Review Article Insulin-Sensitizers, Polycystic Ovary Syndrome and …downloads.hindawi.com/journals/ije/2016/8671762.pdf · 2019-07-30 · Insulin-sensitizers improve the metabolic

Review ArticleInsulin-Sensitizers Polycystic Ovary Syndrome andGynaecological Cancer Risk

Rosa Lauretta1 Giulia Lanzolla2 Patrizia Vici3 Luciano Mariani4

Costanzo Moretti2 and Marialuisa Appetecchia1

1Unit of Endocrinology Regina Elena National Cancer Institute Rome Italy2Unit of Endocrinology Department of Systemsrsquo Medicine University of Rome Tor Vergata Section of Reproductive EndocrinologyFatebenefratelli Hospital ldquoSan Giovanni Calibitardquo Rome Italy3Division of Medical Oncology B Regina Elena National Cancer Institute Rome Italy4Department of Gynaecologic Oncology HPV-Unit Regina Elena National Cancer Institute Rome Italy

Correspondence should be addressed to Marialuisa Appetecchia marialuisaappetecchiaifogovit

Received 13 May 2016 Revised 12 July 2016 Accepted 8 August 2016

Academic Editor Vittorio Unfer

Copyright copy 2016 Rosa Lauretta et al This is an open access article distributed under the Creative Commons Attribution Licensewhich permits unrestricted use distribution and reproduction in any medium provided the original work is properly cited

Preclinical early phase clinical trials and epidemiological evidence support the potential role of insulin-sensitizers in cancerprevention and treatment Insulin-sensitizers improve the metabolic and hormonal profile in PCOS patients and may also actas anticancer agents especially in cancers associated with hyperinsulinemia and oestrogen dependent cancers Several lines ofevidence support the protection against cancer exerted by dietary inositol in particular inositol hexaphosphate Metforminthiazolidinediones and myoinositol postreceptor signaling may exhibit direct inhibitory effects on cancer cell growth AMPKthe main molecular target of metformin is emerging as a target for cancer prevention and treatment PCOS may be correlated toan increased risk for developing ovarian and endometrial cancer (up to threefold) Several studies have demonstrated an increasein mortality rate from ovarian cancer among overweightobese PCOS women compared with normal weight women Long-termuse of metformin has been associated with lower rates of ovarian cancer Considering the evidence supporting a higher risk ofgynaecological cancer in PCOS women we discuss the potential use of insulin-sensitizers as a potential tool for chemopreventionhypothesizing a possible rationale through which insulin-sensitizers may inhibit tumourigenesis

1 Introduction to Polycystic Ovary Syndrome

Polycystic ovary syndrome (PCOS) is one of the most com-mon endocrine disorders in women of reproductive age withan estimated incidence rate of 5ndash10 [1 2] The syndromehas a heterogeneous presentation which includes hirsutismoften related to hypersecretion of ovarian androgens anovu-lation menstrual irregularity infertility and pregnancy com-plications PCOS may predispose women to cardiovascularand metabolic dysfunction as well as an increased risk oftype 2 diabetes [3] The excess of ovarian androgen secretion[4] may affect raised pituitary luteinizing hormone (LH)production and in addition contributes to the mechanisms ofanovulation Insulin sensitivity and secretion can be affectedby hyperandrogenism however dietary factors and indepen-dent genetic seem to have also a role [5] Hyperinsulinemia

and peripheral insulin resistance are present in about half ofPCOS women mainly in adipose tissue and skeletal musclewhile ovarian theca and granulosa cells have been reportedto be highly sensitive to insulin Insulin stimulates ovariantheca cells to produce androgen (ie testosterone) throughthe stimulation of the insulin receptor (IR) like LH [6] Bothhypersecretion of LH and hyperinsulinemia cooperate toincrease ovarian theca cell androgen production contributingto androgen dependent hirsutism also by suppression ofhepatic secretion of sex hormone binding globulin (SHBG)which increases the bioavailability of circulating testosterone[7]The use of antihyperglycemic drugs enhancing peripheralinsulin sensitivity is widely used to treat metabolic aspectsin PCOS women often from a long time [8] However thecorrection of hyperinsulinemia leads to a decreased ovarian

Hindawi Publishing CorporationInternational Journal of EndocrinologyVolume 2016 Article ID 8671762 17 pageshttpdxdoiorg10115520168671762

2 International Journal of Endocrinology

androgen production Chan indicates that using insulin-sensitizers may have a role as a tool for cancer prevention[9] In the present review we try to hypothesize a possi-ble rationale through which insulin-sensitizers may inhibittumourigenesis (Figure 1)

2 Insulin Receptor Signaling andPhosphoinositide Pathways

Insulin receptor is a transmembrane receptor encoded by asingle gene belonging to the large class of tyrosine kinasereceptors [3] It is activated by insulin insulin growth factor1 (IGF-I) and insulin growth factor 2 (IGF-II) [16] The mainactivity of the IR when bound by an insulin molecule isinducing glucose uptake For this reason a decreased sensi-tivity in insulin receptor signaling associated with impairedglycogen synthesis and inhibition of glycogen breakdownprogressively leads tometabolic disorders and type 2 diabetesmellitus [17] Peripheral insulin resistance is then definedby a decrease in insulin-dependent glucose transport atthe level of target tissues [18] due to defects at both theinsulin receptor andor postreceptor signaling [19] Followinghormone binding the IR undergoes conformational changeswhich allow autophosphorylation of its tyrosine residuesdocking sites for insulin receptor substrates (IRSs) involved inphosphatidylinositol-3-kinase (PI3K) activation and recruit-ment to the plasma membrane of the serinethreonine pro-tein kinase AktPKB which represents the main intracellularinterconnecting pathway activated to ensure insulin biologi-cal action together with the mitogen-activated protein kinase(MAPK)extracellular-signaling regulated protein kinase 12(ERK 12) pathway [20 21] Inmammals almost five isoformsof the regulatory subunit of PI3K interact with IRSs activatingthe catalytic subunit and phosphorylating the phosphatidyli-nositol 45-biphosphate [PI(45)P2] which in turn enablesother phosphoinositide dependent kinases [mainly phos-phatidylinositol 345-trisphosphate PI(345)P3] involved inthe phosphoinositide signaling system and in the signaling ofthe glucose transporter type 4 (GLUT4) the main GLUT-likeprotein identified in mammals [22] The phosphoinositidesignaling system plays a pivotal role in the regulation ofcellular processes such as vesicle transport cell proliferationand cytoskeletal remodeling [23] and its deregulation maylead to many diseases including cancer [24] Glucose uptakefor cellular function is additionally regulated by a sensor ofintracellular energy level the 51015840 adenosine monophosphate-activated protein kinase (AMPK) pathway AMPK is a highlyconserved serinethreonine protein kinase that appears touniversally exist as heterotrimeric complex comprised of cat-alytic 120572-subunit and regulatory 120573- and 120574-subunits [25] Likeseveral other protein kinases AMPK and its orthologues areonly significantly active when phosphorylated by upstreamkinases at the level of a conserved threonine (Thr172) withinthe kinase domain [26] In mammals the main upstreamkinase phosphorylating Thr172 is the liver kinase 1-Ste20-Related Adaptor-Mouse protein 25 (LKB1-STRAD-MO25)heterotrimeric complex a biologically active unit containingthe tumour suppressor kinase LKB1 [27 28]This complex isconstitutively active and presents a high basal activity [29]

however its ability to phosphorylate Thr172 is improved byconformational changes in its AMPK substrate due to thebinding of 51015840 adenosine monophosphate (AMP) active toits 120574-subunit Moreover kinases that can activate AMPKalso include calciumcalmodulin-dependent protein kinase(CaMKK) [30] and transforming growth factor 120573-activatedkinase 1 (TAK1) [31] Overall AMPK maintains cellularenergy homeostasis and its activation by metabolic stress(accountable of energy depletion) leads to inhibition of cellgrowth and promotion of adenosine-51015840-triphosphate (ATP)production Indeed once activated AMPK can encouragecatabolic pathways and inhibit anabolic pathways to restoreenergy stores [32] Furthermore many of the biosyntheticpathways such as synthesis of triglycerides fatty acidsphospholipids sterols glycogen proteins and ribosomalRNA are switched off by AMPK These pathways are sub-ject to a AMPK dependent downregulation via multiplemechanisms involving both phosphorylation of pathway keyenzymes and longer-term effects on gene expression [32]As a molecular target of metformin AMPK is a known keypoint in the treatment of metabolic syndrome and type 2diabetes Recently AMPK is emerging as a possiblemetabolictumour suppressor and a target for cancer prevention andtreatment Moreover it has been observed that AMPKdownstream targets can influence many effector proteinsinvolved in various regulatory processes that contribute to thepathogenesis of cancer Even if AMPK negatively regulatescyclooxygenase 2 (COX-2) a proinflammatory enzyme asso-ciated with tumourigenesis and can induce phosphorylationof tumour suppressor p53 resulting in cell cycle arrestthe main molecular mechanism involved in the AMPK-mediated tumour suppression is the negative regulation ofPI3KAktmTOR signaling pathway [33] mTOR is a ser-inethreonine protein kinase that regulates cellular processesincluding proliferation growth motility survival proteinsynthesis and transcription [34 35] mTOR forms two func-tionally distinct complexes mTORC1 andmTOR2 mTORC1a central signaling node that integrates signals arising fromgrowth factors nutrient availability and energy status [36]promotes cell growth by phosphorylating ribosomal proteinS6 kinase 1 (S6K1) and Eukaryotic Translation InitiationFactor 4E-Binding Protein 1 (4E-BP1) [37 38] Inhibitionof mTORC1 signaling by AMPK occurs via dual pathwaysFirst AMPK phosphorylates tuberous sclerosis complex-2(TSC2) [39] which converts the Ras homolog enriched in thebrain (RHEB) a GTP-binding protein activating upstreammTORC1 to its inactive GDP-bound form In a second timeAMPK phosphorylates a regulatory-associated protein ofmTOR (RPTOR or Raptor) a subunit of the mTORC1 com-plex inhibiting it [40 41] As AMPK is considered the mostimportant molecular effector of metformin it may functionas an important key-regulator of cellular energy homeostasisTherefore it is activated in response to a shortage of energyin order to boost cellular catabolic activities [42] On thecontrary insulin which is an anabolic hormone releasedby nutrient intake induces cell growth and energy storageIt is therefore not surprising that there is an antagonismbetween these two pathways AMPK negatively modulatesmTOR through the phosphorylation of TSC2 and Raptor

International Journal of Endocrinology 3

Gynaecological cancer prevention

uarr AMPK

uarr AMPATP

Aromatase

CYP17

Theca cells

Insulin resistance anddiabetes risk in PCOS

Growth of cancersstimulated by type 2diabetes and obesity

uarr gluconeogenesis uarr fat synthesis

Increases ATPgeneration

uarr estrogen effects

uarr testosterone

darr SHBG

OCT1

Insulinsensitizers

Insulinsensitizers

Insulinsensitizers

Polycystic ovary

Liver

Mitochondrial oxidativephosphorylation

effects

Androgens

LH

Stimulates growth of estrogen-dependent cancers

Hyperinsulinemia

Anteriorpituitary

Stimulation pathwaysInhibition pathways

darr insulinIGF-1and glucose

Figure 1 The combined action of insulin-sensitizers on the liver and ovary and the supposed protecting effect on endocrine-relatedgynaecological cancer In the liver metformin inhibits mitochondrial respiratory complex 1 promoting AMPK activation which improvesthe metabolic profile reducing hyperglycemia hyperinsulinemia and insulin resistance Insulin-sensitizers have a positive effect in PCOSpatients through normalization of hyperinsulinaemia that otherwise amplifies the excessive androgen production from the ovary theca cellsvia CYP17 phosphorylation and lower levels of SHBG Metformin and inositols may play an anticancer role both as insulin-sensitizers andas aromatase inhibitors Indeed they improve metabolic profile inhibiting the growth of tumoural cells stimulated by hyperinsulinemia andnormalize estrogen production inhibiting the growth of estrogen-dependent cancers OCT1 Organic Cation Transporter 1 LH luteinizinghormone ISF-1 insulin sensitivity factor CYP17 Cytochrome P-45017 SHBG sex hormone binding globulin IGF-1 insulin-like growthfactor PCOS polycystic ovary syndrome


Cytokinereceptor

Insulin

GPCR

IRS

p110

PTEN

PI3K

IR

P P

P

PI(34)P2 PI(45)P2PI(345)P3

IP3 DAG

RAC1

Cytoskeletalrearrangement

PKC

Transformation

PDK1

Survival

AKT

PmTOR Protein synthesis

Protein translation

Cell cycle Glucose metabolism

BAD

Apoptosis

Stimulation pathways

NF-120581B

GSK3120573

PLC120574

P85120572

Figure 2 Insulin receptor and phosphatidylinositol (345)-trisphosphate formation The activation of PI3K by insulin G-protein coupledreceptor or growth factors generates different 31015840 phosphorylated inositol products which in turn recruit effector molecules regulating manycellular functions involved in cells survival and metabolism GPCR G-protein coupled receptor IR insulin receptor IRS insulin receptorsubstrate PI3K phosphatidylinositol 3-kinase PI(45)P2 phosphatidylinositol 45-bisphosphate PI(345)P3 phosphatidylinositol 345-triphosphate PI(34)P2 phosphatidylinositol 34-bisphosphate PLC120574 Phospholipase C 120574 IP3 inositol trisphosphate DAG diacylglycerolPKC protein kinase C PTEN phosphatase and tensin homolog Akt protein kinase B RAC1 Ras-Related C3 Botulinum Toxin Substrate 1PDK1 phosphoinositide dependent protein kinase-1 mTOR mammalian target of rapamycin GSK3120573 glycogen synthase kinase 3 NF-120581Bnuclear factor 120581B BAD Bcl2-Antagonist of cell Death

A similar but functionally opposite dual approach is used bythe insulin-signaling pathway to activate mTORC1 and thuscontrast AMPKeffects [36] It has been demonstrated that theinsulin-activated kinase Akt phosphorylates TSC2 at distinctsites from those specific for AMPK blocking its RHEB-GAPfunction [36 43 44] and also phosphorylates proline-richAkt substrate of 40 kDa (PRAS40) enhancing its inhibitoryeffect on the mTORC1 complex [45] Hence AMPK and Aktreciprocally control mTOR pathway As demonstrated in ratmodel the insulin-activated kinase Akt has been shown tophosphorylate the 1205721 catalytic subunit of AMPK at Ser485reducing the rate of subsequent Thr172 phosphorylation andthe LKB1 induced activation in cell-free assay whereas thepretreatment with insulin may bluntThr172 phosphorylationduring ischemia in perfused rat hearts [46] The signalingrelationship between Akt and AMPK is quite complexAkt positively regulates mTORC1 and negatively regulatesAMPK while some conditions activating AMPK may silenceAkt signaling suggesting a bidirectional cross-talk betweenAMPK and Akt even if the functional consequence in termsof tumour progression is unclear [33] For instance thisbidirectional feedbackmechanismwas shown by Choudhuryet al using a number of prostate cancer cell lines [47]

Therefore activated AMPK may inhibit or promote Aktsignaling depending on the cellular microenvironment andthe following phenotypic consequences may dependent onthe tumour and cellular context [33] (Figure 2)

Translating into clinical practice the current researchdata discussed above it is possible to support the evidencethat metformin might induce growth-static effect on sev-eral cancers including pancreatic cancer [48] glioma [49]prostate and colon cancer [50] The metformin antiprolif-erative effect may be exerted through the inhibition of thePI3KAktmTOR signaling transduction pathway [35 51ndash54]Finally AMPK can also regulate p53 [55] and modulates theactivity of transcription factors and coregulators that controlthe cell cycle [56 57] Current evidence suggests that AMPKcan act as a tumour suppressor by modulating inflamma-tions contrasting the metabolic changes that occur duringtumourigenesis and directly inducing cell cycle arrest [58]

3 Insulin-Sensitizers in PCOS andCancer Prevention

PCOS is associated with insulin resistance [59] and witha certain number of metabolic disorders [60] Insulin


resistance is a dysmetabolic condition in which a greateramount of insulin is required to exert a physiological cellularresponse It is characterized by increased secretion of insulinfrom pancreatic 120573-cells and compensatory hyperinsulinemiaThe treatment of insulin resistance and hyperinsulinemiaincludes the use of insulin-sensitizers (metformin thiazo-lidinediones and inositols) [8]

31 Metformin Metformin is a synthetically derived bigua-nide off-label used in the management of dysmetabolicdisorders and insulin resistance in PCOS It has been demon-strated that metformin when used in addition to changes inthe life-style may restore ovulation in women with PCOSand reduces the risk of ovarian hyperstimulation syndrome[8]The effects of metformin on glucose metabolism seem tobe secondary to its actions on the mitochondrial respiratorychain inhibiting themitochondrial respiratory complex I [6162] Therefore it leads to a reduction in ATP production andoxidative phosphorylation resulting in a higher AMPATPratio which in turn inhibits gluconeogenesis and modulatesAMPK AMPK activation by metformin induces fatty acidoxidation reduces lipid synthesis and inhibits gluconeogene-sis [63 64] AMPK is regulated bymetformin via an upstreamkinase LKB1 which is produced by a tumour suppressor geneand controls cell growth Although AMP-activated proteinkinase is one of the most important molecular targets ofmetformin this drug also has AMPK-independent effectson glucose metabolism as it has been shown in mice thatdeficiency of LKB1 and AMPK following treatment withmetformin leads to a reduction of serum glucose levelsTheseeffects might be the result of the change in AMPATP ratiothat regulates hepatic glucose output upstream of AMPKand suppresses cyclic-AMP-protein kinase A signaling [8]Although the primary action of metformin is the metabolichomeostasis its putative role in treating different types ofcancer is under investigation [65 66] Currently metformineffect in preventing a number of cancers has been demon-strated by many epidemiological and clinical data [37 67 68]but the molecular mechanisms are yet to be elucidated Thetreatment of endometrial cancer cells with metformin leadsto displacement of constitutively active K-Ras from the cellmembrane uncoupling the mitogen-activated protein kinase(MAPK) signaling pathway [69] Additional anticancer activ-ity could be its antiaromatase activity [38] which leads toa reduction in circulating estrogen levels in obese womenand an upregulation of progesterone receptor expression byendometrial cancer cells [70] Furthermore metformin hasantiangiogenic effects directly scavenging free radicals andblocking endogenous reactive oxygen species [71] A studyin vitro has shown that it significantly reduces DNA damageand mutation rates [72] this might be the explanation ofthe reduced risk of cancer that has been shown by manyepidemiological studies through the use of metformin Thepotential preventive and therapeutic role of this drug onbreast cancer has also been studied For instance Jiralersponget al in a retrospective study of 2529 diabetic patientsincluding 68 on metformin and 87 not showed that diabeticpatients affected with breast cancer and treated with met-formin had higher rates of complete response to neoadjuvant

chemotherapy than those not taking metformin [73] In cellculture the proliferation of a wide range of cancer cells suchas breast cancer cells is inhibited by metformin [74 75] andLiu et al reported the apoptotic effect of metformin in triplenegative breast cancer cells [76] Recently it has been shownthat metformin may also target cancer-initiating cells Inparticular it was shown that its use in a subpopulation ofbreast cancer cells suppressed their growth and decreasedthe ability of these cells to form tumours in mice [77] itscombinationwith trastuzumab leads to a reduction of cancer-initiating cell population in Her2-amplified breast cancercells [78] Moreover metformin can regulate breast cancer-initiating cell ontogeny through repression of the process ofepithelial to mesenchymal transition (EMT) [79] Overallmetformin benefits to breast cancer may be due to its roleon cellular cycle and PI3KAktmTOR signaling pathway andnegative insulin effects on tumour development and growth

32 Thiazolidinediones Thiazolidinediones (TZDs) used inthe treatment of metabolic diseases are a class of drugs alsoknown as glitazones including troglitazone rosiglitazoneand pioglitazone [80] Troglitazone was withdrawn from theworldwide market in 2000 due to an increased incidence ofdrug-induced hepatitis [81] Glitazones are synthetic ligandscontaining a functional group in which thiazolidine serves asa dione and acts as an agonist of the peroxisome proliferator-activated receptor gamma (PPAR120574) whose endogenous lig-ands are free fatty acids (FFA) and eicosanoids [82] ActivatedPPAR120574 shapes a heterodimeric complex with retinoid Xreceptor (RXR) and binds to peroxisome proliferator hor-mone response elements upregulating specific target genesand downregulating others [83] Thiazolidinediones act asinsulin-sensitizing agents increasing fatty acid uptake andstorage in adipose tissue promoting adiponectin expressionand decreasing expression of 11120573-hydroxysteroid dehydro-genase type 1 (11120573-HSD) which converts cortisone to activecortisol [84] PPAR120574 can regulate the transcription andorthe activity of different key regulators of energy homeostasiswhere it can be considered as a control element of the cellularenergy status [82] Beneficial effects of these drugs are alsostudied in polycystic ovary syndrome showing that TZDs canreduce insulin resistance in PCOS women mainly acting onthe adipocytes and the muscle cells [85 86] In addition toimproving insulin resistance and compensatory hyperinsu-linemia administration of TZDs may increase the ovulationrate and pregnancy in patients affected with PCOS [87] Ithas been observed that TZDs can modulate secretion of sev-eral endocrine hormones reducing androgen production orimproving gonadotropins secretion [81] Moreover Hu et alshowed aweak PPAR120574mRNAexpression in granulosa cells ofPCOS patients that varied in relation to the clinical featuresof the disease and was upregulated following administrationof different dosages of insulin andor rosiglitazone [88] Invitro experiments run on human ovarian cells demonstratethe negative regulation exerted by TZDs on steroidogenicenzymes 3-120573-hydroxysteroid-dehydrogenase (3120573-HSD) andaromatase [80 89 90]

Interestingly as with metformin glitazones can activateAMPK indirectly and regardless of PPAR120574 involvement [91]


through an increase of intracellular ADP ATP ratio whichleads to the inhibition of respiratory chain and subsequentAMPK phosphorylation [62]

Considering the potential effects of glitazones on gynae-cological tumorigenesis Shah et al showed that thiazolidine-diones decrease vascular endothelial growth factor (VEGF)production by human luteinized granulosa cells in vitro[92] On the contrary another study which characterizedthe response of ovarian xenograft tumours to the nonhy-percalcemic vitamin-D2 derived anticancer agent (MT19c)observed a reduced efficacy of MT19c and cisplatin followingstimulation of PPAR120574 with rosiglitazone suggesting thatPPAR120574 promotes survival for some ovarian tumour cells [93]Overall these lines of evidencemdashalthough limited and con-trasting in some aspectsmdashindicate that in some conditionsthese drugs may be considered as protective agents even ifdue to their side effects their use should come as a secondaryoption in the treatment of the metabolic problems linked toPCOS

33 Inositols Inositol (cyclohexane-123456) is a polyolof cyclohexane with six hydroxyl groups identified for thefirst time in animal muscle tissue by J J Scherer in 1850In the past it has been considered as a member of thevitamin B complex but inositol cannot be considered a ldquotruerdquoessential nutrient as it can be synthesized by the humanbody Indeed cells can activate inositol biosynthesis startingfrom glucose through two enzymatic reactionsThe first stepconsists of the conversion of D-glucose 6-phosphate to L-inositol-1P catalyzed by 1L-myoinositol-1-phosphate synthase(MIPS) Subsequently L-Ins(1)P-phosphatase hydrolyzes L-inositol-1P forming myoinositol (myo-Ins) and orthophos-phoric acid [94] Inositols exist under nine stereoisomericforms depending on the spatial orientation of their sixhydroxyl groups Myo-Ins and D-chiro-inositol (D-chiro-Ins) are the twomain inositol stereoisomers naturally presentin animal and plant cells either in their free form or asbound-components of phospholipids or inositol phosphatederivatives Myo-Ins is abundantly present in many plantsources and in certain high-fiber diets such as cereals andlegumes When ingested it is actively absorbed at the level ofthe gastrointestinal tract involving an Na+K+-ATPasi [95]Inositol transporters are involved in uptake and intracellulardistribution of inositols that according to their transportmechanism can be classified as sodium ion coupled andproton coupled inositol transporters [96] Myo-Ins is presentin the cell embedded in the phospholipids docked to theplasmamembrane and it is even a component of the glycosyl-phosphoinositides layered on the inner surface of the cellularmembrane acting as important component of the calciumtrafficking [97 98] The discovery of the second-messengerfunction of phosphatidylinositol generated by the actionof cytidine diphosphate diacylglycerol (CDP-DAG) inositolphosphatidyltransferase and its phosphorylated derivativesthe phosphoinositides marked a turning point in studies ofhormone function [99] Myo-Ins plays an important role inthe insulin signal transduction lipid metabolism calciumions flow regulation and assembly of cytoskeletal proteinsRecently a substantial body of research evidenced its role in

PCOS as an insulin-sensitizing agent affecting different path-ways at both ovarian and nonovarian level [100] In additionto being found in some food myo-Ins is formed in the cellsits biosynthesis deriving from the conversion of D-glucose-6 phosphatase to L-inositol-1-phosphate [101] Myo-Ins is animportant component of the structural lipids and its variousphosphates including the phosphatidylinositol phosphate(PIP) lipids [102ndash104] are essential inmaintaining the cellularmembrane bilayer Moreover myo-Ins is the structural basisfor many secondary messengers including inositol triphos-phates (InsP3) phosphatidylinositol (PI) polyphosphoinosi-tides [ie PI(4)P PI(45)P2 and PI(345)P3] and inositolphosphoglycans (IPGs) which controls several physiologicalevents including regulation of hormone activities [105] Inos-itol pyrophosphates act as a controlling factor of PI3KAktsignaling pathway [106] Myo-Ins is involved in mTORC1and AMPK signaling activities [99] Currently myo-Insis involved in inositol polyphosphate multikinase (IPMK)activity a key enzyme for inositol polyphosphate biosynthesisand metformin-induced AMPK activation [107] (Figure 3)

In mammals IPMK is also known as a physiologicallyimportant phosphatidylinositol 3 kinase (PI3K) that formsPI(345)P3 which activates Akt signaling pathway [108]Recently Kim et al suggested the role of IPMK as a novelcofactor for mTORC1 signaling [109] Moreover IPMK alsoappears to be a novel AMPK-binding protein whose bindingaffinity for AMPK is dynamically controlled by glucoselevels [107] Myo-Ins intracellular homeostasis is adjusted bysome processes mainly the extracellular uptake via special-ized myo-Ins transporters phosphoinositide cycle de novobiosynthesis from glucose-6-phosphate by 1-D-myoinositol-phosphate synthase (MIPS) and inositol monophosphatase(IMPase) efflux and degradation [110] Abnormalities in oneor several of these processes lead to myo-Ins intracellulardepletion found in conditions of hyperglycemia and insulinresistance as observed in diabetes mellitus [99] Inositoltransporters were identified in bacteria protozoa fungiplants and animals According to their transport mech-anisms they can be classified into two groups sodium-dependent myo-inositol transporters 1 and 2 (SMIT12) andproton coupled inositol transporters (HMIT) [105] Manylines of evidence support the benefits of myo-Ins supple-mentation for some metabolic disorders associated withinsulin resistance because of its insulin mimetic propertiesAs mentioned above PCOS is characterized by metabolicfeatures such as central obesity and insulin resistance withcompensatory hyperinsulinemia that also are key factorsin the pathogenesis of chronic anovulation [111ndash113] Myo-Ins through its insulin-sensitizing effect plays an importantrole in improving metabolic and hormonal parameters inwomen affected with PCOS [114 115] However the besttherapy for this disorder is constituted by the treatmentwith myo-Ins plus D-chiro-Ins combined in agreement withthe physiological myo-InsD-chiro-Ins plasma ratio (40 1)[116ndash119] which allows obtaining very interesting resultsand also avoids some detrimental effects due to D-chiro-Insalone at high concentrations [120] Myo-Ins involvement inthe reproductive axis function is highlighted by the pivotalrole played by inositol (145)-triphosphate [Ins(145)P3] in


Insulin resistance

GlucoseInsulinTNF 120572IL-6

Myo-Insmetformin

AMP

LKB1

CAMMK120573

ACC P53 COX2

darr lipid andfatty acidsynthesis

Cell cyclearrest

Tumorigenesis

Stimulation pathwaysInhibition pathwaysSupposed inhibition pathways

IR

IRS-1PIP3

PKC JNKNF-120581B

GLUT4

AKTAMPK

TSC1

TSC2

Pras40

RHEBGDP

RHEBGTP mTORC1

mTOR Raptor

6SK1 4EBP1

Figure 3 Negative regulation exerted by insulin-sensitizing on the molecular mechanism feeding insulin resistance Role of AMPK as ametformin andmyo-Ins molecular target AMPK activation induces COX2 inhibition p53 expression andmTORC1 silencing through TSC2and Raptor phosphorylation The regulating activity of AMPK in processes of tumour induction and progression suggest that metforminmay be proposed as an anticancer agent TNF120572 Tumour Necrosis Factor 120572 IL-6 interleukin 6 IR insulin receptor PKC protein kinaseC JNK c-Jun N-terminal Kinase NF120581B nuclear factor 120581B IRS-1 insulin receptor substrate 1 PI(345)P3 phosphatidylinositol 345-trisphosphate Akt protein kinase B GLUT4 glucose transporter type 4 TSC1 tuberous sclerosis 1 TSC2 tuberous sclerosis 2 AMPK 51015840adenosinemonophosphate-activated protein kinase AMP adenosinemonophosphate LKB1 liver kinase B1 CaMKK120573 calciumcalmodulin-dependent protein kinase 120573 Pras40 Proline-Rich AktPKB Substrate 40 kDa RHEB Ras Homolog Enriched in Brain mTOR mammaliantarget of rapamycin Raptor regulatory-associated protein of mTOR mTORC1 mammalian target of rapamycin complex 1 6SK1 6S Kinase1 4EBP1 Eukaryotic Translation Initiation Factor 4E-Binding Protein 1 ACC Acetyl-CoA Carboxylase p53 Tumour Protein 53 COX2cyclooxygenase 2

the regulation of calcium ion (Ca2+) release during oocytesdevelopment and its role in meiotic competence and the finalstage of oocyte maturation [121] In PCOS patients a defectin tissue availability or an altered metabolism of inositolor IPGs mediators may contribute to insulin resistance[122 123] As myo-Ins involvement in PI3KAktmTOR andAMPK signaling pathway [124] plays important roles in theregulation of cellular growth and survival it is interestingto examine its possible role in cancer development Hanet al have shown that regression of bronchial dysplasticlesions can be caused by myo-Ins through inhibition ofactive Akt and ERK and its molecular target in vivo andin vitro [125] Furthermore a phase 1 clinical study carriedout in order to determine the potential chemopreventiveeffect ofmyo-Ins in smokers with bronchial dysplasia showed

a potential positive effect at the oral daily dose of 18 gr forthree months [126] without significant adverse events despitethe high doses used Indeed myo-Ins may work throughmultiple mechanisms to inhibit tumour progression Interestis growing for inositol hexaphosphate (InsP6) a naturaloccurring polyphosphorylated carbohydrate contained inhigh-fiber diets and present in mammalian cells and for itsrole in cancer prevention as well as control of experimentaltumour growth progression andmetastasis [127] Dong et alreported that InsP6 strongly inhibited cellular transformationinduced by epidermal growth factor (EGF) ERK and PI3Kactivation [128] Based on the synergic activity ofmyo-Ins andmetformin in metabolic disorders characterized by insulinresistance and according to the suggested antitumouraleffect of metformin treatment the possibility that myo-Ins


might have some ability to inhibit tumour growth also ingynaecological cancer should be considered More studiesare needed to clarify a possible anticancer role of myo-Ins inpatients affected with PCOS

4 Insulin-Sensitizers in PCOS andOvarian Cancer

Ovarian cancer (OC) is the eighth most common cancer andthe seventh most common cause of death from cancer inwomen worldwide There are factors that increase the risk todevelop OC but they are still not well validated The onsetof OC can be caused by many factors such as age familyhistory of OC infertility treatment and assisted fertilizationhormonal substitution in menopause and obesity [129]Endocrine disorder associatedwith hypersecretion of ovarianandrogens anovulation and menstrual irregularity in PCOSseem to be the cause of higher risk of the epithelial ovariancancer development due to the abnormal hormonal envi-ronment In fact in PCOS we see hormonal alteration withabnormal concentrations of unopposed oestrogens Severalhypotheses are made to explain ovarian carcinogenesis Themajority of malignant ovarian tumours seem to have steroidhormone receptors (62 for oestrogen 49 progesteroneand 69 for androgen) [130] Berchuck et al proposed thatan interference in the local concentration of growth factorsand steroids conducts malignant changes in the ovarianepithelium [131] Oestrogens prevent apoptosis through Bcl-2 upregulation and this may lead to ovarian carcinogenesiswhereas progesterone has a proapoptotic effect on ovarianepithelium through either the modulation of transforminggrowth factor 120573 (TGF 120573) isoform expression or the activationof the FasFas Ligand signaling pathway [132] Also andro-gens seem to be involved in ovarian carcinogenesis in animalmodels and testosterone may intensify the ovarian epithelialtumours growth [133] Androgens decrease TGF 120573 receptorlevels allowing tumour cells to escape TGF1205731 mediatedgrowth inhibition thus promoting ovarian cancer progres-sion [134] Repeated anovulatory cycles with the generationof inclusion cysts may increase the risk of genetic damagebecause of exposure of the epithelial cells to high concen-trations of oestrogens in follicular fluid [135] Likewise highlevels of circulating gonadotropins increase the risk of devel-oping ovarian cancer especially in early postmenopausalyears [136] In the literature few and conflicting studiesaddressing the possibility of an association between ovariancancer and PCOS are reported [137] with the additionalproblem raising from uncertainties in PCOS diagnostic cri-teria as most of such studies have been conducted before theRotterdam ESHREASRM PCOS Consensus 2003 [138] In1996 Schildkraut et al demonstrated in a population-basedcase-control study a 25-fold increase in the risk of ovariancancer among women with PCOS [139] A stratified analysisadjusted for age found that oral contraceptive use plays aprotective role in women with PCOS [139] Stratified age-adjusted analysis also showed that younger women reportingto have PCOS were at much greater risk for developingovarian cancer [139] However the small number of womenwith PCOS (119899 = 31) limited the interpretation of these

findings with the possibility of recall bias in subjects affectedwith ovarian cancer [140] An Australia-wide population-based case-control study of subjects aged 18ndash79 years withnew diagnosis of invasive epithelial ovarian cancer (119899 =315) versus controls (119899 = 1508) tested the hypothesis thathyperandrogenism is associated with the genesis of ovariancancer The authors found no evidence that self-reportedhistories of PCOS were associated with an increased ovariancancer risk although women with PCOS who were also over-weight had a significantly increased risk of serious borderlinetumours [141] A case-control analysis of 1611 patients versus9170 controls with a diagnosis of ovarian cancer shows thatPCOS (OR 163 95 CI 065ndash408) was associated with atendency towards an increased risk of ovarian cancer Aretrospective case-control analysis has shown that long-termuse of metformin was associated with lower rates of ovariancancer (OR 061 95 CI 03ndash125) [142] Identification of anumber of proteins overexpressed in both PCOS and ovariancancer such as superoxide dismutase calreticulin vimentinfibrinogen 120574 lamin B2 and malate dehydrogenase assuredthe identification of women with PCOS with an increasedrisk of developing this malignancy [143] A systematic reviewand meta-analysis of observational studies considered forPCOS association and ovarian cancer only three studies [144]The OR resulted significantly higher in the single study ofwomen aged lt54 years [139] however the increased risk ofovarian cancer in women with PCOS was not significant[144] This is in line with a nationwide population-basedretrospective cohort study conducted in Taiwan where alsothe increased risk of ovarian cancer in the PCOS group wasnot reported [145] The analysis of a large cohort study fromthe Danish National Patient Register compared the womenrsquoscancer incidence with that of the general Danish femalepopulation by means of standardized incidence ratios (SIRs)and found no association between PCOS and ovarian cancer[146]The associationwith obesity is not pronounced asmuchas the association with endometrial cancer however a recentmeta-analysis and a systematic review found that ovariancancer was barely more common in women with a BMI ge30 kgm2 [147 148] and a prospective cohort study showedincreased mortality from ovarian cancer among overweightand obese women compared with normal weight women[149] Lee at al reported a higher risk of ovarian cancer indiabetic women which persisted after adjusting for BMI agealcohol intake and smoking [148] Numerous prospectiveobservational studies suggested that not only patients withtype 2 diabetes taking metformin were at lower risk ofdeveloping cancer [150] but also mortality was less common[151] Stadtmauer et al suggested that insulin-sensitizingagents use as well as improving reproductive function pro-duces long-term health benefits [152] Also myo-Ins acts as acontrolling factor of PI3KAkt signaling pathway [99] and itis also involved inmTORC1 andAMPK signaling [107]Thusbesides its insulin-sensitizing effect it plays an importantrole in improving metabolic and hormonal parameters inwomen affected with PCOS and a possible chemopreventiveeffect can be hypothesized The identification of a high riskgroup is important and this may include women with PCOS


impaired glucose tolerance morbid obesity endometrialhyperplasia and risk for developing ovarian cancer

5 Insulin-Sensitizers in PCOS andEndometrial Cancer

A growing scientific interest towards addressing the risk ofendometrial cancer in women affected by polycystic ovariansyndrome is emerging in endocrinology and gynaecologiconcology Currently endometrial cancer (EC) is the mostcommon gynaecological malignancy in Europe and NorthAmerica with a global tendency to further increase over timemainly involving postmenopausal women [153] The mainrisk factors regarding hormone-related cancer are recognizedin exposure to unopposed estrogen therapy overweight andobesity late-age menopause and nulliparity [114 115] andtherapy with Tamoxifen as well [154] Since EC risk isstrongly associated with high circulating oestrogen levelsall of the pathological conditions leading to this hormonalstatus may promote endometrial proliferation This is thecase of women affected by PCOS that show a high risk ofdeveloping atypical endometrial hyperplasia (EH) which isconsidered a precancerous lesion which may progress to ECAn assessment of the prevalence of EH in PCOS women stillremains a widely debated issue Although the hyperplasticrate has been reported as high as over 48 [155] others [156]did not confirm it referring to an overall prevalence closeto 1 As already mentioned [157] such a wide range of EHprevalence in PCOS patients may reflect the heterogeneousnature of the PCOS phenotypes and the varying diagnosticcriteria over time The biological relationship between PCOSand EC although still unclear refers to a combinationof complex reproductive and metabolic disorders likewisechronic anovulation obesity and hyperinsulinemia resultingin progesterone deficiency Consequently the endometriumtends to remain in an oestrogen dominant proliferative stateincreasing the risk of developing uterine cancer [158 159]Furthermore metabolic impairment in PCOS consists ininsulin resistance accompanied by an increase of IGF-I bothplaying a pivotal role in the endometrial cell proliferation anddifferentiation promoting the development of EC [160 161]as follows

Speculated Pathogenesis of Endometrial Cancer in PCOSWomen (Mod from Gadducci et al [132])

Chronic anovulationrarr unopposed estrogen stimula-tion

uarr serum LHuarr endometrial LH receptor expression

Insulin resistancerarr chronic hyperinsulinemia

uarr serum IGF-1

The estimated risk of PCOS women in developingendometrial cancer has been evaluated in some observationalcase-series case-control studies systematic reviews and

meta-analysis as well With only a few exceptions [162] themajority of such studies [144 159 163ndash166] confirmed ahigher EC risk for PCOS women In the early 90s one ofthe first case-control studies [167] managed by the NationalCancer Institute program of the Surveillance Epidemiologyand End Result assigned to PCOS women an odd ratio (OR)for endometrial cancer of 27 compared to the control groupIn a further retrospective study Wild et al [163] evaluatedthe long-term endometrial consequences in PCOS womenreporting over 30 years of follow-up a higher OR (up to 53)for developing EC A systematic review and a meta-analysisby Chittenden et al [166] explored the long-term outcomeof PCOS patients Among four observational studies theyreported that women with PCOS appear to be three timesmore likely to developwell-differentiated endometrial cancerMore recently Haoula et al [159] performed a meta-analysiscomparing previous observational studies and confirmed thatthe risk of developing EC is three timesmore likely comparedwith general population Furthermore Barry et al [144] ina case-control study have reported a significantly increasedOR of 279 for endometrial cancer in women with PCOS andendometrial hyperplasia Moreover when the meta-analysiswas restricted to women younger than 54 years the risk esti-mate further increased (OR of 405) In a large Danish cohortstudy using the National Patient and Cancer Registry [146]during the period 1977ndash2012 the incidence of endometrialcancer was significantly higher in PCOS-affected women lessthan 50 years of age with a standardized incidence ratio of39 Most of these cases were type I endometrial cancer afinding that supports the pathogenetic mechanism of long-term exposure to unopposed oestrogen

Finally a high-scale nationwide population-based cohortstudy conducted in Taiwan [145] retrospectively estimatedthe risk for EC of 842 times higher for women with PCOSthan for the comparison cohort All these lines of evidencesuggest as stated by the 3rd PCOS Consensus Group [168]that there are moderate-quality data supporting the high riskof PCOS women for developing endometrial cancer withconsequent need for increased awareness for surveillancestrategies As metformin increases signaling by the insulinreceptor leading to an improvement in insulin resistanceand a reduction in circulating insulin levels it is regularlyused as an insulin sensitizer Furthermore metformin playsan essential role in the inhibition of hepatic gluconeogenesis[169] with the consequent decrease in insulin levels Thusmetformin is a cornerstone in treatment of PCOS women forimproving reproductive abnormalities restoring ovulationand improving fertility [170 171] The recognition of PCOSas a risk factor for endometrial cancer has some althoughstill debated therapeutic implications Progesterone and itsanalogues as well as a levonorgestrel-releasing intrauterinedevice are effectively used to inhibit oestrogen-inducedendometrial proliferation while promoting synchronousgrowth development and shedding of a structurally stableendometrium However it has been documented that upto 30 of PCOS women with endometrial hyperplasia donot correctly respond to this type of hormonal approach[172 173] possibly due to a progesterone-resistance whichin turn determines persistence of endometrial hyperplasia


Table 1 Metformin and endometrial proliferative pathology

Author Ref Year Study Results

Session et al [10] 2003 Human clinical study MTF regresses atypical endometrialhyperplasia in one patient

Legro et al [11] 2007 Human clinical study MTF resolved simple hyperplasia in twopatients

Shen et al [12] 2008 Human clinical study MTF regresses atypical endometrialhyperplasia in two women

Cantrell et al [13] 2010 Endometrial cell line experimentalMTF is a potent inhibitor of cell

proliferation in endometrial cancer celllines

Tan et al [14] 2011 Human experimental study MTF reduces in vitro endometrialinvasion

Li et al [15] 2014 Human clinical studyMTF reverts stage IA endometrial

carcinoma into normal in five youngPCOS patients

MTF metformin

and further possible cancer transformation Such hormonal-resistance may be defined as the clinical failure after high-dose progesterone treatment for 3 months resulting in theacceleration of atypical EH [14] To overcome this resis-tance metformin therapy may be used in PCOS womenaffected by proliferative endometrial pathologies Glucosemetabolism in PCOS women and reversing endometrialproliferation as well as modulation of insulin sensitivity arefunctions of metformin very commonly described Indeedan endometrial cancer model has described that exposureof EC cells to sera from PCOS under metformin therapyreduces cell growth altering signaling pathways involvingtumour invasion [14] Thus a pivotal biological pathwayleading to endometrial cancermay be theoretically controlledby metformin to reduce the risk of EH progression [174]Given this background metformin therapy withwithoutprogesterone-based oral contraceptives has been adopted insmall anecdotal studies to reverse atypical EH or early-stageEC as well (Table 1) In an early case-report following thefailure of progestogen therapy Session et al [10] reported EHregression after metformin Some year later Shen et al [12]confirmed metformin and progestin-based contraceptivesas being effective therapeutic combination in two womenaffected by atypical EH with progestin-resistance

However in regard to endometrial cancer outcomesdata concerning a protective efficacy of metformin are stillinsufficient [157] In a large retrospective cohort study [175]the use of metformin among diabetic patients with nonen-dometrioid EC was associated with a statistically improvedoverall survival (OS) Similarly in another retrospectivecohort analysis EC diabetic patients using metformin had animproved recurrence-free survival and OS than those whodid not use metformin [176] Conversely other results fromobservational case-control analysis [177] did not confirm adecreased risk of endometrial cancer in metformin usersIn addition to this due to the lack of studies a systematicreview carried out using the Cochrane Library database[178] did not reach any firm conclusion about a preven-tive role of metformin in endometrial cancer Some datasupport that metformin treatment for 6 months results in

decreased incidence progression and even cancer-relatedmortality with regard to endometrial cancer Li et al [15]described the efficacy of a combination strategy with hor-monal therapy (cyproterone acetate and ethinyl estradiolDiane) and metformin in five PCOS women affected bystage IA endometrial cancer After 6 months all of thewomen reverted to normal endometrium Even though itwas suggested that metformin might become an importantpharmacological asset in early-stage endometrial cancer [54]further prospective investigations are needed For this rea-son the North Carolina Lineberger Comprehensive CancerCenter started a pilot study to evaluate the effectivenessof metformin in reverse endometrial hyperplasia Currentlythe study is still ongoing recruiting participants with anestimated study completion date in December 2018 [179]Furthermore at the same Cancer Center another study is inprogress to assess the conservative treatment of EH with oralprogestin or levonorgestrel-intrauterine device (LNG-IUS)plus metformin therapy [180]

6 Conclusions

Several preclinical cancer models including studies onendometrial cancers cell lines have shown that insulin-sensitizers might act as anticancer agents in ovarian andendometrial cancers and their ability to act on a varietyof pathways with wide-ranging effects should be takeninto consideration Although a lot of evidences supportthe potential role of insulin-sensitizers in prevention andtreatment of certain gynaecological cancer further researchefforts are required to confirm their clinical usefulness Infact it has been demonstrated that they activate AMPK apotent inhibitor of the PI3KAktmTOR pathway promptG1 cell cycle arrest induce apoptosis and decrease humantelomerase reverse transcriptase expression Furthermorethey seem to inhibit mTOR through AMPK-independentpathways which interfere with the development and DNAdamage response mechanisms Insulin-sensitizers antian-giogenetic effects reduce DNA damage and mutation ratesoffering an explanation for the reduced risk of cancer seen


in metformin users across several epidemiological studiesPCOS seems to be associated with an increased risk fordeveloping epithelial ovarian cancer due to the abnormalhormonal environment with abnormal concentrations ofunopposed oestrogen even if few studies support the factthat the association between them is limited Androgens suchas testosterone can enhance the growth of ovarian epithelialtumours in animal models and may promote ovarian cancerprogression by decreasing TGF120573 receptor levels therebyallowing tumour cells to escape TGF120573 1 mediated growthinhibition Recently a number of proteins overexpressed inboth PCOS and ovarian cancer such as superoxide dis-mutase fibrinogen 120574 vimentin calreticulin malate dehy-drogenase and lamin B2 have been identified revealingsubgroups of womenwith PCOS andwith an increased risk ofdeveloping this malignancy Metformin appears to decreaseendometrial cancer incidence progression and even mor-tality in particular at an early stage It appears reasonableto assume that insulin-sensitizers drugs by reducing thecarcinogenic effects of obesity and insulin resistance mightbe employed for long-term chemoprevention in women athigh risk of endometrial cancer It is necessary to carryout new retrospective epidemiological research and meta-analysis on wide population of PCOS patients organizedin groups based on reproductive axis function hormonaland metabolic profile and drugs therapies Therefore eventhough tumoural cell cultures and mouse models have beenused to explain insulin-sensitizersrsquo mechanism of action andtheir potential inhibitory effect on tumourigenesis new andmore physiologically relevant in vitro human models areneeded to fully elucidate themolecularmechanisms exploitedby these drugs and shape clinical studies Additional researchwould be useful to better define cytokines and growthfactors that are activated in gynaecological cancers and maymodulate cellular responses to insulin-sensitizers in womensuffering from PCOS This is an important key point inidentifying the most suitable patients to be treated with thesedrugs and plan adequate clinical trials

Abbreviations

ACC Acetyl-CoA CarboxylaseAktPKB Protein kinase BAMP Adenosine monophosphateAMPK 51015840 Adenosine monophosphate-activated

protein kinaseATP Adenosine-51015840-triphosphateBAD Bcl2-Antagonist of cell DeathCa2+ Calcium ionsCDP-DAG Cytidine diphosphate diacylglycerolCaMKK Calciumcalmodulin-dependent protein

kinaseCOX-2 Cyclooxygenase 2CYP17 Cytochrome P-45017DAG DiacylglycerolD-chiro-Ins D-Chiro-inositolEC Endometrial cancerEGF Epidermal growth factorEH Endometrial hyperplasia

EMT Epithelial to mesenchymal transitionERK Extracellular-signaling regulated protein

kinase4E-BP1 Eukaryotic Translation Initiation Factor

4E-Binding Protein 1FFA Free fatty acidsGLUT Glucose transporterGPCR G-protein coupled receptorGSK3120573 Glycogen synthase kinase 3HIF Hypoxia inducible factorHMIT Proton coupled inositol transporters11120573-HSD 11120573-Hydroxysteroid dehydrogenase3120573-HSD 3120573-Hydroxysteroid-dehydrogenaseIGF-I Insulin growth factor 1IGF-II Insulin growth factor 2IL-6 Interleukin 6IR Insulin receptorIns(145)P3 Inositol (145)-triphosphateInsP6 Inositol hexaphosphateIPMK Inositol polyphosphate multikinaseIRSs Insulin receptor substratesISF-1 Insulin sensitivity factor 1JNK c-Jun N-terminal KinaseK-RasV-Ki-ras2

Kirsten rat sarcoma viral oncogene homolog

LH Luteinizing hormoneLKB1 Liver kinase 1MAPK Mitogen active proteins kinaseMIPS 1L-Myoinositol-1-phosphate synthaseMO25 Mouse protein 25myo-Ins MyoinositolMT19c Nonhypercalcemic vitamin-D2 derived

anticancer agentmTOR Mammalian target of rapamycinmTORC1 Mammalian target of rapamycin complex 1MTF MetforminNF-120581B Nuclear factor 120581BOCT1 Organic Cation Transporter 1OR Odd ratiop53 Tumour Protein 53PCOS Polycystic ovary syndromePDK1 Phosphoinositide dependent protein kinase-1PI PhosphatidylinositolPI(45)P2 Phosphatidylinositol 45-biphosphatePI(345)P3 Phosphatidylinositol 345-trisphosphatePI3K Phosphatidylinositol-3-kinasePIP Phosphatidylinositol phosphatePKC Protein kinase CPLC120574 Phospholipase C 120574PPAR120574 Peroxisome proliferator-activated receptor

gammaPRAS40 Proline-Rich AktPKB Substrate 40 kDaPTEN Phosphatase and tensin homologRAC1 Ras-Related C3 Botulinum Toxin Substrate 1REDD1 Regulated in development and DNA damage

responses 1RHEB Ras Homolog Enriched in BrainRPTOR Regulatory-associated protein of mTORRR Relative risk


RXR Retinoid X receptorS6K1 Ribosomal protein S6 kinase 1TAK1 Transforming growth factor 120573-activated

kinase 1SHBG Sex hormone binding globulinSMIT12 Sodium-dependent myoinositol transporters

1 and 2STRAD STe20-Related AdaptorTGF120573 Transforming growth factor 120573TNF120572 Tumour Necrosis Factor 120572TSC2 Tuberous sclerosis complex-2TZDs ThiazolidinedionesVEGF Vascular endothelial growth factor

Competing Interests

The authors declare that there are no competing interestsregarding the publication of this paper

Authorsrsquo Contributions

Rosa Lauretta and Giulia Lanzolla are authors with equalcontribution

Acknowledgments

The authors are deeply grateful to Professor Gregorio Sir-acusa MD for his critical reading of the manuscript andhelpful suggestions

References

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[2] R Azziz K S Woods R Reyna T J Key E S Knochenhauerand B O Yildiz ldquoThe prevalence and features of the polycysticovary syndrome in an unselected populationrdquo The Journal ofClinical Endocrinology amp Metabolism vol 89 no 6 pp 2745ndash2749 2004

[3] D Glintborg ldquoEndocrine and metabolic characteristics inpolycystic ovary syndromerdquo The Danish Medical Journal vol63 no 4 Article ID B5232 2016

[4] R Pasquali L Zanotti F Fanelli et al ldquoDefining hyper-androgenism in women with polycystic ovary syndrome achallenging perspectiverdquo The Journal of Clinical Endocrinologyamp Metabolism vol 101 no 5 pp 2013ndash2022 2016

[5] S M De Sousa and R J Norman ldquoMetabolic syndrome dietand exerciserdquo Best Practice amp Research Clinical Obstetrics ampGynaecology 2016

[6] D Heimark J McAllister and J Larner ldquoDecreased myo-inositol to chiro-inositol (MC) ratios and increased MCepimerase activity in PCOS theca cells demonstrate increasedinsulin sensitivity compared to controlsrdquoEndocrine Journal vol61 no 2 pp 111ndash117 2014

[7] C N Jayasena and S Franks ldquoThemanagement of patients withpolycystic ovary syndromerdquoNature Reviews Endocrinology vol10 no 10 pp 624ndash636 2014

[8] V N Sivalingam J Myers S Nicholas A H Balen and EJ Crosbie ldquoMetformin in reproductive health pregnancy andgynaecological cancer established and emerging indicationsrdquoHuman Reproduction Update vol 20 no 6 pp 853ndash868 2014

[9] A T Chan ldquoMetformin for cancer prevention a reason foroptimismrdquoTheLancetOncology vol 17 no 4 pp 407ndash409 2016

[10] D R Session K R Kalli I S Tummon M A Damario andD A Dumesic ldquoTreatment of atypical endometrial hyperplasiawith an insulin-sensitizing agentrdquoGynecological Endocrinologyvol 17 no 5 pp 405ndash407 2003

[11] R S Legro R J Zaino L M Demers et al ldquoThe effects ofmetformin and rosiglitazone alone and in combination onthe ovary and endometrium in polycystic ovary syndromerdquoAmerican Journal of Obstetrics and Gynecology vol 196 no 4pp 402ndash410 2007

[12] Z-Q Shen H-T Zhu and J-F Lin ldquoReverse of progestin-resistant atypical endometrial hyperplasia by metformin andoral contraceptivesrdquoObstetricsampGynecology vol 112 no 2 part2 pp 465ndash467 2008

[13] L A Cantrell C Zhou A Mendivil K M Malloy P AGehrig and V L Bae-Jump ldquoMetformin is a potent inhibitor ofendometrial cancer cell proliferationmdashimplications for a noveltreatment strategyrdquoGynecologic Oncology vol 116 no 1 pp 92ndash98 2010

[14] B K Tan R Adya J Chen H Lehnert L J Sant Cassia andH S Randeva ldquoMetformin treatment exerts antiinvasive andantimetastatic effects in human endometrial carcinoma cellsrdquoThe Journal of Clinical Endocrinology ampMetabolism vol 96 no3 pp 808ndash816 2011

[15] X Li Y-R Guo J-F Lin Y Feng H Billig and R Shao ldquoCom-bination of diane-35 and metformin to treat early endometrialcarcinoma in PCOS women with insulin resistancerdquo Journal ofCancer vol 5 no 3 pp 173ndash181 2014

[16] CWWard andM C Lawrence ldquoLigand-induced activation ofthe insulin receptor a multi-step process involving structuralchanges in both the ligand and the receptorrdquo BioEssays vol 31no 4 pp 422ndash434 2009

[17] TheDiabetes Control and Complications Trial Research GroupldquoThe effect of intensive treatment of diabetes on the develop-ment and progression of long-term complications in insulin-dependent diabetes mellitusrdquo The New England Journal ofMedicine vol 329 no 14 pp 977ndash986 1993

[18] J A Levine K A Kaihara B T Layden and B WicksteedldquoLong-term activation of PKA in beta-cells provides sustainedimprovement to glucose control insulin sensitivity and bodyweightrdquo Islets In press

[19] D H Bedinger and S H Adams ldquoMetabolic anabolic andmitogenic insulin responses a tissue-specific perspective forinsulin receptor activatorsrdquoMolecular and Cellular Endocrinol-ogy vol 415 pp 143ndash156 2015

[20] J Dupont and R J Scaramuzzi ldquoInsulin signalling and glucosetransport in the ovary and ovarian function during the ovariancyclerdquo Biochemical Journal vol 473 no 11 pp 1483ndash1501 2016

[21] C M Taniguchi B Emanuelli and C R Kahn ldquoCritical nodesin signalling pathways insights into insulin actionrdquo NatureReviews Molecular Cell Biology vol 7 no 2 pp 85ndash96 2006

[22] H-G Joost and B Thorens ldquoThe extended GLUT-familyof sugarpolyol transport facilitators nomenclature sequencecharacteristics and potential function of its novel membersrdquoMolecular Membrane Biology vol 18 no 4 pp 247ndash256 2001

[23] H J Kim S Y Lee and S C Oh ldquoThe inositide signalingpathway as a target for treating gastric cancer and colorectalcancerrdquo Frontiers in Physiology vol 7 article 168 2016


[24] J A Engelman J Luo and L C Cantley ldquoThe evolutionof phosphatidylinositol 3-kinases as regulators of growth andmetabolismrdquoNature Reviews Genetics vol 7 no 8 pp 606ndash6192006

[25] L Xu and JDAsh ldquoThe role ofAMPKpathway in neuroprotec-tionrdquo Advances in Experimental Medicine and Biology vol 854pp 425ndash430 2016

[26] F A Ross T E Jensen and D G Hardie ldquoDifferentialregulation by AMP and ADP of AMPK complexes containingdifferent 120574 subunit isoformsrdquo Biochemical Journal vol 473 no2 pp 189ndash199 2016

[27] S A Hawley J Boudeau J L Reid et al ldquoComplexes betweenthe LKB1 tumor suppressor STRAD120572120573 and MO25120572120573 areupstream kinases in the AMP-activated protein kinase cascaderdquoThe Journal of Biology vol 2 no 4 article 26 2003

[28] A Woods S R Johnstone K Dickerson et al ldquoLKB1 is theupstream kinase in the AMP-activated protein kinase cascaderdquoCurrent Biology vol 13 no 22 pp 2004ndash2008 2003

[29] K Sakamoto O Goransson D G Hardie and D R AlessildquoActivity of LKB1 and AMPK-related kinases in skeletal muscleeffects of contraction phenformin and AICARrdquo AmericanJournal of PhysiologymdashEndocrinology and Metabolism vol 287no 2 pp E310ndashE317 2004

[30] R J ShawMKosmatkaN Bardeesy et al ldquoThe tumor suppres-sor LKB1 kinase directly activates AMP-activated kinase andregulates apoptosis in response to energy stressrdquo Proceedings ofthe National Academy of Sciences of the United States of Americavol 101 no 10 pp 3329ndash3335 2004

[31] Z Chen L Wang and Y Chen ldquoAntitumor mechanism ofmetformin via adenosine monophosphate-activated proteinkinase (AMPK) activationrdquoChinese Journal of Lung Cancer vol16 no 8 pp 427ndash432 2013

[32] D G Hardie ldquoAMP-activated protein kinase a key regulator ofenergy balance with many roles in human diseaserdquo Journal ofInternal Medicine vol 276 no 6 pp 543ndash559 2014

[33] W Li S M SaudM R Young G Chen and B Hua ldquoTargetingAMPK for cancer prevention and treatmentrdquoOncotarget vol 6no 10 pp 7365ndash7378 2015

[34] M Showkat M A Beigh and K I Andrabi ldquomTOR signalingin protein translation regulation implications in cancer genesisand therapeutic interventionsrdquoMolecular Biology Internationalvol 2014 Article ID 686984 14 pages 2014

[35] R N Eskander and K S Tewari ldquoExploiting the therapeuticpotential of the PI3K-AKT-mTOR pathway in enriched popu-lations of gynecologic malignanciesrdquo Expert Review of ClinicalPharmacology vol 7 no 6 pp 847ndash858 2014

[36] R Zoncu A Efeyan and D M Sabatini ldquomTOR from growthsignal integration to cancer diabetes and ageingrdquo NatureReviews Molecular Cell Biology vol 12 no 1 pp 21ndash35 2011

[37] D RMorales andADMorris ldquoMetformin in cancer treatmentand preventionrdquoTheAnnual Review ofMedicine vol 66 pp 17ndash29 2015

[38] K A Brown N I Hunger M Docanto and E R SimpsonldquoMetformin inhibits aromatase expression in human breastadipose stromal cells via stimulation of AMP-activated proteinkinaserdquo Breast Cancer Research and Treatment vol 123 no 2pp 591ndash596 2010

[39] K Inoki T Zhu and K-L Guan ldquoTSC2 mediates cellularenergy response to control cell growth and survivalrdquo Cell vol115 no 5 pp 577ndash590 2003

[40] D M Gwinn D B Shackelford D F Egan et al ldquoAMPKphosphorylation of raptor mediates a metabolic checkpointrdquoMolecular Cell vol 30 no 2 pp 214ndash226 2008

[41] D G Hardie ldquoAMPK and Raptor matching cell growth toenergy supplyrdquoMolecular Cell vol 30 no 3 pp 263ndash265 2008

[42] N E van der Sligte F J G Scherpen T G J Meeuwsen-deBoer et al ldquoKinase activity profiling reveals active signal trans-duction pathways in pediatric acute lymphoblastic leukemia anew approach for target discoveryrdquo Proteomics vol 15 no 7 pp1245ndash1254 2015

[43] B D Manning A R Tee M N Logsdon J Blenis and LC Cantley ldquoIdentification of the tuberous sclerosis complex-2 tumor suppressor gene product tuberin as a target of thephosphoinositide 3-kinaseAkt pathwayrdquoMolecular Cell vol 10no 1 pp 151ndash162 2002

[44] C J Potter L G Pedraza and T Xu ldquoAkt regulates growth bydirectly phosphorylating Tsc2rdquoNature Cell Biology vol 4 no 9pp 658ndash665 2002

[45] Y Sancak C C Thoreen T R Peterson et al ldquoPRAS40 isan insulin-regulated inhibitor of the mTORC1 protein kinaserdquoMolecular Cell vol 25 no 6 pp 903ndash915 2007

[46] S Horman D Vertommen R Heath et al ldquoInsulin antagonizesischemia-induced Thr172 phosphorylation of AMP-activatedprotein kinase 120572-subunits in heart via hierarchical phosphory-lation of Ser485491rdquoThe Journal of Biological Chemistry vol 281no 9 pp 5335ndash5340 2006

[47] Y Choudhury Z Yang I Ahmad C Nixon I P Salt andH Y Leung ldquoAMP-activated protein kinase (AMPK) as apotential therapeutic target independent of PI3KAkt signalingin prostate cancerrdquoOncoscience vol 1 no 6 pp 446ndash456 2014

[48] K Kisfalvi G Eibl J Sinnett-Smith and E Rozengurt ldquoMet-formin disrupts crosstalk between G protein-coupled receptorand insulin receptor signaling systems and inhibits pancreaticcancer growthrdquo Cancer Research vol 69 no 16 pp 6539ndash65452009

[49] A Isakovic L Harhaji D Stevanovic et al ldquoDual antigliomaaction of metformin cell cycle arrest and mitochondria-dependent apoptosisrdquo Cellular and Molecular Life Sciences vol64 no 10 pp 1290ndash1302 2007

[50] M Zakikhani R J ODowlingN Sonenberg andMN PollakldquoThe effects of adiponectin and metformin on prostate andcolon neoplasia involve activation of AMP-activated proteinkinaserdquo Cancer Prevention Research vol 1 no 5 pp 369ndash3752008

[51] B Markman R Dienstmann and J Tabernero ldquoTargeting thePI3KAktmTOR pathwaymdashbeyond rapalogsrdquo Oncotarget vol1 no 7 pp 530ndash543 2010

[52] I A Mayer and C L Arteaga ldquoThe PI3KAKT pathway as atarget for cancer treatmentrdquoAnnual Review of Medicine vol 67pp 11ndash28 2016

[53] R Rattan R P Graham J L Maguire S Giri and V ShridharldquoMetformin suppresses ovarian cancer growth and metastasiswith enhancement of cisplatin cytotoxicity in vivordquo Neoplasiavol 13 no 5 pp 483ndash491 2011

[54] R Shao X Li and H Billig ldquoPromising clinical practices ofmetformin in women with PCOS and early-stage endometrialcancerrdquo BBA Clinical vol 2 pp 7ndash9 2014

[55] R G Jones D R Plas S Kubek et al ldquoAMP-activatedprotein kinase induces a p53-dependent metabolic checkpointrdquoMolecular Cell vol 18 no 3 pp 283ndash293 2005

[56] I Leclerc C Lenzner L Gourdon S Vaulont A Kahn andB Viollet ldquoHepatocyte nuclear factor-4120572 involved in type 1


maturity-onset diabetes of the young is a novel target of AMP-activated protein kinaserdquo Diabetes vol 50 no 7 pp 1515ndash15212001

[57] J Liang S H Shao Z X Xu et al ldquoThe energy sensing LKB1-AMPK pathway regulates p27(kip1) phosphorylationmediatingthe decision to enter autophagy or apoptosisrdquo Nature CellBiology vol 9 no 2 pp 218ndash224 2007

[58] L A J OrsquoNeill and D G Hardie ldquoMetabolism of inflammationlimited by AMPK and pseudo-starvationrdquo Nature vol 493 no7432 pp 346ndash355 2013

[59] A Gambineri C Pelusi V Vicennati U Pagotto and RPasquali ldquoObesity and the polycystic ovary syndromerdquo Inter-national Journal of Obesity and RelatedMetabolic Disorders vol26 no 7 pp 883ndash896 2002

[60] E Carmina ldquoMetabolic syndrome in polycystic ovary syn-dromerdquoMinerva Ginecologica vol 58 no 2 pp 109ndash114 2006

[61] M-Y El-Mir V Nogueira E Fontaine N Averet M Rigouletand X Leverve ldquoDimethylbiguanide inhibits cell respiration viaan indirect effect targeted on the respiratory chain complex IrdquoThe Journal of Biological Chemistry vol 275 no 1 pp 223ndash2282000

[62] M R Owen E Doran and A P Halestrap ldquoEvidence thatmetformin exerts its anti-diabetic effects through inhibition ofcomplex 1 of the mitochondrial respiratory chainrdquo BiochemicalJournal vol 348 no 3 pp 607ndash614 2000

[63] J D McGarry and N F Brown ldquoThe mitochondrial carnitinepalmitoyltransferase system From concept to molecular analy-sisrdquo European Journal of Biochemistry vol 244 no 1 pp 1ndash141997

[64] Y Li S Xu M M Mihaylova et al ldquoAMPK phosphorylatesand inhibits SREBP activity to attenuate hepatic steatosis andatherosclerosis in diet-induced insulin-resistant micerdquo CellMetabolism vol 13 no 4 pp 376ndash388 2011

[65] C Tebbe J Chhina S A Dar et al ldquoMetformin limits theadipocyte tumor-promoting effect on ovarian cancerrdquoOncotar-get vol 5 no 13 pp 4746ndash4764 2014

[66] Z-J Zhang and S Li ldquoThe prognostic value of metformin forcancer patients with concurrent diabetes a systematic reviewand meta-analysisrdquo Diabetes Obesity and Metabolism vol 16no 8 pp 707ndash710 2014

[67] J Kasznicki A Sliwinska and J Drzewoski ldquoMetformin incancer prevention and therapyrdquo The Annals of TranslationalMedicine vol 2 no 6 p 57 2014

[68] Z-J Zhang Z-J Zheng R Shi Q Su Q Jiang and K E KipldquoMetformin for liver cancer prevention in patients with type 2diabetes a systematic review and meta-analysisrdquoThe Journal ofClinical Endocrinology amp Metabolism vol 97 no 7 pp 2347ndash2353 2012

[69] D A Iglesias M S Yates D van der Hoeven et al ldquoAnothersurprise frommetformin novel mechanism of action via k-Rasinfluences endometrial cancer response to therapyrdquo MolecularCancer Therapeutics vol 12 no 12 pp 2847ndash2856 2013

[70] Y Xie Y-L Wang L Yu et al ldquoMetformin promotes proges-terone receptor expression via inhibition of mammalian targetof rapamycin (mTOR) in endometrial cancer cellsrdquoThe Journalof Steroid Biochemistry and Molecular Biology vol 126 no 3ndash5pp 113ndash120 2011

[71] H Liao Q Zhou Y Gu T Duan and Y Feng ldquoLuteinizinghormone facilitates angiogenesis in ovarian epithelial tumorcells and metformin inhibits the effect through the mTORsignaling pathwayrdquo Oncology Reports vol 27 no 6 pp 1873ndash1878 2012

[72] C Algire OMoiseeva X Deschenes-Simard et al ldquoMetforminreduces endogenous reactive oxygen species and associatedDNA damagerdquo Cancer Prevention Research vol 5 no 4 pp536ndash543 2012

[73] S Jiralerspong S L Palla S H Giordano et al ldquoMetformin andpathologic complete responses to neoadjuvant chemotherapyin diabetic patients with breast cancerrdquo Journal of ClinicalOncology vol 27 no 20 pp 3297ndash3302 2009

[74] R J O Dowling M Zakikhani I G Fantus M Pollakand N Sonenberg ldquoMetformin inhibits mammalian target ofrapamycin-dependent translation initiation in breast cancercellsrdquo Cancer Research vol 67 no 22 pp 10804ndash10812 2007

[75] M Zakikhani R Dowling I G Fantus N Sonenberg andM Pollak ldquoMetformin is an AMP kinase-dependent growthinhibitor for breast cancer cellsrdquo Cancer Research vol 66 no21 pp 10269ndash10273 2006

[76] B Liu Z Fan S M Edgerton et al ldquoMetformin induces uniquebiological and molecular responses in triple negative breastcancer cellsrdquo Cell Cycle vol 8 no 13 pp 2031ndash2040 2009

[77] H A Hirsch D Iliopoulos P N Tsichlis and K Struhl ldquoMet-formin selectively targets cancer stem cells and acts togetherwith chemotherapy to block tumor growth and prolong remis-sionrdquo Cancer Research vol 69 no 19 pp 7507ndash7511 2009

[78] A Vazquez-Martin C Oliveras-Ferraros S Del Barco BMartin-Castillo and J A Menendez ldquoThe anti-diabeticdrug metformin suppresses self-renewal and proliferationof trastuzumab-resistant tumor-initiating breast cancer stemcellsrdquo Breast Cancer Research and Treatment vol 126 no 2 pp355ndash364 2011

[79] A Vazquez-Martin C Oliveras-Ferraros S Cufı S Del BarcoB Martin-Castilloand and J A Menendez ldquoMetformin regu-lates breast cancer stem cell ontogeny by transcriptional regu-lation of the epithelial-mesenchymal transition (EMT) statusrdquoCell Cycle vol 9 no 18 pp 3807ndash3814 2010

[80] G Stabile I Borrielli A C Artenisio et al ldquoEffects of theinsulin sensitizer pioglitazone onmenstrual irregularity insulinresistance and hyperandrogenism in young women with poly-cystic ovary syndromerdquoThe Journal of Pediatric and AdolescentGynecology vol 27 no 3 pp 177ndash182 2014

[81] P Froment and P Touraine ldquoThiazolidinediones and fertility inpolycystic ovary syndrome (PCOS)rdquo PPAR Research vol 2006Article ID 73986 8 pages 2006

[82] B Desvergne andW Wahli ldquoPeroxisome proliferator-activatedreceptors nuclear control of metabolismrdquo Endocrine Reviewsvol 20 no 5 pp 649ndash688 1999

[83] D J Kojetin E Matta-Camacho T S Hughes et al ldquoStructuralmechanism for signal transduction in RXR nuclear receptorheterodimersrdquo Nature Communications vol 6 article 80132015

[84] H Yki-Jarvinen ldquoThiazolidinedionesrdquo The New England Jour-nal of Medicine vol 351 no 11 pp 1106ndash1118 2004

[85] J Girard ldquoMechanisms of action of thiazolidinedionesrdquo Dia-betes amp Metabolism vol 27 part 2 pp 271ndash278 2001

[86] A Dunaif and A Thomas ldquoCurrent concepts in the polycysticovary syndromerdquo Annual Review of Medicine vol 52 pp 401ndash419 2001

[87] R Azziz D Ehrmann R S Legro et al ldquoTroglitazone improvesovulation and hirsutism in the polycystic ovary syndrome amulticenter double blind placebo-controlled trialrdquo Journal ofClinical Endocrinology and Metabolism vol 86 no 4 pp 1626ndash1632 2001


[88] W H Hu L Chen J Tong C Y Zhao S Mao and JQiao ldquoExpression of PPAR120574 mRNA in granulosa cells andits correlation with clinical characteristics of polycystic ovarysyndromerdquo Beijing Da Xue Xue Bao vol 45 no 6 pp 859ndash8632013

[89] S GasicMNagamani A Green and R J Urban ldquoTroglitazoneis a competitive inhibitor of 3120573-hydroxysteroid dehydrogenaseenzyme in the ovaryrdquo American Journal of Obstetrics andGynecology vol 184 no 4 pp 575ndash579 2001

[90] Y-M Mu T Yanase Y Nishi et al ldquoInsulin sensitizer trogli-tazone directly inhibits aromatase activity in human ovariangranulosa cellsrdquo Biochemical and Biophysical Research Commu-nications vol 271 no 3 pp 710ndash713 2000

[91] N K LeBrasseur M Kelly T-S Tsao et al ldquoThiazolidinedionescan rapidly activate AMP-activated protein kinase in mam-malian tissuesrdquoAmerican Journal of PhysiologymdashEndocrinologyand Metabolism vol 291 no 1 pp E175ndashE181 2006

[92] D K Shah K M J Menon L M Cabrera A Vahratian SK Kavoussi and D I Lebovic ldquoThiazolidinediones decreasevascular endothelial growth factor (VEGF) production byhuman luteinized granulosa cells in vitrordquo Fertility and Sterilityvol 93 no 6 pp 2042ndash2047 2010

[93] A Stuckey A Fischer D H Miller et al ldquoIntegrated genomicsof ovarian xenograft tumor progression and chemotherapyresponserdquo BMC Cancer vol 11 article 308 2011

[94] T M Livermore C Azevedo B Kolozsvari M S C Wilsonand A Saiardi ldquoPhosphate inositol and polyphosphatesrdquo Bio-chemical Society Transactions vol 44 no 1 pp 253ndash259 2016

[95] K S Robinson K Lai T A Cannon and P McGraw ldquoInositoltransport in Saccharomyces cerevisiae is regulated by tran-scriptional and degradative endocytic mechanisms during thegrowth cycle that are distinct from inositol-induced regulationrdquoMolecular Biology of the Cell vol 7 no 1 pp 81ndash89 1996

[96] S Schneider ldquoInositol transport proteinsrdquo FEBS Letters vol589 no 10 pp 1049ndash1058 2015

[97] C P Downes and C H Macphee ldquomyo-inositol metabolites ascellular signalsrdquo European Journal of Biochemistry vol 193 no1 pp 1ndash18 1990

[98] K Strange R Morrison C W Heilig S DiPietro and S RGullans ldquoUpregulation of inositol transport mediates inositolaccumulation in hyperosmolar brain cellsrdquoThe American Jour-nal of PhysiologymdashCell Physiology vol 260 no 4 part 1 ppC784ndashC790 1991

[99] M L Croze and C O Soulage ldquoPotential role and therapeuticinterests of myo-inositol in metabolic diseasesrdquo Biochimie vol95 no 10 pp 1811ndash1827 2013

[100] A Bevilacqua and M Bizzarri ldquoPhysiological role and clinicalutility of inositols in polycystic ovary syndromerdquo Best Practiceamp Research Clinical Obstetrics amp Gynaecology 2016

[101] P Manna and S K Jain ldquoPhosphatidylinositol-345-triphosphate and cellular signaling implications for obesityand diabetesrdquo Cellular Physiology and Biochemistry vol 35 no4 pp 1253ndash1275 2015

[102] J M Stevenson I Y Perera I Heilmann S Persson and WF Boss ldquoInositol signaling and plant growthrdquo Trends in PlantScience vol 5 no 6 pp 252ndash258 2000

[103] R Valluru and W Van den Ende ldquoMyo-inositol and beyondmdashemerging networks under stressrdquo Plant Science vol 181 no 4pp 387ndash400 2011

[104] T Balla ldquoPhosphoinositides tiny lipids with giant impact oncell regulationrdquo Physiological Reviews vol 93 no 3 pp 1019ndash1137 2013

[105] D Maag M J Maxwell D A Hardesty et al ldquoInositolpolyphosphate multikinase is a physiologic PI3-kinase thatactivates AktPKBrdquo Proceedings of the National Academy ofSciences of the United States of America vol 108 no 4 pp 1391ndash1396 2011

[106] A Chakraborty M A Koldobskiy N T Bello et al ldquoInositolpyrophosphates inhibit akt signaling thereby regulating insulinsensitivity and weight gainrdquo Cell vol 143 no 6 pp 897ndash9102010

[107] S Bang Y Chen R S Ahima and S F Kim ldquoConvergenceof IPMK and LKB1-AMPK signaling pathways on metforminactionrdquo Molecular Endocrinology vol 28 no 7 pp 1186ndash11932014

[108] J-Y Lee Y-R Kim J Park and S Kim ldquoInositol polyphosphatemultikinase signaling in the regulation of metabolismrdquo Annalsof the New York Academy of Sciences vol 1271 no 1 pp 68ndash742012

[109] S Kim S F Kim D Maag et al ldquoAmino acid signaling tomTOR mediated by inositol polyphosphate multikinaserdquo CellMetabolism vol 13 no 2 pp 215ndash221 2011

[110] R M Deranieh and M L Greenberg ldquoCellular consequencesof inositol depletionrdquo Biochemical Society Transactions vol 37no 5 pp 1099ndash1103 2009

[111] J E Nestler D J Jakubowicz P Reamer R D Gunn and GAllan ldquoOvulatory and metabolic effects of D-chiro-inositol inthe polycystic ovary syndromerdquo The New England Journal ofMedicine vol 340 no 17 pp 1314ndash1320 1999

[112] J-P Baillargeon M J Iuorno T Apridonidze and J E NestlerldquoUncoupling between insulin and release of a d-chiro-inositol-containing inositolphosphoglycan mediator of insulin actionin obese women with polycystic ovary syndromerdquo MetabolicSyndrome and Related Disorders vol 8 no 2 pp 127ndash136 2010

[113] V Unfer G Carlomagno G Dante and F Facchinetti ldquoEffectsof myo-inositol in women with PCOS a systematic review ofrandomized controlled trialsrdquoGynecological Endocrinology vol28 no 7 pp 509ndash515 2012

[114] S Gerli E Papaleo A Ferrari and G C Di Renzo ldquoRan-domized double blind placebo-controlled trial effects of myo-inositol on ovarian function and metabolic factors in womenwith PCOSrdquo European Review for Medical and PharmacologicalSciences vol 11 no 5 pp 347ndash354 2007

[115] P G Artini O M Di Berardino F Papini et al ldquoEndocrineand clinical effects of myo-inositol administration in poly-cystic ovary syndrome A randomized studyrdquo GynecologicalEndocrinology vol 29 no 4 pp 375ndash379 2013

[116] F Facchinetti G Dante and I Neri ldquoThe ratio of MI toDCI and its impact in the treatment of polycystic ovarysyndrome experimental and literature evidencesrdquo in Frontiersin Gynecological Endocrinology Volume 3 Ovarian Functionand ReproductionmdashFrom Needs to Possibilities ISGE Series pp103ndash109 Springer Berlin Germany 2016

[117] M Nordio and E Proietti ldquoThe combined therapy with myo-inositol and D-chiro-inositol reduces the risk of metabolicdisease in PCOS overweight patients compared to myo-inositolsupplementation alonerdquo European Review for Medical andPharmacological Sciences vol 16 no 5 pp 575ndash581 2012

[118] M Minozzi M Nordio and R Pajalich ldquoThe combinedtherapy myo-inositol plus D-chiro-inositol in a physiologicalratio reduces the cardiovascular risk by improving the lipidprofile in PCOS patientsrdquo European Review for Medical andPharmacological Sciences vol 17 no 4 pp 537ndash540 2013


[119] S Colazingari M Treglia R Najjar and A Bevilacqua ldquoThecombined therapy myo-inositol plus D-chiro-inositol ratherthan D-chiro-inositol is able to improve IVF outcomes resultsfrom a randomized controlled trialrdquoArchives of Gynecology andObstetrics vol 288 no 6 pp 1405ndash1411 2013

[120] R Isabella and E Raffone ldquoDoes ovary need D-chiro-inositolrdquoJournal of Ovarian Research vol 5 no 1 article 14 2012

[121] E Papaleo V Unfer J-P Baillargeon et al ldquoMyo-inositol inpatients with polycystic ovary syndrome a novel method forovulation inductionrdquo Gynecological Endocrinology vol 23 no12 pp 700ndash703 2007

[122] J-P Baillargeon J E Nestler R E Ostlund T Apridonidzeand EDiamanti-Kandarakis ldquoGreek hyperinsulinemicwomenwith or without polycystic ovary syndrome display alteredinositols metabolismrdquo Human Reproduction vol 23 no 6 pp1439ndash1446 2008

[123] K I Cheang J-P Baillargeon P A Essah et al ldquoInsulin-stimulated release of d-chiro-inositol-containing inositolphos-phoglycan mediator correlates with insulin sensitivity inwomen with polycystic ovary syndromerdquo Metabolism Clinicaland Experimental vol 57 no 10 pp 1390ndash1397 2008

[124] M Falasca D Chiozzotto H Y Godage et al ldquoA novel inhibitorof the PI3KAkt pathway based on the structure of inositol13456-pentakisphosphaterdquo British Journal of Cancer vol 102no 1 pp 104ndash114 2010

[125] W Han J J Gills R M Memmott S Lam and P A DennisldquoThe chemopreventive agent myoinositol inhibits Akt andextracellular signal-regulated kinase in bronchial lesions fromheavy smokersrdquo Cancer Prevention Research vol 2 no 4 pp370ndash376 2009

[126] S LamAMcWilliams J LeRiche CMacAulay LWattenbergand E Szabo ldquoA phase I study of myo-inositol for lungcancer chemopreventionrdquo Cancer Epidemiology Biomarkers ampPrevention vol 15 no 8 pp 1526ndash1531 2006

[127] I Vucenik and A M Shamsuddin ldquoProtection against cancerby dietary IP6 and inositolrdquoNutrition and Cancer vol 55 no 2pp 109ndash125 2006

[128] Z Dong C Huang and W-Y Ma ldquoPI-3 kinase in signaltransduction cell transformation and as a target for chemopre-vention of cancerrdquo Anticancer Research vol 19 no 5 pp 3743ndash3747 1999

[129] Z Liu T-T Zhang J-J Zhao et al ldquoThe association betweenoverweight obesity and ovarian cancer a meta-analysisrdquo TheJapanese Journal of Clinical Oncology vol 45 no 12 pp 1107ndash1115 2015

[130] B R Rao and B J Slotman ldquoEndocrine factors in commonepithelial ovarian cancerrdquo Endocrine Reviews vol 12 no 1 pp14ndash26 1991

[131] A Berchuck G J Olt L Everitt A P Soisson R C Bast Jr andC M Boyer ldquoThe role of peptide growth factors in epithelialovarian cancerrdquoObstetrics amp Gynecology vol 75 no 2 pp 255ndash262 1990

[132] A Gadducci A Gargini E Palla A Fanucchi andA R Genaz-zani ldquoPolycystic ovary syndrome and gynecological cancers isthere a linkrdquo Gynecological Endocrinology vol 20 no 4 pp200ndash208 2005

[133] E G Silva C Tornos H A Fritsche Jr et al ldquoThe inductionof benign epithelial neoplasms of the ovaries of guinea pigsby testosterone stimulation a potential animal modelrdquoModernPathology vol 10 no 9 pp 879ndash883 1997

[134] A Evangelou S K Jindal T J Brown and M LetarteldquoDown-regulation of transforming growth factor 120573 receptors by

androgen in ovarian cancer cellsrdquo Cancer Research vol 60 no4 pp 929ndash935 2000

[135] M F Fathalla ldquoIncessant ovulationmdasha factor in ovarian neopla-siardquoThe Lancet vol 298 no 7716 p 163 1971

[136] T Riman S Nilsson and I R Persson ldquoReview of epidemiolog-ical evidence for reproductive and hormonal factors in relationto the risk of epithelial ovarian malignanciesrdquo Acta Obstetriciaet Gynecologica Scandinavica vol 83 no 9 pp 783ndash795 2004

[137] D A Dumesic and R A Lobo ldquoCancer risk and PCOSrdquoSteroids vol 78 no 8 pp 782ndash785 2013

[138] The Rotterdam ESHREASRM-Sponsored PCOS ConsensusWorkshop Group ldquoRevised 2003 consensus on diagnosticcriteria and long-term health risks related to polycystic ovarysyndromerdquo Fertility and Sterility vol 81 no 1 pp 19ndash25 2004

[139] J M Schildkraut P J Schwingl E Bastos A Evanoff and CHughes ldquoEpithelial ovarian cancer risk among women withpolycystic ovary syndromerdquo Obstetrics amp Gynecology vol 88no 4 part 1 pp 554ndash559 1996

[140] A Balen ldquoPolycystic ovary syndrome and cancerrdquo HumanReproduction Update vol 7 no 6 pp 522ndash525 2001

[141] C M Olsen A C Green C M Nagle et al ldquoEpithelial ovariancancer testing the lsquoandrogens hypothesisrsquordquo Endocrine-RelatedCancer vol 15 no 4 pp 1061ndash1068 2008

[142] M Bodmer C Becker C Meier S S Jick and C R MeierldquoUse ofmetformin and the risk of ovarian cancer a case-controlanalysisrdquo Gynecologic Oncology vol 123 no 2 pp 200ndash2042011

[143] N Galazis O Olaleye Z Haoula R Layfield and W AtiomoldquoProteomic biomarkers for ovarian cancer risk in women withpolycystic ovary syndrome a systematic review and biomarkerdatabase integrationrdquo Fertility and Sterility vol 98 no 6 pp1590e1ndash1601e1 2012

[144] J A Barry M M Azizia and P J Hardiman ldquoRisk of endome-trial ovarian and breast cancer in women with polycystic ovarysyndrome a systematic review and meta-analysisrdquo HumanReproduction Update vol 20 no 5 pp 748ndash758 2014

[145] C-C Shen A C Yang J-H Hung L-Y Hu and S-J TsaildquoA nationwide population-based retrospective cohort study ofthe risk of uterine ovarian and breast cancer in women withpolycystic ovary syndromerdquo Oncologist vol 20 no 1 pp 45ndash49 2015

[146] M Gottschau S K Kjaer A Jensen C Munk and L Mellemk-jaer ldquoRisk of cancer among women with polycystic ovarysyndrome a Danish cohort studyrdquo Gynecologic Oncology vol136 no 1 pp 99ndash103 2015

[147] D J Joly A M Lilienfeld E L Diamond and I D J BrossldquoAn epidemiologic study of the relationship of reproductiveexperience to cancer of the ovaryrdquo The American Journal ofEpidemiology vol 99 no 3 pp 190ndash209 1974

[148] J-Y Lee I Jeon J W Kim Y-S Song J-M Yoon andS M Park ldquoDiabetes mellitus and ovarian cancer risk asystematic review and meta-analysis of observational studiesrdquoInternational Journal of Gynecological Cancer vol 23 no 3 pp402ndash412 2013

[149] C Rodriguez E E Calle D Fakhrabadi-Shokoohi E J Jacobsand M J Thun ldquoBody mass index height and the risk of ovar-ian cancer mortality in a prospective cohort of postmenopausalwomenrdquoCancer Epidemiology Biomarkers amp Prevention vol 11no 9 pp 822ndash828 2002

[150] G Libby L A Donnelly P T Donnan D R Alessi A DMorris and J M M Evans ldquoNew users of metformin are at low


risk of incident cancer a cohort study among people with type2 diabetesrdquo Diabetes Care vol 32 no 9 pp 1620ndash1625 2009

[151] JMM Evans L A Donnelly AM Emslie-Smith D R Alessiand A D Morris ldquoMetformin and reduced risk of cancer indiabetic patientsrdquo BritishMedical Journal vol 330 no 7503 pp1304ndash1305 2005

[152] L A Stadtmauer B C Wong and S Oehninger ldquoShouldpatients with polycystic ovary syndrome be treated with met-formin Benefits of insulin sensitizing drugs in polycystic ovarysyndromemdashbeyond ovulation inductionrdquo Human Reproduc-tion vol 17 no 12 pp 3016ndash3026 2002

[153] httpwwwcancerorgresearchcancerfactsstatisticscancer-factsfigures2015

[154] T Fornander B Cedermark A Mattsson et al ldquoAdjuvanttamoxifen in early breast cancer occurrence of new primarycancersrdquoThe Lancet vol 333 no 8630 pp 117ndash120 1989

[155] Y Tingthanatikul W Choktanasiri M Rochanawutanon andSWeerakeit ldquoPrevalence and clinical predictors of endometrialhyperplasiain anovulatory women presenting with amenor-rheardquo Gynecological Endocrinology vol 22 no 2 pp 101ndash1052006

[156] N S L Holm D Glintborg M S Andersen D Schledermannand P Ravn ldquoThe prevalence of endometrial hyperplasia andendometrial cancer in women with polycystic ovary syndromeor hyperandrogenismrdquoActa Obstetricia et Gynecologica Scandi-navica vol 91 no 10 pp 1173ndash1176 2012

[157] M N Shafiee G Khan R Ariffin et al ldquoPreventing endome-trial cancer risk in polycystic ovarian syndrome (PCOS)women couldmetformin helprdquoGynecologic Oncology vol 132no 1 pp 248ndash253 2014

[158] P Hardiman O S Pillay and W Atiomo ldquoPolycystic ovarysyndrome and endometrial carcinomardquoTheLancet vol 361 no9371 pp 1810ndash1812 2003

[159] Z Haoula M Salman and W Atiomo ldquoEvaluating the asso-ciation between endometrial cancer and polycystic ovary syn-dromerdquoHuman Reproduction vol 27 no 5 pp 1327ndash1331 2012

[160] G Zhang X Li L Zhang et al ldquoThe expression and roleof hybrid insulininsulin-like growth factor receptor type 1 inendometrial carcinoma cellsrdquoCancer Genetics and Cytogeneticsvol 200 no 2 pp 140ndash148 2010

[161] E E Sheets J C M Tsibris N I Cook S D Virgin RM DeMay and W N Spellacy ldquoIn vitro binding of insulinand epidermal growth factor to human endometrium andendocervixrdquo American Journal of Obstetrics and Gynecologyvol 153 no 1 pp 60ndash65 1985

[162] A Zucchetto D Serraino J Polesel et al ldquoHormone-relatedfactors and gynecological conditions in relation to endometrialcancer riskrdquo European Journal of Cancer Prevention vol 18 no4 pp 316ndash321 2009

[163] S Wild T Pierpoint H Jacobs and P McKeigue ldquoLong-termconsequences of polycystic ovary syndrome results of a 31 yearfollow-up studyrdquoHumanFertility vol 3 no 2 pp 101ndash105 2000

[164] E J Fearnley L Marquart A B Spurdle P Weinstein andP M Webb ldquoPolycystic ovary syndrome increases the riskof endometrial cancer in women aged less than 50 years anAustralian case-control studyrdquoCancer Causes amp Control vol 21no 12 pp 2303ndash2308 2010

[165] K Niwa A Imai M Hashimoto et al ldquoA case-control studyof uterine endometrial cancer of pre- and post-menopausalwomenrdquo Oncology Reports vol 7 no 1 pp 89ndash93 2000

[166] B G Chittenden G Fullerton A Maheshwari and S Bhat-tacharya ldquoPolycystic ovary syndrome and the risk of gynaeco-logical cancer a systematic reviewrdquo Reproductive BioMedicineOnline vol 19 no 3 pp 398ndash405 2009

[167] L G Escobedo N C Lee H B Peterson and P A WingoldquoInfertility-associated endometrial cancer riskmay be limited tospecific subgroups of infertile womenrdquoObstetricsampGynecologyvol 77 no 1 pp 124ndash128 1991

[168] B C J M Fauser B C Tarlatzis R W Rebar et al ldquoConsen-sus on womenrsquos health aspects of polycystic ovary syndrome(PCOS) the Amsterdam ESHREASRM-Sponsored 3rd PCOSConsensus Workshop Grouprdquo Fertility and Sterility vol 97 no1 pp 28ndashe25 2012

[169] R J Shaw K A Lamia D Vasquez et al ldquoThe kinase LKB1mediates glucose homeostasis in liver and therapeutic effects ofmetforminrdquo Science vol 310 no 5754 pp 1642ndash1646 2005

[170] S Dronavalli and D A Ehrmann ldquoPharmacologic therapy ofpolycystic ovary syndromerdquo Clinical Obstetrics and Gynecologyvol 50 no 1 pp 244ndash254 2007

[171] T Sinai T Tang and E Yasmin ldquoRole of metformin in womenrsquoshealth review of its current place in clinical practice andemerging indications for futurerdquo Obstetrical amp GynecologicalSurvey vol 71 no 5 pp 307ndash317 2016

[172] L Aghajanova M C Velarde and L C Giudice ldquoAltered geneexpression profiling in endometrium evidence for progesteroneresistancerdquo Seminars in ReproductiveMedicine vol 28 no 1 pp51ndash58 2010

[173] X Li Y Feng J-F Lin H Billig and R Shao ldquoEndometrial pro-gesterone resistance and PCOSrdquo Journal of biomedical sciencevol 21 article 2 2014

[174] R Sarfstein Y Friedman Z Attias-Geva A Fishman IBruchim and H Werner ldquoMetformin downregulates theinsulinIGF-I signaling pathway and inhibits different uterineserous carcinoma (USC) cells proliferation and migration inp53-dependent or -independent mannersrdquo PLoS ONE vol 8no 4 Article ID e61537 2013

[175] N S Nevadunsky A Van Arsdale H D Strickler et alldquoMetformin use and endometrial cancer survivalrdquo GynecologicOncology vol 132 no 1 pp 236ndash240 2014

[176] E M Ko P Walter A Jackson et al ldquoMetformin is associatedwith improved survival in endometrial cancerrdquo GynecologicOncology vol 132 no 2 pp 438ndash442 2014

[177] C Becker S S Jick C R Meier and M Bodmer ldquoMetforminand the risk of endometrial cancer a case-control analysisrdquoGynecologic Oncology vol 129 no 3 pp 565ndash569 2013

[178] M Costello B Shrestha J Eden P Sjoblom and N JohnsonldquoInsulin-sensitising drugs versus the combined oral contracep-tive pill for hirsutism acne and risk of diabetes cardiovasculardisease and endometrial cancer in polycystic ovary syndromerdquoThe Cochrane Database of Systematic Reviews vol 1 Article IDCD005552 2007

[179] ldquoMetformin for the Treatment of Endometrial HyperplasiardquoClinicalTrialsgov Identifier NCT01685762 2016 httpsclini-caltrialsgovct2home

[180] UNC Lineberger Comprehensive Cancer Center ldquoMetforminwith the levonorgestrel-releasing intrauterine device for thetreatment of complex atypical hyperplasia (CAH) and endome-trial cancer (EC) in non-surgical patientsrdquo clinical trialgovidentifier NCT 02035787 2016

Submit your manuscripts athttpwwwhindawicom

Stem CellsInternational

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014


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of


Behavioural Neurology

EndocrinologyInternational Journal of



Disease Markers


BioMed Research International

OncologyJournal of



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The Scientific World JournalHindawi Publishing Corporation httpwwwhindawicom Volume 2014

Immunology ResearchHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

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Parkinsonrsquos Disease

Evidence-Based Complementary and Alternative Medicine

Volume 2014Hindawi Publishing Corporationhttpwwwhindawicom


androgen production Chan indicates that using insulin-sensitizers may have a role as a tool for cancer prevention[9] In the present review we try to hypothesize a possi-ble rationale through which insulin-sensitizers may inhibittumourigenesis (Figure 1)

2 Insulin Receptor Signaling andPhosphoinositide Pathways

Insulin receptor is a transmembrane receptor encoded by asingle gene belonging to the large class of tyrosine kinasereceptors [3] It is activated by insulin insulin growth factor1 (IGF-I) and insulin growth factor 2 (IGF-II) [16] The mainactivity of the IR when bound by an insulin molecule isinducing glucose uptake For this reason a decreased sensi-tivity in insulin receptor signaling associated with impairedglycogen synthesis and inhibition of glycogen breakdownprogressively leads tometabolic disorders and type 2 diabetesmellitus [17] Peripheral insulin resistance is then definedby a decrease in insulin-dependent glucose transport atthe level of target tissues [18] due to defects at both theinsulin receptor andor postreceptor signaling [19] Followinghormone binding the IR undergoes conformational changeswhich allow autophosphorylation of its tyrosine residuesdocking sites for insulin receptor substrates (IRSs) involved inphosphatidylinositol-3-kinase (PI3K) activation and recruit-ment to the plasma membrane of the serinethreonine pro-tein kinase AktPKB which represents the main intracellularinterconnecting pathway activated to ensure insulin biologi-cal action together with the mitogen-activated protein kinase(MAPK)extracellular-signaling regulated protein kinase 12(ERK 12) pathway [20 21] Inmammals almost five isoformsof the regulatory subunit of PI3K interact with IRSs activatingthe catalytic subunit and phosphorylating the phosphatidyli-nositol 45-biphosphate [PI(45)P2] which in turn enablesother phosphoinositide dependent kinases [mainly phos-phatidylinositol 345-trisphosphate PI(345)P3] involved inthe phosphoinositide signaling system and in the signaling ofthe glucose transporter type 4 (GLUT4) the main GLUT-likeprotein identified in mammals [22] The phosphoinositidesignaling system plays a pivotal role in the regulation ofcellular processes such as vesicle transport cell proliferationand cytoskeletal remodeling [23] and its deregulation maylead to many diseases including cancer [24] Glucose uptakefor cellular function is additionally regulated by a sensor ofintracellular energy level the 51015840 adenosine monophosphate-activated protein kinase (AMPK) pathway AMPK is a highlyconserved serinethreonine protein kinase that appears touniversally exist as heterotrimeric complex comprised of cat-alytic 120572-subunit and regulatory 120573- and 120574-subunits [25] Likeseveral other protein kinases AMPK and its orthologues areonly significantly active when phosphorylated by upstreamkinases at the level of a conserved threonine (Thr172) withinthe kinase domain [26] In mammals the main upstreamkinase phosphorylating Thr172 is the liver kinase 1-Ste20-Related Adaptor-Mouse protein 25 (LKB1-STRAD-MO25)heterotrimeric complex a biologically active unit containingthe tumour suppressor kinase LKB1 [27 28]This complex isconstitutively active and presents a high basal activity [29]

however its ability to phosphorylate Thr172 is improved byconformational changes in its AMPK substrate due to thebinding of 51015840 adenosine monophosphate (AMP) active toits 120574-subunit Moreover kinases that can activate AMPKalso include calciumcalmodulin-dependent protein kinase(CaMKK) [30] and transforming growth factor 120573-activatedkinase 1 (TAK1) [31] Overall AMPK maintains cellularenergy homeostasis and its activation by metabolic stress(accountable of energy depletion) leads to inhibition of cellgrowth and promotion of adenosine-51015840-triphosphate (ATP)production Indeed once activated AMPK can encouragecatabolic pathways and inhibit anabolic pathways to restoreenergy stores [32] Furthermore many of the biosyntheticpathways such as synthesis of triglycerides fatty acidsphospholipids sterols glycogen proteins and ribosomalRNA are switched off by AMPK These pathways are sub-ject to a AMPK dependent downregulation via multiplemechanisms involving both phosphorylation of pathway keyenzymes and longer-term effects on gene expression [32]As a molecular target of metformin AMPK is a known keypoint in the treatment of metabolic syndrome and type 2diabetes Recently AMPK is emerging as a possiblemetabolictumour suppressor and a target for cancer prevention andtreatment Moreover it has been observed that AMPKdownstream targets can influence many effector proteinsinvolved in various regulatory processes that contribute to thepathogenesis of cancer Even if AMPK negatively regulatescyclooxygenase 2 (COX-2) a proinflammatory enzyme asso-ciated with tumourigenesis and can induce phosphorylationof tumour suppressor p53 resulting in cell cycle arrestthe main molecular mechanism involved in the AMPK-mediated tumour suppression is the negative regulation ofPI3KAktmTOR signaling pathway [33] mTOR is a ser-inethreonine protein kinase that regulates cellular processesincluding proliferation growth motility survival proteinsynthesis and transcription [34 35] mTOR forms two func-tionally distinct complexes mTORC1 andmTOR2 mTORC1a central signaling node that integrates signals arising fromgrowth factors nutrient availability and energy status [36]promotes cell growth by phosphorylating ribosomal proteinS6 kinase 1 (S6K1) and Eukaryotic Translation InitiationFactor 4E-Binding Protein 1 (4E-BP1) [37 38] Inhibitionof mTORC1 signaling by AMPK occurs via dual pathwaysFirst AMPK phosphorylates tuberous sclerosis complex-2(TSC2) [39] which converts the Ras homolog enriched in thebrain (RHEB) a GTP-binding protein activating upstreammTORC1 to its inactive GDP-bound form In a second timeAMPK phosphorylates a regulatory-associated protein ofmTOR (RPTOR or Raptor) a subunit of the mTORC1 com-plex inhibiting it [40 41] As AMPK is considered the mostimportant molecular effector of metformin it may functionas an important key-regulator of cellular energy homeostasisTherefore it is activated in response to a shortage of energyin order to boost cellular catabolic activities [42] On thecontrary insulin which is an anabolic hormone releasedby nutrient intake induces cell growth and energy storageIt is therefore not surprising that there is an antagonismbetween these two pathways AMPK negatively modulatesmTOR through the phosphorylation of TSC2 and Raptor



uarr AMPK

uarr AMPATP

Aromatase

CYP17

Theca cells






uarr testosterone

darr SHBG

OCT1

Insulinsensitizers

Insulinsensitizers

Insulinsensitizers

Polycystic ovary

Liver


effects

Androgens

LH


Hyperinsulinemia

Anteriorpituitary





Cytokinereceptor

Insulin

GPCR

IRS

p110

PTEN

PI3K

IR

P P

P

PI(34)P2 PI(45)P2PI(345)P3

IP3 DAG

RAC1


PKC

Transformation

PDK1

Survival

AKT


Protein translation


BAD

Apoptosis


NF-120581B

GSK3120573

PLC120574

P85120572




















Insulin resistance


Myo-Insmetformin

AMP

LKB1

CAMMK120573

ACC P53 COX2


Cell cyclearrest

Tumorigenesis


IR

IRS-1PIP3

PKC JNKNF-120581B

GLUT4

AKTAMPK

TSC1

TSC2

Pras40

RHEBGDP

RHEBGTP mTORC1

mTOR Raptor

6SK1 4EBP1

















uarr serum IGF-1















MTF metformin




6 Conclusions




Abbreviations
















Competing Interests




Acknowledgments


References


































































































































































































of






Disease Markers



OncologyJournal of





PPAR Research



Journal of

ObesityJournal of


















uarr AMPK

uarr AMPATP

Aromatase

CYP17

Theca cells






uarr testosterone

darr SHBG

OCT1

Insulinsensitizers

Insulinsensitizers

Insulinsensitizers

Polycystic ovary

Liver


effects

Androgens

LH


Hyperinsulinemia

Anteriorpituitary





Cytokinereceptor

Insulin

GPCR

IRS

p110

PTEN

PI3K

IR

P P

P

PI(34)P2 PI(45)P2PI(345)P3

IP3 DAG

RAC1


PKC

Transformation

PDK1

Survival

AKT


Protein translation


BAD

Apoptosis


NF-120581B

GSK3120573

PLC120574

P85120572




















Insulin resistance


Myo-Insmetformin

AMP

LKB1

CAMMK120573

ACC P53 COX2


Cell cyclearrest

Tumorigenesis


IR

IRS-1PIP3

PKC JNKNF-120581B

GLUT4

AKTAMPK

TSC1

TSC2

Pras40

RHEBGDP

RHEBGTP mTORC1

mTOR Raptor

6SK1 4EBP1

















uarr serum IGF-1















MTF metformin




6 Conclusions




Abbreviations
















Competing Interests




Acknowledgments


References


































































































































































































of






Disease Markers



OncologyJournal of





PPAR Research



Journal of

ObesityJournal of

















Cytokinereceptor

Insulin

GPCR

IRS

p110

PTEN

PI3K

IR

P P

P

PI(34)P2 PI(45)P2PI(345)P3

IP3 DAG

RAC1


PKC

Transformation

PDK1

Survival

AKT


Protein translation


BAD

Apoptosis


NF-120581B

GSK3120573

PLC120574

P85120572




















Insulin resistance


Myo-Insmetformin

AMP

LKB1

CAMMK120573

ACC P53 COX2


Cell cyclearrest

Tumorigenesis


IR

IRS-1PIP3

PKC JNKNF-120581B

GLUT4

AKTAMPK

TSC1

TSC2

Pras40

RHEBGDP

RHEBGTP mTORC1

mTOR Raptor

6SK1 4EBP1

















uarr serum IGF-1















MTF metformin




6 Conclusions




Abbreviations
















Competing Interests




Acknowledgments


References


































































































































































































of






Disease Markers



OncologyJournal of





PPAR Research



Journal of

ObesityJournal of





























Insulin resistance


Myo-Insmetformin

AMP

LKB1

CAMMK120573

ACC P53 COX2


Cell cyclearrest

Tumorigenesis


IR

IRS-1PIP3

PKC JNKNF-120581B

GLUT4

AKTAMPK

TSC1

TSC2

Pras40

RHEBGDP

RHEBGTP mTORC1

mTOR Raptor

6SK1 4EBP1

















uarr serum IGF-1















MTF metformin




6 Conclusions




Abbreviations
















Competing Interests




Acknowledgments


References


































































































































































































of






Disease Markers



OncologyJournal of





PPAR Research



Journal of

ObesityJournal of























Insulin resistance


Myo-Insmetformin

AMP

LKB1

CAMMK120573

ACC P53 COX2


Cell cyclearrest

Tumorigenesis


IR

IRS-1PIP3

PKC JNKNF-120581B

GLUT4

AKTAMPK

TSC1

TSC2

Pras40

RHEBGDP

RHEBGTP mTORC1

mTOR Raptor

6SK1 4EBP1

















uarr serum IGF-1















MTF metformin




6 Conclusions




Abbreviations
















Competing Interests




Acknowledgments


References


































































































































































































of






Disease Markers



OncologyJournal of





PPAR Research



Journal of

ObesityJournal of

















Insulin resistance


Myo-Insmetformin

AMP

LKB1

CAMMK120573

ACC P53 COX2


Cell cyclearrest

Tumorigenesis


IR

IRS-1PIP3

PKC JNKNF-120581B

GLUT4

AKTAMPK

TSC1

TSC2

Pras40

RHEBGDP

RHEBGTP mTORC1

mTOR Raptor

6SK1 4EBP1

















uarr serum IGF-1















MTF metformin




6 Conclusions




Abbreviations
















Competing Interests




Acknowledgments


References


































































































































































































of






Disease Markers



OncologyJournal of





PPAR Research



Journal of

ObesityJournal of





























uarr serum IGF-1















MTF metformin




6 Conclusions




Abbreviations
















Competing Interests




Acknowledgments


References


































































































































































































of






Disease Markers



OncologyJournal of





PPAR Research



Journal of

ObesityJournal of
























uarr serum IGF-1















MTF metformin




6 Conclusions




Abbreviations
















Competing Interests




Acknowledgments


References


































































































































































































of






Disease Markers



OncologyJournal of





PPAR Research



Journal of

ObesityJournal of



























MTF metformin




6 Conclusions




Abbreviations
















Competing Interests




Acknowledgments


References


































































































































































































of






Disease Markers



OncologyJournal of





PPAR Research



Journal of

ObesityJournal of


















Abbreviations
















Competing Interests




Acknowledgments


References


































































































































































































of






Disease Markers



OncologyJournal of





PPAR Research



Journal of

ObesityJournal of




















Competing Interests




Acknowledgments


References


































































































































































































of






Disease Markers



OncologyJournal of





PPAR Research



Journal of

ObesityJournal of


























































































































































































of






Disease Markers



OncologyJournal of





PPAR Research



Journal of

ObesityJournal of
























































































































































of






Disease Markers



OncologyJournal of





PPAR Research



Journal of

ObesityJournal of























































































































of






Disease Markers



OncologyJournal of





PPAR Research



Journal of

ObesityJournal of























































































of






Disease Markers



OncologyJournal of





PPAR Research



Journal of

ObesityJournal of





















































of






Disease Markers



OncologyJournal of





PPAR Research



Journal of

ObesityJournal of





















of






Disease Markers



OncologyJournal of





PPAR Research



Journal of

ObesityJournal of
















Documents

Review Article Insulin-Sensitizers, Polycystic Ovary Syndrome and …downloads.hindawi.com/journals/ije/2016/8671762.pdf · 2019-07-30 · Insulin-sensitizers improve the metabolic