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Accepted Manuscript
Cervical cancer cells (HeLa) response to photodynamic therapyusing a zinc phthalocyanine photosensitizer
Natasha Hodgkinson, Cherie Ann Kruger, Mpho Mokwena, HeidiAbrahamse
PII: S1011-1344(17)30103-3DOI: doi:10.1016/j.jphotobiol.2017.10.004Reference: JPB 11007
To appear in: Journal of Photochemistry & Photobiology, B: Biology
Received date: 23 January 2017Revised date: 25 August 2017Accepted date: 2 October 2017
Please cite this article as: Natasha Hodgkinson, Cherie Ann Kruger, Mpho Mokwena,Heidi Abrahamse , Cervical cancer cells (HeLa) response to photodynamic therapy usinga zinc phthalocyanine photosensitizer. The address for the corresponding author wascaptured as affiliation for all authors. Please check if appropriate. Jpb(2017), doi:10.1016/j.jphotobiol.2017.10.004
This is a PDF file of an unedited manuscript that has been accepted for publication. Asa service to our customers we are providing this early version of the manuscript. Themanuscript will undergo copyediting, typesetting, and review of the resulting proof beforeit is published in its final form. Please note that during the production process errors maybe discovered which could affect the content, and all legal disclaimers that apply to thejournal pertain.
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Cervical Cancer Cells (HeLa) Response to Photodynamic Therapy using a Zinc
Phthalocyanine Photosensitizer
Natasha Hodgkinson1*, Cherie Ann Kruger1, Mpho Mokwena1, Heidi Abrahamse1
1Laser Research Centre, Faculty of Health Sciences, University of Johannesburg,
Doornfontein, 2028, South Africa
All Correspondence and reprints should be addressed to:
*Dr. Natasha Hodgkinson PhD Biomedical Technology Laser Research Centre Faculty of Health Sciences University of Johannesburg P.O. Box 17011 Doornfontein 2028 South Africa Tel: +27 11 559-6926 Fax: +27 11 559-6558 Email: [email protected] Running title:
Cervical Cancer Cells Response to Photodynamic therapy
Declaration
This manuscript has not been published, nor has it been submitted elsewhere for
publication.
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Abstract
Cervical cancer is the most common gynecological malignancy worldwide, and the
leading cause of cancer related deaths among females. Conventional treatment for
early cervical cancer is radical hysterectomy. In locally advanced cancer the
treatment of choice is concurrent chemo radiation. Although such treatment methods
show promise, they do have adverse side effects. To minimize these effects, as well
as prevent cancer re-occurrence, new treatment methods are being investigated.
Photodynamic therapy (PDT) involves the selective uptake of a photosensitizer (PS)
by cancer cells, illumination with light of an appropriate wavelength that triggers a
photochemical reaction leading to the generation of reactive oxygen and subsequent
tumor regression. The effect of PDT on a cervical cancer cell line (HeLa) was
assessed by exposing cultured cells to a sulphonated zinc phthalocyanine PS
(ZnPcSmix) and irradiating the cells using a 673 nm diode laser. The effects were
measured using the Trypan blue viability assay, adenosine triphosphate assay (ATP)
luminescence assay for proliferation, Lactate Dehydrogenase (LDH) membrane
integrity cytotoxicity assay, and fluorescent microscopy to assess PS cellular
localization and nuclear damage. Fluorescent microscopy revealed localization of the
PS in the cytoplasm and perinuclear region of HeLa cells. PDT treated cellular
responses showed dose dependent structural changes, with decreased cell viability
and proliferation, as well as considerable membrane damage. Hoechst stained cells
also revealed DNA damage in PDT treated cells. The final findings from this study
suggest that ZnPcSmix is a promising PS for the PDT treatment of cervical cancer in
vitro, where a significant 85% cellular cytotoxicity with only 25% cellular viability was
noted in cells which received 1µM ZnPcSmix when an 8 J/cm2 fluence was applied.
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Keywords: Cervical cancer, photodynamic therapy, zinc phthalocyanine
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1 Introduction
Cervical cancer is one of most common causes of cancer related deaths in women
worldwide (Chen et al., 2015). It is the third most common cancer that develops in
women, and nearly half a million new cases are reported each year (Ordikhani et al.,
2016). Despite advances in current therapies for the treatment of cervical cancer,
roughly 35% of women diagnosed with cervical cancer have recurrent disease, in
both advanced and early stage patients, with 90% of these found within 3 years after
the initial treatment (Hou et al., 2015; Lopez et al., 2012). There are also adverse
side effects of current treatment modalities which could decrease patient quality of
life (Ordikhani et al., 2016).
Radical hysterectomy is the treatment is currently the treatment of choice in early
cervical cancer. Concurrent chemo radiation is the favored modality for the cure of
locally advanced cancer (Lee et al., 2016). Although these modalities have shown
promise, the side effects are vast. Radiation therapy has been shown to induce DNA
damage in cells, leading to the loss of cell recovery, arrest of cell cycle, and
consequently cell destruction (Lomax et al., 2013). Chemotherapy, a primary
treatment of metastatic cancer, and alternative treatment for recurrent cervical
cancer, also comes with toxicity and adverse side effects.
In search of alternative, methods of treatment to effectively treat cancer, reduce side
effects and prevent cancer recurrence and metastasis, alternative methods of
treatment are being investigated (Portilho et al., 2013). One such treatment modality
is photodynamic therapy (PDT). PDT is an emerging therapy that is non-invasive and
involves a photosensitizer (PS), a drug which is taken up readily by cancer cells, and
an external light source which activates the drug and can treat diseases (Huang et
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al., 2015). The three components that are involved in PDT are: light, a
photosensitizer (PS), and oxygen (Wan and Lin, 2014). After a PS drug has been
administered either topically or systematically, and absorbed by the tumour cells, the
PS is irradiated by a light of a particular wavelength (Portilho et al., 2013; de Paula et
al., 2015). The excited PS’s then generate singlet oxygen and other reactive oxygen
species (ROS), which can damage different biomolecules, including proteins, DNA
and lipids and so leads to tumor cell death (Fang et al., 2015; Calixto et al., 2016).
Currently PDT is being used to treat patients who want to preserve their fertility and
those who would rather avoid having surgery. Previous studies have utilized PS’s
Photofrin and 5-ALA in the treatment/prevention of cervical cancer. Although the use
of systemic Photofrin was effective, Photofrin caused skin photosensitivity.
Conversely, 5-ALA was used topically to treat cervical lesions which could lead to
cancer, as well as to eradicate Human Papilloma Virus (HPV) infection (Shishkova et
al., 2012). Phthalocyanines are common PS’s used in PDT due to their high tumor
uptake efficiencies, their high ROS production and strong absorption in the
wavelength range between 650 and 850 nm (Pereira et al., 2014). A second
generation PS, Zinc (II) phthalocyanine has absorption Q bands at longer
wavelengths (670 - 770 nm) that allows maximum penetration of the light into the
tissues (Ocakoglu et al., 2016). There is limited literature on the use of
phthalocyanines in PDT and the treatment of cervical cancer, therefore, this study
aimed to investigate the PDT effects of a sulphonated zinc phthalocyanine PS
(ZnPcSmix) on the survival of HeLa cells, in vitro, to determine its potential as a
cancer treatment option.
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2 Materials and Methods
2.1 Cell culture
Cervical cancer cells (HeLa, (ATCC® CCL2™) were grown in Eagles Minimum
Essential Medium (MEM) (Sigma Aldrich: M2279) medium supplemented with Foetal
Bovine Serum (FBS) 10% (Sigma Aldrich: F0804), penicillin and streptomycin (100
mg) (Sigma Aldrich: P4333-100ML), and Amphotericin B (100 mg) (Sigma Aldrich:
A2942-100ML). All cells were incubated at 37°C with 5% CO2 and 85% humidity.
2.2 Treatment with Photosensitizer
The ZnPcSmix PS used in this study is a mixed isomer of sulfonated phthalocyanines,
and was synthesized from (OH2) ZnPc and fuming sulfuric acid (30% SO3) at
Rhodes University in South Africa and donated by Prof Tebello Nyokong (Ogunsipe
and Nyokong, 2005). The photochemical and photophysical properties were
determined and the PS had a fluorescence quantum yield of 0.16 (Φ??); triplet
quantum yield of 0.53 (Φ??); singlet oxygen quantum yield of 0.45 (ΦΔ), and triplet
lifetime (????) of 2.95 μs (Ogunsipe and Nyokong, 2005). Stock solutions of 0.0005 M
ZnPcSmix re-suspended in Phosphate Buffered Saline (PBS: Sigma Aldrich P5493-
1L) has a peak absorbance of 680 nm. Three different concentrations of ZnPcSmix
(0.25; 0.5; and 1 µM) diluted in supplemented cell culture media was used to
determine which would be the most toxic and induce cell death when PDT was
applied.
2.3 Cell preparation and Photosensitizer doses
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Cells from culture were seeded into 3.3 cm2 culture plates at a density of 5 x 105
cells/cm2 and incubated for 4 hours in supplemented growth medium to allow for
attachment. After 4 hours the growth medium was removed from all culture plates
and replaced, however within PS experimental plates, supplemented culture media
with ZnPcSmix was added at varying concentrations (0.25; 0.5; and 1 µM) and both
control groups not treated with ZnPcSmix and experimental groups were incubated, in
the dark, for 24 hours at 37˚C with 5% CO2 and 85% humidity.
2.4 Subcellular Localization
Fluorescent staining was performed to determine subcellular localization and uptake
of the PS (ZnPcSmix). HeLa cells were grown on glass coverslips in 35 mm culture
dishes in the conditions previously described. An hour prior to observation, cells
were fixed with 200 µl of 3.5% (v/v) Paraformaldehyde (Sigma Aldrich P6148) in
DMEM, and permeabilized with 200 µl of 0.5% (v/v) TrixtonX-100 (Sigma–Aldrich
T9284) in distilled water, then washed three times with HBSS. Fifty microliters of 1
µg/ml 40-6-Diamidino-2-phenylindole (DAPI: Invitrogen, D1306) was used to
counter-stain the nuclei. After 5 min incubation, the samples were rinsed with HBSS
and the coverslips were inverted onto glass microscope slides onto which a 30 µl of
20% Fluoromount™ Aqueous Mounting Medium (Sigma Aldrich, F4680) in distilled
water had been added. Coverslip borders were sealed with nail polish and slides
were examined using the fluorescent settings of a Carl Zeiss Axio Z1 Observer. The
358Ex/461Em filter was used to detect blue DAPI counter stained nuclei, and the
589Ex/610Em filter was used to detect any Texas red auto fluorescent signal
produced from cells that had absorbed ZnPcSmix.
2.5 Laser Irradiation
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Semi-confluent monolayers of HeLa cells in supplemented medium were irradiated
from above with the lid off in the dark at room temperature with a 673 nm diode laser
(Oriel, USA). On average a power output of 96 mW was measured using the
Coherent Fieldmate detector and sensor, this value was used to calculate the
duration (time) of each exposure for the different irradiation fluences (2, 4 and 8
J/cm2) which were used. All the laser parameters are described in Table i. Non-
irradiated cells (0 J/cm2) were used as controls and were kept under the same
conditions. Both irradiated and non-irradiated samples were re-incubated at 37°C in
a humidified atmosphere of 5% CO2 for 24, 48 or 72 hrs.
Table i: Laser Parameters used for Irradiation using the 673 nm Diode Laser
Parameter Description/Value
Laser Type Semiconductor diode
Wavelength (nm) 673 nm
Wave Emission Continuous
Power Output (mW) 96 mW
Power Density (mW/cm2) 10.5 mW/cm2
Spot Size (cm2) 9.1 cm2
Fluence (J/cm2) 2; 4; 8
Irradiation times 3 mins; 6 mins; 13 mins
2.6 Cell Morphology
Changes in cellular morphology in control and experimental groups of cervical cells
were observed using an inverted light microscope (Wirsam, Olympus CKX41) 24
hours post-irradiation. Pictures were taken with the SC30 Olympus camera. Images
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of the treated cells were compared to those of the control cells and any
morphological changes were recorded.
2.7 Trypan Blue assay
The Trypan blue staining method was used to determine the percentage of viable
cells. The assay is used to identify dead cells. Cells that are viable have intact
membranes and can effectively exclude the dye, whereas dead cells, with damaged
membranes take up the stain. Equal volumes of 0.4% Trypan blue (Sigma Aldrich:
T8154-20ML) and cell suspension were mixed and loaded into a counting chamber,
where the number of viable and dead cells were counted using the CountessTM
Automated Cell Counter (Invitrogen, C10227). Percent viability was determined by
calculating the number of viable cells from the total number of cells counted.
2.8 Adenosine Triphosphate (ATP) assay
The CellTiter-Glo luminescent cell viability assay (AnaTech: Promega, PRG7571)
was used to determine the number of metabolically active cells post irradiation. The
assay employs the properties of a proprietary thermostable luciferase, which
generates a luminescent signal proportional to the amount of ATP released upon cell
lysis. According to the manufacturer’s protocol, 50 µl of reconstituted reagent was
added to an equal volume of cell suspension. The contents was added into a white
walled 96 well plate and mixed on a shaker for 2 min to induce cell lysis. The plate
was then incubated at room temperature for 10 min to stabilize the luminescent
signal. The amount of ATP was quantified, and luminescence was recorded using
the Perkin Elmer, VICTOR3™ Multilabel Counter (Model 1420).
2.9 Lactose Dehydrogenase (LDH) Assay
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Membrane damage post irradiation was evaluated using the Cyto-Tox96 X assay
(Anatech: Promega, PRG1780). The assay quantitatively measures lactate
dehydrogenase (LDH), a stable cytosolic enzyme that is released upon cell lysis.
LDH catalyses the conversion of lactate to pyruvate via NAD+ reduction to NADH.
Diaphorase then uses NADH to reduce a tetrazolium salt (INT) to a red formazan
product which is measured at 490 nm. The level of formazan formation is directly
proportional to the amount of LDH released into the medium, which indicates
cytotoxicity. Fifty µl of reconstituted reagent and culture medium post irradiation was
transferred into a clear 96 well-plate, incubated for 30 min in dark and the
colorimetric complex was measured at 490 nm using Perkin Elmer, VICTOR3™
Multilabel Counter (Model 1420).
2.10 DNA Damage Induced by PDT
HeLa cells were grown on glass coverslips in 35 mm culture dishes and categorized
into two groups: [1] control of cells only and [2] cells + 1 µg/ml ZnPcSmix + 4 J/cm2.
Cells were incubated at 37°C with 5% CO2 and 80% humidity for 4 hours to allow for
cellular attachment. Both groups were incubated in the dark for an additional 20
hours. Cells were then washed (3x with HBSS) and fixed with 200 µl of 3.5% (v/v)
Paraformaldehyde (Sigma Aldrich P6148) in DMEM for 10 min and permeabilized for
8 min with 200 µl of 0.5% (v/v) TrixtonX-100 (Sigma Aldrich T9284) in distilled water.
The samples were rinsed with HBSS and 1 ml of culture media that contained 1 µl of
1ug/ml (w/v) Hoechst dye was added to both groups for 15 min. The coverslips were
then inverted onto glass microscope slides onto which a 30 µl of 20% Fluoromount™
Aqueous Mounting Medium (Sigma Aldrich, F4680) in distilled water had been
added. Coverslip borders were sealed with nail polish and slides were examined at
40X magnification using the Carl Zeiss Axio Z1 Observer. Hoechst 33258
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352Ex/461Em blue filter was used to track this fluorescent dye uptake in nucleic
acids and so quantitatively analyse DNA damage in cells which received PDT when
compared to control cells only.
2.11 Statistical Analysis
Experiments were repeated three times (n = 3). All assays were performed in
triplicate, and the average was used for statistical calculations. Results were
analysed using Sigma Plot Version 12, and the mean, standard deviation, and
standard error were calculated. The student t test and one way ANOVA were
performed to detect differences between control groups and experimental groups.
Statistical significances are indicated in the figures as p < 0.05 (*), p < 0.01, (**) and
p < 0.001 (***).
3 Results
Subcellular Localization
Fluorescent microscopy revealed significant uptake of the photosensitizer by the
HeLa cells, as seen in Figure i below. The PS (stained in red) appeared to
accumulate within the cytoplasm and perinuclear region of the cells (nuclei stained in
blue). A similar study by Avaștar et al., 2016 showed ZnPcSmix PS localized in
the cytoplasm of MCF-7 cells. Previous studies have also confirmed perinuclear
localization of PS’s in HeLa cells (Soriano et al., 2014). Additionally, studies by Ge et
al. (2013) have noted that the cytoplasmic localization of PSs in HeLa cells is usually
restricted to mitochondrial cells only.
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Figure i: Texas red auto fluorescent signal produced from HeLa cells which
absorbed ZnPcSmix is shown in red. HeLa cells nuclei were counter
stained with DAPI as shown in blue. The merged image showing
localisation of the PS in relation to the nucleus. Magnification 40X and
Scale bar: 20 µm.
Cell Morphology
HeLa cells were examined for morphological changes after treatment, as per the
relevant experimental groups shown in Figure ii. Untreated HeLa cells remained
intact and maintained normal cell morphology. Cells treated with either laser
irradiation or non-activated ZnPcSmix presented morphological changes of cellular
damage as the dosage of PS and fluence increased. The most significant
morphological changes were observed within cells which received either 1 µM alone
or 8 J/cm2 alone. The experimental groups that received PDT yielded the most
significant dose dependent morphological changes indicative of cellular damage, as
the cells began to lose their characteristic shape, became rounded up, detached and
appeared to be free-floating structures in the culture medium. Studies by Manoto et
al. (2015 and 2012), reported similar morphological changes in human lung (A549)
and colon cancer cells (DLD-1) when exposed to 680 nm PDT induced zinc
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sulfophthalocyanine photosensitization at a concentration of 10 µM, and a fluence of
5 J/cm2.
Figure ii: Human cervical cancer cells (HeLa), showing a reduction in cell
sustainability with a dose dependent trend. PDT groups at a higher
fluence and increased PS concentration showed a visible difference in
cellular morphology when compared to control or experimental cells
which only received PS, whereby cell rounding, shrinkage and
detachment from the flask were observed, indicative of cell death.
Magnification 40X.
Trypan Blue assay
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The viability assay (Trypan Blue) showed a significant dose dependent decrease in
cellular viability within experimental groups, which were exposed to increasing
concentrations of either ZnPcSmix only or laser light alone, when compared to control
cells (Figure iii). In the experimental groups which were exposed to PDT, the change
in percentage viability when compared to control cells already noted 50 % cell
damage when HeLa cells received 1 µM of ZnPcSmix at a fluence of 4 J/cm2. These
results became increasingly significant (P < 0.001) in cells that received 1 µM of
ZnPcSmix when the fluence was increased to 8 J/cm2, as only 25% of cells were
reported to be viable. A similar study by Chen et al. (2015) applied 1.5 µM of ZnPcS
to cervical cancer cells and noted a 40% decrease in cell viability, when using a
480nm light emitting diode.
Figure iii: Trypan blue cellular viability assay. The cell viability decreased in all
experimental groups, and showed a dose dependent trend. Both the
ZnPcSmix and laser irradiation groups alone had an effect on the cellular
viability. However, when combined in the PDT application of 2 J/cm2 slight
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proliferation of cells was reported, and as the fluence of laser light and PS
increased so the viability of cells decreased, when compared to control
cells.
Adenosine Triphosphate assay
Cellular proliferation, as shown in Figure iv, was measured using the ATP assay,
significantly decreased in a dose dependent manner in HeLa experimental groups
which were exposed to ZnPcSmix alone as its concentration increased. However, in
experimental groups which were exposed to laser irradiation alone no significant
decrease in cell proliferation was noted as the fluence increased. The experimental
PDT groups which were exposed to a concentration of 1 µM ZnPcSmix in combination
with either 4 J/cm2 or 8 J/cm2, the most significant decrease (P < 0.001) in cellular
proliferation was noted when compared to any of the other experimental or control
groups. Similar findings were noted in studies performed by Tynga et al. (2014 and
2015), within MCF-7 human breast cancer cells when PDT was applied at 680nm,
with a 0.5 µM ZnPcSmix concentration using a fluence of 10 J/cm2. The study
concluded that ZnPcSmix mediated PDT led to an apoptotic cell death pathway,
which initiate programmed cell death in cells and so hindered further cellular
proliferation.
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Figure iv: Adenosine triphosphate assay (ATP) for proliferation. There was a very
significant decrease in cellular proliferation in experimental groups which
received 1 µM ZnPcSmix alone, however laser irradiation alone reported
no effects. The PDT combination of PS and laser irradiation indicated a
dose dependent decrease in proliferation, with the most significant
decrease being noted at a PDT combination concentration of 1 µM
ZnPcSmix at 8 J/cm2.
Lactose Dehydrogenase assay
Cellular damage induced by PDT was measured by evaluating the level of LDH
released into the culture media post irradiation. After 24 hours incubation,
experimental groups that received PDT treatment showed an increase in cell
membrane damage, as noted by the significant increase in the level of LDH
detected, when compared to control cells. In the experimental groups which received
either ZnPcSmix or laser dose treatment alone, no significant cellular cytotoxicity was
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noted. Overall, the cytotoxic effects of ZnPcSmix mediated PDT were dependent on
the concentration of PS used, as well as the fluence that was applied, with the most
significant cytotoxicity of 90% (P < 0.0002) being noted within cells, which received a
concentration of 1 µM ZnPcSmix and were irradiated at a fluence of 8 J/cm2.
Similarly, within studies performed by Manoto et al. (2012), significant in vitro
phototoxicity was noted in human lung (A549) and colon cancer cells (DLD-1) when
exposed to 680nm PDT 10µM induced ZnPcSmix photosensitization at fluence of 5
J/cm2, when compared to inactivated ZnPcSmix control cells.
Figure v: Lactose dehydrogenase assay for cytotoxicity. The ZnPcSmix and laser
irradiation alone showed little cytotoxicity when compared to control cells.
The PDT combination experimental groups reported a dose dependent
increase in cytotoxicity, with the most significant cytotoxicity observed in
cells which received 1 µM PS at a fluence of 8 J/cm2.
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Fluorescent Imaging for DNA damage
The blue Hoechst stained nuclear damage of HeLa cells post incubation which
received 1 µM ZnPcSmix at a PDT fluence of 4 J/cm2, when compared to control cells
is shown in Figure vi. Control cells showed no morphological changes. In contrast,
HeLa cells which received ZnPcSmix PDT treatment presented a small nucleus with
highly condensed chromatin, suggesting DNA damage was present. Studies
performed by Soriano et al (2014) and Acedo et al. (2014) in HeLa cells described
cell shrinkage, chromatin condensation, and nuclear fragmentation, which are typical
apoptotic features of PS laser activated induced cell damage. Similar studies
performed by El-Hussein et al. (2012), noted marked PDT induced DNA damage at
wavelength of 636nm when 10 µM ZnPcSmix was applied to human lung (A549),
breast (MCF-7), and esophageal (SNO) cancer cells at a fluence of 10 J/cm2. This
study proved that cytotoxic singlet oxygen, which is produced by the activation of the
ZnPcSmix during PDT, directly damaged the DNA in cells by causing single and
double-strand breaks which lead to cell death.
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Figure vi: Hoechst DNA detected damage after PDT (blue stain). Untreated cells
showed no morphological changes in the nuclei, however cells which
received ZnPcSmix and laser irradiation, showed highly condensed
chromatin granules, indicative of cellular DNA damage.
Conclusion
In conclusion, the results presented in this paper exhibit the effective
phototherapeutic activities of ZnPcSmix to induce cell damage in cervical cancer cells,
in vitro. This is supported by findings such as obvious changes in cell morphology,
with significantly decreased cellular viability and proliferation, increased cytotoxicity,
and DNA fragmentation noted in experimental groups which received PDT treatment
in comparison to those that didn’t. The significant effects on cellular morphology,
viability, cytotoxicity and DNA damage were seen to increase and proliferation
decrease in dose dependent manner with the most significant effect being observed
at a concentration of 1 µM PS when a fluence of 8 J/cm2 was applied. Hence,
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ZnPcSmix is an effective photodynamic agent, in vitro, for the treatment of cervical
cancer cells. Studies reported by Tynga and Abrahamse (2015), have noted that
metallated phthalocyanine-mediated PDT has been shown to induce autophagy
mode of cell death in various types of cancer cells and this study is suggestive of
this. However, in terms of the future applications of this sulphonated metal
phthalocyanine, further investigation in terms of its in vitro and in vivo drug delivery
(Abrahamse and Hamblin, 2016) through structural modifications (Dabroski et al.
2016), such as the addition of biocompatible antibodies (Iqbal et al. 2016) and
biodegradable nanoparticles (Sundar et al. 2016) should be evaluated. Additionally,
further investigation will include the incorporation of a control cervical cell line for
comparative PS cellular uptake studies to determine the retention rate in normal
versus cancerous cells as well as elucidation of the cell death induction mechanism
which will require extensive comparative research with normal cervical cells. Only
once this is complete could this form of specifically targeted PS PDT induced cell
damage be entirely considered as a prospective means of managing cancer.
Acknowledgements
The authors would like to acknowledge the following institutions for their
contributions: The Laser Research Centre, the National Research foundation,
National Laser Centre, and the University of Johannesburg.
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Highlights
Photodynamic therapy a new less invasive treatment for cervical cancer.
Photosensitizers of choice inlude phthalocyanines due to high tumour uptake.
Zinc phthalocyanine is a promising new photosensitizer for cervical cancer
treatment.
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