PARP Inhibitors:PARP Inhibitors:Usurping DNA repair to target Usurping DNA repair to target

cancercancer

Lee Schwartzberg MD, FACP

Chief Medical Officer

The West Clinic

Question 1

DNA repair mechanisms are important in

1. Cancer cells only

2. Both cancer and normal eukaryotic cells

3. Predominantly in rapidly growing cells like bone marrow precursors

4. Predominantly cancer cells with BRCA mutations

Question 2

PARP inhibitors have demonstrated activity in:

1. BRCA 1 mutation carrier breast cancer

2. BRCA 2 mutation carrier breast cancer

3. Triple negative breast cancer

4. 1 and 3 only

5. 1 and 2 only

6. All of the above

All cells are under constant risk of All cells are under constant risk of DNA damageDNA damage

Ultraviolet light Ionizing radiation Man-made and natural chemicals Reactive oxygen species

most are generated “endogenously”

10,000 Single Strand Breaks/ cell/day ~100,000,000,000,000,000 DNA lesions in a

human body every day1-3

1. Jackson SP. Biochem Soc Trans 2001;29:655-6612. Lindahl T. Nature 1993;362:709-715

3. Jackson SP, Bishop CL. Drug Discovery World 2003;(Fall):41-45

Cellular Response To DNA Cellular Response To DNA DamageDamage

Cancer cells are highly susceptible Cancer cells are highly susceptible to DNA repair inhibitionto DNA repair inhibition Undergo deregulated proliferation

Less time for DNA repair than in normal cells Grow under stress, which causes ongoing DNA

damage Have DNA repair defects

P53, BRCA1, BRCA 2, ATM, Fanconi’s Anemia Allow growth despite ongoing genome instability

Are reliant on the DNA repair pathways they still retain

DNA Excision Repair MechanismsDNA Excision Repair Mechanisms

Lig3XRCC1

PolßPNK

Poly(ADP-Ribose) Polymerase (PARP)Poly(ADP-Ribose) Polymerase (PARP)

A key role in the repair of DNA single-strand breaks Through the base excision repair pathway (BER) Binds directly to sites of DNA damage Once activated, it uses NAD as a substrate, and generates

large, branched chains of poly (ADP-ribose) polymers on multiple target proteins

Recruits other DNA repair enzymes

PAR

Base Excision RepairBase Excision Repair

Inhibiting PARP-1 Increases Double-Strand DNA Inhibiting PARP-1 Increases Double-Strand DNA DamageDamage

PARP

Inhibition of PARP-1 prevents -recruitment of DNA repair enzymes-leads to failure of SSB repair-accumulation of SSBs

XRCC1

LigIII

PNK 1

pol β

During S-phase, replication fork

is arrested at site of SSB

DNA single strand break (SSB)damage

Degeneration into Double strand breaks

BRCA1 And 2 Are Required for Efficient BRCA1 And 2 Are Required for Efficient Repair of Double Stranded DNA BreaksRepair of Double Stranded DNA Breaks

DNA DSB

ATM/R

Ligase IVXRCC4

DNA-PKcs

Ku 70/80

ERCC1XRCC3

Rad 52/4RPA

Rad 51BRCA2

NBS1MRE11

Rad50BRCA1

H2AX

Non-homologous end-joining Homologous recombination

Predominant in G1Error-proneGross Genomic instability

Major pathway for repair Error-free

Cells with BRCA mutations are deficient in homologous recombination and lack the ability to efficiently repair DSBs.

Cancer cell death

Cellsurvival

The Concept of Synthetic LethalityThe Concept of Synthetic Lethality

(PARP)(BRCA)

Ashworth, A. J Clin Oncol; 26:3785-3790 2008

Farmer H et al. Nature 2005;434:917-920Personal communication, Alan Ashworth

BRCA1 and BRCA2 -/- cells are very BRCA1 and BRCA2 -/- cells are very sensitive to PARP inhibitionsensitive to PARP inhibition

BRCA2 +/-

BRCA2 -/-

Wild type

Log surviving fraction

0-4

-3

-2

-1

0

PARP inhibitor concentration (M)10-9 10-8 10-7 10-6 10-5 10-4

Control + PARP inhibitor

Control + PARP inhibitor

Wild type

BRCA2 -/-

Increased levels of chromosomal aberrations in PARP inhibitor treated BRCA2 -/- cells

PARP Inhibitors in Clinical PARP Inhibitors in Clinical DevelopmentDevelopment

Differing chemical structures

Differing toxicity

Differing schedules and routes of administration

Chemotherapeutic Agents:Chemotherapeutic Agents: Double Strand DNA Breaks Double Strand DNA Breaks

Alkylators DNA interstrand cross-links double strand (DS) DNA breaks

Cyclophosphamide

Platinums Forms adducts with DNA Cisplatin

Carboplatin

Oxaliplatin

Topoisomerase I poisons

Arrest of DNA replication forks

Etoposide

Irinotecan

Topotecan

Mitoxantrone

Topoisomerase II poisons

DNA interstrand cross-linking, generation of O2 free radicals

Doxorubicin

Epirubicin

Bleomycin Directly damages DNA DS DNA breaks

Kennedy R et al. JNCI 2004; 96:1659-1668

PARP Inhibitors in BRCA 1/2 PARP Inhibitors in BRCA 1/2 Mutated TumorsMutated Tumors

Phase I Trial of Olaparib in Phase I Trial of Olaparib in Patients with Solid TumorsPatients with Solid Tumors

Escalation and expansion phase, n = 60 Recommended phase II dose: 400 mg PO BID Toxicities

Nausea (32%), fatigue (30%), vomiting (20%), taste alteration (13%), anorexia (12%), anemia (5%)

Clinical activity = 12/19 patients with BRCA mutations

Tumor BRCA No. of pts Response

Breast 2 2 1 CR, 1 SD

Ovarian 1 or 2 8 8 PRs

Fallopian tube 1 1 PR

Prostate 2 1 PR

Fong PC et al. N Engl J Med 2009; 361:123-134

Phase II Trial of Olaparib in BRCA-deficient Phase II Trial of Olaparib in BRCA-deficient Metastatic Breast CancerMetastatic Breast Cancer

Eligibility

Confirmed BRCA1 or 2 mutation

Stage IIIB/C or IV BC after progression ≥ 1 prior chemotherapy for advanced disease

Cohort 2*

Olaparib 100 mg po bid (maximal PARP inhibition)

28-day cycles

Cohort 1

Olaparib 400 mg po bid (MTD)

28-day cycles

* Following an interim review, patients in the 100 mg bid cohort were permitted to crossover to receive 400 mg bid

(Non-randomized sequential cohorts)

Tutt A et al. J Clin Oncol 2009;27(18S):803s (abstr CRA501)

Primary Endpoint: Response rate

Olaparib 400 mg BID(n = 27)

Olaparib 100 mg BID(n = 27)

Grade 1/2 Grade 3 Grade 1/2 Grade 3

Fatigue 15 (56) 4 (15) 15 (56) 2 (7)

Nausea 11 (41) 5 (19) 15 (56) 0

Vomiting 7 (26) 3 (11) 6 (22) 0

Headache 10 (37) 0 5 (19) 1 (4)

Constipation 6 (22) 0 8 (30) 0

Olaparib in BRCA-deficient Metastatic Breast Cancer: Select Toxicities

Tutt A et al. J Clin Oncol 2009;27(18S):803s (abstr CRA501)

Olaparib in BRCA-deficient Olaparib in BRCA-deficient Metastatic Breast Cancer: ResultsMetastatic Breast Cancer: Results

ITT cohort 400 mg BID

N = 27

100 mg BID

N = 27

ORR 11 (41%) 6 (22%)

CR 1 (4%) 0

PR 10 (37%) 6 (22%)

Median PFS

5.7 mo

(4.6-7.4)

3.8 mo

(1.9 – 5.6)

Tutt A et al. J Clin Oncol 2009;27(18S):803s (abstr CRA501)

Best percent change from baseline in target lesions

by genotype

Median 3 prior lines of therapy

PARPi Monotherapy in BRCA Mutated PARPi Monotherapy in BRCA Mutated tumorstumors

Drug Phase Dose Tumor N CBR (%)

RR (%)

MDR (MOS)

PFS (MOS)

Olapirib 1 Varies Ovarian 50 46 40 6.5 NR

Olapirib 2 400 mg BID

Ovarian 33 NR 35 9.6 NR

Olapirib 2 100 mgBID

Ovarian 24 NR 13 9.0 NR

Olapirib 2 400 mgBID

Breast 27 NR 41 NR 5.7

Olapirib 2 100 mg BID

Breast 27 NR 22 NR 3.8

MK-4827

1 Varies Ovarian 19 45

MK-4827

1 Varies Breast 4 50

Prior response to platinum may predict response Prior response to platinum may predict response to olaparib in BRCA mutated Ovarian Cancerto olaparib in BRCA mutated Ovarian Cancer

Gelmon K, et al J Clin Onc 2010

PARP Inhibitors beyond BRCA PARP Inhibitors beyond BRCA mutation carriersmutation carriers

Triple Negative Breast Cancer Triple Negative Breast Cancer (TNBC)(TNBC)

‘Triple negative’: ER-negative, PR-negative, HER2-negative Depending on thresholds used to define ER and PR

positivity and methods for HER2 testing

TNBC accounts for 10–17% of all breast carcinomas

Significantly more aggressive than other molecular subtype tumors

Higher relapse rate than other subtypes No specific targeted therapy

Reis-Filho JS, et al. Histopathology 2008;52:108-118.

Characteristics Hereditary BRCA1 Triple Negative/Basal-Like1,2,3

ER/PR/HER2 status Negative Negative

TP53 status Mutant Mutant

BRCA1 status Mutational inactivation* Diminished expression*

Gene-expression pattern Basal-like Basal-like

Tumor histologyPoorly differentiated

(high grade)Poorly differentiated

(high grade)

Chemosensitivity to DNA-damaging agents

Highly sensitive Highly sensitive

TNBC Shares Clinical and Pathologic Features with TNBC Shares Clinical and Pathologic Features with BRCA-1-Related Breast Cancers (“BRCAness”)BRCA-1-Related Breast Cancers (“BRCAness”)

3Sorlie et al. Proc Natl Acad Sci U S A 2001;98:10869-744 Miyoshi et al. Int J Clin Oncol 2008;13:395-400

*BRCA1 dysfunction due to germline mutations, promoter methylation, or overexpression of HMG or ID44

1Perou et al. Nature. 2000; 406:747-7522Cleator et al.Lancet Oncol 2007;8:235-44

Targeting DNA Repair Pathway in Targeting DNA Repair Pathway in TNBCTNBC

Clustering analyses of microarray RNA expression have shown that familial BRCA-1 tumors strongly segregate with basal-like/ triple-negative tumors

Suggests that sporadic TNBC may have acquired defects in BRCA1-related functions in DNA repair

= BRCA1+ = BRCA2+

Basal-like

Sorlie T et al. PNAS 2003;100:8418-8423

Predictors of Response to Cisplatin in Predictors of Response to Cisplatin in TNBCTNBC

Silver, D. P. et al. J Clin Oncol; 28:1145-1153 2010

Phase II Study of the PARP inhibitor Iniparib in Phase II Study of the PARP inhibitor Iniparib in Combination with Gemcitabine/Carboplatin in Combination with Gemcitabine/Carboplatin in Triple Negative Metastatic Breast CancerTriple Negative Metastatic Breast Cancer

Background and Rationale

PARP1 Upregulated in majority of triple negative human breast cancers1

Iniparib (BSI-201)

Small molecule IV PARP inhibitor

Potentiates effects of chemotherapy-induced DNA damage

No dose-limiting toxicities in Phase I studies of BSI-201 alone or in combination with chemotherapy

Marked and prolonged PARP inhibition in PBMCs

O’Shaughnessy J, et al. NEJM 2011

Phase II TNBC Study: Treatment Schema Phase II TNBC Study: Treatment Schema

21-DayCycle

* Patients randomized to gem/carbo alone could crossover to receive gem/carbo + BSI-201 at disease progression

RANDOMIZE

BSI-201 (5.6 mg/kg, IV, d 1, 4, 8, 11)

Gemcitabine (1000 mg/m2, IV, d 1, 8)

Carboplatin (AUC 2, IV, d 1, 8)

BSI-201 (5.6 mg/kg, IV, d 1, 4, 8, 11)

Gemcitabine (1000 mg/m2, IV, d 1, 8)

Carboplatin (AUC 2, IV, d 1, 8)

Gemcitabine (1000 mg/m2, IV, d 1, 8)

Carboplatin (AUC 2, IV, d 1, 8)

Gemcitabine (1000 mg/m2, IV, d 1, 8)

Carboplatin (AUC 2, IV, d 1, 8)

RESTAGINGEvery 2 Cycles

Metastatic TNBCN = 120

1st -3rd line MBC Eligible

Safety – Hematologic ToxicitySafety – Hematologic ToxicityPhase II Gem Carbo +/- IniparibPhase II Gem Carbo +/- Iniparib

Gem/Carbo(n = 59)

BSI-201 + Gem/Carbo(n = 57)

Grade 2 Grade 3 Grade 4 Grade 2 Grade 3 Grade 4

Anemia, n (%)12

(20.3%)7 (11.9%)

0 (0.0%)

15(26.3%)

7 (12.3%)

0 (0.0%)

Thrombocytopenia, n (%) 7 (11.9%)6

(10.2%)6

(10.2%)4

(7.0%)6

(10.5%)7

(12.3%)

Neutropenia, n (%) 7 (11.9%)18

(30.5%)13

(22.0%)7 (12.3%)

18 (31.6%)

7(12.3%)

Febrile neutropenia, n (%)0

(0.0%)3

(5.1%)1

(1.7%)0

(0.0%)0

(0.0%)0

(0.0%)

RBC treatment*, n (%)5

(8.5%)5

(8.5%)2

(3.4%)3

(5.3%)5

(8.8%)2

(3.5%)

G-CSF Use, n (%)6

(10.2%)6

(10.2%)3

(5.1%)4

(7.0%)5

(8.8%)1

(1.8%)

*Transfusion and/or EPO use

O’Shaughnessy J, et al. NEJM 2011

Gem/Carbo(n = 59)

BSI-201 + Gem/Carbo(n = 57)

Grade 2 Grade 3 Grade 4 Grade 2 Grade 3 Grade 4

Nausea, n (%)10

(16.9%)2

(3.4%)0

(0.0%)7

(12.3%)0

(0.0%)0

(0.0%)

Vomiting, n (%)9

(15.3%)0

(0.0%)0

(0.0%)4

(7.0%)1

(1.8%)0

(0.0%)

Fatigue, n (%)10

(16.9%)6

(10.2%)0

(0.0%)10

(17.5%)1

(1.8%)0

(0.0%)

Neuropathy, n (%)2

(3.4%)0

(0.0%)0

(0.0%)1

(1.8%)0

(0.0%)0

(0.0%)

Diarrhea, n (%)6

(10.2%)1

(1.7%)0

(0.0%)1

(1.8%)1

(1.8%)0

(0.0%)

Safety – Non-Hematologic ToxicitySafety – Non-Hematologic ToxicityPhase II Gem Carbo +/- IniparibPhase II Gem Carbo +/- Iniparib

O’Shaughnessy J, et al. NEJM 2011

Final Results:Final Results:Phase II: Gem Carbo +/- Iniparib in TNBCPhase II: Gem Carbo +/- Iniparib in TNBC

O’Shaughnessy J et.al. NEJM 2011

Final Results:Final Results:Phase II Gem Carbo +/- Iniparib in TNBCPhase II Gem Carbo +/- Iniparib in TNBC

O’Shaughnessy J, et.al. NEJM 2011

Phase I: Olaparib + Paclitaxel in 1Phase I: Olaparib + Paclitaxel in 1stst and 2and 2ndnd line MBC line MBC

BKG: Olaparib single agent activity in BRCA 1/2 mutated MBC

Olaparib + paclitaxel, N=19, 70% 1st line, unselected for BRCA mutations

33-40% RR; no CRs Median PFS: 5.2-6.3 months Hematologic toxicity high, requires G-CSF Dose reductions common Unclear whether combination be taken forward

Resistance to PARP Inhibitors: Resistance to PARP Inhibitors: Reversion of BRCA2 mutationsReversion of BRCA2 mutations

Partial function of BRCA2 is restored and cells become competent for homologous recombination repair

Edwards SL et al. Nature 2008; 451:1111-1115

The Future of PARP inhibitors: The Future of PARP inhibitors: Many Unanswered QuestionsMany Unanswered Questions

Can we use these agents more broadly? To treat other tumors with specific DNA repair defects,

i.e. sporadic loss of BRCA 1/2, tumors with PTEN mutations

Challenge is to identify them

Timing of PARP inhibitor in relation to cytotoxic agent (before it, with it, how long to continue it?)

ConclusionsConclusions

Targeting DNA repair mechanisms in tumor cells is a rational target

PARP is an integral enzyme in DNA repair Multiple PARP inhibitors are available Preliminary results show activity in BRCA mutated

cancers (Breast and Ovarian) Preliminary results show activity of iniparib with

chemotherapy in TNBC Phase III results forthcoming