PARP Inhibitors: Usurping DNA repair to target cancer

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PARP InhibitorsUsurping DNA repair to target
cancer

• Lee Schwartzberg MD, FACP
• Chief Medical Officer
• The West Clinic

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Question 1

• DNA repair mechanisms are important in
• Cancer cells only
• Both cancer and normal eukaryotic cells
• Predominantly in rapidly growing cells like bone
  marrow precursors
• Predominantly cancer cells with BRCA mutations

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Question 2

• PARP inhibitors have demonstrated activity in
• BRCA 1 mutation carrier breast cancer
• BRCA 2 mutation carrier breast cancer
• Triple negative breast cancer
• 1 and 3 only
• 1 and 2 only
• All of the above

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All cells are under constant risk of DNA 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
200129655-661 2. Lindahl T. Nature
1993362709-715 3. Jackson SP, Bishop CL. Drug
Discovery World 2003(Fall)41-45
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Cellular Response To DNA Damage
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Cancer cells are highly susceptible to 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, Fanconis Anemia
• Allow growth despite ongoing genome instability
• Are reliant on the DNA repair pathways they
  still retain

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DNA Excision Repair Mechanisms
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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
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Base Excision Repair
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Inhibiting PARP-1 Increases Double-Strand DNA
Damage
Degeneration into Double strand breaks
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BRCA1 And 2 Are Required for Efficient Repair of
Double Stranded DNA Breaks
DNA DSB
ATM/R
gH2AX
BRCA1
Rad50
NBS1
MRE11
Non-homologous end-joining
Homologous recombination
Ku 70/80
BRCA2
Rad 51
RPA
Rad 52/4
DNA-PKcs
ERCC1 XRCC3
XRCC4
Ligase IV
Predominant in G1 Error-prone Gross 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.
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The Concept of Synthetic Lethality
(PARP)
(BRCA)
Ashworth, A. J Clin Oncol 263785-3790 2008
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BRCA1 and BRCA2 -/- cells are very sensitive to
PARP inhibition
Increased levels of chromosomal aberrations in
PARP inhibitor treated BRCA2 -/- cells
Wild type
Control
PARP inhibitor
BRCA2 -/-
Control
PARP inhibitor
Farmer H et al. Nature 2005434917-920 Personal
communication, Alan Ashworth
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PARP Inhibitors in Clinical Development

• Differing chemical structures
• Differing toxicity
• Differing schedules and routes of administration

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Chemotherapeutic Agents 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 961659-1668
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PARP Inhibitors in BRCA 1/2 Mutated Tumors
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Phase I Trial of Olaparib in Patients 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 361123-134
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Phase II Trial of Olaparib in BRCA-deficient
Metastatic Breast Cancer
Eligibility
Confirmed BRCA1 or 2 mutation Stage IIIB/C or IV BC after progression 1 prior chemotherapy for advanced disease
(Non-randomized sequential cohorts)
Cohort 2 Olaparib 100 mg po bid (maximal PARP
inhibition) 28-day cycles
Cohort 1 Olaparib 400 mg po bid (MTD) 28-day
cycles
Primary Endpoint Response rate
Following an interim review, patients in the
100 mg bid cohort were permitted to crossover to
receive 400 mg bid
Tutt A et al. J Clin Oncol 200927(18S)803s
(abstr CRA501)
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Olaparib in BRCA-deficient Metastatic Breast
Cancer Select Toxicities
Olaparib 400 mg BID (n 27) Olaparib 400 mg BID (n 27) Olaparib 400 mg BID (n 27) Olaparib 400 mg BID (n 27) Olaparib 100 mg BID (n 27) Olaparib 100 mg BID (n 27) Olaparib 100 mg BID (n 27)
Grade 1/2 Grade 3 Grade 1/2 Grade 3
Fatigue Fatigue 15 (56) 4 (15) 15 (56) 2 (7)
Nausea Nausea 11 (41) 5 (19) 15 (56) 0
Vomiting Vomiting 7 (26) 3 (11) 6 (22) 0
Headache Headache 10 (37) 0 5 (19) 1 (4)
Constipation Constipation 6 (22) 0 8 (30) 0
Tutt A et al. J Clin Oncol 200927(18S)803s
(abstr CRA501)
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Olaparib in BRCA-deficient Metastatic Breast
Cancer Results
Best percent change from baseline in target
lesions by genotype
Median 3 prior lines of therapy
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 200927(18S)803s
(abstr CRA501)
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PARPi Monotherapy in BRCA Mutated tumors
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 mg BID Ovarian 24 NR 13 9.0 NR
Olapirib 2 400 mg BID 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
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Prior response to platinum may predict response
to olaparib in BRCA mutated Ovarian Cancer
Gelmon K, et al J Clin Onc 2010
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PARP Inhibitors beyond BRCA mutation carriers
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Triple Negative Breast Cancer (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 1017 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
200852108-118.
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TNBC Shares Clinical and Pathologic Features with
BRCA-1-Related Breast Cancers (BRCAness)
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 histology Poorly differentiated (high grade) Poorly differentiated (high grade)
Chemosensitivity to DNA-damaging agents Highly sensitive Highly sensitive
BRCA1 dysfunction due to germline mutations,
promoter methylation, or overexpression of HMG or
ID44
3Sorlie et al. Proc Natl Acad Sci U S A
20019810869-74 4 Miyoshi et al. Int J Clin
Oncol 200813395-400
1Perou et al. Nature. 2000 406747-752 2Cleator
et al.Lancet Oncol 20078235-44
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Targeting DNA Repair Pathway in TNBC

• 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

Basal-like
BRCA1
BRCA2
Sorlie T et al. PNAS 20031008418-8423
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Predictors of Response to Cisplatin in TNBC

• Silver, D. P. et al. J Clin Oncol 281145-1153
  2010

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Phase II Study of the PARP inhibitor Iniparib in
Combination with Gemcitabine/Carboplatin in
Triple 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

OShaughnessy J, et al. NEJM 2011
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Phase II TNBC Study Treatment Schema
RANDOMIZE
Metastatic TNBC N 120
1st -3rd line MBC Eligible
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)
21-Day Cycle
RESTAGING Every 2 Cycles
Patients randomized to gem/carbo alone could
crossover to receive gem/carbo BSI-201 at
disease progression
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Safety Hematologic ToxicityPhase II Gem Carbo
/- Iniparib
Gem/Carbo (n 59) Gem/Carbo (n 59) Gem/Carbo (n 59) BSI-201 Gem/Carbo (n 57) BSI-201 Gem/Carbo (n 57) 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
OShaughnessy J, et al. NEJM 2011
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Safety Non-Hematologic ToxicityPhase II Gem
Carbo /- Iniparib
Gem/Carbo (n 59) Gem/Carbo (n 59) Gem/Carbo (n 59) BSI-201 Gem/Carbo (n 57) BSI-201 Gem/Carbo (n 57) 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)
OShaughnessy J, et al. NEJM 2011
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Final ResultsPhase II Gem Carbo /- Iniparib
in TNBC
OShaughnessy J et.al. NEJM 2011
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Final ResultsPhase II Gem Carbo /- Iniparib in
TNBC
OShaughnessy J, et.al. NEJM 2011
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Phase I Olaparib Paclitaxel in 1st and 2nd
line MBC

• BKG Olaparib single agent activity in BRCA 1/2
  mutated MBC
• Olaparib paclitaxel, N19, 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

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Resistance to PARP Inhibitors Reversion of BRCA2
mutations

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

Edwards SL et al. Nature 2008 4511111-1115
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The Future of PARP inhibitors Many 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?)

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Conclusions

• 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