PARP Inhibitors:
Usurping DNA repair to target cancer
Lee Schwartzberg MD, FACP
Chief Medical Officer
The West Clinic

DNA repair mechanisms are important in
1.
2.
Cancer cells only
Both cancer and normal eukaryotic cells
3.
4.
Predominantly in rapidly growing cells like bone marrow precursors
Predominantly cancer cells with BRCA mutations

PARP inhibitors have demonstrated activity in:
1.
2.
BRCA 1 mutation carrier breast cancer
BRCA 2 mutation carrier breast cancer
3.
4.
5.
6.
Triple negative breast cancer
1 and 3 only
1 and 2 only
All of the above





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 day 1-3
1. Jackson SP. Biochem Soc Trans 2001;29:655-661
2. Lindahl T. Nature 1993;362:709-715
3. Jackson SP, Bishop CL. Drug Discovery World 2003;(Fall):41-45

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, Fanconi’s Anemia

Allow growth despite ongoing genome instability
 Are reliant on the DNA repair pathways they still retain

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
XRCC1
Lig3

Inhibiting PARP-1 Increases Double-Strand DNA
Damage pol
β
PNK 1
PARP
XRCC1
LigIII
During S-phase, replication fork is arrested at site of SSB
DNA single strand break (SSB) damage
Inhibition of
PARP-1 prevents
recruitment of
DNA repair enzymes
leads to failure of SSB repair
-accumulation of SSBs
Degeneration into
Double strand breaks

BRCA1 And 2 Are Required for Efficient
Repair of Double Stranded DNA Breaks
DNA DSB
ATM/R g H2AX
BRCA1
Rad50
MRE11 NBS1
Non-homologous end-joining Homologous recombination
Ku 70/80
DNA-PKcs
XRCC4 Ligase IV
BRCA2
RPA
Rad
51
Rad
52/4
ERCC1
XRCC3
Cancer cell
Predominant in G1 death
Error-prone
Gross Genomic instability
Major pathway for repair
Error-free
Cell survival
Cells with BRCA mutations are deficient in homologous recombination and lack the ability to efficiently repair DSBs.

(BRCA) (PARP)
Ashworth, A. J Clin Oncol; 26:3785-3790 2008

BRCA1 and BRCA2 -/- cells are very sensitive to PARP inhibition
Increased levels of chromosomal aberrations in PARP inhibitor treated BRCA2 -/- cells
Log surviving fraction
0
-1
Wild type
Control + PARP inhibitor -2
-3
Wild type
BRCA2 +/-
BRCA2 -/-
-4
0 10 -9 10 -8 10 -7 10 -6 10 -5 10 -4
PARP inhibitor concentration (M)
Control + PARP inhibitor
BRCA2 -/-
Farmer H et al. Nature 2005;434:917-920
Personal communication, Alan Ashworth

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

Chemotherapeutic Agents:
Double Strand DNA Breaks
Alkylators
Platinums
Topoisomerase I poisons
Topoisomerase II poisons
Bleomycin
DNA interstrand crosslinks
 double strand
(DS) DNA breaks
Cyclophosphamide
Forms adducts with DNA Cisplatin
Carboplatin
Oxaliplatin
Arrest of DNA replication forks
DNA interstrand crosslinking, generation of O
2 free radicals
Directly damages DNA

DS DNA breaks
Kennedy R et al. JNCI 2004; 96:1659-1668
Etoposide
Irinotecan
Topotecan
Mitoxantrone
Doxorubicin
Epirubicin

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
Breast
Ovarian
Fallopian tube
Prostate
Fong PC et al. N Engl J Med 2009; 361:123-134
BRCA
2
1 or 2
1
2
No. of pts
2
8
1
1
Response
1 CR, 1 SD
8 PRs
PR
PR

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 1
Cohort 2*
Olaparib 400 mg po bid (MTD)
Olaparib 100 mg po bid
(maximal PARP inhibition)
28-day cycles
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 2009;27(18S):803s (abstr CRA501)

Olaparib in BRCA-deficient Metastatic
Breast Cancer: Select Toxicities
Olaparib 400 mg BID
(n = 27)
Grade 1/2 Grade 3
Olaparib 100 mg BID
(n = 27)
Grade 1/2 Grade 3
Fatigue 15 (56) 4 (15) 15 (56) 2 (7)
Nausea
Vomiting
Headache
Constipation
11 (41)
7 (26)
10 (37)
6 (22)
5 (19)
3 (11)
0
0
15 (56)
6 (22)
5 (19)
8 (30)
0
0
1 (4)
0
Tutt A et al. J Clin Oncol 2009;27(18S):803s (abstr CRA501)

Olaparib in BRCA-deficient
Metastatic Breast Cancer: Results
Median 3 prior lines of therapy
Best percent change from baseline in target lesions by genotype
ITT cohort
ORR
400 mg BID
N = 27
11 (41%)
100 mg BID
N = 27
6 (22%)
CR
PR
Median
PFS
1 (4%)
10 (37%)
5.7 mo
(4.6-7.4)
0
6 (22%)
3.8 mo
(1.9 – 5.6)
Tutt A et al. J Clin Oncol 2009;27(18S):803s (abstr CRA501)

PARPi Monotherapy in BRCA Mutated tumors
Drug
Olapirib 1
Olapirib 2
Olapirib 2
Olapirib
Phase Dose Tumor N
2
Olapirib 2
1 MK-
4827
MK-
4827
1
Varies
100 mg
BID
400 mg
BID
Ovarian
Breast
50
400 mg
BID
Ovarian 33
Ovarian 24
27
100 mg
BID
Breast 27
Varies Ovarian 19
Varies Breast 4
CBR
(%)
46
NR
RR
(%)
40
35
NR 13
NR
NR
41
22
45
50
MDR
(MOS)
6.5
9.6
PFS
(MOS)
NR
NR
9.0
NR
NR
NR
5.7
3.8

Prior response to platinum may predict response to olaparib in BRCA mutated Ovarian Cancer
Gelmon K, et al J Clin Onc 2010





‘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.

TNBC Shares Clinical and Pathologic Features with
BRCA-1Related Breast Cancers (“BRCAness”)
Characteristics
ER/PR/HER2 status
TP53 status
BRCA1 status
Gene-expression pattern
Tumor histology
Chemosensitivity to DNAdamaging agents
Hereditary BRCA1
Negative
Mutant
Mutational inactivation*
Basal-like
Poorly differentiated
(high grade)
Highly sensitive
Triple Negative/Basal-Like 1,2,3
Negative
Mutant
Diminished expression*
Basal-like
Poorly differentiated
(high grade)
Highly sensitive
*BRCA1 dysfunction due to germline mutations, promoter methylation, or overexpression of HMG or ID4 4
1 Perou et al. Nature. 2000; 406:747-752
2 Cleator et al.Lancet Oncol 2007;8:235-44
3 Sorlie et al. Proc Natl Acad Sci U S A 2001;98:10869-74
4 Miyoshi et al. Int J Clin Oncol 2008;13:395-400



Clustering analyses of microarray RNA expression have shown that familial BRCA-1 tumors strongly segregate with basal-like/ triplenegative tumors
Suggests that sporadic TNBC may have acquired defects in BRCA1related functions in DNA repair
Basal-like
= BRCA1+ = BRCA2+
Sorlie T et al. PNAS 2003;100:8418-8423

Predictors of Response to Cisplatin in
TNBC
Silver, D. P. et al. J Clin Oncol; 28:1145-1153 2010

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 cancers 1
 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
Metastatic TNBC
N = 120
RANDOMIZE
1 st -3 rd line MBC
Eligible
Gemcitabine (1000 mg/m 2 , IV, d 1, 8)
Carboplatin ( AUC 2, IV, d 1, 8)
21-Day
Cycle
BSI-201 (5.6 mg/kg, IV, d 1, 4, 8, 11)
Gemcitabine ( 1000 mg/m 2 , IV, d 1, 8)
Carboplatin ( AUC 2, IV, d 1, 8)
RESTAGING
Every 2 Cycles
* Patients randomized to gem/carbo alone could crossover to receive gem/carbo + BSI-201 at disease progression

Safety – Hematologic Toxicity
Phase II Gem Carbo +/- Iniparib
Anemia, n (%)
Thrombocytopenia, n (%)
Neutropenia, n (%)
Febrile neutropenia, n (%)
RBC treatment*, n (%)
G-CSF Use, n (%)
Gem/Carbo
(n = 59)
Grade 2 Grade 3 Grade 4
12
(20.3%)
7 (11.9%)
0
(0.0%)
7 (11.9%)
7 (11.9%)
6
(10.2%)
18
(30.5%)
6
(10.2%)
13
(22.0%)
0
(0.0%)
5
(8.5%)
6
(10.2%)
3
(5.1%)
5
(8.5%)
6
(10.2%)
1
(1.7%)
2
(3.4%)
3
(5.1%)
BSI-201 + Gem/Carbo
(n = 57)
Grade 2 Grade 3 Grade 4
15
(26.3%)
7
(12.3%)
0
(0.0%)
4
(7.0%)
7 (12.3%)
6
(10.5%)
18
(31.6%)
7
(12.3%)
7
(12.3%)
0
(0.0%)
3
(5.3%)
4
(7.0%)
0
(0.0%)
5
(8.8%)
5
(8.8%)
0
(0.0%)
2
(3.5%)
1
(1.8%)
*Transfusion and/or EPO use
O’Shaughnessy J, et al. NEJM 2011

Safety – Non-Hematologic Toxicity
Phase II Gem Carbo +/- Iniparib
Nausea, n (%)
Vomiting, n (%)
Fatigue, n (%)
Neuropathy, n (%)
Diarrhea, n (%)
Gem/Carbo
(n = 59)
Grade 2 Grade 3 Grade 4
10
(16.9%)
2
(3.4%)
0
(0.0%)
9
(15.3%)
10
(16.9%)
2
(3.4%)
6
(10.2%)
0
(0.0%)
6
(10.2%)
0
(0.0%)
1
(1.7%)
0
(0.0%)
0
(0.0%)
0
(0.0%)
0
(0.0%)
BSI-201 + Gem/Carbo
(n = 57)
Grade 2 Grade 3 Grade 4
7
(12.3%)
0
(0.0%)
0
(0.0%)
4
(7.0%)
10
(17.5%)
1
(1.8%)
1
(1.8%)
1
(1.8%)
1
(1.8%)
0
(0.0%)
1
(1.8%)
0
(0.0%)
0
(0.0%)
0
(0.0%)
0
(0.0%)
O’Shaughnessy J, et al. NEJM 2011

Final Results:
Phase II: Gem Carbo +/- Iniparib in TNBC
O’Shaughnessy J et.al. NEJM 2011

Final Results:
Phase II Gem Carbo +/- Iniparib in TNBC
O’Shaughnessy J, et.al. NEJM 2011

Phase I: Olaparib + Paclitaxel in 1 st and 2 nd line MBC





 BKG: Olaparib single agent activity in BRCA 1/2 mutated MBC
 Olaparib + paclitaxel, N=19, 70% 1 unselected for BRCA mutations st line,
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

 Partial function of
BRCA2 is restored and cells become competent for homologous recombination repair
Edwards SL et al. Nature 2008; 451:1111-1115

 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?)





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