Transcript Triple Negative Breast Cancer (TNBC)
PARP Inhibitors: Usurping DNA repair to target cancer
Lee Schwartzberg MD, FACP Chief Medical Officer The West Clinic
Question 1
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
Question 2
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
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 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
Cellular Response To DNA Damage
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
DNA Excision Repair Mechanisms
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
Base Excision Repair
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.
The Concept of Synthetic Lethality
(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 PARP inhibitor concentration (M) -5 10 -4 Control + PARP inhibitor BRCA2 -/ Farmer H et al. Nature 2005;434:917-920 Personal communication, Alan Ashworth
PARP Inhibitors in Clinical Development
Differing chemical structures Differing toxicity Differing schedules and routes of administration
Chemotherapeutic Agents: Double Strand DNA Breaks Alkylators DNA interstrand cross links
double strand (DS) DNA breaks Forms adducts with DNA Cyclophosphamide Platinums Topoisomerase I poisons Arrest of DNA replication forks Topoisomerase II poisons Bleomycin DNA interstrand cross linking, generation of O 2 free radicals Directly damages DNA
DS DNA breaks
Kennedy R et al. JNCI 2004; 96:1659-1668
Cisplatin Carboplatin Oxaliplatin Etoposide Irinotecan Topotecan Mitoxantrone Doxorubicin Epirubicin
PARP Inhibitors in BRCA 1/2 Mutated Tumors
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) 28-day cycles Olaparib 100 mg po bid (maximal PARP inhibition) 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 Olapirib 1 2 Olapirib 2 Olapirib Olapirib MK 4827 MK 4827
Phase Dose Tumor N
2 2 1 1 Varies Ovarian 400 mg BID Ovarian 100 mg BID 400 mg BID Ovarian Breast 100 mg BID Breast Varies Ovarian 50 33 24 27 27 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
PARP Inhibitors beyond BRCA mutation carriers
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 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-1 Related Breast Cancers (“BRCAness”) Characteristics ER/PR/HER2 status TP53 status BRCA1 status Gene-expression pattern Tumor histology Chemosensitivity to DNA damaging 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
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 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 Eligible line MBC
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 (%) Grade 2
12 (20.3%)
Gem/Carbo (n = 59) Grade 3
7 (11.9%)
Grade 4
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
15 (26.3%)
Grade 3
7 (12.3%)
Grade 4
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 (%) Grade 2
10 (16.9%)
Gem/Carbo (n = 59) Grade 3
2 (3.4%)
Grade 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
7 (12.3%)
Grade 3
0 (0.0%)
Grade 4
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
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; 451:1111-1115
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?)
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