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. 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
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 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
PNK
Polß
Base Excision Repair
Inhibiting PARP-1 Increases Double-Strand DNA
Damage
DNA single strand
break (SSB)
damage
PNK 1
XRCC1
pol β
LigIII
PARP
During S-phase,
replication fork
is arrested at
site of SSB
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
gH2AX
BRCA1
MRE11
Non-homologous end-joining
Ku 70/80
DNA-PKcs
XRCC4
Cancer cell
death
Ligase IV
Predominant in G1
Error-prone
Gross Genomic instability
Rad50
NBS1
Homologous recombination
BRCA2
Rad 51
RPA Rad 52/4
ERCC1
XRCC3
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
0
Log
surviving
fraction
-1
Wild type
Control
-2
Wild type
BRCA2 +/BRCA2 -/-
-3
-4
0
10-9 10-8 10-7 10-6 10-5
PARP inhibitor concentration (M)
+ PARP inhibitor
BRCA2 -/-
10-4
Control
+ PARP inhibitor
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 crosslinks  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 DNA interstrand crosspoisons
linking, generation of O2
free radicals
Bleomycin
Directly damages DNA 
DS DNA breaks
Kennedy R et al. JNCI 2004; 96:1659-1668
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
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
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
28-day cycles
28-day cycles
(maximal PARP inhibition)
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)
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
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
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
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 Ovarian
BID
33
NR
35
9.6
NR
Olapirib
2
100 mg Ovarian
BID
24
NR
13
9.0
NR
Olapirib
2
400 mg Breast
BID
27
NR
41
NR
5.7
Olapirib
2
100 mg Breast
BID
27
NR
22
NR
3.8
MK4827
1
Varies
Ovarian
19
45
MK4827
1
Varies
Breast
4
50
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 DNAdamaging agents
Hereditary BRCA1
Triple Negative/Basal-Like1,2,3
Negative
Negative
Mutant
Mutant
Mutational inactivation*
Diminished expression*
Basal-like
Basal-like
Poorly differentiated
(high grade)
Poorly differentiated
(high grade)
Highly sensitive
Highly sensitive
*BRCA1 dysfunction due to germline mutations, promoter methylation, or overexpression of HMG or ID44
1Perou
et al. Nature. 2000; 406:747-752
et al.Lancet Oncol 2007;8:235-44
2Cleator
3Sorlie
4
et al. Proc Natl Acad Sci U S A 2001;98:10869-74
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/ triplenegative tumors
 Suggests that sporadic TNBC may have acquired defects in BRCA1related functions in DNA repair
Basal-like
= BRCA1+
Sorlie T et al. PNAS 2003;100:8418-8423
= BRCA2+
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 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
Metastatic TNBC
N = 120
RANDOMIZE
Gemcitabine (1000 mg/m2, IV, d 1, 8)
Carboplatin (AUC 2, IV, d 1, 8)
21-Day
Cycle
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)
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
Gem/Carbo
(n = 59)
BSI-201 + Gem/Carbo
(n = 57)
Grade 2
Grade 3
Grade 4
Grade 2
Grade 3
Grade 4
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%)
Anemia, n (%)
*Transfusion and/or EPO use
O’Shaughnessy J, et al. NEJM 2011
Safety – Non-Hematologic Toxicity
Phase 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
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%)
2
(3.4%)
0
(0.0%)
0
(0.0%)
1
(1.8%)
0
(0.0%)
0
(0.0%)
6
(10.2%)
1
(1.7%)
0
(0.0%)
1
(1.8%)
1
(1.8%)
0
(0.0%)
Neuropathy, n (%)
Diarrhea, n (%)
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 1st
and 2nd 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:
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