AZIENDA OSPEDALIERO-UNIVERSITARIA DI MODENA Targeted therapies in hereditary cancer with PARP-inhibitors: a new biological approach. PARP Antonio Frassoldati Dept Oncology, Hematology and Lung diseases Policlinico - Modena Modena, 19 novembre 2010
DNA damage response has a key role in cancer Excessive DNA damage can result in human cancers, as seen with acute toxic exposures (X-rays) and with chronic environmental exposures (cigarettes, asbestos). Inheritance of mutations in human genes involved in the DDR results in a much higher genomic instability and risk of developing certain cancers. Many of the acute and late normal tissue toxicities from using CT and/or RT are a consequence of the DDR.
DNA Damage Response/Repair Pathways double-strand breaks, single-strand breaks, base damages, bulky adducts, intra-and interstrand cross-links. Kinsella, PASCO 2009
Cancer Susceptibility Syndromes Linked to Defective DNA Damage/Repair Responses Syndrome Defects Tumor risk Li-Fraumeni (AD, p53 heterozigote) Lynch/HNPCC (AD, 1 degrees MLH1/MSH2) BRAC1, BRCA2 (AD, gene heterozigote) AT (AR, AT mutated) Cell cycle regulation, apoptosis Mismatch repair HR and other DNA repair pathways DSB repair, cell cycle regulation Breast, sarcoma, others Colorectal, uterine, others Breast, Ovary Acute leukemia, lymphomas XP (AR, XP variants) NER Skin cancers Fanconi s anemia (AR) Cross-link repair Acute myeloid leukemia AD, autosomal dominant; AR, autosomal recessive; AT, ataxia-telangiectasia; DSB, double-strand breaks; HNPCC, hereditary nonpolyposis colorectal cancer; HR, homologous recombination; NER, nucleotide excision repair; XP, xeroderma pigmentosum.
Types of DNA damage and repair Type of damage: Singlestrand breaks (SSBs) Doublestrand breaks (DSBs) Bulky adducts Insertions & deletions O6- alkylguanine Mismatch repair Repair pathway: Base excision repair Recombinational repair Nucleotideexcision repair Direct reversal HR NHEJ Repair enzymes: PARP ATM DNA-PK XP, MSH2, polymerases MLH1 AGT
potentially resulting in gross chromosomal rearrangements Two main pathways contribute to repair of DNA double-strand breaks accurate repair of the break NHEJ is the most important pathway for the repair of DSBs during G0, G1 and early S phases of the cell cycle HR is cell cycle regulated and is most active in S-G2 phases of the cell cycle. Anders, Clin Cancer Res 2010
Turner, Nat Rev Cancer 2004; Carey, Clin Canc Rev 2010 DNA-repair mechanisms in normal and HR-deficient cells. HR-deficient cells
PARP-1 poly(adenosine diphosphate ribose) polymerase. Key component in the base excision repair of DNA Abundant and highly conserved chromatinbound enzyme Binds to nicked DNA as homodimer Mediates protection against SSB DNA damage HR-deficienct cells are more sensitive to PARP inhibition Cepeda V, et al. Recent Pat Anticancer Drug Discov. 2006;1:39-53.
PARP-1 is a key enzyme involved in the repair of single-strand DNA breaks DNA damage PARP PAR chains are degraded via PARG Repaired DNA Binds directly to SSBs NAD+ Nicotinamide +padpr Repair enzyme recruitment PAR Once bound to damaged DNA, PARP modifies itself producing large branched chains of PAR
Familial/Hereditary BC
TNBC classified as basal like by gene expression 80% of the time, distinct risk factors: aggressive and early patterns of metastases, unique molecular characteristics, association with BRCA1 mutations, relative lack of targeted therapeutics, poor prognosis
Features differentiating familial BRCA from sporadic breast cancers Turner, Nat Rev Canc 2004
Alternative mechanism of DDR can be targeted in BRCA deficient cancers Synthetic lethality Anders, Clin Cancer Res 2010
Inhibiting PARP Increases Double-Strand DNA Breaks and Death of HR-Deficient Cells DNA SSB damage pol β PNK 1 PARP XRCC1 LigIII Inhibition of PARP-1 Prevents recruitment of DNA repair enzymes Leads to failure of SSB repair During S-phase, replication fork is arrested at site of SSB Leads to accumulation of SSBs Degeneration into double-strand breaks and cell death if HR deficient
Poly(ADP-Ribose) Polymerase Inhibitors in Current Clinical Trial Testing
Inhibition of Poly(ADP-Ribose) Polymerase with Olaparib in Tumors From BRCA Mutation Carriers Phase I study Characteristic Value Sex, n (%) Male/Female 20/40 (33/67) Tumor type, n (%)* Ovarian 21 (35) Breast 9 (15) Colorectal 8 (13) Melanoma 4 (7) Sarcoma 4 (7) Prostate 3 (5) Other 11 (18) Previous treatment regimens, n (%) 1 6 (10) 2-3 22(36) 4 32 (53) Fong, N Engl J Med. 2009
Clinical Responses in Study Patients Subgroup and Dose Patients N Partial or Complete Radiologic Response Radiologically SD All patients, N 60 9 7 Patients with BRCA1 or BRCA2 ovarian, breast, or prostate cancer, n 19 9 (8 with ovarian cancer, 1 with breast cancer) 2 (1 with ovarian cancer, 1 with breast cancer) < 100 mg BID continuously, n 1 0 0 100 mg BID 2 of every 3 wks, n 2 1 0 100 mg BID continuously, n 1 0 0 200 mg BID continuously, n 10 4 2 (actual duration: 6 and 7 mos) 400 mg BID continuously, n 4 4 0 600 mg BID continuously 1 0 0 Fong PC, et al. N Engl J Med. 2009
Measuring PARP inhibition Effect on peripheral blood mononuclear cells Tutt, ASCO 2007
Measuring PARP inhibition Formation of foci of γh2ax, the phosphorylated form of histone H2A histone family member X (H2AX) at serine 139, is a marker of DNA double-strand breaks Fong, N Engl J Med. 2009
Olaparib in patients with BRCA1 or BRCA2 mutation and advanced breast cancer: a proof of concept trial Olaparib 400 mg twice daily (first cohort) Olaparib 100 mg twice daily* (second cohort) (23 escalated to higher dosage, 47% after PD) Median chemotherapy regimens: 3 (1-5) 3 (2-4) (taxane, anthra, capecitabine, platinum) BRCA1: 67% - 56% BRCA2: 33% - 41% TN: 50% - 64% ER+: 41% - 15% HER2+: 8% - 19% Maximum tolerated dose; * Dose sufficient to saturate inhibition of the target in PMNcells in phase I trial Tutt, Lancet 2010
Best overall tumor response rate* Olaparib 400 mg twice daily Olaparib 100 mg twice daily N=27 N=27 Objective response 11 (41%) 6 (22%) CR 1 (4%) 0 PR 10 (37%) 6 (22%) Stable disease 12 (44%) 12 (44%) Progressive disease 4 (15%) 9 (33%) * Intention to treat; all but 1 within first 4 courses Tutt, Lancet 2010
Best change from baseline 100 Olaparib 400 mg bid Increasing tumor shrinkage BRCA1 BRCA2 Olaparib 100 mg bid Increasing tumor shrinkage 0 Median: - 30% Median: - 7% -100 % Tutt, Lancet 2010
Olaparib in BRCA1 or 2 mutant advanced breast cancer patients Median 3.8 mos 5.7 mos Tutt, Lancet 2010
Olaparib in BRCA-Deficient Metastatic Breast Cancer: Selected Toxicities Toxicities, n (%) 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 (0) Vomiting 7 (26) 3 (11) 6 (22) 0 (0) Headache 10 (37) 0 (0) 5 (19) 1 (4) Constipation 6 (22) 0 (0) 8 (30) 0 (0) Tutt A, et al. ASCO 2009. Abstract CRA501.
Selective effect of PARP-i Farmer, Nature 2005
Olaparib in BRCA1 or BRCA2 mutated advanced ovarian cancer Median 29% Median 0% Median 5.8m; 1.9m 400 mg bid 100 mg bid 70 pts with advaced ovarian cancer, progressing after 3-4 median previous chemotherapy regimens BRCA1 mut: 64% and 79% in 400 mg and 100 mg (bid) cohorts Objective response: 33% - 13%; CB 52% - 21% Audeh, Lancet 2010
Activity in BRCA1 or 2 mutated does not explain the whole story The magnitude of effect is lower than that observed in other targeted therapies towards driving pathways (c-kit, EGFRm, ALK) Various mutations may induce different defects in HR with different sensitivity to PARP-inhibitors Secondary BRCA2 mutations may restore BRCA function Other molecular events may reactivate DNA repair and offset the synthetic lethality
Benefit of PARP-inhibitors migth not be restricted only to patients with germline BRCA mutation Loss of function of proteins different from BRCA1 and 2: RAD51, ataxia-ataxia telangiectasia mutated (ATM), ataxia telangiectasia and Rad3 related (ATR), and checkpoint kinase 1 and 2 homologue (CHK1 and CHK2) proteins, components of the Fanconi s anemia repair pathway Epigenetic silencing of BRCA1 BRCAness in sporadic cancer
Some sporadic tumors are phenocopies of BRCA1 or BRCA2 deficient tumors without bearing germline mutations The BRCAness tumors
BRCA phenotype and sporadic Breast Cancer Turner, Nat Rev Cancer 2004
Randomized Phase II Trial of BSI-201 + Gem/Carbo in Triple-Negative MBC Key inclusion criteria: 2 previous chemotherapies for MBC No previous gemcitabine, platinum agent, or PARP inhibitor N = 123 BSI-201 5.6 mg/kg, Days 1, 4, 8, 11 Gemcitabine 1000 mg/m 2, Days 1, 8 Carboplatin AUC 2, Days 1, 8 q 3 wks (n = 61) Gemcitabine 1000 mg/m 2, Days 1, 8 Carboplatin AUC = 2, Days 1, 8 q 3 wks (n = 62) Crossover to experimental arm allowed at progression Restage every 2 cycles Primary endpoints: CBR (CR + PR + SD 6 mos), safety Secondary endpoints: ORR, PFS, OS O Shaughnessy J, et al. SABCS 2009. Abstract 3122.
Gem/Carbo BSI-201 + Gem/Carbo P- value 1st line 38/59 (64%) 32/57 (56%) Therapy 2nd line 13/59 (22%) 19/57 (33%) 3rd line 8/59 (14%) 6/57 (11%) ORR (%) 7/44 (16%) 20/42 (48%) 0.002 Clinical Benefit Rate (%) 9/44 (21%) 26 (62%) 0.0002
PARP inhibitors: a new way to treat cancer by targeting a cell weakness WHAT WE KNOW Important activity as a class in BRCA1/2 mutant tumors in clinic Enhanced activity of DNA damaging agents in xenograft, possibly potentiated DNA damage by alkylating agents in early sudies Increased marrow toxicity of certain topo-i poisons, and gem/platinum WHAT WE NEED TO KNOW What degree/duration of PARP inhibition required to produce clinical benefit? Role of off-target effects Effect of PARP inhibition vs other DNA repair defects Unclear mechanism of resistance to agents as a class: Role of restoration of HR or alternative DNA repair pathways? Why only certain classes of DNA damaging drugs potentiated? Doroshow, ASCO 2010
Conclusions The DNA damage response (DDR) is a complex response to DNA-damaging cancer therapy. Genetic and epigenetic alterations to the DDR predispose to cancer development but may also provide opportunities for more targeted cancer therapeutics. PARP inhibitors represent a new way to treat cancer by targeting a cell weakness Ongoing trials will hopefully clarify their role in BRCA mutated and in BRCAness cancers, the best way of administration and the mechanisms of resistance.