Abstract IS04: PARP INHIBITOR COMBINATIONS FOR THE TREATMENT OF OVARIAN CANCER

Poly(ADP-ribose) polymerase (PARP) inhibitors have shown promising single-agent activity in ovarian cancers with BRCA1 and BRCA2 mutations (C. Scott, JCO 33:1397, 2015). Ongoing studies are testing the efficacy of PARP inhibitors in ovarian cancers with other genetic or epigenetic alterations that impair the homologous recombination (HR) pathway of DNA repair. It is less clear whether PARP inhibitor clinical activity can be enhanced in HR deficient cancers or even extended to HR proficient ovarian cancers through judicious combinations. Our preclinical studies have demonstrated that PARP inhibitors enhance the cytotoxic effects of selected therapeutic agents through a variety of mechanisms: By trapping PARP at sites of DNA damage, PARP inhibitors enhance the cytotoxicity of topotecan (A. Patel, J. Biol. Chem. 287: 4198, 2012). By inhibiting base excision repair, PARP inhibitors enhance the cytotoxicity of floxuridine (A. Huehls, Cancer Res. 71: 4944, 2011), an agent previously shown to have clinical activity in ovarian cancer. Building on the first of these observations, we conducted a phase 1 clinical trial of topotecan weekly x 3 in combination with veliparib (NCT01012817). Using a standard 3+3 design, patients were treated with veliparib PO twice daily on days 1-3, 8-10 and 15-17 and topotecan IV on days 2, 9 and 16 every 28 days. The dose-limiting toxicity was neutropenia. The MTD was veliparib 300 mg PO twice daily and topotecan 3 mg/m 2 /dose. Among 52 evaluable patients, objective responses (1 CR, 3 PRs) and stable disease (22 patients, 6 lasting ≥ 8 cycles) were observed. While there was no clear correlation between germline BRCA1 or BRCA2 mutations and clinical benefit, a patient with a germline RAD51D mutation had stable disease for 14 cycles. A phase 2 cohort in platinum-resistant ovarian cancer has just opened. Building on the second set of preclinical observations, we are also conducting a phase 1 trial of veliparib and IP floxuridine in patients with recurrent ovarian cancer confined to the peritoneal cavity (NCT01749397). Using a rolling 6 design, patients are treated with veliparib PO twice daily on days 1-10 and floxuridine IP on days 3-5 every 21 days. The trial is currently enrolling at dose level 5 (veliparib 300 mg PO twice daily on days 1-10 and floxuridine 3 gm/dose IP on days 3-5). Grade 3 toxicities in any cycle have included nausea (1), fatigue (1) and neutropenia (3). Among 20 evaluable patients, treatment duration has ranged from 2-33 cycles. These studies, which build on two different aspects of PARP1 function, illustrate two different approaches to potentially enhancing the activity of PARP inhibitors in relapsed ovarian cancer. These studies were funded in part by NIH grants P50 CA136393, R01 CA190423, and UM1 CA186686 as well as SU2C-AACR DT16-15. Citation Format: Scott H. Kaufmann, Andrea E. Wahner Hendrickson, Maria I Harrell, Michael E. Menefee, Edward J. Tanner, David G, Mutch, Elizabeth M. Swisher, and Larry M. Karnitz. PARP INHIBITOR COMBINATIONS FOR THE TREATMENT OF OVARIAN CANCER [abstract]. In: Proceedings of the 11th Biennial Ovarian Cancer Research Symposium; Sep 12-13, 2016; Seattle, WA. Philadelphia (PA): AACR; Clin Cancer Res 2017;23(11 Suppl):Abstract nr IS04.