Human cancer cells or xenograft tumors with mutated or epigenetically silenced BRCA1/2 were sensitive to AG014699 monotherapy, indicating a potential role for PARP inhibitors in sporadic human cancers.

Up to 50% of epithelial ovarian cancers (EOC) display defects in the homologous recombination (HR) pathway. We sought to determine the ramifications of the homologous recombination-deficient (HRD) status on the clinicopathologic features, chemotherapy response, and survival outcomes of patients with EOCs. HR status was determined in primary cultures from ascitic fluid in 50 chemotherapy-na€ ve patients by a functional RAD51 immunofluorescence assay and correlated with in vitro sensitivity to the PARP inhibitor (PARPi), rucaparib. All patients went on to receive platinum-based chemotherapy; platinum sensitivity, tumor progression, and overall survival were compared prospectively in HR-competent versus HRD patients. Compared with HR-competent patients, the HRD group was predominantly serous with a higher median CA125 at presentation. HRD was associated with higher ex vivo PARPi sensitivity and clinical platinum sensitivity. Median follow-up duration was 14 months; patients in the HRD group had lower tumor progression rates at 6 months, lower overall/diseasespecific death rates at 12 months, and higher median survival. We therefore suggest that HRD as predicted by a functional RAD51 assay correlates with in vitro PARPi sensitivity, clinical platinum sensitivity, and improved survival outcome. Cancer Res; 72(22); 5675-82. Ó2012 AACR.

Purpose: Temozolomide, a DNA methylating agent used to treat melanoma, induces DNA damage, which is repaired by O 6 -alkylguanine alkyltransferase (ATase) and poly(ADP-ribose) polymerase-1 (PARP-1)^dependent base excision repair. The current study was done to define the effect of temozolomide on DNA integrity and relevant repair enzymes as a prelude to a phase I trial of the combination of temozolomide with a PARP inhibitor. Experimental Design: Temozolomide (200 mg/m 2 oral administration) was given to 12 patients with metastatic malignant melanoma. Peripheral blood lymphocytes (PBL) were analyzed for PARP activity, DNA single-strand breakage, ATase levels, and DNA methylation. PARP activity was also measured in tumor biopsies from 9 of 12 patients and in PBLs from healthy volunteers. Results: Temozolomide pharmacokinetics were consistent with previous reports. Temozolomide therapy caused a substantial and sustained elevation of N 7 -methylguanine levels, a modest and sustained reduction in ATase activity, and a modest and transient increase in DNA strand breaks and PARP activity in PBLs. PARP-1activity in tumor homogenates was variable (828 F 599 pmol PAR monomer/mg protein) and was not consistently affected by temozolomide treatment. Conclusions:The effect of temozolomide reported here are consistent with those documented in previous studies with temozolomide and similar drug, dacarbazine, demonstrating that a representative patient population was investigated. Furthermore, PARP activity was not inhibited by temozolomide treatment and this newly validated pharmacodynamic assay is therefore suitable for use in a proof-of-principle phase I trial a PARP-1inhibitor in combination with temozolomide.Intrinsic or acquired resistance remains a major limitation in the use of cytotoxic chemotherapy. A variety of cancer cell resistance mechanisms have been described or proposed, including decreased drug uptake into cells, increased drug efflux intracellular drug inactivation, alteration of the cellular target, repair of drug-induced damage, or development of tolerance to drug-induced lesions (1). Strategies directed at overcoming these mechanisms of drug resistance are being evaluated, including the targeting of DNA repair pathways, in an attempt to improve on the efficacy of existing cytotoxic drugs.Temozolomide is an orally available monofunctional DNA alkylating agent used to treat gliomas and malignant melanoma (2). Temozolomide is rapidly absorbed and undergoes spontaneous breakdown to form the active monomethyl triazene, 5-(3-methyl-1-triazeno)imidazole-4-carboxamide. Monomethyl triazene forms several DNA methylation products, the predominate species being N 7 -methylguanine (70%), N 3 -methyladenine (9%), and O system signals G 2 -M cell cycle arrest and the initiation of apoptosis (5 -7). The quantitatively more important N 7 -methylguanine and N 3 -methyladenine lesions formed by temozolomide are rapidly repaired by base excision repair.The nuclear enzyme poly(ADP-ribose) polymerase-1 (PARP-1) plays a ...

Purpose: High-risk neuroblastoma is characterized by poor survival rates, and the development of improved therapeutic approaches is a priority. Temozolomide and topotecan show promising clinical activity against neuroblastoma. Poly(ADP-ribose) polymerase-1 (PARP-1) promotes DNA repair and cell survival following genotoxic insult; we postulated that its inhibition may enhance the efficacy of these DNA-damaging drugs in pediatric cancers. Experimental Design: We evaluated the chemosensitizing properties of the PARP inhibitor AG014699 (Pfizer, Inc.) in combination with temozolomide and topotecan, against human neuroblastoma cells and xenografts, alongside associated pharmacologic and toxicologic indices. Results: Addition of PARP-inhibitory concentrations of AG014699 significantly potentiated growth inhibition by both topotecan (1.5-to 2.3-fold) and temozolomide (3-to 10-fold) in vitro, with equivalent effects confirmed in clonogenic assays. In two independent in vivo models (NB1691 and SHSY5Y xenografts), temozolomide caused a xenograft growth delay, which was enhanced by co-administration of AG014699, and resulted in complete and sustained tumor regression in the majority (6 of 10; 60%) of cases. Evidence of enhanced growth delay by topotecan/AG014699 co-administration was observed in NB1691 xenografts. AG014699 metabolites distributed rapidly into the plasma (C max , 1.2-1.9 nmol/L at 30 min) and accumulated in xenograft tissues (C max ,1-2 Amol/L at 120 min), associated with a sustained suppression of PARP-1enzyme activity. Doses of AG014699 required for potentiation were not toxic per se. Conclusions: These data show enhancement of temozolomide and topotecan efficacy by PARP inhibition in neuroblastoma. Coupled with the acceptable pharmacokinetic, pharmacodynamic, and toxicity profiles of AG014699, our findings provide strong rationale for investigation of PARP inhibitors in pediatric early clinical studies.