Niraparib - CAS 1038915-60-4

Malignant pleural mesotheliomas (MPM) are most often surgically unresectable, and they respond poorly to current chemotherapy and radiation therapy. Between 23 and 64% of malignant pleural mesothelioma have somatic inactivating mutations in the BAP1 gene. BAP1 is a homologous recombination (HR) DNA repair component found in the BRCA1/BARD1 complex. Similar to BRCA1/2 deficient cancers, mutation in the BAP1 gene leads to a deficient HR pathway and increases the reliance on other DNA repair pathways. We hypothesized that BAP1-mutant MPM would require PARP1 for survival, similar to the BRCA1/2 mutant breast and ovarian cancers. Therefore, we used the clinical PARP1 inhibitors niraparib and olaparib to assess whether they could induce synthetic lethality in MPM. Surprisingly, we found that all MPM cell lines examined, regardless of BAP1 status, were addicted to PARP1-mediated DNA repair for survival. We found that niraparib and olaparib exposure markedly decreased clonal survival in multiple MPM cell lines, with and without BAP1 mutations. This clonal cell death may be due to the extensive replication fork collapse and genomic instability that PARP1 inhibition induces in MPM cells. The requirement of MPM cells for PARP1 suggests that they may generally arise from defects in HR DNA repair.

Niraparib is an investigational oral, once daily, selective poly(ADP-Ribose) polymerase (PARP)-1 and PARP-2 inhibitor. In the pivotal Phase 3 NOVA/ENGOT/OV16 study, niraparib met its primary endpoint of improving progression-free survival (PFS) for adult patients with recurrent, platinum sensitive, ovarian, fallopian tube, or primary peritoneal cancer in complete or partial response to platinum-based chemotherapy. Significant improvements in PFS were seen in all patient cohorts regardless of biomarker status. This study evaluates the absorption, metabolism and excretion (AME) of ;14;C-niraparib, administered to six patients as a single oral dose of 300 mg with a radioactivity of 100 μCi. Total radioactivity (TRA) in whole blood, plasma, urine and faeces was measured using liquid scintillation counting (LSC) to obtain the mass balance of niraparib. Moreover, metabolite profiling was performed on selected plasma, urine and faeces samples using liquid chromatography - tandem mass spectrometry (LC-MS/MS) coupled to off-line LSC. Mean TRA recovered over 504 h was 47.5% in urine and 38.8% in faeces, indicating that both renal and hepatic pathways are comparably involved in excretion of niraparib and its metabolites.

INTRODUCTION: ;Poly(ADP-ribose) polymerase (PARP) inhibitors are a targeted therapy option for ovarian cancer. The goal of this review was to organize and summarize the clinical trials evaluating PARP inhibitor therapy in ovarian cancer as monotherapy, maintenance therapy after partial or complete remission to therapy or as a part of a combination regimen.;EVIDENCE ACQUISITION: ;PubMed, ClinicalTrials.gov, data from the United States Food and Drug Administration (US FDA) and proceedings from scientific conferences were searched for published and unpublished data pertaining to clinical trials and approvals of PARP inhibitor use in ovarian cancer.;EVIDENCE SYNTHESIS: ;There have been 36 published phase 1, 2 and 3 studies evaluating the use of olaparib, niraparib, veliparib and rucaparib in ovarian cancer. Olaparib and rucaparib have been approved by the US FDA as monotherapy for advanced recurrent ovarian cancer. Niraparib and olaparib have been approved by the US FDA for maintenance therapy after partial or complete remission in recurrent ovarian cancer. There are currently ten phase 3 trials evaluating PARP inhibitors at various timepoints in ovarian cancer therapy including at the time of primary adjuvant therapy, as maintenance therapy after primary chemotherapy, as monotherapy for recurrent cancer and as maintenance therapy after chemotherapy for recurrence.