The poly (ADP ribose) polymerase inhibitor niraparib: Management of toxicities

Niraparib is an oral poly(ADP ribose) polymerase (PARP) inhibitor that is currently approved by the United States Food and Drug Administration (US FDA) as well as recently approved by the European Medicines Agency (EMA) for the maintenance treatment of women with recurrent ovarian cancer who are in complete or partial response to platinum-based chemotherapy. The mechanisms of action of niraparib include inhibition of PARP enzymatic activity as well as increased formation of PARP-DNA complexes through "trapping" the PARP enzyme on damaged DNA. Phase I and III studies have demonstrated activity and benefit of niraparib in both BRCA mutated (BRCAm) and BRCA wild-type (BRCAwt) cancers. Phase I testing of niraparib established the maximally tolerated dose of 300mg by mouth (PO) daily, and the phase 3 ENGOT-OV16/NOVA study demonstrated the benefit of niraparib maintenance therapy compared to placebo after completion of and response to platinum-based chemotherapy in both BRCAm and BRCAwt ovarian cancer patient populations. Toxicities seen with niraparib include hematologic, gastrointestinal, fatigue, and cardiovascular. Hematologic toxicities include thrombocytopenia, anemia, neutropenia and leukopenia; upfront dose modification to 200mg niraparib for patients with baseline weight of ≤77kg and/or baseline platelets of ≤150,000K/uL should be considered to avoid significant hematologic toxicity, especially thrombocytopenia, based on recent analyses of the ENGOT-OV16/NOVA study. Cardiovascular toxicities include hypertension, tachycardia, as well as palpitations, and patients should be monitored for hypertension. PARP inhibitors have been associated with low risks of acute myelogenous leukemia (AML) and myelodysplastic syndrome (MDS), and the overall risk of AML and MDS is 0.9% of all patients treated with niraparib. Niraparib testing is ongoing in newly diagnosed ovarian cancer patients as maintenance therapy following completion of platinum-based chemotherapy, in BRCAwt cancers as treatment, as well as in combinations with other biologic drugs such as immunotherapy and anti-angiogenic agents.