Niraparib is an orally active and potent PARP inhibitor being developed for the treatment of ovarian, breast and other cancers.


Niraparib, formerly known as MK-4827, is an orally active and potent poly (ADP-ribose) polymerase, or PARP, inhibitor. A Phase 1/2 monotherapy study has been completed in more than 100 patients with advanced solid tumors. Based upon the results of the Phase 1/2 study and published data from other trials of PARP inhibitors, TESARO is evaluating niraparib at a dose of 300 milligrams once daily in two Phase 3 studies.

Mechanism of Action

PARP is a family of proteins involved in many functions in a cell, including DNA repair, gene expression, cell cycle control, intracellular trafficking and energy metabolism. PARP proteins play key roles in single strand break repair through the base excision repair pathway.

PARP inhibitors have shown activity as a monotherapy against tumors with existing DNA repair defects, such as BRCA1 and BRCA2, and as a combination therapy when administered together with anti-cancer agents that induce DNA damage.

Ovarian Cancer Opportunity

Despite several advances in treatment of ovarian cancer, most patients eventually relapse, and subsequent responses to additional treatment are often limited in duration. Women with germline BRCA1 or BRCA2 mutations have an increased risk for developing high grade serous ovarian cancer (HGSOC), and their tumors appear to be particularly sensitive to treatment with a PARP inhibitor. In addition, published scientific literature indicates that patients with platinum sensitive HGSOC who do not have germline BRCA1 or BRCA2 mutations may also experience clinical benefit from treatment with a PARP inhibitor.

Breast Cancer Opportunity

It is estimated that 5% to 10% of women who are diagnosed with breast cancer, or more than 15,000 women each year, carry a germline mutation in either their BRCA1 or BRCA2 genes. The development of cancer in these women involves the dysfunction of a key DNA repair pathway known as homologous recombination. While cancer cells can maintain viability despite disruption of the homologous recombination pathway, they become particularly vulnerable to chemotherapy if an alternative DNA repair pathway is disrupted. This is known as synthetic lethality – a situation where the individual loss of either repair pathway is compatible with cell viability; but the simultaneous loss of both pathways results in cancer cell deaths. Since PARP inhibitors block DNA repair, in the context of cancer cells with the BRCA mutation, PARP inhibition results in synthetic lethality. For this reason, patients with germline mutations in a BRCA gene show marked clinical benefit that follows treatment with a PARP inhibitor.