CEP-9722

Poly-ADP-ribosylation, that is, adding ADP-ribose moieties to a protein, is a unique type of protein post-translational modification that regulates various cellular processes such as DNA repair, mitosis, transcription, and cell growth. Small-molecule inhibitors of poly-ADP-ribose polymerase 1 (PARP1) have been developed as anticancer agents because inhibition of PARP enzymes may be a synthetic lethal strategy for cancers with or BRCA2 mutations. However, there are still questions surrounding PARP inhibitors.

Data were collected from Pubmed, Medline, through searching of these keywords: “PARP”, “BRCA”, “Synthetic lethal” and “Tankyrase inhibitors”. We describe the current knowledge of PARP inhibition and its effects on DNA damage; mechanisms of resistance to PARP inhibitors; the evolution of PARP inhibitors; and the potential use of PARP5a/b (tankyrases) inhibitors in cancer treatment.

PARP inhibitors are already showing promise as therapeutic tools, especially in the management of BRCA-mutated breast and ovarian cancers but also in tumors with dysfunctional BRCA genes. Small-molecule tankyrase inhibitors are important for increasing our understanding of tankyrase biology.

Use of poly(ADP-ribose) polymerase (PARP) inhibitors has greatly increased over the past 5 years. With several new Food and Drug Administration (FDA) approvals, three PARP inhibitors have entered into standard of care treatment for epithelial ovarian cancer (including ovarian, fallopian tube, and primary peritoneal cancer). Olaparib and rucaparib currently have indications for treatment of recurrent BRCA mutant ovarian cancer. Olaparib, rucaparib, and niraparib all have indications for maintenance therapy in recurrent platinum-sensitive ovarian cancer after response to platinum-based therapy. In our practice, we use both olaparib and rucaparib in the recurrent setting, and all three PARP inhibitors in the maintenance setting. Choice of which PARP inhibitor to use in either setting is largely based upon baseline laboratory values, number of prior therapies, and presence of a BRCA mutation and/or homologous recombination deficiency (HRD). As (HRD) and other biomarker assessments continue to improve, we anticipate being able to better identify which patients might most benefit from PARP inhibitor therapy in the future. The clinically available PARP inhibitors are currently undergoing extensive investigations in clinical trials. Other newer agents such as talazoparib, veliparib, 2X-121, and CEP-9722 are in earlier stages of development. As more FDA-approved indications for PARP inhibitor therapy in ovarian cancer become available, we anticipate the decision of which PARP inhibitor to use will become increasingly complex.