Enhancing the Cytotoxic Effect of PARP Inhibitors with DNA Demethylating Agents - A Potential Therapy for Ovarian Cancer?

Abstract

Ovarian Cancer (OC) is the fifth most common cause of death in women, and the leading cause of gynecological death in the United States. Although some OC patients are responsive to initial treatment (surgery and chemotherapeutic agents such as platinum compounds and taxane), majority of these patients later develop drug resistance and relapse. Initial results of PARP inhibitor (PARPi) therapy in hereditary OC with defects in DNA repair from BRCA1/2 mutations have shown promising results. However, PARPi treatment in OC with intact BRCA1/2 genes has been disappointing. Recent studies have shown that the cytotoxicity of PARPis correlate to its ability to trap PARP in chromatin, with BMN-673 (Talazoparib) demonstrating the most potent trapping activity. Given that DNA methyl transferases (DNMTs) bind PARP and DNMT inhibitors (DNMTi) trap DNMT, we determined whether combination of low, non-cytotoxic doses of the PARPi (Talazoparib) and DNMTi (Azacytidine, 5-AZA) show a significant increase in cytotoxic activity compared to monotherapy with these drugs. We show here that in BRCA1/2-wt OC cells (A2780 and TyKNu), combination treatment with PARPi and DNMTi decreased clonogenicity, in comparison to single agent treatments. In keeping with these findings, we also show that combination therapy leads to increased PARP "trapping" and apoptosis in OC cells. Finally, to develop reagents to test OC more accurately in-vivo, we have generated OC cells with YFP+ luciferase imaging capability, using lentiviral transduction, and determined the optimal conditions in which to test these two drugs in tumor xenografts. Future in-vivo studies with low non-toxic doses of these two drugs will hopefully provide a novel strategy to target OC with intact BRCA1/2 genes, while reducing adverse effects.