Abstract 5336: Olaparib potentiates the anti-proliferative and anti-metastatic effects of ONC206 in ovarian cancer cells

Objectives: Olaparib is a poly ADP-ribose polymerase inhibitor (PARPi) approved for use as maintenance and treatment in advanced and recurrent ovarian cancer (OC). The imipridone ONC206, a chemical derivative of ONC201, is a bioavailable dopamine receptor D2 (DRD2) antagonist that has anti-tumorigenic effects via induction of apoptosis and activation of the integrated stress response. ONC206 exhibits differentiated receptor pharmacology, nanomolar potency, and enhanced bioavailability relative to ONC201. Both olaparib and imipridones (i.e. ONC201) are being evaluated in OC clinical trials, but have yet to be explored in combination. Thus, we sought to examine the effects of olaparib in combination with ONC206 in human OC cell lines. Methods: The OC cell lines, OVCAR3 and OVCAR5, were used. Both cell lines were treated with varying doses of ONC206 (Oncoceutics) and olaparib (MedChemExpress) alone and in combination. Cell proliferation and apoptosis were assessed by MTT and cleaved caspase assays, respectively. Synergy between olaparib and ONC206 was evaluated by the combination index (CI) method of Chou-Talalay. Reactive oxygen species (ROS) was determined by DCFDA assay. Adhesion and migration were assessed by laminin and wound healing assays, respectively. Western blotting was performed to evaluate the effects of olaparib and ONC206 on apoptotic and invasion-related proteins in both OC cell lines. Results: Both drugs inhibited OC cell proliferation in a dose-dependent manner after 72 hrs of exposure (IC50 for olaparib of 15-25 µM for both OVCAR3 and OVCAR5; IC50 1.5 µM and 0.4µM for ONC206 in OVCAR3 and OVCAR5, respectfully). Simultaneous exposure of ONC206 with olaparib resulted in a synergistic anti-proliferative effect (CI