Abstract 4844: Evidence of PARP-1 Dependent Cytotoxic Agents with Low Target Affinity

Abstract Introduction: Inhibition of nuclear protein poly (ADP-ribose) polymerase-1 (PARP1) is synthetically lethal in BRCA mutated cancers. However, the mechanism by which PARPi exert cytotoxic effects is not fully understood. In this study, we compare 16 olaparib analogs and measured their potency in a radioligand binding assay to measure their affinity for PARP1, and in a cytotoxicity assay to measure their ability to serve as a chemotherapeutic. Methods: Compounds were prepared by replacing the piperazine core on olaparib with a series of diazaspiro ring systems. PARP1 affinity was assessed using radioligand binding competition assays. In vitro cytotoxicity was performed on BRCA1 methylated and PARP1-/- ovarian cancer cell lines to evaluate the relative potency of the analog compounds. Results: The 16 analogs displayed lower affinity to PARP1 but comparable or higher potency in cell kill assays when compared to olaparib. Of the 16 compounds, those that contained the diazaspiro core with an N-Boc-functional group displayed the highest degree of potency. Cytotoxicity assays were performed for each compound using PARP1 -/- and PARP2 -/- cells to assess off-target effects. Dose response curves for PARP1-/- cells resulted in a rightward shift; no changes in the dose-response curves were detected for PARP2 -/- cells. Conclusion: Radioligand binding assays demonstrated that these compounds have low PARP1 affinity. Evaluation of the relative potency of these compounds revealed that compounds having a lower PARP1 affinity relative to olaparib still retained a high potency in cell kill assays. In vitro cytotoxicity assays on PARP1 -/- and PARP2 -/- cells confirmed that these compounds are PARP1 but not PARP2 dependent. Future studies will focus on assessing catalytic inhibition of PARP1 and PARP1 trapping in order to better elucidate the antiproliferative effects of these compounds. Citation Format: Laura Puentes, Sean Reilly. Evidence of PARP-1 dependent cytotoxic agents with low target affinity [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 4844.