Abstract 1233: Preclinical profile of RP12146, a novel, selective, and potent small molecule inhibitor of PARP1/2
Authors: Viswanadha Srikant , Eleswarapu Satyanarayana , Rasamsetti Kondababu , Bhuniya Debnath , Merikapudi Gayatriswaroop , Veeraraghavan Sridhar , Vakkalanka Swaroop 
Published: July 2021

Background: Poly (ADP-ribose) polymerase (PARP) activity involves synthesis of Poly-ADP ribose (PAR) polymers that recruit host DNA repair proteins leading to correction of DNA damage and maintenance of cell viability. Upon combining with DNA damaging cytotoxic agents, PARP inhibitors have been reported to demonstrate chemo- and radio-potentiation albeit with incidences of myelosuppression. A need therefore exists for the development selective PARP1/2 inhibitors with a high therapeutic window to fully exploit their potential as a single agent or in combination with established therapy across various tumor types. Additionally, with the emerging concept of ‘synthetic lethality', the applicability PARP inhibitors can be expanded to cancers beyond the well-defined BRCA defects. Herein, we describe the preclinical profile of RP12146, a novel and selective small molecule inhibitor of PARP1 and PARP2.

Methods: Enzymatic potency was evaluated using a PARP Chemiluminescent Activity Assay Kit (BPS biosciences). Cell growth was determined following incubation with RP12146 in BRCA1 mutant and wild-type cell lines across indications. Apoptosis was evaluated following incubation of cell lines with compound for 120 h, subsequent staining with Annexin-V-PE and 7-AAD, and analysis by flow cytometry. For cell cycle, cells were incubated with compound for 72 h, and stained with Propidium Iodide prior to analysis by flow cytometry. Expression of downstream PAR, PARP-trapping, phospho-γH2AX and cleaved PARP expression were determined in UWB1.289 (BRCA1 null) cells by Western blotting. Anti-tumor potential of RP12146 was tested in OVCAR-3 Xenograft model. Pharmacokinetic properties of the molecule were also evaluated. Results: RP12146 demonstrated equipotent inhibition of PARP1 (0.6 nM) and PARP2 (0.5 nM) with several fold selectivity over the other members of the PARP family. Compound caused a dose-dependent growth inhibition of both BRCA mutant and non-mutant cancer cell lines with GI50 in the range of 0.04 µM to 9.6 µM. Incubation of UWB1.289 cells with RP12146 caused a G2/M arrest with a corresponding dose-dependent increase in the percent of apoptotic cells. Expression of PAR was inhibited by 86% at 10 nM with a 2.3-fold increase in PARP-trapping observed at 100 nM in presence of RP12146. A four-fold increase in phospho-γH2AX and &gt; 2-fold increase in cleaved PARP expression was observed at 3 µM of the compound. RP12146 exhibited anti-tumor potential with TGI of 28% as a single agent in OVCAR-3 xenograft model. Efficay was superior compared to Olaparib tested at an equivalent dose. Pharmacokinetic studies in rodents indicated high bioavailability with favorable plasma concentrations relevant for efficacy

Conclusions: Data demonstrate the therapeutic potential of RP12146 in BRCA mutant tumors. Testing in patients is planned in H1 2021.

Citation Format: Srikant Viswanadha, Satyanarayana Eleswarapu, Kondababu Rasamsetti, Debnath Bhuniya, Gayatriswaroop Merikapudi, Sridhar Veeraraghavan, Swaroop Vakkalanka. Preclinical profile of RP12146, a novel, selective, and potent small molecule inhibitor of PARP1/2 [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2021; 2021 Apr 10-15 and May 17-21. Philadelphia (PA): AACR; Cancer Res 2021;81(13_Suppl):Abstract nr 1233.