Abstract 2597: Inhibition of BARD1-PLK1 axis enhances PARP inhibitor/platinum sensitivity in homologous repair proficient pancreatic ductal adenocarcinoma
Authors: Coats Carolyn , Arkala Anoohya , Londin Eric , Nevler Avinoam , Brody Jonathan R. , Yeo Charles J. , Jain Aditi 
Published: June 2022

Abstract
Pancreatic ductal adenocarcinoma (PDAC) is an aggressive cancer with a grim prognosis. Though the overall 5-year survival rates have recently improved to 10%, there is still an unmet need for better therapies. PARP inhibitors (PARPi)/platinum therapies have demonstrated clinical efficacy in BRCA1/2 mutated PDAC and has recently led to the FDA approval of PARPi (olaparib) in the maintenance setting, offering the best personalized treatment approach for such patients. Although promising, the benefits of these therapeutic strategies are currently limited to only a few patients. We have recently established that BARD1 (BRCA1- Associated-Ring-Domain-1), the main binding partner of BRCA1 in regulating homologous recombination repair is upregulated in PDAC cells exposed to PARPi/platinum compounds, by a post-transcriptional RNA binding mechanism. We therefore hypothesized that inhibition of BARD1 will sensitize cells to these agents. We found that inhibition of BARD1 (both by siRNA/shRNA and CRISPR-KO) not only sensitized the cells to olaparib or oxaliplatin but enhanced DNA damage in cells, as analyzed by comet assays and γ-H2AX immunofluorescence staining. BARD1 inhibition led to a decrease in homologous repair efficiency of cells as analyzed by the well established pDRGFP assay. To further understand BARD1 dependent downstream signaling, we performed comparative transcriptomic analysis of BARD1 silenced cells compared to scramble control. RNA seq analysis revealed modulation of several cell cycle checkpoints and DNA damage response pathways. Notably, through gene set enrichment analysis (GSEA), we found that silencing BARD1 causes de-enrichment of pathway regulating Polo-Like-Kinase-1 (PLK1, a serine/threonine kinase) activity (p-val=0.05, FDR=0.07). PLK1 is frequently upregulated in PDAC cells and promotes progression of cells through mitosis. Based on these results, we found that a PLK1 specific inhibitor (onvansertib) synergized with olaparib to reduce cell survival of homologous repair proficient (HR-P) PDAC cells. Importantly, the mechanism of drug synergy involved induction of apoptosis and DNA damage, as assessed by cleaved caspase-3 and γ-H2AX protein analysis. These results are suggestive of targeting the BARD1-PLK1 axis in order to enhance sensitivity of PARPi/platinums in HR proficient cells. Our ongoing and future studies are aimed at understanding the interaction of BARD1 and PLK1 in PDAC cells and analyze the effects of onvansertib and olaparib on tumor growth in vivo. Accomplishment of these studies will establish novel therapeutic targets and synthetic lethal combinations that have not been explored yet for deadly pancreatic cancers, ultimately benefiting patient survival in the long run.
Citation Format: Carolyn Coats, Anoohya Arkala, Eric Londin, Avinoam Nevler, Jonathan R. Brody, Charles J. Yeo, Aditi Jain. Inhibition of BARD1-PLK1 axis enhances PARP inhibitor/platinum sensitivity in homologous repair proficient pancreatic ductal adenocarcinoma [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 2597.