Abstract 6102: Targeting BARD1 slows PDAC growth in vitro and in vivo and sensitizes cells to DNA damaging agents
Authors: Patel Sohum , Arkala Anoohya , Nevler Avinoam , Coats Carolyn , Yeo Charles J. , Jain Aditi 
Published: April 2023

Abstract
Pancreatic ductal adenocarcinoma (PDAC) is the most prevalent malignant neoplasm of the pancreas, responsible for over 90% of pancreatic cancer cases. Despite recent therapeutic advances, the five-year overall survival rate for PDAC is only 11% and therapies remain limited. It is now known that deficiency in DNA damage repair (DDR) renders PDAC cells vulnerable to certain DNA damage agents, for example, poly (ADP-ribose) polymerase inhibitors (PARPi). Most of the DDR genes mutated in PDAC are crucial for the proper functioning of the homologous recombination repair (HRR) pathway, and loss-of-function alterations in DDR genes sensitize cells to DNA-damaging agents. Since this treatment strategy is currently limited to 5-10% of PDAC cases with known mutations in the DDR genes, it underscores a dire need to understand new therapeutic avenues and expand the PDAC patient population that could benefit from this therapeutic approach. We have recently published that BARD1 (BRCA1- Associated- Ring- Domain- 1), an obligate binding partner of BRCA1, is upregulated in PDAC cells exposed to PARPi/platinums. We found that transient inhibition of BARD1 rendered PDAC cells extremely sensitive to olaparib (PARPi)/oxaliplatin (platinum), and enhanced DNA damage. Based on these results, we created two genetic models of BARD1 inhibition and utilized these model systems to investigate if loss of BARD1 chemo-sensitizes PDAC cells to other PARPis and DNA damage agents. Doxycycline inducible shRNA and BARD1 CRISPR KO models were created to inhibit gene expression of BARD1 in PDAC cells. We first characterized these model systems to confirm the loss of BARD1 protein and mRNA expression by western blot and qRT-PCR analyses. Using colony formation and Pico green cell survival assays, we found that inhibiting BARD1 resulted in slower growth of pancreatic cancer cells in vitro. Moreover, expression of several cell cycle genes from G2-M phase was significantly decreased (p=0.05). These studies were recapitulated in a mouse xenograft subcutaneous model, where BARD1 KO and WT PDAC cells were injected subcutaneously and tumor growth was analyzed over 25-30 days. Kaplan-Meier curves were calculated and plotted using Log-rank test. We found that inhibiting BARD1 significantly (p=0.026) delayed formation of PDAC tumors in vivo. Next, we analyzed the efficacies of various DNA damaging agents when BARD1 was inhibited. Silencing or CRISPR KO of BARD1 enhanced efficacy of mitomycin C, irinotecan, as well as other PARPis, which are currently in clinical trials (rucaparib, veliparib) in vitro and lowered their IC50s. These results indicate that targeting BARD1 has the potential to benefit patients in terms of novel or improved treatments. Our ongoing and future studies will expand on these findings to understand BARD1-mediated pathway and evaluate sensitivity of multiple DNA damage agents by screening a library of &gt; 250 compounds.
Citation Format: Sohum Patel, Anoohya Arkala, Avinoam Nevler, Carolyn Coats, Charles J. Yeo, Aditi Jain. Targeting BARD1 slows PDAC growth in vitro and in vivo and sensitizes cells to DNA damaging agents. [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 6102.