Abstract 7600: Synergy of ZEN3694 and VIP152 for dual transcriptional targeting of BET and CDK9 in patient derived organoid models of pancreatic cancer

Abstract Background: Pancreatic ductal adenocarcinoma (PDAC) remains a leading cause of cancer related mortality in the United States, largely due to ineffective systemic therapy. While novel KRAS target strategies are in development, few agents have been investigated to target the transcriptional machinery for global inhibition of expression. Recent small molecule inhibitors targeting transcription (i.e., CDK7) have shown preliminary evidence of disease control; however, combination therapies have lagged, likely due to uncertainty in clinical toxicity. Text mining analysis suggests combination BET and CDK9 inhibition may be promising against PDAC. Here, we present preclinical evidence of synergistic activity for the combination of bromodomain and extraterminal (BET) inhibitor (ZEN3694) and CDK9 inhibitor (VIP152) using patient derived cancer organoids (PCOs). Methods: Dose response curves were generated for ZEN3694 and VIP152 to assess their single agent activity against PCOs using a low volume format. ZEN3694 was treated continuously while VIP152 was removed after 24h to mimic pharmacokinetics with assay endpoint at 144h. Synergy assays were designed using a combination dose titration grid. Viability was determined in all assays using 3D CellTiter Glo (CTG, 50% v/v). Synergy scores were produced using SynergyFinder 3.0 including Zero Interaction Potency (ZIP), Bliss Independence (Bliss), Highest Single Agent (HSA), and Loewe Additivity (Loewe). Western blot analysis was performed against global markers of active RNA polymerase II (phosphorylation at serine 2, 5, 7) and antiapoptotic protein, BCL xL, and MCL 1. Results: ZEN3694 was observed to have a single agent IC50 in the single uM range across 3 independent PDAC PCO lines (PDAC1 3.7uM, PDAC2 1.1uM, PDAC3 2.9uM). VIP152 showed significant potency in the same 3 PDAC PCO lines (PDAC1 140.2nM, PDAC2 30.5nM, PDAC3 43.4nM). The combination of ZEN3694 and VIP152 was found to have increased therapeutic activity with double digit synergy scores across all reference models: PDAC1 (Loewe 17.3, HSA 19.8, ZIP 20.2, and Bliss 17.2) and PDAC2 (Loewe 34.7, HSA 28.3, ZIP 19.7, and Bliss 19.6). Western blots of protein collected from organoids treated for 48h showed on target activity, including decrease in the phosphorylation of Rbp1 (Ser 2, Ser 5, and Ser 7) compared to both control and single agents and decreased expression in antiapoptotic proteins (MCL 1 and BCL xL). Conclusion: Here, we show the activity of dual transcription targeting with BET and CDK9 inhibition in patient derived pancreatic cancer organoid models. The combination of ZEN3694 and VIP152 has in vitro synergy in PDAC PCO models with on target activity. Ongoing work is validating this combination in animal models to assess toxicity, in vivo activity, and RNA expression profiling to understand transcriptional pathway dependency and therapeutic resistance. Citation Format: Lucas J. Koeppel, Austin Stram, Robert J. Millikin, Ellie Riedl, Md Shahadat Hossan, Ethan Samuel Lin, Ron Stewart, Jeremy D. Kratz. Synergy of ZEN3694 and VIP152 for dual transcriptional targeting of BET and CDK9 in patient derived organoid models of pancreatic cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(6_Suppl):Abstract nr 7600.