Abstract C032: De novo pyrimidine biosynthesis inhibition synergizes with BCL-XL targeting in pancreatic cancer

Abstract Oncogenic KRAS, the genetic driver of 90% of PDAC, induces a metabolic rewiring characterized, in part, by dependency on de novo pyrimidine biosynthesis. Dihydroorotate dehydrogenase (DHODH) is the enzymatic ‘chokepoint’ of the de novo pyrimidine biosynthesis pathway and an in vivo metabolic liability in pancreatic ductal adenocarcinoma (PDAC). Targeting enzymes in the de novo pyrimidine synthesis pathway such as dihydroorotate dehydrogenase (DHODH) with clinically available inhibitor brequinar (BQ) starved the tumor of nucleotide synthesis and restrained growth of PDAC cells in vitro. However, therapeutic resistance limited BQ long-term effects in PDAC xenografts, which suggests compensatory pathways and that combinatorial strategies are required for enhanced efficacy. Here, we integrated a mass spectrometry (MS)-based quantitative temporal proteomics workflow, LC/MS- based metabolomics and in vitro and in vivo drug-anchored CRISPR/Cas9 genetic screens to identify compensatory pathways to DHODH inhibition (DHODHi) and targets for combination strategies. We demonstrate that DHODHi alters the apoptotic regulatory proteome thereby enhancing sensitivity to inhibitors of the anti-apoptotic BCL2L1 (BCL-XL) protein. Combinatorial regimens with DHODH and BCL-XL inhibition synergistically induce apoptosis in PDAC cell lines and patient-derived PDAC organoids. In vivo DHODH inhibition with Brequinar and BCL-XL degradation with DT2216, a proteolysis targeting chimera (PROTAC), significantly inhibits the growth of PDAC tumors. Our data defines mechanisms of adaptation to DHODH inhibition and identifies a combination therapy strategy in PDAC. Citation Format: huan zhang, Qijia yu, Naiara Santana-Codina, Clara Poupault, Claudia Campos, Xingping Qin, Aparna Padhye, Nicole Sindoni, Miljan Kuljanin, Junning Wang, Matthew J. Dorman, Andrew J. Aguirre, Stephanie K. Dougan, Kristopher A. Sarosiek, Joseph D. Mancias. De novo pyrimidine biosynthesis inhibition synergizes with BCL-XL targeting in pancreatic cancer [abstract]. In: Proceedings of the AACR Special Conference in Cancer Research: Advances in Pancreatic Cancer Research; 2024 Sep 15-18; Boston, MA. Philadelphia (PA): AACR; Cancer Res 2024;84(17 Suppl_2):Abstract nr C032.