Enhancer-Gene Regulation's Role In 5-Fluorouracil Toxicity And Resistance

Abstract 5-Fluorouracil (5FU)-based chemotherapy remains a front-line treatment for most patients with colorectal cancer. However, approximately 30% of patients who receive 5FU experience severe, life-threatening toxicity. Dihydropyrimidine dehydrogenase (DPD, DPYD gene) mediates the rate determining step in 5FU catabolism. Deleterious genetic variations in DPYD have been associated with elevated concentrations of circulating 5FU and significantly increased risk for 5FU toxicity. Five deleterious variants in DPYD have been identified as clinical biomarkers of toxicity and have led to prospective genotyping and differential dosing recommendations for carriers of these variants, as noted on recent updates to the FDA label for the 5-FU prodrug capecitabine. Our previous studies also established the importance of epigenetic control of DPD expression. In this study, we used existing epigenetic repositories to identify candidate enhancer elements for DPYD. We selected 20 novel high-priority putative enhancers for further study using a combination of reporter assays and CRISPRi applied across multiple cell models. Further studies will investigate means to target these regulatory mechanisms as a means to increase localized efficacy of 5-FU-based therapies in colorectal cancer. Citation Format: Hannah Marie Krause, Julia Magee, Kelly Bouchonville, Lauryn Allyn Hahn, Ryan Jonathan Swartz, Brianna Bembenek, Lulu Jiang, Steven M. Offer. Characterizing the critical role of enhancer-gene regulation in 5-fluorouracil toxicity and resistance [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2026; Part 1 (Regular Abstracts); 2026 Apr 17-22; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2026;86(7 Suppl):Abstract nr 3140.