Abstract 5420: DPYD enhancer variant confers increased risk of severe toxicity in 5-FU chemotherapy

Abstract Genetic variants in the DPYD gene that are deleterious to dihydropyrimidine dehydrogenase (DPD) enzyme function have demonstrated clinical validity as predictive biomarkers for severe (i.e., CTCAE grade ≥3) and potentially lethal toxicity to fluorouracil (5-FU) and capecitabine chemotherapies. Variants within the coding region only explain 5-10% of 5-FU-related toxicities; and GWAS approaches have been unable to identify validated predictive biomarkers to date. Our previous studies demonstrated that DPD expression was controlled by multiple epigenetic processes; considerable variation was also noted in liver DPYD/DPD levels. Using CRISPR-interference (CRISPRi) and CRISPR-activation (CRISPRa), we identified functional enhancer regions within liver tissues and cells. Epigenetic status at these regions was shown to correlate with DPYD expression in cell models and human liver tissues. Chromosome conformation capture (3C) confirmed direct promoter-enhancer interactions. A multi-omics analysis of >1000 human liver specimens identified a proximal eQTL for DPYD expression within an enhancer, with a global minor allele frequency of 27%. This variant was subsequently shown to directly alter DPYD expression in knock-in cell line models. The variant disrupts transcription factor binding at the DPYD enhancer, leading to reduced enhancer-promoter interaction, reduced DPD expression, and increased cellular sensitivity to 5-FU. Collectively, our data suggest that the variant could represent a novel predictive biomarker for severe 5-FU toxicity. The evaluation of this marker in the clinical setting is currently underway. Citation Format: Ting Zhang, Alisa Ambrodji, Huixing Huang, Kelly Bouchonville, Amy Etheridge, Remington Schmidt, Jose Cardiel Nunez, Zoey Temesgen, Federico Innocenti, Robert Diasio, Carlo Largiadèr, Steven M. Offer. DPYD enhancer variant confers increased risk of severe toxicity in 5-FU chemotherapy [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 5420.