Characterization of Genetic Polymorphisms Related to 5-FU Metabolizing Enzymes in Japanese Populations

Fluoropyrimidine anticancer agents, exemplified by 5-fluorouracil (5-FU), induce severe adverse effects-such as myelosuppression, emesis, diarrhea, and hand-foot syndrome-in approximately 10-30% of patients. As such toxicities can result in delays or discontinuation of therapy, accurate prediction of drug response prior to treatment initiation is of critical importance. The metabolic degradation of 5-FU is primarily mediated by the drug-metabolizing enzymes dihydropyrimidine dehydrogenase (DPD) and dihydropyrimidinase (DHPase). These enzymes are encoded by the DPYD and DPYS genes, respectively; polymorphisms in these genes that reduce or abolish enzymatic activity lead to elevated systemic concentrations of 5-FU, thereby increasing the risk of severe toxicity. In Caucasian populations, four DPYD polymorphisms have been identified as predictive markers of adverse drug reactions. However, these variants are rarely observed in Japanese individuals, and reliable pharmacogenomic biomarkers remain largely unreported in this population. To address this gap, we conducted a comprehensive in vitro functional analysis of DPD and DHPase activity of DPYD and DPYS variants identified through large-scale whole-genome sequencing databases. This review summarizes our findings and elucidates the underlying mechanisms affecting the function of 5-FU-metabolizing enzymes, as revealed by our prior research.