Dunlap, Garrett S.

Abstract The antimetabolite 5-fluorouracil (5-FU) is one of the most widely used chemotherapy drugs. Dihydropyrimidine dehydrogenase (DPD) is a major determinant of 5-FU response and toxicity. Although DPYD variants may affect 5-FU metabolism, they do not completely explain the reported variability in DPD function or the resultant differences in treatment response. Here, we report that H3K27 trimethylation (H3K27me3) at the DPYD promoter regulated by Ezh2 and UTX suppresses DPYD expression by inhibiting transcription factor PU.1 binding, leading to increased resistance to 5-FU. Enrichment of H3K27me3 at the DPYD promoter was negatively correlated with both DPYD expression and DPD enzyme activity in peripheral blood specimens from healthy volunteers. Lastly, tumor expression data suggest that DPYD repression by Ezh2 predicts poor survival in 5-FU–treated cancers. Collectively, the findings of the present article suggest that a previously uncharacterized mechanism regulates DPD expression and may contribute to tumor resistance to 5-FU. Cancer Res; 76(21); 6362–73. ©2016 AACR.

Abstract Dihydropyrimidine dehydrogenase (DPD) is a major determinant of the efficacy and toxicity of 5-fluorouracil in various cancer therapies. Single nucleotide polymorphisms (SNPs) within DPYD have been studied extensively for years. However, known SNPs do not explain most cases of altered DPD activity and response to 5-FU. Furthermore, variations of DPYD expression in cancer patients have been reported; however, the underlying molecular mechanism is unclear. This suggests that regulation of DPYD expression may be an additional mechanism to control DPD activity. In this study, we focused on epigenetic regulation of DPD and specifically investigated the role of histone methylation on DPYD expression. Inhibition of the H3K27 methyl-transferase Ezh2 by either GSK-126 or a dominant-negative histone H3 mutant significantly increased DPYD expression in various cell lines. The expression of thymidylate synthetase, a major target of 5-fluorouracil toxicity, was not altered. Consistent with elevated DPYD expression, cells that lost H3K27me3 were more resistant to 5-fluorouracil. Furthermore, we demonstrated that Ezh2 and H3K27me3 were enriched on the promoter and the first exon of DPYD in low-DPD expressing cells, but not in cell lines with high DPD levels. Additionally, the enrichment of H3K27me3 on the DPYD promoter was negatively correlated with cellular DPD activity in peripheral mononuclear cells from healthy volunteers. Finally, CRISPR/Cas9-mediated targeting of Ezh2 to the DPYD promoter artificially increased H3K27me3 and suppressed DPYD expression. Collectively, these data suggest that histone methylation can regulate DPYD expression, providing a previously unrecognized mechanism of 5-fluorouracil sensitivity. The tri-methylation of H3K27 is a potential biomarker for guiding individualized 5-FU therapy. Citation Format: Rentian Wu, Steven Offer, Calvin Jerde, Garrett Dunlap, Robert Diasio. Histone H3K27 tri-methylation regulates DPYD expression and cellular sensitivity of 5-fluorouracil. [abstract]. In: Proceedings of the AACR Special Conference on Chromatin and Epigenetics in Cancer; Sep 24-27, 2015; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2016;76(2 Suppl):Abstract nr B49.