Butterfield, Gabriel L.

Abstract 5-fluorouracil (5-FU) is a commonly administered chemotherapy drug used for the treatment of various aggressive cancers. Dihydropyrimidine dehydrogenase (DPD, encoded by the DPYD gene) is the rate limiting enzyme of the 5-flourouracil (5-FU) catabolic pathway, and as such limits the amount of drug available for conversion into active metabolites. Reduced expression of DPD has been linked to severe adverse toxicity to 5-FU, including mucositis, diarrhea, hematological toxicities, and, in extreme cases, death. DPD has been previously shown to follow circadian patterns of expression in rodent models and in humans. Many microRNAs also exhibit circadian variations in expression and have been suggested to control oscillations in target protein expression. Using in silico prediction, we identified two putative binding domains for the microRNAs mir-27a and mir-27b within the DPYD gene. One of these sites is located in the 3’ untranslated region (UTR) and the other is located within the coding region just upstream from the stop codon. Using a reporter system, we show that mir-27a and mir-27b are able to bind to both predicted binding sites. Furthermore, over-expression of either microRNA reduced endogenous DPD protein levels in the HT-29 colon cancer cell line. To investigate mir-27a/b as a potential circadian regulator of DPD expression, expression was measured in livers collected at 4-hour intervals from chrono-synchronized mice. As expected, the circadian pattern of DPD enzyme activity closely matched that of DPD expression. The expression patterns for mir-27a and mir-27b were inverse of those for DPD expression and activity. These data suggest that mir-27a and mir-27b may direct circadian variations in DPD enzyme activity. Citation Format: Gabriel L. Butterfield, Steven M. Offer, Robert B. Diasio. Possible circadian modulation of dihydropyrimidine dehydrogenase by mir-27a and mir-27b. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 2198. doi:10.1158/1538-7445.AM2013-2198

Abstract Dihydropyrimidine dehydrogenase (DPD) is the initial and rate-limiting enzyme of the uracil catabolic pathway, being critically important for inactivation of the commonly prescribed anti-cancer drug 5-fluorouracil (5-FU). DPD impairment leads to increased exposure to 5-FU and, in turn, increased anabolism of 5-FU to cytotoxic nucleotides, resulting in more severe clinical adverse effects. Numerous variants within the gene coding for DPD, DPYD, have been described, although only a few have been demonstrated to reduce DPD enzyme activity. To identify DPYD variants that alter enzyme function, we expressed 80 protein-coding variants in an isogenic mammalian system and measured their capacities to convert 5-FU to dihydro-fluorouracil, the product of DPD catabolism. The M166V, E828K, K861R, and P1023T variants exhibited significantly higher enzyme activity than wild-type DPD (120%, P = 0.025; 116%, P = 0.049; 130%, P = 0.0077; 138%, P = 0.048, respectively). Consistent with clinical association studies of 5-FU toxicity, the D949V substitution reduced enzyme activity by 41% (P = 0.0031). Enzyme activity was also significantly reduced for 30 additional variants, 19 of which had <25% activity. None of those 30 variants have been previously reported to associate with 5-FU toxicity in clinical association studies, which have been conducted primarily in populations of European ancestry. Using publicly available genotype databases, we confirmed the rarity of these variants in European populations but showed that they are detected at appreciable frequencies in other populations. These data strongly suggest that testing for the reported deficient DPYD variations could dramatically improve predictive genetic tests for 5-FU sensitivity, especially in individuals of non-European descent. Cancer Res; 74(9); 2545–54. ©2014 AACR.

Abstract Dihydropyrimidine dehydrogenase (DPD, encoded by DPYD) is the rate-limiting enzyme in the uracil catabolic pathway and has a pivotal role in the pharmacokinetics of the commonly prescribed anticancer drug 5-fluorouracil (5-FU). Deficiency of DPD, whether due to inadequate expression or deleterious variants in DPYD, has been linked to severe toxic responses to 5-FU. Little is known about the mechanisms governing DPD expression in the liver. In this report, we show increased accumulation of RNA-induced silencing complex (RISC) proteins on DPYD mRNA in cells overexpressing the highly homologous microRNAs (miRNA) miR-27a and miR-27b. These miRNAs were shown to repress DPD expression through two conserved recognition sites in DPYD. The IC50 of 5-FU for HCT116 cells overexpressing miR-27a or miR-27b was 4.4 μmol/L (both), significantly lower than that for cells expressing a nontargeting (scramble) control miRNA (14.3 μmol/L; P = 3.3 × 10−5 and P = 1.5 × 10−7, respectively). Mouse liver DPD enzyme activity was inversely correlated with expression levels of miR-27a (R2 = 0.49; P = 0.0012) and miR-27b (R2 = 0.29; P = 0.022). A common variant in the hairpin loop region of hsa-mir-27a (rs895819) was also shown to be associated with elevated expression of the miR-27a in a panel of cell lines (P = 0.029) and in a transgenic overexpression model (P = 0.0011). Furthermore, rs895819 was associated with reduced DPD enzyme activity (P = 0.028) in a cohort of 40 healthy volunteers. Taken together, these results suggest that miR-27a and miR-27b expression may be pharmacologically relevant modulators of DPD enzyme function in the liver. Furthermore, our data suggest that rs895819 may be a potential risk allele for 5-FU sensitivity. Mol Cancer Ther; 13(3); 742–51. ©2014 AACR.