Purpose: Complete or partial loss of dihydropyrimidine dehydrogenase (DPD) function has been described in cancer patients with intolerance to fluoropyrimidine drugs like 5-fluorouracil (5-FU) or Xeloda. The intention of this population study is to assess and to evaluate gene variations in the entire coding region of the dihydropyrimidine dehydrogenase gene (DPYD), which could be implicated in DPD malfunction. Experimental Design: A cohort of 157 individuals was genotyped by denaturing highperformance liquid chromatography; 100 of these genotypes were compared with functional studies on DPD activity and mRNA expression. Results: Twenty-three variants in coding and noncoding regions of the DPYD gene were detected, giving rise to15 common haplotypes with a frequency of >1%. Rare sequence alterations included a frameshift mutation (295-298delTCAT) and three novel point mutations, 1218G>A (Met Ser). DPD enzyme activity showed high variation in the analyzed population and correlated with DPD mRNA expression. In particular, the novel variants were not accompanied with decreased enzyme activity. However, a statistically significant deviation from the median DPD activity of the population was associated with the mutations 1601G>A (Ser Dihydropyrimidine dehydrogenase (DPD; EC 1.3.1.2) is the initial and rate-limiting enzyme in the catabolism of pyrimidines. The homodimeric protein catalyzes the reduction of uracil and thymine in an NADPH-dependent manner and, furthermore, plays a critical role in the pharmacokinetics of fluoropyrimidine-based anticancer drugs. Eighty percent to 85% of administered standard doses of the common chemotherapeutic agent 5-fluorouracil (5-FU) are rapidly degraded by DPD to inactive compounds followed by excretion of a-fluoroh-alanine within 24 hours (1 -3). The rationally designed orally administered fluoropyrimidine drug Xeloda (capecitabine) is converted in situ into 5-FU due to intracellular thymidine phosphorylase activity. Capecitabine has been shown to be safer and more effective than 5-FU and has greater patient convenience (4, 5).

M166V, S534N, I543V) displayed significantly reduced DPD activity. The rare combination of the highly conserved mutation sites M166V and S534N was additionally found in one of the other patients. DPD enzyme activity was low, but yet within normal range. The K259E mutation did not provoke a decrease in DPD function in a heterozygous individual. Based on the protein structure of crystalline pig DPD and the deduced homology models, we have additionally investigated the amino acid positions in their three-dimensional network which correspond to the five missense mutations discovered in the patients.

No abstract