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).

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PTH and PTHrP have been shown to inhibit maturation of growth plate chondrocytes and the expression of type X collagen. In order to examine the regulatory mechanisms involved, fetal bovine growth plate chondrocytes were incubated for 24-48 h under serum-free conditions with PTH and PTHrP and various aminoterminal, midregional, and carboxyterminal fragments of these hormones. Analysis of type X collagen mRNA levels by Northern hybridization showed a significant suppression by PTH (1-84), PTH (1-34), and PTHrP (1-40), but not by PTH (28-48) or PTH (53-84). PTH fragment (3-34) did not reduce alpha1(X) mRNA levels, while bis-indolylmaleimide, an inhibitor of the protein-kinase C pathway, did not affect alpha1(X) mRNA suppression by PTH, supporting the notion that the inhibition of type X collagen expression by PTH involves predominantly the adenylate cyclase pathway of the PTH/PTHrP-receptor. Since PTH and PTHrP have been shown to induce c-fos in osteoblasts and chondrocytes, the possibility was tested that c-fos mediated the suppressive effect of PTH/PTHrP on collagen X expression. In fetal bovine hypertrophic chondrocytes PTH (1-34), but not PTH (3-34) nor the midregional or C-terminal PTH fragments induced c-fos expression. In order to identify cis- and trans-acting elements in the COL10A1 gene involved in c-fos-mediated inhibition of collagen X expression by PTH/PTHrP, reporter gene constructs carrying various fragments of the human COL10A1 promoter coupled to the luciferase gene were transfected into hypertrophic chondrocytes. A tissue-specific, strong enhancer region, which we had previously located in the promoter of the human type X collagen gene COL10A1, was further narrowed down to a 530-bp sequence, located between - 1,870- and - 2,407 bp upstream of the transcription start site. The transcriptional activity of this enhancer element in transfected hypertrophic chondrocytes was significantly reduced after incubation with PTH (1-34) or PTHrP (1-40). Transcription of these reporter genes was also inhibited when chondrocytes were cotransfected with a c-fos expression vector. These results indicate the presence of a PTH/PTHrP responsive element in the human COL10A1 enhancer, which may be represented by multiple putative AP-1 sites located in this region.

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