Anti-UPB1 monoclonal antibody, clone FQS0244(C)

Aims: To assess the association of DPYS and UPB1 genetic variation, encoding the catabolic enzymes downstream of dihydropyrimidine dehydrogenase, with early-onset toxicity from fluoropyrimidine-based chemotherapy. Patients & methods: The coding and exon-flanking regions of both genes were sequenced in a discovery subset (164 patients). Candidate variants were genotyped in the full cohort of 514 patients. Results & conclusions: Novel rare deleterious variants in DPYS (c.253C > T and c.1217G > A) were detected once each in toxicity cases and may explain the occurrence of severe toxicity in individual patients, and associations of common variants in DPYS (c.1-1T > C: p(adjusted) = 0.003; OR = 2.53; 95% CI: 1.39-4.62, and c.265-58T > C: p(adjusted) = 0.039; OR = 0.61; 95% CI: 0.38-0.97) with 5-fluorouracil toxicity were replicated.

Objective: Dihydropyrimicline dehydrogenase (DPD) deficiency accounts for approximately 43% of grade 3-4 toxicity to 5-fluorouracil. There, however, remain a number of patients presenting with 5-fluorouracil-associated toxicity despite normal DPD enzyme activity, suggesting possible deficiencies in clihydropyrimidinase (DHP), encoded by the DPYS gene, and/or beta-ureidopropionase (BUP-1), encoded by the UPB1 gene. This study investigates the role of DPYS sequence variations in individuals with unexplained molecular basis of altered uracil catabolism. Methods: This study included 219 asymptornatic healthy volunteers with known DPD enzyme activity and [2-C-13]- uracil breath test (UraBT) profiles. All samples were genotyped for sequence variations in the DPYS gene using denaturing high-performance liquid chromatography (DHPLC) and Surveyor enzyme digestion with confirmation by direct sequencing. Site-directed mutagenesis and expression analysis were performed to determine the effect of the identified nonconservative mutations on DHP enzyme activity. Results: Seven previously reported and 11 novel sequence variations were identified, including three nonconservative mutations; two of which (L7V and 1635delC) demonstrated decreased DHP activity when expressed in the RKO cell line (P= 0.25). The P values were not significant due to the small sample size (n=3); however, a modified [2-C-13]- uracil breath test, the C-13-dihydrouracil breath test, was administered to four volunteers to confirm that the 1635delC mutation does in fact reduce in-vivo DHP activity. Conclusion: Data presented in this study demonstrate that alterations of uracil catabolism are not limited to DPD deficiency, and that inactivating mutations in DHP might impair uracil catabolism in cases of normal DPD activity.