ABSTRACT
Thymidylate synthetase (TS) catalyzes the reductive methylation of deoxyuridylate to form thymidylate in the de novo biosynthetic pathway. The therapeutic effectiveness of the TS inhibitors is limited by the emergence of drug-resistant clones within the tumor cell population. TS is an essential enzyme in proliferating mammalian cells that are not supplied with exogenous thymidine. TS normally represents only a tiny fraction of total cellular protein, as expected for a housekeeping enzyme. The mechanism by which these analogues inhibit TS activity has been elucidated. The analogues are first converted to the nucleotide 5-fluorodeoxyuridylate. TS gene amplification has also been observed in a human cell line that was selected for resistance to high concentrations of FdUrd. Sequence analysis revealed that the unamplified fragment closely resembled TS mRNA, indicating that the unamplified TS sequence represents a processed TS pseudogene.
