Abstract
Thymidylate synthase (TS) is an essential enzyme in the de novo synthesis of thymidine, a pyrimidine nucleoside necessary for the synthesis and maintenance of integrity of DNA. Since 1950, a number of drugs have been discovered that have inhibitory effects on this enzyme. The most widely used are 5-fluorouracil (5-FU) and FUDR (floxuridine). Currently, several classes of newer and more specific TS inhibitors are under development in the hope of enhancing the efficacy and reducing the toxicity of these agents. Each new drug has unique structural and biologic characteristics which can be exploited to yield different clinical characteristics.