[Thymidine kinase and thymidylate synthetase activities in human gastric cancer].

Thymidine kinase (TK) and thymidylate synthetase (TS) are known to catalyse the phosphorylation of thymidine for the salvage synthesis of dTMP and the methylation of dUMP for the de novo synthesis of dTMP, respectively. High TK and TS activities and the existence of TK isozymes have been observed in rapidly proliferating tissues. In this work I measured TK, TK-isozyme and TS activities, and DNA and RNA in human gastric cancer tissue. Tissue containing gastric cancer, (well differentiated adenocarcinoma (well: n = 29), poorly differentiated adenocarcinoma (por: n = 28)), and noninvolved paired normal gastric mucosa were obtained from fresh surgical specimens. Total TK and peak A TK activity of gastric cancer increased to 184% and 299% of activity of normal gastric mucosa. TK activity of "well" was higher than that of "por". On the other hand TS activity of gastric cancer increased to 122% of activity of normal gastric mucosa. TS activity of "por" was higher than that of "well". DNA and RNA content of gastric cancer increased to 294% and 228% than that of normal gastric mucosa. But difference wasn't observed between "well" and "por". These characteristics of gastric cancer suggest its susceptibility to control by inhibition of TK and TS.