[Relationship between antitumor activity and the inhibition of thymidylate synthase after oral administration of UFT in nude mice bearing human tumor].

We studied the relationship between antitumor efficacy of UFT, which is a most widely used drug among fluorinated pyrimidines recently, and its effect on the content and the inhibition rate of thymidylate synthase (TS) in 15 human tumor xenografts derived from stomach, colon, breast and pancreatic cancer patients. There was a linear relationship between the content of TS and tumor mass doubling time (MDT). It may be shown that TS content reflects the growth rate of tumor cells. It should be stressed that tumor growth inhibition rate (TGIR), induced by UFT, correlated well with the inhibition of TS (TSI), particularly in the stomach and breast cancer. These results demonstrate that the measurement of inhibition rate of TS is important for the prediction and evaluation of clinical efficacy of UFT.