Thymidylate synthetase-positive and -negative murine mammary FM3A carcinoma cells as a useful system for detecting thymidylate synthetase inhibitors.

The murine mammary FM3A/O and the thymidylate (dTMP) synthetase-deficient FM3A/TS- carcinoma cell lines can be considered as a novel and useful test system for the detection of nucleoside analogues which are directly aimed at the thymidylate synthetase. These compounds should be inhibitory for FM3A/O but not for FM3A/TS- cells, and their inhibitory effects on FM3A/O cell growth should be readily reversed by exogenous dThd within the concentration range of 5-20 microM.