[The role of thymidylate synthetase in sequential dose of MTX and 5-FU in the advanced scirrhous type gastric cancer].

The biochemical rationale for the potentiation of the effects of 5-FU by MTX is based on an increased PRPP level or MTX polyglutamate produced by MTX. The cytotoxic action of MTX results not only from inhibition of DHFR but also depends upon thymidylate synthetase (TS), a key enzyme in DNA synthesis. We obtained a monoclonal antibody to TS using a hydrophilic peptide consisting of 20 amino acids in the TS amino acid sequence and demonstrated by PAP that TS was detectable in poorly differentiated adenocarcinoma cells but not in well differentiated adenocarcinoma cells. Upon clinical application of sequential doses of MTX and 5-FU, the median survival durations were 318 days and 156 days for scirrhous-type gastric cancer patients and non-scirrhous-type gastric cancer patients respectively. These results suggest that immunohistochemistry with TS antibody is available as an indicator of the effect of this drug regimen.