A quinazoline antifolate as inhibitor of folate metabolism in mouse L-cells

The effects of quinazoline antifolate CB 3703 on folate metabolism in mouse L-cells were examined by measuring the amount of 14C label in folate derivatives and its distribution in separated folylmono- and polyglutamates in the cells grown in the presence of radioactive folate and quinazoline. The total radioactivity of folyl derivatives in the quinazoline-treated cells did not exceed 15% of the radioactivity extracted from the control cells, in spite of the fact that quinazoline CB 3703 did not interfere with the uptake of folate into L-cells. Analysis of folylmono- and polyglutamate derivatives, either incubated or not incubated with gamma-glutamylcarboxypeptidase, by chromatography on Sephadex G-25, G-15 or DEAE-cellulose revealed that in the quinazoline-treated cells practically all radioactivity was found in the position of unmetabolized folate. It seems probable, therefore, that quinazoline CB 3703 impairs in L-cells folate reduction and conversion to its coenzymatic forms and their subsequent polyglutamation. These facts seem to be responsible for a decrease in retention of folate derivatives in the quinazoline CB 3703-treated cells.