Effects of folinic acid on amethopterin-induced inhibition of the Ehrlich ascites carcinoma.

The effects of folinic acid on amethopterin-induced inhibition of growth, purine nucleotide biosynthesis, and DNA thymine formation were measured in Ehrlich ascites cells in vivo. Folinic acid prevented the amethopterin-induced prolongation of survival time of tumor-bearing mice at folinic acid levels which caused complete reversal of the inhibition of glycine-2-C14 incorporation into purines by the folie acid antagonist. In contrast, the depression in the rate of conversion of orotic acid-6-C14 to DNA thymine by amethopterin was only partially spared by folinic acid. The prevention of amethopterin's inhibitory effects by folinic acid did not appear to be due to prevention of the