The influence of homologs of riboflavin on the growth of Walker rat carcinoma 256.

a potent antagonist of riboflavin in the rat, has been found to be nonspecific in the inhibition of the growth of Walker rat Carci noma 256. 7-Ethyl-8-methyl-10-(r-D-ribityl)isoalloxazine (7ethyl-8-methyIflavin) and 7-methyl-8-ethy 1-10-(1' -D-ribityl) isoalloxazine (7-methyl-8-ethylflavin) have been found to replace riboflavin for the growth of and the efficiency of utilization of food by the riboflavin-deficient Sprague-Dawley rat. These 2 flavins do not, however, show the same interchangeability with riboflavin in the growth of Walker rat Carcinoma 256 in this rat. The growth rate of the tumor in the presence of 7-methyl-8ethylflavin is indistinguishable from that observed in the pres ence of riboflavin. The growth rate of the tumor in the presence of 7-ethyl-8-methylflavin is 0.5 that observed in the presence of riboflavin.