The activity of 6-selenopurine and related compounds against some experimental mouse tumors.

A series of selenium analogs of physiologically active thiopurines and thiopyrimidines has recent ly been prepared (9). The well established antitumor activity of some of the analogous mercapto compounds, particularly 6-mercaptopurine, which has enjoyed wide clinical use in the treatment of various types of leukemia (3,12), indicated the desirability of comparing the chemical and biologi cal properties of these isosterically related com pounds. The selenium compounds, sterically very similar to the corresponding mercapto compounds, are known to be rather different in terms of elec tron distribution, the carbon-selenium double bond being more highly polarized than the carbon-sulfur double bond (9,10). The antimicrobial activity of 6-selenopurine (which, for Lactobacillus casei, was shown to be a purine antagonist) against a wide range of micro organisms was consistently much higher than that of 6-mercaptopurine.1 Similar differences in anti microbial activity had been observed previously in studies of analogous thioand seleno-carbamyl compounds (11). Selenopurine was found to be 5 times more active than mercaptopurine in inhibit ing the growth of mouse leukemia L5178 cells in tissue culture.2 Selenopurine was also found to be considerably more active than mercaptopurine as an inhibitor of chicken kidney xanthine dehydrogenase.3 These results, coupled with the recent findings of Weisberger and Suhrland (17) that "selenium cystine" produced dramatic decreases