Observations on the anticancer activity of 6-mercaptopurine.

Elion, Burgi, and Hitchings (3) synthesized 6-mercaptopurine and found it to be a purine an tagonist in Laclobacillus casei which was reversible by adenine, guanine, xanthine, and hypoxanthine, but not by folie acid (4). They also observed that resistance of L. casei to 6-mercaptopurine was not accompanied by resistance to adenine antagonists such as 2,6-diaminopurine, 8-azaadenine, and purine, or to the guanine antagonist, 8-azaguanine (5, 6). Clarke and co-workers (2) have reported on the effects of 6-mercaptopurine against Sarcoma 180, which were characterized by only moderate in hibition during the initial period of treatment, but, more important, by the eventual nonviability of the tumor as measured by transplantation and a significant number of complete tumor regressions. Burchenal et al. (1) have observed that 6-mercaptopurine will cause temporary remissions in certain cases of acute leukemia, including those which have become resistant to A-methopterin. The present paper reports certain results ob tained with 6-mercaptopurine in several mouse neoplasms.