Abstract
The effect of prior administration of aminophylline, caffeine, or propranolol on the antitumor activity of 6-mercaptopurine (6-MP) or 6-mercaptopurine riboside (6-MPR) against Ehrlich solid tumor in ddY male mice was studied. These three drugs each weakened the action of 6-MP but had less effect on the action of 6-MPR. Considering the variation in the activities of hypoxanthine-guanine phosphoribosyltransferase and xanthine oxidase, we suggest that higher doses of aminophylline and propranolol may promote the conversion from 6-MP to biologically inactive thiouric acid or hypoxanthine rather than to biologically active thioinosinic acid.
