(4) MR Atkinsun,. JF Jackson and RK Morton,. Vatwe, 19B, 046 (IHGI), and references listed therein. as the basis of antitumor activity exhibited by the purine antagonists. Accordingly, the inhibition of tumor growth might be expected from compounds that are riboflavin antagonists since riboflavin is directly concerned with the biosynthesis of the oxidation- reduction enzyme FAD. Compounds exerting anti-riboflavin activity should then act ...