4-Nitrobenzyloxycarbonyl Derivatives of O6-Benzylguanine as Hypoxia-Activated Prodrug Inhibitors of O6-Alkylguanine-DNA Alkyltransferase (AGT) which Produces Resistance to Agents Targeting the O-6 Position of DNA Guanine

摘要

A series of 4-nitrobenzyloxycarbonyl prodrug derivatives of O⁶-benzylguanine (O⁶-BG), conceived as prodrugs of O⁶-BG, an inhibitor of the resistance protein O⁶-alkylguanine-DNA alkyltransferase (AGT), were synthesized and evaluated for their ability to undergo bioreductive activation by reductase enzymes under oxygen deficiency. Three agents of this class, 4-nitrobenzyl (6-(benzyloxy)-9H-purin-2-yl)carbamate (>1), and its monomethyl (>2) and gem-dimethyl analogues (>3) were tested for activation by reductase enzyme systems under oxygen deficient conditions. Compound >3, the most water-soluble of these agents, gave the highest yield of O⁶-BG following reduction of the nitro group trigger. Compound >3 was also evaluated for its ability to sensitize 1,2-bis(methylsulfonyl)-1-(2-chloroethyl)-2-[(methylamino)carbonyl]hydrazine (laromustine)-resistant DU145 human prostate carcinoma cells, which express high levels of AGT, to the cytotoxic effects of this agent under normoxic and oxygen deficient conditions. While >3 had little or no effect on laromustine cytotoxicity under aerobic conditions, significant enhancement occurred under oxygen deficiency, providing evidence for the preferential release of the AGT inhibitor O⁶-BG under hypoxia.