STRUCTURAL FEATURES OF SUBSTITUTED PURINE DERIVATIVES COMPATIBLE WITH DEPLETION OF HUMAN O-6-ALKYLGUANINE-DNA ALKYLTRANSFERASE

A series of O6- and S6-substituted purine derivatives were tested for their ability to deplete the human DNA repair protein O6-alkylguanine-DNA alkyltransferase (AGT) in cell-free extracts from HT29 colon tumor cells and intact HT29 cells. The order of potency was O6-(p-Y-benzyl)-guanine (Y = H, F, Cl, and CH3) > O6-benzyl-2'-deoxyguanosine > O6-(p-Y-benzyl)guanosine (Y = H, Cl, and CH3) greater-than-or-equal-to a series of 9-substituted O6-benzylguanine derivatives greater-than-or-equal-to O6-allylguanine > O6-benzylhypoxanthine > O6-methylguanine. A series of 7-substituted O6-benzylguanine derivatives, 2-amino-6-(p-Y-benzylthio)purine (Y = H, CH3),2-amino-6-[(p-nitrobenzyl)thiol-9-beta-D-ribofuranosylpurine, and 7-benzylguanine were inactive. It is concluded that for efficient AGT depletion, an allyl or benzyl group attached through exocyclic oxygen at position 6 of a 2-aminopurine derivative is required. Activity is preserved with a variety of substituent groups attached to position 9 while substitution at position 7 leads to a complete loss of activity.