title: Metabolism and metabolic effects of 2-azahypoxanthine and 2-azaadenosine.
abstract: The metabolism and metabolic effects of 2-azahypoxanthine and 2-azaadenosine were studied to elucidate the biochemical basis for their known cytotoxicities. 2-Azaadenosine is a known substrate for adenosine kinase. That 2-azahypoxanthine is a substrate for hypoxanthine (guanine) phosphoribosyltransferase is shown by the observations that, in cell-free fractions from HEp-2 cells supplemented with 5-phosphoribosyl-1-pyrophosphate, 2-azahypoxanthine inhibited the conversion of hypoxanthine to IMP but not the conversion of adenine to AMP, and hypoxanthine, but not adenine, inhibited the conversion of 2-azahypoxanthine to 2-azaIMP. [8-14C]2-Azahypoxanthine was synthesized from [8-14C]hypoxanthine via [2-14C]-4-amino-5-imidazolecarboxamide. In HEp-2 cells in culture, the principal metabolite of [8-14C]-2-azahypoxanthine was 2-azaATP; there was no detectable 14C in deoxynucleotides or in DNA or RNA fractions. 2-Azaadenosine was much more toxic than 2-azahypoxanthine, and, when used in the presence of an adenosine deaminase inhibitor, 2'-deoxycoformycin, was converted in HEp-2 cells to 2-azaATP in amounts that exceeded those of ATP in control cells. The pool of ATP was reduced by as much as 75% as 2-azaATP accumulated. In a short-term experiment (4 hr), 2-azaadenosine selectively reduced the pools of adenine nucleotides, whereas 2-azahypoxanthine reduced the pools of guanine nucleotides selectively. Both 2-azahypoxanthine and 2-azaadenosine inhibited the incorporation of formate into purine nucleotides and were without effect on the conversion of thymidine and uridine to nucleotides. 2-Azahypoxanthine inhibited the incorporation of thymidine into macro-molecules but not that of uridine or leucine; 2-azaadenosine inhibited the incorporation of all three of these precursors non-selectively. 2-AzaIMP inhibited IMP dehydrogenase competitively with IMP (Ki = 66 microM). The difference in effects of 2-azahypoxanthine and 2-azaadenosine perhaps may be due to the production, from 2-azahypoxanthine but not from 2-azaadenosine + 2'-deoxycoformycin, of 2-azaIMP, which inhibits synthesis of guanine nucleotides and thereby results in inhibition of DNA synthesis. Specific sites of action for 2-azaadenosine are yet undefined.
authors.forename: L L
authors.initials: LL
authors.lastname: Bennett
authors.forename: D
authors.initials: D
authors.lastname: Smithers
authors.forename: L M
authors.initials: LM
authors.lastname: Rose
authors.forename: D J
authors.initials: DJ
authors.lastname: Adamson
authors.forename: S C
authors.initials: SC
authors.lastname: Shaddix
authors.forename: H J
authors.initials: HJ
authors.lastname: Thomas
mesh_terms: D000241:Adenosine / Q000031:analogs & derivatives* / Q000378:metabolism / Q000494:pharmacology; D000818:Animals; D000970:Antineoplastic Agents / Q000378:metabolism* / Q000494:pharmacology; D002294:Carcinoma, Squamous Cell; D002460:Cell Line; D002851:Chromatography, High Pressure Liquid; D003854:Deoxyribonucleotides / Q000096:biosynthesis; D006801:Humans; D007041:Hypoxanthine Phosphoribosyltransferase / Q000378:metabolism; D007042:Hypoxanthines / Q000378:metabolism* / Q000494:pharmacology; D007168:IMP Dehydrogenase / Q000037:antagonists & inhibitors; D007822:Laryngeal Neoplasms; D007939:Leukemia L1210; D046911:Macromolecular Substances; D051379:Mice; D011119:Polynucleotides / Q000096:biosynthesis; D012265:Ribonucleotides / Q000096:biosynthesis
chemical_list: D000970:Antineoplastic Agents; D003854:Deoxyribonucleotides; D007042:Hypoxanthines; D046911:Macromolecular Substances; D011119:Polynucleotides; D012265:Ribonucleotides; C045138:2-azaadenosine; D007168:IMP Dehydrogenase; D007041:Hypoxanthine Phosphoribosyltransferase; D000241:Adenosine; C012759:2-azahypoxanthine