title: Formation of 6-thioguanine and 6-mercaptopurine from their 9-alkyl derivatives in mice.
abstract: Several 9-alkyl, 6-thiopurines have been reported to have more favorable therapeutic indexes than do the parent drugs, 6-mercaptopurine (MP) and 6-thioguanine (TG). Some of these compounds were reported to be active against cells in culture resistant to 6-thiopurines, and it has been assumed that their mechanisms of action may differ from those of TG and MP. 9-(n-Butyl)-6-thioguanine was essentially inactive toward Chinese hamster ovary cells in vitro when compared with TG (50% effective dose, 250 and 1 microM, respectively). However, lethal doses of 9-(n-butyl)-6-thioguanine and TG in mice were similar when these agents were given i.p. daily for 9 consecutive days (50% lethal dose, 13 and 9 mg/kg/day). Similar organ toxicities were observed upon histopathological examination of dying animals. The cumulative, daily urinary excretion of TG was virtually identical in mice given 20- and 10-mg/kg/day of doses of 9-(n-butyl)-6-thioguanine or TG, respectively, for 9 days. The TG formed was identified by ultraviolet light (340 nm) detection following separation on a reverse phase high performance liquid chromatography system and by fluorescent detection of the permanganate oxidation product separated on a strong anion-exchange system. Dealkylation of 9-(n-butyl)-6-mercaptopurine and 9-ethyl-6-mercaptopurine also occurred in AKR mice. At near equitoxic doses, the daily cumulative urinary excretion of MP from 9-(n-butyl)-6-mercaptopurine and 9-ethyl-6-mercaptopurine was about 20-30% of that observed in mice receiving MP. The MP was confirmed in each case by enzymatic peak-shift of MP to 6-thiouric acid and ultraviolet light detection using the high performance liquid chromatography systems referred to above. The results suggest that these 9-alkyl derivatives serve as prodrugs for TG and MP, a finding that explains a number of their pharmacological and toxicological properties.
mesh_terms: D000818:Animals; D002470:Cell Survival / Q000187:drug effects; D004305:Dose-Response Relationship, Drug; D015122:Mercaptopurine / Q000031:analogs & derivatives* / Q000378:metabolism / Q000627:therapeutic use / Q000633:toxicity / Q000652:urine; D051379:Mice; D012513:Sarcoma, Experimental / Q000188:drug therapy; D013329:Structure-Activity Relationship; D013866:Thioguanine / Q000031:analogs & derivatives* / Q000378:metabolism / Q000627:therapeutic use / Q000633:toxicity / Q000652:urine
chemical_list: C047359:9-(n-butyl)-6-thioguanine; D015122:Mercaptopurine; C047358:9-(n-butyl)-6-mercaptopurine; D013866:Thioguanine; C047357:9-ethyl-6-mercaptopurine