Conversion of the oncogenic 1-methylguanine 3-oxide to 3-hydroxy-1-methylxanthine.

Deamination of the oncogenic 1-methylguanine 3-oxide occurs to a significant extent in rats to yield 3-hydroxy-1-methylxanthine and its metabolites. When 3-hydroxy-1-methylxanthine is administered, 1-methyl-8-methylthioxanthine can be recovered from urine and released from hepatic protein. No 1-methyl-8-methylthioguanine was detected in urine or bound to protein. There is no evidence of significant activation of 1-methylguanine 3-oxide by sulfotransferase, but deamination to the oncogenic 3-hydroxy-1-methylxanthine suffices to explain its oncogenicity.