Characterization of the urinary metabolites of 5-azacytidine in mice

The metabolism of 5-azacytidine, radiolabeled in the 4- or 6-position with carbon-14, was studied in mice. High pressure liquid Chromatographic analysis of urine from mice given [4- 14 C]- or [6- 14 C]-5-azacytidine showed that six radioactive peaks were present and that peaks V and VI were the major peaks excreted. Similar analysis of urine from mice given the labeled compounds and tetrahydrouridine, a deaminase inhibitor, indicated that peaks I, II and V were deaminated metabolites. Peak V appeared to contain components with the 6-carbon absent, whereas peak VI contained components, in a 1:1 ratio, with the 6-carbon either present or absent. Co-chromatography of urine from treated mice with authentic standards indicated that peaks I, III, IV were 5-azauracil, 5-azacytosine and 5-azacytidine, respectively. These data, along with the characterization of peaks V and VI by gasliquid chromatography and mass spectrometry, indicated that the metabolism of 5-azacytidine in mice is similar to that proposed by other investigators.