Phenotypic analysis of 1-B-D-arabinofuranosylcytosine deamination in patients treated with high doses and correlation with response.

Two phenotypes for 1-B-D-arabinofuranosylcytosine (ara-C) deamination corresponding to a ratio of distribution for "slow" (ratio, less than or equal to 14) vs "fast" (ratio, greater than 14) deaminators of 70%:30%, have been determined on the basis of studies on plasma ratios of 1-B-D-arabinofuranosyluracil/ara-C (ara-U/ara-C) in 56 subjects treated with high-dose ara-C (3 g/m2 infused i.v. over 3 h). A positive correlation of age with the concentration of ara-U was observed. In a subgroup of 36 patients with leukemia, the ara-U/ara-C pattern was similar to that observed for all 56 subjects. In these leukemic patients, who were treated with combinations of ara-C plus other conventional agents, a tendency toward a positive response (complete response + partial response) was found for those showing low ara-U/ara-C ratios (slow deaminators). The phenotypic effect of deamination in acute leukemia needs to be evaluated prospectively.