Production of N4-succinyl-1-beta-D-arabinofuranosylcytosine, a novel metabolite of N4-behenoyl-1-beta-D-arabinofuranosylcytosine, in mice and its biological significance.

A novel metabolite was found in the urine and bile of mice given i.v. injections of N4-behenoyl-1-beta-D-arabinofuranosylcytosine (behenoyl-ara-C). Acid and alkaline hydrolysis of this metabolite resulted in the production of 1-beta-D-arabinofuranosylcytosine and succinic acid, as determined by thin-layer chromatography and high-performance liquid chromatography. Mass spectrometry identified this metabolite as N4-succinyl-1-beta-D-arabinofuranosylcytosine (succinyl-ara-C). This conclusion was supported by thin-layer chromatography and by the ultraviolet spectrum, upon which the characteristics of this metabolite agreed with those of succinyl-ara-C. Only a very small amount, if any, of this metabolite was found in the urine and bile of mice given injections of N4-stearoyl- or N4-palmitoyl-1-beta-D-arabinofuranosylcytosine, suggesting that behenoyl-ara-C was metabolized differently from the other two analogs. Comparison of the metabolites of behenoyl-ara-C, radiolabeled at different positions of the behenoyl-residue, suggested that behenoyl-ara-C was degraded by omega-oxidation and then by beta-oxidation, resulting in the production of succinyl-ara-C. This metabolite was more potent than behenoyl-ara-C in suppressing the in vitro proliferation of murine L1210 cells. The high therapeutic potency of behenoyl-ara-C in L1210-bearing mice may be ascribable to the contribution of succinyl-ara-C to the efficacy of behenoyl-ara-C, either by suppressing the proliferation of L1210 cells or by protecting 1-beta-D-arabinofuranosylcytosine, the possible eventual metabolite, from inactivation by deaminase.