Production of N⁴-Succinyl-1-β-d-arabinofuranosylcytosine, a Novel Metabolite of N⁴-Behenoyl-1-β-d-arabinofuranosylcytosine, in Mice and Its Biological Significance¹

A novel metabolite was found in the urine and bile of mice given i.v. injections of N⁴-behenoyl-1-β-d-arabinofuranosylcytosine (behenoyl-ara-C). Acid and alkaline hydrolysis of this metabolite resulted in the production of 1-β-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-β-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-β-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 ω-oxidation and then by β-oxidation, resulting in the production of succinyl-ara-C.

This metabolite was more potent then 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-β-d-arabinofuranosylcytosine, the possible eventual metabolite, from inactivation by deaminase.