DISTRIBUTION AND METABOLISM OF LIPSOME-ENCAPSULATED AND FREE 1-BETA-D-ARABINOFURANOSYLCYTOSINE (ARA-C) IN DOG AND MOUSE-TISSUES

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Abstract
The effect of liposome encapsulation on the metabolic activation (phosphorylation) and degradation (deamination) or arabinofuranosylcytosine (Ara-C) [an antitumor agent] in liver and spleen of dogs and mice was investigated. Ara-C in free or liposome-encapsulated form was administered i.v. to dogs and DBA2/CR mice bearing leukemia L1210. At various times after injection the concentration of Ara-C and Ara-C metabolites in the blood, liver and spleen was measured. Liposome encapsulation results in an increased Ara-C/arabinofuranosyluracil ratio in the liver and spleen of dogs and leukemic mice and that encapsulated Ara-C generates a sustained level of Ara-C triphosphate in the liver and spleen of leukemic mice. Apparently encapsulated Ara-C is protected against deamination in the liver; encapsulated Ara-C is slowly released from liposomes in liver and spleen; and liposomes may act as a local depot for Ara-C in these tissues.