Metabolism and Toxicity of Electroporated 1‐β‐d‐Arabinofuranosylcytosine Triphosphate in a Human Leukemia Cell Line

The metabolism and toxicity of 1‐β‐d‐arabinofuranosylcytosine triphosphate (ara‐CTP) directly injected into cells by electroporation was studied in human leukemia cell lines. The intracellular accumulation of ara‐CTP (ara‐CTP‐Ep) was dependent on the cell type, extracellular ara‐CTP concentration and pulse voltage on electroporation. In a promyelocytic leukemia cell line, HL‐60, ara‐CTP‐Ep revealed a cytotoxic effect in a dose‐dependent manner, although electroporation alone did not have any significant toxicity. Furthermore, simultaneous injection of dCTP, or continuous exposure to deoxycytidine, but not to other deoxyribonucleosides, immediately after electroporation rescued the cells from the toxicity of ara‐CTP‐Ep. The degradation of ara‐CTP‐Ep consisted of an early rapid phase followed by a slower phase with a half life of 1.5 h. The addition of dipyridamole (10 μM), an inhibitor of nucleoside transport, retarded this degradation process. These data indicate that transfer of ara‐CTP by electroporation is a useful method for the study of ara‐CTP metabolism.