165 GENETIC ANALYSIS OF 2′,3′-DIDEOXYCYTIDINE METABOLISM IN HUMAN CEM T LYMPHOBLASTS

Abstract

2′,3′-Dideoxycytidine (ddC) is known to inhibit the in vitro infectivity and growth of HTLV-III/LAV, the causative agent of acquired immunodeficiency syndrome (AIDS). The cellular determinants that mediate the action of ddC in cultured human CEM thymic lymphoblasts were analyzed by somatic cell genetic approaches. Whereas ddC at a concentration of 5 micromolar inhibited the growth of wild type CEM cells by 50%, two nucleoside transport-deficient clones were 4-fold resistant to the pyrimidine analog. A deoxycytidine kinase-deficient CEM cell derivative was completely refractory to growth inhibition by I millimolar ddC. An 80% diminished rate of ddC influx into the two nucleoside transport-deficient cell lines could account for their resistance to the dideoxynucleoside, while the resistance of the deoxycytidine kinase-deficient cells to ddC toxicity could be explained by a complete failure to incorporate ddC in situ. NBMPR and DPA, two potent inhibitors of nucleoside transport in mammalian cells, mimicked the effects of the genetic deficiency in nucleoside transport with respect to ddC toxicity and ddC incorporation. These data indicate that the intracellular metabolism of ddC in CEM cells is initiated by the nucleoside transport system and deoxycytidine kinase and has important implications for the design of biochemically rational chemotherapeutic regimens exploiting antiretroviral nucleoside analogs in the treatment of AIDS.