Dideoxycytidine permeation and salvage by mouse leukemia cells and human erythrocytes.

Transmembrane equilibration of dideoxycytidine (ddCyd) in P388 mouse leukemia cells and human erythrocytes was only 1% as rapid as that of uridine and 2'-deoxycytidine which is mediated by the facilitated nucleoside transporter of these cells. ddCyd entry was nonsaturable up to a concentration of 1 mM but was partially inhibited by dipyridamole, nitrobenzylthioinosine and nucleosides, but not by nucleobases. Thus, entry was partly (70-80%) mediated, though very inefficiently, by the nucleoside carrier. Intracellular phosphorylation of ddCyd in P388 cells was also very inefficient compared to that of 2'-deoxycytidine and uridine and not rate limited by its slow entry into the cells.