DIFFERENTIAL PHOSPHORYLATION OF AZIDOTHYMIDINE, DIDEOXYCYTIDINE, AND DIDEOXYINOSINE IN RESTING AND ACTIVATED PERIPHERAL-BLOOD MONONUCLEAR-CELLS

The antiviral activity of azidothymidine (AZT), dideoxycytidine (ddC), and dideoxyinosine (ddl) against HIV-1 was comparatively evaluated in PHA-stimulated PBM. The mean drug concentrations which yielded 50% p2 4 Gag negative cultures were substantially different: 0.06, 0.2, and 6 muM for AZT, ddC, and ddl, respectively. We found that AZT was prefer entially phosphorylated to its triphosphate (TP) form in PHA-PBM rathe r than unstimulated, resting PBM (R-PBM), producing 10- to 17-fold hig her ratios of AZTTP/dTTP in PHA-PBM than in R-PBM. The phosphorylation of ddC and ddl to their TP forms was, however, much less efficient in PHA-PBM, resulting in approximately 5-fold and approximately 15-fold lower ratios of ddCTP/dCTP and ddATP/dATP, respectively, in PHA-PBM th an in R-PBM. The comparative order of PHA-induced increase in cellular enzyme activities examined was: thymidine kinase > uridine kinase > d eoxycytidine kinase > adenosine kinase > 5'-nucleotidase. We conclude that AZT, ddC, and ddl exert disproportionate antiviral effects depend ing on the activation state of the target cells, i.e., ddI and ddC exe rt antiviral activity more favorably in resting cells than in activate d cells, while AZT preferentially protects activated cells against HIV infection. Considering that HIV-1 proviral DNA synthesis in resting l ymphocytes is reportedly initiated at levels comparable with those of activated lymphocytes, the current data should have practical relevanc e in the design of anti-HIV chemotherapy, particularly combination che motherapy.