PERMEATION AND METABOLISM OF ANTI-HIV AND ENDOGENOUS NUCLEOSIDES IN HUMAN IMMUNE EFFECTOR-CELLS

Numerous anti-HIV drugs are synthetic analogs of endogenous nucleoside s. Therefore it is of interest to see if a facilitated nucleoside tran sport system exists to mediate their uptake into human immune effector cells that are known HIV targets. Nucleoside permeation and metabolis m in lymphocytes, macrophages and bone marrow cells isolated from heal thy human volunteers were studied, using uridine as the prototype endo genous nucleoside. There are saturable broad specificity nucleoside tr ansport systems in all three cell types, all of which were inhibited b y dipyridamole. The V(max) and K(m) values for uridine transport were 0.05 +/- 0.01 pmol/sec/10(6) cells and 18.4 +/- 4.2 muM, respectively, for lymphocytes, 0.04 +/- 0.01 pmol/sec/10(6) cells and 25.3 +/- 6.6 muM, respectively, for macrophages, and 0.03 +/- 0.01 pmol/sec/106 cel ls and 90.2 +/- 10.1 muM, respectively, for bone marrow mononuclear ce lls. Anti-HIV dideoxynucleosides such as azidothymidine (AZT), 2',3'-d ideoxycytidine (DDC), 2',3'-dideoxyinosine (DDI), 2',3'-dideoxyadenosi ne (DDA), and 2',3'-dideoxythymidine (DDT) are not substrates of this nucleoside transport system; hence, little or no drug accumulated insi de the cells after 60 sec. Equilibration of cells with uridine or dide oxynucleosides for 2 hr resulted in high levels of cellular uridine an d DDA, low levels of cellular AZT, but undetectable levels of the othe r analogs in all three cell types. Active metabolite levels in lymphoc ytes as assayed by HPLC correlated with the drug permeation results. O ur data demonstrated that DDC, DDI, and DDT are not substrates for the nucleoside transporter and cannot diffuse readily across the cell mem brane of human immune effector cells. Future anti-HIV drug development efforts should consider drugs that are substrates of the nucleoside t ransporter to ensure rapid and complete uptake into target cells.