MECHANISM OF ANTI-HIV ACTION OF MASKED ALANINYL D4T-MP DERIVATIVES

So324 is a -dideoxy-2',3'-didehydrothymidine-5'-monophosphate (d4T-MP) prodrug containing at the phosphate moiety a phenyl group and the met hylester of alanine linked to the phosphate through a phosphoramidate linkage. So324 has anti-HIV activity in human GEM, MT4, and monocyte/m acrophage cells that is superior to that of d4T. In contrast to d4T, S o324 is also able to inhibit HIV replication in thymidine kinase-defic ient CEM cells, After uptake of So324 by intact human lymphocytes, d4T -MP is released and subsequently converted intracellularly to d4T-TP. In addition, accumulation of substantial amounts of a novel d4T deriva tive has been found. This d4T metabolite has been characterized as ala ninyl d4T-MP. The latter metabolite accumulates at approximate to 13- to 200-fold higher levels than d4T-TP depending the experimental condi tions. Alaninyl d4T-MP should be considered as an intra- and/or extrac ellular depot form of d4T and/or d4T-MP. These findings may explain th e superior anti-retroviral activity of So324 over d4T in cell culture.