Kinetic studies with the non-nucleoside HIV-1 reverse transcriptase inhibitor U-88204E.

The bis(heteroaryl)piperazine U-88204E is a potent inhibitor of HIV-1 reverse transcriptase (RT) and possesses excellent anti-HIV activity in HIV-1-infected lymphocytes grown in tissue culture. Enzymatic kinetic studies of the RNA- and DNA-dependent DNA polymerases of RT were carried out in order to determine whether the inhibitor interacts directly with the template:primer or deoxyribonucleotide triphosphate (dNTP) binding sites of the polymerase. The experimental results were analyzed using steady-state or Briggs-Haldane kinetics, by assuming that the template:primer binds to the enzyme first followed by the dNTP and that the polymerase functions processively. The results of the analysis show that the inhibitor acts as a mixed to noncompetitive inhibitor with respect to both the template:primer and the dNTP binding sites. The potency of U-88204E on the RNA-directed DNA polymerase activity depends on the base composition of the template:primer. The Ki values for the poly(rC):(dG)10-directed reactions were at least 7 times lower than the ones for reactions directed by poly(rA):(dT)10. The inhibitor did not inhibit the RNase H function of HIV-1 RT nor did it impair the RNA-directed DNA polymerase activity of HIV-2 RT. These data thus demonstrate the unique specificity of U-88204E for HIV-1 RT.