Enhanced fidelity of 3TC-selected M184V HIV reverse transcriptase.
Originally Published on May 12, 1999
Wainberg MA; Hsu M; Gu Z; Inouye P; Quan Y
Int Conf AIDS. 1996 Jul 7-12;11(1):11 (abstract no. Mo.A.380).
ABSTRACT: Objective: To determine the basis of success of 3TC in recent clinical trials that have reported increased CD4 counts and diminished viral burden. Specifically, we asked whether these findings might be attributable to an increase in fidelity of HIV reverse transcriptase conferred by the M184V substitution responsible for resistance to 3TC. Methods: Recombinant viruses containing the M184V substitution were grown in the presence of other drugs. In addition, antisera obtained from patients at baseline were tested for ability to neutralize sequential autologous HIV clinical isolates. We also studied fidelity directly using purified recombinant RT enzyme.
Results: Individuals treated with 3TC monotherapy had lower viral burden in plasma than at baseline, even after high level resistance had been documented. Furthermore, sera obtained from early time points continued to have neutralizing activity against viruses isolated up to twelve months later. We further asked whether recombinant viruses, that contain M184V RT, can be grown in the presence of other drugs, such as AZT, d4T, and saquinavir, using procedures previously shown to select for resistance in tissue culture. We found that wild-type virus could grow in the presence of increasing concentrations of these drugs to yield variants that possessed previously described resistance-conferring mutations. In contrast, viruses containing the M184V substitution failed to replicate RT that contained the M184V mutation and displayed significantly higher fidelity in RDDP assays than wild-type enzyme. Finally, the ratio of TCID50:p24 was substantially higher in viruses containing the M184V mutation than in viruses with a M184I substitution, also associated with 3TC resistance, which in turn had a higher ratio than wild-type virus. Conclusions: The success of 3TC in clinical trials is due to selection of a higher fidelity RT. Future drug trials should involve the use of 3TC in patients with high CD4 counts to qualitatively alter viral populations to ones that contain the M184V substitution, following which the use of other antivirals and/or immune stimulators should be considered.
