Multi-step inhibition explains HIV-1 protease inhibitor pharmacodynamics and resistance
S. Alireza Rabi, … , Richard D. Moore, Robert F. Siliciano
S. Alireza Rabi, … , Richard D. Moore, Robert F. Siliciano
Published August 27, 2013
Citation Information: J Clin Invest. 2013;123(9):3848-3860. https://doi.org/10.1172/JCI67399.
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Research Article

Multi-step inhibition explains HIV-1 protease inhibitor pharmacodynamics and resistance

Abstract

HIV-1 protease inhibitors (PIs) are among the most effective antiretroviral drugs. They are characterized by highly cooperative dose-response curves that are not explained by current pharmacodynamic theory. An unresolved problem affecting the clinical use of PIs is that patients who fail PI-containing regimens often have virus that lacks protease mutations, in apparent violation of fundamental evolutionary theory. Here, we show that these unresolved issues can be explained through analysis of the effects of PIs on distinct steps in the viral life cycle. We found that PIs do not affect virion release from infected cells but block entry, reverse transcription, and post–reverse transcription steps. The overall dose-response curves could be reconstructed by combining the curves for each step using the Bliss independence principle, showing that independent inhibition of multiple distinct steps in the life cycle generates the highly cooperative dose-response curves that make these drugs uniquely effective. Approximately half of the inhibitory potential of PIs is manifest at the entry step, likely reflecting interactions between the uncleaved Gag and the cytoplasmic tail (CT) of the Env protein. Sequence changes in the CT alone, which are ignored in current clinical tests for PI resistance, conferred PI resistance, providing an explanation for PI failure without resistance.

Authors

S. Alireza Rabi, Gregory M. Laird, Christine M. Durand, Sarah Laskey, Liang Shan, Justin R. Bailey, Stanley Chioma, Richard D. Moore, Robert F. Siliciano

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Figure 3

Median effect plots illustrating the effects of the PIs ATV, DRV, and LPV on HIV-1 entry, reverse transcription, all postentry events, and overall infectivity.

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Median effect plots illustrating the effects of the PIs ATV, DRV, and LP...
(A, E, and I) Effect of PIs on viral entry. The dose-response curves of PIs at the entry step from Figure 2 were linearized by plotting log[(1 – fu)/fu)] vs. log(D/IC50). (B, F, and J) Effect of PIs on reverse transcription. qPCR was used to measure production of early reverse transcripts in primary CD4+ T lymphoblasts infected with pseudoviruses carrying an X4-tropic Env truncated in the CT of gp41 CT. PIs were present at the indicated concentration during virus production. (C, G, and K) Effect of PIs on all postentry steps. Flow cytometry was used to detect infection of primary CD4+ T lymphoblasts by pseudoviruses carrying a VSV-G. PIs were present at the indicated concentration during virus production. (D, H, and L) Reconstruction of overall dose-response curve of PIs by combining the dose-response curves at entry and postentry steps. A 2-step form of Equation 3 was used to combine best fit dose-response curves for PI effects on entry (blue line) and all postentry steps (red line). The resulting curves (dotted black lines) were compared with experimental results for the inhibition of infectivity by PIs (black circles).