Evaluation of cutpoints for phenotypic hypersusceptibility to efavirenz

In vitro HIV-1 evolution in response to triple reverse transcriptase inhibitors & in silico phenotypic analysis

BACKGROUND

Effectiveness of ART regimens strongly depends upon complex interactions between the selective pressure of drugs and the evolution of mutations that allow or restrict drug resistance.

METHODS

Four clinical isolates from NRTI-exposed, NNRTI-naive subjects were passaged in increasing concentrations of NVP in combination with 1 µM 3 TC and 2 µM ADV to assess selective pressures of multi-drug treatment. A novel parameter inference procedure, based on a stochastic viral growth model, was used to estimate phenotypic resistance and fitness from in vitro combination passage experiments.

RESULTS

Newly developed mathematical methods estimated key phenotypic parameters of mutations arising through selective pressure exerted by 3 TC and NVP. Concentrations of 1 µM 3 TC maintained the M184V mutation, which was associated with intrinsic fitness deficits. Increasing NVP concentrations selected major NNRTI resistance mutations. The evolutionary pathway of NVP resistance was highly dependent on the viral genetic background, epistasis as well as stochasticity. Parameter estimation indicated that the previously unrecognized mutation L228Q was associated with NVP resistance in some isolates.

CONCLUSION

Serial passage of viruses in the presence of multiple drugs may resemble the selection of mutations observed among treated individuals and populations in vivo and indicate evolutionary preferences and restrictions. Phenotypic resistance estimated here "in silico" from in vitro passage experiments agreed well with previous knowledge, suggesting that the unique combination of "wet-" and "dry-lab" experimentation may improve our understanding of HIV-1 resistance evolution in the future.

Use of new T-cell-based cell lines expressing two luciferase reporters for accurately evaluating susceptibility to anti-human immunodeficiency virus type 1 drugs

Two new T-cell-based reporter cell lines were established to measure human immunodeficiency virus type 1 (HIV-1) infectivity. One cell line naturally expresses CD4 and CXCR4, making it susceptible to X4-tropic viruses, and the other cell line, in which a CCR5 expression vector was introduced, is susceptible to both X4- and R5-tropic viruses. Reporter cells were constructed by transfecting the human T-cell line HPB-Ma, which demonstrates high susceptibility to HIV-1, with genomes expressing two different luciferase reporters, HIV-1 long terminal repeat-driven firefly luciferase and cytomegalovirus promoter-driven renilla luciferase. Upon HIV infection, the cells expressed firefly luciferase at levels that were highly correlated (r2=0.91 to 0.98) with the production of the capsid antigen p24. The cells also constitutively expressed renilla luciferase, which was used to monitor cell numbers and viability. The reliability of the cell lines for two in vitro applications, drug resistance phenotyping and drug screening, was confirmed. As HIV-1 efficiently replicated in these cells, they could be used for multiple-round replication assays as an alternative method to a single-cycle replication protocol. Coefficients of variation for drug susceptibility evaluated with the cell lines ranged from 17 to 41%. The new cell lines were beneficial for evaluating antiretroviral drug resistance. Firefly luciferase gave a wider dynamic range for evaluating virus infectivity, and the introduction of renilla luciferase improved assay reproducibility. The cell lines were also beneficial for screening new antiretroviral agents, as false inhibition caused by the cytotoxicity of test compounds was easily detected by monitoring renilla luciferase activity.

Efavirenz for HIV-1 infection in adults: an overview

Efavirenz (Sustiva), Bristol-Myers Squibb) is a non-nucleoside reverse transcriptase inhibitor that has been used successfully since the late 1990s to treat HIV-1 infection, and has since become a cornerstone of antiretroviral therapy. The efficacy and potency of efavirenz has been established in many clinical trials and cohort studies, where it has been compared with unboosted or ritonavir (Norvir, Abbott Laboratories Ltd)-boosted protease inhibitors, nevirapine (Viramune, Boehringer Ingelheim Ltd); and three nucleoside analog-based regimens. Pharmacokinetics allowing for a convenient once-daily administration make efavirenz one of the first agents to be included in once-daily regimens. Tolerability of efavirenz is satisfactory, although CNS-related toxicity can occur, and is still poorly understood. New insights into the pharmacokinetics of efavirenz could help to manage this unwanted toxicity. This drug profile will examine the principal data concerning the efficacy, pharmacokinetics and safety that have made efavirenz a standard of care in HIV-1 therapy, and will comment on new data that could change the way efavirenz is used in the near future.