HIV-1 reverse transcriptase inhibitor resistance mutations and fitness: a view from the clinic and ex vivo

A high-affinity inhibitor of human CD59 enhances complement-mediated virolysis of HIV-1: implications for treatment of HIV-1/AIDS

Many pathogenic enveloped viruses, including HIV-1, escape complement-mediated virolysis by incorporating host cell regulators of complement activation into their own viral envelope. The presence of complement regulators including CD59 on the external surface of the viral envelope confers resistance to complement-mediated virolysis, which may explain why human pathogenic viruses such as HIV-1 are not neutralized by complement in human fluids, even in the presence of high Ab titers against the viral surface proteins. In this study, we report the development of a recombinant form of the fourth domain of the bacterial toxin intermedilysin (the recombinant domain 4 of intermedilysin [rILYd4]), a 114 aa protein that inhibits human CD59 function with high affinity and specificity. In the presence of rILYd4, HIV-1 virions derived from either cell lines or peripheral blood mononuclear cells of HIV-1-infected patients became highly sensitive to complement-mediated lysis activated by either anti-HIV-1 gp120 Abs or by viral infection-induced Abs present in the plasma of HIV-1-infected individuals. We also demonstrated that rILYd4 together with serum or plasma from HIV-1-infected patients as a source of anti-HIV-1 Abs and complement did not mediate complement-mediated lysis of either erythrocytes or peripheral blood mononuclear cells. These results indicate that rILYd4 may represent a novel therapeutic agent against HIV-1/AIDS.

Select resistance-associated mutations in blood are associated with lower CSF viral loads and better neuropsychological performance

BACKGROUND

When antiretroviral therapy does not fully suppress HIV replication, suboptimal levels of antiretrovirals can select for antiretroviral resistant variants of HIV. These variants may exhibit reduced replication capacity and result in lower viral loads in blood. Our study evaluated whether antiretroviral resistance was associated with viral loads in the cerebrospinal fluid (CSF) and better neuropsychological (NP) performance.

METHODS

We enrolled 94 participants and each participant underwent a comprehensive neuromedical evaluation that used structured clinical assessments of medical history, ART and other medication use, comprehensive NP testing, and neurological and general physical signs of disease. Blood was collected by venipuncture, and all participants were offered lumbar puncture. Univariate and multivariate statistical methods were used to analyze the relationship between antiretroviral resistance, blood and CSF HIV RNA levels, substance use, and NP performance.

RESULTS

Antiretroviral resistance, detected in blood, was associated with lower CSF viral loads (p<0.01) and better NP performance (p=0.04) in multivariate analyses, independent of past and current ARV use and blood viral loads (model: p<0.01). However, HIV RNA levels in CSF did not independently correlate with NP performance. Low viral loads in the CSF limited our ability to investigate the relationship between antiretroviral resistance detected in CSF and NP performance.

CONCLUSIONS

Even in the absence of ART, antiretroviral resistance-associated mutations correlate with better NP performance possibly because these mutations reflect reduced neurovirulence compared with wild-type HIV.

The utilization of humanized mouse models for the study of human retroviral infections

The development of novel techniques and systems to study human infectious diseases in both an in vitro and in vivo settings is always in high demand. Ideally, small animal models are the most efficient method of studying human afflictions. This is especially evident in the study of the human retroviruses, HIV-1 and HTLV-1, in that current simian animal models, though robust, are often expensive and difficult to maintain. Over the past two decades, the construction of humanized animal models through the transplantation and engraftment of human tissues or progenitor cells into immunocompromised mouse strains has allowed for the development of a reconstituted human tissue scaffold in a small animal system. The utilization of small animal models for retroviral studies required expansion of the early CB-17 scid/scid mouse resulting in animals demonstrating improved engraftment efficiency and infectivity. The implantation of uneducated human immune cells and associated tissue provided the basis for the SCID-hu Thy/Liv and hu-PBL-SCID models. Engraftment efficiency of these tissues was further improved through the integration of the non-obese diabetic (NOD) mutation leading to the creation of NODSCID, NOD/Shi-scid IL2rγ^-/-, and NOD/SCID β2-microglobulin^null animals. Further efforts at minimizing the response of the innate murine immune system produced the Rag2^-/-γ_c^-/- model which marked an important advancement in the use of human CD34+ hematopoietic stem cells. Together, these animal models have revolutionized the investigation of retroviral infections in vivo.

[Resistance to integrase inhibitors]

Integrase inhibitors are the most recently approved family of antiretroviral agents for the treatment of HIV infection. As with other antiretroviral agents, under pharmacological pressure, the virus selects resistance mutations if viral suppression is incomplete. Mutations are selected in the integrase gene, specifically in positions proximal to the catalytic center. Because clinical experience with these drugs is scarce, information on resistance is limited. Virologic failure with raltegravir is associated with selection of primary mutations such as N155H (40%) and distinct changes in position Q148 (28%). Less frequently, Y143R (6.6%) and E92Q are selected. The most frequently observed mutations in failure with elvitegravir are E92Q, E138K, Q148R/K/H and N155H, and less frequently S147G and T66A/I/K. The most common resistance pattern seems to be E138K + E147G + Q148R. There is a high grade of cross resistance between raltegravir and elvitegravir, making sequencing between these two drugs impossible.

Effect of the human immunodeficiency virus type 1 reverse transcriptase polymorphism Leu-214 on replication capacity and drug susceptibility

A negative association between polymorphism Leu-214 and type-1 thymidine analogue mutations (TAM1) and a positive association with a clinically favorable virological response to thymidine analogue-based combination antiretroviral therapy have been described. In this study, the impact of Leu-214 on replication capacity and resistance to zidovudine (ZDV) of viruses containing TAM1 or TAM2 was determined. Leu-214 decreased the growth rate of viruses bearing Tyr-215, as well as their resistance to ZDV. This observation was confirmed by structural and molecular modeling data, suggesting a regulatory role for Leu-214 in the emergence and phenotypic resistance of TAM1.

Molecular basis of human immunodeficiency virus drug resistance: an update

Antiretroviral therapy has led to a significant decrease in human immunodeficiency virus (HIV)-related mortality. Approved antiretroviral drugs target different steps of the viral life cycle including viral entry (coreceptor antagonists and fusion inhibitors), reverse transcription (nucleoside and non-nucleoside inhibitors of the viral reverse transcriptase), integration (integrase inhibitors) and viral maturation (protease inhibitors). Despite the success of combination therapies, the emergence of drug resistance is still a major factor contributing to therapy failure. Viral resistance is caused by mutations in the HIV genome coding for structural changes in the target proteins that can affect the binding or activity of the antiretroviral drugs. This review provides an overview of the molecular mechanisms involved in the acquisition of resistance to currently used and promising investigational drugs, emphasizing the structural role of drug resistance mutations. The optimization of current antiretroviral drug regimens and the development of new drugs are still challenging issues in HIV chemotherapy. This article forms part of a special issue of Antiviral Research marking the 25th anniversary of antiretroviral drug discovery and development, Vol 85, issue 1, 2010.

Mother to child transmission of HIV-1 in a Thai population: role of virus characteristics and maternal humoral immune response

The objective of this study was to investigate factors influencing mother to child transmission of HIV-1 in Thailand, where HIV-1 CRF01_AE, the major subtype in Southeast Asia, predominates. Samples from 84 HIV-1 infected, anti-retroviral treatment-naïve, non-breast feeding mothers, 28 who transmitted HIV-1 to their babies (transmitters) and 56 who did not (non-transmitters), were studied for maternal humoral immune response and virus characteristics. Maternal humoral immune response was measured by lymphocyte phenotyping; neutralizing antibodies to laboratory HIV-1 MN strain and two clinical isolates; peptide binding antibody to gp41 and V3 from strains CRF01_AE, B, and MN; autologous antibodies; and quasispecies diversity. Virus characteristics studied were viral load, co-receptor usage, and viral replication capacity. No significant difference between transmitters and non-transmitters was found for any parameter of maternal humoral immune response. However, viral load and viral replication capacity were significantly higher in transmitters versus non-transmitters and were not correlated with each other. This suggests that viral replication capacity may be a transmission factor independent of viral load, which is already well established as a risk factor for transmission of HIV-1. All except four viral isolates used the CCR5 co-receptor. This is one of few studies of vertical transmission in a population where HIV-1 CRF01_AE predominates. The data suggest that in this population the maternal humoral immune response was not important in preventing transmission at parturition, but that virus characteristics were key factors, and that viral replication capacity may contribute to birth-associated mother to child transmission of HIV-1.

Variability in the Plasma Concentration of Efavirenz and Nevirapine is Associated with Genotypic Resistance after Treatment Interruption

Background

Selection and persistence of non-nucleoside reverse transcriptase inhibitor (NNRTI)-associated mutations during treatment interruptions (TIs) has been attributed to the long plasma half-life of these drugs. However, little is known about the contribution of variable NNRTI plasma levels before a TI. We evaluated the selection of NNRTI-related mutations and the coefficient of variation of NNRTI plasma concentrations during different TI periods.

Methods

The selection of NNRTI-related mutations was examined in 50 HIV type-1 (HIV-1)-infected patients on a virologically suppressive regimen who underwent TI guided by CD4+ T-cell counts and plasma viraemia. Population and clone-based sequencing of the reverse transcriptase coding region was performed using plasma HIV-1 RNA samples during TI and proviral DNA from peripheral blood mononuclear cells before TI. NNRTI plasma concentrations were determined by HPLC.

Results

In 7/50 treated patients, de novo and transient NNRTI-related mutations appeared when treatment was interrupted. Emergence of resistant variants (including K103N, Y181C or G190S) after interruption was associated with a higher coefficient of variation in NNRTI plasma concentrations during the treatment period. Moreover, minority HIV-1 variants containing different resistance patterns (V106I/A, K103R/E or Y188C/D/H) were detected regardless of NNRTI concentrations.

Conclusions

The emergence of NNRTI-associated mutations during TI appears to be associated with the variation of NNRTI plasma concentrations during the preceding treatment period. The selection of minority HIV-1 variants with different patterns of NNRTI resistance in the absence of drug pressure should be considered for the efficacy of future NNRTI-containing antiretroviral regimens.

Quantitative structure-activity relationship studies on 1-aryl-tetrahydroisoquinoline analogs as active anti-HIV agents

Predictive quantitative structure-activity relationship analysis was developed for a diverse series of recently synthesized 1-aryl-tetrahydroisoquinoline analogs with anti-HIV activities in this study. The conventional 2D-QSAR models were developed by genetic function approximation (GFA) and stepwise multiple linear regression (MLR) with acceptable explanation of 94.9% and 95.5% and good predicted power of 91.7% and 91.7%, respectively. The results of the 2D-QSAR models were further compared with 3D-QSAR model generated by molecular field analysis (MFA), investigating the substitutional requirements for the favorable receptor-drug interaction and quantitatively indicating the important regions of molecules for their activities. The results obtained by combining these methodologies give insights into the key features for designing more potent analogs against HIV.

Novel HIV-1 reverse transcriptase inhibitors

HIV-1 reverse transcriptase (RT) was the first viral enzyme to be targeted by anti-HIV drugs. Despite 20 years of experience with RT inhibitors, new ways to inhibit this target and address viral resistance continue to emerge. In both licensed RT inhibitor classes, nucleosides (NRTIs) and non-nucleosides (NNRTIs), compounds with better resistance, pharmacokinetic and toxicity profiles are being developed. Second-generation NNRTIs active against HIV-1 strains resistant to current NNRTIs are being clinically evaluated. Beyond the classical NRTIs, nucleoside analogs that are no longer obligate chain terminators but nevertheless impede reverse transcription or even lead to viral ablation after several replication cycles, are being studied. RT inhibitor research has also yielded additional mechanisms to block RT. Driven by new insights the RNase H field remains in evolution. In addition, the binding of both substrates (deoxynucleotide and primer/template) to RT is now subject to competition by novel inhibitors. Further development of aptamers bears promise for gene therapy but perhaps more importantly, reveals additional new platforms for the development of small-molecule RT inhibitors. This promising research provides much optimism that RT inhibitors will continue to evolve with subsequent clinical benefit.