Recent advances in antiretroviral treatment and prevention in HIV-infected patients

Darunavir/cobicistat once daily for the treatment of HIV

A current focus in HIV management is improving adherence by minimizing pill burden with convenient formulations, including fixed-dose combinations (FDCs). Darunavir, a HIV protease inhibitor, co-administered with low-dose ritonavir (800/100 mg once daily), is recommended in guidelines in combination with other antiretrovirals for HIV patients with no darunavir resistance-associated mutations. Cobicistat is an alternative agent to ritonavir for boosting plasma drug levels of darunavir among other antiretrovirals. Cobicistat is a more specific cytochrome P450 3A inhibitor than ritonavir without enzyme-inducing properties. This review describes the differing effects of cobicistat and ritonavir on metabolic enzymes, which explains their differing drug-drug interactions, and summarizes some of the studied drug-drug interactions for cobicistat. It also outlines the clinical development and data for a once-daily darunavir/cobicistat FDC. This FDC thus allows for a once-daily treatment regimen (including background antiretrovirals) with reduced pill burden.

A single-loop recombinant pseudotyped-virus-based assay to detect HIV-1 phenotypic resistance

HIV/AIDS is a leading public health concern throughout the world. Currently, treatment of HIV/AIDS still depends on highly active antiretroviral therapy (HAART); however, there is increasing evidence showing the emergence of resistance to antiretroviral drugs in HIV-1 strains, making ART less effective over time. Intensive monitoring of HIV-1 drug resistance is therefore of great importance to evaluate the current sensitivity of antiretroviral agents and is urgently needed. The aim of this study was to develop a single-loop recombinant pseudotyped-virus-based assay to detect phenotypic resistance in clinical HIV-1 strains. HIV-1 RNA was extracted from HIV-1-infected human plasma samples, and an approximately 3-kb fragment containing p7/p1/p6 cleavage sites and full-length protease (PR), reverse transcriptase (RT), thermonuclease (TNase), and integrase (1-280 aa) genes was amplified by nested RT-PCR. A retroviral vector was constructed using the HIV-1 infectious molecular clone pLWJ to test antiretroviral drug susceptibility. pLWJ-SV40-Luc contained a luciferase expression cassette inserted within a deleted region of the envelope (env) gene as an indicator gene. Resistance test vectors (RTVs) were constructed by incorporating amplified target genes into pLWJ-SV40-Luc by using ApaI or AgeI and AarI restriction sites and conventional cloning methods. The virus stocks used for drug susceptibility test were produced by co-transfecting 293T cells with RTVs and a plasmid that provided vesicular stomatitis virus glycoprotein (VSV-G). Viral replication was monitored by measuring luciferase activity in infected target cells at approximately 48 h postinfection. A total of 35 clinical plasma samples from HIV-1-infected humans were tested, and target fragments were successfully amplified from 34 samples (97.1 %) and 33 RTVs were successfully constructed by directional cloning, with an overall success rate of 94.3 %. A clear-cut dose-dependent relationship was detected between virus production and luciferase activity in the constructed phenotypic resistance testing system. The highest coefficient of determination (R(2)) was found between luciferase activity and drug concentration and viral inhibition at 293T cell concentrations of 5 × 10(4) cells per well. The phenotypic profiles of the viruses from 29 clinical samples almost completely matched the observed genotypes. The results demonstrate that a single-loop recombinant pseudotyped-virus-based assay was successfully developed, and this testing system has high stability and appears to be applicable for testing phenotypic resistance of clinical HIV-1 strains to commonly used antiretroviral agents.

Cost-effectiveness analysis of antiretroviral therapy in a cohort of HIV-infected patients starting first-line highly active antiretroviral therapy during 6 years of observation

Objectives

Costs may play a role in deciding how and when to start highly active antiretroviral therapy (HAART) in a naïve patient. The aim of the present study was to assess the cost- effectiveness of treatment with HAART in a large clinical cohort of naïve adults to determine the potential role of single-tablet regimens in the management of patients with human immunodeficiency virus (HIV). An incremental cost-effectiveness ratio analysis was performed, including a quality-adjusted life year approach.

Results

In total, 741 patients (females comprising 25.5%) were retrospectively included. The mean age was 39 years, the mean CD4 cell count was 266 cells/μL, and the mean viral load was 192,821 copies/mL. The most commonly used backbone was tenofovir + emtricitabine (77.6%); zidovudine + lamivudine was used in 10%, lamivudine + abacavir in 3%, and other nucleoside reverse transcriptase inhibitor (NRTI) or NRTI-free regimens in 9.4% of patients. NNRTIs were used in 52.8% of cases, boosted protease inhibitors in 44.1%, and unboosted protease inhibitors and integrase inhibitors in 0.7% and 2.4%, respectively. Starting therapy at CD4 >500 cells/μL and CD4 351–500 cells/μL rather than at <201 cells/μL was the more cost-effective approach. The same consideration was not true comparing current indications with the possibility to start HAART at any CD4 value (eg, >500 cells per μL); in this case, the incremental cost-effectiveness ratio value was €199,130 per quality-adjusted life year gained, a higher value than the one suggested in guidelines. The single-tablet regimen (STR) invariably dominated any other therapeutic approach. Sensitivity analysis was performed, and starting right away with an STR was cost-effective even when compared with therapeutic strategies contemplating STR as simplification.

Conclusion

By integrating clinical data with economic variables, our study offers an estimate of the cost-effectiveness of the various first-line treatment strategies for patients infected with HIV and provides significant evidence to be used in future prospective pharmacoeconomic evaluations.

Darunavir: a review of its use in the management of HIV-1 infection

The latest HIV-1 protease inhibitor (PI) darunavir (Prezista™) has a high genetic barrier to resistance development and is active against wild-type HIV and HIV strains no longer susceptible to some older PIs. Ritonavir-boosted darunavir, as a component of antiretroviral therapy (ART), is indicated for the treatment of HIV-1 infection in adult and paediatric patients (aged ≥3 years), with or without treatment experience (details vary depending on region of approval). Several open-label or partially-blinded trials have evaluated the efficacy of ritonavir-boosted darunavir ART regimens for up to 192 weeks in these settings. In treatment-naïve adults, once-daily boosted darunavir was no less effective in establishing virological suppression than once- or twice-daily boosted lopinavir, yet was more effective at maintaining suppression long term. Moreover, treatment-experienced adults with no darunavir resistance-associated mutations (RAMs) had no less effective viral load suppression with once-daily than with twice-daily boosted darunavir. In treatment-experienced adults, including some with multiple major PI RAMs, twice-daily boosted darunavir was more effective than twice-daily boosted lopinavir or boosted control PIs in reducing viral load, and provided virological benefit as part of a salvage regimen in those with few remaining treatment options. Boosted darunavir also reduced viral load when administered once-daily in treatment-naïve adolescents or twice-daily in treatment-experienced children and adolescents. Boosted darunavir is generally well tolerated, with gastrointestinal disturbances and lipid abnormalities among the most common tolerability issues. It has a lipid profile more favourable than that of boosted lopinavir in terms of total cholesterol and triglyceride changes and, when administered once daily, its lipid effects are generally similar to those of boosted atazanavir. Thus, boosted darunavir is a useful option for the ART regimens of adult and paediatric patients with HIV-1 infection.

Ethical issues for late-stage trials of multipurpose prevention technologies for HIV and pregnancy

Multipurpose prevention technologies (MPTs) designed to simultaneously prevent pregnancy and HIV could provide urgently needed tools to address unmet sexual and reproductive health needs of women worldwide. Late-stage clinical trials will be complex given the need to demonstrate efficacy for HIV and contraceptive indications simultaneously from a single product. Currently, HIV and pregnancy prevention trials have distinctive design features that will need to be reconciled in MPT trials. This article identifies several ethical issues uniquely associated with this research that will benefit from future deliberation and guidance to ensure that this globally important research can proceed efficiently and expeditiously.

[Microbicides for preventing sexually transmitted infections: Current status and strategies for preclinical evaluation of new candidates]

Microbicides are a new tool, still under investigation, which could help prevent infection by the human immunodeficiency virus (HIV) and other sexually transmitted infections (STIs). Increasing evidence shows that the complexity of sexual transmission of viral pathogens requires the identification of compounds able to block the early events during the cycle of viral infection. In this manuscript we provide a comprehensive review of the different microbicide strategies that have been studied or are currently being considered for STI prevention, particularly emphasizing those having the potential to block HIV infection. The manuscript also reviews the complex process that is required to conduct future clinical studies in humans and concludes with a brief discussion of the strategies that could be part of the immediate future in microbicide research.

Modeling the allosteric modulation of CCR5 function by Maraviroc

Maraviroc is a non-peptidic, low molecular weight CC chemokine receptor 5 (CCR5) ligand that has recently been marketed for the treatment of HIV infected individuals. This review discusses recent molecular modeling studies of CCR5 by homology to CXC chemokine receptor 4, their contribution to the understanding of the allosteric mode of action of the inhibitor and their potential for the development of future drugs with improved efficiency and preservation of CCR5 biological functions.

Initiation of antiretroviral therapy

With the widespread availability of antiretroviral therapy, there is a dramatic decline in HIV related morbidity and mortality in both developed and developing countries. Further, the current antiretroviral drug combinations are safer and the availability of newer monitoring assays and guidelines has vastly improved the patient management. The clinician needs to evaluate several key issues prior to institution of antiretroviral regimen including the correct stage of starting the treatment and the kind of regimen to initiate. In addition to various disease related factors, it is also critical to assess the patient's general condition including nutritional status, presence of co-morbidities and mental preparedness prior to starting the therapy. The patients need to develop an overall understanding of the treatment and its benefits and the importance of lifelong adherence to the drugs. The presence of special situations like pediatric age, older patients, pregnancy, lactation and presence of opportunistic infections also require modification of the therapy. This review briefly summarizes issues relevant to the clinician prior to the initiation of antiretroviral therapy.

An immunomodulating motif of the HIV-1 fusion protein is chirality-independent: implications for its mode of action

An immunosuppressive motif was recently found within the HIV-1 gp41 fusion protein (termed immunosuppressive loop-associated determinant core motif (ISLAD CM)). Peptides containing the motif interact with the T-cell receptor (TCR) complex; however, the mechanism by which the motif exerts its immunosuppressive activity is yet to be determined. Recent studies showed that interactions between protein domains in the membrane milieu are not always sterically controlled. Therefore, we utilized the unique membrane leniency toward association between D- and L-stereoisomers to investigate the detailed mechanism by which ISLAD CM inhibits T-cell activation. We show that a D-enantiomer of ISLAD CM (termed ISLAD D-CM) inhibited the proliferation of murine myelin oligodendrocyte glycoprotein (MOG)-(35-55)-specific line T-cells to the same extent as the l-motif form. Moreover, the D- and L-forms preferentially bound spleen-derived T-cells over B-cells by 13-fold. Furthermore, both forms of ISLAD CM co-localized with the TCR on activated T-cells and interacted with the transmembrane domain of the TCR. FRET experiments revealed the importance of basic residues for the interaction between ISLAD CM forms and the TCR transmembrane domain. Ex vivo studies demonstrated that ISLAD D-CM administration inhibited the proliferation (72%) and proinflammatory cytokine secretion of pathogenic MOG(35-55)-specific T-cells. This study provides insights into the immunosuppressive mechanism of gp41 and demonstrates that chirality-independent interactions in the membrane can take place in diverse biological systems. Apart from HIV pathogenesis, the D-peptide reported herein may serve as a potential tool for treating T-cell-mediated pathologies.

Emtricitabine/rilpivirine/tenofovir disoproxil fumarate single-tablet regimen: a guide to its use in HIV-1 infection

The once-daily, single-tablet regimen of emtricitabine/rilpivirine/tenofovir disoproxil fumarate (Eviplera™ [EU]; Complera™ [US]) provides a convenient option for antiretroviral therapy in treatment-naive patients with HIV-1 infection. In well designed trials in this patient population, rilpivirine plus emtricitabine/tenofovir disoproxil fumarate was noninferior to efavirenz plus emtricitabine/tenofovir disoproxil fumarate in terms of reducing viral HIV-1 RNA level to <50 copies/mL and was generally better tolerated than efavirenz plus emtricitabine/tenofovir disoproxil fumarate.

Triple-combination rilpivirine, emtricitabine, and tenofovir (Complera™/Eviplera™) in the treatment of HIV infection

The combination rilpivirine (RPV)/emtricitabine (FTC)/tenofovir (TDF) is a once-daily, single-tablet regimen (STR) containing one nonnucleoside reverse-transcriptase inhibitor associated with two nucleos(t)ide reverse transcriptase inhibitors. It is approved by regulatory agencies (eg, US Food and Drug Association, European Medicines Agency) in all countries in which it is manufactured, except Switzerland, as first-line highly active antiretroviral therapy (HAART) for the treatment of naïve patients with HIV infection and a viral load HIV-RNA level of ≤100,000 copies/mL. Two large trials (ECHO and THRIVE) comparing RPV with efavirenz, along with different background regimens, led to approval of the drug, while a more recent trial (STaR) explored the use of STR. RPV showed noninferiority to efavirenz in all the studies, including superiority as an STR in patients with HIV-RNA ≤100,000 copies/mL in the STaR study. A positive CD4 cell response was observed in all the studies, both in the RPV and efavirenz groups. The incidence of virologic failures was higher for RPV, but was mostly referred to patients with HIV-RNA >100,000 copies/mL. There were fewer adverse events (AEs) with the RPV-based regimens versus efavirenz-based regimens, with a lower discontinuation rate because of AEs, especially psychiatric-neurological AEs, and a significantly lower rate of blood-lipid abnormalities. In the SPIRIT study (a switch study), significantly greater improvements from baseline in serum total cholesterol, low-density lipoprotein cholesterol, and trygliceride were demonstrated in patients switching to RPV/FTC/TDF from a ritonavir-boosted protease inhibitor (PI/r)-based regimen, than in those who continued treatment with a PI/r regimen. RPV's better tolerability, associated with its once-daily STR formulation, is key to improving patients' adherence and quality of life, which are among the most important factors affecting the therapeutic efficacy of an antiretroviral regimen. In summary, RPV/FTC/TDF STR is a valuable treatment option for the majority of antiretroviral-naïve HIV-infected patients. Furthermore, the use of this STR in the therapeutic switch, like in the SPIRIT study, can result in another valuable option by which to reduce AEs and improve patients' quality of life.

Designing a soluble near full-length HIV-1 gp41 trimer

The HIV-1 envelope spike is a trimer of heterodimers composed of an external glycoprotein gp120 and a transmembrane glycoprotein gp41. gp120 initiates virus entry by binding to host receptors, whereas gp41 mediates fusion between viral and host membranes. Although the basic pathway of HIV-1 entry has been extensively studied, the detailed mechanism is still poorly understood. Design of gp41 recombinants that mimic key intermediates is essential to elucidate the mechanism as well as to develop potent therapeutics and vaccines. Here, using molecular genetics and biochemical approaches, a series of hypotheses was tested to overcome the extreme hydrophobicity of HIV-1 gp41 and design a soluble near full-length gp41 trimer. The two long heptad repeat helices HR1 and HR2 of gp41 ectodomain were mutated to disrupt intramolecular HR1-HR2 interactions but not intermolecular HR1-HR1 interactions. This resulted in reduced aggregation and improved solubility. Attachment of a 27-amino acid foldon at the C terminus and slow refolding channeled gp41 into trimers. The trimers appear to be stabilized in a prehairpin-like structure, as evident from binding of a HR2 peptide to exposed HR1 grooves, lack of binding to hexa-helical bundle-specific NC-1 mAb, and inhibition of virus neutralization by broadly neutralizing antibodies 2F5 and 4E10. Fusion to T4 small outer capsid protein, Soc, allowed display of gp41 trimers on the phage nanoparticle. These approaches for the first time led to the design of a soluble gp41 trimer containing both the fusion peptide and the cytoplasmic domain, providing insights into the mechanism of entry and development of gp41-based HIV-1 vaccines.

Emtricitabine/rilpivirine/tenofovir disoproxil fumarate single-tablet regimen: a guide to its use in HIV-1 infection

The once-daily, single-tablet regimen of emtricitabine/rilpivirine/tenofovir disoproxil fumarate (Eviplera™ [EU]; Complera™ [US]) provides a convenient option for antiretroviral therapy in treatment-naive patients with HIV-1 infection. In well designed trials in this patient population, rilpivirine plus emtricitabine/tenofovir disoproxil fumarate was noninferior to efavirenz plus emtricitabine/tenofovir disoproxil fumarate in terms of reducing viral HIV-1 RNA level to <50 copies/mL and was generally better tolerated than efavirenz plus emtricitabine/tenofovir disoproxil fumarate.

A GxxxG-like motif within HIV-1 fusion peptide is critical to its immunosuppressant activity, structure, and interaction with the transmembrane domain of the T-cell receptor

To thrive in the human body, HIV fuses to its target cell and evades the immune response via several mechanisms. The fusion cascade is initiated by the fusion peptide (FP), which is located at the N-terminal of gp41, the transmembrane protein of HIV. Recently, it has been shown that the HIV-1 FP, particularly its 5-13 amino acid region (FP(5-13)), suppresses T-cell activation and interacts with the transmembrane domain (TMD) of the T-cell receptor (TCR) complex. Specific amino acid motifs often contribute to such interactions in TMDs of membrane proteins. Using bioinformatics and experimental studies, we report on a GxxxG-like motif (AxxxG), which is conserved in the FP throughout different clades and strains of HIV-1. Biological activity studies and FTIR spectroscopy revealed that HIV FP(5-13)-derived peptides, in which the motif was altered either by randomization or by a single amino acid shift, lost their immunosuppressive activity concomitant with a loss of the β-sheet structure in a membranous environment. Furthermore, fluorescence studies revealed that the inactive mutants lost their ability to interact with their target site, namely, the TMD of TCRα, designated CP. Importantly, lipotechoic acid activated macrophages (lacking TCR) were not affected by FP, further demonstrating the specificity of the immunosuppressant activity of CP. Finally, although the AxxxG WT and the GxxxG analog both associated with the CP and immunosuppressed T-cells, the AxxxG WT but not the GxxxG analog induced lipid mixing. Overall, the data support an important role for the AxxxG motif in the function of FP and might explain the natural selection of the AxxxG motif rather than the classical GxxxG motif in FP.