Emerging pharmacology: inhibitors of human immunodeficiency virus integration

Doing More With Less: Review of Dolutegravir-Lamivudine, a Novel Single-Tablet Regimen for Antiretroviral-Naïve Adults With HIV-1 Infection

OBJECTIVE

To review data on efficacy and safety of dolutegravir (DTG) and lamivudine (3TC) in treatment-naïve adults with HIV-1 infection.

DATA SOURCES

Phase III clinical trials and review articles were identified through PubMed (1996 to March 2020) and ClinicalTrials.gov (2000 to May 2020) using the keywords dolutegravir, lamivudine, and HIV.

STUDY SELECTION AND DATA EXTRACTION

Relevant clinical trials and review articles available in English evaluating efficacy and safety of DTG and 3TC were included.

DATA SYNTHESIS

The once-daily, single-tablet regimen of DTG/3TC is the first dual antiretroviral therapy (ART) recommended for initial therapy in treatment-naïve adults with HIV-1 infection. DTG and 3TC were compared with a regimen of DTG and tenofovir disoproxil fumarate/emtricitabine in the GEMINI studies and demonstrated noninferiority for the primary end point of virological suppression at up to 96 weeks. No treatment-emergent resistance mutations were identified in a small group of participants who did not reach virological suppression. The regimen is well tolerated, and the most common adverse events reported in trials include headache, diarrhea, nausea, insomnia, and fatigue.

RELEVANCE TO PATIENT CARE AND CLINICAL PRACTICE

This dual-ART regimen is a favorable treatment option for ART-naïve patients with HIV-1 RNA <500 000 copies/mL, absence of hepatitis B virus, and no resistance to DTG or 3TC. Benefits of dual ART include reduction in treatment-related adverse events and toxicities, drug interactions, and cost. In addition, the once-daily, single-tablet formulation promotes adherence.

CONCLUSIONS

DTG/3TC has demonstrated efficacy in maintaining virological suppression in ART-naïve patients at up to 96 weeks while minimizing treatment-related adverse events and toxicities.

O papel do dolutegravir na terapia antiretroviral

Os inibidores da integrase são a mais nova classe de antirretroviral aprovada, que agem impedindo a incorporação do DNA do HIV no genoma do linfócito T CD4+ (LTCD4+) do hospedeiro, limitando a propagação do vírus. O Dolutegravir e o inibidor da integrase mais moderno e como os demais inibidores apresenta de alta performance, boa tolerância; alta barreira genética para mutações de resistência, além de apresentar eficácia em pacientes já submetidos a tratamento antirretroviral anterior. Neste contexto o presente estudo trata-se de um estudo de revisão bibliográfica realizada de janeiro a junho de 2018, de artigos científicos de artigos científicos que abordam aspectos exclusivos do dolutegravir na terapia antirretroviral em comparação com outros esquemas terapêuticos. Concluindo que o tratamento com dolutegravir apresenta como principais vantagens à rápida supressão virológica; boa tolerância e alta barreira genética para mutações de resistência.

Two-long terminal repeat (LTR) DNA circles are a substrate for HIV-1 integrase

Integration of the HIV-1 DNA into the host genome is essential for viral replication and is catalyzed by the retroviral integrase. To date, the only substrate described to be involved in this critical reaction is the linear viral DNA produced in reverse transcription. However, during HIV-1 infection, two-long terminal repeat DNA circles (2-LTRcs) are also generated through the ligation of the viral DNA ends by the host cell's nonhomologous DNA end-joining pathway. These DNAs contain all the genetic information required for viral replication, but their role in HIV-1's life cycle remains unknown. We previously showed that both linear and circular DNA fragments containing the 2-LTR palindrome junction can be efficiently cleaved in vitro by recombinant integrases, leading to the formation of linear 3'-processed-like DNA. In this report, using in vitro experiments with purified proteins and DNAs along with DNA endonuclease and in vivo integration assays, we show that this circularized genome can also be efficiently used as a substrate in HIV-1 integrase-mediated integration both in vitro and in eukaryotic cells. Notably, we demonstrate that the palindrome cleavage occurs via a two-step mechanism leading to a blunt-ended DNA product, followed by a classical 3'-processing reaction; this cleavage leads to integrase-dependent integration, highlighted by a 5-bp duplication of the host genome. Our results suggest that 2-LTRc may constitute a reserve supply of HIV-1 genomes for proviral integration.

Digoxin reveals a functional connection between HIV-1 integration preference and T-cell activation

HIV-1 integrates more frequently into transcribed genes, however the biological significance of HIV-1 integration targeting has remained elusive. Using a selective high-throughput chemical screen, we discovered that the cardiac glycoside digoxin inhibits wild-type HIV-1 infection more potently than HIV-1 bearing a single point mutation (N74D) in the capsid protein. We confirmed that digoxin repressed viral gene expression by targeting the cellular Na⁺/K⁺ ATPase, but this did not explain its selectivity. Parallel RNAseq and integration mapping in infected cells demonstrated that digoxin inhibited expression of genes involved in T-cell activation and cell metabolism. Analysis of >400,000 unique integration sites showed that WT virus integrated more frequently than N74D mutant within or near genes susceptible to repression by digoxin and involved in T-cell activation and cell metabolism. Two main gene networks down-regulated by the drug were CD40L and CD38. Blocking CD40L by neutralizing antibodies selectively inhibited WT virus infection, phenocopying digoxin. Thus the selectivity of digoxin depends on a combination of integration targeting and repression of specific gene networks. The drug unmasked a functional connection between HIV-1 integration and T-cell activation. Our results suggest that HIV-1 evolved integration site selection to couple its early gene expression with the status of target CD4+ T-cells, which may affect latency and viral reactivation.

HIV-1 integrates more frequently within transcribed host genes, however we do not understand the biological significance of this. We found that a drug called digoxin inhibits wild type HIV-1 more potently than an HIV-1 bearing a single point mutation in the capsid protein. Here we show that digoxin represses HIV-1 gene expression and in parallel inhibits CD4+ T-cell activation and metabolism. When we analysed the integration sites of wild type and mutant HIV-1, we discovered that wild type virus integrates within or near genes involved in CD4⁺ T-cell activation and metabolism more often than the mutant virus. Because these are the very same genes repressed by digoxin, the integration bias of wild type virus makes it more susceptible than mutant virus to silencing by the drug. Digoxin unmasked a functional link between HIV-1 integration and T-cell activation, which may affect HIV-1 latency and reactivation.

Lack of impact of pre-existing T97A HIV-1 integrase mutation on integrase strand transfer inhibitor resistance and treatment outcome

T97A is an HIV-1 integrase polymorphism associated with integrase strand transfer inhibitor (INSTI) resistance. Using pooled data from 16 clinical studies, we investigated the prevalence of T97A (pre-existing and emergent) and its impact on INSTI susceptibility and treatment response in INSTI-naive patients who enrolled on elvitegravir (EVG)- or raltegravir (RAL)-based regimens. Prior to INSTI-based therapy, primary INSTI resistance-associated mutations (RAMs) were absent and T97A pre-existed infrequently (1.4%; 47 of 3367 integrase sequences); most often among non-B (5.3%) than B (0.9%) HIV-1 subtypes. During INSTI-based therapy, few patients experienced virologic failure with emergent INSTI RAMs (3%; 122 of 3881 patients), among whom T97A emerged infrequently in the presence (n = 6) or absence (n = 8) of primary INSTI RAMs. A comparison between pre-existing and emergent T97A patient populations (i.e., in the absence of primary INSTI RAMs) showed no significant differences in EVG or RAL susceptibility in vitro. Furthermore, among all T97A-containing viruses tested, only 38-44% exhibited reduced susceptibility to EVG and/or RAL (all of low magnitude; <11-fold), while all maintained susceptibility to dolutegravir. Of the patients with pre-existing T97A, 17 had available clinical follow-up: 16 achieved virologic suppression and 1 maintained T97A and INSTI sensitivity without further resistance development. Overall, T97A is an infrequent integrase polymorphism that is enriched among non-B HIV-1 subtypes and can confer low-level reduced susceptibility to EVG and/or RAL. However, detection of T97A does not affect response to INSTI-based therapy with EVG or RAL. These results suggest a very low risk of initiating INSTI-based therapy in patients with pre-existing T97A.

Relative Bioavailability of a Dolutegravir Dispersible Tablet and the Effects of Low- and High-Mineral-Content Water on the Tablet in Healthy Adults

Dolutegravir (DTG) is approved in the United States to treat HIV‐1‐infected patients weighing ≥30 kg. A dispersible DTG tablet formulation was recently developed for pediatric patients. This study compares the pharmacokinetics (PK) of the dispersible tablet with that of a previously evaluated granule formulation. In this randomized, open‐label, crossover study, 15 healthy adults received single oral doses of DTG 20 mg every 7 days across 5 treatment arms: granules consumed immediately after mixture with purified water, dispersible DTG consumed immediately after reconstitution in low‐mineral‐content (LMC) or high‐mineral‐content (HMC) water, and dispersible DTG consumed 30 minutes after dispersal in LMC or HMC water. Primary endpoints were bioavailability of immediately consumed dispersible tablet in LMC water relative to granule formulation reconstituted in purified water and PK of the dispersible tablet. Secondary endpoints included tolerability and palatability. The DTG dispersible tablet showed equivalent exposures to the granule formulation with geometric least‐squares mean treatment ratios of 1.06 and 1.12 for AUC_0‐∞ and C_max, respectively. DTG PK parameters were unaffected by mineral content or the 30‐minute delay. Adverse events were mild; only nausea (n = 1) was considered drug related. DTG exposure observed with the dispersible tablet supports evaluation of this formulation for further development.

Protein expression from unintegrated HIV-1 DNA introduces bias in primary in vitro post-integration latency models

To understand the persistence of latently HIV-1 infected cells in virally suppressed infected patients, a number of in vitro models of HIV latency have been developed. In an attempt to mimic the in vivo situation as closely as possible, several models use primary cells and replication-competent viruses in combination with antiretroviral compounds to prevent ongoing replication. Latency is subsequently measured by HIV RNA and/or protein production after cellular activation. To discriminate between pre- and post-integration latency, integrase inhibitors are routinely used, preventing novel integrations upon cellular activation. Here, we show that this choice of antiretrovirals may still cause a bias of pre-integration latency in these models, as unintegrated HIV DNA can form and directly contribute to the levels of HIV RNA and protein production. We further show that the addition of reverse transcriptase inhibitors effectively suppresses the levels of episomal HIV DNA (as measured by 2-LTR circles) and decreases the levels of HIV transcription. Consequently, we show that latency levels described in models that only use integrase inhibitors may be overestimated. The inclusion of additional control conditions, such as 2-LTR quantification and the addition of reverse transcriptase inhibitors, is crucial to fully elucidate the actual levels of post-integration latency.

HIV-1 capsid is involved in post-nuclear entry steps

Background

HIV-1 capsid influences viral uncoating and nuclear import. Some capsid is detected in the nucleus but it is unclear if it has any function. We reported that the antibiotic Coumermycin-A1 (C-A1) inhibits HIV-1 integration and that a capsid mutation confers resistance to C-A1, suggesting that capsid might affect post-nuclear entry steps.

Results

Here we report that C-A1 inhibits HIV-1 integration in a capsid-dependent way. Using molecular docking, we identify an extended binding pocket delimited by two adjacent capsid monomers where C-A1 is predicted to bind. Isothermal titration calorimetry confirmed that C-A1 binds to hexameric capsid. Cyclosporine washout assays in Jurkat CD4+ T cells expressing engineered human TRIMCyp showed that C-A1 causes faster and greater escape from TRIMCyp restriction. Sub-cellular fractionation showed that small amounts of capsid accumulated in the nuclei of infected cells and C-A1 reduced the nuclear capsid. A105S and N74D capsid mutant viruses did not accumulate capsid in the nucleus, irrespective of C-A1 treatment. Depletion of Nup153, a nucleoporin located at the nuclear side of the nuclear pore that binds to HIV-1 capsid, made the virus less susceptible to TRIMCyp restriction, suggesting that Nup153 may help maintain some integrity of the viral core in the nucleus. Furthermore C-A1 increased binding of CPSF6, a nuclear protein, to capsid.

Conclusions

Our results indicate that capsid is involved in post-nuclear entry steps preceding integration.

Electronic supplementary material

The online version of this article (doi:10.1186/s12977-016-0262-0) contains supplementary material, which is available to authorized users.

Pharmacokinetic and pharmacodynamic evaluation of raltegravir and experience from clinical trials in HIV-positive patients

INTRODUCTION

Raltegravir was the first available integrase inhibitor for treating HIV-positive patients. This review aims to provide an overview of its role in the management of HIV-1 infection, highlighting its key pharmacokinetic and pharmacodynamic properties.

AREAS COVERED

This review covers material searched and obtained through Medline and PubMed up to April 2015.

EXPERT OPINION

Raltegravir for its tolerability, efficacy, few drug-to-drug interactions and for the amount of available data in difficult subgroups of patients is a key drug in the antiretroviral armamentarium. For its weak genetic barrier to resistance and erratic pharmacokinetic profile, it should be administered twice daily and with fully active companion antiretrovirals.

Antiviral Drugs

Viruses are major pathogenic agents causing a variety of serious diseases in humans, other animals, and plants.

Drugs that combat viral infections are called antiviral drugs. There are no effective antiviral drugs for many viral infections. However, there are several drugs for influenza, a couple of drugs for herpesviruses, and some new antiviral drugs for treatment of HIV and hepatitis C infections.

The arsenal of antivirals is complex. As of March 2014, it consists of approximately 50 drugs approved by the FDA, approximately half of which are directed against HIV. Antiviral drug creation strategies are focused on two different approaches: targeting the viruses themselves or targeting host cell factors.

Direct virus-targeting antiviral drugs include attachment inhibitors, entry inhibitors, uncoating inhibitors, protease inhibitors, polymerase inhibitors, nucleoside and nucleotide reverse transcriptase inhibitors, nonnucleoside reverse-transcriptase inhibitors, and integrase inhibitors.

Protease inhibitors (darunavir, atazanavir, and ritonavir), viral DNA polymerase inhibitors (acyclovir, valacyclovir, valganciclovir, and tenofovir), and an integrase inhibitor (raltegravir) are included in the list of Top 200 Drugs by sales for the 2010s.

Clinical pharmacokinetics and pharmacodynamics of dolutegravir used as a single tablet regimen for the treatment of HIV-1 infection

INTRODUCTION

With the introduction of the coformulated dolutegravir, abacavir and lamivudine , a new single tablet regimen (STR) is made available for the use in treatment-naive and treatment-experienced HIV-infected patients. This drug combination is the fourth STR that will be positioned next to the STRs with efavirenz, rilpivirine or elvitegravir as third agents, respectively.

AREAS COVERED

The objective of this review is to provide an overview of the efficacy and safety of the combined dolutegravir/abacavir/lamivudine coformulation. The review will focus on dolutegravir and includes both published data as well as data presented at recent major international HIV/AIDS conferences.

EXPERT OPINION

The dolutegravir/abacavir/lamivudine regimen is highly effective in achieving sustained suppression of HIV-1 RNA plasma concentrations. The STR has a favorable safety profile and a low potential for drug interactions, which will contribute to a prominent role in therapy. As this STR contains abacavir as backbone component, the use requires patients to be HLA-B*5701 negative, with good hepatic function. Other first-line treatment combinations are preferred for patients with hepatitis B co-infection or with a high cardiovascular risk.

The hepatitis B virus ribonuclease H as a drug target

Chronic hepatitis B virus (HBV) infection is a leading cause of hepatitis, liver failure, and hepatocellular carcinoma. An outstanding vaccine is available; however, the number of infections remains high. Current anti-HBV treatments with interferon α and nucleos(t)ide analogs clear the infection in only a small minority of patients, and either induce serious side-effects or are of very long duration. HBV is a small, enveloped DNA virus that replicates by reverse transcription via an RNA intermediate. The HBV ribonuclease H (RNaseH) is essential for viral replication, but it has not been exploited as a drug target. Recent low-throughput screening of compound classes with anti-Human Immunodeficiency Virus RNaseH activity led to identification of HBV RNaseH inhibitors in three different chemical families that block HBV replication. These inhibitors are promising candidates for development into new anti-HBV drugs. The RNaseH inhibitors may help improve treatment efficacy enough to clear the virus from the liver when used in combination with existing anti-HBV drugs and/or with other novel inhibitors under development. This article forms part of a symposium in Antiviral Research on "An unfinished story: from the discovery of the Australia antigen to the development of new curative therapies for hepatitis B."

Integrase inhibitor reversal dynamics indicate unintegrated HIV-1 dna initiate de novo integration

BACKGROUND

Genomic integration, an obligate step in the HIV-1 replication cycle, is blocked by the integrase inhibitor raltegravir. A consequence is an excess of unintegrated viral DNA genomes, which undergo intramolecular ligation and accumulate as 2-LTR circles. These circularized genomes are also reliably observed in vivo in the absence of antiviral therapy and they persist in non-dividing cells. However, they have long been considered as dead-end products that are not precursors to integration and further viral propagation.

RESULTS

Here, we show that raltegravir action is reversible and that unintegrated viral DNA is integrated in the host cell genome after raltegravir removal leading to HIV-1 replication. Using quantitative PCR approach, we analyzed the consequences of reversing prolonged raltegravir-induced integration blocks. We observed, after RAL removal, a decrease of 2-LTR circles and a transient increase of linear DNA that is subsequently integrated in the host cell genome and fuel new cycles of viral replication.

CONCLUSIONS

Our data highly suggest that 2-LTR circles can be used as a reserve supply of genomes for proviral integration highlighting their potential role in the overall HIV-1 replication cycle.

The combined anti-HIV-1 activities of emtricitabine and tenofovir plus the integrase inhibitor elvitegravir or raltegravir show high levels of synergy in vitro

Highly active antiretroviral therapy (HAART) involves combination treatment with three or more antiretroviral agents. The antiviral effects of combinations of emtricitabine (FTC) plus tenofovir (TFV) plus antiretroviral agents of all the major drug classes were investigated. Combinations of FTC and TFV with a nonnucleoside reverse transcriptase inhibitor (NNRTI) (efavirenz or rilpivirine) or with a protease inhibitor (PI) (atazanavir, lopinavir, or darunavir) showed additive to synergistic anti-HIV-1 activity. FTC-TFV with an HIV-1 integrase strand transfer inhibitor (INSTI) (elvitegravir or raltegravir) showed the strongest synergy. Anti-HIV-1 synergy suggests enhancement of individual anti-HIV-1 activities within cells that may contribute to potent treatment efficacy and open new areas of research into interactions between reverse transcriptase (RT) and integrase inhibitors.

Dolutegravir: a new integrase strand transfer inhibitor for the treatment of HIV

The first two integrase strand transfer inhibitors (INSTIs) approved for treatment of patients infected with human immunodeficiency virus (HIV) were raltegravir and elvitegravir. Both raltegravir and elvitegravir are now guideline-preferred agents as part of an antiretroviral regimen for treatment-naive patients. However, raltegravir is dosed twice/day. Elvitegravir is available in a single-tablet regimen and dosed once/day because it is administered with the pharmacokinetic booster cobicistat, a potent CYP3A4 inhibitor that can lead to clinically significant drug-drug interactions. In addition, raltegravir and elvitegravir have a low genetic barrier to resistance and are associated with cross-resistance. Dolutegravir is a new-generation INSTI administered once/day without a pharmacokinetic booster and can be coformulated in a single-tablet regimen. Phase III studies have demonstrated the efficacy and safety of dolutegravir for treatment-naive and treatment-experienced patients. Compared with other INSTIs, dolutegravir has a higher genetic barrier to resistance. Dolutegravir was approved by the U.S. Food and Drug Administration in August 2013 and joins raltegravir and elvitegravir as guideline-preferred agents for the management for HIV-infected treatment-naive patients.

Treatment with suboptimal doses of raltegravir leads to aberrant HIV-1 integrations

Integration of the DNA copy of the HIV-1 genome into a host chromosome is required for viral replication and is thus an important target for antiviral therapy. The HIV-encoded enzyme integrase (IN) catalyzes two essential steps: 3' processing of the viral DNA ends, followed by the strand transfer reaction, which inserts the viral DNA into host DNA. Raltegravir binds to IN and blocks the integration of the viral DNA. Using the Rous sarcoma virus-derived vector RCAS, we previously showed that mutations that cause one viral DNA end to be defective for IN-mediated integration led to abnormal integrations in which the provirus had one normal and one aberrant end, accompanied by rearrangements in the host genome. On the basis of these results, we expected that suboptimal concentrations of IN inhibitors, which could block one of the ends of viral integration, would lead to similar aberrant integrations. In contrast to the proviruses from untreated cells, which were all normal, ∼10-15% of the proviruses isolated after treatment with a suboptimal dose of raltegravir were aberrant. The aberrant integrations were similar to those seen in the RCAS experiments. Most of the aberrant proviruses had one normal end and one aberrant end and were accompanied by significant rearrangements in the host genome, including duplications, inversions, deletions and, occasionally, acquisition of sequences from other chromosomes. The rearrangements of the host DNA raise concerns that these aberrant integrations might have unintended consequences in HIV-1-infected patients who are not consistent in following a raltegravir-containing treatment regimen.

Fragment-based discovery of 8-hydroxyquinoline inhibitors of the HIV-1 integrase-lens epithelium-derived growth factor/p75 (IN-LEDGF/p75) interaction

On the basis of an initial molecular modeling study suggesting the favorable binding of the "privileged" fragment 8-hydroxyquinoline with HIV-1 integrase (IN) at the IN-lens epithelium-derived growth factor/p75 (LEDGF/p75) interface , we developed a set of modified 8-hydroxyquinoline fragments demonstrating micromolar IC50 values for inhibition of the IN-LEDGF/p75 interaction, but significant cytotoxicity was associated with these initial compounds. Diverse modifications at the C5 and C7 carbons of the 8-hydroxyquinoline core improved potency, but reduction of diversity to only modifications at the C5 position ultimately yielded potent inhibitors with low cytotoxicity. Two of these particular compounds, 5-((p-tolylamino)methyl)quinolin-8-ol and 5-(((3,4-dimethylphenyl)amino)methyl)quinolin-8-ol, inhibited viral replication in MT-4 cells with low micromolar EC50. This is the first study providing evidence for 8-hydroxyquinolines as novel inhibitors of the IN-LEDGF/p75 interaction. Our lead compounds are druglike, have low molecular weights, and are amenable to various substitutions suitable for enhancing their potency and selectivity.

HIV Drug Resistance and the Advent of Integrase Inhibitors

This review focuses on the topic of HIV integrase inhibitors that are potent antiretroviral drugs that efficiently decrease viral load in patients. However, emergence of resistance mutations against this new class of drugs represents a threat to their long-term efficacy. Here, we provide new information about the most recent mutations identified and other mutations that confer resistance to several integrase inhibitors, such as new resistance mutations-for example, G118R, R263K, and S153Y-that have been identified through in vitro selection studies with second-generation integrase strand transfer inhibitors (INSTIs). These add to the three main resistance pathways involving mutations at positions Y143, N155, and Q148. Deep sequencing, structural modeling, and biochemical analyses are methods that currently help in the understanding of the mechanisms of resistance conferred by these mutations. Although the new resistance mutations appear to confer only low levels of cross-resistance to second-generation drugs, the Q148 pathway with numerous secondary mutations has the potential to significantly decrease susceptibility to all drugs of the INSTI family of compounds.

HIV integrase inhibitors: 20-year landmark and challenges

Since the discovery of HIV as the cause for AIDS 30 years ago, major progress has been made, including the discovery of drugs that now control the disease. Here, we review the integrase (IN) inhibitors from the discovery of the first compounds 20 years ago to the approval of two highly effective IN strand transfer inhibitors (INSTIs), raltegravir (Isentress) and elvitegravir (Stribild), and the promising clinical activity of dolutegravir. After summarizing the molecular mechanism of action of the INSTIs as interfacial inhibitors, we discuss the remaining challenges. Those include: overcoming resistance to clinical INSTIs, long-term safety of INSTIs, cost of therapy, place of the INSTIs in prophylactic treatments, and the development of new classes of inhibitors (the LEDGINs) targeting IN outside its catalytic site. We also discuss the role of chromatin and host DNA repair factor for the completion of integration.

Antiviral agents: structural basis of action and rational design

During the last 30 years, significant progress has been made in the development of novel antiviral drugs, mainly crystallizing in the establishment of potent antiretroviral therapies and the approval of drugs inhibiting hepatitis C virus replication. Although major targets of antiviral intervention involve intracellular processes required for the synthesis of viral proteins and nucleic acids, a number of inhibitors blocking virus assembly, budding, maturation, entry or uncoating act on virions or viral capsids. In this review, we focus on the drug discovery process while presenting the currently used methodologies to identify novel antiviral drugs by using a computer-based approach. We provide examples illustrating structure-based antiviral drug development, specifically neuraminidase inhibitors against influenza virus (e.g. oseltamivir and zanamivir) and human immunodeficiency virus type 1 protease inhibitors (i.e. the development of darunavir from early peptidomimetic compounds such as saquinavir). A number of drugs in preclinical development acting against picornaviruses, hepatitis B virus and human immunodeficiency virus and their mechanism of action are presented to show how viral capsids can be exploited as targets of antiviral therapy.

The Need for Development of New HIV-1 Reverse Transcriptase and Integrase Inhibitors in the Aftermath of Antiviral Drug Resistance

The use of highly active antiretroviral therapy (HAART) involves combinations of drugs to achieve maximal virological response and reduce the potential for the emergence of antiviral resistance. There are two broad classes of reverse transcriptase inhibitors, the nucleoside reverse transcriptase inhibitors (NRTIs) and nonnucleoside reverse transcriptase inhibitors (NNRTIs). Since the first classes of such compounds were developed, viral resistance against them has necessitated the continuous development of novel compounds within each class. This paper considers the NRTIs and NNRTIs currently in both preclinical and clinical development or approved for second line therapy and describes the patterns of resistance associated with their use, as well as the underlying mechanisms that have been described. Due to reasons of both affordability and availability, some reverse transcriptase inhibitors with low genetic barrier are more commonly used in resource-limited settings. Their use results to the emergence of specific patterns of antiviral resistance and so may require specific actions to preserve therapeutic options for patients in such settings. More recently, the advent of integrase strand transfer inhibitors represents another major step forward toward control of HIV infection, but these compounds are also susceptible to problems of HIV drug resistance.

Novel method to assess antiretroviral target trough concentrations using in vitro susceptibility data

Durable suppression of HIV-1 replication requires the establishment of antiretroviral drug concentrations that exceed the susceptibility of the virus strain(s) infecting the patient. Minimum plasma drug concentrations (C(trough)) are correlated with response, but determination of target C(trough) values is hindered by a paucity of in vivo concentration-response data. In the absence of these data, in vitro susceptibility measurements, adjusted for serum protein binding, can provide estimations of suppressive in vivo drug concentrations. We derived serum protein binding correction factors (PBCF) for protease inhibitors, nonnucleoside reverse transcriptase inhibitors, and an integrase inhibitor by measuring the effect of a range of human serum concentrations on in vitro drug susceptibility measured with the PhenoSense HIV assay. PBCFs corresponding to 100% HS were extrapolated using linear regression and ranged from 1.4 for nevirapine to 77 for nelfinavir. Using the mean 95% inhibitory concentration (IC(95)) for ≥1,200 drug-susceptible viruses, we calculated protein-bound IC(95) (PBIC(95)) values. PBIC(95) values were concordant with the minimum effective C(trough) values that were established in well-designed pharmacodynamic studies (e.g., indinavir, saquinavir, and amprenavir). In other cases, the PBIC(95) values were notably lower (e.g., darunavir, efavirenz, and nevirapine) or higher (nelfinavir and etravirine) than existing target recommendations. The establishment of PBIC(95) values as described here provides a convenient and standardized approach for estimation of the minimum drug exposure that is required to maintain viral suppression and prevent the emergence of drug-resistant variants, particularly when in vivo concentration-response relationships are lacking.

Identification of HIV inhibitors guided by free energy perturbation calculations

Free energy perturbation (FEP) theory coupled to molecular dynamics (MD) or Monte Carlo (MC) statistical mechanics offers a theoretically precise method for determining the free energy differences of related biological inhibitors. Traditionally requiring extensive computational resources and expertise, it is only recently that its impact is being felt in drug discovery. A review of computer-aided anti-HIV efforts employing FEP calculations is provided here that describes early and recent successes in the design of human immunodeficiency virus type 1 (HIV-1) protease and non-nucleoside reverse transcriptase inhibitors. In addition, our ongoing work developing and optimizing leads for small molecule inhibitors of cyclophilin A (CypA) is highlighted as an update on the current capabilities of the field. CypA has been shown to aid HIV-1 replication by catalyzing the cis/trans isomerization of a conserved Gly-Pro motif in the Nterminal domain of HIV-1 capsid (CA) protein. In the absence of a functional CypA, e.g., by the addition of an inhibitor such as cyclosporine A (CsA), HIV-1 has reduced infectivity. Our simulations of acylurea-based and 1-indanylketone-based CypA inhibitors have determined that their nanomolar and micromolar binding affinities, respectively, are tied to their ability to stabilize Arg55 and Asn102. A structurally novel 1-(2,6-dichlorobenzamido) indole core was proposed to maximize these interactions. FEP-guided optimization, experimental synthesis, and biological testing of lead compounds for toxicity and inhibition of wild-type HIV-1 and CA mutants have demonstrated a dose-dependent inhibition of HIV-1 infection in two cell lines. While the inhibition is modest compared to CsA, the results are encouraging.

Novel therapeutic strategies targeting HIV integrase

Integration of the viral genome into host cell chromatin is a pivotal and unique step in the replication cycle of retroviruses, including HIV. Inhibiting HIV replication by specifically blocking the viral integrase enzyme that mediates this step is an obvious and attractive therapeutic strategy. After concerted efforts, the first viable integrase inhibitors were developed in the early 2000s, ultimately leading to the clinical licensure of the first integrase strand transfer inhibitor, raltegravir. Similarly structured compounds and derivative second generation integrase strand transfer inhibitors, such as elvitegravir and dolutegravir, are now in various stages of clinical development. Furthermore, other mechanisms aimed at the inhibition of viral integration are being explored in numerous preclinical studies, which include inhibition of 3' processing and chromatin targeting. The development of new clinically useful compounds will be aided by the characterization of the retroviral intasome crystal structure. This review considers the history of the clinical development of HIV integrase inhibitors, the development of antiviral drug resistance and the need for new antiviral compounds.

Study of genotypic and phenotypic HIV-1 dynamics of integrase mutations during raltegravir treatment: a refined analysis by ultra-deep 454 pyrosequencing

BACKGROUND

The dynamics of raltegravir-resistant variants and their impact on virologic response in 23 HIV-1-infected patients, who started a salvage raltegravir-containing regimen, were investigated.

METHODS

Integrase population sequencing and Ultra-Deep-454 Pyrosequencing (UDPS) were performed on plasma samples at baseline and at raltegravir failure. All integrase mutations detected at a frequency ≥1% were considered to be reliable for the UDPS analyses. Phylogenetic and phenotypic resistance analyses were also performed.

RESULTS

At baseline, primary resistance mutations were not detected by both population and UDPS genotypic assays; few secondary mutations (T97A-V151I-G163R) were rarely detected and did not show any statistically association either with virologic response at 24-weeks or with the development of resistant variants at failure. At UDPS, not all resistant variants appearing early during treatment evolved as major populations during failure; only specific resistance pathways (Y143R-Q148H/R-N155H) associated with an increased rate of fitness and phenotypic resistance were selected.

CONCLUSIONS

Resistance to raltegravir in integrase strand transfer inhibitor-naive patients remains today a rare event, which might be changed by future extensive use of such drugs. In our study, pathways of resistance at failure were not predicted by baseline mutations, suggesting that evolution plus stochastic selection plays a major role in the appearance of integrase-resistance mutations, whereas fitness and resistance are dominant factors acting for the late selection of resistant quasispecies.

Design of HIV-1 integrase inhibitors targeting the catalytic domain as well as its interaction with LEDGF/p75: a scaffold hopping approach using salicylate and catechol groups

HIV-1 integrase (IN) is a validated therapeutic target for antiviral drug design. However, the emergence of viral strains resistant to clinically studied IN inhibitors demands the discovery of novel inhibitors that are structurally as well mechanistically different. Herein, we describe the design and discovery of novel IN inhibitors targeting the catalytic domain as well as its interaction with LEDGF/p75, which is essential for the HIV-1 integration as an IN cofactor. By merging the pharmacophores of salicylate and catechol, the 2,3-dihydroxybenzamide (5a) was identified as a new scaffold to inhibit the strand transfer reaction efficiently. Further structural modifications on the 2,3-dihydroxybenzamide scaffold revealed that the heteroaromatic functionality attached on the carboxamide portion and the piperidin-1-ylsulfonyl substituted at the phenyl ring are beneficial for the activity, resulting in a low micromolar IN inhibitor (5p, IC(50)=5 μM) with more than 40-fold selectivity for the strand transfer over the 3'-processing reaction. More significantly, this active scaffold remarkably inhibited the interaction between IN and LEDGF/p75 cofactor. The prototype example, N-(cyclohexylmethyl)-2,3-dihydroxy-5-(piperidin-1-ylsulfonyl) benzamide (5u) inhibited the IN-LEDGF/p75 interaction with an IC(50) value of 8 μM. Using molecular modeling, the mechanism of action was hypothesized to involve the chelation of the divalent metal ions inside the IN active site. Furthermore, the inhibitor of IN-LEDGF/p75 interaction was properly bound to the LEDGF/p75 binding site on IN. This work provides a new and efficient approach to evolve novel HIV-1 IN inhibitors from rational integration and optimization of previously reported inhibitors.

Targeting viral reservoirs: ability of antiretroviral therapy to stop viral replication

PURPOSE OF REVIEW

HIV infection is controlled but not cured by combination antiretroviral therapy. HIV may persist for a number of reasons, including ongoing cycles of HIV infection or viral persistence as latent, or HIV replication in long-lived cells containing HIV proviruses. Therapeutic consequences of these alternative mechanisms are significant and distinct. If ongoing replication remains during current antiretroviral therapy, then improvements in potency will be useful in eradication strategies. Alternatively, long-lived cells with integrated proviruses will not be affected by improvements in therapy directed against active infection, and new strategies will be necessary for HIV eradication. Technologic advances have made it possible to carry out a series of drug intensification protocols in well suppressed patients; these and other analyses for HIV replication have been useful to elucidate the nature of HIV persistence on therapy.

RECENT FINDINGS

A number of clinical studies intensifying antiretroviral therapy carried out in the last several years have yielded new findings regarding the ability to detect the presence of ongoing replication. Decreases in persistent viremia have not been consistently detected in individuals on potent combination antiretroviral therapy. Evidence for persistent replication has been reported in patients using sensitive assays of cell-associated HIV.

SUMMARY

HIV viremia persists despite combination antiretroviral therapy. Antiretroviral drug intensification does not lower the level of HIV measured in plasma, suggesting current therapy arrests active virus replication. HIV eradication will most likely require therapy in addition to potent antiretroviral therapy.

Potential of novel antiretrovirals to modulate expression and function of drug transporters in vitro

OBJECTIVES

The chemokine receptor antagonists maraviroc and vicriviroc and the integrase inhibitors elvitegravir and raltegravir are novel antiretroviral agents for the treatment of HIV-1 infections. ATP-binding cassette (ABC) transporters as modulators of the effectiveness and safety of therapy can mediate viral resistance and drug-drug interactions. To expand knowledge on drug-drug interactions of these antiretrovirals we investigated whether these compounds are substrates, inhibitors or inducers of important ABC transporters.

METHODS

We evaluated P-glycoprotein (P-gp/ABCB1) inhibition by the calcein assay in P388/dx and L-MDR1 cells, breast cancer resistance protein (BCRP/ABCG2) inhibition in MDCKII-BCRP cells by pheophorbide A efflux, and inhibition of the multidrug resistance-associated protein 2 (MRP2/ABCC2) by using the MRP2 PREDIVEZ™ Vesicular Transport Kit. Substrate characteristics were evaluated by growth inhibition assays in MDCKII cells overexpressing particular ABC transporters. Induction of transporters was quantified by real-time RT-PCR in LS180 cells and for ABCB1 also at the functional level.

RESULTS

Elvitegravir and vicriviroc inhibited ABCB1 in P388/dx and L-MDR1 cells (f2 values 1.9±0.2 µmol/L and 8.5±3.6 µmol/L, respectively). The IC50 for ABCG2 inhibition was 15.7±5.7 µmol/L for elvitegravir and 236.7±93.3 µmol/L for vicriviroc. Raltegravir and maraviroc showed no evidence of ABCB1 or ABCG2 inhibition. Maraviroc and vicriviroc stimulated ABCC2 transport function. Growth inhibition assays suggest that elvitegravir, raltegravir and vicriviroc are substrates of ABCB1. Induction assays demonstrate that mRNA expression of several ABC transporters is induced by these antiretrovirals in LS180 cells.

CONCLUSIONS

The new antiretrovirals bear the potential to modulate expression and function of several ABC transporters, with elvitegravir revealing the highest interaction potential.

Effect of antacids on the pharmacokinetics of raltegravir in human immunodeficiency virus-seronegative volunteers

Raltegravir's divalent metal ion chelating motif may predispose the drug to interactions with divalent cations. We determined whether a divalent cation-containing antacid interacted with raltegravir. Twelve HIV-1-seronegative subjects were enrolled in this randomized, prospective, crossover study of single-dose raltegravir (400 mg) with and without an antacid. Subjects underwent two intensive pharmacokinetic visits in the fasted state separated by a 5- to 12-day washout period. With simultaneous antacid administration, time to peak raltegravir concentration occurred 2 h sooner (P = 0.002) and there was a 67% lower raltegravir concentration at 12 h postdose (P < 0.0001) than with administration of raltegravir alone. The raltegravir area under the-concentration-time curve from 0 to 12 h and maximum concentration were unchanged with the addition of an antacid. Studies are needed to determine the clinical relevance of this interaction, whether it remains after multiple dosing to steady state, whether it is mitigated by temporal separation, and whether raltegravir interacts with divalent cation-containing vitamins, supplements, or foods.

Deciphering the code for retroviral integration target site selection

Upon cell invasion, retroviruses generate a DNA copy of their RNA genome and integrate retroviral cDNA within host chromosomal DNA. Integration occurs throughout the host cell genome, but target site selection is not random. Each subgroup of retrovirus is distinguished from the others by attraction to particular features on chromosomes. Despite extensive efforts to identify host factors that interact with retrovirion components or chromosome features predictive of integration, little is known about how integration sites are selected. We attempted to identify markers predictive of retroviral integration by exploiting Precision-Recall methods for extracting information from highly skewed datasets to derive robust and discriminating measures of association. ChIPSeq datasets for more than 60 factors were compared with 14 retroviral integration datasets. When compared with MLV, PERV or XMRV integration sites, strong association was observed with STAT1, acetylation of H3 and H4 at several positions, and methylation of H2AZ, H3K4, and K9. By combining peaks from ChIPSeq datasets, a supermarker was identified that localized within 2 kB of 75% of MLV proviruses and detected differences in integration preferences among different cell types. The supermarker predicted the likelihood of integration within specific chromosomal regions in a cell-type specific manner, yielding probabilities for integration into proto-oncogene LMO2 identical to experimentally determined values. The supermarker thus identifies chromosomal features highly favored for retroviral integration, provides clues to the mechanism by which retrovirus integration sites are selected, and offers a tool for predicting cell-type specific proto-oncogene activation by retroviruses.

When HIV-1, murine leukemia virus (MLV), or other retroviruses infect a cell, the virus generates a DNA copy of the viral RNA genome and ligates the cDNA within host chromosomal DNA. This integration reaction occurs at sites throughout the host cell genome, but little is known about how integration sites are selected. We attempted to identify markers predictive of retroviral integration by comparing the genome-wide binding sites for more than 60 factors with 14 retroviral integration datasets. We borrowed Precision-Recall methods from the Information Retrieval field for extracting information from highly skewed datasets such as these. For MLV and other gammaretroviruses, strong association was observed with STAT1, acetylation of H3 and H4 at several positions, and methylation of H2AZ, H3K4, and K9. We generated a supermarker by combining high scoring markers. The supermarker localized within 2 kB of 75% of MLV proviruses and predicted the likelihood of integration within specific chromosomal regions in a cell-type specific manner. This study identified chromosomal features highly favored for retroviral integration. It also provides clues to the mechanism by which retrovirus integration sites are selected, and offers a tool for predicting cell-type specific proto-oncogene activation by retroviruses.

Gyrase B inhibitor impairs HIV-1 replication by targeting Hsp90 and the capsid protein

Chemical genetics is an emerging approach to investigate the biology of host-pathogen interactions. We screened several inhibitors of ATP-dependent DNA motors and detected the gyrase B inhibitor coumermycin A1 (C-A1) as a potent antiretroviral. C-A1 inhibited HIV-1 integration and gene expression from acutely infected cell, but the two activities mapped to distinct targets. Target discovery identified Hsp90 as the C-A1 target affecting viral gene expression. Chromatin immunoprecipitation revealed that Hsp90 associates with the viral promoter and may directly regulate gene expression. Molecular docking suggested that C-A1 binds to two novel pockets at the C terminal domain of Hsp90. C-A1 inhibited Hsp90 dimer formation, suggesting that it impairs viral gene expression by preventing Hsp90 dimerization at the C terminus. The inhibition of HIV-1 integration imposed by C-A1 was independent of Hsp90 and mapped to the capsid protein, and a point mutation at residue 105 made the virus resistant to this block. HIV-1 susceptibility to the integration block mediated by C-A1 was influenced by cyclophilin A. Our chemical genetic approach revealed an unexpected function of capsid in HIV-1 integration and provided evidence for a role of Hsp90 in regulating gene expression in mammalian cells. Both activities were amenable to inhibition by small molecules and represent novel antiretroviral drug targets.

Pharmacokinetics and pharmacogenomics of once-daily raltegravir and atazanavir in healthy volunteers

Atazanavir inhibits UDP-glucuronyl-transferase-1A1 (UGT1A1), which metabolizes raltegravir, but the magnitude of steady-state inhibition and role of the UGT1A1 genotype are unknown. Sufficient inhibition could lead to reduced-dose and -cost raltegravir regimens. Nineteen healthy volunteers, age 24 to 51 years, took raltegravir 400 mg twice daily (arm A) and 400 mg plus atazanavir 400 mg once daily (arm B), separated by ≥3 days, in a crossover design. After 1 week on each regimen, raltegravir and raltegravir-glucuronide plasma and urine concentrations were measured by liquid chromatography-tandem mass spectrometry in multiple samples obtained over 12 h (arm A) or 24 h (arm B) and analyzed by noncompartmental methods. UGT1A1 promoter variants were detected with a commercially available kit and published primers. The primary outcome was the ratio of plasma raltegravir C(tau), or concentration at the end of the dosing interval, for arm B (24 h) versus arm A (12 h). The arm B-to-arm A geometric mean ratios (95% confidence interval, P value) for plasma raltegravir C(tau), area under the concentration-time curve from 0 to 12 h (AUC(0-12)), and raltegravir-glucuronide/raltegravir AUC(0-12) were 0.38 (0.22 to 0.65, 0.001), 1.32 (0.62 to 2.81, 0.45), and 0.47 (0.38 to 0.59, <0.001), respectively. Nine volunteers were heterozygous and one was homozygous for a UGT1A1 reduction-of-function allele, but these were not associated with metabolite formation. Although atazanavir significantly reduced the formation of the glucuronide metabolite, its steady-state boosting of plasma raltegravir did not render the C(tau) with a once-daily raltegravir dose of 400 mg similar to the C(tau) with the standard twice-daily dose. UGT1A1 promoter variants did not significantly influence this interaction.

Susceptibility of the human retrovirus XMRV to antiretroviral inhibitors

Background

XMRV (xenotropic murine leukemia virus-related virus) is the first known example of an exogenous gammaretrovirus that can infect humans. A limited number of reports suggest that XMRV is intrinsically resistant to many of the antiretroviral drugs used to treat HIV-1 infection, but is sensitive to a small subset of these inhibitors. In the present study, we used a novel marker transfer assay to directly compare the antiviral drug sensitivities of XMRV and HIV-1 under identical conditions in the same host cell type.

Results

We extend the findings of previous studies by showing that, in addition to AZT and tenofovir, XMRV and HIV-1 are equally sensitive to AZddA (3'-azido-2',3'-dideoxyadenosine), AZddG (3'-azido-2',3'-dideoxyguanosine) and adefovir. These results indicate that specific 3'-azido or acyclic nucleoside analog inhibitors of HIV-1 reverse transcriptase (RT) also block XMRV infection with comparable efficacy in vitro. Our data confirm that XMRV is highly resistant to the non-nucleoside RT inhibitors nevirapine and efavirenz and to inhibitors of HIV-1 protease. In addition, we show that the integrase inhibitors raltegravir and elvitegravir are active against XMRV, with EC₅₀ values in the nanomolar range.

Conclusions

Our analysis demonstrates that XMRV exhibits a distinct pattern of nucleoside analog susceptibility that correlates with the structure of the pseudosugar moiety and that XMRV is sensitive to a broader range of antiretroviral drugs than has previously been reported. We suggest that the divergent drug sensitivity profiles of XMRV and HIV-1 are partially explained by specific amino acid differences in their respective protease, RT and integrase sequences. Our data provide a basis for choosing specific antiretroviral drugs for clinical studies in XMRV-infected patients.

Inhibition of HIV-1 replication by isoxazolidine and isoxazole sulfonamides

Targeting host factors is a complementary strategy for the development of new antiviral drugs. We screened a library of isoxazolidine and isoxazole sulfonamides and found four compounds that inhibited HIV-1 infection in human CD4+ lymphocytic T cells with no toxicity at IC₉₀ concentrations. Structure-activity relationship showed that benzyl sulfonamides and a halo-substituted aromatic ring on the heterocycle scaffold were critical for antiretroviral activity. The size and position of the incorporated halogen had a marked effect on the antiretroviral activity. The sulfonamide derivatives had no significant effect on HIV-1 entry, reverse transcription and integration but impaired a step necessary for activation of viral gene expression. This step was Tat-independent, strongly suggesting that the target is a cell factor. A virus partially resistant to the least potent compounds could be selected but could not be propagated in the long term, consistent with the possibility that HIV-1 may be less likely to develop resistance against drugs targeting some host factors. Here, we provide evidence that novel synthetic methods can be applied to develop small molecules with antiretroviral activity that target host factors important for HIV-1 replication.

Raltegravir: The evidence of its therapeutic value in HIV-1 infection

Introduction:

The antiretroviral treatment paradigm for human immunodeficiency virus-1 (HIV-1) infection has undergone a significant change with the addition of a new class of therapeutic agents targeting HIV-1 integrase (IN). IN inhibitors prevent the integration of viral DNA into the human genome and terminate the viral life cycle. As the first member of this new class of anti-HIV drugs, raltegravir has shown promising results in the clinic.

Aims:

To review the emerging evidence for the use of the IN inhibitor raltegravir in the treatment of HIV-1 infection.

Evidence review:

Strong evidence shows that raltegravir is effective in reducing the viral load to less than 50 copies/mL and increasing CD4 cell count in treatment-experienced patients with triple-drug class-resistant HIV-1 infection. Substantial evidence also indicates that while raltegravir is able to achieve treatment response in patients with drug-resistant HIV-1, it is susceptible to development of resistance. Raltegravir should be used with at least one other active drug. In addition to its use in salvage therapy upon failure of first-line antiretroviral treatment, a raltegravir-based treatment regimen may also be effective as initial therapy. Substantial evidence also shows that raltegravir-based treatment regimen is well tolerated with minimal clinically severe adverse events and toxicities. Modeling studies suggest a cost-effectiveness of US$21,339 per quality-adjusted life year gained with raltegravir use, though further direct evidence on quality of life and cost-effectiveness is needed.

Place in therapy:

Raltegravir shows significant and sustained virologic and immunologic response in combination with other antiretrovirals in treatment-experienced HIV-1 infected patients who show evidence of viral replication or multidrug-resistant HIV-1 strains, without any significant tolerability issues.

Raltegravir: molecular basis of its mechanism of action

Integration of the HIV-1 viral DNA generated by reverse transcription of the RNA genome into the host cell chromosomes is a key step of viral replication, catalyzed by the viral integrase. In October 2007, the first integrase inhibitor, raltegravir, was approved for clinical use under the name of Isentress™. The results of the various clinical trials that have evaluated raltegravir have been very encouraging with regard to the immunological and virological efficacy and tolerance. However, as observed for other anti-retrovirals, specific resistance mutations have been identified in patients failing to respond to treatment with raltegravir. Although knowledge of the integrase structural biology remains fragmentary, the structures and modeling data available might provide relevant clues on the origin of the emergence of these resistance mutations. In this review, we describe the mechanism of action of this drug and the main data relating to its use in vivo, together with recent structural data important to our understanding of the origin of viral resistance.

Integrase inhibitors in salvage therapy regimens for HIV-1 infection

PURPOSE OF REVIEW

To review current knowledge and the role of integrase inhibitors in the setting of HIV salvage therapy. We will discuss results from recent studies and literature and comment on the potential for integrase inhibitors in defined clinical settings.

RECENT FINDINGS

Raltegravir has been studied most intensively in treatment-experienced patients and is the first integrase inhibitor that has been licensed for use in this patient group. Most studies have shown good tolerability data and very potent virus suppression. In patients with limited treatment options, switching from enfuvirtide appears to be well tolerated, whereas switching from a protease inhibitor-based regimen may increase the rates of viral failure. Elvitegravir also showed good results in early phase clinical trials and is currently undergoing phase III clinical trials.

SUMMARY

Given that integrase inhibitors belong to a new class of antiretroviral agents with a diverse drug resistance profile, and are active against both chemokine (C-C motif) receptor 5 and chemokine (C-X-C motif) receptor 4 strains, they are exciting additions to salvage therapy regimen. Raltegravir and elvitegravir are metabolized via different pathways, which will affect their respective use. The major limitation for the use of integrase inhibitors is a potentially low threshold for viral drug resistance, so functional monotherapy must be avoided.