International perspectives on antiretroviral resistance. Nonnucleoside reverse transcriptase inhibitor resistance

Mutation patterns, cross resistance and virological failure among HIV type-1 patients in Alexandria, Egypt

Aim: The main purpose of this cross-sectional study was to detect the prevalence of drug resistance mutations related to nonnucleoside/nucleoside reverse transcriptase inhibitors (NNRTIs/NRTIs) and protease inhibitors (PIs). Patients & methods: Patients (n = 45) with HIV type-1 were recruited, 30 of whom were treatment naive and 15 treatment experienced. A partial pol gene covering the protease/reverse transcriptase (PRRT) region was amplified and then sequenced by the Sanger method. Results & conclusion: The most common NNRTI/NRTI-related mutations were ‘V179I (24%) and K103N (14.3%)’ and ‘M41L and V75M’ (14.3% each). M36I and H69K were the most prevalent PI-related mutations (86% each). The results of the current study serve as an initial crucial step in defining the overall prevalence of HIV type-1 drug resistance in Egypt.

Antiretroviral resistance in HIV-1 patients at a tertiary medical institute in Saudi Arabia: a retrospective study and analysis

Background

Since the early 90’s antiretroviral drugs have been available at King Faisal Specialist Hospital and Research Centre (KFSH&RC), a referral hospital in Riyadh, Saudi Arabia, for the treatment of both adults and children infected with HIV-1. However, up to date, there are no genetic profiling data for the resistance-causing mutations in HIV-1 virus in patients on antiretroviral drugs therapy. This paper presents an initial report and a profiling survey of drug resistance-associated mutations of 103 HIV-1 patients seen at KFSH&RC.

Methods

This is a retrospective study on Patients treated at KFSH&RC since 2003 up to 2016. The analysis was done on the drug resistance mutations profiles of 103 patients who were undergoing highly active antiretroviral therapy protocols.

Results

Our analysis shows that the drug resistance mutations reported in our treatment cohort of HIV-infected adults patients is similar what is internationally reported to some extent. Additionally, we have identified novel drug resistance causing mutations. Furthermore, different profile of drug resistance causing mutations was also observed.

Conclusion

Patients showed both similar and new drug resistant causing mutations, early identification of these mutations is crucial to guide and avoid failure future therapy.

Switching to Efavirenz Versus Remaining on Ritonavir-boosted Lopinavir in Human Immunodeficiency Virus-infected Children Exposed to Nevirapine: Long-term Outcomes of a Randomized Trial

Background

We previously demonstrated the noninferiority of switching to efavirenz (EFV) versus remaining on ritonavir-boosted lopinavir (LPV/r) for virologic control in children infected with human immunodeficiency virus (HIV) and exposed to nevirapine (NVP) for prevention of mother-to-child transmission. Here we assess outcomes up to 4 years post-randomization.

Methods

From 2010-2013, 298 NVP-exposed HIV-infected children ≥3 years of age were randomized to switch to EFV or remain on LPV/r in Johannesburg, South Africa (Clinicaltrials.gov NCT01146873). After trial completion, participants were invited to enroll into observational follow-up. We compared HIV RNA levels, CD4 counts and percentages, lipids, and growth across groups through four years post-randomization.

Results

HIV RNA levels 51-1000 copies/mL were less frequently observed in the EFV group than the LPV/r group (odds ratio [OR] 0.67, 95% confidence interval [CI]: 0.51-0.88, P = .004), as was HIV RNA >1000 copies/mL (OR 0.52 95% CI: 0.28-0.98, P = .04). The probability of confirmed HIV RNA >1000 copies/mL by 48 months was 0.07 and 0.12 in the EFV and LPV/r groups, respectively (P = .21). Children randomized to EFV had a reduced risk of elevated total cholesterol (OR 0.45 95% CI: 0.27-0.75, P = .002) and a reduced risk of abnormal triglycerides (OR 0.42, 95% CI 0.29-0.62, P < .001).

Conclusions

Our results indicate that the benefits of switching virologically suppressed NVP-exposed HIV-infected children ≥3 years of age from LPV/r to EFV are sustained long-term. This approach has several advantages, including improved palatability, reduced metabolic toxicity, simplified cotreatment for tuberculosis, and preservation of second line options.

Clinical Trials Registration

NCT01146873.

Efavirenz or nevirapine in three-drug combination therapy with two nucleoside or nucleotide-reverse transcriptase inhibitors for initial treatment of HIV infection in antiretroviral-naïve individuals

BACKGROUND

The advent of highly active antiretroviral therapy (ART) has reduced the morbidity and mortality due to HIV infection. The World Health Organization (WHO) ART guidelines focus on three classes of antiretroviral drugs, namely nucleoside or nucleotide reverse transcriptase inhibitors (NRTI), non-nucleoside reverse transcriptase inhibitors (NNRTI) and protease inhibitors. Two of the most common medications given as first-line treatment are the NNRTIs, efavirenz (EFV) and nevirapine (NVP). It is unclear which NNRTI is more efficacious for initial therapy. This systematic review was first published in 2010.

OBJECTIVES

To determine which non-nucleoside reverse transcriptase inhibitor, either EFV or NVP, is more effective in suppressing viral load when given in combination with two nucleoside reverse transcriptase inhibitors as part of initial antiretroviral therapy for HIV infection in adults and children.

SEARCH METHODS

We attempted to identify all relevant studies, regardless of language or publication status, in electronic databases and conference proceedings up to 12 August 2016. We searched MEDLINE, Embase, the Cochrane Central Register of Controlled Trials (CENTRAL), the World Health Organization (WHO) International Clinical Trials Registry Platform (ICTRP) and ClinicalTrials.gov to 12 August 2016. We searched LILACS (Latin American and Caribbean Health Sciences Literature) and the Web of Science from 1996 to 12 August 2016. We checked the National Library of Medicine (NLM) Gateway from 1996 to 2009, as it was no longer available after 2009.

SELECTION CRITERIA

We included all randomized controlled trials (RCTs) that compared EFV to NVP in people with HIV without prior exposure to ART, irrespective of the dosage or NRTI's given in combination.The primary outcome of interest was virological success. Other primary outcomes included mortality, clinical progression to AIDS, severe adverse events, and discontinuation of therapy for any reason. Secondary outcomes were change in CD4 count, treatment failure, development of ART drug resistance, and prevention of sexual transmission of HIV.

DATA COLLECTION AND ANALYSIS

Two review authors assessed each reference for inclusion using exclusion criteria that we had established a priori. Two review authors independently extracted data from each included trial using a standardized data extraction form. We analysed data on an intention-to-treat basis. We performed subgroup analyses for concurrent treatment for tuberculosis and dosage of NVP. We followed standard Cochrane methodological procedures.

MAIN RESULTS

Twelve RCTs, which included 3278 participants, met our inclusion criteria. None of these trials included children. The length of follow-up time, study settings, and NRTI combination drugs varied greatly. In five included trials, participants were receiving concurrent treatment for tuberculosis.There was little or no difference between EFV and NVP in virological success (RR 1.04, 95% CI 0.99 to 1.09; 10 trials, 2438 participants; high quality evidence), probably little or no difference in mortality (RR 0.84, 95% CI 0.59 to 1.19; 8 trials, 2317 participants; moderate quality evidence) and progression to AIDS (RR 1.23, 95% CI 0.72 to 2.11; 5 trials, 2005 participants; moderate quality evidence). We are uncertain whether there is a difference in all severe adverse events (RR 0.91, 95% CI 0.71 to 1.18; 8 trials, 2329 participants; very low quality evidence). There is probably little or no difference in discontinuation rate (RR 0.93, 95% CI 0.69 to 1.25; 9 trials, 2384 participants; moderate quality evidence) and change in CD4 count (MD -3.03; 95% CI -17.41 to 11.35; 9 trials, 1829 participants; moderate quality evidence). There may be little or no difference in treatment failure (RR 0.97, 95% CI 0.76 to 1.24; 5 trials, 737 participants; low quality evidence). Development of drug resistance is probably slightly less in the EFV arms (RR 0.76, 95% CI 0.60 to 0.95; 4 trials, 988 participants; moderate quality evidence). No studies were found that looked at sexual transmission of HIV.When we examined the adverse events individually, EFV probably is associated with more people with impaired mental function (7 per 1000) compared to NVP (2 per 1000; RR 4.46, 95% CI 1.65 to 12.03; 6 trials, 2049 participants; moderate quality evidence) but fewer people with elevated transaminases (RR 0.52, 95% CI 0.35 to 0.78; 3 trials, 1299 participants; high quality evidence), fewer people with neutropenia (RR 0.48, 95% CI 0.28 to 0.82; 3 trials, 1799 participants; high quality evidence), and probably fewer people withrash (229 per 100 with NVP versus 133 per 1000 with EFV; RR 0.58, 95% CI 0.34 to 1.00; 7 trials, 2277 participants; moderate quality evidence). We found that there may be little or no difference in gastrointestinal adverse events (RR 0.76, 95% CI 0.48 to 1.21; 6 trials, 2049 participants; low quality evidence), pyrexia (RR 0.65, 95% CI 0.15 to 2.73; 3 trials, 1799 participants; low quality evidence), raised alkaline phosphatase (RR 0.65, 95% CI 0.17 to 2.50; 1 trial, 1007 participants; low quality evidence), raised amylase (RR 1.40, 95% CI 0.72 to 2.73; 2 trials, 1071 participants; low quality evidence) and raised triglycerides (RR 1.10, 95% CI 0.39 to 3.13; 2 trials, 1071 participants; low quality evidence). There was probably little or no difference in serum glutamic oxaloacetic transaminase (SGOT; MD 3.3, 95% CI -2.06 to 8.66; 1 trial, 135 participants; moderate quality evidence), serum glutamic- pyruvic transaminase (SGPT; MD 5.7, 95% CI -4.23 to 15.63; 1 trial, 135 participants; moderate quality evidence) and raised cholesterol (RR 6.03, 95% CI 0.75 to 48.78; 1 trial, 64 participants; moderate quality evidence).Our subgroup analyses revealed that NVP slightly increases mortality when given once daily (RR 0.34, 95% CI 0.13 to 0.90; 3 trials, 678 participants; high quality evidence). There were little or no differences in the primary outcomes for patients who were concurrently receiving treatment for tuberculosis.

AUTHORS' CONCLUSIONS

Both drugs have similar benefits in initial treatment of HIV infection when combined with two NRTIs. The adverse events encountered affect different systems, with EFV more likely to cause central nervous system adverse events and NVP more likely to raise transaminases, cause neutropenia and rash.

Prevalence of Transmitted HIV Drug Resistance Among Recently Infected Persons in San Diego, CA 1996-2013

BACKGROUND

Transmitted drug resistance (TDR) remains an important concern when initiating antiretroviral therapy (ART). Here, we describe the prevalence and phylogenetic relationships of TDR among ART-naive, HIV-infected individuals in San Diego from 1996 to 2013.

METHODS

Data were analyzed from 496 participants of the San Diego Primary Infection Cohort who underwent genotypic resistance testing before initiating therapy. Mutations associated with drug resistance were identified according to the WHO-2009 surveillance list. Network and phylogenetic analyses of the HIV-1 pol sequences were used to evaluate the relationships of TDR within the context of the entire cohort.

RESULTS

The overall prevalence of TDR was 13.5% (67/496), with an increasing trend over the study period (P = 0.005). TDR was predominantly toward nonnucleoside reverse transcriptase inhibitors (NNRTIs) [8.5% (42/496)], also increasing over the study period (P = 0.005). By contrast, TDR to protease inhibitors and nucleos(t)ide reverse transcriptase inhibitors were 4.4% (22/496) and 3.8% (19/496), respectively, and did not vary with time. TDR prevalence did not differ by age, gender, race/ethnicity, or risk factors. Using phylogenetic analysis, we identified 52 transmission clusters, including 8 with at least 2 individuals sharing the same mutation, accounting for 23.8% (16/67) of the individuals with TDR.

CONCLUSIONS

Between 1996 and 2013, the prevalence of TDR significantly increased among recently infected ART-naive individuals in San Diego. Around one-fourth of TDR occurred within clusters of recently infected individuals. These findings highlight the importance of baseline resistance testing to guide selection of ART and for public health monitoring.

HIV-1 Antiretroviral Drug Resistance in Pregnant Women in Jamaica: A Preliminary Report

This preliminary report sought to provide insight into the genetic diversity of human immunodeficiency virus drug resistance (HIVDR) in Jamaica. This was done by investigating the genetic diversity associated with drug resistance in pregnant women living with HIV attending antenatal clinics in Kingston, Jamaica. Blood samples were collected and viral RNA were extracted and analysed. The protease and reverse transcriptase (Pro-RT) genes were amplified using the nested polymerase chain reaction (PCR) method. Polymerase chain reaction amplicons were obtained for nine of 16 patients (56%), of which five (55%) were antiretroviral (ARV) drug naïve and four (45%) were treatment experienced. Three minor protease resistant-conferring mutations (A71AT, A71V, A71T) and five mutations conferring high to low-level resistance (K219EK, T69S, K103S, G190A and K103N) were detected in the RT region. More than 50% of the resistance mutations found were detected in ARV drug naïve individuals, implying that viruses are being transmitted with the ARV resistance. These preliminary results will inform the health practitioners of the level of drug resistance that is being transmitted as well as strengthen the need to initiate a national baseline survey on HIVDR in Jamaica.

Impact of CYP polymorphisms, ethnicity and sex differences in metabolism on dosing strategies: the case of efavirenz

PURPOSE

Differences in drug metabolism due to cytochrome P450 (CYP) polymorphisms may be significant enough to warrant different dosing strategies in carriers of specific cytochrome P450 (CYP) polymorphisms, especially for drugs with a narrow therapeutic index. The impact of such polymorphisms on drug plasma concentrations and the resulting dosing strategies are presented in this review, using the example of efavirenz (EFV).

METHODS

A structured literature search was performed to extract information pertaining to EFV metabolism and the influence of polymorphisms of CYP2B6, ethnicity, sex and drug interactions on plasma concentrations of EFV. The corresponding dosing strategies developed for carriers of specific CYP2B6 genotypes were also reviewed.

RESULTS

The polymorphic CYP2B6 enzyme, which is the major enzyme in the EFV metabolic pathway, is a key determinant for the significant inter-individual differences seen in EFV pharmacokinetics and pharmacodynamics (PKPD). Ethnic differences and the associated prevalence of CYP2B6 polymorphisms result in significant differences in the PKPD associated with a standard 600 mg per day dose of EFV, warranting dosage reduction in carriers of specific CYP2B6 polymorphisms. Drug interactions and auto-induction also influence EFV PKPD significantly.

CONCLUSION

Using EFV as an example of a drug with a narrow therapeutic index and a high inter-patient variability in plasma concentrations corresponding to a standard dose of the drug, this review demonstrates how genotyping of the primary metabolising enzyme can be useful for appropriate dosage adjustments in individuals. However, other variables such as drug interactions and auto-induction may necessitate plasma concentration measurements as well, prior to personalising the dose.

HIV-1 antiretroviral drug therapy

The most significant advance in the medical management of HIV-1 infection has been the treatment of patients with antiviral drugs, which can suppress HIV-1 replication to undetectable levels. The discovery of HIV-1 as the causative agent of AIDS together with an ever-increasing understanding of the virus replication cycle have been instrumental in this effort by providing researchers with the knowledge and tools required to prosecute drug discovery efforts focused on targeted inhibition with specific pharmacological agents. To date, an arsenal of 24 Food and Drug Administration (FDA)-approved drugs are available for treatment of HIV-1 infections. These drugs are distributed into six distinct classes based on their molecular mechanism and resistance profiles: (1) nucleoside-analog reverse transcriptase inhibitors (NNRTIs), (2) non-nucleoside reverse transcriptase inhibitors (NNRTIs), (3) integrase inhibitors, (4) protease inhibitors (PIs), (5) fusion inhibitors, and (6) coreceptor antagonists. In this article, we will review the basic principles of antiretroviral drug therapy, the mode of drug action, and the factors leading to treatment failure (i.e., drug resistance).

The M230L nonnucleoside reverse transcriptase inhibitor resistance mutation in HIV-1 reverse transcriptase impairs enzymatic function and viral replicative capacity

The M230L mutation in HIV-1 reverse transcriptase (RT) is associated with resistance to first-generation nonnucleoside reverse transcriptase inhibitors (NNRTIs). The present study was designed to determine the effects of M230L on enzyme function, viral replication capacity (RC), and the extent to which M230L might confer resistance to the second-generation NNRTI etravirine (ETR) as well as to the first-generation NNRTIs efavirenz (EFV) and nevirapine (NVP). Phenotyping assays with TZM-bl cells confirmed that M230L conferred various degrees of resistance to each of the NNRTIs tested. Recombinant viruses containing M230L displayed an 8-fold decrease in RC compared to that of the parental wild-type (WT) virus. Recombinant HIV-1 WT and M230L mutant RT enzymes were purified; and both biochemical and cell-based phenotypic assays confirmed that M230L conferred resistance to each of EFV, NVP, and ETR. RT that contained M230L was also deficient in regard to each of minus-strand DNA synthesis, both DNA- and RNA-dependent polymerase activities, processivity, and RNase H activity, suggesting that this mutation contributes to diminished viral replication kinetics.

Detecting and understanding combinatorial mutation patterns responsible for HIV drug resistance

We propose a systematic approach for a better understanding of how HIV viruses employ various combinations of mutations to resist drug treatments, which is critical to developing new drugs and optimizing the use of existing drugs. By probabilistically modeling mutations in the HIV-1 protease or reverse transcriptase (RT) isolated from drug-treated patients, we present a statistical procedure that first detects mutation combinations associated with drug resistance and then infers detailed interaction structures of these mutations. The molecular basis of our statistical predictions is further studied by using molecular dynamics simulations and free energy calculations. We have demonstrated the usefulness of this systematic procedure on three HIV drugs, (Indinavir, Zidovudine, and Nevirapine), discovered unique interaction features between viral mutations induced by these drugs, and revealed the structural basis of such interactions.

Role of etravirine in the management of treatment-experienced patients with human immunodeficiency virus type 1

Etravirine is an oral diarylpyrimidine compound, a second-generation human immunodeficiency virus type 1 (HIV-1) non-nucleoside reverse transcriptase inhibitor (NNRTI) with expanded antiviral activity against NNRTI-resistant HIV-1, to be used in combination therapy for treatment-experienced patients. Compared with first-generation NNRTIs, etravirine has a high genetic barrier to resistance, and is better tolerated without the neuropsychiatric and hepatic side effects of efavirenz and nevirapine, respectively. Its safety profile is comparable to placebo with the exception of rash, which has been mild and self-limited in the great majority of patients. In phase III clinical trials among treatment-experienced patients harboring NNRTI-resistant HIV-1, etravirine in combination with an optimized background regimen (OBR) that included ritonavir-boosted darunavir demonstrated superior antiviral activity than the control OBR. In addition, patients on the etravirine arm had fewer AIDS-defining conditions, hospitalizations, and lower mortality compared with the OBR control arm.

Optimization of allele-specific PCR using patient-specific HIV consensus sequences for primer design

Allele-specific PCR based on subtype consensus sequences is a powerful technique for detecting low frequency drug resistant mutants in HIV-1 infected patients. However, this approach can be limited by genetic variation in the region complementary to the primers, leading to variability in allele detection. The goals of this study were to quantify this effect and then to improve assay performance.

Reverse transcriptase inhibitors as potential colorectal microbicides

We investigated whether reverse transcriptase (RT) inhibitors (RTI) can be combined to inhibit human immunodeficiency virus type 1 (HIV-1) infection of colorectal tissue ex vivo as part of a strategy to develop an effective rectal microbicide. The nucleotide RTI (NRTI) PMPA (tenofovir) and two nonnucleoside RTI (NNRTI), UC-781 and TMC120 (dapivirine), were evaluated. Each compound inhibited the replication of the HIV isolates tested in TZM-bl cells, peripheral blood mononuclear cells, and colorectal explants. Dual combinations of the three compounds, either NRTI-NNRTI or NNRTI-NNRTI combinations, were more active than any of the individual compounds in both cellular and tissue models. Combinations were key to inhibiting infection by NRTI- and NNRTI-resistant isolates in all models tested. Moreover, we found that the replication capacities of HIV-1 isolates in colorectal explants were affected by single point mutations in RT that confer resistance to RTI. These data demonstrate that colorectal explants can be used to screen compounds for potential efficacy as part of a combination microbicide and to determine the mucosal fitness of RTI-resistant isolates. These findings may have important implications for the rational design of effective rectal microbicides.

Antiretroviral therapy in HIV-infected patients with multidrug-resistant virus: applying the guidelines to practice

Abstract Current treatment guidelines recommend maintenance of HIV-1 viral load below detectable levels (<50 copies per milliliter), even in extensively treated patients with multidrug-resistant HIV-1. Given recent advances in drug development and the availability of new agents with activity against antiretroviral-resistant HIV-1 viral strains, this goal is increasingly attainable for treatment-experienced patients. A stepwise approach to management of patients harboring antiretroviral-resistant HIV is presented, including assessment of adherence, a description of the use of resistance testing and utilization of new antiretroviral agents.

Pharmacokinetics of BILR 355 after multiple oral doses coadministered with a low dose of ritonavir

The pharmacokinetics and safety of BILR 355 following oral repeated dosing coadministered with low doses of ritonavir (RTV) were investigated in 12 cohorts of healthy male volunteers with a ratio of 6 to 2 for BILR 355 versus the placebo. BILR 355 was given once a day (QD) coadministered with 100 mg RTV (BILR 355/r) at 5 to 50 mg in a polyethylene glycol solution or at 50 to 250 mg as tablets. BILR 355 tablets were also dosed at 150 mg twice a day (BID) coadministered with 100 mg RTV QD or BID. Following oral dosing, BILR 355 was rapidly absorbed, with the mean time to maximum concentration of drug in serum reached within 1.3 to 5 h and a mean half-life of 16 to 20 h. BILR 355 exhibited an approximately linear pharmacokinetics for doses of 5 to 50 mg when given as a solution; in contrast, when given as tablets, BILR 355 displayed a dose-proportional pharmacokinetics, with a dose range of 50 to 100 mg; from 100 to 150 mg, a slightly downward nonlinear pharmacokinetics occurred. The exposure to BILR 355 was maximized at 150 mg and higher due to a saturated dissolution/absorption process. After oral dosing of BILR 355/r, 150/100 mg BID, the values for the maximum concentration of drug in plasma at steady state, the area under the concentration-time curve from 0 to the dose interval at steady state, and the minimum concentration of drug in serum at steady state were 1,500 ng/ml, 12,500 h.ng/ml, and 570 ng/ml, respectively, providing sufficient suppressive concentration toward human immunodeficiency virus type 1. Based on pharmacokinetic modeling along with the in vitro virologic data, several BILR 355 doses were selected for phase II trials using Monte Carlo simulations. Throughout the study, BILR 355 was safe and well tolerated.

Analyses of HIV-1 drug-resistance profiles among infected adolescents experiencing delayed antiretroviral treatment switch after initial nonsuppressive highly active antiretroviral therapy

Treatment failure and drug resistance create obstacles to long-term management of HIV-1 infection. Nearly 60% of infected persons fail their first highly active antiretroviral therapy (HAART) regimen, partially because of nonadherence, requiring a switch to a second regimen to prevent drug resistance. Among HIV-infected youth, a group with rising infection rates, treatment switch is often delayed; virologic and immunologic consequences of this delay are unknown. We conducted a retrospective, longitudinal study of drug resistance outcomes of initial HAART in U.S. youth enrolled between 1999-2001 in a multicenter, observational study and experiencing delayed switch in their first nonsuppressive treatment regimen for up to 3 years. HIV-1 genotyping was performed on plasma samples collected longitudinally, and changes in drug resistance mutations, CD4+ T cell numbers and viral replication capacity were assessed. Forty-four percent (n = 18) of youth in the parent study experiencing virologic nonsuppression were maintained on their initial HAART regimen for a median of 144 weeks. Drug resistance was detected in 61% (11/18) of subjects during the study. Subjects on non-nucleoside reverse transcriptase inhibitor (NNRTI) regimens developed more (8/10) drug resistance mutations than those on protease-inhibitor (PI) regimens (2/7) (p = 0.058). Subjects developing NNRTI-resistance (NNRTI-R), showed a trend toward lower CD4+ T cell gains (median: -6 cells/mm(3) per year) than those without detectable NNRTI-R (median: +149 cells/mm(3) per year) (p = 0.16). HIV-1-infected youth maintained on initial nonsuppressive NNRTI-based HAART regimens are more likely to develop drug-resistant viremia than with PI-based HAART. This finding may have implications for initial treatment regimens and transmission risk in HIV-infected youth, a group with rising infection rates.

HIV-1-Resistant Strains during 8-Week on 8-Week off Intermittent Therapy and their Effect on CD4+ T-cell Counts and Antiviral Response

Background

We aimed here to study drug-associated HIV resistance mutations in peripheral blood mononuclear cells (PBMC) and plasma during intermittent therapy.

Methods

A substudy of 86 patients randomized to the intermittent treatment arm (8-week on/8-week off) of the ANRS 106 Window trial. HIV reverse transcriptase and protease genes were sequenced and resistance mutations identified according to the International AIDS Society list.

Results

Resistance mutations were detected in PBMC of 27/86 (31%) patients at baseline and 25/72 (35%) patients at week 96. Resistance mutations were detected in plasma of 28/86 (33%), 24/83 (29%) and 33/80 (41%) patients at weeks 8, 40 and 88, respectively. The detection of nucleoside reverse transcriptase inhibitor and protease inhibitor associated resistance mutations in plasma remained stable over time, but there was an increase in non-nucleoside reverse transcriptase inhibitor (NNRTI)-associated resistance mutations in patients on an NNRTI-based regimen: 1/33 (3%) versus 7/26 patients (27%) at weeks 8 and 88, respectively ( P=0.02). The proportions of patients with plasma HIV RNA levels ≤400 copies/ml after 8 weeks of treatment at weeks 16, 48 and 96 in patients with drug-resistant and wild-type viruses were 93% versus 74% ( P=0.04), 96% versus 88% ( P=0.43) and 70% versus 84% ( P=0.13), respectively. Patients with drug-resistant virus had a lower CD4+ T-cell decrease from baseline at weeks 40 and 88 as compared to patients with wild-type virus ( P=0.05 and 0.002, respectively).

Conclusions

NNRTI-associated resistance mutations increased over time in plasma of patients who were given NNRTIs. Drug-associated HIV resistance mutations did not seem to impair short-term antiviral response and might be associated with reduced CD4+ T-cell loss during interruptions.

The World Health Organization's global strategy for prevention and assessment of HIV drug resistance

Antiretroviral treatment (ART) for HIV is being scaled up rapidly in resource-limited countries. Treatment options are simplified and standardized, generally with one potent first-line regimen and one potent alternate first-line regimen recommended. Widespread HIV drug resistance (HIVDR) was initially feared, but reports from resource-limited countries suggest that initial ART programmes are as effective as in resource-rich countries, which should limit HIV drug resistance if programme effectiveness continues during scale-up. ART interruptions must be minimized to maintain viral suppression on the first-line regimen for as long as possible. Lack of availability of appropriate second-line drugs is a concern, as is the additional accumulation of resistance mutations in the absence of viral load testing to determine failure. The World Health Organization (WHO) recommends a minimum-resource strategy for prevention and assessment of HIVDR in resource-limited countries. The WHO's Global Network HIVResNet provides standardized tools, training, technical assistance, laboratory quality assurance, analysis of results and recommendations for guidelines and public health action. National strategies focus on assessments to guide immediate public health action to improve ART programme effectiveness in minimizing HIVDR and to guide regimen selection. Globally, WHO HIVResNet collects and analyses data to support evidence-based international policies and guidelines. Financial support is provided by major international organizations and technical support from HIVDR experts worldwide. As of December 2007, 25 countries were planning or implementing the strategy; seven countries report results in this supplement.

Protease inhibitor associated mutations compromise the efficacy of therapy in human immunodeficiency virus-1 (HIV-1) infected pediatric patients: a cross-sectional study

Background

Although the introduction of combined therapy with reverse transcriptase and protease inhibitors has resulted in considerable decrease in HIV related mortality; it has also induced the development of multiple drug-resistant HIV-1 variants.

The few studies on HIV-1 mutagenesis in HIV infected children have not evaluated the impact of HIV-1 mutations on the clinical, virological and immunological presentation of HIV disease that is fundamental to optimizing the treatment regimens for these patients.

Results

A cross sectional study was conducted to evaluate the impact of treatment regimens and resistance mutation patterns on the clinical, virological, and immunological presentation of HIV disease in 41 children (25 male and 16 female) at the Robert Wood Johnson Pediatric AIDS Program in New Brunswick, New Jersey. The study participants were symptomatic and had preceding treatment history with combined ARV regimens including protease inhibitors (PIs), nucleoside reverse transcriptase inhibitors (NRTIs) and non-nucleoside reverse transcriptase inhibitors (NNRTIs). Fifteen (36.6%) children were treated with NRTI+NNRTI+ PI, 6 (14.6%) with NRTI+NNRTIs, 13 (31.7%) with NRTI+PIs, and the remaining 7 (17.1%) received NRTIs only.

Combined ARV regimens did not significantly influence the incidence of NRTI and NNRTI associated mutations. The duration of ARV therapy and the child's age had no significant impact on the ARV related mutations. The clinico-immunological presentation of the HIV disease was not associated with ARV treatment regimens or number of resistance mutations. However, primary mutations in the protease (PR) gene increased the likelihood of plasma viral load (PVL) ≥ 10,000 copies/mL irrespective of the child's age, duration of ARV therapy, presence of NRTI and NNRTI mutation. Viremia ≥ 10,000 copies/mL was recorded in almost all the children with primary mutations in the PR region (n = 12/13, 92.3%) as compared with only 50.0% (n = 14/28) of HIV infected children without (PR-), P < 0.008. However, CD-4 T cells were not affected by the mutations in the PR gene of the HIV-1 isolates.

Conclusion

Primary PR resistance mutations significantly increase the likelihood for high viral replication in pediatric patients with moderate/severe HIV-1 infection, which may affect the long-term clinical prognosis of the HIV infected children.

Novel 2-chloro-8-arylthiomethyldipyridodiazepinone derivatives with activity against HIV-1 reverse transcriptase

Based on the molecular modeling analysis against Y181C HIV-1 RT, dipyridodiazepinone derivatives containing an unsubstituted lactam nitrogen and 2-chloro-8-arylthiomethyl were synthesized via an efficient route. Some of them were evaluated for their antiviral activity against HIV-1 RT subtype E and were found to exhibit virustatic activity comparable to some clinically used therapeutic agents.

High levels of primary antiretroviral resistance genotypic mutations and B/F recombinants in Santos, Brazil

This study characterized HIV-1 among antiretroviral-naïve populations presenting recent infection (RI) or long-standing infection (LSI). Sera collected from January 1999 to December 2001 at an anonymous HIV testing site in Santos, Brazil, were submitted to serologic testing algorithm for recent HIV seroconversion (STARHS). The STARHS methodology uses a combination of a sensitive and a less sensitive version of an anti-HIV enzyme immunoassay (EIA), and specimens found to be positive on the sensitive EIA and negative on the less sensitive EIA are considered to represent RI. HIV-1 V3 and pol regions of those with RI and LSI were compared. Antiretroviral resistance was defined solely by genotypic analysis. Ninety samples were evaluated representing those taken from an original cohort of 345 individuals, for whom adequate samples were available. Of 90 HIV-positive individuals, 25 presented RI. Cumulatively, 36.8% of those with RI and 25% of those with LSI presented resistance to at least one antiretroviral class. In the pol and V3 regions, 47% and 53% of those with RI presented clade B viruses and B/F recombinant viruses, respectively, whereas 56.2%, 41.7%, and 2.1% of those with LSI harbored clades B, B/F, and clade C viruses, respectively. Primary resistance and the prevalence of B/F recombinants was high in this population. Monitoring HIV-1 genetic diversity is important for developing vaccines and treatment strategies.

Determinants of HAART discontinuation among injection drug users

The objective of this study was to identify psychosocial determinants of, and self-reported reasons for, HAART discontinuation among HIV-positive injection drug users (IDUs). We examined correlates between sociodemographic characteristics, drug use and risk behaviors, outcome expectations, adherence self-efficacy, social support and HAART discontinuation among 160 HIV-positive participants in the Vancouver Injection Drug Users' Study (VIDUS). Logistic regression was used to identify the factors independently associated with discontinuation of HAART. Seventy-one (44%) study participants discontinued HAART during the study period. Factors independently associated with discontinuation of HAART included recent incarceration (OR = 4.84, p = 0.022), negative outcome expectations (OR = 1.41, p = 0.001), adherence efficacy expectations (OR = 0.70, p = 0.003) and self-regulatory efficacy (OR = 0.86, p = 0.050). The most frequently cited reasons provided for discontinuing HAART were being in jail (44%) and medication side effects (41%). The results of this study suggest that psychological constructs derived from self-efficacy theory are highly germane to the understanding of HAART discontinuation behavior and interventions that may change it. Incarceration may result in interruptions in HAART among IDUs, and programmatic changes may be needed to promote optimal retention on HAART among incarcerated HIV-infected IDUs.

Persistence of nevirapine-resistant HIV-1 in women after single-dose nevirapine therapy for prevention of maternal-to-fetal HIV-1 transmission

Single-dose nevirapine (sdNVP) for prevention of mother-to-child transmission of HIV-1 can select nevirapine (NVP)-resistant variants, but the frequency, duration, and clinical significance of this resistance is not well defined. We used a sensitive allele-specific PCR assay to assess the emergence and persistence of NVP-resistant variants in plasma samples from 22 women with HIV-1 subtype C infection who participated in a study of sdNVP for prevention of mother-to-child transmission of HIV-1. The women were categorized into three groups on the basis of detection of NVP resistance by standard genotype analysis. Group 1 (n = 6) had NVP resistance detected at 2 and 6 mo after sdNVP, but not at 12 mo. Group 2 (n = 9) had NVP resistance detected at 2 mo, but not 6 mo. Group 3 (n = 7) had no NVP resistance detected at any time point. Allele-specific PCR analysis for the two most common NVP resistance mutations (K103N and Y181C) detected NVP-resistant variants in most (16 of 21) samples that were negative for NVP resistance by standard genotype, at levels ranging from 0.1% to 20% 1 yr after treatment. The frequency of NVP-resistant mutations decreased over time, but persisted above predose levels for more than 1 yr in > or = 23% of the women. These findings highlight the urgent need for studies assessing the impact of sdNVP on the efficacy of subsequent antiretroviral therapy containing NVP or other nonnucleoside reverse transcriptase inhibitors.

Virus fitness: concept, quantification, and application to HIV population dynamics

Viral fitness has been broadly studied during the past three decades, mainly to test evolutionary models and population theories difficult to analyze and interpret with more complex organisms. More recent studies, however, are focused in the role of fitness on viral transmission, pathogenesis, and drug resistance. Here, we used human immunodeficiency virus (HIV) as one of the most relevant models to evaluate the importance of viral quasispecies and fitness in HIV evolution, population dynamics, disease progression, and potential clinical implications.

Suppression of virus load by highly active antiretroviral therapy in rhesus macaques infected with a recombinant simian immunodeficiency virus containing reverse transcriptase from human immunodeficiency virus type 1

We have modeled highly active antiretroviral therapy (HAART) for AIDS in rhesus macaques infected with a chimera (RT-SHIV) of simian immunodeficiency virus containing reverse transcriptase from human immunodeficiency virus type-1 (HIV-1). Seven RT-SHIV-infected macaques were treated with a combination of efavirenz (200 mg orally once daily), lamivudine (8 mg/kg subcutaneously once daily), and tenofovir (30 mg/kg subcutaneously once daily). Plasma viral RNA levels in all animals were reduced by more than 1,000-fold after 4 weeks and, in six of the seven animals, were reduced to undetectable levels after 10 weeks. Virus loads increased slightly between 12 and 16 weeks of treatment, associated with problems with the administration of efavirenz. After a change in the method of efavirenz administration, virus loads declined again and remained undetectable in the majority of animals for the duration of therapy. Treatment was stopped for three animals after 36 weeks of therapy, and virus loads increased rapidly. Posttreatment RT-SHIV isolates had no mutations associated with resistance to any of the three drugs. Efavirenz treatment was stopped, but lamivudine and tenofovir treatment for two other macaques was continued. The virus load in one of these two animals rebounded; virus from this animal was initially free of drug-resistance mutations but acquired the K65R mutation in reverse transcriptase at 11 weeks after efavirenz treatment was withdrawn. These results mimic HAART of HIV-1-infected humans. The RT-SHIV/rhesus macaque model should be useful for studies of tissue reservoirs and sites of residual replication that are not possible or practical with humans.

Gln145Met/Leu changes in human immunodeficiency virus type 1 reverse transcriptase confer resistance to nucleoside and nonnucleoside analogs and impair virus replication

The frequencies of multidrug resistance-associated mutations at codons 145, 151, and 69 of the human immunodeficiency virus (HIV) reverse transcriptase (RT) gene in strains from a group of 3,595 highly active antiretroviral therapy (HAART)-experienced patients were 0.22, 2.36, and 0.86%, respectively. Several amino acid substitutions different from the recently reported Gln145Met change (S. Paolucci, F. Baldanti, M. Tinelli, G. Maga, and G. Gerna, AIDS 17:924-927, 2003) were detected at position 145. Thus, amino acid substitutions selected at position 145 were introduced into the wild-type HIV type 1 (HIV-1) RT gene by site-directed mutagenesis, and recombinant HIV strains were assayed for their drug susceptibilities. Only Met and Leu substitutions at position 145 of the HIV-1 RT conferred multidrug resistance, while other amino acid changes did not. Lower levels of replication of the Gln145Met recombinant strain compared with those of both Gln151Met and wild-type recombinant strains were observed. In in vitro inhibition assays, expression and purification of the recombinant Gln145Met HIV-1 RT revealed a strong loss of catalytic efficiency of the mutated enzyme, as well as significant resistance to both zidovudine and efavirenz. Specific amino acid substitutions in the HIV RT nucleotide-binding pocket might affect both antiretroviral drug recognition and binding and decrease the level of virus replication, possibly by interfering with the enzyme activity. This finding may explain the lower frequency of Gln145Met/Leu mutations observed compared with the frequencies of Gln151Met/Leu mutations and the insertion at position 69 in HAART-experienced patients.

TMC125, a novel next-generation nonnucleoside reverse transcriptase inhibitor active against nonnucleoside reverse transcriptase inhibitor-resistant human immunodeficiency virus type 1

Nonnucleoside reverse transcriptase inhibitors (NNRTIs) are potent inhibitors of human immunodeficiency virus type 1 (HIV-1); however, currently marketed NNRTIs rapidly select resistant virus, and cross-resistance within the class is extensive. A parallel screening strategy was applied to test candidates from a series of diarylpyrimidines against wild-type and resistant HIV strains carrying clinically relevant mutations. Serum protein binding and metabolic stability were addressed early in the selection process. The emerging clinical candidate, TMC125, was highly active against wild-type HIV-1 (50% effective concentration [EC50] = 1.4 to 4.8 nM) and showed some activity against HIV-2 (EC50 = 3.5 microM). TMC125 also inhibited a series of HIV-1 group M subtypes and circulating recombinant forms and a group O virus. Incubation of TMC125 with human liver microsomal fractions suggested good metabolic stability (15% decrease in drug concentration and 7% decrease in antiviral activity after 120 min). Although TMC125 is highly protein bound, its antiviral effect was not reduced by the presence of 45 mg of human serum albumin/ml, 1 mg of alpha1-acid glycoprotein/ml, or 50% human serum. In an initial screen for activity against a panel of 25 viruses carrying single and double reverse transcriptase amino acid substitutions associated with NNRTI resistance, the EC50 of TMC125 was <5 nM for 19 viruses, including the double mutants K101E+K103N and K103N+Y181C. TMC125 also retained activity (EC50 < 100 nM) against 97% of 1,081 recent clinically derived recombinant viruses resistant to at least one of the currently marketed NNRTIs. TMC125 is a potent next generation NNRTI, with the potential for use in individuals infected with NNRTI-resistant virus.

Efavirenz therapy in rhesus macaques infected with a chimera of simian immunodeficiency virus containing reverse transcriptase from human immunodeficiency virus type 1

The specificity of nonnucleoside reverse transcriptase (RT) inhibitors (NNRTIs) for the RT of human immunodeficiency virus type 1 (HIV-1) has prevented the use of simian immunodeficiency virus (SIV) in the study of NNRTIs and NNRTI-based highly active antiretroviral therapy. However, a SIV-HIV-1 chimera (RT-SHIV), in which the RT from SIVmac239 was replaced with the RT-encoding region from HIV-1, is susceptible to NNRTIs and is infectious to rhesus macaques. We have evaluated the antiviral activity of efavirenz against RT-SHIV and the emergence of efavirenz-resistant mutants in vitro and in vivo. RT-SHIV was susceptible to efavirenz with a mean effective concentration of 5.9 +/- 4.5 nM, and RT-SHIV variants selected with efavirenz in cell culture displayed 600-fold-reduced susceptibility. The efavirenz-resistant mutants of RT-SHIV had mutations in RT similar to those of HIV-1 variants that were selected under similar conditions. Efavirenz monotherapy of RT-SHIV-infected macaques produced a 1.82-log-unit decrease in plasma viral-RNA levels after 1 week. The virus load rebounded within 3 weeks in one treated animal and more slowly in a second animal. Virus isolated from these two animals contained the K103N and Y188C or Y188L mutations. The RT-SHIV-rhesus macaque model may prove useful for studies of antiretroviral drug combinations that include efavirenz.

Transmission of HIV-1 drug resistance

BACKGROUND

The use of highly-active anti-retroviral therapy (HAART) for treating HIV infections is increasing. Recent studies have demonstrated that HAART is improving both the length and quality of life in HIV-infected patients. Resistant strains of HIV arise when drug adherence is poor. This can lead to the transmission of drug-resistant strains of HIV to susceptible individuals. This can lead to suboptimal first-line therapy, if the resistance profile of the transmitted virus is unknown.

OBJECTIVES

To review the mechanisms of how drug resistance arises; the methods used to characterise drug resistance; the problems arising with compliance leading to the development of drug-resistant HIV strains; the evidence for the incidence, prevalence and trends in the transmission of resistant HIV strains in different risk groups; and the evidence of suboptimal response to first-line therapy where transmission of a resistant HIV strain has occurred. On the basis of this, a case is presented for the routine resistance testing of all newly diagnosed HIV-infected individuals.

STUDY DESIGN

Literature review.

RESULTS AND CONCLUSIONS

There is evidence, though limited at present, that transmission of drug-resistant HIV strains can lead to suboptimal response to first-line therapy in newly diagnosed HIV-infected individuals. As the use of HAART can only increase in the future, and compliance will always be a problem in such HAART-treated patients, baseline resistance testing should become a routine part of their management.

Principles of antiretroviral treatment of children and adolescents with human immunodeficiency virus infection

Human immunodeficiency virus (HIV) infection requires life-long therapy to attain durable suppression of HIV replication and prevent or reverse HIV-related symptoms or immune system dysfunction. Combination therapy with 3 or more antiretroviral medications is currently widely recommended for treatment of children and adolescents with HIV infection. While potent regimens can initially reduce virus load to below assay quantitation limits in the majority of persons with HIV infection, 30% to 80% of children will have regimen failure and return of detectable plasma virus within 1 year. Adherence to therapy is critical to regimen success. Optimal treatment requires careful use of potent combinations of drugs, with attention to adherence, palatability, toxicity, and pharmacokinetics. Practitioners with experience caring for children and adolescents with HIV infection should be involved.

High prevalence of antiretroviral resistance in treated Ugandans infected with non-subtype B human immunodeficiency virus type 1

This study examined the emergence and prevalence of drug-resistant mutations in reverse transcriptase and protease coding regions in human immunodeficiency virus type 1 (HIV-1)-infected Ugandans treated with antiretroviral drugs (ARV). Genotypic resistance testing was performed on 50 and 16 participants who were enrolled in a cross-sectional and longitudinal observational cohort, respectively. The majority of the 113 HIV-1 PR-RT sequences were classified as subtypes A and D. Drug resistance mutations were prevalent in 52% of ARV-experienced individuals, and 17 of 27 ARV-resistant isolates had three mutations or more in reverse transcriptase. Resistance mutations in protease were less prevalent but only 17 of the 50 patients were receiving a protease inhibitor upon sample collection. Mutations conferring drug resistance were also selected in 3 of 16 participants in the longitudinal cohort, i.e., less than 8 months after the initiation of ARV treatment. Rapid emergence of ARV resistance was associated with poor adherence to treatment regimens, which was related to treatment costs. ARV resistance did, however, appear at a slightly higher prevalence in HIV-1 subtype D (21 of 33) than subtype A (7 of 25) infected individuals. Overall, this observational study suggests that ARV-resistant HIV-1 isolates are emerging rapidly in ARV-treated individual in Uganda and possibly other developing countries.

Psychosocial Determinants of Adherence to Highly Active Antiretroviral Therapy among Injection Drug Users in Vancouver

Background

Sub-optimal adherence to highly active antiretroviral therapy (HAART) among injection drug users (IDUs) is a significant concern. As such, there is an urgent need to identify psychosocial determinants of adherence that can be incorporated into interventions designed to promote optimal adherence.

Objective

To identify psychosocial determinants of adherence to HAART, as well as self-reported reasons for missing doses of HAART among HIV-infected IDUs.

Methods

We developed an eight-item adherence self-efficacy scale comprised of two sub-scales: adherence efficacy and self-regulatory efficacy. We examined correlates between adherence self-efficacy, outcome expectations, socio-demographic characteristics, drug use and risk behaviours, social support and HAART adherence among 108 HIV-infected participants in the Vancouver Injection Drug Users Study (VIDUS). Pharmacy-based adherence to HAART was obtained through a confidential record linkage to the province of British Columbia's HIV/AIDS Drug Treatment Program. Participants were defined as adherent if they picked-up 95% of their HAART prescriptions. Participants were also asked to indicate reasons for missing doses of HAART. Logistic regression was used to identify the factors independently associated with adherence to HAART.

Results

Seventy-one (66%) HIV-infected IDUs were less than 95% adherent. Forgetting was the most frequently cited reason (27%) for missing doses of HAART. Factors independently associated with adherence to HAART included adherence efficacy expectations [OR=1.8 (95% CI: 1.0–3.1); P=0.039] and negative outcome expectations [OR=0.8 (95% CI: 0.7–0.9); P=0.027].

Conclusions

We found low rates of adherence to HAART among IDUs. Psychological constructs derived from self-efficacy theory are highly germane to the understanding of adherence behaviour, and interventions that address these constructs should be developed and tested among HIV-infected drug users.

Drug resistance in non-subtype B HIV-1

Treatment of HIV-1 with antiretroviral therapy may select mutations in the pol gene associated with resistance to reverse transcriptase inhibitors and protease inhibitors. To provide durable clinical benefit, emergence of drug resistance is countered by prescription of alternative drug regimens. Data on sequential treatments that are effective after virologic failure and the selection of drug resistance is largely confined to HIV-1 subtype B, the clade that has circulated in North America and Europe. However, HIV-1 subtype B currently accounts for only 12% of the estimated 40 million HIV infected individuals worldwide. The global HIV-1 epidemic includes infection with nine identified HIV-1 group M subtypes (A-K), as well as distinct sub-subtypes and numerous chimerical or recombinant forms. Increasing access to treatment of HIV-1 in the developing world and increasing non-subtype B infection through travel and migration pose new questions about the susceptibility and response of these diverse HIV-1 viruses to antiretroviral drugs. Here we review HIV diversity and the published literature on drug resistance, comparing the known resistance mutations in individuals infected with subtype B to the growing experience in the treatment of non-subtype B HIV-1 worldwide.

Evolution of human immunodeficiency virus type 1 (HIV-1) resistance mutations in nonnucleoside reverse transcriptase inhibitors (NNRTIs) in HIV-1-infected patients switched to antiretroviral therapy without NNRTIs

We studied the evolution of nonnucleoside reverse transcriptase inhibitor (NNRTI) resistance mutations among 29 human immunodeficiency virus type 1 (HIV-1)-infected patients who experienced virologic failure when receiving an NNRTI-containing regimen (nevirapine, delavirdine, or efavirenz) and subsequently switched to antiretroviral therapy without NNRTIs. Genotypic resistance was determined from plasma samples collected at the time of NNRTI withdrawal (baseline) and during follow-up. At baseline, 83% of patients had more than two thymidine analog resistance mutations (TAMs), and all had NNRTI resistance mutations. Mutations at codons 103, 181, and 190 were found in 62, 62, and 34% of the patients, respectively. Follow-up samples were available after a median time of 6 months in all patients and at 12 months in 22 patients. The mean number of resistance mutations to NNRTIs was significantly lower at months 6 (1.34 +/- 1.04) and 12 (1.18 +/- 1.05) than at month 0 (2.03 +/- 1.02) (P < 0.009). The percentages of patients with at least one NNRTI resistance mutation were 100, 76, and 73% at baseline, month 6, and month 12, respectively (P < 0.0044). Overall, 70% of the patients had a mutation at codon 103 or 181 at month 12. The mean number of TAMs did not vary significantly during follow-up. Our data show that, in the context of maintained antiretroviral therapy, NNRTI resistance mutations persist in two-thirds of the patients in spite of NNRTI withdrawal. These results argue for the low impact of NNRTI resistance mutations on viral fitness and suggest that resistance mutations to different classes of drugs are associated on the same genome, at least in some of the resistant strains.

Virological significance, prevalence and genetic basis of hypersusceptibility to nonnucleoside reverse transcriptase inhibitors

Nonnucleoside reverse transcriptase inhibitors (NNRTI) are used to treat HIV-infected individuals in combination with nucleoside analogues (NRTI) and protease inhibitors. Long-term treatment with antiretroviral agents results in the emergence of strains with decreased susceptibility (resistance) to the drugs and is one of the major factors in loss of drug efficacy. Conversely, there have been recent reports of HIV strains with increased susceptibility (hypersusceptibility) to NNRTIs. These isolates emerge in patients on long-term antiretroviral therapy particularly in individuals receiving NRTIs. The prevalence of NNRTI hypersusceptibility ranges between 17.5 and 50% in NRTI-treatment experienced compared to 10% in NRTI-naïve patients. There is an inverse correlation between NNRTI hypersusceptibility and phenotypic NRTI resistance and a direct correlation between the number of NRTI resistance mutations present in the HIV reverse transcriptase. Re-sensitisation of phenotypic NNRTI resistance has been reported by NRTI mutations and is not likely to be detected using genotypic resistance assays. Recent studies demonstrate that NNRTI hypersusceptible virus at baseline is likely to predict better virological outcomes in patients on NNRTI-based salvage regimens compared to patients with NNRTI susceptible virus. These studies have implications for the sequence of antiretroviral drug use where patients may benefit from NRTI therapy before the introduction of NNRTIs, however more studies are needed to examine this treatment rationale.

Survival in an urban HIV-1 clinic in the era of highly active antiretroviral therapy: a 5-year cohort study

OBJECTIVE

To examine the implications of early virologic response to highly active antiretroviral therapy (HAART) on long-term HAART utilization patterns, development of diabetes or hyperlipidemia, and mortality in an urban HIV-1 clinic.

DESIGN

A cohort of 444 patients in an urban HIV-1 clinic, who started HAART prior to January 1, 1999, were categorized by virologic response in the first 18 months of therapy: durable viral suppression, initial suppression followed by rebound, and failure to achieve suppression. Antiretroviral exposure, HIV-1 RNA levels, CD4 cell counts, development of diabetes or hyperlipidemia, and survival were compared in the three groups.

RESULTS

Over 4 years of follow-up, patients in the durable suppression group used HAART 82% of the time compared with 60% in the rebound group (p <.001) and 23% in the failure to suppress group (p <.001). Through 4 years of follow-up, patients in the rebound group had a cumulative exposure to a median of seven antiretroviral drugs (interquartile range [IQR]: 6-9) compared with five drugs in the durable suppression group (IQR: 4-6) and five drugs in the failure to suppress group (IQR: 3-7) (p <.001 for both comparisons with the rebound group). At 5 years, the estimated proportions surviving were 89% in the durable suppression group, 76% in the rebound group (p =.04), and 56% in the failure to suppress group (p <.001). During follow-up, 35% in the durable suppression group developed diabetes or hyperlipidemia compared with 24% in the rebound group (p =.15) and 8% in the failure to suppress group (p <.001).

CONCLUSIONS

This study highlights the long-term implications of early virologic response to HAART for survival, accumulation of triple-class antiretroviral exposure, and development of HAART-associated toxicities.

Interruption of nonnucleoside reverse transcriptase inhibitor (NNRTI) therapy for 2 months has no effect on levels of human immunodeficiency virus type 1 in plasma of patients harboring viruses with mutations associated with resistance to NNRTIs

A 2-month interruption of only nonnucleoside reverse transcriptase inhibitors (NNRTIs) for patients carrying mutations associated with resistance to NNRTIs was followed by no change in either viral load or CD4 cell counts. These data suggest that these compounds have lost all of their in vivo antiviral activity in such cases.

Changes in the human immunodeficiency virus p7-p1-p6 gag gene in drug-naive and pretreated patients

Resistance to antiretroviral agents often results from mutations within the human immunodeficiency virus (HIV) pol gene. Moreover, insertions within the p6 gag-pol region have recently been found to be involved with resistance to nucleoside analogs. Overall, we found that 21% of 156 specimens collected from HIV-infected individuals (17.6% from 74 drug-naive patients and 24.4% from 82 pretreated patients) harbored these insertions. Insertions around the KQE (Lys-Gln-Glu) motif were found in 12.2% of the pretreated patients but in none of the drug-naive subjects (P = 0.002). In contrast, insertions around the PTAP (Prol-Thre-Ala-Prol) motif were seen at similar rates ( approximately 15%) among drug-naive and pretreated patients, which supports the idea that they may be natural polymorphisms.

Reversion of the M184V mutation in simian immunodeficiency virus reverse transcriptase is selected by tenofovir, even in the presence of lamivudine

The methionine-to-valine mutation in codon 184 (M184V) in reverse transcriptase (RT) of human immunodeficiency virus type 1 (HIV-1) or simian immunodeficiency virus (SIV) confers resistance to (-)-2'-deoxy-3'-thiacytidine (3TC; lamivudine) and increased sensitivity to 9-[2-(phosphonomethoxy)propyl]adenine (PMPA; tenofovir). We have used the SIV model to evaluate the effect of the M184V mutation on the emergence of resistance to the combination of 3TC plus PMPA. A site-directed mutant of SIVmac239 containing M184V (SIVmac239-184V) was used to select for resistance to both 3TC and PMPA by serial passage in the presence of increasing concentrations of both drugs. Under these selection conditions, the M184V mutation reverted in the majority of the selections. Variants resistant to both drugs were found to have the lysine-to-arginine mutation at codon 65 (K65R), which has previously been associated with resistance to PMPA in both SIV and HIV. Similarly, in rhesus macaques infected with SIVmac239-184V for 46 weeks and treated daily with (-)-2'-deoxy-5-fluoro-3'-thiacytidine [(-)-FTC], there was no reversion of M184V, but this mutation reverted to 184 M in all three animals within 24 weeks of treatment with (-)-FTC and PMPA. Although the addition of PMPA to the (-)-FTC therapy induced a decrease in virus loads in plasma, these loads eventually returned to pre-PMPA levels in each case. All animals receiving this combination developed the K65R mutation. These results demonstrate that the combination of PMPA with 3TC or (-)-FTC selects for the K65R mutation and against the M184V mutation in SIV RT.

Fitness of drug resistant HIV-1: methodology and clinical implications

Recent studies of human immunodeficiency virus type 1 (HIV-1) fitness have examined the potential relationship with plasma viral load, drug resistance, and disease progression. For example, treatment of HIV-1 infected individuals with antiretroviral drugs may result in the selection and emergence of inhibitor-resistant variants with reduced replicative capacity. However, it is still unclear whether in vitro HIV-1 fitness has any direct relationship to in vivo disease progression or treatment success. A related question is which in vitro assay of viral fitness is the most appropriate for comparison with in vivo HIV-1 fitness. Characterization of the relative viral fitness of drug-resistant HIV-1 strains may lead to a better understanding of whether or not less fit viruses pose a clinical benefit to the patient.

No evidence for persistence of multidrug-resistant viral strains after a 7-month treatment interruption in an HIV-1-infected individual

The number of HIV-1-infected patients harboring multidrug-resistant viruses is increasing. Since new antiretroviral drugs with favorable resistance profiles are limited, innovative strategies are urgently needed. Treatment interruptions can lead to a loss in HIV resistance followed by improved response to reinitiated therapy. The authors report the case of a patient with sustained antiretroviral response for 3.5 years after a 7-month treatment interruption. Concomitant with an increase in replication capacity, multidrug-resistant viruses gradually disappeared during treatment interruption. Resistance to protease inhibitors (PI) was completely lost, and resistance to reverse transcriptase inhibitors was still present when therapy was reinitiated. PI-resistant variants were not detected at four time points after treatment reinitiation. The alignment of the nucleic acid sequences from all different time points suggested that the viruses obtained after treatment reinitiation evolved from less-resistant variants prior to treatment interruption. This was supported by in vitro propagation of the viral plasma population and an individual clone derived from the time point of treatment interruption. This is consistent with a model favoring reversible binding of HIV-1 to reservoirs, as has recently been proposed for follicular dendritic cells. Understanding of this process could help to exploit the reduced fitness of drug-resistant viruses for treatment interruptions.

Origin of human immunodeficiency virus type 1 quasispecies emerging after antiretroviral treatment interruption in patients with therapeutic failure

The emergence of antiretroviral (ARV) drug-resistant human immunodeficiency virus type 1 (HIV-1) quasispecies is a major cause of treatment failure. These variants are usually replaced by drug-sensitive ones when the selective pressure of the drugs is removed, as the former have reduced fitness in a drug-free environment. This was the rationale for the design of structured ARV treatment interruption (STI) studies for the management of HIV-1 patients with treatment failure. We have studied the origin of drug-sensitive HIV-1 quasispecies emerging after STI in patients with treatment failure due to ARV drug resistance. Plasma and peripheral blood mononuclear cell samples were obtained the day of treatment interruption (day 0) and 30 and 60 days afterwards. HIV-1 pol and env were partially amplified, cloned, and sequenced. At day 60 drug-resistant variants were replaced by completely or partially sensitive quasispecies. Phylogenetic analyses of pol revealed that drug-sensitive variants emerging after STI were not related to their immediate temporal ancestors but formed a separate cluster, demonstrating that STI leads to the recrudescence and reemergence of a sequestrated viral population rather than leading to the back mutation of drug-resistant forms. No evidence for concomitant changes in viral tropism was seen, as deduced from env sequences. This study demonstrates the important role that the reemergence of quasispecies plays in HIV-1 population dynamics and points out the difficulties that may be found when recycling ARV therapies with patients with treatment failure.

The impact of the M184V substitution in HIV-1 reverse transcriptase on treatment response

The M184V mutation in the HIV-1 reverse transcriptase gene is primarily associated with rapid, high-level lamivudine (3TC) resistance. It has also been observed to arise under selective pressure by abacavir, to which it confers low-level resistance. Although the development of viral drug resistance remains a major concern in antiretroviral therapy, it is known that some immunological and clinical benefit can still be derived from highly active antiretroviral therapy (HAART) regimens despite resistance-associated virological failure. This residual benefit on a failing regimen is commonly attributed to the preservation of fitness-reducing protease inhibitor (PI) resistance mutations under continued drug pressure. However, fitness-reducing nucleoside reverse transcriptase inhibitor (NRTI) mutations may also contribute to the effect. M184V is both common in the treated population and fitness-reducing. A number of studies, both of dual nucleoside therapy and HAART, have noted a residual treatment effect for 3TC despite the assumed or observed presence of M184V and high-level phenotypic resistance. The speed and consistency with which this mutation is selected by 3TC under suboptimal viral suppression therefore makes M184V a particularly interesting model for further clinical studies on the association of drug resistance with ongoing treatment benefit. While fitness considerations are likely to be a major contributor to the clinical observations noted, there are a number of other potential mechanisms that may contribute to a continuing response to 3TC in the presence of M184V. These include the delay and reversal of zidovudine (ZDV) resistance, hypersensitization to other NRTIs, reduced reverse transcriptase (RT) processivity and a possible reduction in RT pyrophosphorolysis. The full impact of M184V on therapeutic prospects will require further elucidation; ideally, the risk/benefit of preserving this substitution would be investigated in randomized trials. However, existing data suggest that the presence of this mutation may preserve some benefit in spite of the loss of 3TC susceptibility which, with further study, may prove valuable.

Genotypic testing for human immunodeficiency virus type 1 drug resistance

There are 16 approved human immunodeficiency virus type 1 (HIV-1) drugs belonging to three mechanistic classes: protease inhibitors, nucleoside and nucleotide reverse transcriptase (RT) inhibitors, and nonnucleoside RT inhibitors. HIV-1 resistance to these drugs is caused by mutations in the protease and RT enzymes, the molecular targets of these drugs. Drug resistance mutations arise most often in treated individuals, resulting from selective drug pressure in the presence of incompletely suppressed virus replication. HIV-1 isolates with drug resistance mutations, however, may also be transmitted to newly infected individuals. Three expert panels have recommended that HIV-1 protease and RT susceptibility testing should be used to help select HIV drug therapy. Although genotypic testing is more complex than typical antimicrobial susceptibility tests, there is a rich literature supporting the prognostic value of HIV-1 protease and RT mutations. This review describes the genetic mechanisms of HIV-1 drug resistance and summarizes published data linking individual RT and protease mutations to in vitro and in vivo resistance to the currently available HIV drugs.