Role of baseline human immunodeficiency virus genotype as a predictor of viral response to tenofovir in heavily pretreated patients

Infection with the frequently transmitted HIV-1 M41L variant has no influence on selection of tenofovir resistance

OBJECTIVES

In ∼10% of newly diagnosed HIV-1 patients, drug-resistant viral variants are detected. In such transmitted HIV-1 variants, the thymidine analogue mutation (TAM) M41L is frequently observed as a single resistance mutation and these viral variants often belong to phylogenetic transmission clusters. The presence of at least three TAMs, in particular patterns with M41L/L210W, impairs the efficacy of the extensively used drug tenofovir. We investigated whether the presence of a single M41L mutation at baseline influences the selection of resistance to tenofovir and emtricitabine in vitro and in vivo.

METHODS

The impact of M41L on the development of drug resistance to tenofovir and emtricitabine was determined by extensive in vitro selection experiments and investigation of the virological outcome of patients on a first-line regimen.

RESULTS

The presence of a single M41L mutation did not influence the selected mutational profile or the genetic barrier to resistance to tenofovir and/or emtricitabine during long-term in vitro selection experiments. In vivo, virological outcome of first-line regimens containing tenofovir and emtricitabine was comparable between patients diagnosed with HIV-1 harbouring M41L (n=17, 16 were part of one transmission cluster) and WT virus (n=248).

CONCLUSIONS

Detection of a single M41L reverse transcriptase mutation at baseline did not influence the development of resistance in vitro or virological outcome on tenofovir-containing regimens in patients belonging to a large transmission cluster. Our results indicate that a high genetic barrier regimen may not be required when patients are diagnosed with HIV variants containing a single M41L mutation in reverse transcriptase.

Clinical, virological and biochemical evidence supporting the association of HIV-1 reverse transcriptase polymorphism R284K and thymidine analogue resistance mutations M41L, L210W and T215Y in patients failing tenofovir/emtricitabine therapy

Background

Thymidine analogue resistance mutations (TAMs) selected under treatment with nucleoside analogues generate two distinct genotypic profiles in the HIV-1 reverse transcriptase (RT): (i) TAM1: M41L, L210W and T215Y, and (ii) TAM2: D67N, K70R and K219E/Q, and sometimes T215F. Secondary mutations, including thumb subdomain polymorphisms (e.g. R284K) have been identified in association with TAMs. We have identified mutational clusters associated with virological failure during salvage therapy with tenofovir/emtricitabine-based regimens. In this context, we have studied the role of R284K as a secondary mutation associated with mutations of the TAM1 complex.

Results

The cross-sectional study carried out with >200 HIV-1 genotypes showed that virological failure to tenofovir/emtricitabine was strongly associated with the presence of M184V (P < 10^-10) and TAMs (P < 10^-3), while K65R was relatively uncommon in previously-treated patients failing antiretroviral therapy. Clusters of mutations were identified, and among them, the TAM1 complex showed the highest correlation coefficients. Covariation of TAM1 mutations and V118I, V179I, M184V and R284K was observed. Virological studies showed that the combination of R284K with TAM1 mutations confers a fitness advantage in the presence of zidovudine or tenofovir. Studies with recombinant HIV-1 RTs showed that when associated with TAM1 mutations, R284K had a minimal impact on zidovudine or tenofovir inhibition, and in their ability to excise the inhibitors from blocked DNA primers. However, the mutant RT M41L/L210W/T215Y/R284K showed an increased catalytic rate for nucleotide incorporation and a higher RNase H activity in comparison with WT and mutant M41L/L210W/T215Y RTs. These effects were consistent with its enhanced chain-terminated primer rescue on DNA/DNA template-primers, but not on RNA/DNA complexes, and can explain the higher fitness of HIV-1 having TAM1/R284K mutations.

Conclusions

Our study shows the association of R284K and TAM1 mutations in individuals failing therapy with tenofovir/emtricitabine, and unveils a novel mechanism by which secondary mutations are selected in the context of drug-resistance mutations.

N348I in HIV-1 reverse transcriptase decreases susceptibility to tenofovir and etravirine in combination with other resistance mutations

We previously demonstrated that N348I in HIV-1 reverse transcriptase confers zidovudine and nevirapine resistance. However, both of these inhibitors are currently infrequently used in developed countries, and the impact of N348I on newer reverse transcriptase inhibitors, such as tenofovir and etravirine, is unknown. In this study, we demonstrate that N348I alone confers no resistance to tenofovir and low-level resistance to etravirine. However, N348I significantly decreases tenofovir susceptibility when combined with thymidine analogue mutations and etravirine susceptibility when combined with Y181C.

Changing patterns in HIV reverse transcriptase resistance mutations after availability of tenofovir

Assessment of 1177 human immunodeficiency virus (HIV) resistance genotypes at an HIV/AIDS clinic showed a decrease in the incidence of the K65R mutation, from 15.2% of isolates during the period 2002-2004 to 2.7% of isolates during the period 2005-2006 (P < .001), despite elevated and stable rates of tenofovir use. A reduction in the rate of coadministration of didanosine (from 41.6% of patients in 2004 to 0.8% of patients in 2006; P < .001) largely explained this observation.

Antiviral Efficacy and Genotypic Resistance Patterns of Combination Therapy with Stavudine/Tenofovir in Highly Active Antiretroviral Therapy Experienced Patients

Objectives

To evaluate antiviral efficacy of stavudine/tenofovir (d4T/TDF) backbone combination in late-line antiretroviral therapy, and to assess clinical and virological determinants of treatment success.

Design

Multicentric retrospective analysis on patients starting d4T/TDF after highly active antiretroviral therapy (HAART) failure.

Methods

The primary endpoint was the change in plasma HIV-1 RNA from the baseline (time of d4T/TDF initiation) to 6 months of therapy; secondary endpoint was the risk of virological failure.

Results

Among 172 patients included, a mean change in HIV-1 RNA of -1.69 (+1.23) and -1.53 (+1.43) log10 cp/ml was observed respectively at weeks 24 and 48 after starting d4T/TDF combination. Any single type-1 thymidine analogue mutation (TAM; M41L, L210W, T215Y) had a negative effort on the change in HIV RNA at 6 months, whereas among type-2 TAMs (D67N, K70R, K219Q), only D67N showed a trend for a negative effect. Presence of M184V mutation was related with a greater reduction in HIV RNA during d4T/TDF exposure. The risk of virological failure at 6 months after d4T/TDF starting was 22%. Type-1 TAMs were associated with a greater risk of failure (adjusted hazard ratio [HR]=1.65; 95% confidence interval [CI] 1.19–2.29). Conversely, M184V showed a protective effect. In 17 genotypic tests available at failure, no K65R mutation was detected, whereas a trend for an increasing prevalence of d4T-associated mutations was found.

Conclusions

Combining TDF with a thymidine analogue as d4T may be effective as component of antiretroviral rescue regimens in HIV-infected patients with previous exposure to nucleoside analogue reverse transcriptase inhibitor. Previous selection of type-1 TAMs induces a detrimental effect over virological response.

Short-term safety and pharmacodynamics of amdoxovir in HIV-infected patients

OBJECTIVES

To evaluate the pharmacodynamics and safety of escalating doses of amdoxovir (DAPD) monotherapy administered to treatment-naive and experienced HIV-1-infected patients over 15 days.

DESIGN

Ninety patients with plasma HIV-1 RNA levels between 5000 and 250,000 copies/ml were randomized to DAPD 25, 100, 200, 300 or 500 mg twice daily or 600 mg once daily monotherapy [antiretroviral therapy (ART)-naive and ART-experienced] or to add DAPD 300 or 500 mg twice daily to existing ART. After 15 days of dosing, patients were followed for an additional 7 days.

METHODS

Antiviral activity was compared between treatment arms using log10 HIV-1 RNA based on average area under the curve minus baseline to day 15. Safety and tolerability was analyzed by incidence of grade 1 to 4 clinical and laboratory adverse events.

RESULTS

In ART-naive patients receiving short-term DAPD monotherapy, a median reduction in plasma HIV-1 RNA of 1.5 log10 copies/ml at the highest doses was observed. In ART-experienced patients, the reduction in viral load observed at each dose was less than that observed in treatment-naive patients (reduction of 0.7 log10 at 500 mg twice daily). The incidence of adverse events was similar across groups with the majority of adverse events reported as mild or moderate in severity. Steady-state plasma concentrations of DAPD and dioxolane guanosine followed linear kinetics.

CONCLUSIONS

DAPD was well tolerated and produced antiviral activity in treatment-naive and in some treatment-experienced patients. In ART-experienced patients, the antiviral activity was significant in those with no thymidine-analogue mutations and higher baseline CD4+ cell counts.

Impact of drug resistance genotypes on CD4+ counts and plasma viremia in heavily antiretroviral-experienced HIV-infected patients

The number of HIV-infected individuals with prior multiple treatment failures is increasing as time passes by. The success of antiretroviral therapy in these patients is often compromised by the selection of drug-resistant viruses. Despite initial concerns, a rebound in AIDS cases among heavily treatment-experienced patients failing virologically their antiretroviral therapy has not occurred yet. In a multicenter study conducted in Spain, HIV-infected patients were assessed with prior failure to antiretrovirals from the three main drug families who presented during the last semester of the year 2003 with plasma HIV-RNA values above 1,000 copies/ml, despite good treatment adherence. The relationships between CD4+ T cell counts, viral loads and drug-resistant genotypes were examined. A total of 273 patients were identified in 12 centers (78% male, median age: 41 years). The mean viral load was 50,438 copies/ml and the mean CD4+ count was 328 cells/mul. Only 19.5% had less than 200 CD4+ T cells/mul. Most patients (95%) were receiving nucleoside reverse transcriptase inhibitors (NRTI) in their last antiretroviral regimen, while 63% were treated with protease inhibitors (PI) and 27% on non-nucleoside reverse transcriptase inhibitors (NNRTI). Overall, 97.4% had at least one drug resistance mutation (87.2% for NRTI, 68.5% for NNRTI, and 92.7% for PI). Using the virtual phenotype, resistance to three or more drugs within each class was recognized in 45.8% for NRTI, 40.7% for NNRTI, and 44.7% for PI. Moreover, cross-resistance to compounds from two or three drug families was recognized in 41% and 19.4% of patients, respectively. Nearly half of the patients had plasma HIV-RNA below 10,000 copies/ml and they showed significantly higher CD4 + counts than those with greater viremia (408 versus 259 cells/mul; P < 0.001). Patients with higher plasma viremia had significantly more drug resistance mutations than those with lower viremia. No favorable effect on viral load could be recognized for individual drug resistance mutations known to reduce viral fitness in vitro (i.e., rtM184V, rtL74V, rtK65R, proD30N, or proI50L). In summary, a large proportion of treatment-experienced patients failing their current antiretroviral regimen carry viruses with broad cross-resistant genotypes. Nearly half of the patients with these multi-drug resistant viruses had < 10,000 HIV-RNA copies/ml and 80% have more than 200 CD4 + T cells/mul. Thus, maintaining treatment HIV-infected individuals failing virologically and harboring drug-resistant viruses might ameliorate immunological deterioration until new drugs became available. J. Med. Virol. 77:23-28, 2005. (c) 2005 Wiley-Liss, Inc.