Effectiveness of etravirine-based therapy for treatment-experienced HIV- infected patients

Introduction: Treatment options are limited for HIV-1-infected individuals who have received extensive previous antiretroviral therapy. ETV has shown significant clinical benefits in treatment-experienced HIV-1+ patients with antiretroviral resistance. The aim of this study was to evaluate the effectiveness of ETV plus optimized background regimen in real-life conditions in a cohort of highly HIV-1 antiretroviralexperienced patients. Methodology: Retrospective cohort of treatment-experienced HIV-1-infected adults with virological failure who started therapy with an ETVcontaining regimen. The effectiveness was evaluated using HIV-1 RNA viral load and changes in CD4+ cell count after 48 weeks of treatment. Results: Forty-two patients ≥ 16 years of age were included; 74% were men, and the median age was 45 years (IQR 41–53). All participants had prior non-nucleoside reverse transcriptase inhibitor use (55% nevirapine, 83%, efavirenz, and 28% both). Baseline median HIV-1 RNA viral load was 15,598 copies/mL (IQR 2651–84,175) and CD4+ cell count was 276 cells/L (IQR 155–436). After 48 weeks of treatment, 90.5% (95% CI 78–96) of patients had HIV-1 RNA viral load < 200 copies/mL and 76% (95% CI 61–86) had < 50 copies/mL. CD4+ cell counts increased from baseline to 48 weeks of treatment to a median of 407 cells/L (IQR 242–579); p < 0.001. Virological outcome was associated with virological failure at baseline HIV-1 RNA viral load ≥ 100,000 copies/mL (OR 7.6; 95% CI 1.2–44.80; p = 0.025). Conclusions: Our study provides clinically important evidence of the effectiveness and safety of ETV in highly antiretroviral-experienced HIV1-infected patients.


Introduction
Current antiretroviral therapy (ART) for HIV has improved treatment durability for a substantial proportion of patients; however, for some patients, therapy fails and viral rebound occurs with progression of disease and mortality [1].Among HIV-infected patients, 21% of treatment-experienced and 11% of treatment-naive patients experience triple-class virological failure six years after starting ART [2].Furthermore, once patients have triple-class virological failure, treatment options are extremely limited and patients are at increased risk of mortality [3].Thus, there is a need for new antiretroviral agents with which to construct active treatment regimens for patients infected with drug-resistant HIV strains who have experienced triple-class treatment failure [4].
Etravirine (ETV) has shown significant clinical benefits in treatment-experienced HIV type-1 (HIV-1)infected patients with antiretroviral resistance in phase III DUET-1 and DUET-2 trials.These parallel, multicenter, randomized studies evaluated the use of ETV versus placebo, each combined with a darunavir/ritonavir (DRV/r)-containing optimized background regimen (OBR), in 1,203 patients experiencing virological failure on ART with evidence of multiclass resistance.The pooled 96-week DUET-1 and -2 data demonstrated that 57% of patients in the ETV group achieved HIV-1 RNA < 50 copies/mL compared with 36% in the placebo group (p < 0.001) [4,5].
Important data regarding combination therapies, especially with DRV/r, came from the subset of DUET patients who had no ETV resistance-associated mutations (RAMs); those with as many as three DRV RAMs (a subgroup with diminished response to DRV/r) had a high 24-week response rate of 78%, the same response rate observed in patients with no DRV RAMs [6].
ETV was approved for use in treatmentexperienced adult patients who have evidence of viral replication and HIV-1 strains resistant to nonnucleoside reverse transcriptase inhibitor (NNRTI) and other antiretroviral agents [7].Several clinical trials have reported a dramatic increase in the proportion of patients safely achieving virological response despite harboring multidrug-resistant HIV-1 viruses [8][9][10].Among these investigations, the ANRS 139 TRIO trial reported that 86% of patients reached HIV-1 RNA < 50 copies/mL at week 48 with a salvage regimen containing raltegravir (RAL), ETV and DRV/r, and OBR with NRTIs or enfuvirtide [9].
The present observational study in antiretroviral treatment-experienced, HIV-1-infected adults explored the efficacy of ETV plus OBR.

Design
This study was based on a retrospective cohort of treatment-experienced HIV-1-infected adults who started therapy with an ETV-containing regimen.The first analysis end-point was an HIV-1 RNA viral load < 50 copies/mL (by reverse transcription polymerase chain reaction [RT-PCR) after patients completed 48 weeks of treatment.Secondary end-points were the evaluation of HIV-1 RNA viral load < 200 copies/mL (by RT-PCR) and an increase of CD4+ cell counts at 48 weeks of treatment.

Patients
Patients were recruited for HIV treatment from seven referral centres in four Mexican states.Patients were  16 years of age with confirmed HIV-1 infection by enzyme-linked immunosorbent assay and western blot and had virological failure and mutations detected from three classes of antiviral drugs.Patients had previous treatment with at least three classes of antiretroviral drugs including nucleos(t)ide reversetranscriptase inhibitors (NRTIs), NNRTIs, and protease inhibitors (PIs), with mutation resistance documented for each class known by genotype.
The regimen included three to four ARV agents, according to HIV-1 resistance testing and previous antiretroviral drug experience.

Measurements
Clinical history regarding ARV regimens, CD4+ cell count, HIV-1 RNA viral load, and serum laboratory parameters at the beginning of the therapy with ETV at baseline, 24, and 48 weeks were recorded.Once provided with each patient's genotype, tropism-testing, and previous regimens, an expert committee evaluated each case to decide the better option for a salvage regimen using ETV plus an OBR, considering the previous use of ARV regimens.
The effects of salvage treatment susceptibility on HIV-1 RNA viral load suppression were analyzed using the genotypic susceptibility score (GSS) for the salvage regimen, calculated based on the drug resistance scores extracted from the Stanford HIVdb.Each antiretroviral drug was assigned a score according to the five-level Stanford HIVdb interpretation: 1.00, 0.75, 0.50, 0.25, and 0.00 for susceptible, potential low-level resistance, low-level resistance, intermediate resistance, and highlevel resistance, respectively.GSS was defined as the sum of the genotypic sensitivities for all the drugs in a patient's treatment regimen.The GSS was defined as the total number of drugs (excluding ETV) in a participant's OBR antiretroviral regimen to which their HIV isolate had genotypic sensitivity, as evaluated by gene sequence and mutation analyses.
Once genotyping and tropism testing was done and the previous use of antiretroviral regimens was considered, an expert committee evaluated each case to decide the better option for a salvage regimen, namely ETV plus OBR.
The effectiveness of ETV treatment was evaluated with percentage of HIV-1 RNA viral load < 50 copies/mL after 48 weeks of treatment.Changes in CD4+ cell counts were also evaluated.
RAMs associated with ETV at baseline, RAMs associated with DRV, OBR, GSS, and the ETV Stanford score were analyzed for potential risk factors of virological failure.
Other evaluations were changes in fasting lipids levels (total cholesterol, triglycerides) and creatinine from baseline to 48 weeks.

Statistical analysis
Baseline characteristics were analyzed for medians and interquartile ranges (IQR) for continuous variables and proportions for categorical variables.Explorative statistical methods were used to determine the efficacy end-points and changes in safety-relevant laboratory parameters.Significant changes from baseline were tested using the Wilcoxon signed-rank test.
Baseline differences between patients who reached or did not reach viral load < 50 copies/mL at week 48 were tested in a bivariate analysis, including crude odds ratios (ORs), Fisher's exact test, and the Chi-squared test.Independent risk factors associated with virological response at week 48 were identified in a multivariate logistic regression analysis that included variables from bivariate analyses.All analyses were conducted using SPSS software version 17 (SPSS Inc, Chicago, USA).

Results
Forty-two multidrug-experienced patients who started ETV-based salvage therapy between 2009 and 2013 were identified.Forty-two patients who were followed through the 48-week analyses were included.The median age of the overall cohort at ETV initiation was 45 years (IQR 41-53), and 74% of the patients were men.Centers for Disease Control Class C AIDS was found in 50% of patients, and the median years of previous ARV treatment was six (IQR 4-7); all had prior NNRTI use (55% nevirapine, 83% efavirenz, and 28% both) (Table 1).
The most common regimens associated with ETV were DRV/r-RAL (47.6%),DRV/r-TDF (12%), and DRV/r-RAL-tenofovir disoproxil fumarate (TDF) (9.5%), with the rest at 5% or less.Thirteen (31%) of the patients who had two or more RAMs for DRV/r had < 50 copies/mL at week 48, ten had no ETV RAMS, and the other three had one ETV RAM (two with Y181C and one with L100I).
The number of baseline ETV RAMs showed by genotype and the baseline ETV GSS were not associated with virological failure.None of the NNRTI RAMs present at baseline affected the virological response to ETV (Table 4).

Discussion
Our study provides evidence for the effectiveness and safety of ETV among ARV-experienced patients in a clinical setting.Therapy with ETV regimens was associated with high levels of HIV-1 RNA viral load suppression over 48 weeks, with 90.4% in highly treatment-experienced patients with viral load < 200 copies/mL and 76% in those with < 50 copies/mL, which appears to be independent of SS of OBR.The outcome of 76% of patients with viral load < 50 copies/mL at week 48 is superior to the outcomes of some randomized clinical trials (60%) [5] but similar to an observational study of antiretroviral treatmentexperienced patients by a different PI in the OBR in which week-48 responses were 75% [10].
What was striking in this analysis was that among the subset of DUET patients who had no ETV RAMs, those with as many as three DRV RAMs, a subgroup with less response to DRV, had a high week-48 response rate of 60%, similar to the rate observed in DUET 48-week analysis [5].These data show the potency of ETV and its high genetic barrier to resistance since it was able to produce a high response rate even in patients in whom DRV/r was not a fully active agent.However, we must take into account that it is difficult to determine which of the OBR components has a greater impact when a salvage therapy is used in highly experienced patients.
Although the response rate decreased in patients who had four or more ETV or DRV RAMs, in this study, we did not find statistical significance.Existing  for DRV, it is imperative that the activity of ETV not be compromised so that the regimen does not fail [9].If both drugs had reasonable activity, even with one or two resistance mutations, the responses would be adequate.For certain patients, the combination of ETV and DRV/r plus NRTIs may be sufficient to achieve an undetectable HIV-1 RNA viral load.
Towner et al. provided data about the tolerability of ETV in a real-world setting [8].
With respect to metabolic situation, we found, in our study, an increase in total triglycerides after the new regimen was started, but not in total cholesterol.Regimens in highly experienced patients often include different combinations of ARV and the variety of combinations associated with ETV could complicate the interpretation of metabolic data.However, ETV is associated with a low rate of serious adverse events (11.6%) and a very low rate of discontinuation (1.9%) as a result of adverse events [4][5][6].These results confirm that an ETV-containing regimen is well tolerated in this difficult-to-treat population.
The response rates were high across the different regimen backgrounds; however, we must be cautious in attributing the response to ETV efficacy alone because of the absence of data on baseline resistance in patients with genotyping test without NNRTI pressure.
We found a direct association between baseline HIV-1 RNA  100,000 copies/mL and risk of failure in this small sample size, which emphasizes the importance of early ARV change.This is the first multicenter cohort in Mexico to evaluate the effectiveness of ETV in highly experienced patients.However, this study has some limitations, such as its small sample size and the use of a retrospective method to enrol patients; in addition, we could not assess adherence to antiretroviral drugs in our population.

Conclusions
In summary, this study suggests that the use of ETV-based regimens for salvage therapy is an effective strategy in the clinical care setting of a developing country.

Table 2 .
End-points after 24 and 48 weeks of treatment.
*At both 24 and 48 weeks.Blood values are statistically significant.

Table 3 .
Bivariate and multivariate analysis of risk factors associated with virological failure (HIV-1 RNA < 200 copies/mL) at week 48 of antiretroviral treatment.

Table 4 .
Bivariate and multivariate analyses of risk factors associated with virological failure (HIV-1 RNA < 50 copies/mL) at week 48 of antiretroviral treatment.