Interruption of enfuvirtide in HIV-1 infected adults with incomplete viral suppression on an enfuvirtide-based regimen

Many antiretroviral drugs continue to exert an anti-human immunodeficiency virus (HIV) benefit in the presence of drug resistance mutations. The degree to which enfuvirtide exerts continued antiviral activity in the presence of incomplete viral suppression has not been defined. To address this question, 25 subjects interrupted enfuvirtide while remaining on a stable background regimen. Enfuvirtide interruption was associated with an immediate but limited increase in plasma HIV-1 RNA levels. Enfuvirtide resistance waned rapidly in the absence of drug pressure and was no longer detectable by week 16 in most individuals. These data indicate that enfuvirtide has measurable antiviral activity in the setting of incomplete viral suppression. Although enfuvirtide resistance mutations are associated with significant fitness defects in vivo, the clinical significance of these mutations remains undefined.

Assay of HIV gp41 amino acid sequence to identify baseline variation and mutation development in patients with virologic failure on enfuvirtide

In this study, we retrospectively assessed a gp41 genotypic assay in 404 enfuvirtide-naïve individuals (340 clade B, 64 non-B clade) to determine the prevalence of baseline polymorphisms and in 41 patients virologically failing enfuvirtide to determine correlates of resistance to this agent. Conserved and polymorphic regions of gp41 were identified in clade B isolates, with 127 of 328 codons (38.7%) being highly conserved (<1.0% variation) and 74 of 328 codons (22.6%) being partially conserved (1.0-5.0% variation). Polymorphisms were observed throughout gp41 in non-B clade virus sequences compared to the clade B reference strain, ranging from 53 natural substitutions in clade D to 76 in clade A. Insertions were common at positions 3, 105, 215 and 276. In the patients failing enfuvirtide, mutations were detected in the 10 amino acid region at positions 36-45 in all plasma virus sequences. Six additional mutations were selected outside of the common region which may be clinically significant at positions 33, 73, 75, 126, and 138. Two or three mutations at positions 36-45 were observed in the majority of plasma virus sequences from patients with virologic failure following the use of enfuvirtide. Further study is required to determine the clinical relevance of the clade related polymorphisms and the new mutations identified in the patients with virologic failure.

Pharmacokinetic Bioequivalence of Enfuvirtide Using a Needle-Free Device versus Standard Needle Administration

STUDY OBJECTIVES

To compare the relative bioavailability of enfuvirtide, a human immunodeficiency virus type 1 (HIV-1) fusion inhibitor, injected with the Biojector 2000 (B2000) needle-free device versus a 27-gauge half-inch needle-syringe; and to assess safety, tolerability, and patient preference for the two devices.

DESIGN

Open-label, randomized, two-period crossover bioequivalence evaluation.

SETTING

Clinical research center.

PATIENTS

Twenty-seven adults with HIV-1 viral loads below 1000 copies/ml.

INTERVENTION

Each patient received enfuvirtide 90 mg subcutaneously with the B2000 and with the needle-syringe, with a 1-week washout between treatments.

MEASUREMENTS AND MAIN RESULTS

Twenty-six and 27 patients were included in the bioequivalence and safety analyses, respectively. Plasma enfuvirtide concentrations were measured at baseline and at several intervals after each injection. The B2000:needle-syringe ratios of maximum concentration (C(max)), area under the concentration-time curve from time zero extrapolated to infinity (AUC(0-infinity)), and AUC from time zero to tau (dosing interval) (AUC(0-tau)) served as criteria for bioequivalence determination. The two drug delivery systems were considered bioequivalent if the 90% confidence intervals (CIs) for the ratios were within 0.8-1.25. Safety and tolerability were evaluated based on documentation of adverse events, graded laboratory toxicities, and local injection-site reactions. Patient surveys provided feedback on device preference. Ratios of C(max), AUC(0-infinity), and AUC(0-tau) were 0.95 (90% CI 0.84-1.09), 0.99 (90% CI 0.93-1.05), and 0.99 (90% CI 0.93-1.05), respectively. The frequency of injection-site reactions was low, and severity was generally mild for both devices. Survey results showed 18 patients (69%) had a positive overall impression of the B2000 and 14 (54%) felt safer injecting with this device. Overall, 17 patients (65%) preferred the B2000 over the needle-syringe.

CONCLUSION

Bioavailability of enfuvirtide with the B2000 and needle-syringe was equivalent based on C(max), AUC(0-tau), and AUC(0-infinity). Safety profiles and injection-site reactions were comparable between the devices, but patients preferred the B2000. Delivery of enfuvirtide with the B2000 is a feasible alternative to standard needle administration and warrants further evaluation.

The Lifetime Cost of Current Human Immunodeficiency Virus Care in the United States

OBJECTIVE

We sought to project the lifetime cost of medical care for human immunodefiency virus (HIV)-infected adults using current antiretroviral therapy (ART) standards.

METHODS

Medical visits and hospitalizations for any reason were from the HIV Research Network, a consortium of high-volume HIV primary care sites. HIV treatment drug regimen efficacies were from clinical guidelines and published sources; data on other drugs used were not available. In a computer simulation model, we projected HIV medical care costs in 2004 U.S. dollars.

RESULTS

From the time of entering HIV care, per person projected life expectancy is 24.2 years, discounted lifetime cost is Dollars 385,200, and undiscounted cost is Dollars 618,900 for adults who initiate ART with CD4 cell count < 350/microL. Seventy-three percent of the cost is antiretroviral medications, 13% inpatient care, 9% outpatient care, and 5% other HIV-related medications and laboratory costs. For patients who initiate ART with CD4 cell count < 200/microL, projected life expectancy is 22.5 years, discounted lifetime cost is Dollars 354,100 and undiscounted cost is Dollars 567,000. Results are sensitive to drug manufacturers' discounts, ART efficacy, and use of enfuvirtide for salvage. If costs are discounted to the time of infection, the discounted lifetime cost is Dollars 303,100.

CONCLUSIONS

Effective ART regimens have substantially improved survival and have increased the lifetime cost of HIV-related medical care in the U.S.

Performance of human immunodeficiency virus type 1 gp41 assays for detecting enfuvirtide (T-20) resistance mutations

The performance of a gp41 assay, created using reagents designed for use with the OpenGene DNA Sequencing System, was evaluated using a panel of plasma samples obtained from enfuvirtide-naive and -experienced human immunodeficiency virus type 1-infected subjects. Resulting sequence data were highly accurate compared to a "home brew" assay and clonal sequence analysis.

Rapid emergence of enfuvirtide resistance in HIV-1-infected patients: results of a clonal analysis

OBJECTIVES

To study the dynamics of enfuvirtide (T-20) resistance development in HIV-1-infected subjects.

PATIENTS AND METHODS

Clonal analysis of gp41 sequences was performed on serial samples obtained from HIV-1-infected subjects with early virologic failure of T-20-based regimens.

RESULTS

Enfuvirtide resistance mutations at codons 36 to 45 in the first heptad repeat of gp41 emerged within 2 weeks in most subjects and were associated with the return of plasma HIV-1 RNA level toward baseline by weeks 4 to 8. Mutations at codons 36 (G36E, G36D, or G36S) and 38 (V38A, V38G, or V38M) were the most commonly detected resistance mutations at week 2. Mutations at codons 40 (Q40H) and 43 (N43D) were more prevalent at week 4 than at week 2 and seemed to emerge more slowly than mutations at codons 36 and 38.

CONCLUSIONS

The rapid emergence of mutations associated with T-20 resistance in the absence of a fully suppressive antiretroviral regimen demonstrates a low genetic barrier to resistance and underscores the importance of combining T-20 with other active drugs when constructing regimens for highly treatment-experienced patients.

Genetic evolution of gp41 reveals a highly exclusive relationship between codons 36, 38 and 43 in gp41 under long-term enfuvirtide-containing salvage regimen

OBJECTIVE

To analyse the genetic changes in the gp41 protein in HIV-infected patients with detectable plasma viraemia receiving a long-term salvage enfuvirtide regimen.

METHODS

We studied 13 heavily antiretroviral-experienced patients receiving a salvage regimen containing enfuvirtide. Substitutions in gp41 were analysed by population-based sequencing at baseline and longitudinally after the initiation of enfuvirtide treatment. To investigate sequence evolution we also analysed multiple gp41 clones from four selected patients. A Fisher's two-tailed test was used to assess the distribution of resistance-associated mutations in the clonal sequences.

RESULTS

Mutations at positions 36 and 38 in gp41 (HR1) emerged rapidly (median emerging time 10 weeks), but disappeared at subsequent timepoints in most of the patients. Amino acid changes did not accumulate over time, with no patient having more than two mutations in HR1 after 6 months of treatment. The mutation N43D was not observed together with changes at positions 36 or 38 in any patient. Clonal analysis showed that the three main gp41 resistance mutations were highly mutually exclusive (P < 0.001), being present in individual clones and constituting independent populations.

CONCLUSION

Substitutions at positions 36 and 38 are rapidly selected but disappear thereafter in HIV-1-infected patients failing an enfuvirtide-containing salvage therapy. We found a highly exclusive relationship between the three main enfuvirtide resistance-associated mutations (amino acids 36, 38 and 43), suggesting that the genetic evolution of HIV-1 gp41 protein is a dynamic and much more complex process than previously though.

Unexpected drug-drug interaction between tipranavir/ritonavir and enfuvirtide

Fifty-five patients placed on tipranavir/ritonavir 500/200 mg twice a day (27 with enfuvirtide and 28 without) underwent tipranavir and ritonavir plasma concentration measurements by high-pressure liquid chromatography. Markedly higher tipranavir and ritonavir trough concentrations were observed in enfuvirtide recipients. The modelling of sparse plasma samples using a first order absorption and elimination monocompartmental model without time lag predicted higher tipranavir elimination half-life and volume of distribution in enfuvirtide takers. This unexpected drug-drug interaction warrants further investigation.

Selective increase in serum IgE following enfuvirtide administration in HIV-1 infected multidrug resistant patients

Enfuvirtide (ENF) is the first HIV-1 entry inhibitor used in clinical practice and is currently administered via the subcutaneous route. We here evaluated whether ENF administration leads to a change in humoral parameters, including IgE, possibly related to ENF-associated injection site reactions (ISRs). A 24-week prospective study was conducted in multidrug resistant patients enrolled in the ENF Early Access Program characterized by CD4 counts < or =100 cells/microlitre and no other active antiretroviral drug. Licensed commercial laboratory assays were used to measure the parameters considered in this study. Results are reported as medians (interquartiles IQR). Statistical analyses were performed using Wilcoxon sign rank, Wilcoxon rank sum and Kruskall Wallis tests. Total IgM, IgA and IgG did not change significantly throughout the study. Conversely, a significant increase in IgE was observed in all patients, in those with normal as well as in those with altered IgE at baseline (BL). ISRs such as induration and number of nodules were more frequent in patients with altered BL IgE. IgE increased significantly in all patients, regardless of the different stratifications in their BL CD4 counts. Of note, the ENF-induced increase in CD4 occurred significantly in all patients, independently of their BL IgE levels. The immunological response associated with ENF treatment is accompanied by a selective increase in IgE levels. Determination of IgE could be used in the monitoring ISRs associated with ENE

Viral failure in HIV-infected patients with long-lasting viral suppression who discontinued enfuvirtide

The aim of this pilot study was to assess whether enfuvirtide can be discontinued in patients on long-term viral suppression. Eight patients with multidrug-resistant virus were randomly assigned to stop and 10 subjects to continue enfuvirtide. At week 48, viral rebound occurred in five (62.5%) and in no patients, respectively, (P = 0.007). The CD4 cell decrease in failure patients was 5% (P = ns). These results suggest that enfuvirtide should be maintained until new active drugs became available.

Human immunodeficiency virus (HIV) entry inhibitors (CCR5 specific blockers) in development: are they the next novel therapies?

Since the introduction of the nucleoside reverse transcriptase inhibitor zidovudine in 1987, the number of the available antiretroviral medications has grown to about 20. Despite the efficacy of these medications, treatment-limiting adverse events are frequent. During the last several years, a new class of antiretroviral drugs often referred to as entry inhibitors, specifically the CCR5 blockers, have moved from the basic science laboratories and are now in the clinical phases of drug development. There are three agents in phase 2/3 development that inhibit viral entry by binding to CCR5, disrupting the interaction between the co-receptor and viral glycoprotein (gp) 120. They are aplaviroc (GW-873140), maraviroc (UK-427,857), and vicriviroc (SCH 417690). The development of these new antiviral agents that target different aspects of the viral life cycle is likely to make it possible to suppress viral strains that are resistant to the currently available antiretroviral drugs. There is a growing need for a new class of antiretrovirals with reduced toxicity and improved tolerability. However, currently available information suggests further pharmacokinetics, resistance, safety, and efficacy data are needed to understand how these agents may be effectively used in the clinical setting.

Current status of antiretroviral therapy

At present, there are 22 FDA-approved antiretroviral agents, which are categorised into four classes of drugs. Several others are in various stages of basic and clinical development. The authors of this paper review the general characteristics of each class of antiretrovirals, as well as individual investigational agents that are in advanced clinical development. A brief synopsis of US and WHO antiretroviral treatment guidelines is also provided.

Biology of CCR5 and its role in HIV infection and treatment

Chemokine receptors are found on cell surfaces and promote cellular migration by chemotaxis. The CC chemokine receptor 5 (CCR5) is used by the human immunodeficiency virus (HIV) to infect cells. Strategies that target human CCR5 are therefore being developed to prevent and treat HIV infection. Antiviral strategies that target a host element necessary for viral replication may be predicted to interfere with the function of that element and may therefore adversely affect the host. We conducted a review of the literature between November 2005 and April 2006 with a focus on articles addressing the genetics and function of CCR5, the effects of CCR5 deletion in human and murine systems, and treatment strategies for HIV infection that target this coreceptor. English-language articles in the human and murine literature published between March 1996 and April 2006 were identified through a search of MEDLINE using CCR5 as the search term. Relevant articles as judged by their titles and abstracts were reviewed in detail. In addition, based on our knowledge of the field and with permission, unpublished work was also reviewed. In this article, we explore the effects that targeting CCR5 may have on host defenses in individuals with immunity already compromised by HIV infection.

Durable efficacy of tipranavir-ritonavir in combination with an optimised background regimen of antiretroviral drugs for treatment-experienced HIV-1-infected patients at 48 weeks in the Randomized Evaluation of Strategic Intervention in multi-drug reSistant patients with Tipranavir (RESIST) studies: an analysis of combined data from two randomised open-label trials

BACKGROUND

Treatment options for HIV-1 infected individuals who have received extensive previous antiretroviral therapy are limited. We compared efficacy and safety of the novel non-peptidic protease inhibitor tipranavir co-administered with ritonavir plus an optimised background regimen with that of an investigator-selected ritonavir-boosted comparator protease inhibitor (CPI-ritonavir) in such patients.

METHODS

We did a combined analysis of 48-week data from two ongoing, randomised, open-label, multinational, phase III, RESIST studies. HIV-1-infected adults with 3 months or longer previous triple antiretroviral class experience, two or more previous protease inhibitor regimens, HIV-1 RNA 1000 copies per mL or greater, and genotypically demonstrated primary resistance to protease inhibitor, were eligible. Primary endpoints were proportion of treatment responders (with reduction in viral load of 1 log(10) copies per mL or greater below baseline without treatment change) at 48 weeks and time to treatment failure through 48 weeks (intention-to-treat analysis). The RESIST studies are registered with ClinicalTrials.gov, numbers NCT00054717 (RESIST-1) and NCT00144170 (RESIST-2).

FINDINGS

3324 patients were screened; 746 received tipranavir-ritonavir and 737 CPI-ritonavir. 486 (65.1%) patients on tipranavir-ritonavir and 192 (26.1%) on CPI-ritonavir remained on assigned treatment until week 48. At week 48, more patients achieved and maintained treatment response in the tipranavir-ritonavir group than in the CPI-ritonavir group (251 [33.6%] vs 113 [15.3%]; p<0.0001). Median time to treatment failure was significantly longer in the tipranavir-ritonavir group than in the CPI-ritonavir group (113 days vs 0 days; p<0.0001). Gastrointestinal system disorders and raised transaminase, cholesterol, and triglycerides were more frequent in the tipranavir-ritonavir group than in the CPI-ritonavir group.

INTERPRETATION

Compared with CPI-ritonavir, tipranavir-ritonavir with an optimised background regimen provides better virological and immunological responses over 48 weeks in patients who have received extensive previous antiretroviral treatment.

Specific mutations in HIV-1 gp41 are associated with immunological success in HIV-1-infected patients receiving enfuvirtide treatment

OBJECTIVES

To investigate gp41 variability and correlation with viro-immunological parameters in 54 HIV-1-infected patients receiving enfuvirtide added as single active drug to a failing regimen.

METHODS

One hundred and two HIV-1 gp41 sequences and clinical follow-up from 54 enfuvirtide-treated patients were analysed from baseline to week 36 of treatment. The association of mutations with viraemia/CD4 count was assessed by Mann-Whitney test.

RESULTS

The addition of enfuvirtide to the failing regimen induced at week 4 a viraemia decrease from 5.1 to 4.3 log(10)/mL (P = 0.0002) and a CD4 increase from 48 to 106 cells/mm(3) (P = 0.008). While viraemia rebounded to 4.8 and 4.6 log(10)/mL at week 12 and 36, respectively, CD4 continued to increase to 136 cells/mm(3) at week 36. Enfuvirtide resistance mutations, rarely found at baseline, occurred in 45/54 (83.3%) enfuvirtide-treated patients. V38A/E were the most represented mutations at all time-points. The presence of V38A/E was significantly associated with a 4.5-fold CD4 increase from baseline to week 24 and with a 6-fold increase at week 36 (P = 0.004 and 0.02 compared without V38A/E, respectively), without significant correlation with viraemia. In contrast, Q40H + L45M (present in six enfuvirtide-treated patients at week 36) correlated with CD4 loss from baseline to week 36 (P = 0.02), without significant correlation with viraemia. Mutation N126K (observed in six enfuvirtide-treated patients, never found at baseline) abrogates the fourth gp41 glycosylation site and correlates with a 2.1-fold CD4 increase at week 24.

CONCLUSIONS

Specific enfuvirtide resistance mutations (V38A/E) are associated with a sustained CD4 increase, without remarkable effects upon viraemia. This CD4 recovery, due to virus- and immune-mediated mechanisms most probably not applicable to protease/reverse transcriptase inhibitors, is important for innovative therapeutic strategies.

Cellular entry of HIV: Evaluation of therapeutic targets

In the absence of a vaccine which could stop the HIV/AIDS pandemic, the development of therapeutic options is of utmost interest. The combined use of inhibitors of reverse transcriptase and protease as highly active antiretroviral therapy (HAART) provided the first effective treatment of HIV/AIDS and significantly decreased the number of AIDS related deaths in industrialized countries. However, the emergence of resistant viruses and the toxic side effects of HAART highlights that novel therapies are urgently required. The inhibition of HIV-1 entry is a promising option. Entry of HIV-1 into target cells involves interactions of the viral envelope protein (Env) with CD4 and a coreceptor, usually CCR5 or CXCR4. Env binding to receptor triggers several conformational rearrangements in Env, which involve the creation and/or exposure of structural intermediates pivotal to fusion of the viral and cellular membranes. Both, cellular receptors and structures in Env associated with membrane fusion are targets for therapeutic intervention. Here, we will discuss how HIV-1 enters cells and introduce strategies how this process can be inhibited.

Genotypic changes in human immunodeficiency virus type 1 envelope glycoproteins on treatment with the fusion inhibitor enfuvirtide and their influence on changes in drug susceptibility in vitro

BACKGROUND

Previous studies have established the importance of substitutions at amino acids 36-45 of HIV-1 gp41 in the development of viral resistance to the peptide fusion inhibitor enfuvirtide. However, the influence of other loci in the HIV-1 envelope is not well established.

OBJECTIVE

To identify positions showing genotypic changes that are associated with particularly high levels of changes in enfuvirtide susceptibility.

STUDY DESIGN

We examined full-length baseline and on treatment sequences of gp120 and gp41 for isolates from 369 patients in Phase III studies of enfuvirtide, including 281 patients receiving ENF+OB and 88 patients receiving OB alone. Individual changes in gp41 and gp120 were evaluated for correlations with on treatment phenotype changes by analysis of variance (ANOVA). This modeling was done with (two-way) and without (one-way) ANOVA adjusting for the effects of any changes in gp41 amino acids 36-45 modeled as a single variable (ANY(36-45)). Positions displaying significance levels of p<0.05 by either one- or two-way ANOVA were then studied by multi-way ANOVA (stepwise regression).

RESULTS

In addition to changes at gp41 amino acids 36-45, changes at three positions in the HR2 domain (126, 129 and 133) occurred significantly more often in patients undergoing virologic failure on enfuvirtide. However, ANY(36-45) alone accounted for slightly more than 90% of the variation in phenotype explained by the ANOVA models. Relative to ANY(36-45) alone, significant increases in the geometric mean of the fold-change in inhibitory concentration (19.6-236.3-fold higher) were observed for amino acid changes at positions gp41: 18, 42,126, 247, 256 and 312; gp120: 330, 389 and 424 and significant reductions (18.8-29.7-fold lower) for gp41: 3, 46, 165, 232 and 324.

CONCLUSIONS

This study represents a statistical approach to highlight positions in HIV envelope that undergo mutations in the presence of enfuvirtide. Several of the identified positions have been implicated in the viral fusion process by other studies. The specific impact of positions 330. Three hundred and eighty-nine and 424 on viral fusion kinetics remains to be studied further by site-directed mutagenesis experiments.

Antiretroviral therapy 2006: Pharmacology, applications, and special situations

As we approach the completion of the first 25 years of the human immunodeficiency virus (HIV) epidemic, there have been dramatic improvements in the care of patients with HIV infection. These have prolonged life and decreased morbidity. There are twenty currently available antiretrovirals approved in the United States for the treatment of this infection. The medications, including their pharmacokinetic properties, side effects, and dosing are reviewed. In addition, the current approach to the use of these medicines is discussed. We have included a section addressing common comorbid conditions including hepatitis B and C along with tuberculosis.

Anti-HIV Therapy: Current and Future Directions

Although combinations of drugs that target the HIV reverse transcriptase and protease enzymes have clearly revolutionized the treatment of HIV/AIDS, problems with these agents, such as viral escape mutants, persistence of viral reservoirs, poor patient compliance due to complicated regimens, and toxic side effects, have emphasized the need for development of new drugs with novel mechanisms of action, as well as an HIV vaccine. Recently two new classes of drugs have been identified that interfere with the membrane fusion reaction required for HIV entry of target cells. Two such agents, T-20 (enfuvirtide) and T-1249, which have been approved by the Food and Drug Administration (FDA), block the action of the fusogenic envelope glycoprotein gp41. Others target the HIV coreceptors CCR5 and CXCR4, and are now in clinical trials. Also under development are novel agents that target the HIV integrase and HIV regulatory gene products as well as immunomodulators such as IL-12 and IL-2. This article will focus on these and other novel approaches to HIV therapeutics.