Primary genotypic resistance of HIV-1 to the fusion inhibitor T-20 in long-term infected patients

Broad-spectrum anti-HIV activity and high drug resistance barrier of lipopeptide HIV fusion inhibitor LP-19

Lipopeptide-19, a HIV fusion inhibitor (LP-19), has showed potent anti-HIV activity. However, there is still limited information of the antiviral activity against different subtype clinical isolates and the drug resistance barrier of LP-19. Therefore, 47 HIV clinical isolates were selected for this study. The viral features were identified, in which 43 strains are CCR5 tropisms, and 4 strains are CCR5/CXCR4 tropisms, and there are 6 subtype B', 15 CRF01_AE, 14 CRF07_BC, 2 CRF08_BC and 10 URF strains. These 47 viruses were used to detected and analyze the inhibitory activities of LP-19. The results showed that the average 50% inhibitory concentration (IC₅₀) and 90% inhibitory concentration (IC₉₀) of LP-19 were 0.50 nM and 1.88 nM, respectively. The average IC₅₀ of LP-19 to B', CRF01_AE, CRF07_BC, CRF08_BC, and URF strains was 0.76 nM, 0.29 nM, 0.38 nM, 0.85 nM, and 0.44 nM, respectively. C34 and Enfuvirtide (T-20), two fusion inhibitors, were compared on the corresponding strains simultaneously. The antiviral activity of LP-19 was 16.7-fold and 86-fold higher than that of C34 and T-20. The antiviral activity of LP-19, C34, and T-20 were further detected and showed IC₅₀ was 0.15 nM, 1.02 nM, and 66.19 nM, respectively. IC₅₀ of LP-19 was about 7-fold and 441-fold higher compared to C34 and T-20 against HIV-1 NL4-3 strains. NL4-3 strains were exposed to increasing concentrations of LP-19 and C34 in MT-2 cell culture. The culture virus was sequenced and analyzed. The results showed that A243V mutation site identified at weeks 28, 32, 38, and 39 of the cell culture in the gp41 CP (cytoplasmic domain) region. NL4-3/A243V viruses containing A243V mutation were constructed. Comparing the antiviral activities of LP-19 against HIV NL4-3 to HIV strains (only 1.3-fold), HIV did not show drug resistance when LP-19 reached 512-fold of the initial concentration under the drug pressure for 39 weeks. This study suggests that LP-19 has broad-spectrum anti-HIV activity, and high drug resistance barrier.

Functional characteristics of the natural polymorphisms of HIV-1 gp41 in HIV-1 isolates from enfuvirtide-naïve Korean patients

HIV-1 gp41 plays a key role in viral entry. The insertion of Thr at position 4 and Met/Val/Phe substitutions at position 7 are frequently observed in the fusion peptide (FP) motif of gp41 without major enfuvirtide resistance associated with mutation in heptad repeats 1/2 (HR1/2) of HIV-1 isolates from Korean patients. Here, the influence of these mutations on their biological function was evaluated by employing HIV-1 variants with mutant FPs as shown previously and with recombinant HIV-1 using the env genes of 20 HIV-1 isolates from Korean patients. In an infectivity assay, all FP mutants showed lower infectivity than the wild-type NL4-3. In particular, the substitutions at position 7 led to much greater reductions in infectivity than the insertions at position 4. Nevertheless, the replication kinetics of most mutants were similar to those of the wild type, except that the FP mutants with an Ile insertion at position 4 and a Phe substitution at position 7 showed reduced replication. Moreover, most point mutants showed lower IC50 values for enfuvirtide than the wild type, whereas the L7M substitution resulted in a slightly increased IC50 value. The infectivity using the HIV-1 env recombinant viruses decreased in 14 cases but increased slightly in six cases compared with the wild type. Most recombinants were more susceptible to enfuvirtide than the wild type, except for three recombinants that showed slight resistance. Our findings may help to explain the potential mechanisms corresponding to the natural polymorphism of gp41 and to predict the efficiency of enfuvirtide in treatment of HIV-1-infected patients in Korea.

Enfuvirtide: Antiretroviral Class 4, Drug 1

With the licensing of enfuvirtide, physicians prescribing antiretroviral medications now have available the first of a new class of drugs, the fusion inhibitors. In this article, enfuvirtide is discussed with particular emphasis on the clinical trials that led to the drug's licensing. The possible placement of enfuvirtide in the sequence of treatment is also discussed.

Escape from human immunodeficiency virus type 1 (HIV-1) entry inhibitors

The human immunodeficiency virus (HIV) enters cells through a series of molecular interactions between the HIV envelope protein and cellular receptors, thus providing many opportunities to block infection. Entry inhibitors are currently being used in the clinic, and many more are under development. Unfortunately, as is the case for other classes of antiretroviral drugs that target later steps in the viral life cycle, HIV can become resistant to entry inhibitors. In contrast to inhibitors that block viral enzymes in intracellular compartments, entry inhibitors interfere with the function of the highly variable envelope glycoprotein as it continuously adapts to changing immune pressure and available target cells in the extracellular environment. Consequently, pathways and mechanisms of resistance for entry inhibitors are varied and often involve mutations across the envelope gene. This review provides a broad overview of entry inhibitor resistance mechanisms that inform our understanding of HIV entry and the design of new inhibitors and vaccines.

Mutation L33M in the HR1 region of HIV-1 gp41 may play a role in T20 resistance

BACKGROUND

Although Enfuvirtide (T20) has not been used in China, investigating the natural occurrence of primary resistance mutations in the HR1 region of the gp41 sequence from T20 naïve patients would help in determining treatment strategies for AIDS patients.

OBJECTIVES

To investigate natural mutations in the HR1 region of the gp41 sequence in China and evaluate their biological function.

STUDY DESIGN

The amino acid sequences in the HR1 region of 27 isolates including subtypes AE, BC and B' from Chinese T20 naïve patients were analyzed. All 27 isolates were constructed into pseudoviruses and their susceptibility to T20 was measured by using recombinant virus assays.

RESULTS

Mutations in a 10 amino acid motif, such as N42S and N42R, and those outside this motif, such as L33M, R46S, A50V, Q52H and L54M, were found in the 27 isolates. N in position 42 was mutated to S in all three AE subtype strains and 17 of 18 subtype BC strains, whilst it was mutated to R in all 6 subtypes B strains. Compared to the SF162 strain, the susceptibility of the mutants, except for L33M, to T20 was not significantly different. After L was mutated to M in position 33 of six strains by site directed mutagenesis, their IC50 values were increased by 3.7-7.9-fold.

CONCLUSIONS

Mutations outside a 10 amino acid motif in HR1, such as L33M, may cause T20 resistance.

SC29EK, a peptide fusion inhibitor with enhanced alpha-helicity, inhibits replication of human immunodeficiency virus type 1 mutants resistant to enfuvirtide

Peptides derived from the alpha-helical domains of human immunodeficiency virus (HIV) type 1 (HIV-1) gp41 inhibit HIV-1 fusion to the cell membrane. Enfuvirtide (T-20) is a peptide-based drug that targets the step of HIV fusion, and as such, it effectively suppresses the replication of HIV-1 strains that are either wild type or resistant to multiple reverse transcriptase and/or protease inhibitors. However, HIV-1 variants with T-20 resistance have emerged; therefore, the development of new and potent inhibitors is urgently needed. We have developed a novel HIV fusion inhibitor, SC34EK, which is a gp41-derived 34-amino-acid peptide with glutamate (E) and lysine (K) substitutions on its solvent-accessible site that stabilize its alpha-helicity. Importantly, SC34EK effectively inhibits the replication of T-20-resistant HIV-1 strains as well as wild-type HIV-1. In this report, we introduce SC29EK, a 29-amino-acid peptide that is a shorter variant of SC34EK. SC29EK blocked the replication of T-20-resistant HIV-1 strains and maintained antiviral activity even in the presence of high serum concentrations (up to 50%). Circular dichroism analysis revealed that the alpha-helicity of SC29EK was well maintained, while that of the parental peptide, C29, which showed moderate and reduced inhibition of wild-type and T-20-resistant HIV-1 strains, was lower. Our results show that the alpha-helicity in a peptide-based fusion inhibitor is a key factor for activity and enables the design of short peptide inhibitors with improved pharmacological properties.

Selection of T1249-resistant human immunodeficiency virus type 1 variants

Human immunodeficiency virus type 1 (HIV-1) entry is an attractive target for therapeutic intervention. Two drugs that inhibit this process have been approved: the fusion inhibitor T20 (enfuvirtide [Fuzeon]) and, more recently, the CCR5 blocker maraviroc (Selzentry). T1249 is a second-generation fusion inhibitor with improved antiviral potency compared to the first-generation peptide T20. We selected T1249-resistant HIV-1 variants in vitro by serial virus passage in the presence of increasing T1249 doses after passage with wild-type and T20-resistant variants. Sequence analysis revealed the acquisition of substitutions within the HR1 region of the gp41 ectodomain. The virus acquired mutations of residue V38 to either E or R in 10 of 19 cultures. Both E and R at position 38 were confirmed to cause resistance to T1249, as well as cross-resistance to T20 and C34, but not to the third-generation fusion inhibitor T2635. We also observed substitutions at residues 79 and 90 (Q79E and K90E), which provide modest resistance to T1249 and, interestingly, T2635. Thus, the gp41 amino acid position implicated in T20 resistance (V38 replaced by A, G, or W) is also responsible for T1249 resistance (V38 replaced by E, R, or K). These results indicate that T20 and T1249 exhibit very similar inhibition modes that call for similar but not identical resistance mutations. All T1249-resistant viruses with changes at position 38 are cross resistant to T20, but not vice versa. Furthermore, substitutions at position 38 do not provide resistance to the third-generation inhibitor T2635, while substitution at positions 79 and 90 do, suggesting different resistance mechanisms.

HIV-1 drug-resistance and drug-dependence

In this review, we will describe several recent HIV-1 studies in which a drug-dependent virus variant was selected. A common evolutionary route to the drug-dependence phenotype is proposed. First, the selection of a drug-resistance mutation that also affects the function of the targeted viral protein. Second, a compensatory mutation that repairs the protein function, but in the presence of the drug, which becomes an intrinsic part of the mechanism. The clinical relevance of drug-dependent HIV-1 variants is also discussed.

Transmembrane protein polymorphisms and resistance to T-20 (Enfuvirtide, Fuzeon®) in HIV-1 infected therapy-naive seroconverters and AIDS patients under HAART-T-20 therapy

The human immunodeficiency virus type 1 fusion inhibitor T-20 (Enfuvirtide, Fuzeon) has recently been introduced into clinical practice. T-20 in combination with HAART efficiently inhibits HIV-1 replication, however T-20 resistance has been reported and the number of confirmed resistant-associated mutations is growing. In this study we aimed to analyze HIV-1 gp41 transmembrane protein (TM) variability and primary resistance to T-20 in plasma viruses from 10 HIV-1 subtype B infected homosexuals. Nine out of ten were documented seroconverters. Nine individuals (including one long time infected therapy naïve individual) were part of four linked virus infection chains. We also examined TM polymorphism in two AIDS patients under HAART and T-20 therapy. Obtained TM amplicons were examined for minor variants by clonal analysis.Sequences polymorphism of the N-terminal regions of the fusion domain (FD) and the heptad repeat 2 (HR2) domain were demonstrated in examined seroconverters. Analysis of the heptad repeat 1 (HR1) domain revealed T-20 resistance in cloned sequences from 3/10 individuals. In two individuals these mutations were present as minor viral quasispecies. Transmission of the resistant virus to the sexual partner was traced in virus infection chain.Baseline TM amplicons (population sequence) and clones from two patients under HAART did not contain T-20 resistance associated mutations. After onset of T-20 therapy only resistant viruses were identified in plasma from the patients. As shown by clonal analysis of plasma from one patient, treatment interruption results in viruses reverting to a T-20-sensitive genotype.

Recomendaciones españolas sobre el uso adecuado de enfuvirtida

Enfuvirtide is a high-cost, parenterally administered drug commonly used in late phases of HIV infection, when its efficacy may be compromised. To optimize enfuvirtide use, consensus recommendations for this purpose have been formulated by 247 physicians attending patients with HIV infection in Spain. A literature review was performed in which grades of evidence and recommendations were defined according to the origin of the data (randomized clinical trials, non-randomized studies, expert opinion). Twenty-eight local consensus meetings were held between May and September 2005 to discuss the most important aspects related to the use of enfuvirtide, following a pre-established system used in all the meetings. The main conclusions were as follows: a) enfuvirtide use is often excessively delayed and is given to patients with little chance of treatment success; b) enfuvirtide is indicated in patients who require antiretroviral treatment and for whom an optimum treatment with three other fully effective drugs cannot be designed; c) the most important prognostic factor is the availability of at least one other completely active drug; d) there is no infallible method to avoid the development of local reactions, but measures are available to decrease their incidence and severity; and e) patient counseling and training for correct administration of the drug are essential to improve adherence, the repercussions of local reactions and, of course, the efficacy of the treatment.

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.

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.

Natural resistance-associated mutations to Enfuvirtide (T20) and polymorphisms in the gp41 region of different HIV-1 genetic forms from T20 naive patients

BACKGROUND

The natural occurrence of primary resistance mutations in reverse transcriptase (RT) and protease (PR) genes of HIV-1 isolates from untreated patients has been reported and it may have important implications for the response to drug treatment. It is predictable that the same occurs in the HR1 region of gp41 sequence from patients who have never received T20 therapy, and in this regard it would be important to know not only the mutation frequencies at HR1 region but also the natural polymorphisms at resistance-associated positions present in the absence of this drug.

OBJECTIVES

The objectives of this study are to investigate the existence of natural resistance-associated mutations to T20 in HR1 gp41 region corresponding to different HIV-1 genetic forms from T20 naive patients and to determine their prevalence.

STUDY DESIGN

Two hundred HIV-1 gp41 sequences were included: subtype B: 164 (81.3%); subtype A: 15 (8.2%); subtype G: 10 (4.6%); subtype F: 6 (3.5%); subtype C: 3 (1.8%); subtype K: 1 (0.6%); and subtype D: 1 (0.6%). We analyzed the resistance-associated mutations previously described: Q32H/R, G36D/S, I37V, V38A/M, Q39R/H, Q40H, N42T/D/Q/H, N43D/S/K/Q, L44M, L45M, R46M and V69I.

RESULTS

Natural resistance mutations to T20 were found at a high frequency: 10.5%, corresponding to 9.1% in subtype B and 16.7% in non-B subtype samples. Polymorphisms were more frequent in non-B and recombinant forms than in subtype B (p<0.001). Different substitutions were related to subtypes: N42S in subtypes A, B, G and C, but not in F, Q56R in subtype A from CRF02_AG, and L54M in subtype B from CRF14_BG.

CONCLUSIONS

To our knowledge this is the first study describing natural-resistance to T20 among different HIV-1 subtypes, warranting a study of the biological significance of this mutations and their clinical relevance. The detection of differences between subtypes may have an influence on the rate and patterns of resistance in patients undergoing T20 treatment.

Effect of naturally-occurring gp41 HR1 variations on susceptibility of HIV-1 to fusion inhibitors

BACKGROUND

Sequence variations in the gp41 heptad repeat 1 (HR1) region have been identified in some treatment-naive HIV-1-infected patients but it remained elusive whether they confer resistance to fusion inhibitors.

OBJECTIVE

To evaluate whether naturally occurring sequence variations in the HIV-1 group M gp41 HR1 region affect the sensitivity to inhibition by T-20 and T-1249.

METHODS

Site-directed mutagenesis was used to generate HIV-1 NL4-3 mutants containing changes in the gp41 HR1 domain which have been previously identified in treatment-naive patients infected with various HIV-1 group M subtypes. HIV-1 variants were produced by transient transfection of 293T cells and used to determine viral infectivity and sensitivity to the fusion inhibitors T-20 and T-1249.

RESULTS

Most naturally occurring sequence variations in the HR1 domain did not reduce viral infectivity. Three of the 10 HIV-1 variants analysed containing a single substitution of L33V, which is frequently present in subtype D isolates, or combined changes of L54M/Q56K or L34M/L54M/Q56R showed about fivefold reduced sensitivity to inhibition by T-20. In comparison, none of these HR1 sequence variations conferred resistance to T-1249.

CONCLUSION

Some naturally occurring sequence variations in the gp41 HR1 region reduce sensitivity of HIV-1 to inhibition by T-20 but not T-1249.

The appealing story of HIV entry inhibitors : from discovery of biological mechanisms to drug development

Current therapeutic intervention in HIV infection relies upon 20 different drugs. Despite the impressive efficacy shown by these drugs, we are confronted with an unexpected frequency of adverse effects, such as mitochondrial toxicity and lipodystrophy, and resistance, not only to individual drugs but to entire drug classes.Thus, there is now a great need for new antiretroviral drugs with reduced toxicity, increased activity against drug-resistant viruses and a greater capacity to reach tissue sanctuaries of the virus. Two different HIV molecules have been selected as targets of drug inhibition so far: reverse transcriptase and protease. Drugs that target the interactions between the HIV envelope and the cellular receptor complex are a 'new entry' into the scenario of HIV therapy and have recently raised great interest because of their activity against multidrug-resistant viruses. There are several compounds that are at different developmental stages in the pipeline to counter HIV entry, among them: (i) the attachment inhibitor dextrin-2-sulfate; (ii) the inhibitors of the glycoprotein (gp) 120/CD4 interaction PRO 542, TNX 355 and BMS 488043; (iii) the co-receptor inhibitors subdivided in those targeting CCR5 (SCH 417690 [SCH D], UK 427857 GW 873140, PRO 140, TAK 220, AMD 887) and those targeting CXCR4 (AMD 070, KRH 2731); and (iv) the fusion inhibitors enfuvirtide (T-20) and tifuvirtide (T-1249). The story of the first of these drugs, enfuvirtide, which has successfully completed phase III clinical trials, has been approved by the US FDA and by the European Medicines Agency, and is now commercially available worldwide, is an example of how the knowledge of basic molecular mechanisms can rapidly translate into the development of clinically effective molecules.

Emergence and evolution of enfuvirtide resistance following long-term therapy involves heptad repeat 2 mutations within gp41

The objective of this study was to track the evolution of sequence changes in both the heptad region 1 (HR1) and HR2 domains of gp41 associated with resistance to enfuvirtide (ENF) in a patient cohort receiving long-term ENF treatment. We studied 17 highly antiretroviral agent-experienced patients receiving long-term ENF treatment with virological rebound or a lack of suppression. Sixty-two samples obtained after between 5 and 107 weeks of ENF therapy were analyzed. Baseline samples from 15 of these 17 patients were available for analysis. Viruses from five samples from four patients were also sequenced after the cessation of ENF therapy. Drug susceptibilities were assessed by a pseudotype virus reporter assay. We identified HR1 and HR2 sequence changes over time in relation to the baseline sequences. Mutations in HR1 (amino acids 36 to 45) were noted in all cases, including previously unreported changes N42Q/H and N43Q. In addition to a range of HR2 sequence changes at polymorphic sites, isolates from 6 of 17 (35%) patients developed an S138A substitution in the HR2 domain at least 8 weeks after the start of ENF treatment and also subsequent to the first emergence of HR1 mutations. In most, but not all, cases the S138A mutation accompanied HR1 mutations at position 43. Molecular modeling demonstrates the close proximity of S138A with amino acids 40 and 45 in HR1. Of note, isolates in samples available from four patients demonstrated the loss of both the HR1 and the S138A HR2 mutations following the cessation of therapy. We show that the S138A HR2 mutation increased the level of resistance by approximately threefold over that conferred by the HR1 mutation N43D. Continual evolution of HR1 in the domain from amino acids 36 to 45 was observed during long-term ENF therapy. We have identified, for the first time, an ENF resistance-associated HR2 mutation, S138A, which appeared in isolates from 6 of 17 patients with virological failure and demonstrated its potential to contribute to drug resistance. We propose that this represents a possible secondary and/or compensatory mutation, particularly when it coexists with mutations at position 43 in HR-1.

Enfuvirtide: the first HIV fusion inhibitor

Highly active antiretroviral therapy, a combination of antiretrovirals to treat HIV-infected individuals, may fail for a number of reasons, including the selection of genetic mutations which confer resistance to the antiretroviral drugs, and poor adherence or treatment discontinuation resulting from drug toxicity. Treatment-experienced patients, who have failed therapy owing to the emergence of drug-resistant virus, have a significant unmet medical need. Enfuvirtide (T-20), the first of a new class of antiretroviral agents known as HIV fusion inhibitors, has a unique mechanism of action involving disruption of HIV entry at the stage of membrane fusion. The potent antiviral activity and favourable safety and tolerability profile of enfuvirtide has been demonstrated in combination with other agents. Its novel mechanism of action offers a low potential for cross-resistance with conventional classes of antiretrovirals, and its extracellular distribution means that drug interactions and intracellular metabolic disturbances are unlikely. Targeting viral fusion or entry will hopefully provide respite for patients who have limited treatment options following the emergence of multi-drug resistance.

Emergence of a drug-dependent human immunodeficiency virus type 1 variant during therapy with the T20 fusion inhibitor

The fusion inhibitor T20 belongs to a new class of anti-human immunodeficiency virus type 1 (HIV-1) drugs designed to block entry of the virus into the host cell. However, the success of T20 has met with the inevitable emergence of drug-resistant HIV-1 variants. We describe an evolutionary pathway taken by HIV-1 to escape from the selective pressure of T20 in a treated patient. Besides the appearance of T20-resistant variants, we report for the first time the emergence of drug-dependent viruses with mutations in both the HR1 and HR2 domains of envelope glycoprotein 41. We propose a mechanistic model for the dependence of HIV-1 entry on the T20 peptide. The T20-dependent mutant is more prone to undergo the conformational switch that results in the formation of the fusogenic six-helix bundle structure in gp41. A premature switch will generate nonfunctional envelope glycoproteins (dead spikes) on the surface of the virion, and T20 prevents this abortive event by acting as a safety pin that preserves an earlier prefusion conformation.

Enfuvirtide: a fusion inhibitor for the treatment of HIV infection

BACKGROUND

Drug resistance continues to be a major challenge in the treatment of HIV-1 infection. Virtually all currently available antiretroviral medications inhibit the viral reverse transcriptase or protease. Enfuvirtide is the first fusion inhibitor approved by the US Food and Drug Administration for use in combination with other antiretroviral agents for the treatment of HIV-1 infection in treatment-experienced patients.

OBJECTIVE

This paper describes the pharmacologic properties and clinical usefulness of enfuvirtide.

METHODS

Relevant information was identified through searches of MEDLINE (1990 to October 2003), International Pharmaceutical Abstracts (1970 to October 2003), and meeting abstracts of major HIV/AIDS conferences (1996-2003) using the search terms enfuvirtide, pentafuside, T-20, DP-178, and fusion inhibitor.

RESULTS

In vitro, enfuvirtide exhibits activity against HIV-1 isolates that are resistant to all other classes of anti-retroviral medications. Enfuvirtide blocks the entry of HIV-1 into host cells by interfering with virus-cell fusion, making it unique among licensed antiretroviral medications. In human adults, enfuvirtide has a volume of distribution of 5.48 L, is highly bound to plasma protein (92%), has a plasma elimination half-life of 3.8 hours, and is catabolized by peptidases and proteinases in various tissues. Dose adjustment does not appear necessary on the basis of age, race, or body weight, but may be warranted in women weighing <50 kg. A literature review did not identify any data on the disposition of enfuvirtide in patients with hepatic or renal insufficiency. Clinical trials suggest that enfuvirtide reduces plasma HIV-1 RNA levels in highly treatment-experienced patients taking an optimized antiretroviral regimen. Pivotal trials indicated a mean change in HIV-1 RNA of -1.48 log(10) copies/mL in the enfuvirtide arm at week 48, compared with -0.63 log(10) copy/mL in the control arm ( P<0.001 ). The mean absolute increase on CD4 cell count was 46 cells/mm(3) (91 cells/mm(3)) in the enfuvirtide arm vs 45 cells/mm(3) in the control arm; P<0.001 ). The most commonly reported (>15 cases per 100 patient-years of exposure) adverse events (AEs) in clinical trials included injection-site reactions, diarrhea, nausea, fatigue, insomnia, peripheral neuropathy, headache, vomiting, and fever. The most commonly reported (> or =2%) laboratory abnormalities (grade III or IV) were eosinophilia, anemia, and increases in amylase, lipase, triglycerides, creatine phosphokinase, alanine aminotransferase, aspartate aminotransferase, and gamma-glutamyl transferase. In clinical trials, serious AEs leading to study discontinuation occurred in 12.9% ( 114/885 ) of patients in the enfuvirtide arm, compared with 10.7% ( 12/112 ) in the control arm ( P = NS ). The recommended dosage of enfuvirtide is 90 mg SC BID in adults and 2 mg/kg SC BID in children. Efficacy studies in children are ongoing.

CONCLUSION

Although additional studies are needed, enfuvirtide appears to be a promising agent, in combination with other antiretroviral agents, for the treatment of HIV infection in treatment-experienced patients.

Peptide inhibitors of virus-cell fusion: enfuvirtide as a case study in clinical discovery and development

The peptidic antiretroviral enfuvirtide (Fuzeon) is the first clinically approved antiviral fusion inhibitor and the first antiretroviral that must routinely be administered parenterally. Its extracellular activity results both in activity against current drug-resistant strains of HIV-1 and a low potential for systemic toxicities. As a peptide, enfuvirtide also exhibits few interactions with other antiretrovirals and concomitant medications used in HIV disease. Enfuvirtide shows potent antiretroviral activity and significantly improves medical outcomes in highly treatment-experienced patients with HIV-1 infection, but like other antiretrovirals must be given as part of a carefully selected combination regimen to minimise the risk of emergent drug resistance. Despite its subcutaneous route of administration, clinical data indicate that most patients can accept long-term enfuvirtide treatment with little difficulty or impact on daily activities. The only common adverse event associated with enfuvirtide use is injection-site reactions of generally mild-to-moderate severity, which are seldom treatment-limiting.

Safety, tolerability, and plasma pharmacokinetics of high-strength formulations of enfuvirtide (T-20) in treatment-experienced HIV-1-infected patients

BACKGROUND

Enfuvirtide, a HIV-1 membrane fusion inhibitor, is the first viral entry inhibitor approved for the treatment of HIV-1 infected patients in the USA. Parenteral administration of enfuvirtide in clinical trials has been safe and has resulted in significant decreases in plasma viral load, even in the setting of extensive previous treatment and multi-drug resistance to conventional antiretroviral (ARV) therapy. Previous formulations have required two injections administered twice-daily (BID).

OBJECTIVES

The primary objectives of this study were to evaluate the safety, tolerability, and pharmacokinetics of two high-strength 100 mg/ml formulations of enfuvirtide (carbonate [CO(3)] and tromethamine [TRIS] buffer) and of the current formulation (50 mg/ml CO(3) formulation) at doses of 90 mg (deliverable) BID and 67.5 mg (deliverable) BID in treatment-experienced patients.

STUDY DESIGN

This was a phase II, multi-center, open-label, sequential cross-over pharmacokinetic, efficacy, and safety study. Study design included two treatment variables; dose (90 mg or 67.5 mg BID) and formulation (A: 50 mg/ml CO(3), B: 100 mg/ml CO(3) or C; 100 mg/ml TRIS).

RESULTS

Forty-six treatment-experienced participants were sequentially enrolled into three treatment cohorts. All cohorts had similar safety profiles and only one patient discontinued due to an adverse event. Pharmacokinetic data indicated that the high-strength 100 mg/ml CO(3) formulation was bioequivalent to the 50 mg/ml CO(3) formulation whereas the TRIS formulation was not. At 48 weeks, 59.1%, 66.7% and 16.7% had <400 copies per milliliter HIV-1 RNA in the 90 MgCO(3), 67.5 MgCO(3) and 90 mg TRIS cohorts with median suppression of HIV-1 RNA of 2.97, 3.48, and 0.87 log(10)copies per milliliter, respectively.

CONCLUSIONS

Based upon bioequivalence data and the convenience and similarity in safety and virological effect with the 50 mg/ml formulation, the 100 mg/ml CO(3) formulation was selected for use in clinical efficacy studies of enfuvirtide.

Enfuvirtide

Enfuvirtide is the first of a new class of drugs, the fusion inhibitors. It is a synthetic peptide which binds to the HIV glycoprotein 41 (gp41), blocking fusion of the viral and cellular membranes. HIV isolates with reduced susceptibility to enfuvirtide have been recovered from patients receiving enfuvirtide in combination with other antiretroviral agents. Enfuvirtide 90mg (subcutaneously, twice daily) in combination with optimised background (OB) antiretroviral therapy significantly reduced plasma HIV RNA levels compared with OB alone after treatment for 24 weeks in two randomised trials involving adults with advanced HIV infection. The antiviral efficacy of enfuvirtide was maintained through to 48 weeks. At 24 and 48 weeks, the increase from baseline in the CD4+ cell count was significantly greater for patients receiving enfuvirtide plus OB than for those receiving OB alone. Enfuvirtide 30 mg/m(2) or 60 mg/m(2) in combination with other antiretroviral agents reduced plasma HIV RNA levels and increased CD4+ cell counts in a small trial involving paediatric patients with HIV infection. Local injection-site reactions were common. Lymphadenopathy and pneumonia occurred more often in patients receiving enfuvirtide plus OB than in the control group. The incidence of most other events was similar in each group.

Neutralization of infectivity of diverse R5 clinical isolates of human immunodeficiency virus type 1 by gp120-binding 2'F-RNA aptamers

Human immunodeficiency virus type 1 (HIV-1) has evolved a number of strategies to resist current antiretroviral drugs and the selection pressures of humoral and cellular adaptive immunity. For example, R5 strains, which use the CCR5 coreceptor for entry and are the dominant viral phenotype for HIV-1 transmission and AIDS pathogenesis, are relatively resistant to neutralization by antibodies, as are other clinical isolates. In order to overcome these adaptations, we raised nucleic acid aptamers to the SU glycoprotein (gp120) of the R5 strain, HIV-1(Ba-L). These not only bound gp120 with high affinity but also neutralized HIV-1 infectivity in human peripheral blood mononuclear cells (PBMCs) by more than 1,000-fold. Furthermore, these aptamers were able to neutralize the infectivity of R5 clinical isolates of HIV-1 derived from group M (subtypes A, C, D, E, and F) and group O. One aptamer defined a site on gp120 that overlaps partially with the conserved, chemokine receptor-binding, CD4-induced epitope recognized by monoclonal antibody 17b. In contrast to the antibody, the site is accessible to aptamer in the absence of CD4 binding. Neutralizing aptamers such as this could be exploited to provide leads in developing alternative, efficacious anti-HIV-1 drugs and lead to a deeper understanding of the molecular interactions between the virus and its host cell.

Uncommon mutations at residue positions critical for enfuvirtide (T-20) resistance in enfuvirtide-naive patients infected with subtype B and non-B HIV-1 strains

Enfuvirtide (T-20) is the lead compound of the new class of antiretroviral drugs called fusion inhibitors. T-20 resistance-associated mutations located in the heptad repeat 1 (HR-1) domain of gp41 have been described in vitro and in clinical trials. In this study, the authors investigated the primary genotypic T-20 resistance in subtype B and non-B HIV-1 strains from patients at the beginning of their follow-up in the Luxembourg HIV Cohort as well as the emergence of primary resistance to T-20 in patients who had long-term infection with subtype B HIV-1 strains. HR-1 fragments including the gp41 amino acid 36-45, T-20-sensitive region were screened for amino acid variation. No classic T-20 resistance-associated mutations were identified in subtype B or non-B isolates. However, several uncommon mutations were found at residues 37, 39, and 42 for subtype B isolates and at residue 42 for a subtype non-B isolate. The results indicate that primary genotypic T-20 resistance seems to be rare in HIV-1, regardless of subtype or prior antiretroviral therapy (excluding fusion inhibitors). However, episodic variation within HR-1 can occur and needs further phenotypic evaluation in accurate fusion inhibitor resistance assays.

Primary resistance mutations to fusion inhibitors and polymorphisms in gp41 sequences of HIV-1 non-B subtypes and recombinants

Primary resistance mutations to fusion inhibitors and polymorphisms in gp41 sequences of non-B subtypes and recombinant HIV-1 isolates were analysed. L91H to RPR103611 was detected in one DGpol/Denv/Dgp41 recombinant; L9F and K144R, rarely reported previously, were frequent in the B region of CRF14_BG recombinants. V194I and V318A, not described in the G subtype, were detected in the G region of BG recombinants and in G subtype viruses that also show the rare mutations T115L, M118V and K90R.

Baseline susceptibility of primary human immunodeficiency virus type 1 to entry inhibitors

Human immunodeficiency virus type 1 plasma viruses from 29 entry inhibitor-naive patients were characterized for their susceptibilities to T-20, AMD3100, and RANTES. A strikingly wide range of susceptibilities to T-20 was observed that was influenced by coreceptor usage but not by the susceptibilities of the viruses to inhibitors that target the chemokine receptors or by polymorphisms in the gp41 N helix.

Minimal variation in T-20 binding domain of different HIV-1 subtypes from antiretroviral-naive and -experienced patients

In-vitro differences in T-20 susceptibility among HIV-1 subtypes have been reported. We therefore studied the T-20 binding domain of a variety of virus subtypes from both antiretroviral-naive and -experienced patients. Minimal variation in the HR-1 region of gp41 was observed, especially within the region responsible for T-20 resistance. Any subtype differences in T-20 susceptibility do not appear to be related to HR-1 genetic variation.

Variability of critical epitopes within HIV-1 heptad repeat domains for selected entry inhibitors in HIV-infected populations worldwide [corrected]

BACKGROUND

Two of the fusion inhibitors T-20 and 5-helix polypeptide have been shown to be potent inhibitors of cell-to-cell fusion and are currently under investigation as therapy for HIV-1.

OBJECTIVES

To examine variability of HIV-1 gp41 heptads repeat regions (HR1 and HR2), with special emphasis on the presence of T-20 resistance mutations and 5-helix variability at critical epitopes, in treatment-naive patients infected with diverse HIV-1 subtypes from different geographic regions.

METHODS

A total of 150 specimens representing HIV-1 group M subtypes (A-G) from persons naive to HIV-1 viral entry inhibitor therapy were used to amplify and sequence a 506 bp segment of transmembrane protein.

RESULTS

In general, both HR1 (a.a. 540-593) and HR2 (a.a. 628-673) domains were highly conserved. Sequence analysis of the T-20 resistant domain (a.a. 547-549, GIV) revealed that 99% of the specimens (149 of 150) carried a T-20 sensitive genotype. The critical epitopes involved in the 5-helix interaction include residues at positions 628W, 631W, 635I, 638Y, 642I, 645L, 649S, 652Q, 656N, and 659E. Analysis of the 150 specimens revealed that all had identical residues at six of these positions, whereas two positions had minor variations (635 and 649) and two (645 and 659) appeared to have subtype-specific substitutions.

CONCLUSIONS

This data indicates that there is limited resistance to T-20 in these worldwide populations and that the critical epitopes for effective 5-helix binding are highly conserved across all subtypes. Taken together, these data suggest that T-20 and 5-helix should provide useful additives to current antiretroviral therapy for clinical management of HIV disease.