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

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.

Genetic variation in the HR region of the env gene of HIV: A perspective for resistance to HIV fusion inhibitors

HIV fusion inhibitors may be classified into three groups. Peptides binding to HR1 include T1249, C30, and T20 (enfuvirtide). Peptides binding to HR2 include 5-helix. XTT formazan, NB-2, and NB-64 are nonpeptide fusion inhibitors. Genotypic testing for drug resistance is used more commonly than phenotypic testing because of its lower cost, wider availability, and shorter turnaround time. The aim of the study was to predict the efficacy of fusion inhibitors for AIDS patients in our population. A total of 100 specimens were collected. The viral RNA was isolated and nucleotides of the required regions were sequenced using the BigDye terminator method. It is concluded from this study that viruses in our population may show resistance to C30 and T20 whereas the other fusion inhibitors may be effectively used for our population.

Short communication: high polymorphism rates in the HR1 and HR2 gp41 and presence of primary resistance-related mutations in HIV type 1 circulating in Brazil: possible impact on enfuvirtide efficacy

We analyzed the gp41 sequences of 80 HIV-infected enfuvirtide-naive individuals who were eligible to receive this antiretroviral according to Brazilian guidelines. We analyzed the genetic diversity of pol and the heptad repeat 1 and 2 (HR1 and HR2) regions of gp41, and compared the genetic profile of HR1 and HR2 found in PBMCs with the profile found in plasma. The similarity between sequences obtained from DNA and RNA in the HR1 and HR2 regions was, on average, 98.6% and 98.9%, respectively. We detected mutations related to enfuvirtide resistance (L44M or N43K) in HR1 DNA samples from three individuals (3.8%) and RNA samples from three individuals (4.6%). Other polymorphisms frequently detected were E137K (10% and 13.8%), L130I (8.8% and 9.2%), S129N (6.3% and 10.8%), L44M (2.5% and 4.6%), S138A (2.5% and 1.5%), and N43K (1.3% and 0%) in DNA and RNA, respectively. Subtype B was identified in 68.8% of the samples [protease (PR) B, reverse transcriptase (RT) B, gp41 B], subtype F in 5.0%, subtype C in 1.3%, and the remaining sequences presented with a mosaic profile. These results suggest that genotyping the gp41 region prior to introducing an expensive and complex approach, such as enfuvirtide, may be cost effective. Moreover, assessment of proviral DNA may be less expensive than RNA, as well as being sufficient for this purpose.

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.

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.

Natural variability in the HR-1 and HR-2 domains of HIV type 1 gp41 from different clades circulating in Italy

The human immunodeficiency virus type 1 (HIV-1) HR-1 and HR-2 gp41 regions were sequenced in a total of 228 plasma or peripheral blood mononuclear cell samples obtained from an equal number of enfuvirtide-naive subjects for pol genotypic resistance testing in clinical practice. Phylogenetic analysis of the env sequences indicated that 102 belonged to subtype B and 95 to non-B subtypes (31 CRF02_AG, 21 F1, 14 C, 11 A1/A2/A3, 9 CRF01_AE, 9 others) while the remaining 31 were unique recombinant forms. There was considerable variability in the consensus sequence of different clades, particularly in HR-2. The HR-1 amino acid region 36-45, containing all of the enfuvirtide resistance mutations so far characterized, was well conserved except for position 42 where serine and asparagine were unevenly distributed in different subtypes. Enfuvirtide resistance mutations were not present in any sample, reinforcing the expectation that enfuvirtide is effective against many different HIV-1 clades and recombinants. However, some of the mutations outside the amino acid 36-45 region and provisionally suggested to play a role in modulating resistance were detected in a minority of cases. Molecular epidemiological surveys coupled with long-term observation of in vivo response to enfuvirtide and future fusion inhibitors are required to clarify the clinical significance of gp41 natural variability.

Increased polymorphism in the HR-1 gp41 env gene encoding the enfuvirtide (T-20) target in HIV-1 variants harboring multiple antiretroviral drug resistance mutations in the pol gene

BACKGROUND

Sequence variations in HR-1 gp41 env gene region encoding the target for T-20 have previously been reported among patients naive to inhibitory fusion.

OBJECTIVE

To evaluate whether a previous therapeutic history of patients could have an impact on a differential evolution of the gp41 polymorphism.

METHODS

We assessed the genetic polymorphism within the critical HR-1 gp41 env gene region in HIV-1 variants from 108 T-20-naive patients (Groups I-III) and 12 patients receiving T-20 as part of a salvage regimen (Group IV). T-20-naive patients included 50 patients exhibiting variants harboring resistance mutations to NRTIs, NNRTIs, and PIs (Group I), 24 patients with variants harboring resistance mutations for NRTIs and/or NNRTIs (Group II), and 34 antiretroviral drug-naive patients (Group III).

RESULTS

In T-20-naive patients whose HIV harbored resistance mutations to NRTIs, NNRTIs, and/or PIs, the mean number of synonymous mutations (ds) per patient was decreased and the mean number of nonsynonymous (da) mutations per patient was increased, resulting in a significant decrease in the mean Sigmads/Sigmada ratio as compared with antiretroviral drug-naive patients (Group III; 4.1 vs. 11.6; P < 0.0001). The mean number of polymorphic mutations in HR-1 gp41 per patient was two-fold higher in patients exhibiting antiretroviral drug resistance mutations (Groups I and II) than in antiretroviral drug-naive patients (Group III; 0.41 vs. 0.20; P < 0.05).

CONCLUSION

Our observations indicate that the HR-1 gp41 T-20 target is subjected to high genetic variability, including intrinsic polymorphism and selection of T-20 resistance mutations under T-20 intake, that is increased by the presence of resistance mutations to NRTIs, NNRTIs, and/or PIs. Our data provide a basis for a potential impact of previous antiretroviral drug history on the therapeutic efficacy of T-20.

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.

Enfuvirtide in HIV-1-Infected Individuals Changing Therapy to A Nucleoside Reverse Transcriptase Inhibitor Sparing Regimen: The Alliance Study

The role of the fusion inhibitor enfuvirtide in nucleoside reverse transcriptase inhibitor (NRTI)-sparing regimens was assessed in an open-label study of fifty-nine highly antiretroviral drug exposed HIV-1-infected individuals. There was a reduction in plasma HIV-1 RNA of 1.43 (95% confidence interval [CI]: -2.06, -1.22) log10 copies/ml plasma over 96 weeks, and 44% (95% CI: 31, 58) of individuals had a viral load less than 400 copies/ml. A viral load below detection at 96 weeks was predicted by a baseline genotypic sensitivity score greater than 1. There was an average increase of 67 cells/μl (95% CI: 15, 120) from baseline CD4+ T-cell count to week 96, and the percentage of patients with CD4+ T-cell counts above 100 and 200 cells/μl increased over the trial. Injection site reactions (ISRs) were less common in people with CD4+ T-cell counts >250 cells/μl at any time during follow-up, and were more severe in patients with lower baseline peripheral fat. Adherence over 48 weeks to enfuvirtide injections ranged from 96.3-99.5%. During the 96 week trial there were two discontinuations due to ISRs and two discontinuations following hypersensitivity reactions. Over the 96 weeks of study lean body mass increased by an average 2.7 kg (95% CI; 1.7, 3.6 kg). Mean peripheral fat increased by 0.2 kg (95% CI; -0.2, 0.6 kg). Baseline NRTI-associated toxicities resolved in 17% of participants during follow-up. Enfuvirtide is an important component of antiretroviral therapy in highly treatment-experienced individuals where NRTI sparing may be desirable.

Susceptibility to antiretroviral drugs of CRF01_AE, CRF02_AG, and subtype C viruses from untreated patients of Africa and Asia: comparative genotypic and phenotypic data

Non-B HIV-1 viruses are predominant in developing countries where access to antiretroviral drugs (ARVs) is progressively being intensified. It is important to obtain more data on the susceptibility of these viruses to available ARVs. CRF01_AE, CRF02_AG, and subtype C strains of HIV-1 obtained from untreated patients from Vietnam, Cote d'Ivoire, and India were analyzed for their in vitro susceptibility to NRTIs, NNRTIs, PIs, and an entry inhibitor (T-20) using a recombinant viral assay (PHENOSCRIPT). The corresponding viruses, which had been previously sequenced in reverse transcriptase (RT), protease (prot), plus envelope (env) C2/V3 genes and had therefore been fully characterized, were further sequenced in env HR1 + HR2 regions. CRF01_AE isolates are sensitive to NRTIs and NNRTIs with the exception of one isolate that exhibits a decreased susceptibility to NNRTIs associated with a I135T substitution in RT. CRF02_AG and subtype C viruses are sensitive to NRTIs and NNRTIs but some CRF02_AG isolates tend to be resistant to abacavir, potentially related to associated substitutions of RT at positions 123 (D123N) plus 135 (I135V). Whereas all but one CRF01_AE isolates are fully susceptible to PIs, some CRF02_AG and, more frequently, some subtype C isolates are resistant to atazanavir. The role of substitutions in prot at positions of secondary resistance mutations 20, 36, 63, and 82 is raised with a potentially crucial role of the V82I substitution. Finally, all viruses tested, regardless of the CRF or subtype, are fully susceptible to T-20.

A cohort study of enfuvirtide immunological and virological efficacy in clinical practice

The aim of the study was to evaluate, under routine circumstances, the immunological and virological efficacy of antiretroviral regimens containing enfuvirtide in multi-class experienced HIV-1 infected patients. This retrospective monocentric study analyzed the clinical, immunological, and virological data of 18 HIV-1 infected patients who started enfuvirtide and completed at least 3 months of therapy. Following 3 months of enfuvirtide therapy, 11 (61%) patients had HIV-1 RNA below 400 copies/ml, among whom 8 (44%) patients below 50 copies/ml. In the ten patients still receiving enfuvirtide after 12 months, the median increase in CD4 cell count was 159 cells/microl (range, -25 to +301) and the mean decrease in HIV-1 RNA was 2.5 +/- 1.4 log(10) copies/ml; in six of these patients, viral load remained below 50 copies/ml. Five patients discontinued enfuvirtide for virological failure but none as a consequence of adverse event. Mutations located within the 36-45 amino acid domain of HR1 region of gp41 and associated to enfuvirtide resistance were found in all seven patients with persistent viral replication. In addition, a new mutation, A50V, emerged in one patient with late viral rebound. Its disappearance after treatment discontinuation suggests that it could play a role in resistance to enfuvirtide. In conclusion, enfuvirtide may be a good therapeutic option as rescue therapy in treatment-experienced patients. However, the mutations conferring resistance to enfuvirtide develop rapidly when viral load is not controlled confirming that enfuvirtide should be prescribed in association with an active background regimen.

HIV-1 tropism for the central nervous system: Brain-derived envelope glycoproteins with lower CD4 dependence and reduced sensitivity to a fusion inhibitor

We previously described envelope glycoproteins of an HIV-1 isolate adapted in vitro for growth in microglia that acquired a highly fusogenic phenotype and lower CD4 dependence, as well as resistance to inhibition by anti-CD4 antibodies. Here, we investigated whether similar phenotypic changes are present in vivo. Envelope clones from the brain and spleen of an HIV-1-infected individual with neurological disease were amplified, cloned, and sequenced. Phylogenetic analysis demonstrated clustering of sequences according to the tissue of origin, as expected. Functional clones were then used in cell-to-cell fusion assays to test for CD4 and co-receptor utilization and for sensitivity to various antibodies and inhibitors. Both brain- and spleen-derived envelope clones mediated fusion in cells expressing both CD4 and CCR5 and brain envelopes also used CCR3 as co-receptor. We found that the brain envelopes had a lower CD4 dependence, since they efficiently mediated fusion in the presence of low levels of CD4 on the target cell membrane, and they were significantly more resistant to blocking by anti-CD4 antibodies than the spleen-derived envelopes. In contrast, we observed no difference in sensitivity to the CCR5 antagonist TAK-779. However, brain-derived envelopes were significantly more resistant than those from spleen to the fusion inhibitor T-1249 and concurrently showed slightly greater fusogenicity. Our results suggest an increased affinity for CD4 of brain-derived envelopes that may have originated from in vivo adaptation to replication in microglial cells. Interestingly, we note the presence of envelopes more resistant to a fusion inhibitor in the brain of an untreated, HIV-1-infected individual.

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.

In vitro generation of HIV type 1 subtype C isolates resistant to enfuvirtide

Enfuvirtide (ENF) is the first in a new class of antiretroviral agents targeting the fusion process of the viral life cycle. ENF is a synthetic 36-amino acid peptide that binds to the HR-1 region of gp41 preventing fusion of viral and cellular membranes. With the introduction of ENF there are now four classes of antiretrovirals each with distinct and different resistance pathways. Resistance to ENF among subtype B HIV-1 isolates is associated with amino acid changes mainly in the HR-1 region, although other regions of envelope have also been implicated. To determine whether subtype C viruses developed resistance mutations similar to subtype B viruses, 11 subtype C and 4 subtype B viruses were passaged in the presence of increasing concentrations of ENF. The subtype C isolates showed varying levels of replication at 1 microg/ml ENF by day 18, but by day 29 all replicated efficiently at 10 microg/ml ENF. All subtype C isolates showed evidence of genotypic changes in gp41 HR-1 following exposure to ENF that included G36S/E/D, I37T, V38M/A/L/E, N/S42D, N43K, L45R/M, and A50T/V. Three subtype C viruses had compensatory changes in the HR-2 region, which corresponds to the ENF sequence, and two isolates had changes in the V3 region. Mutational patterns among the four subtype B viruses were similar to those for subtype C and those previously published in the literature. These data indicate that in vitro resistance to ENF develops rapidly among HIV-1 subtype C isolates. In general, mutational patterns for subtype C were similar to those described for subtype B, suggesting that the mechanism of action for ENF is similar for HIV-1 subtype B and C isolates.

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 binding domain is highly conserved in non-B HIV type 1 strains from Cameroon, West Central Africa

Recently T-20 or enfuvirtide, the first drug of a new class of antiretrovirals targeting the entry stage of the virus life cycle, has been clinically approved. Enfuvirtide is a peptide derived from the HR2 region of the transmembrane glycoprotein from the HXB2 HIV-1 subtype B prototype strain that binds to the HR1 region. Drug resistance seems to occur in the HR1 region between amino acids 36 and 45. We examined to what extent this region is conserved in 184 non-B strains from Cameroon: 132 (71.7%) CRF02-AG, 14 (7.6%) subtype A, 11 (5.9%) F2, 9 (4.8%) subtype D, 8 (4.3%) subtype G, 4 (2.1%) CRF01-AE, 4 (2.1%) CRF11-cpx, and 2 (1.1%) CRF06-cpx. Among the 184 strains studied, no amino acid mutation was found in the highly conserved three amino acid motif at codons 36-38 (GIV) that are important determinants of viral susceptibility to enfuvirtide. Other common substitutions like Q40H and N42T were also absent. The N42S polymorphism was present in 148 (80.4%) strains. Analysis of the HR2 domain, from which the peptide is derived, indicated a much greater genetic variability as compared to HR1.

Different susceptibility of human immunodeficiency virus type 1 to Env gp41-derived synthetic peptides corresponding to the C-terminal heptad repeat region

Two functional domains, alpha-helical heptad repeat 1 (HR-1) and HR-2, located in the N-terminal and C-terminal regions of human immunodeficiency virus type 1 (HIV-1) Env gp41, respectively, play an important role in the fusion process. Synthetic 34-amino-acid peptide that contains the HR-2 region, named C34, has been shown to inhibit the HIV-1 fusion process. Here, we prepared six representative peptides (C34-B1, -B2, -A, -C1, -C2, and -E from subtypes B, A, C, and E, respectively) according to the sequences from the HIV sequence database of Los Alamos. All the C34 peptides had lower ability to inhibit the primary isolates (subtypes B and CRF01_AE) than subtype B laboratory strain LAI. On the other hand, the L-2 cell clone, isolated from persistently LAI-infected MT-4 cells (MT-4/LAI), showed unique C34 peptide sensitivities. L-2 virus has the same sequences at HR-1 and HR-2 regions as LAI, but showed higher syncytia formation activity than LAI. Interestingly, the sensitivity of L-2 was higher to C34-B2 and -A but slightly lower to C34-C1 at higher concentrations than MT-4/LAI, while C34-B1, -C2, and -E showed similar activity against both viruses. Thus, in addition to the sequences of the C34 peptide as well as of the HR-1 and HR-2 regions in target viruses used for fusion assays, the fusion inhibitory activities of C34 peptides seem to be affected by viral factor(s) other than the gp41 alpha-helical heptad repeats.

A genotypic resistance assay for the detection of drug resistance in the human immunodeficiency virus type 1 envelope gene

Since it is not clear yet whether enfuvirtide resistance is restricted to gp41, it was decided to develop a genotypic assay for the detection of drug resistance in the entire human immunodeficiency virus type 1 (HIV-1) env gene. Given the increasing prevalence of HIV-1 non-B subtypes in Europe, it is important to evaluate the performance of the assay on a panel of genetically divergent samples. A panel of 1 laboratory and 10 clinical isolates from 10 patients was tested, all enfuvirtide naive and chosen according to the subtype as determined in the pol region (A, B, C, H, CRF01-AE, CRF02-AG, CRF05-DF, CRF11-cpx and U), while their env sequences belonged to subtypes A, B, C, H, A/G recombinant, B/H recombinant, CRF01-AE, CRF02-AG, CRF05-DF and CRF11-cpx. The detection limits of the gp120 and the gp41 PCRs ranged between 500 and 5000 RNA copies/ml plasma. The highest sensitivity was obtained for the laboratory strain, whereas the detection limit for all patient samples, except for the subtype C sample, was 1000 RNA copies/ml. The numerous insertions and deletions in the gp120 gene, that were often present as quasi-species, necessitated the sequencing of cloned PCR products. The gp41 gene displayed less diversity and less insertions/deletions. Especially, the heptad repeat 1 was highly conserved and none of the enfuvirtide naive samples contained any of the already known enfuvirtide resistance mutations at amino acid positions 36-45. This study demonstrates that the assay is able to genotype genetically diverse HIV-1 strains with a good sensitivity.

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.

Impairment by mucosal adjuvants and cross-reactivity with variant peptides of the mucosal immunity induced by injection of the fusion peptide PADRE-ELDKWA

Secretory immunity protects against mucosal transmission of viruses, as demonstrated with the oral poliovirus vaccine. In a previous study we showed that this immunity could be induced in mice by injection of a fusion peptide consisting of an unnatural peptide-like sequence (PADRE) and a viral epitope (ELDKWASLW). PADRE is a T-helper-cell epitope able to bind most major histocompatibility complex class II molecules of different haplotypes in mice and humans and to increase antibody responses. ELDKWA is a well-known consensual sequence of gp41 involved in a key structure of human immunodeficiency virus (HIV) type 1. Here, the antibody response to the native form of ELDKWA was mainly of the immunoglobulin A isotype and selectively occurred in mucosa. Adjuvants, such as cholera toxin and cytosine polyguanine, were useless and even competed with PADRE for the response. Interestingly, these antibodies were cross-reactive with the three major variants of the epitope, as shown both by direct enzyme-linked immunosorbent assay and by inhibition. This unconventional route of mucosal immunization allows control of the administered dose. The lack of adjuvant and the cross-reactivity of the antibodies increase the safety and the spectrum of the candidate vaccine, respectively. The drug-like nature of the construct suggests further improvements by synthesis of more antigenic sequences. The reasonable cost of short peptides at the industrial level and their purity make this approach of interest for future vaccines against mucosal transmission of HIV or other pathogens.

Characterization of determinants of genotypic and phenotypic resistance to enfuvirtide in baseline and on-treatment HIV-1 isolates

BACKGROUND

Enfuvirtide (ENF) is the first of a novel class of drugs that block HIV gp41-mediated viral fusion to host cells. Viruses with mutations at positions 36-38 in HIV-1 gp41 and/or reduced susceptibility to ENF have been selected both in vitro and in vivo.

METHODS

An analysis of baseline and on-treatment ENF susceptibility in virus samples from Phase II clinical trial patients treated with ENF as functional monotherapy for 28 days (TRI-003) or in combination with oral antiretrovirals for >/= 48 weeks (T20-205, T20-206 and T20-208). Population sequencing identified amino acid (aa) substitutions at positions 36-45 of gp41 in plasma HIV-1. ENF susceptibility of virus isolates was tested in the cMAGI assay and viral DNA was sequenced for selected isolates.

RESULTS

HIV-1 gp41 aa 36-45 were highly conserved in virus from ENF-naive patients, except for a 15% incidence of N42S which did not reduce sensitivity to ENF. Virus from patients experiencing viral load rebound exhibited reduced susceptibility to ENF and substitutions in gp41 aa 36-45. The most common substitutions observed on treatment were at positions 36, 38, 40, 42 and 43. On-treatment changes in the phenotypic susceptibility of virus isolates to ENF were generally associated with genotypic changes in aa 36-45. There was a relatively lower incidence of ENF resistance in patients with baseline sensitivity to more oral antiretrovirals in comparison to patients sensitive to fewer antiretrovirals.

CONCLUSIONS

These data identify the importance of HIV-1 gp41 aa 36-45 in the emergence of resistance to ENF.

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.

Sensitivity of HIV type 1 subtype C isolates to the entry inhibitor T-20

T-20 is the first in a new class of antiretroviral drugs targeting the entry stage of the virus life cycle. It is a 36 amino acid peptide that binds to the HR1 region of gp41 preventing gp41-mediated fusion with the host cell membrane. T-20 was designed based on the HR2 sequence of HIV-1 subtype B gp41, a region that shows significant genetic variation with HIV-1 subtype C sequences. In order to assess the efficacy of T-20 to inhibit subtype C isolates, a total of 23 isolates were tested for their ability to replicate in the presence of T-20. This included 15 isolates that used CCR5, five that used both CCR5 and CXCR4, and three that used CXCR4. Five of these were from patients failing other antiretroviral therapies. Sequence analysis of the HR2 region indicated that there were 10-16 amino acid changes in the region corresponding to T-20. However, all isolates were effectively inhibited by T-20 at 1 microg/ml. There were no significant differences between viruses that used CCR5 or CXCR4 to enter cells. All isolates, except one, had GIV at positions 36-38 in the HR1 region. One isolate had a GVV motif but this did not affect its sensitivity to T-20. Therefore, T-20 inhibited subtype C viruses despite significant genetic differences in the HR2 region and there was no evidence for baseline resistance to T-20. These data suggest that T-20 would be highly effective in patients with HIV-1 subtype C infection, including those failing existing antiretroviral drug regimens.

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.

Are fusion inhibitors active against all HIV variants?

Genetic sequence alignment of the transmembrane region from HIV-1 group O and HIV-2 isolates was performed to examine their potential susceptibility to fusion inhibitors enfuvirtide (T-20) and T-1249. A high genetic diversity within the HRI and HR2 domains was found, which should compromise any antiviral effect of T-20 on HIV-2 and HIV-1 group O viruses. However, conserved sequences in the gp41 regions from HIV-1 group O involved in T-1249 susceptibility might result in a much broader antiviral effect of T-1249 on HIV-1 variants. In contrast, genetic diversity in those regions make unlikely any activity of these compounds on HIV-2.

New patterns of HIV-1 resistance during HAART

HIV-1 resistance and subsequent virologic failure occur in a substantial proportion of HIV-infected patients receiving HAART regimens. In the present article, we summarize new data on resistance to current and forthcoming antiretroviral drugs which will help in the interpretation of the results of resistance tests and the individualization of therapy. Nucleoside analog mutations (NAMs) (M41L, D67N, K70R, L210W, T215Y/F and K219Q/E) are associated with reduced susceptibility to most nucleoside analogs and the nucleotide tenofovir. This recently approved drug has shown a reduced virologic response in the presence of three or more NAMs, including M41L or L210W, as well as in the presence of T69 insertions. Hypersusceptibility (IC50 < 0.5) to non-nucleoside reverse transcriptase inhibitors (NNRTIs) has recently been described in association with increased resistance to nucleoside analogs, and it seems to enhance the immunologic and virologic reponses in patients receiving efavirenz-containing regimens. New protease inhibitors (PIs) have a lower cross-resistance profile, although more clinical data are needed to establish appropriate PI sequencing to promote sustained virologic success. Cross-resistance between amprenavir (APV) and lopinavir (LPV/r) in the presence of only four APV-related mutations has been described, suggesting that phenotypic tests should be applied before prescribing LPV/r to APV-experienced patients. Resistance to the new entry inhibitor class compound T-20 (enfuvirtide) has also been detected.

Enfuvirtide (T-20): a novel human immunodeficiency virus type 1 fusion inhibitor

The development of highly active antiretroviral therapy has improved life expectancy and reduced progression to acquired immunodeficiency syndrome in human immunodeficiency virus (HIV)-infected patients. However, resistance to currently available classes of antiretroviral drugs has become a problem, limiting the options for patients with advanced disease who have been heavily treated. Enfuvirtide (T-20; ENF), a synthetic peptide, is the first of a new class of antiretrovirals that block entry of virus into host cells. ENF interferes with conformational changes required for membrane fusion and injection of virus into the host cell. Optimal treatment of HIV infection will likely require combinations of drugs that target novel stages of HIV type 1 entry and replication.

Protein grafting of an HIV-1-inhibiting epitope

Protein grafting, the transfer of a binding epitope of one ligand onto the surface of another protein, is a potentially powerful technique for presenting peptides in preformed and active three-dimensional conformations. Its utility, however, has been limited by low biological activity of the designed ligands and low tolerance of the protein scaffolds to surface substitutions. Here, we graft the complete binding epitope (19 nonconsecutive amino acids with a solvent-accessible surface area of >2,000 A2) of an HIV-1 C-peptide, which is derived from the C-terminal region of HIV-1 gp41 and potently inhibits HIV-1 entry into cells, onto the surface of a GCN4 leucine zipper. The designed peptide, named C34coil, displays a potent antiviral activity approaching that of the native ligand. Moreover, whereas the linear C-peptide is unstructured and sensitive to degradation by proteases, C34coil is well structured, conformationally stable, and exhibits increased resistance to proteolytic degradation compared with the linear peptide. In addition to being a structured antiviral inhibitor, C34coil may also serve as the basis for the development of an alternative class of immunogens. This study demonstrates that "one-shot" protein grafting, without subsequent rounds of optimization, can be used to create ligands with structural conformations and improved biomedical properties.

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.

Targeting therapeutics to an exposed and conserved binding element of the HIV-1 fusion protein

There is an urgent need for new drugs that can kill HIV type 1 (HIV-1)-infected cells. HIV-1 glycoprotein Env, which promotes viral membrane fusion through receptor-mediated conformational changes, is an attractive target for such agents because it is expressed on the surface of both virions and infected cells. Unfortunately, conserved binding elements on this protein frequently are buried under a canopy of flexible, glycosylated peptide loops or exposed only transiently during the fusion process. Here, we investigate the exposure of the C-terminal region of the Env ectodomain outside the context of membrane fusion. This binding element is the target of the 5-Helix protein, a designed entry inhibitor that disrupts conformational changes in Env subunit gp41, essential for the fusion process. We show that 5-Helix is capable of interacting with HIV-1 Env in a receptor-independent fashion and that a chimeric 5-Helix/Pseudomonas exotoxin protein recognizes cells expressing Env from a broad spectrum of HIV-1 strains including primary isolates from clades B, D, E, G, and H. This recombinant toxin selectively kills HIV-1-infected cells and blocks spreading infection while still maintaining potent inhibitory activity against membrane fusion. Our results demonstrate that the C-terminal region of the gp41 ectodomain is an accessible target on HIV-1-infected cells for the development of antiviral therapeutics and neutralizing antibodies.