Prolonged therapy with the fusion inhibitor T-20 in combination with oral antiretroviral agents in an HIV-infected individual

Fusion/entry inhibitors as therapies for HIV

A combination of three or more antiretroviral drugs, commonly termed 'highly active antiretroviral therapy' (HAART), has become the standard-of-care treatment for HIV-related disease in the developed world. Since its initiation in the mid 1990s, HAART has led to substantial reductions in both mortality and morbidity. There are, however, significant problems associated with existing therapies including high pill burdens and serious side effects in many patients, as well as the emergence and transmission of drug-resistant HIV variants. There is, therefore, a need for new medicines to treat HIV infections, both from the existing drug classes and, perhaps more importantly, a need for medicines that act against the virus in entirely new ways. In recent years, much has been learned about how HIV enters its target cells and this work has led to the identification of compounds that potently inhibit the individual steps of viral entry. The status of current research focussed on preventing HIV entry is described below.

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.

Novel reporter T-cell line highly susceptible to both CCR5- and CXCR4-using human immunodeficiency virus type 1 and its application to drug susceptibility tests

CCR5-using (R5) human immunodeficiency virus type 1 (HIV-1) is a major viral population that is transmitted by sexual intercourse and that replicates in infected individuals during the asymptomatic stage of HIV-1 infection, suggesting that agents effective against R5 HIV-1 can be expected to prevent viral transmission and delay disease progression. However, R5 HIV-1 is unable to replicate in human T-cell lines, which is an apparent obstacle to efficient and reliable susceptibility tests of compounds for their activities against R5 HIV-1. To establish a simple and rapid assay system for the monitoring of R5 HIV-1 replication and drug susceptibility, we have established a novel reporter T-cell line, MOCHA (which represents MOLT-4 cells stably expressing CCR5 and carrying the HIV-1 long terminal repeat-driven secretory alkaline phosphatase). Cells of this cell line express CD4, CXCR4, and CCR5 on their surfaces and secrete human placental alkaline phosphatase into the culture supernatants during HIV-1 infection. MOCHA cells proved to be highly permissive for the replication of R5 HIV-1 as well as CXCR4-using (X4) HIV-1, and the alkaline phosphatase activity increased in parallel with increasing HIV-1 p24 antigen levels in the culture supernatants. When HIV-1 reverse transcriptase inhibitors, protease inhibitors, and entry inhibitors, including the CCR5 antagonist TAK-779 and the CXCR4 antagonist AMD3100, were examined for their inhibitory effects on R5 and X4 HIV-1 replication in MOCHA cells, the antiviral activities of these compounds were found to be almost identical to those previously reported in peripheral blood mononuclear cells. Thus, MOCHA cells are an extremely useful tool for detection of R5 and X4 HIV-1 replication and drug susceptibility tests.

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.

A phase II clinical study of the long-term safety and antiviral activity of enfuvirtide-based antiretroviral therapy

OBJECTIVES

The primary objective was to determine the long-term safety of the subcutaneous self-administration of enfuvirtide. Secondary objectives included the determination of enfuvirtide pharmacokinetics and antiviral activity and the immunological response to the enfuvirtide-containing regimen.

METHODS

A multicenter 48-week uncontrolled open-label rollover study was conducted on 71 HIV-infected adults recruited from previous enfuvirtide clinical trials. Patients with extensive previous use of protease and reverse transcriptase inhibitors received a twice-daily dose of 50 mg enfuvirtide subcutaneously (45 mg deliverable) combined with two or more antiretroviral drugs selected for each individual, guided by resistance testing and previous treatment history.

RESULTS

The mean baseline plasma HIV-RNA level was 4.81 log(10) copies/ml and the mean CD4 cell count was 134.8 cells/microl. The majority (86.9%) of treatment-emergent adverse events were grade 2 or less in severity. Injection site reactions were common, but no patients discontinued treatment. A mean HIV-RNA change of -1.33 log(10) was achieved within 14 days of treatment initiation. At week 48, approximately one-third of all patients in the intent-to-treat population maintained significant suppression of plasma HIV RNA, with either less than 400 copies/ml or more than a 1.0 log(10) decline from baseline. The mean gain in absolute CD4 cell counts at 48 weeks was 84.9 cells/microl. Trough plasma concentrations of enfuvirtide were consistently higher than target concentrations.

CONCLUSION

Self-administration of enfuvirtide is not associated with unexpected toxicities for up to one year, and combined with oral antiretroviral drugs was associated with a significant decrease in HIV RNA and an increase in CD4 cell counts.

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.

Safety and antiretroviral activity of chronic subcutaneous administration of T-20 in human immunodeficiency virus 1-infected children

BACKGROUND

Entry inhibitors, a new class of antiretroviral agents, interfere with the attachment, coreceptor interaction or fusion of HIV-1 with host target cells. The fusion inhibitor T-20 is the first in this new class, and the present study is the first to examine chronic s.c. administration of T-20 to HIV-1-infected children.

METHODS

Fourteen children, 4 to 12 years of age, with incompletely suppressed HIV-1 were studied. The median plasma viral load at baseline was 26,866 copies/ml (4.4 log10), and the median CD4 count was 523 cells/mm3. T-20 was administered twice daily by s.c. injection at 30 or 60 mg per m2 of body surface area per dose. For 7 days T-20 was added to the patients' background antiretroviral regimens; at Day 7 each subject's background therapy was changed to a regimen that was predicted to be virologically active, while T-20 was continued. Results are presented for the first 24 weeks of chronic T-20 dosing.

RESULTS

T-20 was generally well-tolerated. One child discontinued the drug because of aversion to injections, but no child discontinued because of adverse events. Eleven (79%) of 14 children had local injection site reactions at some time during the chronic T-20 dosing. Eleven of 14 subjects achieved the protocol-specified milestone of at least a 0.7-log10 reduction in plasma HIV-1 RNA by Day 7. In 10 subjects (71%) virologic suppression of 1.0 log10 or greater was achieved at 24 weeks; 6 subjects (43%) had viral loads <400 copies/ml and 3 (21%) had fewer than 50 copies/ml at 24 weeks.

CONCLUSIONS

These results indicate that a 24-week regimen of twice daily s.c. dosing of T-20 in HIV-1-infected children is safe and tolerable and that it is associated with suppression of HIV-1 replication during 24 weeks of administration.

Long-term treatment with subcutaneous T-20, a fusion inhibitor, in HIV-infected patients: patient satisfaction and impact on activities of daily living

T-20 is a novel antiretroviral agent that inhibits the fusion of human immunodeficiency virus (HIV) with target cell membranes. It is delivered by self-administered, twice-daily, subcutaneous injections. The impact of this mode of administration on patients' ability to conduct normal activities of daily living (ADL) and comply with a T-20 treatment regimen was assessed as part of a 48-week, phase 2 trial (T20-205). Patients' opinions on the impact of T-20 on ADL, ease of use of T-20, and choice to continue with T-20 were assessed by two questionnaires completed at baseline and week 48 (or study withdrawal). ADL were measured using a Likert-type scale based on established instruments with questions added to assess HIV-specific issues. Seventy previously treated patients received T-20 in combination with an average of five oral antiretroviral agents. Relative to other HIV/AIDS drugs, T-20 had little impact on ADL, with the majority of patients (54%-96%) agreeing (somewhat or strongly) that subcutaneous injections had not limited ADL. Patients found the injections relatively easy to perform with more than 47% of patients stating that each aspect of the injections (ease of injection, storage, reconstitution, and disposal of sharps) were very easy or easy. If medically indicated, 98% of patients stated that they would choose to continue with T-20. The most common reasons for this were the perceived effectiveness of T-20 and lack of side effects. In conclusion, the need to deliver T-20 via twice-daily subcutaneous injections was not considered an important barrier by HIV-positive patients seeking improvement or stabilization of their condition.

Anti-human immunodeficiency virus interactions of SCH-C (SCH 351125), a CCR5 antagonist, with other antiretroviral agents in vitro

SCH-C (SCH 351125) is a small-molecule antagonist of the human immunodeficiency virus type 1(HIV-1) coreceptor CCR5. It has in vitro activity against R5 viruses with 50% inhibitory concentrations ranging from 1.0 to 30.9 nM. We have studied anti-HIV-1 interactions of SCH-C with other antiretroviral agents in vitro. Synergistic interactions were seen with nucleoside reverse transcriptase inhibitors (zidovudine and lamivudine), nonnucleoside reverse transcriptase inhibitors (efavirenz), and protease inhibitors (indinavir) at all inhibitory concentrations evaluated. We have also studied antiviral interactions between the HIV-1 fusion inhibitor T-20 and SCH-C against a panel of R5 HIV-1 isolates. We found synergistic interactions against all the viruses tested, some of which harbored resistance mutations to reverse transcriptase and protease inhibitors. Anti-HIV-1 synergy was also observed between SCH-C and another R5 virus inhibitor, aminooxypentane-RANTES. These findings suggest that SCH-C may be a useful anti-HIV drug in combination regimens and that a combination of chemokine coreceptor/fusion inhibitors may be useful in the treatment of multidrug-resistant viruses.

SCH-C (SCH 351125), an orally bioavailable, small molecule antagonist of the chemokine receptor CCR5, is a potent inhibitor of HIV-1 infection in vitro and in vivo

We describe here the identification and properties of SCH-C (SCH 351125), a small molecule inhibitor of HIV-1 entry via the CCR5 coreceptor. SCH-C, an oxime-piperidine compound, is a specific CCR5 antagonist as determined in multiple receptor binding and signal transduction assays. This compound specifically inhibits HIV-1 infection mediated by CCR5 in U-87 astroglioma cells but has no effect on infection of CXCR4-expressing cells. SCH-C has broad and potent antiviral activity in vitro against primary HIV-1 isolates that use CCR5 as their entry coreceptor, with mean 50% inhibitory concentrations ranging between 0.4 and 9 nM. Moreover, SCH-C strongly inhibits the replication of an R5-using HIV-1 isolate in SCID-hu Thy/Liv mice. SCH-C has a favorable pharmacokinetic profile in rodents and primates with an oral bioavailability of 50-60% and a serum half-life of 5-6 h. On the basis of its novel mechanism of action, potent antiviral activity, and in vivo pharmacokinetic profile, SCH-C is a promising new candidate for therapeutic intervention of HIV infection.

Metabolic complications associated with antiretroviral therapy

Mortality rates in the HIV-infected patient population have decreased with the advent of highly active antiretroviral therapy (HAART) for the treatment of AIDS. Due to the chronic nature of HAART, long-term metabolic complications are associated with therapy, such as hyperlipidemia, fat redistribution and diabetes mellitus. Currently, all of these symptoms are classified as the lipodystrophy (LD) syndrome(s). However, hyperlipidemia and fat redistribution occur independently, indicating there may be multiple syndromes associated with HAART. Although fat gain/loss and dyslipidemia occur in protease inhibitor (PI) naïve patients treated with nucleoside reverse transcriptase inhibitors (NRTIs), combination therapies (PI and NRTI) accelerate the syndrome. Recent clinical trials, cell culture and animal studies indicate that these effects are not drug class specific and select PIs, NRTIs and non-nucleoside reverse transcriptase inhibitors (NNRTIs) can be associated with metabolic complications. Moreover, the effects can vary between various members of the same class of antiretroviral agents (i.e. not all PIs cause the same adverse reactions) and may be influenced by duration of infection, genetics and environmental factors. Although HAART increases the risk of metabolic complications, this does not outweigh the benefits of survival. In this review, we summarize the latest clinical and scientific information on these metabolic complications, examine current hypotheses explaining the syndromes and comment on the existing methods available to manage these metabolic side effects.

Mode of action of an antiviral peptide from HIV-1. Inhibition at a post-lipid mixing stage

DP178, a synthetic peptide corresponding to a segment of the transmembrane envelope glycoprotein (gp41) of human immunodeficiency virus, type 1 (HIV-1), is a potent inhibitor of viral infection and virus-mediated cell-cell fusion. Nevertheless, DP178 does not contain gp41 coiled-coil cavity binding residues postulated to be essential for inhibiting HIV-1 entry. We find that DP178 inhibits phospholipid redistribution mediated by the HIV-1 envelope glycoprotein at a concentration 8 times greater than that of solute redistribution (the IC(50) values are 43 and 335 nm, respectively). In contrast, C34, a synthetic peptide which overlaps with DP178 but contains the cavity binding residues, did not show this phenomenon (11 and 25 nm, respectively). The ability of DP178 to inhibit membrane fusion at a post-lipid mixing stage correlates with its ability to bind and oligomerize on the surface of membranes. Furthermore, our results are consistent with a model in which DP178 inhibits the formation of gp41 viral hairpin structure at low affinity, whereas C34 inhibits its formation at high affinity: the failure to form the viral hairpin prevents both lipid and solute from redistributing between cells. However, our data also suggest an additional membrane-bound inhibitory site for DP178 in the ectodomain of gp41 within a region immediately adjacent to the membrane-spanning domain. By binding to this higher affinity site, DP178 inhibits the recruitment of several gp41-membrane complexes, thus inhibiting fusion pore formation.

Strong in vitro synergy between the fusion inhibitor T-20 and the CXCR4 blocker AMD-3100

Attachment and entry of HIV-1 into CD4 cells involve a series of events in which different viral envelope proteins interact with specific cell receptors, culminating in fusion of viral and cell membranes. AMD-3100 is a small molecule inhibitor of HIV-1 attachment to the CXCR4 chemokine receptor, and T-20 is a synthetic peptide corresponding to a region of HIV-1 gp41 that blocks fusion to cell membranes. To evaluate the interaction between agents acting at two different steps of the entry process, we conducted in vitro studies of the combination of T-20 and AMD-3100 against an X4 HIV-1 isolate. Single drugs or multiply diluted fixed ratio combinations of drugs were added to peripheral blood mononuclear cells infected with a clinical isolate, 14aPre. Drug interactions were evaluated using the median-effect principle and the combination index technique. The 50% inhibitory concentration (IC50) for T-20 was 0.10 microg/ml and for AMD-3100 was 0.19 microg/ml. Synergy was observed between T-20 and AMD-3100 and this increased with higher inhibitory concentrations, with combination indices ranging from 0.62 at IC50 to 0.02 at IC95. Whether these synergistic interactions translate into clinical benefit will need to be addressed in the context of clinical trials.

Novel compounds in preclinical/early clinical development for the treatment of HIV infections

Virtually all the compounds that are currently used, or under advanced clinical trial, for the treatment of HIV infections, belong to one of the following classes: (i) nucleoside/nucleotide reverse transcriptase inhibitors (NRTIs), (ii) non-nucleoside reverse transcriptase inhibitors (NNRTIs) and (iii) protease inhibitors (PIs). In addition to the reverse transcriptase and protease step, various other events in the HIV replicative cycle are potential targets for chemotherapeutic intervention: (i) viral adsorption, through binding to the viral envelope glycoprotein gp120 (polysulphates, polysulphonates, polyoxometalates, zintevir, negatively charged albumins); (ii) viral entry, through blockade of the viral coreceptors CXCR4 and CCR5 [bicyclams (AMD3100), polyphemusins (T22), TAK-779]; (iii) virus-cell fusion, through binding to the viral glycoprotein gp41 [T-20 (DP-178), siamycins, betulinic acid derivatives]; (iv) viral assembly and disassembly, through NCp7 zinc finger-targeted agents [2,2'-dithiobisbenzamides (DIBAs), azadicarbonamide (ADA)]; (v) proviral DNA integration, through integrase inhibitors such as L-chicoric acid; (vi) viral mRNA transcription, through inhibitors of the transcription (transactivation) process (peptoid CGP64222, fluoroquinolone K-12, Streptomyces product EM2487). Also, in recent years new NRTIs, NNRTIs and PIs have been developed that possess, respectively, improved metabolic characteristics (i.e. phosphoramidate and cyclosaligenyl pronucleotides of d4T), or increased activity against NNRTI-resistant HIV strains, or, in the case of PIs, a different, non-peptidic scaffold. Given the multitude of molecular targets with which anti-HIV agents can interact, one should be cautious in extrapolating from cell-free enzymatic assays to the mode of action of these agents in intact cells. A number of compounds (i.e. zintevir and L-chicoric acid, on the one hand; and CGP64222 on the other hand) have recently been found to interact with virus-cell binding and viral entry in contrast to their proposed modes of action targeted at the integrase and transactivation process, respectively.

The HIV-1 cell entry inhibitor T-20 potently chemoattracts neutrophils by specifically activating the N-formylpeptide receptor

T-20, a synthetic peptide corresponding to the heptad repeat sequence of HIV-1 gp41, blocks HIV-1 entry by targeting gp41, and is currently in clinical trials as an anti-retroviral agent. We recently reported that in vitro T-20 also functions as a phagocyte chemoattractant and a chemotactic agonist at the phagocyte N-formylpeptide receptor (FPR). Here we show that T-20 is also a potent chemotactic agonist in vitro at a related human phagocyte receptor FPRL1R. To test the relative importance of FPR and FPRL1R in primary cells, we identified the corresponding mouse T-20 receptors, mFPR and FPR2, which are both expressed in neutrophils, and compared T-20 action on neutrophils from wild type and mFPR knockout mice. Surprisingly, although T-20 activates mFPR and FPR2 in transfected cells with equal potency and efficacy in both calcium flux and chemotaxis assays, neutrophils from mFPR knockout mice did not respond to T-20. These results provide genetic evidence that FPR is the major phagocyte T-20 receptor in vivo and point to the potential feasibility of studying T-20 effects on immunity in a mouse model. This may help define the cause of local inflammation after T-20 injection that has recently been reported in Phase I clinical trials.