Multiparametric assay to screen and dissect the mode of action of anti-human immunodeficiency virus envelope drugs

Discovery of Ten Anti-HIV Hit Compounds and Preliminary Pharmacological Mechanisms Studies

BACKGROUND

The research and development of HIV drugs is very important, but at the same time it is a long cycle and expensive system project. High-throughput drug screening systems and molecular libraries of potential hit compounds remain the main ways for the discovery of hit compounds with anti-HIV activity.

OBJECTIVE

The aim of this study was to screen out the hit compounds against HIV-1 in the natural product molecule library and the antiviral molecule library, and elucidate the molecular mechanism of their inhibition of HIV-1, so as to provide a new choice for AIDS drug research.

METHODS

In this study, a drug screening system using HIV Rev-dependent indicator cell line (Rev-A3R5-GFP reporter cells) with pseudoviruses (pNL4-3) was used. The natural drug molecule library and antiviral molecule library were screened, and preliminary drug mechanism studies were performed.

RESULTS

Ten promising hit compounds were screened. These ten molecules and their drug inhibitory IC50 were as follows: Cephaeline (0.50 μM), Yadanziolide A (8.82 μM), Bruceine D (2.48 μM), Astragaloside IV (4.30 μM), RX-3117 (1.32 μM), Harringtonine (0.63 μM), Tubercidin (0.41 μM), Theaflavine-3, 3'-digallate (0.41 μM), Ginkgetin (10.76 μM), ZK756326 (5.97 μM). The results of the Time of additions showed that except for Astragaloside IV and Theaflavine-3, 3'-digallate had a weak entry inhibition effect, and it was speculated that all ten compounds had an intracellular inhibition effect. Cephaeline, Harringtonine, Astragaloside IV, Bruceine D, and Tubercidin may have pre-reverse transcriptional inhibition. Yadanziolide A, Theaflavine-3, 3'-digallate, Ginkgetin and RX-3117 may be in the post-reverse transcriptional inhibition. The inhibitory effect of ZK 75632 may be in the reverse transcriptional process.

CONCLUSION

A drug screening system using Rev-A3R5-GFP reporter cells with pseudoviruses (pNL4-3) is highly efficient. This study provided potential hit compounds for new HIV drug research.

Design of Small Molecules with HIV Fusion Inhibitory Property Based on Gp41 Interaction Assay

BACKGROUND

Gp41 of HIV (Human Immunodeficiency Virus) is a protein that mediates fusion between viral and cellular membranes. The agent, T-20, which has been approved for HIV inhibition, can restrain Gp41 function in the fusion process; nevertheless, it has disadvantages like instability, high cost of production and injection form to be delivered twice a day.

METHODS

Several molecules like NB-2 and NB-64 have been discovered that can inhibit HIV infection. These molecules were used as template compounds to design and develop more effective small molecules functioning as HIV-1 fusion inhibitors targeting Gp41. The process included in silico docking protocols using HEX and ArgusLab applications. A multisource database was created, after choosing the best molecules; they were tested in vitro for inhibitory activity by HIV-1 single-cycle model, transfected in HEK cells (293T).

RESULTS

Computational analysis and experimental data were combined to explore molecular properties and the most potent ones were found, with the best suitable criteria for interaction with Gp41. Several examples (DAA-6, DAA-9 and DAA-12) could inhibit infection in vitro as effective as NB-2, NB-64.

CONCLUSION

Since disadvantages of available fusion inhibitor (T-20), it seems necessary to find similar molecules to be approved and have small size providing suitable bioactivity profile. The molecules explored in this study can be good candidates for further investigations to be used as oral HIV fusion inhibitors in the future.

Development of resistance to VIR-353 with cross-resistance to the natural HIV-1 entry virus inhibitory peptide (VIRIP)

OBJECTIVE

Virus-inhibitory peptide (VIRIP) has been identified as a component of human hemofiltrate that blocks HIV-1 gp41-dependent fusion by interacting with the fusion peptide. A VIRIP analogue (VIR-576) has been shown to be effective in a phase I/II clinical trial. We have evaluated the activity and mechanism of HIV-1 resistance to VIRIP and its analogue, VIR-353.

METHODS

Anti-HIV activity and passage of HIV-1 strains in cell culture were used to generate and identify mutations that confer resistance to VIRIP and VIR-353. Recombinant viruses harboring the most relevant mutations were generated and characterized.

RESULTS

VIRIP and VIR-353 showed anti-HIV-1 activity with EC(50) of 28 and 0.3 μmol/l, respectively, and were active against virus resistant to BMS-155, AMD3100, T20, TAK-779 or nevirapine. Time of addition experiments showed that VIR-353 targets a time/site of action corresponding to gp41-dependent fusion. VIR-353-resistant virus was generated after 450 days in cell culture, suggesting a high genetic barrier for resistance. The VIR-353-resistant virus was cross-resistant to VIRIP but remained sensitive to T20, AMD3100 or zidovudine. Recombination of gp41 into a wild-type backbone partially recovered the resistant phenotype, but both gp120 and gp41 from the resistant virus were necessary to restore resistance to VIRIP or VIR-353. Site-directed mutagenesis confirmed the role of specific mutations and identified a combination of three mutations (A433T/V489I/V570I) as the most relevant to VIRIP resistance.

CONCLUSION

VIRIP may interact with a region of gp41 that is essential for fusion but not the fusion peptide. Our results highlight interactions between gp41 and gp120 that may be required during the fusion process.

A cell-to-cell HIV transfer assay identifies humoral responses with broad neutralization activity

BACKGROUND

Cell-to-cell HIV spread through virological synapses proceeds in two steps, first HIV particles are rapidly transferred to target cells in a CD4-dependent manner and then coreceptor-dependent events allow for infection or death of single target cells and cell-to-cell fusion.

METHODS

293T or MOLT cells producing HIV particles were cocultured with primary CD4 T-cells or reporter cell lines. The extent of HIV transfer, cell fusion and target cell death was assessed. Inhibition by sera from 19 HIV-infected patients was evaluated and compared with cell-free HIV neutralization using different envelopes from clades A, B, C and E.

RESULTS

Sera showed different abilities to protect CD4 T-cells from cell-to-cell transfer, fusion or death when cocultured with HIV producing 293T cells. Some sera were able to block all parameters (a property of IgGb12), while other showed lower activity against HIV transfer despite being able to block fusion and death (a property of antibodies blocking post-CD4 binding steps). Neutralization of cell-to-cell HIV transfer strongly correlated with IgG binding to native Env. Interestingly, sera that efficiently blocked HIV transfer showed broader neutralizing response, as they neutralized a higher percentage of the viruses tested compared with sera showing low CD4 binding site responses (P=0.01). Similar results were observed in a model of T cell-T cell HIV transmission, although this experimental model showed lower capacity to discriminate broadly neutralizing responses.

CONCLUSION

Cell-to-cell HIV transfer assays identify sera with broadly neutralizing capacity and may help to characterize anti-HIV humoral responses.

Identification of low-molecular weight inhibitors of HIV-1 reverse transcriptase using a cell-based high-throughput screening system

A cell-based drug screening system that utilizes a green fluorescent protein (GFP)-tagged recombinant lentiviral vector has been used to screen a chemical library of 34,000 small molecules for antiretroviral compounds. Thirty-three initial hits were analyzed and four compounds were selected based on their anti-human immunodeficiency virus type 1 (HIV-1) activity (EC(50) values ranging from 0.17 to 1.9 μM) and low cellular toxicity (CC(50) values >50 μM). The four compounds blocked reverse transcription and were able to inhibit the replication of a panel of different HIV-1 strains, including non-B subtype and viruses resistant to different drug classes. Serial in vitro passages of HIV-1(B-HXB2) in the presence of increasing drug concentrations selected for viruses with reduced susceptibility. Mutations previously associated with resistance to non-nucleoside reverse transcriptase (RT) inhibitors (L100I and Y181C for CBL-17 and CBL-21, respectively) or linked to nucleoside analogue resistance (A62V for CBL-4.0 and CBL-4.1) were identified. Viruses with reduced susceptibility to CBL-17 and CBL-21 but not the ones resistant to CBL-4.0 or CBL-4.1 showed a decrease in replicative fitness. Interestingly, two of the small molecules (CBL-4.0 and CBL-4.1) are indolopyridinones that were previously described as nucleotide-competing RT inhibitors.

Endocytosis of HIV: anything goes

The major pathway for HIV internalization in CD4+ T cells has been thought to be the direct fusion of virus and cell membranes, because the cell surface is the point of entry of infectious particles. However, the exact contribution of endocytic pathways to the infection of CD4+ T lymphocytes is unknown, and the mechanisms involved in endocytosis of HIV particles are unclear. Recent evidence suggests that endocytosis of cell-free and cell-associated virus particles could lead to effective virus entry and productive infections. Such observations have, in turn, spurred a debate on the relevance of endosomal entry as a mechanism of escape from the immune system and HIV entry inhibitors. In this paper, we review the endocytosis of HIV and discuss its role in HIV infection and pathogenesis.

ADS-J1 inhibits HIV-1 entry by interacting with gp120 and does not block fusion-active gp41 core formation

We had shown that virus resistance to ADS-J1 was associated with amino acid changes in the envelope glycoprotein, mostly located in the gp120 coding region. Time-of-addition and endocytic virus transfer assays clearly demonstrated that ADS-J1 behaved as a gp120 inhibitor. ADS-J1-resistant virus was cross-resistant to the polyanion dextran sulfate, and recombination of gp120 recovered only the ADS-J1-resistant phenotype. In summary, ADS-J1 blocks an early step of virus entry that appears to be driven by gp120 alone.

Novel targets for antiretroviral therapy: clinical progress to date

The advent of HIV-1 resistance to antiretroviral medications, the need for lifelong antiretroviral therapy (ART) for HIV-infected individuals, and the goal of minimizing ART-related adverse effects and toxicity all drive the need for new antiretroviral drugs. Two new classes of antiretroviral medications for HIV treatment, the CCR5 and integrase inhibitors, have recently been approved for use in patients in whom previous HIV treatment regimens have failed. These new agent classes are a welcome addition to other antiretroviral classes, which include nucleoside reverse transcriptase inhibitors, non-nucleoside reverse transcriptase inhibitors, protease inhibitors and fusion inhibitors. Maraviroc is a CCR5 co-receptor antagonist that blocks HIV binding to the CCR5 receptor, which is a CD4 co-receptor necessary for cell entry. It is approved for use in ART-experienced patients with CCR5-tropic HIV, and was found to significantly reduce HIV viral load and increase CD4+ cell count when combined with an optimized background ART regimen (OBR). Treatment failure with maraviroc has been described and is primarily associated with the presence of CXCR4-tropic virus. Vicriviroc is another CCR5 co-receptor antagonist that is in late clinical trials. Raltegravir is the first US FDA-approved HIV-1 integrase inhibitor. It is approved for use in ART-experienced patients and was found to significantly reduce HIV viral load and increase CD4+ cell counts compared with placebo in combination with an OBR. Raltegravir has also been studied in treatment-naive patients and was found to be non-inferior to an efavirenz-based regimen. Elvitegravir is another HIV-1 integrase inhibitor in clinical development. Other new antiretroviral agents in clinical development include PRO140, a monoclonal antibody against CCR5, and bevirimat, a maturation inhibitor that prevents late-stage gag polyprotein processing. A number of other drug targets, such as CCR5 co-receptor agonists, CXCR4 co-receptor antagonists, novel fusion inhibitors, and alternative antiretroviral strategies, such as immune stimulation and gene therapy, are under investigation.

Anti-HIV activity and resistance profile of the CXC chemokine receptor 4 antagonist POL3026

We have studied the mechanism of action of Arg(*)-Arg-Nal(2)-Cys(1x)-Tyr-Gln-Lys-(d-Pro)-Pro-Tyr-Arg-Cit-Cys(1x)-Arg-Gly-(d-Pro)(*) (POL3026), a novel specific beta-hairpin mimetic CXC chemokine receptor (CXCR)4 antagonist. POL3026 specifically blocked the binding of anti-CXCR4 monoclonal antibody 12G5 and the intracellular Ca(2+) signal induced by CXC chemokine ligand 12. POL3026 consistently blocked the replication of human immunodeficiency virus (HIV), including a wide panel of X4 and dualtropic strains and subtypes in several culture models, with 50% effective concentrations (EC(50)) at the subnanomolar range, making POL3026 the most potent CXCR4 antagonist described to date. However, 1-[[4-(1,4,8,11-tetrazacyclotetradec-1-ylmethyl)phenyl]methyl]-1,4,8,11-tetrazacyclotetradecane (AMD3100)-resistant and stromal cell-derived factor-1alpha-resistant HIV-1 strains were cross-resistant to POL3026. Time of addition experiments and a multiparametric evaluation of HIV envelope function in the presence of test compounds confirmed the activity of POL3026 at an early step of virus replication: interaction with the coreceptor. Generation of HIV-1 resistance to POL3026 led to the selection of viruses 12- and 25-fold less sensitive and with mutations in gp120, including the V3 loop region. However, POL3026 prevented the emergence of CXCR4-using variants from an R5 HIV-1 strain that may occur in the presence of anti-HIV agents targeting CC chemokine receptor 5.

Inhibition of coreceptor-independent cell-to-cell human immunodeficiency virus type 1 transmission by a CD4-immunoglobulin G2 fusion protein

We have previously shown (J. Blanco et al., J. Biol. Chem. 279:51305-51314, 2004) that the contact between HIV producing cells and primary CD4(+) T cells may induce the uptake of human immunodeficiency virus (HIV) particles by target cells in the absence of HIV envelope-mediated membrane fusion or productive HIV replication. HIV uptake by CD4(+) T cells was dependent on cellular contacts mediated by the binding of gp120 to CD4 but was independent of the expression of the appropriate HIV coreceptor, CCR5 or CXCR4. Here, we have characterized the effect of agents blocking gp120 binding to CD4 on cell-to-cell HIV transmission. A recombinant CD4-based protein (CD4-immunoglobulin G2 [IgG2]), that is currently being evaluated in clinical trials, completely inhibited the uptake of HIV particles by CD4(+) T cells from persistently infected cells expressing R5, X4, or X4/T-20-resistant HIV-1 envelope glycoproteins. Consequently, both the release of viral particles from endocytic vesicles and the infection of reporter U87-CD4 cells were also prevented. The polyanionic anti-HIV agent dextran sulfate failed to prevent the intracellular uptake of virions by CD4(+) T cells. Indeed, it increased HIV uptake in a dose-dependent manner, suggesting functional differences between the specific gp120-targeting CD4-IgG2 agent and nonspecific HIV binding inhibitors. Thus, the inhibition of the specific interaction between gp120 and CD4 protein could be an effective strategy to inhibit HIV binding to CD4(+) T cells, and the mechanism by which CD4(+) T cells lacking the appropriate coreceptor may be converted in HIV carriers.