Rotten to the core: antivirals targeting the HIV-1 capsid core

WEDAP: A Python Package for Streamlined Plotting of Molecular Simulation Data

Given the growing interest in path sampling methods for extending the timescales of molecular dynamics (MD) simulations, there has been great interest in software tools that streamline the generation of plots for monitoring the progress of large-scale simulations. Here, we present the WEDAP Python package for simplifying the analysis of data generated from either conventional MD simulations or the weighted ensemble (WE) path sampling method, as implemented in the widely used WESTPA software package. WEDAP facilitates (i) the parsing of WE simulation data stored in highly compressed, hierarchical HDF5 files, and (ii) incorporates trajectory weights from WE simulations into all generated plots. Our Python package consists of multiple user-friendly interfaces: a command-line interface, a graphical user interface, and a Python application programming interface. We demonstrate the plotting features of WEDAP through a series of examples using data from WE and conventional MD simulations that focus on the HIV-1 capsid protein C-terminal domain dimer as a showcase system. The source code for WEDAP is freely available on GitHub at https://github.com/chonglab-pitt/wedap .

A Tag-Free Platform for Synthesis and Screening of Cyclic Peptide Libraries

In the realm of high-throughput screening (HTS), macrocyclic peptide libraries traditionally necessitate decoding tags, essential for both library synthesis and identifying hit peptide sequences post-screening. Our innovation introduces a tag-free technology platform for synthesizing cyclic peptide libraries in solution and facilitates screening against biological targets to identify peptide binders through unconventional intramolecular CyClick and DeClick chemistries (CCDC) discovered through our research. This combination allows for the synthesis of diverse cyclic peptide libraries, the incorporation of various amino acids, and facile linearization and decoding of cyclic peptide binder sequences. Our sensitivity-enhancing derivatization method, utilized in tandem with nano LC-MS/MS, enables the sequencing of peptides even at exceedingly low picomolar concentrations. Employing our technology platform, we have successfully unearthed novel cyclic peptide binders against a monoclonal antibody and the first cyclic peptide binder of HIV capsid protein responsible for viral infections as validated by microscale thermal shift assays (TSA), biolayer interferometry (BLI) and functional assays.

Discovery of low-molecular-weight phenylalanine derivatives as novel HIV capsid modulators with improved antiretroviral activity and metabolic stability

The HIV capsid (CA) protein is a promising target for anti-AIDS treatment due to its critical involvement in viral replication. Herein, we utilized the well-documented CA inhibitor PF74 as our lead compound and designed a series of low-molecular-weight phenylalanine derivatives. Among them, compound 7t exhibited remarkable antiviral activity with a high selection index (EC50 = 0.040 µM, SI = 2815), surpassing that of PF74 (EC50 = 0.50 µM, SI = 258). Furthermore, when evaluated against the HIV-2 strain, 7t (EC50 = 0.13 µM) demonstrated approximately 14-fold higher potency than that of PF74 (EC50 = 1.76 µM). Insights obtained from surface plasmon resonance (SPR) revealed that 7t exhibited stronger target affinity to the CA hexamer and monomer in comparison to PF74. The potential interactions between 7t and the HIV-1 CA were further elucidated using molecular docking and molecular dynamics simulations, providing a plausible explanation for the enhanced target affinity with 7t over PF74. Moreover, the metabolic stability assay demonstrated that 7t (T1/2 = 77.0 min) significantly outperforms PF74 (T1/2 = 0.7 min) in human liver microsome, exhibiting an improvement factor of 110-fold. In conclusion, 7t emerges as a promising drug candidate warranting further investigation.

Design and Synthesis of New GS-6207 Subtypes for Targeting HIV-1 Capsid Protein

HIV-1 capsid protein (CA) is the molecular target of the recently FDA-approved long acting injectable (LAI) drug lenacapavir (GS-6207). The quick emergence of CA mutations resistant to GS-6207 necessitates the design and synthesis of novel sub-chemotypes. We have conducted the structure-based design of two new sub-chemotypes combining the scaffold of GS-6207 and the N-terminal cap of PF74 analogs, the other important CA-targeting chemotype. The design was validated via induced-fit molecular docking. More importantly, we have worked out a general synthetic route to allow the modular synthesis of novel GS-6207 subtypes. Significantly, the desired stereochemistry of the skeleton C2 was confirmed via an X-ray crystal structure of the key synthetic intermediate 22a. Although the newly synthesized analogs did not show significant potency, our efforts herein will facilitate the future design and synthesis of novel subtypes with improved potency.

A Review of FDA-Approved Anti-HIV-1 Drugs, Anti-Gag Compounds, and Potential Strategies for HIV-1 Eradication

Acquired immunodeficiency syndrome (AIDS) is an enormous global health threat stemming from human immunodeficiency virus (HIV-1) infection. Up to now, the tremendous advances in combination antiretroviral therapy (cART) have shifted HIV-1 infection from a fatal illness into a manageable chronic disorder. However, the presence of latent reservoirs, the multifaceted nature of HIV-1, drug resistance, severe off-target effects, poor adherence, and high cost restrict the efficacy of current cART targeting the distinct stages of the virus life cycle. Therefore, there is an unmet need for the discovery of new therapeutics that not only bypass the limitations of the current therapy but also protect the body's health at the same time. The main goal for complete HIV-1 eradication is purging latently infected cells from patients' bodies. A potential strategy called "lock-in and apoptosis" targets the budding phase of the life cycle of the virus and leads to susceptibility to apoptosis of HIV-1 infected cells for the elimination of HIV-1 reservoirs and, ultimately, for complete eradication. The current work intends to present the main advantages and disadvantages of United States Food and Drug Administration (FDA)-approved anti-HIV-1 drugs as well as plausible strategies for the design and development of more anti-HIV-1 compounds with better potency, favorable pharmacokinetic profiles, and improved safety issues.

Identification of clickable HIV-1 capsid-targeting probes for viral replication inhibition

Of the targets for HIV-1 therapeutics, the capsid core is a relatively unexploited but alluring drug target due to its indispensable roles throughout virus replication. Because of this, we aimed to identify "clickable" covalent modifiers of the HIV-1 capsid protein (CA) for future functionalization. We screened a library of fluorosulfate compounds that can undergo sulfur(VI) fluoride exchange (SuFEx) reactions, and five compounds were identified as hits. These molecules were further characterized for antiviral effects. Several compounds impacted in vitro capsid assembly. One compound, BBS-103, covalently bound CA via a SuFEx reaction to Tyr145 and had antiviral activity in cell-based assays by perturbing virus production, but not uncoating. The covalent binding of compounds that target the HIV-1 capsid could aid in the future design of antiretroviral drugs or chemical probes that will help study aspects of HIV-1 replication.

HIV-1 Capsid Uncoating Is a Multistep Process That Proceeds through Defect Formation Followed by Disassembly of the Capsid Lattice

The HIV-1 core consists of a cone-shaped capsid shell made of capsid protein (CA) hexamers and pentamers encapsulating the viral genome. HIV-1 capsid disassembly, referred to as uncoating, is important for productive infection; however, the location, timing, and regulation of uncoating remain controversial. Here, we employ amber codon suppression to directly label CA. In addition, a fluid phase fluorescent probe is incorporated into the viral core to detect small defects in the capsid lattice. This double-labeling strategy enables the visualization of uncoating of single cores in vitro and in living cells, which we found to always proceed through at least two distinct steps─the formation of a defect in the capsid lattice that initiates gradual loss of CA below a detectable level. Importantly, intact cores containing the fluid phase and CA fluorescent markers enter and uncoat in the nucleus, as evidenced by a sequential loss of both markers, prior to establishing productive infection. This two-step uncoating process is observed in different cells, including a macrophage line. Notably, the lag between the release of fluid phase marker and terminal loss of CA appears to be independent of the cell type or reverse transcription and is much longer (>5-fold) for nuclear capsids compared to cell-free cores or cores in the cytosol, suggesting that the capsid lattice is stabilized by capsid-binding nuclear factors. Our results imply that intact HIV-1 cores enter the cell nucleus and that uncoating is initiated through a localized defect in the capsid lattice prior to a global loss of CA.

HIV-1-induced translocation of CPSF6 to biomolecular condensates

Cleavage and polyadenylation specificity factor subunit 6 (CPSF6, also known as CFIm68) is a 68 kDa component of the mammalian cleavage factor I (CFIm) complex that modulates mRNA alternative polyadenylation (APA) and determines 3' untranslated region (UTR) length, an important gene expression control mechanism. CPSF6 directly interacts with the HIV-1 core during infection, suggesting involvement in HIV-1 replication. Here, we review the contributions of CPSF6 to every stage of the HIV-1 replication cycle. Recently, several groups described the ability of HIV-1 infection to induce CPSF6 translocation to nuclear speckles, which are biomolecular condensates. We discuss the implications for CPSF6 localization in condensates and the potential role of condensate-localized CPSF6 in the ability of HIV-1 to control the protein expression pattern of the cell.

HIV-1 capsid and viral DNA integration

IMPORTANCE

HIV-1 capsid protein (CA)-independently or by recruiting host factors-mediates several key steps of virus replication in the cytoplasm and nucleus of the target cell. Research in the recent years have established that CA is multifunctional and genetically fragile of all the HIV-1 proteins. Accordingly, CA has emerged as a validated and high priority therapeutic target, and the first CA-targeting antiviral drug was recently approved for treating multi-drug resistant HIV-1 infection. However, development of next generation CA inhibitors depends on a better understanding of CA's known roles, as well as probing of CA's novel roles, in HIV-1 replication. In this timely review, we present an updated overview of the current state of our understanding of CA's multifunctional role in HIV-1 replication-with a special emphasis on CA's newfound post-nuclear roles, highlight the pressing knowledge gaps, and discuss directions for future research.

Molecular docking and simulation studies of Chloroquine, Rimantadine and CAP-1 as potential repurposed antivirals for decapod iridescent virus 1 (DIV1)

Drug repurposing is a methodology of identifying new therapeutic use for existing drugs. It is a highly efficient, time and cost-saving strategy that offers an alternative approach to the traditional drug discovery process. Past in-silico studies involving molecular docking have been successful in identifying potential repurposed drugs for the various treatment of diseases including aquaculture diseases. The emerging shrimp hemocyte iridescent virus (SHIV) or Decapod iridescent virus 1 (DIV1) is a viral pathogen that causes severe disease and high mortality (80 %) in farmed shrimps caused serious economic losses and presents a new threat to the shrimp farming industry. Therefore, effective antiviral drugs are critically needed to control DIV1 infections. The aim of this study is to investigate the interaction of potential existing antiviral drugs, Chloroquine, Rimantadine, and CAP-1 with DIV1 major capsid protein (MCP) with the intention of exploring the potential of drug repurposing. The interaction of the DIV1 MCP and three antivirals were characterised and analysed using molecular docking and molecular dynamics simulation. The results showed that CAP-1 is a more promising candidate against DIV1 with the lowest binding energy of -8.46 kcal/mol and is more stable compared to others. We speculate that CAP-1 binding may induce the conformational changes in the DIV1 MCP structure by phosphorylating multiple residues (His123, Tyr162, and Thr395) and ultimately block the viral assembly and maturation of DIV1 MCP. To the best of our knowledge, this is the first report regarding the structural characterisation of DIV1 MCP docked with repurposing drugs.

HIV-1 binds dynein directly to hijack microtubule transport machinery

Viruses exploit host cytoskeletal elements and motor proteins for trafficking through the dense cytoplasm. Yet the molecular mechanism that describes how viruses connect to the motor machinery is unknown. Here, we demonstrate the first example of viral microtubule trafficking from purified components: HIV-1 hijacking microtubule transport machinery. We discover that HIV-1 directly binds to the retrograde microtubule-associated motor, dynein, and not via a cargo adaptor, as previously suggested. Moreover, we show that HIV-1 motility is supported by multiple, diverse dynein cargo adaptors as HIV-1 binds to dynein light and intermediate chains on dynein's tail. Further, we demonstrate that multiple dynein motors tethered to rigid cargoes, like HIV-1 capsids, display reduced motility, distinct from the behavior of multiple motors on membranous cargoes. Our results introduce a new model of viral trafficking wherein a pathogen opportunistically 'hijacks' the microtubule transport machinery for motility, enabling multiple transport pathways through the host cytoplasm.

Anti-CD4 antibody and dendrimeric peptide based targeted nano-liposomal dual drug formulation for the treatment of HIV infection

AIMS

Development and characterization of LAM and DTG loaded liposomes conjugated anti-CD4 antibody and peptide dendrimer (PD2) to improve the therapeutic efficacy and to achieve targeted treatment for HIV infection.

MAIN METHODS

A 2-level full factorial design was used to optimize the preparation of dual drug loaded liposomes. Optimized dual drug loaded ligand conjugated liposomes were assessed for their cytotoxicity and cell internalization on TZM-bl cells. Anti-HIV efficiency of the dual drug loaded liposomes were screened for their inhibitory potential in TZM-bl cells and the activities were confirmed using Peripheral Blood Mononuclear Cells (PBMCs).

KEY FINDINGS

The particle size of the optimized dual drug-loaded liposomes was 133.7 ± 4.04 nm, and the spherical morphology of the liposomes was confirmed by TEM analysis. The entrapment efficiency was 34 ± 4.9 % and 54 ± 1.8 % for LAM and DTG, respectively, and a slower in vitro release of LAM and DTG was observed when entrapped into liposomes. The cytotoxicity of the dual drug loaded liposomes was similar to the cytotoxicity of free drug solutions. Conjugation of anti-CD4 antibody and PD2 did not significantly influence the cytotoxicity but it enhanced the uptake of liposomes into the cells. Conjugated dual drug loaded liposomes exhibited better HIV inhibition with lower IC50 values (0.0003 ± 0.0002 μg/mL) compared to their free drug solutions (0.002 ± 0.001 μg/mL). The liposomal formulations have shown similar activities in both screening and confirmatory cell-based assays.

SIGNIFICANCE

The results demonstrated the cell targeting ability of dual drug loaded liposomes conjugated with anti-CD4 antibody and peptide dendrimer. Conjugated liposomes also improved anti-HIV efficiency of LAM and DTG.

Label-free imaging of nuclear membrane for analysis of nuclear import of viral complexes

HIV-1 enters the nucleus of non-dividing cells through the nuclear pore complex where it integrates into the host genome. The mechanism of HIV-1 nuclear import remains poorly understood. A powerful means to investigate the docking of HIV-1 at the nuclear pore and nuclear import of viral complexes is through single virus tracking in live cells. This approach necessitates fluorescence labeling of HIV-1 particles and the nuclear envelope, which may be challenging, especially in the context of primary cells. Here, we leveraged a deep neural network model for label-free visualization of the nuclear envelope using transmitted light microscopy. A training image set of cells with fluorescently labeled nuclear Lamin B1 (ground truth), along with the corresponding transmitted light images, was acquired and used to train our model to predict the morphology of the nuclear envelope in fixed cells. This protocol yielded accurate predictions of the nuclear membrane and was used in conjunction with virus infection to examine the nuclear entry of fluorescently labeled HIV-1 complexes. Analyses of HIV-1 nuclear import as a function of virus input yielded identical numbers of fluorescent viral complexes per nucleus using the ground truth and predicted nuclear membrane images. We also demonstrate the utility of predicting the nuclear envelope based on transmitted light images for multicolor fluorescence microscopy of infected cells. Importantly, we show that our model can be adapted to predict the nuclear membrane of live cells imaged at 37 °C, making this approach compatible with single virus tracking. Collectively, these findings demonstrate the utility of deep learning approaches for label-free imaging of cellular structures during early stages of virus infection.

Use of TSAR, Thermal Shift Analysis in R, to identify Folic Acid as a Molecule that Interacts with HIV-1 Capsid

Thermal shift assay (TSA) is a versatile biophysical technique for studying protein interactions. Here, we report a free, open-source software tool TSAR (Thermal Shift Analysis in R) to expedite and automate the analysis of thermal shift data derived either from individual experiments or large screens of chemical libraries. The TSAR package incorporates multiple, dynamic workflows to facilitate the analysis of TSA data and returns publication-ready graphics or processed results. Further, the package includes a graphic user interface (GUI) that enables easy use by non-programmers, aiming to simplify TSA analysis while diversifying visualization. To exemplify the utility of TSAR we screened a chemical library of vitamins to identify molecules that interact with the capsid protein (CA) of human immunodeficiency virus type 1 (HIV-1). Our data show that hexameric CA interacts with folic acid in vitro.

Modulation of HIV-1 capsid multimerization by sennoside A and sennoside B via interaction with the NTD/CTD interface in capsid hexamer

Small molecules that bind to the pocket targeted by a peptide, termed capsid assembly inhibitor (CAI), have shown antiviral effects with unique mechanisms of action. We report the discovery of two natural compounds, sennoside A (SA) and sennoside B (SB), derived from medicinal plants that bind to this pocket in the C-terminal domain of capsid (CA CTD). Both SA and SB were identified via a drug-screening campaign that utilized a time-resolved fluorescence resonance energy transfer assay. They inhibited the HIV-1 CA CTD/CAI interaction at sub-micromolar concentrations of 0.18 μM and 0.08 μM, respectively. Mutation of key residues (including Tyr 169, Leu 211, Asn 183, and Glu 187) in the CA CTD decreased their binding affinity to the CA monomer, from 1.35-fold to 4.17-fold. Furthermore, both compounds induced CA assembly in vitro and bound directly to the CA hexamer, suggesting that they interact with CA beyond the CA CTD. Molecular docking showed that both compounds were bound to the N-terminal domain (NTD)/CTD interface between adjacent protomers within the CA hexamer. SA established a hydrogen-bonding network with residues N57, V59, Q63, K70, and N74 of CA1-NTD and Q179 of CA2-CTD. SB formed hydrogen bonds with the N53, N70, and N74 residues of CA1-NTD, and the A177and Q179 residues of CA2-CTD. Both compounds, acting as glue, can bring αH4 in the NTD and αH9 in the CTD of the NTD/CTD interface close to each other. Collectively, our research indicates that SA and SB, which enhance CA assembly, could serve as novel chemical tools to identify agents that modulate HIV-1 CA assembly. These natural compounds may potentially lead to the development of new antiviral therapies with unique mechanisms of action.

Multidisciplinary studies with mutated HIV-1 capsid proteins reveal structural mechanisms of lattice stabilization

HIV-1 capsid (CA) stability is important for viral replication. E45A and P38A mutations enhance and reduce core stability, thus impairing infectivity. Second-site mutations R132T and T216I rescue infectivity. Capsid lattice stability was studied by solving seven crystal structures (in native background), including P38A, P38A/T216I, E45A, E45A/R132T CA, using molecular dynamics simulations of lattices, cryo-electron microscopy of assemblies, time-resolved imaging of uncoating, biophysical and biochemical characterization of assembly and stability. We report pronounced and subtle, short- and long-range rearrangements: (1) A38 destabilized hexamers by loosening interactions between flanking CA protomers in P38A but not P38A/T216I structures. (2) Two E45A structures showed unexpected stabilizing CANTD-CANTD inter-hexamer interactions, variable R18-ring pore sizes, and flipped N-terminal β-hairpin. (3) Altered conformations of E45Aa α9-helices compared to WT, E45A/R132T, WTPF74, WTNup153, and WTCPSF6 decreased PF74, CPSF6, and Nup153 binding, and was reversed in E45A/R132T. (4) An environmentally sensitive electrostatic repulsion between E45 and D51 affected lattice stability, flexibility, ion and water permeabilities, electrostatics, and recognition of host factors.

Structural insights into HIV-1 polyanion-dependent capsid lattice formation revealed by single particle cryo-EM

The HIV-1 capsid houses the viral genome and interacts extensively with host cell proteins throughout the viral life cycle. It is composed of capsid protein (CA), which assembles into a conical fullerene lattice composed of roughly 200 CA hexamers and 12 CA pentamers. Previous structural analyses of individual CA hexamers and pentamers have provided valuable insight into capsid structure and function, but detailed structural information about these assemblies in the broader context of the capsid lattice is lacking. In this study, we combined cryoelectron tomography and single particle analysis (SPA) cryoelectron microscopy to determine structures of continuous regions of the capsid lattice containing both hexamers and pentamers. We also developed a method of liposome scaffold-based in vitro lattice assembly ("lattice templating") that enabled us to directly study the lattice under a wider range of conditions than has previously been possible. Using this approach, we identified a critical role for inositol hexakisphosphate in pentamer formation and determined the structure of the CA lattice bound to the capsid-targeting antiretroviral drug GS-6207 (lenacapavir). Our work reveals key structural details of the mature HIV-1 CA lattice and establishes the combination of lattice templating and SPA as a robust strategy for studying retroviral capsid structure and capsid interactions with host proteins and antiviral compounds.

HIV-1 Group M Capsid Amino Acid Variability: Implications for Sequence Quality Control of Genotypic Resistance Testing

BACKGROUND

With the approval of the HIV-1 capsid inhibitor, lenacapavir, capsid sequencing will be required for managing lenacapavir-experienced individuals with detectable viremia. Successful sequence interpretation will require examining new capsid sequences in the context of previously published sequence data.

METHODS

We analyzed published HIV-1 group M capsid sequences from 21,012 capsid-inhibitor naïve individuals to characterize amino acid variability at each position and influence of subtype and cytotoxic T lymphocyte (CTL) selection pressure. We determined the distributions of usual mutations, defined as amino acid differences from the group M consensus, with a prevalence ≥ 0.1%. Co-evolving mutations were identified using a phylogenetically-informed Bayesian graphical model method.

RESULTS

162 (70.1%) positions had no usual mutations (45.9%) or only conservative usual mutations with a positive BLOSUM62 score (24.2%). Variability correlated independently with subtype-specific amino acid occurrence (Spearman rho = 0.83; p < 1 × 10-9) and the number of times positions were reported to contain an HLA-associated polymorphism, an indicator of CTL pressure (rho = 0.43; p = 0.0002).

CONCLUSIONS

Knowing the distribution of usual capsid mutations is essential for sequence quality control. Comparing capsid sequences from lenacapavir-treated and lenacapavir-naïve individuals will enable the identification of additional mutations potentially associated with lenacapavir therapy.

Targeting the HIV-1 and HBV Capsids, an EnCore

Not many structures are common among all viruses: only nucleic acid and a protein coat [...].

[Genetic diversity of capsid protein (p24) in human immunodeficiency virus type-1 (HIV-1) variants circulating in the Russian Federation]

INTRODUCTION

The human immunodeficiency virus (HIV) protein p24 plays an important role in the life cycle of the virus, and also is a target for diagnostic tests and for new antiretroviral drugs and therapeutic vaccines. The most studied variant of HIV-1 in the world is subtype B. In Russia, the most common variant is A6, the spread of recombinant forms (CRF63_02A6, CRF03_A6B) is observed as well as circulation of G and CRF02_AG variants. However, a detailed study of the p24 protein in these variants has not yet been conducted. The aim was to study the features of the p24 protein in HIV-1 variants circulating in Russia and estimate the frequency of occurrence of pre-existing mutations associated with resistance to lenacapavir, the first antiretroviral drug in the class of capsid inhibitors.

MATERIALS AND METHODS

The objects of the study were the nucleotide sequences obtained from the Los Alamos international database and clinical samples from HIV infected patients.

RESULTS AND DISCUSSION

The features of HIV-1 variants circulating in Russia have been determined. V86A, H87Q, I91F are characteristic substitutions in A6 genome. It is shown that the presence of preexisting mutations associated with resistance to lenacapavir is unlikely.

CONCLUSION

Features of the p24 protein in HIV-1 variants circulating in Russia allow them to be distinguished from others variants and among themselves. The prognosis for the use of lenacapavir in Russia is generally favorable. The results obtained could be taken into account in developing and using antiretroviral drugs and therapeutic vaccines.

A Broad-Spectrum Antiviral Molecule, Protoporphyrin IX, Acts as a Moderator of HIV-1 Capsid Assembly by Targeting the Capsid Hexamer

The capsid protein (CA), an essential component of human immunodeficiency virus type 1 (HIV-1), represents an appealing target for antivirals. Small molecules targeting the CAI-binding cavity in the C-terminal domain of HIV-1 CA (CA CTD) confer potent antiviral activities. In this study, we report that a small molecule, protoporphyrin IX (PPIX), targets the HIV-1 CA by binding to this pocket. PPIX was identified via in vitro drug screening, using a homogeneous and time-resolved fluorescence-based assay. CA multimerization and a biolayer interferometry (BLI) assay showed that PPIX promoted CA multimerization and bound directly to CA. The binding model of PPIX to CA CTD revealed that PPIX forms hydrogen bonds with the L211and E212 residues in the CA CTD. Moreover, the BLI assay demonstrated that this compound preferentially binds to the CA hexamer versus the monomer. The superposition of the CAI CTD-PPIX complex and the hexameric CA structure suggests that PPIX binds to the interface formed by the NTD and the CTD between adjacent protomers in the CA hexamer via the T72 and E212 residues, serving as a glue to enhance the multimerization of CA. Taken together, our studies demonstrate that PPIX, a hexamer-targeted CA assembly enhancer, should be a new chemical probe for the discovery of modulators of the HIV-1 capsid assembly. IMPORTANCE CA and its assembled viral core play essential roles in distinct steps during HIV-1 replication, including reverse transcription, integration, nuclear entry, virus assembly, and maturation through CA-CA or CA-host factor interactions. These functions of CA are fundamental for HIV-1 pathogenesis, making it an appealing target for antiviral therapy. In the present study, we identified protoporphyrin IX (PPIX) as a candidate CA modulator that can promote CA assembly and prefers binding the CA hexamer versus the monomer. PPIX, like a glue, bound at the interfaces between CA subunits to accelerate CA multimerization. Therefore, PPIX could be used as a new lead for a CA modulator, and it holds potential research applications.

Potent Long-Acting Inhibitors Targeting the HIV-1 Capsid Based on a Versatile Quinazolin-4-one Scaffold

Long-acting (LA) human immunodeficiency virus-1 (HIV-1) antiretroviral therapy characterized by a ≥1 month dosing interval offers significant advantages over daily oral therapy. However, the criteria for compounds that enter clinical development are high. Exceptional potency and low plasma clearance are required to meet dose size requirements; excellent chemical stability and/or crystalline form stability is required to meet formulation requirements, and new antivirals in HIV-1 therapy need to be largely free of side effects and drug-drug interactions. In view of these challenges, the discovery that capsid inhibitors comprising a quinazolinone core tolerate a wide range of structural modifications while maintaining picomolar potency against HIV-1 infection in vitro, are assembled efficiently in a multi-component reaction, and can be isolated in a stereochemically pure form is reported herein. The detailed characterization of a prototypical compound, GSK878, is presented, including an X-ray co-crystal structure and subcutaneous and intramuscular pharmacokinetic data in rats and dogs.

The HIV-1 Gag Protein Displays Extensive Functional and Structural Roles in Virus Replication and Infectivity

Once merely thought of as the protein responsible for the overall physical nature of the human immunodeficiency virus type 1 (HIV-1), the Gag polyprotein has since been elucidated to have several roles in viral replication and functionality. Over the years, extensive research into the polyproteins’ structure has revealed that Gag can mediate its own trafficking to the plasma membrane, it can interact with several host factors and can even aid in viral genome packaging. Not surprisingly, Gag has also been associated with HIV-1 drug resistance and even treatment failure. Therefore, this review provides an extensive overview of the structural and functional roles of the HIV-1 Gag domains in virion integrity, functionality and infectivity.

Nuclear Capsid Uncoating and Reverse Transcription of HIV-1

After cell entry, human immunodeficiency virus type 1 (HIV-1) replication involves reverse transcription of the RNA genome, nuclear import of the subviral complex without nuclear envelope breakdown, and integration of the viral complementary DNA into the host genome. Here, we discuss recent evidence indicating that completion of reverse transcription and viral genome uncoating occur in the nucleus rather than in the cytoplasm, as previously thought, and suggest a testable model for nuclear import and uncoating. Multiple recent studies indicated that the cone-shaped capsid, which encases the genome and replication proteins, not only serves as a reaction container for reverse transcription and as a shield from innate immune sensors but also may constitute the elusive HIV-1 nuclear import factor. Rupture of the capsid may be triggered in the nucleus by completion of reverse transcription, by yet-unknown nuclear factors, or by physical damage, and it appears to occur in close temporal and spatial association with the integration process. Expected final online publication date for the Annual Review of Virology, Volume 9 is September 2022. Please see http://www.annualreviews.org/page/journal/pubdates for revised estimates.

HIV Capsid Protein Genetic Diversity Across HIV-1 Variants and Impact on New Capsid-Inhibitor Lenacapavir

The HIV p24 capsid protein has an essential, structural, and functional role in the viral replication cycle, being an interesting target for vaccine design, diagnostic tests, and new antiretroviral drugs (ARVs). The HIV-1 variability poses a challenge for the accuracy and efficiency of diagnostic and treatment tools. This study analyzes p24 diversity among HIV-1 variants and within its secondary structure in HIV-1 M, O, P, and N groups. All available HIV-1 p24 nucleotide sequences were downloaded from the Los Alamos HIV Sequence Database, selecting 23,671 sequences belonging to groups O, N, P, and M (9 subtypes, 7 sub-sub types, and 109 circulating recombinant forms or CRFs). Using a bioinformatics tool developed in our laboratory (EpiMolBio program), we analyzed the amino acid conservation compared to the HXB2 subtype B reference sequence and the V-markers, or amino acid changes that were specific for each variant with at least 10 available sequences. We inferred the p24 consensus sequence for HIV-1 and for each group to analyze the overall conservation in p24 main structural regions, reporting the percentage of substitutions per variant affecting the capsid assembly and molecule-binding, including those associated with resistance to the new capsid-inhibitor lenacapavir, and the key residues involved in lenacapavir-p24 interaction, according to the bibliography. Although the overall structure of p24 was highly conserved, the conservation in the secondary structure varied between HIV-1 variants and the type of secondary structure. All HIV-1 variants presented >80% amino acid conservation vs. HXB2 reference sequence, except for group M sub-subtype F1 (69.27%). Mutants affecting the capsid assembly or lenacapavir capsid-binding were found in <1% of the p24 consensus sequence. Our study reports the HIV-1 variants carrying 14 unique single V-markers in 9/38 group M variants and the level of p24 conservation in each secondary structure region among the 4 HIV-1 groups and group M variants, revealing no natural resistance to lenacapavir in any HIV-1 variant. We present a thorough analysis of p24 variability among all HIV-1 variants circulating to date. Since p24 genetic variability can impact the viral replication cycle and the efficacy of new p24-based diagnostic, therapeutic, and vaccine strategies, conservation studies must consider all HIV-1 variants circulating worldwide.