Unmet therapeutic needs in the new era of combination antiretroviral therapy for HIV-1

Design, synthesis, and structure activity relationship analysis of new betulinic acid derivatives as potent HIV inhibitors

Prior modification of betulinic acid (1), a natural product lead with promising anti-HIV activity, produced 3-O-(3',3'-dimethylsuccinyl)betulinic acid (bevirimat, 3), the first-in-class HIV maturation inhibitor. After 3-resistant variants were found during Phase I and IIa clinical trials, further modification of 3 produced 4 with improved activity against wild-type and 3-resistant HIV-1. In continued efforts to optimize 1, 63 final products have now been designed, synthesized, and evaluated for anti-HIV-1 replication activity against HIV-1_NL4-3 infected MT-4 cell lines. Five known and 21 new derivatives were as or more potent than 3 (EC₅₀ 0.065 μM), while eight new derivatives were as or more potent than 4 (EC₅₀ 0.019 μM). These derivatives feature expanded structural diversity and chemical space that may improve the antiviral activity and address the growing resistance crisis. Structure-Activity Relationship (SAR) correlations were thoroughly analyzed, and a 3D Quantitative SAR model with high predictability was constructed to facilitate further rational design and development of new potent derivatives.

An Adherence-Enhancing Program Increases Retention in Care in the Swiss HIV Cohort

Background

This study tested a theory-based adherence-enhancing intervention: the “Interprofessional Medication Adherence Program” (IMAP) to increase human immunodeficiency virus (HIV) retention in care.

Methods

We retrospectively compared our intervention center (intervention group [IG]) with a standard of care center (control group [CG]) both participating in the Swiss HIV Cohort Study between 2004 and 2012. Endpoints were defined as >6-month and >12-month gaps in care for intervals of care longer than 6 and 12 months without any blood draw. Inverse probability of treatment weights was used to adjust for differences between patients at the 2 centers. Viral failure was defined as ribonucleic acid ≥50 copies/mL after 24+ weeks on antiretrovirals.

Results

The IG included 451 patients, CG 311. In the IG, 179 (40%) patients took part in the IMAP for a median of 27 months (interquartile range, 12–45). Gaps in care of ≥6 months were significantly more likely to happen in the CG versus IG (74.6% vs 57%, P < .001). The median time until the first treatment gap was longer in the IG vs CG (120 vs 84 weeks, P < .001). Gaps in care of ≥12 months evaluated in 709 (93%) patients were significantly more likely to occur in the CG compared with the IG (22.6% vs 12.5%, P < .001). The rate of viral failure was significantly lower in the IG (8.3% vs 15.1%, P = .003).

Conclusions

This study, in a real-world setting, shows the effectiveness of the IMAP to reduce 6- and 12-month gaps in follow up among people with HIV. These results should be confirmed by studies in other settings.

Development and Validation of a Specific RP-HPLC Method for Simultaneous Estimation of Anti-retroviral Drugs: Application to Nanoparticulate Formulation System

Objective:

A simple, accurate and economical reverse phase- high performance liquid chromatographic method has been developed for the simultaneous quantitative estimation of two anti-retro viral drugs, Etravirine and Elvitegravir in nanoparticulate formulations for the first time. This method is a novel analytical technique for the detection of the both the drugs concurrently, as there is no method available for their simultaneous quantification, to the best of our knowledge.

Methods:

Optimization and validation of the chromatographic conditions were completed according to the standard ICH guidelines. The separation was done on a C18 column (250 mm x 4.6mm, 5μm) using methanol and phosphate buffer of pH (5.6) as the mobile phase in the ratio 78:22 v/v at a flow rate of 1ml/min for a short run time of 13 min. The detection wavelength was 285nm and the column temperature was maintained at 32oC.

Results:

The developed method was linear over 10 to 160 μg/ml with a regression coefficient of 0.999 for each. The LOD values were 4.83 and 9.25 µg/ml while LOQ values were 14.63 and 28.01 µg/ml for etravirine and elvitegravir respectively. The recovery values obtained by etravirine and elvitegravir were between 97.6% and 100.8%.

Conclusion:

The method was specific, precise, fast and accurate with good inter and intra day precision. The method was also effectively employed for the characterization and simultaneous quantification of both drugs in nanoparticulate formulation.

Computational design, synthesis and evaluation of new sulphonamide derivatives targeting HIV-1 gp120

Attachment of envelope glycoprotein gp120 to the host cell receptor CD4 is the first step during the human immunodeficiency virus-1 (HIV-1) entry into the host cells that makes it a promising target for drug design. To elucidate the crucial three dimensional (3D) structural features of reported HIV-1 gp120 CD4 binding inhibitors, 3D pharmacophores were generated and receptor based approach was employed to quantify these structural features. A four-partial least square factor model with good statistics and predictive ability was generated for the dataset of 100 molecules. To further ascertain the structural requirement for gp120-CD4 binding inhibition, molecular interaction studies of inhibitors with gp120 was carried out by performing molecular docking using Glide 5.6. Based on these studies, structural requirements were drawn and new molecules were designed accordingly to yield new sulphonamides derivatives. A water based green synthetic approach was adopted to obtain these compounds which were evaluated for their HIV-1 gp120 CD4 binding inhibition. The newly synthesized compounds exhibited remarkable activity (10-fold increase) when compared with the standard BMS 806. Further the stability of newly synthesized derivatives with HIV-1 gp120 was also investigated through molecular dynamics simulation studies. This provides a proof of concept for molecular modeling based design of new inhibitors for inhibition of HIV-1 gp120 CD4 interaction.

The Membrane-Active Phytopeptide Cycloviolacin O2 Simultaneously Targets HIV-1-infected Cells and Infectious Viral Particles to Potentiate the Efficacy of Antiretroviral Drugs

Background: Novel strategies to increase the efficacy of antiretroviral (ARV) drugs will be of crucial importance. We hypothesize that membranes of HIV-1-infected cells and enveloped HIV-1 particles may be preferentially targeted by the phytopeptide, cycloviolacin O2 (CyO2) to significantly enhance ARV efficacy. Methods: Physiologically safe concentrations of CyO2 were determined via red blood cell (RBC) hemolysis. SYTOX-green dye-uptake and radiolabeled saquinavir (³H-SQV) uptake assays were used to measure pore-formation and drug uptake, respectively. ELISA, reporter assays and ultracentrifugation were conducted to analyze the antiviral efficacy of HIV-1 protease and fusion inhibitors alone and co-exposed to CyO2. Results: CyO2 concentrations below 0.5 μM did not show substantial hemolytic activity, yet these concentrations enabled rapid pore-formation in HIV-infected T-cells and monocytes and increased drug uptake. ELISA for HIV-1 p24 indicated that CyO2 enhances the antiviral efficacy of both SQV and nelfinavir. CyO2 (< 0.5 μM) alone decreases HIV-1 p24 production, but it did not affect the transcription regulatory function of the HIV-1 long terminal repeat (LTR). Ultracentrifugation studies clearly showed that CyO2 exposure disrupted viral integrity and decreased the p24 content of viral particles. Furthermore, direct HIV-1 inactivation by CyO2 enhanced the efficacy of enfuvirtide. Conclusions: The membrane-active properties of CyO2 may help suppress viral load and augment antiretroviral drug efficacy.

The New Paradigms in Clinical Research: From Early Access Programs to the Novel Therapeutic Approaches for Unmet Medical Needs

Despite several innovative medicines gaining worldwide approval in recent years, there are still therapeutic areas for which unsatisfied therapeutic needs persist. For example, high unmet clinical need was observed in patients diagnosed with type 2 diabetes mellitus and hemophilia, as well as in specific age groups, such as the pediatric population. Given the urgent need to improve the therapy of clinical conditions for which unmet clinical need is established, clinical testing, and approval of new medicines are increasingly being carried out through accelerated authorization procedures. Starting from 1992, the Food and Drug Administration and the European Medicines Agency have supported the so-called Early Access Programs (EAPs). Such procedures, which can be based on incomplete clinical data, allow an accelerated marketing authorization for innovative medicines. The growth in pharmaceutical research has also resulted in the development of novel therapeutic approaches, such as biotech drugs and advanced therapy medicinal products, including new monoclonal antibodies for the treatment of asthma, antisense oligonucleotides for the treatment of Duchenne muscular dystrophy and spinal muscular atrophy, and new anticancer drugs that act on genetic biomarkers rather than any specific type of cancer. Even though EAPs and novel therapeutic approaches have brought huge benefits for public health, their implementation is limited by several challenges, including the high risk of safety-related label changes for medicines authorized through the accelerated procedure, the high costs, and the reimbursement and access concerns. In this context, regulatory agencies should provide the best conditions for the implementation of the described new tools.

Design, Synthesis, and SAR of C-3 Benzoic Acid, C-17 Triterpenoid Derivatives. Identification of the HIV-1 Maturation Inhibitor 4-((1 R,3a S,5a R,5b R,7a R,11a S,11b R,13a R,13b R)-3a-((2-(1,1-Dioxidothiomorpholino)ethyl)amino)-5a,5b,8,8,11a-pentamethyl-1-(prop-1-en-2-yl)-2,3,3a,4,5,5a,5b,6,7,7a,8,11,11a,11b,12,13,13a,13b-octadecahydro-1 H-cyclopenta[ a]chrysen-9-yl)benzoic Acid (GSK3532795, BMS-955176)

GSK3532795, formerly known as BMS-955176 (1), is a potent, orally active, second-generation HIV-1 maturation inhibitor (MI) that advanced through phase IIb clinical trials. The careful design, selection, and evaluation of substituents appended to the C-3 and C-17 positions of the natural product betulinic acid (3) was critical in attaining a molecule with the desired virological and pharmacokinetic profile. Herein, we highlight the key insights made in the discovery program and detail the evolution of the structure-activity relationships (SARs) that led to the design of the specific C-17 amine moiety in 1. These modifications ultimately enabled the discovery of 1 as a second-generation MI that combines broad coverage of polymorphic viruses (EC₅₀ <15 nM toward a panel of common polymorphisms representative of 96.5% HIV-1 subtype B virus) with a favorable pharmacokinetic profile in preclinical species.

HIV and the Macrophage: From Cell Reservoirs to Drug Delivery to Viral Eradication

Macrophages serve as host cells, inflammatory disease drivers and drug runners for human immunodeficiency virus infection and treatments. Low-level viral persistence continues in these cells in the absence of macrophage death. However, the cellular microenvironment changes as a consequence of viral infection with aberrant production of pro-inflammatory factors and promotion of oxidative stress. These herald viral spread from macrophages to neighboring CD4⁺ T cells and end organ damage. Virus replicates in tissue reservoir sites that include the nervous, pulmonary, cardiovascular, gut, and renal organs. However, each of these events are held in check by antiretroviral therapy. A hidden and often overlooked resource of the macrophage rests in its high cytoplasmic nuclear ratios that allow the cell to sense its environment and rid it of the cellular waste products and microbial pathogens it encounters. These phagocytic and intracellular killing sensing mechanisms can also be used in service as macrophages serve as cellular carriage depots for antiretroviral nanoparticles and are able to deliver medicines to infectious disease sites with improved therapeutic outcomes. These undiscovered cellular functions can lead to reductions in persistent infection and may potentially facilitate the eradication of residual virus to eliminate disease.

Recent progress in the antiviral activity and mechanism study of pentacyclic triterpenoids and their derivatives

Viral infections cause many serious human diseases with high mortality rates. New drug‐resistant strains are continually emerging due to the high viral mutation rate, which makes it necessary to develop new antiviral agents. Compounds of plant origin are particularly interesting. The pentacyclic triterpenoids (PTs) are a diverse class of natural products from plants composed of three terpene units. They exhibit antitumor, anti‐inflammatory, and antiviral activities. Oleanolic, betulinic, and ursolic acids are representative PTs widely present in nature with a broad antiviral spectrum. This review focuses on the recent literatures in the antiviral efficacy of this class of phytochemicals and their derivatives. In addition, their modes of action are also summarized.

Nanocarriers for brain specific delivery of anti-retro viral drugs: challenges and achievements

HIV/AIDS is a global pandemic and the deleterious effects of human immunodeficiency virus in the brain cannot be overlooked. Though the current anti-retro viral therapy is able to reduce the virus load in the peripheral tissues of the body, the inability of the anti-retro viral drugs to cross the blood brain barrier, as such, limits its therapeutic effect in the brain. The development of newer, successful nanoparticulate drug delivery systems to enhance the feasibility of the anti-retro viral drugs to the brain, offers a novel strategy to treat the AIDS-related neuronal degradation. This review summarised the neuropathogenesis of neuroAIDS, the challenges and achievements made in the delivery of therapeutics across the BBB and the use of nanocarriers as a safe and effective way for delivering anti-retro viral drugs to the brain.

HIV-infected patients' beliefs about their chronic co-treatments in comparison with their combined antiretroviral therapy

Objectives

Thanks to the success of combination antiretroviral therapy (cART), HIV‐infected patients can have almost a normal life expectancy. This has resulted in an aging HIV‐infected population with other chronic comorbidities such as cardiovascular diseases, osteoporosis, and depression. Our hypothesis is that patients' perceptions of and attitudes towards their cART, which is perceived as crucial to their survival, differ from their beliefs about their co‐treatments, and this may have an impact on their medication adherence.

Methods

We used the French version of the Beliefs about Medicine Questionnaire (BMQ‐f) to measure the perceptions of patients about their co‐treatments and the Beliefs about Medicine Questionnaire for Highly Active Antiretroviral Therapy (BMQ‐HAART) to measure their beliefs about their cART in a representative sample (n = 150) of patients enrolled in the Swiss HIV Cohort Study (SHCS) and followed at the Infectious Disease Service at the University Hospital in Lausanne, Switzerland. The survey was administered to all eligible patients by the order of their scheduled appointments at the end of their medical visit. The BMQ comprises two subscores: Specific‐Necessity (5 identical items in BMQ‐f and BMQ‐HAART) and Specific‐Concerns (also 5 identical items in BMQ‐f and BMQ‐HAART). The subscores were standardized by dividing the score scale by the number of questions in the scale, resulting in a range of responses between 1 (low) and 5 (high). Self‐reported medication adherence was measured using the SHCS Adherence Questionnaire (SHCS‐AQ). Adherence was defined as not missing any dose or missing one dose of the treatment in the past 4 weeks. Sociodemographic variables were retrieved by reviewing the SHCS database.

Results

A response rate of 73% (109 of 150) was achieved. A total of 105 patients were included in the analysis: their median age was 56 [interquartile range (IQR) 51, 63] years and 74 were male (70%). Eighty‐seven patients (83%) were adherent to cART and 75 (71%) were adherent to their co‐treatments (P = 0.0001). The standardized mean responses for the BMQ Specific‐Necessity subscores were 4.46 [standard deviation (SD): 0.58] and 2.86 (SD: 1.02) for cART and co‐treatments, respectively (P < 0.0001). For Specific‐Concerns, the standardized mean responses were 2.9 (SD: 1.02) for cART and 4.09 (SD: 1.02) (P < 0.0001) for co‐treatments. cART and co‐treatment concerns increased as the number of co‐treatments increased (P = 0.03 and P < 0.0001, respectively).

Conclusions

Patients had higher Necessity and lower Concerns scores for their cART in comparison with their co‐treatments. A higher percentage of patients reported being adherent to cART compared with the co‐treatments that they reported they were most likely to miss. Further research using a bigger sample size and more objective measures of adherence is needed to explore the association between adherence and patients' perceptions.

Investigating the effects of point mutations on the affinity between the cyanobacterial lectin microvirin and high mannose-type glycans present on the HIV envelope glycoprotein

Human immunodeficiency virus (HIV) infections continue to exert an enormous impact on global human health. This led experts to emphasize the importance of new measures for preventing HIV infections, including the development of vaccines and novel drugs. In this context, a promising approach involves the use of lectins that can bind the surface envelope glycoprotein gp120 of HIV with high affinity, preventing viral entry. The cyanobacterial lectin microvirin (MVN) has been proposed as a candidate for development as a topical microbicide because of its ability to bind to high mannose-type glycans, potently inhibiting HIV-1 entry. Thus, the aim of this computational study was to investigate the effects of four point mutations (D53Q, D53E, D53K, and D53W) on the structure and affinity of MVN with di-mannose (MAN). Molecular dynamics simulations followed by binding free energy calculations using MM-GBSA were employed. The calculated binding free energy of ligand-receptor complexation of MVN with MAN was -26.02 kcal mol^-1. We identified in the wild-type protein that residues I45, T59, and Q81 have a major contribution to the binding free energy of di-mannose. Among the investigated mutants, the most promising one was the D53W mutation, with a theoretical binding free energy value of -29.16 kcal mol^-1. We suggest that this increased stability is due to the introduction of extra rigidity on the hinge region connecting two key structural elements of the MVN binding site.

Improving combination antiretroviral therapy by targeting HIV-1 gene transcription

INTRODUCTION

Combination Antiretroviral Therapy (cART) has not allowed the cure of HIV. The main obstacle to HIV eradication is the existence of quiescent reservoirs. Several other limitations of cART have been described, such as strict life-long treatment and high costs, restricting it to Western countries, as well as the development of multidrug resistance. Given these limitations and the impetus to find a cure, the development of new treatments is necessary. Areas covered: In this review, we discuss the current status of several efficient molecules able to suppress HIV gene transcription, including NF-kB and Tat inhibitors. We also assess the potential of new proteins belonging to the intriguing DING family, which have been reported to have potential anti-HIV-1 activity by inhibiting HIV gene transcription. Expert opinion: Targeting HIV-1 gene transcription is an alternative approach, which could overcome cART-related issues, such as the emergence of multidrug resistance. Improving cART will rely on the identification and characterization of new actors inhibiting HIV-1 transcription. Combining such efforts with the use of new technologies, the development of new models for preclinical studies, and improvement in drug delivery will considerably reduce drug toxicity and thus increase patient adherence.

Discovery of BMS-955176, a Second Generation HIV-1 Maturation Inhibitor with Broad Spectrum Antiviral Activity

HIV-1 maturation inhibition (MI) has been clinically validated as an approach to the control of HIV-1 infection. However, identifying an MI with both broad polymorphic spectrum coverage and good oral exposure has been challenging. Herein, we describe the design, synthesis, and preclinical characterization of a potent, orally active, second generation HIV-1 MI, BMS-955176 (2), which is currently in Phase IIb clinical trials as part of a combination antiretroviral regimen.

C-3 benzoic acid derivatives of C-3 deoxybetulinic acid and deoxybetulin as HIV-1 maturation inhibitors

A series of C-3 phenyl- and heterocycle-substituted derivatives of C-3 deoxybetulinic acid and C-3 deoxybetulin was designed and synthesized as HIV-1 maturation inhibitors (MIs) and evaluated for their antiviral activity and cytotoxicity in cell culture. A 4-subsituted benzoic acid moiety was identified as an advantageous replacement for the 3'3'-dimethylsuccinate moiety present in previously disclosed MIs that illuminates new aspects of the topography of the pharmacophore. The new analogs exhibit excellent in vitro antiviral activity against wild-type (wt) virus and a lower serum shift when compared with the prototypical HIV-1 MI bevirimat (1, BVM), the first MI to be evaluated in clinical studies. Compound 9a exhibits comparable cell culture potency toward wt virus as 1 (WT EC50=16 nM for 9a compared to 10nM for 1). However, the potency of 9a is less affected by the presence of human serum, while the compound displays a similar pharmacokinetic profile in rats to 1. Hence 9a, the 4-benzoic acid derivative of deoxybetulinic acid, represents a new starting point from which to explore the design of a 2nd generation MI.

Potent in vitro antiviral activity of Cistus incanus extract against HIV and Filoviruses targets viral envelope proteins

Novel therapeutic options are urgently needed to improve global treatment of virus infections. Herbal products with confirmed clinical safety features are attractive starting material for the identification of new antiviral activities. Here we demonstrate that Cistus incanus (Ci) herbal products inhibit human immunodeficiency virus (HIV) infections in vitro. Ci extract inhibited clinical HIV-1 and HIV-2 isolates, and, importantly, a virus isolate with multiple drug resistances, confirming broad anti-HIV activity. Antiviral activity was highly selective for virus particles, preventing primary attachment of the virus to the cell surface and viral envelope proteins from binding to heparin. Bioassay-guided fractionation indicated that Ci extract contains numerous antiviral compounds and therefore has favorably low propensity to induce virus resistance. Indeed, no resistant viruses emerged during 24 weeks of continuous propagation of the virus in the presence of Ci extracts. Finally, Ci extracts also inhibited infection by virus particles pseudotyped with Ebola and Marburg virus envelope proteins, indicating that antiviral activity of Ci extract extends to emerging viral pathogens. These results demonstrate that Ci extracts show potent and broad in vitro antiviral activity against viruses that cause life-threatening diseases in humans and are promising sources of agents that target virus particles.

Capsid proteins of enveloped viruses as antiviral drug targets

Viral proteins have enabled the design of selective and efficacious treatments for viral diseases. While focus in this area has been on viral enzymes, it appears that multifunctional viral proteins may be even more susceptible to small molecule interference. As exemplified by HIV capsid, small molecule inhibitors can bind to multiple binding sites on the capsid protein and induce or prevent protein interactions and conformational changes. Resistance selection is complicated by the fact that the capsid proteins have to engage in different protein interactions at different times of the life cycle. Viral capsid assembly and disassembly have therefore emerged as highly sensitive processes that could deliver a new generation of antiviral agents across viral diseases.

Design and evaluation of clinically relevant SOFA-HDV ribozymes targeting HIV RNA

Nucleic acid therapies targeting HIV replication have the potential to be used in conjunction with or in place of the standard small-molecule therapies. Among the different classes of nucleic acid therapies, several ribozymes (Rzs, RNA enzymes) have been developed to target HIV RNA. The design of Rzs targeting HIV RNA is complicated by the sequence diversity of viral strains and the structural diversity of their target sites. Using the SOFA-HDV Rz as an example, this chapter describes methods that can be used to design Rzs for controlling HIV replication. We describe how to (1) identify highly conserved Rz target sites in HIV RNA; (2) generate a set of Rzs with the potential to be used as therapeutics; and (3) screen these Rzs for activity against HIV production.

Eradication of HIV and Cure of AIDS, Now and How?

Recent studies have highlighted the importance of eradication of human immunodeficiency virus (HIV) and cure of acquired immunodeficiency syndrome (AIDS). However, a pivotal point that the patient immunity controls HIV reactivation after highly active anti-retroviral therapy [HAART or combination anti-retroviral therapy (cART)] remains less well addressed. In spite of the fact that both innate and adaptive immunities are indispensable and numerous cells participate in the anti-HIV immunity, memory CD4 T-cells are indisputably the key cells organizing all immune actions against HIV while being the targets of HIV. Here we present a view and multidisciplinary approaches to HIV/AIDS eradication and cure. We aim at memory CD4 T-cells, utilizing the stem cell properties of these cells to reprogram an anti-HIV memory repertoire to eliminate the viral reservoir, toward achieving an AIDS-free world.

Nano-NRTIs demonstrate low neurotoxicity and high antiviral activity against HIV infection in the brain

Antiviral therapy using nucleoside reverse transcriptase inhibitors (NRTIs) is neurotoxic and has low efficiency in eradication of HIV-1 harbored in central nervous system (CNS). Previously, we reported that active 5'-triphosphates of NRTIs encapsulated in cationic nanogels (nano-NRTIs) suppress HIV-1 activity more efficiently than NRTIs and exhibit reduced mitochondrial toxicity [Vinogradov SV, Poluektova LY, Makarov E, Gerson T, Senanayake MT. Nano-NRTIs: efficient inhibitors of HIV type-1 in macrophages with a reduced mitochondrial toxicity. Antivir Chem Chemother. 2010; 21:1-14. Makarov E, Gerson T, Senanayake T, Poluektova LY, Vinogradov. Efficient suppression of Human Immunodeficiency Virus in Macrophages by Nano-NRTIs. Antiviral Res. 2010; 86(1):A38-9]. Here, we demonstrated low neurotoxicity and excellent antiviral activity of nano-NRTIs decorated with the peptide (AP) binding brain-specific apolipoprotein E receptor. Nano-NRTIs induced lower levels of apoptosis and formation of reactive oxygen species, a major cause of neuron death, than free NRTIs. Optimization of size, surface decoration with AP significantly increased brain accumulation of nano-NRTIs. The efficient CNS delivery of nano-NRTIs resulted in up to 10-fold suppression of retroviral activity and reduced virus-associated inflammation in humanized mouse model of HIV-1 infection in the brain. Our data provide proof of the advanced efficacy of nano-NRTIs as safer alternative of current antiviral drugs.

FROM THE CLINICAL EDITOR

This team of investigators demonstrated low neurotoxicity and excellent anti-HIV activity of nano-nucleoside reverse transcriptase inhibitors decorated with the peptide (AP) binding brain-specific apolipoprotein E receptor, providing proof of enhanced efficacy and a safer alternative compared with current antiviral drugs.

A novel inhibitor-binding site on the HIV-1 capsid N-terminal domain leads to improved crystallization via compound-mediated dimerization

Despite truly impressive achievements in the global battle against HIV there remains a need for new drugs directed against novel targets, and the viral capsid protein (CA) may represent one such target. Intense structural characterization of CA over the last two decades has provided unprecedented insight into the structure and assembly of this key viral protein. Furthermore, several inhibitor-binding sites that elicit antiviral activity have been reported on CA, two of which are located on its N-terminal domain (CANTD). In this work, the binding of a novel capsid-assembly inhibitor that targets a unique inhibitory site on CANTD is reported. Moreover, whereas cocrystallization of CANTD in complex with ligands has proven to be challenging in the past, the use of this inhibitor as a tool compound is shown to vastly facilitate ternary cocrystallizations with CANTD. This improvement in crystallization is likely to be achieved through the formation of a compound-mediated homodimer, the intrinsic symmetry of which greatly increases the prospect of generating a crystal lattice. While protein engineering has been used in the literature to support a link between the inherent symmetry of a macromolecule and its propensity to crystallize, to our knowledge this work represents the first use of a synthetic ligand for this purpose.

Discovery and structural characterization of a new inhibitor series of HIV-1 nucleocapsid function: NMR solution structure determination of a ternary complex involving a 2:1 inhibitor/NC stoichiometry

The nucleocapsid (NC) protein is an essential factor with multiple functions within the human immunodeficiency virus type 1 (HIV-1) replication cycle. In this study, we describe the discovery of a novel series of inhibitors that targets HIV-1 NC protein by blocking its interaction with nucleic acids. This series was identified using a previously described capsid (CA) assembly assay, employing a recombinant HIV-1 CA-NC protein and immobilized TG-rich deoxyoligonucleotides. Using visible absorption spectroscopy, we were able to demonstrate that this new inhibitor series binds specifically and reversibly to the NC with a peculiar 2:1 stoichiometry. A fluorescence-polarization-based binding assay was also developed in order to monitor the inhibitory activities of this series of inhibitors. To better characterize the structural aspect of inhibitor binding onto NC, we performed NMR studies using unlabeled and (13)C,(15)N-double-labeled NC(1-55) protein constructs. This allowed the determination of the solution structure of a ternary complex characterized by two inhibitor molecules binding to the two zinc knuckles of the NC protein. To the best of our knowledge, this represents the first report of a high-resolution structure of a small-molecule inhibitor bound to NC, demonstrating sub-micromolar potency and moderate antiviral potency with one analogue of the series. This structure was compared with available NC/oligonucleotide complex structures and further underlined the high flexibility of the NC protein, allowing it to adopt many conformations in order to bind its different oligonucleotide/nucleomimetic targets. In addition, analysis of the interaction details between the inhibitor molecules and NC demonstrated how this novel inhibitor series is mimicking the guanosine nucleobases found in many reported complex structures.

Monitoring binding of HIV-1 capsid assembly inhibitors using (19)F ligand-and (15)N protein-based NMR and X-ray crystallography: early hit validation of a benzodiazepine series

The emergence of resistance to existing classes of antiretroviral drugs underlines the need to find novel human immunodeficiency virus (HIV)-1 targets for drug discovery. The viral capsid protein (CA) represents one such potential target. Recently, a series of benzodiazepine inhibitors was identified via high-throughput screening using an in vitro capsid assembly assay (CAA). Here, we demonstrate how a combination of NMR and X-ray co-crystallography allowed for the rapid characterization of the early hits from this inhibitor series. Ligand-based (19)F NMR was used to confirm inhibitor binding specificity and reversibility as well as to identify the N-terminal domain of the capsid (CA(NTD)) as its molecular target. Protein-based NMR ((1)H and (15)N chemical shift perturbation analysis) identified key residues within the CA(NTD) involved in inhibitor binding, while X-ray co-crystallography confirmed the inhibitor binding site and its binding mode. Based on these results, two conformationally restricted cyclic inhibitors were designed to further validate the possible binding modes. These studies were crucial to early hit confirmation and subsequent lead optimization.

Inhibitors of human immunodeficiency virus type 1 (HIV-1) attachment. 12. Structure-activity relationships associated with 4-fluoro-6-azaindole derivatives leading to the identification of 1-(4-benzoylpiperazin-1-yl)-2-(4-fluoro-7-[1,2,3]triazol-1-yl-1h-pyrrolo[2,3-c]pyridin-3-yl)ethane-1,2-dione (BMS-585248)

A series of highly potent HIV-1 attachment inhibitors with 4-fluoro-6-azaindole core heterocycles that target the viral envelope protein gp120 has been prepared. Substitution in the 7-position of the azaindole core with amides (12a,b), C-linked heterocycles (12c-l), and N-linked heterocycles (12m-u) provided compounds with subnanomolar potency in a pseudotype infectivity assay and good pharmacokinetic profiles in vivo. A predictive model was developed from the initial SAR in which the potency of the analogues correlated with the ability of the substituent in the 7-position of the azaindole to adopt a coplanar conformation by either forming internal hydrogen bonds or avoiding repulsive substitution patterns. 1-(4-Benzoylpiperazin-1-yl)-2-(4-fluoro-7-[1,2,3]triazol-1-yl-1H-pyrrolo[2,3-c]pyridin-3-yl)ethane-1,2-dione (BMS-585248, 12m) exhibited much improved in vitro potency and pharmacokinetic properties than the previous clinical candidate BMS-488043 (1). The predicted low clearance in humans, modest protein binding, and good potency in the presence of 40% human serum for 12m led to its selection for human clinical studies.

A new system for parallel drug screening against multiple-resistant HIV mutants based on lentiviral self-inactivating (SIN) vectors and multi-colour analyses

Background

Despite progress in the development of combined antiretroviral therapies (cART), HIV infection remains a significant challenge for human health. Current problems of cART include multi-drug-resistant virus variants, long-term toxicity and enormous treatment costs. Therefore, the identification of novel effective drugs is urgently needed.

Methods

We developed a straightforward screening approach for simultaneously evaluating the sensitivity of multiple HIV gag-pol mutants to antiviral drugs in one assay. Our technique is based on multi-colour lentiviral self-inactivating (SIN) LeGO vector technology.

Results

We demonstrated the successful use of this approach for screening compounds against up to four HIV gag-pol variants (wild-type and three mutants) simultaneously. Importantly, the technique was adapted to Biosafety Level 1 conditions by utilising ecotropic pseudotypes. This allowed upscaling to a large-scale screening protocol exploited by pharmaceutical companies in a successful proof-of-concept experiment.

Conclusions

The technology developed here facilitates fast screening for anti-HIV activity of individual agents from large compound libraries. Although drugs targeting gag-pol variants were used here, our approach permits screening compounds that target several different, key cellular and viral functions of the HIV life-cycle. The modular principle of the method also allows the easy exchange of various mutations in HIV sequences. In conclusion, the methodology presented here provides a valuable new approach for the identification of novel anti-HIV drugs.

Inhibitors of HIV-1 attachment. Part 9: an assessment of oral prodrug approaches to improve the plasma exposure of a tetrazole-containing derivative

7-(2H-Tetrazol-5-yl)-1H-indole 3 was found to be a potent inhibitor of HIV-1 attachment but the compound lacked oral bioavailability in rats. The cause of the low exposure was believed to be poor absorption attributed to the acidic nature of the tetrazole moiety and, in an effort to address this liability, three more lipohilic tetrazole analogs, N-acetoxymethyl 4, N-pivaloyloxymethyl 5, and N-methyl 6, were evaluated as potential oral prodrugs in rats. Prodrug 5 was ineffective in improving the plasma concentration of 3 in vivo but compound 4 provided a 15-fold enhancement of the plasma concentration of 3. Most interestingly, oral dosing of analog 6 afforded a substantial increase in the plasma concentration of the parent in rats when compared to dosing of parent. This represents a novel example of a methyl tetrazole that acts as a prodrug for a free NH tetrazole-containing compound.

Inhibitors of HIV-1 attachment. Part 10. The discovery and structure-activity relationships of 4-azaindole cores

A series of 4-azaindole oxoacetic acid piperazine benzamides was synthesized and evaluated in an effort to identify an oral HIV-1 attachment inhibitor with the potential to improve upon the pre-clinical profile of BMS-378806 (7), an initial clinical compound. Modifications at the 7-position of the 4-azaindole core modulated potency significantly and SAR showed that certain compounds with a 5-membered ring heteroaryl group at that position were the most potent. Four of the compounds with the best profiles were evaluated in a rat pharmacokinetic model and all had superior oral bioavailability and lower clearance when compared with 7.

Inhibitors of HIV-1 attachment. Part 11: the discovery and structure-activity relationships associated with 4,6-diazaindole cores

A series of HIV-1 attachment inhibitors containing a 4,6-diazaindole core were examined in an effort to identify a compound which improved upon the potency and oral exposure of BMS-488043 (2). BMS-488043 (2) is a 6-azaindole-based HIV-1 attachment inhibitor which established proof-of-concept for this mechanism in human clinical studies but required high doses and concomitant administration of a high fat meal to achieve efficacious exposures. Based on previous studies in indole and azaindole scaffolds, SAR investigation was concentrated around the key 7-position in the 4,6-diazaindole series and led to the discovery of molecules with 5- to 20-fold increases in potency and three- to seven-fold increases in exposure over 2 in a rat PK studies.

Distinct effects of two HIV-1 capsid assembly inhibitor families that bind the same site within the N-terminal domain of the viral CA protein

The emergence of resistance to existing classes of antiretroviral drugs necessitates finding new HIV-1 targets for drug discovery. The viral capsid (CA) protein represents one such potential new target. CA is sufficient to form mature HIV-1 capsids in vitro, and extensive structure-function and mutational analyses of CA have shown that the proper assembly, morphology, and stability of the mature capsid core are essential for the infectivity of HIV-1 virions. Here we describe the development of an in vitro capsid assembly assay based on the association of CA-NC subunits on immobilized oligonucleotides. This assay was used to screen a compound library, yielding several different families of compounds that inhibited capsid assembly. Optimization of two chemical series, termed the benzodiazepines (BD) and the benzimidazoles (BM), resulted in compounds with potent antiviral activity against wild-type and drug-resistant HIV-1. Nuclear magnetic resonance (NMR) spectroscopic and X-ray crystallographic analyses showed that both series of inhibitors bound to the N-terminal domain of CA. These inhibitors induce the formation of a pocket that overlaps with the binding site for the previously reported CAP inhibitors but is expanded significantly by these new, more potent CA inhibitors. Virus release and electron microscopic (EM) studies showed that the BD compounds prevented virion release, whereas the BM compounds inhibited the formation of the mature capsid. Passage of virus in the presence of the inhibitors selected for resistance mutations that mapped to highly conserved residues surrounding the inhibitor binding pocket, but also to the C-terminal domain of CA. The resistance mutations selected by the two series differed, consistent with differences in their interactions within the pocket, and most also impaired virus replicative capacity. Resistance mutations had two modes of action, either directly impacting inhibitor binding affinity or apparently increasing the overall stability of the viral capsid without affecting inhibitor binding. These studies demonstrate that CA is a viable antiviral target and demonstrate that inhibitors that bind within the same site on CA can have distinct binding modes and mechanisms of action.

Beyond virological suppression: the role of adherence in the late HAART era

HAART has increased the life expectancy of HIV-infected individuals significantly. Optimal adherence to HAART results in viral suppression and immune recovery in the majority of HIV-infected persons. Data from the early HAART era suggest that adherence levels of greater than 95% are necessary to achieve and maintain virological suppression. However, the optimal threshold of adherence required to maximize the pharmacological benefits of contemporary antiretroviral regimens, particularly in the virologically suppressed patient, is unknown. This review examines new data on the role of adherence in the late HAART era, focusing on virological, immunological and epidemiological aspects. We begin with a discussion of the impact of adherence on viral dynamics and immunological parameters in the virologically suppressed patient. We then review the importance of adherence in emerging antiretroviral treatment strategies. Finally, we summarize accumulating data on the role of antiretroviral adherence in the prevention of HIV transmission. Taken together, the data reviewed reinforce the critical importance of adherence in the management of HIV infection in the late HAART era.

Inhibitors of human immunodeficiency virus type 1 (HIV-1) attachment 6. Preclinical and human pharmacokinetic profiling of BMS-663749, a phosphonooxymethyl prodrug of the HIV-1 attachment inhibitor 2-(4-benzoyl-1-piperazinyl)-1-(4,7-dimethoxy-1H-pyrrolo[2,3-c]pyridin-3-yl)-2-oxoethanone (BMS-488043)

BMS-663749, a phosphonooxymethyl prodrug 4 of the HIV-1 attachment inhibitor 2-(4-benzoyl-1-piperazinyl)-1-(4,7-dimethoxy-1H-pyrrolo[2,3-c]pyridin-3-yl)-2-oxoethanone (BMS-488043) (2) was prepared and profiled in a variety of preclinical in vitro and in vivo models designed to assess its ability to deliver parent drug following oral administration. The data showed that prodrug 4 had excellent potential to significantly reduce dissolution rate-limited absorption following oral dosing in humans. Clinical studies in normal healthy subjects confirmed the potential of 4, revealing that the prodrug significantly increased both the AUC and C(max) of 2 compared to a solid capsule formulation containing the parent drug upon dose escalation. These data provided guidance for further efforts to obtain an effective HIV-1 attachment inhibitor.

Comparative frequencies of HIV low-level viremia between real-time viral load assays at clinically relevant thresholds

BACKGROUND

The introduction of new real-time PCR HIV-1 assays with higher sensitivity and broader dynamic range has resulted in detection of low-level viremia (LLV) (≥ 50 copies/mL) in some patients who previously had undetectable HIV-1 viral load (VL) (<50 copies/mL) with end-point PCR assays. It is therefore important to compare the performance of end-point and newer real-time PCR assays at medically relevant decision points.

OBJECTIVES

The study compared the results obtained with the end-point COBAS(®) AMPLICOR HIV-1 MONITOR Test, v1.5 to those obtained by three real-time PCR assays COBAS(®) AmpliPrep/COBAS(®) TaqMan(®) HIV-1 Test; the COBAS(®) AmpliPrep/COBAS(®) TaqMan(®) HIV-1 Test, v2.0; and the Abbott RealTime™ HIV-1 test.

STUDY DESIGN

A total of 391 plasma specimens from HIV-1-infected patients from three US cities were tested with all four assays. The correlation and concordance of results between real-time and end-point PCR assays were calculated.

RESULTS

There was a consistent and similar proportion (11.8-14.0%) of HIV-1 VL ≥ 50 copies/mL with the three real-time PCR assays for specimens recording <50 copies/mL on the end-point PCR assay. The real-time PCR assays correlated with the end-point PCR assay within generally accepted limits, but consistently quantified higher than the end-point PCR assay between 50 and 200 copies/mL. Discrepancies in results were associated with patient CD4+ cell count and antiviral medication class.

CONCLUSIONS

The clinical interpretation of VL results from real-time PCR assays should take into account their higher sensitivity at the lower quantitation range when assessing patients for disease progression and monitoring response to therapy in HIV-1-infected patients, in line with current treatment guidelines.

Solution structure of the monovalent lectin microvirin in complex with Man(alpha)(1-2)Man provides a basis for anti-HIV activity with low toxicity

Lectins that bind surface envelope glycoprotein gp120 of HIV with high avidity can potently inhibit viral entry. Yet properties such as multivalency that facilitate strong interactions can also cause nonspecific binding and toxicity. The cyanobacterial lectin microvirin (MVN) is unusual as it potently inhibits HIV-1 with negligible toxicity compared with cyanovirin-N (CVN), its well studied antiviral homolog. To understand the structural and mechanistic basis for these differences, we solved the solution structure of MVN free and in complex with its ligand Manα(1-2)Man, and we compared specificity and time windows of inhibition with CVN and Manα(1-2)Man-specific mAb 2G12. We show by NMR and analytical ultracentrifugation that MVN is monomeric in solution, and we demonstrate by NMR that Manα(1-2)Man-terminating carbohydrates interact with a single carbohydrate-binding site. Synchronized infectivity assays show that 2G12, MVN, and CVN inhibit entry with distinct kinetics. Despite shared specificity for Manα(1-2)Man termini, combinations of the inhibitors are synergistic suggesting they recognize discrete glycans and/or dynamic glycan conformations on gp120. Entry assays employing amphotropic viruses show that MVN is inactive, whereas CVN potently inhibits both. In addition to demonstrating that HIV-1 can be inhibited through monovalent interactions, given the similarity of the carbohydrate-binding site common to MVN and CVN, these data suggest that gp120 behaves as a clustered glycan epitope and that multivalent-protein interactions achievable with CVN but not MVN are required for inhibition of some viruses.

Inhibition of both HIV-1 reverse transcription and gene expression by a cyclic peptide that binds the Tat-transactivating response element (TAR) RNA

The RNA response element TAR plays a critical role in HIV replication by providing a binding site for the recruitment of the viral transactivator protein Tat. Using a structure-guided approach, we have developed a series of conformationally-constrained cyclic peptides that act as structural mimics of the Tat RNA binding region and block Tat-TAR interactions at nanomolar concentrations in vitro. Here we show that these compounds block Tat-dependent transcription in cell-free systems and in cell-based reporter assays. The compounds are also cell permeable, have low toxicity, and inhibit replication of diverse HIV-1 strains, including both CXCR4-tropic and CCR5-tropic primary HIV-1 isolates of the divergent subtypes A, B, C, D and CRF01_AE. In human peripheral blood mononuclear cells, the cyclic peptidomimetic L50 exhibited an IC₅₀ ∼250 nM. Surprisingly, inhibition of LTR-driven HIV-1 transcription could not account for the full antiviral activity. Timed drug-addition experiments revealed that L-50 has a bi-phasic inhibition curve with the first phase occurring after HIV-1 entry into the host cell and during the initiation of HIV-1 reverse transcription. The second phase coincides with inhibition of HIV-1 transcription. Reconstituted reverse transcription assays confirm that HIV-1 (−) strand strong stop DNA synthesis is blocked by L50-TAR RNA interactions in-vitro. These findings are consistent with genetic evidence that TAR plays critical roles both during reverse transcription and during HIV gene expression. Our results suggest that antiviral drugs targeting TAR RNA might be highly effective due to a dual inhibitory mechanism.

The HIV-1 transactivator protein (Tat), together with the elongation factor P-TEFb binds to an HIV-1 RNA secondary structure in the 5′-UTRs of nascent viral mRNAs (TAR) and promotes transcription elongation. This process has been an attractive target for drug development but previous inhibitors that bind either Tat or TAR have been plagued by poor inhibition of virus replication, limited cell penetration, and off-target effects. In this article, we describe a series of rationally designed cyclic peptides that block Tat-TAR interactions. L50, the most potent of these compounds, inhibits a wide range of HIV-1 strains from around the world. Remarkably, L50 inhibits two distinct steps in the HIV-1 lifecycle. As expected, L50 inhibits Tat-dependent HIV-1 transcription, but the majority of its anti-HIV activity is due to a block in reverse transcription, i.e. synthesis of the proviral DNA from the RNA genome. L50 inhibition of reverse transcription reveals an important role for TAR RNA during reverse transcription as well as providing one of first examples of a drug with a dual mechanism of action.

Potential use of rapamycin in HIV infection

The strong need for the development of alternative anti-HIV agents is primarily due to the emergence of strain-resistant viruses, the need for sustained adherence to complex treatment regimens and the toxicity of currently used antiviral drugs. This review analyzes proof of concept studies indicating that the immunomodulatory drug rapamycin (RAPA) possesses anti-HIV properties both in vitro and in vivo that qualifies it as a potential new anti-HIV drug. It represents a literature review of published studies that evaluated the in vitro and in vivo activity of RAPA in HIV. RAPA represses HIV-1 replication in vitro through different mechanisms including, but not limited, to down regulation of CCR5. In addition RAPA synergistically enhances the anti-HIV activity of entry inhibitors such as vicriviroc, aplaviroc and enfuvirtide in vitro. RAPA also inhibits HIV-1 infection in human peripheral blood leucocytes-SCID reconstituted mice. In addition, a prospective nonrandomized trial of HIV patient series receiving RAPA monotherapy after liver transplantation indicated significantly better control of HIV and hepatitis C virus (HCV) replication among patients taking RAPA monotherapy. Taken together, the evidence presented in this review suggests that RAPA may be a useful drug that should be evaluated for the prevention and treatment of HIV-1 infection.

Macrophage endocytic trafficking of antiretroviral nanoparticles

AIM

Nanoformulated antiretroviral therapy can improve drug compliance for people infected with HIV. Additional benefits would include specific drug deliveries to viral reservoirs and reduction in systemic toxicities.

METHODS

In this article, we describe mechanisms of crystalline antiretroviral nanoparticle (NP) uptake, intracellular trafficking and release in human monocyte-derived macrophages.

RESULTS

Following clathrin-dependent endocytosis NPs bypassed lysosomal degradation by sorting from early endosomes to recycling endosome pathways. Disruption of this pathway by siRNAs or brefeldin-A impaired particle release. Proteomic and biological analysis demonstrated that particle recycling was primarily Rab11 regulated. Particles were released intact and retained complete antiretroviral efficacy.

CONCLUSION

These results suggest possible pathways of subcellular transport of antiretroviral nanoformulations that preserve both particle integrity and antiretroviral activities demonstrating the potential utility of this approach for targeted drug delivery.

Influence of mutagenesis and viral load on the sustained low-level replication of an RNA virus

Lethal mutagenesis is an antiviral strategy that aims to extinguish viruses as a consequence of enhanced mutation rates during virus replication. The molecular mechanisms that underlie virus extinction by mutagenic nucleoside analogues are not well understood. When mutagenic agents and antiviral inhibitors are administered sequentially or in combination, interconnected and often conflicting selective constraints can influence the fate of the virus either towards survival through selection of mutagen-escape or inhibitor-escape mutants or towards extinction. Here we report a study involving the mutagenesis of foot-and-mouth disease virus (FMDV) by the nucleoside analogue ribavirin (R) and the effect of R-mediated mutagenesis on the selection of FMDV mutants resistant to the inhibitor of RNA replication, guanidine hydrochloride (GU). The results show that under comparable (and low) viral load, an inhibitory activity by GU could not substitute for an equivalent inhibitory activity by R in driving FMDV to extinction. Both the prior history of R mutagenesis and the viral population size influenced the selection of GU-escape mutants. A sufficiently low viral load allowed continued viral replication without selection of inhibitor-escape mutants, irrespective of the history of mutagenesis. These observations imply that reductions of viral load as a result of a mutagenic treatment may provide an opportunity either for immune-mediated clearing of a virus or for an alternative antiviral intervention, even if extinction is not initially achieved.