HIV microbicides: state-of-the-art and new perspectives on the development of entry inhibitors

Automated Solution-Phase Synthesis of S-Glycosides for the Production of Oligomannopyranoside Derivatives

Thioglycosides are more resistant to enzymatic hydrolysis than their O-linked counterparts, thereby becoming attractive targets for carbohydrate-based therapeutic development. We report the first development of methods for the site-selective incorporation of S-linkages into automated solution-phase oligosaccharide protocols. The protocols were shown to be compatible with the formation of S- or O-glycosides for the synthesis of mannopyranoside trimmers that incorporate both S- and O-linkages to allow the selective incorporation of an S-glycoside in various stages in an automated program.

Straightforward synthesis of Man9, the relevant epitope of the high-mannose oligosaccharide

The high-mannose oligosaccharide (or its corresponding Man₉ epitope) is the most abundant structure present in pathogen envelope glycoproteins. In this work, a very efficient synthetic alternative was described to access this relevant Man₉ epitope in a very straightforward manner.

Dendronized Anionic Gold Nanoparticles: Synthesis, Characterization, and Antiviral Activity

Anionic carbosilane dendrons decorated with sulfonate functions and one thiol moiety at the focal point have been used to synthesize water-soluble gold nanoparticles (AuNPs) through the direct reaction of dendrons, gold precursor, and reducing agent in water, and also through a place-exchange reaction. These nanoparticles have been characterized by NMR spectroscopy, TEM, thermogravimetric analysis, X-ray photoelectron spectroscopy (XPS), UV/Vis spectroscopy, elemental analysis, and zeta-potential measurements. The interacting ability of the anionic sulfonate functions was investigated by EPR spectroscopy with copper(II) as a probe. Different structures and conformations of the AuNPs modulate the availability of sulfonate and thiol groups for complexation by copper(II). Toxicity assays of AuNPs showed that those produced through direct reaction were less toxic than those obtained by ligand exchange. Inhibition of HIV-1 infection was higher in the case of dendronized AuNPs than in dendrons.

Rapid and efficient synthesis of α(1–2)mannobiosides

A very rapid, versatile and high yield synthesis of Manα1,2Man derivatives using a common orthogonal benzoyl/acetyl protection strategy compatible with the presence of azido groups and the use of CuAAC for conjugating the α(1–2)mannobiosides to different scaffolds, reducing the cost and time of the synthesis and improving the overall yield.

Recent advances on anti-HIV vaginal delivery systems development

A review of the recent outcomes regarding technologies to prevent vaginal transmission of HIV, mainly by using antiretroviral (ARV) drugs formulated as microbicides. An introduction about the HIV transmission mechanisms by the vaginal route is included, together with the recent challenges faced for development of successful microbicide products. The outcomes of clinical evaluations are mentioned, and the different formulation strategies studied to-date, with the requirements, advantages, disadvantages and limitations of each dosage-form type, are presented. Finally, the recent attempts to apply various types of nanotechnologies in order to develop advanced microbicide-products and overcome existing limitations, are discussed.

Nanotech-derived topical microbicides for HIV prevention: the road to clinical development

More than three decades since its discovery, HIV infection remains one of the most aggressive epidemics worldwide, with more than 35 million people infected. In sub-Saharan Africa, heterosexual transmissions represent nearly 80% of new infections, with 50% of these occurring in women. In an effort to stop the dramatic spread of the HIV epidemic, new preventive treatments, such as microbicides, have been developed. Nanotechnology has revolutionized this field by designing and engineering novel highly effective nano-sized materials as microbicide candidates. This review illustrates the most recent advances in nanotech-derived HIV prevention strategies, as well as the main steps required to translate promising in vitro results into clinical trials.

Unique DC-SIGN clustering activity of a small glycomimetic: A lesson for ligand design

DC-SIGN is a dendritic cell-specific C-type lectin receptor that recognizes highly glycosylated ligands expressed on the surface of various pathogens. This receptor plays an important role in the early stages of many viral infections, including HIV, which makes it an interesting therapeutic target. Glycomimetic compounds are good drug candidates for DC-SIGN inhibition due to their high solubility, resistance to glycosidases, and nontoxicity. We studied the structural properties of the interaction of the tetrameric DC-SIGN extracellular domain (ECD), with two glycomimetic antagonists, a pseudomannobioside (1) and a linear pseudomannotrioside (2). Though the inhibitory potency of 2, as measured by SPR competition experiments, was 1 order of magnitude higher than that of 1, crystal structures of the complexes within the DC-SIGN carbohydrate recognition domain showed the same binding mode for both compounds. Moreover, when conjugated to multivalent scaffolds, the inhibitory potencies of these compounds became uniform. Combining isothermal titration microcalorimetry, analytical ultracentrifugation, and dynamic light scattering techniques to study DC-SIGN ECD interaction with these glycomimetics revealed that 2 is able, without any multivalent presentation, to cluster DC-SIGN tetramers leading to an artificially overestimated inhibitory potency. The use of multivalent scaffolds presenting 1 or 2 in HIV trans-infection inhibition assay confirms the loss of potency of 2 upon conjugation and the equal efficacy of chemically simpler compound 1. This study documents a unique case where, among two active compounds chemically derived, the compound with the lower apparent activity is the optimal lead for further drug development.

Can plant biotechnology help break the HIV-malaria link?

The population of sub-Saharan Africa is at risk from multiple, poverty-related endemic diseases. HIV and malaria are the most prevalent, but they disproportionately affect different groups of people, i.e. HIV predominantly affects sexually-active adults whereas malaria has a greater impact on children and pregnant women. Nevertheless, there is a significant geographical and epidemiological overlap which results in bidirectional and synergistic interactions with important consequences for public health. The immunosuppressive effects of HIV increase the risk of infection when individuals are exposed to malaria parasites and also the severity of malaria symptoms. Similarly, acute malaria can induce a temporary increase in the HIV viral load. HIV is associated with a wide range of opportunistic infections that can be misdiagnosed as malaria, resulting in the wasteful misuse of antimalarial drugs and a failure to address the genuine cause of the disease. There is also a cumulative risk of toxicity when antiretroviral and antimalarial drugs are given to the same patients. Synergistic approaches involving the control of malaria as a strategy to fight HIV/AIDS and vice versa are therefore needed in co-endemic areas. Plant biotechnology has emerged as a promising approach to tackle poverty-related diseases because plant-derived drugs and vaccines can be produced inexpensively in developing countries and may be distributed using agricultural infrastructure without the need for a cold chain. Here we explore some of the potential contributions of plant biotechnology and its integration into broader multidisciplinary public health programs to combat the two diseases in developing countries.

Development of sulphated and naphthylsulphonated carbosilane dendrimers as topical microbicides to prevent HIV-1 sexual transmission

OBJECTIVES

For the last 20 years, the idea of alternative prevention strategies based on the use of topical vaginally products to inhibit HIV-1 infection in women has been established. The concept of a 'microbicide' product has been born out of the unavailability of a vaccine against HIV-1 and the problems of women in negotiating the use of preventive prophylaxis by their partners, especially in developing countries.

DESIGN

We have developed and evaluated polyanionic carbosilane dendrimers G3-S16 and G2-NF16 with sulphated and naphthylsulphonated end groups as nonspecific microbicides.

METHODS

Cellular in-vitro or in-vivo models were used to evaluate the safety, biocompatibility and anti-HIV ability of two polyanionic carbosilane dendrimers.

RESULTS

Both dendrimers showed high biosafety in human epithelial cell lines derived from uterus and vagina and in primary blood human cells (PBMC). These dendrimers not only have a partial capacity to block the entry of different X4 and R5 HIV-1 isolates inside epithelial cells but protect the epithelial monolayer from cell disruption and also reduce HIV-1 infection of activated PBMC. Additionally, treatment of epithelial cells with G3-S16 or G2-NF16 dendrimers did not produce changes in proinflammatory cytokines profile, in proliferation of PBMC, on microbiota or sperm survival. Finally, no irritation or vaginal lesions were detected in female CD1(ICR) mice after dendrimers vaginal administration.

CONCLUSION

These interesting results suggest that G3-S16 or G2-NF16 could be effective to inhibit HIV infection and transmission within genital mucosa as well as the spread of HIV transmission to human PBMC.

Glycodendritic structures: tools to interact with DC-SIGN

The key role of carbohydrates in many biological events has attracted the interest of the scientific community. This fact has demanded the access to new tools necessary to understand this role and the interaction of carbohydrates with their corresponding receptors, lectins. Glycodendrimers and glycodendritic structures in general, have demonstrated to be very efficient and interesting tools to intervene in those processes where carbohydrates participate. In this review, we discuss the different glycodendritic structures that have been used to interfere with DC-SIGN, a very attractive lectin involved in infection processes and in the regulation of the immune response.

Plant made anti-HIV microbicides--a field of opportunity

HIV remains a significant global burden and without an effective vaccine, it is crucial to develop microbicides to halt the initial transmission of the virus. Several microbicides have been researched with various levels of success. Amongst these, the broadly neutralising antibodies and peptide lectins are promising in that they can immediately act on the virus and have proven efficacious in in vitro and in vivo protection studies. For the purpose of development and access by the relevant population groups, it is crucial that these microbicides be produced at low cost. For the promising protein and peptide candidate molecules, it appears that current production systems are overburdened and expensive to establish and maintain. With recent developments in vector systems for protein expression coupled with downstream protein purification technologies, plants are rapidly gaining credibility as alternative production systems. Here we evaluate the advances made in host and vector system development for plant expression as well as the progress made in expressing HIV neutralising antibodies and peptide lectins using plant-based platforms.

Microbicides: still a long road to success

The development of efficient microbicides, the topically applied compounds that protect uninfected individuals from acquiring HIV-1, is a promising strategy to contain HIV-1 epidemics. Such microbicides should of course possess anti-HIV-1 activity, but they should also act against other genital pathogens, which facilitate HIV-1 transmission. The new trend in microbicide strategy is to use drugs currently used in HIV-1 therapy. The success of this strategy is mixed so far and is impaired by our limited knowledge of the basic mechanisms of HIV-1 transmission as well as by the inadequacy of the systems in which microbicides are tested in preclinical studies.

Quinoxalinone Inhibitors of the Lectin DC-SIGN

The C-type lectin dendritic cell-specific intercellular adhesion molecule 3-grabbing nonintegrin (DC-SIGN) can serve as a docking site for pathogens on the surface of dendritic cells. Pathogen binding to DC-SIGN can have diverse consequences for the host. DC-SIGN can facilitate HIV-1 dissemination, but the interaction of Mycobacterium tuberculosis with DC-SIGN is important for host immunity. The ability of pathogens to target DC-SIGN provides impetus to identify ligands that can perturb these interactions. Here, we describe the first stable small molecule inhibitors of DC-SIGN. These inhibitors were derived from a collection of quinoxalinones, which were assembled using a tandem cross metathesis-hydrogenation sequence. To assess the ability of these small molecules to block DC-SIGN-mediated glycan adhesion and internalization, we developed a sensitive flow cytometry assay. Our results reveal that the quinoxalinones are effective inhibitors of DC-SIGN-glycan interactions. These compounds block both glycan binding to cells and glycan internalization. We anticipate that these non-carbohydrate inhibitors can be used to elucidate the role of DC-SIGN in pathogenesis and immune function.

A glycomimetic compound inhibits DC-SIGN-mediated HIV infection in cellular and cervical explant models

OBJECTIVE

Dendritic cell-specific intercellular adhesion molecule (ICAM)-3 grabbing nonintegrin (DC-SIGN) participates in the initial stages of sexually transmitted HIV-1 infection by recognizing highly mannosylated structures presented in multiple copies on HIV-1 gp120 and promoting virus dissemination. Inhibition of HIV interaction with DC-SIGN thus represents a potential therapeutic approach for viral entry inhibition at the mucosal level.

DESIGN

Herein we evaluate the efficacy in inhibiting HIV-1 infection and the potential toxicity of a multimeric glycomimetic DC-SIGN ligand (Dendron 12).

METHODS

The ability of Dendron 12 to block HIV-1 infection was assessed in cellular and human cervical explant models. Selectivity of Dendron 12 towards DC-SIGN and langerin was evaluated by surface plasmon resonance studies. β chemokine production following stimulation with Dendron 12 was also analyzed. Toxicity of the compound was evaluated in cellular and tissue models.

RESULTS

Dendron 12 averted HIV-1 trans infection of CD4(+) T lymphocytes in presence of elevated viral loads and prevented HIV-1 infection of human cervical tissues, under conditions mimicking compromised epithelial integrity, by multiple clades of R5 and X4 tropic viruses. Treatment with Dendron 12 did not interfere with the activity of langerin and also significantly elicited the production of the β chemokines MIP-1α, MIP-1β and RANTES.

CONCLUSION

Dendron 12 thus inhibits HIV-1 infection by competition with binding of HIV to DC-SIGN and stimulation of β-chemokine production. Dendron 12 represents a promising lead compound for the development of anti-HIV topical microbicides.

A novel VSV/HIV pseudotype approach for the study of HIV microbicides without requirement for level 3 biocontainment

Studies of potential HIV mucosal microbicides are difficult to undertake due to the requirement for a suitable animal model and the use of biosafety level 3 containment, which are not always available to researchers. Here we show the use of a mouse model of vaginal and rectal transmission of an HIV chimeric virus that does not require level 3 biosafety containment, to test the ex vivo efficacy of soluble Gb3 analogs for the prevention of mucosal HIV infection. The model uses a pseudoenvelope-typed vesicular stomatitis virus (VSV)/HIV recombinant virus that can infect all murine cell types. We demonstrate that the envelope glycoproteins VSV-G of VSV and gp-120 of HIV both bind Gb3. We show that soluble Gb3 analogs inhibit in vitro infection of cervical and vaginal-derived cell lines by both intact HIV and the VSV/HIV recombinant virus. Soluble Gb3 analogs incorporated into gel or used alone and applied directly to the vaginal and rectal mucosal tissue of mice were able to resist viral infection as monitored by PCR and quantitative real-time PCR copy number of HIV cDNA extracted from mouse tissue. Only a trend towards significant efficacy for prevention of mucosal transmission through lower copy number in the treatment groups was evident from these studies; however, this finding warrants further evaluation. In addition, we illustrate a methodology to evaluate inflammatory responses in either vagina or rectum after administration of soluble microbicidal compounds. These studies provide a potential new ex vivo methodology suitable for animal facilities in general, to screen microbicide drug candidates, including drug candidates that target viral proteins, for efficacy and safety, in order to accelerate development and discovery of prophylactic and therapeutic agents for HIV/AIDS.

Modelling the impact of treatment with individual antiretrovirals

PURPOSE OF REVIEW

The aim of this paper is to review the recent literature on HIV mathematical models that evaluate the effect of antiretroviral treatment on mortality, morbidity, HIV and other key outcomes. The focus of our attention is models which explicitly model specific effects of individual antiretroviral drugs.

RECENT FINDINGS

The number of studies that use mathematical models to evaluate the impact of antiretroviral drugs as a treatment or prevention strategy is increasing.Many mathematical models are deterministic compartmental models, and do not have the level of detail of specific effects of individual drugs. However, models that include specific antiretroviral drugs have been increasingly employed to assess the cost-effectiveness of prevention interventions, to evaluate benefits and harms (toxicities, side-effects, resistance development) of different regimens and different intervention timing and to predict long-term outcomes of randomized controlled trials (RCTs) that are not usually measured in the time frame of a trial.

SUMMARY

The number of models that consider specific antiretroviral drugs, with their own peculiarities, is limited. This factor is particularly the case for dynamic individual-based stochastic models. In order to address some research questions it is necessary to accurately take into consideration implications of toxicities, side-effects, and resistance acquisition, and hence to model specific drugs or at least specific drug classes.