Vaginal microbicides: A novel approach to preventing sexual transmission of HIV

The AIDS epidemic continues its unrelentless expansion. According to the Joint United Nations Programme on HIV/AIDS, there are more than 40 million people living with HIV, and more than 15,000 new infections occur every day. One approach to curbing HIV is the development of topical microbicidal agents or microbicides. These are compounds designed to protect the body’s mucosal surfaces from infection by sexually transmitted diseasecausing pathogens, including HIV. Several candidates are in preclinical stages; however, only a handful have been tested in humans for safety, and even fewer are ready for clinical efficacy trials. In this update, we describe microbicide research and development, including preclinical screening algorithms, ideal properties, compounds in the pipeline, and future prospects. This review is based on a previous work, which has been updated to contain new information, especially regarding microbicide candidates in preclinical and clinical stages of development.     

Mucosal innate immunity as a determinant of HIV susceptibility

Most human immunodeficiency virus (HIV) is acquired during sex, across a mucosal membrane. Despite many advances in our understanding of HIV pathogenesis, the initial events during mucosal transmission have been poorly characterized, and a better understanding of these events will probably be a key to the development of successful microbicide(s) and/or a preventative HIV vaccine. While a vast majority of mucosal HIV exposures do not result in productive infection, implying that innate mucosal immune defenses are highly protective, failure of these mucosal defenses resulted in over 3 million new HIV infections in 2006. We review recent findings regarding HIV mucosal immunopathogenesis, emphasizing the importance of innate immunity in natural protection from infection, and examine how natural or induced perturbations in the mucosal innate system may underpin HIV transmission. Given the great challenges to the development of HIV microbicides and vaccines, identification and enhancement of 'natural' innate immune defenses present attractive avenues for development of safe, non-toxic microbicides.     

Microbicide Research and Development—Where To?

Abstract

Purpose: Against the backdrop of increasing numbers of HIV infections in women and the limitations of current safer sex messages, several calls have been made for the development of women-initiated methods of prevention as an essential component of the armamentarium to reduce women’s vulnerability of acquiring infection with HIV. An effective microbicide is a critical survival tool in instances and situations where existing proven prevention strategies have failed to be adopted. Method: The results of published N-9 clinical trials in terms of anti-HIV activity, safety data, and anti-sexually transmitted infection (STI) activity are discussed. Results: There is no evidence of efficacy against HIV in three clinical trials, there is scanty evidence for protection against STIs, and there is considerable evidence of dose-related adverse effects. Conclusion: During this time, a vast array of potential microbicides with differing modes of action have been discovered, and some have undergone preclinical and early clinical testing. Effort, time, and resources might be better spent on advancing preclinical and clinical testing of these other candidate microbicides.     

Methodological Lessons from Clinical Trials and the Future of Microbicide Research

Interpretation of microbicide trial results has been compromised by challenges to accurate measurement of product adherence and sexual risk behaviors. This article provides an evaluation of the methods used to measure adherence and other sensitive behaviors relevant to assessment of product safety and effectiveness in recently completed trials of vaginal and rectal microbicides. We review the strengths and limitations of existing and novel behavioral measurement strategies and provide recommendations for future trial design with the goal of facilitating the development and identification of safe and effective microbicides for HIV prevention.     

Impact of microbicides and sexually transmitted infections on mucosal immunity in the female genital tract

Human immunodeficiency virus, genital herpes, and other sexually transmitted infections are a critical national and global health priority requiring the rapid development of safe and effective control methods. Topical microbicides, self-administered agents designed for vaginal use, that block transmission at the mucosal surface may provide a realistic method of intervention that could be distributed worldwide. An optimal microbicide should protect against infection but must also be safe, without adversely affecting the mucosal environment, including mediators of host defense. Thus, a critical component in microbicides development is to identify optimal assays that could serve as surrogate markers to predict safety of microbicides prior to embarking on large-scale clinical trials. This will require a greater understanding of the mediators of mucosal immunity in the female genital tract.     

Microbicides for preventing transmission of genital herpes

Available technologies for preventing sexual transmission of genital herpes infection are limited. This article focuses on the ongoing development of a new technology, topical microbicides, for preventing sexually transmitted infection. Recent data evaluating detergent-based spermicides as potential microbicides are reviewed. The first generation of broad-spectrum, non-detergent microbicides that are currently in clinical development, including the sulphated polymer-based inhibitors and acid buffers, are discussed. Finally, the potential of monoclonal antibodies as an example of a specific microbicide in late pre-clinical development is considered.     

Hydrogels containing monocaprin prevent intravaginal and intracutaneous infections with HSV-2 in mice: impact on the search for vaginal microbicides

Hydrogel formulations containing the 1-monoglyceride of capric acid (monocaprin) possess potent in vitro microbicidal activity against HIV and HSV, Chlamydia trachomatis and Neisseria gonorrhoeae. These formulations were studied to determine whether they prevent intracutaneous and intravaginal infections of mice with HSV-2, a virus that is in vitro as sensitive to the virucidal action of the compound as is HIV. In mice intravaginal infection with HSV-2 and the associated mortality was prevented completely when the infection was carried out in the presence of a 20 mM monocaprin containing gel formulation. Similarly, virtually complete protection of lesion development and associated mortality was observed when mice were infected intracutaneously with HSV-2 in the presence of gels containing 10 or 20 mM monocaprin. No irritation or toxicity was observed following application of the gel to the skin or the vaginal mucosa. Hydrogel formulations of monocaprin could thus be pursued as vaginal microbicides for the prevention of sexual transmission of HSV, HIV and other infectious pathogens.     

Using objective markers to assess participant behavior in HIV prevention trials of vaginal microbicides

The need to verify participant behavior exists in any study in which behavior may affect outcomes. In vaginal microbicide trials, the act of having sex and the use of study products and condoms all affect the risk of acquiring HIV/sexually transmitted infections (STIs). Until now, these behaviors have been assessed using self-reports. But self-reports are limited by participant cooperation in answering questions, imperfect recall, and social desirability biases. Biomarkers are increasingly being used in medicine to reduce the time and resources needed to bring a drug to market. The use of biomarkers in vaginal microbicide trials has been proposed as a means of assessing factors that affect the risk of sexual acquisition of HIV/STIs, namely, the presence of preexisting infection, cervicovaginal inflammation, and the presence of HIV/STIs. Biomarkers for some of these already exist. What are needed are validated markers of behaviors that might affect risk, namely, markers for sexual behavior and for the use of study products and condoms. Validating and working out the logistics of collecting such markers in large trials will be a challenge. But finding objective markers for behavior may help improve adherence measurement during a trial and is a rate-limiting step in the field of vaginal microbicides. Resources and funding should be mobilized to develop and validate markers of sexual behavior and product use as a high priority in vaginal microbicide research.     

Female genital tract secretions and semen impact the development of microbicides for the prevention of HIV and other sexually transmitted infections

Pharmacologic strategies for the prevention of HIV include vaccines, post-exposure prophylaxis with antiretroviral therapy, and topical microbicides. Vaginal microbicides have the potential to augment innate defenses in the genital tract but may also disrupt endogenous protection and increase HIV acquisition risk, as observed in clinical trials of nonoxynol-9. The initially disappointing results of microbicide clinical trials stimulated the development of more sensitive and comprehensive pre-clinical safety studies, which include dual-chamber culture systems to model the epithelial barrier and post-coital studies to evaluate the effects of semen and sexual intercourse on microbicide efficacy. This review discusses the key factors that contribute to a healthy female genital tract environment, the impact of semen on mucosal defense, and how our understanding of these mediators informs the development of effective vaginal microbicides.     

Recommendations for the nonclinical development of topical microbicides for prevention of HIV transmission: an update

The development of methods to prevent HIV infection is critical to curbing the rising epidemic. Topical microbicides represent a potential new strategy for reduction of HIV transmission. The purpose of this article is to update and expand upon the nonclinical recommendations of a previously published document on the development of microbicides prepared by the International Working Group on Microbicides. The nonclinical studies discussed here represent general concepts and regulatory considerations that are pertinent to the development of topical microbicides for prevention or reduction of HIV transmission. Essential early steps in product development include the determination of antiviral activity, cytotoxicity, mechanism of action, pathways to resistance, and cross-resistance to approved drugs. Other parameters to consider include activity against vaginal microflora and pathogens that cause sexually transmitted diseases. Before and during clinical trials, nonclinical data on toxicology and pharmacokinetics should be obtained. Finally, product quality issues, including microbicide formulation characteristics, interaction with other products, and stability, should be addressed.     

Bioengineering lactic acid bacteria to secrete the HIV-1 virucide cyanovirin

An urgent need exists to prevent the sexual transmission of HIV-1. With prevalence rates exceeding 35% in parts of sub-Saharan Africa, increasing attention has been placed on developing and testing microbicidal agents capable of preventing virus transmission at mucosal sites. HIV-1 microbicides must meet several requirements before their widespread use. The drugs must be able to neutralize a diversity of HIV-1 strains, not induce mucosal inflammation, be associated with minimal side effects, and be effective for a prolonged period after a single application. Recent work has demonstrated the utility of recombinant lactic acid bacteria (LAB) as agents of mucosal drug delivery. Here, we describe the bioengineering of strains of LAB to secrete the prototypic virucidal compound cyanovirin (CV-N) and demonstrate the anti-HIV-1 activity of secreted CV-N. Our results suggest that recombinant LAB may serve as effective microbicidal compounds and deserve in vivo testing in simian immunodeficiency virus models of mucosal virus transmission.     

Preservation HIV-1-specific IFNγ+ CD4+ T-cell responses in breakthrough infections after exposure to tenofovir gel in the CAPRISA 004 microbicide trial

The Centre for the AIDS Program of Research in South Africa 004 trial demonstrated reduction of sexual HIV-1 acquisition in women using a vaginal microbicide containing tenofovir. A better understanding of the consequences of antiretroviral-containing microbicides for immune responses in individuals with intercurrent HIV-1 infection is needed for future trials combining the use of microbicides with HIV-1 vaccines. Investigation of immune responses in women who acquired HIV-1 although using tenofovir gel showed significantly higher (P = 0.01) Gag-specific IFNγ+ CD4+ T-cell responses. The use of tenofovir-containing gel around the time of infection can modulate HIV-1 immunity, and these immunological changes need to be considered in future trials combining vaccines and microbicides.     

Distribution of a spermicide containing Nonoxynol-9 in the vaginal canal and the upper female reproductive tract

Topical, intravaginal microbicides and spermicides are greatly needed to prevent transmission of sexually transmitted diseases and/or unwanted pregnancies. The development of such compounds is a high research priority. The presumed method of action of existing, or novel, microbicides/spermicides is to provide a chemical barrier to the vaginal epithelium preventing exposure to micro-organisms. Other intravaginal products are used to treat vaginal bacteria of fungal infections. Little is known, however, about the actual or optimal initial distribution and subsequent spread of medications placed in the vagina. We describe a sensitive new technique to quantify the spread of a gel placed in the vagina using magnetic resonance imaging (MRI). Five millilitres of an over-the-counter spermicide containing Nonoxynol-9 was mixed with Gadolinium. MRI was used to quantify spread of the mixture 10 min after insertion with a standard applicator. We demonstrated contiguous spread of gel throughout the vagina. The coverage of material was thicker in the upper vagina than in the lower vagina. We also demonstrated, for the first time, that spermicidal compounds may migrate from the vaginal canal into the endocervix within 10 min of insertion. This finding suggests that topical microbicides/spermicides may act both in the vaginal canal and in the upper female genital tract.     

Microbicides: an emerging science of HIV‐1 prevention in women—15th Conference on Retroviruses and Opportunistic Infections,Boston, USA, 3–6 February 2008

Women account for almost 60% of human immunodeficiency virus type 1 (HIV‐1) infections in Sub‐Saharan Africa. HIV‐1 prevention tools such as condoms, abstinence and monogamy are not always feasible options for women due to various socio‐economic and cultural factors. Microbicides are anti‐microbial medications formulated for topical administration to prevent the sexual transmission of HIV‐1 and other pathogens. Ideally, they will afford bidirectional protection to both men and women who are engaged in vaginal or anal sex. Since the use of condom is often difficult or impossible, this multifunctional role of microbicides will be crucial in the fight against AIDS. The 15th Conference on Retroviruses and Opportunistic Infections (CROI) was recently held in Boston, USA, where one of the most interesting subject area discussed by researchers from all around the world was the latest developments and understandings in microbicide‐related basic science and pre‐clinical product development as well as in product manufacturing and formulation that address the issue of user adherence. Copyright © 2008 John Wiley & Sons, Ltd.     

Safety and anti-HIV assessments of natural vaginal cleansing products in an established topical microbicides <Emphasis Type="Italic">in vitro</Emphasis> testing algorithm

Background  

At present, there is no effective vaccine or other approved product for the prevention of sexually transmitted human immunodeficiency virus type 1 (HIV-1) infection. It has been reported that women in resource-poor communities use vaginally applied citrus juices as topical microbicides. These easily accessible food products have historically been applied to prevent pregnancy and sexually transmitted diseases. The aim of this study was to evaluate the efficacy and cytotoxicity of these substances using an established topical microbicide testing algorithm. Freshly squeezed lemon and lime juice and household vinegar were tested in their original state or in pH neutralized form for efficacy and cytotoxicity in the CCR5-tropic cell-free entry and cell-associated transmission assays, CXCR4-tropic entry and fusion assays, and in a human PBMC-based anti-HIV-1 assay. These products were also tested for their effect on viability of cervico-vaginal cell lines, human cervical explant tissues, and beneficial Lactobacillus species.     

Entry inhibitor-based microbicides are active in vitro against HIV-1 isolates from multiple genetic subtypes

Inhibitors of viral entry are under consideration as topical microbicides to prevent HIV-1 sexual transmission. Small molecules targeting HIV-1 gp120 (BMS-378806) or CCR5 (CMPD167), and a peptide fusion inhibitor (C52L), each blocks vaginal infection of macaques by a SHIV. A microbicide, however, must be active against multiple HIV-1 variants. We therefore tested BMS-C (a BMS-378806 derivative), CMPD167, C52L and the CXCR4 ligand AMD3465, alone and in combination, against 25 primary R5, 12 X4 and 7 R5X4 isolates from subtypes A-G. At high concentrations (0.1-1 microM), the replication of most R5 isolates in human donor lymphocytes was inhibited by >90%. At lower concentrations, double and triple combinations were more effective than individual inhibitors. Similar results were obtained with X4 viruses when AMD3465 was substituted for CMPD167. The R5X4 viruses were inhibited by combining AMD3465 with CMPD167, or by the coreceptor-independent compounds. Thus, combining entry inhibitors may improve microbicide effectiveness.     

Liposomes for HIV prophylaxis

There are approximately 33.4 million adults living with HIV worldwide of which an estimated 15.7 million are women. Although there has been enormous progress in the therapy of HIV/AIDS, treatment is not curative. Prevention is therefore of paramount importance, but vaccine-based and microbicidal approaches are still in their infancy. Since women acquire the virus largely through sexual intercourse, we developed liposomal systems potentially suitable for intra-vaginal use to prevent HIV-1 infection. We formulated liposomes from a range of naturally-occurring and synthetic lipids with varying physicochemical properties, and tested their ability to inhibit infection of transformed cells that express receptors specific to the virus. We identified formulations with the most favorable balance between decreasing HIV infection and causing cytotoxicity (i.e. therapeutic index). The therapeutic index improved with increasing cardiolipin content, and degree of unsaturation. Tissue reaction to these formulations was benign after intra-vaginal instillation in an in vivo female mouse model. These results support the potential use of cardiolipin-based liposomes enriched with synthetic lipids as microbicides for the prevention of HIV infection in women.     

Guiding the vaginal microbicide trials with biomarkers of inflammation

This article discusses cytokine patterns as potential biomarkers of vaginal inflammation, which are needed for the safety evaluation of topical microbicide products for the prevention of sexually transmitted HIV-1 infection. In order to be effective, the vaginal anti-HIV-1 microbicides should avoid proinflammatory responses that facilitate transepithelial viral penetration and replication. Pro-inflammatory and anti-inflammatory cytokines play bi-directional roles in HIV-1 pathogenesis, transmission, susceptibility and resistance. Previous research has shown that many of these key mediators of mucosal barrier function (e.g. IL-1, IL-1 receptor antagonist, IL-6, TNF-alpha, TNF-receptor II, transforming growth factor beta, IL-10, IL-12, IL-8, macrophage inhibitory protein 1, etc.) can be detected in the vaginal secretions of healthy or infected individuals using non-invasive sampling techniques. As part of two microbicide trials, we measured IL-lalpha, IL-1beta, IL-1 receptor antagonist, TNF-alpha and IL-8 in 291 cervicovaginal lavage samples obtained before product use and at the seventh and 14th day after product use. We showed that vaginal formulations, temperature and matrix-specific factors in the vaginal fluids may interfere with cytokine detection, and therefore specific protocols must be validated for various collection procedures and cytokine assays. Our results suggest that combined patterns of cytokine dynamics rather than individual measurements might distinguish proinflammatory product-related effects in microbicide safety trials. More research is needed to establish cytokine mucosal baselines and modulation by genetic factors, sexual intercourse, menstrual cycle, exercise, hormones, stress and infections before guidelines can be established for clinical trial enrollment criteria, the prediction of side/adverse events and ultimately microbicide benefit prognostication.     

Protective effect of vaginal application of neutralizing and nonneutralizing inhibitory antibodies against vaginal SHIV challenge in macaques

Definition of antibody (Ab) functions capable of preventing mucosal HIV transmission may be critical to both effective vaccine development and the prophylactic use of monoclonal Abs. Although direct antibody-mediated neutralization is highly effective against cell-free virus, increasing evidence suggests an important role for immunoglobulin G (IgG) Fcγ receptor (FcγR)–mediated inhibition of HIV replication. Thus, a panel of well-known neutralizing (NAbs) and nonneutralizing Abs (NoNAbs) were screened for their ability to block HIV acquisition and replication in vitro in either an independent or FcγR-dependent manner. Abs displaying the highest Fc-mediated inhibitory activity in various in vitro assays were selected, formulated for topical vaginal application in a microbicide gel, and tested for their antiviral activity against SHIVSF162P3 vaginal challenge in non-human primates (NHPs). A combination of three NAbs, 2G12, 2F5, and 4E10, fully prevented simian/human immunodeficiency virus (SHIV) vaginal transmission in 10 out of 15 treated NHPs, whereas a combination of two NoNAbs, 246-D and 4B3, although having no impact on SHIV acquisition, reduced plasma viral load. These results indicate that anti-HIV Abs with distinct neutralization and inhibitory functions differentially affect in vivo HIV acquisition and replication, by interfering with early viral replication and dissemination. Therefore, combining diverse Ab properties may potentiate the protective effects of anti-HIV-Ab-based strategies.