An algorithm for the preclinical development of anti-HIV topical microbicides

Throughout the world, and especially in countries comprising the developing world, women are now bearing the brunt of the HIV pandemic, with over 50% living with HIV infection primarily contracted through sexual transmission in monogamous relationships. Thus, effective chemical or physical means of preventing HIV transmission are urgently needed and in the absence of an approved and effective vaccine, microbicides have become the strategy of choice to provide women with the ability to prevent HIV transmission from their infected partners. Topical microbicides include agents specifically developed and formulated for use in either the vaginal or rectal environment to prevent the sexual transmission of infectious organisms, including pathogenic viruses, bacteria and fungi. Although a microbicide product will have many of the same properties as other anti-infective therapeutic agents and would be similarly developed through a defined preclinical program leading to human clinical trials, microbicide development bears its own challenges related to appropriate and informative preclinical investigation, formulation and delivery, and the complex biological environment in which the product must act, as well as the requirement to develop a product that is acceptable to the user. Following years of microbicide development and a series of unsuccessful human clinical trials, a preclinical microbicide development algorithm has been continuously evolving as greater understanding of the required properties of a successful microbicide are defined through laboratory and clinical experience. Herein, we discuss currently accepted practices required for the development of a successful microbicide product which will prevent cell-free and cell-associated virus transmission in the vaginal and rectal vaults.     

The future of HIV prevention: prospects for an effective anti-HIV microbicide

Topical microbicides are self-administered products for prevention of HIV transmission, and they present one of the most promising strategies for combating the HIV-AIDS epidemic. The development of microbicides is a long and complicated process, with many hurdles that are unique to this class of product, including challenges in product design, in the conduct and design of clinical trials, and in obtaining licensure of a new class of products intended for use almost exclusively in developing countries. Once they have been registered, there are additional challenges to the marketing and distribution of microbicides. An overview of the types of microbicide currently in development, and a summary of the issues and the approaches being taken to address them, are provided.     

Microbicides to prevent heterosexual transmission of HIV: ten years down the road

The development of topical microbicides for HIV prevention originated in response to the unabated spread of HIV despite the availability of an effective HIV prevention tool (condoms), as well as the lack of an effective HIV vaccine. Initially, hopes were pinned on existing over-the-counter spermicides containing nonoxynol-9. Concern about the toxicity of nonoxynol-9 with frequent use, and its small or nonexistent protective effect against HIV and other sexually transmitted infections (STIs), has spurred the development of new microbicides with a number of novel mechanisms of action. Significant progress has been made in the last decade. The microbicides pipeline currently contains approximately 34 products in preclinical development, 15 in Phase I safety trials, four in Phase II expanded safety and preliminary effectiveness trials, and three in Phase II/III or Phase III effectiveness trials. Laboratory and clinical research has been complemented by a growing body of research and literature on microbicide acceptability, harm reduction and dual protection strategies, and potential markets. However, many challenges remain, including the need for a significant increase in investment to accelerate product development and complementary research, and to plan for availability and access once effective microbicides are available.     

Knowledge and acceptability of alternative HIV prevention bio-medical products among MSM who bareback

Condom use is the best available strategy to prevent HIV infection during sexual intercourse. However, since many people choose not to use condoms in circumstances in which HIV risk exists, alternatives to condom use for HIV prevention are needed. Currently there are several alternative bio-medical HIV-prevention products in different stages of development: microbicides, vaccines, post-exposure prophylaxis (PEP) and pre-exposure prophylaxis (PrEP). Seventy-two men who have sex with men (MSM) who took part in a study on Internet use and intentional condomless anal intercourse were asked about these four products during a semi-structured interview. The questions explored knowledge and acceptability of all the products and willingness to participate in microbicide and vaccine trials. Qualitative analysis of the data suggests that these men had virtually no knowledge of PrEP, very limited knowledge of microbicides, some information about PEP and considerably more knowledge about vaccines. Reactions towards the products were generally positive except for PrEP, for which reactions were polarized as either enthusiastic or negative. With the exception of PrEP, many men expressed willingness to use the products in the future. Most men would be willing to participate in trials for microbicides and vaccines if given basic reassurances. Concerns over negative side effects and preoccupation with possible infection were some of the motives given for non-willingness to participate in a vaccine trial. These results should inform the development of future trials of biomedical prevention products.     

Past, present, and future of entry inhibitors as HIV microbicides

Preventing the transmission of human immunodeficiency virus (HIV) is the main goal of numerous studies trying to develop an effective vaccine and microbicide agents. Here we review the use of antiretroviral drugs to inhibit viral entry as potential HIV microbicides. After the failure of nonoxynol-9 microbicide strategies shifted towards the use of compounds creating a physical barrier to virus attachment (e.g., surfactants) or inhibit the virus in the vaginal milieu (e.g., polyanions). These early, non-specific inhibitors showed promise in both in vitro and in vivo(non-human primates) studies but provided only modest protection from HIV transmission in clinical efficacy trials. The next generation of HIV entry microbicides was based on specifically blocking virus from entering host cells by targeting CD4 attachment, gp120 binding, and virus-cell membrane fusion events. Although protection from an SIV-HIV hybrid was evident in non-human primates treated and challenged in the vaginal cavity, none of these compounds have advanced to clinical trials as a microbicide. Here we will discuss the reasons for these failures, including the selection of drug resistant HIV variants, which raises questions as to the future of broadly effective microbicides based on HIV entry inhibitors. The outcome of continued research and potential efficacy trials on the next generation of entry inhibitors might reveal whether or not an effective entry microbicide can be developed.     

The development of microbicides for clinical use to prevent sexually transmitted diseases

Approximately 60 vaginal microbicides are under development for the prevention of HIV/AIDS and other sexually transmitted pathogens. The history and current status of the field are discussed with emphasis on the lessons learned from recent clinical trials, along with an emphasis on the mechanisms involved in the sexual transmission of HIV and how this information influences microbicide development. Additionally, the current status of in vitro and animal systems used for evaluating microbicide efficacy, as well as the challenges involved in developing more appropriate and practical assays, are discussed. Also discussed are the challenges that face the microbicide product development field in meeting US Food and Drug Administration requirements regarding product safety and stability.     

From the Cover: Scaleable manufacture of HIV-1 entry inhibitor griffithsin and validation of its safety and efficacy as a topical microbicide component

To prevent sexually transmitted HIV, the most desirable active ingredients of microbicides are antiretrovirals (ARVs) that directly target viral entry and avert infection at mucosal surfaces. However, most promising ARV entry inhibitors are biologicals, which are costly to manufacture and deliver to resource-poor areas where effective microbicides are urgently needed. Here, we report a manufacturing breakthrough for griffithsin (GRFT), one of the most potent HIV entry inhibitors. This red algal protein was produced in multigram quantities after extraction from Nicotiana benthamiana plants transduced with a tobacco mosaic virus vector expressing GRFT. Plant-produced GRFT (GRFT-P) was shown as active against HIV at picomolar concentrations, directly virucidal via binding to HIV envelope glycoproteins, and capable of blocking cell-to-cell HIV transmission. GRFT-P has broad-spectrum activity against HIV clades A, B, and C, with utility as a microbicide component for HIV prevention in established epidemics in sub-Saharan Africa, South Asia, China, and the industrialized West. Cognizant of the imperative that microbicides not induce epithelial damage or inflammatory responses, we also show that GRFT-P is nonirritating and noninflammatory in human cervical explants and in vivo in the rabbit vaginal irritation model. Moreover, GRFT-P is potently active in preventing infection of cervical explants by HIV-1 and has no mitogenic activity on cultured human lymphocytes.     

In vitro and in vivo characterization of a potential universal placebo designed for use in vaginal microbicide clinical trials

The development of vaginal microbicides for the prevention of sexual transmission of HIV is becoming an increasingly important strategy in the battle against the AIDS epidemic. Several first generation microbicide candidates are entering Phase III efficacy trials, and several other candidates are in earlier stages of clinical development. The capacity to make accurate clinical assessments of the safety and efficacy of microbicide formulations is critical. Since microbicide trials will rely on a blinded, randomized, placebo-controlled design, it is important to employ a placebo formulation that does not distort either safety or efficacy assessments. Efficacy of the microbicide would be underestimated if the placebo itself provided a degree of protection. Conversely, a placebo with epithelial toxicity that increased susceptibility would cause an overestimation of microbicide efficacy. To address these issues, a hydroxyethylcellulose (HEC) placebo formulation has been developed and has been adopted for use in clinical evaluations of investigational microbicides as a "universal" placebo. In this report, the chemical and physical properties of this formulation are described, as well as its in vitro and in vivo effects on safety and efficacy. The results show that this "universal" placebo has adequate physical properties, is sufficiently stable as a vaginal gel formulation, and is safe and sufficiently inactive for use in the clinical study of investigational microbicides.     

Influences of geo-spatial location on pre-exposure prophylaxis use in South Africa: positioning microbicides for better product uptake

Young women bear a disproportionately high burden of HIV infection in sub-Saharan Africa, prioritising pre-exposure prophylaxis (PrEP) can be an integral part of HIV prevention combination strategies. Women initiated HIV prevention technology options will require consistent adherence, an imperative for product effectiveness. With several PrEP clinical trials underway; exploring women’s acceptability to advances in HIV prevention technologies can better facilitate demand creation for future PrEP roll out. This study utilised the opportunity of post-trial access to CAPRISA 008 women (trial) and non-trial women from three geo-spatial settings (urban, rural and peri-urban) to identify microbicide acceptability and how product associations of microbicides can influence future HIV prevention choices. Six participatory workshops using participatory action research with art-based activities and discussion groups were conducted in KwaZulu-Natal with 104 women from various geo-spatial locations and social status to understand microbicide acceptability and product associations. The data were analysed using thematic analysis. The study found that women’s acceptability and product association of the tenofovir gel microbicide differed according to rural and urban areas. Most urban women identified confidence, sexiness and classiness as key associations that will encourage microbicide acceptability and use, while rural women identified respect, responsibility and confidence as the key product associations, with increased focus on the individual and collective family/community benefits of product acceptance and use. Urban–rural differences suggest a market segmentation that is contextualised to be locally responsive to promote HIV prevention technologies. Various sexual encounters further determined the types of HIV prevention technologies women would consider. In line with WHO’s recommendation that PrEP should be an additional prevention choice for people at risk of HIV, this study underscores the importance of user engagement, understanding product associations and how this can influence product acceptability and promotion of HIV prevention technologies.     

Rectal Microbicides: Can We Make Them and Will People Use Them?

The results of the CAPRISA 004 and iPrEx HIV prevention studies have demonstrated that topical or systemic use of antiretroviral agents can significantly reduce the risk of HIV acquisition associated with unprotected vaginal or anal sexual intercourse. However, the effect size in these studies was relatively modest and product adherence was generally poor. These observations suggest the need for new approaches to HIV prevention, especially for high risk MSM. Rates of lubricant use are high in MSM practicing receptive anal sex. Consequently, the development of an antiretroviral rectal microbicide gel may provide a safe and effective means of preventing HIV infection with an intervention that is likely to have high acceptability among the target population. The purpose of this article is to describe the challenges and progress in the development of rectal microbicides for HIV prevention.     

Rectal microbicides: can we make them and will people use them?

The results of the CAPRISA 004 and iPrEx HIV prevention studies have demonstrated that topical or systemic use of antiretroviral agents can significantly reduce the risk of HIV acquisition associated with unprotected vaginal or anal sexual intercourse. However, the effect size in these studies was relatively modest and product adherence was generally poor. These observations suggest the need for new approaches to HIV prevention, especially for high risk MSM. Rates of lubricant use are high in MSM practicing receptive anal sex. Consequently, the development of an antiretroviral rectal microbicide gel may provide a safe and effective means of preventing HIV infection with an intervention that is likely to have high acceptability among the target population. The purpose of this article is to describe the challenges and progress in the development of rectal microbicides for HIV prevention.     

Biologic approaches to the prevention of sexual transmission of human immunodeficiency virus

HIV prevention science has made progress, especially in Thailand and some sub-Saharan African countries. New cases of HIV in the United States, however, have not diminished and explosive epidemics in India and the People's Republic of China seem inevitable. Therefore, HIV prevention activities must move forward in parallel. Funding for biologic and behavioral research efforts must be balanced. Behavioral research must inform biologic strategies. In addition, HIV prevention efforts have been distorted by forces that require further consideration. First, the stigmatization associated with a diagnosis of HIV infection led to prevention efforts that virtually ignore the index case. Focusing entirely on the susceptible population puts intense and unrealistic pressure on behavior change and vaccine development. Although development of an HIV vaccine is desirable, there is no evidence that this goal can be achieved in the near future. Blind faith in vaccine technology detracts from pursuit of alternative aspects of prevention science. Vaccine development is but one of several key components to a broad-based prevention strategy. The history of control of infectious diseases has shown the need for targeting index cases. This certainly will prove important in HIV over the next few years. In developed countries, antiretroviral therapy for established HIV infection has become the standard of care. Increased knowledge of the biology of transmission of HIV suggests use of ART to prevent transmission. Such intervention must be accompanied by safer sex behavior in the index cases, and ultimately could lead to some form of monitoring and directly observed therapy. At this time, the latter approach seems unrealistic in developing countries, where the expense of drugs renders them unavailable. But there is every reason to believe that cheaper, more appropriate drugs will be developed before an effective vaccine. Furthermore, targeted use of ART might have disproportionate benefits in some countries. Women are the fastest growing HIV risk group. Several issues, both biologic and social, make this trend a concern. Increases in the number of HIV-infected women will lead to greater vertical transmission. Women possibly have different risk factors for acquisition and transmission than men. Information about the effects of vaginal ecology, specifically, the role of bacterial vaginosis, in the acquisition of HIV is essential because bacterial vaginosis can be reversed, at least transiently. To allow women to take an active role in HIV prevention methods, development of a topical microbicide is vital and may prove easier than a vaccine. Finally, HIV prevention efforts require knowledgeable, central leadership. All prevention efforts should be developed and implemented in parallel, to gain a synergistic result. Few vaccine experts are enthusiastic about microbicides, and HIV caregivers only rarely focus on the public health considerations of their patients. Stopping the spread of HIV requires a coordinated, concerted efforts using "all the tools in the toolbox."     

Perceptions of acceptability and utility of microbicides in Ghana,West Africa: A qualitative,exploratory study

Vaginal microbicides, substances that may substantially decrease transmission of sexually transmitted infections (STI) including human immunodeficiency virus (HIV), are currently in clinical trials. They are being presented as woman-initiated prevention methods that have the potential to be used without partners' knowledge. However, it is recognised that covert use may be challenging, due to the accompanying increase in vaginal lubrication. This study explored factors that may influence acceptability and utilisation of vaginal microbicides in Ghana, a sub-Saharan West African country with relatively low rates of HIV.

Qualitative research methods were employed in Accra, Ghana in 2005. Individual interviews were conducted with 10 staff working in reproductive health settings, and two focus groups were conducted with young women aged 24–28. Three main topics emerged during the interviews and focus groups, including issues related to available contraceptive and prevention methods, perceptions of microbicide interest and acceptability, and cultural influences on microbicide acceptability and use. Participants discussed issues associated with available contraceptive options that may influence microbicide uptake. All respondents suggested that Ghanaian women would have a high level of interest in microbicides, with varying interest in formulas with different contraceptive and disease prevention properties. Cultural factors that may impact on microbicide use, often related to gender and power issues, were also discussed. Thus, as microbicides are being developed, cultural issues and behavioral correlates will need to be assessed to help ensure acceptability and use. In addition, gendered negotiation power and the implications of covert use need to be addressed in microbicide education and social marketing.     

The last decade of microbicide clinical trials in Africa: from hypothesis to facts

Microbicide clinical trials have dominated biomedical HIV prevention research in the past decade. Two generations of microbicides have gone through large-scale human clinical trials. Candidate microbicides assessed in clinical trials in Africa have fallen into the categories of surfactants, polyanionic entry inhibitors, or vaginal milieu protectors. These include compounds such as nonoxynol-9, SAVVY, cellulose sulphate, Carraguard, PRO 2000, and BufferGel. Disappointingly, none of the products have shown efficacy against HIV. Each successive trial has benefited from the lessons learned in preceding trials. The trials have provided important lessons in basic, clinical, social, and behavioural science. More importantly, we have learned that the concept of a vaginally inserted product for HIV prevention is acceptable by women. We have now reached an end of an era of clinical testing with non-HIV-specific microbicides and move forward to testing novel strategies of antiretroviral therapeutic products such as preexposure prophylaxis (PrEP) for HIV prevention. PrEP for vaginal administration in various formulations is being tested to continue our commitment to providing more HIV prevention options to millions of women worldwide.     

Mechanisms and modifications of naturally occurring host defense peptides for anti-HIV microbicide development

Despite advances in the treatment of HIV infection, heterosexual transmission of HIV remains high, and vaccines to prevent HIV acquisition have been unfruitful. Vaginal microbicides, on the other hand, have demonstrated considerable potential for HIV prevention, and a variety of compounds have been screened for their activity and safety as anti-HIV microbicides. Among these are the naturally occurring host defense peptides, small peptides from diverse lineages with intrinsic antiviral activity. Naturally occurring host defense peptides with anti-HIV activity are promising candidates for vaginal microbicide development. Their structural variance and accompanying mechanistic diversity provide a wide range of inhibitors whose antiviral activity can be exerted at nearly every stage of the HIV lifecycle. Additionally, peptide modification has been explored as a method for improving the anti-HIV activity of host defense peptides. Structure- and sequence-based alterations have achieved varying success in improving the potency and specificity of anti-HIV peptides. Overall, peptides have been discovered or engineered to inhibit HIV with therapeutic indices of > 1000, encouraging their advancement toward clinical trials. Here we review the naturally occurring anti-HIV host defense peptides, demonstrating their breadth of mechanistic diversity, and exploring approaches to enhance and optimize their activity in order to expedite their development as safe and effective anti-HIV vaginal microbicides.     

Intravaginal and Menstrual Practices among Women Working in Food and Recreational Facilities in Mwanza,Tanzania: Implications for Microbicide Trials

Intravaginal and menstrual practices may potentially influence results of trials of microbicides for HIV prevention through effects on the vaginal environment and on adherence to microbicide and placebo products. As part of the feasibility study for the Microbicides Development Programme Phase 3 trial of a vaginal microbicide in Mwanza, a variety of quantitative and qualitative methods were used to describe these practices, associations with behaviour and underlying social norms among women working in food and recreational facilities. Intravaginal cleansing by inserting fingers and either water alone or soap and water was thought necessary to remove “uchafu” (dirt), referring to vaginal secretions, including menstrual blood and post-coital discharge. Vaginal cleansing was carried out within 2 hours after 45% of sex acts. Sexual enhancement practices were less common. Intravaginal and menstrual practices and associated behaviours and demographic factors should be measured and monitored throughout microbicide trials to enable analyses of their impacts on microbicide effectiveness.     

Willingness of Clinicians to Integrate Microbicides into HIV Prevention Practices in Southern Africa

The first vaginal microbicide was recently proven effective in clinical trials. We assessed the willingness of clinicians to integrate microbicides into HIV prevention practices in Southern Africa, where women face elevated HIV risks. We conducted in-depth interviews (n?=?60) and nationally representative surveys (n?=?1,444) in South Africa and Zimbabwe with nurses and physicians. Over half of clinicians (58%) were aware of microbicides, with physicians far more likely than nurses to be familiar. Clinicians, including those in rural areas, were generally willing to discuss microbicides, a female-initiated method less effective than the condom, particularly when condom use was unlikely (70%). Fewer would include microbicides while counseling adolescents (51%). Most clinicians (85%) thought their patients would use microbicides; greater clinician familiarity with microbicides was significant for support. Training for both nurses and physicians prior to introduction is critical, so they have sufficient knowledge and skills to offer a microbicide upon availability.