The international Microbicides conference was held in 2006 in Cape Town, South Africa. Notably the first time it has ever been held in a developing country, the conference attracted over 1300 researchers, public health workers, advocates and members of civil society organisations.

The conference focused on the vulnerability of women to HIV infection and the need to find better ways for women to protect themselves. Microbicides are products that could reduce the transmission of HIV and other sexually transmitted infections (STIs) when used in the vagina or rectum. Since they can be applied by a woman before sex without the man being present, they are being labelled as a true female-controlled prevention method.

This extended treatment brief collates news and scientific information presented at the conference.

Challenges for the clinical development of microbicides

Even though the clinical development of microbicides has advanced dramatically in the last few years, study investigators are concerned that a number of challenges could potentially undermine their ability to show whether these products truly work or not. As a result, large pharmaceutical companies have been hesitant to enter the field in the first place — the studies are in resource-limited settings with limited infrastructure, and must enrol large numbers of high risk and often disadvantaged women. The participants speak many different languages and have different levels of literacy; they have to understand and provide consent to the study and continue coming to their scheduled clinic visits, adhere to the study protocol and not get pregnant.

Products in the pipeline

Although scientists have identified a great number of ways to disrupt HIV transmission, “the near term pipeline of microbicides ready to enter [early clinical studies] is fairly modest and... needs to be expanded rapidly,” Professor Sharon Hillier of the University of Pittsburgh and Magee-Women’s Hospital said.

Prof. Hillier gave a plenary talk on the evolving microbicide product pipeline and novel mechanisms to deliver microbicidal compounds, preparing the audience for some of the new developments presented later in the week.

The need for new strategies is great, because the handful of microbicides that have advanced into large scale human trials have relatively low potency against HIV (compared to antiretroviral drugs) — and there is no guarantee that they will actually work in practice. “We need to have a lot of different approaches in the race,” Prof. Hillier said.

Fortunately, many ways to prevent HIV and other STIs in the vagina or rectum have been identified — each with its own set of strengths and challenges for development.

Surface active agents

Surface active agents (or membrane disruptive agents) could prevent HIV and STI transmission and pregnancy by forming a protective barrier in the vagina or rectum. Surface active agents are also cheap to make.

Nonoxynol-9 (N-9) was an early surface active microbicide that has been abandoned because it was abrasive to mucosal tissue and actually increased the risk of HIV transmission. Newer surface active products have been shown to have very low toxicity. However, such compounds are not specific for HIV and their effectiveness will depend on how thoroughly they coat the vagina or rectum (even with the best gel formulations, bare spots are likely), as well as how consistently they are used.

Furthermore, these products need to be applied shortly before sex (and may not be on hand when intercourse has not been planned). If too closely linked to sex, products could be stigmatised in some cultures in the same way that condoms have been — although a study of 200 people in Nigeria presented at the conference suggested that this may not be a problem for the leading product, Savvy, and that acceptance of this microbicide was very high (90 per cent). Even so, there were complaints about excessive wetness, and in other cultures where dry sex (sex without lubricants) is the norm such in as parts of Southern Africa, men may insist that women not use such products.

USAID-sponsored efficacy trials of Savvy are ongoing. However, a major Savvy study in Ghana had to be discontinued when observed rates of HIV transmission were determined to be too low in both the Savvy and placebo-controlled arm for the study to reach a statistically significant conclusion. A related study in Nigeria is continuing, while a study comparing Savvy and tenofovir (Viread) gel vs. placebo is being planned.

Two other new surface active agents in development include cellulose acetate 1,2-benzenedicarboxylate (CAP), a polymer mixture with a long history of safe use in humans as enteric coating for capsules and tablets, and octylglycerol, a naturally occurring antimicrobial lipid found in human breast milk.

Acid/buffering agents

The vagina is acidic, but semen contains strong alkalinizing properties to protect sperm from the vagina’s natural defences. Unfortunately, increasing the pH in the vagina also protects microbes such as HIV and increases the likelihood of their transmission. Acid or buffering agents, such as leading products, BufferGel (which has a pH of 3.9), and Acidform, are sometimes called vaginal defence enhancers because they restore the vagina to its naturally acidic state. Buffering agents may also protect against both pregnancy and STIs by killing sperm and by inactivating acid-sensitive pathogens.

But the buffering agents in commercial development have low local toxicity and no systemic activity. They are active, in vitro, against bacterial vaginosis (BV) and several STIs. However, their potency is rather low; although it could be improved by combining them with other products such as cervical barrier delivery devices (see below).

Fusion/entry inhibitors

Most of the products in advanced clinical trials are simple entry or fusion inhibitors such as cellulose sulfate, PRO 2000 and Carraguard. In test tube studies, the negatively charged active molecules in these gels have been shown to interfere with the binding of HIV, HSV-2 and other enveloped viruses to CD4 and other receptors on macrophages and dendritic cells.

Though these compounds are more directly microbicidal than surface active agents, they are fairly non-specific for HIV and may have a relatively low potency in the presence of seminal fluid and vaginal flora. While they may persist in the vagina longer than surface active agents, they are still generally formulated in gels which have to be applied (with plastic applicators) prior to sex.

But thus far they appear to be quite safe and have moved into large clinical efficacy studies.

Antiretrovirals

One solution to the low potency potential of the previous microbicides would be to use antiretrovirals, which already have proven efficacy as therapeutics. Drugs such as oral tenofovir are being tested in advanced studies worldwide as pre-exposure prophylaxis (PREP) to prevent HIV transmission, but tenofovir and many other antiretrovirals can also be formulated as topical microbicides.

One drawback of formulating antiretrovirals into microbicides is that they only work against HIV — with no activity against other STIs or other benefits for vaginal health or contraception. Thus, unless it is combined with products that offer such attributes, a man who discovers that a woman is using an antiretrovirals -only microbicide, may conclude that she doesn’t trust him — and this could spell trouble for the product’s use once it is marketed.

Another potential weakness for antiretroviral microbicides, at least for those containing only a single antiretroviral compound, is drug resistance. For example, if a woman’s partner has HIV which is resistant to the antiretroviral in her microbicide, she may not be as protected as she thinks. Also, if a woman who is unaware that she is HIV-infected takes a single drug like tenofovir for PREP, she could develop resistance to the drug and possibly limit her future treatment options. It is unclear, however, whether that would happen with a microbicide containing a single antiretroviral that is not systemically absorbed. Drug levels would probably be too low to select for drug resistant virus, but no one knows for certain yet. One possible solution to the resistance problem would be to use combination antiretrovirals in the microbicide.
Fortunately, there is a host of antiretroviral compounds to choose from, including many whose clinical development as oral drugs was halted when they were found to have poor systemic absorption. For example, previous animal and human studies have shown that one compound being considered for development, MIV-150, is non-toxic, and although the compound is well tolerated, it was found to be poorly absorbed orally. Another conference presentation was on zinc-finger inhibitors, which never worked out in clinical development as oral compounds, but still look promising as topical microbicides.

Many of the antiretrovirals have been licensed to the International Partnership for Microbicides (IPM). IPM is a non-profit public-private partnership established to accelerate the development of microbicides for resource-limited countries, with funding from the Bill and Melinda Gates Foundation, the Rockefeller Foundation, and various international governments and multilateral organisations.

IPM identifies the most promising antiretroviral candidates for microbicidal development, licenses them from the big pharmaceutical companies and handles their clinical development. If the microbicides are shown to be effective, IPM has the right to distribute the microbicides at affordable prices in the developing world while the originator pharmaceutical company retains the right to market the products in the western industrialised countries.

IPM’s first product dapirivine (TMC 120) was licensed from Tibotec/Johnson & Johnson only two years ago, and now a gel formulation of the non-nucleoside reverse transcriptase inhibitor (NNRTI) is slated to enter a very large (10,000 plus participants) efficacy study in 2007. IPM is also studying a sustained release formulation of drugs (see below). A benefit of such delivery forms is that antiretroviral-containing microbicides can be effective even when applied or delivered long (or even shortly) before coitus.

CCR5 antagonists

CCR5 antagonists, including PSC-RANTES, aplaviroc, maraviroc and Merck-167, are a new class of highly potent antiretrovirals that could be effective even when applied as a topical microbicide days before coitus. CCR5 antagonists bind to CCR5 receptors and specifically block HIV fusion to cells for up to five days — and the virus finds it difficult to develop resistance to them.

gp120 binders

Although some microbicides in clinical development may block fusion by binding to gp120, a number of more sophisticated and potent HIV fusion inhibitors have been identified including Cyanovirin-N, dendrimers (SPL, VivaGel), and a couple of BMS compounds that have now been licensed to IPM.

Current gp120 binder formulations (gels) must be used shortly before sex, but in the future these may be formulated for once-daily use or in rings which will allow for non-coital use such as once daily contraception or feminine hygiene.

Lime juice?

Douching the vagina (with soap and water, or other liquids such as vinegar, diluted lemon or lime juice – even soft drinks) is a common cultural practice in Africa, particularly after sex. Previous studies have documented that sex workers in Nigeria commonly use high concentrations (50 per cent or 100 percent) of lime juice intravaginally to prevent HIV, STIs or pregnancy.

A laboratory study of lime juice presented at the conference found that it does kill HIV. At a 10 percent concentration, lime juice can inactivate HIV within five minutes. But in the presence of semen, it takes a 50 per cent concentration at least 30 minutes to kill the virus – shorter time periods or lower concentrations failed to demonstrate significant inactivation.

But the study also found some suggestions that lime juice might damage mucosal tissues — particularly if the tissue was already irritated. A second preclinical study, which also looked at lemon juice, found that both juices were markedly toxic to a variety of human cells, and concluded that while the juice might kill HIV in the cultures, it killed everything in the culture.

Two studies set out to determine the safety of douching with lime juice using different concentrations. One, conducted by Dr Anke Hemmerling of the University of California, Berkeley, concluded that the practice was relatively safe at lower concentrations.

In her trial, 25 women were randomly assigned to apply a tampon soaked either without juice or with a 10 per cent or 20 per cent concentration of lime juice for 14 consecutive days. None of the participants showed signs of severe vaginal irritation, although more than 70 per cent of women in all groups reported minor and temporary side effects such as dryness. No other significant problems were observed. However, in light of the preclinical activity studies, these concentrations would be unlikely to affect HIV transmission.

A different study, conducted by Dr Mauck, compared three concentrations of lime juice (25 per cent, 50 per cent and 100 per cent) to plain water in 47 abstinent women who applied 24ml of their assigned fluid twice daily for six consecutive days in two consecutive menstrual cycles, using either a douche or a fluid-saturated modified tampon in each cycle. All study arms experienced some genital irritation — even with water. But at the two higher concentrations of lime juice, there were deep abrasions to the women’s vaginal epithelium. At the highest dose, more than 65 per cent had genital irritation, 50 per cent experienced deep epithelial abrasions and more than 70 per cent reported experiencing pain.

According to Dr. Mauck, high concentrations of lime juice are even more harmful than nonoxynol-9, which despite being used as a microbicide for years, was shown to so irritate the mucosa that it actually increased HIV transmission.

“There’s a very small level of safety and a low therapeutic index — that’s the biggest problem with lime juice. While lime juice is inexpensive and available, this does not justify holding it to a lower standard of safety and efficacy than a microbicide being developed as a drug. To do so would be unfair to the women who so desperately need and deserve a safe and effective prevention method,” Dr. Mauck concluded.

Poor adherence reported in some of the microbicide studies

Women randomised to microbicides currently being evaluated in the clinical efficacy studies report that they do not always use the products as consistently as they should, and in one study, adherence to the microbicides has been lower without condoms than when condoms are being used.

Self-reported behaviour, particularly around microbicide and condom use (and sexual behaviour in general), is not always reliable but if these trends continue, it could make it more difficult for those studies to provide clear answers as to whether the products work or not. Numerous presentations at the Microbicides 2006 Conference focused on ways to improve acceptance, encourage longer-term adherence and to verify whether the products are being used or not in the ongoing trials.

The investigators in the clinical efficacy trials of microbicides are in the awkward position of needing to encourage participants in their studies to use both the product to which they’ve been randomised (microbicide or placebo) and practice safer sex and use condoms — but the trials would have a better chance of reaching a clear conclusion about the effectiveness of the microbicide if people did not actually use the condoms. Yet just the reverse — better adherence to condoms than the microbicide — is being reported in some studies.

Acceptability studies are usually conducted in the early stages of product development and clinical testing, in order to understand women (and men’s) preferences about a product, to help product developers find acceptable formulations, delivery mechanisms, and packaging designs. All of the current crop of microbicides had been extensively tested before proceeding into advanced stage trials, and in general, product acceptance has been high. These studies have been cross-sectional, however, and haven’t tracked temporal changes in adherence.

Even so, a number of acceptability studies presented at the conference suggested that could be room for improvement in the design of some of the products — especially the diaphragms, which are not widely available in many resource limited settings or familiar to the women there.

Who will control microbicides?

Microbicides have been billed as a female-controlled HIV prevention method; but even though most women like the idea that they could use such a product without informing their partners, most would nevertheless prefer to tell their regular partners if they are using a microbicide, according to studies presented at the conference. Some want to disclose the use of microbicides to enhance intimacy while others believe that gel-based lubricants would be detectable to their partners — and fear negative consequences.

Such consequences have already been observed in some of the clinical efficacy studies as researchers reported that failure to involve men in the clinical trials of microbicides has sometimes contributed to poorer adherence to microbicide use and has even led to some women dropping out of the studies. As a result, researchers are increasingly looking at ways of involving regular male partners in the trials from early on.

Future directions

Future studies within the community at large will be essential to get the exact picture of how male involvement could affect microbicide use — and what sort of community-based marketing might be necessary to change attitudes. In the meantime, the job might be made easier if the microbicidal products that eventually go to the market have broader applications than simply being anti-HIV or anti-STI. Combination products for female hygiene or contraception might raise fewer eyebrows and allow women more freedom to use a product without raising suspicion. Also, slow-release technologies such as intravaginal rings or even oral drugs that a woman can use without the man knowing may better deliver on the promise of women-controlled devices.

Challenges for development of microbicides

Problems of study design and size — especially in light of lower than expected incidence rates.
Recruitment of high risk women.

How to provide a high standard of HIV care to women who test HIV positive at screening or during these clinical trials.

What to do when women in microbicide trials become pregnant.

The benefits and challenges involved in measuring a microbicide's effect on other sexually STIs.
Poor adherence to the studies’ experimental arms.

If a somewhat effective microbicide is identified, approved and makes it to the market, how will this affect other ongoing or planned clinical trials?

Products in the pipeline

VivaGel is a vaginal microbicide developed to prevent the transmission of genital herpes and HIV and is currently being tested in Melbourne. Vivagel was awarded US$20 million by the US based NIAID (a division of the National Institutes of Health (NIH) to accelerate its development.
The Carraguard study is one of the furthest along in implementation. Carraguard contains a seaweed extract that acts as an HIV fusion or entry inhibitor. Formulated as a gel, the microbicide is being compared to placebo in a randomised controlled trial by the Population Council at three sites in South Africa (Cape Town, Durban and Limpopo). The study will be unblinded for final efficacy analysis in the second quarter of 2007.

Cellulose Sulfate (CS) is another entry inhibitor formulated as a gel.Trials of celulose sulfate were halted on January 31 2007 when an interim analysis of the CONRAD study showed that the product may increase risk of HIV. Participants on the active arm (those receiving cellulose sulfate rather than the placebo gel) were more likely to seroconvert. A total of 35 seroconversions were reported in the interim analysis of 1333 participants. It has not yet been reported how many of these occurred in the active arm.

A second study of the product sponsored by Family Health International was also halted, though its interim analysis did not show any safety concern. This decision was made as a precaution based on the findings in CONRAD.

HIV Prevention Trials Network (HPTN) study 035 is comparison of 0.5% PRO 2000 (another gel entry inhibitor) and BufferGel (an acidic buffering gel) versus two controls -- a placebo gel and open label no gel arm. The trial is looking at safety and efficacy against HIV and also bacterial vaginosis, a number STIs and pregnancy at six sites in Malawi, South Africa, Zimbabwe, Zambia, and one site in the US. The trial is currently in a safety analysis phase, but rolled over uninterrupted into the efficacy phase in October 2006, with primary effectiveness results expected by early 2009.

Microbicides Development Programme (MDP) 301, is a study funded by the UK’s medical research council and UK Department for International Development (DFID) looking at two strengths of PRO 2000 (0.5%, and 2.0%) versus placebo at six sites in South Africa, Uganda and Tanzania. The trial is expected to continue until March 2009 with results due later that year.
Methods for Reproductive Health in Africa (MIRA) is conducting a study of the Ortho All-Flex diaphragm containing Replens gel (an acidifying buffer) in Harare, Zimbabwe, and in Soweto and Durban, South Africa. The study is fully enrolled, and final results are projected for Autumn 2007.

Two trials of Savvy, a surface active agent formulated as a gel that provides a protective coating within the vagina, have begun: Savvy Nigeria, conducted in Lagos and Ibadan, Nigeria, began in October 2004 and is expected to continue until May 2007. Savvy Ghana was discontinued when it was discovered that the HIV incidence among trial participants (in both placebo and microbicide arm) would be too low to reach any clear conclusion about the effectiveness (or lack of effect) of Savvy.

Link: http://afao.org.au/view_articles.asp?pxa=ve&pxs=103&pxsc=127&pxsgc=158&id=606