Image courtesy of Starpharma Pty Ltd

Women account for 50 per cent of HIV infection, with more than 60 per cent of those infected living in Sub-Saharan Africa. In these environments, negotiating use of male condoms can be difficult for women and abstaining from intercourse is not an option for women who want to have children or who are at risk of sexual violence.

Head of Burnet’s Retroviral Biology and Antiviral Laboratory, Associate Professor Gilda Tachedjian and her team are investigating methods of protection that women can initiate themselves.

“It is precisely in these most affected environments where the development of female-initiated strategies, such as microbicides, is desperately needed. We need to offer women a chance to protect themselves,” she said.

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Microbicides are chemical entitites that can block infection by HIV and other STIs that enter via the female genital tract. Globally, more than 60 products have been evaluated as potential microbicide candidates, but the challenge lies in the myriad of criteria that a microbicide must meet in order to be successful. Most importantly, it must be safe for use and not cause any irritation or discomfort to the user.

For a microbicide to become successful it must also be socially acceptable to women and their partners, affordable for use in low-income settings, and easy to apply.

Ideally, it would provide protection for several days or even weeks at a time and be available in both contraceptive and non-contraceptive formulations. Microbicides must remain stable at high temperatures, preferably be odourless, colourless, tasteless, compatible for use with latex, and able to be used without partner knowledge.

Leading Australian microbicide efforts

In collaboration with the Australian biotechnology company Starpharma Pty Ltd, Professor Tachedjian and her team have been undertaking the preclinical evaluation of dendrimer microbicides for the inhibition of HIV and genital herpes. The laboratory is also studying how dendrimers interact with the virus and host cells to block infection.

These studies have identified a fourth-generation dendrimer, SPL7013, as the most potent in blocking HIV and genital herpes in cell culture tests, achieving a broad-spectrum activity against different HIV strains and herpes virus (HSV) by inhibiting viral attachment and entry.

The Tachedjian Laboratory has also discovered that SPL7013 directly kills some HIV strains. In 2011, Starpharma and the Tachedjian laboratory published results for a study investigating VivaGel®, a topical gel containing SPL7013, in healthy women.

This study found that VivaGel’s® antiviral activity against HIV and HSV was sustained in cervico-vaginal samples for at least three hours post application in all women, and up to 24 hours in 50 per cent of participants. This prolonged high-level efficacy suggests that VivaGel® does not need to be used immediately prior to intercourse.

“While these results are encouraging, further studies will need to evaluate VivaGel®’s effect in the body and determine the product’s effectiveness in real-life settings,” Associate Professor Tachedjian said.

“There are also exciting results indicating that daily application of VivaGel® for seven days clears bacterial vaginosis (BV) which is a relatively common imbalance in the vaginal microflora.

“Curing this condition is critical because BV can increase the risk of acquiring HIV and other STIs. If confirmed in phase III clinical trials, this property of VivaGel® will make it highly attractive for use in combination with specific antiretroviral agents, such as tenofovir, forming a multi-prevention microbicide with potential efficacy against HIV, other STIs and BV.”

Lactic Acid: Another approach

The Tachedjian Laboratory in collaboration with Professor Richard Cone (Johns Hopkins University, Baltimore, USA) and Dr Thomas Moench (ReProtect, Baltimore, USA) are determining the potential for lactic acid as a topical vaginal microbicide.

“We are studying the ability of lactic acid to inactivate microbes associated with BV, HIV and HSV, and assessing its potential to be combined with specific anti-retrovirals,” Associate Professor Tachedjian said.

Lactic acid is produced by bacteria that are normally present in the healthy vaginal tract and has been found to be potent in inactivation of HIV.