A bacterium with a live biotherapeutic grows into a microbicide candidate
by Chael Needle
LifeGuide [Treatment Horizons]
The development of female-initiated HIV prevention methods—female condoms, antiretroviral treatment as prevention, vaginal and rectal microbicide candidates—has been guided by the idea that the empowerment of women and girls is key to improving their health. Effective safer sex methods may be useless if the context surrounding the individual still puts her at risk. For example, an individual may want to use a particular product but may not be able to afford the expense or have ready access to it. Or an individual’s sexual partner(s) may not support her decision to use prophylaxis, or demand sex without her consent. Social stigma surrounding AIDS may convince an individual to set aside prevention strategies for fear of being associated with the virus.
A new topical microbicide candidate seems to hold the potential to not only be effective but to address many of the barriers that thwart prevention. Developed at Osel Inc., a biopharmaceutical company, and the National Cancer Institute, MucoCept is a novel, first-in-class candidate that genetically enhances the ability of naturally occurring vaginal bacteria to inhibit HIV and block transmission.
The bacterium used is a common strain of lactobacilli called Lactobacillus jensenii, which is a member of the normal vaginal flora. The live recombinant lactobacilli are engineered to express an HIV entry inhibitor called cyanovirin-N on the cervical/vaginal mucosa. Cyanovirin-N binds to HIV’s entry-seeking protein gp120 and inhibits HIV transmission.
It’s the product of ten years of work, says Dr. Laurel Lagenaur, MucoCept’s principal investigator at Osel. One of the most recent steps was to test the therapeutic in a macaque challenge model. Explains Dr. Lagenaur: “In these models you repeatedly challenge the animals and you look for infection. You look for the drawn-out survival curve. If you had a couple who was disparate—for instance, the man had HIV and the woman did not and they’re in a [sexual] relationship—what you want your product to do is increase the time that it takes for the person to get infected, to the point where you increase it infinitely. In an animal model you give a much higher dose of virus so that they get infected at a more advanced rate and then you look at whether your product slows down the rate of infection. In this case it slowed it down sixty-three percent and that’s good.” A reduction in the viral load of infected macaques receiving the product was also noted.
A class apart
In the context of antiretroviral-based and non-antiretroviral based microbicides, MucoCept is set to distinguish itself. Like antiretroviral-based candidates, MucoCept inhibits the virus in a specific way. Yet, the potential for an individual to develop drug resistance with an antiretroviral-based microbicide is present. If drug resistance develops, the user would have to change therapies, says Dr. Lagenaur. Antiretroviral-based microbicides might be effective, in other words, but also might be date-stamped.
“Other microbicides that have been out in the field have been non-specific inhibitors, like all of the early-tested microbicides: N-9, cellulose sulfate, PRO 2000, Carraguard. Many of those were polyanions or detergents, so either they kind of worked against the membrane of the virus or they bound to the virus. But—none of those worked,” Dr. Lagenaur explains, adding that one positive result of these studies is that researchers have learned that combining contraception and HIV prevention, which some of the candidates tried to do, may not be harder than we thought.
“Our product is a really novel class of microbicides because it’s a biologic. First of all, this product will only work in women because this product is meant to colonize the female reproductive tract. [Yet], there could be future products that could colonize both the vagina and the rectum. This product [so far] only colonizes the vagina well,” says Dr. Lagenaur.
Novel and natural
As a biologic, a therapy derived from living organisms, the cyanovirin-N-expressing lactobacilli naturally colonize the female reproductive tract and could potentially offer protection for weeks at a time. “This particular protein, cyanovirin, was found in a drug screen at the National Cancer Institute many years ago and kind of languished because there wasn’t a good way to make this antiviral protein cheaply and efficiently,” says Dr. Lagenaur, adding that if it were developed as a conventional microbicide it would be limited by its coital dependence, the need to apply it every time you engaged in vaginal sex. “By linking this protein to a bacterium…the bacterium is the factory for you. You put the bacterium into the vagina and it will continue to make this antiviral protein….”
The capacity of bacteria to grow and multiply makes it unnecessary to apply a microbicide like this around the time of sexual activity, as well as makes it efficient and affordable to produce. Gone would be much of the costs associated with traditional therapeutic manufacturing, purifying, formulating, and so on, says Dr. Lagenaur. A big batch of bacteria may be grown in multi-liter fermenters, freeze-dried, and then delivered in a dried capsule.
We can think of MucoCept as a “second-generation probiotic,” says Dr. Lagenaur, different from some of the other probiotics in that the lactobacilli is “capable of coming back alive and then it grows and it produces your antiretroviral so you don’t have to worry about fresh drug. Once you have the bacteria, it’s making fresh drug….You use the bacteria to do your bidding!”
Overproduction is not a concern. “MucoCept tends to replace the [resident] Lactobacillus that is already [in the vagina] but if there’s no Lactobacillus it will become the normal flora there….It doesn’t really overgrow because it’s not a pathogenic organism. It’s what’s called a commensal organism, kind of the native species of what’s supposed to be there. So, it grows to a certain level that the body tolerates…,” notes Dr. Lagenaur. “And in this case it produces the antiviral at a low level and we know that the level we produce is at a level that can inhibit the virus but it’s not so great that it would be toxic. It’s the self-limitation of the system—the bacteria can produce only so much protein.” The settled-on level of antiviral has been tested in an animal model.
A double benefit
Improving vaginal health lowers the risk of HIV transmission and MucoCept’s Lactobacillus is protective, controlling various vaginal infections and safeguarding against inflammation.
Referring to the CAPRISA 004 trial, which found that a one-percent tenofovir gel provided moderate protection against the sexual transmission of HIV for women, she says, “For the group of women who had tenofovir and had no vaginal inflammation, no infections occurred. Women who had tenofovir and had vaginal inflammation is where they saw infections, and of course women who got placebo also had infections.
“Vaginal inflammation was a big cofactor for infection. And this can be caused by a number of things—a viral infection, or another bacterial infection, or something called bacterial vaginosis, which is an overgrowth of bacteria, other than lactobacillus, in the vagina. By actually putting in the Lactobacillus as part of the product, we are giving women what they need to have there anyway. There’s a high level of bacterial vaginosis in women in developing countries. It’s actually as high as twenty-five to thirty percent of women worldwide who may have bacterial vaginosis, but not recognize it. So they have a low level of inflammation and levels of inflammation bring in white cells [of which] one component is the CD4 T cell and that’s what HIV infects.”
Usability of any product in a real-life situation is a factor of its viability as a prevention method and MucoCept addresses the concerns many women have about more conspicuous products.
“What I like about MucoCept is that a woman could use this very covertly. What’s more covert and natural than what already lives in the vaginal tract? You could deliver this in a form that would be invisible to the user. It’s not gelatinous; it’s not sticky; it has no odor…,” she notes. “Another aspect is that it could always be female-initiated and not coital dependent so it could be applied well in advance or any time she wants…[T]hat makes it very much more in a person’s control. So it gives a woman more options….
“Secondly, there’s a stigma associated with using anti-HIV products,” says Dr. Lagenaur, noting that often the presence of a prevention method sometimes translates to partners as evidence of infection. “However, MucoCept is [not only an HIV inhibitor but] also a women’s health product because it’s a Lactobacillus and women could use it to prevent bacterial vaginosis or ‘to enhance vaginal health,’ if you want to say it that way. So, a woman in a developing country could seek a product like this and tell a partner that it’s for vaginal health…and yet it’s protecting her in two ways—it’s improving vaginal health and there’s the anti-HIV component to it.”
Future potential, next steps
The next step in Dr. Lagenaur’s research is animal-based preclinical safety testing, a process necessary to make sure it has no toxic effects on the reproductive tract or liver, and so on, in order to be able to give it to humans as part of a trial. Later, the team will work on formulating the biologic and finding the right dosage. “Then there will be acceptability studies,” says Dr. Lagenaur. “Do women prefer to have the product as a capsule? Do they prefer it in an applicator? Do they want it as a film? Do they want it as a gel? How do they want it delivered? And that’s a little bit on the advocacy and consumer side:You have people ask, what do you think about a product like this, and if you were using a product like this how would you take it? It’s very important because you’d want a product that women would feel comfortable using. Or men, for that matter, if you develop a similar product for them.”
Notes Dr. Lagenaur: “Our product is sort of a first in class. It’s not a me-too product. If you look at some of the antiretrovirals out there, it’s like, try this one, try that one, but they’re all basically similar. MucoCept is a very different kind of product. In that way, we have a little bit of a higher hurdle because it’s a very novel approach and people might not be as comfortable using a modified bacterium. But if you think about it, it’s a natural bacterium with one little change—and that’s a lot more natural than a drug. It’s a bacterium with one additional protein, so, if you think about it in that way, it may end up being safer than other things out there.”
Chael Needle wrote about a statin in the context of drug-drug interaction for the August issue.