Group to test Merck AIDS drug in gel

(Adds Merck comment, paragraph 11)

By Maggie Fox, Health and Science Editor

WASHINGTON, March 11 (Reuters) - A group working to develop a gel or cream women could use to protect themselves against the AIDS virus said on Tuesday they have permission to use an experimental drug from Merck and Co (MRK.N).

It is the sixth HIV drug to be tested by the International Partnership for Microbicides, said the group's chief executive officer, Dr. Zeda Rosenberg.

The drug is known only by its experimental name L'644. It is a member of a class of drugs known as gp41 fusion inhibitors. They stop the AIDS virus from attaching to the immune system cells it targets.

"It's a completely different mechanism of action to what we have currently under development and what the field has under development," Rosenberg told Reuters in a telephone interview.

"It's pretty early in the life cycle for HIV. Most of us feel that, for a microbicide to be really effective, it has to get at the infection in its earliest timepoints."

Microbicides are products, such as gels or creams, that could be applied vaginally or anally to prevent transmission of the human immunodeficiency virus that causes AIDS.

So far, attempts to create a microbicide have failed.

The AIDS virus has infected 33 million people globally, according to the World Health Organization. It has killed 25 million, and there is no vaccine to prevent the fatal and incurable virus.

Condoms can protect men and women, but health experts note that many men refuse to use them. In many countries, a women who demands that her husband or partner use a condom can face refusal or even a beating.

According to the United Nations, in sub-Saharan Africa almost 61 percent of adults infected with HIV are women. Most cases of HIV are transmitted sexually.

Merck said it was not developing the drug to treat HIV infection. "L'644 is a peptide that would need to be injected to act as an effective antiviral. As such, it was not deemed to have a favorable profile for patient convenience," said Dr. Daria Hazuda, vice president of scientific affairs for infectious disease and HIV at Merck Research Laboratories.

The nonprofit IPM has another agreement with Merck for a royalty-free license to develop another compound, called L'167/CMPD167, which belongs to the class of molecules known as CCR5 blockers.

The microbicides group also has agreements with Pfizer to develop its CCR5 blocker maraviroc; with Gilead Sciences to develop tenofovir, a licensed HIV drug; with Bristol-Myers Squibb; and with Johnson & Johnson subsidiary Tibotec Pharmaceuticals to try to make a microbicide out of its HIV drug dapivirine.

The field could use some successes.

Last month a study showed one microbicide candidate, called Carraguard, did not protect women from infection.

Two other potential microbicides have made women more likely to become infected -- a spermicide called nonoxynol-9 and a product called Ushercell, made by Toronto-based Polydex Pharmaceuticals. (Editing by Mohammad Zargham and Jackie Frank)