* AIDS gel ineffective in largest trial to date
* Scientists say results disappointing but definitive
* Result adds to setbacks for Endo Pharmaceuticals (Adds background, details on Gilead's product)
By Kate Kelland
LONDON, Dec 14 (Reuters) - U.S. drug company Endo Pharmaceuticals' (ENDP.O) gel designed to prevent infection with the AIDS virus was ineffective in trials in Africa, Britain's Medical Research Council (MRC) said on Monday.
The large international trial of vaginal microbicide Pro 2000 in more than 9,000 women in four African countries found no evidence that it reduces the risk of HIV infection.
The result is a setback for the specialty drugmaker, whose shares were hit earlier in the month when U.S. health regulators declined to approve its Aveed drug for low testosterone. [ID:nN0387831]
To date, no such gel, known as a microbicide, has been shown to prevent HIV infection and this trial "showed conclusively that Pro 2000 gel was of no added benefit," the council said in a statement.
"This result is disheartening, particularly in light of the results of a smaller trial sponsored by the U.S. National Institutes of Health which suggested that Pro 2000 could reduce the risk of HIV infection by 30 per cent," the council's Sheena McCormack, who led the trial, said in a statement.
"Nevertheless we know this is an important result and it shows clearly the need to undertake trials which are large enough to provide definitive evidence for whether or not a product works."
The findings also were a setback to researchers trying to find a microbicide -- a gel or cream that women and perhaps men can use to protect against the AIDS virus when their partners cannot or will not use a condom.
Studies presented at an AIDS conference in Canada in February suggested the Pro 2000 gel, which ENDO acquired through its purchase of Indevus Pharmaceuticals earlier this year, could cut transmission rates by a third [ID:nN09513969].
Almost 60 million people have been infected with HIV and 25 million people have died of HIV-related causes since the beginning of the AIDS epidemic. There is no cure and no vaccine, although drug cocktails can keep patients healthy.
United Nations data have shown that globally that 33.4 million people had HIV in 2008 and 2 million people died.
The latest trial, which took place between September 2005 and September 2009, involved 9,385 women and was carried out by the Microbicides Development Programme (MDP), a not-for-profit partnership of 16 African and European research institutions.
It found that the risk of HIV infection in women who were given PRO 2000 to use was not significantly different than in women supplied with a placebo gel.
Jonathan Weber of the MDP said the result was disappointing but added: "The trial itself was very well designed and undertaken, so we know that the results are definitive.
"It is unfortunate that this microbicide is ineffective at preventing HIV infection but it's still vital for us as scientists to continue to look for new ways of preventing HIV," Weber said in a statement.
Dozens of potential microbicides are being tested, including a formulation using Gilead Sciences Inc's (GILD.O) HIV drug Viread, or tenofovir. (Additional reporting by Ed Cropley in Johannesburg and Maggie Fox in Washington, editing by Karen Foster and Carol Bishopric)