United Press International; Wednesday July 1 10:53 PM EDT
Michael Smith, UPI Science News

Daniel Kuritzkes of the University of Colorado said there are a tremendous number of new anti-AIDS drugs in the pipeline and the challenge for researchers is to make them simpler to use, with fewer side-effects andlower toxicity.

"We talk about triple therapy but there's really nothing magic about the number three," said Kuritzkes, associate professor of medicine, who helped write new AIDS treatment guidelines released Wednesday. "If two drugs are potent, we could use just twoand reserve a class of drugs for future use."

Current treatment standards call for people infected with the human immunodeficiency virus (HIV) to be treated with three drugs, attacking the virus' ability to reproduce in two different ways.

The two points of attack are the enzymes reverse transcriptase and protease, Kuritzkes said, and there are at least nine new drugs in the early stages of clinical trials that may soon join the 11 drugs already approved.

But researchers are also studying other ways of attacking the virus. The most promising research at the moment, he said, aims at preventing the virus from entering a cell in the first place. A virus must enter a cell before it can reproduce.

HIV uses two pathways to enter the cell _ proteins known as CCR5 and CXCR4 that lie on the surface of the target cell. So-called 'fusion blockers,' Kuritzkes said, could block those proteins on the cell surface. As well, a fusion blocker could bind to the virus itself, preventing it from using the pathways.

Kuritzkes said several fusion blockers are under development, including one at the University of Alabama dubbed T20 that has already been shown to block HIV from getting into cells in culture.

A report on T20 a few months ago "was actually the first evidence that fusion could be blocked," Kuritzkes said.

One advantage of fusion blockers, he said, is that they might possibly have a preventive role _ stopping an infection from starting as well as a therapeutic role in preventing the virus from reproducing.

Investigators are also studying the possibility of blocking another HIV enzyme, called integrase, which allows the virus to integrate itself into the DNA of the host cell. But Kuritzkes said those drugs are likely to further down the pipeline, because integrase is a "very difficult protein to work with."

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