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Integrase Inhibitors- 2 new drugs
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Drug hits key part of HIV virus
By ED SUSMAN
DENVER, Feb. 8 (UPI) -- Doctors said Wednesday that they are impressed by a new class of drug that destroys the virus that causes AIDS by attacking one of its key functions.
In early trials, two of these experimental "integrase inhibitors" were able to kill off more than 95 percent of the virus in just a few days of treatments - even in patients who were harboring virus resistant to other classes of drugs.
"This is some of the best data we have seen in salvage therapy in a long time," said Robin Isaacs, executive director for infectious diseases-clinical research at Merck, based in West Point, Penn.
"Today we have seen the fruition of more than 10 years of development," said John Mellors, professor of medicine at the University of Pittsburgh. "These are very impressive results."
In a presentation at the 13th Conference on Retroviruses and Opportunistic Infections in Denver, Isaacs told United Press International that work on the integrase inhibitor has been going on for more than a decade.
A previous Merck compound that had been through preliminary testing in people was discarded when toxicities appeared in animal models. The new compound, MK0518, appears to have few adverse side effects, despite a potent antiviral impact on human immunodeficiency virus (HIV), the pathogen that causes AIDS.
In a clinical trial, 80 patients were given MK0518 on top of their regular antiretroviral therapy - a therapy that wasn't holding the virus in check.
Depending on the experimental dosage of MK0518, 57 percent to 72 percent of the patients were able to reduce virus in their blood to levels that could not be detected by sensitive assays.
In contrast, only 5 of 27 patients - 19 percent - who were given a placebo pill in addition to the best available treatment could reduce their bloodstream levels of virus to undetectable levels.
"Integrase is absolutely essential for the virus to replicate," said Isaacs. The integrase enzyme is required to allow the virus to splice its RNA into the DNA of the host cell, turning the host cell into a factory to produce more viruses.
Integrase is one of the three main enzymes in the make-up of HIV. Scientists have already produced numerous drugs that interfere with the reverse transcriptase and protease enzymes. The integrase inhibitors have been eagerly awaited as another weapon to control HIV infection.
Isaacs said that further testing is underway and if those advanced studies go well, Merck will seek Food and Drug Administration approval for MK0518 in 2007. "We are very excited about these results," he told UPI.
Another study of a second integrase inhibitor also shows promise, according to Andrew Cheng, vice president for clinical research for Gilead Sciences, Forster City, Calif.
Cheng said his company's candidate, GS9137, appeared to reduce circulating HIV in every dosage used in a 10-day monotherapy trial.
He said that in his company's early studies, GS9137 was able to reduce bloodstream virus by as much as 99 percent in the 10 days of study. Further studies are also underway with this compound.
"The fact that Gilead's integrase inhibitor also worked well shows that this strategy is not a fluke," Mellors said in offering perspective. "This is a real target. This is validated. These results are as impressive as I've ever seen in the treatment of experienced patients."
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