BARCELONA, Spain — Trials of the first completely new AIDS drug in six years indicate it is an effective weapon for treating HIV infections that are resistant to other families of medications, researchers will report here today.
The drug, called T-20, is the first member of a long-awaited family of drugs called fusion inhibitors that block the entry of HIV into cells. The four existing classes of drugs block enzymes that enable the virus to replicate, so T-20 represents an alternative approach to halting viral spread within the body.
Researchers will report on two major trials of more than 1,000 patients who were not responding well to treatment with other AIDS drugs. T-20 reduced blood virus levels by nearly three-quarters and doubled the percentage of patients in which the virus fell to undetectable levels, the teams will tell the 14th International AIDS Conference.
The results are considered quite powerful because the study was conducted "among heavily treatment-experienced patients, a population for whom treatment options are limited," Dr. Jay Lalezari of Quest Clinical Research in San Francisco, who headed one of the studies, said in an interview here. The findings are "exciting and encouraging," he added.
The drug is a "major step forward" in HIV treatment, added Dr. Carl Dieffenbach of the National Institute of Allergy and Infectious Diseases.
T-20 was developed by Trimeris Inc. and will be marketed by Hoffmann-La Roche Inc. Based on the test results, the companies hope to obtain Food and Drug Administration approval for it by the end of the year.
There are 16 drugs in the four classes approved for treating HIV infection. Three of the classes are different families of drugs that block a crucial viral enzyme called reverse transcriptase. Members of the fourth family block a second enzyme, called protease. Both enzymes are crucial to viral replication within cells.
T-20, in contrast, prevents the virus from entering cells, which it does by fusing with the membrane of a target cell, a crucial step in infection. That fusion is carried out by a viral protein called gp 41.
The new drug is a small protein that blends with gp 41, thereby preventing it from fusing with the cellular membrane. Because it is a protein, however, T-20 cannot be given orally. Instead, it is administered twice daily by injections.
But also because it is a protein, the drug does not interfere with cellular metabolic processes or interact with other AIDS medications, said Dr. Dani Bolognesi, CEO of Trimeris. So there are very few side effects, he said.
In fact, the most common adverse effect has been a rash or other mild reaction at the injection site. Only 3% of subjects chose to discontinue drug use because of side effects.
The subjects in the two studies had all been treated with an average of 11 or 12 other AIDS drugs before entering the trials. For each patient, physicians devised a regimen of three new AIDS drugs that appeared to offer the best hope of reducing HIV. Half of these patients received T-20 as well.
After 24 weeks, 37% of the patients who received T-20 in one study had undetectable blood levels of HIV, compared with 16% of those who received just the three-drug cocktail. In the second study, the corresponding figures were 28% and 14%. Patients in earlier studies have sustained such reductions for 96 weeks or longer, said Dr. James A. Thommes, medical director of Roche.