HIV Develops Resistance to Experimental Drug T-20

The experimental AIDS drug T-20, which researchers hope will benefit people whose HIV infections have become resistant to other medications, may itself sometimes cause HIV resistance to develop, suggests a new study in Antimicrobial Agents and Chemotherapy (2002;46:1896-1905). The resistance developed in a study of patients taking T-20 alone, not in combination with other medications. Recently, Roche Holding AG, which is developing the drug with Trimeris Inc., reported encouraging results of studies of T-20 used in combination with other AIDS drugs.

"Both studies indicate that T-20 significantly enhances the activity of HIV combination therapy," said Dr. Dani Bolognesi, CEO and chief scientific officer of Trimeris. The cases of HIV resistance developed in an early-phase trial designed to test the safety of the drug in humans, he said. That resistance was only in patients taking a lower dose than is being tested in later trials of T-20, which are ongoing. Resistant viruses have not developed in those studies, according to Bolognesi. Further details of T-20 studies will be presented at the upcoming international AIDS meeting in Spain, he said.

Unlike current AIDS drugs that target HIV once it has already entered cells, the fusion inhibitor T-20 works by keeping HIV from entering cells in the first place.

In the study, Dr. John C. Kappes and colleagues at the University of Alabama-Birmingham studied 16 HIV-positive patients. Patients took 3 mg, 10 mg, 30 mg or 100 mg of T-20 twice a day for two weeks. In patients taking the two lowest doses, there was no noticeable effect on the viral load. In all patients taking the highest dose, however, viral load dropped below detectable levels. Resistance developed in patients taking the 30 mg dose. These patients experienced some decline in viral load, though not as large as the drop seen in the 100 mg group. At the end of the study, though, the researchers detected HIV mutations in two of the four patients in the 30 mg group.

"Our study of patients receiving T-20 monotherapy provided the first evidence for the rapid emergence of clinical resistance to a novel class of entry inhibitors," Kappes said. "These findings are highly relevant to ongoing and future treatment strategies involving these agents," he said.

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