Panacos' PA-457 effective against drug-resistant HIV strains, study says

By Angela McDaniels

Seattle, Feb. 9 - Panacos Pharmaceuticals Inc. said that PA-457, the company's HIV maturation inhibitor, showed potent anti-HIV activity in vitro against a number of commonly occurring HIV strains that are resistant to approved drugs, including nucleoside reverse transcriptase inhibitors, non-nucleoside reverse transcriptase inhibitors, protease inhibitors and fusion inhibitors.

In a second study, completed at the National Cancer Institute in collaboration with Panacos, results showed that there may be a high genetic barrier to developing resistance to PA-475.

Finally, a more detailed analysis of data from a phase 2a clinical trial of PA-457 found that 88% of the modeled variability in antiviral response among patients could be explained by plasma concentrations of the drug.

Panacos said the analysis also suggested that doses higher than 200 mg may lead to greater antiviral responses.

The original phase 2a study data, announced in August, demonstrated that PA-457 had potent anti-HIV activity following 10 days of once-daily dosing in HIV-infected patients, meeting its primary endpoint with a statistically significant median reduction in viral load of greater than 10 times at 200 mg, the highest dose level in the study.

Data from all three studies was presented at the 13th Conference on Retroviruses and Opportunistic Infections held this week in Denver.

"We believe that these data on the phase 2a study, resistance profile and synergistic activity of PA-457 continue to be encouraging indicators for future development," president and chief executive officer Samuel Ackerman said in a news release.

"Of particular interest are the pharmacodynamic modeling results, which support our plan to go higher in dose in an upcoming phase 2b study of PA-457, with the likelihood of achieving an even greater antiviral response than we saw in phase 2a."

Watertown, Mass.-based Panacos develops small molecule oral drugs for the treatment of HIV and other major viral diseases.

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