Panacos Pharmaceuticals, Inc. has commenced a phase IIa clinical trial of PA-457, the first in a new class of HIV drug candidates called Maturation Inhibitors. Institutional Review Board (IRB) and other approvals have been received and the study is now open for enrolment. Panacos plans to complete dosing of all patients during first quarter, 05.

The study, to be performed at several sites in the US, is designed to demonstrate the antiviral potency of PA-457 following once-daily oral dosing for 10 days in HIV-infected patients who are not on other antiretroviral therapy. Panacos recently announced positive results from a phase I/II clinical trial in HIV-infected patients. Following a single oral dose of PA-457, a significant reduction in viral load from baseline, of up to approximately 0.7 log10, was seen in patients receiving the higher dose levels.

The Company also recently completed a phase Ib clinical trial of PA-457 administered orally once a day for 10 days to uninfected volunteers. The drug candidate was well tolerated and plasma concentrations of PA-457 reached levels significantly greater than those predicted to provide a therapeutic benefit in HIV-infected patients. Both of those studies have been selected for presentation at the 12th Conference on Retroviruses and Opportunistic Infections to be held in Boston, MA during February 2005, the company release said.

"Initiation of phase 2 development of PA-457 is a major milestone for the Company," Dr. David E. Martin, VP, Drug Development at Panacos said adding, "This study builds on our recent rapid progress, generating encouraging safety and pharmacokinetic data from the phase Ib study and demonstrating a reduction in viral load following a single oral dose in HIV-infected patients in the phase I/II study. PA-457 has a long half-life in the body, resulting in significantly increased plasma concentrations following repetitive daily dosing. Therefore, we expect to see an even greater viral load reduction when PA-457 is administered on a daily basis for several days or more."

Results of the Phase 2a clinical trial are expected in Q2, 2005. During the second half of 2005, Panacos intends to initiate Phase 2b studies of PA-457 designed to pave the way for pivotal Phase 3 studies.

PA-457 is the first in a new class of oral HIV drugs discovered by Panacos scientists that inhibit virus maturation, the last stage of the virus life cycle. It is designed to combat drug resistance, which occurs in most HIV patients treated with currently available drugs and is the leading cause of treatment failure. PA-457 works by a mechanism different from that of any approved drug or other drug in development, by blocking a key step in the processing of a viral core protein called capsid. Preclinical studies have shown that PA-457 retains full activity against drug-resistant virus, is effective in an animal model of HIV infection and should be suitable for use in combination therapy with other drugs.