• Initial results on next-generation HIV fusion inhibitor consistent with target profile for convenient, once-daily, low-volume injection

Durham, NC -- August 7, 2008

Preliminary Results from the Phase 1 Clinical Study of TRI-1144

Trimeris also today announced preliminary results from study TRI-1144-101, a Phase 1 study of the next-generation HIV fusion inhibitor, TRI-1144. Results of the study indicate TRI-1144 was well tolerated at all doses tested. Plasma concentrations at 24 hours suggested that a dose of approximately 25 mg of TRI-1144 could be sufficient for a convenient, once-daily, low-volume injection. In addition, this dose produced no injection-site reactions (ISRs) in this study.

"We are very pleased with the results from this first-in-human study of TRI-1144," said Martin Mattingly, CEO of Trimeris, Inc. "The initial safety and pharmacokinetic results from this study, together with the excellent solution stability of TRI-1144, continue to suggest that this peptide will meet the target profile of a safe and convenient once-daily fusion inhibitor. As previously communicated, we are no longer funding research and development at Trimeris and are seeking a licensor to develop this promising candidate."

Conducted in 24 healthy subjects, study TRI 1144-101 was a placebo-controlled, double-blind, single-dose trial that explored the safety, tolerability and pharmacokinetics of four doses of TRI-1144. A total of 18 subjects received TRI-1144, ranging from 25 mg to 250 mg while 6 subjects received placebo. Pharmacokinetic analyses showed that the plasma half-life ranged from 13 to 20 hours depending on the dose administered, with a time to maximal exposure ranging from 10 to 13 hours.

There were no serious adverse events observed during the trial. Eight subjects experienced a total of 13 adverse events. Of these eight subjects, five were in the TRI-1144 group (5/18 or 28%) while three subjects were in the placebo group (3/6 or 50%). With respect to the events observed in the TRI-1144 group, five were considered mild (5/6 or 83%) and one was moderate (1/6 or 17%) (backache; unrelated). With respect to adverse events observed in the placebo group, five events were considered mild (5/7 or 71%) and two were moderate in intensity (2/7 or 29%). No serious injection-site reactions (ISRs) were observed. Two out of 6 (33%) and 15/18 (83%) of subjects receiving placebo or TRI-1144, respectively, experienced mild or moderate ISRs. No ISRs were experienced in the TRI-1144 25 mg group. Erythema and pain/discomfort were the most frequent signs/symptoms observed and most ISRs resolved by 96 hours. No ISRs were experienced in the 25 mg group. Full data from the trial will be presented at an upcoming medical conference.

Next Generation Fusion Inhibitor Program -- TRI-1144 (TR-0291144)

Our next generation fusion inhibitor, TRI-1144, has been developed with the specific goal of achieving durable suppression of HIV by increasing the potency and raising the genetic barrier to the development of resistance. Also, key to the development program was improving patient convenience via more patient-friendly administration with less frequent dosing and reduction of the injection site reactions associated with Fuzeon. TRI-1144 (TR-0291144) is currently under investigation in a Phase 1 clinical trial. TRI-1144 is a 38 amino acid peptide derived from the HIV gp41 sequence shown to be the most potent in inhibiting viral fusion; its sequence partially overlaps that of enfuvirtide. Through discovery efforts undertaken at Trimeris, the nascent gp41 sequence was intentionally altered allowing the peptide to exist as a stable alpha helix of three peptide molecules known as a trimer. The key contact residues required for viral fusion were maintained or conservatively changed -- the result of all of the modifications is TRI-1144. These alterations are believed to give TRI 1144 its unique properties of high genetic barrier to resistance, enhanced pharmacokinetic properties, and excellent physical chemical properties.

In preclinical studies, TRI-1144 has proven to be as or more potent than enfuvirtide, have a much higher genetic barrier to resistance, and have approximately a ten-fold longer half-life in cynomolgus monkeys than enfuvirtide. The potency, improved genetic barrier, and pharmacokinetic properties suggest that TRI-1144 will be administered less frequently than Fuzeon and possibly at a lower dose. In the appropriate sustained release formulations, it is envisaged that TRI-1144 could have a once weekly dosing profile.

No safety issues were identified in a full battery of IND supporting toxicology studies. The physical chemical properties of TRI-1144 indicate that a stable solution formulation should be achievable removing the requirement for the onerous reconstitution needed for Fuzeon for a patient-friendly once daily administration from an auto-injector such as a pre-filled pen device.

An IND was filed in January 2008 for the clinical study of TRI-1144. Currently, one clinical protocol is in progress (TRI 1144-101). TRI 1144-101 is a single dose escalation study in healthy volunteers that is investigating the safety, including injection site reactions, tolerability and pharmacokinetics of TRI-1144. Results are expected in the third quarter of 2008.

For more information, visit www.trimeris.com.