Presidio Pharmaceuticals, Inc. selects PPI-461 as a Clinical Candidate in their Hepatitis C Virus NS5A Program

San Francisco, CA – July 7, 2009 – Presidio Pharmaceuticals, Inc. announced today that they have selected one of the lead compounds in their hepatitis C virus (HCV) NS5A program to advance toward clinical development.

Inhibitors of the HCV NS5A protein are novel and distinct from those currently being pursued by others against the two enzymatic targets of HCV, protease or replicase. With response rates of approximately 50% and tolerance issues associated with standard of care treatments involving the combination of pegylated IFN and ribavirin, there is a clear need for potent, small molecule inhibitors that target multiple viral targets and can be administered orally in future combination therapies.

The selected Presidio NS5A inhibitor, PPI-461, exhibits potent and selective activity against all HCV genotypes and showed good oral bioavailability and was well tolerated in animal studies, with elevated liver concentrations relative to serum levels, and potential for once daily dosing in humans. Resistance studies to date suggest that the compound will likely have a high resistance barrier requiring multiple substitutions within the NS5A gene.

IND-enabling studies for PPI-461are currently underway and the Company expects to commence clinical studies in 2010. Additional preclinical research continues on other distinct classes of compounds in the Company’s NS5A program.

About Presidio
Presidio Pharmaceuticals, Inc. is a specialty pharmaceutical company focused on the discovery, in-licensing, development and commercialization of novel therapeutics for viral infections, including HIV-1 and HCV. For more information, please visit our website at www.presidiopharma.com.