SAN DIEGO – Conatus Pharmaceuticals Inc. announced today 24-week interim results from a clinical trial with CTS-1027 in combination with Peginterferon Alpha-2a (Pegasys®) and ribavirin (Copegus®) in a treatment experienced, hepatitis C virus (HCV) null-responder patient population. Null-responder patients are the most difficult to treat patient population and are clinically defined as those patients failing to achieve an early virologic response (EVR) when undergoing treatment with the current standard of care (SOC; pegylated interferon and ribavirin). EVR is defined as at least a 2 log decline in HCV-RNA by week 12 of SOC treatment. The CTS-1027-04 clinical trial enrolled 67 HCV genotype 1 null-responder patients. The clinical trial is a single arm and open label design with sustained viral response (SVR; no detectable virus 24 weeks after the end of treatment) as its primary end point. At week 12, 51% (31/61) of patients receiving 15 mg twice a day of CTS-1027 in addition to standard doses of Pegasys® and Copegus® achieved an EVR on a per protocol (PP) basis. HCV-RNA was below quantifiable limit (BQL) in 5 patients (8.2%, PP) at week 12 and increased to 17 patients (34%, 17/50, PP) at week 24. This clinical trial is ongoing and final SVR results are expected in 2011.

Data from the CTS-1027-04 clinical trial were presented at the 46th annual meeting of the European Association for the Study of the Liver (EASL) held in Berlin, Germany, as Abstract 468. The full abstract is available at www.conatuspharma.com.

Consistent with expectations, the majority of patients tested for genetic analysis of IL-28B (95%, 58/61) carried the CT or TT allelic variant. Patients possessing these genetic variants are predicted to be less responsive to the antiviral actions of interferon.

“Most other approaches to treat HCV infection are direct-acting anti-viral drugs whose activity is directed against virus proteins or enzymes with the objective of reducing the production of virus in infected cells. CTS-1027, by comparison, is distinctly different in that its activity is hypothesized to facilitate the immune clearance of virus-infected cells and decrease the frequency of new infections, both of which are of key importance in curing HCV infections.”

said Alfred P. Spada, Ph.D., Senior Vice President of R & D of Conatus.

“Clearance of infected cells is a slow but essential process to achieving a sustained viral response. It is intriguing to observe this significant improvement in viral load reduction at such a low dose of CTS-1027. A recently initiated Phase 2b clinical trial (CTS-1027-05) will test CTS-1027 at higher doses in combination with Pegasys® and Copegus® in the null-responder patient population.”

said Steven J. Mento, Ph.D, President and CEO of Conatus.

Conatus Pharmaceuticals Inc. is a privately-held biopharmaceutical company engaged in the development of innovative human therapeutics to treat liver disease and oncology. Conatus’ lead drug candidate, CTS-1027 is in multiple Phase 2 clinical trials for the treatment of hepatitis C virus (HCV). Conatus was founded by the executive management team of Idun Pharmaceuticals in July 2005 following the sale of Idun to Pfizer. For additional information, please visit www.conatuspharma.com.

Pegasys® and Copegus® are registered trademarks of F. Hoffman-La Roche, Inc.

Contact:

Steven J. Mento, Ph.D.
President and CEO
Conatus Pharmaceuticals Inc.
(858) 457-7222
smento@conatuspharma.com

Alfred P. Spada, Ph.D.
Sr. VP, R&D
Conatus Pharmaceuticals Inc.
(858) 457-7223
aspada@conatuspharma.com