Phase II HELIX-1 Trial is First HCV Clinical Study to Commence Through Collaboration Agreement With Janssen Pharmaceuticals, Inc.

CAMBRIDGE, MA, USA I May 30, 2013 I Idenix Pharmaceuticals, Inc. (IDIX), a biopharmaceutical company engaged in the discovery and development of drugs for the treatment of human viral diseases, today announced the initiation of the phase II HELIX-1 clinical trial evaluating an all-oral, direct-acting antiviral (DAA) HCV combination regimen of samatasvir (IDX719), Idenix’s once-daily pan-genotypic NS5A inhibitor, and simeprevir (TMC435), a once-daily protease inhibitor jointly developed by Janssen R&D Ireland and Medivir AB.

The HELIX-1 trial is a 12-week, randomized, double-blind, parallel group study evaluating the safety and tolerability of samatasvir and simeprevir in addition to antiviral activity endpoints, with a target enrollment of 90 treatment-naive, non-cirrhotic, genotype 1b or 4 HCV-infected patients. Patients will be randomized equally across three treatment arms, receiving either 50, 100, or 150 mg samatasvir once-daily for 12 weeks in combination with simeprevir plus ribavirin. The HELIX-1 trial is the first study in HCV-infected patients to commence under a non-exclusive collaboration agreement signed with Janssen in January 2013. A second trial (HELIX-2) of samatasvir, simeprevir and TMC647055, a once-daily non-nucleoside polymerase inhibitor boosted with low-dose ritonavir being developed by Janssen, is expected to initiate in the second half of 2013.

“We are pleased with the progress of our samatasvir program and its advancement into phase II following successful completion of a drug-drug interaction study with simeprevir earlier this year,” said Ron Renaud, Idenix’s President and Chief Executive Officer. “Our goal is to initiate multiple two- and three-DAA trials of samatasvir through the Janssen collaboration. Additionally, we look forward to advancing our own internal combination of samatasvir with our lead uridine nucleotide analog by the end of this year.”

ABOUT THE IDENIX/JANSSEN COLLABORATION

In January 2013, Idenix entered into a non-exclusive collaboration with Janssen Pharmaceuticals, Inc. for the clinical development of all-oral direct-acting antiviral (DAA) HCV combination therapies. The collaboration will evaluate combinations including samatasvir, simeprevir, and TMC647055. In addition to the HELIX-1 phase II trial, the companies also plan to initiate HELIX-2 which will evaluate a three-DAA combination of samatasvir, simeprevir and TMC647055/r, with and without ribavirin. The clinical trials will be conducted by Idenix. Both Idenix and Janssen retain all rights to their respective compounds under the agreement.

ABOUT SAMATASVIR (IDX719)

Samatasvir is an NS5A inhibitor with low picomolar, pan-genotypic antiviral activity in vitro. To date, samatasvir has been safe and well-tolerated after single and multiple doses of up to 150 mg in healthy volunteers for up to 14 days duration and up to 100 mg in HCV-infected patients up to 3 days duration. There have been no treatment-emergent serious adverse events reported in the program. Samatasvir has demonstrated potent pan-genotypic antiviral activity in HCV-infected patients with mean maximal viral load reductions up to approximately 4.0 log10 IU/mL across HCV genotypes 1-4 in a proof-of-concept, three-day monotherapy study.

ABOUT SIMEPREVIR (TMC435)

Simeprevir is a once-daily potent investigational hepatitis C protease inhibitor in late phase III clinical development being jointly developed by Janssen R&D Ireland and Medivir AB to treat chronic hepatitis C virus infections. Simeprevir is being investigated in combination with PegIFN/RBV in phase III trials and is also being evaluated with direct-acting antiviral (DAA) agents in three other phase II interferon-free combinations both with and without ribavirin (RBV). For further details please visit  http://www.medivir.com.

ABOUT HEPATITIS C

Hepatitis C virus is a common blood-borne pathogen infecting three to four million people worldwide annually. The World Health Organization (WHO) estimates that more than 170 million people worldwide are chronically infected with HCV, representing a nearly 5-fold greater prevalence than human immunodeficiency virus.

ABOUT IDENIX

Idenix Pharmaceuticals, Inc., headquartered in Cambridge, Massachusetts, is a biopharmaceutical Company engaged in the discovery and development of drugs for the treatment of human viral diseases. Idenix’s current focus is on the treatment of patients with hepatitis C virus (HCV) infection. For further information about Idenix, please refer to www.idenix.com.

SOURCE: Idenix Pharmaceuticals