SciClone Pharmaceuticals Inc. and Sigma-Tau SpA reported "promising" interim results from a Phase III study of a Zadaxin (thymalfasin)-based regimen for hepatitis C virus (HCV).

Full data are expected in the third quarter of 2008.

The blinded interim data showed that 171 of 553 total patients in both the treatment and control groups responded to treatment after 48 weeks. A response to treatment is defined as having no detectable HCV RNA in the blood at the end of 48 weeks of therapy.

The treated group received a triple-therapy regimen, containing pegylated interferon alpha, ribavirn and Zadaxin. Patients were randomized, in a one-to-one ratio, to receive either thymalfasin or a placebo, and all patients received pegylated interferon alpha and ribavirin.

After 48 weeks of treatment, patients were followed up during a 24-week observation period, for a total of 72 weeks. All patients will complete the observation period by the end of the second quarter.

Of the 171 patients who responded after 48 weeks of therapy, 150 patients have completed the 24-week follow-up period, and 54 patients have achieved a sustained virologic response (SVR). The study's primary endpoint is SVR, defined as the absence of hepatitis C virus in the blood after the 24-week follow-up period.

SciClone, of Foster City, Calif., and Sigma-Tau, of Rome, pointed out that those data included both treated and control group patients. Still, the companies said the "trend is promising" for nonresponder patients with HCV SVR rates in other recent trials were 3 percent to 8 percent at the 72-week point.

If the final results of the trial are positive, SciClone and Sigma-Tau said they plan to meet with the regulatory authorities in the U.S. and Europe to discussion bringing Zadaxin to the market.

The study's lead researcher, Mario Rizzetto, professor of gastroenterology at the University of Torino in Italy, acknowledged that "we do not know the breakdown between thymalfasin-treated and control group patients who have achieved an SVR." But there is a strong overall response for nonresponder patients, he said in a company news release.

An estimated nearly 1 million U.S. patients with hepatitis C virus have failed or will fail currently approved therapy, particularly those who have not done well on prior therapy, Friedhelm Blodel, president and CEO of SciClone, said in the release. "We believe that thymalfasin could represent an important advance in the treatment of hepatitis C patients and address a growing and acute unmet need," he said.

Blodel noted that the combination of thymalfasin, pegylated interferon and ribavirin is patent protected by SciClone in most major markets, including the U.S. and Europe until 2021.

In 2005 and 2006, SciClone completed two Phase III clinical trials using thymalfasin in combination with pegylated interferon without ribavirin. Although those trials did not show statistical significance in the thymalfasin treatment arm, a positive thymalfasin-related trend was observed in SVR.

In June 2007, SciClone reported positive Phase II clinical trial results from Sigma-Tau's 488-patient study of thymalfasin in Stage IV malignant melanoma. That study met its primary endpoint in tumor response and showed promise in extending survival for those patients, according to the companies.

They are planning a Phase III melanoma trial and expect to file a special protocol assessment with the FDA. However, before proceeding further with the melanoma trial, SciClone and Sigma-Tau said they will review the final 72-week results for the current HCV clinical trial in the third quarter to determine the next steps for thymalfasin development program for HCV and malignant melanoma indications.