UPDATE 1-Schering-Plough HIV drug begins late-stage trials

(Adds new long-term safety data, updates shares)

By Ransdell Pierson

NEW YORK, Sept 17 (Reuters) - Schering-Plough Corp. SGP.N said on Monday that it had begun late-stage trials of an experimental HIV drug that showed promising effectiveness in earlier studies but aroused safety concerns because of cancers seen in some patients taking it.

The U.S. drugmaker said it had begun two Phase III trials of vicriviroc, a once-daily tablet that works through the same mechanism as Pfizer Inc's (PFE.N) recently approved Selzentry, or maraviroc. Both potentially can help patients whose virus has become resistant to earlier HIV treatments.

The new class of medicines is designed to keep the HIV virus that causes AIDS from entering immune cells, specifically by blocking the CCR5 co-receptor protein that is the virus's main doorway. Older HIV drugs, including a family of medicines called protease inhibitors, attack the virus itself.

Schering-Plough said in a release that it had begun the pair of international trials, each with 375 patients. They followed a 48-week study in which vicriviroc showed "potent and sustained viral suppression" among patients whose virus had not been adequately controlled by earlier treatments, the company said.

A monitoring committee in early 2006 cited reports of five malignancies among vicriviroc recipients in a Phase II study, according to Cowen and Co., including four cases of lymphoma and one of stomach cancer. But the committee said it could not conclude the drug had caused the tumors.

Patients in the mid-stage trial were notified of the malignancies, but allowed to remain in the study.

Data from a two-year follow-up of the patients were slated to be presented Tuesday in Chicago at the annual Interscience Conference on Antimicrobial Agents and Chemotherapy (ICAAC).

According to an abstract, or brief summary of the data, vicriviroc proved potent and durable against HIV and was generally well tolerated. No drug-related new lymphomas, liver problems or heart attacks were seen among patients who had taken it for an average of more than three years, although one patient developed tuberculosis.

Two cases of skin cancer were observed, but deemed unlikely to be related to the drug.

Subjects in the larger new trials will take the Schering-Plough drug with other HIV treatments -- including two protease inhibitors.

Cowen earlier this year said vicriviroc has potential to garner annual sales of $200 million by 2012.

Pfizer's Selzentry, which is given twice daily, has its own safety concerns. U.S. regulators approved the drug last month with the provision that its label carries a "black box" warning about the risk of liver toxicity and mentions its potential to increase the risk of heart attack.

Shares of Schering-Plough were down 26 cents at $30.12 in afternoon trading on the New York Stock Exchange, in line with a decline for the drug sector.