GTx muscle drug boosts lean body mass in mid-stage trial

* Cancer patients gained 1.5 kg after 16 weeks

* No pivotal trial before early 2010

By Deena Beasley

LOS ANGELES, June 11 (Reuters) - GTx Inc (GTXI.O) said patients with cancer-induced muscle loss, or cancer cachexia, gained as much as 1.5 kilograms of muscle in a mid-stage trial of its experimental drug Ostarine.

GTx had announced in October that the 159-patient trial met its main goal of increasing lean body mass, as well as the secondary goal of improved muscle function.

Measured by a dual energy X-ray absorptiometry scan, patients taking 1 mg Ostarine gained 1.5 kg (3.3 lbs) of lean body mass and patients on the 3 mg dose gained 1.3 kg (2.9 lbs) at the end of the 16-week trial. Patients given a placebo gained 0.1 kg.

GTx, which is developing the drug with Merck & Co Inc (MRK.N), said the participants had lost an average of 8.8 percent of their weight before entering the trial.

The most common side effects seen were fatigue, anemia, nausea and diarrhea, the company said.

Ostarine is a member of a family of medicines called SARMs, or selective androgen receptor modulators, now in mid-stage trials to treat muscle loss related to cancer or to the normal process of aging.

Merck expects to have Phase II results for another SARM, known as MK-0773 by the end of the year.

"We are waiting to get information from that trial to decide how to move forward," said Mitchell Steiner, chief executive at GTx.

As a result, he said a pivotal trial of Ostarine would be launched no earlier than early 2010. (Reporting by Deena Beasley; editing by Carol Bishopric)