Osiris Therapeutics will wait for 12-month data on its Phase I/II stem cell treatment Chondrogen before announcing further development of the knee repair therapy, CEO C. Randal Mills said.

On Feb. 13, the Baltimore firm released top-line data on Chondrogen, which is in development for regeneration of the meniscus, or cartilage, of the knee. Results showed the therapy did not lead to significant change in meniscus tissue regeneration at six months, the primary efficacy endpoint.

"We do not think that there was sufficient quantity of meniscus regenerated ... to allow us to use meniscus regeneration as a surrogate endpoint in this trial," Mills said during a same-day conference call.

The 55 patients in the double-blind trial were randomized to receive an injection of placebo, or either 50 million cells or 150 million cells of Chondrogen one week following meniscetomy surgery. Patients were enrolled beginning in March, and the last patient was treated in April.

Mills, however, said he was buoyed by results in 30 percent of patients in the treatment arms, who showed improvement in their baseline cartilage or joint condition while no placebo patients showed any improvement. The exec noted, however, that patients with severe osteoarthritis were prescreened out of the study.

"Most of the patients in the trial had very subtle osteoarthritic changes," he said. "That's interesting because in this patient population, we would not expect to pick up any changes. ...There really wasn't room for major improvement because these patients were prescreened ... so most of the improvements we saw were small."

Going forward, Mills says he is focused on three areas: fully evaluating the six-month data; evaluating global joint score, underlying cartilage changes and quality of life data at 12 months; and investigating the use of the therapy for treatment of osteoarthritis.

"If we are able to use Chondrogen for the treatment of osteoarthritis, that would be a significant market opportunity for us," the exec said, noting that about 20 million cases are diagnosed annually.

Osiris' other stem cell-derived therapies in development include Prochymal ,in Phase III for acute Graft-versus-Host disease and slated to enter Phase III for Crohn's disease, and Provacel ,in Phase I for acute myocardial infarction.

The firm markets the bone matrix agent Osteocel for regenerating bone in orthopedic indications.

- Jonathan M. Block (j.block@elsevier.com)

Osiris Stem Cell Knee Therapy Misses Endpoint

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