Osiris discontinues enrollment in Phase III Crohn’s trial

Osiris Therapeutics has elected to end enrollment at 210 patients in its Phase III trial evaluating Prochymal for Crohn’s disease.

The company believes there is a design flaw in the trial resulting in significantly higher than expected placebo response rates. The decision was made after the trial’s final scheduled interim analysis showed that one of the two Prochymal dose arms had crossed a futility boundary.

The dose arm was unlikely to achieve the primary endpoint of remission because of the high placebo response rate. This latest analysis continued to show no serious safety concerns with the therapy and safety was not a factor in the decision to stop enrollment, the company said.

The Prochymal Crohn’s program consists of two separate but related double-blinded trials. The first trial evaluates patients’ initial response to two dose levels of Prochymal as compared to placebo. The trial was originally designed to enroll 270 subjects.

The potential trial design flaw may be related to the fact that patients responding to the initial therapy were eligible to participate in a second, longer-term trial evaluating Prochymal as a maintenance therapy. It is reported that because the current standard for determining response of Crohn’s patients to therapy is largely subjective, there may have been response bias to meet the eligibility requirements for continuation of therapy in the longer-term maintenance trial.

Randal Mills, president and CEO of Osiris, said: After careful discussion with the FDA, we elected to discontinue enrollment rather than attempt to re-power the trial. We will keep the trial blinded and expect a solid data package for use in designing future trials in Crohn’s disease and to bolster Prochymal’s safety database.