By Lisa Seachrist

Washington Editor

CytRx Corp.'s sickle cell anemia drug Flocor failed to meet its primary efficacy endpoint of decreasing the length of sickle cell anemia-associated vascular occlusive crisis in a multicenter Phase III clinical trial.

The Atlanta-based company's stock (NASDAQ:CYTR) fell 58 percent on the news Tuesday, closing at $1.156, down $1.593.

While the study did show Flocor (purified poloxamer 188) helped patients achieve resolution of crisis, the failure to meet the primary endpoint means the study can't be considered a pivotal trial. The company intends to pursue additional studies to support a marketing application.

"We got mixed results in this study," said company spokesman Mark Reynolds. "The bottom line is we didn't meet the hurdles necessary for FDA to consider this a pivotal trial."

Sickle cell anemia affects approximately 60,000 Americans of African, Caribbean, Middle Eastern and South American descent. The genetic disease shortens life span by approximately 15 to 20 years and causes chronic pain. In addition, patients suffer from vascular occlusive crisis, a painful condition resulting from misshapen red blood cells clogging arteries and veins, on average two times a year.

Flocor is a surfactant molecule that alters the way cells interact with water. The drug is made by polymerizing propylene oxide with propylene glycol and works by preventing red blood cells from sticking to each other or adhering to the lining of blood vessels.

The double-blind, placebo-controlled Phase III study included 255 patients in 52 centers across the U.S. Patients who entered the hospital in crisis received standard therapy plus a 48-hour infusion of Flocor or placebo. The primary endpoint was a decrease in the time it took for the crisis to resolve.

"Our underlying assumption was that it took between four and five days for a crisis to resolve," said J. Michael Grindel, vice president of drug development for CytRx. "Data from this study indicates crisis resolves in six to seven days."

As a result, the company was able to show Flocor could provide a statistically significant increase in the number of patients who had resolution of crisis in seven days compared to patients on placebo. In addition, the company found patients who were on hydroxyurea or patients under the age of 15 enjoyed a statistically significant decrease in the length of crisis.

"The younger patients may not have experienced as much damage as adults," Grindel said. "What we saw in kids was very significant."

Grindel said the company needed to analyze the data more thoroughly in order to devise an additional clinical trial and try to ascertain whether crisis resolution is as slow as the current study indicates. The company is also testing the drug in a Phase I/II study for a particularly serious pulmonary complication of vascular occlusive crisis known as "acute chest."

CytRx had entertained the possibility of taking Flocor to market without a partner; however, the need for additional clinical studies means the company will intensify its efforts to find a marketing and development partner for the drug.