Crippled by 2 deaths, Zafgen says obesity drug cut weight in PhIII

Zafgen CEO Tom Hughes

With its clinical development program for a new obesity drug in limbo following the unexplained deaths of two patients, Zafgen reported today that the troubled Phase III study hit its co-primary efficacy endpoints in treating a rare eating disorder.

Beloranib, a MetAP2 inhibitor, successfully knocked the weight off of patients suffering from Prader-Willi syndrome in the late-stage trial, offering what the biotech called a "clear efficacy outcome" that would help define talks with the FDA about the possibility of moving forward.

Zafgen's ($ZFGN) shares soared 67% in premarket trading.

The safety of the drug, though, remains under a dark cloud. Zafgen stayed silent for days back in October as investors started demanding to know why it had suddenly scrapped plans for a road show. It was only after a rising crescendo of criticism that the company finally revealed that one patient in the drug arm had died, crashing the stock. And the company's shares were battered again following a second death.

The FDA clamped a complete hold on trial work in early December, citing an imbalance of severe venous thromboembolic events, including the two patient deaths. But the biotech says it had gone far enough into the Phase III to wrap the study and read out the results.

Investigators took two doses of the drug into Phase III. They found that the drug was able to reduce weight by 5.3% in the 2.4-mg dose group and 4.05% for the 1.8-mg dose, compared to an average weight gain of 4.15% in the placebo arm. The study also hit a primary endpoint for a reduction in hyperphagia-related behaviors.

Six patients in the drug arms withdrew from the study for a variety of reasons, including several psychiatric disorders. Zafgen noted that these side effects are common among Prader-Willi patients, and has noted in the past that patients with the genetic disease also have a high mortality rate. Regulators, though, have been clearly alarmed by the concentration of adverse events in the drug arm. And there's no certainty how long the trial hold will last.

"This clear efficacy outcome is a crucial first step in moving discussions forward with the Food and Drug Administration regarding continued development of beloranib," stated Thomas Hughes, chief executive officer of Zafgen. "While we take the previously reported adverse events very seriously, we now have the robust data to provide greater perspective on the benefit/risk relationship of beloranib in this high-risk patient population. We thank our investigators, and the patients and their families for participating in the bestPWS ZAF-311 clinical trial."

- here's the release

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