After death, Zafgen clinical trial of obesity drug halted

Zafgen Inc., the Boston pharmaceutical developer whose stock tumbled after a patient enrolled in one of its clinical trials died, lost more than half its value Friday after regulators temporarily halted the trial.

The company said early Friday morning that the Food and Drug Administration ordered a “partial clinical hold” on the trial to screen patients for thrombotic diseases, which form internal clots that can block blood flow. The company also confirmed that the dead patient was taking its experimental drug, not a placebo.

Zafgen’s stock dropped 51 percent Friday to $10.36, capping a tumultuous week in which the company lost two-thirds of its value, falling from $932 million to $281 million. The company’s management reportedly canceled a public appearance Monday, and rumors began to appear in online message boards that it had gone quiet because a patient taking beloranib, its lead drug candidate meant to treat a rare disease called Prader-Willi syndrome, had died.

The company confirmed the death on Wednesday but provided few other details. In a Friday conference call, Zafgen officials said the patient who died was 23 years old and obese and died about two weeks ago, but said the cause of death was unknown. People with Prader-Willi syndrome are often obese because the illness causes feelings of chronic hunger. The FDA imposed the hold orally, the company said.

Dr. Dennis Kim, the company’s chief medical officer, said the FDA would allow patients to resume their trial as soon as they obtained informed consent from them and screened them for blood-clot disorders, a process he estimated would take no more than two weeks. He said three-quarters of patients in the trial — one of two important trials planned by the company to show the drug’s effectiveness — had already completed the six-month treatment regimen.

Jur Strobos, a Washington attorney at the firm Olsson Frank and Weeda, said the FDA required clinical holds in about 50 percent of cases in which unexpected deaths or other serious consequences occur that are related to a drug. In some trials, such as for cancer drugs, some deaths are expected, but drug companies such as Zafgen have to be careful to follow both medical and market regulations when events happen, he said.

“There’s a period of time where the company doesn’t know what’s going on, and that creates what I refer to as a silent period,” said Strobos, who added he could only speak generally because he was not familiar with the details of Zafgen’s case. “You’ve heard about this death. You have no details. You don’t know at this point whether it’s unexpected.”

Dr. Thomas Hughes, Zafgen’s chief executive, said the company reported the patient’s death within a week of learning about it, as required by FDA regulations. A company spokeswoman said “it would have been inappropriate to discuss this event publicly while the company was in initial dialogue with the FDA.”

Hughes added that the company had actually expected “one or two deaths” during the trial based on the known mortality rate of people with Prader-Willi syndrome.

The company said it plans to report the results of the clinical trial in the first three months of 2016.

Publicly traded companies also are required to disclose “material” information about their companies to investors. Strobos, the attorney, said the term isn’t described in regulations written by the Securities and Exchange Commission, but said several events could cross that threshold for small drug developers that are working on only a few drugs, including deaths of individual patients or big movements in their stock prices.

Zafgen, backed by investors that include the venture capital firms Atlas Venture of Cambridge and Third Rock Ventures of Boston, raised $96 million in last year’s initial public offering. It was formed in 2005 and is developing treatments for obesity and metabolic disorders.