FDA REJECTS ALNYLAM PLAN TO EXPAND USE OF DRUG

The Food and Drug Administration refused to expand its approval of a gene-silencing medicine from Alnylam Pharmaceuticals to treat a rare progressive heart disease after concluding that the benefits to patients weren’t “clinically meaningful,” the firm said Monday. Yvonne Greenstreet, Alnylam’s chief executive, told analysts in a conference call that she was “quite surprised” by the FDA decision, which was received in a letter to the Cambridge company. She said Alnylam designed the study of the medicine, called Onpattro, with regulators and the drug met multiple goals in a clinical trial. In a pivotal study, she said, Onpattro met its primary goal by helping patients with the debilitating disease, called ATTRCM, walk about 14.7 meters more in six minutes compared to those given a placebo. Alnylam said that was a statistically significant difference suggesting the medicine was slowing the progression of the deadly disease. As a result of the FDA decision, Greenstreet said, Alnylam will no longer pursue expanded use of Onpattro for ATTR-CM, a progressive form of cardiomyopathy that causes abnormal proteins to build up in the heart and can lead to heart failure if left untreated. Given as an infusion, Onpattro was the first drug approved in a new class of medicines that rely on RNA interference, or RNAi, a Nobel Prize-winning approach to mute disease-causing genes. Alnylam has persuaded drug regulators to approve five RNAi drugs for rare diseases. The medicines, which have annual list prices of six figures per patient, work by silencing disease-causing genes in the liver. Alnylam is one of the state’s biggest homegrown drug firms by headcount, with 1,159 employees in Massachusetts, according to a report last month by the nonprofit Massachusetts Biotechnology Council trade group.