FDA greenlights Regeneron drug for rare bone disease

The FDA has officially granted approval for Regeron's garetosmab-grts, to be sold under the brand name Pasatru. A monoclonal anitbody that blocks the protein Activin A, Pasatru is the second treatment to be approved for the ultra-rare disease fibrodysplasia ossificans progressiva (FOP), a disorder characterised by rogue bone formation in the muscles and other connective tissue.

Up until now, Ipsen had the only approved treatment for FOP on the market, Sohonos (palovarotene), which secured approval in 2023 after a rocky road with the agency. But Sohonos has not lived up to its sales potential, despite being the only drug on the market, perhaps owing to relatively low efficacy and a concerning side effect profile.

Pasatru might be well-positioned against the older Ipsen drug: the OPTIMA trial on which the FDA clearance is based demonstrated a 90% or greater reduction in new lesions at 56 weeks, compared to just a 60% reduction in Sohonos's pivotal trial. The OPTIMA trial also demonstrated a "dramatic reduction" in clinician-assessed flare-ups -- an 88% reduction compared to placebo at the 10 mg/kg dose level.

“For people living with FOP, every irregular new bone formation is a step toward disability and potential loss of mobility,” Dr. Kathryn Dahir, a professor at Vanderbilt University, and a primary investigator for the OPTIMA trial, said in a statement. “With the ability to reduce the number of new bone lesions and flare-ups, we now have a new treatment that can positively affect patients.”

The drug continues to be under review at the European Medicines Agency, with another submission planned in Japan.

Regeneron has not yet announced a list price for the drug. Sohonos was priced at $624,000 per year. 

About 900 patients worldwide live with FOP, and the disease leaves most patients wheelchair-bound by the age of 30, with a median survival age of 56, according to Regeneron. Pasatru is only approved for adult FOP patients.

There are several more trials underway that could lead to additional treatment options for FOP, including one from Ipsen for the investigational drug fidrisertib, as well as ashibio's andecaliximab and Incyte's zilurgisertib. None of these employ Regeneron's protein-blocking approach. All three trials are currently in phase 2.