Regeneron Pharmaceuticals has received approval from the US Food and Drug Administration (FDA) for Pasatru (garetosmab-grts) to reduce the formation of new Heterotopic Ossification (HO) lesions and clinician-assessed flare-ups in adults with Fibrodysplasia Ossificans Progressiva (FOP).

FOP is an ultra-rare genetic disorder in which muscles, tendons, ligaments and other connective tissues progressively develop abnormal bone, a process known as heterotopic ossification. The formation of bone in areas such as the jaw, spine, hips and rib cage can progressively restrict movement and make essential activities, including speaking, eating, walking and breathing, increasingly difficult.

Approximately 900 people worldwide are diagnosed with FOP. Most patients become wheelchair-dependent by the age of 30, while the median survival age is approximately 56 years.

Pasatru is a fully human monoclonal antibody derived using Regeneron's VelocImmune technology. The therapy blocks Activin A, a protein discovered by Regeneron scientists to play a critical role in the development of HO lesions in people with FOP.

The recommended starting dose is 10 mg/kg administered intravenously over 60 minutes once every four weeks. For patients who do not tolerate the starting dose, the dosage may be reduced to 3 mg/kg once monthly, also administered over 60 minutes. Given the significant mobility challenges associated with FOP, Pasatru may be administered across different care settings, including home infusion where appropriate.

The FDA approval is based on efficacy and safety findings from the Phase 3 OPTIMA trial, which evaluated Pasatru in adults with FOP.

At week 56, both evaluated Pasatru doses met the trial's primary endpoint, demonstrating substantial reductions in the total number of new HO lesions compared with placebo.

Patients receiving 10 mg/kg Pasatru experienced a 90 percent reduction in new HO lesions, with two lesions reported compared with 19 in the placebo group. The 3 mg/kg dose produced a 94 percent reduction, with one lesion compared with 19 for placebo, as assessed by CT scans.

Clinician-assessed flare-ups, a key secondary endpoint, also declined. The 10 mg/kg group recorded nine flare-ups, representing an 88 percent reduction compared with placebo, while the 3 mg/kg group recorded 53 flare-ups, a 15 percent reduction compared with placebo. The placebo group recorded 66 clinician-assessed flare-ups.

However, changes in the proportion of patients experiencing patient-reported flare-ups through week 56 were not statistically significantly different between the Pasatru and placebo groups.

The OPTIMA trial included 63 participants. At week 56, serious treatment-emergent adverse events were reported in two patients receiving 10 mg/kg Pasatru, one patient receiving 3 mg/kg and two patients receiving placebo.

Among adults treated with Pasatru, the most common adverse reactions occurring in at least 10 percent of patients included abscess, acne, increased hair growth, madarosis (eyebrow loss), oral ulcers, nosebleeds, folliculitis, paronychia and rash.

Pasatru's regulatory development is continuing internationally. In the European Union, a marketing authorisation application is currently under review by the European Medicines Agency (EMA), while additional regulatory submissions are planned in other countries, including Japan.

The therapy has previously received Fast Track and Orphan Drug designations from the FDA, as well as Orphan Designation from the EMA and Japan's Ministry of Health, Labour and Welfare.