Ipsen’s fidrisertib has failed to show meaningful benefit above placebo in a Phase II trial in patients with fibrodysplasia ossificans progressiva (FOP).
In the FALKON study (NCT05039515), fidrisertib, an oral, highly selective and potent small molecule ALK2 kinase inhibitor, failed to meet its primary endpoint of reducing new heterotopic ossification (HO) in adults and children living with FOP.
While there were no safety concerns identified, based on the efficacy data, Ipsen will be terminating the trial about four years early. The FALKON trial was conducted over five years and enrolled 113 patients globally.
Dr Christelle Huguet, EVP and head of R&D, said: “These results are disappointing for the FOP community and patients living with this devastating disease. However, we do believe that these data will contribute to the growing body of research on FOP, giving new insights into managing this disease for patients and their care providers.”
It is unclear whether Ipsen will continue to develop the drug following the Phase II trial, as there are no other planned or ongoing clinical trials, according to GlobalData’s Pharmaceutical Intelligence Center. GlobalData is the parent company of Clinical Trials Arena.
Ipsen gained rights to develop fidrisertib from Blueprint Medicines Corp in 2019. The agreement was signed by Ipsen’s subsidiary, Clementia Pharmaceuticals.
FOP is an ultra-rare, genetic condition caused by pathogenic variants of ALK2 kinase that leads to bone formation in soft and connective tissues, like muscles, tendons and ligaments, a process known as HO, which is irreversible once formed.
The average age of diagnosis is five years old and FOP shortens the life expectancy to a median of 56 years, with death frequently linked to bone formation around the ribcage, leading to breathing problems and thoracic insufficiency.
There are limited treatment options for patients with FOP. Treatment currently includes corticosteroids, with evidence showing that when initiated within a short period of a flare-up, it may help reduce the intense inflammation and tissue oedema seen in the early stages of the disease. Non-steroidal anti-inflammatory medications COX-2 inhibitors and paracetamol may be useful in managing pain and chronic discomfort.
In 2023, Ipsen gained approval from the US Food and Drug Administration (FDA) for its retinoid therapy Sohonos (palovarotene), an oral RAR gamma agonist, in FOP. Sales of the drug reached €20.8m ($24.4m) in 2024, with GlobalData analysis forecasting sales to reach $30m in 2031.
Regeneron has seen success in the indication, with its candidate garetosmab meeting its endpoints in a Phase III trial in September 2025. In the study, the anti-activin A antibody reduced the rate of lesions, with just three reported across the low and high doses compared to 19 in the placebo cohort. There was also a reduction in flare-ups, with 53 reported in the treated patients compared with 70 in the placebo arm. Based on this, Regeneron will be submitting for approval of the drug to the FDA in FOP by the end of 2025.
