UK-based Mereo BioPharma Group has released six-month data from the open-label arm of the Phase IIb ASTEROID study evaluating setrusumab (BPS-804) in adult patients with Type I, III or IV osteogenesis imperfecta (OI).

Setrusumab is a fully humanised monoclonal antibody (mAb) designed to inhibit the sclerostin protein, which slows down the activity of bone-forming cells.

The dose-ranging Phase IIb study assessed the therapeutic in 112 patients, comprising 69 with Type I, 29 with Type IV and 14 with Type III OI.

Patients in the open-label arm received the highest of the three prospectively defined doses of the study drug administered in the blinded arms.

Changes in patients’ baseline trabecular volumetric bone mineral density (Tr vBMD) at the radius (wrist) was assessed at three and six months.

At the interim data cut-off, 12 subjects had the Tr vBMD measurements available at baseline and three months, while 11 had data recorded at baseline and six months.

A mean increase of 1.4% over baseline was observed at three months, while the rise was 3.2% at six months. The percentage change over baseline in Tr vBMD of the radius at 12 months is the primary endpoint of the Phase IIb trial.

The study’s secondary endpoint is change over baseline in areal bone mineral density (BMD) at the lumbar spine at six and 12 months.

Top-line 12-month data from the blinded arms of the study are expected in Q4 2019.

Mereo BioPharma CEO Denise Scots-Knight said: “The data from this open-label arm of our Phase IIb study is clear and encouraging and in line with our expectations.

“Osteogenesis Imperfecta is quite distinct from osteoporosis and is a rare and devastating orphan disease, where there exists a significant need for an effective treatment. We are committed to advancing setrusumab for both adult and paediatric patients with this condition.”

Of the 112 patients in the Phase IIb study, nine have discontinued to date. The most frequent adverse event (AE) is headaches, and there have not been any drug-related cardiovascular serious adverse events (SAE) or AEs.