FDA Grants Mereo's Setrusumab Rare Pediatric Disease Designation

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The U.S. Food and Drug Administration (FDA) granted Mereo BioPharma’s setrusumab Rare Pediatric Disease designation for the treatment of osteogenesis imperfecta. Under that designation, Mereo may qualify for a voucher that can be used for a priority review of a subsequent marketing application for a different product.

Osteogenesis imperfecta (OI) is a rare genetic disease marked by fragile bones and decreased bone mass. This causes bones to break easily, have loose joints and weakened teeth. Patients with the most severe cases may have hundreds of fractures over their lifetime. They also suffer muscle weakness, early hearing loss, fatigue, curved bones, scoliosis, respiratory problems and short stature. About 90% are caused by a dominant mutation in a gene coding for type 1 collagen, which is critical for healthy bone.

There are no FDA or European Medicines Agency (EMA) approved treatments. Treatments consist of supportive care and minimizing fractures and maximizing mobility.

Setrusumab is a fully humanized monoclonal antibody that inhibitors sclerostin. Sclerostin is a protein that inhibits the activity of the cells that form bone. The drug has received orphan drug designation for OI in both the U.S. and Europe. It was also accepted into the EMA’s Adaptive Pathways program and the EMA’s Priority Medicines (PRIME) scheme.

“Receiving Rare Pediatric Disease designation from the FDA highlights the significant unmet medical need facing children with OI and underscores the potential of setrusumab to become the first approved treatment option specifically for these patients,” said Denise Scots-Knight, Mereo’s chief executive officer. “Following the completion of our Phase IIb ASTEROID study, we are pleased that both the FDA and EMA have agreed on the principles of a design of a single Phase III pivotal pediatric study in OI. We believe there is a clear path forward for setrusumab in OI and are continuing discussions with potential partners prior to the initiation of a Phase III study consistent with our company strategy.”

On January 14, 2020, the company announced additional endpoint data from its Phase IIb dose-ranging ASTEROID trial of setrusumab for Type I, III or IV OI. The 12-month topline data had been announced in November 2019. The drug showed a dose-dependent, statistically significant bone building effect of setrusumab at multiple anatomical sites in adults with OI, regardless of subtype.

The ASTEROID study was a 12-month, randomized, double-blind, Phase IIb dose-finding study in 112 adults with OI and a confirmed COL1A1/COL1A2 mutation who have fractured over the previous five years. The primary endpoint was the change over baseline in Tr vBMD of the wrist at 12 months, followed by bone strength measured by Fine Element Analysts (hierarchical) assessed using HR-pQCT.

At the time, Alastair MacKinnon, Mereo’s chief medical officer, stated, “Based upon our review of the comprehensive data set from the Phase IIb ASTEROID study, these additional prespecified analyses support our previous conclusions that setrusumab is building bone at the lumbar spine and is increasing bone strength at multiple peripheral sites in adult OI patients. We believe these additional endpoint data, together with the totality of the 12-month topline data and trend in fracture rate reduction in the high dose cohort, are fully supportive of moving forward with our planned pivotal trial in children with OI.”

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