Ultragenyx and Mereo BioPharma announce collaboration and license agreement for setrusumab in osteogenesis imperfecta.

Ultragenyx Pharmaceutical Inc. and Mereo BioPharma Group plc announced a license and collaboration agreement for setrusumab, a monoclonal antibody in clinical development for osteogenesis imperfecta (OI). Setrusumab is an investigational anti-sclerostin fully human monoclonal antibody that has shown the ability to improve bone production and density leading to greater bone strength in animal models of OI. Data from a Phase IIb study of setrusumab conducted by Mereo demonstrated a dose-dependent increase in bone formation, density, and strength in adults with OI. Osteogenesis imperfecta (OI) is a group of genetic disorders including types I, III and IV, of which approximately 85-90% are caused by mutations in the COL1A1 or COL1A2 genes leading to either a reduced amount of normal collagen or collagen with abnormal structure and changes in bone metabolism. Since collagen molecules represent the foundation upon which bone is formed, these abnormalities lead to increased bone resorption, reduced bone mass, and bone fragility and weakness. Although the abnormal or deficient collagen weakens bone, these collagen abnormalities also set off a maladaptive cascade of bone remodeling signals that enhance bone resorption, or the breaking down of bone, with inadequate production of new bone, which compounds the bone fragility. These genetic defects and their consequences lead to systemic clinical manifestations such as decreased bone mass, bone brittleness leading to a high rate of fractures, including at atypical sites, or bone deformities, including abnormal spine curvature, as well as pain, decreased mobility, and short stature. OI affects approximately 60,000 patients in the developed world and has no approved treatments. Setrusumab is a fully human monoclonal antibody that inhibits sclerostin, a protein that acts on a key bone-signaling pathway and inhibits the activity of bone-forming cells. By blocking inhibitory effects of sclerostin, the anti-sclerostin antibody causes new bone formation, increased production of collagen, and increased bone mineral density and strength. Sclerostin inhibition also reduces excessive bone resorption, further enhancing the impact on bone density. In various mouse models of OI, the use of anti-sclerostin antibodies was shown to stimulate bone formation, improve bone mass and density, reduce bone fragility, increase long bone stiffness and strength, and reduce the number of fractures. Overall, improvements in bone mass and strength were enhanced when an anti-sclerostin antibody was used in combination with bisphosphonates, the current standard of care in OI. Mereo has completed the Phase IIb ASTEROID study of setrusumab across three dose groups monthly for 12 months in 90 adults with OI types I, III, and IV. Results from the study indicated improvements in bone mineral density across multiple measures and at multiple anatomical sites on a dose-dependent basis after 12 months. Improvements were also observed in serum P1NP (procollagen type I N propeptide), a biomarker of bone formation and direct measure of collagen production. The bone mineral density and P1NP results were consistent across OI types studied. In addition, there was a dose-dependent improvement in trabecular bone architecture and bone strength by measuring wrist bone failure load and stiffness. In the per protocol population at the high dose, there was a trend toward improvement of ankle failure load and a statistically significant improvement in ankle bone stiffness. While the study was not powered to show a difference in fracture rates, there was a trend toward a reduction in fractures in the highest dose relative to the lower doses. In the study, setrusumab was generally well tolerated with no cardiac-related safety concerns observed. The companies will expand and initially prioritize the development of setrusumab for pediatric patients with OI. Development plans are being finalized which may include changes to current study designs, and will require discussions with regulatory agencies, for a pediatric Phase II/III study that first focuses on determining the optimal dose based on increases in collagen production using serum P1NP levels and an acceptable safety profile. Following determination of the dose, the study is intended to adapt into a pivotal Phase III stage, evaluating fracture reduction over an estimated 15 to 24 months as the primary endpoint pending regulatory review. The pediatric Phase II/III study is expected to start in 2021. A separate pivotal study is also being planned for adults with OI. Under the terms of the collaboration, Ultragenyx will lead future global development of setrusumab in both pediatric and adult patients. Mereo granted Ultragenyx an exclusive license to develop and commercialize setrusumab in the US and rest of the world, excluding Europe where Mereo retains commercial rights. Each party will be responsible for post-marketing commitments in their respective territories. Ultragenyx will make an upfront payment of $50 million to Mereo and will fund global development of the program until approval, and has agreed to pay a total of up to $254 million upon achievement of certain clinical, regulatory, and commercial milestones. Ultragenyx will pay tiered double digit percentage royalties to Mereo on net sales outside of Europe, and Mereo will pay a fixed double digit percentage royalty to Ultragenyx on net sales in Europe. Under the terms of its 2015 agreement with Novartis, Mereo will pay Novartis a percentage of proceeds, subject to certain deductions, with Mereo receiving a substantial majority of the payments from Ultragenyx.