6820 Assessing The Efficacy And Safety Of Setrusumab For Osteogenesis Imperfecta: Updated Phase 2 Data From The Phase 2/3 Orbit Study
Authors: Gottesman G S , Carpenter T O , Wallace M , Smith P , Imel E A , Wang H , Byers H M , Krolczyk S , Lewiecki E M 
Published: October 2024

Abstract
Disclosure: G.S. Gottesman: Advisory Board Member; Self; Ultragenyx, Kyowa Kirin, Inc. Consulting Fee; Self; Ultragenyx. Research Investigator; Self; Alexion Pharmaceuticals, Inc., Ultragenyx. T.O. Carpenter: Advisory Board Member; Self; Ultragenyx. Consulting Fee; Self; Ultragenyx. Research Investigator; Self; Ultragenyx. M. Wallace: Advisory Board Member; Self; Ultragenyx. Consulting Fee; Self; Novosteo. P. Smith: Grant Recipient; Self; Ultragenyx. Research Investigator; Self; Ultragenyx. E.A. Imel: Consulting Fee; Self; Ultragenyx. Grant Recipient; Self; Ultragenyx. Research Investigator; Self; Ultragenyx. H. Wang: Employee; Self; Ultragenyx. Stock Owner; Self; Ultragenyx. H.M. Byers: Employee; Self; Ultragenyx. Stock Owner; Self; Ultragenyx. S. Krolczyk: Employee; Self; Ultragenyx. Stock Owner; Self; Ultragenyx. E.M. Lewiecki: Consulting Fee; Self; Amgen Inc, Radius Health, Inc. Grant Recipient; Self; Amgen Inc, Radius Health, Inc, Ultragenyx. Research Investigator; Self; Amgen Inc, Radius Health, Inc, Ultragenyx. Speaker; Self; Amgen Inc, Kyowa Kirin, Inc.
Osteogenesis imperfecta (OI) is a rare genetic disorder characterized by bone fragility and low bone mass with no universally accepted treatment. Setrusumab is a fully human anti-sclerostin monoclonal antibody that improved bone mineral density (BMD), bone strength, and bone turnover markers in adults with OI (ASTEROID; NCT03118570). In the ongoing Phase 2/3 Orbit study (NCT05125809), Phase 2 evaluated the efficacy and safety of setrusumab in pediatric and young-adult cohorts with OI based on PK/PD, safety, and BMD data, to determine the dosing strategy for the Phase 3 portion. Subjects with OI Types I, III, or IV, ages 5 to &lt;26 years, were randomized 1:1 to receive 20 or 40 mg/kg setrusumab intravenously monthly. Six-month data as of August 2023 are presented. Twenty-four subjects (50% female, 75% &lt;18 years of age) with OI Type I (n=17/24, 71%) or III/IV (n=7/24, 29%) were enrolled and randomized to receive 20 mg/kg (n=14/24) or 40 mg/kg (n=10/24) of setrusumab. The mean (SD) baseline-corrected area under the effect curve (AUEC) for serum P1NP in the 20 mg/kg setrusumab group was 4153 (4407) µg/(L*day) over month one of treatment, and 5256 (5521) µg/(L*day) in the 40 mg/kg group. Mean (SE) change from baseline in lumbar spine BMD in the 20 mg/kg group was 9.1% (1.8%) and 12.8% (2.5%) at M3 and M6, respectively (all p&lt;0.05 vs baseline) and 9.3% (2.4%) and 16.1% (3.9%) in the 40 mg/kg group (M6 p&lt;0.05 vs baseline). Mean (SE) baseline BMD Z-score in the 20 mg/kg group of 2.1 (0.8) improved by 0.6 (0.8) at M3 and 0.9 (0.8) at M6, and improved from 1.1 (0.4) at baseline by 0.5 (0.4) and 0.9 (0.4) at M3 and M6, respectively, in the 40 mg/kg group (all p&lt;0.05 vs baseline). The median annualized fracture rate (excluding fingers, toes, face, and skull) was reduced significantly from 0.7 to 0 (p=0.042) after setrusumab initiation (calculated reduction of 67%). No new radiographically confirmed fractures excluding fingers, toes, face, and skull were reported in 20/24 (83%) subjects after starting setrusumab, while only 4/24 (17%) reported fractures (precipitating events: one subject: slipped on ice, stubbed toe, one subject each: fell off of tricycle, bending over in bed, tripped and fell). Setrusumab treatment resulted in no unexpected adverse events. Treatment-related adverse events included infusion-related reaction (7/24, 29%), headache (3/24, 13%) infusion site pain, bone pain, and upper respiratory tract infection (each 1/24, 4%). In Orbit Phase 2, we observed significant improvements from baseline in lumbar spine BMD at M3 and M6 at both 20 and 40 mg/kg doses, with no marked differences between dose groups. Fracture rates significantly decreased with setrusumab initiation, with 83% of subjects reporting no new fractures.
Presentation: 6/1/2024