Modeling-Based Bone Formation After 2 Months of Romosozumab Treatment: Results From the FRAME Clinical Trial
J Bone Miner Res. 2021 Oct 11. doi: 10.1002/jbmr.4457. Online ahead of print.
The bone-forming agent romosozumab is a monoclonal antibody that inhibits sclerostin, leading to increased bone formation and decreased resorption. The highest levels of bone formation markers in human patients are observed in the first 2 months of treatment. Histomorphometric analysis of bone biopsies from the phase 3 FRAME trial (NCT01575834) showed an early significant increase in bone formation with concomitant decreased resorption. Preclinical studies demonstrated that most new bone formation following romosozumab treatment was modeling-based bone formation (MBBF). Here we analyzed bone biopsies from FRAME to assess the effect of 2 months of romosozumab vs placebo on the surface extent of MBBF and remodeling-based bone formation (RBBF). In FRAME, postmenopausal women aged ≥55 years with osteoporosis were randomized 1:1 to 210 mg romosozumab or placebo SC QM for 12 months, followed by 60 mg denosumab SC Q6M for 12 months. Participants in the bone biopsy substudy received quadruple tetracycline labeling and underwent transiliac biopsies at month 2. A total of 29 biopsies were suitable for histomorphometry. Using fluorescent microscopy, bone formation at cancellous, endocortical, and periosteal envelopes was classified based on the appearance of underlying cement lines as modeling (smooth) or remodeling (scalloped). Data were compared using the Wilcoxon rank-sum test, without multiplicity adjustment. After 2 months, the median percentage of MBBF referent to the total bone surface was significantly increased with romosozumab vs placebo on cancellous (18.0% vs 3.8%; p = 0.005) and endocortical (36.7% vs 3.0%; p = 0.001), but not on periosteal (5.0% vs 2.0%; p = 0.37) surfaces, with no significant difference in the surface extent of RBBF on all three bone surfaces. These data show that stimulation of bone formation in the first 2 months of romosozumab treatment in postmenopausal women with osteoporosis is predominately due to increased MBBF on endocortical and cancellous surfaces. This article is protected by copyright. All rights reserved.