Robert R. Recker, Charles T. Benson, Toshio Matsumoto, Michael A. Bolognese, Deborah A. Robins, Jahangir Alam, Alan Y Chiang, Leijun Hu, John H Krege, Hideaki Sowa, Bruce H. Mitlak, Stephen L. Myers

Sclerostin, a SOST protein secreted by osteocytes, negatively regulates formation of mineralized bone matrix and bone mass. We report the results of a randomized, double-blind, placebo-controlled multicenter phase 2 clinical trial of blosozumab, a humanized monoclonal antibody targeted against sclerostin, in postmenopausal women with low bone mineral density (BMD). Postmenopausal women with a lumbar spine T-score -2.0 to -3.5, inclusive, were randomized to subcutaneous blosozumab 180 mg every 4 weeks (Q4W), 180 mg Q2W, 270 mg Q2W, or matching placebo for one year, with calcium and vitamin D. Serial measurements of spine and hip BMD and biochemical markers of bone turnover were performed. Overall, 120 women enrolled in the study (mean age 65.8y, mean lumbar spine T-score -2.8). Blosozumab treatment resulted in statistically significant dose-related increases in spine, femoral neck, and total hip BMD as compared with placebo. In the highest dose group, BMD increases from baseline reached 17.7% at the spine, and 6.2% at the total hip. Biochemical markers of bone formation increased rapidly during blosozumab treatment, and trended toward pretreatment levels by study end. However, bone specific alkaline phosphatase remained higher than placebo at study end in the highest dose group. CTx, a biochemical marker of bone resorption, decreased early during blosozumab treatment to a concentration less than placebo by 2 weeks, and remained reduced throughout blosozumab treatment. Mild injection site reactions were reported more frequently with blosozumab than placebo. In conclusion, treatment of postmenopausal women with an antibody targeted against sclerostin resulted in substantial increases in spine and hip BMD. These results support further study of blosozumab as a potential anabolic therapy for osteoporosis. NCT01144377 © 2014 American Society for Bone and Mineral Research.