Effects of long term treatment with high doses of odanacatib on bone mass, bone strength, and remodeling/modeling in newly ovariectomized monkeys

The objectives here were to evaluate the effects of odanacatib (ODN) at doses exceeding the clinical exposure on biomechanical properties of lumbar vertebrae (LV), hip and central femur (CF), and compare ODN to alendronate (ALN) on bone remodeling/modeling in ovariectomized (OVX) monkeys. Ten days post-surgery, animals were treated with vehicle (VEH), ODN-L (2 mg/kg/day, p.o.), ODN-H (8/4 mg/kg/day), or ALN (30 μg/kg/week, s.c.) for 20 months. An intact group was also included. ODN-L provided systemic exposures of 1.8-fold of clinical exposure. ODN-H started at 20-fold for 5.5 months, and then reduced to 7.8-fold of clinical exposure, compared to ALN at approximated clinical exposure. From cross sectional analyses, LV density and peak load in ODN at both doses or ALN were not different from VEH or Intact. However, cortical thickness of femoral neck (FN) and CF in ODN were higher (21-34%, p < 0.05) than VEH, due to smaller endocortical (Ec) perimeter of FN (10-11%; p < 0.05) and CF (9-12%; ODN-L, p < 0.05), and larger CF periosteal (Ps) perimeter (2-12%; ODN-H, p < 0.001) versus VEH. ODN groups also showed slightly higher cortical porosity and Ps non-lamellar bone in CF. ODN-H treatment resulted in higher CF peak load (p < 0.05) versus VEH. For all bone sites analyzed, a positive, linear relationship (r2 = 0.46-0.69, p < 0.0001) of peak load to density or structural parameters was demonstrated. No treatment-related differences in the derived intrinsic strength properties were evidenced as compared between groups. ALN reduced all remodeling surfaces without affecting Ps modeling. Trabecular and intracortical remodeling were reduced in ODN groups, similar to ALN. Ec mineralizing surface in ODN-H trended to be lower than VEH by month 20, but Ec bone formation indices in ODN groups generally were not different from VEH. Ps modeling in ODN groups was significantly higher than other treatment groups. This study overall demonstrated the bone safety profile of ODN and its unique mechanism on cortical bone supporting the clinical application for osteoporosis treatment.