Cortical bone mineral density is increased by the cathepsin K inhibitor ONO-5334, which leads to a robust increase in bone strength: results from a 16-month study in ovariectomised cynomolgus monkeys.

This study evaluated the long-term effects of the cathepsin K inhibitor ONO-5334 on bone mass and strength in ovariectomised (OVX) cynomolgus monkeys. Animals were assigned to one of the following six groups: Sham (non-OVX), OVX control treated with vehicle, ONO-5334 1.2, 6 or 30 mg/kg/day, p.o., or alendronate (ALN) 0.05 mg/kg/2 weeks, i.v. for 16 months. Peripheral quantitative computed tomography (pQCT) analysis revealed that ONO-5334 increased not only trabecular bone mineral density (BMD) but also cortical BMD in the distal radius and the lumbar vertebra. ONO-5334 and ALN suppressed the deterioration of trabecular architecture by micro-CT analysis in the distal radius. Assessments of bone strength showed that ONO-5334 increased maximum load at the distal and midshaft radius. The linear regression lines between bone mass and strength in the lumbar vertebra were tended to be shifted towards increasing bone strength in the ONO-5334 6 and 30 mg/kg groups compared with the ALN groups. This indicated that bone strength was higher in the ONO-5334 groups than the ALN group, even though bone mineral content (BMC) and BMD were comparable. Subpopulation analysis revealed that, at similar integral BMC or BMD level, cortical bone mass for ONO-5334 was higher than for ALN; the opposite effects were observed for trabecular bone. In conclusion, ONO-5334 preferentially increased cortical bone, which may provide a greater contribution to bone strength. Since these results support a different mode of action for ONO-5334 compared with that of ALN, ONO-5334 may offer new therapeutic options to patients with osteoporosis.