Effects of eight-month treatment with ONO-5334, a cathepsin K inhibitor, on bone metabolism, strength and microstructure in ovariectomized cynomolgus monkeys.

This study examined the effect of ONO-5334, a cathepsin K inhibitor, on bone turnover, mineral density (BMD), mechanical strength and microstructure in ovariectomized (OVX) cynomolgus monkeys. Vehicle, ONO-5334 (3, 10 or 30 mg/kg) or alendronate (0.5 mg/kg) was orally administered for eight months to sham- and OVX-operated monkeys. ONO-5334 dose-dependently suppressed OVX-induced increase in bone turnover markers (urinary C-terminal cross-linking telopeptide of type I collagen (CTX) and serum osteocalcin). At the dose of 30 mg/kg, ONO-5334 maintained urinary CTX at nearly zero level and kept serum osteocalcin around the level of the sham animals. Marker levels in the alendronate-treated animals were similar to those in the sham animals throughout the study. ONO-5334 dose-dependently reversed the effect of OVX on vertebral BMD as measured by dual-energy X-ray absorptiometry (DXA) with improvement of bone mechanical strength. Both ONO-5334 and alendronate suppressed OVX-induced changes in vertebral microstructure and turnover state. In the femoral neck, peripheral quantitative computed tomography (pQCT) analysis showed that ONO-5334 increased total and cortical BMD. In particular, ONO-5334 significantly increased cortical BMD with improvement of bone mechanical strength. In microstructural analysis, alendronate suppressed OVX-induced increase in femoral mid-shaft osteonal bone formation rate (BFR) to a level below that recorded in the sham group, whereas ONO-5334 at 30 mg/kg did not suppress periosteal, osteonal and endocortical BFR. This finding supports the significant effect of ONO-5334 on cortical BMD and mechanical strength in the femoral neck. The results of this study suggest that ONO-5334 has good therapeutic potential for the treatment of osteoporosis.

Effects of ONO-5334, a novel orally-active inhibitor of cathepsin K, on bone metabolism.

In the present study, we examined the in vitro and in vivo pharmacological effects of ONO-5334, a novel inhibitor of cathepsin K, on bone metabolism. In vitro experiments indicated that ONO-5334 is a potent inhibitor of cathepsin K with Ki value of 0.1 nM. Although this compound inhibited other cysteine proteases, such as cathepsin S, L and B, its inhibitory activity for these enzymes was 8 to 320 fold lower than that for cathepsin K. ONO-5334 also inhibited human osteoclasts bone resorption in vitro at a concentration more than 100 fold lower than that of alendronate, a bisphosphonate. While alendronate disrupted actin ring and induced pyknotic nuclei in osteoclasts, ONO-5334 did not have such effects, suggesting that this compound does not affect osteoclasts viability. In in vivo experiments, oral administration of ONO-5334 dose-dependently reduced plasma calcium level increased by parathyroid hormone related peptide in thyroparathyroidectomized rats. Furthermore, in vivo experiment using normal monkeys demonstrated that ONO-5334 decreases serum and urine C-telopeptide of type I collagen level, a bone resorption marker, soon after oral dosing. These levels were consistently decreased below pre-dose levels by repeated oral dosing with ONO-5334 for 7 days. ONO-5334 on the other hand did not affect bone formation markers, serum osteocalcin and bone specific alkaline phosphatase. These findings indicate that ONO-5334 is a specific inhibitor for cathepsin K and thus may be a novel therapeutic agent for metabolic bone diseases.