Inhibition of cathepsin K reduces bone erosion, cartilage degradation and inflammation evoked by collagen-induced arthritis in mice

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Cathepsin K (EC is expressed by osteoclasts and synovial fibroblasts and its proteolytic activity is hypothesized to play a role in the pathology of rheumatoid arthritis. This study explored the effects of the cathepsin K inhibitor N-(1-{[(Cyanomethyl)amino]carbonyl}cyclohexyl)-4-[2-(4-methylpiperazin-1-yl)-1,3-thiazol-4-yl]benzamide (L-006235) in murine collagen-induced arthritis. L-006235 is a potent inhibitor of recombinant human and murine cathepsin K, enzymes (Ki:0.073 nM and IC50: 2.4 nM, respectively) and at the cellular level in human osteoclasts (IC50: 28 nM) with ˜ 1000-fold selectivity against cathepsin S. L-006235 did not result in splenic invariant chain p10 accumulation, a specific marker of cathepsin S inhibition. L-006235 was dosed daily (25 mg/kg, p.o.), either prophylactically (days 0–42) or therapeutically (14 days post onset of disease) to DBA/1J mice subjected to collagen-induced arthritis. Disease severity was scored during the course of the study. Histological evaluation of cartilage and bone degradation together with related biomarkers namely, deoxypyridinoline, cartilage oligomeric matrix protein and C-terminal telopeptide degradation product of type I collagen (CTX-I) were analyzed after the study. After prophylactic or therapeutic administration, L-006235 significantly reduced biomarkers reflecting bone and cartilage degradation. Pathological changes at the histological level were significantly reduced after prophylactic treatment (P < 0.01), but not after therapeutic treatment. Prophylactic treatment with L-006235 delayed disease onset (P < 0.01) and reduced the disease severity score (P < 0.05). Inhibition of cathepsin K activity exerts beneficial effects on collagen-induced arthritis in mice and thus warrants further investigation as a therapeutic intervention in human rheumatoid arthritis.

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