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

Abstract

Cathepsin K (EC 3.4.22.38) 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 (K_i: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.

Introduction

Rheumatoid arthritis is a chronic inflammatory disease that results in synovial hyperplasia and subsequent destruction of bone and cartilage in joints. Many cell types actively contribute to the disease process, including T and B-lymphocytes (Bugatti et al., 2007, Cope et al., 2007), synovial fibroblasts (Pap et al., 2000) and osteoclasts (Gravallese, 2002, Schett, 2008). Proteases derived from such cells may play a role in disease pathology (Jones et al., 2008). Prevention of structural damage in rheumatoid arthritis is of importance since destructive arthritis with bone erosion is a common outcome for most patients. Indeed, there is specific interest in developing new therapeutic agents that specifically target bone and cartilage degradation (Moreland, 2005, Schwarz et al., 2006).

Cathepsin K (EC 3.4.22.38) a cysteine protease expressed by osteoclasts and synovial fibroblasts degrades key components of bone and cartilage such as type I and type II collagen (Salminen-Mankonen et al., 2007), osteonectin (Bossard et al., 1996) and aggrecan (Hou et al., 2003). Cathepsin K expression is elevated in the synovium of rheumatoid arthritis patients (Hou et al., 2002) and a positive correlation is seen between the extent of radiological destruction and the serum levels of cathepsin K (Skoumal et al., 2005). Expression of cathepsin K is also localized within a range of cells at the site of cartilage erosion in rheumatoid arthritis (Hou et al., 2002). Inhibition of cathepsin K protease activity may be beneficial for the prevention of bone erosion and cartilage degradation in rheumatoid arthritis (Salminen-Mankonen et al., 2007, Weidauer et al., 2007, Yasuda et al., 2005b). Cathepsin S (EC 3.4.22.27), another cysteine protease, is also upregulated within cells in the synovium of rheumatoid arthritis patients (Hou et al., 2002). It plays a pivotal role in major histocompatibility complex class II-restricted antigen presentation (Riese et al., 1998, Riese et al., 1996, Villadangos et al., 1999) and is also a potential therapeutic target in rheumatoid arthritis (Vasiljeva et al., 2007, Yasuda et al., 2005a).

Murine collagen-induced arthritis is a validated model for exploring the potential of new disease-modifying drugs for the treatment of human rheumatoid arthritis. It shares many features with rheumatoid arthritis including mononuclear cell infiltration, synovial cell hyperplasia and subsequent destruction of bone and cartilage (Trentham et al., 1977). A number of studies have highlighted the suitability of this model for examining the possible role of compounds that affect osteoclast activity and cathepsin K (Ibrahim et al., 2002, Lubberts et al., 2002). Other modulators of osteoclast function, namely bisphosphonates and receptor activator of nuclear factor-κB ligand modulators also prevent bone loss in rodent collagen-induced arthritis models (Romas et al., 2002, Saidenberg-Kermanac'h et al., 2004).

L-006235 is a potent and selective inhibitor of human cathepsin K, that also inhibits murine cathepsin K (Desmarais et al., 2008, Falgueyret et al., 2005). This study therefore sought to directly examine the efficacy of L-006235, in a murine collagen-induced arthritis experimental model of human rheumatoid arthritis, primarily examining the effects on bone and cartilage degradation, but also exploring the effects on the inflammatory disease process.