Inhibitory effects of KP-A159, a thiazolopyridine derivative, on osteoclast differentiation, function, and inflammatory bone loss via suppression of RANKL-Induced MAP Kinase signaling pathway

Abnormally elevated formation and activation of osteoclasts are primary causes for a majority of skeletal diseases. In this study, we found that KP-A159, a newly synthesized thiazolopyridine derivative, inhibited osteoclast differentiation and function in vitro, and inflammatory bone loss in vivo. KP-A159 did not cause a cytotoxic response in bone marrow macrophages (BMMs), but significantly inhibited the formation of multinucleated tartrateresistant acid phosphatase (TRAP)-positive osteoclasts induced by macrophage colonystimulating factor (M-CSF) and receptor activator of nuclear factor-κB ligand (RANKL). KPA159 also dramatically inhibited the expression of marker genes related to osteoclast differentiation, including TRAP (Acp5), cathepsin K (Ctsk), dendritic cell-specific transmembrane protein (Dcstamp), matrix metallopeptidase 9 (Mmp9), and nuclear factor of activated Tcells, cytoplasmic 1 (Nfatc1). Moreover, actin ring and resorption pit formation were inhibited by KP-A159. Analysis of the signaling pathway involved showed that KP-A159 inhibited RANKL-induced activation of extracellular signal-regulated kinase (ERK), c-Jun N-terminal kinase (JNK), and mitogen-activated protein kinase kinase1/2 (MEK1/2). In a mouse inflammatory bone loss model, KP-A159 significantly rescued lipopolysaccharide (LPS)-induced bone loss by suppressing osteoclast numbers. Therefore, KP-A159 targets osteoclasts, and may be a potential candidate compound for prevention and/or treatment of inflammatory bone loss.