PP121 suppresses RANKL-Induced osteoclast formation in vitro and LPS-Induced bone resorption in vivo.

Bone resorption, caused by osteoclasts (OCs), is important to bone homeostasis. The abnormalities of bone resorption may induce a series of diseases, including osteoarthritis, osteoporosis and aseptic peri-implant loosening. The latest research developed,a novel tyrosine and phosphoinositide kinase dual inhibitor, named PP121, inhibited Src in anaplastic thyroid carcinoma cell. However, the therapeutic function of PP121 on abnormal bone resorption is still uncertain. In the present study, we showed that PP121 could potently suppress osteoclast differentiation, osteoclast-specific gene expression and bone resorption via suppressing Src/MAPK (ERK and p38)/Akt-mediated NFATc1 induction in vitro. \It was found that PP121 could suppress the formation of osteoclasts from bone marrow macrophages (BMMs) without causing cytotoxicity, inhibit bone resorption and downregulate the mRNA level of osteoclast-specific markers, including calcitonin receptor (CTR), tartrate resistant acid phosphatase (TRAP), cathepsin K (CTSK), matrix metalloproteinase 3 (MMP3), Cellular oncogene fos (C-Fos) and nuclear factor of activated T-cells cytoplasmic 1 (NFATc1). Consistent with in vitro observation, we found that PP121 greatly ameliorated LPS-induced bone resorption. Our results provide promising evidence of the therapeutic potential of PP121 for osteolytic diseases related to excessive osteoclast-mediated bone resorption.