Ki20227, a novel quinoline-urea derivative, is a c-Fms tyrosine kinase inhibitor. The IC50s of Ki20227 to inhibit c-Fms, vascular endothelial growth factor receptor-2 (KDR), stem cell factor receptor (c-Kit), and platelet-derived growth factor receptor B are found to be 2, 12, 451, and 217 nmol/L, respectively. Ki20227 is also found to inhibit the M-CSFdependent growth of M-NFS-60 cells but not the M-CSFindependent growth of A375 human melanoma cells in vitro. Furthermore, in an osteoclast-like cell formation assay using mouse bone marrow cells, Ki20227 inhibits the development of tartrate-resistant acid phosphatase-positive osteoclast-like cells in a dose-dependent manner.^[1]

In in vivo studies, oral administration of Ki20227 suppresses osteoclast-like cell accumulation and bone resorption induced by metastatic tumor cells in nude rats following intracardiac injection of A375 cells. Moreover, Ki20227 decreases the number of tartrate-resistant acid phosphatase–positive osteoclast-like cells on bone surfaces in ovariectomized (ovx) rats. These findings suggest that Ki20227 inhibits osteolytic bone destruction through the suppression of M-CSF-induced osteoclast accumulation in vivo.^[1]