Ki20227 is an orally active, potent and selective M-CSF receptor c-Fms (CSF-1R) tyrosine kinase inhibitor (IC50 = 2 nM vs. 12 nM/KDR, 451 nM/c-Kit, 217 nM/PDGFβ; >1 µM/BTK, EGFR, FGFR2, FLT3, Fyn, Met, c-Src, PKA, PKCα) that inhibits M-CSF-dependent (50 ng/mL) c-Fms phosphorylation (by >90% at 10 nM; RAW264.7) and cell growth (IC50 = 14 nM; M-NFS-60). Ki20227 prevents osteolysis in a rat model of bone metastasis (50 mg/kg/day p.o.) by inhibiting A375 tumor-induced osteoclast formation and decreases the number of osteoclast-like cells on bone surfaces in ovariectomized rats (20 mg/kg/day p.o.) in vivo.