Sunitinib is a potent inhibitor of CSF-1 receptor kinase in an enzyme assay, with an IC50 of 7 nM, and inhibits receptor phosphorylation in a cellular assay with an IC50 of 61 nM. Sunitinib inhibits SCF-induced phosphotyrosine levels on KIT (IC50 = 1 - 10 nM) and reduced SCF-stimulated ERK1/2 phosphorylation with an IC50 value consistent with that for inhibition of KIT phosphotyrosine levels. Sunitinib also inhibited SCF-stimulated proliferation in NCI-H526 cells (IC50 = 2 nM). MW: 532.56. Purity ≥99% by HPLC