KX2-391 is an orally bioavailable small molecule Src kinase inhibitor with potential antineoplastic activity. Unlike other Src kinase inhibitors which bind to the ATP-binding site, Src kinase inhibitor KX2-391 specifically binds to the peptide substrate binding site of Src kinase; inhibition of kinase activity may result in the inhibition of primary tumor growth and the suppression of metastasis. Src tyrosine kinases are upregulated in many tumor cells and play important roles in tumor cell proliferation and metastasis.