A Src/Abl Kinase Inhibitor, SKI-606, Blocks Breast Cancer Invasion, Growth, and Metastasis in Vitro and in Vivo

The central role of Src in the development of several malignancies, including breast cancer, and the accumulating evidence of its interaction with receptor tyrosine kinases, integrins, and steroid receptors have identified it as an attractive therapeutic target. In the current study, we have evaluated the effect of a Src/Abl kinase inhibitor, SKI-606, on breast cancer growth, migration, invasion, and metastasis. Treatment of human breast cancer cells MDA-MB-231 with SKI-606 caused a marked inhibition of cell proliferation, invasion, and migration by inhibiting mitogen-activated protein kinase and Akt phosphorylation. For in vivo studies, MDA-MB-231 cells transfected with the plasmid encoding green fluorescent protein (GFP; MDA-MB-231-GFP) were inoculated into the mammary fat pads of female BALB/c nu/nu mice. Once tumor volume reached 30 to 50 mm(3), animals were randomized and treated with vehicle alone or 150 mg/kg SKI-606 by daily oral gavage. Experimental animals receiving SKI-606 developed tumors of significantly smaller volume (45-54%) compared with control animals receiving vehicle alone. Analysis of lungs, liver, and spleen of these animals showed a significant decrease in GFP-positive tumor metastasis in animals receiving SKI-606 at a dose that was well tolerated. Western blot analysis and immunohistochemical analysis of primary tumors showed that these effects were due to the ability of SKI-606 to block tumor cell proliferation, angiogenesis, growth factor expression, and inhibition of Src-mediated signaling pathways in vivo. Together, the results from these studies provide compelling evidence for the role of Src inhibitors as therapeutic agents for blocking breast cancer growth and metastasis.