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. [Cancer Res 2007;67(4):1580-8] IntroductionSrc belongs to a non-receptor tyrosine kinase family that comprises nine members in vertebrates (1). It is overexpressed in several human cancers, including carcinomas of the breast, lung, colon, esophagus, skin, parotid, cervix, as well as gastric tissues (2-4). For breast cancer, increased Src activity is believed to play an important role in its development and progression. Furthermore, elevated expression of Src has been associated with poor prognosis (2). Src plays a role in several signaling pathways that are involved in cell proliferation and survival (5). Additionally, the ability of Src to promote tumor cell invasion can lead to the development of tumor metastasis (6). Collectively, Src plays a major role in regulating important mechanisms of specific receptor pathways where their activation can influence the biological activities of the tumor cell (1).In the vascular endothelial growth factor (VEGF) signaling pathway, phosphorylation of VE-cadherin on Tyr 685 by Src plays a pivotal role in regulating VE-cadherin adhesive activity (7). In addition, Src has been shown to regulate phosphatidylinositol 3-kinase and Akt pathways (8). Several growth factors and proteases, including parathyroid hormone-related protein (PTHrP) and urokinase-type plasminogen...

In the current study, we have examined the efficacy of a Src/Abl kinase inhibitor SKI-606 (Bosutinib) for its effect on prostate cancer growth and skeletal metastasis. Treatment of highly invasive human prostate cancer cells PC-3 and DU-145 with different doses of SKI-606 decreased Src activation, cell proliferation, migration, and invasion as determined by Matrigel Boyden chamber invasion assay. For in vivo studies, PC-3 cells were inoculated through s.c. or i.t. route into male BALB/c nu/nu or Fox Chase severe combined immunodeficient mice, respectively. Experimental animals treated with SKI-606 developed tumors of a significantly smaller volume and a significant decrease (50%) in experimental skeletal lesion area. A marked increase (32%) in bone volume to tumor volume ratio was also seen by micro-computed tomography analysis of tibias from control and experimental groups of animals. Western blot analysis showed the ability of SKI-606 to significantly decrease the phosphorylation of signaling molecules (AKT, mitogen-activated protein kinase, focal adhesion kinase) and the expression of tumor progression-associated genes uPAR, MMP-2, MMP-9, N-cadherin, fibronectin, BMP-2 (bone morphogenetic protein 2), BMP-6 (bone morphogenetic protein 6), IL-8 (interleukin 8), and TGF-β (transforming growth factor β) in prostate cancer cells. SKI-606 is currently in clinical trials for breast cancer and chronic myelogenous leukemia. Results from these studies provide convincing evidence for evaluating its efficacy in prostate cancer patients. Mol Cancer Ther; 9(5); 1147-57.