Targeting focal adhesion kinase inhibits cell migration and non-angiogenic vascularization in malignant breast cancer.

[BACKGROUND] High-grade carcinomas, including breast cancer, are associated with angiogenesis and non-angiogenic vascularization. Non-angiogenic vascularization enhances blood flow, tumor growth, and metastasis. Although inhibition of focal adhesion kinase (FAK) is a promising anticancer strategy, its effect on non-angiogenic vascularization remains unknown. We aimed to determine if defactinib, an oral selective FAK inhibitor, suppresses tumor growth by inhibiting non-angiogenic vascularization via reduced cell migration in malignant breast cancer cell lines.

[METHODS] Non-angiogenic vascularization was evaluated in JIMT-1 and MDA-MB-231 cells. Western blotting, fluorescent immunocytochemistry, cell migration assay, time-lapse microscopy, and tube formation assays were performed to evaluate the effects of defactinib. Cells were transfected with siFAK to evaluate off-target effects. The in vivo effects were assessed in orthotopic mouse tumor models, followed by immunohistochemical staining of excised tumor samples.

[RESULTS] Defactinib induced changes in cell morphology, migration, and the formation of vascular-like structures in JIMT-1 and MDA-MB-231 cells. Phosphorylation of FAK/PTK2 and its downstream effectors was reduced in defactinib-treated cells. SiRNA-mediated FAK knockdown produced similar effects. Treatment with defactinib suppressed tumor growth in orthotopic mouse tumor models, resulting in tumor shrinkage and reduced macroscopic blood-rich areas. Immunohistochemical staining also revealed a significant reduction in the number of vessels characterized by human serpin family E member 2-a potential indicator of non-angiogenic vascularization-in the defactinib-treated group, with no significant increase in apoptosis.

[CONCLUSIONS] FAK inhibition was shown to suppress non-angiogenic vascularization. Defactinib has the potential to serve as a novel treatment for malignant breast cancer which is resistant to conventional therapies.