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

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.

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.

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.

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.