Selective and effective killing of angiogenic vascular endothelial cells and cancer cells by targeting tissue factor using a factor VII-targeted photodynamic therapy for breast cancer

The cell surface receptor tissue factor (TF) is regarded as a common but specific target on angiogenic tumor vascular endothelial cells (VECs) and tumor cells in many types of cancer including breast cancer. The purpose of this study is to develop a selective and effective TF-targeting photodynamic therapy (PDT) by using its natural ligand factor VII (fVII)-conjugated Sn(IV) chlorin e6 (SnCe6) for the treatment of breast cancer. A cross linker EDC was used to covalently conjugate fVII protein to SnCe6, and the binding activity and phototoxicity was confirmed by ELISA and in vitro PDT. The efficacy of fVII-tPDT was assessed in vitro by crystal violet staining assay and in vivo by measuring tumor size in mice carrying murine or human breast cancer xenografts. We show that active site-mutated (K341A) fVII protein can be internalized into breast cancer cells and vascular endothelial growth factor (VEGF)-stimulated human umbilical vein endothelial cells (HUVECs) as angiogenic VECs. fVII-tPDT not only enhances 12-fold the in vitro efficacy but also selectively and effectively kills angiogenic HUVECs and breast cancer cells via specifically binding of fVII to TF and inducing apoptosis and necrosis as the underlying mechanism. Furthermore, fVII-tPDT can significantly inhibit the tumor growth of murine and human breast cancer without obvious toxicities in mice. We conclude that fVII-tPDT using fVII–SnCe6 conjugate can selectively and effectively kill angiogenic VECs and breast cancer cells in vitro and significantly inhibit the tumor growth of murine and human breast cancer in mice.