The potential of a novel antiangiogenic VEGFR1-D2 binding peptide in oncology therapeutics

Background Tumor growth depends on pro-angiogenic vascular endothelial growth factors (VEGF-A/-B) via binding to VEGF receptors (VEGFR1 and VEGFR2) that are biomarkers of tumor angiogenesis. Importantly, interfering with this interaction by small molecules impairs tumor growth and angiogenesis. Methods A novel peptide (known as VGB3) was synthesized using a solid-phase peptide synthesis (SPPS) procedure on 2-chlorotrityl chloride (2-CTC) resin. A disulfide bridge was formed in the peptide and it was purified using RP-HPLC. Recombinant His-tagged VEGFR1D2 obtained from inclusion bodies and purified on a Ni2+-NTA agarose resin. The equilibrium constant for the binding of VGB3 to VEGFR1-D2 molecule was determined by microscale thermophoresis (MST). The accumulation of the peptide in 4T1 mammary carcinoma tumors (MCTs) was assessed using 2D optical imaging. Anti-angiogenic activity of VGB3 were investigated using MTT, scratch assay, and two- as well as three-dimensional angiogenesis assays. Downstream signaling pathways were assessed by quantitative estimation of protein expression using western blotting and immunohistochemistry. (IHC). Results We have indicated that VGB3 is able to block VEGFR1-D2 in human umbilical vein endothelial cells (HUVECs) and 4T1 mammary carcinoma tumor (MCT) cells. This resulted in inhibition in proliferation of HUVEC, 4T1 MCT, and U87 glioblastoma cells and MST results reveals that VGB3 is a high-affinity (Kd=1.96± 0.69 µM, n = 3, P < 0.0001) binder to VEGFR1-D2. Moreover, fluorescence imaging in Balb/c mice demonstrated that fluorescein isothiocyanate (FITC)-VGB3 accumulated in tumors. VEGFA-stimulated proliferation, migration, and 2 and 3D tube formation in HUVECs were strongly inhibited by VGB3 (n = 3, P < 0.0001). In a murine 4T1 MCT model, VGB3 strongly inhibited AKT and ERK1/2 phosphorylation and tumor cell downstream signaling pathways associated with proliferation, migration, and angiogenesis, and led to the increased apoptosis index and suppression of systematic spreading of the tumor compared to PBS-treated controls. Conclusions These results indicate that VGB3 may be applicable for antiangiogenic and antitumor therapy.