Creation of different bioluminescence resonance energy transfer based biosensors with high affinity to VEGF

Abstract

In age-related macular degeneration (AMD) or diabetic retinopathy (DR), hypoxia and inflammatory processes lead to an upregulation of the vascular endothelial growth factor (VEGF) expression and thereby to pathological neovascularisation with incorrectly formed vessels prone to damage, thus increasing the vascular permeability and the risk of bleeding and oedema in the retina. State of the art treatment is the repeated intraocular injection of anti-VEGF molecules. For developing improved individualized treatment approaches, a minimally invasive, repeatable method for in vivo quantification of VEGF in the eye is necessary. Therefore, we designed single molecule eBRET2 VEGF biosensors by directly fusing a Renilla luciferase mutant (Rluc8) N-terminal and a green fluorescent protein (GFP2) C-terminal to a VEGF binding domain. In total, 10 different VEGF biosensors (Re01-Re10) were generated based on either single domains or full length of VEGF receptor 1 or 2 extracellular regions as VEGF binding domains. Full length expression of the biosensors in HEK293-T cells was verified via Western Blot employing an anti-Rluc8-IgG. Expression of alternative splice variants was eliminated through the deletion of the donor splice site by introduction of a silent point mutation. In all ten biosensors the energy transfer from the Rluc8 to the GFP2 occurs and generates a measurable eBRET2 ratio. Four biosensors show a relevant change of the BRET ratio (ΔBR) after VEGF binding. Furthermore, each biosensor shows a unique detection range for VEGF quantification and especially Re06 and Re07 have a high sensitivity in the range of in vivo VEGF concentrations in the eye, previously measured by invasive methods. In conclusion, we generated several eBRET2 biosensors that are suitable for VEGF quantification in vitro and could identify two eBRET2 biosensors, which may be suitable for non-invasive in vivo VEGF quantification with an implantable device.