Synthesis and characterization of scVEGF-PEG-[68Ga]NOTA and scVEGF-PEG-[68Ga]DOTA PET tracers


Långström Bengt, Department of Biochemistry and Organic Chemistry Box 967, SE-751 09 Uppsala, Sweden.


Vascular endothelial growth factor (VEGF) signaling via vascular endothelial growth factor receptor 2 (VEGFR-2) on tumor endothelial cells is a critical driver of tumor angiogenesis. Novel anti-angiogenic drugs target VEGF/VEGFR-2 signaling and induce changes in VEGFR-2 prevalence. To monitor VEGFR-2 prevalence in the course of treatment, we are evaluating 68Ga positron emission tomography imaging agents based on macrocyclic chelators, site-specifically conjugated via polyethylene glycol (PEG) linkers to engineered VEGFR-2 ligand, single-chain (sc) VEGF. The 68Ga-labeling was performed at room temperature with NOTA (2,2′,2′′-(1,4,7-triazonane-1,4,7-triyl) triacetic acid) conjugates or at 90 °C by using either conventional or microwave heating with NOTA and DOTA (2,2′,2′′,2′′′-(1,4,7,10-tetraazacyclododecane-1,4,7,10-tetrayl) tetraacetic acid) conjugates. The fastest (~2 min) and the highest incorporation (>90%) of 68Ga into conjugate that resulted in the highest specific radioactivity (~400 MBq/nmol) was obtained with microwave heating of the conjugates. The bioactivity of the NOTA- and DOTA-containing tracers was validated in 3-D tissue culture model of 293/KDR cells engineered to express high levels of VEGFR-2. The NOTA-containing tracer also displayed a rapid accumulation (~ 20 s after intravenous injection) to steady-state level in xenograft tumor models. A combination of high specific radioactivity and maintenance of functional activity suggests that scVEGF-PEG-[68 Ga]NOTA and scVEGF-PEG-[68 Ga]DOTA might be promising tracers for monitoring VEGFR-2 prevalence and should be further explored. Copyright © 2011 John Wiley & Sons, Ltd.