A vascular endothelial growth factor 121 (VEGF121)-based dual PET/optical probe for in vivo imaging of VEGF receptor expression

We have developed a vascular endothelial growth factor 121 (VEGF121)-based, dual positron emission tomography (PET)/optical imaging probe for monitoring VEGF receptor (VEGFR) expression using a streptavidin (SAv)-biotin platform. 64Cu-1,4,7,10-tetraazacyclododecane-N,N′,N″,N′″-tetraacetic acid (DOTA)-conjugated Alexa Fluor 680 (AF)-SAv/biotin-PEG-VEGF121 (64Cu-labeled dual probe) was prepared with a radiochemical yield of 31.40 ± 3.30% and was stable for 24 h in serum. A human aortic endothelial cell binding study showed avid, time-dependent cellular uptake of the 64Cu-labeled dual probe. MicroPET imaging of U87MG tumor-bearing mice injected with 64Cu-labeled dual probe showed rapid, high accumulation of radioactivity in tumors, which reached 3.90 ± 0.17 %ID/g and 4.93 ± 0.80 %ID/g at 1 and 22 h after injection, respectively. Subsequent optical imaging of mice revealed strong fluorescence signals in tumors. Biodistribution studies performed after in vivo imaging demonstrated tumor uptake of 4.19 ± 0.14 %ID/g. Tumor uptake was blocked by 28% in the presence of VEGF121, confirming the VEGFR specificity of the 64Cu-labeled dual probe. Ex vivo microPET images of major tissues showed the signal intensities consistent with optical images of the corresponding tissues. Moreover, it was shown that tumor uptake of the 64Cu-labeled dual probe was not due to non-specific uptake by 64Cu-DOTA-conjugated AF-SAv (tumor uptake; 1.57 ± 0.09 %ID/g). Taken together, these results suggest that the 64Cu-labeled dual probe is a promising candidate for dual PET/optical imaging of VEGFR expression.