⁶⁸Ga-NODAGA-VEGF₁₂₁ for in vivo imaging of VEGF receptor expression

Purpose: Vascular endothelial growth factor (VEGF) is a crucial regulator of angiogenesis. In this study, we labeled VEGF₁₂₁ with ⁶⁸Ga using a hydrophilic chelating agent, NODAGA and evaluated the resulting ⁶⁸Ga-NODAGA-VEGF₁₂₁ for in vivo imaging of VEGF receptor (VEGFR) expression. Methods: NODAGA-VEGF₁₂₁ was prepared and its binding affinity for VEGFR2 was measured using ¹²⁵I-VEGF₁₂₁. ⁶⁸Ga-NODAGA-VEGF₁₂₁ was prepared by labeling NODAGA-VEGF₁₂₁ with ⁶⁸GaCl₃ followed by purification using a PD-10 column. Human aortic endothelial cell (HAEC) binding studies of ⁶⁸Ga-NODAGA-VEGF₁₂₁ were performed at 37°C for 4h. MicroPET imaging followed by biodistribution studies were performed in U87MG tumor-bearing mice injected with ⁶⁸Ga-NODAGA-VEGF₁₂₁. Immunofluorescence staining of the tumor tissues was performed to verify VEGFR2 expression. Results: Binding affinity of NODAGA-VEGF₁₂₁ for VEGFR2 was found to be comparable to that of VEGF₁₂₁. ⁶⁸Ga-NODAGA-VEGF₁₂₁ was prepared in 47.8% yield with specific activity of 3.4GBq/mg. ⁶⁸Ga-NODAGA-VEGF₁₂₁ was avidly taken up by HAECs with a time-dependent increase from 9.88 %ID at 1h to 20.86 %ID at 4h. MicroPET imaging of mice demonstrated high liver and spleen uptake with clear visualization of tumor at 1h after injection. ROI analysis of tumors revealed 2.53±0.11 %ID/g at 4h after injection. In the blocking study, tumor uptake was inhibited by 29% at 4h. Subsequent biodistribution studies demonstrated tumor uptake of 2.38±0.15 %ID/g. Immunofluorescence staining of the tumor tissues displayed high level of VEGFR2 expression. Conclusions: These results demonstrate that ⁶⁸Ga-NODAGA-VEGF₁₂₁ led to VEGFR-specific distribution in U87MG tumor-bearing mice. This study also suggests that altered physicochemical properties of VEGF₁₂₁ after radiolabeling may affect biodistribution of the radiolabeled VEGF₁₂₁.