Preliminary evaluation of ⁶⁸Ga-NOTA-VEGF₁₂₁ for the imaging of VEGF receptor expression

Objectives VEGF receptor (VEGFR) is known to be associated with advanced tumor growth and the induction of tumor angiogenesis and is also shown to be over-expressed in various human tumors. Therefore, expression levels of the receptor could be a valuable indicator of tumor diagnosis and response to anticancer treatment. In the present study, we prepared and evaluated ⁶⁸Ga-NOTA-VEGF₁₂₁ for the in vivo imaging of VEGFR expression.

Methods NOTA-VEGF₁₂₁ was prepared by conjugation of recombinant human VEGF₁₂₁ (PeproTech) and p-SCN-Bn-NOTA (Macrocyclics) and then purified using a PD-10 column. The NOTA-VEGF₁₂₁ was radiolabeled with ⁶⁸Ga at room temperature for 30 min, and the product was purified using a PD-10 column. In vitro cell binding affinity was assessed by incubating ⁶⁸Ga-NOTA-VEGF₁₂₁ with U87MG cells at 37 ^oC for 1, 2, or 4 h (n = 3). For the blocking study, the cells were incubated with ⁶⁸Ga-NOTA-VEGF₁₂₁ in the presence of human VEGFR-2 antibody (5 μg/mL) for 2 h. For microPET imaging, ⁶⁸Ga-NOTA-VEGF₁₂₁ was injected into mice bearing U87MG cells. Static microPET images were acquired for 20 min at 1 h, 2 h, and 4 h post-injection, and the images were reconstructed using 3D-OSEM. ROIs were drawn over the tumors and the average signal level in the ROIs was measured.

Results The overall radiochemical yield of ⁶⁸Ga-NOTA-VEGF₁₂₁ was 40-50% after purification and the radiochemical purity was higher than 98%. The average number of NOTA conjugated to VEGF₁₂₁ was 0.9-1. In the cell binding study, ⁶⁸Ga-NOTA-VEGF₁₂₁ was found to be taken up by the U87MG cells in a time-dependent manner (195% at 2 h and 230% at 4 h; relative to a value of 100% at 1 h). Tumor uptake of ⁶⁸Ga-NOTA-VEGF121 was slightly blocked in the presence of VEGFR-2 antibody. In microPET images, tumors were clearly visualized and their ROI analyses revealed 3.7% ID/g at 1 h and 4.6% ID/g at 2 h post-injection.

Conclusions The preliminary result suggests that ⁶⁸Ga-NOTA-VEGF₁₂₁ has potential for the in vivo imaging of VEGFR expression