Angiogenesis is essential to tumor progression, and the precise imaging of the angiogenic marker vascular endothelial growth factor receptor 2 (VEGFR-2) may provide an accurate evaluation for angiogenesis during a therapeutic response. With the use of molecular magnetic resonance imaging (mMRI), an in vitro cell assay indicated significantly decreased T1 relaxation values when tumor endothelial cells (TEC), which positively expressed VEGFR-2 (Western blot), were in the presence of the VEGFR-2 probe compared to TEC alone (P < 0.001). For in vivo mMRI evaluations, we assessed VEGFR-2 levels in untreated and OKN-007-treated GL261 mouse gliomas. Regarding treatment response, OKN-007 was also able to significantly decrease tumor volumes (P < 0.01) and increase survival (P < 0.001) in treated animals. Regarding in vivo detection of VEGFR-2, OKN-007 was found to significantly decrease the amount of VEGFR-2 probe (P < 0.05) compared to an untreated control group. Fluorescence imaging for the VEGFR-2 probe indicated that there was colocalization with the endothelial marker CD31 in an untreated tumor bearing mouse and decreased levels for an OKN-007-treated animal. Immuno-fluorescence imaging for VEGFR-2 indicated that OKN-007 treatment significantly decreased VEGFR-2 levels (P < 0.0001) when compared to untreated tumors. Immuno-electron microscopy was used with gold-labeled anti-biotin to detect the anti-VEGFR-2 probe within the plasma membrane of GL261 tumor endothelial cells. This is the first attempt at detecting in vivo levels of VEGFR-2 in a mouse GL261 glioma model and assessing the anti-angiogenic capability of an anticancer nitrone. The results indicate that OKN-007 treatment substantially decreased VEGFR-2 levels in a GL261 glioma model, and can be considered as an anti-angiogenic therapy in human gliomas.
Keywords: GL261; Molecular magnetic resonance imaging; VEGFR-2; angiogenesis; glioma; in vivo.