Non-invasive monitoring of tumor-vessel infarction by retargeted truncated tissue factor tTF–NGR using multi-modal imaging

The fusion protein tTF–NGR consists of the extracellular domain of the thrombogenic human tissue factor (truncated tissue factor, tTF) and the peptide GNGRAHA (NGR), a ligand of the surface protein CD13 (aminopeptidase N), upregulated on endothelial cells of tumor vessels. tTF–NGR preferentially activates blood coagulation within tumor vasculature, resulting in tumor vessel infarction and subsequent tumor growth retardation/regression. The anti-vascular mechanism of the tTF–NGR therapy approach was verified by quantifying the reduced tumor blood-perfusion with contrast-enhanced ultrasound, the reduced relative tumor blood volume by ultrasmall superparamagnetic iron oxide-enhanced magnetic resonance imaging, and by in vivo-evaluation of hemorrhagic bleeding with fluorescent biomarkers (AngioSense⁶⁸⁰) in fluorescence reflectance imaging. The accumulation of tTF–NGR within the tumor was proven by visualizing the distribution of the iodine-123-labelled protein by single-photon emission computed tomography. Use of these multi-modal vascular and molecular imaging tools helped to assess the therapeutic effect even at real time and to detect non-responding tumors directly after the first tTF–NGR treatment. This emphasizes the importance of imaging within clinical studies with tTF–NGR. The imaging techniques as used here have applicability within a wider scope of therapeutic regimes interfering with tumor vasculature. Some even are useful to obtain predictive biosignals in personalized cancer treatment.