PhotoAcoustic Imaging (PAI) is a biomedical imaging modality currently under evaluation in preclinical and clinical settings. In this work, ICG is coupled to an integrin binding vector (ICG-RGD) to combine the good photoacoustic properties of ICG and the favourable αvβ3-binding capabilities of a small RGD cyclic peptidomimetic. ICG-RGD is characterized in terms of physicochemical properties, biodistribution and imaging performance. Tumor uptake was assessed in subcutaneous xenograft mouse models of human glioblastoma (U-87MG, high αvβ3 expression) and epidermoid carcinoma (A431, low αvβ3 expression). ICG and ICG-RGD showed high PA signal in tumors already after 15 min post-injection. At later time points the signal of ICG rapidly decreased, while ICG-RGD showed sustained uptake in U-87MG but not in A431 tumors, likely due to the integrin-mediated retention of the probe. In conclusion, ICG-RGD is a novel targeted contrast agents for PAI with superior biodistribution, tumor uptake properties and diagnostic value compared to ICG.
Keywords: Contrast agents; Indocyanine green; Optoacoustic imaging; Photoacoustic imaging; Tumor targeting; αvβ3-Integrin.