Protein Based Ligands For Tumor Targeting

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In addition to peptides, protein-based ligands such as Affibody proteins have been utilized for tumor targeting. Anti-epidermal growth factor receptor (EGFR) Affibody protein (e.g., Ac-Cys-ZEGFR:1907, amino acid sequence: Ac-CVDNKFNKEMWAAWEEIRNLPNLNGWQMTAFIASLVDDPSQSANLLAEAKKLNDAQAPK-NH2) is used to target EGFR that is overexpressed in a wide variety of human tumors. Cheng and co-workers used anti-EGFR Affibody protein as tumor-targeting ligand on 64Cu–Au-IO nanoparticles (PET component: 64Cu, MRI component: iron oxide, specific for EGFR) surface.[63] In their work, A431 tumor cells were subcutaneously implanted in the right shoulders of nude mice; and 64Cu-NOTA-Au-IONP-Affibody nanoparticles were administered via tail vain injection. Rather low resolution PET image showed that these nanoparticles were taken by EGFR positive A431 (human epithelial carcinoma cell line) cells reaching 4.6% ID/g at 24 h after injection, significantly higher than that obtained from the blocking experiment (1.9% ID/g) indicating the specificity of the probe. This difference in % ID/g values corroborated with 44% drop in MRI signal intensity that was observed for the tumor. In this study, the use of an Affibody protein as ligand for EGFR-expressing tumor in small animals was demonstrated to be successful; however, the benefit of multimodality was not demonstrated. The unique chemistry of this dumbbell-shaped Au–IO nanoprobe could pave the way for targeted drug delivery into EGFR-expressing tumors
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