Recent advances in receptor-targeted fluorescent probes for in vivo cancer imaging.

Receptor-targeted optical imaging of cancer is emerging as an attractive strategy for early cancer diagnosis and surgical guidance. The success of such strategy depends largely upon the development of receptor-targeted fluorescent probes with high specificity and binding affinity to the target receptors. Recently, a host of such probes have been reported to target cancer-specific receptors, such as somatostatin receptors (SSTRs), integrin receptors, cholecystokinin-2 (CCK(2)) receptor, gastrin-releasing peptide (GRP) receptor, endothelin A (ET(A)) receptor, translocator protein (TSPO) receptor, epidermal growth factor (EGF) receptor, human epidermal growth factor receptor 2 (HER2), vascular endothelial growth factor (VEGF) receptor, folate receptor (FR), transferrin receptor (TFR), low-density lipoprotein (LDL) receptors, type I insulin-like growth factor receptor (IGF1R), vasoactive intestinal peptide (VIP) receptors, urokinase plasminogen activator (uPA) and estrogen receptor (ER). This review will describe the recent advances in synthetic targeting optical imaging probes and demonstrate their in vivo imaging potentials. Moreover, current status of near infrared (NIR) fluorescent dyes, targeting moieties and coupling reactions, as well as strategies for designing targeted probes, will also be discussed.