A Novel Conjugable Translocator Protein Ligand Labeled with a Fluorescence Dye for in Vitro Imaging

A conjugable analogue of the benzodiazepine 4' '-chlorodiazepam (Ro5-4864), C6Ro5-4864 was synthesized to probe the binding sites of translocator protein (18 kDa; TSPO), previously known as the peripheral benzodiazepine receptor for molecular imaging. The amino group in this analogue allows universal conjugation to signaling molecules. Lissamine-C6Ro5-4864, synthesized from C6Ro5-4864 and a lissamine fluorescence dye, was investigated in this study. This imaging agent exhibited micromolar binding affinity (Ki = 2.6 microM) to TSPO and was successfully imaged in TSPO rich glioma and breast cancer cell lines. These findings suggest that C6Ro5-4864 may provide opportunities in imaging disease states where TSPO levels are affected, such as cancer and neurologic diseases.