Chemical Delivery System of MIBG to the Central Nervous System: Synthesis, C-Radiosynthesis, and Evaluation.

The norepinephrine transporter (NET) plays an important role in neurotransmission and is involved in a multitude of psychiatric and neurodegenerative diseases. [I/I]-iodobenzylguanidine (MIBG) is a widely used radiotracer in the diagnosis and follow-up of peripheral neuroendocrine tumors overexpressing the norepinephrine transporter. MIBG does not cross the blood-brain barrier (BBB), and we have demonstrated the "proof-of-concept" that 1,4-dihydroquinoline/quinolinium salt as chemical delivery system (CDS) is a promising tool to deliver MIBG to the brain. To improve BBB passage, various substituents on the 1,4-dihydroquinoline moiety and a linker between CDS and MIBG were added. A series of CDS-MIBG - was synthesized, labeled with carbon-11, and evaluated into rats. The results demonstrated that, although adding substituents on CDS in - is of no benefit for brain delivery of MIBG, the presence of a linker in CDS-MIBG greatly improved both brain penetration and the release rate of MIBG in the central nervous system.