Radiochemical Synthesis and Radio-Ligand Receptor Binding Assay of ⁹⁹Tc^m-NCAM as a Potential NMDA Receptor Imaging Agent

A new radio-ligand ⁹⁹Tc^m-NCAM was synthesized by labeling a derivative of memantine N₂S₂-memantine (N2-(N-(2-mercapotoethyl))aminoformylmethylN-(2-mercapotoethyl)-3, 5-dimethyladamantyl aminoacetamide, NCAM), and its radiochemical purity was greater than 95% determined by TLC under optimized labeling conditions. The radio-ligand receptor binding assay was shown that the binding of radio-ligand ⁹⁹Tc^m-NCAM to NMDA receptor was saturable with a dissociation constant K_d of 706.3 nmol/L and a B_maxof 56.8 μmol/g calculated by a computer program written based on the receptor theory in B region. The competitive analysis show that such specific binding could be inhibited by specific inhibitors of NMDA receptor. Its oil/water partition coefficient is 1.90. In conclusion, the new radio-ligand ⁹⁹Tc^m-NCAM, which was systhesized by the method of directly labelling NCAM with ⁹⁹Tc^m, has a moderate affinity and specific binding to NMDA receptor, and can easily transported through the blood-brain barrier(BBB). Therefore, it may be a potential NMDA receptor imaging agent.