Acetylated Benzothiazolone as Homobivalent SPECT Metallo-Radiopharmaceutical 99mTc-(6-AcBTZ)2DTPA: Design, Synthesis, and Preclinical Evaluation for Mapping 5-HT1A/7 Receptors

Mapping different structural forms of serotonin subtypes 5-HT 1A -5-HT 7 using a selective-specific ligand with good pharmacokinetics and brain permeability can open avenues for personalized medication in depressed population. Herein, the selective 5-HT 1A/7 antagonist, modified for enhanced brain permeation, is developed as a homobivalent ligand, (6-AcBTZ) 2 DTPA. After in-depth computational studies to probe the binding mechanism, two-step synthesis lead to (6-AcBTZ) 2 DTPA. Biocompatibility studies indicated cytocompatibility with 3.6-1.64% cell death (0.1 mM-1 pM) and hemocompatibility with 2.33% hemolysis of human erythrocytes. When 99m Tc-radiolabeled in a quantitative yield (98%), a stable preparation was obtained with 7.4 and 3.5% dissociation upon incubation with human serum and excess cysteine. The single-photon-emission computed tomography (SPECT) tracer 99m Tc-(6-AcBTZ) 2 DTPA showed biphasic clearance ( t 1/2, distribution = 0.5 min and t 1/2, elimination = 482 min) and maximum brain uptake of 0.42 ± 0.02% ID/g with the regional localization (hippocampus: 11.38% ID/g; cortex: 26.42% ID/g; cerebellum: 25.23% ID/g). Thus, the 99m Tc-metal-based SPECT neurotracer holds potential for neuroreceptor mapping.