Design, synthesis, characterization and evaluation of methionine-ABO based TSPO ligand

Abstract

A novel series of molecules based on the acetamidobenzoxazolone (ABO) skeleton has been developed for diagnosing pathological conditions characterized by over-expression of the 18 kDa translocator protein (TSPO) in organs. To enhance the targeting of TSPO, methionine methyl ester was incorporated into the ABO structure, yielding ABMO 2-[2-(2-oxo-benzoxazol-3-yl)-acetylamino]-4-methylsulfanyl-butyric acid methyl ester, for potential biomedical applications. Two analogs, ABMO-Br and ABMO-Cl, with halogen substitutions at the 5th position of benzoxazolone, were designed and validated in silico for their pharmacokinetic properties, adherence to drug-like criteria, and blood-brain barrier penetration ability.Docking studies revealed the affinity of the designed molecules towards both native and mutant forms of TSPO. Based on in silico analysis, halogen derivatives were selected for synthesis. An efficient three-step synthetic procedure was employed to produce ABMO-Cl/Br, which were purified by column chromatography and characterized by NMR spectroscopy.The resultant ligands were radiolabeled with 99mTc, exhibiting significant stability in saline solution for up to 24 hours. Blood kinetic studies conducted on New Zealand rabbits demonstrated substantial clearance from blood within 1 hr. Ex vivo and in vivo biodistribution studies confirmed uptake of the ligands in TSPO-rich organs. In conclusion, these studies validated the ability of these compounds to cross the blood-brain barrier in animal models. These findings underscore the potential of ABMO-Cl/Br as SPECT markers targeting TSPO. Further investigations using animal models are warranted to fully elucidate the utility of these ligands in diagnosing TSPO-related conditions.