^99mTc-Labeled 2-Arylbenzothiazoles: Aβ Imaging Probes with Favorable Brain Pharmacokinetics for Single-Photon...

A series of 2-arylbenzothiazole derivatives conjugated with bis(aminoethanethiol) (BAT) chelating groups were designed and synthesized. A competitive binding assay-based screening was used to select seven rhenium complexes with potent binding affinity toward Aβ_1-42 aggregates (K_i < 50 nM) for ^99mTc labeling and further evaluation. The ^99mTc-labeled probes showed good affinity and specificity to Aβ plaques in Tg mouse brain tissue in in vitro autoradiography studies. Moreover, [^99mTc]14b exhibited favorable brain pharmacokinetics in normal mice (2.11% ID/g at 2 min and 0.62% ID/g at 60 min). Ex vivo autoradiography revealed extensive labeling of Aβ plaques by [^99mTc]14b in the brain of Tg mice. Furthermore, we performed the first single-photon emission computed tomography (SPECT) imaging study in nonhuman primates with ^99mTc-labeled Aβ probes. The semiquantitative data showed that [^99mTc]14b penetrated the brains of rhesus monkeys. These results indicate that [^99mTc]14b could be utilized as a SPECT imaging probe for Aβ plaques.