nhua Jia

Novel Cyclopentadienyl Tricarbonyl Complexes of 99mTc Mimicking Chalcone as Potential Single-Photon Emission Computed Tomography Imaging Probes for β-Amyloid Plaques in Brain

Rhenium and technetium-99m cyclopentadienyl tricarbonyl complexes mimicking the chalcone structure were prepared. These complexes were proved to have affinity to β-amyloid (Aβ) in fluorescent staining on brain sections of Alzheimers Disease (AD) patient and binding assay using Aβ(1-42) aggregates, with K(i) values ranging from 899 to 108 nM as the extension of conjugated π system. In vitro autoradiograpy on sections of transgenic mouse brain confirmed the affinity of [(99m)Tc]5 (K(i) = 108 nM). In biodistribution, all compounds showed good initial uptakes into the brain and fast blood clearance, while the decreasing of initial brain uptakes correspond to increasing of conjugation length, from 4.10 ± 0.38% ID/g ([(99m)Tc]3) to 1.11 ± 0.34% ID/g ([(99m)Tc]5). These small technetium-99m complexes (<500 Da) designed by an integrated approach provide encouraging evidence that development of a promising (99m)Tc-labeled agent for imaging Aβ plaques in the brain may be feasible.

99mTc-labeled dibenzylideneacetone derivatives as potential SPECT probes for in vivo imaging of β-amyloid plaque

Four (99m)Tc-labeled dibenzylideneacetone derivatives and corresponding rhenium complexes were successfully synthesized and biologically evaluated as potential imaging probes for Aβ plaques using SPECT. All rhenium complexes (5a-d) showed affinity for Aβ(1-42) aggregates (Ki = 13.6-120.9 nM), and selectively stained the Aβ plaques on brain sections of transgenic mice. Biodistribution in normal mice revealed that [(99m)Tc]5a-d exhibited moderate initial uptake (0.31%-0.49% ID/g at 2 min) and reasonable brain washout at 60 min post-injection. Although additional optimizations are still needed to facilitate its penetration through BBB, the present results indicate that [(99m)Tc]5a may be a potential SPECT probe for imaging Aβ plaques in Alzheimers brains.

99mTc(CO)3-Labeled Benzothiazole Derivatives Preferentially Bind Cerebrovascular Amyloid: Potential Use as Imaging Agents for Cerebral Amyloid Angiopathy.

Cerebral amyloid angiopathy (CAA) is a disorder affecting the elderly that is characterized by amyloid-β (Aβ) deposition in blood vessel walls of the brain. A series of 99mTc(CO)3-labeled benzothiazole derivatives as potential SPECT imaging probes for cerebrovascular Aβ deposition is reported. Rhenium surrogate displayed high affinities to Aβ aggregates with Ki values ranging from 106 to 42 nM, and they strongly stained Aβ deposits in transgenic mice (Tg) and Alzheimers disease (AD) patients. In vitro autoradiography on brain sections of Tg and AD patients confirmed that [99mTc]24 possessed sufficient affinity for Aβ plaques, and [99mTc]24 could only label Aβ deposition in blood vessels but not Aβ plaques in the parenchyma of the brain of AD patients. Moreover, [99mTc]24 possessed favorable initial uptake (1.21% ID/g) and fast blood washout (blood2 min/blood60 min=23) in normal mice. These preliminary results suggest that [99mTc]24 may be used as an Aβ imaging probe for the detection of CAA.

99mTc-labeled benzothiazole and stilbene derivatives as imaging agents for Aβ plaques in cerebral amyloid angiopathy

β-Amyloid (Aβ) plaques in the blood vessels of the brain are associated with cerebral amyloid angiopathy (CAA), which is a common cause of stroke and vascular diseases. Imaging agents that can differentiate between Aβ plaques in the brain and those on the walls of cerebrovascular vessels will provide non-invasive biomarkers to interrogate the pathogenesis of CAA and give insights into the mechanisms, significance and impact of Aβ-CAA for developing effective therapies for CAA and stroke. A new series of 99mTc-labeled benzothiazole and stilbene derivatives with positive charge were developed and evaluated for selectively targeting Aβ plaques in the blood vessels of the brain. The rhenium complexes 6, 7, 13 and 14 displayed medium binding affinity to Aβ1–42 aggregates with Ki values of 162, 37, 366 and 78 nM, respectively. In vitro fluorescence staining of 7 and 14 demonstrated an intense labeling of Aβ plaques associated with blood vessel walls on brain sections of a patient with Alzheimers diseases. A relatively low initial brain uptake for [99mTc]7 and [99mTc]14, 0.18 and 0.24 ID% per gram, respectively, suggests that they may be useful SPECT imaging agents for selectively detecting Aβ plaques associated with cerebral vessels in the living human brain.

Synthesis and biological evaluation of 18F-labled 2-phenylindole derivatives as PET imaging probes for β-amyloid plaques

A novel series of fluorinated 2-phenylindole derivatives were synthesized and evaluated as β-amyloid imaging probes for PET. The in vitro inhibition assay demonstrated that their binding affinities for Aβ(1-42) aggregates ranged from 28.4 to 1097.8 nM. One ligand was labeled with (18)F ([(18)F]1a) for its high affinity (K(i)=28.4 nM), which was also confirmed by in vitro autoradiography experiments on brain sections of transgenic mouse (C57BL6, APPswe/PSEN1, 11 months old, male). In vivo biodistribution experiments in normal mice showed that this radiotracer displayed high initial uptake (5.82±0.51% ID/g at 2 min) into and moderate washout (2.77±0.31% ID/g at 60 min) from the brain. [(18)F]1a could be developed as a promising new PET imaging probe for Aβ plaques although necessary modifications are still needed.

18F-Labeled 2-phenylquinoxaline derivatives as potential positron emission tomography probes for in vivo imaging of β-amyloid plaques

In continuation of our study on the 2-phenylquinoxaline scaffold as potential β-amyloid imaging probes, two [(18)F]fluoro-pegylated 2-phenylquinoxaline derivatives, 2-(4-(2-[(18)F]fluoroethoxy)phenyl)-N-methylquinoxalin-6-amine ([(18)F]4a) and 2-(4-(2-(2-(2-[(18)F]fluoroethoxy)ethoxy)ethoxy)phenyl)-N-methylquinoxalin-6-amine ([(18)F]4b) were prepared. Both of them displayed high binding affinity to Aβ(1-42) aggregates (K(i) = 10.0 ± 1.4 nM for 4a, K(i) = 5.3 ± 3.2 nM for 4b). The specific and high binding of [(18)F]4a and [(18)F]4b to Aβ plaques was confirmed by in vitro autoradiography on brain sections of AD human and transgenic mice. In biodistribution in normal mice, [(18)F]4a displayed high initial brain uptake (8.17% ID/g at 2 min) and rapid washout from the brain. These preliminary results suggest [(18)F]4a may be a potential PET imaging agent for Aβ plaques in the living human brain.

Optically Pure Diphenoxy Derivatives as More Flexible Probes for β-Amyloid Plaques

The highly rigid and planar scaffold with π-conjugated systems has been widely considered to be indispensable for Aβ binding probes. However, the flexible benzyloxybenzene derivative [(125)I]BOB-4 represents an excellent lead candidate for targeting Aβ in AD brains. Based on that, we designed two pairs of more flexible and optically pure diphenoxy derivatives with a chiral center as novel Aβ probes. These compounds possessed high affinity (Ki = 15.8-45.0 nM) for Aβ1-42 aggregates, and (R)-enantiomers showed slightly better binding ability than (S)-enantiomers. In addition, the competition binding assay implied that the optically pure diphenoxy derivatives with more flexible geometry shared the same binding site as IMPY, a classical rigid and planar Aβ probe. For (125)I-radiolabeled enantiomers, (S)-[(125)I]5 and (R)-[(125)I]5, specific plaque labeling on brain sections of Tg mice and AD patients were observed in in vitro autoradiography, persuasively proving the excellent affinity of the probes. In biodistribution, (S)-[(125)I]5 and (R)-[(125)I]5 with relatively low lipophilicity exhibited moderate initial brain uptake (4.37% and 3.72% ID/g at 2 min, respectively) and extremely fast washout from normal mice brain (brain2min/brain60min = 19.0 and 17.7, respectively). In summary, the separate enantiomers displayed similar properties in vitro and in vivo, and (S/R)-[(123)I]5 may be potential SPECT probes for recognizing Aβ plaques in AD brains.