Boli Liu

Smart near-infrared fluorescence probes with donor-acceptor structure for in vivo detection of β-amyloid deposits.

The deposition of β-amyloid (Aβ) plaques in the parenchymal and cortical brain is accepted as the main pathological hallmark of Alzheimers disease (AD); however, early detection of AD still presents a challenge. With the assistance of molecular imaging techniques, imaging agents specifically targeting Aβ plaques in the brain may lead to the early diagnosis of AD. Herein, we report the design, synthesis, and evaluation of a series of smart near-infrared fluorescence (NIRF) imaging probes with donor-acceptor architecture bridged by a conjugated π-electron chain for Aβ plaques. The chemical structure of these NIRF probes is completely different from Congo Red and Thioflavin-T. Probes with a longer conjugated π system (carbon-carbon double bond) displayed maximum emission in PBS (>650 nm), which falls in the best range for NIRF probes. These probes were proved to have affinity to Aβ plaques in fluorescent staining of brain sections from an AD patient and double transgenic mice, as well as in an in vitro binding assay using Aβ(1-42) aggregates. One probe with high affinity (K(i) = 37 nM, K(d) = 27 nM) was selected for in vivo imaging. It can penetrate the blood-brain barrier of nude mice efficiently and is quickly washed out of the normal brain. Moreover, after intravenous injection of this probe, 22-month-old APPswe/PSEN1 mice exhibited a higher relative signal than control mice over the same period of time, and ex vivo fluorescent observations confirmed the existence of Aβ plaques. In summary, this probe meets most of the requirements for a NIRF contrast agent for the detection of Aβ plaques both in vitro and in vivo.

18F-FDG PET as a Tool to Predict the Clinical Outcome of Infliximab Treatment of Rheumatoid Arthritis: An Explorative Study

18F-FDG PET is a sensitive, promising method for visualizing disease activity in rheumatoid arthritis. This study aimed to assess the association between changes in 18F-FDG joint uptake after 2 wk of infliximab treatment and clinical outcome. Methods: Scans were obtained at the initiation of treatment and at 2 wk. Uptake in metacarpophalangeal and wrist joints was quantified using standardized uptake values. Results: Changes in mean standardized uptake value at 0–2 wk significantly correlated with the disease activity score (DAS) at 14 and 22 wk and contributed significantly to the prediction of DAS at these time points. No significant correlation was found between changes in acute-phase reactants at 0–2 wk and the DAS at later time points. Conclusion: Early changes in 18F-FDG uptake in joints during infliximab treatment of rheumatoid arthritis patients, using PET, may predict clinical outcome.

Synthesis and structure-affinity relationships of novel dibenzylideneacetone derivatives as probes for β-amyloid plaques.

A new and extensive set of dibenzylideneacetone derivatives was synthesized and screened for affinity toward Aβ(1-42) aggregates. Structure-activity relationships revealed the binding of dibenzylideneacetones to be affected by various substituents. The introduction of a substituent group in the ortho position reduced or abolished the binding. However, the para position was highly tolerant of sterically demanding substitutions. Three radioiodinated ligands (6, 70, and 71) and two (18)F fluoro-pegylated (FPEG) ligands (83 and 85) were prepared, all of which displayed high affinity for Aβ(1-42) aggregates (K(i) ranging from 0.9 to 7.0 nM). In biodistribution experiments, they exhibited good initial penetration (1.59, 4.68, 4.56, 4.13, and 5.15% ID/g, respectively, at 2 min) of and fast clearance from the brain. Autoradiography with sections of postmortem AD brain and transgenic mouse brain confirmed the high affinity of these tracers. These preliminary results strongly suggest the dibenzylideneacetone structure to be a potential new scaffold for β-amyloid imaging probes.

Synthesis and biological evaluation of 99mTc, Re-monoamine-monoamide conjugated to 2-(4-aminophenyl)benzothiazole as potential probes for β-amyloid plaques in the brain

The benzothiazole aniline (BTA) conjugated with monoamine-monoamide (MAMA) was synthesized and then labeled with (99m)Tc. Its corresponding rhenium analogue was synthesized, and the fluorescent staining was performed in brain sections of both Tg mouse and Alzheimers disease (AD) patient. The fluorescent rhenium complex Re-MAMA-BTA selectively bound to the amyloid aggregates in the brain sections of both APP Tg mouse and AD patient. The analogous (99m)Tc-MAMA-BTA complex could enter the normal mouse brain with high initial uptake. These results are encouraging for further exploration of their derivatives as imaging agents for Abeta plaques in the brain.

Synthesis and Evaluation of Novel 18F Labeled 2-Pyridinylbenzoxazole and 2-Pyridinylbenzothiazole Derivatives as Ligands for Positron Emission Tomography (PET) Imaging of β-Amyloid Plaques

A series of fluoro-pegylated (FPEG) 2-pyridinylbenzoxazole and 2-pyridinylbenzothiazole derivatives were synthesized and evaluated as novel β-amyloid (Aβ) imaging probes for PET. They displayed binding affinities for Aβ(1-42) aggregates that varied from 2.7 to 101.6 nM. Seven ligands with high affinity were selected for (18)F labeling. In vitro autoradiography results confirmed the high affinity of these radiotracers. In vivo biodistribution experiments in normal mice indicated that the radiotracers with a short FPEG chain (n = 1) displayed high initial uptake into and rapid washout from the brain. One of the 2-pyridinylbenzoxazole derivatives, [(18)F]-5-(5-(2-fluoroethoxy)benzo[d]oxazol-2-yl)-N-methylpyridin-2-amine ([(18)F]32) (K(i) = 8.0 ± 3.2 nM) displayed a brain(2min)/brain(60min) ratio of 4.66, which is highly desirable for Aβ imaging agents. Target specific binding of [(18)F]32 to Aβ plaques was validated by ex vivo autoradiographic experiment with transgenic model mouse. Overall, [(18)F]32 is a promising Aβ imaging agent for PET and merits further evaluation in human subjects.

Highly Sensitive Near-Infrared Fluorophores for in Vivo Detection of Amyloid-β Plaques in Alzheimer’s Disease

Alzheimers disease (AD) is pathologically characterized by the accumulation of β-amyloid (Aβ) deposits in the parenchymal and cortical brain. In this work, we designed, synthesized, and evaluated a series of near-infrared (NIR) probes with electron donor-acceptor end groups interacting through a π-conjugated system for the detection of Aβ deposits in the brain. Among these probes, 3b and 3c had excellent fluorescent properties (emission maxima > 650 nm and high quantum yields) and displayed high sensitivity and high affinities to Aβ aggregates (3b, Kd = 8.8 nM; 3c, Kd = 1.9 nM). Both 3b and 3c could readily penetrate the blood-brain barrier with high initial brain uptake and fast to moderate washout from the brain. In vivo NIR imaging revealed that 3b and 3c could efficiently differentiate transgenic and wild-type mice. In summary, our research provides new hints for developing smarter and more activatable NIR probes targeting Aβ.

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.

Fluorine-18 labeled galactosylated chitosan for asialoglycoprotein-receptor-mediated hepatocyte imaging

Galactosylated chitosan (GC) was prepared by reacting lactobionic acid with water-soluble chitosan. GC was labeled with fluorine-18 by conjugation with N-succinimidyl-4-(18)F-fluorobenzoate ([(18)F]SFB) under a slightly basic condition. After rapid purification with HiTrap desalting column, [(18)F]FB-GC was obtained with high radiochemical purity (>97%) determined by radio-HPLC. The total reaction time for [(18)F]FB-GC was about 150 min. Typical decay-corrected radiochemical yield was about 4-8%. Ex vivo biodistribution in normal mice showed that [(18)F]FB-GC had moderate activity accumulation in liver with very good retention (11.13+/-1.63, 10.97+/-1.90 and 10.77+/-0.95%ID/g at 10, 60, 120 min after injection, respectively). The other tissues except kidney showed relative low radioactivity accumulation. The high liver/background ratio affords promising biological properties to get clear images. The specific binding of this radiotracer to the ASGP receptor was confirmed by blocking experiment in mice. Compared with the non-blocking group the hepatic uptake of [(18)F]FB-GC significantly declined in all selected time points. The better liver retention properties of [(18)F]FB-GC than that of albumin based imaging agents may improve imaging quality and simplify pharmacokinetic model of liver function in the future application with PET imaging.

Novel 18F-Labeled Benzoxazole Derivatives as Potential Positron Emission Tomography Probes for Imaging of Cerebral β-Amyloid Plaques in Alzheimer’s Disease

Two radiofluoro-pegylated phenylbenzoxazole derivatives, 4-(5-(2-(2-(2-[(18)F]fluoroethoxy)ethoxy)ethoxy)benzo[d]oxazol-2-yl)-N-methylaniline ([(18)F]24) and 4-(5-(2-(2-(2-[(18)F]fluoroethoxy)ethoxy)ethoxy)benzo[d]oxazol-2-yl)-N,N-dimethylaniline ([(18)F]32), were synthesized and evaluated as probes for imaging cerebral β-amyloid (Aβ) plaques in living brain tissue by PET. [(18)F]24 and [(18)F]32 displayed high affinity for Aβ(1-42) aggregates (K(i) = 9.3 and 3.9 nM, respectively). In vitro autoradiography with sections of post-mortem AD brain and transgenic mouse brain confirmed the affinity of these tracers. Initial high uptake into and rapid washout from the brain in normal mice were observed. [(18)F]24 also displayed excellent binding to Aβ plaques in ex vivo autoradiographic experiments with Tg2576 mice. Furthermore, small-animal PET studies demonstrated significant differences in the clearance profile after the administration of [(18)F]24 between Tg2576 and wild-type mice. The results suggest [(18)F]24 to be a useful PET agent for detecting Aβ plaques in the living human brain.

Copolymer-Based Hepatocyte Asialoglycoprotein Receptor Targeting Agent for SPECT

Poly(vinylbenzyl-O-β-D-galactopyranosyl-D-gluconamide) (PVLA) can be specifically internalized by hepatocytes via the asialoglycoprotein receptor. In this study, we synthesized and characterized galactose-carrying copolymers with hydrazinonicotinamide chains as bifunctional groups to radiolabel PVLA with 99mTc for SPECT targeting specific hepatocytes. Methods: Poly(N-p-vinylbenzyl-[O-β-D-galactopyranosyl-(1→4)-D-gluconamide]-co-N-p-vinylbenzyl-6-[2-(4-dimethylamino)benzaldehydehydrazono]nicotinate) (P(VLA-co-VNI)) was first prepared via copolymerization of N-p-vinylbenzyl-O-β-D-galactopyranosyl-D-gluconamide with 5% (mol) of N-p-vinylbenzyl-(4-dimethylaminobenzaldehyde hydrazono)nicotinamide. The copolymer was labeled with 99mTc using tricine as a coligand. Then 99mTc[P(VLA-co-VNI)](tricine)2 was evaluated by in vivo metabolic stability and biodistribution in normal mice. SPECT was performed in normal New Zealand White rabbits and rabbits with liver cancer. Results: 99mTc[P(VLA-co-VNI)](tricine)2 was prepared in high labeling yield (>95%) and radiochemical purity (>99%), with good stability. The results of biodistribution in mice demonstrated that the liver uptake was 125.33 ± 10.99 percentage injected dose per gram at 10 min after injection and could be blocked significantly by preinjecting free neogalactosylalbumin or P(VLA-co-VNI). SPECT images with high quality were obtained at 15, 30, 60, and 120 min after injection of the radiotracer. Significant radioactivity defect was observed in the liver cancer model. Conclusion: The bifunctional coupling agent hydrazinonicotinamide was introduced to PVLA via copolymerization and labeled with 99mTc. The promising biologic properties of 99mTc[P(VLA-co-VNI)](tricine)2 afford potential applications for the assessment of hepatocyte function in the future.