Smart Near-Infrared Fluorescence Probes with Donor–Acceptor Structure for in Vivo Detection of β-Amyloid Deposits

Abstract

The deposition of β-amyloid (Aβ) plaques in the parenchymal and cortical brain is accepted as the main pathological hallmark of Alzheimer's 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.

Near-infrared fluorescence molecular imaging of amyloid beta species and monitoring therapy in animal models of Alzheimer’s disease

“…Fluorescence molecular imaging is appealing for small animal studies because of its low cost, easy operation, and stable imaging probes. In the past decade, the development of fluorescent imaging probes for AD has been actively pursued, and several probes showed capacity for imaging Aβs (37)(38)(39)(40)(41)(42)(43)(44)(45) and Tau tangles (64) in mice. Nonetheless, none has been used to monitor the effectiveness of drug therapy.…”

“…Several NIRF probes for insoluble Aβs have been reported (37)(38)(39)(40)(41)(42)(43)(44)(45). It has been almost 10 y since the first report of NIRF imaging of Aβs by Hintersteiner et al in 2005 (41).…”

<i>In Vivo</i> Molecular Imaging

“…Thus we designed molecular probes for nuclear medicinal imaging the distribution of aggregates of Aβ and hyperphosphorylated tau protein in the brain of a patient with AD, which satisfied the following requirements: 1) high blood-brain barrier permeability; 2) high and specific binding ability to Aβ and tau aggregates; and 3) rapid elimination from normal regions of the brain. Consequently, we succeeded in developing 18 F-labeled pyridyl benzofuran derivative, 18 F-FPYBF-2, as a probe for PET imaging of Aβ plaques [28][29][30][31][32][33][34][35][36] and 123 I-labeled benzo imidazopyridine (BIP) derivative, BIP-3, as a probe for SPECT imaging of tau aggregates [37][38][39][40][41] (Fig. 3).…”

Quantification of Two Fluorophores’ Concentration Ratio in a Mice Model in Preparation for a Proposed Method for Early Detection of Alzheimer’s Disease

“…They demonstrated in vivo the correlation between the intensity of the THK-265 signal and the plaque burden, indicating its utility for direct monitoring of Aβ aggregation progression. Cui et al [28] report the synthesis, characteristics, and biological evaluations of a series of donor-acceptor molecules (DANIRs) as smart NIRF imaging probes for Aβ plaques in AD. These probes were proved to have affinity to Aβ plaques ex vivo, in vitro, and in vivo, with a significant fluorescence intensity increase and a blue-shift in the emission spectra.…”

“…The method includes several stages. First, fluorescent probes [23][24][25][26][27][28][29][30]32], which bind specifically to the two biomarkers in the CSF, are injected to the blood. Second, a miniature needle with an optical fiber is inserted into the epidural fat, which is located several millimeters from the CSF, without penetrating the dura matter.…”