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Metal chelates targeted to amyloid peptides are widely explored as diagnostic tools or therapeutic agents. The attachment of a metal complex to amyloid recognition units typically leads to a decrease in peptide affinity. We show here that by separating a macrocyclic GdL chelate and a PiB targeting unit with a long hydrophobic C10 linker, it is possible to attain nanomolar affinities for both Aβ1‐40 (Kd=4.4 nm) and amylin (Kd=4.5 nm), implicated, respectively in Alzheimer's disease and diabetes. The Scatchard analysis of surface plasmon resonance data obtained for a series of amphiphilic, PiB derivative GdL complexes indicate that their Aβ1‐40 or amylin binding affinity varies with their concentration, thus micellar aggregation state. The GdL chelates also affect peptide aggregation kinetics, as probed by thioflavin‐T fluorescence assays. A 2D NMR study allowed identifying that the hydrophilic region of Aβ1‐40 is involved in the interaction between the monomer peptide and the Gd3+ complex. Finally, ex vivo biodistribution experiments were conducted in healthy mice by using 111In labeled analogues. Their pancreatic uptake, ∼3 %ID g−1, is promising to envisage amylin imaging in diabetic animals. [ABSTRACT FROM AUTHOR]

Background: Amyloidoses are characterized by the extracellular deposition of insoluble fibrillar proteinaceous aggregates highly organized into cross-β structure and referred to as amyloid fibrils. Nowadays, the diagnosis of these diseases remains tedious and involves multiple examinations while an early and accurate protein typing is crucial for the patients' treatment. Routinely used neuroimaging techniques such as magnetic resonance imaging (MRI) and positron emission tomography (PET) using Pittsburgh compound B, [11C]PIB, provide structural information and allow to assess the amyloid burden, respectively, but cannot discriminate between different amyloid deposits. Therefore, the availability of efficient multimodal imaging nanoparticles targeting specific amyloid fibrils would provide a minimallyinvasive imaging tool useful for amyloidoses typing and early diagnosis. In the present study, we have functionalized gadolinium-based MRI nanoparticles (AGuIX) with peptides highly specific for Aβ amyloid fibrils, LPFFD and KLVFF. The capacity of such nanoparticles grafted with peptide to discriminate among different amyloid proteins, was tested with Aβ(1-42) fibrils and with mutated-(V30M) transthyretin (TTR) fibrils. Results: The results of surface plasmon resonance studies showed that both functionalized nanoparticles interact with Aβ(1-42) fibrils with equilibrium dissociation constant (Kd) values of 403 and 350 μM respectively, whilst they did not interact with V30M-TTR fibrils. Similar experiments, performed with PIB, displayed an interaction both with Aβ(1-42) fibrils and V30M-TTR fibrils, with Kd values of 6 and 10 μM respectively, confirming this agent as a general amyloid fibril marker. Thereafter, the ability of functionalized nanoparticle to target and bind selectively Aβ aggregates was further investigated by immunohistochemistry on AD like-neuropathology brain tissue. Pictures clearly indicated that KLVFF-grafted or LPFFD-grafted to AGuIX nanoparticle recognized and bound the Aβ amyloid plaque localized in the mouse hippocampus. Conclusion: These results constitute a first step for considering these functionalized nanoparticles as a valuable multimodal imaging tool to selectively discriminate and diagnose amyloidoses. [ABSTRACT FROM AUTHOR]

Metal complexes are increasingly explored as imaging probes in amyloid peptide related pathologies. We report the first detailed study on the mechanism of interaction between a metal complex and both the monomer and the aggregated form of Aβ1-40 peptide. We have studied lanthanide(III) chelates of two PiB-derivative ligands (PiB=Pittsburgh compound B), L1 and L2, differing in the length of the spacer between the metal-complexing DO3A macrocycle (DO3A= 1,4,7,10-tetraazacyclododecane-1,4,7-triacetic acid) and the peptide-recognition PiB moiety. Surface plasmon resonance (SPR) and saturation transfer difference (STD) NMR spectroscopy revealed that they both bind to aggregated Aβ1-40 ( KD=67-160 μ M), primarily through the benzothiazole unit. HSQC NMR spectroscopy on the 15N-labeled, monomer Aβ1-40 peptide indicates nonsignificant interaction with monomeric Aβ. Time-dependent circular dichroism (CD), dynamic light scattering (DLS), and TEM investigations of the secondary structure and of the aggregation of Aβ1-40 in the presence of increasing amounts of the metal complexes provide coherent data showing that, despite their structural similarity, the two complexes affect Aβ fibril formation distinctly. Whereas GdL1, at higher concentrations, stabilizes β-sheets, GdL2 prevents aggregation by promoting α-helical structures. These results give insight into the behavior of amyloid-targeted metal complexes in general and contribute to a more rational design of metal-based diagnostic and therapeutic agents for amyloid- associated pathologies. [ABSTRACT FROM AUTHOR]