Synthesis and evaluation of a (18)F-curcumin derivate for ß-amyloid plaque imaging.

INTRODUCTION: Curcumin is a neuroprotective compound that inhibits the formation of amyloid oligomers and fibrils and binds to ß-amyloid plaques in Alzheimer's disease (AD). We aimed to synthesize an (18)F-labeled curcumin derivate ([(18)F]4) and to characterize its positron emission tomography (PET) tracer-binding properties to ß-amyloid plaques in a transgenic APP23 mouse model of AD. METHODS: We utilized facile one-pot synthesis of [(18)F]4 using nucleophilic (18)F-fluorination and click chemistry. Binding of [(18)F]4 to ß-amyloid plaques in the transgenic APP23 mouse brain cryosections was studied in vitro using heterologous competitive binding against PIB. [(18)F]4 uptake was studied ex vivo in rodents and in vivo using PET/computed tomography of transgenic APP23 and wild-type control mice. RESULTS: The radiochemical yield of [(18)F]4 was 21 ± 11%, the specific activity exceeded 1TBq/µmol, and the radiochemical purity exceeded 99.3% at the end of synthesis. In vitro studies of [(18)F]4 with the transgenic APP23 mouse revealed high ß-amyloid plaque binding. In vivo and ex vivo studies demonstrated that [(18)F]4 has fast clearance from the blood, moderate metabolism but low blood-brain barrier (BBB) penetration. CONCLUSIONS: [(18)F]4 was synthesized in high yield and excellent quality. In vitro studies, metabolite profile, and fast clearance from the blood indicated a promising tracer for Aß imaging. However, [(18)F]4 has low in vivo BBB penetration and thus further studies are needed to reveal the reason for this and to possibly overcome this issue.

Natural glycoconjugates with antitumor activity.

Cancer is one of the major causes of death worldwide. As a consequence, many different therapeutic approaches, including the use of glycosides as anticancer agents, have been developed. Various glycosylated natural products exhibit high activity against a variety of microbes and human tumors. In this review we classify glycosides according to the nature of their aglycone (non-saccharidic) part. Among them, we describe anthracyclines, aureolic acids, enediyne antibiotics, macrolide and glycopeptides presenting different strengths and mechanisms of action against human cancers. In some cases, the glycosidic residue is crucial for their activity, such as in anthracycline, aureolic acid and enediyne antibiotics; in other cases, Nature has exploited glycosylation to improve solubility or pharmacokinetic properties, as in the glycopeptides. In this review we focus our attention on natural glycoconjugates with anticancer properties. The structure of several of the carbohydrate moieties found in these conjugates and their role are described. The structure­activity relationship of some of these compounds, together with the structural features of their interaction with the biological targets, are also reported. Taken together, all this information is useful for the design of new potential anti-tumor drugs.

Functionalization of liposomes with ApoE-derived peptides at different density affects cellular uptake and drug transport across a blood-brain barrier model.

A promising strategy to enhance blood-brain barrier penetration by drugs is the functionalization of nanocarriers with uptake-facilitating ligands. We studied the cellular uptake, by cultured RBE4 brain capillary endothelial cells, of nanoliposomes (NLs) covalently coupled with monomer or tandem dimer of apolipoprotein E (ApoE)-derived peptides (residues 141-150), at various densities. NLs without functionalization did not show either relevant membrane accumulation or cellular uptake, as monitored by confocal microscopy and quantified by fluorescence-activated cell sorting. Functionalization with peptides mediated an efficient NLs uptake that increased with peptide density; NLs carrying monomeric peptide performed the best. Moreover, we studied the ability of ApoE-NLs to enhance the transport of a drug payload through a RBE4 cell monolayer. The permeability of a tritiated curcumin derivative was enhanced after its entrapment into ApoE-NLs, in particular those functionalized with the dimer (+83% with respect to free drug, P < 0.01). Thus, these NLs appear particularly suitable for implementing further strategies for drug brain targeting.

Effect of curcumin-associated and lipid ligand-functionalized nanoliposomes on aggregation of the Alzheimer's Aß peptide.

The effect of various types of nanoliposomes (associated with curcumin, phosphatidic acid, cardiolipin, or GM1 ganglioside) on the aggregation of the amyloid-ß(1-42) (Aß(1-42)) peptide was investigated. Nanoliposomes incorporating curcumin (curcumin-liposomes) were prepared by adding curcumin in the lipid phase during liposome preparation, whereas curcumin surface-decorated liposomes were prepared by using a curcumin-lipid conjugate (lipid-S-curcumin liposomes) or by attaching a curcumin derivative on preformed liposomes by click chemistry (click-curcumin liposomes). The lipid ligands (phosphatidic acid, cardiolipin, or GM1) were also incorporated into nanoliposomes during their formation. All nanoliposomes with curcumin, or the curcumin derivative, were able to inhibit the formation of fibrillar and/or oligomeric Aß in vitro. Of the three forms of curcumin liposomes tested, the click-curcumin type was by far the most effective. Liposomes with lipid ligands only inhibited Aß fibril and oligomer formation at a very high ratio of liposome to peptide. Curcumin-based liposomes could be further developed as a novel treatment for Alzheimer's disease.

(18)F-labeling syntheses and preclinical evaluation of functionalized nanoliposomes for Alzheimer's disease.

The aim of the present study was to synthesize functionalized (18)F-labeled NLs ((18)F-NLs) and evaluate their biological behavior in mouse models of Alzheimer's disease (AD) using positron emission tomography (PET) and ex vivo brain autoradiography. (18)F-fluorine was introduced to (18)F-NLs either by using a core forming (18)F-lipid or by encapsulating a (18)F-tracer, (18)F-treg-curcumin inside the NLs. Phosphatidic acid (PA) and curcumin derivative (Curc) functionalized (18)F-NLs with or without additional mApoE functionalization were produced using thin film hydration. The biodistribution and ß-amyloid plaque-binding ability of (18)F-NLs were studied in wild type mice and AD mouse models using in vivo PET imaging and ex vivo brain autoradiography at 60min after (18)F-NL injection. Functionalized (18)F-NLs were successfully synthesized. The preclinical evaluation in mice showed that the functional group affected the biodistribution of (18)F-NLs. Further functionalization with mApoE increased the brain-to-blood ratio of (18)F-NLs but the overall brain uptake remained low with all functionalized (18)F-NLs. The liposomal encapsulation of (18)F-treg-curcumin was not successful and preclinical results of encapsulated (18)F-treg-curcumin and plain (18)F-treg-curcumin were identical. Although the studied functionalized (18)F-NLs were not suitable for PET imaging as such, the synthesis techniques introduced in this study can be utilized to modify the biological behavior of (18)F-labeled NLs.

Comparison of Various Types of Ligand Decorated Nanoliposomes for their Ability to Inhibit Amyloid Aggregation and to Reverse Amyloid Cytotoxicity.

Three different amyloid targeting ligands, previously shown to exhibit amyloid specific properties, have been used to develop amyloid -targeted nanoliposomes (AT-NLs. For this a MAb against Aß-peptides (Aß-MAb (immobilized on NLs at 0.015 and 0.05 mol %, and two different curcumin-lipid derivatives were attached to the surface of preformed NLs or incorporated in NL membranes during their formation. Following physicochemical characterization, these AT-NLs were studied for their ability to inhibit or delay amyloid peptide aggregation -using the thioflavin-T assay, and for their potential to reverse amyloid-induced (and Zn, or, amyloid + Zn cytotoxicity, on wild type (N2aWT and transformed (N2aAPP neuroblastoma cells, applying the MTT assay. Experimental results reveal that all formulations were found to strongly delay amyloid peptide aggregation (with no significant differences between the different AT-NL types. However, although Aß-MAb-NLs significantly reversed amyloid-induced cytotoxicity in all cases, both curcumin-NL types did not reverse Zn-induced, nor Zn+Aß-induced cytotoxicity in N2aWT cells, suggesting lower activity against synthetic-Aß peptides (compared to endogenous Aß peptides; perhaps due to different affinity towards different (aggregation stages of peptide species (monomers, oligomers, fibrils, etc. Taken into account that the aggregation stage of amyloid species is an important determinant of their toxicity, the importance of the affinity of each AT-NL type towards specific species, is highlighted.

Nanoliposomes presenting on surface a cis-glycofused benzopyran compound display binding affinity and aggregation inhibition ability towards Amyloid ß1-42 peptide.

Nanoliposomes decorated on their surface with ligands for Aß-peptides, the key morphological features of Alzheimer's disease (AD), have been synthesized and characterized for their ability to target Aß-peptide aggregates. A tricyclic benzopyrane-glycofused structure has been exploited as Aß-peptide ligand, which was linked to liposomes via a copper-free, chemoselective, biocompatible click chemistry reaction. The tricyclic-decorated liposomes presented a mean diameter in the nanomolar range (150-200 nm), a negative z-potential and a good stability, at least up to one month. Integrity studies performed in the presence of serum proteins indicated that these decorated nanoliposomes fulfill the requirements for in vivo applications. NMR experiments carried out with Aß1-42 oligomers using both surface functionalized and plain (control) liposomes, revealed that the binding ability of the nanoliposomes was mediated by the presence of the tricyclic ligand on their surface. Finally ThT assay carried out with tricyclic-decorated liposomes showed significant decrease in thioflavine T fluorescence after 24 h, suggesting a significant inhibition/delay of Aß1-42 aggregation.

Versatile and efficient targeting using a single nanoparticulate platform: application to cancer and Alzheimer's disease.

A versatile and efficient functionalization strategy for polymeric nanoparticles (NPs) has been reported and successfully applied to PEGylated, biodegradable poly(alkyl cyanoacrylate) (PACA) nanocarriers. The relevance of this platform was demonstrated in both the fields of cancer and Alzheimer's disease (AD). Prepared by copper-catalyzed azide-alkyne cycloaddition (CuAAC) and subsequent self-assembly in aqueous solution of amphiphilic copolymers, the resulting functionalized polymeric NPs exhibited requisite characteristics for drug delivery purposes: (i) a biodegradable core made of poly(alkyl cyanoacrylate), (ii) a hydrophilic poly(ethylene glycol) (PEG) outer shell leading to colloidal stabilization, (iii) fluorescent properties provided by the covalent linkage of a rhodamine B-based dye to the polymer backbone, and (iv) surface functionalization with biologically active ligands that enabled specific targeting. The construction method is very versatile and was illustrated by the coupling of a small library of ligands (e.g., biotin, curcumin derivatives, and antibody), resulting in high affinity toward (i) murine lung carcinoma (M109) and human breast cancer (MCF7) cell lines, even in a coculture environment with healthy cells and (ii) the ß-amyloid peptide 1-42 (Aß(1-42)), believed to be the most representative and toxic species in AD, both under its monomeric and fibrillar forms. In the case of AD, the ligand-functionalized NPs exhibited higher affinity toward Aß(1-42) species comparatively to other kinds of colloidal systems and led to significant aggregation inhibition and toxicity rescue of Aß(1-42) at low molar ratios.

Curcumin derivatives as new ligands of Aß peptides.

Curcumin derivatives with high chemical stability, improved solubility and carrying a functionalized appendage for the linkage to other entities, have been synthesized in a straightforward manner. All compounds retained Curcumin ability to bind Aß peptide oligomers without inducing their aggregation. Moreover all Curcumin derivatives were able to stain very efficiently Aß deposits.

Curcumin-decorated nanoliposomes with very high affinity for amyloid-ß1-42 peptide.

Amyloid ß (Aß) aggregates are considered as possible targets for therapy and/or diagnosis of Alzheimer disease (AD). It has been previously shown that curcumin targets Aß plaques and interferes with their formation, suggesting a potential role for prevention or treatment of AD. Herein, a click chemistry method was used to generate nanoliposomes decorated with a curcumin derivative, designed to maintain the planar structure required for interaction with Aß, as directly confirmed by Surface Plasmon Resonance experiments. Another type of liposomes was formed starting from curcumin-phospholipid conjugate, in which the planar structure of curcumin is disrupted. Both types of generated curcumin-decorated vesicles had mean diameters in the nano range (131-207 nm) and slightly negative ζ-potential values according to their lipid composition, and were stable for periods up to 20 days. They also demonstrated high integrity during incubation in presence of plasma proteins. Surface Plasmon Resonance experiments, measuring the binding of flowing liposomes to immobilized Aß1-42, indicated that the liposomes exposing the curcumin derivative (maintaining the planarity) have extremely high affinity for Aß1-42 fibrils (1-5 nM), likely because of the occurrence of multivalent interactions, whereas those exposing non-planar curcumin did not bind to Aß1-42. In summary, we describe here the preparation and characterization of new nanoparticles with a very high affinity for Aß1-42 fibrils, to be exploited as vectors for the targeted delivery of new diagnostic and therapeutic molecules for AD.

Carbohydrate mimetics and scaffolds: sweet spots in medicinal chemistry.

Several glycoprocessing enzymes and glycoreceptors have been recognized as important targets for therapeutic intervention. This concept has inspired the development of important classes of therapeutics, such as anti-influenza drugs inhibiting influenza virus neuraminidase, anti-inflammatory drugs targeting lectin-sialyl-Lewis X interaction and glycosidase inhibitors against HIV, Gaucher's disease, hepatitis and cancer. These therapeutics are mainly carbohydrate mimics in which proper modifications permit stronger interactions with the target protein, higher stability, better pharmacokinetic properties and easier synthesis. Furthermore, the conformational rigidity and polyfunctionality of carbohydrates stimulate their use as scaffolds for the generation of libraries by combinatorial decoration with different pharmacophores. This mini-review will present examples of how to exploit carbohydrates mimics and scaffolds in drug research.

Carbohydrate scaffolds in chemical genetic studies.

Small molecules altering protein functions as inhibitors, agonists or antagonists, find application in systems biology enabling an analysis of the in vivo consequences of these alterations. In this context carbohydrates are ideal tools, not only because they are involved in a variety of recognition phenomena of biological relevance, but also because they are ideal scaffolds to generate libraries of bioactive compounds. Examples of design, synthesis and biological assays of different carbohydrate based inhibitors or protein ligands are reported. Exploiting NMR methods, the binding between a small molecules (inhibitor or ligand) and a protein can be detected, the affinity measured, and the interaction topology defined. This set of information is useful not only to clarify the mechanism of protein-ligand interaction, but also to improve the design of new inhibitors/ligands. The multifunctionality and the conformational rigidity of carbohydrates make this class of compounds the ideal scaffolds to generate libraries exploiting the combinatorial approach. An example of solid phase combinatorial synthesis of a library of 37 compounds is reported.