Utilization of dendritic framework as a multivalent ligand: a functionalized gadolinium(III) carrier with glycoside cluster periphery

MRI Contrast Agents in Glycobiology

Molecular recognition involving glycoprotein-mediated interactions is ubiquitous in both normal and pathological natural processes. Therefore, visualization of these interactions and the extent of expression of the sugars is a challenge in medical diagnosis, monitoring of therapy, and drug design. Here, we review the literature on the development and validation of probes for magnetic resonance imaging using carbohydrates either as targeting vectors or as a target. Lectins are important targeting vectors for carbohydrate end groups, whereas selectins, the asialoglycoprotein receptor, sialic acid end groups, hyaluronic acid, and glycated serum and hemoglobin are interesting carbohydrate targets.

Polyhydroxylated GdDTPA-derivatives as high relaxivity magnetic resonance imaging contrast agents

Novel GdDTPA-like complexes bearing differently branched, highly hydrophilic, gluconyl moieties were synthesized to obtain high relaxivity agents (∼20 mM⁻¹ s⁻¹ at 25 °C) over a wide range of imaging fields (0.5–3 T).

The role of cerium(iii)/yttrium(iii) nitrate hexahydrate salts on electroactive β phase nucleation and dielectric properties of poly(vinylidene fluoride) thin films

Electroactive β phase nucleation in cerium/yttrium nitrate hexahydrate salt modified PVDF thin filmsviaformation of hydrogen bonds.

Synthesis, in vitro and in vivo studies of Gd-DTPA-XDA-D1-Glc(OH) complex as a new potential MRI contrast agent

A new type of dendritic molecules Gd-DTPA-XDA-D1-Glc(OH), which work as a functionalized ligand coordinating gadolinium(III) ion at the center of their frameworks with two glucose moieties on the molecular surfaces, were readily synthesized with high yield. The structures were established by IR, (1)H, (13)C NMR, and mass spectral studies. Its bio-distribution patterns were evaluated on rats.

Dendritic polymers in biomedical applications: from potential to clinical use in diagnostics and therapy

Dendrimers are characterized by a combination of high end-group functionality and a compact, precisely defined molecular structure. These characteristics can be used in biomedical applications, for example, for the amplification or multiplication of effects on a molecular level, or to create extremely high local concentrations of drugs, molecular labels, or probe moieties. A brief summary of the current state of the art in the field is given, and focuses on the application of dendrimers both in diagnostics as well as in therapy. In diagnostics, dendrimers that bear GdIII complexes are used as contrast agents in magnetic resonance imaging. DNA dendrimers have potential for routine use in high-throughput functional genomic analysis, as well as for DNA biosensors. Dendrimers are also being investigated for therapeutics, for example, as carriers for controlled drug delivery, in gene transfection, as well as in boron neutron-capture therapy. Furthermore, the antimicrobial activity of dendrimers has been studied.

Glyconanoparticles allow pre-symptomatic in vivo imaging of brain disease

Initial recruitment of leukocytes in inflammation associated with diseases such as multiple sclerosis (MS), ischemic stroke, and HIV-related dementia, takes place across intact, but activated brain endothelium. It is therefore undetectable to symptom-based diagnoses and cannot be observed by conventional imaging techniques, which rely on increased permeability of the blood-brain barrier (BBB) in later stages of disease. Specific visualization of the early-activated cerebral endothelium would provide a powerful tool for the presymptomatic diagnosis of brain disease and evaluation of new therapies. Here, we present the design, construction and in vivo application of carbohydrate-functionalized nanoparticles that allow direct detection of endothelial markers E-/P-selectin (CD62E/CD62P) in acute inflammation. These first examples of MRI-visible glyconanoparticles display multiple copies of the natural complex glycan ligand of selectins. Their resulting sensitivity and binding selectivity has allowed acute detection of disease in mammals with beneficial implications for treatment of an expanding patient population suffering from neurological disease.

A glycosylated complex of gadolinium, a new potential contrast agent for magnetic resonance angiography?

A new low-molecular weight dendrimer-like MRI contrast agent (Gd-D1) has been synthesized and characterized in vitro by proton and oxygen-17 relaxometry. Its pharmacokinetic parameters and biodistribution patterns were evaluated on rats. Its in vitro and in vivo properties, that is, the longitudinal relaxivity (defined as the increase of the water proton longitudinal relaxation rate induced by one millimole per liter of Gd-D1) equal to 5.6s(-1)mM(-1) at 20 MHz and 310 K, the elimination half-time equal to 85 min, and its low accumulation in liver and spleen, underline its potential as a blood-pool MRI contrast agent.

Glycoconjugates of gadolinium complexes for MRI applications

Examples of C-4 symmetric, medium MW conjugates incorporating 12 glucose or galactose groups linked via four dendritic wedges to a central Gd complex have been characterised; their enhanced relaxivity is interpreted in terms of effective motional coupling and large contributions from second sphere water molecules.

Synthesis and biological evaluation of mannose-6-phosphate-coated multivalent dendritic cluster glycosides

The synthesis of multivalent dendritic cluster glycosides of mannopyranosyl-6-phosphate is presented. Poly(amido amine)-based dendrimers of 0.5-3.5 generations, containing carboxylic acid peripheral functionalities, were utilized so as to install 4, 8, 16 and 32 mannopyranosyl-6-phosphate residues at the peripheries of the dendrimers. Amide bond formation between an amine-tethered mannopyranosyl-6-phosphate monomer unit and carboxylic acid-functionalized dendrimers was conducted to synthesize the dendritic cluster glycosides. The constitutions of the Man-6-P-containing dendrimers were assessed by 1H, 13C and 31P NMR spectroscopies and the sugar content analysis by a resorcinol assay. Preliminary biological studies with few newly synthesized Man-6-P-containing dendrimers showed that these compounds could bind the purified goat liver mannose 6-phosphate receptor (MPR 300) protein.

Synthesis of DTPA-conjugated (1,4)-linked 2-aminoglycosides varying in the anomeric configuration and their MRI contrast effect

We describe the efficient synthesis of DTPA-conjugated oligosaccharides composed of alpha- and/or beta-linked tri to monoglucosamines. Gd(iii) complex with DTPA-conjugated chitotriitol has been reported to be an effective MRI contrast agent. In order to elucidate the structure-property relationships, we planned to synthesize the DTPA-conjugated 2-amino-tri-, di-, and monosaccharides varying in configuration at the anomeric positions and the C2 position on the reducing end. Our strategy for the synthesis of the DTPA-conjugated oligosaccharides involves O-perbenzyl protected 2-amino-tri-, di-, and monosaccharides as key intermediates. The 2-aminoglycosides were prepared by non-selective glycosidation of 2-azido-2-deoxyglycosyl donors, followed by separation of two anomeric isomers. Although the synthesis involves separation of the stereoisomers, it circumvents not only the careful tuning of reaction conditions, but also the time-consuming preparation of glycosyl donors attached to different protecting groups. The protected 2-aminoglycosides were converted to the fully deprotected DTPA-conjugated tri- to monosaccharides by the same operation. MRI phantom study using the Gd(III) complexes of DTPA-conjugated oligosaccharides indicates that the number of the monosaccharide units was critical for enhancing the relative signal intensity of water protons per Gd, and various stereoisomers would be candidate scaffolds for MRI contrast agents.

Enabling ScFvs as multi-drug carriers: a dendritic approach

To enable scFvs as multi-drug carriers, we designed and synthesized dendritic linker molecules bearing up to nine chlorambucil residues at the branch ends. A maleimide group was used at the focal point of the dendron for easy linkage to the scFv. Originally designed molecules showed poor water solubility. To address this problem, a lysine residue with an unprotected carboxylic acid group was inserted into the dendron branches. The new molecules showed excellent water solubility and are now suitable for conjugation. Such dendritic molecules will allow studies to understand the relationship between the drug/antibody ratio and the potency of the immunoconjugates. The dendritic approach could also be applied to drugs other than chlorambucil and carriers other than scFvs to greatly increase the drug/carrier ratio.

Luminescent lanthanide ions hosted in a fluorescent polylysin dendrimer. Antenna-like sensitization of visible and near-infrared emission

We have investigated the complexation of the luminescent Nd(3+), Eu(3+), Gd(3+), Tb(3+), Er(3+), and Yb(3+) ions by a polylysin dendrimer containing 21 amide groups in the interior and, in the periphery, 24 chromophoric dansyl units which show an intense fluorescence band in the visible region. Most of the experiments were performed in 5:1 acetonitrile/dichloromethane solution at 298 K. On addition of the lanthanide ions to dendrimer solutions, the fluorescence of the dansyl units is quenched; in Nd(3+), Er(3+), and Yb(3+), a sensitized near-infrared emission of the lanthanide ion is observed. At low metal ion concentrations, each dendrimer hosts only one metal ion and when the hosted metal ion is Nd(3+) or Eu(3+), the fluorescence of all the 24 dansyl units of the dendrimer is quenched with unitary efficiency. Quantitative measurements were performed in a variety of experimental conditions, including protonation of the dansyl units and measurements in rigid matrix at 77 K where a sensitized Eu(3+) emission could also be observed. The results obtained have been interpreted on the basis of the energy levels and redox potentials of dendrimer and metal ions.