Dendritic MRI Contrast Agents: An Efficient Prelabeling Approach Based on CuAAC

Synthesis of well-defined glycopolymers with highly ordered sugar units in the side chain via combining CuAAC reaction and ROMP: lectin interaction study in homo- and hetero-glycopolymers

The design of novel heterogeneous glycopolymers with different sugar motifs is of critical importance in the glycopolymer field.

Synthetic methodologies and spatial organization of metal chelate dendrimers and star and hyperbranched polymers

The synthetic methodologies, physico-chemical peculiarities, properties, and structure of metal chelate dendrimers and star and hyperbranched polymers are considered.

Dendrimer mediated clustering of bacteria: improved aggregation and evaluation of bacterial response and viability

Here, we evaluate how cationic gallic acid-triethylene glycol (GATG) dendrimers interact with bacteria and their potential to develop new antimicrobials. We demonstrate that GATG dendrimers functionalised with primary amines in their periphery can induce the formation of clusters in Vibrio harveyi, an opportunistic marine pathogen, in a generation dependent manner. Moreover, these cationic GATG dendrimers demonstrate an improved ability to induce cluster formation when compared to poly(N-[3-(dimethylamino)propyl]methacrylamide) [p(DMAPMAm)], a cationic linear polymer previously shown to cluster bacteria. Viability of the bacteria within the formed clusters and evaluation of quorum sensing controlled phenotypes (i.e. light production in V. harveyi) suggest that GATG dendrimers may be activating microbial responses by maintaining a high concentration of quorum sensing signals inside the clusters while increasing permeability of the microbial outer membranes. Thus, the reported GATG dendrimers constitute a valuable platform for the development of novel antimicrobial materials that can target microbial viability and/or virulence.

MRI-visible polymer based on poly(methyl methacrylate) for imaging applications

Macromolecular contrast agents are very attractive to afford efficient magnetic resonance imaging (MRI) visualization of implantable medical devices.

Easy access to heterobimetallic complexes for medical imaging applications via microwave-enhanced cycloaddition

The Cu(I)-catalysed Huisgen cycloaddition, known as “click” reaction, has been applied to the synthesis of a range of triazole-linked porphyrin/corrole to DOTA/NOTA derivatives. Microwave irradiation significantly accelerates the reaction. The synthesis of heterobimetallic complexes was easily achieved in up to 60% isolated yield. Heterobimetallic complexes were easily prepared as potential MRI/PET (SPECT) bimodal contrast agents incorporating one metal (Mn, Gd) for the enhancement of contrast for MRI applications and one “cold” metal (Cu, Ga, In) for future radionuclear imaging applications. Preliminary relaxivity measurements showed that the reported complexes are promising contrast agents (CA) in MRI.

In situ nanofabrication of hybrid PEG-dendritic-inorganic nanoparticles and preliminary evaluation of their biocompatibility

An in situ template fabrication of inorganic nanoparticles using carboxylated PEG-dendritic block copolymers of the GATG family is described as a function of the dendritic block generation, the metal (Au, CdSe) and metal molar ratio. The biocompatibility of the generated nanoparticles analysed in terms of their aggregation in physiological media, cytotoxicity and uptake by macrophages relates to the PEG density of the surface of the hybrids.

GATG dendrimers and PEGylated block copolymers: from synthesis to bioapplications

Dendrimers are synthetic macromolecules composed of repetitive layers of branching units that emerge from a central core. They are characterized by a tunable size and precise number of peripheral groups which determine their physicochemical properties and function. Their high multivalency, functional surface, and globular architecture with diameters in the nanometer scale makes them ideal candidates for a wide range of applications. Gallic acid-triethylene glycol (GATG) dendrimers have attracted our attention as a promising platform in the biomedical field because of their high tunability and versatility. The presence of terminal azides in GATG dendrimers and poly(ethylene glycol) (PEG)-dendritic block copolymers allows their efficient functionalization with a variety of ligands of biomedical relevance including anionic and cationic groups, carbohydrates, peptides, or imaging agents. The resulting functionalized dendrimers have found application in drug and gene delivery, as antiviral agents and for the treatment of neurodegenerative diseases, in diagnosis and as tools to study multivalent carbohydrate recognition and dendrimer dynamics. Herein, we present an account on the preparation and recent applications of GATG dendrimers in these fields.

Responsive linear-dendritic block copolymers

The combination of dendritic and linear polymeric structures in the same macromolecule opens up new possibilities for the design of block copolymers and for applications of functional polymers that have self-assembly properties. There are three main strategies for the synthesis of linear-dendritic block copolymers (LDBCs) and, in particular, the emergence of click chemistry has made the coupling of preformed blocks one of the most efficient ways of obtaining libraries of LDBCs. In these materials, the periphery of the dendron can be precisely functionalised to obtain functional LDBCs with self-assembly properties of interest in different technological areas. The incorporation of stimuli-responsive moieties gives rise to smart materials that are generally processed as self-assemblies of amphiphilic LDBCs with a morphology that can be controlled by an external stimulus. Particular emphasis is placed on light-responsive LDBCs. Furthermore, a brief review of the biomedical or materials science applications of LDBCs is presented.

Fast conversion of terminal thiocarbonylthio groups of RAFT polymers to “clickable” thiol groups via versatile sodium azide

A facile and fast way of converting thiocarbonylthio end groups of RAFT polymers to thiol groups was demonstrated.

Demonstration of a sucrose-derived contrast agent for magnetic resonance imaging of the GI tract

A scaffold bearing eight terminal alkyne groups was synthesized from sucrose, and copies of an azide-terminated Gd-DOTA complex were attached via copper(I)-catalyzed azide-alkyne cycloaddition. The resulting contrast agent (CA) was administered by gavage to C3H mice. Passage of the CA through the gastrointestinal (GI) tract was followed by T1-weighted magnetic resonance imaging (MRI) over a period of 47h, by which time the CA had exited the GI tract. No evidence for leakage of the CA from the GI tract was observed. Thus, a new, orally administered CA for MRI of the GI tract has been developed and successfully demonstrated.

Macromolecular Imaging Agents Containing Lanthanides: Can Conceptual Promise Lead to Clinical Potential?

Macromolecular magnetic resonance imaging (MRI) contrast agents are increasingly being used to improve the resolution of this noninvasive diagnostic technique. All clinically-approved T₁ contrast agents are small molecule chelates of gadolinium [Gd(III)] that affect bound water proton relaxivity. Both the small size and monomeric nature of these agents ultimately limits the image resolution enhancement that can be achieved for both contrast enhancement and pharmacokinetic/biodistribution reasons. The multimeric nature of macromolecules, such as polymers, dendrimers, and noncovalent complexes of small molecule agents with proteins, have been shown to significantly increase the image contrast and resolution due to their large size and ability to incorporate multiple Gd(III) chlelation sites. Also, macromolecular agents are advantageous as they have the ability to be designed to be nontoxic, hydrophilic, easily purified, aggregation-resistant, and have controllable three-dimensional macromolecular structure housing the multiple lanthanide chelation sites. For these reasons, large molecule diagnostics have the ability to significantly increase the relaxivity of water protons within the targeted tissues and thus the image resolution for many diagnostic applications. The FDA approval of a contrast agent that consists of a reversible, non-covalent coupling of a small Gd(III) chelate with serum albumin for blood pool imaging (marketed under the trade names of Vasovist and Ablivar) proved to be one of the first diagnostic agent to capitalize on these benefits from macromolecular association in humans. However, much research and development is necessary to optimize the safety of these unique agents for in vivo use and potential clinical development. To this end, recent work in the field of polymer, dendrimer, and noncovalent complex-based imaging agents are reviewed herein and the future outlook of this field is discussed.

Exploring the efficiency of gallic acid-based dendrimers and their block copolymers with PEG as gene carriers

The synthesis of a new family of amino-functionalized gallic acid-triethylene glycol (GATG) dendrimers and their block copolymers with polyethylene glycol (PEG) has recently being disclosed. In addition, these dendrimers have shown potential for gene delivery applications, as they efficiently complex nucleic acids and form small and homogeneous dendriplexes. On this basis, the present study aimed to explore the interaction of the engineered dendriplexes with blood components, as well as their stability, cytotoxicity and ability to enter and transfect mammalian cells. Results show that GATG dendrimers can form stable dendriplexes, protect the associated pDNA from degradation, and are biocompatible with HEK-293T cells and erythrocytes. More importantly, dendriplexes are effectively internalized by HEK-293T cells, which are successfully transfected. Besides, PEGylation has a marked influence on the properties of the resulting dendriplexes. While PEGylated GATG dendrimers have improved biocompatibility, the long PEG chains limit their uptake by HEK-293T cells, and thus, their ability to transfect them. As a consequence, the degree of PEGylation in dendriplexes containing dendrimer/block copolymer mixtures emerges as an important parameter to be modulated in order to obtain an optimized stealth formulation able to effectively induce the expression of the encoded protein.

Original submitted 29 November 2011; Revised submitted 8 March 2012; Published online 20 July 2012

Peripheral functionalization of dendrimers regulates internalization and intracellular trafficking in living cells

GATG (gallic acid-triethylene glycol) dendrimers represent appealing nanostructures for biomedical applications. The incorporation of specific ligands and targeting and imaging agents on their surface has resulted in promising tools in diagnosis and drug delivery. With the aim to further explore the versatility of GATG dendrimers in the biomedical field, in this work we study the effect of peripheral substitution on their uptake and intracellular trafficking in living cells. To this end, peripheral groups with different physicochemical properties and biological relevance have been installed on the surface of GATG dendrimers, and their interactions, uptake efficacy, and specificity for certain cell populations studied by confocal microscopy. Finally, this information was used to design a pH-sensitive drug delivery system for the selective release of cargo molecules inside cells after lysosomal localization. These results along with the easy functionalization and modular architecture of GATG dendrimers reveal these systems as promising nanotools in biomedicine.