Alejandro Díaz-Moscoso

Polycationic amphiphilic cyclodextrins for gene delivery: synthesis and effect of structural modifications on plasmid DNA complex stability, cytotoxicity, and gene expression.

A molecular-diversity-oriented approach for the preparation of well-defined polycationic amphiphilic cyclodextrins (paCDs) as gene-delivery systems is reported. The synthetic strategy takes advantage of the differential reactivity of primary versus secondary hydroxyl groups on the CD torus to regioselectively decorate each rim with cationic elements and lipophilic tails, respectively. Both the charge density and the hydrophobic-hydrophilic balance can be finely tuned in a highly symmetrical architecture that is reminiscent of both cationic lipids and cationic polymers, the two most prominent types of nonviral gene vectors. The monodisperse nature of paCDs and the modularity of the synthetic scheme are particularly well suited for structure-activity relationship studies. Gel electrophoresis revealed that paCDs self-assemble in the presence of plasmid DNA (pDNA) to provide homogeneous, stable nanoparticles (CDplexes) of 70-150 nm that fully protect pDNA from the environment. The transfection efficiency of the resulting CDplexes has been investigated in vitro on BNL-CL2 and COS-7 cell lines in the absence and presence of serum and found to be intimately dependent on architectural features. Facial amphiphilicity and the presence of a cluster of cationic and hydrogen-bonding centers for cooperative and reversible complexation of the polyanionic DNA chain is crucial to attain high transgene expression levels with very low toxicity profiles. Further enhancement of gene expression, eventually overcoming that of polyplexes from commercial polyethyleneimine (PEI) polymers (22 kDa), is achieved by building up space-oriented dendritic polycationic constructs.

Mannosyl-coated nanocomplexes from amphiphilic cyclodextrins and pDNA for site-specific gene delivery

Fully homogeneous facial amphiphiles consisting in a cyclodextrin (CD) platform onto which a polycationic cluster and a multi-tail hydrophobic moiety have been installed (polycationic amphiphilic CDs; paCDs) self-organized in the presence of plasmid DNA to form nanometric complexes (CDplexes) which exhibit broad-range transfection capabilities. We hypothesized that biorecognizable moieties located at the hydrophilic rim in the CD scaffold would be exposed at the surface of the corresponding nanoparticles after DNA-promoted aggregation, endowing the system with molecular recognition abilities towards cell receptors. This concept has been demonstrated by developing an efficient synthetic strategy for the preparation of multivalent polycationic glyco-amphiphilic CDs (pGaCDs). Self-assembled nanoparticles obtained from mannosylated pGaCDs and pDNA (average hydrodynamic diameter 80 nm) have been shown to be specifically recognized by mannose-specific lectins, including concanavalin A (Con A) and the human macrophage mannose receptor (MMR). Further macrophage adhesion studies indicated that unspecific binding, probably due to electrostatic interactions with negatively charged cell membrane components, can also operate. The relative specific versus non-specific internalization is dependent on the pGaCD:pDNA proportion, being optimal at a protonable nitrogen/phosphate (N/P) ratio of 5. The resulting GlycoCDplexes were shown to specifically mediate transfection in Raw 264.7 (murine macrophage) cells expressing the mannose-fucose receptor in vitro. FACS experiments confirmed that transfection using these nanoparticles is mannose-dependent, supporting the potential of the approach towards vectorized gene delivery.

Insights in cellular uptake mechanisms of pDNA–polycationic amphiphilic cyclodextrin nanoparticles (CDplexes)

It is generally recognized that the major obstacle to efficient gene delivery is cellular internalization and endosomal escape of the DNA. Recently, we have developed a modular strategy for the preparation of well-defined polycationic amphiphilic cyclodextrins (paCDs) capable of complexing and compacting DNA into homogeneous nanoparticles (<70nm). Since paCDs resemble both cationic polymers and cationic lipids, it is conceivable that the corresponding pDNA-paCD nanoparticles (CDplexes) might use the cell internalization and endosomal escape mechanisms described for both lipoplexes and polyplexes. To verify this hypothesis, we have now investigated the uptake and transfection efficiencies of CDplexes in the presence of several inhibitors of endocytosis, namely chlorpromazine, genistein, dynasore and methylated beta-cyclodextrin (MbCD). Our data show that CDplexes obtained from paCD 1, which ranks among the most efficient paCD gene vectors reported up to date, are internalized by both clathrin-dependent (CDE) and clathrin-independent endocytosis (CIE), both processes being cholesterol- and dynamin-dependent. We observed that the largest fraction of gene complexes is taken up via CDE, but this fraction is less relevant for transfection. The smaller fraction that is internalized via the CIE pathway is predominantly responsible for successful transfection.

Efficient Transfection of Hepatocytes Mediated by mRNA Complexed to Galactosylated Cyclodextrins

In this study, we aimed at specific targeting of polycationic amphiphilic cyclodextrins (paCDs) to HepG2 cells via the asialoglycoprotein receptor (ASGPr). The transfection efficiencies of paCDs modified with galactose moieties were evaluated. In preliminary experiments, attempts to transfect HepG2 cells with pDNA complexed with different modified paCDs resulted in very low transfection levels. In additional series of experiments, we found out that nucleic acid/cyclodextrin complexes (CDplexes) were efficiently taken up by the cells and that photochemical internalization, which facilitates release from endosomes, did not improve transfection. Further experiments showed that pDNA can be readily released from the CDplexes when exposed to negatively charged vesicles. These observations imply that the lack of transfection cannot be attributed to a lack of internalization, release of CDplexes from the endosomal compartment, or release of free pDNA from the CDplexes. This in turn suggests that the nuclear entry of the pDNA represents the main limiting factor in the transfection process. To verify that HepG2 cells were transfected with targeted CDplexes containing mRNA, which does not require entry into the nucleus for being translated. With mRNA encoding the green fluorescent protein, fractions of GFP-positive cells of up to 31% were obtained. The results confirmed that the galactosylated complexes are specifically internalized via the ASGPr.

Symmetry Complementarity-Guided Design of Anthrax Toxin Inhibitors Based on β-Cyclodextrin: Synthesis and Relative Activities of Face-Selective Functionalized Polycationic Clusters

Three new series of potential anthrax toxin inhibitors based on the β‐cyclodextrin (βCD) scaffold were developed by exploiting face‐selective CuI‐catalyzed azide–alkyne 1,3‐cycloadditions, amine–isothiocyanate coupling, and allyl group hydroboration–oxidation/hydroxy → amine replacement reactions. The molecular design follows the “symmetry–complementarity” concept between homogeneously functionalized polycationic βCD derivatives and protective antigen (PA), a component of anthrax toxin known to form C7‐symmetric pores on the cell membrane used by lethal and edema factors to gain access to the cytosol. The synthesis and antitoxin activity of a collection of βCD derivatives differing in the number, arrangement, and face location of the cationic elements are reported herein. These results set the basis for a structure–activity relationship development program of new candidates to combat the anthrax threat.

Cell uptake mechanisms of glycosylated cationic pDNA–cyclodextrin nanoparticles

The incorporation of carbohydrate functional elements in the architecture of polycationic amphiphilic cyclodextrins (paCDs) provides glycosylated paCDs (pGaCDs) that form transfectious nanocomplexes (glycoCDplexes) with pDNA. In this study, we aimed at elucidating the internalization mechanisms at play and their incidence in transfection efficiency for glycoCDplexes formulated with 6-amino-6-deoxy-β-D-glucopyranosyl-appended pGaCDs in comparison with mannosylated and non-glycosylated congeners. Preliminary data showed a relatively high uptake of the 6-aminoglucosylated nanocomplexes by BNL-CL2 hepatocytes that correlated with a strong affinity towards the galactose-specific peanut agglutinin (PNA) lectin, suggesting that the galactose-binding asialoglycoprotein receptor at the surface of hepatocytes might be involved in glycoCDplex internalization. Transfection kinetics, internalization rates and protein expression data in BNL-CL2 ASGPR-expressing cells and COS-7 ASGPR-devoid epithelial cells in the absence and presence of different inhibitors of clathrin-dependent (chlorpromazine), caveolae-dependent (genistein) and macropinocytosis (amiloride) endocytic routes evidenced significant differences in cell uptake pathways and fate of glycoCDplexes as compared with CDplexes. Most importantly, such differences were dependent on the cell type and on the carbohydrate coating moiety. Clathrin-mediated uptake in BNLCL-2 cells is particularly favored for the 6-amino-6-deoxyglucose CDplexes, supporting the interplay of specific recognition phenomena. Competitive uptake and transfection experiments conducted in the presence of asialofetuin or of a polyclonal ASGPR-antibody, as well as siRNA-mediated ASGPR-specific gene knockdown, supported the involvement of ASGPR, firmly demonstrating the dual role of the 6-amino-6-deoxyglucose motif as DNA and lectin receptor ligand. The results reinforce the use of carbohydrates in glycoCDplexes to modulate cellular uptake and transfection capabilities in a cell-dependent manner.

Stereoselective Synthesis of Lower and Upper Rim Functionalized Tetra-α Isomers of Calix[4]pyrroles

Hydroxyaryl alkyl ketones with functionalized alkyl chains often fail to produce the corresponding tetra-α calix[4]pyrroles in Brönsted acid mediated condensations with pyrrole. A remarkable effect exerted by the addition of methyltrialkylammonium chloride during the acid-mediated syntheses of a series of meso-(tetrahydroxyaryl)-meso-tetraalkylcalix[4]pyrroles featuring alkyl terminal chloro or ester groups is reported. The ammonium salt enhances the cyclocondensation reaction and induces the almost exclusive formation of the tetra-α isomers.

Synthesis and Dimerization Studies of a Lipophilic Photoresponsive Aryl‐Extended Tetraurea‐Calix[4]pyrrole

We describe the syntheses of the lipophilic aryl-extended α,α,α,α-tetraurea-phenyl-calix[4]pyrrole 1, featuring four appended azo-phenyl groups with two tert-butoxy carbonyl meta-substituents and its photo-inactive counterpart 2. In CD2 Cl2 solutions, both tetraurea-calix[4]pyrroles self-assemble into dimeric capsules by encapsulating one molecule of a suitable bis-N-oxide or two molecules of a mono-N-oxide. The dimeric capsules are mainly stabilized by a cyclic array of sixteen hydrogen bonds established between the eight unidirectionally oriented urea groups. Photoirradiation experiments demonstrated the trans-to-cis isomerization of the azo-phenyl groups and the formation of a plethora of stereo isomeric cis-azo-enriched capsular assemblies. The highly cis-azo enriched capsular assemblies seem to show a reduced stability and their involvement in equilibria with non-capsular counterparts that also bind the N-oxides. The thermally induced cis-to-trans interconversion processes demonstrated the reversibility of the photoisomerization and the photostability of most binding partners. An equimolar mixture of the two tetraureas produced two homodimeric capsules and the heterodimeric counterpart in a ratio close to statistical distribution.

Harmonized tuning of nucleic acid and lectin binding properties with multivalent cyclodextrins for macrophage-selective gene delivery

Polycationic amphiphilic cyclodextrins (paCDs) have been shown to behave as efficient non-viral gene carriers paralleling the efficacy of commercial vectors towards a variety of cell lines. Their molecular framework and modular design allow the installation of saccharidic antennae to promote specific carbohydrate–protein interactions, thus potentially endowing them with selective targeting abilities. Yet, the presence of these additional functionalities onto the polycationic cluster may hamper paCD self-assembly and nucleic acid condensation. In this report we describe the influence of paCD mannosylation extent on paCD-pDNA nanocomplex stability as well as the consequences of varying glycotope density on mannose-specific lectin recognition and gene delivery capabilities. The work aims at exploring the potential of this approach to optimize both properties in order to modulate cell transfection selectivity.