Copper(II) complexes with 4-carbomethoxypyrrolidone functionalized PAMAM-dendrimers: an EPR study

The advanced synthetic modifications and applications of multifunctional PAMAM dendritic composites

The profound advances in dendrimer chemistry have led to new horizons in polymer science.

Characterization of a fluorescent 1,8-naphthalimide-functionalized PAMAM dendrimer and its Cu(ii) complexes as cytotoxic drugs: EPR and biological studies in myeloid tumor cells

The activity and interacting ability of a polyamidoamine (PAMAM) dendrimer modified with 4-N-methylpiperazine-1,8-naphthalimide units (termed D) and complexed by Cu(ii) ions, towards healthy and cancer cells were studied. Comparative electron paramagnetic resonance (EPR) studies of the Cu(ii)-D complex are presented: coordination mode, chemical structure, flexibility and stability of these complexes, in the absence and presence of myeloid cancer cells and peripheral blood mononuclear cells (PBMC). The interactions of Cu(ii) ions in the biological media at different equilibrium times were studied, highlighting different stability and interacting conditions with the cells. Furthermore, flow cytometry and confocal analysis, trace the peculiar properties of the dendrimers in PBMC and U937 cells. Indeed, a new probe (Fly) was used as a potential fluorescent tool for biological imaging of Cu(ii). The study highlights that dendrimer and, mainly, the Cu(ii) metallodendrimer are cytotoxic agents for the cells, specifically for U937 tumor cells, inducing mitochondrial dysfunction, ROS increase and lysosome involvement. The metallodendrimer shows antitumor selectivity, fewer affecting healthy PBMC, inducing a massive apoptotic cell death on U937 cells, in line with the high stability of this complex, as verified by EPR studies. The results underline the potentiality of this metallodendrimer to be used as anticancer drug.

Elaborated study of Cu(II) carbosilane metallodendrimers bearing substituted iminopyridine moieties as antitumor agents

Iminopyridine-decorated carbosilane metallodendrimers have recently emerged as a promising strategy in the treatment of cancer diseases. Their unique features such as the nanometric size, the multivalent nature and the structural perfection offer an extraordinary platform to explore structure-to-property relationships. Herein, we showcase the outstanding impact on the antitumor activity of a parameter not explored before: the iminopyridine substituents in meta position. New Cu(II) carbosilane metallodendrimers, bearing methyl or methoxy substituents in the pyridine ring, were synthesized and thoroughly characterized. Electron Paramagnetic Resonance (EPR) was exploited to unveil the properties of the metallodendrimers. This study confirmed the presence of different coordination modes of the Cu(II) ion (Cu-N₂O₂, Cu-N₄ and Cu-O₄), whose ratios were determined by the structural features of the dendritic molecules. These metallodendrimers exhibited IC₅₀ values in the low micromolar range (<6 μM) in tumor cell lines such as HeLa and MCF-7. The subsequent in vitro assays on both healthy (PBMC) and tumor (U937) myeloid cells revealed two key facts which improved the cytotoxicity and selectivity of the metallodrug: First, maximizing the Cu-N₂O₂ coordination mode; second, adequately selecting the pair ring-substituent/metal-counterion. The most promising candidates, G₁(-CH₃)Cl (8) and G₁(-OCH₃)NO₃(17), exhibited a substantial increase in the antitumor activity in U937 tumor cells, compared to the non-substituted counterparts, probably through two different ROS-production pathways.

DOTA Glycodendrimers as Cu(II) Complexing Agents and Their Dynamic Interaction Characteristics toward Liposomes

Copper (Cu)(II) ions, mainly an excess amount, play a negative role in the course of several diseases, like cancers, neurodegenerative diseases, and the so-called Wilson disease. On the contrary, Cu(II) ions are also capable of improving anticancer drug efficiency. For this reason, it is of great interest to study the interacting ability of Cu(II)-nanodrug and Cu(II)-nanocarrier complexes with cell membranes for their potential use as nanotherapeutics. In this study, the complex interaction between 1,4,7,10-tetraazacyclododecan-N,N',N'',N'''-tetraacetic acid (DOTA)-functionalized poly(propyleneimine) (PPI) glycodendrimers and Cu(II) ions and/or neutral and anionic lipid membrane models using different liposomes is described. These interactions were investigated via dynamic light scattering (DLS), ζ-potential (ZP), electron paramagnetic resonance (EPR), fluorescence anisotropy, and cryogenic transmission electron microscopy (cryo-TEM). Structural and dynamic information about the PPI glycodendrimer and its Cu(II) complexes toward liposomes was obtained via EPR. At the binding site Cu-N₂O₂ coordination prevails, while at the external interface, this coordination partially weakens due to competitive dendrimer-liposome interactions, with only small liposome structural perturbation. Fluorescence anisotropy was used to evaluate the membrane fluidity of both the hydrophobic and hydrophilic parts of the lipid bilayer, while DLS and ZP allowed us to determine the distribution profile of the nanoparticle (PPI glycodendrimer and liposomes) size and surface charge, respectively. From this multitechnique approach, it is deduced that DOTA-PPI glycodendrimers selectively extract Cu(II) ions from the bioenvironment, while these complexes interact with the liposome surface, preferentially with even more negatively charged liposomes. However, these complexes are not able to cross the cell membrane model and poorly perturb the membrane structure, showing their potential for biomedical use.

Insight into the antitumor activity of carbosilane Cu(ii)-metallodendrimers through their interaction with biological membrane models

Current cancer therapies present serious drawbacks including severe side-effects and development of drug resistance. Strategies based on nanosized metallodrugs combine the structural diversity and non-classical modes of action of metal complexes with the selectivity arising from the unique interaction of nanoparticles with biological membranes. A new family of water-soluble copper(ii) carbosilane metallodendrimers was synthesized and characterized as a nanotechnological alternative to current therapies. The interactions occurring over time between the dendrimers, at different generations (G₀ to G₂) and with different Cu(ii) counter-ions (nitrate vs. chloride), and cell-membrane models (cethyl-trimethylammonium bromide (CTAB) micelles and lecithin liposomes) were investigated using a computer-aided analysis of the electron paramagnetic resonance (EPR) spectra. The EPR analysis provided structural and dynamical information on the systems indicating that the increase in generation and the change of the Cu(ii) contra-ion - from nitrate to chloride - produce an increased relative amount and strength of interaction of the dendrimer with the model membranes. Interestingly, the stabilization effect produced a lower toxicity towards cancer cells. The cytotoxic effect of Cu(ii) metallodendrimers was verified by an in vitro screening in a selection of tumor cell lines, revealing the impact of multivalency on the effectivity and selectivity of the metallodrugs. As a proof-of-concept, first-generation dendrimer G₁-Cu(ONO₂)₂ was selected for in-depth in vitro and in vivo antitumor evaluation towards resistant prostate cancer. The Cu(ii)-metallodendrimers produced a significant tumor size reduction with no signs of toxicity during the experiment, confirming their promising potential as anticancer metallodrugs.

Advanced Drug Delivery Nanosystems for Shikonin: A Calorimetric and Electron Paramagnetic Resonance Study

Drug delivery is considered a mature scientific and technological platform for producing innovative medicines with nanosystems composed of intelligent bio-materials that carry active pharmaceutical ingredients forming advanced drug delivery nanosystems (aDDnSs). Shikonin and its enantiomer alkannin are natural products that have been extensively studied in vitro and in vivo for, among others, their antitumor activity, and various efforts have been made to prepare shikonin-loaded drug delivery systems. This study is focused on chimeric aDDnSs and specifically on liposomal formulations combining three lipids (egg-phosphatidylcholine; dipalmitoyl phosphatidylcholine; and distearoyl phosphatidylcholine) and a hyperbranched polymer (PFH-64-OH). Furthermore, PEGylated liposomal formulations of all samples were also prepared. Calorimetric techniques and electron paramagnetic resonance were used to explore and evaluate the interactions and stability of the liposomal formulations, showing that the presence of hyperbranched polymers promote the overall stability of the chimeric aDDnSs based on the drug release profile enhancement. Furthermore, results showed that polyethylene glycol enhances drug stabilization inside the liposomes, forming a stable and promising carrier for shikonin with improved characteristics.

EPR Characterization of Copper(II) Complexes of PAMAM-Py Dendrimers for Biocatalysis in the Absence and Presence of Reducing Agents and a Spin Trap

Polyamidoamine (PAMAM) dendrimers at different generations (from G2 to G6) were functionalized with pyridine (Py) groups at the external surface, and their complexation behavior with Cu(II) at increasing molar ratios between the ions and the Py groups was analyzed in the absence and presence of reducing agents and a spin trap. These Cu(II)-dendrimer complexes may be used as antitumor and antiamyloidogenesis drugs, similarly to other Cu(II)-dendrimer complexes, and as biocatalysts. Indeed, they have revealed to selectively catalyze molecular oxygen reduction to generate reactive oxygen species (ROS). A computer-aided electron paramagnetic resonance (EPR) study of these complexes allowed us to identify different complexes by increasing the Cu(II)/Py molar ratio for the different generations. Binuclear EPR-silent complexes were formed at the highest generations. The differently complexed Cu(II) ions showed a different capability to be reduced, starting from the most exposed at the dendrimer surface bearing a stable Cu(II)-Py₂ coordination. Cu(II)-G5 showed peculiar structural properties which probably favored its activity as biocatalyst. The spin trap was able to capture hydroxyl radicals, which became clearly EPR visible after all Cu(II) ions were reduced to Cu(I). This method may be used as a platform to study interactions of Cu(II) in nanosized macromolecules for biomedical purposes, mainly in biocatalysis involving redox reactions and formation of ROS.

Carbosilane metallodendrimers based on copper (II) complexes: Synthesis, EPR characterization and anticancer activity

A series of new organometallic carbosilane dendrimers functionalized with Copper(II) complex on the surface were synthesized and characterized as potential anticancer agents. These metallodendrimers were synthesized through the reaction of dendritic ligands containing N,N- and N,O- donor atoms able to act as chelating agents with CuCl₂ as metallic ion precursor. The structural characterization of these complexes was addressed through the use of different analytical and spectroscopical techniques. Particularly, an electron paramagnetic resonance study was performed to corroborate the coordination properties of these dendritic ligands. A preliminary study was carried out to establish the cytotoxicity of the new synthesized compounds in human prostate (PC3) and human cervical (HeLa) cancer cell lines in order to evaluate their potential as anticancer agents and compare their activity with other copper or analogous ruthenium metallodendrimers.

Being two is better than one—catalytic reductions with dendrimer encapsulated copper- and copper–cobalt-subnanoparticles

Copper and copper–cobalt subnanoparticles have been synthesized using 4-carbomethoxypyrrolidone terminated PAMAM-dendrimers as templates.

Multi-technique characterization of poly-L-lysine dendrigrafts-Cu(II) complexes for biocatalysis

Poly-L-lysine is a biocompatible polymer used for drug or gene delivery, for transport through cellular membranes, and as nanosized magnetic resonance imaging contrast agents. Cu(II)-poly-L-lysine complexes are of particular interest for their role in biocatalysis. In this study, poly-L-lysine dendrigrafts (DGLs) at different generations (G2, G3, and G4) are synthesized and characterized in absence and presence of Cu(II) by means of electron paramagnetic resonance (EPR), UV-Vis, potentiometric titration and circular dichroism (CD). The analysis is performed as a function of the [Cu(II)]/[Lys] (=R) molar ratio, pH and generation by identifying differently flexible complexes in different dendrimer regions. The amine sites in the lateral chains become increasingly involved with the increase of pH. The good agreement and complementarity of the results from the different techniques provide an integrate view of the structural and dynamic properties of Cu(II)-DGL complexes implementing their use as biocatalysts.

Combined EPR and molecular modeling study of PPI dendrimers interacting with copper ions: effect of generation and maltose decoration

Understanding the early onset of neurodegeneration is crucial to deploy specific treatments for patients before the process becomes irreversible. Copper has been proposed as a biomarker for many neurodegenerative disorders, being the ion released by pathologically unfolded proteins involved in many biochemical pathways. Dendrimers are macromolecules that bind metal ions with a large ion/ligand ratio, thus, allowing a massive collection of copper. This work provides structural information, obtained via molecular modeling and EPR, for the binding sites of copper in polypropyleneimine (PPI) dendrimers, especially in the maltose decorated form that has potential applications in diagnosis and therapies for various types of neurodegenerations. The analysis of the EPR spectra showed that, at the lowest Cu concentrations, the results are well supported by the calculations. Moreover, EPR analysis at increasing Cu(II) concentration allowed us to follow the saturation behavior of the interacting sites identified by the modeling study.

Comparative EPR studies of Cu(ii)-conjugated phosphorous-dendrimers in the absence and presence of normal and cancer cells

EPR analysis revealed peculiar structural and dynamical properties of anticancer-activeG3B–Cu(ii) in absence and presence of normal and cancer cells.

Study of the complexation of oxacillin in 1-(4-carbomethoxypyrrolidone)-terminated PAMAM dendrimers

The complexation of oxacillin to three generations of 1-(4-carbomethoxypyrrolidone)-terminated PAMAM dendrimers was studied with NMR in CD3OD and CDCl3. The stochiometries, which were determined from Job plots, were found to be both solvent- and generation-dependent. The dissociation constants (K(d)) and Gibbs energies for complexation of oxacillin into the 1-(4-carbomethoxypyrrolidone)-terminated PAMAM dendrimer hosts were determined by (1)H NMR titrations and showed weaker binding of oxacillin upon increasing the size (generation) of the dendrimer.