Marcelo Calderón

Stimuli-responsive nanogel composites and their application in nanomedicine

Nanogels are nanosized crosslinked polymer networks capable of absorbing large quantities of water. Specifically, smart nanogels are interesting because of their ability to respond to biomedically relevant changes like pH, temperature, etc. In the last few decades, hybrid nanogels or composites have been developed to overcome the ever increasing demand for new materials in this field. In this context, a hybrid refers to nanogels combined with different polymers and/or with nanoparticles such as plasmonic, magnetic, and carbonaceous nanoparticles, among others. Research activities are focused nowadays on using multifunctional hybrid nanogels in nanomedicine, not only as drug carriers but also as imaging and theranostic agents. In this review, we will describe nanogels, particularly in the form of composites or hybrids applied in nanomedicine.

Degradable Self-Assembling Dendrons for Gene Delivery – Experimental and Theoretical Insights into the Barriers to Cellular Uptake

This paper uses a combined experimental and theoretical approach to gain unique insight into gene delivery. We report the synthesis and investigation of a new family of second-generation dendrons with four triamine surface ligands capable of binding to DNA, degradable aliphatic-ester dendritic scaffolds, and hydrophobic units at their focal points. Dendron self-assembly significantly enhances DNA binding as monitored by a range of experimental methods and confirmed by multiscale modeling. Cellular uptake studies indicate that some of these dendrons are highly effective at transporting DNA into cells (ca. 10 times better than poly(ethyleneimine), PEI). However, levels of transgene expression are relatively low (ca. 10% of PEI). This indicates that these dendrons cannot navigate all of the intracellular barriers to gene delivery. The addition of chloroquine indicates that endosomal escape is not the limiting factor in this case, and it is shown, both experimentally and theoretically, that gene delivery can be correlated with the ability of the dendron assemblies to release DNA. Mass spectrometric assays demonstrate that the dendrons, as intended, do degrade under biologically relevant conditions over a period of hours. Multiscale modeling of degraded dendron structures suggests that complete dendron degradation would be required for DNA release. Importantly, in the presence of the lower pH associated with endosomes, or when bound to DNA, complete degradation of these dendrons becomes ineffective on the transfection time scale-we propose this explains the poor transfection performance of these dendrons. As such, this paper demonstrates that taking this kind of multidisciplinary approach can yield a fundamental insight into the way in which dendrons can navigate barriers to cellular uptake. Lessons learned from this work will inform future dendron design for enhanced gene delivery.

In vivo delivery of small interfering RNA to tumors and their vasculature by novel dendritic nanocarriers

New targets for RNA interference (RNAi)‐based cancer therapy are constantly emerging from the increasing knowledge on key molecular pathways that are paramount for carcinogenesis. Nevertheless, in vivo delivery of small interfering RNA (siRNA) remains a crucial challenge for therapeutic success. siRNAs on their own are not taken up by most mammalian cells in a way that preserves their activity. Moreover, when applied in vivo, siRNA‐based approaches are all limited by poor penetration into the target tissue and low silencing efficiency. To circumvent these limitations, we have developed novel polymerized polyglycerol‐based dendrimer core shell structures to deliver siRNA to tumors in vivo. These cationic dendrimers can strongly improve the stability of the siRNA, its intracellular trafficking, its silencing efficacy, and its accumulation in the tumor environment owing to the enhanced permeability and retention effect. Here, we show that our dendritic nanocarriers exhibited low cytotoxicity and high efficacy in delivering active siRNA into cells. With use of human glioblastoma and murine mammary adenocarcinoma cell lines as model systems, these siRNA‐dendrimer polyplexes silenced the luciferase gene, ectopically overexpressed in these cells. Importantly, significant gene silencing was accomplished in vivo within 24 h of treatment with our luciferase siRNA‐nanocarrier polyplexes, as measured by noninvasive intravital bioluminescence imaging. Moreover, our siRNA‐nanocarriers show very low levels of toxicity as no significant weight loss was observed after intravenous administration of the polyplexes. We show a proof of concept for siRNA delivery in vivo using a luciferase‐based model. We predict that in vivo silencing of important cell growth and angiogenesis regulator genes in a selective manner will justify this approach as a successful anticancer therapy.—Ofek, P., Fischer, W., Calderón, M., Haag, R., Satchi‐Fainaro, R. In vivo deliveryof small interfering RNAto tumors and their vasculature by novel dendritic nanocarriers. FASEB J. 24, 3122–3134 (2010). www.fasebj.org

Structure-biocompatibility relationship of dendritic polyglycerol derivatives.

Nanocarriers possess advanced physicochemical properties that improve bioavailability, enhance cellular dynamics, and control targetability in drug delivery. In particular, dendritic polyglycerol is a promising new biocompatible scaffold for drug delivery. The present explores the structure-biocompatibility relationship of dendritic polyglycerol (dPG) derivatives possessing neutral, cationic, and anionic charges. The effect of solution pH on the surface charge was studied in buffered aqueous solution between pH 4.8 and 7.4. Surface charge properties of dPG derivatives are discussed in terms of surface functionalities and compared with amine and hydroxyl terminated polyamidoamine (PAMAM) dendrimers. Zeta potential measurements and fluorescence quenching studies address the binding interactions of dPGs to bovine serum albumin in order to explore the applicability of dPG derivatives for systemic delivery. Cellular entry of dPG-dye conjugate was evaluated using A549 lung epithelial cells, while in vitro toxicity was studied for various dPGs and compared to PAMAM dendrimers, polyethyleneimine (PEI), dextran, and linear polyethylene glycol (PEG) using human hematopoietic cell line U-937. Cellular uptake studies of dye labelled dPGs inferred that the charged derivatives (dPG-sulfate and dPG-amine) are more rapidly internalized primarily inside the cytosol of A549 cells compared to the neutral dPG. The cell compatibility results show that the dendritic polyglycerols are as safe as linear PEG polymer or dextran, which indicates the suitability of dPG derivatives in delivering therapeutic agents systemically.

Functional dendritic polymer architectures as stimuli-responsive nanocarriers

Stimuli-responsive polymer architectures are molecular systems which evolve with an external signal. The observed changes are mainly decomposition, isomerization, polymerization, activation, supramolecular aggregation, and structural modifications of these molecules. The external stimuli, which can be combined in order to provoke these molecular changes, are numerous. In this review, we have chosen to present an overview on different mechanisms to impart responsiveness to dendritic polymers, with the particular aim of delivery and release of bioactive molecules.

Development of efficient acid cleavable multifunctional prodrugs derived from dendritic polyglycerol with a poly(ethylene glycol) shell

In an attempt to explore the potential of dendritic systems for the development of effective anticancer drug delivery systems, we explored a simple modular approach of preparing polyglycerol doxorubicin prodrugs, with flexibility for drug loading using an acid-sensitive hydrazone linker and further post-modification with poly(ethylene glycol) shell. The resulting drug polymer conjugates showed optimal properties for in vitro and in vivo applications because of their high water solubility, an appropriate size for passive tumor targeting, a high stability at physiological conditions, pronounced acid-sensitive properties, cellular internalization, and a favorable toxicity profile. Doxorubicin polyglycerol conjugates with a high drug loading ratio showed clearly improved antitumor efficacy over doxorubicin in an ovarian xenograft tumor model (A2780) inducing transient complete remissions thus demonstrating the potential of developing efficient multifunctional dendritic drug delivery using our modular approach.

Development of enzymatically cleavable prodrugs derived from dendritic polyglycerol

In this Letter we report the synthesis and in vitro studies of cleavable polymer-drug conjugates derived from dendritic polyglycerol and maleimide-bearing prodrugs of doxorubicin and methotrexate that are cleaved by cathepsin B. Cleavage properties and cytotoxicity of the new conjugates are presented.

Dendritic Polyglycerols with Oligoamine Shells Show Low Toxicity and High siRNA Transfection Efficiency in Vitro

RNA interference provides great opportunities for treating diseases from genetic disorders, infection, and cancer. The successful application of small interference RNA (siRNA) in cells with high transfection efficiency and low cytotoxicity is, however, a major challenge in gene-mediated therapy. Several pH-responsive core shell architectures have been designed that contain a nitrogen shell motif and a polyglycerol core, which has been prepared by a two-step protocol involving the activation of primary and secondary hydroxyl groups by phenyl chloroformate and amine substitution. Each polymer was analyzed by particle size and ζ potential measurements, whereas the respective polyplex formation was determined by ethidium bromide displacement assay, atomic force microscopy (AFM), and surface charge analysis. The in vitro gene silencing properties of the different polymers were evaluated by using a human epithelial carcinoma cell (HeLaS3) line with different proteins (Lamin, CDC2, MAPK2). Polyplexes yielded similar knockdown efficiencies as HiPerFect controls, with comparably low cytotoxicity. Therefore, these efficient and highly biocompatible dendritic polyamines are promising candidates for siRNA delivery in vivo.

Glycine-Terminated Dendritic Amphiphiles for Nonviral Gene Delivery

Development of nonviral vectors for the successful application of gene therapy through siRNA/DNA transfection of cells is still a great challenge in current research. (1, 2) In the present study, we have developed multivalent polyglycerol dendron based amphiphiles with well-defined molecular structures that express controlled glycine arrays on their surfaces. The structure-activity relationships with respect to the siRNA complexation, toxicity, and transfection profiles were studied with synthesized amphiphilic polycations. Our findings revealed that a second-generation amphiphilic dendrimer (G2-octaamine, 4) that has eight amine groups on its surface and a hydrophobic C-18 alkyl chain at the core of the dendron, acts as an efficient vector to deliver siRNA and achieve potent gene silencing by investigating the knockdown of luciferase and GAPDH gene activity in HeLa cells. Interestingly, the amphiphilic vector is nontoxic even at higher ratio of N/P 100. To the best of our knowledge this is the first example of successful in vitro siRNA transfection using dendritic amphiphiles. We believe that this supramolecular complex may serve as a new promising alternative for nonviral siRNA delivery systems and will be investigated for in vivo siRNA delivery in the future.

Thermosensitive nanogels based on dendritic polyglycerol and N-isopropylacrylamide for biomedical applications

In this paper we describe a methodology for the synthesis of thermoresponsive polyglycerol-based nanogels through precipitation polymerization. A systematic analysis of the preparative conditions and composition regarding the nanogel size is presented. The thermoresponsive properties of the synthesized nanogels, as well as the cytotoxicity and uptake in three different cell lines were investigated. The thermoresponsive behavior, the enhanced biocompatible profile, and the cell penetrating properties of the nanogels highlight the potential of such constructs for application as smart, environmentally-responsive materials.