Elizabeth R. Gillies

Dendrimers and dendritic polymers in drug delivery.

The unique properties of dendrimers, such as their high degree of branching, multivalency, globular architecture and well-defined molecular weight, make them promising new scaffolds for drug delivery. In the past decade, research has increased on the design and synthesis of biocompatible dendrimers and their application to many areas of bioscience including drug delivery, immunology and the development of vaccines, antimicrobials and antivirals. Recent progress has been made in the application of biocompatible dendrimers to cancer treatment, including their use as delivery systems for potent anticancer drugs such as cisplatin and doxorubicin, as well as agents for both boron neutron capture therapy and photodynamic therapy.

A single dose of doxorubicin-functionalized bow-tie dendrimer cures mice bearing C-26 colon carcinomas

The antitumor effect of doxorubicin (DOX) conjugated to a biodegradable dendrimer was evaluated in mice bearing C-26 colon carcinomas. An asymmetric biodegradable polyester dendrimer containing 8–10 wt % DOX was prepared. The design of the dendrimer carrier optimized blood circulation time through size and molecular architecture, drug loading through multiple attachment sites, solubility through PEGylation, and drug release through the use of pH-sensitive hydrazone linkages. In culture, dendrimer–DOX was >10 times less toxic than free DOX toward C-26 colon carcinoma cells after exposure for 72 h. Upon i.v. administration to BALB/c mice with s.c. C-26 tumors, dendrimer–DOX was eliminated from the serum with a half-life of 16 ± 1 h, and its tumor uptake was ninefold higher than i.v. administered free DOX at 48 h. In efficacy studies performed with BALB/c mice bearing s.c. C-26 tumors, a single i.v. injection of dendrimer–DOX at 20 mg/kg DOX equivalents 8 days after tumor implantation caused complete tumor regression and 100% survival of the mice over the 60-day experiment. No cures were achieved in tumor-implanted mice treated with free DOX at its maximum tolerated dose (6 mg/kg), drug-free dendrimer, or dendrimer–DOX in which the DOX was attached by means of a stable carbamate bond. The antitumor effect of dendrimer–DOX was similar to that of an equimolar dose of liposomal DOX (Doxil). The remarkable antitumor activity of dendrimer–DOX results from the ability of the dendrimer to favorably modulate the pharmacokinetics of attached DOX.

A new approach towards acid sensitive copolymer micelles for drug delivery.

A new micellar system capable of selective release of its contents under mildly acidic conditions is described.

Enhanced cell uptake of superparamagnetic iron oxide nanoparticles functionalized with dendritic guanidines.

Magnetic resonance imaging (MRI) is a powerful tool for the diagnosis of disease and the study of biological processes such as cancer metastasis and inflammation. Superparamagnetic iron oxide (SPIO) nanoparticles have been shown to be effective contrast agents for labeling cells to provide high sensitivity in MRI, but this sensitivity depends on the ability to label cells with sufficient quantities of SPIO, which can be challenging for nonphagocytic cells such as cancer cells. To address this issue, a novel cell-penetrating polyester dendron with peripheral guanidines was developed and conjugated to the surface of SPIO. The functionalized nanoparticles were characterized by transmission electron microscopy, infrared spectroscopy, and dynamic light scattering, and it was found that the surface functionalization reaction proceeded to completion and did not have any adverse effects on the SPIO. In GL261 mouse glioma cells, the dendritic guanidine exhibited remarkably similar cell-penetrating capabilities to the HIV-Tat(47-57) peptide for the transport of fluorescein, and when conjugated to SPIO, it provided significantly enhanced uptake in comparison with nanoparticles having no dendron or dendrons with hydroxyl or amine peripheries. This uptake led to substantial decreases in the transverse relaxation time (T(2)) of labeled cells relative to control cells. While the nanoparticles functionalized with dendritic guanidines exhibited somewhat greater toxicity than those functionalized with dendrons having hydroxyl or amine peripheries, they were still relatively nontoxic at the low concentrations required for labeling.

Development of acid-sensitive copolymer micelles for drug delivery*

In recent years, supramolecular micellar assemblies formed from amphiphilic block copolymers have been receiving attention as potential drug carriers. The size of the carriers is ideal for avoiding rapid renal exclusion and reticuloendothelial uptake, and enables them to be targeted to certain tissues such as tumors. One important issue determining the effectiveness of a micellar drug carrier is the ability to control the time over which drug release takes place, or to possibly trigger drug release at a specific location or time. The mildly acidic pH encountered in tumor and inflammatory tissues as well as in the endosomal and lysosomal compartments of cells has inspired the development of micellar carriers capable of releasing their drug load in response to small changes in pH. One approach to the development of these systems has been to incorporate “titratable” groups such as amines and carboxylic acids into the copolymer backbone, thus altering the solubility of the polymer upon protonation and disrupting micelle formation. Another approach has been to incorporate acid-degradable linkages into the copolymer, either for direct attachment of the drug, or to cause a structural change of such magnitude that micellar integrity is lost and the drug is released.

Surface Functionalization of Nanomaterials with Dendritic Groups: Toward Enhanced Binding to Biological Targets

A diverse array of nanomaterials ranging from polymer assemblies to nanoparticles has been under development for biomedical applications in recent years. A key aspect of these applications is the ability to target the materials to the desired locations in vivo by exploiting their size or through the conjugation of active targeting groups. While nanoscale scaffolds may provide advantages such as the multivalent presentation of targeting ligands, the binding of these ligands may also be inhibited by interfering polymer chains at their surfaces. This aspect was investigated here by preparing poly(butadiene-block-ethylene oxide) vesicles and dextran-coated iron oxide nanoparticles functionalized with dendritic and nondendritic displays of mannose, a well-known multivalent ligand. The binding of these systems to the mannose-binding protein Concanavalin A was compared using a hemagglutination assay. It was found that the dendritic systems exhibited 1-2 orders of magnitude enhancement in binding affinity relative to the nondendritic displays. This result is attributed to the ability of the dendritic groups to overcome steric inhibition by polymer chains at the material surface and also to the presentation of ligands in localized clusters. It is anticipated that these results should be applicable to a wide range of nanomaterials with polymers at their surfaces and that the method by which biological ligands are conjugated to the surfaces of nanoparticles and polymer assemblies should be carefully considered.

Amplified release through the stimulus triggered degradation of self-immolative oligomers, dendrimers, and linear polymers

In recent years, numerous delivery systems based on polymers, dendrimers, and nano-scale assemblies have been developed to improve the properties of drug molecules. In general, for the drug molecules to be active, they must be released from these delivery systems, ideally in a selective manner at the therapeutic target. As the changes in physiological conditions are relatively subtle from one tissue to another and the concentrations of specific enzymes are often quite low, a release strategy involving the amplification of a biological signal is particularly attractive. This article describes the development of oligomers, dendrimers, and linear polymers based on self-immolative spacers. This new class of molecules is designed to undergo a cascade of intramolecular reactions in response to the cleavage of a trigger moiety, resulting in molecular fragmentation and the release of multiple reporter or drug molecules. Progress in the development of these materials as drug delivery vehicles and sensors will be highlighted.

Curcumin, a promising anti-cancer therapeutic: a review of its chemical properties, bioactivity and approaches to cancer cell delivery

The development of new anti-cancer treatments with greater efficacy and fewer side effects remains a significant challenge of modern scientific and medical research. Curcumin, a natural polyphenol found in the dietary spice turmeric, has been demonstrated to inhibit cancer cell survival and proliferation, and to induce apoptosis without promoting the development of side effects. However, due to its sparing solubility and low bioavailability, curcumin has not yet been clinically used to treat cancer. This review describes the main physicochemical properties of curcumin, including its chemical structure, stability, and degradation products as a function of pH and temperature. It also describes the proposed mechanisms by which curcumin exhibits anti-cancer activity. Finally, we review the various approaches that have been studied to enhance the solubility and bioavailability of curcumin, including the preparation of co-crystals, and the development of delivery systems based on liposomes, micelles, exosomes, nanoparticles and dendrimers.

NON-COVALENTLY FUNCTIONALIZED SINGLE-WALLED CARBON NANOTUBE FOR TOPICAL SIRNA DELIVERY INTO MELANOMA

RNAi can specifically regulate gene expression, but efficient delivery of siRNA in vivo is difficult while it has been shown that modified carbon nanotubes (CNT) protect siRNA, facilitate entry into cells and enhance transdermal drugs delivery. Single-walled carbon nanotubes (SWCNT) were functionalized non-covalently with succinated polyethyleimine (PEI-SA). In this study, the water soluble CNT, PEI-SA/CNT (IS/C) were isolated and characterized, the gene silencing induced by IS/C/siRNA complexes was achieved in vitro in B16-F10 cells. In vivo delivery was topically applied to shaved mouse skin, as well as topically to a C57BL/6 mice melanoma model. We found significant uptake of Cy3-labeled siRNA specific to Braf (siBraf) and gene silencing in the tumor tissue. Treatment with IS/C/siBraf resulted in attenuation of tumor growth over a 25-day period. This new delivery method has provided a new possibility for future siRNA delivery and therapy, which providing insight for the potential application and development of CNT-based siRNA delivery.

Raman enhancement of azobenzene monolayers on substrates prepared by Langmuir-Blodgett deposition and electron-beam lithography techniques.

Nanostructured metallic platforms for Raman enhancement were fabricated using Langmuir-Blodgett and electron beam (e-beam) lithography techniques. The gold platforms were inscribed on thin glass slides with the purpose of using them in a transmission geometry experimental setup under a confocal microscope. The plasmon frequency of the gold nanostructures was determined in the visible-near-infrared range for various pattern sizes prepared by Langmuir-Blodgett transfer and e-beam lithography. The surface Raman enhancement factors were determined for a monolayer of azobenzene molecules adsorbed on gold through thiol bonding and compared for both LB transfer and e-beam samples for nanostructures of comparable geometries.