Dendrimers have unique molecular architectures and properties that make them attractive materials for the development of nanomedicines. Key properties such as defined architecture and a high ratio of multivalent surface moieties to molecular volume also make these nanoscaled materials highly interesting for the development of synthetic (non-viral) vectors for therapeutic nucleic acids. Rational development of such vectors requires the link to be made between dendrimer structure and the morphology and physicochemistry of the respective nucleic acid complexes and, furthermore, to the biological performance of these systems at the cellular and systemic level. The review focuses on the current understanding of the role of dendrimers in those aspects of synthetic vector development. Dendrimer-based transfection agents have become routine tools for many molecular and cell biologists but therapeutic delivery of nucleic acids remains a challenge.

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As 95% of all prescriptions are for orally administered drugs, the issue of oral absorption is central to the development of pharmaceuticals. Oral absorption is limited by a high molecular weight (>500 Da), a high log P value (>2.0) and low gastrointestinal permeability. We have designed a triple action nanomedicine from a chitosan amphiphile: quaternary ammonium palmitoyl glycol chitosan (GCPQ), which significantly enhances the oral absorption of hydrophobic drugs (e.g., griseofulvin and cyclosporin A) and, to a lesser extent, the absorption of hydrophilic drugs (e.g., ranitidine). The griseofulvin and cyclosporin A C(max) was increased 6- and 5-fold respectively with this new nanomedicine. Hydrophobic drug absorption is facilitated by the nanomedicine: (a) increasing the dissolution rate of hydrophobic molecules, (b) adhering to and penetrating the mucus layer and thus enabling intimate contact between the drug and the gastrointestinal epithelium absorptive cells, and (c) enhancing the transcellular transport of hydrophobic compounds. Although the C(max) of ranitidine was enhanced by 80% with the nanomedicine, there was no appreciable opening of tight junctions by the polymer particles.

Amphiphilic chitosan-based polymers (Mw < 20 kDa) self-assemble in aqueous media at low micromolar concentrations to give previously unknown micellar clusters of 100-300 nm in size. Micellar clusters comprise smaller 10-30 nm aggregates, and the nanopolarity/drug incorporation efficiency of their hydrophobic domains can be tailored by varying the degree of lipidic derivatization and molecular weight of the carbohydrate. The extent of drug incorporation by these novel micellar clusters is 1 order of magnitude higher than is seen with triblock copolymers, with molar polymer/drug ratios of 1:48 to 1:67. On intravenous injection, the pharmacodynamic activity of a carbohydrate propofol formulation is increased by 1 order of magnitude when compared to a commercial emulsion formulation, and on topical ocular application of a carbohydrate prednisolone formulation, initial drug aqueous humor levels are similar to those found with a 10-fold dose of prednisolone suspension.

The generation 2 polypropylenimine dendrimer combines a sufficient level of DNA binding with a low level of cell cytoxicity to give it optimum in vitro gene transfer activity.

Neurological diseases such as neurodegeneration, pain, psychiatric disorders, stroke, and brain cancers would greatly benefit from the use of highly potent and specific peptide pharmaceuticals. Peptides are especially desirable because of their low inherent toxicity. The presence of the blood brain barrier (BBB), their short duration of action, and their need for parenteral administration limits their clinical use. However, over the past decade there have been significant advances in delivering peptides to the central nervous system. Angiopep peptides developed by Angiochem (Montreal, Canada), transferrin antibodies developed by ArmaGen (Santa Monica, USA), and cell penetrating peptides have all shown promise in delivering therapeutic peptides across the BBB after intravenous administration. Noninvasive methods of delivering peptides to the brain include the use of chitosan amphiphile nanoparticles for oral delivery and nose to brain strategies. The uptake of the chitosan amphiphile nanoparticles by the gastrointestinal epithelium is important for oral peptide delivery. Finally protecting peptides from plasma degradation is integral to the success of most of these peptide delivery strategies.