ABSTRACT
References ........................................................................................................ 214
The direct intracellular delivery of large hydrophilic therapeutic agents such as
proteins, active peptide domains, or nucleic acids has, until recently, been difficult to
achieve due primarily to the bioavailability barrier of the plasma membrane, which
effectively prevents the uptake of such macromolecules by limiting their passive
entry. Traditional approaches to modulate protein function have largely relied on the
serendipitous discovery of specific drugs and small molecules, which could be
delivered easily into the cell. However, the usefulness of these pharmacological
agents is limited by their tissue distribution and, unlike “information-rich”
macromolecules, they often suffer from poor target specificity, unwanted side
effects, and toxicity. Likewise, over the past several decades, the development of
molecular techniques for gene delivery and expression of proteins has provided for
tremendous advances in our understanding of cellular processes but has been of
surprisingly little benefit for the management of genetic disorders. Apart from these
gains, however, the transfer of genetic material into eukaryotic cells in vivo either
using viral vectors or by nonviral methods, such as microinjection, electroporation,
or chemical transfection, and the use of liposomes, remains problematic. Moreover,
in vivo, gene therapy approaches relying on adenoviral vectors are associated with
significant difficulties relating to toxicity and immunogenicity which have
contributed to poor performance in several clinical trials.1
