Chupi

4158–4171 Nucleic Acids Research, 2008, Vol. 36, No. 12
doi:10.1093/nar/gkn342

Published online 16 June 2008

SURVEY AND SUMMARY
Mechanisms and strategies for effective delivery
of antisense and siRNA oligonucleotides
Rudy Juliano*, Md. Rowshon Alam, Vidula Dixit and Hyumin Kang
Department of Pharmacology, University of North Carolina, Chapel Hill, NC 27599, USA
Received April 2, 2008;Revised May 9, 2008; Accepted May 12, 2008

ABSTRACT
The potential use of antisense and siRNA oligonucleotides as therapeutic agents has elicited a
great deal of interest. However, a major issue for
oligonucleotide-based therapeutics involves effective intracellular delivery of the active molecules. In
this Survey and Summary, we review recent reports
on delivery strategies, includingconjugates of
oligonucleotides with various ligands, as well as
use of nanocarrier approaches. These are discussed
in the context of intracellular trafficking pathways
and issues regarding in vivo biodistribution of molecules and nanoparticles. Molecular-sized chemical
conjugates and supramolecular nanocarriers each
display advantages and disadvantages in terms of
effective and nontoxicdelivery. Thus, choice of an
optimal delivery modality will likely depend on the
therapeutic context.

antisense or siRNA effects. However, the large size
and/or considerable toxicity (16,17) of cationic lipid
particles and cationic polymers may render them problematic candidates for in vivo utilization. In contrast, many
animal studies and virtually all of the clinical studies thus
far have used‘free’ antisense or siRNA compounds
(without a delivery agent), thereby demonstrating that
oligonucleotides can function in that form. However,
many investigators believe that appropriate delivery platforms could be very helpful for oligonucleotide-based
therapeutics (18–20). In this Survey and Summary, we
review and analyze chemically based approaches to
oligonucleotide delivery, includinguse of nanocarriers
and molecular conjugates. These approaches will be considered both in terms of intracellular delivery to cultured
cells and in terms of in vivo biodistribution. Obviously,
another important therapeutic strategy will be to use viral
vectors for siRNA expression (10,12,21–24), but we will
not further consider the viral approach in this review.
BACKGROUND

OVERVIEWAntisense and siRNA mechanisms

Antisense and siRNA oligonucleotides hold great promise
as therapeutic agents. Several first generation (phosphorothioate) antisense oligonucleotides are in late phase
clinical testing (1–4), while newer oligonucleotide chemistries are providing antisense molecules with higher binding
affinities, greater stability and lower toxicity as clinical
candidates (5–7). Therapid development of mammalian
RNA interference (RNAi) opens the path to a powerful
new strategy for therapeutic regulation of gene expression
(8–12). Promising results have been attained with small
interfering RNAs (siRNAs) in animal models (13–15) and
several clinical trials are underway (13). However, despite
abundant promise, a number of problems and hurdles
remain foroligonucleotide-based therapeutics. Perhaps
the most important issue concerns the effective delivery of
antisense or siRNA oligonucleotides to their respective
sites of action in the nucleus or cytoplasm. In studies of
cells in culture, delivery agents such as cationic lipids or
polymers are required in order to attain significant

Here, we briefly summarize aspects of the chemistry and
biology of antisense andsiRNA oligonucleotides that are
salient to their potential as therapeutic agents.
Antisense. RNaseH-mediated degradation of complementary mRNA is the major mode of action of antisense
oligonucleotides. However, oligonucleotides that do not
support RNaseH can affect gene expression by translation
arrest or by altering splicing (25). Target site selection in the
mRNA is an important issue...