Biomedical Engineering Reference
In-Depth Information
6-10
III.
The structural characteristics of the stems and loops may
vary depending on the promoters, but more often shRNA produce
efficient target gene silencing.
11
Finally, microRNA interacts partially
with mismatched sequences in the 3
-untranslated regions of the
target mRNA, and this results in the suppression or degradation of
the target mRNA.
′
12
Despite the recognized potential of the nucleic-acid-based
therapeutics, there are still several limitations to overcome in
order to achieve sufficient therapeutic effects. So far, most of the
in
vivo
studies for nucleic acid have used high doses of unformulated
or
“naked”
nucleic
acid
delivered
through
a
hydrodynamic
13-17
injection.
When naked nucleic acid is systemically administered,
it is highly susceptible to a rapid enzymatic degradation by serum
nucleases, resulting in a short half-life ranging from several minutes
to about an hour.
18-21
Also, due to its highly charged nature, it does
not freely diffuse through the cell membranes, which might be
responsible for a low efficiency.
22
Other serious problems for non-
targeted nucleic acid are the difficulty in delivering it specifically
to target cells and rapid excretion through the urine.
A biodistri-
bution study of Cy3-labeled siRNA suggested that it was found
primarily in the kidney within 20 minutes after injection and was
not detected in any other major organs.
23
23
Extracellular level
Intracellular level
Target Ligand
g
g
Receptor
ձ
H
+
Recycling
ղ
ղ
H
Endosome
ճ
Lysosome
degradation
մ
Nucleus
g
ձ
Opsonization - RES
ղ
Degradation of nucleic acid
ճ
Off target effect
ձ
Cellular uptake
ղ
Endosomal escape
ճ
Intracellular trafficking
g
մ
Immunogenic response
մ
Nuclear delivery
Figure 3.1
Scheme outlining the barriers for gene delivery.
In order to overcome these barriers (Fig. 3.1) and to achieve
successful pharmacological effects, an effective and efficient
Search WWH ::
Custom Search