Delivery to Intracellular Targets by Nanosized Particles - Intracellular Delivery: Fundamentals and Applications - page 87

that it was delivered to endosomes. In vivo, these NC containing AS-ODN targeted
to the EWS-Fli-1 spliced gene showed a true antisense effect against Ewing's sar-
coma in mice (Maksimenko et al. 2003 ).
Nanoparticles encapsulating nucleic acids have also been prepared from the well
known PLGA polymer. Thus, the uptake of AS-ODN directed against VEGF
mRNA by ARPE-19 human retinal pigment epithelial cells was increased 4-fold by
encapsulation and protein expression was thereby inhibited (Aukunuru et al. 2003 ).
More recently, intracellular delivery of siRNA was achieved by PLGA nanoparti-
cles, silencing the GFP gene in 293 T cells (Yuan et al. 2006 ).
Coating of PLGA nanoparticles with the positively charged polysaccharide
chitosan promoted their uptake by A549 lung cancer cells (Beisner et al. 2010 ). In
this way, 2¢-O-methyl RNA was able to inhibit telomerase activity in a sequence-
specific way in these cells. Chitosan alone has also been used to form particles for
siRNA delivery, by ionic gelation with tripolyphosphate (Katas and Alpar 2006 ).
These particles were efficient at silencing the marker gene luciferase expression in
CHO K1 and HEK 293 cells and showed better activity than simple chitosan-RNA
complexes. Later, the same group combined PLGA and PEI in nanoparticles. These
were able to adsorb siRNA and allow a good gene silencing effect in CHO K1 cells,
showing better activity and lower toxicity than PEI alone (Katas et al. 2008 ).
Finally, methacrylic polymers, such as those in the Eudragit series, are attractive as
nucleic acid delivery systems because of their positive charge. Yessine et al. ( 2006 )
showed that complexes between these polymers and AS-ODN could deliver the
nucleic acid to the cytoplasm, probably because of an endosome-perturbing effect.
Recently, nanoparticles for gene delivery have been formulated from Eudragit poly-
mers and shown to be able to transfect some tumor cells lines (Gargouri et al. 2009 ).

5 Conclusion

Particulate nanocarriers have shown their potential for intracellular delivery of bio-
logically interesting substances in numerous studies over the past decades. However,
a number of unresolved issues remain, such as the choice of truly specific ligands
for in-vivo applications and the formulation of systems which allow the cargo to
escape from the lysosomes while remaining non toxic and stable in biological fluids.
Therefore, this is likely to remain an active research field in the years to come.

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