Biomedical Engineering Reference
In-Depth Information
at 24 h, which decreased over the remaining 48 h period, which may
reflect RNA degradation or dilution due to cellular division events.
The reducible polyplexes followed a temporal incremental decrease
suggestive of a sustained release effect. The rHB 50% showed
incremental decreases at 24, 48, and 72 h and exhibited the most
prominent change (25%) for the 24-72 h period, which could be due
to a slower decomplexation process despite the highest disulphide
content. The rHB 25% and rHB 17% showed a nominal decrease in
EGFP silencing between 48 and 72 h, which was near to maximal at
24 h, suggesting faster decomplexation with the less redox-
susceptible nanoparticle. The inherent instability of polyplexes due
to low charge density contributed by short RNA adds to the difficulty
in tuning the RNAi effects of system based on disulphide levels.
Furthermore, the different cellular uptake and distribution patterns
between the nanoparticles highlight the difficulty in reducing
differences in RNAi effects solely to intracellular assembly and that
other factors are involved in the multistep process of gene silencing.
This approach, however, does suggest a role of disulphide content
for modulation of the biological activity.
6.6
Conclusion
Delivery is central to realizing the clinical potential of RNAi
therapeutics. Much attention has been focused on the extracellular
delivery requirements of extended blood circulation, stability,
and accumulation in target tissue. The RNAi process, however,
depends on intracellular engagement, and so, intracellular delivery
considerations of cellular uptake, cellular trafficking, and target
interaction need to be addressed. The wide repertoire of potential
RNAi therapeutics that engages at different levels of the RNAi
cascade within different subcellular sites requires modulation of
intracellular trafficking. Nanoparticle-based delivery is a promising
approach to overcome both extracellular and intracellular
barriers. A major challenge is to install extracellular stability
without compromising intracellular disassembly and availability
for siRNA target interaction. These requirements may be fulfilled
by bioresponsive polycation-based nanoparticles whose action
is triggered by local biological stimuli. The ability to incorporate
functional components during polymer synthesis or by post-
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