Biomedical Engineering Reference
In-Depth Information
were toxic
. Contrasting this was potent, non-toxic silencing
when a tail consisting of PEG monomer, an amine, and an acrylate
was added. Although the precise mechanism governing tolerability
was not identified, these results demonstrate that small changes
in chemical structure can dramatically influence function. Despite
promising results
in vitro
in vitro
, new structures were outperformed by
98N
-5
in vivo
, which reduced F7 expression by nearly 90% at
12
18
2 mg/kg.
7.5
Optimization: Formulation Parameters
Greatly Influence Carrier Efficacy
During the original investigation of 98N
-5, delivery was enhanced
by purifying a chemical mixture into constituents differentiated by
the number of tails attached to the amine backbone.
12
13
However,
this chemical optimization neglects the effect of both PEG-lipid
and cholesterol on delivery. Since these components are known to
influence the stability, half-life, and distribution of nanoparticles, we
investigated how the lipidoid:siRNA mass ratio, type of PEG-lipid,
and particle size influenced delivery.
17
The first variable modified was the lipidoid:siRNA mass ratio.
High mass ratios increase the amount of lipid injected into the animal,
which could cause toxic effects. Conversely, lowering the mass ratio
could reduce the amount of siRNA entrapped by the particle, since
fewer positive amines would be available to interact with the anionic
RNA backbone. Non-entrapped siRNA would remain free in solution,
effectively wasted. Consequently, siRNA entrapment was measured
at mass ratios between 5 and 30. Entrapment was almost 100% at
mass ratios between 10 and 30 but decreased dramatically at a mass
ratio equal to 5. Consequently, efficacy and toxicity were tested at
ratios of 7.5, 10, 15, 20, and 30. At a mass ratio of 7.5, compounds
were well tolerated at all doses, while larger ratios resulted in weight
loss at 10 mg/kg. Since efficacy decreased modestly, a mass ratio of
7.5 was selected for additional studies.
After optimizing the lipidoid:siRNA mass ratio, efficacy and
tolerability as a function of the PEG-lipid tail length was evaluated
at 2.5 and 25 mg/kg. PEG-lipids are anchored into the nanoparticle
membrane via hydrophobic interactions. Consequently, adjusting
the PEG tail length influences how securely PEG inserts into the
Search WWH ::
Custom Search