Lipidoids: A Combinatorial Approach to siRNA Delivery - RNA Interference from Biology to Therapeutics - page 150

in liver and decreases plasma LDL cholesterol (LDLc). A single dose of lipidoid-
formulated siRNA targeting PCSK9 in NHP resulted in a rapid and durable—lasting
3 weeks—reduction of plasma PCSK9, ApoB, and LDLc, without measurable
effects on either high-density lipoprotein cholesterol (HDLc) or triglycerides. The
silencing of ApoB similarly reduced LDLc in a specific and persistent manner.
While these approaches might be useful for the treatment of hypercholesterolemia,
the utility of siRNA in addressing this and other disease types requires a safe plat-
form technology.
The lipidoid platform was used to verify the safety of siRNA as a therapeutic
modality [ 11 ]. shRNAs had previously been shown to impart morbidity and mortal-
ity in mice owing to saturation of the endogenous microRNA processing pathway
[ 10 ]. It was thus important to confirm that synthetic siRNAs, which enter the path-
way downstream of miRNA biogenesis, do not induce deleterious consequences.
Systemic administration of lipidoid-formulated siRNA resulted in robust target
knockdown in mouse liver without any demonstrable effect on miRNA levels or
activity, as determined by Northern blotting and qRT-PCR. These findings were also
confirmed following multiple administrations in hamsters using a nuclease protec-
tion assay. The results of this study were significant because they established that
siRNA-mediated gene silencing could be achieved either acutely or chronically
without altering cellular miRNA biogenesis or function [ 11 ] .
These studies confirmed the safety and utility of siRNA in addressing the
pathophysiology of an isolated organism. Lipidoids were next applied to affect the
biology of an organism in the context of its environment, influencing its interaction
with a pathogen. Specifically, lipidoids were shown to decrease the pathogenicity of
invading parasites by facilitating the knockdown of host proteins involved in the
in fl ammatory response [ 43 ]. Mice treated with lipidoid-formulated siRNA targeting
heme oxygenase 1 (HO-1) were protected from the development of blood-stage
malaria infection after infection with Plasmodium berghei sporozoites. In contrast,
all mice treated with control siRNA developed patent parasitemia. In addition to
being suggestive of a therapeutic application in the mitigation of infectious diseases,
these data validated that the induction of HO-1 in the liver is required for the efficient
establishment of malarial infection, representing an important biological insight.
While lipidoids are very effective mediators of siRNA delivery to the liver, they
are also adept at transfecting other cell types, including peritoneal macrophages
[ 18 ] and ovarian cancer cells following intraperitoneal (i.p.) administration [ 44, 45 ] .
Injection into the i.p. space minimizes systemic exposure and clearance of the drug
and serves to concentrate the treatment at the intended site of action. Indeed, it has
been shown that i.p. administration provides improved outcomes for ovarian cancer
patients treated with the standard-of-care chemotherapeutic regimen relative to
intravenous administration [ 46 ] .
Multiple lipidoids were shown to be effective in this context. 98N 12 -5(1) lipi-
doids loaded with siRNA targeting the tight junction protein Claudin-3 was deliv-
ered to the i.p. cavity of mice bearing either autochthonous ovarian tumors or tumors
derived from mouse ovarian surface epithelial cells, resulting in decreased tumor
growth [ 44 ]. The concomitant reduction of ascites development suggested that the
treatment suppressed metastasis. 100N 11 -3 lipidoids loaded with siRNA targeting