Despite the therapeutic potential of small interfering RNA (siRNA) and a growing prevalence of lung diseases for which innovative therapies are needed, a safe and effective siRNA inhalation therapy remains non-existing due to a lack of suitable formulations. We identified surfactant protein B (SP-B) as a potent enhancer of siRNA delivery by proteolipid coated nanogel formulations in vitro in a lung epithelial cell line. The developed nanocomposites have a low in vivo toxicity and show a high uptake by alveolar macrophages, a main target cell type for treatment of inflammatory pulmonary pathologies. Importantly, in vivo SP-B is also critical for the developed formulation to obtain a significant silencing of TNFα in a murine LPS-induced acute lung injury model.
Small
nucleic acid (NA) therapeutics, such as small interfering
RNA (siRNA), are generally formulated in nanoparticles (NPs) to overcome
the multiple extra- and intracellular barriers upon in vivo administration. Interaction with target cells typically triggers
endocytosis and sequesters the NPs in endosomes, thus hampering the
pharmacological activity of the encapsulated siRNAs that occurs in
the cytosol. Unfortunately, for most state-of-the-art NPs, endosomal
escape is largely inefficient. As a result, the bulk of the endocytosed
NA drug is rapidly trafficked toward the degradative lysosomes that
are considered as a dead end for siRNA nanomedicines. In contrast
to this paradigm, we recently reported that cationic amphiphilic drugs
(CADs) could strongly promote functional siRNA delivery from the endolysosomal
compartment via transient induction of lysosomal
membrane permeabilization. However, many questions still remain regarding
the broader applicability of such a CAD adjuvant effect on NA delivery.
Here, we report a drug repurposing screen (National Institutes of
Health Clinical Collection) that allowed identification of 56 CAD
adjuvants. We furthermore demonstrate that the CAD adjuvant effect
is dependent on the type of nanocarrier, with NPs that generate an
appropriate pool of decomplexed siRNA in the endolysosomal compartment
being most susceptible to CAD-promoted gene silencing. Finally, the
CAD adjuvant effect was verified on human ovarian cancer cells and
for antisense oligonucleotides. In conclusion, this study strongly
expands our current knowledge on how CADs increase the cytosolic release
of small NAs, providing relevant insights to more rationally combine
CAD adjuvants with NA-loaded NPs for future therapeutic applications.
Two decades since the discovery of the RNA interference (RNAi) pathway, we are now witnessing the approval of the first RNAi-based treatments with small interfering RNA (siRNA) drugs. Nevertheless, the widespread use of siRNA is limited by various extra- and intracellular barriers, requiring its encapsulation in a suitable (nanosized) delivery system. On the intracellular level, the endosomal membrane is a major barrier following endocytosis of siRNA-loaded nanoparticles in target cells and innovative materials to promote cytosolic siRNA delivery are highly sought after. We previously identified the endogenous lung surfactant protein B (SP-B) as siRNA delivery enhancer when reconstituted in (proteo) lipid-coated nanogels. It is known that the surface-active function of SP-B in the lung is influenced by the lipid composition of the lung surfactant. Here, we investigated the role of the lipid component on the siRNA delivery-promoting activity of SP-B proteolipid-coated nanogels in more detail. Our results clearly indicate that SP-B prefers fluid membranes with cholesterol not exceeding physiological levels. In addition, SP-B retains its activity in the presence of different classes of anionic lipids. In contrast, comparable fractions of SP-B did not promote the siRNA delivery potential of DOTAP:DOPE cationic liposomes. Finally, we demonstrate that the beneficial effect of lung surfactant on siRNA delivery is not limited to lung-related cell types, providing broader therapeutic opportunities in other tissues as well.
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