Nanocarrier Lipid Composition Modulates the Impact of Pulmonary Surfactant Protein B (SP-B) on Cellular Delivery of siRNA

Abstract

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.

Surfactant Protein B Promotes Cytosolic SiRNA Delivery by Adopting a Virus-like Mechanism of Action

“…84 In addition to the well-known function of SP-B at the alveolar spaces, we recently discovered a previously unknown property of SP-B in its ability to promote siRNAmediated gene knockdown, suggesting that this highly specialized protein can also interfere with (intra)cellular membranes. 16,17,19,20 In this work, it was demonstrated that SP-B can promote cytosolic siRNA delivery via electrostatic interaction and subsequent fusion with anionic lipid membranes, typically found in late endosomal compartments. In contrast to using viral-derived peptides or membrane-perturbing toxins, repurposing an endogenous membrane-active protein such as SP-B as an siRNA delivery-promoting agent offers the opportunity to achieve safe and efficient siRNA delivery, in particular for local administration such as inhalation therapy.…”

“…Considering that SP-B does neither enhance the cellular uptake of the nanocomposites nor impact the exploited endocytic route, we hypothesized that SP-B could rather improve the cytosolic delivery of the encapsulated siRNA at the level of the endosomes. 19,20 The cells treated with the lipid-coated formulation (siNGs-LIP) only showed a punctuate pattern of Cy5-labeled siRNA, indicating accumulation in endosomal/lysosomal organelles (Figure 1g). 39 In contrast, inserting SP-B into the lipid-coat also resulted in diffuse staining of the cytoplasm with Cy5-labeled siRNA (Figure 1h).…”

“…described the use of Curosurf ® as a biomaterial to promote RNAi. [15][16][17][18][19][20] More specifically, layering siRNA-loaded biodegradable dextran nanogels with Curosurf ® improved both their colloidal stability and siRNA-induced target gene knockdown efficiency in vitro and in vivo. 18 PS is a complex mixture of lipids and proteins that plays an essential role in surface tension dynamics at the alveolar air-liquid interface.…”

Inhaled RNA Therapy: From Promise to Reality

“…The authors also compared naked mRNA with the use of polyethyleneimine (PEI, a synthetic cationic polymer discussed later) derivatives as delivery vectors and noticed that the transfection efficiency of naked mRNA was either better than, or comparable to, these polymers. Despite the promising effect of pulmonary naked RNA delivery, the exact mechanism of how naked RNA crosses the cell membrane barrier in the lung remains unclear, although it has been suggested that the pulmonary surfactant has a significant role in facilitating RNA uptake [25,26]. Some studies also showed that the use of delivery vectors could significantly improve RNA transfection compared with naked RNA in the airways [27][28][29][30][31].…”

Targeting Tumor Cells with Nanoparticles for Enhanced Co-Drug Delivery in Cancer Treatment

“…Cancer nanotechnology is being vigorously developed for applications in cancer imaging, molecular diagnosis, and targeted therapy [ 10 , 11 , 12 ]. Compared with their single- or dual-ligand-targeting nanoparticle (NP) counterparts, non-targeted NPs significantly increase metastasis deposition.…”