Uptake and intracellular traffic of siRNA dendriplexes in glioblastoma cells and macrophages

Dual-mRNA Delivery Using Tumor Cell Lysate-Based Multifunctional Nanoparticles as an Efficient Colon Cancer Immunogene Therapy

Background

Messenger RNA (mRNA)-based immunogene therapy holds significant promise as an emerging tumor therapy approach. However, the delivery efficiency of existing mRNA methods and their effectiveness in stimulating anti-tumor immune responses require further enhancement. Tumor cell lysates containing tumor-specific antigens and biomarkers can trigger a stronger immune response to tumors. In addition, strategies involving multiple gene therapies offer potential optimization paths for tumor gene treatments.

Methods

Based on the previously developed ideal mRNA delivery system called DOTAP-mPEG-PCL (DMP), which was formed through the self-assembly of 1.2-dioleoyl-3-trimethylammonium-propane (DOTAP) and methoxypoly (ethylene glycol)-b-poly (ε-caprolactone) (mPEG-PCL), we introduced a fused cell-penetrating peptide (fCPP) into the framework and encapsulated tumor cell lysates to form a novel nanovector, termed CLSV system (CLS: CT26 tumor cell lysate, V: nanovector). This system served a dual purpose of facilitating the delivery of two mRNAs and enhancing tumor immunogene therapy through tumor cell lysates.

Results

The synthesized CLSV system had an average size of 241.17 nm and a potential of 39.53 mV. The CLSV system could not only encapsulate tumor cell lysates, but also deliver two mRNAs to tumor cells simultaneously, with a transfection efficiency of up to 60%. The CLSV system effectively activated the immune system such as dendritic cells to mature and activate, leading to an anti-tumor immune response. By loading Bim-encoded mRNA and IL-23A-encoded mRNA, CLSV/Bim and CLSV/IL-23A complexes were formed, respectively, to further induce apoptosis and anti-tumor immunity. The prepared CLSV/dual-mRNA complex showed significant anti-cancer effects in multiple CT26 mouse models.

Conclusion

Our results suggest that the prepared CLSV system is an ideal delivery system for dual-mRNA immunogene therapy.

Analyzing siRNA Concentration, Complexation and Stability in Cationic Dendriplexes by Stem-Loop Reverse Transcription-qPCR

RNA interference (RNAi) is a powerful therapeutic approach for messenger RNA (mRNA) level regulation in human cells. RNAi can be triggered by small interfering RNAs (siRNAs) which are delivered by non-viral carriers, e.g., dendriplexes. siRNA quantification inside carriers is essential in drug delivery system development. However, current siRNA measuring methods either are not very sensitive, only semi-quantitative or not specific towards intact target siRNA sequences. We present a novel reverse transcription real-time PCR (RT-qPCR)-based application for siRNA quantification in drug formulations. It enables specific and highly sensitive quantification of released, uncomplexed target siRNA and thus also indirect assessment of siRNA stability and concentration inside dendriplexes. We show that comparison with a dilution series allows for siRNA quantification, exclusively measuring intact target sequences. The limit of detection (LOD) was 4.2 pM (±0.2 pM) and the limit of quantification (LOQ) 77.8 pM (±13.4 pM) for uncomplexed siRNA. LOD and LOQ of dendriplex samples were 31.6 pM (±0 pM) and 44.4 pM (±9.0 pM), respectively. Unspecific non-target siRNA sequences did not decrease quantification accuracy when present in samples. As an example of use, we assessed siRNA complexation inside dendriplexes with varying nitrogen-to-phosphate ratios. Further, protection of siRNA inside dendriplexes from RNase A degradation was quantitatively compared to degradation of uncomplexed siRNA. This novel application for quantification of siRNA in drug delivery systems is an important tool for the development of new siRNA-based drugs and quality checks including drug stability measurements.

Microfluidic-Based Cationic Cholesterol Lipid siRNA Delivery Nanosystem: Highly Efficient In Vitro Gene Silencing and the Intracellular Behavior

Safe and efficient delivery of small interfering RNA (siRNA) is essential to gene therapy towards intervention of genetic diseases. Herein, we developed a novel cationic cholesterol lipid derivative (CEL) in which cholesterol hydrophobic skeleton was connected to L-lysine cationic headgroup via a hexanediol linker as the non-viral siRNA delivery carrier. Well-organized CEL/siRNA nanocomplexes (100-200 nm) were prepared by microfluidic-assisted assembly of CEL and siRNA at various N/P ratios. The CEL and CEL/siRNA nanocomplexes have lower cytotoxicity compared with bPEI25k. Delightfully, we disclosed that, in Hela-Luc and H1299-Luc cell lines, the micro-fluidic-based CEL/siRNA nanocomplexes exhibited high siRNA transfection efficiency under both serum-free condition (74-98%) and low-serum circumstances (80-87%), higher than that of lipofectamine 2000. These nanocomplexes also showed high cellular uptake through the caveolae/lipid-raft mediated endocytosis pathway, which may greatly contribute to transfection efficiency. Moreover, the time-dependent (0-12 h) dynamic intracellular imaging demonstrated the efficient delivery to cytoplasm after lysosomal co-localization. The results indicated that the microfluidic-based CEL/siRNA nanosystems possessed good stability, low cytotoxicity, high siRNA delivery efficiency, rapid cellular uptake and caveolae/lipid raft-dependent internalization. Additionally, this study provides a simple approach for preparing and applying a "helper lipid-free" cationic lipid siRNA delivery system as potential nanotherapeutics towards gene silencing treatment of (tumor) diseases.

Induction of Cytokines by Nucleic Acid Nanoparticles (NANPs) Depends on the Type of Delivery Carrier

Recent insights into the immunostimulatory properties of nucleic acid nanoparticles (NANPs) have demonstrated that variations in the shape, size, and composition lead to distinct patterns in their immunostimulatory properties. While most of these studies have used a single lipid-based carrier to allow for NANPs' intracellular delivery, it is now apparent that the platform for delivery, which has historically been a hurdle for therapeutic nucleic acids, is an additional means to tailoring NANP immunorecognition. Here, the use of dendrimers for the delivery of NANPs is compared to the lipid-based platform and the differences in resulting cytokine induction are presented.

Design of 18 nm Doxorubicin-Loaded 3-Helix Micelles: Cellular Uptake and Cytotoxicity in Patient-Derived GBM6 Cells

The fate of nanocarrier materials at the cellular level constitutes a critical checkpoint in the development of effective nanomedicines, determining whether tissue level accumulation results in therapeutic benefit. The cytotoxicity and cell internalization of ∼18 nm 3-helix micelle (3HM) loaded with doxorubicin (DOX) were analyzed in patient-derived glioblastoma (GBM) cells in vitro. The half-maximal inhibitory concentration (IC₅₀) of 3HM-DOX increased to 6.2 μg/mL from <0.5 μg/mL for free DOX in patient-derived GBM6 cells, to 15.0 μg/mL from 6.5 μg/mL in U87MG cells, and to 21.5 μg/mL from ∼0.5 μg/mL in LN229 cells. Modeling analysis of previous 3HM biodistribution results predicts that these cytotoxic concentrations are achievable with intravenous injection in rodent GBM models. 3HM-DOX formulations were internalized intact and underwent intracellular trafficking distinct from free DOX. 3HM was quantified to have an internalization half-life of 12.6 h in GBM6 cells, significantly longer than that reported for some liposome and polymer systems. 3HM was found to traffic through active endocytic processes, with clathrin-mediated endocytosis being the most involved of the pathways studied. Inhibition studies suggest substantial involvement of receptor recognition in 3HM uptake. As the 3HM surface is PEG-ylated with no targeting functionalities, protein corona-cell surface interactions, such as the apolipoprotein-low-density lipoprotein receptor, are expected to initiate internalization. The present work gives insights into the cytotoxicity, pharmacodynamics, and cellular interactions of 3HM and 3HM-DOX relevant for ongoing preclinical studies. This work also contributes to efforts to develop predictive mathematical models tracking the accumulation and biodistribution kinetics at a systemic level.

RNA Interference Nanotherapeutics for Treatment of Glioblastoma Multiforme

Nucleic acid therapeutics for RNA interference (RNAi) are gaining attention in the treatment and management of several kinds of the so-called "undruggable" tumors via targeting specific molecular pathways or oncogenes. Synthetic ribonucleic acid (RNAs) oligonucleotides like siRNA, miRNA, shRNA, and lncRNA have shown potential as novel therapeutics. However, the delivery of such oligonucleotides is significantly hampered by their physiochemical (such as hydrophilicity, negative charge, and instability) and biopharmaceutical features (in vivo serum stability, fast renal clearance, interaction with extracellular proteins, and hindrance in cellular internalization) that markedly reduce their biological activity. Recently, several nanocarriers have evolved as suitable non-viral vectors for oligonucleotide delivery, which are known to either complex or conjugate with these oligonucleotides efficiently and also overcome the extracellular and intracellular barriers, thereby allowing access to the tumoral micro-environment for the better and desired outcome in glioblastoma multiforme (GBM). This Review focuses on the up-to-date advancements in the field of RNAi nanotherapeutics utilized for GBM treatment.

Co-delivery of IKBKE siRNA and cabazitaxel by hybrid nanocomplex inhibits invasiveness and growth of triple-negative breast cancer

IKBKE is an oncogene in triple-negative breast cancer (TNBC), and we demonstrate that IKBKE small interfering RNA (siRNA) inhibits the proliferation, migration, and invasion of TNBC cells. Despite the recent success of siRNA therapeutics targeting to the liver, there still remains a great challenge to deliver siRNAs to solid tumors. Here, we report a hybrid nanocomplex to co-deliver the IKBKE siRNA and cabazitaxel to TNBC to achieve an optimal antitumor effect. The nanocomplex is modified with hyaluronic acid to target CD44 on TNBC cells. The nanocomplex shows higher cellular uptake and better tumor penetration of the encapsulated cargos. The nanocomplex also exhibits high tumor accumulation and antitumor activity in an orthotopic TNBC mouse model. Encapsulation of cabazitaxel in the nanocomplex enhances the activity of the IKBKE siRNA. The hybrid nanocomplex provides a novel and versatile platform for combination therapies using siRNAs and chemotherapy.

PAMAM Dendrimer Nanomolecules Utilized as Drug Delivery Systems for Potential Treatment of Glioblastoma: A Systematic Review

Glioblastoma (GB) is a grade IV astrocytoma that maintains a poor prognosis with respect to current treatment options. Despite major advancements in the fields of surgery and chemoradiotherapy over the last few decades, the life expectancy for someone with glioblastoma remains virtually unchanged and warrants a new approach for treatment. Poly(amidoamine) (PAMAM) dendrimers are a type of nanomolecule that ranges in size (between 1 and 100 nm) and shape and can offer a new viable solution for the treatment of intracranial tumors, including glioblastoma. Their ability to deliver a variety of therapeutic cargo and penetrate the blood-brain barrier (BBB), while preserving low cytotoxicity, make them a favorable candidate for further investigation into the treatment of glioblastoma. Here, we present a systematic review of the current advancements in PAMAM dendrimer technology, including the wide spectrum of dendrimer generations formulated, surface modifications, core modifications, and conjugations developed thus far to enhance tumor specificity and tumor penetration for treatment of glioblastoma. Furthermore, we highlight the extensive variety of therapeutics capable of delivery by PAMAM dendrimers for the treatment of glioblastoma, including cytokines, peptides, drugs, siRNAs, miRNAs, and organic polyphenols. While there have been prolific results stemming from aggressive research into the field of dendrimer technology, there remains a nearly inexhaustible amount of questions that remain unanswered. Nevertheless, this technology is rapidly developing and is nearing the cusp of use for aggressive tumor treatment. To that end, we further highlight future prospects in focus as researchers continue developing more optimal vehicles for the delivery of therapeutic cargo.

Complexes of Pro-Apoptotic siRNAs and Carbosilane Dendrimers: Formation and Effect on Cancer Cells

This paper examines the complexation of anti-cancer small interfering RNAs (siRNAs) by cationic carbosilane dendrimers, and the interaction of the formed complexes with HeLa and HL-60 cancer cells. Stepwise formation of the complexes accompanied by the evolution of their properties has been observed through the increase of the charge ratio (dendrimer/siRNA). The complexes decrease the viability of both “easy-to-transfect” cells (HeLa) and “hard-to transfect” ones (HL-60), indicating a high potential of the cationic carbosilane dendrimers for siRNA delivery into tumor cells.

Au-CGKRK Nanoconjugates for Combating Cancer through T-Cell-Driven Therapeutic RNA Interference

Numerous prior studies on fighting cancer have been based on using inhibitors of JAK-STAT pathway (signal transducer and activator of transcription 3 (STAT3) inhibitor in particular), a signaling pathway responsible for progression of many types of cancer cells. However, recent studies have shown that STAT3 activation leads to upregulation of program death receptor-ligand 1 (PD-L1, an immune checkpoint protein that plays a major role behind evasion of immune systems by growing tumors) expression levels in tumor cells, leading to enhanced immune suppression. This is why global efforts are being witnessed in combating cancer through use of immune checkpoint inhibitors. Herein, we report on the design, synthesis, physicochemical characterizations, and bioactivity evaluation of novel tumor- and tumor-vasculature-targeting noncytotoxic Au-CGKRK nanoconjugates (17-80 nm) for combating tumor. Using a syngeneic mouse tumor model, we show that intraperitoneal (i.p.) administration of the Au-CGKRK nanoparticles (NPs) complexed with both PD-L1siRNA (the immune checkpoint inhibitor) and STAT3siRNA (the JAK-STAT pathway inhibitor) results in significant (>70%) enhancement in overall survivability (OS) in melanoma-bearing mice (n = 5) when compared to the OS in the untreated mice group. The expression levels of CD8 and CD4 proteins in the tumor lysates of differently treated mice groups (by Western blotting) are consistent with the observed OS enhancement being a T-cell-driven process. Biodistribution study using near-infrared dye-loaded Au-CGKRK nanoconjugates revealed selective accumulation of the dye in mouse tumor. Notably, the overall survival benefits were significantly less (∼35%) when melanoma-bearing mice were treated (i.p.) with Au-CGKRK NPs complexed with only PD-L1siRNA or with STAT3siRNA alone. The presently described Au-CGKRK nanoconjugates are expected to find future use in therapeutic RNA-interference-based cancer immunotherapy.

Cholesterol and Morpholine Grafted Cationic Amphiphilic Copolymers for miRNA-34a Delivery

miR-34a is a master tumor suppressor playing a key role in the several signaling mechanisms involved in cancer. However, its delivery to the cancer cells is the bottleneck in its clinical translation. Herein we report cationic amphiphilic copolymers grafted with cholesterol (chol), N, N-dimethyldipropylenetriamine (cation chain) and 4-(2-aminoethyl)morpholine (morph) for miR-34a delivery. The copolymer interacts with miR-34a at low N/P ratios (∼2/1) to form nanoplexes of size ∼108 nm and a zeta potential ∼ +39 mV. In vitro studies in 4T1 and MCF-7 cells indicated efficient transfection efficiency. The intracellular colocalization suggested that the copolymer effectively transported the FAM labeled siRNA into the cytoplasm within 2 h and escaped from the endo-/lysosomal environment. The developed miR-34a nanoplexes inhibited the breast cancer cell growth as confirmed by MTT assay wherein 28% and 34% cancer cell viability was observed in 4T1 and MCF-7 cells, respectively. Further, miR-34a nanoplexes possess immense potential to induce apoptosis in both cell lines.

Preferential and Increased Uptake of Hydroxyl-Terminated PAMAM Dendrimers by Activated Microglia in Rabbit Brain Mixed Glial Culture

Polyamidoamine (PAMAM) dendrimers are multifunctional nanoparticles with tunable physicochemical features, making them promising candidates for targeted drug delivery in the central nervous system (CNS). Systemically administered dendrimers have been shown to localize in activated glial cells, which mediate neuroinflammation in the CNS. These dendrimers delivered drugs specifically to activated microglia, producing significant neurological improvements in multiple brain injury models, including in a neonatal rabbit model of cerebral palsy. To gain further insight into the mechanism of dendrimer cell uptake, we utilized an in vitro model of primary glial cells isolated from newborn rabbits to assess the differences in hydroxyl-terminated generation 4 PAMAM dendrimer (D4-OH) uptake by activated and non-activated glial cells. We used fluorescently-labelled D4-OH (D-Cy5) as a tool for investigating the mechanism of dendrimer uptake. D4-OH PAMAM dendrimer uptake was determined by fluorescence quantification using confocal microscopy and flow cytometry. Our results indicate that although microglial cells in the mixed cell population demonstrate early uptake of dendrimers in this in vitro system, activated microglia take up more dendrimer compared to resting microglia. Astrocytes showed delayed and limited uptake. We also illustrated the differences in mechanism of uptake between resting and activated microglia using different pathway inhibitors. Both resting and activated microglia primarily employed endocytotic pathways, which are enhanced in activated microglial cells. Additionally, we demonstrated that hydroxyl terminated dendrimers are taken up by primary microglia using other mechanisms including pinocytosis, caveolae, and aquaporin channels for dendrimer uptake.

Survivin as a novel target protein for reducing the proliferation of cancer cells

Survivin, also known as baculoviral inhibitor of apoptosis repeat-containing 5, is a novel member of the inhibitor of apoptosis protein family. Survivin is highly expressed in tumors and embryonic tissues and is associated with tumor cell differentiation, proliferation, invasion and metastasis; however, survivin is expressed at low levels in normal terminally differentiated adult tissues. Meanwhile, the expression level of survivin is also a negative prognostic factor for patients with cancer. These unique characteristics of survivin make it an exciting potential therapeutic target for cancer treatment. This review will discuss the biological characteristics of survivin and its potential use as a treatment target to reduce cancer cell proliferation.

Dendrimers as Nanocarriers for Nucleic Acid and Drug Delivery in Cancer Therapy

Dendrimers are highly branched polymers with easily modifiable surfaces. This makes them promising structures for functionalization and also for conjugation with drugs and DNA/RNA. Their architecture, which can be controlled by different synthesis processes, allows the control of characteristics such as shape, size, charge, and solubility. Dendrimers have the ability to increase the solubility and bioavailability of hydrophobic drugs. The drugs can be entrapped in the intramolecular cavity of the dendrimers or conjugated to their functional groups at their surface. Nucleic acids usually form complexes with the positively charged surface of most cationic dendrimers and this approach has been extensively employed. The presence of functional groups in the dendrimer's exterior also permits the addition of other moieties that can actively target certain diseases and improve delivery, for instance, with folate and antibodies, now widely used as tumor targeting strategies. Dendrimers have been investigated extensively in the medical field, and cancer treatment is one of the greatest areas where they have been most used. This review will consider the main types of dendrimer currently being explored and how they can be utilized as drug and gene carriers and functionalized to improve the delivery of cancer therapy.

Tunable Surface Properties of Temperature-Responsive Polymer-Modified Liposomes Induce Faster Cellular Uptake

Drug delivery by nanoparticle carriers has been limited by inefficient intracellular drug delivery. Temperature-responsive poly(N-isopropylacrylamide) (PNIPAAm)-modified liposomes can release their content following heating. In this study, we synthesized the temperature-responsive polymer poly(N-isopropylacrylamide)-co-N,N'-dimethylaminopropylacrylamide (P(NIPAAm-co-DMAPAAm)) and investigated the properties of liposomes modified with P(NIPAAm-co-DMAPAAm) for intracellular drug carriers. The copolymer displayed a thermosensitive transition at a lower critical solution temperature (LCST) that is higher than body temperature. Above the LCST, the temperature-responsive liposomes started to aggregate and release. The liposomes showed a fixed aqueous layer thickness (FALT) at the surface below the LCST, and the FALT decreased with increasing temperature. Above 37 °C, cytosolic release from the temperature-responsive liposomes was higher than that from the PEGylated liposomes, indicating intracellular uptake. Here, we showed that the tunable surface properties of the temperature-responsive polymer-modified liposomes possibly enabled their dehydration by heating, which likely induced a faster cellular uptake and release. Therefore, the liposomes could be highly applicable for improving intracellular drug-delivery carriers.

Insight into the relationship between the cell culture model, cell trafficking and siRNA silencing efficiency

Despite research efforts, cell uptake processes determining siRNA silencing efficiency remain unclear. Here, we examine the relationship between in vitro cell culture models, cellular trafficking and siRNA silencing efficiency to provide a mechanistic insight on siRNA delivery system design. Model siRNA-polyplexes, based on chitosan as a ‘classical’ condensing agent, were applied to a panel of lung epithelial cell lines, H1299, A549 and Calu-3 and cell internalization levels, trafficking pathways and gene silencing assessed on exposure to pharmacological inhibitors. The data reveal striking differences in the internalization behaviour and gene silencing efficiency in the tested cell lines, despite their common lung epithelial origins. The model system’s silencing was lower where clathrin internalization pathway predominated in Calu-3, relative to silencing in H1299 cells where a non-clathrin internalization appears dominant. Increased silencing on endosomal disruption was apparent in Calu-3 cells, but absent when cellular internalization was not predominantly clathrin-mediated in A549 cells. This highlights that identifying cell trafficking pathways before incorporation of functional components to siRNA delivery systems (e.g. endosomolytic compounds) is crucial. The study hence stresses the importance of selection of appropriate cell culture model, relevant to in vivo target, to assess the gene silencing efficiency and decide which functionalities the ‘stratified siRNA silencing vector’ requires.

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Relationship between cell type, uptake path and silencing examined to inform siRNA vector design.

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Notable differences observed in cell uptake pathways and silencing despite cells’ common origin.

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Addition of endosomolytic functionality shows no effect when non-clathrin pathways dominate.

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Cell model important to assess silencing and decide which functionalities siRNA vector requires.

Cationic Nanoparticles Assembled from Natural-Based Steroid Lipid for Improved Intracellular Transport of siRNA and pDNA

Developing new functional biomaterials from biocompatible natural-based resources for gene/drug delivery has attracted increasing attention in recent years. In this work, we prepared a series of cationic nanoparticles (Diosarg-DOPE NPs) by assembly of a natural steroid diosgenin-based cationic lipid (Diosarg) with commercially-available helper lipid 1,2-dioleoyl-sn-glycero-3-phosphorethanolamine (DOPE). These cationic Diosarg-DOPE NPs were able to efficiently bind siRNA and plasmid DNA (pDNA) via electrostatic interactions to form stable, nano-sized cationic lipid nanoparticles instead of lamellar vesicles in aqueous solution. The average particle size, zeta potentials and morphologies of the siRNA and pDNA complexes of the Diosarg-DOPE NPs were examined. The in vitro cytotoxicity of NPs depends on the dose and assembly ratio of the Diosarg and DOPE. Notably, the intracellular transportation efficacy of the exogenesis siRNA and pDNA could be greatly improved by using the Diosarg-DOPE NPs as the cargoes in H1299 cell line. The results demonstrated that the self-assembled Diosarg-DOPE NPs could achieve much higher intracellular transport efficiency for siRNA or pDNA than the cationic lipid Diosarg, indicating that the synergetic effect of different functional lipid components may benefit the development of high efficiency nano-scaled gene carriers. Moreover, it could be noted that the traditional "lysosome localization" involved in the intracellular trafficking of the Diosarg and Diosarg-DOPE NPs, indicating the co-assembly of helper lipid DOPE, might not significantly affect the intracellular localization features of the cationic lipids.

Intracellular trafficking and exocytosis of a multi-component siRNA nanocomplex

Despite the importance of siRNA delivery systems, understanding of their intracellular fate remains elusive. We recently developed a multi-component siRNA nanocomplex to deliver siRNA to hepatic stellate cells (HSCs). The objective of this study is to study post-internalization trafficking of this siRNA nanocomplex and its multiple components like siRNA, protamine, and streptavidin, in HSCs. After internalization, the nanocomplex entrapped in early endosomes undergoes three possible routes including endosomal escape, exocytosis, and entrapment in lysosomes. Significant amount of siRNA dissociates from the nanocomplex to exert silencing activity. After escaping from endosomes, protamine dissociates from the nanocomplex and stays inside the cytoplasm. Golgi complex plays an important role in exocytosis of the nanocomplex. We also demonstrate that exocytosis is one of the major reasons accounting for the transient silencing activity of nonviral siRNA delivery. Incorporation of exocytosis inhibitors in nonviral siRNA delivery systems may extend the silencing activity of siRNA.

Nanometer-scale siRNA carriers incorporating peptidomimetic oligomers: physical characterization and biological activity

Synthetic short interfering RNA (siRNA) oligonucleotides can trigger the RNA interference pathway and lead to selective gene silencing. Despite considerable enthusiasm and investment, formidable challenges remain that may deter translating this breakthrough discovery into clinical applications. In particular, the development of efficient, nontoxic, nonimmunogenic methods for delivering siRNA in vivo has proven to be exceptionally challenging. Thorough analysis of the relationship between the structure and function of siRNA carrier systems, both in isolation and in complex with RNA, will facilitate the design of efficient nonviral siRNA delivery vehicles. In this study, we explore the relationship between the physicochemical characteristics and the biological activity of “lipitoid” compounds as potent siRNA delivery vehicles. Lipitoids are cationic peptidomimetic oligomers incorporating a peptoid and a phospholipid moiety. Lipitoids can associate with siRNA oligonucleotides and self-assemble into spherical lipitoid-based nanoparticles (LNPs), with dimensions that are dependent upon the medium and the stoichiometric ratio between the cationic monomers of the lipitoid and anionic siRNA oligonucleotides. The morphology, gene silencing efficiency, and cytotoxicity of the siRNA-loaded LNPs are similarly sensitive to the stoichiometry of the complexes. The medium in which the LNPs are formed affects the assembled cargo particles’ characteristics such as particle size, transfection efficiency, and stability. Formation of the LNPs in the biological, serum-free medium OptiMEM resulted in LNPs an order of magnitude larger than LNPs formed in water, and were twice as efficient in siRNA transfection compared to LNPs formed in water. Inhibitor studies were conducted to elucidate the efficiency of lysosomal escape and the uptake mechanism of the siRNA-loaded LNPs. Our results suggest that these lipitoid-based, siRNA-loaded spherical LNPs are internalized through a lipid raft-dependent and dynamin-mediated pathway, circumventing endosomal and lysosomal encapsulation. The lipitoid-siRNA nanospheres proved to be suitable platforms for investigating the critical parameters determining the efficiency of transfection agents, revealing the necessity for conducting characterization studies in biological media. The investigation of the LNP internalization pathway points to an alternative uptake route that bypasses the lysosome, explaining the surprisingly high efficiency of LNPs and suggesting that the uptake mechanism should be probed rather than assumed for the next generation of rationally designed transfection agents.

Dendrimers as carriers for siRNA delivery and gene silencing: a review

RNA interference (RNAi) was first literaturally reported in 1998 and has become rapidly a promising tool for therapeutic applications in gene therapy. In a typical RNAi process, small interfering RNAs (siRNA) are used to specifically downregulate the expression of the targeted gene, known as the term "gene silencing." One key point for successful gene silencing is to employ a safe and efficient siRNA delivery system. In this context, dendrimers are emerging as potential nonviral vectors to deliver siRNA for RNAi purpose. Dendrimers have attracted intense interest since their emanating research in the 1980s and are extensively studied as efficient DNA delivery vectors in gene transfer applications, due to their unique features based on the well-defined and multivalent structures. Knowing that DNA and RNA possess a similar structure in terms of nucleic acid framework and the electronegative nature, one can also use the excellent DNA delivery properties of dendrimers to develop effective siRNA delivery systems. In this review, the development of dendrimer-based siRNA delivery vectors is summarized, focusing on the vector features (siRNA delivery efficiency, cytotoxicity, etc.) of different types of dendrimers and the related investigations on structure-activity relationship to promote safe and efficient siRNA delivery system.

Anti-prion drug mPPIg5 inhibits PrP(C) conversion to PrP(Sc)

Prion diseases, also known as transmissible spongiform encephalopathies, are a group of fatal neurodegenerative diseases that include scrapie in sheep, bovine spongiform encephalopathy (BSE) in cattle and Creutzfeldt-Jakob disease (CJD) in humans. The ‘protein only hypothesis’ advocates that PrP^Sc, an abnormal isoform of the cellular protein PrP^C, is the main and possibly sole component of prion infectious agents. Currently, no effective therapy exists for these diseases at the symptomatic phase for either humans or animals, though a number of compounds have demonstrated the ability to eliminate PrPSc in cell culture models. Of particular interest are synthetic polymers known as dendrimers which possess the unique ability to eliminate PrP^Sc in both an intracellular and in vitro setting. The efficacy and mode of action of the novel anti-prion dendrimer mPPIg5 was investigated through the creation of a number of innovative bio-assays based upon the scrapie cell assay. These assays were used to demonstrate that mPPIg5 is a highly effective anti-prion drug which acts, at least in part, through the inhibition of PrP^C to PrP^Sc conversion. Understanding how a drug works is a vital component in maximising its performance. By establishing the efficacy and method of action of mPPIg5, this study will help determine which drugs are most likely to enhance this effect and also aid the design of dendrimers with anti-prion capabilities for the future.

Caveolin-1, caveolae, and glioblastoma

Glioblastoma multiforme (GBM) is the most common malignant brain tumor and is characterized by high invasiveness, poor prognosis, and limited therapeutic options. Biochemical and morphological experiments have shown the presence of caveolae in glioblastoma cells. Caveolae are flask-shaped plasma membrane subdomains that play trafficking, mechanosensing, and signaling roles. Caveolin-1 is a membrane protein that participates in the formation of caveolae and binds a multitude of signaling proteins, compartmentalizing them in caveolae and often directly regulating their activity via binding to its scaffolding domain. Caveolin-1 has been proposed to behave either as a tumor suppressor or as an ongogene depending on the tumor type and progress. This review discusses the existing information on the expression and function of caveolin-1 and caveolae in GBM and the role of this organelle and its defining protein on cellular signaling, growth, and invasiveness of GBM. We further analyze the available data suggesting caveolin-1 could be a target in GBM therapy.

Increased brain radioactivity by intranasal P-labeled siRNA dendriplexes within in situ-forming mucoadhesive gels

BACKGROUND

Molecules taken up by olfactory and trigeminal nerve neurons directly access the brain by the nose-to-brain pathway. In situ-forming mucoadhesive gels would increase the residence time of intranasal material, favoring the nose-to-brain delivery. In this first approach, brain radioactivity after intranasal administration of (32)P-small interference RNA (siRNA) complexed with poly(amidoamine) G7 dendrimers (siRNA dendriplexes) within in situ-forming mucoadhesive gels, was determined.

MATERIALS

(32)P-siRNA dendriplexes were incorporated into in situ-forming mucoadhesive gels prepared by blending thermosensitive poloxamer (23% w/w) with mucoadhesive chitosan (1% w/w, PxChi) or carbopol (0.25% w/w, PxBCP). Rheological properties, radiolabel release profile, and local toxicity in rat nasal mucosa were determined. The best-suited formulation was intranasally administered to rats, and blood absorption and brain distribution of radioactivity were measured.

RESULTS

The gelation temperature of both formulations was 23°C. The PxChi liquid showed non-Newtonian pseudoplastic behavior of high consistency and difficult manipulation, and the gel retained 100% of radiolabel after 150 minutes. The PxCBP liquid showed a Newtonian behavior of low viscosity and easy manipulation, while in the gel phase showed apparent viscosity similar to that of the mucus but higher than that of aqueous solution. The gel released 35% of radiolabel and the released material showed silencing activity in vitro. Three intranasal doses of dendriplexes in PxCBP gel did not damage the rat nasal mucosa. A combination of (32)P-siRNA complexation with dendrimers, incorporation of the dendriplexes into PxCBP gel, and administration of two intranasal doses was necessary to achieve higher brain radioactivity than that achieved by intravenous dendriplexes or intranasal naked siRNA.

CONCLUSION

The increased radioactivity within the olfactory bulb suggested that the combination above mentioned favored the mediation of a direct brain delivery.