Polyethylenimine–DNA Ratio Strongly Affects Their Nanoparticle Formation: A Large-Scale Coarse-Grained Molecular Dynamics Study

Chitosan nanocarriers for non-coding RNA therapeutics: A review

Non-coding RNA (ncRNA)-based therapies entail delivering ncRNAs to cells to regulate gene expression and produce proteins that combat infections, cancer, neurological diseases, and bone abnormalities. Nevertheless, the therapeutic potential of these ncRNAs has been limited due to the difficulties in delivering them to specific cellular targets within the body. Chitosan (CS), a biocompatible cationic polymer, interacts with negatively charged RNA molecules to form stable complexes. It is a promising biomaterial to develop nanocarriers for ncRNA delivery, overcoming several disadvantages of traditional delivery systems. CS-based nanocarriers can protect ncRNAs from degradation and target-specific delivery by surface modifications and intracellular release profiles over an extended period. This review briefly summarizes the recent developments in CS nanocarriers' synthesis and design considerations and their applications in ncRNA therapeutics for treating various diseases. We also discuss the challenges and limitations of CS-based nanocarriers for ncRNA therapeutics and potential strategies for overcoming these challenges.

A study of complexation and biological fate of polyethyleneimine-siRNA polyplexes in vitro and in vivo by fluorescence correlation spectroscopy and positron emission tomography imaging

A deeper knowledge on the formation and biological fate of polymer based gene vectors is needed for their translation into therapy. Here, polyplexes of polyethyleneimine (PEI) and silencing RNA (siRNA) are formed with theoretical N/P ratios of 2, 4 and 12. Fluorescence correlation spectroscopy (FCS) is used to study the formation of polyplexes from fluorescently labelled PEI and siRNA. FCS proves the presence of free PEI. From the analysis of the autocorrelation functions it was possible to determine the actual stoichiometry of polyplexes. FCS and fluorescence cross correlation spectroscopy (FCCS) are used to follow the fate of the polyplexes intracellularly. Polyplexes disassemble after 1 day inside cells. Positron emission tomography (PET) studies are conducted with radiolabelled polyplexes prepared with siRNA or PEI labelled with 2,3,5,6-tetrafluorophenyl 6-[18F]-fluoronicotinate ([18F]F-PyTFP). PET studies in healthy mice show that [18F]siRNA/PEI and siRNA/[18F]PEI polyplexes show similar biodistribution patterns with limited circulation in the bloodstream and accumulation in the liver. Higher activity for [18F]PEI in the kidney and bladder suggests the presence of free PEI.

Trends in the synthetic polymer delivery of RNA

Ribonucleic acid (RNA) has emerged as one of the most promising therapeutic payloads in the field of gene therapy. There are many unique types of RNA that allow for a range of applications including vaccination, protein replacement therapy, autoimmune disease treatment, gene knockdown and gene editing. However, RNA triggers the host immune system, is vulnerable to degradation and has a low proclivity to enter cells spontaneously. Therefore, a delivery vehicle is required to facilitate the protection and uptake of RNA therapeutics into the desired host cells. Lipid nanoparticles have emerged as one of the only clinically approved vehicles for genetic payloads, including in the COVID-19 messenger RNA vaccines. While lipid nanoparticles have distinct advantages, they also have drawbacks, including strong immune stimulation, complex manufacturing and formulation heterogeneity. In contrast, synthetic polymers are a widely studied group of gene delivery vehicles and boast distinct advantages, including biocompatibility, tunability, inexpensiveness, simple formulation and ease of modification. Some classes of polymers enhance efficient transfection efficiency, and lead to lower stimulation of the host immune system, making them more viable candidates for non-vaccine-related applications of RNA medicines. This review aims to identify the most promising classes of synthetic polymers, summarize recent research aimed at moving them into the clinic and postulate the future steps required for unlocking their full potential.

Polymeric Carriers for Delivery of RNA Cancer Therapeutics

As research uncovers the underpinnings of cancer biology, new targeted therapies have been developed. Many of these therapies are small molecules, such as kinase inhibitors, that target specific proteins; however, only 1% of the genome encodes for proteins and only a subset of these proteins has ‘druggable’ active binding sites. In recent decades, RNA therapeutics have gained popularity due to their ability to affect targets that small molecules cannot. Additionally, they can be manufactured more rapidly and cost-effectively than small molecules or recombinant proteins. RNA therapeutics can be synthesised chemically and altered quickly, which can enable a more personalised approach to cancer treatment. Even though a wide range of RNA therapeutics are being developed for various indications in the oncology setting, none has reached the clinic to date. One of the main reasons for this is attributed to the lack of safe and effective delivery systems for this type of therapeutic. This review focuses on current strategies to overcome these challenges and enable the clinical utility of these novel therapeutic agents in the cancer clinic.

Polyethylenimine-DNA Nanoparticles under Endosomal Acidification and Implication to Gene Delivery

Non-viral gene delivery using polyethylenimine (PEI) has shown tremendous promise as a therapeutic technique. Through the formation of nanoparticles (NPs), PEIs protect genetic material such as DNA from degradation. Escape of the NPs from endosomes and lysosomes is facilitated by PEI's buffering capacity over a wide range of pH. However, little is known about the effects of endosomal acidification on the morphology of the NPs. In this work, large-scale coarse-grained simulations performed to mimic endosomal acidification reveal that NPs undergo a resizing process that is highly dependent on the N/P ratio (ratio of PEI nitrogen to DNA phosphate) at which they are prepared. With a low N/P ratio, NPs further aggregate after endosomal acidification, whereas with a high N/P ratio they dissociate. The mechanisms behind such NP resizing and its consequences on endosomal escape and nuclear trafficking are discussed. Based on the findings, suggestions are made on the PEI architecture that may enhance NP dissociation driven by endosomal acidification.

DNA Framework-Engineered Long-Range Electrostatic Interactions for DNA Hybridization Reactions

Long-range electrostatic interactions beyond biomolecular interaction interfaces have not been extensively studied due to the limitation in engineering electric double layers in physiological fluids. Here we find that long-range electrostatic interactions play an essential role in kinetic modulation of DNA hybridizations. Protein and gold nanoparticles with different charges are encapsulated in tetrahedral frameworks to exert diverse electrostatic effects on site-specifically tethered single DNA strands. Using this strategy, we have successfully modulated the hybridization kinetics in both bulk solution and single molecule level. Experimental and theoretical studies reveal that long-range Coulomb interactions are the key factor for hybridization rates. This work validates the important role of long-range electrostatic forces in nucleic acid-biomacromolecule complexes, which may encourage new strategies of gene regulation, antisense therapy, and nucleic acid detection.

In silico prediction of the in vitro behavior of polymeric gene delivery vectors

Non-viral gene delivery vectors have increasingly come under the spotlight, but their performaces are still far from being satisfactory. Therefore, there is an urgent need for forecasting tools and screening methods to enable the development of ever more effective transfectants. Here, coarse-grained (CG) models of gold standard transfectant poly(ethylene imine)s (PEIs) have been profitably used to investigate and highlight the effect of experimentally-relevant parameters, namely molecular weight (2 vs. 10 kDa) and topologies (linear vs. branched), protonation state, and ammine-to-phosphate ratios (N/Ps), on the complexation and the gene silencing efficiency of siRNA molecules. The results from the in vitro screening of cationic polymers and conditions were used to validate the in silico platform that we developed, such that the hits which came out of the CG models were of high practical relevance. We show that our in silico platform enables to foresee the most suitable conditions for the complexation of relevant siRNA-polycation assemblies, thereby providing a reliable predictive tool to test bench transfectants in silico, and foster the design and development of gene delivery vectors.

A dendritic, redox-responsive, supramolecular (Dr.S) system for lysis-triggered delivery for drug-resistant renal cancer

Purpose: Aiming to improve the drug loading capacity of dendritic nanoparticles and enhance delivery efficacy in drug-resistant cancer, we developed and optimized a more advanced dendritic, redox-responsive, supramolecular (Dr.S) system for intravenous RAD001 administration. Materials and methods: The Dr.S system was engineered by linking 3^rd generation polyamidoamine dendrimers (G3 PAMAM) with 8-arm polyethylene glycol (PEG) to encapsulate a molecular targeted agent RAD001. The drug-loading capacity was measured by ultraviolet-visible spectrophotometry. In vitro release behavior was determined with a two-compartment model, and the in vivo distribution pattern was tracked by Cy5.5 fluorescence. The therapeutic effect of Dr.S/RAD001 was evaluated in RAD001-resistant cancer cells and tumor-bearing nude mice, respectively. Results: The Dr.S system encapsulating RAD001 with a loading efficiency of 10.6% formed a core–shell structure, by shifting hydrophobic PAMAM/RAD001 components towards inner space and exposing the hydrophilic PEG on the surface. The Dr.S/RAD001 system could respond to a lysis-mimicking reduction stimulus, and functionally release cargoes to facilitate tumor accumulation and cellular internalization. These features contributed to the enhanced anti-tumor activity of RAD001 in renal cancers in vitro and in vivo. The Dr.S/RAD001 system also reversed acquired RAD001-resistance by a 60-fold increase in tumor accumulation of the therapeutics. Conclusion: The functional Dr.S/RAD001 system enables lysis-triggered release of RAD001 to achieve better tumor accumulation, which helps overcome acquired drug resistance in renal cancers.

Aiming to improve the drug loading capacity of dendritic nanoparticles and enhance delivery efficacy in drug-resistant cancer, we developed and optimized a more advanced dendritic, redox-responsive, supramolecular (Dr.S) system for intravenous RAD001 administration.