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4-2 Progress in siRNA Delivery Using Multifunctional Nanoparticles-II
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Welcome to Creative Biolabs, 100% of the effort, 100% of the service. As a dynamic contract research organization, we are based in New York and serve the whole world. Our seasoned scientists are skilled in antibody discovery, antibody engineering, and biomanufacturing solutions. Good evening, dear friends. Thanks for joining us again. At the end of the last program, we said that SIRNA needs a suitable, safe, and effective in vivo delivery system to play a good therapeutic role. Today, we will continue to educate us on the SIRNA packaging. David, great to have you here with us. Thank you for inviting me. I'm very excited to be here. And let's continue our discussion. We already know from our last program that the delivery strategies of SIRNA are mainly divided into physical strategies. Covalent binding strategies, and viral and non-viral vector delivery strategies. Nanoparticles made from synthetic polymers have been developed for SIRNA delivery. When using polymer nanoparticles for delivery, effective encapsulation and subsequent release of the RNA are essential. Why are polymer nanoparticles considered qualified carriers? A qualified carrier needs to both carry SIRNAs and protect them from degradation. And polymer nanoparticles can achieve both functions. What can you tell us about SIRNAs encapsulating conventional cationic polymers? Several traditional cationic polymers are used to encapsulate SIRNAs, such as polyethylene imine and poly-L-lysine. Because they can condense negatively charged small interfering RNA into small particles by electrostatic interaction, they have been widely studied in SIRNA delivery. What are some of the advantages or disadvantages associated with them? These cationic polymers can bind to negatively charged mammalian cell membranes and promote the entry of related nucleic acids into cells. I think these can be counted as their advantages. However, the application of cationic segments in vivo is not popular due to the toxicity of materials, which is a major disadvantage. Any strategy to overcome this disadvantage? The main strategy has been focused on their modification, such as polyethylene glycol of polymers. Polyethylene glycol shielding can provide a barrier to reduce the nonspecific binding caused by positive charge, and cross-linked polyethylene imine with a reversible disulfide bond is another one. The nanoparticles are therefore prone to be degraded into small fragments, which are less toxic. Some researchers have reported simple amine modifications, such as acetylation of primary amine and the introduction of negatively charged propionic acid or succinic acid groups into polyethylene imine polymer structure. The resulting siRNA delivery system maintained high efficiency in gene knockdown. In particular, succinylation of branched polyethylene imine resulted in up to tenfold lower polymer toxicity, in comparison to unmodified polyethylene imine. I found that some studies have used kettle-branched polyethylene imine to reduce polymer toxicity. Have you heard about this experiment? Yes. In that study, siRNA efficiently dissociated from the polyplexes made of catalyzed polyethylene imine upon hydrolysis. In vitro studies further demonstrated that catalyzation enhanced the transfection efficiency of the polyplexes and reduced cellular toxicity. Is there any other methods to improve the transfection efficiency of polymer and reduce its cytotoxicity? People have been committed to the rational design and synthesis of novel polymers. Some of the new polymer systems have shown good results in delivering siRNA. Actually, a novel amphiphilic and cationic tri-block copolymer, consisting of monomathoxy polyethylene glycol, poly-3-coprolactone, and poly-2-aminoethyl ethylene phosphate, was designed and synthesized for siRNA delivery. What are the benefits of nanoparticles made from this polymer? They can load siRNAs through charge interaction after the nanoparticles are formed, without changing the spherical shape of the nanoparticles. This way, siRNAs can effectively silence the expression of green fluorescent protein in certain cells, without obvious cytotoxicity. And of course, other methods are under development as well. For example, one team reported the development of a new polymer based on beta-propionamide cross-linked oligoethylene imine. Using transferrin as the target ligand, the complex can effectively regulate the expression of nucleoprotein, without obvious cytotoxicity. Other teams have recently developed a reducible poly-amidoethylene imine, synthesized by the addition copolymerization of triethylene tetramine and cysteine b-sacralamide. Any results or good outcome yet? In the study of siRNA composite vector formed by new polymer and linear polyethylene imine, a large amount of siRNA dissociation and intracellular distribution were observed after 5 hours, but linear polyethylene imine preparation did not. Is there any new design for packing siRNA? Poly-beta-amino ester is another class of pH-sensitive and biodegradable cationic polymers that may be utilized for intracellular pH-dependent drug release. Poly-beta-amino ester was synthesized by Michael addition reaction of terminal amine and acrylate monomer. In an acidic microenvironment, studies found that poly-beta-amino ester dissolved rapidly and released its content. Poly-beta-amino ester nanoparticles have been used to deliver small molecule drugs, DNA and small interfering RNA. We know that liposomes also play an important role in the encapsulation and delivery of virus into cells. Can they also be used for siRNA delivery? Good question. There is a similar strategy. Lipidoids is another new type of biomaterial for siRNA delivery. They are lipid-like molecules containing tertiary amines and can be mixed to form small interfering RNA lipidoid complexes. Has the safety of lipidoids been tested? Only in animal studies. The safety and efficacy of lipidoids have been evaluated in rodents and non-human primates, indicating their potential for local and systemic RNA therapy. Can non-cationic polymers be used to deliver small interfering RNA? Absolutely. In order to avoid the toxicity associated with cationic polymers, non-cationic polymers were also explored for siRNA delivery. For example, some researchers have reported a nanopreparation using biodegradable non-cationic polyazobutyl cyanoacrylate to form liposomes for small interfering RNA delivery. Such preparation can effectively deliver small interfering RNA to the target, effectively inhibiting tumor growth. Polylactic co-glycolic acid, as another example of non-cationic polymers, has been widely used in drug delivery, including siRNA delivery. What are the advantages here? Polylactic co-glycolic acid is biodegradable, biocompatible, and allows sustained release of siRNA in the site of interest. Since polylactic co-glycolic acid has been approved by FDA for clinical use, they have the potential for rapid clinical translation. Have researchers applied polylactic co-glycolic acid to siRNA delivery? Yes. One team has done that. Target gene silencing successfully inhibited tumor growth in a rat model of hereditary renal cell carcinoma. Another team used polylactic co-glycolic acid nanoparticles to load large amounts of small interfering RNA. In their study, a single dose of siRNA nanoparticles injected into the female genital tract of mice resulted in effective and sustained gene silencing. The downregulation of gene expression was observed in the proximal and distal of the delivery site. Nanoparticles were found penetrated into epithelial tissue. How are siRNA and polymer bound in the process of encapsulation? In nanopreparations, siRNA is physically embedded in the polymer matrix through charge interaction with the polymer. Also, siRNA can be directly linked to the polymer chain for transmission. siRNA has been directly linked to small targeted ligands, including peptides, cholesterol, and aptamers. And reversible crosslinkers have also been used to couple siRNA to small polymeric chains for delivery. Right. It is a direct synthesis method. Pyridine disulfide terminal functionalized polyethylene glycolacrolate was prepared by reversible addition fragmentation chain transfer polymerization for the coupling and delivery of siRNA. To improve the efficiency of siRNA delivery, this group coupled siRNA to pH sensitive polymers. Interesting to see all these new methods. And another one recently, a company has developed a rational siRNA delivery method. They call it the dynamic polycoupling. Can you elaborate more on this? Yeah, I saw that as well. This company designed an amphiphilic polyvinyl ether consisting of butyl vinyl ether and amino vinyl ether as the backbone of the carrier. siRNA is grafted onto the skeleton via reversible disulfide bonds, which prevent the substitution of siRNA from the polymer in the process of reaching the target cell. Likewise, other functional components, including polyethylene glycol, targeting ligands, and endosomalytic components, were also reversibly conjugated to the polymer backbone to form a delivery vehicle. And was it effective? From what they have published, it effectively knocked down two endogenous liver genes, apolipoprotein B and peroxisome proliferator activated receptor alpha. That was it for today's program. Thank you for sharing your knowledge with us. Thank you everyone for listening. We will see you next time.
