Degradable poly(amido amine)s as gene delivery carriers

Recent Advances in Engineering Carriers for siRNA Delivery

RNA interference (RNAi) technology has been a promising treatment strategy for combating intractable diseases. However, the applications of RNAi in clinical are hampered by extracellular and intracellular barriers. To overcome these barriers, various siRNA delivery systems have been developed in the past two decades. The first approved RNAi therapeutic, Patisiran (ONPATTRO) using lipids as the carrier, for the treatment of amyloidosis is one of the most important milestones. This has greatly encouraged researchers to work on creating new functional siRNA carriers. In this review, the recent advances in siRNA carriers consisting of lipids, polymers, and polymer-modified inorganic particles for cancer therapy are summarized. Representative examples are presented to show the structural design of the carriers in order to overcome the delivery hurdles associated with RNAi therapies. Finally, the existing challenges and future perspective for developing RNAi as a clinical modality will be discussed and proposed. It is believed that the addressed contributions in this review will promote the development of siRNA delivery systems for future clinical applications.

Redox-Responsive Polymeric Nanoparticle for Nucleic Acid Delivery and Cancer Therapy: Progress, Opportunities, and Challenges

Cancer development and progression of cancer are closely associated with the activation of oncogenes and loss of tumor suppressor genes. Nucleic acid drugs (e.g., siRNA, mRNA, and DNA) are widely used for cancer therapy due to their specific ability to regulate the expression of any cancer-associated genes. However, nucleic acid drugs are negatively charged biomacromolecules that are susceptible to serum nucleases and cannot cross cell membrane. Therefore, specific delivery tools are required to facilitate the intracellular delivery of nucleic acid drugs. In the past few decades, a variety of nanoparticles (NPs) are designed and developed for nucleic acid delivery and cancer therapy. In particular, the polymeric NPs in response to the abnormal redox status in cancer cells have garnered much more attention as their potential in redox-triggered nanostructure dissociation and rapid intracellular release of nucleic acid drugs. In this review, the important genes or signaling pathways regulating the abnormal redox status in cancer cells are briefly introduced and the recent development of redox-responsive NPs for nucleic acid delivery and cancer therapy is systemically summarized. The future development of NPs-mediated nucleic acid delivery and their challenges in clinical translation are also discussed.

Advancing nucleic acid delivery through cationic polymer design: non-cationic building blocks from the toolbox

The rational integration of non-cationic building blocks into cationic polymers can be devised to enhance the performance of the resulting gene delivery vectors, improving cell targeting behavior, uptake, endosomal escape, toxicity, and transfection efficiency.

Cell uptake and intracellular trafficking of bioreducible poly(amidoamine) nanoparticles for efficient mRNA translation in chondrocytes

Disulfide-containing poly(amidoamine) (PAA) is a cationic and bioreducible polymer, with potential use as a nanocarrier for mRNA delivery in the treatment of several diseases including osteoarthritis (OA). Successful transfection of joint cells with PAA-based nanoparticles (NPs) was shown previously, but cell uptake, endosomal escape and nanoparticle biodegradation were not studied in detail. In this study, C28/I2 human chondrocytes were transfected with NPs co-formulated with a PEG-polymer coating and loaded with EGFP mRNA for confocal imaging of intracellular trafficking and evaluation of transfection efficiency. Compared with uncoated NPs, PEG-coated NPs showed smaller particle size, neutral surface charge, higher colloidal stability and superior transfection efficiency. Furthermore, endosomal entrapment of these PEG-coated NPs decreased over time and mRNA release could be visualized both in vitro and in live cells. Importantly, cell treatment with modulators of the intracellular reducing environment showed that glutathione (GSH) concentrations affect translation of the mRNA payload. Finally, we applied a D-optimal experimental design to test different polymer-to-RNA loading ratios and dosages, thus obtaining an optimal formulation with up to ≈80% of GFP-positive cells and without toxic effects. Together, the biocompatibility and high transfection efficiency of this system may be a promising tool for intra-articular delivery of therapeutical mRNA in OA treatment.

Excipient-Free Ionizable Polyester Nanoparticles for Lung-Selective and Innate Immune Cell Plasmid DNA and mRNA Transfection

Extrahepatic nucleic acid delivery using polymers typically requires the synthesis and purification of custom monomers, post-synthetic modifications, and incorporation of additional excipients to augment their stability, endosomal escape, and in vivo effectiveness. Here, we report the development of a single-component and excipient-free, polyester-based nucleic acid delivery nanoparticle platform comprising ionizable N-methyldiethanolamine (MDET) and various hydrophobic alkyl diols (Cp) that achieves lung-selective nucleic acid transfection in vivo. PolyMDET and polyMDET-Cp polyplexes displayed high serum and enzymatic stability, while delivering pDNA or mRNA to "hard-to-transfect" innate immune cells. PolyMDET-C4 and polyMDET-C6 mediated high protein expression in lung alveolar macrophages and dendritic cells without inducing tissue damage or systemic inflammatory responses. Improved strategies using readily available starting materials to produce a simple, excipient-free, non-viral nucleic acid delivery platform with lung-selective and innate immune cell tropism has the potential to expedite clinical deployment of polymer-based genetic medicines.

The effects of fluoroalkyl chain length and density on siRNA delivery of bioreducible poly(amido amine)s

Fluorination is an attractive strategy for the improvement of transfection efficiency of nucleic acid delivery vectors. Bioreducible poly(amido amine)s (bPAAs) are an important class of biomaterials exhibited to effectively deliver multiple nucleic acids. However, still, the effects of fluoroalkyl chain length and density of bPAA on siRNA delivery are unveiled. Here, we synthesized bPAAs and grafted with different chain lengths and densities of fluorocarbon compounds. Furthermore, we prepared a library of complexes of fluorinated bPAA and siRNA, and investigated the effects of fluorination on the siRNA delivery in vitro and in vivo. We found that all the synthesized bPAAs readily formed complexes with siRNA and the fluorinated complexes considerably achieved improved gene silencing efficacies both in vitro and in vivo. Dramatically, the gene silencing efficacy was increased with increasing fluorine contents. Heptafluorobutyric anhydride (HF) modified bPAAs achieved better gene silencing efficacy when compared with bPAAs fluorinated by trifluoroacetic anhydride (TF) and pentafluoropropionic anhydride (PF) providing the evidence for choosing of best one among fluorocarbon compounds. In addition, a combination of fluorination with bioreducibility enables efficient and safe siRNA delivery.

Biodegradable Polymers for Gene-Delivery Applications

Gene-based therapies have emerged as a new modality for combating a myriad of currently incurable diseases. However, the fragile nature of gene therapeutics has significantly hampered their biomedical applications. Correspondingly, the development of gene-delivery vectors is of critical importance for gene-based therapies. To date, a variety of gene-delivery vectors have been created and utilized for gene delivery. In general, they can be categorized into viral- and non-viral vectors. Due to safety issues associated with viral vectors, non-viral vectors have recently attracted much more research focus. Of these non-viral vectors, polymeric vectors, which have been preferred due to their low immunogenicity, ease of production, controlled chemical composition and high chemical versatility, have constituted an ideal alternative to viral vectors. In particular, biodegradable polymers, which possess advantageous biocompatibility and biosafety, have been considered to have great potential in clinical applications. In this context, the aim of this review is to introduce the recent development and progress of biodegradable polymers for gene delivery applications, especially for their chemical structure design, gene delivery capacity and additional biological functions. Accordingly, we first define and categorize biodegradable polymers, followed by describing their corresponding degradation mechanisms. Various types of biodegradable polymers resulting from natural and synthetic polymers will be introduced and their applications in gene delivery will be examined. Finally, a future perspective regarding the development of biodegradable polymer vectors will be given.

Alterations in Cellular Processes Involving Vesicular Trafficking and Implications in Drug Delivery

Endocytosis and vesicular trafficking are cellular processes that regulate numerous functions required to sustain life. From a translational perspective, they offer avenues to improve the access of therapeutic drugs across cellular barriers that separate body compartments and into diseased cells. However, the fact that many factors have the potential to alter these routes, impacting our ability to effectively exploit them, is often overlooked. Altered vesicular transport may arise from the molecular defects underlying the pathological syndrome which we aim to treat, the activity of the drugs being used, or side effects derived from the drug carriers employed. In addition, most cellular models currently available do not properly reflect key physiological parameters of the biological environment in the body, hindering translational progress. This article offers a critical overview of these topics, discussing current achievements, limitations and future perspectives on the use of vesicular transport for drug delivery applications.

Redox-responsive polymeric micelles formed by conjugating gambogic acid with bioreducible poly(amido amine)s for the co-delivery of docetaxel and MMP-9 shRNA

A novel redox-sensitive system for co-delivering hydrophobic drugs and hydrophilic siRNA or shRNA was developed by conjugating gambogic acid (GA) with poly(amido amine)s (PAAs) through amide bonds, which is called GA-conjugated PAAs (PAG). PAG can self-assemble into micelles as amphiphilic block copolymers, which exhibits an excellent loading ability for the co-delivery of docetaxel (DTX) and MMP-9 shRNA with adjustable dosing ratios. In addition, confocal microscopy, flow cytometry and in vitro transfection analyses demonstrated more efficient cellular internalization of DTX and MMP-9 shRNA after incubation with PAG/DTX- MMP-9 shRNA micelles (PAG/DTX-shRNA) than with free drugs. Unlike traditional amphiphilic copolymer micelles, GA conjugated in PAG possesses an intrinsic anticancer efficacy. The presence of disulfide bonds in PAAs enables rapid disassembly of PAG micelles in response to reducing agents, inducing the release of loaded drugs (DTX, GA and MMP-9 shRNA). In vitro cellular assays revealed that PAG/DTX-shRNA micelles inhibited MCF-7 cell proliferation more efficiently than the single drug or single drug-loaded micelles. In vivo biodistribution and anti-tumor effect studies using an MCF-7 breast cancer xenograft mouse model have indicated that PAG/DTX-shRNA micelles can enhance drug accumulation compared with the free drug, thereby sustaining the therapeutic effect on tumors. Additionally, PAG/DTX-shRNA micelles displayed a greater anti-tumor efficacy than Taxotere® and PAG-shRNA micelles. These results suggest that the redox-sensitive PAG platform is a promising co-delivery system for combining drugs and gene therapy for the treatment of cancer.

STATEMENT OF SIGNIFICANCE

The PAG micelles were designed by conjugating gambogic acid (GA) with poly(amido amine)s (PAAs), which would serve dual purposes as both gene and drugs co-delivery carrier and an anti-tumor prodrug. Unlike traditional amphiphilic micelles, GA conjugated in PAG could exert its intrinsic efficacy and provide synergistic antiproliferative effects with docetaxel (DTX) on MCF-7 cells. Disulfide bonds in PAG enables a rapid disassembly of PAG micelles in response to reducing agents and to release all loaded drugs (DTX, GA and MMP-9 shRNA) at tumor sites. PAG/DTX-shRNA micelles displayed greater anti-tumor efficacy than that of Taxotere®, indicating the design concept for PAG works well. And the strategy for PAG could be used to develop a series of similar co-delivery systems through conjugations of other small-molecule drugs with PAAs, such as doxorubicin, methotrexate and other drugs with carboxy groups in their structure.

Novel guanidinylated bioresponsive poly(amidoamine)s designed for short hairpin RNA delivery

Two different disulfide (SS)-containing poly(amidoamine) (PAA) polymers were constructed using guanidino (Gua)-containing monomers (ie, arginine [Arg] and agmatine [Agm]) and N,N′-cystamine bisacrylamide (CBA) by Michael-addition polymerization. In order to characterize these two Gua-SS-PAA polymers and investigate their potentials as short hairpin RNA (shRNA)-delivery carriers, pSilencer 4.1-CMV FANCF shRNA was chosen as a model plasmid DNA to form complexes with these two polymers. The Gua-SS-PAAs and plasmid DNA complexes were determined with particle sizes less than 90 nm and positive ζ-potentials under 20 mV at nucleic acid:polymer weight ratios lower than 1:24. Bioresponsive release of plasmid DNA was observed from both newly constructed complexes. Significantly lower cytotoxicity was observed for both polymer complexes compared with polyethylenimine and Lipofectamine 2000, two widely used transfection reagents as reference carriers. Arg-CBA showed higher transfection efficiency and gene-silencing efficiency in MCF7 cells than Agm-CBA and the reference carriers. In addition, the cellular uptake of Arg-CBA in MCF7 cells was found to be higher and faster than Agm-CBA and the reference carriers. Similarly, plasmid DNA transport into the nucleus mediated by Arg-CBA was more than that by Agm-CBA and the reference carriers. The study suggested that guanidine and carboxyl introduced into Gua-SS-PAAs polymers resulted in a better nuclear localization effect, which played a key role in the observed enhancement of transfection efficiency and low cytotoxicity. Overall, two newly synthesized Gua-SS-PAAs polymers demonstrated great potential to be used as shRNA carriers for gene-therapy applications.

Guanidinylated bioresponsive poly(amido amine)s designed for intranuclear gene delivery

Guanidinylated poly(amido amine)s with multiple disulfide linkages (Gua-SS-PAAs) were designed and constructed as nonviral gene carriers. The main chains of these novel carriers were synthesized based on monomers containing guanidino groups (guanidine hydrochloride and chlorhexidine), which could avoid complicated side-chain-modification reactions while introducing the guanidino groups. The synthesized Gua-SS-PAAs polymers were characterized by ¹H nuclear magnetic resonance, molecular weight, and polydispersity. Furthermore, Gua-SS-PAAs polymers were complexed with pDNA, and the properties of the complexes were determined, including entrapment efficiency, particle size, ζ-potential, atomic force microscopy images, stability, DNA complexation ability, reduction sensitivity, cytotoxicity, and transfection efficiency. The new Gua-SS-PAAs carriers exhibited higher transfection efficiency and lower cytotoxicity compared with two widely used gene delivery carriers, polyethylenimine and lipofectamine 2000. Furthermore, the relationship between the side-chain structure and morphological/biological properties was extrapolated, and the results showed that guanidine in the side chain aids in the improvement of transfection efficiency. In addition, the introduction of guanidino group might confer the new carriers with nuclear localization function compared to carriers without it.

Peptide-like Polymers Exerting Effective Glioma-Targeted siRNA Delivery and Release for Therapeutic Application

Lipopolymer 49, a solid-phase synthesized T-shaped peptide-like oligoamide containing two central oleic acids, 20 aminoethane, and two terminal cysteine units, is identified as very potent and biocompatible small interfering RNA (siRNA) carrier for gene silencing in glioma cells. This carrier is combined with a novel targeting polymer 727, containing a precise sequence of Angiopep 2 targeting peptide, linked with 28 monomer units of ethylene glycol, 40 aminoethane, and two terminal cysteines in siRNA complex formation. Angiopep-polyethylene glycol (PEG)/siRNA polyplexes exhibit good nanoparticle features, effective glioma-targeting siRNA delivery, and intracellular siRNA release, resulting in an outstanding gene downregulation both in glioma cells and upon intravenous delivery in glioma model nude mice without significant biotoxicity. Therefore, this novel siRNA delivery system is expected to be a promising strategy for targeted and safe glioma therapy.

Surfactant-Free Emulsion-Based Preparation of Redox-Responsive Nanogels

A surfactant-free emulsion-based approach is developed for preparation of nanogels. A water-in-oil emulsion is generated feasibly from a mixture of water and a solution of disulfide-containing hyperbranched PEGylated poly(amido amine)s, poly(BAC2-AMPD1)-PEG, in chloroform. The water droplets in the emulsion are stabilized and filled with poly(BAC2-AMPD1)-PEG, and the crosslinked poly(amido amine)s nanogels are formed via the intermolecular disulfide exchange reaction. FITC-dextran is loaded within the nanogels by dissolving the compound in water before emulsification. Transmission electron microscopy and dynamic light scattering are applied to characterize the emulsion and the nanogels. The effects of the homogenization rate and the ratio of water/polymer are investigated. Redox-induced degradation and FITC-dextran release profile of the nanogels are monitored, and the results show efficient loading and redox-responsive release of FITC-dextran. This is a promising approach for the preparation of nanogels for drug delivery, especially for neutral charged carbohydrate-based drugs.

pH- and redox-responsive self-assembly of amphiphilic hyperbranched poly(amido amine)s for controlled doxorubicin delivery

Vinyl-terminated hyperbranched poly(amido amine)s is obtained by Michael addition polymerization of 4-(aminomethyl)piperidine (AMPD) with a double molar N,N-cystaminebis(acrylamide) (BAC). Then an amphiphilic hyperbranched poly(BAC2-AMPD1)-PEG is produced via converting the vinyl groups to amines followed by PEGylation. Transmission electron microscopy (TEM), dynamic light scattering (DLS), and (1)H nuclear magnetic resonance (NMR) results indicate that the micelles can be obtained via self-assembly of hyperbranched poly(BAC2-AMPD1)-PEG. Further an anti-cancer drug, doxorubicin (DOX), can be loaded into the micelles. pH- and redox-response of the micelles of hyperbranched poly(BAC2-AMPD1)-PEG without and with DOX are investigated. The results of confocal microscopy and flow cytometry reflect that FITC tagged or DOX loaded micelles of hyperbranched poly(BAC2-AMPD1)-PEG can enter HepG2 and MCF-7 cells, and DOX can be observed in the nucleus of the cells. The cytotoxicity of the micelles without and with DOX is evaluated in HepG2 and MCF-7 cells, and the efficacy to kill the cancer cells is discussed in comparison with free DOX.

Safety profiles and antitumor efficacy of oncolytic adenovirus coated with bioreducible polymer in the treatment of a CAR negative tumor model

Adenovirus (Ad) vectors show promise as cancer gene therapy delivery vehicles, but immunogenic safety concerns and coxsackie and adenovirus receptor (CAR)-dependency have limited their use. Alternately, biocompatible and bioreducible nonviral vectors, including arginine-grafted cationic polymers, have been shown to deliver nucleic acids through a cell penetration peptide (CPP) and protein transduction domain (PTD) effect. We utilized the advantages of both viral and nonviral vectors to develop a hybrid gene delivery vehicle by coating Ad with mPEG-PEI-g-Arg-S-S-Arg-g-PEI-mPEG (Ad/PPSA). Characterization of Ad/PPSA particle size and zeta potential showed an overall size and cationic charge increase in a polymer concentration-dependent manner. Ad/PPSA also showed a marked transduction efficiency increase in both CAR-negative and -positive cells compared to naked Ad. Competition assays demonstrated that Ad/PPSA produced higher transgene expression levels than naked Ad and achieved CAR-independent transduction. Oncolytic Ad (DWP418)/PPSA was able to overcome the nonspecificity of polymer-only therapies by demonstrating cancer-specific killing effects. Furthermore, the DWP418/PPSA nanocomplex elicited a 2.24-fold greater antitumor efficacy than naked Ad in vivo. This was supported by immunohistochemical confirmation of Ad E1As accumulation in MCF7 xenografted tumors. Lastly, intravenous injection of DWP418/PPSA elicited less innate immune response compared to naked Ad, evaluated by interleukin-6 cytokine release into the serum. The increased antitumor effect and improved vector targeting to both CAR-negative and -positive cells make DWP418/PPSA a promising tool for cancer gene therapy.

Polyamidoamine and polyglycerol; their linear, dendritic and linear–dendritic architectures as anticancer drug delivery systems

This review covers the latest advances in the conjugation of chemotherapeutics such as doxorubicin, paclitaxel, methotrexate, fluorouracil and cisplatin to dendritic polymers, including polyamidoamine dendrimers, hyperbranched polyglycerols and their linear analogues, with a focus on their cytotoxicity, biodistribution and biodegradability.

pH- and redox-responsive poly(ethylene glycol) and cholesterol-conjugated poly(amido amine)s based micelles for controlled drug delivery

An optimized condition is identified to prepare linear poly(amido amine)s via Michael Addition polymerization of trifunctional amine, 4-(aminomethyl)piperidine (AMPD), with an equimolar diacrylamide, N,N-cystaminebis(acrylamide) (BAC). Poly(ethylene glycol) (PEG) and cholesterol (CE) are conjugated to linear poly(BAC-AMPD) through the reactions with the secondary amino groups in the backbone, respectively, to form poly(BAC-AMPD)-g-PEG-g-CE. The chemical structures of poly(BAC-AMPD) and poly(BAC-AMPD)-g-PEG-g-CE are characterized using NMR and gel permeation chromatography (GPC). Transmission electron microscopy (TEM), dynamic light scattering (DLS) and (1)H NMR results show that micelles with PEG shells and hydrophobic cores composed of poly(BAC-AMPD) and CE are formed via self-assembly of poly(BAC-AMPD)-g-PEG-g-CE in aqueous solution, and the micelles of poly(BAC-AMPD)-g-PEG-g-CE can be degraded by the presence of L-dithiothreitol and show a limited cytotoxicity in vitro. The anti-cancer drug, doxorubicin (DOX), can be loaded into the micelles. The DOX loaded micelles of poly(BAC-AMPD)-g-PEG-g-CE show pH- and redox-responsive drug release and redox-induced formation of aggregates, and it is shown that the DOX loaded micelles can deliver DOX into cells and show a higher efficacy in killing cancer cells than free drug.

2011 Rita Schaffer lecture: nanoparticles for intracellular nucleic acid delivery

Nanoparticles are a promising technology for delivery of new types of therapeutics. A polymer library approach has allowed engineering of polymeric particles that are particularly effective for the delivery of DNA and siRNA to human cells. Certain chemical structural motifs, degradable linkages, hydrophobicity, and biophysical properties are key for successful intracellular delivery. Small differences to biomaterial structure, and especially the type of degradable linkage in the polymers, can be critical for successful delivery of siRNA vs. DNA. Furthermore, subtle changes to biomaterial structure can facilitate cell-type gene delivery specificity between human brain cancer cells and healthy cells as well as between human retinal endothelial cells and epithelial cells. These polymeric nanoparticles are effective for nucleic acid delivery in a broad range of human cell types and have applications to regenerative medicine, ophthalmology, and cancer among many other biomedical research areas.