Dendrimer-grafted bioreducible polycation/DNA multilayered films with low cytotoxicity and high transfection ability

Controlled release of incorporated foreign DNA from multilayered films plays an important role in surface-mediated gene delivery. Herein, multilayered polyelectrolyte complex thin films, composed of dendrimer-grafted bio-reducible cationic poly(disulfide amine) and plasmid DNA, were fabricated via layer-by-layer (LBL) assembly for in vitro localized gene delivery. The UV absorbance and thickness of the LBL films were found to have linear correlation with the numbers of poly(disulfide amine)/DNA bilayers. Although LBL films were stable in PBS buffer, their degradation could be triggered by reducing agents (i.e. glutathione, GSH). The degradation rate of the films is directly proportional to the GSH concentration, which in turn affected the corresponding gene expression. All poly(disulfide amine)/DNA films exhibited lower cytotoxicity and higher transfection activity in comparison with PEI/DNA multilayered films. Moreover, LBL films showed the highest transfection efficiency in the presence of 2.5 mM GSH when cultured with 293T cells, with ~36% GFP-positive 293T cells after 5-days of co-culture. These DNA-containing reducible films could potentially be useful in gene therapy and tissue engineering by controlling the release of incorporated DNA.

Stimuli-responsive dendrimers in drug delivery

Dendrimers have shown great promise as carriers in drug delivery due to their unique structures and superior properties. However, the precise control of payload release from a dendrimer matrix still presents a great challenge. Stimuli-responsive dendrimers that release payloads in response to a specific trigger could offer distinct clinical advantages over those dendrimers that release payloads passively. These smart polymers are designed to specifically release their payloads at targeted regions or at constant release profiles for specific therapies. They represent an attractive alternative to targeted dendrimers and enable dendrimer-based therapeutics to be more effective, more convenient, and much safer. The wide range of stimuli, either endogenous (acid, enzyme, and redox potentials) or exogenous (light, ultrasound, and temperature change), allows great flexibility in the design of stimuli-responsive dendrimers. In this review article, we will highlight recent advances and opportunities in the development of stimuli-responsive dendrimers for the treatment of various diseases, with emphasis on cancer. Specifically, the applications of stimuli-responsive dendrimers in drug delivery as well as their mechanisms are intensively reviewed.

Two-component reduction-sensitive lipid–polymer hybrid nanoparticles for triggered drug release and enhanced in vitro and in vivo anti-tumor efficacy

Two-component reduction-sensitive lipid–polymer hybrid nanoparticles composed of DLPE-S-S-MPEG and PCL were developed for intracellular reduction triggered delivery of DOX.

A dendritic catiomer with an MOF motif for the construction of safe and efficient gene delivery systems

The dendritic catiomer using biocompatible Zr-MOFs as the core exhibited a markedly higher transfection efficiency and lower cytotoxicity than the commercial gold standard branched PEI_25k in A549 cells.

Challenges in CRISPR/CAS9 Delivery: Potential Roles of Nonviral Vectors

CRISPR/Cas9 genome editing platforms are widely applied as powerful tools in basic research and potential therapeutics for genome regulation. The appropriate alternative of delivery system is critical if genome editing systems are to be effectively performed in the targeted cells or organisms. To date, the in vivo delivery of the Cas9 system remains challenging. Both physical methods and viral vectors are adopted in the delivery of the Cas9-based gene editing platform. However, physical methods are more applicable for in vitro delivery, while viral vectors are generally concerned with safety issues, limited packing capacities, and so on. With the robust development of nonviral drug delivery systems, lipid- or polymer-based nanocarriers might be potent vectors for the delivery of CRISPR/Cas9 systems. In this review, we look back at the delivery approaches that have been used for the delivery of the Cas9 system and outline the recent development of nonviral vectors that might be potential carriers for the genome editing platform in the future. The efforts in optimizing cationic nanocarriers with structural modification are described and promising nonviral vectors under clinical investigations are highlighted.

Clustering Small Dendrimers into Nanoaggregates for Efficient DNA and siRNA Delivery with Minimal Toxicity

Cationic dendrimers are widely used as nonviral gene vectors, however, current gene materials based on dendrimers are either little effective or too toxic on the transfected cells. Here, a facile strategy is presented to prepare high efficient dendrimers with low transfection toxicity. Small dendrimers with 2 nm are clustered into nanoaggregates (≈100 nm) via phenylboronic acid modification and the self-assembled materials enable efficient DNA and siRNA delivery on several cell lines. The clustered nanostructures can disassemble into small dendrimers in acidic conditions thus exerting significantly less toxicity on the transfected cells. Further structure-function relationship studies reveal that both the phenyl group and boronic acid group play essential roles in the self-assembly and gene delivery processes. The transfection efficacy of phenylboronic acid-modified dendrimers can be down-regulated by blocking the boronic acid groups on dendrimers with diols or degrading the groups with hydrogen peroxide. This study provides a facile strategy in the development of efficient and biocompatible gene vectors based on low molecular weight polymers and clearly demonstrates the structure-function relationship of phenylboronic acid-modified polymers in gene delivery.

Nanocomplexes from RGD-modified generation 1.0 polyamidoamine based copolymers used for intravascular gene release to prevent restenosis

Aim: To validate the efficacy of nanocomplexes from RGD-modified polyamidoamine (PAMAM G1) copolymer for prevention of restenosis. Materials & methods: Generation 1.0 polyamidoamine (PAMAM G1)-based copolymers (PGP) and RGD modified PGP (PGP-RGD) were synthesized and its properties were evaluated. Intravascular VEGF165 release tests were performed. Results: The PGP-RGD1 (2.6% grafting rate) exhibited lower cytotoxicity and larger combining ability with pDNA. The complexes had sizes of 80–160 nm and zeta potentials of 3–20 mV. Transfection efficiency of PGP-RGD1 complexes in human umbilical vein endothelial cells was larger than that of PGP complexes. Patency and expression level of artery in PGP-RGD1 group were higher than that in saline group. Conclusion: PGP-RGD1 will be a promising targeted gene vector.

Synergetic enhancement of antitumor efficacy with charge-reversal and reduction-sensitive polymer micelles

An amphiphilic block copolymer PLA-SS-PAEMA/DMMA was used to encapsulate and deliver Doxorubicin for synergetic enhancement of antitumor efficacy by the combinational effect of charge-reversal on cellular uptake and reduction-sensitivity on intracellular DOX release.

Bioreducible polyethylenimine nanoparticles for the efficient delivery of nucleic acids

Electrostatically crosslinked bioreducible nanoparticles of polyethylenimine (DP NPs) have been prepared and evaluated for their cytotoxicity and capability to transport nucleic acids inside the cells.

Small cyclen-imidazolium-containing molecules and their interactions with DNA

Three small organic molecules containing different numbers of cyclen and imidazolium units were synthesized. Their interactions with plasmid DNA and their potential for gene delivery vectors were investigated. Agarose gel retardation and ethidium bromide exclusion assays revealed that these molecules can effectively condense DNA, and compounds with higher molecular weights are needed to lower w/w ratio for full condensation. Dynamic light scattering (DLS) and transmission electron microscopy (TEM) indicated that these compounds may form nanosized spherical particles with DNA. Furthermore, the complex formed from 10, i.e., 10/DNA, can partially release DNA from compact state at a relatively higher concentration of NaCl (200 mM). In the presence of the lipid 1,2-dioleoyl-sn-glycero-3-phosphoethanolamine (DOPE), 10 could transfer plasmid DNA into BEL-7402 cells. In addition, these compounds exhibited much lower cytotoxicity than PEI 25 kDa.

Oligoamine-tethered low generation polyamidoamine dendrimers as potential nucleic acid carriers

Oligoamine-tethered low generation PAMAM dendrimers (mG2–mG4) have been synthesized, which showed significantly higher transfection efficiency with minimal cytotoxicity in vitro.

Molecular weight and architectural dependence of well-defined star-shaped poly(lysine) as a gene delivery vector

A series of well-defined star-shaped polypeptides were successfully synthesised by the ring opening polymerisation (ROP) of the N-carboxyanhydride (NCA) of ε-carbobenzyloxy-l-lysine (ZLL) using a range of generations of polypropylene imine (PPI) dendrimers as multifunctional initiators. The monomer feed ratio and dendrimer generation were varied to afford a series of polypeptide dendrimer hybrids with superior structural versatility and functionality. Subsequent protecting group removal yielded star-shaped poly(lysine) of controlled variation in polypeptide chain length and arm multiplicity. Star-shaped PLL polymers were used to prepare pDNA and siRNA to form "polyplexes" to determine their ability to complex different nucleic acid cargoes and were compared with linear PLL polyplex controls. Significant differences in size and surface charge were seen between star-shaped PLL polyplexes and linear PLL polyplexes for both cargoes. The star-shaped polypeptides were capable of more effective complexation of both nucleic acids at low N/P ratios compared to linear PLL as evidenced by zeta potential and electrophoretic data. This was particularly evident in siRNA polyplexes as linear PLL failed to completely complex siRNA into nanocomplexes of appropriate size for cell transfection i.e. <200 nm in size, while star poly(lysine) formed siRNA polyplexes <100 nm at certain N/P ratios, albeit strongly dependent on the particular molecular weight and architecture, as analysed by dynamic light scattering (DLS). Atomic force microscopy (AFM) identified discrete spherically shaped polyplexes for all star-shaped polypeptide-based polyplexes while linear PLL formed elongated irregular shaped complexes. This difference in morphology may go some way towards explaining the 300-fold increase in luciferase expression seen for star-shaped PLL polyplexes G5(64)-PLL₄₀ compared to linear PLL pGLuc polyplexes in epithelial cells. Each of the PPI-PLL polymers appeared to be capable of protecting the nucleic acid cargoes from degradation by the relevant nuclease enzyme as effectively as the positive control polyethyleneimine (PEI) polyplexes. Overall the promising nucleic acid complexation, sizing, morphology and protection capacity of two different genetic "cargoes" highlight the potential of polypeptide dendrimer hybrids as gene delivery vectors.

Reduction biodegradable brushed PDMAEMA derivatives synthesized by atom transfer radical polymerization and click chemistry for gene delivery

Novel reducible and degradable brushed poly(2-(dimethylamino) ethyl methacrylate) (PDMAEMA) derivatives were synthesized and evaluated as non-viral gene delivery vectors. First, alkyne-functionalized poly(aspartic acid) with a disulfide linker between the propargyl group and backbone poly([(propargyl carbamate)-cystamine]-α,β-aspartamide) (P(Asp-SS-AL)) was synthesized. Second, linear low molecular weight (LMW) monoazido-functionalized PDMAEMAs synthesized via atom transfer radical polymerization were conjugated to the polypeptide side-chains of P(Asp-SS-AL) via click chemistry to yield high molecular weight (HMW) polyaspartamide-based disulfide-containing brushed PDMAEMAs (PAPDEs). The PAPDEs were able to condense plasmid DNA to form 100 to 200nm polyplexes with positive ζ-potentials. Moreover, in the presence of dithiothreitol the PAPDEs degraded into LMW PDAMEMA, resulting in disintegration of the PAPDE/DNA polyplexes and subsequent release of plasmid DNA. In vitro experiments revealed that the PAPDEs were less cytotoxic and more effective in gene transfection than control 25kDa poly(ethyleneimine) and HMW linear PDMAEMA. In conclusion, reducible and degradable polycations composed of LMW PDMAEMAs coupled to a polypeptide backbone via reduction-sensitive disulfide bonds are effective gene vectors with an excellent cytocompatibility.

A Serum-Resistant Low-Generation Polyamidoamine with PEI 423 Outer Layer for Gene Delivery Vector

A new derivative of polyamidoamine and polyethylenimine, G2.5-PEI 423 or G1.5-PEI 423, is prepared by an amidation reaction of PAMAM G2.5 or PAMAM G1.5 using PEI 423. The polycations show a great ability to combine with pDNA to form complexes, which protect the pDNA from nuclease degradation. The polymers display stronger buffer capacity and lower cytotoxicity. The complexes have particle sizes of 120-180 nm and zeta potentials of 20-40 mV. The G2.5-PEI 423 complexes display much higher transfection efficiencies than PAMAM G5 and Lipo-2k, and the G1.5-PEI 423 complexes display higher transfection efficiencies than PAMAM G4 and PEI-25k. The complexes possess better serum-resistant capacity. The G2.5-PEI 423 has a great potential to be used as a serum-resistant gene vector.

Cationic polymers and their therapeutic potential

The last decade has witnessed enormous research focused on cationic polymers. Cationic polymers are the subject of intense research as non-viral gene delivery systems, due to their flexible properties, facile synthesis, robustness and proven gene delivery efficiency. Here, we review the most recent scientific advances in cationic polymers and their derivatives not only for gene delivery purposes but also for various alternative therapeutic applications. An overview of the synthesis and preparation of cationic polymers is provided along with their inherent bioactive and intrinsic therapeutic potential. In addition, cationic polymer based biomedical materials are covered. Major progress in the fields of drug and gene delivery as well as tissue engineering applications is summarized in the present review.

Disulfide-containing brushed polyethylenimine derivative synthesized by click chemistry for nonviral gene delivery

Polyaspartamide-based disulfide-containing brushed polyethylenimine derivatives P(Asp-Az)X-SS-PEIs were synthesized via click chemistry and evaluated as nonviral gene delivery carrier. First, azide-functional poly(aspartic acid) derivatives with various azide-group densities and monoalkyne-terminated PEI with disulfide linkages were synthesized. Then, click reaction between the azide-functional poly(aspartic acid) derivative as main chain and the monoalkyne-terminated PEI as branched chain resulted in high-molecular-weight disulfide-containing brushed PEI derivative. The structure of obtained polymers was confirmed by (1)H NMR and FTIR. It was shown that the disulfide-containing P(Asp-Az)X-SS-PEIs were able to bind plasmid DNA and condense DNA into small positive nanoparticles. The reduction-sensitivity of the P(Asp-Az)X-SS-PEI/DNA polyplexes was confirmed by gel retardation assay and dynamic light scattering (DLS) in the presence of DTT. In vitro experiments revealed that the reducible P(Asp-Az)X-SS-PEI not only had much lower cytotoxicity, but also posed high transfection activity (both in the presence and absence of serum) as compared to the control nondegradable 25 kDa PEI. This study indicates that a reducibly degradable brushed polymer P(Asp-Az)X-SS-PEI composed of low-molecular-weight (LMW) PEI via a disulfide-containing linkage can be a promising gene delivery carrier.

Intracellular organelle-targeted non-viral gene delivery systems

Gene therapy is a rapidly growing approach for the treatment of various diseases. To achieve successful gene therapy, a gene delivery system is necessary to overcome several barriers in the extracellular and intracellular spaces. Polymers, peptides, liposomes and nanoparticles developed as gene carriers have achieved efficient cellular uptake of genes. Among these carriers, cationic polymers and peptides have been further developed as intracellular organelle-targeted delivery systems. The cytoplasm, nucleus and mitochondria have been considered primary targets for gene delivery using targeting moieties or environment-responsive materials. In this review, we explore recently developed non-viral gene carriers based on reducible systems specialized to target the cytoplasm, nucleus and mitochondria.

Biocleavable Polycationic Micelles as Highly Efficient Gene Delivery Vectors

An amphiphilic disulfide-containing polyamidoamine was synthesized by Michael-type polyaddition reaction of piperazine to equimolar N, N'-bis(acryloyl)cystamine with 90% yield. The polycationic micelles (198 nm, 32.5 mV), prepared from the amphiphilic polyamidoamine by dialysis method, can condense foreign plasmid DNA to form nanosized polycationic micelles/DNA polyelectrolyte complexes with positive charges, which transfected 293T cells with high efficiency. Under optimized conditions, the transfection efficiencies of polycationic micelles/DNA complexes are comparable to, or even higher than that of commercially available branched PEI (Mw 25 kDa).