Revisiting Complexation between DNA and Polyethylenimine: Does the Disulfide Linkage Play a Critical Role in Promoting Gene Delivery?

Enhancing the in vivo stability of polyanion gene carriers by using PEGylated hyaluronic acid as a shielding system

To increase the in vivo stability of cationic gene carriers and avoid the adverse effects of their positive charge, we synthesized a new shielding material by conjugating low molecular weight polyethylene glycol (PEG) to a hyaluronic acid (HA) core. The HA-PEG conjugate assembled with the positively charged complex, forming a protective layer through electrostatic interactions. DNA/polyetherimide/HA-PEG (DNA/PEI/HA-PEG) nanoparticles had higher stability than both DNA/polyethyleneimine (DNA/PEI) and DNA/PEI/HA complexes. Furthermore, DNA/PEI/HA-PEG nanoparticles also showed a diminished nonspecific response toward serum proteins in vivo. The in vivo transfection efficiency was also enhanced by the low cytotoxicity and the improved stability; therefore, this material might be promising for use in gene delivery applications.

Integrating disulfides into a polyethylenimine gene carrier selectively boosts significant transfection activity in lung tissue enabling robust IL-12 gene therapy against metastatic lung cancers

Bioreducible polyethylenimines (SSPEIs) are promising non-viral carriers for cancer gene therapy. However, the availability of significant gene transfection activity by SSPEIs remains a challenge. Herein, an essential step was taken to ascertain whether or not the disulfide bonds of SSPEIs play a critical role in promoting significant gene transfection activity in different tissues. Initially, a disulfide-linked linear polyethylenimine (denoted as SSLPEI) consisting of one 5.0 kDa LPEI main chain and three disulfide-linked 5.7 kDa LPEI grafts was designed and prepared to possess similar molecular weight with commercialized 25 kDa LPEI as a positive control. The SSLPEI could induce superior in vitro transfection activity in different cells to the LPEI control as well as low cytotoxicity. Notably, such enhanced in vitro transfection effect by the SSLPEI was more marked in type-II alveolar epithelial cells compared to different cancer cells. In a Balb/c nude mouse model bearing SKOV-3 tumor, the SSLPEI caused parallel level of transgene expression with the LPEI control in the tumor but significantly higher level in the mouse lung. Furthermore, the SSLPEI and LPEI groups afforded an identical antitumor efficacy against the SKOV-3 tumor via intravenous delivery of a shRNA for silencing VEGF expression in the tumor. However, via intravenous delivery of an interleukin-12 (IL-12) gene into metastatic lung cancers in a C57BL/6 mouse model, the SSLPEI group exerted markedly higher IL-12 expression level in the mouse lung and peripheral blood as compared to the LPEI group, thereby boosting IL-12 immunotherapy against the lung metastasis with longer medium survival time. The results of this work elicit that the disulfide bonds of SSPEIs play a pivotal role in enhancing gene transfection activity selectively in the lung tissue rather than solid tumor, enabling high translational potential of SSPEIs for non-viral gene therapy against metastatic lung cancers.

Block copolymers comprising degradable poly(2-ethyl-2-oxazoline) analogues via copper-free click chemistry

We present the synthesis development of amphiphilic, degradable poly(2-ethyl-2-oxazoline) (PEtOx) analogue block copolymers in a modular fashion utilizing the strain-promoted azide–alkyne cycloaddition (SPAAC).

Cationic cell penetrating peptide modified SNARE protein VAMP8 as free chains for gene delivery

Previously, our group carried out a series of studies using branched polyethyleneimine with 25 000 g mol-1 molar mass (bPEI-25k) as a gene delivery vector and came up with the theory that free cationic chains un-complexed with plasmid DNA (pDNA) can greatly increase the gene transfection efficiency and influence the intracellular delivery process. These free chains can penetrate the membrane quickly, with some of them embedded inside the lipid bi-layers. The "stuck-out" cationic chain ends would shield the signal protein, prevent/delay the development of the later endolysosomes and enhance the efficiency of gene delivery. To mimic the effect of cationic polymers, we selected to use vesicle associated membrane protein-8 (VAMP8) and modified its N-terminus with different cationic cell penetrating peptides (CPPs). The modified fusion proteins are expressed in an Escherichia coli system and purified after extraction. These modified VAMP8 proteins are used as free chains for gene transfection, while using bPEI-25k to condense the pDNA. The results show that the gene transfection efficiency of bPEI-25k/pDNA polyplexes is obviously enhanced in the 293 T cell line. Furthermore, the gene sequences encoding these modified VAMP8 proteins are sub-cloned to pcDNA-3.1 vector and then transferred to 293 T before the treatment with bPEI-25k/pDNA polyplexes. From the result, the transfection efficiency of bPEI-25k/pDNA complexes is enhanced at a similar level to that using modified VAMP8 as free chains. Our current results prove that free cationic chains are probably embedded with the membrane and influence intracellular trafficking, pointing out a new idea to design an effective non-viral gene delivery system.

Antimicrobial activity of nano-sized silver colloids stabilized by nitrogen-containing polymers: the key influence of the polymer capping

Synthesis of stable silver colloids was achieved using nitrogen-containing polymers acting simultaneously as a reducing and stabilizer agent. The polymers polyethyleneimine (PEI), polyvinylpyrrolidone (PVP) and poly(2-vinyl pyridine)-b-poly(ethylene oxide) (PEO-b-P2VP) were used in the procedures. The influence of the surface chemistry and chemical nature of the stabilizer on the cytotoxicity and antimicrobial properties have been evaluated. The produced nanomaterials were found to be non-toxic up to the highest evaluated concentration (1.00 ppm). Nevertheless, at this very low concentration, the AgNPs stabilized by PVP and PEO-b-P2VP were found to be remarkable biocides against bacteria and fungus. On the other hand, we have surprisingly evidenced negligible antimicrobial activity of AgNPs stabilized by positively charged PEI although both (AgNPs and PEI) materials separately are known for their antimicrobial activity as also evidenced in the current investigation. The evidence is claimed to be related to the blocking of Ag+ kinetic release. Accordingly, the antimicrobial effect of nano-sized silver colloids largely depends on the chemical nature of the polymer coating. Possibly, the outstanding colloid stabilization provided by polyethyleneimine slows down Ag+ release thereby hampering its biological activity whereas the poorer stabilization and good ionic transport property of PVP and PEO-b-P2VP allows much faster ion release and cell damage.

Gene Transfection Mediated by Catiomers Requires Free Highly Charged Polymer Chains To Overcome Intracellular Barriers

The prospective use of the block copolymers poly(ethylene oxide)₁₁₃-b-poly[2-(diethylamino)ethyl methacrylate]₅₀ (PEO₁₁₃-b-PDEA₅₀) and poly[oligo(ethylene glycol)methyl ether methacrylate]₇₀-b-poly[oligo(ethylene glycol)methyl ether methacrylate₁₀-co-2-(diethylamino)ethyl methacrylate₄₇-co-2-(diisopropylamino)ethyl methacrylate₄₇] (POEGMA₇₀-b-P(OEGMA₁₀-co-DEA₄₇-co-DPA₄₇)) as nonviral gene vectors was evaluated. The polymers are able to properly condense DNA into nanosized particles (R_H ≈ 75 nm), which are marginally cytotoxic and can be uptaken by cells. However, the green fluorescent protein (GFP) expression assays evidenced that DNA delivery is essentially negligible meaning that intracellular trafficking hampers efficient gene release. Subsequently, we demonstrate that cellular uptake and particularly the quantity of GFP-positive cells are substantially enhanced when the block copolymer polyplexes are produced and further supplemented by BPEI chains (branched polyethylenimine). The dynamic light scattering/electrophoretic light scattering/isothermal titration calorimetry data suggest that such a strategy allows the adsorption of BPEI onto the surface of the polyplexes, and this phenomenon is responsible for increasing the size and surface charge of the assemblies. Nevertheless, most of the BPEI chains remain freely diffusing in the systems. The biological assays confirmed that cellular uptake is enhanced in the presence of BPEI and principally, the free highly charged polymer chains play the central role in intracellular trafficking and gene transfection. These investigations pointed out that the transfection efficiency versus cytotoxicity issue can be balanced by a mixture of BPEI and less cytotoxic agents such as for instance the proposed block copolymers.