Linear polyethylenimine produced by partial acid hydrolysis of poly(2-ethyl-2-oxazoline) for DNA and siRNA delivery in vitro

Thermoresponsive Polyoxazolines as Vectors for Transfection of Nucleic Acids

Poly(2-oxazoline)s (POx) are an attractive platform for the development of non-viral gene delivery systems. The combination of POx moieties, exhibiting excellent biocompatibility, with DNA-binding polyethyleneimine (PEI) moieties into a single copolymer chain is a promising approach to balance toxicity and transfection efficiency. The versatility of POx in terms of type of substituent, copolymer composition, degree of polymerization, degree of hydrolysis, and chain architecture, as well as the introduction of stimuli-responsive properties, provides opportunities to finely tune the copolymer characteristics and physicochemical properties of the polyplexes to increase the biological performance. An overview of the current state of research in the POx-PEI-based gene delivery systems focusing particularly on thermosensitive POx is presented in this paper.

PEGylated Polyethylenimine Derivative-Mediated Local Delivery of the shSmad3 Inhibits Intimal Thickening after Vascular Injury

Intimal hyperplasia is a complex process which contributes to several clinical problems such as atherosclerosis and postangioplasty restenosis. Inhibition of Smad3 expression inhibits intimal thickening. Our previous study has modified biscarbamate cross-linked polyethylenimine derivative (PEI-Et) through PEGylation thus obtained polyethylene glycol-graft-polyethylenimine derivative (PEG-Et 1:1), which has lower cytotoxicity and higher gene transfection efficiency compared with PEI-Et. In this study, PEG-Et 1:1 was employed in Smad3 shRNA (shSmad3) delivery for preventing intimal hyperplasia after vascular injury. It was observed that PEG-Et 1:1 could condense shSmad3 gene into nanoparticles with particle size of 115–168 nm and zeta potential of 3–6 mV. PEG-Et 1:1 displayed remarkably lower cytotoxicity, higher transfection efficiency, and shRNA silencing efficiency than PEI-Et and PEI 25 kDa in vascular smooth muscle cells (VSMCs). Moreover, PEG-Et 1:1/shSmad3 polyplex treatment significantly inhibited collagen, matrix metalloproteinase 1 (MMP1), MMP2 and MMP9 expression, and upregulated tissue inhibitor of metalloproteinase 1 (TIMP1) expression both in vitro and in vivo. Furthermore, intravascular delivery of shSmad3 with PEG-Et 1:1 polyplex efficiently reduced Smad3 expression and inhibited intimal thickening 14 days after vascular injury. Ultimately, this study indicated that PEG-Et 1:1-mediated local delivery of shSmad3 is a promising strategy for preventing intimal thickening.

Novel Oligo-Guanidyl-PEG Carrier Forming Rod-Shaped Polyplexes

A novel unconventional supramolecular oligo-cationic structure (Agm₆-M-PEG-OCH₃) has been synthesized to yield high efficiency therapeutic oligonucleotide (ON) delivery. Agm₆-M-PEG-OCH₃ was obtained by a multistep protocol that included the conjugation of agmatine (Agm) moieties to maltotriose (M), which was further derivatized with one poly(ethylene glycol) (PEG) chain. Gel electrophoresis analysis showed that the 19 base pairs dsDNA model ON completely associates with Agm₆-M-PEG-OCH₃ at 3 N/P molar ratio, which is in agreement with the in silico molecular predictions. Isothermal titration calorimetry (ITC) analyses showed that the Agm₆-M-PEG-OCH₃/ON association occurs through a combination of mechanisms depending on the N/P ratios resulting in different nanostructures. Dynamic light scattering (DLS) and transmission electron microscopy (TEM) revealed that the Agm₆-M-PEG-OCH₃/ON polyplexes have rod-shape structure with a mean diameter of 50-75 nm and aspect ratio depending on the N/P ratio. The polyplexes were stable over time in buffer, while a slight size increase was observed in the presence of serum proteins. Cell culture studies showed that neither Agm₆-M-PEG-OCH₃ nor polyplexes displayed cytotoxic effects. Cellular uptake depended on the cell line and polyplex composition: cellular internalization was higher in the case of MCF-7 and KB cells compared to MC3T3-E1 cells and polyplexes with smaller aspect ratio were taken-up by cells more efficiently than polyplexes with higher aspect ratio. Finally, preliminary studies showed that our novel carrier efficiently delivered ONs into cells providing gene silencing.

"Grafting-from" synthesis and characterization of poly (2-ethyl-2-oxazoline)-b-poly (benzyl L-glutamate) micellar nanoparticles for potential biomedical applications

Introduction: Recent advances in the field of poly (2-oxazolines) as bio-inspired synthetic pseudopeptides have proven their potential biomedical applications such as drug delivery and tissue engineering. Methods: In order to fabricate a biodegradable micellar nanoparticle of poly (2-ethyl 2-oxazoline)-b-poly (benzyl L-glutamate) or pEOx-b-pBLG, "grafting-from" synthesis approach was used involving consecutive steps of cationic ring-opening polymerization of 2-ethyl-2-oxazoline, amine functionalization of pEOx using 1-Boc-piperazine and N-carboxyanhydride polymerization of γ-benzyl- L-glutamate. Following hydrolysis of the copolymer, the protecting γ-benzyl groups were removed yielding a double-hydrophilic block ionomer of pEOx-b-poly (L-glutamic acid). The polymers were characterized by FTIR, 1H-NMR, size exclusion chromatography and differential scanning calorimetry (DSC). Aqueous assembly of the polymers was investigated by pyrene assay, dynamic light scattering, and transmission electron microscopy. MTT cytotoxicity assay was also performed to determine the cytocompatibility in various tumor cell lines. Results: The polymeric micelles presented a uni-modal size distribution with mean hydrodynamic diameter of 149.8 ± 10.6 nm and critical aggregation concentration of 60 µg/mL. The average molecular weight of pEOx increased from ~ 14 to 20 kDa for pEOx-b-poly (L-glutamic acid) as determined by light scattering (Debye plot), indicating a successful copolymerization. MTT assay showed little to no practical cytotoxicity at concentrations below 1 mg/mL. Conclusion: Multi-step synthesis of pEOx-b-pBLG and subsequent alkaline hydrolysis were performed to obtain the block ionomer pEOx-b-poly (L-glutamic acid). Both pEOx-based copolymers can be considered for various potential applications such as loading and delivery of drugs, genes, and contrast agents either by chemical conjugation or physical loading.

Reversal of multidrug resistance in MCF-7/Adr cells by codelivery of doxorubicin and BCL2 siRNA using a folic acid-conjugated polyethylenimine hydroxypropyl-β-cyclodextrin nanocarrier

Systemic administration of chemotherapy for cancer often faces drug resistance, limiting its applications in cancer therapy. In this study, we developed a simple multifunctional nanocarrier based on polyethylenimine (PEI) to codeliver doxorubicin (DOX) and BCL2 small interfering RNA (siRNA) for overcoming multidrug resistance (MDR) and enhancing apoptosis in MCF-7/Adr cancer cells by combining chemotherapy and RNA interference (RNAi) therapy. The low-molecular-weight branch PEI was used to conjugate hydroxypropyl-β-cyclodextrin (HP-β-CD) and folic acid (FA), forming the codelivery nanocarrier (FA-HP-β-CD-PEI) to encapsulate DOX with the cavity HP-β-CD and bind siRNA with the positive charge of PEI for tumor-targeting codelivering drugs. The drug-loaded nanocomplexes (FA-HP-β-CD-PEI/DOX/siRNA) showed uniform size distribution, high cellular uptake, and significant gene suppression of BCL2, displaying the potential of overcoming MDR for enhancing the effect of anticancer drugs. Furthermore, the nanocomplexes achieved significant cell apoptosis through a mechanism of downregulating the antiapoptotic protein BCL2, resulted in improving therapeutic efficacy of the coadministered DOX by tumor targeting and RNA interference. Our study indicated that combined RNAi therapy and chemotherapy using our functional codelivery nanocarrier could overcome MDR and enhance apoptosis in MDR cancer cells for a potential application in treating MDR cancers.

In vitro study of partially hydrolyzed poly(2-ethyl-2-oxazolines) as materials for biomedical applications

Polymers based on 2-oxazoline, such as poly(2-ethyl-2-oxazolines) (PETOx), are considered to be a type of 'pseudopeptide' with the ability to form novel biomaterials. The hydrolysis of PETOx was carried out to evaluate its use in biomedical applications. In the present work, PETOx samples with a range of molar masses were prepared by living cationic polymerization. Hydrolysis was carried out at time intervals ranging from 15 to 180 min to prepare copolymers with different amounts of ethylene imine units. (1)H NMR spectroscopy was used to identify the structure of the hydrolyzed polymers. The dependence of in vitro cell viability on the degree of hydrolysis was determined using three different model cell lines, namely, mouse embryonic 3T3 fibroblasts, pancreatic βTC3 cells, and mouse lymphoid macrophages P388.D1. It was demonstrated that increasing the degree of hydrolysis decreased cell viability for all cell types. Fibroblast cells displayed the highest tolerance; additionally, the effect of polymer size showed no observable significance. Macrophage cells, immune system representatives, displayed the highest sensitivity to contact with hydrolyzed PETOx. The effect of polymer hydrolysis, polymer concentration and the incubation time on cell viability was experimentally observed. Confocal laser-scanning microscopy provided evidence of cellular uptake of pyrene-labeled (co)polymers.

Cross-linked polyethylenimine-tripolyphosphate nanoparticles for gene delivery

The high transfection efficiency of polyethylenimine (PEI) makes it an attractive potential nonviral genetic vector for gene delivery and therapy. However, the highly positive charge of PEI leads to cytotoxicity and limits its application. To reduce the cytotoxicity of PEI, we prepared anion-enriched nanoparticles that combined PEI with tripolyphosphate (TPP). We then characterized the PEI-TPP nanoparticles in terms of size, zeta potential, and Fourier-transform infrared (FTIR) spectra, and assessed their transfection efficiency, cytotoxicity, and ability to resist deoxyribonuclease (DNase) I digestion. The cellular uptake of PEI-TPP with phosphorylated internal ribosome entry site–enhanced green fluorescent protein C1 or FAM (fluorouracil, Adriamycin [doxorubicin] and mitomycin)-labeled small interfering ribonucleic acids (siRNAs) was monitored by fluorescence microscopy and confocal laser microscopy. The efficiency of transfected delivery of plasmid deoxyribonucleic acid (DNA) and siRNA in vitro was 1.11- to 4.20-fold higher with the PEI-TPP particles (7.6% cross-linked) than with the PEI, at all N:P ratios (nitrogen in PEI to phosphorus in DNA) tested. The cell viability of different cell lines was more than 90% at the chosen N:P ratios of PEI-TPP/DNA complexes. Moreover, PEI-TPP nanoparticles resisted digestion by DNase I for more than 2 hours. The time-dependent absorption experiment showed that 7.6% of cross-linked PEI-TPP particles were internalized by 293T cells within 1 hour. In summary, PEI-TPP nanoparticles effectively transfected cells while conferring little or no toxicity, and thus have potential application in gene delivery.

Glial cell line-derived neurotrophic factor gene delivery via a polyethylene imine grafted chitosan carrier

Parkinson’s disease is known to result from the loss of dopaminergic neurons. Direct intracerebral injections of high doses of recombinant glial cell line-derived neurotrophic factor (GDNF) have been shown to protect adult nigral dopaminergic neurons. Because GDNF does not cross the blood–brain barrier, intracerebral gene transfer is an ideal option. Chitosan (CHI) is a naturally derived material that has been used for gene transfer. However, the low water solubility often leads to decreased transfection efficiency. Grafting of highly water-soluble polyethylene imines (PEI) and polyethylene glycol onto polymers can increase their solubility. The purpose of this study was to design a non-viral gene carrier with improved water solubility as well as enhanced transfection efficiency for treating Parkinsonism. Two molecular weights (Mw =600 and 1,800 g/mol) of PEI were grafted onto CHI (PEI600-g-CHI and PEI1800-g-CHI, respectively) by opening the epoxide ring of ethylene glycol diglycidyl ether (EX-810). This modification resulted in a non-viral gene carrier with less cytotoxicity. The transfection efficiency of PEI600-g-CHI/deoxyribonucleic acid (DNA) polyplexes was significantly higher than either PEI1800-g-CHI/DNA or CHI/DNA polyplexes. The maximal GDNF expression of PEI600-g-CHI/DNA was at the polymer:DNA weight ratio of 10:1, which was 1.7-fold higher than the maximal GDNF expression of PEI1800-g-CHI/DNA. The low toxicity and high transfection efficiency of PEI600-g-CHI make it ideal for application to GDNF gene therapy, which has potential for the treatment of Parkinson’s disease.