PEGylation improves nanoparticle formation and transfection efficiency of messenger RNA.

PURPOSE: Cationic polymers have been intensively investigated for plasmid-DNA (pDNA), but few studies addressed their use for messenger-RNA (mRNA) delivery. We analyzed two types of polymers, linear polyethylenimine (l-PEI) and poly-N,N-dimethylaminoethylmethacrylate P(DMAEMA), to highlight specific requirements for the design of mRNA delivery reagents. The effect of PEGylation was investigated using P(DMAEMA-co-OEGMA) copolymer. METHODS: The influence of polymer structure on mRNA binding and particle formation was assessed in a side-by-side comparison with pDNA by methods such as agarose-retardation assay and scanning probe microscopy. Transfection studies were performed on bronchial epithelial cells. RESULTS: Binding of cationic polymers inversely correlated with type of nucleic acid. Whereas P(DMAEMA) bound strongly to pDNA, only weak mRNA binding was observed, which was vice versa for l-PEI. Both polymers resulted in self-assembled nanoparticles forming pDNA complexes of irregular round shape; mRNA particles were significantly smaller and more distinct. Surprisingly, PEGylation improved mRNA binding and transfection efficiency contrary to observations made with pDNA. Co-transfections with free polymer improved mRNA transfection. CONCLUSIONS: Gene delivery requires tailor-made design for each type of nucleic acid. PEGylation influenced mRNA-polymer binding efficiency and transfection and may provide a method of further improving mRNA delivery.

Characterization of tailor-made copolymers of oligo(ethylene glycol) methyl ether methacrylate and N,N-dimethylaminoethyl methacrylate as nonviral gene transfer agents: influence of macromolecular structure on gene vector particle properties and transfection efficiency.

Oligo(ethylene glycol) methyl ether methacrylates (OEGMA) of various chain lengths (i.e., 9, 23, or 45 EG units) and N,N-dimethylaminoethyl methacrylate (DMAEMA) were copolymerized by atom transfer radical polymerization (ATRP), yielding well-defined P(DMAEMA-co-OEGMA) copolymers with increasing OEGMA molar fractions (F(OEGMA)) but a comparable degree of polymerization (DP approximately 120). Increase of both F(OEGMA) and OEGMA chain lengths correlated inversely with gene vector size, morphology, and zeta potential. P(DMAEMA-co-OEGMA) copolymers prevented gene vector aggregation at high plasmid DNA (pDNA) concentrations in isotonic solution and did not induce cytotoxicity even at high concentrations. Transfection efficiency of the most efficient P(DMAEMA-co-OEGMA) copolymers was found to be >10-fold lower compared with branched polyethylenimine (PEI) 25 kDa. Although OEGMA copolymerization largely reduced gene vector binding with the cell surface, cellular internalization of the bound complexes was less affected. These observations suggest that inefficient endolysosomal escape limits transfection efficiency of P(DMAEMA-co-OEGMA) copolymer gene vectors. Despite this observation, optimized p(DMAEMA-co-OEGMA) gene vectors remained stable under conditions for in vivo application leading to 7-fold greater gene expression in the lungs compared with PEI. Tailor-made P(DMAEMA-co-OEGMA) copolymers are promising nonviral gene transfer agents that fulfill the requirements for successful in vivo gene delivery.

Targeting of the beta(2)-adrenoceptor increases nonviral gene delivery to pulmonary epithelial cells in vitro and lungs in vivo.

Coupling of targeting ligands to polyethylenimine (PEI) has been previously used to improve transfection efficiency of PEI gene vectors. Here, we show that the beta(2)-adrenoceptor (beta(2)-AR) agonist, clenbuterol (Clen), can be used to improve gene transfer efficiency of PEI gene vectors on alveolar epithelial cells in vitro and in the lungs of mice in vivo. Clenbuterol conjugated to fluorescein-labeled bovine serum albumin resulted in clenbuterol-specific cellular uptake predominantly into alveolar but not bronchial epithelial cells. Clen-g-PEI (4/1) conjugates were combined with increasing molar ratios of PEI for transfection. At optimized PEI-g-Clen/PEI composition, transfection efficiency on alveolar epithelial cells was up to 14-fold higher than for unmodified PEI and could be inhibited by an excess of free clenbuterol. No increase of transfection efficiency was observed on bronchial epithelial cells. Increasing the PEI-g-Clen/PEI molar ratio resulted in an increase of gene vector size, decrease of the zeta potential and cytotoxicity. Aerosol delivery of optimized PEI-g-Clen/PEI (1/5) gene vectors resulted in a significant 3-fold increase of gene expression in the lungs of mice compared with unmodified PEI gene vectors. We suggest that coupling of beta(2)-adrenoceptor ligands to nonviral gene vectors represents a promising approach to improve gene delivery to the lungs.

Optimization of Streptomyces bacteriophage phi C31 integrase system to prevent post integrative gene silencing in pulmonary type II cells.

phi C31 integrase has emerged as a potent tool for achieving long-term gene expression in different tissues. The present study aimed at optimizing elements of phi C31 integrase system for alveolar type II cells. Luciferase and beta-galactosidase activities were measured at different time points post transfection. 5-Aza-2'deoxycytidine (AZA) and trichostatin A (TSA) were used to inhibit DNA methyltransferase and histone deacetylase complex (HDAC) respectively. In A549 cells, expression of the integrase using a CMV promoter resulted in highest integrase activity, whereas in MLE12 cells, both CAG and CMV promoter were equally effective. Effect of polyA site was observed only in A549 cells, where replacement of SV40 polyA by bovine growth hormone (BGH) polyA site resulted in an enhancement of integrase activity. Addition of a C-terminal SV40 nuclear localization signal (NLS) did not result in any significant increase in integrase activity. Long-term expression studies with AZA and TSA, provided evidence for post-integrative gene silencing. In MLE12 cells, both DNA methylases and HDACs played a significant role in silencing, whereas in A549 cells, it could be attributed majorly to HDAC activity. Donor plasmids comprising cellular promoters ubiquitin B (UBB), ubiquitin C (UCC) and elongation factor 1 alpha (EF1 alpha) in an improved backbone prevented post-integrative gene silencing. In contrast to A549 and MLE12 cells, no silencing could be observed in human bronchial epithelial cells, BEAS-2B. Donor plasmid coding for murine erythropoietin under the EF1 alpha promoter when combined with phi C31 integrase resulted in higher long-term erythropoietin expression and subsequently higher hematocrit levels in mice after intravenous delivery to the lungs. These results provide evidence for cell specific post integrative gene silencing with C31 integrase and demonstrate the pivotal role of donor plasmid in long-term expression attained with this system.