Polycation-mediated delivery of siRNAs for prophylaxis and treatment of influenza virus infection

Research progress of siRNA in anti-influenza viral infection

The harms of seasonal flu and global pandemic influenza have generally attracted attention. However, the currently administered influenza drugs and flu vaccines have certain limitations. Since the discovery of the small interfering RNA (siRNA) and its mediated RNA interference process, this molecule has been widely used in the study of anti-influenza viral infections because of its high specificity and strong selectivity. The results provided new concepts for the prevention and treatment of influenza virus. However, the siRNA still faces an enormous challenge despite extensive studies on this molecule. The research progress of siRNA in anti-influenza viral infection was reviewed in this study.

A possible strategy to produce pigs resistant to porcine reproductive and respiratory syndrome virus

The purpose of this study was to enhance the production of transgenic cloned embryos with porcine reproductive and respiratory syndrome virus (PRRSV) shRNA expression cassettes. To construct transgenic vector with expression targeting against PRRSV, PRRSV shRNA expression cassettes were inserted into pEGFP-N1 and the ability of resulting recombinant plasmid pEGFP-G1 inhibiting virus replication was examined in Marc-145 cells. Results showed that PRRSV replication could be significantly inhibited by pEGFP-G1 in Marc-145 cells compared with the control. The pEGFP-G1 plasmid was used to deliver a transgene expressing EGFP and the PRRSV shRNA into porcine fetal fibroblasts (PFF). Fluorescent-positive cells were used as nuclear donors for somatic cell nuclear transfer (SCNT) to produce shRNA-EGFP transgenic cloned embryos. The effects of trichostatin A (TSA) on production of transgenic cloned embryos were investigated. Reconstructed embryos were designed into 4 groups: Donor cells of Group A were treated with 50nM TSA for 24h before SCNT. Reconstructed embryos of Group B were treated with 50nM TSA for 24h after activation. Both donor cells and reconstructed embryos in Group C were treated with TSA and Group D were the control without TSA treatment. The results showed no difference (p>0.05) in cleavage rates among the 4 groups; however, blastocyst developmental rates of Group B and C (30.9% and 42.0%, respectively) were higher than for Group A and D (21.2% and 22.1%, respectively) with Group C highest among groups (p<0.05). Interestingly, EGFP expression intensity of transgenic cloned blastocysts of Group A was the highest. Our results provide promising evidence toward a new approach for production of transgenic cloned pigs with resistance to PRRSV and possibly a wide variety of other porcine diseases.

Insight into alternative approaches for control of avian influenza in poultry, with emphasis on highly pathogenic H5N1

Highly pathogenic avian influenza virus (HPAIV) of subtype H5N1 causes a devastating disease in poultry but when it accidentally infects humans it can cause death. Therefore, decrease the incidence of H5N1 in humans needs to focus on prevention and control of poultry infections. Conventional control strategies in poultry based on surveillance, stamping out, movement restriction and enforcement of biosecurity measures did not prevent the virus spreading, particularly in developing countries. Several challenges limit efficiency of the vaccines to prevent outbreaks of HPAIV H5N1 in endemic countries. Alternative and complementary approaches to reduce the current burden of H5N1 epidemics in poultry should be encouraged. The use of antiviral chemotherapy and natural compounds, avian-cytokines, RNA interference, genetic breeding and/or development of transgenic poultry warrant further evaluation as integrated intervention strategies for control of HPAIV H5N1 in poultry.

A potential therapeutic for pandemic influenza using RNA interference

RNA interference (RNAi) involves sequence-specific downregulation of target genes, leading to gene silencing in vitro and in vivo. Synthetic small interfering RNAs (siRNAs), formulated with appropriate delivery agents, can serve as effective tools for RNAi-based therapeutics. The potential of siRNA to provide antiviral activity has been studied extensively in many respiratory viruses, including influenza virus, wherein specific siRNAs target highly-conserved regions of influenza viral genome, leading to potent inhibition of viral RNA replication. Despite various delivery strategies, such as polycations and liposomes that have been employed to formulate siRNAs, effective delivery modalities are still needed. Although current strategies can provide significant biodistribution and delivery into lungs allowing gene silencing, complete protection and prolonged survival rates against multiple strains of influenza virus still remains a key challenge. Here, we describe methods and procedures pertaining to screening and selection of highly effective influenza-specific siRNAs in cell culture, in mice, and in the ferret model. This will be potentially useful to evaluate RNAi as a therapeutic modality for future clinical application.

A novel mechanism is involved in cationic lipid-mediated functional siRNA delivery

A key challenge for therapeutic application of RNA interference is to efficiently deliver synthetic small interfering RNAs (siRNAs) into target cells that will lead to the knockdown of the target transcript (functional siRNA delivery). To facilitate rational development of nonviral carriers, we have investigated by imaging, pharmacological and genetic approaches the mechanisms by which a cationic lipid carrier mediates siRNA delivery into mammalian cells. We show that ∼95% of siRNA lipoplexes enter the cells through endocytosis and persist in endolysosomes for a prolonged period of time. However, inhibition of clathrin-, caveolin-, or lipid-raft-mediated endocytosis or macropinocytosis fails to inhibit the knockdown of the target transcript. In contrast, depletion of cholesterol from the plasma membrane has little effect on the cellular uptake of siRNA lipoplexes, but it abolishes the target transcript knockdown. Furthermore, functional siRNA delivery occurs within a few hours and is gradually inhibited by lowering temperatures. These results demonstrate that although endocytosis is responsible for the majority of cellular uptake of siRNA lipoplexes, a minor pathway, probably mediated by fusion between siRNA lipoplexes and the plasma membrane, is responsible for the functional siRNA delivery. Our findings suggest possible directions for improving functional siRNA delivery by cationic lipids.

Optimized protocol for the large scale production of HIV pseudovirions by transient transfection of HEK293T cells with linear fully deacylated polyethylenimine

HIV vaccine strategies which employ pseudovirions (PVs) as the source of antigen require large amounts of particles. These are typically generated by transient transfection of mammalian cells and purification of the released PVs from the culture supernatant. Since efficiency and cost of transfection are key issues, in this report the transfection efficiencies, achieved by employing a panel of high-molecular-weight linear polyethylenimines (PEIs) and small cross-linked PEIs, were analyzed and compared to those obtained by transfections with calcium phosphate or the commercial reagent Polyfect. High efficiencies were obtained using several of the modified PEIs, and the transfections with these inexpensive reagents were very robust. The observed efficiencies (as quantitated by amounts of expressed gene product) were two to four fold superior to calcium phosphate transfection and approximately equal to that achieved using Polyfect which is, however, prohibitively expensive for large scale applications. An optimized and rapid protocol for the large scale production and purification of HIV-PVs from 293T cells growing in so-called cell stacks and transfected with the best reagent identified, PEI87, is described here. The generated PVs, obtained with a yield in the range of 0.4mg virion-associated HIV-CA/liter culture supernatant, exhibited only very minimal contamination with non-viral proteins and were thus suitable for vaccination applications.