Development of a targeted siRNA delivery system using FOL-PEG-PEI conjugate

Small interfering RNA for cancer treatment: overcoming hurdles in delivery

In many ways, cancer cells are different from healthy cells. A lot of tactical nano-based drug delivery systems are based on the difference between cancer and healthy cells. Currently, nanotechnology-based delivery systems are the most promising tool to deliver DNA-based products to cancer cells. This review aims to highlight the latest development in the lipids and polymeric nanocarrier for siRNA delivery to the cancer cells. It also provides the necessary information about siRNA development and its mechanism of action. Overall, this review gives us a clear picture of lipid and polymer-based drug delivery systems, which in the future could form the base to translate the basic siRNA biology into siRNA-based cancer therapies.

Polymeric siRNA gene delivery - transfection efficiency versus cytotoxicity

Within the field of gene therapy, there is a considerable need for the development of non-viral vectors that are able to compete with the efficiency obtained by viral vectors, while maintaining a good toxicity profile and not inducing an immune response within the body. While there have been many reports of possible polymeric delivery systems, few of these systems have been successful in the clinical setting due to toxicity, systemic instability or gene regulation inefficiency, predominantly due to poor endosomal escape and cytoplasmic release. The objective of this review is to provide an overview of previously published polymeric non-coding RNA and, to a lesser degree, oligo-DNA delivery systems with emphasis on their positive and negative attributes, in order to provide insight in the numerous hurdles that still limit the success of gene therapy.

Current prospects and challenges of nanomedicine delivery in prostate cancer therapy

Management of prostate cancer is currently being pursued by systemic delivery of anticancer drugs, but it has drawbacks like nonspecific distribution, decreased bioavailability, coupled with adverse side effects. These problems have been resolved using nanomedicine-based anticancer drug delivery to improve the therapeutic index with higher drug dose and reduced nonspecific distribution. Targeting prostate tumor by delivering nanomedicine through locoregional route is more effective, than the systemic delivery, which can decrease systemic exposure of the therapeutics significantly. Therefore, in this article, we have reviewed the current prospects and challenges of prostate cancer therapy using nanomedicine, by providing a comprehensive description of advantages and limitations of the systemic route and locoregional route. Eventually, we have emphasized on the need for localized prostate cancer therapy developments using nanomedicines.

Polyethylene glycol-poly(ε-benzyloxycarbonyl-l-lysine)-conjugated VEGF siRNA for antiangiogenic gene therapy in hepatocellular carcinoma

A polyethylene glycol-poly(ε-benzyloxycarbonyl-l-lysine) (PEG-SS-PLL) block copolymer based on a disulfide-linked, novel biodegradable catiomer bearing a PEG-sheddable shell was developed to avoid "PEG dilemma" in nanoparticle intracellular tracking of PEG-PLL where PEG was nondegradable. However, PEG-SS-PLL catiomers have not been used to deliver small interfering VEGF RNA (siVEGF) in antiangiogenesis gene therapy. In this study, we aimed to investigate whether this novel biodegradable catiomer can deliver siVEGF into cancer cells and at the same time have an antitumor effect in a xenograft mouse model. It was found that PEG-SS-PLL efficiently delivered siVEGF with negligible cytotoxicity, and significantly decreased the expression of VEGF at both the messenger-RNA and protein levels both in vitro and in vivo, and thus tumor growth was inhibited. Our findings demonstrated that PEG-SS-PLL/siVEGF could potentially be applied to antiangiogenesis gene therapy for hepatocellular carcinoma.

Ternary complexes of folate-PEG-appended dendrimer (G4)/α-cyclodextrin conjugate, siRNA and low-molecular-weight polysaccharide sacran as a novel tumor-selective siRNA delivery system

We previously developed a tumor-selective siRNA carrier by preparing polyamidoamine dendrimer (generation 4, G4) conjugates with α-cyclodextrin and folate-polyethylene glycol (Fol-PαC (G4)). In the present study, we developed ternary complexes of Fol-PαC (G4)/siRNA with low-molecular-weight-sacrans to achieve more effective siRNA transfer activity. Among the different molecular-weight sacrans, i.e. sacran 100, 1000 and 10,000 (MW 44,889Da, 943,692Da and 1,488,281Da, respectively), sacran 100 significantly increased the cellular uptake and the RNAi effects of Fol-PαC (G4)/siRNA binary complex with negligible cytotoxicity in KB cells (folate receptor-α positive cells). In addition, the ζ-potential and particle size of Fol-PαC (G4)/siRNA complex were decreased by the ternary complexation with sacran 100. Importantly, the in vivo RNAi effect of the ternary complex after the intravenous administration to tumor-bearing BALB/c mice was significantly higher than that of the binary complex. In conclusion, Fol-PαC (G4)/siRNA/sacran 100 ternary complex has a potential as a novel tumor-selective siRNA delivery system.

Peptide-Mediated Tumor Targeting by a Degradable Nano Gene Delivery Vector Based on Pluronic-Modified Polyethylenimine

Polyethylenimine (PEI) is considered to be a promising non-viral gene delivery vector. To solve the toxicity versus efficacy and tumor-targeting challenges of PEI used as gene delivery vector, we constructed a novel non-viral vector DR5-TAT-modified Pluronic-PEI (Pluronic-PEI-DR5-TAT), which was based on the attachment of low-molecular-weight polyethylenimine (LMW-PEI) to the amphiphilic polymer Pluronic to prepare Pluronic-modified LMW-PEI (Pluronic-PEI). This was then conjugated to a multifunctional peptide containing a cell-penetrating peptide (TAT) and a synthetic peptide that would bind to DR5-a receptor that is overexpressed in cancer cells. The vector showed controlled degradation, favorable DNA condensation and protection performance. The Pluronic-PEI-DR5-TAT/DNA complexes at an N/P ratio of 15:1 were spherical nanoparticles of 122 ± 11.6 nm and a zeta potential of about 22 ± 2.8 mV. In vitro biological characterization results indicated that Pluronic-PEI-DR5-TAT/DNA complexes had a higher specificity for the DR5 receptor and were taken up more efficiently by tumor cells than normal cells, compared to complexes formed with PEI 25 kDa or Pluronic-PEI. Thus, the novel complexes showed much lower cytotoxicity to normal cells and higher gene transfection efficiency in tumor cells than that exhibited by PEI 25 kDa and Pluronic-PEI. In summary, our novel, degradable non-viral tumor-targeting vector is a promising candidate for use in gene therapy.

Conjugates of small targeting molecules to non-viral vectors for the mediation of siRNA

To use siRNA (small interfering RNA) for gene therapy, a gene delivery system is often necessary to overcome several challenging requirements including rapid excretion, low stability in blood serum, non-specific accumulation in tissues, poor cellular uptake and inefficient intracellular release. Active and/or passive targeting should help the delivery system to reach the desired tissue or cell, to be internalized, and to deliver siRNA to the cytoplasm so that siRNA can inhibit protein synthesis. This review covers conjugates of small targeting molecules and non-viral delivery systems for the mediation of siRNA, with a focus on their transfection properties in order to help the development of new and efficient siRNA delivery systems, as the therapeutic solutions of tomorrow.

STATEMENT OF SIGNIFICANCE

The delivery of siRNA into cells or tissues remains to be a challenge for its applications, an alternative strategy for siRNA delivery systems is direct conjugation of non-viral vectors with targeting moieties for cellular delivery. In comparison to macromolecules, small targeting molecules have attracted great attention due to their many potential advantages including significant simplicity and ease of production, good repeatability and biodegradability. This review will focus on the most recent advances in the delivery of siRNA using conjugates of small targeting molecules and non-viral delivery systems. Based the editor's suggestions, we hope the revised manuscript could provide more profound understanding to the conjugates of targeting molecules to vectors for mediation of siRNA.

Non-covalent complexes of folic acid and oleic acid conjugated polyethylenimine: An efficient vehicle for antisense oligonucleotide delivery

Polyethylenimine (PEI) was conjugated to oleic acid (PEI-OA) and evaluated as a delivery agent for LOR-2501, an antisense oligonucleotide against ribonucleotide reductase R1 subunit. PEI-OA/LOR-2501 complexes were further coated with folic acid (FA/PEI-OA/LOR-2501) and evaluated in tumor cells. The level of cellular uptake of FA/PEI-OA/LOR-2501 was more than double that of PEI/LOR-2501 complexes, and was not affected by the expression level of folate receptor (FR) on the cell surface. Efficient delivery was seen in several cell lines. Furthermore, pathway specific cellular internalization inhibitors and markers were used to reveal the principal mechanism of cellular uptake. FA/PEI-OA/LOR-2501 significantly induced the downregulation of R1 mRNA and R1 protein. This novel formulation of FA/PEI-OA provides a reliable and highly efficient method for delivery of oligonucleotide and warrants further investigation.

A mannosylated cell-penetrating peptide-graft-polyethylenimine as a gene delivery vector

Polyethylenimine (PEI) is widely applied in non-viral gene delivery vectors. PEI with high molecular weight is highly effective in gene transfection but is high cytotoxic. Conversely, PEI with low molecular weight displays lower cytotoxicity but less delivering efficiency. To overcome this issue, a novel copolymer with mannosylated, a cell-penetrating peptide (CPP), grafting into PEI with molecular weight of 1800 (Man-PEI1800-CPP) were prepared in this study to target antigen-presenting cells (APCs) with mannose receptors and enhance transfection efficiency with grafting CPP. The copolymer was characterized by (1)H NMR and FTIR. Spherical nanoparticles were formed with diameters of about 80-250 nm by mixing the copolymer and DNA at various charge ratios of copolymer/DNA(N/P). Gel retardation assays indicated that Man-PEI1800-CPP polymers efficiently condensed DNA at low N/P ratios. Cytotoxicity studies showed that Man-PEI1800-CPP/DNA complexes maintained in a high percentage of cell viability compared to the PEI with molecular weight of 25 k (PEI25k). Laser scan confocal microscopy and flow cytometry confirmed that Man-PEI1800-CPP/DNA complexes resulted in higher cell uptake efficiency on DC2.4 cells than on Hela cells line. The transfection efficiency of Man-PEI1800-CPP was significantly higher than that of PEI25k on DC2.4 cells. More importantly, the complexes were mainly distributed in the epidermis and dermis of skin and targeted on splenocytes after percutaneous coating based on microneedles in vivo. These results indicated that Man-PEI1800-CPP was a potential APCs targeted of non-virus vector for gene therapy.

Vaccination of mice using the West Nile virus E-protein in a DNA prime-protein boost strategy stimulates cell-mediated immunity and protects mice against a lethal challenge

West Nile virus (WNV) is a mosquito-borne flavivirus that is endemic in Africa, the Middle East, Europe and the United States. There is currently no antiviral treatment or human vaccine available to treat or prevent WNV infection. DNA plasmid-based vaccines represent a new approach for controlling infectious diseases. In rodents, DNA vaccines have been shown to induce B cell and cytotoxic T cell responses and protect against a wide range of infections. In this study, we formulated a plasmid DNA vector expressing the ectodomain of the E-protein of WNV into nanoparticles by using linear polyethyleneimine (lPEI) covalently bound to mannose and examined the potential of this vaccine to protect against lethal WNV infection in mice. Mice were immunized twice (prime – boost regime) with the WNV DNA vaccine formulated with lPEI-mannose using different administration routes (intramuscular, intradermal and topical). In parallel a heterologous boost with purified recombinant WNV envelope (E) protein was evaluated. While no significant E-protein specific humoral response was generated after DNA immunization, protein boosting of DNA-primed mice resulted in a marked increase in total neutralizing antibody titer. In addition, E-specific IL-4 T-cell immune responses were detected by ELISPOT after protein boost and CD8⁺ specific IFN-γ expression was observed by flow cytometry. Challenge experiments using the heterologous immunization regime revealed protective immunity to homologous and virulent WNV infection.

Nanoparticle-Based Delivery of RNAi Therapeutics: Progress and Challenges

RNA interference (RNAi) is an evolutionarily conserved, endogenous process for post-transcriptional regulation of gene expression. Although RNAi therapeutics have recently progressed through the pipeline toward clinical trials, the application of these as ideal, clinical therapeutics requires the development of safe and effective delivery systems. Inspired by the immense progress with nanotechnology in drug delivery, efforts have been dedicated to the development of nanoparticle-based RNAi delivery systems. For example, a precisely engineered, multifunctional nanocarrier with combined passive and active targeting capabilities may address the delivery challenges for the widespread use of RNAi as a therapy. Therefore, in this review, we introduce the major hurdles in achieving efficient RNAi delivery and discuss the current advances in applying nanotechnology-based delivery systems to overcome the delivery hurdles of RNAi therapeutics. In particular, some representative examples of nanoparticle-based delivery formulations for targeted RNAi therapeutics are highlighted.

Alkane-modified low-molecular-weight polyethylenimine with enhanced gene silencing for siRNA delivery

Small interfering RNA (siRNA) has tremendous potential as a therapeutic agent for diverse diseases; however, due to its susceptibility to degradation and poor cellular uptake, the low efficiency of administration has been the most important limiting factor for clinical applications of siRNA. Herein, we synthesized alkyl chain modified low-molecular-weight polyethylenimines (LMW PEIs) and found that hydrophobically modified PEIs displayed enhanced efficiency in siRNA-mediated knockdown of target genes. To elucidate the mechanism for increased delivery, we characterized the polymers' physicochemical properties and bioactivity via nuclear magnetic resonance (NMR), gel retardation assay, dynamic laser scattering (DLS) analysis, confocal laser scanning microscopy and flow cytometry. The hydrophobic modification reduced siRNA binding affinity but facilitated the formation of nanoparticles in contrast to the original PEI. The PEIs with eight and thirteen alkyl tails were able to self-assemble into nanoparticles and yielded higher cellular uptake, which leaded to even similar efficiencies of 80-90% knockdown as Lipofectamine™ 2000 control. These results suggested that the status of polymers in aqueous solution, which depended on the degree of hydrophobic modification, played an important role in the uptake of siRNA. Therefore, we provided new information on the role of hydrophobic content in the enhanced gene silencing activity.

Vehicles for Small Interfering RNA transfection: Exosomes versus Synthetic Nanocarriers

Therapies based on RNA interference (RNAi) hold a great potential for targeted interference of the expression of specific genes. Small-interfering RNAs (siRNA) and micro-RNAs interrupt protein synthesis by inducing the degradation of messenger RNAs or by blocking their translation. RNAibased therapies can modulate the expression of otherwise undruggable target proteins. Full exploitation of RNAi for medical purposes depends on efficient and safe methods for delivery of small RNAs to the target cells. Tremendous effort has gone into the development of synthetic carriers to meet all requirements for efficient delivery of nucleic acids into particular tissues. Recently, exosomes unveiled their function as a natural communication system which can be utilized for the transport of small RNAs into target cells. In this review, the capabilities of exosomes as delivery vehicles for small RNAs are compared to synthetic carrier systems. The step by step requirements for efficient transfection are considered: production of the vehicle, RNA loading, protection against degradation, lack of immunogenicity, targeting possibilities, cellular uptake, cytotoxicity, RNA release into the cytoplasm and gene silencing efficiency. An exosomebased siRNA delivery system shows many advantages over conventional transfection agents, however, some crucial issues need further optimization before broad clinical application can be realized.

Intracellular Delivery of siRNA by Polycationic Superparamagnetic Nanoparticles

The siRNA transfection efficiency of nanoparticles (NPs), composed of a superparamagnetic iron oxide core modified with polycationic polymers (poly(hexamethylene biguanide) or branched polyethyleneimine), were studied in CHO-K1 and HeLa cell lines. Both NPs demonstrated to be good siRNA transfection vehicles, but unmodified branched polyethyleneimine (25 kD) was superior on both cell lines. However, application of an external magnetic field during transfection (magnetofection) increased the efficiency of the superparamagnetic NPs. Furthermore, our results reveal that these NPs are less toxic towards CHO-K1 cell lines than the unmodified polycationic-branched polyethyleneimine (PEI). In general, the external magnetic field did not alter the cell's viability nor it disrupted the cell membranes, except for the poly(hexamethylene biguanide)-modified NP, where it was observed that in CHO-K1 cells application of the external magnetic field promoted membrane damage. This paper presents new polycationic superparamagnetic NPs as promising transfection vehicles for siRNA and demonstrates the advantages of magnetofection.

Nanoparticles for intracellular-targeted drug delivery

Nanoparticles (NPs) are very promising for the intracellular delivery of anticancer and immunomodulatory drugs, stem cell differentiation biomolecules and cell activity modulators. Although initial studies in the area of intracellular drug delivery have been performed in the delivery of DNA, there is an increasing interest in the use of other molecules to modulate cell activity. Herein, we review the latest advances in the intracellular-targeted delivery of short interference RNA, proteins and small molecules using NPs. In most cases, the drugs act at different cellular organelles and therefore the drug-containing NPs should be directed to precise locations within the cell. This will lead to the desired magnitude and duration of the drug effects. The spatial control in the intracellular delivery might open new avenues to modulate cell activity while avoiding side-effects.

Polymers in small-interfering RNA delivery

This review will cover the current strategies that are being adopted to efficiently deliver small interfering RNA using nonviral vectors, including the use of polymers such as polyethylenimine, poly(lactic-co-glycolic acid), polypeptides, chitosan, cyclodextrin, dendrimers, and polymers-containing different nanoparticles. The article will provide a brief and concise account of underlying principle of these polymeric vectors and their structural and functional modifications which were intended to serve different purposes to affect efficient therapeutic outcome of small-interfering RNA delivery. The modifications of these polymeric vectors will be discussed with reference to stimuli-responsiveness, target specific delivery, and incorporation of nanoconstructs such as carbon nanotubes, gold nanoparticles, and silica nanoparticles. The emergence of small-interfering RNA as the potential therapeutic agent and its mode of action will also be mentioned in a nutshell.

Synthesis and characterization of mannosylated pegylated polyethylenimine as a carrier for siRNA

Regulation of gene expression using small interfering RNA (siRNA) is a promising strategy for research and treatment of numerous diseases. In this study, we develop and characterize a delivery system for siRNA composed of polyethylenimine (PEI), polyethylene glycol (PEG), and mannose (Man). Cationic PEI complexes and compacts siRNA, PEG forms a hydrophilic layer outside of the polyplex for steric stabilization, and mannose serves as a cell binding ligand for macrophages. The PEI-PEG-mannose delivery system was constructed in two different ways. In the first approach, mannose and PEG chains are directly conjugated to the PEI backbone. In the second approach, mannose is conjugated to one end of the PEG chain and the other end of the PEG chain is conjugated to the PEI backbone. The PEI-PEG-mannose delivery systems were synthesized with 3.45-13.3 PEG chains and 4.7-3.0 mannose molecules per PEI. The PEI-PEG-Man-siRNA polyplexes displayed a coarse surface in Scanning Electron Microscopy (SEM) images. Polyplex sizes were found to range from 169 to 357 nm. Gel retardation assays showed that the PEI-PEG-mannose polymers are able to efficiently complex with siRNA at low N/P ratios. Confocal microscope images showed that the PEI-PEG-Man-siRNA polyplexes could enter cells and localized in the lysosomes at 2h post-incubation. Pegylation of the PEI reduced toxicity without any adverse reduction in knockdown efficiency relative to PEI alone. Mannosylation of the PEI-PEG could be carried out without any significant reduction in knockdown efficiency relative to PEI alone. Conjugating mannose to PEI via the PEG spacer generated superior toxicity and gene knockdown activity relative to conjugating mannose and PEG directly onto the PEI backbone.

siRNA targeting Notch-1 decreases glioma stem cell proliferation and tumor growth

Glioblastoma multiforme (GBM), the most common brain tumor in adults, is neurologically destructive and has a dismal response to virtually all therapeutic modalities. One phenomenon that can contribute to this complexity is the presence of a relatively small subset of glioma stem cells (GSCs) within the tumor and the activation of pathways that control cellular differentiation. The Notch signaling pathway, which is responsible for maintaining a balance between cell proliferation and apoptosis, is believed to be deregulated in cancer stem cells (CSCs), leading to tumor growth through the generation or expansion of CSCs. In this study, Notch-1 small interfering RNA (siRNA) was used to silence Notch-1 gene expression in GSCs. An MTT assay demonstrated inhibitory effects on the proliferation of GSCs in vitro. Real-time PCR showed that Notch-1 expression levels were markedly decreased in GSCs transfected with Notch-1 siRNA in vitro. Notch-1 silenced GSCs engrafted on Balb/c nude mice showed a significantly greater reduction in oncogenicity than the control group (P < 0.05). Furthermore, direct intratumoral injections of Notch-1-siRNA/PEI significantly delayed the growth of pre-established tumors in nude mice (P < 0.05). These results suggest that siRNA-mediated silencing of the Notch-1 gene may represent a novel target for gene therapy of GBM.