Targeting of Synthetic Gene Delivery Systems

Targeted gene delivery systems for T-cell engineering

T lymphocytes are indispensable for the host systems of defense against pathogens, tumors, and environmental threats. The therapeutic potential of harnessing the cytotoxic properties of T lymphocytes for antigen-specific cell elimination is both evident and efficacious. Genetically engineered T-cells, such as those employed in CAR-T and TCR-T cell therapies, have demonstrated significant clinical benefits in treating cancer and autoimmune disorders. However, the current landscape of T-cell genetic engineering is dominated by strategies that necessitate in vitro T-cell isolation and modification, which introduce complexity and prolong the development timeline of T-cell based immunotherapies. This review explores the complexities of gene delivery systems designed for T cells, covering both viral and nonviral vectors. Viral vectors are known for their high transduction efficiency, yet they face significant limitations, such as potential immunogenicity and the complexities involved in large-scale production. Nonviral vectors, conversely, offer a safer profile and the potential for scalable manufacturing, yet they often struggle with lower transduction efficiency. The pursuit of gene delivery systems that can achieve targeted gene transfer to T cell without the need for isolation represents a significant advancement in the field. This review assesses the design principles and current research progress of such systems, highlighting the potential for in vivo gene modification therapies that could revolutionize T-cell based treatments. By providing a comprehensive analysis of these systems, we aim to contribute valuable insights into the future development of T-cell immunotherapy.

Second-Generation Polyamidoamine Dendrimer Conjugated with Oligopeptides Can Enhance Plasmid DNA Delivery In Vitro

Poly(amidoamine) (PAMAM) dendrimers have attracted considerable attention in the field of gene therapy due to their flexibility in introducing different functional moieties and reduced toxicity at low generations. However, their transfection efficiency remains a limitation. Therefore, an essential approach for improving their transfection efficiency as gene carriers involves modifying the structure of PAMAM by conjugating functional groups around their surface. In this study, we successfully conjugated an RRHRH oligopeptide to the surface of PAMAM generation 2 (PAMAM G2) to create RRHRH-PAMAM G2. This construction aims to condense plasmid DNA (pDNA) and facilitate its penetration into cell membranes, leading to its promising potential for gene therapy. RRHRH-PAMAM G2/pDNA complexes were smaller than 100 nm and positively charged. Nano-polyplexes can enter the cell and show a high transfection efficiency after 24 h of transfection. The RRHRH-PAMAM G2 was non-toxic to HeLa, NIH3T3, A549, and MDA-MB-231 cell lines. These results strongly suggest that RRHRH-PAMAM G2 holds promise as a gene carrier for gene therapy owing to its biocompatibility and ability to deliver genes to the cell.

Polymeric Delivery of Therapeutic Nucleic Acids

The advent of genome editing has transformed the therapeutic landscape for several debilitating diseases, and the clinical outlook for gene therapeutics has never been more promising. The therapeutic potential of nucleic acids has been limited by a reliance on engineered viral vectors for delivery. Chemically defined polymers can remediate technological, regulatory, and clinical challenges associated with viral modes of gene delivery. Because of their scalability, versatility, and exquisite tunability, polymers are ideal biomaterial platforms for delivering nucleic acid payloads efficiently while minimizing immune response and cellular toxicity. While polymeric gene delivery has progressed significantly in the past four decades, clinical translation of polymeric vehicles faces several formidable challenges. The aim of our Account is to illustrate diverse concepts in designing polymeric vectors towards meeting therapeutic goals of in vivo and ex vivo gene therapy. Here, we highlight several classes of polymers employed in gene delivery and summarize the recent work on understanding the contributions of chemical and architectural design parameters. We touch upon characterization methods used to visualize and understand events transpiring at the interfaces between polymer, nucleic acids, and the physiological environment. We conclude that interdisciplinary approaches and methodologies motivated by fundamental questions are key to designing high-performing polymeric vehicles for gene therapy.

Antibody-targeted chromatin enables effective intracellular delivery and functionality of CRISPR/Cas9 expression plasmids

We report a novel system for efficient and specific targeted delivery of large nucleic acids to and into cells. Plasmid DNA and core histones were assembled to chromatin by salt gradient dialysis and subsequently connected to bispecific antibody derivatives (bsAbs) via a nucleic acid binding peptide bridge. The resulting reconstituted vehicles termed 'plasmid-chromatin' deliver packaged nucleic acids to and into cells expressing antigens that are recognized by the bsAb, enabling intracellular functionality without detectable cytotoxicity. High efficiency of intracellular nucleic acid delivery is revealed by intracellular expression of plasmid encoded genes in most (∼90%) target cells to which the vehicles were applied under normal growth/medium conditions in nanomolar concentrations. Specific targeting, uptake and transgene expression depends on antibody-mediated cell surface binding: plasmid chromatin of identical composition but with non-targeting bsAbs or without bsAbs is ineffective. Examples that demonstrate applicability, specificity and efficacy of antibody-targeted plasmid chromatin include reporter gene constructs as well as plasmids that enable CRISPR/Cas9 mediated genome editing of target cells.

Hepatocellular targeted α-tocopherol based pH sensitive galactosylated lipids: design, synthesis and transfection studies

Receptor mediated gene delivery to the liver offers advantages in treating genetic disorders such as hemophilia and hereditary tyrosinemia type I (HTI). Prior findings demonstrated that tethering the d-galactose head group to cationic lipids directs genes to the liver via asialoglycoprotein receptors (ASGPRs). In our continued efforts to develop safer and efficient lipofectins, we demonstrated that cationic lipids bearing α-tocopherol, an antioxidant, as a hydrophobic domain could deliver genes efficiently with high safety profiles in multiple cell lines. Towards developing ASGPR targeted pH sensitive cationic lipids, we have designed a galactosylated cationic lipid (Toc-Gal) with α-tocopherol as the hydrophobic core covalently connected with a pH responsive triazole moiety and a non-targeting control lipid (Toc-OH) without the galactose head group. In this study, we present the design and synthesis of a pH sensitive galactosylated cationic lipid (Toc-Gal), its comparative transfection biology, cellular uptake studies, serum stability and cytotoxicity profiles in both ASGPR positive and negative liver cells, i.e. HepG2 and SK-Hep-1, respectively.

Peptide vectors for gene delivery: from single peptides to multifunctional peptide nanocarriers

The therapeutic use of nucleic acids relies on the availability of sophisticated delivery systems for targeted and intracellular delivery of these molecules. Such a gene delivery should possess essential characteristics to overcome several extracellular and intracellular barriers. Peptides offer an attractive platform for nonviral gene delivery, as several functional peptide classes exist capable of overcoming these barriers. However, none of these functional peptide classes contain all the essential characteristics required to overcome all of the barriers associated with successful gene delivery. Combining functional peptides into multifunctional peptide vectors will be pivotal for improving peptide-based gene delivery systems. By using combinatorial strategies and high-throughput screening, the identification of multifunctional peptide vectors will accelerate the optimization of peptide-based gene delivery systems.

Polymers for nucleic acid transfer-an overview

For the last five decades cationic polymers have been used for nucleic acids transfection. Our understanding of polymer-nucleic acid interactions and their rational use in delivery has continuously increased. The great improvements in macromolecular chemistry and the recognition of distinct biological extra- and intracellular delivery hurdles triggered several breakthrough developments, including the discovery of natural and synthetic polycations for compaction of nucleic acids into stable nanoparticles termed polyplexes; the incorporation of targeting ligands and surface-shielding of polyplexes to enable receptor-mediated gene delivery into defined target tissues; and strongly improved intracellular transfer efficacy by better endosomal escape of vesicle-trapped polyplexes into the cytosol. These experiences triggered the development of second-generation polymers with more dynamic properties, such as endosomal pH-responsive release mechanisms, or biodegradable units for improved biocompatibility and intracellular release of the nucleic acid pay load. Despite a better biological understanding, significant challenges such as efficient nuclear delivery and persistence of gene expression persist. The therapeutic perspectives widened from pDNA-based gene therapy to application of novel therapeutic nucleic acids including mRNA, siRNA, and microRNA. The finding that different therapeutic pay loads require different tailor-made carriers complicates preclinical developments. Convincing evidence of medical efficacy still remains to be demonstrated. Bioinspired multifunctional polyplexes resembling "synthetic viruses" appear as attractive opportunity, but provide additional challenges: how to identify optimum combinations of functional delivery units, and how to prepare such polyplexes reproducibly in precise form? Design of sequence-defined polymers, screening of combinatorial polymer and polyplex libraries are tools for further chemical evolution of polyplexes.

Noncovalently associated cell-penetrating peptides for gene delivery applications

The use of various cell-penetrating peptides (CPPs) to deliver genetic material for gene therapy applications has been a topic of interest for more than 20 years. The delivery of genetic material by using CPPs can be divided into two categories: covalently bound and electrostatically bound. Complexity of the synthesis procedure can be a significant barrier to translation when using a strategy requiring covalent binding of CPPs. In contrast, electrostatically complexing CPPs with genetic material or with a viral vector is relatively simple and has been demonstrated to improve gene delivery in both in vitro and in vivo studies. This review highlights gene therapy applications of complexes formed noncovalently between CPPs and genetic material or viruses.

Enhanced in vivo gene transfer into the placenta using RGD fiber-mutant adenovirus vector

Among viral vectors, the fiber-mutant adenovirus vector carrying the Arg-Gly-Asp (RGD) peptide sequence (Ad-RGD) seems to have potential for both clinical gene therapy and basic research. As a part of a thorough evaluation of Ad-RGD in preclinical studies, we designed an experiment to investigate in detail the distribution of Ad-RGD compared with conventional adenovirus vector (WT-Ad) in pregnant mice. Surprisingly, Ad-RGD had substantial placental tropism, at 10-100 times that of WT-Ad. Transgene expression was sustained for at least 7 days, and Ad-RGD expressing firefly luciferase or red fluorescent protein has so far caused no placental dysfunction leading to fetal death. Ad-RGD showed high levels of transduction efficiency in in vitro-differentiated trophoblast stem cells, in which higher expression of αvβ3 integrin than in undifferentiated cells was observed. Our results suggest that the use of Ad-RGD or another RGD-mediated targeting strategy holds promise for drug delivery to the placenta.

Aggregation and particle formation of tRNA by dendrimers

Major attention has been focused on dendrimer-DNA complexes because of their applications in gene delivery systems. Dendrimers are also used to transport miRNA and siRNA in vitro. We examine the interaction of tRNA with several dendrimers of different compositions, mPEG-PAMAM (G3), mPEG-PAMAM (G4), and PAMAM (G4) under physiological conditions using constant tRNA concentration and various dendrimer contents. FTIR, UV-visible, and CD spectroscopic methods as well as atomic force microscopy (AFM) were used to analyze the macromolecule binding mode, the binding constant, and the effects of dendrimer complexation on RNA stability, aggregation, particle formation, and conformation. Structural analysis showed that dendrimer-tRNA complexation occurred via RNA bases and the backbone phosphate group with both hydrophilic and hydrophobic contacts. The overall binding constants of K(mPEG-G3) = 7.6 (± 0.9) × 10(3) M(-1), K(mPEG-G4) = 1.5 (± 0.40) × 10(4) M(-1), and K(PAMAM-G4) = 5.3 (± 0.60) × 10(4) M(-1) show stronger polymer-RNA complexation by PAMAM-G4 than pegylated dendrimers. RNA remains in the A-family structure, whereas biopolymer aggregation and particle formation occurred at high polymer concentrations.

Reconstitutable charged polymeric (PLGA)(2)-b-PEI micelles for gene therapeutics delivery

This study investigated the potential of creating a charged polymeric micelle-based nucleic acid delivery system that could easily be reconstituted by the addition of water. (PLGA(36kDa))(2)-b-bPEI(25kDa) (PLGA MW 36 kDa, bPEI M(w) 25 kDa, PLGA:bPEI block ratio = 2) was synthesized and used to prepare cationic micelles. The copolymer retained proton-buffering capability from the bPEI block within the endosomal pH range. Micelle/pDNA complexes retained their particle size (100-150 nm) and surface charge (30-40 mV) following reconstitution. It was found that adding a small amount of low molecular weight bPEI (1.8 kDa) completely shielded pDNA in the micelle/pDNA complexes and enhanced transfection efficiency 50-100 fold for both fresh and reconstituted complexes without affecting complex size. Transfection efficiency for "reconstituted" micelle/pDNA/bPEI(1.8kDa) (WR 1) complexes was 16-fold higher than its "fresh" counterpart. Although transfection levels achieved using "reconstituted" micelle/pDNA/bPEI(1.8kDa) complexes were 3.6-fold lower than control "fresh" bPEI(25kDa)/pDNA (N/P 5) complexes, transfection levels were 39-fold higher than "reconstituted" bPEI(25kDa)/pDNA (N/P 5) complexes. The micelle/pDNA/bPEI(1.8kDa) system showed very low cytotoxicity in MCF7 cells even with pDNA doses up to 20 μg, and transfection levels increased linearly with increasing pDNA dose. These results indicate that this PLGA-b-bPEI polymeric micelle-based system is well suited as a reconstitutable gene delivery system, and has high potential for use as a delivery system for gene therapy applications.

Targeting of Cancer Cells Using Quantum Dot-Polypeptide Hybrid Assemblies that Function as Molecular Imaging Agents and Carrier Systems

We report a highly tunable quantum dot (QD)-polypeptide hybrid assembly system with potential uses for both molecular imaging and delivery of biomolecular cargo to cancer cells. In this work, we demonstrate the tunability of the assembly system, its application for imaging cancer cells, and its ability to carry a biomolecule. The assemblies are formed through the self-assembly of carboxyl-functionalized QDs and poly(diethylene glycol-L-lysine)-poly(L-lysine) (PEGLL-PLL) diblock copolypeptide molecules, and they are modified with peptide ligands containing a cyclic arginine-glycine-aspartate [c(RGD)] motif that has affinity for α_vβ₃ and α_vβ₅ integrins overexpressed on the tumor vasculature. To illustrate the tunability of the QD-polypeptide assembly system, we show that binding to U87MG glioblastoma cells can be modulated and optimized by changing either the conditions under which the assemblies are formed or the relative lengths of the PEGLL and PLL blocks in the PEGLL-PLL molecules. The optimized c(RGD)-modified assemblies bind integrin receptors on U87MG cells and are endocytosed, as demonstrated by flow cytometry and live-cell imaging. Binding specificity is confirmed by competition with an excess of free c(RGD) peptide. Finally, we show that the QD-polypeptide assemblies can be loaded with fluorescently labeled ovalbumin, as a proof-of-concept for their potential use in biomolecule delivery.

Revisit the complexation of PEI and DNA - how to make low cytotoxic and highly efficient PEI gene transfection non-viral vectors with a controllable chain length and structure?

The commercially available branched polyethyleneimine (PEI) with a molar mass of 25 kD (PEI-25K) is an effective in vitro vector to transfer genes, but its cytotoxicity limits its applications in bio-related research. To solve such an efficiency-versus-cytotoxicity catch-22 problem, the disulfide bond has been previously used to link less toxic short PEI chains (2 kD), but previous literature results are controversial. Recently, we found that it is vitally important to remove both carbon dioxide and water in the linking reaction as well as to control the structure of the resultant chains linked by dithiobis(succinimidyl propionate) (DSP). Under a programmable mixing of PEI and DSP, we can use laser light scattering (LLS) to in-situ monitor the linking reaction kinetics in DMSO in terms of the change of the average molar mass (M(w)). Therefore, we were able to withdraw a series of linked PEI chains with different molar masses from one reaction mixture. Two such linked PEI samples (M(w) approximately 7 kD, PEI-7K-L and approximately 400 kD, PEI-400K-L) were used to illustrate the effect of the sample preparation and the chain structure on the in vitro gene transfection and cytotoxicity. Our results reveal that PEI-7K-L is less cytotoxic and more effective in the gene transfection than both PEI-25K and Lipofectamine 2000 in the in vitro gene transfection. However, PEI-400K-L has no gene transfection efficiency even though it is non-toxic.

Effect of transferrin as a ligand of pH-sensitive fusogenic liposome-lipoplex hybrid complexes

We previously developed potent nonviral vectors based on complexation of lipoplexes and pH-sensitive fusogenic liposomes, which achieve efficient transfection through membrane fusion with intracellular acidic compartments such as endosomes. Because transferrin receptor is known to be overexpressed in cancer cells, in this study, we investigated the effect of transferrin as a ligand for transfection of various cancer-derived cell lines mediated by the liposome-lipoplex hybrid complexes. Results showed that these hybrid complexes with transferrin exhibited higher transfection efficiency toward these cells than complexes without transferrin, but the extent of the transferrin-induced enhancement was dependent on the cell line. Conjugation of transferrin increased their transfection activity for HeLa and KB cells, although it only slightly enhanced transfection for HT1080, HepG2, and K562. Transferrin receptors in HT1080, HepG2, and K562 cells were internalized slowly, whereas those in HeLa and KB cells were internalized quickly and actively. These results indicate that transfection mediated by the ligand-attached hybrid complex does not correlate with the amount of transferrin receptor in the cell surface but correlate with the activity of internalization of transferrin receptor into the cells.

Impact of tumor-specific targeting and dosing schedule on tumor growth inhibition after intravenous administration of siRNA-containing nanoparticles

This study addresses issues of relevance for siRNA nanoparticle delivery by investigating the functional impact of tumor-specific targeting and dosing schedule. The investigations are performed using an experimental system involving a syngeneic mouse cancer model and a theoretical system based on our previously described mathematical model of siRNA delivery and function. A/J mice bearing subcutaneous Neuro2A tumors approximately 100 mm(3) in size were treated by intravenous injection with siRNA-containing nanoparticles formed with cyclodextrin-containing polycations (CDP). Three consecutive daily doses of transferrin (Tf)-targeted nanoparticles carrying 2.5 mg/kg of two different siRNA sequences targeting ribonucleotide reductase subunit M2 (RRM2) slowed tumor growth, whereas non-targeted nanoparticles were significantly less effective when given at the same dose. Furthermore, administration of the three doses on consecutive days or every 3 days did not lead to statistically significant differences in tumor growth delay. Mathematical model calculations of siRNA-mediated target protein knockdown and tumor growth inhibition are used to elucidate possible mechanisms to explain the observed effects and to provide guidelines for designing more effective siRNA-based treatment regimens regardless of delivery methodology and tumor type.

Delivery of DNA HIV-1 vaccine to the liver induces high and long-lasting humoral immune responses

The quality of immune responses induced by DNA vaccination depends on the site of DNA administration, the expression, and the properties of the encoded antigen. In the present study, we demonstrate that intravenous hydrodynamic HIV-1 envelope DNA injection resulted in high levels of expression of HIV-1 envelope antigen in the liver. When compared to the administration of DNA by i.n., i.d., i.m., and i.splenic routes, hydrodynamic vaccination induced, upon DNA boosting, levels of HIV-1 envelope-specific antibodies 40-fold higher than those elicited by the other routes tested. Hydrodynamic vaccination with 1 microg DNA induced higher humoral responses than 100 microg DNA given intramuscularly in the prime-boost regimen. High levels of envelope-specific IgG and IgA antibodies were induced in genital tract secretions after two doses of DNA followed by intranasal boosting with recombinant HIV-1 gp120 protein. Furthermore, two doses of 100 microg DNA generated interferon-gamma production in approximately 4.3+/-1.7% of CD8(+) splenocytes after in vitro stimulation with HIV-1 envelope peptides. These results demonstrate that DNA vaccines targeted to tissues with high proteosynthetic activity, such as the liver, results in enhanced immune responses.

Enhancement of immunity to an Escherichia coli vaccine in mice orally inoculated with a fusion gene encoding porcine interleukin 4 and 6

Experiments were conducted to investigate the effect of a fusion gene of porcine IL-4 and IL-6 (PIL4/IL6) packaged with chitosan nanoparticles (CNPs) in terms of the development of a novel effective adjuvant. The IL4/PIL6 fusion gene was constructed and inserted into a eukaryotic expression vector. The plasmid was bound to CNP and then utilized to orally inoculate 21-day-old female Kunming mice that simultaneously received intramuscular injection of inactivated Escherichia coli vaccine. At 35 days post-vaccination, the mice were challenged by oral feeding with virulent O139: K88 strain EPEC E. coli bacteria. Compared with those of control mice, the content of immunoglobulins and specific antibodies to E. coli increased significantly in the sera of mice immunized with VPIL4/IL6-CNP (P<0.05). Furthermore, the levels of IL-2, IL-4 and IL-6 increased remarkably in the sera of immunized mice (P<0.05). After challenge, these immunological markers were elevated to different degrees in the mice immunized with the fusion gene construct (IL4/VPIL6-CNP) or individual plasmids (VPIL4+VPIL6-CNP). The immunized mice all survived the challenge and did not show any symptoms or lesion, whereas the VR1020-CNP control mice manifested obvious clinical symptoms and hemorrhagic lesions in the digestive tracts. These results demonstrated that VPIL4/IL6 entrapped with CNP is a novel promising adjuvant to promote specific immunity and resistance of animals against infectious pathogen.

Polymer-based siRNA delivery: Perspectives on the fundamental and phenomenological distinctions from polymer-based DNA delivery

Gene therapy holds tremendous promise in the treatment of many genetic and acquired diseases. The future of gene therapy in humans, however, is contingent upon the discovery of safe and effective carriers of genetic material. Polymers represent a class of materials that can be extensively modified to meet the needs of a particular gene delivery system. A variety of polymer formulations have been proposed in the literature as potential carriers, most of which facilitate gene delivery by encapsulating, and in some cases, condensing nucleic acids into nano-sized particles which can then be taken up by cells. Crucial to successful delivery of the gene to a cell is the polymer's ability to protect its contents from degradation in the extracellular environment. A well-designed carrier will also promote cellular uptake and intracellular release of the nucleic acid. In the past, a common approach to gene therapy has been to transfect cells with a polymer-encapsulated DNA plasmid designed to replace a defective gene in the target-cell genome. Within the last few years, however, RNA interference (RNAi) has emerged as a novel therapeutic pathway by which harmful genes can be "silenced" by delivering complementary short interfering RNA (siRNA) to target cells. siRNA delivery facilitated by polymers, although very promising, suffers from many of the same limitations as DNA delivery. This review will (1) highlight the similarities and differences between these two methods of gene therapy and (2) discuss how some of the remaining challenges in siRNA delivery facilitated by polymers can be addressed by applying knowledge from the longer-studied problem of DNA delivery.

Mannan-mediated gene delivery for cancer immunotherapy

Recent years have seen a resurgence in interest in the development of efficient non-viral delivery systems for DNA vaccines and gene therapy. We have previously used oxidized and reduced mannan as carriers for protein delivery to antigen-presenting cells by targeting the receptors that bind mannose, resulting in efficient induction of cellular responses. In the present study, oxidized mannan and reduced mannan were used as receptor-mediated gene transfer ligands for cancer immunotherapy. In vivo studies in C57BL/6 mice showed that injection of DNA encoding ovalbumin (OVA) complexed to oxidized or reduced mannan-poly-L-lysine induced CD8 and CD4 T-cell responses as well as antibody responses leading to protection of mice from OVA+ tumours. Both oxidized and reduced mannan delivery was superior to DNA alone or DNA-poly-L-lysine. These studies demonstrate the potential of oxidized and reduced mannan for efficient receptor-mediated gene delivery in vivo, particularly as DNA vaccines for cancer immunotherapy.

Optimizing targeted gene delivery: chemical modification of viral vectors and synthesis of artificial virus vector systems

In comparison to classical medicines, gene therapy has the potential to mediate the highest possible level of therapeutic specificity. Every normal or diseased cell can switch on or off a gene expression cassette in a tissue-, disease-, and time-dependent fashion, by use of specific transcription factors that are active only in a given unique situation. In practice, we face the problem in realizing the concept: the delivery of nucleic acids into target cells is very ineffective and presents a formidable challenge. Key issues for future developments include improved targeting, enhanced intracellular uptake, and reduced toxicity of gene vectors. The currently used classes of vectors have complementary characteristics, such as high intracellular efficiency of viral vectors on the one hand and low immunogenicity and greater flexibility of nonviral vectors on the other hand. The merge of viral and nonviral vector technologies is highlighted as an encouraging strategy for the future; concepts include chemically modified viral vectors ("chemo-viruses") and synthesis of virus-like systems ("synthetic viruses"). Examples for the development of vectors toward artificial synthetic viruses are presented.

Physicochemical and biological characterization of targeted, nucleic acid-containing nanoparticles

Nucleic acid-based therapeutics have the potential to provide potent and highly specific treatments for a variety of human ailments. However, systemic delivery continues to be a significant hurdle to success. Multifunctional nanoparticles are being investigated as systemic, nonviral delivery systems, and here, we describe the physicochemical and biological characterization of cyclodextrin-containing polycations (CDP) and their nanoparticles formed with nucleic acids including plasmid DNA (pDNA) and small interfering RNA (siRNA). These polycation/nucleic acid complexes can be tuned by formulation conditions to yield particles with sizes ranging from 60 to 150 nm, zeta potentials from 10 to 30 mV, and molecular weights from approximately 7 x 107 to 1 x 109 g mol-1 as determined by light scattering techniques. Inclusion complexes formed between adamantane (AD)-containing molecules and the beta-cyclodextrin molecules enable the modular attachment of poly(ethylene glycol) (AD-PEG) conjugates for steric stabilization and targeting ligands (AD-PEG-transferrin) for cell-specific targeting. A 70 nm particle can contain approximately 10 000 CDP polymer chains, approximately 2000 siRNA molecules, approximately 4000 AD-PEG5000 molecules, and approximately 100 AD-PEG5000-Tf molecules; this represents a significant payload of siRNA and a large ratio of siRNA to targeting ligand (20:1). The particles protect the nucleic acid payload from nuclease degradation, do not aggregate at physiological salt concentrations, and cause minimal erythrocyte aggregation and complement fixation at the concentrations typically used for in vivo application. Uptake of the nucleic acid-containing particles by HeLa cells is measured by flow cytometry and visualized by confocal microscopy. Competitive uptake experiments show that the transferrin-targeted particles display enhanced affinity for the transferrin receptor through avidity effects (multiligand binding). Functional efficacy of the delivered pDNA and siRNA is demonstrated through luciferase reporter protein expression and knockdown, respectively. The analysis of the CDP delivery vehicle provides insights that can be applied to the design of targeted nucleic acid delivery vehicles in general.

Peptide-guided gene delivery

Although currently less efficient than their viral counterparts, nonviral vectors are under intense investigation as a safer alternative for gene therapy. For successful delivery, the nonviral vector must be able to overcome many barriers to protect DNA and specifically deliver it for efficient gene expression in target cells. The use of peptides as gene delivery vectors is advantageous over other nonviral agents in that they are able to achieve all of these goals. This review will focus on the application of peptides to mediate nonviral gene delivery. By examining the literature over the past 20 years, it becomes clear that no other class of biomolecules are simultaneously capable of DNA condensation, blocking metabolism, endosomal escape, nuclear localization, and receptor targeting. Based on virtually limitless diversity of peptide sequence and function information from nature, it is increasingly clear that peptide-guided gene delivery is still in its infancy.

Lipoplexes with biotinylated transferrin accessories: Novel, targeted, serum-tolerant gene carriers

Novel transfecting assemblies comprising biotinylated cationic liposomes, DNA and tribiotinylated transferrin-streptavidin (streptavidin(bio3-transferrin)) accessories have been prepared, characterized and evaluated for toxicity and DNA delivery capability in human cervical carcinoma cells (HeLa). Two new lipophilic cholesteryl-based biotin derivatives, biotinylcholesterylformylhydrazide (MSB1) and aminohexanoylbiotinylcholesterylformylhydrazide (MSB2) provided docking points for streptavidin(bio3-transferrin) on cationic liposomes which were formulated with N,N-dimethylaminopropylaminylsuccinylcholesterylformylhydrazide (MS09) and dioleoylphosphatidylethanolamine (DOPE) in a 2:48:50 molar ratio. Ethidium dye displacement assays and gel retardation studies suggest that in ternary complexes, the DNA is electrostatically bound to the cationic liposomes while transferrins remain liposome-bound through streptavidin-biotin interactions. Assemblies fully protected plasmid DNA from serum nuclease digestion over a range of liposome:pGL3 DNA ratios (3-8:1, w/w) and exhibited low growth inhibition of HeLa cells (circa 5%) at the optimal transfection composition for streptavidin(bio3-transferrin):liposome:pGL3 DNA of 10:6:1 (w/w/w). Transfection levels, which were twice those of untargeted lipoplexes containing MSB1 or MSB2, were not significantly diminished in the presence of 10% foetal bovine serum. Excess transferrin (200 microg per well) reduced transfection levels to those of untargeted complexes, supporting the notion that at least 50% of ternary complexes gained entry into the cervical carcinoma cells by receptor mediation. Conversely, transfection levels with untargeted lipoplexes were only slightly reduced in the presence of transferrin at the same concentration.

Delivering cancer stem cell therapies - a role for nanomedicines?

Cancer stem cells (CSCs), i.e. cancer cells that can self-renew, constitute only a minority of the cells of a tumour, but, because of their ability to initiate and repopulate tumours, failure to control CSCs can potentially lead to tumour re-growth, even though the bulk tumour may have been treated successfully. Nanomedicines improve spatio-temporal control over drug kinetics and distribution, thus opening the prospect of safer and more specific therapies to address the challenges posed by CSCs. In particular, these systems have the potential to facilitate CSC-aware therapy by overcoming resistance to conventional cytotoxic drugs and by targeting novel therapies to the tumour and CSC-marker positive cells. This review examines the implications of the CSC paradigm specifically for the development of nanomedicines, i.e. therapies based on macromolecules or supramolecular aggregates.

Synthesis and characterization of polyaminoacidic polycations for gene delivery

The properties as non viral gene vector of a protein-like polymer, the alpha,beta-poly(N-2-hydroxyethyl)-d,l-aspartamide (PHEA) were exploited after its derivatization with 3-(carboxypropyl)trimethyl-ammonium chloride (CPTA) as molecule bearing a cationic group, in order to obtain stable polycations able to condense DNA. PHEA was firstly functionalized with aminic pendant groups by reaction with ethylenediamine (EDA) obtaining the alpha,beta-poly(N-2-hydroxyethyl)(2-aminoethylcarbamate)-d,l-aspartamide (PHEA-EDA) copolymer. We demonstrated that polymer functionalization degree is easily modulable by varying reaction conditions, so allowing to produce two PHEA-EDA derivatives at different molar percentage of amine groups. Subsequently, the condensation reaction of PHEA-EDA copolymers with CPTA yielded alpha,beta-poly(N-2-hydroxyethyl)(2-[3-(trimethylammonium chloride)propylamide]-amidoethylcarbamate)-d,l-aspartamide (PHEA-EDA-CPTA) polycation derivatives. In vitro studies were carried out to evaluate polycations ability to complex DNA and to protect it from nuclease degradation. Obtained results demonstrated the good ability of our new PHEA polycationic derivatives, PHEA-EDA-CPTA, to complex and condense genomic material, neutralizing its anionic charge even at very low polycation/DNA weight ratio. Finally, PHEA-EDA-CPTA polycations were characterized by in vitro cytotoxicity studies to evaluate their effects on the viability of HuH-6 human hepatocellular carcinoma cells by MTS assay. No cytotoxicity was evidenced by both polycationic derivatives after 48h of incubation at all tested concentrations.

Nanotechnology in otolaryngology

This article provides a background on nanotechnology and discusses the applications of nanotechnology to medicine, specifically to otolaryngology.

Tumor-targeted gene delivery using poly(ethylene glycol)-modified gelatin nanoparticles: in vitro and in vivo studies

PURPOSE

To develop safe and effective systemically administered nonviral gene therapy vectors for solid tumors, DNA-containing poly(ethylene glycol)-modified (PEGylated) gelatin nanoparticles were fabricated and evaluated in vitro and in vivo.

METHODS

Reporter plasmid DNA encoding for beta-galactosidase (pCMV-beta) was encapsulated in gelatin and PEGylated gelatin nanoparticles using a water-ethanol solvent displacement method under controlled pH and temperature. Lewis lung carcinoma (LLC) cells in culture were transfected with the pCMV-beta in the control and nanoparticle formulations. Periodically, the expression of beta-galactosidase in the cells was measured quantitatively using an enzymatic assay for the conversion of o-nitrophenyl-beta-D: -galactopyranoside (ONPG) to o-nitrophenol (ONP). Qualitative expression of beta-galactosidase in LLC cells was observed by staining with 5-bromo-4-chloro-3-indolyl-beta-D: -galactopyranoside (X-gal). Additionally, the plasmid DNA-encapsulated gelatin and PEGylated gelatin nanoparticles were administered intravenously (i.v.) and intratumorally (i.t.) to LLC-bearing female C57BL/6J mice. At various time points postadministration, the animals were sacrificed and transgene expression in the tumor and liver was determined quantitatively by the ONPG to ONP enzymatic conversion assay and qualitatively by X-gal staining.

RESULTS

Almost 100% of the pCMV-beta was encapsulated in gelatin and PEGylated gelatin nanoparticles (mean diameter 200 nm) at 0.5% (w/w) concentration. PEGylated gelatin nanoparticles efficiently transfected the LLC cells and the beta-galactosidase expression, as measured by the ONPG to ONP enzymatic conversion assay at 420 nm absorbance, increased starting from 12 h until 96 h post-transfection. The efficient expression of LLC cells was also evident by the X-gal staining method that shows blue color formation. The in vivo studies showed significant expression of beta-galactosidase in the tumor following administration of DNA-containing PEGylated gelatin nanoparticles to LLC-bearing mice by both i.v. and i.t. routes. Following i.v. administration of pCMV-beta in PEGylated gelatin nanoparticles, for instance, the absorbance at 420 nm per gram of tumor increased from 0.60 after 12 h to 0.85 after 96 h of transfection. After i.t. administration, the absorbance values increased from 0.90 after 12 h to almost 1.4 after 96 h.

CONCLUSIONS

The in vitro and in vivo results of this study clearly show that a long-circulating, biocompatible and biodegradable, DNA-encapsulating nanoparticulate system would be highly desirable for systemic delivery of genetic constructs to solid tumors.

Cationic polymethacrylates with covalently linked membrane destabilizing peptides as gene delivery vectors

A membrane-disrupting peptide derived from the influenza virus was covalently linked to different polymethacrylates (pDMAEMA, pDAMA and the degradable pHPMA-DMAE, monomers depicted in Fig. 1) using N-succinimidyl 3-(2-pyridyldithio)propionate (SPDP) as coupling agent to increase the transfection efficiency of polyplexes based on these polymers. It was shown by circular dichroism (CD) measurements that the polymer-conjugated peptide was, as the free peptide, able to undergo a conformational change of a random coil to an alpha helix upon lowering the pH to 5.0. This indicates that the property of the peptide to destabilize the endosomal membrane was preserved after its conjugation to the cationic polymers. In line herewith, a liposome leakage assay revealed that the polymer-bound peptide has comparable activity as the free peptide. The DNA condensing properties of the synthesized polymer-peptide conjugates were studied with dynamic light scattering and zeta-potential measurements, and it was shown that small (100 to 250 nm), positively charged (+15 to +20 mV) particles were formed. In vitro transfection and toxicity was tested in COS-7 cells, and these experiments showed that the polyplexes with grafted peptide had a substantially higher transfection activity than the control polyplexes, while the toxicity remained unchanged. Cellular uptake of the polyplexes was visualized with confocal laser scanning microscopy, and no differences in cellular uptake could be determined between the peptide containing systems and the control formulation. This shows that the increased transfection activity is indeed due to a better endosomal escape of the peptide grafted polyplexes. This study demonstrates that it is possible to covalently conjugate an endosome disruptive peptide to cationic gene delivery polymers with preservation of its membrane destabilization activity, making these conjugates suitable for in vivo DNA delivery.

Targeting of Polyplexes: Toward Synthetic Virus Vector Systems

Dominating issues in gene vector optimization are specific in recognizing the target cells and exploiting the proper intracellular trafficking routes. Any progress in this area will result in improved specific gene transfer, reduce the required therapeutic vector doses and, in consequence, lower the overall toxicity to the host. To provide polyplexes with the ability to distinguish between non-target and target cells, cell-binding ligands have been incorporated which recognize target-specific cellular receptors. In addition, polyplex domains with unspecific binding capacity (such as surface charges) have to be shielded or removed. Cell-binding ligands can be small molecules, vitamins, carbohydrates, peptides or proteins such as growth factors or antibodies. Such ligands have been incorporated into polyplexes after chemical conjugation to cationic polymers. The choice of the ligand and physical properties of the DNA formulation strongly influence extracellular routing (circulation in blood, tissue distribution), uptake and intracellular delivery of polyplexes. Recent efforts are discussed that aim at the development of polyplexes into virus-like supramolecular complexes; such particles should undergo structural changes compatible with extracellular and intracellular targeting.

Nonviral gene delivery systems: From simple transfection agents to artificial viruses

The introduction of nucleic acids into cells for therapeutic intervention is greatly impeded by the size and charge of these molecules and therefore requires sophisticated vectors that facilitate cellular uptake. Both viral and nonviral vectors have been developed for this purpose, each with their own advantages and shortcomings. The engineering of artificial viruses by dismantling virus particles or incorporating viral features into nonviral vectors represents a novel strategy to combine "the best of both worlds".:

Cyclodextrin-polyethylenimine conjugates for targeted in vitro gene delivery

Many human gene therapies will require cell-specific targeting. Though recombinant viruses are much more efficient than nonviral vectors, the latter, especially polymers, have the advantage of being targetable via conjugation of cell-specific ligands, including sugars, peptides, and antibodies, which can be covalently attached to the polymer using a variety of chemistries. Cyclodextrin, which forms inclusion complexes with small hydrophobic molecules, has been incorporated into a gene-delivery polymer and may provide a facile and versatile attachment site for targeting ligands. Polyethylenimine (PEI) was derivatized with beta-cyclodextrin on approximately 10% of the polymer's amines (termed CD-PEI). Human insulin was also derivatized with a hydrophobic palmitate group (pal-HI), which could anchor the protein to CD-PEI/DNA polyplexes. CD-PEI was essentially nontoxic to HEK293 cells at concentrations optimal for gene delivery and mediated nearly 4-fold higher gene expression than unmodified PEI, which is relatively toxic to these cells. More importantly, addition of the pal-HI to CD-PEI enhanced gene expression by more than an order of magnitude compared to unmodified PEI, either with or without the pal-HI. Because of the relative ease with which CD-binding moieties may be attached to various types of ligands, CD-PEI may be a generally useful material for testing novel cell-specific targeting compounds.