In vitro cytotoxicity of poly(amidoamine)s: relevance to DNA delivery

ROS-responsive polyprodrug micelles carrying suicide genes in combination with chemotherapy and gene therapy for prostate cancer treatment

Prostate cancer is the most common malignant tumor in the male reproductive system, and its incidence increases with age. Chemotherapy is one of the main strategies for treating prostate cancer, but it often comes with unavoidable side effects. Nanocarriers can improve drug utilization and targeting, and cationic carriers can also carry nucleic acids for gene therapy. In this study, we prepared a cationic micelle constructed from a polyprodrug that can deliver both chemotherapeutic drugs and nucleic acids simultaneously. The typical chemotherapeutic drug hydroxycamptothecin (HCPT) was linked by reactive oxygen species (ROS)-responsive coupling agents and forms amphiphilic block polymers with low molecular weight polyethyleneimine (PEI). The resulting cationic micelles can be triggered by high levels of ROS in tumor cells and collapse to release HCPT and suicide genes to kill tumor cells. At the same time, it reduces the killing of normal cells. In prostate cancer cells, it has been confirmed that the co-delivery carriers combined with chemotherapy and a suicide gene prodrug system have shown an ideal therapeutic effect on prostate cancer.

Synthesis and Characterization of Click Nucleic Acid Conjugated Polymeric Microparticles for DNA Delivery Applications

Microparticle-mediated nucleic acid delivery is a popular strategy to achieve therapeutic outcomes via antisense gene therapy. However, current methods used to fabricate polymeric microparticles suffer from suboptimal properties such as particle polydispersity and low encapsulation efficiency. Here, a new particulate delivery system based on step-growth thiol-Michael dispersion polymerization is reported in which a low polydispersity microparticle is functionalized with a synthetic nucleic acid mimic, namely, click nucleic acids (CNA). CNA oligomers, exhibiting an average length of approximately four nucleic acid repeat units per chain for both adenine and thymine bases, were successfully conjugated to excess thiols present in the microparticles. Effective DNA loading was obtained by simple mixing, and up to 6 ± 2 pmol of complementary DNA/mg of particle was achieved, depending on the length of DNA used. In addition, DNA loading was orders of magnitude less for noncomplementary sequences and sequences containing an alternating base mismatch. The DNA release properties were evaluated, and it was found that release could be triggered by sudden changes in temperature but was unaffected over a range of pH. Finally, phagocytosis of loaded microparticles was observed by confocal microscopy and corroborated by an increase in cellular metabolic activity up to 90%. Overall, this work suggests that CNA functionalized microparticles could be a promising platform for controlled DNA delivery.

Light-Triggered Trafficking to the Cell Nucleus of a Cationic Polyamidoamine Functionalized with Ruthenium Complexes

Strategies for endosomal escape and access to the cell nucleus are highly sought for nanocarriers to deliver their load efficiently following endocytosis. In this work, we have studied the uptake and intracellular trafficking of a polycationic polyamidoamine (PAA) endowed with a luminescent Ru complex, Ru-PhenAN, that shows unique trafficking to the cell nucleus. Live cell imaging confirmed the capacity of this polymer to access the nucleus, excluding artifacts due to cell fixation, and clarified that the mechanism of escape is light-triggered and relies on the presence of the Ru complexes and their capacity to absorb light and act as photosensitizers for singlet oxygen production. These results open up the possibility to use PAA-ruthenium complexes for targeted light-triggered delivery of genetic material or drugs to the cytosol and nucleus.

Cancer-Targeting Nanoparticles for Combinatorial Nucleic Acid Delivery

Nucleic acids are a promising type of therapeutic for the treatment of a wide range of conditions, including cancer, but they also pose many delivery challenges. For efficient and safe delivery to cancer cells, nucleic acids must generally be packaged into a vehicle, such as a nanoparticle, that will allow them to be taken up by the target cells and then released in the appropriate cellular compartment to function. As with other types of therapeutics, delivery vehicles for nucleic acids must also be designed to avoid unwanted side effects; thus, the ability of such carriers to target their cargo to cancer cells is crucial. Classes of nucleic acids, hurdles that must be overcome for effective intracellular delivery, types of nonviral nanomaterials used as delivery vehicles, and the different strategies that can be employed to target nucleic acid delivery specifically to tumor cells are discussed. Additonally, nanoparticle designs that facilitate multiplexed delivery of combinations of nucleic acids are reviewed.

Comparison of Gene Transfection and Cytotoxicity Mechanisms of Linear Poly(amidoamine) and Branched Poly(ethyleneimine) Polyplexes

PURPOSE

This study aimed to further explore the mechanisms behind the ability of certain linear polyamidoamines (PAAs) to transfect cells with minimal cytotoxicity.

METHODS

The transfection efficiency of DNA complexed with a PAA of a molecular weight over 10 kDa or 25 kDa branched polyethyleneimine (BPEI) was compared in A549 cells using a luciferase reporter gene assay. The impact of endo/lysosomal escape on transgene expression was investigated by transfecting cells in presence of bafilomycin A1 or chloroquine. Cytotoxicity caused by the vectors was evaluated by measuring cell metabolic activity, lactate dehydrogenase release, formation of reactive oxygen species and changes in mitochondrial membrane potential.

RESULTS

The luciferase activity was ~3-fold lower after transfection with PAA polyplexes than with BPEI complexes at the optimal polymer to nucleotide ratio (RU:Nt). However, in contrast to BPEI vectors, PAA polyplexes caused negligible cytotoxic effects. The transfection efficiency of PAA polyplexes was significantly reduced in presence of bafilomycin A1 while chloroquine enhanced or decreased transgene expression depending on the RU:Nt.

CONCLUSIONS

PAA polyplexes displayed a pH-dependent endo/lysosomal escape which was not associated with cytotoxic events, unlike observed with BPEI polyplexes. This is likely due to their greater interactions with biological membranes at acidic than neutral pH.

The AGMA1 polyamidoamine mediates the efficient delivery of siRNA

AGMA1, a prevailingly cationic, guanidine-bearing, linear, amphoteric polyamidoamine is an effective siRNA condensing agent. Here two AGMA1 samples of different molecular weight, i.e. AGMA1-5 and AGMA1-10 were evaluated as siRNA condensing agents and transfection promoters. AGMA1-10 formed stable polyplexes with a size lower than 50 nm and positive zeta potential. AGMA1-5 polyplexes were larger, about 100 nm in size. AGMA1-10 polyplexes, but not AGMA1-5 proved to be an effective intracellular siRNA carrier, able to trigger gene silencing in Hela and PC3 cell lines without eliciting cytotoxic effects. AGMA1-10 knocked down AKT-1 expression upon transfection with an AKT-1 specific siRNA. The polyplex entry mechanism was investigated and was mediated by macropinocytosis. In conclusion, AGMA1 has potential as an efficient, non-toxic tool for the intracellular delivery of siRNA and warrants further investigation.

Cytotoxicity of polycations: Relationship of molecular weight and the hydrolytic theory of the mechanism of toxicity

The mechanism of polycation cytotoxicity and the relationship to polymer molecular weight is poorly understood. To gain an insight into this important phenomenon a range of newly synthesised uniform (near monodisperse) linear polyethylenimines, commercially available poly(l-lysine)s and two commonly used PEI-based transfectants (broad 22kDa linear and 25kDa branched) were tested for their cytotoxicity against the A549 human lung carcinoma cell line. Cell membrane damage assays (LDH release) and cell viability assays (MTT) showed a strong relationship to dose and polymer molecular weight, and increasing incubation times revealed that even supposedly "non-toxic" low molecular weight polymers still damage cell membranes. The newly proposed mechanism of cell membrane damage is acid catalysed hydrolysis of lipidic phosphoester bonds, which was supported by observations of the hydrolysis of DOPC liposomes.

Study of the RAFT homopolymerization and copolymerization of N-[3-(dimethylamino)propyl]methacrylamide hydrochloride and evaluation of the cytotoxicity of the resulting homo- and copolymers

Well-defined p(DMAPMA·HCl) homopolymers with good chain extension ability were obtained by the RAFT in acidic conditions and precipitation in acetone.

Polyamine derivatives: a revival of an old neglected scaffold to fight resistant Gram-negative bacteria?

Emergence of multidrug-resistant pathogens was responsible for microbial infections and inefficacy of numerous antimicrobial therapies has induced a need for the research of new classes of antibiotics. In this review, we will focus our interest toward the biological properties of polyamino antimicrobial agents.

The Effect of the Molecular Architecture on the Antioxidant Properties of Chitosan Gallate

To elucidate the structure-antioxidant activity relationships of chitosan gallate (CG), a series of CG derivatives with different degrees of substitution (DS's) and molecular weights (MWs) were synthesized from chitosan (CS) and gallic acid (GA) via a free radical graft reaction. A higher MW led to a lower DS of CG. The structures of CG were characterized by FT-IR and ¹H NMR, and results showed that GA was mainly conjugated to the C-2 and C-6 positions of the CS chain. The antioxidant activity (the DPPH radical scavenging activity and reducing power) were enhanced with an increased DS and a decreased MW of CG. A correlation between antioxidant activities and the DS and MW of CG was also established. In addition, a suitable concentration (0~250 μg/mL) of CG with different MWs (32.78~489.32 kDa) and DS's (0~92.89 mg·GAE/g CG) has no cytotoxicity. These results should provide a guideline to the application of CG derivatives in food or pharmacology industries.

Exploring the role of polymer structure on intracellular nucleic acid delivery via polymeric nanoparticles

Intracellular nucleic acid delivery has the potential to treat many genetically-based diseases, however, gene delivery safety and efficacy remains a challenging obstacle. One promising approach is the use of polymers to form polymeric nanoparticles with nucleic acids that have led to exciting advances in non-viral gene delivery. Understanding the successes and failures of gene delivery polymers and structures is the key to engineering optimal polymers for gene delivery in the future. This article discusses the polymer structural features that enable effective intracellular delivery of DNA and RNA, including protection of nucleic acid cargo, cellular uptake, endosomal escape, vector unpacking, and delivery to the intracellular site of activity. The chemical properties that aid in each step of intracellular nucleic acid delivery are described and specific structures of note are highlighted. Understanding the chemical design parameters of polymeric nucleic acid delivery nanoparticles is important to achieving the goal of safe and effective non-viral genetic nanomedicine.

Synthesis and evaluation of degradable polyurea block copolymers as siRNA delivery agents

Chain extension by diisocyanate condensation provides a versatile and convenient means for preparing block copolymers. We have utilized this chemistry to prepare reducible multiblock polycations for siRNA delivery. This approach, an alternative to oxidative coupling, was suitable for preparing multiblock polycations with defined molecular weight and architecture. The polymer, PEG-b-multi-(polyhexylurea-co-oligo-L-lysine)-b-PEG, was capable of electrostatically condensing siRNA to form nano-sized polyplexes across a broad compositional range. We demonstrated that the polyplexes enter the cells via endocytosis and interact with the endosome membrane leading to destabilization and hence endosome escape. Another feature of these polymers is their multiple intra-chain disulfide linkages. This enables weakening of the polyplex via chain scission within the cytosol's reductive environment. In addition to the controlled preparation of the polymer, the polyplexes were capable of delivering siRNA in vitro to silence greater than 50% green fluorescent protein expression with negligible toxicity.

Bioengineered nanoparticles for siRNA delivery

Short interfering RNA (siRNA) has been an important laboratory tool in the last two decades and has allowed researchers to better understand the functions of nonprotein-coding genes through RNA interference (RNAi). Although RNAi holds great promise for this purpose as well as for treatment of many diseases, efforts at using siRNA have been hampered by the difficulty of safely and effectively introducing it into cells of interest, both in vitro and in vivo. To overcome this challenge, many biomaterials and nanoparticles (NPs) have been developed and optimized for siRNA delivery, often taking cues from the DNA delivery field, although different barriers exist for these two types of molecules. In this review, we discuss general properties of biomaterials and nanoparticles that are necessary for effective nucleic acid delivery. We also discuss specific examples of bioengineered materials, including lipid-based NPs, polymeric NPs, inorganic NPs, and RNA-based NPs, which clearly illustrate the problems and successes in siRNA delivery.

Poly(amidoamine) polymers: soluble linear amphiphilic drug-delivery systems for genes, proteins and oligonucleotides

Polymer-drug and polymer-protein conjugates are emerging as a robust and well-characterized class of therapeutic entity. Although there are no low-molecular-weight soluble polymer conjugates in routine clinical use, there are many examples of routinely used high-molecular-weight drugs conjugated to soluble polymers (e.g., Oncospar). Advances in synthetic polymer chemistry have fostered the development of linear poly(amidoamine)s (PAA)s that impart both biodegradability, 'smart' (pH responsive) biological activity and biocompatibility. In their linear form, such as hyper-branched poly(amidoamine) (PAMAM) dendrimers, linear PAAs can be used to deliver large therapeutic entities such as peptides, proteins and genes to either the cytosol or nucleus. Furthermore, these polymers offer great potential in vivo due to their ability to either target the liver or be directed away from the liver and enter tumor mass via the enhanced permeability and retention (EPR) effect. PAAs also exhibit minimal toxicity (dependent upon backbone chemistry), relative to well-characterized polymers used for gene delivery. The propensity of PAAs to modulate intracellular trafficking resulting in their cytosolic translocation has also recently been quantified in vivo and is the primary focus of this article.

EphA2 targeting peptide tethered bioreducible poly(cystamine bisacrylamide-diamino hexane) for the delivery of therapeutic pCMV-RAE-1γ to pancreatic islets

The pathogenesis of type-1 diabetes is complicated, and a clear, single mechanism has yet to be identified. Reports have indicated that the activating receptor NKG2D plays an important role in the development of disease. Exploiting a natural phenomenon observed in tumors, plasmid DNA encoding for a soluble ligand to NKG2D (sRAE-1γ) was isolated and engineered into a plasmid expression system. A polymeric gene delivery system was developed to deliver the soluble RAE-1 plasmid locally to the pancreatic islets for the prevention of type-1 diabetes. The bioreducible cationic polymer poly(cystamine bisacrylamide-diamino hexane) (p(CBA-DAH)) was modified with poly(ethylene glycol) (PEG) and the targeting peptide CHVLWSTRC, known to target the EphA2 and EphA4 receptors. The PEG serves to improve stability and tissue selectivity, while the peptide will target EphA2 and A4, overexpressed in the pancreatic microvasculature. The targeting polymer Eph-PEG-p(CBA-DAH) shows selective uptake by the target cell line, indicative of the targeting properties that will be seen in systemic administration. Using the delivery system, the therapeutic plasmid can be delivered to the pancreas, reduce interactions between the beta-cells and infiltrating NKG2D positive lymphocytes, and effectively protect beta-cells from autoimmune destruction and prevent type 1 diabetes.

Gene silencing activity of siRNA polyplexes based on thiolated N,N,N-trimethylated chitosan

N,N,N-Trimethylated chitosan (TMC) is a biodegradable polymer emerging as a promising nonviral vector for nucleic acid and protein delivery. In the present study, we investigated whether the introduction of thiol groups in TMC enhances the extracellular stability of the complexes based on this polymer and promotes the intracellular release of siRNA. The gene silencing activity and the cellular cytotoxicity of polyplexes based on thiolated TMC were compared with those based on the nonthiolated counterpart and the regularly used lipidic transfection agent Lipofectamine. Incubation of H1299 human lung cancer cells expressing firefly luciferase with siRNA/thiolated TMC polyplexes resulted in 60-80% gene silencing activity, whereas complexes based on nonthiolated TMC showed less silencing (40%). The silencing activity of the complexes based on Lipofectamine 2000 was about 60-70%. Importantly, the TMC-SH polyplexes retained their silencing activity in the presence of hyaluronic acid, while nonthiolated TMC polyplexes hardly showed any silencing activity, demonstrating their stability against competing anionic macromolecules. Under the experimental conditions tested, the cytotoxicity of the thiolated and nonthiolated siRNA complexes was lower than those based on Lipofectamine. Given the good extracellular stability and good silencing activity, it is concluded that polyplexes based on TMC-SH are attractive systems for further in vivo evaluations.

Plasmid DNA delivery into MDA-MB-453 cells mediated by recombinant Her-NLS fusion protein

A major rate-limiting step in nonviral gene delivery is the entry of nucleic acids across various membrane barriers and eventually into the nucleus where it must be transcribed. Cell-penetrating peptides and proteins are employed to generate formulations that overcome these challenges to facilitate DNA delivery into cells efficiently. However, these are limited by their inability to deliver nucleic acids selectively due to lack of specificity because they deliver to both cancer and normal cells. In this study, through modular design, we generated a recombinant fusion protein designated as Her-nuclear localization sequence (Her-NLS), where heregulin-α (Her), a targeting moiety, was cloned in frame with cationic NLS peptide to obtain a cell-specific targeting biomolecule for nucleic acid delivery. The heregulin-α₁ isoform possesses the epidermal growth factor-like domain and binds to HER2/3 heterodimers which are overexpressed in certain breast cancers. Purified recombinant Her-NLS fusion protein binds plasmid DNA and specifically transfects MDA-MB-453 cells overexpressing the epidermal growth factor receptors HER2/3 in vitro. The approach described would also permit replacement of heregulin ligand with other targeting moieties that would be suited to cell-specific nucleic acid delivery mediated via receptor-ligand interactions.

Induction of human alveolar epithelial cell growth factor receptors by dendrimeric nanostructures

Although nonviral dendrimeric nanostructures have been widely used as gene delivery systems, key questions about target cells responses to these nanostructures are yet to be answered. Here, we report the responsiveness of A431 and A549 cells upon treatment with polypropylenimine diaminobutane (DAB) dendrimers nanosystems. Complexation of DAB dendrimers with DNA reduced the zeta potential of nanostructures, but increased their size. Fluorescence microscopy revealed high transfection efficiency in both cell lines treated with DAB dendrimers with induced cytotoxicity evidenced by MTT assay. The A549 cells showed upregulation of epidermal growth factor receptor (EGFR) and its downstream signalling biomolecule Akt kinase upon treatment with DAB dendrimers, while no changes were observed in A431 cells. Based on our findings, the biological impacts of these nanosystems appeared to be cell dependent. Thus, the biological responses of target cells should be taken into account when these nanostructures are used as gene delivery system.

Sterically stabilized self-assembling reversibly cross-linked polyelectrolyte complexes with nucleic acids for environmental and medical applications

One of the principal problems facing nucleic acid delivery systems using polyplexes is the instability of the complexes in the presence of proteins and high salt concentrations. We have used a cross-linking polymer to overcome this problem. Pendant thiol moieties have been incorporated into a PAA (polyamidoamine) homopolymer and a PEG [poly(ethylene glycol)]–PAA–PEG copolymer reported previously as a self-assembling system. When mixed with DNA, small monodisperse sterically stabilized particles are formed in quantitative yields. Optimization of the formulation resulted in nanoparticles which are stable in seawater. This cross-linked formulation has been successfully tested in both freshwater and estuarine field trials as a water tracer. Future work will develop these particles as a groundwater tracer and also for therapeutic applications of nucleic acid delivery.

Estimation of toxicity of ionic liquids in Leukemia Rat Cell Line and Acetylcholinesterase enzyme by principal component analysis, neural networks and multiple lineal regressions

Multiple linear regression (MLR), radial basis network (RB), and multilayer perceptron (MLP) neural network (NN) models have been explored for the estimation of toxicity of ammonium, imidazolium, morpholinium, phosphonium, piperidinium, pyridinium, pyrrolidinium and quinolinium ionic liquid salts in the Leukemia Rat Cell Line (IPC-81) and Acetylcholinesterase (AChE) using only their empirical formulas (elemental composition) and molecular weights. The toxicity values were estimated by means of decadic logarithms of the half maximal effective concentration (EC(50)) in microM (log(10)EC(50)). The model's performances were analyzed by statistical parameters, analysis of residuals and central tendency and statistical dispersion tests. The MLP model estimates the log(10)EC(50) in IPC-81 and AchE with a mean prediction error less than 2.2 and 3.8%, respectively.

Comparison of the efficiency and toxicity of sonoporation with branched polyethylenimine-mediated gene transfection in various cultured cell lines

OBJECTIVE

The objective of this study is to evaluate transfection efficiency and safety for gene delivery by sonoporation in comparison with cationic polymer gene carrier branched polyethylenimine (BPEI).

METHODS

The cDNA expressing VEGF(165) was cloned under chicken beta-actin promoter. The plasmid DNA was transfected into the CHO, HEK293, and NIH3T3 cells using microbubble-based sonoporation and BPEI (25 kDa) under various conditions. Enzyme-linked immunosorbent assay (ELISA) was used to determine the expressed protein level. Cytotoxicities of transfection methods were compared by Cell Counting Kit-8.

RESULTS

At 1 MHz intensity, transfection efficiency of sonoporation was enhanced by microbubble concentration with no detrimental effects. By contrast, BPEI exacerbated cell viability, despite its high transgene expression efficiency.

CONCLUSION

Sonoporation gene therapy might be the safest technique to be used in actual clinical practice.

Development of a slow non-viral DNA release system from PDLLA scaffolds fabricated using a supercritical CO2 technique

Polyamidoamine polymers (PAA) comprising methylene-bisacrylamide/dimethylethylene-diamine monomers were synthesized, complexed with DNA and incorporated into porous P(DL)LA scaffolds by using a supercritical CO(2) (scCO(2)) technique. Scaffolds were made in a dry state consequently there was a need to lyophilize the complexes. A statistically significant reduction of the transfection efficiency was observed in the absence of trehalose when compared to the original complex after freeze-drying. Increasing concentrations (0-10% w/v) of trehalose were added to the complex prior to freeze-drying. Structure dependent differences in DNA binding were evaluated by gel electrophoresis and thermal transition analysis. TEM and PCS showed aggregate formation after freeze-drying without trehalose. Scaffolds were characterized by pore sizes of 173 +/- 73 microm and a porosity of 71%. The transfection potential of the released DNA was investigated by seeding scaffolds with A549 cells and following firefly luciferase as a marker gene after 48 h exposure. Low but continuous levels of transfection were observed for PAA complexes during a 60-day study. Complexes made with Lipofectaminetrade mark gave initially higher levels of DNA release but no further expression was seen after 40 days. Uncomplexed DNA showed background levels of transfection. Culturing cells on 3D scaffolds showed a benefit in retention of transfection activity with time compared to 2D controls. Transfection levels could be increased when cells were grown in OptiMEM. This study demonstrated that PAA/DNA complexes incorporated into a P(DL)LA scaffold made by using scCO(2) processing exhibited a slow release and extended gene expression profile.

Investigation of in vitro biocompatibility of novel pentablock copolymers for gene delivery

Novel pentablock copolymers of poly(diethylaminoethylmethacrylate) (PDEAEM), poly(ethylene oxide) (PEO), and poly(propylene oxide) (PPO), (PDEAEM-b-PEO-b-PPO-b-PEO-b-PDEAEM), were synthesized as vectors for gene delivery, and were tested for their biocompatibility on SKOV3 (human ovarian carcinoma) and A431 (human epidermoid cancer) cell lines under different in vitro conditions using various assays to elucidate the mechanism of cell death. These copolymers form micelles in aqueous solutions and can be tuned for their cytotoxicity by tailoring the weight percentage of their cationic component, PDEAEM. Copolymers with higher PDEAEM content were found to be more cytotoxic, though their polyplexes were less toxic than the polycations alone. Pentablock copolymers displayed higher cell viability than commercially available ExGen 500 at similar N:P ratios. While cell death with ExGen was found to be accompanied by an early loss of cell membrane integrity, pentablock copolymers caused very little membrane leakage. Caspase-3/7 assay confirmed that none of these polymers induced apoptosis in the cells. These pentablock copolymers form thermo-reversible gels at physiological temperatures, thereby enabling controlled gene delivery. Toxicity of the polymer gels was tested using an agarose-matrix, simulating an in vivo tumor model where injected polyplex gels would dissolve to release polyplexes, diffusing through tumor mass to reach the target cells. Twenty five weight percent of copolymer gels were found to be nontoxic or mildly cytotoxic after 24 h incubation. Transfection efficiency of the copolymers was found to be critically correlated to cytotoxicity and depended on DNA dose, polymer concentration, and N:P ratios. Transgene expression obtained was comparable to that of ExGen, but ExGen exhibited greater cell death.

Biodegradable poly(2-dimethylamino ethylamino)phosphazene for in vivo gene delivery to tumor cells. Effect of polymer molecular weight

PURPOSE

Previously, we have shown that complexes of plasmid DNA with the biodegradable polymer poly(2-dimethylamino ethylamino)phosphazene (p(DMAEA)-ppz) mediated tumor selective gene expression after intravenous administration in mice. In this study, we investigated the effect of p(DMAEA)-ppz molecular weight on both in vitro and in vivo tumor transfection, as well as on complex induced toxicity.

MATERIALS AND METHODS

p(DMAEA)-ppz with a broad molar mass distribution was fractionated by preparative size exclusion chromatography. Polyplexes consisting of plasmid DNA and the collected polymer fractions were tested for biophysical properties, (cyto)toxicity and transfection activity.

RESULTS

Four p(DMAEA)-ppz fractions were collected with weight average molecular weights ranging from 130 to 950 kDa, and with narrow molecular mass distributions (Mw/Mn from 1.1 to 1.3). At polymer-to-DNA (N/P) ratios above 6, polyplexes based on these polymers were all positively charged (zeta potential 25-29 mV), and had a size of 80-90 nm. The in vitro cytotoxicity of the polyplexes positively correlated with polymer molecular weight. The in vitro transfection activity of the different polyplexes depended on their N/P ratio, and was affected by the degree of cytotoxicity, as well as the colloidal stability of the different polyplexes. Intravenous administration of polyplexes based on the high molecular weight polymers led to apparent toxicity, as a result of polyplex-induced erythrocyte aggregation. On the other hand, administration of polyplexes based on low molecular weight p(DMAEA)-ppz's (Mw 130 kDa) did not show signs of toxicity and resulted in tumor selective gene expression.

CONCLUSION

Polymer molecular weight fractionation enabled us to optimize the transfection efficiency/toxicity ratio of p(DMAEA)-ppz polyplexes for in vitro and in vivo tumor transfection.

Polylysine-functionalised thermoresponsive chitosan hydrogel for neural tissue engineering

Foetal mouse cortical cells were cultured on 2D films and within 3D thermally responsive chitosan/glycerophosphate salt (GP) hydrogels. The biocompatibility of chitosan/GP 2D films was assessed in terms of cell number and neurites per cell. Osmolarity of the hydrogel was a critical factor in promoting cell survival with isotonic GP concentrations providing optimal conditions. To improve cell adhesion and neurite outgrowth, poly-D-lysine (PDL) was immobilised onto chitosan via azidoaniline photocoupling. Increase in PDL concentrations did not alter cell survival in 2D cultures but neurite outgrowth was significantly inhibited. Neurons exhibited a star-like morphology typical of 2D culture systems. The effects of PDL attachment on cell number, cell morphology and neurite outgrowth were more distinct in 3D culture conditions. Neurones exhibited larger cell bodies and sent out single neurites within the macroporous gel. Immobilised PDL improved cell survival up to an optimum concentration of 0.1%, however, further increases resulted in drops in cell number and neurite outgrowth. This was attributed to a higher cell interaction with PDL within a 3D hydrogel compared to the corresponding 2D surface. The results show that thermally responsive chitosan/GP hydrogels provide a suitable 3D scaffolding environment for neural tissue engineering.

NANOMEDICINES: DELIVERING DRUGS USING BOTTOM UP NANOTECHNOLOGY

The use of nanosized materials changes the way in which drugs are handled by the body and offers opportunities to improve drug delivery. The physiological mechanisms controlling the distribution of nanosized materials (enhanced permeability and retention effect, cellular uptake pathways and opsonisation/elimination of nanoparticles) are described. Two different nanosized drug delivery systems are considered; drug delivery and DNA delivery. The deficiencies of currently available biodegradable polymers for preparation of drug containing nanoparticles are mainly the amount of drug that can be incorporated and the rapid rate of drug release. The development of new biodegradable polymers which can interact with the drug and so significantly increase drug loading and decrease the rate of drug release are outlined. DNA delivery necessitates overcoming a variety of biological barriers. We are developing polyelectrolyte complexes of DNA with cationic polyamidoamines (PAA) as a delivery system. Complexing PAA with DNA results in good transfection of cells in vitro. However, in vivo, a more complex arrangement of PAA, Polyethylene glycol-PAA copolymers, DNA and the use of ligands will be required. Despite these efforts, further developments will be needed in nanotechnology for both drug and DNA nanoparticle delivery systems to achieve our clinical objectives.

A versatile reducible polycation-based system for efficient delivery of a broad range of nucleic acids

Synthetic vectors based on reducible polycations consisting of histidine and polylysine residues (HIS RPCs) were evaluated for their ability to deliver nucleic acids. Initial experiments showed that RPC-based vectors with at least 70% histidine content mediated efficient levels of gene transfer without requirement for the endosomolytic agent chloroquine. Significant gene transfer was observed in a range of cell types achieving up to a 5-fold increase in the percentage of transfected cells compared to 25 kDa PEI, a gold standard synthetic vector. In contrast to 25 kDa PEI, HIS RPCs also mediated efficient transfer of other nucleic acids, including mRNA encoding green fluorescent protein in PC-3 cells and siRNA directed against the neurotrophin receptor p75^NTR in post-mitotic cultures of rat dorsal root ganglion cell neurons. Experiments to elevate intracellular glutathione and linear profiling of cell images captured by multiphoton fluorescent microscopy highlighted that parameters such as the molecular weight and rate of cleavage of HIS RPCs were important factors in determining transfection activity. Altogether, these results demonstrate that HIS RPCs represent a novel and versatile type of vector that can be used for efficient cytoplasmic delivery of a broad range of nucleic acids. This should enable different or a combination of therapeutic strategies to be evaluated using a single type of polycation-based vector.

Trimethylated chitosans as non-viral gene delivery vectors: Cytotoxicity and transfection efficiency

Chitosans are linear polysaccharides of natural origin that show potential as carriers in drug and gene delivery. Introducing quaternisation on the chitosan backbone renders the polymer soluble over a wider pH range and confers controlled cationic character. This study aims to investigate the effect of increasing quaternisation and therefore, positive charge on cell viability and transfection. Oligomeric and polymeric chitosans were trimethylated, the toxicity and transfection efficiency of these derivatives were tested with respect to increasing degree of trimethylation. The cytoxicity of polymer and oligomer derivatives alone and of their complexes with plasmid DNA were determined using the 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl tetrazolium bromide (MTT) assay on COS-7 (monkey kidney fibroblasts) and MCF-7 (epithelial breast cancer) cells. Transfection efficiency was investigated using the pGL3 luciferase reporter gene on the same cell lines. Complexes were characterised for their stability by gel electrophoresis. Cytotoxicity results showed that all derivatives were significantly less toxic than linear polyethylenimine (PEI). A general trend of increasing toxicity with increasing degree of trimethylation was seen. However, higher toxicity was seen in polymeric chitosan derivatives over oligomeric chitosan derivatives at similar degrees of trimethylation. All derivatives complexed pGL3 luc plasmid DNA efficiently at 10:1 ratio and three (TMO44, TMC57 and TMC93) were able to transfect MCF-7 cells with greater efficiency than PEI; 16, 23 and 50-fold, respectively. TMC57, TMC93 and all TMOs gave appreciable transfection of COS-7 cells.

Structure–function relationships of gene delivery vectors in a limited polycation library

A library of 13 polylysine-graft-imidazoleacetic acid conjugates was synthesized to examine the collective effects of polymer molecular weight, side chain substitution, and DNA:polymer ratio on cytotoxicity, transfection efficiency, and polycation-DNA interaction. In general, the relationships between the physicochemical characteristics and the gene transfer capabilities of these polycations appear nonlinear. The in vitro cytotoxicity of these polymers decreased, while total protein expression increased, with decreasing molecular weight and increasing imidazole content. Flow cytometry experiments indicated, however, that an increase in marker gene expression does not always correlate with the total number of cells transfected, even when similar polymer structures are used for transfection. The maximum level of luciferase gene expression was mediated by transfection with a low molecular weight, high imidazole content (9400 Mw, 95 mol% imidazole) polymer. The extent of DNA condensation, as determined by ethidium bromide fluorescence quenching, also decreased with decreasing polymer molecular weight and increasing imidazole content. Relative binding affinity between DNA and the polycations, measured via competitive binding in the presence of a synthetic polyanion, decreased with decreasing polymer molecular weight; however, the relative affinity also appeared to increase with increasing imidazole, suggesting that electrostatic contributions are not solely responsible for DNA-polycation binding interactions. This limited library and corresponding structure/function analysis forms the foundation upon which larger, more comprehensive polycationic libraries can be designed and evaluated to further understand how polycation transfection reagents function.

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.

Partial acetylation of polyethylenimine enhances in vitro gene delivery

PURPOSE

Polyethylenimine (PEI) is a highly effective gene delivery vector, but because it is an off-the shelf material, its properties may not be optimal. To investigate the effects of the protonation properties of the polymer, we generated PEI derivatives by acetylating varying fractions of the primary and secondary amines to form secondary and tertiary amides, respectively.

METHODS

Reaction of PEI with increasing amounts of acetic anhydride at 60 degrees C for 4.5 h yielded polymers with 15%, 27%, and 43% of the primary amines modified with acetyl groups. Polymer-DNA complexes were characterized by dynamic light scattering and zeta potential measurements. Cytotoxicity of the polymers was assessed by XTT assay for metabolic activity, and gene delivery efficiency was determined as the relative expression of a luciferase gene in MDA-MB-231 and C2C12 cell lines.

RESULTS

Acetylation of PEI decreased the "physiological buffering capacity," defined as the moles of protons absorbed per mole of nitrogen on titration from pH 7.5 to 4.5, from 0.29 mol H+/mol N to 0.17 mol H+/mot N, 0.12 mol H+/mol N, and 0.090 mol H+/mol N for PEI-Ac15, PEI-Ac27, and PEI-Ac43, respectively. In addition, acetylation decreased the zeta potential of polyplexes from 14 mV to 8-11 mV and increased the polyplex diameter by two- to threefold. Surprisingly, acetylation had a negligible effect on cytotoxicity of the polymers and increased gene delivery effectiveness by up to 21-fold compared to unmodified PEI, both in the presence and absence of serum.

CONCLUSIONS

Reduction of the buffering capacity of PEI greatly enhanced the gene delivery activity of the polymer. The mechanism is not yet understood, but the enhancement may be caused by more effective polyplex unpackaging, altered endocytic trafficking, and/or increased lipophilicity of acetylated PEI-DNA complexes. Future studies will address these possibilities in more detail.

Polyfection as Nonviral Gene Transfer Method —Design of Novel Nonviral Vector Using α-Cyclodextrin—

Due to the growing concerns over the toxicity and immunogenicity of viral DNA delivery systems, DNA delivery via nonviral routes has become more desirable and advantageous. In particular, polycation complexes with DNA (polyplex) are attractive nonviral vectors. To design novel polycationic vectors, we prepared polyamidoamine starburst dendrimer (dendrimer) conjugates with three cyclodextrins (CDE conjugates) and three generations (G2, G3, and G4) of dendrimers. Of seven CDE conjugates, an alpha-CDE conjugate (G3) with an average degree of substitution (DS) of alpha-CyD of 2.4 [alpha-CDE conjugate (G3, DS 2.4)] showed greater gene transfer activity than dendrimers and other alpha-CDE conjugates with less cytotoxicity. These results suggest the potential use of alpha-CDE conjugate (G3, DS 2.4) as a polycationic vector in vitro and in vivo. Herein, I review a recent polyfection method, with special focus on alpha-CDE conjugate (G3, DS 2.4).

Development of multicomponent DNA delivery systems based upon poly(amidoamine)-PEG co-polymers

PEGylated polyamidoamine (PAA) polymers were investigated for the production of sterically stabilised DNA delivery systems. Comparison of a PEGylated polymer (NG47) with a non-PEGylated polymer (NG49) showed similar binding of co-polymer to DNA by displacement of ethidium bromide (EB) and DNA melting studies. Gel electrophoresis, turbidimetric analysis and PCS demonstrated differences in the colloidal properties of the complexes, which were attributable to the formation of soluble complexes by the PEGylated co-polymer. However, transmission electron microscopy (TEM) showed that the resulting complexes containing poly(ethylene glycol) (PEG) were not well condensed, susceptible to degradation by nucleases, and thus not suited for in vivo delivery. The poor properties of the PEGylated co-polymer were attributed to an excess of PEG. However, polymer blends of NG47 and NG49 at defined ratios of polymer to co-polymer and total repeating units (RUs) to nucleotide, spontaneously formed complexes with a range of desirable properties. These included small size and polydispersity, high particle density, low surface charge and resistance to nuclease degradation. Complexes made with PEGylated polymer alone, and the polymer blends both suffered from a reduced polyfection activity. This was attributed to a low surface charge on the complex, which reduced interactions with the cell membrane and consequent uptake of the particles into the cell.