Nano-carriers for DNA delivery to the lung based upon a TAT-derived peptide covalently coupled to PEG-PEI

Cell penetrating peptide-modified pharmaceutical nanocarriers for intracellular drug and gene delivery

Cell-penetrating peptides (CPPs) including TAT peptide (TATp) have been successfully used for intracellular delivery of a broad variety of cargos including various nanoparticulate pharmaceutical carriers (liposomes, micelles, nanoparticles). Here, we will consider the main results in this area, with a special emphasis on TATp-mediated delivery of liposomes and DNA. We will also address the development of "smart" stimuli-sensitive nanocarriers, where cell-penetrating function can be activated by the decreased pH only inside the biological target minimizing thus the interaction of drug-loaded nanocarriers with nontarget cells.

Preparation of polyethyleneimine incorporated poly(D,L-lactide-co-glycolide) nanoparticles by spontaneous emulsion diffusion method for small interfering RNA delivery

Gene therapy based on small interfering RNA (siRNA) has emerged as an exciting new therapeutic approach. However, insufficient cellular uptake and poor stability have limited its usefulness. Polyethyleneimine (PEI) has been extensively studied as a vector for nucleic acids and incorporation of PEI into poly(d,l-lactide-co-glycolide) (PLGA) particles has been shown to be useful in the development of gene delivery. PEI was incorporated into the PLGA particles by spontaneous modified emulsification diffusion method. Incorporation of PEI into PLGA particles with the PLGA to PEI weight ratio 29:1 was found to produce spherical and positively charged nanoparticles where type of polymer, type and concentration of surfactant could affect their physical properties. Particle size of around 100nm was obtained when 5% (m/v) PVA was used as a stabiliser. PLGA-PEI nanoparticles were able to completely bind siRNA at N/P ratio 20:1 and to provide protection for siRNA against nuclease degradation. In vitro cell culture studies subsequently revealed that PLGA-PEI nanoparticles with adsorbed siRNA could efficiently silence the targeted gene in mammalian cells, better than PEI alone, with acceptable cell viability. PLGA-PEI nanoparticles have been found to be superior to its cationising parent compound; PEI polymer.

Effect of cell-penetrating peptides on the nasal absorption of insulin

The goal of this study was to evaluate whether cell-penetrating peptides (CPPs) affect the nasal absorption of insulin. L- or D-forms of penetratin, or the L- or D-forms of octaarginine (L- or D-R8), was used as first time for nasal insulin delivery. Furthermore, the concentration of lactate dehydrogenase (LDH) in nasal lavage fluid was determined and a histopathological study of nasal respiratory epithelium was conducted. CPPs dramatically increased nasal insulin absorption, and it was more pronounced for L- and D-penetratin than L- or D-R8. L-penetratin was the most effective promoter of insulin absorption compared with others CPPs. A dose-dependent relationship of L-penetratin and insulin bioavailability was statically significant. The pharmacological availability and bioavailability of nasally administered insulin was up to 76.7% and 50.7% relative to the subcutaneous route, respectively. In contrast, increasing the D-penetratin concentration decreased the efficiency of nasal insulin absorption. There was no significant difference in the release of LDH in nasal lavage fluid and the integrity of nasal respiratory epithelium when L-penetratin was present. In conclusion, these data demonstrate that L-penetratin markedly increased the permeability of insulin across the nasal membrane without causing detectable damage to the integrity of cells in the nasal respiratory mucosa.

Selective gene transfer to endometrial cancer cells by a polymer against matrix metalloproteinase 2 (MMP-2)

A novel cancer-cell-specific gene delivery vector with high transfection efficiency was designed and tested with an in vitro coculture consisting of the human endometrial adenocarcinoma cell line, HEC-1A cells, and normal endometrial stromal cells. For the cancer-cell targeting, polyethylenimine (PEI), a cationic polymer that can be easily combined with anionic DNA to form a particulate complex, polyplex, being capable of transferring a gene into a variety of cells, was covalently conjugated with antibodies against matrix metalloproteinase 2 (MMP-2), a typical surface-marker protein on cancer cells known for its close correlation with angiogenesis and invasion in many types of cancer, using the heterofunctional cross-linker, n-succinimidyl 3-(2-pyridyldithio)-propionamide. Biophysical properties and transfection efficiencies of anti-MMP-2-conjugated PEI were analyzed by means of dynamic light scattering, laser Doppler anemometry, and flow cytometry. Our results reveal that (1) the PEI-anti-MMP-2 antibody conjugate maintains physical parameters, including sizes and surface charges, which appear to be favorable for gene transfer and (2) when the pEGFP-N3 plasmid complexes of the PEI-anti-MMP-2 antibody conjugate are applied to the coculture consisting of HEC-1A cells and human stromal cells, a high level of green fluorescent protein expression occurs in HEC-1A cells over stromal cells, suggesting a specific gene transfer targeting cancer cells. Therefore, targeting invading cancer cells with the PEI-anti-MMP-2 antibody conjugate could be promising in endometrial cancer treatment, and this gene delivery system deserves further optimization in the context of targeted therapeutic gene delivery.

Pulmonary applications and toxicity of engineered nanoparticles

Because of their unique physicochemical properties, engineered nanoparticles have the potential to significantly impact respiratory research and medicine by means of improving imaging capability and drug delivery, among other applications. These same properties, however, present potential safety concerns, and there is accumulating evidence to suggest that nanoparticles may exert adverse effects on pulmonary structure and function. The respiratory system is susceptible to injury resulting from inhalation of gases, aerosols, and particles, and also from systemic delivery of drugs, chemicals, and other compounds to the lungs via direct cardiac output to the pulmonary arteries. As such, it is a prime target for the possible toxic effects of engineered nanoparticles. The purpose of this article is to provide an overview of the potential usefulness of nanoparticles and nanotechnology in respiratory research and medicine and to highlight important issues and recent data pertaining to nanoparticle-related pulmonary toxicity.

Inhalable siRNA: potential as a therapeutic agent in the lungs

RNA interference (RNAi) is gaining increasing popularity both as a molecular biology tool and as a potential therapeutic agent. RNAi is a naturally occurring gene regulatory mechanism, which has a number of advantages over other gene/antisense therapies including specificity of inhibition, potency, the small size of the molecules and the diminished risk of toxic effects, e.g., immune responses. Targeted, local delivery of RNAi to the lungs via inhalation offers a unique opportunity to treat a range of previously untreatable or poorly controlled respiratory conditions. In this timely review we look at the potential applications of RNAi in the lungs for the treatment of a range of diseases including inflammatory and immune conditions, cystic fibrosis, infectious disease and cancer. In 2006 Alnylam initiated the first phase 1 clinical study of an inhaled siRNA for the treatment of respiratory syncytial virus. If its potential as a therapeutic is to be realized, then safe and efficient means of targeted delivery of small interfering RNA (siRNA) to the lungs must be developed. Therefore in this review we also present the latest developments in siRNA delivery to airway cells in vitro and the work to date on in vivo delivery of siRNA to the lungs for the treatment of a range of diseases.

Bioconjugation of oligonucleotides for treating liver fibrosis

Liver fibrosis results from chronic liver injury due to hepatitis B and C, excessive alcohol ingestion, and metal ion overload. Fibrosis culminates in cirrhosis and results in liver failure. Therefore, a potent antifibrotic therapy is urgently needed to reverse scarring and eliminate progression to cirrhosis. Although activated hepatic stellate cells (HSCs) remain the principle cell type responsible for liver fibrosis, perivascular fibroblasts of portal and central veins as well as periductular fibroblasts are other sources of fibrogenic cells. This review will critically discuss various treatment strategies for liver fibrosis, including prevention of liver injury, reduction of inflammation, inhibition of HSC activation, degradation of scar matrix, and inhibition of aberrant collagen synthesis. Oligonucleotides (ODNs) are short, single-stranded nucleic acids, which disrupt expression of target protein by binding to complementary mRNA or forming triplex with genomic DNA. Triplex forming oligonucleotides (TFOs) provide an attractive strategy for treating liver fibrosis. A series of TFOs have been developed for inhibiting the transcription of alpha1(I) collagen gene, which opens a new area for antifibrotic drugs. There will be in-depth discussion on the use of TFOs and how different bioconjugation strategies can be utilized for their site-specific delivery to HSCs or hepatocytes for enhanced antifibrotic activities. Various insights developed in individual strategy and the need for multipronged approaches will also be discussed.

Tat peptide-mediated intracellular delivery of pharmaceutical nanocarriers

Cell-penetrating peptides (CPPs) including TAT peptide (TATp) have been successfully used for intracellular delivery of a broad variety of cargoes including various nanoparticulate pharmaceutical carriers (liposomes, micelles, nanoparticles). Here, we will consider the main results in this area, with a special emphasis on TATp-mediated delivery of liposomes and DNA. We will also address the development of "smart" stimuli-sensitive nanocarriers, where cell-penetrating function can be activated by the decreased pH only inside the biological target minimizing thus the interaction of drug-loaded nanocarriers with non-target cells.

Characterization of PLL-g-PEG-DNA nanoparticles for the delivery of therapeutic DNA

Local and controlled DNA release is a critical issue in current gene therapy. As viral gene delivery systems are associated with severe security problems, nonviral gene delivery vehicles were developed. Here, DNA-nanoparticles using grafted copolymers of PLL and PEG to increase their biocompatibility and stealth properties were systematically studied. Ten different PLL-based polymers with no, low, and high PEG grafting and PEG molecular weights as well as different PLL backbone lengths were complexed with plasmids containing 3200 to 10,100 base pairs. Stable complexes were formed and selected for cytotoxicity and transfection efficiency. Predominantly, PLL-g-PEG-DNA nanoparticles grafted with 4 or 5% PEG moieties of 5 kDa transfected 40% COS-7 cells without reduction of cell viability when formed at N/P ratios between 0.1 and 12.5. The molecular weight of PLL did not significantly affect transfection efficiency or cytotoxicity indicating that a specific cationic charge-density-to-PEG-ratio is important for efficient transfection and low cytotoxicity. The PLL-g-PEG-DNA nanoparticles were spherical with a diameter of approximately 100 nm and did not aggregate over 2 weeks. Moreover, they protected included plasmid DNA against serum components and DNase I digestion. Therefore, such storage stable and versatile PLL-g-PEG-DNA nanoparticles might be useful to deliver differently sized therapeutic DNA for in vivo applications.

Poly(ethylene glycol)-block-polyethylenimine copolymers as carriers for gene delivery: Effects of PEG molecular weight and PEGylation degree

An ideal gene carrier is required both in safety and efficiency for transfection. Polyethylenimine (PEI), a well-studied cationic polymer, has been proved with high transfection efficiency, but is reported as toxicity in many cell lines. In this study, PEI was coupled with polyethylene glycol (PEG) to reduce its cytotoxicity. PEG-PEI copolymers were synthesized with isoporon diisocyanate (IPDI) in two steps. A set of PEG-PEI with different PEG molecular weights (MWs) and amounts of PEG were synthesized. The molecular structure of the resulting copolymers was evaluated by nuclear magnetic resonance spectroscopy ((1)H NMR), infrared spectroscopy (IR), and gel permeation chromatography (GPC), all of which had successfully verified formation of the copolymers. The particle size and zeta potential of polymer/DNA complexes were measured, and their cytotoxicity and transfection efficiency in Hela cells were evaluated. We found that the copolymer block structure significantly influenced not only the physicochemical properties of complexes, but also their cytotoxicity and transfection efficiency. PEG (5 kDa) significantly reduced the diameter of the spherical complexes. The zeta potential of complexes was reduced with increasing amount of PEG grafting. Cytotoxicity was dependent not on PEG MW but on the amount of PEG grafting. Copolymer PEG-PEI (2-25-1) with 1.89 PEG (2 kDa) was proved to be more efficient for in vitro gene transfer. In conclusion, PEG MW and the degree of PEGylation were found to significantly influence the biological activity of PEG-PEI/DNA complexes. These results provide new sights into the studies using block copolymer as gene delivery systems.

Polymers and nanoparticles: Intelligent tools for intracellular targeting?

In recent years, a new generation of drugs has entered the pharmaceutical market. Some are more potent, but some are also more toxic and thus, therapeutical efficacy may be hindered, and severe side effects may be observed, unless they are delivered to their assigned place of effect. Those targets are not only certain cell types, moreover, in cancer therapy for example, some drugs even have to be targeted to a specific cell organelle. Those targets in eukaryotic cells include among others endo- and lysosomes, mitochondria, the so-called power plants of the cells, and the biggest compartment with almost all the genetic information, the nucleus. In this review, we describe how the drugs can be directed to specific subcellular organelles and focus especially on synthetic polymers and nanoparticles as their carriers. Furthermore, we portray the progress that has been accomplished in recent years in the field of designing the carriers for efficient delivery into these target structures. Yet, we do not fail to mention the obstacles that still exist and are preventing polymeric and nanoparticular drug carrier systems from their broad application in humans.

Bioreversibly crosslinked polyplexes of PEI and high molecular weight PEG show extended circulation times in vivo

Copolymers consisting of branched PEI 25 kDa grafted with high molecular weight PEG at a low degree of substitution were successfully synthesized using a simple two-step procedure. The resulting AB-type and ABA-type copolymers were tested for cytotoxicity and DNA condensation and complexation properties. Their polyplexes with plasmid DNA were characterized in terms of DNA size and surface charge, transfection efficiency and blood compatibility. Pharmacokinetic profiles of the complexes containing (32)P-labeled plasmid were assessed before and after surface crosslinking. A set of four copolymers containing one or two PEG 20 kDa or PEG 30 kDa chains was obtained. The cytotoxicity of PEI was strongly reduced after copolymerization. The copolymer polyplexes showed hydrodynamic diameters of less than 200 nm, comparable to PEI 25. Similarly, no reduction in DNA condensation and complexation properties was found. In fact, PEI-PEG(30 k) copolymers exhibited better condensation and complexation properties than PEI 25. The transfection efficiency of copolymer polyplexes was increased 10-fold compared to PEI 25 control and the hemolytic activity was markedly reduced. After intravenous injection into mice, plasmids complexed to PEI-PEG(30 k) copolymers resulted in significantly increased circulation times. After stabilizing the polyplexes with a redox sensitive, biodegradable crosslinker, blood levels of plasmid could be further increased up to 125% compared to PEI. These results demonstrate that polyplexes prepared using a combined strategy of surface crosslinking and PEGylation seem to provide promising properties as stable, long circulating vectors.

Enhanced transfection of tumor cells in vivo using "Smart" pH-sensitive TAT-modified pegylated liposomes

Liposomes have been prepared loaded with DNA (plasmid encoding for the green fluorescent protein, GFP) and additionally modified with TATp and PEG, with PEG being attached to the liposome surface via both pH-sensitive hydrazone and non-pH-sensitive bonds. The pGFP-loaded liposomal preparations have been administered intratumorarly in tumor-bearing mice and the efficacy of tumor cell transfection was followed after 72 h. The administration of pGFP-TATp-liposomes with non-pH-sensitive PEG coating has resulted in only minimal transfection of tumor cells because of steric hindrances for the liposome-to-cell interaction created by the PEG coat, which shielded the surface-attached TATp. At the same time, the administration of pGFP-TATp-liposomes with the low pH-detachable PEG resulted in at least three times more efficient transfection since the removal of PEG under the action of the decreased intratumoral pH leads to the exposure of the liposome-attached TATp residues, enhanced penetration of the liposomes inside tumor cells and more effective intracellular delivery of the pGFP. This result can be considered as an important step in the development of tumor-specific stimuli-sensitive drug and gene delivery systems.

Nanotechnology in the diagnosis and management of heart, lung and blood diseases

Heart, lung and blood diseases exert an enormous toll, accounting for almost half of the deaths in the USA each year. In addition to the morbidity and mortality resulting from these diseases, there is also a high economic burden, estimated at 560 billion US dollars for 2006. Nanotechnology offers a broad range of opportunities to improve diagnosis and therapy for cardiovascular, pulmonary and hematopoietic diseases, thereby decreasing these burdens. This review will focus on four areas of particular promise for the application of nanotechnology: imaging, diagnostics and biosensors, drug delivery and therapy, and tissue engineering and repair. The goal is to summarize the current state of science and technology in these areas and to look at future directions that the field is likely to move in to enhance the diagnosis and treatment of heart, lung and blood diseases.

Biodegradable nanoparticles for cytosolic delivery of therapeutics

Many therapeutics require efficient cytosolic delivery either because the receptors for those drugs are located in the cytosol or their site of action is an intracellular organelle that requires transport through the cytosolic compartment. To achieve efficient cytosolic delivery of therapeutics, different nanomaterials have been developed that consider the diverse physicochemical nature of therapeutics (macromolecule to small molecule; water soluble to water insoluble) and various membrane associated and intracellular barriers that these systems need to overcome to efficiently deliver and retain therapeutics in the cytoplasmic compartment. Our interest is in investigating PLGA and PLA-based nanoparticles for intracellular delivery of drugs and genes. The present review discusses the various aspects of our studies and emphasizes the need for understanding of the molecular mechanisms of intracellular trafficking of nanoparticles in order to develop an efficient cytosolic delivery system.

Design of fine particles for pulmonary drug delivery

Particle design for inhalation is characterized by advances in particle processing methods and the utilization of new excipients. Processing methods such as spray drying allow control over critical particle design features, such as particle size and distribution, surface energy, surface rugosity, particle density, surface area, porosity and microviscosity. Control of these features has enabled new classes of therapeutics to be delivered by inhalation. These include therapeutics that have a narrow therapeutic index, require a high delivered dose, and/or elicit their action systemically. Engineered particles are also being utilized for immune modulation, with exciting advances being made in the delivery of antibodies and inhaled vaccines. Continued advances are expected to result in 'smart' therapeutics capable of active targeting and intracellular trafficking.

Cell Penetrating Peptides: Intracellular Pathways and Pharmaceutical Perspectives

Cell penetrating peptides, generally categorized as amphipathic or cationic depending on their sequence, are increasingly drawing attention as a non-invasive delivery technology for macromolecules. Delivery of a diverse set of cargo in terms of size and nature ranging from small molecules to particulate cargo has been attempted using different types of cell penetrating peptides (CPPs) in vitro and in vivo. However, the internalization mechanism of CPPs is an unresolved issue to date, with dramatic changes in view regarding the involvement of endocytosis as a pathway of internalization. A key reason for the lack of consensus on the mechanism can be attributed to the methodology in deciphering the internalization mechanism. In this review, we highlight some of the methodology concerns, focus more on the internalization pathway and also provide a novel perspective about the intracellular processing of CPPs, which is a crucial aspect to consider when selecting a cell penetrating peptide as a drug delivery system. In addition, recent applications of cell penetrating peptides for the delivery of small molecules, peptides, proteins, oligonucleotides, nanoparticles and liposomes have been reviewed.

Crosslinked nanocarriers based upon poly(ethylene imine) for systemic plasmid delivery: In vitro characterization and in vivo studies in mice

Crosslinked poly(ethylene imine) (PEI) polyplexes for intracellular DNA release were generated using a low molecular weight crosslinking reagent, Dithiobis(succinimidyl propionate) (DSP). Disulfide bonds of the crosslinked polyplexes were susceptible to intracellular redox conditions and DNA release was observed using an ethidium bromide exclusion assay and dynamic light scattering. Transfection experiments were performed to elucidate the effect of extra- and intracellular redox conditions. Pharmacokinetics and organ accumulation of uncrosslinked and crosslinked polyplexes were compared and gene expression patterns were measured in mice 24 h after intravenous injection. Crosslinked PEI and plasmid DNA formed stable polyplexes in a size range of 100-300 nm, with zeta potentials between +16.4 and +26.1 mV. DNA release occurred after cleavage of the disulfide bonds. Cell culture experiments under reducing conditions as well as with glutathione loaded cells confirmed the proposed intracellular activation. A significant influence of the intracellular glutathione status on the transfection efficiency was observed. Pharmacokinetic profiles of crosslinked PEI/DNA polyplexes in mice after intravenous administration showed higher blood levels for crosslinked polyplexes. These polyplexes accumulated mainly in the liver and the lungs. In vivo transfection data revealed significantly reduced (unwanted) lung transfection while liver transfection predominated. These studies suggest that crosslinked polyplexes are more stable in circulation and retain their transfection efficiency after intravenous administration.

Poly(ethylene glycol)-modified nanocarriers for tumor-targeted and intracellular delivery

The success of anti-cancer therapies largely depends on the ability of the therapeutics to reach their designated cellular and intracellular target sites, while minimizing accumulation and action at non-specific sites. Surface modification of nanoparticulate carriers with poly(ethylene glycol) (PEG)/poly(ethylene oxide) (PEO) has emerged as a strategy to enhance solubility of hydrophobic drugs, prolong circulation time, minimize non-specific uptake, and allow for specific tumor-targeting through the enhanced permeability and retention effect. Furthermore, PEG/PEO modification has emerged as a platform for incorporation of active targeting ligands, thereby providing the drug and gene carriers with specific tumor-targeting properties through a flexible tether. This review focuses on the recent developments surrounding such PEG/PEO-surface modification of polymeric nanocarriers to promote tumor-targeting capabilities, thereby enhancing efficacy of anti-cancer therapeutic strategies.

'Click' Bioconjugation of a Well-Defined Synthetic Polymer and a Protein Transduction Domain

The copper-catalyzed 1,3-dipolar ‘click’ cycloaddition of azides and alkynes was studied to link a model synthetic polymer to a sequence-defined protein transduction domain (PTD). The bromine chain-ends of a well-defined polystyrene (PS) sample synthesized by atom transfer radical polymerization (Mn 2200 g mol–1, Mw/Mn 1.21) were first transformed into azide functions by substitution with sodium azide, and subsequently reacted with an alkyne-functionalized PTD (i.e., the oligopeptide sequence GGYGRKKRRQRRRG, also known as the TAT peptide). The click bioconjugation proceeded successfully at room temperature, thus affording the targeted PS-b-GGYGRKKRRQRRRG bioconjugate in high yields. However, a slight molar excess of polystyrene was required for optimal coupling.

Stabilized Nanocarriers for Plasmids Based Upon Cross-linked Poly(ethylene imine)

Stabilized PEI/DNA polyplexes were generated by cross-linking PEI with biodegradable disulfide bonds. The reaction conversion of different PEIs with the amine reactive cross-linker dithiobis(succinimidyl propionate) (DSP) was investigated, and the molecular weight of the reaction products was identified. Light scattering and microelectrophoresis were employed to assess size and zeta potential of the resulting polyplexes. Polyplex morphology and mechanic stability were investigated using atomic force microscopy. Finally, albumin and erythrocyte interactions and stability against polyanions and high ionic strength were checked. Polyplexes of PEI and DNA were prepared by two different formulation methods, either using pre-cross-linked polymers or by cross-linking polyplexes after complexation. Only the latter method yielded small (100-300 nm) polyplexes with a positive zeta potential when HMW PEI was used, whereas cross-linked LMW PEI resulted in polyplexes with increased size (>1000 nm) and zeta potentials down to -20 mV. In addition, only cross-linking after polyplex formation was able to enhance resistance against polyanion exchange and high ionic strength. AFM images revealed no changes in the morphology of cross-linked HWM PEI polyplexes, and indentation force measurements using AFM significantly increased mechanical stability of cross-linked HMW PEI polyplexes. These polyplexes also displayed significantly reduced interactions with major blood components like albumin and erythrocytes. The resulting biocompatible particles offer a means of combining enhanced polyplex stability with redox-triggered activation for in vivo application.