A novel peptide, THALWHT, for the targeting of human airway epithelia

Adeno-Associated Virus Engineering and Load Strategy for Tropism Modification, Immune Evasion and Enhanced Transgene Expression

Gene therapy aims to add, replace or turn off genes to help treat disease. To date, the US Food and Drug Administration (FDA) has approved 14 gene therapy products. With the increasing interest in gene therapy, feasible gene delivery vectors are necessary for inserting new genes into cells. There are different kinds of gene delivery vectors including viral vectors like lentivirus, adenovirus, retrovirus, adeno-associated virus et al, and non-viral vectors like naked DNA, lipid vectors, polymer nanoparticles, exosomes et al, with viruses being the most commonly used. Among them, the most concerned vector is adeno-associated virus (AAV) because of its safety, natural ability to efficiently deliver gene into cells and sustained transgene expression in multiple tissues. In addition, the AAV genome can be engineered to generate recombinant AAV (rAAV) containing transgene sequences of interest and has been proven to be a safe gene vector. Recently, rAAV vectors have been approved for the treatment of various rare diseases. Despite these approvals, some major limitations of rAAV remain, namely nonspecific tissue targeting and host immune response. Additional problems include neutralizing antibodies that block transgene delivery, a finite transgene packaging capacity, high viral titer used for per dose and high cost. To deal with these challenges, several techniques have been developed. Based on differences in engineering methods, this review proposes three strategies: gene engineering-based capsid modification (capsid modification), capsid surface tethering through chemical conjugation (surface tethering), and other formulations loaded with AAV (virus load). In addition, the major advantages and limitations encountered in rAAV engineering strategies are summarized.

Advanced approaches to overcome biological barriers in respiratory and systemic routes of administration for enhanced nucleic acid delivery to the lung

INTRODUCTION

Numerous delivery strategies, primarily novel nucleic acid delivery carriers, have been developed and explored to enable therapeutically relevant lung gene therapy. However, its clinical translation is yet to be achieved despite over 30 years of efforts, which is attributed to the inability to overcome a series of biological barriers that hamper efficient nucleic acid transfer to target cells in the lung.

AREAS COVERED

This review is initiated with the fundamentals of nucleic acid therapy and a brief overview of previous and ongoing efforts on clinical translation of lung gene therapy. We then walk through the nature of biological barriers encountered by nucleic acid carriers administered via respiratory and/or systemic routes. Finally, we introduce advanced strategies developed to overcome those barriers to achieve therapeutically relevant nucleic acid delivery efficiency in the lung.

EXPERT OPINION

We are now stepping close to the clinical translation of lung gene therapy, thanks to the discovery of novel delivery strategies that overcome biological barriers via comprehensive preclinical studies. However, preclinical findings should be cautiously interpreted and validated to ultimately realize meaningful therapeutic outcomes with newly developed delivery strategies in humans. In particular, individual strategies should be selected, tailored, and implemented in a manner directly relevant to specific therapeutic applications and goals.

Novel Lung Tropic Adeno-Associated Virus Capsids for Therapeutic Gene Delivery

Efforts to identify mutations that underlie inherited genetic diseases combined with strides in the development of gene therapy vectors over the last three decades have culminated in the approval of several adeno-associated virus (AAV)-based gene therapies. Genetic diseases that manifest in the lung such as cystic fibrosis (CF) and surfactant deficiencies, however, have so far proven to be elusive targets. Early clinical trials in CF using AAV serotype 2 (AAV2) achieved safety, but not efficacy endpoints; however, importantly, these studies provided critical information on barriers that need to be surmounted to translate AAV lung gene therapy toward clinical success. Bolstered with an improved understanding of AAV biology and more clinically relevant lung models, next-generation molecular biology and bioinformatics approaches have given rise to novel AAV capsid variants that offer improvements in transduction efficiency, immunological profile, and the ability to circumvent physical barriers in the lung such as mucus. This review discusses the principal limiting barriers to clinical success in lung gene therapy and focuses on novel engineered AAV capsid variants that have been developed to overcome those challenges.

Phage nanofibers in nanomedicine: Biopanning for early diagnosis, targeted therapy, and proteomics analysis

Display of a peptide or protein of interest on the filamentous phage (also known as bacteriophage), a biological nanofiber, has opened a new route for disease diagnosis and therapy as well as proteomics. Earlier phage display was widely used in protein-protein or antigen-antibody studies. In recent years, its application in nanomedicine is becoming increasingly popular and encouraging. We aim to review the current status in this research direction. For better understanding, we start with a brief introduction of basic biology and structure of the filamentous phage. We present the principle of phage display and library construction method on the basis of the filamentous phage. We summarize the use of the phage displayed peptide library for selecting peptides with high affinity against cells or tissues. We then review the recent applications of the selected cell or tissue targeting peptides in developing new targeting probes and therapeutics to advance the early diagnosis and targeted therapy of different diseases in nanomedicine. We also discuss the integration of antibody phage display and modern proteomics in discovering new biomarkers or target proteins for disease diagnosis and therapy. Finally, we propose an outlook for further advancing the potential impact of phage display on future nanomedicine. This article is categorized under: Biology-Inspired Nanomaterials > Protein and Virus-Based Structures.

Towards Safe Nanoparticle Technologies for Nucleic Acid Therapeutics

Nucleic acid therapeutics (or gene therapy) has to date failed to deliver on promise but rapid improvements in the understanding and use of delivery technologies should reverse this situation. In this review of work performed in and in collaboration with the Imperial College Genetic Therapies Centre, progress towards safe nanoparticles for efficient delivery of functional nucleic acids in vivo is described. The intention is to demonstrate the fruits of a journey from the results of initial studies in animal models of disease that suggested that so much should be possible so quickly, to the realization that new technologies are rarely successful so quickly, through to developments in the present day that appear to be approaching the preclinical/clinical threshold with realism but measured confidence. New chemistry is central to the design and formulation of safe nanotechnologies. Chemistry should have a central role to play in ensuring that nucleic acid therapeutics truly live up to their potential for therapy and cure, none more so than in the derivation of newer and better therapies for cancers.

Nanomedicine therapeutics and diagnostics are the goal

Understanding and exploiting molecular mechanisms in biology is central to chemical biology. In 20 years, chemical biology research has advanced from simple mechanistic studies using isolated biological macromolecules to molecular-level and nanomolecular-level mechanistic studies involving whole organisms. This review documents the best of my personal and collaborative academic research work that has made use of a solid organic chemistry and chemical biology approach toward nanomedicine, in which my focus has been on the design, creation and use of synthetic, self-assembly lipid-based nanoparticle technologies for the functional delivery of active pharmaceutical ingredients to target cells in vivo. This research is now leading to precision therapeutics approaches (PTAs) for the treatment of diseases that may define the future of nanomedicine.

Barriers to inhaled gene therapy of obstructive lung diseases: A review

Knowledge of genetic origins of obstructive lung diseases has made inhaled gene therapy an attractive alternative to the current standards of care that are limited to managing disease symptoms. Initial lung gene therapy clinical trials occurred in the early 1990s following the discovery of the genetic defect responsible for cystic fibrosis (CF), a monogenic disorder. However, despite over two decades of intensive effort, gene therapy has yet to help patients with CF or any other obstructive lung disease. The slow progress is due in part to poor understanding of the biological barriers to inhaled gene therapy. Encouragingly, clinical trials have shown that inhaled gene therapy with various viral vectors and non-viral gene vectors is well tolerated by patients, and continued research has provided valuable lessons and resources that may lead to future success of this therapeutic strategy. In this review, we first introduce representative obstructive lung diseases and examine limitations of currently available therapeutic options. We then review key components for successful execution of inhaled gene therapy, including gene delivery systems, primary physiological barriers and strategies to overcome them, and advances in preclinical disease models with which the most promising systems may be identified for human clinical trials.

PEGylation improves the receptor-mediated transfection efficiency of peptide-targeted, self-assembling, anionic nanocomplexes

Non-viral vector formulations comprise typically complexes of nucleic acids with cationic polymers or lipids. However, for in vivo applications cationic formulations suffer from problems of poor tissue penetration, non-specific binding to cells, interaction with serum proteins and cell adhesion molecules and can lead to inflammatory responses. Anionic formulations may provide a solution to these problems but they have not been developed to the same extent as cationic formulations due to difficulties of nucleic acid packaging and poor transfection efficiency. We have developed novel PEGylated, anionic nanocomplexes containing cationic targeting peptides that act as a bridge between PEGylated anionic liposomes and plasmid DNA. At optimized ratios, the components self-assemble into anionic nanocomplexes with a high packaging efficiency of plasmid DNA. Anionic PEGylated nanocomplexes were resistant to aggregation in serum and transfected cells with a far higher degree of receptor-targeted specificity than their homologous non-PEGylated anionic and cationic counterparts. Gadolinium-labeled, anionic nanoparticles, administered directly to the brain by convection-enhanced delivery displayed improved tissue penetration and dispersal as well as more widespread cellular transfection than cationic formulations. Anionic PEGylated nanocomplexes have widespread potential for in vivo gene therapy due to their targeted transfection efficiency and ability to penetrate tissues.

Oral delivery of macromolecules: rationale underpinning Gastrointestinal Permeation Enhancement Technology (GIPET)

Oral delivery of macromolecular drugs, particularly peptides and proteins, is the focus of many academic and industrial laboratories. Armed with an increased understanding of the structure and regulation of intestinal epithelial junctional complexes of the paracellular barrier, the development of permeation enhancement technology initially focused on the specific and reversible opening of tight junctions in order to enable oral delivery. Despite intense research, none of these specific tight junction-opening technologies has yet been approved in an oral drug product, likely because of poor efficacy. Less specific enhancer technologies with a long history of safe use in man have additional surfactant-like effects on the transcellular pathway that lead to improved efficacy. These are likely to be the first to market for selected poorly permeable peptides. This review presents a summary of some approaches taken to intestinal permeation enhancement and explores in detail the oral delivery system developed by Merrion Pharmaceuticals, Gastrointestinal Permeation Enhancement Technology (GIPET).

Current Status of Gene Therapy for Cystic Fibrosis Pulmonary Disease

Cystic fibrosis (CF) is a common lethal genetic disorder that affects all ethnic populations; however, it is most prevalent in Caucasians. Intensive basic research over the last 20 years has resulted in a wealth of information regarding the CF gene, its protein product and the mutational basis of disease. This increased understanding has lead to the development of gene therapy for the treatment of CF pulmonary disease. Delivery of the CF gene to the airway requires direct in vivo transfer using vectors encoding for normal CF transmembrane regulator (CFTR) protein. Several vectors are currently available for CF gene transfer and include both viral (adenoviruses, adeno-associated viruses) and non-viral (liposomal) systems. Initial clinical trials with each of these vectors have demonstrated that gene transfer to the CF airway is possible. The efficiency of transfer and duration of expression, however, have been limited. The effects of gene transfer on correction of the basic ion transport defects have also been highly variable and inconsistent, irrespective of the vector. Currently, the risk of severe immunological reactions is the primary factor limiting the clinical advancement of gene therapy. Both the adenoviral and liposomal vectors are associated with significant acute inflammatory reactions. The adenoviruses and adeno-associated viruses also elicit humoral immune responses that significantly reduce the efficiency of transgene expression and increase the risk of readministration. Several strategies are under investigation to improve the efficiency of gene transfer to the CF airway. These include overcoming local barriers in the lung, circumventing the immune response and improving vector internalization and/or uptake. Application of gene transfer in the child and possibly the fetus are also potential future clinical applications of gene therapy. However, despite considerable research with gene therapy, there is little evidence to suggest that a well tolerated and effective gene transfer method is imminent and aggressive use of conventional pharmacological therapies currently offer the greatest promise in the treatment of patients with CF.

Enhanced pulmonary absorption of a macromolecule through coupling to a sequence-specific phage display-derived peptide

With the aim of identifying a peptide sequence that promotes pulmonary epithelial transport of macromolecule cargo we used a stringent peptide-phage display library screening protocol against rat lung alveolar epithelial primary cell cultures. We identified a peptide-phage clone (LTP-1) displaying the disulphide-constrained 7-mer peptide sequence, C-TSGTHPR-C, that showed significant pulmonary epithelial translocation across highly restrictive polarised cell monolayers. Cell biological data supported a differential alveolar epithelial cell interaction of the LTP-1 peptide-phage clone and the corresponding free synthetic LTP-1 peptide. Delivering select phage-clones to the intact pulmonary barrier of an isolated perfused rat lung (IPRL) resulted in 8.7% of lung deposited LTP-1 peptide-phage clone transported from the IPRL airways to the vasculature compared (p<0.05) to the cumulative transport of less than 0.004% for control phage-clone groups. To characterise phage-independent activity of LTP-1 peptide, the LTP-1 peptide was conjugated to a 53kDa anionic PAMAM dendrimer. Compared to respective peptide-dendrimer control conjugates, the LTP-1-PAMAM conjugate displayed a two-fold (bioavailability up to 31%) greater extent of absorption in the IPRL. The LTP-1 peptide-mediated enhancement of transport, when LTP-1 was either attached to the phage clone or conjugated to dendrimer, was sequence-dependent and could be competitively inhibited by co-instillation of excess synthetic free LTP-1 peptide. The specific nature of the target receptor or mechanism involved in LTP-1 lung transport remains unclear although the enhanced transport is enabled through a mechanism that is non-disruptive with respect to the pulmonary transport of hydrophilic permeability probes. This study shows proof-of principle that array technologies can be effectively exploited to identify peptides mediating enhanced transmucosal delivery of macromolecule therapeutics across an intact organ.

A FQHPSFI peptide selectively binds to LPS-activated alveolar macrophages and inhibits LPS-induced MIP-2 production

OBJECTIVE

The goal of this study was to identify peptides selectively binding to lipopolysaccharide (LPS)-activated alveolar macrophages (AMs) and to characterize their effects on the production of LPS-induced cytokines.

METHODS

A phage display library was sequentially screened by binding phages to unmanipulated AMs and then to LPS-activated AMs. Individual phage clones were identified by cell-based ELISA. Positive phage clones were characterized by DNA sequencing and bioinformatics analysis. Binding specificity of the selected phage to LPS-activated AMs was tested using immunofluorescent staining. The selected candidate peptide was chemically synthesized to determine whether it could modulate LPS-induced cytokine production in AMs.

RESULTS

Twenty-two out of 40 phage clones selected randomly after four rounds of biopanning bound selectively to LPS-activated AMs, and 12 of them displayed novel peptides. A phage clone displaying FQHPSFI peptide bound effectively to LPS-activated AMs, but not to other cells tested. Furthermore, the synthetic FQHPSFI peptide, but not seven point mutants tested, competitively inhibited the binding of the phage clone to LPS-activated AMs. Importantly, the FQHPSFI peptide significantly inhibited LPS-stimulated microphage inflammatory protein 2 (MIP-2) production in vitro.

CONCLUSIONS

Our data demonstrate that phage display technology is a powerful tool for the identification of bioactive peptides. The identified FQHPSFI peptide may be used for the modulation of LPS-stimulated MIP-2 production in AMs.

Genetic modification of adeno-associated viral vector type 2 capsid enhances gene transfer efficiency in polarized human airway epithelial cells

Cystic fibrosis (CF) is a common genetic disease characterized by defects in the expression of the CF transmembrane conductance regulator (CFTR) gene. Gene therapy offers better hope for the treatment of CF. Adeno-associated viral (AAV) vectors are capable of stable expression with low immunogenicity. Despite their potential in CF gene therapy, gene transfer efficiency by AAV is limited because of pathophysiological barriers in these patients. Although a few AAV serotypes have shown better transduction compared with the AAV2-based vectors, gene transfer efficiency in human airway epithelium has still not reached therapeutic levels. To engineer better AAV vectors for enhanced gene delivery in human airway epithelium, we developed and characterized mutant AAV vectors by genetic capsid modification, modeling the well-characterized AAV2 serotype. We genetically incorporated putative high-affinity peptide ligands to human airway epithelium on the GH loop region of AAV2 capsid protein. Six independent mutant AAV were constructed, containing peptide ligands previously reported to bind with high affinity for known and unknown receptors on human airway epithelial cells. The vectors were tested on nonairway cells and nonpolarized and polarized human airway epithelial cells for enhanced infectivity. One of the mutant vectors, with the peptide sequence THALWHT, not only showed the highest transduction in undifferentiated human airway epithelial cells but also indicated significant transduction in polarized cells. Interestingly, this modified vector was also able to infect cells independently of the heparan sulfate proteoglycan receptor. Incorporation of this ligand on other AAV serotypes, which have shown improved gene transfer efficiency in the human airway epithelium, may enhance the application of AAV vectors in CF gene therapy.

Polyethylenimine-mediated gene delivery to the lung and therapeutic applications

Nonviral gene delivery is now considered a promising alternative to viral vectors. Among nonviral gene delivery agents, polyethylenimine (PEI) has emerged as a potent candidate for gene delivery to the lung. PEI has some advantages over other polycations in that it combines strong DNA compaction capacity with an intrinsic endosomolytic activity. However, intracellular (mainly the nuclear membrane) and extracellular obstacles still hamper its efficiency in vitro and in vivo, depending on the route of administration and the type of PEI. Nuclear delivery has been increased by adding nuclear localization signals. To overcome nonspecific interactions with biological fluids, extracellular matrix components and nontarget cells, strategies have been developed to protect polyplexes from these interactions and to increase target specificity and gene expression. When gene delivery into airway epithelial cells of the conducting airways is necessary, aerosolization of complexes seems to be better suited to guarantee higher transgene expression in the airway epithelial cells with lower toxicity than observed with either intratracheal or intravenous administration. Aerosolization, indeed, is useful to target the alveolar epithelium and pulmonary endothelium. Proof-of-principle that PEI-mediated gene delivery has therapeutic application to some genetic and acquired lung disease is presented, using as genetic material either plasmidic DNA or small-interfering RNA, although optimization of formulation and delivery protocols and limitation of toxicity need further studies.

Recombinant AAV serotype and capsid mutant comparison for pulmonary gene transfer of alpha-1-antitrypsin using invasive and noninvasive delivery

Recombinant adeno-associated viral (rAAV) vectors have been widely used in pulmonary gene therapy research. In this study, we evaluated the transduction and expression efficiencies of several AAV serotypes and AAV2 capsid mutants with specific pulmonary targeting ligands in the mouse lung. The noninvasive intranasal delivery was compared with the traditional intratracheal lung delivery. The rAAV8 was the most efficient serotype at expressing alpha-1-antitrypsin (AAT) in the lung among all the tested serotypes and mutants. A dose of 1 x 10(10) vg of rAAV8-CB-AAT transduced a high percentage of cells in the lung when delivered intratrachealy. The serum and the broncho-alveolar lavage fluid (BALF) levels of human AAT (hAAT) were about 6- and 2.5-fold higher, respectively, than those of rAAV5 group. Among the rAAV2 capsid mutants, the rAAV2 capsid mutants that display a peptide sequence from hAAT ("long serpin") indicated a twofold increase in transgene expression. For most vectors, the serum hAAT levels achieved after intranasal delivery were 1/2 to 1/3 of those with the intratracheal method. Overall, rAAV8 was the most promising vector for the future application in gene therapy of pulmonary diseases such as AAT deficiency-related emphysema.

Neuronal affinity of a C7C loop peptide identified through phage display

Phage display is a promising tool for the screening of peptides with high affinity for specific cells. Here we describe a novel peptide with neuronal affinity isolated from a C7C library. We designed a two-tiered biopanning strategy initially selecting for ganglioside binding and subsequently selecting for binding to PC12 cells. At the completion of biopanning, 54.8% of phage clones bore the identical peptide (Tet.C7C.1). Immunofluorescence confirmed selective binding of this clone to differentiated PC12 cells. Tet.C7C.1 was synthesized and fluorescein conjugated. The synthetic peptide binds neuronal cell lines (SH-SY5Y, NSC-34 and PC12 cells) and tissue (DRG and spinal cord). The C7C structure creates a loop that minimizes the impact of peptide insertion on the confirmation of the recipient protein. Small loop peptides have the ideal characteristics for modification of viral vector capsids without undermining genome packaging. The neuronal binding properties of this peptide may be applied in the development of neurotropic viral vectors.

Identification of an Internalising Peptide in Differentiated Calu-3 Cells by Phage Display Technology; Application to Gene Delivery to the Airways

Differentiated, human submucosal-gland carcinoma, Calu-3 cell monolayers were used as in vitro model for the airway epithelium. Internalised phage were selected from a recombinant pComb8 phage library by repetitive cycles of bio-panning on Calu-3 monolayers, protease K degradation, cell-lysis and amplification. After four selection rounds, sequence analysis of 15 enriched phage colonies revealed two clones of 73 and 27% abundancy, named IB1 and IB2, respectively. The IB2 sequence was eliminated due to a frame shift. IB1-phage internalisation at 4 degrees C was significantly lower (P < 0.05) than at 37 degrees C, suggesting involvement of a receptor-mediated endocytosis pathway. The IB1 peptide was synthesised, biotinylated and complexed to streptavidin. IB1/streptavidin-complexes co-administrated with PEI/DNA-polyplexes, enhanced polyplex transfection efficiency, dose dependently, by 6- and 4-fold in Calu-3 cells. IB1/Alexa488-streptavidin complexes were used for confocal laser-scanning microscopy (CLSM) visualisation and showed basolateral localisation in membrane associated and internalising vesicles. This study demonstrates the potential of phage display technology for identification of internalising peptide-epitopes that can enhance gene delivery efficiency in differentiated airway epithelial cells.

Phage display screening of epithelial cell monolayers treated with EGTA: identification of peptide FDFWITP that modulates tight junction activity

Phage display was used to screen for peptides that modulate the activity of epithelial cell tight junctions. Panning with a phage library that displays random 7-mers was performed using monolayers of human bronchial epithelial cells (16HBE14o(-)) treated with a calcium chelator, ethylene glycol-bis(2-aminoethylether)- N, N, N', N'-tetraacetic acid (EGTA), to increase accessibility to the junctional complex/paracellular space, followed by subtractive panning. A novel peptide, FDFWITP, identified as a potential tight junction modulator, was synthesized in linear and cyclic forms with lysine residues added to improve solubility. The cyclic form of the peptide reduced transepithelial electrical resistance (TER) in a concentration-dependent manner (80% reduction at 100 microM and 95% reduction at 500 microM) and was reversible within 2 h; the linear form only affected TER at the highest concentration. Interestingly, the constrained peptide did not increase permeation of the model small molecule, fluorescein. The highly selective activity of FDFWITP supports the hypothesis that ions and small molecules may be transported paracellularly across tight junctions by separate pathways.

Gene delivery to vascular endothelium using chemical vectors: implications for cardiovascular gene therapy

The vascular endothelium is an attractive target for gene therapy because of its accessibility and its importance in the pathophysiology of a wide range of cardiovascular conditions. In general, viral methods have been shown to be very effective at delivering genes to endothelium. The immunogenicity and pathogenicity associated with viral vectors have led increased efforts to seek alternative means of 'ferrying' therapeutic genes to endothelium or to decrease the short-comings of viral vectors. This paper reviews developments in non-viral technology. In addition, discussion also covers the mechanisms whereby existing chemical vectors deliver DNA to cells. Understanding the pathways of vector internalisation and intracellular traffic is important in developing strategies to improve vector technology. The authors propose that the chemical vector may represent a robust and versatile technology to 'ferry' therapeutic genes to vascular endothelium in order to modify the endothelial dysfunction associated with many cardiovascular diseases.

Targeted polymers for gene delivery

Over the past decade, significant research has been done in the area of polymer-mediated gene delivery. Synthesis of new polymers and modifications to existing polymers has resulted in polyplexes with improved in vitro and in vivo transfection efficiencies. Targeting has been an important aspect of this research, and various strategies for obtaining selective and enhanced gene delivery to the target site have been evaluated. This review covers the different aspects involved in polyplex targeting. Development of targeted polyplexes involves a careful consideration of the target site, the targeting ligand and the physicochemical properties of the polyplex itself. The need to redirect the polyplexes by using the 'shield and target' approach by reducing nonspecific interactions with negatively charged components, while conferring specificity by incorporating targeting ligands, is discussed. Basic chemistry involved in modifying polymers is covered and examples of targeting strategies used for tissue-specific gene delivery are discussed. Targeting is also discussed in the broader context of developing safe and effective polymeric vectors for in vivo gene delivery. Maximum benefit of targeting can be obtained when it is used as part of a multi-functional complex containing elements designed to improve gene delivery and reduce overall toxicity of the polyplex.

Carrier-based strategies for targeting protein and peptide drugs to the lungs

With greater interest in delivery of protein and peptide-based drugs to the lungs for topical and systemic activity, a range of new devices and formulations are being investigated. While a great deal of recent research has focused on the development of novel devices, attention must now be paid to the formulation of these macromolecular drugs. The emphasis in this review will be on targeting of protein/peptide drugs by inhalation using carriers and ligands.

Targeted gene delivery to human airway epithelial cells with synthetic vectors incorporating novel targeting peptides selected by phage display

Human airway epithelial cell targeting peptides were identified by biopanning on 1HAEo-cells, a well characterised epithelial cell line. Bound phage were recovered after three rounds of binding, high stringency washing and elution, leading to the production of an enriched phage peptide population. DNA sequencing of 56 clones revealed 14 unique sequences. Subsequent binding analysis revealed that 13 of these peptides bound 1HAEo-cells with high affinity. Three peptides, SERSMNF, YGLPHKF and PSGAARA were represented at high frequency. Three clearly defined families of peptide were identified on the basis of sequence motifs including (R/K)SM, L(P/Q)HK and PSG(A/T)ARA. Two peptides, LPHKSMP and LQHKSMP contained two motifs. Further detailed sequence analysis by comparison of peptide sequences with the SWISSPROT protein database revealed that some of the peptides closely resembled the cell binding proteins of viral and bacterial pathogens including Herpes Simplex Virus, rotavirus, Mycoplasma pneumoniae and rhinovirus, the latter two being respiratory pathogens, as well as peptide YGLPHKF having similarity to a protein of unknown function from the respiratory pathogen Legionella pneumophila. Peptides were incorporated into gene delivery formulations with the cationic lipid Lipofectin and plasmid DNA and shown to confer a high degree of transfection efficiency and specificity in 1HAEo-cells. Improved transfection efficiency and specificity was also observed in human endothelial cells, fibroblasts and keratinocytes. Therefore, on the basis of clone frequency after biopanning, cell binding affinity, peptide sequence conservation and pathogenic similarity, we have identified 3 novel peptide families and 5 specific peptides that have the potential for gene transfer to respiratory epithelium in vivo as well as providing useful in vitro transfection reagents for primary human cell types of scientific and commercial interest.

Non-viral vectors in cystic fibrosis gene therapy: progress and challenges

Although the viability of cystic fibrosis (CF) gene transfer to airway epithelium has been demonstrated in vitro and in animal models, so far none of the clinical investigations using adenovirus, adeno-associated virus, lentivirus, cationic lipids or polymers has shown a persistent correction of the ion transport defects that occur in CF. Despite disappointing results, these studies have shown that non-viral vectors could represent a viable alternative for gene therapy in CF airway epithelium. The transfer efficiency of non-viral vectors is currently low, however, and thus these systems are not clinically relevant as yet. Before clinical application, several limitations encountered by non-viral delivery systems must be addressed. Recent progress has been made towards overcoming these limitations and towards making non-viral gene therapy a more realistic option for CF.

Selective targeting of cancer cells using synthetic peptides

To establish efficient and reliable therapeutic delivery into cancer cells, a number of delivery agents and concepts have been investigated in the recent years. Among many improvements in targeted and controlled delivery of therapeutics, cell-targeting peptides have emerged as the most valuable non-immunogenic approach to target cancer cells. Peptides can be incorporated into multicomponent gene-delivery complexes for cell-specific targeting. In contrast to larger molecules such as monoclonal antibodies, peptides have an excellent tumor penetration, which make them ideal carriers of therapeutics to the site of primary tumor and the distant metastatic sites. Here we give an update on the progress made during the last two years on the identification and potential of specific synthetic tumor targeting peptides.

Phage-displayed peptides bind to the malarial protein apical membrane antigen-1 and inhibit the merozoite invasion of host erythrocytes

Apical membrane antigen-1 (AMA1) is a transmembrane protein present on the surface of merozoites that is thought to be involved in the process of parasite invasion of host erythrocytes. Although it is the target of a natural immune response that can inhibit invasion, little is known about the molecular mechanisms by which AMA1 facilitates the invasion process. In an attempt to identify peptides that specifically interact with and block the function of AMA1, a random peptide library displayed on the surface of filamentous phage was panned on recombinant AMA1 from Plasmodium falciparum. Three peptides with affinity for AMA1 were isolated, and characterization of their fine binding specificities indicated that they bind to a similar region on the surface of AMA1. One of these peptides was found to be a potent inhibitor of the invasion of P. falciparum merozoites into human erythrocytes. We propose that this peptide blocks interaction between AMA1 and a ligand on the erythrocyte surface that is involved in a critical step in malarial invasion. The identification and characterization of these peptide inhibitors now permit an evaluation of the essential requirements that are necessary for efficient neutralization of merozoite invasion by blocking AMA1 function.

Barriers to and new approaches for gene therapy and gene delivery in cystic fibrosis

Clinical trials of gene therapy for cystic fibrosis suggest that current levels of gene transfer efficiency are probably too low to result in clinical benefit, largely as a result of the barriers faced by gene transfer vectors within the airways. The respiratory epithelium has evolved a complex series of extracellular barriers (mucus, lack of receptors, immune surveillance, etc.) aimed at preventing penetration of lumenally delivered materials, including gene therapy vectors. In addition, once in the cell, further hurdles have to be overcome, including DNA degradation, nuclear import and the ability to maintain long-term transgene expression. Strategies to overcome these barriers will be addressed in this review and include the use of: (i) clinically relevant adjuncts to overcome the extra- and intracellular barriers; (ii) less-conventional delivery routes, such as intravenous or in utero administration; (iii) more efficient non-viral vectors and 'stealth' viruses which can be re-administered; and (iv) new approaches to prolong transgene expression by means of alternative promoters or integrating vectors. These advances have the potential to improve the efficiency of gene delivery to the airway epithelium, thus making gene therapy a more realistic option for cystic fibrosis.

Gene therapy progress and prospects: cystic fibrosis

Since the cloning of the cystic fibrosis gene (CFTR) in 1989, 18 clinical trials have been carried out, including five in the 2 years reviewed here. Most trials demonstrated proof-of-principle for gene transfer to the airway. However, gene transfer efficiency with each of the three gene transfer agents (adenovirus (Ad), adeno-associated virus 2 (AAV2) and cationic liposomes) was low, and most likely insufficient to achieve clinical benefit. Here, we will review the clinical and pre-clinical progress for the last 2 years (2000-2001) and briefly speculate on future prospects for the next 2 in CF gene therapy.

Intranasal gene delivery with a polyethylenimine-PEG conjugate

Polyethylenimines (PEIs) are among the most efficient synthetic DNA carriers. High levels of reporter gene expression can be obtained with these agents on a variety of cells. Nevertheless, the gap between their efficiency and that required for therapeutic approaches is still important. With the aim to improve the in vivo transfection properties of PEIs, we have synthesized a conjugate consisting of the linear polymer of 22 kDa covalently modified with polyethyleneglycol (PEG) residues. The resulting conjugate was able to complex DNA and allowed the preparation of highly concentrated polyplexes, in contrast to non-modified PEIs. Administration by nasal instillation of PEI-PEG/DNA complexes in mice resulted in significant levels of transgene expression. Luciferase activity was greatest 24 h after delivery and decreased thereafter. Our results show that the grafting of PEGs can improve some of the properties of PEIs.

One from column A and two from column B: the benefits of phage display in molecular-recognition studies

Recent uses of phage-displayed combinatorial peptide and cDNA libraries have proven invaluable in mapping protein-protein interactions, protein-drug interactions, and the generation of 'molecular therapeutics'. This article reviews some of the findings of the past year and points out some of the pros and cons of phage display as compared with those of yeast two-hybrid screening.

Perspectives on gene therapy for cystic fibrosis airway disease

Since the discovery of the cystic fibrosis transmembrane conductance regulator (CFTR) gene nearly 12 years ago, cystic fibrosis (CF) has become one of the most intensively investigated monogenetic disorders considered approachable by gene therapy. This has resulted in over 20 clinical trials currently under way, concluded or awaiting approval. Despite the initial promise of gene therapy for CF, and the demonstration of successful gene transfer to the nose and airways of individuals, it has not so far been as effective as initially projected. Here we discuss the rationale behind CF gene therapy and dissect the vast array of literature representing the work that ultimately brought about the current phase I/II clinical trials. In the context of human trials, we review the limitations of current vector systems for CF gene therapy. We come to the conclusion that at present none of the application methods and vector systems are able to achieve the level and persistence of CFTR gene expression in the affected epithelia of CF patients that is required for therapeutic success. We also outline the challenges that must be overcome and describe some of the novel approaches to be taken in order to attain the curative therapy that was originally envisaged for this disease.