Single chain Fv: a ligand in receptor-mediated gene delivery

Discovery and characterization of single-domain antibodies for polymeric Ig receptor-mediated mucosal delivery of biologics

Mucosal immunity is dominated by secretory IgA and IgM, although these are less favorable compared to IgG molecules for therapeutic development. Polymeric IgA and IgM are actively transported across the epithelial barrier via engagement of the polymeric Ig receptor (pIgR), but IgG molecules lack a lumen-targeted active transport mechanism, resulting in poor biodistribution of IgG therapeutics in mucosal tissues. In this work, we describe the discovery and characterization of single-domain antibodies (VHH) that engage pIgR and undergo transepithelial transport across the mucosal epithelium. The anti-pIgR VHH panel displayed a broad range of biophysical characteristics, epitope diversity, IgA competition profiles and transcytosis activity in cell and human primary lung tissue models. Making use of this diverse VHH panel, we studied the relationship between biophysical and functional properties of anti-pIgR binders targeting different domains and epitopes of pIgR. These VHH molecules will serve as excellent tools for studying pIgR-mediated transport of biologics and for delivering multispecific IgG antibodies into mucosal lumen, where they can target and neutralize mucosal antigens.

High yield of human monoclonal antibody produced by stably transfected Drosophila schneider 2 cells in perfusion culture using wave bioreactor

Since it was first introduced in late 1990s Wave bioreactor has been used for protein production by mammalian and insect cell lines. However, using Wave bioreactor to produce human monoclonal antibody by stable Drosophila Schneider 2 (S2) cell transfectants has not been reported before. In this study, S2 cells were co-transfected with an inducible vector expressing human monoclonal antibody heavy and light chains, respectively, specific for hemagglutinin (HA) of H5N1 influenza virus. Stable S2 transfectant clone was selected by limiting dilution assay. Stable S2 transfectant clone that produce the highest amount of human monoclonal antibody was inoculated into two 2-l disposable cellbags, where cell growth and antibody production were compared between batch and perfusion cultures using Wave bioreactor. Here, we report that maximum viable cell density reached 1.06 × 10(7) cells/ml in batch culture; whereas 1.04 × 10(8) cells/ml was achieved in perfusion culture. The maximum volumetric antibody productivity in batch culture was 52 mg/l/day; while perfusion culture yielded 1,437 mg/l/day. As a result, the total antibody production was 201 mg in batch culture and 8,212 mg in perfusion culture. The antibody produced by both cultures displays full neutralizing activity. Thus, our results provide strong support for using Wave bioreactor in perfusion culture for a large-scale production of human monoclonal antibody by stable S2 cell transfectants.

Lipophilic siRNAs mediate efficient gene silencing in oligodendrocytes with direct CNS delivery

Conjugation of small interfering RNA (siRNA) with lipophilic molecules has been demonstrated to enhance cellular uptake in cell culture and to produce efficient endogenous gene silencing in the liver after systemic administration and in neurons after direct local injection. Here, we evaluated the in vivo delivery of siRNAs conjugated with different linkers to cholesterol by targeting CNPase (2'-3'-cyclic nucleotide 3'-phosphodiesterase) in oligodendrocytes. Cholesterol-conjugated siRNAs administered to the rat corpus callosum by intraparenchymal central nervous system (CNS) infusion show improved silencing ability compared with unconjugated siRNA. Furthermore, conjugation of siRNA to cholesterol with a cleavable disulfide linker appears to be beneficial for improving the potency of silencing of CNPase mRNA in oligodendrocytes in vivo. Taken together, these findings indicate that cholesterol-conjugated siRNAs are effective for direct CNS delivery to oligodendrocytes, and that the biocleavable disulfide linker appears to be beneficial for improving the potency of silencing of target mRNA in vivo.

Real-time imaging of gene delivery and expression with DNA nanoparticle technologies

The construction of safe, efficient, and modifiable synthetic DNA nanoparticles is an emerging technology that has achieved important milestones of success in the past 5 years. Advances in chemical conjugation, purification, and controlled synthesis have allowed researchers to produce uniform and stable particles, whose physical characteristics can be well characterized and monitored. As a result of these improvements, DNA nanoparticles have now been cleared for clinical testing, and show good potential for human gene therapy. A very important recent development in the study of DNA nanoparticles is the use of small-animal imaging. Real-time imaging has become a valuable technique for tracking particle biodistribution and gene transfer efficacy. In this chapter, we discuss how bioluminescent, positron emission tomography, and magnetic resonance imaging can be used separately or in concert to study particle delivery, localization, and magnitude of gene expression in vivo.

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.

Antibodies to the polymeric immunoglobulin receptor with different binding and trafficking patterns

The polymeric immunoglobulin receptor (pIgR) has been proposed as a therapeutic target, but its potential depends on the efficiency of uptake and trafficking of the receptor ligand. Mouse monoclonal antibodies (Mabs) directed against pIgR, selected for strong binding to secretory component (SC) and secretory IgA (sIgA), were tested in a transcytosis assay in 16HBEo--cells (human bronchial epithelial cell line) transfected with human pIgR. Intracellular trafficking was followed by confocal microscopy. Mabs fell into two classes. For two Mabs, transcytosis from basolateral to apical surface is rapid, unidirectional, and little Mab is retained in the cell. For three Mabs, basolateral to apical transcytosis occurs to a significantly lesser extent, reverse transcytosis is permitted, and some of the Mab is retained in the perinuclear region even after 24 h. When tested for their ability to recognize and immunoprecipitate pIgR with systematic truncations and deletions of the five immunoglobulin (Ig)-like domains, all Mabs bound to the fifth Ig-like domain, but three of them also bound to the C-terminal region of pIgR near the plasma membrane. Different binding sites probably account for the different trafficking of these Mabs and may predict differential therapeutic utility.

Intermolecular interaction between R domains of cystic fibrosis transmembrane conductance regulator

The function of the R domain of cystic fibrosis transmembrane conductance regulator (CFTR) has not yet been fully established. The cis-trans proline isomerase cyclophilin A stimulates channel activity, and stimulation depends on the presence of highly conserved prolines at positions 740, 750, and 759. When the prolines at these positions, which normally exist in the cis conformation, are locked into the trans conformation by mutation to alanine (the P3A mutant), the open probability of P3A is high and is not further increased by cyclophilin A. We speculated that one mechanism by which this could occur was by promoting CFTR dimerization, which has been shown to increase open probability, and that the P3A-CFTR might favor dimerization more strongly than the native sequence. To test the hypothesis that R-R interaction occurs and is stronger in the P3A-R mutants, we investigated R-R interactions. GST-R and StrepII-R proteins expressed in Escherichia coli could interact with R domain protein translated in vitro as well as with full-length CFTR. In similar assays, the P3A mutant of R domain also interacts with R domain and P3A-R. The P3A-R-P3A-R interaction is stronger than the R-R interaction, which corroborates our data from the channel study and supports our hypothesis. Studies of deletion constructs of the isolated R domain and of full-length CFTR localize the region of interaction to the C-terminal portion of R (after amino acid 708). Particularly, the last 22 a.a. residues (838-859) of R are essential for this binding. R-R interaction possibly plays a role in channel gating.

Targeting of Synthetic Gene Delivery Systems

Safe, efficient, and specific delivery of therapeutic genes remains an important bottleneck for the development of gene therapy. Synthetic, nonviral systems have a unique pharmaceutical profile with potential advantages for certain applications. Targeting of the synthetic vector improves the specificity of gene medicines through a modulation of the carriers' biodistribution, thus creating a dose differential between healthy tissue and the target site. The biodistribution of current carrier systems is being influenced to a large extent by intrinsic physicochemical characteristics, such as charge and size. Consequently, such nonspecific interactions can interfere with specific targeting, for example, by ligands. Therefore, a carrier complex should ideally be inert, that is, free from intrinsic properties that would bias its distribution away from the target site. Strategies such as coating of DNA carrier complexes with hydrophilic polymers have been used to mask some of these intrinsic targeting effects and avoid nonspecific interactions. Preexisting endogenous ligand-receptor interactions have frequently been used for targeting to certain cell types or tumours. Recently exogenous ligands have been derived from microorganisms or, like antibodies or phage-derived peptides, developed de novo. In animal models, such synthetic vectors have targeted remote sites such as a tumour. Furthermore, the therapeutic proof of the concept has been demonstrated for fitting combinations of synthetic vectors and therapeutic gene.

Drug delivery strategy utilizing conjugation via reversible disulfide linkages: role and site of cellular reducing activities

The first disulfide linkage-employing drug conjugate that exploits the reversible nature of this unique covalent bond was recently approved for human use. Increasing numbers of drug formulations that incorporate disulfide bonds have been reported, particularly in the next generation macromolecular pharmaceuticals. These are designed to exploit differences in the reduction potential at different locations within and upon cells. The recent characterization of a novel redox enzyme in endosomes and lysosomes adds more excitement to this approach. This review focuses on understanding where and how the disulfide bond in the bioconjugate is reduced upon contact with biological milieu, which affects delivery design and the interpretation of the delivery strategies.