Immobilization of plasmid DNA in bacterial ghosts

Bacteria from Infectious Particles to Cell Based Anticancer Targeted Drug Delivery Systems

Bacterial ghosts (BGs) are empty cell envelopes of nonliving evacuated bacterial cells. They are free from their cytoplasmic contents; however, they sustain their cellular 3D morphology and antigenic structures, counting on bioadhesive properties. Lately, they have been tested as an advanced drug delivery system (DDS) for different materials like DNA, peptides, or drugs, either single components or combinations. Different studies have revealed that, BG DDS were paid the greatest attention in recent years. The current review explores the impact of BGs on the field of drug delivery and drug targeting. BGs have a varied area of applications, including vaccine and tumor therapy. Moreover, the use of BGs, their synthesis, their uniqueness as a delivery system and application principles in cancer are discussed. Furthermore, the safety issues of BGs and stability aspects of using ghost bacteria as delivery systems are discussed. Future perspective efforts that must be followed for this important system to continue to grow are important and promising.

The development of ghost vaccines trials

INTRODUCTION

Bacterial ghosts are intact bacterial cell envelopes that are emptied of their content by gentle biological or chemical poring methods. Ghost techniques increase the safety of the killed vaccines, while maintaining their antigenicity due to mild preparation procedures. Moreover, ghost-platforms may express and/or carry several antigens or plasmid-DNA encoding for protein epitopes.

AREAS COVERED

In this review, the development in ghost-vaccine production over the last 30 years is classified and discussed. The different applications of ghost-vaccines, how they trigger the immune system, their advantages and limitations are displayed. The phage-mediated lysis, molecular manipulation of the lysis-genes, and the biotechnological production of ghosts are described. The trials are classified according to the pattern of lysis and to the type of bacteria. Further subdivision includes chronological ordered application of the ghost as alternative-killed vaccine, recombinant antigen platform, plasmid DNA carrier, adjuvants, and dendritic cell inducer. Particular trials for specific pathogens or from distinct research schools are gathered.

EXPERT OPINION

Ghosts are highly qualified to act as immune-presenting platforms that express and/or carry several recombinant and DNA vaccines, as well as, being efficient alternative-killed vaccines. The coming years will show more molecular advances to develop ghost-production and to express more antigens.

Biomimetic and bioinspired strategies for oral drug delivery

Oral drug delivery remains the most preferred approach due to its multiple advantages. Recently there has been increasing interest in the development of advanced vehicles for oral delivery of different therapeutics. Among them, biomimetic and bioinspired strategies are emerging as novel approaches that are promising for addressing biological barriers encountered by traditional drug delivery systems. Herein we provide a state-of-the-art review on the current progress of biomimetic particulate oral delivery systems. Different biomimetic nanoparticles used for oral drug delivery are first discussed, mainly including ligand/antibody-functionalized nanoparticles, transporter-mediated nanoplatforms, and nanoscale extracellular vesicles. Then we describe bacteria-derived biomimetic systems, with respect to oral delivery of therapeutic proteins or antigens. Subsequently, yeast-derived oral delivery systems, based on either chemical engineering or bioengineering approaches are discussed, with emphasis on the treatment of inflammatory diseases and cancer as well as oral vaccination. Finally, bioengineered plant cells are introduced for oral delivery of biological agents. A future perspective is also provided to highlight the existing challenges and possible resolution toward clinical translation of currently developed biomimetic oral therapies.

Bacterial components as naturally inspired nano-carriers for drug/gene delivery and immunization: Set the bugs to work?

Drug delivery is a rapidly growing area of research motivated by the nanotechnology revolution, the ideal of personalized medicine, and the desire to reduce the side effects of toxic anti-cancer drugs. Amongst a bewildering array of different nanostructures and nanocarriers, those examples that are fundamentally bio-inspired and derived from natural sources are particularly preferred. Delivery of vaccines is also an active area of research in this field. Bacterial cells and their components that have been used for drug delivery, include the crystalline cell-surface layer known as "S-layer", bacterial ghosts, bacterial outer membrane vesicles, and bacterial products or derivatives (e.g. spores, polymers, and magnetic nanoparticles). Considering the origin of these components from potentially pathogenic microorganisms, it is not surprising that they have been applied for vaccines and immunization. The present review critically summarizes their applications focusing on their advantages for delivery of drugs, genes, and vaccines.

Pushing the Right Buttons: Improving Efficacy of Therapeutic DNA Vectors

Gene therapy represents a potent therapeutical application for regenerative medicine. So far, viral and nonviral approaches suffer from major drawbacks hindering efficient gene therapeutic applicability: the immunogenicity of viral systems on the one hand, and the low gene transfer efficiency of nonviral systems on the other hand. Therefore, there is a high demand for improvements of therapeutical systems at several levels. This review summarizes different DNA vector modifications to enhance biological efficacy and efficiency of therapeutical vectors, aiming for low toxicity, high specificity, and biological efficacy-the cornerstones for successful translation of gene therapy into the clinic. We aim to provide a step-by-step instruction to optimize their vectors to achieve the desired outcome of gene therapy. Our review provides the means to either construct a potent gene therapeutic vector de novo or to specifically address a bottleneck in the chain of events mandatory for therapeutic success. Although most of the introduced techniques can be translated into different areas, this review primarily addresses improvements for applications in transient gene therapy in the field of tissue engineering.

Helicobacter pylori outer inflammatory protein DNA vaccine-loaded bacterial ghost enhances immune protective efficacy in C57BL/6 mice

Helicobacter pylori (H. pylori) infection is associated with incidents of gastrointestinal diseases in half of the human population. However, management of its infection remains a challenge. Hence, it is necessary to develop an efficient vaccine to fight against this pathogen. In the present study, a novel vaccine based on the production of attenuated Salmonella typhimurium bacterial ghost (SL7207-BG), delivering H. pylori outer inflammatory protein gene (oipA) encoded DNA vaccine was developed, and the efficiency was evaluated in C57BL/6 mice. Significant higher levels of IgG2a/IgG1 antibodies and IFN-γ/IL-4 cytokines were detected after mice were oral administered with oipA DNA vaccine loaded SL7207-BG, indicating that a mixed Th1/Th2 immune response was elicited. When challenged with infective doses H. pylori strain SS1, the ghost based vaccine was capable of reducing bacterium colonization in the vaccinated mice. In addition, codon-optimized oipA plasmid loaded SL7207-BG significantly eliminates H. pylori colonization density in mice model. Thus, it has been demonstrated that this novel bacterial ghost based DNA vaccine could be used as a promising vaccine candidate for the control of H. pylori infection.

Harnessing the potential of bacterial ghost for the effective delivery of drugs and biotherapeutics

It seems to be a necessary need to develop an effective drug carrier system for targeted delivery of pharmaceuticals. Bacterial ghosts are emerging drug delivery platform that are capable of delivery of proteins, antigens, nucleic acids, and pharmaceuticals. Bacterial ghosts are generally produced by lysis of gram-negative bacteria. Pharmaceutically, these ghosts could be utilized to deliver proteins peptides, vaccines, drugs effectively. However, this technology is at initial stage and systematic studies are required to implement such system over humans.

Sponge-like: a new protocol for preparing bacterial ghosts

Bacterial Ghosts (BGs) received an increasing interest in the recent years for their promising medicinal and pharmaceutical applications. In this study, for the first time we introduce a new protocol for BGs production. E. coli BL21 (DE3) pLysS (Promega) was used as a model to establish a general protocol for BGs preparation. The protocol is based on using active chemical compounds in concentrations less than the Minimum Inhibition Concentration (MIC). Those chemical compounds are SDS, NaOH, and H2O2. Plackett-Burman experimental design was used to map the best conditions for BGs production. Normal and electronic microscopes were used to evaluate the BGs quality (BGQ). Spectrophotometer was used to evaluate the amount of the released protein and DNA. Agarose gel electrophoresis was used to determine the existence of any residue of DNA after each BGs preparation. Viable cells, which existed after running this protocol, were subjected to lysis by inducing the lysozyme gene carried on pLysS plasmid. This protocol is able to produce BGs that can be used in different biotechnological applications.

The Bacterial Ghost platform system: production and applications

The Bacterial Ghost (BG) platform technology is an innovative system for vaccine, drug or active substance delivery and for technical applications in white biotechnology. BGs are cell envelopes derived from Gram-negative bacteria. BGs are devoid of all cytoplasmic content but have a preserved cellular morphology including all cell surface structures. Using BGs as delivery vehicles for subunit or DNA-vaccines the particle structure and surface properties of BGs are targeting the carrier itself to primary antigen-presenting cells. Furthermore, BGs exhibit intrinsic adjuvant properties and trigger an enhanced humoral and cellular immune response to the target antigen. Multiple antigens of the native BG envelope and recombinant protein or DNA antigens can be combined in a single type of BG. Antigens can be presented on the inner or outer membrane of the BG as well as in the periplasm that is sealed during BG formation. Drugs or supplements can also be loaded to the internal lumen or periplasmic space of the carrier. BGs are produced by batch fermentation with subsequent product recovery and purification via tangential flow filtration. For safety reasons all residual bacterial DNA is inactivated during the BG production process by the use of staphylococcal nuclease A and/or the treatment with β-propiolactone. After purification BGs can be stored long-term at ambient room temperature as lyophilized product. The production cycle from the inoculation of the pre-culture to the purified BG concentrate ready for lyophilization does not take longer than a day and thus meets modern criteria of rapid vaccine production rather than keeping large stocks of vaccines. The broad spectrum of possible applications in combination with the comparably low production costs make the BG platform technology a safe and sophisticated product for the targeted delivery of vaccines and active agents as well as carrier of immobilized enzymes for applications in white biotechnology.

Relevant uses of surface proteins--display on self-organized biological structures

Proteins are often found attached to surfaces of self‐assembling biological units such as whole microbial cells or subcellular structures, e.g. intracellular inclusions. In the last two decades surface proteins were identified that could serve as anchors for the display of foreign protein functions. Extensive protein engineering based on structure–function data enabled efficient display of technically and/or medically relevant protein functions. Small size, diversity of the anchor protein as well as support structure, genetic manipulability and controlled cultivation of phages, bacterial cells and yeasts contributed to the establishment of designed and specifically functionalized tools for applications as sensors, catalysis, biomedicine, vaccine development and library‐based screening technologies. Traditionally, phage display is employed for library screening but applications in biomedicine and vaccine development are also perceived. For some diagnostic purposes phages are even too small in size so other carrier materials where needed and gave way for cell and yeast display. Only recently, intracellular inclusions such as magnetosomes, polyhydroxyalkanoate granules and lipid bodies were conceived as stable subcellular structures enabling the display of foreign protein functions and showing potential as specific and tailor‐made devices for medical and biotechnological applications.

Use of minicircle plasmids for gene therapy

A large number of cancer gene therapy clinical trials are currently being performed that are attempting to evaluate novel approaches to eliminate tumor cells by the introduction of genetic material into patients. One of the most important objectives in gene therapy is the development of highly safe and efficient vector systems for gene transfer in eukaryotic cells. Currently, viral and nonviral vector systems are used, both having their advantages and limitations. Minicircles are novel supercoiled minimal expression cassettes, derived from conventional plasmid DNA by site-specific recombination in vivo in Escherichia coli for the use in nonviral gene therapy and vaccination. Minicircle DNA lacks the bacterial backbone sequence consisting of an antibiotic resistance gene, an origin of replication, and inflammatory sequences intrinsic to bacterial DNA. In addition to their improved safety profile, minicircles have been shown to greatly increase the efficiency oftransgene expression in various in vitro and in vivo studies. In this chapter, we describe the production, purification, and application of minicircle DNA and discuss the rationale of the improved gene transfer efficiencies compared to conventional plasmid DNA.

Minicircle-DNA production by site specific recombination and protein-DNA interaction chromatography

BACKGROUND

Conventional plasmid-DNA (pDNA) used in gene therapy and vaccination can be subdivided into a bacterial backbone and a transcription unit. Bacterial backbone sequences are needed for pDNA production in bacteria. However, for gene transfer application, these sequences are dispensable, reduce the overall efficiency of the DNA agent and, most importantly, represent a biological safety risk. For example, the dissemination of antibiotic resistance genes, as well as the uncontrolled expression of backbone sequences, may have profound detrimental effects and unmethylated CpG motifs have been shown to contribute to silencing of episomal transgene expression. Therefore, an important goal in nonviral vector development is to produce supercoiled pDNA lacking bacterial backbone sequences.

METHODS

A method is described to provide circular, supercoiled minimal expression cassettes (minicircle-DNA) based on two processes: (i) an inducible, sequence specific, in vivo recombination process that is almost 100% efficient and (2) a novel affinity-based chromatographic purification approach for the isolation of the minicircle-DNA.

RESULTS

Quantitative real-time polymerase chain reaction analysis, capillary gel electrophoresis and restriction analysis of the recombination products, and the minicircle-DNA revealed a recombination efficiency greater than 99.5% and a purity of the isolated minicircle-DNA of more than 98.5%.

CONCLUSIONS

The results obtained in the present study demonstrate that the described technology facilitates the production of highly pure minicircle-DNA for direct application in gene therapy and vaccination. The process described is efficient, stable and suitable for further scale-up in industrial large-scale manufacturing.

Effective gene transfer to melanoma cells using bacterial ghosts

Bacterial ghosts (BG) are cell envelopes preparations of Gram-negative bacteria devoid of cytoplasmic content produced by controlled expression of PhiX174 plasmid-encoded lysis gene E. Eight melanoma cell lines were investigated for their capacity to bind and phagocyte BG derived from Escherichia coli NM522 and Mannheimia haemolytica A23. High capability to bind BG was observed in almost all of the analyzed cell lines, furthermore cells were able to take up BG independently of the used bacterial species. Further, transfection efficiency of BG loaded with DNA in vitro was measured. The Bowes cells exhibited a high expression level of GFP and the incubation of cells with plasmid loaded BG led up to 82% transfection efficiency.

Bacterial ghosts as adjuvant particles

The development of more advanced and effective vaccines is of great interest in modern medicine. These new-generation vaccines, based on recombinant proteins or DNA, are often less reactogenic and immunogenic than traditional vaccines. Thus, there is an urgent need for the development of new and improved adjuvants. Besides many other immunostimulatory components, the bacterial ghost (BG) system is currently under investigation as a potent vaccine delivery system with intrinsic adjuvant properties. BGs are nonliving cell envelope preparations from Gram-negative cells, devoid of cytoplasmic contents, while their cellular morphology and native surface antigenic structures remain preserved. Owing to the particulate nature of BGs and the fact that they contain many well known immune-stimulating compounds, BGs have the potential to enhance immune responses against ghost-delivered target antigens.

Optimization and delivery of plasmid DNA for vaccination

Vaccination with DNA is one of the most promising novel immunization techniques against a variety of pathogens and tumors, for which conventional vaccination regimens have failed. DNA vaccines are able to stimulate both arms of the immune system simultaneously, without carrying the safety risks associated with live vaccines, therefore representing not only an alternative to conventional vaccines but also significant progress in the prevention and treatment of fatal diseases and infections. However, translation of the excellent results achieved in small animals to similar success in primates or large animals has so far proved to be a major hurdle. Moreover, biosafety issues, such as the removal of antibiotic resistance genes present in plasmid DNA used for vaccination, remain to be addressed adequately. This review describes strategies to improve the design and production of conventional plasmid DNA, including an overview of safety and regulatory issues. It further focuses on novel systems for the optimization of plasmid DNA and the development of diverse plasmid DNA delivery systems for vaccination purposes.

Bacterial ghosts as a novel advanced targeting system for drug and DNA delivery

Although there are powerful drugs against infectious diseases and cancer on the market, delivery systems are needed to decrease serious toxic and noncurative side effects. In order to enhance compliance, several delivery systems such as polymeric micro- and nanoparticles, liposomal systems and erythrocyte ghosts have been developed. Bacterial ghosts representing novel advanced delivery and targeting vehicles suitable for the delivery of hydrophobic or water-soluble drugs, are the main focus of this review. They are useful nonliving carriers, as they can carry different active substances in more than one cellular location separately and simultaneously. Bacterial ghosts combine excellent natural or engineered adhesion properties with versatile carrier functions for drugs, proteins and DNA plasmids or DNA minicircles. The simplicity of both bacterial ghost production and packaging of drugs and/or DNA makes them particularly suitable for the use as a delivery system. Further advantages of bacterial ghost delivery vehicles include high bioavailability and a long shelf life without the need of cold-chain storage due to the possibility to freeze-dry the material.

Minicircle DNA immobilized in bacterial ghosts: in vivo production of safe non-viral DNA delivery vehicles

DNA as an active agent is among the most promising technologies for vaccination and therapy. However, plasmid backbone sequences needed for the production of pDNA in bacteria are dispensable, reduce the efficiency of the DNA agent and, most importantly, represent a biological safety risk. In this report we describe a novel technique where a site-specific recombination system based on the ParA resolvase was applied to a self-immobilizing plasmid system (SIP). In addition, this system was combined with the protein E-specific lysis technology to produce non-living bacterial carrier vehicles loaded with minicircle DNA. The in vivo recombination process completely divided an origin plasmid into a minicircle and a miniplasmid. The replicative miniplasmid containing the origin of replication and the antibiotic resistance gene was lost during the subsequently induced PhiX174 gene E-mediated lysis process, which results in bacterial ghosts. The minicircle DNA was retained in these empty bacterial cell envelopes during the lysis process via the specific interaction of a membrane anchored protein with the minicircle DNA. Using this novel platform technology, a DNA delivery vehicle--consisting of a safe bacterial carrier with known adjuvant properties and minicircle DNA with an optimized safety profile--can be produced in vivo in a continuous process. Furthermore, this study provides the basis for the development of an efficient in vitro minicircle purification process.

Strategies for DNA vaccine delivery

Strategies for gene delivery comprise a diverse range of live and synthetic approaches; DNA delivery for the purposes of immunisation in turn comprises a large part of this research. This review mainly discusses synthetic systems for application in the delivery of plasmid DNA vaccines, outlining polylactide-co-glycolide, liposome, chitosan and complex combination delivery systems. Areas of promise for DNA vaccine candidates include immune modulation of allergic responses and veterinarian application. The potential for realistic consideration of DNA vaccines as an alternative to existing approaches is dependent on the development of efficient DNA vaccine vectors and improved systems for DNA vaccine delivery. DNA vaccine technology may yet prove to be an important asset in an environment where there is a critical need for therapeutic and prophylactic strategies to combat a wide range of disease states.

Bacterial ghosts as antigen delivery vehicles

The bacterial ghost system is a novel vaccine delivery system unusual in that it combines excellent natural intrinsic adjuvant properties with versatile carrier functions for foreign antigens. The efficient tropism of bacterial ghosts (BG) for antigen presenting cells promotes the generation of both cellular and humoral responses to heterologous antigens and carrier envelope structures. The simplicity of both BG production and packaging of (multiple) target antigens makes them particularly suitable for use as combination vaccines. Further advantages of BG vaccines include a long shelf-life without the need of cold-chain storage due to their freeze-dried status, they are safe as they do not involve host DNA or live organisms, they exhibit improved potency with regard to target antigens compared to conventional approaches, they are versatile with regards to DNA or protein antigen choice and size, and as a delivery system they offer high bioavailability.