Roderick A. Slavcev

Immunocompatibility of Bacteriophages as Nanomedicines

Bacteriophage-based medical research provides the opportunity to develop targeted nanomedicines with heightened efficiency and safety profiles. Filamentous phages also can and have been formulated as targeted drug-delivery nanomedicines, and phage may also serve as promising alternatives/complements to antibiotics. Over the past decade the use of phage for both the prophylaxis and the treatment of bacterial infection, has gained special significance in view of a dramatic rise in the prevalence of antibiotic resistance bacterial strains. Two potential medical applications of phages are the treatment of bacterial infections and their use as immunizing agents in diagnosis and monitoring patients with immunodeficiencies. Recently, phages have been employed as gene-delivery vectors (phage nanomedicine), for nearly half a century as tools in genetic research, for about two decades as tools for the discovery of specific target-binding proteins and peptides, and for almost a decade as tools for vaccine development. As phage applications to human therapeutic development grow at an exponential rate, it will become essential to evaluate host immune responses to initial and repetitive challenges by therapeutic phage in order to develop phage therapies that offer suitable utility. This paper examines and discusses phage nanomedicine applications and the immunomodulatory effects of bacteriophage exposure and treatment modalities.

Bacteriophage recombination systems and biotechnical applications

Bacteriophage recombination systems have been widely used in biotechnology for modifying prokaryotic species, for creating transgenic animals and plants, and more recently, for human cell gene manipulation. In contrast to homologous recombination, which benefits from the endogenous recombination machinery of the cell, site-specific recombination requires an exogenous source of recombinase in mammalian cells. The mechanism of bacteriophage evolution and their coexistence with bacterial cells has become a point of interest ever since bacterial viruses’ life cycles were first explored. Phage recombinases have already been exploited as valuable genetic tools and new phage enzymes, and their potential application to genetic engineering and genome manipulation, vectorology, and generation of new transgene delivery vectors, and cell therapy are attractive areas of research that continue to be investigated. The significance and role of phage recombination systems in biotechnology is reviewed in this paper, with specific focus on homologous and site-specific recombination conferred by the coli phages, λ, and N15, the integrase from the Streptomyces phage, ΦC31, the recombination system of phage P1, and the recently characterized recombination functions of Yersinia phage, PY54. Key steps of the molecular mechanisms involving phage recombination functions and their application to molecular engineering, our novel exploitations of the PY54-derived recombination system, and its application to the development of new DNA vectors are discussed.

Addressing the Challenge: Current and Future Directions in Ovarian Cancer Therapy

Numerous ovarian gene therapy strategies are in clinical phases based on concepts of replacement/ knock out of deregulated gene, suicide gene strategies, strengthening of the immune response against a tumor, inhibition of tumor angiogenesis and growth factors. Non-viral delivery systems have potential advantages over currently widely used viral vectors and other classical vectors for delivering therapeutic gene of interest. The present review provides a comprehensive overview of potential of various delivery systems currently in use. Non-viral formulations used in ovarian gene therapy include injecting naked DNA, liposomes, polyplexes, lipopolyplexes, nanoparticles, gene gun and ultrasound/microbubble mediated gene delivery. In addition to improving vector delivery, the DNA constructs need to be optimised for both efficient and long-term transgene expression. Minicircles using minimal immunological defined gene expression (MIDGE) technology, are a promising future alternative to plasmid for use in non-viral ovarian gene therapy in terms of biosafety, improved gene transfer, potential bioavailability, minimal size and little immune reaction. The review explores the best route of administration for ovarian cancer gene therapy given its peritoneal dissemination which poses a major challenge in treating ovarian cancer patients. Enhancement of therapeutic index can be further achieved by overcoming barriers both at cellular and nuclear levels. Selective tumor targeting with minimal toxicity using folate modified, incorporating nuclear localization signal and PEGylated stealth liposomes represents a popular approach and needs to be exploited in ovarian gene therapy.

Construction and Characterization of an in-vivo Linear Covalently Closed DNA Vector Production System

BackgroundWhile safer than their viral counterparts, conventional non-viral gene delivery DNA vectors offer a limited safety profile. They often result in the delivery of unwanted prokaryotic sequences, antibiotic resistance genes, and the bacterial origins of replication to the target, which may lead to the stimulation of unwanted immunological responses due to their chimeric DNA composition. Such vectors may also impart the potential for chromosomal integration, thus potentiating oncogenesis. We sought to engineer an in vivo system for the quick and simple production of safer DNA vector alternatives that were devoid of non-transgene bacterial sequences and would lethally disrupt the host chromosome in the event of an unwanted vector integration event.ResultsWe constructed a parent eukaryotic expression vector possessing a specialized manufactured multi-target site called “Super Sequence”, and engineered E. coli cells (R-cell) that conditionally produce phage-derived recombinase Tel (PY54), TelN (N15), or Cre (P1). Passage of the parent plasmid vector through R-cells under optimized conditions, resulted in rapid, efficient, and one step in vivo generation of mini lcc—linear covalently closed (Tel/TelN-cell), or mini ccc—circular covalently closed (Cre-cell), DNA constructs, separated from the backbone plasmid DNA. Site-specific integration of lcc plasmids into the host chromosome resulted in chromosomal disruption and 105 fold lower viability than that seen with the ccc counterpart.ConclusionWe offer a high efficiency mini DNA vector production system that confers simple, rapid and scalable in vivo production of mini lcc DNA vectors that possess all the benefits of “minicircle” DNA vectors and virtually eliminate the potential for undesirable vector integration events.

Bacteriophage lambda display systems: developments and applications

Bacteriophage (phage) Lambda (λ) has played a key historic role in driving our understanding of molecular genetics. The lytic nature of λ and the conformation of its major capsid protein gpD in capsid assembly offer several advantages as a phage display candidate. The unique formation of the λ capsid and the potential to exploit gpD in the design of controlled phage decoration will benefit future applications of λ display where steric hindrance and avidity are of great concern. Here, we review the recent developments in phage display technologies with phage λ and explore some key applications of this technology including vaccine delivery, gene transfer, bio-detection, and bio-control.

DNA ministrings: highly safe and effective gene delivery vectors.

Conventional plasmid DNA vectors play a significant role in gene therapy, but they also have considerable limitations: they can elicit adverse immune responses because of bacterial sequences they contain for maintenance and amplification in prokaryotes, their bioavailability is compromised because of their large molecular size, and they may be genotoxic. We constructed an in vivo platform to produce ministring DNA—mini linear covalently closed DNA vectors—that are devoid of unwanted bacterial sequences and encode only the gene(s) of interest and necessary eukaryotic expression elements. Transfection of rapidly and slowly dividing human cells with ministring DNA coding for enhanced green fluorescent protein resulted in significantly improved transfection, bioavailability, and cytoplasmic kinetics compared with parental plasmid precursors and isogenic circular covalently closed DNA counterparts. Ministring DNA that integrated into the genome of human cells caused chromosomal disruption and apoptotic death of possibly oncogenic vector integrants; thus, they may be safer than plasmid and circular DNA vectors.

Construction and analysis of a genetically tuneable lytic phage display system

The Bacteriophage λ capsid protein gpD has been used extensively for fusion polypeptides that can be expressed from plasmids in Escherichia coli and remain soluble. In this study, a genetically controlled dual expression system for the display of enhanced green fluorescent protein (eGFP) was developed and characterized. Wild-type D protein (gpD) expression is encoded by λ Dam15 infecting phage particles, which can only produce a functional gpD protein when translated in amber suppressor strains of E. coli in the absence of complementing gpD from a plasmid. However, the isogenic suppressors vary dramatically in their ability to restore functional packaging to λDam15, imparting the first dimension of decorative control. In combination, the D-fusion protein, gpD::eGFP, was supplied in trans from a multicopy temperature-inducible expression plasmid, influencing D::eGFP expression and hence the availability of gpD::eGFP to complement for the Dam15 mutation and decorate viable phage progeny. Despite being the worst suppressor, maximal incorporation of gpD::eGFP into the λDam15 phage capsid was imparted by the SupD strain, conferring a gpDQ68S substitution, induced for plasmid expression of pD::eGFP. Differences in size, fluorescence and absolute protein decoration between phage preparations could be achieved by varying the temperature of and the suppressor host carrying the pD::eGFP plasmid. The effective preparation with these two variables provides a simple means by which to manage fusion decoration on the surface of phage λ.

Identification and Characterization of a Novel Allele of Escherichia coli dnaB Helicase That Compromises the Stability of Plasmid P1

Bacteriophage P1 lysogenizes Escherichia coli cells as a plasmid with approximately the same copy number as the copy number of the host chromosome. Faithful inheritance of the plasmids relies upon proper DNA replication, as well as a partition system that actively segregates plasmids to new daughter cells. We genetically screened for E. coli chromosomal mutations that influenced P1 stability and identified a novel temperature-sensitive allele of the dnaB helicase gene (dnaB277) that replaces serine 277 with a leucine residue (DnaB S277L). This allele conferred a severe temperature-sensitive phenotype to the host; dnaB277 cells were not viable at temperatures above 34 degrees C. Shifting dnaB277 cells to 42 degrees C resulted in an immediate reduction in the rate of DNA synthesis and extensive cell filamentation. The dnaB277 allele destabilized P1 plasmids but had no significant influence on the stability of the F low-copy-number plasmid. This observation suggests that there is a specific requirement for DnaB in P1 plasmid maintenance in addition to the general requirement for DnaB as the replicative helicase during elongation.

Solid Lipid Nanoparticles: Tuneable Anti-Cancer Gene/Drug Delivery Systems

With the advent of multifunctional nano delivery systems, simultaneous imaging and therapy aspires to detect and treat tumors at a very early stage with promising out‐ comes. In this context, numerous anti-cancer drug/gene delivery systems have been ex‐ plored with the primary aim to increase the treatment efficacy without compromising safety. Secondary goals include enhancing bioavailability, specific targeting, apart from the enhanced stability of the formulation [1]. The multifaceted applications of nanoparti‐ cles are the direct result of their ability to deliver high pay loads of drugs or biomarkers to the desired sites within the body. Design and development of tumor specific nanopar‐ ticles could significantly amplify the delivering capacity to a specific target of interest, without affecting healthy cells [2]. Technological advances in nanomaterials and nano‐ technology have paved the way for several carriers such as liposomes [3], dendrimers [4], and micelles [5], solid lipid nanoparticles (SLN) [6] and recently nanostructured lipid carriers [1, 7]. Polymeric micelles, or nanosized (~10–100 nm) supramolecular constructs composed of amphiphilic block-copolymers, are emerging as powerful drug delivery ve‐ hicles for hydrophobic drugs. Liposomes are currently the most popular nanosized drug delivery systems, with one or several lipid bilayers enclosing an aqueous core. Liposomeencapsulated formulations of doxorubicin earlier approved for the treatment of Kaposi’s sarcoma, are now used against breast cancer and refractory ovarian cancer. Breast cancer in particular has been the focus of many studies involving liposome-based chemothera‐ peutics, in part due to the clinical success of various drugs such as Doxil, which is a lip‐ osomal formulation currently used to treat recurrent breast cancer [7]. The anthracycline doxorubicin is the active cytotoxic agent and is contained within the internal aqueous core of the liposome. The encapsulation of doxorubicin within liposomes significantly re‐

Graphical analysis of flow cytometer data for characterizing controlled fluorescent protein display on λ phage

As native virus particles typically cannot be resolved using a flow cytometer, the general practice is to use fluorescent dyes to label the particles. In this work, an attempt was made to use a common commercial flow cytometer to characterize a phage display strategy that allows for controlled levels of protein display, in this case, eGFP. To achieve this characterization, a number of data processing steps were needed to ensure that the observed phenomena were indeed capturing differences in the phages produced. Phage display of eGFP resulted in altered side scatter and fluorescence profile, and sub‐populations could be identified within what would otherwise be considered uniform populations. Surprisingly, this study has found that side scatter may be used in the future to characterize the display of nonfluorescent proteins.