Mammalian cell binding and transfection mediated by surface-modified bacteriophage lambda

Engineered Bacteriophage T7 as a Potent Anticancer Agent in vivo

Oncolytic viruses (OVs) induce antitumor effect by both direct lysis of target cells and eliciting immunogenic response to the virus and ultimately to the target cells. These viruses are usually natural human pathogens. Bacteriophages are natural pathogens of bacteria that do not infect human and have greater advantages in safety, manipulation, and production over human viruses. We constructed an engineered bacteriophage T7 displaying a peptide, which targets murine melanoma cells and harbors a mammalian expression cassette of the cytokine granulocyte macrophage-colony stimulating factor (GM-CSF) in viral genomic DNA. The engineered phage was successfully transduced to B16F10 melanoma cells both in vitro and in vivo. GM-CSF was expressed from the transduced phage DNA. All mice treated with the phage intravenously survived for 25 days until the end of experiment, while only 40% of those not treated survived. During the 16 days of phage treatment, phage T7 displaying homing peptide and expressing GM-CSF inhibited tumor growth by 72% compared to the untreated control. Serum cytokine levels of IL-1α, TNF-α, and GM-CSF were seen to increase during the treatment. Immunohistochemical analysis of tumor tissue revealed infiltration by macrophages, dendritic cells (DCs), and CD8⁺ T cells. Migration of murine macrophages to bacteriophages was also observed in in vitro transwell assays in both time- and dose-dependent manners. Taken together, the recombinant bacteriophage T7 efficiently inhibited tumor growth by changing the tumor microenvironment and recruiting anti-tumor immune cells.

Factors determining phage stability/activity: challenges in practical phage application

Introduction: Phages consist of nucleic acids and proteins that may lose their activity under different physico-chemical conditions. The production process of phage formulations may decrease phage infectivity. Ingredients present in the preparation may influence phage particles, although preparation and storage conditions may also cause variations in phage titer. Significant factors are the manner of phage application, the patient's immune system status, the type of medication being taken, and diet. Areas covered: We discuss factors determining phage activity and stability, which is relevant for the preparation and application of phage formulations with the highest therapeutic efficacy. Our article should be helpful for more insightful implementation of clinical trials, which could pave the way for successful phage therapy. Expert opinion: The number of naturally occurring phages is practically unlimited and phages vary in their susceptibility to external factors. Modern methods offer engineering techniques which should lead to enhanced precision in phage delivery and anti-bacterial activity. Recent data suggesting that phages may also be used in treating nonbacterial infections as well as anti-inflammatory and immunomodulatory agents add further weight to such studies. It may be anticipated that different phage activities could have varying susceptibility to factors determining their actions.

Bacteriophages and phage-inspired nanocarriers for targeted delivery of therapeutic cargos

The main goal of drug delivery systems is to target therapeutic cargoes to desired cells and to ensure their efficient uptake. Recently a number of studies have focused on designing bio-inspired nanocarriers, such as bacteriophages, and synthetic carriers based on the bacteriophage structure. Bacteriophages are viruses that specifically recognize their bacterial hosts. They can replicate only inside their host cell and can act as natural gene carriers. Each type of phage has a particular shape, a different capacity for loading cargo, a specific production time, and their own mechanisms of supramolecular assembly, that have enabled them to act as tunable carriers. New phage-based technologies have led to the construction of different peptide libraries, and recognition abilities provided by novel targeting ligands. Phage hybridization with non-organic compounds introduces new properties to phages and could be a suitable strategy for construction of bio-inorganic carriers. In this review we try to cover the major phage species that have been used in drug and gene delivery systems, and the biological application of phages as novel targeting ligands and targeted therapeutics.

Engineered M13 bacteriophage nanocarriers for intracellular delivery of exogenous proteins to human prostate cancer cells

The size, well-defined structure, and relatively high folding energies of most proteins allow them to recognize disease-relevant receptors that present a challenge to small molecule reagents. While multiple challenges must be overcome in order to fully exploit the use of protein reagents in basic research and medicine, perhaps the greatest challenge is their intracellular delivery to a particular diseased cell. Here, we describe the genetic and enzymatic manipulation of prostate cancer cell-penetrating M13 bacteriophage to generate nanocarriers for the intracellular delivery of functional exogenous proteins to a human prostate cancer cell line.

Binary gene vectors based on hyperbranched poly(l-lactide-co-polyglycerol) and polyethylenimine for prolonged transgene expression via co-assembly with DNA into fiber core-shell triplexes

Hyper-branched PG6-PLA polymers based on hydrophilic hyperbranched polyglycerol (PG6) and the ester chain poly(l-lactide) (PLA) were synthesized and facilitated to develop a novel biocompatible release-controlled gene vector. The hyper-branched structure of PG6-PLA was verified by NMR, FT-IR and SEC-MALLS analysis. The co-assembly of PG6-PLA with high molecular weight polyethylenimine (PEI) of 25 kDa was discussed. The results of TEM, fluorescence tracking and size/zeta-potential analysis revealed that the PG6-PLA/PEI25k/DNA could co-assemble to generate a novel fiber core-shell conformation. In vitro cell experiment demonstrated that PG6-PLA significantly enhanced the ability of PEI25k to remain within cells and mediate luciferase and EGFP expression in the human embryonic kidney cell line 293T and human cervical carcinoma cell line HeLa, which was accompanied by improved cell biocompatibility and an extended period of transgene expression. Importantly, the binary vector PG6-PLA/PEI25k exhibited specific affinity to some tumour cell lines including HeLa and the HepG2 human hepatoma cell line. These results suggested that the novel gene delivery system based on fiber core-shell PG6-PLA/PEI25k/DNA can serve as a gene delivery system to mediate more efficient transgene expression.

Going viral: next-generation sequencing applied to phage populations in the human gut

Over the past decade, researchers have begun to characterize viral diversity using metagenomic methods. These studies have shown that viruses, the majority of which infect bacteria, are probably the most genetically diverse components of the biosphere. Here, we briefly review the incipient rise of a phage biology renaissance, which has been catalysed by advances in next-generation sequencing. We explore how work characterizing phage diversity and lifestyles in the human gut is changing our view of ourselves as supra-organisms. Finally, we discuss how a renewed appreciation of phage dynamics may yield new applications for phage therapies designed to manipulate the structure and functions of our gut microbiomes.

Bacteriophages and their implications on future biotechnology: a review

Recently it has been recognized that bacteriophages, the natural predators of bacteria can be used efficiently in modern biotechnology. They have been proposed as alternatives to antibiotics for many antibiotic resistant bacterial strains. Phages can be used as biocontrol agents in agriculture and petroleum industry. Moreover phages are used as vehicles for vaccines both DNA and protein, for the detection of pathogenic bacterial strain, as display system for many proteins and antibodies. Bacteriophages are diverse group of viruses which are easily manipulated and therefore they have potential uses in biotechnology, research, and therapeutics. The aim of this review article is to enable the wide range of researchers, scientists, and biotechnologist who are putting phages into practice, to accelerate the progress and development in the field of biotechnology.

Proteasome inhibitors enhance bacteriophage lambda (lambda) mediated gene transfer in mammalian cells

Bacteriophage lambda vectors can transfer their genomes into mammalian cells, resulting in expression of phage-encoded genes. However, this process is inefficient. Experiments were therefore conducted to delineate the rate limiting step(s) involved, using a phage vector that contains a mammalian luciferase reporter gene cassette. The efficiency of phage-mediated gene transfer in mammalian cells was quantitated, in the presence or absence of pharmacologic inhibitors of cell uptake and degradation pathways. Inhibitors of lysosomal proteases and proteasome inhibitors strongly enhanced phage-mediated luciferase expression, suggesting that these pathways contribute to the destruction of intracellular phage particles. In contrast, inhibition of endosome acidification had no effect on phage-mediated gene transfer, presumably because phage lambda is tolerant to extended exposure to low pH. These findings provide insights into the pathways by which phage vectors enter and transduce mammalian cells, and suggest that it may be possible to pharmacologically enhance the efficiency of phage-mediated gene transfer in mammalian cells. Finally, the data also suggest that the proteasome complex may serve as an innate defense mechanism that restricts the infection of mammalian cells by diverse viral agents.

In vivo gene delivery and expression by bacteriophage lambda vectors

Aims

Bacteriophage vectors have potential as gene transfer and vaccine delivery vectors because of their low cost, safety and physical stability. However, little is known concerning phage-mediated gene transfer in mammalian hosts. We therefore performed experiments to examine phage-mediated gene transfer in vivo.

Methods and Results

Mice were inoculated with recombinant lambda phage containing a mammalian expression cassette encoding firefly luciferase (luc). Efficient, dose-dependent in vivo luc expression was detected, which peaked within 24 h of delivery and declined to undetectable levels within a week. Display of an integrin-binding peptide increased cellular internalization of phage in vitro and enhanced phage-mediated gene transfer in vivo. Finally, in vivo depletion of phagocytic cells using clodronate liposomes had only a minor effect on the efficiency of phage-mediated gene transfer.

Conclusions

Unmodified lambda phage particles are capable of transducing mammalian cells in vivo, and may be taken up – at least in part – by nonphagocytic mechanisms. Surface modifications that enhance phage uptake result in more efficient in vivo gene transfer.

Significance and Impact of the Study

These experiments shed light on the mechanisms involved in phage-mediated gene transfer in vivo, and suggest new approaches that may enhance the efficiency of this process.

Purification and concentration of bacteriophage T4 using monolithic chromatographic supports

Phages are gaining importance due to their wide usage. In this work strong anion exchange monolithic chromatographic column was used for single step phage purification. Most of the proteins and DNA were removed and recovery of approximately 70% of infective virus was reproducibly achieved. 30 ml of phage sample was purified in around 10 min.

A tractable method for simultaneous modifications to the head and tail of bacteriophage lambda and its application to enhancing phage-mediated gene delivery

There is considerable interest in the use of bacteriophage vectors for mammalian cell gene transfer applications, due to their stability, excellent safety profile and inexpensive mass production. However, to date, phage vectors have been plagued by mediocre performance as gene transfer agents. This may reflect the complexity of the viral infection process in mammalian cells and the need to refine each step of this process in order to arrive at an optimal, phage-based gene transfer system. Therefore, a flexible system was designed that alowed for the introduction of multiple modifications on the surface of bacteriophage lambda. Using this novel method, multiple peptides were displayed simultaneously from both the phage head and tail. Surface head display of an ubiquitinylation motif greatly increased the efficiency of phage-mediated gene transfer in a murine macrophage cell line. Gene transfer was further increased when this peptide was displayed in combination with a tail-displayed CD40-binding motif. Overall, this work provides a novel system that can be used to rationally improve bacteriophage gene transfer vectors and shows it may be possible to enhance the efficiency of phage-mediated gene transfer by targeting and optimizing multiple steps within the viral infection pathway.

Bacteriophages and biotechnology: vaccines, gene therapy and antibacterials

In recent years it has been recognized that bacteriophages have several potential applications in the modern biotechnology industry: they have been proposed as delivery vehicles for protein and DNA vaccines; as gene therapy delivery vehicles; as alternatives to antibiotics; for the detection of pathogenic bacteria; and as tools for screening libraries of proteins, peptides or antibodies. This diversity, and the ease of their manipulation and production, means that they have potential uses in research, therapeutics and manufacturing in both the biotechnology and medical fields. It is hoped that the wide range of scientists, clinicians and biotechnologists currently researching or putting phages to practical use are able to pool their knowledge and expertise and thereby accelerate progress towards further development in this exciting field of biotechnology.

Production in Saccharomyces cerevisiae of MS2 virus-like particles packaging functional heterologous mRNAs

Recently, DNA bacteriophages (M13, lambda) have been genetically engineered to transfer genes into mammalian cells. Although efficiencies observed are still relatively low, this opens the possibility of using these viruses as a new class of transfection agents not only for fundamental research purposes but also in gene therapy protocols or in other applications like vaccination. In this respect, it has been shown that a lambda bacteriophage engineered to express the hepatitis B surface antigen in mammalian cells could elicit an immune response against this antigen in mice and rabbits without any specific targeting of the bacteriophage. These impressive results would be even more encouraging if they could be obtained with an RNA bacteriophage, as RNA vaccines are preferred over DNA vaccines for safety reasons. Up to now, RNA bacteriophages have never been engineered for gene delivery. In this paper, we have sought to determine whether such a vector could be obtained by engineering the RNA bacteriophage MS2. We show that MS2 can be produced as virus-like particles (VLPs) in Saccharomyces cerevisiae and is able to package functional heterologous mRNAs, provided that these mRNAs contain the MS2 packaging sequence. For instance, linking the MS2 packaging sequence to the human growth hormone (hGH) mRNA enabled the packaging of this particular mRNA in MS2 VLPs. Functionality in eukaryotic systems of packaged mRNAs was confirmed by showing that mRNAs purified from VLPs can be efficiently translated in vitro and in cell cultures. The high stability of MS2 could, therefore, make MS2 VLPs a very powerful carrier for RNA vaccines.

Construction and exploitation in model experiments of functional selection of a landscape library expressed from a phagemid

Phage display has evolved during the past 15 years as a powerful technique to select, from libraries of peptides or proteins, binders for various targets or to evolve new functions in proteins. In recent years, the knowledge acquired in phage display technology was exploited to engineer phages as vehicles for receptor-mediated gene delivery. The first vectors generated provided the proof of the concept that development of gene delivery vehicles based on phages was feasible. Results obtained showed that the level of receptor ligand display was an essential factor that determines the efficiency of transduction and suggested that phagemids might be more appropriate than phages for gene delivery. However, due to the limitations of the existing display systems, vectors constructed up to now allowed only relatively low levels of ligand display. The transduction efficiency of these vectors was relatively poor. Here, we describe the construction and optimization of a new phagemid display system that was designed to allow the functional selection of peptides that promote gene delivery from phagemids in a high display format. Peptides are displayed on every copy of the major coat protein pVIII and are expressed from the phagemid itself. The phagemid is rescued as particles by a modified R408 helper phage, deficient in pVIII production. Besides an expression cassette for pVIII, the phagemid also contains the SV40 origin of replication, the GFP gene and the neomycin resistance marker. As a model we constructed a library of octapeptides and showed that the library is amenable to selection on cos-7 cells. Several selection approaches were investigated and a preliminary analysis of the peptides selected was carried out.

Protein transduction domain of HIV-1 Tat protein promotes efficient delivery of DNA into mammalian cells

The plasma membrane of mammalian cells is one of the tight barriers against gene transfer by synthetic delivery systems. Various agents have been used to facilitate gene transfer by destabilizing the endosomal membrane under acidic conditions, but their utility is limited, especially for gene transfer in vivo. In this article, we report that the protein transduction domain of human immunodeficiency virus type 1 Tat protein (Tat peptide) greatly facilitates gene transfer via membrane destabilization. We constructed recombinant lambda phage particles displaying Tat peptide on their surfaces and carrying mammalian marker genes as part of their genomes (Tat-phage). We demonstrate that, when animal cells are briefly exposed to Tat-phage, significant expression of phage marker genes is induced with no harmful effects to the cells. In contrast, recombinant phage displaying other functional peptides, such as the integrin-binding domain or a nuclear localization signal, could not induce detectable marker gene expression. The expression of marker genes induced by Tat-phage is not affected by endosomotropic agents but is partially impaired by inhibitors of caveolae formation. These data suggest that Tat peptide will become a useful component of synthetic delivery vehicles that promote gene transfer independently of the classical endocytic pathway.

Gene transfer to mammalian cells using genetically targeted filamentous bacteriophage

We have genetically modified filamentous bacteriophage to deliver genes to mammalian cells. In previous studies we showed that noncovalently attached fibroblast growth factor (FGF2) can target bacteriophage to COS-1 cells, resulting in receptor-mediated transduction with a reporter gene. Thus, bacteriophage, which normally lack tropism for mammalian cells, can be adapted for mammalian cell gene transfer. To determine the potential of using phage-mediated gene transfer as a novel display phage screening strategy, we transfected COS-1 cells with phage that were engineered to display FGF2 on their surface coat as a fusion to the minor coat protein, pIII. Immunoblot and ELISA analysis confirmed the presence of FGF2 on the phage coat. Significant transduction was obtained in COS-1 cells with the targeted FGF2-phage compared with the nontargeted parent phage. Specificity was demonstrated by successful inhibition of transduction in the presence of excess free FGF2. Having demonstrated mammalian cell transduction by phage displaying a known gene targeting ligand, it is now feasible to apply phage-mediated transduction as a screen for discovering novel ligands.

Targeted delivery of multivalent phage display vectors into mammalian cells

Novel peptide motives targeting endocytosing receptors were isolated from phage display libraries of random peptides by recovering internalized phage from mammalian cells. The peptide-presenting phage selected by internalization in HEp-2 and ECV304 human cells were taken up 1000- to 100,000-fold more efficiently than their parent libraries, and from 10 to 100 times faster than phage particles displaying integrin-binding peptides. A high degree of selectivity of phage uptake was observed in these cells: phage selected in ECV304 cells were internalized approximately 100-fold more efficiently in ECV304 cells than in HEp-2 cells. Likewise, phage selected in HEp-2 cells were subsequently taken up approximately 40-fold more efficiently by HEp-2 cells than by ECV304 cells. In multiple independent trials using a cyclic peptide library, an identical peptide sequence displayed on phage was internalized by and recovered from ECV304 cells. These findings indicate that the internalization process is highly selective, and is capable of capturing a specific peptide from 2 x 10(7) peptide variants. Immunofluorescence microscopy showed juxtanuclear localization of internalized phage. These results demonstrate the feasibility of using multivalent phage-display libraries to identify new targeting ligands for the intracellular delivery of macromolecules.

Uptake and intracellular fate of phage display vectors in mammalian cells

Receptor-mediated endocytosis is exploited in experimental systems for selective delivery of genes and drugs into specific cells. To improve targeting efficiency of delivery vectors, we have used phage display technology to isolate novel ligands for endocytosed receptors. We show here that phage vectors internalized by mammalian cells via integrin-mediated endocytosis can be rescued by cell lysis and quantitated by infection of bacteria. Immediately following uptake, phage enter an intracellular compartment where they remain intact, with phage titer unaffected by the addition of chloroquine. Phage are then translocated to a second intracellular compartment in which they are inactivated and their titer affected by chloroquine. Immunofluorescence microscopy showed an association of the second compartment with supranuclear organelles. The ability to recover internalized phage in an infectious form from two distinctive intracellular compartments provides a means to select novel ligands from phage libraries for targeted delivery of macromolecules into mammalian cells.

Targeting bacteriophage to mammalian cell surface receptors for gene delivery

Filamentous bacteriophages represent one of nature's most elegant ways of packaging and delivering DNA. In an effort to develop novel methods for ligand discovery via phage gene delivery, we conferred mammalian cell tropism to filamentous bacteriophages by attaching basic fibroblast growth factor (FGF2), transferrin, or epidermal growth factor (EGF) to their coat proteins and measuring CMV promoter-driven reporter gene expression in target cells. In this system, FGF2 was a more effective targeting agent than transferrin or EGF. The detection of green fluorescent protein (GFP) or beta-galactosidase (beta-Gal) activity in cells required FGF2 targeting and was phage concentration dependent. Specificity of the targeting for high-affinity FGF receptors was demonstrated by competing the targeted phage with FGF2, by the failure of FGF2-targeted bacteriophage to transduce high-affinity FGF receptor-negative cells, and by their ability to transduce these same cells when stably transfected with FGFR1, a high-affinity FGF receptor. Long-term transgene expression was established by selecting colonies for G418 resistance, suggesting that with the appropriate targeted tropism, filamentous bacteriophage can serve as a vehicle for targeted gene delivery to mammalian cells.