Gene therapy for cancer: bacteria-mediated anti-angiogenesis therapy. Gene Ther. 2011;18:425-431. [PMID: 21228886 DOI: 10.1038/gt.2010.176]

Pragmatic Expectancy on Microbiota and Non-Small Cell Lung Cancer: A Narrative Review

It is well known that lung cancer relies on a number of genes aberrantly expressed because of somatic lesions. Indeed, the lungs, based on their anatomical features, are organs at a high risk of development of extremely heterogeneous tumors due to the exposure to several environmental toxic agents. In this context, the microbiome identifies the whole assemblage of microorganisms present in the lungs, as well as in distant organs, together with their structural elements and metabolites, which actively interact with normal and transformed cells. A relevant amount of data suggest that the microbiota plays a role not only in cancer disease predisposition and risk but also in its initiation and progression, with an impact on patients’ prognosis. Here, we discuss the mechanistic insights of the complex interaction between lung cancer and microbiota as a relevant component of the microenvironment, mainly focusing on novel diagnostic and therapeutic objectives.

Genetically modified cancer vaccines: Current status and future prospects

Vaccines can stimulate the immune system to protect individuals from infectious diseases. Moreover, vaccines have also been applied to the prevention and treatment of cancers. Due to advances in genetic engineering technology, cancer vaccines could be genetically modified to increase antitumor efficacy. Various genes could be inserted into cells to boost the immune response, such as cytokines, T cell costimulatory molecules, tumor-associated antigens, and tumor-specific antigens. Genetically modified cancer vaccines utilize innate and adaptive immune responses to induce durable antineoplastic capacity and prevent the recurrence. This review will discuss the major approaches used to develop genetically modified cancer vaccines and explore recent advances to increase the understanding of engineered cancer vaccines.

Bacteria and bacterial derivatives as delivery carriers for immunotherapy

There is growing interest in the role of microorganisms in human health and disease, with evidence showing that new types of biotherapy using engineered bacterial therapeutics, including bacterial derivatives, can address specific mechanisms of disease. The complex interactions between microorganisms and metabolic/immunologic pathways underlie many diseases with unmet medical needs, suggesting that targeting these interactions may improve patient treatment. Using tools from synthetic biology and chemical engineering, non-pathogenic bacteria or bacterial products can be programmed and designed to sense and respond to environmental signals to deliver therapeutic effectors. This review describes current progress in biotherapy using live bacteria and their derivatives to achieve therapeutic benefits against various diseases.

The Evolution and Future of Targeted Cancer Therapy: From Nanoparticles, Oncolytic Viruses, and Oncolytic Bacteria to the Treatment of Solid Tumors

While many classes of chemotherapeutic agents exist to treat solid tumors, few can generate a lasting response without substantial off-target toxicity despite significant scientific advancements and investments. In this review, the paths of development for nanoparticles, oncolytic viruses, and oncolytic bacteria over the last 20 years of research towards clinical translation and acceptance as novel cancer therapeutics are compared. Novel nanoparticle, oncolytic virus, and oncolytic bacteria therapies all start with a common goal of accomplishing therapeutic drug activity or delivery to a specific site while avoiding off-target effects, with overlapping methodology between all three modalities. Indeed, the degree of overlap is substantial enough that breakthroughs in one therapeutic could have considerable implications on the progression of the other two. Each oncotherapeutic modality has accomplished clinical translation, successfully overcoming the potential pitfalls promising therapeutics face. However, once studies enter clinical trials, the data all but disappears, leaving pre-clinical researchers largely in the dark. Overall, the creativity, flexibility, and innovation of these modalities for solid tumor treatments are greatly encouraging, and usher in a new age of pharmaceutical development.

Emerging applications of bacteria as antitumor agents

Bacteria are associated with the human body and colonize the gut, skin, and mucous membranes. These associations can be either symbiotic or pathogenic. In either case, bacteria derive more benefit from their host. The ability of bacteria to enter and survive within the human body can be exploited for human benefit. They can be used as a vehicle for delivering or producing bioactive molecules, such as toxins and lytic enzymes, and eventually for killing tumor cells. Clostridium and Salmonella have been shown to infect and survive within the human body, including in tumors. There is a need to develop genetic circuits, which enable bacterial cells to carry out the following activities: (i) escape the human immune system, (ii) invade tumors, (iii) multiply within the tumorous cells, (iv) produce toxins via quorum sensing at low cell densities, and (v) express suicide genes to undergo cell death or cell lysis after the tumor has been lysed. Thus, bacteria have the potential to be exploited as anticancer agents.

Microbes as Medicines: Harnessing the Power of Bacteria in Advancing Cancer Treatment

Conventional anti-cancer therapy involves the use of chemical chemotherapeutics and radiation and are often non-specific in action. The development of drug resistance and the inability of the drug to penetrate the tumor cells has been a major pitfall in current treatment. This has led to the investigation of alternative anti-tumor therapeutics possessing greater specificity and efficacy. There is a significant interest in exploring the use of microbes as potential anti-cancer medicines. The inherent tropism of the bacteria for hypoxic tumor environment and its ability to be genetically engineered as a vector for gene and drug therapy has led to the development of bacteria as a potential weapon against cancer. In this review, we will introduce bacterial anti-cancer therapy with an emphasis on the various mechanisms involved in tumor targeting and tumor suppression. The bacteriotherapy approaches in conjunction with the conventional cancer therapy can be effective in designing novel cancer therapies. We focus on the current progress achieved in bacterial cancer therapies that show potential in advancing existing cancer treatment options and help attain positive clinical outcomes with minimal systemic side-effects.

Oncolytic bacteria: past, present and future

More than a century ago, independent groups raised the possibility of using bacteria to selectively infect tumours. Such treatment induces an immune reaction that can cause tumour rejection and protect the patient against further recurrences. One of the first holistic approximations to use bacteria in cancer treatment was performed by William Coley, considered the father of immune-therapy, at the end of XIX century. Since then, many groups have used different bacteria to test their antitumour activity in animal models and patients. The basis for this reactivity implies that innate immune responses activated upon bacteria recognition, also react against the tumour. Different publications have addressed several aspects of oncolytic bacteria. In the present review, we will focus on revisiting the historical aspects using bacteria as oncolytic agents and how they led to the current clinical trials. In addition, we address the molecules present in oncolytic bacteria that induce specific toxic effects against the tumors as well as the activation of host immune responses in order to trigger antitumour immunity. Finally, we discuss future perspectives that could be considered in the different fields implicated in the implementation of this kind of therapy in order to improve the current use of bacteria as oncolytic agents.

Bioengineered smart bacterial carriers for combinational targeted therapy of solid tumours

Despite many endeavours for the development of new anticancer drugs, effective therapy of solid tumours remains a challenging issue. The current cancer chemotherapies may associate with two important limitations, including the lack/trivial specificity of treatment modalities towards diseased cells/tissues resulting in undesired side effects, and the emergence of drug-resistance mechanisms by tumour cells causing the failure of the treatment. Much attention, therefore, has currently been paid to develop smart and highly specific anticancer agents with maximal therapeutic impacts and minimal side effects. Among various strategies used to target cancer cells, bacteria-based cancer therapies (BCTs) have been validated as potential gene/drug delivery carriers, which can also be engineered to be used in diagnosis processes. They can be devised to selectively target the tumour microenvironment (TME), within which they may preferentially proliferate in the necrotic and anaerobic parts - often inaccessible to other therapeutics. BCTs are capable to sense and respond to the environmental signals, upon which they are considered as smart microrobots applicable in the controlled delivery of therapeutic agents to the TME. In this review, we aimed to provide comprehensive insights into the potentials of the bioengineered bacteria as smart and targeted bio-carriers and discuss their applications in cancer therapy.

The role of bacterial toxins and spores in cancer therapy

Cancer is one of the leading causes of human death worldwide. Conventional anticancer therapies are ineffective in treating cancer patients due to various reasons. Thus, more effective and accessible alternative anticancer strategies have been evolved with time with high specificity towards tumor cells and with less or no adverse effects to normal cells. One such promising therapy is the use of bacterial toxins and spores to treat advanced solid tumors. Initially, Coley paved the way towards the bacterial anticancer therapy several decades ago and now it has emerged as a potential tool to eliminate tumor cells. Bacterial spores of obligate anaerobes exclusively germinate in the hypoxic/necrotic areas and not in the well-oxygenated areas of the body. This unique phenomenon has been exploited in using bacterial spores as a remedy for cancer. Bacterial toxins also play a significant role in either directly killing tumor cells or altering the cellular processes of the tumor cells which ultimately leads to the inhibition and regression of the solid tumor. With the advancement of molecular techniques, a number of genetically-modified non-pathogenic bacteria have been developed to use in bacterial anticancer strategies. Although promising results have shown so far, further investigations are required to ensure the efficacy and the safety of the bacterial spores and toxins in treating cancer.

A microfluidic device for studying chemotaxis mechanism of bacterial cancer targeting

Bacterial cancer targeting may become an efficacious cancer therapy, but the mechanisms underlying bacterial specificity for cancer cells need to be explored prior to adopting it as a new clinical application. To characterize the mechanism of bacterial chemotactic preference towards cancer cells, we developed a microfluidic device for in vitro study. The device consists of a cell culture chamber on both sides of a central bacteria channel, with micro-channels used as barriers between them. The device, when used as model for lung cancer, was able to provide simultaneous three-dimensional co-culture of multiple cell lines in separate culture chambers, and when used as model for bacterial chemotaxis, established constant concentration gradients of biochemical compounds in a central channel by diffusion through micro-channels. Fluorescence intensity of green fluorescence protein (GFP)-encoding bacteria was used to measure bacterial taxis behavior due to established chemotactic gradients. Using this platform, we found that Escherichia coli (E. coli) clearly illustrated the preference for lung cancer cells (NCI-H460) which was attributed to biochemical factors secreted by carcinoma cells. Furthermore, by secretome analysis and validation experiments, clusterin (CLU) was found as a key regulator for the chemotaxis of E. coli in targeting lung cancer.

The role of bacteria in cancer therapy - enemies in the past, but allies at present

In recent decades, bacteria’s therapeutic role has aroused attention in medicinal and pharmaceutical research. While bacteria are considered among the primary agents for causing cancer, recent research has shown intriguing results suggesting that bacteria can be effective agents for cancer treatment – they are the perfect vessels for targeted cancer therapy. Several bacterial strains/species have been discovered to possess inherent oncolytic potentials to invade and colonize solid tumors in vivo. The therapeutic strategy of using bacteria for treating cancer is considered to be effective; however, the severe side effects encountered during the treatment resulted in the abandonment of the therapy. State-of-the-art genetic engineering has been recently applied to bacteria therapy and resulted in a greater efficacy with minimum side effects. In addition, the anti-cancer potential of tumor-targeting bacteria through oral administration circumvents the use of the intravenous route and the associated adverse effects. This review aims to provide a comprehensive summary of the latest literature on the role of bacteria in cancer treatment.

Isolation and screening of proangiogenic and antiangiogenic metabolites producing rare actinobacteria from soil

AIMS

Angiogenesis is a physiological process that has important impacts on the pathology and healing of various diseases, and its induction or inhibition by bioactive actinobacterial metabolites can help the treatment of some diseases. In this study, the effects of actinobacterial extract in the process of angiogenesis have been explored.

METHODS AND RESULTS

In this research, proangiogenic and antiangiogenic metabolites producing actinobacteria were isolated from soil samples and their fermentation broth were extracted and after evaluation of their toxicity by MTT assay, antiangiogenic and proangiogenic activities were screened against human umbilical vein endothelial cells (HUVECs) by in vitro tube formation and migration assay. Isolated strains were identified through molecular techniques. The results showed that Nocardiopsis arvandica UTMC 103 and Nonomuraea sp. UTMC 2180 extracts had a high potential of anti-angiogenic activity on HUVECs.

CONCLUSIONS

For the first time proangiogenic potency of a rare actinobacterium, Kribbella sp. UTMC 522, was reported, and N. arvandica UTMC 103 and Nonomuraea sp. UTMC 2180 extracts inhibits the proliferation, migration and angiogenesis activity of HUVECs with reasonable potency.

SIGNIFICANCE AND IMPACT OF THE STUDY

Metabolites of the introduced rare actinobacteria are potent proangiogenic and angiogenic inhibitors. Identification of angiogenic-antiangiogenic mechanisms and purification of the extracts would be useful in therapeutic angiogenesis.

Tumor rim cells: From resistance to vascular targeting agents to complete tumor ablation

Current vascular targeting strategies pursue two main goals: anti-angiogenesis agents aim to halt sprouting and the formation of new blood vessels, while vascular disrupting agents along with coaguligands seek to compromise blood circulation in the vessels. The ultimate goal of such therapies is to deprive tumor cells out of oxygen and nutrients long enough to succumb cancer cells to death. Most of vascular targeting agents presented promising therapeutic potential, but the final goal which is cure is rarely achieved. Nevertheless, in both preclinical and clinical settings, tumors tend to grow back, featuring a highly invasive, metastatic, and extremely resistant form. This review highlights the critical significance of tumor rim cells as the main factor, determining therapy success with vascular targeting agents. We present an overview of different single and combination treatments with vascular targeting agents that enable efficient targeting of tumor rim cells and long-lasting tumor cure. Understanding the nature of tumor rim cells, how they establish, how they manage to survive of vascular targeting agents, and how they contribute in tumor refractoriness, may open new avenues to the development of beneficial strategies, capable to eliminate residual rim cells, and enable tumor ablation once and forever.

Ultrasound-targeted microbubble destruction in gene therapy: A new tool to cure human diseases

Human gene therapy has made significant advances in less than two decades. Within this short period of time, gene therapy has proceeded from the conceptual stage to technology development and laboratory research, and finally to clinical trials for the treatment of a variety of deadly diseases. Cardiovascular disease, cancer, and stroke are leading causes of death worldwide. Despite advances in medical, interventional, radiation and surgical treatments, the mortality rate remains high, and the need for novel therapies is great. Gene therapy provides an efficient approach to disease treatment. Notable advances in gene therapy have been made for genetic disorders, including severe combined immune deficiency, chronic granulomatus disorder, hemophilia and blindness, as well as for acquired diseases, including cancer and neurodegenerative and cardiovascular diseases. However, lack of an efficient delivery system to target cells as well as the difficulty of sustained expression of transgenes has hindered advancements in gene therapy. Ultrasound targeted microbubble destruction (UTMD) is a promising approach for target-specific gene delivery, and it has been successfully investigated for the treatment of many diseases in the past decade. In this paper, we review UTMD-mediated gene delivery for the treatment of cardiovascular diseases, cancer and stroke.

Combined prokaryotic-eukaryotic delivery and expression of therapeutic factors through a primed autocatalytic positive-feedback loop

Progress in bacterial therapy for cancer and infectious diseases is hampered by the absence of safe and efficient vectors. Sustained delivery and high gene expression levels are critical for the therapeutic efficacy. Here we developed a Salmonella typhimrium strain to maintain and safely deliver a plasmid vector to target tissues. This vector is designed to allow dual transcription of therapeutic factors, such as cytotoxic proteins, short hairpin RNAs or combinations, in the nucleus or cytoplasm of eukaryotic cells, with this expression sustained by an autocatalytic positive-feedback loop. Mechanisms to prime the system and maintain the plasmid in the bacterium are also provided. Synergistic effects of attenuated Salmonella and our inter-kingdom system allow the precise expression of Diphtheria toxin A chain (DTA) gene in tumor microenvironment and eradicate large established tumors in immunocompetent animals. In the experiments reported here, 26% of mice (n=5/19) with aggressive tumors were cured and the others all survived until the end of the experiment. We also demonstrated that ST4 packaged with shRNA-encoding plasmids has sustained knockdown effects in nude mice bearing human MDA-MB-231 xenografts. Three weeks after injection of 5×10(6) ST4/pIKT-shPlk, PLK1 transcript levels in tumors were 62.5±18.6% lower than the vector control group (P=0.015). The presence of PLK1 5' RACE-PCR cleavage products confirmed a sustained RNAi-mediated mechanism of action. This innovative technology provides an effective and versatile vehicle for efficient inter-kingdom gene delivery that can be applied to cancer therapy and other purposes.

Effect of DSS on Bacterial Growth in Gastrointestinal Tract

Inflammatory bowel disease is an idiopathic autoimmune disorder that is mainly divided into ulcerative colitis and Crohn's disease. Probiotics are known for their beneficial effect and used as a treatment option in different gastrointestinal problems. The aim of our study was to find suitable bacterial vectors for gene therapy of inflammatory bowel disease. Salmonella enterica serovar Typhimurium SL7207 and Escherichia coli Nissle 1917 were investigated as potential vectors. Our results show that the growth of Escherichia coli Nissle 1917 was inhibited in the majority of samples collected from dextran sodium sulphate-treated animals compared with control growth in phosphate-buffered saline. The growth of Salmonella enterica serovar Typhimurium SL7207 in all investigated samples was enhanced or unaffected in comparison with phosphate-buffered saline; however, it did not reach the growth rates of Escherichia coli Nissle 1917. Dextran sodium sulphate treatment had a stimulating effect on the growth of both strains in homogenates of distant small intestine and proximal colon samples. The gastrointestinal tract contents and tissue homogenates did not inhibit growth of Salmonella enterica serovar Typhimurium SL7207 in comparison with the negative control, and provided more suitable environment for growth compared to Escherichia coli Nissle 1917. We therefore conclude that Salmonella enterica serovar Typhimurium SL7207 is a more suitable candidate for a potential bacterial vector, even though it has no known probiotic properties.

Live-Attenuated Bacterial Vectors: Tools for Vaccine and Therapeutic Agent Delivery

Genetically attenuated microorganisms, including pathogenic and commensal bacteria, can be engineered to carry and deliver heterologous antigens to elicit host immunity against both the vector as well as the pathogen from which the donor gene is derived. These live attenuated bacterial vectors have been given much attention due to their capacity to induce a broad range of immune responses including localized mucosal, as well as systemic humoral and/or cell-mediated immunity. In addition, the unique tumor-homing characteristics of these bacterial vectors has also been exploited for alternative anti-tumor vaccines and therapies. In such approach, tumor-associated antigen, immunostimulatory molecules, anti-tumor drugs, or nucleotides (DNA or RNA) are delivered. Different potential vectors are appropriate for specific applications, depending on their pathogenic routes. In this review, we survey and summarize the main features of the different types of live bacterial vectors and discussed the clinical applications in the field of vaccinology. In addition, different approaches for using live attenuated bacterial vectors for anti-cancer therapy is discussed, and some promising pre-clinical and clinical studies in this field are outlined.

Pathological and therapeutic interactions between bacteriophages, microbes and the host in inflammatory bowel disease

The intestinal microbiome is a dynamic system of interactions between the host and its microbes. Under physiological conditions, a fine balance and mutually beneficial relationship is present. Disruption of this balance is a hallmark of inflammatory bowel disease (IBD). Whether an altered microbiome is the consequence or the cause of IBD is currently not fully understood. The pathogenesis of IBD is believed to be a complex interaction between genetic predisposition, the immune system and environmental factors. In the recent years, metagenomic studies of the human microbiome have provided useful data that are helping to assemble the IBD puzzle. In this review, we summarize and discuss current knowledge on the composition of the intestinal microbiota in IBD, host-microbe interactions and therapeutic possibilities using bacteria in IBD. Moreover, an outlook on the possible contribution of bacteriophages in the pathogenesis and therapy of IBD is provided.

Tumor-targeting bacterial therapy: A potential treatment for oral cancer (Review)

Certain obligate or facultative anaerobic bacteria, which exhibit an inherent ability to colonize solid tumors in vivo, may be used in tumor targeting. As genetically manipulated bacteria may actively and specifically penetrate into the tumor tissue, bacterial therapy is becoming a promising approach in the treatment of tumors. However, to the best of our knowledge, no reports have been published thus far regarding the bacterial treatment of oral cancer, one of the most common types of cancer worldwide. In this review, the progress in the understanding of bacterial strategies used in tumor-targeted therapy is discussed and particular bacterial strains that may have great therapeutic potential in oral squamous cell carcinoma (OSCC) tumor-targeted therapy are predicted as determined by previous studies.

Effect of nonviral plasmid delivered basic fibroblast growth factor and low intensity pulsed ultrasound on mandibular condylar growth: a preliminary study

OBJECTIVE

Basic fibroblast growth factor (bFGF) is an important regulator of tissue growth. Previous studies have shown that low intensity pulsed ultrasound (LIPUS) stimulates bone growth. The objective of this study was to evaluate the possible synergetic effect of LIPUS and local injection of nonviral bFGF plasmid DNA (pDNA) on mandibular growth in rats.

DESIGN

Groups were control, blank pDNA, bFGF pDNA, LIPUS, and bFGF pDNA + LIPUS. Treatments were performed for 28 days. Significant increase was observed in mandibular height and condylar length in LIPUS groups. MicroCT analysis showed significant increase in bone volume fraction in bFGF pDNA + LIPUS group. Histomorphometric analysis showed increased cell count and condylar proliferative and hypertrophic layers widths in bFGF pDNA group.

RESULTS

Current study showed increased mandibular condylar growth in either bFGF pDNA or LIPUS groups compared to the combined group that showed only increased bone volume fraction.

CONCLUSION

It appears that there is an additive effect of bFGF + LIPUS on the mandibular growth.

A novel microfluidic co-culture system for investigation of bacterial cancer targeting

Although bacterial cancer targeting in animal models has been previously demonstrated and suggested as a possible therapeutic tool, a thorough understanding of the mechanisms responsible for cancer specificity would be required prior to clinical applications. To visualize bacterial preference for cancer cells over normal cells and to elucidate the cancer-targeting mechanism, a simple microfluidic platform has been developed for in vitro studies. This platform allows simultaneous cultures of multiple cell types in independent culture environments in isolated chambers, and creates a stable chemical gradient across a collagen-filled passage between each of these cell culture chambers and the central channel. The established chemical gradient induces chemotactic preferential migration of bacteria toward a particular cell type for quantitative analysis. As a demonstration, we tested differential bacterial behavior on a two-chamber device where we quantified bacterial preference based on the difference in fluorescence intensities of green fluorescence protein (GFP)-expressing bacteria at two exits of the collagen-filled passages. Analysis of the chemotactic behavior of Salmonella typhimurium toward normal versus cancer hepatocytes using the developed platform revealed an apparent preference for cancer hepatocytes. We also demonstrate that alpha-fetoprotein (AFP) is one of the key chemo-attractants for S. typhimurium in targeting liver cancer.

Therapeutic DNA vaccination and RNA interference in inflammatory bowel disease

Angiogenesis plays a significant role in numerous diseases. Recently, dysbalanced angiogenesis was found to be a component of pathogenesis of inflammatory bowel disease (IBD). Therefore, inhibition of angiogenesis is a novel therapeutic strategy that alleviates the inflammation and clinical outcomes of IBD. Bacteria act as vectors for the delivery of therapeutic sequences, a process that is particularly suitable in IBD, due to the natural occurrence of bacteria in gut. The main focus of the present study was the application of bacterial gene therapy in the modulation of angiogenesis in IBD. As a target molecule we used the main proangiogenic factor, vascular endothelial growth factor (VEGF). Bacterial strain Salmonella typhimurium SL7207 was used as a gene delivery vector for oral application. DNA vaccination and RNA interference were examined and their efficiency in improving the course of the disease in dextran sulfate sodium-induced colitis in mice was compared. The two approaches yielded similar beneficial results in evaluation of the disease activity parameters (stool consistency, weight loss and colon length) as well as VEGF expression and tumor necrosis factor-α (TNF-α). Improvement in all of the parameters compared with the control groups not treated by therapeutic bacterial strains was also observed. All the bacterial groups showed similar improvement in histopathological scoring. Results of this study are consistent with the literature and provide a basis for additional studies on the modulation of angiogenesis in IBD.

Optimization of Ultrasound-mediated Anti-angiogenic Cancer Gene Therapy

Ultrasound-targeted microbubble destruction (UTMD) can be used to deliver silencing gene therapy to tumors. We hypothesized that UTMD would be effective in suppressing angiogenesis within tumors, and that modulation of the ultrasound pulsing intervals (PI) during UTMD would affect the magnitude of target knockdown. We performed UTMD of vascular endothelial growth factor receptor-2 (VEGFR2) short hairpin (sh)RNA plasmid in an heterotopic mammary adenocarcinoma model in rats, evaluating PIs of 2, 5, 10, and 20 seconds. We demonstrated that UTMD with a PI of 10 seconds resulted in the greatest knockdown of VEGFR2 by PCR, immunostaining, western blotting, smaller tumor volumes and perfused areas, and lower tumor microvascular blood volume (MBV) and flow by contrast-enhanced ultrasound (CEU) compared with UTMD-treated tumors at 2, 5, and 20 seconds, control tumors, tumors treated with intravenous shRNA plasmid and scrambled plasmid. CEU perfusion assessment using the therapeutic probe demonstrated that tumors were fully replenished with microbubbles within 10 seconds, but incompletely replenished at PI-2 and PI-5 seconds. In conclusion, for anti-VEGFR2 cancer gene therapy by UTMD, PI of 10 seconds results in higher target knockdown and a greater anti-angiogenic effect. Complete replenishment of tumor vasculature with silencing gene-bearing microbubbles in between destructive pulses of UTMD is required to maximize the efficacy of anti-angiogenic cancer gene therapy.Molecular Therapy - Nucleic Acids (2013) 2, e94; doi:10.1038/mtna.2013.20; published online 21 May 2013.

Recombinant attenuated Salmonella typhimurium carrying a plasmid co-expressing ENDO-VEGI151 and survivin siRNA inhibits the growth of breast cancer in vivo

The aim of this study was to investigate the antitumor effect of a plasmid co-expressing ENDO-VEGI151 and survivin siRNA on breast cancer in nude mice, and to explore the feasibility of attenuated Salmonella typhimurium (S. typhimurium) as a delivery vector for cancer gene therapy in vivo. Three recombinant expression plasmids pENDO‑VEGI151 (pEV), pSurvivin-siRNA (psi-survivin) and co-expressing plasmid pENDO-VEGI151/survivin‑siRNA (pEV/si-survivin), were transferred into the attenuated S. typhimurium strain SL7207, respectively. MDA-MB-231 cells were infected with these recombinants in vitro, and the expression of ENDO-VEGI151 and survivin was detected. In order to detect S. typhimurium distribution and gene delivery efficiency in vivo, the plasmid pEGFP-N1 which encodes green fluorescent protein was transferred into SL7207, and the recombinant known as SL-pEGFP was orally administered to tumor-bearing nude mice. The gene transfer efficiency, distribution and survival time of the SL-pEGFP in vivo were evaluated by detection of GFP fluorescence. SL-pEGFP not only infected the cancer cells effectively, but also allowed the survival and expression of specific genes mainly in the xenografts of nude mice. To further identify the anticancer effects of these recombinants in vivo, mice burdened with xenografts were randomly divided into 6 groups, which were subjected to intragastric administration of vehicle, SL7207, SL-pcDNA3.1, SL-pEV, SL-psi-survivin and SL-pEV/si-survivin, respectively. Eight weeks after implantation, tumor size, weight, inhibition rate, intratumoral microvessel density (MVD), apoptotic index (AI), ENDO‑VEGI151 and survivin expression were evaluated. Compared with the SL-pEV or SL-psi-survivin-treated groups, the growth of tumors was significantly reduced in the SL-pEV/si-survivin group with an inhibition rate of 90.28 vs. 69.12 and 65.61%, respectively. MVD and the expression of survivin were decreased significantly in the SL-pEV/si-survivin-treated group, while AI increased significantly in the SL-pEV/si-survivin-treated group. These results indicated that attenuated S. typhimurium carrying the dual function plasmid pEV/si-survivin cannot only be specifically enriched in the tumor tissue, but also showed a synergistic antitumor effect in vivo.

Double-blind, placebo-controlled first in human study to investigate an oral vaccine aimed to elicit an immune reaction against the VEGF-Receptor 2 in patients with stage IV and locally advanced pancreatic cancer

Background

The investigational oral DNA vaccine VXM01 targets the vascular endothelial growth factor receptor 2 (VEGFR-2) and uses Salmonella typhi Ty21a as a vector. The immune reaction elicited by VXM01 is expected to disrupt the tumor neovasculature and, consequently, inhibit tumor growth. VXM01 potentially combines the advantages of anti-angiogenic therapy and active immunotherapy.

Methods/Design

This phase I trial examines the safety, tolerability, and immunological and clinical responses to VXM01. The randomized, placebo-controlled, double blind dose-escalation study includes up to 45 patients with locally advanced and stage IV pancreatic cancer. The patients will receive four doses of VXM01 or placebo in addition to gemcitabine as standard of care. Doses from 10⁶ cfu up to 10¹⁰ cfu of VXM01 will be evaluated in the study. An independent data safety monitoring board (DSMB) will be involved in the dose-escalation decisions. In addition to safety as primary endpoint, the VXM01-specific immune reaction, as well as clinical response parameters will be evaluated.

Discussion

The results of this study shall provide the first data regarding the safety and immunogenicity of the oral anti-VEGFR-2 vaccine VXM01 in cancer patients. They will also define the recommended dose for phase II and provide the basis for further clinical evaluation, which may also include additional cancer indications.

Trial registration

EudraCT No.: 2011-000222-29, NCT01486329, ISRCTN68809279

Suicide gene therapy in cancer: where do we stand now?

Suicide gene therapy is based on the introduction into tumor cells of a viral or a bacterial gene, which allows the conversion of a non-toxic compound into a lethal drug. Although suicide gene therapy has been successfully used in a large number of in vitro and in vivo studies, its application to cancer patients has not reached the desirable clinical significance. However, recent reports on pre-clinical cancer models demonstrate the huge potential of this strategy when used in combination with new therapeutic approaches. In this review, we summarize the different suicide gene systems and gene delivery vectors addressed to cancer, with particular emphasis on recently developed systems and associated bystander effects. In addition, we review the different strategies that have been used in combination with suicide gene therapy and provide some insights into the future directions of this approach, particularly towards cancer stem cell eradication.

Inducing pluripotency using in vivo gene therapy

Since the original study of Takahashi and Yamanaka in 2006 [1], the field of induced pluripotent stem (iPS) cells has made a great progress. Since then, a number of different cell types have been successfully brought to a state of pluripotency and a different set of transcription factors have been reported to be sufficient to reprogram mouse and human somatic cells. Although still with low efficiency of reprogramming, the patient- and disease-specific therapy represents the most valuable outcome of the whole area of iPS cells. Herein we hypothesize that inducing pluripotency in vivo might be an interesting alternative to the standard ex vivo methods. In vivo reprogramming would benefit from the direct administration of the DNA encoding the reprogramming factors into the target tissue/organ of an individual. The target cells that are to be reprogrammed would be transduced in their natural environment that can provide all the necessary molecular and spatial factors that could be missing during ex vivo reprogramming. However, since no available data exist on in vivo induced pluripotency, it is difficult to predict if testing the hypothesis will provide any promising results. On the way to this point, a number of pilot experiments have to be performed to overcome many limitations and pitfalls that are arising from such a risky concept. Safety issues, such as the risk of somatic tumor formation, will likely be the crucial point to focus on during the process of proving the validity of the hypothesis. However, initial data from the study on inflammatory bowel disease suggest that there might be some beneficial effect of in vivo gene therapy based on reprogramming the target cells.

A bioluminescent transposon reporter-trap identifies tumor-specific microenvironment-induced promoters in Salmonella for conditional bacterial-based tumor therapy

Salmonella specifically localize to malignant tumors in vivo, a trait potentially exploitable as a delivery system for cancer therapeutics. To characterize mechanisms and genetic responses of Salmonella during interaction with living neoplastic cells, we custom-designed a promoterless transposon reporter containing bacterial luciferase. Analysis of a library containing 7,400 independent Salmonella transposon insertion mutants in coculture with melanoma or colon carcinoma cells identified five bacterial genes specifically activated by cancer cells: adiY, yohJ, STM1787, STM1791, and STM1793. Experiments linked acidic pH, a common characteristic of the tumor microenvironment, to a strong, specific, and reversible stimulus for activation of these Salmonella genes in vitro and in vivo. Indeed, a Salmonella reporter strain encoding a luciferase transgene regulated by the STM1787 promoter, which contains a tusp motif, showed tumor-induced bioluminescence in vivo. Furthermore, Salmonella expressing Shiga toxin from the STM1787 promoter provided potent and selective antitumor activity in vitro and in vivo, showing the potential for a conditional bacterial-based tumor-specific therapeutic.

SIGNIFICANCE

Salmonella, which often encounter acidic environments during classical host infection, may co-opt evolutionarily conserved pathways for tumor colonization in response to the acidic tumor microenvironment. We identified specific promoter sequences that provide a platform for targeted Salmonella-based tumor therapy in vivo.

Therapeutic antitumor potential of endoglin-based DNA vaccine combined with immunomodulatory agents

Therapy targeting tumor blood vessels ought to inhibit tumor growth. However, tumors become refractory to antiangiogenic drugs. Therefore, therapeutic solutions should be sought to address cellular resistance to antiangiogenic therapy. In this regard, reversal of the proangiogenic and immunosuppressive phenotype of cancer cells, and the shift of the tumor microenvironment towards more antiangiogenic and immune-stimulating phenotype may hold some promise. In our study, we sought to validate the effects of a combination therapy aimed at reducing tumor blood vessels, coupled with the abrogation of the immunosuppressive state. To achieve this, we developed an oral DNA vaccine against endoglin. This antigen was carried by an attenuated Salmonella Typhimurium and applied before or after tumor cell inoculation into immunocompetent mice. Our results show that this DNA vaccine effectively inhibited tumor growth, in both the prophylactic and therapeutic settings. It also activated both specific and nonspecific immune responses in immunized mice. Activated cytotoxic T-lymphocytes were directed specifically against endothelial and tumor cells overexpressing endoglin. The DNA vaccine inhibited angiogenesis but did not affect wound healing. In combination with interleukin-12-mediated gene therapy, or with cyclophosphamide administration, the DNA vaccine resulted in reduced microvessel density and lowered the level of Treg lymphocytes in the experimental tumors. This effectively inhibited tumor growth and prolonged survival of the treated animals. Polarization of tumor milieu, from proangiogenic and immunosuppressive, towards an immunostimulatory and antiangiogenic profile represents a promising avenue in anticancer therapy.

New generation of plasmid backbones devoid of antibiotic resistance marker for gene therapy trials

Since it has been established that the injection of plasmid DNA can lead to an efficient expression of a specific protein in vivo, nonviral gene therapy approaches have been considerably improved, allowing clinical trials. However, the use of antibiotic resistance genes as selection markers for plasmid production raises safety concerns which are often pointed out by the regulatory authorities. Indeed, a horizontal gene transfer to patient's bacteria cannot be excluded, and residual antibiotic in the final product could provoke allergic reactions in sensitive individuals. A new generation of plasmid backbones devoid of antibiotic resistance marker has emerged to increase the safety profile of nonviral gene therapy trials. This article reviews the existing strategies for plasmid maintenance and, in particular, those that do not require the use of antibiotic resistance genes. They are based either on the complementation of auxotrophic strain, toxin-antitoxin systems, operator-repressor titration, RNA markers, or on the overexpression of a growth essential gene. Minicircles that allow removing of the antibiotic resistance gene from the initial vector will also be discussed. Furthermore, reported use of antibiotic-free plasmids in preclinical or clinical studies will be listed to provide a comprehensive view of these innovative technologies.

The role of innate immune-stimulated epithelial apoptosis during gastrointestinal inflammatory diseases

The maintenance of mucosal barrier equilibrium in the intestine requires a delicate and dynamic balance between enterocyte loss by apoptosis and the generation of new cells by proliferation from stem cell precursors at the base of the intestinal crypts. When the balance shifts towards either excessive or insufficient apoptosis, a broad range of gastrointestinal diseases can manifest. Recent work from a variety of laboratories has provided evidence in support of a role for receptors of the innate immune system, including Toll-like receptors 2, 4, and 9 as well as the intracellular pathogen recognition receptor NOD2/CARD15, in the initiation of enterocyte apoptosis. The subsequent induction of enterocyte apoptosis in response to the activation of these innate immune receptors plays a key role in the development of various intestinal diseases, including necrotizing enterocolitis, Crohn's disease, ulcerative colitis, and intestinal cancer. This review will detail the regulatory pathways that govern enterocyte apoptosis, and will explore the role of the innate immune system in the induction of enterocyte apoptosis in gastrointestinal disease.