Facultative or obligate anaerobic bacteria have the potential for multimodality therapy of solid tumours

Combinations of TLR ligands: a promising approach in cancer immunotherapy

Toll-like receptors (TLRs), a family of pattern recognition receptors recognizing molecules expressed by pathogens, are typically expressed by immune cells. However, several recent studies revealed functional TLR expression also on tumor cells. Their expression is a two-sided coin for tumor cells. Not only tumor-promoting effects of TLR ligands are described but also direct oncopathic and immunostimulatory effects. To clarify TLRs' role in colorectal cancer (CRC), we tested the impact of the TLR ligands LPS, Poly I:C, R848, and Taxol on primary human CRC cell lines (HROC40, HROC60, and HROC69) in vitro and in vivo (CT26). Taxol, not only a potent tumor-apoptosis-inducing, but also TLR4-activating chemotherapeutic compound, inhibited growth and viability of all cell lines, whereas the remaining TLR ligands had only marginal effects (R848 > LPS > Poly I:C). Combinations of the substances here did not improve the results, whereas antitumoral effects were dramatically boosted when human lymphocytes were added. Here, combining the TLR ligands often diminished antitumoral effects. In vivo, best tumor growth control was achieved by the combination of Taxol and R848. However, when combined with LPS, Taxol accelerated tumor growth. These data generally prove the potential of TLR ligands to control tumor growth and activate immune cells, but they also demonstrate the importance of choosing the right combinations.

Bacteria and tumours: causative agents or opportunistic inhabitants?

Associations between different bacteria and various tumours have been reported in patients for decades. Studies involving characterisation of bacteria within tumour tissues have traditionally been in the context of tumourigenesis as a result of bacterial presence within healthy tissues, and in general, dogma holds that such bacteria are causative agents of malignancy (directly or indirectly). While evidence suggests that this may be the case for certain tumour types and bacterial species, it is plausible that in many cases, clinical observations of bacteria within tumours arise from spontaneous infection of established tumours. Indeed, growth of bacteria specifically within tumours following deliberate systemic administration has been demonstrated for numerous bacterial species at preclinical and clinical levels. We present the available data on links between bacteria and tumours, and propose that besides the few instances in which pathogens are playing a pathogenic role in cancer, in many instances, the prevalent relationship between solid tumours and bacteria is opportunistic rather than causative, and discuss opportunities for exploiting tumour-specific bacterial growth for cancer treatment.

Efficient tumor targeting by anaerobic butyrate-producing bacteria

Butyrate as an important short chain fatty acid has been shown to affect different kinds of cancer cells. Butyrate exerts its anti-cancerous effects by several mechanisms and has lead to successful outcomes in phase I and II clinical trials. Moreover, since solid tumors grow rapidly, multiple regions of hypoxia and anoxia forms within them that provide good niches for the growth of anaerobic bacteria. It has been shown that bacterial tumor targeting is an applicable strategy for tumor-selective therapy. Therefore, we propose that nonpathogenic anaerobic butyrate-producing bacteria may be a versatile tool in tumor therapy as they can grow in anoxic and hypoxic regions of tumors and influence tumor cells by producing butyric acid. Moreover, this approach may overcome the existing problems of butyrate delivery to the sites of tumor and enhance its bioavailability. Also reversion of cancer drug resistance by butyrate will be plausible. Tumor targeting with nonpathogenic anaerobic bacteria with a higher capacity to produce butyrate could be the focus of future research.

Explicit hypoxia targeting with tumor suppression by creating an "obligate" anaerobic Salmonella Typhimurium strain

Using bacteria as therapeutic agents against solid tumors is emerging as an area of great potential in the treatment of cancer. Obligate and facultative anaerobic bacteria have been shown to infiltrate the hypoxic regions of solid tumors, thereby reducing their growth rate or causing regression. However, a major challenge for bacterial therapy of cancer with facultative anaerobes is avoiding damage to normal tissues. Consequently the virulence of bacteria must be adequately attenuated for therapeutic use. By placing an essential gene under a hypoxia conditioned promoter, SalmonellaTyphimurium strain SL7207 was engineered to survive only in anaerobic conditions (strain YB1) without otherwise affecting its functions. In breast tumor bearing nude mice, YB1 grew within the tumor, retarding its growth, while being rapidly eliminated from normal tissues. YB1 provides a safe bacterial vector for anti-tumor therapies without compromising the other functions or tumor fitness of the bacterium as attenuation methods normally do.

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.

Targeting tumors with salmonella Typhimurium- potential for therapy

When one considers the organism Salmonella enterica serotype Typhimurium (S. Typhimurium), one usually thinks of the Gram-negative enteric pathogen that causes the severe food borne illness, gastroentertitis. In this context, the idea of Salmonella being exploited as a cancer therapeutic seems pretty remote. However, there has been an escalating interest in the development of tumor-therapeutic bacteria for use in the treatment of a variety of cancers. This strategy takes advantage of the remarkable ability of certain bacteria to preferentially replicate and accumulate within tumors. In the case of S. Typhimurium, this organism infects and selectively grows within implanted tumors, achieving tumor/normal tissue ratios of approximately 1,000:1. Salmonella also has some attractive properties well suited for the design of a chemotherapeutic agent. In particular, this pathogen can easily be manipulated to carry foreign genes, and since this species is a facultative anaerobe, it is able to survival in both oxygenated and hypoxic conditions, implying this organism could colonize both small metastatic lesions as well as larger tumors. These observations are the impetus to a burgeoning field focused on the development of Salmonella as a clinically useful anti-cancer agent. We will discuss three cutting edge technologies employing Salmonella to target tumors.

TransKingdom RNA interference: a bacterial approach to challenges in RNAi therapy and delivery

Since its discovery in 1998 RNA interference (RNAi), a potent and highly selective gene silencing mechanism, has revolutionized the field of biological science. The ability of RNAi to specifically down-regulate the expression of any cellular protein has had a profound impact on the study of gene function in vitro. This property of RNAi also holds great promise for in vivo functional genomics and interventions against a wide spectrum of diseases, especially those with "undruggable" therapeutic targets. Despite the enormous potential of RNAi for medicine, development of in vivo applications has met with significant problems, particularly in terms of delivery. For effective gene silencing to occur, silencing RNA must reach the cytoplasm of the target cell. Consequently, various strategies using chemically modified siRNA, liposomes, nanoparticles and viral vectors are being developed to deliver silencing RNA. These approaches, however, can be expensive and in many cases they lack target cell specificity or clinical compatibility. Recently, we have shown that RNAi can be activated in vitro and in vivo by non-pathogenic bacteria engineered to manufacture and deliver silencing shRNA to target cells. This new approach, termed TransKingdom RNAi (tkRNAi), has several key advantages. First, tkRNAi may provide a viable means to accomplish therapeutic RNAi since non-pathogenic bacteria have a proven safety record in clinical applications. Second, tkRNAi eliminates the cost of siRNA manufacture since silencing shRNA are produced inside bacteria. Moreover, the intracellular mechanism of shRNA release inherent to tkRNAi may circumvent, or mitigate, the activation of host immune responses. Finally, tkRNAi may facilitate high-throughput in vivo functional genomics screening since bacteria-based RNAi libraries can be easily constructed, stored, reproduced and amplified, thereby allowing for the creation of a stable gene silencing system.

Gene therapy for cancer: bacteria-mediated anti-angiogenesis therapy

Several bacterial species have inherent ability to colonize solid tumors in vivo. However, their natural anti-tumor activity can be enhanced by genetic engineering that enables these bacteria express or transfer therapeutic molecules into target cells. In this review, we summarize latest research on cancer therapy using genetically modified bacteria with particular emphasis on blocking tumor angiogenesis. Despite recent progress, only a few recent studies on bacterial tumor therapy have focused on anti-angiogenesis. Bacteria-mediated anti-angiogenesis therapy for cancer, however, is an attractive approach given that solid tumors are often characterized by increased vascularization. Here, we discuss four different approaches for using modified bacteria as anti-cancer therapeutics--bactofection, DNA vaccination, alternative gene therapy and transkingdom RNA interference--with a specific focus on angiogenesis suppression. Critical areas and future directions for this field are also outlined.

Reconstitution of the FK228 biosynthetic pathway reveals cross talk between modular polyketide synthases and fatty acid synthase

Functional cross talk between fatty acid biosynthesis and secondary metabolism has been discovered in several cases in microorganisms; none of them, however, involves a modular biosynthetic enzyme. Previously, we reported a hybrid modular nonribosomal peptide synthetase (NRPS)-polyketide synthase (PKS) pathway for the biosynthesis of FK228 anticancer depsipeptide in Chromobacterium violaceum strain 968. This pathway contains two PKS modules on the DepBC enzymes that lack a functional acyltransferase (AT) domain, and no apparent AT-encoding gene exists within the gene cluster or its vicinity. We report here that, through reconstitution of the FK228 biosynthetic pathway in Escherichia coli cells, two essential genes, fabD1 and fabD2, both encoding a putative malonyl coenzyme A (CoA) acyltransferase component of the fatty acid synthase complex, are positively identified to be involved in FK228 biosynthesis. Either gene product appears sufficient to complement the AT-less PKS modules on DepBC for polyketide chain elongation. Concurrently, a gene (sfp) encoding a putative Sfp-type phosphopantetheinyltransferase was identified to be necessary for FK228 biosynthesis as well. Most interestingly, engineered E. coli strains carrying variable genetic components produced significant levels of FK228 under both aerobic and anaerobic cultivation conditions. Discovery of the trans complementation of modular PKSs by housekeeping ATs reveals natural product biosynthesis diversity. Moreover, demonstration of anaerobic production of FK228 by an engineered facultative bacterial strain validates our effort toward the engineering of novel tumor-targeting bioagents.

Targeting tumors with salmonella Typhimurium- potential for therapy

When one considers the organism Salmonella enterica serotype Typhimurium (S. Typhimurium), one usually thinks of the Gram-negative enteric pathogen that causes the severe food borne illness, gastroentertitis. In this context, the idea of Salmonella being exploited as a cancer therapeutic seems pretty remote. However, there has been an escalating interest in the development of tumor-therapeutic bacteria for use in the treatment of a variety of cancers. This strategy takes advantage of the remarkable ability of certain bacteria to preferentially replicate and accumulate within tumors. In the case of S. Typhimurium, this organism infects and selectively grows within implanted tumors, achieving tumor/normal tissue ratios of approximately 1,000:1. Salmonella also has some attractive properties well suited for the design of a chemotherapeutic agent. In particular, this pathogen can easily be manipulated to carry foreign genes, and since this species is a facultative anaerobe, it is able to survival in both oxygenated and hypoxic conditions, implying this organism could colonize both small metastatic lesions as well as larger tumors. These observations are the impetus to a burgeoning field focused on the development of Salmonella as a clinically useful anti-cancer agent. We will discuss three cutting edge technologies employing Salmonella to target tumors.

Enterobacterial tumor colonization in mice depends on bacterial metabolism and macrophages but is independent of chemotaxis and motility

Despite promising results and increasing attention in bacterial cancer therapy, surprisingly little is known about initial tumor colonization and the interaction between bacteria and surrounding tumor tissue. Here, we analyzed the role of chemotaxis, motility, and metabolism both in Escherichia coli and Salmonella enterica serovar Typhimurium strains upon intravenous injection into tumor-bearing mice. In contrast to previous models, we found that chemotaxis and motility do not play a significant role in tumor colonization and bacterial distribution within the tumor. Rather, the whole colonization and intratumoral migration process seems to be a passive mechanism that is influenced by the reticuloendothelial system of the host, by the tumor microenvironment and by the bacterial metabolism. These conclusions were supported by experimental data demonstrating that disruption of the basic branch of the aromatic amino acid biosynthetic pathway and depletion of macrophages, in contrast to flagellar mutations, led to significant changes in bacterial accumulation in tumors of live mice.

Bacteria in cancer therapy: a novel experimental strategy

Resistance to conventional anticancer therapies in patients with advanced solid tumors has prompted the need of alternative cancer therapies. Moreover, the success of novel cancer therapies depends on their selectivity for cancer cells with limited toxicity to normal tissues. Several decades after Coley's work a variety of natural and genetically modified non-pathogenic bacterial species are being explored as potential antitumor agents, either to provide direct tumoricidal effects or to deliver tumoricidal molecules. Live, attenuated or genetically modified non-pathogenic bacterial species are capable of multiplying selectively in tumors and inhibiting their growth. Due to their selectivity for tumor tissues, these bacteria and their spores also serve as ideal vectors for delivering therapeutic proteins to tumors. Bacterial toxins too have emerged as promising cancer treatment strategy. The most potential and promising strategy is bacteria based gene-directed enzyme prodrug therapy. Although it has shown successful results in vivo yet further investigation about the targeting mechanisms of the bacteria are required to make it a complete therapeutic approach in cancer treatment.

Cancer immunoediting and "spontaneous" tumor regression

The combination of host protective and tumor-promoting actions of the immune system throughout tumor development is termed cancer immunoediting. This review briefly summarizes the currently vast evidence supporting the immune system's role in not only protecting against developing cancer, but also sculpting tumor immunogenicity and immune escape. We also briefly summarize the history of immunotherapy and discuss the immunoediting process in the context of spontaneous tumor regression and whether this observation can be utilized in future treatment regimens.

Myristoylation negative msbB-mutants of probiotic E. coli Nissle 1917 retain tumor specific colonization properties but show less side effects in immunocompetent mice

Specific colonization of solid tumors by bacteria opens the way to novel approaches in both tumor diagnosis and therapy. However, even non-pathogenic bacteria induce responses by the immune system, which could be devastating for a tumor bearing patient. As such effects are caused e.g., by the lipid A moiety of the lipopolysaccharide, a msbB-mutant of the probiotic E. coli Nissle 1917 strain was investigated. Bacteria of the mutant strain did not show any growth defects in culture media when compared to wild-type E. coli Nissle 1917 but were unable to myristoylate lipid A, had less toxic effects on immunocompetent BALB/c mice, and were still able to specifically colonize tumors. Therefore, the modification of lipid A could result in bacterial strains that might be better suited for diagnosis and therapy of tumors than the corresponding wild-type strains, even if those are not considered pathogenic or are of probiotic background.

Effect of LTA isolated from bifidobacteria on D-galactose-induced aging

BACKGROUND

Bifidobacteria are a natural part of the bacterial flora in the human body and have a symbiotic bacteria-host relationship with human beings. Aging is associated with reduced number of beneficial colonic bifidobacteria and impaired immunity. Lipoteichoic acid is a major constituent of the cell wall of bifidobacteria which is important for bacterial survival, growth, and function. The possible anti-aging effects of lipoteichoic acid isolated from bifidobacteria is presently unknown.

OBJECTIVE

The aim of the present study was to investigate possible anti-aging effects of lipoteichoic acid isolated from bifidobacteria on senescent mice artificially induced by chronic injection of d-galactose and explore potential anti-aging's mechanisms.

METHODS

Mice were artificially induced senescence by consecutive injection of d-galactose (100mg/kg) once daily for 7weeks and lipoteichoic acid from bifidobacterium bifidum, was simultaneously administered to them once a week by intraperitoneal infusion. Mice were sacrificed, blood and other samples were collected at the indicated time. Anti-oxidation activity in brain, histology of tissue, gene expression, lymphocyte's DNA damage and cytokine production of lymphocytes in vitro and in vivo were measured.

RESULTS

Lipoteichoic acid could significantly improve general appearance of the aging model mice, improve anti-oxidation activity in brain, increase IL-2 level and decrease TNF-alpha level in vitro and in vivo, respectively. Besides, LTA remarkably inhibited DNA damage in the both splenic lymphocytes and circulating lymphocytes. Moreover, LTA could decrease p16 expression while increase c-fos expression in the d-galactose treated mice.

CONCLUSION

Taken together, the results indicated, for the first time, that LTA could suppress the aging process via the following several mechanisms, including enhancement of anti-oxidation activity in brain, improvement of immune function and alteration of gene expression.

Bacterial targeted tumour therapy-dawn of a new era

Original observation of patients' spontaneous recovery from advanced tumours after an infection or a "fever" inspired extensive research. As a result, Coley's toxin for the therapy of sarcomas and live Bacillus Calmette-Guerin (BCG) for bladder cancer were born. In addition, three genera of anaerobic bacteria have been shown to specifically and preferentially target solid tumours and cause significant tumour lyses. Initial research had focused on determining the best tumour colonizing bacteria, and assessing the therapeutic efficacy of different strategies either as a single or combination treatment modalities. However, although clinical trials were carried out as early as the 1960s, lack of complete tumour lyses with injection of Clostridial spores had limited their further use. Recent progress in the field has highlighted the rapid development of new tools for genetic manipulation of Clostridia which have otherwise been a hurdle for a long time, such as plasmid transformation using electroporation that bore the problems of inefficiency, instability and plasmid loss. A new Clostridium strain, C. novyi-NT made apathogenic by genetic modification, is under clinical trials. New genetic engineering tools, such as the group II intron has shown promise for genetic manipulation of bacteria and forecast the dawn of a new era for a tumour-targeted bacterial vector system for gene therapy of solid tumours. In this review we will discuss the potential of genetically manipulated bacteria that will usher in the new era of bacterial therapy for solid tumours, and highlight strategies and tools used to improve the bacterial oncolytic capability.

Clostridial spores as live 'Trojan horse' vectors for cancer gene therapy: comparison with viral delivery systems

Solid tumours account for 90% of all cancers. Gene therapy represents a potential new modality for their treatment. Up to now, several approaches have been developed, but the most efficient ones are the viral vector based gene therapy systems. However, viral vectors suffer from several deficiencies: firstly most vectors currently in use require intratumoural injection to elicit an effect. This is far from ideal as many tumours are inaccessible and many may have already spread to other parts of the body, making them difficult to locate and inject gene therapy vectors into. Second, because of cell heterogeneity within a given cancer, the vectors do not efficiently enter and kill every cancer cell. Third, hypoxia, a prevalent characteristic feature of most solid tumours, reduces the ability of the viral vectors to function and decreases viral gene expression and production. Consequently, a proportion of the tumour is left unaffected, from which tumour regrowth occurs. Thus, cancer gene therapy has yet to realise its full potential. The facultative or obligate anaerobic bacteria have been shown to selectively colonise and regerminate in solid tumours when delivered systemically. Among them, the clostridial spores were easy to produce, stable to store and safe to use as well as having extensive oncolytic ability. However, research in animals and humans has shown that oncolysis was almost always interrupted sharply at the outer rim of the viable tumour tissue where the blood supply was sufficient. These clostridial spores, though, could serve as "Trojan horse" for cancer gene therapy. Indeed, various spores harbouring genes for cancerstatic factors, prodrug enzymes, or proteins or cytokines had endowed with additional tumour-killing capability. Furthermore, combination of these "Trojan horses" with conventional chemotherapy or radiation therapies often significantly perform better, resulting in the "cure" of solid tumours in a high percentage of animals. It is, thus, not too difficult to predict the potential outcomes for the use of clostridial spores as "Trojan horse" vectors for oncolytic therapy when compared with viral vector-mediated cancer therapy for it be replication-deficient or competent. However, to move the "Trojan horse" to a clinic, though, additional requirements need to be satisfied (i) target tumours only and not anywhere else, and (ii) be able to completely kill primary tumours as well as metastases. Current technologies are in place to achieve these goals.

Colonization of experimental murine breast tumours by Escherichia coli K-12 significantly alters the tumour microenvironment

The successful application of live bacteria in cancer therapy requires a more detailed understanding of bacterial interaction with the tumour microenvironment. Here, we analysed the effect of Escherichia coli K-12 colonization on the tumour microenvironment by immunohistochemistry and fluorescence microscopy in the murine 4T1 breast carcinoma model. We described the colonization of tumour-bearing mice, as well as the spatiotemporal distribution of E. coli K-12 in the 4T1 tumour tissue over a period of 14 days. The colonization resulted within 3 days in large avascular necrotic tissue, redistribution of hypoxic areas and an enhanced collagen IV deposition within the colonized tumour tissue, which changed the tumoral perfusion of systemically injected immunoglobulins. In addition, E. coli K-12 colonization led to the redistribution of tumour-associated macrophages, forming a granulation tissue around bacterial colonies, and also to an increase in TNFalpha and matrix metalloproteinase 9 expression. Colonization of 4T1 tumours by E. coli K-12 resulted in strong reduction of pulmonary metastatic events. These new insights will contribute to the general understanding of the tumour-microbe cross-talk and to the design of bacterial strains with enhanced anticancer efficiency.