Orally administered bifidobacteria as vehicles for delivery of agents to systemic tumors

Unveiling intratumoral microbiota: An emerging force for colorectal cancer diagnosis and therapy

Microbes, including bacteria, viruses, fungi, and other eukaryotic organisms, are commonly present in multiple organs of the human body and contribute significantly to both physiological and pathological processes. Nowadays, the development of sequencing technology has revealed the presence and composition of the intratumoral microbiota, which includes Fusobacterium, Bifidobacteria, and Bacteroides, and has shed light on the significant involvement in the progression of colorectal cancer (CRC). Here, we summarized the current understanding of the intratumoral microbiota in CRC and outline the potential translational and clinical applications in the diagnosis, prevention, and treatment of CRC. We focused on reviewing the development of microbial therapies targeting the intratumoral microbiota to improve the efficacy and safety of chemotherapy and immunotherapy for CRC and to identify biomarkers for the diagnosis and prognosis of CRC. Finally, we emphasized the obstacles and potential solutions to translating the knowledge of the intratumoral microbiota into clinical practice.

Untangling the web of intratumor microbiota in lung cancer

Microbes are pivotal in contemporary cancer research, influencing various biological behaviors in cancer. The previous notion that the lung was sterile has been destabilized by the discovery of microbiota in the lower airway and lung, even within tumor tissues. Advances of biotechnology enable the association between intratumor microbiota and lung cancer to be revealed. Nonetheless, the origin and tumorigenicity of intratumor microbiota in lung cancer still remain implicit. Additionally, accumulating evidence indicates that intratumor microbiota might serve as an emerging biomarker for cancer diagnosis, prognosis, and even a therapeutic target across multiple cancer types, including lung cancer. However, research on intratumor microbiota's role in lung cancer is still nascent and warrants more profound exploration. Herein, this paper provides an extensive review of recent advancements in the following fields, including 1) established and emerging biotechnologies utilized to study intratumor microbiota in lung cancer, 2) causation between intratumor microbiota and lung cancer from the perspectives of translocation, cancerogenesis and metastasis, 3) potential application of intratumor microbiota as a novel biomarker for lung cancer diagnosis and prognosis, and 4) promising lung cancer therapies via regulating intratumor microbiota. Moreover, this review addresses the limitations, challenges, and future prospects of studies focused on intratumor microbiota in lung cancer.

Understanding the role of gut microfloral bifidobacterium in cancer and its potential therapeutic applications

Gut microbiota research has gained a tremendous amount of attention from the scientific community because of its contribution to gut homeostasis, human health, and various pathophysiological conditions. The early colonizer of the human gut, i.e., bifidobacteria, has emerged as an efficient probiotic in various diseased conditions, including cancer. This review explores the pros and cons of Bifidobacterium in various malignancies and various therapeutic strategies. We have illustrated the controversial role of bifidobacteria participating in various malignancies as well as described the current knowledge regarding its use in anticancer therapies. Ultimately, this article also addresses the need for further extensive research in elucidating the mechanism of how bifidobacteria is involved and is indirectly affecting the tumor microenvironment. Exhaustive and large-scale research is also required to solve the controversial questions regarding the involvement of bifidobacteria in cancer research.

Refined control of CRISPR-Cas9 gene editing in Clostridium sporogenes: the creation of recombinant strains for therapeutic applications

Despite considerable clinical success, the potential of cancer immunotherapy is restricted by a lack of tumour-targeting strategies. Treatment requires systemic delivery of cytokines or antibodies at high levels to achieve clinically effective doses at malignant sites. This is exacerbated by poor penetration of tumour tissue by therapeutic antibodies. High-grade immune-related adverse events (irAEs) occur in a significant number of patients (5-15%, cancer- and therapeutic-dependent) that can lead to lifelong issues and can exclude from treatment patients with pre-existing autoimmune diseases. Tumour-homing bacteria, genetically engineered to produce therapeutics, is one of the approaches that seeks to mitigate these drawbacks. The ability of Clostridium sporogenes to form spores that are unable to germinate in the presence of oxygen (typical of healthy tissue) offers a unique advantage over other vectors. However, the limited utility of existing gene editing tools hinders the development of therapeutic strains. To overcome the limitations of previous systems, expression of the Cas9 protein and the gRNA was controlled using tetracycline inducible promoters. Furthermore, the components of the system were divided across two plasmids, improving the efficiency of cloning and conjugation. Genome integrated therapeutic genes were assayed biochemically and in cell-based functional assays. The potency of these strains was further improved through rationally-conceived gene knock-outs. The new system was validated by demonstrating the efficient addition and deletion of large sequences from the genome. This included the creation of recombinant strains expressing two pro-inflammatory cytokines, interleukin-2 (IL-2) and granulocyte macrophage-colony stimulating factor (GM-CSF), and a pro-drug converting enzyme (PCE). A comparative, temporal in vitro analysis of the integrant strains and their plasmid-based equivalents revealed a substantial reduction of cytokine activity in chromosome-based constructs. To compensate for this loss, a 7.6 kb operon of proteolytic genes was deleted from the genome. The resultant knock-out strains showed an 8- to 10-fold increase in cytokine activity compared to parental strains.

Intratumor microbiome: selective colonization in the tumor microenvironment and a vital regulator of tumor biology

The polymorphic microbiome has been proposed as a new hallmark of cancer. Intratumor microbiome has been revealed to play vital roles in regulating tumor initiation and progression, but the regulatory mechanisms have not been fully uncovered. In this review, we illustrated that similar to other components in the tumor microenvironment, the reside and composition of intratumor microbiome are regulated by tumor cells and the surrounding microenvironment. The intratumor hypoxic, immune suppressive, and highly permeable microenvironment may select certain microbiomes, and tumor cells may directly interact with microbiome via molecular binding or secretions. Conversely, the intratumor microbiomes plays vital roles in regulating tumor initiation and progression via regulating the mutational landscape, the function of genes in tumor cells and modulating the tumor microenvironment, including immunity, inflammation, angiogenesis, stem cell niche, etc. Moreover, intratumor microbiome is regulated by anti-cancer therapies and actively influences therapy response, which could be a therapeutic target or engineered to be a therapy weapon in the clinic. This review highlights the intratumor microbiome as a vital component in the tumor microenvironment, uncovers potential mutual regulatory mechanisms between the tumor microenvironment and intratumor microbiome, and points out the ongoing research directions and drawbacks of the research area, which should broaden our view of microbiome and enlighten further investigation directions.

A comprehensive review of Bifidobacterium spp: as a probiotic, application in the food and therapeutic, and forthcoming trends

Recently, more consumers are interested in purchasing probiotic food and beverage products that may improve their immune health. The market for functional foods and beverages that include Bifidobacterium is expanding because of their potential uses in both food and therapeutic applications. However, maintaining Bifidobacterium's viability during food processing and storage remains a challenge. Microencapsulation technique has been explored to improve the viability of Bifidobacterium. Despite the technical, microbiological, and economic challenges, the market potential for immune-supporting functional foods and beverages is significant. Additionally, there is a shift toward postbiotics as a solution for product innovation, a promising postbiotic product that can be incorporated into various food and beverage formats is also introduced in this review. As consumers become more health-conscious, future developments in the functional food and beverage market discussed in this review could serve as a reference for researchers and industrialist.

Blautia coccoides JCM1395T Achieved Intratumoral Growth with Minimal Inflammation: Evidence for Live Bacterial Therapeutic Potential by an Optimized Sample Preparation and Colony PCR Method

We demonstrate that Blautia coccoides JCM1395^T has the potential to be used for tumor-targeted live bacterial therapeutics. Prior to studying its in vivo biodistribution, a sample preparation method for reliable quantitative analysis of bacteria in biological tissues was required. Gram-positive bacteria have a thick outer layer of peptidoglycans, which hindered the extraction of 16S rRNA genes for colony PCR. We developed the following method to solve the issue; the method we developed is as follows. The homogenates of the isolated tissue were seeded on agar medium, and bacteria were isolated as colonies. Each colony was heat-treated, crushed with glass beads, and further treated with restriction enzymes to cleave DNAs for colony PCR. With this method, Blautia coccoides JCM1395^T and Bacteroides vulgatus JCM5826^T were individually detected from tumors in mice intravenously receiving their mixture. Since this method is very simple and reproducible, and does not involve any genetic modification, it can be applied to exploring a wide range of bacterial species. We especially demonstrate that Blautia coccoides JCM1395^T efficiently proliferate in tumors when intravenously injected into tumor-bearing mice. Furthermore, these bacteria showed minimal innate immunological responses, i.e., elevated serum tumor necrosis factor α and interleukin-6, similar to Bifidobacterium sp., which was previously studied as a therapeutic agent with a small immunostimulating effect.

Understanding and harnessing triple-negative breast cancer-related microbiota in oncology

Bacterial inhabitants of the body have the potential to play a role in various stages of cancer initiation, progression, and treatment. These bacteria may be distal to the primary tumour, such as gut microbiota, or local to the tissue, before or after tumour growth. Breast cancer is well studied in this context. Amongst breast cancer types, Triple Negative Breast Cancer (TNBC) is more aggressive, has fewer treatment options than receptor-positive breast cancers, has an overall worse prognosis and higher rates of reoccurrence. Thus, an in-depth understanding of the bacterial influence on TNBC progression and treatment is of high value. In this regard, the Gut Microbiota (GM) can be involved in various stages of tumour progression. It may suppress or promote carcinogenesis through the release of carcinogenic metabolites, sustenance of proinflammatory environments and/or the promotion of epigenetic changes in our genome. It can also mediate metastasis and reoccurrence through interactions with the immune system and has been recently shown to influence chemo-, radio-, and immune-therapies. Furthermore, bacteria have also been found to reside in normal and malignant breast tissue. Several studies have now described the breast and breast tumour microbiome, with the tumour microbiota of TNBC having the least taxonomic diversity among all breast cancer types. Here, specific conditions of the tumour microenvironment (TME) - low O2, leaky vasculature and immune suppression - are supportive of tumour selective bacterial growth. This innate bacterial ability could enable their use as delivery agents for various therapeutics or as diagnostics. This review aims to examine the current knowledge on bacterial relevance to TNBC and potential uses while examining some of the remaining unanswered questions regarding mechanisms underpinning observed effects.

Probiotic Spore-Based Oral Drug Delivery System for Enhancing Pancreatic Cancer Chemotherapy by Gut-Pancreas-Axis-Guided Delivery

The chemotherapeutic effectiveness of pancreatic ductal adenocarcinoma (PDAC) is severely hampered by insufficient intratumoral delivery of antitumor drugs. Here, we demonstrate that enhanced pancreatic cancer chemotherapy can be achieved by probiotic spore-based oral drug delivery system via gut-pancreas axis translocation. Clostridium butyricum spores resistant to harsh external stress are extracted as drug carriers, which are further covalently conjugated with gemcitabine-loaded mesoporous silicon nanoparticles (MGEM). The spore-based oral drug delivery system (SPORE-MGEM) migrates upstream into pancreatic tumors from the gut, which increases intratumoral drug accumulation by ∼3-fold compared with MGEM. In two orthotopic PDAC mice models, tumor growth is markedly suppressed by SPORE-MGEM without obvious side effects. Leveraging the biological contact of the gut-pancreas axis, this probiotic spore-based oral drug delivery system reveals a new avenue for enhancing PDAC chemotherapy.

Bioinformatic Analysis of the Genetic Mechanism of Biomineralization of Biogenic Magnetic Nanoparticles in Bacteria Capable of Tumor-Specific Accumulation

Background. Current methods of targeted cancer therapy are not always effective enough and can lead to side effects, such as an increased risk of autoimmune diseases. It is known that some bacteria are capable of specific accumulation in malignant tumors, and therefore can be used as an alternative means of targeted drug delivery. However, the genetic mechanism of tumor-specific accumulation of bacteria is not fully understood and needs to be studied in more detail. Objective. This work aims to identify, by methods of comparative genomics methods, magnetically controlled bacteria among those for which tumor-specific accumulation has already been experimentally shown. Methods. To identify magnetically controlled bacterial strains, i.e., bacteria that biomineralize biogenic magnetic nanoparticles (BMN), the method of comparative genomics was used, namely: pairwise alignment of proteomes with amino acid sequences of Mam-proteins of required for biomineralization of BMN in magneto­tactic bacteria Magnetospirillum gryphiswaldense MSR-1. Sequence alignments were performed in the BLAST program of the US National Center for Biotechnology Information (NCBI). Results. The conducted bioinformatic analysis showed that strains of bacteria in which the ability to accumulate specifically in tumors has been experimentally proven are potential producers of BMN of different types. Among them there are potential producers of intracellular crystalline BMN, potential producers of intracellular amorphous BMN, and extracellular crystalline BMN Conclusions. It is expedient to use bacteria-producing BMN as gene vectors and systems of targeted drug delivery to tumors that biomineralize BMN.

Recent Development of Probiotic Bifidobacteria for Treating Human Diseases

Bifidobacterium is a non-spore-forming, Gram-positive, anaerobic probiotic actinobacterium and commonly found in the gut of infants and the uterine region of pregnant mothers. Like all probiotics, Bifidobacteria confer health benefits on the host when administered in adequate amounts, showing multifaceted probiotic effects. Examples include B. bifidum, B. breve, and B. longum, common Bifidobacterium strains employed to prevent and treat gastrointestinal disorders, including intestinal infections and cancers. Herein, we review the latest development in probiotic Bifidobacteria research, including studies on the therapeutic impact of Bifidobacterial species on human health and recent efforts in engineering Bifidobacterium. This review article would provide readers with a wholesome understanding of Bifidobacteria and its potentials to improve human health.

Bacterial-Based Cancer Therapy (BBCT): Recent Advances, Current Challenges, and Future Prospects for Cancer Immunotherapy

Currently approximately 10 million people die each year due to cancer, and cancer is the cause of every sixth death worldwide. Tremendous efforts and progress have been made towards finding a cure for cancer. However, numerous challenges have been faced due to adverse effects of chemotherapy, radiotherapy, and alternative cancer therapies, including toxicity to non-cancerous cells, the inability of drugs to reach deep tumor tissue, and the persistent problem of increasing drug resistance in tumor cells. These challenges have increased the demand for the development of alternative approaches with greater selectivity and effectiveness against tumor cells. Cancer immunotherapy has made significant advancements towards eliminating cancer. Our understanding of cancer-directed immune responses and the mechanisms through which immune cells invade tumors have extensively helped us in the development of new therapies. Among immunotherapies, the application of bacteria and bacterial-based products has promising potential to be used as treatments that combat cancer. Bacterial targeting of tumors has been developed as a unique therapeutic option that meets the ongoing challenges of cancer treatment. In comparison with other cancer therapeutics, bacterial-based therapies have capabilities for suppressing cancer. Bacteria are known to accumulate and proliferate in the tumor microenvironment and initiate antitumor immune responses. We are currently well-informed regarding various methods by which bacteria can be manipulated by simple genetic engineering or synthetic bioengineering to induce the production of anti-cancer drugs. Further, bacterial-based cancer therapy (BBCT) can be either used as a monotherapy or in combination with other anticancer therapies for better clinical outcomes. Here, we review recent advances, current challenges, and prospects of bacteria and bacterial products in the development of BBCTs.

Microbiome in drug resistance to colon cancer

Metagenomic analyses have revealed microbial dysbiosis in the gut of patients with colorectal cancer (CRC). The gut microbiota influences CRC via a variety of mechanisms, including microbial-derived factors such as metabolites or genotoxins. Pathogenic drivers and opportunistic passenger bacteria may underlie direct effect of the gut microbiota on carcinogenesis. We posit that metabolites generated by gut microbiota can influence CRC through a multitude of epigenetic or genetic effects on malignant transformation. A closer look at the cross talks between the commensals, epithelial cells, immune regulators etc., needs to be established with more substantiated studies. The recurrence of chemoresistant disease following therapy undoubtedly provides the impetus for morbidity and mortality; yet, the role of gut microbiome in drug resistance remains to be fully investigated. We review the current literature on microbial dysbiosis during CRC and discuss the mechanistic basis of CRC-associated bacteria in tumor initiation, progression and drug resistance.

Optimized Doxycycline-Inducible Gene Expression System for Genetic Programming of Tumor-Targeting Bacteria

PURPOSE

In the programming of tumor-targeting bacteria, various therapeutic or reporter genes are expressed by different gene-triggering strategies. Previously, we engineered pJL87 plasmid with an inducible bacterial drug delivery system that simultaneously co-expressed two genes for therapy and imaging by a bidirectional tet promoter system only in response to the administration of exogenous doxycycline (Doxy). In this multi-cassette expression approach, tetA promoter (P_tetA) was 100-fold higher in expression strength than tetR promoter (P_tetR). In the present study, we developed pJH18 plasmid with novel Doxy-inducible gene expression system based on a tet promoter.

PROCEDURES

In this system, Tet repressor (TetR) expressed by a weak constitutive promoter binds to tetO operator, resulting in the tight repression of gene expressions by P_tetA and P_tetR, and Doxy releases TetR from tetO to de-repress P_tetA and P_tetR.

RESULTS

In Salmonella transformed with pJH18, the expression balance of bidirectional tet promoters in pJH18 was remarkably improved (P_tetA:P_tetR = 4~6:1) compared with that of pJL87 (P_tetA:P_tetR = 100:1) in the presence of Doxy. Also, the expression level by novel tet system was much higher in Salmonella transformed with pJH18 than in those with pJL87 (80-fold in rluc8 and 5-fold in clyA). Interestingly, pJH18 of the transformed Salmonella was much more stably maintained than pJL87 in antibiotic-free tumor-bearing mice (about 41-fold), because only pJH18 carries bom sequence with an essential role in preventing the plasmid-free population of programmed Salmonella from undergoing cell division.

CONCLUSIONS

Overall, doxycycline-induced co-expression of two proteins at similar expression levels, we exploited bioluminescence reporter proteins with preclinical but no clinical utility. Future validation with clinically compatible reporter systems, for example, suitable for radionuclide imaging, is necessary to develop this system further towards potential clinical application.

Bacteria-mediated cancer therapies: opportunities and challenges

In recent years, cancer therapy strategies utilizing live tumor-targeting bacteria have presented unique advantages. Engineered bacteria have the particular ability to distinguish tumors from normal tissues with less toxicity. Live bacteria are naturally capable of homing to tumors, resulting in high levels of local colonization because of insufficient oxygen and low pH in the tumor microenvironment. Bacteria initiate their antitumor effects by directly killing the tumor or by activating innate and adaptive antitumor immune responses. The bacterial vectors can be reprogrammed following advanced DNA synthesis, sophisticated genetic bioengineering, and biosensors to engineer microorganisms with complex functions, and then produce and deliver anticancer agents based on clinical needs. However, because of the lack of knowledge on the mechanisms and side effects of microbial cancer therapy, developing such smart microorganisms to treat or prevent cancer remains a significant challenge. In this review, we summarized the potential, status, opportunities and challenges of this growing field. We illustrated the mechanism of tumor regression induced by engineered bacteria and discussed the recent advances in the application of bacteria-mediated cancer therapy to improve efficacy, safety and drug delivery. Finally, we shared our insights into the future directions of tumor-targeting bacteria in cancer therapy.

Application of bacterial directed enzyme prodrug therapy as a targeted chemotherapy approach in a mouse model of breast cancer

Cancer is the second leading cause of death in the world. Some of the usual cancer treatments include surgery, chemotherapy, and radiotherapy. However, due to low efficacy and side effects of these treatments, novel targeted therapeutic methods are needed. One of the common drawbacks of cancer chemotherapy is off-target toxicity. In order to overcome this problem, many investigations have been conducted. One of the new targeted therapy methods known as bacterial directed enzyme-prodrug therapy (BDEPT) employs bacteria as enzyme carriers to convert a pro-drug to a drug specifically within the tumor site. In the present study, we used Escherichia coli DH5α carrying luxCDABE gene cluster and overexpressing β-glucuronidase for luminescent emission and enzyme expression, respectively. Enzyme expression can lead to the conversion of glycyrrhizic acid as a prodrug to glycyrrhetinic acid, a potent anti-cancer agent. DH5α-lux/βG was characterized and its stability was also evaluated. Bacteria colonization in the tumor site was measured by tissue homogenate preparation and colony counting method. Histopathological studies on the liver, spleen, and tumor were also conducted. According to the results, co-treatment of 4T1, a highly metastatic mouse breast cancer cell line, with GL and DH5α-lux/βG could significantly decrease the IC₅₀ values. Moreover, increased number of bacteria could lead to a dramatic drop in IC₅₀ value. Specific colonization of DH5α-lux/βG was observed in the tumor site compared with other tissues (p< 0.0001). Moreover, the biocompatibility evaluation proved that DH5α-lux/βG had no adverse effects on normal tissues. Furthermore, concurrent usage of GL and bacteria in the treatment of induced 4T1 tumors in BALB/c mice significantly delayed tumor growth (p<0.001) during 16 days of investigation. Based on these findings, BDEPT might be useful for targeted breast cancer therapy, although further investigations are required to confirm this.

Bifidobacterium Transformation

The protocol presented in this chapter describes a generic method for electrotransformation of Bifidobacterium spp., outlining a technique that is ideal for conferring selective properties onto strains as well as allowing the user to introduce or knock out/in selected genes for phenotypic characterization purposes. We have generalized on the plasmid chosen for transformation and antibiotic selection marker, but the protocol is versatile in this respect and we are able to achieve transformation efficiencies up to 10⁷ transformants/μg of DNA.

The Gut‒Breast Axis: Programming Health for Life

The gut is a pivotal organ in health and disease. The events that take place in the gut during early life contribute to the programming, shaping and tuning of distant organs, having lifelong consequences. In this context, the maternal gut plays a quintessence in programming the mammary gland to face the nutritional, microbiological, immunological, and neuroendocrine requirements of the growing infant. Subsequently, human colostrum and milk provides the infant with an impressive array of nutrients and bioactive components, including microbes, immune cells, and stem cells. Therefore, the axis linking the maternal gut, the breast, and the infant gut seems crucial for a correct infant growth and development. The aim of this article is not to perform a systematic review of the human milk components but to provide an insight of their extremely complex interactions, which render human milk a unique functional food and explain why this biological fluid still truly remains as a scientific enigma.

Suppressing Sart1 to modulate macrophage polarization by siRNA-loaded liposomes: a promising therapeutic strategy for pulmonary fibrosis

Idiopathic pulmonary fibrosis (IPF) is a chronic and diffuse form of interstitial lung disease of unknown etiology with a fatal outcome. Although various strategies for IPF have been developed over the last few decades, no significant positive impact on the prognosis of IPF has been observed. According to the current paradigm, macrophages have been recognized to play a significant role in IPF pathogenesis. Here, we report a potential nanomedicine-based gene therapy for IPF based on regulate macrophage polarization.

Method: C57BL/6 mice were obtained and used to establish a bleomycin (BLM)-induced pulmonary fibrosis animal model, and Sart1 siRNA-loaded liposomes were designed for in vivo experiment. The experimental animals were administered BLM intratracheally on day 0 and treated with Sart1 siRNA on days 14 and 17. In the in vitro experiment, we further examined the function of Sart1 in macrophages.

Results: Our data indicated that the liposomes could passively target the fibrotic area in the lung and efficiently accumulate in macrophages. The suppression of Sart1 by siRNA-loaded liposomes significantly protected mice against BLM-induced lung injury and fibrosis, which was attributed to attenuated M2 macrophage infiltration in the lung.

Conclusion: Our study provides a valuable reference for modulating macrophage polarization and a promising strategy for the treatment of pulmonary fibrosis in clinical settings.

Protoblock - A biological standard for formalin fixed samples

BACKGROUND

Formalin-fixed, paraffin-embedded (FFPE) tissue is the gold standard in pathology tissue storage, representing the largest collections of patient material. Their reliable use for DNA analyses could open a trove of potential samples for research and are currently being recognised as a viable source material for bacterial analysis. There are several key features which limit bacterial-related data generation from this material: (i) DNA damage inherent to the fixing process, (ii) low bacterial biomass that increases the vulnerability to contamination and exacerbates the host DNA effects and (iii) lack of suitable DNA extraction methods, leading to data bias. The development and systematic use of reliable standards is a key priority for microbiome research. More than perhaps any other sample type, FFPE material urgently requires the development of standards to ensure the validity of results and to promote reproducibility.

RESULTS

To address these limitations and concerns, we have developed the Protoblock as a biological standard for FFPE tissue-based research and method optimisation. This is a novel system designed to generate bespoke mock FFPE 'blocks' with a cell content that is user-defined and which undergoes the same treatment conditions as clinical FFPE tissues. The 'Protoblock' features a mix of formalin-fixed cells, of known number, embedded in an agar matrix which is solidified to form a defined shape that is paraffin embedded. The contents of various Protoblocks populated with mammalian and bacterial cells were verified by microscopy. The quantity and condition of DNA purified from blocks was evaluated by qPCR, 16S rRNA gene amplicon sequencing and whole genome sequencing. These analyses validated the capability of the Protoblock system to determine the extent to which each of the three stated confounding features impacts on eventual analysis of cellular DNA present in FFPE samples.

CONCLUSION

The Protoblock provides a representation of biological material after FFPE treatment. Use of this standard will greatly assist the stratification of biological variations detected into those legitimately resulting from experimental conditions, and those that are artefacts of the processed nature of the samples, thus enabling users to relate the outputs of laboratory analyses to reality. Video Abstract.

Immunotherapy in Colorectal Cancer: Potential of Fecal Transplant and Microbiota-augmented Clinical Trials

PURPOSE OF REVIEW

This review summarizes the role of the microbiome in colorectal cancer (CRC) in the setting of immunotherapy and emphasizes the potential of microbiota-influencing strategies with a focus on the use of fecal microbiota transplant (FMT).

RECENT FINDINGS

Observations from preclinical and clinical studies suggest that the human gut microbiome is implicated in the CRC carcinogenesis and is integral in determining the clinical response and toxicity to immunotherapy. Among the therapeutic methods devised to exploit the microbiome, FMT is the most direct method and is backed by the highest level of evidence of efficacy in nonneoplastic disease settings. Furthermore, a favorable microbiome has the potential to overcome immunotherapy resistance and ameliorate immune-related adverse events (irAEs). To this end, clinical trials are underway to evaluate the potential of FMT and microbiota-augmented methods in the setting of immunotherapy in CRC.

SUMMARY

Evidence from animal studies, retrospective studies, and smaller-scale prospective human studies have led to initiation of a number of microbiota-augmented clinical trials in CRC. Given the intimate relationship between the gut microbiota and the immune system as well as antitumor immune responses, potentiating immunotherapy and managing its toxicity are major areas of research in microbiota-augmented therapies in cancer. Therefore, evaluation of the patient microbiome as a routine part of clinical outcome analysis is warranted in future clinical trials.

The Microbiome in Immuno-oncology

The field of cancer therapy has been revolutionized through the use of immunotherapy, and treatment with these therapies now spans from early to late stage, and even into prevention. However, there are still a significant proportion of patients who do not derive long-term benefit from monotherapy and even combined therapy regimens, and novel approaches are needed to enhance therapeutic responses. Additionally, ideal biomarkers of response to immunotherapy are lacking and are critically needed. An emerging area of interest in immuno-oncology (IO) is the microbiome, which refers to the collection of microbes (and their genomes) that inhabit an individual and live in symbiosis. There is now evidence that these microbes (particularly those within the gut) impact host physiology and can impact responses to immunotherapy. The field of microbiome research in immuno-oncology is quickly emerging, with the potential use of the microbiome (in the gut as well as in the tumor) as a biomarker for response to IO as well as a therapeutic target. Notably, the microbiome may even have a role in toxicity to therapy. The state of the science in microbiome and IO are discussed and caveats and future directions are outlined to provide insights as we move forward as a field.

Feasibility between Bifidobacteria Targeting and Changes in the Acoustic Environment of tumor Tissue for Synergistic HIFU

High intensity focused ultrasound (HIFU) has been recently shown as a rapidly developing new technique for non-invasive ablation of local tumors whose therapeutic efficiency can be significantly improved by changing the tissue acoustic environment (AET). Currently, the method of changing AET is mainly to introduce a medium with high acoustic impedance, but there are some disadvantages such as low retention of the introduced medium in the target area and a short residence time during the process. In our strategy, anaerobic bacterium Bifidobacterium longum (B. longum) which can colonize selectively in hypoxic regions of the animal body was successfully localized and shown to proliferate in the hypoxic zone of tumor tissue, overcoming the above disadvantages. This study aimed to explore the effects of Bifidobacteria on AET (including the structure and acoustic properties of tumor tissues) and HIFU ablation at different time. The results show that the injection of Bifidobacteria increased the collagen fibre number, elastic modulus and sound velocity and decreased neovascularization in tumor tissues. The number of collagen fibres and neovascularization decreased significantly over time. Under the same HIFU irradiation intensity, the B. longum injection increased the coagulative necrosis volume and decreased the energy efficiency factor (EEF). This study confirmed that Bifidobacteria can change the AET and increase the deposition of ultrasonic energy and thereby the efficiency of HIFU. In addition, the time that Bifidobacteria stay in the tumor area after injection is an important factor. This research provides a novel approach for synergistic biologically targeted HIFU therapy.

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.

Molecular principles of metastasis: a hallmark of cancer revisited

Metastasis is the hallmark of cancer that is responsible for the greatest number of cancer-related deaths. Yet, it remains poorly understood. The continuous evolution of cancer biology research and the emergence of new paradigms in the study of metastasis have revealed some of the molecular underpinnings of this dissemination process. The invading tumor cell, on its way to the target site, interacts with other proteins and cells. Recognition of these interactions improved the understanding of some of the biological principles of the metastatic cell that govern its mobility and plasticity. Communication with the tumor microenvironment allows invading cancer cells to overcome stromal challenges, settle, and colonize. These characteristics of cancer cells are driven by genetic and epigenetic modifications within the tumor cell itself and its microenvironment. Establishing the biological mechanisms of the metastatic process is crucial in finding open therapeutic windows for successful interventions. In this review, the authors explore the recent advancements in the field of metastasis and highlight the latest insights that contribute to shaping this hallmark of cancer.

Sequence-Based Characterization of Intratumoral Bacteria-A Guide to Best Practice

Tumors are hospitable environments to bacteria and several recent studies on cancer patient samples have introduced the concept of an endogenous tumor microbiome. For a variety of reasons, this putative tumor microbiome is particularly challenging to investigate, and a failure to account for the various potential pitfalls will result in erroneous results and claims. Before this potentially extremely medically-significant habitat can be accurately characterized, a clear understanding of all potential confounding factors is required, and a best-practice approach should be developed and adopted. This review summarizes all of the potential issues confounding accurate bacterial DNA sequence analysis of the putative tumor microbiome, and offers solutions based on related research with the hope of assisting in the progression of research in this field.

Designing a light-activated recombinant alpha hemolysin for colorectal cancer targeting

Introduction: Colorectal cancer (CRC) is one of the main health burden worldwide, which can cause major economic and physiological problems along with relatively high rate of mortality. It is important to develop new methods for the localized delivery of recombinant protein therapeutics, in large part due to the failure of conventional therapies in most cases. Since E. coli Nissle 1917 (EcN) does not produce any virulence factors, here we used these bacteria with the light-activated promoter system to deliver therapeutic agents in the desired location and time. Methods: In this study, Staphylococcus aureus alpha hemolysin (SAH), after codon usage optimization, was cloned into blue light activating vector (pDawn) and transferred to EcN strain. Then, the functionality and cytotoxicity of secreted alpha hemolysin was evaluated in the SW480 colon cancer cell line by using different experiments, including blood agar test, flow cytometry analysis, and DAPI staining. Results: Our findings revealed that EcN can produce functional SAH under the blue light irradiation against SW480 cancer cells. Moreover, cytotoxicity assays confirmed the dose- and time-dependent toxicity of this payload (SAH) against SW480 cancer cells. Conclusion: Based on our results, EcN is proposed as an appropriate light-activated vehicle for delivery of anticancer agents to the target cancer cells/tissues.

Bifidobacterium spp: the promising Trojan Horse in the era of precision oncology

Selective delivery of therapeutic agents into solid tumors has been a major challenge impeding the achievement of long-term disease remission and cure. The need to develop alternative drug delivery routes to achieve higher drug concentration in tumor tissue, reduce unwanted off-target side effects and thus achieve greater therapeutic efficacy, has resulted in an explosive body of research. Bifidobacterium spp. are anaerobic, nonpathogenic, Gram-positive bacteria, commensal to the human gut that are a possible anticancer drug-delivery vehicle. In this review, we describe Bifidobacterium's microbiology, current clinical applications, overview of the preclinical work investigating Bifidobacterium's potential to deliver anticancer therapy, and review the different strategies used up to date. Finally, we discuss both current challenges and future prospects.

Biomimetic and bioinspired strategies for oral drug delivery

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

The microbiome and cancer for clinicians

The human microbiome is an emerging target in cancer development and therapeutics. It may be directly oncogenic, through promotion of mucosal inflammation or systemic dysregulation, or may alter anti-cancer immunity/therapy. Microorganisms within, adjacent to and distant from tumors may affect cancer progression, and interactions and differences between these populations can influence the course of disease. Here we review the microbiome as it pertains to cancer for clinicians. The microbiota of cancers including colorectal, pancreas, breast and prostate are discussed. We examine "omics" technologies, microbiota associated with tumor tissue and tumor-site fluids such as feces and urine, as well as indirect effects of the gut microbiome. We describe roles of the microbiome in immunotherapy, and how it can be modulated to improve cancer therapeutics. While research is still at an early stage, there is potential to exploit the microbiome, as modulation may increase efficacy of treatments, reduce toxicities and prevent carcinogenesis.

[Targeted binding of estradiol with ESR1 promotes proliferation of human chondrocytes in vitro by inhibiting activation of ERK signaling pathway]

OBJECTIVE

To investigate the effect of estradiol (E2)/estrogen receptor 1 (ESR1) on the proliferation of human chondrocytes in vitro and explore the molecular mechanism.

METHODS

The Ad-Easy adenovirus packaging system was used to construct and package the ESR1-overexpressing adenovirus Ad-ESR1. Western blotting and qPCR were used to detect the expression of ESR1 protein and mRNA in human chondrocyte C28I2 cells. In the cells treated with different adenoviruses, the effects of E2 were tested on the expressions of proteins related with cell autophagy and apoptosis and the phosphorylation of ERK signaling pathway using Western blotting. Immunofluorescence assay was used to observe the intracellular autophagic flow, flow cytometry was performed to analyze the cell apoptosis rate and the cell cycle changes, and qPCR was used to detect the expressions of PCNA, cyclin B1 and cyclin D1 mRNAs. The inhibitory effect of the specific inhibitor of ERK on the expressions of autophagy- and apoptosis-related genes at both the protein and mRNA levels were detected using Western blotting and qPCR.

RESULTS

Transfection with the recombinant adenovirus overexpressing ESR1 and E2 treatment of C28I2 cells significantly enhanced the expressions of autophagy-related proteins LC3, ATG7, promoted the colocalization of LC3 and LAMP1 in the cytoplasm, increased the expressions of the proliferation-related marker genes PCNA, cyclin B1 and cyclin D1, and supressed the expressions of cleaved caspase-3, caspase-12 and pERK. RNA interference of ESR1 obviously lowered the expression levels of autophagy-related proteins in C28I2 cells, causing also suppression of the autophagic flow, increments of the expressions of apoptosis-related proteins and pERK, and down-regulated the expressions of the proliferation marker genes. Blocking ERK activation with the ERK inhibitor obviously inhibited the effects of E2/ESR1 on autophagy, proliferationrelated gene expressions and cell apoptosis.

CONCLUSIONS

The targeted binding of E2 with ESR1 promotes the proliferation of human chondrocytes in vitro possibly by inhibiting the activation of ERK signaling pathway to promote cell autophagy and induce cell apoptosis.

A platform of genetically engineered bacteria as vehicles for localized delivery of therapeutics: Toward applications for Crohn's disease

For therapies targeting diseases of the gastrointestinal tract, we and others envision probiotic bacteria that synthesize and excrete biotherapeutics at disease sites. Toward this goal, we have engineered commensal E. coli that selectively synthesize and secrete a model biotherapeutic in the presence of nitric oxide (NO), an intestinal biomarker for Crohn's disease (CD). This is accomplished by co‐expressing the pore forming protein TolAIII with the biologic, granulocyte macrophage‐colony stimulating factor (GM‐CSF). We have additionally engineered these bacteria to accumulate at sites of elevated NO by engineering their motility circuits and controlling pseudotaxis. Importantly, because we have focused on in vitro test beds, motility and biotherapeutics production are spatiotemporally characterized. Together, the targeted recognition, synthesis, and biomolecule delivery comprises a “smart” probiotics platform that may have utility in the treatment of CD. Further, this platform could be modified to accommodate other pursuits by swapping the promoter and therapeutic gene to reflect other disease biomarkers and treatments, respectively.

Synthetic Biology Approaches to Engineer Probiotics and Members of the Human Microbiota for Biomedical Applications

An increasing number of studies have strongly correlated the composition of the human microbiota with many human health conditions and, in several cases, have shown that manipulating the microbiota directly affects health. These insights have generated significant interest in engineering indigenous microbiota community members and nonresident probiotic bacteria as biotic diagnostics and therapeutics that can probe and improve human health. In this review, we discuss recent advances in synthetic biology to engineer commensal and probiotic lactic acid bacteria, bifidobacteria, and Bacteroides for these purposes, and we provide our perspective on the future potential of these technologies.

Physiological Translocation of Lactic Acid Bacteria during Pregnancy Contributes to the Composition of the Milk Microbiota in Mice

The human milk microbiota is a complex and diverse ecosystem that seems to play a relevant role in the mother-to-infant transmission of microorganisms during early life. Bacteria present in human milk may arise from different sources, and recent studies suggest that at least some of them may be originally present in the maternal digestive tract and may reach the mammary gland through an endogenous route during pregnancy and lactation. The objective of this work was to elucidate whether some lactic acid bacteria are able to translocate and colonize the mammary gland and milk. For this purpose, two lactic acid bacteria strains (Lactococcus lactis MG1614 and Lactobacillus salivarius PS2) were transformed with a plasmid containing the lux genes; subsequently, the transformed strains were orally administered to pregnant mice. The murine model allowed the visualization, isolation, and Polymerase Chain Reaction (PCR)-detection of the transformed bacteria in different body locations, including mammary tissue and milk, reinforcing the hypothesis that physiological translocation of maternal bacteria during pregnancy and lactation may contribute to the composition of the mammary and milk microbiota.

Influence of Particle Geometry on Gastrointestinal Transit and Absorption following Oral Administration

Geometry has been considered as one of the important parameters in nanoparticle design because it affects cellular uptake, transport across the physiological barriers, and in vivo distribution. However, only a few studies have been conducted to elucidate the influence of nanoparticle geometry in their in vivo fate after oral administration. This article discloses the effect of nanoparticle shape on transport and absorption in gastrointestinal (GI) tract. Nanorods and nanospheres were prepared and labeled using fluorescence resonance energy transfer molecules to track the in vivo fate of intact nanoparticles accurately. Results demonstrated that nanorods had significantly longer retention time in GI tract compared with nanospheres. Furthermore, nanorods exhibited stronger ability of penetration into space of villi than nanospheres, which is the main reason of longer retention time. In addition, mesenteric lymph transported 1.75% nanorods within 10 h, which was more than that with nanospheres (0.98%). Fluorescent signals arising from nanoparticles were found in the kidney but not in the liver, lung, spleen, or blood, which could be ascribed to low absorption of intact nanoparticles. In conclusion, nanoparticle geometry influences in vivo fate after oral delivery and nanorods should be further investigated for designing oral delivery systems for therapeutic drugs, vaccines, or diagnostic materials.

Designer bacteria as intratumoural enzyme biofactories

Bacterial-directed enzyme prodrug therapy (BDEPT) is an emerging form of treatment for cancer. It is a biphasic variant of gene therapy in which a bacterium, armed with an enzyme that can convert an inert prodrug into a cytotoxic compound, induces tumour cell death following tumour-specific prodrug activation. BDEPT combines the innate ability of bacteria to selectively proliferate in tumours, with the capacity of prodrugs to undergo contained, compartmentalised conversion into active metabolites in vivo. Although BDEPT has undergone clinical testing, it has received limited clinical exposure, and has yet to achieve regulatory approval. In this article, we review BDEPT from the system designer's perspective, and provide detailed commentary on how the designer should strategize its development de novo. We report on contemporary advancements in this field which aim to enhance BDEPT in terms of safety and efficacy. Finally, we discuss clinical and regulatory barriers facing BDEPT, and propose promising approaches through which these hurdles may best be tackled.

Intratumoural production of TNFα by bacteria mediates cancer therapy

Systemic administration of the highly potent anticancer therapeutic, tumour necrosis factor alpha (TNFα) induces high levels of toxicity and is responsible for serious side effects. Consequently, tumour targeting is required in order to confine this toxicity within the locality of the tumour. Bacteria have a natural capacity to grow within tumours and deliver therapeutic molecules in a controlled fashion. The non-pathogenic E. coli strain MG1655 was investigated as a tumour targeting system in order to produce TNFα specifically within murine tumours. In vivo bioluminescence imaging studies and ex vivo immunofluorescence analysis demonstrated rapid targeting dynamics and prolonged survival, replication and spread of this bacterial platform within tumours. An engineered TNFα producing construct deployed in mouse models via either intra-tumoural (i.t.) or intravenous (i.v.) administration facilitated robust TNFα production, as evidenced by ELISA of tumour extracts. Tumour growth was impeded in three subcutaneous murine tumour models (CT26 colon, RENCA renal, and TRAMP prostate) as evidenced by tumour volume and survival analyses. A pattern of pro-inflammatory cytokine induction was observed in tumours of treated mice vs. controls. Mice remained healthy throughout experiments. This study indicates the therapeutic efficacy and safety of TNFα expressing bacteria in vivo, highlighting the potential of non-pathogenic bacteria as a platform for restricting the activity of highly potent cancer agents to tumours.

Engineered Probiotics: Applications and Biological Containment

Bioengineered probiotics represent the next generation of whole cell-mediated biotherapeutics. Advances in synthetic biology, genome engineering, and DNA sequencing and synthesis have enabled scientists to design and develop probiotics with increased stress tolerance and the ability to target specific pathogens and their associated toxins, as well as to mediate targeted delivery of vaccines, drugs, and immunomodulators directly to host cells. Herein, we review the most significant advances in the development of this field. We discuss the critical issue of biological containment and consider the role of synthetic biology in the design and construction of the probiotics of the future.

Tumor-targeted delivery of a C-terminally truncated FADD (N-FADD) significantly suppresses the B16F10 melanoma via enhancing apoptosis

Fas-associated protein with death domain (FADD), a pivotal adaptor protein transmitting apoptotic signals, is indispensable for the induction of extrinsic apoptosis. However, overexpression of FADD can form large, filamentous aggregates, termed death effector filaments (DEFs) by self-association and initiate apoptosis independent of receptor cross-linking. A mutant of FADD, which is truncated of the C-terminal tail (m-FADD, 182–205 aa) named N-FADD (m-FADD, 1–181 aa), can dramatically up-regulate the strength of FADD self-association and increase apoptosis. In this study, it was found that over-expression of FADD or N-FADD caused apoptosis of B16F10 cells in vitro, even more, N-FADD showed a more potent apoptotic effect than FADD. Meanwhile, Attenuated Salmonella Typhimurium strain VNP20009 was engineered to express FADD or N-FADD under the control of a hypoxia-induced NirB promoter and each named VNP-pN-FADD and VNP-pN-N-FADD. The results showed both VNP-pN-FADD and VNP-pN-N-FADD delayed tumor growth in B16F10 mice model, while VNP-pN-N-FADD suppressed melanoma growth more significantly than VNP-pN-FADD. Additionally, VNP-pN-FADD and VNP-pN-N-FADD induced apoptosis of tumor cells by activating caspase-dependent apoptotic pathway. Our results show that N-FADD is a more potent apoptotic inducer and VNP20009-mediated targeted expression of N-FADD provides a possible cancer gene therapeutic approach for the treatment of melanoma.

Gut Bifidobacteria Populations in Human Health and Aging

The intestinal microbiota has increasingly been shown to have a vital role in various aspects of human health. Indeed, several studies have linked alterations in the gut microbiota with the development of different diseases. Among the vast gut bacterial community, Bifidobacterium is a genus which dominates the intestine of healthy breast-fed infants whereas in adulthood the levels are lower but relatively stable. The presence of different species of bifidobacteria changes with age, from childhood to old age. Bifidobacterium longum, B. breve, and B. bifidum are generally dominant in infants, whereas B. catenulatum, B. adolescentis and, as well as B. longum are more prevalent in adults. Increasingly, evidence is accumulating which shows beneficial effects of supplementation with bifidobacteria for the improvement of human health conditions ranging from protection against infection to different extra- and intra-intestinal positive effects. Moreover, bifidobacteria have been associated with the production of a number of potentially health promoting metabolites including short chain fatty acids, conjugated linoleic acid and bacteriocins. The aim of this mini-review is to describe the bifidobacteria compositional changes associated with different stages in life, highlighting their beneficial role, as well as their presence or absence in many disease states.

Programmable probiotics for detection of cancer in urine

Rapid advances in the forward engineering of genetic circuitry in living cells has positioned synthetic biology as a potential means to solve numerous biomedical problems, including disease diagnosis and therapy. One challenge in exploiting synthetic biology for translational applications is to engineer microbes that are well tolerated by patients and seamlessly integrate with existing clinical methods. We use the safe and widely used probiotic Escherichia coli Nissle 1917 to develop an orally administered diagnostic that can noninvasively indicate the presence of liver metastasis by producing easily detectable signals in urine. Our microbial diagnostic generated a high-contrast urine signal through selective expansion in liver metastases (10(6)-fold enrichment) and high expression of a lacZ reporter maintained by engineering a stable plasmid system. The lacZ reporter cleaves a substrate to produce a small molecule that can be detected in urine. E. coli Nissle 1917 robustly colonized tumor tissue in rodent models of liver metastasis after oral delivery but did not colonize healthy organs or fibrotic liver tissue. We saw no deleterious health effects on the mice for more than 12 months after oral delivery. Our results demonstrate that probiotics can be programmed to safely and selectively deliver synthetic gene circuits to diseased tissue microenvironments in vivo.

In Vivo Bioluminescence Imaging of Intratumoral Bacteria

This chapter describes the use of whole-body bioluminescent imaging (BLI) for the study of bacterial trafficking in live mice, with an emphasis on the use of bacteria in therapy of cancer. Bacteria present an attractive class of vector for cancer therapy, possessing a natural ability to grow preferentially within tumors following systemic administration. Bacteria engineered to express the lux gene cassette permit BLI detection of the bacteria and tumor sites concurrently. The location and levels of bacteria within tumors over time can be readily examined, visualized in two or three dimensions. The method is applicable to a wide range of bacterial species and tumor xenograft types. This article describes the protocol for analysis of bioluminescent bacteria within subcutaneous tumor-bearing mice. This powerful, and inexpensive, real-time imaging strategy represents an ideal method for the study of bacteria in vivo in the context of cancer research. This protocol outlines the procedure for studying lux-tagged Escherichia coli and Bifidobacterium breve in mice, demonstrating the spatial and temporal readout from 2D and 3D BLI achievable with whole-body in vivo luminescence imaging.

Three-dimensional tumor spheroids for in vitro analysis of bacteria as gene delivery vectors in tumor therapy

Background

Several studies in animal models demonstrated that obligate and facultative anaerobic bacteria of the genera Bifidobacterium, Salmonella, or Clostridium specifically colonize solid tumors. Consequently, these and other bacteria are discussed as live vectors to deliver therapeutic genes to inhibit tumor growth. Therapeutic approaches for cancer treatment using anaerobic bacteria have been investigated in different mouse models. In the present study, solid three-dimensional (3D) multicellular tumor spheroids (MCTS) of the colorectal adenocarcinoma cell line HT-29 were generated and tested for their potential to study prodrug-converting enzyme therapies using bacterial vectors in vitro.

Results

HT-29 MCTS resembled solid tumors displaying all relevant features with an outer zone of proliferating cells and hypoxic and apoptotic regions in the core. Upon incubation with HT-29 MCTS, Bifidobacterium bifidum S17 and Salmonella typhimurium YB1 selectively localized, survived and replicated in hypoxic areas inside MCTS. Furthermore, spores of the obligate anaerobe Clostridium sporogenes germinated in these hypoxic areas. To further evaluate the potential of MCTS to investigate therapeutic approaches using bacteria as gene delivery vectors, recombinant bifidobacteria expressing prodrug-converting enzymes were used. Expression of a secreted cytosine deaminase in combination with 5-fluorocytosine had no effect on growth of MCTS due to an intrinsic resistance of HT-29 cells to 5-fluorouracil, i.e. the converted drug. However, a combination of the prodrug CB1954 and a strain expressing a secreted chromate reductase effectively inhibited MCTS growth.

Conclusions

Collectively, the presented results indicate that MCTS are a suitable and reliable model to investigate live bacteria as gene delivery vectors for cancer therapy in vitro.

Electronic supplementary material

The online version of this article (doi:10.1186/s12934-015-0383-5) contains supplementary material, which is available to authorized users.

Activation of multiple chemotherapeutic prodrugs by the natural enzymolome of tumour-localised probiotic bacteria

Some chemotherapeutic drugs (prodrugs) require activation by an enzyme for efficacy. We and others have demonstrated the ability of probiotic bacteria to grow specifically within solid tumours following systemic administration, and we hypothesised that the natural enzymatic activity of these tumour-localised bacteria may be suitable for activation of certain such chemotherapeutic drugs. Several wild-type probiotic bacteria; Escherichia coli Nissle, Bifidobacterium breve, Lactococcus lactis and Lactobacillus species, were screened against a panel of popular prodrugs. All strains were capable of activating at least one prodrug. E. coli Nissle 1917 was selected for further studies because of its ability to activate numerous prodrugs and its resistance to prodrug toxicity. HPLC data confirmed biochemical transformation of prodrugs to their toxic counterparts. Further analysis demonstrated that different enzymes can complement prodrug activation, while simultaneous activation of multiple prodrugs (CB1954, 5-FC, AQ4N and Fludarabine phosphate) by E. coli was confirmed, resulting in significant efficacy improvement. Experiments in mice harbouring murine tumours validated in vitro findings, with significant reduction in tumour growth and increase in survival of mice treated with probiotic bacteria and a combination of prodrugs. These findings demonstrate the ability of probiotic bacteria, without the requirement for genetic modification, to enable high-level activation of multiple prodrugs specifically at the site of action.