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

Paving the way for bacteria-based drug delivery: biohybrid microrobots emerging from microrobotics and synthetic biology

Advances in microrobotics and synthetic biology are paving the way for innovative solutions to long-standing challenges in drug delivery. Both fields have independently worked on engineering bacteria as a therapeutic system, focusing on enhancing propulsion, cargo delivery, detection, and biocompatibility. Bacteria, with their inherent adaptability and functional versatility, serve as an ideal foundation for these efforts, enabling them to navigate complex biological environments such as the human body. This review explores the convergence of microrobotics and synthetic biology, which has catalysed the development of biohybrid bacterial microrobots that integrate the strengths of both disciplines. By incorporating external control modalities - such as light, ultrasound, and magnetic fields - these hybrid systems address the limitations of purely microrobotic or biological approaches, offering new opportunities to enhance precision and efficacy in targeted therapies. However, realising the full potential of biohybrid bacterial microrobots requires overcoming critical challenges, such as ensuring compatibility between biological and synthetic components, scaling manufacturing processes, and defining regulatory pathways tailored to living therapeutics. Addressing these hurdles through joint, interdisciplinary research efforts, can unlock the transformative possibilities of these systems in modern medicine.

Prospects of engineered bacteria-assisted CAR T Cell therapy in gastrointestinal cancers

The high incidence and mortality rates associated with gastrointestinal cancers represent a significant global health challenge. In recent years, CAR T cell therapy has emerged as a promising immunotherapeutic approach, demonstrating favorable clinical outcomes. However, the application of traditional CAR T cell therapy in gastrointestinal cancers faces numerous challenges, including the suppressive tumor microenvironment and limitations in anti-tumor efficacy. The application of engineered bacteria offers a novel strategy to enhance CAR T cell therapy by modulating the tumor microenvironment and boosting immune responses, potentially leading to improved therapeutic outcomes. This review synthesizes the current research advancements related to engineered bacteria-assisted CAR T cell therapy in gastrointestinal cancers, exploring its underlying mechanisms, clinical applications, and future developmental directions.

Bacterial immunotherapy leveraging IL-10R hysteresis for both phagocytosis evasion and tumor immunity revitalization

Bacterial immunotherapy holds promising cancer-fighting potential. However, unlocking its power requires a mechanistic understanding of how bacteria both evade antimicrobial immune defenses and stimulate anti-tumor immune responses within the tumor microenvironment (TME). Here, by harnessing an engineered Salmonella enterica strain with this dual proficiency, we unveil an underlying singular mechanism. Specifically, the hysteretic nonlinearity of interleukin-10 receptor (IL-10R) expression drives tumor-infiltrated immune cells into a tumor-specific IL-10Rhi state. Bacteria leverage this to enhance tumor-associated macrophages producing IL-10, evade phagocytosis by tumor-associated neutrophils, and coincidently expand and stimulate the preexisting exhausted tumor-resident CD8+ T cells. This effective combination eliminates tumors, prevents recurrence, and inhibits metastasis across multiple tumor types. Analysis of human samples suggests that the IL-10Rhi state might be a ubiquitous trait across human tumor types. Our study unveils the unsolved mechanism behind bacterial immunotherapy's dual challenge in solid tumors and provides a framework for intratumoral immunomodulation.

Genetically Engineered Bacteria as a Promising Therapeutic Strategy Against Cancer: A Comprehensive Review

As a significant cause of global mortality, the cancer has also economic impacts. In the era of cancer therapy, mitigating side effects and costs and overcoming drug resistance is crucial. Microbial species can grow inside the tumor microenvironment and inhibit cancer growth through direct killing of tumor cells and immunoregulatory effects. Although microbiota or their products have demonstrated anticancer effects, the possibility of acting as pathogens and exerting side effects in certain individuals is a risk. Hence, several genetically modified/engineered bacteria (GEB) have been developed to this aim with ability of diagnosing and selective targeting and destruction of cancers. Additionally, GEB are expected to be considerably more efficient, safer, more permeable, less costly, and less invasive theranostic approaches compared to wild types. Potential GEB strains such as Escherichia coli (Nissle 1917, and MG1655), Salmonella typhimurium YB1 SL7207 (aroA gene deletion), VNP20009 (∆msbB/∆purI) and ΔppGpp (PTet and PBAD), and Listeria monocytogenes Lmat-LLO have been developed to combat cancer cells. When used in tandem with conventional treatments, GEB substantially improve the efficacy of anticancer therapy outcomes. In addition, public acceptance, optimal timing (s), duration (s), dose (s), and strains identification, interactions with other strains and the host cells, efficacy, safety and quality, and potential risks and ethical dilemmas include major challenges.

Nanobiohybrid Oncolytic Bacteria with Optimized Intratumoral Distribution for Combined Sono-Photodynamic/Immunotherapy

"Living therapeutic carriers" present a promising avenue for cancer research, but it is still challenging to achieve uniform and durable distribution of payloads throughout the solid tumor owing to the tumor microenvironment heterogeneity. Herein, a living drug sprinkle biohybrid (YB1-HCNs) was constructed by hitching acid/enzyme-triggered detachable nanoparticles (HCNs) backpack on the surface of metabolic oligosaccharide-engineered oncolytic bacteria YB1. Along with the process of tumor penetration by bacterial hypoxia navigation, YB1-HCNs responsively and continuously release HCNs, achieving a uniform distribution of loaded agents throughout the tumor. Upon successive irradiation of laser and ultrasound (US), the HCNs can separately generate type II and type I ROS for superior sono-photodynamic therapy (SPDT), which enables HCNs to synergize with YB1 for a satisfactory therapeutic effect in both superficial normoxic and deep hypoxic regions of the tumor. After a single dose, this efficient combination realized 98.3% primary tumor inhibition rate and prolonged survival of mice for 90 days with no recurrence, further inducing a powerful immunological memory effect to completely suppress tumor rechallenge in cured mice. Such a bacterial hybridization vector enables optimization of the spatial distribution of YB1 and HCNs, providing an innovative strategy to maximize therapeutic outcomes and evoke durable antitumor immunity.

Innovative Applications of Bacteria and Their Derivatives in Targeted Tumor Therapy

Despite significant progress in cancer treatment, traditional therapies still face considerable challenges, including poor targeting, severe toxic side effects, and the development of resistance. Recent advances in biotechnology have revealed the potential of bacteria and their derivatives as drug delivery systems for tumor therapy by leveraging their biological properties. Engineered bacteria, including Escherichia coli, Salmonella, and Listeria monocytogenes, along with their derivatives─outer membrane vesicles (OMVs), bacterial ghosts (BGs), and bacterial spores (BSPs)─can be loaded with a variety of antitumor agents, enabling precise targeting and sustained drug release within the tumor microenvironment (TME). These bacteria and their derivatives possess intrinsic properties that stimulate the immune system, enhancing both innate and adaptive immune responses to further amplify therapeutic effects. The ability of bacteria to naturally accumulate in hypoxic tumor regions and their versatility in genetic modifications allow for tailored drug delivery strategies that synergistically enhance the effectiveness of chemotherapy, immunotherapy, and targeted therapies. This review comprehensively examines the fundamental principles of bacterial therapy, focusing on the strategies employed for bacterial engineering, drug loading, and the use of bacteria and their derivatives in targeted tumor therapy. It also discusses the challenges faced in optimizing bacterial delivery systems, such as safety concerns, unintended immune responses, and scalability for clinical applications. By exploring these aspects, this review provides a theoretical framework for improving bacterial-based drug delivery systems, contributing to the development of more effective and personalized cancer treatments.

Bacterial and bacterial derivatives-based drug delivery systems: a novel approach for treating central nervous system disorders

INTRODUCTION

Bacteria and their derivatives show great potential as drug delivery systems due to their unique chemotaxis, biocompatibility, and targeting abilities. In CNS disease treatment, bacterial carriers can cross the blood-brain barrier (BBB) and deliver drugs precisely, overcoming limitations of traditional methods. Advances in genetic engineering, synthetic biology, and nanotechnology have transformed these systems into multifunctional platforms for personalized CNS treatment.

AREAS COVERED

This review examines the latest research on bacterial carriers for treating ischemic brain injury, neurodegenerative diseases, and gliomas. Bacteria efficiently cross the blood-brain barrier via active targeting, endocytosis, paracellular transport, and the nose-to-brain route for precise drug delivery. Various bacterial drug delivery systems, such as OMVs and bacterial ghosts, are explored for their design and application. Databases were searched in Google Scholar for the period up to December 2024.

EXPERT OPINION

Future developments in bacterial drug delivery will rely on AI-driven design and high-throughput engineering, enhancing treatment precision. Personalized medicine will further optimize bacterial carriers for individual patients, but challenges such as biosafety, immune rejection, and scalability must be addressed. As multimodal diagnostic and therapeutic strategies advance, bacterial carriers are expected to play a central role in CNS disease treatment, offering novel precision medicine solutions.

Precision tumor treatment utilizing bacteria: principles and future perspectives

Bacteria-based tumor therapy, which releases therapeutic payloads or remodels the tumor's immune-suppressive microenvironment and directly kills tumor cells or initiates an anti-tumor immune response, is recently recognized as a promising strategy. Bacteria could be endowed with the capacities of tumor targeting, tumor cell killing, and anti-tumor immune activating by established gene engineering. Furthermore, the integration of synthetic biology and nanomedicine into these engineered bacteria could further enhance their efficacy and controllability. This comprehensive review systematically elucidates the classification and mechanisms of bacterial gene expression induction systems, as well as strategies for constructing bacterial-nanomaterial nanobiohybrids. The review concludes by highlighting the challenges associated with quality control and regulation of bacteria-based tumor therapy while also providing insights into the future prospects of this therapeutic technology. KEY POINTS: • A comprehensive overview of the current status of research on bacteria-based tumor therapy. • The classification and mechanisms of bacterial gene expression induction systems are summarized. • The challenges and perspectives in clinical translation.

The guided fire from within: intratumoral administration of mRNA-based vaccines to mobilize memory immunity and direct immune responses against pathogen to target solid tumors

We investigated a novel cancer immunotherapy strategy that effectively suppresses tumor growth in multiple solid tumor models and significantly extends the lifespan of tumor-bearing mice by introducing pathogen antigens into tumors via mRNA-lipid nanoparticles. The pre-existing immunity against the pathogen antigen can significantly enhance the efficacy of this approach. In mice previously immunized with BNT162b2, an mRNA-based COVID-19 vaccine encoding the spike protein of the SARS-CoV-2 virus, intratumoral injections of the same vaccine efficiently tagged the tumor cells with mRNA-expressed spike protein. This action rapidly mobilized the pre-existing memory immunity against SARS-CoV-2 to kill the cancer cells displaying the spike protein, while concurrently reprogramming the tumor microenvironment (TME) by attracting immune cells. The partial elimination of tumor cells in a normalized TME further triggered extensive tumor antigen-specific T cell responses through antigen spreading, eventually resulting in potent and systemic tumor-targeting immune responses. Moreover, combining BNT162b2 treatment with anti-PD-L1 therapy yielded a more substantial therapeutic impact, even in "cold tumor" types that are typically less responsive to treatment. Given that the majority of the global population has acquired memory immunity against various pathogens through infection or vaccination, we believe that, in addition to utilizing the widely held immune memory against SARS-CoV-2 via COVID-19 vaccine, mRNA vaccines against other pathogens, such as Hepatitis B Virus (HBV), Common Human Coronaviruses (HCoVs), and the influenza virus, could be rapidly transitioned into clinical use and holds great promise in treating different types of cancer. The extensive selection of pathogen antigens expands therapeutic opportunities and may also overcome potential drug resistance.

A Review of Clinical Trials Involving Genetically Modified Bacteria, Bacteriophages and Their Associated Risk Assessments

Introduction

Discussion of gene-modified investigational products (IPs) in clinical trials has largely focused on nucleic acid-based vectors, viral vectors, and gene-modified cellular products involving mammalian cells. Use of bacteria and bacteriophages as IPs is resurgent, and discussion of the risks associated with genetic modification of these organisms has become pertinent to the biosafety community.

Methods

This review article summarizes the United States Food and Drug Administration classification for IPs comprising bacteria or bacteriophages and provides an overview of clinical trials conducted to date involving genetically modified bacteria. The risk assessment for bacterial or bacteriophage-based IPs is discussed.

Conclusion

The risk assessment process for bacterial or bacteriophage-based IPs is different from that of gene expression vectors and mammalian cells. Greater consideration must be given to the attenuating mutations affecting virulence, replication competency, antibiotic susceptibility, and persistence in the environment. With the recent growth in clinical trials involving genetically modified bacteria, biosafety professionals and Institutional Biosafety Committees with responsibilities including oversight of clinical trials must become familiar with the associated risk assessment.

The Rational Engineered Bacteria Based Biohybrid Living System for Tumor Therapy

Living therapy based on bacterial cells has gained increasing attention for their applications in tumor treatments. Bacterial cells can naturally target to tumor sites and active the innate immunological responses. The intrinsic advantages of bacteria attribute to the development of biohybrid living carriers for targeting delivery toward hypoxic environments. The rationally engineered bacterial cells integrate various functions to enhance the tumor therapy and reduce toxic side effects. In this review, the antitumor effects of bacteria and their application are discussed as living therapeutic agents across multiple antitumor platforms. The various kinds of bacteria used for cancer therapy are first introduced and demonstrated the mechanism of antitumor effects as well as the immunological effects. Additionally, this study focused on the genetically modified bacteria for the production of antitumor agents as living delivery system to treat cancer. The combination of living bacterial cells with functional nanomaterials is then discussed in the cancer treatments. In brief, the rational design of living therapy based on bacterial cells highlighted a rapid development in tumor therapy and pointed out the potentials in clinical applications.

Tumor-targeting bacteria as immune stimulants - the future of cancer immunotherapy?

Cancer immunotherapies have been widely hailed as a breakthrough for cancer treatment in the last decade, epitomized by the unprecedented results observed with checkpoint blockade. Even so, only a minority of patients currently achieve durable remissions. In general, responsive patients appear to have either a high number of tumor neoantigens, a preexisting immune cell infiltrate in the tumor microenvironment, or an 'immune-active' transcriptional profile, determined in part by the presence of a type I interferon gene signature. These observations suggest that the therapeutic efficacy of immunotherapy can be enhanced through strategies that release tumor neoantigens and/or produce a pro-inflammatory tumor microenvironment. In principle, exogenous tumor-targeting bacteria offer a unique solution for improving responsiveness to immunotherapy. This review discusses how tumor-selective bacterial infection can modulate the immunological microenvironment of the tumor and the potential for combination with cancer immunotherapy strategies to further increase therapeutic efficacy. In addition, we provide a perspective on the clinical translation of replicating bacterial therapies, with a focus on the challenges that must be resolved to ensure a successful outcome.

Targeting Tumor Hypoxia with Nanoparticle-Based Therapies: Challenges, Opportunities, and Clinical Implications

Hypoxia is a crucial factor in tumor biology, affecting various solid tumors to different extents. Its influence spans both early and advanced stages of cancer, altering cellular functions and promoting resistance to therapy. Hypoxia reduces the effectiveness of radiotherapy, chemotherapy, and immunotherapy, making it a target for improving therapeutic outcomes. Despite extensive research, gaps persist, necessitating the exploration of new chemical and pharmacological interventions to modulate hypoxia-related pathways. This review discusses the complex pathways involved in hypoxia and the associated pharmacotherapies, highlighting the limitations of current treatments. It emphasizes the potential of nanoparticle-based platforms for delivering anti-hypoxic agents, particularly oxygen (O2), to the tumor microenvironment. Combining anti-hypoxic drugs with conventional cancer therapies shows promise in enhancing remission rates. The intricate relationship between hypoxia and tumor progression necessitates novel therapeutic strategies. Nanoparticle-based delivery systems can significantly improve cancer treatment efficacy by targeting hypoxia-associated pathways. The synergistic effects of combined therapies underscore the importance of multimodal approaches in overcoming hypoxia-mediated resistance. Continued research and innovation in this area hold great potential for advancing cancer therapy and improving patient outcomes.

Veillonella parvula as an anaerobic lactate-fermenting bacterium for inhibition of tumor growth and metastasis through tumor-specific colonization and decrease of tumor's lactate level

High tumor's lactate level directly associates with high tumor growth, metastasis, and patients' poor prognosis. Therefore, many studies have focused on the decrease of tumor's lactate as a novel cancer treatment. In the present study for the first time, a strictly anaerobic lactate-fermenting bacterium, Veillonella parvula, was employed for the decrease of tumor's lactate level. At first, 4T1 breast tumor-bearing BALB/c mice were administered with 106 V. parvula bacteria intravenously, orally, intraperitoneally, and intratumorally. Then, the bacteria biodistribution was evaluated. The best administration route according to tumor colonization was selected and its safety was assessed. Then, the therapeutic effect of V. parvula administration through the best route was investigated according to 4T1 murine breast tumor's growth and metastasis in vivo. In addition, histopathological and immunohistochemistry evaluations were done to estimate microscopic changes at the inner of the tumor and tumor's lactate level was measured after V. parvula administration. V. parvula exhibited considerable tumor-targeting and colonization efficacy, 24 h after intravenous administration. Normal organs were free of the bacteria after 72 h and no side effect was observed. Tumor colonization by V. parvula significantly decreased the tumors' lactate level for about 46% in comparison with control tumors which caused 44.3% and 51.6% decline (P < 0.05) in the mean tumors' volume and liver metastasis of the treatment group in comparison with the control group, respectively. The treatment group exhibited 35% inhibition in the cancer cell proliferation in comparison with the control according to the Ki-67 immunohistochemistry staining. Therefore, intravenous administration of V. parvula is a tumor-specific and safe treatment which can significantly inhibit tumors' growth and metastasis by decreasing the tumor lactate level.

Systematic review on the role of the gut microbiota in tumors and their treatment

Tumors present a formidable health risk with limited curability and high mortality; existing treatments face challenges in addressing the unique tumor microenvironment (hypoxia, low pH, and high permeability), necessitating the development of new therapeutic approaches. Under certain circumstances, certain bacteria, especially anaerobes or parthenogenetic anaerobes, accumulate and proliferate in the tumor environment. This phenomenon activates a series of responses in the body that ultimately produce anti-tumor effects. These bacteria can target and colonize the tumor microenvironment, promoting responses aimed at targeting and fighting tumor cells. Understanding and exploiting such interactions holds promise for innovative therapeutic strategies, potentially augmenting existing treatments and contributing to the development of more effective and targeted approaches to fighting tumors. This paper reviews the tumor-promoting mechanisms and anti-tumor effects of the digestive tract microbiome and describes bacterial therapeutic strategies for tumors, including natural and engineered anti-tumor strategies.

Exploiting bacteria for cancer immunotherapy

Immunotherapy has revolutionized the treatment of cancer but continues to be constrained by limited response rates, acquired resistance, toxicities and high costs, which necessitates the development of new, innovative strategies. The discovery of a connection between the human microbiota and cancer dates back 4,000 years, when local infection was observed to result in tumour eradication in some individuals. However, the true oncological relevance of the intratumoural microbiota was not recognized until the turn of the twentieth century. The intratumoural microbiota can have pivotal roles in both the pathogenesis and treatment of cancer. In particular, intratumoural bacteria can either promote or inhibit cancer growth via remodelling of the tumour microenvironment. Over the past two decades, remarkable progress has been made preclinically in engineering bacteria as agents for cancer immunotherapy; some of these bacterial products have successfully reached the clinical stages of development. In this Review, we discuss the characteristics of intratumoural bacteria and their intricate interactions with the tumour microenvironment. We also describe the many strategies used to engineer bacteria for use in the treatment of cancer, summarizing contemporary data from completed and ongoing clinical trials. The work described herein highlights the potential of bacteria to transform the landscape of cancer therapy, bridging ancient wisdom with modern scientific innovation.

Cancer therapy with the viral and bacterial pathogens: The past enemies can be considered the present allies

Cancer continues to be one of the leading causes of mortality worldwide despite significant advancements in cancer treatment. Many difficulties have arisen as a result of the detrimental consequences of chemotherapy and radiotherapy as a common cancer therapy, such as drug inability to penetrate deep tumor tissue, and also the drug resistance in tumor cells continues to be a major concern. These obstacles have increased the need for the development of new techniques that are more selective and effective against cancer cells. Bacterial-based therapies and the use of oncolytic viruses can suppress cancer in comparison to other cancer medications. The tumor microenvironment is susceptible to bacterial accumulation and proliferation, which can trigger immune responses against the tumor. Oncolytic viruses (OVs) have also gained considerable attention in recent years because of their potential capability to selectively target and induce apoptosis in cancer cells. This review aims to provide a comprehensive summary of the latest literature on the role of bacteria and viruses in cancer treatment, discusses the limitations and challenges, outlines various strategies, summarizes recent preclinical and clinical trials, and emphasizes the importance of optimizing current strategies for better clinical outcomes.

The Role of Bacteria in Central Nervous System Tumors: Opportunities and Challenges

Tumors of the central nervous system (CNS) are severe and refractory diseases with poor prognosis, especially for patients with malignant glioblastoma and brain metastases. Currently, numerous studies have explored the potential role of bacteria and intestinal flora in tumor development and treatment. Bacteria can penetrate the blood-brain barrier (BBB), targeting the hypoxic microenvironment at the core of tumors, thereby eliminating tumors and activating both the innate and adaptive immune responses, rendering them promising therapeutic agents for CNS tumors. In addition, engineered bacteria and derivatives, such as bacterial membrane proteins and bacterial spores, can also be used as good candidate carriers for targeted drug delivery. Moreover, the intestinal flora can regulate CNS tumor metabolism and influence the immune microenvironment through the "gut-brain axis". Therefore, bacterial anti-tumor therapy, engineered bacterial targeted drug delivery, and intervention of the intestinal flora provide therapeutic modalities for the treatment of CNS tumors. In this paper, we performed a comprehensive review of the mechanisms and therapeutic practices of bacterial therapy for CNS tumors and discussed potential future research directions in this field.

Progress of engineered bacteria for tumour therapy

Finding novel therapeutic modalities, improving drug delivery efficiency and targeting, and reducing the immune escape of tumor cells are currently hot topics in the field of tumor therapy. Bacterial therapeutics have proven highly effective in preventing tumor spread and recurrence, used alone or in combination with traditional therapies. In recent years, a growing number of researchers have significantly improved the targeting and penetration of bacteria by using genetic engineering technology, which has received widespread attention in the field of tumor therapy. In this paper, we provide an overview and assessment of the advancements made in the field of tumor therapy using genetically engineered bacteria. We cover three major aspects: the development of engineered bacteria, their integration with other therapeutic techniques, and the current state of clinical trials. Lastly, we discuss the limitations and challenges that are currently being faced in the utilization of engineered bacteria for tumor therapy.

Synergistic Brilliance: Engineered Bacteria and Nanomedicine Unite in Cancer Therapy

Engineered bacteria are widely used in cancer treatment because live facultative/obligate anaerobes can selectively proliferate at tumor sites and reach hypoxic regions, thereby causing nutritional competition, enhancing immune responses, and producing anticancer microbial agents in situ to suppress tumor growth. Despite the unique advantages of bacteria-based cancer biotherapy, the insufficient treatment efficiency limits its application in the complete ablation of malignant tumors. The combination of nanomedicine and engineered bacteria has attracted increasing attention owing to their striking synergistic effects in cancer treatment. Engineered bacteria that function as natural vehicles can effectively deliver nanomedicines to tumor sites. Moreover, bacteria provide an opportunity to enhance nanomedicines by modulating the TME and producing substrates to support nanomedicine-mediated anticancer reactions. Nanomedicine exhibits excellent optical, magnetic, acoustic, and catalytic properties, and plays an important role in promoting bacteria-mediated biotherapies. The synergistic anticancer effects of engineered bacteria and nanomedicines in cancer therapy are comprehensively summarized in this review. Attention is paid not only to the fabrication of nanobiohybrid composites, but also to the interpromotion mechanism between engineered bacteria and nanomedicine in cancer therapy. Additionally, recent advances in engineered bacteria-synergized multimodal cancer therapies are highlighted.

Hypoxia-targeting bacteria in cancer therapy

Tumor hypoxia plays a crucial role in driving cancer progression and fostering resistance to therapies by contributing significantly to chemoresistance, radioresistance, angiogenesis, invasiveness, metastasis, altered cell metabolism, and genomic instability. Despite the challenges encountered in therapeutically addressing tumor hypoxia with conventional drugs, a noteworthy alternative has emerged through the utilization of anaerobic oncolytic bacteria. These bacteria exhibit a preference for accumulating and proliferating within the hypoxic regions of tumors, where they can initiate robust antitumor effects and immune responses. Through simple genetic manipulation or sophisticated synthetic bioengineering, these bacteria can be further optimized to improve safety and antitumor activities, or they can be combined synergistically with chemotherapies, radiation, or other immunotherapies. In this review, we explore the potential benefits and challenges associated with this innovative anticancer approach, addressing issues related to clinical translation, particularly as several strains have progressed to clinical evaluation.

Self-propelling bacteria-based magnetic nanoparticles (BacMags) for targeted magnetic hyperthermia therapy against hypoxic tumors

Magnetic hyperthermia-based cancer therapy (MHCT) holds great promise as a non-invasive approach utilizing heat generated by an alternating magnetic field for effective cancer treatment. For an efficacious therapeutic response, it is crucial to deliver therapeutic agents selectively at the depth of tumors. In this study, we present a new strategy using the naturally occurring tumor-colonizing bacteria Escherichia coli (E. coli) as a carrier to deliver magnetic nanoparticles to hypoxic tumor cores for effective MHCT. Self-propelling delivery agents, "nano-bacteriomagnets" (BacMags), were developed by incorporating anisotropic magnetic nanocubes into E. coli which demonstrated significantly improved hyperthermic performance, leading to an impressive 85% cell death in pancreatic cancer. The in vivo anti-cancer response was validated in a syngeneic xenograft model with a 50% tumor inhibition rate within 20 days and a complete tumor regression within 30 days. This proof-of-concept study demonstrates the potential of utilizing anaerobic bacteria for the delivery of magnetic nanocarriers as a smart therapeutic approach for enhanced MHCT.

Promising dawn in tumor microenvironment therapy: engineering oral bacteria

Despite decades of research, cancer continues to be a major global health concern. The human mouth appears to be a multiplicity of local environments communicating with other organs and causing diseases via microbes. Nowadays, the role of oral microbes in the development and progression of cancer has received increasing scrutiny. At the same time, bioengineering technology and nanotechnology is growing rapidly, in which the physiological activities of natural bacteria are modified to improve the therapeutic efficiency of cancers. These engineered bacteria were transformed to achieve directed genetic reprogramming, selective functional reorganization and precise control. In contrast to endotoxins produced by typical genetically modified bacteria, oral flora exhibits favorable biosafety characteristics. To outline the current cognitions upon oral microbes, engineered microbes and human cancers, related literatures were searched and reviewed based on the PubMed database. We focused on a number of oral microbes and related mechanisms associated with the tumor microenvironment, which involve in cancer occurrence and development. Whether engineering oral bacteria can be a possible application of cancer therapy is worth consideration. A deeper understanding of the relationship between engineered oral bacteria and cancer therapy may enhance our knowledge of tumor pathogenesis thus providing new insights and strategies for cancer prevention and treatment.

Bacteria-Based Nanoprobes for Cancer Therapy

Surgical removal together with chemotherapy and radiotherapy has used to be the pillars of cancer treatment. Although these traditional methods are still considered as the first-line or standard treatments, non-operative situation, systemic toxicity or resistance severely weakened the therapeutic effect. More recently, synthetic biological nanocarriers elicited substantial interest and exhibited promising potential for combating cancer. In particular, bacteria and their derivatives are omnipotent to realize intrinsic tumor targeting and inhibit tumor growth with anti-cancer agents secreted and immune response. They are frequently employed in synergistic bacteria-mediated anticancer treatments to strengthen the effectiveness of anti-cancer treatment. In this review, we elaborate on the development, mechanism and advantage of bacterial therapy against cancer and then systematically introduce the bacteria-based nanoprobes against cancer and the recent achievements in synergistic treatment strategies and clinical trials. We also discuss the advantages as well as the limitations of these bacteria-based nanoprobes, especially the questions that hinder their application in human, exhibiting this novel anti-cancer endeavor comprehensively.

Enhancing tumor-specific recognition of programmable synthetic bacterial consortium for precision therapy of colorectal cancer

Probiotics hold promise as a potential therapy for colorectal cancer (CRC), but encounter obstacles related to tumor specificity, drug penetration, and dosage adjustability. In this study, genetic circuits based on the E. coli Nissle 1917 (EcN) chassis were developed to sense indicators of tumor microenvironment and control the expression of therapeutic payloads. Integration of XOR gate amplify gene switch into EcN biosensors resulted in a 1.8-2.3-fold increase in signal output, as confirmed by mathematical model fitting. Co-culturing programmable EcNs with CRC cells demonstrated a significant reduction in cellular viability ranging from 30% to 50%. This approach was further validated in a mouse subcutaneous tumor model, revealing 47%-52% inhibition of tumor growth upon administration of therapeutic strains. Additionally, in a mouse tumorigenesis model induced by AOM and DSS, the use of synthetic bacterial consortium (SynCon) equipped with multiple sensing modules led to approximately 1.2-fold increased colon length and 2.4-fold decreased polyp count. Gut microbiota analysis suggested that SynCon maintained the abundance of butyrate-producing bacteria Lactobacillaceae NK4A136, whereas reducing the level of gut inflammation-related bacteria Bacteroides. Taken together, engineered EcNs confer the advantage of specific recognition of CRC, while SynCon serves to augment the synergistic effect of this approach.

Salmonella immunotherapy engineered with highly efficient tumor antigen coating establishes antigen-specific CD8+ T cell immunity and increases in antitumor efficacy with type I interferon combination therapy

Bacteria-based cancer therapy employs various strategies to combat tumors, one of which is delivering tumor-associated antigen (TAA) to generate specific immunity. Here, we utilized a poly-arginine extended HPV E7 antigen (9RE7) for attachment on Salmonella SL7207 outer membrane to synthesize the bacterial vaccine Salmonella-9RE7 (Sal-9RE7), which yielded a significant improvement in the amount of antigen presentation compared to the previous lysine-extended antigen coating strategy. In TC-1 tumor mouse models, Sal-9RE7 monotherapy decreased tumor growth by inducing E7 antigen-specific immunity. In addition, pairing Sal-9RE7 with adjuvant Albumin-IFNβ (Alb-IFNβ), a protein cytokine fusion, the combination significantly increased the antitumor efficacy and enhanced immunogenicity in the tumor microenvironment (TME). Our study made a significant contribution to personalized bacterial immunotherapy via TAA delivery and demonstrated the advantage of combination therapy.

Salmonella enterica and outer membrane vesicles are current and future options for cancer treatment

Conventional cancer therapies have many limitations. In the last decade, it has been suggested that bacteria-mediated immunotherapy may circumvent the restrictions of traditional treatments. For example, Salmonella enterica is the most promising bacteria for treating cancer due to its intrinsic abilities, such as killing tumor cells, targeting, penetrating, and proliferating into the tumor. S. enterica has been genetically modified to ensure safety and increase its intrinsic antitumor efficacy. This bacterium has been used as a vector for delivering anticancer agents and as a combination therapy with chemotherapy, radiotherapy, or photothermic. Recent studies have reported the antitumor efficacy of outer membrane vesicles (OMVs) derived from S. enterica. OMVs are considered safer than attenuated bacteria and can stimulate the immune system as they comprise most of the immunogens found on the surface of their parent bacteria. Furthermore, OMVs can also be used as nanocarriers for antitumor agents. This review describes the advances in S. enterica as immunotherapy against cancer and the mechanisms by which Salmonella fights cancer. We also highlight the use of OMVs as immunotherapy and nanocarriers of anticancer agents. OMVs derived from S. enterica are innovative and promising strategies requiring further investigation.

Bacteria-driven cancer therapy: Exploring advancements and challenges

Cancer, a serious fatal disease caused by the uncontrolled growth of cells, is the biggest challenge flagging around medicine and health fields. Conventionally, various treatments-based strategies such as radiotherapy, chemotherapy, and alternative cancer therapies possess drugs that cannot reach the cancerous tissues and make them toxic to noncancerous cells. Cancer immunotherapy has made outstanding achievements in reducing the chances of cancer. Our considerable attention towards cancer-directed immune responses and the mechanisms behind which immune cells kill cancer cells have progressively been helpful in the advancement of new therapies. Among them, bacteria-based cancer immunotherapy has achieved much more attention due to smart and robust mechanisms in activating the host anti-tumor response. Moreover, bacterial-based therapy can be utilized as a single monotherapy or in combination with multiple anticancer immunotherapies to accelerate productive clinical results. Herein, we comprehensively reviewed recent advancements, challenges, and future perspectives in developing bacterial-based cancer immunotherapies.

Targeted IFNγ induction by a genetically engineered Salmonella typhimurium is the key to the liver metastasis inhibition in a mouse model of pancreatic neuroendocrine tumor

Background

Liver metastasis is one of the primary causes of death for the patients with pancreatic neuroendocrine tumors (PNETs). However, no curative therapy has been developed so far.

Methods

The anti-tumor efficacy of a genetically engineered tumor-targeting Salmonella typhimurium YB1 was evaluated on a non-functional INR1G9 liver metastasis model. Differential inflammatory factors were screened by Cytometric Bead Array. Antibody depletion assay and liver-targeted AAV2/8 expression vector were used for functional evaluation of the differential inflammatory factors.

Results

We demonstrated that YB1 showed significant anti-tumor efficacy as a monotherapy. Since YB1 cannot infect INR1G9 cells, its anti-tumor effect was possibly due to the modulation of the tumor immune microenvironment. Two inflammatory factors IFNγ and CCL2 were elevated in the liver after YB1 administration, but only IFNγ was found to be responsible for the anti-tumor effect. Liver-targeted expression of IFNγ caused the activation of macrophages and NK cells, and reproduced the therapeutic effect of YB1 on liver metastasis.

Conclusion

We demonstrated that YB1 may exhibit anti-tumor effect mainly based on IFNγ induction. Targeted IFNγ therapy can replace YB1 for treating liver metastasis of PNETs.

Breast cancer vaccination: Latest advances with an analytical focus on clinical trials

Breast cancer (BC) is one of the main causes of cancer-related death worldwide. The heterogenicity of breast tumors and the presence of tumor resistance, metastasis, and disease recurrence make BC a challenging malignancy. A new age in cancer treatment is being ushered in by the enormous success of cancer immunotherapy, and therapeutic cancer vaccination is one such area of research. Nevertheless, it has been shown that the application of cancer vaccines in BC as monotherapy could not induce satisfying anti-tumor immunity. Indeed, the application of various vaccine platforms as well as combination therapies like immunotherapy could influence the clinical benefits of BC treatment. We analyzed the clinical trials of BC vaccination and revealed that the majority of trials were in phase I and II meaning that the BC vaccine studies lack favorable outcomes or they need more development. Furthermore, peptide- and cell-based vaccines are the major platforms utilized in clinical trials according to our analysis. Besides, some studies showed satisfying outcomes regarding carbohydrate-based vaccines in BC treatment. Recent advancements in therapeutic vaccines for breast cancer were promising strategies that could be accessible in the near future.

Revolutionizing cancer treatment: The power of cell-based drug delivery systems

Intravenous administration of drugs is a widely used cancer therapy approach. However, the efficacy of these drugs is often hindered by various biological barriers, including circulation, accumulation, and penetration, resulting in poor delivery to solid tumors. Recently, cell-based drug delivery platforms have emerged as promising solutions to overcome these limitations. These platforms offer several advantages, including prolonged circulation time, active targeting, controlled release, and excellent biocompatibility. Cell-based delivery systems encompass cell membrane coating, intracellular loading, and extracellular backpacking. These innovative platforms hold the potential to revolutionize cancer diagnosis, monitoring, and treatment, presenting a plethora of opportunities for the advancement and integration of pharmaceuticals, medicine, and materials science. Nevertheless, several technological, ethical, and financial barriers must be addressed to facilitate the translation of these platforms into clinical practice. In this review, we explore the emerging strategies to overcome these challenges, focusing specifically on the functions and advantages of cell-mediated drug delivery in cancer treatment.

Hacking the Immune Response to Solid Tumors: Harnessing the Anti-Cancer Capacities of Oncolytic Bacteria

Oncolytic bacteria are a classification of bacteria with a natural ability to specifically target solid tumors and, in the process, stimulate a potent immune response. Currently, these include species of Klebsiella, Listeria, Mycobacteria, Streptococcus/Serratia (Coley's Toxin), Proteus, Salmonella, and Clostridium. Advancements in techniques and methodology, including genetic engineering, create opportunities to "hijack" typical host-pathogen interactions and subsequently harness oncolytic capacities. Engineering, sometimes termed "domestication", of oncolytic bacterial species is especially beneficial when solid tumors are inaccessible or metastasize early in development. This review examines reported oncolytic bacteria-host immune interactions and details the known mechanisms of these interactions to the protein level. A synopsis of the presented membrane surface molecules that elicit particularly promising oncolytic capacities is paired with the stimulated localized and systemic immunogenic effects. In addition, oncolytic bacterial progression toward clinical translation through engineering efforts are discussed, with thorough attention given to strains that have accomplished Phase III clinical trial initiation. In addition to therapeutic mitigation after the tumor has formed, some bacterial species, referred to as "prophylactic", may even be able to prevent or "derail" tumor formation through anti-inflammatory capabilities. These promising species and their particularly favorable characteristics are summarized as well. A complete understanding of the bacteria-host interaction will likely be necessary to assess anti-cancer capacities and unlock the full cancer therapeutic potential of oncolytic bacteria.

Engineered Salmonella inhibits GPX4 expression and induces ferroptosis to suppress glioma growth in vitro and in vivo

PURPOSE

Glioma is a life-threatening malignancy where conventional therapies are ineffective. Bacterial cancer therapy has shown potential for glioma treatment, in particular, the facultative anaerobe Salmonella has been extensively studied. Meanwhile, ferroptosis is a newly characterized form of cell death. Nevertheless, the role of ferroptosis in Salmonella-induced tumour cell death remains unclear. Therefore, we aim to elucidate whether Salmonella YB1 exerts therapeutic effects via inducing ferroptosis in glioma.

METHODS

Following Salmonella YB1 infection, mRNA sequencing was applied to detect ferroptosis-related gene expression and the levels of reactive oxygen species, malondialdehyde, and glutathione were quantified. Transmission electron microscopy (TEM) was then used to observe the changes in the mitochondrial morphology of glioma cells. The role of ferroptosis in the anti-tumor effect of YB1 was assessed in vivo in mouse tumor xenograft models.

RESULTS

Whole-transcriptome analysis revealed that Salmonella YB1 infection alters ferroptosis-related gene expression in the U87 glioma cell line. Moreover, we found that Salmonella-induced ferroptosis is correlated with reduced levels of glutathione and glutathione peroxidase-4 (GPX4) and increased levels of reactive oxygen species and malondialdehyde in vitro. Meanwhile, TEM revealed that mitochondria are shrunken and mitochondrial membrane density increases in infected glioma cells. Experiments in vivo further showed that tumor growth in the Salmonella-treated group was significantly slower compared to the control and Fer-1 groups. However, Salmonella-induced tumor suppression can be reversed in vivo by Fer-1 treatment.

CONCLUSION

Salmonella YB1 inhibits GPX4 expression and induces ferroptosis to suppress glioma growth. Hence, ferroptosis regulation might represent a promising strategy to improve the efficacy of bacterial cancer therapy.

Synthetic bacterial therapies for intestinal diseases based on quorum-sensing circuits

Bacterial therapy has become a key strategy against intestinal infectious diseases in recent years. Moreover, regulating the gut microbiota through traditional fecal microbiota transplantation and supplementation of probiotics faces controllability, efficacy, and safety challenges. The infiltration and emergence of synthetic biology and microbiome provide an operational and safe treatment platform for live bacterial biotherapies. Synthetic bacterial therapy can artificially manipulate bacteria to produce and deliver therapeutic drug molecules. This method has the advantages of solid controllability, low toxicity, strong therapeutic effects, and easy operation. As an essential tool for dynamic regulation in synthetic biology, quorum sensing (QS) has been widely used for designing complex genetic circuits to control the behavior of bacterial populations and achieve predefined goals. Therefore, QS-based synthetic bacterial therapy might become a new direction for the treatment of diseases. The pre-programmed QS genetic circuit can achieve a controllable production of therapeutic drugs on particular ecological niches by sensing specific signals released from the digestive system in pathological conditions, thereby realizing the integration of diagnosis and treatment. Based on this as well as the modular idea of synthetic biology, QS-based synthetic bacterial therapies are divided into an environmental signal sensing module (senses gut disease physiological signals), a therapeutic molecule producing module (plays a therapeutic role against diseases), and a population behavior regulating module (QS system). This review article summarized the structure and function of these three modules and discussed the rational design of QS gene circuits as a novel intervention strategy for intestinal diseases. Moreover, the application prospects of QS-based synthetic bacterial therapy were summarized. Finally, the challenges faced by these methods were analyzed to make the targeted recommendations for developing a successful therapeutic strategy for intestinal diseases.

Current advances in microbial-based cancer therapies

Microbes have an immense metabolic capability and can adapt to a wide variety of environments; as a result, they share complicated relationships with cancer. The goal of microbial-based cancer therapy is to treat patients with cancers that are not easily treatable, by using tumor-specific infectious microorganisms. Nevertheless, a number of difficulties have been encountered as a result of the harmful effects of chemotherapy, radiotherapy, and alternative cancer therapies, such as the toxicity to non-cancerous cells, the inability of medicines to penetrate deep tumor tissue, and the ongoing problem of rising drug resistance in tumor cells. Due to these difficulties, there is now a larger need for designing alternative strategies that are more effective and selective when targeting tumor cells. The fight against cancer has advanced significantly owing to cancer immunotherapy. The researchers have greatly benefited from their understanding of tumor-invading immune cells as well as the immune responses that are specifically targeted against cancer. Application of bacterial and viral cancer therapeutics offers promising potential to be employed as cancer treatments among immunotherapies. As a novel therapeutic strategy, microbial targeting of tumors has been created to address the persisting hurdles of cancer treatment. This review outlines the mechanisms by which both bacteria and viruses target and inhibit the proliferation of tumor cells. Their ongoing clinical trials and possible modifications that can be made in the future have also been addressed in the following sections. These microbial-based cancer medicines have the ability to suppress cancer that builds up and multiplies in the tumor microenvironment and triggers antitumor immune responses, in contrast to other cancer medications.

TLR5 agonists enhance anti-tumor immunity and overcome resistance to immune checkpoint therapy

Primary and adaptive resistance to immune checkpoint therapies (ICT) represent a considerable obstacle to achieving enhanced overall survival. Innate immune activators have been actively pursued for their antitumor potential. Herein we report that a syngeneic 4T1 mammary carcinoma murine model for established highly-refractory triple negative breast cancer showed enhanced survival when treated intra-tumorally with either the TLR5 agonist flagellin or CBLB502, a flagellin derivative, in combination with antibodies targeting CTLA-4 and PD-1. Long-term survivor mice showed immunologic memory upon tumor re-challenge and a distinctive immune activating cytokine profile that engaged both innate and adaptive immunity. Low serum levels of G-CSF and CXCL5 (as well as high IL-15) were candidate predictive biomarkers correlating with enhanced survival. CBLB502-induced enhancement of ICT was also observed in poorly immunogenic B16-F10 melanoma tumors. Combination immune checkpoint therapy plus TLR5 agonists may offer a new therapeutic strategy to treat ICT-refractory solid tumors.

Hypoxia-responsive nanomaterials for tumor imaging and therapy

Hypoxia is an important component of tumor microenvironment and plays a pivotal role in cancer progression. With the distinctive physiochemical properties and biological effects, various nanoparticles targeting hypoxia had raised great interest in cancer imaging, drug delivery, and gene therapy during the last decade. In the current review, we provided a comprehensive view on the latest progress of novel stimuli-responsive nanomaterials targeting hypoxia-tumor microenvironment (TME), and their applications in cancer diagnosis and therapy. Future prospect and challenges of nanomaterials are also discussed.

Anti-Tumor Effects of Engineered VNP20009-Abvec-Igκ-mPD-1 Strain in Melanoma Mice via Combining the Oncolytic Therapy and Immunotherapy

Programmed cell death protein 1/Programmed cell death ligand 1 (PD-1/PD-L1) immune checkpoint inhibitors are the most promising treatments for malignant tumors currently, but the low response rate limits their further clinical utilization. To address this problem, our group constructed an engineered strain of VNP20009-Abvec-Igκ-mPD-1 [V-A-mPD-1 (mPD-1, murine PD-1)] to combine oncolytic bacterial therapy with immunotherapy. Further, we evaluated its growth performance and mPD-1 expression ability in vitro while establishing the melanoma mice model to explore its potential anti-cancer effects in tumor therapy. Our results indicated that the V-A-mPD-1 strain has superior growth performance and can invade B16F10 melanoma cells and express PD-1. In addition, in the melanoma mice model, we observed a marked reduction in tumor volume and the formation of a larger necrotic area. V-A-mPD-1 administration resulted in a high expression of mPD-1 at the tumor site, inhibiting tumor cell proliferation via the down-regulation of the expression of rat sarcoma (Ras), phosphorylated mitogen-activated protein kinase (p-MEK)/MEK, and phosphorylated extracellular signal-regulated kinase (p-ERK)/ERK expression significantly inhibited tumor cell proliferation. Tumor cell apoptosis was promoted by down-regulating phosphoinositide 3 kinase (PI3K) and protein kinase B (AKT) signaling pathways, as evidenced by an increased Bcl-2-associated X protein/B cell lymphoma-2 (Bax/Bcl-2) expression ratio. Meanwhile, the expression levels of systemic inflammatory cytokines, such as interleukin-6 (IL-6), interleukin-1β (IL-1β), and tumor necrosis factor-α (TNF-α), were substantially reduced. In conclusion, our research demonstrated that V-A-mPD-1 has an excellent anti-tumor effect, prompting that the combined application of microbial therapy and immunotherapy is a feasible cancer treatment strategy.

Engineering bacteria as interactive cancer therapies

With increasing evidence that microbes colonize tumors, synthetic biology tools are being leveraged to repurpose bacteria as tumor-specific delivery systems. These engineered systems can modulate the tumor microenvironment using a combination of their inherent immunogenicity and local payload production. Here, we review genetic circuits that enhance spatial and temporal control of therapeutic bacteria to improve their safety and efficacy. We describe the engineering of interactions among bacteria, tumor cells, and immune cells, and the progression from bacteria as single agents toward their rational combination with other modalities. Together, these efforts are building toward an emerging concept of engineering interactions between programmable medicines using synthetic biology.

Bacterial Metabolism-Initiated Nanocatalytic Tumor Immunotherapy

The low immunogenicity of tumors remains one of the major limitations of cancer immunotherapy. Herein, we report a bacterial metabolism-initiated and photothermal-enhanced nanocatalytic therapy strategy to completely eradicate primary tumor by triggering highly effective antitumor immune responses. Briefly, a microbiotic nanomedicine, designated as Cu₂O@ΔSt, has been constructed by conjugating PEGylated Cu₂O nanoparticles on the surface of an engineered Salmonella typhimurium strain (ΔSt). Owing to the natural hypoxia tropism of ΔSt, Cu₂O@ΔSt could selectively colonize hypoxic solid tumors, thus minimizing the adverse effects of the bacteria on normal tissues. Upon bacterial metabolism within the tumor, Cu₂O@ΔSt generates H₂S gas and other acidic substances in the tumor microenvironment (TME), which will in situ trigger the sulfidation of Cu₂O to form CuS facilitating tumor-specific photothermal therapy (PTT) under local NIR laser irradiation on the one hand. Meanwhile, the dissolved Cu⁺ ions from Cu₂O into the acidified TME enables the nanocatalytic tumor therapy by catalyzing the Fenton-like reaction of decomposing endogenous H₂O₂ into cytotoxic hydroxyl radicals (·OH) on the other hand. Such a bacterial metabolism-triggered PTT-enhanced nanocatalytic treatment could effectively destroy tumor cells and induce a massive release of tumor antigens and damage-associated molecular patterns, thereby sensitizing tumors to checkpoint blockade (ICB) therapy. The combined nanocatalytic and ICB therapy results in the much-inhibited growth of distant and metastatic tumors, and more importantly, induces a powerful immunological memory effect after the primary tumor ablation.

Neospora caninum inhibits tumor development by activating the immune response and destroying tumor cells in a B16F10 melanoma model

Background

Melanoma is a malignant tumor with a high mortality rate. Some microorganisms have been shown to activate the immune system and limit cancer progression. The objective of this study is to evaluate the anti-melanoma effect of Neospora caninum, a livestock pathogen with no pathogenic activity in humans.

Methods

Neospora caninum tachyzoites were inoculated into a C57BL/6 mouse melanoma model by intratumoral and distal subcutaneous injections. Tumor volumes were measured, and cell death areas were visualized by hematoxylin and eosin staining and quantified. Apoptosis in cell cultures and whole tumors was detected by propidium iodide (PI) and TUNEL staining, respectively. Cytokine and tumor-associated factor levels in tumors and spleens were detected by real-time quantitative polymerase chain reaction. Infiltration of macrophages and CD8⁺ T cells in the tumor microenvironment (TME) were detected by immunohistochemistry with anti-CD68 and anti-CD8 antibodies, respectively. Finally, 16S rRNA sequencing of mice cecal contents was performed to evaluate the effect of N. caninum on gut microbial diversity.

Results

Intratumoral and distal subcutaneous injections of N. caninum resulted in significant inhibition of tumor growth (P < 0.001), and more than 50% of tumor cells were dead without signs of apoptosis. Neospora caninum treatment significantly increased the mRNA expression levels of IL-12, IFN-γ, IL-2, IL-10, TNF-α, and PD-L1 in the TME, and IL-12 and IFN-γ in the spleen of tumor-bearing mice (P < 0.05). An increase in the infiltration of CD8⁺ T cells and macrophages in the TME was observed with these cytokine changes. Neospora caninum also restored the abundance of gut microbiota Lactobacillus, Lachnospiraceae, Adlercreutzia, and Prevotellaceae associated with tumor growth, but the changes were not significant.

Conclusion

Neospora caninum inhibits B16F10 melanoma by activating potent immune responses and directly destroying the cancer cells. The stable, non-toxic, and efficacious properties of N. caninum demonstrate the potential for its use as a cancer treatment.

Graphical Abstract

Supplementary Information

The online version contains supplementary material available at 10.1186/s13071-022-05456-8.

A novel tumor-targeting strain of Xenorhabdus stockiae exhibits potent biological activities

Xenorhabdus are symbionts of soil entomopathogenic nematodes of the genus Steinernema presenting two distinct forms in their life cycle, and can produce a broad range of bioactive compounds. In this study, a novel Xenorhabdus stockiae strain HN_xs01 was isolated from a soil sample via an entrapment method using Galleria melonella nematodes. The supernatants of strain HN_xs01 exhibited antimicrobial properties against Gram-negative and Gram-positive bacteria, and insecticidal properties against Helicoverpa armigera larvae, and antitumor properties as well. Moreover, three linear rhabdopeptides (1, 2 and 3) were identified from strain HN_xs01 using nuclear magnetic resonance analysis, which exhibited significant cytotoxic activity against the human epithelial carcinoma cell line A431 and the human chronic myelogenous leukemia cell line K562. Some bacteria have been reported to colonize the tumor region, and we determined that HN_xs01 could grow in tumor xenografts in this study. HN_xs01 invaded and replicated in B16 melanoma cells grafted into C57BL/6 mice, resulting in tumor inhibition. Moreover, strain HN_xs01 not only merely aggregated in the tumor environment, but also prevented pulmonary metastasis. It caused fragmentation of vessels and cell apoptosis, which contributed to its antitumor effect. In conclusion, X. stockiae HN_xs01 is a novel tumor-targeting strain with potential applications in medicinal and agricultural fields.

Recent advances in bacterial therapeutics based on sense and response

Intelligent drug delivery is a promising strategy for cancer therapies. In recent years, with the rapid development of synthetic biology, some properties of bacteria, such as gene operability, excellent tumor colonization ability, and host-independent structure, make them ideal intelligent drug carriers and have attracted extensive attention. By implanting condition-responsive elements or gene circuits into bacteria, they can synthesize or release drugs by sensing stimuli. Therefore, compared with traditional drug delivery, the usage of bacteria for drug loading has better targeting ability and controllability, and can cope with the complex delivery environment of the body to achieve the intelligent delivery of drugs. This review mainly introduces the development of bacterial-based drug delivery carriers, including mechanisms of bacterial targeting to tumor colonization, gene deletions or mutations, environment-responsive elements, and gene circuits. Meanwhile, we summarize the challenges and prospects faced by bacteria in clinical research, and hope to provide ideas for clinical translation.

Recombinant Attenuated Salmonella enterica as a Delivery System of Heterologous Molecules in Cancer Therapy

Simple Summary

Cancer is among the main causes of death of millions of individuals worldwide. Although survival has improved with conventional treatments, the appearance of resistant cancer cells leads to patient relapses. It is, therefore, necessary to find new antitumor therapies that can completely eradicate transformed cells. Bacteria-based tumor therapy represents a promising alternative treatment, particularly the use of live-attenuated Salmonella enterica, with its potential use as a delivery system of antitumor heterologous molecules such as tumor-associated antigens, cytotoxic molecules, immunomodulatory molecules, pro-apoptotic proteins, nucleic acids, and nanoparticles. In this review, we present the state of the art of current preclinical and clinical research on the use of Salmonella enterica as a potential therapeutic ally in the war against cancer.

Abstract

Over a century ago, bacterial extracts were found to be useful in cancer therapy, but this treatment modality was obviated for decades. Currently, in spite of the development and advances in chemotherapies and radiotherapy, failure of these conventional treatments still represents a major issue in the complete eradication of tumor cells and has led to renewed approaches with bacteria-based tumor therapy as an alternative treatment. In this context, live-attenuated bacteria, particularly Salmonella enterica, have demonstrated tumor selectivity, intrinsic oncolytic activity, and the ability to induce innate or specific antitumor immune responses. Moreover, Salmonella enterica also has strong potential as a delivery system of tumor-associated antigens, cytotoxic molecules, immunomodulatory molecules, pro-apoptotic proteins, and nucleic acids into eukaryotic cells, in a process known as bactofection and antitumor nanoparticles. In this review, we present the state of the art of current preclinical and clinical research on the use of Salmonella enterica as a potential therapeutic ally in the war against cancer.

Acid-Directed Electrostatic Self-Assembly Generates Charge-Reversible Bacteria for Enhanced Tumor Targeting and Low Tissue Trapping

Despite recent preclinical progress with oncolytic bacteria in cancer therapy, dose-limiting toxicity has been a long-standing challenge for clinical application. Genetic and chemical modifications for enhancing the bacterial tumor-targeting ability have been unable to establish a balance between increasing its specificity and effectiveness while decreasing side effects. Herein, we report a simple, highly efficient method for rapidly self-assembling a clinically used lipid on bacterium and for reducing its minimum effective dose and toxicity to normal organs. The resultant bacteria present the ability to reverse-charge between neutral and acidic solutions, thus enabling weak interactions with the negatively charged normal cells, hence increasing their biocompatibility with blood cells and with the immune system. Additionally, the lipid-coated bacteria exhibit a longer blood circulation lifetime and low tissue trapping compared with the wild-type strains. Thereby, the engineered bacteria show enhanced tumor specificity and effectiveness even at low doses. Multiple visualization techniques are used for vividly demonstrating the time course of bacterial circulation in the blood and normal organs after intravenous administration. We believe that these methods for biointerfacial lipid self-assembly and evaluation of bacterial systemic circulation possess vast potential in exquisitely fabricating engineered bacteria for cancer therapy in the future.

A rapid screening platform to coculture bacteria within tumor spheroids

The prevalence of tumor-colonizing bacteria along with advances in synthetic biology are leading to a new generation of living microbial cancer therapies. Because many bacterial systems can be engineered to recombinantly produce therapeutics within tumors, simple and high-throughput experimental platforms are needed to screen the large collections of bacteria candidates and characterize their interactions with cancer cells. Here, we describe a protocol to selectively grow bacteria within the core of tumor spheroids, allowing for their continuous and parallel profiling in physiologically relevant conditions. Specifically, tumor spheroids are incubated with bacteria in a 96-well low-adhesion plate followed by a series of washing steps and an antibiotic selection protocol to confine bacterial growth within the hypoxic and necrotic core of tumor spheroids. This bacteria spheroid coculture (BSCC) system is stable for over 2 weeks, does not require specialized equipment and is compatible with time-lapse microscopy, commercial staining assays and histology that uniquely enable analysis of growth kinetics, viability and spatial distribution of both cellular populations, respectively. We show that the procedure is applicable to multiple tumor cell types and bacterial species by varying protocol parameters and is validated by using animal models. The BSCC platform will allow the study of bacteria-tumor interactions in a continuous manner and facilitate the rapid development of engineered microbial therapies.

Current Status and Future Directions of Bacteria-Based Immunotherapy

With the in-depth understanding of the anti-cancer immunity, immunotherapy has become a promising cancer treatment after surgery, radiotherapy, and chemotherapy. As natural immunogenicity substances, some bacteria can preferentially colonize and proliferate inside tumor tissues to interact with the host and exert anti-tumor effect. However, further research is hampered by the infection-associated toxicity and their unpredictable behaviors in vivo. Due to modern advances in genetic engineering, synthetic biology, and material science, modifying bacteria to minimize the toxicity and constructing a bacteria-based immunotherapy platform has become a hotspot in recent research. This review will cover the inherent advantages of unedited bacteria, highlight how bacteria can be engineered to provide greater tumor-targeting properties, enhanced immune-modulation effect, and improved safety. Successful applications of engineered bacteria in cancer immunotherapy or as part of the combination therapy are discussed as well as the bacteria based immunotherapy in different cancer types. In the end, we highlight the future directions and potential opportunities of this emerging field.

Advances in Salmonella Typhimurium-based drug delivery system for cancer therapy

The clinical application of bacteria-mediated immune therapy dates back over a century ago. In recent years, these strategies have advanced greatly with the rapid development of synthetic biology and nanotechnology. Several bacterial therapies have been developed allowing for more effective treatments for cancers, and Salmonella is one of the most studied bacterial species. Here, we review the advances in the bioengineered and functionalized Salmonella Typhimurium strains as drug delivery carries, including the various genetic circuits for programing these bacteria, the surface modification strategies using nanoparticles or other therapeutic agents for richer and broader features, and the bacterial component-based vehicles for cancer immunotherapy. This review will include the promises and challenges of these optimized Salmonella-based delivery systems and their related clinical trials. Ultimately, we hope to provide a spark of thought in the field of drug delivery and find important crosstalk between bacteria-mediated therapy and other different forms of treatments.

Bacterially mediated drug delivery and therapeutics: Strategies and advancements

It was already clinically apparent 150 years ago that bacterial therapy could alleviate diseases. Recently, a burgeoning number of researchers have been using bacterial regimens filled with microbial therapeutic leads to diagnose and treat a wide range of disorders and diseases, including cancers, inflammatory diseases, metabolic disorders and viral infections. Some bacteria that were designed to have low toxicity and high efficiency in drug delivery have been used to treat diseases successfully, especially in tumor therapy in animal models or clinical trials, thanks to the progress of genetic engineering and synthetic bioengineering. Therefore, genetically engineered bacteria can serve as efficient drug delivery vehicles, carrying nucleic acids or genetic circuits that encode and regulate therapeutic payloads. In this review, we summarize the development and applications of this approach. Strategies for genetically modifying strains are described in detail, along with their objectives. We also describe some controlled strategies for drug delivery and release using these modified strains as carriers. Furthermore, we discuss treatment methods for various types of diseases using engineered bacteria. Tumors are discussed as the most representative example, and other diseases are also briefly described. Finally, we discuss the challenges and prospects of drug delivery systems based on these bacteria.

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.