Search

Abstract Cancer is measured as a major threat to human life and is a leading cause of death. Millions of cancer patients die every year, although a burgeoning number of researchers have been making tremendous efforts to develop cancer medicine to fight against cancer. Owing to the complexity and heterogeneity of cancer, lack of ability to treat deep tumor tissues, and high toxicity to the normal cells, it complicates the therapy of cancer. However, bacterial derivative-mediated drug delivery has raised the interest of researchers in overcoming the restrictions of conventional cancer chemotherapy. In this review, we show various examples of tumor-targeting bacteria and bacterial derivatives for the delivery of anticancer drugs. This review also describes the advantages and limitations of delivering anticancer treatment drugs under regulated conditions employing these tumor-targeting bacteria and their membrane vesicles. This study highlights the substantial potential for clinical translation of bacterial-based drug carriers, improve their ability to work with other treatment modalities, and provide a more powerful, dependable, and distinctive tumor therapy. Graphical Abstract

Cancer is measured as a major threat to human life and is a leading cause of death. Millions of cancer patients die every year, although a burgeoning number of researchers have been making tremendous efforts to develop cancer medicine to fight against cancer. Owing to the complexity and heterogeneity of cancer, lack of ability to treat deep tumor tissues, and high toxicity to the normal cells, it complicates the therapy of cancer. However, bacterial derivative-mediated drug delivery has raised the interest of researchers in overcoming the restrictions of conventional cancer chemotherapy. In this review, we show various examples of tumor-targeting bacteria and bacterial derivatives for the delivery of anticancer drugs. This review also describes the advantages and limitations of delivering anticancer treatment drugs under regulated conditions employing these tumor-targeting bacteria and their membrane vesicles. This study highlights the substantial potential for clinical translation of bacterial-based drug carriers, improve their ability to work with other treatment modalities, and provide a more powerful, dependable, and distinctive tumor therapy. [ABSTRACT FROM AUTHOR]

Autologous cancer vaccine that stimulates tumor-specific immune responses for personalized immunotherapy holds great potential for tumor therapy. However, its efficacy is still suboptimal due to the immunosuppressive tumor microenvironment (ITM). Here, we report a new type of bacteria-based autologous cancer vaccine by employing calcium carbonate (CaCO3) biomineralized Salmonella (Sal) as an in-situ cancer vaccine producer and systematical ITM regulator. CaCO3 can be facilely coated on the Sal surface with calcium ionophore A23187 co-loading, and such biomineralization did not affect the bioactivities of the bacteria. Upon intratumoral accumulation, the CaCO3 shell was decomposed at an acidic microenvironment to attenuate tumor acidity, accompanied by the release of Sal and Ca2+/A23187. Specifically, Sal served as a cancer vaccine producer by inducing cancer cells' immunogenic cell death (ICD) and promoting the gap junction formation between tumor cells and dendritic cells (DCs) to promote antigen presentation. Ca2+, on the other hand, was internalized into various types of immune cells with the aid of A23187 and synergized with Sal to systematically regulate the immune system, including DCs maturation, macrophages polarization, and T cells activation. As a result, such bio-vaccine achieved remarkable efficacy against both primary and metastatic tumors by eliciting potent anti-tumor immunity with full biocompatibility. This work demonstrated the potential of bioengineered bacteria as bio-active vaccines for enhanced tumor immunotherapy.

Autologous cancer vaccine that stimulates tumor-specific immune responses for personalized immunotherapy holds great potential for tumor therapy. However, its efficacy is still suboptimal due to the immunosuppressive tumor microenvironment (ITM). Here, we report a new type of bacteria-based autologous cancer vaccine by employing calcium carbonate (CaCO 3) biomineralized Salmonella (Sal) as an in-situ cancer vaccine producer and systematical ITM regulator. CaCO 3 can be facilely coated on the Sal surface with calcium ionophore A23187 co-loading, and such biomineralization did not affect the bioactivities of the bacteria. Upon intratumoral accumulation, the CaCO 3 shell was decomposed at an acidic microenvironment to attenuate tumor acidity, accompanied by the release of Sal and Ca2+/A23187. Specifically, Sal served as a cancer vaccine producer by inducing cancer cells' immunogenic cell death (ICD) and promoting the gap junction formation between tumor cells and dendritic cells (DCs) to promote antigen presentation. Ca2+, on the other hand, was internalized into various types of immune cells with the aid of A23187 and synergized with Sal to systematically regulate the immune system, including DCs maturation, macrophages polarization, and T cells activation. As a result, such bio-vaccine achieved remarkable efficacy against both primary and metastatic tumors by eliciting potent anti-tumor immunity with full biocompatibility. This work demonstrated the potential of bioengineered bacteria as bio-active vaccines for enhanced tumor immunotherapy. A new type of bacteria-based autologous cancer vaccine was developed by employing calcium carbonate biomineralized Salmonella as in-situ cancer vaccine producer and systematical immunosuppressive tumor microenvironment regulator. [Display omitted] [ABSTRACT FROM AUTHOR]

Bacteria‐based microbial immunotherapy shows various unique properties for tumor therapy owing to their active tropism to tumor and multiple anti‐tumor mechanisms. However, its clinical benefit is far from satisfactory, which is limited by rapid systemic clearance and neutrophils‐mediated immune restriction to compromise the efficacy, as well as non‐specific distribution to cause toxicity. To address all these limitations, herein we reported a polyserotonin (PST) coated Salmonella (Sal) with surface adsorption of DNAzyme (Dz)‐functionalized MnO2 nanoparticles (DzMN) for tumor therapy. PST could facilely coat on Sal surface via oxidation and self‐polymerization of its serotonin monomer, which enabled surface stealth to avoid rapid systemic clearance while maintaining the tumor homing effect. Upon targeting to tumor, the PST was degraded and exfoliated in response to acidic tumor microenvironment, thus liberating Sal to recover its anti‐tumor activities. Meanwhile, the DzMN was also delivered into tumor via hitchhiking Sal, which could release Dz and Mn2+ after tumor cells internalization. The Dz was then activated by its cofactor of Mn2+ to cleave target PD‐L1 mRNA, thus serving as a self‐activated system for gene silencing. Combining Sal and Dz for immune activation and PD‐L1 knockdown, respectively, anti‐tumor immunotherapy was achieved with enhanced efficacy. Notably, PST coating could significantly decrease infection potential and non‐specific colonization of Sal at normal organs, achieving high in vivo biosafety. This work addresses the key limitations of Sal for in vivo application via biomaterials modification, and provides a promising platform for better microbial immunotherapy. [ABSTRACT FROM AUTHOR]

Abstract Bacteria‐based microbial immunotherapy shows various unique properties for tumor therapy owing to their active tropism to tumor and multiple anti‐tumor mechanisms. However, its clinical benefit is far from satisfactory, which is limited by rapid systemic clearance and neutrophils‐mediated immune restriction to compromise the efficacy, as well as non‐specific distribution to cause toxicity. To address all these limitations, herein we reported a polyserotonin (PST) coated Salmonella (Sal) with surface adsorption of DNAzyme (Dz)‐functionalized MnO2 nanoparticles (DzMN) for tumor therapy. PST could facilely coat on Sal surface via oxidation and self‐polymerization of its serotonin monomer, which enabled surface stealth to avoid rapid systemic clearance while maintaining the tumor homing effect. Upon targeting to tumor, the PST was degraded and exfoliated in response to acidic tumor microenvironment, thus liberating Sal to recover its anti‐tumor activities. Meanwhile, the DzMN was also delivered into tumor via hitchhiking Sal, which could release Dz and Mn2+ after tumor cells internalization. The Dz was then activated by its cofactor of Mn2+ to cleave target PD‐L1 mRNA, thus serving as a self‐activated system for gene silencing. Combining Sal and Dz for immune activation and PD‐L1 knockdown, respectively, anti‐tumor immunotherapy was achieved with enhanced efficacy. Notably, PST coating could significantly decrease infection potential and non‐specific colonization of Sal at normal organs, achieving high in vivo biosafety. This work addresses the key limitations of Sal for in vivo application via biomaterials modification, and provides a promising platform for better microbial immunotherapy.

Abstract Tumors are presently a major threat to human life and health. Malignant tumors are conventionally treated through radiotherapy and chemotherapy. However, traditional therapies yield unsatisfactory results due to high toxicity to the normal cells, inability to treat deep tumor tissues, and the possibility of inducing drug resistance in the tumor cells. This has caused immunotherapy to emerge as an effective and alternate treatment strategy. To overcome the limitations of the conventional treatments as well as to avert the risk of various drug resistance and cytotoxicity, bacterial anti‐tumor immunotherapy has raised the interest of researchers. This therapeutic strategy employs bacteria to specifically target and colonize the tumor tissues with preferential accumulation and proliferation. Such bacterial accumulation initiates a series of anti‐tumor immune responses, effectively eliminating the tumor cells. This immunotherapy can use the bacteria alone or concomitantly with the other methods. For example, the bacteria can deliver the anti‐cancer effect mediators by regulating the expression of the bacterial genes or by synthesizing the bioengineered bacterial complexes. This review will discuss the mechanism of utilizing bacteria in treating tumors, especially in terms of immune mechanisms. This could help in better integrating the bacterial method with other treatment options, thereby, providing a more effective, reliable, and unique treatment therapy for tumors.

Tumors are presently a major threat to human life and health. Malignant tumors are conventionally treated through radiotherapy and chemotherapy. However, traditional therapies yield unsatisfactory results due to high toxicity to the normal cells, inability to treat deep tumor tissues, and the possibility of inducing drug resistance in the tumor cells. This has caused immunotherapy to emerge as an effective and alternate treatment strategy. To overcome the limitations of the conventional treatments as well as to avert the risk of various drug resistance and cytotoxicity, bacterial anti‐tumor immunotherapy has raised the interest of researchers. This therapeutic strategy employs bacteria to specifically target and colonize the tumor tissues with preferential accumulation and proliferation. Such bacterial accumulation initiates a series of anti‐tumor immune responses, effectively eliminating the tumor cells. This immunotherapy can use the bacteria alone or concomitantly with the other methods. For example, the bacteria can deliver the anti‐cancer effect mediators by regulating the expression of the bacterial genes or by synthesizing the bioengineered bacterial complexes. This review will discuss the mechanism of utilizing bacteria in treating tumors, especially in terms of immune mechanisms. This could help in better integrating the bacterial method with other treatment options, thereby, providing a more effective, reliable, and unique treatment therapy for tumors. [ABSTRACT FROM AUTHOR]

Bacteria are important symbionts for humans, which sustain substantial influences on our health. Interestingly, some bastrains have been identified to have therapeutic applications, notably for antitumor activity. Thereby, oncologists have developed various therapeutic models and investigated the potential antitumor mechanisms for bacteria-mediated cancer therapy (BCT). Even though BCT has a long history and exhibits remarkable therapeutic efficacy in pre-clinical animal models, its clinical translation still lags and requires further breakthroughs. This review aims to focus on the established strains of therapeutic bacteria and their antitumor mechanisms, including the stimulation of host immune responses, direct cytotoxicity, the interference on cellular signal transduction, extracellular matrix remodeling, neoangiogenesis, and metabolism, as well as vehicles for drug delivery and gene therapy. Moreover, a brief discussion is proposed regarding the important future directions for this fantastic research field of BCT at the end of this review. [ABSTRACT FROM AUTHOR]

Salmonella: mediated cancer therapy has achieved remarkable anti-tumor effects in experimental animal models, but the detailed mechanism remains unsolved. In this report, the active involvement of the host immune response in this process was confirmed by comparing the tumor-suppressive effects of Salmonella in immunocompetent and immunodeficient mice bearing melanoma allografts. Since flagella are key inducers of the host immune response during bacterial infection, flagella were genetically disrupted to analyse their involvement in Salmonella-mediated cancer therapy. The results showed that flagellum-deficient strains failed to induce significant anti-tumor effects, even when more bacteria were administered to offset the difference in invasion efficiency. Flagella mainly activate immune cells via Flagellin/Toll-like receptor 5 (TLR5) signalling pathway. Indeed, we showed that exogenous activation of TLR5 signalling by recombinant Flagellin and exogenous expression of TLR5 both enhanced the therapeutic efficacy of flagellum-deficient Salmonella against melanoma. Our study highlighted the therapeutic value of the interaction between Salmonella and the host immune response through Flagellin/TLR5 signalling pathway during Salmonella-mediated cancer therapy, thereby suggesting the potential application of TLR5 agonists in the cancer immune therapy.

The major reason for the failure of conventional therapies is the heterogeneity and complexity of tumor microenvironments (TMEs). Many malignant tumors reprogram their surface antigens to evade the immune surveillance, leading to reduced antigen-presenting cells and hindered T-cell activation. Bacteria-mediated cancer immunotherapy has been extensively investigated in recent years. Scientists have ingeniously modified bacteria using synthetic biology and nanotechnology to enhance their biosafety with high tumor specificity, resulting in robust anticancer immune responses. To enhance the antitumor efficacy, therapeutic proteins, cytokines, nanoparticles, and chemotherapeutic drugs have been efficiently delivered using engineered bacteria. This review provides a comprehensive understanding of oncolytic bacterial therapies, covering bacterial design and the intricate interactions within TMEs. Additionally, it offers an in-depth comparison of the current techniques used for bacterial modification, both internally and externally, to maximize their therapeutic effectiveness. Finally, we outlined the challenges and opportunities ahead in the clinical application of oncolytic bacterial therapies. [Display omitted] [ABSTRACT FROM AUTHOR]

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. [Display omitted] • Oncolytic bacteria (OBs) and oncolytic viruses (OVs) are demonstrating potential as a novel approach to cancer therapy. • OVs selectively infect and destroy cancer cells, activating both innate and adaptive immune responses. • Endotoxins and other products of OBs have shown promise in tumor removal. • Bacteria can influence the immune response and enhance the effectiveness of OVs by producing therapeutic agents like cytokines or checkpoint inhibitors. [ABSTRACT FROM AUTHOR]

mediated cancer therapy has achieved remarkable anti-tumor effects in experimental animal models, but the detailed mechanism remains unsolved. In this report, the active involvement of the host immune response in this process was confirmed by comparing the tumor-suppressive effects of Salmonella in immunocompetent and immunodeficient mice bearing melanoma allografts. Since flagella are key inducers of the host immune response during bacterial infection, flagella were genetically disrupted to analyse their involvement in Salmonella -mediated cancer therapy. The results showed that flagellum-deficient strains failed to induce significant anti-tumor effects, even when more bacteria were administered to offset the difference in invasion efficiency. Flagella mainly activate immune cells via Flagellin/Toll-like receptor 5 (TLR5) signalling pathway. Indeed, we showed that exogenous activation of TLR5 signalling by recombinant Flagellin and exogenous expression of TLR5 both enhanced the therapeutic efficacy of flagellum-deficient Salmonella against melanoma. Our study highlighted the therapeutic value of the interaction between Salmonella and the host immune response through Flagellin/TLR5 signalling pathway during Salmonella -mediated cancer therapy, thereby suggesting the potential application of TLR5 agonists in the cancer immune therapy. Flagella play a critical role in Salmonella -mediated cancer therapy by activating host immune response through Flagellin/TLR5/NF- κ B signalling pathway, indicating Flagellin's potential application in cancer immune therapy. [Display omitted] [ABSTRACT FROM AUTHOR]

Over the years, conventional cancer treatments, such as chemotherapy with only a limited specificity for tumors, have undergone significant improvement. Moreover, newer therapies such as immunotherapy have undergone a revolution to stimulate the innate as well as adaptive immune responses against the tumor. However, it has been found that tumors can be selectively colonized by certain bacteria, where they can proliferate, and exert direct oncolytic effects as well as stimulating the immune system. Bacterial-mediated cancer therapy (BMCT) is now one example of a hot topic in the antitumor field. Salmonella typhimurium is a Gram-negative species that generally causes self-limiting gastroenteritis in humans. This species has been designed and engineered in order to be used in cancer-targeted therapeutics. S. typhimurium can be used in combination with other treatments such as chemotherapy or radiotherapy for synergistic modification of the tumor microenvironment. Considerable benefits have been shown by using engineered attenuated strains for the diagnosis and treatment of tumors. Some of these treatment approaches have received FDA approval for early-phase clinical trials. This review summarizes the use of Salmonella bacteria for cancer therapy, which could pave the way towards routine clinical application. The benefits of this therapy include an automatic self-targeting ability, and the possibility of genetic manipulation to produce newly engineered attenuated strains. Nevertheless, Salmonella-mediated anticancer therapy has not yet been clinically established, and requires more research before its use in cancer treatment.

Over the years, conventional cancer treatments, such as chemotherapy with only a limited specificity for tumors, have undergone significant improvement. Moreover, newer therapies such as immunotherapy have undergone a revolution to stimulate the innate as well as adaptive immune responses against the tumor. However, it has been found that tumors can be selectively colonized by certain bacteria, where they can proliferate, and exert direct oncolytic effects as well as stimulating the immune system. Bacterial-mediated cancer therapy (BMCT) is now one example of a hot topic in the antitumor field. Salmonella typhimurium is a Gram-negative species that generally causes self-limiting gastroenteritis in humans. This species has been designed and engineered in order to be used in cancer-targeted therapeutics. S. typhimurium can be used in combination with other treatments such as chemotherapy or radiotherapy for synergistic modification of the tumor microenvironment. Considerable benefits have been shown by using engineered attenuated strains for the diagnosis and treatment of tumors. Some of these treatment approaches have received FDA approval for early-phase clinical trials. This review summarizes the use of Salmonella bacteria for cancer therapy, which could pave the way towards routine clinical application. The benefits of this therapy include an automatic self-targeting ability, and the possibility of genetic manipulation to produce newly engineered attenuated strains. Nevertheless, Salmonella- mediated anticancer therapy has not yet been clinically established, and requires more research before its use in cancer treatment. [ABSTRACT FROM AUTHOR]

Conventional chemotherapies have some limitations, including the lack of selectivity, high toxicity to normal tissues, multidrug resistance, and tumor relapse. Recently, great progress was made in immunotherapies for anticancer research, with bacteria-mediated cancer therapy one of the most promising approaches among them. Attenuated Salmonella have very specific targeting to various solid cancers, making them ideal vectors for the delivery and expression of immunostimulators. They have native bacterial immunogenicity and induce strong anticancer immunity in vivo. In this review, the recent advances in Salmonella-mediated cancer immunotherapies and the related mechanisms of Salmonella-based cancer therapies are summarized. [ABSTRACT FROM AUTHOR]

Summary: Use of bacteria in cancer therapy, despite being considered as a potent strategy, has not really picked up the way other methods of cancer therapies have evolved. However, in recent years, the interest on use of bacteria to kill cancer cells has renewed considerably. The standard and widely followed strategies of cancer treatment often fail either due to the complexity of tumour biology or because of the accompanying side effects. In contrast, these limitations can be easily overcome in a bacteria‐mediated approach. Salmonella is a bacterium, which is known for its ability to colonize solid or semisolid tumours more efficiently than any other bacteria. Among more than 2500 serovars of Salmonella, S. Typhimurium has been widely studied for its antagonistic effects on cancer cells. Here in, we review the current status of the preclinical and the clinical studies with a focus on the mechanisms that attribute the anticancer properties to nontyphoidal Salmonella. [ABSTRACT FROM AUTHOR]

Bacteria-mediated cancer therapy (BMCT) is an emerging tool that may advance potential approaches in cancer immunotherapy, whereby tumors are eradicated by the hosts’ immune system upon recruitment and activation by bacteria such as Salmonella. This paper provides an emphasis on the immunomodulatory effects that encompasses both the innate and adaptive immune responses inherently triggered by Salmonella. Furthermore, modifications of Salmonella-based treatment in the attempt to improve tumor-specific immune responses including cytokine therapy, gene therapy, and DNA vaccine delivery are likewise discussed. The majority of the findings described herein incorporate cell-based experiments and murine model studies, and only a few accounts describe clinical trials. Salmonella-based cancer therapy is still under development; nonetheless, the pre-clinical research and early-phase clinical trials that have been completed so far have shown promising and convincing results. Certainly, the continuous development of, and innovation on, Salmonella-based therapy could pave the way for its eventual emergence as one of the mainstream therapeutic interventions addressing various types of cancer.

Bacteria are important symbionts for humans, which sustain substantial influences on our health. Interestingly, some bastrains have been identified to have therapeutic applications, notably for antitumor activity. Thereby, oncologists have developed various therapeutic models and investigated the potential antitumor mechanisms for bacteria-mediated cancer therapy (BCT). Even though BCT has a long history and exhibits remarkable therapeutic efficacy in pre-clinical animal models, its clinical translation still lags and requires further breakthroughs. This review aims to focus on the established strains of therapeutic bacteria and their antitumor mechanisms, including the stimulation of host immune responses, direct cytotoxicity, the interference on cellular signal transduction, extracellular matrix remodeling, neoangiogenesis, and metabolism, as well as vehicles for drug delivery and gene therapy. Moreover, a brief discussion is proposed regarding the important future directions for this fantastic research field of BCT at the end of this review., Competing Interests: The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest., (Copyright © 2022 Luo, Chen, Gao, Yang, Chen and Qiao.)

Bacteria-mediated cancer therapy (BMCT) is an emerging tool that may advance potential approaches in cancer immunotherapy, whereby tumors are eradicated by the hosts' immune system upon recruitment and activation by bacteria such as Salmonella. This paper provides an emphasis on the immunomodulatory effects that encompasses both the innate and adaptive immune responses inherently triggered by Salmonella. Furthermore, modifications of Salmonella-based treatment in the attempt to improve tumor-specific immune responses including cytokine therapy, gene therapy, and DNA vaccine delivery are likewise discussed. The majority of the findings described herein incorporate cell-based experiments and murine model studies, and only a few accounts describe clinical trials. Salmonella-based cancer therapy is still under development; nonetheless, the pre-clinical research and early-phase clinical trials that have been completed so far have shown promising and convincing results. Certainly, the continuous development of, and innovation on, Salmonella-based therapy could pave the way for its eventual emergence as one of the mainstream therapeutic interventions addressing various types of cancer. [ABSTRACT FROM AUTHOR]

Salmonella selectively colonizes into the hypoxic tumor region and exerts antitumor effects via multiple mechanisms, while the tumor colonized Salmonella recruits host neutrophils into the tumor, presenting a key immunological restraint to compromise the Salmonella efficacy. Here, we develop a combinatorial strategy by employing silver nanoparticles (AgNPs) to improve the efficacy and biosafety of Salmonella . The AgNPs were decorated with sialic acid (SA) to allow selective recognition of L-selectin on neutrophil surfaces, based on which the tumor-homing of AgNPs was achieved by neutrophil infiltration in the Salmonella colonized tumor. The tumor-targeting AgNPs exert the functions of (1) local depletion of neutrophils in tumors to boost the efficacy of Salmonella , (2) direct killing tumor cells via L-selectin-mediated intracellular delivery, and (3) clearing the residual Salmonella after complete tumor eradication to minimize the side effects. With a single tail vein injection of such combination treatment, the tumor was eliminated with high biosafety, resulting in a superior therapeutic outcome.

Bacteria-based anticancer therapies aim to overcome the limitations of current cancer therapy by actively targeting and efficiently removing cancer. To achieve this goal, new approaches that target and maintain bacterial drugs at sufficient concentrations during the therapeutic window are essential. Here, we examined the tumor tropism of attenuated Salmonella typhimurium displaying the RGD peptide sequence (ACDCRGDCFCG) on the external loop of outer membrane protein A (OmpA). RGD-displaying Salmonella strongly bound to cancer cells overexpressing αvβ3, but weakly bound to αvβ3-negative cancer cells, suggesting the feasibility of displaying a preferential homing peptide on the bacterial surface. In vivo studies revealed that RGD-displaying Salmonellae showed strong targeting efficiency, resulting in the regression in αvβ3-overexpressing cancer xenografts, and prolonged survival of mouse models of human breast cancer (MDA-MB-231) and human melanoma (MDA-MB-435). Thus, surface engineering of Salmonellae to display RGD peptides increases both their targeting efficiency and therapeutic effect.

Although strains of attenuated Salmonella typhimurium and wild-type Escherichia coli show similar tumor-targeting capacities, only S. typhimurium significantly suppresses tumor growth in mice. The aim of the present study was to examine bacteria-mediated immune responses by conducting comparative analyses of the cytokine profiles and immune cell populations within tumor tissues colonized by E. coli or attenuated Salmonellae. CT26 tumor-bearing mice were treated with two different bacterial strains: S. typhimurium defective in ppGpp synthesis (ΔppGpp Salmonellae) or wild-type E. coli MG1655. Cytokine profiles and immune cell populations in tumor tissue colonized by these two bacterial strains were examined at two time points based on the pattern of tumor growth after ΔppGpp Salmonellae treatment: 1) when tumor growth was suppressed ('suppression stage') and 2) when they began to re-grow ('re-growing stage'). The levels of IL-1β and TNF-α were markedly increased in tumors colonized by ΔppGpp Salmonellae. This increase was associated with tumor regression; the levels of both IL-1β and TNF-α returned to normal level when the tumors started to re-grow. To identify the immune cells primarily responsible for Salmonellae-mediated tumor suppression, we examined the major cell types that produce IL-1β and TNF-α. We found that macrophages and dendritic cells were the main producers of TNF-α and IL-1β. Inhibiting IL-1β production in Salmonellae-treated mice restored tumor growth, whereas tumor growth was suppressed for longer by local administration of recombinant IL-1β or TNF-α in conjunction with Salmonella therapy. These findings suggested that IL-1β and TNF-α play important roles in Salmonella-mediated cancer therapy. A better understanding of host immune responses in Salmonella therapy may increase the success of a given drug, particularly when various strategies are combined with bacteriotherapy.