Targeted deprivation of methionine with engineered Salmonella leads to oncolysis and suppression of metastasis in broad types of animal tumor models

Metabolic reprogramming of tumor microenviroment by engineered bacteria

The tumor microenvironment (TME) is a complex ecosystem that plays a crucial role in tumor progression and response to therapy. The metabolic characteristics of the TME are fundamental to its function, influencing not only cancer cell proliferation and survival but also the behavior of immune cells within the tumor. Metabolic reprogramming-where cancer cells adapt their metabolic pathways to support rapid growth and immune evasion-has emerged as a key factor in cancer immunotherapy. Recently, the potential of engineered bacteria in cancer immunotherapy has gained increasing recognition, offering a novel strategy to modulate TME metabolism and enhance antitumor immunity. This review summarizes the metabolic properties and adaptations of tumor and immune cells within the TME and summarizes the strategies by which engineered bacteria regulate tumor metabolism. We discuss how engineered bacteria can overcome the immunosuppressive TME by reprogramming its metabolism to improve antitumor therapy. Furthermore, we examine the advantages, potential challenges, and future clinical translation of engineered bacteria in reshaping TME metabolism.

Methionine Dependency and Restriction in Cancer: Exploring the Pathogenic Function and Therapeutic Potential

Methionine, an essential amino acid, is obtained by dietary intake to fulfill the requirements of our bodies. Accumulating evidence indicates that methionine plays a pivotal role in various biological processes, including protein synthesis, energy metabolism, redox balance maintenance, and methylation modifications. Numerous advances underscore the heightened dependence of cancer cells on methionine, which is a significant factor in cancer pathogenesis and development. A profound comprehension of the intricate relationship between methionine metabolism and tumorigenesis is imperative for advancing the field of cancer therapeutics. Herein, we delve into the role of methionine in supporting cancer growth, the impact on epigenetic modifications, and the interaction between methionine and the tumor microenvironment. Additionally, we provide insights into the development of various methionine-targeted therapy strategies. This paper summarizes the current state of research and its translational potential, emphasizing the challenges and opportunities associated with harnessing methionine dependence as a target for innovative cancer treatments.

Engineered VNP20009 expressing IL-15&15Rα augments anti-tumor immunity for bladder cancer treatment

Surgical resection combined with intravesical instillation of chemotherapeutics or Bacillus Calmette-Guerin (BCG) to remove residual cancer cells is the gold standard for the clinical treatment of patients with bladder cancer. In a recent clinical trial, a new super-agonist complex of IL-15 - N803, has shown promising results when used in combination with BCG to treat patients with bladder cancer who do not respond to BCG. Herein, we used temperature-controlled pBV220 plasmid encoding Interleukin-15 and its receptor alpha subunit (IL-15&15Rα) to transform VNP20009, an attenuated salmonella typhimurium strain, obtaining engineered bacteria named 15&15Rα@VNP. After induction at 42 °C, 15&15Rα@VNP can secrete functional IL-15&15Rα stably. It was found that intravesical instillation of thermally activated 15&15Rα@VNP could inhibit the growth of bladder tumors if used alone. Moreover, the sequential intravesical instillation of epirubicin (EPI), a first-line bladder cancer drug, followed by thermally activated 15&15Rα@VNP, could achieve further improved therapeutic responses, without causing significant side effects. Therefore, this study shows that 15&15Rα@VNP can be effectively used in the treatment of bladder cancer and can be used as a complementary therapy to chemotherapy agents, promising for potential clinical translation in bladder cancer treatment.

Xenotopic synthetic biology: Prospective tools for delaying aging and age-related diseases

Metabolic dysregulation represents one of the major driving forces in aging. Although multiple genetic and pharmacological manipulations are known to extend longevity in model organisms, aging is a complex trait, and targeting one's own genes may be insufficient to prevent age-dependent deterioration. An alternative strategy could be to use enzymes from other species to reverse age-associated metabolic changes. In this review, we discuss a set of enzymes from lower organisms that have been shown to affect various metabolic parameters linked to age-related processes. These enzymes include modulators of steady-state levels of amino acids (METase, ASNase, and ADI), NADPH/NADP+ and/or reduced form of coenzyme Q (CoQH2)/CoQ redox potentials (NDI1, AOX, LbNOX, TPNOX, EcSTH, RquA, LOXCAT, Grubraw, and ScURA), GSH (StGshF), mitochondrial membrane potential (mtON and mito-dR), or reactive oxygen species (DAAO and KillerRed-SOD1). We propose that leveraging non-mammalian enzymes represents an untapped resource that can be used to delay aging and age-related diseases.

Engineered Methioninase-expressing Tumor-targeting Salmonella typhimurium A1-R Inhibits Syngeneic-Cancer Mouse Models by Depleting Tumor Methionine

BACKGROUND/AIM

We previously developed Salmonella typhimurium A1-R, which selectively targets and kills tumors. In the present study, we established recombinant methioninase (rMETase)-producing Salmonella typhimurium A1-R (A1-R-rMETase), by transfer of the Pseudomonas putida methioninase gene, to target methionine addiction of syngeneic-cancer mouse models.

MATERIALS AND METHODS

A plasmid containing the Pseudomonas putida methioninase gene was extracted from METase-producing recombinant E. coli and inserted into Salmonella typhimurium A1-R using electroporation. Lewis Lung Carcinoma (LLC) cells (106) were injected subcutaneously in male C57BL/6 mice aged 4-6 weeks. We determined that 108 Salmonella typhimurium A1-R-rMETase administered iv was a safe dosage in C57BL/6 mice and was used for efficacy studies on LLC tumors in C57BL/6 mice. Tumor size was measured with calipers three times per week for 3 weeks. On day 22, tumor methionine levels were measured using HPLC in the control mice injected with phosphate-buffered saline (PBS) and the mice injected with Salmonella typhimurium A1-R-rMETase.

RESULTS

The mean LLC tumor size of each group on day 22 was as follows: PBS control: 741.5 mm3; mice injected with Salmonella typhimurium A1-R: 566.3 mm3 (p=0.370); and mice injected with Salmonella typhimurium A1-R-rMETase: 198.8 mm3 (p=0.0003 vs control and p=0.0117 vs. Salmonella A1-R). The mice injected with Salmonella typhimurium A1-R-rMETase showed a significantly lower mean tumor methionine level than mice injected with PBS (5.9 nM/mg protein vs 11.1 nM/mg protein, p=0.0095). Salmonella typhimurium A1-R-rMETase grew continuously in the tumors but not in the liver or spleen.

CONCLUSION

Tumor-targeting Salmonella typhimurium A1-R engineered to express the Pseudomonas putida methioninase gene, inhibited LLC tumor growth in a syngeneic mouse model and reduced the methionine level in the tumor. Salmonella typhimurium A1-R-rMETase combines the tumor targeting and killing capability of Salmonella typhimurium A1-R plus rMETase which targets the methionine addiction of cancer.

Studying the Oncolytic Activity of Streptococcus pyogenes Strains Against Hepatoma, Glioma, and Pancreatic Cancer In Vitro and In Vivo

BACKGROUND

Cancer remains a leading cause of mortality globally. Conventional treatment modalities, including radiation and chemotherapy, often fall short of achieving complete remission, highlighting the critical need for novel therapeutic strategies. One promising approach involves the oncolytic potential of Group A Streptococcus (GAS) strains for tumor treatment. This study aimed to investigate the oncolytic efficacy of S. pyogenes GUR and its M protein knockout mutant, S. pyogenes strain GURSA1, which was genetically constructed to minimize overall toxicity, against mouse hepatoma 22A, pancreatic cancer PANC02, and human glioma U251 cells, both in vitro and in vivo, using the C57BL/6 mouse model.

METHODS

The in vitro oncolytic cytotoxic activity of GAS strains was studied against human glioma U251, pancreatic cancer PANC02, murine hepatoma 22a, and normal skin fibroblast cells using the MTT assay and the real-time xCELLigence system. A syngeneic mouse model of hepatoma and pancreatic cancer was used to evaluate the in vivo oncolytic effect of GAS strains. Statistical analysis was conducted using Student's t-test and Mann-Whitney U-test with GraphPad Prism software.

RESULTS

The in vitro model showed that the live S. pyogenes GUR strain had a strong cytotoxic effect (67.4 ± 1.9%) against pancreatic cancer PANC02 cells. This strain exhibited moderate (38.0 ± 1.8%) and weak (16.3 ± 5.4%) oncolytic activities against glioma and hepatoma cells, respectively. In contrast, the S. pyogenes GURSA1 strain demonstrated strong (86.5 ± 1.6%) and moderate (36.5 ± 1.8%) oncolytic activities against glioma and hepatoma cells. Additionally, the S. pyogenes GURSA1 strain did not exhibit cytotoxic activity against healthy skin fibroblast cells (cell viability 104.2 ± 1.3%, p = 0.2542). We demonstrated that tumor treatment with S. pyogenes GURSA1 significantly increased the lifespan of C57BL/6 mice with hepatoma (34 days, p = 0.040) and pancreatic cancer (32 days, p = 0.039) relative to the control groups (24 and 28 days, respectively). Increased lifespan was accompanied by a slowdown in tumor progression, as evidenced by a reduction in the growth of hepatoma and pancreatic cancer tumors under treatment with GAS strains in mice.

CONCLUSIONS

Both S. pyogenes GUR and S. pyogenes GURSA1 strains demonstrated strong oncolytic activity against murine hepatoma 22a, pancreatic cancer PANC02, and human U251 glioma cells in vitro. In contrast, S. pyogenes GUR and GURSA1 did not show toxicity against human normal skin fibroblasts. The overall survival rate and lifespan of mice treated with S. pyogenes GURSA1, a strain lacking the M protein on its surface, were significantly higher compared to the control and S. pyogenes GUR strain groups.

Salmonella-based therapeutic strategies: improving tumor microenvironment and bringing new hope for cancer immunotherapy

Immunotherapy has revolutionized cancer treatment, yet its effectiveness is limited by immunosuppressive tumor microenvironment (TME). To overcome this challenge, innovative strategies to effectively modulate the TME are urgently needed. Over the past decades, bacteria-mediated cancer immunotherapy has recaptured increasing attention, driven by advances in synthetic biology, genetic engineering and our knowledge of host-pathogen interactions. Among various bacterial species, Salmonella has emerged as a leading candidate with significant therapeutic potential due to its broad-spectrum anti-tumor activity, tumor-targeting ability, immunomodulatory effects, oncolytic properties, genetic programmability, and engineering flexibility. These characteristics enable Salmonella to reshape the immunosuppressive TME, thereby enhancing anti-tumor efficacy. This review elaborates the regulatory effects of Salmonella on key components of the TME, the versatile engineering strategies for optimizing Salmonella's ability to modulate the TME, and recent advancements in combination cancer therapies. We also summarize current clinical applications and discuss challenges of developing safer and more effective Salmonella-based cancer immunotherapy.

Genetic engineering of Salmonella spp. for novel vaccine strategies and therapeutics

Salmonella enterica is a diverse species that infects both humans and animals. S. enterica subspecies enterica consists of more than 1,500 serovars. Unlike typhoidal Salmonella serovars which are human host-restricted, non-typhoidal Salmonella (NTS) serovars are associated with foodborne illnesses worldwide and are transmitted via the food chain. Additionally, NTS serovars can cause disease in livestock animals causing significant economic losses. Salmonella is a well-studied model organism that is easy to manipulate and evaluate in animal models of infection. Advances in genetic engineering approaches in recent years have led to the development of Salmonella vaccines for both humans and animals. In this review, we focus on current progress of recombinant live-attenuated Salmonella vaccines, their use as a source of antigens for parenteral vaccines, their use as live-vector vaccines to deliver foreign antigens, and their use as therapeutic cancer vaccines in humans. We also describe development of live-attenuated Salmonella vaccines and live-vector vaccines for use in animals.

Advances in Microbiome-Based Therapeutics for Dermatological Disorders: Current Insights and Future Directions

The human skin hosts an estimated 1000 bacterial species that are essential for maintaining skin health. Extensive clinical and preclinical studies have established the significant role of the skin microbiome in dermatological disorders such as atopic dermatitis, psoriasis, diabetic foot ulcers, hidradenitis suppurativa and skin cancers. In these conditions, the skin microbiome is not only altered but, in some cases, implicated in disease pathophysiology. Microbiome-based therapies (MBTs) represent an emerging category of live biotherapeutic products with tremendous potential as a novel intervention platform for skin diseases. Beyond using established wild-type strains native to the skin, these therapies can be enhanced to express targeted therapeutic molecules, offering more tailored treatment approaches. This review explores the role of the skin microbiome in various common skin disorders, with a particular focus on the development and therapeutic potential of MBTs for treating these conditions.

Programmable Bacteria with Dynamic Virulence Modulation System for Precision Antitumor Immunity

Engineered bacteria-mediated antitumor approaches have been proposed as promising immunotherapies for cancer. However, the off-target bacterial toxicity narrows the therapeutic window. Living microbes will benefit from their controllable immunogenicity within tumors for safer antitumor applications. In this study, a genetically encoded microbial activation strategy is reported that uses tunable and dynamic expression of surface extracellular polysaccharides to improve bacterial biocompatibility while retaining therapeutic efficacy. Based on screening of genes associated with Salmonella survival in macrophages, a novel attenuated Salmonella chassis strain AIS (htrA gene-deficient) highly enriched in tumors after administration and rapidly cleared from normal organs are reported. Subsequently, an engineered bacterial strain, AISI-H, is constructed based on the AIS strain and an optimized quorum-sensing regulatory system. The AISI-H strain can achieve recovery of dynamic tumor-specific bacterial virulence through a novel HTRA-RCSA axis-based and quorum-sensing synthetic gene circuit-mediated increase in extracellular polysaccharide content. These strains act "off" in normal organs to avoid unwanted immune activation and "on" in tumors for precise tumor suppression in mice. The AISI-H strain shows significant tumor inhibition and potent activation of anticancer immunity in a melanoma mouse model. The AISI-H strain exhibits excellent biocompatibility. This bacterial regulation strategy expands the applications of microbe-based antitumor therapeutics.

Bacteria-based cancer therapy: Looking forward

The field of bacteria-based cancer therapy, which focuses on the key role played by the prevalence of bacteria, specifically in tumors, in controlling potential targets for cancer therapy, has grown enormously over the past few decades. In this review, we discuss, for the first time, the global cancer situation and the timeline for using bacteria in cancer therapy. We also explore how interdisciplinary collaboration has contributed to the evolution of bacteria-based cancer therapies. Additionally, we address the challenges that need to be overcome for bacteria-based cancer therapy to be accepted in clinical trials and the latest advancements in the field. The groundbreaking technologies developed through bacteria-based cancer therapy have opened up new therapeutic strategies for a wide range of therapeutics in cancer.

Image-Guided Photothermal and Immune Therapy of Tumors via Melanin-Producing Genetically Engineered Bacteria

Photothermal therapy (PTT) is a new treatment modality for tumors. However, the efficient delivery of photothermal agents into tumors remains difficult, especially in hypoxic tumor regions. In this study, an approach to deliver melanin, a natural photothermal agent, into tumors using genetically engineered bacteria for image-guided photothermal and immune therapy is developed. An Escherichia coli MG1655 is transformed with a recombinant plasmid harboring a tyrosinase gene to produce melanin nanoparticles. Melanin-producing genetically engineered bacteria (MG1655-M) are systemically administered to 4T1 tumor-bearing mice. The tumor-targeting properties of MG1655-M in the hypoxic environment integrate the properties of hypoxia targeting, photoacoustic imaging, and photothermal therapeutic agents in an "all-in-one" manner. This eliminates the need for post-modification to achieve image-guided hypoxia-targeted cancer photothermal therapy. Tumor growth is significantly suppressed by irradiating the tumor with an 808 nm laser. Furthermore, strong antitumor immunity is triggered by PTT, thereby producing long-term immune memory effects that effectively inhibit tumor metastasis and recurrence. This work proposes a new photothermal and immune therapy guided by an "all-in-one" melanin-producing genetically engineered bacteria, which can offer broad potential applications in cancer treatment.

Deprivation of methionine inhibits osteosarcoma growth and metastasis via C1orf112-mediated regulation of mitochondrial functions

Osteosarcoma is a malignant bone tumor that primarily inflicts the youth. It often metastasizes to the lungs after chemotherapy failure, which eventually shortens patients' lives. Thus, there is a dire clinical need to develop a novel therapy to tackle osteosarcoma metastasis. Methionine dependence is a special metabolic characteristic of most malignant tumor cells that may offer a target pathway for such therapy. Herein, we demonstrated that methionine deficiency restricted the growth and metastasis of cultured human osteosarcoma cells. A genetically engineered Salmonella, SGN1, capable of overexpressing an L-methioninase and hydrolyzing methionine led to significant reduction of methionine and S-adenosyl-methionine (SAM) specifically in tumor tissues, drastically restricted the growth and metastasis in subcutaneous xenograft, orthotopic, and tail vein-injected metastatic models, and prolonged the survival of the model animals. SGN1 also sharply suppressed the growth of patient-derived organoid and xenograft. Methionine restriction in the osteosarcoma cells initiated severe mitochondrial dysfunction, as evident in the dysregulated gene expression of respiratory chains, increased mitochondrial ROS generation, reduced ATP production, decreased basal and maximum respiration, and damaged mitochondrial membrane potential. Transcriptomic and molecular analysis revealed the reduction of C1orf112 expression as a primary mechanism underlies methionine deprivation-initiated suppression on the growth and metastasis as well as mitochondrial functions. Collectively, our findings unraveled a molecular linkage between methionine restriction, mitochondrial function, and osteosarcoma growth and metastasis. A pharmacological agent, such as SGN1, that can achieve tumor specific deprivation of methionine may represent a promising modality against the metastasis of osteosarcoma and potentially other types of sarcomas as well.

Intratumoral delivery of immunotherapy to treat breast cancer: current development in clinical and preclinical studies

Breast cancer poses one of the largest threats to women's health. Treatment continues to improve for all the subtypes of breast cancer, but some subtypes, such as triple negative breast cancer, still present a significant treatment challenge. Additionally, metastasis and local recurrence are two prevalent problems in breast cancer treatment. A newer type of therapy, immunotherapy, may offer alternatives to traditional treatments for difficult-to-treat subtypes. Immunotherapy engages the host's immune system to eradicate disease, with the potential to induce long-lasting, durable responses. However, systemic immunotherapy is only approved in a limited number of indications, and it benefits only a minority of patients. Furthermore, immune related toxicities following systemic administration of potent immunomodulators limit dosing and, consequently, efficacy. To address these safety considerations and improve treatment efficacy, interest in local delivery at the site of the tumor has increased. Numerous intratumorally delivered immunotherapeutics have been and are being explored clinically and preclinically, including monoclonal antibodies, cellular therapies, viruses, nucleic acids, cytokines, innate immune agonists, and bacteria. This review summarizes the current and past intratumoral immunotherapy clinical landscape in breast cancer as well as current progress that has been made in preclinical studies, with a focus on delivery parameters and considerations.

Salmonella-mediated methionine deprivation drives immune activation and enhances immune checkpoint blockade therapy in melanoma

BACKGROUND

Although immune checkpoint inhibitor (ICI)-based therapy is advantageous for patients with advanced melanoma, resistance and relapse are frequent. Thus, it is crucial to identify effective drug combinations and develop new therapies for the treatment of melanoma. SGN1, a genetically modified Salmonella typhimurium species that causes the targeted deprivation of methionine in tumor tissues, is currently under investigation in clinical trials. However, the inhibitory effect of SGN1 on melanoma and the benefits of SGN1 in combination with ICIs remain largely unexplored. Therefore, this study aims to investigate the antitumor potential of SGN1, and its ability to enhance the efficacy of antibody-based programmed cell death-ligand 1 (PD-L1) inhibitors in the treatment of murine melanoma.

METHODS

The antitumor activity of SGN1 and the effect of SGN1 on the efficacy of PD-L1 inhibitors was studied through murine melanoma models. Further, The Cancer Genome Atlas-melanoma cohort was clustered using ConsensusClusterPlus based on the methionine deprivation-related genes, and immune characterization was performed using xCell, Microenvironment Cell Populations-counter, Estimation of Stromal and Immune cells in MAlignant Tumor tissues using Expression data, and immunophenoscore (IPS) analyses. The messenger RNA data on programmed death-1 (PD-1) immunotherapy response were obtained from the Gene Expression Omnibus database. Gene Set Enrichment Analysis of methionine deprivation-up gene set was performed to determine the differences between pretreatment responders and non-responders.

RESULTS

This study showed that both, the intratumoral and the intravenous administration of SGN1 in subcutaneous B16-F10 melanomas, suppress tumor growth, which was associated with an activated CD8+T-cell response in the tumor microenvironment. Combination therapy of SGN1 with systemic anti-PD-L1 therapy resulted in better antitumor activity than the individual monotherapies, respectively, and the high therapeutic efficacy of the combination was associated with an increase in the systemic level of tumor-specific CD8+ T cells. Two clusters consisting of methionine deprivation-related genes were identified. Patients in cluster 2 had higher expression of methionine_deprivation_up genes, better clinical outcomes, and higher immune infiltration levels compared with patients in cluster 1. Western blot, IPS analysis, and immunotherapy cohort study revealed that methionine deficiency may show a better response to ICI therapy CONCLUSIONS：: This study reports Salmonella-based SGN1 as a potent anticancer agent against melanoma, and lays the groundwork for the potential synergistic effect of ICIs and SGN1 brought about by improving the immune microenvironment in melanomas.

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.