Bacteria as tumor therapeutics?

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.

Alzheimer's Disease Immunotherapy: Current Strategies and Future Prospects

Alzheimer's disease (AD) is an extremely complex and heterogeneous pathology influenced by many factors contributing to its onset and progression, including aging, amyloid-beta (Aβ) plaques, tau fibril accumulation, inflammation, etc. Despite promising advances in drug development, there is no cure for AD. Although there have been substantial advancements in understanding the pathogenesis of AD, there have been over 200 unsuccessful clinical trials in the past decade. In recent years, immunotherapies have been at the forefront of these efforts. Immunotherapy alludes to the immunological field that strives to identify disease treatments via the enhancement, suppression, or induction of immune responses. Interestingly, immunotherapy in AD is a relatively new approach for non-infectious disease. At present, antibody therapy (passive immunotherapy) that targets anti-Aβ aimed to prevent the fibrillization of Aβ peptides and disrupt pre-existing fibrils is a predominant AD immunotherapy due to the continuous failure of active immunotherapy for AD. The most rational and safe strategies will be those targeting the toxic molecule without triggering an abnormal immune response, offering therapeutic advantages, thus making clinical trial design more efficient. This review offers a concise overview of immunotherapeutic strategies, including active and passive immunotherapy for AD. Our review encompasses approved methods and those presently under investigation in clinical trials, while elucidating the recent challenges, complications, successes, and potential treatments. Thus, immunotherapies targeting Aβ throughout the disease progression using a mutant oligomer-Aβ stimulated dendritic cell vaccine may offer a promising therapy in AD.

Bacterial cancer therapy using the attenuated fowl-adapted Salmonella enterica serovar Gallinarum

We report here a novel anti-cancer therapy based on an avian-host-specific serotype Salmonella enterica serovar Gallinarum (S. Gallinarum) deficient in ppGpp synthesis. To monitor the tumor targeting, a bioluminescent ΔppGpp S. Gallinarum was constructed and injected intravenously into mice bearing syngeneic and human xenograft tumors. Strong bioluminescent signals were detected specifically in all grafted tumors at 2 days post-injection (dpi). The bacterial counts in normal and tumor tissue at 1 dpi revealed that ΔppGpp S. Gallinarum reached >108 CFU/g in tumor tissue and 106-107 CFU/g in endothelial organs; counts were much lower in other organs. At 16 dpi, ΔppGpp S. Gallinarum counts in tumor tissue decreased to ∼106 CFU/g, while those in the other organs became undetectable. A strong anti-cancer effect was observed after the injection of ΔppGpp S. Gallinarum into BALB/c mice grafted with CT26 colon cancer cells. This could be attributed to reduced virulence, which allowed the administration of at least a 10-fold greater dose (108 CFU) of ΔppGpp S. Gallinarum than other attenuated strains of S. enterica serovar Typhimurium (≤107 CFU). An advantage of the avian-specific S. Gallinarum as a cancer therapeutic should be a reduced capacity to cause infections or harm in humans.

Bacterial immunotherapy: is it a weapon in our arsenal in the fight against cancer?

Advances in understanding the genetic basis of cancer have driven alternative treatment approaches. Recent findings have demonstrated the potential of bacteria and it's components to serve as robust theranostic agents for cancer eradication. Compared to traditional cancer therapies like surgery, chemotherapy, radiotherapy, bacteria mediated tumor therapy has exhibited superior cancer suppressing property which is attributed a lot to it's tumor proliferating and accumulating characteristics. Genetically modified bacteria has reduced inherent toxicity and enhanced specificity towards tumor microenvironment. This anti- tumor activity of bacteria is attributed to its toxins and other active components from the cell membrane, cell wall and spores. Furthermore, bacterial genes can be regulated to express and deliver cytokines, antibodies and cancer therapeutics. Although there is less clinical data available, the pre- clinical research clearly indicates the feasibility and potential of bacteria- mediated cancer therapy.

Emerging applications of cancer bacteriotherapy towards treatment of pancreatic cancer

Pancreatic cancer is a highly aggressive form of cancer with a five-year survival rate of only ten percent. Pancreatic ductal adenocarcinoma (PDAC) accounts for ninety percent of those cases. PDAC is associated with a dense stroma that confers resistance to current treatment modalities. Increasing resistance to cancer treatments poses a challenge and a need for alternative therapies. Bacterial mediated cancer therapies were proposed in the late 1800s by Dr. William Coley when he injected osteosarcoma patients with live streptococci or a fabrication of heat-killed Streptococcus pyogenes and Serratia marcescens known as Coley's toxin. Since then, several bacteria have gained recognition for possible roles in potentiating treatment response, enhancing anti-tumor immunity, and alleviating adverse effects to standard treatment options. This review highlights key bacterial mechanisms and structures that promote anti-tumor immunity, challenges and risks associated with bacterial mediated cancer therapies, and applications and opportunities for use in PDAC management.

Microbial cancer therapeutics: A promising approach

The success of conventional cancer therapeutics is hindered by associated dreadful side-effects of antibiotic resistance and the dearth of antitumor drugs' selectivity and specificity. Hence, the conceptual evolution of anti-cancerous therapeutic agents that selectively target cancer cells without impacting the healthy cells or tissues, has led to a new wave of scientific interest in microbial-derived bioactive molecules. Such strategic solutions may pave the way to surmount the shortcomings of conventional therapies and raise the potential and hope for the cure of wide range of cancer in a selective manner. This review aims to provide a comprehensive summary of anti-carcinogenic properties and underlying mechanisms of bioactive molecules of microbial origin, and discuss the current challenges and effective therapeutic application of combinatorial strategies to attain minimal systemic side-effects.

The Immune System as a Therapeutic Target for Alzheimer’s Disease

Alzheimer’s disease (AD) is a heterogeneous neurodegenerative disorder and is the most common cause of dementia. Furthermore, aging is considered the most critical risk factor for AD. However, despite the vast amount of research and resources allocated to the understanding and development of AD treatments, setbacks have been more prominent than successes. Recent studies have shown that there is an intricate connection between the immune and central nervous systems, which can be imbalanced and thereby mediate neuroinflammation and AD. Thus, this review examines this connection and how it can be altered with AD. Recent developments in active and passive immunotherapy for AD are also discussed as well as suggestions for improving these therapies moving forward.

Bacterial-Based Methods for Cancer Treatment: What We Know and Where We Are

A severe disease, cancer is caused by the exponential and uncontrolled growth of cells, leading to organ dysfunction as well as disorders. This disease has been recognized as one of the significant challenges to health and medicine. Various treatment procedures for cancer are associated with diverse side effects; the most conventional cancer treatments include chemotherapy, surgery, and radiotherapy, among others. Numerous adverse and side effects, low specificity and sensitivity, narrow therapeutic windows, and, recently, the emergence of tumor cells resistant to such treatments have been documented as the shortcomings of conventional treatment strategies. As a group of prokaryotic microorganisms, bacteria have great potential for use in cancer therapy. Currently, utilizing bacteria for cancer treatment has attracted the attention of scientists. The high potential of bacteria to become non-pathogenic by genetic manipulation, their distinguished virulence factors (which can be used as weapons against tumors), their ability to proliferate in tissues, and the contingency to control their population by administrating antibiotics, etc., have made bacteria viable candidates and live micro-medication for cancer therapies. However, the possible cytotoxicity impacts of bacteria, their inability to entirely lyse cancerous cells, as well as the probability of mutations in their genomes are among the significant challenges of bacteria-based methods for cancer treatment. In this article, various available data on bacterial therapeutics, along with their pros and cons, are discussed.

Periodontitis pathogen Porphyromonas gingivalis promotes pancreatic tumorigenesis via neutrophil elastase from tumor-associated neutrophils

Intratumor microbiome shapes the immune system and influences the outcome of various tumors. Porphyromonas gingivalis (P. gingivalis), the keystone periodontal pathogen, is highly epidemically connected with pancreatic cancer (PC). However, its causative role and the underlining mechanism in promoting PC oncogenesis remain unclear. Here, we illustrated the landscape of intratumor microbiome and its bacterial correlation with oral cavity in PC patients, where P. gingivalis presented both in the oral cavity and tumor tissues. When exposed to P. gingivalis, tumor development was accelerated in orthotopic and subcutaneous PC mouse model, and the cancerous pancreas exhibited a neutrophils-dominated proinflammatory tumor microenvironment. Mechanistically, the intratumoral P. gingivalis promoted PC progression via elevating the secretion of neutrophilic chemokines and neutrophil elastase (NE). Collectively, our study disclosed the bacterial link between periodontitis and PC, and revealed a previously unrecognized mechanism of P. gingivalis in PC pathophysiology, hinting at therapeutic implications.

Bacteria-driven hypoxia targeting delivery of chemotherapeutic drug proving outcome of breast cancer

Local hypoxia is a common feature of many solid tumors and may lead to unsatisfactory chemotherapy outcomes. Anaerobic bacteria that have an affinity to hypoxic areas can be used to achieve targeted drug delivery in tumor tissues. In this study, we developed a biocompatible bacteria/nanoparticles biohybrid (Bif@DOX-NPs) platform that employs the anaerobic Bifidobacterium infantis (Bif) to deliver adriamycin-loaded bovine serum albumin nanoparticles (DOX-NPs) into breast tumors. The Bif@DOX-NPs retained the targeting ability of B. infantis to hypoxic regions, as well as the cytotoxicity of DOX. The biohybrids were able to actively colonize the hypoxic tumors and significantly increased drug accumulation at the tumor site. The DOX concentration in the tumor masses colonized by Bif@DOX-NPs was 4 times higher than that in the free DOX-treated tumors, which significantly prolonged the median survival of the tumor-bearing mice to 69 days and reduced the toxic side-effects of DOX. Thus, anaerobic bacteria-based biohybrids are a highly promising tool for the targeted treatment of solid tumors with inaccessible hypoxic regions.

Innate Immunity and Cancer Pathophysiology

Chronic inflammation increases the risk of several cancers, including gastric, colon, and hepatic cancers. Conversely, tumors, similar to tissue injury, trigger an inflammatory response coordinated by the innate immune system. Cellular and molecular mediators of inflammation modulate tumor growth directly and by influencing the adaptive immune response. Depending on the balance of immune cell types and signals within the tumor microenvironment, inflammation can support or restrain the tumor. Adding to the complexity, research from the past two decades has revealed that innate immune cells are highly heterogeneous and plastic, with variable phenotypes depending on tumor type, stage, and treatment. The field is now on the cusp of being able to harness this wealth of data to (a) classify tumors on the basis of their immune makeup, with implications for prognosis, treatment choice, and clinical outcome, and (b) design therapeutic strategies that activate antitumor immune responses by targeting innate immune cells.

Fighting Cancer with Bacteria and Their Toxins

Cancer is one of the most important global health problems that continues to demand new treatment strategies. Many bacteria that cause persistent infections play a role in carcinogenesis. However, since bacteria are well studied in terms of molecular mechanisms, they have been proposed as an interesting solution to treat cancer. In this review, we present the use of bacteria, and particularly bacterial toxins, in cancer therapy, highlighting the advantages and limitations of bacterial toxins. Proteomics, as one of the omics disciplines, is essential for the study of bacterial toxins. Advances in proteomics have contributed to better characterization of bacterial toxins, but also to the development of anticancer drugs based on bacterial toxins. In addition, we highlight the current state of knowledge in the rapidly developing field of bacterial extracellular vesicles, with a focus on their recent application as immunotherapeutic agents.

BCG turns 100: its nontraditional uses against viruses, cancer, and immunologic diseases

First administered to a human subject as a tuberculosis (TB) vaccine on July 18, 1921, Bacillus Calmette-Guérin (BCG) has a long history of use for the prevention of TB and later the immunotherapy of bladder cancer. For TB prevention, BCG is given to infants born globally across over 180 countries and has been in use since the late 1920s. With about 352 million BCG doses procured annually and tens of billions of doses having been administered over the past century, it is estimated to be the most widely used vaccine in human history. While its roles for TB prevention and bladder cancer immunotherapy are widely appreciated, over the past century, BCG has been also studied for nontraditional purposes, which include (a) prevention of viral infections and nontuberculous mycobacterial infections, (b) cancer immunotherapy aside from bladder cancer, and (c) immunologic diseases, including multiple sclerosis, type 1 diabetes, and atopic diseases. The basis for these heterologous effects lies in the ability of BCG to alter immunologic set points via heterologous T cell immunity, as well as epigenetic and metabolomic changes in innate immune cells, a process called "trained immunity." In this Review, we provide an overview of what is known regarding the trained immunity mechanism of heterologous protection, and we describe the current knowledge base for these nontraditional uses of BCG.

Dual Gate-Controlled Therapeutics for Overcoming Bacterium-Induced Drug Resistance and Potentiating Cancer Immunotherapy

The presence of bacteria in the tumor can cause cancer resistance to chemotherapeutics. To fight against bacterium-induced drug resistance, herein we design self-traceable nanoreservoirs that are simultaneously loaded with gemcitabine (an anticancer drug) and ciprofloxacin (an antibiotic) and are decorated with hyaluronic acid for active tumor targeting. The nanoreservoirs have a pH-sensitive gate and an enzyme-responsive gate that can be opened in the acidic and hyaluronidase-abundant tumor microenvironment to control drug release rates. Moreover, the nanoreservoirs can specifically target the tumor regions without eliciting evident toxicity to normal tissues, kill the intratumoral bacteria, and inhibit the tumor growth even in the presence of the bacteria. Unexpectedly, the nanoreservoirs can activate T cell-mediated immune responses through promoting antigen-presenting dendritic cell maturation and depleting immunosuppressive myeloid-derived suppressor cells in bacterium-infected tumors.

Clinical Experience and Recent Advances in the Development of Listeria-Based Tumor Immunotherapies

The promise of tumor immunotherapy to significantly improve survival in patients who are refractory to long-standing therapies, such as chemotherapy and radiation, is now being realized. While immune checkpoint inhibitors that target PD-1 and CTLA-4 are leading the charge in clinical efficacy, there are a number of other promising tumor immunotherapies in advanced development such as Listeria-based vaccines. Due to its unique life cycle and ability to induce robust CTL responses, attenuated strains of Listeria monocytogenes (Lm) have been utilized as vaccine vectors targeting both infectious disease and cancer. In fact, preclinical studies in a multitude of cancer types have found Listeria-based vaccines to be highly effective at activating anti-tumor immunity and eradicating tumors. Several clinical trials have now recently reported their results, demonstrating promising efficacy against some cancers, and unique challenges. Development of the Lm-based immunotherapies continues with discovery of improved methods of attenuation, novel uses, and more effective combinatorial regimens. In this review, we provide a brief background of Listeria monocytogenes as a vaccine vector, discuss recent clinical experience with Listeria-based immunotherapies, and detail the advancements in development of improved Listeria-based vaccine platforms and in their utilization.

Cell primitive-based biomimetic functional materials for enhanced cancer therapy

Cell primitive-based functional materials that combine the advantages of natural substances and nanotechnology have emerged as attractive therapeutic agents for cancer therapy. Cell primitives are characterized by distinctive biological functions, such as long-term circulation, tumor specific targeting, immune modulation etc. Moreover, synthetic nanomaterials featuring unique physical/chemical properties have been widely used as effective drug delivery vehicles or anticancer agents to treat cancer. The combination of these two kinds of materials will catalyze the generation of innovative biomaterials with multiple functions, high biocompatibility and negligible immunogenicity for precise cancer therapy. In this review, we summarize the most recent advances in the development of cell primitive-based functional materials for cancer therapy. Different cell primitives, including bacteria, phages, cells, cell membranes, and other bioactive substances are introduced with their unique bioactive functions, and strategies in combining with synthetic materials, especially nanoparticulate systems, for the construction of function-enhanced biomaterials are also summarized. Furthermore, foreseeable challenges and future perspectives are also included for the future research direction in this field.

Dual Role of Bacteria in Carcinoma: Stimulation and Inhibition

Although what unifies the carcinogenic microorganisms has not been determined by multiple studies, the role of bacteria in the development of neoplasms has not been properly elucidated. In this review, we discuss links between the bacterial species and cancer, with focus on immune responses for the stimulation of tumor cells such as induction of inflammation. Finally, we will describe the potential therapeutic strategies of bacteria on target tumors to improve treatment while mitigating adverse reactions. Cancer is a series of genetic changes that transform normal cells into tumor cells. These changes come from several reasons, including smoking, drinking alcohol, sunlight, exposure to chemical or physical factors, and finally chronic infection with microorganisms, including bacteria. In fact, bacterial infections are not carcinogenic, but recently it was discovered that the association between bacteria and cancer is through two mechanisms, the first stimulating chronic inflammation and the second producing carcinogenic metabolites. While bacteria are carcinogenic agents also, they have a dual role eliminating and removing tumor cells. However, the traditional cancer treatments that include chemotherapy, radiotherapy, surgery, and immunotherapy increase the chances of survival, and there are many side effects of these therapies, including the high toxicity of tissues and normal cells, could not penetrate the tumor cells, and resistance of these therapies by tumor cells. Therefore, the world has turned to an alternative solution, which is the use of genetically engineered microorganisms; thus, the use of living bacteria targeting cancerous cells is the unique option to overcome these challenges. Bacterial therapies, whether used alone or combination with chemotherapy, give a positive effect to treat multiple conditions of cancer. Also, bacteria can be used as vectors for drug, gene, or therapy, and this is a great step to treat cancer. Thus, we review the mechanisms underlying the interaction of the microbiota residents with cancer. Cancer-associated bacteria differ from those in healthy human and are linked with gene-expression profile. We also discuss how live bacteria interact with tumor microenvironments to induce tumor regression through colonization and spread. Finally, we provide past and ongoing clinical trials that include bacteria targeting tumors.

Mycobacteria-Based Vaccines as Immunotherapy for Non-urological Cancers

The arsenal against different types of cancers has increased impressively in the last decade. The detailed knowledge of the tumor microenvironment enables it to be manipulated in order to help the immune system fight against tumor cells by using specific checkpoint inhibitors, cell-based treatments, targeted antibodies, and immune stimulants. In fact, it is widely known that the first immunotherapeutic tools as immune stimulants for cancer treatment were bacteria and still are; specifically, the use of Mycobacterium bovis bacillus Calmette-Guérin (BCG) continues to be the treatment of choice for preventing cancer recurrence and progression in non-invasive bladder cancer. BCG and also other mycobacteria or their components are currently under study for the immunotherapeutic treatment of different malignancies. This review focuses on the preclinical and clinical assays using mycobacteria to treat non-urological cancers, providing a wide knowledge of the beneficial applications of these microorganisms to manipulate the tumor microenvironment aiming at tumor clearance.

[Intestinal microbiom modulates the response to antitumor immunotherapy]

Numerous studies confirm the high degree of involvement of the intestinal microbiota in most processes in the human body. There is evidence for the effect of intestinal microbiota on the success of chemo and immunotherapy of oncological diseases. It is assumed that the intestinal microbiota exhibits an indirect effect on the antitumor therapy through such mechanisms as general immunomodulation, an increase in cells that specifically respond to antigens of both microbial and tumor origin, metabolism, degradation (utilization) of drug compounds. The intestinal microbiota is currently considered as an additional, but important target for studying the effective use of antitumor therapy and reducing its toxicity, as well as a predictor of the success of immunotherapy. In this review, we highlight the results of studies published to date that confirm the relationship between gut microbiome and antitumor efficacy of immune checkpoint inhibitors. Despite the promising and theoretically substantiated conclusions, there are still some discrepancies among the existing data that will have to be addressed in order to facilitate the further development of this direction.

Bioinspired and Biomimetic Nanomedicines

Nanomedicine development aims to enhance the efficacy, accuracy, safety, and/or compliance of diagnosis and treatment of diseases by leveraging the unique properties of engineered nanomaterials. To this end, a multitude of organic and inorganic nanoparticles have been designed to facilitate drug delivery, sensing, and imaging, some of which are currently in clinical trials or have been approved by the Food and Drug Administration (FDA). In the process, the increasing knowledge in understanding how natural particulates, including cells, pathogens, and organelles, interact with body and cellular systems has spurred efforts to mimic their morphology and functions for developing new generations of nanomedicine formulations. In addition, the advances in bioengineering tools, bioconjugation chemistries, and bio-nanotechnologies have further enabled researchers to exploit these natural particulates for theranostic purposes. In this Account, we will discuss the recent progress in our lab on engineering bioinspired and biomimetic synthetic and cellular systems toward rational design of nanomedicine platforms for treating diabetes and cancer. Inspired by the structure and response mechanism of pancreatic β-cells, we synthesized a series of insulin granule-like vesicles that can respond to high blood or intestinal glucose levels for aiding in transdermal or oral insulin delivery, respectively. Then, to more closely mimic the multicompartmental architecture of β-cells, we further developed synthetic artificial cells with vesicle-in-vesicle superstructures which can sense blood glucose levels and dynamically release insulin via a membrane fusion process. Meanwhile, clues drawn from the traits of anaerobic bacteria that selectively invade and proliferate in solid tumors inspired the synthesis of a light-tuned hypoxia-responsive nanovesicle for implementing synergistic cancer therapy. In parallel, we also studied how autologous particulates could be recruited for developing advanced drug delivery systems. Through combination of genetic engineering and top-down cell engineering technologies, biomimetic nanomedicines derived from cytoplasmic membrane with programmed death 1 (PD-1) receptors expressed on surfaces were generated and employed for cancer immunotherapy. Based on our earlier study where aPD-L1 (antibodies against PD ligand 1)-conjugated platelets could release aPD-L1-bearing particles in situ and inhibit postsurgical tumor recurrence, we further genetically engineered megakaryocytes, the precursor cells of platelets, to express PD-1 receptors. In this way, platelets born with checkpoint blocking activity could be produced directly in vitro, avoiding post chemical modification processes while exerting similar therapeutic impact. As a further extension, by virtue of the bone marrow-homing ability of hematopoietic stem cells (HSCs), we recently conceived a cell-combination strategy by conjugating HSCs with platelets decorated with antibodies against PD1 (aPD-1) to suppress the growth and recurrence of leukemia. While we are still on the way of digging deep to understand and optimize bioinspired and biomimetic drug carriers, we expect that the strategies summarized in this Account would contribute to the development of advanced nanomedicines.

Advances in Stimulus-Responsive Polymeric Materials for Systemic Delivery of Nucleic Acids

Polymeric materials that respond to a variety of endogenous and external stimuli are actively developed to overcome the main barriers to successful systemic delivery of therapeutic nucleic acids. Here, an overview of viable stimuli that are proved to improve systemic delivery of nucleic acids is provided. The main focus is placed on nucleic acid delivery systems (NADS) based on polymers that respond to pathological or physiological changes in pH, redox state, enzyme levels, hypoxia, and reactive oxygen species levels. Additional discussion is focused on NADS suitable for applications that use external stimuli, such as light, ultrasound, and local hyperthermia.

Bacterial Therapy of Cancer: Promises, Limitations, and Insights for Future Directions

Spontaneous tumors regression has been associated with microbial infection for 100s of years and inspired the use of bacteria for anticancer therapy. Dr. William B. Coley (1862-1936), a bone- sarcoma surgeon, was a pioneer in treating his patients with both live bacterial-based and mixture of heat-killed bacteria known as "Coley's toxins." Unfortunately, Coley was forced to stop his work which interrupted this field for about half a century. Currently, several species of bacteria are being developed against cancer. The bacterial species, their genetic background and their infectious behavior within the tumor microenvironment are thought to be relevant factors in determining their anti-tumor effectiveness in vivo. In this perspective article we will update the most promising results achieved using bacterial therapy (alone or combined with other strategies) in clinically-relevant animal models of cancer and critically discuss the impact of the bacterial variants, route of administration and mechanisms of bacteria-cancer-cell interaction. We will also discuss strategies to apply this information using modern mouse models, molecular biology, genetics and imaging for future bacterial therapy of cancer patients.

The power of combining adoptive cell therapy (ACT) and pathogen-boosted vaccination to treat solid tumors

Recent advancements in adoptive cell therapy (ACT) are opening up new frontiers for cancer immunotherapy. CAR T cells targeting CD19 have emerged as a remarkable T cell-based therapy for the successful treatment of certain types of leukemia and lymphomas. Despite these clinical successes, as well as significant breakthroughs in T cell engineering, the treatment of solid tumors with ACT remains a relentless challenge. Thus, the current consensus of the field is that an urgent need exists for the design of innovative approaches that can improve the efficacy of ACT in treating solid cancers while maintaining a high degree of reliability and safety.

Anaerobe-Inspired Anticancer Nanovesicles

Anaerobic bacteria, such as Clostridium and Salmonella, can selectively invade and colonize in tumor hypoxic regions (THRs) and deliver therapeutic products to destroy cancer cells. Herein, we present an anaerobe nanovesicle mimic that can not only be activated in THRs but also induce hypoxia in tumors by themselves. Moreover, inspired by the oxygen metabolism of anaerobes, we construct a light-induced hypoxia-responsive modality to promote dissociation of vehicles and activation of bioreductive prodrugs simultaneously. In vitro and in vivo experiments indicate that this anaerobe-inspired nanovesicle can efficiently induce apoptotic cell death and significantly inhibit tumor growth. Our work provides a new strategy for engineering stimuli-responsive drug delivery systems in a bioinspired and synergistic fashion.

A Salmonella nanoparticle mimic overcomes multidrug resistance in tumours

Salmonella enterica serotype Typhimurium is a food-borne pathogen that also selectively grows in tumours and functionally decreases P-glycoprotein (P-gp), a multidrug resistance transporter. Here we report that the Salmonella type III secretion effector, SipA, is responsible for P-gp modulation through a pathway involving caspase-3. Mimicking the ability of Salmonella to reverse multidrug resistance, we constructed a gold nanoparticle system packaged with a SipA corona, and found this bacterial mimic not only accumulates in tumours but also reduces P-gp at a SipA dose significantly lower than free SipA. Moreover, the Salmonella nanoparticle mimic suppresses tumour growth with a concomitant reduction in P-gp when used with an existing chemotherapeutic drug (that is, doxorubicin). On the basis of our finding that the SipA Salmonella effector is fundamental for functionally decreasing P-gp, we engineered a nanoparticle mimic that both overcomes multidrug resistance in cancer cells and increases tumour sensitivity to conventional chemotherapeutics.

Solid tumors provide niche-specific conditions that lead to preferential growth of Salmonella

Therapeutic attenuated strains of Salmonella Typhimurium target and eradicate tumors in mouse models. However, the mechanism of S. Typhimurium for tumor targeting is still poorly understood. We performed a high-throughput screening of single-gene deletion mutants of S. Typhimurium in an orthotopic, syngeneic murine mammary model of breast cancer. The mutants under selection in this system were classified into functional categories to identify bacterial processes involved in Salmonella accumulation within tumors. Niche-specific genes involved in preferential tumor colonization were identified and exemplars were confirmed by competitive infection assays. Our results show that the chemotaxis gene cheY and the motility genes motAB confer an advantage for colonization of Salmonella within orthotopic syngeneic breast tumors. In addition, eutC, a gene belonging to the ethanolamine metabolic pathway, also confers an advantage for Salmonella within tumors, perhaps by exploiting either ethanolamine or an alternative nutrient in the inflamed tumor environment.

Targeting the tumor microenvironment to enhance antitumor immune responses

The identification of tumor-specific antigens and the immune responses directed against them has instigated the development of therapies to enhance antitumor immune responses. Most of these cancer immunotherapies are administered systemically rather than directly to tumors. Nonetheless, numerous studies have demonstrated that intratumoral therapy is an attractive approach, both for immunization and immunomodulation purposes. Injection, recruitment and/or activation of antigen-presenting cells in the tumor nest have been extensively studied as strategies to cross-prime immune responses. Moreover, delivery of stimulatory cytokines, blockade of inhibitory cytokines and immune checkpoint blockade have been explored to restore immunological fitness at the tumor site. These tumor-targeted therapies have the potential to induce systemic immunity without the toxicity that is often associated with systemic treatments. We review the most promising intratumoral immunotherapies, how these affect systemic antitumor immunity such that disseminated tumor cells are eliminated, and which approaches have been proven successful in animal models and patients.