The microbiome in anti-cancer therapy

Targeting the gut microbiota to enhance the antitumor efficacy and attenuate the toxicity of CAR-T cell therapy: a new hope?

Chimeric antigen receptor (CAR) -T cell therapy has achieved tremendous efficacy in the treatment of hematologic malignancies and represents a promising treatment regimen for cancer. Despite the striking response in patients with hematologic malignancies, most patients with solid tumors treated with CAR-T cells have a low response rate and experience major adverse effects, which indicates the need for biomarkers that can predict and improve clinical outcomes with future CAR-T cell treatments. Recently, the role of the gut microbiota in cancer therapy has been established, and growing evidence has suggested that gut microbiota signatures may be harnessed to personally predict therapeutic response or adverse effects in optimizing CAR-T cell therapy. In this review, we discuss current understanding of CAR-T cell therapy and the gut microbiota, and the interplay between the gut microbiota and CAR-T cell therapy. Above all, we highlight potential strategies and challenges in harnessing the gut microbiota as a predictor and modifier of CAR-T cell therapy efficacy while attenuating toxicity.

What if amoxicillin/clavulanic acid reduces the cisplatin anticancer impact on oral cancer treatment?

Antibiotics-chemotherapeutics combination have become on the table for many cancer treatments. For this reason, we thought that further progress and development of studies to support chemotherapeutic approaches with the use of antibiotics may be beneficial in the clinical field. Cell lines (SCC-15, HTB-41, and MRC-5) were treated with 5-100 μM/ml concentrations of cisplatin (cisp) and amoxicillin/clavulanic acid (amx/cla) with combination (amx/cla-cisp) and alone in three different incubation periods. The all-cells viability was examined with WST-1 and apoptotic activity of the drugs were investigated via cell death ELISA assay kit. The cytotoxic impact of the 100 μM amx/cla-cisp combination was found to be reduced by up to 21.8%, which was significant given that the cytotoxic effect of only cisplatin therapy was 86.1%. Because our findings demonstrated that solo amx/cla therapy have almost no impact on proliferation or death, we focused on the amx/cla-cisp combination effect. It was found that the amx/cla-cisp combination has reduced the apoptotic fragment when comparing with the solely cisp-treated cells. Due to amx/cla-cisp combination on both cells but significantly on SCC-15 recovered the sole cisplatin effect, we believe that there might be a second thought when prescribing antibiotics while treating cancer patients. Not only the antibiotic's type but also the cancer type might interact to lessen the chemotherapeutic agent's impact which is clinically a dilemma to focus on.

Microbiota as a New Target in Cancer Pathogenesis and Treatment

The microbial ecosystem of humans is an integral part of human health and disease. A significant percentage of tumors worldwide are thought to be microbially induced. The relationship between cancer and microbes is complex. In this article review, we aim to give an overview of human microbiota and its role in carcinogenesis, emphasize the relation between microbiota and cancer immunity, and highlight its role in the future of cancer therapy. The term microbiota refers to the collection of microorganisms that are located in an individual, whereas the total genome of these microorganisms is referred to as the microbiome. The microbiota in humans has many physiological functions. The microbiota within the gut lumen has a profound effect on the local and systemic immune system. The immune system can change the gut microbiota. Microbiota may induce carcinogenesis by several mechanisms. It also affects tumor progression. Thus, microbiota modulation may aid in the prevention and treatment of cancer. Intentionally introducing microorganisms into the oncological patient is assumed to mobilize the immune system to become able to, at least, limit the development of cancer. Microbes are used as vectors which are carriers of particular antineoplastic agents that reduce the side effects of chemotherapy. Inflammation and tumor microenvironment play an essential role in promoting chemo-resistance. There is now considerable evidence, both in humans as well as in laboratory animals, that the commensal microbiota has important effects on carcinogenesis, tumor growth, and therapy response.

Social Isolation and Breast Cancer

Although the role of life stressors in breast cancer remains unclear, social isolation is consistently associated with increased breast cancer risk and mortality. Social isolation can be defined as loneliness or an absence of perceived social connections. In female mice and rats, social isolation is mimicked by housing animals 1 per cage. Social isolation causes many biological changes, of which an increase in inflammatory markers and disruptions in mitochondrial and cellular metabolism are commonly reported. It is not clear how the 2 traditional stress-induced pathways, namely, the hypothalamic-pituitary-adrenocortical axis (HPA), resulting in a release of glucocorticoids from the adrenal cortex, and autonomic nervous system (ANS), resulting in a release of catecholamines from the adrenal medulla and postganglionic neurons, could explain the increased breast cancer risk in socially isolated individuals. For instance, glucocorticoid receptor activation in estrogen receptor positive breast cancer cells inhibits their proliferation, and activation of β-adrenergic receptor in immature immune cells promotes their differentiation toward antitumorigenic T cells. However, activation of HPA and ANS pathways may cause a disruption in the brain-gut-microbiome axis, resulting in gut dysbiosis. Gut dysbiosis, in turn, leads to an alteration in the production of bacterial metabolites, such as short chain fatty acids, causing a systemic low-grade inflammation and inducing dysfunction in mitochondrial and cellular metabolism. A possible causal link between social isolation-induced increased breast cancer risk and mortality and gut dysbiosis should be investigated, as it offers new tools to prevent breast cancer.

Immunity orchestrates a bridge in gut-brain axis of neurodegenerative diseases

Neurodegenerative diseases, in particular for Alzheimer's disease (AD), Parkinson's disease (PD) and Multiple sclerosis (MS), are a category of diseases with progressive loss of neuronal structure or function (encompassing neuronal death) leading to neuronal dysfunction, whereas the underlying pathogenesis remains to be clarified. As the microbiological ecosystem of the intestinal microbiome serves as the second genome of the human body, it is strongly implicated as an essential element in the initiation and/or progression of neurodegenerative diseases. Nevertheless, the precise underlying principles of how the intestinal microflora impact on neurodegenerative diseases via gut-brain axis by modulating the immune function are still poorly characterized. Consequently, an overview of initiating the development of neurodegenerative diseases and the contribution of intestinal microflora on immune function is discussed in this review.

The Debate between the Human Microbiota and Immune System in Treating Aerodigestive and Digestive Tract Cancers: A Review

The human microbiota comprises a group of microorganisms co-existing in the human body. Unbalanced microbiota homeostasis may impact metabolic and immune system regulation, shrinking the edge between health and disease. Recently, the microbiota has been considered a prominent extrinsic/intrinsic element of cancer development and a promising milestone in the modulation of conventional cancer treatments. Particularly, the oral cavity represents a yin-and-yang target site for microorganisms that can promote human health or contribute to oral cancer development, such as Fusobacterium nucleatum. Moreover, Helicobacter pylori has also been implicated in esophageal and stomach cancers, and decreased butyrate-producing bacteria, such as Lachnospiraceae spp. and Ruminococcaceae, have demonstrated a protective role in the development of colorectal cancer. Interestingly, prebiotics, e.g., polyphenols, probiotics (Faecalibacterium, Bifidobacterium, Lactobacillus, and Burkholderia), postbiotics (inosine, butyrate, and propionate), and innovative nanomedicines can modulate antitumor immunity, circumventing resistance to conventional treatments and could complement existing therapies. Therefore, this manuscript delivers a holistic perspective on the interaction between human microbiota and cancer development and treatment, particularly in aerodigestive and digestive cancers, focusing on applying prebiotics, probiotics, and nanomedicines to overcome some challenges in treating cancer.

Immunological consequences of microbiome-based therapeutics

The complex network of microscopic organisms living on and within humans, collectively referred to as the microbiome, produce wide array of biologically active molecules that shape our health. Disruption of the microbiome is associated with susceptibility to a range of diseases such as cancer, diabetes, allergy, obesity, and infection. A new series of next-generation microbiome-based therapies are being developed to treat these diseases by transplanting bacteria or bacterial-derived byproducts into a diseased individual to reset the recipient's microbiome and restore health. Microbiome transplantation therapy is still in its early stages of being a routine treatment option and, with a few notable exceptions, has had limited success in clinical trials. In this review, we highlight the successes and challenges of implementing these therapies to treat disease with a focus on interactions between the immune system and microbiome-based therapeutics. The immune activation status of the microbiome transplant recipient prior to transplantation has an important role in supporting bacterial engraftment. Following engraftment, microbiome transplant derived signals can modulate immune function to ameliorate disease. As novel microbiome-based therapeutics are developed, consideration of how the transplants will interact with the immune system will be a key factor in determining whether the microbiome-based transplant elicits its intended therapeutic effect.

Maternal obesity and resistance to breast cancer treatments among offspring: Link to gut dysbiosis

BACKGROUND

About 50 000 new cases of cancer in the United States are attributed to obesity. The adverse effects of obesity on breast cancer may be most profound when affecting the early development; that is, in the womb of a pregnant obese mother. Maternal obesity has several long-lasting adverse health effects on the offspring, including increasing offspring's breast cancer risk and mortality. Gut microbiota is a player in obesity as well as may impact breast carcinogenesis. Gut microbiota is established early in life and the microbial composition of an infant's gut becomes permanently dysregulated because of maternal obesity. Metabolites from the microbiota, especially short chain fatty acids (SCFAs), play a critical role in mediating the effect of gut bacteria on multiple biological functions, such as immune system, including tumor immune responses.

RECENT FINDINGS

Maternal obesity can pre-program daughter's breast cancer to be more aggressive, less responsive to treatments and consequently more likely to cause breast cancer related death. Maternal obesity may also induce poor response to immune checkpoint inhibitor (ICB) therapy through increased abundance of inflammation associated microbiome and decreased abundance of bacteria that are linked to production of SCFAs. Dietary interventions that increase the abundance of bacteria producing SCFAs potentially reverses offspring's resistance to breast cancer therapy.

CONCLUSION

Since immunotherapies have emerged as highly effective treatments for many cancers, albeit there is an urgent need to enlarge the patient population who will be responsive to these treatments. One of the factors which may cause ICB refractoriness could be maternal obesity, based on its effects on the microbiota markers of ICB therapy response among the offspring. Since about 40% of children are born to obese mothers in the Western societies, it is important to determine if maternal obesity impairs offspring's response to cancer immunotherapies.

The impact of the microbiome in cancer: Targeting metabolism of cancer cells and host

Abnormal metabolic alterations of cancer cells and the host play critical roles in the occurrence and development of tumors. Targeting cancer cells and host metabolism can provide novel diagnosis indicators and intervention targets for tumors. In recent years, it has been found that gut microbiota is involved in the metabolism of the host and cancer cells. Increasingly, gut microbiome and their metabolites have been demonstrated great influence on the tumor formation, prognosis and treatment. Specific gut microbial composition and metabolites are associated with the status of tumor in the host. Interventions on the gut microbiota can exert the protective effects on the tumor, through the manipulation of structure and its related metabolites. This may be the new approach to improve the efficacy of tumor prevention and treatment. Here, we discuss the effects and the underlying mechanisms of gut microbiota and microbial-derived metabolites in tumor progression and treatment.

Diet-microbiome interactions in cancer treatment: Opportunities and challenges for precision nutrition in cancer

Dietary patterns contribute to cancer risk. Separately, microbial factors influence the development of several cancers. However, the interaction of diet and the microbiome and their joint contribution to cancer treatment response needs more research. The microbiome significantly impacts drug metabolism, immune activation, and response to immunotherapy. One of the critical factors affecting the microbiome structure and function is diet. Data demonstrate that the diet and microbiome composition affects the immune response. Moreover, malnutrition is a significant confounder to cancer therapy response. There is little understanding of the interaction of malnutrition with the microbiome in the context of cancer. This review aims to address the current knowledge of dietary intake patterns and malnutrition among cancer patients and the impact on treatment outcomes. Second, this review will provide evidence linking the microbiome to cancer treatment response and provide evidence of the potentially strong effect that diet could have on this interaction. This review will formulate critical questions that will need further research to understand the diet-microbiome relationship in cancer treatment response and directions for future research to guide us to precision nutrition therapy to improve cancer outcomes.

Gut Microbiome in Anesthesiology and Pain Medicine

The gut microbiome plays critical roles in human health and disease. Recent studies suggest it may also be associated with chronic pain and postoperative pain outcomes. In animal models, the composition of the gut microbiome changes after general anesthesia and affects the host response to medications, including anesthetics and opioids. In humans, the gut microbiome is associated with the development of postoperative pain and neurocognitive disorders. Additionally, the composition of the gut microbiome has been associated with pain conditions including visceral pain, nociplastic pain, complex regional pain syndrome, and headaches, partly through altered concentration of circulating bacterial-derived metabolites. Furthermore, animal studies demonstrate the critical role of the gut microbiome in neuropathic pain via immunomodulatory mechanisms. This article reviews basic concepts of the human gut microbiome and its interactions with the host and provide a comprehensive overview of the evidence linking the gut microbiome to anesthesiology, critical care, and pain medicine.

Gut Microbiome Alterations Affect Glioma Development and Foxp3 Expression in Tumor Microenvironment in Mice

Glioma is the most common malignant tumor of the central nervous system (CNS), with high degree of malignancy and poor prognosis. The gut microbiome (GM) is composed of microorganisms with different properties and functions, which play an important role in human physiology and biological activities. It has been proved that GM can affect the development of glioma through natural immunity, but whether GM can affect glioma through adaptive immunity and whether there are some microorganisms in the GM that may affect glioma growth still remain unclear. In our study, we evaluated the relationship between GM and glioma. We proved that (I) glioma growth can induce structural changes of mouse GM, including the decreased abundance of Bacteroidia and increased abundance of Firmicutes. (II) GM dysbiosis can downregulate Foxp3 expression in the brain and promote glioma growth. A balanced environment of GM can upregulate the expression of Foxp3 in the brain and delay the development of glioma. (III) The increased abundance of Bacteroidia is associated with accelerated glioma progression, while its decreased abundance is associated with delayed glioma progression, which may be one of the key microorganisms affecting glioma growth. This study is helpful to reveal the relationship between GM and glioma development and provide new ideas for adjuvant therapy of glioma.

Bugs as Drugs: Understanding the Linkage between Gut Microbiota and Cancer Treatment Microbiome in Cancer Therapy

BACKGROUND

The commensal microbiota is known to regulate host physiology. Dysbiosis or compromised Resilience in the microbial ecology is related to the impending risk of cancer. A potential link between cancer and microbiota is indicated by a lot of evidence.

OBJECTIVE

The current review explores in detail the various links leading to and /or facilitating oncogenesis, providing sound reasoning or a basis for its utilization as potential therapeutic targets. The present review emphasizes the existing knowledge of the microbiome in cancer and further elaborates on the factors like genetic modifications, effects of dietary components, and environmental agents that are considered to assess the direct and indirect effect of microbes in the process of oncogenesis and on the host's health. Strategies modulating the microbiome and novel biotherapeutics are also discussed. Pharmacomicrobiomics is one such niche accounting for the interplay between the microbiome, xenobiotic, and host responses is also looked upon.

METHODS

The literature search strategy for this review was conducted by following the methodology of the Preferred Reporting Items for Systematic reviews and Meta-Analyses (PRISMA). The method includes the collection of data from different search engines like PubMed, ScienceDirect, SciFinder etc. to get coverage of relevant literature for accumulating appropriate information regarding microbiome, cancer, and their linkages.

RESULTS

These considerations are made to expand the existing literature on the role of gut microbiota on the host's health, the interaction between host and microbiota, and the reciprocal relationship between the microbiome and modified neoplastic cells.

CONCLUSION

Potential therapeutic implications of cancer microbiomes that are yet unexplored and have rich therapeutic dividends improving human health are discussed in detail in this review.

Microbiomics in Collusion with the Nervous System in Carcinogenesis: Diagnosis, Pathogenesis and Treatment

The influence of the naturally occurring population of microbes on various human diseases has been a topic of much recent interest. Not surprisingly, continuously growing attention is devoted to the existence of a gut brain axis, where the microbiota present in the gut can affect the nervous system through the release of metabolites, stimulation of the immune system, changing the permeability of the blood–brain barrier or activating the vagus nerves. Many of the methods that stimulate the nervous system can also lead to the development of cancer by manipulating pathways associated with the hallmarks of cancer. Moreover, neurogenesis or the creation of new nervous tissue, is associated with the development and progression of cancer in a similar manner as the blood and lymphatic systems. Finally, microbes can secrete neurotransmitters, which can stimulate cancer growth and development. In this review we discuss the latest evidence that support the importance of microbiota and peripheral nerves in cancer development and dissemination.

The intratumoural microbiota in cancer: new insights from inside

The human body harbors a vast array of microbiota that modulates host pathophysiological processes and modifies the risk of diseases including cancer. With the advent of metagenomic sequencing studies, the intratumoural microbiota has been found as a component of the tumor microenvironment, imperceptibly affecting the tumor progression and response to current antitumor treatments. The underlying carcinogenic mechanisms of intratumoural microbiota, mainly including inducing DNA damages, activating oncogenic signaling pathways and suppressing the immune response, differ significantly in varied organs and are not fully understood. Some native or genetically engineered microbial species can specifically accumulate and replicate within tumors to initiate antitumor immunity, which will be conducive to pursue precise cancer therapies. In this review, we summarized the community characteristics and therapeutic potential of intratumoural microbiota across diverse tumor types. It may provide new insights for a better understanding of tumor biology and hint at the significance of manipulating intratumoural microbiota.

Increase in Akkermansiaceae in Gut Microbiota of Prostate Cancer-Bearing Mice

Gut microbiota are reported to be associated with many diseases, including cancers. Several bacterial taxa have been shown to be associated with cancer development or response to treatment. However, longitudinal microbiota alterations during the development of cancers are relatively unexplored. To better understand how microbiota changes, we profiled the gut microbiota composition from prostate cancer-bearing mice and control mice at five different time points. Distinct gut microbiota differences were found between cancer-bearing mice and control mice. Akkermansiaceae was found to be significantly higher in the first three weeks in cancer-bearing mice, which implies its role in the early stage of cancer colonization. We also found that Bifidobacteriaceae and Enterococcaceae were more abundant in the second and last sampling week, respectively. The increments of Akkermansiaceae, Bifidobacteriaceae and Enterococcaceae were previously found to be associated with responses to immunotherapy, which suggests links between these bacteria families and cancers. Additionally, our function analysis showed that the bacterial taxa carrying steroid biosynthesis and butirosin and neomycin biosynthesis were increased, whereas those carrying naphthalene degradation decreased in cancer-bearing mice. Our work identified the bacteria taxa altered during prostate cancer progression and provided a resource of longitudinal microbiota profiles during cancer development in a mouse model.

S-Nitrosylation in Tumor Microenvironment

S-nitrosylation is a selective and reversible post-translational modification of protein thiols by nitric oxide (NO), which is a bioactive signaling molecule, to exert a variety of effects. These effects include the modulation of protein conformation, activity, stability, and protein-protein interactions. S-nitrosylation plays a central role in propagating NO signals within a cell, tissue, and tissue microenvironment, as the nitrosyl moiety can rapidly be transferred from one protein to another upon contact. This modification has also been reported to confer either tumor-suppressing or tumor-promoting effects and is portrayed as a process involved in every stage of cancer progression. In particular, S-nitrosylation has recently been found as an essential regulator of the tumor microenvironment (TME), the environment around a tumor governing the disease pathogenesis. This review aims to outline the effects of S-nitrosylation on different resident cells in the TME and the diverse outcomes in a context-dependent manner. Furthermore, we will discuss the therapeutic potentials of modulating S-nitrosylation levels in tumors.

Intestinal microbiota: A potential target for enhancing the antitumor efficacy and reducing the toxicity of immune checkpoint inhibitors

Accumulating evidence suggests that the intestinal microbiota is associated with the antitumor efficacy of immune checkpoint inhibitors (ICIs) and the occurrence of immune-related adverse events (irAEs) following ICI treatment. However, the mechanisms underlying these interactions remain unclear. Recent technological advances have allowed more extensive investigation into the interplay between the intestinal microbiota and the tumor immune microenvironment. Breakthroughs by two research groups revealed that Bifidobacterium enhanced the efficacy of ICIs via the stimulator of interferon genes (STING) and adenosine 2A receptor (A_2AR) signaling pathways, highlighting the molecular mechanisms through which the intestinal microbiota modulates immunotherapy. In this review, we summarize recent findings related to the potential role and mechanisms of the gut microbiota in ICI therapy, available microbiota-targeting strategies, and ongoing clinical trials. Further we discuss the associated challenges that remain in this field of research. The current review aims to evaluate the potential of the intestinal microbiota in maximizing the antitumor efficacy of ICIs while minimizing their toxic effects and guiding the development of more specific treatment regimens.

The role of the microbiome in ovarian cancer: mechanistic insights into oncobiosis and to bacterial metabolite signaling

Ovarian cancer is characterized by dysbiosis, referred to as oncobiosis in neoplastic diseases. In ovarian cancer, oncobiosis was identified in numerous compartments, including the tumor tissue itself, the upper and lower female genital tract, serum, peritoneum, and the intestines. Colonization was linked to Gram-negative bacteria with high inflammatory potential. Local inflammation probably participates in the initiation and continuation of carcinogenesis. Furthermore, local bacterial colonies in the peritoneum may facilitate metastasis formation in ovarian cancer. Vaginal infections (e.g. Neisseria gonorrhoeae or Chlamydia trachomatis) increase the risk of developing ovarian cancer. Bacterial metabolites, produced by the healthy eubiome or the oncobiome, may exert autocrine, paracrine, and hormone-like effects, as was evidenced in breast cancer or pancreas adenocarcinoma. We discuss the possible involvement of lipopolysaccharides, lysophosphatides and tryptophan metabolites, as well as, short-chain fatty acids, secondary bile acids and polyamines in the carcinogenesis of ovarian cancer. We discuss the applicability of nutrients, antibiotics, and probiotics to harness the microbiome and support ovarian cancer therapy. The oncobiome and the most likely bacterial metabolites play vital roles in mediating the effectiveness of chemotherapy. Finally, we discuss the potential of oncobiotic changes as biomarkers for the diagnosis of ovarian cancer and microbial metabolites as possible adjuvant agents in therapy.

Host immunity modulates the efficacy of microbiota transplantation for treatment of Clostridioides difficile infection

Fecal microbiota transplantation (FMT) is a successful therapeutic strategy for treating recurrent Clostridioides difficile infection. Despite remarkable efficacy, implementation of FMT therapy is limited and the mechanism of action remains poorly understood. Here, we demonstrate a critical role for the immune system in supporting FMT using a murine C. difficile infection system. Following FMT, Rag1 heterozygote mice resolve C. difficile while littermate Rag1^-/- mice fail to clear the infection. Targeted ablation of adaptive immune cell subsets reveal a necessary role for CD4⁺ Foxp3⁺ T-regulatory cells, but not B cells or CD8⁺ T cells, in FMT-mediated resolution of C. difficile infection. FMT non-responsive mice exhibit exacerbated inflammation, impaired engraftment of the FMT bacterial community and failed restoration of commensal bacteria-derived secondary bile acid metabolites in the large intestine. These data demonstrate that the host's inflammatory immune status can limit the efficacy of microbiota-based therapeutics to treat C. difficile infection.

Gut microbiota of animals living in polluted environments are a potential resource of anticancer molecules

Cancer is a prominent cause of morbidity and mortality worldwide, in spite of advances in therapeutic interventions and supportive care. In 2018 alone, there were 18·1 million new cancer cases and 9·6 million deaths indicating the need for novel anticancer agents. Plant-based products have often been linked with protective effects against communicable and non-communicable diseases. Recently, we have shown that animals such as crocodiles thrive in polluted environments and are often exposed to carcinogenic agents, but still benefit from prolonged lifespan. The protective mechanisms shielding them from cancer could be attributed to the immune system, and/or it is possible that their gut microbiota produce anticancer molecules. In support, several lines of evidence suggest that gut microbiota plays a critical role in the physiology of its host. Here, we reviewed the available literature to assess whether the gut microbiota of animals thriving in polluted environment possess anticancer molecules.

The microbiota-microglia axis in central nervous system disorders

The innate immune system in the central nervous system (CNS) is mainly represented by specialized tissue-resident macrophages, called microglia. In the past years, various species-, host- and tissue-specific as well as environmental factors were recognized that essentially affect microglial properties and functions in the healthy and diseased brain. Host microbiota are mostly residing in the gut and contribute to microglial activation states, for example, via short-chain fatty acids (SCFAs) or aryl hydrocarbon receptor (AhR) ligands. Thereby, the gut microorganisms are deemed to influence numerous CNS diseases mediated by microglia. In this review, we summarize recent findings of the interaction between the host microbiota and the CNS in health and disease, where we specifically highlight the resident gut microbiota as a crucial environmental factor for microglial function as what we coin "the microbiota-microglia axis."

Association between the gut microbiota and patient responses to cancer immune checkpoint inhibitors

Studies are increasingly investigating the association between the gut microbiota and the outcomes of immunotherapy in patients with cancer. Notably, certain studies have demonstrated that the gut microbiota serves a key role in regulating a patient's response to immunotherapy. In the present review, the potential associations between the gut microbiota, and cancer, host immunity and cancer immunotherapy are reviewed. Furthermore, the effects of fecal microbiota transplantation, antibiotics, probiotics, prebiotics, synbiotics, components of traditional Chinese medicine and various lifestyle factors on the gut microbiota and cancer immunotherapy outcomes are discussed. Certain dominant bacterial groups in the context of cancer immunotherapy and certain effective methods for optimizing immunotherapy by regulating the gut microbiota have been identified. Further investigation may enable the rapid conversion of these discoveries into practical products and clinically applicable methods.

Microbiota and Cancer: The Emerging Beneficial Role of Bifidobacteria in Cancer Immunotherapy

Many intestinal bacteria are believed to be involved in various inflammatory and immune processes that influence tumor etiology because of their metabolic properties and their ability to alter the microbiota homeostasis. Although many functions of the microbiota are still unclear, there is compelling experimental evidence showing that the intestinal microbiota is able to modulate carcinogenesis and the response to anticancer therapies, both in the intestinal tract and other body sites. Among the wide variety of gut-colonizing microorganisms, various species belonging to the Bifidobacterium genus are believed to elicit beneficial effects on human physiology and on the host-immune system. Recent findings, based on preclinical mouse models and on human clinical trials, have demonstrated the impact of gut commensals including bifidobacteria on the efficacy of tumor-targeting immunotherapy. Although the underlying molecular mechanisms remain obscure, bifidobacteria and other microorganisms have become a promising aid to immunotherapeutic procedures that are currently applied to treat cancer. The present review focuses on strategies to recruit the microbiome in order to enhance anticancer responses and develop therapies aimed at fighting the onset and progression of malignancies.

The pint- sized powerhouse: Illuminating the mighty role of the gut microbiome in improving the outcome of anti- cancer therapy

Cancer persists as a major health catastrophe and a leading cause of widespread mortality across every nation. Research of several decades has increased our understanding of the pivotal pathways and key players of the host during tumor development and progression, which has enabled generation of precision therapeutics with improved efficacy. Despite such tremendous advancements in our combat against this fatal disease, a majority of the cancer patients suffer from poor tumor- free survival owing to the increased incidence of recurrent tumor. This is primarily due to the development of resistance against contemporary anti- cancer strategies. Recent studies have pointed towards the involvement of the human symbiotic gut microbiota in regulating the outcome of chemotherapy and immunotherapy. It does so primarily by modulating the metabolism of the drugs and host immune response, thereby enhancing the efficacy and ameliorating the toxicity. The interactions between the therapeutic agents, microbial community and host immunity may provide a new avenue for the clinical management of cancer. In addition, consumption of dietary pro-, pre- and synbiotics has been recognized to confer protection against tumor genesis and also promote improved response to traditional tumor suppressive strategies. Naturally, the use of various combinatorial regimes containing dietary supplements that improve the gut microbiome in amalgamation with conventional cancer treatment methods may significantly augment the therapeutic outcome of cancer patients and circumnavigate the resistance mechanisms that confound traditional therapies. In this review, we have summarized the role of the gut microbiome, which is the largest assembly of commensals within the human body, in regulating the efficacy and toxicity of various existing anti- cancer therapies including chemotherapy, immunotherapy and surgery. Furthermore, we have discussed how novel strategies integrating the application of probiotics, prebiotics, synbiotics and antibiotics in combination with the aforementioned anti- cancer modules manipulate the gut microbiota and, therefore, augment their therapeutic outcome. Together, such innovative anti- tumorigenic approaches may prove highly effective in improving the prognosis of cancer patients.

The promise and challenge of cancer microbiome research

Many microbial agents have been implicated as contributors to cancer genesis and development, and the search to identify and characterize new cancer-related organisms is ongoing. Modern developments in methodologies, especially culture-independent approaches, have accelerated and driven this research. Recent work has shed light on the multifaceted role that the community of organisms in and on the human body plays in cancer onset, development, detection, treatment, and outcome. Much remains to be discovered, however, as methodological variation and functional testing of statistical correlations need to be addressed for the field to advance.

Deficient Resident Memory T Cell and CD8 T Cell Response to Commensals in Inflammatory Bowel Disease

BACKGROUND AND AIMS

The intestinal microbiota is closely associated with resident memory lymphocytes in mucosal tissue. We sought to understand how acquired cellular and humoral immunity to the microbiota differ in health versus inflammatory bowel disease [IBD].

METHODS

Resident memory T cells [Trm] in colonic biopsies and local antibody responses to intraepithelial microbes were analysed. Systemic antigen-specific immune T and B cell memory to a panel of commensal microbes was assessed.

RESULTS

Systemically, healthy blood showed CD4 and occasional CD8 memory T cell responses to selected intestinal bacteria, but few memory B cell responses. In IBD, CD8 memory T cell responses decreased although B cell responses and circulating plasmablasts increased. Possibly secondary to loss of systemic CD8 T cell responses in IBD, dramatically reduced numbers of mucosal CD8+ Trm and γδ T cells were observed. IgA responses to intraepithelial bacteria were increased. Colonic Trm expressed CD39 and CD73 ectonucleotidases, characteristic of regulatory T cells. Cytokines/factors required for Trm differentiation were identified, and in vitro-generated Trm expressed regulatory T cell function via CD39. Cognate interaction between T cells and dendritic cells induced T-bet expression in dendritic cells, a key mechanism in regulating cell-mediated mucosal responses.

CONCLUSIONS

A previously unrecognised imbalance exists between cellular and humoral immunity to the microbiota in IBD, with loss of mucosal T cell-mediated barrier immunity and uncontrolled antibody responses. Regulatory function of Trm may explain their association with intestinal health. Promoting Trm and their interaction with dendritic cells, rather than immunosuppression, may reinforce tissue immunity, improve barrier function, and prevent B cell dysfunction in microbiota-associated disease and IBD aetiology.

Novel Forms of Immunomodulation for Cancer Therapy

In recent years immunotherapy has provided new hope for cancer patients. However, some patients eventually relapse. Immunological responses are thought to underlie the long-term effects of conventional or targeted therapies. Whether this influence emerges from direct effects on cancer cells through immunogenic cell death (ICD) or by modulating the immune environment requires further clarification. ICD-related molecular mechanisms are also shared by cell-intrinsic defense responses that combat foreign intrusions. Indeed, we could potentially mimic and harness these processes to improve cancer immunogenicity. In addition, the microbiome is materializing as a missing factor in the cancer-immune therapy axis. The emerging idea of manipulating the gut microbiota to improve responses to anticancer therapy is becoming increasingly popular, but further clinical authentication is needed.

Recycling the Interspecific Relations with Epithelial Cells: Bacteria and Cancer Metabolic Symbiosis

Several aspects of the human physiology are controlled by the microbiota that plays a key role in health and disease. In fact, microbial dysbiosis is associated with numerous diseases, including several types of cancer such as colon, gastric, esophageal, pancreatic, laryngeal, breast and gallbladder carcinomas.Metabolic symbiosis between non-malignant cells and the resident microbita is crucial for the host homeostasis. However, cancer cells are able to repurpose the pre-existing metabolic symbiosis, being able to recycle those relations and also create novel metabolic symbiosis, leading to profound alterations on the local microenvironment.In here we will explore some of these symbiotic metabolic interactions between bacteria and non-malignant cells in two different contexts: colon and uterine cervix. The way malignant cells are able to recycle these normal interactions and also create novel types of symbiotic metabolic relations will also be discussed.The knowledge of these complex interactions and recycling mechanisms is of extreme importance for cancer treatment, as new therapeutic targets could be developed.

A Phase Ib Study of Preoperative, Locoregional IRX-2 Cytokine Immunotherapy to Prime Immune Responses in Patients with Early-Stage Breast Cancer

PURPOSE

To evaluate the safety and feasibility of preoperative locoregional cytokine therapy (IRX-2 regimen) in early-stage breast cancer, and to evaluate for intratumoral and peripheral immunomodulatory activity.

PATIENTS AND METHODS

Sixteen patients with stage I-III early-stage breast cancer (any histology type) indicated for surgical lumpectomy or mastectomy were enrolled to receive preoperative locoregional immunotherapy with the IRX-2 cytokine biological (2 mL subcutaneous × 10 days to periareolar skin). The regimen also included single-dose cyclophosphamide (300 mg/m²) on day 1 to deplete T-regulatory cells and oral indomethacin to modulate suppressive myeloid subpopulations. The primary objective was to evaluate feasibility (i.e., receipt of therapy without surgical delays or grade 3/4 treatment-related adverse events). The secondary objective was to evaluate changes in stromal tumor-infiltrating lymphocyte score. The exploratory objective was to identify candidate pharmacodynamic changes for future study using a variety of assays, including flow cytometry, RNA and T-cell receptor DNA sequencing, and multispectral immunofluorescence.

RESULTS

Preoperative locoregional cytokine administration was feasible in 100% (n = 16/16) of subjects and associated with increases in stromal tumor-infiltrating lymphocytes (P < 0.001). Programmed death ligand 1 (CD274) was upregulated at the RNA (P < 0.01) and protein level [by Ventana PD-L1 (SP142) and immunofluorescence]. Other immunomodulatory effects included upregulation of RNA signatures of T-cell activation and recruitment and cyclophosphamide-related peripheral T-regulatory cell depletion.

CONCLUSIONS

IRX-2 is safe in early-stage breast cancer. Potentially favorable immunomodulatory changes were observed, supporting further study of IRX-2 in early-stage breast cancer and other malignancies.

Intestinal Microbiota: A Novel Target to Improve Anti-Tumor Treatment?

Recently, preclinical and clinical studies targeting several types of cancer strongly supported the key role of the gut microbiota in the modulation of host response to anti-tumoral therapies such as chemotherapy, immunotherapy, radiotherapy and even surgery. Intestinal microbiome has been shown to participate in the resistance to a wide range of anticancer treatments by direct interaction with the treatment or by indirectly stimulating host response through immunomodulation. Interestingly, these effects were described on colorectal cancer but also in other types of malignancies. In addition to their role in therapy efficacy, gut microbiota could also impact side effects induced by anticancer treatments. In the first part of this review, we summarized the role of the gut microbiome on the efficacy and side effects of various anticancer treatments and underlying mechanisms. In the second part, we described the new microbiota-targeting strategies, such as probiotics and prebiotics, antibiotics, fecal microbiota transplantation and physical activity, which could be effective adjuvant therapies developed in order to improve anticancer therapeutic efficiency.

The cancer microbiome

Collectively known as the microbiota, the commensal bacteria and other microorganisms that colonize the epithelial surfaces of our body have been shown to produce small molecules and metabolites that have both local and systemic effects on cancer onset, progression and therapy response. To date, most studies focusing on the microbiome have used traditional preclinical mouse models and identified correlative relationships between microbial species and cancer phenotypes. Now, the profound influence of the microbiota on the efficacy of cancer treatments, such as immunotherapies, has begun to be extensively characterized in humans. Paramount to the development of microbiota-based therapeutics, the next challenge in microbiome research will be to identify individual microbial species that causally affect cancer phenotypes and unravel the underlying mechanisms. In this Viewpoint article, we asked four scientists working on the cancer microbiome for their opinions on the current state of the field, where the research is heading and how we can advance our understanding to rationally design microbial-based therapeutics to transform treatment strategies for patients with cancer.

Microbiome-Microbial Metabolome-Cancer Cell Interactions in Breast Cancer-Familiar, but Unexplored

Breast cancer is a leading cause of death among women worldwide. Dysbiosis, an aberrant composition of the microbiome, characterizes breast cancer. In this review we discuss the changes to the metabolism of breast cancer cells, as well as the composition of the breast and gut microbiome in breast cancer. The role of the breast microbiome in breast cancer is unresolved, nevertheless it seems that the gut microbiome does have a role in the pathology of the disease. The gut microbiome secretes bioactive metabolites (reactivated estrogens, short chain fatty acids, amino acid metabolites, or secondary bile acids) that modulate breast cancer. We highlight the bacterial species or taxonomical units that generate these metabolites, we show their mode of action, and discuss how the metabolites affect mitochondrial metabolism and other molecular events in breast cancer. These metabolites resemble human hormones, as they are produced in a "gland" (in this case, the microbiome) and they are subsequently transferred to distant sites of action through the circulation. These metabolites appear to be important constituents of the tumor microenvironment. Finally, we discuss how bacterial dysbiosis interferes with breast cancer treatment through interfering with chemotherapeutic drug metabolism and availability.

Microbiome diurnal rhythmicity and its impact on host physiology and disease risk

Host-microbiome interactions constitute key determinants of host physiology, while their dysregulation is implicated in a wide range of human diseases. The microbiome undergoes diurnal variation in composition and function, and this in turn drives oscillations in host gene expression and functions. In this review, we discuss the newest developments in understanding circadian host-microbiome interplays, and how they may be relevant in health and disease contexts. We summarize the molecular mechanisms by which the microbiome influences host function in a diurnal manner, and inversely describe how the host orchestrates circadian rhythmicity of the microbiome. Furthermore, we highlight the future perspectives and challenges in studying this new and exciting facet of host-microbiome interactions. Finally, we illustrate how the elucidation of the microbiome chronobiology may pave the way for novel therapeutic approaches.

Impact of microbiota on central nervous system and neurological diseases: the gut-brain axis

Development of central nervous system (CNS) is regulated by both intrinsic and peripheral signals. Previous studies have suggested that environmental factors affect neurological activities under both physiological and pathological conditions. Although there is anatomical separation, emerging evidence has indicated the existence of bidirectional interaction between gut microbiota, i.e., (diverse microorganisms colonizing human intestine), and brain. The cross-talk between gut microbiota and brain may have crucial impact during basic neurogenerative processes, in neurodegenerative disorders and tumors of CNS. In this review, we discuss the biological interplay between gut-brain axis, and further explore how this communication may be dysregulated in neurological diseases. Further, we highlight new insights in modification of gut microbiota composition, which may emerge as a promising therapeutic approach to treat CNS disorders.

Recurrent bacterial translocation from gut and sepsis in Head and neck cancer patients and its prevention by probiotics

Head and neck cancers are the 6th most common cancer type in human malignant tumors and treated with chemoradiotherapy and surgery. Chemotherapy during these treatment modalities leads to damage of intestinal epithelial barriers and results in translocation of intestinal bacteria in bloodstream through invasion in these damaged regions. In this report, we report two cases of hypopharyngeal cancer patients, both of whom received chemotherapy before surgery. The patients demonstrated repeated sepsis before and after surgery, supporting translocation of intestinal bacteria. Proper continuous probiotic use prevented proliferation and intestinal bacterial translocation. Hypothesis of bacterial translocation and prevention by probiotics are discussed.

Genomics and emerging biomarkers for immunotherapy of colorectal cancer

Colorectal cancer (CRC) is a common and lethal disease with a high therapeutic need. For most patients with metastatic CRC, chemotherapy is the only viable option. Currently, immunotherapy is restricted to the particular genetic subgroup of mismatch-repair deficient (MMRd)/microsatellite instable (MSI) CRC. Anti-PD1 therapy was recently FDA-approved as a second-line treatment in this subgroup. However, in a metastatic setting, these MMRd/MSI tumors are vastly outnumbered by mismatch-repair proficient (MMRp)/microsatellite stable (MSS) tumors. These MMRp/MSS tumors do not meaningfully respond to any traditional immunotherapy approach including checkpoint blockade, adoptive cell transfer and vaccination. This resistance to immunotherapy is due to a complex tumor microenvironment that counteracts antitumor immunity through a combination of poorly antigenic tumor cells and an immunosuppressive tumor microenvironment. To find ways of overcoming immunotherapy resistance in the majority of CRC patients, it is necessary to analyze the immunological makeup in an in-depth and personalized way and in the context of their tumor genetic makeup. Flexible, biomarker-guided early-phase immunotherapy trials are needed to optimize this workflow. In this review, we detail key mechanisms for immune evasion and emerging immune biomarkers for personalized immunotherapy in CRC. Also, we present a template for biomarker-guided clinical trials that are needed to move new immunotherapy approaches closer to clinical application.

Intratumoral bacteria may elicit chemoresistance by metabolizing anticancer agents

We recently reported that bacteria can be found within pancreatic ductal adenocarcinoma (PDAC) tumors. Some of these bacteria can metabolize and thereby inactivate the nucleoside analog gemcitabine. We demonstrated that the long isoform of the bacterial enzyme cytidine deaminase (CDD) mediates the metabolism of gemcitabine. The clinical effect of overcoming this potential mechanism of drug resistance has yet to be studied.

Tumor Targeting by Fusobacterium nucleatum: A Pilot Study and Future Perspectives

Colorectal adenocarcinoma (CRC) is a common tumor with high mortality rates. Interestingly, CRC was found to be colonized by the oral anaerobic bacteria Fusobacterium nucleatum, which accelerates tumor progression and enables immune evasion. The CRC-specific colonization by fusobacteria is mediated through the recognition of tumor displayed Gal-GalNAc moieties by the fusobacterial Fap2 Gal-GalNAc lectin. Here, we show high Gal-GalNAc levels in additional adenocarcinomas including those found in the stomach, prostate, ovary, colon, uterus, pancreas, breast, lung, and esophagus. This observation coincides with recent reports that found fusobacterial DNA in some of these tumors. Given the tumorigenic role of fusobacteria and its immune evasion properties, we suggest that fusobacterial elimination might improve treatment outcome of the above tumors. Furthermore, as fusobacteria appears to specifically home-in to Gal-GalNAc—displaying tumors, it might be engineered as a platform for treating CRC and the above common, lethal, adenocarcinomas.