The impact of tumor and gut microbiotas on cancer therapy: Beneficial or detrimental?

Influence of Gut Microbiota-Mediated Immune Regulation on Response to Chemotherapy

The involvement of the gut microbiota in anti-cancer treatment has gained increasing attention. Alterations to the structure and function of the gut bacteria are important factors in the development of cancer as well as the efficacy of chemotherapy. Recent studies have confirmed that the gut microbiota and related metabolites influence the pharmacological activity of chemotherapeutic agents through interactions with the immune system. This review aims to summarize the current knowledge of how malignant tumor and chemotherapy affect the gut microbiota, how the gut microbiota regulates host immune response, and how interactions between the gut microbiota and host immune response influence the efficacy of chemotherapy. Recent advances in strategies for increasing the efficiency of chemotherapy based on the gut microbiota are also described. Deciphering the complex homeostasis maintained by the gut microbiota and host immunity provides a solid scientific basis for bacterial intervention in chemotherapy.

The role of the gut microbiome in gastrointestinal cancers

The gut microbiota present in the human digestive system is incredibly varied and is home to trillions of microorganisms. The gut microbiome is shaped at birth, while numerous genetic, dietary, and environmental variables primarily influence the microbiome composition. The importance of gut microbiota on host health is becoming more widely acknowledged. Digestion, intestinal permeability, and immunological and metabolism responses can all be affected by changes in the composition and function of the gut microbiota. There is mounting evidence that the microbial population's complex traits are important biomarkers and indicators of patient outcomes in cancer and its therapies. Numerous studies have demonstrated that changed commensal gut microorganisms contribute to the development and spread of cancer through various routes. Despite the ongoing controversy surrounding the gut microbiome and gastrointestinal cancer, accumulating evidence points to a potentially far more intricate connection than a simple cause-and-effect relationship. SIMPLE SUMMARY: Due to their high frequency and fatality rate, gastrointestinal cancers are regarded as a severe public health issue with complex medical and economic burdens. The gut microbiota may directly or indirectly interact with existing therapies like immunotherapy and chemotherapy, affecting how well a treatment works. The gut microbiome influences the immune response's activity, function, and development. Generally, certain gut bacteria impact the antitumor actions during cancer by creating particular metabolites or triggering T-cell responses. Yet, certain bacterial species have been found to promote cellular proliferation and metastasis in cancer, and comprehending these interactions in the context of cancer may help identify possible treatment targets. Notwithstanding the improvements in the field, additional research is still required to comprehend the underlying processes, examine the effects on existing therapies, and pinpoint certain bacteria and immune cells that can cause this interaction.

Gut microbiota and tumor-associated macrophages: potential in tumor diagnosis and treatment

Avoiding immune destruction and polymorphic microbiomes are two key hallmarks of cancer. The tumor microenvironment (TME) is essential for the development of solid tumors, and the function of tumor-associated macrophages (TAMs) in the TME is closely linked to tumor prognosis. Therefore, research on TAMs could improve the progression and control of certain tumor patients. Additionally, the intestinal flora plays a crucial role in metabolizing substances and maintaining a symbiotic relationship with the host through a complex network of interactions. Recent experimental and clinical studies have suggested a potential link between gut microbiome and TME, particularly in regulating TAMs. Understanding this association could improve the efficacy of tumor immunotherapy. This review highlights the regulatory role of intestinal flora on TAMs, with a focus on gut microbiota and their metabolites. The implications of this association for tumor diagnosis and treatment are also discussed, providing a promising avenue for future clinical treatment strategies.

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.

Gut microbiome and cancer implications: Potential opportunities for fermented foods

There is a critical opportunity to improve response to immunotherapies and overall cancer survivorship via dietary interventions targeted to modify the gut microbiome, and in turn, potentially enhance anti-cancer immunity. A promising dietary intervention is fermented foods, which may alter gut microbiome composition and, in turn, improve immunity. In this article, we summarize the state of the literature pertaining to the gut microbiome and response to immunotherapy and other cancer treatments, potential clinical implications of utilizing a fermented foods dietary approach to improve cancer treatment outcomes, and existing gaps in the literature regarding the implementation of fermented food interventions among individuals with cancer or with a history of cancer. This review synthesizes a compelling rationale across different disciplines to lay a roadmap for future fermented food dietary intervention research aimed at modulating the gut microbiome to reduce cancer burden.

Effect of antimicrobial therapy on progression-free survival of immunotherapy and chemo-/immunotherapy in patients with non-small cell lung cancer

BACKGROUND

The choice between immunotherapy with a checkpoint inhibitor (CPI) and chemo-/immunotherapy (CIT) in patients with NSCLC stage IV is often discussed. There are some data that the effect of CPI therapy is impaired by antimicrobial therapy (AMT). Little is known about the influence of AMT on CIT.

PATIENTS AND METHODS

We retrospectively analysed 114 patients (age 68 ± 8.5 years) with NSCLC stage IV. Patients were treated according to the guidelines with either CPI alone (pembrolizumab, nivolumab, atezolizumab, cemiplimab) or CIT (Carboplatin/Pemetrexed/Pembrolizumab, Carboplatin/Paclitaxel/Pembrolizumab). We registered patients' characteristics including presence and timing of AMT. Group 1 consisted of 42 patients with AMT in the month before CPI or CIT, group 2 were 49 patients with AMT during CPI or CIT, and group 3 were 64 patients without AMT and CPI or CIT.

RESULTS

Group 1-3 showed comparable patients characteristics. Using cox-regression analysis, we found that AMT in the month before CPI resulted in a decreased progression-free survival (PFS) compared to patients with CPI and no AMT (14 ± 1.02 vs. 4 ± 1.02 months, p = 0.002, 95% CI 1.88-9). In patients, who were treated with CIT, there was no difference in PFS in those with or without AMT in the month before therapy (10 ± 2.5 vs. 6 ± 1.2 months, p = 0.7). Interestingly, AMT during CIT or CPI therapy showed no effect on PFS.

CONCLUSIONS

In a real-life setting, we found that AMT reduces PFS when given in the month before CIT therapy. AMT before or during CIT does not seem to influence PFS. As a consequence, AMT before start of therapy might be a factor that could lead to a preference of CIT instead of CPI in NSCLC stage IV patients.

Inosine, gut microbiota, and cancer immunometabolism

This article briefly reviews cancer immunity and the role of gut microbiota in carcinogenesis, followed by an understanding of mechanisms by which inosine is involved in cancer immunometabolism. The immune system plays a paradoxical role in cancer treatment. Antitumor immunity depends on the T-cell priming against tumor antigens, whereas inflammatory mediators trigger the protumor signaling in the tumor microenvironment. Studies link the microbiome with metabolism and immunity-two main factors implicated in carcinogenesis. Gut microbiota has been shown to affect both antitumor immunity and protumor immune signaling. There is mounting evidence that the human microbiome can play a role in the immunotherapeutic effects, both response and resistance. Inosine-5'-monophosphate dehydrogenase (IMPDH) is a highly conservative enzyme widely expressed in mammals. Cell signaling pathways use molecular inosine, a crucial secondary metabolite in purine metabolism and a molecular messenger. Recent research has identified inosine as a critical regulator of immune checkpoint inhibition (ICI) therapeutic response in various tumor types. Some bacterial species were found to produce inosine or its metabolite hypoxanthine and induce T-helper 1 differentiation and effector functions via the inosine-A2AR-cAMP-PKA pathway upon ICI therapy. Also, inosine acts as a substitute carbon source for T-cell metabolism in glucose-restricted environments, i.e., the tumor microenvironment, assisting T-cell proliferation and differentiation while enhancing sensitivity to ICI, reinforcing the notion that inosine metabolism might contribute to antitumor immunity. Also, inosine is a potent agonist of the adenosine receptor, A2AR, and A2AR signaling can affect T-cell responses and antitumor immunity, making the inosine-A2AR pathway blockage a candidate for cancer treatment. Further research is required to investigate inosine as a cancer immunometabolism therapy.

New Insights into the Relationship between Gut Microbiota and Radiotherapy for Cancer

Cancer is the second most common cause of death among humans in the world, and the threat that it presents to human health is becoming more and more serious. The mechanisms of cancer development have not yet been fully elucidated, and new therapies are changing with each passing day. Evidence from the literature has validated the finding that the composition and modification of gut microbiota play an important role in the development of many different types of cancer. The results also demonstrate that there is a bidirectional interaction between the gut microbiota and radiotherapy treatments for cancer. In a nutshell, the modifications of the gut microbiota caused by radiotherapy have an effect on tumor radiosensitivity and, as a result, affect the efficacy of radiotherapy and show a certain radiation toxicity, which leads to numerous side effects. What is of new research significance is that the "gut-organ axis" formed by the gut microbiota may be one of the most interesting potential mechanisms, although the relevant research is still very limited. In this review, we combine new insights into the relationship between the gut microbiota, cancer, and radiotherapy. Based on our current comprehensive understanding of this relationship, we give an overview of the new cancer treatments based on the gut microbiota.

The impact of antibiotic selection and interval time among advanced non-small cell lung cancer patients receiving prior antibacterial treatment and first-line chemotherapy

BACKGROUND

To determine whether antibiotic use before chemotherapy is associated with chemotherapy responses and patient outcomes among NSCLC patients and define the optimal interval between chemotherapy initiation and antibiotic treatment.

MATERIALS AND METHODS

One thousand four hundred and four advanced NSCLC patients receiving first-line platinum-based doublets therapy were retrospectively analyzed. Kaplan-Meier curve evaluated the impact of antibiotic use and type of antibiotics on the survival of patients. The factors affect the patient's prognosis were further confirmed by Cox regression. The optimal interval between antibiotic treatment and the initiation of chemotherapy was determined by the X-tile program.

RESULTS

NSCLC patients of 33.5% advanced underwent broad-spectrum antibiotic treatment prior to chemotherapy. In the chemotherapy only (Chemo) and chemotherapy plus antiangiogenesis (Chemo-angio) treatment groups, prior antibiotic treatment was associated with worse OS (Chemo: 13.8 vs. 17.6 months, p < 0.001; Chemo-angio:11.9 vs. 18.1 months, p = 0.012) and PFS (Chemo: 3.7 vs. 5.8 months, p < 0.001; Chemo-angio: 3.1 vs. 5.9 months, p < 0.001). Cox regression analysis revealed prior antibiotic administration as an independent predictor of OS and PFS (HR for PFS/OS: 1.925/1.452, both p < 0.001). Antibiotic usage duration (HR for PFS/OS: 1.030/1.036, p = 0.009/0.001) and type (PFS/OS: p < 0.001/p = 0.01) also showed significant association with patient prognosis, with calculated interval time cutoff values of 2, 4, and 2 days for fluoroquinolones, β-lactamase inhibitors, and cephalosporins, respectively.

CONCLUSION

Antibiotic use before first-line chemotherapy was associated with poor results in advanced NSCLC patients; treatment length and type being strongly correlated with patient outcomes. Appropriate prolongation of the time between two treatments may enhance patient survival. Further prospective research is however necessary.

Effect of antimicrobial therapy on progression-free survival of patients with non-small cell lung cancer receiving checkpoint inhibitor- and chemotherapy

BACKGROUND

Checkpoint inhibitor therapy (CPI) has significantly changed therapy in non-small cell lung cancer (NSCLC) in recent years. There are some data that the effect of CPI therapy is influenced by the microbiome. Little is known about the influence and timing of antimicrobial therapy (AMT) on the microbiome-mediated effect on CPI therapy.

PATIENTS AND METHODS

We retrospectively analysed 70 patients (age 68 ± 9.2 years) with NSCLC stage IV. Patients were treated according to the guidelines with either CPI alone (pembrolizumab, nivolumab, atezolizumab) or chemotherapy (platin doublet or docetaxel/nintedanib or pemetrexed). We registered patient's characteristics including presence and timing of AMT. Group 1 consisted of 27 patients with AMT in the month before CPI- or chemotherapy, group 2 was 30 patients with AMT during CPI- or chemotherapy, and group 3 was 43 patients without AMT.

RESULTS

Groups 1-3 showed comparable patient characteristics. Using cox-regression analysis, we found that AMT in the month before CPI resulted in a decreased progression-free survival (PFS) compared to patients with CPI and no AMT (14 ± 1.56 vs. 5 ± 0.99, p = 0.005, 95% CI: 0.13-0.67). In patients, who were treated with chemotherapy alone, there was no difference in PFS in those with or without AMT in the month before therapy (5 ± 0.99 vs. 6 ± 0.81 months, p = 0.3). Interestingly, AMT during chemotherapy or CPI therapy showed no effect on PFS.

CONCLUSIONS

In a real-life setting, we found that AMT reduces PFS when given in the month before CPI therapy. AMT before chemotherapy and during CPI and chemotherapy seems not to influence PFS. The best PFS was seen in patients without AMT before CPI therapy. This implies the need for an even more restrictive use of AMT in the context of patients with NSCLC stage IV disease.

From microbiota toward gastro-enteropancreatic neuroendocrine neoplasms: Are we on the highway to hell?

Gut microbiota is represented by different microorganisms that colonize the intestinal tract, mostly the large intestine, such as bacteria, fungi, archaea and viruses. The gut microbial balance has a key role in several functions. It modulates the host's metabolism, maintains the gut barrier integrity, participates in the xenobiotics and drug metabolism, and acts as protection against gastro-intestinal pathogens through the host's immune system modulation. The impaired gut microbiota, called dysbiosis, may be the result of an imbalance in this equilibrium and is linked with different diseases, including cancer. While most of the studies have focused on the association between microbiota and gastrointestinal adenocarcinomas, very little is known about gastroenteropancreatic (GEP) neuroendocrine neoplasms (NENs). In this review, we provide an overview concerning the complex interplay between gut microbiota and GEP NENs, focusing on the potential role in tumorigenesis and progression in these tumors.

Chemotherapy-Induced Intestinal Microbiota Dysbiosis Impairs Mucosal Homeostasis by Modulating Toll-like Receptor Signaling Pathways

Chemotherapy-induced intestinal mucositis, a painful debilitating condition affecting up to 40–100% of patients undergoing chemotherapy, can reduce the patients’ quality of life, add health care costs and even postpone cancer treatment. In recent years, the relationships between intestinal microbiota dysbiosis and mucositis have drawn much attention in mucositis research. Chemotherapy can shape intestinal microbiota, which, in turn, can aggravate the mucositis through toll-like receptor (TLR) signaling pathways, leading to an increased expression of inflammatory mediators and elevated epithelial cell apoptosis but decreased epithelial cell differentiation and mucosal regeneration. This review summarizes relevant studies related to the relationships of mucositis with chemotherapy regimens, microbiota, TLRs, inflammatory mediators, and intestinal homeostasis, aiming to explore how gut microbiota affects the pathogenesis of mucositis and provides potential new strategies for mucositis alleviation and treatment and development of new therapies.

Enzymatic Conversion of Mannan-Rich Plant Waste Biomass into Prebiotic Mannooligosaccharides

A growing demand in novel food products for well-being and preventative medicine has attracted global attention on nutraceutical prebiotics. Various plant agro-processes produce large amounts of residual biomass considered "wastes", which can potentially be used to produce nutraceutical prebiotics, such as manno-oligosaccharides (MOS). MOS can be produced from the degradation of mannan. Mannan has a main backbone consisting of β-1,4-linked mannose residues (which may be interspersed by glucose residues) with galactose substituents. Endo-β-1,4-mannanases cleave the mannan backbone at cleavage sites determined by the substitution pattern and thus give rise to different MOS products. These MOS products serve as prebiotics to stimulate various types of intestinal bacteria and cause them to produce fermentation products in different parts of the gastrointestinal tract which benefit the host. This article reviews recent advances in understanding the exploitation of plant residual biomass via the enzymatic production and characterization of MOS, and the influence of MOS on beneficial gut microbiota and their biological effects (i.e., immune modulation and lipidemic effects) as observed on human and animal health.

Selenium-rich royal jelly inhibits hepatocellular carcinoma through PI3K/AKT and VEGF pathways in H22 tumor-bearing mice

Royal jelly (RJ) and selenium (Se)-rich foods have well-known health benefits that are attributable to a broad range of pharmacological effects including antioxidant, anti-tumor, and immunoregulatory activities. However, the physiological effects of Se-rich RJ, which is produced by feeding Apis mellifera (Hymenoptera: Apidae) sodium selenite sucrose solution, are not well understood. The anti-hepatoma activity and mechanism of Se-rich RJ in H22 tumor-bearing mice were investigated in the current study. The findings showed that the content of organic and inorganic Se in Se-rich RJ was significantly higher than that in RJ. Furthermore, interleukin-2 (IL-2) levels and tumor necrosis factor-α (TNF-α) production in serum were increased and the malondialdehyde (MDA) content in liver was decreased in mice fed RJ and Se-rich RJ. 16SrRNA sequencing and serum untargeted metabolomics showed that RJ and Se-rich RJ could modulate the gut microbiota, and fisetin and l-glutathione oxidized were the main anti-tumor components in RJ and Se-rich RJ. Further analysis showed 11-deoxy prostaglandin F1β was the specific anti-tumor metabolite in mice treated with Se-rich RJ compared with RJ. The results indicated that RJ and Se-rich RJ could inhibit the expression of PI3K and phosphorylation of AKT, induce cell apoptosis through the activation of caspase-9 and caspase-3, and regulate Bcl-2/Bax expression. RJ and Se-rich RJ also inhibited the expression of COX-2 and VEGF. To summarize, the findings clearly demonstrate that Se-rich RJ could inhibit tumor growth by inducing apoptosis and inhibiting angiogenesis as well as exhibit anti-tumor effects by improving immune function and antioxidant activities. The results indicated that Se-rich RJ could be a potential functional food for the management and prevention of cancer.

Prospective correlation between the patient microbiome with response to and development of immune-mediated adverse effects to immunotherapy in lung cancer

BACKGROUND

Though the gut microbiome has been associated with efficacy of immunotherapy (ICI) in certain cancers, similar findings have not been identified for microbiomes from other body sites and their correlation to treatment response and immune related adverse events (irAEs) in lung cancer (LC) patients receiving ICIs.

METHODS

We designed a prospective cohort study conducted from 2018 to 2020 at a single-center academic institution to assess for correlations between the microbiome in various body sites with treatment response and development of irAEs in LC patients treated with ICIs. Patients must have had measurable disease, ECOG 0-2, and good organ function to be included. Data was collected for analysis from January 2019 to October 2020. Patients with histopathologically confirmed, advanced/metastatic LC planned to undergo immunotherapy-based treatment were enrolled between September 2018 and June 2019. Nasal, buccal and gut microbiome samples were obtained prior to initiation of immunotherapy +/- chemotherapy, at development of adverse events (irAEs), and at improvement of irAEs to grade 1 or less.

RESULTS

Thirty-seven patients were enrolled, and 34 patients were evaluable for this report. 32 healthy controls (HC) from the same geographic region were included to compare baseline gut microbiota. Compared to HC, LC gut microbiota exhibited significantly lower α-diversity. The gut microbiome of patients who did not suffer irAEs were found to have relative enrichment of Bifidobacterium (p = 0.001) and Desulfovibrio (p = 0.0002). Responders to combined chemoimmunotherapy exhibited increased Clostridiales (p = 0.018) but reduced Rikenellaceae (p = 0.016). In responders to chemoimmunotherapy we also observed enrichment of Finegoldia in nasal microbiome, and increased Megasphaera but reduced Actinobacillus in buccal samples. Longitudinal samples exhibited a trend of α-diversity and certain microbial changes during the development and resolution of irAEs.

CONCLUSIONS

This pilot study identifies significant differences in the gut microbiome between HC and LC patients, and their correlation to treatment response and irAEs in LC. In addition, it suggests potential predictive utility in nasal and buccal microbiomes, warranting further validation with a larger cohort and mechanistic dissection using preclinical models.

TRIAL REGISTRATION

ClinicalTrials.gov, NCT03688347 . Retrospectively registered 09/28/2018.

Diet, Microbiome, and Cancer Immunotherapy-A Comprehensive Review

The immune system plays a key role in cancer suppression. Immunotherapy is widely used as a treatment method in patients with various types of cancer. Immune checkpoint blockade using antibodies, such as anti-PD-1, anti-PD-L1, and anti-CTLA-4, is currently gaining popularity. A systematic literature search was executed, and all available data was summarized. This review shows that specific dietary patterns (such as, e.g., animal-based, vegetarian, or Mediterranean diet) alter the gut microbiome's composition. An appropriate intestinal microbiota structure might modulate the function of human immune system, which affects the bodily anti-cancer response. This paper shows also that specific bacteria species inhabiting the gastrointestinal tract can have a beneficial influence on the efficacy of immunotherapy. Antibiotics weaken gut bacteria and worsen the immune checkpoint blockers' efficacy, whereas a faecal microbiota transplant or probiotics supplementation may help restore bacterial balance in the intestine. Other factors (like vitamins, glucose, or BMI) change the cancer treatment response, as well. This review demonstrates that there is a strong association between one's diet, gut microbiome composition, and the outcome of immunotherapy. However, further investigation on this subject is required.

The Gut Microbiome and Gastrointestinal Toxicities in Pelvic Radiation Therapy: A Clinical Review

Simple Summary

A substantial proportion of cancer patients receive radiotherapy (RT) during their cancer trajectory. One of the most challenging pelvic RT-related toxicities are gastrointestinal (GI) toxicities (e.g., abdominal pain, rectal bleeding, faecal incontinence, and diarrhoea) which impair the quality of life (QoL) of patients. Mounting evidence suggests that gut microbiota plays a pivotal role in health and disease, including cancer. Our current clinical review aims to assess the impact of RT on gut microbiota and GI toxicities in cancer patients to provide useful information, in addition to standard care, for clinicians and patients.

Abstract

Background: Gastrointestinal (GI) toxicities are common adverse effects of pelvic radiotherapy (RT). Several recent studies revealed that toxicity of RT is associated with dysbiosis of the gut microbiome. Method: A literature search was conducted in electronic databases Medline, PubMed, and ScienceDirect, with search terms “microbiome and/or microbiota” and “radiotherapy (RT) and/or chemoradiation therapy (CRT)” and “cancer”, and the relevant literature were selected for use in this article. Results: Eight prospective cohort studies were selected for review with a total of 311 participants with a range of 15–134 participants within these studies. The selected studies were conducted in patients with gynaecological (n = 3), rectal (n = 2), or prostate cancers (n = 1), or patients with various types of malignancies (n = 2). Three studies reported that cancer patients had significantly lower alpha diversity compared with healthy controls. Seven studies found that lower alpha diversity and modulated gut microbiome were associated with GI toxicities during and after pelvic RT (n = 5) and CRT (n = 2), whereas one study found that beta diversity was related to a complete response following CRT. Two further studies reported that fatigue was associated with dysbiosis of the gut microbiome and low alpha diversity during and after RT, and with dysbiosis of the gut microbiome and diarrhoea, respectively. Conclusion: Gut microbiome profiles are associated with GI toxicities and have the potential to predict RT/CRT-induced toxicities and quality of life (QoL) in patients undergoing those treatments. Further robust randomized controlled trials (RCTs) are required to elucidate the effect of gut microbiome profiles on RT-related adverse effects and responses to RT.

Exploring the Modulatory Effects of Gut Microbiota in Anti-Cancer Therapy

In the recent decade, gut microbiota has received growing interest due to its role in human health and disease. On the one hand, by utilizing the signaling pathways of the host and interacting with the immune system, the gut microbiota is able to maintain the homeostasis in human body. This important role is mainly modulated by the composition of microbiota, as a normal microbiota composition is responsible for maintaining the homeostasis of human body, while an altered microbiota profile could contribute to several pathogenic conditions and may further lead to oncogenesis and tumor progression. Moreover, recent insights have especially focused on the important role of gut microbiota in current anticancer therapies, including chemotherapy, radiotherapy, immunotherapy and surgery. Research findings have indicated a bidirectional interplay between gut microbiota and these therapeutic methods, in which the implementation of different therapeutic methods could lead to different alterations in gut microbiota, and the presence of gut microbiota could in turn contribute to different therapeutic responses. As a result, manipulating the gut microbiota to reduce the therapy-induced toxicity may provide an adjuvant therapy to achieve a better therapeutic outcome. Given the complex role of gut microbiota in cancer treatment, this review summarizes the interactions between gut microbiota and anticancer therapies, and demonstrates the current strategies for reshaping gut microbiota community, aiming to provide possibilities for finding an alternative approach to lower the damage and improve the efficacy of cancer therapy.

Radiotherapy and the gut microbiome: facts and fiction

An ever-growing body of evidence has linked the gut microbiome with both the effectiveness and the toxicity of cancer therapies. Radiotherapy is an effective way to treat tumors, although large variations exist among patients in tumor radio-responsiveness and in the incidence and severity of radiotherapy-induced side effects. Relatively little is known about whether and how the microbiome regulates the response to radiotherapy. Gut microbiota may be an important player in modulating “hot” versus “cold” tumor microenvironment, ultimately affecting treatment efficacy. The interaction of the gut microbiome and radiotherapy is a bidirectional function, in that radiotherapy can disrupt the microbiome and those disruptions can influence the effectiveness of the anticancer treatments. Limited data have shown that interactions between the radiation and the microbiome can have positive effects on oncotherapy. On the other hand, exposure to ionizing radiation leads to changes in the gut microbiome that contribute to radiation enteropathy. The gut microbiome can influence radiation-induced gastrointestinal mucositis through two mechanisms including translocation and dysbiosis. We propose that the gut microbiome can be modified to maximize the response to treatment and minimize adverse effects through the use of personalized probiotics, prebiotics, or fecal microbial transplantation. 16S rRNA sequencing is the most commonly used approach to investigate distribution and diversity of gut microbiome between individuals though it only identifies bacteria level other than strain level. The functional gut microbiome can be studied using methods involving metagenomics, metatranscriptomics, metaproteomics, as well as metabolomics. Multiple ‘-omic’ approaches can be applied simultaneously to the same sample to obtain integrated results. That said, challenges and remaining unknowns in the future that persist at this time include the mechanisms by which the gut microbiome affects radiosensitivity, interactions between the gut microbiome and combination treatments, the role of the gut microbiome with regard to predictive and prognostic biomarkers, the need for multi “-omic” approach for in-depth exploration of functional changes and their effects on host-microbiome interactions, and interactions between gut microbiome, microbial metabolites and immune microenvironment.

Novel insights into the role of Clostridium novyi-NT related combination bacteriolytic therapy in solid tumors

Several solid tumors (for example leiomyosarcoma, melanoma and hepatocellular carcinoma) possess areas of hypoxia, which underlies one of the primary reasons of failure of conventional anticancer therapies. The areas of poor vascularization are insensitive to radiotherapy and chemotherapeutic drugs. Conversely, the hypoxic regions of tumors provide an ideal environment for anaerobic bacteria. The attenuated anaerobic bacterium, Clostridium novyi-NT (C. novyi-NT), is highly sensitive to oxygen and can target the destruction of hypoxic and necrotic areas of tumors, inducing oncolysis and characteristics indicative of an immune response. Theoretically, chemotherapy, radiotherapy and immunotherapy combined with bacterial therapy can be used as a novel means of treating solid tumors, promoting tumor regression and inhibiting metastasis formation with a notable beneficial effect. The present review discusses the molecular mechanisms of combined bacteriolytic therapy, predominantly focusing on C. novyi-NT, and summarizes the findings of previous studies on experimental animal models, including its efficacy and safety via different drug delivery routes. This strategy has great potential to overcome the limitations of conventional cancer therapy, resulting in improved treatments, and thus potentially improved outcomes for patients.

Gut Microbiome Components Predict Response to Neoadjuvant Chemoradiotherapy in Patients with Locally Advanced Rectal Cancer: A Prospective, Longitudinal Study

PURPOSE

The gut microbiome is involved in antitumor immunotherapy and chemotherapy responses; however, evidence-based research on the role of gut microbiome in predicting response to neoadjuvant chemoradiotherapy (nCRT) in patients with locally advanced rectal cancer (LARC) remains scarce. This prospective, longitudinal study aimed to evaluate the feasibility of the gut microbiome in predicting nCRT responses.

EXPERIMENTAL DESIGN

We collected 167 fecal samples from 84 patients with LARC before and after nCRT and 31 specimens from healthy individuals for 16S rRNA sequencing. Patients were divided into responders and nonresponders according to pathologic response to nCRT. After identifying microbial biomarkers related to nCRT responses, we constructed a random forest classifier for nCRT response prediction of a training cohort of baseline samples from 37 patients and validated the classifier in another cohort of 47 patients.

RESULTS

We observed significant microbiome alterations represented by a decrease in LARC-related pathogens and an increase in Lactobacillus and Streptococcus during nCRT. Furthermore, a prominent microbiota difference between responders and nonresponders was noticed in the baseline samples. Microbes related with butyrate production, including Roseburia, Dorea, and Anaerostipes, were overrepresented in responders, whereas Coriobacteriaceae and Fusobacterium were overrepresented in nonresponders. Ten biomarkers were selected for the response-prediction classifier, including Dorea, Anaerostipes, and Streptococcus, which yielded an area under the curve value of 93.57% [95% confidence interval (CI), 85.76%-100%] in the training cohort and 73.53% (95% CI, 58.96%-88.11%) in the validation cohort.

CONCLUSIONS

The gut microbiome offers novel potential biomarkers for predicting nCRT responses, which has important manifestations in the clinical management of these patients.

The role of the microbiome in drug resistance in gastrointestinal cancers

Introduction: The microbiota is recognized for its impact on both human health and disease. The human microbiota is made up of trillions of cells, including bacteria, viruses, and fungi. The largest population of microbes reside in the gut, prompting research for better understanding of the impact of gastrointestinal microbiota in different diseases. Evidence from numerous studies has pointed out the role of commensal microbes as key determinants of cancer pathogenesis. Moreover, gut microbiota may play an important role in chemoresistance; consequently, this knowledge might be important for novel strategies to improve anticancer treatment efficacy.Areas covered: We describe the role of microbiota in different gastrointestinal cancer types (esophageal, gastric, colorectal, hepatocellular and pancreatic-biliary tract cancers). Moreover, we analyzed the impact of the microbiota on resistance to anticancer therapies, and, lastly, we focused on possibilities of microbiota modulation to enhance anticancer therapy efficacy.Expert opinion: Increasing evidence shows that gut microbiota might influence resistance to anticancer treatment, including conventional chemotherapy, immunotherapy, radiotherapy, and surgery. Therefore, a better knowledge of gut microbiota and its interactions with anticancer drugs will enable us to develop novel anticancer treatment strategies and subsequently improve the cancer patients' outcome.

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.

Impact of Polypharmacy for Chronic Ailments in Colon Cancer Patients: A Review Focused on Drug Repurposing

Colorectal cancer is characterized by high incidence worldwide. Despite increased awareness and early diagnosis thanks to screening programmes, mortality remains high, particularly for patients with metastatic involvement. Immune checkpoint inhibitors or poly (ADP-ribose) polymerase (PARP)-inhibitors have met with disappointing results when used in this setting, opposed to other malignancies. New drugs with different mechanisms of action are needed in this disease. Drug repurposing might offer new therapeutic options, as patients with metastatic colorectal cancer often share risk factors for other chronic diseases and thus frequently are on incidental therapy with these drugs. The aim of this review is to summarise the published results of the activity of drugs used to treat chronic medications in patients affected by colorectal cancer. We focused on antihypertensive drugs, Non-Steroid Anti-inflammatory Drugs (NSAIDs), metformin, antidepressants, statins and antibacterial antibiotics. Our review shows that there are promising results with beta blockers, statins and metformin, whereas data concerning antidepressants and antibacterial antibiotics seem to show a potentially harmful effect. It is hoped that further prospective trials that take into account the role of these drugs as anticancer medications are conducted.

Presence of constipation predicts the therapeutic efficacy of pembrolizumab in metastatic urothelial cancer patients

OBJECTIVES

To study bowel function in urothelial cancer patients treated with pembrolizumab and to assess its association with treatment efficacy.

METHODS

This retrospective study was analyzed for patients with metastatic urothelial cancer who received immune checkpoint inhibitor treatment between December 2017 and June 2019 at Nagoya University and affiliated hospitals in Japan. The association between bowel dysfunction (defined as constipation or need for laxatives) and treatment efficacy was investigated.

RESULTS

We retrospectively enrolled 73 patients with metastatic urothelial cancer who received immune checkpoint inhibitor treatment. All patients received pembrolizumab at 200 mg per bodyweight administered intravenously every 3 weeks. Performance status was 0-1 in 58 patients (79.5%), and liver metastasis was detected in 22 patients (30.1%). The median age was 72 years (range 40-89 years). A total of 45 patients had constipation. The median progression-free survival and overall survival from the start of immune checkpoint inhibitor treatment was 4.0 months (95% confidence interval 1.0-17.3) and 6.6 months (95% confidence interval 1.0-18.0), respectively. Patients with constipation had a significantly higher risk of disease progression (P = 0.005). There was no significant association between constipation and overall survival (P = 0.131). However, complete response was observed among two patients treated with immune checkpoint inhibitor, both of whom did not present constipation.

CONCLUSION

The presence of constipation might be a prognostic factor for urothelial cancer patients undergoing immune checkpoint inhibitor treatment.

Gut microbiota; an overlooked effect of phosphate binders

Hyperphosphatemia is a mineral bone-disease that increases cardiovascular complications and all-cause mortality in chronic kidney disease (CKD) patients. Oral phosphate binders absorb the dietary phosphate to prevent its high plasma levels. Moreover, they can adsorb some uremic toxins and decrease inflammation. A few recent studies highlight an ignored effect of phosphate binders on gut microbiota. Phosphorous is a major nutrient for survival and reproduction of bacteria and its intestinal concentration may impact the activity and composition of the gut microbiota. CKD is a state of an altered gut microbiome and bacterial-derived uremic toxins stimulate cardiovascular disease and systemic inflammation. The identification of the impact of phosphate binders on gut opens a new era in nephrology and fill the existing gap in interpretation of beneficial effects of phosphate binders. This review aims to highlight the impact of oral phosphate binders on the gut microbiome in CKD.

Dietary Recombinant Phycoerythrin Modulates the Gut Microbiota of H22 Tumor-Bearing Mice

Normal intestinal flora is widely involved in many functions of the host: nutritional metabolism; maintenance of intestinal microecological balance; regulation of intestinal endocrine function and nerve signal transduction; promotion of intestinal immune system development and maturation; inhibition of pathogenic bacteria growth and colonization, reduction of its invasion to intestinal mucosa, and so on. In recent years, more and more studies have shown that intestinal flora is closely related to the occurrence, development, and treatment of various tumors. It is indicated that recombinant phycoerythrin (RPE) has significant anti-tumor and immunomodulatory effects. However, little is known about the mechanism of the effect of oral (or intragastric) administration of RPE on gut microbiota in tumor-bearing animals. In this study, using high-throughput 16S rDNA sequencing, we examined the response of gut microbiota in H22-bearing mice to dietary RPE supplementation. The results showed that the abundance of beneficial bacteria in the mice intestinal flora decreased and that of the detrimental flora increased after inoculation with tumor cells (H22); following treatment with dietary RPE, the abundance of beneficial bacteria in the intestinal flora significantly increased and that of detrimental bacteria decreased. In this study, for the first time, it was demonstrated that dietary RPE could modulate the gut microbiota of the H22 bearing mice by increasing the abundance of beneficial bacteria and decreasing that of detrimental bacteria among intestinal bacteria, providing evidence for the mechanism by which bioactive proteins affect intestinal nutrition and disease resistance in animals.

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.