Microbiota and radiation-induced bowel toxicity: lessons from inflammatory bowel disease for the radiation oncologist

Probiotic Consortia Protect the Intestine Against Radiation Injury by Improving Intestinal Epithelial Homeostasis

PURPOSE

Radiation-induced intestinal injury (RIII) commonly occur during abdominal-pelvic cancer radiation therapy; however, no effective prophylactic or therapeutic agents are available to manage RIII currently. This study aimed to clarify the potential of probiotic consortium supplementation in alleviating RIII.

METHODS AND MATERIALS

Male C57BL/6J mice were orally administered a probiotic mixture comprising Bifidobacterium longum BL21, Lactobacillus paracasei LC86, and Lactobacillus plantarum Lp90 for 30 days before exposure to 13 Gy of whole abdominal irradiation. The survival rates, clinical scores, and histologic changes in the intestines of mice were assessed. The impacts of probiotic consortium treatment on intestinal stem cell proliferation, differentiation, and epithelial barrier function; oxidative stress; and inflammatory cytokines were evaluated. A comprehensive examination of the gut microbiota composition was conducted through 16S rRNA sequencing, while changes in metabolites were identified using liquid chromatography-mass spectrometry.

RESULTS

The probiotic consortium alleviated RIII, as reflected by increased survival rates, improved clinical scores, and mitigated mucosal injury. The probiotic consortium treatment exhibited enhanced therapeutic effects at the histologic level compared with individual probiotic strains, although there was no corresponding improvement in survival rates and colon length. Moreover, the probiotic consortium stimulated intestinal stem cell proliferation and differentiation, enhanced the integrity of the intestinal epithelial barrier, and regulated redox imbalance and inflammatory responses in irradiated mice. Notably, the treatment induced a restructuring of the gut microbiota composition, particularly enriching short-chain fatty acid-producing bacteria. Metabolomic analysis revealed distinctive metabolic changes associated with the probiotic consortium, including elevated levels of anti-inflammatory and antiradiation metabolites.

CONCLUSIONS

The probiotic consortium attenuated RIII by modulating the gut microbiota and metabolites, improving inflammatory symptoms, and regulating oxidative stress. These findings provide new insights into the maintenance of intestinal health with probiotic consortium supplementation and will facilitate the development of probiotic-based therapeutic strategies for RIII in clinical practice.

Intestinal microbiota composition is predictive of radiotherapy-induced acute gastrointestinal toxicity in prostate cancer patients

BACKGROUND

The search for factors beyond the radiotherapy dose that could identify patients more at risk of developing radio-induced toxicity is essential to establish personalised treatment protocols for improving the quality-of-life of survivors. To investigate the role of the intestinal microbiota in the development of radiotherapy-induced gastrointestinal toxicity, the MicroLearner observational cohort study characterised the intestinal microbiota of 136 (discovery) and 79 (validation) consecutive prostate cancer patients at baseline radiotherapy.

METHODS

Gastrointestinal toxicity was assessed weekly during RT using CTCAE. An average grade >1.3 over time points was used to identify patients suffering from persistent acute toxicity (endpoint). The microbiota of patients was quantified from the baseline faecal samples using 16S rRNA gene sequencing technology and the Ion Reporter metagenomic pipeline. Statistical techniques and computational and machine learning tools were used to extract, functionally characterise, and predict core features of the bacterial communities of patients who developed acute gastrointestinal toxicity.

FINDINGS

Analysis of the core bacterial composition in the discovery cohort revealed a cluster of patients significantly enriched for toxicity, displaying a toxicity rate of 60%. Based on selected high-risk microbiota compositional features, we developed a clinical decision tree that could effectively predict the risk of toxicity based on the relative abundance of genera Faecalibacterium, Bacteroides, Parabacteroides, Alistipes, Prevotella and Phascolarctobacterium both in internal and external validation cohorts.

INTERPRETATION

We provide evidence showing that intestinal bacteria profiling from baseline faecal samples can be effectively used in the clinic to improve the pre-radiotherapy assessment of gastrointestinal toxicity risk in prostate cancer patients.

FUNDING

Italian Ministry of Health (Promotion of Institutional Research INT-year 2016, 5 × 1000, Ricerca Corrente funds). Fondazione Regionale per la Ricerca Biomedica (ID 2721017). AIRC (IG 21479).

Disrupted gut microecology after high-dose 131I therapy and radioprotective effects of arachidonic acid supplementation

BACKGROUND

Despite the potential radiotoxicity in differentiated thyroid cancer (DTC) patients with high-dose 131I therapy, the alterations and regulatory mechanisms dependent on intestinal microecology remain poorly understood. We aimed to identify the characteristics of the gut microbiota and metabolites in DTC patients suffering from high-dose 131I therapy and explore the radioprotective mechanisms underlying arachidonic acid (ARA) treatment.

METHODS

A total of 102 patients with DTC were recruited, with fecal samples collected before and after 131I therapy for microbiome and untargeted and targeted metabolomic analyses. Mice were exposed to total body irradiation with ARA replenishment and antibiotic pretreatment and were subjected to metagenomic, metabolomic, and proteomic analyses.

RESULTS

131I therapy significantly changed the structure of gut microbiota and metabolite composition in patients with DTC. Lachnospiraceae were the most dominant bacteria after 131I treatment, and metabolites with decreased levels and pathways related to ARA and linoleic acid were observed. In an irradiation mouse model, ARA supplementation not only improved quality of life and recovered hematopoietic and gastrointestinal systems but also ameliorated oxidative stress and inflammation and preserved enteric microecology composition. Additionally, antibiotic intervention eliminated the radioprotective effects of ARA. Proteomic analysis and ursolic acid pretreatment showed that ARA therapy greatly influenced intestinal lipid metabolism in mice subjected to irradiation by upregulating the expression of hydroxy-3-methylglutaryl-coenzyme A synthase 1.

CONCLUSION

These findings highlight that ARA, as a key metabolite, substantially contributes to radioprotection. Our study provides novel insights into the pivotal role that the microbiota-metabolite axis plays in radionuclide protection and offers effective biological targets for treating radiation-induced adverse effects.

Gut Microbiota-Derived 3-Hydroxybutyrate Blocks GPR43-Mediated IL6 Signaling to Ameliorate Radiation Proctopathy

Radiation proctopathy (RP) is a common complication of radiotherapy for pelvic malignancies with high incidence. RP accompanies by microbial dysbiosis. However, how the gut microbiota affects the disease remains unclear. Here, metabolomics reveals that the fecal and serous concentrations of microbiota-derived 3-hydroxybutyrate (3HB) are significantly reduced in RP mice and radiotherapeutic patients. Moreover, the concentration of 3HB is negatively associated with the expression of proinflammatory IL6 that is increased along with the severity of radiation damage. 3HB treatment significantly downregulates IL6 expression and alleviates IL6-mediated radiation damage. Irradiated cell-fecal microbiota co-culture experiments and in vivo assays show that such a radioprotection of 3HB is mediated by GPR43. Microbiome analysis reveals that radiation leads to a distinct bacterial community compared to untreated controls, in which Akkermansia muciniphila is significantly reduced in RP mice and radiotherapeutic patients and is associated with lower 3HB concentration. Gavage of A. muciniphila significantly increases 3HB concentration, downregulates GPR43 and IL6 expression, and ameliorates radiation damage. Collectively, these results demonstrate that the gut microbiota, including A. muciniphila, induce higher concentrations of 3HB to block GPR43-mediated IL6 signaling, thereby conferring radioprotection. The findings reveal a novel implication of the gut-immune axis in radiation pathophysiology, with potential therapeutic applications.

The Tumor Microbiome Reacts to Hypoxia and Can Influence Response to Radiation Treatment in Colorectal Cancer

Tumor hypoxia has been shown to predict poor patient outcomes in several cancer types, partially because it reduces radiation's ability to kill cells. We hypothesized that some of the clinical effects of hypoxia could also be due to its impact on the tumor microbiome. Therefore, we examined the RNA sequencing data from the Oncology Research Information Exchange Network database of patients with colorectal cancer treated with radiotherapy. We identified microbial RNAs for each tumor and related them to the hypoxic gene expression scores calculated from host mRNA. Our analysis showed that the hypoxia expression score predicted poor patient outcomes and identified tumors enriched with certain microbes such as Fusobacterium nucleatum. The presence of other microbes, such as Fusobacterium canifelinum, predicted poor patient outcomes, suggesting a potential interaction between hypoxia, the microbiome, and radiation response. To experimentally investigate this concept, we implanted CT26 colorectal cancer cells into immune-competent BALB/c and immune-deficient athymic nude mice. After growth, in which tumors passively acquired microbes from the gastrointestinal tract, we harvested tumors, extracted nucleic acids, and sequenced host and microbial RNAs. We stratified tumors based on their hypoxia score and performed a metatranscriptomic analysis of microbial gene expression. In addition to hypoxia-tropic and -phobic microbial populations, analysis of microbial gene expression at the strain level showed expression differences based on the hypoxia score. Thus, hypoxia gene expression scores seem to associate with different microbial populations and elicit an adaptive transcriptional response in intratumoral microbes, potentially influencing clinical outcomes.

SIGNIFICANCE

Tumor hypoxia reduces radiotherapy efficacy. In this study, we explored whether some of the clinical effects of hypoxia could be due to interaction with the tumor microbiome. Hypoxic gene expression scores associated with certain microbes and elicited an adaptive transcriptional response in others that could contribute to poor clinical outcomes.

Host microbiome depletion attenuates biofluid metabolite responses following radiation exposure

Development of novel biodosimetry assays and medical countermeasures is needed to obtain a level of radiation preparedness in the event of malicious or accidental mass exposures to ionizing radiation (IR). For biodosimetry, metabolic profiling with mass spectrometry (MS) platforms has identified several small molecules in easily accessible biofluids that are promising for dose reconstruction. As our microbiome has profound effects on biofluid metabolite composition, it is of interest how variation in the host microbiome may affect metabolomics based biodosimetry. Here, we 'knocked out' the microbiome of male and female C57BL/6 mice (Abx mice) using antibiotics and then irradiated (0, 3, or 8 Gy) them to determine the role of the host microbiome on biofluid radiation signatures (1 and 3 d urine, 3 d serum). Biofluid metabolite levels were compared to a sham and irradiated group of mice with a normal microbiome (Abx-con mice). To compare post-irradiation effects in urine, we calculated the Spearman's correlation coefficients of metabolite levels with radiation dose. For selected metabolites of interest, we performed more detailed analyses using linear mixed effect models to determine the effects of radiation dose, time, and microbiome depletion. Serum metabolite levels were compared using an ANOVA. Several metabolites were affected after antibiotic administration in the tryptophan and amino acid pathways, sterol hormone, xenobiotic and bile acid pathways (urine) and lipid metabolism (serum), with a post-irradiation attenuative effect observed for Abx mice. In urine, dose×time interactions were supported for a defined radiation metabolite panel (carnitine, hexosamine-valine-isoleucine [Hex-V-I], creatine, citric acid, and Nε,Nε,Nε-trimethyllysine [TML]) and dose for N1-acetylspermidine, which also provided excellent (AUROC ≥ 0.90) to good (AUROC ≥ 0.80) sensitivity and specificity according to the area under the receiver operator characteristic curve (AUROC) analysis. In serum, a panel consisting of carnitine, citric acid, lysophosphatidylcholine (LysoPC) (14:0), LysoPC (20:3), and LysoPC (22:5) also gave excellent to good sensitivity and specificity for identifying post-irradiated individuals at 3 d. Although the microbiome affected the basal levels and/or post-irradiation levels of these metabolites, their utility in dose reconstruction irrespective of microbiome status is encouraging for the use of metabolomics as a novel biodosimetry assay.

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.

The role of microbiomes in gastrointestinal cancers: new insights

Gastrointestinal (GI) cancers constitute more than 33% of new cancer cases worldwide and pose a considerable burden on public health. There exists a growing body of evidence that has systematically recorded an upward trajectory in GI malignancies within the last 5 to 10 years, thus presenting a formidable menace to the health of the human population. The perturbations in GI microbiota may have a noteworthy influence on the advancement of GI cancers; however, the precise mechanisms behind this association are still not comprehensively understood. Some bacteria have been observed to support cancer development, while others seem to provide a safeguard against it. Recent studies have indicated that alterations in the composition and abundance of microbiomes could be associated with the progression of various GI cancers, such as colorectal, gastric, hepatic, and esophageal cancers. Within this comprehensive analysis, we examine the significance of microbiomes, particularly those located in the intestines, in GI cancers. Furthermore, we explore the impact of microbiomes on various treatment modalities for GI cancer, including chemotherapy, immunotherapy, and radiotherapy. Additionally, we delve into the intricate mechanisms through which intestinal microbes influence the efficacy of GI cancer treatments.

Gut microbiota interactions with antitumor immunity in colorectal cancer: From understanding to application

Colorectal cancer (CRC) is one of highly prevalent cancer. Immunotherapy with immune checkpoint inhibitors (ICIs) has dramatically changed the landscape of treatment for many advanced cancers, but CRC still exhibits suboptimal response to immunotherapy. The gut microbiota can affect both anti-tumor and pro-tumor immune responses, and further modulate the efficacy of cancer immunotherapy, particularly in the context of therapy with ICIs. Therefore, a deeper understanding of how the gut microbiota modulates immune responses is crucial to improve the outcomes of CRC patients receiving immunotherapy and to overcome resistance in nonresponders. The present review aims to describe the relationship between the gut microbiota, CRC, and antitumor immune responses, with a particular focus on key studies and recent findings on the effect of the gut microbiota on the antitumor immune activity. We also discuss the potential mechanisms by which the gut microbiota influences host antitumor immune responses as well as the prospective role of intestinal flora in CRC treatment. Furthermore, the therapeutic potential and limitations of different modulation strategies for the gut microbiota are also discussed. These insights may facilitate to better comprehend the interplay between the gut microbiota and the antitumor immune responses of CRC patients and provide new research pathways to enhance immunotherapy efficacy and expand the patient population that could be benefited by immunotherapy.

Released dsDNA-triggered inflammasomes serve as intestinal radioprotective targets

Objectives

Intestinal mucositis is the major side effect during abdominal or pelvic radiotherapy, but the underlying immunogen remains to be further characterised and few radioprotective agents are available. This study investigated the role of dsDNA-triggered inflammasomes in intestinal mucositis during radiotherapy.

Methods

Pro-inflammatory cytokines were detected by ELISA. Radiation-induced intestinal injury in mice was analyzed by means of survival curves, body weight, HE staining of intestines, and intestinal barrier integrity. Western blot, immunofluorescence staining, co-immunoprecipitation assay and flow cytometry were used to investigate the regulatory role of dsDNA on inflammasomes.

Results

Here, we show that a high level of IL-1β and IL-18 is associated with diarrhoea in colorectal cancer (CRC) patients during radiotherapy, which accounts for intestinal radiotoxicity. Subsequently, we found that the dose-dependently released dsDNA from the intestinal epithelial cells (IECs) serves as the potential immunogenic molecule for radiation-induced intestinal mucositis. Our results further indicate that the released dsDNA transfers into the macrophages in an HMGB1/RAGE-dependent manner and then triggers absent in melanoma 2 (AIM2) inflammasome activation and the IL-1β and IL-18 secretion. Finally, we show that the FDA-approved disulfiram (DSF), a newly identified inflammasome inhibitor, could mitigate intestinal radiotoxicity by controlling inflammasome.

Conclusion

These findings indicate that the extracellular self-dsDNA released from the irradiated IECs is a potential immunogen to stimulate immune cells and trigger the subsequent intestinal mucositis, while blunting the dsDNA-triggered inflammasome in macrophages may represent an exciting therapeutic strategy for side effects control during abdominal radiotherapy.

Interactions between extracellular vesicles and microbiome in human diseases: New therapeutic opportunities

In recent decades, accumulating research on the interactions between microbiome homeostasis and host health has broadened new frontiers in delineating the molecular mechanisms of disease pathogenesis and developing novel therapeutic strategies. By transporting proteins, nucleic acids, lipids, and metabolites in their versatile bioactive molecules, extracellular vesicles (EVs), natural bioactive cell-secreted nanoparticles, may be key mediators of microbiota-host communications. In addition to their positive and negative roles in diverse physiological and pathological processes, there is considerable evidence to implicate EVs secreted by bacteria (bacterial EVs [BEVs]) in the onset and progression of various diseases, including gastrointestinal, respiratory, dermatological, neurological, and musculoskeletal diseases, as well as in cancer. Moreover, an increasing number of studies have explored BEV-based platforms to design novel biomedical diagnostic and therapeutic strategies. Hence, in this review, we highlight the recent advances in BEV biogenesis, composition, biofunctions, and their potential involvement in disease pathologies. Furthermore, we introduce the current and emerging clinical applications of BEVs in diagnostic analytics, vaccine design, and novel therapeutic development.

Adhesive Ergothioneine Hyaluronate Gel Protects against Radiation Gastroenteritis by Alleviating Apoptosis, Inflammation, and Gut Microbiota Dysbiosis

Radiation gastroenteritis represents one of the most prevalent and hazardous complications of abdominopelvic radiotherapy, which not only severely reduces patients' life quality but also restricts radiotherapy efficacy. However, there is currently no clinically available oral radioprotector for this threatening disease due to its complex pathogenesis and the harsh gastrointestinal environment. To this end, this study developed a facile but effective oral radioprotector, ergothioneine hyaluronate (EGT@HA) gel, protecting against radiation gastroenteritis by synergistically regulating oxidative stress, inflammation, and gut microbiota. In vitro and cellular experiments verified the chemical stability and free radical scavenging ability of EGT and its favorable cellular radioprotective efficacy by inhibiting intracellular reactive oxidative species (ROS) generation, DNA damage, mitochondrial damage, and apoptosis. At the in vivo level, EGT@HA with prolonged gastrointestinal residence mitigated radiation-induced gastrointestinal tissue injury, apoptosis, neutrophil infiltration, and gut flora dysbiosis. For the first time, this work investigated the protective effects of EGT@HA gel on radiation gastroenteritis, which not only hastens the advancement of the novel gastrointestinal radioprotector but also provides a valuable gastrointestinal radioprotection paradigm by synergistically modulating oxidative stress, inflammation, and gut microbiota disturbance.

The Influence of the Microbiome on Metastatic Colorectal Cancer

The microbiome (bacteria, viruses, and fungi) that exist within a patient's gastrointestinal tract and throughout their body have been increasingly understood to play a critical role in a variety of disease, including a number of cancer histologies. These microbial colonies are reflective of a patient's overall health state, their exposome, and germline genetics. In the case of colorectal adenocarcinoma, significant progress has been made in understanding the mechanism the microbiome plays beyond mere associations in both disease initiation and progression. Importantly, this improved understanding holds the potential to further identify the role these microbes play in colorectal cancer. We hope this improved understanding will be able to be leveraged in the future through either biomarkers or next-generation therapeutics to augment contemporary treatment algorithms through the manipulation of a patient's microbiome-whether through diet, antibiotics, prebiotics, or novel therapeutics. Here we review the role of the microbiome in the setting of patients with stage IV colorectal adenocarcinoma in both the development and progression or disease as well as response to therapeutics.

Gut microbiota-mediated nucleotide synthesis attenuates the response to neoadjuvant chemoradiotherapy in rectal cancer

Preoperative neoadjuvant chemoradiotherapy (nCRT) is a standard treatment for locally advanced rectal cancer (LARC) patients, yet little is known about the mediators underlying the heterogeneous patient response. In this longitudinal study, we performed 16S rRNA sequencing on 353 fecal specimens and find reduced microbial diversity after nCRT. Multi-omics data integration reveals that Bacteroides vulgatus-mediated nucleotide biosynthesis associates with nCRT resistance in LARC patients, and nonresponsive tumors are characterized by the upregulation of genes related to DNA repair and nucleoside transport. Nucleosides supplementation or B. vulgatus gavage protects cancer cells from the 5-fluorouracil or irradiation treatment. An analysis of 2,205 serum samples from 735 patients suggests that uric acid is a potential prognosis marker for LARC patients receiving nCRT. Our data unravel the role of intestinal microbiota-mediated nucleotide biosynthesis in the response of rectal tumors to nCRT, and highlight the importance of deciphering the cross-talk between cancer cells and gut microorganisms during cancer therapies.

Clinical Radiobiology for Radiation Oncology

This chapter is focused on radiobiological aspects at the molecular, cellular, and tissue level which are relevant for the clinical use of ionizing radiation (IR) in cancer therapy. For radiation oncology, it is critical to find a balance, i.e., the therapeutic window, between the probability of tumor control and the probability of side effects caused by radiation injury to the healthy tissues and organs. An overview is given about modern precision radiotherapy (RT) techniques, which allow optimal sparing of healthy tissues. Biological factors determining the width of the therapeutic window are explained. The role of the six typical radiobiological phenomena determining the response of both malignant and normal tissues in the clinic, the 6R’s, which are Reoxygenation, Redistribution, Repopulation, Repair, Radiosensitivity, and Reactivation of the immune system, is discussed. Information is provided on tumor characteristics, for example, tumor type, growth kinetics, hypoxia, aberrant molecular signaling pathways, cancer stem cells and their impact on the response to RT. The role of the tumor microenvironment and microbiota is described and the effects of radiation on the immune system including the abscopal effect phenomenon are outlined. A summary is given on tumor diagnosis, response prediction via biomarkers, genetics, and radiomics, and ways to selectively enhance the RT response in tumors. Furthermore, we describe acute and late normal tissue reactions following exposure to radiation: cellular aspects, tissue kinetics, latency periods, permanent or transient injury, and histopathology. Details are also given on the differential effect on tumor and late responding healthy tissues following fractionated and low dose rate irradiation as well as the effect of whole-body exposure.

Exploiting dietary fibre and the gut microbiota in pelvic radiotherapy patients

With an ageing population, there is an urgent need to find alternatives to current standard-of-care chemoradiation schedules in the treatment of pelvic malignancies. The gut microbiota may be exploitable, having shown a valuable role in improving patient outcomes in anticancer immunotherapy. These bacteria feed on dietary fibres, which reach the large intestine intact, resulting in the production of beneficial metabolites, including short-chain fatty acids. The gut microbiota can impact radiotherapy (RT) treatment responses and itself be altered by the radiation. Evidence is emerging that manipulation of the gut microbiota by dietary fibre supplementation can improve tumour responses and reduce normal tissue side effects following RT, although data on tumour response are limited to date. Both may be mediated by immune and non-immune effects of gut microbiota and their metabolites. Alternative approaches include use of probiotics and faecal microbiota transplantation (FMT). Current evidence will be reviewed regarding the use of dietary fibre interventions and gut microbiota modification in improving outcomes for pelvic RT patients. However, data regarding baseline (pre-RT) gut microbiota of RT patients and timing of dietary fibre manipulation (before or during RT) is limited, heterogenous and inconclusive, thus more robust clinical studies are required before these strategies can be applied clinically.

NMN ameliorated radiation induced damage in NRF2-deficient cell and mice via regulating SIRT6 and SIRT7

Risk of cancer often increases with aging, and radiotherapy is an essential component of treatment. As for abdominal and pelvic cancer, radiotherapy always inevitably causes injury to intestines through direct DNA damage or overload of reactive oxygen species (ROS). Nuclear factor erythroid 2-related factor 2 (NRF2) has been identified as a key protective factor against ionizing-radiation induced damage through promoting DNA damage repair and antioxidant modulation. However, the level of NRF2 always decreases with aging. Here, we demonstrated that NRF2 deficiency aggravated cellular DNA damage and the intestinal pathological lesion. Overexpression of SIRT6 or SIRT7 could improve cell proliferation and protect against radiation injury in NRF2 knock-out (KO) cells by modulating oxidative-stress and DNA damage repair. Consistently, supplement of nicotinamide mononucleotide (NMN), the agonist of sirtuins, increased the level of SIRT6 and SIRT7 in NRF2 KO cells, concomitant with reduced cellular ROS level and ameliorated DNA damage. In vivo, long-term oral administration of NMN attenuated the radiation-induced injury of jejunum, increased the number of intestinal stem cells, and promoted the ability of intestinal proliferation in NRF2-/- mice. Together, our results indicated that SIRT6 and SIRT7 had involved in scavenging ROS and repairing DNA damage, and NMN could be a promising candidate for preventing radiation damage when NRF2 is lacking.

Radioprotective effect of mistletoe extract on intestinal toxicity: in vivo study using adult zebrafish

PURPOSE

The intestine is a dose-limiting organ in the treatment of intra-abdominal cancer. We previously reported that the extract of mistletoe parasites on Quercus had a more potent radioprotective effect than amifostine in reducing the developmental toxicities of zebrafish embryos. In this study, radioprotection against intestinal toxicity was investigated in adult zebrafish.

METHODS

Wild-type adult AB zebrafish were exposed to 45-50 Gy of photon beam irradiation and/or treated with mistletoe extract orally 1 h before. The main endpoints of the study were survival and degree of deformation of the intestinal villi.

RESULTS

The median follow-up period was 10 d post-irradiation (range: 7-11 d). A total of 105 zebrafish were used, including 42 in the radiation alone, 42 in the radiation and mistletoe arms, and 21 control subjects (mistletoe alone, mock-irradiated arm). The rate of both significant deformity and death was 53% in the radiation-alone arm, whereas the corresponding rate was 30% in the radiation and mistletoe arms. Significant deformity-free survival rates at 10 d post-irradiation in the radiation alone, and radiation and mistletoe arms were 44.7% (95% confidence interval [CI]:20-54.3) and 68.4% (95% CI:53.8-86.8), respectively (p=.046). The radiation and mistletoe arms showed decreased expression of two of three inflammatory genes (IL-1β and IL-6) compared to the radiation alone group (p<.05).

CONCLUSION

The radioprotective effect against intestinal toxicity was successfully shown in an adult zebrafish model. This result suggests the possibility of clinical use of mistletoe extract for the treatment of abdominal cancers.

The microbiota and radiotherapy for head and neck cancer: What should clinical oncologists know?

Radiotherapy is a linchpin in head and neck squamous cell carcinoma (HN-SCC) treatment. Modulating tumour and/or normal tissue biology offers opportunities to further develop HN-SCC radiotherapy. The microbiota, which can exhibit homeostatic properties and be a modulator of immunity, has recently received considerable interest from the Oncology community. Microbiota research in head and neck oncology has also flourished. However, available data are difficult to interpret for clinical and radiation oncologists. In this review, we focus on how microbiota research can contribute to the improvement of radiotherapy for HN-SCC, focusing on how current and future research can be translated back to the clinic. We include in-depth discussions about the microbiota, its multiple habitats and relevance to human physiology, mechanistic interactions with HN-SCC, available evidence on microbiota and HNC oncogenesis, efficacy and toxicity of treatment. We discuss clinically-relevant areas such as the role of the microbiota as a predictive and prognostic biomarker, as well as the potential of leveraging the microbiota and its interactions with immunity to improve treatment results. Importantly, we draw parallels with other cancers where research is more mature. We map out future directions of research and explain clinical implications in detail.

Life style and interaction with microbiota in prostate cancer patients undergoing radiotherapy: study protocol for a randomized controlled trial

Background

Prostate cancer (PCa) is the second most common cancer in men worldwide. The standard non-surgical approach for localized PCa is radiotherapy (RT), but one of the limitations of high-dose RT is the potential increase in gastrointestinal and genitourinary toxicities. We present the protocol of the Microstyle study, a multicentre randomized two-arm crossover clinical trial. The primary outcome will be assessed at the end of 6-month intervention, by measuring the change in adherence to a healthy lifestyle score. The hypothesis is that modifying lifestyle we change microbiome and improve quality of life and decrease side effects of RT.

Methods

Study participants will be recruited among men undergoing RT in two Italian centers (Milan and Naples). We foresee to randomize 300 patients in two intervention arms: Intervention Group (IG) and Control Group (CG). Participants allocated to the IG will meet a dietitian and a physiotherapist before RT to receive personalized diet and exercise recommendations, according to their health status, to improve overall lifestyle and reduce side effects (bowel and/or urinary problems). Dietitian and physiotherapist will work together to set individualized goals to reduce or eliminate side effects and pain according to their health status. All participants (IG) will be given a pedometer device (steps counter) in order to monitor and to spur participants to increase physical activity and reduce sedentary behavior. Participants included in the CG will receive baseline general advice and materials available for patients undergoing RT. According to the cross-over design, the CG will cross to the intervention approach after 6-month, to actively enhance compliance towards suggested lifestyle recommendations for all patients.

Discussion

This trial is innovative in its design because we propose a lifestyle intervention during RT, that includes both dietary and physical activity counselling, as well as monitoring changes in microbiome and serum biomarkers. The promotion of healthy behaviour will be initiated before initiation of standard care, to achieve long lasting effects, controlling side effects, coping with feelings of anxiety and depression and improve efficacy of RT.

Trial registration

ClincalTrial.gov registration number: NCT05155618. Retrospectively registered on December 13, 2021. The first patient was enrolled on October 22, 2021.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12885-022-09521-4.

Gut microbiome in gastrointestinal cancer: a friend or foe?

The impact of the gut microbiome on host health is becoming increasingly recognized. To date, there is growing evidence that the complex characteristics of the microbial community play key roles as potential biomarkers and predictors of responses in cancer therapy. Many studies have shown that altered commensal bacteria lead to cancer susceptibility and progression in diverse pathways. In this review, we critically assess the data for gut microbiota related to gastrointestinal cancer, including esophageal, gastric, pancreatic, colorectal cancer, hepatocellular carcinoma and cholangiocarcinoma. Importantly, the underlying mechanisms of gut microbiota involved in cancer occurrence, prevention and treatment are elucidated. The purpose of this review is to provide novel insights for applying this understanding to the development of new therapeutic strategies in gastrointestinal cancer by targeting the microbial community.

The microbiome and precision oncology: an emerging paradigm in anticancer therapy

Understanding the host-microbiome interactions has emerged as an essential factor in improving human health and disease. Recent advances in understanding the intimate relationship of microbes with the host have uncovered various previously unknown underlying causes of disease development, progression, and treatment failure. The dynamic behaviour of the microbiome confers the heterogeneity in treatment response by modulating the immune response and inflammation in various diseases, including cancer. The growing insights into the microbial modulation of cancer through immunoregulation, xenometabolism, and increase in toxicity open a new era of personalised medicine. In the current review, we discuss the essential roles played by the microbiome in modulating the efficacy and toxicity of anticancer therapies (immunotherapy, chemotherapy, and radiotherapy). We also outline the current state of personalised medicine in the context of cancer and microbiome modulation. The knowledge about the role of cancer-microbiome communication will lead to designing other precise microbial modulation strategies for cancer treatment through enhanced efficacy and decreased toxicity.

Immunomodulation by radiotherapy in tumour control and normal tissue toxicity

Radiotherapy (RT) is a highly effective anticancer treatment that is delivered to more than half of all patients with cancer. In addition to the well-documented direct cytotoxic effects, RT can have immunomodulatory effects on the tumour and surrounding tissues. These effects are thought to underlie the so-called abscopal responses, whereby RT generates systemic antitumour immunity outside the irradiated tumour. The full scope of these immune changes remains unclear but is likely to involve multiple components, such as immune cells, the extracellular matrix, endothelial and epithelial cells and a myriad of chemokines and cytokines, including transforming growth factor-β (TGFβ). In normal tissues exposed to RT during cancer therapy, acute immune changes may ultimately lead to chronic inflammation and RT-induced toxicity and organ dysfunction, which limits the quality of life of survivors of cancer. Here we discuss the emerging understanding of RT-induced immune effects with particular focus on the lungs and gut and the potential immune crosstalk that occurs between these tissues.

Strategies for the treatment of colorectal cancer caused by gut microbiota

Colorectal cancer (CRC), also named as colon and rectal or bowel cancer, is one of the leading neoplasia diagnosed in the world. Genetic sequencing studies of microorganisms from the intestinal microbiota of patients with CRC revealed that changes in its composition occur with the development of the disease, which can play a fundamental role in its development, being mediated by the production of metabolites and toxins that damage enterocytes. Some microorganisms are frequently reported in the literature as the main agents of this process, such as the bacteria Fusobacterium nucleatum, Escherichia coli and Bacteroides fragilis. Thus, understanding the mechanisms and function of each microorganism in CRC is essential for the development of treatment tools that focus on the gut microbiota. This review verifies current research aimed at evaluating the microorganisms present in the microbiota that can influence the development of CRC, as well as possible forms of treatment that can prevent the initiation and/or spread of this disease. Due to the incidence of CRC, alternatives have been launched considering factors beyond those already known in the disease development, such as diet, fecal microbiota transplantation, use of probiotics and antibiotics, which have been widely studied for this purpose. However, despite being promising, the studies that focus on the development of new therapeutic approaches targeting the microorganisms that cause CRC still need to be improved and better developed, involving new techniques to elucidate the effectiveness and safety of these new methods.

Impact of Pelvic Radiation Therapy for Prostate Cancer on Global Metabolic Profiles and Microbiota-Driven Gastrointestinal Late Side Effects: A Longitudinal Observational Study

PURPOSE

Radiation therapy to the prostate and pelvic lymph nodes (PLNRT) is part of the curative treatment of high-risk prostate cancer. Yet, the broader influence of radiation therapy on patient physiology is poorly understood. We conducted comprehensive global metabolomic profiling of urine, plasma, and stools sampled from patients undergoing PLNRT for high-risk prostate cancer.

METHODS AND MATERIALS

Samples were taken from 32 patients at 6 timepoints: baseline, 2 to 3 and 4 to 5 weeks of PLNRT; and 3, 6, and 12 months after PLNRT. We characterized the global metabolome of urine and plasma using 1H nuclear magnetic resonance spectroscopy and ultraperformance liquid chromatography-mass spectrometry, and of stools with nuclear magnetic resonance. Linear mixed-effects modeling was used to investigate metabolic changes between timepoints for each biofluid and assay and determine metabolites of interest.

RESULTS

Metabolites in urine, plasma and stools changed significantly after PLNRT initiation. Metabolic profiles did not return to baseline up to 1 year post-PLNRT in any biofluid. Molecules associated with cardiovascular risk were increased in plasma. Pre-PLNRT fecal butyrate levels directly associated with increasing gastrointestinal side effects, as did a sharper fall in those levels during and up to 1 year postradiation therapy, mirroring our previous results with metataxonomics.

CONCLUSIONS

We showed for the first time that an overall metabolic effect is observed in patients undergoing PLNRT up to 1 year posttreatment. These metabolic changes may effect on long-term morbidity after treatment, which warrants further investigation.

Radiotherapy-Induced Digestive Injury: Diagnosis, Treatment and Mechanisms

Radiotherapy is one of the main therapeutic methods for treating cancer. The digestive system consists of the gastrointestinal tract and the accessory organs of digestion (the tongue, salivary glands, pancreas, liver and gallbladder). The digestive system is easily impaired during radiotherapy, especially in thoracic and abdominal radiotherapy. In this review, we introduce the physical classification, basic pathogenesis, clinical characteristics, predictive/diagnostic factors, and possible treatment targets of radiotherapy-induced digestive injury. Radiotherapy-induced digestive injury complies with the dose-volume effect and has a radiation-based organ correlation. Computed tomography (CT), MRI (magnetic resonance imaging), ultrasound (US) and endoscopy can help diagnose and evaluate the radiation-induced lesion level. The latest treatment approaches include improvement in radiotherapy (such as shielding, hydrogel spacers and dose distribution), stem cell transplantation and drug administration. Gut microbiota modulation may become a novel approach to relieving radiogenic gastrointestinal syndrome. Finally, we summarized the possible mechanisms involved in treatment, but they remain varied. Radionuclide-labeled targeting molecules (RLTMs) are promising for more precise radiotherapy. These advances contribute to our understanding of the assessment and treatment of radiation-induced digestive injury.

Altered Gut Microbiota Associated With Hemorrhage in Chronic Radiation Proctitis

Pelvic cancer radiotherapy may cause chronic radiation proctitis (CRP) that adversely affects patient's quality of life, especially in patients with prolonged hematochezia. However, previous studies of radiation enteropathy mainly focused on acute irradiation hazards, and the detailed pathogenesis process and mechanism of prolonged hematochezia associated with radiation-induced toxicity remain unclear. In this study, we characterized the gut microbiota of 32 female CRP patients with or without hematochezia. Differential patterns of dysbiosis were observed. The abundance of Peptostreptococcaceae, Eubacterium, and Allisonella was significantly higher in CRP patients with hematochezia, while the compositions of the Lachnospiraceae, Megasphera, Megamonas, and Ruminococcaceae were lower in the microbiota of non-hematochezia patients. Functional prediction suggested significant difference in the expression of mineral absorption and the arachidonic acid metabolism proteins between hematochezia and non-hematochezia patients, possibly interdependent on radiation-induced inflammation. This study provides new insight into the altered composition and function of gut microbiota in patients with hematochezia, implying the potential use of probiotics and prebiotics for assessment and treatment of CRP.

The brain-gut axis in gastrointestinal cancers

Recent developments have given more credence into the brain-gut-microbiota axis and its role in the development of tumor genesis. The microbiota have multiple functions including maintenance of the epithelial barrier, immune response, digestion, cortisol regulation, and control of neurotransmitters and their metabolism [e.g., serotonin, dopamine, noradrenaline and gamma-Aminobutyric Acid (GABA)]. Changes in gut microbiota can interfere with homeostasis leading to dysbiosis microbiota, which is linked to colorectal cancer. Microbiota composition can cause pronounced effect on medical interventions including medications, chemotherapy, and radiation. Altered primary immune system is associated with microbiota disassociation and development of colorectal cancer. This article reviews the current research in brain-gut axis with focus on microbiota and its role in the development of gastrointestinal cancers. We conducted a literature review on PubMed, Cochrane, and Science direct using English language. We begin by reviewing the brain-gut axis and its function and then discuss its effect on the development of gastrointestinal cancers. We reviewed 70 manuscripts and found association between microbiota dysfunction and development of colorectal cancers predisposing to psychiatric manifestations. Lasting disturbances in the microbiota can lead to systemic inflammation with implications on disease development or treatment modifications. These disruptions of the intestinal flora can play an important role in the pathogenesis of cancers. Most psychological reactions to cancer are similar across cancer types but each cancer when examined individually has its own unique features associated with it. Correlation between fear of recurrence and the level of pathological distress is viewed as an indicator of overall adjustment to cancer survival.

Review: Effect of Gut Microbiota and Its Metabolite SCFAs on Radiation-Induced Intestinal Injury

Gut microbiota is regarded as the second human genome and forgotten organ, which is symbiotic with the human host and cannot live and exist alone. The gut microbiota performs multiple physiological functions and plays a pivotal role in host health and intestinal homeostasis. However, the gut microbiota can always be affected by various factors and among them, it is radiotherapy that results in gut microbiota ¹²dysbiosis and it is often embodied in a decrease in the abundance and diversity of gut microbiota, an increase in harmful bacteria and a decrease in beneficial bacteria, thereby affecting many disease states, especially intestine diseases. Furthermore, gut microbiota can produce a variety of metabolites, among which short-chain fatty acids (SCFAs) are one of the most abundant and important metabolites. More importantly, SCFAs can be identified as second messengers to promote signal transduction and affect the occurrence and development of diseases. Radiotherapy can lead to the alterations of SCFAs-producing bacteria and cause changes in SCFAs, which is associated with a variety of diseases such as radiation-induced intestinal injury. However, the specific mechanism of its occurrence is not yet clear. Therefore, this review intends to emphasize the alterations of gut microbiota after radiotherapy and highlight the alterations of SCFAs-producing bacteria and SCFAs to explore the mechanisms of radiation-induced intestinal injury from the perspective of gut microbiota and its metabolite SCFAs.

Intervention on gut microbiota may change the strategy for management of colorectal cancer

Dysbiosis in the gut microbiota composition due to environmental or genetic variations can disrupt the immune system and may promote several diseases such as colorectal cancer (CRC). Gut microbiota can alter the toxicity and efficiency of an extensive range of CRC treatment methods, especially surgery, chemotherapy, radiotherapy, and immunotherapy. The recent scientific evidence suggested that gut microbiota modulation exhibits an essential positive influence on inhibition and treatment of CRC. The literature survey revealed that modulating the gut microbiota composition by probiotics, prebiotics, and diets protects CRC patients from treatment-associated adverse effects. This review summarizes the recent advancements in the association between interventions on gut microbiota and CRC to provide innovative strategies for enhancing the safety and efficiency of CRC therapy.

Gastrointestinal Toxicity of Pelvic Radiotherapy: Are We Letting Women Down?

For all cancers there are four areas of importance: prevention, early diagnosis, optimising therapy and living with and beyond. For women diagnosed with gynaecological cancers, progress in these first three areas has been immense. However, living with and beyond has largely been ignored as a significant issue. As a group, patients treated for gynaecological cancer are more often young and more often suffer the most difficult long-term issues. Despite the growing number of long-term survivors, little has been done to ensure appropriate assessment and treatment of side-effects of cancer therapies, especially when radiotherapy has been used. For many affected patients their symptoms become part of everyday life, 'normality' is adjusted and these changes are tolerated even when severely limiting activities. Data show that even expert clinicians frequently do not appreciate the true impact of these problems and the focus of treatment and of follow-up remains fixed on 5-year survival and cancer recurrence, respectively. Many clinicians are unaware of what experts can do for toxicity and do not know where to refer their patients. However, rapid identification of patients with significant symptoms can lead to earlier diagnosis of treatable pathologies and improvement in patients' quality of life. In addition, the underlying pathophysiology of radiation-induced damage is potentially amenable to disease-modifying therapies. This review focuses on the factors that contribute to patients developing pelvic radiation disease, what can be done to mitigate the toxicity of treatment and highlights the challenges that must be addressed to reduce the gastrointestinal toxicity of pelvic radiotherapy.

Changes in the gut microbiome community of nonhuman primates following radiation injury

BACKGROUND

Composition and maintenance of the microbiome is vital to gut homeostasis. However, there is limited knowledge regarding the impact of high doses of radiation, which can occur as a result of cancer radiation therapy, nuclear accidents or intentional release of a nuclear or radioactive weapon, on the composition of the gut microbiome. Therefore, we sought to analyze alterations to the gut microbiome of nonhuman primates (NHPs) exposed to high doses of radiation. Fecal samples were collected from 19 NHPs (Chinese rhesus macaques, Macaca mulatta) 1 day prior and 1 and 4 days after exposure to 7.4 Gy cobalt-60 gamma-radiation (LD_70-80/60). The 16S V4 rRNA sequences were extracted from each sample, followed by bioinformatics analysis using the QIIME platform.

RESULTS

Alpha Diversity (Shannon Diversity Index), revealed no major difference between pre- and post-irradiation, whereas Beta diversity analysis showed significant differences in the microbiome after irradiation (day + 4) compared to baseline (pre-irradiation). The Firmicutes/Bacteriodetes ratio, a factor known to be associated with disruption of metabolic homeostasis, decreased from 1.2 to less than 1 post-radiation exposure. Actinobacillus, Bacteroides, Prevotella (Paraprevotellaceae family) and Veillonella genera were significantly increased by more than 2-fold and Acinetobacter and Aerococcus genus were decreased by more than 10-fold post-irradiation. Fifty-two percent (10/19) of animals exposed to radiation demonstrated diarrhea at day 4 post-irradiation. Comparison of microbiome composition of feces from animals with and without diarrhea at day 4 post-irradiation revealed an increase in Lactobacillus reuteri associated with diarrhea and a decrease of Lentisphaerae and Verrucomicrobioa phyla and Bacteroides in animals exhibiting diarrhea. Animals with diarrhea at day 4 post-irradiation, had significantly lower levels of Lentisphaere and Verrucomicrobia phyla and Bacteroides genus at baseline before irradiation, suggesting a potential association between the prevalence of microbiomes and differential susceptibility to radiation-induced diarrhea.

CONCLUSIONS

Our findings demonstrate that substantial alterations in the microbiome composition of NHPs occur following radiation injury and provide insight into early changes with high-dose, whole-body radiation exposure. Future studies will help identify microbiome biomarkers of radiation exposure and develop effective therapeutic intervention to mitigate the radiation injury.

Suppression of local type I interferon by gut microbiota-derived butyrate impairs antitumor effects of ionizing radiation

The antitumor effects of ionizing radiation (IR) are mediated in part through activation of innate and adaptive immunity. Here we report that gut microbiota influences tumor control following IR. Vancomycin decreased the abundance of butyrate-producing gut bacteria and enhanced antitumor responses to IR. Oral administration of Lachnospiraceae, a family of vancomycin-sensitive bacteria, was associated with increased systemic and intratumoral butyric acid levels and impaired the efficacy of IR in germ-free (GF) mice. Local butyrate inhibited STING-activated type I IFN expression in dendritic cells (DCs) through blockade of TBK1 and IRF3 phosphorylation, which abrogated IR-induced tumor-specific cytotoxic T cell immune responses without directly protecting tumor cells from radiation. Our findings demonstrate that the selective targeting of butyrate-producing microbiota may provide a novel therapeutic option to enhance tumor radiation sensitivity.

Association of Radiotherapy-Related Intestinal Injury and Cancer-related Fatigue: A Brief Review and Commentary

Radiotherapy treatment-induced intestinal injury and gut microbial perturbation/dysbiosis have been implicated in the pathobiology of cancer-related fatigue. The objective of this brief review was to explore the available evidence of the relationship between intestinal injury and self-reported fatigue, especially among cancer patients. The scientific evidence-including our own-linking gut mucosal barrier dysfunction and gut microbial perturbation/dysbiosis induced by cancer treatment with worsening of cancer related fatigue (perhaps through the gut-brain axis) is limited but promising. Emerging data suggest that lifestyle interventions and the administration of specific probiotics may favorably modulate the gut microbiota and potentially mediate beneficial effects leading to improvements in fatigue.

Dietary Methionine Supplementation Exacerbates Gastrointestinal Toxicity in a Mouse Model of Abdominal Irradiation

BACKGROUND AND PURPOSE

Identification of appropriate dietary strategies for prevention of weight and muscle loss in cancer patients is crucial for successful treatment and prolonged patient survival. High-protein oral nutritional supplements decrease mortality and improve indices of nutritional status in cancer patients; however, high-protein diets are often rich in methionine, and experimental evidence indicates that a methionine-supplemented diet (MSD) exacerbates gastrointestinal toxicity after total body irradiation. Here, we sought to investigate whether MSD can exacerbate gastrointestinal toxicity after local abdominal irradiation, an exposure regimen more relevant to clinical settings.

MATERIALS AND METHODS

Male CBA/CaJ mice fed either a methionine-adequate diet or MSD (6.5 mg methionine/kg diet vs 19.5 mg/kg) received localized abdominal X-irradiation (220 kV, 13 mA) using the Small Animal Radiation Research Platform, and tissues were harvested 4, 7, and 10 days after irradiation.

RESULTS

MSD exacerbated gastrointestinal toxicity after local abdominal irradiation with 12.5 Gy. This was evident as impaired nutrient absorption was paralleled by reduced body weight recovery. Mechanistically, significant shifts in the gut ecology, evident as decreased microbiome diversity, and substantially increased bacterial species that belong to the genus Bacteroides triggered proinflammatory responses. The latter were evident as increases in circulating neutrophils with corresponding decreases in lymphocytes and associated molecular alterations, exhibited as increases in mRNA levels of proinflammatory genes Icam1, Casp1, Cd14, and Myd88. Altered expression of the tight junction-related proteins Cldn2, Cldn5, and Cldn6 indicated a possible increase in intestinal permeability and bacterial translocation to the liver.

CONCLUSIONS

We report that dietary supplementation with methionine exacerbates gastrointestinal syndrome in locally irradiated mice. This study demonstrates the important roles registered dieticians should play in clinical oncology and further underlines the necessity of preclinical and clinical investigations in the role of diet in the success 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.

The Gut Microbiome Is Associated With Therapeutic Responses and Toxicities of Neoadjuvant Chemoradiotherapy in Rectal Cancer Patients-A Pilot Study

Responses to neoadjuvant chemoradiotherapy (nCRT) and therapy-related toxicities in rectal cancer vary among patients. To provide the individualized therapeutic option for each patient, predictive markers of therapeutic responses and toxicities are in critical need. We aimed to identify the association of gut microbiome with and its potential predictive value for therapeutic responses and toxicities. In the present study, we collected fecal microbiome samples from patients with rectal cancer at treatment initiation and just after nCRT. Taxonomic profiling via 16S ribosomal RNA gene sequencing was performed on all samples. Patients were classified as responders versus non-responders. Patients were grouped into no or mild diarrhea and severe diarrhea. STAMP and high-dimensional class comparisons via linear discriminant analysis of effect size (LEfSe) were used to compare the compositional differences between groups. Phylogenetic Investigation of Communities by Reconstruction of Unobserved States (PICRUSt) was utilized to predict differences in metabolic function between groups. Ten patients were classified as responders and 12 patients were classified as non-responders. Fourteen patients experienced no or mild diarrhea and 8 patients experienced severe diarrhea. Several bacteria taxa with significantly different relative abundances before and after nCRT were identified. Similarly, several baseline bacteria taxa and predicted pathways with significantly different relative abundances between responders and non-responders or between patients no or mild diarrhea and severe diarrhea were identified. Specifically, Shuttleworthia was identified as enriched in responders and several bacteria taxa in the Clostridiales order etc. were identified as enriched in non-responders. Pathways including fatty acid metabolism were predicted to be enriched in responders. In addition, Bifidobacterium, Clostridia, and Bacteroides etc. were identified as enriched in patients with no or mild diarrhea. Pathways including primary bile acid biosynthesis were predicted to be enriched in patients with no or mild diarrhea. Together, the microbiota and pathway markers identified in this study may be utilized to predict the therapeutic responses and therapy-related toxicities of nCRT in patients with rectal cancer. More patient data is needed to verify the current findings and the results of metagenomic, metatranscriptomic, and metabolomic analyses will further mine key biomarkers at the compositional and functional level.

A Minireview on Gastrointestinal Microbiota and Radiosusceptibility

Gastrointestinal (GI) microbiota maintains a symbiotic relationship with the host and plays a key role in modulating many important biological processes and functions of the host, such as metabolism, inflammation, immune and stress response. It is becoming increasingly apparent that GI microbiota is susceptible to a wide range of environmental factors and insults, for examples, geographic location of birth, diet, use of antibiotics, and exposure to radiation. Alterations in GI microbiota link to various diseases, including radiation-induced disorders. In addition, GI microbiota composition could be used as a biomarker to estimate radiosusceptibility and radiation health risk in the host. In this minireview, we summarized the documented studies on radiation-induced alterations in GI microbiota and the relationship between GI microbiota and radiosusceptibility of the host, and mainly discussed the possible mechanisms underlying GI microbiota influencing the outcome of radiation response in humans and animal models. Furthermore, we proposed that GI microbiota manipulation may be used to reduce radiation injury and improve the health of the host.

Prophylactic Faecalibacterium prausnitzii treatment prevents the acute breakdown of colonic epithelial barrier in a preclinical model of pelvic radiation disease

Every year, millions of people around the world benefit from radiation therapy to treat cancers localized in the pelvic area. Damage to healthy tissue in the radiation field can cause undesirable toxic effects leading to gastrointestinal complications called pelvic radiation disease. A change in the composition and/or function of the microbiota could contribute to radiation-induced gastrointestinal toxicity. In this study, we tested the prophylactic effect of a new generation of probiotic like Faecalibacterium prausnitzii (F. prausnitzii) on acute radiation-induced colonic lesions. Experiments were carried out in a preclinical model of pelvic radiation disease. Rats were locally irradiated at 29 Gray in the colon resulting in colonic epithelial barrier rupture. Three days before the irradiation and up to 3 d after the irradiation, the F. prausnitzii A2-165 strain was administered daily (intragastrically) to test its putative protective effects. Results showed that prophylactic F. prausnitzii treatment limits radiation-induced para-cellular hyperpermeability, as well as the infiltration of neutrophils (MPO+ cells) in the colonic mucosa. Moreover, F. prausnitzii treatment reduced the severity of the morphological change of crypts, but also preserved the pool of Sox-9+ stem/progenitor cells, the proliferating epithelial PCNA+ crypt cells and the Dclk1+/IL-25+ differentiated epithelial tuft cells. The benefit of F. prausnitzii was associated with increased production of IL-18 by colonic crypt epithelial cells. Thus, F. prausnitzii treatment protected the epithelial colonic barrier from colorectal irradiation. New-generation probiotics may be promising prophylactic treatments to reduce acute side effects in patients treated with radiation therapy and may improve their quality of life.

The role of the gut microbiome on radiation therapy efficacy and gastrointestinal complications: A systematic review

Radiation therapy (RT) is an essential component of therapy either curative or palliative armamentarium in oncology, but its efficacy varies considerably among patients through many extrinsic and intrinsic mechanisms of the tumour, which are beginning to be better understood. Recent studies have shown that the gut microbiome represents a key factor in the modulation of the systemic immune response and consequently on patients' outcome. Moreover, the emergence of biomarkers that are derived from the gut microbiota has fuelled the development of adjuvant strategies for patients treated with immunotherapy in combination or not with RT. Despite progress in development of more precise radiotherapy techniques, almost all patients undergoing RT to the abdomen, pelvis, or rectum develop acute adverse events as a consequence of several dose-limiting parameters such as the location of irradiation that may subsequently damage normal tissue including the intestinal epithelium. Several lines of evidence in preclinical models identified that vancomycin improves RT-induced gastrointestinal toxicities such as diarrhea and oral mucositis. In order to gain further insight into this rapidly evolving field, we have systematically reviewed the studies that have described how the gut microbiome may directly or indirectly modulate RT efficacy and its gastro-intestinal toxicities. Lastly, we outline current knowledge gaps and discuss potentially more satisfactory therapeutic options to restore the functionality of the gut microbiome of patients treated with RT.

Bacterial dysbiosis incites Th17 cell revolt in irradiated gut

Th17 cells are critical members in mediating immune responses of adaptive immunity. In humans and mice, gut is a main site where Th17 cells are resided, and Th17 cell polarization also occurs in the gut. This process can be mediated by many factors, such as commensal bacteria, dendritic cells and cytokines, such as TGF-β and IL-6. Physiologically, polarized Th17 cells function in anti-infection and maintaining the integrity of intestinal epithelium. However, Th17 cells are plastic. For example, they will become pro-inflammatory cells if being exposed to IL-23. The pathogenic roles of Th17 cells have been well documented in inflammatory bowel disease. Besides, Th17 cells can accumulate in irradiated gut as well. Critically, radiation enteritis and inflammatory bowel disease present several similarities in disease pathology and pathophysiology. Herein, bacterial dysbiosis highly correlates with the pathogenicity of Th17 cells in inflammatory bowel disease. To our knowledge, radiation serves as a factor in inducing bacterial dysbiosis. Using this action, can Th17 cells be incited to promote inflammation in irradiated gut? In this review, we will sequentially introduce polarization of Th17 cells at steady state, radiation-induced Th17 accumulation in the gut, and advances in the management of radiation enteritis by using pharmacological therapy for bacterial dysbiosis.

[Treatment of radiation-induced late effects: What's new?]

Mechanisms of late radio-induced lesions are the result of multiple and complex phenomena, with many entangled cellular and tissue factors. The biological continuum between acute and late radio-induced effects will be described, with firstly a break in homeostasis that leads to cellular redistributions. New insights into late toxicity will finally be addressed. Individual radiosensitivity is a primary factor for the development of late toxicity, and clinicians urgently need predictive tests to offer truly personalized radiation therapy. An update will be made on the various functional and genetic tests currently being validated. The management of radio-induced side effects remains a frequent issue for radiation oncologists, and an update will be made for certain specific clinical situations. Finally, an innovative management for patients with significant side effects after pelvic radiotherapy will be developed, involved mesenchymal stem cell transplantation, with the presentation of the "PRISME" protocol currently open to patients recruitment.

Metformin mitigates gastrointestinal radiotoxicity and radiosensitises P53 mutation colorectal tumours via optimising autophagy

BACKGROUND AND PURPOSE

There is an urgent but unmet need for mitigating radiation-induced intestinal toxicity while radio sensitising tumours for abdominal radiotherapy. We aimed to investigate the effects of metformin on radiation-induced intestinal toxicity and radiosensitivity of colorectal tumours.

EXPERIMENTAL APPROACH

Acute and chronic histological injuries of the intestine from mice were used to assess radioprotection and IEC-6 cell line was used to investigate the mechanisms in vitro. The fractionated abdominal radiation model of HCT116 and HT29 tumour grafts was used to determine the effects on colorectal cancer.

KEY RESULTS

Metformin alleviated radiation-induced acute and chronic intestinal toxicity by optimising mitophagy which was AMPK-dependent. In addition, our data indicated that metformin increased the radiosensitivity of colorectal tumours with P53 mutation both in vitro and in vivo.

CONCLUSION AND IMPLICATIONS

Metformin may be a radiotherapy adjuvant agent for colorectal cancers especially those carrying P53 mutation. Our findings provide a new strategy for further precise clinical trials for metformin on radiotherapy.

Bi-Directional interactions between microbiota and ionizing radiation in head and neck and pelvic radiotherapy - clinical relevance

Purpose: Rapid developments in high throughput screening technology for the detection and identification of the human microbiota have helped in understanding its influence on human health and disease. In the recent past, several seminal studies have demonstrated the influence of microbiota on outcomes of therapy-associated radiation exposure. In this review, we highlight the concepts related to the mechanisms by which radiation alters the microbiota composition linked with radiation-associated toxicity in head and neck and pelvic regions. We further discuss specific microbial changes that can be employed as a biomarker for radiation and tumor response.Conclusion: Knowledge of the influence of microbiota in radiation response and advances in microbiota manipulation techniques would help to design personalized treatment augmenting the efficacy of radiotherapy.

Total body irradiation-induced colon damage is prevented by nitrate-mediated suppression of oxidative stress and homeostasis of the gut microbiome

Inorganic dietary nitrate plays vital roles in biological functions via the exogenous NO3^-/NO2^-/NO pathway under hypoxia and ischemia. We previously verified the antioxidative effects of inorganic nitrate in a mouse model of total body irradiation (TBI). Accordingly, in this study, we evaluated the effects of inorganic nitrate on prevention of TBI-induced colon injury and dysbiosis of the gut microbiome. Nitrate significantly rescued the abnormal biological indexes (body weight, white blood cell, red blood cell, platelet, hemoglobin level and intestinal canal lengths) induced by TBI. Then, we detected oxidative stress and DNA damage indexes (phospho-histone H2AX and p53 binding protein 1), which were both increased by irradiation (IR) and alleviated by nitrate. IR-induced apoptosis and senescence were ameliorated by inorganic nitrate. The distribution of the gut microbiome differed for mice with TBI and those receiving inorganic nitrate. The average abundance of Lactobacillus significantly increased, and that of Bacteroidales decreased at the genus level in the nitrate group compared with that in the IR alone group. At 30 days after TBI, the abundances of Bacteroides and Faecalibaculum decreased, whereas that of Lactobacillus increased in the IR + nitrate group compared with that in the IR alone group. Inorganic nitrate efficiently prevents TBI-induced colon epithelium injury and maintains the homeostasis of the gut microbiome. Thus, our results showed that inorganic nitrate might be a promising treatment for TBI induced colon injury.

Microbes and Cancer: Friends or Faux?

Cancer is one of the most aggressive and deadly diseases in the world, representing the second leading cause of death. It is a multifactorial disease, in which genetic alterations play a key role, but several environmental factors also contribute to its development and progression. Infections induced by certain viruses, bacteria, fungi and parasites constitute risk factors for cancer, being chronic infection associated to the development of certain types of cancer. On the other hand, susceptibility to infectious diseases is higher in cancer patients. The state of the host immune system plays a crucial role in the susceptibility to both infection and cancer. Importantly, immunosuppressive cancer treatments increase the risk of infection, by decreasing the host defenses. Furthermore, alterations in the host microbiota is also a key factor in the susceptibility to develop cancer. More recently, the identification of a tumor microbiota, in which bacteria establish a symbiotic relationship with cancer cells, opened a new area of research. There is evidence demonstrating that the interaction between bacteria and cancer cells can modulate the anticancer drug response and toxicity. The present review focuses on the interaction between microbes and cancer, specifically aiming to: (1) review the main infectious agents associated with development of cancer and the role of microbiota in cancer susceptibility; (2) highlight the higher vulnerability of cancer patients to acquire infectious diseases; (3) document the relationship between cancer cells and tissue microbiota; (4) describe the role of intratumoral bacteria in the response and toxicity to cancer therapy.

Derivation of Dose/Volume Constraints for the Anorectum from Clinician- and Patient-Reported Outcomes in the CHHiP Trial of Radiation Therapy Fractionation

PURPOSE

The CHHiP trial randomized 3216 men with localized prostate cancer (1:1:1) to 3 radiation therapy fractionation schedules: 74 Gy in 37 fractions over 7.4 weeks; 60 Gy in 20 fractions over 4 weeks; and 57 Gy in 19 fractions over 3.8 weeks. Literature-based dose constraints were applied with arithmetic adjustment for the hypofractionated arms. This study aimed to derive anorectal dose constraints using prospectively collected clinician-reported outcomes (CROs) and patient-reported outcomes (PROs) and to assess the added predictive value of spatial dose metrics.

METHODS AND MATERIALS

A case-control study design was used; 7 CRO and 5 PRO bowel symptoms were evaluated. Cases experienced a moderate or worse symptom 1 to 5 years after-radiation therapy and did not have the symptom before radiation therapy. Controls did not experience the symptom at baseline or between 1 to 5 years after radiation therapy. The anorectum was recontoured from the anal verge to the rectosigmoid junction; dose/volume parameters were extracted. Univariate logistic regression, atlases of complication indices, and bootstrapped receiver-operating-characteristic analysis (1000 replicates, balanced outcomes) were used to derive dose constraints for the whole cohort (hypofractionated schedules were converted to 2-Gy equivalent schedules using α/β = 3 Gy) and separate hypofractionated/conventional fractionation cohorts. Only areas under the curve with 95% confidence interval lower limits >0.5 were considered statistically significant. Any constraint derived in <95% to 99% of bootstraps was excluded.

RESULTS

Statistically significant dose constraints were derived for CROs but not PROs. Intermediate to high doses were important for rectal bleeding, whereas intermediate doses were important for increased bowel frequency, fecal incontinence, and rectal pain. Spatial dose metrics did not improve prediction of CROs or PROs. A new panel of dose constraints for hypofractionated schedules to 60 Gy or 57 Gy are V20Gy <85%, V30Gy <57%, V40Gy <38%, V50Gy <22%, and V60Gy <0.01%.

CONCLUSIONS

Dose constraints differed among symptoms, indicating potentially different pathogenesis of radiation-induced side effects. Derived dose constraints were stricter than those used in CHHiP and may reduce bowel symptoms after radiation therapy.

Gut commensal bacteria, Paneth cells and their relations to radiation enteropathy

In steady state, the intestinal epithelium forms an important part of the gut barrier to defend against luminal bacterial attack. However, the intestinal epithelium is compromised by ionizing irradiation due to its inherent self-renewing capacity. In this process, small intestinal bacterial overgrowth is a critical event that reciprocally alters the immune milieu. In other words, intestinal bacterial dysbiosis induces inflammation in response to intestinal injuries, thus influencing the repair process of irradiated lesions. In fact, it is accepted that commensal bacteria can generally enhance the host radiation sensitivity. To address the determination of radiation sensitivity, we hypothesize that Paneth cells press a critical “button” because these cells are central to intestinal health and disease by using their peptides, which are responsible for controlling stem cell development in the small intestine and luminal bacterial diversity. Herein, the most important question is whether Paneth cells alter their secretion profiles in the situation of ionizing irradiation. On this basis, the tolerance of Paneth cells to ionizing radiation and related mechanisms by which radiation affects Paneth cell survival and death will be discussed in this review. We hope that the relevant results will be helpful in developing new approaches against radiation enteropathy.

Efficacy and safety of sacral nerve modulation for faecal incontinence after pelvic radiotherapy

OBJECTIVE

To assess the efficacy and safety of sacral nerve modulation (SNM) in patients with faecal incontinence (FI) after pelvic radiotherapy in comparison with results of SNM for FI related to other conditions.

METHODS

Prospectively collected data from patients who underwent SNM therapy between January 2010 and December 2015 at 7 tertiary colorectal units were reviewed retrospectively. Patients with FI following pelvic radiotherapy were identified and matched (1:2) for age and sex with 38 patients implanted over the same period for FI without previous radiotherapy. The treatment was considered favourable if the patient reported any therapeutic benefit from SNM, had no further complaints or interventions and did not consider stopping the treatment. Long-term results, surgical revision and definitive explantation rates were compared.

RESULTS

Among 352 patients who received a permanent SNM implant, 19 (5.4%) had FI following pelvic radiotherapy. After a mean follow-up of 3.5 ± 1.9 years, the cumulative successful treatment rates were similar between the groups (p = 0.60). For patients with FI following pelvic radiotherapy, the cumulative success rates were 99.4% [85.4-99.8], 96.7% [78.1-99.6], 91.7% [70.4-98.1] and 74.6% [48.4-94.8] at 1, 2, 3 and 5 years respectively. The revision and definitive explantation rates for infection did not differ significantly.

CONCLUSION

The long-term success rate of SNM for FI after pelvic radiotherapy is similar to that of SNM for FI related to other more frequent conditions. Our study suggests that FI after pelvic radiotherapy could be improved with SNM without an increased risk of complication.