Gut microbiome-driven colorectal cancer via immune, metabolic, neural, and endocrine axes reprogramming.

Colorectal cancer (CRC) is a multifactorial disease increasingly recognized for its complex interplay with the gut microbiota. The disruption of microbial homeostasis-dysbiosis-has profound implications for intestinal barrier integrity and host immune function. Pathogenic bacterial species such as Fusobacterium nucleatum, Escherichia coli harboring polyketide synthase (pks) island, and enterotoxigenic Bacteroides fragilis are implicated in CRC through mechanisms involving mucosal inflammation, epithelial barrier disruption, and immune evasion. These pathogens promote pro-tumorigenic inflammation, enhance DNA damage, and suppress effective anti-tumor immunity. Conversely, commensal and probiotic bacteria, notably Lactobacillus and Bifidobacterium species, exert protective effects by preserving epithelial barrier function and priming host immune responses. These beneficial microbes can promote the maturation of dendritic cells, stimulate CD8+ T cell cytotoxicity, and modulate regulatory T cell populations, thereby enhancing anti-tumor immunity. The dichotomous role of the microbiota underscores its potential as both a biomarker and a therapeutic target in CRC. Recent advances in studies have explored microbiota-modulating strategies-ranging from dietary interventions and prebiotics to fecal microbiota transplantation (FMT) and microbial consortia-as adjuncts to conventional therapies. Moreover, the composition of the gut microbiome has been shown to influence the responses to immunotherapy and chemotherapy, raising the possibility of microbiome-informed precision oncology therapy. This review synthesizes the current findings on the pathogenic and protective roles of bacteria in CRC and evaluates the translational potential of microbiome-based interventions in shaping future therapeutic paradigms.

Enterotoxigenic anaerobic Bacteroides fragilis is a significant source of inflammatory diarrheal disease and a risk factor for colorectal cancer. Two distinct metalloproteinase types (the homologous 1, 2, and 3 isoforms of fragilysin (FRA1, FRA2, and FRA3, respectively) and metalloproteinase II (MPII)) are encoded by the B. fragilis pathogenicity island. FRA was demonstrated to be important to pathogenesis, whereas MPII, also a potential virulence protein, remained completely uncharacterized. Here, we, for the first time, extensively characterized MPII in comparison with FRA3, a representative of the FRA isoforms. We employed a series of multiplexed peptide cleavage assays to determine substrate specificity and proteolytic characteristics of MPII and FRA. These results enabled implementation of an efficient assay of MPII activity using a fluorescence-quenched peptide and contributed to structural evidence for the distinct substrate cleavage preferences of MPII and FRA. Our data imply that MPII specificity mimics the dibasic Arg↓Arg cleavage motif of furin-like proprotein convertases, whereas the cleavage motif of FRA (Pro-X-X-Leu-(Arg/Ala/Leu)↓) resembles that of human matrix metalloproteinases. To the best of our knowledge, MPII is the first zinc metalloproteinase with the dibasic cleavage preferences, suggesting a high level of versatility of metalloproteinase proteolysis. Based on these data, we now suggest that the combined (rather than individual) activity of MPII and FRA is required for the overall B. fragilis virulence in vivo.

Comment on: Wu S, et al. Nat Med 2009; 15:1016-22.

Colorectal cancer (CRC) is the third most common malignant tumor worldwide. The incidence and mortality rates of CRC have been increasing in China, possibly due to economic development, lifestyle, and dietary changes. Evidence suggests that gut microbiota plays an essential role in the tumorigenesis of CRC. Gut dysbiosis, specific pathogenic microbes, metabolites, virulence factors, and microbial carcinogenic mechanisms contribute to the initiation and progression of CRC. Gut microbiota biomarkers have potential translational applications in CRC screening and early diagnosis. Gut microbiota-related interventions could improve anti-tumor therapy’s efficacy and severe intestinal toxic effects. Chinese researchers have made many achievements in the relationship between gut microbiota and CRC, although some challenges remain. This review summarizes the current evidence from China on the role of gut microbiota in CRC, mainly including the gut microbiota characteristics, especially Fusobacterium nucleatum and Parvimonas micra, which have been identified to be enriched in CRC patients; microbial pathogens such as F. nucleatum and enterotoxigenic Bacteroides fragilis, and P. micra, which Chinese scientists have extensively studied; diagnostic biomarkers especially F. nucleatum; therapeutic effects, including microecological agents represented by certain Lactobacillus strains, fecal microbiota transplantation, and traditional Chinese medicines such as Berberine and Curcumin. More efforts should be focused on exploring the underlying mechanisms of microbial pathogenesis of CRC and providing novel gut microbiota-related therapeutic and preventive strategies.

Colorectal cancer (CRC) represents a predominant global malignancy, characterized by increasing incidence and mortality rates. Recent investigations have underscored the gut microbiota as a pivotal element in the pathogenesis and progression of CRC. This review synthesizes current evidence regarding the association between gut microbial dysbiosis and CRC, with a particular emphasis on pathogenic bacteria such as Fusobacterium nucleatum, enterotoxigenic Bacteroides fragilis, pks⁺ Escherichia coli, and Enterococcus faecalis, among others. The mechanisms through which these microbes contribute to tumorigenesis include the induction of DNA damage, the promotion of chronic inflammation, and the induction of immunosuppression, and the production of oncogenic metabolites. Additionally, the review examines the clinical implications of gut microbiota, highlighting their potential as non-invasive biomarkers for early CRC detection and their impact on the efficacy and toxicity of chemotherapy, radiotherapy, and immunotherapy. Furthermore, emerging microbiota-targeted interventions, such as fecal microbiota transplantation, dietary modification, and probiotics, are evaluated for their therapeutic potential. Despite substantial progress, challenges remain in standardizing microbial markers and optimizing individualized microbiota modulation strategies. Future studies integrating multi-omics and machine learning approaches may pave the way for microbiome-based precision medicine in CRC.

The colonic microbiome perhaps aided by specific bacterial species is hypothesized to contribute to colorectal cancer (CRC) pathogenesis, possibly acting as an initiator and/or promoter of colon oncogenesis. Potential mechanisms include induction of specific mucosal pro-carcinogenic immune responses and the biologic action of specific microbial, particularly bacterial, virulence factors. Among specific bacterial species, Escherichia coli possessing the pks island with the DNA-damaging colibactin toxin, Fusobacterium nucleatum and enterotoxigenic Bacteroides fragilis (ETBF) that secrete the DNA-damaging B. fragilis toxin are carcinogenic species of particular interest. To address the hypothesis that microbial species or communities contribute to CRC pathogenesis, we are prospectively studying the microbial associations of human CRC together with parameters of mucosal immunity. Paired surgical CRC samples and normal colon mucosa are studied along with colon biopsies (right and left) of healthy controls undergoing screening colonoscopy. In both United States (Johns Hopkins) and Malaysian cohorts, our data demonstrate that sporadic colon tumors located proximal to the hepatic flexure are characterized by invasive polymicrobial biofilms that extend to normal colon tissue far distant from the tumor. In contrast, biofilm formation is infrequent in colon tumors distal to the hepatic flexure and in the mucosa of colonoscopy controls. Importantly, biofilm formation in colonoscopy controls occurs with similar frequency in the right and left colon demonstrating that the right colon is not inherently prone to biofilm formation. Biofilms induce colonic epithelial cell (CEC) and mucosal biologic changes. Namely, biofilm-containing normal tissues of CRC patients display significantly reduced crypt cell E-cadherin as well as increased CEC IL-6 and Stat3 activation that are not observed in biofilm-negative normal tissues from CRC hosts. Mucosal biofilms in colonoscopy controls are also associated with redistribution of E-cadherin and increased mucosal IL-6. Remarkably, biofilm formation on normal colon tissues from either CRC or healthy hosts is associated with increased crypt epithelial proliferation, a marker for CEC transformation. Collectively, these data indicate that biofilm formation promotes biologic changes known to increase colonic permeability, Wnt signaling, angiogenesis and CEC proliferation, all consistent with mucosal procarcinogenesis. To further identify the microbial links to human CRC, in these same cohorts, we have analyzed in more detail the association of Fusobacterium with CRC finding that a Fusobacterium bloom, largely consisting of F. nucleatum or closely related species, is associated with a subset of early stage CRC. F. nucleatum detection is rare in the normal colon mucosa of either CRC or healthy hosts. The Bacteroides fragilis toxin gene (bft) that identifies oncogenic ETBF is detected by PCR significantly more often on left (86%) and right (92%) tumor and/or paired normal tissues compared with left and right colon biopsies from individuals undergoing screening colonoscopy (53% and 55%, respectively; P<0.04 for each comparison). In contrast to the dominance of bft1-secreting ETBF in diarrheal disease that occurs across the globe, bft2, the most carcinogenic variant of bft in murine models, is the most frequent bft isotype in the mucosa of both cases and controls. Further multiple bft isotypes are detected more frequently in the colonic mucosa of CRC cases (P<0.02). Lastly, in contrast to children with and without colitis where pks+ E. coli can be isolated nearly universally from colonic mucosa, pks+ E. coli were isolated from the colon mucosa of ∼80% of sporadic CRC patients compared to 22% of biopsies from colonoscopy controls (P<0.001). Together our studies support a model whereby biofilm formation enhances epithelial permeability that increases direct access of bacterial antigens/mutagens to an unshielded epithelial surface and promotes procarcinogenic tissue inflammation. Collectively these events are predicted to induce epithelial cell mutations with consequent increased proliferation of transformed CECs. We postulate that the additive or synergistic actions of procarcinogenic bacteria may trigger initiation of CRC in non-biofilm-associated CRC. Co-colonization with procarcinogenic bacteria and/or biofilm formation may predict increased risk for development of sporadic CRC. Citation Format: Cynthia L. Sears. Colon cancer: Alpha-bugs or community as disease drivers. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr SY34-03. doi:10.1158/1538-7445.AM2015-SY34-03

Fecal Microbiota Transplantation for Ulcerative Colitis: Not Just Yet

Diet-mediated gut microbial community modulation and signature metabolites as potential biomarkers for early diagnosis, prognosis, prevention and stage-specific treatment of colorectal cancer

In recent years, it has been shown that some bacteria may be associated with colorectal cancer (CRC). In this study, it was aimed to investigate the role of Fusobacterium nucleatum and enterotoxigenic Bacteroides fragilis (ETBF) in the etiology of CRC by comparing the amounts of these bacteria in colon biopsy tissues of patients with CRC and healthy individuals. The amounts of F.nucleatum and ETBF were determined by quantitative polymerase chain reaction (qPCR) in colon biopsy samples taken from 35 CRC and 35 healthy individuals, and the results were compared in the patient and control groups. The detection rate and amounts of F.nucleatum were found to be statistically significantly higher in tissues of female patients with CRC compared to male patients (p= 0.003, p= 0.013, respectively). There was no statistically significant difference between the tissues of female and male patients with CRC in terms of detection rate and amount of ETBF (p= 0.521, p= 0.515, respectively). It was found that in the 50-74 age group, the amount of ETBF was statistically significantly higher in women and men with CRC compared to the controls (p= 0.005, p= 0.047, respectively), while the amount of F.nucleatum was statistically significantly higher in female patients compared to controls. However, no difference was found between male patients and controls (p= 0.009, p= 0.083). It was determined that the detection rate and amount of F.nucleatum in the tissues of patients with CRC, regardless of age and gender, were not statistically different from the controls (p= 0.473, p= 0.995, respectively), however, the detection rate of ETBF and the amount of ETBF were found to be statistically significantly higher (p= 0.002, p= 0.004, respectively). It has been determined that ETBF can play a role in the etiology of CRC in both men and women, and F.nucleatum only in women, in the age range of 50-74 years, when routine screenings for CRC are performed.

Colorectal cancer (CRC) is a common malignancy of the gastrointestinal tract, accounting for the second most common cause of gastrointestinal tumors. As one of the intestinal barriers, gut bacteria form biofilm, participate in intestinal work, and form the living environment of intestinal cells. Metagenomic next-generation sequencing (mNGS) of the gut bacteria in a large number of CRC patients has been established, enabling specific microbial signatures to be associated with colorectal adenomato-carcinoma. Gut bacteria are involved in both benign precursor lesions (polyps), in situ growth and metastasis of CRC. Therefore, the term tumorigenic bacteria was proposed in 2018, such as Escherichia coli, Fusobacterium nucleatum, enterotoxigenic Bacteroides fragilis, etc. Meanwhile, bacteria toxins (such as cytolethal distending toxin (CDT), Colibactin (Clb), B. fragilis toxin) affect the tumor microenvironment and promote cancer occurrence and tumor immune escape. It is important to note that there are differences in the bacteria of different types of CRC. In this paper, the role of tumorigenic bacteria in the polyp-cancer transformation and the effects of their secreted toxins on the tumor microenvironment will be discussed, thereby further exploring new ideas for the prevention and treatment of CRC.

Exploring the therapeutic potential of bacteriophage-mediated modulation of gut microbiota towards colorectal cancer.

The intestinal microbiota, composed of a large population of microorganisms, is often considered a “forgotten organ” in human health and diseases. Increasing evidence indicates that dysbiosis of the intestinal microbiota is closely related to colorectal cancer (CRC). The roles for intestinal microorganisms that initiated and facilitated the CRC process are becoming increasingly clear. Hypothesis models have been proposed to illustrate the complex relationship between the intestinal microbiota and CRC. Recent studies have identified Streptococcus bovis, enterotoxigenic Bacteroides fragilis, Fusobacterium nucleatum, Enterococcus faecalis, Escherichia coli, and Peptostreptococcus anaerobius as CRC candidate pathogens. In this review, we summarized the mechanisms involved in microbiota-related colorectal carcinogenesis, including inflammation, pathogenic bacteria, and their virulence factors, genotoxins, oxidative stress, bacterial metabolites, and biofilm. We also described the clinical values of intestinal microbiota and novel strategies for preventing and treating CRC.

Gut microbiota as a mediator of cancer development and management: From colitis to colitis-associated dysplasia and carcinoma.

Background: Colorectal cancer (CRC) incidence has increased in those 50 years or younger compared to older individuals in recent decades. While the intra-tumoral microbiome is a potent facilitator of tumorigenesis, the role of the microbiome in early onset (eo)CRC is unclear. Identification of the intra-tumoral microbiome may enhance prediction of adverse outcomes to improve survival of CRC overall age groups and eoCRC. Methods: We performed targeted sequencing of tumor and matched normal DNA samples from 3695 colorectal cancer cases within the Genetics and Colorectal Cancer Consortium (GECCO) and the Colon Cancer Family Registry (CCFR). Tumor DNA was extracted from formalin fixed paraffin embedded (FFPE) or fresh frozen tissue. Normal tissue DNA was extracted from blood or normal surrounding colorectal tissue. We designed probes for the bacterial pathogens enterotoxigenic Bacteroides fragilis (ETBF), polyketide synthase positive E. coli (pks+ EC), and Fusobacterium nucleatum (Fn). We used logistic regression to assess tumor-associated bacteria and clinical parameters, tumor molecular characteristics, and tumor stage adjusted for age, sex, and study and a Cox promotional hazard to assess association with CRC-specific survival, overall and in eoCRC, adjusted for age at diagnosis, sex, mutational burden, and microsatellite instability (MSI) and stratified baseline hazards by study. Survival data were available for 2357 and 308 patients, overall and in eoCRC, respectively. Results: The prevalence of different bacteria in tumors differed slightly overall vs. in eoCRC tumors: ETBF (5.2%, 6.3%), pks+ EC (12.9%, 14.8%), and Fn (10.4%, 8.2%). Overall, men had a lower probability of tumors with Fn (odds ratio (OR)=0.8, 95% confidence interval (CI)=0.64-0.99, p=0.04) but higher odds of tumors with pks+ EC (OR=1.38, CI=1.14-1.68, p=0.001), compared to women. The odds of prevalent Fn were higher for proximal vs distal tumors (OR=1.76, CI=1.38-2.26, p<0.001), but there was no association between tumor site and pks+ EC or ETBF. MSI-high tumors were more likely to carry Fn (OR=2.79, CI=2.08-3.75, p<0.001) and less likely to carry pks+ EC (OR=0.63, CI=0.44-0.88, p=0.008) when compared to patients with MSS tumors. In patients with non-hypermutated tumors, we observed that pks+ EC positive tumors were associated with better CRC-specific survival (HR=0.73, CI=0.57-0.93, p=0.01), whereas ETBF positive tumors (HR=1.99, CI=1,18-3.36,p=0.009) and Fn positive tumors (HR=1.33, CI=1.04-1.72, p=0.03) were associated with poorer survival. In eo-CRC patients, Fn positive status was associated with poorer survival (HR=2.4, CI= 1.056 - 5.492, p=0.026). Conclusions: We showed that the intra-tumoral microbiome differs in distribution across patient populations and patient survival over all age groups and, specifically, in eoCRC. Citation Format: Meredith A. Hullar, Keith R. Curtis, Tabitha Harrison, Yi Lin, Robert Steinfelder, Sonja I. Berndt, Daniel D. Buchanan, Andrew T. Chan, David A. Drew, Jane Figueiredo, Amy J. French, Tabitha A. Harrison, Mark A. Jenkins, Johannes Melaku, Victor Moreno, Tomotaka Ugai, Shuji Ogino, Conghui Qu, Chenxu Qu, Steven Thibodeau, Syed Zaidi, Amanda I. Phipps, Ulrike Peters, on behalf of GECCO and CCFR investigators. Evaluation of intra-tumoral pks+ E. coli, enterotoxigenic B. fragilis and Fusobacterium nucleatum, overall and in early onset disease, in colorectal cancer cases [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 3039.

Gut microbiota and their derivatives in the progression of colorectal cancer: Mechanisms of action, genome and epigenome contributions