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Simple Summary Gut microbiota is emerging as new diagnostic and prognostic marker and/or therapeutic target to improve the management of cancer. This review aims to summarize microbial signatures that have been associated with digestive and other cancers. We report the clinical relevance of these microbial markers to predict the response to cancer therapy. Among these biomarkers, colibactin-producing E. coli are prevalent in the colonic mucosa of patients with colorectal cancer and they promote colorectal carcinogenesis in several pre-clinical models. Here we discuss the promising use of colibactin-producing E. coli as a new predictive factor and a therapeutic target in colon cancer management. Abstract The gut microbiota is crucial for physiological development and immunological homeostasis. Alterations of this microbial community called dysbiosis, have been associated with cancers such colorectal cancers (CRC). The pro-carcinogenic potential of this dysbiotic microbiota has been demonstrated in the colon. Recently the role of the microbiota in the efficacy of anti-tumor therapeutic strategies has been described in digestive cancers and in other cancers (e.g., melanoma and sarcoma). Different bacterial species seem to be implicated in these mechanisms: F. nucleatum, B. fragilis, and colibactin-associated E. coli (CoPEC). CoPEC bacteria are prevalent in the colonic mucosa of patients with CRC and they promote colorectal carcinogenesis in susceptible mouse models of CRC. In this review, we report preclinical and clinical data that suggest that CoPEC could be a new factor predictive of poor outcomes that could be used to improve cancer management. Moreover, we describe the possibility of using these bacteria as new therapeutic targets.

International audience; Colorectal cancer (CRC) is the second leading cause of cancer worldwide. CRC is still associated with a poor prognosis among patients with advanced disease. On the contrary, due to its slow progression from detectable precancerous lesions, the prognosis for patients with early stages of CRC is encouraging. While most robust methods are invasive and costly, actual patient-friendly screening methods for CRC suffer of lack of sensitivity and specificity. Therefore, the development of sensitive, non-invasive and cost-effective methods for CRC detection and prognosis are necessary for increasing the chances of a cure. Beyond its beneficial functions for the host, increasing evidence suggests that the intestinal microbiota is a key factor associated with carcinogenesis. Many clinical studies have reported a disruption in the gut microbiota balance and an alteration in the faecal metabolome of CRC patients, suggesting the potential use of a microbial-based test as a non-invasive diagnostic and/or prognostic tool for CRC screening. This review aims to discuss the microbial signatures associated with CRC known to date, including dysbiosis and faecal metabolome alterations, and the potential use of microbial variation markers for non-invasive early diagnosis and/or prognostic assessment of CRC and advanced adenomas. We will finally discuss the possible use of these markers as predicators for treatment response and their limitations.

International audience; Colibactin-producing E. coli (CoPEC) are frequently detected in colorectal cancer (CRC) and exhibit procarcinogenic properties. Because increasing evidence show the role of immune environment and especially of antitumor T-cells in CRC development, we investigated the impact of CoPEC on these cells in human CRC and in the APC(Min/+) mice colon. T-cell density was evaluated by immunohistochemistry in human tumors known for their CoPEC status. APC(min/+) mice were chronically infected with a CoPEC strain (11G5). Immune cells (neutrophils and T-cell populations) were then quantified by immunofluorescent staining of the colon. The quantification of lymphoid populations was also performed in the mesenteric lymph nodes (MLNs). Here, we show that the colonization of CRC patients by CoPEC is associated with a decrease of tumor-infiltrating T lymphocytes (CD3(+) T-cells). Similarly, we demonstrated, in mice, that CoPEC chronic infection decreases CD3(+) and CD8(+) T-cells and increases colonic inflammation. In addition, we noticed a significant decrease in antitumor T-cells in the MLNs of CoPEC-infected mice compared to that of controls. Moreover, we show that CoPEC infection decreases the antimouse PD-1 immunotherapy efficacy in MC38 tumor model. Our findings suggest that CoPEC could promote a procarcinogenic immune environment through impairment of antitumor T-cell response, leading to tumoral resistance to immunotherapy. CoPEC could thus be a new biomarker predicting the anti-PD-1 response in CRC.

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

Introduction. Retinol (RO) and its active metabolite, all-trans retinoic acid (atRA), have been widely studied as cancer chemotherapeutic agents. atRA is a critical immunoregulatory molecule reported to decrease cancer cell proliferation and inhibit tumor-promoting inflammation. However, recent studies report a loss of efficacy of atRA treatment to counteract colorectal cancer (CRC) progress, and the mechanisms underlying this failure are not fully understood. Alcohol dehydrogenase 1B (ADH1B), a major isoform of alcohol dehydrogenase expressed in normal colon, is responsible for the conversion of RO to atRA. We recently reported that stromal (myo)fibroblasts are major ADH1B expressers in normal colonic mucosa and that this expression is lost during the neoplastic transformation process of CRC. Thus, we hypothesized that aberrant retinoid signaling in cancer-associated fibroblasts (CAFs) is among key processes supporting tumor-promoting inflammation in CRC. Methods. Real-time PCR, confocal microscopy and cytokine luminex arrays were used to evaluate alterations in retinoid pathway gene expression and activity to define its relevance to the tumor-associated inflammation in human normal and CRC colonic tissues, and in normal primary (myo)fibroblasts (N-CMFs) and CAFs. Results. We observed a strong downregulation of ADH1B expression in CAFs in situ and in culture along with an increased expression of the tumor growth promoting inflammatory cytokine IL-6. Addition of the ADH1B substrate, RO, or its metabolite, atRA, to N-CMF cultures decreased the LPS-inducible IL-6 expression by N-CMFs. No downregulation of LPS-inducible IL-6 expression by RO was observed in CAFs, while atRA treatment partially inhibits IL-6 expression. Silencing of adh1b gene in N-CMFs led to the increased production of the LPS-inducible IL-6. This suggests that lack of ADH1B expression in CAFs prevents conversion of RO into atRA, resulting in the disruption of the negative regulation of IL-6. A decrease in downstream enzyme ALDH1A expression, which converts ADH1B’s byproduct retinaldehyde, to atRA, was also observed in CAFs. Finally, only a partial inhibition of IL-6 production by exogenous atRA was observed in CAFs. When compared to N-CMFs, CAFs expressed higher levels of CYP26B1, a cytochrome that is responsible for atRA degradation. Treatment of CAFs with atRA resulted in an eight fold higher upregulation of CYP26B1 expression than in N-CMFs. Conclusions. Taken together, our data suggests that CYP26B1 overexpression in CAFs along with ADH1B downregulation support aberrant retinoic acid metabolism in CRC. Adh1blow/Cyp26b1high activity of CAFs leads to a decrease of atRA availability in the tumor microenvironment, supporting IL-6-driven tumor growth promoting inflammation and resistance to exogenous atRA as a chemotherapeutic agent in CRC. Citation Format: Romain Villeger, Gabriella Uribe, Judy A. Trieu, Paul Johnson, Suimmin Qiu, Don W. Powell, Ellen J. Beswick, Iryna V. Pinchuk. Adh1blow/Cyp26b1high activity of CD90+ (myo)fibroblasts supports tumor-promoting inflammation in colorectal cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 4924. doi:10.1158/1538-7445.AM2017-4924