The Pancreatic Cancer Microbiome Promotes Oncogenesis by Induction of Innate and Adaptive Immune Suppression

Modulating the microbiome to improve therapeutic response in cancer

Although novel therapies, including immunotherapy, have dramatically improved outcomes for many patients with cancer, overall outcomes are heterogeneous and existing biomarkers do not reliably predict response. To date, predictors of response to cancer therapy have largely focused on tumour-intrinsic features; however, there is growing evidence that other host factors (eg, host genomics and the microbiome) can substantially affect therapeutic response. The microbiome, which refers to microbiota within a host and their collective genomes, is becoming increasingly recognised for its influence on host immunity, as well as therapeutic responses to cancer treatment. Importantly, microbiota can be modified via several different strategies, affording new angles in cancer treatment to improve outcomes. In this Review, we examine the evidence on the role of the microbiome in cancer and therapeutic response, factors that influence and shape host microbiota, strategies to modulate the microbiome, and present key unanswered questions to be addressed in ongoing and future research.

The Microbiomes of Pancreatic and Duodenum Tissue Overlap and Are Highly Subject Specific but Differ between Pancreatic Cancer and Noncancer Subjects

BACKGROUND

In mice, bacteria from the mouth can translocate to the pancreas and impact pancreatic cancer progression. In humans, oral bacteria associated with periodontal disease have been linked to pancreatic cancer risk. It is not known if DNA bacterial profiles in the pancreas and duodenum are similar within individuals.

METHODS

Tissue samples were obtained from 50 subjects with pancreatic cancer or other conditions requiring foregut surgery at the Rhode Island Hospital (RIH), and from 34 organs obtained from the National Disease Research Interchange. 16S rRNA gene sequencing was performed on 189 tissue samples (pancreatic duct, duodenum, pancreas), 57 swabs (bile duct, jejunum, stomach), and 12 stool samples.

RESULTS

Pancreatic tissue samples from both sources (RIH and National Disease Research Interchange) had diverse bacterial DNA, including taxa typically identified in the oral cavity. Bacterial DNA across different sites in the pancreas and duodenum were highly subject specific in both cancer and noncancer subjects. Presence of genus Lactobacillus was significantly higher in noncancer subjects compared with cancer subjects and the relative abundance of Fusobacterium spp., previously associated with colorectal cancer, was higher in cancer subjects compared with noncancer subjects.

CONCLUSIONS

Bacterial DNA profiles in the pancreas were similar to those in the duodenum tissue of the same subjects, regardless of disease state, suggesting that bacteria may be migrating from the gut into the pancreas. Whether bacteria play a causal role in human pancreatic cancer needs to be further examined.

IMPACT

Identifying bacterial taxa that differ in cancer patients can provide new leads on etiologically relevant bacteria.

Tongue coating microbiome data distinguish patients with pancreatic head cancer from healthy controls

Background: The microbiota plays a critical role in the process of human carcinogenesis. Pancreatic head carcinoma (PHC)-associated tongue coating microbiome dysbiosis has not yet been clearly defined.Objective: Our aim is to reveal the bacterial composition shifts in the microbiota of the tongue coat of PHC patients.Design: The tongue coating microbiota was analyzed in 30 PHC patients and 25 healthy controls using 16S rRNA gene sequencing technology.Results: The microbiome diversity of the tongue coat in PHC patients was significantly increased, as shown by the Shannon, Simpson, inverse Simpson, Obs and incidence-based coverage estimators. Principal component analysis revealed that PHC patients were colonized by remarkably different tongue coating microbiota than healthy controls and liver cancer patients. Linear discriminant analysis effect size revealed that Leptotrichia, Fusobacterium,Rothia, Actinomyces, Corynebacterium, Atopobium, Peptostreptococcus, Catonella, Oribacterium, Filifactor, Campylobacter, Moraxella and Tannerella were overrepresented in the tongue coating of PHC patients, and Haemophilus, Porphyromonas and Paraprevotella were enriched in the tongue coating microbiota of healthy controls. Strikingly, Haemophilus, Porphyromonas, Leptotrichia and Fusobacterium could distinguish PHC patients from healthy subjects, and Streptococcus and SR1 could distinguish PHC patients from liver cancer patients. Conclusions: These findings identified the microbiota dysbiosis of the tongue coat in PHC patients, and provide insight into the association between the human microbiome and pancreatic cancer.

Alteration in gut microbiota associated with hepatitis B and non-hepatitis virus related hepatocellular carcinoma

BACKGROUND

The onset of hepatocellular carcinoma (HCC) ranked fifth malignancies all over the world. Increasing evidences showed that the distribution of HCC was related to the incidence of chronic hepatitis B virus (HBV) infection and other factors, such as alcoholism, aflatoxin B1 ingestion and obesity. Recent studies demonstrated that gut dysbiosis plays an important role in liver diseases. However, the researches on gut microbiota of HBV and non-HBV non-HCV related HCC have not been reported. In this study, we investigated the differences between the gut microbiota of HBV related HCC (B-HCC) and non-HBV non-HCV related HCC (NBNC-HCC), finally found some potential bacteria, linking different pathological mechanism of both types of HCCs.

RESULTS

We carried out 16S rRNA analyses in a cohort of 33 healthy controls, 35 individuals with HBV related HCC (B-HCC) and 22 individuals with non-HBV non-HCV (NBNC) related HCC (NBNC-HCC). We found that the species richness of fecal microbiota of B-HCC patients was much higher than other two groups. Interestingly, the feces of NBNC-HCC patients harbored more potential pro-inflammatory bacteria (Escherichia-Shigella, Enterococcus) and reduced levels of Faecalibacterium, Ruminococcus, Ruminoclostridium which results in decrease potential of anti-inflammatory short-chain fatty acids. The feces of NBNC-HCC patients had relatively fewer abundance of multiple biological pathways related to amino acid and glucose metabolism, but high level of transport and secretion in some types. However, the B-HCC patients had opposite results of bacterial composition and associated multiple biological pathways versus NBNC-HCC patients. Meanwhile, we found that aberrant network of gut microbiota occurred differently in B-HCC and NBNC-HCC patients.

CONCLUSIONS

Our study indicated that B-HCC and NBNC-HCC patients showed differential abundance of bacteria involved in different functions or biological pathways. We suggested the modification of specific gut microbiota may provide the therapeutic benefit for B-HCC and NBNC-HCC.

The Gut Microbiome in Pancreatic Disease

The gut microbiome increasingly is recognized for its role in human health and disease. Initial evidence has indicated that gut microbial dysbiosis is associated with several pancreatic diseases. Although it is not known if these associations are causative, gut dysbiosis is hypothesized to mediate chronic proinflammatory changes in the pancreas. Further mechanistic and epidemiologic studies of the microbiome are needed. Ultimately, targeted modulation of the microbiota could have therapeutic value.

Human Microbiota and Personalized Cancer Treatments: Role of Commensal Microbes in Treatment Outcomes for Cancer Patients

The human gut microbiota consists of about 3.8 × 10¹³ microorganisms that play an essential role in health, metabolism, and immunomodulation. These gut microbes alter therapeutic response and toxicity to cancer therapies including cytotoxic chemotherapy, radiation therapy, kinase inhibitors, and immunotherapy agents. The gut microbiota generates short-chain fatty acids that are significant regulators of histone post-translational modifications that fundamentally regulate gene expression, linking the microbiota to cellular metabolism and transcriptional regulation. The short-chain fatty acids not only act locally but can be taken up in the blood stream to inhibit the activity of histone deacetylases, regulate gene expression in distant organs as well as the effector function of CD8+ T cells. Cancer and the treatments for it negatively impact the microbiome often resulting in dysbiosis. This can diminish a patient's response to treatment as well as increase systemic toxicities from these therapies. In addition to the gut microbiota, microbes have been detected in tumors that can modulate chemotherapeutic drug response and can result in immune suppression. The gut microbiota and tumor-associated bacteria may be a significant contributor to the interindividual differences and heterogeneous responses to cancer therapies and drug tolerability and strategies that support and/or manipulate the microbiota to improve therapeutic outcome is an emerging area for personalized cancer treatment.

Fecal microbiota transplantation in cancer management: Current status and perspectives

The human gut is home to a large and diverse microbial community, comprising about 1,000 bacterial species. The gut microbiota exists in a symbiotic relationship with its host, playing a decisive role in the host's nutrition, immunity and metabolism. Accumulating studies have revealed the associations between gut dysbiosis or some special bacteria and various cancers. Emerging data suggest that gut microbiota can modulate the effectiveness of cancer therapies, especially immunotherapy. Manipulating the microbial populations with therapeutic intent has become a hot topic of cancer research, and the most dramatic manipulation of gut microbiota refers to fecal microbiota transplantation (FMT) from healthy individuals to patients. FMT has demonstrated remarkable clinical efficacy against Clostridium difficile infection (CDI) and it is highly recommended for the treatment of recurrent or refractory CDI. Lately, interest is growing in the therapeutic potential of FMT for other diseases, including cancers. We briefly reviewed the current researches about gut microbiota and its link to cancer, and then summarized the recent preclinical and clinical evidence to indicate the potential of FMT in cancer management as well as cancer‐treatment associated complications. We also presented the rationale of FMT for cancer management such as reconstruction of intestinal microbiota, amelioration of bile acid metabolism, and modulation of immunotherapy efficacy. This article would help to better understand this new therapeutic approach for cancer patients by targeting gut microbiota.

Systemic treatment of pancreatic cancer revisited

Pancreatic cancer is considered to be one of the most aggressive cancers. For unknown reasons, the incidence of pancreatic cancer is slowly rising and so too are mortality rates. Over 75% of patients are diagnosed with locally advanced disease or with metastases; and more than 95% of patients have metastases at diagnosis or will develop metastases during their follow-up. Despite recent improvements in the therapy of pancreatic cancer, initially with demonstration of the activity of the FOLFIRINOX regimen and subsequently the approval of nab-paclitaxel in combination with gemcitabine, prognosis remains poor and the 5-year survival rate is less than 5%. To date, neither personalized medicine nor immunotherapy, the 2 recent revolutions of cancer treatment, have delivered major positive results in the treatment of pancreatic cancer; and it is especially clear that immune checkpoint inhibitors will not become a major tool in the treatment of pancreatic cancer. There are many ongoing studies, including those exploring combinations of chemotherapy with immunotherapy. Vaccines or T cells modified with a chimeric antigen receptor (CAR-T cells) could also play a role in the treatment of cancer in the future. The aim of this review is to discuss recent improvements in standard of care, major obstacles to overcome, recent results of new treatment combinations, and the most interesting innovative approaches.

Pancreatic cancer associated with obesity and diabetes: an alternative approach for its targeting

BACKGROUND

Pancreatic cancer (PC) is among foremost causes of cancer related deaths worldwide due to generic symptoms, lack of effective screening strategies and resistance to chemo- and radiotherapies. The risk factors associated with PC include several metabolic disorders such as obesity, insulin resistance and type 2 diabetes mellitus (T2DM). Studies have shown that obesity and T2DM are associated with PC pathogenesis; however, their role in PC initiation and development remains obscure.

MAIN BODY

Several biochemical and physiological factors associated with obesity and/or T2DM including adipokines, inflammatory mediators, and altered microbiome are involved in PC progression and metastasis albeit by different molecular mechanisms. Deep understanding of these factors and causal relationship between factors and altered signaling pathways will facilitate deconvolution of disease complexity as well as lead to development of novel therapies. In the present review, we focuses on the interplay between adipocytokines, gut microbiota, adrenomedullin, hyaluronan, vanin and matrix metalloproteinase affected by metabolic alteration and pancreatic tumor progression.

CONCLUSIONS

Metabolic diseases, such as obesity and T2DM, contribute PC development through altered metabolic pathways. Delineating key players in oncogenic development in pancreas due to metabolic disorder could be a beneficial strategy to combat cancers associated with metabolic diseases in particular, PC.

Myalgic Encephalomyelitis/Chronic Fatigue Syndrome in the Era of the Human Microbiome: Persistent Pathogens Drive Chronic Symptoms by Interfering With Host Metabolism, Gene Expression, and Immunity

The illness ME/CFS has been repeatedly tied to infectious agents such as Epstein Barr Virus. Expanding research on the human microbiome now allows ME/CFS-associated pathogens to be studied as interacting members of human microbiome communities. Humans harbor these vast ecosystems of bacteria, viruses and fungi in nearly all tissue and blood. Most well-studied inflammatory conditions are tied to dysbiosis or imbalance of the human microbiome. While gut microbiome dysbiosis has been identified in ME/CFS, microbes and viruses outside the gut can also contribute to the illness. Pathobionts, and their associated proteins/metabolites, often control human metabolism and gene expression in a manner that pushes the body toward a state of illness. Intracellular pathogens, including many associated with ME/CFS, drive microbiome dysbiosis by directly interfering with human transcription, translation, and DNA repair processes. Molecular mimicry between host and pathogen proteins/metabolites further complicates this interference. Other human pathogens disable mitochondria or dysregulate host nervous system signaling. Antibodies and/or clonal T cells identified in patients with ME/CFS are likely activated in response to these persistent microbiome pathogens. Different human pathogens have evolved similar survival mechanisms to disable the host immune response and host metabolic pathways. The metabolic dysfunction driven by these organisms can result in similar clusters of inflammatory symptoms. ME/CFS may be driven by this pathogen-induced dysfunction, with the nature of dysbiosis and symptom presentation varying based on a patient's unique infectious and environmental history. Under such conditions, patients would benefit from treatments that support the human immune system in an effort to reverse the infectious disease process.

The microbiome of pancreatic cancer: from molecular diagnostics to new therapeutic approaches to overcome chemoresistance caused by metabolic inactivation of gemcitabine

Introduction: Pancreatic cancer is a complex disease, with an extremely poor response to chemotherapy. Emerging evidence indicates that the tumor microenvironment (TME) might play an important role in mediating chemoresistance. Areas covered: The evaluated study by Geller and collaborators describes several bacterial species within pancreatic tumor tissues and TME and investigated their roles in gemcitabine chemoresistance. Intratumor bacteria express the enzyme cytidine deaminase (CDD), whose long form (CDDL) was shown to metabolize gemcitabine into its inactive metabolite. CDDL is mostly expressed by Gammaproteobacteria and this was among the most common species in pancreatic cancer tissues. Interestingly, mouse models of colorectal cancer injected with bacterial CDDL displayed a reduced response to gemcitabine, but this resistance was neutralized by the antibiotic ciprofloxacin. Expert Commentary: The increased knowledge on the microbiome in pancreatic tissues, as well as its role in chemoresistance, will provide innovative prognostic and therapeutic strategies.

Combination systemic therapies with immune checkpoint inhibitors in pancreatic cancer: overcoming resistance to single-agent checkpoint blockade

Immune checkpoint inhibitors have demonstrated broad single-agent antitumor activity and a favorable safety profile that render them attractive agents to combine with other systemic anticancer therapies. Pancreatic cancer has been fairly resistant to monotherapy blockade of programmed cell death protein 1 receptor, programmed death ligand 1, and cytotoxic T-lymphocyte associated protein 4. However, there is a growing body of preclinical evidence to support the rational combination of checkpoint inhibitors and various systemic therapies in pancreatic cancer. Furthermore, early clinical evidence has begun to support the feasibility and efficacy of checkpoint inhibitor-based combination therapy in advanced pancreatic cancer. Despite accumulating preclinical and clinical data, there remains several questions as to the optimal dosing and timing of administration of respective agents, toxicity of combination strategies, and mechanisms by which immune resistance to single-agent checkpoint blockade are overcome. Further development of biomarkers is also important in the advancement of combination systemic therapies incorporating checkpoint blockade in pancreatic cancer. Results from an impressive number of ongoing prospective clinical trials are eagerly anticipated and will seek to validate the viability of combination immuno-oncology strategies in pancreatic cancer.

The hallmarks of successful anticancer immunotherapy

Immunotherapy is revolutionizing the clinical management of multiple tumors. However, only a fraction of patients with cancer responds to immunotherapy, and currently available immunotherapeutic agents are expensive and generally associated with considerable toxicity, calling for the identification of robust predictive biomarkers. The overall genomic configuration of malignant cells, potentially favoring the emergence of immunogenic tumor neoantigens, as well as specific mutations that compromise the ability of the immune system to recognize or eradicate the disease have been associated with differential sensitivity to immunotherapy in preclinical and clinical settings. Along similar lines, the type, density, localization, and functional orientation of the immune infiltrate have a prominent impact on anticancer immunity, as do features of the tumor microenvironment linked to the vasculature and stroma, and systemic factors including the composition of the gut microbiota. On the basis of these considerations, we outline the hallmarks of successful anticancer immunotherapy.

Fusobacterium nucleatum in Colorectal Cancer Relates to Immune Response Differentially by Tumor Microsatellite Instability Status

The presence of Fusobacterium nucleatum (F. nucleatum) in colorectal carcinoma tissue has been associated with microsatellite instability (MSI), lower-level T-cell infiltrates, and poor clinical outcomes. Considering differences in the tumor-immune microenvironment between MSI-high and non-MSI-high carcinomas, we hypothesized that the association of F. nucleatum with immune response might differ by tumor MSI status. Using samples from 1,041 rectal and colon cancer patients within the Nurses' Health Study and Health Professionals Follow-up Study, we measured F. nucleatum DNA in tumor tissue by a quantitative polymerase chain reaction assay. Multivariable logistic regression models were used to examine the association between F. nucleatum status and histopathologic lymphocytic reactions or density of CD3⁺ cells, CD8⁺ cells, CD45RO (PTPRC)⁺ cells, or FOXP3⁺ cells in strata of tumor MSI status. We adjusted for potential confounders, including CpG island methylator phenotype; LINE-1 methylation; and KRAS, BRAF, and PIK3CA mutations. The association of F. nucleatum with tumor-infiltrating lymphocytes (TIL) and intratumoral periglandular reaction differed by tumor MSI status (P _interaction = 0.002). The presence of F. nucleatum was negatively associated with TIL in MSI-high tumors [multivariable odds ratio (OR), 0.45; 95% confidence interval (CI), 0.22-0.92], but positively associated with TIL in non-MSI-high tumors (multivariable OR 1.91; 95% CI, 1.12-3.25). No significant differential association was observed for peritumoral lymphocytic reaction, Crohn-like lymphoid reaction, or T-cell densities. In conclusion, the association of F. nucleatum with immune response to colorectal carcinoma differs by tumor MSI status, suggesting that F. nucleatum and MSI status interact to affect antitumor immune reactions. Cancer Immunol Res; 6(11); 1327-36. ©2018 AACR See related Spotlight on p. 1290.

Targeting the IDO1 pathway in cancer: from bench to bedside

Indoleamine 2, 3-dioxygenases (IDO1 and IDO2) and tryptophan 2, 3-dioxygenase (TDO) are tryptophan catabolic enzymes that catalyze the conversion of tryptophan into kynurenine. The depletion of tryptophan and the increase in kynurenine exert important immunosuppressive functions by activating T regulatory cells and myeloid-derived suppressor cells, suppressing the functions of effector T and natural killer cells, and promoting neovascularization of solid tumors. Targeting IDO1 represents a therapeutic opportunity in cancer immunotherapy beyond checkpoint blockade or adoptive transfer of chimeric antigen receptor T cells. In this review, we discuss the function of the IDO1 pathway in tumor progression and immune surveillance. We highlight recent preclinical and clinical progress in targeting the IDO1 pathway in cancer therapeutics, including peptide vaccines, expression inhibitors, enzymatic inhibitors, and effector inhibitors.

Intestinal microbiota enhances pancreatic carcinogenesis in preclinical models

Pancreatic ductal adenocarcinoma (PDAC) is the third leading cause of cancer death in the United States yet data are scant regarding host factors influencing pancreatic carcinogenesis. Increasing evidence support the role of the host microbiota in carcinogenesis but its role in PDAC is not well established. Herein, we report that antibiotic-mediated microbial depletion of KrasG12D/PTENlox/+ mice showed a decreased proportion of poorly differentiated tumors compared to microbiota-intact KrasG12D/PTENlox/+ mice. Subsequent 16S rRNA PCR showed that ~50% of KrasG12D/PTENlox/+ mice with PDAC harbored intrapancreatic bacteria. To determine if a similar observation in humans correlates with presence of PDAC, benign and malignant human pancreatic surgical specimens demonstrated a microbiota by 16S bacterial sequencing and culture confirmation. However, the microbial composition did not differentiate PDAC from non-PDAC tissue. Furthermore, murine pancreas did not naturally acquire a pancreatic microbiota, as germ-free mice transferred to specific pathogen-free housing failed to acquire intrapancreatic bacteria over time, which was not augmented by a murine model of colitis. Finally, antibiotic-mediated microbial depletion of Nod-SCID mice, compared to microbiota-intact, showed increased time to PDAC xenograft formation, smaller tumors, and attenuated growth. Interestingly, both xenograft cohorts were devoid of intratumoral bacteria by 16S rRNA PCR, suggesting that intrapancreatic/intratumoral microbiota is not the sole driver of PDAC acceleration. Xenografts from microbiota-intact mice demonstrated innate immune suppression by immunohistochemistry and differential regulation of oncogenic pathways as determined by RNA sequencing. Our work supports a long-distance role of the intestinal microbiota on PDAC progression and opens new research avenues regarding pancreatic carcinogenesis.

The Microbiome and Pancreatic Cancer: An Evidence-based Association?

Many risk factors for pancreatic cancer are related with microbiome alteration. In the past few years, the human microbiome and its relation with the immune system have been linked with carcinogenesis of different organs distant from the gut, including the pancreas. Patterns of oral microbiome associated with periodontitis are associated with an increased risk of pancreatic cancer, possibly because of the increased systemic inflammatory response, or to the capacity of some specific bacteria to alter the host immune response, making it more favorable to cancer cells. Helicobacter pylori infection when affecting the gastric body mucosa with subsequent hypochlorhydria also seems associated with an increased risk of pancreatic cancer. The composition of the intestinal microbiome is different in animal models and in humans with pancreatic cancer who have a distinct microbiome population compared with controls. Some specific bacteria can migrate from the intestine to the pancreas, and their ablation restores the immune system activity through its reprogramming with a switch toward a Th1 response and displays a protective effect toward tumor growth. More research in this area might lead to progress in terms of pancreatic cancer prevention and treatment, possibly in association with immunotherapy.