Cyclooxygenases and Prostaglandins in Tumor Immunology and Microenvironment of Gastrointestinal Cancer.

Chronic inflammation is a known risk factor for gastrointestinal cancer. The evidence that nonsteroidal anti-inflammatory drugs suppress the incidence, growth, and metastasis of gastrointestinal cancer supports the concept that a nonsteroidal anti-inflammatory drug target, cyclooxygenase, and its downstream bioactive lipid products may provide one of the links between inflammation and cancer. Preclinical studies have demonstrated that the cyclooxygenase-2-prostaglandin E2 pathway can promote gastrointestinal cancer development. Although the role of this pathway in cancer has been investigated extensively for 2 decades, only recent studies have described its effects on host defenses against transformed epithelial cells. Overcoming tumor-immune evasion remains one of the major challenges in cancer immunotherapy. This review summarizes the impacts of the cyclooxygenase-2-prostaglandin E2 pathway on gastrointestinal cancer development. Our focus was to highlight recent advances in our understanding of how this pathway induces tumor immune evasion.

Prostaglandin E2 Induces miR675-5p to Promote Colorectal Tumor Metastasis via Modulation of p53 Expression.

BACKGROUND & AIMS: Prostaglandin E2 (PGE2) promotes colorectal tumor formation and progression by unknown mechanisms. We sought to identify microRNAs (miRNAs) that might mediate the effects of PGE2 on colorectal cancer (CRC) development. METHODS: We incubated LS174T colorectal cancer cells with PGE2 or without (control) and used miRNA-sequencing technology to compare expression patterns of miRNAs. We knocked down levels of specific miRNAs or proteins in cells using small interfering RNAs or genome editing. Cells were analyzed by immunoblot, quantitative polymerase chain reaction, chromosome immunoprecipitation, cell invasion, and luciferase reporter assays; we measured gene expression, binding activity, cell migration and invasion, and transcriptional activity of transcription factors. NOD-scidIL-2Rg-/- mice were given injections of LS174T cells, and growth of primary tumors and numbers of liver and lung metastases were quantified and analyzed by histology. We used public databases to identify correlations in gene expression pattern with patient outcomes. RESULTS: We identified miRNA 675-5p (miR675-5p) as the miRNA most highly up-regulated by incubation of colorectal cancer cells with PGE2. PGE2 increased expression of miR675-5p by activating expression of Myc, via activation of protein kinase B, also known as (AKT), nuclear factor κB, and ß-catenin. PGE2 increased the invasive activities of cultured CRC cells. LS174T cells incubated with PGE2 formed more liver and lung metastases in mice than control LS174T cells. We identified a 3' untranslated region in the TP53 messenger RNA that bound miR675-5p; binding resulted in loss of the p53 protein. Expression of miR675-5p or its precursor RNA, H19, correlated with expression of cyclooxygenase-1 and cyclooxygenase-2 and shorter survival times of patients with CRC. CONCLUSIONS: We found that treatment of mice with PGE2 increased CRC cells invasive activity and ability to form liver and lung metastases. PGE2 down-regulates expression of p53 by increasing expression of miR675-5p, which binds to and prevents translation of TP53 messenger RNA. These findings provide insight into the mechanisms by which PGE2 promotes tumor development and progression. Strategies to target PGE2 might be developed for treatment of CRC.

Peroxisome proliferator-activated receptor δ promotes colonic inflammation and tumor growth.

Although epidemiologic and experimental evidence strongly implicates chronic inflammation and dietary fats as risk factors for cancer, the mechanisms underlying their contribution to carcinogenesis are poorly understood. Here we present genetic evidence demonstrating that deletion of peroxisome proliferator-activated receptor δ (PPARδ) attenuates colonic inflammation and colitis-associated adenoma formation/growth. Importantly, PPARδ is required for dextran sodium sulfate induction of proinflammatory mediators, including chemokines, cytokines, COX-2, and prostaglandin E2 (PGE2), in vivo. We further show that activation of PPARδ induces COX-2 expression in colonic epithelial cells. COX-2-derived PGE2 stimulates macrophages to produce proinflammatory chemokines and cytokines that are responsible for recruitment of leukocytes from the circulation to local sites of inflammation. Our results suggest that PPARδ promotes colonic inflammation and colitis-associated tumor growth via the COX-2-derived PGE2 signaling axis that mediates cross-talk between tumor epithelial cells and macrophages.

Prostaglandin E2 Promotes Colorectal Cancer Stem Cell Expansion and Metastasis in Mice.

BACKGROUND & AIMS: Inflammation may contribute to the formation, maintenance, and expansion of cancer stem cells (CSCs), which have the capacity for self-renewal, differentiation, and resistance to cytotoxic agents. We investigated the effects of the inflammatory mediator prostaglandin E2 (PGE2) on colorectal CSC development and metastasis in mice and the correlation between levels of PGE2 and CSC markers in human colorectal cancer (CRC) specimens. METHODS: Colorectal carcinoma specimens and matched normal tissues were collected from patients at the Mayo Clinic (Scottsdale, AZ) and analyzed by mass spectrometry and quantitative polymerase chain reaction. Human primary CRC cells and mouse tumor cells were isolated using microbeads or flow cytometry and analyzed for sphere-formation and by flow cytometry assays. LS-174T cells were sorted by flow cytometry (for CD133(+)CD44(+) and CD133(-)CD44(-) cells) and also used in these assays. NOD-scidIL-2Rγ(-/-) (NSG) mice were given cecal or subcutaneous injections of LS-174T or human primary CRC cells. Apc(Min/+) mice and NSG mice with orthotopic cecal tumors were given vehicle (controls), PGE2, celecoxib, and/or Ono-AE3-208. PGE2 downstream signaling pathways were knocked down with small hairpin RNAs, expressed from lentiviral vectors in LS-174T cells, or blocked with inhibitors in human primary CRC cells. RESULTS: Levels of PGE2 correlated with colonic CSC markers (CD133, CD44, LRG5, and SOX2 messenger RNAs) in human colorectal carcinoma samples. Administration of PGE2 to Apc(Min/+) mice increased tumor stem cells and tumor burden, compared with controls. NSG mice given PGE2 had increased numbers of cecal CSCs and liver metastases compared with controls after intracecal injection of LS-174T or human primary CRC cells. Alternatively, celecoxib, an inhibitor of prostaglandin-endoperoxide synthase 2, reduced polyp numbers in Apc(Min/+) mice, liver metastasis in NSG mice with orthotopic tumors, and numbers of CSCs in Apc(Min/+) and NSG mice. Inhibitors or knockdown of PGE2 receptor 4 (EP4), phosphoinositide 3-kinase (PI3K) p85α, extracellular signal-regulated kinase 1 (ERK1), or nuclear factor (NF)-κB reduced PGE2-induced sphere formation and expansion of LS-174T and/or human primary CRC cells. Knockdown of ERK1 or PI3K p85α also attenuated PGE2-induced activation of NF-κB in LS-174T cells. An EP4 antagonist reduced the ability of PGE2 to induce CSC expansion in orthotopic tumors and to accelerate the formation of liver metastases. Knockdown experiments showed that NF-κB was required for PGE2 induction of CSCs and metastasis in mice. CONCLUSIONS: PGE2 induces CSC expansion by activating NF-κB, via EP4-PI3K and EP4-mitogen-activated protein kinase signaling, and promotes the formation of liver metastases in mice. The PGE2 signaling pathway therefore might be targeted therapeutically to slow CSC expansion and colorectal cancer progression.

Immunosuppression associated with chronic inflammation in the tumor microenvironment.

Chronic inflammation contributes to cancer development via multiple mechanisms. One potential mechanism is that chronic inflammation can generate an immunosuppressive microenvironment that allows advantages for tumor formation and progression. The immunosuppressive environment in certain chronic inflammatory diseases and solid cancers is characterized by accumulation of proinflammatory mediators, infiltration of immune suppressor cells and activation of immune checkpoint pathways in effector T cells. In this review, we highlight recent advances in our understanding of how immunosuppression contributes to cancer and how proinflammatory mediators induce the immunosuppressive microenvironment via induction of immunosuppressive cells and activation of immune checkpoint pathways.

The role of anti-inflammatory drugs in colorectal cancer.

A large body of evidence indicates that genetic mutations, epigenetic changes, chronic inflammation, diet, and lifestyle are key risk factors for colorectal cancer (CRC). Prevention of CRC has long been considered a plausible approach for the population and individuals at high risk for developing this disease. A significant effort has been made in the development of novel drugs for both prevention and treatment over the past two decades. This review highlights recent advances in our understanding of the role of nonsteroidal anti-inflammatory drugs in CRC prevention and adjuvant treatment. Moreover, we focus on the molecular mechanisms underlying the antitumor effects of these drugs in CRC. The knowledge of how anti-inflammatory agents inhibit cancer formation and progression may provide a rationale for the development of more effective chemopreventive and chemotherapeutic agents with less toxicity.

The Jeremiah Metzger Lecture: Inflammation, Immune Modulators, and Chronic Disease.

Chronic inflammation is a risk factor for many different diseases. It is clear that inflammation is associated with degenerative brain diseases, obesity, metabolic syndrome, cardiovascular disease, diabetes, and cancer. Throughout the past 100 years, changes in the causes of death in the US have been dramatic. The most recent data indicate that cardiovascular disease and cancer are now responsible for 63% of mortality in the US population. Although progression of these diseases is related to diet, lifestyle, and genetic factors, a common but often unrecognized link is the presence of underlying chronic inflammation. As of 2014, 83.6 million people were living with some form of cardiovascular disease, 29.1 million people have been diagnosed with diabetes, 14 million people carried the diagnosis of cancer, and 5.2 million people were living with Alzheimer disease. These diseases are a huge burden on our health care system and all have been associated with chronic inflammation.

CG100649, a novel COX-2 inhibitor, inhibits colorectal adenoma and carcinoma growth in mouse models.

Nonsteroidal anti-inflammatory drugs (NSAIDs) and selective cyclooxygenase-2 (COX-2) inhibitors (COXIBs) can reduce the risk of developing colorectal cancer (CRC) and are being considered for use as adjuvant therapy for treatment of CRC patients. However, long-term use of most NSAIDs, except aspirin, increases cardiovascular risk, hampering use of these drugs in CRC prevention and possibly for treatment. CG100649 is a new member of the COXIB family, which is proposed to inhibit both COX-2 and carbonic anhydrase-I/-II (CA-I/-II) activity. Using mouse models, we show here that CG100649 inhibits premalignant and malignant colorectal lesions in mouse models, partly through inhibiting tumor cell proliferation. These pre-clinical findings suggest a need for further exploration of CG100649 for CRC prevention and treatment. The long-term safety profile of CG100649, particularly regarding its effect on cardiovascular risk, is yet to be determined.

Connecting COX-2 and Wnt in cancer.

Both the cyclooxygenase-2 (COX-2) and Wnt signaling cascades are active in the majority of colorectal cancers. Nevertheless, a direct link between these two key pathways has remained elusive. Recent reports show that one of the bioactive products of COX-2, prostaglandin E2, activates components of the canonical Wnt signaling system. The findings reviewed below reveal important crosstalk between these pathways, which may provide opportunities for the development of new drugs for treatment and/or prevention of colorectal cancer.

Role of inflammation and inflammatory mediators in colorectal cancer.

Chronic inflammation is a risk factor for several different cancers including colorectal cancer (CRC). However, the mechanisms underlying the contribution of inflammation to cancer remain elusive. Pro-inflammatory mediators such as cyclooxygenase 2 (COX-2) and prostaglandin E2 (PGE2) contribute to cancer progression. Here, we show that COX-2 is an immediate-early response gene induced by growth factors and pro-inflammatory cytokines and its levels are elevated in human CRCs. Furthermore, we show that COX-2-derived PGE2 promotes colonic tumor growth via silencing certain tumor suppressors and DNA repair genes by DNA methylation in colonic epithelial tumor cells. We also report that C-X-C motif chemokine receptor 2 accelerates colonic inflammation and colitis-associated tumorigenesis by mediating myeloid-derived suppressor cell recruitment to the tumor microenvironment. These findings not only support a rationale to target these pro-inflammatory pathways for cancer prevention and treatment but also provide support for developing new therapeutic approaches to subvert chronic inflammation- and tumor-induced immunosuppression.

Prostaglandin Gbetagamma signaling stimulates gastrulation movements by limiting cell adhesion through Snai1a stabilization.

Gastrulation movements form the germ layers and shape them into the vertebrate body. Gastrulation entails a variety of cell behaviors, including directed cell migration and cell delamination, which are also involved in other physiological and pathological processes, such as cancer metastasis. Decreased Prostaglandin E(2) (PGE(2)) synthesis due to interference with the Cyclooxygenase (Cox) and Prostaglandin E synthase (Ptges) enzymes halts gastrulation and limits cancer cell invasiveness, but how PGE(2) regulates cell motility remains unclear. Here we show that PGE(2)-deficient zebrafish embryos, impaired in the epiboly, internalization, convergence and extension gastrulation movements, exhibit markedly increased cell-cell adhesion, which contributes to defective cell movements in the gastrula. Our analyses reveal that PGE(2) promotes cell protrusive activity and limits cell adhesion by modulating E-cadherin transcript and protein, in part through stabilization of the Snai1a (also known as Snail1) transcriptional repressor, an evolutionarily conserved regulator of cell delamination and directed migration. We delineate a pathway whereby PGE(2) potentiates interaction between the receptor-coupled G protein betagamma subunits and Gsk3beta to inhibit proteasomal degradation of Snai1a. However, overexpression of beta-catenin cannot stabilize Snai1a in PGE(2)-deficient gastrulae. Thus, the Gsk3beta-mediated and beta-catenin-independent inhibition of cell adhesion by Prostaglandins provides an additional mechanism for the functional interactions between the PGE(2) and Wnt signaling pathways during development and disease. We propose that ubiquitously expressed PGE(2) synthesizing enzymes, by promoting the stability of Snai1a, enable the precise and rapid regulation of cell adhesion that is required for the dynamic cell behaviors that drive various gastrulation movements.

Dual Blockade of EP2 and EP4 Signaling is Required for Optimal Immune Activation and Antitumor Activity Against Prostaglandin-Expressing Tumors.

While the role of prostaglandin E2 (PGE2) in promoting malignant progression is well established, how to optimally block the activity of PGE2 signaling remains to be demonstrated. Clinical trials with prostaglandin pathway targeted agents have shown activity but without sufficient significance or dose-limiting toxicities that have prevented approval. PGE2 signals through four receptors (EP1-4) to modulate tumor progression. EP2 and EP4 signaling exacerbates tumor pathology and is immunosuppressive through potentiating cAMP production. EP1 and EP3 signaling has the opposite effect through increasing IP3 and decreasing cAMP. Using available small-molecule antagonists of single EP receptors, the cyclooxygenase-2 (COX-2) inhibitor celecoxib, or a novel dual EP2/EP4 antagonist generated in this investigation, we tested which approach to block PGE2 signaling optimally restored immunologic activity in mouse and human immune cells and antitumor activity in syngeneic, spontaneous, and xenograft tumor models. We found that dual antagonism of EP2 and EP4 together significantly enhanced the activation of PGE2-suppressed mouse and human monocytes and CD8+ T cells in vitro as compared with single EP antagonists. CD8+ T-cell activation was dampened by single EP1 and EP3 antagonists. Dual EP2/EP4 PGE2 receptor antagonists increased tumor microenvironment lymphocyte infiltration and significantly reduced disease burden in multiple tumor models, including in the adenomatous polyposis coli (APC)min+/- spontaneous colorectal tumor model, compared with celecoxib. These results support a hypothesis that redundancy of EP2 and EP4 receptor signaling necessitates a therapeutic strategy of dual blockade of EP2 and EP4. Here we describe TPST-1495, a first-in-class orally available small-molecule dual EP2/EP4 antagonist. Significance: Prostaglandin (PGE2) drives tumor progression but the pathway has not been effectively drugged. We demonstrate significantly enhanced immunologic potency and antitumor activity through blockade of EP2 and EP4 PGE2 receptor signaling together with a single molecule.

Nuclear orphan receptor NR4A2 modulates fatty acid oxidation pathways in colorectal cancer.

Although cancer cells have traditionally been thought to rely on the glycolytic pathway to generate ATP, recent studies suggest that cancer cells can shift to the fatty acid oxidation pathway as an alternative energy source. All of the factors that induce and regulate this adaptive shift in metabolism are not known. Cyclooxygenase-2-derived prostaglandin E(2) (PGE(2)) is produced at high levels in colon cancer, and multiple lines of evidence from human-, animal-, and cell line-based studies indicate that PGE(2) plays a pro-oncogenic role in colorectal cancer progression. We have shown previously that exposure of colon cancer cells to PGE(2) promotes cell survival, in part by inducing the expression of the nuclear orphan receptor NR4A2. Here, we report that PGE(2)-induced NR4A2 increased fatty acid oxidation by inducing the expression of multiple proteins in the fatty acid oxidation pathway. NR4A2 was found to bind directly to Nur77-binding response elements located within the regulatory region of these genes. Nur77-binding response element binding also resulted in the recruitment of transcriptional coactivators and induction of gene expression. Collectively, our findings suggest that NR4A2 plays a key role as a transcriptional integration point between the eicosanoid and fatty acid metabolic pathways. Thus, PGE(2) is a potential regulator of the adaptive shift to energy utilization via fatty acid oxidation that has been observed in several types of cancer.

CXCL1 induced by prostaglandin E2 promotes angiogenesis in colorectal cancer.

Chronic inflammation is a well-known risk factor for cancer. Proinflammatory mediators such as prostaglandin E2 (PGE2) promote colorectal tumor growth by stimulating angiogenesis, cell invasion, and cell growth, and inhibiting apoptosis. Molecules that regulate tumor-associated angiogenesis provide promising therapeutic targets for treatment of colorectal cancer (CRC) as indicated by the recent development of the novel anti-angiogenic agent bevacizumab (Avastin). However, use of this drug only prolongs survival by several months, highlighting the importance of finding more effective treatment regimens. We report here that PGE2 induces expression of CXCL1 (growth-regulated oncogene alpha), a pro-angiogenic chemokine, in human CRC cells. More importantly, CXCL1 released from carcinoma cells induces microvascular endothelial cell migration and tube formation in vitro. Furthermore, PGE2 promotes tumor growth in vivo by induction of CXCL1 expression, which results in increased tumor microvessel formation. These results have potential clinical significance because we found that CXCL1 expression correlates with PGE2 levels in human CRCs. Collectively, our findings show for the first time that CXCL1 is regulated by PGE2 and indicate that CXCL1 inhibitors should be evaluated further as potential anti-angiogenic agents for treatment of CRC.

Prostaglandin E(2) promotes colorectal adenoma growth via transactivation of the nuclear peroxisome proliferator-activated receptor delta.

Cyclooxygenase-derived prostaglandin E(2) (PGE(2)) is the predominant prostanoid found in most colorectal cancers (CRC) and is known to promote colon carcinoma growth and invasion. However, the key downstream signaling pathways necessary for PGE(2)-induced intestinal carcinogenesis are unclear. Here we report that PGE(2) indirectly transactivates PPARdelta through PI3K/Akt signaling, which promotes cell survival and intestinal adenoma formation. We also found that PGE(2) treatment of Apc(min) mice dramatically increased intestinal adenoma burden, which was negated in Apc(min) mice lacking PPARdelta. We demonstrate that PPARdelta is a focal point of crosstalk between the prostaglandin and Wnt signaling pathways which results in a shift from cell death to cell survival, leading to increased tumor growth.

Role of Prostaglandin E2 in the Progression of Gastrointestinal Cancer.

Chronic inflammation is a well-established risk factor for several diseases, including cancer. It influences tumor cell biology and the type and density of immune cells in the tumor microenvironment (TME), promoting cancer development. While proinflammatory cytokines and chemokines modulate cancer development, emerging evidence has shown that prostaglandin E2 (PGE2) is a known mediator connecting chronic inflammation to cancerization. This review highlights recent advances in our understanding of how the elevation of PGE2 production promotes gastrointestinal cancer initiation, progression, invasion, metastasis, and recurrence, including modulation of immune checkpoint signaling and the type and density of immune cells in the tumor/tissue microenvironment.

The First Lady Presses for Cancer Screening to Get Back On Track.

The First Lady of the United States, Dr. Jill Biden, visited the Hollings Cancer Center at the Medical University of South Carolina on October 25, 2021. This Commentary remarks on the administration's goal of directing public attention to cancer screening and prevention as part of an overall effort to recover ground lost in the COVID-19 pandemic, particularly in underserved communities.

The COX-2-PGE2 Pathway Promotes Tumor Evasion in Colorectal Adenomas.

The mechanisms underlying the regulation of a checkpoint receptor, PD-1, in tumor-infiltrating immune cells during the development of colorectal cancer are not fully understood. Here we demonstrate that COX-2-derived PGE2, an inflammatory mediator and tumor promoter, induces PD-1 expression by enhancing NFκB's binding to the PD-1 promoter via an EP4-PI3K-Akt signaling pathway in both CD8+ T cells and macrophages. Moreover, PGE2 suppresses CD8+ T-cell proliferation and cytotoxicity against tumor cells and impairs macrophage phagocytosis of cancer cells via an EP4-PI3K-Akt-NFκB-PD-1 signaling pathway. In contrast, inhibiting the COX-2-PGE2-EP4 pathway increases intestinal CD8+ T-cell activation and proliferation and enhances intestinal macrophage phagocytosis of carcinoma cells accompanied by reduction of PD-1 expression in intestinal CD8+ T cells and macrophages in ApcMin/+ mice. PD-1 expression correlates well with COX-2 levels in human colorectal cancer specimens. Both elevated PD-1 and COX-2 are associated with poorer overall survival in patients with colorectal cancer. Our results uncover a novel role of PGE2 in tumor immune evasion. They may provide the rationale for developing new therapeutic approaches to subvert this process by targeting immune checkpoint pathways using EP4 antagonists. In addition, our findings reveal a novel mechanism explaining how NSAIDs reduce colorectal cancer risk by suppressing tumor immune evasion. PREVENTION RELEVANCE: These findings provide a potential explanation underlying the chemopreventive effect of NSAIDs on reducing colorectal cancer incidence during premalignancy and provide a rationale for developing EP4 antagonists for colorectal cancer prevention and treatment. Simply targeting PGE2 signaling alone may be efficacious in colorectal cancer prevention and treatment, avoiding side effects associated with NSAIDs.

Activation of nuclear hormone receptor peroxisome proliferator-activated receptor-delta accelerates intestinal adenoma growth.

We treated Apc(min) mice, which are predisposed to intestinal polyposis, with a selective synthetic agonist of peroxisome proliferator-activated receptor-delta (PPAR-delta). Exposure of Apc(min) mice to the PPAR-delta ligand GW501516 resulted in a significant increase in the number and size of intestinal polyps. The most prominent effect was on polyp size; mice treated with the PPAR-delta activator had a fivefold increase in the number of polyps larger than 2 mm. Our results implicate PPAR-delta in the regulation of intestinal adenoma growth.

Aberrant cannabinoid signaling impairs oviductal transport of embryos.

Ectopic pregnancy is a major reproductive health issue. Although other underlying causes remain largely unknown, one cause of ectopic pregnancy is embryo retention in the fallopian tube. Here we show that genetic or pharmacologic silencing of cannabinoid receptor CB1 causes retention of a large number of embryos in the mouse oviduct, eventually leading to pregnancy failure. This is reversed by isoproterenol, a beta-adrenergic receptor agonist. Impaired oviductal embryo transport is also observed in wild-type mice treated with methanandamide. Collectively, the results suggest that aberrant cannabinoid signaling impedes coordinated oviductal smooth muscle contraction and relaxation crucial to normal oviductal embryo transport. Colocalization of CB1 and beta2-adrenergic receptors in the oviduct muscularis implies that a basal endocannabinoid tone in collaboration with adrenergic receptors coordinates oviductal motility for normal journey of embryos into the uterus. Besides uncovering a new regulatory mechanism, this study could be clinically relevant to ectopic pregnancy.