Abstract
Background
Colorectal cancer (CRC) with a high prevalence is recognized as the fourth most common cause of cancer‐related death globally. Over the past decade, there has been growing interest in the network of tumor cells, stromal cells, immune cells, blood vessel cells, and fibroblasts that comprise the tumor microenvironment (TME) to identify new therapeutic interventions.
Methods
Databases, such as Google Scholar, PubMed, and Scopus, were searched to provide an overview of the recent research progress related to targeting the TME as a novel therapeutic approach.
Results
Tumor microenvironment as a result of the cross talk between these cells may result in either advantages or disadvantages in tumor development and metastasis, affecting the signals and responses from the surrounding cells. Whilst chemotherapy has led to an improvement in CRC patients' survival, the metastatic aspect of the disease remains difficult to avoid.
Conclusions
The present review emphasizes the structure and function of the TME, alterations in the TME, its role in the incidence and progression of CRC, the effects on tumor development and metastasis, and also the potential of its alterations as therapeutic targets. It should be noted that providing novel studies in this field of research might help us to achieve practical therapeutic strategies based on their interaction.
Keywords: blood vessel cells, colorectal cancer, potential therapeutic approaches, tumor microenvironment
Inflammatory pathways play a role in tumor microenvironments and can be considered as therapeutic targets.
1. INTRODUCTION
Colorectal cancer (CRC) is a prevalent and widespread cancer, the fourth most frequent leading cause of death, with one or two million newly diagnosed cases yearly. 1 , 2 Although the development of therapeutic strategies such as chemotherapy (CHT) and targeted agents (TA) has resulted in the improvement of patients' survival and mortality rates, metastatic CRC is still incurable, with only a 12% survival rate. 3 , 4 , 5 Furthermore, in early‐stage patients, surgical resection of the tumor frequently results in relapse and is not applicable to advanced‐stage patients. 3 In recent years, the limited knowledge of the factors underlying the progression mechanisms and lack of tumor targeting has led to a greater focus on the role of the tumor microenvironment (TME) in the development of many cancers, including: breast, cervical, ovarian, prostate, gastric, pancreatic, and CRC to find an effective therapeutic approach. 6 Tumors contain infiltrating inflammatory cells, proliferating cancer cells, blood vessels, tumor stroma, and an assortment of related tissue cells that comprise the tissue microenvironment. 7 The fate of cancer cells is influenced by specific molecular interactions between cancer cells and their microenvironment, which controls cellular and molecular events in adjacent tissues. 8
The seed and soil theory was proposed more than a century ago. 9 Based on this theory, there is an interaction between the microenvironment and cancer cells in the distant organ, and it would be practical to investigate their crosstalk. 10 Despite the determination of molecular features of the cancer cells, there remains a long way to go to fully understand the role of the microenvironment in the original site of the tumor and in relation to metastasis to distant organs. Inflammatory cells, vascular cells, and cancer‐associated fibroblasts (CAFs) are essential components of the TME, which results in the final phenotype of cancer cells, recurrence, metastasis, and drug resistance entity of CRC. 11 , 12 It has been shown that long‐term targeting of cyclooxygenase‐2 (COX‐2) by nonsteroidal anti‐inflammatory drugs, which is overexpressed in the majority of CRCs, reduces the risk of CRC. 13 This treatment results in mediating tumor cell proliferation, supportive tumor microenvironment, survival, and migration/invasion. 13 Another important characteristic of the TME is to reduce or suppress activated immune cells in response to the tumor invasion. 14 Therefore, enhancement of the antitumor response of the immune system by targeting checkpoint blockade pathways would be promising. There are a few FDA‐approved drugs such as Pembrolizumab, Nivolumab, and Atezolizumab that target PD‐L1 and PD‐1 for producing tumor‐specific T‐cell responses. 15
In this review, we will discuss the role of the tumor microenvironment in the incidence of CRC, its impact on tumor progression, and recent therapeutic and management approaches based on their interaction. Figure 1 showed the selection of articles used in constructing the manuscript. First, we searched PubMed, Scopus, and Google Scholar to find articles related to our main keywords, including colorectal cancer, microenvironment, therapeutic approach, and molecular mechanisms. Then, the titles and abstracts of articles were screened in order to include proper articles. To assort the included articles, we read their full texts and put them under the suitable headlines. Finally, we chose the most recent and frequently cited publications in order to summarize and include.
FIGURE 1.
Articles selection process of the present study
2. THE MOLECULAR MECHANISMS BEHIND THE MICROENVIRONMENT IN TUMORIGENESIS
One of the most important characteristics of cancer cells is their ability to proliferate indefinitely and to survive in a variety of harsh conditions. Furthermore, tumor cells are supported by normal stroma called TME. TME has recently been shown to be responsible for tumor growth by providing specific circumstances such as maintaining cancer cell initiators and neutralizing metastatic factors. Inflammation and immune‐related cells in the TME are other determining factors in the tumor‐specific phenotype. Thus, understanding the cellular and molecular mechanisms underlying tumor microenvironment is critical for facilitating the identification of new therapeutic targets.
2.1. The relationship of wound healing and tumor microenvironment
Involvement of TME and cells of TME, which are known as the stroma, reactive stroma, and cancer‐associated fibroblasts (CAFs; also known as tumor stromal fibroblasts) during wound healing is a key event in tumorigenesis. 16 Some of the well‐known underlying molecular mechanisms are fibroblast‐to‐myofibroblast differentiation, as well as activation of inflammatory components. 17 , 18 The repair of damaged tissue produces paracrine signals, which results in the activation of myofibroblast differentiation. 17 Transforming growth factor‐beta (TGF‐β) is the most important signal during this process. 19 Myofibroblasts, by inducing angiogenesis factor and ECM remodeling, play a vital role in the healing process. 16 During normal conditions, myofibroblasts would degrade by apoptosis; however, in cancerous states, they would resist as chronic wounds. 20
Embryonic mesenchymal cells traditionally are considered as the direct origin of adult fibroblasts. 21 , 22 During fibrosis (pathological wound healing), one of the main promoters of fibroblasts' accumulation is the epithelial‐mesenchymal transition (EMT), which is the loss of epithelial cells' features in order to gain mesenchymal cells' features and occurs in up to 40% of tumor‐associated fibroblasts. 23 , 24 Integration of malignant epithelial cells into the tumor stroma after undertaking the EMT process can also increase the CAF population. 25 TGF‐ and BMP‐7 collaboration also promotes it as a mediator and inhibitor, respectively. 26 STAT3 enables the epithelial‐to‐mesenchymal transition through stimulation of matrix metalloproteinases (e.g., MMP2, MMP7, and MMP9) and disintegration of the extracellular matrix. STAT3 also, by activation of hypoxia‐inducible factor‐1 (HIF1) and vascular endothelial growth factor (VEGF), plays a vital role in self‐renewal maintenance of diversified types of tissue. 27 , 28 , 29
During wound healing, the inflammation in the tumor microenvironment was enriched by GP130 cytokines via Th17 cell differentiation to induce the malignant feature of the epithelium, aberrant STAT3 activity, and suppress the immune system's antitumor response. 30 Here, tumor formation could be initiated by the continuous wound‐healing process in TME and CAF (Figure 2). Therefore, myofibroblast formation could serve as a potential target for the therapeutic approach.
FIGURE 2.
Processes involved in wound healing in the tumor microenvironment. VEGF, vascular endothelial growth factor; HIF1, hypoxia‐inducible factor‐1; TGF‐β, transforming growth factor‐beta; ECM, extracellular matrix; MMPs, matrix metalloproteinases; RBC, red blood cell
2.2. Immune cells and tumor microenvironment
The weakness of the anti‐tumor response may result from the lack of proper reorganization of a primary signal to pathogens, down‐regulation of the immune system to avoid self‐harm or the involvement of the microenvironment to hinder any assessment of the immune system to the tumor cells. 8 , 31 , 32 Regulating immune cell infiltration into the pre‐metastatic niches or tumor is another way that direct tumor cells and TME interaction can affect inflammation. 33 Microenvironment cells stimulate the secretion of matrix remodeling enzymes, cytokines, chemokines, and growth factors. 34 Although cytokines are in charge of tumor suppression based on tumor microenvironment, they initiate cell transformation and progression in constant inflammation responses that result in a disrupted balance of pro‐ and anti‐inflammatory cytokines. 35 Then, STAT3 and NF‐κB pathways are activated to regulate the release of the cytokines and mediate the progression and inflammation response that per se becomes a promoting factor in releasing more cytokines. 36 , 37 , 38
Tumor necrosis factor‐alpha (TNF‐α) is a pro‐inflammatory cytokine that has been identified to play a critical role in tumorigenesis. This cytokine can bind to one of two receptors, of which TNF‐αR1 is constitutionally expressed while TNF‐αR2 expression is mainly restricted to immune cells. The activation of TNF‐α results in the activation of an antiapoptotic pathway induced by the cellular inhibitor of apoptosis protein‐1 (cIAP1) and induced NF‐κB. 39 , 40 TNF‐α promotes tumor growth by producing reactive nitrogen species (RNS) and reactive oxygen species (ROS). 41 , 42
Interleukin 6 (IL‐6) is another pro‐inflammatory cytokine which involves stimulating proliferation and inhibition of apoptosis in tumorigenesis. As IL‐6 binds to the IL‐6R receptor and glycoprotein 130 co‐receptor (gp130), the Janus kinase (JAK)/STAT signaling pathway becomes active. 43 , 44 , 45 The IL‐6R/JAK/STAT3 signaling pathway activation leads to the up‐regulation of Oct4 gene expression. STATs family are transcription factors that their relation with the tumorigenesis process has been shown. 46 All in all, IL‐6 has become an attractive target therapy. Targeting IL‐6 by a monoclonal antibody named Siltuximab (CNTO 328) has been revealed to have favorable outcomes. 47 , 48
IL‐10 is an anti‐inflammatory factor that is produced by different cells, including tumor cells and infiltrating‐macrophages from tumors. 49 , 50 IL‐10 binds to its receptors (Jak1 and Tyk2), and leads to the activation of STAT signaling pathway as well as inhibition of the NF‐κB signaling pathway, 51 which results in the protumorigenic effect and down‐regulated of pro‐inflammatory cytokines, respectively. By suppressing the immune system, IL‐10 contributes to tumor cells' escape from immune surveillance mechanisms. 52
Through the initiation of the inflammatory response, anti‐inflammatory cytokines suppress the signaling pathways as well as cancer progression. Hence, TGF‐β and IL‐10 have a complicated role in tumorigenesis. Therefore, it is of great importance to determine their role in the context of colorectal cancer in order to properly target them as a part of the therapeutic approach.
2.3. Inflammation as a potential mechanism in tumorigenesis
One of the most important promoters of tumorigenesis in colon cancer is inflammation. 53 Inflammation starts as a response of the immune system to pathogens or tissue damage; however, perpetuating this response results in increasing the incidence of cancer due to the weakness of the anti‐tumor response because it can release bioactive molecules from tumor microenvironment cells such as chemokines, cytokines, and growth factors—that contribute to constant proliferation and cell survival signals to prevent apoptosis‐metalloproteinases,—as a modifier of extracellular matrix to initiate epithelial‐mesenchymal transition (EMT)—pro‐angiogenic factors, and it can also facilitate other tumorigenesis mechanisms such as genome instability. 34 , 54 , 55 Although fibroblasts, immune cells, and endothelial cells produce a large portion of pro‐inflammatory signals as tumor microenvironment components, they have also been shown to play an important role in tumorigenesis promotion through the secretion of cytokines and proteases from CAFs. 34
It has been shown that fibroblasts adjacent to the CRC cells express IL‐6, FAPα, and SPINK3 as an inflammation‐induced factor in CRC. 47 , 53 , 56 Another function of IL‐6 is the involvement in cell survival by stimulating the phosphorylation and acetylation of Ku70, production of sClusterin and organization of Bax‐Ku70‐sCLU in the cytoplasm. This process finally results in inhibition of the pro‐apoptotic activity of Bax. 57 IL‐6 expression also results in increased expression of VEGF and, eventually, angiogenesis stimulation while IL‐6 and SPINK3 both have a regulatory role in various cellular functions such as differentiation, growth, proliferation, and motility. 56 , 58 , 59 , 60 The IL‐6 family acts through IL6ST/gp130 and leads to phosphorylation of STAT3 at tyrosine 705 residue and makes STAT3 active. Finally, fibroblast‐derived IL‐6 results in the high secretion of SPINK1 in CRC cells via the STAT3 signaling pathway. 59 IL‐6–STAT3 signaling is known as a promoter of cancer‐related inflammation (CRI) by cytokines producing and stimulating angiogenesis and tissue transformation, while the SPINK1 signaling pathway is a mediator of CRI that has a critical role in tumorigenesis. 61 Hereto, lots of STAT3 inhibitors have been used to block its phosphorylation and hinder its activation. However, none of these inhibitors have revealed an appropriate outcome due to the absence of specificity, cell penetrance, and rapid degradation. 59 , 60 , 61 , 62
As was mentioned earlier, in the tumor microenvironment, ROS is one by‐product of inflammatory cells. ROS is one of the regulatory factors in chronic inflammation that can regulate other relevant factors in this process, such as activator protein 1 (AP‐1), NF‐κB, β‐catenin/Wnt (wingless related integration site), chemokines, inflammatory cytokines, peroxisome proliferator‐activated receptor‐gamma (PPAR‐γ), and growth factors. 63 , 64 , 65 , 66 In the presence of elevated ROS in the microenvironment, the secretion of VEGF and HIF1 would stimulate and activate cellular signaling related to migration and proliferation. 67 , 68 Therefore, targeting of ROS becomes another factor to consider as a therapeutic approach to modulate proliferative signaling and angiogenesis. 69 , 70 Figure 3 summarized the role of various inflammatory pathways in the TME.
FIGURE 3.
The schematic of inflammatory pathways involved in the tumor microenvironment. ROS, reactive oxygen species; AP1, activating protein 1; TGF‐β, transforming growth factor‐beta; TNF‐α, tumor necrosis factor‐alpha; cIAP1, cellular inhibitor of apoptosis protein‐1; RNS, reactive nitrogen species; IL‐6, interleukin 6; PPAR‐γ, peroxisome proliferator‐activated receptor‐gamma; NF‐κB, nuclear factor‐kappa B; VEGF, vascular endothelial growth factor; HIF1, hypoxia‐inducible factor‐1; ECM, extracellular matrix; IL‐10, interleukin 10; JAK, Janus kinase; STAT, signal transducer and activator of transcription; RBC, red blood cell
2.4. TGF‐β signaling and tumor microenvironment
Stromal cells, which include immune cells and fibroblasts, are an important source of TGF‐β in the tumor microenvironment. TGF‐β attachment to TGF‐β RII results in TGF‐β RI activation and, eventually, activation of SMAD transcription factors. 71 SMADs family activation has various cellular consequences, such as cytostatic effects, invasion, cell proliferation, extracellular matrix synthesis, suppression of migration, and cell cycle. 51 However, the role of TGF‐β varies according to cell type and stage of cancer. TGF‐β suppression causes tumorigenesis in the early stages due to its role in the up‐regulation of the cyclin‐dependent kinase inhibitor (CKI) p21 and the down‐regulation of c‐Myc. 51 As the tumor starts to progress, TGF‐β by activation EMT plays a critical role in increasing the invasion and metastasis. 72 Although targeting of TGF‐β and has revealed favorable outcomes in progressive cancers, serious side effects have been reported heretofore. 73
Activated TGF‐β in the Tumor Microenvironment is involved in the differentiation of mesenchymal stem cells (MSCs) to cancer‐associated fibroblast CAFs through activation of STAT3 by stimulating of TGF‐β2 and then nuclear translocation of p‐STAT3 due to the activation of JAK/STAT pathway. Activated CAFs also participate in the acceleration of metastasis by increasing the production of chemokine CXCL12, interact with CXCR4+ CRC cells, activation of IL‐11 induced‐GP130/STAT signaling pathway, and positive feedback on TGF‐β ligand production in the tumor microenvironment, therefore, CAF plays an major role in tumorigenesis and metastasis. 74
2.5. Estrogen regulatory impact on tumor microenvironment and immune surveillance
There is a hypothesis around the inhibitory role of estrogen on the inflammatory signal and thereupon modulation of the tumor microenvironment in CRC, but the exact underlying mechanism has not been understood yet. 75 The tumor microenvironment leads to the release of cytokines through inflammation; these cytokines increase the biosynthesis of steroid hormones by enhancing the expression of the 3b‐hydroxysteroid dehydrogenase gene. 75 A genome‐wide study showed that the transfected ERβ in SW480 cells results in the down‐regulation of the IL‐6 signaling pathway. 76 As mentioned previously, by considering the role of IL‐6 in the STAT3 transcription factor's activation and promotion of CRC tumorigenesis, the potential consequence of ERβ expression could be the reduction of tumor progression in the microenvironment. 77 ERβ also plays a role in the anti‐inflammatory response by suppressing IL‐6, TNF‐a, and CSF2 expression induced by TNF‐a and enhancing CD4C T cell responses on monocytes and macrophages. 78 , 79 Estrogen signaling plays a role in tumor suppression in CRC via pro‐apoptotic signaling activation by ERβ, adjusting the tumor microenvironment and immune surveillance mechanisms by inhibiting inflammatory signals. 80 Therefore, the absence of ERβ could result in tumorigenesis and then provides a suitable therapeutic target.
3. INFLAMMATION/FIBROBLASTS ASSOCIATED WITH TUMOR MICROENVIRONMENT
The initial description of the chronic inflammatory responses' involvement in tumorigenesis was done by Virchow in 1863. 81 Since the incidence rate of CRC, Crohn's disease, or ulcerative colitis is higher in patients with inflammatory bowel disease (IBD) than in the unaffected population, and the important role of chronic inflammation in sporadic CRC's incidence, the CRC was introduced as an inflammation‐dependent cancer. 82 The inflammatory response is initiated by the activation of specific oncogenes, which results in the exertion of immune cells and the generation of chemokines and cytokines. 83 The inflammatory microenvironment is responsible for invasion, fibroblast activation, matrix remodeling, angiogenesis, metastasis, and the survival of malignant cells. 84 , 85 B cell, lymphotoxin, and CD40 ligand as pro‐inflammatory cytokines lead to the activation of the TNF family and NF‐κB. 86 NF‐κB participates in tumorigenesis and development by causing chromosomal instability, DNA damage, aneuploidy, mutation, and epigenetic changes, along with the production of reactive nitrogen and reactive oxygen species (ROS). 87 Nuclear transcription factors such as STAT3 and NF‐κB produce numerous pro‐inflammatory cytokines, proliferation modulating, survival, angiogenesis, and invasion in the nucleus, targeting critical genes in modulating cancer‐promoting inflammatory responses and so have a great influence on producing the tumorigenic microenvironment. 86 , 88 Moreover, they also play a role in autoactivation by the chemokines' generation, and therefore, in the tumor microenvironment, they cause a sustained inflammatory response. 84 Alternatively, the loss of p53, which is the most prevalent mutation in colorectal cancer, is another promoting factor of NF‐κB production, so it initiates epithelial‐mesenchymal transition and inflammation in the microenvironment. 89 Another result of inflammatory factors' activation and the existence of oxidative stress is the prevention of MSH3 protein's (DNA mismatch repair protein) displacement from nuclear to cytosolic, which promotes inflammatory‐associated microsatellite alterations in the tumor microenvironment. 90
As we have already discussed, tumor microenvironment consists of a wide variety of cell types, including endothelial cells, leukocytes, and fibroblasts. As an initiator of the chronic inflammatory condition, epithelial cells can undergo an epithelial‐mesenchymal transition in order to produce the fibrotic matrix. 91 Fibroblasts in the tumor microenvironment express α‐SMA marker just like phenotype, are presented by myofibroblasts; and are known as cancer‐associated fibroblasts (CAFs). CAFs can assist in the progression and development of tumors by raising a plethora of growth factors' secretion. 92 , 93 In the case of the exact origin of CAFs, there is controversy, as it is obvious that the most possible origin in the colon tissues of CRC patients is fibroblasts. In colon cancer, as well as various types of cancers, CAFs demonstrated functional heterogeneity, which could influence the clinical outcome of patients. 94 In colon cancer, CAFs secrete various cytokines and growth factors like hepatocyte growth factor (HGF) and make a colony of cancer stem cells. 95 On the other hand, cancer cells and CAFs increase the growth of CAFs by producing growth factors and accelerating the proliferation of tumors. 96 TGF‐β derived from cancer cell make CAFs produce IL‐11, to promote gp130/STAT3 signaling and help the tumor to more progression. 97 In CAFs, the expression of MMPs is associated with the basement membrane's degradation and PAR1 cleavage; therefore, CAFs also play a critical role in the invasion and migration of cancer cells. 98 , 99 Although the CAFs are the outcome of chronic inflammation, they can also influence the increased inflammation by modulating pro‐inflammatory genes such as NF‐κB. 100 All in all, CAFs play a various role in making the best conditions for the tumor to become malignant.
4. CROSSTALK BETWEEN CANCER‐ASSOCIATED FIBROBLASTS AND IMMUNE CELLS
Cancer is regarded as a promoting factor for inflammation because it results in severe immune cell reactions. A better understanding of how the CAFs interact with immune cells is crucial for our understanding of the tumor‐based prognostic and therapeutic aspects of many malignancies. The data suggest that CAFs interact with cancer cells and immune cells through different mechanisms. 101 , 102 For instance, several tumor‐promoting factors such as chemokines and cytokines are secreted by CAFs, resulting in tumor cell survival, immune suppression, and resistance to therapy. 103 These immune cells include natural killer (NK) cells, macrophages, T cells, and dendritic cells which have a significant role in TME. There is a controversial issue regarding the role of immune cells in TME and controlling the growth of a tumor, which influences all aspects of cancer diseases, from tumorigenesis to treatment. 104 , 105 The interaction between immune cells and CAFs to regulate the TME has been summarized in some kinds of literature. 101 , 102 , 106 However, the importance of this issue convinced us to provide this section for a better understanding of the fundamental aspects of immunology's role in cancer.
In tumor tissue, fibroblasts have the ability to secret lots of immune suppressants such as TGF‐B and VEGF. CAFs are thought to be the primary source of TGF‐β in the TME, 102 , 107 and TGF‐β inhibits NK cell and cytotoxic T lymphocyte (CTL) activation (CTLs) activation. 106 NK cells are the main cause of the tumor‐infiltrating leukocyte population, which acts as the first immune response against tumors. Furthermore, TGF‐β not only inhibits DAP12 (DNAX‐activating protein of 12 kDa) transcription (a critical protein for NK cell signaling) by inducing miR‐183, but it also inhibits NKp30 and NK Group 2D (NKG2D) expression. 108 Thus, NK cells are inhibited by CAFs through various signaling blockage pathways, which leads to tumor progression. The inhibiting properties of CAFs on the operation of NK cells may be exerted in different ways, including NK receptor activation, cytokine production, and cytotoxic activity. 8 Furthermore, CAFs decrease the cytotoxic effect of NK cells versus their tumor target cells via secretion of PGE2, perforin, IDO, as well as granzyme B. 101 , 108 Li et al. reported that the release of pro‐inflammatory cytokine prostaglandin E2 (PGE2) by CAFs is a novel mechanism for the suppression of antitumor NK cell immunity in TME, which binds the pro‐inflammatory response to immune tolerance. 109 Moreover, it has been suggested that inhibition of PGE2 confers chemotherapeutic properties in numerous cancers, especially CRC. 109 , 110 , 111
Macrophages have a vital role in angiogenesis, tumor progression, and enhancement of tissue repair. Accumulation and infiltration of macrophages in TME are related to tumor development, worse prognosis, and metastasis. 112 , 113 According to the different phenotypes, classically activated macrophages (M1) and alternatively activated macrophages (M2) are the two types of tumor associated macrophages (TAMs). M1 macrophages activate the immune system by producing lots of inflammatory cytokines (TNF‐α, IL‐22, IL‐12, and IL‐6) and reactive oxygen species, TNF, and NO. M2 macrophages have an impact on the immune system by promoting tissue repair and angiogenesis, which are involved in malignant development. 114 , 115 Furthermore, M2 macrophages promote the production of immunosuppressive cytokines (IL‐10, TGF‐β, Arginase, and IDO) that inhibit inflammation and the immune response of cytotoxic CD8+ T cells in the TME. 108 , 116 M2 macrophage and CAFs can interact with each other bilaterally, and M2 macrophage can facilitate the conversion of CAFs to myofibroblasts. Pieces of advice indicate there is an essential relationship between CAFs and TAMs, causing the tumor to develop. Notably, CAFs and TAMs are frequently identified in the same location in a number of tumor forms. CAFs have a significant role in immunosuppressive cancers because they promote monocyte recruitment to the TME (via stromal cell‐derived factor‐1 (SDF‐1) and monocyte chemotactic protein‐1 (MCP‐1)) and monocytes divided into M2 macrophages with higher IL‐10 expression. 117 Moreover, CAFs can secrete IL‐6, CCL2/MCP‐1, CXCL12/SDF1, and M‐CSF (macrophage colony‐stimulating factor which is also recognized as CSF‐1) which leads to an increase in the influx of monocytes into the TME as well as M2 immunosuppressive differentiation. 117 Overall, the expression of these factors is considered as a poor prognostic factor for patients with many cancers, particularly colorectal cancer.
Another critical immune cell type is mast cells, which are involved in CAFs‐TAE interaction. It has been documented that activation and accumulation of mast cells release a wide variety of chemokines and cytokines (such as IL‐6, IL‐10, IL‐13, IL‐17, VEGF, and TNF‐α) and exacerbate the inflammation that modulates tumor growth and immunosuppression. 108 , 118 Evidence suggests that mast cells can be recruited and activated by different agents produced by different tumors. Activation of mast cells enhances CAFs differentiation and proliferation by secreting TGF‐B, tryptase, IL‐13, and adenosine, which are all favored in tumor progression and immunosuppression. 119 Adenosine, which is produced by both tumor cells and mast cells, inhibits T‐cell function and has a critical role as an immunosuppressive factor in TME. Mast cells could also increase the expression of IL‐13 and activate STAT‐3, leading to M2 polarization and contributing to immunosuppressive effects. 118 , 119 , 120 , 121
CAFs also participated in the gathering of neutrophils into the TME and increased the activation and survival of them via secreting IL‐6 and STAT‐3. 122 Then, in association with CAFs, tumor‐associated neutrophils (TANs) expressed more programmed death‐ligand 1(PDL1), IL‐8, TNF‐α, and CCL2, which all of them are linked to increasing the tumor cell migration and poor prognosis of patients in many cancers, especially colorectal cancer. 101 , 108 , 123 Moreover, these TANs derived factors have many roles in tumor cells; for example, they have the ability to facilitate invasion, proliferation, and migration as well as produce pro‐angiogenic factors, leading to tumor vascularization. 108 , 124
5. TUMOR CELL MUTATIONS/CHROMOSOME INSTABILITY AND TUMOR MICROENVIRONMENT
The TME surrounding tumors consists of various immune cells, vessels, and fibroblasts. There is an important relationship between TME and tumor cells that together leads to cancer development. So, it is important to recognize the abnormal genetic changes in TME, which might be critical factors in the development of colorectal cancer or metastasis by influencing signaling pathways in the process of CRC pathogenesis, such as chronic inflammation. Therefore, understanding the genetic alternations that may promote CRC is important for identifying novel therapeutic targets and drug development. In the following paragraphs, some of the genetic mutations in TME that may have a role in the CRC's incidence are summarized.
5.1. SLIT/ROBO signaling pathway and tumorigenesis
Previous studies have shown significantly overexpressed ROBO1 and ROBO4 in colorectal cancer compared to normal patients, and there is a relation between the expression of SLIT2 and ROBO1 and a high risk of metastatic incidence and poor prognosis in these patients. 125 ROBO1 and ROBO4 are chiefly expressed in tumor cells and the endothelial cells of tumor vessels, respectively. 125 The SLIT/ROBO pathway is critical for regulating tumorigenesis by modulating migration, tumor proliferation, tumor microenvironment, and angiogenesis; it could play both tumor‐suppressor and oncogenic functions in this process. One of the main consequences of the overexpression of the SLIT/ROBO pathway is EMT, a major activator of metastasis and tumor invasion. The activation of ROBO1 by recombinant SLIT2 in colorectal epithelial carcinoma cells results in ubiquitination of E‐cadherin by ubiquitin ligase Hakai that together lead to lysosomal degradation and then stimulate the EMT. 126 Moreover, the SLIT/ROBO pathway has a further role in the tumor microenvironment, such as angiogenesis and inflammation. The regulatory effect of SLIT2 on ROBO1 and ROBO4 results in the activation of ROBO4, then the blockage of VEGF, resulting in increased vascularization and permeability. 127 In the same way as SLIT2 regulated vascularization, it could affect inflammation by down‐regulation of lipopolysaccharide or VEGF. 128 , 129 Taking these together, it is suggested that the SLIT/ROBO signaling pathway might play a role in the tumor microenvironment.
5.2. PD‐L1 gene locus and resistance to the adaptive immune response
In CRC, amplification of the PD‐L1 gene locus has been reported recently, which is known as a cause of resistance to the adaptive immune response to local inflammatory signals. 130 , 131 Up‐regulation of PD‐L1 has a strong correlation with chromosomal instability, which is caused by mutation in the mismatch repair (MMR) gene (responsible for the occurrence of MSI). 130 Within the tumor microenvironment, the anti‐tumor immune activation stimulated the secretion of IFN‐γ, which results in abnormal expression of PD‐L1. 132 CD8+ cells are an important anti‐cancer immunity response to cancer cells and are produced by tumor‐infiltrating lymphocytes (TIL). 133 Besides, infiltrating CD8+ cells are the main consequence of microsatellite instability, high neo‐antigen content, or active chronic inflammation pathways. 134 Another possible mechanism under the up‐regulation for PD‐L1 is the constant expression of NF‐κB, the major cause of chronic inflammation. Because the PD‐L1 gene has a binding site for NF‐κB on its promoter, continued activation of NF‐B in cancer cells results in sustained expression of PD‐L. 135 High PD‐L1 expression bestows the advantage of an increased survival rate for colorectal carcinoma through a negative impact on the immune response. 136 It could be a useful tool to evaluate the prognosis of patients with high levels of microsatellite instability and provide them with the therapeutic benefit of PD‐1/PD‐L1 blockade.
5.3. NF‐κB, IL‐6/STAT3, and inflammation
As we mentioned earlier, inflammation is one of the progressive factors in the incidence of CRC. There are lots of factors in the microenvironment that participate in the secretion of pro‐inflammatory cytokines, among which NF‐κB, IL‐6/STAT3, and epigenetic changes help them to make it worse and irreversible, 137 are a contributing signal in promoting inflammatory response in the microenvironment, and we discussed their plausible epigenetic changes during tumorigenesis of CRC. 138 IL‐6 induces DNA methylation mechanisms by increasing the expression levels of DNMT1; therefore, it suppresses the negative regulator of the STAT3 signaling pathway, which is SOCS3 (suppressor of cytokine signaling 3). 139 On the other hand, IL‐6, in the same way, suppresses miR‐27b expression, which targets CYP1B1 (cytochrome P450 enzymes) and results in altered metabolic competency of epithelial cells. Overall, their silencing leads to the incidence of CRC. 140 Another epigenetic component with the ability to silence SOCS3 is miR‐196b‐5p. As a result, overexpression of miR‐196b‐5p in CRC is associated with a poor prognosis and resistance to 5‐fluorouracil (5‐FU). 141 The activation of NF‐κB by TNF‐α, which is a leading factor in chronic inflammatory and tumorigenesis by regulation of the Wnt/β catenin signaling pathway. This pathway employs both anti and pro‐inflammatory functions during the development of CRC, and constantly remains active due to the suppression of DACT3 (a negative regulator of Wnt/beta‐catenin) by histone modification. 77 TNF‐α also increases the expression of miR‐105 and miR‐19a, which activate NF‐κB signaling and contribute to the progression of colitis, CAC, and CRC. 142 , 143
5.4. Long non‐coding RNAs (lncRNAs) and tumor microenvironment
LncRNAs may play a regulatory role in tumor progression by affecting angiogenesis and metastasis through adjustment of the biological processes of endothelial cells as critical elements of stroma in TME. 131 , 144 For example, lncRNA APC1 decreases the stability of Rab5b mRNA through reduced production of exosomes in CRC cells, which results in the suppression of tumor angiogenesis by inhibition of the MAPK pathway in endothelial cells. 134 Another regulatory role of lncRNAs is the adjustment of activation, development, and differentiation of T cells. T cells are one of the major immune cells in the TME, of which CD8+ (cytotoxic T‐cell) with an anti‐tumor role in the TME is a predominant percentage of T cells. 84 , 145 , 146 LncRNA SOX5 through adjustment of indoleamine 2,3‐dioxygenase 1 (IDO1) expression by regulating the secretion of CD8+T cells and cytotoxicity can impact on colorectal cancer progress. 147
LncRNAs have a critical role in tumor microenvironment regulation by modulating angiogenesis, and cancer stem cell self‐renewal. 148 , 149 Aberrant expression of SATB2‐AS1 has been shown in CRC. The expression of SATB2‐AS1 was down‐regulated in tissue and cells of CRC patients, which has a positive correlation with progression and poor prognostic in patients. Besides, SATB2‐AS1 is able to suppress the metastasis and regulate the immune response in the tumor microenvironment of CRC through the modulation of immune cell infiltration by cis‐activating SATB2. 150 In addition, lncRNAs are another progressive factor in turning chronic inflammation into CRC. In comparison to normal CRC tissue, higher expression of LncRNA FEZF1‐AS1 and abnormal expression of LncRNA AB073614 has been observed in CRC. LncRNA FEZF1‐AS1 and lncRNA AB073614 cause the up‐regulation of STAT3, which induces the transformation of inflammation into cancer and EMT in CRC, respectively 151 , 152 (see Table 1).
TABLE 1.
A summary of dysregulated non‐coding RNAs related to the TME of CRC
Non‐coding RNA | Type | Clinical level | Regulated by/Regulating | Reference |
---|---|---|---|---|
miR‐183 | miRNA | Up | TGF‐β/DAP12 | 1 |
APC1 | lncRNA | Up | Rab5b | 75 |
SOX5 | lncRNA | Up | IDO1 | 79 |
SATB2‐AS1 | lncRNA | Down | SATB2 | 139 |
FEZF1‐AS1 | lncRNA | Up | STAT3 | 140 |
AB073614 | lncRNA | Up | STAT3 | 141 |
miR‐27b | miRNA | Down | IL‐6/CYP1B1 | 146 |
miR‐196b‐5p | miRNA | Up | SOCS3 | 147 |
miR‐105 | miRNA | Up | TNF‐α | 126 |
miR‐19a | miRNA | Up | TNF‐α | 127 |
Abbreviations: APC1, adenomatous polyposis coli 1; CRC, colorectal cancer; CYP1B1, cytochrome P450 enzyme 1; DAP12, DNAX‐activating protein of 12 kDa; FEZF1, FEZ Family Zinc Finger 1; IDO1, indoleamine 2,3‐dioxygenase 1; IL‐6, interleukin 6; lncRNA, long non‐coding RNA; miR, miRNA, microRNA; RAB5B, member RAS oncogene family; SATB2, special AT‐rich binding protein 2; SOCS3, suppressor of cytokine signaling 3; STAT3, signal transducer and activator of transcription 3; TGF‐β, transforming growth factor‐beta; TME, tumor microenvironment; TNF‐α, tumor necrosis factor‐alpha.
6. THERAPEUTIC APPROACH OF COLORECTAL CANCER BY TARGETING TME COMPONENTS
Two factors influence tumor growth and progression: genetic and epigenetic alteration in tumor cells and the related and active interaction that reorganizes the components of the TME. Tumor cells, as the center of TME, employ sophisticated signaling networks to alter the purpose of cellular and non‐cellular parts in order to exploit non‐cancerous cells. A complicated network of various components is the source of intercellular communication, and the result of such interaction is tumor growth and progression, drug resistance, and ineffective treatment response. Recent developments in tumor biology have shown that understanding the various underlying mechanisms of tumor growth and progression requires a complete investigation of the complex interactions between tumor cells and their surrounding microenvironment. Understanding how cancer cells interact can help researchers create therapeutic strategies to predict and combat cancer cells' strategies for surviving and resisting anti‐cancer treatments. As a result, a variety of approaches have been used to attack malignant tumors by interrupting their interactions with stromal cells, and we summarized a few of them in the following paragraph.
However, the most significant challenge in this field is recognizing and determining the heterogeneity of TIME by investigating a wide variety of patients with different cancer types at either the cellular or the molecular level. This can result in functional solutions for extensive clinical application, such as increasing the therapeutic effectiveness of targeting TIME components.
6.1. Anti‐cancer‐associated fibroblast therapies
Anti‐cancer‐associated fibroblast treatments have recently received considerable attention. Although many reports have shown the pro‐tumorigenic characteristics of CAFs, the therapeutic aspects of CAFs are still a challenging issue. In this regard, many drugs have been discovered and used with the aim of anti‐CAFs therapies and have had anti‐tumor effects in some clinical research. According to different specific targets, these agents can be divided into several classes. 153
6.1.1. Class 1 of anti‐CAFs
Class 1 agents suppress signal transduction pathways and affect the interaction between CAF and the tumor. Inhibitors of VEGF, TGF‐, VEGFR, IGF‐1R, PDGFR, and HGF/MET are examples of this class. After binding to their receptors, TGF‐, IL‐6, and PDGF are important factors for activating fibroblasts as well as participating in cell signaling circuits. 154 , 155 Activation of these receptors leads to increase proliferation and invasive characteristics of CAFs. Along with the role of CAFs in secreting plenty of growth factors and pro‐inflammatory chemokines and cytokines mentioned above, they can also increase IL‐6, CCL2, and TGF‐β, which help immune evasion by enrolling immune cells. 56 , 156
CAFs are the main cellular source of TGF‐β, which is known as an immunosuppressive cytokine and leads to polarization of immune cells (both adaptive and innate cells) to promote immunosuppressive cells. 156 Galunisertib (LY2157299) is an anti‐cancer agent that targets TGF‐β signaling and has been used in a variety of cancers. 157 Calon and colleagues reported that TGF‐β inhibition may be associated with the prevention of CRC metastasis, particularly when patients are treated early phase of the disease. 97
VEGF is highly expressed in advanced CRC. Neovascularization, supported by increased VEGF expression, is needed to provide nutrients and hematogenous supply for tumor spread. 158 It has been demonstrated that in colorectal adenocarcinoma, higher levels of VEGF have been linked to a higher risk of hepatic metastasis and a worse prognosis. 158 , 159 By restoring vessel integrity, expanding tumor perfusion, and decreasing interstitial fluid pressure, VEGF inhibitors increase the number of immune cells entering the tumor. Some of the anti‐VEGF agents, including Aflibercept, Regorafenib, and Bevacizumab, have been used successfully in the treatment of malignant CRC. 160
Another growth factor that activates c‐Met (mesenchymal‐epithelial transition factor) on cancer cells, HGF, is mainly secreted by fibroblasts. 93 Activation of the c‐Met, which is a cell surface tyrosine kinase receptor, regulates signaling cascades, including cellular motility, angiogenesis, proliferation, development of cancer cells, and epithelial‐mesenchymal transition. 161 Recently, anti‐Met agents have become a topic of interest as a new strategy for both therapeutic management and prediction of CRC patients' prognosis. In this respect, several drugs have been used in different phases of trials to target the c‐MET/HGF signaling pathway with different results. These drugs are divided into small‐molecule tyrosine kinase inhibitors (TKIs), including NK4, 162 , 163 Cabozantinib, 164 as well as Onartuzumab and also monoclonal antibodies (mAbs). For a review of c‐Met inhibitors in colorectal cancer, see ref (161).
6.1.2. Class 2 of anti‐CAFs
Class 2 anti‐CAFs agents are more focused on CAFs and CAF products, and thus include inhibitors of MMPs, tenascin‐c, cathepsin, and serine proteases. 153 Although clinical trials in this group are not too many, we discuss them in brief as the following.
Cathepsins are a group of globular proteases that belong to the cysteine, serine, or aspartic proteases and are not only identified as intracellular peptide hydrolases, but some of them also have extracellular functions. There are several cathepsin families, including cathepsin A‐H, K L, O, S, V, and W. Cathepsins are synthesized and processed as inactive proenzymes to be converted to mature and active enzymes. 165 , 166 Since cathepsins are able to degrade extracellular matrix proteins, they are involved in colorectal cancer invasion and metastasis. Evidence suggests that some cathepsins are expressed in CRC and enhance development and tumor progression. 165 , 166 , 167 , 168 For instance, cathepsin S is a lysosomal cysteine protease with a critical role in cell migration, angiogenesis, and cancer cell invasion. This, in turn, can provide a valuable prognostic indicator and a possible target for noninvasive therapy. Burden et al. demonstrated that Fsn0503, which is a monoclonal antibody, could block CRC angiogenesis and tumor development in vivo and might improve the effectiveness of chemotherapy by inhibition of catepsin S. 168
MMPs are zinc‐dependent proteolytic metalloenzymes that have a significant role in the deterioration of ECM and are needed for metastasis and tumor development. During the inactive period, they are secreted and activated in the extracellular environment. Based on preclinical studies, different MMPs, including MMP1‐13 and MT1‐MMP, have been found abundantly in CRC. Although overexpression of some MMPs is related to bad prognosis and metastasis in CRC, overexpression of MMP‐12 is associated with a higher improved survival rate in patients with CRC due to its inhibitory effects on angiogenesis. 169 , 170 Prinomastat/AG‐3340 is an MMP inhibitor and effective against a variety of MMPs, including MMPs 2, 3, 9, 13, and 14. AG‐3340 might be able to stop angiogenesis and tumor growth, which results in apoptosis in different cancers, especially colon cancer. However, the utility of this drug is limited due to its lack of effectiveness and unwanted side effects. 171 Curcumin is another anti‐cancer agent that suppresses MMP expression and significantly inhibits MMP‐9 activity in CRC. 172 Notably, the inhibitory effect of curcumin on AP‐1 and NF‐KB cell signaling results in down‐regulation of MMP‐9 expression. 173
Serine protease inhibitors (serpins) belong to a protein superfamily, which can be used as a powerful strategy in cancer treatments. They have been classified into six groups: serine, glutamic acid, threonine, cysteine, aspartate proteases, and matrix metalloproteinase. SPINK1 (Serine protease inhibitor Kazal Type 1) is an inhibitor of trypsin kinase, which plays a role in cell proliferation, cancer metastasis, and inflammation. It seems that SPINK1 has participated in tumor progression and malignancy via EGFR signaling. 174 Overexpression of SPINK1 has been seen in 50% of patients with CRC and is related to a bad prognosis. 58 Thus, SPINK1 could be a useful biomarker for targeted therapy in CRC. FAP (Fibroblast activation protein) is a serine proteinase found in CRC cancers at both the protein and mRNA levels, and its expression levels are linked to angiogenesis, collagen degradation, poor prognosis, and aggressive cancer progression stages. 58
Moreover, it has been reported that FAP in CAFs by inducing tumor‐promoting inflammation may be critical in controlling an antitumor immune response. 175 Consequently, treatment with anti‐FAPα antibodies inhibited progression and tumor growth, which might be facilitated by T‐cell immunotherapy. 101 In this regard, ValboroPro (Talabostat) was used in metastatic colorectal cancer, which prevents fibroblast activation protein (FAP). 176
6.1.3. Class 3 of anti‐CAFs
Class 3 of anti‐CAFs is COX‐2, which is triggered by a huge number of cytokines and growth factors. COX‐2 is overexpressed in many cancers, and COX‐2 inhibitors can decrease the growth of tumor by several pathways such as the production of 1‐PGE1 (inhibition of prostaglandin E1) in fibroblasts, and 2‐down‐regulation of HDM2, which is an oncogenic E3 ligase that targets P53 for degradation and ubiquitination. 153 On this point, NSAIDs, which are COX‐2 inhibitors, have been used successfully in CRC treatment and have an anti‐tumor effect on the progression of tumors (see Table 2). 177
TABLE 2.
Pharmacological anti‐tumorigenic agents against CAFs in CRC treatment
Class | Name | Target | Pathway | References |
---|---|---|---|---|
Class 1 of anti‐CAFs | Galunisertib (LY2157299) | TGF‐βRI kinase | TGF‐β signaling pathway | 97 |
Aflibercept | VEGF | Angiogenesis | 178 | |
Regorafenib | ||||
Bevacizumab (Avastin) | ||||
NK4 | c‐Met | c‐MET/HGF signaling pathway | 38, 179, 180 | |
Cabozantinib | ||||
Onartuzumab | ||||
Class 2 of anti‐CAFs | Fsn0503 | Catepsin S | Proteolysis | 181 |
Prinomastat/AG‐3340 | MMPs 2, 3, 9, 13 and 14 | 182 | ||
Curcumin | MMP‐9 | 48 | ||
Class 3 of anti‐CAFs | NSAIDs | COX‐2 | Inflammatory pathway | 49 |
Abbreviations: CAFs, cancer‐associated fibroblasts; COX‐2, cyclooxygenase‐2; CRC, Colorectal cancer; EGCG, epigallocatechin‐3‐gallate; HGF, hepatocyte growth factor; MMPs, matrix metalloproteinases; NSAIDs, nonsteroidal anti‐inflammatory drugs; TGF‐β, transforming growth factor‐beta; VEGF, vascular endothelial growth factor.
6.2. Targeting the tumor vasculature
Angiogenesis is needed for the metastasis and growth of solid tumors in cancer, and it demands the balance of lots of inhibitory and stimulatory factors. Even though different mechanisms are responsible for the pathogeneses of angiogenesis, the inhibition of angiogenesis may be a practical therapeutic approach in the management of cancers. Measuring microvessel density (MVD) is commonly used to evaluate angiogenesis. Furthermore, MVD is based on endothelial markers such as CD31, endoglin (CD105), CD34, and von Willebrand's factor (Factor VIII related antigen or F. VIII Ag) and is also associated with the distant site, lymph node involvement, depth of invasion, and tumor metastasis stage. 183 There is a relationship between MVD and VEGF with a higher incidence of metastases and decreased survival of CRC. However, it is challenging to relate MVD and VEGF with overall survival (OS) as prognostic biomarkers for CRC patients. 183
Inhibitors of angiogenesis such as antibodies or small molecules are used in the standard treatment of CRC. Bevacizumab (Avastin) is the first angiogenesis inhibitor with a specific effect on VEGF, which avoids its binding to specific receptors. Previous studies have demonstrated that adding bevacizumab to chemotherapy increases OS and response rate. 184 , 185 However, this kind of treatment is expensive and, in some cases, it could be accompanied by some side effects such as proteinuria, hypertension, as well as bowel perforation without producing an effective response. 186
Endoglin, also known as CD105, is a TGF‐β accessory receptor that is overexpressed in endothelial cells of tissues involved in angiogenesis. Consequently, CD105 is a good predictor of tumor‐related angiogenesis. It has been documented that MVD determined by monoclonal antibodies to CD105 can be utilized to differentiate low‐grade from high‐grade dysplasia and also between high‐grade dysplasia from CRC. On the other hand, MVD determined by monoclonal antibodies to CD34, cannot be utilized to differentiate between these pathologies. 187
6.3. Targeting the tumor microenvironment
In a patient with colorectal cancer, some special features of tumor cells can change the tumor microenvironment (TME) and vice versa. The TME consists of cellular components (fibroblasts, osteoblasts, mesenchymal stem cells, blood, fat cells, and immune cells and ECM). The TME has been proven to play a significant role in providing cytokines, growth factors, and other anti‐apoptotic and pro‐metastatic factors that modulate tumor cells' ability to migrate. 188
Several treatment approaches based on tumor microenvironment targeting have been established, including TGF‐signaling pathway targeting, angiogenesis targeting, CAF targeting, cancer stem cell (CSC) therapies, and immunotherapy. In the following, some of these therapies and their targets will be discussed in more detail.
6.3.1. Targeting TGF‐β signaling in colorectal cancer
The multifunctional TGF‐β has a crucial role in proliferation, embryonic development of normal tissues and differentiation as well as cellular immune responses, cell motility, angiogenesis, and extracellular matrix production. 189 Basically, cells in tissues synthesize and secrete this factor into the microenvironment where it attaches to special TGF‐β receptors for paracrine and autocrine signaling. The TGF‐β signaling pathway begins with the attachment of TGF‐β molecule to its receptor and consequent activation of downstream molecules where they can move to the nucleus and change several genes' expression. 190 There are three major TGF‐β receptors, each of which plays a specific role in transmitting the signal into the cytosol. Following TGF‐β receptor II (TBR II) activation by TGF‐ I, TGF‐ receptor I (ALK5) is activated and a heterodimeric complex is formed. 191 TBRII is a fundamental active serine/threonine kinase while transphosphorylation of the glycine/serine‐rich domain of TBRI by TBRII after complex formation, activates TBRI kinase. TBRIIIs, endoglin, which lacks kinase signaling motifs, also participates in the activation process of TGF‐β1 kinase receptors as the accessory receptor. 192 Phosphorylated receptors then activate separate pathways, including canonical and non‐canonical pathways. The canonical pathway is also referred to as the SMAD‐dependent pathway in which SMAD2 and SMAD3 molecules are phosphorylated and then assembled into heterodimeric and trimeric complexes with SMAD4 molecules. The complex is then translocated to the nucleus to regulate the expression of TGF‐β target genes. 193
TGF‐β has been shown to have dual activity in CRC, acting as a tumor suppressor factor in the early stages and increasing disease progression in the later stages. Kawata et al. reported in a study that TGF‐β signaling has a positive effect on disease development and that its serum level predicts recurrence in CRC patients. 194 It has also been shown that increased TGF‐β signaling in the tumor microenvironment is associated with a poor prognosis in CRC patients, and that stromal TGF‐response causes an increase in ECM proteins, cytokines, and growth factors, many of which play important roles in metastasis and the development of various cancers. 194
Several TGF‐targeting therapeutic options are currently being studied in clinical trials, including monoclonal antibodies, chimeric proteins, small molecule receptor kinase inhibitors, vaccines, and antisense oligonucleotides (ASOs). 195 In the case of colorectal cancer, the first priority has been to block the receptor with small molecules such as Galunisertib (LY2157299), which inhibits TGF‐RI kinase and thus blocks SMAD2 phosphorylation (NCT04031872, NCT02688712). In a study, Jonathan M. Yingling et al. reported that Galunisertib has anti‐tumor activity, including suppressing mesenchymal phenotype and tumor cell migration, postponement of tumor growth, and reversal TGFβ‐mediated immune‐suppression. 195 It has been demonstrated that this molecule prevents the growth of hepatocellular, colon, lung, and breast cancers in animal models. 196
6.3.2. Targeting CAFs and angiogenesis in CRC
CAFs are also the most crucial elements of the tumor microenvironment that induce metastasis and tumor growth via various mechanisms. Basically, CAFs secrete many cytokines and growth factors in the tumor microenvironment, leading to the enhancement of cancer cell growth and invasiveness. In addition to CAFs, TAMs also exist in the tumor microenvironment and, together with CAFs, they prepare a better niche for cancer cells. IL‐6 secreted by CAFs is one of the inflammatory cytokines primarily and helps the growth and invasiveness of cancer by activating STAT3. 197
STAT3 is an important mediator for malignant progression in colorectal cancer. Retained STAT3 activation in CRC is actively contributed to immune cells and cancer‐associated fibroblasts. 198 TGF‐β‐stimulated CAF and TAM induce STAT3 signaling in tumor cells by secretion of IL‐11 and IL‐6, respectively. In a study, E Sanchez‐Lopez et.al investigated the potential of NT157, which is a new tyrphostin, for targeting cancer cells and their microenvironment at once in a sporadic CRC mouse model. NT157 at least inhibits IGF/1R/IRS and JAK/STAT3 as oncogenetic signaling pathways. By doing so, it was demonstrated that NT157 efficiently decreased tumor size and multiplicity. 197
In another study performed by Jin et al. JAK/STAT3/IL‐8 pathway was inhibited using (−)‐epigallocatechin‐3‐gallate and curcumin's combination in order to stop microenvironment‐induced angiogenesis. In this study, JAK/STAT3 signaling was repressed by curcumin combination with EGCG and subsequently inhibited the conditioned medium‐induced transition of normal endothelial cells (NECs) to tumor endothelial cells (TECs). 199
7. CONCLUSIONS
With respect to the great heterogeneity in the TME of CRC and the following metastasis, there is a pressing need to consider targeted therapy. In addition, there are several therapeutic molecules that could be used to target TME components in preclinical investigations and also in clinical trials. We have evaluated studies reporting the cell composition and other various components in TME along with their characteristics and functions with respect to CRC to provide new diagnostic biomarkers and novel personalized therapeutic approaches.
CONFLICT OF INTEREST
The authors declare that there is no conflict of interest in this study.
Supporting information
Appendix S1
ACKNOWLEDGMENT
All authors have read the journal's authorship agreement and agree that the manuscript has been reviewed and approved by all named authors.
Zafari N, Khosravi F, Rezaee Z, et al. The role of the tumor microenvironment in colorectal cancer and the potential therapeutic approaches. J Clin Lab Anal. 2022;36:e24585. doi: 10.1002/jcla.24585
Narges Zafari and Fatemeh Khosravi contributed equally to the current manuscript.
Contributor Information
Narges Zafari, Email: narges_zafari@yahoo.com.
Afshin Bahramy, Email: bahramy_afshin@yahoo.com.
Amir Avan, Email: avana@mums.ac.ir.
DATA AVAILABILITY STATEMENT
All data used to support the findings of this study are included in the article.
REFERENCES
- 1. Aghabozorgi AS, Ebrahimi R, Bahiraee A, et al. The genetic factors associated with Wnt signaling pathway in colorectal cancer. Life Sci. 2020;256:118006. [DOI] [PubMed] [Google Scholar]
- 2. Weiderpass E, Stewart BW. World Cancer Report. The International Agency for Research on Cancer (IARC); 2020. [Google Scholar]
- 3. Hung H‐Y, Chen J‐S, Tang R, et al. Preoperative alkaline phosphatase elevation was associated with poor survival in colorectal cancer patients. Int J Colorectal Dis. 2017;32(12):1775‐1778. [DOI] [PubMed] [Google Scholar]
- 4. Liu W, Zhang M, Wu J, Tang R, Hu L. Oncologic outcome and efficacy of chemotherapy in colorectal cancer patients aged 80 years or older. Front Med. 2020;7:525421. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 5. Xie Y‐H, Chen Y‐X, Fang J‐Y. Comprehensive review of targeted therapy for colorectal cancer. Signal Transduct Target Ther. 2020;5(1):1‐30. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 6. Herrera M, Galindo‐Pumariño C, García‐Barberán V, Peña C. A snapshot of the tumor microenvironment in colorectal cancer: the liquid biopsy. Int J Mol Sci. 2019;20(23):6016. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 7. Jahanban‐Esfahlan R, Seidi K, Zarghami N. Tumor vascular infarction: prospects and challenges. Int J Hematol. 2017;105(3):244‐256. [DOI] [PubMed] [Google Scholar]
- 8. Anderson NM, Simon MC. The tumor microenvironment. Curr Biol. 2020;30(16):R921‐R925. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 9. Paget S. The distribution of secondary growths in cancer of the breast. Lancet. 1889;133(3421):571‐573. [PubMed] [Google Scholar]
- 10. Dai C, Sun B, Kang J. Is seed and soil theory suitable for metastatic spread of pituitary carcinomas? Front Endocrinol. 2021;11:607405. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 11. Chen W‐J, Ho C‐C, Chang Y‐L, et al. Cancer‐associated fibroblasts regulate the plasticity of lung cancer stemness via paracrine signalling. Nat Commun. 2014;5(1):1‐17. [DOI] [PubMed] [Google Scholar]
- 12. Joshi RS, Kanugula SS, Sudhir S, Pereira MP, Jain S, Aghi MK. The role of cancer‐associated fibroblasts in tumor progression. Cancers. 2021;13(6):1399. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 13. Sheng J, Sun H, Yu F‐B, Li B, Zhang Y, Zhu Y‐T. The role of cyclooxygenase‐2 in colorectal cancer. Int J Med Sci. 2020;17(8):1095‐1101. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 14. Xiong Y, Wang Y, Tiruthani K. Tumor immune microenvironment and nano‐immunotherapeutics in colorectal cancer. Nanomed Nanotechnol Biol Med. 2019;21:102034. [DOI] [PubMed] [Google Scholar]
- 15. De Velasco G, Je Y, Bossé D, et al. Comprehensive meta‐analysis of key immune‐related adverse events from CTLA‐4 and PD‐1/PD‐L1 inhibitors in cancer patients. Cancer Immunol Res. 2017;5(4):312‐318. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 16. Foster DS, Jones RE, Ransom RC, Longaker MT, Norton JA. The evolving relationship of wound healing and tumor stroma. JCI insight. 2018;3(18):e99911. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 17. Liu T, Zhou L, Li D, Andl T, Zhang Y. Cancer‐associated fibroblasts build and secure the tumor microenvironment. Front Cell Dev Biol. 2019;7:60. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 18. Wang Z, Qi F, Luo H, Xu G, Wang D. Inflammatory microenvironment of skin wounds. Front Immunol. 2022;13:789274. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 19. Chung JY‐F, Chan MK‐K, Li JS‐F, et al. Tgf‐β signaling: From tissue fibrosis to tumor microenvironment. Int J Mol Sci. 2021;22(14):7575. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 20. Dvorak HF. Tumors: wounds that do not heal—a historical perspective with a focus on the fundamental roles of increased vascular permeability and clotting. Semin Thromb Hemost. 2019;45(6):576‐592. [DOI] [PubMed] [Google Scholar]
- 21. Lang H, Fekete DM. Lineage analysis in the chicken inner ear shows differences in clonal dispersion for epithelial, neuronal, and mesenchymal cells. Dev Biol. 2001;234(1):120‐137. [DOI] [PubMed] [Google Scholar]
- 22. Maric C, Ryan GB, Alcorn D. Embryonic and postnatal development of the rat renal interstitium. Anat Embryol. 1997;195(6):503‐514. [DOI] [PubMed] [Google Scholar]
- 23. Lamouille S, Xu J, Derynck R. Molecular mechanisms of epithelial–mesenchymal transition. Nat Rev Mol Cell Biol. 2014;15(3):178‐196. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 24. LeBleu VS, Neilson EG. Origin and functional heterogeneity of fibroblasts. FASEB J. 2020;34(3):3519‐3536. [DOI] [PubMed] [Google Scholar]
- 25. Zeisberg EM, Potenta S, Xie L, Zeisberg M, Kalluri R. Discovery of endothelial to mesenchymal transition as a source for carcinoma‐associated fibroblasts. Cancer Res. 2007;67(21):10123‐10128. [DOI] [PubMed] [Google Scholar]
- 26. Zhang Y, Wu X, Li Y, et al. Endothelial to mesenchymal transition contributes to arsenic‐trioxide‐induced cardiac fibrosis. Sci Rep. 2016;6(1):1‐12. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 27. Hwang S, Seong H, Ryu J, et al. Phosphorylation of STAT3 and ERBB2 mediates hypoxia‐induced VEGF release in ARPE‐19 cells. Mol Med Rep. 2020;22(4):2733‐2740. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 28. Jin W. Role of JAK/STAT3 signaling in the regulation of metastasis, the transition of cancer stem cells, and chemoresistance of cancer by epithelial–mesenchymal transition. Cell. 2020;9(1):217. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 29. Zhao T, Jin F, Di Xiao HW, et al. IL‐37/STAT3/HIF‐1α negative feedback signaling drives gemcitabine resistance in pancreatic cancer. Theranostics. 2020;10(9):4088‐4100. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 30. Kortylewski M, Kujawski M, Wang T, et al. Inhibiting Stat3 signaling in the hematopoietic system elicits multicomponent antitumor immunity. Nat Med. 2005;11(12):1314‐1321. [DOI] [PubMed] [Google Scholar]
- 31. Gallucci S, Matzinger P. Danger signals: SOS to the immune system. Curr Opin Immunol. 2001;13(1):114‐119. [DOI] [PubMed] [Google Scholar]
- 32. Li C, Jiang P, Wei S, Xu X, Wang J. Regulatory T cells in tumor microenvironment: new mechanisms, potential therapeutic strategies and future prospects. Mol Cancer. 2020;19(1):1‐23. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 33. Plundrich D, Chikhladze S, Fichtner‐Feigl S, Feuerstein R, Briquez PS. Molecular mechanisms of tumor immunomodulation in the microenvironment of colorectal cancer. Int J Mol Sci. 2022;23(5):2782. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 34. Hanahan D, Weinberg RA. Hallmarks of cancer: the next generation. Cell. 2011;144(5):646‐674. [DOI] [PubMed] [Google Scholar]
- 35. Zamarron BF, Chen W. Dual roles of immune cells and their factors in cancer development and progression. Int J Biol Sci. 2011;7(5):651‐658. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 36. Dev A, Iyer S, Razani B, Cheng G. NF‐κB and innate immunity. Curr Top Microbiol Immunol. 2010;349:115‐143. [DOI] [PubMed] [Google Scholar]
- 37. Dorrington MG, Fraser ID. NF‐κB signaling in macrophages: dynamics, crosstalk, and signal integration. Front Immunol. 2019;10:705. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 38. Rius J, Guma M, Schachtrup C, et al. NF‐κB links innate immunity to the hypoxic response through transcriptional regulation of HIF‐1α. Nature. 2008;453(7196):807‐811. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 39. Jang D‐i, Lee A‐H, Shin H‐Y, et al. The role of tumor necrosis factor alpha (TNF‐α) in autoimmune disease and current TNF‐α inhibitors in therapeutics. Int J Mol Sci. 2021;22(5):2719. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 40. Khodarahmian M, Amidi F, Moini A, et al. A randomized exploratory trial to assess the effects of resveratrol on VEGF and TNF‐α 2 expression in endometriosis women. J Reprod Immunol. 2021;143:103248. [DOI] [PubMed] [Google Scholar]
- 41. Kastl L, Sauer S, Ruppert T, et al. TNF‐α mediates mitochondrial uncoupling and enhances ROS‐dependent cell migration via NF‐κB activation in liver cells. FEBS Lett. 2014;588(1):175‐183. [DOI] [PubMed] [Google Scholar]
- 42. Zafari N, Tarafdari AM, Izadi P, et al. A panel of plasma miRNAs 199b‐3p, 224‐5p and Let‐7d‐3p as non‐invasive diagnostic biomarkers for endometriosis. Reprod Sci. 2021;28(4):991‐999. [DOI] [PubMed] [Google Scholar]
- 43. Bahiraee A, Ebrahimi R, Halabian R, Aghabozorgi AS, Amani J. The role of inflammation and its related microRNAs in breast cancer: a narrative review. J Cell Physiol. 2019;234(11):19480‐19493. [DOI] [PubMed] [Google Scholar]
- 44. Lin Y, He Z, Ye J, et al. Progress in understanding the IL‐6/STAT3 pathway in colorectal cancer. Onco Targets Ther. 2020;13:13023‐13032. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 45. Xu J, Lin H, Wu G, Zhu M, Key HP, Li M. IL‐6/STAT3 is a promising therapeutic target for hepatocellular carcinoma. Front. Oncologia. 2021;11:760971. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 46. Chatterjee M, Stühmer T, Herrmann P, Bommert K, Dörken B, Bargou RC. Combined disruption of both the MEK/ERK and the IL‐6R/STAT3 pathways is required to induce apoptosis of multiple myeloma cells in the presence of bone marrow stromal cells. Blood. 2004;104(12):3712‐3721. [DOI] [PubMed] [Google Scholar]
- 47. Koczorowska M, Tholen S, Bucher F, et al. Fibroblast activation protein‐α, a stromal cell surface protease, shapes key features of cancer associated fibroblasts through proteome and degradome alterations. Mol Oncol. 2016;10(1):40‐58. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 48. Rossi J, Négrier S, James N, et al. A phase I/II study of siltuximab (CNTO 328), an anti‐interleukin‐6 monoclonal antibody, in metastatic renal cell cancer. Br J Cancer. 2010;103(8):1154‐1162. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 49. Gastl GA, Abrams JS, Nanus DM, et al. Interleukin‐10 production by human carcinoma cell lines and its relationship to interleukin‐6 expression. Int J Cancer. 1993;55(1):96‐101. [DOI] [PubMed] [Google Scholar]
- 50. O'Sullivan E. Prevalence of oral mucosal abnormalities in addiction treatment centre residents in Southern Ireland. Oral Oncol. 2011;47(5):395‐399. [DOI] [PubMed] [Google Scholar]
- 51. Finbloom DS, Winestock KD. IL‐10 induces the tyrosine phosphorylation of tyk2 and Jak1 and the differential assembly of STAT1 alpha and STAT3 complexes in human T cells and monocytes. J Immunol. 1995;155(3):1079‐1090. [PubMed] [Google Scholar]
- 52. Sheikhpour E, Noorbakhsh P, Foroughi E, Farahnak S, Nasiri R, Neamatzadeh H. A survey on the role of interleukin‐10 in breast cancer: A narrative. Rep Biochem Mol Biol. 2018;7(1):30‐37. [PMC free article] [PubMed] [Google Scholar]
- 53. Ida S, Ozaki N, Araki K, et al. SPINK1 status in colorectal cancer, impact on proliferation, and role in colitis‐associated cancer. Mol Cancer Res. 2015;13(7):1130‐1138. [DOI] [PubMed] [Google Scholar]
- 54. Bahramy A, Zafari N, Izadi P, Soleymani F, Kavousi S, Noruzinia M. The Role of miRNAs 340‐5p, 92a‐3p, and 381‐3p in Patients with Endometriosis: A Plasma and Mesenchymal Stem‐Like Cell Study. Biomed Res Int. 2021;2021:1‐15. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 55. Saliba J, Coutaud B, Makhani K, et al. Loss of NFE2L3 protects against inflammation‐induced colorectal cancer through modulation of the tumor microenvironment. Oncogene. 2022;41(11):1563‐1575. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 56. Nagasaki T, Hara M, Nakanishi H, Takahashi H, Sato M, Takeyama H. Interleukin‐6 released by colon cancer‐associated fibroblasts is critical for tumour angiogenesis: anti‐interleukin‐6 receptor antibody suppressed angiogenesis and inhibited tumour–stroma interaction. Br J Cancer. 2014;110(2):469‐478. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 57. Pucci S, Mazzarelli P, Sesti F, Boothman DA, Spagnoli LG. Interleukin‐6 affects cell death escaping mechanisms acting on Bax‐Ku70‐Clusterin interactions in human colon cancer progression. Cell Cycle. 2009;8(3):473‐481. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 58. Räsänen K, Itkonen O, Koistinen H, Stenman U‐H. Emerging roles of SPINK1 in cancer. Clin Chem. 2016;62(3):449‐457. [DOI] [PubMed] [Google Scholar]
- 59. Räsänen K, Lehtinen E, Nokelainen K, et al. Interleukin‐6 increases expression of serine protease inhibitor Kazal type 1 through STAT3 in colorectal adenocarcinoma. Mol Carcinog. 2016;55(12):2010‐2023. [DOI] [PubMed] [Google Scholar]
- 60. Taniguchi K, Karin M. IL‐6 and related cytokines as the critical lynchpins between inflammation and cancer. Semin Immunol. 2014;26:54‐74. [DOI] [PubMed] [Google Scholar]
- 61. Hirano T. IL‐6 in inflammation, autoimmunity and cancer. Int Immunol. 2021;33(3):127‐148. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 62. Wake MS, Watson CJ. STAT 3 the oncogene–still eluding therapy? FEBS J. 2015;282(14):2600‐2611. [DOI] [PubMed] [Google Scholar]
- 63. Ebrahimi R, Bahiraee A, Niazpour F, Emamgholipour S, Meshkani R. The role of microRNAs in the regulation of insulin signaling pathway with respect to metabolic and mitogenic cascades: A review. J Cell Biochem. 2019;120(12):19290‐19309. [DOI] [PubMed] [Google Scholar]
- 64. Emamgholipour S, Ebrahimi R, Bahiraee A, Niazpour F, Meshkani R. Acetylation and insulin resistance: a focus on metabolic and mitogenic cascades of insulin signaling. Crit Rev Clin Lab Sci. 2020;57(3):196‐214. [DOI] [PubMed] [Google Scholar]
- 65. Rashidi Z, Khosravizadeh Z, Talebi A, Khodamoradi K, Ebrahimi R, Amidi F. Overview of biological effects of Quercetin on ovary. Phytother Res. 2021;35(1):33‐49. [DOI] [PubMed] [Google Scholar]
- 66. Valipour J, Nashtaei MS, Khosravizadeh Z, et al. Effect of sulforaphane on apoptosis, reactive oxygen species and lipids peroxidation of human sperm during cryopreservation. Cryobiology. 2020;99:122‐130. [DOI] [PubMed] [Google Scholar]
- 67. Alhayaza R, Haque E, Karbasiafshar C, Sellke FW, Abid MR. The relationship between reactive oxygen species and endothelial cell metabolism. Front Chem. 2020;8:592688. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 68. Hagen T. Oxygen versus reactive oxygen in the regulation of HIF‐1: the balance tips. Biochem Res Int. 2012;2012:1‐5. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 69. Ahn KS, Sethi G, Chaturvedi MM, Aggarwal BB. Simvastatin, 3‐hydroxy‐3‐methylglutaryl coenzyme A reductase inhibitor, suppresses osteoclastogenesis induced by receptor activator of nuclear factor‐κB ligand through modulation of NF‐κB pathway. Int J Cancer. 2008;123(8):1733‐1740. [DOI] [PubMed] [Google Scholar]
- 70. Nair AS, Shishodia S, Ahn KS, Kunnumakkara AB, Sethi G, Aggarwal BB. Deguelin, an Akt inhibitor, suppresses IκBα kinase activation leading to suppression of NF‐κB‐regulated gene expression, potentiation of apoptosis, and inhibition of cellular invasion. J Immunol. 2006;177(8):5612‐5622. [DOI] [PubMed] [Google Scholar]
- 71. Xie F, Ling L, van Dam H, Zhou F, Zhang L. TGF‐β signaling in cancer metastasis. Acta Biochim Biophys Sin. 2018;50(1):121‐132. [DOI] [PubMed] [Google Scholar]
- 72. Morrison CD, Parvani JG, Schiemann WP. The relevance of the TGF‐β Paradox to EMT‐MET programs. Cancer Lett. 2013;341(1):30‐40. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 73. Connolly EC, Freimuth J, Akhurst RJ. Complexities of TGF‐β targeted cancer therapy. Int J Biol Sci. 2012;8(7):964‐978. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 74. Itatani Y, Kawada K, Sakai Y. Transforming growth factor‐β signaling pathway in colorectal cancer and its tumor microenvironment. Int J Mol Sci. 2019;20(23):5822. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 75. Simard J, Gingras S. Crucial role of cytokines in sex steroid formation in normal and tumoral tissues. Mol Cell Endocrinol. 2001;171(1–2):25‐40. [DOI] [PubMed] [Google Scholar]
- 76. Edvardsson K, Ström A, Jonsson P, Gustafsson J‐Å, Williams C. Estrogen receptor β induces antiinflammatory and antitumorigenic networks in colon cancer cells. Mol Endocrinol. 2011;25(6):969‐979. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 77. Dong C, Yuan T, Wu Y, et al. Loss of FBP1 by Snail‐mediated repression provides metabolic advantages in basal‐like breast cancer. Cancer Cell. 2013;23(3):316‐331. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 78. Cvoro A, Tatomer D, Tee M‐K, Zogovic T, Harris HA, Leitman DC. Selective estrogen receptor‐β agonists repress transcription of proinflammatory genes. J Immunol. 2008;180(1):630‐636. [DOI] [PubMed] [Google Scholar]
- 79. Kovats S, Carreras E. Regulation of dendritic cell differentiation and function by estrogen receptor ligands. Cell Immunol. 2008;252(1–2):81‐90. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 80. Caiazza F, Ryan EJ, Doherty G, Winter DC, Sheahan K. Estrogen receptors and their implications in colorectal carcinogenesis. Front Oncol. 2015;5:19. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 81. Coussens LM, Werb Z. Inflammation and cancer. Nature. 2002;420(6917):860‐867. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 82. Pedersen N, Duricova D, Elkjaer M, Gamborg M, Munkholm P, Jess T. Risk of extra‐intestinal cancer in inflammatory bowel disease: meta‐analysis of population‐based cohort studies. Am J Gastroenterol. 2010;105(7):1480‐1487. [DOI] [PubMed] [Google Scholar]
- 83. Mantovani A, Allavena P, Sica A, Balkwill F. Cancer‐related inflammation. Nature. 2008;454(7203):436‐444. [DOI] [PubMed] [Google Scholar]
- 84. Grivennikov SI, Greten FR, Karin M. Immunity, inflammation, and cancer. Cell. 2010;140(6):883‐899. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 85. Joyce JA, Pollard JW. Microenvironmental regulation of metastasis. Nat Rev Cancer. 2009;9(4):239‐252. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 86. Taniguchi K, Karin M. NF‐κB, inflammation, immunity and cancer: coming of age. Nat Rev Immunol. 2018;18(5):309‐324. [DOI] [PubMed] [Google Scholar]
- 87. Mussbacher M, Salzmann M, Brostjan C, et al. Cell type‐specific roles of NF‐κB linking inflammation and thrombosis. Front Immunol. 2019;10:85. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 88. West NR, McCuaig S, Franchini F, Powrie F. Emerging cytokine networks in colorectal cancer. Nat Rev Immunol. 2015;15(10):615‐629. [DOI] [PubMed] [Google Scholar]
- 89. Schwitalla S, Ziegler PK, Horst D, et al. Loss of p53 in enterocytes generates an inflammatory microenvironment enabling invasion and lymph node metastasis of carcinogen‐induced colorectal tumors. Cancer Cell. 2013;23(1):93‐106. [DOI] [PubMed] [Google Scholar]
- 90. Koi M, Tseng‐Rogenski SS, Carethers JM. Inflammation‐associated microsatellite alterations: mechanisms and significance in the prognosis of patients with colorectal cancer. World J Gastrointest Oncol. 2018;10(1):1‐14. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 91. Sisto M, Ribatti D, Lisi S. Organ fibrosis and autoimmunity: the role of inflammation in TGFβ‐dependent EMT. Biomolecules. 2021;11(2):310. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 92. Servais C, Erez N. From sentinel cells to inflammatory culprits: cancer‐associated fibroblasts in tumour‐related inflammation. J Pathol. 2013;229(2):198‐207. [DOI] [PubMed] [Google Scholar]
- 93. Tao L, Huang G, Song H, Chen Y, Chen L. Cancer associated fibroblasts: An essential role in the tumor microenvironment. Oncol Lett. 2017;14(3):2611‐2620. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 94. Mukaida N, Sasaki S. Fibroblasts, an inconspicuous but essential player in colon cancer development and progression. World J Gastroenterol. 2016;22(23):5301‐5316. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 95. Vermeulen L, De Sousa E, Melo F, et al. Wnt activity defines colon cancer stem cells and is regulated by the microenvironment. Nat Cell Biol. 2010;12(5):468‐476. [DOI] [PubMed] [Google Scholar]
- 96. Xiao L, Zhu H, Shu J, Gong D, Zheng D, Gao J. Overexpression of TGF‐β1 and SDF‐1 in cervical cancer‐associated fibroblasts promotes cell growth, invasion and migration. Arch Gynecol Obstet. 2022;305(1):179‐192. [DOI] [PubMed] [Google Scholar]
- 97. Calon A, Espinet E, Palomo‐Ponce S, et al. Dependency of colorectal cancer on a TGF‐β‐driven program in stromal cells for metastasis initiation. Cancer Cell. 2012;22(5):571‐584. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 98. Kessenbrock K, Plaks V, Werb Z. Matrix metalloproteinases: regulators of the tumor microenvironment. Cell. 2010;141(1):52‐67. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 99. Zhao J, Jin G, Liu X, et al. PAR1 and PAR4 exert opposite effects on tumor growth and metastasis of esophageal squamous cell carcinoma via STAT3 and NF‐κB signaling pathways. Cancer Cell Int. 2021;21(1):1‐14. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 100. Erez N, Truitt M, Olson P, Hanahan D. Cancer‐associated fibroblasts are activated in incipient neoplasia to orchestrate tumor‐promoting inflammation in an NF‐κB‐dependent manner. Cancer Cell. 2010;17(2):135‐147. [DOI] [PubMed] [Google Scholar]
- 101. An Y, Liu F, Chen Y, Yang Q. Crosstalk between cancer‐associated fibroblasts and immune cells in cancer. J Cell Mol Med. 2020;24(1):13‐24. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 102. Wei T, Song J, Liang K, et al. Identification of a novel therapeutic candidate, NRK, in primary cancer‐associated fibroblasts of lung adenocarcinoma microenvironment. J Cancer Res Clin Oncol. 2021;147(4):1049‐1064. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 103. Liu T, Han C, Wang S, et al. Cancer‐associated fibroblasts: an emerging target of anti‐cancer immunotherapy. J Hematol Oncol. 2019;12(1):1‐15. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 104. Guo G, Wang Y, Zhou Y, et al. Immune cell concentrations among the primary tumor microenvironment in colorectal cancer patients predicted by clinicopathologic characteristics and blood indexes. J Immunother Cancer. 2019;7(1):1‐13. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 105. Markman JL, Shiao SL. Impact of the immune system and immunotherapy in colorectal cancer. J Gastrointest Oncol. 2015;6(2):208. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 106. Sun Q, Zhang B, Hu Q, et al. The impact of cancer‐associated fibroblasts on major hallmarks of pancreatic cancer. Theranostics. 2018;8(18):5072‐5087. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 107. Zhuang J, Lu Q, Shen B, et al. TGFβ1 secreted by cancer‐associated fibroblasts induces epithelial‐mesenchymal transition of bladder cancer cells through lncRNA‐ZEB2NAT. Sci Rep. 2015;5(1):1‐13. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 108. Ziani L, Chouaib S, Thiery J. Alteration of the antitumor immune response by cancer‐associated fibroblasts. Front Immunol. 2018;9:414. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 109. Li T, Yi S, Liu W, et al. Colorectal carcinoma‐derived fibroblasts modulate natural killer cell phenotype and antitumor cytotoxicity. Med Oncol. 2013;30(3):1‐7. [DOI] [PubMed] [Google Scholar]
- 110. Balsamo M, Scordamaglia F, Pietra G, et al. Melanoma‐associated fibroblasts modulate NK cell phenotype and antitumor cytotoxicity. Proc Natl Acad Sci U S A. 2009;106(49):20847‐20852. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 111. Kim R, Emi M, Tanabe K. Cancer immunosuppression and autoimmune disease: beyond immunosuppressive networks for tumour immunity. Immunology. 2006;119(2):254‐264. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 112. Grossman JG, Nywening TM, Belt BA, et al. Recruitment of CCR2+ tumor associated macrophage to sites of liver metastasis confers a poor prognosis in human colorectal cancer. Onco Targets Ther. 2018;7(9):e1470729. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 113. Mazur A, Holthoff E, Vadali S, Kelly T, Post SR. Cleavage of type I collagen by fibroblast activation protein‐α enhances class A scavenger receptor mediated macrophage adhesion. PLoS One. 2016;11(3):e0150287. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 114. Chiarugi P. Cancer‐associated fibroblasts and macrophages: Friendly conspirators for malignancy. Onco Targets Ther. 2013;2(9):e25563. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 115. Tiainen S, Tumelius R, Rilla K, et al. High numbers of macrophages, especially M2‐like (CD 163‐positive), correlate with hyaluronan accumulation and poor outcome in breast cancer. Histopathology. 2015;66(6):873‐883. [DOI] [PubMed] [Google Scholar]
- 116. Ge P, Wang W, Li L, et al. Profiles of immune cell infiltration and immune‐related genes in the tumor microenvironment of colorectal cancer. Biomed Pharmacother. 2019;118:109228. [DOI] [PubMed] [Google Scholar]
- 117. Gok Yavuz B, Gunaydin G, Gedik ME, et al. Cancer associated fibroblasts sculpt tumour microenvironment by recruiting monocytes and inducing immunosuppressive PD‐1+ TAMs. Sci Rep. 2019;9(1):1‐15. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 118. Varricchi G, Galdiero MR, Loffredo S, et al. Are mast cells MASTers in cancer? Front Immunol. 2017;8:424. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 119. Ma Y, Hwang RF, Logsdon CD, Ullrich SE. Dynamic mast cell–stromal cell interactions promote growth of pancreatic cancer. Cancer Res. 2013;73(13):3927‐3937. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 120. Marquardt D, Gruber H, Wasserman S. Adenosine release from stimulated mast cells. Proc Natl Acad Sci U S A. 1984;81(19):6192‐6196. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 121. Martinez‐Nunez RT, Louafi F, Sanchez‐Elsner T. The interleukin 13 (IL‐13) pathway in human macrophages is modulated by microRNA‐155 via direct targeting of interleukin 13 receptor α1 (IL13Rα1). J Biol Chem. 2011;286(3):1786‐1794. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 122. Cheng Y, Li H, Deng Y, et al. Cancer‐associated fibroblasts induce PDL1+ neutrophils through the IL6‐STAT3 pathway that foster immune suppression in hepatocellular carcinoma. Cell Death Dis. 2018;9(4):1‐11. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 123. Zhu Q, Zhang X, Zhang L, et al. The IL‐6–STAT3 axis mediates a reciprocal crosstalk between cancer‐derived mesenchymal stem cells and neutrophils to synergistically prompt gastric cancer progression. Cell Death Dis. 2014;5(6):e1295. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 124. Ocana A, Nieto‐Jiménez C, Pandiella A, Templeton AJ. Neutrophils in cancer: prognostic role and therapeutic strategies. Mol Cancer. 2017;16(1):1‐7. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 125. Gröne J, Doebler O, Loddenkemper C, Hotz B, Buhr H‐J, Bhargava S. Robo1/Robo4: differential expression of angiogenic markers in colorectal cancer. Oncol Rep. 2006;15(6):1437‐1443. [PubMed] [Google Scholar]
- 126. Zhou W‐J, Geng ZH, Chi S, et al. Slit‐Robo signaling induces malignant transformation through Hakai‐mediated E‐cadherin degradation during colorectal epithelial cell carcinogenesis. Cell Res. 2011;21(4):609‐626. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 127. Marlow R, Binnewies M, Sorensen LK, et al. Vascular Robo4 restricts proangiogenic VEGF signaling in breast. Proc Natl Acad Sci U S A. 2010;107(23):10520‐10525. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 128. Jones CA, London NR, Chen H, et al. Robo4 stabilizes the vascular network by inhibiting pathologic angiogenesis and endothelial hyperpermeability. Nat Med. 2008;14(4):448‐453. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 129. Zhao H, Anand AR, Ganju RK. Slit2–Robo4 pathway modulates lipopolysaccharide‐induced endothelial inflammation and its expression is dysregulated during endotoxemia. J Immunol. 2014;192(1):385‐393. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 130. Dosset M, Vargas TR, Lagrange A, et al. PD‐1/PD‐L1 pathway: an adaptive immune resistance mechanism to immunogenic chemotherapy in colorectal cancer. Onco Targets Ther. 2018;7(6):e1433981. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 131. Junttila MR, De Sauvage FJ. Influence of tumour micro‐environment heterogeneity on therapeutic response. Nature. 2013;501(7467):346‐354. [DOI] [PubMed] [Google Scholar]
- 132. Thiem A, Hesbacher S, Kneitz H, et al. IFN‐gamma‐induced PD‐L1 expression in melanoma depends on p53 expression. J Exp Clin Cancer Res. 2019;38(1):1‐15. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 133. Raskov H, Orhan A, Christensen JP, Gögenur I. Cytotoxic CD8+ T cells in cancer and cancer immunotherapy. Br J Cancer. 2021;124(2):359‐367. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 134. Wang F‐W, Cao C‐H, Han K, et al. APC‐activated long noncoding RNA inhibits colorectal carcinoma pathogenesis through reduction of exosome production. J Clin Invest. 2021;131(7):e149666. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 135. Antonangeli F, Natalini A, Garassino MC, Sica A, Santoni A, Di Rosa F. Regulation of PD‐L1 expression by NF‐κB in cancer. Front Immunol. 2020;11:584626. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 136. Hidalgo M, Amant F, Biankin AV, et al. Patient‐derived xenograft models: an emerging platform for translational cancer research. Cancer Discov. 2014;4(9):998‐1013. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 137. Chen X‐W, Zhou S‐F. Inflammation, cytokines, the IL‐17/IL‐6/STAT3/NF‐κB axis, and tumorigenesis. Drug Des Devel Ther. 2015;9:2941. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 138. Zafari N, Bahramy A, Majidi Zolbin M, et al. MicroRNAs as novel diagnostic biomarkers in endometriosis patients: a systematic review and meta‐analysis. Expert Rev Mol Diagn. 2022;22(4):479‐495. [DOI] [PubMed] [Google Scholar]
- 139. Li Y, Deuring J, Peppelenbosch MP, Kuipers EJ, de Haar C, van der Woude CJ. IL‐6‐induced DNMT1 activity mediates SOCS3 promoter hypermethylation in ulcerative colitis‐related colorectal cancer. Carcinogenesis. 2012;33(10):1889‐1896. [DOI] [PubMed] [Google Scholar]
- 140. Patel SA, Bhambra U, Charalambous MP, et al. Interleukin‐6 mediated upregulation of CYP1B1 and CYP2E1 in colorectal cancer involves DNA methylation, miR27b and STAT3. Br J Cancer. 2014;111(12):2287‐2296. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 141. Ren D, Lin B, Zhang X, et al. Maintenance of cancer stemness by miR‐196b‐5p contributes to chemoresistance of colorectal cancer cells via activating STAT3 signaling pathway. Oncotarget. 2017;8(30):49807‐49823. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 142. Shen Z, Zhou R, Liu C, et al. MicroRNA‐105 is involved in TNF‐α‐related tumor microenvironment enhanced colorectal cancer progression. Cell Death Dis. 2017;8(12):1‐13. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 143. Wang T, Xu X, Xu Q, et al. miR‐19a promotes colitis‐associated colorectal cancer by regulating tumor necrosis factor alpha‐induced protein 3‐NF‐κB feedback loops. Oncogene. 2017;36(23):3240‐3251. [DOI] [PubMed] [Google Scholar]
- 144. Jia P, Cai H, Liu X, et al. Long non‐coding RNA H19 regulates glioma angiogenesis and the biological behavior of glioma‐associated endothelial cells by inhibiting microRNA‐29a. Cancer Lett. 2016;381(2):359‐369. [DOI] [PubMed] [Google Scholar]
- 145. Gonzalez H, Hagerling C, Werb Z. Roles of the immune system in cancer: from tumor initiation to metastatic progression. Genes Dev. 2018;32(19–20):1267‐1284. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 146. Heward JA, Lindsay MA. Long non‐coding RNAs in the regulation of the immune response. Trends Immunol. 2014;35(9):408‐419. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 147. Wu K, Zhao Z, Liu K, Zhang J, Li G, Wang L. Long noncoding RNA lnc‐sox5 modulates CRC tumorigenesis by unbalancing tumor microenvironment. Cell Cycle. 2017;16(13):1295‐1301. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 148. Huarte M. The emerging role of lncRNAs in cancer. Nat Med. 2015;21(11):1253‐1261. [DOI] [PubMed] [Google Scholar]
- 149. Spizzo R, Almeida MI, Colombatti A, Calin GA. Long non‐coding RNAs and cancer: a new frontier of translational research? Oncogene. 2012;31(43):4577‐4587. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 150. Xu M, Xu X, Pan B, et al. LncRNA SATB2‐AS1 inhibits tumor metastasis and affects the tumor immune cell microenvironment in colorectal cancer by regulating SATB2. Mol Cancer. 2019;18(1):1‐16. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 151. Bian Z, Zhang J, Li M, et al. LncRNA–FEZF1‐AS1 promotes tumor proliferation and metastasis in colorectal cancer by regulating PKM2 signaling. Clin Cancer Res. 2018;24(19):4808‐4819. [DOI] [PubMed] [Google Scholar]
- 152. Xue J, Liao L, Yin F, Kuang H, Zhou X, Wang Y. LncRNA AB073614 induces epithelial‐mesenchymal transition of colorectal cancer cells via regulating the JAK/STAT3 pathway. Cancer Biomark. 2018;21(4):849‐858. [DOI] [PubMed] [Google Scholar]
- 153. Takebe N, Ivy P, Timmer W, Khan N, Schulz T, Harris PJ. Review of cancer–associated fibroblasts and therapies that interfere with their activity. Tumor Microenviron Ther. 2013;1:19‐36. [Google Scholar]
- 154. Barrett R, Puré E. Cancer‐associated fibroblasts: key determinants of tumor immunity and immunotherapy. Curr Opin Immunol. 2020;64:80‐87. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 155. Kuzet S‐E, Gaggioli C. Fibroblast activation in cancer: when seed fertilizes soil. Cell Tissue Res. 2016;365(3):607‐619. [DOI] [PubMed] [Google Scholar]
- 156. Chen X, Song E. Turning foes to friends: targeting cancer‐associated fibroblasts. Nat Rev Drug Discov. 2019;18(2):99‐115. [DOI] [PubMed] [Google Scholar]
- 157. Yingling JM, Blanchard KL, Sawyer JS. Development of TGF‐β signalling inhibitors for cancer therapy. Nat Rev Drug Discov. 2004;3(12):1011‐1022. [DOI] [PubMed] [Google Scholar]
- 158. Buka D, Dvořák J, Richter I, Škrobánek P, Buchler T, Melichar B. Interactions between anti‐Vegf therapy and antitumor immunity as a potential therapeutic strategy in colorectal cancer. Acta Medica. 2019;62(3):127‐130. [DOI] [PubMed] [Google Scholar]
- 159. Mohamed SY, Mohammed HL, Ibrahim HM, Mohamed EM, Salah M. Role of VEGF, CD105, and CD31 in the prognosis of colorectal cancer cases. J Gastrointest Cancer. 2019;50(1):23‐34. [DOI] [PubMed] [Google Scholar]
- 160. Ganji PN, Park W, Wen J, et al. Antiangiogenic effects of ganetespib in colorectal cancer mediated through inhibition of HIF‐1α and STAT‐3. Angiogenesis. 2013;16(4):903‐917. [DOI] [PubMed] [Google Scholar]
- 161. Parizadeh SM, Jafarzadeh‐Esfehani R, Fazilat‐Panah D, et al. The potential therapeutic and prognostic impacts of the c‐MET/HGF signaling pathway in colorectal cancer. IUBMB Life. 2019;71(7):802‐811. [DOI] [PubMed] [Google Scholar]
- 162. Shali H, Ahmadi M, Kafil HS, Dorosti A, Yousefi M. IGF1R and c‐met as therapeutic targets for colorectal cancer. Biomed Pharmacother. 2016;82:528‐536. [DOI] [PubMed] [Google Scholar]
- 163. Wen J, Matsumoto K, Taniura N, Tomioka D, Nakamura T. Hepatic gene expression of NK4, an HGF‐antagonist/angiogenesis inhibitor, suppresses liver metastasis and invasive growth of colon cancer in mice. Cancer Gene Ther. 2004;11(6):419‐430. [DOI] [PubMed] [Google Scholar]
- 164. Sun Y, Sun L, An Y, Shen X. Cabozantinib, a novel c‐Met inhibitor, inhibits colorectal cancer development in a xenograft model. Med Sci Monit. 2015;21:2316‐2321. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 165. Kuester D, Lippert H, Roessner A, Krueger S. The cathepsin family and their role in colorectal cancer. Pathol Res Pract. 2008;204(7):491‐500. [DOI] [PubMed] [Google Scholar]
- 166. Tan G‐J, Peng Z‐K, Lu J‐P, Tang F‐Q. Cathepsins mediate tumor metastasis. World J Biol Chem. 2013;4(4):91‐101. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 167. Abdulla M‐H, Valli‐Mohammed M‐A, Al‐Khayal K, et al. Cathepsin B expression in colorectal cancer in a Middle East population: Potential value as a tumor biomarker for late disease stages. Oncol Rep. 2017;37(6):3175‐3180. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 168. Burden RE, Gormley JA, Kuehn D, et al. Inhibition of Cathepsin S by Fsn0503 enhances the efficacy of chemotherapy in colorectal carcinomas. Biochimie. 2012;94(2):487‐493. [DOI] [PubMed] [Google Scholar]
- 169. Said AH, Raufman J‐P, Xie G. The role of matrix metalloproteinases in colorectal cancer. Cancers. 2014;6(1):366‐375. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 170. Zucker S, Vacirca J. Role of matrix metalloproteinases (MMPs) in colorectal cancer. Cancer Metastasis Rev. 2004;23(1):101‐117. [DOI] [PubMed] [Google Scholar]
- 171. Mondal S, Adhikari N, Banerjee S, Amin SA, Jha T. Matrix metalloproteinase‐9 (MMP‐9) and its inhibitors in cancer: A minireview. Eur J Med Chem. 2020;194:112260. [DOI] [PubMed] [Google Scholar]
- 172. Xiang L, He B, Liu Q, et al. Antitumor effects of curcumin on the proliferation, migration and apoptosis of human colorectal carcinoma HCT‐116 cells. Oncol Rep. 2020;44(5):1997‐2008. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 173. Park J, Conteas CN. Anti‐carcinogenic properties of curcumin on colorectal cancer. World J Gastrointest Oncol. 2010;2(4):169‐176. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 174. Chen Y‐T, Tsao S‐C, Yuan S‐SF, Tsai H‐P, Chai C‐Y. Serine protease inhibitor kazal type 1 (SPINK1) promotes proliferation of colorectal cancer through the epidermal growth factor as a prognostic marker. Pathol Oncol Res. 2015;21(4):1201‐1208. [DOI] [PubMed] [Google Scholar]
- 175. Coto‐Llerena M, Ercan C, Kancherla V, et al. High expression of FAP in colorectal cancer is associated with angiogenesis and immunoregulation processes. Front Oncol. 2020;10:979. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 176. Narra K, Mullins SR, Lee H‐O, et al. Phase II trial of single agent Val‐boroPro (Talabostat) inhibiting Fibroblast Activation Protein in patients with metastatic colorectal cancer. Cancer Biol Ther. 2007;6(11):1691‐1699. [DOI] [PubMed] [Google Scholar]
- 177. Gungor H, Ilhan N, Eroksuz H. The effectiveness of cyclooxygenase‐2 inhibitors and evaluation of angiogenesis in the model of experimental colorectal cancer. Biomed Pharmacother. 2018;102:221‐229. [DOI] [PubMed] [Google Scholar]
- 178. Zhang B. Targeting the stroma by T cells to limit tumor growth. Cancer Res. 2008;68(23):9570‐9573. [DOI] [PubMed] [Google Scholar]
- 179. Karin M. Nuclear factor‐κB in cancer development and progression. Nature. 2006;441(7092):431‐436. [DOI] [PubMed] [Google Scholar]
- 180. Popa C, Netea MG, Van Riel PL, Van Der Meer JW, Stalenhoef AF. The role of TNF‐α in chronic inflammatory conditions, intermediary metabolism, and cardiovascular risk. J Lipid Res. 2007;48(4):751‐762. [DOI] [PubMed] [Google Scholar]
- 181. Hodge DR, Hurt EM, Farrar WL. The role of IL‐6 and STAT3 in inflammation and cancer. Eur J Cancer. 2005;41(16):2502‐2512. [DOI] [PubMed] [Google Scholar]
- 182. Kurzrock R, Voorhees PM, Casper C, et al. A phase I, open‐label study of siltuximab, an anti–IL‐6 monoclonal antibody, in patients with B‐cell non‐Hodgkin lymphoma, multiple myeloma, or Castleman disease. Clin Cancer Res. 2013;19(13):3659‐3670. [DOI] [PubMed] [Google Scholar]
- 183. Fridman WH, Miller I, Sautès‐Fridman C, Byrne AT. Therapeutic targeting of the colorectal tumor stroma. Gastroenterology. 2020;158(2):303‐321. [DOI] [PubMed] [Google Scholar]
- 184. Botrel TEA, Clark LGO, Paladini L, Clark OAC. Efficacy and safety of bevacizumab plus chemotherapy compared to chemotherapy alone in previously untreated advanced or metastatic colorectal cancer: a systematic review and meta‐analysis. BMC Cancer. 2016;16(1):1‐19. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 185. Hurwitz H. Integrating the anti–VEGF‐A humanized monoclonal antibody bevacizumab with chemotherapy in advanced colorectal cancer. Clin Colorectal Cancer. 2004;4:S62‐S68. [DOI] [PubMed] [Google Scholar]
- 186. Sliesoraitis S, Tawfik B. Bevacizumab‐induced bowel perforation. J Am Osteopath Assoc. 2011;111(7):437‐441. [PubMed] [Google Scholar]
- 187. Cho T, Shiozawa E, Urushibara F, et al. The role of microvessel density, lymph node metastasis, and tumor size as prognostic factors of distant metastasis in colorectal cancer. Oncol Lett. 2017;13(6):4327‐4333. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 188. Zessner‐Spitzenberg J, Thomas AL, Krett NL, Jung B. TGFβ and activin A in the tumor microenvironment in colorectal cancer. Gene Rep. 2019;17:100501. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 189. Gu S, Feng X‐H. TGF‐β signaling in cancer. Acta Biochim Biophys Sin. 2018;50(10):941‐949. [DOI] [PubMed] [Google Scholar]
- 190. Tzavlaki K, Moustakas A. TGF‐β signaling. Biomolecules. 2020;10(3):487. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 191. Vander Ark A, Cao J, Li X. TGF‐β receptors: In and beyond TGF‐β signaling. Cell Signal. 2018;52:112‐120. [DOI] [PubMed] [Google Scholar]
- 192. Maeda H, Wada N, Tomokiyo A, Monnouchi S, Akamine A. Prospective potency of TGF‐β1 on maintenance and regeneration of periodontal tissue. Int Rev Cell Mol Biol. 2013;304:283‐367. [DOI] [PubMed] [Google Scholar]
- 193. Colak S, Ten Dijke P. Targeting TGF‐β signaling in cancer. Trends Cancer. 2017;3(1):56‐71. [DOI] [PubMed] [Google Scholar]
- 194. Bahrami A, Khazaei M, Hassanian SM, et al. Targeting the tumor microenvironment as a potential therapeutic approach in colorectal cancer: Rational and progress. J Cell Physiol. 2018;233(4):2928‐2936. [DOI] [PubMed] [Google Scholar]
- 195. Yingling JM, McMillen WT, Yan L, et al. Preclinical assessment of galunisertib (LY2157299 monohydrate), a first‐in‐class transforming growth factor‐β receptor type I inhibitor. Oncotarget. 2018;9(6):6659‐6677. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 196. Villalba M, Evans SR, Vidal‐Vanaclocha F, Calvo A. Role of TGF‐β in metastatic colon cancer: it is finally time for targeted therapy. Cell Tissue Res. 2017;370(1):29‐39. [DOI] [PubMed] [Google Scholar]
- 197. Sanchez‐Lopez E, Flashner‐Abramson E, Shalapour S, et al. Targeting colorectal cancer via its microenvironment by inhibiting IGF‐1 receptor‐insulin receptor substrate and STAT3 signaling. Oncogene. 2016;35(20):2634‐2644. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 198. Park S‐Y, Lee C‐J, Choi J‐H, et al. The JAK2/STAT3/CCND2 Axis promotes colorectal Cancer stem cell persistence and radioresistance. J Exp Clin Cancer Res. 2019;38(1):1‐18. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 199. Jin G, Yang Y, Liu K, et al. Combination curcumin and (−)‐epigallocatechin‐3‐gallate inhibits colorectal carcinoma microenvironment‐induced angiogenesis by JAK/STAT3/IL‐8 pathway. Oncogenesis. 2017;6(10):e384. [DOI] [PMC free article] [PubMed] [Google Scholar]
Associated Data
This section collects any data citations, data availability statements, or supplementary materials included in this article.
Supplementary Materials
Appendix S1
Data Availability Statement
All data used to support the findings of this study are included in the article.