1、Mechanisms that drive inflammatory tumor microenvironment,tumor heterogeneity,and metastatic progressionLi Yanga,*and P.Charles Linb,*aLaboratory of Cancer Biology and Genetics,National Cancer Institute,NIH,37 Convent Drive,Bethesda,MD 20892,USAbCancer and Inflammation Program,Center for Cancer Rese
2、arch,National Cancer Institute,NIH,Frederick,MD,21702,USAAbstractTreatment of cancer metastases has been largely ineffective.It is paramount to understand the mechanisms underlying the metastatic process,of which the tumor microenvironment is an indispensable participant.What are the critical cellul
3、ar and molecular players at the primary tumor site where metastatic cascade initiates?How is tumor-associated inflammation regulated?How do altered vasculatures contribute to metastasis?What is the dynamic nature or heterogeneity of primary tumors and what are the challenges to catch a moving target
4、?This review summarizes recent progress,mechanistic understanding,and options for metastasis-targeted therapy.KeywordsTumor metastasis;Microenvironment;Tumor suppressor;Inflammation/Immune;Heterogeneity1.IntroductionTumor metastasis accounts for most cancer-associated deaths in patients.Currently,th
5、ere are very few effective treatment options 1.During metastasis,tumor cells must disseminate,intravasate into circulation,travel through vascular networks,arrest in vascular beds of target organs,and subsequently extravasate into the organ parenchyma 2.In a hostile distant organ,they must escape ho
6、st immune surveillance,adapt to supportive niches,survive as latent tumor-initiating seeds,and eventually break out to grow 3.Evidence from recent years strongly suggests that the tumor microenvironment(TME)is an indispensable participant in the metastatic process 3,4,allowing the tumor cells not on
7、ly to escape from host immune surveillance,but also induce the formation of new blood vessels and invade the*Corresponding author at:Laboratory of Cancer Biology and Genetics,National Cancer Institute,NIH,37 Convent Drive,Bethesda,MD 20892,USA.yangl3mail.nih.gov(L.Yang),Phone numbers:240-760-6809.*C
8、orresponding author at:Cancer and Inflammation Program,Center for Cancer Research,National Cancer Institute,NIH,Frederick,MD,21702,USA,p.linnih.gov(P.C.Lin),Phone numbers:301-228-4688.Publishers Disclaimer:This is a PDF file of an unedited manuscript that has been accepted for publication.As a servi
9、ce to our customers we are providing this early version of the manuscript.The manuscript will undergo copyediting,typesetting,and review of the resulting proof before it is published in its final citable form.Please note that during the production process errors may be discovered which could affect
10、the content,and all legal disclaimers that apply to the journal pertain.HHS Public AccessAuthor manuscriptSemin Cancer Biol.Author manuscript;available in PMC 2018 December 01.Published in final edited form as:Semin Cancer Biol.2017 December;47:185195.doi:10.1016/j.semcancer.2017.08.001.Author Manus
11、criptAuthor ManuscriptAuthor ManuscriptAuthor Manuscriptvasculature 5.This review will focus on the primary tumor site where the initiating step of metastatic cascade occurs,and provide updates on the critical cellular and molecular players,as well as potential targeting options.2.Players in the pri
12、mary tumor microenvironmentTumor is described as an unhealed chronically inflamed wound.In addition to the tumor cells at a primary tumor site,there are a variety of inflammatory cells including both innate and adoptive immune cells,and myeloid and lymphoid lineages(Fig.1).They impact diverse biolog
13、ical functions and tumor phenotypes(Fig.1).Of tumor-infiltrating myeloid cells,there are three major types:Gr-1+CD11b+immature myeloid cells,tumor-associated macrophages(TAM),and tumor-associated neutrophils(TAN).Gr-1+CD11b+cells are a heterogeneous set of immature myeloid cells,while TAM and TAN ar
14、e well-differentiated.It remains to be seen how these three populations of cells are interrelated in phenotype and function in the TME.Gr-1+CD11b+cells are also called myeloid-derived suppressor cells(MDSCs)for their well-known immune suppressive activities 6,7.In addition,MDSCs produce matrix metal
15、lopeptidase 9(MMP9)and transforming factor beta(TGF),executing a profound impact on tumor progression and metastasis through modulation of tumor vascularization and tumor cell invasion 8,9.TAMs are identified as Mac-1(CD11b+)and/or F4/80+myeloid cells.They promote tumor progression and metastasis 10
16、12 through elevated colony stimulating factor 1(CSF-1)production and enhanced epithelial growth factor(EGF)signaling in cancer cells 13,14.TAN,identified as CD11b+Ly6G+cells,have only recently been reported to possess tumor-promoting functions 1517.However,in early stages of human lung cancer,subset
17、s of TANs exhibit anti-tumor properties with characteristics of both neutrophils and antigen-presenting cells 17.TGF regulates N1N2 polarization of neutrophils 15.This N1N2 polarization of neutrophils may mirror the M1M2 polarization of macrophages that are defined by interferon-and IL-4 production
18、as Th1 and Th2 cells,respectively 18.Tissue-residing lymphoid cells are very important in tissue repair and integrity 19.In tumor tissues,a number of lymphoid cells are found,including cytotoxic T lymphocytes(CTL),regulatory T cells(Treg),and B cells.CTL proliferation and function are usually suppre
19、ssed under tumor conditions through various mechanisms including decreased perforin,granzymes,and cytotoxins 20,21;lost co-localization of the T cell receptor and CD8 22;the development of other T cell types such as gamma/delta T cells that suppress T and dendritic cell functions 23;aberrant express
20、ion of stress-inducible NKG2D ligands;and expansion of immunosuppressive T cells 24.Importantly,activation of immune inhibitory pathways through programmed cell death protein 1 and its ligand(PDL-1/PD1)impairs cytotoxic T cell functions 25,26.CD4+CD25+Treg cells are induced in the TME through TGF-pr
21、omoted Foxp3 expression and possess strong immune suppressive functions 27,28.Cytotoxic T-lymphocyte-associated antigen 4(CTLA4)is identified as an important inhibitory mediator particularly in CD4+Treg cells.Drugs targeting CTLA4 unleashes anti-tumor immunity 25,29.Chronic activation of B cells is
22、indicated in potentiating carcinoma development in the transgenic mouse model K14-HPV16 30.In fact,B cells,humoral immunity,and activating FcyRs are required for establishing chronic inflammatory programs that promote de novo carcinogenesis 31.TGF(and/or IL-10)is Yang and LinPage 2Semin Cancer Biol.
23、Author manuscript;available in PMC 2018 December 01.Author ManuscriptAuthor ManuscriptAuthor ManuscriptAuthor Manuscriptresponsible for B cell-mediated immune suppression 32,33.In addition,complement C5a in a TME recruits MDSCs,thus suppressing CTL function and promoting tumor growth 34.Beyond the i
24、mmune cells,there is also an abundance of cancer-associated fibroblasts(CAFs)35,36,and their gene expression predicts clinical outcomes 36,37.CAFs produce chemokines and cytokines such as stromal-derived factor 1(SDF-1 or CXCL12)38 and platelet-derived growth factor C 39,and promote tumor progressio
25、n and resistance to therapy such as anti-VEGF(vascular endothelial growth factor)39.TGF is a critical mediator in the CAF tumor-promoting function 4042.Tumor infiltrating immune cells crosstalk with each other and with tumor cells.For example,tumor cells and macrophages produce PDL-1(ligand for PD-1
26、)that activates PD1-(programmed cell death protein 1)mediated inhibitory immune checkpoint in T cells;immune therapies blocking immune-inhibitory checkpoints(PDL1/PD1 and CTLA-4)lead to T cell activation and tumor regression 25,26.IL-4-expressing CD4+T lymphocytes regulate phenotype and function of
27、CD11b+F4/80+macrophages,which in turn enhance epithelial growth factor receptor(EGFR)signaling in mammary epithelial cells and promote tumor invasion and metastasis 43.Recently studies show TAM also express PD1,which impairs their phagocytic activity 44.In addition,TAMs capture the PD-1 mAbs on the
28、T cell surface thus compromise the effectiveness of immune therapeutics 45.These insights should be helpful in addressing relapse and resistance in immune checkpoint blockade.TGF-mediated inflammatory response is critical in the crosstalk between myeloid cells and metastatic breast cancer cells 9,46
29、,47.In addition,epithelial cells and CAFs influence one another and enhance tumor progression 4042.Some studies have shown genetic alterations/somatic mutations in stromal fibroblasts and support a tumor-stroma coevolution 4852;however,such findings remain highly controversial 53,54.Nevertheless,it
30、is clear that host-derived stromal cells collectively create an environment that favors tumor progression by providing growth factors,pro-angiogenic factors,proteases,and adhesion molecules that facilitate tumor cell proliferation,angiogenesis,invasion,and metastasis as well as therapeutic resistanc
31、e 55,56.This very dynamic TME likely serves as a selective pressure for tumor cell variants through genomic instability,genomic heterogeneity,and epigenetic alterations 57,58.3.Mechanisms of inflammationChronic inflammation is a hallmark of cancer 59.Different from acute inflammation that can clear
32、infection,heal wounds,and maintain tissue homeostasis,tumor-associated inflammation is often low in grade and chronic.Many factors can trigger inflammatory response in tumors,including infection,tissue damage,activation of oncogenes,and loss of tumor suppressors(TS)(Fig.2).Oncogenes like those encod
33、ing protein tyrosine kinases(RTKs)are often persistently activated in a ligand-independent manner 60,61.Emerging literature supports a role of RTKs in inflammation induction.RET(REarranged during Transfection),an RTK with cadherin-like domains in its extracellular region,is altered in cancers in the
34、 forms of fusion(thyroid and non-small cell lung cancer),overexpression(breast,prostate,pancreatic cancers,and several more),and point mutations(in multiple Yang and LinPage 3Semin Cancer Biol.Author manuscript;available in PMC 2018 December 01.Author ManuscriptAuthor ManuscriptAuthor ManuscriptAuth
35、or Manuscriptendocrine neoplasia type 2A and familial medullary thyroid carcinoma)62,63.Activation of RET,either by oncogenic mutations or binding of ligands and co-receptors,stimulates pro-inflammatory gene expression and increases tumor-associated inflammation 6366.This biological property may exp
36、lain higher malignancy and resistance to endocrine therapies in patients with breast cancer exhibiting increased RET expression 63.EGFR signaling activates NF-B through MALT1,a scaffold protein,via recruiting E3 ligase TRAF6 to IB kinase (IKK)complex 67.Overexpression of Neu or Her2 driven by the MM
37、TV promoter induced inflammatory response through Stat3-dependent overexpression of C-terminal tensin-like(Cten)focal adhesion protein,which disrupts cell-cell junctions and enhances tumor cell metastatic ability 68.In addition to RTKs,publications also support a role of oncogenic Ras in inflammatio
38、n induction.Ras activation exacerbated pro-malignant paracrine activities through IL-6 and IL-8 69.High Ras activity leads to acinar cell senescence and increased inflammation and fibrosis,subsequently resulting in the formation of pancreatic intraepithelial neoplasia and progression to both cystic
39、papillary carcinoma and metastatic pancreatic ductal adenocarcinoma 70.In the presence of oncogenic Ras,inflammatory stimuli trigger an NF-B-mediated positive feedback mechanism involving cyclooxygenase 2 that amplifies Ras activity 71.In skin carcinogenesis,Ras activation induces inflammation throu
40、gh IL-1R-MyD88 signaling 72.Activation of oncogenic Ras enhances the expression of squamous cell carcinoma antigens and IL-6 via NF-B inflammatory pathway 73.In pancreatic cancer,oncogenic KRAS(G12D)accelerates inflammation-induced carcinogenesis through NFATc1-STAT3 cooperativity in gene transcript
41、ion 74.Lastly,p53 mutant,with gain-of-oncogenic activity,such as p53R273H,is capable of activating NF-B,which leads to chronic inflammation,tissue damage,and accelerated tumor development 75,76.Together these studies suggest that oncogene activation promotes inflammation and tumor progression throug
42、h production of cytokines,chemokines,growth factors,prostaglandins,reactive oxygen,and nitrogen species,as well as recruitment of inflammatory cells in tumor tissues(Fig.2).Tumor suppressors are powerful transcriptional and signaling regulators counteracting the growth-promoting activity of oncogene
43、s 77.Loss or silencing of TS promotes neoplastic transformation and malignant progression.To date,most work on TS has focused on cell-autonomous effects.We recently proposed an important non-cell-autonomous role for TS in the control of tumor-associated inflammation 78.These TSs include p53,APC(aden
44、omatous polyposis coli),and TGF.p53 mutations are documented in over 50%of human cancers.Loss of normal p53 function is frequently associated with an increased susceptibility to inflammation-driven cancers such as ulcerative colitis-associated colorectal cancer 7981.A strong association of p53 mutat
45、ion and NF-B activity has been observed in patients with head and neck squamous cell carcinoma(HNSCC)82.In mouse models,p53 mutations induced inflammation in several tumor models 8385.Thus,the ability of WT p53 to inhibit tumor-associated inflammation is critical in its tumor suppressive activities
46、8688.APC germ line allelic loss is a hallmark of human familial adenomatous polyposis syndrome as well as sporadic colorectal cancer.Studies suggest a strong correlation between colon cancer progression and tumor-associated inflammation 11,89.Yang and LinPage 4Semin Cancer Biol.Author manuscript;ava
47、ilable in PMC 2018 December 01.Author ManuscriptAuthor ManuscriptAuthor ManuscriptAuthor ManuscriptIn mouse models,mono-allelic deletion of Apc in intestinal epithelial cells(Apc+/)results in tumor development upon inactivation of the wt Apc allele due to a loss of heterozygocity(LOH)9092.When Apc+/
48、mice are crossed with transgenic mice expressing constitutively active IKK in intestinal epithelial cells(IECs),the compound mice exhibit more-catenin positive(+)early lesions and small intestinal and colonic tumors relative to the parental Apc+/line 93.Targeted deletion of Apc allelic by Cdx2-Cre t
49、ransgene in mice leads to colorectal tumors with upregulation of several pro-inflammatory cytokines,including IL-23 and IL-17A 94.Interestingly,loss of APC in this model(which is also due to LOH)results in rapid epithelial barrier deterioration and microbial invasion,thus providing a major impetus f
50、or tumor-elicited inflammation 94.TGF possesses potent anti-inflammatory activity;loss or down-regulation of TGF signaling in epithelial cells induces inflammation in mouse models of mammary,pancreatic,intestinal,colon,and head-and-neck squamous cell carcinomas,and accelerates malignant progression
