Emerging roles of the tumor-associated stroma in promoting tumor metastasis

The stroma in human carcinomas consists of extracellular matrix and various types of non-carcinoma cells, mainly leukocytes, endothelial cells, fibroblasts, myofibroblasts and bone marrow-derived progenitors. The tumor-associated stroma actively supports tumor growth by stimulating neo-angiogenesis, as well as proliferation and invasion of apposed carcinoma cells. It has long been accepted that alterations within carcinoma cells mediate metastasis in a cell-autonomous fashion. Recent studies have, however, suggested an additional notion that cancer cells instigate local and systemic changes in the tumor microenvironment and contribute to niche formation for metastasis. Research, aiming to establish the roles of the tumor-associated stroma in facilitating the spread of carcinoma cells into distant organs, has provided an abundance of data and greater knowledge of the biology of metastatic carcinoma cells and associated stromal cells. This has stimulated further advances in the development of novel therapeutic approaches targeting tumor metastasis.     

结缔组织生成和肿瘤

肿瘤的发生并不只是由肿瘤细胞本身恶化引起的,肿瘤基质也发挥了非常重要的作用,肿瘤发生是肿瘤细胞和围绕它的肿瘤基质相互作用的产物。肿瘤细胞可以通过各种途径激活与其相邻的间质,促进成纤维细胞的增生、细胞外基质的沉积、免疫细胞浸润和血管生成,这种现象被称为结缔组织生成。结缔组织生成形成了一个支持肿瘤发展的微环境,通过多种途径促进了肿瘤的发生、发展和转移。针对结缔组织生成进行肿瘤治疗可以为肿瘤的临床治疗提供新的思路。     

结缔组织生成和肿瘤

肿瘤的发生并不只是由肿瘤细胞本身恶化引起的,肿瘤基质也发挥了非常重要的作用,肿瘤发生是肿瘤细胞和围绕它的肿瘤基质相互作用的产物。肿瘤细胞可以通过各种途径激活与其相邻的间质,促进成纤维细胞的增生、细胞外基质的沉积、免疫细胞浸润和血管生成,这种现象被称为结缔组织生成。结缔组织生成形成了一个支持肿瘤发展的微环境,通过多种途径促进了肿瘤的发生、发展和转移。针对结缔组织生成进行肿瘤治疗可以为肿瘤的临床治疗提供新的思路。     

综述: 细胞外基质与肿瘤相关成纤维细胞

肿瘤的发生发展是一个肿瘤细胞与其微环境相互促进,共同演化的动态过程．实体肿瘤的发生发展过程伴随细胞外基质的过量沉积及其组织形式的异常以及成纤维细胞的活化和富集．细胞外基质与肿瘤相关成纤维细胞不仅是实体肿瘤的重要病理特征,同时也是恶性肿瘤发展的重要驱动力量．细胞外基质与肿瘤相关成纤维细胞通过多种机制促进了肿瘤的发生、发展和转移．针对细胞外基质与肿瘤相关成纤维细胞进行肿瘤治疗,可以为肿瘤的临床治疗提供新的思路．     

黏着斑激酶与肿瘤微环境

黏着斑激酶（focal adhesion kinase, FAK）是一种胞质非受体酪氨酸激酶。FAK和肿瘤密切相关,在多种癌细胞中高表达,促进癌细胞的发生、生长、存活、增殖、粘附、转移和侵袭以及血管生成等过程。肿瘤微环境包括肿瘤细胞、周围血管、免疫细胞、纤维母细胞、内皮细胞、信号分子和细胞外基质,它对癌症的发展和恶化具有重要作用。肿瘤细胞可以通过分泌细胞外信号影响微环境,使其有利于肿瘤生存和发展|肿瘤微环境中的基质细胞能通过产生趋化因子、基质降解酶和生长因子促进肿瘤侵袭和转移。本文综述肿瘤微环境在癌症发生发展过程中的作用及FAK在肿瘤微环境中的调控作用,为肿瘤疾病的治疗提供新思路。     

Components of the hepatocellular carcinoma microenvironment and their role in tumor progression

This review summarizes recently published data on the mechanisms of tumor cell interaction with the tumor microenvironment. Tumor stroma influences the processes of hepatocarcinogenesis, epithelial-to-mesenchymal transition, invasion, and metastasis. The tumor microenvironment includes both cellular and noncellular components. Main cellular components of hepatocellular carcinoma (HCC) stroma are tumor-associated fibroblasts, hepatic stellate cells, immune cells, and endothelial cells that produce extracellular components of tumor microenvironment such as extracellular matrix, various proteins, proteolytic enzymes, growth factors, and cytokines. The noncellular components of the stroma modulate signaling pathways in tumor cells and stimulate invasion and metastasis. The tumor microenvironment composition and organization can serve as prognostic factors in HCC pathogenesis. Current approaches in HCC targeted therapy are aimed at creating efficient strategies for interrupting tumor interactions with the stroma. Recent data on the composition and role of the microenvironment in HCC pathogenesis, as well as new developments in antitumor drug design are discussed.     

Cancer Associated Fibroblasts Promote Tumor Growth and Metastasis by Modulating the Tumor Immune Microenvironment in a 4T1 Murine Breast Cancer Model

Background

Local inflammation associated with solid tumors commonly results from factors released by tumor cells and the tumor stroma, and promotes tumor progression. Cancer associated fibroblasts comprise a majority of the cells found in tumor stroma and are appealing targets for cancer therapy. Here, our aim was to determine the efficacy of targeting cancer associated fibroblasts for the treatment of metastatic breast cancer.

Methodology/Principal Findings

We demonstrate that cancer associated fibroblasts are key modulators of immune polarization in the tumor microenvironment of a 4T1 murine model of metastatic breast cancer. Elimination of cancer associated fibroblasts in vivo by a DNA vaccine targeted to fibroblast activation protein results in a shift of the immune microenvironment from a Th2 to Th1 polarization. This shift is characterized by increased protein expression of IL-2 and IL-7, suppressed recruitment of tumor-associated macrophages, myeloid derived suppressor cells, T regulatory cells, and decreased tumor angiogenesis and lymphangiogenesis. Additionally, the vaccine improved anti-metastatic effects of doxorubicin chemotherapy and enhanced suppression of IL-6 and IL-4 protein expression while increasing recruitment of dendritic cells and CD8⁺ T cells. Treatment with the combination therapy also reduced tumor-associated Vegf, Pdgfc, and GM-CSF mRNA and protein expression.

Conclusions/Significance

Our findings demonstrate that cancer associated fibroblasts promote tumor growth and metastasis through their role as key modulators of immune polarization in the tumor microenvironment and are valid targets for therapy of metastatic breast cancer.     

Frequent allelic losses in tumor-associated stromal cells and tumor epitelium of prostate cancer

It has become increasingly clear that tumor microenvironment plays a critical role in carcinogenesis. Accumulation of genetic alterations is typical not only for cancer epithelial cells but tumor-associated fibroblasts as well. Tumor epithelia, tumor-associated stroma from prostatectomy specimens of patients with prostate cancer and cells from prostatic intraepithelial neoplasia (PIN) and adjacent stroma from males with PIN were isolated by using laser capture microdissection. Microsatellite allelotyping was evaluated using 4 highly polymorphic markers for chromosomal regions 8p22, 16q23-24 and 13q14. Incidences of alterations (loss of heterozygosity or allelic imbalance) were 48% for region 8p22, 72% for 16q23 and 37% for 13q14. The LOH frequencies in tumor-associated stroma cells were very similar. Alterations at chromosome 13q were significantly associated with advanced tumor stage, whereas AI at 16q was also associated with high Gleason score and lymph node metastasis. We find some incidences of allelic imbalance in premalignant lesions in epithelial (16-27%) and stromal (7-22%) components. Our results show that the frequencies of genetic aberrations are as high in stromal cells as in tumor cells.     

ADAM12 produced by tumor cells rather than stromal cells accelerates breast tumor progression

Expression of ADAM12 is low in most normal tissues but is markedly increased in numerous human cancers, including breast carcinomas. We have previously shown that overexpression of ADAM12 accelerates tumor progression in a mouse model of breast cancer (PyMT). In this study, we found that ADAM12 deficiency reduces breast tumor progression in the PyMT model. However, the catalytic activity of ADAM12 seems to be dispensable for its tumor-promoting effect. Interestingly, we show that ADAM12 endogenously expressed in tumor-associated stroma in the PyMT model does not influence tumor progression, but that ADAM12 expression by tumor cells is necessary for tumor progression in these mice. This finding is consistent with our observation that in human breast carcinoma, ADAM12 is almost exclusively located in tumor cells and, only rarely, seen in the tumor-associated stroma. We hypothesized, however, that the tumor-associated stroma may stimulate ADAM12 expression in tumor cells, on the basis of the fact that TGF-β1 stimulates ADAM12 expression and is a well-known growth factor released from tumor-associated stroma. TGF-β1 stimulation of ADAM12-negative Lewis lung tumor cells induced ADAM12 synthesis, and growth of these cells in vivo induced more than 200-fold increase in ADAM12 expression. Our observation that ADAM12 expression is significantly higher in the terminal duct lobular units (TDLU) adjacent to human breast carcinoma compared with TDLUs found in normal breast tissue supports our hypothesis that tumor-associated stroma triggers ADAM12 expression.     

Decreased Peritoneal Ovarian Cancer Growth in Mice Lacking Expression of Lipid Phosphate Phosphohydrolase 1

Lysophosphatidic acid (LPA) is a bioactive lipid that enhances ovarian cancer cell proliferation, migration and invasion in vitro and stimulates peritoneal metastasis in vivo. LPA is generated through the action of autotaxin or phospholipases, and degradation begins with lipid phosphate phosphohydrolase (LPP)-dependent removal of the phosphate. While the effects of LPA on ovarian cancer progression are clear, the effects of LPA metabolism within the tumor microenvironment on peritoneal metastasis have not been reported. We examined the contribution of lipid phosphatase activity to ovarian cancer peritoneal metastasis using mice deficient in LPP1 expression. Homozygous deletion of LPP1 (LPP1 KO) results in elevated levels and decreased turnover of LPA in vivo. Within 2 weeks of intraperitoneal injection of syngeneic mouse ovarian cancer cells, we observed enhanced tumor seeding in the LPP1 KO mice compared to wild type. However, tumor growth plateaued in the LPP1 KO mice by 3 weeks while tumors continued to grow in wild type mice. The decreased tumor burden was accompanied by increased apoptosis and no change in proliferation or angiogenesis. Tumor growth was restored and apoptosis reversed with exogenous administration of LPA. Together, these observations demonstrate that the elevated levels of LPA per se in LPP1 KO mice do not inhibit tumor growth. Rather, the data support the notion that either elevated LPA concentration or altered LPA metabolism affects other growth-promoting contributions of the tumor microenvironment.     

Systems Analysis of a Mouse Xenograft Model Reveals Annexin A1 as a Regulator of Gene Expression in Tumor Stroma

Annexin A1 is a multi functional molecule which is involved in inflammation, innate and adaptive immune systems, tumor progression and metastasis. We have previously showed the impaired tumor growth, metastasis, angiogenesis and wound healing in annexin A1 knockout mice. While tumor is a piece of heterogeneous mass including not only malignant tumor cells but also the stroma, the importance of the tumor stroma for tumor progression and metastasis is becoming increasingly clear. The tumor stroma is comprised by various components including extracellular matrix and non-malignant cells in the tumor, such as endothelial cells, fibroblasts, immune cells, inflammatory cells. Based on our previous finding of pro-angiogenic functions for annexin A1 in vascular endothelial cell sprouting, wound healing, tumor growth and metastasis, and the previously known properties for annexin A1 in immune cells and inflammation, this study hypothesized that annexin A1 is a key functional player in tumor development, linking the various components in tumor stroma by its actions in endothelial cells and immune cells. Using systems analysis programs commercially available, this paper further compared the gene expression between tumors from annexin A1 wild type mice and annexin A1 knockout mice and found a list of genes that significantly changed in the tumor stroma that lacked annexin A1. This revealed annexin A1 to be an effective regulator in tumor stroma and suggested a mechanism that annexin A1 affects tumor development and metastasis through interaction with the various components in the microenvironment surrounding the tumor cells.     

Ovarian Tumor-Induced T Cell Suppression Is Alleviated by Vascular Leukocyte Depletion

The ovarian cancer microenvironment recruits an array of immune cells to the site of tumor growth. Within the peritoneal ascites of both humans and mice, the predominant population of tumor-infiltrating leukocytes is a CD11c⁺CD11b⁺ population variably referred to as vascular leukocytes (VLCs), tumor-associated macrophages, and immature dendritic cells. We have previously shown that these cells are critical for tumor growth because their selective elimination from the peritoneal tumor microenvironment inhibited tumor progression. However, the underlying mechanism by which this therapy was efficacious is poorly understood. Here, we use the murine ID8 ovarian tumor model to demonstrate that the tumor microenvironment induces in vivo immunosuppression of T cells and that the SR-A⁺ VLCs mediate this suppression. Importantly, the elimination of SR-A⁺ VLCs from the peritoneum of tumor-bearing mice relieves the T cell suppression. Moreover, the profound changes that VLC elimination has on the immune system are T cell-dependent because the protective antitumor effect of VLC elimination does not occur when CD8 T cells are concomitantly depleted. These results were confirmed and extended with the use of a genetic model for VLC depletion, which demonstrated that short-term therapeutic depletion of VLCs alleviates immunosuppression and allows for efficacious vaccination against model tumor antigens in tumor-bearing mice. These studies provide a mechanistic explanation for how leukocytes contribute to ovarian tumor progression and, correspondingly, how leukocyte depletion inhibits tumor growth.     

The tumor microenvironment and its contribution to tumor evolution toward metastasis

Cancer cells acquire cell-autonomous capacities to undergo limitless proliferation and survival through the activation of oncogenes and inactivation of tumor suppressor genes. Nevertheless, the formation of a clinically relevant tumor requires support from the surrounding normal stroma, also referred to as the tumor microenvironment. Carcinoma-associated fibroblasts, leukocytes, bone marrow-derived cells, blood and lymphatic vascular endothelial cells present within the tumor microenvironment contribute to tumor progression. Recent evidence indicates that the microenvironment provides essential cues to the maintenance of cancer stem cells/cancer initiating cells and to promote the seeding of cancer cells at metastatic sites. Furthermore, inflammatory cells and immunomodulatory mediators present in the tumor microenvironment polarize host immune response toward specific phenotypes impacting tumor progression. A growing number of studies demonstrate a positive correlation between angiogenesis, carcinoma-associated fibroblasts, and inflammatory infiltrating cells and poor outcome, thereby emphasizing the clinical relevance of the tumor microenvironment to aggressive tumor progression. Thus, the dynamic and reciprocal interactions between tumor cells and cells of the tumor microenvironment orchestrate events critical to tumor evolution toward metastasis, and many cellular and molecular elements of the microenvironment are emerging as attractive targets for therapeutic strategies.     

Role of myofibroblasts at the invasion front

Tumor progression occurs within a microecosystem, where cancer cells and myofibroblasts exchange proteinases and cytokines that promote growth directly through stimulation of proliferation and survival, as well as invasion through local proteolysis of the extracellular matrix and stimulation of motility. Myofibroblasts maintain the capacity of fibroblasts to induce differentiation. Fibroblasts are the main source of tumor-associated myofibroblasts. The transition to myofibroblasts also occurs in noncancerous situations. This transition is modulated by mechanical stress and cytokines, amongst which transforming growth factor-beta. The cross-talk between cancer cells and myofibroblasts illustrates the microecosystem of tumor invasion. In order to consider myofibroblasts as a possibly new target for cancer therapy, further characterization of the molecular cross-talk between myofibroblasts and cancer cells is required.     

Distinct Patterns of Stromal and Tumor Expression of ROR1 and ROR2 in Histological Subtypes of Epithelial Ovarian Cancer

OBJECTIVE: The ROR1 and ROR2 receptor tyrosine kinases have both been implicated in ovarian cancer progression and have been shown to drive migration and invasion. There is an increasing importance of the role of stroma in ovarian cancer metastasis; however, neither ROR1 nor ROR2 expression in tumor or stromal cells has been analyzed in the same clinical cohort. AIM: To determine ROR1 and ROR2 expression in ovarian cancer and surrounding microenvironment and examine associations with clinicopathological characteristics. METHODS: Immunohistochemistry for ROR1 and ROR2 was used to assess receptor expression in a cohort of epithelial ovarian cancer patients (n = 178). Results were analyzed in relation to clinical and histopathological characteristics and survival. Matched patient sample case studies of normal, primary, and metastatic lesions were used to examine ROR expression in relation to ovarian cancer progression. RESULTS: ROR1 and ROR2 are abnormally expressed in malignant ovarian epithelium and stroma. Higher ROR2 tumor expression was found in early-stage, low-grade endometrioid carcinomas. ROR2 stromal expression was highest in the serous subtype. In matched patient case studies, metastatic samples had higher expression of ROR2 in the stroma, and a recurrent sample had the highest expression of ROR2 in both tumor and stroma. CONCLUSION: ROR1 and ROR2 are expressed in tumor-associated stroma in all histological subtypes of ovarian cancer and hold potential as therapeutic targets which may disrupt tumor and stroma interactions.     

Hereditary ovarian cancer and two-compartment tumor metabolism

Mutations in the BRCA1 tumor suppressor gene are commonly found in hereditary ovarian cancers. Here, we used a co-culture approach to study the metabolic effects of BRCA1-null ovarian cancer cells on adjacent tumor-associated stromal fibroblasts. Our results directly show that BRCA1-null ovarian cancer cells produce large amounts of hydrogen peroxide, which can be abolished either by administration of simple antioxidants (N-acetyl-cysteine; NAC) or by replacement of the BRCA1 gene. Thus, the BRCA1 gene normally suppresses tumor growth by functioning as an antioxidant. Importantly, hydrogen peroxide produced by BRCA1-null ovarian cancer cells induces oxidative stress and catabolic processes in adjacent stromal fibroblasts, such as autophagy, mitophagy and glycolysis, via stromal NFκB activation. Catabolism in stromal fibroblasts was also accompanied by the upregulation of MCT4 and a loss of Cav-1 expression, which are established markers of a lethal tumor microenvironment. In summary, loss of the BRCA1 tumor suppressor gene induces hydrogen peroxide production, which then leads to metabolic reprogramming of the tumor stroma, driving stromal-epithelial metabolic coupling. Our results suggest that new cancer prevention trials with antioxidants are clearly warranted in patients that harbor hereditary/familial BRCA1 mutations.     

Hereditary ovarian cancer and two-compartment tumor metabolism: Epithelial loss of BRCA1 induces hydrogen peroxide production,driving oxidative stress and NFκB activation in the tumor stroma

Mutations in the BRCA1 tumor suppressor gene are commonly found in hereditary ovarian cancers. Here, we used a co-culture approach to study the metabolic effects of BRCA1-null ovarian cancer cells on adjacent tumor-associated stromal fibroblasts. Our results directly show that BRCA1-null ovarian cancer cells produce large amounts of hydrogen peroxide, which can be abolished either by administration of simple antioxidants (N-acetyl-cysteine; NAC) or by replacement of the BRCA1 gene. Thus, the BRCA1 gene normally suppresses tumor growth by functioning as an antioxidant. Importantly, hydrogen peroxide produced by BRCA1-null ovarian cancer cells induces oxidative stress and catabolic processes in adjacent stromal fibroblasts, such as autophagy, mitophagy and glycolysis, via stromal NFκB activation. Catabolism in stromal fibroblasts was also accompanied by the upregulation of MCT4 and a loss of Cav-1 expression, which are established markers of a lethal tumor microenvironment. In summary, loss of the BRCA1 tumor suppressor gene induces hydrogen peroxide production, which then leads to metabolic reprogramming of the tumor stroma, driving stromal-epithelial metabolic coupling. Our results suggest that new cancer prevention trials with antioxidants are clearly warranted in patients that harbor hereditary/familial BRCA1 mutations.     

Adipose-derived stem cells in ovarian cancer progression, metastasis,and chemoresistance

Ovarian cancer is the deadliest gynecological malignancy due to its symptomless early stage, metastasis, and high recurrence rate. The tumor microenvironment contributes to the ovarian cancer progression, metastasis, and chemoresistance. Adipose-derived stem cell in the tumor microenvironment of ovarian cancer, as a key player, interacts with ovarian cancer cells to form the cancer-associated fibroblasts and cancer-associated adipocytes, and secretes soluble factors to activate tumor cell signaling, which can promote ovarian cancer metastasis and chemoresistance. We summarize in this review the recent progress in the studies of interactions between adipose-derived stem cell and ovarian cancer, thus, to provide some insight for ovarian cancer therapy through targeting adipose-derived stem cell.