Microenvironmental regulation of cancer development

Mesenchymal stem cells enhance growth and metastasis of colon cancer

Recently, mesenchymal stem cells (MSCs) were reported to migrate to tumor stroma as well as injured tissue. We examined the role of human MSCs in tumor stroma using an orthotopic nude mice model of KM12SM colon cancer. In in vivo experiments, systemically injected MSCs migrated to the stroma of orthotopic colon tumors and metastatic liver tumors. Orthotopic transplantation of KM12SM cells mixed with MSCs resulted in greater tumor weight than did transplantation of KM12SM cells alone. The survival rate was significantly lower in the mixed-cell group, and liver metastasis was seen only in this group. Moreover, tumors resulting from transplantation of mixed cells had a significantly higher proliferating cell nuclear antigen labeling index, significantly greater microvessel area and significantly lower apoptotic index. Splenic injection of KM12SM cells mixed with MSCs, in comparison to splenic injection of KM12SM cells alone, resulted in a significantly greater number of liver metastases. MSCs incorporated into the stroma of primary and metastatic tumors expressed α-smooth muscle actin and platelet-derived growth factor receptor-β as carcinoma-associated fibroblast (CAF) markers. In in vitro experiments, KM12SM cells recruited MSCs, and MSCs stimulated migration and invasion of tumor cells through the release of soluble factors. Collectively, MSCs migrate and differentiate into CAFs in tumor stroma, and they promote growth and metastasis of colon cancer by enhancing angiogenesis, migration and invasion and by inhibiting apoptosis of tumor cells.

Co-evolution of cancer microenvironment reveals distinctive patterns of gastric cancer invasion: laboratory evidence and clinical significance

Background

Cancer invasion results from constant interactions between cancer cells and their microenvironment. Major components of the cancer microenvironment are stromal cells, infiltrating inflammatory cells, collagens, matrix metalloproteinases (MMP) and newly formed blood vessels. This study was to determine the roles of MMP-9, MMP-2, type IV collagen, infiltrating macrophages and tumor microvessels in gastric cancer (GC) invasion and their clinico-pathological significance.

Methods

Paraffin-embedded tissue sections from 37 GC patients were studied by Streptavidin-Peroxidase (SP) immunohistochemical technique to determine the levels of MMP-2, MMP-9, type IV collagen, macrophages infiltration and microvessel density (MVD). Different invasion patterns were delineated and their correlation with major clinico-pathological information was explored.

Results

MMP2 expression was higher in malignant gland compared to normal gland, especially nearby the basement membrane (BM). High densities of macrophages at the interface of cancer nests and stroma were found where BM integrity was destroyed. MMP2 expression was significantly increased in cases with recurrence and distant metastasis (P = 0.047 and 0.048, respectively). Infiltrating macrophages were correlated with serosa invasion (P = 0.011) and TNM stage (P = 0.001). MVD was higher in type IV collagen negative group compared to type IV collagen positive group (P = 0.026). MVD was related to infiltrating macrophages density (P = 0.040). Patients with negative MMP9 expression had better overall survival (OS) compared to those with positive MMP9 expression (Median OS 44.0 vs 13.5 mo, P = 0.036). Median OS was significantly longer in type IV collagen positive group than negative group (Median OS 25.5 vs 10.0 mo, P = 0.044). The cumulative OS rate was higher in low macrophages density group than in high macrophages density group (median OS 40.5 vs 13.0 mo, P = 0.056). Median OS was significantly longer in low MVD group than high MVD group (median OS 39.0 vs 8.5 mo, P = 0.001). The difference of disease-free survival (DFS) between low MVD group and high MVD group was not statistically significant (P = 0.260). Four typical patterns of cancer invasion were identified based on histological study of the cancer tissue, including Washing pattern, Ameba-like pattern, Spindle pattern and Linear pattern.

Conclusions

Proteolytic enzymes MMP9, MMP2 and macrophages in stroma contribute to GC progression by facilitating the angiogenesis. Cancer invasion patterns may help predict GC metastasis.

The origins of cancer robustness and evolvability

Unless diagnosed early, many adult cancers remain incurable diseases. This is despite an intense global research effort to develop effective anticancer therapies, calling into question the use of rational drug design strategies in targeting complex disease states such as cancer. A fundamental challenge facing researchers and clinicians is that cancers are inherently robust biological systems, able to survive, adapt and proliferate despite the perturbations resulting from anticancer drugs. It is essential that the mechanisms underlying tumor robustness be formally studied and characterized, as without a thorough understanding of the principles of tumor robustness, strategies to overcome therapy resistance are unlikely to be found. Degeneracy describes the ability of structurally distinct system components (e.g. proteins, pathways, cells, organisms) to be conditionally interchangeable in their contribution to system traits and it has been broadly implicated in the robustness and evolvability of complex biological systems. Here we focus on one of the most important mechanisms underpinning tumor robustness and degeneracy, the cellular heterogeneity that is the hallmark of most solid tumors. Based on a combination of computational, experimental and clinical studies we argue that stochastic noise is an underlying cause of tumor heterogeneity and particularly degeneracy. Drawing from a number of recent data sets, we propose an integrative model for the evolution of therapy resistance, and discuss recent computational studies that propose new therapeutic strategies aimed at defeating the adaptable cancer phenotype.

Can inhibition of angiogenesis and stimulation of immune response be combined into a more effective antitumor therapy?

Cancer initiation and progression is strongly influenced by the tumor microenvironment consisting of various types of host cells (inflammatory cells, vascular cells and fibroblasts), extracellular matrix and non-matrix molecules. Host cells play a defining role in two major processes crucial for tumor growth: angiogenesis and escape from immune surveillance. The interdependence of these processes resemble the principles of Yin and Yang, as the stimulation of tumor angiogenesis inhibits effective immune responses, while angiogenesis inhibition may have the opposite effect. These considerations may be useful in developing anticancer strategies based on the potentially synergistic combinations of antiangiogenic and immunostimulatory drugs.

Quantitative analysis of the secretome of TGF-beta signaling-deficient mammary fibroblasts

Transforming growth factor beta (TGF-beta) is a master regulator of autocrine and paracrine signaling pathways between a tumor and its microenvironment. Decreased expression of TGF-beta type II receptor (TbetaRII) in stromal cells is associated with increased tumor metastasis and shorter patient survival. In this study, SILAC quantitative proteomics was used to identify differentially externalized proteins in the conditioned media from the mammary fibroblasts with or without intact TbetaRII. Over 1000 proteins were identified and their relative differential levels were quantified. Immunoassays were used to further validate identification and quantification of the proteomic results. Differential expression was detected for various extracellular proteins, including proteases and their inhibitors, growth factors, cytokines, and extracellular matrix proteins. CXCL10, a cytokine found to be up-regulated in the TbetaRII knockout mammary fibroblasts, is shown to directly stimulate breast tumor cell proliferation and migration. Overall, this study revealed hundreds of specific extracellular protein changes modulated by deletion of TbetaRII in mammary fibroblasts, which may play important roles in the tumor microenvironment. These results warrant further investigation into the effects of inhibiting the TGF-beta signaling pathway in fibroblasts because systemic inhibition of TGF-beta signaling pathways is being considered as a potential cancer therapy.

Tumour stromal cells derived from paediatric malignancies display MSC-like properties and impair NK cell cytotoxicity

Background

Tumour growth and metastatic infiltration are favoured by several components of the tumour microenvironment. Bone marrow-derived multipotent mesenchymal stromal cells (MSC) are known to contribute to the tumour stroma. When isolated from healthy bone marrow, MSC exert potent antiproliferative effects on immune effector cells. Due to phenotypic and morphological similarities of MSC and tumour stromal cells (TStrC), we speculated that immunotherapeutic approaches may be hampered if TStrC may still exhibit immunomodulatory properties of MSC.

Methods

In order to compare immunomodulatory properties of MSC and tumour stromal cells (TStrC), we established and analyzed TStrC cultures from eleven paediatric tumours and MSC preparations from bone marrow aspirates. Immunophenotyping, proliferation assays and NK cell cytotoxicity assays were employed to address the issue.

Results

While TStrC differed from MSC in terms of plasticity, they shared surface expression of CD105, CD73 and other markers used for MSC characterization. Furthermore, TStrC displayed a strong antiproliferative effect on peripheral blood mononuclear cells (PBMC) in coculture experiments similar to MSC. NK cell cytotoxicity was significantly impaired after co-culture with TStrC and expression of the activating NK cell receptors NKp44 and NKp46 was reduced.

Conclusions

Our data show that TStrC and MSC share important phenotypic and functional characteristics. The inhibitory effect of TStrC on PBMC and especially on NK cells may facilitate the immune evasion of paediatric tumours.

Cancer-associated fibroblasts enhance the gland-forming capability of prostate cancer stem cells

Signals originating from cancer-associated fibroblasts (CAF) may positively regulate proliferation and tumorigenicity in prostate cancer. In this study, we investigated whether CAFs may regulate the biology of prostate cancer stem cells (CSC) by using a conditional Pten deletion mouse model of prostate adenocarcinoma to isolate both CAF cultures and CSC-enriched cell fractions from the tumors. CSCs that were isolated possessed self-renewal, spheroid-forming, and multipotential differentiation activities in tissue culture, segregating with a cell fraction exhibiting a signature expression phenotype, including SCA-1 (high), CD49f (high), CK5 (high), p63 (high), Survivin (high), RUNX2 (high), CD44 (low), CD133 (low), CK18 (low), and Androgen Receptor (low). CSC spheroid-forming efficiency was differentially influenced by the nature of fibroblasts in a coculture system: Compared with mouse urogenital sinus mesenchyme or normal prostate fibroblasts, CAFs enhanced spheroid formation, with the spheroids displaying generally larger sizes and more complex histology. Graft experiments showed that CSCs admixed with CAFs produced prostatic glandular structures with more numerous lesions, high proliferative index, and tumor-like histopathologies, compared with those formed in the presence of normal prostate fibroblasts. Together, our findings underscore a significant role of CAFs in CSC biology.

Breast cancer characteristics are modified by first trimester human placenta: in vitro co-culture study

BACKGROUND

Pregnant women with breast cancer present with a more advanced disease compared with non-pregnant women. Nevertheless, breast cancer metastasis to the placenta is rare. Trophoblast/tumor implantations share the same biochemical mediators, while only the first is stringently controlled. We hypothesized that the same mechanisms that affect/restrain placental implantation may inhibit metastatic growth in the placenta. We aimed to analyze the effects of human placenta on breast cancer cells.

METHODS

First trimester human placental explants were co-cultured with MCF-7/T47D-eGFP tagged cells. Following culture, placenta/cancer cells/both were fixed, paraffin embedded and sliced for immunohistochemical analysis or sorted by their eGFP expression for future analysis. The tested parameters were: proliferation (immunohistochemistry)/cell cycle (FACS), apoptosis (immunohistochemistry/FACS), cell count/adhesion/distribution around the placenta (cell sorter, visual observation and counting), matrix metalloproteinase activity (zymogram) and estrogen receptor (ER) expression (western blotting, immunohistochemistry).

RESULTS

Reduced breast cancer cell numbers (45%↓, 48%↓ for MCF-7/T47D, respectively, P < 0.05) were observed near the placenta. The placenta elevated MCF-7 sub-G1 phase and modestly elevated apoptosis (3-17%↑ for T47D/MCF-7, respectively, P < 0.05). Our findings demonstrate breast cancer cell migration from the placenta as: (i) T47D/MCF-7 cells changed their morphology to that of motile cells; (ii) elevated MMPs activity was found in the co-culture; (iii) placental soluble factors detached breast cancer cells; and (4) the placenta reduced MCF-7/T47D cells' ER expression (a characteristic of motile cells).

CONCLUSIONS

MCF-7/T47D cells are eliminated from the placental surroundings. Analyzing the causes of these phenomena may suggest biological pathways for this event and raise new therapeutic targets.

Molecular signaling of the epithelial to mesenchymal transition in generating and maintaining cancer stem cells

The epithelial to mesenchymal transition (EMT) is a highly conserved cellular program that allows polarized, well-differentiated epithelial cells to convert to unpolarized, motile mesenchymal cells. EMT is critical for appropriate embryogenesis and plays a crucial role in tumorigenesis and cancer progression. Recent studies revealed that there is a direct link between the EMT program and the gain of epithelial stem cell properties. EMT is sufficient to induce a population with stem cell characteristics from well-differentiated epithelial cells and cancer cells. In this review, we briefly introduce the biology of EMT inducers and transcription factors in tumorigenesis and then focus on the role of these key players of the EMT in generating and maintaining cancer stem cells.

Molecular diversity in ductal carcinoma in situ (DCIS) and early invasive breast cancer

Ductal carcinoma in situ (DCIS) is a non-invasive form of breast cancer where cells restricted to the ducts exhibit an atypical phenotype. Some DCIS lesions are believed to rapidly transit to invasive ductal carcinomas (IDCs), while others remain unchanged. Existing classification systems for DCIS fail to identify those lesions that transit to IDC. We studied gene expression patterns of 31 pure DCIS, 36 pure invasive cancers and 42 cases of mixed diagnosis (invasive cancer with an in situ component) using Agilent Whole Human Genome Oligo Microarrays 44k. Six normal breast tissue samples were also included as controls. qRT-PCR was used for validation. All DCIS and invasive samples could be classified into the "intrinsic" molecular subtypes defined for invasive breast cancer. Hierarchical clustering establishes that samples group by intrinsic subtype, and not by diagnosis. We observed heterogeneity in the transcriptomes among DCIS of high histological grade and identified a distinct subgroup containing seven of the 31 DCIS samples with gene expression characteristics more similar to advanced tumours. A set of genes independent of grade, ER-status and HER2-status was identified by logistic regression that univariately classified a sample as belonging to this distinct DCIS subgroup. qRT-PCR of single markers clearly separated this DCIS subgroup from the other DCIS, and contains samples from several histopathological and intrinsic molecular subtypes. The genes that differentiate between these two types of DCIS suggest several processes related to the re-organisation of the microenvironment. This raises interesting possibilities for identification of DCIS lesions both with and without invasive characteristics, which potentially could be used in clinical assessment of a woman's risk of progression, and lead to improved management that would avoid the current over- and under-treatment of patients.

TNFα-exposed bone marrow-derived mesenchymal stem cells promote locomotion of MDA-MB-231 breast cancer cells through transcriptional activation of CXCR3 ligand chemokines

Bone marrow-derived mesenchymal stem cells (BM-MSCs) are often recruited to solid tumors, integrate into the tumor stroma, and contribute to tumor development. TNFα is a major inflammatory cytokine present in the tumor microenvironment and has a profound influence on the progression of tumor development. This study was aimed to investigate the role of BM-MSCs in tumor promotion in response to TNFα. Quantitative real-time PCR arrays show that diverse cytokines/chemokines were induced in TNFα-treated BM-MSCs; in particular, CXCR3 ligand chemokines, including CXCL9, CXCL10, and CXCL11, were potently induced. A serial and site-directed mutation analysis in the CXCL9, CXCL10, and CXCL11 promoters revealed that NF-κB binding elements were responsible for TNFα-induced promoter activation of CXCR3 ligand chemokines. TNFα stimulated NF-κB activity, and ectopic expression of NF-κB enhanced TNFα-induced promoter activities of the CXCR3 ligand chemokines. Gel shift and supershift assays showed that NF-κB was associated with CXCR3 ligand chemokine promoters in response to TNFα treatment. All three CXCR3 ligand chemokines enhanced the migration and invasive motility of MDA-MB-231 breast cancer cells expressing CXCR3. Treatment of MDA-MB-231 cells with CXCL10 activated small GTPase of Rho family proteins, such as RhoA and Cdc42. CXCL9-, CXCL10-, or CXCL11-induced invasive capability of MDA-MB-231 cells was completely abrogated in the presence of a neutralizing anti-CXCR3 antibody in the culture medium. Moreover, CXCL9, CXCL10, and CXCL11 stimulated the expression of MMP-9, but not MMP-2, in MDA-MB-231 cells. These results suggest that BM-MSCs promote the locomotion of breast cancer cells through CXCR3 ligand-mediated actin rearrangement by TNFα in the tumor microenvironment.

Metastatic growth from dormant cells induced by a col-I-enriched fibrotic environment

Breast cancer that recurs as metastatic disease many years after primary tumor resection and adjuvant therapy seems to arise from tumor cells that disseminated early in the course of disease but did not develop into clinically apparent lesions. These long-term surviving, disseminated tumor cells maintain a state of dormancy, but may be triggered to proliferate through largely unknown factors. We now show that the induction of fibrosis, associated with deposition of type I collagen (Col-I) in the in vivo metastatic microenvironment, induces dormant D2.0R cells to form proliferative metastatic lesions through beta1-integrin signaling. In vitro studies using a three-dimensional culture system modeling dormancy showed that Col-I induces quiescent D2.0R cells to proliferate through beta1-integrin activation of SRC and focal adhesion kinase, leading to extracellular signal-regulated kinase (ERK)-dependent myosin light chain phosphorylation by myosin light chain kinase and actin stress fiber formation. Blocking beta1-integrin, Src, ERK, or myosin light chain kinase by short hairpin RNA or pharmacologic approaches inhibited Col-I-induced activation of this signaling cascade, cytoskeletal reorganization, and proliferation. These findings show that fibrosis with Col-I enrichment at the metastatic site may be a critical determinant of cytoskeletal reorganization in dormant tumor cells, leading to their transition from dormancy to metastatic growth. Thus, inhibiting Col-I production, its interaction with beta1-integrin, and downstream signaling of beta1-integrin may be important strategies for preventing or treating recurrent metastatic disease.

Inoculated mammary carcinoma-associated fibroblasts: contribution to hormone independent tumor growth

Background

Increasing evidence has underscored the role of carcinoma associated fibroblasts (CAF) in tumor growth. However, there are controversial data regarding the persistence of inoculated CAF within the tumors. We have developed a model in which murine metastatic ductal mammary carcinomas expressing estrogen and progesterone receptors transit through different stages of hormone dependency. Hormone dependent (HD) tumors grow only in the presence of progestins, whereas hormone independent (HI) variants grow without hormone supply. We demonstrated previously that CAF from HI tumors (CAF-HI) express high levels of FGF-2 and that FGF-2 induced HD tumor growth in vivo. Our main goal was to investigate whether inoculated CAF-HI combined with purified epithelial (EPI) HD cells can induce HD tumor growth.

Methods

Purified EPI cells of HD and HI tumors were inoculated alone, or together with CAF-HI, into female BALB/c mice and tumor growth was evaluated. In another set of experiments, purified EPI-HI alone or combined with CAF-HI or CAF-HI-GFP were inoculated into BALB/c or BALB/c-GFP mice. We assessed whether inoculated CAF-HI persisted within the tumors by analyzing inoculated or host CAF in frozen sections of tumors growing in BALB/c or BALB/c-GFP mice. The same model was used to evaluate early stages of tumor development and animals were euthanized at 2, 7, 12 and 17 days after EPI-HI or EPI-HI+CAF-HI inoculation. In angiogenesis studies, tumor vessels were quantified 5 days after intradermal inoculation.

Results

We found that admixed CAF-HI failed to induce epithelial HD tumor growth, but instead, enhanced HI tumor growth (p < 0.001). Moreover, inoculated CAF-HI did not persist within the tumors. Immunofluorescence studies showed that inoculated CAF-HI disappeared after 13 days. We studied the mechanisms by which CAF-HI increased HI tumor growth, and found a significant increase in angiogenesis (p < 0.05) in the co-injected mice at early time points.

Conclusions

Inoculated CAF-HI do not persist within the tumor mass although they play a role during the first stages of tumor formation promoting angiogenesis. This angiogenic environment is unable to replace the hormone requirement of HD tumors that still need the hormone to recruit the stroma from the host.

Microdialysis combined with proteomics for protein identification in breast tumor microenvironment in vivo

Tumor microenvironment constitutes a reservoir for proteins released from tumor cells and the host, which can contribute significantly to tumor growth and invasion. This study aims to apply a method of combining in vivo microdialysis and proteomics to identify proteins in mammary tumor interstitial fluids, a major component of tumor microenvironment. In vivo microdialysis was performed in polyomavirus middle T antigen (PyVmT) transgenic mouse mammary tumors and age-matched control wild-type mammary glands. Over four hundred proteins were identified from the microdialysis perfusates, using the Multidimensional Protein Identification Technology. Osteopontin (OPN) is one of the proteins overexpressed in breast tumor perfusates, as confirmed with immunoassays. OPN was also found to be present in tumor-associated stroma in both PyVmT and human breast tumors, using immunohistochemistry. Specifically, fibroblasts were further shown to express OPN at both mRNA and protein levels. In vitro assays showed that OPN can stimulate PyVmT breast carcinoma cell proliferation and migration. Finally, the expression of OPN was significantly higher in the peripheral blood of mice bearing breast tumors, compared to wild-type mice. Overall, microdialysis combined with proteomics is a unique technique for identifying proteins in a tumor microenvironment in vivo. Mammary fibroblasts can secrete OPN, and its overexpression in mammary tumor microenvironment may contribute significantly to mammary tumor progression.

ELECTRONIC SUPPLEMENTARY MATERIAL

The online version of this article (doi:10.1007/s12307-010-0046-3) contains supplementary material, which is available to authorized users.

Enhanced tumor growth in the NaS1 sulfate transporter null mouse

Sulfate plays an important role in maintaining normal structure and function of tissues, and its content is decreased in certain cancers including lung carcinoma. In this study, we investigated tumor growth in a mouse model of hyposulfatemia (Nas1(-/-)) and compared it to wild-type (Nas1(+/+)) mice. Lung epithelial tumor cells (TC-1 cell line) were injected subcutaneously into male Nas1(-/-) and Nas1(+/+) mice on a mixed 129Sv and C57BL/6 genetic background. Tumor sections were stained with anti-glycosaminoglycan antibodies to assess the distribution of proteoglycans and Gomori's trichrome to detect collagen. After 14 days, tumor weights were markedly increased (by approximately 12-fold) in Nas1(-/-) mice when compared with Nas1(+/+) mice. Histological analyses of tumors revealed increased (by approximately 2.4-fold) vessel content, as well as markedly reduced collagen and immunoreactivity against glycosaminoglycan structural epitopes in the tumors from Nas1(-/-) mice. No significant differences were found for the growth of cultured TC-1 cells supplemented with Nas1(-/-) or Nas1(+/+) serum, as determined by (3)H-thymidine incorporation, implying that the cell culture conditions may not reflect the in vivo situation of enhanced tumor growth. This study has revealed increased tumor growth and an altered extracellular tumor matrix in hyposulfatemic Nas1(-/-) mice. These findings highlight the importance of blood sulfate levels as a possible modulator of tumor growth, and could lead to future cancer studies in humans with altered sulfate homeostasis.

Lack of an endogenous anti-inflammatory protein in mice enhances colonization of B16F10 melanoma cells in the lungs

Emerging evidence indicates a link between inflammation and cancer metastasis, but the molecular mechanism(s) remains unclear. Uteroglobin (UG), a potent anti-inflammatory protein, is constitutively expressed in the lungs of virtually all mammals. UG-knock-out (UG-KO) mice, which are susceptible to pulmonary inflammation, and B16F10 melanoma cells, which preferentially metastasize to the lungs, provide the components of a model system to determine how inflammation and metastasis are linked. We report here that B16F10 cells, injected into the tail vein of UG-KO mice, form markedly elevated numbers of tumor colonies in the lungs compared with their wild type littermates. Remarkably, UG-KO mouse lungs overexpress two calcium-binding proteins, S100A8 and S100A9, whereas B16F10 cells express the receptor for advanced glycation end products (RAGE), which is a known receptor for these proteins. Moreover, S100A8 and S100A9 are potent chemoattractants for RAGE-expressing B16F10 cells, and pretreatment of these cells with a blocking antibody to RAGE suppressed migration and invasion. Interestingly, in UG-KO mice S100A8/S100A9 concentrations in blood are lowest in tail vein and highest in the lungs, which most likely guide B16F10 cells to migrate to the lungs. Further, B16F10 cells treated with S100A8 or S100A9 overexpress matrix metalloproteinases, which are known to promote tumor invasion. Most notably, the metastasized B16F10 cells in UG-KO mouse lungs express MMP-2, MMP-9, and MMP-14 as well as furin, a pro-protein convertase that activates MMPs. Taken together, our results suggest that a lack of an anti-inflammatory protein leads to increased pulmonary colonization of melanoma cells and identify RAGE as a potential anti-metastatic drug target.

Antitumor activity of targeting SRC kinases in endothelial and myeloid cell compartments of the tumor microenvironment

PURPOSE

Several Src family kinase (SFK) inhibitors have entered clinical trials based on their direct effects against tumor cells. Here, we characterize the effects of targeting Src kinases on the tumor microenvironment and how these effects influence tumor growth.

EXPERIMENTAL DESIGN

Human cancer cells grown in cell culture or in mice were treated with dasatinib, a small-molecule inhibitor of SFKs. Tumor cell, endothelial cell, and myeloid cell compartments within the tumor microenvironment were analyzed. Primary human endothelial cells and freshly isolated CD11b+/CD11c- myeloid cells from mice were treated with dasatinib in cell culture. Cellular functions and signaling pathways affected by dasatinib were evaluated.

RESULTS

Dasatinib was not cytotoxic in cell culture against the human cancer cell lines investigated here. However, dasatinib administration in human tumor-bearing mice suppressed tumor growth associated with increased tumor cell apoptosis, decreased microvessel density, and reduced intratumoral CD11b+ myeloid cells. Dasatinib directly inhibited motility and other functions of endothelial and myeloid cells, accompanied by the inhibition of phosphorylation of SFKs and downstream signaling. Tumor-infiltrating myeloid cells were identified as the major source of matrix metalloproteinase (MMP)-9 in the tumor microenvironment. Dasatinib treatment reduced MMP-9 levels in the tumor microenvironment through the simultaneous inhibition of recruitment of MMP9+ myeloid cells and MMP-9 gene expression in tumor-infiltrating myeloid cells.

CONCLUSIONS

These findings suggest that Src kinase inhibitors such as dasatinib possess a previously unrecognized anticancer mechanism of action by targeting both host-derived endothelial and myeloid cell compartments within the tumor microenvironment.

The role of genetic diversity in cancer

The role of genetic heterogeneity within neoplasms is increasingly recognized as important for understanding the dynamics of cancer progression, cancer stem cells, and therapeutic resistance, and there is interest in intratumoral heterogeneity measurements as potential biomarkers for risk stratification. In this issue of the JCI, Park et al. characterize this genetic diversity in carcinoma in situ and in invasive regions from 3 types of human breast cancers and lay the groundwork for translation of these measures to the clinic.

Molecular biology of cancer-associated fibroblasts: can these cells be targeted in anti-cancer therapy?

It is increasingly recognized that the non-neoplastic stromal compartment in most solid cancers plays an active role in tumor proliferation, invasion and metastasis. Cancer-associated fibroblasts (CAFs) are one of the most abundant cell types in the tumor stroma, and these cells are pro-tumorigenic. Evidence that CAFs are epigenetically and possibly also genetically distinct from normal fibroblasts is beginning to define these cells as potential targets of anti-cancer therapy. Here, we review the cell-of-origin and molecular biology of CAFs, arguing that such knowledge provides a rational basis for designing therapeutic strategies to coordinately and synergistically target both the stromal and malignant epithelial component of human cancers.

Characterisation of normal and cancer stem cells: one experimental paradigm for two kinds of stem cells

The characterisation of normal stem cells and cancer stem cells uses the same paradigm. These cells are isolated by a fluorescence-activated cell sorting step and their stemness is assayed following implantation into animals. However, differences exist between these two kinds of stem cells. Therefore, the translation of the experimental procedures used for normal stem cell isolation into the research field of cancer stem cells is a potential source of artefacts. In addition, normal stem cell therapy has the objective of regenerating a tissue, while cancer stem cell-centred therapy seeks the destruction of the cancer tissue. Taking these differences into account is critical for anticipating problems that might arise in cancer stem cell-centred therapy and for upgrading the cancer stem cell paradigm accordingly.

The invasive potential of human melanoma cell lines correlates with their ability to alter fibroblast gene expression in vitro and the stromal microenvironment in vivo

The tumor microenvironment is thought to play an important role in invasion and metastasis. Previously, we have shown that signaling from melanoma cells can alter the gene expression profiles of fibroblasts in vitro and in vivo. To investigate whether the capacity to signal fibroblasts and alter host gene expression profiles is correlated to the invasive potential of specific human melanoma cell lines, we assayed changes in gene expression of fibroblasts when cocultured with the human melanoma cell lines BLM, MV3, A2058, SK-mel28 and WM164. Results indicated that the gene expression of key chemokines and cytokines, such as IL-1B, IL-8, IL-6 and CCL2/MCP1, was significantly upregulated in fibroblasts cocultured with the invasive melanoma lines BLM and MV3 compared to fibroblasts cocultured with noninvasive WM164 cells. The results were verified by quantitative RT-PCR as well as by protein assay and supported by immunohistochemistry of human invasive melanoma. Furthermore, a role for fibroblast-secreted IL-1B in the invasion of melanoma was demonstrated in vitro, where siRNA silencing of IL-1B in melanoma-stimulated fibroblasts resulted in a diminution of melanoma invasion. Although CCL2/MCP1, a chemoattractant for macrophages, was shown to be upregulated in fibroblasts cocultured with metastatic melanoma cell lines, immunohistochemical analysis of human melanoma also indicated CCL2/MCP1 production associated with the melanoma. In summary, these experiments indicate that the invasiveness of melanoma can partly be correlated to its ability to stimulate host stromal fibroblasts to give rise to the secretion of chemokines that generate a microenvironment that is conductive for melanoma invasion and metastasis.

Adhesion-mediated apoptosis resistance in cancer

Adhesion-mediated apoptosis resistance (AMAR) is an emerging concept that may explain the observed differences in survival between cells within the three-dimensional structure of a tumor and the standard monolayer culture conditions in the laboratory. Not only the cancer cells' motility and invasiveness are different in a three-dimensional tumor, but - crucially - the cells' sensitivity towards apoptosis, a form of programmed cell death, varies widely between the in vivo and in vitro situation. Tumor cells interacting either with a specific extracellular matrix protein substrate or with each other or with non-transformed cells, such as fibroblasts, exhibit increased resistance towards a wide variety of therapeutic approaches. In this review we discuss the molecular basis of these interactions and the main downstream effectors that are involved in the enhancement of the tumor cells' survival. In particular, we show that the pathways activated by adhesion are not unique, but involve the MAPK/ERK and PI3K/Akt pathways, which are reused between different forms of AMAR and are also found in adhesion-independent modes of resistance. Thus, the tools to overcome AMAR are already at our disposal and using them in this novel context of AMAR should lead to significant therapeutic benefit.

Cancer attractors: a systems view of tumors from a gene network dynamics and developmental perspective

Cell lineage commitment and differentiation are governed by a complex gene regulatory network. Disruption of these processes by inappropriate regulatory signals and by mutational rewiring of the network can lead to tumorigenesis. Cancer cells often exhibit immature or embryonic traits and dysregulated developmental genes can act as oncogenes. However, the prevailing paradigm of somatic evolution and multi-step tumorigenesis, while useful in many instances, offers no logically coherent reason for why oncogenesis recapitulates ontogenesis. The formal concept of "cancer attractors", derived from an integrative, complex systems approach to gene regulatory network may provide a natural explanation. Here we present the theory of attractors in gene network dynamics and review the concept of cell types as attractors. We argue that cancer cells are trapped in abnormal attractors and discuss this concept in the light of recent ideas in cancer biology, including cancer genomics and cancer stem cells, as well as the implications for differentiation therapy.

Clonal mutations in the cancer-associated fibroblasts: the case against genetic coevolution

It is well established that carcinoma-associated fibroblasts (CAFs) differ phenotypically from fibroblasts associated with normal tissue, but the mechanisms underlying these differences remain controversial. Because CAFs can be propagated in vitro for extended periods and still maintain their cancer promoting phenotype, it has been proposed that they might have acquired somatic genetic alterations analogous to those observed in malignant epithelium. Whereas some investigators have reported frequent and profound genomic alterations in CAFs, other groups have found no such evidence. One striking common trait of those studies reporting frequent clonal somatic alterations in CAFs is the use of tissues and techniques which are well known to be highly prone to generating artefacts, such as limiting and poor quality DNA followed by highly multiplexed PCR-based analysis. We conclude that reported frequent clonal somatic mutations in CAFs are likely to be artefacts and are not the biological basis of the cancer promoting attributes of CAFs. [corrected]

Induction of myeloid-derived suppressor cells by tumor exosomes

Myeloid-derived suppressor cells (MDSCs) promote tumor progression. The mechanisms of MDSC development during tumor growth remain unknown. Tumor exosomes (T-exosomes) have been implicated to play a role in immune regulation, however the role of exosomes in the induction of MDSCs is unclear. Our previous work demonstrated that exosomes isolated from tumor cells are taken up by bone marrow myeloid cells. Here, we extend those findings showing that exosomes isolated from T-exosomes switch the differentiation pathway of these myeloid cells to the MDSC pathway (CD11b(+)Gr-1(+)). The resulting cells exhibit MDSC phenotypic and functional characteristics including promotion of tumor growth. Furthermore, we demonstrated that in vivo MDSC mediated promotion of tumor progression is dependent on T-exosome prostaglandin E2 (PGE2) and TGF-beta molecules. T-exosomes can induce the accumulation of MDSCs expressing Cox2, IL-6, VEGF, and arginase-1. Antibodies against exosomal PGE2 and TGF-beta block the activity of these exosomes on MDSC induction and therefore attenuate MDSC-mediated tumor-promoting ability. Exosomal PGE2 and TGF-beta are enriched in T-exosomes when compared with exosomes isolated from the supernatants of cultured tumor cells (C-exosomes). The tumor microenvironment has an effect on the potency of T-exosome mediated induction of MDSCs by regulating the sorting and the amount of exosomal PGE2 and TGF-beta available. Together, these findings lend themselves to developing specific targetable therapeutic strategies to reduce or eliminate MDSC-induced immunosuppression and hence enhance host antitumor immunotherapy efficacy.

Upregulated expression of periostin by hypoxia in non-small-cell lung cancer cells promotes cell survival via the Akt/PKB pathway

Periostin is a secreted protein and has been shown to be frequently overexpressed in various types of human cancers. We have previously reported that periostin potently promotes metastatic growth of colon cancer by augmenting cell survival. However, little is known about the functions of periostin in non-small-cell lung cancer. Here, we revealed that increased expression of periostin in non-small-cell lung cancer A549 cells was one kind of cellular responses to the stress of chemical-mimic hypoxia, and this effect could be regulated by hypoxia inducible growth factors, such as TGF-alpha and bFGF. We further demonstrated that RTK/PI3-K pathway activated by TGF-alpha and bFGF was evoked in upregulating the expression of periostin, and then periostin promoted the survival of A549 cells under hypoxic microenvironment via activation of Akt/PKB pathway. Therefore, periostin and the pathway that it involved might provide a target for lung cancer treatment.

Principles of cancer therapy: oncogene and non-oncogene addiction

Cancer is a complex collection of distinct genetic diseases united by common hallmarks. Here, we expand upon the classic hallmarks to include the stress phenotypes of tumorigenesis. We describe a conceptual framework of how oncogene and non-oncogene addictions contribute to these hallmarks and how they can be exploited through stress sensitization and stress overload to selectively kill cancer cells. In particular, we present evidence for a large class of non-oncogenes that are essential for cancer cell survival and present attractive drug targets. Finally, we discuss the path ahead to therapeutic discovery and provide theoretical considerations for combining orthogonal cancer therapies.

Role of COX-2 in epithelial-stromal cell interactions and progression of ductal carcinoma in situ of the breast

Epithelial-stromal cell interactions have an important role in breast tumor progression, but the molecular mechanisms underlying these effects are just beginning to be understood. We previously described that fibroblasts promote, whereas normal myoepithelial cells inhibit, the progression of ductal carcinoma in situ (DCIS) to invasive breast carcinomas by using a xenograft model of human DCIS. Here, we report that the tumor growth and progression-promoting effects of fibroblasts are at least in part due to increased COX-2 expression in tumor epithelial cells provoked by their interaction with fibroblasts. Up-regulation of COX-2 in DCIS xenografts resulted in increased VEGF and MMP14 expression, which may contribute to the larger weight and invasive histology of COX-2-expressing tumors. Administration of celecoxib, a selective COX-2 inhibitor, to tumor-bearing mice decreased xenograft tumor weight and inhibited progression to invasion. Coculture of fibroblasts with DCIS epithelial cells enhanced their motility and invasion, and this change was associated with increased MMP14 expression and MMP9 protease activity. We identified the NF-kappaB pathway as one of the mediators of stromal fibroblast-derived signals regulating COX-2 expression in tumor epithelial cells. Inhibition of NF-kappaB and COX-2 activity and down-regulation of MMP9 expression attenuated the invasion-promoting effects of fibroblasts. These findings support a role for COX-2 in promoting the progression of DCIS to invasive breast carcinomas, and suggest that therapeutic targeting of the NF-kappaB and prostaglandin signaling pathways might be used for the treatment and prevention of breast cancer.

Cancer-associated fibroblasts and tumor growth--bystanders turning into key players

Novel mechanisms, and molecular mediators, of the pro-tumorigenic effects of cancer-associated fibroblasts (CAFs) have been identified. These include CXCL12/SDF-1-mediated recruitment of bone marrow-derived endothelial precursor cell and pro-metastatic effects of CCL5. Co-culture experiments also suggest that CAFs can influence the drug-sensitivity of cancer cells. Comparisons of CAFs from different tumors have started to identify tumor-type specific differences in CAF gene expression and marker protein profiling indicates the existence of multiple distinct co-existing CAF-subsets. Studies in animal models have demonstrated that CAFs can be derived from bone marrow-derived cells or from epithelial or endothelial cells undergoing mesenchymal transition. The genetic status of CAFs remains controversial following conflicting findings. Meanwhile, analyses of CAFs from human tumors have revealed consistent epigenetic changes. An increasing number of translational studies have emphasized the prognostic significance of different CAF-related tumor characteristics. Clinical studies aiming at CAF-targeting can now be envisioned based on findings from experimental intervention studies with agents targeting, for example FAP or PDGF-, TGF-beta- or hedgehog-signaling.

Relationships between cancer and aging: a multilevel approach

The incidence of cancer increases with age in humans and in laboratory animals alike. There are different patterns of age-related distribution of tumors in different organs and tissues. Aging may increase or decrease the susceptibility of various tissues to initiation of carcinogenesis and usually facilitates promotion and progression of carcinogenesis. Aging may predispose to cancer in two ways: tissue accumulation of cells in late stages of carcinogenesis and alterations in internal homeostasis, in particular, alterations in immune and endocrine systems. Increased susceptibility to the effects of tumor promoters is found both in aged animals and aged humans, as predicted by the multistage model of carcinogenesis. Aging is associated with a number of events at the molecular, cellular and physiological levels that influence carcinogenesis and subsequent cancer growth. An improved understanding of age-associated variables impacting on the tumor microenvironment, as well as the cancer cells themselves, will result in improved treatment modalities in geriatric oncology.

Stroma-epithelium crosstalk in prostate cancer

The critical role played by stroma-epithelium crosstalk in carcinogenesis and progression of prostate cancer has been increasingly recognized. These interactions are mediated by a variety of paracrine factors secreted by cancer cells and/or stromal cells. In human prostate cancer, reactive stroma is characterized by an increase in myofibroblasts and a corresponding amplification of extracellular matrix production and angiogenesis. Permanent genetic mutations have been reported in stromal cells as well as in tumour cells. Transforming growth factor-beta, vascular endothelial growth factor, platelet-derived growth factor and fibroblast growth factor signalling pathways are involved in the process of angiogenesis, whereas hepatocyte growth factor, insulin-like growth factor-1, epidermal growth factor, CXC12 and Interleukin-6 play active roles in the progression, androgen-independent conversion and distal metastasis of prostate cancer. Some soluble factors have reciprocal interactions with androgens and the androgen receptor (AR), and can even activate AR in the absence of the androgen ligand. In this article, we review the complex interactions between cancer cells and the surrounding microenvironment, and discuss the potential therapeutic targets in the stromal compartment of prostate cancer.

Co-evolution of tumor cells and their microenvironment

Increasing evidence indicates that tumor-stromal cell interactions have a crucial role in tumor initiation and progression. These interactions modify cellular compartments, leading to the co-evolution of tumor cells and their microenvironment. Although the importance of microenvironmental alterations in tumor development is recognized, the molecular mechanisms underlying these changes are only now beginning to be understood. Epigenetic and gene expression changes have consistently been reported in cancer-associated stromal cells and the influence of the host genotype on tumorigenesis is also well documented. However, the presence of clonally selected somatic genetic alterations within the tumor microenvironment has been controversial. A thorough understanding of the co-evolution of these two cellular compartments will require carefully executed molecular studies combined with mathematical modeling.

Ecological therapy for cancer: defining tumors using an ecosystem paradigm suggests new opportunities for novel cancer treatments

We propose that there is an opportunity to devise new cancer therapies based on the recognition that tumors have properties of ecological systems. Traditionally, localized treatment has targeted the cancer cells directly by removing them (surgery) or killing them (chemotherapy and radiation). These modes of therapy have not always been effective because many tumors recur after these therapies, either because not all of the cells are killed (local recurrence) or because the cancer cells had already escaped the primary tumor environment (distant recurrence). There has been an increasing recognition that the tumor microenvironment contains host noncancer cells in addition to cancer cells, interacting in a dynamic fashion over time. The cancer cells compete and/or cooperate with nontumor cells, and the cancer cells may compete and/or cooperate with each other. It has been demonstrated that these interactions can alter the genotype and phenotype of the host cells as well as the cancer cells. The interaction of these cancer and host cells to remodel the normal host organ microenvironment may best be conceptualized as an evolving ecosystem. In classic terms, an ecosystem describes the physical and biological components of an environment in relation to each other as a unit. Here, we review some properties of tumor microenvironments and ecological systems and indicate similarities between them. We propose that describing tumors as ecological systems defines new opportunities for novel cancer therapies and use the development of prostate cancer metastases as an example. We refer to this as "ecological therapy" for cancer.

Molecular aspects of tumour hypoxia

Hypoxia is an important feature of the microenvironment of a wide range of solid tumours. Its critical role in radio- and chemoresistance and its significance as an adverse prognostic factor have been well established over the last decades. On a cellular level, hypoxia evokes a complex molecular response with a central role for the HIF-1 pathway. The cellular processes under control of HIF-1 contain important prognostic information and comprise potential candidates for directing hypoxia-modifying therapies. This review will provide an overview of the current knowledge on the molecular aspects of tumour hypoxia and the link to clinical practice.