Increased survival, proliferation, and migration in metastatic human pancreatic tumor cells expressing functional CXCR4

High expression of CXCR4 may predict poor survival in resected pancreatic adenocarcinoma

Chemokines and their receptors are involved in tumourigenicity and clinicopathological significance of chemokines receptor expression in pancreatic adenocarcinoma (PA) is not fully understood. This study was conducted to determine patients' outcome according to the expressions of CXCR4, CXCR7 and HIF-1alpha after resection of PA. Immunohistochemistry for CXCR4, CXCR7 and HIF-1alpha expressions as well as cell proliferative index (Ki-67) was conducted in 71 resected (R0) PA and their 48 related lymph nodes (LN) using tissue microarray. CXCR4 and CXCR7 expressions were positively correlated to HIF-1alpha suggesting a potential role of HIF-1alpha in CXCR4 and CXCR7 transcription activation. Patients with CXCR4(high) tumour expression had shorter OS than those with low expression (median survival: 9.7 vs 43.2 months, P=0.0006), a higher risk of LN metastases and liver recurrence. In multivariate analysis, high CXCR4 expression, LN metastases and poorly differentiated tumour are independent negative prognosis factors. In a combining analysis, patients with a CXCR7(high)/CXCR4(high) [corrected] tumour had a significantly shorter DFS and OS than patients with a CXCR4(low)/CXCR7(low) [corrected] tumour. CXCR4 in resected PA may represent a valuable prognostic factor as well as an attractive target for therapeutic purpose.

CXCR4 chemokine receptor antagonists: perspectives in SCLC

Small-cell lung cancer (SCLC) is a particularly aggressive form of lung cancer characterized by early and widespread metastases and the ability to rapidly develop resistance against chemotherapeutic agents. Tumor cell migration and metastasis share many similarities with leukocyte trafficking, which is critically regulated by chemokine receptors and adhesion molecules. SCLC cells express high levels of CXCR4 (CD184), a seven-transmembrane G-protein-coupled chemokine receptor. Stromal cells within the bone marrow microenvironment and at extramedullary sites constitutively secrete stromal cell-derived factor-1 (CXCL12), the ligand for CXCR4. Activation of CXCR4 induces SCLC cell migration and adhesion to stromal cells that secrete CXCL12, which in turn provides growth- and drug resistance-signals to the tumor cells. CXCR4 antagonists, such as Plerixafor (AMD3100) and T140 analogues (TN14003/ BKT140), disrupt CXCR4-mediated SCLC cell-adhesion to stromal cells. In stromal cell co-cultures, CXCR4 antagonists also sensitize SCLC cells to cytotoxic drugs, such as etoposide, and thereby antagonize cell adhesion-mediated drug resistance. Therefore, targeting the CXCR4-CXCL12 axis is a novel, attractive therapeutic approach in SCLC. Here, we summarize preclinical data about CXCR4 in SCLC, and the current status of the preclinical and clinical development of CXCR4 antagonists.

CCR5 proinflammatory allele in prostate cancer risk: a pilot study in patients and centenarians from Sicily

Prostate cancer (PCa) is the most common malignant neoplasm in older men in Western countries. The number of affected older men is increasing. Therefore, strategies for prevention of prostate cancer are crucial. To this purpose it is essential to know the mechanisms involved in development and progression of this malignancy. Recently, an increasing body of genetic and epidemiological studies proposed new hypotheses for prostate carcinogenesis. It has been suggested that genetic factors as well as exposure to environmental factors such as infectious agents, dietary carcinogens, and hormonal imbalances participate in PCa development. Besides, chronic inflammation plays a key role in PCa. Taking into consideration this complex scenario, in the present study we evaluated whether CCR5Delta32 deletion of CCR5 gene might be associated with PCa susceptibility. For the control group we used centenarians, since they represent a disease-free human model. These preliminary results suggest that the CCR5Delta32 anti-inflammatory variant might be a resistance factor for the development of PCa.

CXCL12/SDF-1 over-expression in human insulinomas and its biological relevance

This study was performed on the basis of previously obtained investigative gene array data concerning the over-expression of CXCL12/SDF-1 in human insulinomas versus human pancreatic islet preparations. The presence of CXCL12/SDF-1 was studied by RT-qPCR in human insulinomas (n=8) versus pancreatic islets (n=3), and was found to be significantly up-regulated in the former (p<0.012). The mRNA data were confirmed by immunostaining and confocal microscopy of human normal pancreatic islets, which showed the absence of CXCL12 protein and high expression in insulinoma tissue. Individual human insulinoma cells at cytospins stained positive for CXCL12 in the paranuclear region. These morphological data were extended by consecutive immunoblotting for cell-compartment-specific marker proteins of fractions obtained by sucrose gradient fractionation using Rin-5F insulinoma cells. CXCL12-containing fractions were positive for the membrane marker NSF but negative for SNAP-25 and appeared at a lighter density in the gradient than heavy insulin granules, suggesting packaging in specific granules different from insulin. In order to determine the biological relevance of the protein in insulinomas, we investigated the colony-forming potential of human CXCL12 stable-transfected rat Rin-5F insulinoma cells. These clones secreted human CXCL12 and contained 50-1000-fold higher copy numbers compared to its endogenous rat homologue. In colony-forming assays, these transfectant clones developed greater colony numbers, which were larger than wild-type and sham transfectants. To elucidate the mechanism of action, we identified a CXCL12 transfectant-specific increase in the pro-survival factor Mn-SOD, which is considered important for the inactivation of reactive oxygen species, thereby prolonging cell survival. These data demonstrate the importance of CXCL12 in the tumor biology of insulinoma.

64Cu-AMD3100--a novel imaging agent for targeting chemokine receptor CXCR4

CXCR4 is a chemokine receptor which has been shown to be exploited by various tumors for increased survival, invasion, and homing to target organs. We developed a one step radiosynthesis for labeling the CXCR4-specific antagonist AMD3100 with Cu-64 to produce (64)Cu-AMD3100 with a specific activity of 11.28Ci/ micromol (417GBq/ micromol) at the end of radiosynthesis. Incorporation of Cu(II) ion into AMD3100 did not change its ability to inhibit cellular migration in response to the (only) CXCR4 ligand, SDF-1/CXCL12. (64)Cu-AMD3100 binding affinity to CXCR4 was found to be 62.7 microM. Biodistribution of (64)Cu-AMD3100 showed accumulation in CXCR4-expressing organs and tissues, a renal clearance pathway, and an anomalous specific accumulation in the liver. We conclude that (64)Cu-AMD3100 exhibits promise as a potential PET imaging agent for visualization of CXCR4-positive tumors and metastases and might be used to guide and monitor anti-CXCR4 tumor therapy.

CXCL8/IL-8 and CXCL12/SDF-1alpha co-operatively promote invasiveness and angiogenesis in pancreatic cancer

CXC-chemokines are involved in the chemotaxis of neutrophils, lymphocytes and monocytes. However, role of these chemokines in tumorigenesis, especially with regard to interaction between tumor and its microenvironment, has not been clearly elucidated. The purpose of this study was to analyze the co-operative role of CXCL8 and CXCL12 in the tumor-stromal interaction in pancreatic cancer (PaCa). Using enzyme-linked immunosorbent assay (ELISA) and reverse transcription polymerase chain reaction (RT-PCR), we initially confirmed the expression of ligands and receptors, respectively, of CXC-chemokines in PaCa and stromal cells. We examined the co-operative role of CXCL8 and CXCL12 in proliferation/invasion of PaCa and human umbilical vein endothelial cells (HUVECs), and in HUVEC tube-formations through tumor-stromal interaction by MTS, Matrigel invasion, and angiogenesis assays, respectively. We detected expression of CXCR4, but not CXCR2, in all PaCa cells and fibroblasts. PaCa cells secreted CXCL8, and fibroblast cells secreted CXCL12. CXCL8 production in PaCa was significantly enhanced by CXCL12, and CXCL12 production in fibroblasts was significantly enhanced by co-culturing with PaCa. CXCL8 enhanced proliferation/invasion of HUVECs but did not promote proliferation/invasion of PaCa. Both recombinant and PaCa-derived CXCL8 enhanced tube formation of HUVECs that were co-cultured with fibroblast cells. CXCL12 enhanced the proliferation/invasion of HUVECs and the invasion of PaCa cells but had no effect on tube formation of HUVEC. We showed that PaCa-derived CXCL8 and fibroblast-derived CXCL12 cooperatively induced angiogenesis in vitro by promoting HUVEC proliferation, invasion, and tube formation. Thus, corresponding receptors CXCR2 and CXCR4 are potential antiangiogenic and antimetastatic therapeutic targets in PaCa.

CXCR4 antagonists: targeting the microenvironment in leukemia and other cancers

Hematopoietic and epithelial cancer cells express CXCR4, a seven-transmembrane G-protein-coupled chemokine receptor. Stromal cells within the bone marrow microenvironment constitutively secrete stromal cell-derived factor-1 (SDF-1/CXCL12), the ligand for CXCR4. Activation of CXCR4 induces leukemia cell trafficking and homing to the marrow microenvironment, where CXCL12 retains leukemia cells in close contact with marrow stromal cells that provide growth and drug resistance signals. CXCR4 antagonists, such as Plerixafor (AMD3100) and T140 analogs, can disrupt adhesive tumor-stroma interactions and mobilize leukemia cells from their protective stromal microenvironment, making them more accessible to conventional drugs. Therefore, targeting the CXCR4-CXCL12 axis is a novel, attractive therapeutic approach that is explored in ongoing clinical trials in leukemia patients. Initially, CXCR4 antagonists were developed for the treatment of HIV, where CXCR4 functions as a co-receptor for virus entry into T cells. Subsequently, CXCR4 antagonists were noticed to induce leukocytosis, and are currently used clinically for mobilization of hematopoietic stem cells. However, because CXCR4 plays a key role in cross-talk between leukemia cells (and a variety of other tumor cells) and their microenvironment, cancer treatment may become the ultimate application of CXCR4 antagonists. Here, we summarize the development of CXCR4 antagonists and their preclinical and clinical activities, focusing on leukemia and other cancers.

The chemokine receptor CX3CR1 is involved in the neural tropism and malignant behavior of pancreatic ductal adenocarcinoma

Tumor perineural dissemination is a hallmark of human pancreatic ductal adenocarcinoma (PDAC) and represents a major source of local tumor recurrence after surgery. In this study, we provide in vitro and in vivo evidence that the chemokine receptor CX3CR1 may be involved in the neurotropism of PDAC cells to local peripheral nerves. Neoplastic cells from PDAC cell lines and surgical specimens express the chemokine receptor CX3CR1, absent in normal pancreatic ducts. Its unique ligand, the transmembrane chemokine CX3CL1, is expressed by neurons and nerve fibers. CX3CR1 + PDAC cell lines migrated in response to human recombinant CX3CL1 and specifically adhered to CX3CL1-expressing cells of neural origin via mechanisms involving activation of G proteins, beta1 integrins, and focal adhesion kinase. In vivo experiments with transplanted PDAC showed that only CX3CR1-transfected tumor cells infiltrated the local peripheral nerves. Immunohistochemistry of CX3CR1 in PDAC specimens revealed that 90% of the samples were positive with a heterogeneous pattern of expression. High receptor score was significantly associated with more prominent tumor perineural infiltration evaluated histologically (P = 0.026). Regression analyses (univariate and multivariate) showed that high CX3CR1 expression and perineural invasion were strongly associated with local and earlier tumor recurrence (P = 0.007). Collectively, this study shows that the CX3CR1 receptor may be involved in PDAC tumor neurotropism and is a relevant and independent risk factor to predict an early local tumor relapse in resected patients. Thus, the CX3CR1-CX3CL1 axis could represent a valuable therapeutic target to prevent tumor perineural dissemination in pancreatic cancer.

Zerumbone down-regulates chemokine receptor CXCR4 expression leading to inhibition of CXCL12-induced invasion of breast and pancreatic tumor cells

CXC chemokine receptor 4 (CXCR4), initially linked with leukocyte trafficking, is now known to be expressed in various tumors including breast, ovary, prostate, gastrointestinal, head and neck, bladder, brain, and melanoma. This receptor mediates homing of tumor cells to specific organs that express the ligand CXCL12 for this receptor. Thus, agents that can down-regulate CXCR4 expression have potential against cancer metastasis. In this study, we report the identification of zerumbone, a component of subtropical ginger (Zingiber zerumbet), as a regulator of CXCR4 expression. This sesquiterpene down-regulated the expression of CXCR4 on HER2-overexpressing breast cancer cells in a dose- and time-dependent manner. The decrease in CXCR4 by zerumbone was found to be not cell type specific as its expression was abrogated in leukemic, skin, kidney, lung, and pancreatic cancer cell lines. The down-regulation of CXCR4 was not due to proteolytic degradation but rather to transcriptional regulation, as indicated by down-regulation of mRNA expression, inhibition of nuclear factor-kappaB activity, and suppression of chromatin immunoprecipitation activity. Suppression of CXCR4 expression by zerumbone correlated with the inhibition of CXCL12-induced invasion of both breast and pancreatic cancer cells. An analogue of zerumbone, alpha-humulene, which lacks the carbonyl group, was found to be inactive in inducing CXCR4 down-regulation. Overall, our results show that zerumbone is a novel inhibitor of CXCR4 expression and thus has a potential in the suppression of cancer metastasis.

Secreted trefoil factor 2 activates the CXCR4 receptor in epithelial and lymphocytic cancer cell lines

The secreted trefoil factor family 2 (TFF2) protein contributes to the protection of the gastrointestinal mucosa from injury by strengthening and stabilizing mucin gels, stimulating epithelial restitution, and restraining the associated inflammation. Although trefoil factors have been shown to activate signaling pathways, no cell surface receptor has been directly linked to trefoil peptide signaling. Here we demonstrate the ability of TFF2 peptide to activate signaling via the CXCR4 chemokine receptor in cancer cell lines. We found that both mouse and human TFF2 proteins (at approximately 0.5 microm) activate Ca2+ signaling in lymphoblastic Jurkat cells that could be abrogated by receptor desensitization (with SDF-1alpha) or pretreatment with the specific antagonist AMD3100 or an anti-CXCR4 antibody. TFF2 pretreatment of Jurkat cells decreased Ca2+ rise and chemotactic response to SDF-1alpha. In addition, the CXCR4-negative gastric epithelial cell line AGS became highly responsive to TFF2 treatment upon expression of the CXCR4 receptor. TFF2-induced activation of mitogen-activated protein kinases in gastric and pancreatic cancer cells, KATO III and AsPC-1, respectively, was also dependent on the presence of the CXCR4 receptor. Finally we demonstrate a distinct proliferative effect of TFF2 protein on an AGS gastric cancer cell line that expresses CXCR4. Overall these data identify CXCR4 as a bona fide signaling receptor for TFF2 and suggest a mechanism through which TFF2 may modulate immune and tumorigenic responses in vivo.

Chemokine receptor CXCR4 as a therapeutic target for neuroectodermal tumors

Chemokines (chemotactic cytokines) are a family of proteins associated with the trafficking and activation of leukocytes and other cell types in immune surveillance and inflammatory response. Besides their roles in the immune system, they play pleiotropic roles in tumor initiation, promotion, and progression. Chemokines can be classified into four subfamilies of chemokines, CXC, CC, C, or CX3C, based on their number and spacing of conserved cysteine residues near the N-terminus. This CXC subfamily can be further subclassified into two groups, depending on the presence or absence of a tripeptide motif glutamic acid-leucine-arginine (ELR) in the N-terminal domain. ELR(-)CXCL12, which binds to CXCR4 has been frequently implicated in various cancers. Over the past several years, studies have increasingly shown that the CXCR4/CXCL12 axis plays critical roles in tumor progression, such as invasion, angiogenesis, survival, homing to metastatic sites. This review focuses on involvement of CXCR4/CXCL12 interaction in neuroectodermal cancers and their therapeutic potentials. As an attractive therapeutic target of CXCR4/CXCL12 axis for cancer chemotherapy, development history and application of CXCR4 antagonists are described.

Characterization of the CXCR4 signaling in pancreatic cancer cells

CXCL12 and its receptor, CXCR4, are emerging as promising targets for modulating growth, angiogenesis, and metastasis in several human cancers. Indeed, blocking the receptor is sufficient to prevent metastasis and angiogenesis in experimental breast cancer xenografts. Recently, the biological effect of the CXCR4 in pancreatic cancer, one of the most deadly neoplastic diseases, has been reported. However, the molecular mechanism by which CXCR4 contributes to these properties is not completely understood. In this paper, we characterize the signaling pathways activated by CXCR4 in pancreatic cancer. We show that after CXCR4 activation, EGFR becomes tyrosine phosphorylated, and the kinase activity of this receptor, together with the activation of MMPs, Src, and PI3-Kinase, is required for CXCR4-mediated ERK activation. Analysis of this cascade in pancreatic cancer cells revealed that the ERK-mediated pathway regulates genes involved in angiogenesis, such as VEGF, CD44, HIF1alpha, and IL-8. Furthermore, ERK blockage inhibits the migration and tube formation of endothelial cells induced by CXCL12. Considering that inhibitors for several components of this pathway, including CXCR4 itself, are at different stages of clinical trials, this study provides theoretical justification for the clinical testing of these drugs in pancreatic cancer, thus extending the list of potential targets for treating this dismal disease.

Cancer-related inflammation

The mediators and cellular effectors of inflammation are important constituents of the local environment of tumours. In some types of cancer, inflammatory conditions are present before a malignant change occurs. Conversely, in other types of cancer, an oncogenic change induces an inflammatory microenvironment that promotes the development of tumours. Regardless of its origin, 'smouldering' inflammation in the tumour microenvironment has many tumour-promoting effects. It aids in the proliferation and survival of malignant cells, promotes angiogenesis and metastasis, subverts adaptive immune responses, and alters responses to hormones and chemotherapeutic agents. The molecular pathways of this cancer-related inflammation are now being unravelled, resulting in the identification of new target molecules that could lead to improved diagnosis and treatment.

The critical role of SDF-1/CXCR4 axis in cancer and cancer stem cells metastasis

Chemokines exert their multifunctional role in several physiologic and pathologic processes through interaction with their specific receptors. Much evidence have revealed that metastatic spread tumor cells may use chemokine-mediated mechanisms. In particular, an involvement of stromal cell-derived factor-1 (SDF-1) in growth of primary tumors and in metastatic process has been demonstrated. Indeed, it has been suggested that CXCR4 expression by tumor cells, plays a critical role in cell metastasis by a chemotactic gradient to organs expressing the ligand SDF-1. Moreover, CXCR4 overexpression correlated with poor prognosis in many types of cancer. In physiologic condition, SDF-1 also plays an essential role modulating stem cell proliferation, survival, and homing through its canonical receptor CXCR4. Recently, several studies have demonstrated the existence of a small subset of cancer cells which share many characteristics with stem cells and named cancer stem cells (CSC). They constitute a reservoir of self-sustaining cells with the ability to maintain the tumor growth. In particular, most of them express CXCR4 receptor and respond to a chemotactic gradient of its specific ligand SDF-1, suggesting that CSC probably represent a subpopulation capable of initiating metastasis. This review focuses on the role of SDF-1/CXCR4 axis in cancer and in the metastatic progression by tumoral cells, as well as the role of CSC in tumor pathogenesis and in metastatic process. A better understanding of migratory mechanism involving cancer cells and CSC provides a powerful tool for developing novel therapies reducing both local and distant recurrences.

FGF10/FGFR2 signal induces cell migration and invasion in pancreatic cancer

Pancreatic cancer has one of the highest mortalities among all malignancies and there is an urgent need for new therapy. This might be achieved by resolving the detailed biological mechanism, and in this study we examined how pancreatic cancer cells develop aggressive properties by focusing on signalling through the fibroblast growth factor (FGF)10 and FGF receptor (FGFR)2, which play important roles in pancreatic organogenesis. Immunostaining of pancreatic cancer tissues showed that FGFR2 was expressed in cancer cells, whereas FGF10 was expressed in stromal cells surrounding the cancer cells. Patients with high FGFR2 expression in cancer cells had a shorter survival time compared to those with low FGFR2 expression. Fibroblast growth factor 10 induced cell migration and invasion of CFPAC-1 and AsPC-1 pancreatic cancer cells through interaction with FGFR2-IIIb, a specific isoform of FGFR2. Fibroblast growth factor 10 also induced expression of mRNA for membrane type 1-matrix metalloproteinase (MT1-MMP) and transforming growth factor (TGF)-β1, and increased secretion of TGF-β1 protein from these cell lines. These data indicate that stromal FGF10 induces migration and invasion in pancreatic cancer cells through interaction with FGFR2, resulting in a poor prognosis. This suggests that FGF10/FGFR2 signalling is a promising target for new molecular therapy against pancreatic cancer.

Cytoplasmic trapping of CXCR4 in hepatocellular carcinoma cell lines

PURPOSE

The chemokine receptor CXCR4 plays a role in the metastasis and progression of a broad range of malignant tumors; however, its influence on hepatocellular carcinoma (HCC) is not well defined. Thus, we analyzed the expression of CXCR4 and its functions in HCC cell lines in vitro.

MATERIALS AND METHODS

Five HCC cell lines (HepG2, Hep3B, SK-HEP-1, NCI-H630 and PLC/PRF5) were investigated. The CXCR4 expression was analyzed by RT-PCR, Western blotting, flow cytometry and immunofluorescence staining. In addition, the effects of stromal cell-derived factor-1 (SDF-1) on the migration, proliferation and survival of the cells were investigated, as well as the SDF-1-induced phosphorylation of signaling molecules.

RESULTS

All five cell lines had abundant CXCR4 in their cytoplasm, whereas a cell surface CXCR4 expression was only detected in a very small population of PLC/PRF5 cells. In contrast, SDF-1 bound to all the cells. SDF-1 induced the phosphorylation of AKT and ERK1/2 in the PLC/PRF5 cells and the phosphorylation of Stat3, AKT and ERK1/2 in the Hep3B cells. Nonetheless, SDF-1 did not induce migration or proliferation in any of the cells, nor did it rescue the cells from serum deprivation-induced apoptosis. Recruitment of CXCR4 from the cytoplasm to the cell surface was not elicited by dexamethasone, proinflammatory cytokines or VEGF. Hypoxia increased both the cytoplasmic and cell surface expressions of CXCR4 in only the PLC/PRF5 cells.

CONCLUSIONS

CXCR4 is trapped in the cytoplasm and it is not recruited to the cell surface by standard extrinsic stimuli in the majority of HCC cell lines, and the result of this is a negligible response to SDF-1.

pVHL co-ordinately regulates CXCR4/CXCL12 and MMP2/MMP9 expression in human clear-cell renal cell carcinoma

Loss of pVHL function, characteristic for clear-cell renal cell carcinoma (ccRCC), causes increased expression of CXCR4 chemokine receptor, which triggers expression of metastasis-associated MMP2/MMP9 in different human cancers. The impact of pVHL on MMP2/MMP9 expression and their relationship to CXCR4 and its ligand CXCL12 in ccRCC is unclear. By using reverse transcription PCR, immunofluorescence and immunohistochemistry, strong mRNA and protein expression of CXCR4, CXCL12, MMP2, MMP9 and MMP inhibitors TIMP1 and TIMP2 was found in VHL-null 786-O ccRCC cells. Loss of CXCR4/CXCL12 expression after restoration of VHL function in these cells was accompanied by a significant reduction of MMP2 and MMP9 expression, whereas neither TIMP1 nor TIMP2 expression was affected. Using real-time PCR analysis, higher MMP2 (p = 0.0134) and MMP9 (p = 0.067) mRNA expression levels were detected in primary ccRCC with strong CXCR4 compared to cases with weak CXCR4 expression. There was no association between CXCR4 and TIMP1 or TIMP2 mRNA expression. MMP2 protein expression data obtained by immunohistochemistry on a tissue microarray uncovered positive cytoplasmic staining in 290/380 (76%) primary ccRCCs. Co-expression of CXCR4 and MMP2 was found in 282 of these tumours (74%). Our in vitro and in vivo data strongly indicate that pVHL coordinately regulates expression of metastasis-associated genes CXCR4/CXCL12 and MMP2/MMP9 but the exact molecular mechanism of this regulation remains to be determined. Co-expression of CXCR4 and CXCL12, as demonstrated in VHL-null 786-O cells, might enable ccRCC progression and metastatic dissemination by autocrine receptor stimulation, even in the absence of exogenous CXCL12.

CXCR4 and CXCL12 down-regulation: a novel mechanism for the chemoprotection of 3,3'-diindolylmethane for breast and ovarian cancers

Cruciferous vegetables are thought to protect against numerous types of cancer. 3,3'-Diindolylmethane (DIM) is an acid-catalyzed product generated during the consumption of cruciferous vegetables and appears to be chemoprotective for breast cancer. The interaction between the chemokine receptor, CXCR4, and its unique ligand, CXCL12, is known to mediate the progression and metastasis of breast and other cancers. Organs to which these cancers metastasize secrete CXCL12, which binds to CXCR4 expressed on the surface of primary cancer cells. This process subsequently stimulates the invasive properties of the cancer cells and attracts them to the preferred organ sites of metastases. We have found that DIM down-regulates both CXCR4 and CXCL12 in MCF-7 and MDA-MB-231 breast cancer cells as well as in BG-1 ovarian cancer cells at the transcriptional level and in an estrogen-independent manner. We demonstrate that the potential of MDA-MB-231 and BG-1 cells for chemotaxis and invasion towards CXCL12, but not towards IL-6 or fetal bovine serum, respectively, is inhibited by DIM. Furthermore, we show that DIM down-regulates CXCR4 under hypoxia and CXCL12 under estradiol-inducing conditions. Our data suggest that one mechanism whereby DIM protects against breast, ovarian, and possibly other cancers is through the repression of CXCR4 and/or CXCL12, thereby lowering the invasive and metastatic potential of these cells.

Chemokines and cancer: migration, intracellular signalling and intercellular communication in the microenvironment

Inappropriate chemokine/receptor expression or regulation is linked to many diseases, especially those characterized by an excessive cellular infiltrate, such as rheumatoid arthritis and other inflammatory disorders. There is now overwhelming evidence that chemokines are also involved in the progression of cancer, where they function in several capacities. First, specific chemokine–receptor pairs are involved in tumour metastasis. This is not surprising, in view of their role as chemoattractants in cell migration. Secondly, chemokines help to shape the tumour microenvironment, often in favour of tumour growth and metastasis, by recruitment of leucocytes and activation of pro-inflammatory mediators. Emerging evidence suggests that chemokine receptor signalling also contributes to survival and proliferation, which may be particularly important for metastasized cells to adapt to foreign environments. However, there is considerable diversity and complexity in the chemokine network, both at the chemokine/receptor level and in the downstream signalling pathways they couple into, which may be key to a better understanding of how and why particular chemokines contribute to cancer growth and metastasis. Further investigation into these areas may identify targets that, if inhibited, could render cancer cells more susceptible to chemotherapy.

Eotaxin-2 and colorectal cancer: a potential target for immune therapy

PURPOSE

To study the production of chemokines by colorectal hepatic metastases.

EXPERIMENTAL DESIGN

Biopsies of resected colorectal hepatic metastases and nonneoplastic adjacent liver tissue were screened for chemokines using protein arrays and results were confirmed by ELISA and immunohistochemistry.

RESULTS

Two chemokines, eotaxin-2 and MCP-1, were found at elevated levels within the tumor biopsy compared with adjacent liver. The relative increase in expression from tumor was much higher for eotaxin-2 than MCP-1, with 10 of 25 donors having a >100-fold increase in expression compared with 0 of 24 donors for MCP-1. In a parallel analysis, eotaxin-2 was also found at elevated levels in the tumor region of primary colorectal cancer biopsies. Immunohistochemical staining indicated that carcinoembryonic antigen-positive tumor cells stained strongly for eotaxin-2, implicating these cells as the predominant source of the chemokine. In vitro studies confirmed that several colorectal tumor lines produce eotaxin-2 and that secretion of this chemokine could be depressed by IFN-gamma and enhanced by the Th2-type cytokines interleukin-4 and interleukin-13. Jurkat T cells were engineered to express the receptor for eotaxin-2 (CCR3). These cells effectively migrated in response to eotaxin-2 protein, suggesting that immune cells gene modified to express a chemokine receptor may have improved abilities to home to tumor.

CONCLUSIONS

Taken together, these observations confirm eotaxin-2 as a chemokine strongly associated with primary and metastatic tumors of colorectal origin. Furthermore, the importance of this result may be a useful tool in the development of targeted therapeutic approaches to colorectal tumors.

AMD3100 mobilizes endothelial progenitor cells in mice, but inhibits its biological functions by blocking an autocrine/paracrine regulatory loop of stromal cell derived factor-1 in vitro

Endothelial progenitor cells (EPCs), a CXCR4-bearing cell line, are thought to positively influence reendothelialization, vascular repair, and angiogenesis. AMD3100, a highly selective antagonist of stromal cell derived factor (SDF)-1 that binds to its receptor, CXCR4, has been shown to induce rapid mobilization of hematopoietic stem cells in mice, dogs, and humans. Results of this study indicate that AMD3100 injection can induce a rapid and potent mobilization of EPCs in mice compared with saline injection. The study demonstrates that murine spleen-derived EPCs can produce high levels of SDF-1 in vitro. Blocking this endogenous SDF-1 with AMD3100 decreases the number of EPCs; inhibits the proliferation, migration, and adhesion of EPCs; and induces EPC apoptosis. In addition, AMD3100 inhibits ectogenous SDF-1alpha induced improvement of EPC functions. However, AMD3100 incubation does not change the functions of CXCR4-negative cell line HPDE6. In conclusion, AMD3100 can be regarded as a potent mobilizer of EPCs in mice. EPCs have an autocrine/paracrine SDF-1 loop, and breaking this loop with AMD3100 can inhibit the EPC functions in vitro.

The CXCR5 chemokine receptor is expressed by carcinoma cells and promotes growth of colon carcinoma in the liver

The chemokine receptor CXCR5 is expressed by B cells and certain T cells and controls their migration into and within lymph nodes. Its ligand BCA-1/CXCL13 is present in lymph nodes and spleen and also in the liver. Surprisingly, we detected CXCR5 in several mouse and human carcinoma cell lines. CXCR5 was particularly prominent in pancreatic carcinoma cell lines and was also detected by immunohistochemistry in 7 of 18 human pancreatic carcinoma tissues. Expression in CT26 colon carcinoma was low in vitro, up-regulated in vivo, and rapidly lost when cells were explanted in vitro. CXCL13 strongly promoted proliferation of CXCR5-transfected CT26 cells in vitro. In the liver, after intrasplenic injection, these CXCR5 transfectants initially grew faster than controls, but the growth rate of control tumors accelerated later to become similar to the transfectants, likely due to the up-regulation of CXCR5. Inhibition of CXCR5 function, by trapping CXCR5 in the endoplasmic reticulum using a CXCL13-KDEL "intrakine," had no effect on initial growth of liver foci but later caused a prolonged growth arrest. In contrast, s.c. and lung tumors of CXCR5- and intrakine-transfected cells grew at similar rates as controls. We conclude that expression of CXCR5 on tumor cells promotes the growth of tumor cells in the liver and, at least for CT26 cells, seems to be required for outgrowth to large liver tumors. Given the limited expression on normal cells, CXCR5 may constitute an attractive target for therapy, particularly for pancreatic carcinoma.

Silencing of CXCR4 inhibits the proliferation, adhesion, chemotaxis and invasion of salivary gland mucoepidermoid carcinoma Mc3 cells in vitro

Mucoepidermoid carcinoma is the most common malignant tumor in salivary glands and high-grade mucoepidermoid carcinoma is often accompanied with poor prognosis. Many recent research works demonstrated that stromal cell-derived factor-1 (SDF-1) and its receptor CXC chemokine receptor-4 (CXCR4) interaction was critical for metastasis of various cancers. In this study, the immunoexpression of CXCR4 in human salivary gland mucoepidermoid carcinoma in different grades was detected by immunohistochemical analysis and the expression of CXCR4 and its ligand SDF-1 in mucoepidermoid carcinoma MEC-1 cell line and its highly metastatic clone Mc3 was examined by RT-PCR, flow cytometry and immunocytochemical analysis. It was found that CXCR4 was over-expressed in Mc3 cell line and SDF-1 was expressed in both cell lines at a nearly equal level. We further constructed CXCR4-shRNA expression vector to stably transfect Mc3 cells. We found that silencing of endogenous CXCR4 gene expression in Mc3 cells resulted in inhibition of the proliferation, adhesion, chemotaxis and invasion of Mc3 cells in vitro. This study implies that CXCR4 molecule is a potential factor controlling the proliferation and metastasis of Mc3 cells.

The inflammatory micro-environment in tumor progression: the role of tumor-associated macrophages

The link between inflammation and cancer proposed more than a century ago by Rudolf Virchow, who noticed the infiltration of leukocytes in malignant tissues, has recently found a number of genetic and molecular confirmations. Experimental, clinical and epidemiological studies have revealed that chronic inflammation contributes to cancer progression and even predisposes to different types of cancer. Cancer-associated inflammation includes: the presence of leukocyte infiltration; the expression of cytokines such as tumor necrosis factor (TNF) or interleukin (IL)-1; chemokines such as CCL2 and CXCL8; active tissue remodelling and neo-angiogenesis. Tumor-associated macrophages (TAM) are key regulators of the link between inflammation and cancer. Many observations indicate that, in the tumor micro-environment, TAM have several protumoral functions, including expression of growth factors, matrix proteases, promotion of angiogenesis and suppression of adaptive immunity. In this review we will discuss the role of TAM in the inflammatory micro-environment of solid tumors and will try to identify potential target for future therapeutic approaches.

The chemokine receptor CXCR4 strongly promotes neuroblastoma primary tumour and metastatic growth, but not invasion

Neuroblastoma (NB) is a heterogeneous, and particularly malignant childhood neoplasm in its higher stages, with a propensity to form metastasis in selected organs, in particular liver and bone marrow, and for which there is still no efficient treatment available beyond surgery. Recent evidence indicates that the CXCR4/CXCL12 chemokine/receptor axis may be involved in promoting NB invasion and metastasis. In this study, we explored the potential role of CXCR4 in the malignant behaviour of NB, using a combination of in vitro functional analyses and in vivo growth and metastasis assessment in an orthotopic NB mouse model. We show here that CXCR4 overexpression in non-metastatic CXCR4-negative NB cells IGR-NB8 and in moderately metastatic, CXCR4 expressing NB cells IGR-N91, strongly increased tumour growth of primary tumours and liver metastases, without altering the frequency or the pattern of metastasis. Moreover shRNA-mediated knock-down experiments confirmed our observations by showing that silencing CXCR4 in NB cells impairs in vitro and almost abrogates in vivo growth. High levels of CXCL12 were detected in the mouse adrenal gland (the primary tumour site), and in the liver suggesting a paracrine effect of host-derived CXCL12 on NB growth. In conclusion, this study reveals a yet unreported NB-specific predominant growth and survival-promoting role of CXCR4, which warrants a critical reconsideration of the role of CXCR4 in the malignant behaviour of NB and other cancers.

Stepping out of the flow: capillary extravasation in cancer metastasis

In order for cancer cells to successfully colonize a metastatic site, they must detach from the primary tumor using extracellular matrix-degrading proteases, intravasate and survive in the circulation, evade the immune response, and extravasate the vasculature to invade the target tissue parenchyma, where metastatic foci are established. Though many of the steps of metastasis are widely studied, the precise cellular interactions and molecular alterations associated with extravasation are unknown, and further study is needed to elucidate the mechanisms inherent to this process. Studies of leukocytes localized to inflamed tissue during the immune response may be used to elucidate the process of cancer extravasation, since leukocyte diapedesis through the vasculature involves critical adhesive interactions with endothelial cells, and both leukocytes and cancer cells express similar surface receptors capable of binding endothelial adhesion molecules. Thus, leukocyte extravasation during the inflammatory response has provided a model for transendothelial migration (TEM) of cancer cells. Leukocyte extravasation is characterized by a process whereby rolling mediated by cytokine-activated endothelial selectins is followed by firmer adhesions with beta1 and beta2 integrin subunits to an activated endothelium and subsequent diapedesis, which most likely involves activation of Rho GTPases, regulators of cytoskeletal rearrangements and motility. It is controversial whether such selectin-mediated rolling is necessary for TEM of cancer cells. However, it has been established that similar stable adhesions between tumor and endothelial cells precede cancer cell transmigration through the endothelium. Additionally, there is support for the preferential attachment of tumor cells to the endothelium and, accordingly, site-specific metastasis of cancer cells. Rho GTPases are critical to TEM of cancer cells as well, and some progress has been made in understanding the specific roles of the Rho GTPase family, though much is still unknown. As the mechanisms of cancer TEM are elucidated, new approaches to study and target metastasis may be utilized and developed.

Adhesion molecules and chemokines: the navigation system for circulating tumor (stem) cells to metastasize in an organ-specific manner

To date, cancer is still the second most prevalent cause of death after cardiovascular diseases in the industrialized word, whereby the primary cause of cancer is not attributed to primary tumor formation, but rather to the growth of metastases at distant organ sites. For several years it was considered that the well-known phenomenon of organ-specific spreading of tumor cells is mostly a mechanical process either directed passively due to size constraints (mechanical trapping theory) or due to a fertile environment provided by the organ in which tumor cells can proliferate (seed and soil hypothesis). Both mechanisms strongly depend on the adhesive properties of tumor cells either to endothelial cells and/or cancer cells, which are facilitated by a variety of cell adhesion molecules including carbohydrates and integrins. Within the past years it became evident that the organ-specific metastatic spreading of tumor cells does not only rely on heterotypic and homotypic adhesive interactions, but also on the interplay of chemokines and their appropriate receptors. Moreover, the identification of cancer stem cells in various tumor tissues has opened new questions. Cancer stem cells possess self-renewal, differentiation, and tumor-initiating capacities. Thus these cells are ideal candidates to be the seed of a secondary tumor. In the present review we will give a brief overview about the complex process of organ-specific metastasis formation depending on the interplay of adhesion molecules, chemokines, and the putative role of cancer stem cells in metastasis formation.

The CXCR4-SDF1alpha axis is a critical mediator of rhabdomyosarcoma metastatic signaling induced by bone marrow stroma

Rhabdomyosarcoma (RMS) is the most common malignant soft-tissue tumor of childhood. Nearly 15% of children present with metastatic disease, frequently involving the lungs and bone marrow. The prognosis for patients with metastatic RMS is dismal, with an estimated 3-year overall survival of 30%. Stromal-cell derived factor 1-alpha (SDF1alpha, CXCL12) is a chemokine that plays a crucial role in the metastatic attraction of tumor cells expressing its receptor, CXCR4. We investigated the role of the bone marrow microenvironment on RMS signaling through the CXCR4/SDF1alpha pathway in cell lines and primary tumors. Conditioned media (CM) isolated from cultured patient-derived bone marrow stromal cells (BMS) induced migration and proliferation in multiple RMS cell lines. CXCR4 was expressed in RMS cell lines and primary tumors, with higher expression in alveolar subtype RMS. Further, SDF1alpha was secreted by all BMS cultures and potently induced the migration and proliferation of RMS cells. Small molecule or blocking antibody-mediated inhibition of CXCR4 or SDF1alpha suppressed RMS cell migration towards BMS-CM, confirming the activity of this axis. Our study provides strong evidence for the involvement of the bone marrow microenvironment and CXCR4/SDF1alpha signaling in metastasis of RMS. These results form the basis for future studies to delineate the mechanisms of bone marrow metastasis in RMS.

CCR2 expression correlates with prostate cancer progression

Although the primary role of chemokines and their receptors is controlling the trafficking of leukocytes during inflammatory responses, they also play pleoitropic roles in cancer development. There is emerging evidence that cancer cells produce chemokines that induce tumor cell proliferation or chemotaxis in various cancer types. We have previously reported that MCP-1 acts as a paracrine and autocrine factor for prostate cancer (PCa) growth and invasion. As the cellular effects of MCP-1 are mediated by CC chemokine receptor 2 (CCR2), we hypothesized that CCR2 may contribute PCa progression. Accordingly, we first determined CCR2 mRNA and protein expression in various cancer cell lines, including PCa and other cancer types. All cells expressed CCR2 mRNA and protein, but in PCa, more aggressive cancer cells such as C4-2B, DU145, and PC3 expressed a higher amount of CCR2 compared with the less aggressive cancer cells such as LNCaP or non-neoplastic PrEC and RWPE-1 cells. Further, we found a positive correlation between CCR2 expression and PCa progression by analyzing an ONCOMINE gene array database. We confirmed that CCR2 mRNA was highly expressed in PCa metastatic tissues compared with the localized PCa or benign prostate tissues by real-time RT-PCR. Finally, CCR2 protein expression was examined by immunohistochemical staining on tissue microarray specimens from 96 PCa patients and 31 benign tissue controls. We found that CCR2 expression correlated with Gleason score and clinical pathologic stages, whereas lower levels of CCR2 were expressed in normal prostate tissues. These results suggest that CCR2 may contribute to PCa development.

Rho activation regulates CXCL12 chemokine stimulated actin rearrangement and restitution in model intestinal epithelia

Chemokines are critical regulatory factors that direct migration, proliferation and maturation of receptor expressing target cells within gut mucosa. The aim of the present study was to define the cellular mechanisms whereby engagement of the essential chemokine CXCL12 to CXCR4 regulates restitutive epithelial cell migration. Non-transformed IEC-6 cells or polarized T84 epithelial monolayers were wounded and F-actin accumulation assessed using fluorescence microscopy and flow cytometry. Immunoblot analysis, pull-down assays, fluorescence microscopy and wound healing assays defined activation of Rho, Rho-kinase (ROCK), and myosin light chain (MLC) and the role for those Rho effectors in CXCL12-regulated epithelial restitution. CXCL12 increased RhoGTP and F-actin localization to the leading edge of wounded IEC-6 and T84 monolayers. CXCL12 congruently stimulated an increase in active MLC that was inhibited by blockade of ROCK and myosin light chain kinase and regulated epithelial migration. Our data in model intestinal epithelia suggest CXCR4 and CXCL12 may function as an autocrine and paracrine mucosal signaling network regulating the competency of the epithelial barrier to withstand injury and mediate repair following damage.

Synergistic effect of cyclin D1 and c-Myc leads to more aggressive and invasive mammary tumors in severe combined immunodeficient mice

Cyclin D1 is one of the most commonly overexpressed oncogenes in breast cancer; yet, it is not clear whether cyclin D1 alone is capable of causing malignant transformation of mammary epithelial cells. Here, we show that ectopic expression of cyclin D1 in benign mouse mammary epithelial cells promotes cell proliferation, anchorage-independent growth in soft agar, and tumorigenesis in severe combined immunodeficient mice. To address the possible interaction of cyclin D1 and c-myc in malignant transformation, we used cyclin D1/c-myc dual-expressing clones, which displayed more aggressive and invasive phenotype than cyclin D1-expressing clones. These data provide evidence that overexpression of cyclin D1 or coexpression with c-myc could cause invasive malignant transformation of benign mouse mammary epithelial cells. Furthermore, microarray analysis of cyclin D1 and cyclin D1/c-myc clones showed that these two tumor-producing clones might use distinct invasive pathways. In summary, overexpression of cyclin D1 may commit mammary epithelia to a tumor-prone phenotype in which cooperation with other genes, such as synergy with c-myc, may lead to a more aggressive phenotype.

Integrin-mediated laminin-1 adhesion upregulates CXCR4 and IL-8 expression in pancreatic cancer cells

BACKGROUND

We have shown recently that alpha(2)beta(1) integrin-mediated type I collagen adhesion promotes a more malignant phenotype in pancreatic cancer cell lines than other extracellular matrix (ECM) proteins. MiaPaCa-2 cells, by contrast, do not express collagen-binding integrins, but are metastatic in our orthotopic mouse model and migrate maximally on laminin-1 (Ln-1). It has also been shown that CXCR4 and IL-8 expression correlates directly with metastasis in pancreatic cancer in vivo. We therefore examined the potential of the ECM to regulate CXCR4 and IL-8 expression in pancreatic cancer cells.

METHODS

We cultured 8 pancreatic cancer cell lines on fibronectin (Fn), types I and IV collagen, Ln-1 and vitronectin (Vn), and examined cell lysates for CXCR4 by immunoblotting and media for IL-8 by ELISA. We also conducted cell migration assays with stromal-derived factor-1 (SDF-1) as the chemoattractant to examine integrin-binding specificity and CXCR4 function.

RESULTS

All cell lines expressed CXCR4 protein. MiaPaCa-2 cell growth on Ln-1 increased significantly CXCR4 and IL-8 expression relative to other ECM proteins. Migration inhibition studies showed that both the alpha(6)beta(1) and alpha(3)beta(1) integrins mediate MiaPaCa-2 migration on Ln-1. Growth studies showed further that CXCR4 expression on Ln-1 was mediated by the alpha(6)beta(1) integrin whereas IL-8 expression was mediated by both the alpha(6)beta(1) and alpha(3)beta(1) integrins. The expression of functional CXCR4 was also shown in migration assays, where SDF-1 significantly increased pancreatic cancer cell chemotaxis on Ln-1.

CONCLUSIONS

These data indicate that integrin-mediated Ln-1 adhesion upregulates CXCR4 and IL-8 expression and may play a mechanistic role in pancreatic cancer metastases.

Profiles of chemokine receptors in melanocytic lesions: de novo expression of CXCR6 in melanoma

Selective expression of certain chemokine receptors by melanoma cells and the presence of their ligands in tissues might govern organ site-specific metastasis. Because the expression profile of chemokine receptors in tissues of melanocytic origin is unknown, we performed a comprehensive study on melanocytic tissue samples investigating the expression of 18 chemokine receptors at the mRNA level by real-time polymerase chain reaction, using a semiquantitative approach, and of 3 chemokine receptors (CXCR6, CCR9, and XCR1) at the protein level. We report on the de novo expression of CXCR6 in primary melanomas and melanoma metastases, but absence in melanoma cell lines and congenital nevi. CXCR4 and CCR1 were the only 2 chemokine receptors that were consistently expressed in melanocytes, melanoma cell lines, primary, and metastatic melanoma; CCR1 expression increased significantly over progression. CCR9 and XCR1 transcripts were found in melanocytic lesions, and expression was confirmed by immunohistochemistry. Transcripts for CCR10 were not found in any of the lesions, but in some melanoma cell lines. Expression of CCR7 was observed in primary melanomas and some metastases. CCR5 was exclusively expressed in primary melanomas and some cutaneous metastases. Results revealed a restricted and differential pattern of chemokine receptor expression in melanoma tissue, which varies substantially from the expression profile of melanoma cell lines and warrants functional studies on some receptors.

CXCR4expression is associated with pelvic lymph node metastasis in cervical adenocarcinoma

The aim of this study is to investigate the expression of CXCR4 receptor in cervical adenocarcinoma and related mechanisms involved in pelvic lymph node metastasis. Immunohistochemistry was used to evaluate the expression of CXCR4 and the association of pelvic lymph node metastasis in archived tissue from clinical stage IB cervical adenocarcinomas (n = 37) and from benign specimens obtained at hysterectomy for other causes (n = 48). The HeLa cell (cervical adenocarcinoma-derived cell) line that expresses CXCR4 was used to study the interaction between the CXCR4 receptor and stromal cell-derived factor 1alpha (SDF-1alpha). Cell migration assays, cell numbers, flow cytometry, cell proliferation assay, and western blot were used to study the function of CXCR4 and its downstream signal transduction. The positive cases were semiquantitatively divided into three score classes according to their staining. Tumors with strong CXCR4 stainings were more likely to have pelvic lymph node metastasis than those with weak or negative stainings (87.5% vs 34.5%; P = 0.014). Only 25% of the benign specimens had weak or negative staining for CXCR4. Functioning CXCR4 receptor was expressed on HeLa cells. SDF-1alpha provoked significant signal transduction events, including chemotaxis and rescue from apoptosis. These actions were apparently mediated by the activation and phosphorylation of the extracellular signal-regulated kinase 1/2 and AKT pathways. We conclude CXCR4 expression is associated with cervical adenocarcinoma cell migration and proliferation, and primary cervical adenocarcinoma cells expressing CXCR4 are significantly more likely to metastasize to pelvic lymph nodes.

Current update of cytokines in pancreatic cancer: pathogenic mechanisms, clinical indication, and therapeutic values

Pancreatic cancer is the fourth leading cause of cancer death with a 5-year survival less than 5 percent despite rigorous interventions. This largely is due to its late presentation, aggressive metastasis, and a lack of effective adjuvant therapies. Cytokines have been studied in many tumor types, where they have been shown to be an important influence in cancer cell behavior and to have potential as tumor markers, therapeutic targets, or as treatments themselves. Recently, the roles cytokines play in pancreatic cancer have become the subject of intense investigation. However, the story is complicated, largely because of the pleiotropic and overlapping nature of cytokine functions. This article attempts to provide a focused review of recent discoveries in this area by organizing the material along the pathophysiologic tasks a cancer cell must accomplish to achieve malignancy. We examined how cytokines act to create a microenvironment conducive to tumor cell survival and growth, discussed how cytokines affect proliferation, invasion, metastasis, and apoptosis in pancreatic cancer cells, and we summarized how this knowledge has been applied either to target cytokines or use them therapeutically.

β-Catenin is a promising key factor in the SDF-1/CXCR4 axis on metastasis of pancreatic cancer

Metastasis is recently the most fearsome of cancer. Pancreatic cancer is the fourth leading cause of cancer death. Morbidity and mortality from pancreatic cancer is conspicuously associated with metastasis. However, the mechanism of metastasis is not well described. Early studies mostly focus on the "soil and seed" hypothesis. Recently, the chemotaxis hypothesis has been paid more attention. Cancer cell with high expression of chemokine receptor will spread to the specific sites where the ligand is highly secreted. It has been demonstrated that SDF-1/CXCR4 signaling, one of the most important chemokine receptor-ligand complexes, was considered to play a critical role in pancreatic cancer organ-specific metastasis through some possible pathways. However, studies do not clarify the mechanism of SDF-1/CXCR4 signaling on pancreatic cancer progression. Beta-catenin, an important factor in canonical Wnt signaling pathway, also makes great contributions on cancer invasion and metastasis. It seems that Wnt/beta-catenin has a significant role in pancreatic cancer progression through interactions with different protein complexes. In the previous study of neural development, the relationship between SDF-1/CXCR4 signaling and beta-catenin has been described. It gave a clue to describe the correlation between SDF-1/CXCR4 signaling and Wnt/beta-catenin pathway. According to this, we postulate that beta-catenin is a promising key factor of SDF-1/CXCR4 signaling to regulate the metastasis of pancreatic cancer. With the stimulation of SDF-1 on highly metastatic pancreatic cancer cells, beta-catenin will separate from different complexes, translocate into the nucleus, trigger the expression of target genes and finally promote the migration of pancreatic cancer cells to specific sites. Through the observation of this crosstalk, it is possible to understand more clearly about the pancreatic cancer specific metastasis and to make some contributions on gene therapy of pancreatic cancer.

Chemokines and cancer

The chemokines and their receptors are a superfamily of small secreted molecules that control the migration of many cell types in the body. Several years ago it became clear that some chemokines and receptors regulate the migration of certain cells in the lymphoid system, and this raised the possibility that chemokines could also control the migration of tumor cells in the body. Breast cancer cells were found to express chemokine receptors in a nonrandom manner, and these observations pointed to several chemokine/receptor pairs that control tumor-cell migration. The most important ligand/receptors pairs in these phenomena include CXCL12/CXCR4 and CCL21/CCR7. Since then, there has been intense interest in this area and many studies have been published, especially on CXCR4. These studies point to the following conclusions: (i) Tumors express chemokine receptors in a nonrandom manner. (ii) CXCR4 is the most widely expressed chemokine receptor in many different cancers. (iii) CCR7 is also expressed by many cancers, and is likely to mediate metastasis to the lymph nodes in selected cancers. (iv) The effects of CXCL12 on CXCR4-bearing tumor cells likely include many other functions (growth, differentiation) besides migration. During normal development, the interaction CXCL12/CXCR4 is known to be involved in organogenesis. This process shares many characteristics with metastasis, and represents one of the key areas of future research.

Human melanoma metastases express functional CXCR4

PURPOSE

The chemokine receptor CXCR4 was identified as an independent predictor of poor prognosis in primary melanoma. The aim of the study was to investigate the role of CXCR4 in human melanoma metastases.

EXPERIMENTAL DESIGN

CXCR4 expression was evaluated in melanoma metastases and in metastatic cell lines through immunohistochemistry, immunoblotting, immunofluorescence, and reverse transcription-PCR. The function of CXCR4 was tested in the presence of the ligand, CXCL12, through induction of extracellular signal-regulated kinase-1 and -2 (Erk-1 and -2) phosphorylation, proliferation, apoptosis, and migration capabilities.

RESULTS

CXCR4 expression was detected in 33 out of 63 (52.4%) metastases from cutaneous melanomas. Metastatic melanoma cell lines expressed cell surface CXCR4; PES 43, Alo 40, and COPA cell lines showed the highest levels of CXCR4 (>90% of positive cells); PES 41, Alo 39, PES 47, POAG, and CIMA cell lines showed low to moderate degrees of expression (5-65% of positive cells). Other chemokine receptors, CCR7 and CCR10, were detected on the melanoma cell lines; CXCL12 activated Erk-1 and Erk-2, the whose induction was specifically inhibited by AMD3100 treatment. CXCL12 increased the growth in PES 41, PES 43, and PES 47 cells under suboptimal (1% serum) and serum-free culture conditions; AMD3100 (1 mumol/L) inhibited the spontaneous and CXCL12-induced proliferation. No rescue from apoptosis was shown but PES 41, PES 43, and PES 47 cells migrate toward CXCL12.

CONCLUSIONS

These findings indicate that CXCR4 is expressed and active in human melanoma metastases, suggesting that active inhibitors such as AMD3100 may be experienced in human melanoma.

CXCR4 chemokine receptor mediates prostate tumor cell adhesion through alpha5 and beta3 integrins

The mechanisms leading to prostate cancer metastasis are not understood completely. Although there is evidence that the CXC chemokine receptor (CXCR) 4 and its ligand CXCL12 may regulate tumor dissemination, their role in prostate cancer is controversial. We examined CXCR4 expression and functionality, and explored CXCL12-triggered adhesion of prostate tumor cells to human endothelium or to extracellular matrix proteins laminin, collagen, and fibronectin. Although little CXCR4 was expressed on LNCaP and DU-145 prostate tumor cells, CXCR4 was still active, enabling the cells to migrate toward a CXCL12 gradient. CXCL12 induced elevated adhesion to the endothelial cell monolayer and to immobilized fibronectin, laminin, and collagen. Anti-CXCR4 antibodies or CXCR4 knock out significantly impaired CXCL12-triggered tumor cell binding. The effects observed did not depend on CXCR4 surface expression level. Rather, CXCR4-mediated adhesion was established by alpha5 and beta3 integrin subunits and took place in the presence of reduced p38 and p38 phosphorylation. These data show that chemoattractive mechanisms are involved in adhesion processes of prostate cancer cells, and that binding of CXCL12 to its receptor leads to enhanced expression of alpha5 and beta3 integrins. The findings provide a link between chemokine receptor expression and integrin-triggered tumor dissemination.

Stroma-derived factor (SDF-1/CXCL12) and human tumor pathogenesis

The chemokine stroma-derived factor (SDF-1/CXCL12) plays multiple roles in tumor pathogenesis. It has been demonstrated that CXCL12 promotes tumor growth and malignancy, enhances tumor angiogenesis, participates in tumor metastasis, and contributes to immunosuppressive networks within the tumor microenvironment. Therefore, it stands to reason that the CXCL12/CXCR4 pathway is an important target for the development of novel anti-cancer therapies. In this review, we consider the pathological nature and characteristics of the CXCL12/CXCR4 pathway in the tumor microenvironment. Strategies for therapeutically targeting the CXCL12/CXCR4 axis also are discussed.

Possible regulation of migration of intrahepatic cholangiocarcinoma cells by interaction of CXCR4 expressed in carcinoma cells with tumor necrosis factor-alpha and stromal-derived factor-1 released in stroma

Intrahepatic cholangiocarcinoma (ICC) is highly fatal because of early invasion, widespread metastasis, and lack of an effective therapy. We examined roles of CXCR4 and its ligand, stromal cell-derived factor (SDF)-1, in migration of ICC with respect to tumor-stromal interaction by using two ICC cell lines, a fibroblast cell line (WI-38), and 28 human ICC tissues. The two ICC cell lines expressed CXCR4 mRNA and protein, and WI-38 fibroblasts expressed SDF-1 mRNA and protein. Migration of cultured ICC cells in Matrigel was induced by co-culture with WI-38 fibroblasts and by incubation with SDF-1. Anti-SDF-1 antibody suppressed migration, demonstrating that SDF-1 released from WI-38 fibroblasts was responsible for this migration. Tumor necrosis factor (TNF)-alpha pretreatment of ICC cells up-regulated CXCR4 mRNA and protein expression in a concentration-dependent manner. Administration of SDF-1 and TNF-alpha increased synergistically ICC cell migration, which was suppressed by the CXCR4 antagonist AMD3100. In ICC tissue, TNF-alpha was mainly expressed in infiltrated macrophages, CXCR4 in ICC cells, and SDF-1 in stromal fibroblasts. In conclusion, the interaction of SDF-1 released from fibroblasts and CXCR4 expressed on ICC cells may be actively involved in ICC migration, and TNF-alpha may enhance ICC cell migration by increasing CXCR4 expression. CXCR4 could be a therapeutic target to prevent ICC invasion.

Differential Functional Activation of Chemokine Receptor CXCR4 Is Mediated by G Proteins in Breast Cancer Cells

CXCR4 is a G protein-coupled receptor of considerable biological significance, and among its numerous functions, it is suggested to play a critical role in cancer metastasis. We have investigated the expression and function of CXCR4 in a range of breast cancer cell lines covering a spectrum of invasive phenotypes and found that, while surface levels of CXCR4 were uniform across the entire panel, only highly invasive cells that are metastatic in immunocompromised mice expressed functional receptors. CXCL12/SDF-1 induced cellular responses such as calcium mobilization, actin polymerization, and chemotaxis in metastatic cells, whereas noninvasive cells were unresponsive. Moreover, CXCL12 activated multiple signaling pathways downstream of G proteins in highly invasive cells but failed to activate any of the examined kinase cascades in noninvasive cell lines. This blockade in nonmetastatic cell lines seems to be due to the inability of G protein alpha and beta subunits to form a heterotrimeric complex with CXCR4. Galpha and Gbeta were able to bind to CXCR4 independently in all cell lines, but the association of G protein alphabetagamma heterotrimers with the receptor, a prerequisite for signal transduction downstream from G protein-coupled receptors, was only observed in the highly invasive cell lines. Our findings show, for the first time, that CXCR4 function is subject to complex and potentially tightly controlled regulation in breast cancer cells via differential G protein-receptor complex formation, and this regulation may play a role in the transition from nonmetastatic to malignant tumors.

Role of the CXCL12/CXCR4 axis in peritoneal carcinomatosis of gastric cancer

Peritoneal carcinomatosis is a frequent cause of death in patients with advanced gastric carcinoma. Because chemokines are now considered to play an important role in the metastasis of various malignancies, we hypothesized that they may be involved in the development of peritoneal carcinomatosis by gastric carcinoma. Human gastric carcinoma cell lines, which were all highly efficient in generating malignant ascites in nude mice upon i.p. inoculation, selectively expressed CXCR4 mRNA and protein. In particular, NUGC4 cells expressed CXCR4 mRNA at high levels and showed vigorous migratory responses to its ligand CXCL12. CXCL12 enhanced proliferation and rapid increases in phosphorylation of protein kinase B/Akt and extracellular signal-regulated kinase of NUGC4 cells. We also showed that AMD3100 (a specific CXCR4 antagonist) effectively reduced tumor growth and ascitic fluid formation in nude mice inoculated with NUGC4 cells. Additionally, we examined human clinical samples. Malignant ascitic fluids from patients with peritoneal carcinomatosis contained high concentrations of CXCL12 (4.67 ng/mL). Moreover, immunohistochemical analysis showed that 22 of 33 primary gastric tumors with peritoneal metastasis were positive for CXCR4 expression (67%), whereas only 4 of 16 with other distant metastasis were positive (25%). Notably, 22 of 26 CXCR4-expressing primary tumors developed peritoneal metastases (85%). CXCR4 positivity of primary gastric carcinomas significantly correlated with the development of peritoneal carcinomatosis (P < 0.001). Collectively, our results strongly suggest that the CXCR4/CXC12 axis plays an important role in the development of peritoneal carcinomatosis from gastric carcinoma. Thus, CXCR4 may be a potential therapeutic target for peritoneal carcinomatosis of gastric carcinoma.

Therapeutic potential of cytokine and chemokine antagonists in cancer therapy

A new paradigm is becoming widely accepted, that chronic inflammation, driven in part by chemokines and cytokines at the site of a tumour, may facilitate tumour progression instead of promoting anti-tumour immunity. Tumours and activated stromal cells secrete pro-inflammatory chemokines and cytokines that act either directly or indirectly through stimulation of the vascular endothelium to recruit leukocytes to the tumour. After activation, these tumour-associated leukocytes release angiogenic factors, mitogens, proteolytic enzymes, and chemotactic factors, recruiting more inflammatory cells and stimulating angiogenesis to sustain tumour growth and facilitate tumour metastasis. Breaking this cycle by inhibiting targets such as cytokines, chemokines and other inflammatory mediators, either alone, or more realistically, in combination with other therapies, such as anti-angiogenic or cytotoxic agents, may provide highly efficacious therapeutic regimens for the treatment of malignancies. This article reviews anti-cytokine and anti-chemokine therapies being pursued in cancer, and discusses in more detail anti-tumour necrosis factor-alpha (TNF) approaches.

Tumour-associated macrophages are a distinct M2 polarised population promoting tumour progression: potential targets of anti-cancer therapy

Tumour-associated macrophages (TAM) represent the major inflammatory component of the stroma of many tumours, and can affect different aspects of the neoplastic tissue. Many observations indicate that TAM express several M2-associated pro-tumoural functions, including promotion of angiogenesis, matrix remodelling and suppression of adaptive immunity. The pro-tumoural role of TAM in cancer is further supported by clinical studies that found a correlation between the high macrophage content of tumours and poor patient prognosis. Evidence is presented here supporting the view that TAM represent a unique and distinct M2-skewed myeloid population and are a potential target for anti-cancer therapy.

Inflammatory chemokines in cancer growth and progression

Leukocyte infiltration is a cardinal feature of almost all cancers. Chemokines are generally responsible for eliciting local accumulation of inflammatory cells and they appear to play the same role in the formation of peri- and intra-tumoural infiltrates. Chronic inflammation predisposes to cancer formation and progression, and it is likely that the chemokine system contributes to this process. In part, this may be a consequence of its ability to attract mononuclear cells to cancer sites, where they provide growth or angiogenic factors that enhance cancer development. However, accumulating evidence also points to a direct effect of chemokines on cancer cells that express chemokine receptors. In particular, some chemokines can activate anti-apoptotic pathways in these cells. By either mechanism, tumour cells that secrete and/or respond to chemokines would have a selective advantage. This provides another example of cancer's ability to co-opt host systems in order to promote tumour progression.

CXCL12 does not attract CXCR4+ human metastatic neuroblastoma cells: clinical implications

PURPOSE

The role of CXCR4 in bone marrow localization of neuroblastoma cells has been recently proposed. The aim of this study was to investigate the expression and chemotactic functionality of CXCR4 in human metastatic neuroblastoma cells isolated from the bone marrow and, for comparison, in a panel of neuroblastoma cell lines.

EXPERIMENTAL DESIGN

CXCR4 expression and chemotactic functionality were investigated in metastatic neuroblastoma cells isolated from patient bone marrow and in neuroblastoma cell lines. The former cells were isolated as CD45- or GD2+ cells by immunomagnetic bead manipulation. Chemotactic assays were done in a transwell system. Regulator of G protein signaling expression was investigated by reverse transcription-PCR.

RESULTS

Metastatic neuroblastoma cells consistently expressed CXCR4, which was also detected in 5 of 10 neuroblastoma cell lines. CXCL12 did not stimulate the chemotaxis of primary tumor cells or cell lines in either normoxia or hypoxia, irrespective of CXCR4 up-regulation detected under the latter condition. Accordingly, neuroblastoma cells failed to modulate filamentous actin and to activate mitogen-activated protein kinase upon treatment with CXCL12. RGS16 mRNA was consistently expressed in primary tumor cells and cell lines, but its down-regulation by RNA interference did not restore CXCR4 chemotactic functionality.

CONCLUSIONS

These results show unambiguously that CXCR4 expressed in human metastatic neuroblastoma cells is not functional and do not support the clinical use of CXCR4 antagonists to prevent neuroblastoma metastasis.