Chemokines in neuroectodermal tumour progression and metastasis

Molecular cloning and functional analyses of C-C motif chemokine ligand 3 (CCL3) in mandarin fish Siniperca chuatsi

Chemokines are critical molecules involved in immune reaction and immune system homeostasis, and some chemokines play a role in antiviral immunity. It is not known if the C-C motif chemokine ligand 3 (CCL3), a member of the CC chemokine family, possesses antiviral properties in fish. In this study, a ccl3 was cloned from the mandarin fish (Siniperca chuatsi), and it has an open reading frame (ORF) of 276 base pairs, which are predicted to encode a 91-amino acid peptide. Mandarin fish CCL3 revealed conserved sequence features with four cysteine residues and closely relationships with the CCL3s from other vertebrates based on the sequence alignment and phylogenetic analysis. The transcripts of ccl3 were notably enriched in immune-related organs, such as spleen and gills in healthy mandarin fish, and the ccl3 was induced in the isolated mandarin fish brain (MFB) cells following infection with infectious spleen and kidney necrosis virus (ISKNV). Moreover, in MFB cells, overexpression of CCL3 induced immune factors, such as IL1β, TNFα, MX, IRF1 and IFNh, and exhibited antiviral activity against ISKNV. This study sheds light on the immune role of CCL3 in immune response of mandarin fish, and its antiviral defense mechanism is of interest for further investigation.

Impacts of Chemokine (C-X-C Motif) Receptor 2 C1208T Polymorphism on Cancer Susceptibility

Background

The CXC chemokines belong to a unique family of cytokines that participates in the progression and development of many malignant tumors. Evidence for the relationship between chemokine (C-X-C motif) receptor 2 (CXCR2) C1208T polymorphism and susceptibility to cancer remains inconsistent.

Methods

Odds ratios (ORs), 95% confidence intervals (CIs), and combined analysis were used to investigate the effect of CXCR2 variation on cancer risk. Gene Set Enrichment Analysis (GSEA) and enzyme-linked immunosorbent assay (ELISA) were also used to evaluate the expression of CXCR2 in prostate cancer (PCA).

Results

Across 11 case-control studies, 4,909 cases and 5,884 controls were involved in the current analysis. Individuals with a TT genotype were associated with increased risk of digestive cancer, compared to those with a TC+CC genotype (OR = 1.16, 95%CI = 1.02-1.31, P = 0.025). Individuals carrying the TT genotype had a 39% higher risk of urinary cancer than those carrying CC genotype (OR = 1.39, 95%CI = 1.04-1.87, P = 0.025). Individuals with a TT genotype showed a 56% augmented breast cancer risk, compared to those with a CC genotype (OR = 1.56, 95%CI = 1.03-2.35, P = 0.034). It was found that CXCR2 expression was downregulated in PCA. Compared with PCA subjects carrying the CC genotype, the expression of CXCR2 was decreased in patients with the TT genotype.

Conclusions

The CXCR2 C1208T variation was associated with elevated risk of urinary, breast, and digestive cancer. However, the C1208T polymorphism was correlated with attenuated risk of lung cancer.

Effect of interleukin-8 receptor B (IL8RB) rs1126579 C>T variation on the risk to cancer

Chemokines are a type of cytokine that participate in the migration of macrophages and monocytes to inflammatory cells. In particular, CXC chemokines are involved in the development of many cancers. Evidence for the association between interleukin-8 receptor B (IL8RB) rs1126579 C > T variation and cancer risk remains contradictory. Here, we utilized a comprehensive analysis containing odds ratios (ORs), regression, and in silico tools to evaluate the effect of IL8RB polymorphism on cancer risk. We further employed Gene set enrichment analysis combined with ELISA to evaluate the IL8RB expression in patients with prostate cancer (PRAD). A total of 5,187 cancer cases and 6,691 controls were included in the present analysis. Individuals with the TT genotype were associated with an increased risk of cancer compared to those with the TC+CC genotype. In a subgroup analysis by type of cancer, individuals with the TT genotype had a 39% increased risk of urinary cancer compared to those with the CC genotype. A subgroup analysis by ethnicity showed that Asians carrying the TC genotype had a 26% lower risk of cancer than those carrying the CC genotype. We found that the expression of IL8RB was down-regulated in PRAD. Compared to that in PRAD subjects carrying the CC genotype, the expression of IL8RB was decreased in patients with the TT+TC genotype. In conclusion, the IL8RB rs1126579 C > T variation may be associated with cancer risk, especially in Asian populations and patients with PRAD.

Modulating the SDF-1/CXCL12-induced cancer cell growth and adhesion by sulfated K5 polysaccharides in vitro

Stromal cell-derived factor-1 (SDF-1)/chemokine (CXC motif) ligand 12 (CXCL12) is involved in the process of tumor progression. Sulfated K5 polysaccharides have shown anti-cancer activity by acting on multiple targets, though it remains unclear whether sulfated K5 polysaccharides would disrupt SDF-1/CXCL12-stimulated cancer biology. This study aimed to investigate the effects of sulfated K5 polysaccharides on cell growth, adhesion in murine B16 melanoma cells and the underlying mechanism by targeting SDF-1/CXCL12. Results indicated that K5-NS,OS inhibited the proliferation of B16 melanoma cells, induced the cell cycle arrest mainly at the G0/G1 phase, and suppressed cancer cell proliferation or adhesion induced by SDF-1/CXCL12. It was possible that K5-NS,OS appeared to interact with CXCL12 and block the subsequent biological functions. This work suggests that the existence of O- and N-sulfate groups is more effective in targeting CXCL12 and exhibiting anti-cancer activity.

Role of chemokine CX3CL1 in progression of multiple myeloma via CX3CR1 in bone microenvironments

Several chemokines/chemokine receptors such as CXCL12, CCL3, CXCR4 and CCR1 attract multiple myelomas to specific microenvironments. In the present study, we investigated whether the CX3CL1/CX3CR1 axis is involved in the interaction of the multiple myeloma cells with their microenvironment. The expression of CX3CR1 (also known as fractalkine) was detected in three of the seven human myeloma cell lines. CX3CL1-induced phosphorylation of Akt and ERK1/2 was detected in the CX3CR1-positive cell lines, but not in the CX3CR1-negative cell lines. In addition, CX3CL1-induced cell adhesion to fibronectin and vascular cell adhesion molecule-1 (VCAM-1) in the human myeloma RPMI-8226 cell line. We also investigated whether a relationship existed between myeloma cells and osteoclasts that may function via the CX3CL1/CX3CR1 axis. Conditioned medium from CX3CL1-stimulated RPMI-8226 cells drastically increased the osteoclast differentiation. Collectively, the results from the present study support the concept of the CX3CL1-mediated activation of the progression of the multiple myeloma via CX3CR1. Thus, CX3CR1 may represent a potential therapeutic target for the treatment of multiple myeloma in a bone microenvironment.

Mesenchymal stromal cell secretome up-regulates 47 kDa CXCR4 expression, and induce invasiveness in neuroblastoma cell lines

Neuroblastoma accounts for 15% of childhood cancer deaths and presents with metastatic disease of the bone and the bone marrow at diagnosis in 70% of the cases. Previous studies have shown that the Mesenchymal Stromal Cell (MSC) secretome, triggers metastases in several cancer types such as breast and prostate cancer, but the specific role of the MSC factors in neuroblastoma metastasis is unclear. To better understand the effect of MSC secretome on chemokine receptors in neuroblastoma, and its role in metastasis, we studied a panel of 20 neuroblastoma cell lines, and compared their invasive potential towards MSC-conditioned-RPMI (mRPMI) and their cytokine receptor expression profiles. Western blot analysis revealed the expression of multiple CXCR4 isoforms in neuroblastoma cells. Among the five major isoforms, the expression of the 47 kDa isoform showed significant correlation with high invasiveness. Pretreatment with mRPMI up-regulated the expression of the 47 kDa CXCR4 isoform and also increased MMP-9 secretion, expression of integrin α3 and integrin β1, and the invasive potential of the cell; while blocking CXCR4 either with AMD 3100, a CXCR4 antagonist, or with an anti-47 kDa CXCR4 neutralizing antibody decreased the secretion of MMP-9, the expression of integrin α3 and integrin β1, and the invasive potential of the cell. Pretreatment with mRPMI also protected the 47 kDa CXCR4 isoform from ubiquitination and subsequent degradation. Our data suggest a modulatory role of the MSC secretome on the expression of the 47 kDa CXCR4 isoform and invasion potential of the neuroblastoma cells to the bone marrow.

β-Arrestin1 and distinct CXCR4 structures are required for stromal derived factor-1 to downregulate CXCR4 cell-surface levels in neuroblastoma

CXC chemokine receptor 4 (CXCR4) is a G protein-coupled receptor (GPCR) located on the cell surface that signals upon binding the chemokine stromal derived factor-1 (SDF-1; also called CXCL 12). CXCR4 promotes neuroblastoma proliferation and chemotaxis. CXCR4 expression negatively correlates with prognosis and drives neuroblastoma growth and metastasis in mouse models. All functions of CXCR4 require its expression on the cell surface, yet the molecular mechanisms that regulate CXCR4 cell-surface levels in neuroblastoma are poorly understood. We characterized CXCR4 cell-surface regulation in the related SH-SY5Y and SK-N-SH human neuroblastoma cell lines. SDF-1 treatment caused rapid down-modulation of CXCR4 in SH-SY5Y cells. Pharmacologic activation of protein kinase C similarly reduced CXCR4, but via a distinct mechanism. Analysis of CXCR4 mutants delineated two CXCR4 regions required for SDF-1 treatment to decrease cell-surface CXCR4 in neuroblastoma cells: the isoleucine-leucine motif at residues 328 and 329 and residues 343-352. In contrast, and unlike CXCR4 regulation in other cell types, serines 324, 325, 338, and 339 were not required. Arrestin proteins can bind and regulate GPCR cell-surface expression, often functioning together with kinases such as G protein-coupled receptor kinase 2 (GRK2). Using SK-N-SH cells which are naturally deficient in β-arrestin1, we showed that β-arrestin1 is required for the CXCR4 343-352 region to modulate CXCR4 cell-surface expression following treatment with SDF-1. Moreover, GRK2 overexpression enhanced CXCR4 internalization, via a mechanism requiring both β-arrestin1 expression and the 343-352 region. Together, these results characterize CXCR4 structural domains and β-arrestin1 as critical regulators of CXCR4 cell-surface expression in neuroblastoma. β-Arrestin1 levels may therefore influence the CXCR4-driven metastasis of neuroblastoma as well as prognosis.

IRF-8 controls melanoma progression by regulating the cross talk between cancer and immune cells within the tumor microenvironment

The transcription factor interferon regulatory factor-8 (IRF-8) is crucial for myeloid cell development and immune response and also acts as a tumor suppressor gene. Here, we analyzed the role of IRF-8 in the cross talk between melanoma cells and tumor-infiltrating leukocytes. B16-F10 melanoma cells transplanted into IRF-8-deficient (IRF-8(-/-)) mice grow more rapidly, leading to higher numbers of lung metastasis, with respect to control animals. These events correlated with reduced dendritic cell and T cell infiltration, accumulation of myeloid-derived suppressor cells and a chemokine/chemokine receptor expression profile within the tumor microenvironment supporting tumor growth, angiogenesis, and metastasis. Noticeably, primary tumors developing in IRF-8(-/-) mice displayed a clear-cut inhibition of IRF-8 expression in melanoma cells. Injection of the demethylating agent 5-aza-2'-deoxycytidine into melanoma-bearing IRF-8(-/-) animals induced intratumoral IRF-8 expression and resulted in the re-establishment of a chemokine/ chemokine receptor pattern favoring leukocyte infiltration and melanoma growth arrest. Importantly, intrinsic IRF-8 expression was progressively down-modulated during melanoma growth in mice and in human metastatic melanoma cells with respect to primary tumors. Lastly, IRF-8 expression in melanoma cells was directly modulated by soluble factors, among which interleukin-27 (IL-27), released by immune cells from tumor-bearing mice. Collectively, these results underscore a key role of IRF-8 in the cross talk between melanoma and immune cells, thus revealing its critical function within the tumor microenvironment in regulating melanoma progression and invasiveness.

p38MAPK inhibition: a new combined approach to reduce neuroblastoma resistance under etoposide treatment

Neuroblastoma (NB) is the second most common solid pediatric tumor and is characterized by clinical and biological heterogeneity, and stage-IV of the disease represents 50% of all cases. Considering the limited success of present chemotherapy treatment, it has become necessary to find new and effective therapies. In this context, our approach consists of identifying and targeting key molecular pathways associated with NB chemoresistance. This study has been carried out on three stage-IV NB cell lines with different status of MYCN amplification. Cells were exposed to a standard chemotherapy agent, namely etoposide, either alone or in combination with particular drugs, which target intracellular signaling pathways. Etoposide alone induced a concentration-dependent reduction of cell viability and, at very high doses, totally counteracted cell tumorigenicity and neurosphere formation. In addition, etoposide activated p38 mitogen-activated protein kinase (MAPK), AKT and c-Jun N-terminal kinase. Pre-treatment with SB203580, a p38MAPK inhibitor, dramatically sensibilized NB cells to etoposide, strongly reducing the dosage needed to inhibit tumorigenicity and neurosphere formation. Importantly, SB203580–etoposide cotreatment also reduced cell migration and invasion by affecting cyclooxygenase-2, intercellular adhesion molecule-1, C–X–C chemokine receptor-4 and matrix metalloprotease-9. Collectively, our results suggest that p38MAPK inhibition, in combination with standard chemotherapy, could represent an effective strategy to counteract NB resistance in stage-IV patients.

Self-aggregating TIAF1 in lung cancer progression

Recent studies have demonstrated that transforming growth factor beta (TGF-β1)-induced antiapoptotic factor (TIAF1) is able to form aggregates in the hippocampi of middle-aged normal individuals. The aggregating TIAF1 induces generation of amyloid beta (Aβ) for causing neurodegeneration. Intriguingly, TIAF1 aggregates are shown, together with Smad4 and Aβ, in the cancer stroma and peritumor capsules of many solid tumors. During lung cancer progression, for example, TIAF1 and amyloid fibrils are significantly upregulated in the cancer stroma. Aggregates of TIAF1 and Aβ are shown on the interface between metastatic lung cancer cells and the brain tissues. Conceivably, these peritumor materials are needed for cancer cells to survive. In vitro experiments revealed that TIAF1 is a crucial component for tumor suppressors p53 and WWOX-mediated tumor suppression and apoptosis. While metastatic lung cancer cells are frequently devoid of WWOX and p53, we provide new perspectives regarding the role of TIAF1 in the pathogenesis of lung cancer development, and propose a therapeutic approach for targeting TIAF1.

Induction of cytokines and growth factors by rapamycin in the microenvironment of brain metastases of lung cancer

The association between rapamycin and astrocytes in a tumor-bearing mouse model with brain metastases of non-small cell lung cancer (NSCLC) was investigated. For in vitro experiments, NCI-H358, a human lung adenocarcinoma cell line, was co-cultured with immortalized astrocytes, and treated with rapamycin, an mTOR inhibitor. We evaluated the expression of interleukin-1 (IL-1), interleukin-3 (IL-3), interleukin-6 (IL-6), tumor necrosis factor-α (TNF-α), transforming growth factor-β (TGF-β), insulin-like growth factor-1 (IGF-1), platelet-derived growth factor (PDGF), chemoattractant protein-1 (MCP-1) and macrophage inflammatory protein-1 (MIP-1) in tumor cells in vivo. Rapamycin is cytotoxic in vitro; however, co-culturing tumor cells and astrocytes induced tumor cell survival. IL-1, IL-3, IL-6, TNF-α, TGF-β, PDGF, MCP-1 and MIP-1 expression were higher in rapamycin-treated mice compared to the control group, however, IGF-1 expression was lower. Notably, treatment with rapamycin before inoculating tumor cells affected cytokine expression in the tumor microenvironment. We suggest that growth factors and cytokines in the tumor microenvironment play a role in the survival of cancer cells in brain metastases.

Ethanol promotes mammary tumor growth and angiogenesis: the involvement of chemoattractant factor MCP-1

Alcohol consumption is a risk factor for breast cancer in humans. Experimental studies indicate that alcohol exposure promotes malignant progression of mammary tumors. However, the underlying cellular and molecular mechanisms remain unclear. Alcohol induces a pro-inflammatory response by modulating the expression of cytokines and chemokines. Monocyte chemoattractant protein-1 (MCP-1), also known as chemokine (C-C motif) ligand 2, is a pro-inflammatory chemokine implicated in breast cancer development/malignancy. We investigated the role of MCP-1 in alcohol-promoted mammary tumor progression. Using a xenograft model, we demonstrated that alcohol increased tumor angiogenesis and promoted growth/metastasis of breast cancer cells in C57BL/6 mice. Alcohol up-regulated the expression of MCP-1 and its receptor CCR2 in breast cancer cells in vitro and in vivo. Using a three-dimensional tumor/endothelial cell co-culture system, we demonstrated MCP-1 regulated tumor/endothelial cell interaction and promoted tumor angiogenesis. More importantly, MCP-1 mediated alcohol-promoted angiogenesis; an antagonist of the MCP-1 receptor CCR2 significantly inhibited alcohol-stimulated tumor angiogenesis. The CCR2 antagonist abolished ethanol-stimulated growth of mammary tumors in mice. We further demonstrated that MCP-1 enhanced the migration, but not the proliferation of endothelial cells as well as breast cancer cells. These results suggest that MCP-1 plays an important role in ethanol-stimulated tumor angiogenesis and tumor progression.

An integrated proteomic approach to identifying circulating biomarkers in high-risk neuroblastoma and their potential in relapse monitoring

PURPOSE

Despite intensive treatment regimens, overall survival for high-risk neuroblastoma (HRNB) is still poor. This is in part due to an inability to cure the disease once a patient has reached clinical relapse. Identifying plasma biomarkers of active disease may provide a way of relapse monitoring in HRNB.

EXPERIMENTAL DESIGN

In this study, we developed an integrated proteomic approach to identify plasma biomarkers for HRNB.

RESULTS

We identified seven candidate biomarkers (SAA, APOA1, IL-6, EGF, MDC, sCD40L and Eotaxin) for HRNB. These biomarkers were then used to create a multivariate classifier of HRNB, which showed a specificity of 90% (95% confidence interval (CI), 73%, 98%), and a sensitivity of 81% (95%CI, 54%, 96%) for classifying HRNB in a training set. When evaluated on independent test samples, the classifier exhibited 86% accuracy (95% CI, 42%, 100%) of identifying diagnostic samples, and 86% accuracy (95% CI, 70%, 100%) of detecting post-diagnosis longitudinal samples that having active disease.

CONCLUSION AND CLINICAL RELEVANCE

Further validation of these biomarkers may improve patients' outcomes by developing a simple blood test for the detection of relapse prior to the development of clinically evident disease. Understanding the role of these biomarkers in immune surveillance of neuroblastoma may also provide a new direction of therapeutic strategies.

Prevention of intrahepatic metastasis of liver cancer by suicide gene therapy and chemokine ligand 2/monocyte chemoattractant protein-1 delivery in mice

BACKGROUND

The prognosis of patients with hepatocellular carcinoma (HCC) remains poor, largely as a result of intrahepatic metastasis. Using a mouse model of intrahepatic metastasis, we investigated whether chemokine ligand 2/monocyte chemoattractant protein-1 (CCL2/MCP-1) could potentiate the antitumor effects of the herpes simplex virus thymidine kinase/ganciclovir (HSV-tk/GCV) system.

METHODS

Mouse hepatoma cells infected with recombinant adenovirus vectors expressing HSV-tk, CCL2/MCP-1 and LacZ at multiplicities of infection of Ad-tk/Ad-MCP1 = 3/0.03 (T/M(Low)), 3/3 (T/M(High)) and Ad-tk/Ad-LacZ = 3/3 (T/L) were injected into BALB/c mice.

RESULTS

Intrahepatic tumor growth was significantly lower in T/M(Low) mice. By contrast, no tumor suppression was observed in T/M(High) mice. The tumor-specific cytolytic activities of splenocytes from T/M(Low) and T/M(High) mice were comparable. Immunohistochemical analysis of liver tissues showed similar infiltration by Mac-1(+) and T cells in these animals, whereas the proportions of classical activated (M1) monocytes/macrophages were significantly higher in T/M(Low) mice. In addition, interleukin-12 production was elevated in these tissues. Vascular endothelial growth factor-A expression and CD31(+) microvessels were increased in T/M(High) mice.

CONCLUSIONS

Collectively, these results demonstrate that an adequate amount of CCL2/MCP-1, together with the HSV-tk/GCV system, may induce T helper 1-polarized antitumor effects without inducing tumor angiogenesis in the microenvironment of intrahepatic HCC progression.

A novel role of the CX3CR1/CX3CL1 system in the cross-talk between chronic lymphocytic leukemia cells and tumor microenvironment

Several chemokines/chemokine receptors such as CCR7, CXCR4 and CXCR5 attract chronic lymphocytic leukemia (CLL) cells to specific microenvironments. Here we have investigated whether the CX(3)CR1/CX(3)CL1 axis is involved in the interaction of CLL with their microenvironment. CLL cells from 52 patients expressed surface CX(3)CR1 and CX(3)CL1 and released constitutively soluble CX(3)CL1. One third of these were attracted in vitro by soluble CX(3)CL1. CX(3)CL1-induced phosphorylation of PI3K, Erk1/2, p38, Akt and Src was involved in induction of CLL chemotaxis. Leukemic B cells upregulated CXCR4 upon incubation with CX(3)CL1 and this was paralleled by increased chemotaxis to CXCL12. Akt phosphorylation was involved in CX(3)CL1-induced upregulation of CXCR4 on CLL. In proliferation centers from CLL lymph node and bone marrow, CX(3)CL1 was expressed by CLL cells whereas CX(3)CR1 was detected in CLL and stromal cells. Nurselike cells (NLCs) generated from CLL patient blood co-expressed surface CX(3)CR1 and CX(3)CL1, but did not secrete soluble CX(3)CL1. Only half of NLC cell fractions were attracted in vitro by CX(3)CL1. In conclusion, the CX(3)CR1/CX(3)CL1 system may contribute to interactions between CLL cells and tumor microenvironment by increasing CXCL12-mediated attraction of leukemic cells to NLC and promoting directly adhesion of CLL cells to NLC.

Lung-residing metastatic and dormant neuroblastoma cells

The mechanism by which dormant tumor cells can begin growing after long periods of inactivity and accelerate disease recurrence is poorly understood. The present study characterizes dormant neuroblastoma (NB) cells, as well as metastatic cells, which reside in the same organ microenvironment. A xenograft model of human NB consisting of variants that generate nonmetastatic local tumors in the orthotopic inoculation site and variants that generate lung metastatic NB (MetNB) cells was developed in our laboratory. The present study shows that lungs of mice inoculated with nonmetastatic NB variants contain disseminated neuroblastoma (DisNB) human cells. Both DisNB and MetNB variants expressed a similar tumorigenicty phenotype in vivo, whereas the MetNB variants produced a heavy metastatic load and the DisNB variants produced no or little metastasis. A comparative in vitro characterization of MetNB and DisNB cells revealed similarities and differences. DisNB, but not MetNB cells, expressed the minimal residual disease markers PHOX2B and TH. MetNB cells demonstrated higher migratory capacity, an elevated matrix metalloproteinase (MMP) secretion, and a higher constitutive phosphorylation of extracellular signal-regulated kinase (ERK) than DisNB cells. We suggest that characteristics common to both MetNB and DisNB cells were acquired relatively early in the metastatic process and the characteristics that differ between these variants were acquired later. We hypothesize that the DisNB cells are metastasis precursors, which may progress toward metastasis under certain microenvironmental conditions.

Syk regulates multiple signaling pathways leading to CX3CL1 chemotaxis in macrophages

Several studies have clearly established the importance of the interaction between macrophages and CX3CL1 in the progression of disease. A previous study demonstrated that Syk was required for CX3CL1-mediated actin polymerization and chemotaxis. Here, we delineated the signaling cascade of Syk-mediated cell migration in response to CX3CL1. Inhibition of Syk in bone marrow-derived macrophages or reduction of Syk expression using siRNA in RAW/LR5 cells indicated that Syk was required for the activation of PI3K, Cdc42, and Rac1. Also, reduction in WASP or WAVE2 levels, common downstream effectors of Cdc42 or Rac1, resulted in impaired cell migration to CX3CL1. Syk indirectly regulated WASP tyrosine phosphorylation through Cdc42 activation. Altogether, our data identify that Syk mediated chemotaxis toward CX3CL1 by regulating both Rac1/WAVE2 and Cdc42/WASP pathways, whereas Src family kinases were required for proper WASP tyrosine phosphorylation.

Chemokine signaling in cancer: one hump or two?

Chemokines and their receptors play essential roles in the development and function of multiple tissues. Chemokine expression, particularly CXCL12 and its receptor CXCR4, has prognostic significance in several cancers apparently due to chemokine mediated growth and metastatic spread. These observations provide the rationale for pursuing CXCR4 inhibition for cancer chemotherapy. However, the multiple homeostatic functions of CXCR4 may preclude global inhibition as a therapeutic strategy. Here I review CXCR4 signaling and how it might differ in normal and transformed cells with special emphasis on the role that altered CXCR4 counter-regulation might play in tumor biology. I propose that CXCR4 mediates unique signals in cancer cells as a consequence of abnormal counter-regulation and that this results in novel biological responses. The importance of testing this hypothesis lies in the possibility that targeting abnormal CXCR4 signaling might provide an anti-tumor effect without disturbing normal CXCR4 functions.

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.

Chemokines and the microenvironment in neuroectodermal tumor-host interaction

Chemokines and chemokine receptors play an important role in immune homeostasis and surveillance. Altered or defective expression of chemokines and/or chemokine receptors could lead to a disease state including autoimmune disorder or cancer. Tumors from glioblastoma, melanoma, and neuroblastoma secrete high levels of chemokines that can promote tumor growth and progression or induce stromal cells present in the tumor microenvironment to produce cytokines or chemokines which, in turn, can regulate angiogenesis, tumor growth, and metastasis. On the other hand, chemokines secreted by tumor or stromal cells can also attract leukocytes such as dendritic cells, macrophages, neutrophils, and lymphocytes which may downmodulate tumor growth. New therapies that are aimed at limiting tumor growth and progression by attracting immune effector cells to the tumor site with chemokines may hold the key to the successful treatment of cancer, although this approach may be hampered by possible tumor growth-stimulating effects of chemokines.

The role of chemokines in cancer immune surveillance by the adaptive immune system

Chemokines are key molecules involved in the migration and homeostasis of immune cells. However, also tumor cells use chemokine signals for different processes such as tumor progression and metastasis. It is thus unclear whether chemokines, through their immunostimulatory roles, contribute to the repression of tumor cells by tumor immunosurveillance or whether chemokines act primarily as growth factors and chemoattractants for primary and metastatizing tumors, respectively. Research of recent years, using gene knockout mice, recombinant chemokines, and agents able to block chemokine actions, has provided further insight into the diverse functions of chemokines. Here, we review the current knowledge on the complex actions of chemokines at the interface of the immune system and the tumor.

The roles of chemokine CXCL12 in embryonic and brain tumor angiogenesis

The formation of blood vessels in embryos and tumors are different processes but under the control of common molecular mechanisms. Chemokine CXCL12 involved in both embryonic and tumor angiogenesis. In this review, we summarize recent advances in understanding the roles of CXCL12 in brain tumor angiogenesis/vasculogenesis. CXCL12 and its cognate receptors are abnormally induced in brain tumors, in particular in tumor cells and endothelium. Pathologically enhanced CXCL12 signaling may promote the formation of new vessels through recruiting circulating endothelial progenitor cells or directly enhancing the migration/growth of endothelial cells. Therefore, CXCL12 signaling represents an important mechanism that regulates brain tumor angiogenesis/vasculogenesis and may provide potential targets for anti-angiogenic therapy in malignant gliomas.

Chemokines in neuroectodermal cancers: the crucial growth signal from the soil

Although chemokines and their receptors were initially identified as regulators of cell trafficking during inflammation and immune response, they have emerged as crucial players in all stages of tumor development, primary growth, migration, angiogenesis, and establishment as metastases in distant target organs. Neuroectodermal tumors regroup neoplasms originating from the embryonic neural crest cells, which display clinical and biological similarities. These tumors are highly malignant and rapidly progressing diseases that disseminate to similar target organs such as bone marrow, bone, liver and lungs. There is increasing evidence that interaction of several chemokine receptors with corresponding chemokine ligands are implicated in the growth and invasive characteristics of these tumors. In this review we summarize the current knowledge on the role of CXCL12 chemokine and its CXCR4 and CXCR7 receptors in the progression and survival of neuroectodermal tumors, with particular emphasis on neuroblastoma, the most typical and enigmatic neuroectodermal childhood tumor.