CXCR4 expression heterogeneity in neuroblastoma cells due to ligand-independent regulation

The involvement of a chemokine receptor antagonist CTCE-9908 and kynurenine metabolites in cancer development

Cancer is the second leading cause of mortality worldwide. Skin cancer is the most common cancer in South Africa with nearly 20,000 reported cases every year and 700 deaths. If diagnosed early, the 5-year survival rate is about 90%, however, when diagnosed late, the 5-year survival rate decreases to about 20%. Melanoma is a type of skin cancer with an estimated 5-year survival rate of approximately 90%. Neuroblastoma is a paediatric cancer with a low survival rate. Sixty percent of patients with metastatic disease do not survive 5 years after diagnosis. Despite recent advances in targeted therapies, there is a crucial need to identify reliable prognostic biomarkers which will be able to contribute to the development of more precision-based chemotherapeutic strategies to prevent tumour migration and metastasis. The compound, CTCE-9908 inhibits the binding of CXC chemokine ligand 12 (CXCL12) to the CXC chemokine receptor 4 (CXCR4) receptor leading to reduced metastasis. Kynurenine metabolites are derived tryptophan, which is an essential amino acid. Kynurenine metabolites inhibit T-cell proliferation resulting in cell growth arrest. For this reason, chemokines receptors represent potential targets for the treatment of cancer growth and metastasis. In this review paper, the role of the CXCL12/CXCR4 signalling pathway in the development of cancer is highlighted together with the current available treatments involving the CTCE-9908 compound in combination with microtubule inhibitors like paclitaxel and docetaxel.

MIF/CXCR4 signaling axis contributes to survival, invasion, and drug resistance of metastatic neuroblastoma cells in the bone marrow microenvironment

BACKGROUND

The bone marrow (BM) is the most common site of dissemination in patients with aggressive, metastatic neuroblastoma (NB). However, the molecular mechanisms underlying the aggressive behavior of NB cells in the BM niche are still greatly unknown. In the present study, we explored biological mechanisms that play a critical role in NB cell survival and progression in the BM and investigated potential therapeutic targets.

METHODS

Patient-derived bone marrow (BM) primary cultures were generated using fresh BM aspirates obtained from NB patients. NB cell lines were cultured in the presence of BM conditioned media containing cell-secreted factors, and under low oxygen levels (1% O₂) to mimic specific features of the BM microenvironment of high-risk NB patients. The BM niche was explored using cytokine profiling assays, cell migration-invasion and viability assays, flow cytometry and analysis of RNA-sequencing data. Selective pharmacological inhibition of factors identified as potential mediators of NB progression within the BM niche was performed in vitro and in vivo.

RESULTS

We identified macrophage migration inhibitory factor (MIF) as a key inflammatory cytokine involved in BM infiltration. Cytokine profiling and RNA-sequencing data analysis revealed NB cells as the main source of MIF in the BM, suggesting a potential role of MIF in tumor invasion. Exposure of NB cells to BM-conditions increased NB cell-surface expression of the MIF receptor CXCR4, which was associated with increased cell viability, enhanced migration-invasion, and activation of PI3K/AKT and MAPK/ERK signaling pathways. Moreover, subcutaneous co-injection of NB and BM cells enhanced tumor engraftment in mice. MIF inhibition with 4-IPP impaired in vitro NB aggressiveness, and improved drug response while delayed NB growth, improving survival of the NB xenograft model.

CONCLUSIONS

Our findings suggest that BM infiltration by NB cells may be mediated, in part, by MIF-CXCR4 signaling. We demonstrate the antitumor efficacy of MIF targeting in vitro and in vivo that could represent a novel therapeutic target for patients with disseminated high-risk NB.

Advances in pharmacotherapy for neuroblastoma

INTRODUCTION

Neuroblastoma is the most prevalent cancer type diagnosed within the first year after birth and accounts for 15% of deaths from pediatric cancer. Despite the improvements in survival rates of patients with neuroblastoma, the incidence of the disease has increased over the last decade. Neuroblastoma tumor cells harbor a vast range of variable and heterogeneous histochemical and genetic alterations which calls for the need to administer individualized and targeted therapies to induce tumor regression in each patient.

AREAS COVERED

This paper provides reviews the recent clinical trials which used chemotherapeutic and/or targeted agents as either monotherapies or in combination to improve the response rate in patients with neuroblastoma, and especially high-risk neuroblastoma. It also reviews some of the prominent preclinical studies which can provide the rationale for future clinical trials.

EXPERT OPINION

Although some distinguished advances in pharmacotherapy have been made to improve the survival rate and reduce adverse events in patients with neuroblastoma, a more comprehensive understanding of the mechanisms of tumorigenesis, resistance to therapies or relapse, identifying biomarkers of response to each specific drug, and developing predictive preclinical models of the tumor can lead to further breakthroughs in the treatment of neuroblastoma.

Endosome-triggered ion-releasing nanoparticles as therapeutics to enhance the angiogenic efficacy of human mesenchymal stem cells

Here, we report that Fe ions delivered into human mesenchymal stem cells (hMSCs) by bioreducible metal nanoparticles (NPs) enhance their angiogenic and cell-homing efficacy by controlling ion-triggered intracellular reactive oxygen species (ROS) and improve cell migration, while reducing cytotoxicity. Endosome-triggered iron-ion-releasing nanoparticles (ETIN) were designed to be low-pH responsive to take advantage of the low-pH conditions (4-5) of endosomes for in situ iron-ion release. Due to the different redox potentials of Fe and Au, only Fe could be ionized and released from our novel ETIN, while Au remained intact after ETIN endocytosis. Treatment with an optimal amount of ETIN led to a mild increase in intracellular ROS levels in hMSCs, which enhanced the expression of HIF-1α, a key trigger for angiogenic growth factor secretion from hMSCs. Treatmetn of hMSCs with ETIN significantly enhanced the expression of angiogenesis- and lesion-targeting-related genes and proteins. Transplantation of ETIN-treated hMSCs significantly enhanced angiogenesis and tissue regeneration in a wound-closing mouse model compared with those in untreated mice and mice that underwent conventional hMSC transplantation.

Targeting the Tumor Microenvironment in Neuroblastoma: Recent Advances and Future Directions

Neuroblastoma (NB) is the most common pediatric tumor malignancy that originates from the neural crest and accounts for more than 15% of all the childhood deaths from cancer. The neuroblastoma cancer research has long been focused on the role of MYCN oncogene amplification and the contribution of other genetic alterations in the progression of this malignancy. However, it is now widely accepted that, not only tumor cells, but the components of tumor microenvironment (TME), including extracellular matrix, stromal cells and immune cells, also contribute to tumor progression in neuroblastoma. The complexity of different components of tumor stroma and their resemblance with surrounding normal tissues pose huge challenges for therapies targeting tumor microenvironment in NB. Hence, the detailed understanding of the composition of the TME of NB is crucial to improve existing and future potential immunotherapeutic approaches against this childhood cancer. In this review article, I will discuss different components of the TME of NB and the recent advances in the strategies, which are used to target the tumor microenvironment in neuroblastoma.

The CXCR4 antagonist plerixafor (AMD3100) promotes proliferation of Ewing sarcoma cell lines in vitro and activates receptor tyrosine kinase signaling

BACKGROUND

The CXCR4 receptor antagonist plerixafor (AMD3100) is raising interest as an anti-cancer agent that disrupts the CXCL12-CXCR4 chemokine - receptor interaction between neoplastic cells and their microenvironment in tumor progression and metastasis. Here, we investigated plerixafor for anti-cancer activity in Ewing sarcoma, a rare and aggressive cancer of bone and soft tissues.

METHODS

We used a variety of methods such as cell viability and migration assays, flow cytometry, phospho-tyrosine arrays and western blotting to determine plerixafor effects on five characterized Ewing sarcoma cell lines and a low-passage culture in vitro.

RESULTS

Unexpectedly, plerixafor led to an increase in cell viability and proliferation in standard cell growth conditions, and to chemotactic migration towards plerixafor. Exploring potential molecular mechanisms underlying this effect, we found that Ewing sarcoma cell lines divided into classes of high- and low-level CXCR4 surface expression. Proliferative plerixafor responses were observed in both groups, maintained despite significant CXCR4 down-regulation or inhibition of Gαi-protein signal transduction, and involved activation of multiple receptor tyrosine kinases (DDR2, MERTK, MST1R, NTRK1, RET), the most prominent being platelet-derived growth factor receptor beta (PDGFRB). PDGFRB was activated in response to inhibition of the CXCL12-CXCR4 axis by plerixafor and/or pertussis toxin (Gαi-protein inhibitor). Dasatinib, a multi-kinase inhibitor of both PDGFRB and the CXCR4 downstream kinase SRC, counteracted this activation in some but not all cell lines.

CONCLUSION

These data suggest a feedback interaction between the CXCR4 chemokine receptor and RTK signaling cascades that elicits compensatory cell survival signaling and can shift the net effect of plerixafor towards proliferation. PDGFRB was identified as a candidate driver RTK and potential therapeutic co-target for CXCR4 in Ewing sarcoma. Although as yet limited to in vitro studies, these findings call for further investigation in the cancer - microenvironment interplay in vivo.

CXCR4: A new player in vestibular schwannoma pathogenesis

BACKGROUND

CXCR4 is a chemokine receptor that recruits blood stem cells and increases tumor cell growth and invasiveness. We examined CXCR4 expression in vestibular schwannomas (VS) from patients with and without neurofibromatosis type 2 (NF2) and correlated the levels with the patients' clinical characteristics. The aim was to determine whether CXCR4 can be used as a prognostic marker and as a target for systemic therapy.

RESULTS

Overall, CXCR4 mRNA levels were 4.6-fold higher in VS versus control; the levels were 4.9-fold higher in NF2 patients and 4.2-fold higher in sporadic VS patients. IHC and WB showed heterogeneous protein expression, and CXCR4 was expressed mainly in S100-positive Schwann cells. There was no correlation between the CXCR4 protein levels and tumor extension. However, there was a trend towards correlation between higher expression levels and greater hearing loss.

MATERIALS AND METHODS

CXCR4 mRNA and protein levels were determined in VS samples (n = 60); of these, 30 samples were from patients with NF2. Healthy nerves from autopsies served as controls. CXCR4 mRNA levels were measured by PCR, and protein levels were measured by immunohistochemistry (IHC) and Western blotting (WB). Tumor extension and hearing loss were categorized according to the Hannover Classification as clinical parameters.

CONCLUSIONS

CXCR4 mRNA was overexpressed in VS relative to healthy vestibular nerves, and there was a trend towards higher CXCR4 expression levels being correlated with greater functional impairment. Thus, CXCR4 may be a prognostic marker of VS, and CXCR4 inhibition has potential as a systemic approach for the treatment of VS.

Prognostic and predictive value of circulating tumor cells and CXCR4 expression as biomarkers for a CXCR4 peptide antagonist in combination with carboplatin-etoposide in small cell lung cancer: exploratory analysis of a phase II study

Background Circulating tumor cells (CTCs) and chemokine (C-X-C motif) receptor 4 (CXCR4) expression in CTCs and tumor tissue were evaluated as prognostic or predictive markers of CXCR4 peptide antagonist LY2510924 plus carboplatin-etoposide (CE) versus CE in extensive-stage disease small cell lung cancer (ED-SCLC). Methods This exploratory analysis of a phase II study evaluated CXCR4 expression in baseline tumor tissue and peripheral blood CTCs and in post-treatment CTCs. Optimum cutoff values were determined for CTC counts and CXCR4 expression in tumors and CTCs as predictors of survival outcome. Kaplan-Meier estimates and hazard ratios were used to determine biomarker prognostic and predictive values. Results There was weak positive correlation at baseline between CXCR4 expression in tumor tissue and CTCs. Optimum cutoff values were H-score ≥ 210 for CXCR4⁺ tumor, ≥7% CTCs with CXCR4 expression (CXCR4⁺ CTCs), and ≥6 CTCs/7.5 mL blood. Baseline H-score for CXCR4⁺ tumor was not prognostic of progression-free survival (PFS) or overall survival (OS). Baseline CXCR4⁺ CTCs ≥7% was prognostic of shorter PFS. CTCs ≥6 at baseline and cycle 2, day 1 were prognostic of shorter PFS and OS. None of the biomarkers at their respective optimum cutoffs was predictive of treatment response of LY2510924 plus CE versus CE. Conclusions In patients with ED-SCLC, baseline CXCR4 expression in tumor tissue was not prognostic of survival or predictive of LY2510924 treatment response. Baseline CXCR4⁺ CTCs ≥7% was prognostic of shorter PFS. CTC count ≥6 at baseline and after 1 cycle of treatment were prognostic of shorter PFS and OS.

Comparative miRNA-Based Fingerprinting Reveals Biological Differences in Human Olfactory Mucosa- and Bone-Marrow-Derived Mesenchymal Stromal Cells

Previously we reported that nestin-positive human mesenchymal stromal cells (MSCs) derived from the olfactory mucosa (OM) enhanced CNS myelination in vitro to a greater extent than bone-marrow-derived MSCs (BM-MSCs). miRNA-based fingerprinting revealed the two MSCs were 64% homologous, with 26 miRNAs differentially expressed. We focused on miR-146a-5p and miR-140-5p due to their reported role in the regulation of chemokine production and myelination. The lower expression of miR-140-5p in OM-MSCs correlated with higher secretion of CXCL12 compared with BM-MSCs. Addition of CXCL12 and its pharmacological inhibitors to neural co-cultures supported these data. Studies on related miR-146a-5p targets demonstrated that OM-MSCs had lower levels of Toll-like receptors and secreted less pro-inflammatory cytokines, IL-6, IL-8, and CCL2. OM-MSCs polarized microglia to an anti-inflammatory phenotype, illustrating potential differences in their inflammatory response. Nestin-positive OM-MSCs could therefore offer a cell transplantation alternative for CNS repair, should these biological behaviors be translated in vivo.

•

OM-MSCs share 64% miRNA homology to BM-MSCs and differentially express 26 miRNAs

•

CXCL12 promotes CNS myelination and is negatively regulated by miR-140-5p in BM-MSCs

•

miR-146a-5p negatively regulates IL-6, IL-8, TLR2, and TLR4 on OM-MSCs

•

These properties make OM-MSCs a suitable candidate for transplant-mediated CNS repair

Deregulation of focal adhesion pathway mediated by miR-659-3p is implicated in bone marrow infiltration of stage M neuroblastoma patients

To get insights on the metastatic process of human neuroblastoma (NB), the miRNA expression profile of bone marrow (BM)-infiltrating cells has been determined and compared to that of primary tumors.Twenty-two BM-infiltrating cells, 22 primary tumors, and 4 paired samples from patients with metastatic NB aged > 12 months were analyzed for the expression of 670 miRNAs by stem-loop RT-qPCR. The miRNAs whose expression was significantly different were subjected to selection criteria, and 20 selected miRNAs were tested in 10 additional BM-infiltrating cells and primary tumors. Among the miRNAs confirmed to be differentially expressed, miR-659-3p was further analyzed. Transfection of miR-659-3p mimic and inhibitor demonstrated the specific suppression and over-expression, respectively, of the miR-659-3p target gene CNOT1, a regulator of transcription of genes containing AU-rich element (ARE) sequence. Among the ARE-containing genes, miR-659-3p mimic and inhibitor specifically modified the expression of AKT3, BCL2, CYR61 and THSB2, belonging to the focal adhesion pathway. Most importantly, in BM-infiltrating cells CNOT1 expression was significantly higher, and that of AKT3, BCL2, THSB2 and CYR61 was significantly lower than in primary tumors. Thus, our study suggests a role of the focal adhesion pathway, regulated by miR-659-3p through CNOT1, in the human NB metastatic process.

More than the genes, the tumor microenvironment in neuroblastoma

Neuroblastoma is the second most common solid tumor in children. Since the seminal discovery of the role of amplification of the MYCN oncogene in the pathogenesis of neuroblastoma in the 1980s, much focus has been on the contribution of genetic alterations in the progression of this cancer. However it is now clear that not only genetic events play a role but that the tumor microenvironment (TME) substantially contributes to the biology of neuroblastoma. In this article, we present a comprehensive review of the literature on the contribution of the TME to the ten hallmarks of cancer in neuroblastoma and discuss the mechanisms of communication between neuroblastoma cells and the TME that underlie the influence of the TME on neuroblastoma progression. We end our review by discussing how the knowledge acquired over the last two decades in this field is now leading to new clinical trials targeting the TME.

Heteromerization of chemokine (C-X-C motif) receptor 4 with α1A/B-adrenergic receptors controls α1-adrenergic receptor function

Recent evidence suggests that chemokine (C-X-C motif) receptor 4 (CXCR4) contributes to the regulation of blood pressure through interactions with α1-adrenergic receptors (ARs) in vascular smooth muscle. The underlying molecular mechanisms, however, are unknown. Using proximity ligation assays to visualize single-molecule interactions, we detected that α1A/B-ARs associate with CXCR4 on the cell surface of rat and human vascular smooth muscle cells (VSMC). Furthermore, α1A/B-AR could be coimmunoprecipitated with CXCR4 in a HeLa expression system and in human VSMC. A peptide derived from the second transmembrane helix of CXCR4 induced chemical shift changes in the NMR spectrum of CXCR4 in membranes, disturbed the association between α1A/B-AR and CXCR4, and inhibited Ca(2+) mobilization, myosin light chain (MLC) 2 phosphorylation, and contraction of VSMC upon α1-AR activation. CXCR4 silencing reduced α1A/B-AR:CXCR4 heteromeric complexes in VSMC and abolished phenylephrine-induced Ca(2+) fluxes and MLC2 phosphorylation. Treatment of rats with CXCR4 agonists (CXCL12, ubiquitin) reduced the EC50 of the phenylephrine-induced blood pressure response three- to fourfold. These observations suggest that disruption of the quaternary structure of α1A/B-AR:CXCR4 heteromeric complexes by targeting transmembrane helix 2 of CXCR4 and depletion of the heteromeric receptor complexes by CXCR4 knockdown inhibit α1-AR-mediated function in VSMC and that activation of CXCR4 enhances the potency of α1-AR agonists. Our findings extend the current understanding of the molecular mechanisms regulating α1-AR and provide an example of the importance of G protein-coupled receptor (GPCR) heteromerization for GPCR function. Compounds targeting the α1A/B-AR:CXCR4 interaction could provide an alternative pharmacological approach to modulate blood pressure.

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.

Intracellular trafficking and endocytosis of CXCR4 in fetal mesenchymal stem/stromal cells

Background

Fetal mesenchymal stem/stromal cells (MSC) represent a developmentally-advantageous cell type with translational potential.

To enhance adult MSC migration, studies have focussed on the role of the chemokine receptor CXCR4 and its ligand SDF-1 (CXCL12), but more recent work implicates an intricate system of CXCR4 receptor dimerization, intracellular localization, multiple ligands, splice variants and nuclear accumulation. We investigated the intracellular localization of CXCR4 in fetal bone marrow-derived MSC and role of intracellular trafficking in CXCR4 surface expression and function.

Results

We found that up to 4% of human fetal MSC have detectable surface-localized CXCR4. In the majority of cells, CXCR4 is located not at the cell surface, as would be required for ‘sensing’ migratory cues, but intracellularly. CXCR4 was identified in early endosomes, recycling endosomes, and lysosomes, indicating only a small percentage of CXCR4 travelling to the plasma membrane. Notably CXCR4 was also found in and around the nucleus, as detected with an anti-CXCR4 antibody directed specifically against CXCR4 isoform 2 differing only in N-terminal sequence. After demonstrating that endocytosis of CXCR4 is largely independent of endogenously-produced SDF-1, we next applied the cytoskeletal inhibitors blebbistatin and dynasore to inhibit endocytotic recycling. These increased the number of cells expressing surface CXCR4 by 10 and 5 fold respectively, and enhanced the number of cells migrating to SDF1 in vitro (up to 2.6 fold). These molecules had a transient effect on cell morphology and adhesion, which abated after the removal of the inhibitors, and did not alter functional stem cell properties.

Conclusions

We conclude that constitutive endocytosis is implicated in the regulation of CXCR4 membrane expression, and suggest a novel pharmacological strategy to enhance migration of systemically-transplanted cells.

Stress-induced CXCR4 promotes migration and invasion of ewing sarcoma

Ewing sarcoma is the second most common bone cancer in pediatric patients. Although the primary cause of death in Ewing sarcoma is metastasis, the mechanism underlying tumor spread needs to be elucidated. To this end, the role of the CXCR4/SDF-1a chemokine axis as a mediator of Ewing sarcoma metastasis was investigated. CXCR4 expression status was measured in primary tumor specimens by immunohistochemical staining and in multiple cell lines by quantitative reverse transcriptase PCR and flow cytometry. Migration and invasion of CXCR4-positive Ewing sarcoma cells toward CXCL12/SDF-1a were also determined. Interestingly, while CXCR4 status was disparate among Ewing sarcoma cells, ranging from absent to high-level expression, its expression was found to be highly dynamic and responsive to changes in the microenvironment. In particular, upregulation of CXCR4 occurred in cells that were subjected to growth factor deprivation, hypoxia, and space constraints. This upregulation of CXCR4 was rapidly reversed upon removal of the offending cellular stress conditions. Functionally, CXCR4-positive cells migrated and invaded toward an SDF-1a gradient and these aggressive properties were impeded by both the CXCR4 small-molecule inhibitor AMD3100, and by knockdown of CXCR4. In addition, CXCR4-dependent migration and invasion were inhibited by small-molecule inhibitors of Cdc42 and Rac1, mechanistically implicating these Rho-GTPases as downstream mediators of the CXCR4-dependent phenotype.

IMPLICATIONS

This study reveals the highly plastic and dynamic nature of CXCR4 expression in Ewing sarcoma and supports a model in which stress-induced upregulation of CXCR4 contributes to tumor metastasis to lung and bone marrow, which express high levels of SDF-1a.

Intracellular coexpression of CXC- and CC- chemokine receptors and their ligands in human melanoma cell lines and dynamic variations after xenotransplantation

Background

Chemokines have been implicated in tumor progression and metastasis. In melanoma, chemokine receptors have been implicated in organ selective metastasis by regulating processes such as chemoattraction, adhesion and survival.

Methods

In this study we have analyzed, using flow cytometry, the systems formed by the chemokine receptors CXCR3, CXCR4, CXCR7, CCR7 and CCR10 and their ligands in thirteen human melanoma cell lines (five established from primary tumors and eight established from metastasis from different tissues). WM-115 and WM-266.4 melanoma cell lines (obtained from a primary and a metastatic melanoma respectively) were xenografted in nude mice and the tumors and cell lines derived from them were also analyzed.

Results

Our results show that the melanoma cell lines do not express or express in a low degree the chemokine receptors on their cell surface. However, melanoma cell lines show intracellular expression of all the aforementioned receptors and most of their respective ligands. When analyzing the xenografts and the cell lines obtained from them we found variations in the intracellular expression of chemokines and chemokine receptors that differed between the primary and metastatic cell lines. However, as well as in the original cell lines, minute or no expression of the chemokine receptors was observed at the cell surface.

Conclusions

Coexpression of chemokine receptors and their ligands was found in human melanoma cell lines. However, this expression is intracellular and receptors are not found at the cell membrane nor chemokines are secreted to the cell medium. The levels of expressed chemokine receptors and their ligands show dynamic variations after xenotransplantation that differ depending on the origin of the cell line (from primary tumor or from metastasis).

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.

Human osteosarcoma cells respond to sorafenib chemotherapy by downregulation of the tumor progression factors S100A4, CXCR4 and the oncogene FOS

Osteosarcoma is a rare but aggressive bone neoplasm in humans, which is commonly treated with surgery, classical chemotherapy and radiation. Sorafenib, an inhibitor of a number of kinases targeting the Raf/MEK/ERK pathway, is a promising new chemotherapeutic agent in human medicine that has been approved since 2006 for the therapy of renal cell carcinoma and since 2007 for the treatment of hepatocellular carcinoma. Here, we studied the antimetastatic potential of 4 µM of this multikinase inhibitor in a human osteosarcoma cell line. DNA microarray-based gene expression profiling detected 297 and 232 genes upregulated or downregulated at a threshold of >2-fold expression alteration (P<0.05) in the sorafenib-treated cells. Three genes (CXCR4, FOS and S100A4) that are involved in tumor progression were chosen for validation by quantitative PCR (qPCR) and protein expression analysis. The decrease in RNA expression detected by microarray profiling was confirmed by qPCR for all three genes (P<0.01). On the protein level, sorafenib-induced reduction of S100A4 was verified both by western blotting and immunohistochemistry. For CXCR4 and c-Fos, a reduced protein expression was shown by immunohistochemistry, for c-Fos also by immunoblotting. We conclude that sorafenib could serve as a potent chemotherapeutical agent by which to inhibit the metastatic progression of osteosarcomas.

An isoform of C/EBPβ, LIP, regulates expression of the chemokine receptor CXCR4 and modulates breast cancer cell migration

Metastasis is the primary cause of death in cancer patients. CXCR4/CXCL12 chemokine axis provides directional cues for breast cancer cells to metastasize to specific organs. Despite their potential clinical importance, how CXCR4 expression in breast cancer cells is regulated at the molecular level is not well understood. We identified an isoform of C/EBPβ, liver-enriched inhibitory protein (LIP), as a previously unrecognized transcriptional regulator of CXCR4 in breast cancer cells. LIP up-regulated the transcription of CXCR4 through direct interaction with the CXCR4 promoter. The increase in CXCR4 mRNA was paralleled by an increased cell surface expression of the CXCR4, which in turn promoted CXCR4-mediated breast cancer cell migration. A significant positive correlation between LIP and CXCR4 expression was observed in stage III and IV human breast carcinoma specimens. Neuregulin 1 (or NRG1, hereafter referred to as heregulin) increased CXCR4 expression in breast cancer cells, and this coincided with increased LIP binding on the CXCR4 promoter. These findings may have important implications for understanding the molecular basis of CXCR4-mediated breast cancer cell metastasis and could potentially allow us to develop novel strategies to reduce morbidity and mortality in patients with metastatic breast cancer.

Characterization of neuroblastoma bone invasion/metastasis in established bone metastatic model of SY5Y and KCNR cell lines

OBJECTS

To determine the mechanism of neuroblastoma (NB) bone invasion/metastasis, it is necessary to investigate the bone invasion/metastasis-related factors in the bone invasion/metastasis process. Some evidence has suggested that various proteins were involved in bone osteolytic response. The invasion/metastasis property and gene expression of NB, however, are still unknown.

METHODS

Single-cell suspensions of SY5Y and KCNR cells were injected directly into the femur of nude mice. Radiological and histological analyses, immunohistochemistry analyses, and western blot assay were performed to characterize bone metastasis mechanism in these bone metastasis models.

RESULTS

SY5Y and KCNR NB cells result in osteolytic responses in bone metastasis model. Osteoprotegerin (OPG), receptor activator of NF-kappaB ligand (RANKL), parathyroid hormone-related peptide (PTHrP), endothelin 1 (ET-1), and CXCR4 were examined and compared among in vitro, in vivo, and normal bone, respectively. PTHrP, OPG, RANKL, and ET-1 except CXCR4 in SY5Y and KCNR NB cells xenografts were strikingly upregulated compared with normal bone and NB cells. However, significantly stronger expression of PTHrP and RANKL was presented than ET-1 and OPG; furthermore, the ratios of expression of PTHrP, RANKL to OPG, and ET-1 were also markedly increased in vivo versus in vitro.

CONCLUSIONS

Our study provided evidence that NB cell may enhance bone invasion through PTHrP, OPG, RANKL, and ET-1, especially PTHrP and RANKL which may display stronger effects. CXCR4 appeared not participating in bone invasion, but in tumor growth, and homing to bone. Targeting PTHrP, OPG, ET-1, and RANKL may provide a new insight and method for patient therapy by inhibiting NB bone metastasis and invasiveness.

Perturbation of invadolysin disrupts cell migration in zebrafish (Danio rerio)

Invadolysin is an essential, conserved metalloprotease which links cell division with cell migration and is intriguingly associated with lipid droplets. In this work we examine the expression pattern, protein localisation and gross anatomical consequences of depleting invadolysin in the teleost Danio rerio. We observe that invadolysin plays a significant role in cell migration during development. When invadolysin is depleted by targeted morpholino injection, the appropriate deposition of neuromast clusters and distribution of melanophores are both disrupted. We also observe that blood vessels generated via angiogenesis are affected in invadolysin morphant fish while those formed by vasculogenesis appear normal, demonstrating an unanticipated role for invadolysin in vessel formation. Our results thus highlight a common feature shared by, and a requirement for invadolysin in, these distinct morphological events dependent on cell migration.

Use of a single hybrid imaging agent for integration of target validation with in vivo and ex vivo imaging of mouse tumor lesions resembling human DCIS

Screening of biomarker expression levels in tumor biopsy samples not only provides an assessment of prognostic and predictive factors, but may also be used for selection of biomarker-specific imaging strategies. To assess the feasibility of using a biopsy specimen for a personalized selection of an imaging agent, the chemokine receptor 4 (CXCR4) was used as a reference biomarker.

Establishment and characterization of xenograft models of human neuroblastoma bone metastasis

OBJECTS

To improve the therapy of advanced neuroblastoma (NB), it is critical to develop animal models that mimic NB bone metastases. Unlike the human disease, NB xenograft models rarely metastasize spontaneously to bone from the orthotopic site of primary tumor growth.

METHODS

Single-cell suspensions of SY5Y, KCNR NB cells were injected directly into the femur of nude mice. Radiological and histological analyses and immunohistochemistry analyses were performed to characterize these osseous NB models. SY5Y and KCNR result in osteolytic responses.

RESULTS

We have detected osteoprotegerin, receptor activator of nuclear factor kappa B ligand, parathyroid hormone-related protein, and endothelin-1, proteins associated with bone growth and osteolysis, and C-X-C chemokine receptor type 4 (CXCR4) involved in tumor growth and tumor cell migration in the NB cells grown in the bone.

CONCLUSIONS

These animal models can be used to study biological interactions, pathways, and potential therapeutic targets and also to evaluate new agents for treatment and prevention of NB bone metastasis.

Histone deacetylase inhibitors induce CXCR4 mRNA but antagonize CXCR4 migration

The stromal cell-derived factor-1α SDF-1α (CXCL12)/CXCR4 axis has been linked to poor prognosis in some cancers. As histone deacetylase inhibitors (HDIs) exert antitumor effects by targeting proteins affecting cell migration, we sought to evaluate the effects of the HDIs apicidin, vorinostat, entinostat (MS-275) and romidepsin on the expression and function of CXCR4 in human cancer cell lines. After treatment with romidepsin, CXCR4 mRNA expression increased 12-fold in UOK121 renal cancer cells, 16-fold in H460 non-small cell cancer cells and 4-fold in SF295 glioma cells; treatment with other HDIs yielded similar effects. CXCR4 induction was not observed in MCF7 breast cancer cells or SW620 colon cancer cells. To evaluate the corresponding functional increase, the effect of CXCR4 ligand, CXCL12, on ERK1/2, STAT3 and c-SRC activation and cell migration was examined in UOK121, SF295 and H460 cells. Alone, the HDIs increased pERK1/2, while reducing pSTAT-3 and pSRC. Following CXCL12 exposure, pERK1/2 induction was maintained, but STAT3 and SRC phosphorylation was impaired. These findings resulted in reduced basal and CXCL12-mediated cell migration. In conclusion, HDIs upregulated CXCR4 mRNA expression but impaired CXCL12-dependent signaling cascades through STAT3 and c-SRC, suggesting a potential role for HDIs in delaying or preventing metastatic processes in solid tumors.

Bone marrow of neuroblastoma patients shows downregulation of CXCL12 expression and presence of IFN signature

BACKGROUND

At diagnosis, children with neuroblastoma (NB) present with either localized or metastatic disease. Since the mechanisms responsible for BM invasion are not well known, we investigated the transcriptome of resident BM cells from NB patients as compared to healthy children.

PROCEDURE

Ninety-two and 88 children with localized and metastatic NB, respectively, and 15 healthy children were included in the study. BM resident cells recovered from BM aspirates by immunomagnetic bead manipulation were subjected to genome-wide microarray analysis. After validation in an independent set of samples, the genes significantly modulated in resident BM cells from NB patients were tested for their diagnostic/prognostic values.

RESULTS

BM resident cells, irrespective of neoplastic cell invasion, significantly overexpressed genes involved in innate immune responses, and interferon (IFN) and IFN-DRS signatures were enriched. Genes coding for metallothioneins and zinc finger proteins, and involved in histone and nucleosome/chromatin organization were also overexpressed. Resident BM cells from NB patients significantly downregulated genes involved in cell adhesion, and in erythrocyte, myeloid, and platelet differentiation pathways. Among downregulated genes, CXCL12 expression reached near complete silencing in patients with metastatic disease. The downregulation of CXCL12 expression was independent of contact between NB cell and resident BM cell.

CONCLUSIONS

We demonstrated that NB tumor growth at the primary site can alter the BM microenvironment, and the presence of BM-infiltrating NB cells makes the alterations more pronounced. Therefore, the restoration of a BM physiological state by means of IFN-α monoclonal antibody, Sifalimumab, and selective noradrenaline receptor blockers should be further studied to ameliorate patients' clinical management.

Plerixafor plus granulocyte-colony stimulating factor for autologous hematopoietic stem cell mobilization in patients with metastatic neuroblastoma

Current therapies for high-risk neuroblastoma (NB) necessitate the availability of several aliquots of autologous peripheral blood stem cells to reverse-associated myelosuppression. Priming with the CXCR4 inhibitor plerixafor plus G-CSF was associated with successful stem cell harvest in 5/7 heavily prior-treated patients with stage 4 NB who had previously failed G-CSF priming. Minimal residual disease was not detected in harvested cells from any patient despite the presence of disease in bone/bone marrow in 6/7. Hematopoietic reconstitution was achieved in all three patients receiving plerixafor-primed stem cells after myeloablative therapy. Plerixafor is an effective and safe agent for stem cell collection in patients with NB.

Cytokines in neuroblastoma: from pathogenesis to treatment

Cytokines released by cancer cells or by cells of the tumor microenvironment stimulate angiogenesis, act as autocrine or paracrine growth factors for malignant cells, promote tumor cell migration and metastasis or create an immunosuppressive microenvironment. These tumor-promoting effects of cytokines also apply to neuroblastoma (NB), a pediatric neuroectodermal malignancy with frequent metastatic presentation at diagnosis and poor prognosis. IL-6 and VEGF are the best characterized cytokines that stimulated tumor growth and metastasis, while others such as IFN-γ can exert anti-NB activity by inducing tumor cell apoptosis and inhibiting angiogenesis. On the other hand, cytokines are part of the anti-NB therapeutic armamentarium, as exemplified by IL-2 and granulocyte-macrophage colony stimulating factor that potentiate the activity of anti-NB antibodies. These recent results raise hope for more efficacious treatment of this ominous pediatric malignancy.

The expression of the hypoxia markers CA9 and CXCR4 is correlated with survival in patients with neuroendocrine tumours of the ileum

BACKGROUND/AIM

The hypoxia-inducible factor pathway regulates the expression of a diverse group of molecules such as CA9 and CXCR4. Our aim was to investigate the expression of these markers in a series of patients with an ileal neuroendocrine tumour (IET) at various stages of tumorigenesis.

METHODS

The immunohistochemical expression of CA9 and CXCR4 was examined in 51 patients with a resected IET. A 'hypoxic score' was calculated, integrating the expression of both CA9 and CXCR4 (hypoxic score 0: absence of expression of both molecules; hypoxic score 1: expression of CXCR4 and/or CA9). Results were compared to histoprognostic factors (including tumour size, stage and grade, WHO and TNM classifications, presence of vascular or perineural invasion, presence of a fibrotic stroma and microvascular density) and to survival.

RESULTS

All tumours were well differentiated. 69% of tumours were less than 25 mm. 46% of tumours largely infiltrated the intestinal wall (≥T3, subserosa and serosa) and 90% were classified as N1 and/or 63% as M1. 57% of tumours were of grade G1, 43% of grade G2. Grade G2 (p=0.004) and larger tumour infiltration (≥T4; p=0.03) correlated with lower survival. Hypoxic score 1 correlated with a greater tumour size (p=0.034), larger tumour infiltration (T3 or T4; p=0.001), grade G2 (p=0.046), presence of lymph node metastasis (p=0.0066) and with lower survival of patients (p=0.03).

CONCLUSION

The hypoxia-inducible factors CA9 and CXCR4 were found associated to the malignant progression of neuroendocrine tumours of the ileum. Their expression may reflect higher tumour aggressivity.

Self-renewal gene tracking to identify tumour-initiating cells associated with metastatic potential

Tumour-initiating cells (TICs) are rare cancer cells isolated from tumours of different origins including high-grade tumours that sustain neoplasic progression and development of metastatic disease. They harbour deregulated stem cells pathways and exhibit an unchecked ability to self-renew, a property essential for tumour progression. Among the essential factors maintaining embryonic stem (ES) cells properties, OCT-4 (also known as POU5F1) has been detected in tumours of different origins. Although ectopic expression results in dysplasic growth restricted to epithelial tissues, overexpression expands the proportion of immature cells in teratomas. However, OCT-4-expressing cells have not been purified from spontaneously occurring tumours, thus information concerning their properties is rather scant. Here, using p53-/- mice expressing green fluorescent protein and the puromycin resistance gene under the control of the Oct-4 promoter, we show that OCT-4 is expressed in 5% onwards of the undifferentiated tumour cell populations derived from different organs. OCT-4 expression was low as compared with ES cells, but was associated with a 'stemness' signature and expression of the chemokine receptor CXCR4. These cells displayed cancer stem cell features, including increased self-renewal and differentiation ability in vitro and in vivo. They not only formed allografts containing immature bone regions but also disseminated into different organs, including lung, liver and bone. Experiments based on RNA interference revealed that Oct-4 expression drives both their engraftment and metastasis formation. This work points out the crucial contribution of Oct-4-expressing TICs in the hierarchical organization of the malignant potential, leading to metastasis formation. Consequently, it provides an appropriate model to develop novel therapies aiming to strike down TICs by targeting self-renewal genes, therefore efficient to reduce tumour growth and metastatic disease.

CXC receptor-4 mRNA silencing abrogates CXCL12-induced migration of colorectal cancer cells

BACKGROUND

Interactions between CXCR4 and its ligand CXCL12 have been shown to be involved in cancer progression in colorectal cancer (CRC). We performed a comparative CXCL12/CXCR4 expression analysis and assessed the effect of external CXCL12 stimulation on migration of CRC cells without and with CXCR4 inhibition.

METHODS

Expression of CXCL12/CXCR4 was assessed by quantitative real-time PCR, ELISA and immunohistochemistry in resection specimens of 50 CRC patients as well as in the corresponding normal tissues and in three human CRC cell lines with different metastatic potential (Caco-2, SW480 and HT-29). Migration assays were performed after stimulation with CXCL12 and CXCR4 was inhibited by siRNA and neutralizing antibodies.

RESULTS

In CRC tissues CXCL12 was significantly down-regulated and CXCR4 was significantly up-regulated compared to the corresponding normal tissues. In cell lines CXCR4 was predominantly expressed in SW480 and less pronounced in HT-29 cells. CXCL12 was only detectable in Caco-2 cells. CXCL12 stimulation had no impact on Caco-2 cells but significantly increased migration of CXCR4 bearing SW480 and HT-29 cells. This effect was significantly abrogated by neutralizing anti-CXCR4 antibody as well as by CXCR4 siRNAs (P < 0.05).

CONCLUSIONS

CXCR4 expression was up-regulated in CRC and CXCL12 stimulation increased migration in CXCR4 bearing cell lines. Migration was inhibited by both neutralizing CXCR4 antibodies and CXCR4 siRNAs. Thus, the expression and functionality of CXCR4 might be associated with the metastatic potential of CRC cells and CXCL12/CXCR4 interactions might therefore constitute a promising target for specific treatment interventions.

Neurotrophins modulate the expression of chemokine receptors in the brain

In the central nervous system, chemokines are primarily mediators of inflammatory processes. Their receptors, in particular, CXCR4 and CCR5, serve as co-factors along with CD4 that permit Human immunodeficiency virus-1 (HIV) infection. Moreover, experimental evidence has shown that CXCR4 and CCR5 mediate the neurotoxic effects of the HIV envelope protein gp120, suggesting that these receptors could also promote the neuropathogenesis observed in HIV-positive individuals. Therefore, a better understanding of the molecular mechanisms governing the expression of chemokine receptors in the brain may lead to improved therapies that reduce HIV neurotoxicity. This study presents evidence that the expression of chemokine receptors in the brain is modulated by two neurotrophins in an area-specific manner. This new evidence suggests that the neurotrophins may be an adjunct therapy to reduce HIV-mediated neuronal injury evoked by chemokine receptor activation.