Chemokine receptor CXCR4 expression in breast cancer as a potential predictive marker of isolated tumor cells in bone marrow

New Emerging Chemokine Receptors: CCR5 or CXCR5 on Tumor Is Associated with Poor Response to Chemotherapy and Poor Prognosis in Locally Advanced Triple-Negative Breast Cancer

BACKGROUND

We aim to investigate any possible associations between chemokine receptor expression and responses to neoadjuvant chemotherapy (NAC) along with outcomes in patients with triple-negative breast cancer (TNBC) with locally advanced disease.

METHOD

Expressions of chemokine receptors were examined immunohistochemically after staining archival tissue of surgical specimens (n = 63) using specific antibodies for CCR5, CCR7, CXCR4, and CXCR5.

RESULTS

Patients with high CCR5, CCR7, CXCR4, and CXCR5 expression on tumors and high CXCR4 expression on tumor-infiltrating lymphocytes (TILs) were less likely to have a pathological complete response (pCR) or Class 0-I RCB-Index compared to others. Patients with residual lymph node metastases (ypN-positive), high CCR5TM(tumor), and high CXCR4TM expressions had an increased hazard ratio (HR) compared to others (DFS: HR = 2.655 [1.029-6.852]; DSS: HR = 2.763 [1.008-7.574]), (DFS: HR = 2.036 [0.805-5.148]; DSS: HR = 2.689 [1.020-7.090]), and (DFS: HR = 2.908 [1.080-7.829]; DSS: HR = 2.132 (0.778-5.846)), respectively. However, patients without CXCR5TIL expression had an increased HR compared to those with CXCR5TIL (DFS: 2.838 [1.266-6.362]; DSS: 4.211 [1.770-10.016]).

CONCLUSIONS

High expression of CXCR4TM and CCR5TM was found to be associated with poor prognosis, and CXCR5TM was associated with poor chemotherapy response in the present cohort with locally advanced TNBC. Our results suggest that patients with TNBC could benefit from a chemokine receptor inhibitor therapy containing neoadjuvant chemotherapy protocols.

Demystifying the CXCR4 conundrum in cancer biology: Beyond the surface signaling paradigm

The oncogenic chemokine duo CXCR4-CXCL12/SDF-1 (C-X-C Receptor 4-C-X-C Ligand 12/ Stromal-derived factor 1) has been the topic of intense scientific disquisitions since Muller et al., in her ground-breaking research, described this axis as a critical determinant of organ-specific metastasis in breast cancer. Elevated CXCR4 levels correlate with distant metastases, poor prognosis, and unfavourable outcomes in most solid tumors. Therapeutic impediment of the axis in clinics with Food and Drug Administration (FDA) approved inhibitors like AMD3100 or Plerixafor yield dubious results, contrary to pre-clinical developments. Clinical trials entailing inhibition of CXCR7 (C-X-C Receptor 7), another convicted chemokine receptor that exhibits affinity for CXCL12, reveal outcomes analogous to that of CXCR4-CXCL12 axis blockade. Of note, the cellular CXCR4 knockout phenotype varies largely from that of inhibitor treatments. These shaky findings pique great curiosity to delve further into the realm of this infamous chemokine receptor to provide a probable explanation. A multitude of recent reports suggests the presence of an increased intracellular CXCR4 pool in various cancers, both cytoplasmic and nuclear. This intracellular CXCR4 protein reserve seems active as it correlates with vital tumor attributes, viz. prognosis, aggressiveness, metastasis, and disease-free survival. Diminishing this entire intracellular CXCR4 load apart from the surface signals looks encouraging from a therapeutic point of view. Transcending beyond the classically accepted concept of ligand-mediated surface signaling, this review sheds new light on plausible associations of intracellularly compartmentalised CXCR4 with various aspects of tumorigenesis. Besides, this review also puts forward a comprehensive account of CXCR4 regulation in different cancers.

A feed-forward loop between nuclear translocation of CXCR4 and HIF-1α promotes renal cell carcinoma metastasis

CXC chemokine receptor 4 (CXCR4) has been suggested to play a critical role in cancer metastasis. Some studies have described CXCR4 nuclear localization in metastatic lesions of renal cell carcinoma (RCC), which has been suggested to be correlated with cancer metastasis. However, the underlying mechanism and clinical significance of CXCR4 nuclear localization remains unknown. Here, we show that CXCR4 nuclear localization is more likely to occur in RCC tissues, especially in metastases, and is associated with poor prognosis. CXCR4 nuclear localization requires its nuclear localization sequence (NLS, residues 146-RPRK-149). After the mutation of NLS in CXCR4, CXCR4 nuclear localization in RCC cells is lost. Nuclear localization of CXCR4 promoted RCC tumorigenicity both in vitro and in vivo. Mechanistically, we found that CXCR4 and hypoxia-inducible factor-1α (HIF-1α) colocalized in RCC cells and interacted with each other. Moreover, CXCR4 nuclear localization promoted nuclear accumulation of HIF-1α, thereby promoting the expression of genes downstream of HIF-1α. Reciprocally, nuclear HIF-1α promoted CXCR4 transcription, thus forming a feed-forward loop. Subcellular CXCR4 and HIF-1α expression levels were independent adverse prognostic factors and could be combined with TNM stage to generate a predictive nomogram of the clinical outcome of patients with RCC. Therefore, our findings indicate that CXCR4 nuclear translocation plays a critical role in RCC metastasis and may serve as a prognostic biomarker and potential therapeutic target.

CXCR4 and its ligand CXCL12 display opposite expression profiles in feline mammary metastatic disease, with the exception of HER2-overexpressing tumors

BACKGROUND

The receptor CXCR4 and its ligand CXCL12 play crucial roles in breast cancer. Despite the fact that the spontaneous feline mammary carcinoma (FMC) is considered a suitable model for breast cancer studies, the importance of the CXCR4/CXCL12 axis in FMC is completely unknown. Therefore, this work aims to elucidate the role of CXCR4 and its ligand in the progression of FMC and metastatic disease.

METHODS

CXCR4 and CXCL12 expression was analyzed by immunohistochemistry and immunofluorescence on primary tumors (PT), regional and distant metastases of female cats with mammary carcinoma and correlated with serum CXCL12 levels, tumor molecular subtypes and clinicopathological features.

RESULTS

CXCR4 was more expressed in PT than in metastases (p = 0.0067), whereas CXCL12 was highly expressed in metastatic lesions located in liver and lung (p < 0.0001), as reported for human breast cancer. Moreover, cats with CXCR4 positive PT exhibited significantly lower serum CXCL12 levels than cats with CXCR4 negative mammary carcinomas (p = 0.0324). At metastatic lesions, HER2-overexpressing tumors presented higher CXCR4 expression than the other molecular tumor subtypes (p = 0.012) and significant differences in overall (p = 0.0147) and disease-free survival (p = 0.0279) curves between the cats with CXCL12 positive and CXCL12 negative tumors were found. Indeed, CXCL12 negative PT were associated with unfavorable prognosis in cats with HER2-overexpressing tumors.

CONCLUSIONS

This work exposes part of the complex interaction between CXCR4 and CXCL12 in PT, but also in metastases of a breast cancer model. These findings could uncover novel therapeutic tools to be used in cats and humans.

Cytokine Regulation of Metastasis and Tumorigenicity

The human body combats infection and promotes wound healing through the remarkable process of inflammation. Inflammation is characterized by the recruitment of stromal cell activity including recruitment of immune cells and induction of angiogenesis. These cellular processes are regulated by a class of soluble molecules called cytokines. Based on function, cell target, and structure, cytokines are subdivided into several classes including: interleukins, chemokines, and lymphokines. While cytokines regulate normal physiological processes, chronic deregulation of cytokine expression and activity contributes to cancer in many ways. Gene polymorphisms of all types of cytokines are associated with risk of disease development. Deregulation RNA and protein expression of interleukins, chemokines, and lymphokines have been detected in many solid tumors and hematopoetic malignancies, correlating with poor patient prognosis. The current body of literature suggests that in some tumor types, interleukins and chemokines work against the human body by signaling to cancer cells and remodeling the local microenvironment to support the growth, survival, and invasion of primary tumors and enhance metastatic colonization. Some lymphokines are downregulated to suppress tumor progression by enhancing cytotoxic T cell activity and inhibiting tumor cell survival. In this review, we will describe the structure/function of several cytokine families and review our current understanding on the roles and mechanisms of cytokines in tumor progression. In addition, we will also discuss strategies for exploiting the expression and activity of cytokines in therapeutic intervention.

Chemokine axes in breast cancer: factors of the tumor microenvironment reshape the CCR7-driven metastatic spread of luminal-A breast tumors

Chemokine axes have been shown to mediate site-specific metastasis in breast cancer, but their relevance to different subtypes has been hardly addressed. Here, with the focus on the CCR7-CCL21 axis, patient datasets demonstrated that luminal-A tumors express relatively low CCR7 levels compared with more aggressive disease subtypes. Furthermore, lymph node metastasis was not associated with high CCR7 levels in luminal-A patients. The metastatic pattern of luminal-A breast tumors may be influenced by the way luminal-A tumor cells interpret signals provided by factors of the primary tumor microenvironment. Thus, CCR7-expressing human luminal-A cells were stimulated simultaneously by factors representing 3 tumor microenvironment arms typical of luminal-A tumors, hormonal, inflammatory, and growth stimulating: estrogen + TNF-α + epidermal growth factor. Such tumor microenvironment stimulation down-regulated the migration of CCR7-expressing tumor cells toward CCL21 and inhibited the formation of directional protrusions toward CCL21 in a novel 3-dimensional hydrogel system. CCL21-induced migration of CCR7-expressing tumor cells depended on PI3K and MAPK activation; however, when CCR7-expressing cancer cells were prestimulated by tumor microenvironment factors, CCL21 could not effectively activate these signaling pathways. In vivo, pre-exposure of the tumor cells to tumor microenvironment factors has put restraints on CCL21-mediated lymph node-homing cues and shifted the metastatic pattern of CCR7-expressing cells to the aggressive phenotype of dissemination to bones. Several of the aspects were also studied in the CXCR4-CXCL12 system, demonstrating similar patient and in vitro findings. Thus, we provide novel evidence to subtype-specific regulation of the CCR7-CCL21 axis, with more general implications to chemokine-dependent patterns of metastatic spread, revealing differential regulation in the luminal-A subtype.

Recent aspects for disseminated carcinomatosis of the bone marrow associated with gastric cancer: What has been done for the past, and what will be needed in future?

Disseminated carcinomatosis of the bone marrow is characterized by widespread bone metastasis (bone marrow infiltration) from solid tumors with hematological disorders coexisted. This disease is frequently complicated with gastric cancer among solid tumors although its incidence is very rare. In recent years, technological innovations in diagnosis and treatment for cancer have remarkably improved, which made survival rates of various cancers prolonged. Prognosis of disseminated carcinomatosis of the bone marrow associated with gastric cancer, however, is still poor (less than a year), possibly because this disease has not been given attention due to low incidence. In this review, I summarize the results obtained for the past, and propose ways to improve the prognosis of this disease.

The saponin DT-13 inhibits gastric cancer cell migration through down-regulation of CCR5-CCL5 axis

AIM

To investigate the effect of DT-13 on gastric cancer cell migration, and to explore the possible mechanisms underlying the anti-metastasis activity of DT-13.

METHODS

Growth inhibition of DT-13 was analyzed by the MTT assay. Cell migration was measured by the scratch-wound assay and transwell double chamber assay. To investigate the possible mechanisms underlying the anti-metastasis activity of DT-13, chemokine receptors that are involved in cancer metastasis (CCR2, CCR5, CCR7, CXCR4, and CXCR6) were detected by conventional PCR. The effect of DT-13 on CCR5 and CXCR4 expression was further evaluated by quantitative PCR and Western blot, respectively. The secretion of CCL5 (ligand of CCR5) and SDF-1 (ligand of CXCR4) were detected by enzyme-linked immunosorbent assay (ELISA).

RESULTS

DT-13 inhibited BGC-823 and HGC-27 cell growth in a dose dependent manner, and the estimated IC50 value for 24 h treatment was 23.5 ± 5.1 μmol·L(-1) for BGC-823 cells and 35.6 ± 7.6 μmol·L(-1) for HGC-27 cells. DT-13 also significantly decreased gastric cancer cell migration. DT-13 significantly decreased the gene expression of CCR5 in both BGC-823 and HGC-27 gastric cancer cells, and moderately reduced the expression of CXCR4. Similar to the results of gene expression, significant down-regulation of CCR5 protein was observed, but CXCR4 protein levels were much less affected. CCL5 secretion, but not SDF-1 production, was inhibited by DT-13.

CONCLUSION

DT-13 inhibited gastric cancer cell migration by down-regulation of the CCR5-CCL5 axis.

Coexpression of EGFR and CXCR4 predicts poor prognosis in resected pancreatic ductal adenocarcinoma

BACKGROUND

Epidermal growth factor receptor (EGFR) is highly expressed in pancreatic ductal adenocarcinoma (PDAC) and is involved in tumorigenesis and development. However, EGFR expression alone has limited clinical and prognostic significance. Recently, the cross-talk between EGFR and G-protein-coupled chemokine receptor CXCR4 has become increasingly recognized.

METHODS

In the present study, immunohistochemical staining of EGFR and CXCR4 was performed on paraffin-embedded specimens from 131 patients with surgically resected PDAC. Subsequently, the associations between EGFR expression, CXCR4 expression, EGFR/CXCR4 coexpression and clinicopathologic factors were assessed, and survival analyses were performed.

RESULTS

In total, 64 (48.9%) patients expressed EGFR, 68 (51.9%) expressed CXCR4, and 33 (25.2%) coexpressed EGFR and CXCR4. No significant association between EGFR and CXCR4 expression was observed (P = 0.938). EGFR expression significantly correlated with tumor differentiation (P = 0.031), whereas CXCR4 expression significantly correlated with lymph node metastasis (P = 0.001). EGFR/CXCR4 coexpression was significantly associated with lymph node metastasis (P = 0.026), TNM stage (P = 0.048), and poor tumor differentiation (P = 0.004). By univariate survival analysis, both CXCR4 expression and EGFR/CXCR4 coexpression were significant prognostic factors for poor disease-free survival (DFS) and overall survival (OS). Moreover, EGFR/CXCR4 coexpression significantly increased the hazard ratio for both recurrence and death compared with EGFR or CXCR4 protein expression alone. Multivariate survival analysis demonstrated that EGFR/CXCR4 coexpression was an independent prognostic factor for DFS (HR = 2.33, P<0.001) and OS (HR = 2.48, P = 0.001).

CONCLUSIONS

In conclusion, our data indicate that although EGFR expression alone has limited clinical and prognostic significance, EGFR/CXCR4 coexpression identified a subset of PDAC patients with more aggressive tumor characteristics and a significantly worse prognosis. Our results suggest a potentially important "cross-talk" between CXCR4 and EGFR intracellular pathways and indicate that the simultaneous inhibition of these pathways might be an attractive therapeutic strategy for PDAC.

Chemokine receptor Cxcr4 contributes to kidney fibrosis via multiple effectors

Kidney fibrosis is the final common pathway for virtually every type of chronic kidney disease and is a consequence of a prolonged healing response that follows tissue inflammation. Chronic kidney inflammation ultimately leads to progressive tissue injury and scarring/fibrosis. Several pathways have been implicated in the progression of kidney fibrosis. In the present study, we demonstrate that G protein-coupled chemokine (C-X-C motif) receptor (CXCR)4 was significantly upregulated after renal injury and that sustained activation of Cxcr4 expression augmented the fibrotic response. We demonstrate that after unilateral ureteral obstruction (UUO), both gene and protein expression of Cxcr4 were highly upregulated in tubular cells of the nephron. The increased Cxcr4 expression in tubules correlated with their increased dedifferentiated state, leading to increased mRNA expression of platelet-derived growth factor (PDGF)-α, transforming growth factor (TGF)-β1, and concurrent loss of bone morphogenetic protein 7 (Bmp7). Ablation of tubular Cxcr4 attenuated UUO-mediated fibrotic responses, which correlated with a significant reduction in PDGF-α and TGF-β1 levels and preservation of Bmp7 expression after UUO. Furthermore, Cxcr4(+) immune cells infiltrated the obstructed kidney and further upregulate their Cxcr4 expression. Genetic ablation of Cxcr4 from macrophages was protective against UUO-induced fibrosis. There was also reduced total kidney TGF-β1, which correlated with reduced Smad activation and α-smooth muscle actin levels. We conclude that chronic high Cxcr4 expression in multiple effector cell types can contribute to the pathogenesis of renal fibrosis by altering their biological profile. This study uncovered a novel cross-talk between Cxcr4-TGF-β1 and Bmp7 pathways and may provide novel targets for interrupting the progression of fibrosis.

Evaluation of N-[(11)C]methyl-AMD3465 as a PET tracer for imaging of CXCR4 receptor expression in a C6 glioma tumor model

The chemokine receptor CXCR4 and its ligand CXCL12 play an important role in tumor progression and metastasis. CXCR4 receptors are expressed by many cancer types and provide a potential target for treatment. Noninvasive detection of CXCR4 may aid diagnosis and improve therapy selection. It has been demonstrated in preclinical studies that positron emission tomography (PET) with a radiolabeled small molecule could enable noninvasive monitoring of CXCR4 expression. Here, we prepared N-[(11)C]methyl-AMD3465 as a new PET tracer for CXCR4. N-[(11)C]Methyl-AMD3465 was readily prepared by N-methylation with [(11)C]CH3OTf. The tracer was obtained in a 60 ± 2% yield (decay corrected), the purity of the tracer was >99%, and specific activity was 47 ± 14 GBq/μmol. Tracer stability was tested in vitro using liver microsomes and rat plasma; excellent stability was observed. The tracer was evaluated in rat C6 glioma and human PC-3 cell lines. In vitro cellular uptake of N-[(11)C]methyl-AMD3465 was receptor mediated. The effect of transition metal ions (Cu(2+), Ni(2+), and Zn(2+)) on cellular binding was examined in C6 cells, and the presence of these ions increased the cellular binding of the tracer 9-, 7-, and 3-fold, respectively. Ex vivo biodistribution and PET imaging of N-[(11)C]methyl-AMD3465 were performed in rats with C6 tumor xenografts. Both PET and biodistribution studies demonstrated specific accumulation of the tracer in the tumor (SUV 0.6 ± 0.2) and other CXCR4 expressing organs, such as lymph node (1.5 ± 0.2), liver (8.9 ± 1.0), bone marrow (1.0 ± 0.3), and spleen (1.0 ± 0.1). Tumor uptake was significantly reduced (66%, p < 0.01) after pretreatment with Plerixafor (AMD3100). Biodistribution data indicates a tumor-to-muscle ratio of 7.85 and tumor-to-plasma ratio of 1.14, at 60 min after tracer injection. Our data demonstrated that N-[(11)C]methyl-AMD3465 is capable of detecting physiologic CXCR4 expression in tumors and other CXCR4 expressing tissues. These results warrant further evaluation of N-[(11)C]methyl-AMD3465 as a potential PET tracer for CXCR4 receptor imaging.

AEG-1 promotes anoikis resistance and orientation chemotaxis in hepatocellular carcinoma cells

Metastasis contributes to the poor prognosis of hepatocellular carcinoma (HCC). Anoikis resistance and orientation chemotaxis are two important and sequential events in tumor cell metastasis. The process of tumor metastasis is known to be regulated by AEG-1, an important oncogene that plays a critical role in tumor metastasis, though the effects of this oncogene on anoikis resistance and orientation chemotaxis in HCC cells are currently unknown. To directly assess the role of AEG-1 in these processes, we up-regulated AEG-1 expression via exogenous transfection in SMMC-7721 cells, which express low endogenous levels of AEG-1; and down-regulated AEG-1 expression via siRNA-mediated knockdown in MHCC-97H and HCC-LM3 cells, which express high endogenous levels of AEG-1. Our data directly demonstrate that AEG-1 promotes cell growth as assessed by cell proliferation/viability and cell cycle analysis. Furthermore, the prevention of anoikis by AEG-1 correlates with decreased activation of caspase-3. AEG-1-dependent anoikis resistance is activated via the PI3K/Akt pathway and is characterized by the regulation of Bcl-2 and Bad. The PI3K inhibitor LY294002 reverses the AEG-1 dependent effects on Akt phosphorylation, Bcl-2 expression and anoikis resistance. AEG-1 also promotes orientation chemotaxis of suspension-cultured cells towards supernatant from Human Pulmonary Microvascular Endothelial Cells (HPMECs). Our results show that AEG-1 activates the expression of the metastasis-associated chemokine receptor CXCR4, and that its ligand, CXCL12, is secreted by HPMECs. Furthermore, the CXCR4 antoagonist AMD3100 decreases AEG-1-induced orientation chemotaxis. These results define a pathway by which AEG-1 regulates anoikis resistance and orientation chemotaxis during HCC cell metastasis.

A Comprehensive Analysis of CXCL12 Isoforms in Breast Cancer1,2

CXCL12-CXCR4-CXCR7 signaling promotes tumor growth and metastasis in breast cancer. Alternative splicing of CXCL12 produces isoforms with distinct structural and biochemical properties, but little is known about isoform-specific differences in breast cancer subtypes and patient outcomes. We investigated global expression profiles of the six CXCL12 isoforms, CXCR4, and CXCR7 in The Cancer Genome Atlas breast cancer cohort using next-generation RNA sequencing in 948 breast cancer and benign samples and seven breast cancer cell lines. We compared expression levels with several clinical parameters, as well as metastasis, recurrence, and overall survival (OS). CXCL12-α, -β, and -γ are highly co-expressed, with low expression correlating with more aggressive subtypes, higher stage disease, and worse clinical outcomes. CXCL12-δ did not correlate with other isoforms but was prognostic for OS and showed the same trend for metastasis and recurrence-free survival. Effects of CXCL12-δ remained independently prognostic when taking into account expression of CXCL12,CXCR4, and CXCR7. These results were also reflected when comparing CXCL12-α, -β, and -γ in breast cancer cell lines. We summarized expression of all CXCL12 isoforms in an important chemokine signaling pathway in breast cancer in a large clinical cohort and common breast cancer cell lines, establishing differences among isoforms in multiple clinical, pathologic, and molecular subgroups. We identified for the first time the clinical importance of a previously unstudied isoform, CXCL12-δ.

Expression of CXC chemokine receptor-4 and forkhead box 3 in neuroblastoma cells and response to chemotherapy

Current evidence indicates that the abnormal expression of chemokines or their receptors, such as CXC chemokine receptor-4 (CXCR4), is positively correlated with the development, progression and metastasis of tumor cells. However, the role of CXCR4 in neuroblastoma and its response to chemotherapy remain largely unclear. In addition, forkhead box 3 (Foxp3), a transcription factor associated with T cell tolerance, is expressed in tumor cells and plays a role in the immune evasion of cancers. The present study aimed to examine the expression of CXCR4 and Foxp3 in the LAN-5 and SK-N-SH neuroblastoma cell lines. The effects of chemotherapy drugs, cyclophosphamide (CTX) and pirarubicin (THP), on the expression of these two genes were also investigated. Our findings indicated that CXCR4 and Foxp3 were highly expressed in LAN-5 and SK-N-SH cells. Following treatment with CTX and THP, the protein expression of CXCR4 in LAN-5 and SK-N-SH cells was significantly decreased (P<0.05). The expression of Foxp3 in LAN-5 cells was also significantly downregulated by CTX and THP treatment (P<0.05). Therefore, the high expression of CXCR4 and Foxp3 in LAN-5 and SK-N-SH cells and their subsequent downregulation following administration of the chemotherapy agents suggests that the chemokine receptors, CXCR4 and Foxp3, may be involved in the metastasis and tumor evasion of neuroblastoma. Further studies should investigate the expression of CXCR4 and Foxp3 in patient samples.

Posttranscriptional control of the chemokine receptor CXCR4 expression in cancer cells

We demonstrate that CXCR4 mRNA contains ARE in its 3′-UTR and regulated by the RNA-binding proteins, TTP and HuR. Normalization of the aberrant TTP-HuR axis resulted in reduced invasion and migration of breast cancer cells toward CXCL12.

CXCR4 is a chemokine receptor that is overexpressed in certain cancer types and involved in migration toward distant organs. The molecular mechanisms underlying CXCR4 expression in invasive cancer, particularly posttranscriptional regulation, are poorly understood. Here, we find that CXCR4 harbors AU-rich elements (AREs) in the 3′-untranslated region (3′-UTR) that bind and respond to the RNA-binding proteins, tristetraprolin (TTP/ZFP36) and HuR (ELAVL1). Different experimental approaches, including RNA immunoprecipitation, 3′-UTR reporter, RNA shift and messenger RNA (mRNA) half-life studies confirmed functionality of the CXCR4 ARE. Wild-type TTP, but not the zinc finger mutant, C124R, was able to bind CXCR4 mRNA and ARE. In the invasive breast cancer phenotype, aberrant expression of CXCR4 is linked to both TTP deficiency and HuR overexpression. HuR silencing led to decreased CXCR4 mRNA stability and expression, and significant reduction in migration of the cells toward the CXCR4 ligand, CXCL12. Derepression of TTP using miR-29a inhibitor led to significant reduction in CXCR4 mRNA stability, expression and migration capability of the cells. The study shows that CXCR4 is regulated by ARE-dependent posttranscriptional mechanisms that involve TTP and HuR, and that aberration in this pathway helps cancer cells migrate toward the CXCR4 ligand. Targeting posttranscriptional control of CXCR4 expression may constitute an alternative approach in cancer therapy.

Bioinformatics analysis of breast cancer bone metastasis related gene-CXCR4

OBJECTIVE

To analyze breast cancer bone metastasis related gene-CXCR4.

METHODS

This research screened breast cancer bone metastasis related genes by high-flux gene chip.

RESULTS

It was found that the expressions of 396 genes were different including 165 up-regulations and 231 down-regulations. The expression of chemokine receptor CXCR4 was obviously up-regulated in the tissue with breast cancer bone metastasis. Compared with the tissue without bone metastasis, there was significant difference, which indicated that CXCR4 played a vital role in breast cancer bone metastasis.

CONCLUSIONS

The bioinformatics analysis of CXCR4 can provide a certain basis for the occurrence and diagnosis of breast cancer bone metastasis, target gene therapy and evaluation of prognosis.

The potential of hypoxia markers as target for breast molecular imaging--a systematic review and meta-analysis of human marker expression

Background

Molecular imaging of breast cancer is a promising emerging technology, potentially able to improve clinical care. Valid imaging targets for molecular imaging tracer development are membrane-bound hypoxia-related proteins, expressed when tumor growth outpaces neo-angiogenesis. We performed a systematic literature review and meta-analysis of such hypoxia marker expression rates in human breast cancer to evaluate their potential as clinically relevant molecular imaging targets.

Methods

We searched MEDLINE and EMBASE for articles describing membrane-bound proteins that are related to hypoxia inducible factor 1α (HIF-1α), the key regulator of the hypoxia response. We extracted expression rates of carbonic anhydrase-IX (CAIX), glucose transporter-1 (GLUT1), C-X-C chemokine receptor type-4 (CXCR4), or insulin-like growth factor-1 receptor (IGF1R) in human breast disease, evaluated by immunohistochemistry. We pooled study results using random-effects models and applied meta-regression to identify associations with clinicopathological variables.

Results

Of 1,705 identified articles, 117 matched our selection criteria, totaling 30,216 immunohistochemistry results. We found substantial between-study variability in expression rates. Invasive cancer showed pooled expression rates of 35% for CAIX (95% confidence interval (CI): 26-46%), 51% for GLUT1 (CI: 40-61%), 46% for CXCR4 (CI: 33-59%), and 46% for IGF1R (CI: 35-70%). Expression rates increased with tumor grade for GLUT1, CAIX, and CXCR4 (all p < 0.001), but decreased for IGF1R (p < 0.001). GLUT1 showed the highest expression rate in grade III cancers with 58% (45-69%). CXCR4 showed the highest expression rate in small T1 tumors with 48% (CI: 28-69%), but associations with size were only significant for CAIX (p < 0.001; positive association) and IGF1R (p = 0.047; negative association). Although based on few studies, CAIX, GLUT1, and CXCR4 showed profound lower expression rates in normal breast tissue and benign breast disease (p < 0.001), and high rates in carcinoma in situ. Invasive lobular carcinoma consistently showed lower expression rates (p < 0.001).

Conclusions

Our results support the potential of hypoxia-related markers as breast cancer molecular imaging targets. Although specificity is promising, combining targets would be necessary for optimal sensitivity. These data could help guide the choice of imaging targets for tracer development depending on the envisioned clinical application.

Patterns of metastatic spread in early breast cancer

AIMS

The aim of this study was to prospectively investigate metastatic pathways of spread to lymph node versus bone marrow and identify biological characteristics that determine these patterns in early invasive breast cancer.

PATIENTS AND METHODS

In all, 177 patients with early invasive breast cancer underwent surgical extirpation of the primary tumour with sentinel lymph node biopsy (SLNB). Bone marrow (BM) aspiration was performed to screen for cytokeratin-positive cells by immunocytochemistry. Lymphatic spread was assessed by histopathological examination of lymph nodes (LN). A representative subset of 87 tumours was analysed by tissue microarray (TMA) to evaluate expression of markers that potentially influence haematogenous vs. lymphatic spread. Patients were followed up for a median of 54.7 months.

RESULTS

Of the 177 patients, 114 (64%) were BM-/LN-, 38 (22%) BM-/LN+, 19 (11%) BM+/LN- and 6 (3%) BM+/LN+. Multivariate analysis of histopathological characteristics revealed that increasing tumour size was significantly associated with both LN positivity (p = 0.003) and BM positivity (p = 0.01), the presence of lymphovascular invasion significantly correlated with LN+ (p = 0.01), whereas lower histological grade was significantly associated with BM+ (p = 0.03). LN+ and BM+ were non-significantly negatively related to each other. Univariate analysis of the TMA data showed differential expression patterns for several factors; significant differences between effects on the two metastatic pathways (lymphatic vs. haematogenous) were found for expression of CD54 (p = 0.03), osteopontin (p = 0.04), bone sialoprotein (p = 0.04) and CXCR4 (p = 0.009). High expression of CD54, osteopontin and bone sialoprotein (BSP) was positively associated with BM + but was either not associated, or negatively associated, with LN+. High CXCR4 expression was positively associated with LN+ and negatively with BM+. High VEGF-C expression was associated with both LN+ and BM+, although this did not attain statistical significance. Due to the small number of clinical events during clinical follow-up, no associations were identified between metastatic spread patterns, recurrence and/or death.

CONCLUSION

These findings suggest that distinct lymphatic and haematogenous metastatic pathways exist in early breast cancer and that these pathways are governed by specific biological markers.

[⁹⁹mTc]O₂-AMD3100 as a SPECT tracer for CXCR4 receptor imaging

PURPOSE

CXCR4 plays an important role in HIV infection, tumor progression, neurogenesis, and inflammation. In-vivo imaging of CXCR4 could provide more insight in the role of this receptor in health and disease. The aim of this study was to investigate [(99m)Tc]O₂-AMD3100 as a potential SPECT tracer for imaging of CXCR4.

METHOD

AMD3100 was labelled with [(99m)Tc]pertechnetate. A cysteine challenge assay was performed to test the tracer stability. Heterologous and homologous receptor binding assay and internalization assay were performed in CXCR4 expressing Jurkat-T cells. Ex vivo biodistribution was studied in healthy mice at 30, 60, and 120 min after tracer injection. Tumor uptake of the tracer was determined by microSPECT imaging in nude mice xenografted with human PC-3 prostate tumor. Specificity of tracer uptake was determined by blocking studies using an excess of unlabelled AMD3100.

RESULTS

AMD3100 was labelled with technetium-99m with a radiochemical yield of >98%. The tracer was stable in PBS and mouse plasma for at least 6h at 37 °C. Heterologous and homologous binding assays with AMD3100 showed IC50 values of 240 ± 10 μM, and 92 ± 5 μM for [(125)I]SDF-1α and [(99m)Tc]O₂-AMD3100 respectively, with negligible receptor internalisation. The tracer showed high uptake in liver, lungs, spleen, thymus, intestine and bone. Blocking dose of AMD3100.8HCl (20mg/kg) decreased the uptake in these organs (p<0.05). [(99m)Tc]O2-AMD3100 showed specific tumor accumulation in mice bearing PC-3 xenografts model. Time activity curves (TAC) in AMD3100 pre-treated animals tracer showed 1.7 times less tumor uptake as compared to control animals (p<0.05).

CONCLUSION

[(99m)Tc]O2-AMD3100 is readily labelled, is stable in plasma and displays a favourable binding affinity for the CXCR4 receptors. [(99m)Tc O₂-AMD3100 shows specific binding in organs with high CXCR4 expression and in CXCR4 positive tumors. These results justify further evaluation of this radiopharmaceutical as a potential biomarker for the non-invasive imaging of CXCR4 receptors.

CD133: holy of grail of neuro-oncology or promiscuous red-herring?

The CD133 glycoprotein is a controversial cancer stem cell marker in the field of neuro-oncology, based largely on the now considerable experimental evidence for the existence of both CD133+ve and CD133-ve populations as tumour-initiating cells. It is thought that decreasing oxygen tension enhances the complex regulation and phenotype of CD133 in glioma. In light of these ideologies, establishing the precise functional role of CD133 is becoming increasingly critical. In this article, we review the complex regulation of CD133 and its extracellular epitope AC133, and associated alterations, to tumour cell behaviour by hypoxia. Furthermore, its role in functional modulation of tumours, rather than determination of a specific stem cell type is therefore alluded to, while evidence for and against its ability as a cancer stem cell marker in primary brain tumours, is critically evaluated. Thus, the suggestion that CD133 may be a central 'holy grail' in identifying core cells for propagation of malignant glial neoplasms seems increasingly less convincing. It remains to be seen, however, whether CD133 is randomly expressed on such brain tumour cell populations or whether it is of major significance to brain biological behaviour.

Expression of CXCR4 is an independent prognostic factor for overall survival and progression-free survival in patients with myelodysplastic syndrome

CXCR4 is the receptor of stromal cell-derived factor (SDF-1) and is expressed in many types of cancer cells. It also plays an important role in metastasis of malignant disease. In this study, we detected the expression of CXCR4 in 81 patients with myelodysplastic syndrome (MDS) by flow cytometry. We categorized MDS patients into the high-expression group and low-expression group according to CXCR4 mean florescence intensity ration thresholds. We showed that the high-expression group had a shorter overall survival time and shorter relapse-free survival time compared with those of the low-expression group (21.6 ± 1.9 vs. 46.0 ± 1.6 months, 17.0 ± 1.9 vs. 42.5 ± 2.1 months, respectively, P < 0.05), and Cox regression showed that CXCR4 was an independent prognostic factor. We conclude that the expression of CXCR4 is a useful prognostic factor for patients with MDS.

Emodin inhibits invasion and migration of prostate and lung cancer cells by downregulating the expression of chemokine receptor CXCR4

Emodin (ED), an anthraquinone derivative, has been found to inhibit proliferation, induce apoptosis, suppress angiogenesis, impede metastasis, and enhance chemotherapy. However, the detailed mechanism of ED related to the regulation of CXC chemokine receptor-4 (CXCR4) gene expression that affects cellular migration and invasion in prostate and lung cancer cells are not fully understood. Recent evidence indicates that the CXCR4/CXCL12 axis is involved in promoting invasion and metastasis in tumors. Thus, novel agents that can downregulate CXCR4 expression have therapeutic potential in repressing cancer metastasis. Among ED and its derivatives, it is found that ED downregulated the expression of both CXCR4 and HER2 without affecting cell viability in tumor cells. The suppression of CXCR4 expression by ED was found to correlate with the inhibition of CXCL12-induced migration and invasion of both DU145 and A549 cells. Besides, neither proteasome inhibition nor lysosomal stabilization had any effect on ED-induced decrease in CXCR4 expression. The basic molecular mechanisms unveiled that the downregulation of CXCR4 was at the transcriptional level, as indicated by downregulation of mRNA expression and suppression of NF-κB activation. Overall, our findings suggest that ED is a novel blocker of CXCR4 expression and, thus, has enormous potential as a powerful therapeutic agent for metastatic cancer.

Phosphorylated CXCR4 is associated with poor survival in adults with B-acute lymphoblastic leukemia

BACKGROUND

CXC chemokine receptor 4 (CXCR4) is activated by phosphorylation (pCXCR4) and is essential for the migration of hematopoietic precursors to bone marrow. CXCR4 overexpression predicts a poor prognosis in patients with acute myeloid leukemia. Data regarding the prognostic impact of CXCR4 in patients with B-acute lymphoblastic leukemia (B-ALL) are sparse and limited to the pediatric population.

METHODS

The authors analyzed CXCR4 and pCXCR4 expression in 54 adults with newly diagnosed B-ALL. CXCR4 was assessed by flow cytometry (FC) and immunohistochemistry (IHC) using an anti-CXCR4 antibody. pCXCR4 expression was assessed using an anti-pCXCR4 antibody.

RESULTS

The study group included 30 men and 24 women with a median age of 42 years (range, 17-84 years). Philadelphia chromosome was present in 19 patients. The median follow-up was 16 months (range, 17-84 months). Forty-nine patients had a complete response, and 12 patients relapsed with a median relapse free survival >120 weeks. Fifteen patients (28%) died with a median survival >125 weeks. CXCR4 detected by FC and IHC was highly correlated (P < .001). CXCR4 was not associated with clinical or laboratory findings or survival. In contrast, pCXCR4 was associated with higher leukocyte count (P = .006) and serum bilirubin level (P = .03). In multivariate analysis, pCXCR4 expression (P = .027), high serum creatinine level (P < .01), presence of the Philadelphia chromosome (P = .017), and late clinical response (P < .001) were associated with worse overall survival.

CONCLUSIONS

The current results indicated that detection of the activated form of CXCR4, pCXCR4, provides independent prognostic information in adult patients with B-ALL.

Crosstalk between chemokine receptor CXCR4 and cannabinoid receptor CB2 in modulating breast cancer growth and invasion

Background

Cannabinoids bind to cannabinoid receptors CB₁ and CB₂ and have been reported to possess anti-tumorigenic activity in various cancers. However, the mechanisms through which cannabinoids modulate tumor growth are not well known. In this study, we report that a synthetic non-psychoactive cannabinoid that specifically binds to cannabinoid receptor CB₂ may modulate breast tumor growth and metastasis by inhibiting signaling of the chemokine receptor CXCR4 and its ligand CXCL12. This signaling pathway has been shown to play an important role in regulating breast cancer progression and metastasis.

Methodology/Principal Findings

We observed high expression of both CB₂ and CXCR4 receptors in breast cancer patient tissues by immunohistochemical analysis. We further found that CB₂-specific agonist JWH-015 inhibits the CXCL12-induced chemotaxis and wound healing of MCF7 overexpressing CXCR4 (MCF7/CXCR4), highly metastatic clone of MDA-MB-231 (SCP2) and NT 2.5 cells (derived from MMTV-neu) by using chemotactic and wound healing assays. Elucidation of the molecular mechanisms using various biochemical techniques and confocal microscopy revealed that JWH-015 treatment inhibited CXCL12-induced P44/P42 ERK activation, cytoskeletal focal adhesion and stress fiber formation, which play a critical role in breast cancer invasion and metastasis. In addition, we have shown that JWH-015 significantly inhibits orthotopic tumor growth in syngenic mice in vivo using NT 2.5 cells. Furthermore, our studies have revealed that JWH-015 significantly inhibits phosphorylation of CXCR4 and its downstream signaling in vivo in orthotopic and spontaneous breast cancer MMTV-PyMT mouse model systems.

Conclusions/Significance

This study provides novel insights into the crosstalk between CB₂ and CXCR4/CXCL12-signaling pathways in the modulation of breast tumor growth and metastasis. Furthermore, these studies indicate that CB₂ receptors could be used for developing innovative therapeutic strategies against breast cancer.

Role of RANK, RANKL, OPG, and CXCR4 tissue markers in predicting bone metastases in breast cancer patients

This is a retrospective study on 40 breast cancer patients, of which 20 have bone metastases, 10 have visceral metastases, and 10 have no evidence of disease, aimed at evaluating the role of CXCR4 and the RANK/RANKL/OPG system to predict bone metastases. CXCR4 expression, alone or in combination with RANK, identified patients destined to relapse to bone.

BACKGROUND

The RANK/RANKL/OPG system is active in primary cancers such as breast, prostate, and also in their bone metastases. CXCR4 chemokine receptor is highly expressed in human breast cancer cells and is believed to facilitate the homing of tumor cells to organs such as bone that express high levels of its ligand SDF1. Our study aimed to investigate whether the analysis of these markers with an inexpensive and simple test can help to predict bone metastases in breast cancer patients.

PATIENTS AND METHODS

Marker expression was evaluated by immunohistochemical staining in paraffin-embedded tissue sections of primary breast cancers from 40 individuals: 20 patients with bone metastases (BM), 10 with visceral metastases (VM; considered together as the relapsed group), and 10 with no evidence of disease (NED).

RESULTS

RANKL was not detected in tumor cells. OPG- and RANK-positive tumors are found with similar frequency in NED (20%) and in relapsed patients (23% and 17%, respectively). However, in the latter subgroup, only RANK positivity was always associated with bone relapse. The frequency of CXCR4-positive tumors was three-fold higher in relapsed (30%) than in NED (10%) patients and positivity was always linked to bone metastases. Considering NED and VM patients together versus BM patients, we observed that CXCR4 expression, alone (P = .008) or in combination with RANK (P < .001), identified patients destined to relapse to bone.

CONCLUSION

Our results provide the first clinical evidence to support a pivotal role of combined CXCR4 and RANK expression in predicting bone relapse.

CXCR4 in Cancer and Its Regulation by PPARgamma

Chemokines are peptide mediators involved in normal development, hematopoietic and immune regulation, wound healing, and inflammation. Among the chemokines is CXCL12, which binds principally to its receptor CXCR4 and regulates leukocyte precursor homing to bone marrow and other sites. This role of CXCL12/CXCR4 is “commandeered” by cancer cells to facilitate the spread of CXCR4-bearing tumor cells to tissues with high CXCL12 concentrations. High CXCR4 expression by cancer cells predisposes to aggressive spread and metastasis and ultimately to poor patient outcomes. As well as being useful as a marker for disease progression, CXCR4 is a potential target for anticancer therapies. It is possible to interfere directly with the CXCL12:CXCR4 axis using peptide or small-molecular-weight antagonists. A further opportunity is offered by promoting strategies that downregulate CXCR4 pathways: CXCR4 expression in the tumor microenvironment is modulated by factors such as hypoxia, nucleosides, and eicosanoids. Another promising approach is through targeting PPAR to suppress CXCR4 expression. Endogenous PPARγ such as 15-deoxy-Δ^12,14-PGJ₂ and synthetic agonists such as the thiazolidinediones both cause downregulation of CXCR4 mRNA and receptor. Adjuvant therapy using PPARγ agonists may, by stimulating PPARγ-dependent downregulation of CXCR4 on cancer cells, slow the rate of metastasis and impact beneficially on disease progression.

Annexin-1 interacts with NEMO and RIP1 to constitutively activate IKK complex and NF-κB: implication in breast cancer metastasis

The molecular mechanisms underlying constitutive nuclear factor-κB (NF-κB) activation in solid tumors has not been elucidated. We show that Annexin-1 (ANXA1) is involved in this process, and suppression of ANXA1 in highly metastatic breast cancer cells impedes migration and metastasis capabilities in vitro and in vivo. ANXA1 expression correlates with NF-κB activity, suggesting that ANXA1 may be required for the constitutive activity of IκB kinase (IKK) and NF-κB in highly metatstatic breast cancer. Gel-filtration analysis demonstrated that ANXA1 co-elutes with the members of the IKK complex and NF-κB signaling pathway, and immunoprecipitation confirmed that ANXA1 can bind to and interact with IKKγ or NEMO, but not IKKα or IKKβ. Importantly, silencing of ANXA1 prevents the interaction of NEMO and RIP1, which indicates that ANXA1 is required for the recruitment of RIP1 to the IKK complex, which may be important for the activation of NF-κB. Downstream targets of NF-κB include uPA and CXCR4, which can be modulated by ANXA1 silencing. CXCR4-mediated migration of breast cancer cell lines in response to CXCL12 was significantly modulated by ANXA1, indicating its importance in the tissue-specific migration of breast cancer cells. Chromatin immunoprecipitation experiments confirmed that in ANXA1 overexpressed cells, NF-κB was recruited to CXCR4 promoter without external stimulation, indicating that ANXA1 is critical for the constitutive activation of NF-κB in breast cancer to promote metastasis. Finally, we show that ANXA1 overexpression enhances metastasis and reduces survival in an intracardiac metastasis model, while ANXA1-deficient mice crossed with MMTV-PyMT mice display significantly less metastasis than their heterozygous littermates, indicating that ANXA1 is an important gene in breast cancer metastasis. Our data reveal that ANXA1 can constitutively activate NF-κB in breast cancer cells through the interaction with the IKK complex, and suggests that modulating ANXA1 levels has therapeutic potential to suppress breast cancer metastasis.

Acetyl-11-keto-β-boswellic acid suppresses invasion of pancreatic cancer cells through the downregulation of CXCR4 chemokine receptor expression

Ninety percent of cancer-mediated deaths are due to metastasis of the tumor; however, the mechanisms controlling metastasis remain poorly understood. Thus, no therapy targeting this process has yet been approved. Chemokines and their receptors are mediators of chronic inflammation and have been linked to the metastasis of numerous cancers. More recently, the Cysteine X Cysteine (CXC) chemokine receptor 4 (CXCR4) has emerged as a key mediator of tumor metastasis; therefore, identification of inhibitors of this receptor has the potential to abrogate metastasis. In this report, we demonstrate that acetyl-11-keto-β-boswellic acid (AKBA), a component of the therapeutic plant Boswellia serrata, can downregulate CXCR4 expression in pancreatic cancer cells. The reduction in CXCR4 induced by this terpenoid was found to be cell-type specific, as its expression was also abrogated in leukemia, myeloma and breast cancer cell lines. Neither proteasome inhibitors nor lysosomal stabilization could prevent the AKBA-induced reduction in CXCR4 expression. This downregulation occurred at the transcriptional level. Suppression of CXCR4 by AKBA was accompanied by the inhibition of pancreatic cancer cell invasion, which is induced by CXCL12, the ligand for CXCR4. In addition, abrogation of the expression of chemokine receptor by AKBA was found in human pancreatic tissues from orthotopic animal model. AKBA also abolished breast tumor cell invasion, and this effect correlated with the disappearance of both the CXCR4 messenger RNA and CXCR4 protein. Overall, our results show that AKBA is a novel inhibitor of CXCR4 expression and, thus, has the potential to suppress the invasion and metastasis of cancer cells.

CXCR4 suppression attenuates EGFRvIII-mediated invasion and induces p38 MAPK-dependent protein trafficking and degradation of EGFRvIII in breast cancer cells

Our previous report has shown that the constitutively activated EGFR variant, EGFRvIII, up-regulates the pro-metastatic chemokine receptor CXCR4 in breast cancer cells. Here we evaluated the biological effect and cell signaling effects of silencing CXCR4 expression in EGFRvIII-expressing breast cancer cells. Short hairpin RNA (shRNA)-mediated suppression of CXCR4 expression significantly reduced the invasive potential and proliferation of EGFRvIII-expressing breast cancer cells. These cells exhibited a reduction of EGFRvIII activity and protein expression due to increased protein degradation and altered protein trafficking. In conclusion, suppression of CXCR4 inhibits EGFRvIII-mediated breast cancer cell invasion and proliferation.

CXCR4 expression predicts patient outcome and recurrence patterns after hepatic resection for colorectal liver metastases

BACKGROUND

The purpose of this study was to determine if the expression of the chemokine receptors, CXCR4 and CCR7, and the chemokine ligand, CXCL12, in completely resected colorectal cancer hepatic metastases are predictive of disease-specific survival, recurrence-free survival and patterns of recurrence.

METHODS

Immunohistochemical analysis of CXCR4, CCR7 and CXCL12 expression within resected hepatic metastases was performed and correlated with clinicopathological variables, disease-specific survival, recurrence-free survival and patterns of recurrence.

RESULTS

Seventy-five patients who underwent partial hepatectomy with curative intent were studied. CXCR4 expression (hazard ratio [HR] 3.6, 95% confidence interval [95% CI] 1.4-9.1) and clinical risk score >2 (HR 2.3, 95% CI 1.1-4.7) were independently associated with disease-specific survival by multivariate analysis. The 5-year estimated disease-specific survival rates for positive and negative CXCR4 tumor expression were 44 and 77%, respectively (P = 0.005). CXCR4 expression (HR 2.2, 95% CI 1.2-4.2) and clinical risk score >2 (HR 1.9, 95% CI 1.1-3.4) were independently associated with recurrence-free survival by multivariate analysis. The five year estimated recurrence-free survival rates for positive and negative CXCR4 tumor expression were 20 and 50%, respectively (P = 0.004). Neither CXCL12 nor CCR7 expression in tumors predicted disease-specific survival or recurrence-free survival. Forty-nine patients (65%) developed recurrent disease after initial hepatectomy. Negative CXCR4 tumor expression was associated with favorable recurrence patterns amenable to salvage resection and/or ablation.

CONCLUSIONS

Negative CXCR4 expression in resected colorectal cancer hepatic metastases is independently associated with improved disease-specific and recurrence-free survival and favorable patterns of recurrence.

A critical role of Gbetagamma in tumorigenesis and metastasis of breast cancer

A growing body of evidence indicates that G protein-coupled receptors (GPCRs) are involved in breast tumor progression and that targeting GPCRs may be a novel adjuvant strategy in cancer treatment. However, due to the redundant role of multiple GPCRs in tumor development, it may be necessary to target a common signaling component downstream of these receptors to achieve maximum efficacy. GPCRs transmit signals through heterotrimeric G proteins composed of Gα and Gβγ subunits. Here we evaluated the role of Gβγ in breast tumor growth and metastasis both in vitro and in vivo. Our data show that blocking Gβγ signaling with Gα(t) or small molecule inhibitors blocked serum-induced breast tumor cell proliferation as well as tumor cell migration induced by various GPCRs in vitro. Moreover, induced expression of Gα(t) in MDA-MB-231 cells inhibited primary tumor formation and retarded growth of existing breast tumors in nude mice. Blocking Gβγ signaling also dramatically reduced the incidence of spontaneous lung metastasis from primary tumors and decreased tumor formation in the experimental lung metastasis model. Additional studies indicate that Gβγ signaling may also play a role in the generation of a tumor microenvironment permissive for tumor progression, because the inhibition of Gβγ signaling attenuated leukocyte infiltration and angiogenesis in primary breast tumors. Taken together, our data demonstrate a critical role of Gβγ signaling in promoting breast tumor growth and metastasis and suggest that targeting Gβγ may represent a novel therapeutic approach for breast cancer.

Celastrol suppresses invasion of colon and pancreatic cancer cells through the downregulation of expression of CXCR4 chemokine receptor

Although metastasis accounts for >90% of cancer-related deaths, no therapeutic that targets this process has yet been approved. Because the chemokine receptor CXCR4 is one of the targets closely linked with tumor metastasis, inhibitors of this receptor have the potential to abrogate metastasis. In the current report, we demonstrate that celastrol can downregulate the CXCR4 expression on breast cancer MCF-7 cells stably transfected with HER2, an oncogene known to induce the chemokine receptor. Downregulation of CXCR4 by the triterpenoid was not cell type-specific as downregulation occurred in colon cancer, squamous cell carcinoma, and pancreatic cancer cells. Decrease in CXCR4 expression was not due to proteolysis as neither proteasome inhibitors nor lysosomal stabilization had any effect. Quantitative reverse transcription polymerase chain reaction analysis revealed that downregulation of CXCR4 messenger RNA (mRNA) by celastrol occurred at the translational level. Chromatin immunoprecipitation analysis revealed regulation at the transcriptional level as well. Abrogation of the chemokine receptor by celastrol or by gene-silencing was accompanied by suppression of invasiveness of colon cancer cells induced by CXCL12, the ligand for CXCR4. This effect was not cell type-specific as celastrol also abolished invasiveness of pancreatic tumor cells, and this effect again correlated with the disappearance of both the CXCR4 mRNA and CXCR4 protein. Other triterpenes, such as withaferin A and gedunin, which are known to inhibit Hsp90, did not downregulate CXCR4 expression, indicating that the effects were specific to celastrol. Overall, these results show that celastrol has potential in suppressing invasion and metastasis of cancer cells by down-modulation of CXCR4 expression.

Trastuzumab in Primary Inflammatory Breast Cancer (IBC): High Pathological Response Rates and Improved Outcome

Inflammatory breast cancer (IBC) represents a rare but aggressive and lethal form of locally advanced breast cancer (LABC) and frequently with HER-2 neu overexpressed or amplified. We retrospectively identified 16 newly diagnosed HER-2 ⁄ neu-positive IBC patients who were treated with preoperative trastuzumab. We determined the pathological complete response rate (pCR) when trastuzumab was added to preoperative chemotherapy in patients with HER2⁄ neupositive IBC. Furthermore, we assessed the expression of CXCR4 in metastatic recurrence sites. Ten patients (62.5%)achieved a pCR. Six patients (37.5%) achieved a partial response. Median follow-up of all patients was 24.2 months. Four(25%) patients have experienced a progression, of which three were in the brain. Two-year progression-free survival was 59.4% (95% CI 35–100). High expression of CXCR4 was detected in the brain metastases. We conclude that in spite of high pCR rates among women with HER-2 ⁄ neu-positive IBC treated with neoadjuvant trastuzumab-based regimens the outcome remains dismal and brain recurrences are frequent. CXCR4 may represent a novel therapeutic target.

Butein downregulates chemokine receptor CXCR4 expression and function through suppression of NF-κB activation in breast and pancreatic tumor cells

The CXC chemokine receptor-4 (CXCR4), a Gi protein-coupled receptor for the ligand CXCL12/stromal cell-derived factor-1α (SDF-1α), is known to be expressed in various tumors. This receptor mediates homing of tumor cells to specific organs that express the ligand CXCL12 for this receptor and plays an important role in tumor growth, invasion, metastasis, and angiogenesis. Thus, a priori, agents that can downregulate CXCR4/CXCL12 signaling cascade have potential against cancer metastasis. In this study, we report the identification of butein (3, 4, 2', 4'-tetrahydroxychalcone) as a novel regulator of CXCR4 expression and function. We found that butein downregulated the expression of CXCR4 in HER2-overexpressing breast cancer cells in a dose- and time-dependent manner. The decrease in CXCR4 expression induced by butein was not cell type-specific as the inhibition also occurred in pancreatic, prostate, multiple myeloma, head and neck, and hepatocellular cancer cell lines. When investigated for the molecular mechanism(s), it was found that the downregulation of CXCR4 was not due to proteolytic degradation but rather to transcriptional regulation as indicated by downregulation of mRNA expression, inhibition of NF-κB activation evident by both DNA binding, and reporter assays, and suppression of chromatin immunoprecipitation activity. Suppression of CXCR4 expression by butein correlated with the inhibition of CXCL12-induced migration and invasion of both breast and pancreatic cancer cells. Overall, our results demonstrate for the first time that butein is a novel inhibitor of CXCR4 expression and thus has a potential in suppressing metastasis of cancer.

Expression of stromal derived factor-1 (SDF-1) and chemokine receptor (CXCR4) in bone metastasis of renal carcinoma

Renal cancer is a relatively common malignant carcinoma that metastasizes to bone. The chemokine stromal derived factor-1 (SDF-1) and its corresponding receptor CXCR4 have been shown to regulate organ-specific metastasis in other cancer types. Based on this observation, we predicted that the expressions of SDF-1 and CXCR4 play a role in renal carcinoma metastasis to bone. To investigate the expressions of SDF-1 and CXCR4, and to assess the correlation between SDF-1 and CXCR4 immunoreactivity in bone metastasis of renal carcinoma, we collected 10 in situ renal carcinoma samples and 30 bone metastasis samples. We analyzed SDF-1 and CXCR4 expression with immunohistochemical analysis on paraffin-embedded sections. Compared with primary renal carcinomas, the SDF-1 expression in bone metastases was significantly higher [80% (24/30) vs. 30% (3/10), P = 0.006]; the expression of CXCR4 was also higher [83.3% (25/30) vs. 40% (4/10), P = 0.014]. Pearson correlation analysis supports a positive correlation between SDF-1 and CXCR4 in bone metastasis of renal carcinoma. In addition, RT-PCR demonstrated that, as compared with in situ renal carcinoma tissues, SDF-1 expression was predominant in the bone metastasis samples (P = 0.001), while CXCR4 was overexpressed in the bone metastasis tissues (P = 0.028). Western blot analysis confirmed these trends. Our data suggest that the expression of SDF-1/CXCR4 is high in bone metastases and over-expression of SDF-1/CXCR4 may play important roles in the bone metastasis of renal carcinoma.

Hypoxia increases the metastatic ability of breast cancer cells via upregulation of CXCR4

BACKGROUND

Chemokine SDF1alpha and its unique receptor CXCR4 have been implicated in organ-specific metastases of many cancers including breast cancer. Hypoxia is a common feature of solid tumors and is associated with their malignant phenotype. We hypothesized that hypoxia would upregulate CXCR4 expression and lead to increased chemotactic responsiveness to its specific ligand SDF1alpha.

METHODS

Three breast cancer cell lines MDA-MB-231, MCF7 and 4T1 were subjected to 48 hrs of hypoxia or normoxia. Cell surface receptor expression was evaluated using flow cytometry. An extracellular matrix invasion assay and microporous migration assay was used to assess chemotactic response and metastatic ability.

RESULTS

CXCR4 surface expression was significantly increased in the two human breast cancer cell lines, MDA-MB-231 and MCF7, following exposure to hypoxia. This upregulation of CXCR4 cell surface expression corresponded to a significant increase in migration and invasion in response to SDF1-alpha in vitro. The increase in metastatic potential of both the normoxic and the hypoxic treated breast cancer cell lines was attenuated by neutralization of CXCR4 with a CXCR4 neutralizing mAb, MAB172 or a CXCR4 antagonist, AMD3100, showing the relationship between CXCR4 overexpression and increased chemotactic responsiveness.

CONCLUSIONS

CXCR4 expression can be modulated by the tissue microenvironment such as hypoxia. Upregulation of CXCR4 is associated with increased migratory and invasive potential and this effect can be abrogated by CXCR4 inhibition. Chemokine receptor CXCR4 is a potential therapeutic target in the adjuvant treatment of breast cancer.

Molecular imaging of CXCR4 receptor expression in human cancer xenografts with [64Cu]AMD3100 positron emission tomography

The chemokine receptor CXCR4 and its cognate ligand CXCL12 are pivotal for establishing metastases from many tumor types. Thus, CXCR4 may offer a cell surface target for molecular imaging of metastases, assisting diagnosis, staging, and therapeutic monitoring. Furthermore, noninvasive detection of CXCR4 status of a primary tumor may provide an index of the metastatic potential of the lesion. Here, we report the development and evaluation of [(64)Cu]AMD3100, a positron-emitting analogue of the stem cell mobilizing agent plerixafor to image CXCR4 in human tumor xenografts preselected for graded expression of this receptor. This imaging method was evaluated in lung metastases derived from human MDA-MB-231 breast cancer cells. Ex vivo biodistribution studies, performed to validate the in vivo imaging data, confirmed the ability of [(64)Cu]AMD3100 to image CXCR4 expression. Our findings show the feasibility of imaging CXCR4 by positron emission tomography using a clinically approved agent as a molecular scaffold.

EGFR variant-mediated invasion by enhanced CXCR4 expression through transcriptional and post-translational mechanisms

The expression of the potent, constitutively activated EGFR variant, EGFRvIII, has been linked to breast cancer metastasis, but the mechanisms of EGFRvIII and CXCR4 crosstalk, which may facilitate breast cancer invasion, have never been explored. Here we report that CXCR4 expression is increased in breast cancer cells expressing EGFRvIII regardless of the ER/PgR status of the cells. Treatment of EGFRvIII-expressing breast cancer cells with the tyrosine kinase inhibitor, AG1478, reverses CXCR4 expression back to levels expressed in parental cells. In addition, expressing EGFRvIII enhances CXCL12/CXCR4-mediated invasion, which can be inhibited by CXCR4 inhibitors. Surprisingly, CXCR4 mRNA and its transcriptional regulator, HIF-1alpha, are up-regulated only in ER+/PgR+ estrogen-dependent EGFRvIII-expressing breast cancer cells, but not in ER-/PgR- or estrogen-independent cell lines, suggesting that HIF-1alpha and hormone receptor-mediated actions may have a role in the transcriptional regulation of CXCR4. We also demonstrate that p38 MAPK is one of the major down-stream signaling molecules responsible for EGFRvIII/CXCR4-mediated invasion as p38 MAPK activity was induced by CXCL12 stimulation under both normoxic and hypoxic conditions. More interestingly, inhibition of p38 MAPK activity significantly reduced CXCR4 expression and inhibited the invasive potential of EGFRvIII-expressing breast cancer cells, suggesting an essential role for p38 MAPK in EGFRvIII/CXCR4 induced invasion. Furthermore, CXCR4 is regulated post-translationally through decreased expression of AIP4 and beta-arrestin 1/2, molecules involved in CXCR4 internalization, cellular trafficking and degradation. These results provide a plausible mechanism for EGFRvIII-mediated invasion and establish a functional link between EGFRvIII and CXCR4 signaling pathways.

Evaluation of a CXCR4 antagonist in a xenograft mouse model of inflammatory breast cancer

CXCL12/CXCR4 signaling, being important in the homing of cancer cells to lungs, bone and other organs, is a promising therapeutic target. Our purpose was to determine whether a peptide-based antagonist of CXCR4 would reduce primary tumor growth and/or metastasis in a preclinical mouse model of inflammatory breast cancer. We improved an existing model of inflammatory breast cancer for this study by luciferase transfection of SUM149 cells and the monitoring of such cells in mice by imaging and the luciferase assay. We implanted 2 x 10(6) SUM49-Luc cells along with matrigel into the left thoracic mammary fat pad of nude mice to produce tumors. Our mouse model exhibited important features of inflammatory breast cancer, namely, aggressive local disease, local metastases and distant metastases. To evaluate the efficacy of a CXCR4 antagonist CTCE-9908, by itself or in combination with paclitaxel, we treated groups of ten mice each with CTCE-9908 (25 mg/kg, injected subcutaneously 5 days/week), control peptide SC-9908, paclitaxel (10 mg/kg, injected subcutaneously twice a week), and CTCE-9908 plus paclitaxel concurrently. We assessed all mice weekly by whole-body luciferase imaging to quantify relative primary tumor burden and distant metastases. At the end of the experiment, we quantified primary tumors by weight and lung metastases by luciferase activity assay on tissue lysates. Paclitaxel, a known chemotherapeutic, inhibited primary tumor growth in our model (P < 0.05). CTCE-9908 did not significantly inhibit primary tumor growth or lung metastases as compared to control groups, without or with paclitaxel (P > 0.05). However, CTCE-9908 as a single therapy inhibited organ-specific metastasis to leg (P < 0.05 by chi-squared test and by two-sample t-test).

CXCR4 expression in early breast cancer and risk of distant recurrence

BACKGROUND

Chemokine receptor 4 (CXCR4) has been demonstrated to have a critical role in the early metastatic process. The aim of this study was to evaluate the prognostic value of CXCR4 expression in primary breast tumors and describe correlations with the occurrence of metastasis in organs expressing the CXCR4 ligand stromal cell-derived factor 1 (i.e., liver, lung, brain, and bone).

PATIENTS AND METHODS

CXCR4 expression in primary breast tumors was evaluated by immunohistochemistry in 823 patients included in two prospective clinical trials. CXCR4 expression was considered positive when >1% of tumor cells were stained. The prognostic value of CXCR4 expression was assessed by a Cox regression model adjusted for clinical characteristics. We assessed the association of CXCR4 expression with the rate of distant metastasis to specific organ sites.

RESULTS

CXCR4 was expressed in 92 of 794 primary tumors (12%). CXCR4 expression was not associated with clinical characteristics. CXCR4 was not prognostic for overall survival and showed a nonsignificant trend toward a higher risk for distant metastasis. CXCR4(+) tumors showed a significantly higher risk for bone metastasis. The 10-year incidences of bone metastases were 23% (13.6%-32.6%) and 12% (9.7%-15%) in CXCR4(+) and CXCR4(-) tumors, respectively.

CONCLUSION

This study suggests that expression of CXCR4 in primary breast tumors is associated with a higher likelihood of developing bone metastases. This finding could open new avenues for the development of novel adjuvant strategies, including bone-targeting agents.

The influence of tumor-host interactions in the stromal cell-derived factor-1/CXCR4 ligand/receptor axis in determining metastatic risk in breast cancer

The chemokine stromal cell-derived factor-1 (SDF-1) may function to attract CXCR4-expressing cancer cells to metastatic organs. We have previously demonstrated that low plasma SDF-1, a host-derived marker, increases distant metastatic risk in breast cancer. We therefore hypothesized that tumors overexpressing the SDF-1 receptor CXCR4 have an enhanced ability to metastasize in patients with low plasma SDF-1 levels. In this study, we determined the prognostic significance of activated CXCR4, or phosphorylated CXCR4 (p-CXCR4), and CXCR7, another receptor for SDF-1. Immunohistochemistry was performed on a tissue microarray built using 237 samples from the same cohort of patients for which we measured plasma SDF-1 levels. We found that the prognostic value of p-CXCR4 expression (hazard ratio or HR, 3.95; P = 0.004) was superior to total CXCR4 expression (HR, 3.20; P = 0.03). The rate of breast cancer-specific mortality was much higher in patients with both high p-CXCR4 expression and low plasma SDF-1 levels (HR, 5.96; P < 0.001) than either low plasma SDF-1 (HR, 3.59; P = 0.01) or high p-CXCR4 expression (HR, 3.83; P = 0.005) alone. The added prognostic value of low plasma SDF-1 was only effective in patients with high p-CXCR4 expression, and as such, provides clinical validation for modulation of the metastatic potential of tumor cells by an inherent host-derived metastatic risk factor.

Chemokine receptors in advanced breast cancer: differential expression in metastatic disease sites with diagnostic and therapeutic implications

BACKGROUND

We investigated the expression of CXCR4, CCR7, estrogen receptor (ER), progesterone receptor (PR) and HER2-neu in human metastatic breast cancers to determine whether these biological biomarkers were preferentially expressed in any organ-specific metastases.

MATERIALS AND METHODS

CXCR4, CCR7, ER, PR and HER2-neu expression levels were evaluated by immunohistochemical staining using paraffin-embedded tissue sections of metastatic breast cancers (n = 41) obtained by either diagnostic biopsy or surgical resection.

RESULTS

The metastatic sites included the following: bone (n = 15), brain (n = 14), lung (n = 6), liver (n = 2), and omental metastases (n = 2). CXCR4 was expressed in 41% of cases, CCR7 expression was demonstrated in 10%, and HER2-neu overexpression was present in 27%. CXCR4 was more likely to be expressed in bone metastases than visceral metastases (67% versus 26%, P = 0.020). Visceral sites demonstrated a lower rate of CXCR4 positivity (33% and 23%, respectively, for lung and brain metastases). Similarly, CCR7 was more likely to be found in bone metastases than visceral sites (27% versus 0%, P = 0.037).

CONCLUSIONS

These results indicate that CXCR4 can contribute to the homing of breast cancer cells to the bone. This finding might have important clinical implications since patients with metastatic bone disease may achieve the highest benefit from a CXCR4-targeted therapy.

Topotecan inhibits cancer cell migration by down-regulation of chemokine CC motif receptor 7 and matrix metalloproteinases

AIM

The aim of this study was to investigate the effect of topotecan (TPT) on cancer cell migration.

METHODS

Growth inhibition of TPT was analyzed by MTT assay, and cancer cell migration was measured by transwell double chamber assay. To verify the effect of TPT on the chemokine receptors CXCR4 and CCR7, quantitative PCR, semi-quantitative PCR and Western blot analysis were performed. The secretion of MMP-2 and MMP-9 was detected by enzyme-linked immunosorbent assay (ELISA) and gelatin zymography. To evaluate possible contributions of CCR7 to MMP secretion, the overexpression vectors pcDNA3.1(+)-CCR7 and CCR7 siRNA were transiently transfected into MDA-MB-435 cells.

RESULTS

TPT inhibited cancer cell migration in a dose-dependent manner. Additionally, TPT significantly decreased the expression of CCR7 in both MDA-MB-435 and MDA-MB-231 cells and moderately reduced the expression of CXCR4 in MDA-MB-435 cells. The secretion of MMPs (MMP-2, MMP-9) was also inhibited by TPT. Overexpression of CCR7 increased the secretion of MMP-2/9 and cancer cell migration, whereas knockdown of CCR7 reduced active MMP-2/9 production and migration of MDA-MB-435 cells.

CONCLUSION

TPT inhibited cancer cell migration by down-regulation of CCR7 and MMPs (MMP-2 and MMP-9).

CXCR4 receptor positive spheroid forming cells are responsible for tumor invasion in vitro

Stem cells have been found to be involved in breast cancer growth, but the specific contribution of cancer stem cells in tumor biology, including metastasis, is still uncertain. We found that murine breast cancer cell lines 4T1, 4TO7, 167Farn and 67NR contains cancer stem cells defined by CXCR4 expression and their capability of forming spheroids in suspension culture. Importantly, we showed that CXCR4 expression is essential for tumor invasiveness because both CXCR4 neutralizing antibody and shRNA knockdown of the CXCR4 receptor significantly reduced tumor cell invasion.

Deubiquitination of CXCR4 by USP14 is critical for both CXCL12-induced CXCR4 degradation and chemotaxis but not ERK ativation

The chemokine receptor CXCR4 plays important roles in the immune and nervous systems. Abnormal expression of CXCR4 contributes to cancer and inflammatory and neurodegenerative disorders. Although ligand-dependent CXCR4 ubiquitination is known to accelerate CXCR4 degradation, little is known about counter mechanisms for receptor deubiquitination. CXCL12, a CXCR4 agonist, induces a time-dependent association of USP14 with CXCR4, or its C terminus, that is not mimicked by USP2A, USP4, or USP7, other members of the deubiquitination catalytic family. Co-localization of CXCR4 and USP14 also is time-dependent following CXCL12 stimulation. The physical interaction of CXCR4 and USP14 is paralleled by USP14-catalyzed deubiquitination of the receptor; knockdown of endogenous USP14 by RNA interference (RNAi) blocks CXCR4 deubiquitination, whereas overexpression of USP14 promotes CXCR4 deubiquitination. We also observed that ubiquitination of CXCR4 facilitated receptor degradation, whereas overexpression of USP14 or RNAi-induced knockdown of USP14 blocked CXCL12-mediated CXCR4 degradation. Most interestingly, CXCR4-mediated chemotactic cell migration was blocked by either overexpression or RNAi-mediated knockdown of USP14, implying that a CXCR4-ubiquitin cycle on the receptor, rather than a particular ubiquitinated state of the receptor, is critical for the ligand gradient sensing and directed motility required for chemokine-mediated chemotaxis. Our observation that a mutant of CXCR4, HA-3K/R CXCR4, which cannot be ubiquitinated and does not mediate a chemotactic response to CXCL12, indicates the importance of this covalent modification not only in marking receptors for degradation but also for permitting CXCR4-mediated signaling. Finally, the indistinguishable activation of ERK by wild typeor 3K/R-CXCR4 suggests that chemotaxis in response to CXCL12 may be independent of the ERK cascade.

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.