CX3CR1-fractalkine expression regulates cellular mechanisms involved in adhesion, migration, and survival of human prostate cancer cells

Mechanisms of lymph node metastasis: An extracellular vesicle perspective

In several solid tumors such as breast cancer, prostate cancer, colorectal cancer or melanoma, tumor draining lymph nodes are the earliest tissues where colonization by tumor cells is detected. Lymph nodes act as sentinels of metastatic dissemination, the deadliest phase of tumor progression. Besides hematogenous dissemination, lymphatic spread of tumor cells has been demonstrated, adding more complexity to the mechanisms involved in metastasis. A network of blood and lymphatic vessels surrounds tumors providing routes for tumor soluble factors to mediate regional and long-distance effects. Additionally, extracellular vesicles (EVs), particularly small EVs/exosomes, have been shown to circulate through the blood and lymph, favoring the formation of pre-metastatic niches in the tumor-draining lymph nodes (TDLNs) and distant organs. In this review, we present an overview of the relevance of lymph node metastasis, the structural and immune changes occurring in TDLNs during tumor progression, and how extracellular vesicles contribute to modulating some of these alterations while promoting the formation of lymph node pre-metastatic niches.

Fractalkine in Health and Disease

CX3CL1 is one of the 50 up-to-date identified and characterized chemokines. While other chemokines are produced as small, secreted proteins, CX3CL1 (fractalkine) is synthetized as a transmembrane protein which also leads to a soluble form produced as a result of proteolytic cleavage. The membrane-bound protein and the soluble forms exhibit different biological functions. While the role of the fractalkine/CX3CR1 signaling axis was described in the nervous system and was also related to the migration of leukocytes to sites of inflammation, its actions are controversial in cancer progression and anti-tumor immunity. In the present review, we first describe the known biology of fractalkine concerning its action through its cognate receptor, but also its role in the activation of different integrins. The second part of this review is dedicated to its role in cancer where we discuss its role in anti-cancer or procarcinogenic activities.

Relationship between aggressive features of oral squamous cell carcinoma and the immunoexpression of CX3CR1, CX3CL1 and ITGAV

OBJECTIVE

We aimed to describe the association between CX3CR1, CX3CL1, and ITGAV immunoexpression with PNI and adverse oncologic outcomes in patients with OSCC.

STUDY DESIGN

Expression CX3CR1, CX3CL1, and ITGAV was assessed by immunohistochemistry in a cohort of 50 paraffin-embedded resections of OSCC. Survival analysis, Cox, and binary logistic regressions were undertaken to determine the impact on patient survival and predictive value for PNI.

RESULTS

CX3CL1 positive nerves exhibited a significant association with tumor budding (TB) (P = .043), whereas nerves positive for ITGAV were associated with PNI (P = .021), T3-T4 tumor size (P = .029), and III-IV stage (P = .044). Cases with ITGAV-positive nerves exhibited an odds ratio of 9.603 (P = .008) for PNI, whereas cases with CX3CL1-positive nerves exhibited and odds ratio of 4.682 (P = .033) for TB. A trend toward decreased 5-year overall survival (P = .078) and 5-year disease-specific survival (P = .09) was observed in relation to ITGAV-positive nerves. However, no independent predictors for poor survival were identified.

CONCLUSIONS

The expression of ITGAV was associated with PNI and advanced disease, whereas the expression of CX3CL1 was related to TB, suggesting that ITGAV and CX3CL1 are involved in their respective developments. Therefore, further investigations are encouraged to assess the potential utility of targeted therapies against CX3CL1 receptors in OSCC.

Interruption of KLF5 acetylation promotes PTEN-deficient prostate cancer progression by reprogramming cancer-associated fibroblasts

Inactivation of phosphatase and tensin homolog (PTEN) is prevalent in human prostate cancer and causes high-grade adenocarcinoma with a long latency. Cancer-associated fibroblasts (CAFs) play a pivotal role in tumor progression, but it remains elusive whether and how PTEN-deficient prostate cancers reprogram CAFs to overcome the barriers for tumor progression. Here, we report that PTEN deficiency induced Krüppel-like factor 5 (KLF5) acetylation and that interruption of KLF5 acetylation orchestrated intricate interactions between cancer cells and CAFs that enhance FGF receptor 1 (FGFR1) signaling and promote tumor growth. Deacetylated KLF5 promoted tumor cells to secrete TNF-α, which stimulated inflammatory CAFs to release FGF9. CX3CR1 inhibition blocked FGFR1 activation triggered by FGF9 and sensitized PTEN-deficient prostate cancer to the AKT inhibitor capivasertib. This study reveals the role of KLF5 acetylation in reprogramming CAFs and provides a rationale for combined therapies using inhibitors of AKT and CX3CR1.

CX3CL1 (Fractalkine)-CX3CR1 Axis in Inflammation-Induced Angiogenesis and Tumorigenesis

The chemotactic cytokine fractalkine (FKN, chemokine CX3CL1) has unique properties resulting from the combination of chemoattractants and adhesion molecules. The soluble form (sFKN) has chemotactic properties and strongly attracts T cells and monocytes. The membrane-bound form (mFKN) facilitates diapedesis and is responsible for cell-to-cell adhesion, especially by promoting the strong adhesion of leukocytes (monocytes) to activated endothelial cells with the subsequent formation of an extracellular matrix and angiogenesis. FKN signaling occurs via CX3CR1, which is the only known member of the CX3C chemokine receptor subfamily. Signaling within the FKN-CX3CR1 axis plays an important role in many processes related to inflammation and the immune response, which often occur simultaneously and overlap. FKN is strongly upregulated by hypoxia and/or inflammation-induced inflammatory cytokine release, and it may act locally as a key angiogenic factor in the highly hypoxic tumor microenvironment. The importance of the FKN/CX3CR1 signaling pathway in tumorigenesis and cancer metastasis results from its influence on cell adhesion, apoptosis, and cell migration. This review presents the role of the FKN signaling pathway in the context of angiogenesis in inflammation and cancer. The mechanisms determining the pro- or anti-tumor effects are presented, which are the cause of the seemingly contradictory results that create confusion regarding the therapeutic goals.

Immunophenotypic and Gene Expression Analyses of the Inflammatory Microenvironment in High-Grade Oral Epithelial Dysplasia and Oral Lichen Planus

BACKGROUND

Oral lichen planus (OLP) and oral epithelial dysplasia (OED) present diagnostic challenges due to clinical and histologic overlap. This study explores the immune microenvironment in OED, hypothesizing that immune signatures could aid in diagnostic differentiation and predict malignant transformation.

METHODS

Tissue samples from OED and OLP cases were analyzed using immunofluorescence/immunohistochemistry (IF/IHC) for CD4, CD8, CD163/STAT1, and PD-1/PDL-1 expression. RNA-sequencing was performed on the samples, and data was subjected to CIBERSORTx analysis for immune cell composition. Gene Ontology analysis on the immune differentially expressed genes was also conducted.

RESULTS

In OED, CD8 + T-cells infiltrated dysplastic epithelium, correlating with dysplasia severity. CD4 + lymphocytes increased in the basal layer. STAT1/CD163 + macrophages correlated with CD4 + intraepithelial distribution. PD-1/PDL-1 expression varied. IF/IHC analysis revealed differential immune cell composition between OED and OLP. RNA-sequencing identified upregulated genes associated with cytotoxic response and immunosurveillance in OED. Downregulated genes were linked to signaling, immune cell recruitment, and tumor suppression.

CONCLUSIONS

The immune microenvironment distinguishes OED and OLP, suggesting diagnostic potential. Upregulated genes indicate cytotoxic immune response in OED. Downregulation of TRADD, CX3CL1, and ILI24 implies dysregulation in TNFR1 signaling, immune recruitment, and tumor suppression. This study contributes to the foundation for understanding immune interactions in OED and OLP, offering insights into future objective diagnostic avenues.

Anticancer effects of cell-free culture supernatant of Escherichia coli in bladder cancer cell line: New insight into the regulation of inflammation

Bladder cancer (BC) is the 10th most common malignancy in worldwide, with substantial mortality and morbidity if not treated effectively. According to various research, inflammatory circumstances majorly impact the microenvironment of bladder cancer, and the chronic presence of cytokines and chemokines promotes tumor progression. In this investigation, we explored the impact of cell-free culture supernatant ofEscherichia colistrain 536 on inflammatory cytokines and chemokines in bladder cancer model microarray data (GSE162251). Then we examined in silico outcomes on human bladder cancer cell line 5637 to verify and extrapolate findings. This investigation revealed for the first time that this compound has potent suppressor effects on interleukin 1 beta (IL-1β), C-C motif chemokine ligand 2 (CCL2), and C-X3-C motif chemokine ligand 1 (CX3CL1) gene expression as well as increased NAD(P)H quinone dehydrogenase 1 (NQO1), as an anti-oxidant agent, gene expression in 4, 8, and 24 h. Moreover, we confirmed that c-MYC, a member of the MYC proto-oncogene family, gene expression reduced in 5637 cells in 4 h and then followed up its expression in 8 and 24 h. In addition, our investigation demonstrated that the supernatant raised the BCL2-Associated X Protein/B-cell lymphoma 2 (BAX/BCL2) ratio, and subsequent flow cytometry analysis demonstrated that the supernatant induction apoptosis and necrosis. In conclusion, our findings demonstrate that this compound is a potential candidate for the suppression of bladder cancer progression.

Exploring the role of miR-200 family in regulating CX3CR1 and CXCR1 in lung adenocarcinoma tumor microenvironment: implications for therapeutic intervention

Lung adenocarcinoma (LUAD) is the most common malignant subtype of lung cancer (LC). miR-200 family is one of the prime miR regulators of epithelial-mesenchymal transition (EMT) and worst overall survival (OS) in LC patients. The study aimed to identify and validate the key differentially expressed immune-related genes (DEIRGs) regulated by miR-200 family which may serve for therapeutic aspects in LUAD tumor microenvironment (TME) by affecting cancer progression, invasion, and metastasis. The study identified differentially expressed miRNAs (DEMs) in LUAD, consisting of hsa-miR-200a-3p and hsa-miR-141-5p, respectively. Two highest-degree subnetwork motifs identified from 3-node miRNA FFL were: (i) miR-200a-3p-CX3CR1-SPIB and (ii) miR-141-5p-CXCR1-TBX21. TIMER analysis showed that the expression levels of CX3CR1 and CXCR1 were significantly positively correlated with infiltrating levels of M0-M2 macrophages and natural killer T (NKT) cells. The OS of LUAD patients was significantly affected by lower expression levels of hsa-miR-200a-3p, CX3CR1 and SPIB. These DEIRGs were validated using the human protein atlas (HPA) web server. Further, we validated the regulatory role of hsa-miR-200a-3p in an in-vitro indirect co-culture model using conditioned media from M0, M1 and M2 polarized macrophages (THP-1) and LUAD cell lines (A549 and H1299 cells). The results pointed out the essential role of hsa-miR-200a-3p regulated CX3CL1 and CX3CR1 expression in progression of LC TME. Thus, the study augments a comprehensive understanding and new strategies for LUAD treatment where miR-200 family regulated immune-related genes, especially chemokine receptors, which regulate the metastasis and invasion of LUAD, leading to the worst associated OS.

The CX3CL1-CX3CR1 chemokine axis can contribute to tumor immune evasion and blockade with a novel CX3CR1 monoclonal antibody enhances response to anti-PD-1 immunotherapy

CX3CL1 secreted in the tumor microenvironment serves as a chemoattractant playing a critical role in metastasis of CX3CR1 expressing cancer cells. CX3CR1 can be expressed in both cancer and immune-inhibitory myeloid cells to facilitate their migration. We generated a novel monoclonal antibody against mouse CX3CR1 that binds to CX3CR1 and blocks the CX3CL1-CX3CR1 interaction. We next explored the immune evasion strategies implemented by the CX3CL1-CX3CR1 axis and find that it initiates a resistance program in cancer cells that results in 1) facilitation of tumor cell migration, 2) secretion of soluble mediators to generate a pro-metastatic niche, 3) secretion of soluble mediators to attract myeloid populations, and 4) generation of tumor-inflammasome. The CX3CR1 monoclonal antibody reduces migration of tumor cells and decreases secretion of immune suppressive soluble mediators by tumor cells. In combination with anti-PD-1 immunotherapy, this CX3CR1 monoclonal antibody enhances survival in an immunocompetent mouse colon carcinoma model through a decrease in tumor-promoting myeloid populations. Thus, this axis is involved in the mechanisms of resistance to anti-PD-1 immunotherapy and the combination therapy can overcome a portion of the resistance mechanisms to anti-PD-1.

Plasma fractalkine contributes to systemic myeloid diversity and PD-L1/PD-1 blockade in lung cancer

Recent studies highlight the importance of baseline functional immunity for immune checkpoint blockade therapies. High-dimensional systemic immune profiling is performed in a cohort of non-small-cell lung cancer patients undergoing PD-L1/PD-1 blockade immunotherapy. Responders show high baseline myeloid phenotypic diversity in peripheral blood. To quantify it, we define a diversity index as a potential biomarker of response. This parameter correlates with elevated activated monocytic cells and decreased granulocytic phenotypes. High-throughput profiling of soluble factors in plasma identifies fractalkine (FKN), a chemokine involved in immune chemotaxis and adhesion, as a biomarker of response to immunotherapy that also correlates with myeloid cell diversity in human patients and murine models. Secreted FKN inhibits lung adenocarcinoma growth in vivo through a prominent contribution of systemic effector NK cells and increased tumor immune infiltration. FKN sensitizes murine lung cancer models refractory to anti-PD-1 treatment to immune checkpoint blockade immunotherapy. Importantly, recombinant FKN and tumor-expressed FKN are efficacious in delaying tumor growth in vivo locally and systemically, indicating a potential therapeutic use of FKN in combination with immunotherapy.

Osteoid cell-derived chemokines drive bone-metastatic prostate cancer

One of the greatest challenges in improving prostate cancer (PCa) survival is in designing new therapies to effectively target bone metastases. PCa regulation of the bone environment has been well characterized; however, bone-targeted therapies have little impact on patient survival, demonstrating a need for understanding the complexities of the tumor-bone environment. Many factors contribute to creating a favorable microenvironment for prostate tumors in bone, including cell signaling proteins produced by osteoid cells. Specifically, there has been extensive evidence from both past and recent studies that emphasize the importance of chemokine signaling in promoting PCa progression in the bone environment. Chemokine-focused strategies present promising therapeutic options for treating bone metastasis. These signaling pathways are complex, with many being produced by (and exerting effects on) a plethora of different cell types, including stromal and tumor cells of the prostate tumor-bone microenvironment. ​This review highlights an underappreciated molecular family that should be interrogated for treatment of bone metastatic prostate cancer (BM-PCa).

Differences in Prostate Cancer Transcriptomes by Age at Diagnosis: Are Primary Tumors from Older Men Inherently Different?

Older age at diagnosis is consistently associated with worse clinical outcomes in prostate cancer. We sought to characterize gene expression profiles of prostate tumor tissue by age at diagnosis. We conducted a discovery analysis in The Cancer Genome Atlas prostate cancer dataset (n = 320; 29% of men >65 years at diagnosis), using linear regressions of age at diagnosis and mRNA expression and adjusting for TMPRSS2:ERG fusion status and race. This analysis identified 13 age-related candidate genes at FDR < 0.1, six of which were also found in an analysis additionally adjusted for Gleason score. We then validated the 13 age-related genes in a transcriptome study nested in the Health Professionals Follow-up Study and Physicians' Health Study (n = 374; 53% of men >65 years). Gene expression differences by age in the 13 candidate genes were directionally consistent, and age at diagnosis was weakly associated with the 13-gene score. However, the age-related genes were not consistently associated with risk of metastases and prostate cancer-specific death. Collectively, these findings argue against tumor genomic differences as a main explanation for age-related differences in prostate cancer prognosis.

PREVENTION RELEVANCE

Older age at diagnosis is consistently associated with worse clinical outcomes in prostate cancer. This study with independent discovery and validation sets and long-term follow-up suggests that prevention of lethal prostate cancer should focus on implementing appropriate screening, staging, and treatment among older men without expecting fundamentally different tumor biology.

Rethinking the chemokine cascade in brain metastasis: Preventive and therapeutic implications

Brain metastasis (BrM) is one of the major causes of death in cancer patients and is associated with an estimated 10-40 % of total cancer cases. The survival rate of brain metastatic patients has not improved due to intratumor heterogeneity, the survival adaptations of brain homing metastatic cells, and the lack of understanding of underlying molecular mechanisms that limit the availability of effective therapies. The heterogeneous population of immune cells and tumor-initiating cells or cancer stem cells in the tumor microenvironment (TME) release various factors, such as chemokines that upon binding to their cognate receptors enhance tumor growth at primary sites and help tumor cells metastasize to the brain. Furthermore, brain metastatic sites have unique heterogeneous microenvironment that fuels cancer cells in establishing BrM. This review explores the crosstalk of chemokines with the heterogeneous TME during the progression of BrM and recognizes potential therapeutic approaches. We also discuss and summarize different targeted, immunotherapeutic, chemotherapeutic, and combinatorial strategies (with chemo-/immune- or targeted-therapies) to attenuate chemokines mediated BrM.

Chemokines network in bone metastasis: Vital regulators of seeding and soiling

Chemokines are well equipped with chemo-attractive signals that can regulate cancer cell trafficking to specific organ sites. Currently, updated concepts have revealed the diverse role of chemokines in the biology of cancer initiation and progression. Genomic instabilities and alterations drive tumor heterogeneity, providing more options for the selection and metastatic progression to cancer cells. Tumor heterogeneity and acquired drug resistance are the main obstacles in managing cancer therapy and the primary root cause of metastasis. Studies emphasize that multiple chemokine/receptor axis are involved in cancer cell-mediated organ-specific distant metastasis. One of the persuasive mechanisms for heterogeneity and subsequent events is sturdily interlinked with the crosstalk between chemokines and their receptors on cancer cells and tissue-specific microenvironment. Among different metastatic niches, skeletal metastasis is frequently observed in the late stages of prostate, breast, and lung cancer and significantly reduces the survival of cancer patients. Therefore, it is crucial to elucidate the role of chemokines and their receptors in metastasis and bone remodeling. Here, we review the potential chemokine/receptor axis in tumorigenesis, tumor heterogeneity, metastasis, and vicious cycle in bone microenvironment.

Hallmarks of Cancer Expression in Oral Lichen Planus: A Scoping Review of Systematic Reviews and Meta-Analyses

Oral lichen planus (OLP) is a common chronic inflammatory disease of unknown etiology and likely autoimmune nature that is currently considered an oral potentially malignant disorder, implying that patients suffering from this process are at risk of developing oral cancer in their lifetime. The molecular alterations that develop in OLP and that make the affected oral epithelium predisposed to malignancy are unknown, although, as in other autoimmune diseases (ulcerative colitis, primary biliary cirrhosis, etc.), they may be linked to oncogenesis-promoting effects mediated by the inflammatory infiltrate. So far there is no in-depth knowledge on how these hallmarks of cancer are established in the cells of the oral epithelium affected by OLP. In this scoping review of systematic reviews and meta-analyses the state of evidence based knowledge in this field is presented, to point out gaps of evidence and to indicate future lines of research. MEDLINE, Embase, Cochrane Library and Dare were searched for secondary-level studies published before October 2022. The results identified 20 systematic reviews and meta-analyses critically appraising the hallmarks tumor-promoting inflammation (n = 17, 85%), sustaining proliferative signaling (n = 2, 10%), and evading growth suppressors (n = 1, 5%). No evidence was found for the other hallmarks of cancer in OLP. In conclusion, OLP malignization hypothetically derives from the aggressions of the inflammatory infiltrate and a particular type of epithelial response based on increased epithelial proliferation, evasion of growth-suppressive signals and lack of apoptosis. Future evidence-based research is required to support this hypothesis.

Regulation of Tumor and Metastasis Initiation by Chemokine Receptors

Tumor-initiating cells (TICs) are a rare sub-population of cells within the bulk of a tumor that are major contributors to tumor initiation, metastasis, and chemoresistance. TICs have a stem-cell-like phenotype that is dictated by the expression of master regulator transcription factors, including OCT4, NANOG, and SOX2. These transcription factors are expressed via activation of multiple signaling pathways that drive cancer initiation and progression. Importantly, these same signaling pathways can be activated by select chemokine receptors. Chemokine receptors are increasingly being revealed as major drivers of the TIC phenotype, as their signaling can lead to activation of stemness-controlling transcription factors. Additionally, the cell surface expression of chemokine receptors provides a unique therapeutic target to disrupt signaling pathways that control the expression of master regulator transcription factors and the TIC phenotype. This review summarizes the master regulator transcription factors known to dictate the TIC phenotype, along with the complex signaling pathways that can mediate their expression and the chemokine receptors that are most upstream of this phenotype.

Expression of CX3CL1 and CCL28 in Spinal Metastases of Lung Adenocarcinoma and Their Correlation with Clinical Features and Prognosis

Lung adenocarcinoma is the most common non-small-cell lung cancer. In this paper, we aim to investigate the expression of chemokine ligand 1 (cx3cl1) and chemokine ligand 28 (CCL28) in spinal metastases of lung adenocarcinoma and their correlation with clinical features and prognosis. We analyzed the clinical data of 40 patients with lung adenocarcinoma and spinal metastases who underwent surgery in our hospital from January 2018 to January 2021 retrospectively. The expression levels of cx3cl1 and CCL28 in bone metastases were detected by immunohistochemistry, and the staining results were sorted and classified. Combined with the follow-up results and clinicopathological data, we statistically analyzed the expression of cx3cl1 and CCL28 in spinal bone metastases and their correlation with prognosis. Among the 40 patients with spinal metastasis of lung adenocarcinoma, 7 cases were strongly positive for cx3cl1, 25 cases were moderately positive, and 8 cases were weakly positive and negative. CCL28 was strongly positive in 9 cases, moderately positive in 26 cases, weakly positive and negative in 5 cases. The expression of cx3cl1 was correlated with ECOG score (P = 0.005) and visceral organ metastasis (P = 0.004), but not with age, sex, and the number of bone metastases (P > 0.05). The expression of CCL28 was correlated with ECOG score (P = 0.022) and visceral organ metastasis (P = 0.003), but not with age, sex, and the number of bone metastases (P > 0.05). The OS of patients with strong cx3cl1 positive was significantly shorter than that of patients with medium positive and weak positive (P < 0.001). The survival time was 10, 7, and 4 months, respectively. The OS of patients with strong positive CCL28 was significantly shorter than that of patients with medium positive and weak positive CCL28 (P = 0.004). The survival time was 12, 8, and 4 months, respectively. Univariate analysis showed that ECOG score (P < 0.001), chemotherapy (P = 0.032), visceral organ metastasis (P = 0.002), cx3cl1 expression (P < 0.001), and CCL28 expression (P = 0.004) were the risk factors of OS. Cox regression analysis showed that the expression of cx3cl1 was an independent risk factor for OS in patients with spinal metastasis of lung adenocarcinoma (P = 0.044). Cx3cl1 and CCL28 were highly/strongly positive in spinal metastases of lung adenocarcinoma. The level of cx3cl1 can be used as an index to judge the clinical prognosis of patients with spinal metastasis of lung adenocarcinoma, which can better reflect the prognosis of patients than CCL28.

Subsets of cancer cells expressing CX3CR1 are endowed with metastasis-initiating properties and resistance to chemotherapy

Metastasis-initiating cells (MICs) display stem cell-like features, cause metastatic recurrences and defy chemotherapy, which leads to patients' demise. Here we show that prostate and breast cancer patients harbor contingents of tumor cells with high expression of CX3CR1, OCT4a (POU5F1), and NANOG. Impairing CX3CR1 expression or signaling hampered the formation of tumor spheroids by cell lines from which we isolated small subsets co-expressing CX3CR1 and stemness-related markers, similarly to patients' tumors. These rare CX3CR1High cells show transcriptomic profiles enriched in pathways that regulate pluripotency and endowed with metastasis-initiating behavior in murine models. Cancer cells lacking these features (CX3CR1Low) were capable of re-acquiring CX3CR1-associated features over time, implying that MICs can continuously emerge from non-stem cancer cells. CX3CR1 expression also conferred resistance to docetaxel, and prolonged treatment with docetaxel selected CX3CR1High phenotypes with de-enriched transcriptomic profiles for apoptotic pathways. These findings nominate CX3CR1 as a novel marker of stem-like tumor cells and provide conceptual ground for future development of approaches targeting CX3CR1 signaling and (re)expression as therapeutic means to prevent or contain metastasis initiation.

The Clinical Implications and Molecular Mechanism of CX3CL1 Expression in Urothelial Bladder Cancer

Background

CX3CL1 is a chemokine that may play important roles in cancer immune regulation. Its mechanism in bladder cancer (BCa) is poorly understood. The objective of the current study was to evaluate the association between CX3CL1 and BCa and the related biological mechanisms.

Methods

A total of 277 patients with BCa were enrolled in the present study. The association between CX3CL1 expression and disease outcome was evaluated. In vitro and in vivo experiments were performed using the TCCSUP cell line to investigate the function of CX3CL1 in BCa.

Results

Compared with low expression, high expression of CX3CL1 was significantly associated with poorer progression-free survival (hazard ratio [HR]=2.03, 95% confidence interval [95% CI]: 1.26-3.27, P=0.006), cancer-specific survival (HR=2.16, 95% CI: 1.59-2.93, P<0.001), and overall survival (HR=1.55, 95% CI: 1.08-2.24, P=0.039). Multivariable Cox regression analysis suggested that CX3CL1 was an independent prognostic factor for BCa outcomes. In vitro and in vivo experiments indicated that high expression of CX3CL1 was significantly associated with cell proliferation (P<0.001) and invasion (P<0.001). Gene expression profiling results showed that after CX3CL1 knockdown, CDH1 was significantly upregulated, while ETS1, RAF1, and EIF4E were significantly downregulated. Pathway enrichment analysis suggested that the ERK/MAPK signaling pathway was significantly inhibited (P<0.001).

Conclusions

CX3CL1 is an independent predictor of a poor prognosis in BCa and can promote the proliferation and invasion of BCa cells.

The Role of Post-Translational Modifications of Chemokines by CD26 in Cancer

Chemokines are a large family of small chemotactic cytokines that fulfill a central function in cancer. Both tumor-promoting and -impeding roles have been ascribed to chemokines, which they exert in a direct or indirect manner. An important post-translational modification that regulates chemokine activity is the NH₂-terminal truncation by peptidases. CD26 is a dipeptidyl peptidase (DPPIV), which typically clips a NH₂-terminal dipeptide from the chemokine. With a certain degree of selectivity in terms of chemokine substrate, CD26 only recognizes chemokines with a penultimate proline or alanine. Chemokines can be protected against CD26 recognition by specific amino acid residues within the chemokine structure, by oligomerization or by binding to cellular glycosaminoglycans (GAGs). Upon truncation, the binding affinity for receptors and GAGs is altered, which influences chemokine function. The consequences of CD26-mediated clipping vary, as unchanged, enhanced, and reduced activities are reported. In tumors, CD26 most likely has the most profound effect on CXCL12 and the interferon (IFN)-inducible CXCR3 ligands, which are converted into receptor antagonists upon truncation. Depending on the tumor type, expression of CD26 is upregulated or downregulated and often results in the preferential generation of the chemokine isoform most favorable for tumor progression. Considering the tight relationship between chemokine sequence and chemokine binding specificity, molecules with the appropriate characteristics can be chemically engineered to provide innovative therapeutic strategies in a cancer setting.

RNA editing enzyme adenosine deaminases acting on RNA 1 deficiency increases the sensitivity of non-small cell lung cancer cells to anlotinib by regulating CX3CR1-fractalkine expression

Adenosine deaminases acting on RNA 1 (ADAR1) has been identified to play key roles in non-small cell lung cancer (NSCLC) progression, and can modulate the sensitivity of cancer cells to anticancer drugs. The current study aimed to investigate the effect of ADAR1 on the sensitivity of NSCLC cells to anlotinib. We established anlotinib-resistant NSCLC (NSCLC/AR) cells, including NCI-H1975/AR and A549/AR cells. Results showed that ADAR1 was significantly upregulated in NSCLC/AR cells. Genetic-knockdown of ADAR1 increased the sensitivity of NSCLC/AR cells to anlotinib by inducing cell proliferation suppression, cell cycle arrest, and apoptosis. Furthermore, knockdown of ADAR1 decreased the level of C-X3-C motif chemokine ligand 1 (CX3CL1) in NCI-H1975/AR and A549/AR cells after anlotinib treatment. Introduction of exogenous CX3CL1 significantly reversed the positive effect of ADAR1 deficiency on NSCLC/AR cell sensitivity, exhibited by the increase of cell viability and decrease of apoptosis. Further in-vivo study demonstrated that knockdown of ADAR1 inhibited NCI-H1975/AR cell tumorigenesis by reducing CX3CL1 expression. Collectively, ADAR1 deficiency increased the sensitivity of NSCLC/AR cells to anlotinib by downregulating CX3CL1, which might provide a potential strategy for NSCLC/AR therapy.

CX3 CL1 promotes tumour cell by inducing tyrosine phosphorylation of cortactin in lung cancer

It has been reported that chemokine CX3 CL1 can regulate various tumours by binding to its unique receptor CX3 CR1. However, the effect of CX3 CL1-CX3 CR1 on the lung adenocarcinoma and lung squamous cell carcinoma is still unclear. Here, we showed that CX3 CL1 can further invasion and migration of lung adenocarcinoma A549 and lung squamous cell carcinoma H520. In addition, Western blot and immunofluorescence test indicated CX3 CL1 up-regulated the phosphorylation level of cortactin, which is a marker of cell pseudopodium. Meanwhile, the phosphorylation levels of c-Src and c-Abl, which are closely related to the regulation of cortactin phosphorylation, are elevated. Nevertheless, the src/abl inhibitor bosutinib and mutations of cortactin phosphorylation site could inhibit the promotion effect of CX3 CL1 on invasion and migration of A549 and H520. Moreover, these results of MTT, Hoechst staining and Western blot suggested that CX3 CL1 had no effect on the proliferation and apoptosis of A549 and H520 in vitro. The effects of CX3 CL1 were also verified by the subcutaneous tumour formation in nude mice, which showed that it could promote proliferation and invasion of A549 in vivo. In summary, our results indicated that CX3 CL1 furthered invasion and migration in lung cancer cells partly via activating cortactin, and CX3 CL1 may be a potential molecule in regulating the migration and invasion of lung cancer.

CX3CR1 positively regulates BCR signaling coupled with cell metabolism via negatively controlling actin remodeling

As an important chemokine receptor, the role of CX3CR1 has been studied extensively on the migration of lymphocytes including T and B cells. Although CX3CR1+ B cells have immune suppressor properties, little is known about its role on the regulation of BCR signaling and B cell differentiation as well as the underlying molecular mechanism. We have used CX3CR1 KO mice to study the effect of CX3CR1 deficiency on BCR signaling and B cell differentiation. Interestingly, we found that proximal BCR signaling, such as the activation of CD19, BTK and SHIP was reduced in CX3CR1 KO B cells upon antigenic stimulation. However, the activation of mTORC signaling was enhanced. Mechanistically, we found that the reduced BCR signaling in CX3CR1 KO B cells was due to reduced BCR clustering, which is caused by the enhanced actin accumulation by the plasma membrane via increased activation of WASP. This caused an increased differentiation of MZ B cells in CX3CR1 KO mice and an enhanced generation of plasma cells (PC) and antibodies. Our study shows that CX3CR1 regulates BCR signaling via actin remodeling and affects B cell differentiation and the humoral immune response.

Cytokines and Chemokines as Mediators of Prostate Cancer Metastasis

The consequences of prostate cancer metastasis remain severe, with huge impact on the mortality and overall quality of life of affected patients. Despite the convoluted interplay and cross talk between various cell types and secreted factors in the metastatic process, cytokine and chemokines, along with their receptors and signaling axis, constitute important factors that help drive the sequence of events that lead to metastasis of prostate cancer. These proteins are involved in extracellular matrix remodeling, epithelial-mesenchymal-transition, angiogenesis, tumor invasion, premetastatic niche creation, extravasation, re-establishment of tumor cells in secondary organs as well as the remodeling of the metastatic tumor microenvironment. This review presents an overview of the main cytokines/chemokines, including IL-6, CXCL12, TGFβ, CXCL8, VEGF, RANKL, CCL2, CX3CL1, IL-1, IL-7, CXCL1, and CXCL16, that exert modulatory roles in prostate cancer metastasis. We also provide extensive description of their aberrant expression patterns in both advanced disease states and metastatic sites, as well as their functional involvement in the various stages of the prostate cancer metastatic process.

Fractalkine/CX3CL1 in Neoplastic Processes

Fractalkine/CX3C chemokine ligand 1 (CX3CL1) is a chemokine involved in the anticancer function of lymphocytes-mainly NK cells, T cells and dendritic cells. Its increased levels in tumors improve the prognosis for cancer patients, although it is also associated with a poorer prognosis in some types of cancers, such as pancreatic ductal adenocarcinoma. This work focuses on the 'hallmarks of cancer' involving CX3CL1 and its receptor CX3CR1. First, we describe signal transduction from CX3CR1 and the role of epidermal growth factor receptor (EGFR) in this process. Next, we present the role of CX3CL1 in the context of cancer, with the focus on angiogenesis, apoptosis resistance and migration and invasion of cancer cells. In particular, we discuss perineural invasion, spinal metastasis and bone metastasis of cancers such as breast cancer, pancreatic cancer and prostate cancer. We extensively discuss the importance of CX3CL1 in the interaction with different cells in the tumor niche: tumor-associated macrophages (TAM), myeloid-derived suppressor cells (MDSC) and microglia. We present the role of CX3CL1 in the development of active human cytomegalovirus (HCMV) infection in glioblastoma multiforme (GBM) brain tumors. Finally, we discuss the possible use of CX3CL1 in immunotherapy.

ADAM17-regulated CX3CL1 expression produced by bone marrow endothelial cells promotes spinal metastasis from hepatocellular carcinoma

Spinal metastasis occurs in 50-75% of bone metastases caused by hepatocellular carcinoma (HCC), and HCC-derived spinal metastasis can lead to a less favorable prognosis. Recently, several studies have demonstrated that C-X3-C motif chemokine ligand 1 (CX3CL1) is closely associated with cancer metastasis, and its secretion is modulated by a disintegrin and metalloproteinase 17 (ADAM17). Bone marrow endothelial cells (BMECs) are an essential component of bone marrow. However, little is known about the roles in and effects of BMECs on HCC spinal metastasis. The present study demonstrated that CX3CL1 and C-X-C motif chemokine receptor 3 (CXCR3) expression was upregulated in HCC spinal metastases, and that CX3CL1 promoted the migration and invasion of HCC cells to the spine. Western blot analysis revealed that the Src/protein tyrosine kinase 2 (PTK2) axis participated in CX3CL1-induced HCC cell invasion and migration. CX3CL1 also increased the expression of M2 macrophage markers in THP-1 monocytes. BMECs promoted the migration and invasion of Hep3B and MHCC97H cells by secreting soluble CX3CL1, whereas the neutralization of CX3CL1 inhibited this enhancement. CX3CL1 enhanced the activation of the phosphatidylinositol-4,5-bisphos-phate 3-kinase catalytic subunit alpha (PIK3CA)/AKT serine/threonine kinase 1 (AKT1) and Ras homolog family member A (RHOA)/Rho associated coiled-coil containing protein kinase 2 (ROCK2) signaling pathways through the Src/PTK2 signaling pathway. Furthermore, ADAM17 was activated by mitogen-activated protein kinase (MAPK) z14 in BMECs and significantly promoted the secretion of CX3CL1. HCC cells enhanced the recruitment and proliferation of BMECs. The overexpression of CX3CR1 facilitated the spinal metastasis of HCC in a mouse model in vivo. In addition, in vivo experiments revealed that BMECs promoted the growth of HCC in the spine. The present study demonstrated that CX3CL1 participates in HCC spinal metastasis, and that BMECs play an important role in the regulation of CX3CL1 in the spinal metastatic environment.

Pivotal Involvement of the CX3CL1-CX3CR1 Axis for the Recruitment of M2 Tumor-Associated Macrophages in Skin Carcinogenesis

We previously revealed the crucial roles of a chemokine, CX3CL1, and its receptor, CX3CR1, in skin wound healing. Although repeated wounds frequently develop into skin cancer, the roles of CX3CL1 in skin carcinogenesis remain elusive. Here, we proved that CX3CL1 protein expression and CX3CR1⁺ macrophages were observed in human skin cancer tissues. Similarly, we observed the enhancement of CX3CL1 expression and the abundant accumulation of CX3CR1⁺ tumor-associated macrophages with M2-like phenotypes in the skin carcinogenesis process induced by the combined treatment with 7,12-dimethylbenz[a]anthracene and 12-O-tetradecanoylphorbol-13-acetate. In this mouse skin carcinogenesis process, CX3CR1⁺ tumor-associated macrophages exhibited M2-like phenotypes with the expression of Wnt3a and angiogenic molecules including VEGF and matrix metalloproteinase 9. Compared with wild-type mice, CX3CR1-deficient mice showed fewer numbers of skin tumors with a lower incidence. Concomitantly, M2-macrophage numbers and neovascularization were reduced with the depressed expression of angiogenic factors and Wnt3a. Thus, the CX3CL1-CX3CR1 axis can crucially contribute to skin carcinogenesis by regulating the accumulation and functions of tumor-associated macrophages. Thus, this axis can be a good target for preventing and/or treating skin cancers.

Proteolytic chemokine cleavage as a regulator of lymphocytic infiltration in solid tumors

In the past decade, immune-based therapies such as monoclonal antibodies against tumor epitopes or immune checkpoint inhibitors have become an integral part of contemporary cancer treatment in many entities. However, a fundamental prerequisite for the success of such therapies is a sufficient trafficking of tumor-infiltrating lymphocytes into the tumor microenvironment. This infiltration is facilitated by chemokines, a group of about 50 small proteins capable of chemotactically guiding leukocytes. Proteolytic inactivation of chemokines leading to an impaired infiltration of immune effector cells appears to be an efficient immune escape mechanism of solid cancers.

The CXCR3 and CX3CR1 chemokine receptor ligands CXCL9-11 and CX3CL1, respectively, are mainly responsible for the tumor-suppressive lymphocytic infiltration into the tumor micromilieu. Their structure explains the biochemical basis of their proteolytic cleavage, while in vivo data from mouse models and patient samples shed light on the corresponding processes in cancer. The emerging roles of proteases, e.g., matrix metalloproteinases, cathepsins, and dipeptidyl peptidase 4, in chemokine inactivation define new resistance mechanisms against immunotherapies and identify attractive new targets to enhance immune intervention in cancer.

Novel Techniques to Study the Bone-Tumor Microenvironment

Many cancers commonly metastasize to bone. After entering the bone, cancer cells can interact with surrounding stromal cells, which ultimately influences metastasis progression. Extracellular vesicles, direct cell contact and gap junctions, and cytokines are all mechanisms of intercellular communication that have been observed to occur in the bone microenvironment. These methods of cellular crosstalk can occur between cancer cells and a variety of stromal cells, with each interaction having a different impact on cancer progression. Communication between cancer cells and bone-resident cells has previously been implicated in processes such as cancer cell trafficking and arrest in bone, cancer cell dormancy, cancer cell reactivation, and proliferation. In this chapter we review innovative techniques and model systems that can be used to study bidirectional crosstalk between cancer cells and stromal cells in the bone, with an emphasis specifically on bone-metastatic breast cancer. Investigating how metastatic cancer cells interact with, and are influenced by, the bone microenvironment is crucial to better understanding of the progression of bone metastasis.

Limiting tumor seeding as a therapeutic approach for metastatic disease

Here we propose that therapeutic targeting of circulating tumor cells (CTCs), which are widely understood to be the seeds of metastasis, would represent an effective strategy towards limiting numerical expansion of secondary lesions and containing overall tumor burden in cancer patients. However, the molecular mediators of tumor seeding have not been well characterized. This is in part due to the limited number of pre-clinical in vivo approaches that appropriately interrogate the mechanisms by which cancer cells home to arresting organs. It is critical that we continue to investigate the mediators of tumor seeding as it is evident that the ability of CTCs to colonize in distant sites is what drives disease progression even after the primary tumor has been ablated by local modalities. In addition to slowing disease progression, containing metastatic spread by impeding tumor cell seeding may also provide a clinical benefit by increasing the duration of the residence of CTCs in systemic circulation thereby increasing their exposure to pharmacological agents commonly used in the treatment of patients such as chemotherapy and immunotherapies. In this review we will examine the current state of knowledge about the mechanisms of tumor cells seeding as well as explore how targeting this stage of metastatic spreading may provide therapeutic benefit to patients with advanced disease.

Protein interaction disruption in cancer

Background

Most methods that integrate network and mutation data to study cancer focus on the effects of genes/proteins, quantifying the effect of mutations or differential expression of a gene and its neighbors, or identifying groups of genes that are significantly up- or down-regulated. However, several mutations are known to disrupt specific protein-protein interactions, and network dynamics are often ignored by such methods. Here we introduce a method that allows for predicting the disruption of specific interactions in cancer patients using somatic mutation data and protein interaction networks.

Methods

We extend standard network smoothing techniques to assign scores to the edges in a protein interaction network in addition to nodes. We use somatic mutations as input to our modified network smoothing method, producing scores that quantify the proximity of each edge to somatic mutations in individual samples.

Results

Using breast cancer mutation data, we show that predicted edges are significantly associated with patient survival and known ligand binding site mutations. In-silico analysis of protein binding further supports the ability of the method to infer novel disrupted interactions and provides a mechanistic explanation for the impact of mutations on key pathways.

Conclusions

Our results show the utility of our method both in identifying disruptions of protein interactions from known ligand binding site mutations, and in selecting novel clinically significant interactions.Supporting website with software and data: https://www.cs.cmu.edu/~mruffalo/mut-edge-disrupt/.

Electronic supplementary material

The online version of this article (10.1186/s12885-019-5532-5) contains supplementary material, which is available to authorized users.

Increased CX3CL1 mRNA expression level is a positive prognostic factor in patients with lung adenocarcinoma

Chemokines are a family of small cytokines, which are signalling proteins secreted by cells. The principal role of chemokines is to serve as chemoattractants to guide the migration of their target cells. Chemokine C-X3-C motif ligand 1 (CX3CL1) is a protein-coding gene of fractalkine, which serves as a ligand for chemokine C-X3-C motif receptor 1 (CX3CR1) and integrins. However, the roles of CX3CL1 in different pathological types of lung cancer remain poorly understood. The present study aimed to investigate the potential clinical and biological function of CX3CL1 mRNA expression in patients with lung cancer. In the present study, lung cancer data obtained from the Gene Expression Omnibus database and The Cancer Genome Atlas were downloaded and analysed, and the results demonstrated that an increased CX3CL1 mRNA expression in tumour tissues from lung adenocarcinoma (LUAD) was associated with improved overall survival. However, no significant association was identified between CX3CL1 expression and the prognosis of lung squamous cell carcinoma (LUSC). Furthermore, the genes whose expression levels were correlated with CX3CL1 expression were subjected to enrichment analysis, and the results for the LUAD data demonstrated that the most significant biological processes included ‘positive regulation of cell adhesion’, ‘leukocyte cell-cell adhesion’, ‘leukocyte migration’ and ‘T cell activation’, whereas, the important highly ranked pathways included ‘cell adhesion molecules (CAMs)’, ‘leukocyte transendothelial migration’ and ‘natural killer cell-mediated cytotoxicity’. However, in the patients with LUSC, the genes that were highly correlated with CX3CL1 were not enriched for any biological processes or signalling pathways. Based on the data of the present study, it was hypothesised that CX3CL1 may serve as a prognostic marker for LUAD.

Higher CXCL16 exodomain is associated with aggressive ovarian cancer and promotes the disease by CXCR6 activation and MMP modulation

Ovarian cancer (OvCa) is the leading cause of death from gynecological malignancies. Five-year survival rate of OvCa ranges from 30–92%, depending on the spread of disease at diagnosis. Role of chemokines is well appreciated in cancer, including OvCa. However, their precise role is understudied. Here, we show clinical and biological significance of CXCR6-CXCL16 and ADAM10 in OvCa. Expression of CXCR6 and N-terminal CXCL16 was significantly higher in serous carcinoma tissues compared to endometrioid. OvCa cells (SKOV-3 and OVCAR-3) also showed higher expression of CXCR6 than normal ovarian epithelial cells (IOSE-7576) while CXCL16 was higher in SKOV-3 than IOSE-7576. Furthermore, N-terminal CXCL16 was higher in conditioned media of OvCa cells than IOSE-7576. Compared to OVCAR-3, SKOV-3 cells, which had higher CXCL16, expressed significantly higher transcripts of ADAM10, a protease that cleaves CXCL16. OVCAR-3 cells showed higher CXCR6 specific migration whereas SKOV-3 cells showed more invasion. Difference in invasive potential of these cells was due to modulation of different MMPs after CXCL16 stimulation. Higher CXCR6 expression in serous papillary carcinoma tissues suggests its association with aggressive OvCa. Increased migration-invasion towards CXCL16 implies its role in metastatic spread. Therefore, CXCR6-CXCL16 axis could be used to differentiate between aggressive versus non-aggressive disease and as a target for better prognosis.

Chemokines and Chemokine Receptors: Orchestrating Tumor Metastasization

Metastasis still represents the primary cause of cancer morbidity and mortality worldwide. Chemokine signalling contributes to the overall process of cancer growth and metastasis, and their expression in both primary tumors and metastatic lesions correlate with prognosis. Chemokines promote tumor metastasization by directly supporting cancer cell survival and invasion, angiogenesis, and by indirectly shaping the pre-metastatic niches and antitumor immunity. Here, we will focus on the relevant chemokine/chemokine receptor axes that have been described to drive the metastatic process. We elaborate on their role in the regulation of tumor angiogenesis and immune cell recruitment at both the primary tumor lesions and the pre-metastatic foci. Furthermore, we also discuss the advantages and limits of current pharmacological strategies developed to target chemokine networks for cancer therapy.

CX3CL1 involves in breast cancer metastasizing to the spine via the Src/FAK signaling pathway

C-X3-C chemokine ligand 1 (CX3CL1) has been shown to be involved in the development of multiple tumors. Our previous study demonstrated that CX3CL1 may be involved in the process of metastasis of various malignant tumors to the spine, including breast cancer, but the molecular mechanism was still unknown. In the present study, we found that the receptor CX3CR1 was overexpressed in the spinal metastases of breast cancer than in para-tumor tissue. In terms of CX3CL1, it was significantly more expressed in normal spinal cancellous bone than in limbs. However, CX3CR1 was not expressed at a high level in every breast cancer cell compared with the human mammary epithelial cell line MCF-10A. In addition, CX3CL1 did promote the migration and invasion abilities of MDA-MB-231 cells. However, CX3CL1 has no obvious effect on cell growth. Furthermore, CX3CL1 induced chemotaxis of tumor cells via the Src/FAK signaling pathway. The migration index enhanced by CX3CL1 was dramatically declined using Bosutinib and PF-00562271, which are the inhibitors of Src and FAK signaling pathways, respectively. Therefore, CX3CL1 in spinal cancellous bone attracts CX3CR1-expressing tumor cells to the spine and enhances their migration and invasion abilities through the Src/FAK signaling pathway.

CX3CL1/fractalkine enhances prostate cancer spinal metastasis by activating the Src/FAK pathway

Chemokines serve important roles in the development of cancer. C-X3-C motif chemokine ligand 1 (CX3CL1) has been demonstrated to promote metastases in different types of tumors. The authors' previous studies demonstrated that the CX3CL1 (also termed fractalkine)/steroid receptor coactivator (Src)/focal adhesion kinase (FAK) signaling pathway is associated with spinal metastasis. In the present study, it was observed that CX3CL1/C-X3-C motif chemokine receptor 1 (CX3CR1) was overexpressed in prostate cancer tissues with spinal metastasis compared with primary tumors. Overexpression of CX3CR1 induced cell proliferation, migration and invasion, and inhibited cellular apoptosis. However, repression of CX3CR1 reduced cell proliferation, migration and invasion, and increased cellular apoptosis. In addition, the Src/FAK pathway was activated by CX3CL1, which depends on the Tyr992 residue of epidermal growth factor receptor (EGFR) for phosphorylation. The inhibitors of these kinases repressed the cell migration induced by CX3CL1 or CX3CR1 overexpression. Furthermore, overexpression of CX3CR1 induced the spinal metastasis of prostate cancer in an in vivo mouse model. Therefore, CX3CL1 and its regulation of the EGFR, Src and FAK pathways may be potential targets for the early prevention of spinal metastasis in prostate cancer.

Fatty Acids and Calcium Regulation in Prostate Cancer

Prostate cancer is a widespread malignancy characterized by a comparative ease of primary diagnosis and difficulty in choosing the individualized course of treatment. Management of prostate cancer would benefit from a clearer understanding of the molecular mechanisms behind the transition to the lethal, late-stage forms of the disease, which could potentially yield new biomarkers for differential prognosis and treatment prioritization in addition to possible new therapeutic targets. Epidemiological research has uncovered a significant correlation of prostate cancer incidence and progression with the intake (and often co-intake) of fatty acids and calcium. Additionally, there is evidence of the impact of these nutrients on intracellular signaling, including the mechanisms mediated by the calcium ion as a second messenger. The present review surveys the recent literature on the molecular mechanisms associated with the critical steps in the prostate cancer progression, with special attention paid to the regulation of these processes by fatty acids and calcium homeostasis. Testable hypotheses are put forward that integrate some of the recent results in a more unified picture of these phenomena at the interface of cell signaling and metabolism.

Cancer Metastases to Bone: Concepts, Mechanisms, and Interactions with Bone Osteoblasts

The skeleton is a unique structure capable of providing support for the body. Bone resorption and deposition are controlled in a tightly regulated balance between osteoblasts and osteoclasts with no net bone gain or loss. However, under conditions of disease, the balance between bone resorption and deposition is upset. Osteoblasts play an important role in bone homeostasis by depositing new bone osteoid into resorption pits. It is becoming increasingly evident that osteoblasts additionally play key roles in cancer cell dissemination to bone and subsequent metastasis. Our laboratory has evidence that when osteoblasts come into contact with disseminated breast cancer cells, the osteoblasts produce factors that initially reduce breast cancer cell proliferation, yet promote cancer cell survival in bone. Other laboratories have demonstrated that osteoblasts both directly and indirectly contribute to dormant cancer cell reactivation in bone. Moreover, we have demonstrated that osteoblasts undergo an inflammatory stress response in late stages of breast cancer, and produce inflammatory cytokines that are maintenance and survival factors for breast cancer cells and osteoclasts. Advances in understanding interactions between osteoblasts, osteoclasts, and bone metastatic cancer cells will aid in controlling and ultimately preventing cancer cell metastasis to bone.

Lymphatic exosomes promote dendritic cell migration along guidance cues

Inflammation stimulates lymphatic endothelial cells to release exosomes, which accumulate in the perivascular stroma. Brown et al. show that these exosomes promote the directional migration of dendritic cells along guidance cues in complex environments by enhancing dynamic cellular protrusions in a CX3CL1-dependent manner.

Lymphatic endothelial cells (LECs) release extracellular chemokines to guide the migration of dendritic cells. In this study, we report that LECs also release basolateral exosome-rich endothelial vesicles (EEVs) that are secreted in greater numbers in the presence of inflammatory cytokines and accumulate in the perivascular stroma of small lymphatic vessels in human chronic inflammatory diseases. Proteomic analyses of EEV fractions identified >1,700 cargo proteins and revealed a dominant motility-promoting protein signature. In vitro and ex vivo EEV fractions augmented cellular protrusion formation in a CX3CL1/fractalkine-dependent fashion and enhanced the directional migratory response of human dendritic cells along guidance cues. We conclude that perilymphatic LEC exosomes enhance exploratory behavior and thus promote directional migration of CX3CR1-expressing cells in complex tissue environments.

Functions of chemokines in the perineural invasion of tumors (Review)

The perineural invasion (PNI) of malignant tumors is a form of tumor progression in which cancer cells encroach along nerves. PNI hinders curative resection. Residual tumor cells in or around nerves can bring about local recurrence, infiltration and metastasis. This behavior is usually associated with a poor clinical prognosis. Therefore, it is necessary to investigate novel ligand-receptor crosstalk between nerves and tumor cells that promote the process of PNI. Chemokines are regarded as one of pivotal factors involved in the process of PNI. The present review collates information provided by previous studies with regard to the role of chemokines in PNI. The study presents a definition of PNI in cancer, generalizes the biological characteristics and the expression of chemokines and their receptors in cancer types associated with PNI, and discusses the underlying molecular mechanisms of chemokines, the reciprocal interactions between chemokines and other factors in PNI, and the interconnectivity of the microenvironment and chemokines. The aim of the review is to thoroughly illustrate the molecular cues of chemokines in cancer with PNI and to identify novel antitumor targets.

Inhibition of CX3CR1 reduces cell motility and viability in pancreatic adenocarcinoma epithelial cells

Increased expression of the chemokine CX₃CL1 and its sole receptor, CX₃CR1 have been correlated with poor pancreatic cancer patient survival and time to recurrence, as well as with pancreatic perineural invasion. We have previously shown that metastasis of prostate and breast cancer is in part driven by CX₃CL1, and have developed small molecule inhibitors against the CX₃CR1 receptor that diminish metastatic burden. Here we ask if inhibition of this chemokine receptor affects the phenotype of PDAC tumor cells. Our findings demonstrate that motility, invasion, and contact-independent growth of PDAC cells all increase following CX₃CL1 exposure, and that antagonism of CX₃CR1 by the inhibitor JMS-17-2 reduces each of these phenotypes and correlates with a downregulation of AKT phosphorylation. These data suggest that PDAC tumor cell migration and growth, elements critical in metastatic progression, may susceptible to pharmacologic intervention.

CX3CL1: a potential chemokine widely involved in the process spinal metastases

Objectives

The aim of our study was to investigate the general mechanism of spinal metastases from five different primary cancers: lung cancer, breast cancer, liver cancer, prostate cancer, and kidney cancer.

Results

From microarray analysis and validation by real-time polymerase chain reaction, CX3C chemokine ligand 1 (CX3CL1) appeared to be a potential chemokine widely involved in the process of spinal metastases. Further studies revealed that, compared with normal controls, serum samples from patients with spinal metastases from the lung (P < 0.01), kidney (P < 0.05) and prostate (P < 0.05) contained significantly higher levels of CX3CL1, whereas those from patients with spinal metastases from the liver and breast had a tendency to contain higher levels of CX3CL1 but without significance. Immunohistochemical staining for the expression of CX3C chemokine receptor 1 (CX3CR1), the receptor for CX3CL1, in all spinal metastases samples showed negative staining.

Materials and Methods

Cancellous bone in the spine from patients with and without spinal metastases was collected for mRNA microarray study, and then differentially expressed mRNAs related to chemokines were further confirmed by real-time polymerase chain reaction. Enzyme linked immunosorbent assay was used to detect the serum level of the selected chemokines and immunohistochemical staining was used to detect the expression level of corresponding receptors in tumor.

Conclusions

Our present study showed that CX3CL1 is associated with the process of spinal metastases from different primary cancers.

Fractalkine/CX3CR1 axis modulated the development of pancreatic ductal adenocarcinoma via JAK/STAT signaling pathway

Pancreatic ductal adenocarcinoma (PDAC) is a fatal malignancy with an estimated 5 year survival rate of approximately 5% of all stages combined. High potential of PDAC metastasis is a leading cause for high mortality and poor prognosis. The majority of patients present with distant metastasis at diagnosis. Fractalkine (FKN) is recognized as a chemokine and a specific ligand of CX3CR1. It has been reported that FKN/CX3CR1 system was upregulated in many types of solid tumors. However, role of FKN/CX3CR1 in PDAC development remains unclear. In the current investigation, we found that FKN and CX3CR1 expression was significantly increased in PDAC tissues, especially in the metastatic samples, and was highly-correlated with severity of PDAC. Ectopic expression of FKN promoted the proliferation and migration of PDAC, while knockdown of CX3CR1 reversed the function of FKN. In addition, PDAC cells with FKN-deficiency showed impaired proliferation and migration activity. The underlying mechanism is that FKN/CX3CR1 activated JAK/STAT signaling, which in turn regulated cell growth. Consistently, in vivo tumorigenesis assay validated the regulatory role of FKN/CX3CR1 in PDAC growth. Our investigation helped understanding the pathogenesis of PDAC occurrence, and demonstrated critical role of FKN/CX3CR1 in PDAC development.

Fractalkine/CX3CR1 induces apoptosis resistance and proliferation through the activation of the AKT/NF-κB cascade in pancreatic cancer cells

Fractalkine (FKN, CX3CL1) is highly expressed in a majority of malignant solid tumours. Fractalkine is the only known ligand for CX3CR1. In this study, we performed an analysis to determine the effects of fractalkine/CX3CR1 on modulating apoptosis and explored the related mechanisms. The expression of fractalkine/CX3CR1 was detected by immunohistochemistry and western blotting. The levels of AKT/p-AKT, BCL-xl, and BCL-2 were detected by western blotting. Then, the effects of exogenous and endogenous fractalkine on the regulation of tumour apoptosis and proliferation were investigated. The mechanism of fractalkine/CX3CR1 on modulating apoptosis in cancer cells through the activation of AKT/NF-κB/p65 signals was evaluated. The effect of fractalkine on regulating cell cycle distribution was also tested. Fractalkine, AKT/p-AKT, and apoptotic regulatory proteins BCL-xl and BCL-2 were highly expressed in human pancreatic cancer tissues. In vitro, fractalkine/CX3CR1 promoted proliferation and mediated resistance to apoptosis in pancreatic cancer cells. The antiapoptotic effect of fractalkine was induced by the activation of AKT/NF-κB/p65 signalling in pancreatic cancer cells. The NF-κB/p65 contributes to promote the expressions of BCL-xl and BCL-2 and reduce caspase activity, thereby inhibiting apoptotic processes. Treatment with fractalkine resulted in the enrichment of pancreatic cancer cells in S phase with a concomitant decrease in the number of cells in G1 phase. The present study demonstrated the function of fractalkine in the activation of the AKT/NF-κB/p65 signalling cascade and mediation of apoptosis resistance in pancreatic cancer cells. Fractalkine/CX3CR1 could serve as a diagnostic marker and as a potential target for chemotherapy in early stage pancreatic cancer. Pancreatic cancer is characterized by local recurrence, neural invasion, or distant metastasis. The present study demonstrated the overexpression of fractalkine/CX3CR1 in pancreatic cancer tissues, indicating its important role in the tumourigenesis of pancreatic cancer, and suggested that the overexpression of fractalkine/CX3CR1 could serve as a diagnostic marker for pancreatic cancer. Moreover, we reveal the mechanism that fractalkine functions on the activation of the AKT/NF-κB/p65 signalling cascade and regulation of the antiapoptosis process in pancreatic cancer cells. Fractalkine/CX3CR1 could serve as an effective therapeutic target of chemotherapeutic and biologic agents in early stage pancreatic cancer.

Screening of cancer tissue arrays identifies CXCR4 on adrenocortical carcinoma: correlates with expression and quantification on metastases using 64Cu-plerixafor PET

Expression of the chemokine receptor CXCR4 by many cancers correlates with aggressive clinical behavior. As part of the initial studies in a project whose goal was to quantify CXCR4 expression on cancers non-invasively, we examined CXCR4 expression in cancer samples by immunohistochemistry using a validated anti-CXCR4 antibody. Among solid tumors, we found expression of CXCR4 on significant percentages of major types of kidney, lung, and pancreatic adenocarcinomas, and, notably, on metastases of clear cell renal cell carcinoma and squamous cell carcinoma of the lung. We found particularly high expression of CXCR4 on adrenocortical cancer (ACC) metastases. Microarrays of ACC metastases revealed correlations between expression of CXCR4 and other chemokine system genes, particularly CXCR7/ACKR3, which encodes an atypical chemokine receptor that shares a ligand, CXCL12, with CXCR4. A first-in-human study using ⁶⁴Cu-plerixafor for PET in an ACC patient prior to resection of metastases showed heterogeneity among metastatic nodules and good correlations among PET SUVs, CXCR4 staining, and CXCR4 mRNA. Additionally, we were able to show that CXCR4 expression correlated with the rates of growth of the pulmonary lesions in this patient. Further studies are needed to understand better the role of CXCR4 in ACC and whether targeting it may be beneficial. In this regard, non-invasive methods for assessing CXCR4 expression, such as PET using ⁶⁴Cu-plerixafor, should be important investigative tools.

Pathophysiology of bone metastases from solid malignancies

Bone metastases are common complications of many cancers. Among the mechanisms that set the scene for the development of bone metastases, several are shared by all forms of metastatic dissemination (pre-metastatic niche formation and chemotactic attraction of malignant cells, which invade the host tissue) and others are specific of bone tissue (homing of malignant cells to bone marrow niches and acquisition of an osteomimetic cell phenotype). After a latency period that can last several years, the malignant cells can proliferate into tumors that alter the normal bone remodeling process by inducing dysregulation of osteoblast and osteoclast function. These metastases may be lytic, characterized by major bone destruction; sclerotic, with excess bone formation; or mixed. Osteolysis occurs when the tumor cells stimulate osteoclast activity and inhibit osteoblast activity, whereas the opposite effects lead to bone sclerosis. Moreover, the mineralized bone matrix plays a major role in the formation of bone metastases, as its degradation releases growth factors and calcium that exert mitogenic effects on tumor cells. Thus, bone metastases are the site of a vicious circle in which mechanisms involved in bone resorption/formation promote tumor growth and vice versa.

Bone: A Fertile Soil for Cancer Metastasis

Bone is one of the most common and most dangerous sites for metastatic growth across cancer types, and bone metastasis remains incurable. Unfortunately, the processes by which cancers preferentially metastasize to bone are still not well understood. In this review, we summarize the morphological features, physical properties, and cell signaling events that make bone a unique site for metastasis and bone remodeling. The signaling crosstalk between the tumor cells and bone cells begins a vicious cycle - a self-sustaining feedback loop between the tumor cells and the bone microenvironment composed of osteoclasts, osteoblasts, other bone marrow cells, bone matrix, and vasculature to support both tumor growth and bone destruction. Through this crosstalk, bone provides a fertile microenvironment that can harbor dormant tumor cells, sometimes for long periods, and support their growth by releasing cytokines as the bone matrix is destroyed, similar to providing nutrients for a seed to germinate in soil. However, few models exist to study the late stages of bone colonization by metastatic tumor cells. We describe some of the current methodologies used to study bone metastasis, highlighting the limitations of these methods and alternative future strategies to be used to study bone metastasis. While <i>in vivo</i> animal and patient studies may provide the gold standard for studying metastasis, <i>ex vivo</i> models can be used as an alternative to enable more controlled experiments designed to study the late stages of bone metastasis.

Andrographolide inhibits prostate cancer by targeting cell cycle regulators, CXCR3 and CXCR7 chemokine receptors

Despite state of the art cancer diagnostics and therapies offered in clinic, prostate cancer (PCa) remains the second leading cause of cancer-related deaths. Hence, more robust therapeutic/preventive regimes are required to combat this lethal disease. In the current study, we have tested the efficacy of Andrographolide (AG), a bioactive diterpenoid isolated from Andrographis paniculata, against PCa. This natural agent selectively affects PCa cell viability in a dose and time-dependent manner, without affecting primary prostate epithelial cells. Furthermore, AG showed differential effect on cell cycle phases in LNCaP, C4-2b and PC3 cells compared to retinoblastoma protein (RB(-/-)) and CDKN2A lacking DU-145 cells. G2/M transition was blocked in LNCaP, C4-2b and PC3 after AG treatment whereas DU-145 cells failed to transit G1/S phase. This difference was primarily due to differential activation of cell cycle regulators in these cell lines. Levels of cyclin A2 after AG treatment increased in all PCa cells line. Cyclin B1 levels increased in LNCaP and PC3, decreased in C4-2b and showed no difference in DU-145 cells after AG treatment. AG decreased cyclin E2 levels only in PC3 and DU-145 cells. It also altered Rb, H3, Wee1 and CDC2 phosphorylation in PCa cells. Intriguingly, AG reduced cell viability and the ability of PCa cells to migrate via modulating CXCL11 and CXCR3 and CXCR7 expression. The significant impact of AG on cellular and molecular processes involved in PCa progression suggests its potential use as a therapeutic and/or preventive agent for PCa.