Sensitization of B16 tumor cells with a CXCR4 antagonist increases the efficacy of immunotherapy for established lung metastases

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

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

A protocol for quantifying lymphocyte-mediated cytotoxicity using an impedance-based real-time cell analyzer

Current standard assays to analyze lymphocyte-mediated antitumor cytotoxicity employ radioisotopic or fluorescent labels. However, such assays are not suitable for real-time analysis. Here we describe a protocol that facilitates the analysis of lymphocyte-mediated toxicity using a label-free, impedance-based real-time cell analyzer. This analyzer measures cellular electrical impedance, expressed as the cell index value, noninvasively and continuously. In contrast with label-dependent assays, this protocol simultaneously generates real-time killing curves useful for quantifying lymphocyte-mediated cytotoxicity in real time.

For complete details on the use and execution of this protocol, please refer to Kanemaru et al. (2021).

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A label-independent assay assesses lymphocyte-mediated cytotoxicity

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Cellular electrical impedance expressed as the cell index value

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Continuous and noninvasive measurements of changes in cell number

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Generates real-time killing curves, in contrast to label-dependent assays

Beyond Cell Motility: The Expanding Roles of Chemokines and Their Receptors in Malignancy

The anti-tumor activities of some members of the chemokine family are often overcome by the functions of many chemokines that are strongly and causatively linked with increased tumor progression. Being key leukocyte attractants, chemokines promote the presence of inflammatory pro-tumor myeloid cells and immune-suppressive cells in tumors and metastases. In parallel, chemokines elevate additional pro-cancerous processes that depend on cell motility: endothelial cell migration (angiogenesis), recruitment of mesenchymal stem cells (MSCs) and site-specific metastasis. However, the array of chemokine activities in cancer expands beyond such “typical” migration-related processes and includes chemokine-induced/mediated atypical functions that do not activate directly motility processes; these non-conventional chemokine functions provide the tumor cells with new sets of detrimental tools. Within this scope, this review article addresses the roles of chemokines and their receptors at atypical levels that are exerted on the cancer cell themselves: promoting tumor cell proliferation and survival; controlling tumor cell senescence; enriching tumors with cancer stem cells; inducing metastasis-related functions such as epithelial-to-mesenchymal transition (EMT) and elevated expression of matrix metalloproteinases (MMPs); and promoting resistance to chemotherapy and to endocrine therapy. The review also describes atypical effects of chemokines at the tumor microenvironment: their ability to up-regulate/stabilize the expression of inhibitory immune checkpoints and to reduce the efficacy of their blockade; to induce bone remodeling and elevate osteoclastogenesis/bone resorption; and to mediate tumor-stromal interactions that promote cancer progression. To illustrate this expanding array of atypical chemokine activities at the cancer setting, the review focuses on major metastasis-promoting inflammatory chemokines—including CXCL8 (IL-8), CCL2 (MCP-1), and CCL5 (RANTES)—and their receptors. In addition, non-conventional activities of CXCL12 which is a key regulator of tumor progression, and its CXCR4 receptor are described, alongside with the other CXCL12-binding receptor CXCR7 (RDC1). CXCR7, a member of the subgroup of atypical chemokine receptors (ACKRs) known also as ACKR3, opens the gate for discussion of atypical activities of additional ACKRs in cancer: ACKR1 (DARC, Duffy), ACKR2 (D6), and ACKR4 (CCRL1). The mechanisms involved in chemokine activities and the signals delivered by their receptors are described, and the clinical implications of these findings are discussed.

Emerging role of mTOR in tumor immune contexture: Impact on chemokine-related immune cells migration

During the last few decades, cell-based anti-tumor immunotherapy emerged and it has provided us with a large amount of knowledge. Upon chemokines recognition, immune cells undergo rapid trafficking and activation in disease milieu, with immune cells chemotaxis being accompanied by activation of diverse intercellular signal transduction pathways. The outcome of chemokines-mediated immune cells chemotaxis interacts with the cue of mammalian target of rapamycin (mTOR) in the tumor microenvironment (TME). Indeed, the mTOR cascade in immune cells involves migration and infiltration. In this review, we summarize the available mTOR-related chemokines, as well as the characterized upstream regulators and downstream targets in immune cells chemotaxis and assign potential underlying mechanisms in each evaluated chemokine. Specifically, we focus on the involvement of mTOR in chemokine-mediated immune related cells in the balance between tumor immunity and malignancy.

Therapy-Induced Changes in CXCR4 Expression in Tumor Xenografts Can Be Monitored Noninvasively with N-[11C]Methyl-AMD3465 PET

Purpose

Chemokine CXCL12 and its receptor CXCR4 are constitutively overexpressed in human cancers. The CXCL12-CXCR4 signaling axis plays an important role in tumor progression and metastasis, but also in treatment-induced recruitment of CXCR4-expressing cytotoxic immune cells. Here, we aimed to demonstrate the feasibility of N-[¹¹C]methyl-AMD3465 positron emission tomography (PET) to monitor changes in CXCR4 density in tumors after single-fraction local radiotherapy or in combination with immunization.

Procedure

TC-1 cells expressing human papillomavirus antigens E6 and E7 were inoculated into the C57BL/6 mice subcutaneously. Two weeks after tumor cell inoculation, mice were irradiated with a single-fraction 14-Gy dose of X-ray. One group of irradiated mice was immunized with an alpha-viral vector vaccine, SFVeE6,7, and another group received daily injections of the CXCR4 antagonist AMD3100 (3 mg/kg -intraperitoneal (i.p.)). Seven days after irradiation, all animals underwent N-[¹¹C]methyl-AMD3465 PET.

Results

PET imaging showed N-[¹¹C]methyl-AMD3465 uptake in the tumor of single-fraction irradiated mice was nearly 2.5-fold higher than in sham-irradiated tumors (1.07 ± 0.31 %ID/g vs. 0.42 ± 0.05 % ID/g, p < 0.01). The tumor uptake was further increased by 4-fold (1.73 ± 0.17 % ID/g vs 0.42 ± 0.05 % ID/g, p < 0.01) in mice treated with single-fraction radiotherapy in combination with SFVeE6,7 immunization. Administration of AMD3100 caused a 4.5-fold reduction in the tracer uptake in the tumor of irradiated animals (0.24 ± 0.1 % ID/g, p < 0.001), suggesting that tracer uptake is indeed due to CXCR4-mediated chemotaxis.

Conclusion

This study demonstrates the feasibility of N-[¹¹C]methyl-AMD3465 PET imaging to monitor treatment-induced changes in the density of CXCR4 receptors in tumors and justifies further evaluation of CXCR4 as a potential imaging biomarker for evaluation of anti-tumor therapies.

CXCL12/CXCR4 signal transduction in diseases and its molecular approaches in targeted-therapy

Chemokines are small molecules called "chemotactic cytokines" and regulate many processes like leukocyte trafficking, homing of immune cells, maturation, cytoskeletal rearrangement, physiology, migration during development, and host immune responses. These proteins bind to their corresponding 7-membrane G-protein-coupled receptors. Chemokines and their receptors are anti-inflammatory factors in autoimmune conditions, so consider as potential targets for neutralization in such diseases. They also express by cancer cells and function as angiogenic factors, and/or survival/growth factors that enhance tumor angiogenesis and development. Among chemokines, the CXCL12/CXCR4 axis has significantly been studied in numerous cancers and autoimmune diseases. CXCL12 is a homeostatic chemokine, which is acts as an anti-inflammatory chemokine during autoimmune inflammatory responses. In cancer cells, CXCL12 acts as an angiogenic, proliferative agent and regulates tumor cell apoptosis as well. CXCR4 has a role in leukocyte chemotaxis in inflammatory situations in numerous autoimmune diseases, as well as the high levels of CXCR4, observed in different types of human cancers. These findings suggest CXCL12/CXCR4 as a potential therapeutic target for therapy of autoimmune diseases and open a new approach to targeted-therapy of cancers by neutralizing CXCL12 and CXCR4. In this paper, we reviewed the current understanding of the role of the CXCL12/CXCR4 axis in disease pathology and cancer biology, and discuss its therapeutic implications in cancer and diseases.

C-X-C Chemokine Receptor 4 in Diffuse Large B Cell Lymphoma: Achievements and Challenges

Diffuse large B cell lymphoma (DLBCL), an aggressive cancer of the B cells, is the most common subtype of non-Hodgkin lymphoma (NHL) worldwide. In China, the cases of DLBCL increase yearly. C-X-C chemokine receptor 4 (CXCR4) has been implicated in the migration and trafficking of malignant B cells in several hematological malignancies, and only a few reports have been published on the role of CXCR4 in the metastasis of DLBCL. This review summarizes the relevant perspectives on the functional mechanism, prognostic significance, and therapeutic applications of the CXCL12/CXCR4 axis in DLBCL, in particular DLBCL with bone marrow involvement.

Systematic Review of the Prognostic Role of the Immune System After Surgery of Colorectal Liver Metastases

Background: The current prognostication of patient survival after surgery for colorectal liver metastases is based on clinical characteristics, but low accuracy makes it difficult to guide treatment for the individual patient. Rapidly evolving technologies have led to the expectation that biomarkers will be able to outperform the current clinical scoring systems and provide more effective personalised treatment. Two main topics prevail in cancer treatment, namely the role of the immune system and the prediction and prognostication by application of high-throughput methodology. The aim of this review is to examine the evidence for prognostic immunological and molecular markers studied in tumour tissue obtained at surgical resection for colorectal liver metastases.

Methods: First we analysed immunophenotypical protein markers, that are mainly studied by immunohistochemistry. Second, we review molecular markers by analysing high-throughput studies on tumour mRNA and microRNA expression.

Results: CD3, CD4, and CD8 are the most frequently studied protein markers. High intra-tumoural CD3+ T cell infiltration and low CXCR4 expression have the best association with favourable patient survival. Studies that analysed microRNA or mRNA expression data showed very little overlap in prognostic genes.

Conclusions: Patient prognostication after surgery for colorectal liver metastases by analysing the immune system remains difficult. Current data are based on diverse and heterogeneous patient populations which prohibits drawing firm conclusions.

A framework for the development of effective anti-metastatic agents

Most cancer-related deaths are a result of metastasis, and thus the importance of this process as a target of therapy cannot be understated. By asking 'how can we effectively treat cancer?', we do not capture the complexity of a disease encompassing >200 different cancer types - many consisting of multiple subtypes - with considerable intratumoural heterogeneity, which can result in variable responses to a specific therapy. Moreover, we have much less information on the pathophysiological characteristics of metastases than is available for the primary tumour. Most disseminated tumour cells that arrive in distant tissues, surrounded by unfamiliar cells and a foreign microenvironment, are likely to die; however, those that survive can generate metastatic tumours with a markedly different biology from that of the primary tumour. To treat metastasis effectively, we must inhibit fundamental metastatic processes and develop specific preclinical and clinical strategies that do not rely on primary tumour responses. To address this crucial issue, Cancer Research UK and Cancer Therapeutics CRC Australia formed a Metastasis Working Group with representatives from not-for-profit, academic, government, industry and regulatory bodies in order to develop recommendations on how to tackle the challenges associated with treating (micro)metastatic disease. Herein, we describe the challenges identified as well as the proposed approaches for discovering and developing anticancer agents designed specifically to prevent or delay the metastatic outgrowth of cancer.

CXCR4 Ligands: The Next Big Hit?

The G protein-coupled protein receptor C-X-C chemokine receptor 4 (CXCR4) is an attractive target for cancer diagnosis and treatment, as it is overexpressed in many solid and hematologic cancers. Binding of its ligand, C-X-C chemokine ligand 12 (CXCL12), results in receptor internalization and activation of several signal transduction pathways, such as phosphoinositide 3-kinase/protein kinase B, which are critical in cell proliferation, angiogenesis, development of metastasis, and survival. Also, the CXCR4-CXCL12 axis is involved in the interaction between hematopoietic stem cells (as well as hematologic and solid tumor cells) and their protective microenvironment. This interaction can be disrupted by CXCR4 antagonists. This concept is being used clinically to harvest hematopoietic stem or progenitor cells from bone marrow and to sensitize cancer cells to conventional chemotherapy and radiotherapy, and the potential to overcome tumor microenvironment-driven immunosuppression is being explored. This review focuses on new strategies for improvement of cancer treatment by targeting of the CXCR4-CXCL12 interaction. Because of its critical role in cancer, many peptidic and nonpeptidic ligands with different modes of antagonistic activity against the CXCR4-CXCL12 axis have been developed, with some of them reaching clinical trials. Molecular imaging with recently developed radiolabeled CXCR4 ligands could facilitate the selection of patients who might benefit from directed targeted therapy, including CXCR4-directed endoradiotherapy.

Protein-only, antimicrobial peptide-containing recombinant nanoparticles with inherent built-in antibacterial activity

The emergence of bacterial antibiotic resistances is a serious concern in human and animal health. In this context, naturally occurring cationic antimicrobial peptides (AMPs) might play a main role in a next generation of drugs against bacterial infections. Taking an innovative approach to design self-organizing functional proteins, we have generated here protein-only nanoparticles with intrinsic AMP microbicide activity. Using a recombinant version of the GWH1 antimicrobial peptide as building block, these materials show a wide antibacterial activity spectrum in absence of detectable toxicity on mammalian cells. The GWH1-based nanoparticles combine clinically appealing properties of nanoscale materials with full biocompatibility, structural and functional plasticity and biological efficacy exhibited by proteins. Because of the largely implemented biological fabrication of recombinant protein drugs, the protein-based platform presented here represents a novel and scalable strategy in antimicrobial drug design, that by solving some of the limitations of AMPs offers a promising alternative to conventional antibiotics.

STATEMENT OF SIGNIFICANCE

The low molecular weight antimicrobial peptide GWH1 has been engineered to oligomerize as self-assembling protein-only nanoparticles of around 50nm. In this form, the peptide exhibits potent and broad antibacterial activities against both Gram-positive and Gram-negative bacteria, without any harmful effect over mammalian cells. As a solid proof-of-concept, this finding strongly supports the design and biofabrication of nanoscale antimicrobial materials with in-built functionalities. The protein-based homogeneous composition offer advantages over alternative materials explored as antimicrobial agents, regarding biocompatibility, biodegradability and environmental suitability. Beyond the described prototype, this transversal engineering concept has wide applicability in the design of novel nanomedicines for advanced treatments of bacterial infections.

The CXCR4 antagonist plerixafor enhances the effect of rituximab in diffuse large B-cell lymphoma cell lines

Background

Diffuse large B-cell lymphoma (DLBCL) is an aggressive disease with variable clinical outcome, accounting for at least 25-30 % of adult non-Hodgkin lymphomas. Approximately one third of DLBCL patients are not cured by the currently used treatment regimen, R-CHOP. Hence, new treatment strategies are needed. Antagonizing the CXCR4 receptor might be promising since the CXCR4-CXCL12 axis is implicated in several aspects of tumor pathogenesis as well as in protection from chemotherapeutic response. In Burkitt lymphoma, the CXCR4 antagonist plerixafor has already been shown to enhance the therapeutic effect of rituximab, the immunotherapeutic agent of R-CHOP; but this is yet to be confirmed for DLBCL. We, therefore, investigated the effect of plerixafor on DLBCL cellular response to rituximab.

Methods

In this in vitro study, human DLBCL cell lines were treated with rituximab and/or plerixafor, concomitantly or in sequence. The trypan blue exclusion method and MTS-based assays were used to evaluate cellular proliferation, whereas flow cytometry was used for assessment of apoptosis status and CXCR4 surface expression level. Linear mixed effects models were used to assess statistical significance.

Results

We observed that simultaneous addition of plerixafor and rituximab resulted in a significant decrease in DLBCL cellular proliferation, compared to monotherapeutic response. The effect was dose-dependent, and concomitant administration was observed to be superior to sequential drug administration. Accordingly, the fraction of apoptotic/dead cells significantly increased following addition of plerixafor to rituximab treatment. Furthermore, exposure of DLBCL cells to plerixafor resulted in a significant decrease in CXCR4 fluorescence intensity.

Conclusions

Based on our results, implying that the anti-proliferative/pro-apoptotic effect of rituximab on DLBCL cells can be synergistically enhanced by the CXCR4 antagonist plerixafor, addition of plerixafor to the R-CHOP regimen can be suggested to improve treatment outcome for DLBCL patients.

Electronic supplementary material

The online version of this article (doi:10.1186/s40364-016-0067-2) contains supplementary material, which is available to authorized users.

PAX3 and FOXD3 Promote CXCR4 Expression in Melanoma

Metastatic melanoma is an aggressive and deadly disease. The chemokine receptor CXCR4 is active in melanoma metastasis, although the mechanism for the promotion and maintenance of CXCR4 expression in these cells is mostly unknown. Here, we find melanoma cells express two CXCR4 isoforms, the common version and a variant that is normally restricted to cells during development or to mature blood cells. CXCR4 expression is driven through a highly conserved intronic enhancer element by the transcription factors PAX3 and FOXD3. Inhibition of these transcription factors slows melanoma cell growth, migration, and motility, as well as reduces CXCR4 expression. Overexpression of these transcription factors drives the production of increased CXCR4 levels. Loss of PAX3 and FOXD3 transcription factor activity results in a reduction in cell motility, migration, and chemotaxis, all of which are rescued by CXCR4 overexpression. Here, we discover a molecular pathway wherein PAX3 and FOXD3 promote CXCR4 gene expression in melanoma.

Vascular dysfunction and increased metastasis of B16F10 melanomas in Shb deficient mice as compared with their wild type counterparts

Background

Shb is a signaling protein downstream of vascular endothelial growth factor receptor-2 and Shb deficiency has been found to restrict tumor angiogenesis. The present study was performed in order to assess metastasis in Shb deficiency using B16F10 melanoma cells.

Methods

B16F10 melanoma cells were inoculated subcutaneously on wild type or Shb +/− mice. Primary tumors were resected and lung metastasis determined after tumor relapse. Lung metastasis was also assessed after bone marrow transplantation of wild type bone marrow to Shb +/− recipients and Shb +/− bone marrow to wild type recipients. Primary tumors were subject to immunofluorescence staining for CD31, VE-cadherin, desmin and CD8, RNA isolation and isolation of vascular fragments for further RNA isolation. RNA was used for real-time RT-PCR and microarray analysis.

Results

Numbers of lung metastases were increased in Shb +/− or −/− mice and this coincided with reduced pericyte coverage and increased vascular permeability. Gene expression profiling of vascular fragments isolated from primary tumors and total tumor RNA revealed decreased expression of different markers for cytotoxic T cells in tumors grown on Shb +/− mice, suggesting that vascular aberrations caused altered immune responses.

Conclusions

It is concluded that a unique combinatorial response of increased vascular permeability and reduced recruitment of cytotoxic CD8+ cells occurs as a consequence of Shb deficiency in B16F10 melanomas. These changes may promote tumor cell intravasation and metastasis.

Electronic supplementary material

The online version of this article (doi:10.1186/s12885-015-1269-y) contains supplementary material, which is available to authorized users.

Administration of a plasmid that expresses SDF-1α affects the oncogenic potential of mouse bcr-abl-transformed cells

Stromal-derived factor 1α (SDF‑1α, also known as CXCL12) is a chemokine that exerts its effects through the G-protein coupled receptors, C-X-C chemokine receptor type 4 (CXCR4) and 7 (CXCR7). There is marked evidence that the SDF-1/CXCR4 axis is involved in the pathogenesis of leukemia and therapies that target this axis are under development. The present study aimed to increase the efficacy of a DNA-based bcr-abl vaccine by simultaneously immunizing mice with a plasmid carrying the whole SDF-1α gene. Bcr-abl‑transformed 12B1 cells were used to challenge the mice. These cells have the oncogenic potential to induce both leukemia following intravenous inoculation and lymphoma-type solid tumors after subcutaneous inoculation. Administering an SDF‑1 carrying plasmid together with the bcr-abl vaccine resulted in increased survival following a challenge with subcutaneously administered 12B1 cells, although the difference was not statistically significant. However, there was a difference when the animals that developed subcutaneous tumors were only taken into consideration. In doubly-treated mice, significantly more mice failed to develop solid tumors than mice that had only received the bcr-abl vaccine. By contrast, the occurrence of fatal leukemia was significantly higher in the mice that were treated with the SDF-1 plasmid, regardless of whether they were immunized with the bcr-abl-vaccine. No humoral or cellular immune responses against SDF‑1 were detected in the treated mice, which suggested that the changes in oncogenic potential of 12B1 cells were due to the activity of SDF-1 itself.

Identification of the genomic insertion site of Pmel-1 TCR α and β transgenes by next-generation sequencing

The pmel-1 T cell receptor transgenic mouse has been extensively employed as an ideal model system to study the mechanisms of tumor immunology, CD8⁺ T cell differentiation, autoimmunity and adoptive immunotherapy. The ‘zygosity’ of the transgene affects the transgene expression levels and may compromise optimal breeding scheme design. However, the integration sites for the pmel-1 mouse have remained uncharacterized. This is also true for many other commonly used transgenic mice created before the modern era of rapid and inexpensive next-generation sequencing. Here, we show that whole genome sequencing can be used to determine the exact pmel-1 genomic integration site, even with relatively ‘shallow’ (8X) coverage. The results were used to develop a validated polymerase chain reaction-based genotyping assay. For the first time, we provide a quick and convenient polymerase chain reaction method to determine the dosage of pmel-1 transgene for this freely and publically available mouse resource. We also demonstrate that next-generation sequencing provides a feasible approach for mapping foreign DNA integration sites, even when information of the original vector sequences is only partially known.

Direct T cell activation via CD40 ligand generates high avidity CD8+ T cells capable of breaking immunological tolerance for the control of tumors

CD40 and CD40 ligand (CD40L) are costimulatory molecules that play a pivotal role in the proinflammatory immune response. Primarily expressed by activated CD4⁺ T cells, CD40L binds to CD40 on antigen presenting cells (APCs), thereby inducing APC activation. APCs, in turn, prime cytotoxic T lymphocytes (CTLs). Here, two tumor-associated antigen (TAA) animal models, p53-based and GP100-based, were utilized to examine the ability of CD40-CD40L to improve antigen-specific CTL-mediated antitumor immune responses. Although p53 and GP100 are self-antigens that generate low affinity antigen-specific CD8⁺ T cells, studies have shown that their functional avidity can be improved with CD40L-expressing APCs. Therefore, in the current study, we immunized mice with a DNA construct encoding a TAA in conjunction with another construct encoding CD40L via intramuscular injection followed by electroporation. We observed a significant increase in the antigen-specific CTL-mediated immune responses as well as the potent antitumor effects in both models. Antibody depletion experiments demonstrated that CD8⁺ T cells play a crucial role in eliciting antitumor effects in vaccinated mice. Furthermore, we showed that in vitro stimulation with irradiated tumor cells expressing both TAA and CD40L improved the functional avidity of antigen-specific CD8⁺ T cells. Thus, our data show that vaccination with TAA/CD40L DNA can induce potent antitumor effects against TAA-expressing tumors through the generation of better functioning antigen-specific CD8⁺ T cells. Our study serves as an important foundation for future clinical translation.

Chemokine receptor CXCR4: role in gastrointestinal cancer

Chemokines (CK)s, small proinflammatory chemoattractant cytokines that bind to specific G-protein coupled seven-span transmembrane receptors, are major regulators of cell trafficking and adhesion. The CXCL12 [stromal cell-derived factor-1 (SDF-1)] binds primarily to CXC receptor 4 (CXCR4; CD184). The binding of CXCL12 to CXCR4 induces intracellular signaling through several divergent pathways initiating signals related to chemotaxis, cell survival and/or proliferation, increase in intracellular calcium, and gene transcription. CXCR4 is expressed on multiple cell types including lymphocytes, hematopoietic stem cells, endothelial and epithelial cells, and cancer cells. One of the most intriguing and perhaps important roles that CKs and the CK receptors have is in regulating metastasis. Here, CK receptors may potentially facilitate tumor dissemination at each of the key steps of metastasis, including adherence of tumor cells to endothelium, extravasation from blood vessels, metastatic colonization, angiogenesis, proliferation, and protection from the host response via activation of key survival pathways such as ERK/MAPK, PI-3K/Akt/mTOR, or Jak/STAT, etc. In addition, it is increasingly recognized that CKs play an important role in facilitating communication between cancer cells and non-neoplatic cells in the tumor microenvironment (TME), including endothelial cells and fibroblasts, promoting the infiltration, activation of neutrophils, and tumor-associated macrophages within the TME. In this review, we mainly focus on the roles of chemokines CXCL12 and its cognate receptors CXCR4 as they pertain to cancer progression. In particular, we summarizes our current understanding regarding the contribution of CXCR4 and SDF-1 to gastrointestinal tumor behavior and its role in local progression, dissemination, and immune evasion of tumor cells. Also, describes recent therapeutic approaches that target these receptors or their ligands.

Engineering the assemblies of biomaterial nanocarriers for delivery of multiple theranostic agents with enhanced antitumor efficacy

The rapid development of nanotechnology holds great promise for revolutionizing the current landscape of tumor drug delivery. However, one of the biggest challenges is developing a simple nanocarrier platform to co-deliver various therapeutic agents. Here, a strategy for fabricating nanocarriers with many desirable features is demonstrated. The resulting nanoparticles achieve both high antitumor efficacy and effective inhibition of tumor metastasis with minimal side effects.

Chemokines, costimulatory molecules and fusion proteins for the immunotherapy of solid tumors

In this article, the role of chemokines and costimulatory molecules in the immunotherapy of experimental murine solid tumors and immunotherapy used in ongoing clinical trials are presented. Chemokine networks regulate physiologic cell migration that may be disrupted to inhibit antitumor immune responses or co-opted to promote tumor growth and metastasis in cancer. Recent studies highlight the potential use of chemokines in cancer immunotherapy to improve innate and adaptive cell interactions and to recruit immune effector cells into the tumor microenvironment. Another critical component of antitumor immune responses is antigen priming and activation of effector cells. Reciprocal expression and binding of costimulatory molecules and their ligands by antigen-presenting cells and naive lymphocytes ensures robust expansion, activity and survival of tumor-specific effector cells in vivo. Immunotherapy approaches using agonist antibodies or fusion proteins of immunomodulatory molecules significantly inhibit tumor growth and boost cell-mediated immunity. To localize immune stimulation to the tumor site, a series of fusion proteins consisting of a tumor-targeting monoclonal antibody directed against tumor necrosis and chemokines or costimulatory molecules were generated and tested in tumor-bearing mice. While several of these reagents were initially shown to have therapeutic value, combination therapies with methods to delete suppressor cells had the greatest effect on tumor growth. In conclusion, a key conclusion that has emerged from these studies is that successful immunotherapy will require both advanced methods of immunostimulation and the removal of immunosuppression in the host.

Monomeric and dimeric CXCL12 inhibit metastasis through distinct CXCR4 interactions and signaling pathways

Chemokines and chemokine receptors are extensively and broadly involved in cancer metastasis. Previously, we demonstrated that epigenetic silencing of the chemokine CXCL12 sensitizes breast and colon cancer cells to endocrine signaling and metastasis to distant tissues. Yet, the precise mechanism whereby CXCL12 production by tumor cells regulates dissemination remains unclear. Here, we show that administration of CXCL12 extended survival of tumor-bearing mice by potently limiting metastasis of colorectal carcinoma or murine melanoma. Because secreted CXCL12 is a mixture of monomeric and dimeric species in equilibrium, oligomeric variants that either promote (monomer) or halt (dimer) chemotaxis were used to dissect the mechanisms interrupting carcinoma metastasis. Monomeric CXCL12 mobilized intracellular calcium, inhibited cAMP signaling, recruited β-arrestin-2, and stimulated filamentous-actin accumulation and cell migration. Dimeric CXCL12 activated G-protein-dependent calcium flux, adenylyl cyclase inhibition, and the rapid activation of ERK1/2, but only weakly, if at all, recruited arrestin, stimulated actin polymerization, or promoted chemotaxis. NMR analyses illustrated that CXCL12 monomers made specific contacts with CXCR4 that were lost following dimerization. Our results establish the potential for inhibiting CXCR4-mediated metastasis by administration of CXCL12. Chemokine-mediated migration and β-arrestin responses did not dictate the antitumor effect of CXCL12. We conclude that cellular migration is tightly regulated by selective CXCR4 signaling evoked by unique interactions with distinct ligand quaternary structures.

CXCL12/CXCR4 blockade induces multimodal antitumor effects that prolong survival in an immunocompetent mouse model of ovarian cancer

The chemokine CXCL12 and its receptor CXCR4 are expressed widely in human cancers, including ovarian cancer, in which they are associated with disease progression at the levels of tumor cell proliferation, invasion, and angiogenesis. Here, we used an immunocompetent mouse model of intraperitoneal papillary epithelial ovarian cancer to show that modulation of the CXCL12/CXCR4 axis in ovarian cancer has multimodal effects on tumor pathogenesis associated with induction of antitumor immunity. siRNA-mediated knockdown of CXCL12 in BR5-1 cells that constitutively express CXCL12 and CXCR4 reduced cell proliferation in vitro, and tumor growth in vivo. Similarly, treatment of BR5-1-derived tumors with AMD3100, a selective CXCR4 antagonist, resulted in increased tumor apoptosis and necrosis, reduction in intraperitoneal dissemination, and selective reduction of intratumoral FoxP3(+) regulatory T cells (Treg). Compared with controls, CXCR4 blockade greatly increased T-cell-mediated antitumor immune responses, conferring a significant survival advantage to AMD3100-treated mice. In addition, the selective effect of CXCR4 antagonism on intratumoral Tregs was associated with both higher CXCR4 expression and increased chemotactic responses to CXCL12, a finding that was also confirmed in a melanoma model. Together, our findings reinforce the concept of a critical role for the CXCL12/CXCR4 axis in ovarian cancer pathogenesis, and they offer a definitive preclinical validation of CXCR4 as a therapeutic target in this disease.

CXCL12 (SDF1alpha)-CXCR4/CXCR7 pathway inhibition: an emerging sensitizer for anticancer therapies?

Addition of multiple molecularly targeted agents to the existing armamentarium of chemotherapeutics and radiotherapies represents a significant advance in the management of several advanced cancers. In certain tumor types with no efficacious therapy options, these agents have become the first line of therapy, for example, sorafenib in advanced hepatocellular carcinoma or bevacizumab in recurrent glioblastoma. Unfortunately, in many cases, the survival benefits are modest, lasting only weeks to a few months. Moreover, they may not show benefit in patients with localized disease (i.e., in the adjuvant setting). Recent studies have provided increasing evidence that activation of the chemokine CXCL12 (SDF1α) pathway is a potential mechanism of tumor resistance to both conventional therapies and biological agents via multiple complementary actions: (i) by directly promoting cancer cell survival, invasion, and the cancer stem and/or tumor-initiating cell phenotype; (ii) by recruiting "distal stroma" (i.e., myeloid bone marrow-derived cells) to indirectly facilitate tumor recurrence and metastasis; and (iii) by promoting angiogenesis directly or in a paracrine manner. Here, we discuss recent preclinical and clinical data that support the potential use of anti-CXCL12 agents (e.g., AMD3100, NOX-A12, or CCX2066) as sensitizers to currently available therapies by targeting the CXCL12/CXCR4 and CXCL12/CXCR7 pathways.

Contribution of MyD88 to the tumor exosome-mediated induction of myeloid derived suppressor cells

In this study we observed that mice pretreated with tumor exosomes had a significant acceleration of tumor metastasis in the lung. Tumor metastasis correlated significantly with an increase in recruitment of more Myeloid-derived suppressor cells (MDSCs) in the lung of C57BL/6j (B6) mice pretreated with tumor exosomes. These effects were blunted when MyD88 knockout (KO) mice were pretreated with tumor exosomes. MDSCs induced by tumor exosomes and isolated from wild-type B6 mice also more potently inhibited T cell activation and induction of interleukin-6 and tumor necrosis factor-alpha than MDSCs isolated from the lung of MyD88 KO mice. In vitro, addition of tumor exosomes to bone marrow-derived CD11b(+)Gr-1(+) cells isolated from wild-type B6 mice resulted in more cytokine production, including tumor necrosis factor-alpha, interleukin-6, and the chemokine CCL2, than CD11b(+)Gr-1(+) cells isolated from MyD88 KO mice. Moreover, lower levels of CCL2 were observed in the lungs in MyD88 KO mice pretreated with tumor exosomes than that in wild-type mice. Together these data demonstrate a pivotal role for MyD88 in tumor exosome-mediated expansion of MDSCs and tumor metastasis.

Inhibition of chemokine receptor expression on uveal melanomas by CXCR4 siRNA and its effect on uveal melanoma liver metastases

PURPOSE

To determine whether blocking the expression of the chemokine receptor CXCR4 using siRNA inhibits chemotactic responses of human uveal melanoma cells to liver-derived factors and prevents liver metastases.

METHODS

Human uveal melanoma cells were transfected with CXCR4 siRNA or control siRNA and tested in vitro for chemotactic and invasive behavior in response to soluble factors produced by human liver cells. The effect of CXCR4 siRNA transfection on the formation of liver metastases was tested by injecting transfected melanoma cells into the spleen capsules of NOD-SCID mice, and metastases were quantified by measuring the human housekeeping gene hHPRT in livers.

RESULTS

Blocking CXCR4 interaction with its ligand using anti-CXCL12 antibody resulted in a significant reduction in the chemotactic responses of uveal melanoma cells to soluble factors produced by human liver cells. Similarly, blocking CXCR4 gene expression by transfection with CXCR4 siRNA inhibited both the chemotactic and the invasive properties of uveal melanoma cells exposed to factors produced by human livers. Uveal melanoma cells transfected with CXCR4 siRNA produced fewer liver metastases than untreated uveal melanoma cells or uveal melanoma cells transfected with control siRNA.

CONCLUSIONS

CXCR4 is a key chemokine receptor that may account for the organ-specific homing of human uveal melanomas to the liver, which contains significant quantities of CXCL2, the only known ligand for CXCR4. CXCR4 is a potential therapeutic target for preventing the initial establishment of liver metastases but has limited application for use in advanced liver tumors.

Chemokine receptors in T-cell-mediated diseases of the skin

The chemokine/chemokine receptor network is an integral element of the complex system of homeostasis and immunosurveillance. Initially studied because of their role in coordinating tissue-specific migration and activation of leucocytes, chemokines have been implicated in the pathogenesis of various malignancies and diseases with strong inflammatory components. We discuss recent findings suggesting a critical involvement of chemokine receptor interactions in the immunopathogenesis of classical inflammatory skin disorders such as psoriasis and atopic dermatitis, as well as neoplastic diseases with a T-cell origin, such as mycosis fungoides. A deeper understanding of the underlying contribution of the chemokine network in the disease processes is key for the development of selective targeted immunotherapeutics that may meet the delicate balance between efficacy and safety.

The good and the bad of chemokines/chemokine receptors in melanoma

Chemokine ligand/receptor interactions affect melanoma cell growth, stimulate or inhibit angiogenesis, recruit leukocytes, promote metastasis, and alter the gene expression profile of the melanoma associated fibroblasts. Chemokine/chemokine receptor interactions can protect against tumor development/growth or can stimulate melanoma tumor progression, tumor growth and metastasis. Metastatic melanoma cells express chemokine receptors that play a major role in the specifying the organ site for metastasis, based upon receptor detection of the chemokine gradient elaborated by a specific organ/tissue. A therapeutic approach that utilizes the protective benefit of chemokines involves delivery of angiostatic chemokines or chemokines that stimulate the infiltration of cytotoxic T cells and natural killer T cells into the tumor microenvironment. An alternative approach that tackles the tumorigenic property of chemokines uses chemokine antibodies or chemokine receptor antagonists to target the growth and metastatic properties of these interactions. Based upon our current understanding of the role of chemokine-mediated inflammation in cancer, it is important that we learn to appropriately regulate the chemokine contribution to the tumorigenic 'cytokine/chemokine storm', and to metastasis.

Chemokine–chemokine receptors in cancer immunotherapy

A surge in interest in the chemokine–chemokine receptor network is probably related to the expanding roles that chemokines have now been identified to play in human biology, particularly immunity. Specific tissue microenvironments express distinct chemokines and both hematopoietic and nonhematopoietic cells have receptor expression profiles that permit the coordinated trafficking and organization of cells within these specific tissues. Since the chemokine network plays critical roles in both the function of the immune system and the progression of cancer, it is an attractive target for therapeutic manipulation. This review will focus on chemokine and chemokine receptor network-related therapeutic interventions that utilize host–tumor interactions particularly involving the immune system.

CXCR4 antagonists: targeting the microenvironment in leukemia and other cancers

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

CCR7 regulates B16 murine melanoma cell tumorigenesis in skin

Tumor cell-associated chemokine receptors play distinct roles in cancer biology, including enhancement of lymph node (LN) metastasis. To determine if CCR7 influences tumor formation in skin, we inoculated B16 cells transduced with CCR7 and luciferase (CCR7-luc-B16) or with retroviral vector and luciferase (pLNCX2-luc-B16) into ear skin and footpads of wild-type (WT) mice. In contrast to pLNCX2-luc-B16 cells, 97% of CCR7-luc-B16 cell-inoculated mice formed skin tumors as well as cervical LN metastases by Day 21 following ear inoculation. CCR7-expressing and control B16 cells, however, formed tumors of similar size and with high-efficiency in SCID-beige mice. Cells from both lines accumulated in the skin of WT mice in similar numbers until Day 7. By Day 11, however, control cells decreased tenfold, whereas CCR7-luc-B16 cells formed small tumor nodules. Tumor cells were infrequently detected in draining cervical LNs up to 11 days after injection of both cell lines, but stable nodal metastases were only observed after CCR7-luc-B16 ear tumors had been established (Day 21). ELISPOT assays revealed that IFN--producing cells in draining LNs from CCR7-luc-B16-injected ears were reduced through Day 7. After footpad injection, tumor formation by CCR7-expressing B16 cells was enhanced only with small, initial tumor cell inocula. With larger inocula, tumor formation was equivalent, but the numbers of tumor-infiltrating leukocytes were reduced by approximately sixfold in CCR7-B16 tumors compared with pLNCX2-B16 tumors of equal size. IFN- and CXCL10 were reduced 35- and sixfold, respectively, in CCR7-B16 cell tumors (vs. control tumors). Thus, CCR7 expression enhances tumorigenesis in addition to facilitating LN metastasis.

Immunotherapy for advanced melanoma

Immunotherapy for melanoma has undergone significant change since the first attempts to treat patients with high dose IL-2. Herein, strategies to boost patient antitumor immunity through vaccination, treatment with agents that augment host immunity, and adoptive cell transfer will be discussed. The first two strategies have yielded only limited clinical success, but adoptive cell transfer therapy, particularly following a lymphodepleting, preconditioning regimen has resulted in objective response rates approaching 50%. For a number of reasons, lymphodepletion appears to be critical for maintenance of circulating antitumor T cells following adoptive cell transfer. Balancing antitumor efficacy, autoimmunity, and reconstitution of a functioning immune system remain challenging and potentially life-threatening issues.

Chemokine receptor CXCR4-prognostic factor for gastrointestinal tumors

To review the implication of CXCR4 for gastrointestinal cancer, a “Pubmed” analysis was performed in order to evaluate the relevance of CXCR4 and its ligands for gastrointestinal cancers. Search terms applied were “cancer, malignoma, esophageal, gastric, colon, colorectal, hepatic, pancreatic, CXCR4, SDF-1α, and SDF-1β”. CXCR4 expression correlated with dissemination of diverse gastrointestinal malignomas. The CXCR4 ligand SDF-1α might act as “chemorepellent” while SDF-1β might act as "chemorepellent" for CTLs, inducing tumor rejection. The paracrine expression of SDF-1α was furthermore closely associated with neoangiogenesis. CXCR4 and its ligands influence the dissemination, immune rejection, and neoangiogenesis of human gastrointestinal cancers. Inhibition of CXCR4 might be an interesting therapeutic option.

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

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

Transcriptional modulation using HDACi depsipeptide promotes immune cell-mediated tumor destruction of murine B16 melanoma

With melanoma, as with many other malignancies, aberrant transcriptional repression is a hallmark of refractory cancer. To restore gene expression, use of a histone deacetylase inhibitor (HDACi) is expected to be effective. Our recent DNA micro-array analysis showed that the HDACi depsipeptide (FK228) significantly enhances gp100 antigen expression. Herein, we demonstrate that depsipeptide promotes tumor-specific T-cell-mediated killing of B16/F10 murine melanoma cells. First, by a quantitative assay of caspase-3/7 activity, a sublethal dose of depsipeptide was determined (ED50: 5 nM), in which p21(Waf1/Cip1) and Fas were sufficiently evoked concomitantly with histone H3 acetylation. Second, the sublethal dose of depsipeptide treatment with either a recombinant Fas ligand or tumor-specific T cells synergistically enhanced apoptotic cell death in B16/F10 cells in vitro. Furthermore, we found that depsipeptide increased levels of perforin in T cells. Finally, in vivo metastatic growth of B16/F10 in the lung was significantly inhibited by a combination of depsipeptide treatment and immune cell adoptive transfer from immunized mice using irradiated B16 cells and gp100-specific (Pmel-1) TCR transgenic mice (P<0.05, vs cell transfer alone). Consequently, employment of a transcriptional modulation strategy using HDACis might prove to be a useful pretreatment for human melanoma immunotherapy.

Inhibition of the CXCR4/CXCL12 chemokine pathway reduces the development of murine pulmonary metastases

Metastasis continues to be the leading cause of mortality for patients with cancer. High expression of the chemokine receptor CXCR4 correlates with poor prognosis in many cancers, including osteosarcoma and melanoma. CXCL12, the ligand for CXCR4, is expressed at high levels in the lung and lymph node, which are the primary sites to which these tumors metastasize respectively. These findings suggest that therapy aimed at disruption of this specific receptor/ligand complex may lead to a decrease in metastases. CTCE-9908, a small peptide CXCR4 antagonist was utilized in two murine metastasis models to test this hypothesis. Treatment of osteosarcoma cells in vitro with CTCE-9908 led to the following changes: decreased adhesion, decreased migration, decreased invasion, and decreased growth rate. Following tail vein injection of osteosarcoma cells, mice that were treated with CTCE-9908 had a 50% reduction in the number of gross metastatic lung nodules and a marked decrease in micro-metastatic disease. Similar findings were observed following injection of melanoma cells and treatment with CTCE-9908. However, these results could only be consistently reproduced when the cells were pre-treated with the inhibitor. A novel ex vivo luciferase assay showed decreased numbers of cells in the lung immediately after injection into mice, when treated with CTCE-9908, suggesting the importance of interactions between the receptor and the ligand. Our findings show that inhibition of the CXCR4/CXCL12 pathway decreases metastatic disease in two murine tumor models and expands on previous reports to describe potential mechanisms of action.