Integrin alpha4beta1 involvement in stromal cell-derived factor-1alpha-promoted myeloma cell transendothelial migration and adhesion: role of cAMP and the actin cytoskeleton in adhesion

Cancer metastasis chemoprevention prevents circulating tumour cells from germination

The war against cancer traces back to the signature event half-a-century ago when the US National Cancer Act was signed into law. The cancer crusade costs trillions with disappointing returns, teasing the possibility of a new breakthrough. Cure for cancer post-metastases still seems tantalisingly out of reach. Once metastasized, cancer-related death is extremely difficult, if not impossible, to be reversed. Here we present cancer pre-metastasis chemoprevention strategy that can prevent circulating tumour cells (CTCs) from initiating metastases safely and effectively, and is disparate from the traditional cancer chemotherapy and cancer chemoprevention. Deep learning of the biology of CTCs and their disseminating organotropism, complexity of their adhesion to endothelial niche reveals that if the adhesion of CTCs to their metastasis niche (the first and the most important part in cancer metastatic cascade) can be pharmaceutically interrupted, the lethal metastatic cascade could be prevented from getting initiated. We analyse the key inflammatory and adhesive factors contributing to CTC adhesion/germination, provide pharmacological fundamentals for abortifacients to intervene CTC adhesion to the distant metastasis sites. The adhesion/inhibition ratio (AIR) is defined for selecting the best cancer metastasis chemopreventive candidates. The successful development of such new therapeutic modalities for cancer metastasis chemoprevention has great potential to revolutionise the current ineffective post-metastasis treatments.

Desmoglein-2 expression is an independent predictor of poor prognosis patients with multiple myeloma

Multiple myeloma (MM) is the second most common haematological malignancy and is an incurable disease of neoplastic plasma cells (PC). Newly diagnosed MM patients currently undergo lengthy genetic testing to match chromosomal mutations with the most potent drug/s to decelerate disease progression. With only 17% of MM patients surviving 10‐years postdiagnosis, faster detection and earlier intervention would unequivocally improve outcomes. Here, we show that the cell surface protein desmoglein‐2 (DSG2) is overexpressed in ~ 20% of bone marrow biopsies from newly diagnosed MM patients. Importantly, DSG2 expression was strongly predictive of poor clinical outcome, with patients expressing DSG2 above the 70^th percentile exhibiting an almost 3‐fold increased risk of death. As a prognostic factor, DSG2 is independent of genetic subtype as well as the routinely measured biomarkers of MM activity (e.g. paraprotein). Functional studies revealed a nonredundant role for DSG2 in adhesion of MM PC to endothelial cells. Together, our studies suggest DSG2 to be a potential cell surface biomarker that can be readily detected by flow cytometry to rapidly predict disease trajectory at the time of diagnosis.

Pleiotropic Roles of CXCR4 in Wound Repair and Regeneration

Wound healing is a multi-step process that includes multiple cellular events such as cell proliferation, cell adhesion, and chemotactic response as well as cell apoptosis. Accumulating studies have documented the significance of stromal cell-derived factor-1 (SDF-1)/C-X-C chemokine receptor 4 (CXCR4) signaling in wound repair and regeneration. However, the molecular mechanism of regeneration is not clear. This review describes various types of tissue regeneration that CXCR4 participates in and how the efficiency of regeneration is increased by CXCR4 overexpression. It emphasizes the pleiotropic effects of CXCR4 in regeneration. By delving into the specific molecular mechanisms of CXCR4, we hope to provide a theoretical basis for tissue engineering and future regenerative medicine.

Tumour Dissemination in Multiple Myeloma Disease Progression and Relapse: A Potential Therapeutic Target in High-Risk Myeloma

Simple Summary

Like in solid cancers, the process of dissemination is a critical feature of disease progression in the blood cancer multiple myeloma. At diagnosis, myeloma patients have cancer that has spread throughout the bone marrow, with patients with more disseminatory myeloma having worse outcomes for their disease. In this review, we discuss the current understanding of the mechanisms that underpin the dissemination process in multiple myeloma. Furthermore, we discuss the potential for the use of therapies that target the dissemination process as a novel means of improving outcomes for multiple myeloma patients.

Abstract

Multiple myeloma (MM) is a plasma cell (PC) malignancy characterised by the presence of MM PCs at multiple sites throughout the bone marrow. Increased numbers of peripheral blood MM PCs are associated with rapid disease progression, shorter time to relapse and are a feature of advanced disease. In this review, the current understanding of the process of MM PC dissemination and the extrinsic and intrinsic factors potentially driving it are addressed through analysis of patient-derived MM PCs and MM cell lines as well as mouse models of homing and dissemination. In addition, we discuss how patient cytogenetic subgroups that present with highly disseminated disease, such as t(4;14), t(14;16) and t(14;20), suggest that intrinsic properties of MM PC influence their ability to disseminate. Finally, we discuss the possibility of using therapeutic targeting of tumour dissemination to slow disease progression and prevent overt relapse.

Contribution of the bone marrow stromal cells in mediating drug resistance in hematopoietic tumors

The bone marrow microenvironment (BMM) provides input via production of cytokines, chemokines, extracellular matrixes in the context of lower oxygen levels that influences self-renewal, survival, differentiation, progression, and therapeutic resistance of multiple myeloma and leukemic cells. Within the context of the BMM, tumor cells are supported by osteoblasts, bone marrow stromal cells (BMSCs), fibroblasts, myeloid cells, endothelial cells and blood vessels, as well as extracellular matrix (ECM) that contribute to tumor progression. Environmental mediated-drug resistance (EM-DR) contains cell adhesion-mediated drug resistance (CAM-DR) and soluble factor-mediated drug resistance (SM-DR) that contributes to de novo drug resistance. In this review, we focus on the crosstalk between the BMM and tumor cells as well as mechanisms underlying the BMM contributing to drug resistance in hematologic malignancies.

Clozapine reduces infiltration into the CNS by targeting migration in experimental autoimmune encephalomyelitis

Background

Atypical antipsychotic agents, such as clozapine, are used to treat schizophrenia and other psychiatric disorders by a mechanism that is believed to involve modulating the immune system. Multiple sclerosis is an immune-mediated neurological disease, and recently, clozapine was shown to reduce disease severity in an animal model of MS, experimental autoimmune encephalomyelitis (EAE). However, the mode of action by which clozapine reduces disease in this model is poorly understood.

Methods

Because the mode of action by which clozapine reduces neuroinflammation is poorly understood, we used the EAE model to elucidate the in vivo and in vitro effects of clozapine.

Results

In this study, we report that clozapine treatment reduced the infiltration of peripheral immune cells into the central nervous system (CNS) and that this correlated with reduced expression of the chemokines CCL2 and CCL5 transcripts in the brain and spinal cord. We assessed to what extent immune cell populations were affected by clozapine treatment and we found that clozapine targets the expression of chemokines by macrophages and primary microglia. Furthermore, in addition to decreasing CNS infiltration by reducing chemokine expression, we found that clozapine directly inhibits chemokine-induced migration of immune cells. This direct target on the immune cells was not mediated by a change in receptor expression on the immune cell surface but by decreasing downstream signaling via these receptors leading to a reduced migration.

Conclusions

Taken together, our study indicates that clozapine protects against EAE by two different mechanisms; first, by reducing the chemoattractant proteins in the CNS; and second, by direct targeting the migration potential of peripheral immune cells.

Sialyltransferase inhibition leads to inhibition of tumor cell interactions with E-selectin, VCAM1, and MADCAM1, and improves survival in a human multiple myeloma mouse model

Aberrant glycosylation resulting from altered expression of sialyltransferases, such as ST3 β-galactoside α2-3-sialyltransferase 6, plays an important role in disease progression in multiple myeloma (MM). Hypersialylation can lead to increased immune evasion, drug resistance, tumor invasiveness, and disseminated disease. In this study, we explore the in vitro and in vivo effects of global sialyltransferase inhibition on myeloma cells using the pan-sialyltransferase inhibitor 3F_ax-Neu5Ac delivered as a per-acetylated methyl ester pro-drug. Specifically, we show in vivo that 3F_ax-Neu5Ac improves survival by enhancing bortezomib sensitivity in an aggressive mouse model of MM. However, 3F_ax-Neu5Ac treatment of MM cells in vitro did not reverse bortezomib resistance conferred by bone marrow (BM) stromal cells. Instead, 3Fax-Neu5Ac significantly reduced interactions of myeloma cells with E-selectin, MADCAM1 and VCAM1, suggesting that reduced sialylation impairs extravasation and retention of myeloma cells in the BM. Finally, we showed that 3F_ax-Neu5Ac alters the post-translational modification of the α4 integrin, which may explain the reduced affinity of α4β1/α4β7 integrins for their counter-receptors. We propose that inhibiting sialylation may represent a valuable strategy to restrict myeloma cells from entering the protective BM microenvironment, a niche in which they are normally protected from chemotherapeutic agents such as bortezomib. Thus, our work demonstrates that targeting sialylation to increase the ratio of circulating to BM-resident MM cells represents a new avenue that could increase the efficacy of other anti-myeloma therapies and holds great promise for future clinical applications.

Targeted Approaches to Inhibit Sialylation of Multiple Myeloma in the Bone Marrow Microenvironment

Aberrant glycosylation modulates different aspects of tumor biology, and it has long been recognized as a hallmark of cancer. Among the different forms of glycosylation, sialylation, the addition of sialic acid to underlying oligosaccharides, is often dysregulated in cancer. Increased expression of sialylated glycans has been observed in many types of cancer, including multiple myeloma, and often correlates with aggressive metastatic behavior. Myeloma, a cancer of plasma cells, develops in the bone marrow, and colonizes multiple sites of the skeleton including the skull. In myeloma, the bone marrow represents an essential niche where the malignant cells are nurtured by the microenvironment and protected from chemotherapy. Here, we discuss the role of hypersialylation in the metastatic process focusing on multiple myeloma. In particular, we examine how increased sialylation modulates homing of malignant plasma cells into the bone marrow by regulating the activity of molecules important in bone marrow cellular trafficking including selectins and integrins. We also propose that inhibiting sialylation may represent a new therapeutic strategy to overcome bone marrow-mediated chemotherapy resistance and describe different targeted approaches to specifically deliver sialylation inhibitors to the bone marrow microenvironment.

The role of CXCR4 in multiple myeloma: Cells' journey from bone marrow to beyond

CXCR4 is a pleiotropic chemokine receptor which acts through its ligand CXCL12 to regulate diverse physiological processes. CXCR4/CXCL12 axis plays a pivotal role in proliferation, invasion, dissemination and drug resistance in multiple myeloma (MM). Apart from its role in homing, CXCR4 also affects MM cell mobilization and egression out of the bone marrow (BM) which is correlated with distant organ metastasis. Aberrant CXCR4 expression pattern is associated with osteoclastogenesis and tumor growth in MM through its cross talk with various important cell signalling pathways. A deeper insight into understanding of CXCR4 mediated signalling pathways and its role in MM is essential to identify potential therapeutic interventions. The current therapeutic focus is on disrupting the interaction of MM cells with its protective tumor microenvironment where CXCR4 axis plays an essential role. There are still multiple challenges that need to be overcome to target CXCR4 axis more efficiently and to identify novel combination therapies with existing strategies. This review highlights the role of CXCR4 along with its significant interacting partners as a mediator of MM pathogenesis and summarizes the targeted therapies carried out so far.

Molecular Players in Hematologic Tumor Cell Trafficking

The trafficking of neoplastic cells represents a key process that contributes to progression of hematologic malignancies. Diapedesis of neoplastic cells across endothelium and perivascular cells is facilitated by adhesion molecules and chemokines, which act in concert to tightly regulate directional motility. Intravital microscopy provides spatio-temporal views of neoplastic cell trafficking, and is crucial for testing and developing therapies against hematologic cancers. Multiple myeloma (MM), chronic lymphocytic leukemia (CLL), and acute lymphoblastic leukemia (ALL) are hematologic malignancies characterized by continuous neoplastic cell trafficking during disease progression. A common feature of these neoplasias is the homing and infiltration of blood cancer cells into the bone marrow (BM), which favors growth and survival of the malignant cells. MM cells traffic between different BM niches and egress from BM at late disease stages. Besides the BM, CLL cells commonly home to lymph nodes (LNs) and spleen. Likewise, ALL cells also infiltrate extramedullary organs, such as the central nervous system, spleen, liver, and testicles. The α4β1 integrin and the chemokine receptor CXCR4 are key molecules for MM, ALL, and CLL cell trafficking into and out of the BM. In addition, the chemokine receptor CCR7 controls CLL cell homing to LNs, and CXCR4, CCR7, and CXCR3 contribute to ALL cell migration across endothelia and the blood brain barrier. Some of these receptors are used as diagnostic markers for relapse and survival in ALL patients, and their level of expression allows clinicians to choose the appropriate treatments. In CLL, elevated α4β1 expression is an established adverse prognostic marker, reinforcing its role in the disease expansion. Combining current chemotherapies with inhibitors of malignant cell trafficking could represent a useful therapy against these neoplasias. Moreover, immunotherapy using humanized antibodies, CAR-T cells, or immune check-point inhibitors together with agents targeting the migration of tumor cells could also restrict their survival. In this review, we provide a view of the molecular players that regulate the trafficking of neoplastic cells during development and progression of MM, CLL, and ALL, together with current therapies that target the malignant cells.

The good and bad faces of the CXCR4 chemokine receptor

Chemokines are chemotactic cytokines that promote cell migration and activation under homeostatic and inflammatory conditions. Chemokines bind to seven transmembrane-spanning receptors that are coupled to heterotrimeric guanine nucleotide-binding (G) proteins, which are the responsible for intracellularly transmitting the activating signals for cell migration. Hematopoiesis, vascular development, lymphoid organ morphogenesis, cardiogenesis and neural differentiation are amongst the processes involving chemokine function. In addition, immune cell trafficking from bone marrow to blood circulation, and from blood and lymph to lymphoid and inflamed tissues, is tightly regulated by chemokines both under physiological conditions and also in autoimmune diseases. Furthermore, chemokine binding to their receptors stimulate trafficking to and positioning of cancer cells into target tissues and organs during tumour dissemination. The CXCL12 chemokine (also known as stromal-cell derived factor-1α, SDF-1α) plays key roles in hematopoiesis and lymphoid tissue architecture, in cardiogenesis, vascular formation and neurogenesis, as well as in the trafficking of solid and hematological cancer cell types. CXCL12 binds to the CXCR4 receptor, a multi-facetted molecule which tightly mirrors CXCL12 functions in homeostasis and disease. This review addresses the important roles of the CXCR4-CXCL12 axis in homeostasis, specially focusing in hematopoiesis, as well as it provides a picture of CXCR4 as mediator of cancer cell spreading, and a view of the available CXCR4 antagonists in different cancer types.

Impact of CXCR4/CXCL12 Blockade on Normal Plasma Cells In Vivo

Plasma cells (PCs) are a major source of alloantibody in transplant patients and are resistant to current therapy. Because receptor-ligand interactions in stromal microenvironments play important roles in the localization, development, and survival of normal PCs, we hypothesized that interfering with CXCR4/CXCL12 interactions with plerixafor might cause PC depletion and enhance the efficacy of the proteasome inhibitor bortezomib. PCs in mouse spleen, bone marrow, and peripheral blood demonstrated CXCR4 expression. We then treated with plerixafor in doses ranging from 240 μg/kg in a single dose to a 1-mg/kg daily dose for 10 days. CXCR4/CXCL12 blockade with plerixafor resulted in increased mobilization of PCs into the peripheral blood. Splenectomy completely abrogated this effect, suggesting that all plerixafor-mobilized cells were from the spleen. The total number of PCs in the spleen and marrow remained constant despite treatment with plerixafor. Bortezomib caused a reduction in PCs, but adding plerixafor did not increase killing. We conclude that CXCR4/CXCL12 interactions are important for the retention of a subpopulation of PCs in the spleen, but this interaction has minimal effect on PCs in the marrow. The lack of enhancement of bortezomib-mediated depletion suggests that factors other than CXCR4/CXCL12 interactions are responsible for drug resistance.

Adipocyte-Lineage Cells Support Growth and Dissemination of Multiple Myeloma in Bone

Multiple myeloma (MM) cells reside in the bone marrow microenvironment and form complicated interactions with nonneoplastic, resident stromal cells. We previously found that aggressive MM cells shift osteoblast progenitors toward adipogenesis. In addition, adipocytes are among the most common cell types in the adult skeleton; both mature adipocytes and preadipocytes serve as endocrine cells that secrete a number of soluble molecules into the microenvironment. Therefore, we used a combination of in vivo and in vitro methods to test the hypothesis that an increase in adipocyte lineage cells feeds back to promote MM progression. The results of this study revealed that bone marrow from patients with MM indeed contains increased preadipocytes and significantly larger mature adipocytes than normal bone marrow. We also found that preadipocytes and mature adipocytes secrete many molecules important for supporting MM cells in the bone marrow and directly recruit MM cells through both monocyte chemotactic protein-1 and stromal cell-derived factor-1α. Co-culture experiments found that preadipocytes activate Wnt signaling and decrease cleaved caspase-3, whereas mature adipocytes activate ERK signaling in MM cells. Furthermore, mature adipocyte conditioned medium promotes MM growth, whereas co-culture with preadipocytes results in enhanced MM cell chemotaxis in vitro and increased tumor growth in bone in vivo. Combined, these data reveal the importance of preadipocytes and mature adipocytes on MM progression and represent a unique target in the bone marrow microenvironment.

Bone metastasis: the importance of the neighbourhood

During the past decade preclinical studies have defined many of the mechanisms used by tumours to hijack the skeleton and promote bone metastasis. This has led to the development and widespread clinical use of bone-targeted drugs to prevent skeletal-related events. This understanding has also identified a critical dependency between colonizing tumour cells and the cells of bone. This is particularly important when tumour cells first arrive in bone, adapt to their new microenvironment and enter a long-lived dormant state. In this Review, we discuss the role of different bone cell types in supporting disseminated tumour cell dormancy and reactivation, and highlight the new opportunities this provides for targeting the bone microenvironment to control dormancy and bone metastasis.

In vivo molecular imaging of chemokine receptor CXCR4 expression in patients with advanced multiple myeloma

CXCR4 is a G-protein-coupled receptor that mediates recruitment of blood cells toward its ligand SDF-1. In cancer, high CXCR4 expression is frequently associated with tumor dissemination and poor prognosis. We evaluated the novel CXCR4 probe [(68)Ga]Pentixafor for in vivo mapping of CXCR4 expression density in mice xenografted with human CXCR4-positive MM cell lines and patients with advanced MM by means of positron emission tomography (PET). [(68)Ga]Pentixafor PET provided images with excellent specificity and contrast. In 10 of 14 patients with advanced MM [(68)Ga]Pentixafor PET/CT scans revealed MM manifestations, whereas only nine of 14 standard [(18)F]fluorodeoxyglucose PET/CT scans were rated visually positive. Assessment of blood counts and standard CD34(+) flow cytometry did not reveal significant blood count changes associated with tracer application. Based on these highly encouraging data on clinical PET imaging of CXCR4 expression in a cohort of MM patients, we conclude that [(68)Ga]Pentixafor PET opens a broad field for clinical investigations on CXCR4 expression and for CXCR4-directed therapeutic approaches in MM and other diseases.

In vivo adhesion of malignant B cells to bone marrow microvasculature is regulated by α4β1 cytoplasmic-binding proteins

Multiple myeloma (MM) and chronic lymphocytic leukemia (CLL) cells must attach to the bone marrow (BM) microvasculature before lodging in the BM microenvironment. Using intravital microscopy (IVM) of the BM calvariae we demonstrate that the α4β1 integrin is required for MM and CLL cell firm arrest onto the BM microvasculature, while endothelial P-selectin and E-selectin mediate cell rolling. Talin, kindlin-3 and ICAP-1 are β1-integrin-binding partners that regulate β1-mediated cell adhesion. We show that talin and kindlin-3 cooperatively stimulate high affinity and strength of α4β1-dependent MM and CLL cell attachment, whereas ICAP-1 negatively regulates this adhesion. A functional connection between talin/kindlin-3 and Rac1 was found to be required for MM cell attachment mediated by α4β1. Importantly, IVM analyses with talin- and kindlin-3-silenced MM cells indicate that these proteins are needed for cell arrest on the BM microvasculature. Instead, MM cell arrest is repressed by ICAP-1. Moreover, MM cells silenced for talin and kindlin-3, and cultured on α4β1 ligands showed higher susceptibility to bortezomib-mediated cell apoptosis. Our results highlight the requirement of α4β1 and selectins for the in vivo attachment of MM and CLL cells to the BM microvasculature, and indicate that talin, kindlin-3 and ICAP-1 differentially control physiological adhesion by regulating α4β1 activity.

Targeting SDF-1 in multiple myeloma tumor microenvironment

Multiple myeloma (MM) is a type of B-cell malignancy that remains incurable to date. The bone marrow (BM) microenvironment plays a crucial role in MM progression. The chemokine SDF-1 (CXCL12) is an important actor of the BM microenvironment that has the ability to regulate numerous processes related to its malignant transformation during MM development. The activity of SDF-1 is mainly mediated by its specific receptor CXCR4, which is expressed at the surface of MM cells and various other BM cell types. Current treatments available for MM patients mainly target tumor cells but have limited effects on the BM microenvironment. In this context, SDF-1 and CXCR4 represent ideal targets for the normalization of the MM-supportive BM microenvironment. The present review focuses on the activity of SDF-1 in the MM BM microenvironment and the current efforts carried out to target the SDF-1/CXCR4 axis for treatment of MM.

Chemokine Signaling Controls Integrity of Radial Glial Scaffold in Developing Spinal Cord and Consequential Proper Position of Boundary Cap Cells

Radial glial cells are the neural progenitors of the developing CNS and have long radial processes that guide radially migrating neurons. The integrity of the radial glial scaffold, in particular proper adhesion between the endfeet of radial processes and the pial basement membrane (BM), is important for the cellular organization of the CNS, as indicated by evidence emerging from the developing cortex. However, the mechanisms underlying the maintenance of radial glial scaffold integrity during development, when the neuroepithelium rapidly expands, are still poorly understood. Here, we addressed this issue in the developing mouse spinal cord. We show that CXCR4, a receptor of chemokine CXCL12, is expressed in spinal cord radial glia. Conditional knock-out of Cxcr4 in radial glia caused disrupted radial glial scaffold with gaps at the pial endfeet layer and consequentially led to an invasion of boundary cap (BC) cells into the spinal cord. Because BC cells are PNS cells normally positioned at the incoming and outgoing axonal roots, their invasion into the spinal cord suggests a compromised CNS/PNS boundary in the absence of CXCL12/CXCR4 signaling. Both disrupted radial glial scaffold and invasion of BC cells into the CNS were also present in mice deficient in CXCR7, a second receptor of CXCL12. We further show that CXCL12 signaling promotes the radial glia adhesion to BM components and activates integrin β1 avidity. Our study unravels a novel molecular mechanism that deploys CXCL12/CXCR4/CXCR7 for the maintenance of radial glial scaffold integrity, which in turn safeguards the CNS/PNS boundary during spinal cord development.

The intricate role of CXCR4 in cancer

Chemokines mediate numerous physiological and pathological processes related primarily to cell homing and migration. The chemokine CXCL12, also known as stromal cell-derived factor-1, binds the G-protein-coupled receptor CXCR4, which, through multiple divergent pathways, leads to chemotaxis, enhanced intracellular calcium, cell adhesion, survival, proliferation, and gene transcription. CXCR4, initially discovered for its involvement in HIV entry and leukocytes trafficking, is overexpressed in more than 23 human cancers. Cancer cell CXCR4 overexpression contributes to tumor growth, invasion, angiogenesis, metastasis, relapse, and therapeutic resistance. CXCR4 antagonism has been shown to disrupt tumor-stromal interactions, sensitize cancer cells to cytotoxic drugs, and reduce tumor growth and metastatic burden. As such, CXCR4 is a target not only for therapeutic intervention but also for noninvasive monitoring of disease progression and therapeutic guidance. This review provides a comprehensive overview of the biological involvement of CXCR4 in human cancers, the current status of CXCR4-based therapeutic approaches, as well as recent advances in noninvasive imaging of CXCR4 expression.

C-X-C motif chemokine 12 influences the development of extramedullary hematopoiesis in the spleens of myelofibrosis patients

Myelofibrosis (MF) is characterized by the constitutive mobilization of hematopoietic stem cells (HSC) and hematopoietic progenitor cells (HPC) and the establishment of extramedullary hematopoiesis. The mechanisms underlying this abnormal HSC/HPC trafficking pattern remain poorly understood. We demonstrated that both splenic and peripheral blood (PB) MF CD34(+) cells equally share a defective ability to home to the marrow, but not to the spleens, of NOD/LtSz-Prkdc(scid) mice. This trafficking pattern could not be attributed to discordant expression of integrins or chemokine receptors other than the downregulation of C-X-C chemokine receptor type 4 by both PB and splenic MF CD34(+) cells. The number of both splenic MF CD34(+) cells and HPCs that migrated toward splenic MF plasma was, however, significantly greater than the number that migrated toward PB MF plasma. The concentration of the intact HSC/HPC chemoattractant C-X-C motif chemokine 12 (CXCL12) was greater in splenic MF plasma than PB MF plasma, as quantified using mass spectrometry. Functionally inactive truncated products of CXCL12, which are the product of proteolytic degradation by serine proteases, were detected at similar levels in both splenic and PB MF plasma. Treatment with an anti-CXCL12 neutralizing antibody resulted in a reduction in the degree of migration of splenic MF CD34(+) cells toward both PB and splenic MF plasma, validating the role of CXCL12 as a functional chemoattractant. Our data indicate that the MF splenic microenvironment is characterized by increased levels of intact, functional CXCL12, which contributes to the localization of MF CD34(+) cells to the spleen and the establishment of extramedullary hematopoiesis.

Phosphoinositide 3-kinase p85beta regulates invadopodium formation

The acquisition of invasiveness is characteristic of tumor progression. Numerous genetic changes are associated with metastasis, but the mechanism by which a cell becomes invasive remains unclear. Expression of p85β, a regulatory subunit of phosphoinositide-3-kinase, markedly increases in advanced carcinoma, but its mode of action is unknown. We postulated that p85β might facilitate cell invasion. We show that p85β localized at cell adhesions in complex with focal adhesion kinase and enhanced stability and maturation of cell adhesions. In addition, p85β induced development at cell adhesions of an F-actin core that extended several microns into the cell z-axis resembling the skeleton of invadopodia. p85β lead to F-actin polymerization at cell adhesions by recruiting active Cdc42/Rac at these structures. In accordance with p85β function in invadopodium-like formation, p85β levels increased in metastatic melanoma and p85β depletion reduced invadopodium formation and invasion. These results show that p85β enhances invasion by inducing cell adhesion development into invadopodia-like structures explaining the metastatic potential of tumors with increased p85β levels.

Anti-galectin-3 therapy: a new chance for multiple myeloma and ovarian cancer?

Here we review the role of Galectins in the molecular pathogenesis of multiple myeloma and ovarian cancer, with a special focus on Glectin-3. Multiple myeloma is the second most common hematologic malignancy worldwide. Because the pathogenesis of multiple myeloma is still incompletely understood, there is no ultimately effective cure, and this cancer results fatal. Ovarian cancer is the most lethal gynecologic malignancy worldwide. Due to the lack of screening techniques for early detection, patients are mostly diagnosed with advanced disease, which results ultimately fatal. Multiple myeloma and ovarian cancer have different biologies, but they share a strong dependence on adhesion with extracellular matrix and other cells. Galectin-3 plays a key role in regulating such adhesive abilities of tumor cells. Here we discuss the outcomes and possible mechanism of action of a truncated, dominant negative form of Galectin-3, Galectin-3C, in these malignancies. Overall, we report that Galectin-3C is a promising new compound for effective adjuvant therapies in advanced, refractory multiple myeloma and ovarian cancer.

The detection of risk pathways, regulated by miRNAs, via the integration of sample-matched miRNA-mRNA profiles and pathway structure

The use of genome-wide, sample-matched miRNA (miRNAs)-mRNA expression data provides a powerful tool for the investigation of miRNAs and genes involved in diseases. The identification of miRNA-regulated pathways has been crucial for analysis of the role of miRNAs. However, the classical identification method fails to consider the structural information of pathways and the regulation of miRNAs simultaneously. We proposed a method that simultaneously integrated the change in gene expression and structural information in order to identify pathways. Our method used fold changes in miRNAs and gene products, along with the quantification of the regulatory effect on target genes, to measure the change in gene expression. Topological characteristics were investigated to measure the influence of gene products on entire pathways. Through the analysis of multiple myeloma and prostate cancer expression data, our method was proven to be effective and reliable in identifying disease risk pathways that are regulated by miRNAs. Further analysis showed that the structure of a pathway plays a crucial role in the recognition of the pathway as a factor in disease risk.

Crossing the endothelial barrier during metastasis

During metastasis, cancer cells disseminate to other parts of the body by entering the bloodstream in a process that is called intravasation. They then extravasate at metastatic sites by attaching to endothelial cells that line blood vessels and crossing the vessel walls of tissues or organs. This Review describes how cancer cells cross the endothelial barrier during extravasation and how different receptors, signalling pathways and circulating cells such as leukocytes and platelets contribute to this process. Identification of the mechanisms that underlie cancer cell extravasation could lead to the development of new therapies to reduce metastasis.

Identification of stromal differentially expressed proteins in the colon carcinoma by quantitative proteomics

Tumor microenvironment plays very important roles in the carcinogenesis. A variety of stromal cells in the microenvironment have been modified to support the unique needs of the malignant state. This study was to discover stromal differentially expressed proteins (DEPs) that were involved in colon carcinoma carcinogenesis. Laser capture microdissection (LCM) was captured and isolated the stromal cells from colon adenocarcinoma (CAC) and non-neoplastic colon mucosa (NNCM) tissues, respectively. Seventy DEPs were identified between the pooled LCM-enriched CAC and NNCM stroma samples by iTRAQ-based quantitative proteomics. Gene Ontology (GO) relationship analysis revealed that DEPs were hierarchically grouped into 10 clusters, and were involved in multiple biological functions that were altered during carcinogenesis, including extracellular matrix organization, cytoskeleton, transport, metabolism, inflammatory response, protein polymerization, and cell motility. Pathway network analysis revealed 6 networks and 56 network eligible proteins with Ingenuity pathway analysis. Four significant networks functioned in digestive system development and its function, inflammatory disease, and developmental disorder. Eight DEPs (DCN, FN1, PKM2, HSP90B1, S100A9, MYH9, TUBB, and YWHAZ) were validated by Western blotting, and four DEPs (DCN, FN1, PKM2, and HSP90B1) were validated by immunohistochemical analysis. It is the first report of stromal DEPs between CAC and NNCM tissues. It will be helpful to recognize the roles of stromas in the colon carcinoma microenvironment, and improve the understanding of carcinogenesis in colon carcinoma. The present data suggest that DCN, FN1, PKM2, HSP90B1, S100A9, MYH9, TUBB, and YWHAZ might be the potential targets for colon cancer prevention and therapy.

Sphingosine-1-phosphate activates chemokine-promoted myeloma cell adhesion and migration involving α4β1 integrin function

Myeloma cell adhesion dependent on α4β1 integrin is crucial for the progression of multiple myeloma (MM). The α4β1-dependent myeloma cell adhesion is up-regulated by the chemokine CXCL12, and pharmacological blockade of the CXCL12 receptor CXCR4 leads to defective myeloma cell homing to bone marrow (BM). Sphingosine-1-phosphate (S1P) regulates immune cell trafficking upon binding to G-protein-coupled receptors. Here we show that myeloma cells express S1P1, a receptor for S1P. We found that S1P up-regulated the α4β1-mediated myeloma cell adhesion and transendothelial migration stimulated by CXCL12. S1P promoted generation of high-affinity α4β1 that efficiently bound the α4β1 ligand VCAM-1, a finding that was associated with S1P-triggered increase in talin-β1 integrin association. Furthermore, S1P cooperated with CXCL12 for enhancement of α4β1-dependent adhesion strengthening and spreading. CXCL12 and S1P activated the DOCK2-Rac1 pathway, which was required for stimulation of myeloma cell adhesion involving α4β1. Moreover, in vivo analyses indicated that S1P contributes to optimizing the interactions of MM cells with the BM microvasculture and for their lodging inside the bone marrow. The regulation of α4β1-dependent adhesion and migration of myeloma cells by CXCL12-S1P combined activities might have important consequences for myeloma disease progression.

Microenvironment and tumor cell plasticity: an easy way out

Cancer cells undergo genetic changes allowing their adaptation to environmental changes, thereby obtaining an advantage during the long metastatic route, disseminated of several changes in the surrounding environment. In particular, plasticity in cell motility, mainly due to epigenetic regulation of cancer cells by environmental insults, engage adaptive strategies aimed essentially to survive in hostile milieu, thereby escaping adverse sites. This review is focused on tumor microenvironment as a collection of structural and cellular elements promoting plasticity and adaptive programs. We analyze the role of extracellular matrix stiffness, hypoxia, nutrient deprivation, acidity, as well as different cell populations of tumor microenvironment.

Anti-Notch treatment prevents multiple myeloma cells localization to the bone marrow via the chemokine system CXCR4/SDF-1

Multiple myeloma (MM) is a deadly hematopoietic malignancy characterized by proliferation of malignant plasma cells in the bone marrow (BM) and bone disease. Interactions between myeloma and BM cells facilitate tumor progression and resistance to therapies. CXCR4 and its ligand Stromal cell-derived factor-1 (SDF-1) have a primary role in this process and are associated with poor prognosis. The Notch pathway is active in myeloma cells, resulting in increased proliferation, resistance to apoptosis and osteolytic activity. We hypothesized that the CXCR4/SDF-1 axis mediates the effects of Notch signals in myeloma cells. Here we show that Notch positively controls CXCR4/SDF-1 expression and functions in myeloma cell lines, and that forced CXCR4 activation partially rescues tumor cells from the outcomes of Notch inhibition. Additionally, we provide evidences that Notch blocking in vivo significantly reduces BM infiltration by human myeloma cells in mouse xenografts. This is the first evidence that a Notch-targeted approach effectively prevents MM cell migration, proliferation and resistance to apoptosis by reducing CXCR4 and SDF-1 levels.

Notch-directed microenvironment reprogramming in myeloma: a single path to multiple outcomes

Multiple myeloma is a deadly hematopoietic malignancy. Despite therapeutic advances such as autologous stem cell transplantation and novel chemotherapeutics, multiple myeloma remains incurable. Multiple myeloma cell localization in the bone marrow and the cross-talk with the bone niche trigger dramatic alterations in the bone marrow microenvironment critical for tumor progression, resistance to therapies and osteolytic bone destruction. It does not surprise that the molecular bases of such fatal interaction are under examination as source of novel potential pharmacological targets. Among these, the Notch family of receptors and ligands has gained growing interest in the recent years because of their early deregulation in multiple myeloma and their ability to affect multiple features of the disease, including tumor cell growth, drug resistance, angiogenesis and bone lesions. This review will explore the evidences of Notch deregulation in multiple myeloma, the state of the art of the currently known roles of its signaling in the fatal interaction between multiple myeloma cells, extracellular matrix and cells in the bone marrow stroma. Finally, we will present recent findings concerning the arguments for or against a therapy addressed to Notch signaling inhibition in the cure of multiple myeloma.

Non-invasive imaging provides spatiotemporal information on disease progression and response to therapy in a murine model of multiple myeloma

BACKGROUND

Multiple myeloma (MM) is a B-cell malignancy, where malignant plasma cells clonally expand in the bone marrow of older people, causing significant morbidity and mortality. Typical clinical symptoms include increased serum calcium levels, renal insufficiency, anemia, and bone lesions. With standard therapies, MM remains incurable; therefore, the development of new drugs or immune cell-based therapies is desirable. To advance the goal of finding a more effective treatment for MM, we aimed to develop a reliable preclinical MM mouse model applying sensitive and reproducible methods for monitoring of tumor growth and metastasis in response to therapy.

MATERIAL AND METHODS

A mouse model was created by intravenously injecting bone marrow-homing mouse myeloma cells (MOPC-315.BM) that expressed luciferase into BALB/c wild type mice. The luciferase in the myeloma cells allowed in vivo tracking before and after melphalan treatment with bioluminescence imaging (BLI). Homing of MOPC-315.BM luciferase+ myeloma cells to specific tissues was examined by flow cytometry. Idiotype-specific myeloma protein serum levels were measured by ELISA. In vivo measurements were validated with histopathology.

RESULTS

Strong bone marrow tropism and subsequent dissemination of MOPC-315.BM luciferase(+) cells in vivo closely mimicked the human disease. In vivo BLI and later histopathological analysis revealed that 12 days of melphalan treatment slowed tumor progression and reduced MM dissemination compared to untreated controls. MOPC-315.BM luciferase(+) cells expressed CXCR4 and high levels of CD44 and α4β1 in vitro which could explain the strong bone marrow tropism. The results showed that MOPC-315.BM cells dynamically regulated homing receptor expression and depended on interactions with surrounding cells.

CONCLUSIONS

This study described a novel MM mouse model that facilitated convenient, reliable, and sensitive tracking of myeloma cells with whole body BLI in living animals. This model is highly suitable for monitoring the effects of different treatment regimens.

Myeloma as a model for the process of metastasis: implications for therapy

Multiple myeloma (MM) is a plasma cell dyscrasia characterized by the presence of multiple myelomatous "omas" throughout the skeleton, indicating that there is continuous trafficking of tumor cells to multiple areas in the bone marrow niches. MM may therefore represent one of the best models to study cell trafficking or cell metastasis. The process of cell metastasis is described as a multistep process, the invasion-metastasis cascade. This involves cell invasion, intravasation into nearby blood vessels, passage into the circulation, followed by homing into predetermined distant tissues, the formation of new foci of micrometastases, and finally the growth of micrometastasis into macroscopic tumors. This review discusses the significant advances that have been discovered in the complex process of invasion-metastasis in epithelial carcinomas and cell trafficking in hematopoietic stem cells and how this process relates to progression in MM. This progression is mediated by clonal intrinsic factors that mediate tumor invasiveness as well as factors present in the tumor microenvironment that are permissive to oncogenic proliferation. Therapeutic agents that target the different steps of cell dissemination and progression are discussed. Despite the significant advances in the treatment of MM, better therapeutic agents that target this metastatic cascade are urgently needed.

Chemokine-dependent B cell-T cell interactions in chronic lymphocytic leukemia and multiple myeloma - targets for therapeutic intervention?

INTRODUCTION

Chemokines and their receptors play essential roles in the development, maintenance and proper functioning of the immune system. B cell-T cell interactions are modulated by chemokines. In B cell malignancies, these interactions may have tumor-promoting consequences.

AREAS COVERED

This review summarizes physiological B cell-T cell interactions and discusses their pathological role in the onset and progression of B cell malignancies with a special focus on chronic lymphocytic leukemia and multiple myeloma. Experimental data on chemokine-guided B cell-T cell actions in B cell malignancies from murine models as well as in vitro data are summarized and their potential as future therapeutic targets is critically discussed.

EXPERT OPINION

Direct or indirect targeting of chemokine receptors involved in localization and T-cell-dependent activation of B lymphocytes can provide strong synergisms with conventional or immunomodulatory therapies by disrupting the microenvironmental conditions necessary for survival and proliferation of malignant B lymphocytes. However, further knowledge of these interactions between B and T cells is needed.

Notch-ing from T-cell to B-cell lymphoid malignancies

Notch receptors are transmembrane proteins critically determining cell fate and maintenance of progenitor cells in many developmental systems. Notch signaling is involved in stem cell self-renewal and regulates the main functions of cell life at different levels of development: cell proliferation, differentiation and apoptosis. By virtue of its involvement in the regulation of cell physiology, it is not surprising that a deregulation of the Notch pathway leads to the development of different tumors. In this review, we critically discuss the latest findings concerning Notch roles in hematologic oncology, with a special focus on T-cell acute lymphoblastic leukemia and B-cell malignancies. We also describe the molecular mediators of Notch-driven oncogenic effects and the current pharmacological approaches targeting Notch signaling.

Extranodal dissemination of non-Hodgkin lymphoma requires CD47 and is inhibited by anti-CD47 antibody therapy

Non-Hodgkin lymphoma (NHL) presents as both localized and disseminated disease with spread to secondary sites carrying a worse prognosis. Although pathways driving NHL dissemination have been identified, there are few therapies capable of inhibiting them. Here, we report a novel role for the immunomodulatory protein CD47 in NHL dissemination, and we demonstrate that therapeutic targeting of CD47 can prevent such spread. We developed 2 in vivo lymphoma metastasis models using Raji cells, a human NHL cell line, and primary cells from a lymphoma patient. CD47 expression was required for Raji cell dissemination to the liver in mouse xenotransplants. Targeting of CD47 with a blocking antibody inhibited Raji cell dissemination to major organs, including the central nervous system, and inhibited hematogenous dissemination of primary lymphoma cells. We hypothesized that anti-CD47 antibody-mediated elimination of circulating tumor cells occurred through phagocytosis, a previously described mechanism for blocking anti-CD47 antibodies. As predicted, inhibition of dissemination by anti-CD47 antibodies was dependent on blockade of phagocyte SIRPα and required macrophage effector cells. These results demonstrate that CD47 is required for NHL dissemination, which can be therapeutically targeted with a blocking anti-CD47 antibody. Ultimately, these findings are potentially applicable to the dissemination and metastasis of other solid tumors.

Cancer to bone: a fatal attraction

When cancer metastasizes to bone, considerable pain and deregulated bone remodelling occurs, greatly diminishing the possibility of cure. Metastasizing tumour cells mobilize and sculpt the bone microenvironment to enhance tumour growth and to promote bone invasion. Understanding the crucial components of the bone microenvironment that influence tumour localization, along with the tumour-derived factors that modulate cellular and protein matrix components of bone to favour tumour expansion and invasion, is central to the pathophysiology of bone metastases. Basic findings of tumour-bone interactions have uncovered numerous therapeutic opportunities that focus on the bone microenvironment to prevent and treat bone metastases.

Cancer to bone: a fatal attraction

When cancer metastasizes to bone, considerable pain and deregulated bone remodelling occurs, greatly diminishing the possibility of cure. Metastasizing tumour cells mobilize and sculpt the bone microenvironment to enhance tumour growth and to promote bone invasion. Understanding the crucial components of the bone microenvironment that influence tumour localization, along with the tumour-derived factors that modulate cellular and protein matrix components of bone to favour tumour expansion and invasion, is central to the pathophysiology of bone metastases. Basic findings of tumour-bone interactions have uncovered numerous therapeutic opportunities that focus on the bone microenvironment to prevent and treat bone metastases.

Integrins and bone metastasis: integrating tumor cell and stromal cell interactions

Integrins on both tumor cells and the supporting host stromal cells in bone (osteoclasts, new blood vessels, inflammatory cells, platelets and bone marrow stromal cells) play key roles in enhancing bone metastasis. Tumor cells localize to specific tissues through integrin-mediated contacts with extracellular matrix and stromal cells. Integrin expression and signaling are perturbed in cancer cells, allowing them to "escape" from cell-cell and cell-matrix tethers, invade, migrate and colonize within new tissues and matrices. Integrin signaling through αvβ3 and VLA-4 on tumor cells can promote tumor metastasis to and proliferation in the bone microenvironment. Osteoclast (OC) mediated bone resorption is a critical component of bone metastasis and can promote tumor growth in bone and αvβ3 integrins are critical to OC function and development. Tumors in the bone microenvironment can recruit new blood vessel formation, platelets, pro-tumor immune cells and bone marrow stromal cells that promote tumor growth and invasion in bone. Integrins and their ligands play critical roles in platelet aggregation (αvβ3 and αIIbβ3), hematopoietic cell mobilization (VLA-4 and osteopontin), neoangiogenesis (αvβ3, αvβ5, α6β4, and β1 integrin) and stromal function (osteopontin and VLA-4). Integrins are involved in the pathogenesis of bone metastasis at many levels and further study to define integrin dysregulation by cancer will yield new therapeutic targets for the prevention and treatment of bone metastasis.

Adhesion molecules--The lifelines of multiple myeloma cells

Multiple myeloma is an incurable hematological malignancy of terminally differentiated immunoglobulin-producing plasma cells. As a common presentation of the disease, the malignant plasma cells accumulate and proliferate in the bone marrow, where they disrupt normal hematopoiesis and bone physiology. Multiple myeloma cells and the bone marrow microenvironment are linked by a composite network of interactions mediated by soluble factors and adhesion molecules. Integrins and syndecan-1/CD138 are the principal multiple myeloma receptor systems of extracellular matrix components, as well as of surface molecules of stromal cells. CD44 and RHAMM are the major hyaluronan receptors of multiple myeloma cells. The SDF-1/CXCR4 axis is a key factor in the homing of multiple myeloma cells to the bone marrow. The levels of expression and activity of these adhesion molecules are controlled by cytoplasmic operating mechanisms, as well as by extracellular factors including enzymes, growth factors and microenvironmental conditions. Several signaling responses are activated by adhesive interactions of multiple myeloma cells, and their outcomes affect the survival, proliferation and migration of these cells, and in many cases generate a drug-resistant phenotype. Hence, the adhesion systems of multiple myeloma cells are attractive potential therapeutic targets. Several approaches are being developed to disrupt the activities of adhesion molecules in multiple myeloma cells, including small antagonist molecules, direct targeting by immunoconjugates, stimulation of immune responses against these molecules, and signal transduction inhibitors. These potential novel therapeutics may be incorporated into current treatment schemes, or directed against minimal residual malignant cells during remission.

Bone marrow stromal cell interaction reduces syndecan-1 expression and induces kinomic changes in myeloma cells

CD138 (Syndecan 1) is a heparan sulfate proteoglycan that concentrates heparan sulfate-binding growth factors on the surface of normal and malignant plasma cells (multiple myeloma, MMC). Recent studies have shown the presence of a CD138-negative fraction of MMC within myelomatous bone marrow (BM). We employed kinome array technology to characterize this fraction at a molecular level, using a myeloma cell line model. Compared to CD138-positive cells, CD138-negative MMC showed (i) a reduced activity of kinases involved in cell cycle progression, in agreement with a decreased labeling index and (ii) reduced Rho signaling to F-actin. Interestingly, CD138 mRNA and protein expression was reduced upon interaction of MM cells with stromal cell lines and primary mesenchymal cultures, which was accompanied by the acquisition of an increased Bcl6/Blimp1 ratio. Co-culture induced an increased activity of kinases involved in adhesion and a decreased S-phase transition in both CD138-positive and -negative fractions. In addition, CD138-negative MMC demonstrated an increased STAT3 and ERK1/2 activation compared to CD138+ MMC, in agreement with a lower sensitivity to compound exposure. The presence of a less mature, more resistant CD138-negative myeloma cell fraction within bone marrow microniches might contribute to high incidence of relapse of Myeloma patients.

Hypoxia-inducible factor-2 is a novel regulator of aberrant CXCL12 expression in multiple myeloma plasma cells

BACKGROUND

Multiple myeloma is an incurable malignancy of bone marrow plasma cells. Progression of multiple myeloma is accompanied by an increase in bone marrow angiogenesis. Studies from our laboratory suggest a role for the CXCL12 chemokine in this process, with circulating levels of CXCL12 correlating with bone marrow angiogenesis in patients with multiple myeloma. While the mechanisms responsible for aberrant plasma cell expression of CXCL12 remain to be determined, studies in other systems suggest a role for hypoxia and hypoxia-inducible transcription factors.

DESIGN AND METHODS

The expression of hypoxia-inducible factor protein was examined in patients' bone marrow biopsy specimens using immunohistochemistry. The hypoxic regulation of CXCL12 was examined in multiple myeloma plasma cell lines using polymerase chain reaction and western blotting. The role of hypoxia-inducible factors-1 and -2 in the regulation of CXCL12 expression was examined using over-expression and short hairpin RNA knockdown constructs, electrophoretic mobility shift assays and chromatin immunoprecipitation. The contribution of CXCL12 to hypoxia-induced angiogenesis was examined in vivo using a subcutaneous murine model of neovascularization.

RESULTS

Strong hypoxia-inducible factor-2 protein expression was detected in CD138(+) multiple myeloma plasma cells in patients' biopsy specimens. Prolonged exposure to hypoxia strongly up-regulated CXCL12 expression in multiple myeloma plasma cells and hypoxia-inducible factor-2 was found to play a key role in this response. Promoter analyses revealed increased hypoxia-inducible factor-2 binding to the CXCL12 promoter under hypoxic conditions. Over-expression of hypoxia-inducible factor in multiple myeloma plasma cells strongly induced in vivo angiogenesis, and administration of a CXCL12 antagonist decreased hypoxia-inducible factor-induced angiogenesis.

CONCLUSIONS

Hypoxia-inducible factor-2 is a newly identified regulator of CXCL12 expression in multiple myeloma plasma cells and a major contributor to multiple myeloma plasma cell-induced angiogenesis. Targeting the hypoxic niche, and more specifically hypoxia-inducible factor-2, may represent a viable strategy to inhibit angiogenesis in multiple myeloma and progression of this disease.

Correction of the abnormal trafficking of primary myelofibrosis CD34+ cells by treatment with chromatin-modifying agents

The abnormal trafficking of CD34+ cells is a unique characteristic of primary myelofibrosis (PMF). We have further studied the behavior of PMF CD34+ cells by examining their homing to the marrow and the spleens of nonobese diabetic/severe combined immunodeficient (NOD/SCID) mice. Following the infusion of PMF and normal granulocyte colony-stimulating factor-mobilized peripheral blood (mPB) CD34+ cells into NOD/SCID mice, reduced numbers of PMF CD34+ cells and granulocyte-macrophage colony-forming unit (CFU-GM) compared with mPB were detected in the marrow of these mice, whereas similar numbers of PMF and mPB CD34+ cells and CFU-GM homed to their spleens. The abnormal homing of PMF CD34+ cells was associated with reduced expression of CXCR4, but was not related to the presence of JAK2V617F. The sequential treatment of PMF CD34+ cells with the chromatin-modifying agents 5-aza-2'-deoxycytidine (5azaD) and trichostatin A (TSA), but not treatment with small molecule inhibitors of JAK2, resulted in the generation of increased numbers of CD34+CXCR4+ cells, which was accompanied by enhanced homing of PMF CD34+ cells to the marrow but not the spleens of NOD/SCID mice. Following 5azaD/TSA treatment, JAK2V617F-negative PMF hematopoietic progenitor cells preferentially homed to the marrow but not the spleens of recipient mice. Our data suggest that PMF CD34+ cells are characterized by a reduced ability to home to the marrow but not the spleens of NOD/SCID mice and that this homing defect can be corrected by sequential treatment with chromatin-modifying agents.

CXCR4 regulates the early extravasation of metastatic tumor cells in vivo

Recent studies have demonstrated that the chemokine receptor CXCR4 plays a crucial role in organ-specific metastasis formation. Although a variety of studies showed the expression of chemokine receptors, in particular, CXCR4, by gastrointestinal tumors, the precise mechanisms of chemokine receptor-mediated homing of cancer cells to specific sites of metastasis remained elusive. Here, we used liver metastatic human HEP-G2 hepatoma and HT-29LMM colon cancer cells expressing functional CXCR4 to dissect the metastatic cascade by intravital fluorescence microscopy. Immunohistochemistry revealed that the CXCR4 ligand CXCL12 is expressed by endothelial cells and likely Kupffer cells lining the liver sinusoids. Tumor cell adhesion and extravasation in vivo was quantitatively analyzed using intravital fluorescence microscopy. Treatment of cells with an anti-CXCR4 antibody did not affect cell adhesion but significantly impaired tumor cell extravasation (HEP-G2; isotype control: 22.3% +/- 4.3% vs anti-CXCR4: 6.0% +/- 5.0%, P < .001). In addition, pretreatment of tumor cells with the ligand CXCL12 enhanced the activation of the small GTPases Rho, Rac, and cdc42 as well as tumor cell extravasation without affecting tumor cell adhesion within liver sinusoids. Taken together, the findings of the present study provide first in vivo insights into the early events of chemokine ligand/receptor-mediated liver metastasis formation of tumor cells and define tumor cell extravasation rather than tumor cell arrest as the rate-limiting event.

Stromal cell-derived factor-1/CXCR4 enhanced motility of human osteosarcoma cells involves MEK1/2, ERK and NF-kappaB-dependent pathways

Osteosarcoma is characterized by a high malignant and metastatic potential. The chemokine stromal-derived factor-1alpha (SDF-1alpha) and its receptor, CXCR4, play a crucial role in adhesion and migration of human cancer cells. Integrins are the major adhesive molecules in mammalian cells, and has been associated with metastasis of cancer cells. Here, we found that human osteosarcoma cell lines had significant expression of SDF-1 and CXCR4 (SDF-1 receptor). Treatment of osteosarcoma cells with SDF-1alpha increased the migration and cell surface expression of alphavbeta3 integrin. CXCR4-neutralizing antibody, CXCR4 specific inhibitor (AMD3100) or small interfering RNA against CXCR4 inhibited the SDF-1alpha-induced increase the migration and integrin expression of osteosarcoma cells. Pretreated of osteosarcoma cells with MAPK kinase (MEK) inhibitor PD98059 inhibited the SDF-1alpha-mediated migration and integrin expression. Stimulation of cells with SDF-1alpha increased the phosphorylation of MEK and extracellular signal-regulating kinase (ERK). In addition, NF-kappaB inhibitor (PDTC) or IkappaB protease inhibitor (TPCK) also inhibited SDF-1alpha-mediated cell migration and integrin up-regulation. Stimulation of cells with SDF-1alpha induced IkappaB kinase (IKKalpha/beta) phosphorylation, IkappaB phosphorylation, p65 Ser(536) phosphorylation, and kappaB-luciferase activity. Furthermore, the SDF-1alpha-mediated increasing kappaB-luciferase activity was inhibited by AMD3100, PD98059, PDTC and TPCK or MEK1, ERK2, IKKalpha and IKKbeta mutants. Taken together, these results suggest that the SDF-1alpha acts through CXCR4 to activate MEK and ERK, which in turn activates IKKalpha/beta and NF-kappaB, resulting in the activations of alphavbeta3 integrins and contributing the migration of human osteosarcoma cells.

RhoA and Rac1 GTPases play major and differential roles in stromal cell-derived factor-1-induced cell adhesion and chemotaxis in multiple myeloma

The interaction of multiple myeloma (MM) cells with the bone marrow (BM) milieu plays a crucial role in MM pathogenesis. Stromal cell-derived factor-1 (SDF1) regulates homing of MM cells to the BM. In this study, we examined the role of RhoA and Rac1 GTPases in SDF1-induced adhesion and chemotaxis of MM. We found that both RhoA and Rac1 play key roles in SDF1-induced adhesion of MM cells to BM stromal cells, whereas RhoA was involved in chemotaxis and motility. Furthermore, both ROCK and Rac1 inhibitors reduced SDF1-induced polymerization of actin and activation of LIMK, SRC, FAK, and cofilin. Moreover, RhoA and Rac1 reduced homing of MM cells to BM niches. In conclusion, we characterized the role of RhoA and Rac1 GTPases in SDF1-induced adhesion, chemotaxis, and homing of MM cells to the BM, providing the framework for targeting RhoA and Rac1 GTPases as novel MM therapy.

CXCR4 inhibitor AMD3100 disrupts the interaction of multiple myeloma cells with the bone marrow microenvironment and enhances their sensitivity to therapy

The interaction of multiple myeloma (MM) cells with their microenvironment in the bone marrow (BM) provides a protective environment and resistance to therapeutic agents. We hypothesized that disruption of the interaction of MM cells with their BM milieu would lead to their sensitization to therapeutic agents such as bortezomib, melphalan, doxorubicin, and dexamethasone. We report that the CXCR4 inhibitor AMD3100 induces disruption of the interaction of MM cells with the BM reflected by mobilization of MM cells into the circulation in vivo, with kinetics that differed from that of hematopoietic stem cells. AMD3100 enhanced sensitivity of MM cell to multiple therapeutic agents in vitro by disrupting adhesion of MM cells to bone marrow stromal cells (BMSCs). Moreover, AMD3100 increased mobilization of MM cells to the circulation in vivo, increased the ratio of apoptotic circulating MM cells, and enhanced the tumor reduction induced by bortezomib. Mechanistically, AMD3100 significantly inhibited Akt phosphorylation and enhanced poly(ADP-ribose) polymerase (PARP) cleavage as a result of bortezomib, in the presence of BMSCs in coculture. These experiments provide a proof of concept for the use of agents that disrupt interaction with the microenvironment for enhancement of efficacy of cytotoxic agents in cancer therapy.

Notch: From fly wings to human hematological tumors

Notch history begins in 1919 with Thomas Hunt Morgan studies on fruit fly mutants. From then, this gene aroused lively interest in the scientific community since it is involved in a wide variety of processes, including morphogenesis, tissue homeostasis, and stem cell maintenance. Deregulation of Notch signaling characterizes several human tumors. Hematopoietic system is affected by mutations of Notch receptors, Notch ligands, and proteins controlling their stability. Approximately 60% T acute lymphoblastic leukemia (T-ALL) patients carry activating Notch1 mutations prompting blasts growth. In addition, multiple myeloma is characterized by Notch signaling hyper-activation due to an abnormal expression of the Jagged2 ligand; this affects not only myeloma cells, but also their interaction with bone marrow microenvironment, influencing tumor burden and bone disease. These findings make Notch a rational target of a therapeutic approach. Inhibitors of the Notch activating enzyme, ?-Secretase, have been successfully used in vitro and in vivo and are currently under clinical trials for T-ALL and breast cancer. Yet a wide use of these inhibitors is prevented by frequently occurring drug resistance. To elucidate the mechanism underlying this phenomenon, a number of pathways have been identified mediating Notch biological effects: AKT and c-Myc are frequently deregulated in leukemic patients and account for resistance to ?-Secretase inhibitors by acting downstream Notch receptor. Therefore, the interaction of Notch with other cancer-associated proteins should be clarified to predict the biological outcome of a Notch targeted therapy and possibly, to exploit combined treatments against the key deregulated elements in Notch-associated cancers.

SDF-1/CXCR4 and VLA-4 interaction regulates homing in Waldenstrom macroglobulinemia

Waldenstrom macroglobulinemia (WM) is characterized by widespread involvement of the bone marrow at the time of diagnosis, implying continuous homing of WM cells into the marrow. The mechanisms by which trafficking of the malignant cells into the bone marrow has not been previously elucidated. In this study, we show that WM cells express high levels of chemokine and adhesion receptors, including CXCR4 and VLA-4. We showed that CXCR4 was essential for the migration and trans-endothelial migration of WM cells under static and dynamic shear flow conditions, with significant inhibition of migration using CXCR4 knockdown or the CXCR4 inhibitor AMD3100. Similarly, CXCR4 or VLA-4 inhibition led to significant inhibition of adhesion to fibronectin, stromal cells, and endothelial cells. Decreased adhesion of WM cells to stromal cells by AMD3100 led to increased sensitivity of these cells to cytotoxicity by bortezomib. To further investigate the mechanisms of CXCR4-dependent adhesion, we showed that CXCR4 and VLA-4 directly interact in response to SDF-1, we further investigated downstream signaling pathways regulating migration and adhesion in WM. Together, these studies demonstrate that the CXCR4/SDF-1 axis interacts with VLA-4 in regulating migration and adhesion of WM cells in the bone marrow microenvironment.

The small GTPase Ral mediates SDF-1-induced migration of B cells and multiple myeloma cells

Chemokine-controlled migration plays a critical role in B-cell development, differentiation, and function, as well as in the pathogenesis of B-cell malignancies, including the plasma cell neoplasm multiple myeloma (MM). Here, we demonstrate that stimulation of B cells and MM cells with the chemokine stromal cell-derived factor-1 (SDF-1) induces strong migration and activation of the Ras-like GTPase Ral. Inhibition of Ral, by expression of the dominant negative RalN28 mutant or of RalBPDeltaGAP, a Ral effector mutant that sequesters active Ral, results in impaired SDF-1-induced migration of B cells and MM cells. Of the 2 Ral isoforms, RalA and RalB, RalB was found to mediate SDF-1-induced migration. We have recently shown that Btk, PLCgamma2, and Lyn/Syk mediate SDF-1-controlled B-cell migration; however, SDF-1-induced Ral activation is not affected in B cells deficient in these proteins. In addition, treatment with pharmacological inhibitors against PI3K and PLC or expression of dominant-negative Ras did not impair SDF-1-induced Ral activation. Taken together, these results reveal a novel function for Ral, that is, regulation of SDF-1-induced migration of B cells and MM cells, thereby providing new insights into the control of B-cell homeostasis, trafficking, and function, as well as into the pathogenesis of MM.