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Chemotherapy remains one of the main treatment modalities for cancer. While chemotherapy is mainly known for its ability to kill tumor cells directly, accumulating evidence indicates that it also acts indirectly by enhancing T cell-mediated anti-tumor immunity sometimes through immunogenic cell death. However, the role of immature immune cells in chemotherapy-induced immunomodulation has not been studied. Here, we utilized a mouse pancreatic cancer model to characterize the effects of gemcitabine chemotherapy on immature bone marrow cells in the context of tumor immunogenicity. Single cell RNA sequencing of hematopoietic stem and progenitor cells revealed a 3-fold increase in megakaryocyte-erythroid progenitors (MEPs) in the bone marrow of gemcitabine-treated mice in comparison to untreated control mice. Notably, adoptive transfer of MEPs to pancreatic tumor-bearing mice significantly reduced tumor growth and increased the levels of anti-tumor immune cells in tumors and peripheral blood. Furthermore, MEPs increased the tumor cell killing activity of CD8 + T cells and NK cells, an effect that was dependent on MEP-secreted CCL5 and CXCL16. Collectively, our findings demonstrate that chemotherapy-induced enrichment of MEPs in the bone marrow compartment contributes to anti-tumor immunity., (© 2023. The Author(s).)

Molecular understanding of osteogenic differentiation (OD) of human bone marrow-derived mesenchymal stem cells (hBMSCs) is important for regenerative medicine and has direct implications for cancer. We report that the RNF4 ubiquitin ligase is essential for OD of hBMSCs, and that RNF4-deficient hBMSCs remain as stalled progenitors. Remarkably, incubation of RNF4-deficient hBMSCs in conditioned media of differentiating hBMSCs restored OD. Transcriptional analysis of RNF4-dependent gene signatures identified two secreted factors that act downstream of RNF4 promoting OD: (1) BMP6 and (2) the BMP6 co-receptor, RGMb (Dragon). Indeed, knockdown of either RGMb or BMP6 in hBMSCs halted OD, while only the combined co-addition of purified RGMb and BMP6 proteins to RNF4-deficient hBMSCs fully restored OD. Moreover, we found that the RNF4-RGMb-BMP6 axis is essential for survival and tumorigenicity of osteosarcoma and therapy-resistant melanoma cells. Importantly, patient-derived sarcomas such as osteosarcoma, Ewing sarcoma, liposarcomas, and leiomyosarcomas exhibit high levels of RNF4 and BMP6, which are associated with reduced patient survival. Overall, we discovered that the RNF4~BMP6~RGMb axis is required for both OD and tumorigenesis., (© 2022. The Author(s).)

Myeloid-derived suppressor cells (MDSCs) are known to promote tumor growth in part by their immunosuppressive activities and their angiogenesis support. It has been shown that Bv8 blockade inhibits the recruitment of MDSCs to tumors, thereby delaying tumor relapse associated with resistance to antiangiogenic therapy. However, the impact of Bv8 blockade on tumors resistant to the new immunotherapy drugs based on the blockade of immune checkpoints has not been investigated. Here, we demonstrate that granulocytic-MDSCs (G-MDSCs) are enriched in anti-PD1 resistant tumors. Importantly, resistance to anti-PD1 monotherapy is reversed upon switching to a combined regimen comprised of anti-Bv8 and anti-PD1 antibodies. This effect is associated with a decreased level of G-MDSCs and enrichment of active cytotoxic T cells in tumors. The blockade of anti-Bv8 has shown efficacy also in hyperprogressive phenotype of anti-PD1-treated tumors. In vitro , anti-Bv8 antibodies directly inhibit MDSC-mediated immunosuppression, as evidenced by enhanced tumor cell killing activity of cytotoxic T cells. Lastly, we show that anti-Bv8-treated MDSCs secrete proteins associated with effector immune cell function and T cell activity. Overall, we demonstrate that Bv8 blockade inhibits the immunosuppressive function of MDSCs, thereby enhancing anti-tumor activity of cytotoxic T cells and sensitizing anti-PD1 resistant tumors. Our findings suggest that combining Bv8 blockade with anti-PD1 therapy can be used as a strategy for overcoming therapy resistance., Competing Interests: The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest., (Copyright © 2022 Benguigui, Vorontsova, Timaner, Levin, Haj-Shomaly, Deo, Menachem, Manobla, Cooper, Raviv and Shaked.)

Metastasis is the main cause of cancer-related mortality. Despite intense efforts to understand the mechanisms underlying the metastatic process, treatment of metastatic cancer is still challenging. Here we describe a chemotherapy-induced, host-mediated mechanism that promotes remodeling of the extracellular matrix (ECM), ultimately facilitating cancer cell seeding and metastasis. Paclitaxel (PTX) chemotherapy enhanced rapid ECM remodeling and mechanostructural changes in the lungs of tumor-free mice, and the protein expression and activity of the ECM remodeling enzyme lysyl oxidase (LOX) increased in response to PTX. A chimeric mouse model harboring genetic LOX depletion revealed chemotherapy-induced ECM remodeling was mediated by CD8 + T cells expressing LOX. Consistently, adoptive transfer of CD8 + T cells, but not CD4 + T cells or B cells, from PTX-treated mice to naïve immunodeprived mice induced pulmonary ECM remodeling. Lastly, in a clinically relevant metastatic breast carcinoma model, LOX inhibition counteracted the metastasis-promoting, ECM-related effects of PTX. This study highlights the role of immune cells in regulating ECM and metastasis following chemotherapy, suggesting that inhibiting chemotherapy-induced ECM remodeling represents a potential therapeutic strategy for metastatic cancer. SIGNIFICANCE: Chemotherapy induces prometastatic pulmonary ECM remodeling by upregulating LOX in T cells, which can be targeted with LOX inhibitors to suppress metastasis. See related commentary by Kolonin and Woodward, p. 197 ., (©2021 The Authors; Published by the American Association for Cancer Research.)

Background: Metastasis is the major cause of death in patients with cancer. Myeloid skewing of hematopoietic cells is a prominent promoter of metastasis. However, the reservoir of these cells in the bone marrow (BM) compartment and their differentiation pattern from hematopoietic stem and progenitor cells (HSPCs) have not been explored., Methods: We used a unique model system consisting of tumor cell clones with low metastatic potential or high metastatic potential (met-low and met-high, respectively) to investigate the fate of HSPC differentiation using murine melanoma and breast carcinoma. Single-cell RNA sequencing (scRNA-seq) analysis was performed on HSPC obtained from the BM of met-low and met-high tumors. A proteomic screen of tumor-conditioned medium integrated with the scRNA-seq data analysis was performed to analyze the potential cross talk between cancer cells and HSPCs. Adoptive transfer of tumor-educated HSPC subsets obtained from green fluorescent protein (GFP)+ tagged mice was then carried out to identify the contribution of committed HSPCs to tumor spread. Peripheral mononuclear cells obtained from patients with breast and lung cancer were analyzed for HSPC subsets., Results: Mice bearing met-high tumors exhibited a significant increase in the percentage of HSPCs in the BM in comparison with tumor-free mice or mice bearing met-low tumors. ScRNA-seq analysis of these HSPCs revealed that met-high tumors enriched the monocyte-dendritic progenitors (MDPs) but not granulocyte-monocyte progenitors (GMPs). A proteomic screen of tumor- conditioned medium integrated with the scRNA-seq data analysis revealed that the interleukin 6 (IL-6)-IL-6 receptor axis is highly active in HSPC-derived MDP cells. Consequently, loss of function and gain of function of IL-6 in tumor cells resulted in decreased and increased metastasis and corresponding MDP levels, respectively. Importantly, IL-6-educated MDPs induce metastasis within mice bearing met-low tumors-through further differentiation into immunosuppressive macrophages and not dendritic cells. Consistently, MDP but not GMP levels in peripheral blood of breast and lung cancer patients are correlated with tumor aggressiveness., Conclusions: Our study reveals a new role for tumor-derived IL-6 in hijacking the HSPC differentiation program toward prometastatic MDPs that functionally differentiate into immunosuppressive monocytes to support the metastatic switch., Competing Interests: Competing interests: None declared., (© Author(s) (or their employer(s)) 2021. Re-use permitted under CC BY. Published by BMJ.)

Background: Immunomodulatory agents that induce antitumor immunity have great potential for treatment of cancer. We have previously shown that interleukin (IL)-31, a proinflammatory cytokine from the IL-6 family, acts as an antiangiogenic agent. Here, we characterize the immunomodulatory effect of IL-31 in breast cancer., Methods: In vivo breast carcinoma models including EMT6 and PyMT cell lines were used to analyze the effect of IL-31 on the composition of various immune cells in the tumor microenvironment using high-throughput flow cytometry. In vitro studies using isolated cytotoxic T cells, CD4 + T cells, myeloid-derived suppressor cells (MDSCs) and macrophages were carried out to study IL-31 immunological activity. The generation of recombinant IL-31 bound to IgG backbone was used to test IL-31 therapeutic activity., Results: The growth rate of IL-31-expressing breast carcinomas is decreased in comparison with control tumors due, in part, to antitumor immunomodulation. Specifically, cytotoxic T cell activity is increased, whereas the levels of CD4 + T cells, MDSCs, and tumor-associated macrophages are decreased in IL-31-expressing tumors. These cellular changes are accompanied by a cytokine profile associated with antitumor immunity. In vitro, IL-31 directly inhibits CD4 + Th0 cell proliferation, and the expression of Th2 canonical factors GATA3 and IL-4. It also promotes CD8 + T cell activation through inhibition of MDSC activity and motility. Clinically, in agreement with the mouse data, alterations in immune cell composition in human breast cancer biopsies were found to correlate with high expression of IL-31 receptor A (IL-31Ra) . Furthermore, high coexpression of IL-31Ra, IL-2 and IL-4 in tumors correlates with increased survival. Lastly, to study the therapeutic potential of IL-31, a recombinant murine IL-31 molecule was fused to IgG via a linker region (IL-31-L-IgG). This IL-31-L-IgG therapy demonstrates antitumor therapeutic activity in a murine breast carcinoma model., Conclusions: Our findings demonstrate that IL-31 induces antitumor immunity, highlighting its potential utility as a therapeutic immunomodulatory agent., Competing Interests: Competing interests: YS and AA hold a patent on IL-31 as an anticancer drug., (© Author(s) (or their employer(s)) 2020. Re-use permitted under CC BY. Published by BMJ.)

Pancreatic ductal adenocarcinoma (PDAC) is one of the deadliest cancers worldwide. Late diagnosis, desmoplastic tissue and intrinsic resistance to therapy are among the main reasons for its aggressive phenotype. In addition, it is now appreciated that cancer stem cells - a rare subpopulation of tumor cells highly resistant to therapy - are crucial players in PDAC initiation, progression and resistance to therapy. In a recent article in The Journal of Pathology, Hsu et al elucidated the specific roles of abnormal spindle-like, microcephaly-associated protein (ASPM) isoforms in PDAC. The authors reported that ASPM isoform I (ASPM-iI) is mainly expressed in the cytoplasm of PDAC cells. Its expression is associated with the Wnt signaling pathway, which promotes stemness and maintains the cancer stem cell niche. Clinically, expression of ASPM-iI correlates with poor survival in PDAC patients. Thus, this study revealed a novel prognostic marker as well as a potential therapeutic target for PDAC. © 2019 Pathological Society of Great Britain and Ireland. Published by John Wiley & Sons, Ltd., (© 2019 Pathological Society of Great Britain and Ireland. Published by John Wiley & Sons, Ltd.)

Mesenchymal stem cells (MSCs) are multipotent stem cells derived from the mesoderm that give rise to several mesenchymal lineages, including osteoblasts, adipocytes, chondrocytes and myocytes. Their potent ability to home to tumors coupled with their differentiation potential and immunosuppressive function positions MSCs as key regulators of tumor fate. Here we review the existing knowledge on the involvement of MSCs in multiple tumor-promoting processes, including angiogenesis, epithelial-mesenchymal transition, metastasis, immunosuppression and therapy resistance. We also discuss the clinical potential of MSC-based therapy for cancer., (Copyright © 2019 Elsevier Ltd. All rights reserved.)

Radiotherapy induces immune-related responses in cancer patients by various mechanisms. Here, we investigate the immunomodulatory role of tumor-derived microparticles (TMPs)-extracellular vesicles shed from tumor cells-following radiotherapy. We demonstrate that breast carcinoma cells exposed to radiation shed TMPs containing elevated levels of immune-modulating proteins, one of which is programmed death-ligand 1 (PD-L1). These TMPs inhibit cytotoxic T lymphocyte (CTL) activity both in vitro and in vivo, and thus promote tumor growth. Evidently, adoptive transfer of CTLs pre-cultured with TMPs from irradiated breast carcinoma cells increases tumor growth rates in mice recipients in comparison with control mice receiving CTLs pre-cultured with TMPs from untreated tumor cells. In addition, blocking the PD-1-PD-L1 axis, either genetically or pharmacologically, partially alleviates TMP-mediated inhibition of CTL activity, suggesting that the immunomodulatory effects of TMPs in response to radiotherapy is mediated, in part, by PD-L1. Overall, our findings provide mechanistic insights into the tumor immune surveillance state in response to radiotherapy and suggest a therapeutic synergy between radiotherapy and immune checkpoint inhibitors.

Multiple myeloma (MM) is a plasma cell neoplasia commonly treated with proteasome inhibitors such as bortezomib. Although bortezomib has demonstrated enhanced survival benefit, some patients relapse and subsequently develop resistance to such therapy. Here, we investigate the mechanisms underlying relapse and refractory MM following bortezomib treatment. We show that bortezomib-exposed proinflammatory macrophages promote an enrichment of MM-tumor-initiating cells (MM-TIC) both in vitro and in vivo . These effects are regulated in part by IL1β, as blocking the IL1β axis by a pharmacologic or genetic approach abolishes bortezomib-induced MM-TIC enrichment. In MM patients treated with bortezomib, high proinflammatory macrophages in the bone marrow negatively correlate with survival rates (HR, 1.722; 95% CI, 1.138-2.608). Furthermore, a positive correlation between proinflammatory macrophages and TICs in the bone marrow was also found. Overall, our results uncover a protumorigenic cross-talk involving proinflammatory macrophages and MM cells in response to bortezomib therapy, a process that enriches the MM-TIC population. IMPLICATIONS: Our findings suggest that proinflammatory macrophages in bone marrow biopsies represent a potential prognostic biomarker for acquired MM resistance to bortezomib therapy., (©2019 American Association for Cancer Research.)

Cancer stem cells, also termed tumor initiating cells (TICs), are a rare population of cells within the tumor mass which initiate tumor growth and metastasis. In pancreatic cancer, TICs significantly contribute to tumor re-growth after therapy, due to their intrinsic resistance. Here we demonstrate that copper oxide nanoparticles (CuO-NPs) are cytotoxic against TIC-enriched PANC1 human pancreatic cancer cell cultures. Specifically, treatment with CuO-NPs decreases cell viability and increases apoptosis in TIC-enriched PANC1 cultures to a greater extent than in standard PANC1 cultures. These effects are associated with increased reactive oxygen species (ROS) levels, and reduced mitochondrial membrane potential. Furthermore, we demonstrate that CuO-NPs inhibit tumor growth in a pancreatic tumor model in mice. Tumors from mice treated with CuO-NPs contain a significantly higher number of apoptotic TICs in comparison to tumors from untreated mice, confirming that CuO-NPs target TICs in vivo. Overall, our findings highlight the potential of using CuO-NPs as a new therapeutic modality for pancreatic cancer.

Stromal cells residing in the tumor microenvironment contribute to the development of therapy resistance. Here we show that chemotherapy-educated mesenchymal stem cells (MSC) promote therapy resistance via cross-talk with tumor-initiating cells (TIC), a resistant tumor cell subset that initiates tumorigenesis and metastasis. In response to gemcitabine chemotherapy, MSCs colonized pancreatic adenocarcinomas in large numbers and resided in close proximity to TICs. Furthermore, gemcitabine-educated MSCs promoted the enrichment of TICs in vitro and enhance tumor growth in vivo These effects were dependent on the secretion of CXCL10 by gemcitabine-educated MSCs and subsequent activation of the CXCL10-CXCR3 axis in TICs. In an orthotopic pancreatic tumor model, targeting TICs using nanovesicles (called nanoghosts) derived from MSC membranes and loaded with a CXCR3 antagonist enhanced therapy outcome and delayed tumor regrowth when administered in combination with gemcitabine. Overall, our results establish a mechanism through which MSCs promote chemoresistance, and propose a novel drug delivery system to target TICs and overcome this resistance. Significance: These results establish a mechanism by which mesenchyme stem cells in the tumor microenvironment promote chemoresistance, and they propose a novel drug delivery system to overcome this challenge. Cancer Res; 78(5); 1253-65. ©2018 AACR ., (©2018 American Association for Cancer Research.)

It has recently been suggested that pro-tumorigenic host-mediated processes induced in response to chemotherapy counteract the anti-tumor activity of therapy, and thereby decrease net therapeutic outcome. Here we use experimental data to formulate a mathematical model describing the host response to different doses of paclitaxel (PTX) chemotherapy as well as the duration of the response. Three previously described host-mediated effects are used as readouts for the host response to therapy. These include the levels of circulating endothelial progenitor cells in peripheral blood and the effect of plasma derived from PTX-treated mice on migratory and invasive properties of tumor cells in vitro . A first set of mathematical models, based on basic principles of pharmacokinetics/pharmacodynamics, did not appropriately describe the dose-dependence and duration of the host response regarding the effects on invasion. We therefore provide an alternative mathematical model with a dose-dependent threshold, instead of a concentration-dependent one, that describes better the data. This model is integrated into a global model defining all three host-mediated effects. It not only precisely describes the data, but also correctly predicts host-mediated effects at different doses as well as the duration of the host response. This mathematical model may serve as a tool to predict the host response to chemotherapy in cancer patients, and therefore may be used to design chemotherapy regimens with improved therapeutic outcome by minimizing host mediated effects., Competing Interests: CONFLICTS OF INTEREST The authors declare no conflicts of interest.

Surgery remains the most successful curative treatment for cancer. However, some patients with early-stage disease who undergo surgery eventually succumb to distant metastasis. Here, we show that in response to surgery, the lungs become more vulnerable to metastasis due to extracellular matrix remodeling. Mice that undergo surgery or that are preconditioned with plasma from donor mice that underwent surgery succumb to lung metastases earlier than controls. Increased lysyl oxidase (LOX) activity and expression, fibrillary collagen crosslinking, and focal adhesion signaling contribute to this effect, with the hypoxic surgical site serving as the source of LOX. Furthermore, the lungs of recipient mice injected with plasma from post-surgical colorectal cancer patients are more prone to metastatic seeding than mice injected with baseline plasma. Downregulation of LOX activity or levels reduces lung metastasis after surgery and increases survival, highlighting the potential of LOX inhibition in reducing the risk of metastasis following surgery., (Copyright © 2017 The Author(s). Published by Elsevier Inc. All rights reserved.)

Pro-inflammatory cytokines in the tumor microenvironment are known for their ability to either inhibit or promote cancer progression. Here we evaluated the role of Interleukin-31 (IL31), a protein belonging to the pro-inflammatory IL-6 cytokine family which has been characterized in autoimmune disease, in tumorigenesis. We show that IL31 and its receptor, IL31RA, are highly expressed in various human and mouse cancer cell lines, as well as in tumor specimens from cancer patients. MC38 murine colon carcinoma cells depleted of IL31 exhibit an increase in invasive and migratory properties in vitro, effects that are reversed by supplementing the cells with exogenous IL31. In vivo, IL31-depleted MC38 tumor cells implanted to mice grow faster than control tumors. In contrast, MC38 tumor-bearing mice infused with recombinant IL31, exhibit a significant reduction in tumor growth than control mice. Furthermore, IL31 infusion reduces the number of metastatic lesions in the lungs of mice bearing 4T1 murine metastatic breast carcinoma. Lastly, injecting tumor-bearing, chemotherapy-treated mice with a long-lived IL31-IgG fusion protein reduces tumor growth, angiogenesis and pulmonary metastasis to a greater extent than when chemotherapy is used alone. The IL31 anti-tumor activity is explained, in part, by the anti-angiogenic effects demonstrated both in vitro and in vivo highlighting the potential use of IL31 as an anti-cancer drug.

While chemotherapy strongly restricts or reverses tumor growth, the response of host tissue to therapy can counteract its anti-tumor activity by promoting tumor re-growth and/or metastases, thus limiting therapeutic efficacy. Here, we show that vascular endothelial growth factor receptor 3 (VEGFR3)-expressing macrophages infiltrating chemotherapy-treated tumors play a significant role in metastasis. They do so in part by inducing lymphangiogenesis as a result of cathepsin release, leading to VEGF-C upregulation by heparanase. We found that macrophages from chemotherapy-treated mice are sufficient to trigger lymphatic vessel activity and structure in naive tumors in a VEGFR3-dependent manner. Blocking VEGF-C/VEGFR3 axis inhibits the activity of chemotherapy-educated macrophages, leading to reduced lymphangiogenesis in treated tumors. Overall, our results suggest that disrupting the VEGF-C/VEGFR3 axis not only directly inhibits lymphangiogenesis but also blocks the pro-metastatic activity of macrophages in chemotherapy-treated mice., (Copyright © 2016 The Author(s). Published by Elsevier Inc. All rights reserved.)

Multiple myeloma (MM) is a chronic progressive malignancy of plasma cells. Although treatment with the novel proteasome inhibitor, bortezomib, significantly improves patient survival, some patients fail to respond due to the development of de novo resistance. We have previously shown that cytotoxic drugs can induce pro-tumorigenic host-mediated effects which contribute to tumour re-growth and metastasis, and thus limit anti-tumour efficacy. However, such effects and their impact on tumour cell aggressiveness have not been investigated using cytostatic agents such as bortezomib. Here we show that plasma from bortezomib-treated mice significantly increases migration, viability and proliferation of MM cells in vitro, compared to plasma from vehicle treated mice. In vivo, bortezomib induces the mobilization of pro-angiogenic bone marrow cells. Furthermore, mice treated with bortezomib and subsequently were used as recipients for an injection of MM cells succumb to MM earlier than mice treated with the vehicle. We show that bortezomib promotes pro-inflammatory macrophages which account for MM cell aggressiveness, an effect which is partially mediated by interleukin-16. Accordingly, co-inoculation of MM cells with pro-inflammatory macrophages from bortezomib-treated mice accelerates MM disease progression. Taken together, our results suggest that, in addition to the known effective anti-tumour activity of bortezomib, host-driven pro-tumorigenic effects generated in response to treatment can promote MM aggressiveness, and thus may contribute to the overall limited efficacy. Copyright © 2016 Pathological Society of Great Britain and Ireland. Published by John Wiley & Sons, Ltd., (Copyright © 2016 Pathological Society of Great Britain and Ireland. Published by John Wiley & Sons, Ltd.)

The tumor microenvironment consists of a variety of cell types. The contribution of each cell type to the tumor is an emerging subject in the field of cancer research. Here, we describe protocols for dissociating tumor tissues and Matrigel plugs into single cells for further analysis by flow cytometry. These protocols can be used for evaluating the cellular component of solid tumors from human or mouse origin or Matrigel plugs implanted in mice. The protocols describe the dissociation of tumor tissue with or without dissociation automatic devices. Subsequently, the use of flow cytometry for immunophenotypic analysis of host cells found in the tumor microenvironment, including myeloid derived suppressor cells, endothelial cells, and macrophages is provided. These methods can be used to broaden our understanding of the cross-talk between tumor and host cells in the tumor microenvironment. © 2016 by John Wiley & Sons, Inc., (Copyright © 2016 John Wiley & Sons, Inc.)

The c-Jun Dimerization Protein 2, JDP2, is a basic leucine zipper protein member of the activator protein-1 (AP-1) family of transcription factors. JDP2 typically suppresses gene transcription through multiple mechanisms and plays a dual role in multiple cellular processes, including cell differentiation and proliferation which is dependent on AP-1 function. Whereas the role of JDP2 expression within cancer cells has been studied, its role in stromal cells at the tumor microenvironment is largely unknown. Here we show that mice lacking JDP2 (JDP2-/-) display a reduced rate of metastasis in Lewis lung carcinoma (LLC) and polyoma middle T-antigen (PyMT) breast carcinoma mouse models. The replacement of wild-type bone marrow derived cells (BMDCs) with JDP2-deficient BMDCs recapitulates the metastatic phenotype of JDP2-/- tumor-bearing mice. In vitro, conditioned medium of wild-type BMDCs significantly potentiates the migration and invasion capacity of LLC cells as compared to that of JDP2-/- BMDCs. Furthermore, wild-type BMDCs secrete CCL5, a chemokine known to contribute to metastasis, to a greater extent than JDP2-/- BMDCs. The supplementation of CCL5 in JDP2-/- BMDC conditioned medium was sufficient to potentiate the invasion capacity of LLC. Overall, this study suggests that JDP2-expressing BMDCs within the tumor microenvironment contribute to metastatic spread.

A major therapeutic obstacle in clinical oncology is intrinsic or acquired resistance to therapy, leading to subsequent relapse. We have previously shown that systemic administration of different cytotoxic drugs can induce a host response that contributes to tumor angiogenesis, regrowth and metastasis. Here we characterize the host response to a single dose of local radiation, and its contribution to tumor progression and metastasis. We show that plasma from locally irradiated mice increases the migratory and invasive properties of colon carcinoma cells. Furthermore, locally irradiated mice intravenously injected with CT26 colon carcinoma cells succumb to pulmonary metastasis earlier than their respective controls. Consequently, orthotopically implanted SW480 human colon carcinoma cells in mice that underwent radiation, exhibited increased metastasis to the lungs and liver compared to their control tumors. The irradiated tumors exhibited an increase in the colonization of macrophages compared to their respective controls; and macrophage depletion in irradiated tumor-bearing mice reduces the number of metastatic lesions. Finally, the anti-tumor agent, dequalinium-14, in addition to its anti-tumor effect, reduces macrophage motility, inhibits macrophage infiltration of irradiated tumors and reduces the extent of metastasis in locally irradiated mice. Overall, this study demonstrates the adverse effects of local radiation on the host that result in macrophage-induced metastasis.