VEGFR1-positive haematopoietic bone marrow progenitors initiate the pre-metastatic niche
TL;DR: A requirement for VEGFR1+ haematopoietic progenitor cells that express vascular endothelial growth factor receptor 1 (VEGFR1) home to tumour-specific pre-metastatic sites and form cellular clusters before the arrival of tumour cells is demonstrated.
Abstract: The cellular and molecular mechanisms by which a tumour cell undergoes metastasis to a predetermined location are largely unknown. Here we demonstrate that bone marrow-derived haematopoietic progenitor cells that express vascular endothelial growth factor receptor 1 (VEGFR1; also known as Flt1) home to tumour-specific pre-metastatic sites and form cellular clusters before the arrival of tumour cells. Preventing VEGFR1 function using antibodies or by the removal of VEGFR1(+) cells from the bone marrow of wild-type mice abrogates the formation of these pre-metastatic clusters and prevents tumour metastasis, whereas reconstitution with selected Id3 (inhibitor of differentiation 3)-competent VEGFR1+ cells establishes cluster formation and tumour metastasis in Id3 knockout mice. We also show that VEGFR1+ cells express VLA-4 (also known as integrin alpha4beta1), and that tumour-specific growth factors upregulate fibronectin--a VLA-4 ligand--in resident fibroblasts, providing a permissive niche for incoming tumour cells. Conditioned media obtained from distinct tumour types with unique patterns of metastatic spread redirected fibronectin expression and cluster formation, thereby transforming the metastatic profile. These findings demonstrate a requirement for VEGFR1+ haematopoietic progenitors in the regulation of metastasis, and suggest that expression patterns of fibronectin and VEGFR1+VLA-4+ clusters dictate organ-specific tumour spread.
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TL;DR: The molecular pathways of this cancer-related inflammation are now being unravelled, resulting in the identification of new target molecules that could lead to improved diagnosis and treatment.
Abstract: The mediators and cellular effectors of inflammation are important constituents of the local environment of tumours. In some types of cancer, inflammatory conditions are present before a malignant change occurs. Conversely, in other types of cancer, an oncogenic change induces an inflammatory microenvironment that promotes the development of tumours. Regardless of its origin, 'smouldering' inflammation in the tumour microenvironment has many tumour-promoting effects. It aids in the proliferation and survival of malignant cells, promotes angiogenesis and metastasis, subverts adaptive immune responses, and alters responses to hormones and chemotherapeutic agents. The molecular pathways of this cancer-related inflammation are now being unravelled, resulting in the identification of new target molecules that could lead to improved diagnosis and treatment.
9,282 citations
TL;DR: The principal mechanisms that govern the effects of inflammation and immunity on tumor development are outlined and attractive new targets for cancer therapy and prevention are discussed.
8,664 citations
Cites background from "VEGFR1-positive haematopoietic bone..."
...Some of these cells may already be targeted to the premetastatic niche in response to tumor-generated inflammatory signals prior to the arrival of metastasis-initiating cancer cells (Kaplan et al., 2005)....
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...Recruitment of such cells may be a consequence of tumor necrosis, but as mentioned above certain carcinomas actively secrete factors that upregulate fibronectin and cause migration of VEGF receptor 1 (VEGFR1)-positive hematopoietic progenitors to the premetastatic niche (Kaplan et al., 2005)....
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TL;DR: The paradoxical roles of the tumor microenvironment during specific stages of cancer progression and metastasis are discussed, as well as recent therapeutic attempts to re-educate stromal cells within the TME to have anti-tumorigenic effects.
Abstract: Cancers develop in complex tissue environments, which they depend on for sustained growth, invasion and metastasis. Unlike tumor cells, stromal cell types within the tumor microenvironment (TME) are genetically stable and thus represent an attractive therapeutic target with reduced risk of resistance and tumor recurrence. However, specifically disrupting the pro-tumorigenic TME is a challenging undertaking, as the TME has diverse capacities to induce both beneficial and adverse consequences for tumorigenesis. Furthermore, many studies have shown that the microenvironment is capable of normalizing tumor cells, suggesting that re-education of stromal cells, rather than targeted ablation per se, may be an effective strategy for treating cancer. Here we discuss the paradoxical roles of the TME during specific stages of cancer progression and metastasis, as well as recent therapeutic attempts to re-educate stromal cells within the TME to have anti-tumorigenic effects.
5,396 citations
TL;DR: Preclinical and clinical studies have shown new molecular targets and principles, which may provide avenues for improving the therapeutic benefit from anti-angiogenic strategies.
Abstract: Blood vessels deliver oxygen and nutrients to every part of the body, but also nourish diseases such as cancer. Over the past decade, our understanding of the molecular mechanisms of angiogenesis (blood vessel growth) has increased at an explosive rate and has led to the approval of anti-angiogenic drugs for cancer and eye diseases. So far, hundreds of thousands of patients have benefited from blockers of the angiogenic protein vascular endothelial growth factor, but limited efficacy and resistance remain outstanding problems. Recent preclinical and clinical studies have shown new molecular targets and principles, which may provide avenues for improving the therapeutic benefit from anti-angiogenic strategies.
4,441 citations
TL;DR: In addition to their role in extracellular matrix turnover and cancer cell migration, MMPs regulate signaling pathways that control cell growth, inflammation, or angiogenesis and may even work in a nonproteolytic manner.
4,185 citations
Cites background from "VEGFR1-positive haematopoietic bone..."
...Soluble factors released from the primary tumor appear to trigger the formation of a metastatic niche that is induced initially by the expression of embryonic-type fibronectin, which is most likely produced by fibroblasts at these sites (Kaplan et al., 2005)....
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...Indeed, MMP-9 turns out to be critical for the formation of the metastatic niche (Kaplan et al., 2005), which is most likely linked with its ability to liberate VEGF and thereby support angiogenesis (Bergers et al., 2000)....
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...MMP-9 releases soluble Kit-ligand to recruit stem and progenitor cells from the bone marrow (Heissig et al., 2002), which may be of particular significance in this context, given that the niche-forming progenitor cells express c-Kit (Kaplan et al., 2005)....
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...In fact, MMP-2, -3, and -9 have already been shown to contribute to the establishment of metastasis-prone sites at tumor-distant organs (Erler et al., 2009; Huang et al., 2009; Kaplan et al., 2005)....
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...Recent findings suggest that metastatic tumor cells specifically localize to receptive sites, called premetastatic niches, in a complex interplay with inflammatory cells and hematopoietic progenitor cells (Kaplan et al., 2005)....
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References
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TL;DR: It is now becoming clear that the tumour microenvironment, which is largely orchestrated by inflammatory cells, is an indispensable participant in the neoplastic process, fostering proliferation, survival and migration.
Abstract: Recent data have expanded the concept that inflammation is a critical component of tumour progression. Many cancers arise from sites of infection, chronic irritation and inflammation. It is now becoming clear that the tumour microenvironment, which is largely orchestrated by inflammatory cells, is an indispensable participant in the neoplastic process, fostering proliferation, survival and migration. In addition, tumour cells have co-opted some of the signalling molecules of the innate immune system, such as selectins, chemokines and their receptors for invasion, migration and metastasis. These insights are fostering new anti-inflammatory therapeutic approaches to cancer development.
12,395 citations
TL;DR: It is reported that the chemokine receptors CXCR4 and CCR7 are highly expressed in human breast cancer cells, malignant breast tumours and metastases and their respective ligands CXCL12/SDF-1α and CCL21/6Ckine exhibit peak levels of expression in organs representing the first destinations of breast cancer metastasis.
Abstract: Breast cancer is characterized by a distinct metastatic pattern involving the regional lymph nodes, bone marrow, lung and liver. Tumour cell migration and metastasis share many similarities with leukocyte trafficking, which is critically regulated by chemokines and their receptors. Here we report that the chemokine receptors CXCR4 and CCR7 are highly expressed in human breast cancer cells, malignant breast tumours and metastases. Their respective ligands CXCL12/SDF-1α and CCL21/6Ckine exhibit peak levels of expression in organs representing the first destinations of breast cancer metastasis. In breast cancer cells, signalling through CXCR4 or CCR7 mediates actin polymerization and pseudopodia formation, and subsequently induces chemotactic and invasive responses. In vivo, neutralizing the interactions of CXCL12/CXCR4 significantly impairs metastasis of breast cancer cells to regional lymph nodes and lung. Malignant melanoma, which has a similar metastatic pattern as breast cancer but also a high incidence of skin metastases, shows high expression levels of CCR10 in addition to CXCR4 and CCR7. Our findings indicate that chemokines and their receptors have a critical role in determining the metastatic destination of tumour cells.
5,132 citations
TL;DR: Macrophages are educated by the tumour microenvironment, so that they adopt a trophic role that facilitates angiogenesis, matrix breakdown and tumour-cell motility — all of which are elements of the metastatic process.
Abstract: Evidence from clinical and experimental studies indicates that macrophages promote solid-tumour progression and metastasis. Macrophages are educated by the tumour microenvironment, so that they adopt a trophic role that facilitates angiogenesis, matrix breakdown and tumour-cell motility — all of which are elements of the metastatic process. During an inflammatory response, macrophages also produce many compounds — ranging from mutagenic oxygen and nitrogen radicals to angiogenic factors — that can contribute to cancer initiation and promotion. Macrophages therefore represent an important drug target for cancer prevention and cure.
3,130 citations
TL;DR: The results show that MMP-9 is a component of theAngiogenic switch, and MMP inhibitors reduce angiogenic switching, and tumour number and growth, as does genetic ablation of M MP-9.
Abstract: During carcinogenesis of pancreatic islets in transgenic mice, an angiogenic switch activates the quiescent vasculature Paradoxically, vascular endothelial growth factor (VEGF) and its receptors are expressed constitutively Nevertheless, a synthetic inhibitor (SU5416) of VEGF signalling impairs angiogenic switching and tumour growth Two metalloproteinases, MMP-2/gelatinase-A and MMP-9/gelatinase-B, are upregulated in angiogenic lesions MMP-9 can render normal islets angiogenic, releasing VEGF MMP inhibitors reduce angiogenic switching, and tumour number and growth, as does genetic ablation of MMP-9 Absence of MMP-2 does not impair induction of angiogenesis, but retards tumour growth, whereas lack of urokinase has no effect Our results show that MMP-9 is a component of the angiogenic switch
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