Search

Growing evidence highlights the importance of tumor endothelial cells (TECs) in the tumor microenvironment (TME) for promoting tumor growth and evading immune responses. Immunomodulatory endothelial cells (IMECs) represent a distinct plastic phenotype of ECs that exerts the ability to modulate immunity in health and disease. This review discusses our current understanding of IMECs in cancer biology, scrutinizing insights from single-cell reports to compare their characteristics and function dynamics across diverse tumor types, conditions, and species. We investigate possible implications of exploiting IMECs in the context of cancer treatment, particularly examining their influence on the efficacy of existing therapies and the potential to leverage them as targets in optimizing immunotherapeutic strategies., Competing Interests: Declaration of interests None are declared by the authors., (Copyright © 2024. Published by Elsevier Inc.)

Macrophages are innate immune cells that play key roles during both homeostasis and disease. Depending on the microenvironmental cues sensed in different tissues, macrophages are known to acquire specific phenotypes and exhibit unique features that, ultimately, orchestrate tissue homeostasis, defense, and repair. Within the tumor microenvironment, macrophages are referred to as tumor-associated macrophages (TAMs) and constitute a heterogeneous population. Like their tissue resident counterpart, TAMs are plastic and can switch function and phenotype according to the niche-derived stimuli sensed. While changes in TAM phenotype are known to be accompanied by adaptive alterations in their cell metabolism, it is reported that metabolic reprogramming of macrophages can dictate their activation state and function. In line with these observations, recent research efforts have been focused on defining the metabolic traits of TAM subsets in different tumor malignancies and understanding their role in cancer progression and metastasis formation. This knowledge will pave the way to novel therapeutic strategies tailored to cancer subtype-specific metabolic landscapes. This review outlines the metabolic characteristics of distinct TAM subsets and their implications in tumorigenesis across multiple cancer types., (© 2024 The Authors. Molecular Oncology published by John Wiley & Sons Ltd on behalf of Federation of European Biochemical Societies.)

The prolyl hydroxylase domain/hypoxia-inducible factor (PHD/HIF) pathway has been implicated in a wide range of immune and inflammatory processes, including in the oxygen-deprived tumor microenvironment. To examine the effect of HIF stabilization in antitumor immunity, we deleted Phd2 selectively in T lymphocytes using the cre/lox system. We show that the deletion of PHD2 in lymphocytes resulted in enhanced regression of EG7-OVA tumors, in a HIF-1α-dependent manner. The enhanced control of neoplastic growth correlated with increased polyfunctionality of CD8+ tumor-infiltrating lymphocytes, as indicated by enhanced expression of IFNγ, TNFα, and granzyme B. Phenotypic and transcriptomic analyses pointed to a key role of glycolysis in sustaining CTL activity in the tumor bed and identified the PHD2/HIF-1 pathway as a potential target for cancer immunotherapy., (©2023 American Association for Cancer Research.)

Immunoediting sculpts immunogenicity and thwarts host anti-tumor responses in tumor cells during tumorigenesis; however, it remains unknown whether metabolic programming of tumor cells can be guided by immunosurveillance. Here, we report that T cell-mediated immunosurveillance in early-stage tumorigenesis instructs c-Myc upregulation and metabolic reprogramming in tumor cells. This previously unexplored tumor-immune interaction is controlled by non-canonical interferon gamma (IFNγ)-STAT3 signaling and supports tumor immune evasion. Our findings uncover that immunoediting instructs deregulated bioenergetic programs in tumor cells to empower them to disarm the T cell-mediated immunosurveillance by imposing metabolic tug-of-war between tumor and infiltrating T cells and forming the suppressive tumor microenvironment., Competing Interests: Declaration of interests P.-C.H. is a member of the scientific advisory board for Elixiron Immunotherapeutics and received research grants from Elixiron Immunotherapeutics. P.-C.H. is also a founder of Pilatus Biosciences., (Copyright © 2022 Elsevier Inc. All rights reserved.)

Tumour-associated macrophages (TAMs) are essential players in the tumour microenvironment (TME) and modulate various pro-tumorigenic functions such as immunosuppression, angiogenesis, cancer cell proliferation, invasion and metastasis, along with resistance to anti-cancer therapies. TAMs also mediate important anti-tumour functions and can clear dying cancer cells via efferocytosis. Thus, not surprisingly, TAMs exhibit heterogeneous activities and functional plasticity depending on the type and context of cancer cell death that they are faced with. This ultimately governs both the pro-tumorigenic and anti-tumorigenic activity of TAMs, making the interface between TAMs and dying cancer cells very important for modulating cancer growth and the efficacy of chemo-radiotherapy or immunotherapy. In this review, we discuss the interface of TAMs with cancer cell death from the perspectives of cell death pathways, TME-driven variations, TAM heterogeneity and cell-death-inducing anti-cancer therapies. We believe that a better understanding of how dying cancer cells influence TAMs can lead to improved combinatorial anti-cancer therapies, especially in combination with TAM-targeting immunotherapies.

Cachexia is a wasting syndrome characterized by devastating skeletal muscle atrophy that dramatically increases mortality in various diseases, most notably in cancer patients with a penetrance of up to 80%. Knowledge regarding the mechanism of cancer-induced cachexia remains very scarce, making cachexia an unmet medical need. In this study, we discovered strong alterations of iron metabolism in the skeletal muscle of both cancer patients and tumor-bearing mice, characterized by decreased iron availability in mitochondria. We found that modulation of iron levels directly influences myotube size in vitro and muscle mass in otherwise healthy mice. Furthermore, iron supplementation was sufficient to preserve both muscle function and mass, prolong survival in tumor-bearing mice, and even rescues strength in human subjects within an unexpectedly short time frame. Importantly, iron supplementation refuels mitochondrial oxidative metabolism and energy production. Overall, our findings provide new mechanistic insights in cancer-induced skeletal muscle wasting, and support targeting iron metabolism as a potential therapeutic option for muscle wasting diseases., (© 2022 The Authors. Published under the terms of the CC BY 4.0 license.)

Tumor vessel co-option is poorly understood, yet it is a resistance mechanism against anti-angiogenic therapy (AAT). The heterogeneity of co-opted endothelial cells (ECs) and pericytes, co-opting cancer and myeloid cells in tumors growing via vessel co-option, has not been investigated at the single-cell level. Here, we use a murine AAT-resistant lung tumor model, in which VEGF-targeting induces vessel co-option for continued growth. Single-cell RNA sequencing (scRNA-seq) of 31,964 cells reveals, unexpectedly, a largely similar transcriptome of co-opted tumor ECs (TECs) and pericytes as their healthy counterparts. Notably, we identify cell types that might contribute to vessel co-option, i.e., an invasive cancer-cell subtype, possibly assisted by a matrix-remodeling macrophage population, and another M1-like macrophage subtype, possibly involved in keeping or rendering vascular cells quiescent., Competing Interests: Declaration of interest The authors declare no competing interests., (Copyright © 2021 The Authors. Published by Elsevier Inc. All rights reserved.)

Cancer immunotherapy aims to augment the response of the patient's own immune system against cancer cells. Despite effective for some patients and some cancer types, the therapeutic efficacy of this treatment is limited by the composition of the tumor microenvironment (TME), which is not well-suited for the fitness of anti-tumoral immune cells. However, the TME differs between cancer types and tissues, thus complicating the possibility of the development of therapies that would be effective in a large range of patients. A possible scenario is that each type of cancer cell, granted by its own mutations and reminiscent of the functions of the tissue of origin, has a specific metabolism that will impinge on the metabolic composition of the TME, which in turn specifically affects T cell fitness. Therefore, targeting cancer or T cell metabolism could increase the efficacy and specificity of existing immunotherapies, improving disease outcome and minimizing adverse reactions., (Copyright © 2020 The Author(s). Published by Elsevier Ltd.. All rights reserved.)

IL1β is a central mediator of inflammation. Secretion of IL1β typically requires proteolytic maturation by the inflammasome and formation of membrane pores by gasdermin D (GSDMD). Emerging evidence suggests an important role for IL1β in promoting cancer progression in patients, but the underlying mechanisms are ill-defined. Here, we have shown a key role for IL1β in driving tumor progression in two distinct mouse tumor models. Notably, activation of the inflammasome, caspase-8, as well as the pore-forming proteins GSDMD and mixed lineage kinase domain-like protein in the host were dispensable for the release of intratumoral bioactive IL1β. Inflammasome-independent IL1β release promoted systemic neutrophil expansion and fostered accumulation of T-cell-suppressive neutrophils in the tumor. Moreover, IL1β was essential for neutrophil infiltration triggered by antiangiogenic therapy, thereby contributing to treatment-induced immunosuppression. Deletion of IL1β allowed intratumoral accumulation of CD8 + effector T cells that subsequently activated tumor-associated macrophages. Depletion of either CD8 + T cells or macrophages abolished tumor growth inhibition in IL1β-deficient mice, demonstrating a crucial role for CD8 + T-cell-macrophage cross-talk in the antitumor immune response. Overall, these results support a tumor-promoting role for IL1β through establishing an immunosuppressive microenvironment and show that inflammasome activation is not essential for release of this cytokine in tumors., (©2020 American Association for Cancer Research.)

The tumor microenvironment (TME) not only facilitates cancer progression from the early formation to distant metastasis, but also it differs itself from time to time alongside the tumor evolution. Tumor-associated macrophages (TAMs), whether as pre-existing tissue-resident macrophages or recruited monocytes, are an inseparable part of this microenvironment. As their parents are broadly classified into a dichotomic, simplistic M1 and M2 subtypes, TAMs also exert paradoxical and diverse phenotypes as they are settled in different regions of TME and receive different microenvironmental signals. Briefly, M1 macrophages induce an inflammatory precancerous niche and flame the early oncogenic mutations, whereas their M2 counterparts are reprogrammed to release various growth factors and providing an immunosuppressive state in TME as long as abetting hypoxic cancer cells to set up a new vasculature. Further, they mediate stromal micro-invasion and co-migrate with invasive cancer cells to invade the vascular wall and neural sheath, while another subtype of TAMs prepares suitable niches much earlier than metastatic cells arrive at the target tissues. Accordingly, at the neoplastic transformation, during the benign-to-malignant transition and through the metastatic cascade, macrophages are involved in shaping the primary, micro-invasive and pre-metastatic TMEs. Whether their behavioral plasticity is derived from distinct genotypes or is fueled by microenvironmental cues, it could define these cells as remarkably interesting therapeutic targets.

It is generally accepted that metabolism is able to shape the immune response. Only recently we are gaining awareness that the metabolic crosstalk between different tumor compartments strongly contributes to the harsh tumor microenvironment (TME) and ultimately impairs immune cell fitness and effector functions. The major aims of this review are to provide an overview on the immune system in cancer; to position oxygen shortage and metabolic competition as the ground of a restrictive TME and as important players in the anti-tumor immune response; to define how immunotherapies affect hypoxia/oxygen delivery and the metabolic landscape of the tumor; and vice versa, how oxygen and metabolites within the TME impinge on the success of immunotherapies. By analyzing preclinical and clinical endeavors, we will discuss how a metabolic characterization of the TME can identify novel targets and signatures that could be exploited in combination with standard immunotherapies and can help to predict the benefit of new and traditional immunotherapeutic drugs.

Macrophages play an important role in tissue development and homeostasis. They serve as a nexus between adaptive and innate immunity, and employ considerable plasticity. In cancer, they play a pivotal role in chronic inflammation and tumor growth either by directly stimulating the proliferation of cancer cells or by producing angiogenic and lymphangiogenic factors. Although numerous immune cells play an important role in the tumor microenvironment, tumor-associated macrophages (TAMs) are by far the most extensively studied. A better understanding of the role of TAMs in mediating chemo- and radiotherapy resistance and suppressing immunosurveillance has led to numerous strategies targeting TAMs as an anticancer therapy either by targeting them directly or by polarizing TAMs toward a tumoricidal phenotype.

Research over the last decades has provided strong evidence for the pivotal role of the tumor-associated blood and lymphatic vasculature in supporting immunoevasion and in subverting T cell-mediated immunosurveillance. Conversely, tumor blood and lymphatic vessel growth is in part regulated by the immune system, with infiltrating innate as well as adaptive immune cells providing both immunosuppressive and various angiogenic signals. Thus, tumor angiogenesis and escape of immunosurveillance are two cancer hallmarks that are tightly linked and interregulated by cell constituents from compartments secreting both chemokines and cytokines. In this review, we discuss the implication and regulation of innate and adaptive immune cells in regulating blood and lymphatic angiogenesis in tumor progression and metastases. Moreover, we also highlight novel therapeutic approaches that target the tumor vasculature as well as the immune compartment to sustain and improve therapeutic efficacy in cancer.

Tumor angiogenesis and escape of immunosurveillance are two cancer hallmarks that are tightly linked and reciprocally regulated by paracrine signaling cues of cell constituents from both compartments. Formation and remodeling of new blood vessels in tumors is abnormal and facilitates immune evasion. In turn, immune cells in the tumor, specifically in context with an acidic and hypoxic environment, can promote neovascularization. Immunotherapy has emerged as a major therapeutic modality in cancer but is often hampered by the low influx of activated cytotoxic T-cells. On the other hand, anti-angiogenic therapy has been shown to transiently normalize the tumor vasculature and enhance infiltration of T lymphocytes, providing a rationale for a combination of these two therapeutic approaches to sustain and improve therapeutic efficacy in cancer. In this review, we discuss how the tumor vasculature facilitates an immunosuppressive phenotype and vice versa how innate and adaptive immune cells regulate angiogenesis during tumor progression. We further highlight recent results of antiangiogenic immunotherapies in experimental models and the clinic to evaluate the concept that targeting both the tumor vessels and immune cells increases the effectiveness in cancer patients., (Copyright © 2018 Elsevier Ltd. All rights reserved.)

From the evidence on clinical studies and experimental mouse models we now know that tumor-associated macrophages (TAMs) sustain tumor development in many different ways. They play a role in angiogenesis, tumor cell invasion, and metastasis formation. Additionally, TAMs interfere with natural killer and T-cell antitumoral activities, producing an immune-suppressive environment that protects tumor cell growth. This indicates that the tumoricidal activity of macrophages within the tumor microenviroment is lost due to an imbalance of the regulatory mechanisms underpinning these cells' function. Since metabolism is emerging as a major modulator of macrophage function, metabolic changes in response to signals coming from cancer or other immune cells might promote this imbalance, enhancing the tumorigenic activities of TAMs. In this review we describe the novel, most recent findings on how metabolism shapes TAM functions or conversely, how TAMs influence the activity of other cells through metabolic mechanisms. The complete elucidation of the metabolic switches between pro- and antitumoral properties of macrophages, now still in its infancy, is destined to provide scientists with new instruments not only to understand but also to combat cancer., (© 2017 Federation of European Biochemical Societies.)

Various steady state and inflamed tissues have been shown to contain a heterogeneous DC population consisting of developmentally distinct subsets, including cDC1s, cDC2s and monocyte-derived DCs, displaying differential functional specializations. The identification of functionally distinct tumour-associated DC (TADC) subpopulations could prove essential for the understanding of basic TADC biology and for envisaging targeted immunotherapies. We demonstrate that multiple mouse tumours as well as human tumours harbour ontogenically discrete TADC subsets. Monocyte-derived TADCs are prominent in tumour antigen uptake, but lack strong T-cell stimulatory capacity due to NO-mediated immunosuppression. Pre-cDC-derived TADCs have lymph node migratory potential, whereby cDC1s efficiently activate CD8 + T cells and cDC2s induce Th17 cells. Mice vaccinated with cDC2s displayed a reduced tumour growth accompanied by a reprogramming of pro-tumoural TAMs and a reduction of MDSCs, while cDC1 vaccination strongly induces anti-tumour CTLs. Our data might prove important for therapeutic interventions targeted at specific TADC subsets or their precursors.

Hypoxic tumor-associated macrophages (TAMs) acquire angiogenic and immunosuppressive properties. Yet it remains unknown if metabolic changes influence these functions. Here, we argue that hypoxic TAMs strongly upregulate the expression of REDD1, a negative regulator of mTOR. REDD1-mediated mTOR inhibition hinders glycolysis in TAMs and curtails their excessive angiogenic response, with consequent formation of abnormal blood vessels. Accordingly, REDD1 deficiency in TAMs leads to the formation of smoothly aligned, pericyte-covered, functional vessels, which prevents vessel leakiness, hypoxia, and metastases. Mechanistically, highly glycolytic REDD1-deficient TAMs outcompete endothelial cells for glucose usage that thwarts vascular hyperactivation and promotes the formation of quiescent vascular junctions. Tuning down glycolysis in REDD1 knockout TAMs re-establishes abnormal angiogenesis and metastases. On this basis, we prove that the anti-tumor effect of mTOR inhibitors is partly countered by the deleterious outcome of these drugs on TAMs. Our data provide a functional link between TAM metabolism and tumor angiogenesis., (Copyright © 2016 Elsevier Inc. All rights reserved.)

A lot of attention has been dedicated to investigate the role of the tyrosine kinase receptor MET in tumors. The acquired notion that cancer cells from different histological origin strictly rely on the engagement of this specific oncogene for their growth and survival has certainly justified the development and the use of MET-targeted therapies in the clinic. However, the function and involvement of this pathway in the stroma (that often constitutes >50% of the global cellularity of the tumor) may offer the opportunity to conceive new patient stratification criteria, rational drug design and guided trials of new combination treatments. In this review, we will summarize and discuss the role of MET in cancer cells but especially in different stromal compartments, in light of the results showed by past and recent preclinical and clinical trials with anti-MET drugs.

The role of tumor-associated macrophages (TAMs) in cancer is often correlated with poor prognosis, even though this statement should be interpreted with care, as the effects of macrophages primarily depend on their localization within the tumor. This versatile cell type orchestrates a broad spectrum of biological functions and exerts very complex and even opposing functions on cell death, immune stimulation or suppression, and angiogenesis, resulting in an overall pro- or antitumoral effect. We are only beginning to understand the environmental cues that contribute to transient retention of macrophages in a specific phenotype. It has become clear that hypoxia shapes and induces specific macrophage phenotypes that serve tumor malignancy, as hypoxia promotes immune evasion, angiogenesis, tumor cell survival, and metastatic dissemination. Additionally, TAMs in the hypoxic niches within the tumor are known to mediate resistance to several anticancer treatments and to promote cancer relapse. Thus, a careful characterization and understanding of this macrophage differentiation state is needed in order to efficiently tailor cancer therapy.

Targeting the aberrant, nonfunctional tumor vasculature is one of the most promising approaches of new anticancer therapies. Here, we discuss a recent publication and a novel mechanism by which tumor-associated macrophages can actively induce vessel normalization and junction stability, and improve the distribution of therapeutic drugs into a tumor., (Copyright © 2015 Elsevier Ltd. All rights reserved.)

Several questions about the role of the oxygen sensor prolyl-hydroxylase 2 (PHD2) in cancer have not been addressed. First, the role of PHD2 in metastasis has not been studied in a spontaneous tumor model. Here, we show that global PHD2 haplodeficiency reduced metastasis without affecting tumor growth. Second, it is unknown whether PHD2 regulates cancer by affecting cancer-associated fibroblasts (CAFs). We show that PHD2 haplodeficiency reduced metastasis via two mechanisms: (1) by decreasing CAF activation, matrix production, and contraction by CAFs, an effect that surprisingly relied on PHD2 deletion in cancer cells, but not in CAFs; and (2) by improving tumor vessel normalization. Third, the effect of concomitant PHD2 inhibition in malignant and stromal cells (mimicking PHD2 inhibitor treatment) is unknown. We show that global PHD2 haplodeficiency, induced not only before but also after tumor onset, impaired metastasis. These findings warrant investigation of PHD2's therapeutic potential., (Copyright © 2015 The Authors. Published by Elsevier Inc. All rights reserved.)

Mutations or amplification of the MET proto-oncogene are involved in the pathogenesis of several tumours, which rely on the constitutive engagement of this pathway for their growth and survival. However, MET is expressed not only by cancer cells but also by tumour-associated stromal cells, although its precise role in this compartment is not well characterized. Here we show that MET is required for neutrophil chemoattraction and cytotoxicity in response to its ligand hepatocyte growth factor (HGF). Met deletion in mouse neutrophils enhances tumour growth and metastasis. This phenotype correlates with reduced neutrophil infiltration to both the primary tumour and metastatic sites. Similarly, Met is necessary for neutrophil transudation during colitis, skin rash or peritonitis. Mechanistically, Met is induced by tumour-derived tumour necrosis factor (TNF)-α or other inflammatory stimuli in both mouse and human neutrophils. This induction is instrumental for neutrophil transmigration across an activated endothelium and for inducible nitric oxide synthase production upon HGF stimulation. Consequently, HGF/MET-dependent nitric oxide release by neutrophils promotes cancer cell killing, which abates tumour growth and metastasis. After systemic administration of a MET kinase inhibitor, we prove that the therapeutic benefit of MET targeting in cancer cells is partly countered by the pro-tumoural effect arising from MET blockade in neutrophils. Our work identifies an unprecedented role of MET in neutrophils, suggests a potential 'Achilles' heel' of MET-targeted therapies in cancer, and supports the rationale for evaluating anti-MET drugs in certain inflammatory diseases.

While tumor blood vessels share many characteristics with normal vasculature, they also exhibit morphological and functional aberrancies. For example, the neural adhesion molecule L1, which mediates neurite outgrowth, fasciculation, and pathfinding, is expressed on tumor vasculature. Here, using an orthotopic mouse model of pancreatic carcinoma, we evaluated L1 functionality in cancer vessels. Tumor-bearing mice specifically lacking L1 in endothelial cells or treated with anti-L1 antibodies exhibited decreased angiogenesis and improved vascular stabilization, leading to reduced tumor growth and metastasis. In line with these dramatic effects of L1 on tumor vasculature, the ectopic expression of L1 in cultured endothelial cells (ECs) promoted phenotypical and functional alterations, including proliferation, migration, tubulogenesis, enhanced vascular permeability, and endothelial-to-mesenchymal transition. L1 induced global changes in the EC transcriptome, altering several regulatory networks that underlie endothelial pathophysiology, including JAK/STAT-mediated pathways. In particular, L1 induced IL-6-mediated STAT3 phosphorylation, and inhibition of the IL-6/JAK/STAT signaling axis prevented L1-induced EC proliferation and migration. Evaluation of patient samples revealed that, compared with that in noncancerous tissue, L1 expression is specifically enhanced in blood vessels of human pancreatic carcinomas and in vessels of other tumor types. Together, these data indicate that endothelial L1 orchestrates multiple cancer vessel functions and represents a potential target for tumor vascular-specific therapies.

A lot of effort has been done to study how cancer cells react to low-oxygen tension, a condition known as hypoxia. Indeed, abnormal and dysfunctional blood vessels in the tumor are incapable to restore oxygenation, therefore perpetuating hypoxia, which, in turn, will fuel tumor progression, metastasis and resistance to antitumor therapies. Nevertheless, how stromal components including blood and lymphatic endothelial cells, pericytes and fibroblasts, as well as hematopoietic cells, respond to low-oxygen tension in comparison with their normoxic counterparts has been a matter of investigation in the last few years only and, to date, this field of research remains poorly understood. In general, opposing phenotypes can arise from the same stromal component when embedded in different tumor microenvironments, and, vice versa, different stromal components can have opposite reaction to the same tumor microenvironment. In this article, we will discuss the emerging link between tumor stroma and hypoxia, and how this complexity is translated at the molecular level.

Tumor-associated macrophages (TAM) are exposed to multiple microenvironmental cues in tumors, which collaborate to endow these cells with protumoral activities. Hypoxia, caused by an imbalance in oxygen supply and demand because of a poorly organized vasculature, is often a prominent feature in solid tumors. However, to what extent tumor hypoxia regulates the TAM phenotype in vivo is unknown. Here, we show that the myeloid infiltrate in mouse lung carcinoma tumors encompasses two morphologically distinct CD11b(hi)F4/80(hi)Ly6C(lo) TAM subsets, designated as MHC-II(lo) and MHC-II(hi) TAM, both of which were derived from tumor-infiltrating Ly6C(hi) monocytes. MHC-II(lo) TAM express higher levels of prototypical M2 markers and reside in more hypoxic regions. Consequently, MHC-II(lo) TAM contain higher mRNA levels for hypoxia-regulated genes than their MHC-II(hi) counterparts. To assess the in vivo role of hypoxia on these TAM features, cancer cells were inoculated in prolyl hydroxylase domain 2 (PHD2)-haplodeficient mice, resulting in better-oxygenated tumors. Interestingly, reduced tumor hypoxia did not alter the relative abundance of TAM subsets nor their M2 marker expression, but specifically lowered hypoxia-sensitive gene expression and angiogenic activity in the MHC-II(lo) TAM subset. The same observation in PHD2(+/+) → PHD2(+/-) bone marrow chimeras also suggests organization of a better-oxygenized microenvironment. Together, our results show that hypoxia is not a major driver of TAM subset differentiation, but rather specifically fine-tunes the phenotype of M2-like MHC-II(lo) TAM.

The success of chemotherapy in cancer treatment is limited by scarce drug delivery to the tumor and severe side-toxicity. Prolyl hydroxylase domain protein 2 (PHD2) is an oxygen/redox-sensitive enzyme that induces cellular adaptations to stress conditions. Reduced activity of PHD2 in endothelial cells normalizes tumor vessels and enhances perfusion. Here, we show that tumor vessel normalization by genetic inactivation of Phd2 increases the delivery of chemotherapeutics to the tumor and, hence, their antitumor and antimetastatic effect, regardless of combined inhibition of Phd2 in cancer cells. In response to chemotherapy-induced oxidative stress, pharmacological inhibition or genetic inactivation of Phd2 enhances a hypoxia-inducible transcription factor (HIF)-mediated detoxification program in healthy organs, which prevents oxidative damage, organ failure, and tissue demise. Altogether, our study discloses alternative strategies for chemotherapy optimization., (Copyright © 2012 Elsevier Inc. All rights reserved.)

Secreted Semaphorin 3E (Sema3E) promotes cancer cell invasiveness and metastatic spreading. The pro-metastatic activity of Sema3E is due to its proteolytic fragment p61, capable of transactivating the oncogenic tyrosine kinase ErbB2 that associates with the Sema3E receptor PlexinD1 in cancer cells. Here, we show that a mutated, uncleavable variant of Sema3E (Uncl-Sema3E) binds to PlexinD1 like p61-Sema3E, but does not promote the association of PlexinD1 with ErbB2 nor activates the ensuing signalling cascade leading to metastatic spreading. Furthermore, Uncl-Sema3E competes with endogenous p61-Sema3E produced by tumour cells, thereby hampering their metastatic ability. Uncl-Sema3E also acts independently as a potent anti-angiogenic factor. It activates a PlexinD1-mediated signalling cascade in endothelial cells that leads to the inhibition of adhesion to extracellular matrix, directional migration and cell survival. The putative therapeutic potential of Uncl-Sema3E was validated in multiple orthotopic or spontaneous tumour models in vivo, where either local or systemic delivery of Uncl-Sema3E-reduced angiogenesis, growth and metastasis, even in the case of tumours refractory to treatment with a soluble vascular endothelial growth factor trap. In summary, we conclude that Uncl-Sema3E is a novel inhibitor of tumour angiogenesis and growth that concomitantly hampers metastatic spreading., (Copyright © 2012 EMBO Molecular Medicine.)

Expression of the mannose receptor (MRC1/CD206) identifies macrophage subtypes, such as alternatively activated macrophages (AAMs) and M2-polarized tumor-associated macrophages (TAMs), which are endowed with tissue-remodeling, proangiogenic, and protumoral activity. However, the significance of MRC1 expression for TAM's protumoral activity is unclear. Here, we describe and characterize miR-511-3p, an intronic microRNA (miRNA) encoded by both mouse and human MRC1 genes. By using sensitive miRNA reporter vectors, we demonstrate robust expression and bioactivity of miR-511-3p in MRC1(+) AAMs and TAMs. Unexpectedly, enforced expression of miR-511-3p tuned down the protumoral gene signature of MRC1(+) TAMs and inhibited tumor growth. Our findings suggest that transcriptional activation of Mrc1 in TAMs evokes a genetic program orchestrated by miR-511-3p, which limits rather than enhances their protumoral functions. Besides uncovering a role for MRC1 as gatekeeper of TAM's protumoral genetic programs, these observations suggest that endogenous miRNAs may operate to establish thresholds for inflammatory cell activation in tumors., (Copyright © 2012 The Authors. Published by Elsevier Inc. All rights reserved.)

All human cells, including cancer cells, need oxygen and nutrients to survive. A widely used strategy to combat cancer is therefore the starvation of tumor cells by cutting off the blood supply of tumors. Clinical experience indeed shows that tumor progression can be delayed by anti-angiogenic agents. However, emerging evidence indicates that in certain experimental conditions, hypoxia as a result of pruning of the tumor microvasculature can promote tumor invasion and metastasis, although these findings are contextual and debated. Genetic studies in mice unveiled that vascular-targeting strategies that avoid aggravation of tumor hypoxia or even promote tumor oxygenation might prevent such an invasive metastatic switch. In this article, we will discuss the emerging link between hypoxia signaling and the various steps of metastasis.

The establishment of a functional, integrated vascular system is instrumental for tissue growth and homeostasis. Without blood vessels no adequate nutrition and oxygen would be provided to cells, nor could the undesired waste products be efficiently removed. Blood vessels constitute therefore one of the largest and most complex body network whose assembly depends on the precise balance of growth factors acting in a complementary and coordinated manner with cells of several identities. However, the vessels that are crucial for life can also foster death, given their involvement in cancer progression towards malignancy and metastasis. Targeting tumor vasculature has thus arisen as an appealing anti-cancer therapeutic approach. Since the milestone achievements that vascular endothelial growth factor (VEGF) blockade suppressed angiogenesis and tumor growth in mice and prolonged the survival of cancer patients when administered in combination with chemotherapy, the clinical development of anti-VEGF(R) drugs has accelerated remarkably. FDA has approved the use of bevacizumab - a humanized monoclonal antibody against VEGF - in colorectal, lung and metastatic breast cancers in combination with standard chemotherapy. Additional broad-spectrum VEGF receptor tyrosine kinase inhibitors, such as sunitinib and sorafenib, are used in monotherapy for metastatic renal carcinoma, while sunitinib is also approved for imatinib resistant gastrointestinal stromal tumors and sorafenib for advanced stage hepatocellular carcinoma. Nevertheless, the survival benefit offered by VEGF(R) blockers, either as single agents or in combination with chemotherapy, is calculated merely in the order of months. Posterior studies in preclinical models have reported that despite reducing primary tumor growth, the inhibition of VEGF increased tumor invasiveness and metastasis. The clinical implications of these findings urge the need to reconcile these conflicting results. Anti-angiogenic therapy represents a significant step forth in cancer therapy and in our understanding of cancer biology, but it is also clear that we need to learn how to use it. What is the biological consequence of VEGF-blockade? Does VEGF inhibition starve the tumor to death - as initially postulated - or does it rather foster malignancy? Can anti-VEGF(R) therapy favor tumor vessel formation by VEGF-independent means? Tumors are very diverse and plastic entities, able to adapt to the harshest conditions; this is also reflected by the tumor vasculature. Lessons from the bench to the bedside and vice versa have taught us that the diversity of signals underlying tumor vessel growth will likely be responsive (or resistant) to distinct therapeutic approaches. In this review, we propose a reflection of the different strategies tumors use to grow blood vessels and how these can have impact on the (un)success of current anti-angiogenic therapies., (Copyright © 2011 Elsevier Ltd. All rights reserved.)

Polarization of tumor-associated macrophages (TAMs) to a proangiogenic/immune-suppressive (M2-like) phenotype and abnormal, hypoperfused vessels are hallmarks of malignancy, but their molecular basis and interrelationship remains enigmatic. We report that the host-produced histidine-rich glycoprotein (HRG) inhibits tumor growth and metastasis, while improving chemotherapy. By skewing TAM polarization away from the M2- to a tumor-inhibiting M1-like phenotype, HRG promotes antitumor immune responses and vessel normalization, effects known to decrease tumor growth and metastasis and to enhance chemotherapy. Skewing of TAM polarization by HRG relies substantially on downregulation of placental growth factor (PlGF). Besides unveiling an important role for TAM polarization in tumor vessel abnormalization, and its regulation by HRG/PlGF, these findings offer therapeutic opportunities for anticancer and antiangiogenic treatment., (Copyright © 2011 Elsevier Inc. All rights reserved.)

Anti-angiogenic therapy and therapeutic angiogenesis have been proposed as opposite strategy for the treatment of cancer and ischemic diseases, respectively. However, both approaches do not provide long term solutions of these pathological conditions and have failed in clinical trials. Therefore, novel strategies are needed. In the current work we describe: 1) how vessels sense and re-adapt oxygen supply and, hence, perfusion in case of oxygen shortage, therefore identifying PHD2 oxygen sensor as a novel target to normalize the tumor vasculature, reduce cancer hypoxia and prevent cancer cell extravasations and dissemination; 2) anti-P1GF as a efficient and safe tool in cancer therapy that does not prune excessively pathological vessels and does not affect the normal vasculature; 3) hypoxia tolerance via inhibition of the oxygen sensor PHD1 as alternative strategy to therapeutic angiogenesis. Altogether, our findings provide new alternatives in the treatment of ischemic disorders and cancer, largely unmet medical problems to date.

From the original concepts that tumors require a vascular supply to grow and that blocking angiogenesis could suppress tumor growth, the oncology field has witnessed clinical successes of VEGF-targeted antiangiogenic medicine. The field is now facing the challenge of overcoming resistance to VEGF-targeted therapy, and therefore additional angiogenesis inhibitors are being developed. Studies on how endothelial 'tip, stalk and phalanx cells' form sprouts have identified promising candidate targets with complementary mechanisms to VEGF. This Review provides a conceptual framework in which molecular discoveries and principles are discussed in light of clinical opportunities to develop new antiangiogenic agents.

A key function of blood vessels, to supply oxygen, is impaired in tumors because of abnormalities in their endothelial lining. PHD proteins serve as oxygen sensors and may regulate oxygen delivery. We therefore studied the role of endothelial PHD2 in vessel shaping by implanting tumors in PHD2(+/-) mice. Haplodeficiency of PHD2 did not affect tumor vessel density or lumen size, but normalized the endothelial lining and vessel maturation. This resulted in improved tumor perfusion and oxygenation and inhibited tumor cell invasion, intravasation, and metastasis. Haplodeficiency of PHD2 redirected the specification of endothelial tip cells to a more quiescent cell type, lacking filopodia and arrayed in a phalanx formation. This transition relied on HIF-driven upregulation of (soluble) VEGFR-1 and VE-cadherin. Thus, decreased activity of an oxygen sensor in hypoxic conditions prompts endothelial cells to readjust their shape and phenotype to restore oxygen supply. Inhibition of PHD2 may offer alternative therapeutic opportunities for anticancer therapy.

Clinical practice reveals that therapy with angiogenesis inhibitors often does not prolong survival of cancer patients for more than months, because tumors elicit evasive resistance. In this issue of Cancer Cell, two papers report that VEGF inhibitors reduce primary tumor growth but promote tumor invasiveness and metastasis. These perplexing findings help to explain resistance to these drugs but raise pertinent questions of how to best treat cancer patients with antiangiogenic medicine in the future. We discuss here how VEGF inhibitors can induce such divergent effects on primary tumor growth and metastasis.

Less than 5 years ago, it was still not clear whether anti-angiogenic drugs would prove successful in the clinic. After numerous patients with cancer or age-related macular degeneration have been treated with these drugs, they have now become part of the standard range of therapeutic tools. Despite this milestone, anti-angiogenic therapy still faces a number of clinical hurdles, such as improving efficacy, avoiding escape and resistance, and minimizing toxicity. Hopefully, other agents with complementary mechanisms, such as those that target placental growth factor, will offer novel opportunities for improved treatment.

Gene therapy provides a still poorly explored opportunity to treat cancer by "active" immunotherapy as it enables the transfer of genes encoding antibodies directed against specific oncogenic proteins. By a bidirectional lentiviral vector, we transferred the cDNA encoding the heavy and light chains of a monoclonal anti-Met antibody (DN-30) to epithelial cancer cells. In vitro, the transduced cells synthesized and secreted correctly assembled antibodies with the expected high affinity, inducing down-regulation of the Met receptor and strong inhibition of the invasive growth response. The inhibitory activity resulted (a) from the interference of the antibody with the Met receptor intracellular processing ("cell autonomous activity," in cis) and (b) from the antibody-induced cleavage of Met expressed at the cell surface ("bystander effect," in trans). The monoclonal antibody gene transferred into live animals by systemic administration or by local intratumor delivery resulted in substantial inhibition of tumor growth. These data provide proof of concept both for targeting the Met receptor and for a gene transfer-based immunotherapy strategy.

It has been recognized for more than a century that most tumors tend to become more aggressive in clinical behavior over time, although this time course may be variable. This phenomenon has been termed "cancer progression," a process that appears to develop in a stepwise fashion through qualitatively different stages. Cancer progression relies on the ability of neoplastic cells to abandon their primary site of accretion, trespass tissue boundaries, and penetrate into the vasculature to colonize and repopulate distant sites. Among the various properties associated with cancer progression, the acquisition by neoplastic cells of the capacity to invade locally and to metastasize is of great clinical significance, and is still the fundamental definition of malignancy. This process represents the aberrant counterpart of a physiological morphogenetic program, known as invasive growth, occurring during embryo development and, in some instances, in adulthood for the generation and maintenance of normal organ complexity and architecture. Here we summarize some of the strategies adopted to inhibit cancer cell growth and spreading. We also review the current findings about cancer and metastasis inhibitors. As we suggest possible directions for drug development, we propose the receptor for the hepatocyte growth factor, Met, as an ideal target for tackling cancer progression.

Scatter factor (SF), also known as hepatocyte growth factor, is ubiquitously present in the extracellular matrix of tissues in the form of an inactive precursor (pro-SF). In order to acquire biological activity, pro-SF must be cleaved by specific proteases present on the cell surface. The mature form of SF controls invasive cues in both physiological and pathological processes through activation of its receptor, the Met tyrosine kinase. By substituting a single amino acid in the proteolytic site, we engineered an unprocessable form of pro-SF (uncleavable SF). Using lentivirus vector technology, we achieved local or systemic delivery of uncleavable SF in mice. We provide evidence that (a) uncleavable SF inhibits both protease-mediated pro-SF conversion and active SF-induced Met activation; (b) local expression of uncleavable SF in tumors suppresses tumor growth, impairs tumor angiogenesis, and prevents metastatic dissemination; and (c) systemic expression of uncleavable SF dramatically inhibits the growth of transplanted tumors and abolishes the formation of spontaneous metastases without perturbing vital physiological functions. These data show that proteolytic activation of pro-SF is a limiting step in tumor progression, thus suggesting a new strategy for the treatment or prevention of the malignant conversion of neoplastic lesions.