PDGF-BB modulates hematopoiesis and tumor angiogenesis by inducing erythropoietin production in stromal cells

Targeting Serglycin Prevents Metastasis in Murine Mammary Carcinoma

In hematopoietic cells, serglycin proteoglycans mainly contribute to proper storage and secretion of inflammatory mediators via their negatively charged glycosaminoglycans. Serglycin proteoglycans are also expressed in cancer cells where increased expression has been linked to poor prognosis. However, the serglycin-dependent mediators promoting cancer progression remain to be determined. In the present study we report that genetic ablation of serglycin proteoglycan completely blocks lung metastasis in the MMTV-PyMT-driven mouse breast cancer model, while serglycin-deficiency did not affect primary tumour growth or number of mammary tumours. Although E-cadherin expression was higher in the serglycin-deficient primary tumour tissue, indicating reduced invasiveness, serglycin-deficient tumour cells were still detected in the circulation. These data suggest that serglycin proteoglycans play a role in extravasation as well as colonization and growth of metastatic cells. A microarray expression analysis and functional annotation of differentially expressed genes identified several biological pathways where serglycin may be important. Our results suggest that serglycin and serglycin-dependent mediators are potential drug targets to prevent metastatic disease/dissemination of cancer.

Functional Interference in the Bone Marrow Microenvironment by Disseminated Breast Cancer Cells

Skeletal metastasis of breast cancer is associated with a poor prognosis and significant morbidity. Investigations in other solid tumors have revealed an impairment in hematopoietic function upon bone marrow invasion. However, the interaction between disseminated breast cancer cells and the bone marrow microenvironment which harbors them has not been addressed comprehensively. Employing advanced co-culture assays, proteomic studies, organotypic models as well as in vivo xenotransplant models, we define the consequences of this interaction on the stromal compartment of bone marrow, affected molecular pathways and subsequent effects on the hematopoietic stem and progenitor cells (HSPCs). The results showed a basic fibroblast growth factor (bFGF)-mediated, synergistic increase in proliferation of breast cancer cells and mesenchymal stromal cells (MSCs) in co-culture. The stromal induction was associated with elevated phosphoinositide-3 kinase (PI3K) signaling in the stroma, which coupled with elevated bFGF levels resulted in increased migration of breast cancer cells towards the MSCs. The perturbed cytokine profile in the stroma led to reduction in the osteogenic differentiation of MSCs via downregulation of platelet-derived growth factor-BB (PDGF-BB). Long term co-cultures of breast cancer cells, HSPCs, MSCs and in vivo studies in NOD.Cg-Prkdc(scid) Il2rg(tm1Wjl) /SzJ (NSG) mice showed a reduced support for HSPCs in the altered niche. The resultant non- conducive phenotype of the niche for HSPC support emphasizes the importance of the affected molecular pathways in the stroma as clinical targets. These findings can be a platform for further development of therapeutic strategies aiming at the blockade of bone marrow support to disseminated breast cancer cells. Stem Cells 2016;34:2224-2235.

The PDGF-BB-SOX7 axis-modulated IL-33 in pericytes and stromal cells promotes metastasis through tumour-associated macrophages

Signalling molecules and pathways that mediate crosstalk between various tumour cellular compartments in cancer metastasis remain largely unknown. We report a mechanism of the interaction between perivascular cells and tumour-associated macrophages (TAMs) in promoting metastasis through the IL-33–ST2-dependent pathway in xenograft mouse models of cancer. IL-33 is the highest upregulated gene through activation of SOX7 transcription factor in PDGF-BB-stimulated pericytes. Gain- and loss-of-function experiments validate that IL-33 promotes metastasis through recruitment of TAMs. Pharmacological inhibition of the IL-33–ST2 signalling by a soluble ST2 significantly inhibits TAMs and metastasis. Genetic deletion of host IL-33 in mice also blocks PDGF-BB-induced TAM recruitment and metastasis. These findings shed light on the role of tumour stroma in promoting metastasis and have therapeutic implications for cancer therapy.

Elevated IL-33 levels have been correlated with metastasis and poor prognosis. Here the authors show in mouse tumour xenograft models that PDGF-BB produced by tumour cells induces IL-33 via Sox7 in tumour pericytes, and IL-33 promotes metastasis through its effects on tumour-associated macrophages.

Preventing diet-induced obesity in mice by adipose tissue transformation and angiogenesis using targeted nanoparticles

The incidence of obesity, which is recognized by the American Medical Association as a disease, has nearly doubled since 1980, and obesity-related comorbidities have become a major threat to human health. Given that adipose tissue expansion and transformation require active growth of new blood vasculature, angiogenesis offers a potential target for the treatment of obesity-associated disorders. Here we construct two peptide-functionalized nanoparticle (NP) platforms to deliver either Peroxisome Proliferator-Activated Receptor gamma (PPARgamma) activator rosiglitazone (Rosi) or prostaglandin E2 analog (16,16-dimethyl PGE2) to adipose tissue vasculature. These NPs were engineered through self-assembly of a biodegradable triblock polymer composed of end-to-end linkages between poly(lactic-coglycolic acid)-b-poly(ethylene glycol) (PLGA-b-PEG) and an endothelial-targeted peptide. In this system, released Rosi promotes both transformation of white adipose tissue (WAT) into brown-like adipose tissue and angiogenesis, which facilitates the homing of targeted NPs to adipose angiogenic vessels, thereby amplifying their delivery. We show that i.v. administration of these NPs can target WAT vasculature, stimulate the angiogenesis that is required for the transformation of adipose tissue, and transform WAT into brown-like adipose tissue, by the up-regulation of angiogenesis and brown adipose tissue markers. In a diet-induced obese mouse model, these angiogenesis-targeted NPs have inhibited body weight gain and modulated several serological markers including cholesterol, triglyceride, and insulin, compared with the control group. These findings suggest that angiogenesis-targeting moieties with angiogenic stimulator-loaded NPs could be incorporated into effective therapeutic regimens for clinical treatment of obesity and other metabolic diseases.

NF-YA promotes invasion and angiogenesis by upregulating EZH2-STAT3 signaling in human melanoma cells

The process of angiogenesis is essential for tumor development and metastasis. Vascular endothelial growth factor (VEGF), which is overexpressed in most human cancers, has been demonstrated to be a major modulator of angiogenesis. Thus, inhibition of VEGF signaling has the potential for tumor anti-angiogenic therapy. Signal transducer and activator of transcription-3 (STAT3) is a key regulator for angiogenesis by directly binding to the VEGF promoter to upregulate its transcription. Several factors can enhance STAT3 activity to affect angiogenesis. Here, we found that overexpression of nuclear transcription factor-Y alpha (NF-YA) gene could promote cell invasion and angiogenesis accompanying the increase of STAT3 signaling in human melanoma cells. Moreover, the expression and secretion of VEGF was also found to be upregulated by the overexpression of NF-YA gene in melanoma cells. The STAT3 inhibitor was able to attenuate the upregulation of VEGF induced by NF-YA overexpression. Enhancer of zeste homolog 2 (EZH2), the catalytic subunit of the Polycomb repressive complex 2, enhances STAT3 activity by mediating its lysine methylation. We also showed that NF-YA upregulated the expression of EZH2 and NF-YA‑induced angiogenesis could be inhibited by EZH2 knockdown. Taken together, these findings indicate that overexpression of NF-YA contributes to tumor angiogenesis through EZH2-STAT3 signaling in human melanoma cells, highlighting NF-YA as a potential therapeutic target in human melanoma.

Spheroid-Based In Vitro Angiogenesis Model

In vitro models mimicking capillary sprouting are important tools to investigate the tumor angiogenesis, developmental blood vessel formation, and pathophysiological remodeling processes of the capillary system in the adult. With this focus, in 1998 Korff et al. introduced endothelial cell (EC) spheroids as a three-dimensional in vitro model resembling angiogenic responses and sprouting behavior [1]. As such, EC spheroids are capable of giving rise to capillary-like sprouts which are relatively close to the physiologically and genetically programmed arrangement of endothelial cells in vessels. Co-culture spheroids consisting of endothelial cells and smooth muscle cells form a spheroidal core composed of smooth muscle cells and an outer monolayer of endothelial cells, similar to the physiological architecture of larger blood vessels. In practise, a defined number of endothelial cells are cultured in a round-bottom well plate or in "hanging drops" to allow the formation and arrangement of the spheroidal three-dimensional structure. Subsequently, they are harvested and embedded in a collagen gel to allow outgrowth of endothelial cell sprouts originating from each spheroid. To evaluate the pro- or antiangiogenic impact of a cytokine or compound, the number and length of sprouts is determined.

Cancer anti-angiogenesis vaccines: Is the tumor vasculature antigenically unique?

Angiogenesis is essential for the growth and metastasis of solid tumors. The tumor endothelium exists in a state of chronic activation and proliferation, fueled by the tumor milieu where angiogenic mediators are aberrantly over-expressed. Uncontrolled tumor growth, immune evasion, and therapeutic resistance are all driven by the dysregulated and constitutive angiogenesis occurring in the vasculature. Accordingly, great efforts have been dedicated toward identifying molecular signatures of this pathological angiogenesis in order to devise selective tumor endothelium targeting therapies while minimizing potential autoimmunity against physiologically normal endothelium. Vaccination with angiogenic antigens to generate cellular and/or humoral immunity against the tumor endothelium has proven to be a promising strategy for inhibiting or normalizing tumor angiogenesis and reducing cancer growth. Here we review tumor endothelium vaccines developed to date including active immunization strategies using specific tumor endothelium-associated antigens and whole endothelial cell-based vaccines designed to elicit immune responses against diverse target antigens. Among the novel therapeutic options, we describe a placenta-derived endothelial cell vaccine, ValloVax™, a polyvalent vaccine that is antigenically similar to proliferating tumor endothelium and is supported by pre-clinical studies to be safe and efficacious against several tumor types.

Effect of VEGFR, PDGFR and PI3K/mTOR Targeting in Glioblastoma

Resistance to targeted therapy is a well known obstacle in cancer therapy. The cross-talk between several growth factor receptors generates redundancy in their intracellular pathways that usually mediates resistance to receptor targeted therapy. Simultaneous inactivation of two or more growth factor receptors has been suggested to prevent the cross-talk between their signaling pathways and to better eliminate malignant cells. Here we found that targeted therapy against these receptors induced moderate cell death in glioblastoma cells. More important, dual PDGFR and VEGFR inactivation induced more pronounceable cell death compared to inactivation of each receptor alone but failed to induce synergistic cell death in glioblastoma. PI3K/mTOR dual targeting has been identified as an efficient therapeutic approach in several malignant diseases, including glioblastoma. Therefore, we also investigated the PI3K/mTOR pathways inhibition effect in glioblastoma cells. Our results showed that inactivation of PI3K/mTOR pathways were more efficient than PDGFR or VEGFR single targeting or their dual inhibition.

Autotaxin is an inflammatory mediator and therapeutic target in thyroid cancer

Autotaxin is a secreted enzyme that converts extracellular lysophosphatidylcholine to lysophosphatidate (LPA). In cancers, LPA increases tumour growth, metastasis and chemoresistance by activating six G-protein coupled receptors. We examined >200 human thyroid biopsies. Autotaxin expression in metastatic deposits and primary carcinomas was four- to tenfold higher than in benign neoplasms or normal thyroid tissue. Autotaxin immunohistochemical staining was also increased in benign neoplasms with leukocytic infiltrations. Malignant tumours were distinguished from benign tumours by high tumour autotaxin, LPA levels and inflammatory mediators including IL1β, IL6, IL8, GMCSF, TNFα, CCL2, CXCL10 and platelet-derived growth factor (PDGF)-AA. We determined the mechanistic explanation for these results and revealed a vicious regulatory cycle in which LPA increased the secretion of 16 inflammatory modulators in papillary thyroid cancer cultures. Conversely, treating cancer cells with ten inflammatory cytokines and chemokines or PDGF-AA and PDGF-BB increased autotaxin secretion. We confirmed that this autotaxin/inflammatory cycle occurs in two SCID mouse models of papillary thyroid cancer by blocking LPA signalling using the autotaxin inhibitor ONO-8430506. This decreased the levels of 16 inflammatory mediators in the tumours and was accompanied by a 50-60% decrease in tumour volume. This resulted from a decreased mitotic index for the cancer cells and decreased levels of vascular endothelial growth factor and angiogenesis in the tumours. Our results demonstrate that the autotaxin/inflammatory cycle is a focal point for driving malignant thyroid tumour progression and possibly treatment resistance. Inhibiting autotaxin activity provides an effective and novel strategy for decreasing the inflammatory phenotype in thyroid carcinomas, which should complement other treatment modalities.

Molecularly targeted therapies for recurrent glioblastoma: current and future targets

OBJECT

Glioblastoma is the most aggressive and diffusely infiltrative primary brain tumor. Recurrence is expected and is extremely difficult to treat. Over the past decade, the accumulation of knowledge regarding the molecular and genetic profile of glioblastoma has led to numerous molecularly targeted therapies. This article aims to review the literature and highlight the mechanisms and efficacies of molecularly targeted therapies for recurrent glioblastoma.

METHODS

A systematic search was performed with the phrase "(name of particular agent) and glioblastoma" as a search term in PubMed to identify all articles published up until 2014 that included this phrase in the title and/or abstract. The references of systematic reviews were also reviewed for additional sources. The review included clinical studies that comprised at least 20 patients and reported results for the treatment of recurrent glioblastoma with molecular targeted therapies.

RESULTS

A total of 42 articles were included in this review. In the treatment of recurrent glioblastoma, various targeted therapies have been tested over the past 10-15 years. The targets of interest include epidermal growth factor receptor, vascular endothelial growth factor receptor, platelet-derived growth factor receptor, Ras pathway, protein kinase C, mammalian target of rapamycin, histone acetylation, and integrins. Unfortunately, the clinical responses to most available targeted therapies are modest at best. Radiographic responses generally range in the realm of 5%-20%. Progression-free survival at 6 months and overall survival were also modest with the majority of studies reporting a 10%-20% 6-month progression-free survival and 5- to 8-month overall survival. There have been several clinical trials evaluating the use of combination therapy for molecularly targeted treatments. In general, the outcomes for combination therapy tend to be superior to single-agent therapy, regardless of the specific agent studied.

CONCLUSIONS

Recurrent glioblastoma remains very difficult to treat, even with molecular targeted therapies and anticancer agents. The currently available targeted therapy regimens have poor to modest activity against recurrent glioblastoma. As newer agents are actively being developed, combination regimens have provided the most promising results for improving outcomes. Targeted therapies matched to molecular profiles of individual tumors are predicted to be a critical component necessary for improving efficacy in future trials.

Tollip is a critical mediator of cerebral ischaemia-reperfusion injury

Toll-like receptor (TLR) signalling plays an important role in regulating cerebral ischaemia-reperfusion (I/R) injury. Toll-interacting protein (Tollip) is an endogenous negative modulator of TLR signalling that is involved in several inflammatory diseases. Our previous study showed that Tollip inhibits overload-induced cardiac remodelling. However, the role of Tollip in neurological disease remains unknown. In the present study, we proposed that Tollip might contribute to the progression of stroke and confirmed this hypothesis. We found that Tollip expression was significantly increased in I/R-challenged brain tissue of humans, mice and rats in vivo and in primary neurons subjected to oxygen and glucose deprivation in vitro, indicating the involvement of Tollip in I/R injury. Next, using genetic approaches, we revealed that Tollip deficiency protects mice against I/R injury by attenuating neuronal apoptosis and inflammation, as demonstrated by the decreased expression of pro-apoptotic and pro-inflammatory genes and the increased expression of anti-apoptotic genes. By contrast, neuron-specific Tollip over-expression exerted the opposite effect. Mechanistically, the detrimental effects of Tollip on neuronal apoptosis and inflammation following I/R injury were largely mediated by the suppression of Akt signalling. Additionally, to further support our findings, a Tollip knockout rat strain was generated via CRISPR-Cas9-mediated gene inactivation. The Tollip-deficient rats were also protected from I/R injury, based on dramatic decreases in neuronal apoptosis and ischaemic inflammation through Akt activation. Taken together, our findings demonstrate that Tollip acts as a novel modulator of I/R injury by promoting neuronal apoptosis and ischaemic inflammation, which are largely mediated by suppression of Akt signalling.

Expression of platelet-derived growth factor BB, erythropoietin and erythropoietin receptor in canine and feline osteosarcoma

The discovery of expression of the erythropoietin receptor (EPO-R) on neoplastic cells has led to concerns about the safety of treating anaemic cancer patients with EPO. In addition to its endocrine function, the receptor may play a role in tumour progression through an autocrine mechanism. In this study, the expression of EPO, EPO-R and platelet-derived growth factor BB (PDGF-BB) was analysed in five feline and 13 canine osteosarcomas using immunohistochemistry (IHC) and reverse transcription polymerase chain reaction (RT-PCR).

EPO expression was positive in all tumours by IHC, but EPO mRNA was only detected in 38% of the canine and 40% of the feline samples. EPO-R was expressed in all samples by quantitative RT-PCR (RT-qPCR) and IHC. EPO-R mRNA was expressed at higher levels in all feline tumours, tumour cell lines, and kidney when compared to canine tissues. PDGF-BB expression was variable by IHC, but mRNA was detected in all samples. To assess the functionality of the EPO-R on tumour cells, the proliferation of canine and feline osteosarcoma cell lines was evaluated after EPO administration using an alamarBlue assay and Ki67 immunostaining. All primary cell lines responded to EPO treatment in at least one of the performed assays, but the effect on proliferation was very low indicating only a weak responsiveness of EPO-R. In conclusion, since EPO and its receptor are expressed by canine and feline osteosarcomas, an autocrine or paracrine tumour progression mechanism cannot be excluded, although in vitro data suggest a minimal role of EPO-R in osteosarcoma cell proliferation.

Assessing the carcinogenic potential of low-dose exposures to chemical mixtures in the environment: focus on the cancer hallmark of tumor angiogenesis

One of the important 'hallmarks' of cancer is angiogenesis, which is the process of formation of new blood vessels that are necessary for tumor expansion, invasion and metastasis. Under normal physiological conditions, angiogenesis is well balanced and controlled by endogenous proangiogenic factors and antiangiogenic factors. However, factors produced by cancer cells, cancer stem cells and other cell types in the tumor stroma can disrupt the balance so that the tumor microenvironment favors tumor angiogenesis. These factors include vascular endothelial growth factor, endothelial tissue factor and other membrane bound receptors that mediate multiple intracellular signaling pathways that contribute to tumor angiogenesis. Though environmental exposures to certain chemicals have been found to initiate and promote tumor development, the role of these exposures (particularly to low doses of multiple substances), is largely unknown in relation to tumor angiogenesis. This review summarizes the evidence of the role of environmental chemical bioactivity and exposure in tumor angiogenesis and carcinogenesis. We identify a number of ubiquitous (prototypical) chemicals with disruptive potential that may warrant further investigation given their selectivity for high-throughput screening assay targets associated with proangiogenic pathways. We also consider the cross-hallmark relationships of a number of important angiogenic pathway targets with other cancer hallmarks and we make recommendations for future research. Understanding of the role of low-dose exposure of chemicals with disruptive potential could help us refine our approach to cancer risk assessment, and may ultimately aid in preventing cancer by reducing or eliminating exposures to synergistic mixtures of chemicals with carcinogenic potential.

Targeting Angiogenesis in Cancer Therapy: Moving Beyond Vascular Endothelial Growth Factor

Angiogenesis, or the formation of new capillary blood vessels, occurs primarily during human development and reproduction; however, aberrant regulation of angiogenesis is also a fundamental process found in several pathologic conditions, including cancer. As a process required for invasion and metastasis, tumor angiogenesis constitutes an important point of control of cancer progression. Although not yet completely understood, the complex process of tumor angiogenesis involves highly regulated orchestration of multiple signaling pathways. The proangiogenic signaling molecule vascular endothelial growth factor (VEGF) and its cognate receptor (VEGF receptor 2 [VEGFR-2]) play a central role in angiogenesis and often are highly expressed in human cancers, and initial clinical efforts to develop antiangiogenic treatments focused largely on inhibiting VEGF/VEGFR signaling. Such approaches, however, often lead to transient responses and further disease progression because angiogenesis is regulated by multiple pathways that are able to compensate for each other when single pathways are inhibited. The platelet-derived growth factor (PDGF) and PDGF receptor (PDGFR) and fibroblast growth factor (FGF) and FGF receptor (FGFR) pathways, for example, provide potential escape mechanisms from anti-VEGF/VEGFR therapy that could facilitate resumption of tumor growth. Accordingly, more recent treatments have focused on inhibiting multiple signaling pathways simultaneously. This comprehensive review discusses the limitations of inhibiting VEGF signaling alone as an antiangiogenic strategy, the importance of other angiogenic pathways including PDGF/PDGFR and FGF/FGFR, and the novel current and emerging agents that target multiple angiogenic pathways for the treatment of advanced solid tumors.

IMPLICATIONS FOR PRACTICE

Significant advances in cancer treatment have been achieved with the development of antiangiogenic agents, the majority of which have focused on inhibition of the vascular endothelial growth factor (VEGF) pathway. VEGF targeting alone, however, has not proven to be as efficacious as originally hoped, and it is increasingly clear that there are many interconnected and compensatory pathways that can overcome VEGF-targeted inhibition of angiogenesis. Maximizing the potential of antiangiogenic therapy is likely to require a broader therapeutic approach using a new generation of multitargeted antiangiogenic agents.

PlGF-induced VEGFR1-dependent vascular remodeling determines opposing antitumor effects and drug resistance to Dll4-Notch inhibitors

Inhibition of Dll4 (delta-like ligand 4)-Notch signaling-mediated tumor angiogenesis is an attractive approach in cancer therapy. However, inhibition of Dll4-Notch signaling has produced different effects in various tumors, and no biomarkers are available for predicting the anti-Dll4-Notch-associated antitumor activity. We show that human and mouse tumor cell-derived placental growth factor (PlGF) is a key determinant of the Dll4-Notch-induced vascular remodeling and tumor growth. In natural PlGF-expressing human tumors, inhibition of Dll4-Notch signaling markedly accelerated tumor growth by increasing blood perfusion in nonleaking tumor vasculatures. Conversely, in PlGF-negative tumors, Dll4 inhibition suppressed tumor growth by the formation of nonproductive and leaky vessels. Surprisingly, genetic inactivation of vascular endothelial growth factor receptor 1 (VEGFR1) completely abrogated the PlGF-modulated vascular remodeling and tumor growth, indicating a crucial role for VEGFR1-mediated signals in modulating Dll4-Notch functions. These findings provide mechanistic insights on PlGF-VEGFR1 signaling in the modulation of the Dll4-Notch pathway in angiogenesis and tumor growth, and have therapeutic implications of PlGF as a biomarker for predicting the antitumor benefits of Dll4 and Notch inhibitors.

Macrophages support splenic erythropoiesis in 4T1 tumor-bearing mice

Anemia is a common complication of cancer; a role of spleen in tumor-stress erythropoiesis has been suggested. However, the molecular mechanisms involved in the splenic erythropoiesis following tumor maintenance remain poorly understood. Here we show that tumor development blocks medullar erythropoiesis by granulocyte colony-stimulating factor (G-CSF) and then causes anemia in murine 4T1 breast tumor-bearing mice. Meanwhile, tumor-stress promotes splenic erythropoiesis. Splenectomy worsened tumor-induced anemia, and reduced tumor volume and tumor weight, indicating the essential role of spleen in tumor-stress erythropoiesis and tumor growth. Tumor progression of these mice led to increased amounts of bone morphogenetic protein 4 (BMP4) in spleen. The in vivo role of macrophages in splenic erythropoiesis under tumor-stress conditions was investigated. Macrophage depletion by injecting liposomal clodronate decreased the expression of BMP4, inhibited splenic erythropoiesis, aggravated the tumor-induced anemia and suppressed tumor growth. Our results provide insight that macrophages and BMP4 are positive regulators of splenic erythropoiesis in tumor pathological situations. These findings reveal that during the tumor-stress period, the microenvironment of the spleen is undergoing changes, which contributes to adopt a stress erythropoietic fate and supports the expansion and differentiation of stress erythroid progenitors, thereby replenishing red blood cells and promoting tumor growth.

Molecular mechanism underlying the tumor-promoting functions of carcinoma-associated fibroblasts

Tumor microenvironment is composed of all the untransformed elements in the vicinity of tumor, mainly including a large number of stromal cells and extracellular matrix proteins, which play an active role in most solid tumor initiation and progression. Carcinoma-associated fibroblasts (CAFs), one of the most common stromal cell types in the tumor microenvironment, have been demonstrated to be involved in tumor growth, invasion, and metastasis. Therefore, they are becoming a promising target for anti-cancer therapies. In this review, we firstly summarize the current understandings of CAFs' molecular biology, including the heterogeneous cellular origins and molecular markers, and then, we focus on reviewing their various tumor-promoting phenotypes involved in complex mechanisms, which can be summarized to the CAF-conveyed paracrine signals in tumor cells, cancer stem cells, and metastasis-initiating cancer cells, as well as the CAF-enhanced extrinsic tumor-promoting processes including angiogenesis, extracellular matrix remodeling, and tumor-related inflammation; finally, we describe the available directions of CAF-based target therapy and suggest research areas which need to be further explored so as to deepen the understanding of tumor evolution and provide new therapeutic targets for cancer treatment.

Extramedullary hematopoiesis (EMH) in laboratory animals: offering an insight into stem cell research

Extramedullary hematopoiesis (EMH) is a pathological process secondary to underlying bone marrow (BM) insufficiency in adults. It is characterized by the emergence of multipotent hematopoietic progenitors scattered around the affected tissue, most likely in the spleen, liver, and lymph node, etc. EMH in patients frequently receives less medical attention and is neglected unless a compressive or obstructive hematopoietic mass appears to endanger the patient's life. However, on a biological basis, EMH reflects the alteration of relationships among hematopoietic stem and progenitor cells (HSPCs) and their original and new microenvironments. The ability of hematopoietic stem cells (HSCs) to mobilize from the bone marrow and to accommodate and function in extramedullary tissues is rather complicated and far from our current understanding. Fortunately, many reports from the studies of drugs and genetics using animals have incidentally found EMH to be involved. Thereby, the molecular basis of EMH could further be elucidated from those animals after cross-comparison. A deeper understanding of the extramedullary hematopoietic niche could help expand stem cells in vitro and establish a better treatment in patients for stem cell transplantation.

Broad targeting of angiogenesis for cancer prevention and therapy

Deregulation of angiogenesis – the growth of new blood vessels from an existing vasculature – is a main driving force in many severe human diseases including cancer. As such, tumor angiogenesis is important for delivering oxygen and nutrients to growing tumors, and therefore considered an essential pathologic feature of cancer, while also playing a key role in enabling other aspects of tumor pathology such as metabolic deregulation and tumor dissemination/metastasis. Recently, inhibition of tumor angiogenesis has become a clinical anti-cancer strategy in line with chemotherapy, radiotherapy and surgery, which underscore the critical importance of the angiogenic switch during early tumor development. Unfortunately the clinically approved anti-angiogenic drugs in use today are only effective in a subset of the patients, and many who initially respond develop resistance over time. Also, some of the anti-angiogenic drugs are toxic and it would be of great importance to identify alternative compounds, which could overcome these drawbacks and limitations of the currently available therapy. Finding “the most important target” may, however, prove a very challenging approach as the tumor environment is highly diverse, consisting of many different cell types, all of which may contribute to tumor angiogenesis. Furthermore, the tumor cells themselves are genetically unstable, leading to a progressive increase in the number of different angiogenic factors produced as the cancer progresses to advanced stages. As an alternative approach to targeted therapy, options to broadly interfere with angiogenic signals by a mixture of non-toxic natural compound with pleiotropic actions were viewed by this team as an opportunity to develop a complementary anti-angiogenesis treatment option. As a part of the “Halifax Project” within the “Getting to know cancer” framework, we have here, based on a thorough review of the literature, identified 10 important aspects of tumor angiogenesis and the pathological tumor vasculature which would be well suited as targets for anti-angiogenic therapy: (1) endothelial cell migration/tip cell formation, (2) structural abnormalities of tumor vessels, (3) hypoxia, (4) lymphangiogenesis, (5) elevated interstitial fluid pressure, (6) poor perfusion, (7) disrupted circadian rhythms, (8) tumor promoting inflammation, (9) tumor promoting fibroblasts and (10) tumor cell metabolism/acidosis. Following this analysis, we scrutinized the available literature on broadly acting anti-angiogenic natural products, with a focus on finding qualitative information on phytochemicals which could inhibit these targets and came up with 10 prototypical phytochemical compounds: (1) oleanolic acid, (2) tripterine, (3) silibinin, (4) curcumin, (5) epigallocatechin-gallate, (6) kaempferol, (7) melatonin, (8) enterolactone, (9) withaferin A and (10) resveratrol. We suggest that these plant-derived compounds could be combined to constitute a broader acting and more effective inhibitory cocktail at doses that would not be likely to cause excessive toxicity. All the targets and phytochemical approaches were further cross-validated against their effects on other essential tumorigenic pathways (based on the “hallmarks” of cancer) in order to discover possible synergies or potentially harmful interactions, and were found to generally also have positive involvement in/effects on these other aspects of tumor biology. The aim is that this discussion could lead to the selection of combinations of such anti-angiogenic compounds which could be used in potent anti-tumor cocktails, for enhanced therapeutic efficacy, reduced toxicity and circumvention of single-agent anti-angiogenic resistance, as well as for possible use in primary or secondary cancer prevention strategies.

Novel mechanism of macrophage-mediated metastasis revealed in a zebrafish model of tumor development

Cancer metastasis can occur at early stages of tumor development due to facilitative alterations in the tumor microenvironment. Although imaging techniques have considerably improved our understanding of metastasis, early events remain challenging to study due to the small numbers of malignant cells involved that are often undetectable. Using a novel zebrafish model to investigate this process, we discovered that tumor-associated macrophages (TAM) acted to facilitate metastasis by binding tumor cells and mediating their intravasation. Mechanistic investigations revealed that IL6 and TNFα promoted the ability of macrophages to mediate this step. M2 macrophages were particularly potent when induced by IL4, IL10, and TGFβ. In contrast, IFNγ-lipopolysaccharide-induced M1 macrophages lacked the capability to function in the same way in the model. Confirming these observations, we found that human TAM isolated from primary breast, lung, colorectal, and endometrial cancers exhibited a similar capability in invasion and metastasis. Taken together, our work shows how zebrafish can be used to study how host contributions can facilitate metastasis at its earliest stages, and they reveal a new macrophage-dependent mechanism of metastasis with possible prognostic implications.

Pre-treatment of human umbilical cord-derived mesenchymal stem cells with interleukin-6 abolishes their growth-promoting effect on gastric cancer cells

The inflammatory microenvironment contributes to cancer development and progression. Mesenchymal stem cells (MSCs), as important stromal cells, may be 'educated' by the inflammatory microenvironment to support the development of gastric cancer. Cytokines are a key component of cancer-related inflammation. Interleukin (IL)-6, as an inflammatory cytokine, has multiple roles in cancer. However, whether MSCs can be 'educated' by IL-6 to support gastric cancer remains unknown. In the present study, we focused on the phenotype and function of human umbilical cord-derived MSCs hUC‑MSCs pre-treated with IL-6 in gastric cancer. We found that the protein levels of α-smooth muscle actin (α-SMA) were upregulated, and phosphorylated nuclear factor (NF)-κB protein levels were downregulated in the hUC‑MSCs pre-treated with IL-6, as shown by western blot analysis. The levels of tumor‑promoting cytokines, including chemokine (C-C motif) ligand 5 (CCL5), platelet-derived growth factor‑BB (PDGF‑BB), monocyte chemoattractant protein-1 (MCP-1) and tumor necrosis factor α(TNFα), were markedly reduced in the hUC‑MSCs following treatment with IL-6, as shown by RT-qPCR. In in vitro experiments, we co-cultured MSCs with N-methyl‑N'‑nitro‑N‑nitrosoguanidine (MNNG)‑transformed GES-1 gastric epithelial cells or SGC-7901 gastric cancer cells. Transwell and colony-forming cell assays revealed that the hUC-MSCs significantly promoted gastric cellular migration and proliferation. However, following treatment with IL-6, the hUC-MSCs had no growth-promoting effect on the gastric epithelial cells and gastric cancer cells. In in vivo experiments, we co-transplanted MSCs and SGC-7901 cells into nude mice in order to establish a nude mouse model of gastric cancer. The hUC-MSCs significantly promoted the growth gastric tumors through the promotion of cell proliferation and the inhibition of cell apoptosis. On the contrary, pre-treatment with IL-6 provided the hUC‑MSCs with the ability to inhibit cell proliferation and significantly induce cell apoptosis. Taken together, our findings indicate that pre-treatment with IL-6 significantly abolishes the ability of hUC-MSCs to promote gastric epithelial cell proliferation and migration and provide new insight into the effects of the inflammatory cytokine, IL-6, on the tumor-promoting ability of MSCs and its role in gastric cancer.

Pre-treatment of human umbilical cord-derived mesenchymal stem cells with interleukin-6 abolishes their growth-promoting effect on gastric cancer cells

The inflammatory microenvironment contributes to cancer development and progression. Mesenchymal stem cells (MSCs), as important stromal cells, may be 'educated' by the inflammatory microenvironment to support the development of gastric cancer. Cytokines are a key component of cancer-related inflammation. Interleukin (IL)-6, as an inflammatory cytokine, has multiple roles in cancer. However, whether MSCs can be 'educated' by IL-6 to support gastric cancer remains unknown. In the present study, we focused on the phenotype and function of human umbilical cord-derived MSCs hUC‑MSCs pre-treated with IL-6 in gastric cancer. We found that the protein levels of α-smooth muscle actin (α-SMA) were upregulated, and phosphorylated nuclear factor (NF)-κB protein levels were downregulated in the hUC‑MSCs pre-treated with IL-6, as shown by western blot analysis. The levels of tumor‑promoting cytokines, including chemokine (C-C motif) ligand 5 (CCL5), platelet-derived growth factor‑BB (PDGF‑BB), monocyte chemoattractant protein-1 (MCP-1) and tumor necrosis factor α(TNFα), were markedly reduced in the hUC‑MSCs following treatment with IL-6, as shown by RT-qPCR. In in vitro experiments, we co-cultured MSCs with N-methyl‑N'‑nitro‑N‑nitrosoguanidine (MNNG)‑transformed GES-1 gastric epithelial cells or SGC-7901 gastric cancer cells. Transwell and colony-forming cell assays revealed that the hUC-MSCs significantly promoted gastric cellular migration and proliferation. However, following treatment with IL-6, the hUC-MSCs had no growth-promoting effect on the gastric epithelial cells and gastric cancer cells. In in vivo experiments, we co-transplanted MSCs and SGC-7901 cells into nude mice in order to establish a nude mouse model of gastric cancer. The hUC-MSCs significantly promoted the growth gastric tumors through the promotion of cell proliferation and the inhibition of cell apoptosis. On the contrary, pre-treatment with IL-6 provided the hUC‑MSCs with the ability to inhibit cell proliferation and significantly induce cell apoptosis. Taken together, our findings indicate that pre-treatment with IL-6 significantly abolishes the ability of hUC-MSCs to promote gastric epithelial cell proliferation and migration and provide new insight into the effects of the inflammatory cytokine, IL-6, on the tumor-promoting ability of MSCs and its role in gastric cancer.

Systems biology of cancer: entropy, disorder, and selection-driven evolution to independence, invasion and "swarm intelligence"

Our knowledge of the biology of solid cancer has greatly progressed during the last few years, and many excellent reviews dealing with the various aspects of this biology have appeared. In the present review, we attempt to bring together these subjects in a general systems biology narrative. It starts from the roles of what we term entropy of signaling and noise in the initial oncogenic events, to the first major transition of tumorigenesis: the independence of the tumor cell and the switch in its physiology, i.e., from subservience to the organism to its own independent Darwinian evolution. The development after independence involves a constant dynamic reprogramming of the cells and the emergence of a sort of collective intelligence leading to invasion and metastasis and seldom to the ultimate acquisition of immortality through inter-individual infection. At each step, the probability of success is minimal to infinitesimal, but the number of cells possibly involved and the time scale account for the relatively high occurrence of tumorigenesis and metastasis in multicellular organisms.

Interferon regulatory factor 7 protects against vascular smooth muscle cell proliferation and neointima formation

Background

Interferon regulatory factor 7 (IRF7), a member of the interferon regulatory factor family, plays important roles in innate immunity and immune cell differentiation. However, the role of IRF7 in neointima formation is currently unknown.

Methods and Results

Significant decreases in IRF7 expression were observed in vascular smooth muscle cells (VSMCs) following carotid artery injury in vivo and platelet‐derived growth factor‐BB (PDGF‐BB) stimulation in vitro. Compared with non‐transgenic (NTG) controls, SMC‐specific IRF7 transgenic (IRF7‐TG) mice displayed reduced neointima formation and VSMC proliferation in response to carotid injury, whereas a global knockout of IRF7 (IRF7‐KO) resulted in the opposite effect. Notably, a novel IRF7‐KO rat strain was successfully generated and used to further confirm the effects of IRF7 deletion on the acceleration of intimal hyperplasia based on a balloon injury‐induced vascular lesion model. Mechanistically, IRF7's inhibition of carotid thickening and the expression of VSMC proliferation markers was dependent on the interaction of IRF7 with activating transcription factor 3 (ATF3) and its downstream target, proliferating cell nuclear antigen (PCNA). The evidence that IRF7/ATF3‐double‐TG (DTG) and IRF7/ATF3‐double‐KO (DKO) mice abolished the regulatory effects exhibited by the IRF7‐TG and IRF7‐KO mice, respectively, validated the underlying molecular events of IRF7‐ATF3 interaction.

Conclusions

These findings demonstrated that IRF7 modulated VSMC proliferation and neointima formation by interacting with ATF3, thereby inhibiting the ATF3‐mediated induction of PCNA transcription. The results of this study indicate that IRF7 is a novel modulator of neointima formation and VSMC proliferation and may represent a promising target for vascular disease therapy.

VEGFR2-mediated vascular dilation as a mechanism of VEGF-induced anemia and bone marrow cell mobilization

Molecular mechanisms underlying tumor VEGF-induced host anemia and bone marrow cell (BMC) mobilization remain unknown. Here, we report that tumor VEGF markedly induced sinusoidal vasculature dilation in bone marrow (BM) and BMC mobilization to tumors and peripheral tissues in mouse and human tumor models. Unexpectedly, anti-VEGFR2, but not anti-VEGFR1, treatment completely blocked VEGF-induced anemia and BMC mobilization. Genetic deletion of Vegfr2 in endothelial cells markedly ablated VEGF-stimulated BMC mobilization. Conversely, deletion of the tyrosine kinase domain from Vegfr1 gene (Vegfr1(TK-/-)) did not affect VEGF-induced BMC mobilization. Analysis of VEGFR1(+)/VEGFR2(+) populations in peripheral blood and BM showed no significant ratio difference between VEGF- and control tumor-bearing animals. These findings demonstrate that vascular dilation through the VEGFR2 signaling is the mechanism underlying VEGF-induced BM mobilization and anemia. Thus, our data provide mechanistic insights on VEGF-induced BMC mobilization in tumors and have therapeutic implications by targeting VEGFR2 for cancer therapy.

Novel antibodies directed against the human erythropoietin receptor: creating a basis for clinical implementation

Recombinant human erythropoietin (rHuEPO) is an effective treatment for anaemia but concerns that it causes disease progression in cancer patients by activation of EPO receptors (EPOR) in tumour tissue have been controversial and have restricted its clinical use. Initial clinical studies were flawed because they used polyclonal antibodies, later shown to lack specificity for EPOR. Moreover, multiple isoforms of EPOR caused by differential splicing have been reported in cancer cell lines at the mRNA level but investigations of these variants and their potential impact on tumour progression, have been hampered by lack of suitable antibodies. The EpoCan consortium seeks to promote improved pathological testing of EPOR, leading to safer clinical use of rHuEPO, by producing well characterized EPOR antibodies. Using novel genetic and traditional peptide immunization protocols, we have produced mouse and rat monoclonal antibodies, and show that several of these specifically recognize EPOR by Western blot, immunoprecipitation, immunofluorescence, flow cytometry and immunohistochemistry in cell lines and clinical material. Widespread availability of these antibodies should enable the research community to gain a better understanding of the role of EPOR in cancer, and eventually to distinguish patients who can be treated safely by rHuEPO from those at increased risk from treatment.

TNFR1 mediates TNF-α-induced tumour lymphangiogenesis and metastasis by modulating VEGF-C-VEGFR3 signalling

Inflammation and lymphangiogenesis are two cohesively coupled processes that promote tumour growth and invasion. Here we report that TNF-α markedly promotes tumour lymphangiogenesis and lymphatic metastasis. The TNF-α-TNFR1 signalling pathway directly stimulates lymphatic endothelial cell activity through a VEGFR3-independent mechanism. However, VEGFR3-induced lymphatic endothelial cell tips are a prerequisite for lymphatic vessel growth in vivo, and a VEGFR3 blockade completely ablates TNF-α-induced lymphangiogenesis. Moreover, TNF-α-TNFR1-activated inflammatory macrophages produce high levels of VEGF-C to coordinately activate VEGFR3. Genetic deletion of TNFR1 (Tnfr1(-/-)) in mice or depletion of tumour-associated macrophages (TAMs) virtually eliminates TNF-α-induced lymphangiogenesis and lymphatic metastasis. Gain-of-function experiments show that reconstitution of Tnfr1(+/+) macrophages in Tnfr1(-/-) mice largely restores tumour lymphangiogenesis and lymphatic metastasis. These findings shed mechanistic light on the intimate interplay between inflammation and lymphangiogenesis in cancer metastasis, and propose therapeutic intervention of lymphatic metastasis by targeting the TNF-α-TNFR1 pathway.

VEGF-targeted cancer therapeutics-paradoxical effects in endocrine organs

Systemic administration of antiangiogenic drugs that target components of the vascular endothelial growth factor A (VEGF-A; VEGF) signal transduction pathway has become a viable therapeutic option for patients with various types of cancer. Nevertheless, these drugs can drive alterations in healthy vasculatures, which in turn are associated with adverse effects in healthy tissues. VEGF is crucial for vascular homeostasis and the maintenance of vascular integrity and architecture in endocrine organs. Given these critical physiological functions, systemic delivery of drugs that target VEGF signalling can block VEGF-mediated vascular functions in endocrine organs, such as the thyroid gland, and lead to endocrine dysfunction, including hypothyroidism, adrenal insufficiency and altered insulin sensitivity. This Review discusses emerging evidence from preclinical and clinical studies that contributes to understanding the mechanisms that underlie the vascular changes and subsequent modulations of endocrine function that are induced by targeted inhibition of VEGF signalling. Understanding these mechanisms is crucial for the design of antiangiogenic drugs with minimal associated adverse effects that will enable effective treatment of patients with cancer.

Lymphatic endothelial cells support tumor growth in breast cancer

Tumor lymphatic vessels (LV) serve as a conduit of tumor cell dissemination, due to their leaky nature and secretion of tumor-recruiting factors. Though lymphatic endothelial cells (LEC) lining the LV express distinct factors (also called lymphangiocrine factors), these factors and their roles in the tumor microenvironment are not well understood. Here we employ LEC, microvascular endothelial cells (MEC), and human umbilical vein endothelial cells (HUVEC) cultured in triple-negative MDA-MB-231 tumor-conditioned media (TCM) to determine the factors that may be secreted by various EC in the MDA-MB-231 breast tumor. These factors will serve as endothelium derived signaling molecules in the tumor microenvironment. We co-injected these EC with MDA-MB-231 breast cancer cells into animals and showed that LEC support tumor growth, HUVEC have no significant effect on tumor growth, whereas MEC suppress it. Focusing on LEC-mediated tumor growth, we discovered that TCM-treated LEC (‘tumor-educated LEC') secrete high amounts of EGF and PDGF-BB, compared to normal LEC. LEC-secreted EGF promotes tumor cell proliferation. LEC-secreted PDGF-BB induces pericyte infiltration and angiogenesis. These lymphangiocrine factors may support tumor growth in the tumor microenvironment. This study shows that LV serve a novel role in the tumor microenvironment apart from their classical role as conduits of metastasis.

Global microRNA depletion suppresses tumor angiogenesis

Chen et al. depleted microRNAs from tumors by knocking out Dicer1 and found that these tumors are highly hypoxic but poorly vascularized. Factor inhibiting HIF-1 (FIH1) was derepressed in the tumors and suppressed HIF transcription. Depleting FIH1 reversed the phenotypes of microRNA-deficient cells, including HIF transcription activity, VEGF production, tumor hypoxia, and angiogenesis. This study suggests that microRNAs promote tumor responses to hypoxia and angiogenesis by repressing FIH1.

MicroRNAs delicately regulate the balance of angiogenesis. Here we show that depletion of all microRNAs suppresses tumor angiogenesis. We generated microRNA-deficient tumors by knocking out Dicer1. These tumors are highly hypoxic but poorly vascularized, suggestive of deficient angiogenesis signaling. Expression profiling revealed that angiogenesis genes were significantly down-regulated as a result of the microRNA deficiency. Factor inhibiting hypoxia-inducible factor 1 (HIF-1), FIH1, is derepressed under these conditions and suppresses HIF transcription. Knocking out FIH1 using CRISPR/Cas9-mediated genome engineering reversed the phenotypes of microRNA-deficient cells in HIF transcriptional activity, VEGF production, tumor hypoxia, and tumor angiogenesis. Using multiplexed CRISPR/Cas9, we deleted regions in FIH1 3′ untranslated regions (UTRs) that contain microRNA-binding sites, which derepresses FIH1 protein and represses hypoxia response. These data suggest that microRNAs promote tumor responses to hypoxia and angiogenesis by repressing FIH1.

Tumour PDGF-BB expression levels determine dual effects of anti-PDGF drugs on vascular remodelling and metastasis

Anti-platelet-derived growth factor (PDGF) drugs are routinely used in front-line therapy for the treatment of various cancers, but the molecular mechanism underlying their dose-dependent impact on vascular remodelling remains poorly understood. Here we show that anti-PDGF drugs significantly inhibit tumour growth and metastasis in high PDGF-BB-producing tumours by preventing pericyte loss and vascular permeability, whereas they promote tumour cell dissemination and metastasis in PDGF-BB-low-producing or PDGF-BB-negative tumours by ablating pericytes from tumour vessels. We show that this opposing effect is due to PDGF-β signalling in pericytes. Persistent exposure of pericytes to PDGF-BB markedly downregulates PDGF-β and inactivation of the PDGF-β signalling decreases integrin α1β1 levels, which impairs pericyte adhesion to extracellular matrix components in blood vessels. Our data suggest that tumour PDGF-BB levels may serve as a biomarker for selection of tumour-bearing hosts for anti-PDGF therapy and unsupervised use of anti-PDGF drugs could potentially promote tumour invasion and metastasis.

Erythropoietin promotes breast tumorigenesis through tumor-initiating cell self-renewal

Erythropoietin (EPO) is a hormone that induces red blood cell production. In its recombinant form, EPO is the one of most prescribed drugs to treat anemia, including that arising in cancer patients. In randomized trials, EPO administration to cancer patients has been associated with decreased survival. Here, we investigated the impact of EPO modulation on tumorigenesis. Using genetically engineered mouse models of breast cancer, we found that EPO promoted tumorigenesis by activating JAK/STAT signaling in breast tumor-initiating cells (TICs) and promoted TIC self renewal. We determined that EPO was induced by hypoxia in breast cancer cell lines, but not in human mammary epithelial cells. Additionally, we demonstrated that high levels of endogenous EPO gene expression correlated with shortened relapse-free survival and that pharmacologic JAK2 inhibition was synergistic with chemotherapy for tumor growth inhibition in vivo. These data define an active role for endogenous EPO in breast cancer progression and breast TIC self-renewal and reveal a potential application of EPO pathway inhibition in breast cancer therapy.

Signaling between tumor cells and the host bone marrow microenvironment

Tumor cells with high skeletal homing affinity express numerous cell surface receptors that bind ligands produced in bone. Upon arrival, these cells survive in the host environment, encompassed in close proximity to bone marrow cells. Interactions between tumor cells and cells of the host microenvironment are essential to not only tumor cell survival but also their activation and proliferation into environment-modifying tumors. Through the production of RANKL, PTHrP, cytokines, and integrins, activated tumor cells stimulate osteoclastogenesis, enhance bone resorption, and subsequently release matrix-bound proteins that further promote tumor growth and bone resorption. In addition, alterations in the TGF-β/BMP and Wnt signaling pathways via tumor cell growth can either stimulate or suppress osteoblastic bone formation and function, leading to sclerotic or lytic bone disease, respectively. Hence, the presence of tumor cells in bone dysregulates bone remodeling, dramatically impairing skeletal integrity. Furthermore, through complex mechanisms, cells of the immune system interact with tumor cells to further impact bone remodeling. Lastly, with alterations in bone cell activity, the environment is permissive to promoting tumor growth further, suggesting an interdependence between tumor cells and bone cells in metastatic bone disease and multiple myeloma.

Hydroxymethylation at gene regulatory regions directs stem/early progenitor cell commitment during erythropoiesis

Hematopoietic stem cell differentiation involves the silencing of self-renewal genes and induction of a specific transcriptional program. Identification of multiple covalent cytosine modifications raises the question of how these derivatized bases influence stem cell commitment. Using a replicative primary human hematopoietic stem/progenitor cell differentiation system, we demonstrate dynamic changes of 5-hydroxymethylcytosine (5-hmC) during stem cell commitment and differentiation to the erythroid lineage. Genomic loci that maintain or gain 5-hmC density throughout erythroid differentiation contain binding sites for erythroid transcription factors and several factors not previously recognized as erythroid-specific factors. The functional importance of 5-hmC was demonstrated by impaired erythroid differentiation, with augmentation of myeloid potential, and disrupted 5-hmC patterning in leukemia patient-derived CD34+ stem/early progenitor cells with TET methylcytosine dioxygenase 2 (TET2) mutations. Thus, chemical conjugation and affinity purification of 5-hmC-enriched sequences followed by sequencing serve as resources for deciphering functional implications for gene expression during stem cell commitment and differentiation along a particular lineage.

Targeting the PDGF signaling pathway in tumor treatment

Platelet-derived growth factor (PDGF) isoforms and PDGF receptors have important functions in the regulation of growth and survival of certain cell types during embryonal development and e.g. tissue repair in the adult. Overactivity of PDGF receptor signaling, by overexpression or mutational events, may drive tumor cell growth. In addition, pericytes of the vasculature and fibroblasts and myofibroblasts of the stroma of solid tumors express PDGF receptors, and PDGF stimulation of such cells promotes tumorigenesis. Inhibition of PDGF receptor signaling has proven to useful for the treatment of patients with certain rare tumors. Whether treatment with PDGF/PDGF receptor antagonists will be beneficial for more common malignancies is the subject for ongoing studies.

Angiogenesis stimulated by human kallikrein-related peptidase 12 acting via a platelet-derived growth factor B-dependent paracrine pathway

KLK12, a kallikrein peptidase, is thought to take part in the control of angiogenesis. Our analysis of the secretome of endothelial cells (ECs) that had been treated with KLK12 showed that KLK12 converts the extracellular matrix- or membrane-bound precursor of platelet-derived growth factor B (PDGF-B) into a soluble form. Both PDGF-B and vascular endothelial growth factor A (VEGF-A) take part in the induction of angiogenesis by KLK12 in a coculture model of angiogenesis that mimics endothelial tubule formation. We used a cellular approach to analyze the interplay between KLK12, PDGF-B, and VEGF-A and showed that release of PDGF-B by KLK12 leads to the fibroblast-mediated secretion of VEGF-A. This then stimulates EC differentiation and the formation of capillary tube-like structures. Thus, KLK12 favors the interaction of ECs and stromal cells. The released PDGF-B acts as a paracrine factor that modulates VEGF-A secretion by stromal cells, which ultimately leads to angiogenesis. Moreover, the genes encoding KLK12 and PDGFB are both expressed in ECs and up-regulated in tumor cells kept under hypoxic conditions, which is consistent with the physiological involvement of KLK12 in PDGF-B maturation.

Low differentiated microvascular density and low expression of platelet-derived growth factor-BB (PDGF-BB) predict distant metastasis and poor prognosis in clear cell renal cell carcinoma

OBJECTIVE

To examine the prognostic significance of the expression of platelet-derived growth factor-BB (PDGF-BB) and differentiated microvascular density (MVD) in patients with clear cell renal cell carcinoma (ccRCC).

PATIENTS AND METHODS

We used the vascular marker cluster of differentiation 34 (CD34) to identify tumour blood vessels. The expression of PDGF-BB and CD34 was detected by immunohistochemistry (IHC) in tissue microarrays (TMAs) from 100 ccRCCs. Prognostic effects of individual parameters were calculated using Cox regression models and Harrell's concordance index (c-index).

RESULTS

Higher grade and more advanced stage ccRCCs had significantly less PDGF-BB expression and differentiated MVD (P < 0.05). Higher PDGF-BB expression was an independent prognostic factor for longer survival, and moreover, the final model built by the addition of PDGF-BB expression improved the predictive accuracy for disease-free survival (c-index 0.707) compared with the clinicopathological-based model (c-index 0.695). PDGF-BB expression was positively associated with differentiated MVD assessed by Spearman correlation and factor analysis (r = 0.634, P < 0.001).

CONCLUSION

PDGF-BB is as a novel and promising prognostic marker and antiangiogenic therapeutic target for the treatment of ccRCC.

Therapeutic targeting of platelet-derived growth factor receptors in solid tumors

INTRODUCTION

Genetic aberrations that are associated with platelet-derived growth factor receptor (PDGFR) activity are frequently found in glioblastomas (10 - 15%), dermatofibrosarcoma protuberans (≤ 100%) and gastrointestinal stromal tumors (5%). Sequencing studies have also identified mutations at lower frequency in common cancer types. Preclinical evidence further suggests tumor stimulatory roles of PDGFRs expressed by tumor stroma cells and indicates a deleterious effect of stromal PDGFRs on intratumoral drug uptake.

AREAS COVERED

This review summarizes the present understanding of PDGF signaling in solid tumors based on experimental studies and clinical findings. It also provides a discussion of selected ongoing efforts to develop novel cancer therapies involving PDGFR inhibition with tyrosine kinase inhibitors or PDGFR-targeting monoclonal antibodies.

EXPERT OPINION

An increased molecular understanding of response and resistance mechanisms will be essential for therapeutic advances in PDGFR-directed cancer therapy. Further developments rely on clinical studies where systematic analyses of target status in malignant cells and in cells of the tumor stroma are included. Studies with combination therapies will be facilitated by selective PDGFR inhibitors with reduced side effects. Finally, development of improved companion diagnostics is of critical importance for patient selection and monitoring of therapeutic effects.

Erythropoiesis-stimulating agents in chronic kidney disease: what have we learned in 25 years?

Since the pioneering studies by Eschbach et al in 1987, erythropoiesis-stimulating agents (ESAs) have become the mainstay of anemia therapy in chronic kidney disease (CKD) patients. The introduction of ESAs 25 years ago markedly improved the lives of many patients with CKD, who until then had severe, often transfusion-dependent anemia. However, randomized controlled trials demonstrate an increased risk for cardiovascular events such as stroke, thrombosis, and death at nearly normal hemoglobin concentrations and higher ESA doses in CKD. By contrast, kidney transplant recipients may represent a unique population of CKD patients who may benefit from ESA therapy. This review discusses potential mechanisms involving the erythropoietic and nonerythropoietic effects of ESA treatment and ESA resistance. Further research aimed at elucidating the causal pathways is strongly recommended. Given current knowledge, however, clinical practice should avoid disproportionately high dosages of ESAs to achieve recommended hemoglobin targets, particularly in those with significant cardiovascular morbidity or ESA resistance. The key to CKD anemia management will be individualization of the potential benefits of reducing blood transfusions and anemia-related symptoms against the risks of harm.

Erythropoietin is involved in the angiogenic potential of bone marrow macrophages in multiple myeloma

Erythropoietin (Epo) is the crucial cytokine regulator of red blood cell production, and recombinant human erythropoietin (rHuEpo) is widely used in clinical practice for the treatment of anemia, primarily in kidney disease and in cancer. Increasing evidence suggests several biological roles for Epo and its receptor, Epo-R, unrelated to erythropoiesis, including angiogenesis. Epo-R has been found expressed in various non-haematopoietic cells and tissues, and in cancer cells. Here, we detected the expression of Epo-R in bone marrow-derived macrophages (BMMAs) from multiple myeloma (MM) and monoclonal gammopathy of undetermined significance (MGUS) patients and assessed whether Epo/Epo-R axis plays a role in MM macrophage-mediated angiogenesis. We found that Epo-R is over-expressed in BMMAs from MM patients with active disease compared to MGUS patients. The treatment of BMMAs with rHuEpo significantly increased the expression and secretion of key pro-angiogenic mediators, such as vascular endothelial growth factor, hepatocyte growth factor and monocyte chemotactic protein (MCP-1/CCL-2), through activation of JAK2/STAT5 and PI3 K/Akt pathways. In addition, the conditioned media harvested from rHuEpo-treated BMMAs enhanced bone marrow-derived endothelial cell migration and capillary morphogenesis in vitro, and induced angiogenesis in the chorioallantoic membrane of chick embryos in vivo. Furthermore, we found an increase in the circulating levels of several pro-angiogenic cytokines in serum of MM patients with anemia under treatment with Epo. Our findings highlight the direct effect of rHuEpo on macrophage-mediated production of pro-angiogenic factors, suggesting that Epo/Epo-R pathway may be involved in the regulation of angiogenic response occurring in MM.

Slug promoted vasculogenic mimicry in hepatocellular carcinoma

Vasculogenic mimicry (VM) refers to the unique capability of aggressive tumour cells to mimic the pattern of embryonic vasculogenic networks. Epithelial–mesenchymal transition (EMT) regulator slug have been implicated in the tumour invasion and metastasis of human hepatocellular carcinoma (HCC). However, the relationship between slug and VM formation is not clear. In the study, we demonstrated that slug expression was associated with EMT and cancer stem cell (CSCs) phenotype in HCC patients. Importantly, slug showed statistically correlation with VM formation. We consistently demonstrated that an overexpression of slug in HCC cells significantly increased CSCs subpopulation that was obvious by the increased clone forming efficiency in soft agar and by flowcytometry analysis. Meantime, the VM formation and VM mediator overexpression were also induced by slug induction. Finally, slug overexpression lead to the maintenance of CSCs phenotype and VM formation was demonstrated in vivo. Therefore, the results of this study indicate that slug induced the increase and maintenance of CSCs subpopulation and contributed to VM formation eventually. The related molecular pathways may be used as novel therapeutic targets for the inhibition of HCC angiogenesis and metastasis.

Multifarious functions of PDGFs and PDGFRs in tumor growth and metastasis

Platelet-derived growth factors (PDGFs) and their receptors (PDGFRs) are frequently expressed in various tumors and their expression levels correlate with tumor growth, invasiveness, drug resistance, and poor clinical outcomes. Emerging experimental evidence demonstrates that PDGFs exhibit multiple functions in modulation of tumor growth, metastasis, and the tumor microenvironment by targeting malignant cells, vascular cells, and stromal cells. Understanding PDGF-PDGFR-mediated molecular signaling may provide new mechanistic rationales for optimizing current cancer therapies and the development of future novel therapeutic modalities.

Platelet-derived growth factor-D promotes fibrogenesis of cardiac fibroblasts

Platelet-derived growth factor (PDGF)-D is a newly recognized member of the PDGF family with its role just now being understood. Our previous study shows that PDGF-D and its receptors (PDGFR-β) are significantly increased in the infarcted heart, where PDGFR-β is primarily expressed by fibroblasts, indicating the involvement of PDGF-D in the development of cardiac fibrosis. In continuing with these findings, the current study explored the molecular basis of PDGF-D on fibrogenesis. Rat cardiac fibroblasts were isolated and treated with PDGF-D (200 ng/ml medium). The potential regulation of PDGF-D on fibroblast growth, phenotype change, collagen turnover, and the transforming growth factor (TGF)-β pathway were explored. We found: 1) PDGF-D significantly elevated cardiac fibroblast proliferation, myofibroblast (myoFb) differentiation, and type I collagen secretion; 2) matrix metalloproteinase (MMP)-1, MMP-2, and MMP-9 protein levels were significantly elevated in PDGF-D-treated cells, which were coincident with increased expressions of tissue inhibitor of metalloproteinase (TIMP)-1 and TIMP-2; 3) PDGF-D significantly enhanced TGF-β1 synthesis, which was eliminated by TGF-β blockade with small-interfering RNA (siRNA); 4) the stimulatory role of PDGF-D on fibroblast proliferation and collagen synthesis was abolished by TGF-β blockade; and 5) TGF-β siRNA treatment significantly suppressed PDGF-D synthesis in fibroblasts. These observations indicate that PDGF-D promotes fibrogenesis through multiple mechanisms. Coelevations of TIMPs and MMPs counterbalance collagen degradation. The profibrogenic role of PDGF-D is mediated through activation of the TGF-β1 pathway. TGF-β1 exerts positive feedback on PDGF-D synthesis. These findings suggest the potential therapeutic effect of PDGFR blockade on interstitial fibrosis in the infarcted heart.

Erythropoietin in cancer: a dilemma in risk therapy

Erythropoietin (EPO) is a frequently prescribed drug for treatment of cancer-related and chemotherapy-induced anemia in cancer patients. Paradoxically, recent preclinical and clinical studies indicate that EPO could potentially accelerate tumor growth and jeopardize survival in cancer patients. In this review I critically discuss the current knowledge and broad biological functions of EPO in association with tumor growth, invasion, and angiogenesis. The emphasis is focused on discussing the complex interplay between EPO and other tumor-derived factors in angiogenesis, tumor growth, invasion, and metastasis. Understanding the multifarious functions of EPO and its reciprocal relation with other signaling pathways is crucial for developing more effective agents for cancer therapy and for minimizing risks for cancer patients.