Contrasting effects of VEGF gene disruption in embryonic stem cell-derived versus oncogene-induced tumors

Previous gene targeting studies have implicated an indispensable role of vascular endothelial growth factor (VEGF) in tumor angiogenesis, particularly in tumors of embryonal or endocrine origin. In contrast, we report here that transformation of VEGF-deficient adult fibroblasts (MDF528) with ras or neu oncogenes gives rise to highly tumorigenic and angiogenic fibrosarcomas. These aggressive VEGF-null tumors (528ras, 528neu) originated from VEGF(-/-) embryonic stem cells, which themselves were tumorigenically deficient. We also report that VEGF production by tumor stroma has a modest role in oncogene-driven tumor angiogenesis. Both ras and neu oncogenes down-regulated at least two endogenous inhibitors of angiogenesis [pigment epithelium derived factor (PEDF) and thrombospondin 1 (TSP-1)]. This is functionally important as administration of an antiangiogenic TSP-1 peptide (ABT-526) markedly inhibited growth of VEGF(-/-) tumors, with some ingress of pericytes. These results provide the first definitive genetic demonstration of the dispensability of tumor cell-derived VEGF in certain cases of 'adult' tumor angiogenesis, and thus highlight the importance of considering VEGF-independent as well as VEGF-dependent pathways when attempting to block this process pharmacologically.     

Notch: a key regulator of tumor angiogenesis and metastasis

The Notch signaling pathway is critical for many developmental processes including physiologic angiogenesis. Notch is also implicated in having a key role in tumor angiogenesis. Preclinical and clinical experience with anti-angiogenic strategies indicates that they may be limited by tumor resistance and recurrence, which has led to the search for alternative angiogenic treatment strategies. Significant progress has been made in shedding light on the complex mechanisms by which Notch signaling can influence tumor growth by disrupting vasculature in an array of tumor models (Ridgway et al., 2006). These results have led to the consideration of Notch as an attractive target to block tumor angiogenesis and inhibit growth. However, studies of inhibition of Notch signaling in different tumor models have uncovered similarly variable results, and some unexpected adverse effects. The ability of Notch to function in a context-dependent manner as a determinant of cell fate, a tumor suppressor, and an oncogene may partially explain the complexity in interpreted the role of Notch signaling inhibitors in preclinical tumor studies. In addition, Notch may also play an important role in metastasis via its direct effects on the vasculature and by modulation of epithelial-mesenchymal transition in tumor cells. Here we present a current understanding of Notch signaling in tumor angiogenesis, and discuss recent work on the role of Notch in tumor metastatic progression.     

Genetic background affects susceptibility to tumoral stem cell reprogramming

The latest studies of the interactions between oncogenes and its target cell have shown that certain oncogenes may act as passengers to reprogram tissue-specific stem/progenitor cell into a malignant cancer stem cell state. In this study, we show that the genetic background influences this tumoral stem cell reprogramming capacity of the oncogenes using as a model the Sca1-BCRABLp210 mice, where the type of tumor they develop, chronic myeloid leukemia (CML), is a function of tumoral stem cell reprogramming. Sca1-BCRABLp210 mice containing FVB genetic components were significantly more resistant to CML. However, pure Sca1-BCRABLp210 FVB mice developed thymomas that were not seen in the Sca1-BCRABLp210 mice into the B6 background. Collectively, our results demonstrate for the first time that tumoral stem cell reprogramming fate is subject to polymorphic genetic control.     

Transformation-related growth factors and their receptors

Cellular transformation may be accomplished in vitro and in vivo through the concerted action of growth factors and oncogenes. This association has demonstrated that malignant growth results from aberrations in growth factor-signal transduction pathways that normally operate to control proliferation. Activation of genes that code for growth factors and/or their receptors provides tumor cells with potential mechanisms to maintain their proliferative state. Tumor cells have been shown to produce endogenous substances that augment their growth (autocrine stimulation), as well as responding to exogenous substances (paracrine stimulation). With solid tumor cells these responses have been shown to involve aberrant expression of growth factor and/or receptor genes. The study of the interrelationship of these various growth regulatory molecules is important not only in the identification of gene products essential to cellular proliferation, but also in providing clues as to what forces are driving tumor cell growth.     

Novel VEGFR-2 Kinase Inhibitors as Anticancer Agents: A Review Focusing on SAR and Molecular Docking Studies (2016–2021)

Cancer growth, annexation, and metastatic spread are all aided by the formation of new blood vessels (angiogenesis). The commencement of the VEGF pathway leads to signal transduction that enhances endothelial cell survival, relocation, and divergence from pre-existing vasculature. The ability of solid malignancies to bloom and spread depends critically on their ability to establish their independent blood circulation (tumor angiogenesis). VEGFR is a major receptor tyrosine kinase that regulates angiogenesis, cell growth, and metastasis, diminishing apoptosis, cytoskeletal function, and other biological processes VEGFR has proven to be a remarkable focus for a variety of anticancer medicines in clinical studies. This Review explores the development of anti-VEGF-based antiangiogenic therapies having different scaffolds. This review had focused on SAR and docking studies of previously reported molecules.     

Growth regulation by oncogenes--new insights from model organisms

A great deal of work has focused on how oncogenes regulate the cell cycle during normal development and in cancer, yet their roles in regulating cell growth have been largely unexplored. Recent work in several model organisms has demonstrated that homologs of several oncogenes regulate cell growth and has suggested that some of the effects of oncogenes on the cell cycle may be a result of growth promotion. These studies have also suggested how growth and cell-cycle progression may be coupled.     

A new model of human aortic endothelial cells in vitro

Vascular endothelial cells play an important role in coagulation regulation of vascular tone and in a variety of synthetic and metabolic functions. Endothelial cells also have a pivotal role in immunological diseases atherogenesis and tumor angiogenesis. Endothelial cells are often used as system to study the pathophysiology of late complications in diabetes mellitus atherosclerotic damages and leukocyte adhesion in inflammatory diseases. Most of the studies have been performed on primary arterial and venous endothelial cell cultures with problems such as availability of autoptic material and reproducibility of cell cultures. We have isolated and characterized a novel system of proliferating long-term cultures of human aortic endothelial cells that maintain their differentiated characteristics for many generations in vitro. They produce antithrombotic and thrombotic factors such as t-PA and PAI-1 and respond to TNFalpha, an important factor correlated with the inflammatory process by modifying growth characteristics by producing cytokines such as GM-CSF by expressing ICAM-1 on the surface and by producing large amounts of nitric oxide and endothelin. This new system may be very useful to understand and study the molecular mechanisms involved in many vascular alteration pathologies and in the aging process.     

Endothelial cell survival and apoptosis in the tumor vasculature

Angiogenesis is essential for the growth and metastasis of solid tumors. The balance of endothelial cell (EC) proliferation and apoptosis is a major determinant in tumor angiogenesis. Recently, several studies demonstrated that numerous angiogenic factors not only induce angiogenesis but also function as EC survival factors. Vascular endothelial growth factor (VEGF), a potent angiogenic factor, is also an EC survival factor in embryonic vasculogenesis and tumor angiogenesis. VEGF activates specific intracellular survival pathways in ECs including Bcl-2, A1, IAP, Akt, and Erk. Integrins may function as EC survival factors by preventing anoikis by enhancing binding to the extracellular matrix. In addition, integrins may function in concert with VEGF to promote EC survival. Angiopoietin-1 (Ang-1) has recently been shown to stabilize EC networks by binding to the EC-specific tyrosine kinase receptor Tie-2. Pericytes also function as EC survival factors, by cell-cell contact, secretion of survival factors, or both. Targeting any of the above mechanisms for EC survival may provide novel antineoplastic strategies.     

Regulation of tumor angiogenesis by thrombospondin-1

Angiogenesis plays a critical role in the growth and metastasis of tumors. Thrombospondin-1 (TSP-1) is a potent angiogenesis inhibitor, and down-regulation of TSP-1 has been suggested to alter tumor growth by modulating angiogenesis in a variety of tumor types. Expression of TSP-1 is up-regulated by the tumor suppressor gene, p53, and down-regulated by oncogenes such as Myc and Ras. TSP-1 inhibits angiogenesis by inhibiting endothelial cell migration and proliferation and by inducing apoptosis. In addition, activation of transforming growth factor beta (TGF-beta) by TSP-1 plays a crucial role in the regulation of tumor progression. An understanding of the molecular basis of TSP-1-mediated inhibition of angiogenesis and tumor progression will aid in the development of novel therapeutics for the treatment of cancer.     

Novel anticancer drug discovery.

There is at present, much optimism about the possibility of finding selective anticancer drugs that will eliminate the cytotoxic side effects associated with conventional cancer chemotherapy. This hope is based on uncovering many novel molecular targets that are 'cancer-specific', which will allow the targeting of cancer cells while normal cells are spared. Thus far, encouraging results have been obtained with several of these novel agents at the preclinical level, and clinical trials have begun. These targets are involved at one level or more in tumor biology, including tumor cell proliferation, angiogenesis and metastasis. Novel targets for which advances are being made include the following: growth factor receptor tyrosine kinases such as the epidermal growth factor receptor and HER-2/neu (proliferation); the vascular endothelial growth factor receptor and the basic fibroblast growth factor receptor (angiogenesis); the oncogenic GTP-binding protein Ras (especially agents targeting Ras farnesylation, farnesyltransferase inhibitors) (proliferation); protein kinase C (proliferation and drug resistance); cyclin-dependent kinases (proliferation); and matrix metalloproteinases and angiogenin (angiogenesis and metastasis). Less explored, but potentially useful targets include the receptor tyrosine kinase platelet-derived growth factor receptor, mitogen-activated protein kinase cascade oncogenes such as Raf-1 and mitogen-activated protein kinase kinase, cell adhesion molecules such as integrins, anti-apoptosis proteins such as Bcl-2, MDM2 and survivin, and the cell life-span target telomerase.     

Mutations and epimutations in the origin of cancer

Cancer is traditionally viewed as a disease of abnormal cell proliferation controlled by a series of mutations. Mutations typically affect oncogenes or tumor suppressor genes thereby conferring growth advantage. Genomic instability facilitates mutation accumulation. Recent findings demonstrate that activation of oncogenes and inactivation of tumor suppressor genes, as well as genomic instability, can be achieved by epigenetic mechanisms as well. Unlike genetic mutations, epimutations do not change the base sequence of DNA and are potentially reversible. Similar to genetic mutations, epimutations are associated with specific patterns of gene expression that are heritable through cell divisions. Knudson's hypothesis postulates that inactivation of tumor suppressor genes requires two hits, with the first hit occurring either in somatic cells (sporadic cancer) or in the germline (hereditary cancer) and the second one always being somatic. Studies on hereditary and sporadic forms of colorectal carcinoma have made it evident that, apart from genetic mutations, epimutations may serve as either hit or both. Furthermore, recent next-generation sequencing studies show that epigenetic genes, such as those encoding histone modifying enzymes and subunits for chromatin remodeling systems, are themselves frequent targets of somatic mutations in cancer and can act like tumor suppressor genes or oncogenes. This review discusses genetic vs. epigenetic origin of cancer, including cancer susceptibility, in light of recent discoveries. Situations in which mutations and epimutations occur to serve analogous purposes are highlighted.     

Thrombospondin-1 as an endogenous inhibitor of angiogenesis and tumor growth

Thrombospondin-1 (TSP-1) is a matricellular glycoprotein that influences cellular phenotype and the structure of the extracellular matrix. These effects are important components of the tissue remodeling that is associated with angiogenesis and neoplasia. The genetic mutations in oncogenes and tumor suppressor genes that occur within tumor cells are frequently associated with decreased expression of TSP-1. However, the TSP-1 that is produced by stromal fibroblasts, endothelial cells and immune cells suppresses tumor progression. TSP-1 inhibits angiogenesis through direct effects on endothelial cell migration and survival and through indirect effects on growth factor mobilization. TSP-1 that is present in the tumor microenvironment also acts to suppress tumor cell growth through activation of transforming growth factor β in those tumor cells that are responsive to TGFβ. In this review, the molecular basis for the role of TSP-1 in the inhibition of tumor growth and angiogenesis is summarized.     

Chromosomal approaches to oncogenes and oncogenesis

Cytogenetic studies are providing clues to the growth regulatory genes involved in human carcinogenesis and to mechanisms that alter their function. Investigations of chromosome translocations in B and T cell lymphomas and in chronic myelogenous leukemia have demonstrated the effects on protooncogenes of transposition within the genome, with or without structural change in the gene. These studies have also provided evidence for many previously unidentified human oncogenes. Similarly, the recognition through cytogenetics of gene amplification units in aggressive forms of certain tumors has helped to define another important type of somatic genetic change in neoplasia, again involving both known and previously unknown oncogenes. The observation of nonrandom chromosomal deletions in other malignancies has contributed to the delineation of an additional major class of tumorigenic genes, called suppressor genes, which appear to have a significant role in inherited malignancies and are now being actively sought in many common cancers. Finally, chromosome studies have helped to demonstrate the clonal nature of most neoplasms and the importance, in tumor progression, of sequential somatic genetic changes within the neoplastic clone. This latter phenomenon appears to depend primarily on acquired genetic lability in the tumor cell population. Karyotypic data are providing leads to its basis, as well as to the significance in carcinogenesis of constitutional chromosomal fragility and of specific fragile sites within the genome of different individuals.     

HIF1-alpha functions as a tumor promoter in cancer-associated fibroblasts,and as a tumor suppressor in breast cancer cells

Our recent studies have mechanistically implicated a loss of stromal Cav-1 expression and HIF1-alpha-activation in driving the cancer-associated fibroblast phenotype, through the paracrine production of nutrients via autophagy and aerobic glycolysis. However, it remains unknown if HIF1a-activation is sufficient to confer the cancer-associated fibroblast phenotype. To test this hypothesis directly, we stably-expressed activated HIF1a in fibroblasts and then examined their ability to promote tumor growth using a xenograft model employing human breast cancer cells (MDA-MB-231). Fibroblasts harboring activated HIF1a showed a dramatic reduction in Cav-1 levels and a shift towards aerobic glycolysis, as evidenced by a loss of mitochondrial activity, and an increase in lactate production. Activated HIF1a also induced BNIP3 and BNIP3L expression, markers for the autophagic destruction of mitochondria. Most importantly, fibroblasts expressing activated HIF1a increased tumor mass by ~2-fold and tumor volume by ~3-fold, without a significant increase in tumor angiogenesis. In this context, HIF1a also induced an increase in the lymph node metastasis of cancer cells. Similar results were obtained by driving NFκB activation in fibroblasts, another inducer of autophagy. Thus, activated HIF1a is sufficient to functionally confer the cancer-associated fibroblast phenotype. It is also known that HIF1a expression is required for the induction of autophagy in cancer cells. As such, we next directly expressed activated HIF1a in MDA-MB-231 cells and assessed its effect on tumor growth via xenograft analysis. Surprisingly, activated HIF1a in cancer cells dramatically suppressed tumor growth, resulting in a 2-fold reduction in tumor mass and a 3-fold reduction in tumor volume. We conclude that HIF1a activation in different cell types can either promote or repress tumorigenesis. Based on these studies, we suggest that autophagy in cancer-associated fibroblasts promotes tumor growth via the paracrine production of recycled nutrients, which can directly "feed" cancer cells. Conversely, autophagy in cancer cells represses tumor growth via their "self-digestion." Thus, we should consider that the activities of various known oncogenes and tumor-suppressors may be compartment and cell-type specific, and are not necessarily an intrinsic property of the molecule itself. As such, other "classic" oncogenes and tumor suppressors will have to be re-evaluated to determine their compartment specific effects on tumor growth and metastasis. Lastly, our results provide direct experimental support for the recently proposed "Autophagic Tumor Stroma Model of Cancer."     

Experimental basis of cancer combination chemotherapy with retinoids,cytokines, 1,25-dihydroxyvitamin D3, and analogs

Retinoids, cytokines as well as 1,25-dihydroxyvitamin D₃ [1,25(OH)₂D₃] and analogs possess properties known to contribute potentially to cancer chemopreventive and chemotherapeutic effects. They induce cell differentiation, inhibit cell prolifeation, suppress expression of viral oncogenes, and inhibit angiogenesis nexessary for tumor growth. Since clinical combination chemotherapy of cytotoxic agents has proven superior to monotherapy, This moddality might also be useful for other classes of antitumor drugs. A series of retinoids, such as all-trans-, 13-cis-, 9-cis retinoic acid, and acitreti, cytokines, 1,25(OH)₂D₃, and analogs have been investigated in mocdel systems of defferentiation, proliferation, viral oncogenes, and angiogenesis. The three classes of compounds have common effects but nevertheless show a variance depending on the particular representative of each class. Combination of compounds of the different classes led in the various models to a hegher efficacy compared with the compounds given alone. Cytokines such as IFNα, IFNγ, G-CSF, TNFα, IL-1, and IL-4 markedly potentiate the differentiation-inducing effect of retinoids. Cytokines as well as retinoids combined with 1,25(OH)₂D₃ and analogs synergistically enhanced differentiation induction in human transformed hemopoietic cell lines. On a series of human transformed epithelial cell lines a panel of cytokies, such as IFNα, IFNβ, TNFα, TGFβ, and EGF acted synergistically with retinoies on inhibition of proliferation. This was also observed by combining retinoids with 1,25(OH)₂D₃ and analogs. Retinoids as well as interferons α and γ have the capacity to suppress the capacity to supperess the oncogene expression of human papilloma viruses which are involved in induction and growth of certain malignancies such as cervical cancer. All-trans-, 13-cis-, 9-cis retinoic acid, and acitretin as well as IFNα inhinited the formation of newly formed blood vessels induced by injection of HPV harboring, tumorigenic cell lines into Balb/C mice. The combination of retinoids with IFNα was more efficacious in inhibition angiogenesis than a retinoid or IFNα given alone. Since there is evidence that cell differentiationl, cell proliferation, viral oncogene expression as well as angiogenesis play a role in tumor induction and/or progression of tumor growth, retinoids, cytokines, as well as 1,25(OH)₂D₃ and analogs may be useful in chemoprevention and chemotherapy of neoplasms. based on the superior effect of combinations compared with administration of single compounds of these three classes under experimental conditions there is hope that also clinical application of combination treatment might bring as a step forward in chemopreventio and chemotherapy of cancer. This has already been proven in a very limited number of very limited numberr of clinical trials.     

Cross-Species Array Comparative Genomic Hybridization Identifies Novel Oncogenic Events in Zebrafish and Human Embryonal Rhabdomyosarcoma

Human cancer genomes are highly complex, making it challenging to identify specific drivers of cancer growth, progression, and tumor maintenance. To bypass this obstacle, we have applied array comparative genomic hybridization (array CGH) to zebrafish embryonal rhabdomyosaroma (ERMS) and utilized cross-species comparison to rapidly identify genomic copy number aberrations and novel candidate oncogenes in human disease. Zebrafish ERMS contain small, focal regions of low-copy amplification. These same regions were commonly amplified in human disease. For example, 16 of 19 chromosomal gains identified in zebrafish ERMS also exhibited focal, low-copy gains in human disease. Genes found in amplified genomic regions were assessed for functional roles in promoting continued tumor growth in human and zebrafish ERMS – identifying critical genes associated with tumor maintenance. Knockdown studies identified important roles for Cyclin D2 (CCND2), Homeobox Protein C6 (HOXC6) and PlexinA1 (PLXNA1) in human ERMS cell proliferation. PLXNA1 knockdown also enhanced differentiation, reduced migration, and altered anchorage-independent growth. By contrast, chemical inhibition of vascular endothelial growth factor (VEGF) signaling reduced angiogenesis and tumor size in ERMS-bearing zebrafish. Importantly, VEGFA expression correlated with poor clinical outcome in patients with ERMS, implicating inhibitors of the VEGF pathway as a promising therapy for improving patient survival. Our results demonstrate the utility of array CGH and cross-species comparisons to identify candidate oncogenes essential for the pathogenesis of human cancer.     

Oncogenes and Tumor Suppressor Genes

Breast cancer progression involves multiple genetic events, which can activate dominant-acting oncogenes and disrupt the function of specific tumor suppressor genes. This article describes several key oncogene and tumor suppressor signaling networks that have been implicated in breast cancer progression. Among the tumor suppressors, the article emphasizes BRCA1/2 and p53 tumor suppressors. In addition to these well characterized tumor suppressors, the article highlights the importance of PTEN tumor suppressor in counteracting PI3K signaling from activated oncogenes such as ErbB2. This article discusses the use of mouse models of human breast that recapitulate the key genetic events involved in the initiation and progression of breast cancer. Finally, the therapeutic potential of targeting these key tumor suppressor and oncogene signaling networks is discussed.Karyotypic and epidemiological analyses of mammary tumors at various stages suggest that breast carcinomas become increasingly aggressive through the stepwise accumulation of genetic changes. The majority of genetic changes found in human breast cancer fall into two categories: gain-of-function mutations in proto-oncogenes, which stimulate cell growth, division, and survival; and loss-of-function mutations in tumor suppressor genes that normally help prevent unrestrained cellular growth and promote DNA repair and cell cycle checkpoint activation. Epigenetic deregulation also contributes to the abnormal expression of these genes. For example, genes that encode enzymes involved in histone modification are mutated in primary renal cell carcinoma (Dalgliesh et al. 2010; van Haaften et al. 2009). In addition, the involvement of noncoding RNAs in tumorigenesis and tumor metastasis has been recently documented (Croce 2009; Shimono et al. 2009). These can act as oncogenes or tumor suppressor genes, depending on the context. Here, we discuss genes that are frequently altered in breast cancer, focusing on ErbB2, PI3K (phosphatidylinositol 3 kinase) pathways, TP53, BRCA1/2, and PTEN (phosphatase and tensin homolog deleted on chromosome 10). Genetically engineered mouse models are emphasized because these provide a wealth of biological information. We consider in detail genetic and biochemical studies that have shown that oncogenic proteins and tumor suppressors provide a critical balance in regulation of key pathways that control cell number and cell behavior.     

血管生成素在造血系统恶性肿瘤中的作用及机制

促血管生成因子不仅参与实体肿瘤的发生和进展,而且与非实体瘤(如白血病等)的发生和发展进程密切相关.在众多促血管生成因子中,血管生成素(angiogenin, ANG)可以促进实体瘤细胞的生长和血管生成,然而其引起血管生成异常的详细机制目前还不完全清楚.本文就近年来在非实体瘤中血管生成素的功能及其潜在的治疗作用的研究进展进行综述.