Antiangiogenic agents targeting vascular endothelial growth factor and its receptors in clinical development

There is ample therapeutic opportunity for the use of antiangiogenic inhibitors in the clinic, as there are several human diseases that are dependent upon angiogenesis [1]. However, no disease has attracted as much attention as a target for antiangiogenic therapy as malignant disorders. There is a vast amount of literature acting as proof-of-principle for the use of angiogenic inhibitors as effective agents for blocking tumour-induced angiogenesis and subverting tumour growth and disease dissemination. One of the unique attractions of targeting tumour angiogenesis is that vascular endothelial cells are a genetically stable population in which acquisition of therapeutic resistance might be less efficient than in genetically unstable tumour cells [2,3]. This review covers inhibitors that target the tumour angiogenic agent vascular endothelial growth factor and its receptors as one such antiangiogenic approach. Many agents in this class are in clinical trials with limited reports of toxicity and some early evidence of clinical benefit.     

Inhibition of Tumor Growth and Metastasis by Targeting Tumor-Associated Angiogenesis with Antagonists to the Receptors of Vascular Endothelial Growth Factor

Angiogenesis, the formation of new blood vessels, is essential for both tumor growth and metastasis. Recent advances in our understanding of the molecular mechanisms underlying the angiogenesis process and its regulation have led to the discovery of a variety of pharmaceutical agents with anti-angiogenic activity. The potential application of these angiogenesis inhibitors is currently under intense clinical and pre-clinical investigation. Compelling evidence suggests that vascular endothelial growth factor (VEGF) and its receptors play critical roles in tumor-associated angiogenesis, and that they represent good targets for therapeutic intervention. This has been demonstrated in a variety of animal tumor models in which disabling the function of VEGF and its receptors was shown to inhibit both tumor growth and metastasis. We have produced a panel of antibodies directed against the VEGF receptor 2, KDR/Flk-1. These antibodies potently block VEGF/KDR/Flk-1 interaction, and inhibit VEGF-stimulated activation of the receptor and proliferation of human endothelial cells. Further, the antibodies significantly inhibited tumor-associated angiogenesis in several animal models. Antagonists of VEGF and/or its receptors may offer higher specificity towards tumors with reduced side effects, and may be less likely to elicit drug resistance compared to conventional therapy. Anti-angiogenesis therapy represents a novel strategy for the treatment of cancer and other human disorders where pathological angiogenesis is involved.     

Antiangiogenic agents and targets: A perspective

The first generation of clinically useful antiangiogenic agents focused on VEGF and targets in the VEGF pathway. The strengths and limitations of these therapeutics are now clear. Some tumors do not respond to VEGF-directed therapies de novo and others become non-responsive or resistant over time by switching to other angiogenic pathways. The next generation of angiogenesis-directed therapeutics will expand the field beyond the VEGF pathway and become more disease selective. Placental growth factor, a protein closely related to VEGF, is induced as tumors lose responsiveness to VEGF-directed therapies. Angiopoietins 1 and 2 are being targeted with a unique peptibody, a human recombinant Fc constant region fused to peptides, in clinical trials. The HGF/c-Met pathway is upregulated in some tumors as an alternate angiogenic pathway. The CXCL12 (SDF-1)/CXCR4 pathway represents a stromal chemokine axis involved in tumor angiogenesis. CXCR2 is a G-protein coupled receptor with several ligands including interleukin-8 and other angiogenic cytokines and may represent a useful target for antiangiogenic agents. The notch pathway is being investigated as a target in the setting of tumor angiogenesis. Sphingosine-1-phosphate is a bioactive lipid that can be neutralized with a monoclonal antibody. The anti-S-1-P antibody is under investigation as an antiangiogenic agent. Finally, several multi-targeted kinase inhibitors each with a unique pattern of inhibitory potency are in clinical trial with a focus on antiangiogenic activity. The expansion of the scope of potential antiangiogenic agents in or entering clinical trial should allow the development of antiangiogenic combination regimens and single agents that address diseases refractory to VEGF-directed therapeutics.     

肝纤维化中星状细胞促血管生成分子机制的研究

肝纤维化进程中存在明显的病理性血管生成与重构,阻碍了肝纤维化的逆转与恢复。血管生成及其信号调控系统已成为肝纤维化治疗的潜在靶标,血管生成抑制剂在一些实验研究中已显示出较好的抗肝纤维化疗效。肝星状细胞是肝脏中的周细胞,可以表达血管内皮生长因子、血小板衍生生长因子、瘦素、血管生成素-1等多种血管生成因子,多途径地促进病理性血管生成过程。该文对近年来肝星状细胞促进肝纤维化血管生成分子机制的研究作一综述,可以为抗肝纤维化研究提供新的视角,有助于发现新的治疗靶标。     

血管内皮生长因子及其受体在抗肿瘤治疗应用的研究进展

肿瘤的生长依赖肿瘤新生血管的形成。血管内皮生长因子（VEGF）是一类能促进血管生成的细胞因子，能诱导细胞的有丝分裂和调节内皮细胞的通透性。VEGF及其受体介导的肿瘤血管新生在肿瘤的生长和转移中具有重要的作用。本文综述了VEGF及其受体的分类、作用机制及在抗肿瘤治疗中的应用。     

Tumor angiogenesis: a potential target in cancer control by phytochemicals

It is now well established that angiogenesis is an obligatory event for the growth and progression of solid tumors beyond the size limit (approximately 2 mm diameter) imposed by simple diffusion for the nutrient supply. Human tumors can remain dormant for years owing to a balance between cell proliferation and apoptosis. Several hypotheses have been articulated regarding the critical importance of tumor angiogenesis in the development and metastatic spread of tumors, and how preventive/therapeutic inhibition of angiogenesis might be exploited as a novel means of controlling cancer growth. Anti-angiogenic therapy is suggested as one of the most promising approaches to control cancer, as endothelial cells are generally non-transformed cells and are less prone to acquire drug resistance. Tumor vasculature could be an important prognostic marker, and an independent predictor of pathologic stages and malignant potential of cancer. This review is focused on recent developments and comprehensive mechanistic aspects of phytochemicals related to an interplay of angiogenic promoters and inhibitors, and associated signaling in both tumor as well as endothelial cells. Since, vascular endothelial cells constitute the first line exposure to the blood-borne agents, it is plausible that anti-angiogenic activity of phytochemicals could be associated with lowering the risk of cancer by preventing the growth and metastasis of tumor.     

Tivozanib

肿瘤的增长与扩散依赖于新血管的生成或血管的新生。血管内皮生长因子受体(VEGFR)能促进内皮细胞的增殖,增强血管的渗透性,是控制新生血管生成的重要调控因子之一。Tivozanib是一种新型高选择抑制VEGFR的喹唑啉脲类化合物,体内外实验表明本品具有显著的抗血管生成和抑制抗肿瘤生长的活性,目前对肾细胞癌的治疗正在进行Ⅲ期临床实验。     

Molecular mechanisms of deguelin-induced apoptosis in transformed human bronchial epithelial cells

Increasing evidence has demonstrated that the phosphatidylinositol-3 kinase (PI3K)/Akt signaling pathway plays an important role in cell proliferation, apoptosis, angiogenesis, adhesion, invasion, and migration, functions that are critical to cancer cell survival and metastasis. Increased expression of activated Akt has been observed in the early stages of tobacco-induced lung carcinogenesis. Moreover, blocking the PI3K/Akt pathway specifically inhibits the proliferation of non-small cell lung cancer (NSCLC) cells, indicating that the PI3K/Akt pathway is a potential target for chemoprevention and therapy in lung cancer. The aim of this work is to study the lung cancer chemopreventive potential of PI3K/Akt inhibitors using an in vitro lung carcinogenesis model. We found that genetic or pharmacologic approaches targeting the PI3K/Akt pathway inhibited the proliferation of premalignant and malignant human bronchial epithelial (HBE) cells. After screening several natural products to identify a potential lung cancer chemopreventive agent, we have found that deguelin, a rotenoid isolated from Mundulea sericea (Leguminosae), specifically inhibits the growth of transformed HBE and NSCLC cells by inducing cell-cycle arrest in the G2/M phase and apoptosis, with no detectable toxic effects on normal HBE cells, most likely due to the agent's ability to inhibit PI3K/Akt-mediated signaling pathways. The specific sensitivity of premalignant and malignant HBE and NSCLC cells to deguelin suggests that this drug could be clinically useful for chemoprevention in early-stage lung carcinogenesis and for therapy in confirmed lung cancer.     

Angiogenesis: new targets for the development of anticancer chemotherapies

Angiogenesis is the process by which new blood vessels are formed from preexisting microvasculature. To ensure an adequate blood supply, tumor cells release angiogenic factors that are capable of promoting nearby blood vessels to extend vascular branches to the tumor. In addition, larger tumors have been shown to release angiogeneic inhibitory factors that prevent blood vessels from sending branches to smaller, more distant tumors that compete for oxygen and nutrients. Angiogenesis is a complex multistep biochemical process, and offers several potential molecular targets for non-cytotoxic anticancer therapies. Strategies for exploiting tumor angiogenesis for novel cancer drug discovery include: (i) inhibition of proteolytic enzymes that breakdown the extracellular matrix surrounding existing capillaries; (ii) inhibition of endothelial cell migration; (iii) inhibition of endothelial cell proliferation; (iv) enhancement of tumor endothelial cell apoptosis. There is also a host of miscellaneous agents that inhibit angiogenesis for which the specific mechanisms are not clear. Several methods have been developed for measuring antiangiogenic activity both in vitro and in vivo. Although there has been intensive research efforts focused at the phenomena of angiogenesis, as well as the search for antiangiogenic agents for more than two decades, many questions remain unanswered with regard to the overall biochemical mechanisms of the angiogenesis process and the potential therapeutic utility of angiogenic inhibitors. Nevertheless potent angiogenic inhibitors capable of blocking tumor growth have been discovered, and appear to have potential for development into novel anticancer therapeutics. However there are still hurdles to be overcome before these inhibitors become mainstream therapies.     

A review of the latest clinical compounds to inhibit VEGF in pathological angiogenesis

Angiogenesis plays an important role in the formation of new blood vessels and is crucial for tumour development and progression. Imbalance between pro- and antiangiogenesis factors regulates the biological process of angiogenesis. The best characterised of the proangiogenic factors and the most potent is vascular endothelial growth factor (VEGF). The binding of VEGF to one of its transmembrane tyrosine kinase receptors, which are predominantly found on endothelial cells, results in receptor dimerisation, activation and autophosphorylation of the tyrosine kinase domain. This triggers a cascade of complex downstream signalling pathways. Several strategies targeting the VEGF signalling pathway have been developed. These include neutralising antibodies to VEGF (bevacizumab) or VEGF receptors (VEGFRs) (DC101), soluble VEGFR/VEGFR hybrids (VEGF-Trap), and tyrosine kinase inhibitors of VEGFRs (BAY43-9006, SU11248, ZD6474, AZD2171, PTK/ZK and others). Several of these agents are now being investigated in clinical trials.     

分子靶向药物治疗非小细胞肺癌的临床研究进展

分子靶向药物是利用肿瘤细胞与正常细胞之间分子细胞生物学上的差异,采用封闭受体、抑制血管生成、阻断信号传导通路等方法作用于肿瘤细胞特定的靶点,特异性地抑制肿瘤细胞的生长,促使肿瘤细胞凋亡.分子靶向治疗比传统的化疗特异性强、毒副反应小,将成为今后肿瘤治疗的新趋势.综述了近年来分子靶向药物治疗非小细胞肺癌的临床研究和应用.     

表皮生长因子受体酪氨酸激酶抑制剂在肿瘤治疗中的应用

表皮生长因子受体 (EGFR)酪氨酸激酶 ,是细胞外信号传递到细胞内的重要枢纽 ,它在信号传导、细胞增殖、分化以及各种调节机制中发挥重要作用 ,在多种癌细胞中过度表达。许多研究表明 ,抑制EGFR酪氨酸激酶活性 ,可抑制肿瘤生长。目前 ,已有几种EGFR酪氨酸激酶抑制剂进入了临床试验。本文对几种EGFR酪氨酸激酶小分子抑制剂在肿瘤治疗中的研究进展做一综述。     

Antiangiogenic agents: studies on fumagillin and curcumin analogs

Cancer is a general term used to describe many disease states, each of which are characterized by abnormal cell proliferation. The causes which bring about this abnormal cellular behavior are specific to each type of cancer. The success of tumor-targeted therapy is limited by this diversity. One common denominator for all types of cancer is the requirement of a suitable blood supply. Therefore, tumor vasculature has emerged as a potential target for therapeutic intervention. New blood vessel growth from preexisting vasculature stimulated by biochemical signals is termed angiogenesis. Tumor masses require a constant supply of oxygen and nutrients, and a means of efficient waste removal to ensure sustained development. Diffusion from nearby capillaries can supply adequate nutrition for tumors less than 2 mm in size, but for continued growth the tumors must develop their own blood supply. Alteration of the delicate balance of angiogenic stimulating factors and angiogenic inhibitors results in the phenotypic change from quiescence to active endothelial proliferation. To date, this angiogenic switch is not completely understood. The goal of antiangiogenic therapy is to interfere with these mechanisms and prevent tumor cells from developing a viable blood supply. Fumagillin is a naturally occurring antifungal agent. Curcumin is a natural product isolated from the spice turmeric. Both compounds have been shown to have antiangiogenic properties in vitro and in vivo. This paper describes efforts to design and prepare fumagillin and curcumin analogs and evaluate their corresponding antiangiogenic activities.     

NF-kappaB in solid tumors

Cancer is a multistep process during which cells acquire genetic alterations that drive the progressive transformation of normal cells into highly malignant cells. Self-sufficiency in growth, insensitivity to anti-growth signals, evasion of apoptosis, limitless replicative potential, sustained angiogenesis, tissue invasion and metastasis, are signatures of transformed cells. NF-kappaB is a key actor in tumorigenesis given its ability to control the expression and the function of a number of genes involved in these processes. Indeed, constitutive activation of NF-kappaB is a common feature of many human tumors, while its sustained activation during inflammation predisposes normal cells to neoplastic transformation. Since suppression of NF-kappaB has been shown to inhibit oncogenic potential of transformed cells, targeting it should be effective in the prevention and treatment of cancer.     

Antineovascular therapy, a novel antiangiogenic approach

Angiogenesis is a crucial event in tumour growth, since the growth of tumour cells depends on the supply of essentials such as oxygen and nutrients. Therefore, suppression of angiogenesis is expected to show potent therapeutic effects on various cancers. Additionally, this 'antiangiogenic therapy' is thought not only to eradicate primary tumour cells, but also suppress tumour metastases through disruption of haematogenous metastatic pathways. Tumour dormancy therapy does not aim to disrupt newly formed angiogenic vessels but aims to inhibit further formation of neovessels through inhibiting certain processes of angiogenesis. This raises a question of whether or not these antiangiogenic agents bring complete cure of tumours as complete cut-off of oxygen and nutrients is not expected by the treatment with these agents. This paper will review a novel antiangiogenic therapy, antineovascular therapy (ANET). ANET is categorised in antiangiogenic therapy but is different from tumour dormancy therapy using conventional angiogenic inhibitors: ANET aims to disrupt neovessels rather than to inhibit neovessel formation. ANET is based on the fact that angiogenic endothelial cells are growing cells and would be effectively damaged by cytotoxic agents when the agents are effectively delivered to the neovessels. The complete eradication of angiogenic endothelial cells may cause complete cut-off of essential supplies to the tumour cells and lead to indirect but strong cytotoxicity instead of cytostasis caused by the inhibition of angiogenesis. For the purpose of ANET, an angiogenic vasculature-targeting probe has been developed, by which cytotoxic anticancer agents are actively delivered to the angiogenic endothelial cells by using drug delivery system (DDS) technology. Another way to damage newly formed vessels by cytotoxic agents is achieved by metronomic-dosing chemotherapy. This chemotherapy shifts the target of chemotherapeutic agents from tumour cells to angiogenic endothelial cells by selective dosing schedule. Similarly, the shift of target from tumour cells to angiogenic endothelial cells enhanced therapeutic efficacy of cancer photo-dynamic therapy (PDT): in this antiangiogenic PDT, photosensitizers are delivered more to neovessel endothelial cells than to tumour cells. These therapeutic strategies would be clinically applied in the future.     

表皮生长因子在肿瘤诊疗中的研究进展

表皮生长因子受体（Epidermal growth factor receptor,EGFR）在90％的肿瘤中存在过度表达。EGFR介导的信号通路与肿瘤细胞扩增、凋亡抑制、血管生成、侵袭及转移有关。EGFR是与细胞增殖有关的蛋白质,而EGFR蛋白表达水平与活性的改变不仅影响细胞的生长亦与细胞对化、放疗的敏感性有关。本文综述TEGFR的结构、功能及其靶向抗肿瘤新生血管生成药物及其研究进展。     

Prostaglandin E2 regulates cellular migration via induction of vascular endothelial growth factor receptor-1 in HCA-7 human colon cancer cells

An important event in the development of tumors is angiogenesis, or the formation of new blood vessels. Angiogenesis is also known to be involved in tumor cell metastasis and is dependent upon the activity of the vascular endothelial growth factor (VEGF) signaling pathway. Studies of mice in which the EP3 prostanoid receptors have been genetically deleted have shown a role for these receptors in cancer growth and angiogenesis. In the present study, human colon cancer HCA-7 cells were used as a model system to understand the potential role of EP3 receptors in tumor cell migration. We now show that stimulation of HCA-7 cells with PGE₂ enhanced the up-regulation of VEGF receptor-1 (VEGFR-1) expression by a mechanism involving EP3 receptor-mediated activation of phosphatidylinositol 3-kinase and the extracellular signal-regulated kinases. Moreover, the PGE₂ stimulated increase in VEGFR-1 expression was accompanied by an increase in the cellular migration of HCA-7 cells. Given the known involvement of VEGFR-1 in cellular migration, our results suggest that EP3 receptors may contribute to tumor cell metastasis by increasing cellular migration through the up-regulation of VEGFR-1 signaling.     

血管内皮细胞生长因子受体酪氨酸激酶抑制剂的研究进展

血管内皮细胞生长因子受体（VEGFR）家族的受体酪氨酸激酶与多种恶性肿瘤的发生、发展及预后等密切相关。近年来，许多以此为靶点的新的抗肿瘤药物和治疗方法陆续被开发。综述了作用于VEGFR的酪氨酸激酶抑制剂bevacizumab，PTK787，BAY43-9006，SU11248和ZD6474的研究进展。