血管生成主要信号通路

血管生成是通过人体中存在的诸多互补和复杂的信号途径调节的.血管内皮生长因子(VEGF)-血管内皮生长因子受体(VEGFR)、血管生成素(Ang)-Tie2轴和Dll4-Notch这3个复杂的、相辅相成的信号传导通路可在调节血管生成中发挥重要作用.     

血管内皮生长因子和D114-Notch信号通路在肿瘤血管发生中的作用

抗肿瘤血管发生是一种全新的抗肿瘤治疗策略,目前研究最多的是寻找有效抗血管内皮生长因子（VEGF）信号通路的药物。然而VEGF抑制剂并不是对所有肿瘤有效,因此,有必要进一步探索血管发生的其他信号通路。目前,DH4-Nmch信号通路被认为是抗肿瘤血管发生的新靶点,而且VEGF和DH4-N0tch信号通路在多方面相互作用,在调控血管发生过程中发挥重要作用,对这两条通路的探索和研究,将会使治疗肿瘤的手段更为丰富。     

血管内皮生长因子和Notch信号通路与肿瘤血管生成

血管内皮生长因子(VEGF)和Notch信号通路是血管发育及肿瘤血管生成的重要机制.阻断VEGF可抑制肿瘤生长和血管生成.Notch能抑制内皮形成尖端细胞,减少血管生成.实验证明,两条通路相互作用,联合阻断VEGF和Notch信号通路可协同抑制肿瘤生长.对VEGF和Notch通路的研究,将为肿瘤临床治疗提供新的方法.     

Dll4/Notch通路与肿瘤血管形成

Notch是一个高度保守的跨膜受体蛋白家族,广泛存在于无脊椎以及脊椎动物体内.有5种Notch配体存在于哺乳动物体内,分别为Dll1、Dll3、Dll4、Jagged1和Jag-ged2.它们和Notch1-4的4个受体通过相邻细胞膜表面的接触、结合来激活Notch信号通路,发挥一系列的生物学调控功能[1].     

VEGF与骨肿瘤抗血管生成治疗进展

VEGF和VEGFR因其在肿瘤血管生成中的重要作用而成为抗肿瘤血管生成疗法的重要靶点.目前应用单克隆抗体、小分子抑制物、可溶性受体等方法通过阻断其信号转导通路或耗竭肿瘤细胞产生的VEGF,使VEGF或VEGFR表达减少,从而抑制肿瘤血管生成,切断肿瘤血供,最终达到抑制肿瘤生长及转移的作用.全文综述了VEGF及VEGFR研究历程、分子结构及其最近几年在抗血管生成治疗方面的最新进展和应用前景.     

血管瘤及常见血管畸形致病基因的研究进展

血管瘤是指发生于血管组织的一种良性肿瘤,属于血管生成性疾病,遗传因素在血管瘤及其血管畸形中起着重要的作用。近10年,在基因水平上对血管新生机制的研究取得了较大进步。一系列与血管瘤和血管畸形相关的基因和通路被鉴定出来,如血管内皮生长因子(vascular endothelial growth factor,VEGF)/血管内皮生长因子受体(VEGF receptors,VEGFR)信号通路和Notch信号通路异常对血管瘤发生起着重要作用。本文主要对这些方面的最新研究作一综述。     

DLL4在抗肿瘤新生血管治疗中作用的研究进展

抗新生血管治疗是实体肿瘤治疗中的有效策略，近年来抗VEGFA和VEGFR2受体治疗出现了耐药现象。Notch信号转导是一种细胞间信号通路，在肿瘤新生血管生成中起重要作用。在Notch通路中，Delta样配体4（Deltalike ligand 4，DLL4）在影响肿瘤新生血管生成方面起着重要的作用，它能抑制新生血管分支形成，促进新生血管的成熟;阻断DLL4能增加无功能新生血管数量，加剧恶性肿瘤缺血缺氧，抑制肿瘤的生长。对DLL4蛋白的深入研究为肿瘤新生血管分子靶向治疗 提供新的策略和新的靶标，DLL4有可能成为继VEGF后肿瘤血管分子靶向治疗的重要靶点。     

肿瘤中血管生成信号通路相关药物临床转化研究现状

血管生成在肿瘤发生、增殖、侵袭和转移的全程中都扮演着重要角色,以肿瘤血管生成信号通路中的关键分子为靶点开发抗肿瘤药物是目前药物研发的热点。肿瘤相关的血管生成信号通路包括VEGF/VEEFR、血管生成素及其受体、血小板源生长因子及其受体、Delta-like Ligand/Notch、成纤维细胞生长因子及其受体、肝细胞生长因子及其受体、转化生长因子及其受体、内皮素系统等。与肿瘤血管生成通路相关的药物中,贝伐单抗（bevacizumab)、索拉非尼(sorafenib)、舒尼替尼(sunitinib)等药物已经获得FDA的批准,在直肠癌、肾癌、非小细胞肺癌、肝癌、胃肠间质瘤等肿瘤患者中取得了良好效果,数十种尚未被FDA批准的抗血管生成药物也正在全球进行各期临床试验。本文总结肿瘤血管生成信号通路的基础研究及其相关药物临床转化的研究进展。     

DLLA在抗肿瘤新生血管治疗中作用的研究进展

抗新生血管治疗是实体肿瘤治疗中的有效策略，近年来抗VEGF—A和VEGF—R2受体治疗出现了耐药现象。Notch信号转导是一种细胞问信号通路，在肿瘤新生血管生成中起重要作用。在Notch通路中，Delta样配体4（Delta-likeligand4，DLL4）在影响肿瘤新生血管生成方面起着重要的作用，它能抑制新生血管分支形成，促进新生血管的成熟；阻断DLIA能增加无功能新生血管数量，加剧恶性肿瘤缺血缺氧，抑制肿瘤的生长。对DLIA蛋白的深入研究为肿瘤新生血管分子靶向治疗提供新的策略和新的靶标，DLIA有可能成为继VEGF后肿瘤血管分子靶向治疗的重要靶点。     

Jagged-1在肿瘤新生血管形成中的双重作用

Jagged-1是存在于哺乳动物细胞膜上Notch受体的主要配体之一,在许多组织的生长发育中起着重要作用。研究表明Jagged-1-Notch信号参与肿瘤新生血管化,表现为诱导血管特异性酶活化促进内皮细胞分化,导致内皮-间质细胞移行促进血管发育;上调内皮细胞标志分子如血管内皮钙黏附蛋白、血小板内皮细胞黏附分子-1、血管生成素受体-2、纤维连接蛋白、血小板源生长因子受体和α-平滑肌肌动蛋白等的表达,促进内皮和平滑肌细胞分化;与TGF-α和EGF等生长因子激活的通路共同作用促进血管样结构的形成。但也发现Jagged-1-Notch信号通路下游的HERP1通过阻止myocardin而抑制血管平滑肌细胞标志蛋白SM-MHC和平滑肌22-α的表达,同时通过干扰血清应答因子与SM-MHC中含CArG的启动子结合而抑制血管平滑肌细胞的分化;Jagged-1信号通过p21Cip1抑制cyclinD和cdk4的核定位以及Rb蛋白的磷酸化,从而抑制血管内皮细胞的增殖。Jagged-1所呈现的反向双重作用机制仍有待阐明。     

DLL4-Notch signaling mediates tumor resistance to anti-VEGF therapy in vivo

Resistance to VEGF inhibitors is emerging as a major clinical problem. Notch signaling has been implicated in tumor angiogenesis. Therefore, to investigate mechanisms of resistance to angiogenesis inhibitors, we transduced human glioblastoma cells with retroviruses encoding Notch delta-like ligand 4 (DLL4), grew them as tumor xenografts and then treated the murine hosts with the VEGF-A inhibitor bevacizumab. We found that DLL4-mediated tumor resistance to bevacizumab in vivo. The large vessels induced by DLL4-Notch signaling increased tumor blood supply and were insensitive to bevacizumab. However, blockade of Notch signaling by dibenzazepine, a γ-secretase inhibitor, disrupted the large vessels and abolished the tumor resistance. Multiple molecular mechanisms of resistance were shown, including decreased levels of hypoxia-induced VEGF and increased levels of the VEGF receptor VEGFR1 in the tumor stroma, decreased levels of VEGFR2 in large blood vessels, and reduced levels of VEGFR3 overall. DLL4-expressing tumors were also resistant to a VEGFR targeting multikinase inhibitor. We also observed activation of other pathways of tumor resistance driven by DLL4-Notch signaling, including the FGF2-FGFR and EphB4-EprinB2 pathways, the inhibition of which reversed tumor resistance partially. Taken together, our findings show the importance of classifying mechanisms involved in angiogenesis in tumors, and how combination therapy to block DLL4-Notch signaling may enhance the efficacy of VEGF inhibitors, particularly in DLL4-upregulated tumors, and thus provide a rational base for the development of novel strategies to overcome antiangiogenic resistance in the clinic.     

Delta-like 4/Notch signaling and its therapeutic implications.

Intense research efforts have been focused toward the identification of regulators of angiogenesis and the development of antiangiogenesis-based cancer therapies. The approval of anti-vascular endothelial growth factor (VEGF) monoclonal antibody (bevacizumab) for use in colorectal and lung cancer provides clinical validation for targeting angiogenesis for the treatment of cancer. Delta-like 4 (Dll4)-mediated Notch signaling represents another key pathway essential for vascular development. Recent studies yield substantial insights into the role of Dll4 in angiogenesis. Dll4 is downstream of VEGF signaling and its activation triggers a negative feedback that restrains the effects of VEGF. Attenuation of Dll4/Notch signaling results in chaotic vascular network with excessive branching and sprouting. In preclinical studies, blocking of Dll4/Notch signaling is associated with a paradoxical increase in tumor vessel density, yet causes marked growth inhibition due to functionally defective vasculature. Dll4 blockade holds promise as an additional strategy for angiogenesis-based cancer therapy, especially when resistance to and/or escape from existing therapies evolve.     

VEGF and Delta-Notch: interacting signalling pathways in tumour angiogenesis

Tumour angiogenesis has become an important target for antitumour therapy, with most current therapies aimed at blocking the VEGF pathway. However, not all tumours are responsive to VEGF blockers, and some tumours that are responsive initially may become resistant during the course of treatment, thus there is a need to explore other angiogenesis signalling pathways. Recently, the Delta-Notch pathway, and particularly the ligand Delta-like 4 (Dll4), was identified as a new target in tumour angiogenesis. An important feature in angiogenesis is the manifold ways in which the VEGF and Delta-Notch pathways interact. The emerging picture is that the VEGF pathway acts as a potent upstream activating stimulus for angiogenesis, whereas Delta-Notch helps to guide cell fate decisions that appropriately shape the activation. Here we review the two signalling pathways and what is currently known about the ways in which they interact during tumour angiogenesis.     

Notch signaling regulates tumor angiogenesis by diverse mechanisms

The Notch signaling pathway is fundamental to proper cardiovascular development and is now recognized as an important player in tumor angiogenesis. Two key Notch ligands have been implicated in tumor angiogenesis, Delta-like 4 and Jagged1. We introduce the proteins and how they work in normal developing vasculature and then discuss differing models describing the action of these Notch ligands in tumor angiogenesis. Endothelial Dll4 expression activates Notch resulting in restriction of new sprout development; for instance, in growing retinal vessels. In agreement with this activity, inhibition of Dll4-mediated Notch signaling in tumors results in hypersprouting of nonfunctional vasculature. This Dll4 inhibition may paradoxically lead to increased angiogenesis but poor tumor growth because the newly growing vessels are not functional. In contrast, Jagged1 has been described as a Notch ligand expressed in tumor cells that can have a positive influence on tumor angiogenesis, possibly by activating Notch on tumor endothelium. A novel Notch inhibitor, the Notch1 decoy, which blocks both Dll4 and Jagged1 has been recently shown to restrict tumor vessel growth. We discuss these models and speculate on therapeutic approaches.     

Biological roles of the Delta family Notch ligand Dll4 in tumor and endothelial cells in ovarian cancer

Emerging evidence suggests that the Notch/Delta-like ligand 4 (Dll4) pathway may offer important new targets for antiangiogenesis approaches. In this study, we investigated the clinical and biological significance of Dll4 in ovarian cancer. Dll4 was overexpressed in 72% of tumors examined in which it was an independent predictor of poor survival. Patients with tumors responding to anti-VEGF therapy had lower levels of Dll4 than patients with stable or progressive disease. Under hypoxic conditions, VEGF increased Dll4 expression in the tumor vasculature. Immobilized Dll4 also downregulated VEGFR2 expression in endothelial cells directly through methylation of the VEGFR2 promoter. RNAi-mediated silencing of Dll4 in ovarian tumor cells and tumor-associated endothelial cells inhibited cell growth and angiogenesis, accompanied by induction of hypoxia in the tumor microenvironment. Combining Dll4-targeted siRNA with bevacizumab resulted in greater inhibition of tumor growth, compared with control or treatment with bevacizumab alone. Together, our findings establish that Dll4 plays a functionally important role in both the tumor and endothelial compartments of ovarian cancer and that targeting Dll4 in combination with anti-VEGF treatment might improve outcomes of ovarian cancer treatment.     

Activation of multiple angiogenic signaling pathways in hemangiopericytoma

Hemangiopericytoma (HPC) is a highly vascularized mesenchymal tumor. Local recurrence and distant metastasis are common features of HPC. Considering the remarkable hyper-vasculature phenotype of HPC, we assumed that dysregulated angiogenic signaling pathways were involved in HPC. The key components of angiogenic signaling pathways including VEGF–VEGF-R2, EphrinB2-EphB4 and DLL4-Notch were examined by real-time RT-PCR, Western blotting and immunostaining in 17 surgical specimens of HPC patients and in 6 controls. A significant upregulation of VEGF and VEGF-R2 associated with elevated levels of p-Akt and proliferating cell nuclear antigen (PCNA) was detected in HPC. Moreover, a dramatic increase in the mRNA and protein expression of EphB4 and its downstream factor p-Erk1/2 was found in HPC. A massive activation of core-components of DLL4-Notch signaling was detected in HPC. Double-immunofluorescent staining confirmed the expression of these upregulated key factors in the endothelial cells of tumor vessels. The present study identified the activation of multiple and crucial angiogenic signaling pathways, which could function individually and/or synergistically to stimulate angiogenesis in HPC and eventually contribute to tumor growth and progression. Our findings emphasize the importance to target multiple angiogenic signaling pathways when an anti-angiogenic therapy is considered for this highly vascularized tumor.     

Importance of fibroblast growth factor receptor in neovascularization and tumor escape from antiangiogenic therapy

Therapeutic inhibition of pathways involved in angiogenesis has become the standard of care in renal cell carcinoma (RCC). Most currently available antiangiogenic agents inhibit the vascular endothelial growth factor (VEGF) pathway. Although these drugs have produced exciting benefits, some tumors do not respond to these agents. In addition most if not all tumors that initially respond will eventually develop resistance. Tumor escape from antiangiogenic therapy may include various signaling pathways that are involved in angiogenesis, including the fibroblast growth factor (FGF) signaling pathway. Emerging preclinical data suggest that FGF and VEGF act distinctly and synergistically to promote tumor vascularization. The current review discusses the role of FGF signaling in resistance to anti-VEGF therapies and outlines potential therapeutic implications.