整合素在肿瘤转移中的作用机制研究进展

机体重要的黏附分子整合素(Integrins)在细胞与细胞外基质间及细胞与细胞间的黏附作用已为人共知。以往的研究证实整合素与肿瘤转移有着密切关系,文献分析表明,这一研究领域一直是肿瘤转移方面的研究热点,该文着重概述近5年国际上关于整合素在肿瘤转移的作用机制方面的研究进展,表明整合素介导了大量的非配体依赖的信号转导通路促进了肿瘤转移。这使得整合素在肿瘤转移中的作用机制更加明确和深入,也为整合素抑制剂的开发带来了光明的前景。     

以整合素为靶点的抗肿瘤转移药物研究进展

作为与肿瘤转移密切相关的分子,整合素在肿瘤转移的全过程中起着至关重要的作用.开展以整合素为作用靶点的抗肿瘤转移药物研究有助于最终攻克肿瘤这一顽疾.本文围绕整合素与肿瘤转移之间的关系综述近年研究进展,并对以整合素为靶点的抗肿瘤转移的新药研究进行探讨.     

整合素αvβ3拮抗剂的研究进展

肿瘤生长初期没有新血管生成（无血管期）,其生长到一定程度时依赖新生血管的维持.肿瘤血管生成是肿瘤生长和转移的形态学基础,它不仅向肿瘤提供营养,也向宿主输出大量的肿瘤细胞导致肿瘤的生长和转移.因此对以抑制肿瘤血管生成为目的的抗肿瘤药物的研究方兴未艾,有很多具有抑制肿瘤血管生成作用的化合物如大黄素与青蒿琥酯等被发现.整合素αvβ3介导血管内皮细胞和肿瘤细胞的黏附,参与血管生成和肿瘤转移,在肿瘤生长中起重要作用.当其功能受到抑制时,血管内皮细胞出现凋亡,肿瘤生长受到抑制,甚至肿瘤消退.整合素αvβ3受体拮抗剂作为抗新生血管肿瘤药物的同时,对骨质流失、血栓、风湿性关节炎的治疗也起了重要作用.     

整合素阻断剂抗肿瘤药物研究进展

整合素是存在于细胞表面的跨膜糖蛋白受体,能介导细胞间的黏附,参与血管生成和肿瘤转移,与肿瘤的发生发展密切相关。以整合素为靶点进行抗肿瘤治疗,可有效抑制肿瘤的生长和转移。本文主要从抗肿瘤生长类药物、抗肿瘤转移类药物、抗血管生成类药物等方面对近年来整合素阻断剂抗肿瘤药物研究进展进行综述,并对整合素靶向给药的剂量问题进行了讨论。     

ADAM8在恶性肿瘤转移中的作用研究进展

转移是恶性肿瘤的重要生物学特征之一,与肿瘤患者的预后紧密相关。近年来研究表明,去整合素-金属蛋白酶8(a disintegrin and metalloprotease 8,ADAM8)在多种恶性肿瘤中呈现高表达状态,且在恶性肿瘤的转移中发挥着重要的作用。研究显示,ADAM8过表达可减弱肿瘤细胞间的黏附作用,并促进细胞外基质(extracellular matrix,ECM)降解和细胞膜上细胞因子释放,同时有助于肿瘤部位新生血管生成,从而促进了肿瘤细胞转移。因此,抑制ADAM8有可能对肿瘤转移产生抑制作用,这使得ADAM8成为恶性肿瘤的预后指标和潜在治疗靶点,备受关注。该文对ADAM8与肿瘤转移的研究进展进行综述,探讨ADAM8介导的肿瘤转移的机制和靶向ADAM8进行肿瘤转移治疗的策略,为后续研究和临床治疗提供重要的参考。     

以整合素为靶点的抗肿瘤药物研究进展

整合素作为一类具有信号转导功能的细胞表面粘附分子,与肿瘤的发生、发展密切相关。整合素能与细胞内多种分子相互协调,从多方面影响肿瘤的增殖、侵袭和转移等过程。以整合素为靶点进行的抗肿瘤药物的研发及相应治疗方法的开发已成为当前肿瘤治疗的热点。该文从整合素抗体类药物,含RGD等与整合素高亲和力结合序列的药物以及其他整合素靶向药物3方面综述了近年来以整合素为靶点的抗肿瘤药物研究开发的最新进展,并对整合素的靶向治疗进行了探讨。     

整合素连接激酶(ILK)在肾脏疾病中的研究进展

整合素连接激酶（integrin-linked kinase,ILK）是一种丝氨酸/苏氨酸蛋白激酶,可与整合素β1、β3亚基胞浆域结合,参与整合素、生长因子、Wnt及TGF-β/Smad等多种信号转导,在调节细胞黏附、凋亡、转移、生长、细胞周期、肿瘤形成等过程中起重要作用。细胞中ILK表达异常,将引发病理变化。本文综述了ILK的生物学活性及其与肾脏疾病的关系,提示ILK的表达调控可能成为治疗肾脏疾病的新途径。     

骨桥蛋白与肿瘤转移的关系

骨桥蛋白是一种分泌的磷酸化蛋白,在调控肿瘤转移发面发挥重要作用,并已作为一种重要的肿瘤标志物用于临床和作为一个潜在的调控肿瘤转移的治疗手段。OPN DNA序列高度保守,其中包含几个重要的功能域包括αvβ整合素和CD44结合位点。高OPN的表达水平与肿瘤的浸润、恶化或转移有关。研究表明,骨桥蛋白介导的分子机制在细胞凋亡,细胞外基质蛋白水解和重塑,细胞迁移,对免疫主细胞的逃逸,新生血管的生成等方面与肿瘤的转移有关。OPN的转录调控是复杂的,涉及到多种途径。现阶段对OPN的生物学知识的了解表明,其在分子水平上治疗肿瘤转移方面很有研究价值。     

整合素与肿瘤侵袭和转移的研究进展

整合素（integrin）分布广泛[1],属于细胞黏附分子家族。研究发现整合素可以调节细胞-细胞、细胞-细胞外基质（extracellu-larmatrix,ECM〕间的黏附。整合素所介导的肿瘤细胞与ECM间的相互作用影响肿瘤的发生、增殖、侵袭和转移到其他组织的能力。现就整合素的结构、功能及其对肿瘤侵袭和转移的影响予以综述。     

整合素α5β1与恶性肿瘤侵袭转移关系的研究进展

目的：综述整合素α5β1与恶性肿瘤侵袭转移的关系。方法：查阅国内外相关文献进行分析和归纳。结果：α5β1是整合素家族的一员，参与肿瘤的发生、发展与转移。而这种作用可能是通过影响肿瘤细胞与细胞外基质的黏附、细胞外基质的水解、诱导肿瘤血管的生成、调节肿瘤细胞的凋亡等作用而实现的。结论：深入研究α5β1在恶性肿瘤中的表达与功能，有助于进一步认识恶性肿瘤侵袭转移的分子机制，且有可能为恶性肿瘤的诊断和预后判断提供新的指标。     

Gambogic acid inhibits tumor cell adhesion by suppressing integrin β1 and membrane lipid rafts-associated integrin signaling pathway

Cell adhesion plays an important role in the steps of cancer metastasis. Regulation of cell–cell (intercellular) and cell–matrix adhesion is a promising strategy for cancer progression. Gambogic acid is a xanthone derived from the resin of the Chinese plant Garciania hanburyi, with potent anti-metastasis activity on highly metastatic cells. The aim of this study was to investigate the function and mechanism of gambogic acid on tumor adhesion. We found that gambogic acid strongly inhibited the adhesion of human cancer cells to fibronectin. This inhibition was associated with the deformation of focal adhesion complex, which was mediated by suppressing the expression of integrin β1 and integrin signaling pathway. In vitro, cell lipid rafts clustering was inhibited following treatment of gambogic acid, which induced the suppression of integrin β1 and focal adhesion complex proteins colocalization within rafts. Moreover, gambogic acid significantly decreased cellular cholesterol content, whereas cholesterol replenishment lessened the inhibitory effect of gambogic acid on cell adhesion. Real-time PCR analysis showed that gambogic acid reduced mRNA levels of hydroxymethylglutaryl-CoA reductase and sterol regulatory element binding protein-2, while increased acetyl-CoA acetyltransferase-1/2. Taken together, these results demonstrate that gambogic acid inhibits cell adhesion via suppressing integrin β1 abundance and cholesterol content as well as the membrane lipid raft-associated integrin function, which provide new evidence for the anti-cancer activity of gambogic acid.     

Integrin α3β1 as a breast cancer target

INTRODUCTION: Integrin receptors for cell adhesion to the extracellular matrix have important roles in all stages of cancer progression and metastasis. Since the integrin family was discovered in the early 1980's, many studies have identified critical adhesion and signaling functions for integrins expressed on tumor cells, endothelial cells and other cell types of the tumor microenvironment, in controlling proliferation, survival, migration and angiogenesis. In recent years, the laminin-binding integrin α3β1 has emerged as a potentially promising anti-cancer target on breast cancer cells. AREAS COVERED: Studies from the past decade that implicate integrins as promising anti-cancer targets and the development of integrin antagonists as anti-cancer therapeutics. Recent preclinical studies that have identified the laminin-binding integrin α3β1 as an appealing anti-cancer target and the knowledge gaps that must be closed to fully exploit this integrin as a therapeutic target for breast cancer. EXPERT OPINION: Although the tumor-promoting functions of α3β1 implicate this integrin as a promising therapeutic target on breast cancer cells, successful exploitation of this integrin as an anti-cancer target will require a better understanding of the molecular mechanisms whereby it regulates specific tumor cell behaviors and the identification of the most appropriate α3β1 functions to antagonize on breast cancer cells.     

Integrin α3β1 as a breast cancer target

Introduction: Integrin receptors for cell adhesion to the extracellular matrix have important roles in all stages of cancer progression and metastasis. Since the integrin family was discovered in the early 1980's, many studies have identified critical adhesion and signaling functions for integrins expressed on tumor cells, endothelial cells and other cell types of the tumor microenvironment, in controlling proliferation, survival, migration and angiogenesis. In recent years, the laminin-binding integrin α3β1 has emerged as a potentially promising anti-cancer target on breast cancer cells.

Areas covered: Studies from the past decade that implicate integrins as promising anti-cancer targets and the development of integrin antagonists as anti-cancer therapeutics. Recent preclinical studies that have identified the laminin-binding integrin α3β1 as an appealing anti-cancer target and the knowledge gaps that must be closed to fully exploit this integrin as a therapeutic target for breast cancer.

Expert opinion: Although the tumor-promoting functions of α3β1 implicate this integrin as a promising therapeutic target on breast cancer cells, successful exploitation of this integrin as an anti-cancer target will require a better understanding of the molecular mechanisms whereby it regulates specific tumor cell behaviors and the identification of the most appropriate α3β1 functions to antagonize on breast cancer cells.     

Targeting RGD recognizing integrins: drug development, biomaterial research, tumor imaging and targeting

Integrins constitute an important class of cell adhesion receptors responsible not only for cell-matrix adhesion but also for signaling bidirectionally across the membrane. Integrins are involved in many biological processes such as angiogenesis, thrombosis, inflammation, osteoporosis and cancer. Integrins thus play a key role in many severe human diseases. In this review we will describe recent research and development of RGD-containing integrin ligands for medical applications including drug design, radiolabeling, drug targeting, as well as biomaterial research. Many ligands have been developed for targeting the avb3 integrin in order to block angiogenesis or osteoporosis, but there are also other integrins like avb5 and a5b1 which become more and more interesting for similar purposes. aIIbb3 constitutes a potent target in thrombosis therapy; but the search for suitable ligands is still ongoing. We will reconstruct the drug development process for these integrin subtypes considering selected examples with focus on structure based design. Different structural requirements are pointed out concerning integrin activity and particularly the selectivity towards the distinct integrin types. Furthermore, we will show recent progress in tumor and thrombosis imaging based on radiolabeled RGD-containing ligands binding avb3 or aIIbb3, respectively. Additionally further advances in biomaterial research are presented. We describe the coating of different implant materials with various avb3 recognizing ligands for the purpose of increasing cell attachment and biocompatibility.     

Inhibition of tumor formation by snake venom disintegrin.

The metastasis of tumor cells to bone involves migration, invasion and adhesion to bone. Breast and prostate cancer cells have predilection for spreading to bone. Snake venom-derived arginine-glycine-aspartic acid (RGD)-containing disintegrins (e.g. rhodostomin) have been demonstrated to inhibit cell adhesion. Here, we found that rhodostomin inhibited the adhesion of breast and prostate carcinoma cells to both unmineralized and mineralized bone extracellular matrices in a dose-dependent manner, without affecting the viability of tumor cells. In addition, rhodostomin also inhibited the migration and invasion of breast and prostate carcinoma cells. It specifically inhibited the binding of monoclonal antibody (MoAb) 7E3, which recognizes integrin alphavbeta3, to tumor cells, but not those of other MoAbs against other integrin subunits such as alpha2, alpha3, alpha5 and beta1. As breast cancer cells MDA-MB-231 were locally injected into tibia in nude mice, histological examination of the tibia of control group revealed that most of the cancellous bone had been replaced by the breast cancer cells after 28 days' inoculation. In contrast, co-administration of trigramin with cancer cells markedly inhibited tumor growth and bone destruction. Taken together, disintegrins strongly inhibit the adhesion, migration, invasion of tumor cells and also tumor growth of human breast cancer cells in bone as well. Therefore, disintegrins may be developed as alternate therapy for bone metastasis of cancer cells.     

Volociximab,a chimeric integrin alpha5beta1 antibody,inhibits the growth of VX2 tumors in rabbits

Summary Angiogenesis, the process by which new blood vessels form from existing vasculature, is critical for tumor growth and invasion. Growth factors, such as VEGF, initiate signaling cascades resulting in the proliferation of resting endothelial cells. Blockade of growth factor pathways has proven effective in inhibiting angiogenesis and tumor growth in vivo. Integrins, including the integrin α5β1, are also important mediators of angiogenesis and these adhesion molecules also regulate cancer cell growth and migration in vitro. Volociximab is a high affinity, function-blocking antibody against integrin α5β1 that is currently in multiple Phase II oncology clinical trials. Volociximab displays potent anti-angiogenic activity in a monkey model of choroidal neovascularization. In this study, we explored the consequences of integrin α5β1 blockade on tumorigenesis. Because volociximab does not cross-react with rodent α5β1, the syngeneic rabbit VX2 carcinoma model was utilized as an alternative to standard mouse xenograft models for the assessment of anti-tumor activity of volociximab. Volociximab administered intravenously to rabbits bearing VX2 tumors is detectable on tumor cells and vasculature 45 min post-administration. Volociximab was found to significantly inhibit the growth of tumors growing subcutaneously or intramuscularly, despite a 20-fold lower affinity for rabbit integrin, relative to human. This effect was found to correlate with decreased blood vessel density within these tumors. These results support the use of volociximab in the intervention of malignant disease.     

Integrins in drug targeting-RGD templates in toxins

Integrins are a family of heterodimeric receptors, which modulate many cellular processes including: growth, death (apoptosis), adhesion, migration, and invasion by activating several signaling pathways. Integrin-binding RGD (arginine-glycine-aspartic acid) is found in several important extracellular matrix proteins which serve as adhesive integrin ligands. The RGD motif has also been found in many toxins from snake venom and other sources that specifically inhibit integrin binding function and serve as potent integrin antagonists, particularly of platelet aggregation and integrin-mediated cell adhesion. Many of these proteins have potential as therapeutic agents which can target integrins directly. Structural and functional studies of several RGD-containing toxins suggest that the inhibitory potency of these proteins lies in subtle positional requirements of the tripeptide RGD at the tip of a flexible loop, a structural feature for binding to integrins. In addition, amino acid residues in this loop in close vicinity to the RGD-motif determine the integrin-binding specificity and selectivity. This review will present a review of integrin structure and function, and of disintegrin structural features responsible for their activity as antagonists of integrin function. The use of integrins in drug targeting and integrins as targets for drug delivery by using the RGD as a template structure will also be discussed.     

Philinopside E, a new sulfated saponin from sea cucumber, blocks the interaction between kinase insert domain-containing receptor (KDR) and alphavbeta3 integrin via binding to the extracellular domain of KDR

Vascular endothelial growth factor (VEGF) signaling pathway is essential for tumor angiogenesis and has long been recognized as a promising target for cancer therapy. Current view holds that physical interaction between alpha(v)beta(3) integrin and kinase insert domain-containing receptor (KDR) is important in regulating angiogenesis and tumor development. We have reported previously that a new marine-derived compound, philinopside E (PE), exhibited the antiangiogenic activity via inhibition on KDR phosphorylation and downstream signaling. Herein, we have further demonstrated that PE specifically interacts with KDR extracellular domain, which is distinct from conventional small-molecule inhibitors targeting cytoplasmic kinase domain, to block its interaction with VEGF and the downstream signaling. We also noted that PE markedly suppresses alpha(v)beta(3) integrin-driven downstream signaling as a result of disturbance of the physical interaction between KDR and alpha(v)beta(3) integrin in HMECs, followed by disruption of the actin cytoskeleton organization and decreased cell adhesion to vitronectin. All of these findings substantiate PE to be an unrecognized therapeutic class in tumor angiogenesis and, more importantly, help appeal the interest of the therapeutic potential in angiogenesis and cancer development via targeting integrin-KDR interaction in the future.