HIF-1α调控胃癌肿瘤干细胞向肿瘤血管内皮分化的机制研究

Gastric cancer remains one of the most common cancers and a leading cause of mortality. However the efficiency is lower than 50%, even with the new molecular targeted drug in combination with traditional chemotherapy. Cancer stem cells have been considered as the origin of tumor initiation, relapse and drug resistance. We have identi?ed gastric cancer stem cells from VCR-preconditioned SGC7901 cell line, characterized by high tumorigenicity and the capacity for self-renewal and differentiation. In our recent publised data, we found that gastric cancer stem cells formed 2D tube-like and 3D complex lumen-like structures, which resembled differentiated gastric crypts. And we also observed the stem-like cells give rise to tumour endothelium. The vascular endothelium produced tubular networks, highly vascularized anaplastic tumours in nude mice and up-regulation of CD31. Recent studies show that transdifferentiation of cancer stem cells into vascular endothelial cells is an key player in the resistance to anti-VEGF therapy.However, it is still unknown the key regulatory molecules and the mechanism of drug resistance. We have observed the important role of Hypoxia Inducible Factor 1α（HIF-1α） on enhancing the differentiation ability under hypoxia condition. In this study, we will firstly aim to investigate the function of HIF-1α in the phenotype, abortion and its downstream effect on regulating the differentiated vascular endothelium. In addition, we will effectively screen the new pathway and key factors by RNA-sequence and high-throughput methylation chip. Finally,we will explore the HIF-1α biological function on differentiated vascular endothelium by knockdown, up-regulation, inhibition and rescue. Take together, our study will provide newinsight into the biology of cancer stem cells,as well as the mechanisms and the target therapy of tumour neo-angiogenesis.

胃癌是我国高发肿瘤，即使分子靶向药物联合化疗有效率也不到50%，肿瘤干细胞可能是导致复发及耐药的根源。我们前期研究发现胃癌肿瘤干细胞具有向腺体及肿瘤血管内皮分化的多向分化潜能，表现为管状成型能力增强、瘤体微血管密度增加及高表达内皮标志物CD31等。而最新研究表明肿瘤干细胞向肿瘤血管内皮分化可能是导致肿瘤血管分子靶向治疗失败的关键原因，但具体机制不清。本研究将在前期研究HIF-1α增强肿瘤干细胞血管内皮分化的基础上，研究HIF-1α影响胃癌肿瘤干细胞血管内皮细胞分化的表型变化、内皮功能及HIF-1α下游调控分化机制；并通过RNA-sequence与甲基化芯片共筛选的方法筛选关键的效应分子及信号通路；最后再通过干预手段来验证HIF-1α调控肿瘤干细胞分化的分子机制，为肿瘤干细胞的血管靶向治疗奠定基础。

胃癌是我国最常见的消化道恶性肿瘤之一，发病率高，但是早期诊断困难，以中晚期患者为主，目前进展期胃癌主要采取综合治疗，但是联合化疗有效率仅为40%左右，中晚期胃癌五年生存率在10-15%之间。虽然分子靶向治疗取得的长足进步，被寄以厚望的分子靶向药物疗效在胃癌的治疗中并不理想。治疗肿瘤的热点药物—肿瘤血管靶向治疗药如贝伐单抗，研究发现其联合化疗疗效也仅有46%。因此，研究临床中肿瘤化疗抵抗、多药耐药及肿瘤细胞逃避靶向治疗的机制具有重要意义。我们跟其他实验室的研究均表明在新辅助化疗或者常规治疗后，肿瘤干细胞的数量不仅没有减少反而得到富集，这可能是肿瘤干细胞引起肿瘤复发的主要原因。进一步研究发现肿瘤干细胞也对分子靶向药物如酪氨酸激酶抑制剂等产生多药耐药。因此肿瘤的靶向治疗更应该针对肿瘤干细胞特有的生物学特性开发出更为特异性的分子靶向药物。.在国家自然科学基金（No. 81201674）的支持下，我们通过高通量基因测序对比实验研究表明， 肿瘤干细胞血管分化细胞模型中AKT/mTOR信号通路表达上调，并发现在缺氧条件下HIF-1α高表达是促进肿瘤干细胞向血管内皮分化的重要因素。进一步实验研究发现，随着低氧浓度的变化，AKT/mTOR信号通路活化程度不一致，并伴随肿瘤血管分化机制的不同。同时我们研究发现AKT/mTOR与缺氧及其主要效应分子（HIF-1α）之间存在着反馈环路，除了调控可能的共同下游基因VEGF促进肿瘤血管生成外，还有重要的靶分子调整肿瘤干细胞的分化及增殖过程。.综上所述本研究主要的发现是胃癌肿瘤干细胞向血管内皮细胞分化与缺氧诱导因子HIF-1α密切相关，并且HIF-1α与AKT/mTOR信号通路存在反馈调节，该环路除调控经典血管生成分子VEGF外，还有通过调控不同靶分子来维持肿瘤干细胞分化及增殖的平衡。因此缺氧对AKT/mTOR-HIF1α反馈环路中是影响肿瘤干细胞血管分化的关键分子及分子群，对血管靶向治疗的新靶标及对肿瘤干细胞的治疗具有重要意义。