生长抑素受体在胆囊癌中的表达状况及其调控化疗敏感性的机制研究

In recent years our research group has been investigating the molecular mechanism by which somatostatin (SST) enhanced the chemosensitivity of gallbladder cancer. We found that the combination of SST and doxorubicin (DOX) could significantly inhibit the growth of gallbladder cancer cell line (GBC-SD) and xenograft tumors on nude mice. However, the preliminary results from the clinical trials showed that only a small part of the gallbladder cancers was sensitive to the SST and DOX regimen. The biological activities of SST were mainly mediated by somatostatin receptors (SSTRs) and the activation of different SSTR could lead to different biological activities. Thus, the difference in the expression of SSTRs may cause the difference in the chemosensitivity of cancer cells. Based on the others' and our research, we proposed a hypothesis that SSTR1 is the key role to regulate the chemosensitivity of gallbladder cancer cells. For gallbladder cancer cells, SSTR1 which was selectively activated by SST activated ERK. ICBP90 and TFPI-2 was induced by the activation of ERK. ICBP90 is a promoter of the gene of Topoisomerase IIa which is the target of DOX. TFPI-2 which down-regulated the expression of p-glucoprotein can increase the amount of DOX in cells. The cytotoxity of DOX to gallbladder cancer cells was enhanced by the activation of SSTR1. The cases with high expression of SSTR1 are much more sensitive to SST and DOX regimen than those with low expression of SSTR1. The expression of SSTRs on gallbladder cancer cells and tissues will be examined and the activities and relationship of SSTR1, TFPI-2, ICBP90 etc will be investigated in this study. This study will illuminate the mechanism by which SST enhanced the chemosensitivity of gallbladder cancer and will help us to identify those sensitive cases to SST and DOX regimen.

本课题组近年来致力于研究生长抑素（SST）提高胆囊癌化疗敏感性的分子机制。发现SST联合阿霉素（DOX）显著抑制胆囊癌细胞株GBC-SD和裸鼠荷瘤的生长；但临床中仅少数患者对SST+DOX方案较敏感。SST的生物学作用主要由生长抑素受体（SSTR）介导，SSTR亚型的表达差异可能是导致肿瘤细胞化疗敏感性差异的重要原因。我们提出生长抑素受体亚型1（SSTR1）调控胆囊癌细胞化疗敏感性的假设机制。在胆囊癌细胞上，SST与SSTR1结合，激活ERK蛋白，诱导CCAAT盒结合蛋白（ICBP90）和组织因子途径抑制剂2（TFPI-2）的表达，ICBP90蛋白诱导拓扑异构酶IIa 表达增加，TFPI-2蛋白降低p-gp蛋白表达，提高DOX对肿瘤细胞的杀伤作用。本课题拟通过研究验证所提出的分子机制，阐明SSTR1与胆囊癌细胞化疗增敏之间的关系，为筛选适合SST+DOX方案的胆囊癌患者提供理论依据。

胆囊癌是恶性程度极高的一种恶性肿瘤，其发病隐匿，进展迅速，多数患者在确诊时已经丧失根治性切除的机会。以化疗为主的辅助治疗是多数中晚期胆囊癌患者延长生存时间的主要手段。但是胆囊癌对目前的常规化疗方案并不敏感，实际疗效差，因此探索新的化疗方案势在必行。本项目组前期在细胞和动物研究中发现生长抑素（SST）可以增强胆囊癌细胞GBC-SD的化疗敏感性，而在临床试验中发现仅有部分病人对联合生长抑素的化疗方案敏感。根据以往研究，我们认为生长抑素受体表达差异可能是导致胆囊癌病人敏感性差异的重要原因。本项目希望通过细胞、分子、动物以及临床标本多水平实验研究生长抑素受体对胆囊癌化疗敏感性的影响及机制。. 本项目研究内容分为三部分：第一部分主要研究生长抑素受体在胆囊癌组织和细胞中的表达以及其对化疗敏感性的调控。结果表明SST主要通过SSTR1提高胆囊癌化疗敏感性；SSTR1表达水平影响胆囊癌细胞对化疗药物的敏感性；SSTR1在胆囊癌中表达降低，其表达可能受miR-24调控；miR-24异常增高可能是导致胆囊癌组织和细胞中SSTR1表达降低的机制之一。第二部分主要研究SST联合顺铂协同抑制胆囊癌细胞株的作用研究。结果表明SST通过诱导PTEN基因表达增强顺铂对胆囊癌细胞生长的抑制作用。这是课题组发现的关于SST增强胆囊癌化疗敏感性的一种新机制。第三部分主要研究SST与SSTR1结合后增强胆囊癌化疗敏感性的下游信号通路。结果表明SST作用于胆囊癌细胞后，与生长抑素受体1（SSTR1）选择性结合，激活ERK蛋白，进而分别诱导TFPI-2和ICBP90蛋白表达增加；TFPI-2蛋白可以降低p-gp蛋白的表达，提高细胞内DOX浓度；ICBP90蛋白则可以诱导Topo IIα的表达增加，增加DOX的作用靶酶；二者的共同作用导致胆囊癌化疗敏感性提高。. 本项目的意义在于为SST+DOX化疗方案在胆囊癌患者中的应用提供进一步的理论依据，并通过检测生长抑素受体亚型的表达情况判断和筛选对该方案敏感型和非敏感型患者，对于敏感型患者可采用SST+DOX方案进行治疗，对于非敏感型患者则采用其他化疗方案进行治疗。