EFFICACY STUDIES OF CHEMOPREVENTIVE AGENTS

以往阐明食道癌发生的分子机制的工作主要集中在基因工程动物模型的建立和鉴定(Oncogene 14：1185,1997)，包括EB病毒(Epstein-Barr Virus，EBV)ED-L2启动子的鉴定和在口腔-食道鳞状上皮细胞中唯一活性的证明。这是通过口腔-食道特异性核转录因子的相互作用来调节的。这些角蛋白是角蛋白4和角蛋白13。事实上，靶向破坏小鼠胚胎干细胞中的角蛋白4基因会导致食道上皮细胞分化的严重障碍。EB病毒ED-L2启动子正被用于靶向细胞周期进入G1期的关键基因产物细胞周期蛋白D1癌基因，该基因在转基因小鼠头颈部和食道癌中经常被扩增和过表达。先前的工作表明，这些小鼠在6-8个月时出现轻度不典型增生，在16个月时出现重度不典型增生，并伴随着细胞增殖增加、CDK6优先激活(周期蛋白D1/CDK6的一个靶点是视网膜母细胞瘤蛋白)、P53过表达和EGFR过表达(癌症研究57：5542,1997)。P53突变是头颈部和食道癌中常见的基因改变。将细胞周期蛋白D1与p53基因缺失的小鼠杂交的能力代表了一个独特的机会来分析两个关键的基因改变在多阶段口腔食道癌发生中的组合效应。本研究的目的是利用细胞周期蛋白D1x P53基因缺失的小鼠对口腔和食道组织进行组织学、免疫组织化学和聚合酶链式反应的分析。在这些转基因动物中，化学预防药物对口腔癌和食道癌的影响正在研究中。

Previous work to elucidate the underlying molecular mechanisms of esophageal carcinogenesis, focused on the generation and characterization of genetically engineered animal models (Oncogene 14:1185, 1997), including characterization of the Epstein-Barr virus (EBV) ED-L2 promoter and demonstration that it is uniquely active in oral-esophageal squamous epithelial cells. This is mediated through the interaction of oral-esophageal specific nuclear transcriptional factors. These keratins are keratins 4 and 13. In fact, targeted disruption of the keratin 4 gene in murine embryonic stem cells leads to severe impairment of differentiation in esophageal epithelial cells. The EBV ED-L2 promoter is being used to target the cyclin D1 oncogene, a critical gene product in the progression of cell cycle through G1 phase, and one that is frequently amplified and overexpressed in head/neck and esophageal cancers in transgenic mice. Previous work has revealed that these mice develop histological evidence of mild dysplasia by 6-8 months and severe dysplasia by 16 months with accompanying increased cell proliferation, preferential activation of cdk6 (one target of cyclin D1/cdk6 is the retinoblastoma protein), p53 overexpression and EGFR overexpression (Cancer Res. 57:5542, 1997). P53 mutations are a common genetic alteration in head/neck and esophageal cancers. The ability to cross cyclin D1 with p53 null mice represents a unique opportunity to analyze the combinatorial effects of two critical genetic alterations in their contribution to multistage oral-esophageal carcinogenesis. The objective of this study is to utilize cyclin D1 x p53 null mice for the analysis of oral and esophageal tissues by histology, immunohistochemistry and PCR. The effects of chemopreventive agents on the development of oral and esophageal cancers in these transgenic animals is being studied.