Temporally controlled oncogene expression in a novel pancreatic cancer model

描述(申请人提供)：我们实验室的长期目标是阐明基因改变如何导致正常上皮细胞的恶性转化。我们目前的研究更密切地集中在胰腺导管腺癌(PDAC)恶性进展的后续阶段中，癌症起始突变的持续生物学相关性，这是胰腺恶性肿瘤的主要原因。此外，我们的目标是确定作为肿瘤转化或胰腺癌维持的主要靶点的细胞亚型。先前的研究表明，并不是所有启动肿瘤转化的基因变化对癌细胞的生存都同样重要。因此，选择对癌细胞生长至关重要的合适的分子靶点是至关重要的。在初步研究中，我们发现大多数人导管前体病变(Panins)高表达c-Myc，该癌基因在部分原发和转移性PDAC中也上调。为了评估c-Myc和其他癌基因在肿瘤发生和发展中的作用，我们开发了一种新的小鼠模型，该模型允许在成年动物的胰腺导管细胞中以时间可控的方式进行强烈的配体控制的基因表达。利用这一独特的小鼠模型，我们可以证明c-Myc癌基因的上调足以导致快速转化和短潜伏期后导管肿瘤的出现。这些肿瘤性病变迅速进展为原发性PDAC，并伴有散发性肝转移。用一种配体(多西环素)治疗荷瘤小鼠会抑制c-Myc的表达，从而导致Panin病变和实体胰腺肿瘤内的肿瘤细胞凋亡。这项拟议研究的主要目标是进一步研究c-Myc对于所有或部分转移癌细胞的生存是否同样重要。根据我们的初步数据，我们假设去除侵袭性胰腺癌细胞中c-Myc癌基因的表达将导致荷瘤小鼠转移灶的消退。我们预计绝大多数癌细胞将经历细胞死亡，但少数细胞将保持休眠状态，这可能是疾病复发的前兆。为了在探索性研究(R21)中从实验上解决这一假设，我们将在第一个特定目标中确定c-Myc癌基因在PDAC维持和转移进展中的重要性，以及它在晚期癌症中的重要性如何受到次级遗传事件的影响。在第二个目标中，我们将使用我们独特的癌症模型来识别和表征c-Myc表达消失后存活下来的残留细胞，并评估这些细胞是否与疾病复发有关。总而言之，这两个特定目标的结果将产生新的数据，说明在PDAC进展的最后阶段引发癌症的遗传事件的重要性，以及切除癌基因对可能促进疾病复发的癌细胞亚型的不同影响。

DESCRIPTION (provided by applicant): The long-term objective in our laboratory is to elucidate how genetic alterations contribute to malignant transformation of normal epithelial cells. Our current studies focus more closely on the continuous biological relevance of cancer initiating mutations during subsequent stages of malignant progression of pancreatic ductal adenocarcinoma (PDAC), which accounts for the majority of pancreatic malignancies. In addition, we aim to identify cellular subtypes that are primary targets for neoplastic transformation or for the maintenance of pancreatic cancers. Previous studies have demonstrated that not all genetic alternations that initiate neoplastic transformation are equally important for the survival of cancer cells. Consequently, the selection of appropriate molecular targets that are crucial for the growth of cancer cells is of the utmost importance. In preliminary studies, we found that the majority of human ductal precursor lesions (PanINs) highly express c-Myc, and this oncogene is also upregulated in a subset of primary and metastatic PDACs. To assess the role of c-Myc and other oncogenes during tumor initiation and progression, we have developed a novel mouse model that allows for a strong, ligand-controlled expression of genes in a temporally controlled manner in pancreatic ductal cells of adult animals. Using this unique mouse model, we can demonstrate that the upregulation of the c-Myc oncogene is sufficient to cause rapid transformation and the appearance of ductal neoplasia after a short latency period. These neoplastic lesions progress quickly into primary PDACs with sporadic metastases to the liver. The treatment of tumor-bearing mice with a ligand (doxycycline) results in the suppression of c-Myc expression, which subsequently leads to apoptosis of neoplastic cells within PanIN lesions and solid pancreatic tumors. The primary goal of the proposed studies is to further examine whether c-Myc is equally required for the survival of all or a subset of metastatic carcinoma cells. Based on our preliminary data, we hypothesize that ablating the expression of the c-Myc oncogene in invasive pancreatic adenocarcinoma cells will cause the regression of metastatic lesions in tumor-bearing mice. We anticipate that the vast majority of cancer cells will undergo cell death, but a few cells will remain dormant that might serve as precursors for disease recurrence. To experimentally address the hypothesis in an exploratory-type (R21) study, we will determine in the first specific aim the importance of the c-Myc oncogene during maintenance and metastatic progression of PDAC and how its significance in advanced cancers is affected by secondary genetic events. In the second aim, we will employ our unique cancer model to identify and characterize residual cells that survive the ablation of c- Myc expression, and we will assess whether these cells are responsible for disease recurrence. Collectively, the results of both specific aims will yield novel data about the importance of cancer-initiating genetic events during the final stages of PDAC progression as well the differential effects of the ablation of an oncogene on cancer cell subtypes that may facilitate disease recurrence.