Temporally controlled oncogene expression in a novel pancreatic cancer model

描述（由申请人提供）：我们实验室的长期目标是阐明基因改变如何促进正常上皮细胞的恶性转化。我们目前的研究更密切地关注胰腺导管腺癌（PDAC）恶性进展后续阶段中癌症启动突变的持续生物学相关性，PDAC占胰腺恶性肿瘤的大多数。此外，我们的目标是确定肿瘤转化或维持胰腺癌的主要目标细胞亚型。先前的研究表明，并非所有引发肿瘤转化的基因改变对癌细胞的存活都同样重要。因此，选择对癌细胞生长至关重要的合适分子靶点至关重要。在初步研究中，我们发现大多数人类导管前体病变（PanINs）高度表达c-Myc，并且该癌基因在原发性和转移性pdac的一个亚群中也上调。为了评估c-Myc和其他癌基因在肿瘤发生和发展过程中的作用，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一种暂时受控的方式进行强的、配体控制的基因表达。使用这种独特的小鼠模型，我们可以证明c-Myc癌基因的上调足以引起快速转化，并在短潜伏期后出现导管瘤变。这些肿瘤病变迅速发展为原发性pdac，并伴有零星转移到肝脏。用配体（强力霉素）治疗荷瘤小鼠可抑制c-Myc表达，从而导致PanIN病变和实体胰腺肿瘤内肿瘤细胞凋亡。拟议研究的主要目的是进一步研究c-Myc是否对所有转移癌细胞或一部分转移癌细胞的生存同样必要。根据我们的初步数据，我们假设切除侵袭性胰腺腺癌细胞中c-Myc癌基因的表达会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（R21）研究中通过实验解决这一假设，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，以及其在晚期癌症中的重要性如何受到继发性遗传事件的影响。在第二个目标中，我们将采用我们独特的癌症模型来识别和表征c- Myc表达消融后存活的残余细胞，我们将评估这些细胞是否与疾病复发有关。总的来说，这两个特定目标的结果将产生关于在PDAC进展的最后阶段引发癌症的遗传事件的重要性的新数据，以及癌基因消融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.