Mouse model to study dependence of pancreatic cancer on Pik3ca for progression

 描述(申请人提供)：胰腺导管腺癌(PDA)是全球癌症相关死亡的第四大原因，五年存活率为4%。由于现有的治疗方法对PDA患者的生存影响很小，因此迫切需要为这种致命的癌症寻找新的治疗靶点。超过90%的PDA存在Kras基因的致癌突变，Kras基因启动了肿瘤的发生，并且它的持续存在是PDA进展所必需的。不幸的是，到目前为止，直接靶向Kras癌基因用于癌症治疗还没有成功。磷脂酰肌醇3-激酶(PI3K)是参与肿瘤发生的Kras的关键下游效应因子。我们证明，胰腺特异的PI3K p110α催化亚单位(正式命名为PIK3CA)的消融完全保护小鼠免受致癌KrasG12D诱导的肿瘤形成。然后我们制作了一个新的小鼠模型来测试PIK3CA是否也是维持胰腺肿瘤所必需的。在KrasLSL-G12D/+胰腺肿瘤模型中，该小鼠品系具有四环素调节的PIK3CA基因，该基因可以在胰腺中打开或关闭。KrasLSL-G12D/+小鼠出现了人类胰腺癌所见的全谱胰腺上皮内肿瘤(Panins)，但在这种小鼠模型中，这些早期病变很少进展为侵袭性PDA。我们的初步数据显示，沉默PIK3CA导致早期胰腺肿瘤完全消退。然而，随着恶性肿瘤的进展，继发性突变和表观遗传学变化的积累可能会导致对特定治疗的耐药性。目前尚不清楚侵袭性或转移性胰腺癌是否仍然依赖PIK3CA。我们的驱动假设是，Kras诱导的胰腺癌对PIK3CA的依赖性在疾病进展过程中持续生长变化。为了解决我们的假设，我们将通过将Trp53R172H突变引入表达KrasG12D和可诱导的PIK3CA的小鼠来创建侵袭性PDA模型。沉默PIK3CA对胰腺癌发生的三个特定阶段的影响将被研究。早期被定义为原位癌，即可达Panin 3级，基底膜完好。晚期定义为胰腺大体病变或有侵袭性但无转移性病变的单纯PDA。转移期是指有无转移性疾病，我们将对原发胰腺肿瘤和转移性沉积进行比较。在该小鼠模型中，胰腺肿瘤的表型特征、转录本和外显子组特征将与其对PI3KCA的依赖在肿瘤消退和生存时间方面相关。这一应用的成功完成将产生一个有用的动物模型和对胰腺肿瘤消退机制和对PIK3CA抑制的潜在抵抗的分子洞察力。这一认识将使未来的研究能够阐明针对PIK3CA信号通路的最合适的方法，以及该通路调控的PDA治疗的致癌程序。

 DESCRIPTION (provided by applicant): Pancreatic ductal adenocarcinoma (PDA) is the fourth leading cause of cancer-related death worldwide, with a five-year survival rate of 4%. Because existing therapies have little impact on PDA patient survival, there is great urgency to identify new therapeutic targets for this lethal cancer. More than 90% of PDAs have oncogenic mutations in the Kras gene that initiate tumorigenesis and whose continued presence is required for PDA progression. Unfortunately, direct targeting of the Kras oncogene for cancer treatment has thus far not been successful. Phosphoinositide 3-kinase (PI3K) is a critical downstream effector of Kras involved in oncogenesis. We demonstrated that pancreas-specific ablation of the PI3K p110α catalytic subunit (officially named Pik3ca) completely protected mice from oncogenic KrasG12D-induced tumor formation. We then produced a novel mouse model to test whether Pik3ca is also required for pancreatic tumor maintenance. This mouse strain has a tetracycline-regulated Pik3ca gene that can be turned on or off in the pancreas of the KrasLSL-G12D/+ pancreatic tumor model. KrasLSL-G12D/+ mice develop the full spectrum of pancreatic intraepithelial neoplasias (PanINs) seen in human pancreatic cancer, but these early lesions infrequently progress to invasive PDA in this mouse model. Our preliminary data show that silencing of Pik3ca resulted in complete regression of early stage pancreatic tumors. However, as malignancies progress, accumulation of secondary mutations and epigenetic changes can result in resistance to a particular therapy. It is not known whether invasive or metastatic pancreatic cancer remains dependent on Pik3ca. Our driving hypothesis is that the dependence of Kras-induced pancreatic cancer on Pik3ca for continued growth changes during disease progression. To address our hypothesis, we will create a model of aggressive PDA by introducing the Trp53R172H mutation into mice expressing KrasG12D and inducible Pik3ca. The effect of silencing Pik3ca on three specific stages of pancreatic carcinogenesis will be investigated. Early Stage is defined as carcinoma in situ, i.e., up to PanIN grade 3, where the basement membrane is intact. Advanced Stage is defined as the appearance of gross pancreatic lesions or frank PDA with invasion but without metastatic lesions. Metastatic Stage is defined by the presence of metastatic disease, where we shall compare primary pancreatic tumors with metastatic deposits. The phenotypic features, transcriptomes and exome profiles of pancreatic tumors in this mouse model will be correlated with their dependence on Pi3kca in terms of tumor regression and survival time. Successful completion of this application will produce a useful animal model and molecular insight into the mechanisms of pancreatic tumor regression and potential resistance to Pik3ca inhibition. This understanding will allow future studies to elucidate the most appropriate means of targeting the Pik3ca signaling pathway and the oncogenic program regulated by this pathway for PDA therapy.