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

 描述（由申请人提供）：胰腺导管腺癌（PDA）是全球癌症相关死亡的第四大原因，5年生存率为4%。由于现有的治疗方法对PDA患者的生存率几乎没有影响，因此迫切需要为这种致命的癌症确定新的治疗靶点。超过90%的PDA在Kras基因中具有致癌突变，其启动肿瘤发生，并且其持续存在是PDA进展所需的。不幸的是，直接靶向Kras癌基因用于癌症治疗迄今尚未成功。磷酸肌醇3-激酶（PI 3 K）是参与肿瘤发生的Kras的关键下游效应子。我们证明了胰腺特异性消融PI 3 K p110α催化亚基（正式名称为Pik 3ca）完全保护小鼠免受致癌KrasG 12 D诱导的肿瘤形成。然后，我们产生了一种新的小鼠模型来测试Pik 3ca是否也是胰腺肿瘤维持所必需的。该小鼠品系具有四环素调节的Pik 3ca基因，该基因可以在KrasLSL-G12 D/+胰腺肿瘤模型的胰腺中打开或关闭。KrasLSL-G12 D/+小鼠发生了在人胰腺癌中观察到的全谱胰腺上皮内瘤形成（PanIN），但在该小鼠模型中，这些早期病变很少进展为侵袭性PDA。我们的初步数据表明，Pik 3ca的沉默导致早期胰腺肿瘤的完全消退。然而，随着恶性肿瘤的进展，继发性突变和表观遗传变化的积累可能导致对特定疗法的耐药性。目前尚不清楚侵袭性或转移性胰腺癌是否仍然依赖于Pik 3ca。我们的驱动假设是，Kras诱导的胰腺癌对Pik 3ca的依赖性在疾病进展期间持续生长变化。为了解决我们的假设，我们将通过将Trp 53 R172 H突变引入表达KrasG 12 D和诱导型Pik 3ca的小鼠来创建侵袭性PDA模型。将研究沉默Pik 3ca对胰腺癌发生的三个特定阶段的影响。早期定义为原位癌，即，直到PanIN 3级，其中基底膜是完整的。晚期定义为出现胰腺大体病变或伴有浸润但无转移性病变的明显PDA。转移性分期是指存在转移性疾病，我们将比较原发性胰腺肿瘤与转移性沉积物。该小鼠模型中胰腺肿瘤的表型特征、转录组和外显子组谱将与它们在肿瘤消退和存活时间方面对Pi 3 kca的依赖性相关。该应用的成功完成将产生有用的动物模型和对胰腺肿瘤消退机制和对Pik 3ca抑制的潜在抗性的分子见解。这种理解将使未来的研究能够阐明靶向Pik 3ca信号通路的最合适的方法以及由该通路调节的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.