Evaluating the impact of KRas codon bias on pancreatic cancer

描述（由申请人提供）：胰腺癌是美国癌症死亡的第四大原因，每年有32,993名美国人患有胰腺癌，5年生存率仅为5.6%。只有了解这种疾病的分子病因，才能开发出新的治疗策略来治疗这种侵袭性癌症。为此，约90%的胰腺肿瘤含有KRAS基因的致癌突变。这是其中之一，如果不是最早的突变检测到这种疾病，并被很好地描述为实验诱导胰腺癌。有趣的是，致癌KRas蛋白的水平与肿瘤发生的程度相关，临床研究表明，KRas突变的致癌效力与治疗反应密切相关。在这方面，我们发现由于大量代表性不足（罕见）的密码子会阻碍翻译，KRas的翻译效果很差。此外，通过将这些罕见的密码子改变为常见的密码子，KRas的致瘤潜能在肿瘤发生的异种移植模型中大大增加。然而，与内源性表达的癌蛋白相比，致癌KRas的异位表达可能导致更强大甚至完全不同的表型，并且异种移植模型不能概括胰腺中癌症的自发发展。因此，我们建议敲入KRas基因的致癌版本，其中稀有密码子已被改变为常见密码子。这个突变的等位基因随后会在胰腺中被激活，之后该器官将被移除并进行病变评分。本研究的完成将在具有代表性的胰腺癌动物模型中严格确定罕见密码子对KRas致瘤活性的影响，为进一步探讨KRas密码子偏倚在胰腺癌中的作用提供框架。

DESCRIPTION (provided by applicant): Pancreatic cancer is the fourth leading cause of cancer deaths in the USA, afflicting 32,993 Americans annually with a five-year survival rate of only 5.6%. Only by understanding the molecular etiology of this disease can new therapeutic strategies be developed to treat this aggressive cancer. To this end, ~90% of pancreatic tumors contain an oncogenic mutation in the gene KRAS. This is one of, if not the earliest mutation detected in this disease and is well described to experimentally induce pancreatic cancer. Interestingly, the level of oncogenic KRas protein correlates with the degree of tumorigenesis, and clinically it has been shown that the oncogenic potency of KRas mutations tracks with therapeutic responses. In this regard, we discovered that KRas is poorly translated due to an abundance of underrepresented (rare) codons that can impede translation. Moreover, by altering these rare codons to common codons, the tumorigenic potential of KRas was greatly increased in a xenograft model of tumorigenesis. However, ectopic expression of oncogenic KRas can result in more robust or even completely different phenotypes compared to the endogenously expressed oncoprotein, and xenograft models do not recapitulate the spontaneous development of cancer in the pancreas. We therefore propose to knock into the KRas gene an oncogenic version in which rare codons have been changed to common codons. This mutant allele will then be activated in the pancreas, after which the organ will be removed and scored for lesions. Completion of this study will rigorously determine the impact of rare codons on the tumorigenic activity of KRas in a representative animal model of pancreatic cancer, providing the framework to further explore the role of KRas codon bias in pancreatic cancer.