Activating mutations in RAS genes are associated with approximately 20% of all human cancers. New targeted therapies show preclinical promise in inhibiting the KRAS G12C variant. However, concerns exist regarding the effectiveness of such therapies in vivo given the possibilities of existing intratumor heterogeneity or de novo mutation leading to treatment resistance. We performed deep sequencing of 27 KRAS G12-positive lung tumors to determine the prevalence of other oncogenic mutations within KRAS or within commonly mutated downstream genes that could confer resistance at the time of treatment. We also passaged patient-derived xenografts to assess the potential for novel KRAS mutation to arise during subsequent tumor evolution. Furthermore, we estimate the de novo mutation rate in KRAS position 12 and in genes downstream of KRAS. Finally, we present an approach for estimation of the selection intensity for these point mutations that explains their high prevalence in tumors. We find no evidence of heterogeneity that may compromise KRAS G12C targeted therapy within sequenced lung tumors or passaged xenografts. We find that mutations that confer resistance are even less likely to occur downstream of KRAS than to occur within KRAS. Our approach predicts that BRAF V600E would provide the highest fitness advantage for de novo-resistant subclones. Overall, our findings suggest that resistance to targeted therapy of KRAS G12C-positive tumors is unlikely to be present at the time of treatment and, among the de novo mutations likely to confer resistance, mutations in BRAF, a gene with targeted inhibitors presently available, result in subclones with the highest fitness advantage.

中文翻译：

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KRAS和相关癌基因的异质性和突变：评估针对KRAS G12C的靶向抗性进化的潜力。

RAS基因中的活化突变与所有人类癌症中约20％相关。新的靶向疗法显示出在抑制KRAS G12C变体方面的临床前希望。然而，考虑到现有的肿瘤内异质性或从头突变导致治疗耐药性的可能性，人们对这种疗法在体内的有效性存在担忧。我们对27种KRAS G12阳性肺肿瘤进行了深度测序，以确定在KRAS内或通常突变的下游基因内可能在治疗时产生耐药性的其他致癌突变的患病率。我们还传代了患者来源的异种移植物，以评估新型KRAS突变在随后的肿瘤发展过程中出现的可能性。此外，我们估计KRAS 12位和KRAS下游基因的从头突变率。最后，我们提出了一种估计这些点突变的选择强度的方法，这解释了它们在肿瘤中的高流行率。我们没有发现异质性的证据可能会影响已测序的肺肿瘤或传代异种移植物中的KRAS G12C靶向治疗。我们发现，赋予抗性的突变发生在KRAS下游的可能性比发生在KRAS内部的可能性更低。我们的方法预测，BRAF V600E将为从头耐药的亚克隆提供最高的适应性优势。总体而言，我们的发现表明，在治疗时不太可能出现针对KRAS G12C阳性肿瘤的靶向治疗的耐药性，而且在可能带来耐药性的从头突变中，BRAF突变是目前可利用的具有靶向抑制剂的基因，导致具有最高适应性优势的亚克隆。