Biomedical Research Institute, Ninewells Hospital and Medical School, Dundee, UK.
Br J Cancer. 2010 Feb 16;102(4):693-703. doi: 10.1038/sj.bjc.6605534.
Response to EGFR-targeted therapies in colorectal cancer patients has been convincingly associated with Kirsten-Ras (K-Ras) mutation status. Current mandatory mutation testing for patient selection is limited to the K-Ras 'hotspot' codons 12 and 13.
Colorectal tumours (n=106) were screened for additional K-Ras mutations, phenotypes compared in transformation and Ras GTPase activating assays and gene and pathway changes induced by individual K-Ras mutants identified by microarray analysis. Taqman-based gene copy number and FISH analyses were used to investigate K-Ras gene amplification.
Four additional K-Ras mutations (Leu(19)Phe (1 out of 106 tumours), Lys(117)Asn (1 out of 106), Ala(146)Thr (7 out of 106) and Arg(164)Gln (1 out of 106)) were identified. Lys(117)Asn and Ala(146)Thr had phenotypes similar to the hotspot mutations, whereas Leu(19)Phe had an attenuated phenotype and the Arg(164)Gln mutation was phenotypically equivalent to wt K-Ras. We additionally identified a new K-Ras gene amplification event, present in approximately 2% of tumours.
The identification of mutations outwith previously described hotspot codons increases the K-Ras mutation burden in colorectal tumours by one-third. Future mutation screening to facilitate optimal patient selection for treatment with EGFR-targeted therapies should therefore be extended to codon 146, and in addition should consider the unique molecular signatures associated with individual K-Ras mutations.
在结直肠癌患者中，针对表皮生长因子受体（EGFR）靶向治疗的反应与 Kirsten-Ras（K-Ras）突变状态密切相关。目前，用于患者选择的强制性突变检测仅限于 K-Ras 的“热点”密码子 12 和 13。
筛选了 106 例结直肠肿瘤以检测其他 K-Ras 突变，并在转化和 Ras GTPase 激活测定中比较表型，通过微阵列分析鉴定出的单个 K-Ras 突变体，进行基因和通路变化的分析。Taqman 基因拷贝数和 FISH 分析用于研究 K-Ras 基因扩增。
鉴定出 4 个额外的 K-Ras 突变（亮氨酸 19 苯丙氨酸（106 例肿瘤中的 1 例）、赖氨酸 117 天冬酰胺（106 例中的 1 例）、丙氨酸 146 苏氨酸（106 例中的 7 例）和精氨酸 164 谷氨酰胺（106 例中的 1 例））。赖氨酸 117 天冬酰胺和丙氨酸 146 苏氨酸的表型与热点突变相似，而亮氨酸 19 苯丙氨酸的表型较弱，精氨酸 164 谷氨酰胺突变的表型与 wt K-Ras 相当。我们还发现了一种新的 K-Ras 基因扩增事件，存在于大约 2%的肿瘤中。
在先前描述的热点密码子之外鉴定出的突变使结直肠肿瘤中的 K-Ras 突变负担增加了三分之一。因此，为了优化 EGFR 靶向治疗的患者选择，未来的突变筛选应扩展到密码子 146，并应考虑与个别 K-Ras 突变相关的独特分子特征。
