PNAS:科学家终于找到可以干扰癌基因KRAS活性的分子

KRAS基因可以生成的一种叫做K-Ras的蛋白影响了细胞的分裂时间。K-Ras突变可导致正常细胞失控性分裂以及癌变。这些突变尤其常见于肺癌、胰腺癌和结肠癌中。此外，携带这一突变基因的人对治疗不太敏感。30年来，研究人员都未成功尝试开发出一种药物来抑制K-Ras。

德克萨斯大学Harold C. Simmons癌症中心成员、放射肿瘤学和生物化学助理教授Kenneth Westover实验室调查了癌症的分子基础，以求开发出一些可破坏癌症生物学，并有潜力成为治疗方案的化合物。由于KRAS是癌症中最为常见的突变癌基因，Westover实验室尤其将KRAS作为了靶标。

基于以往的研究工作，Westover和同事们采用一种叫做x射线晶体学的技术，确定了当将SML添加到携带G12C突变的KRAS时发生的事件。这种KRAS突变体是和香烟有关的肺癌的一种标志，其存在于每年美国2.5万新增肺癌病例中。

研究人员发现，SML不可逆地与突变KRAS结合，使得KRAS G12C失活。SML与KRAS自然结合的一些分子GTP和GDP发生了竞争，并且在GTP和GDP处于极高水平的情况下也不能移除它。无论是GDP或是GTP都不能除去它，取而代之，这一特性使得SML成为了一种不可逆抑制剂。

研究人员利用质谱法确定了SML不仅不可逆，且只选择性结合KRAS，而不会结合RAS蛋白家族中具有非常相似结构的其他近100个成员。

Westover 博士说““我们相信SML是KRAS的第一个不可逆的、选择性抑制剂。下一阶段，我们将改造SML化合物，推动在癌细胞，以及最终在动物和人类中开展研究。”

原文摘要：

In situ selectivity profiling and crystal structureof SML-8-73-1, an active site inhibitor of oncogenicK-Ras G12C

John C. Hunter, Deepak Gurbani, Scott B. Ficarro, Martin A. CarrASCo, Sang Min Lim,Hwan Geun Choi, Ting Xie, Jarrod A. Marto, Zhe Chen, Nathanael S. Gray and Kenneth D. Westover

Directly targeting oncogenic V-Ki-ras2 Kirsten rat sarcoma viral oncoGENE homolog (K-Ras) with small-molecule inhibitors has historically been considered prohibitively challenging. Recent reports ofcompounds that bind directly to the K-Ras G12C mutant suggest avenues to overcome key obstacles that stand in the way of developing such compounds. We aim to target the guanine nucleotide (GN)-binding pocket because the natural contents of this pocket dictate the signaling state of K-Ras. Here, we characterize the irreversible inhibitor SML-8-73-1 (SML), which targets the GN-binding pocket of K-RasG12C. We report a high-resolution X-ray crystal structure of G12C K-Ras bound to SML, revealing that the compound binds in a manner similar to GDP, forming a covalent linkage with Cys-12. The resulting conformation renders K-Ras in the open, inactive conformation, which is not predicted to associate productively with or activate downstream effectors. Conservation analysis of the Ras family GN-binding pocket reveals variability in the side chains surrounding the active site and adjacent regions, especially inthe switch I region. This variability may enable building specificity into new iterations of Ras and other GTPase inhibitors. High-resolution in situ chemical proteomic profiling of SML confirms that SML effectively discriminates between K-Ras G12C and other cellular GTP-binding proteins. A biochemical assay provides additional evidence that SML is able to compete with millimolar concentrations of GTP andGDP for the GN-binding site.

作者：生物帮