Direct inhibition of mutant K-Ras for the treatment of cancer

描述（由申请人提供）：抑制K-Ras癌基因的药物开发代表了人类癌症治疗中最大的未满足需求之一。Ras基因是癌症中最常发生突变的致癌基因，在所有癌症类型中，其累积突变频率超过30%。Ras突变的癌症具有侵袭性，对标准治疗反应不佳。先前针对K-Ras的尝试都失败了，因为很难与活性位点的皮摩尔核苷酸亲和力竞争，而且大多数GTPases具有高度相似性。我们的科学联合创始人，Kevan Shokat教授，发现了一种新颖的小分子方法来靶向化学上最易处理的K-Ras突变体它包含了甘氨酸-12到半胱氨酸的突变。G12C突变是肺癌中最常见的K-Ras突变。事实上，43%的K-Ras突变肺癌包含G12C突变。这种突变在K-Ras表面放置了一个化学活性的巯基。我们对与K-rasG12C、H-rasG12C共价结合的分子进行了初步的500个化合物库筛选，并对WT K-Ras进行了反筛选。从筛选文库中鉴定出17个碱基，通过对初始碱基的第一轮优化，发现了有效的抑制剂JO-01-18。我们现在已经解决了JO-01-148与K-Ras G12C结合的晶体结构，并在蛋白质表面与半胱氨酸部分相邻的地方发现了先前未描述的变构口袋。这个口袋使得鉴定不可逆抑制剂成为可能，这些不可逆抑制剂结合在口袋中并选择性地靶向位置12的半胱氨酸。重要的是，这些小分子只抑制

DESCRIPTION (provided by applicant): The development of drugs that inhibit the K-Ras oncogene represents one of the greatest unmet needs in the treatment of human cancer. The Ras gene is the most frequently mutated oncogene in cancer, with a greater than 30% cumulative mutation frequency across all cancer types. Cancers with Ras mutations are aggressive and respond poorly to standard therapies. Previous attempts to target K-Ras have failed due to the difficulty of competing with the picomolar nucleotide affinity for the active sit and due to the high similarity of most GTPases. Our scientific co-founder, Professor Kevan Shokat, has discovered a novel, small molecule approach to target the most chemically tractable K-Ras mutant that contains a glycine-12 to cysteine mutation. The G12C mutation is the most common K-Ras mutation in lung cancer. Indeed, 43% of all lung cancers with K-Ras mutations contain the G12C mutation. This mutation positions a chemically reactive sulfhydryl group on the surface of K-Ras. We have carried out a preliminary 500 compound library screen based on mass spectrometry for molecules which bind covalently to K-rasG12C, H-rasG12C and counterscreened against WT K-Ras. 17 hits were identified from the screening library, and the first round optimization of the initial hits led to the discovery of a potent inhibitor JO-01-18. We have now solved the crystal structure of JO-01-148 bound to K-Ras G12C and identified a previously undescribed allosteric pocket on the surface of the protein adjacent to the cysteine moiety. This pocket makes it possible to identify irreversible inhibitors that bind in the pocket and selectively target the cysteine at position 12. Importantly, these small molecules inhibit only mutant K-Ras and not the normal protein. We have now solved more than 10 X-ray crystal structures of irreversible inhibitors bound to this allosteric pocket and synthesized more than 120 compounds. A clear SAR has been established. We are now proposing to further validate our lead G12C compounds in biochemical and cellular assays. The Phase I specific aims are: (1) Develop assays to evaluate K-Ras effector binding; (2) Demonstrate that the G12C irreversible binders can disrupt K-Ras effector binding; and (3) Demonstrate that the G12C irreversible binders can differentially affect tumor cells with G12C mutation compared to cells with wild type K-Ras and other K-Ras mutations. The Phase I milestone is the identification of K-ras G12C inhibitors that suppress proliferation of tumor cells with G12C K-ras mutation five-fold more potently (as measured by IC50 values) relative to tumor cells with other K-Ras mutations or wild type Ras. Collectively, we expect the Phase I results to demonstrate that we can generate a small molecule inhibitor that will specifically inhibit the growth of tumor cells wih K-Ras G12C mutation. If our approach is successful, our Phase II studies will more fully examine the safety, efficacy, and PK/biodistribution of a lead formulation for advancement to an IND application.