Small Molecule Inhibitors of the MCL-1 Survival Pathway for Cancer Therapy

描述（由申请人提供）：MCL-1是b细胞淋巴瘤2 （BCL-2）蛋白家族的成员，通过线粒体启动的细胞凋亡调节细胞死亡。在正常情况下，抗凋亡的MCL-1及其功能同源物BCL-2和BCL-XL作为促生存调节因子，保护线粒体完整性并防止不必要的细胞死亡。然而，这些蛋白的病理性过表达破坏了自然死亡反应，并有助于肿瘤的发生、进展和对化疗药物的耐药性。促生存BCL-2蛋白因此成为抗肿瘤治疗的有吸引力的靶点。抗凋亡BCL-2家族蛋白的最特异性抑制剂ABT-737及其口服生物利用类似物ABT-263结合BCL-2和BCL-XL的疏水结合槽，释放被困的促凋亡BCL-2成员。然而，ABT-737/263由于其独特的结构不能靶向MCL-1。具有MCL-1扩增的癌细胞已被证明对MCL-1成瘾以维持生存，并且MCL-1是所有人类癌症类型中最常扩增的十大基因之一。因此，选择性小分子靶向MCL-1仍然是癌症治疗的一个有希望的尚未实现的目标。在癌细胞中，BIM是与MCL-1结合最紧密的BH3最相关的激活剂，但目前的小分子MCL-1抑制剂已被报道能够取代tBID，但不能取代MCL-1中的BIM。我们开发了一种基于细胞的高通量筛选策略，以识别MCL-1依赖性生存途径的小分子抑制剂，特别是针对MCL-1/BIM复合物。这种新策略能够识别小分子，这些小分子可以通过破坏BIM与MCL-1疏水结合口袋的结合直接释放BIM，也可以通过靶向MCL-1进行降解间接释放BIM。我们使用NCI Diversity Set的1900种化合物和ChemBridge DiverSet的首批10000种化合物（50,080种化合物）进行了试点筛选，并确定了17种先导化合物，这些先导化合物可在依赖MCL-1存活的癌细胞中引发细胞凋亡。在这里，我们建议使用自上而下的方法来(1)识别MCL-1的任何调控水平的抑制剂，阐明它们的分子作用机制；

DESCRIPTION (provided by applicant): MCL-1 is a member of the B-Cell Lymphoma 2 (BCL-2) protein family that regulates cell death via mitochondrion-initiated apoptosis. Under normal conditions, antiapoptotic MCL-1 and its functional homologs BCL-2 and BCL-XL serve as prosurvival regulators that preserve mitochondrial integrity and protect against unwanted cell death. However, pathologic overexpression of these proteins subverts the natural death response and contributes to tumor initiation, progression, and resistance to chemotherapeutics. Prosurvival BCL-2 proteins have consequently become attractive targets for antitumor therapy. The most specific inhibitors of anti-apoptotic BCL-2 family proteins, ABT-737 and its orally bioavailable analog ABT-263, bind the hydrophobic binding groove of BCL-2 and BCL-XL to liberate trapped proapoptotic BCL-2 members. However, ABT-737/263 are unable to target MCL-1 due to its unique structure. Cancer cells with MCL-1 amplifications have been shown to be addicted to MCL-1 for survival, and MCL-1 is among the top 10 most frequently amplified genes in all human cancer types. Therefore, selective small molecule targeting of MCL-1 remains a promising unfulfilled goal for cancer therapy. In cancer cells, BIM is the most relevant activator BH3 that binds most tightly with MCL-1, yet current small molecule MCL-1 inhibitors have been reported to be able to displace tBID but not BIM from MCL-1. We have developed a cell-based high throughput screening strategy to identify small molecule inhibitors of the MCL-1-dependent survival pathway that focuses specifically on the MCL-1/BIM complex. This novel strategy enables the identification of small molecules that either directly release BIM by disrupting the binding of BIM to the hydrophobic binding pocket of MCL-1 or indirectly through targeting MCL-1 for degradation. We have conducted pilot screens using 1,900 compounds of the NCI Diversity Set and first 10,000 compounds of the ChemBridge DiverSet (50,080 compounds) and identified 17 lead compounds that triggered apoptosis in cancer cells that are addicted to MCL-1 for survival. Here we propose to use a top-down approach to (1) identify inhibitors of MCL-1 at any level of its regulation, elucidate their molecular mechanisms of action, and examine their functional capacities to sensitize cancer cell apoptosis; (2) screen the remaining 40,080 compounds of the ChemBridge DiverSet; (3) study the structure-activity relationship of MCL-1 lead compound inhibitors. We hypothesize that our screen will identify compounds that directly inhibit the hydrophobic binding groove of MCL-1, target MCL-1 for accelerated degradation, or induce proapoptotic BCL-2 proteins.