Development of ATP-competitive inhibitors of KSR for the treatment of cancer

描述（由申请人提供）：缺乏突变型RAS驱动的癌症的有效治疗仍然是现代癌症治疗中未满足的关键需求。最近的几条证据表明，RAS激酶抑制因子（KSR）是小分子治疗的可行靶标。已经确定KSR在活性RAS信号传导期间组成性结合MEK并瞬时结合RAF和Erk，并且这些结合事件都至少部分地通过KSR的蛋白激酶结构域介导。Wellspring的科学联合创始人Kevan Shokat最近的结构研究表明，KSR的激酶结构域作为双功能动态支架发挥作用，将RAS信号传导的关键蛋白（MEK和RAF）聚集在一起，并变构调节RAF介导的MEK磷酸化。Shokat及其同事最近报道了一种能够调节KSR中变构开关的通用激酶抑制剂，这表明开发通过KSR作为Ras化学抑制剂的新型药物可能是一个起点。我们建议利用Shokat及其同事的结构和生物化学发现，再加上已建立的激酶化学生物学策略，以产生KSR ATP位点的小分子结合剂，并确定它们对KSR支持的RAS信号传导和细胞转化的影响。我们的假设是，KSR ATP位点的结合将干扰KSR介导的RAS信号所需的变构转换。如果成功，我们将开发出一种治疗RAS驱动肿瘤的新治疗策略。第一阶段的具体目标是：（1）验证ATP位点定向的小分子阻断KSR功能的能力（2）开发用于分析KSR ATP位点占用的测定法。与阿尔文达尔实验室合作，在第一阶段SBIR资助中概述的工作将为化合物筛选和表征工作提供基础，并扩大我们对KSR介导的RAF-MEK磷酸化的生化要求的了解，以帮助指导化合物设计策略。随后的II期研究旨在鉴定、优化和表征KSR的可逆抑制剂，并选择进入临床开发的候选药物。能够破坏KSR支持的突变RAS信号传导的小分子的成功开发将代表人类癌症治疗的一个重要里程碑。

DESCRIPTION (provided by applicant): The lack of effective treatments for mutant RAS driven cancers remains a critical unmet need in modern cancer therapy. Several lines of recent evidence suggest that Kinase Suppressor of RAS (KSR) is a viable target for small molecule therapeutics. It has been established that KSR binds constitutively to MEK and transiently to RAF and Erk during active RAS signaling, and these binding events are all mediated at least in part through KSR's protein kinase domain. Recent structural studies by Wellspring's scientific co-founder, Kevan Shokat suggest that KSR's kinase domain functions as a bifunctional dynamic scaffold, bringing together key proteins for RAS signaling (MEK and RAF) and allosterically modulating RAF mediated MEK phosphorylation. A generic kinase inhibitor with the ability to modulate the allosteric switch in KSR was recently reported by Shokat and coworkers, suggesting a possible starting point to develop novel drugs that function as chemical suppressors of Ras via KSR. We are proposing to leverage the structural and biochemical findings of Shokat and colleagues, coupled with an established kinase chemical biology strategy, to generate small molecule binders of the KSR ATP site and determine their impact on KSR supported RAS signaling and cellular transformation. Our hypothesis is that binding to the KSR ATP-site will interfere with allosteric transitions required for KSR mediated RAS signaling. If successful, we will have developed a novel therapeutic strategy for the treatment of RAS driven tumors. The Phase I specific aims are: (1) Validate the ability of ATP-site directed small molecules to block KSR function (2) Develop assays for profiling KSR ATP- site occupancy. In collaboration with the Arvin Dar lab, the work outlined in this Phase I SBIR grant will provide a foundation for compound screening and characterization efforts, and expand our knowledge of the biochemical requirements for KSR mediated RAF-MEK phosphorylation to help guide compound design strategy. Subsequent Phase II studies would be aimed at identification, optimization, and characterization of reversible inhibitors of KSR and the selection of a candidate for progression into clinical development. The successful development of small molecules capable of disrupting KSR supported mutant RAS signaling would represent a major milestone in the treatment of human cancers.