Targeting Ras-Dependent Cancers with a Chemical Switch for an Inactive Kinase

描述（由申请人提供）：小GTPase Ras是所有癌症中最常见的突变癌基因之一（20-30%）。Ras家族成员（K-Ras， H-Ras和N-Ras）调节多种生物过程，如发育，生长和蛋白质翻译。Ras的失调从根本上促进了肿瘤的发生、转移过程和化疗耐药的发展。到目前为止，Ras癌基因已经扼杀了直接的药理学方法，Ras直接效应器的抑制剂在患者中表现出有限或没有疗效。基因筛选发现Ras激酶抑制因子（KSR）的点突变是致癌Ras的有效抑制因子，这表明KSR可以为Ras靶向干预提供新的方法。虽然KSR是蛋白激酶家族的一员，但将KSR突变转化为一种可行的化学调控模式尚未实现。KSR属于蛋白激酶的一个亚类，称为假激酶，它是天然无活性的，因此相信传统的激酶抑制剂策略。在最近的研究中，我们发现KSR是一种独特的信号分子，其功能是Ras通路的动态支架（Brennan和Dar等人，Nature, 2011）。在一种状态下，KSR表现为Ras效应物MEK的抑制剂。在另一种状态下，KSR是MEK磷酸化的促进剂，被Ras的下游激酶称为RAF。KSR的单点突变抑制了致癌Ras的转化，解除了KSR两种状态之间的转换，并提出了通过KSR获得Ras化学抑制因子的新途径。使用基于结构的策略，我们将生成小分子来调节KSR，以便我们可以将其稳定在不同的构象状态。我们的目标是表征这些分子，从而在复杂的生物系统中表征KSR的构象状态，包括工程细胞和遗传定义的癌症模型。此外，我们将把我们的目标化学和分析与整个动物的分析和苍蝇的遗传学结合起来。我们最近将这一策略应用于开发ret激酶驱动的癌症的新疗法（Dar和Das等人，Nature, 2012）。在这里，我们将在这一成功的基础上，确定稳定ras抑制构象的KSR分子，作为ras依赖性癌症的新治疗方法。总之，该方法将揭示假激酶KSR的药物靶向与整个癌症动物模型中系统反应之间的功能关系。如果成功，这种方法将极大地扩大药物开发的机会，揭示独立于激酶磷酸化活性的调节功能和控制机制，并培养针对癌症、糖尿病和心脏病等疾病的非活性激酶的新范式。

DESCRIPTION (provided by applicant): The small GTPase, Ras, is one of the most frequently mutated oncogenes (20-30%) across all cancers. Ras family members (K-Ras, H-Ras, and N-Ras) regulate diverse biological processes, such as development, growth and protein translation. Dysregulation of Ras contributes fundamentally to the initiation of tumors, the metastatic process and the development of chemoresistance. To this point, Ras oncogenes have stifled direct pharmacological approaches, and inhibitors for the direct effectors of Ras have demonstrated limited or no efficacy within patients. Genetic screens identified point mutations in Kinase Suppressor of Ras (KSR) as potent suppressors of oncogenic Ras, suggesting that KSR could yield novel approaches for Ras-targeted interventions. Although KSR is a member of the protein kinase family, translating KSR mutations into a viable mode of chemical regulation has not yet been practical. KSR belongs to a subclass of protein kinases, termed pseudokinases, which are naturally inactive and therefore belie conventional kinase inhibitor strategies. In recent studies, we identified KSR as a distinct signaling molecule, which functions as a dynamic scaffold of the Ras pathway (Brennan and Dar et al., Nature, 2011). In one state, KSR behaves as an inhibitor of the Ras effector MEK. In another state, KSR is a facilitator of MEK phosphorylation by the kinase immediately downstream of Ras termed RAF. Single point mutations in KSR, which suppress transformation by oncogenic Ras, uncouple the transition between the two states of KSR and suggest novel paths to a chemical suppressor of Ras via KSR. Using structure-based strategies, we will generate small molecules to modulate KSR so that we may stabilize it in distinct conformational states. We aim to characterize these molecules, and thus the conformational states of KSR, within complex biological systems including engineered cell-based and genetically defined cancer models. Additionally, we will combine our target focused chemistry and profiling with whole animal assays and genetics in the fly. We recently applied this strategy to develop novel therapeutics for Ret-kinase driven cancers (Dar and Das et al., Nature, 2012). Here we will build upon this success to identify molecules that stabilize the Ras-suppressive conformation of KSR as novel treatments for Ras-dependent cancers. Together, this approach will reveal the functional relationship between drug targeting of the pseudokinase KSR and system wide responses within whole animal models of cancer. If successful, this approach will greatly expand opportunities for drug development, reveal regulatory functions and control mechanisms that appear independent of kinase phosphorylation activity, and foster a new paradigm of targeting inactive kinases in diseases including cancer, diabetes, and heart disease.