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

描述(申请人提供)：小的GTP酶，RAS，是所有癌症中最频繁突变的癌基因之一(20%-30%)。RAS家族成员(K-RAS、H-RAS和N-RAS)调节多种生物学过程，如发育、生长和蛋白质翻译。RAS的失调在肿瘤的发生、转移过程和化疗耐药的发展中起着根本性的作用。到目前为止，RAS癌基因已经扼杀了直接的药理学途径，而RAS直接效应的抑制剂在患者中表现出有限的疗效或没有疗效。基因筛查发现，RAS的激酶抑制因子(KSR)的点突变是致癌RAS的有效抑制因子，这表明KSR可能为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还不现实。KSR属于蛋白激酶的一个亚类，称为假激酶，它们自然是不活跃的，因此与传统的激酶抑制剂策略不符。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途径的动态支架(Brennan和Dar等人，自然，2011)。在一种状态下，KSR表现为RAS效应器MEK的抑制剂。在另一种状态下，KSR通过紧邻RAS下游的称为RAF的激酶促进MEK的磷酸化。KSR中的单点突变抑制了致癌RAS的转化，解偶联了KSR两种状态之间的转换，并提出了通过KSR实现RAS化学抑制的新途径。使用基于结构的策略，我们将产生小分子来调节KSR，以便我们可以将其稳定在不同的构象状态。我们的目标是在复杂的生物系统中表征这些分子，从而确定KSR的构象状态，包括基于工程细胞和基因定义的癌症模型。此外，我们将把我们的目标重点化学和特征分析与整个动物的分析和遗传学结合起来。我们最近应用这一策略来开发Ret-Kinase驱动的癌症的新疗法(Dar和Das等人，《自然》，2012年)。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依赖癌症的新治疗方法。总之，这种方法将揭示假性激酶KSR的药物靶向和整个癌症动物模型的全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，揭示似乎独立于激酶磷酸化活性的调节功能和控制机制，并培育一种针对癌症、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.