Targeting the ERK Pathway in KRAS-and BRAF-Driven Lung Cancers

具有突变型BRAF或突变型KRAS的肿瘤依赖于ERK信号传导并且对MEK抑制剂敏感，但仅BRAF突变型肿瘤对RAF抑制剂敏感。我们已经表明，RAF抑制剂变构激活RAS依赖的F？AF在大多数正常和肿瘤细胞中二聚体，因此矛盾地激活信号传导。然而，在具有V600E BRAF突变的肿瘤中，活化的ERK导致RAS. GTP的反馈抑制至太低的水平而不能支持RAF二聚化，并且在这种情况下，V600E作为单体发出信号。RAF抑制剂与单体结合并有效抑制这些肿瘤中的ERK信号传导。这是与MEK抑制剂相比，具有密码子600 BRAF突变的黑素瘤对这些药物的显著治疗反应的基础。然而，肿瘤反应是不完全的，而且往往是暂时的。肿瘤进展是由于获得性抗性，其特征通常是ERK信号传导对RAF抑制剂不敏感。我们已经证明，这可能是由诱导RAS、GTP或RAF的剪接变体介导的，RAF以Ras非依赖性方式二聚化。我们还认为，最初的肿瘤反应是有限的适应肿瘤抑制ERK。在RAS和BRAF突变型肿瘤中，ERK激活导致其他细胞内信号传导途径的反馈抑制，并使细胞依赖于ERK信号传导。这会导致对RAF抑制剂（突变型BRAF肿瘤）或MEK抑制剂（突变型BRAF和一些KRAS肿瘤）的超敏反应。然而，用这些药物抑制ERK信号传导缓解了这种反馈，减弱了ERK输出的抑制，并激活了导致对ERK抑制的适应性抗性的其他促有丝分裂信号传导途径。我们在这项提案中的目标是通过将RAF或MEK抑制剂与防止RAF反馈再激活的选择性MEK和RTK抑制剂组合来开发最大限度地抑制ERK输出的疗法。我们假设，最大限度地抑制ERK输出与这些方案将缓解反馈抑制受体酪氨酸激酶信号传导，并导致耐药的方式。我们将确定这些重新激活的途径，然后开发和测试基于最大ERK抑制结合抑制关键重新激活受体的治疗方法，以预防或限制适应性耐药。

Tumors with mutant BRAF or mutant KRAS are dependent on ERK signaling and sensitive to MEK inhibitors, but only the BRAF mutant tumors are sensitive to RAF inhibitors. We have shown that RAF inhibitors allosterically activate RAS-dependent F?AF dimers in most normal and tumor cells and thus paradoxically activate signaling. However, in tumors with V600E BRAF mutation, activated ERK causes feedback inhibition of RAS.GTP to a levels too low to support RAF dimerization and in this context V600E signals as a monomer. RAF inhibitors bind to the monomer and potently inhibit ERK signaling in these tumors. This is basis for the dramatic therapeutic response of melanomas with codon 600 BRAF mutation to these drugs compared to MEK inhibitors. However, tumor responses are incomplete and often temporary. Tumor progression is due to acquired resistance often characterized by insensitivity of ERK signaling to the RAF inhibitor. We have shown that this may be mediated by induction of RAS.GTP or to splice variants of RAF that dimerize in a Ras-independent manner. We also believe that the initial tumor response is limited by adaptation of the tumor to inhibition of ERK. In RAS and BRAF mutant tumors, ERK activation causes the feedback inhibition of other intracellular signaling pathways and renders the cell dependent on ERK signaling. This causes hypersensitivity to RAF inhibitors (mutant BRAF tumors) or MEK inhibitors (mutant BRAF and some KRAS tumors). However, inhibition of ERK signaling with these drugs relieves this feedback, attenuates inhibition of ERK output, and activates other mitogenic signaling pathway that cause adaptive resistance to ERK inhibition. Our goals in this proposal are to develop therapies that maximally inhibit ERK output by combining RAF or MEK inhibitors with selective MEK and RTK inhibitors that prevent feedback reactivation of RAF. We hypothesize that maximal inhibition of ERK output with these regimens will relieve feedback inhibition of receptor tyrosine kinase signaling and cause resistance in that manner. We will identify these reactivated pathways and then develop and test therapies based on maximal ERK inhibition combined with inhibition of key reactivated receptors to prevent or limit adaptive resistance.