Developing therapeutic strategies for ERK-dependent tumors

描述（由申请方提供）：BRAF突变型或KRAS突变型肿瘤依赖于ERK信号传导，对该通路的抑制剂敏感。选择性RAF、MEK和ERK抑制剂现已被开发作为这些肿瘤的治疗剂，然而，它们的临床疗效受到毒性、获得性抗性和适应性抗性的限制，这归因于释放ERK依赖的促有丝分裂信号传导的反馈抑制。我们以前的工作表明，MEK和ERK抑制剂抑制ERK信号在所有正常和肿瘤细胞，RAF抑制剂只抑制信号在肿瘤与BRAF突变和激活ERK信号在其他组织。因此，RAF抑制剂具有比MEK和ERK抑制剂更宽的治疗指数，但仅在具有突变BRAF的肿瘤中起作用。我们还表明，所有这些抑制剂对ERK信号传导的抑制通过RAF/ERK和非RAF/ERK途径重新激活反馈抑制的信号传导，并且这种反馈激活限制了RAF和MEK抑制剂的抗肿瘤作用。我们在这项提案中的目标是通过将RAF或MEK抑制剂与抑制ERK信号传导的反馈再激活的选择性新型MEK和ERK抑制剂组合来开发最大限度地抑制ERK输出的疗法。我们的数据表明，这是最大抗肿瘤活性所必需的，但它也将缓解RTK激活的反馈抑制，导致其他信号传导途径的有效激活，从而减弱疗效。我们计划识别这些重新激活的通路，然后开发和测试结合联合收割机最大ERK抑制和关键重新激活通路抑制的疗法，以防止或限制适应性耐药。将针对突变型BRAF肿瘤（将使用RAF抑制剂）和对RAF抑制剂具有获得性耐药或RAS突变（将不使用）的肿瘤的初始治疗设计特定方案。虽然临床前模型是强有力的工具，但最终需要在用这些药物治疗的黑色素瘤患者的临床标本中鉴定和验证耐药机制。因此，我们将使用靶向DNA和RNA测序方法，使用治疗前和RAF抑制剂疾病进展时收集的肿瘤样本来确定RAF抑制剂耐药性的基础。后一项研究的一个目标是确定我们是否可以在药物治疗前预测RAF抑制剂耐药的机制，目的是利用这些数据开发个体化治疗策略，延迟或预防耐药克隆的出现。

DESCRIPTION (provided by applicant): Tumors with mutant BRAF or mutant KRAS are dependent on ERK signaling and are sensitive to inhibitors of the pathway. Selective RAF, MEK and ERK inhibitor have now been developed as therapeutics for these tumors, however, their clinical efficacy is limited by toxicity, acquired resistance, and adaptive resistance due to relie of ERK-dependent feedback inhibition of mitogenic signaling. Our previous work shows that whereas MEK and ERK inhibitors suppress ERK signaling in all normal and tumor cells, RAF inhibitors only inhibit signaling in tumors with BRAF mutations and activate ERK signaling in other tissue. Thus, RAF inhibitors have a broader therapeutic index than MEK and ERK inhibitors, but only work in tumors with mutant BRAF. We have also shown that inhibition of ERK signaling by all of these inhibitors reactivates feedback inhibited signaling via RAF/ERK and non-RAF/ERK pathways and that this feedback activation limits the antitumor effects of RAF and MEK inhibitors. Our goals in this proposal are to develop therapies that maximally inhibit ERK output by combining RAF or MEK inhibitors with selective novel MEK and ERK inhibitors that suppress feedback reactivation of ERK signaling. Our data suggests that this is required for maximal antitumor activity, but that it will also relieve feedback inhibition of RTK activation resulting in potent activation of other signaling pathways that can attenuate efficacy. We plan to identify these reactivated pathways and then develop and test therapies that combine maximal ERK inhibition with inhibition of key reactivated pathways to prevent or limit adaptive resistance. Specific regimens will be designed for initial treatment of mutant BRAF tumors (which will employ RAF inhibitors) and for tumors with acquired resistance to RAF inhibitors or with RAS mutation (which will not). While preclinical models are powerful tools, ultimately mechanisms of resistance need to be identified and validated in clinical specimens from melanoma patients treated with these agents. We will thus use targeted DNA and RNA-sequencing methods to define the basis for RAF-inhibitor resistance using tumor samples collected pre-treatment and at the time of disease progression on RAF inhibitors. One goal of these latter studies will be to determine whether we can predict, prior to drug treatment, the mechanism of RAF-inhibitor resistance with the goal of using the data to develop individualized treatment strategies that delay or prevent the emergence of drug resistant clones.