Developing therapeutic strategies for ERK-dependent tumors

描述（由申请人提供）：BRAF突变或KRAS突变的肿瘤依赖于ERK信号，并且对该途径的抑制剂敏感。选择性RAF、MEK和ERK抑制剂现已被开发为这些肿瘤的治疗药物，然而，由于ERK依赖性反馈抑制有丝分裂信号的缓解，它们的临床疗效受到毒性、获得性耐药和适应性耐药的限制。我们之前的研究表明，MEK和ERK抑制剂抑制所有正常细胞和肿瘤细胞中的ERK信号传导，而RAF抑制剂仅抑制BRAF突变肿瘤中的信号传导，并激活其他组织中的ERK信号传导。因此，RAF抑制剂比MEK和ERK抑制剂具有更广泛的治疗指数，但仅对BRAF突变的肿瘤有效。我们还表明，所有这些抑制剂对ERK信号的抑制可以通过RAF/ERK和非RAF/ERK途径重新激活反馈抑制信号，并且这种反馈激活限制了RAF和MEK抑制剂的抗肿瘤作用。我们在本提案中的目标是通过将RAF或MEK抑制剂与抑制ERK信号反馈再激活的选择性新型MEK和ERK抑制剂结合，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，但它也会减轻RTK激活的反馈抑制，从而导致其他信号通路的有效激活，从而减弱疗效。我们计划确定这些再激活途径，然后开发和测试将最大ERK抑制与关键再激活途径抑制相结合的疗法，以预防或限制适应性耐药。将为突变BRAF肿瘤（将使用RAF抑制剂）和对RAF抑制剂具有获得性耐药性或RAS突变（不使用RAF抑制剂）的肿瘤的初始治疗设计特定方案。虽然临床前模型是强大的工具，但最终需要在接受这些药物治疗的黑色素瘤患者的临床标本中确定和验证耐药机制。因此，我们将使用靶向DNA和rna测序方法，利用治疗前和疾病进展时收集的肿瘤样本，确定RAF抑制剂耐药的基础。这些后一项研究的目标之一是确定我们是否可以在药物治疗之前预测raf抑制剂耐药的机制，目的是利用这些数据制定个性化的治疗策略，延迟或防止耐药克隆的出现。

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.