Role of Mcl-1 degradation in colorecal cancer therapy

 描述(申请人提供)：转移性结直肠癌(CRC)是最致命的癌症之一，其特点是预后差，生存率低。多激酶抑制剂regorafenib可以提高患者的存活率，最近已被批准用于治疗转移性结直肠癌。Regorafenib抑制RAS/RAF/MEK/ERK通路，该通路在大多数癌组织中由于普遍存在的RAS和RAF突变而异常激活。然而，瑞格非尼的抗癌机制尚不清楚。目前还没有发现基因改变与大肠癌细胞对瑞格非尼的敏感性或耐药性有关。临床研究中观察到的瑞格非尼有时会产生严重的副作用，这使得识别应答患者成为精确医学的关键任务，以避免不必要的治疗。我们的初步研究表明，瑞格拉非尼对结直肠癌细胞的治疗作用与诱导细胞凋亡和蛋白酶体降解有关，Mcl-1是一种促进生存的Bcl2家族蛋白。对瑞格拉非尼本身不敏感的大肠癌细胞缺乏Mcl-1的降解，并含有肿瘤抑制因子FBW7和E3泛素连接酶的失活突变，泛素连接酶在大肠癌中经常突变。作为对瑞格非尼治疗的反应，FBW7与磷酸化的Mcl-1结合，是其泛素化和随后的降解所必需的。通过基因敲入方法阻断Mcl-1的磷酸化，取消其与FBW7的结合和降解，并抑制雷戈非尼诱导的对CRC细胞的杀伤。此外，具有获得性瑞格非尼耐药的CRC细胞被发现阻止了Mcl-1的降解和FBW7突变的浓缩。我们假设FBW7介导的Mcl-1降解对于瑞格拉非尼的抗癌作用是至关重要的，FBW7突变破坏了Regorafenib诱导的Mcl-1降解，导致了肿瘤细胞对regorafenib的耐药性。我们建议使用遗传学和生物化学方法来检验这一假说及其翻译含义。目的1：研究Mcl-1降解在大肠癌细胞中如何介导瑞格非尼的抗癌活性。目的：研究癌基因突变对瑞格拉非尼敏感性和Mcl-1稳定性的影响。目的：阐明FBW7基因突变和Mcl-1稳定性在获得性耐药中的作用。与正在进行的有关瑞格拉非尼的临床研究同时，这些研究可能确定FBW7突变状态和Mcl-1稳定性是决定大肠癌患者对瑞可非尼敏感性的关键决定因素。它们还可能为瑞格拉非尼与其他药物的有效结合提供理论基础，以及为研究Mcl-1和FBW7在靶向抗癌治疗中的广泛功能作用以及克服由结肠癌细胞基因组不稳定引起的治疗耐药性提供新的工具。

 DESCRIPTION (provided by applicant): Metastatic colorectal cancer (CRC) is one of the most deadly cancers, characterized by poor prognosis and low survival rate. The multi-kinase inhibitor regorafenib can improve patient survival and has recently been approved for the treatment of metastatic CRC. Regorafenib inhibits the RAS/RAF/MEK/ERK pathway, which is aberrantly activated in most CRCs due to prevalent RAS and RAF mutations. However, the anticancer mechanism of regorafenib is not well understood. No genetic alteration has been linked to regorafenib sensitivity or resistance in CRC cells. The sometimes serious side effects of regorafenib observed in clinical studies make identifying responder patients a critical mission of precision medicine, to avoid unnecessary treatment. Our preliminary studies reveal that the therapeutic activity of regorafenib in CRC cells is associated with apoptosis induction and proteasomal degradation of Mcl-1, a pro-survival Bcl-2 family protein. CRC cells that are intrinsically insensitive to regorafenib lack Mcl-1 degradation and contain inactivating mutations of FBW7, a tumor suppressor and E3 ubiquitin ligase that is frequently mutated in CRCs. In response to regorafenib treatment, FBW7 binds to phosphorylated Mcl-1 and is required for its ubiquitination and subsequent degradation. Blocking Mcl-1 phosphorylation by a genetic knock-in approach abrogates its binding to FBW7 and degradation, and suppresses regorafenib-induced killing of CRC cells. Furthermore, CRC cells with acquired regorafenib resistance were found to have blocked Mcl-1 degradation and enrichment of FBW7 mutations. We hypothesize that FBW7-mediated Mcl-1 degradation is crucial for the anticancer effects of regorafenib and that FBW7 mutations disrupt regorafenib-induced Mcl-1 degradation, resulting in regorafenib resistance in CRCs. We propose to test this hypothesis and its translational implications by using genetic and biochemical approaches. Aim 1: Delineate how Mcl-1 degradation mediates the anticancer activity of regorafenib in CRC cells. Aim 2: Determine the effects of oncogenic mutations on regorafenib sensitivity and Mcl-1 stability. Aim 3: Elucidate the roles of FBW7 mutations and Mcl-1 stability in acquired resistance to regorafenib. In parallel with ongoing clinical studies on regorafenib, these studies may establish FBW7 mutational status and Mcl-1 stability as key determinants of regorafenib sensitivity in CRCs. They may also provide a rationale for effective combinations of regorafenib with other drugs, as well as new tools for investigating the broad functional roles of Mcl-1 and FBW7 in targeted anticancer therapies, and for overcoming therapeutic resistance caused by genomic instability in CRC cells.