TOR kinase inhibitors for leukemia therapy: mechanisms of action and resistance

描述（由申请人提供）：大多数癌细胞显示磷酸肌醇3-激酶（PI 3 K）和下游酶AKT和TOR的活化。靶向PI 3 K/AKT/TOR网络是癌症治疗的一种有前途的策略，但目前尚不清楚哪种靶点谱将提供疗效和耐受性的最佳平衡。部分抑制TOR的化合物（例如雷帕霉素）或抑制PI 3 K和TOR两者的化合物（例如PI-103）在功效和/或耐受性方面具有显著限制。该领域的一个重大突破是鉴定出了新型化合物，它们是TOR的高效、选择性、小分子竞争性抑制剂。这些化合物被称为“活性位点TOR抑制剂”，当TOR酶存在于两种不同的多蛋白复合物TORC 1或TORC 2中时，它们完全抑制TOR酶。与雷帕霉素（一种变构抑制剂）相比，活性位点TOR抑制剂对关键信号通路具有更广泛的影响，并且在抑制小鼠和人白血病细胞的存活方面更有效。值得注意的是，尽管这些化合物具有更高的抗白血病功效，但它们的免疫抑制作用低于雷帕霉素。活性位点TOR抑制剂在白血病模型中与选择性较低的PI 3 K/TOR抑制剂同样有效，但在小鼠中耐受性更好。几种活性位点TOR抑制剂处于早期临床试验阶段。该提案的总体目标是完善和扩展我们对活性位点TOR抑制剂的理解，最终目标是改善癌症患者的健康。我们将重点关注B细胞恶性肿瘤，因为活性位点TOR抑制剂在B细胞白血病模型中具有显著作用，但其作用机制仍知之甚少。该提案有两个具体目标。首先，我们将建立活性位点TOR抑制剂触发白血病细胞死亡的机制。在这个目标中，我们将使用遗传方法来测试的假设，即TORC 1和TORC 2介导的白血病细胞的生存信号。这将使用诱导型Cre介导的敲除系统和shRNA介导的敲低来实现。然后，我们将测试TORC 1和TORC 2底物在维持白血病细胞存活中的作用。其次，我们将定义细胞对活性位点TOR抑制剂的抗性机制。与任何靶向分子方法一样，癌细胞的亚型对活性位点TOR抑制剂表现出不同的敏感性。药物开发中的一个新兴主题是需要确定靶向药物的有效组合。使用不发生细胞凋亡的细胞系响应于TOR抑制，我们将使用候选人和全球的方法来确定耐药的药物机制。然后，我们将在体外和体内测试组合策略。确定耐药机制并应用适当的药物组合将拓宽活性位点TOR抑制剂的潜在应用。

DESCRIPTION (provided by applicant): Most cancer cells display activation of phosphoinositide 3-kinase (PI3K) and the downstream enzymes AKT and TOR. Targeting the PI3K/AKT/TOR network is a promising strategy for cancer therapeutics, yet it is not clear which target profile will provide the best balance of efficacy and tolerability. Compounds that partially inhibit TOR (such as rapamycin) or compounds that inhibit both PI3K and TOR (such as PI-103) have significant limitations in efficacy and/or tolerability. A major breakthrough in this field has been the identification of novel compounds that are highly potent, selective, small molecule competitive inhibitors of TOR. Termed "active-site TOR inhibitors", these compounds fully inhibit the TOR enzyme when it is present in TORC1 or TORC2, two distinct multiprotein complexes. Compared to rapamycin, an allosteric inhibitor, active-site TOR inhibitors have a broader effect on key signaling pathways and are more effective at suppressing survival of murine and human leukemia cells. Remarkably, these compounds are less immunosuppressive than rapamycin despite their greater anti-leukemic efficacy. Active-site TOR inhibitors appear equally effective in leukemia models as the less selective PI3K/TOR inhibitors, yet are considerably better tolerated in mice. Several active-site TOR inhibitors are in early stage clinical trials. The overall objective of this proposal is to refine and extend our understanding of active-site TOR inhibitors, with the ultimate goal of improving the health of cancer patients. We will focus on B cell malignancies, since active-site TOR inhibitors have dramatic effects in B cell leukemia models yet the mechanism of action remains poorly understood. The proposal has two specific aims. First, we will establish the mechanisms by which active-site TOR inhibitors trigger leukemia cell death. In this aim we will use genetic approaches to test the hypothesis that both TORC1 and TORC2 mediate survival signaling in leukemia cells. This will be accomplished using inducible Cre-mediated knockout systems and shRNA-mediated knockdown. We will then test the roles of TORC1 and TORC2 substrates in maintaining survival in leukemia cells. Second, we will define mechanisms of cellular resistance to active-site TOR inhibitors. As with any targeted molecular approach, subtypes of cancer cells display differing sensitivity to active-site TOR inhibitors. An emerging theme in drug development is the need to identify effective combinations of targeted agents. Using cell lines that do not undergo apoptosis in response to TOR inhibition, we will use candidate and global approaches to identify druggable mechanisms of resistance. We will then test combination strategies in vitro and in vivo. Identifying mechanisms of resistance and applying appropriate drug combinations will broaden the potential application of active-site TOR inhibitors.