Project 2: Role of FOXO and Chromatin Remodeling in Cell Cycle Therapy for MCL

项目摘要 套细胞淋巴瘤(MCL)是一种B细胞性非霍奇金淋巴瘤，总体预后较差。 目前由于最终发展为耐药而无法治愈。由以下因素推动的无节制扩散 细胞周期蛋白D1的过度表达通常是疾病进展的基础。第一阶段，单剂临床试验 靶向CDK4/CDK6的CDK4/CDK6与帕波西利联合治疗复发的MCL导致 持久的临床反应，部分MCL患者肿瘤消退。在正在进行的临床试验中，帕波西利 与其他针对MCL生存的药物联合使用显示出显著的治疗效果，许多 患者在减少剂量的情况下实现完全应答。然而，CDK4/6的作用机制 抑制可以改善其他靶向药物的疗效，这一点还有待确定。理解这一机制 对于改善对这些病原体的反应和克服耐药性至关重要。在协作式临床和 机制研究与项目1，我们发现，抑制CDK4/6的Palbociclib导致延长 早期G1期停滞(PG1)，通过抑制BTK或PI3K使癌细胞对细胞毒杀伤敏感。这需要 FOXO1转录因子的作用，它被激活并定位于pG1的细胞核。肿瘤 抑制子FOXO1是B细胞受体参与的PI3K信号级联的中心组成部分，并且 对于B细胞的动态平衡是必不可少的。我们认为FOXO1的表达和核定位是必要的 用于帕波西利与BTK或PI3K抑制剂联合使用的细胞毒性杀伤。我们发现pG1诱导了 多梳抑制复合体2(PRC2)抑制染色质重塑及其扰动 在pG1中诱导MCL细胞的协同杀伤。我们推测抑制CDK4/6对MCL中pG1的诱导 细胞引起特定的表观遗传改变，改变FOXO1对其目标基因的访问，改变FOXO1- 介导的细胞毒基因表达。我们预测，这些表观遗传事件的及时扰动应该 增加FOXO1靶基因表达，从而提高帕罗西利及其联合治疗的临床疗效 细胞毒剂诱导的杀伤。因此，我们的建议将定义细胞毒性杀伤的潜在机制 MCL通过靶向细胞周期及其与之协调调节的表观遗传和转录机制 具体目的：(1)阐明PrC2在pG1染色质重塑中的作用；(2)确定pG1的作用。 Foxo1在CDK4抑制剂中对BTK或PI3K抑制增敏。猪瘟病毒下游基因靶点的筛选 Foxo1和它们支持的细胞过程，特别是那些介导细胞毒性的过程，将会推进 合理设计基于机制的、有效的、持久的癌症治疗方法。

Project Summary Mantle cell lymphoma (MCL) is a B cell non-Hodgkin's lymphoma with an overall poor prognosis, and is currently incurable due to the eventual development of drug resistance. Unrestrained proliferation driven by cyclin D1 overexpression often underlies disease progression. The first phase I, single-agent clinical trial targeting the cyclin-dependent kinases CDK4/CDK6 with palbociclib treatment in recurrent MCL resulted in a durable clinical response, with tumor regression in some MCL patients. In ongoing clinical trials, palbociclib, in combination with other drugs targeting MCL survival is showing remarkable therapeutic efficacy, with many patients achieving a complete response at reduced doses. However, the mechanism by which CDK4/6 inhibition improves the efficacy of other targeted agents remains to be defined. Understanding this mechanism is critical to improving the response to these agents and overcoming resistance. In collaborative clinical and mechanistic studies with Project 1, we discovered that inhibition of CDK4/6 by palbociclib leads to prolonged early G1 arrest (pG1), which sensitizes cancer cells to cytotoxic killing by BTK or PI3K inhibition. This requires the action of FOXO1 transcription factor, which is activated and localized to the nucleus in pG1. Tumor suppressor FOXO1 is a central component of the PI3K signaling cascade engaged by the B cell receptor, and is essential for B cell homeostasis. We showed that FOXO1 expression and nuclear localization are necessary for cytotoxic killing by palbociclib in combination with a BTK or PI3K inhibitor. We found that pG1 induced repressive chromatin remodeling by the polycomb repressive complex 2 (PRC2), and that its perturbation induces synergistic killing of MCL cells in pG1. We hypothesize that pG1 induction by CDK4/6 inhibition in MCL cells causes specific epigenetic alterations that modify FOXO1 access to its target genes, altering FOXO1- mediated cytotoxic gene expression. We predict that timely perturbation of these epigenetic events should increase FOXO1 target gene expression, thus enhancing clinical outcomes of palbociclib and combined cytotoxic agent-induced killing. Hence our proposal will define the mechanisms underlying cytotoxic killing of MCL by targeting the cell cycle, and its coordinately regulated epigenetic and transcriptional machinery with specific aims (1) to elucidate the role of PRC2 in chromatin remodeling in pG1, and (2) to define the role of FOXO1 in CDK4 inhibitor sensitization to BTK or PI3K inhibition. Identification of downstream gene targets of FOXO1, and the cellular processes that they support, especially those that mediate cytotoxicity, will advance the rational design of mechanism-based, effective, and durable cancer therapies.