Project 1: Therapeutic targeting of CDK4 in Mantle Cell Lymphoma

套细胞淋巴瘤(MCL)由于耐药性的发展仍然无法治愈，尽管在 靶向治疗。每一次连续的治疗失败都与一种更迅速扩散的疾病有关， 更少的实际治疗选择。例如，BTK抑制剂(BTKi)ibrutinib具有前所未有的活性 但失败几乎是普遍的，并与惨淡的结果相关。了解机制和 因此，耐药的基因组基础是开发卓越的持久疗法的基础，这些疗法 也适用于MCL的患者分层。由于CDK4调节失调(CDK6在MCL中不表达)和 细胞周期蛋白D1的异常表达是MCL增殖的基础，靶向CDK4是一种合理的方法 开发避免MCL中伊布鲁替尼耐药的新疗法。我们之前已经证明过 MCL患者对伊布鲁替尼的临床反应与PI3K失活密切相关。诱导 用Palbociclib(选择性CDK4/6抑制剂)抑制CDK4延长早期G1期停滞(PG1) 仅为G1早期计划的基因表达。这导致了基因表达的不平衡 重新编程的MCL细胞的治疗脆弱性，包括BTK和PI3K抑制。在此基础上，我们 假设靶向CDK4既会限制抗性克隆的扩张，又会对MCL细胞重新编程 以获得对BTKi或PI3Ki更深入、更持久的临床反应。支持这一假设，我们的第一阶段 帕波西利联合伊布鲁替尼治疗复发MCL(PALIBR)的临床试验显示 承诺总有效率为67%，完全有效率为43%(N=27)，而且反应迅速 而且经久耐用；自试验开始以来，只有14%的有反应的患者在大约32个月内进展。大写字母 基于这些令人振奋的发现和即将到来的PALIBR第二阶段临床试验，我们建议定义 治疗易损性的pG1重编程机制及区分的分子生物标志物 MCL对靶向CDK4的敏感性有两个特定目的：1)确定基因组基础 针对联合治疗中靶向CDK4的抵抗力。我们将确定复合拷贝数是否发生变化 (CNV)和克隆选择通过纵向功能基因组学诱导对PALIBR的抗性 通过靶向耐药导致的治疗脆弱性来规避PALIBR耐药性的策略 2)阐明MCL细胞中pG1重编程的机制。我们将检验我们的假设 通过加强E2F1的RB隔离，CDK4抑制扰乱了E2F1-EZH2调节电路， 它维持持久的临床反应所需的pG1状态，并重新编程MCL细胞用于治疗 通过染色质重塑、抑制IRF4和PI3K失活而产生的脆弱性。针对CDK4/6的是 现在FDA批准用于乳腺癌的治疗，并正在积极研究各种人类癌症， 然而，潜在的机制仍不清楚。成功完成拟议的研究应包括 推进MCL治疗，并对靶向人类癌症的细胞周期产生深远影响。

Mantle cell lymphoma (MCL) remains incurable due to the development of drug resistance despite advances in targeted therapy. Each successive treatment failure is associated with a more rapidly proliferating disease and fewer practical treatment options. For example, the BTK inhibitor (BTKi) ibrutinib has unprecedented activity but failure is virtually universal and is associated with dismal outcomes. Understanding the mechanism and genomic basis for therapy resistance is thus fundamental to developing superior durable therapies that are also amenable to patient stratification in MCL. As dysregulation of CDK4 (CDK6 is not expressed in MCL) and aberrant cyclin D1 expression underlie MCL proliferation, targeting CDK4 represents a rational approach to developing novel therapies that circumvent ibrutinib resistance in MCL. We have previously demonstrated that the clinical response to ibrutinib was tightly associated with PI3K inactivation in MCL patients. Induction of prolonged early G1 arrest (pG1) by inhibiting CDK4 with palbociclib (selective CDK4/6 inhibitor) restricts the expression of genes to those scheduled for early G1 only. This led to an imbalance in gene expression that reprogrammed MCL cells for therapeutic vulnerability, including BTK and PI3K inhibition. On this basis, we hypothesize that targeting CDK4 will both restrict the expansion of resistant clones and reprogram MCL cells for a deeper, and more durable clinical response to BTKi or PI3Ki. Supporting this hypothesis, our phase I clinical trial of palbociclib in combination with ibrutinib for patients with recurrent MCL (PALIBR) revealed a promising 67% overall response rate with 43% complete response (N=27), Moreover the response was rapid and durable; only 14% responding patients have progressed in ~32 months since the trial opened. Capitalizing on these exciting findings and the upcoming phase 2 PALIBR clinical trial, we propose to define the mechanism of pG1 reprograming for therapeutic vulnerability and the molecular biomarkers that discriminate sensitivity from resistance to targeting CDK4 in MCL with two specific aims: 1) to determine the genomic basis for resistance to targeting CDK4 in combination therapy. We will determine if composite copy number variation (CNV) and clonal selection causes resistance to PALIBR by longitudinal functional genomics and develop strategies to circumvent PALIBR resistance by targeting the therapeutic vulnerability conferred by resistance biomarkers; 2) to elucidate the mechanism for pG1 reprogramming in MCL cells. We will test our hypothesis that by reinforcing Rb sequestration of E2F1, CDK4 inhibition disrupts the E2F1- EZH2 regulatory circuitry, which sustains the pG1 state needed for a durable clinical response and reprograms MCL cells for therapy vulnerability through chromatin remodeling, repression of IRF4 and inactivation of PI3K. Targeting CDK4/6 is now FDA-approved for treatment of breast cancer and is being actively investigated in diverse human cancers, yet the underlying mechanism remains unknown. Successful completion of the proposed studies should both advance MCL therapy and have a profound impact on targeting the cell cycle in human cancer.