Project 1: Therapeutic targeting of CDK4 in Mantle Cell Lymphoma

套细胞淋巴瘤（MCL）仍然是不可治愈的，由于耐药性的发展，尽管进展， 靶向治疗每一次连续的治疗失败都与更快速增殖的疾病有关， 更少的实际治疗选择。例如，BTK抑制剂（BTKi）伊曲替尼具有前所未有的活性， 但失败实际上是普遍的，并伴随着令人沮丧的结果。了解机制和 因此，治疗抗性的基因组基础是开发上级持久疗法的基础， 也适用于MCL中的患者分层。由于CDK 4调节异常（CDK 6在MCL中不表达）， 异常的细胞周期蛋白D1表达是MCL增殖的基础，靶向CDK 4是一种合理的方法， 开发新的治疗方法，以避免MCL中的伊鲁替尼耐药性。我们之前已经证明， MCL患者对伊鲁替尼的临床反应与PI 3 K失活密切相关。诱导 palbociclib（选择性CDK 4/6抑制剂）通过抑制CDK 4延长早期G1期阻滞（pG 1）， 基因的表达仅限于G1早期。这导致了基因表达的不平衡， 重编程MCL细胞用于治疗脆弱性，包括BTK和PI 3 K抑制。在此基础上 假设靶向CDK 4将限制抗性克隆的扩增和重编程MCL细胞 以获得对BTKi或PI 3 Ki更深入、更持久的临床反应。为了支持这一假设，我们的第一阶段 Palbociclib联合伊曲替尼治疗复发性MCL患者的临床试验（PALIBR）显示， 总有效率为67%，完全缓解率为43%（N=27），且缓解迅速 并且持久;自试验开始以来，只有14%的应答患者在约32个月内进展。资本化 基于这些令人兴奋的发现和即将到来的2期PALIBR临床试验，我们建议定义 pG 1重编程对治疗脆弱性的作用机制和区分治疗脆弱性的分子生物标志物 MCL中靶向CDK 4的抗性的敏感性，具有两个特定目的：1）确定基因组基础 对靶向CDK 4的联合治疗的抗性。我们将确定复合拷贝数变化是否 (CNV)克隆选择通过纵向功能基因组学引起对PALIBR的抗性， 通过靶向耐药带来的治疗脆弱性来规避PALIBR耐药的策略 生物标志物; 2）阐明MCL细胞中pG 1重编程的机制。我们将测试我们的假设 通过加强Rb对E2 F1的螯合，CDK 4抑制破坏了E2 F1-EZH 2调节回路， 维持持久临床反应所需的pG 1状态，并重新编程MCL细胞用于治疗 通过染色质重塑、IRF 4的抑制和PI 3 K的失活而导致的脆弱性。靶向CDK 4/6是 现在FDA批准用于治疗乳腺癌，并且正在各种人类癌症中进行积极的研究， 但其潜在机制仍不清楚。成功完成拟议的研究应 推进MCL治疗，并对靶向人类癌症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.