Mantle cell lymphoma (MCL) is a chronically relapsing malignancy with deregulated cell cycle progression. We analyzed efficacy, mode of action, and predictive markers of susceptibility to palbociclib, an approved CDK 4/6 inhibitor, and its combination with venetoclax, a BCL2 inhibitor. A panel of nine MCL cell lines were used for in vitro experiments. Four patient derived xenografts (PDX) obtained from patients with chemotherapy and ibrutinib-refractory MCL were used for in vivo proof-of-concept studies. Changes of the mitochondrial membrane potential, energy-metabolic pathways, AKT activity, and pro-apoptotic priming of MCL cells were evaluated by JC-1 staining, Seahorse XF analyser, genetically encoded fluorescent AKT reporter, and BH3 profiling, respectively. MCL clones with gene knockout or transgenic (over)expression of CDKN2A, MYC, CDK4, and RB1 were used to estimate impact of these aberrations on sensitivity to palbociclib, and venetoclax. Co-targeting MCL cells with palbociclib and venetoclax induced cytotoxic synergy in vitro and in vivo. Molecular mechanisms responsible for the observed synthetic lethality comprised palbociclib-mediated downregulation of anti-apoptotic MCL1, increased levels of proapoptotic BIM bound on both BCL2, and BCL-XL and increased pro-apoptotic priming of MCL cells mediated by BCL2-independent mechanisms, predominantly palbociclib-triggered metabolic and mitochondrial stress. Loss of RB1 resulted in palbociclib resistance, while deletion of CDKN2A or overexpression of CDK4, and MYC genes did not change sensitivity to palbociclib. Our data strongly support investigation of the chemotherapy-free palbociclib and venetoclax combination as an innovative treatment strategy for post-ibrutinib MCL patients without RB1 deletion.

中文翻译：

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在不缺失 RB1 的套细胞淋巴瘤实验模型中，细胞周期蛋白依赖性激酶 4/6 抑制剂 Palbociclib 与 BCL2 抑制剂 Venetoclax 具有协同作用

套细胞淋巴瘤（MCL）是一种细胞周期进程失调的慢性复发性恶性肿瘤。我们分析了 Palbociclib（一种已批准的 CDK 4/6 抑制剂）及其与 Venetoclax（一种 BCL2 抑制剂）联合用药的疗效、作用方式和敏感性预测标记。一组九种 MCL 细胞系用于体外实验。从化疗和依鲁替尼难治性 MCL 患者获得的四例患者来源的异种移植物 (PDX) 用于体内概念验证研究。分别通过 JC-1 染色、Seahorse XF 分析仪、基因编码荧光 AKT 报告基因和 BH3 分析评估 MCL 细胞线粒体膜电位、能量代谢途径、AKT 活性和促凋亡引发的变化。使用基因敲除或转基因（过度）表达 CDKN2A、MYC、CDK4 和 RB1 的 MCL 克隆来评估这些畸变对 Palbociclib 和 Venetoclax 敏感性的影响。与 Palbociclib 和 Venetoclax 共同靶向 MCL 细胞在体外和体内诱导细胞毒性协同作用。导致观察到的合成致死性的分子机制包括 Palbociclib 介导的抗凋亡 MCL1 下调、BCL2 和 BCL-XL 上结合的促凋亡 BIM 水平增加以及由 BCL2 独立机制介导的 MCL 细胞促凋亡启动增加，主要是palbociclib 触发代谢和线粒体应激。 RB1 缺失导致 palbociclib 耐药，而 CDKN2A 缺失或 CDK4 和 MYC 基因过度表达不会改变对 palbociclib 的敏感性。我们的数据强烈支持对免化疗的 Palbociclib 和 Venetoclax 组合作为一种创新治疗策略的研究，用于治疗依鲁替尼后无 RB1 缺失的 MCL 患者。