Overcoming drug resistance using small molecule activators of protein phosphatase 2A

细胞周期蛋白活性异常导致的细胞增殖失控是癌症的一个标志。 有丝分裂原感受器细胞周期蛋白d1的过度表达是肿瘤中最常见的异常之一， 细胞周期蛋白依赖性蛋白依赖性激酶4和6的活性在→细胞周期中的作用 生存和化疗耐药性。D型细胞周期蛋白的高表达不仅在肿瘤的发生中，而且在肿瘤发生中也是必需的 对肿瘤的维持和发展也有帮助。因此，细胞周期蛋白D-CDK4/6的异常活性代表了一种可操作的 肿瘤治疗的靶点和D-型细胞周期蛋白功能是癌症治疗的首要治疗靶点之一。 CDK4/6活性的抑制剂在临床上显示出良好的前景，Palbociclib、abemaciclib和riociclib是 FDA批准用于患者。目前正在进行数百项临床试验，以评估这种抗肿瘤药物 这些药物在广泛的癌症类型中的作用。然而，CDK4/6的治疗前景 不可避免地会出现耐药性，从而抑制了抑制剂的作用。最近的开创性研究确定了一部小说 自噬和Beclin-1调节因子1缺陷介导的药物耐药机制 (AMBRA1)，一个E3连接酶适配器和细胞周期蛋白D1、D2和D3蛋白稳定性的主要调节因子。丢失或突变 AMBRA1基因在人类癌症的一个重要亚群中被发现，与患者较差的生存有关。AMBRA1 缺乏促进D型细胞周期蛋白的积累，而D型细胞周期蛋白是一种高度增殖的表型，并促进肿瘤的发生 降低肿瘤细胞对FDA批准的所有三种CDK4/6抑制剂的敏感性。有证据表明，上调 D型细胞周期蛋白与非正则细胞周期蛋白D-CDK2和p27-细胞周期蛋白D-CDK4复合体的形成 对这些药物的抵抗构成了这一提议的基础。提出了一些策略，以探索 PP2A小分子激活剂(SMAPs)在抗病机制中的应用 CDK4/6抑制剂在AMBRA1缺乏的背景下。SMAP是一类新型的抗肿瘤药物 选择性地激活PP2A全酶的一个子集，在各种癌症类型中有效地抑制肿瘤。 这个项目建立在我们的发现基础上，SMAP在所有类型的细胞中都能有效地下调细胞周期蛋白D1、D2和D3 测试过。重要的是，SMAP作为AMBRA1非依赖的D-型周期蛋白“降解物”，促进蛋白质的快速降解 通过蛋白酶体依赖的机制，该机制在AMBRA1丢失后仍具有功能。 基于这些发现，我们假设将CDK4/6抑制剂治疗与SMAP的D型周期相结合 降解剂将增强抗肿瘤活性并逆转AMBRA1驱动的CDK4/6抑制剂的耐药性 缺乏症。概念验证研究将在两个具体目标下进行：(1)探索组合的效果 CDK4/6抑制剂和SMAPS在AMBRA1缺乏的背景下，以及(2)评估SMAP-1的作用。 体内肿瘤模型中的CDK4/6抑制剂组合。重要的是，除了解决以下问题的后果之外 AMBRA1缺乏，我们的概念验证结果预计将广泛适用于包含 其他肿瘤相关改变导致D型细胞周期蛋白水平升高和CDK活性异常。

Uncontrolled cell proliferation resulting from aberrant activity of cell cycle proteins is a hallmark of cancer. Overexpression of the mitogen sensor cyclin D1 is among the most frequent abnormalities in tumors, enhancing the activity of cyclin dependent kinases 4 and 6 (CDK4/6) to drive G1→S phase progression and promote cell survival and chemoresistance. Increased expression of D-type cyclins is required not only for tumorigenesis but also for tumor maintenance and progression. Thus, aberrant cyclin D-CDK4/6 activity represents an actionable target for cancer therapy and D-type cyclin function is among the top therapeutic targets for cancer management. Inhibitors of CDK4/6 activity have shown promise in the clinic and palbociclib, abemaciclib, and ribociclib are FDA-approved for use in patients. Several hundred clinical trials are currently ongoing to evaluate the antitumor effects of these agents in a broad spectrum of cancer types. However, the therapeutic promise of CDK4/6 inhibitors is dampened by inevitable emergence of resistance. Recent seminal studies have identified a novel mechanism of resistance to these agents mediated by deficiency of autophagy and beclin 1 regulator 1 (AMBRA1), an E3 ligase adaptor and master regulator of cyclin D1, D2, and D3 protein stability. Loss or mutation of AMBRA1 is seen in a significant subset of human cancers, in association with poor patient survival. AMBRA1 deficiency promotes the accumulation of D-type cyclins, a hyperproliferative phenotype, and tumorigenesis, while reducing the sensitivity of tumor cells to all three FDA-approved CDK4/6 inhibitors. Evidence that upregulation of D-type cyclins and the formation of non-canonical cyclin D-CDK2 and p27-cyclin D-CDK4 complexes underpins resistance to these agents forms the basis of this proposal. Strategies are proposed to explore the mechanism-driven application of Small Molecule Activators of PP2A (SMAPs) for overcoming resistance to CDK4/6 inhibitors in the context of AMBRA1 deficiency. SMAPs are a novel class of antitumor agents that selectively activate a subset of PP2A holoenzymes for potent tumor suppression in a variety of cancer types. This project builds on our discovery that SMAPs potently downregulate cyclins D1, D2 and D3 in all cell types tested. Importantly, SMAPs act as AMBRA1-independent D-type cyclin ‘degraders,’ promoting rapid proteolysis of these molecules via a proteasome-dependent mechanism that remains functional following loss of AMBRA1. Based on these findings, we hypothesize that combining CDK4/6 inhibitor treatment with a SMAP ‘D-type cyclin degrader’ will enhance antitumor activity and reverse resistance to CDK4/6 inhibitors driven by AMBRA1 deficiency. Proof-of-concept studies will be performed in two Specific Aims: (1) Explore the effects of combining CDK4/6 inhibitors and SMAPS in the context of AMBRA1-deficiency, and (2) Evaluate the effects of SMAP- CDK4/6 inhibitor combinations in tumor models in vivo. Importantly, in addition to addressing consequences of AMBRA1-deficiency, our proof-of-concept findings are anticipated to be broadly applicable to tumors harboring increased levels of D-type cyclins and aberrant CDK activity resulting from other tumor-associated alterations.