University Children's Hospital, Ulm and Institute for Experimental Cancer Research in Pediatrics, Goethe-University, Frankfurt, Germany.
Clin Cancer Res. 2011 May 15;17(10):3233-47. doi: 10.1158/1078-0432.CCR-10-2530. Epub 2011 Feb 25.
Because we recently identified Akt activation as a novel poor prognostic indicator in neuroblastoma, we investigated whether phosphoinositide 3'-kinase (PI3K) inhibition sensitizes neuroblastoma cells for TRAIL-induced apoptosis.
The effect of pharmacological or genetic inhibition of PI3K or mTOR was analyzed on apoptosis induction, clonogenic survival, and activation of apoptosis signaling pathways in vitro and in a neuroblastoma in vivo model. The functional relevance of individual Bcl-2 family proteins was examined by knockdown or overexpression experiments.
The PI3K inhibitor PI103 cooperates with TRAIL to synergistically induce apoptosis (combination index < 0.1), to suppress clonogenic survival, and to reduce tumor growth in a neuroblastoma in vivo model. Similarly, genetic silencing of PI3K significantly increases TRAIL-mediated apoptosis, whereas genetic or pharmacological blockage of mTOR fails to potentiate TRAIL-induced apoptosis. Combined treatment with PI103 and TRAIL enhances cleavage of Bid and the insertion of tBid into mitochondrial membranes, and reduces phosphorylation of Bim(EL). Additionally, PI103 decreases expression of Mcl-1, XIAP, and cFLIP, thereby promoting Bax/Bak activation, mitochondrial perturbations, and caspase-dependent apoptosis. Knockdown of Bid or Noxa or overexpression of Bcl-2 rescues cells from PI103- and TRAIL-induced apoptosis, whereas Mcl-1 silencing potentiates apoptosis. Bcl-2 overexpression also inhibits cleavage of caspase-3, caspase-8, and Bid pointing to a mitochondria-driven feedback amplification loop.
PI103 primes neuroblastoma cells for TRAIL-induced apoptosis by shifting the balance toward proapoptotic Bcl-2 family members and increased mitochondrial apoptosis. Thus, PI3K inhibitors represent a novel promising approach to enhance the efficacy of TRAIL-based treatment protocols in neuroblastoma.
因为我们最近发现 Akt 激活是神经母细胞瘤的一个新的不良预后指标，所以我们研究了磷酸肌醇 3-激酶（PI3K）抑制是否能使神经母细胞瘤细胞对 TRAIL 诱导的凋亡敏感。
在体外和神经母细胞瘤体内模型中，分析了药理学或遗传学抑制 PI3K 或 mTOR 对凋亡诱导、集落形成存活和凋亡信号通路激活的影响。通过敲低或过表达实验研究了单个 Bcl-2 家族蛋白的功能相关性。
PI3K 抑制剂 PI103 与 TRAIL 协同作用，协同诱导凋亡（组合指数<0.1），抑制集落形成存活，并减少神经母细胞瘤体内模型中的肿瘤生长。同样，PI3K 的基因沉默显著增加了 TRAIL 介导的凋亡，而 mTOR 的基因或药理学阻断未能增强 TRAIL 诱导的凋亡。PI103 与 TRAIL 联合治疗增强了 Bid 的切割和 tBid 插入线粒体膜，减少了 Bim(EL)的磷酸化。此外，PI103 降低了 Mcl-1、XIAP 和 cFLIP 的表达，从而促进了 Bax/Bak 的激活、线粒体扰动和 caspase 依赖性凋亡。Bid 或 Noxa 的敲低或 Bcl-2 的过表达可使细胞免受 PI103 和 TRAIL 诱导的凋亡，而 Mcl-1 的沉默则增强了凋亡。Bcl-2 的过表达也抑制了 caspase-3、caspase-8 和 Bid 的切割，表明存在线粒体驱动的反馈放大环。
PI103 通过向促凋亡 Bcl-2 家族成员和增加的线粒体凋亡倾斜平衡，使神经母细胞瘤细胞对 TRAIL 诱导的凋亡敏感。因此，PI3K 抑制剂代表了一种增强神经母细胞瘤中基于 TRAIL 的治疗方案疗效的新方法。
