Department of Neurology, University of Ulm, Ulm, Germany.
Mol Cancer Ther. 2011 Oct;10(10):1867-75. doi: 10.1158/1535-7163.MCT-11-0218. Epub 2011 Aug 22.
Evasion of apoptosis contributes to radioresistance of glioblastoma, calling for novel strategies to overcome apoptosis resistance. In this study, we investigated the potential of the small molecule Smac mimetic BV6 to modulate radiosensitivity of glioblastoma cells. Here, we identify a novel proapoptotic function of NF-κB in γ-irradiation-induced apoptosis of glioblastoma cells by showing, for the first time, that NF-κB is critically required for Smac mimetic-mediated radiosensitization. BV6 significantly increases γ-irradiation-triggered apoptosis in several glioblastoma cell lines in a dose- and time-dependent manner. Calculation of combination index (CI) reveals that the interaction of BV6 and γ-irradiation is highly synergistic (CI < 0.3). Molecular studies show that BV6 stimulates NF-κB activation, which is critical for radiosensitization, because genetic inhibition of NF-κB by overexpression of the dominant-negative superrepressor IκBα-SR significantly decreases BV6- and γ-irradiation-induced apoptosis. Also, the BV6-mediated enhancement of γ-irradiation-triggered caspase activation, drop of mitochondrial membrane potential, and cytochrome c release is abolished in cells overexpressing IκBα-SR. Similarly, NF-κB inhibition by ectopic expression of a kinase dead mutant of IKKβ prevents the BV6-mediated sensitization for γ-irradiation. The clinical relevance is underscored by experiments with primary tumor samples showing that BV6 sensitizes primary cultured glioma cells as well as glioblastoma-initiating cancer stem cells derived from surgical specimens for γ-irradiation. In conclusion, we identify NF-κB as a critical mediator of Smac mimetic-conferred radiosensitization of glioblastoma cells. These results have important implications for the development of Smac mimetic-based combination protocols for radiosensitization of glioblastoma.
细胞凋亡逃逸导致脑胶质瘤对放疗产生抵抗，因此需要寻找新的策略来克服这种抵抗。在本研究中，我们研究了小分子 Smac 模拟物 BV6 增强脑胶质瘤细胞放射敏感性的潜力。我们首次发现 NF-κB 在 γ 射线诱导的脑胶质瘤细胞凋亡中具有促进凋亡的新功能，证明 NF-κB 是 Smac 模拟物介导放射增敏所必需的。BV6 以剂量和时间依赖的方式显著增加几种脑胶质瘤细胞系中 γ 射线触发的凋亡。计算合并指数（CI）表明，BV6 和 γ 射线的相互作用具有高度协同作用（CI<0.3）。分子研究表明，BV6 刺激 NF-κB 激活，这对于放射增敏至关重要，因为通过表达显性失活超阻遏物 IκBα-SR 对 NF-κB 的遗传抑制显著降低了 BV6 和 γ 射线诱导的凋亡。此外，在过表达 IκBα-SR 的细胞中，BV6 介导的增强 γ 射线触发的半胱天冬酶激活、线粒体膜电位下降和细胞色素 c 释放被消除。同样，通过表达 IKKβ 的激酶失活突变体抑制 NF-κB 也阻止了 BV6 介导的对 γ 射线的增敏作用。通过用手术标本中分离得到的原代培养脑胶质瘤细胞和脑胶质瘤起始癌症干细胞进行实验，证明了 BV6 对 γ 射线的增敏作用，突出了其临床相关性。总之，我们确定 NF-κB 是 Smac 模拟物赋予脑胶质瘤细胞放射增敏作用的关键介质。这些结果对于开发基于 Smac 模拟物的联合方案以增强脑胶质瘤的放射敏感性具有重要意义。
