Neuroscience Research Center, Lausanne University Hospital and University of Lausanne, Lausanne, Switzerland.
Service of Neurosurgery, Lausanne University Hospital and University of Lausanne, Lausanne, Switzerland.
Cell Death Dis. 2022 Dec 13;13(12):1037. doi: 10.1038/s41419-022-05497-y.
Bromodomain and extra-terminal tail (BET) proteins have been identified as potential epigenetic targets in cancer, including glioblastoma. These epigenetic modifiers link the histone code to gene transcription that can be disrupted with small molecule BET inhibitors (BETi). With the aim of developing rational combination treatments for glioblastoma, we analyzed BETi-induced differential gene expression in glioblastoma derived-spheres, and identified 6 distinct response patterns. To uncover emerging actionable vulnerabilities that can be targeted with a second drug, we extracted the 169 significantly disturbed DNA Damage Response genes and inspected their response pattern. The most prominent candidate with consistent downregulation, was the O-6-methylguanine-DNA methyltransferase (MGMT) gene, a known resistance factor for alkylating agent therapy in glioblastoma. BETi not only reduced MGMT expression in GBM cells, but also inhibited its induction, typically observed upon temozolomide treatment. To determine the potential clinical relevance, we evaluated the specificity of the effect on MGMT expression and MGMT mediated treatment resistance to temozolomide. BETi-mediated attenuation of MGMT expression was associated with reduction of BRD4- and Pol II-binding at the MGMT promoter. On the functional level, we demonstrated that ectopic expression of MGMT under an unrelated promoter was not affected by BETi, while under the same conditions, pharmacologic inhibition of MGMT restored the sensitivity to temozolomide, reflected in an increased level of γ-H2AX, a proxy for DNA double-strand breaks. Importantly, expression of MSH6 and MSH2, which are required for sensitivity to unrepaired O6-methylguanine-lesions, was only briefly affected by BETi. Taken together, the addition of BET-inhibitors to the current standard of care, comprising temozolomide treatment, may sensitize the 50% of patients whose glioblastoma exert an unmethylated MGMT promoter.
溴结构域和末端结构域（BET）蛋白已被确定为癌症（包括神经胶质瘤）中的潜在表观遗传靶标。这些表观遗传修饰物将组蛋白密码与基因转录联系起来，而小分子 BET 抑制剂（BETi）可以破坏这种联系。为了开发针对神经胶质瘤的合理联合治疗方法，我们分析了 BETi 诱导的神经胶质瘤衍生球体中的差异基因表达，并确定了 6 种不同的反应模式。为了揭示可以用第二种药物靶向的新出现的可操作的脆弱性，我们提取了 169 个显著受干扰的 DNA 损伤反应基因，并检查了它们的反应模式。最突出的候选基因是 O-6-甲基鸟嘌呤-DNA 甲基转移酶（MGMT）基因，它是神经胶质瘤烷化剂治疗中已知的耐药因素。BETi 不仅降低了神经胶质瘤细胞中的 MGMT 表达，还抑制了其诱导，这通常在替莫唑胺治疗时观察到。为了确定潜在的临床相关性，我们评估了 BETi 对 MGMT 表达和 MGMT 介导的替莫唑胺治疗耐药性的特异性。BETi 介导的 MGMT 表达下调与 BRD4 和 Pol II 在 MGMT 启动子上的结合减少有关。在功能水平上，我们证明了在无关启动子下异位表达 MGMT 不受 BETi 影响，而在相同条件下，MGMT 的药物抑制恢复了对替莫唑胺的敏感性，反映在 γ-H2AX 水平增加，这是 DNA 双链断裂的替代物。重要的是，对于未修复的 O6-甲基鸟嘌呤损伤敏感所需的 MSH6 和 MSH2 的表达仅受到 BETi 的短暂影响。总之，将 BET 抑制剂添加到当前的标准治疗中，包括替莫唑胺治疗，可能会使 50%的神经胶质瘤未甲基化 MGMT 启动子的患者变得敏感。
