Department of Neurological Surgery, University of California San Francisco, San Francisco, California, USA.
Bioinformatics and Computational Biology, Discovery Oncology, Genentech, San Francisco, California, USA.
Neuro Oncol. 2020 Nov 26;22(11):1580-1590. doi: 10.1093/neuonc/noaa059.
Emerging data suggest that a subset of patients with diffuse isocitrate dehydrogenase (IDH)-mutant low-grade glioma (LGG) who receive adjuvant temozolomide (TMZ) recur with hypermutation in association with malignant progression to higher-grade tumors. It is currently unclear why some TMZ-treated LGG patients recur with hypermutation while others do not. MGMT encodes O6-methylguanine-DNA methyltransferase, a DNA repair protein that removes cytotoxic and potentially mutagenic lesions induced by TMZ. Here, we hypothesize that epigenetic silencing of MGMT by promoter methylation facilitates TMZ-induced mutagenesis in LGG patients and contributes to development of hypermutation at recurrence.
We utilize a quantitative deep sequencing assay to characterize MGMT promoter methylation in 109 surgical tissue specimens from initial tumors and post-treatment recurrences of 37 TMZ-treated LGG patients. We utilize methylation arrays to validate our sequencing assay, RNA sequencing to assess the relationship between methylation and gene expression, and exome sequencing to determine hypermutation status.
Methylation level at the MGMT promoter is significantly higher in initial tumors of patients that develop hypermutation at recurrence relative to initial tumors of patients that do not (45.7% vs 34.8%, P = 0.027). Methylation level in initial tumors can predict hypermutation at recurrence in univariate models and multivariate models that incorporate patient age and molecular subtype.
These findings reveal a mechanistic basis for observed differences in patient susceptibility to TMZ-driven hypermutation. Furthermore, they establish MGMT promoter methylation level as a potential biomarker to inform clinical management of LGG patients, including monitoring and treatment decisions, by predicting risk of hypermutation at recurrence.
新出现的数据表明，接受辅助替莫唑胺（TMZ）治疗的弥漫性异柠檬酸脱氢酶（IDH）突变型低级别胶质瘤（LGG）患者中，有一部分亚组在恶性进展为高级别肿瘤时会出现与恶性进展相关的超突变。目前尚不清楚为什么一些接受 TMZ 治疗的 LGG 患者会发生超突变复发，而另一些患者则不会。MGMT 编码 O6-甲基鸟嘌呤-DNA 甲基转移酶，是一种 DNA 修复蛋白，可清除 TMZ 诱导的细胞毒性和潜在致突变损伤。在这里，我们假设 MGMT 启动子甲基化的表观遗传沉默促进了 LGG 患者 TMZ 诱导的突变，并导致复发时出现超突变。
我们利用定量深度测序检测 37 例接受 TMZ 治疗的 LGG 患者初始肿瘤和治疗后复发的 109 例手术组织标本中的 MGMT 启动子甲基化情况。我们利用甲基化芯片验证我们的测序检测，利用 RNA 测序评估甲基化与基因表达的关系，利用外显子组测序确定超突变状态。
在发生超突变复发的患者的初始肿瘤中，MGMT 启动子的甲基化水平明显高于未发生超突变复发的患者（45.7%对 34.8%，P=0.027）。在单变量模型和包含患者年龄和分子亚型的多变量模型中，初始肿瘤中的甲基化水平可以预测复发时的超突变。
这些发现揭示了观察到的患者对 TMZ 驱动的超突变易感性差异的机制基础。此外，它们确立了 MGMT 启动子甲基化水平作为潜在的生物标志物，通过预测复发时的超突变风险，为 LGG 患者的临床管理提供信息，包括监测和治疗决策。
