Abstract

Background

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.

Methods

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.

Results

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.

Conclusions

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.

中文翻译：

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新诊断的低级别胶质瘤中的 MGMT 启动子甲基化水平是复发时超突变的预测因子。

摘要

背景

新出现的数据表明，一部分接受替莫唑胺 (TMZ) 辅助治疗的弥漫性异柠檬酸脱氢酶 (IDH) 突变低级别胶质瘤 (LGG) 患者复发，并伴有与恶性进展为更高级别肿瘤相关的超突变。目前尚不清楚为什么一些接受 TMZ 治疗的 LGG 患者会因超突变而复发，而另一些则不会。MGMT编码 O6-甲基鸟嘌呤-DNA 甲基转移酶，这是一种 DNA 修复蛋白，可去除由 TMZ 诱导的细胞毒性和潜在诱变损伤。在这里，我们假设通过启动子甲基化对MGMT的表观遗传沉默促进了 LGG 患者中 TMZ 诱导的突变，并有助于复发时超突变的发展。

方法

我们利用定量深度测序分析来表征109 个手术组织标本中的MGMT启动子甲基化，这些标本来自 37 名接受 TMZ 治疗的 LGG 患者的初始肿瘤和治疗后复发。我们利用甲基化阵列来验证我们的测序分析，利用 RNA 测序来评估甲基化与基因表达之间的关系，并利用外显子组测序来确定超突变状态。

结果

在复发时发生超突变的患者的初始肿瘤中，MGMT启动子的甲基化水平显着高于未发生超突变的患者的初始肿瘤（45.7% 对 34.8%，P = 0.027）。在包含患者年龄和分子亚型的单变量模型和多变量模型中，初始肿瘤中的甲基化水平可以预测复发时的超突变。

结论

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，他们将MGMT启动子甲基化水平确立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。