DNA methylation-based age acceleration observed in IDH wild-type glioblastoma is associated with better outcome - including in elderly patients

Elderly patients represent a growing proportion of individuals with glioblastoma, who however, are often excluded from clinical trials owing to poor expected prognosis. Little is known about molecular features that would justify different treatment modalities, not related to frailty and co-morbidities. We investigated the DNA methylome (450k) for age related associations using 4 different glioblastoma datasets (mean age, years: DKFZ, 60; TCGA, 62; Nordic, 71; EORTC-26981/NCIC-CE.3 & Lausanne-Pilot, 54), including two are cohorts from clinical trials. We excluded patient samples not compatible with glioblastoma grade 4 WHO-CNS-5 classification 2021. The combined methylome was interrogated for differences based on age, DNA methylation (DNAm) age acceleration (DNAm age “Horvath-clock” minus patient age), methylation-based classification (Heidelberg), entropy, and functional methylation of DNA damage response (DDR) genes. Age dependent methylation included 19 CpGs (p-value≤0.1, Bonferroni corrected), comprising ELOVL2 that is part of a 13-gene forensic age predictor. Three CpGs met our criteria of functional methylation defined as correlation of methylation with expression (r≤-0.3) of the corresponding gene. Most of the age related CpGs (n=16) were also associated with age acceleration that itself was associated with a large number of CpGs (n=50551). Over 70% age acceleration-associated CpGs (n=36348) overlapped with those associated with the methylation based tumor classification (n=170759). Functional methylation of few DDR genes was associated with age acceleration (n=8), tumor classification (n=12), or both (n=4), the latter including MGMT . DNAm age acceleration was significantly associated with better outcome in the trial cohorts of the EORTC/NCIC & Lausanne Pilot, and Nordic (treating elderly patients). Multivariate analysis included treatment (RT, RT/TMZ→TMZ; TMZ, RT), MGMT promoter methylation status, and interaction with treatment. In conclusion, DNA methylation features of age acceleration are an integrative part of the methylation-based tumor classification (RTK I, RTK II, MES), while age seems hardly reflected in the glioblastoma DNA methylome.