MGMT and glioblastoma: Based on bisulfite sequencing analysis, XAF1 promoter methylation status transitioned from a hypermethylated to a hypomethylated status when MGMT-hyper (U251) GBM cell lines transitioned from the treatment naïve (Ctrl) to adaptively resistant (TMZ-R) status, especially in −1572 to −1781 region (Fig. 4d).