Updated project metadata. Tumor-initiating cells (TICs) play a critical role in glioblastoma (GBM) maintenance being responsible for its heterogeneity and resistance to standard therapy. A step toward clinical translation includes GBM TIC targeting. Among the molecules tested for GBM treatment, are those targeting epigenetic modifiers. By using patient-derived TICs and xenograft orthotopic models, we identified Lysine-specific histone demethylase 1A (LSD1) as a potentially druggable target in GBM. LSD1-directed therapy by means of the selective, orally bioavailable and brain penetrant inhibitor DDP_38003 effectively impairs growth, stem-like features and tumorigenic potential of GBM TICs. Our findings point to LSD1 as a positive regulator of Activating Transcription Factor 4 (ATF4)-dependent response in all stress conditions arising during tumor growth and therapy. Thus, through the downregulation of either ATF4 and its adaptive genes, LSD1 targeting is likely a promising strategy to hit GBM TICs by counteracting the ATF4-mediated adaptation to stress.