P04.84 Lysine-specific Histone Demethylase 1 (LSD1) Contributes to the Maintenance of Glioblastoma Stem Cell Population

Glioblastoma (GBM) is the most common, lethal and recurrent primary brain tumor in adults (median survival: 12–15 months, recurrence rate: 90%). Its dismal prognosis is, at least in part, due to the inefficacy of current therapies against GBM tumor initiating cells (TICs), a sub-population of GBM cells able to sustain GBM growth and relapse owing to their stem cell-like phenotype. Lysine specific histone demethylase 1 (LSD1) is an epigenetic regulator that sustains stem cell-like traits, cell proliferation and tumorigenesis, and whose overexpression has been reported in many tumors, including GBM. Notably, drugs that modify LSD1 activity are already available even if their applications are still at their infancy. Altogether, these observations prompted us to study the role of LSD1 in the GBM TIC maintenance. We targeted LSD1 using a chemical inhibitor and confirming the results by shRNA-mediated silencing and CRISPRCas9-mediated knock-out. We studied the biological significance of LSD1 in GBM TICs isolated from fresh GBM samples in vitro(cell proliferation, clonogenic capacity, stem cell frequency byExtreme Limiting Dilution Assay [ELDA algorithm]) and in vivo (orthotopic injection in immunocompromised mice). RNA-sequencing and Chromatin Immuno-Precipitation(ChIP)-sequencing were used to identify possible molecular targets. Differences in LSD1 expression were analyzed by analysis of variance (ANOVA). Kaplan-Meier analyses and log-rank test were used to assess mice survival. All other statistical tests were two-sided t-tests. We found that LSD1 is up-regulated in human GBM tissues and patient-derived TICs compared to normal counterparts. LSD1 targeting does not affect GBM TIC viability and proliferation, but reduces the stem cell frequency -both in vitroand in vivo-and prolongs the survival of GBM-patient-derived xenograftmodels. Preliminary data from RNA-sequencing and ChIP-sequencing provided a list of putative mediators of LSD1 biological activity, including genes known to be important for GBM biology and stemness maintenance. Our results highlight the importance of LSD1 for GBM TIC maintenance and GBM formation through mechanisms that are now under investigation. The importance of GBM TICs for GBM initiation and progression, together with LSD1 targetable nature, shed light on the therapeutic potential of LSD1 inhibitors for GBM management. Italian Association for Cancer Research (AIRC)