To analyze whether the S1PR1 modulator ACT-209905 influences the growth behavior of GBM cells in vitro, we determined the viability (resazurin assay) and vitality (crystal-violet staining) of both human (LN-18, U-87MG) and mouse (GL251) GBM cell lines, as well as primary human GBM cells. This evidence concerns the gene S1PR1 and glioblastoma.