S1PR1 and glioblastoma: As shown in Supplementary Figure S1, the treatment of LN-18 GBM cells with ACT-209905 also resulted in a strongly reduced S1PR1 protein expression, as determined by immunoblot analysis (Supplementary Figure S1a, 72 h, 10 μM of ACT209905) and immunofluorescence staining in most of the cells (Supplementary Figure S1b, 48 h, 20 μM of ACT-209905).