SOX2 and glioblastoma: The specificity of the effects of the tested drugs against GSC subpopulation was further demonstrated showing that 24 h treatment of GBM1 and GBM2 cultures with metformin, phenformin, cycloguanil, and moroxydine significantly reduced the expression of Sox2 (Supplementary Figure S2), a specific GSC marker, which is down-regulated in differentiated GBM cells (Banelli et al., 2015).