In the present study, we investigated the responsiveness of human GBM cell lines to a novel small-molecule MDM2 inhibitor with a spirooxoindolepyrrolidine core structure, named ISA27, which has been recently shown by nuclear magnetic resonance (NMR) analysis to efficiently dissociate the reconstituted human MDM2-p53 complex [26]. This evidence concerns the gene MDM2 and glioblastoma.