Additionally, in vitro experiments validated the relationship between GLS2 and 5-ALA fluorescence/PpIX accumulation in GBM cell lines, thus demonstrating that insufficient NADPH production, a major determinant of the heterogenous 5-ALA/PpIX fluorescence in correlation with GLS2 underexpression is a major determinant of the heterogeneous 5-ALA/PpIX fluorescence. Here, GLS2 is linked to glioblastoma.