HIF1A and glioblastoma: To further determine the drug sensitivities of hypoxic cell subpopulations in glioblastoma xenografts, Hoechst 33342 staining and HIF-1 activation labeling together with immunofluorescence imaging and fluorescence-activated cell sorting were utilized to isolate hypoxic tumor subpopulations from human glioblastoma xenografts as described in our previous studies [6, 13, 14].