STAT3 and central nervous system cancer: To evaluate whether PS modification is required for high efficiency of PS-modified STAT3 peptide penetration into tumor cells, the cell-penetrating efficiency and fluorescence intensities of fluorescein-labeled (FAM-labeled) PS- and PO-modified acet.-STAT3 peptide in human colon cancer HCT116 (Figure 1A) and human glioma U251 (Supplemental Figure 2) cells were measured by flow cytometry after 15 minutes’ incubation under general cell culture conditions.