Topotecan was capable of significantly decreasing the levels of SUMO-1 conjugation at both the 1 μM and 10 μM doses in all three human GBM lines (Fig. 3A,B and C) and SUMO-2/3 conjugation in all three human GBM lines at the 10 μM dose (Fig. 3A,B and C). Here, SUMO1 is linked to glioblastoma.