GO-203 resensitizes BTZ-resistant cells to BTZ treatment. (A-D) U266/BR (A) and RPMI8226/BR (C) cells were treated with (1) the indicated concentrations of GO-203 alone each day for 72 hours, (2) the indicated concentrations of BTZ alone for 24 hours, and (3) GO-203 for 48 hours combined with BTZ for an additional 24 hours. Mean cell survival was assessed in triplicate by Alamar blue assays. Numbers in the graphs (left) represent combinations listed in the table (right). U266/BR (B) and RPMI8226/BR (D) cells were treated with 2.5 μM GO-203 alone, 20 (U266/BR) or 16 (RPMI8226/BR) nM BTZ alone, and the GO-203/BTZ combination. Cells were incubated with PI and annexin V and analyzed by flow cytometry. The results are expressed as the percentage (mean ± SD of 3 determinations) of dead cells. (E) ANBL-6/BR cells were left untreated (CTL) and treated with 2.5 μM GO-203 alone each day for 48 hours, 5 nM BTZ for 24 hours, or GO-203 for 24 hours combined with BTZ during an additional 24 hours. Cells were incubated with PI and annexin V and analyzed by flow cytometry. The results are expressed as the percentage (mean ± SD of 3 determinations) of dead cells. (F) OPM-2/BR cells were left untreated (CTL) and treated with 2.5 μM GO-203 alone each day for 72 hours, 7 nM BTZ for 24 hours, or GO-203 for 48 hours combined with BTZ during an additional 24 hours. Percentage growth inhibition (mean ± SD of 3 determinations) was determined by Alamar blue staining.