Removal of cell-surface gal-3 with GCS-100 sensitizes DLBCL cells to cell death. (A) To remove cell-surface gal-3, SUDHL-6 and SUDHL-9 cells were treated with 75 μg/mL GCS-100 or buffer alone for 1 hour before addition of dexamethasone (dex) and analyzed for annexin V staining 24 hours later. SUDHL-6 cells were relatively resistant to dex alone (left panel, thin line) compared with control treatment (left panel, gray); however, treatment with GCS-100 before dex increased the fraction of annexin V–positive cells (left panel, thick line). SUDHL-9 cells were resistant to dex alone (right panel, thin line) compared with control treatment (right panel, gray) and no increase in annexin V binding was observed after treatment with GCS-100 plus dex (right panel, thick line). (B-D) SUDHL-6 cells were treated with increasing doses of GCS-100 for 1 hour before treatment with (B) 10μM dex, (C) 5 μg/mL rituximab, or (D) 1μM etoposide for 24 hours. Cells were analyzed for annexin V binding and PI uptake. Viability was determined as described in “Methods”; **P < .001, ***P < .0001. (E-F) Removal of cell-surface gal-3 with GCS-100 permitted caspase-8 activation. Caspase-8 activation was determined in SUDHL-6 cells treated with GCS-100 or buffer control and (E) dex or (F) rituximab; **P < .001. In panels B through F, values are mean ± SD of triplicate samples from 1 representative of 3 independent replicate experiments.