GCS-100 removes cell-surface gal-3 from DLBCL cells. (A) Cytotoxicity of GCS-100. Viability of SUDHL-6 cells treated with GCS-100 for 24 hours over the indicated dose range was determined. At ≤ 75 μg/mL, GCS-100 showed no toxicity, while cell death to GCS-100 alone was observed at > 75 μg/mL. Values are means ± SD of triplicates from 1 of 3 independent experiments. (B) GCS-100 removes cell-surface gal-3. SUDHL-6 cells were treated with 75 μg/mL GCS-100 (thin line) or buffer control (thick line) for 24 hours and cell-surface gal-3 measured by flow cytometry. (C) Cell-surface gal-3 is repopulated by 1 hour after removal of GCS-100. SUDHL-6 cells were treated with 75 μg/mL GCS-100 for 24 hours. GCS-100 was washed out with PBS, and cells were treated with either 75 μg/mL GCS-100 or control for 1 hour at 37°C. Cells were fixed and cell-surface gal-3 was evaluated by flow cytometry. Cells that remained in GCS-100 (thin line) had less cell-surface gal-3 compared with cells that were washed out of GCS-100 (thick line). (D) Total gal-3 was examined by immunoblot after treatment of SUDHL-6 cells with 75 μg/mL GCS-100 or buffer alone. GCS-100 treatment did not appreciably alter the total amount of gal-3 in SUDHL-6 cells.