Microchamber cell viability assay for suspension cells. (A) Calcein AM (green) and ethidium homodimer (red) were used to label live and dead RPMI 8226 cells, respectively, which were cultured and treated with bortezomib for 24 hours. (B) Cell viability after 24-hour treatment with bortezomib was dose-dependent with average IC₅₀ ∼ 22nM. Blue lines indicate dose-responses predicted by each of 3 independent experiments (n = 3; independent averages of duplicates). Error bars represent SE.