Fig. 1.

CoCl₂ increases the resistance of HL-60 to Actinomycin-D (Act-D). (A) HL-60, U937, K562, and CCRF-CEM cells were cultured for 8 hrs with or without CoCl₂ (100 µM) and for additional 15 hrs in the presence of Act-D (1 µg/mL). Cells were then analyzed for PI negative population by flow cytometry. CTR, control. (B) HL-60 cells were pre-treated with various doses of CoCl₂ for 8 hrs and then cultured for 15 hrs with indicated doses of Act-D. Cell viability was evaluated by the MTT assay. The relative viable cell number was calculated as the ratio of each optical density (OD) to the control OD. Results are expressed as relative viability±SEM. An asterisk (*) represents statistical significance when the P-value is lower than 0.05.