Cell viability assay
The cell viability assay was performed using the Cell Counting Kit-8 (Proteintech Group, Inc, USA). Briefly, the ESCC cells were seeded into 96-well plates at 6×103 cells/well and incubated under standard culture conditions for 24 h, then the cells were treated with gradient concentrations of ixazomib for 24-72 h. After treatment, 10 µl of CCK-8 solution was added into each well of the 96-well plate and incubated for 1 h at 37°C. The optical density (OD) values were detected at 450 nm using a microplate reader (Biotek, Winooski, VT, USA). Each experiment was independently repeated three times with five replicates.