Cells were seeded at 1.0×105 cells/well in a 24-well culture plate and incubated for 48 h. Cells were treated with Hoechst 33342 cell-permeable nuclear counterstain dye for 10 min, and images were acquired using a fluorescence microscope equipped with a CoolSnap-Pro color digital camera (Media Cybernetics, Rockville, MD, USA). The apoptotic index was calculated using a formula as described previously (Piao et al., 2019 (link)).