Having ADCs with cleavable and non-cleavable linkers in place, we next assessed there in vitro cytotoxicity activities using SSEA4-expressing ovarian SKVO3 cells and breast cancer cells SKBR3 with a negligible expression of SSEA4 and 293T cells as a control. SK-OV3, SKBR3, and 293T cells (2×103 cells/well) were incubated with ADC-1, ADC-2, and chMC-813-70 for 72 h and then treated with MTS at 37 °C. The conversion of the tetrazolium salt MTS (3- (4,5-dimethylthiazol-2-yl)-5- (3-carboxymethoxyphenyl)-2- (4-sulfophenyl)-2H-tetrazolium) to a purple formazan, as a measure of the percentage of viable cells, was measured by absorbance at 490 nm after 4 h. The untreated cells' absorbance was considered 100 % survival (Figure 4).