Figure 7.
In vitro cytotoxicity assays. (A) m860ADC is more cytotoxic (IC50 0.032nM) than the free drug (nAF) (IC50 0.096nM) to HER2-overexpresing SK-BR-3 cells, while the WT IgG1 m860 does not show any cytotoxicity. (B) m860ADC shows cytotoxicity only at relatively high concentration to MCF-7 cells, while the free drug with linker alone shows significant cytotoxicity to MCF-7 cells (IC50 0.26nM). (C) Cytotoxicity assay on JIMT-1 cells. The JIMT-1 cell line was isolated from a Trastuzumab resistant patient, this cell line shows moderate HER2 expression compared with SK-BR-3. m860ADC can still potently kill JIMT-1 cells (IC50 0.087nM), while the IgG1 m860 alone has little effect on the cells. (D) Cell killing activities of m860ADC and T-DM1 were compared side by side on SK-BR-3 cells, the IgG1 m860 and an irrelevant ADC were used as control. The IC50s for m860ADC and T-DM1 are respectively 0.038nM and 0.095nM under these test conditions. (E and F) Serum stability of m860ADC was evaluated through cell killing assay using m860ADC samples collected after incubation in human serum for up to 30 d on HER2-positive SK-BR-3 cells and samples collected at day 0, 5 and 9 were assayed on HER2-negative Kelly cells. (G) Serum stability of T-DM1 was also evaluated and compared side by side with m860ADC.