MMC survival curves of Dox-responsive clone-derived cell lines. (A) Clone D3–derived cell lines, without Dox, (B) D3-derived cell lines at 500 ng/mL Dox, (C) clone E1–derived cell lines at 31 ng/mL Dox, and (D) clone I15–derived cell lines at 125 ng/mL Dox. Error bars indicate SEM.