(A) (a) The molecular formula of the anthracycline pirarubicin. (b) The morphology of MDA-MB-231 cells treated with 3.0 μM THP for 72 h was intact; 6 days later, all cells died. (c) Cells treated with 5.0 μM THP became round and small after 72 h and ultimately died. (d) All cells treated with 7.0 μM THP for 72 h died. (B) (a and b) Images of MDA-MB-231 cells treated with 0.1 or 0.2 μM THP for 4 days showing slight cell morphology changes. (c) Images of cells treated with 6.0 μM THP for four days. All cells lost their nuclei and became small; the cell morphology changed, and all cells died. (d–f) Images of cells treated with 0.8 μM THP for 4 (d), 7 (e) and 15 (f) days. After treatment with 0.8 μM THP, cells initially became bigger, then smaller, and finally formed greater numbers of larger cells. (C) (a) The parental MDA-MB-231 cells were cultured for 24 h; (b) MDA-MB-231R cells were derived from MDA-MB-231 cells after 20 days of treatment with 0.8 μM THP.