(A) Western blot showing that MDR1 expression was high in MDA-MB-231R cells and almost non-existent in MDA-MB-231 cells. Left panel: image; right panel: quantification. (B) After treatment with 0.01-2.0 μM THP, a higher survival percentage was observed for the MDA-MB-231R subclone than for the parental MDA-MB-231 cells a. (C) CCK-8 assay results. MDA-MB-231R grew more than MDA-MB-231 after treatment with 0.1 μM THP. (D) Treated with 0.3 μM THP, MDA-MB-231R cells maintained the ability to grow, but MDA-MB-231 cells gradually died. (E) MDA-MB-231R cell growth decreased after 48 h of treatment with 0.9 μM THP, and MDA-MB-231 cells rapidly died. (F) After treatment with 0.1, 0.3, and 0.9 μM THP, MDA-MB-231R cells formed more clones than MDA-MB-231 cells did. **P<0.01; ***P<0.001.