Intracellular levels of doxorubicin or doxorubicinol in the presence or absence of 5β-cholanic acid or cyclosporine A, measured by HPLC. MCF-7CC12 and MCF-7DOX2-12 cells were treated for 24 h with 0.5uM doxorubicin or doxorubicinol, 200uM 5β-cholanic acid, and/or 5uM cyclosporine A. After treatment, cellular and media extracts were prepared and assessed for doxorubicin or doxorubicinol content by HPLC: (A) Treatment with doxorubicinol and 5β-cholanic acid: 1 = no treatment; 2 = 0.5uM doxorubicinol; 3 = 0.5uM doxorubicinol and 200uM 5β-cholanic acid, (B) Treatment with doxorubicin, 5β-cholanic acid, and/or cyclosporine A: 1 = no treatment; 2 = 0.5uM doxorubicin; 3 = 0.5uM doxorubicin + 200uM 5β-cholanic acid; 4 = 0.5uM doxorubicin + 5uM cyclosporine A; 5 = 0.5uM doxorubicin + 200uM 5β-cholanic acid + 5uM cyclosporine A. The symbol # represents differences between MCF-7CC12 and MCF-7DOX2-12 cells (treatment 2) with a p value ≤ 0.01. The symbols * and ** represent significant differences between treatments at p values of ≤ 0.05 and ≤ 0.01, respectively.