A–D. CHO K1 and A549 cell lines display increased chemoresistance toward the cytotoxic drugs that are mostly associated with MDR: doxorubicin (panel A), taxol (panel B), vincristine (panel C), and mitoxantrone (panel D).

<p>The U-2 OS cell line demonstrates moderately increased chemoresistance to a few drugs associated to MDR, such as doxorubicin (panel A) and mitoxantrone (panel D). The HeLa cell line was used as a non-chemoresistant control specimen. Cells were seeded in 96 well plates, treated with the different doses of indicated drugs, and a standard MTT viability test was performed 1 and 2 days post-treatment. Results are presented as a ratio of the OD₅₉₅ of treated cells to the OD₅₉₅ of the untreated cells.