FIGURE 3.

Sensitization of resistant cancer cells to chemotherapy by selected 3,4-dihydroisocoumarins. (A) P-gp expressing HCT-15 and (B) BCRP-expressing MCF-7/MX were treated with either doxorubicin or mitoxantrone alone, in combination with positive controls PSC833 or Ko143 or in combination with varying concentrations of test compounds 16 and 14. Cell viability was determined after 48 h. Data represent mean ± SEM normalized to untreated cells of at least three independent experiments performed in quadruplicates.