Resistance to doxorubicin occurs via ABCB1-dependent and ABCB1-independent mechanisms.

<p>(<b>A, B</b>) ABCB1 was inhibited with verapamil (<b>A</b>) or silenced with siRNA (<b>B</b>), cells were treated with imatinib (10 µM) and/or doxorubicin (0.5 µM) for 72 h, and cell viability assessed. Mean±SEM from 3 independent experiments. (A) Dox+imatinib, CI = 0.66±0.19; Dox+verapamil, CI = 0.14±0.04; Dox+imatinib+verapamil, CI = 0.47±0.5. Representative Western blot (right). Some error bars are too small to visualize.