Fig. 1
Doxorubicin sensitivity for various cell lines with or without the autophagy inhibitor chloroquine. The sensitivity of MCF-7DOX2 cells to doxorubicin was measured using a clonogenic assay. Cells were selected in increasing concentrations of doxorubicin to selection doses 7 (6.5 nM), 8 (19 nM), 9 (29 nM), 10 (44 nM), 11 (65 nM) and 12 (98.1 nM). The doxorubicin sensitivity of MCF-7 cells selected in the absence of doxorubicin to a passage number equal to dose level 10 (MCF-7CC10 cells) was also assessed (panels a and b). The sensitivity of the MCF-7DOX2–10 and MCF-7CC10 cell lines to doxorubicin in the absence or presence of chloroquine was also assessed (c). Chloroquine was dissolved in water, thus negating the need for a vehicle control in these experiments. Resistance factors represent the extent of resistance to doxorubicin, as calculated by dividing the IC50 of the drug-selected cell lines by the IC50 for its co-cultured control at the same passage number. The data points in Fig. 1a represent the average (± S. E.) of six independent experiments. The data points in Fig. 1b and c are representative of three independent experiments