Western blot analysis was carried out as described previously.18 (link) Cell lysates were prepared using ice-cold lysis buffer. Total protein was separated by 8% SDS polyacrylamide gel electrophoresis and then transferred into nitrocellulose membranes (Millipore, Shanghai, China). The following antibodies were used: anti-multidrug resistance associated protein 1 (anti-MRP1, ab233383), anti-P-glycoprotein (anti-P-gp, ab216656), anti-lung cancer-related protein (anti-LRP, ab92544), anti-KLF12 (ab129459), anti-β-actin (ab8227) and horseradish peroxidase-conjugated IgG secondary antibody (ab150077, all from Abcam, Cambridge, UK).