ABCB1 and non-small cell lung carcinoma: The cytotoxic activity of 6β,7α-dihydroxyroyleanone (7), 7α-acetoxy-6β-hydroxyroyleanone (8), 7α-formyloxy-6β-hydroxyroyleanone (10), and coleon U (183) was assayed in metastatic breast cancer MDA-MB-231, estrogen-dependent breast carcinoma MCF-7, colorectal carcinoma HCT116, normal human embryonal bronchial epithelial cells MRC-5, non-small cell lung carcinoma NCI-H460, and the multidrug-resistant non-small cell lung carcinoma cell line with P-glycoprotein overexpression NCI-H460/R.