PGP and carcinoma: To do so, we assessed the anti-proliferative activity of three different QA derivatives (denoted by QA1, QA2, and QA3; Figure 1) against ovarian and P-glycoprotein (PGP)-overexpressing human carcinoma cell lines (A2780 and A2780AD, respectively), lung carcinoma A549, and NIH mouse embryo 3T3 cells using an MTT (3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide)-based assay.