To check the ability of the docking protocol in discerning between P-gp binders and non-binder compounds, a small dataset (186 compounds), comprised of 77 binders and 109 non-binders (thereafter referred to as "Validation set 1"), was retrieved from the literature . This dataset was used in a first-tier simulation to test the discriminant power of the docking protocol in classifying P-gp binders and non-binders. Subsequently, a second larger dataset of 3250 compounds with known activity (thereafter referred to as "Validation set 2", including 1243 P-gp inhibitors, 487 substrates, and 1520 non-binders) was retrieved from the literature and used to assess the discriminant power of the docking protocol in classifying substrate and inhibitors. The library used for the VS (thereafter referred to as "Screening set") was downloaded from the ZINC database . In particular, the tridimensional coordinates of 197374 commercially available natural compounds were obtained in mol2 format, which were then converted to PDBQT format using OpenBabel . An overview of the chemical properties of the different sets is reported in table .