To investigate the interactions that involve the two copies of zosuquidar within the site, we performed additional re-docking simulations, using the recently developed version of AutoDock Vina (v1.2.0) , which features the possibility to dock multiple ligands simultaneously. As shown in Fig. , by docking two molecules of zosuquidar, we obtained a significant improvement of the molecule pose in position 2, reducing its RMSD value from 5.3 Å to 2.2 Å. Noticeably, the pose in position 1 showed an RMSD value of 3.8 Å, compared to the original conformation. While for this pose the software still was not able to reproduce the orientation of the quinolone moiety, the RMSD of the DTP moiety alone was 1.5, confirming the ability of Vina to correctly place this portion of the ligand in the binding site. These results further support the assumption that both the docking protocol and the Vina force fields can be considered sufficiently reliable for this target, and therefore Vina was chosen for performing the VS.