Multidrug resistance (MDR) is a common problem when fighting cancer with chemotherapy. P-glycoprotein (P-gp, or MDR1) is an active pump responsible for the efflux of xenobiotics out of the cell, including anti-cancer drugs. It is a validated target against MDR. No crystal structure of the human P-gp is available to date, and only recently several cryo-EM structures have been solved. In this paper, we present a comprehensive computational approach that includes constructing the full-length three-dimensional structure of the human P-gp and its refinement using molecular dynamics. We assessed its flexibility and conformational diversity, compiling a dynamical ensemble that was used to dock a set of lignan compounds, previously reported as active P-gp inhibitors, and disclose their binding modes. Based on the statistical analysis of the docking results, we selected a system for performing the structure-based virtual screening of new potential P-gp inhibitors. We tested the method on a library of 87 natural flavonoids described in the literature, and 10 of those were experimentally assayed. The results reproduced the theoretical predictions only partially due to various possible factors. However, at least two of the predicted natural flavonoids were demonstrated to be effective P-gp inhibitors. They were able to increase the accumulation of doxorubicin inside the human promyelocytic leukemia HL60/MDR cells overexpressing P-gp and potentiate the antiproliferative activity of this anti-cancer drug.

Department of Biology Faculty of Medicine Masaryk University Kamenice 5 A6 625 00 Brno Czech Republic

Department of Natural Drugs Faculty of Pharmacy Masaryk University Palackého 1946 1 612 00 Brno Czech Republic

International Clinical Research Center St Anne's University Hospital Brno Pekarska 53 656 91 Brno Czech Republic

Loschmidt Laboratories Department of Experimental Biology and Research Centre for Toxic Compounds in the Environment RECETOX Faculty of Science Masaryk University Kamenice 5 C13 625 00 Brno Czech Republic

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