To find novel P-gp-inhibitors, a library of pregnane X receptor (PXR) ligands and the ZINC DrugsNow library were superimposed on the P-gp inhibitor (+)-pinoresinol (<b>1</b>) used as a query for a three-dimensional similarity search. After determining the TanimotoCombo index of similarity with <b>1</b>, eight compounds from the PXR library and two ZINC compounds were selected for biological evaluation. The P-gp inhibition study showed that compounds <b>7</b>, <b>8</b>, and <b>9</b> successfully increased intracellular doxorubicin (DOX) accumulation in the P-gp overexpressed Lucena 1 cells from 25, 12.5, and 6.25 μM, respectively. Among a series of analogues of <b>9</b>, compounds <b>26</b>-<b>30</b> were shown to be active, with <b>26</b> and <b>27</b> causing a significant increase in DOX accumulation from 1.56 μM and rendering Lucena 1 sensitive to DOX from 1.56 and 0.78 μM, respectively. Molecular modeling studies showed that both compounds bind to the P-gp at transmembrane helices (TMH) 4, 5, and 6, with <b>27</b> also showing contacts with TMH 3.