Analogues of the Lignan Pinoresinol as Novel Lead Compounds for P-glycoprotein (P-gp) Inhibitors

Abstract

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 (1) used as a query for a three-dimensional similarity search. After determining the TanimotoCombo index of similarity with 1, eight compounds from the PXR library and two ZINC compounds were selected for biological evaluation. The P-gp inhibition study showed that compounds 7, 8, and 9 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 9, compounds 26-30 were shown to be active, with 26 and 27 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 27 also showing contacts with TMH 3.

Figure 1

Chemical structures of (+)-pinoresinol (1), the PXR ligands 2–9, and the ZINC compounds 10–25 showing high similarity with 1 by ROCS analysis.

Figure 2

Chemical structures of the diethylstilbestrol derivatives: 26–34.

Figure 3

Dose–response curves for cytotoxicity of doxorubicin (DOX) in Lucena 1 and K562 cells with and without compounds 26 (A) and 27 (B) as determined by the multidrug resistance reversal assay. Values are expressed as mean ± SE of at least three independent experiments.

Figure 4

(A) Superimposition of the lowest energy poses of the inhibitors 1 (highlighted in red), 26 (in yellow), 27 (in violet), and the reference inhibitor tariquidar (in green). (B) Binding of the most active compound 27 (balls and sticks) showing its main contacts (licorice). The cartoon representation of the α-helices is colored according to the sequence, from TMH 1 (red) to TMH 12 (blue).