Reversal of P-glycoprotein mediated multidrug resistance by pinoresinol in chronic myeloid leukemia cells.

GONZÁLEZ M.; VERA M.; JORAY M.; MACCIONI M.; PALACIOS S; CARPINELLA M

Encuentro; 3° Reunión Internacional de Ciencias Farmacéuticas RICIFA.; 2014

The overexpression of P-glycoprotein (P-gp) in tumor cells is one of the major mechanisms of multidrug resistance (MDR) leading to cancer chemotherapy failures. This MDR pump extrudes out of cells a wide range of anticancer drugs by an ATP-dependent mechanism, resulting in a decreased intracellular concentration of these agents. This fact has encouraged the development of effective MDR reversal agents. Little has been reported about the use of compounds isolated from plants of Argentina as MDR inhibitors. The aim of this study was to evaluate the ability of 15 compounds, isolated from native and naturalized plants of central Argentina, to reverse P-gp mediated MDR using doxorubicin (DOX) as a P-gp substrate. For this purpose, the chronic myeloid leukemia cell line K562 and its MDR variant due to P-gp overexpression, Lucena 1, were used. The effect of the compounds on DOX cytotoxicity in Lucena 1 was evaluated by MTT. Pinoresinol (1), isolated from the ethanolic extract of Melia azedarach, showed a high effectiveness, causing a decrease of 9.4 times in the IC50 of DOX in Lucena 1 at 40 µg/mL, showing the same level of activity as that of the commercial modulator verapamil. This result was confirmed by flow cytometry as a significant increase in the intracellular DOX accumulation in MDR cells treated with 1. Docking studies revealed that 1 binds to aromatic residues of P-gp involved in a "v" vortex formed by the trans-membrane -helices 4, 5 and 6. Also, P-gp ATPase activity was proved to be inhibited by 1 with an IC50 of 7.5 µg/mL. No effect was found on P-gp expression. In addition, 1 did not affect cell viability of fresh human lymphocytes up to 160 µg/mL. The results suggest that compound 1 has great potential to be further developed as a P-gp inhibitor.