Plant extracts and betulin from Ligaria cuneifolia inhibit P-glycoprotein function in leukemia cells

• Published in: Food and chemical toxicology Vol. 147; p. 111922
• Main Authors: Laiolo, Jerónimo, Barbieri, Cecilia L., Joray, Mariana B., Lanza, Priscila A., Palacios, Sara M., Vera, D. Mariano A., Carpinella, María C.
• Format: Journal Article
• Language: English
• Published: England Elsevier Ltd 01.01.2021
• Subjects: Betulin; Betulinic acid; Leukemia cells; Molecular modeling; Multidrug resistance reversal; P-glycoprotein; ABC; Betulin; Leukemia cells; CML; P-gp; Rho123; MEC; RMSD; TMD; Dox; FR; PBMC; FIR; TMH; P-glycoprotein; MFI; PB; Molecular modeling; Betulinic acid; IC50; MD; MDR; GB; Multidrug resistance reversal
• ISSN: 0278-6915; 1873-6351
• DOI: 10.1016/j.fct.2020.111922

Overexpression of P-glycoprotein (P-gp), which is linked to multidrug resistance (MDR), is one of the underlying obstacles to the success of chemotherapy as it reduces the efficacy of anticancer drugs and the side effects of these increase as a result of any increased dose to achieve the therapeutic effect. To identify agents with P-gp inhibitory properties, ethanol extracts from 80 plants were screened for their ability to increase intracellular doxorubicin-associated fluorescence, and the extract of Ligaria cuneifolia was found to be the most effective. Its bioassay-guided isolation yielded the pentacyclic triterpene betulin as active agent. This efficiently inhibited P-gp mediated efflux, as demonstrated by the enhancement of the intracellular accumulation of doxorubicin and rhodamine 123 from 1.56 μM in the P-gp overexpressing MDR leukemia cell, Lucena 1. Betulin was also able to render Lucena 1 sensitive to Dox from 0.39 μM. The docking studies revealed that betulin tightly binds to a key region of the TMDs, with a binding mode overlapping one main site of doxorubicin and, more interestingly, emulating the same contacts as tariquidar, as revealed by the per-residue energetic analysis from molecular dynamics simulations. MTT assay using peripheral blood mononuclear cells and hemolysis assay showed that betulin is devoid of toxicity. These findings provide important evidence that betulin may be a safe and promising entity to be further investigated to develop agents able to overcome P-gp-mediated MDR, resulting in a more effective and less toxic chemotherapy. [Display omitted] •Extracts from 80 mostly native plants from Argentina, were screened for their P-gp inhibitory activity.•The extract from Ligaria cuneifolia was one of the most effective and the bioguided isolation of this yielded the non-cytotoxic betulin as its active principle.•Betulin increased the intracellular accumulation of doxorubicin and rhodamine 123 and render the P-gp overexpressing MDR leukemia cell, Lucena 1, sensitive to doxorubicin.•Betulin tightly binds to a key region of the transmembrane domains of P-gp.