Reversal of P-Glycoprotein-Mediated Multidrug Resistance by Protopanaxatriol Ginsenosides from Korean Red Ginseng

Abstract

The overexpression of P-glycoprotein (Pgp) or the multidrug resistance-associated protein (MRP) confers multidrug resistance (MDR) to cancer cells. MDR cells can be sensitized to anticancer drugs when treated concomitantly with an MDR modulator. In this study, we investigated whether or not ginseng saponins could reverse MDR mediated by Pgp or MRP. The chemosensitization and drug accumulation effects of ginseng saponins such as the total saponin, protopanaxadiol ginsenosides (PDG), protopanaxatriol ginsenosides (PTG), ginsenosides-Rb₁, -Rb₂, -Rc, -Rg₁ and -Re were tested on the daunorubicin- and doxorubicin-resistant acute myelogenous leukemia sublines (AML-2/D100 and AML-2/DX100), which overexpress Pgp and MRP, respectively. PTG showed cytotoxicity in both sublines and was able to reverse resistance in the AML-2/D100 subline in a concentration-dependent manner. Conversely, other ginseng saponins at concentrations less than 300 μg/mL showed neither cytotoxicity nor chemosensitizing activity in both resistant sublines. Flow cytometry analysis showed that the effect of PTG (100 μg/mL) on drug accumulation of daunorubicin in the AML-2/D100 subline was 2-fold higher than that observed in the presence of verapamil (5 μg/mL) and 1.5 times less than cyclosporin A (3 μg/mL). The maximum non-cytotoxic concentrations of PTG did not appear to increase the Pgp levels, which is in contrast to verapamil and cyclosporin A. PTG at 200 μg/mL or more completely inhibited the azidopine photolabeling of Pgp. The results suggest that PTG has a chemosensitizing effect on Pgp-mediated MDR cells by increasing the intracellular accumulation of drugs through direct interaction with Pgp at the azidopine site. In addition, PTG may have a beneficial effect on cancer chemotherapy with respect to the possibility of long-term use without the concern of Pgp activation.

Abbreviations

AML:acute myelogenous leukemia

DX:doxorubicin

MDR:multidrug resistance

MRP:multidrug resistance-associated protein

MTT:3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium
bromide

PAGE:polyacrylamide gel electrophoresis

PDG:protopanaxadiol ginsenosides

Pgp:P-glycoprotein

PTG:protopanaxatriol ginsenosides

SDS:sodium dodecyl sulfate

Key words

Multidrug resistance - P-glycoprotein - multidrug resistance-associated protein - ginseng saponins - ginsenosides - drug accumulation

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