The emergence of multidrug resistance (MDR) is a big challenge to cancer chemotherapy. Plant-derived agents have great potential to prevent onset or delay progression of the carcinogenic process, and enhance the efficacy of mainstream antitumor agents. In this study, fractionated extracts of Curcuma wenyujin and Chrysanthemum indicum were tested for their potential to modulate the MDR phenotype and function of P-gp in MCF-7/ADR and A549/Taxol cells in vitro. Fractions C. wenyujin C10, E10 from Curcuma wenyujin, and C. indicum E10 from Chrysanthemum indicum, exhibited significant effects in sensitization of these resistant cancer cells at non-toxic concentration to doxorubicin and docetaxel by MTT method. They also increased the intracellular doxorubicin accumulation and retention in MCF-7/ADR cells. In mechanism study, an increase of Rh123 accumulation and a decrease of Rh123 efflux were observed in MCF-7/ADR cells treated with these fractions, indicating a blockage of the activity of P-gp. Furthermore, C. wenyujin C10 had the ability to down-regulate the expression of P-gp. All these fractions could enhance the apoptosis induced by doxorubicin in MCF-7/ADR cells, and restore the effect of docetaxel on the induction of G2/M arrest in A549/Taxol cells. C. wenyujin C10 and E10 also owned the ability to induce S phase arrest. These results showed the therapeutic value of the three fractions as potential MDR-reversing agents and warranted further investigations.
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