Brazilein Overcame Abcb1-Mediated Multidrug Resistance In Human Leukaemia K562/Ao2 Cells

Multidrug resistance (MDR) was still a major obstacle to the success of chemotherapy in cancer treatment. One of the underlying mechanisms of MDR was cellular overexpression of ABCB1 transporter which pumped various anticancer drugs out of the cells. Here, we investigated the anticancer activity of brazilein (a compound isolated from Caesalpinia sappan Linn.) against human leukaemia K562 and ABCB1 overexpression K562/AO2 cells. Cytotoxicity of brazilein was examined using 3-(4, 5-dimethylthiazol-yl)-2, 5-diphenyltetrazolium bromide (MTT) assay. FITC-Annexin V/PI staining was used to detect apoptotic cells. The expression of ABCB1 was determined by western blotting and RT-PCR assays, respectively. Flow cytometry was used to determine the intracellular accumulation of doxorubicin. The ATPase activity of ABCB1 was estimated using Pgp-Glo (TM) Assay Systems. MTT and apoptotic analysis showed that brazilein exerted similar cytotoxicity against K562 and K562/AO2 cells. The IC(50) values were 5.45 +/- 0.36 and 5.62 +/- 0.43 mu mol/L for K562 and K562/AO2 cells, respectively. Western blotting and RT-PCR assays showed that brazilein did not affect the expression of ABCB1 in K562/AO2 cells. The fluorescence intensity assay demonstrated that brazilein did not promote the intracellular accumulation of doxorubicin. Luminescent ATPase assays proved that brazilein did not interfere with the ATPase of ABCB1. Our results showed that brazilein was not a substrate of ABCB1 and escaped the excretion of ABCB1 transporter to overcome ABCB1-mediated MDR. The present data suggested that brazilein would be promising to develop as an anticancer candidate for circumventing multidrug resistance.