Reversion of multidrug resistance in a chemoresistant human breast cancer cell line by ß-elemene.

BACKGROUND: Multidrug resistance (MDR) presents a problem in cancer chemotherapy, and developing new agents to overcome MDR is important. This study intends to investigate the reversal effect of -elemene on MDR in human breast carcinoma MCF-7 and doxorubicin-resistant MCF-7 cells. METHODS: MTT cytotoxicity assays, flow cytometry, and Western blot analysis were performed to investigate the antiproliferative effects of the combination of anticancer drugs with -elemene, to study the reversal of drug resistance, and to examine the inhibitory effects on protein expression. RESULTS: The results showed that -elemene (30 µ mol/l) had a strong potency to increase the cytotoxicity of doxorubicin to MCF-7/DOX cells, with a reversal fold of 6.38. In addition, the mechanisms of -elemene in reversing P-glycoprotein (Pgp)-mediated MDR demonstrated that -elemene significantly increases the intracellular accumulations of doxorubicin and Rh123 via inhibition of the P-gp transport function in MCF-7/DOX cells. Flow cytometry and Western blot analyses revealed that -elemene could inhibit the expression of P-gp, while it had little effect on the expression of MRP1 protein. In addition, -elemene had little inhibitory effect on the intracellular GSH levels and GST activities in MCF-7/DOX cells. CONCLUSIONS: -Elemene might represent a promising agent for overcoming MDR in cancer therapy.

Guggulsterone of Commiphora mukul resin reverses drug resistance in imatinib-resistant leukemic cells by inhibiting cyclooxygenase-2 and P-glycoprotein.

The purpose of this study was to investigate the effects of guggulsterone on cyclooxygenase-2 and P-glycoprotein mediated drug resistance in imatinib-resistant K562 cells (K562/IMA). MTT cytotoxicity assay, flow cytometry, western blot analysis, and ELISA were performed to investigate the anti-proliferative effect, the reversal action of drug resistance, and the inhibitory effect on cyclooxygenase-2, P-glycoprotein, BCR/ABL kinase, and PGE2 release in K562/IMA cells by guggulsterone. The results showed that co-administration of guggulsterone resulted in a significant increase in chemo-sensitivity of K562/IMA cells to imatinib, compared with imatinib treatment alone. Rhodamine123 accumulation in K562/IMA cells was significantly enhanced after incubation with guggulsterone (60, 120 µM), compared with untreated K562/IMA cells (p<0.05). When imatinib (1 µM) was combined with guggulsterone (60, 120 µM), the mean apoptotic population of K562/IMA cells was 15.47% and 24.91%. It was increased by 3.82 and 6.79 times, compared with imatinib (1 µM) treatment alone. Furthermore, guggulsterone had significantly inhibitory effects on the levels of cyclooxygenase-2, P-glycoprotein and prostaglandin E2. However, guggulsterone had little inhibitory effect on the activity of BCR/ABL kinase. The present study indicates guggulsterone induces apoptosis by inhibiting cyclooxygenase-2 and down-regulating P-glycoprotein expression in K562/IMA cells.

Guggulsterone regulates the function and expression of P-glycoprotein in rat brain microvessel endothelial cells.

Our previous studies found that guggulsterone could inhibit P-glycoprotein-mediated multidrug resistance in P-glycoprotein over-expressed human cancer cell lines. However, the effects of guggulsterone on the ;P-glycoprotein function and expression in rat brain microvessel endothelial cells (rBMECs) are poorly understood. In the present study, we investigated whether guggulsterone has a modulative effect on the function and expression of P-glycoprotein in rBMECs. rhodamine 123 acts as a good substrate for P-glycoprotein, and agents that block P-glycoprotein have been found to increase the retention of rhodamine in cells. The results showed that the accumulation of rhodamine 123 in rBMECs was potentiated in a time-dependent manner after incubation with 30, 100 µM guggulsterone (P<0.05). Efflux of intracellular rhodamine 123 was decreased in a time-dependent manner from after 30, 100 µM guggulsterone treatment. The inhibitory effect of guggulsterone on P-glycoprotein function was reversible and remained at 120 min after removal of 30, 100 µM guggulsterone from the medium. Further results showed that guggulsterone (30, 100 µM) down-regulated the expression of P-glycoprotein, and had no influence on the expression of breast cancer resistance protein in rBMECs. In addition, the present study revealed that guggulsterone promoted the activity of P-glycoprotein ATPase in a dose-dependent manner. These results indicated that guggulsterone suppressed the function and expression of P-glycoprotein in rBMECs primary cultures.

Reversion of P-glycoprotein-mediated multidrug resistance by guggulsterone in multidrug-resistant human cancer cell lines.

Multidrug resistance (MDR) presents a serious problem in cancer chemotherapy. Our previous studies have shown that guggulsterone could reverse MDR through inhibiting the function and expression of P-glycoprotein (P-gp). The present study is to further investigate the reversal effects of guggulsterone on MDR in drug-resistant cancer cell lines. The effects of guggulsterone on MDR1mRNA gene expression, intracellular pH, P-gp ATPase activity and glucosylceramide synthase (GCS) expression were assessed by RT-PCR, Laser Scanning Confocal Microscope using the pH-sensitive fluorescent probe BCECF-AM, Pgp-Glo assay system, and flow cytometric technology, respectively. The results showed that guggulsterone ranging from 2.5 to 80 µM significantly promoted the activity of P-gp ATPase in a dose-dependent manner. The intracellular pH of K562/DOX cells was found to be higher than K562 cells. After treatment with guggulsterone (1, 3, 10, 30, 100 µM), intracellular pH of K562/DOX cells decreased in a dose- and time-dependent manner. However, the present study revealed that guggulsterone ranging from 3 to 100 µM had little influence on MDR1 gene expression in K562/DOX cells. Further, the isogenic doxorubicin-resistant MCF-7/DOX cells exhibited a 4.9-fold increase in GCS level as compared with parental MCF-7 human breast cancer cells. After treatment with guggulsterone (0.1, 1, 10 µM) for 48 h, MCF-7/DOX cells were found to have no change of GCS protein expression amount. Guggulsterone might be a potent MDR reversal agent, and its mechanism on MDR needs more research.