Mechanism Of Pulsed Magnetic Fields On Reversing Multi-drug Resistance In The Breast Cancer Cell Lines MCF-7/ADR

Breast carcinoma is a popular malignant tumor with 7%-10%of cancer-related death for women according to epidemic statistically analysis,that is second only after uterine cancer-related death among women.40-60 years old women before and after menopause or heredity are more easily to get affected.Generally speaking,early stage before metastasis,it can be treated with ablation or radiotherapeutics,patients survival rate of can be 60%high in 5 years.But patients suffering advanced stage could not survive using such methods.Chemoradiation,herb therapy and chronotherapy are used as the main protocols,but multidrug resisitance(MDR) came behind which may contribute to the main failure of treatment.Several cellular mechanisms can be responsible for MDR, such as reduced apoptosis,advanced DNA damage repair mechanisms or altered drug metabolism.However,the most common mechanism of resistance is the active effiux of drugs by ATP-binding cassette(ABC) transporters.P-gp(P-glycoprotein,ABCB1), MRP1(Multidrug resistance-associated protein,ABCC1) and BCRP(Breast cancer resistance-associated protein,ABCG2)are highly expressed in most cancer cell lines on which are fully focused before.The first chemosensitizer was identified by Tsuruo et al. when the calcium channel blocker verapamil was found to re-sensitize vincristine-resistant P388 leukemia cells to vincristine and vinblastine.A subsequent study was developed very fast.However,designing or finding potent chemosensitizers that are selective,low in intrinsic toxicity and highly effective has been more difficult than expected.Furthermore,many natural products and biological agents have shown promising chemosensitizing effects on ABC drug transporters.However,regardless of the source of the inhibitors,unpredictable pharmacokinetic drug interactions, simultaneous involvement of several drug transporters in tumor tissues,as well as the variability in drug transporter expression levels among individuals,remain major obstacles to using modulators to restore drug sensitivity in the clinic.Pulsed magnetic fields(PMF) performing as an physico-method shows much advantages.In this study,we will investigate its reversing effect and mechanisms using breast cancer cell lines MCF-7.It is including two parts in this article:1 The study of PMF effect on breast cancer cell lines MCF-7/ADR;.2 The study of PMF mechanisms on breast cancer cell lines MCF-7/ADR.Objective:To investigate the optimal frequency and intensity of Pulsed Magnetic Fields(PMF) in reversing multi-drug resisitance in breast cancer cell line MCF-7/ADR both in vitro and in vivo.Methods:MCF-7/ADR cells were exposed to PMF of different frequencies(110Hz and 250Hz)and intensities(40mT and 10mT)for 2 hours.The concentration inhibiting growth by dividing the IC50 of the resistance cell line MCF-7/ADR by that of the parental cell line MCF-7.The reversal index was calculated by dividing the IC50 of the resistant cell line MCF-7/ADR after treatment with PMF by that of the resistant cell line MCF-7/ADR.Cells treated with PMF and untreated cells were incubated in rhodamine123(Rh 123)solution for 2 hours at 37℃and the intracellular accumulation of Rh123 was detected by flow cytometry.Energy-dependent efflux proteins that pump a variety of chemotherapeutic agents from tumor cells such as P-glycoprotein(p-gp) and multidrug resistance-associated protein(mrp1) on the cell membrane were evaluated by flow immunofluorescence.We used semiquantitative PCR(RT-PCR) to detect the expression of MDR1 and MRP1 mRNA and to determine the effect of PMF on the expression of multi-drug resistance genes.An MCF-7/ADR cell xenograft model was established in nude mice.The tumor volume and weight were measured to observe the effect of PMF in vivo.Results:PMF effectively reversed the adriamycin resistance of PMF/ADR cells(P＜0.01),with a maximum five-fold effect using 110Hz and 40mT.PMF increased the intracellular accumulation of Rhl23 by 20%and increased the quatity of p-gp on the cell membrane.PMF combined with ADR inhibited tumor proliferation in our xenograft model(P＜0.01).Conclution:PMF decreases MDR1 and MRP1 gene expression in the MCF-7/ADR breast cancer cell line both in vitro and in vivo.