Effects And Mechanism Of Dexamethasone-induced Resistance To Paclitaxel In Breast Carcinomas

Objective:To observe the probability of drug-resistance and the changes of mitogen-activated protein kinase phosphatase-1(MKP-1) mRNA expression in human breast adenocarcinomal cells(MCF-7) after dexamethasone pretreatment in different concentrations and treatment with paclitaxel. To explore the relationship between dexamethasone and chemotherapy resistance and the possible mechanism of glucocorticoids induced chemotherapy resistance.Methods:1. To filter the IC50 concentration of paclitaxel on MCF-7 cells by MTT assay (methyl thiazolyl tetrazolium assay).Routinely cultured MCF-7 cells seeded in 96-well plate, set the zero wells (complete medium), control wells (cells, complete medium), experimental wells (cells, complete medium), being cultured 24 hours later, the intervention was given in experimental wells with different concentrations of paclitaxel, and the final concentrations of paclitaxel were set respectively at 0.7μmol / L,7μmol / L and 70μmol / L. The control wells by adding an equal volume of PBS solution, and then continue the cultivation for 24 hours. To determinated the cells survival rates of MCF-7 cells which pretreated with paclitaxel and to filter the IC50 concentrations of paclitaxel by MTT assay.2. To determinate responses to paclitaxel in dexamethasone pretreated MCF-7 cells by MTT assay and to detect the expression level of MKP-1mRNA in MCF-7 cells by Reverse Transcriptase-polymerase Chain Reaction(RT-PCR).Routinely cultured MCF-7 cells were seeded in 96-well plate and 24-well plate, and set the zero wells (complete medium), control wells (cells,complete medium), and experimental wells (cells,DEX,complete medium), and the final concentrations of dexamethasone were set respectively at 0.7μmol / L,7μmol / L and 70μmol / L. Being cultured 24 hours later , add paclitaxel to the control wells and the experimental wells respectively with the final concentrations at 0 mol/L, 1 multiple of IC50, and 2 multiple of IC50,and then continue the cultivation for 24 hours. To determinated the cells survival rates of MCF-7 cells and to detect the expression level of MKP-1mRNA in MCF-7 cells by RT-PCR.Results: 1. The inhibition rate of MCF - 7 cells were respectively 36.7%, 53.7% and 76.2% after pretreated with different concentrations (0.7μmol/L,7μmol/L,70μmol/L) of paclitaxel, and the IC50 concentration was 5.0μmol/L.2. Drug-resistance developed after being pretreated with different concentrations of dexamethasone, and the drug-resistance rate increased gradually with the increasing concentrations of dexamethasone: (1)When paclitaxel concentration was 0μmol/L(control wells,the same below)and the concentrations of dexamethasone were 0μmol/L,0.1μmol/L,1μmol/L and 10μmol/L, the cells survival rate were respectively 72.6%, 88%, 93.2% and 99.9% (F =68.6, in each others groups, P < 0.05);(2)When the concentration of paclitaxel was 5μmol/L, and the concentrations of dexamethasone were respectively 0μmol/L, 0.1μmol/L,1μmol/L and 10μmol/L, the cells survival rate were respectively 50.1%, 60.8%, 68.2% and 87% (F =137.735, in each others groups, P < 0.01);(3)When the concentration of paclitaxel was 10μmol/L, and the concentrations of dexamethasone were 0μmol/L, 0.1μmol/L, 1μmol/L and 10μmol/L, and the cells survival rate were respectively 40.7%, 43.9%, 50.3% and 61.5% (F =57.275,compared to concentrations of dexamethasone were 0 and 0.1μmol/L, P < 0.05; the left groups within each others P < 0.01).3.The expression level of MKP-1 mRNA increased gradually with the increasing concentrations of dexamethasone also:(1)When the concentration of paclitaxel was 0μmol/L, and the concentration of dexamethasone were 0μmol/L, 0.1μmol/L, 1μmol/L and 10μmol/L, the cells MKP-1 mRNA expression were respectively 0.017±0.003, 0.043±0.005, 0.168±0.012 and 0.358±0.014 (F =791.836, groups within each others P <0.05);(2)When the concentration of paclitaxel was 5μmol/L, and the concentrations of dexamethasone were 0μmol/L, 0.1μmol/L,1μmol/L and 10μmol/L, the mRNA expression of MKP-1 cells were respectively 0.063±0.006 , 0.393±0.028, 0.512±0.022, 0.851±0.039 (F =461.737,groups within each others P < 0.01);(3)When the concentration of paclitaxel was 0μmol/L, and the concentrations of dexamethasone were 0μmol/L, 0.1μmol/L, 1μmol/L and 10μmol/L, the expression of MKP-1 mRNA cells were respectively 0.035±0.004, 0.109±0.016 , 0.156±0.027 and 0.318±0.025 (F =108.778, groups within each others P < 0.05).Conclusions: Dexamethasone could induce resistance to paclitaxel in MCF-7 cells and the over expression MKP-1 may be one of the mechanism.