Effect of Cyclosporine A and Estrogen-Receptor Inhibitor on the Reversion of Multidrug Resistance of K562/A02 Line.

Objective: This paper was to study the reverse effect of cyclosporine A and the estrogen-receptor inhibitor, raloxifene, on multidrug resistance cell line K562/A02 and to investigate the reversal mechanism of this combination, and to provide theoretic evidence for the clinical application of them as resistance modifying agents.

Method: The IC50 (the concentration causing 50% inhibition of cell growth) of DNR were assayed by MTT method; mdr-1 mRNA was assayed by semi-quantitative reverse transcriptase polymerase chain reaction (RT-PCR).; intracellular DNR concentrations and the apoptosis and p-glycoprotein (p-gp) expression in K562 and K562/A02 were detected by fluorometry .

Results:

1. The IC50 of DNR for K562/A02 and K562 cells were 23.51mg/L and 0.29mg/L respectively. Pretreating K562/A02 cells with CsA(1mg/L) or raloxifene(2.5mg/L) for 48 hours partially restored the sensitivity of K562/A02 cells to DNR (IC50 were5.98mg/L and 8.15mg/L respectively) ,but had no effect on K562 cells;IC50 of combined cyclosporine A and raloxifene was 3.68mg/L

2. The intracellular DNR concentrations( [DNR]i) in K562 cells were higher than that in K562/A02 cells,[DNR]i in K562/A02 cells was 12% of K562. Pretreating K562/A02 cells with cyclosporine A and raloxifene alone or combination for 48 hours induced the enhancement of [DNR]i in K562/A02 cells([DNR]i:CsA alone 33% of K562; raloxifene alone 12.78%of K562;CsA+raloxifene 45.29% of K562

3. Cyclosporine A and raloxifene alone or combination could decrease the expression of P-gp in K562/A02,the effect for 48 hours as follows: control(K562) 3.58,control(K562/A02) 104.96; CsA alone 78.29; raloxifene alone 85.02;CsA+raloxifene 59.89

4. K562/A02 showed apoptotic characteristics after treated with cyclosporine A for 48 hours and no apoptotic characteristics after treated with raloxifene for 48 hours

5. Cyclosporine A and raloxifene alone could down regulate the expression of mdr-1 gene mRNA in K562/A02, cyclosporine A and raloxifene combination could markedly down regulate the expression of mdr-1 gene mRNA in K562/A02, the effect for 48 hours as follows(mdr1/β-action):control 1.313;CsA alone 1.232;raloxifene alone 1.052;CsA+raloxifene 0.449.

Data was analyzed by SPSS 11.0 software and expressed as mean ± SD.

Conclusions:

1. Activation of P-gp may be involved in the mechanism of MDR of K562/A02 cell line;

2. Multidrug resistance (MDR) can be partially reversed by CsA or raloxifene, of which the combination shows a great synergistic reversal effect.