| Chemotherapy plays an important role in the cancer treatment, however, multi-drug resistance (MDR) might lead to the failure of chemotherapy. In order to find new solutions to overcome the problem of MDR, here we explored the reversal effects and mechanism of pulsed electrical field (PEF) treatment on MDR of MLLB-2, MCF-7/ADR and A549/Taxol cell lines.Using anti-cancer drugs ADR and Taxol on drug-sensitive cells MCF-7 and A549, MDR cell models MCF-7/ADR and A549/Taxol were established through continuous inducement of increasing drug concentration. MLLB-2 cells were purchased from ATCC. MTT and flow cytometer analysis were used to detect the effects of MDR of the three kinds of cells. The effect of 50Hz low-frequency pulsed electrical field (LF-PEF) on MLLB-2, MCF-7/ADR and A549/Taxol were explored by MTT analysis, respectively. And the effects of 1000Hz squared-modulation sinusoidal wave electromagnetic fieldâ… (SM-SWEFâ… ) andâ…¡(SM-SWEFâ…¡) on A549/Taxol and MLLB-2 were also studied. Meanwhile the mechanism of reversal effects of 50Hz LF-PEF on cells was also studied through flow cytometer analysis, reverse transcription polymerase chain reaction (RT-PCR), gene chip and the detection of accumulation and efflux of DiOC2(3).After drug inducement MCF-7/ADR cells had very strong MDR effects on VCR and HHT. A549/Taxol cells also had strong MDR effects on 5-FU, DNR and HTT. The results showed that the total MDR activity factor (MAFT) of A549/Taxol and MLLB-2 were 31.80 and 84.91, respectively. It was concluded that all three cells have strong MDR effects.It was shown that the effects of 50Hz LF-PEF on the growth of cells was negligible and the reversal index (RI) of LF-PEF on MLLB-2 and MCF-7/ADR were 1.072-2.140 and 1.473-2.090, respectively. However, LF-PEF treatment had a negligible reversal effects on A549/Taxol. It was also showed that 1000Hz SM-SWEFâ… slightly inhibited the proliferation of cells. The reversal index (RI) of SM-SWEFâ… on A549/Taxol was 1.181-1.948 and the reversal effects of SM-SWEFâ… on MLLB-2 were negligible. 1000Hz SM-SWEFâ…¡slightly promoted the proliferation of cells. Its reversal index (RI) on A549/Taxol was 1.550-2.388 and SM-SWEFâ…¡had a negligible reversal effects on the MLLB-2.Treatment of 50Hz LF-PEF on MLLB-2 cells for 5,15,30 and 45 minutes decreased the activity of P-glycoprotein (P-gp) and increased the activity of multi-drug resistance related protein (MRP). The activity change of P-gp and MRP was the most obvious when treated by LF-PEF for 15 minutes.15 minutes LF-PEF treatment decreased MAFT to some extent (P>0.05), and 30 minutes LF-PEF treatment decreased MAFT obviously (P<0.05). Treatment of LF-PEF on A549/Taxol cells for 45 minutes could decrease the activity of P-gp and increase the activity of MRP. It was found that the instant activity of MRP after LF-PEF treatment was higher than that which incubated for 1 hour. Treatment of LF-PEF for 15 minutes down-regulated the gene expression of mdr1 and up-regulated the gene expression of mrp1 in MLLB-2 cells. However, mdr1 expression reached its lowest point after incubation for 5 hours, and at that time, mrp1 expression regenerated the same level of control. On A549/taxol cells, the gene expression of mdr1 and mrp1 was up-regulated by incubation for 3 hours, but down-regulated by incubation for 5 hours after 45 minutes LF-PEF treatment. It was shown that 50 Hz LF-PEF had a time-dependent effect on the activity and gene expression of P-gp and MRP, and it reversed tumor MDR mainly by the way of down-regulating the P-gp activity and mdrl gene expression.The fluorescent micrographs showed that treatment of LF-PEF on MCF-7/ADR cells for 30 and 45 minutes could significantly promote the accumulation of DiOC2(3) and evidently inhibited the efflux of DiOC2(3). Gene chip result showed that 50Hz LF-PEF had significant reversal effects on MLLB-2 cells and caused the change of gene expression profile.1128 genes were up-regulated or down-regulated among the total 31109 genes.In general, six conclusions were obtained:1. MDR cell models MCF-7/ADR and A549/Taxol were established through continuous inducement of increasing drug concentration.2. 50Hz LF-PEF could induce the reversal effects of MDR in MLLB-2 and MCF-7/ADR, but had a negligible effect on A549/Taxol. 3. 1000Hz SM-SWEF could induce the reversal effects of MDR in A549/Taxol, but had a negligible effects on MLLB-2.4. The activity of P-gp and MRP were regulated time-dependently by treatment of 50Hz LF-PEF. Treatment of LF-PEF could have effects on both drug efflux pumps, finally caused reversal effects of MDR.5. The reversal effects of MDR in MCF-7/ADR after treatment of 50Hz LF-PEF were related to drug accumulation and inhibiting drug efflux caused by LF-PEF treatment.6. Treatment of 50Hz LF-PEF could have effects on signal transduction, stress response, cell cycle, protein degradation and gene expression of ion channel protein and protein that related to cell junction.
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