| Objective:To study the reversal effect of adriamycin(ADM) resistance by orphanin FQ(OFQ) in leukemia multi-drug resistance K562/ADM cells and investigate its possible mechanism.Methods: Cytotoxicity of OFQ and the sensibility to adriamycin of K562/ADM cells were studied through MTT assay. Morphological assessment of apoptosis was performed with light microscope after Wright staining and transmission electron microscope(TEM).We detected the changes of ADM concentration inside the K562/ADM cells with or without OFQ by flow cytometry. The level of P-gp,Fas and Fasl after using OFQ was tested by Flow Cytometry(FCM). DNA Fragmentation was assessed by agarose gel electrophoresis.Results: When the concentration of OFQ was 10-7mol/l, OFQ has no toxicity to K562/ADM cells. We found that OFQ could reverse the ADM resistance of K562/ADM cells. By the treatment of OFQ(10-7mol/l), K562/ADM cell were cultured for 48 hours, the reversal index(RI) was 2.03.Furthermore,it showed that OFQ could significantly increase the intracellular accumulation of ADM in K562/ADM cells and apoptotic percentage in K562/ADM cells. The results showed that OFQ could Down-regulate the level of P-gp with dose-dependently, while the level of Fas and Fasl were up-regulated obviously. It has the significant difference comparing with the control group (P<0.01).Application of OFQ (10-7mol/l) with ADM( (20 ug/ml) to K562/ADM cells for 48 hours could subject the cells apoptotic nuclear fragmentation, which was characterized by the appearance of DNA ladder pattern in genomic DNA agarose gel electrophoresis.Conclusion:(1) OFQ can reverse multi-drug resistance in K562/ADM cells to some extent, they have distinctly synergy with ADM.(2) The mechanism of OFQ reversing multi-drug resistance is probably associated with down-regulating of the expression of P-gp.(3) The mechanism of OFQ reversing multi-drug resistance correlate with inducing the apoptosis of K562/ADM cells.
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