Objective:To observe the changes of expression and activity of multidrug resistance associated protein-1(MRP1)in acute monocytic leukemia THP-1 cells treated by cyclosporin A(CsA)

and to explore the mechanism that the function of MRP1 can be reversed by CsA making the THP-1 cells sensiting to chemotherapy.Methods:Expression of MRP1 in THP-1 cells treated by CsA is detected by Immunocytochemistry and Western blot in sequence.50% inhibiting concentration(IC50)of daunorubicin(DNR)to THP-1 cells

content and distribution of DNR in THP-1 cells treated by CsA are examined by MTT method

Spectrofluorometer method and Confocal laser scanning microscopy method

respectively.Results:Compaed with Control Group

in Group CsA the expression of MRP1 increased both in quality while quantity(P<0.05)and IC50 decreased obviously(1.499 7±0.233 8 vs 0.558 4±0.067 0

P<0.01);content of DNR increased obviously(20.900 0±2.497 5 vs 126.500 0±14.781 5

P<0.01)

and DNR distributed more evenly.Conclusion:CsA can increase the expression of MRP1 and decreased its activity

showing that the resistance of MRP1 is reduced by decreasing the activity of MRP1

not the amount of expression

as well as increasing chemotherapy sensitivity of THP-1 cells.