Abstract: ObjectiveTo study the expression of methyl-DNA-binding proteins(MBDs)in mitoxantrone-induced drug-resistance human breast cancer cells(MCF-7)and to analyze the relationship between multidrug resistance and MBDs.MethodsMitoxantrone at 4 different dosages(0.005,0.01,0.02,and 0.04 μmol/L)was administrated to MCF-7 cells for 15 days;then the expressions of breast cancer resistance protein(BCRP)and MBDs(MBD1,MBD2 and MBD4)in the experimental and control MCF-7 cells were determined with Western blot and compared.ResultsCompared with those of the control cells,the BCRP expression gradually increased with the increment of mitoxantrone,while the expressions of MBDs(especially MBD4)decreased in MCF-7 cells,with the MBD4 expression levels of 0.910±0.049,0.835±0.065,0.708±0.082,and 0.660±0.145(all P<0.05).ConclusionMBDs expression,especially MBD4,in MCF-7 cells decreases after exposed to mitoxantrone continuously and the decrease may be related to the formation of drug resistance.