Abstract: AIM: To investigate the efficacy oflomerizine on multidrug resistance(MDR)reversal and its mechanism.METHODS: Cytotoxicity of daunomycin(DNR)on K562/ADM was assessed by MTT assay in thePresence oflomerizine.Fluorescence ofP-glycoprotein(P-gp)substrate rhodamine123(Rh123)in K562/ADM was measured by fluorescence spectrophotometry and flow cytometry.RESULTS: Lomerizine could significantly increase the chemosensitivity of K562/ADM to DNR and intracellular content of Rh123.No effect was found in K562 cells.CONCLUSION: Lomerizine shows significant inhibition on the activity ofP-gPin K562/ADM,increases intracellular accumulation ofP-gPsubstrates,and enhances cytotoxicity of other anticancer drugs.

Key words: pharmacology, lomerizine, P-glycoprotein, P-glycoprotein inhibitor, multidrug resistance