Melittin suppressed the expression and secretion of MMP-9 induced by CypA. MCF-7 cells were cultured in serum-free medium for 12 h, and then the cells were incubated with 200 ng/ml CypA and 2.5 µg/ml melittin for 24 h. (A) The secretion of MMP-9 in MCF-7 was determined by ELISA using human MMP-9 ELISA kit. Following the calibration standards of the ELISA kit, the concentration of MMP-9 in the samples was determined by comparing the OD of the samples to the standard curve. (B) MMP-9 mRNA transcriptions was evaluated by reverse transcription-polymerase chain reaction. The expression of mRNA copies was normalized against GAPDH mRNA expression (#P<0.05 vs. CON, n=5; *P<0.05 vs. CypA, n=5). MMP-9, matrix metallopeptidase 9; CypA, cyclophilin A; CON, control; Mel, metlittin; OD, optical density.