OBJECTIVE: To investigate the possible inhibitory action of pure quercetin on secretion and gene expression of leptin in the T47 D breast cancer cell line.METHODS: In this experimental study, T47 D cells were cultured in monolayers in RPMI 1640. IC50 was determined by MTT(3-[4,5-dimethylthiazol-2-yl]-2,5-diphenyltetrazolium bromide) assay after 24 h treatment at different concentrations of quercetin.The levels of leptin gene expression were measured by reverse-transcription real-time polymerase chain reaction(PCR). Secreted leptin was measured in the supernatant of cells by an enzyme-linked immuno sorbent assay.RESULTS: Analysis of MTT assay data showed that quercetin has a cytotoxic effect on T47 D breast cancer cells with 40 μM IC50 after 24 h exposure. Dataanalysis of real-time PCR showed that with increases in quercetin concentration, a decreasing trend was seen in m RNA levels of leptin of treated cells compared with the control cells(P < 0.05). Also,measurement of secreted leptin in the culture media showed a similar decreasing trend in the amount of leptin protein in the treated cells compared with the control cells(P < 0.05).CONCLUSION: Quercetin significantly inhibits the growth of T47 D cells through inhibition of leptin secretion and gene expression in T47 D breast cancer cells. Therefore, it might be an alternative approach to breast cancer therapy through leptin targeting. OBJECTIVE: To investigate the possible inhibitory action of pure quercetin on secretion and gene expression of leptin in the T47 D breast cancer cell line. METHODS: In this experimental study, T47 D cells were cultured in monolayers in RPMI 1640. IC50 was determined by MTT (3- [4,5-dimethylthiazol-2-yl] -2,5-diphenyltetrazolium bromide assay after 24 h treatment at different concentrations of quercetin. The levels of leptin gene expression were measured by reverse-transcription real-time polymerase chain reaction (PCR). Secreted leptin was measured in the supernatant of cells by an enzyme-linked immuno sorbent assay .RESULTS: Analysis of MTT assay data showed that quercetin has a cytotoxic effect on T47 D breast cancer cells with 40 μΜ IC50 after 24 h exposure. Dataanalysis of real-time PCR showed that with increasing in quercetin concentration, a decreasing trend was seen in m RNA levels of leptin of treated cells compared with the control cells (P <0.05). Also, measurement of secreted lepti n in the culture media showed a similar decreasing trend in the amount of leptin protein in the treated cells compared with the control cells (P <0.05) .CONCLUSION: Quercetin significantly inhibits the growth of T47 D cells through inhibition of leptin secretion and gene expression in T47 D breast cancer cells. Thus, it might be an alternative approach to breast cancer therapy through leptin targeting.