Abstract: BACKGROUND ＆ AIM: To investigate the reversing effect of Chinese drug thallus laminariae PE on drug resistance B-MD-C1(ADR＋/＋)cell line, and to identify the mechanism of TLPE in reversing the multidrug resistance. MATERIALS AND METHODS: MTT assay was used to determine the reversing effect of TLPE and reversal fold; cytoimmunochemistry and flow cytometry were used to assess the expression of P-gp in the level of protein. RT-PCR was used to detect the level of MDR1 gene treated by TLPE. RESULTS: TLPE had reversing effect on B-MD-C1(ADR＋/＋)in vitro and the reversal fold was 4.65. Cytoimmunochemistry showed that TLPE could decrease the expression of P-gp. Flow cytometry showed that TLPE could decrease the expression of P-gp with dose-dependence. RT-PCR suggested that TLPE could reduce the MDR1 gene of B-MD-C1(ADR＋/＋). CONCLUSION: TLPE could exert reversing effect in B-MD-C1(ADR＋/＋)by decreasing the expression of P-gp.

Key words: thallus laminariae PE, multidrug resistance, P-gp protein, MDR1 gene