BACKGROUND:Present studies on the reversal of multi-drug resistance(MDR) are almost entirely limited to in vitro systems,and are seldom carried out in vivo. In order to study MDR under the in vivo situation,a MDR cell strain was used to establish a model in nude mice via orthotopic implantation directed by B-ultrasonography. This model is expected to provide a good platform for evaluating strategies to reverse the phenomenon of primary hepatocellular carcinoma(HCC) MDR. METHODS:An orthotopic MDR1 hepatoma was obtained by injecting the cell lines HepG2 and HepG2/ADM subserosally into the liver of nude mice(10 control and 20 MDR mice). The injections were made under B-ultrasonographic direction. Ultrasonography and laparotomy were used to assess tumor growth,and the long chain PCR technique was applied to sequence the MDR1 gene from multi-drug resistant human HCC cells,HepG2/ADM,and corresponding implanted tumor tissues. Furthermore,MDR1 mRNA and P-gp protein expression were evaluated by reverse transcriptase-polymerase chain reaction(RT-PCR),Western blotting,and immunohistochemical methods. RESULTS:The success rates of tumor implantation and induction of MDR were 100%(30/30) and 95%(19/20),respectively. The 3.8kbp MDR1 gene band was detected from the HepG2/ADM cell line and the correspondingimplanted tumor tissues,and the MDR1 gene sequence coincided with that reported in GenBank. The expressions of MDR1 mRNA and P-gp protein in MDR mice were significantly higher than those in the control group. There was a significant difference in P-gp protein expression between MDR and control mice. CONCLUSION:A MDR model has been successfully established in nude mice via orthotopic implantation of multi-drug resistant human HCC cells directed by ultrasonography. BACKGROUND: Present studies on the reversal of multi-drug resistance (MDR) are almost entirely limited to in vitro systems, and are seldom carried out in vivo. In order to study MDR under the in vivo situation, a MDR cell strain was used to establish a model in nude mice via orthotopic implantation directed by B-ultrasonography. This model is expected to provide a good platform for evaluating strategies to reverse the phenomenon of primary hepatocellular carcinoma (HCC) MDR. METHODS: An orthotopic murine MDR1 hepatoma was obtained by injecting the cell lines HepG2 and HepG2 / ADM subserosally into the liver of nude mice (10 control and 20 MDR mice). The injections were made under B-ultrasonographic direction. Ultrasonography and laparotomy were used to assess tumor growth, and the long chain PCR technique was applied to sequence the MDR1 gene from multi-drug resistant human HCC cells, HepG2 / ADM, and corresponding implanted tumor tissues. Furthermore, MDR1 mRNA and P-gp protein expression were evaluated by RESULTS: The success rates of tumor implantation and induction of MDR were 100% (30/30) and 95% (19/20), respectively. The 3.8 kbp MDR1 gene band was detected from the HepG2 / ADM cell line and the corresponding implanted tumor tissues, and the MDR1 gene sequence coincided with that reported in GenBank. The expressions of MDR1 mRNA and P-gp protein in MDR mice were significantly higher than those in the control group. There was a significant difference in P-gp protein expression between MDR and control mice. CONCLUSION: A MDR model has been successfully established in nude mice via orthotopic implantation of multi-drug resistant human HCC cells directed by ultrasonography.