Overexpression of multidrug resistance gene, (MDR1) is responsible for the resistance of anticancer agents in cancer cells. In this study, we designed three pairs of DNA primers to clone MDR, cDNA from human normal liver by polymerase chain reaction. The sites of these primers in MDR cDNA are (I)-64-46 (5') and 1680-1698 (3'); (II) 1471-1489 (5') and 2905-2923 (3'); (III)2729-2747 (5') and 3845-3863 (3). The three reactions were underwent after the human normal liver mRNA was reverse transcripted into single strand DNA. The lengths of PCR products are 1762bp, 1452 bp and 1134bp, respectively. The former two products were subcloned in pBluscript SK, respectively and the latter product was subcloned in pGEM7Z (named as pMDR1.7, pMDR1.4 and pMDRl.l, respectively). Cloned genes were certificated as MDR1 cDNA by sequence analysis. Full-length MDR, cDNA was obtained after further subcloning. Full-length MDR1 cDNA we obtained will be a very important tool in molecular diagnosis and gene therapy of anticancer drug resistance.

We have cloned full-length MDR1 cDNA from human normal liver tissue in previous study. Using this MDR1 cDNA as probe, we observed the MDR1 gene expression in human hepatocellular carcinoma treated with and without chemotherapy by Northern blot. The results showed that expression of MDR1 gene in hepatocellular carcinoma tissues was higher than that in their adjacent normal liver tissues; and enhanced MDR1 gene expression was also observed in hepatocellular carcinoma treated with chemotherapic agents. We also explored a method for quantitative analysis of MDR1 gene expression in hepatocellular carcinoma by polymerase chain reaction. This study suggests that overexpression of MDR1 gene may be responsible for the intrinsic and acquired drug resistance of human hepatocellular carcinoma, and PCR is a preferable method for quantitative analysis of MDR1 gene expression in hepatocellular carcinoma.