Human
cancers, including
hepatocellular carcinoma (HCC), are characterized by a high degree of drug resistance. The multidrug resistance (MDR) transporters MDR1-P-glycoprotein and MRP2 (multidrug-associated
protein 2) are expressed in almost 50% of human
cancers, including HCCs. In this study, we analyzed the effect of anti-MDR1
ribozymes, especially AFP promoter-driven anti-MDR1
ribozymes, to specifically chemosensitize HCC cells.
Epirubicin-selected HB8065/R cells were used as MDR1-P-glycoprotein-overexpressing cells. Adenoviral vectors were constructed to allow an efficient gene transfer of anti-MDR1
ribozyme constructs. AFP promoter-driven anti-MDR1
ribozymes reduced the IC(50) 30-fold for
epirubicin in HCC cells, whereas human
colorectal cancer cells were unaffected. Target sequences were either the translational start site or
codon 196 of the human MDR1 gene. Adenoviral delivery of CMV promoter-driven anti-MDR1
ribozymes resulted in a reduced IC(50) for
epirubicin and
doxorubicin (60- and 20-fold, respectively). They completely restored chemosensitivity in stably transfected anti-MDR1
ribozyme-expressing HCC cells as well as in HCC cells transduced with adenoviruses expressing wild-type anti-MDR1
ribozymes. Adenoviral delivery of
ribozymes was so efficient that chemosensitization of HCC cells could be demonstrated in cell cultures without further selection of transduced cells for single anti-MDR1
ribozyme-expressing HCC cell clones. Northern blots showed a decreased MDR1
mRNA expression, and fluorescence-activated cell sorting (FACS) analysis revealed a significantly reduced expression of MDR1-P-glycoprotein on the cell surface of HB8065/R cells after transduction with the anti-MDR1
ribozymes. In conclusion, our data demonstrate that adenoviral delivery of
ribozymes can chemosensitize HCC cells and that chemosensitization can be specifically achieved by
ribozymes driven by an AFP promoter directed against human MDR1.