MDR1 GENE-EXPRESSION - ITS EFFECT ON DRUG-RESISTANCE TO DOXORUBICIN IN HUMAN HEPATOCELLULAR-CARCINOMA CELL-LINES

Background: Hepatic tumors are resistant to many chemotherapeutic agen ts. Although elevated MDR1 (also known as PGY1) gene expression has be en shown in such tumors, no direct association has been established be tween the gene expression and multidrug resistance. Purpose: To evalua te the role of the MDR1 gene in the drug resistance of hepatoma, we te sted nine human hepatoma cell lines for their expression of the MDR1 g ene. Methods: We measured the MDR1 messenger RNA (mRNA) expression by RNA slot-blot analysis and by immunocytochemical staining with a P-gly coprotein-specific monoclonal antibody, MRK16. The in vitro chemosensi tivity of these cell lines to fluorouracil, doxorubicin, mitomycin C, cisplatin, and etoposide (VP-16) was determined using the MTT 4,5-dim ethylthiazol-2-yl-2,5-diphenyltetrazolium bromide) colorimetric assay . For doxorubicin cytotoxicity, we also tested the potentiating effect of several multidrug resistance-reversing agents. Results: Slot-blot analysis and immunocytochemistry showed that two cell lines expressed high levels of MDR1 mRNA, one expressed an intermediate level, and all others were low expressors. The MTT assay results showed that all cel l lines tested were generally resistant to chemotherapeutic agents. Th e assay area under the curve (AUC) was within a clinically achievable range only for VP-16 in one of nine cell lines. When the IC50 values w ere compared among the cell lines, the results revealed a close associ ation with the MDR1 gene expression only for doxorubicin resistance. V erapamil and quinidine lowered the IC50 values of doxorubicin for MDR1 -positive cell lines. The lowered assay AUC levels for both reversing agents, however, were still higher than the clinically achievable rang e. Conclusion: These results indicate that the MDR1 gene probably has a role in doxorubicin resistance in hepatocellular carcinoma and that the resistance can be overcome by some multidrug resistance-reversing agents. Implications: Some widely used anticancer agents might be inef fective for treating hepatocellular carcinoma in clinical situations e ven when combined with reversing agents.