Characterization and Resistance Mechanisms of A 5-fluorouracilresistant Hepatocellular Carcinoma Cell Line

Purpose: The chemoresistance of human hepatocellular carcinoma (HCC) to cytotoxic drugs, especiallyintrinsic or acquired multidrug resistance (MDR), still remains a major challenge in the management of HCC.In the present study, possible mechanisms involved in MDR of HCC were identified using a 5-fluorouracil (5-FU)-resistant human HCC cell line.
Methods: BEL-7402/5-FU cells were established through continuous culturingparental BEL-7402 cells, imitating the pattern of chemotherapy clinically. Growth curves and chemosensitivityto cytotoxic drugs were determined by MTT assay. Doubling times, colony formation and adherence rates werecalculated after cell counting. Morphological alteration, karyotype morphology, and untrastructure were assessedunder optical and electron microscopes. The distribution in the cell cycle and drug efflux pump activity weremeasured by flow cytometry. Furthermore, expression of potential genes involved in MDR of BEL-7402/5-FUcells were detected by immunocytochemistry.
Results: Compared to its parental cells, BEL-7402/5-FU cells hada prolonged doubling time, a lower mitotic index, colony efficiency and adhesive ability, and a decreased drugefflux pump activity. The resistant cells tended to grow in clusters and apparent changes of ultrastructuresoccurred. BEL-7402/5-FU cells presented with an increased proportion in S and G2/M phases with a concomitantdecrease in G0/G1 phase. The MDR phenotype of BEL-7402/5-FU might be partly attributed to increaseddrug efflux pump activity via multidrug resistance protein 1 (MRP1), overexpression of thymidylate synthase(TS), resistance to apoptosis by augmentation of the Bcl-xl/Bax ratio, and intracellular adhesion medicated byE-cadherin (E-cad). P-glycoprotein (P-gp) might play a limited role in the MDR of BEL-7402/5-FU.
Conclusion:Increased activity or expression of MRP1, Bcl-xl, TS, and E-cad appear to be involved in the MDR mechanismof BEL-7402/5-FU.