Abstract:

Objective     To compare multidrug-resistant characteristics of two human colorectal carcinoma cell lines selected／induced by continuous stepwise exposure and pulse drug exposure．Methods     The human colorectal carcinoma cell line LOVO was exposed to continuous stepwise-increased concentration of 5-fluorouracil (5-Fu) and constant high concentration of 5Fu，respectively，and the corresponding new sublines were designated as L2 and L3．Drug-sensitivity was measured by MTT. The cell cycle and apoptosis of cells were determined by flow cytometry．Expression of multidrug resistance 1 (MDR1) mRNA was detected by realtime PCR, and the P-gp expression by Western blot． Results    After 8 months′ stepwise drug exposure, the subline L2 exhibited more resistant features, with a resistance index of 26.53 against 5-Fu．It could normally grow and propagate in the medium with 2.5μg／mL of 5Fu．After several exposures with a high concentration of drug(2.5μg／mL of 5-Fu) for 6 months, the subline L3 presented a resistance index of 13.78 and could normally grow and propagate in the medium with 2.5μg／mL of 5-Fu． MTT assay showed that the two sublines were resistant not only to 5-Fu but also to other chemotherapy agents, manifesting multidrug-resistant characteristics．Compared with L2, L3 was more sensitive to most drugs, the number of cells at the G1 phase was lower，the apoptosis rate greatly increased, and expressions of MDR1 mRNA and P-gp were obviously reduced．Conclusion    After exposure with the two different methods, human multidrug-resistant colorectal carcinoma cell lines were successfully established, and the new sublines L2 and L3 manifest different multidrug-resistant characteristics. The mechanism of multidrug resistance may be related to the inhibition of MDR1 mRNA and P-gp overexpressions.

Key words: Colorectal carcinoma； Apoptosis；Multidrugresistance； P-glycoprotein