Stable reversal of multidrug resistance in colon cancer cells by RNA interference targeting the MDR1 gene

Colon cancer is one of the most common cancers in the world. Overexpression of MDR1 mRNA and P-gp is associated with the classic multidrug resistance of colon cancer cells. In our previous study, we reported on the transient specific reversal of MDR1/P-gp-dependent multidrug resistance by RNA interference (RNAi) in colon cancer cells. In this study, RNAi targeting the MDR1 gene stably reversed MDR1/P-gp-dependent multidrug resistance in colon cancer cells. The plasmid vectors pSilencer-#4029, encoding #4029 MDR1 siRNA, and pSilencer-#4123, encoding #4123 MDR1 siRNA, were constructed and then transfected into COLO 320DM, a colon cancer multidrug-resistant cell line. Clone cells were screened by G418 and identified by RT-PCR and Western blot analysis. Cellular viability was measured using the MTT assay. Cell cycle analysis and intracellular adriamycin accumulation were assessed by flow cytometry. MDR1 mRNA and P-gp expression in positive clone cells, those stably transfected with MDR1 siRNA, was inhibited. The IC₅₀ values of the antitumor drugs were significantly decreased in the positive clones compared to the COLO 320DM parent cell line, and the PI/AI values of positive clones treated with antitumor drugs were significantly decreased compared to the parent cells. In addition, the intracellular adriamycin accumulation of positive clones treated with adriamycin was significantly increased compared with COLO 320DM. This demonstrates that the stable transfection of plasmid vectors encoding MDR1 siRNA can stably reverse the MDR1/P-gp-dependent multidrug resistance of colon cancer cells.