Specific reversal of MDR1/P-gp-dependent multidrug resistance by RNA interference in colon cancer cells.

No control cell line was available for previous RNA interference studies on reversal of multidrug resistance (MDR) in colon cancer cells. Here, human COLO 320DM, with HT-29 as the control, colon cancer cell lines were used to investigate the reversal of MDR1/P-gp-dependent MDR by siRNA (#4123 and #4029 MDR1 siRNAs) targeting to MDR1 mRNA. Both siRNAs inhibited expression of MDR1 and P-gp in COLO 320DM. The minimum inhibition concentrations were 5 nmol/l of #4123 and 25 nmol/l of #4029. #4123 MDR1 siRNA took effect in 4, 5 and 6 days at doses of 5, 25 and 100 nmol/l, respectively. Increased cytotoxicity of the antitumor drugs adriamycin and vincristine with increased intracellular adriamycin accumulation accompanied inhibition of MDR1 mRNA and P-gp expression. No such effects were found in the HT-29 control. MDR1 siRNAs specifically reversed the MDR of colon cancer cells demonstrating a possible new approach for treating MDR1/P-gp-dependent multidrug resistance.