Small interfering RNA-induced suppression of MDR1 (P-glycoprotein) restores sensitivity to multidrug-resistant cancer cells

Overexpression of P-glycoprotein (P-gp), the MDR1 gene product, confers multidrug resistance (MDR) to cancer cells. Clinically, MDR is one of the major causes for chemotherapeutic treatment failure in cancer patients. To explore a new approach to circumventing MDR, we adopted RNA interference to target MDR1 gene expression. RNA interference is a conserved biological response to double-stranded RNA, which results in sequence-specific gene silencing [G. J. Hannon, Nature (Lond.), 418: 244-251, 20021. We report that introduction of an MDR1-targeted small interfering RNA duplex into drug-resistant cancer cells markedly inhibited the expression of MDR1 mRNA and P-gp, as determined by reverse transcription-PCR and Western blot. Inhibition of P-gp expression by small interfering RNA enhanced the intracellular accumulation of and selectively restored sensitivity to drugs transported by P-gp. These studies indicate that RNA interference can modulate MDR in preclinical models.