Complete reversal of ABCG2-depending atypical multidrug resistance by RNA interference in human carcinoma cells.

In the chemotherapeutic treatment of patients with disseminated neoplasms, multidrug resistance (MDR) is a major obstacle. ABCG2 (BCRP/MXR), a member of the superfamily of adenosine triphosphate-binding cassette (ABC) transporters, was demonstrated to be associated with "atypical" forms of multidrug-resistant phenotypes of cancer cells. To overcome the ABCG2-depending MDR, two specific anti-ABCG2 small interfering RNAs (siRNAs) were designed for transient triggering of the gene-silencing RNA interference (RNAi) pathway in the human gastric carcinoma cell line EPG85-257RNOV, exhibiting an atypical MDR phenotype. Because both siRNAs showed biological activity, for stable inhibition of ABCG2 corresponding short hairpin RNA (shRNA) expression vectors were constructed. By treatment of EPG85-257RNOV cells with these constructs, expression of the targeted ABCG2-encoding mRNA and transport protein was inhibited completely. Furthermore, anti-ABCG2 shRNA-treated cells increased cellular drug accumulation to the same level measured in drug-sensitive parental cells. These effects were accompanied by complete reversal of the drug-resistant phenotype. Thus, the data indicate that siRNA- and shRNA-mediated RNAi-based gene therapy may be applicable in preventing and reversing ABCG2-depending atypical MDR.