Knocking Down Breast Cancer Resistance Protein (Bcrp) by Adenoviral Vector-Mediated RNA Interference (RNAi) in Sandwich-Cultured Rat Hepatocytes: A Novel Tool To Assess the Contribution of Bcrp to Drug Biliary Excretion

BCRP transports numerous drugs/derived metabolites and toxins, and exhibits overlapping substrate specificity with P-glycoprotein (P-gp) and multidrug resistance-associated protein 2 (MRP2). Assessing the contribution of BCRP to drug/metabolite biliary excretion in intact hepatocytes remains a challenge. Current studies were designed to develop a novel in vitro tool to specifically assess the contribution of Bcrp to drug biliary excretion. Adenoviral vectors expressing short hairpin (sh) RNA targeting Bcrp (Ad-si01 Bcrp) or a nontarget control (Ad-siNT) were packaged and infected into sandwich-cultured rat hepatocytes (SCRH). Protein levels were detected by immunoblot. Biliary excretion index (BEI) and in vitro biliary clearance (Cl-biliary) of nitrofurantoin (BCRP substrate) and digoxin (P-gp substrate) were compared among noninfected, Ad-siNT- and Ad-si01 Bcrp-infected SCRH. shRNA targeting Bcrp efficiently knocked down Bcrp in SCRH, while levels of other transport proteins (P-gp, Mrp2, Bsep, Mrp4 and Oatp1a1) were unaffected. In SCRH exhibiting Bcrp knockdown, cellular accumulation of nitrofurantoin was increased markedly and nitrofurantoin BEI and in vitro Cl-biliary were decreased to 11% and 14% of control, respectively. Digoxin values were unaffected by knockdown of Bcrp. Results indicated that Bcrp in SCRH contributed predominantly to nitrofurantoin biliary excretion, but played a negligible role in digoxin biliary excretion. In summary, Bcrp knockdown in SCRH is the first in vitro model utilizing intact hepatocytes to assess the contribution of Bcrp to the biliary excretion of drugs. This approach may be useful in predicting drug-drug interactions in biliary excretion and the consequence of impaired BCRP function on the hepatic exposure of drugs/derived metabolites.