Distribution of breast cancer resistance protein (BCRP/ABCG2) mRNA expression along the human GI tract

Human breast cancer resistance protein (BCRP/ABCG2) is an ABC-transporter that is present on the luminal membrane of intestinal epithelial cells and restricts absorption of anticancer drugs such as methotrexate, topotecan, mitoxantrone, and doxorubicin. The exact anatomic distribution of BCRP along the gastrointestinal (GI) tract, however, has not been determined before. The aim of this study was, therefore to investigate BCRP mRNA expression pattern along the GI tract in 14 healthy subjects. Furthermore, BCRP duodenal mRNA expression was compared with MDR1/ABCB1 mRNA. Additionally, BCRP mRNA expression was investigated in two human intestinal cell lines (Caco-2 and LS180). Since previous animal studies have suggested sex specific differences in BCRP expression, we analyzed intestinal BCRP expression with respect to sex. Biopsies were taken from different gut segments (duodenum, terminal ileum and ascending, transverse, descending and sigmoid colon). Gene expression was assessed by quantitative real-time PCR (Taqman). BCRP mRNA expression was maximal in the duodenum and decreased continuously down to the rectum (terminal ileum 93.7%, ascending colon 75.8%, transverse colon 66.6%, descending colon 62.8%, and sigmoid colon 50.1% compared to duodenum, respectively). BCRP expression in the duodenum was comparable to MDR1/ABCB1 gene expression. Caco-2 cells showed a comparable expression of BCRP as human duodenal tissue. Gender specific differences in BCRP expression were not observed. These findings represent the first systematic site-specific analysis of BCRP expression along the GI tract. This information might be helpful to develop target strategies for orally administered anticancer drugs.