title: Determining MDR1/P-glycoprotein expression in breast cancer.
abstract: The mechanism of chemotherapy resistance in breast cancer is unresolved. MDR1/P-glycoprotein (P-Gp) over-expression confers multidrug resistance in vitro and might play a role in clinical breast cancer. Studies using clinical samples have yielded conflicting results. MDR1/P-Gp mRNA expression was determined relative to the expression in normal human liver using TaqMan real-time RT-PCR (corrected for expression of the housekeeping gene PBGD). Immunohistochemistry (IHC) was performed with monoclonal antibodies against P-Gp (JSB1, C219). The positive control was SW1573/2R160, the intermediate control SW1573 and the negative control GLC4/ADR. We assayed 9 breast-cancer cell lines by RT-PCR and IHC, 52 carcinoma samples by RT-PCR and 168 samples by IHC. SW1573/2R160 contained high levels of MDR1/P-Gp mRNA (1.0, equal to liver) and showed strong membranous staining. Expression of MDR1/P-Gp mRNA in SW1573 (0.05) and GLC4/ADR (3.2 x 10(-5)) was not detectable by IHC. Very low levels of MDR1/P-Gp mRNA were measured in breast-cancer cell lines (mean 3.1 x 10(-4), range 1 to 12 x 10(-4)), but P-Gp was not detected by IHC. In 25 specimens from chemotherapy-naive patients, MDR1/P-Gp mRNA levels varied from 1 to 11 x 10(-2) (mean 3.9 x 10(-2)). In sections of 80 chemotherapy-naive tumors, no membrane-bound staining was observed in the tumor cells. Tumors of 27 anthracycline-treated patients had comparable MDR1/P-Gp mRNA expression levels (mean 5.4 x 10(-2)). P-Gp was undetectable in 88 tumor samples of patients who had received anthracycline-based chemotherapy. In breast cancer, MDR1/P-Gp mRNA is low or absent and P-Gp levels in cancer cells are too low to detect by IHC. Chemotherapy exposure does not result in detectable MDR1/P-Gp over-expression.
authors.affiliation: Department of Pathology, The Netherlands Cancer Institute/Antoni van Leeuwenhoek Hospital, Amsterdam, the Netherlands.
authors.forename: I F
authors.initials: IF
authors.lastname: Faneyte
authors.forename: P M
authors.initials: PM
authors.lastname: Kristel
authors.forename: M J
authors.initials: MJ
authors.lastname: van de Vijver
mesh_terms: D020168:ATP Binding Cassette Transporter, Subfamily B, Member 1 / Q000032:analysis / Q000235:genetics*; D000970:Antineoplastic Agents / Q000627:therapeutic use; D001943:Breast Neoplasms / Q000188:drug therapy / Q000235:genetics* / Q000473:pathology; D002462:Cell Membrane / Q000378:metabolism; D018432:Drug Resistance, Multiple / Q000235:genetics*; D005260:Female; D015972:Gene Expression Regulation, Neoplastic; D006801:Humans; D012333:RNA, Messenger / Q000235:genetics; D020133:Reverse Transcriptase Polymerase Chain Reaction; D014158:Transcription, Genetic; D014407:Tumor Cells, Cultured
chemical_list: D020168:ATP Binding Cassette Transporter, Subfamily B, Member 1; D000970:Antineoplastic Agents; D012333:RNA, Messenger