title: Expression of the multidrug resistance-associated protein (MRP) gene in primary non-small-cell lung cancer.
abstract: BACKGROUND
  One of the major problems in the cure of advanced non-small-cell lung cancer (NSCLC) is its lack of response to cytotoxic drug treatment, and the mechanisms underlying this intrinsic drug resistance are unclear.
  
  
  METHODS
  We determined the expression of a newly recognised drug resistance gene, the Multidrug Resistance-associated Protein (MRP) gene, in normal lung tissue and in tumour biopsies from 35 surgically resected NSCLCs (11 adenocarcinomas, 24 squamous cell carcinomas). MRP mRNA levels were quantitated by RNase protection assay and expression of the MRP Mr 190,000 glycoprotein was estimated by immunohistochemistry.
  
  
  RESULTS
  Using the MRP-specific monoclonal antibody MRPr1, MRP expression was detected by immunohistochemistry in epithelial cells lining the bronchi in normal lung. In NSCLC approximately 35% of the samples showed elevated MRP mRNA levels. Based on MRP-specific immunohistochemical staining the tumours were divided into 4 groups: 12% were scored as negative (-), 14% showed weak cytoplasmic staining of the tumour cells (+/-), 40% had a clear cytoplasmic staining (+), and in 34% a strong cytoplasmic as well as membranous staining was observed (++). MRP expression, as estimated by immunohistochemistry, correlated with the MRP mRNA levels quantitated by RNase protection assay (correlation coefficient = 0.745, p = 0.0009), with MRP mRNA levels (mean +/- SD) of 3.0 +/- 1.0 U, 3.5 +/- 0.7 U, 7.5 +/- 5.9 U, and 19.3 +/- 10.7 U, in the (-), (+/-), (+), and (++) immunohistochemistry expression groups, respectively. Among the squamous cell carcinomas a correlation was observed between MRP staining and tumour cell differentiation: the strongest MRP staining was predominantly found in the well differentiated tumours.
  
  
  CONCLUSIONS
  Hyperexpression of MRP is frequently observed in primary NSCLC, especially in the well differentiated squamous cell carcinomas. Further studies are needed to assess the role of MRP in the mechanism of clinical drug resistance in NSCLC.
authors.affiliation: Department of Medical Oncology, University Hospital Rotterdam and Rotterdam Cancer Institute, The Netherlands.
authors.forename: K
authors.initials: K
authors.lastname: Nooter
authors.forename: F T
authors.initials: FT
authors.lastname: Bosman
authors.forename: H
authors.initials: H
authors.lastname: Burger
authors.forename: K E
authors.initials: KE
authors.lastname: van Wingerden
authors.forename: M J
authors.initials: MJ
authors.lastname: Flens
authors.forename: R J
authors.initials: RJ
authors.lastname: Scheper
authors.forename: R G
authors.initials: RG
authors.lastname: Oostrum
authors.forename: A W
authors.initials: AW
authors.lastname: Boersma
authors.forename: A
authors.initials: A
authors.lastname: van der Gaast
authors.forename: G
authors.initials: G
authors.lastname: Stoter
mesh_terms: D018528:ATP-Binding Cassette Transporters / Q000096:biosynthesis* / Q000235:genetics; D002289:Carcinoma, Non-Small-Cell Lung / Q000235:genetics / Q000378:metabolism* / Q000473:pathology; D002454:Cell Differentiation / Q000502:physiology; D018432:Drug Resistance, Multiple; D015870:Gene Expression; D006801:Humans; D007150:Immunohistochemistry; D008168:Lung / Q000378:metabolism; D008175:Lung Neoplasms / Q000235:genetics / Q000378:metabolism* / Q000473:pathology; D027425:ATP-Binding Cassette, Sub-Family C Proteins; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism; D012016:Reference Values; D012260:Ribonucleases / Q000378:metabolism
chemical_list: D018528:ATP-Binding Cassette Transporters; D027425:ATP-Binding Cassette, Sub-Family C Proteins; D012333:RNA, Messenger; D012260:Ribonucleases