Search

Multidrug resistant cancer cells frequently overexpress the 110-kd lung resistance-related protein (LRP) as detected with the monoclonal antibody (MAb) LRP-56. Recently, we identified LRP as the major vault protein (MVP), which is the major constituent of vaults, multisubunit cellular organelles. Clinically, LRP/MVP expression in cancer at time of diagnosis provided a strong and independent prognostic factor for response to chemotherapy and outcome in different tumor types, notably acute myeloid leukemia and ovarian cancer. To facilitate additional immunohistopathological studies, we have optimized LRP/MVP detection in paraffin-embedded tissues using two monoclonal antibodies, LRP-56 and LMR-5. Blocking experiments showed that LRP-56 and LMR-5 MAbs detect different epitopes of LRP/MVP. Immunohistochemical studies with both MAbs in a panel of human multidrug resistant tumor cell lines, normal tissues, and colorectal tumors showed that LRP/MVP expression can be reliably detected after formalin-fixation and paraffm-embedding using overnight incubation at 4 degrees C with the primary MAbs at 5- to 10-fold higher concentrations (ie, 1 to 10 microg/ml) as currently used with frozen sections. Both streptavidin-biotin complex and alkaline phosphatase-anti-alkaline phosphatase techniques could be successfully used for signal-amplification. Staining quality did not benefit from antigen-retrieval pretreatments. The optimized staining methodology facilitates studies in archival material on the putative role of LRP/MVP in clinical drug resistance.

The human multidrug resistance protein (MRP) is a 190 kd membrane glycoprotein that can cause resistance of human tumor cells to various anticancer drugs, by extruding these drugs out of the cell. Three different monoclonal antibodies, directed against different domains of MRP, allowed us to determine the localization of MRP in a panel of normal human tissues and malignant tumors. Whereas in malignant tumors strong plasma membrane MRP staining was frequently observed, in normal human tissues MRP staining was predominantly cytoplasmatic. Here, MRP was detected in several types of epithelia, muscle cells, and macrophages. From the presence of MRP in many epithelia we infer that MRP, like MDR1 P-glycoprotein, may have an excretory function in protecting the organism against xenobiotics. Recent studies indicate a role for MRP as a carrier for transport of glutathione-conjugated endo- and xenobiotics. The presence of MRP in bronchiolar epithelium, heart muscle, and macrophages would agree with the glutathione S-conjugate carrier activity previously detected in these cells. Furthermore, in 46 of 119 untreated tumors from various histogenetic origins MRP staining was seen. In these tumors MRP may contribute to the intrinsic resistance against treatment with chemotherapeutic drugs.