title: Multidrug resistant P-glycoprotein positive L1210/VCR cells are also cross-resistant to cisplatin via a mechanism distinct from P-glycoprotein-mediated drug efflux activity.
abstract: P-glycoprotein (P-gp, a drug transporter found in the plasma membrane)-mediated multidrug resistance of leukemia cells represents a real obstacle in the effective chemotherapeutic treatment of leukemia. While cisplatin (CisPt) is known to be a substance that is untransportable by P-gp, P-gp positive cells were often found to be resistant to CisPt. The aim of the current paper is to study this phenomenon using P-gp positive mouse leukemia cells L1210/VCR in which the overexpression of P-gp was induced by its ability to adapt to growth on vincristine (VCR). L1210/VCR cells are also resistant to CisPt. However, resistance to this substance could not be reversed by addition of the known P-gp inhibitor verapamil. CisPt induced more pronounced entry into apoptosis, as measured using the annexin V/propidium iodide kit, in sensitive L1210 cells than in resistant L1210/VCR cells. In addition, CisPt induced an increase in the proportion of L1210 cells that were in the g2 phase of the cell cycle when compared to L1210/VCR cells, as measured by staining with propidium iodide. Similarly, a higher release of cytochrome c from the mitochondria to the cytosol was induced by CisPt treatment in L1210 than in L1210/VCR cells. While similar levels of Bax and Bcl-2 proteins were observed in sensitive and resistant cells, CisPt induced a more pronounced decrease of the Bcl-2 levels in L1210 cells than in L1210/VCR cells. Consistent with this observation, CisPt induced a larger decrease of the Bcl-2 content in the Bcl-2:Bax heterooligomer in L1210 cells than in L1210/VCR cells. Moreover, CisPt induced a similar apoptotic DNA fragmentation pattern in both resistant and sensitive cells. All of the above observations indicated that L1210/VCR cells are also resistant to CisPt and that this resistance is related to the differences in the regulatory mechanisms responsible for CisPt-induced apoptosis in L1210/VCR cells without any contribution from the drug efflux activity of P-gp.
authors.affiliation: Institute of Molecular Physiology and Genetics, Centre of Excellence of the Slovak Research and Development Agency BIOMEMBRANES 2008, Vlárska 5, 833 34 Bratislava, Slovakia.
authors.forename: Lenka
authors.initials: L
authors.lastname: Gibalová
authors.forename: Ján
authors.initials: J
authors.lastname: Sedlák
authors.forename: Martina
authors.initials: M
authors.lastname: Labudová
authors.forename: Miroslav
authors.initials: M
authors.lastname: Barancík
authors.forename: Alena
authors.initials: A
authors.lastname: Reháková
authors.forename: Albert
authors.initials: A
authors.lastname: Breier
authors.forename: Zdena
authors.initials: Z
authors.lastname: Sulová
mesh_terms: D020168:ATP Binding Cassette Transporter, Subfamily B, Member 1 / Q000378:metabolism*; D000818:Animals; D017209:Apoptosis / Q000187:drug effects; D045744:Cell Line, Tumor; D002945:Cisplatin / Q000494:pharmacology*; D045304:Cytochromes c / Q000378:metabolism; D003593:Cytoplasm / Q000187:drug effects / Q000378:metabolism; D053938:DNA Fragmentation / Q000187:drug effects; D018432:Drug Resistance, Multiple / Q000187:drug effects*; D019008:Drug Resistance, Neoplasm / Q000187:drug effects*; D051379:Mice; D009336:Necrosis / Q000139:chemically induced; D021381:Protein Transport / Q000187:drug effects; D019253:Proto-Oncogene Proteins c-bcl-2 / Q000378:metabolism; D014750:Vincristine / Q000494:pharmacology*; D051028:bcl-2-Associated X Protein / Q000378:metabolism
chemical_list: D020168:ATP Binding Cassette Transporter, Subfamily B, Member 1; D019253:Proto-Oncogene Proteins c-bcl-2; D051028:bcl-2-Associated X Protein; D014750:Vincristine; D045304:Cytochromes c; D002945:Cisplatin