title: Intracellular glutathione determines bortezomib cytotoxicity in multiple myeloma cells.
abstract: Multiple myeloma (myeloma in short) is an incurable cancer of antibody-producing plasma cells that comprise 13% of all hematological malignancies. The proteasome inhibitor bortezomib has improved treatment significantly, but inherent and acquired resistance to the drug remains a problem. We here show that bortezomib-induced cytotoxicity was completely dampened when cells were supplemented with cysteine or its derivative, glutathione (GSH) in ANBL-6 and INA-6 myeloma cell lines. GSH is a major component of the antioxidative defense in eukaryotic cells. Increasing intracellular GSH levels fully abolished bortezomib-induced cytotoxicity and transcriptional changes. Elevated intracellular GSH levels blocked bortezomib-induced nuclear factor erythroid 2-related factor 2 (NFE2L2, NRF2)-associated stress responses, including upregulation of the xCT subunit of the Xc- cystine-glutamate antiporter. INA-6 cells conditioned to increasing bortezomib doses displayed reduced bortezomib sensitivity and elevated xCT levels. Inhibiting Xc- activity potentiated bortezomib-induced cytotoxicity in myeloma cell lines and primary cells, and re-established sensitivity to bortezomib in bortezomib-conditioned cells. We propose that intracellular GSH level is the main determinant of bortezomib-induced cytotoxicity in a subset of myeloma cells, and that combined targeting of the proteasome and the Xc- cystine-glutamate antiporter can circumvent bortezomib resistance.
authors.affiliation: Department of Cancer Research and Molecular Medicine, K.G. Jebsen Center for Myeloma Research, Norwegian University of Science and Technology, Trondheim, Norway.|Department of Cancer Research and Molecular Medicine, Center of Molecular Inflammation Research, Norwegian University of Science and Technology, Trondheim, Norway.
authors.forename: K K
authors.initials: KK
authors.lastname: Starheim
authors.affiliation: Department of Cancer Research and Molecular Medicine, K.G. Jebsen Center for Myeloma Research, Norwegian University of Science and Technology, Trondheim, Norway.
authors.forename: T
authors.initials: T
authors.lastname: Holien
authors.affiliation: Department of Cancer Research and Molecular Medicine, K.G. Jebsen Center for Myeloma Research, Norwegian University of Science and Technology, Trondheim, Norway.
authors.forename: K
authors.initials: K
authors.lastname: Misund
authors.affiliation: Department of Cancer Research and Molecular Medicine, Center of Molecular Inflammation Research, Norwegian University of Science and Technology, Trondheim, Norway.|Department of Laboratory Medicine, Children's and Women's Health, Faculty of Medicine, Norwegian University of Science and Technology, Trondheim, Norway.
authors.forename: I
authors.initials: I
authors.lastname: Johansson
authors.affiliation: Department of Cancer Research and Molecular Medicine, K.G. Jebsen Center for Myeloma Research, Norwegian University of Science and Technology, Trondheim, Norway.
authors.forename: K A
authors.initials: KA
authors.lastname: Baranowska
authors.affiliation: Department of Cancer Research and Molecular Medicine, K.G. Jebsen Center for Myeloma Research, Norwegian University of Science and Technology, Trondheim, Norway.
authors.forename: A-M
authors.initials: AM
authors.lastname: Sponaas
authors.affiliation: Department of Cancer Research and Molecular Medicine, K.G. Jebsen Center for Myeloma Research, Norwegian University of Science and Technology, Trondheim, Norway.
authors.forename: H
authors.initials: H
authors.lastname: Hella
authors.affiliation: Department of Cancer Research and Molecular Medicine, K.G. Jebsen Center for Myeloma Research, Norwegian University of Science and Technology, Trondheim, Norway.
authors.forename: G
authors.initials: G
authors.lastname: Buene
authors.affiliation: Department of Cancer Research and Molecular Medicine, K.G. Jebsen Center for Myeloma Research, Norwegian University of Science and Technology, Trondheim, Norway.|Department of Hematology, St. Olavs University Hospital, Trondheim, Norway.
authors.forename: A
authors.initials: A
authors.lastname: Waage
authors.affiliation: Department of Cancer Research and Molecular Medicine, K.G. Jebsen Center for Myeloma Research, Norwegian University of Science and Technology, Trondheim, Norway.|Department of Cancer Research and Molecular Medicine, Center of Molecular Inflammation Research, Norwegian University of Science and Technology, Trondheim, Norway.
authors.forename: A
authors.initials: A
authors.lastname: Sundan
authors.affiliation: Department of Cancer Research and Molecular Medicine, K.G. Jebsen Center for Myeloma Research, Norwegian University of Science and Technology, Trondheim, Norway.|Department of Cancer Research and Molecular Medicine, Center of Molecular Inflammation Research, Norwegian University of Science and Technology, Trondheim, Norway.|Department of Medical Laboratory Technology, Faculty of Technology, Norwegian University of Science and Technology, Trondheim, Norway.
authors.forename: G
authors.initials: G
authors.lastname: Bjørkøy
mesh_terms: D000970:Antineoplastic Agents / Q000494:pharmacology*; D017209:Apoptosis / Q000187:drug effects; D000069286:Bortezomib / Q000494:pharmacology*; D045744:Cell Line, Tumor; D002470:Cell Survival / Q000187:drug effects; D016000:Cluster Analysis; D003545:Cysteine / Q000378:metabolism; D004305:Dose-Response Relationship, Drug; D020869:Gene Expression Profiling; D005978:Glutathione / Q000378:metabolism*; D006801:Humans; D042541:Intracellular Space / Q000378:metabolism; D009101:Multiple Myeloma / Q000235:genetics / Q000378:metabolism*; D051267:NF-E2-Related Factor 2 / Q000378:metabolism; D046988:Proteasome Endopeptidase Complex / Q000378:metabolism; D013312:Stress, Physiological
chemical_list: D000970:Antineoplastic Agents; D051267:NF-E2-Related Factor 2; D000069286:Bortezomib; D046988:Proteasome Endopeptidase Complex; D005978:Glutathione; D003545:Cysteine