title: Antileukemic activity and mechanism of drug resistance to the marine Salinispora tropica proteasome inhibitor salinosporamide A (Marizomib).
abstract: Salinosporamide A (NPI-0052, marizomib) is a naturally occurring proteasome inhibitor derived from the marine actinobacterium Salinispora tropica, and represents a promising clinical agent in the treatment of hematologic malignancies. Recently, these actinobacteria were shown to harbor self-resistance properties to salinosporamide A by expressing redundant catalytically active mutants of the 20S proteasome β-subunit, reminiscent of PSMB5 mutations identified in cancer cells with acquired resistance to the founding proteasome inhibitor bortezomib (BTZ). Here, we assessed the growth inhibitory potential of salinosporamide A in human acute lymphocytic leukemia CCRF-CEM cells, and its 10-fold (CEM/BTZ7) and 123-fold (CEM/BTZ200) bortezomib-resistant sublines harboring PSMB5 mutations. Parental cells displayed sensitivity to salinosporamide A (IC50 = 5.1 nM), whereas their bortezomib-resistant sublines were 9- and 17-fold cross-resistant to salinosporamide A, respectively. Notably, combination experiments of salinosporamide A and bortezomib showed synergistic activity in CEM/BTZ200 cells. CEM cells gradually exposed to 20 nM salinosporamide A (CEM/S20) displayed stable 5-fold acquired resistance to salinosporamide A and were 3-fold cross-resistant to bortezomib. Consistent with the acquisition of a PSMB5 point mutation (M45V) in CEM/S20 cells, salinosporamide A displayed a markedly impaired capacity to inhibit β5-associated catalytic activity. Last, compared with parental CEM cells, CEM/S20 cells exhibited up to 2.5-fold upregulation of constitutive proteasome subunits, while retaining unaltered immunoproteasome subunit expression. In conclusion, salinosporamide A displayed potent antileukemic activity against bortezomib-resistant leukemia cells. β-Subunit point mutations as a common feature of acquired resistance to salinosporamide A and bortezomib in hematologic cells and S. tropica suggest an evolutionarily conserved mechanism of resistance to proteasome inhibitors.
authors.affiliation: Department of Pediatric Oncology/Hematology (D.N., L.F.V.R., J.v.M., G.J.L.K., J.C.), Department of Rheumatology (G.J.), and Department of Hematology (J.v.M., S.Z., J.C.), VU University Medical Center, Amsterdam, The Netherlands; Scripps Institution of Oceanography and Skaggs School of Pharmacy and Pharmaceutical Sciences, University of California at San Diego, San Diego, California (A.J.K., B.S.M.); The Fred Wyszkowski Cancer Research Laboratory, Technion-Israel Institute of Technology, Haifa, Israel (Y.G.A.); and Research Department, Onyx Pharmaceuticals Inc., South San Francisco, California (J.L.A.).
authors.forename: Denise
authors.initials: D
authors.lastname: Niewerth
authors.affiliation: Department of Pediatric Oncology/Hematology (D.N., L.F.V.R., J.v.M., G.J.L.K., J.C.), Department of Rheumatology (G.J.), and Department of Hematology (J.v.M., S.Z., J.C.), VU University Medical Center, Amsterdam, The Netherlands; Scripps Institution of Oceanography and Skaggs School of Pharmacy and Pharmaceutical Sciences, University of California at San Diego, San Diego, California (A.J.K., B.S.M.); The Fred Wyszkowski Cancer Research Laboratory, Technion-Israel Institute of Technology, Haifa, Israel (Y.G.A.); and Research Department, Onyx Pharmaceuticals Inc., South San Francisco, California (J.L.A.).
authors.forename: Gerrit
authors.initials: G
authors.lastname: Jansen
authors.affiliation: Department of Pediatric Oncology/Hematology (D.N., L.F.V.R., J.v.M., G.J.L.K., J.C.), Department of Rheumatology (G.J.), and Department of Hematology (J.v.M., S.Z., J.C.), VU University Medical Center, Amsterdam, The Netherlands; Scripps Institution of Oceanography and Skaggs School of Pharmacy and Pharmaceutical Sciences, University of California at San Diego, San Diego, California (A.J.K., B.S.M.); The Fred Wyszkowski Cancer Research Laboratory, Technion-Israel Institute of Technology, Haifa, Israel (Y.G.A.); and Research Department, Onyx Pharmaceuticals Inc., South San Francisco, California (J.L.A.).
authors.forename: Lesley F V
authors.initials: LF
authors.lastname: Riethoff
authors.affiliation: Department of Pediatric Oncology/Hematology (D.N., L.F.V.R., J.v.M., G.J.L.K., J.C.), Department of Rheumatology (G.J.), and Department of Hematology (J.v.M., S.Z., J.C.), VU University Medical Center, Amsterdam, The Netherlands; Scripps Institution of Oceanography and Skaggs School of Pharmacy and Pharmaceutical Sciences, University of California at San Diego, San Diego, California (A.J.K., B.S.M.); The Fred Wyszkowski Cancer Research Laboratory, Technion-Israel Institute of Technology, Haifa, Israel (Y.G.A.); and Research Department, Onyx Pharmaceuticals Inc., South San Francisco, California (J.L.A.).
authors.forename: Johan
authors.initials: J
authors.lastname: van Meerloo
authors.affiliation: Department of Pediatric Oncology/Hematology (D.N., L.F.V.R., J.v.M., G.J.L.K., J.C.), Department of Rheumatology (G.J.), and Department of Hematology (J.v.M., S.Z., J.C.), VU University Medical Center, Amsterdam, The Netherlands; Scripps Institution of Oceanography and Skaggs School of Pharmacy and Pharmaceutical Sciences, University of California at San Diego, San Diego, California (A.J.K., B.S.M.); The Fred Wyszkowski Cancer Research Laboratory, Technion-Israel Institute of Technology, Haifa, Israel (Y.G.A.); and Research Department, Onyx Pharmaceuticals Inc., South San Francisco, California (J.L.A.).
authors.forename: Andrew J
authors.initials: AJ
authors.lastname: Kale
authors.affiliation: Department of Pediatric Oncology/Hematology (D.N., L.F.V.R., J.v.M., G.J.L.K., J.C.), Department of Rheumatology (G.J.), and Department of Hematology (J.v.M., S.Z., J.C.), VU University Medical Center, Amsterdam, The Netherlands; Scripps Institution of Oceanography and Skaggs School of Pharmacy and Pharmaceutical Sciences, University of California at San Diego, San Diego, California (A.J.K., B.S.M.); The Fred Wyszkowski Cancer Research Laboratory, Technion-Israel Institute of Technology, Haifa, Israel (Y.G.A.); and Research Department, Onyx Pharmaceuticals Inc., South San Francisco, California (J.L.A.).
authors.forename: Bradley S
authors.initials: BS
authors.lastname: Moore
authors.affiliation: Department of Pediatric Oncology/Hematology (D.N., L.F.V.R., J.v.M., G.J.L.K., J.C.), Department of Rheumatology (G.J.), and Department of Hematology (J.v.M., S.Z., J.C.), VU University Medical Center, Amsterdam, The Netherlands; Scripps Institution of Oceanography and Skaggs School of Pharmacy and Pharmaceutical Sciences, University of California at San Diego, San Diego, California (A.J.K., B.S.M.); The Fred Wyszkowski Cancer Research Laboratory, Technion-Israel Institute of Technology, Haifa, Israel (Y.G.A.); and Research Department, Onyx Pharmaceuticals Inc., South San Francisco, California (J.L.A.).
authors.forename: Yehuda G
authors.initials: YG
authors.lastname: Assaraf
authors.affiliation: Department of Pediatric Oncology/Hematology (D.N., L.F.V.R., J.v.M., G.J.L.K., J.C.), Department of Rheumatology (G.J.), and Department of Hematology (J.v.M., S.Z., J.C.), VU University Medical Center, Amsterdam, The Netherlands; Scripps Institution of Oceanography and Skaggs School of Pharmacy and Pharmaceutical Sciences, University of California at San Diego, San Diego, California (A.J.K., B.S.M.); The Fred Wyszkowski Cancer Research Laboratory, Technion-Israel Institute of Technology, Haifa, Israel (Y.G.A.); and Research Department, Onyx Pharmaceuticals Inc., South San Francisco, California (J.L.A.).
authors.forename: Janet L
authors.initials: JL
authors.lastname: Anderl
authors.affiliation: Department of Pediatric Oncology/Hematology (D.N., L.F.V.R., J.v.M., G.J.L.K., J.C.), Department of Rheumatology (G.J.), and Department of Hematology (J.v.M., S.Z., J.C.), VU University Medical Center, Amsterdam, The Netherlands; Scripps Institution of Oceanography and Skaggs School of Pharmacy and Pharmaceutical Sciences, University of California at San Diego, San Diego, California (A.J.K., B.S.M.); The Fred Wyszkowski Cancer Research Laboratory, Technion-Israel Institute of Technology, Haifa, Israel (Y.G.A.); and Research Department, Onyx Pharmaceuticals Inc., South San Francisco, California (J.L.A.).
authors.forename: Sonja
authors.initials: S
authors.lastname: Zweegman
authors.affiliation: Department of Pediatric Oncology/Hematology (D.N., L.F.V.R., J.v.M., G.J.L.K., J.C.), Department of Rheumatology (G.J.), and Department of Hematology (J.v.M., S.Z., J.C.), VU University Medical Center, Amsterdam, The Netherlands; Scripps Institution of Oceanography and Skaggs School of Pharmacy and Pharmaceutical Sciences, University of California at San Diego, San Diego, California (A.J.K., B.S.M.); The Fred Wyszkowski Cancer Research Laboratory, Technion-Israel Institute of Technology, Haifa, Israel (Y.G.A.); and Research Department, Onyx Pharmaceuticals Inc., South San Francisco, California (J.L.A.).
authors.forename: Gertjan J L
authors.initials: GJ
authors.lastname: Kaspers
authors.affiliation: Department of Pediatric Oncology/Hematology (D.N., L.F.V.R., J.v.M., G.J.L.K., J.C.), Department of Rheumatology (G.J.), and Department of Hematology (J.v.M., S.Z., J.C.), VU University Medical Center, Amsterdam, The Netherlands; Scripps Institution of Oceanography and Skaggs School of Pharmacy and Pharmaceutical Sciences, University of California at San Diego, San Diego, California (A.J.K., B.S.M.); The Fred Wyszkowski Cancer Research Laboratory, Technion-Israel Institute of Technology, Haifa, Israel (Y.G.A.); and Research Department, Onyx Pharmaceuticals Inc., South San Francisco, California (J.L.A.) j.cloos@vumc.nl.
authors.forename: Jacqueline
authors.initials: J
authors.lastname: Cloos
mesh_terms: D039903:Actinobacteria / Q000378:metabolism*; D001897:Boronic Acids / Q000494:pharmacology; D000069286:Bortezomib; D002384:Catalysis / Q000187:drug effects; D045744:Cell Line, Tumor; D019008:Drug Resistance, Neoplasm / Q000187:drug effects* / Q000235:genetics; D006801:Humans; D007783:Lactones / Q000494:pharmacology*; D007938:Leukemia / Q000188:drug therapy* / Q000235:genetics / Q000378:metabolism; D009154:Mutation / Q000187:drug effects / Q000235:genetics; D046988:Proteasome Endopeptidase Complex / Q000235:genetics / Q000378:metabolism; D061988:Proteasome Inhibitors / Q000494:pharmacology*; D011719:Pyrazines / Q000494:pharmacology; D011758:Pyrroles / Q000494:pharmacology*; D015854:Up-Regulation / Q000187:drug effects / Q000235:genetics
chemical_list: D001897:Boronic Acids; D007783:Lactones; D061988:Proteasome Inhibitors; D011719:Pyrazines; D011758:Pyrroles; D000069286:Bortezomib; C475865:marizomib; C088874:PSMB5 protein, human; D046988:Proteasome Endopeptidase Complex
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