title: Proteasome inhibition correlates with intracellular bortezomib concentrations but not with antiproliferative effects after bolus treatment in myeloma cell lines.
abstract: Although bortezomib is successfully used against multiple myeloma, the pharmacodynamics of proteasome inhibition and its association with efficacy or resistance is poorly understood. Using ultra performance liquid chromatography coupled to tandem mass spectrometry, site-specific luminogenic substrate assays and 3-(4,5-dimethylthiazolyl-2)-2,5-diphenyltetrazoliumbromide (MTT) assays, effects of bortezomib on cellular drug concentrations, chymotrypsin- , caspase- , and trypsin-like activities, and cytotoxic efficacy were evaluated in eight myeloma cell lines directly after 1 h of exposure and additionally after a 23-h washout phase. Bortezomib accumulated in myeloma cells by up to 100-fold and concentration-dependently inhibited the proteasomal activities with the chymotrypsin-like activity being the most sensitive. Whereas intracellular concentrations correlated with the inhibition of the chymotrypsin- and the caspase-like activities of the proteasome, the cytotoxic efficacy of bortezomib did not correlate with either intracellular concentrations or proteasomal inhibition. However, the ratio of concentrations measured directly after the exposure and after the washout phase (indicating drug disposition) correlated with efficacy, suggesting that the cell's ability to dispose bortezomib at least in part influences bortezomib's cytotoxicity. In conclusion, this data argues against a direct association of intracellular concentration or proteasomal inhibition with cytotoxic efficacy but advocates for an important role of cellular drug disposition. Moreover, this study underlines the pleiotropic mode of action of bortezomib going beyond proteasome inhibition.
authors.affiliation: Department of Clinical Pharmacology and Pharmacoepidemiology, University Hospital Heidelberg, Im Neuenheimer Feld 410, 69120, Heidelberg, Germany.
authors.forename: Susan
authors.initials: S
authors.lastname: Dettmer
authors.affiliation: Department of Clinical Pharmacology and Pharmacoepidemiology, University Hospital Heidelberg, Im Neuenheimer Feld 410, 69120, Heidelberg, Germany.
authors.forename: Dirk
authors.initials: D
authors.lastname: Theile
authors.affiliation: Department of Clinical Pharmacology and Pharmacoepidemiology, University Hospital Heidelberg, Im Neuenheimer Feld 410, 69120, Heidelberg, Germany.
authors.forename: Julia
authors.initials: J
authors.lastname: Schäfer
authors.affiliation: Department of Internal Medicine V, Oncology, Hematology, and Rheumatology, University Hospital Heidelberg, Im Neuenheimer Feld 410, 69120, Heidelberg, Germany.
authors.forename: Anja
authors.initials: A
authors.lastname: Seckinger
authors.affiliation: Department of Clinical Pharmacology and Pharmacoepidemiology, University Hospital Heidelberg, Im Neuenheimer Feld 410, 69120, Heidelberg, Germany.
authors.forename: Jürgen
authors.initials: J
authors.lastname: Burhenne
authors.affiliation: Department of Clinical Pharmacology and Pharmacoepidemiology, University Hospital Heidelberg, Im Neuenheimer Feld 410, 69120, Heidelberg, Germany. johanna.weiss@med.uni-heidelberg.de.
authors.forename: Johanna
authors.initials: J
authors.lastname: Weiss
mesh_terms: D000970:Antineoplastic Agents / Q000378:metabolism / Q000494:pharmacology*; D000069286:Bortezomib / Q000378:metabolism / Q000494:pharmacology*; D061945:Caspase Inhibitors / Q000378:metabolism / Q000494:pharmacology; D045744:Cell Line, Tumor; D049109:Cell Proliferation / Q000187:drug effects*; D002470:Cell Survival / Q000187:drug effects; D002853:Chromatography, Liquid; D002918:Chymotrypsin / Q000037:antagonists & inhibitors / Q000378:metabolism; D004305:Dose-Response Relationship, Drug; D006801:Humans; D020128:Inhibitory Concentration 50; D009101:Multiple Myeloma / Q000188:drug therapy* / Q000201:enzymology / Q000473:pathology; D046988:Proteasome Endopeptidase Complex / Q000187:drug effects* / Q000378:metabolism; D061988:Proteasome Inhibitors / Q000378:metabolism / Q000494:pharmacology*; D015842:Serine Proteinase Inhibitors / Q000378:metabolism / Q000494:pharmacology; D053719:Tandem Mass Spectrometry; D013997:Time Factors
chemical_list: D000970:Antineoplastic Agents; D061945:Caspase Inhibitors; D061988:Proteasome Inhibitors; D015842:Serine Proteinase Inhibitors; D000069286:Bortezomib; D002918:Chymotrypsin; D046988:Proteasome Endopeptidase Complex
keywords: Bolus; Bortezomib; Intracellular concentration; Proteasome inhibition