title: Proteasome inhibitors induce growth inhibition and apoptosis in myeloma cell lines and in human bone marrow myeloma cells irrespective of chromosome 13 deletion.
abstract: OBJECTIVE
  In this study, we investigated the effects of cell-permeable proteasome inhibitors MG-132, MG-262, PSI, and lactacystin on multiple myeloma cell lines OPM-2, U266, RPMI 8226-S, freshly isolated plasma cells with or without deletion of chromosome 13 from patients with multiple myeloma and plasma cell leukemia, and CD34+ human hematopoietic stem cells. The effects of proteasome inhibitors on cell cycle progression, cell growth, and apoptosis were determined.
  
  
  METHODS
  MTT-assay was used to examine the cytotoxicity, and annexin-V staining to quantify apoptosis. Cell cycle analyses were performed using 7-ADD and Ki-67 staining by flow cytometry.
  
  
  RESULTS
  PSI was the most potent proteasome inhibitor among those tested with a half maximal cytotoxicity (IC(50)) of 5.7 nM, followed by MG-262, MG-132, and lactacystin. Growth inhibition occurred irrespective of chromosome 13 status. Cell cycle arrest occurred in a dose- and time-dependent manner. Low, subapoptotic dosages led to a partial loss of Ki-67 antigen, whereas apoptotic dosages led to reduced Ki-67 levels. Apoptosis was partially dependent on activation of caspase-3, since Ac-DEVD-cho, a caspase-3 inhibitor, could reduce apoptosis significantly. The cytotoxicity of the four proteasome inhibitors tested was significantly lower in human hematopoietic stem cells than in myeloma cells.
  
  
  CONCLUSIONS
  Our results show that proteasome inhibitors induce time- and dose-dependent cell cycle alterations, growth inhibition, and apoptosis in human myeloma cells irrespective of chromosome 13 deletion.
authors.affiliation: Department of Oncology and Hematology, Universitätsklinikum Charité, Humboldt-Universität Berlin, 10098, Berlin, Germany.
authors.forename: Ivana
authors.initials: I
authors.lastname: Zavrski
authors.forename: Cord
authors.initials: C
authors.lastname: Naujokat
authors.forename: Kathrin
authors.initials: K
authors.lastname: Niemöller
authors.forename: Christian
authors.initials: C
authors.lastname: Jakob
authors.forename: Ulrike
authors.initials: U
authors.lastname: Heider
authors.forename: Corinna
authors.initials: C
authors.lastname: Langelotz
authors.forename: Claudia
authors.initials: C
authors.lastname: Fleissner
authors.forename: Jan
authors.initials: J
authors.lastname: Eucker
authors.forename: Kurt
authors.initials: K
authors.lastname: Possinger
authors.forename: Orhan
authors.initials: O
authors.lastname: Sezer
mesh_terms: D018952:Antigens, CD34 / Q000378:metabolism; D017209:Apoptosis / Q000187:drug effects; D053148:Caspase 3; D053179:Caspase 7; D020169:Caspases / Q000378:metabolism; D002453:Cell Cycle / Q000187:drug effects; D002455:Cell Division / Q000187:drug effects; D002872:Chromosome Deletion; D002882:Chromosomes, Human, Pair 13 / Q000502:physiology*; D003546:Cysteine Endopeptidases; D006412:Hematopoietic Stem Cells / Q000187:drug effects* / Q000378:metabolism; D006801:Humans; D009097:Multienzyme Complexes / Q000037:antagonists & inhibitors*; D009101:Multiple Myeloma / Q000201:enzymology / Q000235:genetics / Q000473:pathology*; D046988:Proteasome Endopeptidase Complex; D014407:Tumor Cells, Cultured
chemical_list: D018952:Antigens, CD34; D009097:Multienzyme Complexes; C505407:CASP3 protein, human; C505520:CASP7 protein, human; D053148:Caspase 3; D053179:Caspase 7; D020169:Caspases; D003546:Cysteine Endopeptidases; D046988:Proteasome Endopeptidase Complex