Proteasome inhibitors induce growth inhibition and apoptosis in myeloma cell lines and in human bone marrow myeloma cells irrespective of chromosome 13 deletion.
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.
Zavrski
Ivana
I
Department of Oncology and Hematology, Universitätsklinikum Charité, Humboldt-Universität Berlin, 10098, Berlin, Germany.
Naujokat
Cord
C
Niemöller
Kathrin
K
Jakob
Christian
C
Heider
Ulrike
U
Langelotz
Corinna
C
Fleissner
Claudia
C
Eucker
Jan
J
Possinger
Kurt
K
Sezer
Orhan
O
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
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