The proteasome inhibitor PS-341 inhibits growth and induces apoptosis in Bcr/Abl-positive cell lines sensitive and resistant to imatinib mesylate.
OBJECTIVE
Imatinib mesylate (IM) is the choice treatment for Bcr/Abl-positive malignancies. Emergence of resistance to IM warrants the exploration of novel well-tolerated anticancer agents. We intended to evaluate the effect of PS-341 on proliferation, survival, and cellular events in Bcr/Abl-positive cells sensitive and resistant to IM, and to investigate the effect of PS-341 and IM in conjunction.


METHODS
Bcr/Abl-positive cell lines sensitive (p210Bcr/Abl KBM5, p210Bcr/Abl KBM7, and p190Bcr/Abl Z-119) or resistant (KBM5-R) to IM were treated with PS-341 alone or in combination with IM. The effect on cell growth was determined using the MTT assay. Cell-cycle analysis was performed by propidium iodide staining. Apoptosis was evaluated by measurement of sub-G1 DNA content, annexin V binding, and caspase 3 activity assays. Levels of apoptotic proteins, P-IkBalpha, Bcr/Abl, and phosphorylated Bcr/Abl were determined by western blotting. NF-kappaB activity was evaluated by electromobility gel shift assays.


RESULTS
PS-341 exerted growth inhibition effects in IM-sensitive and -resistant cells. This phenomenon correlated with accumulation of cells in the G2/M phase of cell cycle; transient downregulation of NFkappaB DNA binding activity; downregulation of Bcl-xL; activation of caspase 3, induction of apoptosis; inhibition of expression and phosphorylation of Bcr/Abl. Sequential combination of PS-341 followed by IM demonstrated a synergistic pro-apoptotic effect in IM-sensitive cells; concomitant exposure was antagonistic.


CONCLUSIONS
PS-341 suppresses growth and induces apoptosis in Bcr/Abl-positive cells sensitive and resistant to IM. The use of PS-341 should be explored in patients with chronic myelogenous leukemia resistant to IM. Trials of combinations of PS-341 and IM require cautious design.
Gatto
Simona
S
Department of Leukemia, The University of Texas M. D. Anderson Cancer Center, Houston, Texas, USA.
Scappini
Barbara
B
Pham
Lan
L
Onida
Francesco
F
Milella
Michele
M
Ball
Greg
G
Ricci
Clara
C
Divoky
Vladimir
V
Verstovsek
Srdan
S
Kantarjian
Hagop M
HM
Keating
Michael J
MJ
Cortes-Franco
Jorge E
JE
Beran
Miloslav
M
D017209:Apoptosis / Q000187:drug effects*; D001549:Benzamides; D001897:Boronic Acids / Q000494:pharmacology*; D000069286:Bortezomib; D053148:Caspase 3; D020169:Caspases; D002453:Cell Cycle / Q000187:drug effects; D045744:Cell Line, Tumor; D003546:Cysteine Endopeptidases; D015853:Cysteine Proteinase Inhibitors / Q000494:pharmacology*; D004268:DNA-Binding Proteins / Q000378:metabolism / Q000502:physiology; D004338:Drug Combinations; D019008:Drug Resistance, Neoplasm; D016044:Fusion Proteins, bcr-abl / Q000096:biosynthesis / Q000235:genetics / Q000378:metabolism; D015972:Gene Expression Regulation, Neoplastic / Q000187:drug effects; D016313:Genes, abl; D006801:Humans; D020672:I-kappa B Proteins / Q000378:metabolism; D000068877:Imatinib Mesylate; D007945:Leukemia, Lymphoid / Q000201:enzymology / Q000235:genetics / Q000378:metabolism / Q000473:pathology; D007951:Leukemia, Myeloid / Q000201:enzymology / Q000235:genetics / Q000378:metabolism / Q000473:pathology; D009097:Multienzyme Complexes / Q000037:antagonists & inhibitors*; D000072000:NF-KappaB Inhibitor alpha; D016328:NF-kappa B / Q000037:antagonists & inhibitors / Q000378:metabolism / Q000502:physiology; D010766:Phosphorylation / Q000187:drug effects; D010879:Piperazines / Q000494:pharmacology*; D046988:Proteasome Endopeptidase Complex; D011719:Pyrazines / Q000494:pharmacology*; D011743:Pyrimidines / Q000494:pharmacology*
D001549:Benzamides; D001897:Boronic Acids; D015853:Cysteine Proteinase Inhibitors; D004268:DNA-Binding Proteins; D004338:Drug Combinations; D020672:I-kappa B Proteins; D009097:Multienzyme Complexes; D016328:NF-kappa B; C000606204:NFKBIA protein, human; D010879:Piperazines; D011719:Pyrazines; D011743:Pyrimidines; D000072000:NF-KappaB Inhibitor alpha; D000069286:Bortezomib; D000068877:Imatinib Mesylate; D016044:Fusion Proteins, bcr-abl; C505407:CASP3 protein, human; D053148:Caspase 3; D020169:Caspases; D003546:Cysteine Endopeptidases; D046988:Proteasome Endopeptidase Complex