In vitro studies of the combination of imatinib mesylate (Gleevec) and arsenic trioxide (Trisenox) in chronic myelogenous leukemia.
OBJECTIVE
The aim of this study was the preclinical evaluation of imatinib mesylate (Gleevec, formerly STI571) in conjunction with arsenic trioxide (As2O3, Trisenox) for the treatment of chronic myelogenous leukemia (CML).


METHODS
Tetrazolium-based cell line proliferation assays (MTT assays) were performed to determine the cytotoxicity of As2O3 alone and in combination with imatinib. Cell lines tested in this study were Bcr-Abl-expressing cells (K562, MO7p210, 32Dp210) and parental cells (MO7e, 32D). Isobologram analysis was performed manually and using the median effect method. In vitro cytotoxicity also was determined in colony-forming assays using CML patient cells. Western blot analysis was performed to detect Bcr-Abl protein levels in K562 cells exposed to As2O3 at graded concentrations. Bcr-Abl protein level kinetics were correlated with cell viability (trypan blue count) and activated caspase-3 detected by flow cytometry.


RESULTS
We show additive to synergistic cytotoxicity in Bcr-Abl+ cell lines depending on inhibitory concentrations and cell type. Results obtained by colony-forming assays confirmed the findings in cell line proliferation assays. Flow cytometric detection of activated caspase-3 revealed synergistic activity in K562 cells. Treatment of K562 cells with As2O3 alone led to down-regulation of Bcr-Abl protein within 24 hours, even at low doses. The decline of Bcr-Abl preceded activation of caspase-3 and the loss of viable cells.


CONCLUSIONS
Favorable cytotoxicity and proapoptotic activity of imatinib in conjunction with As2O3 and specific down-regulation of Bcr-Abl protein levels by As2O3 in K562 cells indicate that As2O3 in combination with imatinib might be useful for circumventing resistance to imatinib monotherapy.
Division of Hematology and Medical Oncology, Oregon Health and Science University, Portland, OR 97201, USA.
Paul
P
La Rosée
Kara
K
Johnson
Michael E
ME
O'Dwyer
Brian J
BJ
Druker
D000970:Antineoplastic Agents / Q000494:pharmacology*; D000077237:Arsenic Trioxide; D001152:Arsenicals / Q000494:pharmacology*; D001549:Benzamides; D014408:Biomarkers, Tumor / Q000096:biosynthesis / Q000235:genetics; D053148:Caspase 3; D020169:Caspases / Q000378:metabolism; D002455:Cell Division / Q000187:drug effects; D004305:Dose-Response Relationship, Drug; D019008:Drug Resistance, Neoplasm; D004357:Drug Synergism; D004789:Enzyme Activation / Q000187:drug effects; D016044:Fusion Proteins, bcr-abl / Q000096:biosynthesis / Q000235:genetics; D015972:Gene Expression Regulation, Neoplastic / Q000187:drug effects; D006801:Humans; D000068877:Imatinib Mesylate; D020014:K562 Cells / Q000187:drug effects; D015464:Leukemia, Myelogenous, Chronic, BCR-ABL Positive / Q000235:genetics / Q000473:pathology*; D010087:Oxides / Q000494:pharmacology*; D010879:Piperazines / Q000494:pharmacology*; D011743:Pyrimidines / Q000494:pharmacology*; D014407:Tumor Cells, Cultured / Q000187:drug effects; D014410:Tumor Stem Cell Assay
D000970:Antineoplastic Agents; D001152:Arsenicals; D001549:Benzamides; D014408:Biomarkers, Tumor; D010087:Oxides; D010879:Piperazines; D011743:Pyrimidines; D000068877:Imatinib Mesylate; D016044:Fusion Proteins, bcr-abl; C505407:CASP3 protein, human; D053148:Caspase 3; D020169:Caspases; D000077237:Arsenic Trioxide