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Analysis of gene expression profiles in an imatinib-resistant cell line, KCL22/SR
Ken Ohmine1, Tadashi Nagai, Takahisa Tarumoto
1Divisions of Hematology, Cell Transplantation and Transfusion, and Functional Genomics, Jichi Medical School, Tochigi, Japan.
Abstract:
The BCR/ABL tyrosine kinase inhibitor, imatinib, has shown substantial effects in blast crises of chronic myelogenous leukemia. However, most patients relapse after an initial clinical response, indicating that drug resistance is a major problem for patients being treated with imatinib. In this study, we generated a new imatinib-resistant BCR/ABL-positive cell line, KCL22/SR. The 50% inhibitory concentration of imatinib was 11-fold higher in KCL22/SR than in the imatinib-sensitive parental cell line, KCL22. However, KCL22/SR showed no mutations in the BCR/ABL gene and no increase in the levels of BCR/ABL protein and P-glycoprotein. Furthermore, the level of phosphorylated BCR/ABL protein was suppressed by imatinib treatment, suggesting that mechanisms independent of BCR/ABL signaling are involved in the imatinib resistance in KCL22/SR cells. DNA microarray analyses demonstrated that the signal transduction-related molecules, RAS p21 protein activator and RhoA, which could affect Ras signaling, and a surface tumor antigen, L6, were upregulated, while c-Myb and activin A receptor were downregulated in KCL22/SR cells. Furthermore, imatinib treatment significantly suppressed the level of phosphorylated p44/42 in KCL22 cells but not in KCL22/SR cells, even when BCR/ABL was inhibited by imatinib. These results suggest that various mechanisms, including disturbance of Ras-mitogen-activated protein kinase signaling, are involved in imatinib resistance.
Insights
Drug resistance to imatinib, a BCR/ABL tyrosine kinase inhibitor, is a major challenge in chronic myelogenous leukemia. New research reveals mechanisms of imatinib resistance independent of BCR/ABL signaling, involving altered cell signaling pathways.
Area of Science:
- Oncology
- Molecular Biology
- Pharmacology
Background:
- Imatinib is a crucial BCR/ABL tyrosine kinase inhibitor for chronic myelogenous leukemia (CML).
- Therapeutic resistance to imatinib is a significant clinical challenge, leading to patient relapse.
- Understanding resistance mechanisms is vital for developing effective CML treatments.
Purpose of the Study:
- To investigate the mechanisms underlying imatinib resistance in BCR/ABL-positive cells.
- To characterize a newly generated imatinib-resistant cell line (KCL22/SR).
- To identify molecular alterations associated with imatinib resistance.
Main Methods:
- Generation and characterization of an imatinib-resistant cell line (KCL22/SR).
- Analysis of BCR/ABL gene mutations, protein levels, and phosphorylation status.
- P-glycoprotein expression analysis.
- DNA microarray analysis to identify differentially expressed genes.
- Assessment of p44/42 phosphorylation in response to imatinib.
Main Results:
- KCL22/SR cells exhibited an 11-fold higher imatinib IC50 compared to parental KCL22 cells.
- No BCR/ABL mutations or increased BCR/ABL/P-glycoprotein levels were observed in KCL22/SR.
- Imatinib suppressed BCR/ABL phosphorylation in KCL22/SR, indicating BCR/ABL-independent resistance.
- Upregulation of RAS p21 protein activator, RhoA, and L6, and downregulation of c-Myb and activin A receptor were noted in KCL22/SR.
- Imatinib failed to suppress p44/42 phosphorylation in KCL22/SR cells, unlike in KCL22 cells.
Conclusions:
- Imatinib resistance in KCL22/SR cells involves mechanisms independent of BCR/ABL signaling.
- Disturbances in Ras-mitogen-activated protein kinase (MAPK) signaling pathways contribute to imatinib resistance.
- Further research into these alternative signaling pathways is warranted for overcoming imatinib resistance in CML.