2005 Fiscal Year Final Research Report Summary
Novel mechanisms of drug resistance in leukemia and the new molecular target therapeutic strategies.
| Project/Area Number |
16590959
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| Research Category |
Grant-in-Aid for Scientific Research (C)
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| Allocation Type | Single-year Grants |
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| Section | 一般 |
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| Research Field |
Hematology
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| Research Institution | JICHI MEDICAL SCHOOL |
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Principal Investigator |
OHMINE Ken JICHI MEDICAL SCHOOL, Faculty of Medicine, Research Associate, 医学部, 助手 (90316521)
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| Co-Investigator(Kenkyū-buntansha) |
NAGAI Tadashi JICHI MEDICAL SCHOOL, Faculty of Medicine, Assistant Professor, 医学部, 助教授 (40237483)
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| Project Period (FY) |
2004 – 2005
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| Keywords | CML / Drug resistance / BCR / ABL / imatinib / RhoA / KCL22 / SR / Heme / glutatione |
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| Research Abstract |
The ABL tyrosine kinase inhibitor imatinib mesylate has shown a substantial clinical effect in CML. It is important to determine the potential mechanism of resistance to this compound.
1.We found that RhoA, which plays important roles in signal transduction pathways, is expressed at higher levels in an imatinib-resistant BCR/ABL-positive cell line KCK22/SR, than in the parent cell line KCL22. We cloned new imatinib-resistant cells, K562/SR and KU812/SR. Western blot analysis showed that RhoA was up-regulated in KU812/SR cells.
2.We examined the cytotoxic effect of treatment with a combination of imatinib and Chk1 inhibitor UCN-01. The level of apoptosis of imatinib-resistant BCR/ABL-positive cell lines was not increased by the combination treatment, but G0/G1 accumulation in the cells was increased by the combination treatment. Isoborograms showed that combined treatment of all cells with UCN-01 and imatinib did not result in synergistic inhibition of cell growth. In contrast, some of th
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em showed an antagonistic effect. The results suggest that a cell cycle blockage compound inhibits the imatinib effect.
3.Heme plays an important biomodulating role in various cell systems. We investigated the role of heme in modulation of the sensitivity of leukemia cells to imatinib using human BCR/ABL-positive cells. IC_<50> values of imatinib in KCL22 cells were increased by hemin treatment in a dose-dependent manner. Hemin treatment also suppressed imatinib-mediated induction of apoptosis. Levels of phosphorylated BCR/ABL and phosphorylated ERK1/2 were decreased by imatinib treatment regardless of the presence or absence of hemin, indicating that the hemin-mediated increase in IC_<50> values of imatinib does not involve imatinib-mediated inhibition of BCR/ABL kinase activity. On the other hand, hemin treatment increased the activity of the human γ-GCS light subunit gene promoter and the intracellular glutathione (GSH) concentration. These findings thus indicate that heme plays an essential role in determining the sensitivity of leukemia cells to imatinib and that its effect is mediated, in part, via the GSH modulate pathway. Less
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