Ascorbic acid restores sensitivity to imatinib via suppression of Nrf2-dependent gene expression in the imatinib-resistant cell line.
OBJECTIVE
Imatinib, a BCR/ABL tyrosine kinase inhibitor, has shown remarkable clinical effects in chronic myelogenous leukemia. However, the leukemia cells become resistant to this drug in most blast crisis cases. The transcription factor Nrf2 regulates the gene expression of a number of detoxifying enzymes such as gamma-glutamylcysteine synthetase (gamma-GCS), the rate-limiting enzyme in glutathione (GSH) synthesis, via the antioxidant response element (ARE). In this study, we examined the involvement of Nrf2 in the acquisition of resistance to imatinib. Since oxidative stress promotes the translocation of Nrf2 from the cytoplasm to the nucleus, we also examined whether ascorbic acid, a reducing reagent, can overcome the resistance to imatinib by inhibiting Nrf2 activity.


RESULTS
Binding of Nrf2 to the ARE of the gamma-GCS light subunit (gamma-GCSl) gene promoter was much stronger in the imatinib-resistant cell line KCL22/SR than in the parental imatinib-sensitive cell line KCL22. The levels of gamma-GCSl mRNA and GSH were higher in KCL22/SR cells, a finding consistent with the observation of an increase in Nrf2-DNA binding. Addition of a GSH monoester to KCL22 cells resulted in an increase in the IC(50) value of imatinib. In contrast, addition of ascorbic acid to KCL22/SR cells resulted in a decrease in Nrf2-DNA binding and decreases in levels of gamma-GCSl mRNA and GSH. Consistent with these findings, ascorbic acid partly restored imatinib sensitivity to KCL22/SR.


CONCLUSIONS
Changes in the redox state caused by antioxidants such as ascorbic acid can overcome resistance to imatinib via inhibition of Nrf2-mediated gene expression.
Tarumoto
Takahisa
T
Division of Hematology, Jichi Medical School, Tochigi, Japan.
Nagai
Tadashi
T
Ohmine
Ken
K
Miyoshi
Takuji
T
Nakamura
Makiko
M
Kondo
Takahito
T
Mitsugi
Kenji
K
Nakano
Syuji
S
Muroi
Kazuo
K
Komatsu
Norio
N
Ozawa
Keiya
K
D000970:Antineoplastic Agents / Q000494:pharmacology*; D001205:Ascorbic Acid / Q000494:pharmacology*; D001549:Benzamides; D001752:Blast Crisis / Q000235:genetics / Q000473:pathology*; D004273:DNA, Neoplasm / Q000235:genetics; D004268:DNA-Binding Proteins / Q000502:physiology*; D019008:Drug Resistance, Neoplasm / Q000187:drug effects*; D004791:Enzyme Inhibitors / Q000494:pharmacology*; D015973:Gene Expression Regulation, Leukemic / Q000187:drug effects*; D005721:Glutamate-Cysteine Ligase / Q000096:biosynthesis / Q000235:genetics; D006801:Humans; D000068877:Imatinib Mesylate; D015464:Leukemia, Myelogenous, Chronic, BCR-ABL Positive / Q000235:genetics / Q000473:pathology*; D051267:NF-E2-Related Factor 2; D018384:Oxidative Stress; D010879:Piperazines / Q000494:pharmacology*; D021381:Protein Transport / Q000187:drug effects; D011743:Pyrimidines / Q000494:pharmacology*; D012334:RNA, Neoplasm / Q000235:genetics; D012045:Regulatory Sequences, Nucleic Acid; D015534:Trans-Activators / Q000502:physiology*
D000970:Antineoplastic Agents; D001549:Benzamides; D004273:DNA, Neoplasm; D004268:DNA-Binding Proteins; D004791:Enzyme Inhibitors; D051267:NF-E2-Related Factor 2; C495635:NFE2L2 protein, human; D010879:Piperazines; D011743:Pyrimidines; D012334:RNA, Neoplasm; D015534:Trans-Activators; D000068877:Imatinib Mesylate; D005721:Glutamate-Cysteine Ligase; D001205:Ascorbic Acid