BCR-ABL-independent and RAS / MAPK pathway-dependent form of imatinib resistance in Ph-positive acute lymphoblastic leukemia cell line with activation of EphB4.
OBJECTIVE
We investigated the mechanism responsible for imatinib (IM) resistance in Philadelphia chromosome-positive acute lymphoblastic leukemia (Ph(+) ALL) cell lines.


METHODS
We established cell lines from a patient with Ph(+) ALL at the time of first diagnosis and relapsed phase and designated as NPhA1 and NPhA2, respectively. We also derived IM-resistant cells, NPhA2/STIR, from NPhA2 under gradually increasing IM concentrations.


RESULTS
NPhA1 was sensitive to IM (IC(50) 0.05 microm) and NPhA2 showed mild IM resistance (IC(50) 0.3 microm). NPhA2/STIR could be maintained in the presence of 10 microm IM. Phosphorylation of MEK and ERK was slightly elevated in NPhA2 and significantly elevated in NPhA2/STIR compared to NPhA1 cells. After treatment with IM, phosphorylation of MEK and ERK was not suppressed but rather increased in NPhA2 and NPhA2/STIR. Active RAS was also increased markedly in NPhA2/STIR after IM treatment. The expression of BCL-2 was increased in NPhA2 compared to NPhA1, but no further increase in NPhA2/STIR. Proliferation of NPhA2/STIR was significantly inhibited by a combination of MEK inhibitor and IM. Analysis of tyrosine phosphorylation status with a protein tyrosine kinase array showed increased phosphorylation of EphB4 in NPhA2/STIR after IM treatment. Although transcription of EphB4 was suppressed in NPhA1 and NPhA2 after IM treatment, it was not suppressed and its ligand, ephrinB2, was increased in NPhA2/STIR. Suppression of EphB4 transcripts by introducing short hairpin RNA into NPhA2/STIR partially restored their sensitivity to IM.


CONCLUSIONS
These results suggest a new mechanism of IM resistance mediated by the activation of RAS/MAPK pathway and EphB4.
Suzuki
Momoko
M
Department of Hematology and Oncology, Nagoya University Graduate School of Medicine, Nagoya 466-8550, Japan.
Abe
Akihiro
A
Imagama
Shizuka
S
Nomura
Yuka
Y
Tanizaki
Ryohei
R
Minami
Yosuke
Y
Hayakawa
Fumihiko
F
Ito
Yoshie
Y
Katsumi
Akira
A
Yamamoto
Kazuhito
K
Emi
Nobuhiko
N
Kiyoi
Hitoshi
H
Naoe
Tomoki
T
D001549:Benzamides; D045744:Cell Line, Tumor / Q000187:drug effects / Q000201:enzymology; D019008:Drug Resistance, Neoplasm / Q000502:physiology*; D004789:Enzyme Activation; D004790:Enzyme Induction; D036388:Ephrin-B2 / Q000235:genetics / Q000502:physiology; D005260:Female; D016044:Fusion Proteins, bcr-abl / Q000037:antagonists & inhibitors*; D006801:Humans; D000068877:Imatinib Mesylate; D020935:MAP Kinase Signaling System / Q000502:physiology; D008875:Middle Aged; D009363:Neoplasm Proteins / Q000037:antagonists & inhibitors / Q000235:genetics / Q000502:physiology*; D010766:Phosphorylation / Q000187:drug effects; D010879:Piperazines / Q000494:pharmacology*; D054198:Precursor Cell Lymphoblastic Leukemia-Lymphoma / Q000201:enzymology* / Q000473:pathology; D047428:Protein Kinase Inhibitors / Q000494:pharmacology*; D011499:Protein Processing, Post-Translational / Q000187:drug effects; D011743:Pyrimidines / Q000494:pharmacology*; D034741:RNA, Small Interfering / Q000494:pharmacology; D036224:Receptor, EphB4 / Q000037:antagonists & inhibitors / Q000235:genetics / Q000502:physiology*; D012008:Recurrence; D018631:ras Proteins / Q000502:physiology*
D001549:Benzamides; D036388:Ephrin-B2; D009363:Neoplasm Proteins; D010879:Piperazines; D047428:Protein Kinase Inhibitors; D011743:Pyrimidines; D034741:RNA, Small Interfering; D000068877:Imatinib Mesylate; D036224:Receptor, EphB4; D016044:Fusion Proteins, bcr-abl; D018631:ras Proteins