Loss of PTEN expression by blocking nuclear translocation of EGR1 in gefitinib-resistant lung cancer cells harboring epidermal growth factor receptor-activating mutations.
Gefitinib (Iressa) and erlotinib (Tarceva), which target the epidermal growth factor receptor (EGFR), are approved for treatment of patients with advanced non-small cell lung cancer (NSCLC). Patients whose tumors harbor mutations in the EGFR gene, including delE746-A750 in exon 19 and L858R in exon 21, may benefit in particular from gefitinib treatment. However, acquired resistance to gefitinib has been a serious clinical problem, and further optimization is needed for application of EGFR-targeted drugs in lung cancer patients. In this study, we established gefitinib-resistant NSCLC cells from PC-9 cell line, which harbors the delE746-A750 mutation, by exposing the cell line to gefitinib for over 7 months. Gefitinib-resistant PC-9/GEFs cell lines showed a marked downregulation of PTEN expression and increased Akt phosphorylation. In revertant, gefitinib-sensitive clones (PC-9/Rev) derived from PC-9/GEF1-1 and PC-9/GEF2-1, PTEN expression, as well as sensitivity to gefitinib and erlotinib, was restored. Knockdown of PTEN expression using small interfering RNA specific for PTEN in PC-9 cells resulted in drug resistance to gefitinib and erlotinib. Nuclear translocation of the EGR1 transcription factor, which regulates PTEN expression, was shown to be suppressed in resistant clones and restored in their revertant clones. Reduced PTEN expression was also seen in tumor samples from a patient with gefitinib-refractory NSCLC. This study thus strongly suggests that loss of PTEN expression contributes to gefitinib and erlotinib resistance in NSCLC. Our findings reinforce the therapeutic importance of PTEN expression in the treatment of NSCLC with EGFR-targeted drugs.
Department of Pharmaceutical Oncology and Laboratory of Molecular Cancer Biology, Graduate School of Pharmaceutical Sciences, Kyushu University, Fukuoka, Japan.
Chizuko
C
Yamamoto
Yuji
Y
Basaki
Akihiko
A
Kawahara
Kazutaka
K
Nakashima
Masayoshi
M
Kage
Hiroto
H
Izumi
Kimitoshi
K
Kohno
Hidetaka
H
Uramoto
Kosei
K
Yasumoto
Michihiko
M
Kuwano
Mayumi
M
Ono
D015153:Blotting, Western; D002289:Carcinoma, Non-Small-Cell Lung / Q000188:drug therapy / Q000235:genetics* / Q000473:pathology; D002467:Cell Nucleus / Q000187:drug effects / Q000378:metabolism; D049109:Cell Proliferation / Q000187:drug effects; D019008:Drug Resistance, Neoplasm; D051766:Early Growth Response Protein 1 / Q000235:genetics / Q000378:metabolism*; D066246:ErbB Receptors / Q000037:antagonists & inhibitors / Q000235:genetics*; D000069347:Erlotinib Hydrochloride; D000077156:Gefitinib; D006801:Humans; D007124:Immunoenzyme Techniques; D008175:Lung Neoplasms / Q000188:drug therapy / Q000235:genetics / Q000473:pathology; D009154:Mutation / Q000235:genetics*; D051059:PTEN Phosphohydrolase / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism*; D010766:Phosphorylation / Q000187:drug effects; D047428:Protein Kinase Inhibitors / Q000627:therapeutic use; D021381:Protein Transport / Q000187:drug effects; D011799:Quinazolines / Q000627:therapeutic use*; D012333:RNA, Messenger / Q000235:genetics; D034741:RNA, Small Interfering / Q000494:pharmacology; D020133:Reverse Transcriptase Polymerase Chain Reaction; D014407:Tumor Cells, Cultured
C497325:EGR1 protein, human; D051766:Early Growth Response Protein 1; D047428:Protein Kinase Inhibitors; D011799:Quinazolines; D012333:RNA, Messenger; D034741:RNA, Small Interfering; D000069347:Erlotinib Hydrochloride; C512478:EGFR protein, human; D066246:ErbB Receptors; D051059:PTEN Phosphohydrolase; C494929:PTEN protein, human; D000077156:Gefitinib