title: Mechanisms of acquired resistance to insulin-like growth factor 1 receptor inhibitor in MCF-7 breast cancer cell line.
abstract: The purpose of this study was to clarify the mechanism of acquired resistance to the insulin-like growth factor-1 receptor (IGF-1R) tyrosine kinase inhibitor NVP-AEW541. We developed an acquired resistant model by continuously exposing MCF-7 breast cancer cells to NVP-AEW541 (MCF-7-NR). MCF-7 and MCF-7-NR were comparatively analyzed for cell signaling and cell growth. While phosphorylation of Akt was completely inhibited by 3 μM NVP-AEW541 in both MCF-7 and MCF-7-NR, phosphorylation of S6K remained high only in MCF-7-NR, suggesting a disconnection between Akt and S6K in MCF-7-NR. Consistently, the mTOR inhibitor everolimus inhibited phosphorylation of S6K and cell growth equally in both lines. Screening of both lines for phosphorylation of 42 receptor tyrosine kinases with and without NVP-AEW541 showed that Tyro3 phosphorylation remained high only in MCF-7-NR. Protein expression of Tyro3 was found to be higher in MCF-7-NR than in MCF-7. Gene silencing of Tyro3 using siRNA resulted in reduced cell growth and cyclin D1 expression in both lines. While Tyro3 expression was inhibited by NVP-AEW541 and everolimus in MCF-7, it was reduced only by everolimus in MCF-7-NR. These findings suggested that cyclin D1 expression was regulated in a S6K/Tyro3-dependent manner in both MCF-7 and MCF-7-NR, and that the disconnection between IGF-1R/Akt and S6K may enable MCF-7-NR to keep cyclin D1 high in the presence of NVP-AEW541. In summary, acquired resistance to NVP-AEW541 appears to result from IGF-1R/Akt-independent activation of S6K and expression of Tyro3 and cyclin D1.
authors: Division of Medical Oncology/Hematology, Department of Internal Medicine, Kobe University Graduate School of Medicine, 7-5-2, Kobe 650-0017, Japan.
authors: Roudy Chiminch
authors: RC
authors: Ekyalongo
authors: Toru
authors: T
authors: Mukohara
authors: Yu
authors: Y
authors: Kataoka
authors: Yohei
authors: Y
authors: Funakoshi
authors: Hideo
authors: H
authors: Tomioka
authors: Naomi
authors: N
authors: Kiyota
authors: Yutaka
authors: Y
authors: Fujiwara
authors: Hironobu
authors: H
authors: Minami
mesh_terms: D000971:Antineoplastic Combined Chemotherapy Protocols; D017209:Apoptosis / Q000187:drug effects*; D015153:Blotting, Western; D001943:Breast Neoplasms / Q000188:drug therapy / Q000378:metabolism / Q000473:pathology*; D049109:Cell Proliferation / Q000187:drug effects; D019008:Drug Resistance, Neoplasm / Q000187:drug effects*; D004357:Drug Synergism; D000068338:Everolimus; D005260:Female; D006801:Humans; D007166:Immunosuppressive Agents / Q000494:pharmacology; D010766:Phosphorylation / Q000187:drug effects; D011743:Pyrimidines / Q000494:pharmacology*; D011758:Pyrroles / Q000494:pharmacology*; D017526:Receptor, IGF Type 1 / Q000037:antagonists & inhibitors* / Q000378:metabolism; D019893:Ribosomal Protein S6 Kinases / Q000037:antagonists & inhibitors / Q000378:metabolism; D020123:Sirolimus / Q000031:analogs & derivatives / Q000494:pharmacology; D014407:Tumor Cells, Cultured
chemical_list: D007166:Immunosuppressive Agents; C501177:NVP-AEW541; D011743:Pyrimidines; D011758:Pyrroles; D000068338:Everolimus; D017526:Receptor, IGF Type 1; D019893:Ribosomal Protein S6 Kinases; D020123:Sirolimus