title: Acquired resistance to cetuximab is mediated by increased PTEN instability and leads cross-resistance to gefitinib in HCC827 NSCLC cells.
abstract: EGFR inhibitors, including the small-molecule tyrosine kinase inhibitors such as gefitinib, and the monoclonal antibodies directed at the receptor such as cetuximab, have demonstrated promising effects in non-small cell lung cancer (NSCLC). In this study, we generated cetuximab-resistant cell lines (HCC827-CR) from HCC827 NSCLC cells to investigate acquired resistance mechanisms to cetuximab. In HCC827-CR cells, Akt was hyperactivated and its activity was persistent upon cetuximab treatment. Blockade of PI3K/Akt activity restored cetuximab sensitivity in HCC827-CR cells. Further investigation revealed that increased PTEN instability mediates constitutive Akt activation. By 1microM proteosomal inhibitor, MG-132, PTEN protein levels were restored and Akt activity was dramatically reduced. Overexpression of PTEN by transfection could not restore cetuximab sensitivity in HCC827-CR because overexpressed PTEN was degraded rapidly ( approximately 72h). The increased PTEN instability was confirmed by the treatment of HCC827-CR with a protein synthesis inhibitor, cycloheximide. In the presence of cycloheximide, overexpressed PTEN was degraded more rapidly ( approximately 12h) in HCC827-CR cells. Interestingly, HCC827-CR cells also revealed de novo resistance to gefitinib. Inhibition of PI3K/Akt signaling pathway restored sensitivity to gefitinib in HCC827-CR cells. Taken together, these data show that PTEN instability-mediated constitutive Akt activation is involved in acquired resistance mechanisms to cetuximab and also induces de novo resistance to gefitinib. Importantly, these findings suggest emergence of cross-resistance between two agents as a potential serious problem in the clinical setting.
authors.affiliation: Yonsei University College of Medicine, Seoul, Republic of Korea.
authors.forename: Sun Mi
authors.initials: SM
authors.lastname: Kim
authors.forename: Ji Su
authors.initials: JS
authors.lastname: Kim
authors.forename: Joo-Hang
authors.initials: JH
authors.lastname: Kim
authors.forename: Chae-Ok
authors.initials: CO
authors.lastname: Yun
authors.forename: Eun Mi
authors.initials: EM
authors.lastname: Kim
authors.forename: Hyun Ki
authors.initials: HK
authors.lastname: Kim
authors.forename: Flavio
authors.initials: F
authors.lastname: Solca
authors.forename: Soo-Young
authors.initials: SY
authors.lastname: Choi
authors.forename: Byoung Chul
authors.initials: BC
authors.lastname: Cho
mesh_terms: D000911:Antibodies, Monoclonal / Q000627:therapeutic use*; D061067:Antibodies, Monoclonal, Humanized; D000970:Antineoplastic Agents / Q000627:therapeutic use; D002289:Carcinoma, Non-Small-Cell Lung / Q000188:drug therapy* / Q000473:pathology; D045744:Cell Line, Tumor; D002470:Cell Survival / Q000187:drug effects; D000068818:Cetuximab; D017931:DNA Primers; D019008:Drug Resistance, Neoplasm; D066246:ErbB Receptors / Q000378:metabolism; D005434:Flow Cytometry; D000077156:Gefitinib; D006801:Humans; D008175:Lung Neoplasms / Q000188:drug therapy*; D051059:PTEN Phosphohydrolase / Q000235:genetics* / Q000378:metabolism; D011799:Quinazolines / Q000627:therapeutic use*; D034741:RNA, Small Interfering / Q000235:genetics; D020133:Reverse Transcriptase Polymerase Chain Reaction; D014162:Transfection
chemical_list: D000911:Antibodies, Monoclonal; D061067:Antibodies, Monoclonal, Humanized; D000970:Antineoplastic Agents; D017931:DNA Primers; D011799:Quinazolines; D034741:RNA, Small Interfering; D066246:ErbB Receptors; D051059:PTEN Phosphohydrolase; C494929:PTEN protein, human; D000068818:Cetuximab; D000077156:Gefitinib