title: Multiple molecular mechanisms underlying trastuzumab and lapatinib resistance in JIMT-1 breast cancer cells.
abstract: Trastuzumab plays an important role in breast cancer therapy. However, a significant fraction of patients do not respond to therapy or they tend to develop resistance shortly after beginning therapy. Although some resistance mechanisms have been described, it is unclear whether these mechanisms can coexist. In this study, we analyzed the resistance mechanisms in the breast cancer cell line JIMT-1, a model of intrinsic trastuzumab resistance. We compared the JIMT-1 cell line with a panel of eight HER-2 positive breast cancer cell lines. All cell lines were characterized for the phosphatidylinositol 3-kinase (PIK3CA) mutation status, expression levels of the phosphatase and tensin homolog on chromosome 10 (PTEN) and neuregulin-1 (NRG1) mRNA, HER-2 gene copy number, and protein expression. The results were correlated to the sensitivity to trastuzumab and lapatinib as well as the potency of trastuzumab-mediated antibody-dependent cellular cytotoxicity (ADCC) evoked by trastuzumab. JIMT-1 cells showed several co-existing drug resistance mechanisms, including an activating mutation of the PIK3CA gene, low expression of PTEN, high expression of NRG1, and relatively low expression of HER-2 receptor protein (despite gene amplification). All these features were present at variable levels in other cell lines, whereas JIMT-1 was unique in displaying all these factors at the same time. Unexpectedly, ADCC reaction by normal lymphocytes was equally strong in all HER-2 positive cell lines, without any correlation to molecular markers or direct sensitivity to the drugs. Resistance to trastuzumab and lapatinib is probably caused by several co-existing molecular mechanisms. Direct sensitivity to trastuzumab and lapatinib was not correlated with ADCC.
authors.affiliation: Institute of Medical Technology, University of Tampere, Biokatu 6, Tampere 33014, Finland.
authors.forename: Katri
authors.initials: K
authors.lastname: Köninki
authors.forename: Mark
authors.initials: M
authors.lastname: Barok
authors.forename: Minna
authors.initials: M
authors.lastname: Tanner
authors.forename: Synnöve
authors.initials: S
authors.lastname: Staff
authors.forename: Jukka
authors.initials: J
authors.lastname: Pitkänen
authors.forename: Päivikki
authors.initials: P
authors.lastname: Hemmilä
authors.forename: Joanna
authors.initials: J
authors.lastname: Ilvesaro
authors.forename: Jorma
authors.initials: J
authors.lastname: Isola
mesh_terms: D000911:Antibodies, Monoclonal / Q000494:pharmacology*; D061067:Antibodies, Monoclonal, Humanized; D000920:Antibody-Dependent Cell Cytotoxicity / Q000187:drug effects; D000970:Antineoplastic Agents / Q000494:pharmacology*; D001943:Breast Neoplasms / Q000188:drug therapy* / Q000235:genetics / Q000276:immunology; D045744:Cell Line, Tumor; D058534:Class I Phosphatidylinositol 3-Kinases; D019008:Drug Resistance, Neoplasm; D005260:Female; D005784:Gene Amplification; D006801:Humans; D000077341:Lapatinib; D009154:Mutation; D020890:Neuregulin-1 / Q000096:biosynthesis / Q000235:genetics; D051059:PTEN Phosphohydrolase / Q000096:biosynthesis / Q000235:genetics; D019869:Phosphatidylinositol 3-Kinases / Q000235:genetics; D011799:Quinazolines / Q000494:pharmacology*; D012333:RNA, Messenger / Q000096:biosynthesis / Q000235:genetics; D018719:Erb-b2 Receptor Tyrosine Kinases / Q000096:biosynthesis / Q000235:genetics / Q000378:metabolism; D000068878:Trastuzumab
chemical_list: D000911:Antibodies, Monoclonal; D061067:Antibodies, Monoclonal, Humanized; D000970:Antineoplastic Agents; D058534:Class I Phosphatidylinositol 3-Kinases; D000077341:Lapatinib; D020890:Neuregulin-1; D051059:PTEN Phosphohydrolase; D019869:Phosphatidylinositol 3-Kinases; D011799:Quinazolines; D012333:RNA, Messenger; D018719:Erb-b2 Receptor Tyrosine Kinases; D000068878:Trastuzumab; C094131:NRG1 protein, human; C484760:PIK3CA protein, human; C494929:PTEN protein, human