title: β1 integrin mediates an alternative survival pathway in breast cancer cells resistant to lapatinib.
abstract: BACKGROUND
  The overexpression of human epidermal growth factor receptor (HER)-2 in 20% of human breast cancers and its association with aggressive growth has led to widespread use of HER2-targeted therapies, such as trastuzumab (T) and lapatinib (L). Despite the success of these drugs, their efficacy is limited in patients whose tumors demonstrate de novo or acquired resistance to treatment. The β1 integrin resides on the membrane of the breast cancer cell, activating several elements of breast tumor progression including proliferation and survival.
  
  
  METHODS
  We developed a panel of HER2-overexpressing cell lines resistant to L, T, and the potent LT combination through long-term exposure and validated these models in 3D culture. Parental and L/T/LT-resistant cells were subject to HER2 and β1 integrin inhibitors in 3D and monitored for 12 days, followed by quantification of colony number. Parallel experiments were conducted where cells were either stained for Ki-67 and Terminal deoxynucleotidyl transferase dUTP nick end labeling (TUNEL) or harvested for protein and analyzed by immunoblot. Results were subjected to statistical testing using analysis of variance and linear contrasts, followed by adjustment with the Sidak method.
  
  
  RESULTS
  Using multiple cell lines including BT474 and HCC1954, we reveal that in L and LT resistance, where phosphorylation of EGFR/HER1, HER2, and HER3 are strongly inhibited, kinases downstream of β1 integrin--including focal adhesion kinase (FAK) and Src--are up-regulated. Blockade of β1 by the antibody AIIB2 abrogates this up-regulation and functionally achieves significant growth inhibition of L and LT resistant cells in 3D, without dramatically affecting the parental cells. SiRNA against β1 as well as pharmacologic inhibition of FAK achieve the same growth inhibitory effect. In contrast, trastuzumab-resistant cells, which retain high levels of phosphorylated EGFR/HER1, HER2, and HER3, are only modestly growth-inhibited by AIIB2.
  
  
  CONCLUSIONS
  Our data suggest that HER2 activity, which is suppressed in resistance involving L but not T alone, dictates whether β1 mediates an alternative pathway driving resistance. Our findings justify clinical studies investigating the inhibition of β1 or its downstream signaling moieties as strategies to overcome acquired L and LT resistance.
authors: Lester and Sue Smith Breast Center, Baylor College of Medicine, One Baylor Plaza, Houston, TX 77054, USA.
authors: Catherine
authors: C
authors: Huang
authors: Catherine C
authors: CC
authors: Park
authors: Susan G
authors: SG
authors: Hilsenbeck
authors: Robin
authors: R
authors: Ward
authors: Mothaffar F
authors: MF
authors: Rimawi
authors: Yen-Chao
authors: YC
authors: Wang
authors: Jiang
authors: J
authors: Shou
authors: Mina J
authors: MJ
authors: Bissell
authors: C Kent
authors: CK
authors: Osborne
authors: Rachel
authors: R
authors: Schiff
mesh_terms: D000906:Antibodies / Q000494:pharmacology; D061067:Antibodies, Monoclonal, Humanized / Q000494:pharmacology; D000970:Antineoplastic Agents / Q000494:pharmacology*; D001943:Breast Neoplasms / Q000188:drug therapy* / Q000378:metabolism / Q000473:pathology; D045744:Cell Line, Tumor; D049109:Cell Proliferation; D019008:Drug Resistance, Neoplasm; D066246:ErbB Receptors / Q000378:metabolism; D051417:Focal Adhesion Kinase 1 / Q000378:metabolism; D006801:Humans; D019012:Integrin beta1 / Q000235:genetics / Q000276:immunology / Q000378:metabolism*; D000077341:Lapatinib; D010766:Phosphorylation / Q000187:drug effects; D011799:Quinazolines / Q000494:pharmacology*; D034741:RNA, Small Interfering; D018719:Erb-b2 Receptor Tyrosine Kinases / Q000378:metabolism; D011960:Receptors, Estrogen / Q000378:metabolism; D015398:Signal Transduction / Q000187:drug effects; D000068878:Trastuzumab; D015854:Up-Regulation; D019061:src-Family Kinases / Q000378:metabolism
chemical_list: D000906:Antibodies; D061067:Antibodies, Monoclonal, Humanized; D000970:Antineoplastic Agents; D066246:ErbB Receptors; D051417:Focal Adhesion Kinase 1; D019012:Integrin beta1; D000077341:Lapatinib; D011799:Quinazolines; D034741:RNA, Small Interfering; D018719:Erb-b2 Receptor Tyrosine Kinases; D011960:Receptors, Estrogen; D000068878:Trastuzumab; D019061:src-Family Kinases; C512478:EGFR protein, human; C508053:ERBB2 protein, human; C496050:PTK2 protein, human