Human breast cancer cells harboring a gatekeeper T798M mutation in HER2 overexpress EGFR ligands and are sensitive to dual inhibition of EGFR and HER2.
OBJECTIVE
Mutations in receptor tyrosine kinase (RTK) genes can confer resistance to receptor-targeted therapies. A T798M mutation in the HER2 oncogene has been shown to confer resistance to the tyrosine kinase inhibitor (TKI) lapatinib. We studied the mechanisms of HER2-T798M-induced resistance to identify potential strategies to overcome that resistance.


METHODS
HER2-T798M was stably expressed in BT474 and MCF10A cells. Mutant cells and xenografts were evaluated for effects of the mutation on proliferation, signaling, and tumor growth after treatment with combinations of inhibitors targeting the EGFR/HER2/HER3/PI3K axis.


RESULTS
A low 3% allelic frequency of the T798M mutant shifted 10-fold the IC50 of lapatinib. In mutant-expressing cells, lapatinib did not block basal phosphorylation of HER2, HER3, AKT, and ERK1/2. In vitro kinase assays showed increased autocatalytic activity of HER2-T798M. HER3 association with PI3K p85 was increased in mutant-expressing cells. BT474-T798M cells were also resistant to the HER2 antibody trastuzumab. These cells were sensitive to the pan-PI3K inhibitors BKM120 and XL147 and the irreversible HER2/EGFR TKI afatinib but not the MEK1/2 inhibitor CI-1040, suggesting continued dependence of the mutant cells on ErbB receptors and downstream PI3K signaling. BT474-T798M cells showed increased expression of the EGFR ligands EGF, TGFα, amphiregulin, and HB-EGF. Addition of the EGFR neutralizing antibody cetuximab or lapatinib restored trastuzumab sensitivity of BT474-T798M cells and xenografts, suggesting that increased EGFR ligand production was causally associated with drug resistance.


CONCLUSIONS
Simultaneous blockade of HER2 and EGFR should be an effective treatment strategy against HER2 gene-amplified breast cancer cells harboring T798M mutant alleles.
Authors' Affiliations: Departments of Medicine and Cancer Biology, Breast Cancer Research Program, Vanderbilt-Ingram Cancer Center; Vanderbilt University, Nashville, Tennessee; Massachusetts General Hospital Cancer Center; and Department of Medicine, Harvard Medical School, Boston, Massachusetts.
Brent N
BN
Rexer
Ritwik
R
Ghosh
Archana
A
Narasanna
Mónica Valeria
MV
Estrada
Anindita
A
Chakrabarty
Youngchul
Y
Song
Jeffrey A
JA
Engelman
Carlos L
CL
Arteaga
D019943:Amino Acid Substitution; D000818:Animals; D000970:Antineoplastic Agents / Q000494:pharmacology; D001943:Breast Neoplasms / Q000188:drug therapy / Q000235:genetics* / Q000378:metabolism*; D002384:Catalysis; D045744:Cell Line, Tumor; D049109:Cell Proliferation / Q000187:drug effects; D002470:Cell Survival; D003062:Codon; D004195:Disease Models, Animal; D019008:Drug Resistance, Neoplasm / Q000235:genetics*; D066246:ErbB Receptors / Q000037:antagonists & inhibitors / Q000378:metabolism*; D005260:Female; D005784:Gene Amplification; D015870:Gene Expression; D006801:Humans; D008024:Ligands; D051379:Mice; D009154:Mutation; D019869:Phosphatidylinositol 3-Kinases / Q000378:metabolism; D047428:Protein Kinase Inhibitors / Q000494:pharmacology; D018719:Erb-b2 Receptor Tyrosine Kinases / Q000037:antagonists & inhibitors / Q000235:genetics* / Q000378:metabolism; D020893:Receptor, ErbB-3 / Q000378:metabolism; D023041:Xenograft Model Antitumor Assays
D000970:Antineoplastic Agents; D003062:Codon; D066246:ErbB Receptors; D008024:Ligands; D019869:Phosphatidylinositol 3-Kinases; D047428:Protein Kinase Inhibitors; D018719:Erb-b2 Receptor Tyrosine Kinases; D020893:Receptor, ErbB-3