Differential sensitivities of trastuzumab (Herceptin)-resistant human breast cancer cells to phosphoinositide-3 kinase (PI-3K) and epidermal growth factor receptor (EGFR) kinase inhibitors

Breast Cancer Res Treat. 2005 May;91(2):187-201. doi: 10.1007/s10549-004-7715-1.


Her2 (erbB2/neu) is overexpressed in 25-30% of human breast cancers. Herceptin is a recombinant humanized Her2 antibody used to treat breast cancer patients with Her2 overexpression. Over a 5-month selection process, we isolated clones of BT474 (BT) human breast carcinoma cells (BT/Her(R)) that were resistant to Herceptin in vitro. In BT/Her(R) subclones, cell-surface, phosphorylated and total cellular Her2 protein remained high in the continuous presence of Herceptin. Likewise, the levels of cell-surface, phosphorylated, and total cellular Her3 and EGFR were either unchanged or only slightly elevated in BT/Her(R) subclones relative to BT cells. One BT/Her(R) subclone had substantially upregulated cell-surface EGFR, but this did not correlate with a higher relative resistance to Herceptin. In looking at the downstream PI-3K/Akt signaling pathway, phosphorylated and total Akt levels and Akt kinase activities were all sustained in BT/Her(R) subclones in the presence of Herceptin, but significantly downregulated in BT cells exposed to Herceptin. Whereas BT cells lost sensitivity to the PI-3K inhibitor LY294002 in the presence of Herceptin, BT/Her(R) subclones were equally sensitive to this agent in the presence and absence of Herceptin. This suggests that BT/Her(R) subclones acquired a Herceptin-resistant mechanism of PI-3K signaling. BT/Her(R) subclones were also sensitive to the EGFR kinase inhibitor AG1478 in the presence of Herceptin, to the same extent as BT cells. The BT/Her(R) subclones provide new insights into mechanisms of Herceptin resistance and suggest new treatment strategies in combination with other inhibitors targeted to signal transduction pathways.

Publication types

  • Research Support, N.I.H., Extramural
  • Research Support, U.S. Gov't, Non-P.H.S.
  • Research Support, U.S. Gov't, P.H.S.

MeSH terms

  • Antibodies, Monoclonal / pharmacology*
  • Antibodies, Monoclonal, Humanized
  • Antineoplastic Agents / pharmacology*
  • Antineoplastic Combined Chemotherapy Protocols / pharmacology
  • Breast Neoplasms / drug therapy*
  • Chromones / pharmacology
  • Drug Resistance, Neoplasm*
  • ErbB Receptors / antagonists & inhibitors*
  • Female
  • Humans
  • Morpholines / pharmacology
  • Phosphoinositide-3 Kinase Inhibitors*
  • Phosphorylation / drug effects
  • Protein Serine-Threonine Kinases / metabolism
  • Proto-Oncogene Proteins / metabolism
  • Proto-Oncogene Proteins c-akt
  • Quinazolines
  • Receptor, ErbB-2 / biosynthesis
  • Receptor, ErbB-2 / drug effects*
  • Signal Transduction / drug effects
  • Trastuzumab
  • Tumor Cells, Cultured
  • Tyrphostins / pharmacology


  • Antibodies, Monoclonal
  • Antibodies, Monoclonal, Humanized
  • Antineoplastic Agents
  • Chromones
  • Morpholines
  • Phosphoinositide-3 Kinase Inhibitors
  • Proto-Oncogene Proteins
  • Quinazolines
  • Tyrphostins
  • RTKI cpd
  • 2-(4-morpholinyl)-8-phenyl-4H-1-benzopyran-4-one
  • ErbB Receptors
  • Receptor, ErbB-2
  • AKT1 protein, human
  • Protein Serine-Threonine Kinases
  • Proto-Oncogene Proteins c-akt
  • Trastuzumab