Comparison of the effects of the PI3K/mTOR inhibitors NVP-BEZ235 and GSK2126458 on tamoxifen-resistant breast cancer cells

Cancer Biol Ther. 2011 Jun 1;11(11):938-46. doi: 10.4161/cbt.11.11.15527. Epub 2011 Jun 1.


Background: Treatment with anti-estrogens or aromatase inhibitors is commonly used for patients with estrogen receptor-positive (ER+) breast cancers; however resistant disease develops almost inevitably, requiring a choice of secondary therapy. One possibility is to use inhibitors of the PI3K/mTOR pathway and several candidate drugs are in development. We examined the in vitro effects of two inhibitors of the PI3K/mTOR pathway on resistant MCF-7 cells.

Methods: We cultured MCF-7 cells for prolonged periods either in the presence of the anti-estrogen tamoxifen (3 sub-lines) or in estrogen free medium (2 sub-lines) to mimic the effects of clinical treatment. We then analyzed the effects of two dual PI3K/mTOR phosphoinositide-3-kinase inhibitors, NVP-BEZ235 and GSK2126458, on the growth and signaling pathways of these MCF-7 sub-lines. The functional status of the PI3K, mTOR and ERK pathways was analyzed by measuring phosphorylation of AKT, p70S6K, rpS6 and ERK.

Results: The derived sub-lines showed increased resistance to tamoxifen but none exhibited concomitantly increased sensitivity to the PI3K inhibitors. NVP-BEZ235 and GSK2126458 acted mainly by induction of cell cycle arrest, particularly in G1-phase, rather than by induction of apoptosis. The lines varied considerably in their utilization of the AKT, p70S6K and ERK pathways. NVP-BEZ235 and GSK2126458 inhibited AKT signaling but NVP-BEZ235 showed greater effects than GSK2126458 on p70S6K and rpS6 signaling with effects resembling those of rapamycin.

Conclusion: Increased resistance to tamoxifen in these MCF-7 sub-lines is not associated with hypersensitivity to PI3K inhibitors. While both drugs inhibited AKT signaling, NVP-BEZ235 resembled rapamycin in inhibiting the mTOR pathway.

Publication types

  • Comparative Study
  • Research Support, Non-U.S. Gov't

MeSH terms

  • Antineoplastic Agents, Hormonal / pharmacology*
  • Breast Neoplasms / metabolism
  • Breast Neoplasms / pathology*
  • Cell Line, Tumor
  • Cell Proliferation / drug effects
  • Drug Resistance, Neoplasm / drug effects*
  • Extracellular Signal-Regulated MAP Kinases / metabolism
  • Female
  • G1 Phase / drug effects
  • Humans
  • Imidazoles / pharmacology*
  • Neoplasms, Hormone-Dependent / metabolism
  • Neoplasms, Hormone-Dependent / pathology*
  • Phosphoinositide-3 Kinase Inhibitors*
  • Phosphorylation
  • Poly(ADP-ribose) Polymerases / metabolism
  • Proto-Oncogene Proteins c-akt / metabolism
  • Pyridazines
  • Quinolines / pharmacology*
  • Receptors, Estrogen / metabolism
  • Ribosomal Protein S6 / metabolism
  • Sulfonamides / pharmacology*
  • TOR Serine-Threonine Kinases / antagonists & inhibitors*
  • Tamoxifen / pharmacology*


  • Antineoplastic Agents, Hormonal
  • Imidazoles
  • Phosphoinositide-3 Kinase Inhibitors
  • Pyridazines
  • Quinolines
  • Receptors, Estrogen
  • Ribosomal Protein S6
  • Sulfonamides
  • Tamoxifen
  • omipalisib
  • Poly(ADP-ribose) Polymerases
  • MTOR protein, human
  • Proto-Oncogene Proteins c-akt
  • TOR Serine-Threonine Kinases
  • Extracellular Signal-Regulated MAP Kinases
  • dactolisib