ERK2-dependent reactivation of Akt mediates the limited response of tumor cells with constitutive K-RAS activity to PI3K inhibition

Cancer Biol Ther. 2014 Mar 1;15(3):317-28. doi: 10.4161/cbt.27311. Epub 2013 Dec 9.


K-RAS mutated (K-RASmut) non-small cell lung cancer (NSCLC) cells are resistant to EGFR targeting strategies. We investigated the impact of K-RAS activity irrespective of mutational status in the EGFR-independent increase in clonogenic cell survival. An analysis of the K-RAS activity status revealed a constitutively high K-RAS activity in K-RASmut NSCLC cells and also in head and neck squamous cell carcinoma (HNSCC) cells overexpressing wild-type K-RAS (K-RASwt). Similar to K-RAS-mutated cells, increased K-RAS activity in HNSCC cells overexpressing K-RASwt was associated with the stimulated production of the EGFR ligand amphiregulin and resistance to EGFR tyrosine kinase (EGFR-TK) inhibitors such as erlotinib. Expression of mutated K-RAS stimulated Akt phosphorylation and increased plating efficiency. Conversely, knockdown of K-RAS in K-RASmut NSCLC cells and in HNSCC cells presenting overexpression of K-RASwt resulted in sensitization to the anti-clonogenic activity of erlotinib. K-RAS activity results in EGFR-dependent and EGFR-independent Akt activity. The short-term treatment (2 h) of cells with EGFR-TK or PI3K inhibitors (erlotinib and PI-103) resulted in the repression of Akt activation, whereas long-term treatment (24 h) with inhibitors led to the reactivation of Akt and improved clonogenicity. The Akt re-activation was MAPK-ERK2-dependent and associated with a lack of complete response to anti-clonogenic activity of PI-103. A complete response was observed when PI-103 was combined with MEK inhibitor PD98059. Together, clonogenicity inhibition in tumor cells presenting constitutive K-RAS activity independent of K-RAS mutational status can be achieved by targeting of EGFR downstream pathways, i.e., PI3K alone or the combination of PI3K and MAPK inhibitors.

Keywords: EGFR; HNSCC; K-RAS; MAPK/ERK; NSCLC; PI-103; PI3K/Akt; erlotinib.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Carcinoma, Non-Small-Cell Lung
  • Carcinoma, Squamous Cell
  • Cell Line, Tumor
  • Cell Proliferation / drug effects
  • Cell Survival / drug effects
  • Clone Cells / drug effects
  • Clone Cells / pathology
  • Drug Synergism
  • ErbB Receptors / genetics
  • Erlotinib Hydrochloride
  • Flavonoids / pharmacology
  • Furans / pharmacology
  • Head and Neck Neoplasms
  • Humans
  • Lung Neoplasms
  • Mitogen-Activated Protein Kinase 1 / metabolism*
  • Oncogene Protein v-akt / metabolism*
  • Phosphatidylinositol 3-Kinase / metabolism
  • Phosphoinositide-3 Kinase Inhibitors*
  • Protein Kinase Inhibitors / pharmacology
  • Proto-Oncogene Proteins / genetics
  • Proto-Oncogene Proteins / metabolism*
  • Proto-Oncogene Proteins p21(ras)
  • Pyridines / pharmacology
  • Pyrimidines / pharmacology
  • Quinazolines / pharmacology
  • Signal Transduction / genetics
  • ras Proteins / genetics
  • ras Proteins / metabolism*


  • Flavonoids
  • Furans
  • KRAS protein, human
  • PI103
  • Phosphoinositide-3 Kinase Inhibitors
  • Protein Kinase Inhibitors
  • Proto-Oncogene Proteins
  • Pyridines
  • Pyrimidines
  • Quinazolines
  • Erlotinib Hydrochloride
  • Phosphatidylinositol 3-Kinase
  • EGFR protein, human
  • ErbB Receptors
  • Oncogene Protein v-akt
  • MAPK1 protein, human
  • Mitogen-Activated Protein Kinase 1
  • Proto-Oncogene Proteins p21(ras)
  • ras Proteins
  • 2-(2-amino-3-methoxyphenyl)-4H-1-benzopyran-4-one