Molecular dissection of effector mechanisms of RAS-mediated resistance to anti-EGFR antibody therapy.

Kasper S, Reis H, Ziegler S, Nothdurft S, Mueller A, Goetz M, Wiesweg M, Phasue J, Ting S, Wieczorek S, Even A, Worm K, Pogorzelski M, Breitenbuecher S, Meiler J, Paul A, Trarbach T, Schmid KW, Breitenbuecher F, Schuler M
Oncotarget. 2017 8 (28): 45898-45917

PMID: 28507280 · PMCID: PMC5542236 · DOI:10.18632/oncotarget.17438

Monoclonal antibodies targeting the epidermal growth factor receptor (EGFR), cetuximab and panitumumab, are a mainstay of metastatic colorectal cancer (mCRC) treatment. However, a significant number of patients suffer from primary or acquired resistance. RAS mutations are negative predictors of clinical efficacy of anti-EGFR antibodies in patients with mCRC. Oncogenic RAS activates the MAPK and PI3K/AKT pathways, which are considered the main effectors of resistance. However, the relative impact of these pathways in RAS-mutant CRC is less defined. A better mechanistic understanding of RAS-mediated resistance may guide development of rational intervention strategies. To this end we developed cancer models for functional dissection of resistance to anti-EGFR therapy in vitro and in vivo. To selectively activate MAPK- or AKT-signaling we expressed conditionally activatable RAF-1 and AKT in cancer cells. We found that either pathway independently protected sensitive cancer models against anti-EGFR antibody treatment in vitro and in vivo. RAF-1- and AKT-mediated resistance was associated with increased expression of anti-apoptotic BCL-2 proteins. Biomarkers of MAPK and PI3K/AKT pathway activation correlated with inferior outcome in a cohort of mCRC patients receiving cetuximab-based therapy. Dual pharmacologic inhibition of PI3K and MEK successfully sensitized primary resistant CRC models to anti-EGFR therapy. In conclusion, combined targeting of MAPK and PI3K/AKT signaling, but not single pathways, may be required to enhance the efficacy of anti-EGFR antibody therapy in patients with RAS-mutated CRC as well as in RAS wild type tumors with clinical resistance.

MeSH Terms (17)

Antineoplastic Agents, Immunological Apoptosis Biomarkers Cell Line, Tumor Colorectal Neoplasms Drug Resistance, Neoplasm ErbB Receptors Exons Genes, ras Humans Mitogen-Activated Protein Kinases Mutation Odds Ratio Phosphatidylinositol 3-Kinases Proto-Oncogene Proteins c-akt Proto-Oncogene Proteins c-bcl-2 Signal Transduction

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