Feedback activation of HER3 attenuates response to EGFR inhibitors in colon cancer cells
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Albert Bosch-Vilaró1,*, Bart Jacobs1,*, Valentina Pomella1, Layka Abbasi Asbagh1, Richard Kirkland2, Joe Michel2, Sharat Singh2, Xinjun Liu2, Phillip Kim2, Gregory Weitsman3, Paul R Barber4, Borivoj Vojnovic3,4, Tony Ng3,5,6, Sabine Tejpar1
1Laboratory of Molecular Digestive Oncology, Department of Oncology, KU Leuven, Leuven, Belgium
2Prometheus Laboratories, San Diego, CA, USA
3Richard Dimbleby Department of Cancer Research, Randall Division & Division of Cancer Studies, King’s College London, Guy’s Medical School Campus, London, UK
4Department of Oncology, Cancer Research UK and Medical Research Council Oxford Institute for Radiation Oncology, University of Oxford, Oxford, UK
5Breast Cancer Now Research Unit, King’s College London, London, UK
6UCL Cancer Institute, Paul O'Gorman Building, University College London, London, UK
*These authors contributed equally to this work
Sabine Tejpar, email: [email protected]
Keywords: colorectal cancer, cetuximab resistance, HER3, dimerization, feedback loop
Received: September 14, 2016 Accepted: November 30, 2016 Published: December 09, 2016
The EGFR inhibitor cetuximab is approved for the treatment of colorectal cancer. However, both innate and acquired resistance mechanisms, including compensatory feedback loops, limit its efficacy. Nevertheless, the emergence of these feedback loops has remained largely unexplored to date. Here, we showed feedback upregulation of HER3 and induction of HER3 phosphorylation after cetuximab treatment in colon cancer cells. We also showed that this upregulation occurs, at least partly, through AKT inhibition. Together with this, we observed increased HER2:HER3 dimerization upon cetuximab treatment. Interestingly, lapatinib, a dual EGFR and HER2 tyrosine kinase inhibitor, blocked the increase of cetuximab-induced HER3 phosphorylation. Additionally, we showed that upon HER3 knockdown, cetuximab combined with lapatinib was able to decrease cell viability compared to HER3 expressing cells. These results suggest the existence of a cetuximab-induced feedback HER3 activation that could potentially result in reduced cetuximab efficacy in colorectal cancer patients. Taken together, we provide evidence of the limited effectiveness of cetuximab monotherapy compared to rational combinations.
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