Abstract

   The management of locally advanced head and neck squamous cell
   carcinoma (HNSCC) with Cetuximab, a monoclonal antibody targeting the
   epidermal growth factor receptor (EGFR), achieves only moderate
   response rates, and clinical trials that evaluated EGFR-blockade with
   tyrosine kinase inhibitors (TKI) yielded disappointing results.
   Inter-tumor heterogeneity may hinder the therapeutic efficiency of
   anti-EGFR treatments. HNSCC heterogeneity was addressed in several
   studies, which all converged towards the definition of molecular
   subgroups. They include the basal subgroup, defined by the deregulated
   expression of factors involved in the EGFR signaling pathway, including
   the epiregulin EGFR ligand encoded by the EREG gene. These observations
   indicate that basal tumors could be more sensitive to anti-EGFR
   treatments. To test this hypothesis, we performed a screen of a
   representative collection of basal versus non-basal HNSCC cell lines
   for their sensitivity to several anti-EGFR drugs (Cetuximab, Afatinib,
   and Gefitinib), tested as monotherapy or in combination with drugs that
   target closely-linked pathways [Mitogen-activated protein kinase
   kinase/extracellular signal–regulated kinases (MEK), mammalian Target
   of Rapamycine (mTOR) or Human Epidermal growth factor Receptor 2
   (HER2)]. Basal-like cell lines were found to be more sensitive to EGFR
   blockade alone or in combination with treatments that target MEK, mTOR,
   or HER2. Strikingly, the basal-like status was found to be a better
   predictor of cell response to EGFR blockade than clinically relevant
   mutations [e.g., cyclin-dependent kinase Inhibitor 2A (CDKN2A)].
   Interestingly, we show that EGFR blockade inhibits EREG expression, and
   that EREG knock-down decreases basal cell clonogenic survival,
   suggesting that EREG expression could be a predictive functional marker
   of sensitivity to EGFR blockade in basal-like HNSCC.

   Keywords: head and neck squamous cell carcinoma, cancer subgroups,
   EGFR, EREG, drug sensitivity, treatment combinations

1. Introduction

   Head and neck squamous cell carcinoma (HNSCC) is the sixth most common
   cancer in the world, with over 600,000 cases diagnosed each year
   [[50]1]. They encompass a heterogeneous group of malignancies that
   arise from the epithelium of the upper aero-digestive tract (oral
   cavity, pharynx, and larynx). The major risk factors are heavy
   consumption of tobacco smoke and alcohol, and infection with human
   papillomaviruses (HPV) [[51]2]. Despite aggressive multi-modal
   treatment modalities (involving surgery, radiotherapy, and
   chemotherapy), recurrence occurs in about 50% of patients, mainly
   locoregionally, but also locally and at distance (see [[52]3] and
   references therein). The prognosis of locally advanced HNSCC is poor,