title: The hypoxic tumor microenvironment and drug resistance against EGFR inhibitors: preclinical study in cetuximab-sensitive head and neck squamous cell carcinoma cell lines.
abstract: BACKGROUND
  Increased expression of the epidermal growth factor receptor (EGFR) is observed in more than 90% of all head and neck squamous cell carcinomas (HNSCC). Therefore, EGFR has emerged as a promising therapeutic target. Nevertheless, drug resistance remains a major challenge and an important potential mechanism of drug resistance involves the hypoxic tumor microenvironment. Therefore, we investigated the cytotoxic effect of the EGFR-targeting agents cetuximab and erlotinib under normoxia versus hypoxia.
  
  
  RESULTS
  Three cetuximab-sensitive HNSCC cell lines (SC263, LICR-HN2 and LICR-HN5) were treated with either cetuximab or erlotinib. Cells were incubated under normal or reduced oxygen conditions (<0.1% O2) for 24 or 72 h immediately after drug addition. Cell survival was assessed with the sulforhodamine B assay. Cetuximab and erlotinib established a dose-dependent growth inhibition under both normal and prolonged reduced oxygen conditions in all three HNSCC cell lines. However, a significantly increased sensitivity to cetuximab was observed in SC263 cells exposed to hypoxia for 72 h (p = 0.05), with IC50 values of 2.38 ± 0.59 nM, 0.64 ± 0.38 nM, and 0.10 ± 0.05 nM under normoxia, hypoxia for 24 h and hypoxia for 72 h, respectively. LICR-HN5 cells showed an increased sensitivity towards erlotinib when cells were incubated under hypoxia for 24 h (p = 0.05).
  
  
  CONCLUSIONS
  Our results suggest that both EGFR-inhibitors cetuximab and erlotinib maintain their growth inhibitory effect under hypoxia. These results suggest that resistance to anti-EGFR therapy in HNSCC is probably not the result of hypoxic regions within the tumor and other mechanisms are involved.
authors.affiliation: Center for Oncological Research (CORE) Antwerp, University of Antwerp, Universiteitsplein 1, 2610, Wilrijk, Belgium. carolien.boeckx@uantwerpen.be.
authors.forename: Carolien
authors.initials: C
authors.lastname: Boeckx
authors.affiliation: Center for Oncological Research (CORE) Antwerp, University of Antwerp, Universiteitsplein 1, 2610, Wilrijk, Belgium. jolien.vandenbossche@uantwerpen.be.
authors.forename: Jolien
authors.initials: J
authors.lastname: Van den Bossche
authors.affiliation: Center for Oncological Research (CORE) Antwerp, University of Antwerp, Universiteitsplein 1, 2610, Wilrijk, Belgium. ines.depauw@uantwerpen.be.
authors.forename: Ines
authors.initials: I
authors.lastname: De Pauw
authors.affiliation: Center for Oncological Research (CORE) Antwerp, University of Antwerp, Universiteitsplein 1, 2610, Wilrijk, Belgium. marc.peeters@uza.be.|Department of Oncology, Antwerp University Hospital, Wilrijkstraat 10, 2650, Edegem, Belgium. marc.peeters@uza.be.
authors.forename: Marc
authors.initials: M
authors.lastname: Peeters
authors.affiliation: Center for Oncological Research (CORE) Antwerp, University of Antwerp, Universiteitsplein 1, 2610, Wilrijk, Belgium. filip.lardon@uantwerpen.be.
authors.forename: Filip
authors.initials: F
authors.lastname: Lardon
authors.affiliation: Center for Oncological Research (CORE) Antwerp, University of Antwerp, Universiteitsplein 1, 2610, Wilrijk, Belgium. marc.baay@uantwerpen.be.
authors.forename: Marc
authors.initials: M
authors.lastname: Baay
authors.affiliation: Center for Oncological Research (CORE) Antwerp, University of Antwerp, Universiteitsplein 1, 2610, Wilrijk, Belgium. an.wouters@uantwerpen.be.
authors.forename: An
authors.initials: A
authors.lastname: Wouters
mesh_terms: D002294:Carcinoma, Squamous Cell / Q000473:pathology*; D016923:Cell Death / Q000187:drug effects; D015687:Cell Hypoxia / Q000187:drug effects; D045744:Cell Line, Tumor; D000068818:Cetuximab / Q000494:pharmacology*; D019008:Drug Resistance, Neoplasm / Q000187:drug effects*; D066246:ErbB Receptors / Q000037:antagonists & inhibitors* / Q000378:metabolism; D000069347:Erlotinib Hydrochloride / Q000494:pharmacology; D006258:Head and Neck Neoplasms / Q000473:pathology*; D006801:Humans; D020128:Inhibitory Concentration 50; D047428:Protein Kinase Inhibitors / Q000494:pharmacology*; D000077195:Squamous Cell Carcinoma of Head and Neck; D059016:Tumor Microenvironment / Q000187:drug effects*
chemical_list: D047428:Protein Kinase Inhibitors; D000069347:Erlotinib Hydrochloride; D066246:ErbB Receptors; D000068818:Cetuximab