Dual “mAb” HER family blockade in head and neck cancer human cell lines combined with photon therapy

International audienceHead and neck cancer stem cells (CSCs) are highly resistant to treatment. When EGFR is overexpressed in head and neck squamous cell carcinoma (HNSCC), HER2 and HER3 are also expressed. The aim of the present study was to investigate the effect of HER1/2/3 blockade through a combination of cetuximab and pertuzumab, with or without photon irradiation, on the proliferation and migration/ invasion capabilities of an HNSCC chemo-and radioresistant human cell line (SQ20B) and its corresponding stem cell subpopulation. Cell proliferation, migration and invasion were studied after treatment with cetuximab +/− pertuzumab +/− 10 Gy photon irradiation. EGFR, phospho-EGFR, HER2 and HER3 protein expression levels were studied. Activation or inhibition of the RAS/MAPK and AKT-mTOR downstream signalling cascades was investigated through phospho-AKT and phospho-MEK1/2 expression. Cetuximab strongly inhibited SQ20B and FaDu cell proliferation, migration and invasion, whereas it had little effect on SQ20B-CSCs. Cetuximab–pertuzumab combined with radiation significantly inhibited SQ20B and FaDu cell and SQ20B-CSC proliferation, migration and invasion. Cetuximab–pertuzumab with 10 Gy photon irradiation switched off both phospho-AKT and phospho-MEK1/2 expression in the three populations. The triple therapy is therefore thought to inhibit SQ20B cells, SQ20B-CSCs and FaDu cells through an AKT-mTOR and Ras-MAPK downstream signalling blockade. Head and neck squamous cell carcinoma (HNSCC) still has a dismal prognosis, despite recent biological and technological improvements 1. In the past few years, it has been shown that the epidermal growth factor receptor (EGFR) is overexpressed in more than 90% of HNSCCs 2. Faced with this therapeutic target, cetuximab, a mouse– human chimeric monoclonal antibody directed against EGFR, was developed and shown to significantly improve locoregional control, progression-free survival and overall survival when used concomitantly with radiotherapy (RT) 3,4. These improvements were nevertheless counterbalanced by high rates of local and distant recurrences 4,5 leading to specific mortality in the short or medium term 6. The epithelial-to-mesenchymal process, giving inva-sion/migration capacities to cancer cells, is thought to be the root of all these recurrences. Furthermore, the presence of a subpopulation of cancer cells showing particularly high migratory potential 7 , known as cancer stem cells (CSCs), has been revealed in HNSCC 8. Moncharmont et al. 9 showed that a HNSCC CSC subpopulation with low EGFR expression could resist cetuximab, giving the first biological explanation for clinical reports. Moreover, increasing evidence suggests that cancers that initially respond to EGFR may subsequently become refractory