LSCC lacks effective targeted therapies. EGFR is commonly expressed in LSCC and N, an anti-EGFR monoclonal antibody (mAb), is the only approved targeted therapy that with chemotherapy provides a small (clinically irrelevant) survival benefit as 1st-line treatment in metastatic LSCC. AXL, STAT3 or YAP1 pathway activation, and hedgehog-GLI signaling have been described as mechanisms of resistance to anti-EGFR therapy. p21-activated kinase 1 (PAK1) is overexpressed in LSCC, diminishing the efficacy of anti-EGFR mAbs. Herein, we evaluate the relevance of these pathways in LSCC cell lines, illustrating the potential for synthetic lethal approaches.
AXL (and its ligand GAS6), STAT3, YAP1, GLI1/2 and PAK1 mRNA expression were examined by quantitative real-time PCR in 6 LSCC cell lines: H2286, HCC366, H520, H1703, SK-MES1, and EBC1. Cell viability was assessed by the thiazolyl blue assay after treatment with evodiamine (STAT3i), R428 (AXLi), ivermectin (dual YAP1-PAK1i) or GANT61 and mebendazole (GLIi) alone or in combination with 25ug/ml of N.
EGFR was homogeneously overexpressed in all tested cell lines except H520 that lacks EGFR expression. Moderate STAT3 mRNA expression was detected in SK-MES1 cells in which treatment with evodiamine synergistically increased the effect of N alone. The dual YAP1-PAK1i, ivermectin was more active (IC50 3-7uM) in the H1703 and H2286 YAP1 overexpressing cells in comparison with the rest of YAP1 low expressing cells. No correlation was found between PAK1 expression and sensitivity to ivermectin in the tested LSCC cell lines. High GLI1/2 expression and relative sensitivity to the GLI1/2i, GANT61 or mebendazole (IC50 2-3uM) were detected in the H2286 cells. Among our LSCC cell lines, H2286 also had the highest AXL and GAS6 mRNA expression. Western blotting analysis, as well as further cell viability experiments with drugs alone and in combination with N, are ongoing.
LSCC is a heterogeneous disease, in which common signaling pathways dictate distinct pathologic outputs. The awareness of these differences is necessary while planning efficient strategies to improve the scant clinical benefit with EGFR mAbs.
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This work was supported by grants from the La Caixa Foundation and Red Tematica de Investigacion Cooperativa en Cancer (RTICC; grant RD12/0036/ 0072).
All authors have declared no conflicts of interest.