Lymphotoxin-β interacts with methylated EGFR to mediate acquired resistance to cetuximab in head and neck cancer

Purpose: In head and neck squamous cell carcinoma (HNSCC), the incidence of RAS mutation, which is the major cause of cetuximab resistance, is relatively rare compared with the other types of cancers, and the mechanism mediating acquired resistance is unclear compared with the driver gene mutation–mediated de novo resistance. Here, we investigated the driver gene mutation–independent mechanism for cetuximab resistance in HNSCC. Experimental Design: We used the in vitro-selected and in vivo-selected cetuximab-resistant sublines of HNSCC cell lines for investigating the mechanism of acquired resistance to cetuximab. Zebrafish model was applied for evaluating the synergistic effect of combinatory drugs for overcoming cetuximab resistance. Results: The cetuximab-resistant HNSCC cells undergo a Snail-induced epithelial–mesenchymal transition. Mechanistically, Snail induces the expression of lymphotoxin-b (LTb), a TNF superfamily protein that activates NF-kB, and protein arginine methyltransferase 1 (PRMT1), an arginine methyltransferase that methylates EGFR. LTb interacts with methylated EGFR to promote its ligand-binding ability and dimerization. Furthermore, LTb activates the NF-kB pathway through a LTb receptor–independent mechanism. Combination of an EGFR tyrosine kinase inhibitor and a NF-kB inhibitor effectively suppressed cetuximab-resistant HNSCC and interfering with the EGFR–LTb interaction reverses resistance. Conclusions: Our findings elucidate the mechanism of driver gene mutations–independent mechanism of acquired resistance to cetuximab in HNSCC and also provide potential strategies for combating cetuximab resistance.