Amphiregulin triggered epidermal growth factor receptor activation confers in vivo crizotinib‐resistance of EML4‐ALK lung cancer and circumvention by epidermal growth factor receptor inhibitors

Crizotinib, a first‐generation anaplastic lymphoma kinase (ALK) tyrosine‐kinase inhibitor, is known to be effective against echinoderm microtubule‐associated protein‐like 4 (EML4)‐ALK‐positive non‐small cell lung cancers. Nonetheless, the tumors subsequently become resistant to crizotinib and recur in almost every case. The mechanism of the acquired resistance needs to be deciphered. In this study, we established crizotinib‐resistant cells (A925LPE3‐CR) via long‐term administration of crizotinib to a mouse model of pleural carcinomatous effusions; this model involved implantation of the A925LPE3 cell line, which harbors the EML4‐ALK gene rearrangement. The resistant cells did not have the secondary ALK mutations frequently occurring in crizotinib‐resistant cells, and these cells were cross‐resistant to alectinib and ceritinib as well. In cell clone #2, which is one of the clones of A925LPE3‐CR, crizotinib sensitivity was restored via the inhibition of epidermal growth factor receptor (EGFR) by means of an EGFR tyrosine‐kinase inhibitor (erlotinib) or an anti‐EGFR antibody (cetuximab) in vitro and in the murine xenograft model. Cell clone #2 did not have an EGFR mutation, but the expression of amphiregulin (AREG), one of EGFR ligands, was significantly increased. A knockdown of AREG with small interfering RNAs restored the sensitivity to crizotinib. These data suggest that overexpression of EGFR ligands such as AREG can cause resistance to crizotinib, and that inhibition of EGFR signaling may be a promising strategy to overcome crizotinib resistance in EML4‐ALK lung cancer.