Epithelial-to-Mesenchymal Transition Is a Mechanism of ALK Inhibitor Resistance in Lung Cancer Independent of <i>ALK</i> Mutation Status

Abstract

Mutations in the <i>ALK</i> gene are detectable in approximately 40% of <i>ALK</i>-rearranged lung cancers resistant to ALK inhibitors. Although epithelial-to-mesenchymal transition (EMT) is a mechanism of resistance to various targeted drugs, its involvement in ALK inhibitor resistance is largely unknown. In this study, we report that both <i>ALK</i>-mutant L1196M and EMT were concomitantly detected in a single crizotinib-resistant lesion in a patient with <i>ALK</i>-rearranged lung cancer. Digital PCR analyses combined with microdissection after IHC staining for EMT markers revealed that <i>ALK</i> L1196M was predominantly detected in epithelial-type tumor cells, indicating that mesenchymal phenotype and <i>ALK</i> mutation can coexist as independent mechanisms underlying ALK inhibitor-resistant cancers. Preclinical experiments with crizotinib-resistant lung cancer cells showed that EMT associated with decreased expression of miR-200c and increased expression of ZEB1 caused cross-resistance to new-generation ALK inhibitors alectinib, ceritinib, and lorlatinib. Pretreatment with the histone deacetylase (HDAC) inhibitor quisinostat overcame this resistance by reverting EMT <i>in vitro</i> and <i>in vivo</i>. These findings indicate that HDAC inhibitor pretreatment followed by a new ALK inhibitor may be useful to circumvent resistance constituted by coexistence of resistance mutations and EMT in the heterogeneous tumor. SIGNIFICANCE: These findings show that dual inhibition of HDAC and ALK receptor tyrosine kinase activities provides a means to circumvent crizotinib resistance in lung cancer.