Host-dependent Phenotypic Resistance to EGFR Tyrosine Kinase Inhibitors.

Lung cancers driven by mutant forms of the epidermal growth factor receptor (EGFR) invariably develop resistance to kinase inhibitors, often due to secondary mutations. Here we describe an unconventional mechanism of resistance to dacomitinib, a newly approved covalent EGFR kinase inhibitor, and uncover a previously unknown step of resistance acquisition. Dacomitinib-resistant derivatives of lung cancer cells were established by means of gradually increasing dacomitinib concentrations. These dacomitinib-resistant (DR) cells acquired no secondary mutations in the kinase or other domains of EGFR. Along with resistance to other EGFR inhibitors, DR cells acquired features characteristic to epithelial-mesenchymal transition, including an expanded population of aldehyde dehydrogenase (ALDH)-positive cells and upregulation of AXL, a receptor previously implicated in drug resistance. Unexpectedly, when implanted in animals, DR cells reverted to a dacomitinib-sensitive state. Nevertheless, cell lines derived from regressing tumors displayed renewed resistance when cultured in vitro. 3D and co-cultures along with additional analyses indicated lack of involvement of hypoxia, fibroblasts, and immune cells in phenotype reversal, implying that other host-dependent mechanisms might nullify non-mutational modes of resistance. Thus, similar to the phenotypic resistance of bacteria treated with antibiotics, the reversible resisters described here likely evolve from drug-tolerant persisters and give rise to the irreversible, secondary mutation-driven non-reversible resister state.