Diverse Resistance Mechanisms to the Third-Generation ALK Inhibitor Lorlatinib in ALK-Rearranged Lung Cancer.

Abstract

Lorlatinib is a third-generation anaplastic lymphoma kinase (ALK) tyrosine kinase inhibitor with proven efficacy in patients with ALK-rearranged lung cancer previously treated with first- and second-generation ALK inhibitors. Beside compound mutations in the <i>ALK</i> kinase domain, other resistance mechanisms driving lorlatinib resistance remain unknown. We aimed to characterize the mechanisms of resistance to lorlatinib occurring in patients with <i>ALK</i>-rearranged lung cancer and design new therapeutic strategies in this setting. Resistance mechanisms were investigated in 5 patients resistant to lorlatinib. Longitudinal tumor biopsies were studied using high-throughput next-generation sequencing. Patient-derived models were developed to characterize the acquired resistance mechanisms, and Ba/F3 cell mutants were generated to study the effect of novel <i>ALK</i> compound mutations. Drug combinatory strategies were evaluated <i>in vitro</i> and <i>in vivo</i> to overcome lorlatinib resistance. Diverse biological mechanisms leading to lorlatinib resistance were identified. Epithelial-mesenchymal transition (EMT) mediated resistance in two patient-derived cell lines and was susceptible to dual SRC and ALK inhibition. We characterized three <i>ALK</i> kinase domain compound mutations occurring in patients, L1196M/D1203N, F1174L/G1202R, and C1156Y/G1269A, with differential susceptibility to ALK inhibition by lorlatinib. We identified a novel bypass mechanism of resistance caused by <i>NF2</i> loss-of-function mutations, conferring sensitivity to treatment with mTOR inhibitors. This study shows that mechanisms of resistance to lorlatinib are diverse and complex, requiring new therapeutic strategies to tailor treatment upon disease progression.