As LTK and ALK share nearly 80% protein sequence identity in their respective kinase domains, we established Ba/F3 cells expressing CLIP1-LTK (Ba/F3-CLIP1-LTK) with six different LTK mutations (I565N, F568C, L590M, L592F, G596R, and G663A), all of which are analogous to reported ALK mutations responsible for resistance to lorlatinib....All LTK mutations tested showed resistance to lorlatinib, with IC50s of lorlatinib ranging 2.7 to 31.3 nM, which were higher than that in Ba/F3-CLIP-LTK-WT (1.0 nM) in cell viability assay.