Sequential ALK Inhibitors Can Select for Lorlatinib-Resistant Compound <i>ALK</i> Mutations in ALK-Positive Lung Cancer

Abstract

The cornerstone of treatment for advanced ALK-positive lung cancer is sequential therapy with increasingly potent and selective ALK inhibitors. The third-generation ALK inhibitor lorlatinib has demonstrated clinical activity in patients who failed previous ALK inhibitors. To define the spectrum of <i>ALK</i> mutations that confer lorlatinib resistance, we performed accelerated mutagenesis screening of Ba/F3 cells expressing EML4-ALK. Under comparable conditions, <i>N</i>-ethyl-<i>N</i>-nitrosourea (ENU) mutagenesis generated numerous crizotinib-resistant but no lorlatinib-resistant clones harboring single <i>ALK</i> mutations. In similar screens with EML4-ALK containing single <i>ALK</i> resistance mutations, numerous lorlatinib-resistant clones emerged harboring compound <i>ALK</i> mutations. To determine the clinical relevance of these mutations, we analyzed repeat biopsies from lorlatinib-resistant patients. Seven of 20 samples (35%) harbored compound <i>ALK</i> mutations, including two identified in the ENU screen. Whole-exome sequencing in three cases confirmed the stepwise accumulation of <i>ALK</i> mutations during sequential treatment. These results suggest that sequential ALK inhibitors can foster the emergence of compound <i>ALK</i> mutations, identification of which is critical to informing drug design and developing effective therapeutic strategies.<b>Significance:</b> Treatment with sequential first-, second-, and third-generation ALK inhibitors can select for compound <i>ALK</i> mutations that confer high-level resistance to ALK-targeted therapies. A more efficacious long-term strategy may be up-front treatment with a third-generation ALK inhibitor to prevent the emergence of on-target resistance. <i>Cancer Discov; 8(6); 714-29. ©2018 AACR.</i><i>This article is highlighted in the In This Issue feature, p. 663</i>.