The Potent ALK Inhibitor Brigatinib (AP26113) Overcomes Mechanisms of Resistance to First- and Second-Generation ALK Inhibitors in Preclinical Models

Purpose: Non-small cell lung cancers (NSCLCs) harboring ALK gene rearrangements (ALK⁺) typically become resistant to the first-generation anaplastic lymphoma kinase (ALK) tyrosine kinase inhibitor (TKI) crizotinib through development of secondary resistance mutations in ALK or disease progression in the brain. Mutations that confer resistance to second-generation ALK TKIs ceritinib and alectinib have also been identified. Here, we report the structure and first comprehensive preclinical evaluation of the next-generation ALK TKI brigatinib.

Experimental design: A kinase screen was performed to evaluate the selectivity profile of brigatinib. The cellular and in vivo activities of ALK TKIs were compared using engineered and cancer-derived cell lines. The brigatinib-ALK co-structure was determined.

Results: Brigatinib potently inhibits ALK and ROS1, with a high degree of selectivity over more than 250 kinases. Across a panel of ALK⁺ cell lines, brigatinib inhibited native ALK (IC₅₀, 10 nmol/L) with 12-fold greater potency than crizotinib. Superior efficacy of brigatinib was also observed in mice with ALK⁺ tumors implanted subcutaneously or intracranially. Brigatinib maintained substantial activity against all 17 secondary ALK mutants tested in cellular assays and exhibited a superior inhibitory profile compared with crizotinib, ceritinib, and alectinib at clinically achievable concentrations. Brigatinib was the only TKI to maintain substantial activity against the most recalcitrant ALK resistance mutation, G1202R. The unique, potent, and pan-ALK mutant activity of brigatinib could be rationalized by structural analyses.

Conclusions: Brigatinib is a highly potent and selective ALK inhibitor. These findings provide the molecular basis for the promising activity being observed in ALK⁺, crizotinib-resistant patients with NSCLC being treated with brigatinib in clinical trials. Clin Cancer Res; 22(22); 5527-38. ©2016 AACR.