Abstract 781: The potent ALK inhibitor AP26113 can overcome mechanisms of resistance to first- and second-generation ALK TKIs in preclinical models
Authors: Zhang Sen , Nadworny Sara , Wardwell Scott D. , Eichinger Lindsey , Das Biplab , Ye Emily Y. , Hodgson J. Graeme , Rivera Victor M. 
Published: August 2015

Abstract
Background:
Disease progression in anaplastic lymphoma kinase-positive (ALK+) non-small cell lung cancer (NSCLC) patients (pts) treated with the first-generation tyrosine kinase inhibitor (TKI) crizotinib, or the second-generation inhibitors ceritinib and alectinib, is often associated with secondary resistance mutations in ALK (such as G1202R, linked with resistance to all 3 TKIs in pts), or relapse in the brain. AP26113 is a highly potent ALK inhibitor with promising anti-tumor activity in pts with crizotinib-resistant disease. Here we broadly evaluate AP26113's ability to overcome mechanisms of resistance to first- and second-generation ALK inhibitors, in preclinical models (including brain cancer models), and describe a novel methodology to compare in vitro potency, clinical pharmacokinetic parameters, and clinical efficacy.
Methods:
Ba/F3 cells were engineered to express native EML4-ALK or 17 mutants resistant to crizotinib, ceritinib, and/or alectinib in clinical or preclinical studies. IC50s for all TKIs were compared to “clinically effective” plasma concentrations (Ceff) of each inhibitor, which were derived using average steady-state levels in pts, and corrected for the functional effects of protein binding in vitro. In vivo studies were performed in mice, in which Ba/F3 cells with mutant or native EML4-ALK were injected subcutaneously, or a NSCLC line with EML4-ALK (H2228) was injected into the brain.
Results:
The Ceff of crizotinib was only ∼2-fold above the IC50 for native ALK, suggesting that crizotinib may be susceptible to mutants that inhibit binding by only a few-fold. Indeed, 8/10 mutants previously associated with clinical resistance to crizotinib were found to have IC50s that exceed the Ceff. Similar analyses revealed mutants with IC50s that exceeded the Ceff for ceritinib (e.g. L1198F) and alectinib (e.g. I1171N), with G1202R being the most recalcitrant mutant overall. In contrast, the Ceff of AP26113 was &gt;20-fold above the IC50 for native ALK, and exceeded the IC50 for all 17 mutants, including G2102R. In vivo, among all 4 TKIs tested (at doses effective against native ALK), only AP26113 demonstrated significant efficacy against G1202R-mutant ALK (88% tumor growth inhibition). Finally, compared to crizotinib, AP26113 markedly enhanced survival of mice bearing brain tumors.
Conclusion:
AP26113 inhibits all 17 clinically and preclinically observed crizotinib-, ceritinib-, and/or alectinib-resistant ALK mutants tested in vitro, has potent effects on the recalcitrant G1202R mutant in vivo and has activity in an orthotopic brain model. These results suggest AP26113 may effectively address a broad range of resistance mechanisms identified for other ALK TKIs. AP26113 is currently in a global phase 2 registration trial in patients with locally advanced or metastatic ALK+ NSCLC who were previously treated with crizotinib (NCT02094573).
Citation Format: Sen Zhang, Sara Nadworny, Scott D. Wardwell, Lindsey Eichinger, Biplab Das, Emily Y. Ye, J. Graeme Hodgson, Victor M. Rivera. The potent ALK inhibitor AP26113 can overcome mechanisms of resistance to first- and second-generation ALK TKIs in preclinical models. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 781. doi:10.1158/1538-7445.AM2015-781