Abstract 2855: Identification of optimal treatment sequence and acquired resistance mechanisms of ALK inhibitors using EML4-ALK transgenic mouse model
Authors: Pyo Kyoung-Ho , Min Lim Sun , Kim Jae Hwan , Lee Ji Min , Jo Ha Ni , Cho Jae Soek , Yun Mi-Ran , Kim Sung Eun , Kim Hye Ryun , Xin Chun-Feng , Kim Tae-Min , Cho Byoung Chul 
Published: August 2018

Abstract
Introduction: EML4-ALK is a distinct molecular entity that is highly sensitive to ALK tyrosine kinase inhibitors (TKIs). While many trials have showed the superiority of ALK TKIs over cytotoxic chemotherapy, the optimal sequencing of ALK TKIs is still obscure. Acquired resistance to ALK TKIs remains a key challenge, and unknown mechanisms of resistance need to be resolved. In this study, we aimed to identify optimal treatment sequence and acquired resistance mechanisms of ALK TKIs using EML4-ALK transgenic mice model that recapitulates human EML4-ALK lung adenocarcinoma.
Methods: The tumorigenesis of EML4-ALK transgenic mice was based on Cre-ERT2/Lox system, and intraperitoneal injection with tamoxifen induced lung tumors. When tumor nodules were observed, EML4-ALK transgenic mice were treated with either crizotinib (150mg/kg) followed by ceritinib (75mg/kg) upon progression (N=13) or with ceritinib followed by crizotinib (N=12) upon progression. Tumor response was evaluated weekly using magnetic resonance imaging. Progression-free survival (PFS) was measured to compare the efficacy between two ALK TKIs. For the analysis of acquired resistance mechanism, whole-exome sequencing, RNA sequencing, and targeted sequencing of ALK gene were performed.
Results: Head-to-head comparison of crizotinib and ceritinib was performed in the first-line setting. A total of 13 mice were treated with upfront crizotinib, and mice that showed progressive disease (PD) were crossed over to ceritinib (n=9). A total of 12 mice were treated with upfront ceritinib, and mice that showed PD (n=8) were crossed over to crizotinib. Four mice in each group were sacrificed for analysis of resistance mechanism at the time of PD. The PFS of ceritinib was significantly longer than that of crizotinib [24 weeks (95% CI, 21.4-26.5) vs. 8 weeks (95% CI, 6.5-9.0), P &lt; 0.001]. Subsequent treatment with ceritinib following crizotinib resulted in significantly longer PFS than crizotinib following ceritinib [7 weeks (95% CI, 4.1-9.9) vs 3 weeks (95% CI, 2.5-3.5), P &lt; 0.001]. Altogether, treatment with ceritinib followed by crizotinib showed a prolongation of PFS, compared to crizotinib followed by ceritinib (27 weeks vs. 15 weeks, P &lt; 0.001). We noted that ALK-TKI resistant tumors harbored several copy number variations (CNVs), and nonsynonymous oncogenic mutations, but found no previously reported resistant mechanisms including secondary mutations, or CNVs. Wnt signaling related gene set was increased in both crizotinib- and ceritinib-resistant tumors, and Hippo signaling related gene set was increased in ceritinib-resistant tumors on KEGG pathway-based analysis.
Conclusion: Our findings suggest that ceritinib is superior to crizotinib when used in the first-line setting. Novel mechanisms of acquired resistance such as increased Wnt and Hippo signaling need further validation.
Citation Format: Kyoung-Ho Pyo, Lim Sun Min, Jae Hwan Kim, Ji Min Lee, Ha Ni Jo, Jae Soek Cho, Mi-Ran Yun, Sung Eun Kim, Hye Ryun Kim, Chun-Feng Xin, Tae-Min Kim, Byoung Chul Cho. Identification of optimal treatment sequence and acquired resistance mechanisms of ALK inhibitors using EML4-ALK transgenic mouse model [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 2855.