Abstract 1830: A clinical paired resistant model elucidated novel dual salvage signaling that confers alectinib resistance in ALK-rearranged lung cancer

Conventional drug-resistant cancer cell line models have contributed to the elucidation of drug-resistant mechanisms. However, whether or not these models reflect patients in clinical settings is often controversial. We herein report a patient-derived drug resistant model system named the “clinical paired resistant model”. This model consists of 2 cell lines derived from a treatment-naïve patient (drug sensitive cell line model) and again after disease progression (drug resistant cell line model). The clinical paired resistant model of alectinib, the second generation ALK inhibitor, revealed the properties that cancer cells acquired during treatment using phosphoproteome and immunoblotting analyses; the proto-oncogene protein tyrosine kinase Src and hepatocyte growth factor receptor MET were activated after the development of alectinib resistance. No secondary mutations were detected in the coding region of ALK tyrosine kinase in the alectinib resistant model. In this alectinib-resistant model, the inhibition of Src and MET using saracatinib and PHA-665752 significantly restored alectinib sensitivity in vitro (17.2-fold change in IC50). Downstream signaling molecules for proliferation and survival, phosphorylation of Akt and ERK1/2, were inhibited and caspase 3/7 activity was significantly increased when the cells were treated with all three inhibitors (saracatinib, PHA-665752, and alectinib). Combined knockdown of SRC and MET restored alectinib sensitivity and inhibited downstream signaling in combination with ALK inhibition using alectinib, suggesting that the dual salvage signaling of MET and Src conferred alectinib resistance. A xenograft generated from our paired resistant model (N=5-6, in each group) indicated that combination therapy with a saracatinib and crizotinib, the first generation ALK inhibitor which also inhibits MET, significantly decreased tumor size in vivo as compared with saracatinib or crizotinib monotherapy. We also established a conventional alectinib resistant cell line model in vitro by exposing NCI-H2228 cells (EML4-ALK variant 3a/b) to 300 nM of alectinib for 3 months and found MET and Src were also activated in the model. Our clinical paired resistant model permits the detection of drug-resistant mechanisms without exploring the common characteristics of numerous drug-resistant patients. Our results demonstrate that MET and Src are potential therapeutic targets in patients with alectinib resistance and that the clinical paired resistant model may be a new strategy to elucidate drug-resistant mechanisms in relatively rare cancers. Citation Format: Takahiro Tsuji, Hiroaki Ozasa, Takashi Nomizo, Tomoko Funazo, Yuto Yasuda, Yuichi Sakamori, Hironori Yoshida, Kiyoshi Uemasu, Hitomi Ajimizu, Ryoko Okutani, Shunsuke Aburaya, Wataru Aoki, Mitsuyoshi Ueda, Koh Furugaki, Yasushi Yoshimura, Toyohiro Hirai, Young Hak Kim. A clinical paired resistant model elucidated novel dual salvage signaling that confers alectinib resistance in ALK-rearranged lung cancer [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 1830.