Encouraged by these significant clinical responses (Shaw et al., 2014), ceritinib was approved for clinical use by the US Food and Drug Administration (FDA) in 2014 and European Medicines Agency (EMA) in 2015, and alectinib was approved by the Pharmaceuticals and Medical Devices Agency of Japan in 2014 and FDA in 2015 (Seto et al., 2013). NSCLC patients. Our study suggests that alectinib, PF-06463922, or P-gp inhibitor with ceritinib could overcome the ceritinib or crizotinib resistance mediated by P-gp overexpression. avian ur2 sarcoma virus oncogene homolog 1; PFS, progression-free survival; ORR, overall response rate; EGFR, epidermal growth factor receptor; BBB, bloodCbrain barrier; MRP1, multidrug Resistance-associated Protein 1; BCRP, breast cancer resistance protein; ATP, adenosine triphosphate; ABC, adenosine triphosphate (ATP)-binding cassette; CAF, cyclophosphamide, doxorubicin, and fluorouracil; OS, overall survival; FISH, fluorescence Nr4a1 in situ hybridization; IHC, immunohistochemical; IRB, institutional review board; TNM, tumor-node-metastasis; CT, computed tomography; K562/VCR, K562-derived vincristine-resistant; RPMI, Roswell Park Memorial Institute; FBS, 4′-Ethynyl-2′-deoxyadenosine fetal bovine serum; IC50, half-maximal inhibitory concentration; 4′-Ethynyl-2′-deoxyadenosine (sh)RNA, small hairpin; CSCs, 4′-Ethynyl-2′-deoxyadenosine cancer stem/initiating cells; LCNEC, large cell neuroendocrine carcinoma; BAC, bronchioloalveolar carcinoma; SP, side population (gene rearrangement results in the constitutive expression and activation of an ALK fusion protein, which has been shown to strongly drive oncogenesis. To target ALK-rearranged NSCLC, the oral ALK and avian ur2 sarcoma virus oncogene homolog 1 (ROS1) inhibitor crizotinib have been used. Two randomized phase 3 studies of crizotinib showed significantly longer progression-free survival (PFS; 7.7?months vs 3.0?months in the second-line study and 10.9?months vs 7.0?months in the first-line study) and higher overall response rate [ORR; 65% (113/173) vs 20% (34/174) in the second-line study and 74% (128/172) vs 45% (77/171) in the first-line study] compared with those of chemotherapy (Shaw et al., 2013, Solomon et al., 2014). However, although crizotinib has shown significant treatment efficacy in ALK fusion-positive NSCLC patients, tumor relapse because of acquired resistance has been observed. Crizotinib resistance was shown to be caused by various types of secondary mutations in the ALK kinase domain, by fusion gene amplification, or by activation of the epidermal growth factor receptor (EGFR) or KIT (hardy-zuckerman 4′-Ethynyl-2′-deoxyadenosine 4 feline sarcoma viral oncogene homolog)-mediated bypass pathways (Doebele et al., 2012, Katayama et 4′-Ethynyl-2′-deoxyadenosine al., 2012, Sasaki et al., 2011). Crizotinib has also been shown to be relatively ineffective for cancer that has metastasized to the brain because of poor bloodCbrain barrier (BBB) penetration by P-glycoprotein (P-gp) overexpression (Costa et al., 2011, Chuan Tang et al., 2014). To overcome crizotinib resistance, various next-generation ALK inhibitors have been evaluated in clinical trials. Among these, two ALK-tyrosine kinase inhibitors (TKIs) alectinib and ceritinib, have revealed prominent responses in both ALK-TKI-na?ve and crizotinib-treated patients (Sakamoto et al., 2011, Shaw et al., 2014, Gadgeel et al., 2014, Seto et al., 2013, Marsilje et al., 2013). Encouraged by these significant clinical responses (Shaw et al., 2014), ceritinib was approved for clinical use by the US Food and Drug Administration (FDA) in 2014 and European Medicines Agency (EMA) in 2015, and alectinib was approved by the Pharmaceuticals and Medical Devices Agency of Japan in 2014 and FDA in 2015 (Seto et al., 2013). However, it is expected that next-generation ALK inhibitor-resistant tumors will also eventually develop via multiple mechanisms. To date, a few ceritinib-resistant mutations in the ALK kinase domain have been identified in patients who experienced a relapse during ceritinib therapy (Friboulet et al., 2014). In human cancer, ABCB1/P-gp, ABCC1/multidrug resistance-associated protein 1 (MRP1), and ABCG2/breast cancer resistance protein (BCRP) are well-known causes of multidrug resistance to multiple chemotherapeutic agents, such as taxane and vinca alkaloids (Gottesman et al., 2002). Therefore, much effort has been devoted for developing.