Published OnlineFirst January 6, 2012; DOI: 10.1158/1535-7163.MCT-11-0750 Molecular Cancer Molecular Medicine in Practice Therapeutics The EGFR T790M Mutation in Acquired Resistance to an Irreversible Second-Generation EGFR Inhibitor Youngwook Kim1, Jeonghun Ko1, ZhengYun Cui1, Amir Abolhoda3, Jin Seok Ahn2, Sai-Hong Ou3, Myung-Ju Ahn1,2, and Keunchil Park1,2 Abstract Molecular target therapies using first-generation, reversible epidermal growth factor receptor (EGFR) tyrosine kinase inhibitors (TKI), such as gefitinib or erlotinib, have been shown to be effective for patients with non-small cell lung cancer (NSCLC) who harbor activating mutations in EGFR. However, these patients eventually develop resistance to the reversible TKIs, and this has led to the development of second-generation, irreversible EGFR inhibitors. Currently, the mechanism of acquired resistance to irreversible EGFR inhibitors is not clear. Using an in vitro cell culture system, we modeled the acquired resistance to first-line treatment with second-generation EGFR-TKIs using an EGFR-mutant NSCLC cell line. Here, we report a mechanism of resistance involving T790M secondary mutation as well as a corresponding clinical case. The results of these findings suggest that inhibition of EGFR by currently available second-generation EGFR-TKIs may not be sufficient to physiologically prevent the emergence of cells that are still dependent on EGFR signaling. This finding bears important implications on the limitations of currently available second-generation EGFR-TKIs. Mol Cancer Ther; 11(3); 784–91. Ó2012 AACR. Introduction predictive biomarkers for corresponding molecular tar- The successful clinical usage of imatinib seen in the get inhibitors. In contrast to the case of CML, however, case of patients with chronic myeloid leukemia (CML) has the efficacy of EGFR-TKIs in lung cancer was found to be led to the notion that some cancer cells are dependent on severely compromised by the rapid emergence of targeted a limited number of oncogenic pathways and that tumors therapy-resistant clones; most patients with lung cancer can be controlled by specific inhibition of these critical receiving EGFR-TKI therapy acquire resistance within pathways (1–3). This notion has been further expanded 1 year. Detailed molecular analyses have shown that about to the case of solid tumors, where administration of half of these patients develop resistance through a com- pound T790M EGFR substitution mutation, placed in cis epidermal growth factor receptor (EGFR) tyrosine kinase EGFR inhibitors (TKI) has been shown to produce a dramatic with a primary activating mutant allele (7–10). Efforts to block signaling from the compound mutant clinical response in a subset of patients with lung cancer EGFR (4–6). with small-molecule inhibitors has led to the con- It was subsequently observed that the majority of pati- ceptual introduction of experimental, irreversible EGFR- ents with lung cancer responsive to EGFR-TKIs also harbor TKIs that function primarily by covalently attaching to activating mutations in the EGFR-TK domain (4–6). This the cysteinyl-797 residue in the pocket of the EGFR-kinase further bolsters the notion that searching for genetic domain (11). These compounds have been shown to be signatures related to oncogenic alterations can serve as modestly efficacious in coping with the acquired resis- tance because of T790M mutation in preclinical in vitro model studies (12). Furthermore, pharmacologic efforts led to the development of second-generation EGFR-TKIs fi 1 Authors' Af liations: Medical Nano-Element Development Center, Sam- such as HKI-272, BIBW2992 (afatinib), and PF00299804. sung Biomedical Research Institute; 2Division of Hematology-Oncology, Department of Medicine, Samsung Medical Center, Sungkyunkwan Uni- Various in vitro and in vivo preclinical animal model versity School of Medicine, Seoul, Korea; and 3Irvine Medical Center, studies supported the experimental observation that University of California, Orange, California irreversible EGFR-TKIs could be potentially effective Note: Supplementary data for this article are available at Molecular Cancer in blocking T790M EGFR-derived signaling pathways Therapeutics Online (http://mct.aacrjournals.org/). (13–17). Corresponding Authors: Keunchil Park, Division of Hematology-Oncol- Second-generation, irreversible EGFR-TKIs are cur- ogy, Department of Medicine, Samsung Medical Center, Sungkyunkwan University School of Medicine, 50 Irwon-dong Gangnam-gu, Seoul 135- rently being tested in clinical settings as alternative ther- 710, Korea. Phone: 82-2-3410-3450; Fax: 82-2-3410-1754; E-mail: apeutic options for patients who acquired resistance [email protected]; and Myung-Ju Ahn, [email protected] to gefitinib or erlotinib via T790M mutation (18). It has doi: 10.1158/1535-7163.MCT-11-0750 been shown that the covalent attachment of certain irre- Ó2012 American Association for Cancer Research. versible EGFR-TKIs to the kinase pocket is largely 784 Mol Cancer Ther; 11(3) March 2012 Downloaded from mct.aacrjournals.org on September 28, 2021. © 2012 American Association for Cancer Research. Published OnlineFirst January 6, 2012; DOI: 10.1158/1535-7163.MCT-11-0750 Irreversible EGFR-TKI Resistance nondiscriminatory between the active conformation of phospho-EGFR (Cell Signaling Technology, Tyr1068), wild-type EGFR and that of the mutant, providing ratio- p-ErbB3 (Cell Signaling Technology), p-STAT3 (Cell Sig- nale for the use of these molecules in overcoming the naling Technology), STAT3 (Cell Signaling Technology), enzymatic kinetics problem associated with restored AKT (Cell Signaling Technology), p-AKT (Cell Signaling ATP affinity of T790M EGFR (19,20). This nondiscrimi- Technology, Ser473), extracellular signal-regulated kinase nation, although effective in overcoming kinetics problem (ERK; p44/42 MAP kinase, Cell Signaling Technology), of T790M, raises concern in terms of applicability in p-ERK (p44/42 MAP kinase, Tyr202/Tyr204, Cell Signal- clinical settings, given that nondiscriminatory blockade ing Technology), actin and actinin (Santa Cruz), of wild-type and mutant EGFR can eventually limit p-p70S6kinase (Cell Signaling Technology), PTEN (Cell the effectiveness because of issues related to side effects. Signaling Technology), BIM (Cell Signaling Technology), Thus, applicability of this compound in clinics will be p-cMET (Invitrogen BioSource, 44887G), cMET (Santa largely dictated by the effective serum concentration of Cruz), p-insulin-like growth factor (IGF)-1R (Cell Signal- this class of drugs, which must meet the dual requirement ing Technology), and IGF-1R (Cell Signaling Technology). of tolerability of the patients and functionality against tumors. MTT cell viability In this study, we modeled the treatment with the irre- To measure the sensitivities to anti-cancer drugs, an versible EGFR-TKI, BIBW2992 (afatinib), to gefitinib- or MTT assay was conducted. In brief, PC9 cells (5 Â 103/well) erlotinib-naive EGFR-mutant lung cancer and generated were seeded onto 96-well plates and were preincubated the cells that acquired the trait of resistance to irreversible overnight. The cells were continuously exposed to the indi- EGFR-TKIs. The analysis of the resulting clones provides cated concentrations of drugs with 1% FBS for 3 days. insights into the pharmacologic mechanistic basis under- Absorbance was measured at 540 nm with a microplate lying the requirement for alternative treatment schemes. reader (Molecular Devices, 384 plus). In vivo study Materials and Methods All animals were maintained in a facility at Samsung Cell culture and drug treatments Biomedical Research Institute (specific pathogen free) in Non-small cell lung cancer (NSCLC) PC9 cells (exon 19 accordance with institutional guidelines. A total of 1 Â 106 del E746-A750) were kindly provided by Dr. K. Nishio PC9 or BIBW2992-resistant PC9 cells were inoculated onto (National Cancer Center Hospital, Tokyo, Japan). This cell BALB/c nude mice (n ¼ 4). Daily oral doses of BIBW2992 line was extensively characterized previously (21–24) and (35 mg/kg) in captisol solution were administered to was repeatedly tested in the laboratory for its authenti- tumor-bearing mice. Tumor size was measured twice a cation by genotyping and morphologic observation. PC9 week to follow the drug response in animal model studies. cells or their derivatives were verified by morphology and growth curve analysis and were tested for Mycoplasma. Reagents and constructs NSCLC PC9 cells were maintained in RPMI-1640 (GIBCO) EGFR short interfering RNA (siRNA; sense 50cagagg- with 10% FBS (GIBCO) and 1% antibiotic-antimycotic auguucaauaacu30 antisense 50aguuauugaacauccucu30 UU (GIBCO) in a 37 C incubator. BIBW2992 was kindly pro- overhang) and control siRNA (sense 50gagcgaucuagua- vided by Boehringer Ingelheim. PC9TR3 cells were gen- uaauca30 antisense 50ugauuauacuagaucgcuc30 UU over- erated under the continuous stress of erlotinib treatment. hang) were ordered from Bioneer. The cmet copy number Sanger sequencing of the PC9TR3 EGFR-TK domain was measured by SYBR Green-based real-time PCR revealed the presence of T790M mutation (data not assay with glyceraldehyde-3-phosphate dehydrogenase shown). (GAPDH) as the normalization control. Gene dosage of the T790M allele was determined using molecular beacon- Western blotting and antibodies based fluorescence detection. The detailed protocol was Cells were harvested, washed with PBS, and lysed described by Oh and colleagues (25). The EGFR T790M in lysis buffer [50 mmol/L