Published papers

BACKGROUND: Aldehyde dehydrogenases (ALDHs) play a major role in detoxification of aldehydes. High expression of ALDHs is a marker for stem cells of many organs including the lungs. A common polymorphism in ALDH2 gene (ALDH2*2) results in inactivation of the enzyme and is associated with alcohol flushing syndrome and increased risk for cardiovascular and Alzheimer's diseases and some cancers. The effect of this ALDH2 polymorphism on the lung and its stem cells has not been thoroughly examined. METHODS: We examined the association between the ALDH2*2 allele and lung function parameters in a population of healthy individuals. We also examined its association with the incidence of asthma and COPD in patient cohorts. We used the in vitro colony forming assay to detect the effect of the polymorphism on lung epithelial stem cells from both primary human surgical samples and Aldh2*2 transgenic (Tg) and Aldh2 -/- mice. Response to acute and chronic lung injuries was compared between wild type (WT), Aldh2*2 Tg and Aldh2 -/- mice. RESULTS: In humans, the ALDH2*2 allele was associated with lower FEV1/FVC in the general population, but not with the development of asthma or COPD. Both the bronchial and lung epithelium carrying the ALDH2*2 allele showed a tendency for lower colony forming efficiency (CFE) compared to ALDH2 allele. In mice, the tracheal epithelial thickness, nuclear density, and number of basal stem cells were significantly lower in Aldh2 -/- and Aldh2*2 Tg adult mice than in WT. Electron microscopy showed significantly increased number of morphologically abnormal mitochondria in the trachea of Aldh2 -/- mice. Aldh2 -/- tracheal and lung cells showed higher ROS levels and fewer functional mitochondria than those from WT mice. No significant differences were detected when tracheal and lung epithelial stem cells were examined for their in vitro CFE. When exposed to chronic cigarette smoke, Aldh2*2 Tg mice were resistant to emphysema development, whereas influenza infection caused more epithelial damage in Aldh2 -/- mice than in WT mice. CONCLUSIONS: ALDH2 polymorphism has several subtle effects on the lungs, some of which are similar to changes observed during normal aging, suggesting a "premature lung aging" effect.

Objectives: Fibroblast growth factor (FGF) 9 is a member of the FGF family, which modulates cell proliferation, differentiation, and motility. Recent studies show that the activation of FGF signals including FGF9 is associated with the pathogenesis of several cancers; however, its clinicopathological and biological significance in non-small cell lung cancer (NSCLC) is unclear. The purpose of this study was to clarify the characteristics of NSCLC with FGF9 expression. Materials and Methods: We evaluated the expression of FGF9 in resected NSCLC specimens and corresponding non-tumorous lung tissue samples using cDNA microarray and evaluated its clinicopathological characteristics. Results: Nine out of 90 NSCLC specimens (10%) had "high"FGF9 expression compared with corresponding non-cancerous lung tissues. Histologically, of the 9 NSCLC specimens with high FGF9 expression, 5 were adenocarcinoma, whereas none were squamous cell carcinoma. FGF9 expression was not associated with sex, smoking history, or clinical stage. However, in patients with high and low FGF9 expression, the postoperative recurrence rates were 78% and 24% (p = 0.033), respectively. Overall survival was significantly shorter in patients with high FGF9 expression than in those with low FGF9 expression (p < 0.001). Conclusion: Our data indicate that FGF9 may be a novel unfavorable prognostic indicator and a candidate therapeutic target of NSCLC. (C) 2013 Elsevier Ireland Ltd. All rights reserved.

Aim: Clinical microarray datasets were analyzed to search for new therapeutic targets and prognostic markers of non-small cell lung cancer (NSCLC). Materials and Methods: Microarray datasets from 90 lung cancer specimens, were analyzed with focus on the FOXD1 gene. Levels of FOXDI mRNA were assessed in lung cancer cell lines and these levels were correlated with survival. Results: FOXD1-knockdown led to suppression of cell proliferation. Moreover, patients with high FOXDI expression survived for a significantly shorter time than those with low FOXDI expression. Conclusion: The expression status of FOXD1 is a novel prognostic factor and may lead to new treatment strategies for NSCLC.

Recent advances in the treatment of non-small cell lung cancer (NSCLC) with new agents require accurate histological subtyping at diagnosis to avoid the higher risk of an adverse response and to obtain the maximum therapeutic response. However, interobserver variability, tumor hetero-geneity and the degree of differentiation may affect the decision concerning a pathological diagnosis of NSCLC. Therefore, the aim of this study was to identify specific microRNAs (miRNAs) as standardized biomarkers with high sensitivity and specificity in order to distinguish between squamous cell carcinoma (SCC) and adenocarcinoma (AC). Quantitative polymerase chain reaction (qPCR)-based miRNA array analysis was performed to identify microRNAs differentially expressed between SCC and AC using 86 resected NSCLC samples in addition to adjacent normal tissues. The results were confirmed by independent qRT-PCR assays with the same test samples and 88 additional validation samples, and from this we evaluated the usefulness of the identified miRNAs as biomarkers to distinguish between SCC and AC. Three miRNAs (hsa-miR-196b, hsa-miR-205 and hsa-miR-375) were identified. Discriminant analysis combining the three miRNAs appeared to distinguish SCC from AC accurately in the test and validation samples, demonstrating a sensitivity and specificity of 76 and 80%, and 85 and 83%, respectively. hsa-miR-196b, hsa-miR-205 and hsa-miR-375 were identified as biomarkers capable of distinguishing between lung SCC and lung AC. These newly identified miRNAs may prove to be highly valuable molecular markers for the classification of NSCLC histological subtypes and may contribute to the pathogenesis of each subtype of NSCLC.

EGFR mutated lung cancer accounts for a significant subgroup of non-small-cell lung cancer (NSCLC). Over the last decade, multiple EGFR tyrosine kinase inhibitors (EGFR-TKIs) have been developed to target mutated EGFR. However, there is little information regarding mutation specific potency of EGFR-TKIs against various types of EGFR mutations. The purpose of this study is to establish an in vitro model to determine the "therapeutic window" of EGFR-TKIs against various types of EGFR mutations, including EGFR exon 20 insertion mutations. The potency of 1st (erlotinib), 2nd (afatinib) and 3rd (osimertinib and rociletinib) generation EGFR-TKIs was compared in vitro for human lung cancer cell lines and Ba/F3 cells, which exogenously express mutated or wild type EGFR. An in vitro model of mutation specificity was created by calculating the ratio of IC50 values between mutated and wild type EGFR. The in vitro model identified a wide therapeutic window of afatinib for exon 19 deletions and L858R and of osimertinib and rociletinib for T790M positive mutations. The results obtained with our models matched well with previously reported preclinical and clinical data. Interestingly, for EGFR exon 20 insertion mutations, most of which are known to be resistant to 1st and 2nd generation EGFR-TKIS, osimertinib was potent and presented a wide therapeutic window. To our knowledge, this is the first report that has identified the therapeutic window of osimertinib for EGFR exon 20 insertion mutations. In conclusion, this model will provide a preclinical rationale for proper selection of EGFR-TKIs against clinically-relevant EGFR mutations.

This study was designed to identify epigenetically regulated genes and to clarify the contribution of epigenetic alteration to acquired resistance to epidermal growth factor receptor-tyrosine kinase inhibitors (EGFR-TKIs). We established a gefitinib-resistant lung cancer cell line, PC9, which was originally gefitinib-sensitive, by serial long-term exposure to gefitinib. RNA and DNA were collected from both gefitinib-sensitive and -resistant PC9 cells, and comprehensive DNA methylation and mRNA expression analyses were performed using Infinium HumanMethylation27 Bead Arrays and Agilent SurePrint G3 Human Gene Expression 8x60K Array, respectively. DNA methylation was increased in 640 genes in gefitinib-resistant cells compared to parental cells. Among them, we selected 29 candidate genes that presented a decrease in mRNA expression in resistant PC9. We further studied four of the selected genes (C10orf116, IGFBP3, KL, and S100P) and found that KL or S100P silencing by siRNA induced a decrease in gefitinib sensitivity compared to that in the negative control in PC9. In conclusion, KL and S100P could be potential targets to overcome resistance to EGFR-TKIs.

We identified transmembrane protease, serine 4 (TMPRSS4) as a putative, druggable target by screening surgically resected samples from 90 Japanese non-small-cell lung cancer (NSCLC) patients using cDNA microarray. TMPRSS4 has two druggable domains and was upregulated in 94.5% of the lung cancer specimens. Interestingly, we found that TMPRSS4 expression was associated with tissue factor pathway inhibitor 2 (TFPI-2) expression in these clinical samples. In contrast to TMPRSS4, TFPI-2 expression was downregulated in NSCLC samples. The in vitro induction of TFPI-2 in lung cancer cell lines decreased the expression of TMPRSS4 mRNA levels. Reporter assay showed that TFPI-2 inhibited transcription of TMPRSS4, although partially. Knockdown of TMPRSS4 reduced the proliferation rate in several lung cancer cell lines. When lung cancer cell lines were treated with 5-aza-2-deoxycytidine or trichostatin A, their proliferation rate and TMPRSS4 mRNA expression levels were also reduced through the upregulation of TFPI-2 by decreasing its methylation in vitro. The TFPI-2 methylation level in the low TMPRSS4 group appeared to be significantly low in NSCLC samples (P=0.02). We found a novel molecular mechanism that TFPI-2 negatively regulates cell growth by inhibiting transcription of TMPRSS4. We suggest that TMPRSS4 is upregulated by silencing of TFPI-2 through aberrant DNA methylation and contributes to oncogenesis in NSCLC.

Although the main cellular target of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection is thought to be alveolar cells, the absence of their tractable culture system precludes the development of a clinically relevant SARS-CoV-2 infection model. Here, we establish an efficient human alveolosphere culture method and sphere-based drug testing platform for SARS-CoV-2. Alveolospheres exhibit indolent growth in a Wnt- and R-spondin-dependent manner. Gene expression, immunofluorescence, and electron microscopy analyses reveal the presence of alveolar cells in alveolospheres. Alveolospheres express ACE2 and allow SARS-CoV-2 to propagate nearly 100,000-fold in 3 days of infection. Whereas lopinavir and nelfinavir, protease inhibitors used for the treatment of human immunodeficiency virus (HIV) infection, have a modest anti-viral effect on SARS-CoV-2, remdesivir, a nucleotide prodrug, shows an anti-viral effect at the concentration comparable with the circulating drug level. These results demonstrate the validity of the alveolosphere culture system for the development of therapeutic agents to combat SARS-CoV-2.

The development of molecular targeted therapy has improved clinical outcomes in patients with life-threatening advanced lung cancers with driver oncogenes. However, selective treatment for KRAS-mutant lung cancer remains underdeveloped. We have successfully characterised specific molecular and pathological features of KRAS-mutant lung cancer utilising newly developed cell line models that can elucidate the differences in driver oncogenes among tissues with identical genetic backgrounds. Among these KRAS-mutation-associated specific features, we focused on the IGF2-IGF1R pathway, which has been implicated in the drug resistance mechanisms to AMG 510, a recently developed selective inhibitor of KRAS G12C lung cancer. Experimental data derived from our cell line model can be used as a tool for clinical treatment strategy development through understanding of the biology of lung cancer. The model developed in this paper may help understand the mechanism of anticancer drug resistance in KRAS-mutated lung cancer and help develop new targeted therapies to treat patients with this disease.

Rationale Nontuberculous mycobacteria (NTM) are environmental mycobacteria that can cause a chronic progressive lung disease. Although epidemiological data indicate potential genetic predisposition, its nature remains unclear. Objectives We aimed to identify host susceptibility loci for Mycobacterium avium complex (MAC), the most common NTM pathogen. Methods This genome-wide association study (GWAS) was conducted in Japanese patients with pulmonary MAC and healthy controls, followed by genotyping of candidate single-nucleotide polymorphisms (SNPs) in another Japanese cohort. For verification by Korean and European ancestry, we performed SNP genotyping. Results The GWAS discovery set included 475 pulmonary MAC cases and 417 controls. Both GWAS and replication analysis of 591 pulmonary MAC cases and 718 controls revealed the strongest association with chromosome 16p21, particularly with rs109592 (p=1.64×10−13, OR 0.54), which is in an intronic region of the calcineurin-like EF-hand protein 2 (CHP2). Expression quantitative trait loci analysis demonstrated an association with lung CHP2 expression. CHP2 was expressed in the lung tissue in pulmonary MAC disease. This SNP was associated with the nodular bronchiectasis subtype. Additionally, this SNP was significantly associated with the disease in patients of Korean (p=2.18×10−12, OR 0.54) and European (p=5.12×10−03, OR 0.63) ancestry. Conclusions We identified rs109592 in the CHP2 locus as a susceptibility marker for pulmonary MAC disease.

EGFR-mutated lung cancer accounts for a significant proportion of lung cancer cases worldwide. For these cases, osimertinib, a thirdgeneration EGFR tyrosine kinase inhibitor, is extensively used as a first-line or second-line treatment. However, lung cancer cells acquire resistance to osimertinib in 1 to 2 years. Thus, a thorough clarification of resistance mechanisms to osimertinib is highly anticipated. Recent next-generation sequencing (NGS) of lung cancer samples identified several genetically defined resistance mechanisms to osimertinib, such as EGFR C797S or MET amplification. However, nongenetically defined mechanisms are not well evaluated. For a thorough clarification of osimertinib resistance, both genetic and nongenetic mechanisms are essential. By using our comprehensive protein phosphorylation array, we detected IGF1R bypass pathway activation after EGFR abolishment. Both of our established lung cancer cells and patient-derived lung cancer cells demonstrated IGF2 autocrine-mediated IGF1R pathway activation as a mechanism of osimertinib resistance. Notably, this resistance mechanism was not detected by a previously performed NGS, highlighting the essential roles of living cancer cells for a thorough clarification of resistance mechanisms. Interestingly, the immunohistochemical analysis confirmed the increased IGF2 expression in lung cancer patients who were treated with osimertinib and met the established clinical definition of acquired resistance. The findings highlight the crucial roles of cell-Autonomous ligand expression in osimertinib resistance. Here, we report for the first time the IGF2 autocrine-mediated IGF1R activation as a nongenetic mechanism of osimertinib resistance in lung cancer at a clinically relevant level.

Human lung cancer is a constellation of tumors with various histological and molecular properties. To build a preclinical platform that covers this broad disease spectrum, we obtained lung cancer specimens from multiple sources, including sputum and circulating tumor cells, and generated a living biobank consisting of 43 lines of patient-derived lung cancer organoids. The organoids recapitulated the histological and molecular hallmarks of the original tumors. Phenotypic screening of niche factor dependency revealed that EGFR mutations in lung adenocarcinoma are associated with the independence from Wnt ligands. Gene engineering of alveolar organoids reveals that constitutive activation of EGFR-RAS signaling provides Wnt independence. Loss of the alveolar identity gene NKX2-1 confers Wnt dependency, regardless of EGFR signal mutation. Sensitivity to Wnt-targeting therapy can be stratified by the expression status of NKX2-1. Our results highlight the potential of phenotype-driven organoid screening and engineering for the fabrication of therapeutic strategies to combat cancer.

Direct reprogramming is a breakthrough technology that can alter the fate of cells without the passage of stem cells. However, direct reprogramming of somatic cells into pulmonary alveolar epithelial cells has not yet been achieved. Here, we report the direct reprogramming of mouse tail tips and embryonic fibroblasts into induced pulmonary alveolar epithelial-like cells (iPULs) using four transcription factor-coding genes (Nkx2-1, Foxa1, Foxa2, and Gata6) and three-dimensional culture. The iPULs showed lamellar body-like structures and displayed key properties of pulmonary alveolar epithelial cells. Although the potential for iPULs to morphologically differentiate into alveolar epithelial type 1 cells was limited in vitro, the intratracheal administration of iPULs in a bleomycin-induced mouse model of pulmonary fibrosis led to their integration into the alveolar surface, where they formed both alveolar epithelial type 1 and type 2-like cells. Thus, reprogrammed fibroblasts may represent a new source of pulmonary alveolar epithelial cells for regenerative medicine.

Background: Heterogeneity of neuroendocrine (NE) differentiation in pulmonary high-grade NE carcinoma, mainly small-cell lung cancer (SCLC), has been recently explored based on the expression of lineage transcription factors such as ASCL1, NEUROD1 and POU2F3. However, molecular classification based on these factors remains incomplete, and NE differentiation in lung cancers is more heterogeneous than previously appreciated. Here, we investigated the heterogeneity of NE differentiation using epigenomic profiling across a range of lung cancers with NE components, predominantly large-cell neuroendocrine carcinoma (LCNEC). Methods: We analyzed super-enhancer profiles of 24 formalin-fixed paraffin-embedded tumor tissues from patients with primary lung cancers containing LCNEC components. Associations between epigenomic profiles and NE factors were examined. The functional role of SOX11 was assessed by transcriptomic analysis following CRISPR-Cas9–mediated deletion, as well as by analysis of human LCNEC/SCLC tumor and organoid datasets. Results: We identified a classical NE subtype characterized by high expression of ASCL1 and NKX2-1, along with high positivity for canonical NE markers. In addition, we identified a unique differentiation axis characterized by a neural transcription factor SOX11. Transcriptomic analyses revealed loss of neuronal gene signatures accompanied by induction of immune response-associated genes. Consistent with these findings, analysis of the human LCNEC/SCLC data showed enrichment of neuronal genes among those positively correlated with SOX11 expression and immune-associated genes among those negatively correlated. Furthermore, SOX11 was associated with reduced expression of immune-related genes, including MHC class I components. Conclusions: Our epigenomic profiling identifies a classical ASCL1/NKX2-1 subtype and a SOX11-associated axis linked to tumor immunogenicity in NE lung cancers.

Introduction: Up to 54% of all lung adenocarcinoma (LADC) cases in Asian populations occur in never-smoking women, suggesting that the impact of smoking and other environmental factors on the risk of early-onset LADC is minimal. Genetic factors may play a crucial role in disease development. Methods: The prevalence of germline pathogenic variants (GPVs) of 454 hereditary cancer and DNA repair genes was evaluated by whole-exome and whole-genome sequencing of 348 early-onset LADC (aged ≤ 40 y) and 1425 later-onset LADC (aged ≥ 41 y) cases. A case-control study comprising 10,302 LADC cases and 7898 healthy controls was performed to identify moderate-risk genetic factors for the disease. Analysis of somatic mutations in 1278 patients with LADC, including 31 patients with GPVs, was also performed. Results: The frequency of GPVs of TP53 and BRCA2 was significantly higher in those with early-onset LADC than in those with later-onset LADC. The detection rates for TP53 and BRCA2 GPVs were 2.9% and 1.7%, respectively, in patients with early-onset LADC, and 0.14% and 0.21%, respectively, in patients with later-onset LADC. Patients with BRCA1 GPVs exhibited a high incidence of concurrent TP53 somatic mutations. Patients with BRCA2 GPVs exhibited deficient homologous recombination in tumors by means of loss of the wild-type allele. A germline ALKBH2 variant, p.Glu35Alafs∗54, was associated with the risk of early-onset LADC, and patients with a deleterious variant exhibited a correlation between SBS4-related somatic mutations and the Brinkman index. Conclusion: TP53 and BRCA2 GPVs and the ALKBH2 novel variant are associated with early-onset LADC in Asians.

There are currently no effective treatments available for clear cell ovarian cancer (CCC). In this study, we aimed to identify effective drugs for CCC through high-throughput drug screening (HTDS) using ovarian cancer organoids and determine novel therapeutic targets based on the biological characteristics of CCC through omics analysis. An ovarian cancer organoid biobank was established, and HTDS was conducted using CCC organoids based on libraries of 361 and 4,560 compounds. The efficacy of the identified drugs was verified in in vitro and in vivo experiments using a patient-derived organoid xenograft mouse model. Transcriptome analysis was performed to identify genes related to the pathways targeted by the identified drugs in CCC and to assess their potential as therapeutic targets. Proteasome inhibitors and dinaciclib were extracted using HTDS and shown to inhibit tumorigenesis in vitro and in vivo. CCC, like multiple myeloma, exhibited activated endoplasmic reticulum (ER) stress and unfolded protein response (UPR), and treatment with proteasome inhibitors further enhanced ER stress and UPR, ultimately leading to cell death. Transcriptome analysis identified anterior gradient-2 (AGR2) as a key gene involved in UPR in CCC. CRISPR knockout of AGR2 suppressed cell proliferation, increased sensitivity to proteasome inhibitors, and reversed platinum resistance in CCC. AGR2 knockout also upregulated Schlafen 11, contributing to platinum sensitivity. ER stress and the UPR are activated in CCC, and proteasome inhibitors disrupt this balance, ultimately leading to cell death. AGR2 may serve as a potential therapeutic target in CCC.

We recently reported that a combination of four transcription factors (Nkx2-1, Foxa1, Foxa2, and Gata6) directly reprograms mouse embryonic fibroblasts (MEFs) into differentiated self-renewable alveolar epithelial-like cells in a serum-free 3D organoid system. Here, we aimed to generate induced pulmonary epithelial-like cells in serum-containing culture (iPULsSC) using the same four transcription factors in a serum-containing 3D culture system. We found that the global gene expression profile of iPULsSC was similar to that of alveolar epithelial type II (AT2) and alveolar type I (AT1) cells. Surfactant protein (SP)–C-positive iPULsSC displayed lamellar body-like structures, consistent with the features of AT2 cells. Furthermore, we provide evidence that intratracheal administration of iPULsSC rescued influenza virus-induced acute lung injury in mice. These findings suggest that iPULsSC can provide a potential source of lung epithelial cells for regenerative medicine. Reprogramming fibroblasts using serum-containing media, besides previously established serum-free systems, can provide a potential source of lung epithelial cells.

Introduction: Thymic neuroendocrine tumors (TNETs) are rare malignancies characterized by aggressive clinical behavior and limited therapeutic options. In small cell lung cancer (SCLC), molecular subtypes based on the expression of lineage-defining transcription factors (TFs)—ASCL1, NEUROD1, POU2F3, and YAP1—have been proposed. However, the TF landscape of TNETs remains poorly defined. Given the pathological similarities among neuroendocrine tumors across organs, we aimed to investigate whether the TF-based classification system used in SCLC is applicable to TNETs. Methods: Sixteen pathologically confirmed TNETs—including large cell neuroendocrine carcinoma (LCNEC), thymic small cell carcinoma (TSCC), atypical carcinoid (AC), and typical carcinoid (TC)—were retrospectively analyzed. Immunohistochemistry was performed to evaluate classical neuroendocrine (NE) markers (synaptophysin, chromogranin A, CD56) and TFs (ASCL1, NEUROD1, POU2F3, YAP1). H-scores were calculated, and tumors were categorized according to TFs expression profiles. Results: Synaptophysin was strongly expressed in all cases, while chromogranin A and CD56 showed variable expression, with reduced levels in LCNEC and TSCC. The combined NE score was significantly higher in carcinoid tumors compared to LCNEC and TSCC. For TFs, ASCL1 expression was observed in 93.8 % of cases, whereas NEUROD1 and POU2F3 were rarely or not expressed. YAP1 expression was confined to LCNEC cases, all of which co-expressed ASCL1 and YAP1. Based on H-scores, TNETs were classified into three subgroups: (1) ASCL1-positive/YAP1-negative (n = 12, 75 %), (2) ASCL1/YAP1 double-positive (n = 3, 19 %), and (3) double-negative (n = 1, 6 %). Conclusion: This study reveals molecular heterogeneity among TNETs. Notably, ASCL1 and YAP1 co-expression characterizes all LCNEC cases, making a distinct TF landscape in high-grade TNETs.

Alectinib is a highly selective ALK inhibitor and shows promising efficacy in non-small cell lung cancers (NSCLC) harboring the EML4-ALK gene rearrangement. The precise mechanism of acquired resistance to alectinib is not well defined. The purpose of this study was to clarify the mechanism of acquired resistance to alectinib in ALK-translocated lung cancer cells. We established alectinib-resistant cells (H3122-AR) from the H3122 NSCLC cell line, harboring the EML4-ALK gene rearrangement, by long-term exposure to alectinib. The mechanism of acquired resistance to alectinib in H3122-AR cells was evaluated by phospho-receptor tyrosine kinase (phospho-RTK) array screening and Western blotting. No mutation of the ALK-TK domain was found. Phospho-RTK array analysis revealed that the phosphorylation level of EGFR was increased in H3122-AR cells compared with H3122. Expression of TGF alpha, one of the EGFR ligands, was significantly increased and knockdown of TGF alpha restored the sensitivity to alectinib in H3122-AR cells. We found combination therapy targeting ALK and EGFR with alectinib and afatinib showed efficacy both in vitro and in a mouse xenograft model. We propose a preclinical rationale to use the combination therapy with alectinib and afatinib in NSCLC that acquired resistance to alectinib by the activation of EGFR bypass signaling. (C) 2015 AACR.

Patients with non-small cell lung cancer (NSCLC) that harbors epidermal growth factor receptor (EGFR) mutations initially respond to EGFR-tyrosine kinase inhibitors (TKI) but eventually experience relapse. Acquired resistance to EGFR-TKIs is strongly associated with patient mortality. Thus, elucidation of the mechanism of acquired resistance to EGFR-TKIs is of great importance. In this study, gefitinib-resistant cell line models were established by long-term exposure to gefitinib using the gefitinib-sensitive lung cancer cell lines, PC9 and HCC827. Expression analyses indicated that both FGFR1 and FGF2 were increased in PC9 gefitinib-resistant (PC9 GR) cells as compared with PC9 naive (PC9 na) cells. Importantly, proliferation of gefitinib-resistant cells was dependent on the FGF2 -FGFR1 pathway. Mechanistically, inhibition of either FGF2 or FGFR1 by siRNA or FGFR inhibitor (PD173074) restored gefitinib sensitivity in PC9 GR cells. These data suggest that FGF2 (-)FGFR1 activation through an autocrine loop is a novel mechanism of acquired resistance to EGFR-TKIs.