Shinsuke Hashida

Acquired Resistance to EGFR Inhibitors Is Associated with a Manifestation of Stem Cell–like Properties in Cancer Cells

Acquired resistance to EGF receptor (EGFR) tyrosine kinase inhibitor (TKI) is a critical problem in the treatment of lung cancer. Although several mechanisms have been shown to be responsible for acquired resistance, all mechanisms have not been uncovered. In this study, we investigated the molecular and cellular profiles of the acquired resistant cells to EGFR-TKI in EGFR-mutant lung cancers. Four EGFR-mutant cell lines were exposed to gefitinib by stepwise escalation and high-concentration exposure methods, and resistant sublines to gefitinib were established. The molecular profiles and cellular phenotypes of these resistant sublines were characterized. Although previously reported, alterations including secondary EGFR T790M mutation, MET amplification, and appearance of epithelial-to-mesenchymal transition (EMT) features were observed, these 2 drug-exposure methods revealed different resistance mechanisms. The resistant cells with EMT features exhibited downregulation of miRNA-200c by DNA methylation. Furthermore, the HCC827-derived subline characterized by the high-concentration exposure method exhibited not only EMT features but also stem cell-like properties, including aldehyde dehydrogenase isoform 1 (ALDH1A1) overexpression, increase of side-population, and self-renewal capability. Resistant sublines with stem cell-like properties were resistant to conventional chemotherapeutic agents but equally sensitive to histone deacetylase and proteasome inhibitors, compared with their parental cells. ALDH1A1 was upregulated in clinical samples with acquired resistance to gefitinib. In conclusion, our study indicates that the manner of EGFR-TKI exposure influences the mechanism of acquired resistance and the appearance of stem cell-like property with EGFR-TKI treatment.

Novel germline mutation in the transmembrane domain of HER2 in familial lung adenocarcinomas

We encountered a family of Japanese descent in which multiple members developed lung cancer. Using whole-exome sequencing, we identified a novel germline mutation in the transmembrane domain of the human epidermal growth factor receptor 2 (HER2) gene (G660D). A novel somatic mutation (V659E) was also detected in the transmembrane domain of HER2 in one of 253 sporadic lung adenocarcinomas. Because the transmembrane domain of HER2 is considered to be responsible for the dimerization and subsequent activation of the HER family and downstream signaling pathways, we performed functional analyses of these HER2 mutants. Mutant HER2 G660D and V659E proteins were more stable than wild-type protein. Both the G660D and V659E mutants activated Akt. In addition, they activated p38, which is thought to promote cell proliferation in lung adenocarcinoma. Our findings strongly suggest that mutations in the transmembrane domain of HER2 may be oncogenic, causing hereditary and sporadic lung adenocarcinomas.

Antitumor effect of afatinib, as a human epidermal growth factor receptor 2‐targeted therapy, in lung cancers harboring HER2 oncogene alterations

Human epidermal growth factor receptor 2 (HER2) is a member of the HER family of proteins containing four receptor tyrosine kinases. It plays an important role in the pathogenesis of certain human cancers. In non‐small‐cell lung cancer (NSCLC), HER2 amplification or mutations have been reported. However, little is known about the benefit of HER2‐targeted therapy for NSCLCs harboring HER2 alterations. In this study, we investigated the antitumor effect of afatinib, an irreversible epidermal growth factor receptor (EGFR)–HER2 dual inhibitor, in lung cancers harboring HER2 oncogene alterations, including novel HER2 mutations in the transmembrane domain, which we recently identified. Normal bronchial epithelial cells, BEAS‐2B, ectopically overexpressing wild‐type HER2 or mutants (A775insYVMA, G776VC, G776LC, P780insGSP, V659E, and G660D) showed constitutive autophosphorylation of HER2 and activation of downstream signaling. They were sensitive to afatinib, but insensitive to gefitinib. Furthermore, we examined the antitumor activity of afatinib and gefitinib in several NSCLC cell lines, and investigated the association between their genetic alterations and sensitivity to afatinib treatment. In HER2‐altered NSCLC cells (H2170, Calu‐3, and H1781), afatinib downregulated the phosphorylation of HER2 and EGFR as well as their downstream signaling, and induced an antiproliferative effect through G1 arrest and apoptotic cell death. In contrast, HER2‐ or EGFR‐non‐dependent NSCLC cells were insensitive to afatinib. In addition, these effects were confirmed in vivo by using a xenograft mouse model of HER2‐altered lung cancer cells. Our results suggest that afatinib is a therapeutic option as a HER2‐targeted therapy for NSCLC harboring HER2 amplification or mutations.

Acquisition of cancer stem cell-like properties in non-small cell lung cancer with acquired resistance to afatinib

Afatinib is an irreversible epidermal growth factor receptor (EGFR)‐tyrosine kinase inhibitor (TKI) that is known to be effective against the EGFR T790M variant, which accounts for half of the mechanisms of acquired resistance to reversible EGFR‐TKIs. However, acquired resistance to afatinib was also observed in clinical use. Thus, elucidating and overcoming the mechanisms of resistance are important issues in the treatment of non‐small cell lung cancer. In this study, we established various afatinib‐resistant cell lines and investigated the resistance mechanisms. EGFR T790M mutations were not detected using direct sequencing in established resistant cells. Several afatinib‐resistant cell lines displayed MET amplification, and these cells were sensitive to the combination of afatinib plus crizotinib. As a further investigation, a cell line that acquired resistance to afatinib plus crizotinib, HCC827‐ACR, was established from one of the MET amplified‐cell lines. Several afatinib‐resistant cell lines including HCC827‐ACR displayed epithelial‐to‐mesenchymal transition (EMT) features and epigenetic silencing of miR‐200c, which is a suppresser of EMT. In addition, these cell lines also exhibited overexpression of ALDH1A1 and ABCB1, which are putative stem cell markers, and resistance to docetaxel. In conclusion, we established afatinib‐resistant cells and found that MET amplification, EMT, and stem cell‐like features are observed in cells with acquired resistance to EGFR‐TKIs. This finding may provide clues to overcoming resistance to EGFR‐TKIs.

The degree of microRNA-34b/c methylation in serum-circulating DNA is associated with malignant pleural mesothelioma

OBJECTIVES Malignant pleural mesothelioma (MPM) is an aggressive tumor with a poor prognosis. microRNA-34b/c (miR-34b/c), which plays an important role in the pathogenesis of MPM, is frequently downregulated by DNA methylation in approximately 90% of MPM cases. In this study, we estimated the degree of miR-34b/c methylation in serum-circulating DNA using a digital methylation specific PCR assay (MSP). MATERIALS AND METHODS A real-time MSP assay was performed using the SYBR Green method. The melting temperature (Tm) of each PCR product was examined using a melting curve analysis. For a digital MSP assay, 40 wells were analyzed per sample. A total of 110 serum samples from 48 MPM cases, 21 benign asbestos pleurisy (BAP) cases, and 41 healthy volunteers (HVs) were examined. RESULTS Positive range of Tm value for miR-34b/c methylation was defined as 77.71-78.79 °C which was the mean ± 3 standard deviations of 40 wells of a positive control. The number of miR-34b/c methylated wells was counted per sample according to this criterion. The number of miR-34b/c methylated wells in MPM cases was significantly higher than that in BAP cases (P=0.03) or HVs (P<0.001). Advanced MPM cases tended to have higher number of miR-34b/c methylated wells than early MPM cases. Receiver-operating characteristic (ROC) curve analysis revealed that three number of miR-34b/c methylated wells per sample was the best cut-off of positivity of MPM with a 67% of sensitivity and a 77% specificity for prediction. The area under the ROC curve was 0.77. CONCLUSIONS Our digital MSP assay can quantify miR-34b/c methylation in serum-circulating DNA. The degree of miR-34b/c methylation in serum-circulating DNA is associated with MPM, suggesting that this approach might be useful for the establishment of a new detection system for MPM.

Targeting the miR-200c/LIN28B axis in acquired EGFR-TKI resistance non-small cell lung cancer cells harboring EMT features.

MicroRNA (miR)-200 family members (miR-200s) are frequently silenced in advanced cancer and have been implicated in the process of epithelial-to-mesenchymal transition (EMT). We previously reported that miR-200s were silenced through promoter methylation in acquired EGFR-tyrosine kinase inhibitor (TKI) resistant non-small cell lung cancer (NSCLC) cells harboring EMT features. In this study, we examined the functional role of miR-200s in NSCLC cells and investigated a novel approach to overcoming acquired EGFR-TKI resistance. In the analysis of NSCLC cell lines, each of the miR-200s expression-silenced cell lines showed promoter methylation. Significant correlations between miR-200c silencing and several oncogenic pathway alterations, including EMT-changes and LIN28B overexpression, were observed in the database analysis. In addition, EGFR-wild type cell lines had lower miR-200s expression levels than EGFR-mutant cell lines. The introduction of miR-200c using pre-miR-200c caused LIN28B suppression in cells with acquired EGFR-TKI resistance that harbored EMT features. Interestingly, both the introduction of miR-200c and the knockdown of LIN28B produced an antitumor effect in acquired EGFR-TKI resistance cells, whereas these manipulations were not effective in parental cells. The miR-200c/LIN28B axis plays an important role in cells with acquired resistance to EGFR-TKI that harbor EMT features and might be a useful therapeutic target for overcoming resistance.

A new human lung adenocarcinoma cell line harboring the EML4-ALK fusion gene.

OBJECTIVE The echinoderm microtubule associated protein-like 4 (EML4)-anaplastic lymphoma kinase (ALK) fusion gene was identified in patients with non-small cell lung cancer. To the best of our knowledge, there are only three cell lines harboring the EML4-ALK fusion gene, which have contributed to the development of therapeutic strategies. Therefore, we tried to establish a new lung cancer cell line harboring EML4-ALK. METHODS A 61-year-old Japanese female presented with chest discomfort. She was diagnosed with left lung adenocarcinoma with T4N3M1 Stage IV. Although she was treated with chemotherapy, her disease progressed with massive pleural effusion. Because the EML4-ALK rearrangement was found in a biopsied specimen using fluorescence in situ hybridization, she was treated with crizotinib. She did well for 3 months. RESULTS Tumor cells were obtained from the malignant pleural effusion before treatment with crizotinib. Cells continued to proliferate substantially for several weeks. The cell line was designated ABC-11. The EML4-ALK fusion protein and genes were identified in ABC-11 cells using fluorescence in situ hybridization and immunohistochemistry, respectively. ABC-11 cells were sensitive to crizotinib and next-generation ALK inhibitors (ceritinib and AP26113), as determined by a 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide assay. Phosphorylated ALK protein and its downstream signaling were suppressed by treatment with crizotinib in western blotting. Furthermore, we could transplant ABC-11 cells subcutaneously into BALB/c nu/nu mice. CONCLUSIONS We successfully established a new lung adenocarcinoma cell line harboring the EML4-ALK fusion gene. This cell line could contribute to future research of EML4-ALK-positive lung cancer both in vivo and in vitro.

Hsp90 inhibitor NVP-AUY922 enhances the radiation sensitivity of lung cancer cell lines with Acquired resistance to EGFR-tyrosine kinase inhibitors

Acquired resistance to epidermal growth factor receptor (EGFR)-tyrosine kinase inhibitors (TKIs) is a critical issue that needs to be overcome in the treatment of patients with non-small cell lung cancer (NSCLC) harboring EGFR activating mutations. EGFR and AKT are client proteins of the 90-kDa heat shock protein (Hsp90). Therefore, it was hypothesized that the use of Hsp90 inhibitors might allow the resistance to EGFR-TKIs to be overcome. Furthermore, Hsp90 inhibitors are known to function as radiosensitizers in various types of cancer. In the present study, we evaluated the radiosensitizing effect of the novel Hsp90 inhibitor, NVP-AUY922 (AUY), on NSCLC cell lines harboring EGFR activating mutations and showing acquired resistance to EGFR-TKIs via any of several mechanisms. We used HCC827 and PC-9, which are NSCLC cell lines harboring EGFR exon 19 deletions, and gefitinib-resistant sublines derived from the same cell lines with T790M mutation, MET amplification or stem-cell like properties. AUY was more effective against the gefitinib-resistant sublines with T790M mutation and MET amplification than against the parental cell lines, although the subline with stem cell-like properties showed more than a 10-fold higher resistance to AUY than the parental cell line. AUY exerted a significant radiosensitizing effect on the parental cell line and the MET-amplified subline through inducing G2/M arrest and inhibition of non-homologous end joining (NHEJ). In contrast, the radiosensitizing effect of AUY was limited on the subline with stem cell-like properties, in which it did not induce G2/M arrest or inhibition of NHEJ. In conclusion, combined inhibition of Hsp90 plus radiation was effective, and therefore a promising treatment alternative for overcoming major EGFR-TKI resistance, such as that induced by T790M mutation or MET amplification. However, other approaches are required to overcome minor resistance to EGFR-TKIs, such as that observed in cells with stem cell-like properties.

Presence of the minor EGFR T790M mutation is associated with drug-sensitive EGFR mutations in lung adenocarcinoma patients

The T790M mutation in the epidermal growth factor receptor (EGFR) gene is known to be associated with the acquired resistance of lung adenocarcinoma patients to EGFR-tyrosine kinase inhibitors (EGFR-TKIs). The minor T790M mutant allele is occasionally detected in EGFR-TKI-naive tumor samples, yet findings concerning the clinical impact of the minor T790M mutation vary among previous studies. In the present study, we assessed the clinical impact of the minor T790M mutation using a novel, highly sensitive assay combining high-resolution melting (HRM), mutant-enriched PCR and co-amplification at a lower denaturation temperature (COLD)-PCR. We determined the T790M mutational status in 146 surgically resected lung adenocarcinomas without a history of EGFR-TKI treatment using mutant-enriched COLD-HRM (MEC-HRM) and standard HRM assays. The sensitivities of the MEC-HRM and standard HRM assays for the detection of T790M-mutant alleles among wild-type alleles were 0.01 and 10%, respectively. Although the T790M mutation was not detected using a standard HRM assay, we identified 19 (13%) T790M mutations using the MEC-HRM assay and defined these 19 mutations as minor T790M mutations. The proportion of T790M alleles was <0.1% in 17 (84%) of the 19 samples. Multivariate analyses revealed that a minor T790M mutation was significantly associated with the presence of EGFR exon 19 deletions or the L858R mutation (both of which are drug-sensitive EGFR mutations) (P=0.04). In conclusion, the minor EGFR T790M mutations were present in 13% of EGFR-TKI-naive surgically resected lung adenocarcinomas and were associated with drug-sensitive EGFR mutations.

Interaction of cytokeratin 19 head domain and HER2 in the cytoplasm leads to activation of HER2-Erk pathway

HER2 is a receptor tyrosine kinase and its upregulation via activating mutations or amplification has been identified in some malignant tumors, including lung cancers. Because HER2 can be a therapeutic target in HER2-driven malignancies, it is important to understand the molecular mechanisms of HER2 activation. In the current study, we identified that cytokeratin 19 (KRT19) binds to HER2 at the inside face of plasma membrane. HER2 and KRT19, which were concurrently introduced to a human embryonic kidney 293 T cells, revealed an association with each other and resulted in phosphorylation of HER2 with the subsequent activation of a downstream Erk-associated pathway. A binding assay revealed that both the NH2-terminal head domain of KRT19 and the COOH-terminal domain of HER2 were essential for their binding. To investigate the impact of the interaction between HER2 and KRT19 in lung cancer, we examined their expressions and localizations in lung cancers. We found that KRT19 was highly expressed in HER2-positive lung cancer cells, and KRT19 and HER2 were co-localized at the cell membrane. In conclusion, we found that KRT19 intracellularly binds to HER2, playing a critical role in HER2 activation.