Identification of proteasomal catalytic subunit PSMA6 as a therapeutic target for lung cancer

To identify potential therapeutic targets for lung cancer, we performed semi‐genome‐wide shRNA screening combined with the utilization of genome‐wide expression and copy number data. shRNA screening targeting 5043 genes in NCI‐H460 identified 51 genes as candidates. Pathway analysis revealed that the 51 genes were enriched for the five pathways, including ribosome, proteasome, RNA polymerase, pyrimidine metabolism and spliceosome pathways. We focused on the proteasome pathway that involved six candidate genes because its activation has been demonstrated in diverse human malignancies, including lung cancer. Microarray expression and array CGH data showed that PSMA6, a proteasomal subunit of a 20S catalytic core complex, was highly expressed in lung cancer cell lines, with recurrent gene amplifications in some cases. Therefore, we further examined the roles of PSMA6 in lung cancer. Silencing of PSMA6 induced apoptosis or G2/M cell cycle arrest in cancer cell lines but not in an immortalized normal lung cell line. These results suggested that PSMA6 serves as an attractive target with a high therapeutic index for lung cancer.

Can we predict the development of serious adverse events (SAEs) and early treatment termination in elderly non-small cell lung cancer (NSCLC) patients receiving platinum-based chemotherapy?

PURPOSE

Predicting the feasibility of platinum-based chemotherapy remains an important issue in elderly (over 70 years) patients with non-small cell lung cancer (NSCLC). The aim of this study was to identify the risk factors for the early serious adverse events (SAEs) (during cycles 1-2) in elderly receiving platinum-based chemotherapy, and to explore the clinical characteristics of patients who require early treatment termination without progressive disease (PD).

METHODS

One hundred and ninety-eight consecutive elderly NSCLC patients receiving platinum-based chemotherapy were retrospectively reviewed.

RESULTS

The median age was 73 years (range 70-83). 161 (81 %) were males, and 190 (95 %) were PS 0-1. Fifty-one (29 %) and 39 (19 %) patients developed early non-hematological SAEs and hematological SAEs, respectively. Multivariate analysis identified low serum albumin (<3.0 g/dl) as an independent risk factor for non-hematological SAEs, while low creatinine clearance (<45 ml/min) for hematological SAEs. In all, 24 (12 %) patients needed early treatment termination without PD. The major reason for this event was the development of non-hematological SAEs (4.5 %), followed by grade 2 non-hematological adverse events (AEs) (3 %). In multivariate analysis, age over 75 years and low serum albumin were associated with this event. The median overall survival (OS) in patients with this event was only 6.0 months, while the development of early SAE was not associated with poor OS.

CONCLUSION

Baseline serum albumin might be useful for predicting the feasibility of platinum-based chemotherapy, and the risk estimation of early treatment termination without PD might be beneficial for the treatment selection in elderly NSCLC patients.

Factors Affecting the Diagnostic Yield of Transbronchial Biopsy Using Endobronchial Ultrasonography with a Guide Sheath in Peripheral Lung Cancer

Objective Endobronchial ultrasonography with a guide sheath (EBUS-GS) and virtual bronchoscopic navigation (VBN) improves the diagnostic yield in patients with peripheral pulmonary lesions (PPLs). Most previous reports on EBUS-GS-guided transbronchial biopsy (TBB) have included patients with benign and malignant diseases. We aimed to determine the factors that predicted a successful diagnosis by EBUS-GS-guided TBB diagnostic in patients with small peripheral lung cancer, with a focus on the high-resolution computed tomography (HRCT) findings before bronchoscopy. Methods We retrospectively reviewed the medical records of 173 consecutive patients with 175 small (≤30 mm) PPLs who were diagnosed with primary lung cancer between June 2010 and October 2013 at Nagoya University Hospital. All patients underwent EBUS-GS-guided TBB with VBN using a ZioStation computer workstation (Ziosoft, Osaka, Japan). We analyzed the patient characteristics, HRCT findings, diagnostic yield, and the diagnostic factors in small peripheral lung carcinoma. Results The EBUS probe position was within the PPL in 83 of the 175 lesions (47%) and 112 (64.0%) cases were successfully diagnosed by EBUS-GS-guided TBB. A univariate analysis revealed that the following factors were associated with a significantly higher diagnostic yield: CT bronchus sign positivity, a lesion of >20 mm in diameter, a solid nodule, and a probe position that was within the lesion. The following factors were not significant: the lesion location, the number of biopsies, and the lung cancer histology. A multivariate analysis revealed that the following factors significantly affected the diagnostic yield: CT bronchus sign positivity [odds ratio (OR) =2.479]; a probe position that was within the lesion (OR=2.542); and a solid nodule (OR=2.304). Conclusion The significant factors that were significantly associated with a successful diagnosis using EBUS-GS-guided TBB in small peripheral lung carcinoma were as follows: CT bronchus sign positivity, a solid nodule, and a probe position that was within the lesion.

Growth inhibitory effects of miR-221 and miR-222 in non-small cell lung cancer cells

Both pro- and anti-oncogenic roles of miR-221 and miR-222 microRNAs are reported in several types of human cancers. A previous study suggested their oncogenic role in invasiveness in lung cancer, albeit only one cell line (H460) was used. To further evaluate involvement of miR-221 and miR-222 in lung cancer, we investigated the effects of miR-221 and miR-222 overexpression on six lung cancer cell lines, including H460, as well as one immortalized normal human bronchial epithelial cell line, HBEC4. miR-221 and miR-222 induced epithelial-to-mesenchymal transition (EMT)-like changes in a minority of HBEC4 cells but, unexpectedly, both the microRNAs rather suppressed their invasiveness. Consistent with the prior report, miR-221 and miR-222 promoted growth in H460; however, miR-221 suppressed growth in four other cell lines with no effects in one, and miR-222 suppressed growth in three cell lines but promoted growth in two. These are the first results to show tumor-suppressive effects of miR-221 and miR-222 in lung cancer cells, and we focused on clarifying the mechanisms. Cell cycle and apoptosis analyses revealed that growth suppression by miR-221 and miR-222 occurred through intra-S-phase arrest and/or apoptosis. Finally, lung cancer cell lines transfected with miR-221 or miR-222 became more sensitive to the S-phase targeting drugs, possibly due to an increased S-phase population. In conclusion, our data are the first to show tumor-suppressive effects of miR-221 and miR-222 on lung cancer, warranting testing their potential as therapeutics for the disease.

TIMELESS is overexpressed in lung cancer and its expression correlates with poor patient survival

TIMELESS (TIM) is a mammalian homolog of a Drosophila circadian rhythm gene, but its circadian properties in mammals have yet to be determined. TIM appears to be essential for replication protection and genomic stability. Recently, the involvement of TIM in human malignancies has been reported; therefore, we investigated the role of TIM in lung cancer. Microarray expression analysis of lung cancer cell lines showed that TIM expression was elevated 3.7-fold (P < 0.001) in non-small cell lung cancer cell lines (n = 116) compared to normal lung controls (n = 59). In addition, small cell lung cancer cell lines (n = 29) expressed TIM at levels 2.2-fold (P < 0.001) higher than non-small cell lung cancer. Western blot analysis of 22 lung cancer cell lines revealed that all of them expressed TIM protein and that 20 cell lines (91%) expressed TIM protein at higher levels than a normal control line. Remarkably, immunohistochemistry of 30 surgically resected lung cancer specimens showed that all lung cancer specimens but no matched normal lung tissues were positive for TIM expression. Moreover, immunohistochemistry of surgically resected specimens from 88 consecutive patients showed that high TIM protein levels correlated with poor overall survival (P = 0.013). Mutation analysis for TIM in 23 lung cancer cell lines revealed no mutation. TIM knockdown suppressed proliferation and clonogenic growth, and induced apoptosis in H157 and H460 cells. Taken together, our findings suggest that TIM could be useful as a diagnostic and prognostic marker for lung cancer and targeting it would be of high therapeutic value for this disease.

The circadian clock gene BMAL1 is a novel therapeutic target for malignant pleural mesothelioma

Malignant pleural mesothelioma (MPM) is a highly aggressive neoplasm arising from the mesothelial cells lining the parietal pleura and it exhibits poor prognosis. Although there has been significant progress in MPM treatment, development of more efficient therapeutic approaches is needed. BMAL1 is a core component of the circadian clock machinery and its constitutive overexpression in MPM has been reported. Here, we demonstrate that BMAL1 may serve as a molecular target for MPM. The majority of MPM cell lines and a subset of MPM clinical specimens expressed higher levels of BMAL1 compared to a nontumorigenic mesothelial cell line (MeT-5A) and normal parietal pleural specimens, respectively. A serum shock induced a rhythmical BMAL1 expression change in MeT-5A but not in ACC-MESO-1, suggesting that the circadian rhythm pathway is deregulated in MPM cells. BMAL1 knockdown suppressed proliferation and anchorage-dependent and independent clonal growth in two MPM cell lines (ACC-MESO-1 and H290) but not in MeT-5A. Notably, BMAL1 depletion resulted in cell cycle disruption with a substantial increase in apoptotic and polyploidy cell population in association with downregulation of Wee1, cyclin B and p21(WAF1/CIP1) and upregulation of cyclin E expression. BMAL1 knockdown induced mitotic catastrophe as denoted by disruption of cell cycle regulators and induction of drastic morphological changes including micronucleation and multiple nuclei in ACC-MESO-1 cells that expressed the highest level of BMAL1. Taken together, these findings indicate that BMAL1 has a critical role in MPM and could serve as an attractive therapeutic target for MPM.

Abstract 4678: Silencing of TIMELESS induces growth suppression, apoptosis and enhanced cytotoxicity of cisplatin in H157 lung cancer cells

Background: TIMELSS (TIM) is a circadian clock gene in Drosophila, but its role in mammals in circadian clock systems is not well-understood. Mammalian TIM is involved in Chk1 activation and intra-S checkpoint through genotoxic stress (Unsal-Kaçmaz et.al, Molecular and Cellular Biology, 27(8), 3131-3142(2007)). TIM is also associated with doxorubicin-induced G2/M cell cycle arrest and TIM depletion sensitizes HCT116 colon cancer cells to doxorubicin-induced cytotoxicity (Yang et.al, Journal of Biological Chemistry, 285(5), 3030-3034(2010)). Mutations in TIM in breast cancer were reported (Sjöblom et.al, Science, 314(5797), 268-274(2006)). Methods and Findings: The mRNA expression levels of TIM in 17 non-small cell lung cancer (NSCLC) cell lines and 4 small cell lung cancer (SCLC) cell lines were analyzed by reverse transcriptase PCR. HCC44, H460, H157 (NSCLC), H146 and H740 (SCLC) expressed higher levels of TIM than cdk4/hTERT-immortalized normal human bronchial epithelial cell line HBEC4. Sequencing analysis of TIM revealed no mutation in 21 lung cancer cell lines. RNAi-mediated knockdown of TIM in H157 suppressed proliferation in WST-1 assay and clonogenic growth in liquid colony formation assay. Western blot analysis revealed increased level of cleaved caspase-3 after TIM-knockdown, suggesting that apoptosis was involved in growth inhibition. TIM-knockdown induced increased sensitivity to cisplatin in drug sensitivity assay using WST-1 (IC50 were 1.70μM and 0.91μM in TIM-knocked down H157 compared to 4.87μM in control). Conclusions: TIM inhibition causes growth suppression, apoptosis and enhanced cytotoxicity of cisplatin. Our results suggest that TIM inhibition has a potential utility in the treatment of lung cancer.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr 4678. doi:1538-7445.AM2012-4678

Transient but not stable ZEB1 knockdown dramatically inhibits growth of malignant pleural mesothelioma cells

BACKGROUND

The role of ZEB1, a master epithelial-to-mesenchymal transition gene, in malignant pleural mesothelioma (MPM) is unclear.

METHODS

The expression of ZEB1, E-cadherin, vimentin, and epithelial cell adhesion molecule (EpCAM) in 18 MPM cell lines and a normal pleural mesothelial cell line MeT-5A was determined by quantitative real-time polymerase chain reaction and Western blot testing. RNA interference-mediated transient and/or stable knockdown of ZEB1 and EpCAM was performed. Microarray expression analysis was performed with a TORAY-3D gene chip. Growth was evaluated by colorimetric proliferation and colony formation assays. Luciferase reporter assay was performed to access the effects of ZEB1 knockdown on EpCAM promoter activity.

RESULTS

Most MPM cell lines exhibited mesenchymal phenotype and expressed ZEB1. Transient ZEB1 knockdown suppressed growth in all four cell lines studied (ACC-MESO-1, H2052, Y-MESO-8A, Y-MESO-29) while stable ZEB1 knockdown suppressed growth only in Y-MESO-29. Genome-wide gene expression analysis revealed that EpCAM was the most prominently up-regulated gene by both transient and stable ZEB1 knockdown in ACC-MESO-1, with more marked up-regulation in stable knockdown. We hypothesized that EpCAM up-regulation counteracts the stable ZEB1 knockdown-induced growth inhibition in ACC-MESO-1. Transient EpCAM knockdown suppressed growth dramatically in ACC-MESO-1 cells expressing shZEB1 but only modestly in those expressing shGFP, supporting our hypothesis. Luciferase reporter assay showed that ZEB1 knockdown resulted in increased EpCAM promoter activity. EpCAM was also up-regulated in Y-MESO-29 expressing shZEB1, but this EpCAM up-regulation did not counteract ZEB1knockdown-induced growth suppression, suggesting that the counteracting effects of EpCAM may be cellular context dependent.

CONCLUSIONS

RNA interference-mediated ZEB1 knockdown may be a promising therapeutic strategy for MPM, but one has to consider the possibility of diminished growth inhibitory effects of long-term ZEB1 knockdown, possibly as a result of EpCAM up-regulation and/or other gene expression changes resulting from ZEB1 knockdown.

Abstract C37: BMAL1 depletion represses growth of mesothelioma through induction of mitotic catastrophe

Malignant pleural mesothelioma (MPM) is a highly aggressive neoplasm arising from the mesothelial cells lining the pleura. Asbestos exposure is considered the most important carcinogenic factor that has been mentioned in relation to MPM. Although the incidence of MPM continues to increase, it remains resistant to the currently available therapeutic modalities. Thus, identification of more efficient therapeutics based on its molecular abnormalities is highly recommended. Recently, a genome-wide expression analysis showed deregulation of the circadian rhythm pathway in MPM, including overexpression of BMAL1, a central player in the circadian clock machinery. In this study we explored the consequences of targeting BMAL1 in MPM. This was accomplished by genetic knockdown of BMAL1 with small interference RNA (siRNA) and short hairpin lentiviral expression system. The majority of MPM cell lines expressed higher levels of BMAL1 than the nontumorigenic mesothelial cell line (Met-5A). Immunohistochemical analysis revealed that BMAL1 is constitutively expressed in the cytoplasm with granular pattern in a subset of clinical MPM specimens. Long-term depletion of BMAL1 induced senescence and downregulation of IL-8 and BcL-2 in ACC-MESO-1-cells. Notably, RNAi-mediated knockdown of BMAL1 resulted in suppression of cell growth and induction of apoptosis in MPM cell lines with limited consequences in Met5A. Moreover, ACC-MESO-1 cells, which expressed the highest level of BMAL1, underwent drastic morphological changes including micronucleation, multiple nuclei, and increased cellular volume. Consistently, cell cycle profiling revealed substantial increase in apoptotic and polyploidy cells with concomitant decrease in Wee1, cyclin B, p21, and increase in cleaved caspase 3 and cyclin E proteins by Western blot analysis. Taken together, these results suggest that mitotic catastrophe could be the main cause of cells death in ACC-MESO-1 cells after BMAL1 knockdown. BMAL1 plays an important role in MPM and serves as an attractive therapeutic target for MPM with high therapeutic index.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the Second AACR International Conference on Frontiers in Basic Cancer Research; 2011 Sep 14-18; San Francisco, CA. Philadelphia (PA): AACR; Cancer Res 2011;71(18 Suppl):Abstract nr C37.

Pivotal role of epithelial cell adhesion molecule in the survival of lung cancer cells

Epithelial cell adhesion molecule (EpCAM) is overexpressed in a wide variety of human cancers including lung cancer, and its contribution to increased proliferation through upregulation of cell cycle accelerators such as cyclins A and E has been well established in breast and gastric cancers. Nevertheless, very little is known about its role in supporting the survival of cancer cells. In addition, the functional role of EpCAM in the pathogenesis of lung cancer remains to be explored. In this study, we show that RNAi-mediated knockdown of EpCAM suppresses proliferation and clonogenic growth of three EpCAM-expressing lung cancer cell lines (H3255, H358, and HCC827), but does not induce cell cycle arrest in any of these. In addition, EpCAM knockdown inhibits invasion in the highly invasive H358 but not in less invasive H3255 cells in a Transwell assay. Of note, the EpCAM knockdown induces massive apoptosis in the three cell lines as well as in another EpCAM-expressing lung cancer cell line, HCC2279, but to a much lesser extent in a cdk4/hTERT immortalized normal human bronchial epithelial cell line, HBEC4, suggesting that EpCAM could be a therapeutic target for lung cancer. Finally, EpCAM knockdown partially restores contact inhibition in HCC827, in association with p27(Kip1) upregulation. These results indicate that EpCAM could contribute substantially to the pathogenesis of lung cancer, especially cancer cell survival, and suggest that EpCAM targeted therapy for lung cancer may have potential.

Abstract 1657: A pivotal role for epithelial cell adhesion molecule (EpCAM) in survival of lung cancer cells

Introduction: Epithelial cell adhesion molecule (EpCAM) is overexpressed in a wide variety of human cancers, including lung cancer, and its contribution to increased proliferation through up-regulating cell cycle accelerators such as cyclin A/E is well demonstrated in breast and gastric cancers. Nevertheless, very little is known about its role in survival of cancer cells. In addition, functional role of EpCAM in the pathogenesis of lung cancer remains to be explored.

Matrials and methods: 18 human non-small cell lung cancer cell lines and an immortalized normal human bronchial epithelial cell (HBEC4) lines were used. EpCAM expression was measured by quantitative real-time PCR (qRT-PCR) and FACS. RNA interference (RNAi)-mediated gene silencing for EpCAM was done in three non-small cell lung cancer cell and HBEC4 lines. Cell proliferation was measured by WST-1 and clonogenic growth was measured by liquid and soft agar colony formation assays. Apoptosis was evaluated by annexin V/7-AAD staining. FACS with PI staining was done to examine apoptosis and cell cycle. p27kip1 expression was evaluated by western blot analysis. In vitro invasion assay was done by using transwell chambers layered with matrigel and invading cells were stained and counted.

Results: We analyzed the expression of EpCAM in a panel of lung cancer cell and HBEC4 lines and found that most of lung cancer cell lines expressed EpCAM. EpCAM knockdown suppressed proliferation and clonogenic growth of two EpCAM-expressing lung cancer cell lines in anchorage dependent and independent conditions. EpCAM knockdown suppressed invasiveness in a highly invasive line but not in a lowly invasive cell line. In addition, EpCAM knockdown induced massive apoptosis in both cell lines as well as another EpCAM-expressing lung cancer cell line but to a much lesser extent in HBEC4 line. EpCAM knockdown caused lung cancer cells to have increased responsiveness to contact inhibition in part through up-regulating p27kip1 cyclin dependent kinase inhibitor. Conclusion: These results demonstrate that EpCAM substantially contributes to the pathogenesis of lung cancer, especially in its survival, and the development of EpCAM-targeted therapy for lung cancer may have promise.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 102nd Annual Meeting of the American Association for Cancer Research; 2011 Apr 2-6; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2011;71(8 Suppl):Abstract nr 1657. doi:10.1158/1538-7445.AM2011-1657

Identification of N-terminal regions of wheat leaf ferredoxin NADP+ oxidoreductase important for interactions with ferredoxin

Wheat leaves contain two isoproteins of the photosynthetic ferredoxin:NADP(+) reductase (pFNRI and pFNRII). Truncated forms of both enzymes have been detected in vivo, but only pFNRII displays N-terminal length-dependent changes in activity. To investigate the impact of N-terminal truncation on interaction with ferredoxin (Fd), recombinant pFNRII proteins, differing by deletions of up to 25 amino acids, were generated. During purification of the isoproteins found in vivo, the longer forms of pFNRII bound more strongly to a Fd affinity column than did the shorter forms, pFNRII(ISKK) and pFNRII[N-2](KKQD). Further truncation of the N-termini resulted in a pFNRII protein which failed to bind to a Fd column. Similar k(cat) values (104-140 s(-1)) for cytochrome c reduction were measured for all but the most truncated pFNRII[N-5](DEGV), which had a k(cat) of 38 s(-1). Stopped-flow kinetic studies, examining the impact of truncation on electron flow between mutant pFNRII proteins and Fd, showed there was a variation in k(obs) from 76 to 265 s(-1) dependent on the pFNRII partner. To analyze the sites which contribute to Fd binding at the pFNRII N-terminal, three mutants were generated, in which a single or double lysine residue was changed to glutamine within the in vivo N-terminal truncation region. The mutations affected binding of pFNRII to the Fd column. Based on activity measurements, the double lysine residue change resulted in a pFNRII enzyme with decreased Fd affinity. The results highlight the importance of this flexible N-terminal region of the pFNRII protein in binding the Fd partner.

Formation of the iron-sulfur cluster of ferredoxin in isolated chloroplasts

The formation of the iron-sulfur cluster of ferredoxin was examined in vitro by incubating isolated chloroplasts with [(35)S]cysteine. The ferredoxin molecule was radioactively labeled in chloroplasts without synthesis of its polypeptide and comigrated with holoferredoxin during polyacrylamide gel electrophoresis under nondenaturing conditions. When the labeled ferredoxin was denatured by the addition of trichloroacetic acid, radioactive acid-labile sulfide in the cluster was released from the polypeptide as a gas and trapped in a 0.1 M NaOH solution. These results indicate that the sulfur atom derived from cysteine was incorporated into ferredoxin through formation of the iron-sulfur cluster. This process was stimulated by light and inhibited by the electron transport inhibitor, dichlorophenyldimethylurea, and the uncouplers, atebrin and gramicidin, but not by the protein synthesis inhibitor, chloramphenicol. These inhibitory effects were reversed by the addition of ATP to the incubation mixture. Formation of the iron-sulfur cluster of ferredoxin in chloroplasts is thus dependent on ATP.

Knockdown of ZEB1, a master epithelial-to-mesenchymal transition (EMT) gene, suppresses anchorage-independent cell growth of lung cancer cells

We found that among four master epithelial-to-mesenchymal transition (EMT)-inducing genes (ZEB1, SIP1, Snail, and Slug) ZEB1expression was most significantly correlated with the mesenchymal phenotype (high Vimentin and low E-cadherin expression) in non-small cell lung cancer (NSCLC) cell lines and tumors. Furthermore, ZEB1 knockdown with RNA interference in three NSCLC cell lines with high ZEB1 expression suppressed to varying degrees mass culture growth and liquid colony formation but in all cases dramatically suppressed soft agar colony formation. In addition, ZEB1 knockdown induced apoptosis in one of the three lines, indicating that the growth inhibitory effects of ZEB1 knockdown occurs in part through the activation of the apoptosis pathway. These results suggest that inhibiting ZEB1 function may be an attractive target for NSCLC therapeutic development.

Abstract 2302: Knockdown of ZEB1, a master epithelial-to-mesenchymal transition (EMT) inducing gene, suppresses growth of pleural mesothelioma cell lines

Background and Objective: Malignant pleural mesothelioma (MPM) is a highly aggressive disease, usually caused by asbestos exposure. The underlying molecular mechanism contributing to aggressive phenotype of MPM remains to be fully elucidated. Epithelial-to-mesenchymal transition (EMT), an early developmental program, causes a wide variety of human epithelial cancers to have the ability to invade surrounding tissues and metastasize to distant sites. MPM cells usually exhibit mesenchymal characteristics probably because of their mesodermal origin. Such characteristics include fibroblast-like morphology and expression of master EMT-inducing genes. Thus, EMT may contribute to aggressive phenotype of MPM. Among EMT-inducing genes, ZEB1, a repressor of E-cadherin, has emerged as a key player in the progression of several epithelial cancers. To explore the potential of ZEB1 as a therapeutic target for MPM, we examined the effect of ZEB1 knockdown on growth of MPM cell lines. In addition, we evaluated the effect of ZEB1 knockdown on the levels of IL-6, which is known to induce growth of mesothelioma cells.

Materials and Methods: 18 human MPM cell lines and one non-tumorigenic mesothelial cell line were used. Transient and stable knockdown of ZEB1 were done in two MPM cell lines. Quantitative real-time RT-PCR and western blot of ZEB1, E-cadherin, and Vimentin were done. Soluble IL-6 in cellular supernatants was measured by enzyme-linked immunosorbent assay. Cell proliferation was measured by WST-1 and clonogenic growth was measured by liquid and soft agar colony formation assays. FACS with PI staining was done to examine apoptosis and cell cycle. Apoptosis was also evaluated by western blot of cleaved caspase-3.

Results: The majority of MPM cells expressed higher levels of ZEB1 than a non-tumorigenic mesothelial cell. We performed ZEB1 knockdown experiments in two MPM cells, ACC-MESO-1(MESO-1) and H2052, which express high and moderate levels of ZEB1. Transient knockdown of ZEB1 caused MESO-1 but not H2052 cells to reexpress E-cadherin. Transient ZEB1 knockdown suppressed cell proliferation and liquid colony formation in the two lines. Most importantly, the ZEB1 knockdown dramatically suppressed soft agar colony formation in the two lines. We did not see apoptosis or cell cycle arrest in either of the two lines. Stable knockdown of ZEB1 induced morphologic changes suggestive of mesenchymal-to-epithelial transition (MET) in MESO-1 cells but not in H2052 cells. ZEB1 stable knockdown resulted in a decreased IL-6 production in MESO-1 cells, suggesting that growth inhibition by ZEB1 knockdown may in part due to decreased IL-6 production. Conclusion: These results suggest that ZEB1 serves as an attractive therapeutic target for MPM.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 2302.

Abstract 2295: Knockdown of ZEB1, a master EMT gene, suppresses anchorage-independent cell growth of lung cancer cells

Background: Epithelial-to-mesenchymal transition (EMT), an essential process during embryonic development and in wound healing, has been shown to be a key event in tumor migration, invasion and metastasis. EMT program is controlled by several master regulators including Twist, ZEB1, SIP1, Snail, Slug, and Goosecoid which are called master EMT genes1),2). ZEB1 protein binds E-boxes within the promoter region of E-cadherin gene, leading to its transcriptional repression. Also, it directly represses many other genes encoding components of the epithelial junctional complex and cell polarity factors. ZEB1 was shown to promote metastasis in colorectal cancer and breast cancer3), and the association between ZEB1 and tumor progression has been studied in several human cancers.

Purpose: To evaluate the association between ZEB1 expression and mesenchymal phenotype in lung cancer, and to test the effect of ZEB1 knockdown with RNA interference on the growth of lung cancer cells.

Methods: We analyzed the expression of E-cadherin (epithelial marker), Vimentin (mesenchymal marker), and four master EMT genes (Snail, Slug, ZEB1, SIP1) in 19 NSCLC cell lines and 32 NSCLC tumor tissues. Transient knockdown of ZEB1 with RNA interference was done in three NSCLC cell lines with high expression of ZEB1: H157, H1299, and H460. Quantitative real-time RT-PCR and western blot of ZEB1, E-cadherin and Vimentin were done. Cellular proliferation was measured by WST-1 assay and clonogenic growth was measured by liquid (anchorage-dependent) and soft agar (anchorage-independent) colony formation assays. Apoptosis was evaluated by FACS and western blot of cleaved caspase-3.

Results: In cell lines, of four master EMT genes, only ZEB1 expression significantly correlated with both E-cadherin and Vimentin expression. Most EGFR mutant lines showed epithelial phenotype (ratio of Vimentin to E-cadherin (RVE) &lt; 1.0). ZEB1 expression was also inversely correlated with miR-200c and miR-205. In tumor tissues, ZEB1 and Snail expression correlated with the ratio of Vimentin to E-cadherin, and ZEB1 expression highly significantly correlated with Vimentin expression. After ZEB1 knockdown E-cadherin protein was reexpressed in H460 but not in H1299 and H157 cells. ZEB1 knockdown suppressed cell proliferation and liquid colony formation significantly in H1299 and modestly in H157 and H460. Notably, ZEB1 knockdown dramatically suppressed growth of soft agar in the all three cell lines studied. FACS and western blot of cleaved caspase-3 showed apoptosis induction by ZEB1 knockdown in H460, suggesting that growth inhibitory effect of ZEB1 knockdown in lung cancer was caused in part by apoptosis.

Conclusions: ZEB1 has the dominant role in maintaining mesencymal phenotype in NSCLC and removal of ZEB1 in lung cancer cell lines induces inhibition of soft agar growth. These results suggest that ZEB1 could be a therapeutic target for lung cancer.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 2295.