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.