title: Downregulation of thymidylate synthase and E2F1 by arsenic trioxide in mesothelioma.
abstract: Malignant pleural mesothelioma is a global health issue. Arsenic trioxide (ATO) has been shown to suppress thymidylate synthase (TYMS) in lung adenocarcinoma and colorectal cancer, and induce apoptosis in acute promyelocytic leukemia. With TYMS as a putative therapeutic target, the effect of ATO in mesothelioma was therefore studied. A panel of 5 mesothelioma cell lines was used to study the effect of ATO on cell viability, protein expression, mRNA expression and TYMS activity by MTT assay, western blot, qPCR and tritium-release assay, respectively. The knockdown of TYMS and E2F1 was performed with a specific siRNA. Phosphatidylserine externalization and mitochondrial membrane depolarization were measured by Annexin V and JC-1 staining respectively. The in vivo effect of ATO was studied using a nude mouse xenograft model. Application of ATO demonstrated anticancer effects in the cell line model with clinically achievable concentrations. Downregulation of TYMS protein (except H226 cells and 1.25 µM ATO in H2052 cells) and mRNA expression (H28 cells), pRB1 (H28 cells) and E2F1 and TYMS activity (except H226 cells) were also evident. E2F1 knockdown decreased cell viability more significantly than TYMS knockdown. In general, thymidine kinase 1, ribonucleotide reductase M1, c-myc and skp2 were downregulated by ATO. p-c-Jun was downregulated in H28 cells while upregulated in 211H cells. Phosphatidylserine externalization, mitochondrial membrane depolarization, downregulation of Bcl-2 and Bcl-xL, and upregulation of Bak and cleaved caspase-3 were observed. In the H226 xenograft model, the relative tumor growth was aborted, and E2F1 was downregulated while cleaved caspase-3 was elevated and localized to the nucleus in the ATO treatment group. ATO has potent antiproliferative and cytotoxic effects in mesothelioma in vitro and in vivo, partially mediated through E2F1 targeting (less effect through TYMS targeting). There is sound scientific evidence to support the clinical application of ATO in treatment of mesothelioma.
authors.affiliation: Division of Respiratory Medicine, Department of Medicine, The University of Hong Kong, Queen Mary Hospital, Hong Kong, SAR, P.R. China.
authors.forename: Sze-Kwan
authors.initials: SK
authors.lastname: Lam
authors.affiliation: Division of Respiratory Medicine, Department of Medicine, The University of Hong Kong, Queen Mary Hospital, Hong Kong, SAR, P.R. China.
authors.forename: Yuan-Yuan
authors.initials: YY
authors.lastname: Li
authors.affiliation: Division of Respiratory Medicine, Department of Medicine, The University of Hong Kong, Queen Mary Hospital, Hong Kong, SAR, P.R. China.
authors.forename: Chun-Yan
authors.initials: CY
authors.lastname: Zheng
authors.affiliation: Division of Respiratory Medicine, Department of Medicine, The University of Hong Kong, Queen Mary Hospital, Hong Kong, SAR, P.R. China.
authors.forename: James Chung-Man
authors.initials: JC
authors.lastname: Ho
mesh_terms: D000818:Animals; D000970:Antineoplastic Agents / Q000494:pharmacology* / Q000627:therapeutic use; D000077237:Arsenic Trioxide; D001152:Arsenicals / Q000494:pharmacology* / Q000627:therapeutic use; D045744:Cell Line, Tumor; D015536:Down-Regulation / Q000187:drug effects; D050687:E2F1 Transcription Factor / Q000235:genetics* / Q000378:metabolism; D005260:Female; D015972:Gene Expression Regulation, Neoplastic / Q000187:drug effects; D006801:Humans; D008175:Lung Neoplasms / Q000188:drug therapy / Q000235:genetics* / Q000473:pathology; D008654:Mesothelioma / Q000188:drug therapy / Q000235:genetics* / Q000473:pathology; D000086002:Mesothelioma, Malignant; D051379:Mice; D008807:Mice, Inbred BALB C; D008819:Mice, Nude; D010087:Oxides / Q000494:pharmacology* / Q000627:therapeutic use; D013940:Thymidylate Synthase / Q000235:genetics* / Q000378:metabolism; D023041:Xenograft Model Antitumor Assays
chemical_list: D000970:Antineoplastic Agents; D001152:Arsenicals; D050687:E2F1 Transcription Factor; D010087:Oxides; D013940:Thymidylate Synthase; D000077237:Arsenic Trioxide