Monomethylarsonous Acid Produces Irreversible Events Resulting in Malignant Transformation of a Human Bladder Cell Line Following 12 Weeks of Low-Level Exposure

• Published in: Toxicological sciences Vol. 116; no. 1; pp. 44 - 57
• Main Authors: Wnek, Shawn M., Jensen, Taylor J., Severson, Paul L., Futscher, Bernard W., Gandolfi, A. Jay
• Format: Journal Article
• Language: English
• Published: United States Oxford University Press 01.07.2010
• Subjects: Animals; Arsenic; bladder cancer; Blotting, Western; Carcinogenicity; Cell Line, Tumor; Cell Transformation, Neoplastic; DNA Methylation; Dose-Response Relationship, Drug; epigenetic; Humans; Mice; Mice, SCID; monomethylarsonous acid; Organometallic Compounds - toxicity; Reverse Transcriptase Polymerase Chain Reaction; Urinary Bladder Neoplasms; UROtsa
• ISSN: 1096-6080; 1096-0929
• DOI: 10.1093/toxsci/kfq106

Arsenic is a known human bladder carcinogen; however, the mechanisms underlying arsenical-induced bladder carcinogenesis are not understood. Previous research has demonstrated that exposure of a nontumorigenic human urothelial cell line, UROtsa, to 50nM monomethylarsonous acid (MMAIII) for 52 weeks resulted in malignant transformation. To focus research on the early mechanistic events leading to MMAIII-induced malignancy, the goal of this research was to resolve the critical period in which continuous MMAIII exposure (50nM) induces the irreversible malignant transformation of UROtsa cells. An increased growth rate of UROtsa cells results after 12 weeks of MMAIII exposure. Anchorage-independent growth occurred after 12 weeks with a continued increase in colony formation when 12-week exposed cells were cultured for an additional 12 or 24 weeks without MMAIII exposure. UROtsa cells as early as 12 weeks MMAIII exposure were tumorigenic in severe combined immunodeficiency mice with tumorigenicity increasing when 12-week exposed cells were cultured for an additional 12 or 24 weeks in the absence of MMAIII exposure. To assess potential underlying mechanisms associated with the early changes that occur during MMAIII-induced malignancy, DNA methylation was assessed in known target gene promoter regions. Although DNA methylation remains relatively unchanged after 12 weeks of exposure, aberrant DNA methylation begins to emerge after an additional 12 weeks in culture and continues to increase through 24 weeks in culture without MMAIII exposure, coincident with the progression of a tumorigenic phenotype. Overall, these data demonstrate that 50nM MMAIII is capable of causing irreversible malignant transformation in UROtsa cells after 12 weeks of exposure. Having resolved an earlier timeline in which MMAIII-induced malignant transformation occurs in UROtsa cells will allow for mechanistic studies focused on the critical biological changes taking place within these cells prior to 12 weeks of exposure, providing further evidence about potential mechanisms of MMAIII-induced carcinogenesis.