Abstract 1675: Enhanced cell proliferation and induced autophagy in PC-3 prostate cancer cells by 2,3,7,8-tetrachlorodibenzo-p-dioxin exposure.

Introduction: Prostate cancer (PC) is the most commonly diagnosed cancer in males in the Western world and the third leading cause of cancer in men. The environmental contaminant 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) shows a wide range of severe adverse effects in animal models, including immunotoxicity, developmental and reproductive toxicity, teratogenicity, and carcinogenicity. The exposure to TCDD early in development may increase susceptibility to PC and the exposure to TCDD in aged rats can cause greater epithelial proliferation, accompanied by morphological alterations manifested as lobe-specific prostatic hyperplasia. The administration of TCDD to a variety of cultured cells may alter their ability to proliferate and die. Autophagy is an evolutionarily conserved cellular pathway playing a critical role in cellular homeostasis. Defects of autophagy are involved in the pathogenesis of different diseases, including cancer. One of the well-known autophagy markers is the microtubule associated light chain protein 3 (LC3). We have previously demonstrated that exposure of Madin-Darby Bovine Kidney cells to TCDD increased cell proliferation and autophagy. The aim of this study is to evaluate the biological effects of TCDD exposure on a highly metastatic prostate cancer cell line (PC-3). Methods: PC3 cells were exposed to different concentrations of TCDD (D1=0.1 pg/ml, D2=1 pg/ml and D3=100 pg/ml) and cell viability was assessed by Trypan Blue exclusion after 24, 48, and 72 hours of exposure. Autophagy was evaluated using the following: (a) detection of acidic vesicular organelles (AVOs) by acridine orange staining; (b) immunoflurescence analysis (IF) of LC3; (c) LC3 gene expression by real-time PCR; and (d) study of autophagic flux by chloroquine (CQ) autophagy inhibitor (10μM). Results: When compared with their relative controls, only D3 exposure at 24, 48, and 72 hours caused the following: (1) statistically significant increase of cell proliferation (CP) (CP 24h =20.3%, CP 48h =54.5% and CP 72h =52.4%); (2) detection of AVOs; (3) LC3 IF positivity; and (4) LC3 over expression (expression ratio 24h =1.4, expression ratio 48h =6.2 and expression ratio 72h =11.4). When PC-3 cells were D3 exposed and treated with CQ at 24, 48, and 72 hours, LC3 expression ratios compared with controls (dioxin treatment) decreased (CQ 24h =-12.8, CQ 48h =-28.1 and CQ 72h =-2.8). Conclusions: While increased incidence of PC in men exposed to TCDD is known, the molecular mechanisms of carcinogenesis of this compound have not been fully investigated. Our preliminary study demonstrated that treatment of PC-3 with TCDD results in enhanced cell proliferation and activation of autophagy, potentiating the transformed phenotype of these cancer cells. Comparison of the normal primary prostate epithelial cells with PC-3 will further clarify the oncogenic mechanisms of TCDD in PC. Citation Format: Giovanna Elvira Granato, Roberto Ciarcia, Filomena Fiorito, Salvatore Florio, Ugo Pagnini, Luisa De Martino, Antonio Giordano, Giuseppe Russo. Enhanced cell proliferation and induced autophagy in PC-3 prostate cancer cells by 2,3,7,8-tetrachlorodibenzo-p-dioxin exposure. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 1675. doi:10.1158/1538-7445.AM2013-1675