Abstract 614: Increased oxidative DNA damage in human prostate cancer and its relationship to GSTP1 expression

Abstract

Abstract The pi-class glutathione S-transferase (GSTP1) has been described as a ‘caretaker’ gene, as it actively protects the cell from oxidative genome damage mediated by carcinogens and electrophilic compounds. Loss of GSTP1 expression via promoter hypermethylation is one of the most common epigenetic alterations observed in human prostate cancer. Silencing of GSTP1 can increase prostate epithelial cells more vulnerable to both oxidant and electrophile carcinogens and causes genetic aberrations leading to increased risk of tumor progression. Observations suggest that increased reactive oxygen species (ROS) causes DNA damage in cells, as measured by 8-hydroxy-2′-deoxyguanosine (8-OHdG), contribute to increased incidence of prostate cancer. However there are no studies which demonstrate correlation between GSTP1 protein/activity and DNA damage in prostate cancer. We took a panel of 24 human prostate specimens obtained after surgery which comprised of matched primary tumor and adjacent nontumorous (benign) prostate tissues. Oxidative DNA damage, GSTP1 protein expression and its activity, and GSTP1 promoter methylation was assessed. The 8-OHdG levels in DNA of prostate cancer tissues ranged from 0.307 to 0.609ng/μg DNA, whereas the levels in benign tissue range from 0.156 to 0.322ng/μg DNA, respectively. 8-OHdG and GSTP1 promoter methylation levels were higher in adenocarcinoma compared to their benign counterparts, which positively correlated with the loss of GSTP1 activity. The GSTP1 protein activity of prostate cancer tissues ranged from 738.2 to 1754.4ng/mg protein, whereas the levels in benign tissue range from 1728.6 to 2580.4ng/mg protein. The loss of GSTP1 expression in cells might increase their vulnerability to cytotoxicity and reactive oxygen species (ROS)-mediated DNA damage. In further experiments, human prostate carcinoma LNCaP cells, which contains a silenced GSTP1 gene, was genetically modified to constitutively express high levels of GSTP1. Introduction of GSTP1 lowered endogenous ROS levels in LNCaP cells; treatment with H2O2 significantly reduced ROS and 8-OHdG in LNCaP-GSTP1 cells, compared to parental cell line. Furthermore, treatment with green tea polyphenols to LNCaP cells caused re-expression of GSTP1 which protected the cells from H2O2-mediated DNA damage compared to pretreated cells. These results suggest that oxidative stress-induced DNA damage may be an important measure for primary prevention of prostate 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 614. doi:1538-7445.AM2012-614