Valproic acid inhibits glioblastoma multiforme cell growth via paraoxonase 2 expression

// Jen-Ho Tseng 1, 2 , Cheng-Yi Chen 3 , Pei-Chun Chen 3 , Sheng-Huang Hsiao 1, 4 , Chi-Chen Fan 5 , Yu-Chih Liang 6 , Chie-Pein Chen 3, 7 1 Department of Neurosurgery, Taipei City Hospital, Renai Branch, Taipei 106, Taiwan 2 Graduate Institute of Medical Sciences, College of Medicine, Taipei Medical University, Taipei 110, Taiwan 3 Department of Medical Research, MacKay Memorial Hospital, New Taipei City 251, Taiwan 4 College of Science, National Chengchi University, Taipei 116, Taiwan 5 Department of Physiology, MacKay Memorial Hospital, Taipei 104, Taiwan 6 School of Medical Laboratory Science and Biotechnology, College of Medical Science and Technology, Taipei Medical University, Taipei 110, Taiwan 7 Department of Medicine, Taipei Medical University, Taipei 110, Taiwan Correspondence to: Chie-Pein Chen, email: cpchen@mmh.org.tw Keywords: cell growth, glioblastoma multiforme, histone deacetylase, paraoxonase 2, valproic acid Received: September 30, 2015 Accepted: January 10, 2017 Published: January 18, 2017 ABSTRACT We studied the potential mechanisms of valproic acid (VPA) in the treatment of glioblastoma multiforme (GBM). Using the human U87, GBM8401, and DBTRG-05MG GBM-derived cell lines, VPA at concentrations of 5 to 20 mM induced G2/M cell cycle arrest and increased the production of reactive oxygen species (ROS). Stress-related molecules such as paraoxonase 2 (PON2), cyclin B1, cdc2, and Bcl-xL were downregulated, but p27, p21 and Bim were upregulated by VPA treatment. VPA response element on the PON2 promoter was localized at position -400/-1. PON2 protein expression was increased in GBM cells compared with normal brain tissue and there was a negative correlation between the expression of PON2 and Bim. These findings were confirmed by the public Bredel GBM microarray (Gene Expression Omnibus accession: GSE2223) and the Cancer Genome Atlas GBM microarray datasets. Overexpression of PON2 in GBM cells significantly decreased intracellular ROS levels, and PON2 expression was decreased after VPA stimulation compared with controls. Bim expression was significantly induced by VPA in GBM cells with PON2 silencing. These observations were further shown in the subcutaneous GBM8401 cell xenograft of BALB/c nude mice. Our results suggest that VPA reduces PON2 expression in GBM cells, which in turn increases ROS production and induces Bim production that inhibits cancer progression via the PON2–Bim cascade.