Autophagy Induced By Valproic Acid In Prostate Cancer Cells

BackgroundProstate cancer is the most common malignancy among men in the USA, and the second most common cause of cancer death. Increasing effort has been directed at studying the role of histone deacetylase (HDAC) inhibitors in treating prostate cancer and valproic acid(VPA) appears to have many features of HDAC inhibition, making it an attractive target for study in prostate cancer patients. Multiple clinical trials indicate that VPA has antineoplastic activity. Recent studies revealed that the antineoplastic activity induced by VPA varies by cancer cell line. Our results confirm prior findings that chronic administration of VPA, which is known to be a class Ⅰ and Ⅱ selective HDAC inhibitor, results in profound decreases in proliferation in vitro and in vivo. In this study, we investigate the impact of VPA on the process of autophagy in certain prostate cancer cell lines and assess its essential role in altering Akt/mTOR signaling and regulating SPARCL family protein to affect cancer cells proliferation, migration and invasion process. Our studies demonstrate a novel mechanism by which VPA appears to exert is antineoplastic effect on prostate cancer cells and suggests potential new approaches to the clinical use of VPA in the treatment of prostate cancer. ObjectiveTo observe the autophagy of prostate cancer cells induced by VPA and research the further molecular mechanism. To locate target suppression-relevant gene and demonstrate metastasis suppression regulation. MethodsPC3, DU145and LNCaP prostate cancer cells were cultured with various doses of VPA (0,1.2,2.5and5.0mmol/L). Cells were examined for their inhibition rate, cell cycle arrest, autophagy markers LC3-Ⅱ and Beclin-1, by cell proliferation assay, transmission electron microscopy, fluorescent microscopy and Western blot. The human gene SPARCL1was subcloned into pBMN-1-GFP to obtain a pBMN-SPARCLl-I-GFP plasmid. DNA sequencing was done to verify the sequence of the constructed plasmid. Migration and invasion is detected by transwell assay. Activation of Akt/mTOR signal was also assessed by Western blot. ResultVPA induces autophagosomes, and has an effect on cell proliferation, and cell cycle regulation. The activation of these anti-proliferative pathways may be contingent on autophagy, as confirmed by detection of increased LC3-Ⅱ and Beclin-1in VPA-treated samples when compared with untreated controls. The activity of Akt/mTOR pathway is also suppressed after VPA treatment. Both phosphorylated forms of Akt and mTOR are significantly reduced by VPA treatment. SPARCL1protein also show significant increase after treated by VPA and suppress prostate cancer cell metastasis. ConclusionValproic acid induces autophagy and suppresses metastasis. This process may be related to the development of programmed cell death in the cancer cells and appears to involve supression of PI3K/Akt/mTOR pathway and secretion of SPARCL1protein in our human prostate cancer cell model.