Valproic Acid Enhanced Apoptosis by Promoting Autophagy Via Akt/mTOR Signaling in Glioma

Abstract

Glioma is the most common malignant tumor in the central nervous system with a poor median survival. Valproic acid (VPA), a widely used antiepileptic drug, has been found to have antitumor effects on gliomas, but its role still has not been determined. In this study, we investigated VPA-induced apoptotic and autophagic effects on human U251 and SNB19 cells by cell counting kit-8 assay, flow cytometry, terminal deoxynucleotidyl transferase-mediated nick end labeling staining, western blots, and immunofluorescence assay in vitro, and then we further explored the role of autophagy in apoptosis by using the selective antagonist MHY1485. The data showed that VPA inhibited U251 and SNB19 glioma cells viability in a dose-dependent and time-dependent manner and induced apoptosis through the mitochondria-dependent pathway in vitro. In addition, VPA activated the Akt/mTOR pathway by decreasing their protein phosphorylation to promote cellular apoptosis. Surprisingly, the mTOR agonist MHY1485, causing a strong elevation of mTOR activity, partially reduced apoptosis ratio, which supposing that the autophagy of VPA is involved in the regulation of apoptosis. These findings suggest that VPA enhanced apoptosis by promoting autophagy via Akt/mTOR signaling in glioma, which could be further evaluated as a reliable therapy for glioma.

Valproic Acid: A Promising Therapeutic Agent in Glioma Treatment

“…Since LC3-II is closely associated with the membrane of autophagosomes and p62 is a selective autophagy adaptor/receptor, binding ubiquitinated proteins and LC3 for engulfment, the expression of LC3-II and p62 was examined by Western blot analysis (53). Han et al found that p62 expression was downregulated, while LC3-II expression was obviously upregulated in glioma cells treated with VPA (13). Similar promotion of autophagy could also be seen for Beclin-1 (20).…”

“…Further functional investigation illustrated that VPA upregulated expression of cleaved caspase 3 and cleaved caspase 9. Moreover, the expression of Bcl-2 family protein Bax and Bak was increased, whereas Bcl-2, Bcl-xl, and Mcl-1, the anti-apoptotic members, were decreased by VPA treatment (13,17). Additionally, the release of cytochrome c from the mitochondria under VPA treatment has also been increased.…”

“…Moreover, cellular migration and invasion are also the most important features of malignant tumors, mainly involved in cancer metastasis (44). In most glioma cells and glioma stem cells (GSCs), VPA repressed cell viability in a doseand time-dependent manner (2-10 mM for 48, 72, and 96 h) at varying degrees due to tumor heterogeneity (13,17,20). Subsequently, Trypan Blue dye exclusion assay was utilized to detect proliferative rates.…”

“…Autophagy in cancer is often described as a "double-edged sword", which either promotes tumor survival under microenvironmental stress and increases growth and aggressiveness or suppresses tumorigenesis via its quality control function (52). Results of electron microscopy (EM), MDC staining, and GFP-LC3labeling analyses revealed that autophagic vacuoles increased under treatment with VPA (13,20). Since LC3-II is closely associated with the membrane of autophagosomes and p62 is a selective autophagy adaptor/receptor, binding ubiquitinated proteins and LC3 for engulfment, the expression of LC3-II and p62 was examined by Western blot analysis (53).…”

“…Furthermore, VPA sensitized pancreatic cancer cells to NK cell-mediated lysis by upregulating MICA and MICB via PI3K/Akt signaling pathway (12). Currently, various studies have ascertained that application of VPA is effectively involved in glioma treatment (13)(14)(15). In this review, we generalize the latest advances of VPA in treating glioma and its underlying mechanisms (Figures 1-3 and Tables 1, 2) and clinical implications (Table 3), providing a clearer profile for clinical application of VPA as a therapeutic agent for glioma.…”