In vitro activity: Valproic acid acts through a distinct pathway that involves direct inhibition of histone deacetylase (IC(50) for HDAC1 = 0.4 mM). Valproic acid mimics the histone deacetylase inhibitor trichostatin A, causing hyperacetylation of histones in cultured cells. Valproic acid, like trichostatin A, also activates transcription from diverse exogenous and endogenous promoters. Valproic acid and trichostatin A have remarkably similar teratogenic effects in vertebrate embryos, while non-teratogenic analogues of valproic acid do not inhibit histone deacetylase and do not activate transcription. Valproic acid induces proliferation of peroxisomes in the rodent liver. Valproic acid at a concentration of 1 mM induces relief of this repression by Gal4 fusions of N‐CoR, TR or PPARδ in a cell line expressing the ligand‐inding domain of PPARδ fused to the DNA‐inding domain of the glucocorticoid receptor (GR) together with a GR‐controlled reporter gene. Valproic acid induces accumulation of hyperacetylated histone and inhibits HDAC activity. Valproic acid induces a specific type of differentiation characterized by reduced proliferation, morphological alterations, marker gene expression and particularly the accumulation of the AP-2 transcription factor as a potential marker of neuronal or neural crest cell-like differentiation in F9 teratocarcinoma cells. Valproic acid impairs cell proliferation or survival as indicated by decreased incorporation of [3H]thymidine in F9 and P19 teratocarcinoma cells.

Kinase Assay: The activity of caspase-3, -8 and -9 is assessed using the caspase-3, -8 and -9 colorimetric assay kits, respectively. In brief, 1×106 cells in a 60-mm culture dish are incubated with 10 mM Valproic acid for 24 h. The cells are then washed in PBS and suspended in 5 volumes of lysis buffer provided with the kit. Protein concentrations are determined using the Bradford method. Supernatants containing 50 μg total protein are used to determine caspase-3, -8 and -9 activities. The supernatants are added to each well in 96-well microtiter plates with DEVD-pNA, IETD-pNA or LEHD-pNA as caspase-3, -8 and -9 substrates and the plates are incubated at 37°C for 1 h. The optical density of each well is measured at 405 nm using a microplate reader. The activity of caspase-3, -8 and -9 is expressed in arbitrary absorbance units.

Cell Assay: In brief, 5×105 cells are seeded in 96-well microtiter plates for MTT assays. After exposure to the designated doses of Valproic acid for the indicated times, MTT solution [20 mL: 2 mg/mL in phosphate-buffered saline (PBS)] is added to each well of the 96-well plates. The plates are additionally incubated for 3 h at 37°C. Medium is withdrawn from the plates by pipetting and 200 mL DMSO is added to each well to solubilize the formazan crystals. The optical density is measured at 570 nm using a microplate reader.

J Biol Chem. 2001 Sep 28;276(39):36734-41; EMBO J. 2001 Dec 17;20(24):6969-78; Zhang ZH, et al. Valproic acid inhibits tumor angiogenesis in mice transplanted with Kasumi 1 leukemia cells. Mol Med Rep. 2013 Nov 28.