[CAS NO. 99-66-1]  Valproic acid (VPA)

Valproic acid (VPA), like lithium, activates Wnt-dependent gene expression, but unlike lithium, VPA does not inhibit GSK-3β in vivo. VPA can inhibit GSK-3β-mediated phosphorylation of a CREB peptide in vitro. VPA may activate Wnt-dependent gene expression through inhibition of HDAC, which in turn leads to both increased expression of β-catenin and de-repression of Tcf/Lef (as well as activation of other HDAC-regulated genes). In vitro, VPA can stimulate glutamic acid decarboxylase, which is involved in GABA biosynthesis, and inhibit GABA transaminase, succinic semialdehyde dehydrogenase, and α-ketoglutarate dehydrogenase, enzymes involved in GABA degradation. Valproic acid relieves HDAC-dependent transcriptional repression and causes hyperacetylation of histones in cultured cells and in vivo. VPA induces differentiation and/or apoptosis of carcinoma cells, PML-RAR-transformed hematopoietic progenitor cells and leukemic blasts from AML patients. In addition to selectively inhibiting the catalytic activity of class I HDACs, VPA also induces proteasomal degradation of HDAC2.