Valproic acid (VPA) is an orally active HDAC inhibitor, with IC50 in the range of 0.5 and 2 mM, also inhibits HDAC1 (IC50, 400 µM), and induces proteasomal degradation of HDAC2. Valproic acid activates Notch1 signaling and inhibits proliferation in small cell lung cancer (SCLC) cells. Valproic acid is used in the treatment of epilepsy, bipolar disorder, metabolic disease, HIV infection and prevention of migraine headaches[1][2][3][4][5][6][7].