ABCB1 and hepatocellular carcinoma: In vitro, VPA has been shown to inhibit proliferation in acute myeloid leukaemia cells expressing P-glycoprotein (P-gp) and MDR-associated protein 1 (Tang et al, 2004), and to increase sensitivity towards apoptosis in hepatoma cells resistant to epirubicin (Schuchmann et al, 2006).