Synergistic effect of bortezomib and valproic acid treatment on the proliferation and apoptosis of acute myeloid leukemia and myelodysplastic syndrome cells.

The synergistic effect of proteasome inhibitor bortezomib and valproic acid (VPA), a histone deacetylase inhibitor, were investigated in this study. Co-treatment with VPA and bortezomib on acute myeloid leukemia (AML) and myelodysplastic syndrome (MDS) cell lines resulted in marked inhibition of proliferation and induction of apoptosis, including a striking increase in mitochondrial injury, caspase cascade activation, and altered expression of Bcl-2 family proteins. Moreover, combination treatment inhibited cyto-protective signaling pathways, including inactivation of nuclear factor κB (NF-κB), the extracellular signal-related kinase (ERK) and Akt pathways, and activated stress-related signaling pathway, including the c-jun N-terminal kinase (JNK) and p38 mitogen-activated protein kinase (p38) pathways. In addition, this regimen significantly caused G2/M phase arrest, while downregulating the expression of phospho-CDC2 and CyclinD1 as well as increasing p21(cip1). Furthermore, combination treatment efficiently induced apoptosis in primary AML/MDS cells, with little effect on normal cells. In summary, these findings indicate that combination treatment with VPA and bortezomib may be a potent therapy for AML/MDS malignancies.