TY - JOUR
T1 - Caspase-8 dependent histone acetylation by a novel proteasome inhibitor, NPI-0052
T2 - A mechanism for synergy in leukemia cells
AU - Miller, Claudia P.
AU - Rudra, Sharmistha
AU - Keating, Michael J.
AU - Wierda, William G.
AU - Palladino, Michael
AU - Chandra, Joya
PY - 2009
Y1 - 2009
N2 - Combination studies of histone deacetylase inhibitors (HDACi) and proteasome inhibitors are providing preclinical framework to build better strategies against hematologic malignancies. Our previous work found that a novel proteasome inhibitor, NPI-0052, and HDACi synergistically induce apoptosis in leukemia cells in a caspase-8- and oxidant-dependent manner. Here we extend those observations to primary leukemia cells and identify novel mechanisms of synergy. Because the proximal targets of NPI-0052 and HDACi are inhibition of proteasome activity and histone acetylation, we initially examined those biochemical events. Increased acetylation of histone-H3 was detected in Jurkat and CLL primary cells treated with NPI-0052, alone or in combination with various HDACi (MS/SNDX-275 or vorinostat). Hyperacetylation by NPI-0052 occurred to a lesser extent in caspase-8-deficient cells and in cells treated with an antioxidant. These results indicate that NPI-0052 is eliciting caspase-8 and oxidative stress-dependent epigenetic alterations. In addition, real-time PCR revealed that MS/SNDX-275 repressed expression of the proteasomal β5, β2, and β1 subunits, consequently inhibiting respective enzymatic activities. Overall, our results suggest that crosstalk by NPI-0052 and HDACi are contributing, along with caspase-8 activation and oxidative stress, to their synergistic cytotoxic effects in leukemia cells, reinforcing the potential clinical utility of combining these 2 agents.
AB - Combination studies of histone deacetylase inhibitors (HDACi) and proteasome inhibitors are providing preclinical framework to build better strategies against hematologic malignancies. Our previous work found that a novel proteasome inhibitor, NPI-0052, and HDACi synergistically induce apoptosis in leukemia cells in a caspase-8- and oxidant-dependent manner. Here we extend those observations to primary leukemia cells and identify novel mechanisms of synergy. Because the proximal targets of NPI-0052 and HDACi are inhibition of proteasome activity and histone acetylation, we initially examined those biochemical events. Increased acetylation of histone-H3 was detected in Jurkat and CLL primary cells treated with NPI-0052, alone or in combination with various HDACi (MS/SNDX-275 or vorinostat). Hyperacetylation by NPI-0052 occurred to a lesser extent in caspase-8-deficient cells and in cells treated with an antioxidant. These results indicate that NPI-0052 is eliciting caspase-8 and oxidative stress-dependent epigenetic alterations. In addition, real-time PCR revealed that MS/SNDX-275 repressed expression of the proteasomal β5, β2, and β1 subunits, consequently inhibiting respective enzymatic activities. Overall, our results suggest that crosstalk by NPI-0052 and HDACi are contributing, along with caspase-8 activation and oxidative stress, to their synergistic cytotoxic effects in leukemia cells, reinforcing the potential clinical utility of combining these 2 agents.
UR - http://www.scopus.com/inward/record.url?scp=66149121016&partnerID=8YFLogxK
UR - http://www.scopus.com/inward/citedby.url?scp=66149121016&partnerID=8YFLogxK
U2 - 10.1182/blood-2008-08-174797
DO - 10.1182/blood-2008-08-174797
M3 - Article
C2 - 19182209
AN - SCOPUS:66149121016
SN - 1520-4391
VL - 113
SP - 4289
EP - 4299
JO - Unknown Journal
JF - Unknown Journal
IS - 18
ER -