title: Caspase-8 dependent histone acetylation by a novel proteasome inhibitor, NPI-0052: a mechanism for synergy in leukemia cells.
abstract: 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 beta5, beta2, and beta1 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.
authors.affiliation: Department of Pediatrics Research, University of Texas M D Anderson Cancer Center, Houston, TX, USA.
authors.forename: Claudia P
authors.initials: CP
authors.lastname: Miller
authors.forename: Sharmistha
authors.initials: S
authors.lastname: Rudra
authors.forename: Michael J
authors.initials: MJ
authors.lastname: Keating
authors.forename: William G
authors.initials: WG
authors.lastname: Wierda
authors.forename: Michael
authors.initials: M
authors.lastname: Palladino
authors.forename: Joya
authors.initials: J
authors.lastname: Chandra
mesh_terms: D000107:Acetylation; D000975:Antioxidants / Q000494:pharmacology; D017209:Apoptosis / Q000187:drug effects; D001897:Boronic Acids / Q000494:pharmacology; D000069286:Bortezomib; D053181:Caspase 8 / Q000378:metabolism*; D004357:Drug Synergism; D004359:Drug Therapy, Combination; D056572:Histone Deacetylase Inhibitors; D006655:Histone Deacetylases / Q000378:metabolism; D006801:Humans; D006877:Hydroxamic Acids / Q000494:pharmacology; D015151:Immunoblotting; D047468:Immunoprecipitation; D007783:Lactones / Q000494:pharmacology*; D015451:Leukemia, Lymphocytic, Chronic, B-Cell / Q000188:drug therapy* / Q000378:metabolism / Q000473:pathology; D015470:Leukemia, Myeloid, Acute / Q000188:drug therapy* / Q000378:metabolism / Q000473:pathology; D018384:Oxidative Stress; D011480:Protease Inhibitors / Q000494:pharmacology*; D061988:Proteasome Inhibitors; D011499:Protein Processing, Post-Translational / Q000187:drug effects; D011719:Pyrazines / Q000494:pharmacology; D011758:Pyrroles / Q000494:pharmacology*; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism; D020133:Reverse Transcriptase Polymerase Chain Reaction; D013481:Superoxides / Q000378:metabolism; D014407:Tumor Cells, Cultured; D000077337:Vorinostat
chemical_list: D000975:Antioxidants; D001897:Boronic Acids; D056572:Histone Deacetylase Inhibitors; D006877:Hydroxamic Acids; D007783:Lactones; D011480:Protease Inhibitors; D061988:Proteasome Inhibitors; D011719:Pyrazines; D011758:Pyrroles; D012333:RNA, Messenger; D013481:Superoxides; D000077337:Vorinostat; D000069286:Bortezomib; C475865:marizomib; D053181:Caspase 8; D006655:Histone Deacetylases