marizomib and Leukemia--Myeloid--Acute

Current relapse rates in acute myeloid leukemia (AML) highlight the need for new therapeutic strategies. Panobinostat, a novel pan-histone deacetylase inhibitor, and marizomib, a second-generation proteasome inhibitor, are emerging as valuable therapeutic options for hematological malignancies. Here we evaluated apoptotic effects of this combinatorial therapy in AML models and report earlier and higher reactive oxygen species induction and caspase-3 activation and greater caspase-8 dependence than with other combinations. In a bortezomib refractory setting, panobinostat induced high levels of DNA fragmentation, and its action was significantly augmented when combined with marizomib. These data support further study of this combination in hematological malignancies.

Topics: Antineoplastic Agents; Apoptosis; Blotting, Western; Boronic Acids; Bortezomib; Caspases; Cell Proliferation; Drug Combinations; Drug Resistance, Neoplasm; Flow Cytometry; Humans; Hydroxamic Acids; Indoles; Lactones; Leukemia, Myeloid, Acute; Panobinostat; Proteasome Inhibitors; Pyrazines; Pyrroles; Tumor Cells, Cultured

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.

Topics: Acetylation; Antioxidants; Apoptosis; Boronic Acids; Bortezomib; Caspase 8; Drug Synergism; Drug Therapy, Combination; Histone Deacetylase Inhibitors; Histone Deacetylases; Humans; Hydroxamic Acids; Immunoblotting; Immunoprecipitation; Lactones; Leukemia, Lymphocytic, Chronic, B-Cell; Leukemia, Myeloid, Acute; Oxidative Stress; Protease Inhibitors; Proteasome Inhibitors; Protein Processing, Post-Translational; Pyrazines; Pyrroles; Reverse Transcriptase Polymerase Chain Reaction; RNA, Messenger; Superoxides; Tumor Cells, Cultured; Vorinostat