Proteasomal Inhibition by Ixazomib Induces CHK1 and MYC-Dependent Cell Death in T-cell and Hodgkin Lymphoma

Abstract

Proteasome-regulated NF-kB has been shown to be important for cell survival in T-cell lymphoma and Hodgkin lymphoma models. Several new small-molecule proteasome inhibitors are under various stages of active preclinical and clinical development. We completed a comprehensive preclinical examination of the efficacy and associated biologic effects of a second-generation proteasome inhibitor, ixazomib, in T-cell lymphoma and Hodgkin lymphoma cells and in vivo SCID mouse models. We demonstrated that ixazomib induced potent cell death in all cell lines at clinically achievable concentrations. In addition, it significantly inhibited tumor growth and improved survival in T-cell lymphoma and Hodgkin lymphoma human lymphoma xenograft models. Through global transcriptome analyses, proteasomal inhibition showed conserved overlap in downregulation of cell cycle, chromatin modification, and DNA repair processes in ixazomib-sensitive lymphoma cells. The predicted activity for tumor suppressors and oncogenes, the impact on "hallmarks of cancer," and the analysis of key significant genes from global transcriptome analysis for ixazomib strongly favored tumor inhibition via downregulation of MYC and CHK1, its target genes. Furthermore, in ixazomib-treated lymphoma cells, we identified that CHK1 was involved in the regulation of MYC expression through chromatin modification involving histone H3 acetylation via chromatin immunoprecipitation. Finally, using pharmacologic and RNA silencing of CHK1 or the associated MYC-related mechanism, we demonstrated synergistic cell death in combination with antiproteasome therapy. Altogether, ixazomib significantly downregulates MYC and induces potent cell death in T-cell lymphoma and Hodgkin lymphoma, and we identified that combinatorial therapy with anti-CHK1 treatment represents a rational and novel therapeutic approach.

A single center phase II study of ixazomib in patients with relapsed or refractory cutaneous or peripheral T‐cell lymphomas

“…This is noteworthy, as proteasome inhibition is synergistic when combined with other agents, including HDAC inhibitors 49 . The extent to which the synergy observed with these agents and proteasome inhibitors may be attributed to the effect of proteasome inhibition on the NF-kB/GATA-3 axis, as our findings may suggest, c-myc, 50 or some other proteasome-dependent mechanism, is unknown, but may warrant scrutiny in future studies.…”

Combinatorial ixazomib and belinostat therapy induces NFE2L2‐dependent apoptosis in Hodgkin and T‐cell lymphoma

“…Aliquots (2 × 10 4 cells/100 μl) of lymphoma cell lines and primary tumour cells were plated in a 96‐well plate, treated with appropriate drug concentrations of ixazomib, belinostat, or ixazomib and belinostat combination for 72 h, followed by assessment of MTT‐based cell viability using Cell Titer Aqueous Non‐Radioactive Cell Proliferation assay (Promega, Madison, WI, USA), as described before (Ravi et al , ). IC 50 and combination indices for these assays were determined using method of Chou and Talalay and Calcusyn (Biosoft, Ferguson, MO, USA).…”

“…We previously reported that the proteasome inhibitor ixazomib has in vitro cytotoxic effects and in vivo efficacy in Jurkat (TCL) and L540 (HL) ‐derived mouse SCID xenografts (Ravi et al , ). Transcriptomic analysis performed in ixazomib‐treated cells predicted that targeting histone acetylation would result in synergistic effect in combination with proteasome inhibition (Mitsiades et al, ).…”

“…Transcriptomic analysis performed in ixazomib‐treated cells predicted that targeting histone acetylation would result in synergistic effect in combination with proteasome inhibition (Mitsiades et al, ). Additionally, there was prominence of genes encoding for ubiquitin proteasome components among Jurkat, L540 and L428 cells treated with ixazomib (Ravi et al , ). This observed effect corresponds to previously published reports of upregulated ubiquitin/proteasome genes in bortezomib‐treated multiple myeloma cell lines (Mitsiades et al , ).…”

Inhibition of CHK1 and WEE1 as a new therapeutic approach in diffuse large B cell lymphomas with MYC deregulation

“…Synthetic lethal approaches have been expanded to target essential signalling pathways downstream of MYC. The hypothesis that CHK1 protein kinase (also known as CHEK1), by allowing the repair of the insults caused by MYC (endogenous DNA damage from replicative stress) may be a crucial target to inhibit in MYC‐driven malignancies has been recently demonstrated (Hoglund et al , ; Ravi et al , ). CHK1 inhibitors are strongly synergistic with WEE1 inhibitors in many experimental models (Carrassa et al , ) and both kinase inhibitors are under early clinical investigation (Daud et al , ; Scagliotti et al , ).…”