Pevonedistat, a Small Molecule Inhibitor of NEDD8-Activating Enzyme (NAE), Induces Cell Cycle Deregulation, Anaphase Catastrophe, and Apoptosis in T-Cell Lymphoma Cells

Introduction: Despite the significant progress of targeted therapies in B-cell malignancies, T-cell lymphomas remain an area of unmet medical need. Most patients are diagnosed at an advanced stage and have limited treatment options. Moreover, most patients who relapse following initial chemotherapy ultimately succumb to disease. Recent successes of targeting the proteasome (i.e., bortezomib) and E3 ligases (i.e., lenalidomide) identify the ubiquitin-proteasome system (UPS) as a tractable target in lymphoma. Pevonedistat, an investigational small molecule inhibitor of NEDD8-activating enzyme (NAE), interferes with activation of NEDD8, a ubiquitin-like modifier. This interference ultimately leads to decreased activity of cullin-RING (E3) ligases and accumulation of their substrates, including inhibitor of NFκB (IκB), the replication licensing protein Cdt1, and p27. We previously demonstrated that targeting NAE affected primary neoplastic B cells via several mechanisms: disruption of NFκB activity as well as induction of Cdt1, DNA damage, and cell cycle arrest. Here, we demonstrate that targeting NAE in T-cell lymphoma cells mediates apoptosis via cell cycle deregulation, accompanied by induction of Cdt1 and p27, and induction of anaphase catastrophe.

Methods: Experiments were performed in T-cell lymphoma cell lines (SR, HH, Jurkat, and SUP-T1) as well as circulating primary cells from patients with peripheral T-cell lymphoma and Sezary syndrome. Pevonedistat (TAK-924) was obtained from Millennium Pharmaceuticals, a wholly owned subsidiary of Takeda Pharmaceutical Company Limited (Cambridge, MA). Apoptosis was assessed by Annexin V staining.

Results: SR (PTCL) cells and primary T-cell lymphoma cells were the most sensitive to pevonedistat (IC₅₀of ~250nM at 24 hours); Jurkat and SUP-T1 cells demonstrated low/intermediate sensitivity, whereas HH (CTCL) cells were resistant. Targeting NAE disrupted cullin neddylation in a dose-dependent manner across all tested cell lines and primary neoplastic T cells, followed by accumulation of phospho-IκBα. Upregulation of phospho-IκBα was notable within 2 hours of pevonedistat treatment across both sensitive and resistant cell lines and primary cells. Concomitantly, we observed induction of p27 and Cdt1. Upregulation of Cdt1 was attenuated in HH cells compared with SR, consistent with the low proliferation rate of the former. Treatment of SR cells with pevonedistat led to DNA damage as evidenced by γH2AX and G2/M arrest.

Chromosomal instability is a prominent feature in cancer and poorly studied as a therapeutic target. We have previously shown that cancer cells undergo multipolar anaphase in response to inhibition of cyclin-dependent kinase-2 (CDK2), an interphase CDK, followed by apoptosis and termed this event anaphase catastrophe (Hu et al., 2015; Danilov et al., 2016). As we observed robust accumulation of the endogenous CDK inhibitor p27 in cells treated with pevonedistat, an event presumed to lead to attenuated CDK2 activity, we studied anaphase catastrophe in this setting. We visualized anaphase catastrophe by immunofluorescent staining for nuclear material (DAPI) and γ-tubulin, and scored it in 50 cells per condition. NAE inhibition with pevonedistat induced anaphase catastrophe in SR and Jurkat cells. Upon 24-hour exposure to 250 nM pevonedistat, 9.8±6.0% of SR and 18±4.4% of Jurkat cells demonstrated multipolar anaphases, compared with 1±0.8% and 3.0±2.6% with vehicle control, respectively.

Conclusions: Inhibiting NAE with pevonedistat induces apoptosis of T-cell lymphoma cells. We propose deregulation of Cdt1 and p27, followed by anaphase catastrophe, as a key mechanistic event implicated in pevonedistat-induced apoptosis in neoplastic T cells. Our work provides rationale to further investigate neddylation as a therapeutic target in T-cell lymphoma.