Activity Of Cullin-RING Ligases Research Articles

SMC5/6 Promotes Replication Fork Stability via Negative Regulation of the COP9 Signalosome.

It is widely accepted that DNA replication fork stalling is a common occurrence during cell proliferation, but there are robust mechanisms to alleviate this and ensure DNA replication is completed prior to chromosome segregation. The SMC5/6 complex has consistently been implicated in the maintenance of replication fork integrity. However, the essential role of the SMC5/6 complex during DNA replication in mammalian cells has not been elucidated. In this study, we investigate the molecular consequences of SMC5/6 loss at the replication fork in mouse embryonic stem cells (mESCs), employing the auxin-inducible degron (AID) system to deplete SMC5 acutely and reversibly in the defined cellular contexts of replication fork stall and restart. In SMC5-depleted cells, we identify a defect in the restart of stalled replication forks, underpinned by excess MRE11-mediated fork resection and a perturbed localization of fork protection factors to the stalled fork. Previously, we demonstrated a physical and functional interaction of SMC5/6 with the COP9 signalosome (CSN), a cullin deneddylase that enzymatically regulates cullin ring ligase (CRL) activity. Employing a combination of DNA fiber techniques, the AID system, small-molecule inhibition assays, and immunofluorescence microscopy analyses, we show that SMC5/6 promotes the localization of fork protection factors to stalled replication forks by negatively modulating the COP9 signalosome (CSN). We propose that the SMC5/6-mediated modulation of the CSN ensures that CRL activity and their roles in DNA replication fork stabilization are maintained to allow for efficient replication fork restart when a replication fork stall is alleviated.

A Phase II Trial of Pevonedistat and Docetaxel in Patients With Previously Treated Advanced Non–Small-Cell Lung Cancer

BackgroundPostimmunotherapy (IO) treatment options for stage IV non–small-cell lung cancer (NSCLC) remain limited. Docetaxel alone or in combination with ramucirumab remains a standard of care, but response rates and survival benefit are suboptimal. Cullin-RING ligases (CRL) catalyze degradation of tumor suppressor proteins and are overactivated in NSCLC. Neddylation, which is catalyzed by the NEDD8 activating enzyme (NAE), is required for the activation of CRLs. Pevonedistat, a first-in-class small molecule NAE inhibitor, exerted antitumor activity when combined with docetaxel in preclinical studies. MethodsWe conducted a phase II, single-arm, investigator-initiated study evaluating the efficacy of pevonedistat plus docetaxel in patients with relapsed/refractory stage IV NSCLC. Patients received docetaxel 75 mg/m2 on day 1 and pevonedistat 25 mg/m2 on days 1, 3 and 5 of a 21-day cycle. The primary endpoint was objective response rate (ORR). ResultsFrom March 5, 2018 to January 26, 2021, we enrolled 31 patients. The ORR was 22% (1 CR, 5 PR), median PFS was 4.1 months, and median OS was 13.2 months. The incidence of Grade ≥3 adverse events (AE) was 53% in patients (n = 30) who received at least 1 dose of both drugs, with the most frequent being neutropenia and AST/ALT elevation. One patient was taken off study for a Grade 4 transaminase elevation. There were no Grade 5 toxicities. ConclusionOur data suggest that the combination of docetaxel and pevonedistat is safe and exerts activity in patients with relapsed NSCLC. These encouraging results suggest that the neddylation pathway is an antitumor pathway that should be further studied.

FBXL4 ubiquitin ligase deficiency promotes mitophagy by elevating NIX levels.

Selective autophagy of mitochondria, mitophagy, is linked to mitochondrial quality control and as such is critical to a healthy organism. We have used a CRISPR/Cas9 approach to screen human E3 ubiquitin ligases for influence on mitophagy under both basal cell culture conditions and upon acute mitochondrial depolarization. We identify two cullin-RING ligase substrate receptors, VHL and FBXL4, as the most profound negative regulators of basal mitophagy. We show that these converge, albeit via different mechanisms, on control of the mitophagy adaptors BNIP3 and BNIP3L/NIX. FBXL4 restricts NIX and BNIP3 levels via direct interaction and protein destabilization, while VHL acts through suppression of HIF1α-mediated transcription of BNIP3 and NIX. Depletion of NIX but not BNIP3 is sufficient to restore mitophagy levels. Our study contributes to an understanding of the aetiology of early-onset mitochondrial encephalomyopathy that is supported by analysis of a disease-associated mutation. We further show that the compound MLN4924, which globally interferes with cullin-RING ligase activity, is a strong inducer of mitophagy, thus providing a research tool in this context and a candidate therapeutic agent for conditions linked to mitochondrial dysfunction.

Regulation of NKCC2 ubiquitination by Neddylation of Cullin‐Ring Ligases in Thick Ascending Limb

Hypertension and Vascular Research Division, Department of Internal Medicine, Henry Ford Hospital, Detroit, Michigan. Wayne State University, Physiology department, Detroit, Michigan.The Na/K/2Cl cotransporter (NKCC2) reabsorbs ~30% of the filtered NaCl by the glomeruli. Nitric Oxide and atrial natriuretic peptide decrease NaCl reabsorption in thick ascending limbs (TALs) by increasing the second messenger cyclic guanosine monophosphate (cGMP). cGMP decreases surface NKCC2 levels by increasing NKCC2 ubiquitination and proteasomal degradation. The Cullin‐RING Ligases (CRLs) are the largest family of E3 ubiquitin ligases, responsible for ~20% of protein ubiquitination in mammals. Since the CRLs requires neddylation for its activation, we hypothesized that neddylation of CRLs is required for the cGMP‐dependent increase on NKCC2 ubiquitination in TALs. To test our hypothesis, we pulled down ubiquitinated proteins and biotinylated surface proteins from Sprague‐Dawley (SD) rats and blotted for NKCC2. First, we look at the expression of members of the cullin family and found expression of cullin‐1, ‐2, ‐3, ‐4 and ‐5 in TALs from SD rats. Since activity of CRLs is dynamically regulated by neddylation, we blocked cullin neddylation using (MLN4924, 1 µM) and studied whether cGMP increases NKCC2 ubiquitination. To measure ubiquitination of NKCC2, TALs suspensions were treated with proteasomal inhibitor (MG132, 20 µM). TALs was divided in 4 aliquots and incubated at 37°C with vehicle or MLN4924 for 10 minutes and treated with vehicle or db‐cGMP 500 µM at 37°C for an extra 50 minutes. We found that blockade of cullin neddylation, inhibits the cGMP‐dependent increase in ubiquitinated NKCC2 (baseline: 100%; db‐cGMP 500 µM: 162.5 ± 10.3%; MLN4924: 75.1 ± 20.2%; MLN4924 + db‐cGMP 500 µM: 96.8 ± 19.6 %, p<0.05). As expected, neddylation of cullins was blunted in MLN4924 treated samples (baseline: 100%; db‐cGMP: 120.3 ± 24.4%; MLN4924: 11.0 ± 3.5%; MLN4924 + db‐cGMP: 11.4 ± 5.8 %, p<0.05). These data indicate that neddylation of the CRLs mediates the cGMP‐dependent increase in NKCC2 neddylation. NKCC2 activity is directly related to surface NKCC2 expression. Therefore, we study whether blockade of cullin neddylation prevents the cGMP‐dependent decrease in surface NKCC2 expression. TALs suspensions were divided in 4 aliquots. TALs were incubated at 37°C with vehicle or MLN4924 for 10 minutes and then treated with vehicle or db‐cGMP 500 µM at 37°C for an extra 20 minutes. We found that blockade of cullin neddylation, inhibits the cGMP‐dependent decrease in surface NKCC2 expression. (baseline: 100%; db‐cGMP: 81.0 ± 3.4%; MLN4924: 96.4 ± 2.2%; MLN4924 + db‐cGMP: 99.8 ± 9.3 %, p<0.04). These data indicate that cullin neddylation is required for the cGMP‐dependent decrease in surface NKCC2 expression. To our knowledge, this is the first evidence pointing to the E3 ubiquitin ligase complex involved in the ubiquitination of NKCC2 in native TALs. Identifying the E3 ubiquitin ligases that regulates NKCC2 activity may provide new targets for the development of specific loops diuretics.

NEDD8 Deamidation Inhibits Cullin RING Ligase Dynamics.

Cullin-RING ligases (CRLs) are a significant subset of Ubiquitin E3 ligases that regulate multiple cellular substrates involved in innate immunity, cytoskeleton modeling, and cell cycle. The glutamine deamidase Cycle inhibitory factor (Cif) from enteric bacteria inactivates CRLs to modulate these processes in the host cell. The covalent attachment of a Ubiquitin-like protein NEDD8 catalytically activates CRLs by driving conformational changes in the Cullin C-terminal domain (CTD). NEDDylation results in a shift from a compact to an open CTD conformation through non-covalent interactions between NEDD8 and the WHB subdomain of CTD, eliminating the latter’s inhibitory interactions with the RING E3 ligase-Rbx1/2. It is unknown whether the non-covalent interactions are sufficient to stabilize Cullin CTD’s catalytic conformation. We studied the dynamics of Cullin-CTD in the presence and absence of NEDD8 using atomistic molecular dynamics (MD) simulations. We uncovered that NEDD8 engages in non-covalent interactions with 4HB/αβ subdomains in Cullin-CTD to promote open conformations. Cif deamidates glutamine 40 in NEDD8 to inhibit the conformational change in CRLs by an unknown mechanism. We investigated the effect of glutamine deamidation on NEDD8 and its interaction with the WHB subdomain post-NEDDylation using MD simulations and NMR spectroscopy. Our results suggest that deamidation creates a new intramolecular salt bridge in NEDD8 to destabilize the NEDD8/WHB complex and reduce CRL activity.

Phase 1 study of pevonedistat (MLN4924) a NEDD8 activating enzyme inhibitor, in combination with temozolomide (TMZ) and irinotecan (IRN) in pediatric patients with recurrent or refractory solid tumors (ADVL1615).

10019 Background: Pevonedistat (PEV), a first in class inhibitor of NEDD8 activating enzyme (NAE), prevents the activation of Cullin-RING ligases (CRL) necessary for proteasome mediated degradation of key regulatory proteins important in cell survival. In adults with solid tumors, the maximum tolerated dose (MTD) in combination with chemotherapy is 20-25 mg/m2. Antitumor activity of PEV has been demonstrated in preclinical models of childhood cancer. In vivo additive activity has been demonstrated for PEV in combination with IRN and alkylating agents. The objectives of this study are to determine the MTD and recommended Phase 2 dose of PEV in combination with IRN and TMZ and describe the toxicities, pharmacokinetic (PK), and pharmacodynamics (PD) properties of this combination. Methods: We conducted a phase 1 trial of PEV in combination with IRN and TMZ in pediatric patients (pts) with recurrent or refractory solid tumors and brain tumors. During cycle 1, PEV was administered intravenously on days 1, 8, 10, and 12, with IRN (IV, 50mg/m2) and TMZ (orally, 100mg/m2), on days 8-12 of a 28 day cycle. In subsequent cycles, PEV was administered on days 1, 3, and 5, with IRN and TMZ on days 1-5 of a 21 day cycle. Dose escalation was determined using the Rolling 6 Design. Results: 30 pts enrolled. All pts were eligible and evaluable for cycle 1 dose limiting toxicity (DLT) assessment. Median (range) age was 13 (1-21) years; 19 (63%) were male. Eleven pts had brain tumors, and 19 pts had solid tumors. Six pts each enrolled on PEV dose levels (DL) 1 (15mg/m2), 2 (20mg/m2), 3 (25mg/m2) and 4 (35mg/m2) as well as an expanded PK cohort at DL4. Cycle 1 grade 3/4 toxicities include lymphopenia (n = 5), leukopenia (n = 4), neutropenia (n = 2), elevated ALT (n = 2), elevated AST (n = 1), diarrhea (n = 1), flu-like symptoms (n = 1). The most frequent non-dose limiting AEs in cycle 1 were anemia (87%), WBC decreased (77%), nausea (57%), diarrhea (53%), ALT increased (50%), AST increased (50%), and vomiting (50%). PK analyses showed the mean area under the curve at the 25 mg/m2 dose level on day 8 (in combination with irinotecan and temozolomide) was 1300 hr•ng/mL, half-life (T ½) was 5-6 hours, time to maximum concentration (Tmax) was 1 hour, and mean clearance was 20 L/hr/m2. There were 3 DLTs, 2 of which were related to protocol therapy (diarrhea and thrombocytopenia), among 12 patients on DL4. Thus the MTD was not exceeded at any dose level. PK at the 25 mg/m2 dose level are comparable to those in adult patients. PK from the 12 patients on DL4 (35mg/m2) as well as responses of all patients are pending. Conclusions: PEV in combination with IRN and TMZ is well tolerated in children with solid or brain tumors. PEV PK was not altered by the addition of irinotecan and temozolomide. Further PK and PD analyses are ongoing to establish the recommended phase 2 dose. Clinical trial information: NCT03323034.

Role of NEDD8 in CUL2‐dependent ubiquitination of substrates with distinct sizes

As the largest family of ubiquitin E3 ligases in eukaryotes, cullin-RING ligases (CRLs) play essential roles in a myriad of biological processes by catalyzing the ubiquitination of key regulatory proteins. Neddylation, the conjugation of NEDD8 to cullins, is one of the most important mechanisms regulating the activity of CRLs. Biochemical studies have demonstrated that neddylation promotes the activity of CUL1-based CRL1s, leading to increased rates of substrate ubiquitination. Structural studies further suggested that neddylation triggered a conformational change that potentially bridged a gap between the donor ubiquitin and the acceptor substrate. These findings led to a hypothesis that the ubiquitination of larger CRL substrates may depend less on neddylation because the substrates could close the gap by themselves. Here, we explored the effect of neddylation on CRL2VHL-dependent ubiquitination of substrates with distinct sizes, through ex vivo degradation and in vitro ubiquitination assays. We first found that treating HeLa or HEK293 cells with pevonedistat, a small molecule drug inhibiting neddylation, reduced the degradation rates of small-sized p27 or the ODD domain of HIF1α, but not the full-length HIF1α. Though results from these initial trials support our hypothesis, we further found that inhibiting neddylation did reduce the degradation rate of the full-length HIF1α in RCC4 cells expressing exogenous VHL, in which CRL2VHL-dependent ubiquitination is the primary mechanism for HIF1α degradation. This result suggests that the degradation of HIF1α we observed in HEK293 cells in the presence of pevonedistat was CRL2VHL-independent. To directly test our hypothesis, we reconstituted CRL2VHL substrate ubiquitination in vitro and found that neddylation promotes the ubiquitination of the full-length HIF1α and the degron peptide of HIF1α to similar extents, demonstrating that neddylation activates CRL2VHL-dependent ubiquitination regardless of the substrate sizes. Our findings are consistent with the recently updated structural model of the mechanism for NEDD8-induced CRL activation, suggesting that neddylation not only brings the acceptor substrate in close proximity to the donor ubiquitin, but also tunes the CRL conformation to ensure efficient ubiquitination of different-sized substrates.

Suramin and NF449 are IP5K inhibitors that disrupt inositol hexakisphosphate–mediated regulation of cullin–RING ligase and sensitize cancer cells to MLN4924/pevonedistat

Inositol hexakisphosphate (IP6) is an abundant metabolite synthesized from inositol 1,3,4,5,6-pentakisphosphate (IP5) by the single IP5 2-kinase (IP5K). Genetic and biochemical studies have shown that IP6 usually functions as a structural cofactor in protein(s) mediating mRNA export, DNA repair, necroptosis, 3D genome organization, HIV infection, and cullin-RING ligase (CRL) deneddylation. However, it remains unknown whether pharmacological perturbation of cellular IP6 levels affects any of these processes. Here, we performed screening for small molecules that regulate human IP5K activity, revealing that the antiparasitic drug and polysulfonic compound suramin efficiently inhibits IP5K in vitro and in vivo The results from docking experiments and biochemical validations suggested that the suramin targets IP5K in a distinct bidentate manner by concurrently binding to the ATP- and IP5-binding pockets, thereby inhibiting both IP5 phosphorylation and ATP hydrolysis. NF449, a suramin analog with additional sulfonate moieties, more potently inhibited IP5K. Both suramin and NF449 disrupted IP6-dependent sequestration of CRL by the deneddylase COP9 signalosome, thereby affecting CRL activity cycle and component dynamics in an IP5K-dependent manner. Finally, nontoxic doses of suramin, NF449, or NF110 exacerbate the loss of cell viability elicited by the neddylation inhibitor and clinical trial drug MLN4924/pevonedistat, suggesting synergistic ef-fects. Suramin and its analogs provide structural templates for designing potent and specific IP5K inhibitors, which could be used in combination therapy along with MLN4924/pevonedistat. IP5K is a potential mechanistic target of suramin, accounting for suramin's therapeutic effects.

Targeting DCN1-UBC12 Protein-Protein Interaction for Regulation of Neddylation Pathway.

Protein neddylation is one type of posttranslational modifications that regulates the activity of the substrate proteins. Neddylation modification is catalyzed by NEDD8-activating enzyme (NAE, E1), NEDD8-conjugating enzyme (E2), and NEDD8 ligase (E3) to attach NEDD8, an ubiquitin-like molecule, to a lysine residue of a substrate protein. The best known neddylation substrates are cullin family members, which are scaffold components of cullin-RING ligases (CRLs), and cullin neddylation is required for activation of CRLs. In mammalian cells, there are one E1, two E2s (UBC12/UBE2M and UBE2F), and over a dozen E3s. MLN4924, the first-in-class small-molecule inhibitor of NAE, blocks the entire neddylation modification to inactivate activity of all CRLs. MLN4924 is currently in the Phase I/II clinical trials for anticancer application.In the last few years, targeting protein-protein interactions of the neddylation complexes has been pursued as a potential strategy to selectively inhibit the activity of individual CRL. Analysis of the co-crystal structures of DCN1, a co-E3 for neddylation, and its binding partners UBC12 (a neddylation E2) suggested that it may be amenable for the design of potent, small-molecule inhibitors. In this chapter, we will review the discovery of small-molecule inhibitors that block the interactions of DCN1 with UBC12 (hereafter called DCN1 inhibitors) from a number of laboratories, including ours, leading to selective inactivation of CRL-1 and/or CRL-3. We will also discuss potential therapeutic applications of these small-molecule inhibitors.

Neddylation-Independent Activities of MLN4924.

MLN4924, also known as pevonedistat, is a highly selective small-molecule inhibitor of NEDD8 (neuronal precursor cell-expressed developmentally downregulated protein 8)-activating enzyme (NAE) to block the entire neddylation modification cascade, leading to inactivation of cullin-RING ligases (CRLs), since activation of CRLs requires cullin neddylation. MLN4924 showed impressive anticancer activity in many preclinical studies and is currently in several Phase I/II clinical trials for anticancer therapy as a single agent or in combination with chemotherapeutic drugs.In addition to well-characterized anti-neddylation activity, recent studies showed that MLN4924 has several neddylation-independent activities. First, MLN4924 triggers EGFR dimerization to activate EGFR and its downstream RAS/MAPK and PI3K/AKT1 signals, leading to enhanced tumor sphere formation, accelerated EGF-mediated wound healing, and inhibited ciliogenesis. Second, MLN4924 induces PKM2 tetramerization to promote glycolysis, thus affecting energy metabolism. Third, MLN4924 inhibits the interaction between ACT1 (NF-κB activator 1) and TRAF6 (tumor necrosis factor receptor-associated factor 6) and attenuates IL-17A-mediated activation of NF-κB to reduce pulmonary inflammation. Fourth, MLN4924 inhibits IRF3 binding to the IFN-β promoter to inhibit IFN-β production. And finally, MLN4924 activates the JNK signaling pathway to reduce c-FLIP levels, thus enhancing TRAIL-induced apoptosis. This chapter will summarize these neddylation-independent activities of MLN4924 and discuss the underlying mechanisms and potential therapeutic applications.

Are Inositol Polyphosphates the Missing Link in Dynamic Cullin RING Ligase Regulation by the COP9 Signalosome?

The E3 ligase activity of Cullin RING Ligases (CRLs) is controlled by cycles of neddylation/deneddylation and intimately regulated by the deneddylase COP9 Signalosome (CSN), one of the proteasome lid-CSN-initiation factor 3 (PCI) domain-containing “Zomes” complex. Besides catalyzing the removal of stimulatory Cullin neddylation, CSN also provides a docking platform for other proteins that might play a role in regulating CRLs, notably protein kinases and deubiquitinases. During the CRL activity cycle, CRL–CSN complexes are dynamically assembled and disassembled. Mechanisms underlying complex dynamics remain incompletely understood. Recently, the inositol polyphosphate metabolites (IP6, IP7) and their metabolic enzymes (IP5K, IP6K) have been discovered to participate in CRL–CSN complex formation as well as stimulus-dependent dissociation. Here we discuss these mechanistic insights in light of recent advances in elucidating structural basis of CRL–CSN complexes.

Abstract 4439: MLN4924, a protein neddylation inhibitor, elicits antitumor effect via suppression of angiogenesis

Abstract In the process of tumorigenesis, angiogenesis provide oxygen and nutrients for tumor progression. Anti-angiogenesis has become a promising target of cancer therapy. Cullin-RING ligases (CRLs) are a cullin scaffold RING-finger domain containing E3 and are involved in the ubiquitination of specific substrates which regulate important biological processes. The holoenzyme E3 activity of CRLs is controlled by NEDD8. A novel NEDD8-activating enzyme inhibitor, MLN4924, is reported to block the neddylation of cullins and elicits antitumor effect. MLN4924 has been reported to be assoiciated with antiangiogenesis. In this study, we aim to investigate the role of anti-angiogensis in the antitumor effect of MLN4924. Our results showed that MLN4924 induces the cell cycle arrest, apoptosis and suppresses the cell viability and migration in human umbilical vein endothelial cells (HUVECs). Moreover, MLN4924 inhibits angiogenesis in Matrigel plug assay in vivo and tube-formation assay in vitro. Anti-angiogesis was involved in the antitumor effect on human urothelial carcinoma cells (T24) and colon cancer cells in vivo xenograft model. MLN4924 suppressed the VEGF-mediated VEGFR2 downstream activation. Note: This abstract was not presented at the meeting. Citation Format: Kuan-Lin Kuo, Shao-Ping Yang, Shih-Ming Liao, Yeong-Shiau Pu, Kuo-How Huang. MLN4924, a protein neddylation inhibitor, elicits antitumor effect via suppression of angiogenesis [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 4439.

CSN5 inhibition triggers inflammatory signaling and Rho/ROCK-dependent loss of endothelial integrity

RhoGTPases regulate cytoskeletal dynamics, migration and cell-cell adhesion in endothelial cells. Besides regulation at the level of guanine nucleotide binding, they also undergo post-translational modifications, for example ubiquitination. RhoGTPases are ubiquitinated by Cullin RING ligases which are in turn regulated by neddylation. Previously we showed that inhibition of Cullin RING ligase activity by the neddylation inhibitor MLN4924 is detrimental for endothelial barrier function, due to accumulation of RhoB and the consequent induction of contractility. Here we analyzed the effect of pharmacological activation of Cullin RING ligases on endothelial barrier integrity in vitro and in vivo. CSN5i-3 induced endothelial barrier disruption and increased macromolecule leakage in vitro and in vivo. Mechanistically, CSN5i-3 strongly induced the expression and activation of RhoB and to lesser extent of RhoA in endothelial cells, which enhanced cell contraction. Elevated expression of RhoGTPases was a consequence of activation of the NF-κB pathway. In line with this notion, CSN5i-3 treatment decreased IκBα expression and increased NF-κB-mediated ICAM-1 expression and consequent adhesion of neutrophils to endothelial cells. This study shows that sustained neddylation of Cullin RING-ligases leads to activation the NF-κB pathway in endothelial cells, elevated expression of RhoGTPases, Rho/ROCK-dependent activation of MLC and disruption of the endothelial barrier.

Phase 1 study of pevonedistat (MLN4924) in combination with temozolomide (TMZ) and irinotecan (IRN) in pediatric patients with recurrent or refractory solid tumors (ADVL1615).

e21521 Background: Pevonedistat, a first in class inhibitor of NEDD8 activating enzyme (NAE), prevents the activation of Cullin-RING ligases (CRL) necessary for proteasome mediated degradation of key regulatory proteins important in cell survival. In adults with solid tumors, the maximum tolerated dose (MTD) in combination with chemotherapy is 20-25 mg/m2. Antitumor activity of pevonedistat has been demonstrated in preclinical models of childhood cancer. In vivo additive activity has been demonstrated for pevonedistat in combination with IRN and alkylating agents. The objectives of this study are to determine the MTD and recommended phase 2 dose of pevonedistat in combination with IRN and TMZ and describe the toxicities, pharmacokinetic (PK), and pharmacodynamics (PD) properties of this combination. Methods: Using a rolling six design, we conducted a phase 1 trial of pevonedistat in combination with IRN and TMZ in pediatric patients (pts) with recurrent or refractory solid tumors and brain tumors. During cycle 1, pevonedistat was administered intravenously on days 1, 8, 10, and 12, with IRN (IV, 50mg/m2) and TMZ (orally, 100mg/m2), on days 8-12 of a 28 day cycle. In subsequent cycles, pevonedistat was administered on days 1, 3, and 5, with IRN and TMZ on days 1-5 of a 21 day cycle. Results: 18 pts enrolled. All pts were eligible and evaluable for cycle 1 dose limiting toxicity (DLT) assessment. Median (range) age was 13 (1-21) years; 11 (61%) were male. Six pts had brain tumors, and 12 pts had solid tumors. Six pts each enrolled on pevonedistat dose levels 1 (15mg/m2), 2 (20mg/m2), and 3 (25mg/m2). There were no DLTs; DLT assessment is pending for 1 pt on dose level 3. Grade 3/4 toxicities included grade 4 lymphocyte count decreased (n = 2), grade 3 white blood cell decreased (n = 2), and 1 pt each with grade 3 anemia, elevated AST, and elevated ALT. The most frequent AEs were anemia (83%), nausea (61%), elevated AST (61%), and diarrhea (61%). Pharmacokinetic analysis is pending. Conclusions: Pevonedistat in combination with IRN and TMZ is well tolerated in pts with solid or brain tumors. PK and PD analyses are ongoing to establish the recommended dose. Clinical trial information: NCT03323034.

Immunomodulatory Effects of Pevonedistat, a NEDD8-Activating Enzyme (NAE) Inhibitor, in Chronic Lymphocytic Leukemia (CLL)

Introduction: T cells from patients with CLL and lymphoma show highly impaired immune synapse formation, cytotoxic function, and adhesion and migration capabilities. Recent advances in immunooncology led to the emergence of therapeutic agents that permit reversal of T-cell exhaustion in cancer. However, rational development of novel combination approaches in immunotherapy requires detailed understanding of how targeted therapies influence T-cell function.We have shown that pevonedistat (TAK-924), an investigational NAE inhibitor, abrogates NFκB activation in CLL cells. Pevonedistat forms a covalent adduct with NEDD8, a ubiquitin-like modifier, thereby disrupting its interaction with NAE. This leads to reduced activity of Cullin-RING ligases (CRLs), a group of ubiquitin ligases that require modification by NEDD8 for their function. Ultimately, a decrease in CRL activity leads to reduced ubiquitination and proteasomal degradation of CRL substrates, extending the half-life of these proteins, including inhibitor of NFκB (IκB). Moreover, NFκB is critical in T-cell function. However, limited data exist on the effects of targeting neddylation on T-cell response. Here, we demonstrate that targeting neddylation in vitro preserves T-cell functionality and may lead to favorable T-cell population shifts in CLL.Methods: Peripheral blood mononuclear cells were isolated from patients with CLL (n=50), and T cells were purified using Dynabeads. Pevonedistat was obtained from Millennium Pharmaceuticals, Inc., a wholly owned subsidiary of Takeda Pharmaceutical Company Limited (Cambridge, MA).Results: In vitro T-cell receptor (TCR; CD3/CD28) stimulation induced T-cell activation and proliferation. Continuous treatment of T cells with pevonedistat led to rapid (2 hour) disruption of cullin neddylation, followed by a significant reduction in activity of NFκB and NFAT as assessed by immunoblotting and immunofluorescence. Despite this reduction, CD4 and CD8 T cells continued to respond to TCR stimulation, with relative abundance of early markers of activation (CD40L, CD69). However, we observed reduced expression of CD25 and PD-1 at 72 hours. Continuous treatment with pevonedistat led to a dose-dependent decrease in IL-2 secretion and reduced proliferation of the CD4 T-cell subset (CFSE, Ki-67) but did not induce apoptosis. Unlike CLL cells, CD4 T cells did not undergo DNA re-replication and G2/M arrest in response to pevonedistat.We further analyzed T-cell subsets following TCR stimulation. Concurrent treatment with pevonedistat led to an increase in IFNγ-secreting CD4 T cells, whereas IL-4 production decreased, suggesting a shift toward the Th1 phenotype. Furthermore, we observed a robust decrease of the iTreg population, accompanied by downregulation of FoxP3 mRNA and protein within the CD4 T-cell subset, indicating that targeting neddylation may help to reverse the immunosuppressive phenotype in CLL.To mimic the in vivo pharmacokinetics of pevonedistat, we performed drug washouts where CLL-derived T cells were exposed to 2-hour pulse treatment with 1 µM pevonedistat prior to TCR stimulation. Under these conditions, cullin neddylation and NFκB activity began to recover by 8 hours, with near complete recovery by 24 hours. Moreover, pevonedistat did not disrupt allogeneic (OCI-LY19 cells) or autologous (CD40L-stimulated CLL cells) T-cell cytotoxicity. Meanwhile, CD8 T cells continued to produce perforin and granzyme B.Conclusions: Our data suggest that pharmacologic targeting of NAE preserves T-cell cytotoxic function and may enhance anti-tumor immunity in CLL. Combined with our earlier reports that targeting NAE kills CLL cells under lymph node-mimicking conditions, these data provide a strong rationale for continued investigation of pevonedistat in CLL and lymphoid malignancies. DisclosuresSpurgeon:Bristol Myers Squibb: Research Funding; Gilead Sciences, Inc.: Consultancy, Research Funding; Oncternal: Research Funding; Acerta: Research Funding; Genentech: Research Funding; Janssen: Research Funding; Pharmacyclics: Consultancy, Research Funding; MEI Pharma: Consultancy. Berger:Takeda Pharmaceuticals International Co.: Employment. Danilov:Gilead Sciences: Consultancy, Research Funding; Astra Zeneca: Consultancy; Verastem: Consultancy, Research Funding; Genentech: Consultancy, Research Funding; Aptose Biosciences: Research Funding; Takeda Oncology: Research Funding; TG Therapeutics: Consultancy; Bayer Oncology: Consultancy, Research Funding.

CRL4AMBRA1 targets Elongin C for ubiquitination and degradation to modulate CRL5 signaling.

Multi-subunit cullin-RING ligases (CRLs) are the largest family of ubiquitin E3 ligases in humans. CRL activity is tightly regulated to prevent unintended substrate degradation or autocatalytic degradation of CRL subunits. Using a proteomics strategy, we discovered that CRL4AMBRA1 (CRL substrate receptor denoted in superscript) targets Elongin C (ELOC), the essential adapter protein of CRL5 complexes, for polyubiquitination and degradation. We showed that the ubiquitin ligase function of CRL4AMBRA1 is required to disrupt the assembly and attenuate the ligase activity of human CRL5SOCS3 and HIV-1 CRL5VIF complexes as AMBRA1 depletion leads to hyperactivation of both CRL5 complexes. Moreover, CRL4AMBRA1 modulates interleukin-6/STAT3 signaling and HIV-1 infectivity that are regulated by CRL5SOCS3 and CRL5VIF, respectively. Thus, by discovering a substrate of CRL4AMBRA1, ELOC, the shared adapter of CRL5 ubiquitin ligases, we uncovered a novel CRL cross-regulation pathway.

Targeting the neddylation pathway in cells as a potential therapeutic approach for diseases.

The ubiquitin-proteasome system (UPS) is an important system that regulates the balance of intracellular proteins, and it is involved in the regulation of multiple vital biological processes. The approval of bortezomib for relapsed and refractory multiple myeloma has proven that agents targeting the UPS have the potential to be effective treatment strategies for diseases. Among of all of the components of the UPS, cullin-RING ligases (CRLs) are the focus of research. CRLs are the largest family of ubiquitin E3 ligases and they play a critical role in substrate binding. CRL activity is modulated by many pathways in which neddylation modification is the essential process for cullin activation. Thus, targeting the neddylation pathway of cullins could indirectly affect CRL activity, thereby interfering with substrate protein ubiquitination. In addition to cullin proteins, there are some other target proteins of neddylation, such as p53, mouse double minute 2, and epidermal growth factor receptor. For target proteins, neddylation modification mainly causes functions changes, not degradation. In addition, the level of neddylation is also closely related to disease development and prognosis. In this review, we summarize the research on some target proteins and active target agents of neddylation pathways, and explore the role of neddylation in disease therapy. We came to the conclusion that conducting research on neddylation may be a potential approach to discover some novel targets and agents that could be effective without serious side effects.

High-Affinity Peptidomimetic Inhibitors of the DCN1-UBC12 Protein-Protein Interaction.

The Cullin-RING ligases (CRLs) regulate the turnover of approximately 20% of the proteins in mammalian cells and are emerging therapeutic targets in human diseases. The activation of CRLs requires the neddylation of their cullin subunit, which is controlled by an activation complex consisting of Cullin-RBX1-UBC12-NEDD8-DCN1. Herein, we describe the design, synthesis, and evaluation of peptidomimetics targeting the DCN1-UBC12 protein-protein interaction. Starting from a 12-residue UBC12 peptide, we have successfully obtained a series of peptidomimetic compounds that bind to DCN1 protein with KD values of <10 nM. Determination of a cocrystal structure of a potent peptidomimetic inhibitor complexed with DCN1 provides the structural basis for their high-affinity interaction. Cellular investigation of one potent DCN1 inhibitor, compound 36 (DI-404), reveals that it effectively and selectively inhibits the neddylation of cullin 3 over other cullin members. Further optimization of DI-404 may yield a new class of therapeutics for the treatment of human diseases in which cullin 3 CRL plays a key role.

Regulator of cullins-1 expression knockdown suppresses the malignant progression of muscle-invasive transitional cell carcinoma by regulating mTOR/DEPTOR pathway.

Background:Regulator of cullins-1 (ROC1) is a key subunit in the cullin–RING ligase (CRL) protein complex. Our previous study indicated that ROC1 was essential for bladder cancer cell survival and that ROC1 knockdown inhibited CRL activity, triggering G2 phase arrest and senescence. However, the role of ROC1 in the malignant progression of bladder cancer remained unknown.Methods:ROC1 expression in cancer cells was knocked down by siRNA silencing. The effects of ROC1 silencing were evaluated by in vitro assays for cell migration and by an in vivo mouse metastasis model. Epithelial–mesenchymal transition (EMT) induction was evaluated by immunofluorescence staining and western blotting of EMT-associated proteins. ROC1 expression in human tumours was further evaluated by immunohistochemical analysis.Results:ROC1 knockdown suppresses bladder cancer cell migration by inhibiting EMT. ROC1 knockdown inhibited EMT by inhibiting mammalian target of rapamycin (mTOR) activity via the accumulation of the mTOR-inhibitory protein DEPTOR, a CRL substrate. DEPTOR knockdown partially rescued ROC1 knockdown-inhibited EMT and the ROC1-induced inhibition of cancer cell migration. Furthermore, in vivo studies using a nude mouse metastasis model confirmed the in vitro data. Finally, tissue microarray analysis of clinical bladder cancer specimens indicated a positive correlation between ROC1 expression and EMT.Conclusions:ROC1 has an important role in the malignant progression of bladder cancer via the mTOR/DEPTOR pathway. ROC1 may serve as a novel therapeutic target for the treatment of muscle-invasive transitional cell carcinoma.

Abstract C177: TAS4464, a novel and highly potent inhibitor of NEDD8 activating enzyme, overcomes insensitivity to BTK, PI3Kδ, and IRAK4 inhibitors in activated B-cell like diffuse large B-cell lymphoma via inactivation of the NF-κB pathway

Abstract BACKGROUND: NEDD8 activating enzyme (NAE) regulates NEDD8 conjugation in neddylation pathway, a part of the ubiquitin-proteasome system, and controls cell cycle progression, DNA replication, and signal transduction via activation of cullin-RING ligases (CRLs) and subsequent degradation of their substrates. Through one such pathway, the constitutively active nuclear factor κB (NF-κB) triggers the progression of some types of hematological cancer. Activated B-cell like diffuse large B-cell lymphoma (ABC-DLBCL) remains the least curable form of DLBCL despite recent therapeutic advances. Because either phosphatidylinositol-3 kinase (PI3K)/AKT signaling or NF-κB signaling constitutively activated by B cell receptor signaling and MYD88 are reported to promote cancer cell growth and survival in ABC-DLBCL, the key kinases in these pathways [PI3Kδ, Bruton's tyrosine kinase (BTK), and Interleukin-1 receptor-associated kinases (IRAK)] are considered to be potential targets for ABC-DLBCL therapy. We previously reported an NAE inhibitor, TAS4464, that could inactivate NF-κB by accumulating phosphorylated IκBα (p-IκBα). Here, we report on the possible application of TAS4464 to treat ABC-DLBCL that is insensitive to kinase inhibitors. MATERIALS AND METHODS: Human ABC-DLBCL cell lines, OCI-LY10, SU-DHL-2, and TMD8 were used to evaluate the biological activity of TAS4464. Intracellular ATP levels were measured to assess in vitro cell growth. The effects of TAS4464 on NEDD8 conjugation and levels of CRLs substrates were evaluated by Western blot analysis. The levels of NF-κB-targeted gene transcripts were assessed by qRT-PCR. The antitumor activities of TAS4464 were evaluated in both subcutaneous and systemic xenograft model of TMD8. RESULTS: TAS4464 led to growth arrest and death in ABC-DLBCL cell lines in the nanomolar range through inhibition of cullin neddylation. Similar effects were also observed in a cell line insensitive to the kinase inhibitors that inhibit divergent activator of NF-κB. qRT-PCR analysis revealed TAS4464 inhibited the NF-κB pathway in all ABC-DLBCL cell lines tested through accumulation of p-IκBα, which directly inhibit NF-κB activity. Intravenous administration of TAS4464 showed strong antitumor activity in a TMD8 xenograft model, with inhibited cullin neddylation and activation of caspases 3 and 8 in the tumors. Futhermore, in a TMD8 systemic model, intravenous administration of TAS4464 prolonged mice survival more than two-fold. CONCLUSION: TAS4464 leads to cell growth through inhibition of NF-κB pathway regardless of the activation signaling pathway of NF-κB pathway. Though NF-kB activation signaling is complicated, the downstream inhibition of NF-κB pathway by TAS4464 indicated the potential for treatment of ABC-DLBCL in which NF-kB was dominant for their survival. In addition, TAS4464 demonstrates marked antitumor activity and survival benefit in a human ABC-DLBCL model. Therefore, TAS4464 may be a valuable addition to current options for chemotherapy in ABC-DLBCL. Citation Format: Hiromi Muraoka, Chihoko Yoshimura, Shingo Tsuji, Akihiro Hashimoto, Takashi Mizutani, Shuichi Ohkubo, Kenichi Matsuo, Teruhiro Utsugi, Yoshikazu Iwasawa. TAS4464, a novel and highly potent inhibitor of NEDD8 activating enzyme, overcomes insensitivity to BTK, PI3Kδ, and IRAK4 inhibitors in activated B-cell like diffuse large B-cell lymphoma via inactivation of the NF-κB pathway. [abstract]. In: Proceedings of the AACR-NCI-EORTC International Conference: Molecular Targets and Cancer Therapeutics; 2015 Nov 5-9; Boston, MA. Philadelphia (PA): AACR; Mol Cancer Ther 2015;14(12 Suppl 2):Abstract nr C177.