Initial testing of the investigational NEDD8-activating enzyme inhibitor MLN4924 by the pediatric preclinical testing program

Phase 1 study of NEDD8 activating enzyme inhibitor pevonedistat in combination with chemotherapy in pediatric patients with recurrent or refractory solid tumors (ADVL1615)

PURPOSE

The objective of this study was to determine the recommended Phase 2 dose (RP2D) of pevonedistat, a first in class inhibitor of NEDD8 activating enzyme, in combination with irinotecan (IRN) and temozolomide (TMZ) in children with cancer.

METHODS

This Phase 1 study used a rolling 6 design to evaluate escalating doses of pevonedistat in combination with standard doses of IRN and TMZ in pediatric patients with recurrent/refractory solid or CNS tumors. During cycle 1, pevonedistat was administered intravenously on days 1, 8, 10, and 12, with IRN (IV, 50 mg/m2) and TMZ (orally, 100 mg/m2), on days 8-12 of a 28-day cycle. In subsequent cycles, pevonedistat was administered on days 1, 3, and 5, with IRN/TMZ on days 1-5 of a 21-day cycle.

RESULTS

Thirty patients enrolled; all were eligible and evaluable for toxicity. Six patients each enrolled on pevonedistat dose levels (DL) 1 (15 mg/m2), 2 (20 mg/m2), 3 (25 mg/m2) and 4 (35 mg/m2) as well as an expanded pharmacokinetic (PK) cohort at DL4. The maximum tolerated dose (MTD) was not exceeded. 2/12 (17 %) patients treated at the RP2D (35 mg/m2) experienced a cycle 1 dose limiting toxicity (DLT). IRN is unlikely to affect the pharmacokinetics of pevonedistat. Two patients had a partial response and 6 patients had prolonged stable disease (> 6 cycles).

CONCLUSIONS

Pevonedistat in combination with IRN/TMZ is well tolerated in children with solid or CNS tumors. The RP2D of pevonedistat is 35 mg/m2 on days 1, 3, 5 in combination with IRN/TMZ.

Discovery of small molecule inhibitors of neddylation catalyzing enzymes for anticancer therapy

Protein neddylation, a type of post-translational modifications, involves the transfer of the ubiquitin-like protein NEDD8 to the lysine residues of a target substrate, which is catalyzed by the NEDD8 activating enzyme (E1), NEDD8 conjugating enzyme (E2), and NEDD8 ligase (E3). Cullin family proteins, core components of Cullin-RING E3 ubiquitin ligases (CRLs), are the most well-known physiological substrates of neddylation. CRLs, activated upon cullin neddylation, promote the ubiquitination of a variety of key signaling proteins for proteasome degradation, thereby regulating many critical biological functions. Abnormal activation of neddylation enzymes as well as CRLs has been frequently observed in various human cancers and is associated with poor prognosis for cancer patients. Consequently, targeting neddylation has emerged as a promising strategy for the development of novel anticancer therapeutics. This review first briefly introduces the properties of protein neddylation and its role in cancer, and then systematically summarizes all reported chemical inhibitors of the three neddylation enzymes, providing a focused, up to date, and comprehensive resource in the discovery and development of these small molecule inhibitors.

Glioblastoma vulnerability to neddylation inhibition is dependent on PTEN status, and dysregulation of the cell cycle and DNA replication

Background

Neddylation (NAE) inhibition, affecting posttranslational protein function and turnover, is a promising therapeutic approach to cancer. We report the cytotoxic vulnerability to NAE inhibitors in a subset of glioblastoma (GBM) preclinical models and identify genetic alterations and biological processes underlying differential response.

Methods

GBM DNA sequencing and transcriptomic data were queried for genes associated with response to NAE inhibition; candidates were validated by molecular techniques. Multi-omics and functional assays revealed processes implicated in NAE inhibition response.

Results

Transcriptomics and shotgun proteomics depict PTEN signaling, DNA replication, and DNA repair pathways as significant differentiators between sensitive and resistant models. Vulnerability to MLN4924, a NAE inhibitor, is associated with elevated S-phase populations, DNA re-replication, and DNA damage. In a panel of GBM models, loss of WT PTEN is associated with resistance to different NAE inhibitors. A NAE inhibition response gene set could segregate the GBM cell lines that are most resistant to MLN4924.

Conclusions

Loss of WT PTEN is associated with non-sensitivity to 3 different compounds that inhibit NAE in GBM. A NAE inhibition response gene set largely consisting of DNA replication genes could segregate GBM cell lines most resistant to NAEi and may be the basis for future development of NAE inhibition signatures of vulnerability and clinical trial enrollment within a precision medicine paradigm.

MYOD-SKP2 axis boosts tumorigenesis in fusion negative rhabdomyosarcoma by preventing differentiation through p57Kip2 targeting

Rhabdomyosarcomas (RMS) are pediatric mesenchymal-derived malignancies encompassing PAX3/7-FOXO1 Fusion Positive (FP)-RMS, and Fusion Negative (FN)-RMS with frequent RAS pathway mutations. RMS express the master myogenic transcription factor MYOD that, whilst essential for survival, cannot support differentiation. Here we discover SKP2, an oncogenic E3-ubiquitin ligase, as a critical pro-tumorigenic driver in FN-RMS. We show that SKP2 is overexpressed in RMS through the binding of MYOD to an intronic enhancer. SKP2 in FN-RMS promotes cell cycle progression and prevents differentiation by directly targeting p27Kip1 and p57Kip2, respectively. SKP2 depletion unlocks a partly MYOD-dependent myogenic transcriptional program and strongly affects stemness and tumorigenic features and prevents in vivo tumor growth. These effects are mirrored by the investigational NEDDylation inhibitor MLN4924. Results demonstrate a crucial crosstalk between transcriptional and post-translational mechanisms through the MYOD-SKP2 axis that contributes to tumorigenesis in FN-RMS. Finally, NEDDylation inhibition is identified as a potential therapeutic vulnerability in FN-RMS.

PTEN loss drives resistance to the neddylation inhibitor MLN4924 in glioblastoma and can be overcome with TOP2A inhibitors

BACKGROUND

Neddylation inhibition, affecting posttranslational protein function and turnover, is a promising therapeutic approach to cancer. We report vulnerability to MLN4924 or pevonedistat (a neddylation inhibitor) in a subset of glioblastoma (GBM) preclinical models and identify biomarkers, mechanisms, and signatures of differential response.

METHODS

GBM sequencing data were queried for genes associated with MLN4924 response status; candidates were validated by molecular techniques. Time-course transcriptomics and proteomics revealed processes implicated in MLN4924 response.

RESULTS

Vulnerability to MLN4924 is associated with elevated S-phase populations, re-replication, and DNA damage. Transcriptomics and shotgun proteomics depict PTEN signaling, DNA replication, and chromatin instability pathways as significant differentiators between sensitive and resistant models. Loss of PTEN and its nuclear functions is associated with resistance to MLN4924. Time-course proteomics identified elevated TOP2A in resistant models through treatment. TOP2A inhibitors combined with MLN4924 prove synergistic.

CONCLUSIONS

We show that PTEN status serves as both a novel biomarker for MLN4924 response in GBM and reveals a vulnerability to TOP2A inhibitors in combination with MLN4924.

The Anti-Tumor Activity of the NEDD8 Inhibitor Pevonedistat in Neuroblastoma

Pevonedistat is a neddylation inhibitor that blocks proteasomal degradation of cullin–RING ligase (CRL) proteins involved in the degradation of short-lived regulatory proteins, including those involved with cell-cycle regulation. We determined the sensitivity and mechanism of action of pevonedistat cytotoxicity in neuroblastoma. Pevonedistat cytotoxicity was assessed using cell viability assays and apoptosis. We examined mechanisms of action using flow cytometry, bromodeoxyuridine (BrDU) and immunoblots. Orthotopic mouse xenografts of human neuroblastoma were generated to assess in vivo anti-tumor activity. Neuroblastoma cell lines were very sensitive to pevonedistat (IC50 136–400 nM). The mechanism of pevonedistat cytotoxicity depended on p53 status. Neuroblastoma cells with mutant (p53^MUT) or reduced levels of wild-type p53 (p53si-p53) underwent G2-M cell-cycle arrest with rereplication, whereas p53 wild-type (p53^WT) cell lines underwent G0-G1 cell-cycle arrest and apoptosis. In orthotopic neuroblastoma models, pevonedistat decreased tumor weight independent of p53 status. Control mice had an average tumor weight of 1.6 mg + 0.8 mg versus 0.5 mg + 0.4 mg (p < 0.05) in mice treated with pevonedistat. The mechanism of action of pevonedistat in neuroblastoma cell lines in vitro appears p53 dependent. However, in vivo studies using mouse neuroblastoma orthotopic models showed a significant decrease in tumor weight following pevonedistat treatment independent of the p53 status. Novel chemotherapy agents, such as the NEDD8-activating enzyme (NAE) inhibitor pevonedistat, deserve further study in the treatment of neuroblastoma.

Compact Fat Grafting: A Novel Method to Improve Graft Retention Through Modulation of Adipocyte Size

BACKGROUND

The viable zone where adipocytes and/or adipose-derived stem cells survive is present at the surface of graft fat tissue; however, there is controversy regarding the zone thickness. Graft retention could be improved if more adipocytes are included in the zone.

OBJECTIVES

We hypothesize that a temporary reduction in adipocyte size prior to grafting could increase the number of adipocytes in the viable zone. We reduced the adipocyte size by treatment with MLN4924, which controls lipid accumulation in adipocytes, and investigated the histological and microenvironmental changes in grafted fat.

METHODS

Subcutaneous fat harvested from wild-type C57BL/6J mice was chopped into small pieces; treated with dimethyl sulfoxide (control group), 0.25 μM MLN4924, or 0.5 μM MLN4924 for 4 days; and grafted into recipient C57BL/6J mice at the supraperiosteal plane of the skull.

RESULTS

The reduced adipocyte size in response to MLN4924 treatment was restored within 8 weeks after fat grafting. The MLN4924-treated groups exhibited substantially greater graft volume, lower tissue hypoxia, and higher production of M2 macrophages compared with the control group.

CONCLUSIONS

Grafting with compact fat that had smaller adipocytes improved the microenvironment by modulating tissue hypoxia and macrophage polarization, leading to improved graft retention. Therefore, compact fat grafting may offer a new clinical strategy without the need for stem cell manipulation.

Progress Update in Pediatric Renal Tumors

PURPOSE OF REVIEW

Pediatric renal tumors account for 7% of new cancer diagnoses in children. Here, we will review results from recently completed clinical trials informing the current standard of care and discuss targeted and immune therapies being explored for the treatment of high risk or relapsed/refractory pediatric renal malignancies.

RECENT FINDINGS

Cooperative group trials have continued to make improvements in the care of children with pediatric tumors. In particular, trials that standardize treatment of rare cancers (e.g., bilateral Wilms tumor) have improved outcomes significantly. We have seen improvements in event free and overall survival in recently completed clinical trials for many pediatric renal tumors. Still, there are subsets of rarer cancers where outcomes remain poor and new therapeutic strategies are needed. Future trials aim to balance treatment toxicity with treatment efficacy for those with excellent outcomes while identifying novel therapeutics for those with poor outcomes.

E1 Enzymes as Therapeutic Targets in Cancer

Post-translational modifications of cellular substrates with ubiquitin and ubiquitin-like proteins (UBLs), including ubiquitin, SUMOs, and neural precursor cell-expressed developmentally downregulated protein 8, play a central role in regulating many aspects of cell biology. The UBL conjugation cascade is initiated by a family of ATP-dependent enzymes termed E1 activating enzymes and executed by the downstream E2-conjugating enzymes and E3 ligases. Despite their druggability and their key position at the apex of the cascade, pharmacologic modulation of E1s with potent and selective drugs has remained elusive until 2009. Among the eight E1 enzymes identified so far, those initiating ubiquitylation (UBA1), SUMOylation (SAE), and neddylation (NAE) are the most characterized and are implicated in various aspects of cancer biology. To date, over 40 inhibitors have been reported to target UBA1, SAE, and NAE, including the NAE inhibitor pevonedistat, evaluated in more than 30 clinical trials. In this Review, we discuss E1 enzymes, the rationale for their therapeutic targeting in cancer, and their different inhibitors, with emphasis on the pharmacologic properties of adenosine sulfamates and their unique mechanism of action, termed substrate-assisted inhibition. Moreover, we highlight other less-characterized E1s-UBA6, UBA7, UBA4, UBA5, and autophagy-related protein 7-and the opportunities for targeting these enzymes in cancer. SIGNIFICANCE STATEMENT: The clinical successes of proteasome inhibitors in cancer therapy and the emerging resistance to these agents have prompted the exploration of other signaling nodes in the ubiquitin-proteasome system including E1 enzymes. Therefore, it is crucial to understand the biology of different E1 enzymes, their roles in cancer, and how to translate this knowledge into novel therapeutic strategies with potential implications in cancer treatment.

Neddylation of sterol regulatory element-binding protein 1c is a potential therapeutic target for nonalcoholic fatty liver treatment

Nonalcoholic fatty liver disease (NAFLD) is a risk factor for progression of steatohepatitis, liver cirrhosis, and liver cancer. Although pathological condition of NAFLD, which arises from an excessive accumulation of triglyceride in the liver, is accompanied by elevated sterol regulatory element-binding protein 1c (SREBP1c) level, it is largely unknown which factors are involved in the modification of SREBP1c. In this study, we discovered that neddylation of SREBP1c competes with its ubiquitination and stabilizes SREBP1c protein level, and eventually promotes hepatic steatosis. We also demonstrated that human homolog of mouse double minute 2 (HDM2) acts as an E3 neddylation ligase of SREBP1c. Further, treatment with the neddylation inhibitor, MLN4924, attenuates high-fat diet-induced hepatic steatosis by reducing the levels of SREBP1c protein and hepatic triglyceride. Our results indicate that the blockade of SREBP1c neddylation could be a novel approach in the defense against NAFLD.

Genomic Complexity of Osteosarcoma and Its Implication for Preclinical and Clinical Targeted Therapies

Osteosarcoma is a genomically complex disease characterized by few recurrent single-nucleotide mutations or in-frame fusions. In contrast, structural alterations, including copy number changes, chromothripsis, kataegis, loss of heterozygosity (LOH), and other large-scale genomic alterations, are frequent and widespread across the osteosarcoma genome. These observed structural alterations lead to activation of oncogenes and loss of tumor suppressors which together contribute to oncogenesis. To date, few targeted therapies for osteosarcoma have been identified. It is likely that effectiveness of targeted therapies will vary greatly in subsets of tumors with distinct key driver events. Model systems which can recapitulate the genetic heterogeneity of this disease are needed to test this hypothesis. One possible approach is to use patient-derived xenograft (PDX) models characterized with regards to their similarity to the human tumor samples from which they were derived. Here we review evidence pointing to the genomic complexity of osteosarcoma and how this is reflected in available model systems. We also review the current state of preclinical testing for targeted therapies using these models.

The NEDD8-activating enzyme inhibitor MLN4924 induces DNA damage in Ph+ leukemia and sensitizes for ABL kinase inhibitors

The BCR-ABL1 fusion gene is the driver oncogene in chronic myeloid leukemia (CML) and Philadelphia-chromosome positive (Ph+) acute lymphoblastic leukemia (ALL). The introduction of tyrosine kinase inhibitors (TKIs) targeting the ABL kinase (such as imatinib) has dramatically improved survival of CML and Ph+ ALL patients. However, primary and acquired resistance to TKIs remains a clinical challenge. Ph+ leukemia patients who achieve a complete cytogenetic (CCR) or deep molecular response (MR) (≥4.5log reduction in BCR-ABL1 transcripts) represent long-term survivors. Thus, the fast and early eradication of leukemic cells predicts MR and is the prime clinical goal for these patients. We show here that the first-in-class inhibitor of the Nedd8-activating enzyme (NAE1) MLN4924 effectively induced caspase-dependent apoptosis in Ph+ leukemia cells, and sensitized leukemic cells for ABL tyrosine kinase inhibitors (TKI) and hydroxyurea (HU). We demonstrate that MLN4924 induced DNA damage in Ph+ leukemia cells by provoking the activation of an intra S-phase checkpoint, which was enhanced by imatinib co-treatment. The combination of MLN4924 and imatinib furthermore triggered a dramatic shift in the expression of MCL1 and NOXA. Our data offers a clear rationale to explore the clinical activity of MLN4924 (alone and in combination with ABL TKI) in Ph+ leukemia patients

Cross Talk Networks of Mammalian Target of Rapamycin Signaling With the Ubiquitin Proteasome System and Their Clinical Implications in Multiple Myeloma

Multiple myeloma (MM) is the second most common hematological malignancy and results from the clonal amplification of plasma cells. Despite recent advances in treatment, MM remains incurable with a median survival time of only 5-6years, thus necessitating further insights into MM biology and exploitation of novel therapeutic approaches. Both the ubiquitin proteasome system (UPS) and the PI3K/Akt/mTOR signaling pathways have been implicated in the pathogenesis, and treatment of MM and different lines of evidence suggest a close cross talk between these central cell-regulatory signaling networks. In this review, we outline the interplay between the UPS and mTOR pathways and discuss their implications for the pathophysiology and therapy of MM.

Blocking PD1/PDL1 Interactions Together with MLN4924 Therapy is a Potential Strategy for Glioma Treatment

Objective:

MLN4924, a pharmacological inhibitor of cullin neddylation, resulted in glioma cell apoptosis, deregulation of the S-phase of DNA synthesis and thus, offers great potential for the treatment of brain tumours. However, targeting the neddylation pathway with an MLN4924 treatment stabilized the hypoxia-inducible factor 1A (HIF1A), which is one of the main transcriptional enhancers of the immune checkpoint molecule PDL1 (programmid death ligand-1) in cancer cells. The influence of immune checkpoint molecules on glioma progression has recently been discovered; PDL1 overexpression in gliomas corresponds to a significant shortening of patient survival and a decrease of the anti-tumour immune response. We hypothesize that i) PDL1 is up-regulated in gliomas after treatment with MLN4924 and induces T-cell energy; ii) co-utilization of the PD1/PDL1 blockage with MLN4924 therapy may reduce T-cell energy and may engage MLN4924-induced tumour disruption with the immune response.

Methods:

PDL1 expression and its immunosuppressive role in gliomas, glioma microenvironments, and after treatments with MLN4924 were assessed by utilizing methods of immunohistochemistry, molecular biology, and biochemistry.

Results:

We confirmed PDL1 overexpression in clinical brain tumour samples, PDGx and established glioma cell lines, extracellular media from glioma cells, and CSF (cerebrospinal fluid) samples from tumour-bearing mice. Our primary T-cell based assays verified that the up-regulation of PDL1 in tumour cells protects gliomas from T-cell treatment and reduces T-cell activation. We found that a pharmacological inhibitor of cullin neddylation, MLN4924, exhibited strong cytotoxicity towards PDGx and established glioma cell lines, in vitro, with an IC50’s range from 0.2 to 3 uM. However, we observed a significant increase of HIF1A and PDL1 in mRNA and protein levels in all glioma cell lines after treatment with MLN4924. The MLN4924-dependent induction of PDL1 in gliomas resulted in T-cell energy, which was blocked by a blockage of the PD1/PDL1 interaction.

Conclusion:

We conclude that i) PDL1 up-regulation in gliomas and the glioma microenvironment is an important chemotherapeutic target; ii) MLN4924 therapy, combined with a blockage of the PD1/PDL1 pathway, should be considered as a potential strategy for glioma treatment.

MLN4924 therapy as a novel approach in cancer treatment modalities

MLN4924 is an investigational and a newly discovered small molecule that is a potent and selective inhibitor of the NEDD8 (Neural precursor cell-Expressed Developmentally down-regulated 8) Activating Enzyme (NAE), a pivotal regulator of the Cullin Ring Ligases E3 (CRL), which has been implicated recently in DNA damage. MLN4924 effectively inhibits tumour cell growth by inducing all three common types of death, namely apoptosis, autophagy and senescence and it was also reported that the formation of capillary vessels was significantly suppressed by MLN4924.In this review, we are going to highlight the molecular mechanism of MLN4924 in cancer therapy and its pros and cons in cancer therapy.

The NEDD8-activating enzyme inhibitor pevonedistat activates the eIF2α and mTOR pathways inducing UPR-mediated cell death in acute lymphoblastic leukemia

Acute lymphoblastic leukemia (ALL) is the leading cause of cancer-related death in children, and cure rates for adults remain dismal. Further, effective treatment strategies for relapsed/refractory ALL remain elusive. We previously uncovered that ALL cells are prone to apoptosis via endoplasmic reticulum (ER) stress/unfolded protein response (UPR)-mediated mechanisms. We investigated the antineoplastic activity of pevonedistat^®, a novel NEDD8-activating enzyme inhibitor that targets E3 cullin-RING ligases (CRLs) dependent proteasomal protein degradation, in ALL. Herein, we report that pevonedistat induces apoptosis in ALL cells by dysregulating the translational machinery leading to induction of proteotoxic/ER stress and UPR-mediated cell death. Mechanistically, pevonedistat led to P-eIF2a dephosphorylation causing atypical proteotoxic/ER stress from failure to halt protein translation via the UPR and upregulation of mTOR/p70S6K. Additional studies revealed that pevonedistat re-balanced the homeostasis of pro- and anti-apoptotic proteins to favor cell death through altered expression and/or activity of Mcl-1, NOXA, and BIM, suggesting that pevonedistat has a "priming" effect on ALL by altering the apoptotic threshold through modulation of Mcl-1 activity. Further, we demonstrated that pevonedistat synergizes with selected anti-leukemic agents in vitro, and prolongs survival of NSG mice engrafted with ALL cells, lending support for the use of pevonedistat as part of a multi-agent approach.

A review of new agents evaluated against pediatric acute lymphoblastic leukemia by the Pediatric Preclinical Testing Program

Acute lymphoblastic leukemia (ALL) in children exemplifies how multi-agent chemotherapy has improved the outcome for patients. Refinements in treatment protocols and improvements in supportive care for this most common pediatric malignancy have led to a cure rate that now approaches 90%. However, certain pediatric ALL subgroups remain relatively intractable to treatment and many patients who relapse face a similarly dismal outcome. Moreover, survivors of pediatric ALL suffer the long-term sequelae of their intensive treatment throughout their lives. Therefore, the development of drugs to treat relapsed/refractory pediatric ALL, as well as those that more specifically target leukemia cells, remains a high priority. As pediatric malignancies represent a minority of the overall cancer burden, it is not surprising that they are generally underrepresented in drug development efforts. The identification of novel therapies relies largely on the reappropriation of drugs developed for adult malignancies. However, despite the large number of experimental agents available, clinical evaluation of novel drugs for pediatric ALL is hindered by limited patient numbers and the availability of effective established drugs. The Pediatric Preclinical Testing Program (PPTP) was established in 2005 to provide a mechanism by which novel therapeutics could be evaluated against xenograft and cell line models of the most common childhood malignancies, including ALL, to prioritize those with the greatest activity for clinical evaluation. In this article, we review the results of >50 novel agents and combinations tested against the PPTP ALL xenografts, highlighting comparisons between PPTP results and clinical data where possible.

A phase I study of the investigational NEDD8-activating enzyme inhibitor pevonedistat (TAK-924/MLN4924) in patients with metastatic melanoma

Purpose The therapeutic index of proteasome inhibitors may be improved through selective inhibition of a sub-component of the ubiquitin-proteasome system, such as the NEDD8-conjugation pathway. This multicenter, phase I, dose-escalation study assessed safety and the maximum tolerated dose (MTD), pharmacokinetics, pharmacodynamics, and antitumor activity of pevonedistat, an investigational NEDD8-activating enzyme (NAE) inhibitor, in patients with metastatic melanoma. Methods Patients received intravenous pevonedistat on Days 1, 4, 8, 11 (schedule A) or 1, 8, 15 (schedule B) of 21-day cycles. Results 26 patients received pevonedistat 50–278 mg/m² on schedule A; 11 patients received pevonedistat 157 mg/m² on schedule B. The schedule A MTD was 209 mg/m²: dose-limiting toxicities (DLTs) included grade 3 hypophosphatemia and grade 3 increased blood creatinine (associated with grade 3 hyperbilirubinemia). Two schedule A patients experienced acute organ failure toxicities, one of whom experienced grade 5 acute renal failure. Dose escalation did not occur in schedule B: DLTs included grade 3 myocarditis, grade 2 acute renal failure, and grade 2 hyperbilirubinemia in a single patient. Pevonedistat pharmacokinetics were approximately dose-proportional across the dose range studied, with a biphasic disposition profile characterized by a short elimination half-life (~10 h). Pharmacodynamic studies showed increases in NAE-regulated transcripts post-treatment; all post-dose biopsy samples were positive for pevonedistat-NEDD8 adduct. One schedule A patient achieved a partial response; 15 patients had stable disease (4 lasting ≥6.5 months). Conclusions Pevonedistat was generally well tolerated at the MTD. Anticipated pharmacodynamic effects of NAE inhibition were observed with single-agent pevonedistat in peripheral blood and tumor tissue.

PPARγ neddylation essential for adipogenesis is a potential target for treating obesity

The preadipocyte-to-adipocyte differentiation (adipogenesis) is a key process in fat mass increase and thus it is regarded as a compelling target for preventing or treating obesity. Of adipogenic hormone receptors, peroxisome proliferator-activated receptor gamma (PPARγ) has crucial roles in adipogenesis and lipid accumulation within adipocytes. Here we demonstrate that the NEDD8 (neuronal precursor cell expressed, developmentally downregulated 8)-based post-translation modification (neddylation) of PPARγ is essential for adipogenesis. During adipogenesis, NEDD8 is robustly induced in preadipocytes and conjugates with PPARγ, leading to PPARγ stabilization. When the neddylation process was blocked by NEDD8-targeting siRNAs (or viral vectors) or an inhibitor MLN4924, adipocyte differentiation and fat tissue development were substantially impaired. We also demonstrate that MLN4924 effectively prevents the high-fat diet-induced obesity and glucose intolerance in mice. This study provides a better understanding of how the PPARγ signaling pathway starts and lasts during adipogenesis and a potential anti-obesity strategy that targets the neddylation of PPARγ.

Pediatric brain tumor cell lines

Pediatric brain tumors as a group, including medulloblastomas, gliomas, and atypical teratoid rhabdoid tumors (ATRT) are the most common solid tumors in children and the leading cause of death from childhood cancer. Brain tumor-derived cell lines are critical for studying the biology of pediatric brain tumors and can be useful for initial screening of new therapies. Use of appropriate brain tumor cell lines for experiments is important, as results may differ depending on tumor properties, and can thus affect the conclusions and applicability of the model. Despite reports in the literature of over 60 pediatric brain tumor cell lines, the majority of published papers utilize only a small number of these cell lines. Here we list the approximately 60 currently-published pediatric brain tumor cell lines and summarize some of their central features as a resource for scientists seeking pediatric brain tumor cell lines for their research.

Targeting Neddylation pathways to inactivate cullin-RING ligases for anticancer therapy

SIGNIFICANCE

Protein neddylation is catalyzed by an E1 NEDD8-activating enzyme (NAE), an E2 NEDD8-conjugating enzyme, and an E3 NEDD8 ligase. Known physiological substrates of neddylation are cullin family members. Cullin neddylation leads to activation of cullin-RING ligases (CRLs), the largest family of E3 ubiquitin ligases responsible for ubiquitylation and degradation of many key signaling/regulatory proteins. Thus, through modulating CRLs, neddylation regulates many biological processes, including cell cycle progression, signal transduction, and tumorigenesis. Given that NEDD8 is overexpressed and CRLs are abnormally activated in many human cancers, targeting protein neddylation, in general, and cullin neddylation, in particular, appears to be an attractive anticancer approach.

RECENT ADVANCES

MLN4924, a small molecule inhibitor of NAE, was discovered that inactivates CRLs and causes accumulation of CRL substrates to suppress tumor cell growth both in vitro and in vivo. Promising preclinical results advanced MLN4924 to several clinical trials for anticancer therapy.

CRITICAL ISSUES

In preclinical settings, MLN4924 effectively suppresses tumor cell growth by inducing apoptosis, senescence, and autophagy, and causes sensitization to chemoradiation therapies in a cellular context-dependent manner. Signal molecules that determine the cell fate upon MLN4924 treatment, however, remain elusive. Cancer cells develop MLN4924 resistance by selecting target mutations.

FUTURE DIRECTIONS

In the clinical side, several Phase 1b trials are under way to determine the safety and efficacy of MLN4924, acting alone or in combination with conventional chemotherapy, against human solid tumors. In the preclinical side, the efforts are being made to develop additional neddylation inhibitors by targeting NEDD8 E2s and E3s.

SCF ubiquitin ligase-targeted therapies

The clinical successes of proteasome inhibitors for the treatment of cancer have highlighted the therapeutic potential of targeting this protein degradation system. However, proteasome inhibitors prevent the degradation of numerous proteins, which may cause adverse effects. Increased specificity could be achieved by inhibiting the components of the ubiquitin-proteasome system that target specific subsets of proteins for degradation. F-box proteins are the substrate-targeting subunits of SKP1-CUL1-F-box protein (SCF) ubiquitin ligase complexes. Through the degradation of a plethora of diverse substrates, SCF ubiquitin ligases control a multitude of processes at the cellular and organismal levels, and their dysregulation is implicated in many pathologies. SCF ubiquitin ligases are characterized by their high specificity for substrates, and these ligases therefore represent promising drug targets. However, the potential for therapeutic manipulation of SCF complexes remains an underdeveloped area. This Review explores and discusses potential strategies to target SCF-mediated biological processes to treat human diseases.

Targeting the ubiquitin proteasome system in haematological malignancies

The ubiquitin proteasome system (UPS) plays a central role in cellular protein homeostasis through the targeted destruction of damaged/misfolded proteins and regulatory proteins that control critical cellular functions. The UPS comprises a sequential series of enzymatic activities to covalently attach ubiquitin to proteins to target them for degradation through the proteasome. Aberrancies within this system have been associated with transformation and tumourigenesis and thus, the UPS represents an attractive target for the development of anti-cancer therapies. The use of the first-in-class proteasome inhibitor, bortezomib, in the treatment of Plasma Cell Myeloma and Mantle Cell Lymphoma has validated the UPS as a therapeutic target. Following on its success, efforts are focused on the development of second-generation proteasome inhibitors and small molecule inhibitors of other components of the UPS. This review will provide an overview of the UPS and discuss current and novel therapies targeting the UPS.

A review of targeted therapies evaluated by the pediatric preclinical testing program for osteosarcoma

Osteosarcoma, the most common malignant bone tumor of childhood, is a high-grade primary bone sarcoma that occurs mostly in adolescence. Standard treatment consists of surgery in combination with multi-agent chemotherapy regimens. The development and approval of imatinib for Philadelphia chromosome-positive acute lymphoblastic leukemia in children and the fully human monoclonal antibody, anti-GD2, as part of an immune therapy for high-risk neuroblastoma patients have established the precedent for use of targeted inhibitors along with standard chemotherapy backbones. However, few targeted agents tested have achieved traditional clinical endpoints for osteosarcoma. Many biological agents demonstrating anti-tumor responses in preclinical and early-phase clinical testing have failed to reach response thresholds to justify randomized trials with large numbers of patients. The development of targeted therapies for pediatric cancer remains a significant challenge. To aid in the prioritization of new agents for clinical testing, the Pediatric Preclinical Testing Program (PPTP) has developed reliable and robust preclinical pediatric cancer models to rapidly screen agents for activity in multiple childhood cancers and establish pharmacological parameters and effective drug concentrations for clinical trials. In this article, we examine a range of standard and novel agents that have been evaluated by the PPTP, and we discuss the preclinical and clinical development of these for the treatment of osteosarcoma. We further demonstrate that committed resources for hypothesis-driven drug discovery and development are needed to yield clinical successes in the search for new therapies for this pediatric disease.

p53, SKP2, and DKK3 as MYCN Target Genes and Their Potential Therapeutic Significance

Neuroblastoma is the most common extra-cranial solid tumor of childhood. Despite significant advances, it currently still remains one of the most difficult childhood cancers to cure, with less than 40% of patients with high-risk disease being long-term survivors. MYCN is a proto-oncogene implicated to be directly involved in neuroblastoma development. Amplification of MYCN is associated with rapid tumor progression and poor prognosis. Novel therapeutic strategies which can improve the survival rates whilst reducing the toxicity in these patients are therefore required. Here we discuss genes regulated by MYCN in neuroblastoma, with particular reference to p53, SKP2, and DKK3 and strategies that may be employed to target them.

Cullin-3 regulates vascular smooth muscle function and arterial blood pressure via PPARγ and RhoA/Rho-kinase

Dominant-negative (DN) mutations in the nuclear hormone receptor peroxisome proliferator-activated receptor-γ (PPARγ) cause hypertension by an unknown mechanism. Hypertension and vascular dysfunction are recapitulated by expression of DN PPARγ specifically in vascular smooth muscle of transgenic mice. DN PPARγ increases RhoA and Rho-kinase activity, and inhibition of Rho-kinase restores normal reactivity and reduces arterial pressure. RhoBTB1, a component of the Cullin-3 RING E3 ubiquitin ligase complex, is a PPARγ target gene. Decreased RhoBTB1, Cullin-3, and neddylated Cullin-3 correlated with increased levels of the Cullin-3 substrate RhoA. Knockdown of Cullin-3 or inhibition of cullin-RING ligase activity in aortic smooth muscle cells increased RhoA. Cullin-RING ligase inhibition enhanced agonist-mediated contraction in aortic rings from normal mice by a Rho-kinase-dependent mechanism, and it increased arterial pressure in vivo. We conclude that Cullin-3 regulates vascular function and arterial pressure, thus providing a mechanistic link between mutations in Cullin-3 and hypertension in humans.

MLN4924: a novel first-in-class inhibitor of NEDD8-activating enzyme for cancer therapy

INTRODUCTION

The small ubiquitin-like molecule NEDD8 has been identified as an essential regulator of the activity of the cullin-RING E3 ubiquitin ligases (CRLs), which control the turnover of multiple proteins with fundamental roles in cancer biology. The aberrant function of the NEDD8 cascade within the context of malignancy makes it an attractive target for the development of novel anticancer agents. MLN4924 is a first-in-class inhibitor of the proximal regulator of the NEDD8 system (NEDD8-activating enzyme, NAE) that has entered Phase-I trials for cancer therapy and has established that significant therapeutic benefit can be achieved by antagonizing NEDD8-mediated protein degradation.

AREAS COVERED

This review provides a detailed overview of the NEDD8 system and discusses the mechanisms of action of MLN4924, a novel small molecule NAE inhibitor. Key findings from preclinical investigations of MLN4924 in a broad range of cancer models and preliminary findings from ongoing Phase-I clinical trials with MLN4924 are also discussed.

EXPERT OPINION

Targeting protein NEDDylation represents an exciting new anticancer strategy with demonstrable therapeutic benefit. Ongoing and future studies focused on dissecting the functional status/regulation of the NEDD8 system in individual tumor types will facilitate the design of novel approaches that yield optimal therapeutic benefit.