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PML/retinoic acid receptor alpha (RARα), as a hallmark of acute promyeloid leukemia (APL), is directly related to the outcome of clinical APL remedy. It is reported that arsenicals can effectively degrade PML/RARα, such as arsenic trioxide and realgar. However, the high toxicity or insolubility have hampered their clinical applications. Realgar transforming solution (RTS) was produced from realgar by bioleaching process in our lab. Previous studies demonstrated that RTS had a significant anti-cancer ability on chronic myeloid leukemia through oncoprotein degradation. The capacity of RTS on treating APL is what is focused on in this study. The results showed that RTS had a noticeable sensitivity in NB4 cell, and RTS remarkably down-regulated PML/RARα expression and induced cell differentiation. Further, RTS could accumulate PML/RARα into the nuclear bodies and then execute degradation, which could be reversed by proteasome inhibitor MG132. The results also exhibited that the reduction of RTS-induced PML/RARα expression accompanied by the elevation of ubiquitin and SUMO-1 protein expression. Finally, PML and SUMO-1 had been demonstrated to be co-localized after RTS treatment by immunofluorescence co-localization assay and immunoprecipitation assay. In conclusion, these results suggested that RTS-induced cell differentiation may attribute to the PML/RARα degradation partially through the ubiquitin-proteasome pathway.

Ubiquitination and ubiquitin-like posttranslational modifications (PTM) regulate activity and stability of oncoproteins and tumor suppressors. This implicates PTMs as antineoplastic targets. One way to alter PTMs is to inhibit activity of deubiquitinases (DUB) that remove ubiquitin or ubiquitin-like proteins from substrate proteins. Roles of DUBs in carcinogenesis have been intensively studied, yet few inhibitors exist. Prior work provides a basis for the ubiquitin-specific protease 18 (USP18) as an antineoplastic target. USP18 is the major DUB that removes IFN-stimulated gene 15 (ISG15) from conjugated proteins. Prior work discovered that engineered loss of USP18 increases ISGylation and in contrast to its gain decreases cancer growth by destabilizing growth-regulatory proteins. Loss of USP18 reduced cancer cell growth by triggering apoptosis. Genetic loss of USP18 repressed cancer formation in engineered murine lung cancer models. The translational relevance of USP18 was confirmed by finding its expression was deregulated in malignant versus normal tissues. Notably, the recent elucidation of the USP18 crystal structure offers a framework for developing an inhibitor to this DUB. This review summarizes strong evidence for USP18 as a previously unrecognized pharmacologic target in oncology. Cancer Res; 78(3); 587-92. ©2018 AACR ., (©2018 American Association for Cancer Research.)

Background: The NEDD8 conjugation pathway modulates the ubiquitination and activity of a wide range of intracellular proteins, and its blockade by pevonedistat is emerging as a promising therapeutic approach in various cancer settings. However, systematic characterization of pevonedistat efficacy in specific tumor types and definition of response predictors are still missing., Methods: We investigated in vitro sensitivity to pevonedistat in 122 colorectal cancer (CRC) cell lines by an ATP-based proliferation assay and evaluated apoptosis and DNA content by flow cytometry. Associations between pevonedistat sensitivity and CRC molecular features were assessed by Student's t test. A 184-gene transcriptional predictor was generated in cell lines and applied to 87 metastatic CRC samples for which patient-derived xenografts (PDXs) were available. In vivo reponse to pevonedistat was assessed in PDX models (≥5 mice per group). All statistical tests were two-sided., Results: Sixteen (13.1%) cell lines displayed a marked response to pevonedistat, featuring DNA re-replication, proliferative block, and increased apoptosis. Pevonedistat sensitivity did not statistically significantly correlate with microsatellite instability or mutations in KRAS or BRAF and was functionally associated with low EGFR pathway activity. While ineffective on predicted resistant PDXs, in vivo administration of pevonedistat statistically significantly impaired growth of five out of six predicted sensitive models (P < .01). In samples from CRC patients, transcriptional prediction of pevonedistat sensitivity was associated with poor prognosis after surgery (hazard ratio [HR] = 2.49, 95% confidence interval [CI] = 1.34 to 4.62, P = .003) and early progression under cetuximab treatment (HR = 3.59, 95% CI = 1.60 to 8.04, P < .001). Histological and immunohistochemical analyses revealed that the pevonedistat sensitivity signature captures transcriptional traits of poor differentiation and high-grade mucinous adenocarcinoma., Conclusions: These results highlight NEDD8-pathway inhibition by pevonedistat as a potentially effective treatment for poorly differentiated, clinically aggressive CRC., (© The Author 2016. Published by Oxford University Press. All rights reserved. For Permissions, please email: journals.permissions@oup.com.)

The ubiquitin proteasome system (UPS) plays vital roles in maintaining protein equilibrium mainly through proteolytic degradation of targeted substrates. The archetypical SCF ubiquitin E3 ligase complex contains a substrate recognition subunit F-box protein that recruits substrates to the catalytic ligase core for its polyubiquitylation and subsequent proteasomal degradation. Several well-characterized F-box proteins have been demonstrated that are tightly linked to neoplasia. There is mounting information characterizing F-box protein-substrate interactions with the rationale to develop unique therapeutics for cancer treatment. Here we review that how F-box proteins function in cancer and summarize potential small molecule inhibitors for cancer therapy., (Copyright © 2015 Elsevier Ltd. All rights reserved.)

Purpose: Evaluate the safety, pharmacokinetic profile, pharmacodynamic effects, and antitumor activity of the first-in-class investigational NEDD8-activating enzyme (NAE) inhibitor pevonedistat (TAK-924/MLN4924) in patients with relapsed/refractory lymphoma or multiple myeloma., Experimental Design: Patients with relapsed/refractory myeloma (n = 17) or lymphoma (n = 27) received intravenous pevonedistat 25 to 147 mg/m(2) on days 1, 2, 8, 9 (schedule A; n = 27) or 100 to 261 mg/m(2) on days 1, 4, 8, 11 (schedule B; n = 17) of 21-day cycles., Results: Maximum tolerated doses were 110 mg/m(2) (schedule A) and 196 mg/m(2) (schedule B). Dose-limiting toxicities included febrile neutropenia, transaminase elevations, muscle cramps (schedule A), and thrombocytopenia (schedule B). Common adverse events included fatigue and nausea. Common grade ≥3 events were anemia (19%; schedule A), and neutropenia and pneumonia (12%; schedule B). Clinically significant myelosuppression was uncommon. There were no treatment-related deaths. Pevonedistat pharmacokinetics exhibited a biphasic disposition phase and approximate dose-proportional increases in systemic exposure. Consistent with the short mean elimination half-life of approximately 8.5 hours, little-to-no drug accumulation in plasma was seen after multiple dosing. Pharmacodynamic evidence of NAE inhibition included increased skin levels of CDT-1 and NRF-2 (substrates of NAE-dependent ubiquitin ligases), and increased NRF-2-regulated gene transcript levels in whole blood. Pevonedistat-NEDD8 adduct was detected in bone marrow aspirates, indicating pevonedistat target engagement in the bone marrow compartment. Three lymphoma patients had partial responses; 30 patients achieved stable disease., Conclusions: Pevonedistat demonstrated anticipated pharmacodynamic effects in the clinical setting, a tolerable safety profile, and some preliminary evidence that may be suggestive of the potential for activity in relapsed/refractory lymphoma., (©2015 American Association for Cancer Research.)

Protein neddylation, a newly characterized posttranslational modification that adds the ubiquitin-like molecule NEDD8 to substrates, modulates important biological processes, whereas dysfunction of neddylation may cause several serious diseases, such as cancer. Inhibition of neddylation pathway has emerged as a promising anticancer strategy, as evidenced by development of the NEDD8-activating enzyme (NAE) inhibitor MLN4924. Due to its potent anti-cancer efficacy and well-tolerated toxicity, MLN4924 has been evaluated in multiple Phase I clinical trials for solid tumors and hematologic malignancies. Recently, accumulating evidences indicate that neddylation pathway also plays a pivotal role in the regulation of multiple processes of tumor microenvironment (TME), such as tumor angiogenesis and the function of immune cells. In this review, we briefly summarize the latest progresses in this field and highlight neddylation pathway as an attractive therapeutic target against human cancer.

Background: A number of oncoproteins and tumor suppressors are known to be neddylated, but whether the neddylation pathway is entirely activated in human cancer remains unexplored., Methods: NEDD8-activating enzyme (NAE) (E1) and NEDD8-conjugating enzyme (E2) expression and global-protein neddylation were examined by immunohistochemistry, immunoblotting, and real-time polymerase chain reaction analysis. Cell proliferation, clonogenic survival, migration, and motility in vitro, as well as tumor formation and metastasis in vivo, were determined upon neddylation inhibition by MLN4924, an investigational NEDD8-activating enzyme inhibitor. Survival was analyzed with Kaplan-Meier methods and compared by the log-rank test. All statistical tests were two-sided., Results: The entire neddylation pathway, including NEDD8-activating enzyme E1, NEDD8-conjugating enzyme E2, and global-protein neddylation, is overactivated in both lung adenocarcinoma and squamous-cell carcinoma. Compared with lung adenocarcinoma patients with low expression, those with high expression had worse overall survival (NEDD8-activating enzyme E1 subunit 1 [NAE1]: hazard ratio [HR] = 2.07, 95% confidence interval [CI] = 0.95 to 4.52, P = .07; ubiquitin-conjugating enzyme E2M (UBC12): HR = 13.26, 95% CI = 1.77 to 99.35, P = .01; global protein neddylation: HR = 3.74, 95% CI = 1.65 to 8.47, P = .002). Moreover, inhibition of neddylation by the NAE inhibitor MLN4924 statistically significantly suppressed proliferation, survival, migration, and motility of lung cancer cells in vitro and tumor formation and metastasis in vivo. At the molecular level, MLN4924 inactivated Cullin-RING E3 ligases, led to accumulation of tumor-suppressive Cullin-RING E3 ligase substrates and induced phorbol-12-myristate-13-acetate-induced protein 1 (NOXA)-dependent apoptosis or cellular senescence., Conclusions: Our study highlights the overactivated neddylation pathway in lung cancer development and as a promising therapeutic target., (© The Author 2014. Published by Oxford University Press. All rights reserved. For Permissions, please e-mail: journals.permissions@oup.com.)

Tumor cells frequently promote the dysregulation of the cell cycle and escape from apoptotic cell death triggered by a number of cellular stresses. Programmed proteolytic degradation of regulatory proteins via the ubiquitin-proteasome pathway is crucial for homeostasis of numerous biological processes. Disruption of this system is one of the factors that promote aberrant cell-proliferation. The small ubiquitin-like protein, NEDD8, has been identified as a fundamental regulator of the activity of the E3 ubiquitin ligases called the SCF complex (consisting of Skp-1, cullin, and F-box protein) or CRL (cullin-RING ubiquitin ligase) which control a final step in ubiquitination of diverse substrates associated with cancer biology. The ubiquitin ligase activity of the SCF complex requires NEDD8 to covalently bind to cullins. To a large extent, exploring the negative regulation system of the NEDD8 pathway is expected to lead to the development of novel anticancer targets. This review focuses on the NEDD8 negative regulation system including chemical compounds such as MLN4924 and protein molecules (e.g. COP9 signalosome, CAND1, inactive mutant of Ubc12 and NUB1/NUB1L) and clarifies possible strategies for targeting the NEDD8 cascade in cancer cells.

Side population (SP) cells in cancers, including multiple myeloma, exhibit tumor-initiating characteristics. In the present study, we isolated SP cells from human myeloma cell lines and primary tumors to detect potential therapeutic targets specifically expressed in SP cells. We found that SP cells from myeloma cell lines (RPMI 8226, AMO1, KMS-12-BM, KMS-11) express CD138 and that non-SP cells include a CD138-negative population. Serial transplantation of SP and non-SP cells into NOD/Shi-scid IL-2γnul mice revealed that clonogenic myeloma SP cells are highly tumorigenic and possess a capacity for self-renewal. Gene expression analysis showed that SP cells from five MM cell lines (RPMI 8226, AMO1, KMS-12-BM, KMS-11, JJN3) express genes involved in the cell cycle and mitosis (e.g., CCNB1, CDC25C, CDC2, BIRC5, CENPE, SKA1, AURKB, KIFs, TOP2A, ASPM), polycomb (e.g., EZH2, EPC1) and ubiquitin-proteasome (e.g., UBE2D3, UBE3C, PSMA5) more strongly than do non-SP cells. Moreover, CCNB1, AURKB, EZH2 and PSMA5 were also upregulated in the SPs from eight primary myeloma samples. On that basis, we used an aurora kinase inhibitor (VX-680) and a proteasome inhibitor (bortezomib) with RPMI 8226 and AMO1 cells to determine whether these agents could be used to selectively target the myeloma SP. We found that both these drugs reduced the SP fraction, though bortezomib did so more effectively than VX-680 due to its ability to reduce levels of both phospho-histone H3 (p-hist. H3) and EZH2; VX-680 reduced only p-hist. H3. This is the first report to show that certain oncogenes are specifically expressed in the myeloma SP, and that bortezomib effectively downregulates expression of their products. Our approach may be useful for screening new agents with which to target a cell population possessing strong tumor initiating potential in multiple myeloma.

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.

Macroautophagy and the ubiquitin-proteasome system are two complementary pathways for protein degradation. The former degrades long-lived proteins and damaged organelles while the later degrades short-lived proteins. Recent findings indicate that suppression of the ubiquitin-proteasome system by proteasome inhibitors induces macroautophagy through multiple pathways, including (1) accumulation of ubiquitinated proteins and activation of HDAC6; (2) activation of the IRE1-JNK pathway; (3) proteasomal stabilization of ATF4; (4) inhibition of mTOR complex 1 signaling; (5) reduced proteasomal degradation of LC3. Induction of macroautophagy attenuates the antitumor effect of proteasome inhibitors in various types of cancer. These findings suggest that inhibition of macroautophagy may represent a novel strategy to enhance cellular sensitivity to proteasome inhibition., (Copyright 2010 Elsevier Ltd. All rights reserved.)

Cisplatin is a potent cytotoxic agent commonly used for the treatment of solid tumors. However, tumor cell-acquired resistance to cisplatin-induced apoptosis is a major limitation for efficient therapy, as frequently observed in human lung cancer. Nitric oxide (NO) is a key regulator of apoptosis, but its role in cisplatin-induced cell death and the underlying mechanism are largely unknown. Previous studies indicate increased NO synthase activity and elevated NO production in lung carcinomas, which correlate with the incidence of chemotherapeutic resistance. Here, we show that NO impairs the apoptotic function of cells and increases their resistance to cisplatin-induced cell death in human lung carcinoma H-460 cells. The NO donors sodium nitroprusside and dipropylenetriamine NONOate were able to inhibit cisplatin-induced cell death, whereas the NO inhibitors aminoguanidine and 2-(4-carboxyphenyl)-4,4,5,5-tetra-methylimidazoline-1-oxyl-3-oxide had opposite effect. Cisplatin resistance in H-460 cells is mediated by Bcl-2, and NO up-regulates its expression by preventing the degradation of Bcl-2 via ubiquitin-proteasome pathway. Cisplatin-induced generation of reactive oxygen species causes dephosphorylation and degradation of Bcl-2. In contrast, generation of NO has no effect on Bcl-2 phosphorylation but induces S-nitrosylation of the protein, which inhibits its ubiquitination and subsequent proteasomal degradation. These findings indicate a novel pathway for NO regulation of Bcl-2, which provides a key mechanism for cisplatin resistance and its potential modulation for improved cancer chemotherapy.

The ubiquitin-proteasome pathway is the principal mechanism for the degradation of short-lived proteins in eukaryotic cells. We demonstrated that treatment of THP-1 human monocytic leukemia cells with Z-LLL-CHO, a reversible proteasome inhibitor, induced cell death through an apoptotic pathway. Apoptosis in THP-1 cells induced by Z-LLL-CHO involved a cytochrome c-dependent pathway, which included the release of mitochondrial cytochrome c, activation of caspase-9 and -3, and cleavage of Bcl-2 into a shortened 22-kDa fragment. Induction of apoptosis by protease inhibitor also was detected in U937 and TF-1 leukemia cell lines and cells obtained from acute myelogenous leukemia patients but not in normal human blood monocytes. Treatment of human blood monocytes with Z-LLL-CHO did not induce apoptosis or Bcl-2 cleavage in these cells that rarely proliferate. Interestingly, when THP-1 cells were induced to undergo monocytic differentiation by bryostatin 1, a naturally occurring protein kinase C activator, they were no longer susceptible to apoptosis induced by Z-LLL-CHO. Bryostatin 1-induced differentiation of THP-1 cells was associated with growth arrest, acquisition of adherent capacity, and expression of membrane markers characteristic of blood monocytes. Likewise, differentiated THP-1 cells were refractory to Z-LLL-CHO-induced cytochrome c release, caspase activation, and Bcl-2 cleavage. Resistance to Z-LLL-CHO-induced apoptosis in differentiated THP-1 cells was not due to cell cycle arrest. These findings show that the action of proteasome inhibitors is mediated primarily through a cytochrome c-dependent pathway and induces apoptosis in leukemic cells that are not differentiated.