Chalcone-based small-molecule inhibitors attenuate malignant phenotype via targeting deubiquitinating enzymes

Ubiquitin-Specific Protease Inhibitors for Cancer Therapy: Recent Advances and Future Prospects

Cancer management has traditionally depended on chemotherapy as the mainstay of treatment; however, recent advancements in targeted therapies and immunotherapies have offered new options. Ubiquitin-specific proteases (USPs) have emerged as promising therapeutic targets in cancer treatment due to their crucial roles in regulating protein homeostasis and various essential cellular processes. This review covers the following: (1) the structural and functional characteristics of USPs, highlighting their involvement in key cancer-related pathways, and (2) the discovery, chemical structures, mechanisms of action, and potential clinical implications of USP inhibitors in cancer therapy. Particular attention is given to the role of USP inhibitors in enhancing cancer immunotherapy, e.g., modulation of the tumor microenvironment, effect on regulatory T cell function, and influence on immune checkpoint pathways. Furthermore, this review summarizes the current progress and challenges of clinical trials involving USP inhibitors as cancer therapy. We also discuss the complexities of achieving target selectivity, the ongoing efforts to develop more specific and potent USP inhibitors, and the potential of USP inhibitors to overcome drug resistance and synergize with existing cancer treatments. We finally provide a perspective on future directions in targeting USPs, including the potential for personalized medicine based on specific gene mutations, underscoring their significant potential for enhancing cancer treatment. By elucidating their mechanisms of action, clinical progress, and potential future applications, we hope that this review could serve as a useful resource for both basic scientists and clinicians in the field of cancer therapeutics.

Identification and evaluation of antiviral activity of novel compounds targeting SARS-CoV-2 virus by enzymatic and antiviral assays, and computational analysis

The viral genome of the SARS-CoV-2 coronavirus, the aetiologic agent of COVID-19, encodes structural, non-structural, and accessory proteins. Most of these components undergo rapid genetic variations, though to a lesser extent the essential viral proteases. Consequently, the protease and/or deubiquitinase activities of the cysteine proteases Mpro and PLpro became attractive targets for the design of antiviral agents. Here, we develop and evaluate new bis(benzylidene)cyclohexanones (BBC) and identify potential antiviral compounds. Three compounds were found to be effective in reducing the SARS-CoV-2 load, with EC50 values in the low micromolar concentration range. However, these compounds also exhibited inhibitory activity IC50 against PLpro at approximately 10-fold higher micromolar concentrations. Although originally developed as PLpro inhibitors, the comparison between IC50 and EC50 of BBC indicates that the mechanism of their in vitro antiviral activity is probably not directly related to inhibition of viral cysteine proteases. In conclusion, our study has identified new potential noncytotoxic antiviral compounds suitable for in vivo testing and further improvement.

(E)-2-Benzylidenecyclanones: Part XX-Reaction of Cyclic Chalcone Analogs with Cellular Thiols: Unexpected Increased Reactivity of 4-Chromanone- Compared to 1-Tetralone Analogs in Thia-Michael Reactions

In vitro relative cytotoxicity (IC50 (IIb)/IC50 (IIIb) of (E)-3-(4'-methylbenzylidene)-4-chromanone (IIIb) towards human Molt 4/C8 and CEM T-lymphocytes showed a >50-fold increase in comparison to those of the respective tetralone derivative (IIb). On the other hand, such an increase was not observed in the analogous 4-OCH3 (IIc and IIIc) derivatives. In order to study whether thiol reactivity-as a possible basis of the mechanism of action-correlates with the observed cytotoxicities, the kinetics of the non-enzyme catalyzed reactions with reduced glutathione (GSH) and N-acetylcysteine (NAC) of IIIb and IIIc were investigated. The reactivity of the compounds and the stereochemical outcome of the reactions were evaluated using high-pressure liquid chromatography-mass spectrometry (HPLC-MS). Molecular modeling calculations were performed to rationalize the unexpectedly higher thiol reactivity of the chromanones (III) compared to the carbocyclic analog tetralones (II). The results indicate the possible role of spontaneous thiol reactivity of compounds III in their recorded biological effects.

DUBs in Alzheimer's disease: mechanisms and therapeutic implications

Alzheimer's disease (AD) is a prevalent neurodegenerative disorder characterized by the accumulation of amyloid β protein (Aβ) and the hyper-phosphorylation of the microtubule-associated protein Tau. The ubiquitin-proteasome system (UPS) plays a pivotal role in determining the fate of proteins, and its dysregulation can contribute to the buildup of Aβ and Tau. Deubiquitinating enzymes (DUBs), working in conjunction with activating enzymes (E1), ubiquitin-conjugating enzymes (E2), and ubiquitin ligases (E3), actively maintain the delicate balance of protein homeostasis. DUBs specifically remove ubiquitin tags from proteins marked for degradation, thereby averting their proteasomal breakdown. Several DUBs have demonstrated their capacity to regulate the levels of Aβ and Tau by modulating their degree of ubiquitination, underscoring their potential as therapeutic targets for AD. In this context, we present a comprehensive review of AD-associated DUBs and elucidate their physiological roles. Moreover, we delve into the current advancements in developing inhibitors targeting these DUBs, including the determination of cocrystal structures with their respective targets. Additionally, we assess the therapeutic efficacy of these inhibitors in AD, aiming to establish a theoretical foundation for future AD treatments.

Unraveling the Mechanism of Action of Ubiquitin-Specific Protease 5 and Its Inhibitors in Tumors

Ubiquitin-specific protease 5 (USP5), a member of the ubiquitin-specific proteases (USPs) family, functions by specifically removing ubiquitin chains from target proteins for stabilization and degrading unbound polyubiquitin chains to maintain a steady-state monoubiquitin pool. Ubiquitin-specific protease 5 regulates various cellular activities, including DNA double-strand break repair, transmission of neuropathic and inflammatory pain signals, immune response, and tumor cell proliferation. Furthermore, USP5 is involved in the development of multiple tumors such as liver, lung, pancreatic, and breast cancers as well as melanoma. Downstream regulatory mechanisms associated with USP5 are complex and diverse. Ubiquitin-specific protease 5 has been revealed as an emerging target for tumor treatment. This study has introduced some molecules upstream to control the expression of USP5 at the levels of transcription, translation, and post-translation. Furthermore, the study incorporated inhibitors known to be associated with USP5, including partially selective deubiquitinase (DUB) inhibitors such as WP1130, EOAI3402143, vialinin A, and chalcone derivatives. It also included the ubiquitin-activating enzyme E1 inhibitor, PYR-41. These small molecule inhibitors impact the occurrence and development of various tumors. Therefore, this article comprehensively reviews the pivotal role of USP5 in different signaling pathways during tumor progression and resumes the progress made in developing USP5 inhibitors, providing a theoretical foundation for their clinical translation.

Structural basis for the bi-specificity of USP25 and USP28 inhibitors

The development of cancer therapeutics is often hindered by the fact that specific oncogenes cannot be directly pharmaceutically addressed. Targeting deubiquitylases that stabilize these oncogenes provides a promising alternative. USP28 and USP25 have been identified as such target deubiquitylases, and several small-molecule inhibitors indiscriminately inhibiting both enzymes have been developed. To obtain insights into their mode of inhibition, we structurally and functionally characterized USP28 in the presence of the three different inhibitors AZ1, Vismodegib and FT206. The compounds bind into a common pocket acting as a molecular sink. Our analysis provides an explanation why the two enzymes are inhibited with similar potency while other deubiquitylases are not affected. Furthermore, a key glutamate residue at position 366/373 in USP28/USP25 plays a central structural role for pocket stability and thereby for inhibition and activity. Obstructing the inhibitor-binding pocket by mutation of this glutamate may provide a tool to accelerate future drug development efforts for selective inhibitors of either USP28 or USP25 targeting distinct binding pockets.

Exploring the Role of Ubiquitin-Proteasome System in the Pathogenesis of Parkinson's Disease

Parkinson's disease (PD) is a prevalent neurodegenerative disorder among the elderly population. The pathogenesis of PD encompasses genetic alterations, environmental factors, and age-related neurodegenerative processes. Numerous studies have demonstrated that aberrant functioning of the ubiquitin-proteasome system (UPS) plays a crucial role in the initiation and progression of PD. Notably, E3 ubiquitin ligases serve as pivotal components determining substrate specificity within UPS and are intimately associated with the regulation of various proteins implicated in PD pathology. This review comprehensively summarizes the mechanisms by which E3 ubiquitin ligases and deubiquitinating enzymes modulate PD-associated proteins and signaling pathways, while exploring the intricate relationship between UPS dysfunctions and PD etiology. Furthermore, this article discusses recent research advancements regarding inhibitors targeting PD-related E3 ubiquitin ligases.

The effect of novel nitrogen-based chalcone analogs on colorectal cancer cells: Insight into the molecular pathways

In colorectal cancer (CRC), aberrations in KRAS are associated with aggressive tumorigenesis and an overall low survival rate because of chemoresistance and adverse effects. Ergo, complementary, and integrative medicines are being considered for CRC treatment. Among which is the use of natural chalcones that are known to exhibit anti-tumor activities in KRAS mutant CRC subtypes treatment regimens. Consequently, we examine the effect of two novel compounds (DK13 and DK14) having chalcones with nitrogen mustard moiety on CRC cell lines (HCT-116 and LoVo) with KRAS mutation. These compounds were synthesized in our lab and previously reported to exhibit potent activity against breast cancer cells. Our data revealed that DK13 and DK14 treatment suppress cell growth, disturb the progression of cell cycle, and trigger apoptosis in CRC cell lines. Besides, treatment with both compounds impedes cell invasion and colony formation in both cell lines as compared to 5-FU; this is accompanied by up and down regulations of E-cadherin and Vimentin, respectively. At the molecular level, both compounds deregulate the expression and phosphorylation of β-catenin, Akt and mTOR, which are the main likely molecular mechanisms underlying these biological occurrences. Our findings present DK13 and DK14 as novel chemotherapies against CRC, through β-catenin/Akt/mTOR signaling pathways.

USP5: Comprehensive insights into structure, function, biological and disease-related implications, and emerging therapeutic opportunities

Ubiquitin specific protease 5 (USP5) is a vital deubiquitinating enzyme that regulates various physiological functions by removing ubiquitin chains from target proteins. This review provides an overview of the structural and functional characteristics of USP5. Additionally, we discuss the role of USP5 in regulating diverse cellular processes, including cell proliferation, apoptosis, DNA double-strand damage, methylation, heat stress, and protein quality control, by targeting different substrates. Furthermore, we describe the involvement of USP5 in several pathological conditions such as tumors, pathological pain, developmental abnormalities, inflammatory diseases, and virus infection. Finally, we introduce newly developed inhibitors of USP5. In conclusion, investigating the novel functions and substrates of USP5, elucidating the underlying mechanisms of USP5-substrate interactions, intensifying the development of inhibitors, and exploring the upstream regulatory mechanisms of USP5 in detail can provide a new theoretical basis for the treatment of various diseases, including cancer, which is a promising research direction with considerable potential. Overall, USP5 plays a critical role in regulating various physiological and pathological processes, and investigating its novel functions and regulatory mechanisms may have significant implications for the development of therapeutic strategies for cancer and other diseases.

Clinical Spectrum of USP8 Pathogenic Variants in Cushing's Disease

Cushing's disease (CD) is a life-threatening condition with a challenging diagnostic process and scarce treatment options. CD is caused by usually benign adrenocorticotrophic hormone (ACTH)-secreting pituitary neuroendocrine tumors (PitNETs), known as corticotropinomas. These tumors are predominantly of sporadic origin, and usually derive from the monoclonal expansion of a mutated cell. Somatic activating variants located within a hotspot of the USP8 gene are present in 11-62% of corticotropinomas, making USP8 the most frequent genetic driver of corticotroph neoplasia. In contrast, other somatic defects such as those affecting the glucocorticoid receptor gene (NR3C1), the BRAF oncogene, the deubiquitinase-encoding gene USP48, and TP53 are infrequent. Moreover, patients with familial tumor syndromes, such as multiple endocrine neoplasia, familial isolated pituitary adenoma, and DICER1 rarely develop corticotropinomas. One of the main molecular alterations in USP8-driven tumors is an overactivation of the epidermal growth factor receptor (EGFR) signaling pathway, which induces ACTH production. Hotspot USP8 variants lead to persistent EGFR overexpression, thereby perpetuating the hyper-synthesis of ACTH. More importantly, they condition a characteristic transcriptomic signature that might be useful for the clinical prognosis of patients with CD. Nevertheless, the clinical phenotype associated with USP8 variants is less well defined. Hereby we discuss the current knowledge on the molecular pathogenesis and clinical picture associated with USP8 hotspot variants. We focus on the potential significance of the USP8 mutational status for the design of tailored clinical strategies in CD.

Functionalized Gold Nanoparticles Suppress the Proliferation of Human Lung Alveolar Adenocarcinoma Cells by Deubiquitinating Enzymes Inhibition

Functionalized gold nanoparticles (AuNPs) are widely used in therapeutic applications, but little is known regarding the impact of their surface functionalization in the process of toxicity against cancer cells. This study investigates the anticancer effects of 5 nm spherical AuNPs functionalized with tannate, citrate, and PVP on deubiquitinating enzymes (DUBs) in human lung alveolar adenocarcinoma (A549) cells. Our findings show that functionalized AuNPs reduce the cell viability in a concentration- and time-dependent manner as measured by modified lactate dehydrogenase (mLDH) and 3-[4,5-dimethylthiazole-2-yl]-2,5-diphenyltetrazolium bromide (MTT) assays. An increased generation of intracellular reactive oxygen species (ROS) and depletion of glutathione (GSH/GSSG) ratio was observed with the highest AuNP concentration of 10 μg/mL. The expression of DUBs such as ubiquitin specific proteases (USP7, USP8, and USP10) was slightly inhibited when treated with concentrations above 2.5 μg/mL. Moreover, functionalized AuNPs showed an inhibitory effect on protein kinase B/mammalian target of rapamycin (PI3K/AKT/mTOR) and wingless-related integration site (Wnt) signaling proteins, and this could further trigger mitochondrial related-apoptosis by the upregulation of caspase-3, caspase-9, and PARP in A549 cells. Furthermore, our study shows a mechanistic understanding of how functionalized AuNPs inhibit the DUBs, consequently suppressing cell proliferation, and can be modulated as an approach toward anticancer therapy. The study also warrants the need for future work to investigate the effect of functionalized AuNPs on DUB on other cancer cell lines both in vitro and in vivo.

Endogenous anti-tumorigenic nitro-fatty acids inhibit the ubiquitin-proteasome system by directly targeting the 26S proteasome

Nitro-fatty acids (NFAs) are endogenous lipid mediators causing a spectrum of anti-inflammatory effects by covalent modification of key proteins within inflammatory signaling pathways. Recent animal models of solid tumors have helped demonstrate their potential as anti-tumorigenic therapeutics. This study evaluated the anti-tumorigenic effects of NFAs in colon carcinoma cells and other solid and leukemic tumor cell lines. NFAs inhibited the ubiquitin-proteasome system (UPS) by directly targeting the 26S proteasome, leading to polyubiquitination and inhibition of the proteasome activities. UPS suppression induced the unfolded protein response, resulting in tumor cell death. The NFA-mediated effects were substantial, specific, and enduring, representing a unique mode of action for UPS suppression. This study provides mechanistic insights into the biological actions of NFAs as possible endogenous tumor-suppressive factors, indicating that NFAs might be key structures for designing a novel class of direct proteasome inhibitors.

Targeting the deubiquitinase USP2 for malignant tumor therapy (Review)

The ubiquitin‑proteasome system is a major degradation pathway for >80% of proteins in vivo. Deubiquitylases, which remove ubiquitinated tags to stabilize substrate proteins, are important components involved in regulating the degradation of ubiquitinated proteins. In addition, they serve multiple roles in tumor development by participating in physiological processes such as protein metabolism, cell cycle regulation, DNA damage repair and gene transcription. The present review systematically summarized the role of ubiquitin‑specific protease 2 (USP2) in malignant tumors and the specific molecular mechanisms underlying the involvement of USP2 in tumor‑associated pathways. USP2 reverses ubiquitin‑mediated degradation of proteins and is involved in aberrant proliferation, migration, invasion, apoptosis and drug resistance of tumors. Additionally, the present review summarized studies reporting on the use of USP2 as a therapeutic target for malignancies such as breast, liver, ovarian, colorectal, bladder and prostate cancers and glioblastoma and highlights the current status of pharmacological research on USP2. The clinical significance of USP2 as a therapeutic target for malignant tumors warrants further investigation.

Ubiquitin receptors play redundant roles in the proteasomal degradation of the p53 repressor MDM2

Much remains to be determined about the participation of ubiquitin receptors in proteasomal degradation and their potential as therapeutic targets. Suppression of the ubiquitin receptor S5A/PSMD4/hRpn10 alone stabilises p53/TP53 but not the key p53 repressor MDM2. Here, we observed S5A and the ubiquitin receptors ADRM1/PSMD16/hRpn13 and RAD23A and B functionally overlap in MDM2 degradation. We provide further evidence that degradation of only a subset of ubiquitinated proteins is sensitive to S5A knockdown because ubiquitin receptor redundancy is commonplace. p53 can be upregulated by S5A modulation while degradation of substrates with redundant receptors is maintained. Our observations and analysis of Cancer Dependency Map (DepMap) screens show S5A depletion/loss substantially reduces cancer cell line viability. This and selective S5A dependency of proteasomal substrates make S5A a target of interest for cancer therapy.

Deubiquitinase USP5 promotes non-small cell lung cancer cell proliferation by stabilizing cyclin D1

Background

Cyclin D1 (CCND1) is overexpressed in non-small cell lung cancer (NSCLC) and contributes to its tumorigenesis and progression. Accumulating evidence shows that ubiquitin-specific protease 5 (USP5), an important member of the USP family, acts as a tumor promoter by deubiquitinating and stabilizing oncoproteins. However, neither the mechanism for dysregulated turnover of CCND1 protein nor the association of CCND1 with USP5 in NSCLC is well understood.

Methods

The association of USP5 with CCND1 in human NSCLC cells and clinical tissues was determined by immunoprecipitation/immunoblotting, immunohistochemistry (IHC), and The Cancer Genome Atlas database analyses. The effect of USP5 knockdown or overexpression on NSCLC cell proliferation in vitro was assessed by Cell Counting Kit-8, flow cytometry-based cell cycle, and colony formation assays. The effect of the USP5 inhibitor EOAI3402143 (G9) on NSCLC proliferation in vitro was analyzed by CCK-8 assay. The effect of G9 on NSCLC xenograft tumor growth was also examined in vivo, using athymic BALB/c nude mice.

Results

USP5 physically bound to CCND1 and decreased its polyubiquitination level, thereby stabilizing CCND1 protein. This USP5-CCND1 axis promoted NSCLC cell proliferation and colony formation. Further, knockdown of USP5 led to CCND1 degradation and cell cycle arrest in NSCLC cells. Importantly, this tumor-suppressive effect elicited by USP5 knockdown in NSCLC cells was validated in vitro and in vivo through chemical inhibition of USP5 activity using G9. Consistently, G9 downregulated the protein levels of CCND1 in NSCLC cells and xenograft tumor tissues. Also, the expression level of USP5 was positively associated with the protein level of CCND1 in human clinical NSCLC tissues.

Conclusions

This study has provided the first evidence that CCND1 is a novel substrate of USP5. The USP5-CCND1 axis could be a potential target for the treatment of NSCLC.

USP5 Sustains the Proliferation of Glioblastoma Through Stabilization of CyclinD1

Glioblastoma multiforme (GBM) is one of the most malignant primary tumors in humans. Despite standard therapeutic strategy with tumor resection combined with radiochemotherapy, the prognosis remains disappointed. Recently, deubiquitinating enzymes (DUBs) has been reported as potential cancer therapy targets due to their multifunctions involved in the regulation of tumorigenesis, cell cycle, apoptosis, and autophagy. In this study, we found that knockdown of ubiquitin specific protease (USP5), a family member of DUB, could significantly suppress GBM cell line U251 and DBTRG-05MG proliferation and colony formation by inducing cell cycle G1/S arrest, which was correlated with downregulation of CyclinD1 protein level. CyclinD1 had been reported to play a critical role in the tumorigenesis and development of GBM via regulating cell cycle transition. Overexpression of USP5 could significantly extend the half-life of CyclinD1, while knockdown of USP5 decreased the protein level of CyclinD1, which could be restored by proteasome inhibitor MG-132. Indeed, USP5 was found to directly interact with CyclinD1, and decrease its K48-linked polyubiquitination level. Furthermore, knockdown of USP5 in U251 cells remarkably inhibited tumor growth in vivo. Taken together, these findings demonstrate that USP5 plays a critical role in tumorigenesis and progression of GBM by stabilizing CyclinD1 protein. Targeting USP5 could be a potential therapeutic strategy for GBM.

Novel Nitrogen-Based Chalcone Analogs Provoke Substantial Apoptosis in HER2-Positive Human Breast Cancer Cells via JNK and ERK1/ERK2 Signaling Pathways

Natural chalcones possess antitumor properties and play a role as inducers of apoptosis, antioxidants and cytotoxic compounds. We recently reported that novel nitrogen chalcone-based compounds, which were generated in our lab, have specific effects on triple-negative breast cancer cells. However, the outcome of these two new compounds on human epidermal growth factor receptor 2 (HER2)-positive breast cancer remains nascent. Thus, we herein investigated the effects of these compounds (DK-13 and DK-14) on two HER2-positive breast cancer cell lines, SKBR3 and ZR75. Our data revealed that these compounds inhibit cell proliferation, deregulate cell-cycle progression and significantly induce cell apoptosis in both cell lines. Furthermore, the two chalcone compounds cause a significant reduction in the cell invasion ability of SKBR3 and ZR75 cancer cells. In parallel, we found that DK-13 and DK-14 inhibit colony formation of both cell lines in comparison to their matched controls. On the other hand, we noticed that these two compounds can inhibit angiogenesis in the chorioallantoic membrane model. The molecular pathway analysis of chalcone compounds exposed cells revealed that these compounds inhibit the expression of both JNK1/2/3 and ERK1/2, the major plausible molecular pathways behind these events. Our findings implicate that DK-13 and DK-14 possess effective chemotherapeutic outcomes against HER2-positive breast cancer via the ERK1/2 and JNK1/2/3 signaling pathways.

Ubiquitin-Specific Proteases: Players in Cancer Cellular Processes

Ubiquitination represents a post-translational modification (PTM) essential for the maintenance of cellular homeostasis. Ubiquitination is involved in the regulation of protein function, localization and turnover through the attachment of a ubiquitin molecule(s) to a target protein. Ubiquitination can be reversed through the action of deubiquitinating enzymes (DUBs). The DUB enzymes have the ability to remove the mono- or poly-ubiquitination signals and are involved in the maturation, recycling, editing and rearrangement of ubiquitin(s). Ubiquitin-specific proteases (USPs) are the biggest family of DUBs, responsible for numerous cellular functions through interactions with different cellular targets. Over the past few years, several studies have focused on the role of USPs in carcinogenesis, which has led to an increasing development of therapies based on USP inhibitors. In this review, we intend to describe different cellular functions, such as the cell cycle, DNA damage repair, chromatin remodeling and several signaling pathways, in which USPs are involved in the development or progression of cancer. In addition, we describe existing therapies that target the inhibition of USPs.

Cellular functions regulated by deubiquitinating enzymes in neurodegenerative diseases

Neurodegenerative diseases are one of the most common diseases in mankind. Although there are reports of several candidates that cause neurodegenerative diseases, the exact mechanism of pathogenesis is poorly understood. The ubiquitin-proteasome system (UPS) is an important posttranslational modification for protein degradation and control of homeostasis. Enzymes such as E1, E2, E3 ligases, and deubiquitinating enzymes (DUBs) participating in UPS, regulate disease-inducing proteins by controlling the degree of ubiquitination. Therefore, the development of treatments targeting enzymes for degenerative diseases such as Alzheimer's disease (AD), Parkinson's disease (PD), Huntington's disease (HD), and amyotrophic lateral sclerosis (ALS), is emerging as an attractive perspective. In particular, as DUBs are able to regulate one or more degenerative disease-related proteins, the potential as a therapeutic target is even more evident. DUBs influence the regulation of toxic proteins that cause neurodegenerative diseases by not only their removal, but also by regulating signals associated with mitophagy, autophagy, and endoplasmic reticulum-associated degradation (ERAD). In this review, we analyze not only the cellular processes of DUBs, which control neurodegenerative disease-inducing proteins, but also their potentials as a therapeutic agent for neurodegenerative diseases.

Chalcones as Promising Antitumor Agents by Targeting the p53 Pathway: An Overview and New Insights in Drug-Likeness

The p53 protein is one of the most important tumor suppressors that are frequently inactivated in cancer cells. This inactivation occurs either because the TP53 gene is mutated or deleted, or due to the p53 protein inhibition by endogenous negative regulators, particularly murine double minute (MDM)2. Therefore, the reestablishment of p53 activity has received great attention concerning the discovery of new cancer therapeutics. Chalcones are naturally occurring compounds widely described as potential antitumor agents through several mechanisms, including those involving the p53 pathway. The inhibitory effect of these compounds in the interaction between p53 and MDM2 has also been recognized, with this effect associated with binding to a subsite of the p53 binding cleft of MDM2. In this work, a literature review of natural and synthetic chalcones and their analogues potentially interfering with p53 pathway is presented. Moreover, in silico studies of drug-likeness of chalcones recognized as p53-MDM2 interaction inhibitors were accomplished considering molecular descriptors, biophysiochemical properties, and pharmacokinetic parameters in comparison with those from p53-MDM2 in clinical trials. With this review, we expect to guide the design of new and more effective chalcones targeting the p53 pathway.

The Involvement of Ubiquitination Machinery in Cell Cycle Regulation and Cancer Progression

The cell cycle is a collection of events by which cellular components such as genetic materials and cytoplasmic components are accurately divided into two daughter cells. The cell cycle transition is primarily driven by the activation of cyclin-dependent kinases (CDKs), which activities are regulated by the ubiquitin-mediated proteolysis of key regulators such as cyclins, CDK inhibitors (CKIs), other kinases and phosphatases. Thus, the ubiquitin-proteasome system (UPS) plays a pivotal role in the regulation of the cell cycle progression via recognition, interaction, and ubiquitination or deubiquitination of key proteins. The illegitimate degradation of tumor suppressor or abnormally high accumulation of oncoproteins often results in deregulation of cell proliferation, genomic instability, and cancer occurrence. In this review, we demonstrate the diversity and complexity of the regulation of UPS machinery of the cell cycle. A profound understanding of the ubiquitination machinery will provide new insights into the regulation of the cell cycle transition, cancer treatment, and the development of anti-cancer drugs.

Advances in the Development Ubiquitin-Specific Peptidase (USP) Inhibitors

Ubiquitylation and deubiquitylation are reversible protein post-translational modification (PTM) processes involving the regulation of protein degradation under physiological conditions. Loss of balance in this regulatory system can lead to a wide range of diseases, such as cancer and inflammation. As the main members of the deubiquitinases (DUBs) family, ubiquitin-specific peptidases (USPs) are closely related to biological processes through a variety of molecular signaling pathways, including DNA damage repair, p53 and transforming growth factor-β (TGF-β) pathways. Over the past decade, increasing attention has been drawn to USPs as potential targets for the development of therapeutics across diverse therapeutic areas. In this review, we summarize the crucial roles of USPs in different signaling pathways and focus on advances in the development of USP inhibitors, as well as the methods of screening and identifying USP inhibitors.

Disulfiram and 6-Thioguanine synergistically inhibit the enzymatic activities of USP2 and USP21

Disulfiram is a promising repurposed drug that, combining with radiation and chemotherapy, exhibits effective anticancer activities in several preclinical models. The cellular metabolites of disulfiram have been established, however, the intracellular targets of disulfiram remain largely unexplored. We have previously reported that disulfiram suppresses the coronaviral papain-like proteases through attacking their zinc-finger domains, suggesting an inhibitory function potentially on other proteases with similar catalytic structures. Ubiquitin-specific proteases (USPs) share a highly-conserved zinc-finger subdomain that structurally similar to the papain-like proteases and are attractive anticancer targets as upregulated USPs levels are found in a variety of tumors. Here, we report that disulfiram functions as a competitive inhibitor for both USP2 and USP21, two tumor-related deubiquitinases. In addition, we also observed a synergistic inhibition of USP2 and USP21 by disulfiram and 6-Thioguanine (6TG), a clinical drug for acute myeloid leukemia. Kinetic analyses revealed that both drugs exhibited a slow-binding mechanism, moderate inhibitory parameters, and a synergistically inhibitory effect on USP2 and USP21, suggesting the potential combinatory use of these two drugs for USPs-related tumors. Taken together, our study provides biochemical evidence for repurposing disulfiram and 6TG as a combinatory treatment in clinical applications.

USP2-Related Cellular Signaling and Consequent Pathophysiological Outcomes

Ubiquitin specific protease (USP) 2 is a multifunctional deubiquitinating enzyme. USP2 modulates cell cycle progression, and therefore carcinogenesis, via the deubiquitination of cyclins and Aurora-A. Other tumorigenic molecules, including epidermal growth factor and fatty acid synthase, are also targets for USP2. USP2 additionally prevents p53 signaling. On the other hand, USP2 functions as a key component of the CLOCK/BMAL1 complex and participates in rhythmic gene expression in the suprachiasmatic nucleus and liver. USP2 variants influence energy metabolism by controlling hepatic gluconeogenesis, hepatic cholesterol uptake, adipose tissue inflammation, and subsequent systemic insulin sensitivity. USP2 also has the potential to promote surface expression of ion channels in renal and intestinal epithelial cells. In addition to modifying the production of cytokines in immune cells, USP2 also modulates the signaling molecules that are involved in cytokine signaling in the target cells. Usp2 knockout mice exhibit changes in locomotion and male fertility, which suggest roles for USP2 in the central nervous system and male genital tract, respectively. In this review, we summarize the cellular events with USP2 contributions and list the signaling molecules that are upstream or downstream of USP2. Additionally, we describe phenotypic differences found in the in vitro and in vivo experimental models.

Proteasomal dysfunction and ER stress triggers 2'-hydroxy-retrochalcone-induced paraptosis in cancer cells

Chalcones are biologically active class of compounds, known for their anticancer activities. Here we show for the first time that out of the six synthetic derivatives of chalcone tested, 2'-hydroxy-retrochalcone (HRC) was the most effective in inducing extensive cytoplasmic vacuolation mediated death called paraptosis in malignant breast and cervical cancer cells. The cell death by HRC is found to be nonapoptotic in nature due to the absence of DNA fragmentation, PARP cleavage, and phosphatidylserine externalization. It was also found to be nonautophagic as there was an increase in the levels of autophagic markers LC3I, LC3II and p62. Immunofluorescence with the endoplasmic reticulum (ER) marker protein calreticulin showed that the cytoplasmic vacuoles formed were derived from the ER. This ER dilation was due to ER stress as evidenced from the increase in polyubiquitinated proteins, Bip and CHOP. Docking studies revealed that HRC could bind to the Thr1 residue on the active site of the chymotrypsin-like subunit of the proteasome. The inhibition of proteasomal activity was further confirmed by the fluorescence based assay of the chymotrypsin-like subunit of the 26S proteasome. The cell death by HRC was also triggered by the collapse of mitochondrial membrane potential and depletion of ATP. Pretreatment with thiol antioxidants and cycloheximide were able to inhibit this programmed cell death. Thus our data suggest that HRC can effectively kill cancer cells via paraptosis, an alternative death pathway and can be a potential lead molecule for anticancer therapy.

Chalcone Methoxy Derivatives Exhibit Antiproliferative and Proapoptotic Activity on Canine Lymphoma and Leukemia Cells

Chalcones are interesting candidates for anti-cancer drugs due to the ease of their synthesis and their extensive biological activity. The study presents antitumor activity of newly synthesized chalcone analogues with a methoxy group on a panel of canine lymphoma and leukemia cell lines. The antiproliferative effect of the 2'-hydroxychalcone and its methoxylated derivatives was evaluated in MTT assay after 48 h of treatment in different concentrations. The proapoptotic activity was studied by cytometric analysis of cells stained with Annexin V/FITC and propidium iodide and by measure caspases 3/7 and 8 activation. The DNA damage was evaluated by Western blot analysis of phosphorylated histone H2AX. The new compounds had selective antiproliferative activity against the studied cell lines, the most effective were the 2'-hydroxy-2″,5″-dimethoxychalcone and 2'-hydroxy-4',6'-dimethoxychalcone. 2'-Hydroxychalcone and the two most active derivatives induced apoptosis and caspases participation, but some percentage of necrotic cells was also observed. Comparing phosphatidylserine externalization after treatment with the different compounds it was noted that the addition of two methoxy groups increased the proapoptotic potential. The most active compounds triggered DNA damage even in the cell lines resistant to chalcone-induced apoptosis. The results confirmed that the analogues could have anticancer potential in the treatment of canine lymphoma or leukemia.

Targeting homologous recombination (HR) repair mechanism for cancer treatment: discovery of new potential UCHL-3 inhibitors via virtual screening, molecular dynamics and binding mode analysis

UCHL3 (ubiquitin C-terminal hydrolase-L3) is a de-ubiquitinating enzyme involved in the homologous recombination repair mechanism of double-strand breaks (DBS) of the DNA. Multiple studies indicated that UCHL3 inhibitors could be used in combination therapy with high therapeutic efficacy against cancer thus highlighting the validity of directing research against UCHL3 as a druggable target in oncology. In this study, a combination of virtual screening methods was utilized to identify new potential UCHL3 inhibitors. A series of UCHL3 ligands were identified by applying a combination of cheminformatics and molecular modeling filtration techniques to a ChemBl database of over two million small molecules viz. Lipinski's Rule of Five, Veber's rule, pharmacophore model, Hierarchical molecular docking, Pan-assay Interference Compounds (PAINS) alerts, toxicity filter, and single-point Molecular mechanics Poisson/Boltzmann surface area (MM/PBSA) docking pose rescoring. This multi-layer filtration strategy led to the identification of twenty-one compounds as potential UCHL3 inhibitors that were subsequently subjected to a 50 ns molecular dynamics (MD) simulations predict the stability of their ligand-protein complexes. Furthermore, MM/PBSA calculations based on MD trajectories were performed, and the energy contribution per residue to the binding energy was calculated. Three compounds, 1, 2 and 3, were finally recognized as having the highest potential of being UCHL3 inhibitors. Therefore, those were used for binding mode analysis to the UCHL3 active site, leading to identification of four residues as key for binding viz. Pro8, Leu55, Val166, and Leu168.Communicated by Ramaswamy H. Sarma.

Deubiquitinating Enzyme: A Potential Secondary Checkpoint of Cancer Immunity

The efficacy of cancer immunotherapy depends on the fine interplay between tumoral immune checkpoints and host immune system. However, the up-to-date clinical performance of checkpoint blockers in cancer therapy revealed that higher-level regulation should be further investigated for better therapeutic outcomes. It is becoming increasingly evident that the expression of immune checkpoints is largely associated to the immunotherapeutic response and consequent prognosis. Deubiquitinating enzymes (DUBs) with their role of cleaving ubiquitin from proteins and other molecules, thus reversing ubiquitination-mediated protein degradation, modulate multiple cellular processes, including, but not limited to, transcriptional regulation, cell cycle progression, tissue development, and antiviral response. Accumulating evidence indicates that DUBs also have the critical influence on anticancer immunity, simply by stabilizing pivotal checkpoints or key regulators of T-cell functions. Therefore, this review summarizes the current knowledge about DUBs, highlights the secondary checkpoint-like role of DUBs in cancer immunity, in particular their direct effects on the stability control of pivotal checkpoints and key regulators of T-cell functions, and suggests the therapeutic potential of DUBs-based strategy in targeted immunotherapy for cancer.

Advances in Deubiquitinating Enzyme Inhibition and Applications in Cancer Therapeutics

Since the discovery of the ubiquitin proteasome system (UPS), the roles of ubiquitinating and deubiquitinating enzymes (DUBs) have been widely elucidated. The ubiquitination of proteins regulates many aspects of cellular functions such as protein degradation and localization, and also modifies protein-protein interactions. DUBs cleave the attached ubiquitin moieties from substrates and thereby reverse the process of ubiquitination. The dysregulation of these two paramount pathways has been implicated in numerous diseases, including cancer. Attempts are being made to identify inhibitors of ubiquitin E3 ligases and DUBs that potentially have clinical implications in cancer, making them an important target in the pharmaceutical industry. Therefore, studies in medicine are currently focused on the pharmacological disruption of DUB activity as a rationale to specifically target cancer-causing protein aberrations. Here, we briefly discuss the pathophysiological and physiological roles of DUBs in key cancer-related pathways. We also discuss the clinical applications of promising DUB inhibitors that may contribute to the development of DUBs as key therapeutic targets in the future.

Drug Development Targeting the Ubiquitin-Proteasome System (UPS) for the Treatment of Human Cancers

Cancer cells are characterized by a higher rate of protein turnover and greater demand for protein homeostasis compared to normal cells. In this scenario, the ubiquitin-proteasome system (UPS), which is responsible for the degradation of over 80% of cellular proteins within mammalian cells, becomes vital to cancer cells, making the UPS a critical target for the discovery of novel cancer therapeutics. This review systematically categorizes all current reported small molecule inhibitors of the various essential components of the UPS, including ubiquitin-activating enzymes (E1s), ubiquitin-conjugating enzymes (E2s), ubiquitin ligases (E3s), the 20S proteasome catalytic core particle (20S CP) and the 19S proteasome regulatory particles (19S RP), as well as their mechanism/s of action and limitations. We also discuss the immunoproteasome which is considered as a prospective therapeutic target of the next generation of proteasome inhibitors in cancer therapies.

Role of Deubiquitinases in Human Cancers: Potential Targeted Therapy

Deubiquitinases (DUBs) are involved in various cellular functions. They deconjugate ubiquitin (UBQ) from ubiquitylated substrates to regulate their activity and stability. Studies on the roles of deubiquitylation have been conducted in various cancers to identify the carcinogenic roles of DUBs. In this review, we evaluate the biological roles of DUBs in cancer, including proliferation, cell cycle control, apoptosis, the DNA damage response, tumor suppression, oncogenesis, and metastasis. This review mainly focuses on the regulation of different downstream effectors and pathways via biochemical regulation and posttranslational modifications. We summarize the relationship between DUBs and human cancers and discuss the potential of DUBs as therapeutic targets for cancer treatment. This review also provides basic knowledge of DUBs in the development of cancers and highlights the importance of DUBs in cancer biology.

Effects of selected deubiquitinating enzyme inhibitors on the proliferation and motility of lung cancer and mesothelioma cell lines

The post‑translational modification of proteins by ubiquitinating enzymes plays a central role in a number of cellular functions, such as cell proteolysis, DNA repair, and cell signaling and communication. Deubiquitinating enzymes (DUBs) disassemble ubiquitin chains and remove ubiquitin moieties from proteins. Targeting DUBs in cancer models has revealed an important role for these enzymes in tumorigenesis, and they therefore have emerged as attractive therapeutic targets. In the present study, the effects of three DUB inhibitors, PR‑619, RA‑9 and LDN‑91946, on a non‑small cell lung cancer cell line (A549) and a mesothelioma cell line (H2373) were investigated. PR‑619 significantly inhibited cell adhesion and the proliferation of both cell lines. RA‑9 exerted an inhibitory effect on the adhesion and proliferation of H2373 cells, whereas it had no effect on A549 cells. Notably, however, while PR‑619 attenuated the proliferation of both cell lines, it exerted an opposite effect on cell motility; in the case of A549 cells, there was a significant increase in cell motility, while for the H2373 cells, there was a significant decrease. Furthermore, protein phosphorylation kinetic analyses revealed that the effects were cell line‑specific. In H2373 cells, the phosphorylation of only one peptide corresponding to the P85A protein was significantly affected, and while LDN‑91946 treatment increased phosphorylation, treatment with RA‑9 or PR‑619 decreased its phosphorylation compared to the DMSO control. By contrast, in the case of A549 cells, the phosphorylation of 21 peptides was significantly affected by the same compounds. In light of the potential for the negative side‑effects of DUB inhibition, such as increased cancer cell motility, the data presented herein underscore the dire need for the development of specific DUB inhibitors and to elucidate the individual role of DUB family members in cancer biology before they can be specifically pharmacologically targeted.

Re-Evaluating the Mechanism of Action of α,β-Unsaturated Carbonyl DUB Inhibitors b-AP15 and VLX1570: A Paradigmatic Example of Unspecific Protein Cross-linking with Michael Acceptor Motif-Containing Drugs

Deubiquitinating enzymes (DUBs) are a growing target class across multiple disease states, with several inhibitors now reported. b-AP15 and VLX1570 are two structurally related USP14/UCH-37 inhibitors. Through a proteomic approach, we demonstrate that these compounds target a diverse range of proteins, resulting in the formation of higher molecular weight (MW) complexes. Activity-based proteome profiling identified CIAPIN1 as a submicromolar covalent target of VLX1570, and further analysis demonstrated that high MW complex formation leads to aggregation of CIAPIN1 in intact cells. Our results suggest that in addition to DUB inhibition, these compounds induce nonspecific protein aggregation, providing molecular explanation for general cellular toxicity.

Repurposing old drugs as new inhibitors of the ubiquitin-proteasome pathway for cancer treatment

The ubiquitin-proteasome system (UPS) plays a central role in the degradation of cellular proteins. Targeting protein degradation has been validated as an effective strategy for cancer therapy since 2003. Several components of the UPS have been validated as potential anticancer targets, including 20S proteasomes, 19S proteasome-associated deubiquitinases (DUBs) and ubiquitin ligases (E3s). 20S proteasome inhibitors (such as bortezomib/BTZ and carfilzomib/CFZ) have been approved by the U.S. Food and Drug Administration (FDA) for the treatment of multiple myeloma (MM) and some other liquid tumors. Although survival of MM patients has been improved by the introduction of BTZ-based therapies, these clinical 20S proteasome inhibitors have several limitations, including emergence of resistance in MM patients, neuro-toxicities, and little efficacy in solid tumors. One of strategies to improve the current status of cancer treatment is to repurpose old drugs with UPS-inhibitory properties as new anticancer agents. Old drug reposition represents an attractive drug discovery approach compared to the traditional de novo drug discovery process which is time-consuming and costly. In this review, we summarize status of repurposed inhibitors of various UPS components, including 20S proteasomes, 19S-associated DUBs, and ubiquitin ligase E3s. The original and new mechanisms of action, molecular targets, and potential anticancer activities of these repurposed UPS inhibitors are reviewed, and their new uses including combinational therapies for cancer treatment are discussed.

The role of ubiquitin-specific peptidases in cancer progression

Protein ubiquitination is an important mechanism for regulating the activity and levels of proteins under physiological conditions. Loss of regulation by protein ubiquitination leads to various diseases, such as cancer. Two types of enzymes, namely, E1/E2/E3 ligases and deubiquitinases, are responsible for controlling protein ubiquitination. The ubiquitin-specific peptidases (USPs) are the main members of the deubiquitinase family. Many studies have addressed the roles of USPs in various diseases. An increasing number of studies have indicated that USPs are critical for cancer progression, and some USPs have been used as targets to develop inhibitors for cancer prevention. Herein we collect and organize most of the recent studies on the roles of USPs in cancer progression and discuss the development of USP inhibitors for cancer therapy in the future.

Halogen Substituents in the Isoquinoline Scaffold Switches the Selectivity of Inhibition between USP2 and USP7

Deubiquitinases are important components of the protein regulatory network and, hence, constitute a tempting drug target. We report herein structure-activity relationship studies to develop halogen-substituted isoquionoline-1,3-dione-based inhibitors of the deubiquitinase USP2. In contrast to our previous reports, the best compound discovered was found to act through a reactive oxygen species independent, uncompetitive mechanism with an IC₅₀ of 250 nm. We show the crucial role of halogens in the common scaffold to provide potency and selectivity of our compound, where the introduction of the fluorine atom completely switches the selectivity of the inhibitor between USP2 and USP7. Our cellular studies highlight the potential applicability of the reported compound for in vivo experiments. The discovery of the isoquinoline-1,3-dione core and the knowledge obtained with regard to halogen substituents provide a platform towards understanding USP2 inhibition and the development of highly selective next-generation deubiquitinase inhibitors.

Discovering proteasomal deubiquitinating enzyme inhibitors for cancer therapy: lessons from rational design, nature and old drug reposition

The ubiquitin proteasome system has been validated as a target of cancer therapies evident by the US FDA approval of anticancer 20S proteasome inhibitors. Deubiquitinating enzymes (DUBs), an essential component of the ubiquitin proteasome system, regulate cellular processes through the removal of ubiquitin from ubiquitinated-tagged proteins. The deubiquitination process has been linked with cancer and other pathologies. As such, the study of proteasomal DUBs and their inhibitors has garnered interest as a novel strategy to improve current cancer therapies, especially for cancers resistant to 20S proteasome inhibitors. This article reviews proteasomal DUB inhibitors in the context of: discovery through rational design approach, discovery from searching natural products and discovery from repurposing old drugs, and offers a future perspective.

Metal-based proteasomal deubiquitinase inhibitors as potential anticancer agents

Deubiquitinases (DUBs) play an important role in protein quality control in eukaryotic cells due to their ability to specifically remove ubiquitin from substrate proteins. Therefore, recent findings have focused on the relevance of DUBs to cancer development, and pharmacological intervention on these enzymes has become a promising strategy for cancer therapy. In particular, several DUBs are physically and/or functionally associated with the proteasome and are attractive targets for the development of novel anticancer drugs. The successful clinical application of cisplatin in cancer treatment has prompted researchers to develop various metal-based anticancer agents with new properties. Recently, we have reported that several metal-based drugs, such as the antirheumatic gold agent auranofin (AF), the antifouling paint biocides copper pyrithione (CuPT) and zinc pyrithione (ZnPT), and also our two synthesized complexes platinum pyrithione (PtPT) and nickel pyrithione (NiPT), can target the proteasomal DUBs UCHL5 and USP14. In this review, we summarize the recently reported small molecule inhibitors of proteasomal DUBs, with a focus on discussion of the unique nature of metal-based proteasomal DUB inhibitors and their anticancer activity.

USP8 Mutations in Pituitary Cushing Adenomas-Targeted Analysis by Next-Generation Sequencing

Gain-of-function somatic mutations in the ubiquitin specific protease 8 (USP8) gene have recently been reported as a cause of pituitary adenomas in Cushing disease. Molecular diagnostic testing of tumor tissue may aid in the diagnosis of specimens obtained through therapeutic transsphenoidal surgery; however, for small tumors, availability of fresh tissue is limited, and contamination with normal tissue is frequent. We performed molecular testing of DNA isolated from single formalin-fixed and paraffin-embedded (FFPE) tissue sections of 42 pituitary adenomas from patients with Cushing disease (27 female patients and 15 male patients; mean age at surgery, 42.5 years; mean tumor size, 12.2 mm). By Sanger sequencing, we identified previously reported USP8 missense mutations in six tumors. Targeted next-generation sequencing (NGS) revealed known or previously undescribed missense mutations in three additional tumors (two with two different mutations each), with mutant allele frequencies as low as 3%. Of the nine tumors with USP8 mutations (mutation frequency, 21.4%), seven were from female patients (mutation frequency, 25.9%), and two were from male patients (mutation frequency, 13.3%). Mutant tumors were on average 11.4 mm in size, and patients with mutations were on average 43.9 years of age. The overall USP8 mutation frequency in our cohort was lower than in previously described cohorts, and we did not observe USP8 deletions that were frequent in other cohorts. We demonstrate that testing for USP8 variants can be performed from small amounts of FFPE tissue. NGS showed higher sensitivity for USP8 mutation detection than did Sanger sequencing. Assessment for USP8 mutations may complement histopathological diagnosis.

6-Thioguanine is a noncompetitive and slow binding inhibitor of human deubiquitinating protease USP2

Ubiquitin-specific protease 2 (USP2) belongs to the family of deubiquitinases that can rescue protein targets from proteasomal degradation by reversing their ubiquitination. In various cancers, including prostate cancer and ovarian carcinoma, upregulation of USP2 leads to an increase in the levels of deubiquitinated substrates such as fatty acid synthase, MDM2, cyclin D1 and Aurora-A. USP2 thus plays a critical role in tumor cells’ survival and therefore represents a therapeutic target. Here a leukemia drug, 6-thioguanine, was found to be a potent inhibitor of USP2. Enzyme-kinetic and X-ray crystallographic data suggest that 6-thioguanine displays a noncompetitive and slow-binding inhibitory mechanism against USP2. Our study provides a clear rationale for the clinical evaluation of 6-thioguanine for USP2-upregulated cancers.

The binding landscape of a partially-selective isopeptidase inhibitor with potent pro-death activity, based on the bis(arylidene)cyclohexanone scaffold

Diaryldienone derivatives with accessible β-carbons show strong anti-neoplastic properties, related to their ability to make covalent adducts with free thiols by Michael addition, and low toxicity in vivo. Accumulation of poly-ubiquitylated proteins, activation of the unfolded protein response (UPR) and induction of cell death are universal hallmarks of their activities. These compounds have been characterized as inhibitors of isopeptidases, a family of cysteine-proteases, which de-conjugate ubiquitin and ubiquitin-like proteins from their targets. However, it is unclear whether they can also react with additional proteins. In this work, we utilized the biotin-conjugated diaryldienone-derivative named 2c, as a bait to purify novel cellular targets of these small molecules. Proteomic analyses have unveiled that, in addition to isopeptidases, these inhibitors can form stable covalent adducts with different intracellular proteins, thus potentially impacting on multiple functions of the cells, from cytoskeletal organization to metabolism. These widespread activities can explain the ability of diaryldienone derivatives to efficiently trigger different cell death pathways.

The roles of ubiquitin modifying enzymes in neoplastic disease

The initial experiments performed by Rose, Hershko, and Ciechanover describing the identification of a specific degradation signal in short-lived proteins paved the way to the discovery of the ubiquitin mediated regulation of numerous physiological functions required for cellular homeostasis. Since their discovery of ubiquitin and ubiquitin function over 30years ago it has become wholly apparent that ubiquitin and their respective ubiquitin modifying enzymes are key players in tumorigenesis. The human genome encodes approximately 600 putative E3 ligases and 80 deubiquitinating enzymes and in the majority of cases these enzymes exhibit specificity in sustaining either pro-tumorigenic or tumour repressive responses. In this review, we highlight the known oncogenic and tumour suppressive effects of ubiquitin modifying enzymes in cancer relevant pathways with specific focus on PI3K, MAPK, TGFβ, WNT, and YAP pathways. Moreover, we discuss the capacity of targeting DUBs as a novel anticancer therapeutic strategy.

Emerging role of DUBs in tumor metastasis and apoptosis: Therapeutic implication

Malfunction of ubiquitin-proteasome system is tightly linked to tumor formation and tumor metastasis. Targeting the ubiquitin-pathway provides a new strategy for anti-cancer therapy. Despite the parts played by ubiquitin modifiers, removal of ubiquitin from the functional proteins by the deubiquitinating enzymes (DUBs) plays an important role in governing the multiple steps of the metastatic cascade, including local invasion, dissemination, and eventual colonization of the tumor to distant organs. Both deregulated ubiquitination and deubiquitination could lead to dysregulation of various critical events and pathways such as apoptosis and epithelial-mesenchymal transition (EMT). Recent TCGA study has further revealed the connection between mutations of DUBs and various types of tumors. In addition, emerging drug design targeting DUBs provides a new strategy for anti-cancer therapy. In this review, we will summarize the role of deubiquitination and highlight the recent discoveries of DUBs with regards to multiple metastatic events including anti-apoptosis pathway and EMT. We will further discuss the regulation of deubiquitination as a novel strategy for anti-cancer therapy.

Methoxyphenyl chalcone sensitizes aggressive epithelial cancer to cisplatin through apoptosis induction and cancer stem cell eradication

Current standard chemotherapy for late stage ovarian cancer is found unsuccessful due to relapse after completing the regimens. After completing platinum-based chemotherapy, 70% of patients develop relapse and resistance. Recent evidence proves ovarian cancer stem cells as the source of resistance. Therefore, treatment strategy to target both cancer stem cells and normal stem cells is essential. In this study, we developed a novel chalcone derivative as novel drug candidate for ovarian cancer treatment. We found that methoxyphenyl chalcone was effective to eliminate ovarian cancer cells when given either as monotherapy or in combination with cisplatin. We found that cell viability of ovarian cancer cells was decreased through apoptosis induction. Dephosphorylation of Bcl2-associated agonist of cell death protein was increased after methoxyphenyl chalcone treatment that led to activation of caspases. Interestingly, this drug also worked as a G2/M checkpoint modulator with alternative ways of DNA damage signal-evoking potential that might work to increase response after cisplatin treatment. In addition, methoxyphenyl chalcone was able to suppress autophagic flux and stemness regulator in ovarian spheroids that decreased their survival. Therefore, combination of methoxyphenyl chalcone and cisplatin showed synergistic effects. Taken together, we believe that our novel compound is a promising novel therapeutic agent for effective clinical treatment of ovarian cancer.

Lithocholic Acid Hydroxyamide Destabilizes Cyclin D1 and Induces G0/G1 Arrest by Inhibiting Deubiquitinase USP2a

USP2a is a deubiquitinase responsible for stabilization of cyclin D1, a crucial regulator of cell-cycle progression and a proto-oncoprotein overexpressed in numerous cancer types. Here we report that lithocholic acid (LCA) derivatives are inhibitors of USP proteins, including USP2a. The most potent LCA derivative, LCA hydroxyamide (LCAHA), inhibits USP2a, leading to a significant Akt/GSK3β-independent destabilization of cyclin D1, but does not change the expression of p27. This leads to the defects in cell-cycle progression. As a result, LCAHA inhibits the growth of cyclin D1-expressing, but not cyclin D1-negative cells, independently of the p53 status. We show that LCA derivatives may be considered as future therapeutics for the treatment of cyclin D1-addicted p53-expressing and p53-defective cancer types.

The emerging role of deubiquitinating enzymes in genomic integrity, diseases, and therapeutics

The addition of mono-ubiquitin or poly-ubiquitin chain to signaling proteins in response to DNA damage signal is thought to be a critical event that facilitates the recognition of DNA damage lesion site, the activation of checkpoint function, termination and checkpoint response and the recruitment of DNA repair proteins. Despite the ubiquitin modifiers, removal of ubiquitin from the functional proteins by the deubiquitinating enzymes (DUBs) plays an important role in orchestrating DNA damage response as well as DNA repair processes. Deregulated ubiquitination and deubiquitination could lead to genome instability that in turn causes tumorigenesis. Recent TCGA study has further revealed the connection between mutations in alteration of DUBs and various types of tumors. In addition, emerging drug design based on DUBs provides a new avenue for anti-cancer therapy. In this review, we will summarize the role of deubiquitination and specificity of DUBs, and highlight the recent discoveries of DUBs in the modulation of ubiquitin-mediated DNA damage response and DNA damage repair. We will furthermore discuss the DUBs involved in the tumorigenesis as well as interception of deubiquitination as a novel strategy for anti-cancer therapy.

Targeting Deubiquitinating Enzymes in Glioblastoma Multiforme: Expectations and Challenges

Glioblastoma (GBM) is regarded as the most common primary intracranial neoplasm. Despite standard treatment with tumor resection and radiochemotherapy, the outcome remains gloomy. It is evident that a combination of oncogenic gain of function and tumor-suppressive loss of function has been attributed to glioma initiation and progression. The ubiquitin-proteasome system is a well-orchestrated system that controls the fate of most proteins by striking a dynamic balance between ubiquitination and deubiquitination of substrates, having a profound influence on the modulation of oncoproteins, tumor suppressors, and cellular signaling pathways. In recent years, deubiquitinating enzymes (DUBs) have emerged as potential anti-cancer targets due to their targeting several key proteins involved in the regulation of tumorigenesis, apoptosis, senescence, and autophagy. This review attempts to summarize recent studies of GBM-associated DUBs, their roles in various cellular processes, and discuss the relation between DUBs deregulation and gliomagenesis, especially how DUBs regulate glioma stem cells pluripotency, microenvironment, and resistance of radiation and chemotherapy through core stem-cell transcriptional factors. We also review recent achievements and progress in the development of potent and selective reversible inhibitors of DUBs, and attempted to find a potential GBM treatment by DUBs intervention.

Small Molecule Inhibition of the Ubiquitin-specific Protease USP2 Accelerates cyclin D1 Degradation and Leads to Cell Cycle Arrest in Colorectal Cancer and Mantle Cell Lymphoma Models

Deubiquitinases are important components of the protein degradation regulatory network. We report the discovery of ML364, a small molecule inhibitor of the deubiquitinase USP2 and its use to interrogate the biology of USP2 and its putative substrate cyclin D1. ML364 has an IC₅₀ of 1.1 μm in a biochemical assay using an internally quenched fluorescent di-ubiquitin substrate. Direct binding of ML364 to USP2 was demonstrated using microscale thermophoresis. ML364 induced an increase in cellular cyclin D1 degradation and caused cell cycle arrest as shown in Western blottings and flow cytometry assays utilizing both Mino and HCT116 cancer cell lines. ML364, and not the inactive analog 2, was antiproliferative in cancer cell lines. Consistent with the role of cyclin D1 in DNA damage response, ML364 also caused a decrease in homologous recombination-mediated DNA repair. These effects by a small molecule inhibitor support a key role for USP2 as a regulator of cell cycle, DNA repair, and tumor cell growth.

Gene Expression Analysis Reveals the Concurrent Activation of Proapoptotic and Antioxidant-Defensive Mechanisms in Flavokawain B-Treated Cervical Cancer HeLa Cells

Flavokawain B (FKB) is known to possess promising anticancer abilities. This is demonstrated in various cancer cell lines including HeLa cells. Cervical cancer is among the most widely diagnosed cancer among women today. Though FKB has been shown to be effective in treating cancer cells, the exact molecular mechanism is still unknown. This study is aimed at understanding the effects of FKB on HeLa cells using a microarray-based mRNA expression profiling and proteome profiling of stress-related proteins. The results of this study suggest that FKB induced cell death through p21-mediated cell cycle arrest and activation of p38. However, concurrent activation of antioxidant-related pathways and iron sequestration pathway followed by activation of ER-resident stress proteins clearly indicate that FKB failed to induce apoptosis in HeLa cells via oxidative stress. This effect implies that the protection of HeLa cells by FKB from H₂O₂–induced cell death is via neutralization of reactive oxygen species.