Apoptosis induction resulting from proteasome inhibition

Acetylene containing 2-(2-hydrazinyl)thiazole derivatives: design, synthesis, and in vitro and in silico evaluation of antimycobacterial activity against Mycobacterium tuberculosis

Mycobacterium tuberculosis resistance to commercially available drugs is increasing day by day. To address this issue, various strategies were planned and are being implemented. However, there is a need for new drugs and rapid diagnostic methods. For this endeavour, in this paper, we present the synthesis of acetylene containing 2-(2-hydrazinyl) thiazole derivatives and in vitro evaluation against the H37Rv strain of Mycobacterium tuberculosis. Among the developed 26 acetylene containing 2-(2-hydrazinyl) thiazole derivatives, eight compounds inhibited the growth of Mycobacterium tuberculosis with MIC values ranging from 100 μg ml-1 to 50 μg ml-1. The parent acetylene containing thiosemicarbazones showed promising antimycobacterial activity by inhibiting up to 75% of the Mycobacterium at 50 μg ml-1. In addition, in silico studies were employed to understand the binding mode of all the novel acetylene-containing derivatives against the KasA protein of the Mycobacterium. Interestingly, the KasA protein interactions with the compounds were similar to the interactions of KasA protein with thiolactomycin and rifampicin. Cytotoxicity study results indicate that the compounds tested are non-toxic to human embryonic kidney cells.

Novel versatile europium and terbium complexes as bioprobes and anticancer agents

Focusing on the pertinent research on dual activity (as probes and cancer inhibitors), two novel Eu and Tb lanthanide complexes were prepared in this work alongside their binuclear counterparts holding Cu as the secondary metal.

Mangifera indica (Mango): A Promising Medicinal Plant for Breast Cancer Therapy and Understanding Its Potential Mechanisms of Action

Globally, breast cancer is the most common cancer type and is one of the most significant causes of deaths in women. To date, multiple clinical interventions have been applied, including surgical resection, radiotherapy, endocrine therapy, targeted therapy and chemotherapy. However, 1) the lack of therapeutic options for metastatic breast cancer, 2) resistance to drug therapy and 3) the lack of more selective therapy for triple-negative breast cancer are some of the major challenges in tackling breast cancer. Given the safe nature of natural products, numerous studies have focused on their anti-cancer potentials. Mangifera indica, commonly known as mango, represents one of the most extensively investigated natural sources. In this review, we provide a comprehensive overview of M. indica extracts (bark, kernel, leaves, peel and pulp) and phytochemicals (mangiferin, norathyriol, gallotannins, gallic acid, pyrogallol, methyl gallate and quercetin) reported for in vitro and in vivo anti-breast cancer activities and their underlying mechanisms based on relevant literature from several scientific databases, including PubMed, Scopus and Google Scholar till date. Overall, the in vitro findings suggest that M. indica extracts and/or phytochemicals inhibit breast cancer cell growth, proliferation, migration and invasion as well as trigger apoptosis and cell cycle arrest. In vivo results demonstrated that there was a reduction in breast tumor xenograft growth. Several potential mechanisms underlying the anti-breast cancer activities have been reported, which include modulation of oxidative status, receptors, signalling pathways, miRNA expression, enzymes and cell cycle regulators. To further explore this medicinal plant against breast cancer, future research directions are addressed. The outcomes of the review revealed that M. indica extracts and their phytochemicals may have potential benefits in the management of breast cancer in women. However, to validate its utility in the creation of innovative and potent therapeutic agents to treat breast cancer, more dedicated research, especially clinical studies are needed to explore the anti-breast cancer potentials of M. indica extracts and their phytochemicals.

Natural product scaffolds as inspiration for the design and synthesis of 20S human proteasome inhibitors

The 20S proteasome is a valuable target for the treatment of a number of diseases including cancer, neurodegenerative disease, and parasitic infection. In an effort to discover novel inhibitors of the 20S proteasome, many reseaarchers have looked to natural products as potential leads for drug discovery. The following review discusses the efforts made in the field to isolate and identify natural products as inhibitors of the proteasome. In addition, we describe some of the modifications made to natural products in order to discover more potent and selective inhibitors for potential disease treatment.

Proteasome inhibition for the treatment of glioblastoma

INTRODUCTION

Glioblastoma is a primary brain tumor with a poor prognosis despite multimodal therapy including surgery, radiotherapy and alkylating chemotherapy. Novel therapeutic options are therefore urgently needed; however, there have been various drug failures in late-stage clinical development. The proteasome represents a key target for anti-cancer therapy as successfully shown in multiple myeloma and other hematologic malignancies.

AREAS COVERED

This review article summarizes the preclinical and clinical development of proteasome inhibitors in the context of glioblastoma.

EXPERT OPINION

Early clinical trials with bortezomib ended with disappointing results, possibly because this agent does not cross the blood-brain barrier. In contrast to bortezomib and other proteasome inhibitors, marizomib is a novel drug that displays strong inhibitory properties on all enzymatic subunits of the proteasome and, most importantly, crosses the blood-brain barrier, making it a potentially very active novel agent against intrinsic brain tumors. While preclinical studies have demonstrated significant anti-glioma activity, its clinical benefit has yet to be proven. Exploiting the biological effects of proteasome inhibitors in combination with other therapeutic strategies may represent a key next step in their clinical development.

Anticancer drug discovery by targeting cullin neddylation

Protein neddylation is a post-translational modification which transfers the ubiquitin-like protein NEDD8 to a lysine residue of the target substrate through a three-step enzymatic cascade. The best-known substrates of neddylation are cullin family proteins, which are the core component of Cullin–RING E3 ubiquitin ligases (CRLs). Given that cullin neddylation is required for CRL activity, and CRLs control the turn-over of a variety of key signal proteins and are often abnormally activated in cancers, targeting neddylation becomes a promising approach for discovery of novel anti-cancer therapeutics. In the past decade, we have witnessed significant progress in the field of protein neddylation from preclinical target validation, to drug screening, then to the clinical trials of neddylation inhibitors. In this review, we first briefly introduced the nature of protein neddylation and the regulation of neddylation cascade, followed by a summary of all reported chemical inhibitors of neddylation enzymes. We then discussed the structure-based targeting of protein–protein interaction in neddylation cascade, and finally the available approaches for the discovery of new neddylation inhibitors. This review will provide a focused, up-to-date and yet comprehensive overview on the discovery effort of neddylation inhibitors.

Deciphering novel chemotherapy and its impact on dentistry

In the last few decades, the number of targeted chemotherapies approved for cancer treatment and undergoing clinical trials has risen. In comparison to conventional chemotherapy, targeted therapies (TTs) act on specific molecular targets involved in cancer development and progression, with reduced detrimental effects to normal tissues. TTs have now been recognised as key treatments in a number of common cancers, including solid tumours and haematological malignancies. The number of patients undergoing novel cancer treatment will continue to increase, and a significant population will likely present to the dental environment. This paper aims to provide an insight into TTs currently available, including monoclonal antibodies, fusion proteins, tyrosine kinase inhibitors, histone deacetylase inhibitors, mammalian target of rapamycin inhibitors, phosphoinositide 3-kinase inhibitors, proteasome inhibitors and hedgehog pathway inhibitors. The mechanisms of action, indications for use and how to identify the medications will be summarised. Dental implications of these novel therapies include medication-related osteonecrosis of the jaw, delayed healing, immunosuppression and thrombocytopenia. These will be discussed to ensure oral healthcare providers are aware of their impact in a dental setting.

DDX49 is an RNA helicase that affects translation by regulating mRNA export and the levels of pre-ribosomal RNA

Among the proteins predicted to be a part of the DExD box RNA helicase family, the functions of DDX49 are unknown. Here, we characterize the enzymatic activities and functions of DDX49 by comparing its properties with the well-studied RNA helicase, DDX39B. We find that DDX49 exhibits a robust ATPase and RNA helicase activity, significantly higher than that of DDX39B. DDX49 is required for the efficient export of poly (A)+ RNA from nucleus in a splicing-independent manner. Furthermore, DDX49 is a resident protein of nucleolus and regulates the steady state levels of pre-ribosomal RNA by regulating its transcription and stability. These dual functions of regulating mRNA export and pre-ribosomal RNA levels enable DDX49 to modulate global translation. Phenotypically, DDX49 promotes proliferation and colony forming potential of cells. Strikingly, DDX49 is significantly elevated in diverse cancer types suggesting that the increased abundance of DDX49 has a role in oncogenic transformation of cells. Taken together, this study shows the physiological role of DDX49 in regulating distinct steps of mRNA and pre-ribosomal RNA metabolism and hence translation and potential pathological role of its dysregulation, especially in cancers.

The Deubiquitinase Inhibitor b-AP15 and Its Effect on Phenotype and Function of Monocyte-Derived Dendritic Cells

The ubiquitin-proteasome system is elementary for cellular protein degradation and gained rising attention as a new target for cancer therapy due to promising clinical trials with bortezomib, the first-in class proteasome inhibitor meanwhile approved for multiple myeloma and mantle cell lymphoma. Both bortezomib and next-generation proteasome inhibitors mediate their effects by targeting the 20S core particle of the 26S proteasome. The novel small molecule inhibitor b-AP15 affects upstream elements of the ubiquitin-proteasome cascade by suppressing the deubiquitinase activity of both proteasomal regulatory 19S subunits and showed promising anticancer activity in preclinical models. Nonetheless, effects of inhibitors on the ubiquitin-proteasome system are not exclusively restricted to malignant cells: alteration of natural killer cell-mediated immune responses had already been described for drugs targeting either 19S or 20S proteasomal subunits. Moreover, it has been shown that bortezomib impairs dendritic cell (DC) phenotype and function at different levels. In the present study, we comparatively analyzed effects of bortezomib and b-AP15 on monocyte-derived DCs. In line with previous results, bortezomib exposure impaired maturation, antigen uptake, migration, cytokine secretion and immunostimulation, whereas treatment with b-AP15 had no compromising effects on these DC features. Our findings warrant the further investigation of b-AP15 as an alternative to clinically approved proteasome inhibitors in the therapy of malignancies, especially in the context of combinatorial treatment with DC-based immunotherapies.

PSME3 Promotes TGFB1 Secretion by Pancreatic Cancer Cells to Induce Pancreatic Stellate Cell Proliferation

Pancreatic cancer is a highly malignant disease that is associated with poor prognosis. One hallmark of pancreatic cancer is excessive desmoplasia, characterized by fibrous or connective tissue growth and altered tumor stroma. Pancreatic stellate cells (PSCs) comprise a mesenchymal cell type that contributes to pancreas fibrosis and cancer progression. PSME3 is a regulatory subunit of the proteasome that is expressed in various cancers such as breast, ovarian, and pancreatic. Notably, PSME3 modulates lactate secretion in pancreatic cancer, suggesting a potential function in regulating pancreas fibrosis. However, the role of PSME3 in pancreatic cancer cell (PCC)-PSC interactions remains unclear. The current study, for the first time, explored the mechanism involved in PSME3-mediated PCC-PSC interactions. IHC showed that PSME3 is highly expressed in PCCs, and this was found to correlate with tumor differentiation. RNA interference (RNAi) indicated that PSME3 is involved in PCC apoptosis. PCR array and cell co-culture experiments suggested that conditioned culture medium (CM) from PSME3-knockdown PCCs could suppress PSC proliferation by down-regulating TGFB1 secretion. Transcription factor (TF) activation assays showed that PSME3 regulates TGFB1 production by inhibiting activation protein-1 (AP-1). Together, these data demonstrate that PSME3 interacts with AP-1 to regulate TGFB1 secretion in PCCs and promote PSC proliferation. Our results indicate a novel PSME3-regulated association between PSCs and PCCs and provide a promising therapeutic strategy for this malignancy.

Lipoxidation and cancer immunity

Lipoxidation is a well-known reaction between electrophilic carbonyl species, formed during oxidation of lipids, and specific proteins that, in most cases, causes an alteration in proteins function. This can occur under physiological conditions but, in many cases, it has been associated to pathological process, including cancer. Lipoxidation may have an effect in cancer development through their effects in tumour cells, as well as through the alteration of immune components and the consequent modulation of the immune response. The formation of protein adducts affects different proteins in cancer, triggering different mechanism, such as proliferation, cell differentiation and apoptosis, among others, altering cancer progression. The divergent results obtained documented that the formation of lipoxidation adducts can have either anti-carcinogenic or pro-carcinogenic effects, depending on the cell type affected and the specific adduct formed. Moreover, lipoxidation adducts may alter the immune response, consequently causing either positive or negative alterations in cancer progression. Therefore, in this review, we summarize the effects of lipoxidation adducts in cancer cells and immune components and their consequences in the evolution of different types of cancer.

Application of nanotechnology to target and exploit tumour associated proteases

Proteases are hydrolytic enzymes fundamental for a variety of physiological processes, but the loss of their regulation leads to aberrant functions that promote onset and progression of many diseases including cancer. Proteases have been implicated in almost every hallmark of cancer and whilst widely investigated for tumour therapy, clinical adoption of protease inhibitors as drugs remains a challenge due to issues such as off-target toxicity and inability to achieve therapeutic doses at the disease site. Now, nanotechnology-based solutions and strategies are emerging to circumvent these issues. In this review, preclinical advances in approaches to enhance the delivery of protease drugs and the exploitation of tumour-derived protease activities to promote targeting of nanomedicine formulations is examined. Whilst this field is still in its infancy, innovations to date suggest that nanomedicine approaches to protease targeting or inhibition may hold much therapeutic and diagnostic potential.

Structural and bio-mineralization features of alumina zirconia composite influenced by the combined Ca2+ and PO43- additions

The structural and bioactivity features of alumina zirconia composite (AZC) due to Ca²⁺ and PO₄^3- additions are demonstrated. An in situ synthetic approach, starting from the solution precursors is devised for the powder synthesis in which the assorted range of Ca²⁺ and PO₄^3- additions were done to the equimolar concentrations of Al³⁺ and Zr⁴⁺ precursors. The results witnessed the unique crystallization of tetragonal zirconia (t-ZrO₂) at 1100 °C while Ca²⁺, PO₄^3- and Al₂O₃ remained in their amorphous state in the system. On further heat treatment, α-Al₂O₃ crystallized at 1200 °C, which enforced t- → m-ZrO₂ transformation while Ca²⁺ and PO₄^3- still retained their amorphous state. The immersion tests in simulated body fluid (SBF) solution validated the enhanced bio-mineralization activity of AZC due to Ca²⁺ and PO₄^3- additions. The results from the indentation tests demonstrated good uniformity in the elastic modulus and hardness data of the investigated specimens. Further, in vitro cell culture tests ascertained the bioactivity of all the AZC compositions.

Precoce and opposite response of proteasome activity after acute or chronic exposure of C. elegans to γ-radiation

Species are chronically exposed to ionizing radiation, a natural phenomenon which can be enhanced by human activities. The induced toxicity mechanisms still remain unclear and seem depending on the mode of exposure, i.e. acute and chronic. To better understand these phenomena, studies need to be conducted both at the subcellular and individual levels. Proteins, functional molecules in organisms, are the targets of oxidative damage (especially via their carbonylation (PC)) and are likely to be relevant biomarkers. After exposure of Caenorhabditis elegans to either chronic or acute γ rays we showed that hatching success is impacted after acute but not after chronic irradiation. At the molecular level, the carbonylated protein level in relation with dose was slightly different between acute and chronic exposure whereas the proteolytic activity is drastically modified. Indeed, whereas the 20S proteasome activity is inhibited by acute irradiation from 0.5 Gy, it is activated after chronic irradiation from 1 Gy. As expected, the 20S proteasome activity is mainly modified by irradiation whereas the 26S and 30S activity are less changed. This study provides preliminaries clues to understand the role of protein oxidation and proteolytic activity in the radiation-induced molecular mechanisms after chronic versus acute irradiation in C. elegans.

Size- and defect-controlled anti-oxidant enzyme mimetic and radical scavenging properties of cerium oxide nanoparticles

Improved enzymatic activity and concentration-dependent selective activation of peroxidase and oxidase activity of combustion-synthesized nanoceria.

The Proteasome in Modern Drug Discovery: Second Life of a Highly Valuable Drug Target

As the central figure of the cellular protein degradation machinery, the proteasome is critical for cell survival. Having been extensively targeted for inhibition, the constitutive proteasome has proven its role as a highly valuable drug target. However, recent advances in the protein homeostasis field suggest that additional chapters can be added to this successful story. For example, selective immunoproteasome inhibition promises high clinical efficacy for autoimmune disorders and inflammation, and proteasome inhibitors might serve as novel therapeutics for malaria or other microorganisms. Furthermore, utilizing the destructive force of the proteasome for selective degradation of essential drivers of human disorders has opened up a new and exciting area of drug discovery. Thus, the field of proteasome drug discovery still holds exciting questions to be answered and does not simply end with inhibiting the constitutive proteasome.

Iron doped β-Tricalcium phosphate: Synthesis, characterization, hyperthermia effect, biocompatibility and mechanical evaluation

The ability of β-Tricalcium phosphate [β-TCP, β-Ca₃(PO₄)₂] to host iron at its structural lattice and its associated magnetic susceptibility, hyperthermia effect, biocompatibility and mechanical characteristics is investigated. The studies revealed the ability of β-Ca₃(PO₄)₂ to host 5.02mol% of Fe³⁺ at its Ca²⁺(5) site. Excess Fe³⁺ additions led to the formation of trigonal Ca₉Fe(PO₄)₇ and moreover a minor amount of CaFe₃(PO₄)₃O crystallization was also observed. A gradual increment in the iron content at β-Ca₃(PO₄)₂ results in the simultaneous effect of pronounced hyperthermia effect and mechanical stability. However, the presence of CaFe₃(PO₄)₃O contributes for the reduced hyperthermia effect and mechanical stability of iron substituted β-Ca₃(PO₄)₂. Haemolytic tests, cytotoxicity tests and ALP gene expression analysis confirmed the biocompatibility of the investigated systems.

Structural analysis and magnetic induced hyperthermia of Fe3+and Mn2+substituted β-Ca3(PO4)2

Fe³⁺/Mn²⁺co-substitutions in β-Ca₃(PO₄)₂elicit a good hyperthermia effect and biocompatible features.

Pellino-1 derived cationic antimicrobial prawn peptide: Bactericidal activity, toxicity and mode of action

The antimicrobial peptides (AMPs) are multifunctional molecules which represent significant roles in the innate immune system. These molecules have been well known for decades because of their role as natural antibiotics in both invertebrates and vertebrates. The development of multiple drug resistance against conventional antibiotics brought a greater focus on AMPs in recent years. The cationic peptides, in particular, proven as host defense peptides and are considered as effectors of innate immunity. Among the various innate immune molecules, functions of pellino-1 (Peli-1) have been recently studied for its remarkable role in specific immune functions. In our study, we have identified Peli-1 from the cDNA library of freshwater prawn Macrobrachium rosenbergii (Mr) and analyzed its features using various in-silico methods. Real time PCR analysis showed an induced expression of MrPeli-1 during white spot syndrome virus (WSSV), bacteria (Vibrio harveyi) and lipopolysaccharide (LPS) from Escherichia coli challenge. Also, a cationic AMP named MrDN was derived from MrPeli-1 protein sequence and its activity was confirmed against various pathogenic bacteria. The mode of action of MrDN was determined to be its membrane permeabilization ability against Bacillus cereus ATCC 2106 as well as its DNA binding ability. Further, scanning electron microscopic (SEM) images showed the membrane disruption and leakage of cellular components of B. cereus cells induced by MrDN. The toxicity of MrDN against normal cells (HEK293 cells) was demonstrated by MTT and hemolysis assays. Overall, the results demonstrated the innate immune function of MrPeli-1 with a potential cationic AMP in prawn.

4-(Tert-butyl)-2,6-bis(1-phenylethyl)phenol induces pro-apoptotic activity

Previously, we found that KTH-13 isolated from the butanol fraction of Cordyceps bassiana (Cb-BF) displayed anti-cancer activity. To improve its antiproliferative activity and production yield, we employed a total synthetic approach and derivatized KTH-13 to obtain chemical analogs. In this study, one KTH-13 derivative, 4-(tert-butyl)-2,6-bis(1-phenylethyl)phenol (KTH-13-t-Bu), was selected to test its anti-cancer activity. KTH-13-t-Bu diminished the proliferation of C6 glioma, MDA-MB-231, LoVo, and HCT-15 cells. KTH-13-t-Bu induced morphological changes in C6 glioma cells in a dose-dependent manner. KTH-13-t-Bu also increased the level of early apoptotic cells stained with annexin V-FITC. Furthermore, KTH-13-t-Bu increased the levels of cleaved caspase-3 and -9. In contrast, KTH-13-t-Bu upregulated the levels of pro- and cleaved forms of caspase-3, -8, and -9 and Bcl-2. Phospho-STAT3, phospho-Src, and phospho-AKT levels were also diminished by KTH13-t-Bu treatment. Therefore, these results strongly suggest that KTH-13-t-Bu can be considered a novel anti-cancer drug displaying pro-apoptotic activity.

Deposition, structure, physical and invitro characteristics of Ag-doped β-Ca3(PO4)2/chitosan hybrid composite coatings on Titanium metal

Pure and five silver-doped (0-5Ag) β-tricalcium phosphate [β-TCP, β-Ca3(PO4)2]/chitosan composite coatings were deposited on Titanium (Ti) substrates and their properties that are relevant for applications in hard tissue replacements were assessed. Silver, β-TCP and chitosan were combined to profit from their salient and complementary antibacterial and biocompatible features.The β-Ca3(PO4)2 powders were synthesized by co-precipitation. The characterization results confirmed the Ag(+) occupancy at the crystal lattice of β-Ca3(PO4)2. The Ag-dopedβ-Ca3(PO4)2/chitosan composite coatings deposited by electrophoresis showed good antibacterial activity and exhibited negative cytotoxic effects towards the human osteosarcoma cell line MG-63. The morphology of the coatings was observed by SEM and their efficiency against corrosion of metallic substrates was determined through potentiodynamic polarization tests.

Cefepime, a fourth-generation cephalosporin, in complex with manganese, inhibits proteasome activity and induces the apoptosis of human breast cancer cells

Cefepime (FEP), which is a member of the fourth-generation cephalosporin class, has been extensively studied as a biochemical and antimicrobial reagent in recent years. Manganese (Mn) is important in the biochemical and physiological processes of many living organisms, and it is also high expressed in some tumor tissues. In the present study, we aimed to investigate the proteasome-inhibitory and anti-proliferative properties of 8 metal complexes (FEP‑Cu, FEP-Zn, FEP-Co, FEP-Ni, FEP-Cd, FEP-Cr, FEP-Fe, FEP-Mn) in MDA-MB‑231 human breast cancer cells. The FEP-Mn complex was found to be more potent in its ability to inhibit cell proliferation and proteasome activity than the other compounds tested. Moreover, the FEP-Mn complex inhibited proteasomal chymotrypsin-like (CT-like) activity and induced the apoptosis of breast cancer cells in a dose-and time-dependent manner. Furthermore, the MCF-10A cells were much less sensitive to the FEP complexes compared with the MDA-MB-231 breast cancer cells. These results demonstrated that the FEP-Mn(II) complex has the potential to act as a proteasome inhibitor and apoptosis inducer and therefore has possible future applications in cancer chemotherapy.

Pro-Apoptotic Activity of 4-Isopropyl-2-(1-Phenylethyl) Aniline Isolated from Cordyceps bassiana

Cordyceps species including Cordyceps bassiana are a notable anti-cancer dietary supplement. Previously, we identified several compounds with anti-cancer activity from the butanol fraction (Cb-BF) of Cordyceps bassiana. To expand the structural value of Cb-BF-derived anti-cancer drugs, we employed various chemical moieties to produce a novel Cb-BF-derived chemical derivative, KTH-13-amine-monophenyl [4-isopropyl-2-(1-phenylethyl) aniline (KTH-13-AMP)], which we tested for anti-cancer activity. KTH-13-AMP suppressed the proliferation of MDA-MB-231, HeLa, and C6 glioma cells. KTH-13-AMP also dose-dependently induced morphological changes in C6 glioma cells and time-dependently increased the level of early apoptotic cells stained with annexin V-FITC. Furthermore, the levels of the active full-length forms of caspase-3 and caspase-9 were increased. In contrast, the levels of total forms of caspases-3, caspase-8, caspase-9, and Bcl-2 were decreased in KTH-13-AMP treated-cells. We also confirmed that the phosphorylation of STAT3, Src, and PI3K/p85, which is linked to cell survival, was diminished by treatment with KTH-13-AMP. Therefore, these results strongly suggest that this compound can be used to guide the development of an anti-cancer drug or serve as a lead compound in forming another strong anti-proliferative agent.

Ubiquitylation of nuclear receptors: new linkages and therapeutic implications

The nuclear receptor (NR) superfamily is a group of transcriptional regulators that control multiple aspects of both physiology and pathology and are broadly recognized as viable therapeutic targets. While receptor-modulating drugs have been successful in many cases, the discovery of new drug targets is still an active area of research, because resistance to NR-targeting therapies remains a significant clinical challenge. Many successful targeted therapies have harnessed the control of receptor activity by targeting events within the NR signaling pathway. In this review, we explore the role of NR ubiquitylation and discuss how the expanding roles of ubiquitin could be leveraged to identify additional entry points to control receptor function for future therapeutic development.

Rodent models of chemotherapy-induced peripheral neuropathy

Peripheral neuropathy is a common and dose-limiting side effect of many chemotherapeutic drugs. These include platinum compounds, taxanes, vinca alkaloids, proteasome inhibitors, and others such as thalidomide and suramin. Although many rodent models have been developed using either mice or rats, there is limited consistency in the dose or mode of delivery of the drug; the sex, age, and genetic background of the animal used in the study; and the outcome measures used in evaluation of the peripheral neuropathy. Behavioral assays are commonly used to evaluate evoked sensory responses but are unlikely to be a good representation of the spontaneous sensory paresthesias that the patients experience. Electrophysiologic tests evaluate the integrity of large myelinated populations and are useful in drugs that cause either demyelination or degeneration of large myelinated axons but are insensitive to degeneration of unmyelinated axons in early stages of neuropathy. Histopathologic tools offer an unbiased way to evaluate the degree of axonal degeneration or changes in neuronal cell body but are often time consuming and require processing of the tissue after the study is completed. Nevertheless, use of drug doses and mode of delivery that are relevant to the clinical protocols and use of outcome measures that are both sensitive and objective in evaluation of the length-dependent distal axonal degeneration seen in most chemotherapy-induced peripheral neuropathies may improve the translational utility of these rodent models.

Development of Small Molecular Proteasome Inhibitors Using a Caenorhabditis elegans Screen

We have developed a screening protocol to identify compounds with characteristics of small molecule proteasome inhibitors using the real-time analysis of the Caenorhabditis elegans germ line. This screen is able to identify compounds that induce germ line phenotypes characteristic of a reduction in proteasome function such as changes in polarity, aberrant nuclear morphology, and stimulation of apoptosis. This basic protocol is amenable to a high throughput (96-well) format and has been used successfully to identify multiple compounds for further analysis based on structural elements from the naturally occurring compounds lactacystin and the β-lactone homologs omuralide and salinosporamide A. The further development of this assay system should allow for the generation of novel small molecule proteasome inhibitors in a genetically tractable whole animal amenable to biochemical analysis.

Bortezomib

The ubiquitin-mediated degradation of proteins in numerous cellular processes, such as turnover and quality control of proteins, cell cycle and apoptosis, transcription and cell signaling, immune response and antigen presentation, and inflammation and development makes the ubiquitin-proteosome systems a very interesting target for various therapeutic interventions. Proteosome inhibitors were first synthesized as tools to probe the function and specificity of this particle's proteolytic activities. Most synthetic inhibitors rely on a peptide base, which mimics a protein substrate, attached at a COOH terminal "warhead." Notable warheads include boronic acids, such as bortezomib and epoxy ketones, such as carfilzomib. A variety of natural products also inhibit the proteosome that are not peptide-based, most notably lactacystin, that is related to NPI-0052, or salinosporamide A, another inhibitor in clinical trials. The possibility that proteosome inhibitors could be drug candidates was considered after studies showed that they induced apoptosis in leukemic cell lines. The first proteasome inhibitor in clinical application, bortezomib showed activity in non-small-cell lung and androgen-independent prostate carcinoma, as well as MM and mantle cell and follicular non-Hodgkin's lymphoma. It is now licensed for the treatment of newly diagnosed as well as relapsed/progressive MM and has had a major impact on the improvement in the treatment of MM in the last few years.

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.

Caspase-3 cleaves hnRNP K in erythroid differentiation

Post-transcriptional control of gene expression is crucial for the control of cellular differentiation. Erythroid precursor cells loose their organelles in a timely controlled manner during terminal maturation to functional erythrocytes. Extrusion of the nucleus precedes the release of young reticulocytes into the blood stream. The degradation of mitochondria is initiated by reticulocyte 15-lipoxygenase (r15-LOX) in mature reticulocytes. At that terminal stage the release of r15-LOX mRNA from its translational silenced state induces the synthesis of r15-LOX. Heterogeneous nuclear ribonucleoprotein K (hnRNP K) is a key regulator of r15-LOX mRNA translation. HnRNP K that binds to the differentiation control element (DICE) in the 3′ untranslated region (UTR) inhibits r15-LOX mRNA translation initiation. During erythroid cell maturation, activation of r15-LOX mRNA translation is mediated by post-translational modifications of hnRNP K and a decrease of the hnRNP K level. To further elucidate its function in the post-transcriptional control of gene expression, we investigated hnRNP K degradation employing an inducible erythroid cell system that recapitulates both nuclear extrusion and the timely controlled degradation of mitochondria, mediated by the activation of r15-LOX synthesis. Interestingly, we detected a specific N-terminal cleavage intermediate of hnRNP K lacking DICE-binding activity that appeared during erythroid differentiation and puromycin-induced apoptosis. Employing mass spectrometry and enzymatic analyses, we identified Caspase-3 as the enzyme that cleaves hnRNP K specifically. In vitro studies revealed that cleavage by Caspase-3 at amino acids (aa) D334-G335 removes the C-terminal hnRNP K homology (KH) domain 3 that confers binding of hnRNP K to the DICE. Our data suggest that the processing of hnRNP K by Caspase-3 provides a save-lock mechanism for its timely release from the r15-LOX mRNA silencing complex and activation of r15-LOX mRNA synthesis in erythroid cell differentiation.

Emerging biological insights and novel treatment strategies in multiple myeloma

INTRODUCTION

Survival in multiple myeloma (MM) has improved significantly in the past 10 years due to new treatments, such as thalidomide and lenalidomide (immunomodulatory drugs or IMiDs) bortezomib and advances in supportive care. Nevertheless, almost all MM patients show disease relapse and develop drug resistance.

AREAS COVERED

The authors review the therapeutic approach for untreated MM patients. Furthermore, the prognostic stratification of patients and the proposed risk-adapted strategy are discussed. Finally, preclinical and clinical data regarding newer antimyeloma agents, currently undergoing examination such as proteasome inhibitors (PIs, carfilzomib), IMiDs (pomalidomide), epigenetic agents (histone deacetylase inhibitors vorinostat and panobinostat), humanized monoclonal antibodies (elotuzumab and MOR03087) and targeted therapies (inhibitors of NF-κB, MAPK, HSP90 and AKT) are reported.

EXPERT OPINION

MM patient outcome has remarkably improved due to the use of three to four drug combination therapies including PIs and IMiDs, which target the tumor in its bone marrow microenvironment, however MM treatment remains challenging. The use of high-throughput techniques has allowed to discover new insights into MM biology. The identification of candidate therapeutic targets and availability of respective investigative agents will allow for a substantial progress in the development and implementation of personalized medicine in MM.

1,10-Phenanthroline promotes copper complexes into tumor cells and induces apoptosis by inhibiting the proteasome activity

Indole-3-acetic acid and indole-3-propionic acid, two potent natural plant growth hormones, have attracted attention as promising prodrugs in cancer therapy. Copper is known to be a cofactor essential for tumor angiogenesis. We have previously reported that taurine, L-glutamine, and quinoline-2-carboxaldehyde Schiff base copper complexes inhibit cell proliferation and proteasome activity in human cancer cells. In the current study, we synthesized two types of copper complexes, dinuclear complexes and ternary complexes, to investigate whether a certain structure could easily carry copper into cancer cells and consequently inhibit tumor proteasome activity and induce apoptosis. We observed that ternary complexes binding with 1,10-phenanthroline are more potent proteasome inhibitors and apoptosis inducers than dinuclear complexes in PC-3 human prostate cancer cells. Furthermore, the ternary complexes potently inhibit proteasome activity before induction of apoptosis in MDA-MB-231 human breast cancer cells, but not in nontumorigenic MCF-10A cells. Our results suggest that copper complexes binding with 1,10-phenanthroline as the third ligand could serve as potent, selective proteasome inhibitors and apoptosis inducers in tumor cells, and that the ternary complexes may be good potential anticancer drugs.

Inhibitors of nuclear factor kappa B cause apoptosis in cultured macrophages

The precise role of the transcription factor nuclear factor kappa B (NF- κB) in the regulation of cell survival and cell death is still unresolved and may depend on cell type and position in the cell cycle. The aim of this study was to determine if three pharmacologic inhibitors of NF-κB, pyrrolidine dithiocarbamate, N-tosyl-L-lysl chloromethyl ketone and calpain I inhibitor, induce apoptosis in a murine macrophage cell line (RAW 264.7) at doses similar to those required for NF-κB inhibition. We found that each of the three inhibitors resulted in a dose- and time-dependent increase in morphologic indices of apoptosis in unstimulated, LPS-stimulated and TNF-stimulated cells. Lethal doses were consistent with those required for NF- κB inhibition. We conclude that nuclear NF-κB activation may represent an important survival mechanism in macrophages.

Identification of factors that function in Drosophila salivary gland cell death during development using proteomics

Proteasome inhibitors induce cell death and are used in cancer therapy, but little is known about the relationship between proteasome impairment and cell death under normal physiological conditions. Here, we investigate the relationship between proteasome function and larval salivary gland cell death during development in Drosophila. Drosophila larval salivary gland cells undergo synchronized programmed cell death requiring both caspases and autophagy (Atg) genes during development. Here, we show that ubiquitin proteasome system (UPS) function is reduced during normal salivary gland cell death, and that ectopic proteasome impairment in salivary gland cells leads to early DNA fragmentation and salivary gland condensation in vivo. Shotgun proteomic analyses of purified dying salivary glands identified the UPS as the top category of proteins enriched, suggesting a possible compensatory induction of these factors to maintain proteolysis during cell death. We compared the proteome following ectopic proteasome impairment to the proteome during developmental cell death in salivary gland cells. Proteins that were enriched in both populations of cells were screened for their function in salivary gland degradation using RNAi knockdown. We identified several factors, including trol, a novel gene CG11880, and the cop9 signalsome component cop9 signalsome 6, as required for Drosophila larval salivary gland degradation.

Largazole and its derivatives selectively inhibit ubiquitin activating enzyme (e1)

Protein ubiquitination plays an important role in the regulation of almost every aspect of eukaryotic cellular function; therefore, its destabilization is often observed in most human diseases and cancers. Consequently, developing inhibitors of the ubiquitination system for the treatment of cancer has been a recent area of interest. Currently, only a few classes of compounds have been discovered to inhibit the ubiquitin-activating enzyme (E1) and only one class is relatively selective in E1 inhibition in cells. We now report that Largazole and its ester and ketone analogs selectively inhibit ubiquitin conjugation to p27^Kip1 and TRF1 in vitro. The inhibitory activity of these small molecules on ubiquitin conjugation has been traced to their inhibition of the ubiquitin E1 enzyme. To further dissect the mechanism of E1 inhibition, we analyzed the effects of these inhibitors on each of the two steps of E1 activation. We show that Largazole and its derivatives specifically inhibit the adenylation step of the E1 reaction while having no effect on thioester bond formation between ubiquitin and E1. E1 inhibition appears to be specific to human E1 as Largazole ketone fails to inhibit the activation of Uba1p, a homolog of E1 in Schizosaccharomyces pombe. Moreover, Largazole analogs do not significantly inhibit SUMO E1. Thus, Largazole and select analogs are a novel class of ubiquitin E1 inhibitors and valuable tools for studying ubiquitination in vitro. This class of compounds could be further developed and potentially be a useful tool in cells.

Alternating temperature breaks dormancy in leafy spurge seeds and impacts signaling networks associated with HY5

Non-after-ripened seeds of the herbaceous perennial weed leafy spurge do not germinate when imbibed at a constant temperature (C), but transfer to an alternating temperature (A) induced germination. Changes in the transcriptome of seeds during 1 and 3 days of alternating temperature and germinated seeds were compared with seeds incubated at constant temperature. Statistical analysis revealed that 597, 1,491, and 1,329 genes were differentially expressed (P < 0.05) for the comparisons of 21-day C vs. 21-day C + 1-day A, 21-day C vs. 21-day C + 3-day A, and 21-day C vs. 21-day C + Germ (germination), respectively. Functional classifications based on gene set and sub-network enrichment analysis were performed to identify pathways and gene sub-networks that underlie transcriptome changes in the seeds as they germinate. Sugars, plant hormones, photomorphogenesis, and reactive oxygen species were overrepresented at 21-day C + 1-day A. At 21-day C + 3-day A, an increase in cellular activities was observed as the number of overrepresented pathways greatly increased. Many of the metabolic pathways were involved in the biosynthesis of amino acids, macromolecules, and energy and carbon skeleton production for subsequent germination. The 21-day C + 3-day A and 21-day C + Germ pathways and sub-networks were similar and included an overrepresentation of the amino acid biosynthetic pathways; however, 21-day C + Germ seeds have an even wider array of cellular activities such as translation-related pathways, which are most likely for seedling growth. RT-qPCR analysis indicated that the up- and down-regulation of HISTONE H3, GASA2, DREBIII-1, CHS, AOS, PIF3, PLD α1, and LEA may be germination-related since their expression was dramatically changed only in the 21-day C + Germ seeds. Finally, both short-term alternating temperature and short-term light exposure up-regulated the expression targets of the central hub HY5 in leafy spurge and Arabidopsis, respectively, indicating that a signaling network involving HY5 is important for germination.

Proteasome inhibitors in cancer therapy

The ubiquitin proteasome pathway plays a critical role in regulating many processes in the cell which are important for tumour cell growth and survival. Inhibition of proteasome function has emerged as a powerful strategy for anti-cancer therapy. Clinical validation of the proteasome as a therapeutic target was achieved with bortezomib and has prompted the development of a second generation of proteasome inhibitors with improved pharmacological properties. This review summarises the main mechanisms of action of proteasome inhibitors in cancer, the development of proteasome inhibitors as therapeutic agents and the properties and progress of next generation proteasome inhibitors in the clinic.

Cycloheximide suppresses radiation-induced apoptosis in MOLT-4 cells with Arg72 variant of p53 through translational inhibition of p53 accumulation

The human T-cell leukemia cell line MOLT-4 is highly radiosensitive, and thus it is often used as a model of p53-dependent radiation-induced apoptosis. Two branches of the p53-mediated apoptotic pathway are reported: "transcription-dependent" and "transcription-independent." However, the relative contribution of each in different types of cells is not yet clearly defined. Moreover, recent studies have shown that the codon 72 polymorphic variants of p53 show different sensitivities to apoptosis signals. The Arg72 variant has a more potent apoptosis-inducing activity in mitochondria than the Pro72 variant. Here, we initially investigated the codon 72 polymorphism of p53 in MOLT-4 cells. Analysis of the p53 exon 4 genomic DNA sequence, which includes codon 72, revealed that MOLT-4 cells are homozygous for the allele encoding Arg72. We next investigated the involvement of the transcription-independent function of p53 using an RNA synthesis inhibitor, actinomycin D (ActD), and a protein synthesis inhibitor, cycloheximide (CHX), and found that the apoptosis was suppressed by CHX but not by ActD. We also revealed that the suppressive effect of CHX on apoptosis was specifically mediated by p53, using a p53-knockdown MOLT-4 transfectant. Furthermore, the suppressive effect of CHX on apoptosis was highly correlated with the suppression of p53 protein accumulation, and less correlated with the suppression of p53 target genes expression. These results indicated that p53 transactivation is not necessary to induce apoptosis, and that p53 protein accumulation itself is both necessary and sufficient to do so.

Proteasome inhibition induces developmentally deregulated programs of apoptotic and autophagic cell death during Drosophila melanogaster oogenesis

Ubiquitin/proteasome-mediated degradation of eukaryotic proteins is critically implicated in a number of signalling pathways and cellular processes. To specifically impair proteasome activities, in vitro developing Drosophila melanogaster egg chambers were exposed to the MG132 or epoxomicin proteasome inhibitors, while a GAL4/UAS binary genetic system was employed to generate double transgenic flies overexpressing β2 and β6 conditional mutant proteasome subunits in a cell type-specific manner. MG132 and epoxomicin administration resulted in severe deregulation of in vitro developing egg chambers, which was tightly associated with precocious induction of nurse cell-specific apoptotic and autophagic death programmes, featured by actin cytoskeleton disorganization, nuclear chromatin condensation, DRICE caspase activation and autophagosome accumulation. In vivo targeted overexpression of β2 and β6 conditional mutants, specifically in the nurse cell compartment, led to a notable up-regulation of sporadic apoptosis potency during early and mid-oogenesis 'checkpoints', thus reasonably justifying the observed reduction in eclosion efficiency. Furthermore, in response to the intracellular abundance of β2 and β6 conditional mutant forms, specifically in numerous tissues of third instar larval stage, the developmental course was arrested, and lethal phenotypes were obtained at this particular embryonic period, with the double transgenic heterozygote embryos being unable to further proceed to complete maturation to adult flies. Our data demonstrate that physiological proteasome function is required to ensure normal oogenesis and embryogenesis in D. melanogaster, since targeted and cell type-dependent proteasome inactivation initiates developmentally deregulated apoptotic and autophagic mechanisms.

Proteases implicated in apoptosis: old and new

OBJECTIVES

The role of proteases in the regulation of apoptosis is becoming increasingly apparent. Whilst many of these proteases are already characterised, some have yet to be identified. Traditionally caspases held the traditional role as the prime mediators of apoptosis; however, attention is now turning towards the contribution made by serine proteases.

KEY FINDINGS

As unregulated apoptosis is implicated in various disease states, the emergence of this proteolytic family as apoptotic regulators offers novel and alterative opportunities for therapeutic targets.

SUMMARY

This review presents a brief introduction and overview of proteases in general with particular attention given to those involved in apoptotic processing.