Bortezomib-mediated 26S proteasome inhibition causes cell-cycle arrest and induces apoptosis in CD-30+ anaplastic large cell lymphoma

Synthesis of a Bone-Targeted Bortezomib with In Vivo Anti-Myeloma Effects in Mice

Multiple myeloma (MM) is the most common cancer affecting the bone and bone marrow and remains incurable for most patients; novel therapies are therefore needed. Bortezomib (Btz) is an FDA-approved drug for the treatment of patients with MM. However, its severe side effects require a dose reduction or the potential discontinuation of treatment. To overcome this limitation, we conjugated Btz to a bisphosphonate (BP) residue lacking anti-osteoclastic activity using a novel chemical linker and generated a new bone-targeted Btz-based (BP-Btz) proteasome inhibitor. We demonstrated that BP-Btz, but not Btz, bound to bone slices and inhibited the growth of MM cells in vitro. In a mouse model of MM, BP-Btz more effectively reduced tumor burden and bone loss with less systemic side effects than Btz. Thus, BP-Btz may represent a novel therapeutic approach to treat patients with MM.

The Current Status and Perspectives of Delivery Strategy for Boron-based Drugs

Boron-containing compounds are essential micronutrients for animals and plants despite their low-level natural occurrence. They can strengthen the cell walls of the plants and they play important role in supporting bone health. However, surprisingly, boron-containing compounds are seldom found in pharmaceutical drugs. In fact, there are no inherent disadvantages reported so far in terms of the incorporation of boron into medicines. Indeed, drugs based on boron-containing compounds, such as tavaborole (marked name Kerydin) and bortezomib (trade name Velcade) have been investigated and they are used in clinical treatment. In addition, following the advanced development of boron neutron capture therapy and a new emerging proton boron fusion therapy, more boron-containing medicinals are to be expected. This review discusses the current status and perspectives of delivery strategy for boron-containing drugs.

The Role of Autophagy in the Degradation of Misfolded HLA-B27 Heavy Chains

OBJECTIVE

To determine whether autophagy is involved in the degradation of misfolded HLA-B27 in experimental spondyloarthritis.

METHODS

Bone marrow-derived macrophages from HLA-B27/human β2 -microglobulin (hβ2 m)-transgenic rats were incubated in the presence or absence of interferon-γ and proteasome or autophagy inhibitors. Immunoprecipitation, immunoblotting, and immunofluorescence analysis were used to measure HLA-B27 heavy chains and autophagy. Autophagy was induced using rapamycin. Macrophages from HLA-B7/hβ2 m-transgenic and wild-type rats were used as controls.

RESULTS

HLA-B27-expressing macrophages showed phosphatidylethanolamine-conjugated microtubule-associated protein 1 light chain 3B levels similar to those in both control groups, before and after manipulation of autophagy. Blocking autophagic flux with bafilomycin resulted in the accumulation of misfolded HLA-B27 dimers and oligomers as well as monomers, which was comparable with the results of blocking endoplasmic reticulum-associated degradation (ERAD) with the proteasome inhibitor bortezomib. HLA-B7 monomers also accumulated after blocking each degradation pathway. The ubiquitin-to-heavy chain ratio was 2-3-fold lower for HLA-B27 than for HLA-B7. Activation of autophagy with rapamycin rapidly eliminated ~50% of misfolded HLA-B27, while folded HLA-B27 or HLA-B7 monomeric heavy chains were minimally affected.

CONCLUSION

This study is the first to demonstrate that both autophagy and ERAD play roles in the elimination of excess HLA class I heavy chains expressed in transgenic rats. We observed no evidence that HLA-B27 expression modulated the autophagy pathway. Our results suggest that impaired ubiquitination of HLA-B27 may play a role in the accumulation of misfolded disulfide-linked dimers, the elimination of which can be enhanced by activation of autophagy. Manipulation of the autophagy pathway should be further investigated as a potential therapeutic target in spondyloarthritis.

When nature's robots go rogue: exploring protein homeostasis dysfunction and the implications for understanding human aging disease pathologies

INTRODUCTION

Proteins have been historically regarded as 'nature's robots': Molecular machines that are essential to cellular/extracellular physical mechanical properties and catalyze key reactions for cell/system viability. However, these robots are kept in check by other protein-based machinery to preserve proteome integrity and stability. During aging, protein homeostasis is challenged by oxidation, decreased synthesis, and increasingly inefficient mechanisms responsible for repairing or degrading damaged proteins. In addition, disruptions to protein homeostasis are hallmarks of many neurodegenerative diseases and diseases disproportionately affecting the elderly. Areas covered: Here we summarize age- and disease-related changes to the protein machinery responsible for preserving proteostasis and describe how both aging and disease can each exacerbate damage initiated by the other. We focus on alteration of proteostasis as an etiological or phenomenological factor in neurodegenerative diseases such as Alzheimer's, Parkinson's, and Huntington's, along with Down syndrome, ophthalmic pathologies, and cancer. Expert commentary: Understanding the mechanisms of proteostasis and their dysregulation in health and disease will represent an essential breakthrough in the treatment of many (senescence-associated) pathologies. Strides in this field are currently underway and largely attributable to the introduction of high-throughput omics technologies and their combination with novel approaches to explore structural and cross-link biochemistry.

Targeting Deubiquitinases in Cancer

The ubiquitin-proteasome system (UPS) is a complex and robust metabolic pathway that contributes to the regulation of many key cellular processes including the cell cycle, cell division, and response to external stimuli. Ubiquitin ligases, which tag proteins with ubiquitin, are opposed by deubiquitinase enzymes (DUBs). The relative activity of these enzymes allows for a dynamic balance that determines the abundance and activity of cellular proteins. Targeting the UPS in cancer has proven successful, as evidenced by use of bortezomib, a proteasome inhibitor, in multiple myeloma. However, no pharmacologic inhibitor of the upstream enzymes has yet to reach clinical trials for the treatment of malignancy. Here we present an in vitro DUB assay for use in drug discovery and development that provides a biologically relevant platform for screening and developing lead or tool compounds targeting DUBs.

Therapeutic Strategies against Epstein-Barr Virus-Associated Cancers Using Proteasome Inhibitors

Epstein-Barr virus (EBV) is closely associated with several lymphomas (endemic Burkitt lymphoma, Hodgkin lymphoma and nasal NK/T-cell lymphoma) and epithelial cancers (nasopharyngeal carcinoma and gastric carcinoma). To maintain its persistence in the host cells, the virus manipulates the ubiquitin-proteasome system to regulate viral lytic reactivation, modify cell cycle checkpoints, prevent apoptosis and evade immune surveillance. In this review, we aim to provide an overview of the mechanisms by which the virus manipulates the ubiquitin-proteasome system in EBV-associated lymphoid and epithelial malignancies, to evaluate the efficacy of proteasome inhibitors on the treatment of these cancers and discuss potential novel viral-targeted treatment strategies against the EBV-associated cancers.

Temporally distinct transcriptional regulation of myocyte dedifferentiation and Myofiber growth during muscle regeneration

BACKGROUND

Tissue regeneration requires a series of steps, beginning with generation of the necessary cell mass, followed by cell migration into damaged area, and ending with differentiation and integration with surrounding tissues. Temporal regulation of these steps lies at the heart of the regenerative process, yet its basis is not well understood. The ability of zebrafish to dedifferentiate mature "post-mitotic" myocytes into proliferating myoblasts that in turn regenerate lost muscle tissue provides an opportunity to probe the molecular mechanisms of regeneration.

RESULTS

Following subtotal excision of adult zebrafish lateral rectus muscle, dedifferentiating residual myocytes were collected at two time points prior to cell cycle reentry and compared to uninjured muscles using RNA-seq. Functional annotation (GAGE or K-means clustering followed by GO enrichment) revealed a coordinated response encompassing epigenetic regulation of transcription, RNA processing, and DNA replication and repair, along with protein degradation and translation that would rewire the cellular proteome and metabolome. Selected candidate genes were phenotypically validated in vivo by morpholino knockdown. Rapidly induced gene products, such as the Polycomb group factors Ezh2 and Suz12a, were necessary for both efficient dedifferentiation (i.e. cell reprogramming leading to cell cycle reentry) and complete anatomic regeneration. In contrast, the late activated gene fibronectin was important for efficient anatomic muscle regeneration but not for the early step of myocyte cell cycle reentry.

CONCLUSIONS

Reprogramming of a "post-mitotic" myocyte into a dedifferentiated myoblast requires a complex coordinated effort that reshapes the cellular proteome and rewires metabolic pathways mediated by heritable yet nuanced epigenetic alterations and molecular switches, including transcription factors and non-coding RNAs. Our studies show that temporal regulation of gene expression is programmatically linked to distinct steps in the regeneration process, with immediate early expression driving dedifferentiation and reprogramming, and later expression facilitating anatomical regeneration.

Selective Glucocorticoid Receptor Properties of GSK866 Analogs with Cysteine Reactive Warheads

Synthetic glucocorticoids (GC) are the mainstay therapy for treatment of acute and chronic inflammatory disorders. Due to the high adverse effects associated with long-term use, GC pharmacology has focused since the nineties on more selective GC ligand-binding strategies, classified as selective glucocorticoid receptor (GR) agonists (SEGRAs) or selective glucocorticoid receptor modulators (SEGRMs). In the current study, GSK866 analogs with electrophilic covalent-binding warheads were developed with potential SEGRA properties to improve their clinical safety profile for long-lasting topical skin disease applications. Since the off-rate of a covalently binding drug is negligible compared to that of a non-covalent drug, its therapeutic effects can be prolonged and typically, smaller doses of the drug are necessary to reach the same level of therapeutic efficacy, thereby potentially reducing systemic side effects. Different analogs of SEGRA GSK866 coupled to cysteine reactive warheads were characterized for GR potency and selectivity in various biochemical and cellular assays. GR- and NFκB-dependent reporter gene studies show favorable anti-inflammatory properties with reduced GR transactivation of two non-steroidal GSK866 analogs UAMC-1217 and UAMC-1218, whereas UAMC-1158 and UAMC-1159 compounds failed to modulate cellular GR activity. These results were further supported by GR immuno-localization and S211 phospho-GR western analysis, illustrating significant GR phosphoactivation and nuclear translocation upon treatment of GSK866, UAMC-1217, or UAMC-1218, but not in case of UAMC-1158 or UAMC-1159. Furthermore, mass spectrometry analysis of tryptic peptides of recombinant GR ligand-binding domain (LBD) bound to UAMC-1217 or UAMC-1218 confirmed covalent cysteine-dependent GR binding. Finally, molecular dynamics simulations, as well as glucocorticoid receptor ligand-binding domain (GR-LBD) coregulator interaction profiling of the GR-LBD bound to GSK866 or its covalently binding analogs UAMC-1217 or UAMC-1218 revealed subtle conformational differences that might underlie their SEGRA properties. Altogether, GSK866 analogs UAMC-1217 and UAMC-1218 hold promise as a novel class of covalent-binding SEGRA ligands for the treatment of topical inflammatory skin disorders.

Bortezomib induces neuropathic pain through protein kinase C-mediated activation of presynaptic NMDA receptors in the spinal cord

Chemotherapeutic drugs, including bortezomib, often cause painful peripheral neuropathy, which is a severe dose-limiting adverse effect experienced by many cancer patients. The glutamate N-methyl-d-aspartate receptors (NMDARs) at the spinal cord level are critically involved in the synaptic plasticity associated with neuropathic pain. In this study, we determined whether treatment with bortezomib, a proteasome inhibitor, affects the NMDAR activity of spinal dorsal horn neurons. Systemic treatment with bortezomib in rats did not significantly affect postsynaptic NMDAR currents elicited by puff application of NMDA directly to dorsal horn neurons. Bortezomib treatment markedly increased the baseline frequency of miniature excitatory postsynaptic currents (EPSCs), which was completely normalized by the NMDAR antagonist 2-amino-5-phosphonopentanoic acid (AP5). AP5 also reduced the amplitude of monosynaptic EPSCs evoked by dorsal root stimulation in bortezomib-treated, but not vehicle-treated, rats. Furthermore, inhibition of protein kinase C (PKC) with chelerythrine fully reversed the increased frequency of miniature EPSCs and the amplitude of evoked EPSCs in bortezomib-treated rats. Intrathecal injection of AP5 and chelerythrine both profoundly attenuated mechanical allodynia and hyperalgesia induced by systemic treatment with bortezomib. In addition, treatment with bortezomib induced striking membrane translocation of PKC-βII, PKC-δ, and PKC-ε in the dorsal root ganglion. Our findings indicate that bortezomib treatment potentiates nociceptive input from primary afferent nerves via PKC-mediated tonic activation of presynaptic NMDARs. Targeting presynaptic NMDARs and PKC at the spinal cord level may be an effective strategy for treating chemotherapy-induced neuropathic pain.

Bortezomib Warhead-Switch Confers Dual Activity against Mycobacterial Caseinolytic Protease and Proteasome and Selectivity against Human Proteasome

Mycobacteria harbor two main degradative proteolytic machineries, the caseinolytic protease ClpP1P2 and a proteasome. We recently showed that Bortezomib inhibits ClpP1P2 and exhibits whole cell activity against Mycobacterium tuberculosis. Bortezomib, a dipeptide with a boronic acid warhead, is a human proteasome inhibitor approved for cancer therapy. The boronic acid warhead of the compound has been shown to drive potency against both the human proteasome and ClpP1P2 protease. Selectivity for the bacterial ClpP1P2 protease over the human proteasome is lacking but needs to be achieved to move this new anti-tuberculosis lead forward. In this study we explored whether an alternative warhead could influence Bortezomib's selectivity. We synthesized an analog containing a chloromethyl ketone instead of the boronic acid warhead and determined potencies against the bacterial and human enzymes. Surprisingly, the analog retained activity against mycobacterial ClpP1P2 and was active against the mycobacterial proteasome, but was devoid of activity against the human proteasome. Interrogation of a set of chloromethyl ketone peptides identified three additional compounds similarly inhibiting both ClpP1P2 and the proteasome in the bacteria while leaving the human proteasome untouched. Finally, we showed that these compounds display bactericidal activity against M. tuberculosis with cytotoxicity ranging from acceptable to undetectable. These results suggest that selectivity over the human proteasome is achievable. Selectivity, together with dual-targeting of mycobacterial ClpP1P2 and proteasome makes this new scaffold an attractive starting point for optimization.

Towards Selective Mycobacterial ClpP1P2 Inhibitors with Reduced Activity against the Human Proteasome

Mycobacterium tuberculosis is responsible for the greatest number of deaths worldwide due to a bacterial agent. We recently identified bortezomib (Velcade; compound 1) as a promising antituberculosis (anti-TB) compound. We showed that compound 1 inhibits the mycobacterial caseinolytic proteases P1 and P2 (ClpP1P2) and exhibits bactericidal activity, and we established compound 1 and ClpP1P2 as an attractive lead/target couple. However, compound 1 is a human-proteasome inhibitor currently approved for cancer therapy and, as such, exhibits significant toxicity. Selective inhibition of the bacterial protease over the human proteasome is desirable in order to maintain antibacterial activity while reducing toxicity. We made use of structural data in order to design a series of dipeptidyl-boronate derivatives of compound 1. We tested these derivatives for whole-cell ClpP1P2 and human-proteasome inhibition as well as bacterial-growth inhibition and identified compounds that were up to 100-fold-less active against the human proteasome but that retained ClpP1P2 and mycobacterial-growth inhibition as well as bactericidal potency. The lead compound, compound 58, had low micromolar ClpP1P2 and anti-M. tuberculosis activity, good aqueous solubility, no cytochrome P450 liabilities, moderate plasma protein binding, and low toxicity in two human liver cell lines, and despite high clearance in microsomes, this compound was only moderately cleared when administered intravenously or orally to mice. Higher-dose oral pharmacokinetics indicated good dose linearity. Furthermore, compound 58 was inhibitory to only 11% of a panel of 62 proteases. Our work suggests that selectivity over the human proteasome can be achieved with a drug-like template while retaining potency against ClpP1P2 and, crucially, anti-M. tuberculosis activity.

Investigating Effects of Proteasome Inhibitor on Multiple Myeloma Cells Using Confocal Raman Microscopy

Due to its label-free and non-destructive nature, applications of Raman spectroscopic imaging in monitoring therapeutic responses at the cellular level are growing. We have recently developed a high-speed confocal Raman microscopy system to image living biological specimens with high spatial resolution and sensitivity. In the present study, we have applied this system to monitor the effects of Bortezomib, a proteasome inhibitor drug, on multiple myeloma cells. Cluster imaging followed by spectral profiling suggest major differences in the nuclear and cytoplasmic contents of cells due to drug treatment that can be monitored with Raman spectroscopy. Spectra were also acquired from group of cells and feasibility of discrimination among treated and untreated cells using principal component analysis (PCA) was accessed. Findings support the feasibility of Raman technologies as an alternate, novel method for monitoring live cell dynamics with minimal external perturbation.

Transcriptional Activation of Pericentromeric Satellite Repeats and Disruption of Centromeric Clustering upon Proteasome Inhibition

Heterochromatinisation of pericentromeres, which in mice consist of arrays of major satellite repeats, are important for centromere formation and maintenance of genome stability. The dysregulation of this process has been linked to genomic stress and various cancers. Here we show in mice that the proteasome binds to major satellite repeats and proteasome inhibition by MG132 results in their transcriptional de-repression; this de-repression is independent of cell-cycle perturbation. The transcriptional activation of major satellite repeats upon proteasome inhibition is accompanied by delocalisation of heterochromatin protein 1 alpha (HP1α) from chromocentres, without detectable change in the levels of histone H3K9me3, H3K4me3, H3K36me3 and H3 acetylation on the major satellite repeats. Moreover, inhibition of the proteasome was found to increase the number of chromocentres per cell, reflecting destabilisation of the chromocentre structures. Our findings suggest that the proteasome plays a role in maintaining heterochromatin integrity of pericentromeres.

Commentary on "Proteasome Inhibitors: A Novel Class of Potent and Effective Antitumor Agents"

The relatively recent clinical success of bortezomib, particularly in multiple myeloma, has established the validity of the proteasome as a viable target for anticancer drug development. This highly cited 1999 Cancer Research article from Adams and colleagues was published during the period when this drug was transitioning from preclinical studies to phase I clinical trial status. Their results detail structure-activity analyses using a series of boronic acid proteasome inhibitors and correlate cytotoxicity with inhibition of proteasome activity. In and of itself, the recognition that interference with proteasome functions represented a novel therapeutic approach likely underlies the popularity of this article. In addition, the provision of in vitro (at that time using the NCI 60 cell line panel) and in vivo antitumor activity, toxicology, and mouse pharmacokinetic and pharmacodynamic data provided a solid basis for establishing the future credentials for bortezomib to gain initial FDA approval in 2003. Cancer Res; 76(17); 4916-7. ©2016 AACRSee related article by Adams et al., Cancer Res 1999;59:2615-22Visit the Cancer Research 75(th) Anniversary timeline.

An integrated network platform for contextual prioritization of drugs and pathways

Repurposing of drugs to novel disease indications has promise for faster clinical translation. However, identifying the best drugs for a given pathological context is not trivial. We developed an integrated random walk-based network framework that combines functional biomolecular relationships and known drug-target interactions as a platform for contextual prioritization of drugs, genes and pathways. We show that the use of gene-centric or drug-centric data, such as gene expression data or a phenotypic drug screen, respectively, within this network platform can effectively prioritize drugs and pathways, respectively, to the studied biological context. We demonstrate that various genomic data can be used as contextual cues to effectively prioritize drugs to the studied context, while similarly, phenotypic drug screen data can be used to effectively prioritize genes and pathways to the studied phenotypic context. As a proof-of-principle, we showcase the use of our platform to identify known and novel drug indications against different subsets of breast cancers through contextual prioritization based on genome-wide gene expression, shRNA and drug screen and clinical survival data. The integrated network and associated methods are incorporated into the NetWalker suite for functional genomics analysis ().

Targeted immunotherapy using anti-CD138-interferon α fusion proteins and bortezomib results in synergistic protection against multiple myeloma

Although recent advances have substantially improved the management of multiple myeloma, it remains an incurable malignancy. We now demonstrate that anti-CD138 molecules genetically fused to type I interferons (IFN) synergize with the approved therapeutic bortezomib in arresting the proliferation of human multiple myeloma cell lines both in vitro and in vivo. The anti-CD138-IFNα14 fusion protein was active in inducing increased expression of signal transducer and activator of transcription 1 (STAT1) and its phosphorylation while the cell death pathway induced by bortezomib included generation of reactive oxygen species. Interferon regulatory factor 4 (IRF4), an important survival factor for myeloma cells, was down regulated following combination treatment. Induction of cell death appeared to be caspase-independent because treatment with inhibitors of caspase activation did not decrease the level of cell death. The observed caspase-independent synergistic cell death involved mitochondrial membrane depolarization, and poly(ADP-ribose) polymerase-1 (PARP-1) cleavage, and resulted in enhanced induction of apoptosis. Importantly, using 2 different in vivo xenograft models, we found that combination therapy of anti-CD138-IFNα14 and bortezomib was able to cure animals with established tumors (7 of 8 using OCI-My5 or 8 of 8 using NCI-H929). Thus, the combination of anti-CD138-IFNα with bortezomib shows great promise as a novel therapeutic approach for the treatment of multiple myeloma, a malignancy for which there are currently no cures.

Bortezomib for the treatment of mantle cell lymphoma: an update

Bortezomib is a first in class proteasome inhibitor, initially approved by the US Food and Drug Administration for the treatment of plasma cell myeloma. Bortezomib has been approved for the treatment of relapsed and refractory mantle cell lymphoma (MCL) and, more recently, in the upfront setting as well. Treatment algorithms for MCL have rapidly evolved over the past two decades, and the optimal regimen remains to be defined. The choice of treatment regimen is based on disease risk stratification models, the expected toxicity of antineoplastic agents, the perceived patient ability to tolerate the planned treatments and the availability of novel agents. As new drugs with novel mechanisms of action and variable toxicity profiles come into use, treatment decisions for a given patient have become increasingly complex. This article provides an overview of the evolving use of bortezomib in the rapidly changing management landscape of MCL.

Targeting ubiquitination for cancer therapies

Ubiquitination, the structured degradation and turnover of cellular proteins, is regulated by the ubiquitin-proteasome system (UPS). Most proteins that are critical for cellular regulations and functions are targets of the process. Ubiquitination is comprised of a sequence of three enzymatic steps, and aberrations in the pathway can lead to tumor development and progression as observed in many cancer types. Recent evidence indicates that targeting the UPS is effective for certain cancer treatment, but many more potential targets might have been previously overlooked. In this review, we will discuss the current state of small molecules that target various elements of ubiquitination. Special attention will be given to novel inhibitors of E3 ubiquitin ligases, especially those in the SCF family.

Tumor cell survival pathways activated by photodynamic therapy: a molecular basis for pharmacological inhibition strategies

Photodynamic therapy (PDT) has emerged as a promising alternative to conventional cancer therapies such as surgery, chemotherapy, and radiotherapy. PDT comprises the administration of a photosensitizer, its accumulation in tumor tissue, and subsequent irradiation of the photosensitizer-loaded tumor, leading to the localized photoproduction of reactive oxygen species (ROS). The resulting oxidative damage ultimately culminates in tumor cell death, vascular shutdown, induction of an antitumor immune response, and the consequent destruction of the tumor. However, the ROS produced by PDT also triggers a stress response that, as part of a cell survival mechanism, helps cancer cells to cope with the PDT-induced oxidative stress and cell damage. These survival pathways are mediated by the transcription factors activator protein 1 (AP-1), nuclear factor E2-related factor 2 (NRF2), hypoxia-inducible factor 1 (HIF-1), nuclear factor κB (NF-κB), and those that mediate the proteotoxic stress response. The survival pathways are believed to render some types of cancer recalcitrant to PDT and alter the tumor microenvironment in favor of tumor survival. In this review, the molecular mechanisms are elucidated that occur post-PDT to mediate cancer cell survival, on the basis of which pharmacological interventions are proposed. Specifically, pharmaceutical inhibitors of the molecular regulators of each survival pathway are addressed. The ultimate aim is to facilitate the development of adjuvant intervention strategies to improve PDT efficacy in recalcitrant solid tumors.

Triomics Analysis of Imatinib-Treated Myeloma Cells Connects Kinase Inhibition to RNA Processing and Decreased Lipid Biosynthesis

The combination of metabolomics, lipidomics, and phosphoproteomics that incorporates triple stable isotope labeling by amino acids in cell culture (SILAC) protein labeling, as well as (13)C in vivo metabolite labeling, was demonstrated on BCR-ABL-positive H929 multiple myeloma cells. From 11 880 phosphorylation sites, we confirm that H929 cells are primarily signaling through the BCR-ABL-ERK pathway, and we show that imatinib treatment not only downregulates phosphosites in this pathway but also upregulates phosphosites on proteins involved in RNA expression. Metabolomics analyses reveal that BCR-ABL-ERK signaling in H929 cells drives the pentose phosphate pathway (PPP) and RNA biosynthesis, where pathway inhibition via imatinib results in marked PPP impairment and an accumulation of RNA nucleotides and negative regulation of mRNA. Lipidomics data also show an overall reduction in lipid biosynthesis and fatty acid incorporation with a significant decrease in lysophospholipids. RNA immunoprecipitation studies confirm that RNA degradation is inhibited with short imatinib treatment and transcription is inhibited upon long imatinib treatment, validating the triomics results. These data show the utility of combining mass spectrometry-based "-omics" technologies and reveals that kinase inhibitors may not only downregulate phosphorylation of their targets but also induce metabolic events via increased phosphorylation of other cellular components.

Substrate-guided optimization of the syringolins yields potent proteasome inhibitors with activity against leukemia cell lines

Natural products that inhibit the proteasome have been fruitful starting points for the development of drug candidates. Those of the syringolin family have been underexploited in this context. Using the published model for substrate mimicry by the syringolins and knowledge about the substrate preferences of the proteolytic subunits of the human proteasome, we have designed, synthesized, and evaluated syringolin analogs. As some of our analogs inhibit the activity of the proteasome with second-order rate constants 5-fold greater than that of the methyl ester of syringolin B, we conclude that the substrate mimicry model for the syringolins is valid. The improvements in in vitro potency and the activities of particular analogs against leukemia cell lines are strong bases for further development of the syringolins as anti-cancer drugs.

Therapeutic applications of TRAIL receptor agonists in cancer and beyond

TRAIL/Apo-2L is a member of the TNF superfamily first described as an apoptosis-inducing cytokine in 1995. Similar to TNF and Fas ligand, TRAIL induces apoptosis in caspase-dependent manner following TRAIL death receptor trimerization. Because tumor cells were shown to be particularly sensitive to this cytokine while normal cells/tissues proved to be resistant along with being able to synthesize and release TRAIL, it was rapidly appreciated that TRAIL likely served as one of our major physiologic weapons against cancer. In line with this, a number of research laboratories and pharmaceutical companies have attempted to exploit the ability of TRAIL to kill cancer cells by developing recombinant forms of TRAIL or TRAIL receptor agonists (e.g., receptor-specific mAb) for therapeutic purposes. In this review article we will describe the biochemical pathways used by TRAIL to induce different cell death programs. We will also summarize the clinical trials related to this pathway and discuss possible novel uses of TRAIL-related therapies. In recent years, the physiological importance of TRAIL has expanded beyond being a tumoricidal molecule to one critical for a number of clinical settings - ranging from infectious disease and autoimmunity to cardiovascular anomalies. We will also highlight some of these conditions where modulation of the TRAIL/TRAIL receptor system may be targeted in the future.

Post-translational Down-regulation of Melanoma Antigen-A11 (MAGE-A11) by Human p14-ARF Tumor Suppressor

X-linked primate-specific melanoma antigen-A11 (MAGE-A11) is a human androgen receptor (AR) coactivator and proto-oncogene expressed at low levels in normal human reproductive tract tissues and at higher levels in castration-resistant prostate cancer where it is required for androgen-dependent cell growth. In this report, we show that MAGE-A11 is targeted for degradation by human p14-ARF, a tumor suppressor expressed from an alternative reading frame of the p16 cyclin-dependent kinase inhibitor INK4a/ARF gene. MAGE-A11 degradation by the proteasome was mediated by an interaction with p14-ARF and was independent of lysine ubiquitination. A dose-dependent inverse relationship between MAGE-A11 and p14-ARF correlated with p14-ARF inhibition of the MAGE-A11-induced increase in androgen-dependent AR transcriptional activity and constitutive activity of a splice variant-like AR. Reciprocal stabilization between MAGE-A11 and AR did not protect against degradation promoted by p14-ARF. p14-ARF prevented MAGE-A11 interaction with the E2F1 oncoprotein and inhibited the MAGE-A11-induced increase in E2F1 transcriptional activity. Post-translational down-regulation of MAGE-A11 promoted by p14-ARF was independent of HDM2, the human homologue of mouse double minute 2, an E3 ubiquitin ligase inhibited by p14-ARF. However, MAGE-A11 had a stabilizing effect on HDM2 in the absence or presence of p14-ARF and cooperated with HDM2 to increase E2F1 transcriptional activity in the absence of p14-ARF. We conclude that degradation of MAGE-A11 promoted by the human p14-ARF tumor suppressor contributes to low levels of MAGE-A11 in nontransformed cells and that higher levels of MAGE-A11 associated with low p14-ARF increase AR and E2F1 transcriptional activity and promote the development of castration-resistant prostate cancer.

The oncogenic transcription factor IRF4 is regulated by a novel CD30/NF-κB positive feedback loop in peripheral T-cell lymphoma

Peripheral T-cell lymphomas (PTCLs) are generally aggressive non-Hodgkin lymphomas with poor overall survival rates following standard therapy. One-third of PTCLs express interferon regulatory factor-4 (IRF4), a tightly regulated transcription factor involved in lymphocyte growth and differentiation. IRF4 drives tumor growth in several lymphoid malignancies and has been proposed as a candidate therapeutic target. Because direct IRF4 inhibitors are not clinically available, we sought to characterize the mechanism by which IRF4 expression is regulated in PTCLs. We demonstrated that IRF4 is constitutively expressed in PTCL cells and drives Myc expression and proliferation. Using an inhibitor screen, we identified nuclear factor κB (NF-κB) as a candidate regulator of IRF4 expression and cell proliferation. We then demonstrated that the NF-κB subunits p52 and RelB were transcriptional activators of IRF4. Further analysis showed that activation of CD30 promotes p52 and RelB activity and subsequent IRF4 expression. Finally, we showed that IRF4 transcriptionally regulates CD30 expression. Taken together, these data demonstrate a novel positive feedback loop involving CD30, NF-κB, and IRF4; further evidence for this mechanism was demonstrated in human PTCL tissue samples. Accordingly, NF-κB inhibitors may represent a clinical means to disrupt this feedback loop in IRF4-positive PTCLs.

Target mechanism-based whole-cell screening identifies bortezomib as an inhibitor of caseinolytic protease in mycobacteria

A novel type of antibacterial screening method, a target mechanism-based whole-cell screening method, was developed to combine the advantages of target mechanism- and whole-cell-based approaches. A mycobacterial reporter strain with a synthetic phenotype for caseinolytic protease (ClpP1P2) activity was engineered, allowing the detection of inhibitors of this enzyme inside intact bacilli. A high-throughput screening method identified bortezomib, a human 26S proteasome drug, as a potent inhibitor of ClpP1P2 activity and bacterial growth. A battery of secondary assays was employed to demonstrate that bortezomib indeed exerts its antimicrobial activity via inhibition of ClpP1P2: Down- or upmodulation of the intracellular protease level resulted in hyper- or hyposensitivity of the bacteria, the drug showed specific potentiation of translation error-inducing aminoglycosides, ClpP1P2-specific substrate WhiB1 accumulated upon exposure, and growth inhibition potencies of bortezomib derivatives correlated with ClpP1P2 inhibition potencies. Furthermore, molecular modeling showed that the drug can bind to the catalytic sites of ClpP1P2. This work demonstrates the feasibility of target mechanism-based whole-cell screening, provides chemical validation of ClpP1P2 as a target, and identifies a drug in clinical use as a new lead compound for tuberculosis therapy.

During the last decade, antibacterial drug discovery relied on biochemical assays, rather than whole-cell approaches, to identify molecules that interact with purified target proteins derived by genomics. This approach failed to deliver antibacterial compounds with whole-cell activity, either because of cell permeability issues that medicinal chemistry cannot easily fix or because genomic data of essentiality insufficiently predicted the vulnerability of the target identified. As a consequence, the field largely moved back to a whole-cell approach whose main limitation is its black-box nature, i.e., that it requires trial-and-error chemistry because the cellular target is unknown. We developed a novel type of antibacterial screening method, target mechanism-based whole-cell screening, to combine the advantages of both approaches. We engineered a mycobacterial reporter strain with a synthetic phenotype allowing us to identify inhibitors of the caseinolytic protease (ClpP1P2) inside the cell. This approach identified bortezomib, an anticancer drug, as a specific inhibitor of ClpP1P2. We further confirmed the specific “on-target” activity of bortezomib by independent approaches including, but not limited to, genetic manipulation of the target level (over- and underexpressing strains) and by establishing a dynamic structure-activity relationship between ClpP1P2 and growth inhibition. Identifying an “on-target” compound is critical to optimize the efficacy of the compound without compromising its specificity. This work demonstrates the feasibility of target mechanism-based whole-cell screening methods, validates ClpP1P2 as a druggable target, and delivers a lead compound for tuberculosis therapy.

Corticospinal Motor Neurons Are Susceptible to Increased ER Stress and Display Profound Degeneration in the Absence of UCHL1 Function

Corticospinal motor neurons (CSMN) receive, integrate, and relay cerebral cortex's input toward spinal targets to initiate and modulate voluntary movement. CSMN degeneration is central for numerous motor neuron disorders and neurodegenerative diseases. Previously, 5 patients with mutations in the ubiquitin carboxy-terminal hydrolase-L1 (UCHL1) gene were reported to have neurodegeneration and motor neuron dysfunction with upper motor neuron involvement. To investigate the role of UCHL1 on CSMN health and stability, we used both in vivo and in vitro approaches, and took advantage of the Uchl1^nm3419 (UCHL1^−/−) mice, which lack all UCHL1 function. We report a unique role of UCHL1 in maintaining CSMN viability and cellular integrity. CSMN show early, selective, progressive, and profound cell loss in the absence of UCHL1. CSMN degeneration, evident even at pre-symptomatic stages by disintegration of the apical dendrite and spine loss, is mediated via increased ER stress. These findings bring a novel understanding to the basis of CSMN vulnerability, and suggest UCHL1^−/− mice as a tool to study CSMN pathology.

Bortezomib for the treatment of non-Hodgkin's lymphoma

INTRODUCTION

Bortezomib , the first proteasome inhibitor (PI) to be evaluated in humans, is approved in the USA and Europe for the treatment of patients with multiple myeloma, and in the USA for patients with relapsed mantle cell lymphoma (MCL).

AREAS COVERED

This review examines the role of bortezomib in the therapy of non-Hodgkin's lymphoma (NHL). Bortezomib may be particularly effective against the NF-κB-dependent activated B-cell subtype of diffuse large B-cell lymphoma. The combination of bortezomib with rituximab and dexamethasone represents a standard approach for the treatment of Waldenström's macroglobulinemia, and that with bendamustine and rituximab has demonstrated excellent efficacy in follicular lymphoma. Combinations with other novel agents, such as inhibitors of cyclin-dependent kinases or histone deacetylases, also hold substantial promise in NHL. Unmet needs in NHL, competitor compounds, chemistry, pharmacokinetics, pharmacodynamics and safety and tolerability of bortezomib are also discussed.

EXPERT OPINION

The success of bortezomib in MCL has validated the proteasome as a therapeutic target in NHL. Rational combinations, for example, with Bruton's tyrosine kinase inhibitors or BH3-mimetics, may hold the key to optimizing the therapeutic potential of PIs in NHL. Future trials are likely to involve newer agents with improved pharmacodynamic (e.g., carfilzomib, marizomib) or pharmacokinetic (e.g., ixazomib, oprozomib) properties.

Curcumin as a protector for normal cells during bortezomib therapy

This study evaluated the protective potential of curcumin on the possible side effects of bortezomib (Bt) therapy on normal cells in mice. The mice were segregated into three groups ( n = 10) that included normal control, Bt-treated, and Bt + curcumin-treated groups. The Bt treatment resulted in significant decrease in the enzyme activity of erythrocyte δ-aminolevulinic acid dehydratase (ALAD). Also a significant decrease in the hemoglobin (Hb) was also noticed. On the other hand, curcumin co-treatment improvised enzyme activity of erythrocyte ALAD as well as Hb values. The study, therefore, concludes that curcumin co-treatment with Bt has a potential to take care of possible side effects of Bt therapy on normal cells.

Spinal administration of mGluR5 antagonist prevents the onset of bortezomib induced neuropathic pain in rat

Peripheral neuropathy is a common adverse effect of bortezomib-based chemotherapy. In this study we have investigated the role played by subtype 5 of metabotropic receptors in bortezomib induced peripheral neuropathy. Rats were administered with bortezomib three times weekly at 0.20 mg/kg for a total of 4 weeks in presence or absence of mGluR5 antagonist MPEP. The animals were submitted to paw-pressure test and tail sensory nerve conduction measurement more times during the treatment and follow-up. Bortezomib treatment induced a progressively increasing hyperalgesia in rat which was accompanied by a significant reduction in sensory nerve conduction velocity (SNCV). MPEP prevented the emergence of bortezomib-induced pain and counteracted SNCV reduction when co-administered with bortezomib treatment. Spinal extracellular glutamate levels increased in rats treated with bortezomib. Bortezomib-induced onset of the hyperalgesia and SNCV decrease could be prevented by agents that promote the reuptake of glutamate maintaining spinal glutamate at basal level. Our data support the manipulation of the glutamatergic system through the mGluR5 receptor in bortezomib induced peripheral neuropathy. The use of antagonists at the mGluR5, initiated at the same time as bortezomib-chemotherapy, might reduce the number of patients who develop painful peripheral chemo-neuropathy.

Pharmacological modulation of anti-tumor immunity induced by oncolytic viruses

Oncolytic viruses (OVs) not only kill cancer cells by direct lysis but also generate a significant anti-tumor immune response that allows for prolonged cancer control and in some cases cures. How to best stimulate this effect is a subject of intense investigation in the OV field. While pharmacological manipulation of the cellular innate anti-viral immune response has been shown by several groups to improve viral oncolysis and spread, it is increasingly clear that pharmacological agents can also impact the anti-tumor immune response generated by OVs and related tumor vaccination strategies. This review covers recent progress in using pharmacological agents to improve the activity of OVs and their ability to generate robust anti-tumor immune responses.

Molecular pathways: turning proteasomal protein degradation into a unique treatment approach

Cancer treatment regimens have evolved from single cytotoxic substances affecting all proliferative tissues toward antibodies and kinase inhibitors targeting tumor-specific pathways. Treatment efficacy and cancer survival have improved overall, and side effects have become less frequent. The ubiquitin-proteasome system-mediated proteasomal protein degradation is the most critical pathway to regulate the quantity of signal proteins involved in carcinogenesis and tumor progression. These processes are, as well as protein recycling, highly regulated and offer targets for biomarker and drug development. Unspecific proteasome inhibitors such as bortezomib and carfilzomib have shown clinical efficacy and are approved for clinical use. Inhibitors of more substrate-specific enzymes of degradation processes are being developed and are now in early clinical trials. The novel compounds focus on the degradation of key regulatory proteins such as p53, p27(Kip1), and ß-catenin, and inhibitors specific for growth factor receptor kinase turnover are in preclinical testing.

Pathway analysis for drug repositioning based on public database mining

Sixteen FDA-approved drugs were investigated to elucidate their mechanisms of action (MOAs) and clinical functions by pathway analysis based on retrieved drug targets interacting with or affected by the investigated drugs. Protein and gene targets and associated pathways were obtained by data-mining of public databases including the MMDB, PubChem BioAssay, GEO DataSets, and the BioSystems databases. Entrez E-Utilities were applied, and in-house Ruby scripts were developed for data retrieval and pathway analysis to identify and evaluate relevant pathways common to the retrieved drug targets. Pathways pertinent to clinical uses or MOAs were obtained for most drugs. Interestingly, some drugs identified pathways responsible for other diseases than their current therapeutic uses, and these pathways were verified retrospectively by in vitro tests, in vivo tests, or clinical trials. The pathway enrichment analysis based on drug target information from public databases could provide a novel approach for elucidating drug MOAs and repositioning, therefore benefiting the discovery of new therapeutic treatments for diseases.

Correlation of BAG-3 and heat shock protein 70 with CD30 expression in T-cell lymphomas

T-cell lymphomas are aggressive lymphomas with decreased prognosis and resistance to therapy. BAG-3 and heat shock protein 70 (HSP70) function in chemotherapeutic resistance and cellular survival. Expression of BAG-3 has not been investigated in T cell lymphomas. We investigated fifty cases including benign, systemic and cutaneous T cell lymphomas. Benign T cells were negative for BAG-3 and HSP70 immunohistochemical staining. BAG-3 expression correlated with increased HSP70 expression in a subset of systemic T cell lymphoma cases co-expressing the CD30 antigen. Correlation between BAG-3, HSP70 and CD30 expression was not seen in cutaneous T cell lymphoma cases. However, these cases showed a significant increase in BAG-3 staining when compared to CD30 negative systemic T cell lymphoma cases. The differential protein expression profile of BAG-3 and HSP70 may indicate a specific role for these proteins and the ubiquitin-proteasome system/autophagy in T cell lymphomas which may help guide future targeted therapy.

Discrepant NOXA (PMAIP1) transcript and NOXA protein levels: a potential Achilles' heel in mantle cell lymphoma

Mantle cell lymphoma (MCL) is an aggressive lymphoid neoplasm with transient response to conventional chemotherapy. We here investigated the role of the Bcl-2 homology domain 3-only protein NOXA for life–death decision in MCL. Surprisingly, NOXA (PMAIP1) mRNA and NOXA protein levels were extremely discrepant in MCL cells: NOXA mRNA was found to be highly expressed whereas NOXA protein levels were low. Chronic active B-cell receptor signaling and to a minor degree cyclin D1 overexpression contributed to high NOXA mRNA expression levels in MCL cells. The phoshatidyl-inositol-3 kinase/AKT/mammalian target of rapamycin pathway was identified as the major downstream signaling pathway involved in the maintenance of NOXA gene expression. Interestingly, MCL cells adapt to this constitutive pro-apoptotic signal by extensive ubiquitination and rapid proteasomal degradation of NOXA protein (T_½∼15–30 min). In addition to the proteasome inhibitor Bortezomib, we identified the neddylation inhibitor MLN4924 and the fatty acid synthase inhibitor Orlistat as potent inducers of NOXA protein expression leading to apoptosis in MCL. All inhibitors targeted NOXA protein turnover. In contrast to Bortezomib, MLN4924 and Orlistat interfered with the ubiquitination process of NOXA protein thereby offering new strategies to kill Bortezomib-resistant MCL cells. Our data, therefore, highlight a critical role of NOXA in the balance between life and death in MCL. The discrepancy between NOXA transcript and protein levels is essential for sensitivity of MCL to ubiquitin-proteasome system inhibitors and could therefore provide a druggable Achilles' heel of MCL cells.

Bortezomib-induced painful peripheral neuropathy: an electrophysiological, behavioral, morphological and mechanistic study in the mouse

Bortezomib is the first proteasome inhibitor with significant antineoplastic activity for the treatment of relapsed/refractory multiple myeloma as well as other hematological and solid neoplasms. Peripheral neurological complications manifesting with paresthesias, burning sensations, dysesthesias, numbness, sensory loss, reduced proprioception and vibratory sensitivity are among the major limiting side effects associated with bortezomib therapy. Although bortezomib-induced painful peripheral neuropathy is clinically easy to diagnose and reliable models are available, its pathophysiology remains partly unclear.

In this study we used well-characterized immune-competent and immune-compromised mouse models of bortezomib-induced painful peripheral neuropathy. To characterize the drug-induced pathological changes in the peripheral nervous system, we examined the involvement of spinal cord neuronal function in the development of neuropathic pain and investigated the relevance of the immune response in painful peripheral neuropathy induced by bortezomib.

We found that bortezomib treatment induced morphological changes in the spinal cord, dorsal roots, dorsal root ganglia (DRG) and peripheral nerves. Neurophysiological abnormalities and specific functional alterations in Aδ and C fibers were also observed in peripheral nerve fibers. Mice developed mechanical allodynia and functional abnormalities of wide dynamic range neurons in the dorsal horn of spinal cord. Bortezomib induced increased expression of the neuronal stress marker activating transcription factor-3 in most DRG. Moreover, the immunodeficient animals treated with bortezomib developed a painful peripheral neuropathy with the same features observed in the immunocompetent mice.

In conclusion, this study extends the knowledge of the sites of damage induced in the nervous system by bortezomib administration. Moreover, a selective functional vulnerability of peripheral nerve fiber subpopulations was found as well as a change in the electrical activity of wide dynamic range neurons of dorsal horn of spinal cord. Finally, the immune response is not a key factor in the development of morphological and functional damage induced by bortezomib in the peripheral nervous system.

Bortezomib induces apoptosis and autophagy in osteosarcoma cells through mitogen-activated protein kinase pathway in vitro

Objective

To investigate the effects of bortezomib on human osteosarcoma cells from the HOS cell line, and the underlying associated mechanisms.

Methods

Viability of HOS cells treated with bortezomib (5–20 nM) for different time periods was measured and changes in the cell cycle were assessed. Apoptosis and autophagy in HOS cells treated with bortezomib were analysed using annexin V-fluorescein isothiocyanate assay, transmission electron microscopy and Western blotting. Surges in mitogen-activated protein kinase (MAPK) pathways including MAPK/extracellular signal-regulated kinase (ERK) kinase (MEK1/2), ERK1/2, c-Jun N-terminal kinase (JNK) and p38 MAPK were analysed using Western blotting.

Results

Bortezomib induced growth inhibition in a time- and dose-dependent manner, and autophagy and apoptosis in a dose-dependent manner, in HOS cells. HOS cell autophagy and apoptosis in response to bortezomib, corresponded with changing levels of intracellular MAPK signalling molecules.

Conclusions

This study provided new insights into the mechanisms underlying bortezomib-induced apoptosis in human osteosarcoma HOS cells, and suggests that bortezomib could be a potent chemotherapeutic agent in the treatment of osteosarcoma.

Current state of cardiac amyloidosis

PURPOSE OF REVIEW

Cardiac amyloidosis, an infiltrative restrictive cardiomyopathy once thought to be universally fatal, is now increasingly recognized as less rare than previously thought. This update is intended to provide a review of newer aspects of the presentation, diagnosis and treatment of cardiac amyloidosis.

RECENT FINDINGS

Amyloid involvement of the heart is increasingly seen, especially in the elderly population. Recent data suggest life expectancy has increased from 6 to 16-20 months in the most common subtype, AL amyloid. The clinical presentation is typically one of heart failure in the setting of normal or low normal ejection fraction, inappropriate ventricular hypertrophy and atrial enlargement with or without atrial fibrillation. Diagnosis is now most often made by cardiac MRI, with 2D echocardiography serving more of a screening role in patients with heart failure or a similar family history. The gold standard diagnostic test is right-ventricular biopsy, which demonstrates positivity for Congo Red staining. Due to a propensity for disease progression, typically low systemic blood pressure, frequent extra-cardiac involvement and autonomic dysfunction, cardiac amyloidosis is difficult to treat due to poor tolerance of most cardiovascular medication and poor outcome for transplantation. Newer therapies such as bortezomib, usually given to patients with multiple myeloma and serum light chains, are promising in controlling amyloidosis.

CONCLUSION

Recent advances in diagnosis and treatment of amyloid are associated with improved prognosis. Newer therapies offer future benefits.

Expression and cellular distribution of ubiquitin in response to injury in the developing spinal cord of Monodelphis domestica

Ubiquitin, an 8.5 kDa protein associated with the proteasome degradation pathway has been recently identified as differentially expressed in segment of cord caudal to site of injury in developing spinal cord. Here we describe ubiquitin expression and cellular distribution in spinal cord up to postnatal day P35 in control opossums (Monodelphis domestica) and in response to complete spinal transection (T10) at P7, when axonal growth through site of injury occurs, and P28 when this is no longer possible. Cords were collected 1 or 7 days after injury, with age-matched controls and segments rostral to lesion were studied. Following spinal injury ubiquitin levels (western blotting) appeared reduced compared to controls especially one day after injury at P28. In contrast, after injury mRNA expression (qRT-PCR) was slightly increased at P7 but decreased at P28. Changes in isoelectric point of separated ubiquitin indicated possible post-translational modifications. Cellular distribution demonstrated a developmental shift between earliest (P8) and latest (P35) ages examined, from a predominantly cytoplasmic immunoreactivity to a nuclear expression; staining level and shift to nuclear staining was more pronounced following injury, except 7 days after transection at P28. After injury at P7 immunostaining increased in neurons and additionally in oligodendrocytes at P28. Mass spectrometry showed two ubiquitin bands; the heavier was identified as a fusion product, likely to be an ubiquitin precursor. Apparent changes in ubiquitin expression and cellular distribution in development and response to spinal injury suggest an intricate regulatory system that modulates these responses which, when better understood, may lead to potential therapeutic targets.

A whole-genome RNA interference screen for human cell factors affecting myxoma virus replication

Myxoma virus (MYXV) provides an important model for investigating host-pathogen interactions. Recent studies have also highlighted how mutations in transformed human cells can expand the host range of this rabbit virus. Although virus growth depends upon interactions between virus and host proteins, the nature of these interactions is poorly understood. To address this matter, we performed small interfering RNA (siRNA) screens for genes affecting MYXV growth in human MDA-MB-231 cells. By using siRNAs targeting the whole human genome (21,585 genes), a subset of human phosphatases and kinases (986 genes), and also a custom siRNA library targeting selected statistically significant genes ("hits") and nonsignificant genes ("nonhits") of the whole human genome screens (88 genes), we identified 711 siRNA pools that promoted MYXV growth and 333 that were inhibitory. Another 32 siRNA pools (mostly targeting the proteasome) were toxic. The overall overlap in the results was about 25% for the hits and 75% for the nonhits. These pro- and antiviral genes can be clustered into pathways and related groups, including well-established inflammatory and mitogen-activated protein kinase pathways, as well as clusters relating to β-catenin and the Wnt signaling cascade, the cell cycle, and cellular metabolism. The validity of a subset of these hits was independently confirmed. For example, treating cells with siRNAs that might stabilize cells in G(1), or inhibit passage into S phase, stimulated MYXV growth, and these effects were reproduced by trapping cells at the G(1)/S boundary with an inhibitor of cyclin-dependent kinases 4/6. By using 2-deoxy-D-glucose and plasmids carrying the gene for phosphofructokinase, we also confirmed that infection is favored by aerobic glycolytic metabolism. These studies provide insights into how the growth state and structure of cells affect MYXV growth and how these factors might be manipulated to advantage in oncolytic virus therapy.

Bortezomib regulates the chemotactic characteristics of T cells through downregulation of CXCR3/CXCL9 expression and induction of apoptosis

The chemotactic movement of T lymphocytes mediated by chemokines and their receptors plays an important role in the pathogenesis of graft-versus-host disease (GVHD) post-allogeneic hematopoietic stem cell transplantation (allo-HSCT). CCR7 and CXCR3 are two receptors associated with the development of GVHD. Bortezomib, a proteasome inhibitor, was recently found to prevent GVHD in a mouse model and to decrease the production of Th1 cytokines. Here, we report that bortezomib differentially regulates the expression of CXCR3 and CCR7 on T cells; it significantly decreases CXCR3 expression on T cells as well as its CD4(+)/CD8(+) subsets in a dose-dependent manner, while it does not significantly affect CCR7 expression on T cells and subsets. Moreover, the secretion of CXCL9 by activated T cells is also increasingly downregulated with increasing concentrations of bortezomib. Meanwhile, bortezomib inhibits T-cell chemotactic movements toward CXCL9 in a dose-dependent manner, but has no effect on CCL19-induced T-cell chemotaxis. Additionally, it was found that bortezomib treatment also prompts T-lymphocyte apoptosis through activation of caspase-3 and its downstream PARP cleavage in a dose- and time-dependent manner. These results suggest that bortezomib may act as a suppressor of GVHD by downregulating T-cell chemotatic movement toward GVHD target organs, as well as by inducing apoptosis.

Proteasome inhibition and combination therapy for non-Hodgkin's lymphoma: from bench to bedside

Although patients with B-cell non-Hodgkin's lymphoma (NHL) usually respond to initial conventional chemotherapy, they often relapse and mortality has continued to increase over the last three decades in spite of salvage therapy or high dose therapy and stem cell transplantation. Outcomes vary by subtype, but there continues to be a need for novel options that can help overcome chemotherapy resistance, offer new options as consolidation or maintenance therapy postinduction, and offer potentially less toxic combinations, especially in the elderly population. The bulk of these emerging novel agents for cancer treatment target important biological cellular processes. Bortezomib is the first in the class of proteasome inhibitors (PIs), which target the critical process of intracellular protein degradation or recycling and editing through the proteasome. Bortezomib is approved for the treatment of relapsed or refractory mantle cell lymphoma. The mechanisms of proteasome inhibition are very complex by nature (because they affect many pathways) and not fully understood. However, mechanisms of action shared by bortezomib and investigational PIs such as carfilzomib, marizomib, ONX-0912, and MLN9708 are distinct from those of other NHL treatments, making them attractive options for combination therapy. Preclinical evidence suggests that the PIs have additive and/or synergistic activity with a large number of agents both in vitro and in vivo, from cytotoxics to new biologicals, supporting a growing number of combination studies currently underway in NHL patients, as reviewed in this article. The results of these studies will help our understanding about how to best integrate proteasome inhibition in the management of NHL and continue to improve patient outcomes.