Novel, orally active, proteasome inhibitor, delanzomib (CEP-18770), ameliorates disease symptoms and glomerulonephritis in two preclinical mouse models of SLE

Primed for Interactions: Investigating the Primed Substrate Channel of the Proteasome for Improved Molecular Engagement

Protein homeostasis is a tightly conserved process that is regulated through the ubiquitin proteasome system (UPS) in a ubiquitin-independent or ubiquitin-dependent manner. Over the past two decades, the proteasome has become an excellent therapeutic target through inhibition of the catalytic core particle, inhibition of subunits responsible for recognizing and binding ubiquitinated proteins, and more recently, through targeted protein degradation using proteolysis targeting chimeras (PROTACs). The majority of the developed inhibitors of the proteasome's core particle rely on gaining selectivity through binding interactions within the unprimed substrate channel. Although this has allowed for selective inhibitors and chemical probes to be generated for the different proteasome isoforms, much remains unknown about the interactions that could be harnessed within the primed substrate channel to increase potency or selectivity. Herein, we discuss small molecules that interact with the primed substrate pocket and how their differences may give rise to altered activity. Taking advantage of additional interactions with the primed substrate pocket of the proteasome could allow for the generation of improved chemical tools for perturbing or monitoring proteasome activity.

Promising Experimental Treatments for Lupus Nephritis: Key Talking Points and Potential Opportunities

Lupus nephritis (LN) is a frequent and serious complication of systemic lupus erythematosus (SLE), impairing patients' quality of life and significantly increasing mortality. Despite optimizing the use of conventional immunosuppressants and other biological drugs, its management remains unsatisfactory. This is mainly due to the heterogeneity of SLE, but also to insufficiently effective treatment regimens and clinical trial limitations (strict criteria, low number of patients included, and side effects). Most clinical trials of new biological therapies have failed to meet their primary endpoints in both general SLE and LN, with only two biological drugs (belimumab and anifrolumab) being approved by the Food and Drug Administration (FDA) for the treatment of SLE. Recently, several Phase II randomized controlled trials have evaluated the efficacy and safety of new biologics in LN, and some of them have demonstrated an improvement in clinical and laboratory measures. Multi-target therapies are also being successfully developed and encourage a belief that there will be an improvement in LN outcomes.

Targeted Small Molecules for Systemic Lupus Erythematosus: Drugs in the Pipeline

Despite the uncertainty of the pathogenesis of systemic lupus erythematosus, novel small molecules targeting specific intracellular mechanisms of immune cells are being developed to reverse the pathophysiological processes. These targeted molecules have the advantages of convenient administration, lower production costs, and the lack of immunogenicity. The Janus kinases, Bruton's tyrosine kinases, and spleen tyrosine kinases are important enzymes for activating downstream signals from various receptors on immune cells that include cytokines, growth factor, hormones, Fc, CD40, and B-cell receptors. Suppression of these kinases impairs cellular activation, differentiation, and survival, leading to diminished cytokine actions and autoantibody secretion. Intracellular protein degradation by immunoproteasomes, levered by the cereblon E3 ubiquitin ligase complex, is an essential process for the regulation of cellular functions and survival. Modulation of the immunoproteasomes and cereblon leads to depletion of long-lived plasma cells, reduced plasmablast differentiation, and production of autoantibodies and interferon-α. The sphingosine 1-phosphate/sphingosine 1-phosphate receptor-1 pathway is responsible for lymphocyte trafficking, regulatory T-cell/Th17 cell homeostasis, and vascular permeability. Sphingosine 1-phosphate receptor-1 modulators limit the trafficking of autoreactive lymphocytes across the blood-brain barrier, increase regulatory T-cell function, and decrease production of autoantibodies and type I interferons. This article summarizes the development of these targeted small molecules in the treatment of systemic lupus erythematosus, and the future prospect for precision medicine.

Aberrant B Cell Signaling in Autoimmune Diseases

Aberrant B cell signaling plays a critical in role in various systemic and organ-specific autoimmune diseases. This is supported by genetic evidence by many functional studies in B cells from patients or specific animal models and by the observed efficacy of small-molecule inhibitors. In this review, we first discuss key signal transduction pathways downstream of the B cell receptor (BCR) that ensure that autoreactive B cells are removed from the repertoire or functionally silenced. We provide an overview of aberrant BCR signaling that is associated with inappropriate B cell repertoire selection and activation or survival of peripheral B cell populations and plasma cells, finally leading to autoantibody formation. Next to BCR signaling, abnormalities in other signal transduction pathways have been implicated in autoimmune disease. These include reduced activity of several phosphates that are downstream of co-inhibitory receptors on B cells and increased levels of BAFF and APRIL, which support survival of B cells and plasma cells. Importantly, pathogenic synergy of the BCR and Toll-like receptors (TLR), which can be activated by endogenous ligands, such as self-nucleic acids, has been shown to enhance autoimmunity. Finally, we will briefly discuss therapeutic strategies for autoimmune disease based on interfering with signal transduction in B cells.

Enantioselective synthesis of cyclic α-aminoboronates via copper-catalyzed dearomative borylation of 4-quinolinols

A highly enantioselective and regioselective dearomative borylation of 4-quinolinols was developed using a Cu(I)/(R,R)-Ph-BPE catalyst for efficient synthesis of unprecedented heterocyclic α-amino boronates, a new class of compounds potentially relevant to drug discovery, in generally excellent yields and enantioselectivities. The products were also useful intermediates for highly functionalized tetrahydroquinolines and cyclic α-aminoboronate derivatives.

Delanzomib, a Novel Proteasome Inhibitor, Combined With Adalimumab Drastically Ameliorates Collagen-Induced Arthritis in Rats by Improving and Prolonging the Anti-TNF-α Effect of Adalimumab

Delanzomib is a novel proteasome inhibitor initially developed for treating multiple myeloma. It was found to inhibit the expression of tumor necrosis factor alpha (TNF-α). This study aimed to investigate the ameliorating effect of delanzomib on collagen-induced arthritis (CIA) and to explore the pharmacodynamics and pharmacokinetics (PK) interactions between delanzomib and adalimumab. Rats with CIA were randomly assigned to receive the treatment with delanzomib, adalimumab, delanzomib combined with adalimumab, or placebo. Visual inspection and biochemical examinations including TNF-α, interleukin 6, and C-reactive protein were performed to assess arthritis severity during the treatment. The adalimumab concentration in rats was determined to evaluate the PK interaction between delanzomib and adalimumab. Also, the levels of neonatal Fc receptor (FcRn) and FcRn mRNA were measured to explore the role of FcRn in the PK interaction between delanzomib and adalimumab. As a result, delanzomib combined with adalimumab exhibited stronger anti-arthritis activity than a single drug because both drugs synergistically reduced TNF-α level in vivo. Delanzomib also decreased adalimumab elimination in rats by increasing the level of FcRn. The slower elimination of adalimumab in rats further prolonged the anti-TNF-α effect of adalimumab. Moreover, FcRn level was increased by delanzomib via suppressing FcRn degradation rather than promoting FcRn production. In conclusion, delanzomib combined with adalimumab may be a potential therapeutic approach for treating rheumatoid arthritis. The initial finding that the PK interaction occurred between delanzomib and adalimumab may have clinical relevance for patients who simultaneously take proteasome inhibitors and anti-TNF-α therapeutic proteins.

Deubiquitylating enzymes: potential target in autoimmune diseases

The ubiquitin-proteasome pathway is responsible for the turnover of different cellular proteins, such as transport proteins, presentation of antigens to the immune system, control of the cell cycle, and activities that promote cancer. The enzymes which remove ubiquitin, deubiquitylating enzymes (DUBs), play a critical role in central and peripheral immune tolerance to prevent the development of autoimmune diseases and thus present a potential therapeutic target for the treatment of autoimmune diseases. DUBs function by removing ubiquitin(s) from target protein and block ubiquitin chain elongation. The addition and removal of ubiquitin molecules have a significant impact on immune responses. DUBs and E3 ligases both specifically cleave target protein and modulate protein activity and expression. The balance between ubiquitylation and deubiquitylation modulates protein levels and also protein interactions. Dysregulation of the ubiquitin-proteasome pathway results in the development of various autoimmune diseases such as inflammatory bowel diseases (IBD), psoriasis, multiple sclerosis (MS), systemic lupus erythematosus (SLE) and rheumatoid arthritis (RA). This review summarizes the current understanding of ubiquitination in autoimmune diseases and focuses on various DUBs responsible for the progression of autoimmune diseases.

Low expression of TCP1 (T-Complex 1) and PSMC1 (Proteasome 26S subunit, ATPase 1) in heterotopic ossification during ankylosing spondylitis

Heterotopic ossification (HO) is frequently seen in patients with spinal injuries. Therefore, this study aimed to characterize the association of HO with ankylosing spondylitis (AS) through gene expression profiling. The human transcriptomic datasets (GSE73754 and GSE94683) were obtained from the Gene Expression Omnibus database for analysis. Overlapping differentially expressed genes (DEGs) were identified between AS and HO disease states. Subsequently, weighted gene co-expression network analysis (WGCNA) was performed for constructing and identifying hub genes for each condition. Finally, a consensus of the overlapping DEGs and the hub genes in AS and HO was taken for determining the key genes involved in AS-induced HO. Quantitative real-time polymerase chain reaction and western blotting were used to detect the mRNA and protein expression levels in mesenchymal stem cells of AS patients and controls. Additionally, immunohistochemistry was performed on interspinous ligament samples for experimental validation of genes. DEG analysis identified 355 overlapping genes between HO and AS. WGCNA indicated that the salmon module of the 22 modules constructed, was most significantly correlated with AS-induced HO. Subsequently, Gene Ontology and Kyoto Encyclopedia of Genes and Genomes analysis of the salmon module indicated the presence of genes enriched in proteasome regulatory particle and proteasome pathways. mRNA expression analysis identified TCP1 and PSMC1 as the key genes in AS-induced HO. Further validation of these genes could help elucidate their role in the complex association of AS and HO.

Oral Proteasomal Inhibitors Ixazomib, Oprozomib, and Delanzomib Upregulate the Function of Organic Anion Transporter 3 (OAT3): Implications in OAT3-Mediated Drug-Drug Interactions

Organic anion transporter 3 (OAT3) is mainly expressed at the basolateral membrane of kidney proximal tubules, and is involved in the renal elimination of various kinds of important drugs, potentially affecting drug efficacy or toxicity. Our laboratory previously reported that ubiquitin modification of OAT3 triggers the endocytosis of OAT3 from the plasma membrane to intracellular endosomes, followed by degradation. Oral anticancer drugs ixazomib, oprozomib, and delanzomib, as proteasomal inhibitors, target the ubiquitin-proteasome system in clinics. Therefore, this study investigated the effects of ixazomib, oprozomib, and delanzomib on the expression and transport activity of OAT3 and elucidated the underlying mechanisms. We showed that all three drugs significantly increased the accumulation of ubiquitinated OAT3, which was consistent with decreased intracellular 20S proteasomal activity; stimulated OAT3-mediated transport of estrone sulfate and p-aminohippuric acid; and increased OAT3 surface expression. The enhanced transport activity and OAT3 expression following drug treatment resulted from an increase in maximum transport velocity of OAT3 without altering the substrate binding affinity, and from a decreased OAT3 degradation. Together, our study discovered a novel role of anticancer agents ixazomib, oprozomib, and delanzomib in upregulating OAT3 function, unveiled the proteasome as a promising target for OAT3 regulation, and provided implication of OAT3-mediated drug-drug interactions, which should be warned against during combination therapies with proteasome inhibitor drugs.

Emerging B-Cell Therapies in Systemic Lupus Erythematosus

Systemic lupus erythematosus (SLE) is a chronic, multisystem, autoimmune disease of unknown etiology, whose hallmark is the production of autoantibodies. B cells are promising targets for novel SLE therapies. In 2011, belimumab (Benlysta®), a fully humanized monoclonal antibody inhibiting B-cell activation and proliferation, was the first medication in 50 years to be approved by the US Food and Drug Administration to treat adult SLE. This review discusses the current experience with B-cell-targeted therapies, including those targeting B-cell-surface antigens (rituximab, ocrelizumab, ofatumumab, obinutuzumab, obexelimab, epratuzumab, daratumumab), B-cell survival factors (belimumab, tabalumab, atacicept, blisibimod), or B-cell intracellular functions (ibrutinib, fenebrutinib, proteasome inhibitors), for the management of SLE. It focuses on ongoing clinical trials and real-world post-marketing use, where available, including their safety profiles, and concludes with our recommendations for B-cell-centric approaches to the management of SLE.

A novel BAFF antagonist, BAFF-Trap, effectively alleviates the disease progression of systemic lupus erythematosus in MRL/lpr mice

Abnormal B cells, which produce antibodies against self-antigens, play a key role in the pathogenesis of autoimmune diseases, such as systemic lupus erythematosus (SLE) and rheumatoid arthritis (RA). B-cell activating factor (BAFF) is closely associated with abnormal B cells and participates in B cell-mediated autoimmune diseases; thus, neutralizing BAFF is an effective method for treating these diseases. Our group designed a novel fusion protein, BAFF-Trap, that contains the BAFF-binding domains of two BAFF receptors (TACI and BAFF-R) and the Fc domain of human IgG1. In this study, we showed that BAFF-Trap significantly decreased the autoantibody levels, BAFF concentrations and B cells numbers in MRL/lpr mice. BAFF-Trap suppressed the expression of pro-inflammatory cytokines in the kidney and decreased the frequencies of T cell subsets and dendritic cells. Furthermore, BAFF-Trap reduced proteinuria and IgG deposition, relieved glomerular damage in the kidney, and markedly improved the survival rate of mice. These results indicated that BAFF-Trap may be a potential drug for the treatment of SLE.

Systemic lupus erythematosus (SLE): emerging therapeutic targets

INTRODUCTION

Systemic lupus erythematosus (SLE) is a chronic autoimmune disease with a heterogeneous clinical presentation whose etiologies are multifactorial. A myriad of genetic, hormonal, immunologic, and environmental factors contribute to its pathogenesis, and its diverse biological basis and phenotypic presentations make development of therapeutics difficult. In the past decade, tens of therapeutic targets with hundreds of individual candidate therapeutics have been investigated.

AREAS COVERED

We used a PUBMED database search through April 2020 to review the relevant literature. This review discusses therapeutic targets in the adaptive and innate immune systems, specifically: B cell surface antigens, B cell survival factors, Bruton's tyrosine kinase, costimulators, IL-12/IL-23, the calcineurin pathway, the JAK/STAT pathway, and interferons.

EXPERT OPINION

Our ever-improving understanding of SLE pathophysiology in the past decade has allowed us to identify new therapeutic targets. Multiple new drugs are on the horizon that target different elements of the adaptive and innate immune systems. SLE research remains challenging due to the heterogenous clinical presentation of SLE, confounding from background immunosuppressives being taken by SLE patients, animal models that inadequately recapitulate human disease, and imperfect and complicated outcome measures. Despite these limitations, research is promising and ongoing. The search for new therapies that target specific elements of SLE pathophysiology are discussed as well as key findings, pitfalls, and questions surrounding these targets.

Development of an IL-17A DNA Vaccine to Treat Systemic Lupus Erythematosus in Mice

The interleukin-17 (IL-17) family, especially IL-17A, plays an important role in the pathogenesis of systemic lupus erythematosus (SLE). This study developed an IL-17A epitope vaccine to treat SLE in NZBWF1 and MRL/lpr mouse models. A plasmid vector encoding a hepatitis B core (HBc)-IL-17A epitope fusion protein was injected using electroporation into the skeletal muscle of NZBWF1(New Zealand Black mice x New Zealand White mice F1 hybrid strain) or MRL/lpr mice three times at 2-week intervals. As a result, anti-IL-17A antibodies were successfully produced in the HBc-IL-17A group. Accordingly, serum tumor necrosis factor alpha (TNF-α) concentrations were significantly reduced in the HBc-IL-17A group. According to pathological analysis, the IL-17A DNA vaccine significantly suppressed renal tissue damage and macrophage infiltration. Consequently, the survival rate was significantly improved in the HBc-IL-17A group. In addition, we evaluated the antigen reactivity of splenocytes from IL-17A-immunized mice using an enzyme-linked immune absorbent spot (ELISPot) assay for safety evaluation. Splenocytes from IL-17A-immunized mice were significantly stimulated by the HBc epitope peptide, but not by the IL-17A epitope or recombinant IL-17A. These results indicate that the IL-17A vaccine did not induce autoreactive T cells against endogenous IL-17A. This study demonstrates for the first time that an IL-17A DNA vaccine significantly reduced organ damage and extended survival time in lupus-prone mice.

B-cell therapy in lupus nephritis: an overview

Systemic lupus erythematosus (SLE) is an autoimmune multisystem disease that commonly affects the kidneys. It is characterized by persistent autoantibody production that targets a multitude of self-antigens. B-cells, plasmablasts and plasma cells, as the source of these autoantibodies, play a major role in the development of lupus nephritis (LN), and are therefore promising therapeutic targets. To date, however, randomized clinical trials of B-cell therapies in LN have not lived up to expectations, whereas uncontrolled cohort and observational studies of B-cell antagonists have been more promising. In this article, we will review the current experience with B-cell therapy in LN and highlight the pitfalls that may have limited their success. We will conclude by suggesting B-cell-centric approaches to the management of LN based on what has been learned from the overall B-cell experience in SLE.

Novel Treatments in Lupus

Purpose of Review: The standard treatment options for systemic lupus erythematosus (SLE) are focused on non-specific immunosuppression. Over the past few years, scientific studies and ongoing clinical trials have shifted the paradigm with rapid advances in developing biologics and small molecules. A number of monoclonal antibodies and small molecule inhibitors have been developed to target specific pathways involved in SLE. Many of these novel therapeutic agents are already being tested in clinical trials and they may 1 day reshape the landscape of SLE treatment. Herein we review potential future therapeutic options for SLE.

Therapy for Proliferative Lupus Nephritis

Proliferative lupus nephritis requires prompt diagnosis and treatment with immunosuppressive therapy. Cyclophosphamide is the longest studied agent, but mycophenolate mofetil has recently emerged as an efficacious induction and maintenance treatment that does not impart the risk of infertility. However, overall remission rates remain suboptimal and there is a need for improved therapeutic options. To this end, ongoing clinical studies are focusing on agents that target key molecules and pathways implicated in the pathogenesis of lupus nephritis based on previous animal and human studies. This article reviews key findings of trials supporting established induction and maintenance treatment regimens along with novel therapeutic investigations.

Enantioselective Synthesis of α-Amidoboronates Catalyzed by Planar-Chiral NHC-Cu(I) Complexes

The first highly selective catalytic hydroboration of alkyl-substituted aldimines to provide medicinally relevant α-amidoboronates is disclosed. The Cu(I)-catalyzed borylation proceeds with excellent facial selectivity when a set of planar-chiral N-heterocyclic carbenes (NHCs) were employed as ligands. Density functional theory computations suggest that interactions between BPin and the planar-chiral catalyst are responsible for the observed stereoselectivity. Important pharmacophores, such as the boronate analogue of isoleucine, can be prepared using a chromatography-free protocol starting from commercially available reagents. The application of these NHC ligands in these Cu(I)-catalyzed processes offers a significant contribution to existing strategies for laboratory-scale preparation of enantioenriched α-amidoboronates.

Increase of MZB1 in B cells in systemic lupus erythematosus: proteomic analysis of biopsied lymph nodes

Background

Systemic lupus erythematosus (SLE) is a prototypical autoimmune disease in which dysregulation of B cells has been recognized. Here, we searched for potential biomarkers of SLE using liquid chromatography-tandem mass spectrometry (LC-MS).

Methods

Lymph nodes from SLE patients and controls were analyzed by LC-MS. To validate the identified molecules, immunoblotting and immunohistochemistry were performed and B cells from SLE patients were analyzed by quantitative RT-PCR. B-cell subsets from NZB/W F1 mice, which exhibit autoimmune disease resembling human SLE, were analyzed by flow cytometry. Endoplasmic reticulum (ER) stress was induced by tunicamycin and the serum concentration of anti-dsDNA antibodies was determined by ELISA. TUNEL methods and immunoblotting were used to assess the effect of tunicamycin.

Results

MZB1, which comprises part of a B-cell-specific ER chaperone complex and is a key player in antibody secretion, was one of the differentially expressed proteins identified by LC-MS and confirmed by immunoblotting. Immunohistochemically, larger numbers of MZB1⁺ cells were located mainly in interfollicular areas and scattered in germinal centers in specimens from SLE patients compared with those from controls. MZB1 colocalized with CD138⁺ plasma cells and IRTA1⁺ marginal zone B cells. MZB1 mRNA was increased by 2.1-fold in B cells of SLE patients with active disease (SLE Disease Activity Index 2000 ≥ 6) compared with controls. In aged NZB/W F1 mice, splenic marginal zone B cells and plasma cells showed elevated MZB1 levels. Tunicamycin induced apoptosis of MZB1⁺ cells in target organs, resulting in decreased serum anti-dsDNA antibody levels. Additionally, MZB1⁺ cells were increased in synovial tissue specimens from patients with rheumatoid arthritis.

Conclusions

MZB1 may be a potential therapeutic target in excessive antibody-secreting cells in SLE.

Electronic supplementary material

The online version of this article (10.1186/s13075-018-1511-5) contains supplementary material, which is available to authorized users.

Targeting B Cells and Plasma Cells in Glomerular Diseases: Translational Perspectives

The unique contributions of memory B cells and plasma cells in kidney diseases remain unclear. In this review, we evaluate the clinical experience with treatments directed at B cells, such as rituximab, and at plasma cells, such as proteasome inhibition, to shed light on the role of these two B lineage compartments in glomerular diseases. Specifically, analysis of these targeted interventions in diseases such as ANCA-associated vasculitis, SLE, and antibody-mediated transplant rejection permits insight into the pathogenetic effect of these cells. Notwithstanding the limitations of preclinical models and clinical studies (heterogeneous populations, among others), the data suggest that memory B and plasma cells represent two engines of autoimmunity, with variable involvement in these diseases. Whereas memory B cells and plasma cells appear to be key in ANCA-associated vasculitis and antibody-mediated transplant rejection, respectively, SLE seems likely to be driven by both autoimmune compartments. These conclusions have implications for the future development of targeted therapeutics in immune-mediated renal disease.

Novel Treatments in Lupus

PURPOSE OF REVIEW

The treatment of systemic lupus erythematosus (SLE) still depends on non-specific immunosuppression. Herein, we review promising targeted therapies that have the potential to change this therapeutic paradigm.

RECENT FINDINGS

Besides the FDA-approved B lymphocyte stimulator (BLyS) inhibitor, belimumab, interferon-α represents a promising treatment target, albeit with modest effectiveness primarily in non-renal SLE. Preclinical and early-phase clinical trials using biologics and small molecules targeting B and T cell activation as well as the cross-talk between these cells also show promise. BLyS and interferon targeting show the most promising results in challenging the current treatment status in non-renal SLE.

Bortezomib treatment induces a higher mortality rate in lupus model mice with a higher disease activity

Background

Bortezomib (Bz) is a proteasome inhibitor that directly targets antibody-producing plasma cells. We recently reported the first randomized control trial that evaluated the effects of Bz in patients with systemic lupus erythematosus (SLE). In that study, we demonstrated that Bz treatment is associated with many adverse reactions in patients with refractory disease. In the present study, we examine the therapeutic and toxic effects of Bz on MRL/MpJ-lpr/lpr (MRL/lpr) mice with severe disease activity.

Methods

Female MRL/lpr mice at 10 and 14 weeks of age were treated with phosphate buffered saline (PBS) (n = 19), Bz (750 μg/kg twice weekly) (n = 27), or cyclophosphamide (Cyc) (1 mg/body, once in 2 weeks) (n = 20). Cellular subsets, serum immunoglobulin, anti-double-stranded DNA (anti-dsDNA) antibody titer, and a pathological index of glomerulonephritis were then analyzed at 22 weeks of age. Survival curves of the 10-week-old and 14-week-old Bz-treated groups were compared. Blood counts, creatinine, liver enzymes, and serum cytokine levels were measured 1 week after Bz treatment. Gene expression profiling of spleens from Bz and Cyc treatment mice were compared with those from control mice.

Results

The anti-dsDNA antibody levels were significantly higher in 14-week-old than in 10-week-old mice, indicating a higher disease activity at 14 weeks. A significant decrease in the number of splenic cells and glomerulonephritis index was observed in Bz-treated and Cyc-treated mice. Bz, but not Cyc, significantly decreased serum immunoglobulin and anti-dsDNA antibody titer levels. Survival curve analysis revealed a significantly higher mortality rate in 14-week-old than in 10-week-old Bz-treated and control groups. Following two injections of Bz, serum IL-6 and TNF-α levels were significantly more elevated in 14-week-old than in 10-week-old mice. Potentially immunogenic molecules, such as heat shock proteins, were characteristically upregulated in spleens of Bz-treated but not Cyc-treated mice.

Conclusions

In spite of its therapeutic effect, Bz treatment had more toxic effects associated with increased proinflammatory cytokine levels in mice with a higher disease activity. Understanding the mechanism of the toxicity and developing preventive strategies against it is important for the safe clinical application of Bz in human SLE.

Electronic supplementary material

The online version of this article (doi:10.1186/s13075-017-1397-7) contains supplementary material, which is available to authorized users.

Ubiquitination and the Regulation of Membrane Proteins

Newly synthesized transmembrane proteins undergo a series of steps to ensure that only the required amount of correctly folded protein is localized to the membrane. The regulation of protein quality and its abundance at the membrane are often controlled by ubiquitination, a multistep enzymatic process that results in the attachment of ubiquitin, or chains of ubiquitin to the target protein. Protein ubiquitination acts as a signal for sorting, trafficking, and the removal of membrane proteins via endocytosis, a process through which multiple ubiquitin ligases are known to specifically regulate the functions of a number of ion channels, transporters, and signaling receptors. Endocytic removal of these proteins through ubiquitin-dependent endocytosis provides a way to rapidly downregulate the physiological outcomes, and defects in such controls are directly linked to human pathologies. Recent evidence suggests that ubiquitination is also involved in the shedding of membranes and associated proteins as extracellular vesicles, thereby not only controlling the cell surface levels of some membrane proteins, but also their potential transport to neighboring cells. In this review, we summarize the mechanisms and functions of ubiquitination of membrane proteins and provide specific examples of ubiquitin-dependent regulation of membrane proteins.

Current and Emerging Therapies for Lupus Nephritis

The introduction of corticosteroids and later, cyclophosphamide dramatically improved survival in patients with proliferative lupus nephritis, and combined administration of these agents became the standard-of-care treatment for this disease. However, treatment failures were still common and the rate of progression to ESRD remained unacceptably high. Additionally, treatment was associated with significant morbidity. Therefore, as patient survival improved, the goals for advancing lupus nephritis treatment shifted to identifying therapies that could improve long-term renal outcomes and minimize treatment-related toxicity. Unfortunately, progress has been slow and the current approaches to the management of lupus nephritis continue to rely on high-dose corticosteroids plus a broad-spectrum immunosuppressive agent. Over the past decade, an improved understanding of lupus nephritis pathogenesis fueled several clinical trials of novel drugs, but none have been found to be superior to the combination of a cytotoxic agent and corticosteroids. Despite these trial failures, efforts to translate mechanistic advances into new treatment approaches continue. In this review, we discuss current therapeutic strategies for lupus nephritis, briefly review recent advances in understanding the pathogenesis of this disease, and describe emerging approaches developed on the basis of these advances that promise to improve upon the standard-of-care lupus nephritis treatments.

The proteasome - victim or culprit in autoimmunity

The ubiquitin proteasome system is closely connected to apoptosis, autophagy, signaling of inflammatory cytokines and generation of ligands for MHC class I antigen presentation. Proteasome function in the innate immune response becomes particularly evident in patients with proteasome-associated autoinflammatory syndromes (PRAAS), where disease causing mutations result in reduced proteasome activity. PRAAS can be classified as a novel type of interferonopathy, however the molecular mechanism and signaling pathways leading from impaired proteasome capacity, the accumulation of damaged proteins, and the induction of type I IFN-genes remain to be determined. In contrast, several studies have confirmed an up-regulation of inducible subunits of the proteasome in systemic autoimmune diseases. Since proteasome inhibition was shown to be efficacious in several in-vitro studies and animal models of autoimmune diseases, it is justified to investigate the application of proteasome inhibitors in human disease. In this context, a number of available proteasome inhibitors has been characterized as potent immune-suppressants. The mode of action of proteasome inhibition interferes with the quality control of the huge amounts of synthetized antibodies causing an unfolded protein response. Further effects of proteasome inhibition includes inhibition of NFκB activation as well as direct activation of intrinsic and extrinsic pathways of apoptosis. The preliminary clinical work on proteasome inhibition in autoimmune diseases comprises only few studies in small cohorts with promising effects, which needs to be confirmed in controlled clinical trials.

Maintaining Genome Stability in Defiance of Mitotic DNA Damage

The implementation of decisions affecting cell viability and proliferation is based on prompt detection of the issue to be addressed, formulation and transmission of a correct set of instructions and fidelity in the execution of orders. While the first and the last are purely mechanical processes relying on the faithful functioning of single proteins or macromolecular complexes (sensors and effectors), information is the real cue, with signal amplitude, duration, and frequency ultimately determining the type of response. The cellular response to DNA damage is no exception to the rule. In this review article we focus on DNA damage responses in G2 and Mitosis. First, we set the stage describing mitosis and the machineries in charge of assembling the apparatus responsible for chromosome alignment and segregation as well as the inputs that control its function (checkpoints). Next, we examine the type of issues that a cell approaching mitosis might face, presenting the impact of post-translational modifications (PTMs) on the correct and timely functioning of pathways correcting errors or damage before chromosome segregation. We conclude this essay with a perspective on the current status of mitotic signaling pathway inhibitors and their potential use in cancer therapy.

A pathophysiology-based approach to the diagnosis and treatment of lupus nephritis

Lupus is no longer an unknown chameleon of medicine. Significant progress has been made on unraveling the pathogenesis of lupus and lupus nephritis, and how to treat the disease. Here we provide an update on the pathophysiology of lupus and its related kidney disease, consider areas of controversy in disease management, and discuss the unmet needs of lupus nephritis and how to address these needs. We focus on rethinking how innovative therapies for lupus nephritis should be evaluated and evolving strategies to more efficiently mitigate irreversible nephron loss in patients with lupus nephritis.

Drugs in early clinical development for Systemic Lupus Erythematosus

INTRODUCTION

While immunosuppressive therapy has positively impacted the prognosis of systemic lupus erythematosus (SLE), many patients still do not respond to traditional therapy. Thus, active SLE disease remains a significant problem. Furthermore, conventional immunosuppressive treatments for SLE are associated a high risk of side effects. These issues call for improvement in our current therapeutic armamentarium.

AREAS COVERED

In this review, the authors highlight the recent developments in therapies for SLE, and present an overview of drugs which are in early clinical development for SLE. There are many new therapeutic approaches being developed, including those focused on B-cell targets, T-cell downregulation, co-stimulatory blockade, anti-cytokine agents, and kinase inhibition, and Toll-like receptor inhibition. They also discuss peptide therapy as a potential method to re-establish immune tolerance, and some of the challenges ahead in developing and testing novel agents for SLE.

EXPERT OPINION

Many novel agents are currently in development for SLE, but this encouraging news is tempered by several disappointments in clinical trials and provides a timely moment to reflect on the future of therapeutic development in SLE. It seems likely that biological heterogeneity between patients is a major contributor to difficulty in drug design in SLE.

Drugging the undruggables: exploring the ubiquitin system for drug development

Dynamic modulation of protein levels is tightly controlled in response to physiological cues. In mammalian cells, much of the protein degradation is carried out by the ubiquitin-proteasome system (UPS). Similar to kinases, components of the ubiquitin system are often dysregulated, leading to a variety of diseases, including cancer and neurodegeneration, making them attractive drug targets. However, so far there are only a handful of drugs targeting the ubiquitin system that have been approved by the FDA. Here, we review possible therapeutic intervention nodes in the ubiquitin system, analyze the challenges, and highlight the most promising strategies to target the UPS.

Proteasome inhibitors

Proteasome inhibitors have a 20 year history in cancer therapy. The first proteasome inhibitor, bortezomib (Velcade, PS-341), a break-through multiple myeloma treatment, moved rapidly through development from bench in 1994 to first approval in 2003. Bortezomib is a reversible boronic acid inhibitor of the chymotrypsin-like activity of the proteasome. Next generation proteasome inhibitors include carfilzomib and oprozomib which are irreversible epoxyketone proteasome inhibitors; and ixazomib and delanzomib which are reversible boronic acid proteasome inhibitors. Two proteasome inhibitors, bortezomib and carfilzomib are FDA approved drugs and ixazomib and oprozomib are in late stage clinical trials. All of the agents are potent cytotoxics. The disease focus for all the proteasome inhibitors is multiple myeloma. This focus arose from clinical observations made in bortezomib early clinical trials. Later preclinical studies confirmed that multiple myeloma cells were indeed more sensitive to proteasome inhibitors than other tumor cell types. The discovery and development of the proteasome inhibitor class of anticancer agents has progressed through a classic route of serendipity and scientific investigation. These agents are continuing to have a major impact in their treatment of hematologic malignancies and are beginning to be explored as potential treatment agent for non-cancer indications.

Molecular characterization of the boron adducts of the proteasome inhibitor bortezomib with epigallocatechin-3-gallate and related polyphenols

The green tea polyphenol epigallocatechin-3-gallate (EGCG) was reported to effectively antagonize the ability of Bortezomib (BZM) to induce apoptosis in cancer cells. This interaction was attributed to the formation of a covalent adduct between a phenolic moiety of EGCG with the boronic acid group of Bortezomib. However, the structural details of this boron adduct and the molecular factors that contribute to its formation and its ability to inhibit Bortezomib's activity remain unclear. This paper describes the use of NMR spectroscopy and cell assays to characterize the structures and properties of the boron adducts of EGCG and related polyphenols. The observed boron adducts included both boronate and borate derivatives, and their structural characteristics were correlated with cell-based evaluation of the ability of EGCG and other phenols to antagonize the anticancer activity of Bortezomib. The enhanced stability of the BZM/EGCG adduct was attributed to electronic and steric reasons, and a newly identified intramolecular interaction of the boron atom of BZM with the adjacent amide bond. The reported approach provides a useful method for determining the potential ability of polyphenols to form undesired adducts with boron-based drugs and interfere with their actions.

The proteasome inhibitior bortezomib depletes plasma cells and ameliorates clinical manifestations of refractory systemic lupus erythematosus

Objectives

To investigate whether bortezomib, a proteasome inhibitor approved for treatment of multiple myeloma, induces clinically relevant plasma cell (PC) depletion in patients with active, refractory systemic lupus erythematosus (SLE).

Methods

Twelve patients received a median of two (range 1–4) 21-day cycles of intravenous bortezomib (1.3 mg/m²) with the coadministration of dexamethasone (20 mg) for active SLE. Disease activity was assessed using the SLEDAI-2K score. Serum concentrations of anti–double-stranded DNA (anti-dsDNA) and vaccine-induced protective antibodies were monitored. Flow cytometry was performed to analyse peripheral blood B-cells, PCs and Siglec-1 expression on monocytes as surrogate marker for type-I interferon (IFN) activity.

Results

Upon proteasome inhibition, disease activity significantly declined and remained stable for 6 months on maintenance therapies. Nineteen treatment-emergent adverse events occurred and, although mostly mild to moderate, resulted in treatment discontinuation in seven patients. Serum antibody levels significantly declined, with greater reductions in anti-dsDNA (∼60%) than vaccine-induced protective antibody titres (∼30%). Bortezomib significantly reduced the numbers of peripheral blood and bone marrow PCs (∼50%), but their numbers increased between cycles. Siglec-1 expression on monocytes significantly declined.

Conclusions

These findings identify proteasome inhibitors as a putative therapeutic option for patients with refractory SLE by targeting PCs and type-I IFN activity, but our results must be confirmed in controlled trials.

Proteasome inhibitors in progressive renal diseases

Proteasome (PS) is a sophisticated protein degradation machinery comprising a 20S proteolytic core particle provided with caspase-like, trypsin-like and chymotrypsin-like activities on ubiquitinilated proteins. The products of this selective, complex, controlled and strictly coordinated system play a crucial role in cell cycle progression and apoptosis; activation of transcription factors, cytokines and chemokines; degradation and generation of MHC class I-presented peptides. PS has recently emerged as a promising drug target in cancer therapy, and bortezomib has been approved for refractory multiple myeloma. PS proteolysis is crucial for the degradation of the inhibitory protein IkB of nuclear factor kB (NF-kB), and hence, an interesting field of research has been developed on possible benefits of drugs with anti-PS activity in disease conditions with hyper-expression of NF-kB. PS inhibitors are being adopted in pilot studies in antibody-mediated renal rejection and in AL amyloidosis, with increasing scientific interest in possible applications in lupus, IgA nephropathy, idiopathic nephrotic syndrome and renal fibrosis. The most often used PS inhibitor, bortezomib, has a severe peripheral neurotoxicity, and the search for effective and less toxic PS-targeted drugs is a challenging area also in nephrology.

Linking the activity of bortezomib in multiple myeloma and autoimmune diseases

Since their introduction to the clinic 10 years ago, proteasome inhibitors have become the cornerstone of anti-multiple myeloma therapy. Despite significant progress in understanding the consequences of proteasome inhibition, the unique activity of bortezomib is still unclear. Disappointing results from clinical trials with bortezomib in other malignancies raise the question of what makes multiple myeloma so sensitive to proteasome inhibition. Successful administration of bortezomib in various immunological disorders that exhibit high antibody production suggests that the balance between protein synthesis and degradation is a key determinant of sensitivity to proteasome inhibition because a high rate of protein production is a shared characteristic in plasma and myeloma cells. Initial or acquired resistance to bortezomib remains a major obstacle in the clinic as in vitro data from cell lines suggest a key role for the β5 subunit mutation in resistance; however the mutation was not found in patient samples. Recent studies indicate the importance of selecting for a subpopulation of cells that produce lower amounts of paraprotein during bortezomib therapy.

Update on B-cell targeted therapies for systemic lupus erythematosus

INTRODUCTION

Systemic lupus erythematosus (SLE) is a systemic autoimmune disease characterized by flares and remission, leading to accrual of organ damage over time as a result of persistent tissue inflammation and treatment-related complications. Novel therapies aiming at better treatment response and fewer adverse effects are being tested in the pipeline.

AREAS COVERED

This review summarizes the B-cell abnormalities observed in patients with SLE, and updates recent data on the efficacy and safety of B-cell targeted therapies in the treatment of SLE. The pitfalls of clinical trial design and future directions of the development of SLE therapeutics are discussed.

EXPERT OPINION

The variability of clinical response to treatment in SLE reflects the clinical and immunological heterogeneity of the disease. The treatment plan for patients with SLE should be individualized with the aim of eradicating disease activity, preventing flares and minimizing treatment-related complications. Despite the disappointment of recent clinical trials, B-cell remains the promising target of future SLE therapies. Results from ongoing clinical trials on B-cell targeted biological agents are eagerly awaited.

Emerging biological therapies for systemic lupus erythematosus

INTRODUCTION

Systemic lupus erythematosus (SLE) is a systemic autoimmune disease with unpredictable disease course, intermingled with periods of remission and exacerbation. Current therapies for SLE are not ideal in terms of efficacy and toxicity. Although the prognosis of the disease has improved in the past decades, further improvement is hindered by the occurrence of organ damage as a result of persistent disease activity and treatment-related complications. Novel biological therapies targeting at higher treatment efficacy and fewer adverse effects are being developed.

AREAS COVERED

This review summarizes recent data on novel biological therapies for SLE. The pitfalls of clinical trial design and future directions of the development of SLE therapeutics are discussed.

EXPERT OPINION

The variable therapeutic response observed in SLE reflects the clinical and immunological heterogeneity of the disease. The treatment plan of SLE patients should be individualized, with the target of quenching out disease activity, minimizing disease flares, and treatment related morbidities. Despite the disappointment of recent clinical trials, avenues are being opened for novel agents that intervene at different levels of the pathophysiological cascade of SLE. With the availability of a new treatment armamentarium, it is hoped that the survival rate and quality of life of SLE patients can continue to improve.

Lupus nephritis: the evolving role of novel therapeutics

Immune complex accumulation in the kidney is the hallmark of lupus nephritis and triggers a series of events that result in kidney inflammation and injury. Cytotoxic agents and corticosteroids are standard of care for lupus nephritis treatment, but are associated with considerable morbidity and suboptimal outcomes. Recently, there has been interest in using novel biologic agents and small molecules to treat lupus nephritis. These therapies can be broadly categorized as anti-inflammatory (laquinamod, anti-tumor necrosis factor-like weak inducer of apotosis, anti-C5, and retinoids), antiautoimmunity (anti-CD20, anti-interferon α, and costimulatory blockers), or both (anti-interleukin 6 and proteasome inhibitors). Recent lupus nephritis clinical trials applied biologics or small molecules of any category to induction treatment, seeking short-term end points of complete renal response. These trials in general have not succeeded. When lupus nephritis comes to clinical attention during the inflammatory stage of the disease, the autoimmune stage leading to kidney inflammation will have been active for some time. The optimal approach for using novel therapies may be to initially target kidney inflammation to preserve renal parenchyma, followed by suppression of autoimmunity. In this review, we discuss novel lupus nephritis therapies and how they fit into a combinatorial treatment strategy based on the pathogenic stage.

New approaches for the treatment of lupus nephritis in the 21st century: from the laboratory to the clinic

Systemic lupus erythematosus is a complex autoimmune disorder affecting multiple organ systems. Glomerulonephritis leading to severe proteinuria, chronic renal failure and end-stage renal disease remains one of the most severe complications of systemic lupus erythematosus and is associated with significant morbidity and mortality. Conventional lupus nephritis (LN) treatment based on cyclophosphamide, steroids and, recently, mycophenolatemofetil has improved the outcome of the disease over the last 50 years, although failure to achieve remission or treatment resistance has been reported in 18–57% of patients. Chronic complications such as long-term toxicity dampen their ability to maintain disease remission. There is a need to develop more specific pharmacological agents for patients to provide choices that are equally effective, less toxic and have fewer complications. During the last 10 years, experimental studies based on different pathogenesis pathways of LN have provided an enormous amount of knowledge and have offered the possibility to target the disease with selective approaches. In this article, we summarize the new experimental strategies that have recently been utilized to target LN, focusing on mechanisms of action.

Small molecules in the treatment of systemic lupus erythematosus

Advances in the understanding of the cellular biological events that underlie systemic lupus erythematosus (SLE) have led to the identification of key molecules and signaling pathways that are aberrantly expressed. The parallel development of small molecule drugs that inhibit or interfere with the specific perturbations identified, offers perspective for more rational, effective and less toxic therapy. In this review, we present data from preclinical and clinical studies of such emerging novel therapies with a particular focus on kinase inhibitors and other compounds that modulate signal transduction. Moreover, we highlight the use of chromatin-modifying medications, bringing attention to the central role of epigenetics in SLE pathogenesis.

Synthesis and pharmacology of proteasome inhibitors

Shortly after the discovery of the proteasome it was proposed that inhibitors could stabilize proteins which ultimately would trigger apoptosis in tumor cells. The essential questions were whether small molecules would be able to inhibit the proteasome without generating prohibitive side effects and how one would derive these compounds. Fortunately, "Mother Nature" has generated a wide variety of natural products that provide distinct selectivities and specificities. The chemical synthesis of these natural products finally provided access to analogues and optimized drugs of which two different classes have been approved for the treatment of malignancies. Despite these achievements, additional lead structures derived from nature are under investigation and will be discussed with regard to their biological potential and chemical challenges.

JAK2 inhibition in murine systemic lupus erythematosus

Systemic lupus erythematosus is a systemic autoimmune disease characterized by the presence of myriad autoantibodies, some with pathogenic potential, and diverse clinical manifestations. Involvement of the kidney is a major cause of morbidity and mortality in human lupus patients and in murine models of the disease. It is hoped that more specific inhibition of crucial disease pathways would improve patient response rates, while reducing the considerable rates of drug-related side effects associated with current therapy. IL-6 has a pivotal regulatory role in the development and maturation of long-lived plasma cells, one of the key cell types driving the lupus disease phenotype as the source for the majority of lupus-related autoreactive antibodies. In this study, Lu et al. target the IL-6 signal transduction pathway using a specific JAK2 inhibitor of the JAK-STAT pathway, CEP-33779. In murine lupus models, they show significant improvement in nephritis, and prolonged survival, in mice treated with CEP-33779. The study presents the promise of a novel pathway for therapeutic intervention in systemic lupus erythematosus using a medication administered orally.