Efficiency and Safety of CRAC Inhibitors in Human Rheumatoid Arthritis Xenograft Models

ORAI1 inhibition as an efficient preclinical therapy for tubular aggregate myopathy and Stormorken syndrome

Tubular aggregate myopathy (TAM) and Stormorken syndrome (STRMK) are clinically overlapping disorders characterized by childhood-onset muscle weakness and a variable occurrence of multisystemic signs, including short stature, thrombocytopenia, and hyposplenism. TAM/STRMK is caused by gain-of-function mutations in the Ca2+ sensor STIM1 or the Ca2+ channel ORAI1, both of which regulate Ca2+ homeostasis through the ubiquitous store-operated Ca2+ entry (SOCE) mechanism. Functional experiments in cells have demonstrated that the TAM/STRMK mutations induce SOCE overactivation, resulting in excessive influx of extracellular Ca2+. There is currently no treatment for TAM/STRMK, but SOCE is amenable to manipulation. Here, we crossed Stim1R304W/+ mice harboring the most common TAM/STRMK mutation with Orai1R93W/+ mice carrying an ORAI1 mutation partially obstructing Ca2+ influx. Compared with Stim1R304W/+ littermates, Stim1R304W/+Orai1R93W/+ offspring showed a normalization of bone architecture, spleen histology, and muscle morphology; an increase of thrombocytes; and improved muscle contraction and relaxation kinetics. Accordingly, comparative RNA-Seq detected more than 1,200 dysregulated genes in Stim1R304W/+ muscle and revealed a major restoration of gene expression in Stim1R304W/+Orai1R93W/+ mice. Altogether, we provide physiological, morphological, functional, and molecular data highlighting the therapeutic potential of ORAI1 inhibition to rescue the multisystemic TAM/STRMK signs, and we identified myostatin as a promising biomarker for TAM/STRMK in humans and mice.

Single-Cell Ca2+ Imaging

In rheumatological studies, visualization of Ca2+ dynamics in intact cells as direct experimental evidence of Ca2+-dependent signal pathways is generally used to monitor the function of immune cells at first glance. Ability to monitor Ca2+ signaling in living cells would greatly facilitate advances in the functional dissection of immune cells. In this chapter, we describe a basic technique and methods of data analysis for single-cell real-time Ca2+ monitoring using Fluo-4 labeling, which is a single-wavelength Ca2+ indicator.

Long-Term Constant Subcutaneous Drug Administration

In this chapter, a long-term drug delivery system for preclinical therapeutic research is introduced. By using a subcutaneously implanted ALZET® Osmotic Pumps osmotic pump, continuous zero-order delivery of drugs under investigation that need repeated oral or intravenous dosing is realizable. Compared to traditional delivery systems, implanted osmotic pumps present several advantages, such as that no external connections or researcher intervention is required during infusion and that it is possible to save time by eliminating the need for frequent animal handling and repetitive injection schedules. Most importantly, a stable peripheral concentration of a drug can be obtained using this constant drug delivery system, which would benefit researchers in verifying the efficiency of anti-rheumatoid drugs and establishing safety profiles in preclinical studies.

Human Xenograft Model

Human-SCID grafting is a commonly used technique for the long-term investigation of rheumatoid arthritis (RA) explants. To establish a chimeric immunological system in NOD/SCID mice, RA patient-derived pannus tissue from the synovial membrane, articular cartilage, and bone can be transplanted subcutaneously. Same patient-derived peripheral mononuclear cell chimerism can be successfully achieved by intraperitoneal engraftment. This xenograft model is able to be used for the initial screening of human target-specified biologics.

Production of Immunizing Antigen Proteoliposome Using Cell-Free Protein Synthesis System

Antibodies specifically recognizing integral membrane proteins are essential tools for functional analysis, diagnosis, and therapeutics targeting membrane proteins. However, developing antibodies against membrane proteins remains a big challenge because mass production of membrane proteins is difficult. Recently, we developed a highly efficient cell-free production method of proteoliposome antigen using a cell-free protein synthesis method with liposome and dialysis cup. Here, we introduce practical and efficient integrated procedures to produce a large amount of proteoliposome antigen for anti-membrane protein antibody development.

Orai1 Ca2+ channel modulators as therapeutic tools for treating cancer: Emerging evidence!

In non-excitable cells, Orai proteins represent the main channel for Store-Operated Calcium Entry (SOCE), and also mediate various store-independent Calcium Entry (SICE) pathways. Deregulation of these pathways contribute to increased tumor cell proliferation, migration, metastasis, and angiogenesis. Among Orais, Orai1 is an attractive therapeutic target explaining the development of specific modulators. Therapeutic trials using Orai1 channel inhibitors have been evaluated for treating diverse diseases such as psoriasis and acute pancreatitis, and emerging data suggest that Orai1 channel modulators may be beneficial for cancer treatment. This review discusses herein the importance of Orai1 channel modulators as potential therapeutic tools and the added value of these modulators for treating cancer.

Production of Neutralizing Antibody

Techniques employing monoclonal antibodies (mAbs) are widely used in the initial development phase of biologics. The usefulness of mAbs in basic RA research has been established based on their characteristics, including specificity of binding, homogeneity, and ability to be produced on a large scale. MAb immunoglobulins are the starting material for the generation of smaller antibody fragments and other engineered immunomodulatory antibodies. In this chapter, the basic hybridoma technique, which is a well-established and feasible method for the production of mAbs involving animal immunization, cell fusion, hybridoma screening, expanding positive hybridomas, and purification, is introduced. Aiming at specific affinity to a membrane protein, synthetic proteoliposomes are used in the immunization and screening steps.

Release of Antibodies and Cytokines from B Cells

Autoreactive B cells play a critical role in rheumatoid arthritis (RA). These cells differentiate into long-living memory B cells and autoantibody-producing plasma cells, and also present autoantigens to T cells to amplify misdirected immune responses. The therapeutic benefit of B-cell-deleting depleting therapies suggests that B cells are emerging as important factors in the pathogenesis of RA. Aiming at evaluation of the function of B cells, which are usually derived from peripheral blood of RA patients and healthy donors, it is possible to conduct a series of experiments, such as in vitro assessment of antibody production and BCR-mediated cytokine release. These techniques can also be applied for in vivo application.

Reconstitution of Calcium Channel Protein Orai3 into Liposomes for Functional Studies

Store-operated calcium entry (SOCE) is the main mechanism for the Ca2+ influx in non-excitable cells. The two major components of SOCE are stromal interaction molecule 1 (STIM1) in the endoplasmic reticulum and Ca2+ release-activated Ca2+ channel (CRAC) Orai on the plasma membrane. SOCE requires interaction between STIM1 and Orai. Mammals have three Orai homologs: Orai1, Orai2, and Orai3. Although Orai1 has been widely studied and proven to essential for numerous cellular processes, Orai3 has also attracted a significant attention recently. The gating and activation mechanisms of Orai3 have yet to be fully elucidated. Here, we expressed, purified, and reconstituted Orai3 protein into liposomes and investigated its orientation and oligomeric state in the resulting proteoliposomes. STIM1 interacted with the Orai3-containing proteoliposomes and mediated calcium release from the them, suggesting that the Orai3 channel was functional and that recombinant STIM1 could directly open the Orai3 channel in vitro. The developed in vitro calcium release system could be used to study the structure, function, and pharmacology of Orai3 channel.

Evaluation of Cell-Free Synthesized Human Channel Proteins for In Vitro Channel Research

Despite channel proteins being important drug targets, studies on channel proteins remain limited, as the proteins are difficult to express and require correct complex formation within membranes. Although several in vitro synthesized recombinant channels have been reported, considering the vast diversity of the structures and functions of channel proteins, it remains unclear which classes of channels cell-free synthesis can be applied to. In this study, we synthesized 250 clones of human channels, including ion channel pore-forming subunits, gap junction proteins, porins, and regulatory subunits, using a wheat cell-free membrane protein production system, and evaluated their synthetic efficiency and function. Western blotting confirmed that 95% of the channels were successfully synthesized, including very large channels with molecular weights of over 200 kDa. A subset of 47 voltage-gated potassium ion channels was further analyzed using a planar lipid bilayer assay, out of which 80% displayed a voltage-dependent opening in the assay. We co-synthesized KCNB1 and KCNS3, a known heteromeric complex pair, and demonstrated that these channels interact on a liposome. These results indicate that cell-free protein synthesis provides a promising solution for channel studies to overcome the bottleneck of in vitro protein production.

Nucleic Acids for Potential Treatment of Rheumatoid Arthritis

Rheumatoid arthritis (RA) is a common systemic inflammatory autoimmune disease that severely affects the life quality of patients. Current therapeutics in clinic mainly focus on alleviating the development of RA or relieving the pain of patients. The emerging biological disease-modifying antirheumatic drugs (DMARDs) require long-term treatment to achieve the expected efficacy. With the development of bionanotechnology, nucleic acids fulfill characters as therapeutics or nanocarriers and can therefore be alternatives to combat RA. This review summarizes the therapeutic RNAs developed through RNA interference (RNAi), nucleic acid aptamers, DNA nanostructures-based drug delivery systems, and nucleic acid vaccines for the applications in RA therapy and diagnosis. Furthermore, prospects of nucleic acids for RA therapy are intensively discussed as well.

CRAC Channel Controls the Differentiation of Pathogenic B Cells in Lupus Nephritis

Store-operated Ca²⁺ release-activated Ca²⁺ (CRAC) channel is the main Ca²⁺ influx pathway in lymphocytes and is essential for immune response. Lupus nephritis (LN) is an autoimmune disease characterized by the production of autoantibodies due to widespread loss of immune tolerance. In this study, RNA-seq analysis revealed that calcium transmembrane transport and calcium channel activity were enhanced in naive B cells from patients with LN. The increased expression of ORAI1, ORAI2, and STIM2 in naive B cells from patients with LN was confirmed by flow cytometry and Western blot, implying a role of CRAC channel in B-cell dysregulation in LN. For in vitro study, CRAC channel inhibition by YM-58483 or downregulation by ORAI1-specific small-interfering RNA (siRNA) decreased the phosphorylation of Ca²⁺/calmodulin-dependent protein kinase2 (CaMK2) and suppressed Blimp-1 expression in primary human B cells, resulting in decreased B-cell differentiation and immunoglobulin G (IgG) production. B cells treated with CaMK2-specific siRNA showed defects in plasma cell differentiation and IgG production. For in vivo study, YM-58483 not only ameliorated the progression of LN but also prevented the development of LN. MRL/lpr lupus mice treated with YM-58483 showed lower percentage of plasma cells in the spleen and reduced concentration of anti-double-stranded DNA antibodies in the sera significantly. Importantly, mice treated with YM-58483 showed decreased immune deposition in the glomeruli and alleviated kidney damage, which was further confirmed in NZM2328 lupus mice. Collectively, CRAC channel controlled the differentiation of pathogenic B cells and promoted the progression of LN. This study provides insights into the pathogenic mechanisms of LN and that CRAC channel could serve as a potential therapeutic target for LN.

Applicability and implementation of the collagen-induced arthritis mouse model, including protocols (Review)

Animal models of rheumatoid arthritis (RA) are essential for studying the pathogenesis of RA in vivo and determining the efficacy of anti-RA drugs. During the past decades, numerous rodent models of arthritis have been evaluated as potential models and the modeling methods are relatively well-developed. Among these models, the collagen-induced arthritis (CIA) mouse model is the first choice and the most widely used because it may be generated rapidly and inexpensively and is relatively similar in pathogenesis to human RA. To date, there have been numerous classic studies and reviews discussing related pathogeneses and modeling methods. Based on this knowledge, combined with the latest convenient and effective methods for CIA model construction, the present review aims to introduce the model to beginners and clarify important details regarding its use. Information on the origin and pathogenesis of the CIA model, the protocol for establishing it, the rate of successful arthritis induction and the methods used to evaluate the severity of arthritis are briefly summarized. With this information, it is expected that researchers who have recently entered the field or are not familiar with this information will be able to start quickly, avoid unnecessary errors and obtain reliable results.

Store-Operated Calcium Channels in Physiological and Pathological States of the Nervous System

Store-operated calcium channels (SOCs) are widely expressed in excitatory and non-excitatory cells where they mediate significant store-operated calcium entry (SOCE), an important pathway for calcium signaling throughout the body. While the activity of SOCs has been well studied in non-excitable cells, attention has turned to their role in neurons and glia in recent years. In particular, the role of SOCs in the nervous system has been extensively investigated, with links to their dysregulation found in a wide variety of neurological diseases from Alzheimer’s disease (AD) to pain. In this review, we provide an overview of their molecular components, expression, and physiological role in the nervous system and describe how the dysregulation of those roles could potentially lead to various neurological disorders. Although further studies are still needed to understand how SOCs are activated under physiological conditions and how they are linked to pathological states, growing evidence indicates that SOCs are important players in neurological disorders and could be potential new targets for therapies. While the role of SOCE in the nervous system continues to be multifaceted and controversial, the study of SOCs provides a potentially fruitful avenue into better understanding the nervous system and its pathologies.

Store-Operated Ca2+ Channels: Mechanism, Function, Pharmacology, and Therapeutic Targets

Calcium (Ca²⁺) release-activated Ca²⁺ (CRAC) channels are a major route for Ca²⁺ entry in eukaryotic cells. These channels are store operated, opening when the endoplasmic reticulum (ER) is depleted of Ca²⁺, and are composed of the ER Ca²⁺ sensor protein STIM and the pore-forming plasma membrane subunit Orai. Recent years have heralded major strides in our understanding of the structure, gating, and function of the channels. Loss-of-function and gain-of-function mutants combined with RNAi knockdown strategies have revealed important roles for the channel in numerous human diseases, making the channel a clinically relevant target. Drugs targeting the channels generally lack specificity or exhibit poor efficacy in animal models. However, the landscape is changing, and CRAC channel blockers are now entering clinical trials. Here, we describe the key molecular and biological features of CRAC channels, consider various diseases associated with aberrant channel activity, and discuss targeting of the channels from a therapeutic perspective.

Calcium Permeable Channels in Cancer Hallmarks

Cancer, the second cause of death worldwide, is characterized by several common criteria, known as the “cancer hallmarks” such as unrestrained cell proliferation, cell death resistance, angiogenesis, invasion and metastasis. Calcium permeable channels are proteins present in external and internal biological membranes, diffusing Ca²⁺ ions down their electrochemical gradient. Numerous physiological functions are mediated by calcium channels, ranging from intracellular calcium homeostasis to sensory transduction. Consequently, calcium channels play important roles in human physiology and it is not a surprise the increasing number of evidences connecting calcium channels disorders with tumor cells growth, survival and migration. Multiple studies suggest that calcium signals are augmented in various cancer cell types, contributing to cancer hallmarks. This review focuses in the role of calcium permeable channels signaling in cancer with special attention to the mechanisms behind the remodeling of the calcium signals. Transient Receptor Potential (TRP) channels and Store Operated Channels (SOC) are the main extracellular Ca²⁺ source in the plasma membrane of non-excitable cells, while inositol trisphosphate receptors (IP₃R) are the main channels releasing Ca²⁺ from the endoplasmic reticulum (ER). Alterations in the function and/or expression of these calcium channels, as wells as, the calcium buffering by mitochondria affect intracellular calcium homeostasis and signaling, contributing to the transformation of normal cells into their tumor counterparts. Several compounds reported to counteract several cancer hallmarks also modulate the activity and/or the expression of these channels including non-steroidal anti-inflammatory drugs (NSAIDs) like sulindac and aspirin, and inhibitors of polyamine biosynthesis, like difluoromethylornithine (DFMO). The possible role of the calcium permeable channels targeted by these compounds in cancer and their action mechanism will be discussed also in the review.

Assessment and Comparison of the Efficacy of Methotrexate, Prednisolone, Adalimumab, and Tocilizumab on Multipotency of Mesenchymal Stem Cells

Mesenchymal stem cell (MSC)-based articular regeneration might be beneficial for both protecting and rebuilding cartilaginous tissues in the management of rheumatoid arthritis. However, it is unclear how current immunosuppressive strategies influence the multipotency of MSCs. The present study was undertaken to profile the direct effectiveness of major antirheumatic drugs including methotrexate, prednisolone, adalimumab, and tocilizumab on the multipotency of MSCs, with a special focus on chondrogenesis. The inhibitory effects of methotrexate on adipogenesis, osteogenesis, and chondrogenesis were observed to occur in a dose-dependent manner in an in vitro differentiation system. Prednisolone enhanced adipogenesis, but reduced alkaline phosphatase activity in osteoprogenitors and suppressed the formation of chondrospheroids. Adalimumab suppressed alkaline phosphatase activity, while tocilizumab diminished osteogenesis and chondrogenesis of MSCs in vitro. Chondrogenesis of antirheumatic drug-treated MSCs was also evaluated in vivo using a scaffolded spheroid-engrafted murine model. The biologics examined appeared to be relatively safe for cartilaginous formation, but methotrexate and prednisolone exhibited opposing influences on chondrogenesis. Taken together, these results reveal the direct efficacy of major antirheumatic agents on the multipotency of MSCs. Therefore, our findings suggest that optimization of medication protocols is further required for therapeutic approaches involving cartilaginous tissue engineering.

The FcεRIβ homologue, MS4A4A, promotes FcεRI signal transduction and store-operated Ca2+ entry in human mast cells

Members of the membrane spanning 4A (MS4A) gene family are clustered around 11q12-13, a region linked to allergy and asthma susceptibility. Other than the known functions of FcεRIβ (MS4A2) and CD20 (MS4A1) in mast cell and B cell signaling, respectively, functional studies for the remaining MS4A proteins are lacking. We thus explored whether MS4A4A, a mast cell expressed homologue of FcεRIβ, has related functions to FcεRIβ in FcεRI signaling. We establish in this study that MS4A4A promotes phosphorylation of PLCγ1, calcium flux and degranulation in response to IgE-mediated crosslinking of FcεRI. We previously demonstrated that MS4A4A promotes recruitment of KIT into caveolin-1-enriched microdomains and signaling through PLCγ1. Caveolin-1 itself is an important regulator of IgE-dependent store-operated Ca²⁺ entry (SOCE) and promotes expression of the store-operated Ca²⁺ channel pore-forming unit, Orai1. We thus further report that MS4A4A functions through interaction with caveolin-1 and recruitment of FcεRI and KIT into lipid rafts. In addition to proximal FcεRI signaling, we similarly show that MS4A4A regulates Orai1-mediated calcium entry downstream of calcium release from stores. Both MS4A4A and Orai1 had limited effects with compound 48/80 stimulation, demonstrating some degree of selectivity of both proteins to FcεRI receptor signaling over Mas-related G Protein coupled receptor X2 signaling. Overall, our data are consistent with the conclusion that MS4A4A performs a related function to the homologous FcεRIβ to promote PLCγ1 signaling, SOCE, and degranulation through FcεRI in human mast cells and thus represents a new target in the regulation of IgE-mediated mast cell activation.

Ca2+ signalling plays a role in celastrol-mediated suppression of synovial fibroblasts of rheumatoid arthritis patients and experimental arthritis in rats

Background and Purpose

Celastrol exhibits anti‐arthritic effects in rheumatoid arthritis (RA), but the role of celastrol‐mediated Ca²⁺ mobilization in treatment of RA remains undefined. Here, we describe a regulatory role for celastrol‐induced Ca²⁺ signalling in synovial fibroblasts of RA patients and adjuvant‐induced arthritis (AIA) in rats.

Experimental Approach

We used computational docking, Ca²⁺ dynamics and functional assays to study the sarcoplasmic/endoplasmic reticulum Ca²⁺ ATPase pump (SERCA). In rheumatoid arthritis synovial fibroblasts (RASFs)/rheumatoid arthritis fibroblast‐like synoviocytes (RAFLS), mechanisms of Ca²⁺‐mediated autophagy were analysed by histological, immunohistochemical and flow cytometric techniques. Anti‐arthritic effects of celastrol, autophagy induction, and growth rate of synovial fibroblasts in AIA rats were monitored by microCT and immunofluorescence staining. mRNA from joint tissues of AIA rats was isolated for transcriptional analysis of inflammatory genes, using siRNA methods to study calmodulin, calpains, and calcineurin.

Key Results

Celastrol inhibited SERCA to induce autophagy‐dependent cytotoxicity in RASFs/RAFLS via Ca²⁺/calmodulin‐dependent kinase kinase‐β–AMP‐activated protein kinase–mTOR pathway and repressed arthritis symptoms in AIA rats. BAPTA/AM hampered the in vitro and in vivo effectiveness of celastrol. Inflammatory‐ and autoimmunity‐associated genes down‐regulated by celastrol in joint tissues of AIA rat were restored by BAPTA/AM. Knockdown of calmodulin, calpains, and calcineurin in RAFLS confirmed the role of Ca²⁺ in celastrol‐regulated gene expression.

Conclusion and Implications

Celastrol triggered Ca²⁺ signalling to induce autophagic cell death in RASFs/RAFLS and ameliorated arthritis in AIA rats mediated by calcium‐dependent/‐binding proteins facilitating the exploitation of anti‐arthritic drugs based on manipulation of Ca²⁺ signalling.

The roles of Orai and Stim in bone health and disease

Orai and Stim proteins are the mediators of calcium release-activated calcium signaling and are important in the regulation of bone homeostasis and disease. This includes separate regulatory systems controlling mesenchymal stem cell differentiation to form osteoblasts, which make bone, and differentiation and regulation of osteoclasts, which resorb bone. These systems will be described separately, and their integration and relation to other systems, including Orai and Stim in teeth, will be briefly discussed at the end of this review.

Genetic Manipulation of Calcium Release-Activated Calcium Channel 1 Modulates the Multipotency of Human Cartilage-Derived Mesenchymal Stem Cells

Calcium is a ubiquitous intracellular messenger that has a crucial role in determining the proliferation, differentiation, and functions of multipotent mesenchymal stem cells (MSCs). Our study is aimed at elucidating the influence of genetically manipulating Ca²⁺ release-activated Ca²⁺ (CRAC) channel-mediated intercellular Ca²⁺ signaling on the multipotency of MSCs. The abilities of genetically engineered MSCs, including CRAC-overexpressing and CRAC-knockout MSCs, to differentiate into multiple mesenchymal lineages, including adipogenic, osteogenic, and chondrogenic lineages, were evaluated. CRAC channel-mediated Ca²⁺ influx into these cells was regulated, and the differentiation fate of MSCs was modified. Upregulation of intracellular Ca²⁺ signals attenuated the adipogenic differentiation ability and slightly increased the osteogenic differentiation potency of MSCs, whereas downregulation of CRACM1 expression promoted chondrogenic differentiation potency. The findings demonstrated the effects of genetically manipulating MSCs by targeting CRACM1. CRAC-modified MSCs had distinct differentiation fates to adipocytes, osteoblasts, and chondrocytes. To aid in the clinical implementation of tissue engineering strategies for joint regeneration, these data may allow us to identify prospective factors for effective treatments and could maximize the therapeutic potential of MSC-based transplantation.

Human Xenograft Model

Human-SCID grafting is a commonly used technique for the long-term investigation of rheumatoid arthritis (RA) explants. To establish a chimeric immunological system in NOD/SCID mice, RA patient-derived pannus tissue from the synovial membrane, articular cartilage, and bone can be transplanted subcutaneously. The same patient-derived peripheral blood mononuclear cell chimerism can be successfully achieved by intraperitoneal engraftment. This xenograft model is able to be used for initial screening of human target-specified biologics.

Single-Cell Ca2+ Imaging

In rheumatological studies, visualization of Ca²⁺ dynamics in intact cells as direct experimental evidence of Ca²⁺-dependent signal pathways is generally used to monitor the function of immune cells at first glance. Ability to monitor Ca²⁺ signaling in living cells would greatly facilitate advances in the functional dissection of immune cells. In this chapter, we describe a basic technique and methods of data analysis for single-cell real-time Ca²⁺ monitoring using Fluo-4 labeling, which is a single-wavelength Ca²⁺ indicator.

Long-Term Constant Subcutaneous Drug Administration

In this chapter, a long-term drug delivery system for preclinical therapeutic research is introduced. By using a subcutaneously implanted ALZET^® osmotic pump, continuous zero-order delivery of drugs under investigation that need repeated oral or intravenous dosing is realizable. Compared to traditional delivery systems, implanted osmotic pumps present several advantages such as that no external connections or researcher intervention is required during infusion and that it is possible to save time by eliminating the need for frequent animal handling and repetitive injection schedules. Most importantly, a stable peripheral concentration of drug is able to be obtained using this constant drug delivery system, which would benefit researchers to verify the efficiency of antirheumatoid drugs and establish safety profiles in preclinical studies.

CRAC channels as targets for drug discovery and development

Calcium release-activated calcium (CRAC) channels have been the target of drug discovery for many years. The identification of STIM and Orai proteins as key components of CRAC channels greatly facilitated this process because their co-expression in cell lines produced electrophysiological currents (I_CRAC) much larger than those in native cells, making it easier to confirm and characterize the effects of modulatory compounds. A driving force in the quest for CRAC channel drugs has been the immunocompromised phenotype displayed by humans and mice with null or loss-of-function mutations in STIM1 or Orai1, suggesting that CRAC channel inhibitors could be useful therapeutics for autoimmune or inflammatory conditions. Emerging data also suggests that other therapeutic conditions may benefit from CRAC channel inhibition. However, only recently have CRAC channel inhibitors reached clinical trials. This review discusses the challenges associated with drug discovery and development on CRAC channels and the approaches employed to date, as well as the results, starting from initial high-throughput screens for CRAC channel modulators and progressing through target selection and justification, descriptions of pharmacological, safety and toxicological profiles of compounds, and finally the entry of CRAC channel inhibitors into clinical trials.

Engineered membrane protein antigens successfully induce antibodies against extracellular regions of claudin-5

The production of antibodies against the extracellular regions (ECR) of multispanning membrane proteins is notoriously difficult because of the low productivity and immunogenicity of membrane proteins due to their complex structure and highly conserved sequences among species. Here, we introduce a new method to generate ECR-binding antibodies utilizing engineered liposomal immunogen prepared using a wheat cell-free protein synthesis system. We used claudin-5 (CLDN-5) as the target antigen, which is a notoriously difficult to produce and poorly immunogenic membrane protein with two highly conserved extracellular loops. We drastically improved the productivity of CLDN-5 in the cell-free system after suppressing and normalizing mRNA GC content. To overcome its low immunogenicity, two engineered antigens were designed and synthesized as proteoliposomes: a human/mouse chimeric CLDN-5, and a CLDN-5-based artificial membrane protein consisting of symmetrically arranged ECRs. Intraperitoneal immunization of both engineered CLDN-5 ECR antigens induced ECR-binding antibodies in mice with a high success rate. We isolated five monoclonal antibodies that specifically recognized CLDN-5 ECR. Antibody clone 2B12 showed high affinity (<10 nM) and inhibited CLDN-5-containing tight junctions. These results demonstrate the effectiveness of the methods for monoclonal antibody development targeting difficult-to-produce membrane proteins such as CLDNs.

Release of Antibodies and Cytokines from B Cells

Autoreactive B cells play a critical role in rheumatoid arthritis. These cells differentiate into long-living memory B cells and autoantibody-producing plasma cells and also present autoantigens to T cells to amplify misdirected immune responses. The therapeutic benefit of B-cell-deleting therapies suggests that B cells are emerging as important factors in the pathogenesis of RA. Aiming at evaluation of the function of B cells, which are usually derived from peripheral blood of RA patients and healthy donors, it is possible to conduct a series of experiments, such as in vitro assessment of antibody production and BCR-mediated cytokine release. These techniques can also be applied for in vivo application.

Production of Neutralizing Antibody

Techniques employing monoclonal antibodies (mAbs) are widely used in the initial development phase of biologics. The usefulness of mAbs in basic RA research has been established based on their characteristics, including specificity of binding, homogeneity, and ability to be produced on a large scale. MAb immunoglobulins are the starting material for the generation of smaller antibody fragments and other engineered immunomodulatory antibodies. In this chapter, the basic hybridoma technique, which is a well-established and feasible method for the production of mAbs involving animal immunization, cell fusion, hybridoma screening, expanding positive hybridomas, and purification, is introduced. Aiming at specific affinity to a membrane protein, synthetic proteoliposomes are used in the immunization and screening steps.