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Sigma receptor is a transmembrane non-GPCR protein expressed mainly in the endoplasmic reticulum membrane associated with mitochondria. It is classified into two types: Sigma-1 (S1R) and Sigma-2 (S2R) based on their biological functions. S1R has been implicated in many neurological disorders such as anxiety, schizophrenia, and depression. Therefore, S1R ligands possess a variety of potential clinical applications with a great interest in the treatment of neuropathic pain. In this study, we report the discovery of a novel lead compound for S1R binding, based on the thiazolidine-2,4-dione nucleus. We have explored hydrophobic groups of different sizes on both sides of the five-membered ring scaffold guided by the crystal structure of S1R. Six compounds showed more than 50% displacement of the radioligand at 10 µM concentration with compound 6c resulting in 100% displacement and a K

Recent studies have revealed that glial sigma-1 receptor (Sig-1R) in the spinal cord may be a critical factor to mediate sensory function. However, the functional role of Sig-1R in astrocyte has not been clearly elucidated. Here, we determined whether Sig-1Rs modulate calcium responses in primary cultured astrocytes and pathological changes in spinal astrocytes, and whether they contribute to pain hypersensitivity in naive mice and neuropathic pain following chronic constriction injury (CCI) of the sciatic nerve in mice. Sig-1R was expressed in glial fibrillary acidic protein (GFAP)-positive cultured astrocytes. Treatment with the Sig-1R agonist, PRE-084 or neurosteroid dehydroepiandrosterone (DHEA) increased intracellular calcium responses in cultured astrocytes, and this increase was blocked by the pretreatment with the Sig-1R antagonist, BD-1047 or neurosteroid progesterone. Intrathecal administration of PRE-084 or DHEA for 10 days induced mechanical and thermal hypersensitivity and increased the number of Sig-1R-immunostained GFAP-positive cells in the superficial dorsal horn (SDH) region of the spinal cord in naive mice, and these changes were inhibited by administration with BD-1047 or progesterone. In CCI mice, intrathecal administration of BD-1047 or progesterone at post-operative day 14 suppressed the developed mechanical allodynia and the number of Sig-1R-immunostained GFAP-positive cells that were increased in the SDH region of the spinal cord following CCI of the sciatic nerve. These results demonstrate that Sig-1Rs play an important role in the modulation of intracellular calcium responses in cultured astrocytes and pathological changes in spinal astrocytes and that administration of BD-1047 or progesterone alleviates the Sig-1R-induced pain hypersensitivity and the peripheral nerve injury-induced mechanical allodynia.

The σ(2) receptor has attracted intense interest in cancer imaging(1), psychiatric disease(2), neuropathic pain(3–5), and other areas of biology(6,7). We determined the crystal structure of this receptor in complex with the clinical candidate roluperidone(2) and the tool compound PB28(8). These structures templated a large-scale docking screen of 490 million virtual molecules, of which 484 compounds were synthesized and tested. 127 new chemotypes with affinities superior to 1 μM were identified, 31 of which had affinities superior to 50 nM. Hit rate fell smoothly and monotonically with docking score. We optimized three hits for potency and selectivity, achieving affinities ranging from 3 to 48 nM with up to 250-fold selectivity versus the σ(1) receptor. Crystal structures of two new ligands bound to the σ(2) receptor confirmed the docked poses. To investigate the contribution of the σ(2) receptor in pain, two potent σ(2)-selective ligands and one potent σ(1)/σ(2) non-selective ligand were tested for efficacy in a mouse neuropathic pain model. All three ligands demonstrated time-dependent decreases in mechanical hypersensitivity in the spared nerve injury model(9), supporting a role for the σ(2) receptor in nociception. This study illustrates the opportunities for rapid discovery of in vivo probes to study under-explored areas of biology using structure-based screens of diverse, ultra-large libraries.

Allosteric modulation represents an important approach in drug discovery because of its advantages in safety and selectivity. SOMCL-668 is the first selective and potent sigma-1 receptor allosteric modulator, discovered in our laboratory. The present work investigates the potential therapeutic effects of SOMCL-668 on phencyclidine (PCP)-induced schizophrenia-related behavior in mice and further elucidates underlying mechanisms for its antipsychotic-like effects. SOMCL-668 not only attenuated acute PCP-induced hyperactivity and PPI disruption, but also ameliorated social deficits and cognitive impairment induced by chronic PCP treatment. Pretreatment with the selective sigma-1 receptor antagonist BD1047 blocked the effects of SOMCL-668, indicating sigma-1 receptor-mediated responses. This was confirmed using sigma-1 receptor knockout mice, in which SOMCL-668 failed to ameliorate PPI disruption and hyperactivity induced by acute PCP and social deficits and cognitive impairment induced by chronic PCP treatment. Additionally, in vitro SOMCL-668 exerted positive modulation of sigma-1 receptor agonist-induced intrinsic plasticity in brain slices recorded by patch-clamp. Furthermore, in vivo lower dose of SOMCL-668 exerted positive modulation of improvement in social deficits and cognitive impairment induced by the selective sigma-1 agonist PRE084. Also, SOMCL-668 reversed chronic PCP-induced down-regulation in expression of frontal cortical p-AKT/AKT, p-CREB/CREB and BDNF in wide-type but not sigma-1 knockout mice. Moreover, administration of the PI3K/AKT inhibitor LY294002 abolished amelioration by SOMCL-668 of chronic PCP-induced schizophrenia-related behaviors by inhibition of BDNF expression. The present data provide initial, proof-of-concept evidence that allosteric modulation of the sigma-1 receptor may be a novel approach for the treatment of psychotic illness.

Background: Sigma receptors (Rs), initially classified as an additional class of opioid receptors, are now recognized as a unique entity with no homology to opioid receptors divided into two distinct subtypes, namely σ1R and σ2R. σ1R-targeting ligands have been conceived and explored for the treatment of various neurodegenerative disorders and neuropathic pain. Activation of the σ2R appears to be involved in the regulation of cellular proliferation and cell death. Objective: Up to now, the rational design of novel σ1R ligands was efficiently guided by computational methods, especially relying on homology modeling studies. Conversely, the limited number of in silico studies was applied in the search of σ2R-targeting compounds. Herein we explored several series of σ1R ligands, by computational methods, featuring variable selectivity profile towards σ1R and σ2R in order to gain useful information guiding the rational design of more selective ligands. Methods: Based on the recent X-ray crystallographic structure of the human σ1R, in-depth molecular docking studies on different series of σR ligands have been performed. These calculations have been followed by molecular dynamic simulations (MD) and two pharmacophore analyses, taking into account the activity levels towards σ1R and σ2R. Results: Structure-based studies revealed key contacts to be achieved in order to guide selectivity of σ1R-targeting compounds while the two pharmacophore models described the main features turning into effective σ1R or σ2R ligands. Conclusion: The applied computational approach allowed a more comprehensive exploration of the structure-activity relationship (SAR) within the herein analyzed σR ligands, deriving useful guidelines for the rational design of more selective compounds.

Sigma‐2 receptor/TMEM97 is overexpressed in many tumours, and sigma‐2 receptor ligands are under investigation for cancer therapy. We intended to evaluate the effect of PB28 on renal cancer in proliferation, migration and invasion in vitro and in vivo. Invasive renal cancer cell lines treated with PB28 (or sigma‐2 receptor antagonist 1) were subjected to cell proliferation, migration and invasion assays. The therapeutic effect of PB28 was performed on nude mice. Western blot for proteins in the PI3K‐AKT‐mTOR signalling pathway was conducted. A CCK‐8 assay was used to examine the effect of the combination of PB28 and cisplatin on renal cancer cells. Significant inhibitory effects were observed on proliferation, migration and invasion of 786‐O and ACHN cells after culturing with PB28. But, the outcomes of sigma‐2 receptor antagonist 1 presented the opposite tendency. PB28 significantly inhibited the proliferative and invasive ability of OS‐RC‐2 cells in vivo. Treatment resulted in decreased phosphorylation of constituents of the PI3K‐AKT‐mTOR pathway. The combination of PB28 and cisplatin showed enhanced efficacy in the inhibition of renal cancer cell proliferation. Taken together, PB28 inhibited the tumorigenic behaviours of renal cancer cells by regulating the PI3K‐AKT‐mTOR signalling pathway and was expected to be a sensitizer of cisplatin.

金沢大学疾患モデル総合研究センター, Background: This study chronologically evaluated the expression of the intensity and distribution of the sigma-1 receptor (σ1R) demonstrated by radiolabeled 2-[4-(2-iodophenyl)piperidino]cyclopentanol (OI5V) in a rat model of myocardial ischemia and reperfusion. Methods and Results: The left coronary artery was occluded for 30 min, followed by reperfusion. Dual-tracer autoradiography with 125I-OI5V and 99 mTc-MIBI was performed to assess the spatiotemporal changes in 125I-OI5V uptake (n=5-6). Significant and peaked 125I-OI5V uptake in the ischemic area was observed at 3 days after reperfusion, and the 125I-OI5V uptake ratio of ischemic area to normally perfused left ventricular area decreased gradually from 3 to 28 days (mean value ± SD; 0.90±0.12 at 1 day, 1.89±0.19 at 3 days, 1.52±0.17 at 7 days, 1.34±0.13 at 14 days, and 1.16±0.14 at 28 days, respectively). Triple-tracer autoradiography with 125I-OI5V, 99 mTc-MIBI, and 201TlCl was performed to evaluate 125I-OI5V uptake in the ischemic area in relation to the residual perfusion at 7 days (n=4). The 125I-OI5V uptake ratio of the non-salvaged area was higher compared to that of the salvaged area in the ischemic area. 123I-OI5V and 99 mTc-MIBI SPECT/CT was performed 3 days after reperfusion (n=3), and the in vivo images showed clear uptake of 123I-OI5V in the perfusion defect area. Conclusions: The present study confirmed the spatiotemporal expression pattern of σ1R expression. Non-invasive σ1R imaging with 123I or 125I-OI5V was feasible to monitor the expression of σ1R after myocardial ischemia and reperfusion. © 2021 Japanese Circulation Society. All rights reserved.

The sigma 1 receptor (S1R) is an enigmatic ligand-operated chaperone involved in many important biological processes, and its functions are not fully understood yet. Herein, we developed a novel series of bitopic S1R ligands as versatile tools to investigate binding processes, allosteric modulation, and the oligomerization mechanism. These molecules have been prepared in the enantiopure form and subjected to a preliminary biological evaluation, while in silico investigations helped to rationalize the results. Compound 7 emerged as the first bitopic S1R ligand endowed with low nanomolar affinity (Ki = 2.6 nM) reported thus far. Computational analyses suggested that 7 may stabilize the open conformation of the S1R by simultaneously binding the occluded primary binding site and a peripheral site on the cytosol-exposed surface. These findings pave the way to new S1R ligands with enhanced activity and/or selectivity, which could also be used as probes for the identification of a potential allosteric site.

International audience; Multiple Sclerosis (MS) is an autoimmune demyelinating and neurodegenerative disease of the central nervous system (CNS). Current management strategies suppress or modulate immune function, all with consequences and known side effects. They demonstrate a high level of success in limiting new relapses. However, the neurodegenerative process still affects both grey and white matter in the central nervous system. The sigma1 (S1R) ligand-regulated chaperone is implicated in many biological processes in various CNS-targeted diseases, acting on neural plasticity, myelination and neuroinflammation. Among the proteins involved in MS, S1R has therefore emerged as a promising new target. Standard and robust methods have been adopted to analyze the adsorption, distribution, metabolism, excretion (ADME) properties, safety pharmacology and toxicology of a previously synthetized simple benzamide-derived compound with nanomolar affinity for S1R, high selectivity, no cytotoxicity and good metabolic stability. The compound was also characterized as an agonist based on well-validated assays prior to in vivo investigations. Interestingly, we found that the oral administration of this compound resulted in an overall significant reduction in clinical progression in an MS experimental model. This effect is mediated through S1R action. Our results further suggest the potential use of this compound in the treatment of MS.

Purpose Association of the metal chelating portion of thiosemicarbazone with the cytotoxic activity of sigma-2 receptors appears a promising strategy for the treatment of pancreatic tumors. Here, we developed a novel sigma-2 receptor targeting thiosemicarbazone (FA4) that incorporates a moiety associated with lysosome destabilization and ROS increase in order to design more efficient antitumor agents. Methods The density of sigma receptors in pancreatic cancer cells was evaluated by flow cytometry. In these cells, cytotoxicity (MTT assay) and activation of ER- and mitochondria-dependent cell death pathways (mRNA expression of GRP78, ATF6, IRE1, PERK; ROS levels by MitoSOX and DCFDA-AM; JC-1 staining) induced by the thiosemicarbazones FA4, MLP44, PS3 and ACthio-1, were evaluated. The expression of autophagic proteins (ATG5, ATG7, ATG12, beclin, p62 and LC3-I) was also studied. In addition, the in vivo effect of FA4 in xenograft models with and without gemcitabine challenge was investigated. Results We found that FA4 exerted a more potent cytotoxicity than previously studied thiosemicarbazones (MLP44, PS3 and ACthio-1), which were found to display variable effects on the ER or the mitochondria-dependent pro-apoptotic axis. By contrast, FA4 activated pro-apoptotic pathways and decreased autophagy, except in MiaPaCa2 cells, in which autophagic proteins were expressed at lower levels and remained unmodified by FA4. FA4 treatment of PANC-1 xenografted mouse models, poorly responsive to conventional chemotherapy, significantly reduced tumor volumes and increased intratumor apoptosis compared to gemcitabine, with no signs of toxicity. Conclusions Our data indicate that FA4 exhibits encouraging activity in pancreatic cancer cells unresponsive to gemcitabine. These results warrant further investigation in patient-derived pancreatic cancers, and hold promise for the development of therapies that can more efficiently target the specific characteristics of individual tumor types.

Sigma-2 receptor plays key roles in promoting tumor cell apoptosis, enhancing efficacy of anti-tumor drugs, blocking signal transduction controlled by Aβ oligomers, regulating Ca2+ homeostasis and protecting nerve cells. Studies indicated that sigma-2 receptor may be closely coupled with ROS, LDL, mTOR, RAS, PLC/PKC, lysosomal autophagy and mitochondrial super oxidative stress. In addition, the high expression of this receptor in proliferating cells and nerve cells indicates that sigma-2 receptor is an ideal molecular target for imaging and therapeutic development for cancer, Alzheimer's disease, schizophrenia and traumatic brain injury. Various sigma-2 agonists have shown promising anticancer activities, while sigma-2 antagonists have displayed neuroprotection and inhibition of Aβ oligomers in the brain of Alzheimer's disease patients. Thus, both sigma-2 agonists and antagonists are potentially useful therapeutics for the management of cancer and neurodegenerative disorders.

BACKGROUND Alcohol use disorder (AUD) is a complex psychiatric disease characterized by high alcohol intake as well as hyperkatifeia and hyperalgesia during withdrawal. A role for Sigma-1 receptors (Sig-1Rs) in the rewarding and reinforcing effects of alcohol has started to emerge in recent years, as rat studies have indicated that Sig-1R hyperactivity may result in excessive alcohol drinking. Sig-1R studies in mice are very scarce, and its potential role in alcohol-induced hyperalgesia is also unknown. METHODS In this study, we investigated the role of Sig-1R in alcohol drinking and associated hyperalgesia in male mice, using an intermittent access 2-bottle choice model of heavy drinking. RESULTS The Sig-1R antagonist BD-1063 was found dose dependently to reduce both alcohol intake and preference, without affecting either water or sucrose intake, suggesting that the effects are specific for alcohol. Notably, the ability of BD-1063 to suppress ethanol intake correlated with the individual baseline levels of alcohol drinking, suggesting that the treatment was more efficacious in heavy drinking animals. In addition, BD-1063 reversed alcohol-induced hyperalgesia during withdrawal, assessed using an automatic Hargreaves test, without affecting thermal sensitivity in alcohol-naive animals or locomotor activity in either group. CONCLUSIONS These data show that Sig-1R antagonism dose-dependently reduced ethanol consumption in heavy drinking mice as well as its efficacy in reducing alcohol-induced hyperalgesia. These findings provide a foundation for the development of novel treatments for AUD and associated pain states.

Obesity is increasing at epidemic rates across the US and worldwide, as are its co-morbidities, including type-2 diabetes and cardiovascular disease. Thus, targeted interventions to reduce the prevalence of obesity are of the utmost importance. The sigma-1 receptor (S1R) and sigma-2 receptor (S2R; encoded by Tmem97) belong to the same class of drug-binding sites, yet they are genetically distinct. There are multiple ongoing clinical trials focused on sigma receptors, targeting diseases ranging from Alzheimer’s disease through chronic pain to COVID-19. However, little is known regarding their gene-specific role in obesity. In this study, we measured body composition, used a comprehensive laboratory-animal monitoring system, and determined the glucose and insulin tolerance in mice fed a high-fat diet. Compared to Sigmar1+/+ mice of the same sex, the male and female Sigmar1−/− mice had lower fat mass (17% and 12% lower, respectively), and elevated lean mass (16% and 10% higher, respectively), but S1R ablation had no effect on their metabolism. The male Tmem97−/− mice exhibited 7% lower fat mass, 8% higher lean mass, increased volumes of O2 and CO2, a decreased respiratory exchange ratio indicating elevated fatty-acid oxidation, and improved insulin tolerance, compared to the male Tmem97+/+ mice. There were no changes in any of these parameters in the female Tmem97−/− mice. Together, these data indicate that the S1R ablation in male and female mice or the S2R ablation in male mice protects against diet-induced adiposity, and that S2R ablation, but not S1R deletion, improves insulin tolerance and enhances fatty-acid oxidation in male mice. Further mechanistic investigations may lead to translational strategies to target differential S1R/S2R regulations and sexual dimorphism for precision treatments of obesity.

Huntington’s disease (HD) is a genetic neurodegenerative disease caused by an expanded CAG repeat in the Huntingtin (HTT) gene that codes for an expanded polyglutamine (polyQ) repeat in exon-1 of the human mutant huntingtin (mHTT) protein. The presence of this polyQ repeat results in neuronal degeneration for which there is no cure nor treatment that modifies disease progression. In previous studies we have shown that small molecules that bind selectively to σ(2)R/TMEM97 can have significant neuroprotective effects in models of Alzheimer’s disease, traumatic brain injury and several other neurodegenerative diseases. In the present work we extend these investigations and show that certain σ(2)R/TMEM97-selective ligands decrease mHTT induced neuronal toxicity. We first synthesized a set of compounds designed to bind to σ(2)R/TMEM97 and determined their binding profiles (K(i) values) for σ(2)R/TMEM97 and other proteins in the central nervous system. Modulators with high affinity and selectivity for σ(2)R/TMEM97 were then tested in our HD cell model. Primary cortical neurons were cultured in vitro for seven days and then co-transfected with either a normal HTT construct (Htt N-586–22Q/GFP) or the mHTT construct Htt-N586–82Q/GFP. Transfected neurons were treated with either σ(2)R/TMEM97 or σ(1)R modulators for 48 h. After treatment, neurons were fixed and stained with Hoechst, and condensed nuclei were quantified to assess cell death in the transfected neurons. Significantly, σ(2)R/TMEM97 modulators reduce the neuronal toxicity induced by mHTT, and their neuroprotective effects are not blocked by NE-100, a selective σ(1)R antagonist known to block neuroprotection by σ(1)R ligands. These results indicate for the first time that σ(2)R/TMEM97 modulators can protect neurons from mHTT-induced neuronal toxicity, suggesting that targeting σ(2)R/TMEM97 may lead to a novel therapeutic approach to treat patients with HD.

Haloperidol is a widely used antipsychotic agent that exerts antipsychotic effects through a strong antagonism of dopamine D2 receptors. In addition, haloperidol is classified as a sigma-1 receptor (S1R) antagonist that prevents endogenous oxidative stress in cultured cells. However, pharmacological activities of haloperidol against oxidative stress remain unclear. Oxytosis/ferroptosis are iron-dependent nonapoptotic oxidative cell deaths that are regarded as two names for the same cell death pathway and the potential physiological relevance of oxytosis/ferroptosis in multiple diseases is suggested. In the present study, the effects of haloperidol on oxytosis/ferroptosis were investigated in S1R-knockdown mouse hippocampal HT22 cells. The results indicate that haloperidol is a strong inhibitor of oxytosis/ferroptosis independent of S1R. Imaging of HT22 cells with a newly developed fluorescent probe showed that haloperidol was localized to late endosomes and lysosomes and reduced the accumulation of lysosomal ferrous ions, resulting in reduced production of intracellular reactive oxygen species and inhibition of cell death. These results indicate that haloperidol is useful not only as an antipsychotic agent but also as a neuroprotective agent against endogenous oxidative stress via distinct mechanisms. Furthermore, lysosome-targeting ferroptosis inhibitors could be useful for the treatment of various diseases, including cancers, ischemia-reperfusion injury, and neurodegenerative disorders, which have been associated with ferroptosis.

Human salivary histatin 1 (Hst1) exhibits a series of cell-activating properties, such as promoting cell spreading, migration, and metabolic activity. We recently have shown that fluorescently labeled Hst1 (F-Hst1) targets and activates mitochondria, presenting an important molecular mechanism. However, its regulating signaling pathways remain to be elucidated. We investigated the influence of specific inhibitors of G protein-coupled receptors (GPCR), endocytosis pathways, extracellular signal-regulated kinases 1/2 (ERK1/2) signaling, p38 signaling, mitochondrial respiration and Na+/K+-ATPase activity on the uptake, mitochondria-targeting and -activating properties of F-Hst1. We performed a siRNA knockdown (KD) to assess the effect of Sigma-2 receptor (S2R) /Transmembrane Protein 97 (TMEM97)—a recently identified target protein of Hst1. We also adopted live cell imaging to monitor the whole intracellular trafficking process of F-Hst1. Our results showed that the inhibition of cellular respiration hindered the internalization of F-Hst1. The inhibitors of GPCR, ERK1/2, phagocytosis, and clathrin-mediated endocytosis (CME) as well as siRNA KD of S2R/TMEM97 significantly reduced the uptake, which was accompanied by the nullification of the promoting effect of F-Hst1 on cell metabolic activity. Only the inhibitor of CME and KD of S2R/TMEM97 significantly compromised the mitochondria-targeting of Hst1. We further showed the intracellular trafficking and targeting process of F-Hst1, in which early endosome plays an important role. Overall, phagocytosis, CME, GPCR, ERK signaling, and S2R/TMEM97 are involved in the internalization of Hst1, while only CME and S2R/TMEM97 are critical for its subcellular targeting. The inhibition of either internalization or mitochondria-targeting of Hst1 could significantly compromise its mitochondria-activating property.

Although opioids and nonsteroidal anti-inflammatory drugs (NSAIDs) are the most common drugs used in persistent pain treatment; they have shown many side effects. The development of new analgesics endowed with mu opioid receptor/delta opioid receptor (MOR/DOR) activity represents a promising alternative to MOR-selective compounds. Moreover, new mechanisms, such as sigma-1 receptor (σ1R) antagonism, could be an opioid adjuvant strategy. The in vitro σ1R and σ2R profiles of previous synthesized MOR/DOR agonists (−)-2R/S-LP2 (1), (−)-2R-LP2 (2), and (−)-2S-LP2 (3) were assayed. To investigate the pivotal role of N-normetazocine stereochemistry, we also synthesized the (+)-2R/S-LP2 (7), (+)-2R-LP2 (8), and (+)-2S-LP2 (9) compounds. (−)-2R/S-LP2 (1), (−)-2R-LP2 (2), and (−)-2S-LP2 (3) compounds have Ki values for σ1R ranging between 112.72 and 182.81 nM, showing a multitarget opioid/σ1R profile. Instead, (+)-2R/S-LP2 (7), (+)-2R-LP2 (8), and (+)-2S-LP2 (9) isomers displayed a nanomolar affinity for σ1R, with significative selectivity vs. σ2R and opioid receptors. All isomers were evaluated using an in vivo formalin test. (−)-2S-LP2, at 0.7 mg/kg i.p., showed a significative and naloxone-reversed analgesic effect. The σ1R selective compound (+)-2R/S-LP2 (7), at 5.0 mg/kg i.p., decreased the second phase of the formalin test, showing an antagonist σ1R profile. The multitarget or single target profile of assayed N-normetazocine derivatives could represent a promising pharmacological strategy to enhance opioid potency and/or increase the safety margin.

The overexpression of σ receptors (σRs) in various types of tumors has prompted a deep investigation of their role in cancer pathophysiology. Consequently, σR ligands have been widely studied in vitro and in vivo for their antiproliferative effects as a novel potential class of chemotherapeutic agents, both alone and in combination with other anticancer drugs. A growing body of evidence highlights that σR ligands can inhibit cancer cells' survival, migration, and proliferation, thanks to the modulation of a wide panel of tumorigenic pathways. In addition to their antitumor activity, σR ligands are gaining momentum as radiotracers for PET and SPECT imaging applications. The purpose of this review is to report on recent advances in the development of σR ligands. In particular, herein, we describe the structure-activity relationships of structurally diverse mixed σ

The sigma 1 receptor is a multifunctional receptor with wide distribution in the nervous system and its function has been implicated with a number of neurological disorders including dementia and Alzheimer's disease (AD) and other neurodegenerative disorders. In addition, modulators of σ1 have been advanced into clinical trials for the treatment of pain. Starting from our previously disclosed piperidine scaffold, we have identified a class of potent sigma 1 modulators. This work highlights the key SAR components that lead to the divergence in D

Background: Lymphatic endothelium plays significant roles in lymph transport and maintaining a barrier between the lymph and interstitial compartments. Lymphatic endothelial dysfunction is suspected to be a key factor in the pathogenesis of lymphatic diseases such as lymphedema. Sigma receptor-1 (σ1) was recently identified to promote endothelial-dependent production of nitric oxide and relaxation of collecting lymphatic vessels. In this study, we investigated the potential role of σ1 in lymphatic endothelial barrier function. Methods and Results: Cultured adult human dermal lymphatic endothelial cells (HDLEC) were grown into confluent monolayers. Transendothelial electrical resistance (TER) served as an index of barrier function. Glycolytic rate of HDLEC was determined with the Agilent Seahorse system. The σ1-selective agonist PRE-084 was used to test the impact of σ1 on HDLEC monolayer barrier function and endothelial bioenergetics, whereas the contribution of basal σ1 activity was assessed with small interfering RNA (siRNA)-mediated knockdown of σ1 expression. The ability of σ1 activation to counteract interleukin (IL)-1β-induced barrier dysfunction was also tested. The results show that PRE-084 increases HDLEC TER in a concentration-dependent manner, whereas reducing σ1 expression with siRNA decreases HDLEC TER. PRE-084 also enhances glycolytic rate parameters in HDLEC. Moreover, PRE-084 treatment partially counteracts IL-1β-induced HDLEC monolayer barrier dysfunction. Conclusions: Collectively, the results suggest that σ1 contributes to basal lymphatic endothelial barrier function, potentially through its ability to enhance glycolytic energy production. Our work also highlights the therapeutic potential of σ1 agonists for preventing lymphatic barrier dysfunction caused by inflammatory mediators.

σ-1 receptors (σ1R) modulate nociceptive signaling, driving the search for selective antagonists to take advantage of this promising target to treat pain. In this study, a new series of benzylpiperazinyl derivatives has been designed, synthesized, and characterized for their affinities toward σ1R and selectivity over the σ-2 receptor (σ2R). Notably, 3-cyclohexyl-1-{4-[(4-methoxyphenyl)methyl]piperazin-1-yl}propan-1-one (15) showed the highest σ1R receptor affinity (Ki σ1 = 1.6 nM) among the series with a significant improvement of the σ1R selectivity (Ki σ2/Ki σ1 = 886) compared to the lead compound 8 (Ki σ2/Ki σ1 = 432). Compound 15 was further tested in a mouse formalin assay of inflammatory pain and chronic nerve constriction injury (CCI) of neuropathic pain, where it produced dose-dependent (3-60 mg/kg, i.p.) antinociception and anti-allodynic effects. Moreover, compound 15 demonstrated no significant effects in a rotarod assay, suggesting that this σ1R antagonist did not produce sedation or impair locomotor responses. Overall, these results encourage the further development of our benzylpiperazine-based σ1R antagonists as potential therapeutics for chronic pain.

Cerebral ischemia-reperfusion injury (CIRI) mainly arises from the clinical treatment of ischemic stroke, induced by the blood-brain barrier (BBB) disruption and infiltrated inflammation. The Sigma-1 receptor (Sigma-1R) is a novel target for neuroprotection, and the α2-receptor agonist pain medication dexmedetomidine displays a neuroprotective effect through activating Sigma-1R. The present study aims to investigate the potential therapeutic effect of dexmedetomidine in a mouse stroke model and hypoxia/reoxygenation(OGD/R)-induced brain endothelial dysfunction. First, we found that Sigma-1R was significantly upregulated in middle cerebral artery occlusion (MCAO) mice by the administration of dexmedetomidine. In vivo experiments revealed that dexmedetomidine ameliorated hyperpermeability of the blood-brain barrier (BBB), lowered the expression level of Occludin, and impaired brain function as measured by neurological scores in MCAO mice. In vitro assays show that dexmedetomidine alleviated OGD/R-caused cytotoxicity, hyperpermeability, abnormal expression of Occludin, and inflammatory factors in human brain microvascular endothelial cells (HBMVECs). Moreover, blockage of Sigma-1R by its antagonist BD1047 abolished the neuroprotective property of dexmedetomidine in both animal and cell culture experiments. On the basis of these findings, we conclude that dexmedetomidine therapy shows neuroprotection in MCAO mice. Mechanistically, dexmedetomidine alleviated hypoxia/reoxygenation-induced cerebral endothelial dysfunction by activating the Sigma-1R-mediated signaling pathway.

Autophagy is a cellular catabolic mechanism that helps clear damaged cellular components and is essential for normal cellular and tissue function. The sigma-1 receptor (σ-1R) is a chaperone protein involved in signal transduction, neurite outgrowth, and plasticity, improving memory, and neuroprotection. Recent evidence shows that σ-1R can promote autophagy. Autophagy activation by the σ-1Rs along with other neuroprotective effects makes it an interesting target for the treatment of Alzheimer's disease. AF710B, T-817 MA, and ANAVEX2-73 are some of the σ-1R agonists which have shown promising results and have entered clinical trials. These molecules have also been found to induce autophagy and show cytoprotective effects in cellular models.This review provides insight into the current understanding of σ-1R functions related to autophagy and their role in alleviating AD.We propose a mechanism through which the activation of σ-1R and autophagy could alter amyloid precursor protein processing to inhibit amyloid-β production by reconstituting cholesterol and gangliosides in the lipid raft to offer neuroprotection against AD. Future AD treatment could involve the combined targeting of the σ-1R and autophagy activation. We suggest that future studies investigate the link between autophagy the σ-1R and AD.

Huntington's disease (HD) is a neurodegenerative, dominantly inherited genetic disease caused by expansion of the polyglutamine tract in the huntingtin gene. At the cellular level, HD is characterized by the accumulation of mutant huntingtin protein in brain cells, resulting in the development of the HD phenotype, which includes mental disorders, decreased cognitive abilities, and progressive motor impairments in the form of chorea. Despite numerous studies, no unambigous connection between the accumulation of mutant protein and selective death of striatal neurons has yet been established. Recent studies have shown impairments in the calcium homeostasis in striatal neurons in HD. These cells are extremely sensitive to changes in the cytoplasmic concentration of calcium and its excessive increase leads to their death. One of the possible ways to normalize the balance of calcium in striatal neurons is through the sigma 1 receptor (S1R), which act as a calcium sensor that also exhibits modulating chaperone activity upon the cell stress observed during the development of many neurodegenerative diseases. The fact that S1R is a ligand-operated protein makes it a new promising molecular target for the development of drug therapy of HD based on the agonists of this receptor.

Sigma-1 receptors (Sig-1Rs) are endoplasmic reticulum (ER) chaperones implicated in neuropathic pain. Here we examine if the Sig-1R may relate to neuropathic pain at the level of dorsal root ganglia (DRG). We focus on the neuronal excitability of DRG in a “spare nerve injury” (SNI) model of neuropathic pain in rats and find that Sig-1Rs likely contribute to the genesis of DRG neuronal excitability by decreasing the protein level of voltage-gated Cav2.2 as a translational inhibitor of mRNA. Specifically, during SNI, Sig-1Rs translocate from ER to the nuclear envelope via a trafficking protein Sec61β. At the nucleus, the Sig-1R interacts with cFos and binds to the promoter of 4E-BP1, leading to an upregulation of 4E-BP1 that binds and prevents eIF4E from initiating the mRNA translation for Cav2.2. Interestingly, in Sig-1R knockout HEK cells, Cav2.2 is upregulated. In accordance with those findings, we find that intra-DRG injection of Sig-1R agonist (+)pentazocine increases frequency of action potentials via regulation of voltage-gated Ca2+ channels. Conversely, intra-DRG injection of Sig-1R antagonist BD1047 attenuates neuropathic pain. Hence, we discover that the Sig-1R chaperone causes neuropathic pain indirectly as a translational inhibitor. Supplementary Information The online version contains supplementary material available at 10.1007/s12035-020-02276-8.

There is an urgent need to identify therapies that prevent SARS-CoV-2 infection and improve the outcome of COVID-19 patients. Although repurposed drugs with favorable safety profiles could have significant benefit, widely available prevention or treatment options for COVID-19 have yet to be identified. Efforts to identify approved drugs with invitro activity against SARS-CoV-2 resulted in identification of antiviral sigma-1 receptor ligands, including antihistamines in the histamine-1 receptor binding class. We identified antihistamine candidates for repurposing by mining electronic health records of usage in population of more than 219,000 subjects tested for SARS-CoV-2. Usage of diphenhydramine, hydroxyzine and azelastine was associated with reduced incidence of SARS-CoV-2 positivity in subjects greater than age 61. We found diphenhydramine, hydroxyzine and azelastine to exhibit direct antiviral activity against SARS-CoV-2 invitro. Although mechanisms by which specific antihistamines exert antiviral effects is not clear, hydroxyzine, and possibly azelastine, bind Angiotensin Converting Enzyme-2 (ACE2) and the sigma-1 receptor as off-targets. Clinical studies are needed to measure the effectiveness of diphenhydramine, hydroxyzine and azelastine for disease prevention, for early intervention, or as adjuvant therapy for severe COVID-19.

Initially associated with cancer diagnosis and therapy, the sigma 2 receptor (σ

A series of σ2R compounds containing benzimidazolone and diazacycloalkane cores was synthesized and evaluated in radioligand binding assays. Replacing the piperazine moiety in a lead compound with diazaspiroalkanes and the fused octahydropyrrolo[3,4-b] pyrrole ring system resulted in a loss in affinity for the σ2R. On the other hand, the bridged 2,5-diazabicyclo[2.2.1]heptane, 1,4-diazepine, and a 3-aminoazetidine analog possessed nanomolar affinities for the σ2R. Computational chemistry studies were also conducted with the recently published crystal structure of the σ2R/TMEM97 and revealed that hydrogen bond interactions with ASP29 and π-stacking interactions with TYR150 were largely responsible for the high binding affinity of small molecules to this protein.

N,N-dimethyltryptamine (DMT) is a potent psychedelic naturally produced by many plants and animals, including humans. Whether or not DMT is significant to mammalian physiology, especially within the central nervous system, is a debate that started in the early 1960s and continues to this day. This review integrates historical and recent literature to clarify this issue, giving special attention to the most controversial subjects of DMT’s biosynthesis, its storage in synaptic vesicles and the activation receptors like sigma-1. Less discussed topics, like DMT’s metabolic regulation or the biased activation of serotonin receptors, are highlighted. We conclude that most of the arguments dismissing endogenous DMT’s relevance are based on obsolete data or misleading assumptions. Data strongly suggest that DMT can be relevant as a neurotransmitter, neuromodulator, hormone and immunomodulator, as well as being important to pregnancy and development. Key experiments are addressed to definitely prove what specific roles DMT plays in mammalian physiology.

Retinal degenerative diseases are the major factors leading to severe visual impairment and even irreversible blindness worldwide. The therapeutic approach for retinal degenerative diseases is one extremely urgent and hot spot in science research. The sigma-1 receptor is a novel, multifunctional ligand-mediated molecular chaperone residing in endoplasmic reticulum (ER) membranes and the ER-associated mitochondrial membrane (ER-MAM); it is widely distributed in numerous organs and tissues of various species, providing protective effects on a variety of degenerative diseases. Over three decades, considerable research has manifested the neuroprotective function of sigma-1 receptor in the retina and has attempted to explore the molecular mechanism of action. In the present review, we will discuss neuroprotective effects of the sigma-1 receptor in retinal degenerative diseases, mainly in aspects of the following: the localization in different types of retinal neurons, the interactions of sigma-1 receptors with other molecules, the correlated signaling pathways, the influence of sigma-1 receptors to cellular functions, and the potential therapeutic effects on retinal degenerative diseases.

Sigma-1 receptor (Sigmar1) is a specific chaperone located in the mitochondria-associated endoplasmic reticulum membrane (MAM) and plays a role in several physiological processes. However, the role of Sigmar1 in bone homeostasis remains unknown. Here, we show that mice lacking Sigmar1 exhibited severe osteoporosis in an ovariectomized model. In contrast, overexpression of Sigmar1 locally alleviated the osteoporosis phenotype. Treatment with Sigmar1 agonists impaired both human and mice osteoclast formation in vitro. Mechanistically, SERCA2 was identified to interact with Sigmar1 based on the immunoprecipitation-mass spectrum (IP-MS) and co-immunoprecipitation (co-IP) assays, and Q615 of SERCA2 was confirmed to be the critical residue for their binding. Furthermore, Sigmar1 promoted SERCA2 degradation through Hrd1/Sel1L-dependent ER-associated degradation (ERAD). Ubiquitination of SERCA2 at K460 and K541 was responsible for its proteasomal degradation. Consequently, inhibition of SERCA2 impeded Sigmar1 deficiency enhanced osteoclastogenesis. Moreover, we found that dimemorfan, an FDA-approved Sigmar1 agonist, effectively rescued bone mass in various established bone-loss models. In conclusion, Sigmar1 is a negative regulator of osteoclastogenesis, and activation of Sigmar1 by dimemorfan may be a potential treatment for osteoporosis in clinical practice.

Many studies involving compounds that enhance histamine release, such as histamine H

We aimed to investigate the hypothesis that sigma receptor ligands, haloperidol and ifenprodil, attenuate hypoxia-induced striatal dopamine release in vitro and determine the possible mechanisms.Extracellular concentrations of dopamine were measured using acute brain slices method under hypoxic, aglycemic and ischemic conditions. Sigma receptor ligands haloperidol and ifenprodil attenuate striatal dopamine release induced by hypoxia in contrast to aglycemia and ischemia. To determine the possible contribution of glutamatergic system on this effect, we compared the effect of NMDA receptor antagonist MK-801 and haloperidol in hypoxia induced by Na-K-ATPaz enzyme inhibitor ouabain. Also, we compared the effect of dopamine uptake blocker nomifensine and haloperidol to determine the role of dopamine transporter on this effect.Haloperidol and nomifensine almost completely abolish ouabain-induced dopamine release unlike MK-801. Different effects of sigma ligands and glutamate receptor antagonists on the hypoxia and ouabain induced dopamine release show that glutamate receptor blockade is partial involved in inhibitory effect of sigma ligand on dopamine release under hypoxic conditions. Similar effect of dopamine uptake blocker nomifensine and sigma receptor ligand haloperidol on ouabain induced dopamine release supports the possibility that inhibition of reverse dopamine transport by sigma ligands might be involved in their protective effect.Data in this study suggest that sigma ligands may be a new therapeutic intervention for the management of hypoxic conditions.

Background Angiogenesis plays a critical role on post-infarction heart failure (PIHF), the presence of which facilitates additional blood supply to maintain the survival of residual cardiomyocytes. The sigma-1 receptor (S1R) has been substantiated to stimulate angiogenesis, with the effect on a model of PIHF remaining unknown. Aims This study aims to investigate the effects of S1R on PIHF and the underlying mechanisms involved. Methods Rats were implemented left anterior descending artery ligation followed by rearing for 6 weeks to induce a phenotype of heart failure. Daily intraperitoneal injection of S1R agonist or antagonist for 5 weeks was applied from 2nd week after surgery. The effects exerted by S1R were detected by echocardiography, hemodynamic testing, western blot, Sirius red dyeing, ELISA, immunohistochemistry and fluorescence. We also cultured HUVECs to verify the mechanisms in vitro. Results Stimulation of S1R significantly ameliorated the cardiac function resulted from PIHF, in addition to the observation of reduced fibrosis in the peri-infarct region and the apoptosis of residual cardiomyocytes, which were associated with augmentation of microvascular density in peri-infarct region through activation of the JAK2/STAT3 pathway. We also indicated that suppression of JAK2/STAT3 pathway by specific inhibitor in vitro reversed the pro-angiogenic effects of S1R on HUVECs, which further confirmed that angiogenesis, responsible for PIHF amelioration, by S1R stimulation was in a JAK2/STAT3 pathway-dependent manner. Conclusion S1R stimulation improved PIHF-induced cardiac dysfunction and ventricular remodeling through promoting angiogenesis by activating the JAK2/STAT3 pathway.

Endothelial dysfunction is an important mechanism involved in myocardial ischemia-reperfusion (I/R) injury. We aimed to explore the effects of Oxycodone on myocardial I/R injury in vivo and in vitro to reveal its mechanisms related to Sigma-1 Receptor (SIGMAR1). A rat model of I/R-induced myocardial injury was developed. The ischemic area and myocardial histopathological changes after oxycodone addition were evaluated by TTC staining and HE staining. LDH, CK-MB and cTnI levels were used to assess myocardial function. Then, the endothelial integrity was reflected by the expressions of ZO-1, Claudin-1 and Occludin. Afterward, ELISA, RT-qPCR, western blot and immunofluorescence assays were adopted for the detection of inflammation-related genes. SIGMAR1 expression in myocardial tissues induced by I/R and cardiac microvascular endothelial cells (CMECs) under hypoxic/reoxygenation (H/R) was determined using RT-qPCR and western blotting. Subsequently, after SIGMAR1 silencing or BD1047 addition (a SIGMAR1 antagonist), cell apoptosis and endothelial integrity were analyzed in the presence of Oxycodone in H/R-stimulated CMECs. Results indicated that Oxycodone decreased the ischemic area and improved myocardial function in myocardial I/R injury rat. Oxycodone improved myocardial histopathological injury and elevated endothelial integrity, evidenced by upregulated ZO-1, Claudin-1 and Occludin expressions. Moreover, inflammatory response was alleviated after Oxycodone administration. Molecular docking suggested that SIGMAR1 could directly bind to Oxycodone. Oxycodone elevated SIGMAR1 expression and SIGMAR1 deletion or BD1047 addition attenuated the impacts of Oxycodone on apoptosis and endothelial integrity of CMECs induced by H/R. Collectively, Oxycodone alleviates myocardial I/R injury in vivo and in vitro by binding to SIGMAR1.

In this study, a panel of 46 compounds containing five different scaffolds known to have high σ

Sigma-1 receptor (S1R) is an important endoplasmic reticulum chaperone with various functions in health and disease. The purpose of the current work was to elucidate the involvement of S1R in cancer energy metabolism under its basal, activated, and inactivated states. For this, two cancer cell lines that differentially express S1R were treated with S1R agonist, (+)-SKF10047, and antagonist, BD1047. The effects of the agonist and antagonist on cancer energy metabolism were studied using single-cell fluorescence microscopy analysis of real-time ion and metabolite fluxes. Our experiments revealed that S1R activation by agonist increases mitochondrial bioenergetics of cancer cells while decreasing their reliance on aerobic glycolysis. S1R antagonist did not have a major impact on mitochondrial bioenergetics of tested cell lines but increased aerobic glycolysis of S1R expressing cancer cell line. Our findings suggest that S1R plays an important role in cancer energy metabolism and that S1R ligands can serve as tools to modulate it.

The sigma 1 receptor (S1R) is a molecular chaperone protein located in the endoplasmic reticulum and plasma membranes and has been shown to play important roles in various pathological disorders including pain and, as recently discovered, COVID-19. Employing structure- and QSAR-based drug design strategies, we rationally designed, synthesized, and biologically evaluated a series of novel triazole-based S1R antagonists. Compound 10 exhibited potent binding affinity for S1R, high selectivity over S2R and 87 other human targets, acceptable in vitro metabolic stability, slow clearance in liver microsomes, and excellent blood-brain barrier permeability in rats. Further in vivo studies in rats showed that 10 exhibited negligible acute toxicity in the rotarod test and statistically significant analgesic effects in the formalin test for acute inflammatory pain and paclitaxel-induced neuropathic pain models during cancer chemotherapy. These encouraging results promote further development of our triazole-based S1R antagonists as novel treatments for pain of different etiologies.

Genetic mutations related to ALS, a progressive neurological disease, have been discovered in the gene encoding σ-1 receptor (σ1R). We previously reported that σ1RE102Q elicits toxicity in cells. The σ1R forms oligomeric states that are regulated by ligands. Nevertheless, little is known about the effect of ALS-related mutations on oligomer formation. Here, we transfected NSC-34 cells, a motor neuronal cell line, and HEK293T cells with σ1R-mCherry (mCh), σ1RE102Q-mCh, or nontagged forms to investigate detergent solubility and subcellular distribution using immunocytochemistry and fluorescence recovery after photobleaching. The oligomeric state was determined using crosslinking procedure. σ1Rs were soluble to detergents, whereas the mutants accumulated in the insoluble fraction. Within the soluble fraction, peak distribution of mutants appeared in higher sucrose density fractions. Mutants formed intracellular aggregates that were co-stained with p62, ubiquitin, and phosphorylated pancreatic eukaryotic translation initiation factor-2-α kinase in NSC-34 cells but not in HEK293T cells. The aggregates had significantly lower recovery in fluorescence recovery after photobleaching. Acute treatment with σ1R agonist SA4503 failed to improve recovery, whereas prolonged treatment for 48 h significantly decreased σ1RE102Q-mCh insolubility and inhibited apoptosis. Whereas σ1R-mCh formed monomers and dimers, σ1RE102Q-mCh also formed trimers and tetramers. SA4503 reduced accumulation of the four types in the insoluble fraction and increased monomers in the soluble fraction. The σ1RE102Q insolubility was diminished by σ1R-mCh co-expression. These results suggest that the agonist and WT σ1R modify the detergent insolubility, toxicity, and oligomeric state of σ1RE102Q, which may lead to promising new treatments for σ1R-related ALS.

Background: No pharmacological treatment has been demonstrated to provide a functional benefit for persons with Huntington’s disease (HD). Pridopidine is a sigma-1-receptor agonist shown to have beneficial effects in preclinical models of HD. Objective: To further explore the effect of pridopidine on Total Functional Capacity (TFC) in the recent double-blind, placebo-controlled PRIDE-HD study. Methods: We performed post-hoc analyses to evaluate the effect of pridopidine on TFC at 26 and 52 weeks. Participants were stratified according to baseline TFC score and analyzed using repeated measures (MMRM) and multiple imputation assuming missing not-at-random (MNAR) and worst-case scenarios. Results: The pridopidine 45 mg bid dosage demonstrated a beneficial effect on TFC for the entire population at week 52 of 0.87 (nominal p = 0.0032). The effect was more pronounced for early HD participants (HD1/HD2, TFC = 7–13), with a change from placebo of 1.16 (nominal p = 0.0003). This effect remained nominally significant using multiple imputation with missing not at random assumption as a sensitivity analysis. Responder analyses showed pridopidine 45 mg bid reduced the probability of TFC decline in early HD patients at Week 52 (nominal p = 0.02). Conclusion: Pridopidine 45 mg bid results in a nominally significant reduction in TFC decline at 52 weeks compared to placebo, particularly in patients with early-stage HD.