The Molecular Function of σ Receptors: Past, Present, and Future

The σ1 and σ2 receptors are enigmatic proteins that have attracted attention for decades due to the chemical diversity and therapeutic potential of their ligands. However, despite ongoing clinical trials with σ receptor ligands for multiple conditions, relatively little is known regarding the molecular function of these receptors. In this review, we revisit past research on σ receptors and discuss the interpretation of these data in light of recent developments. We provide a synthesis of emerging structural and genetic data on the σ1 receptor and discuss the recent cloning of the σ2 receptor. Finally, we discuss the major questions that remain in the study of σ receptors.

Tetrahydro-3-benzazepines with fluorinated side chains as NMDA and σ1 receptor antagonists: Synthesis, receptor affinity, selectivity and antiallodynic activity

The class of tetrahydro-1H-3-benzazepines was systematically modified in 1-, 3- and 7-position. In particular, a F-atom was introduced in β- or γ-position of the 4-phenylbutyl side chain in 3-position. Ligands with the F-atom in γ-position possess higher GluN2B affinity than analogs bearing the F-atom in β-position. This effect was attributed to the reduced basicity of β-fluoro amines. 3-Benzazepines with a benzylic OH moiety show moderate GluN2B affinity, but considerable selectivity over the σ2 receptor. However, removal of the benzylic OH moiety led to increased GluN2B affinity, but reduced GluN2B/σ2 selectivity. With respect to GluN2B affinity the phenol 17b with a γ-fluorophenylbutyl moiety in 3-position represents the most interesting fluorinated ligand (Ki(GluN2B) = 16 nM). Most of the synthesized ligands reveal either similar GluN2B and σ1 affinity or higher σ1 affinity than GluN2B affinity. The methyl ether 16b shows high σ1 affinity (Ki(σ1) = 6.6 nM) and high selectivity over a broad panel of receptors and transporters. The high antiallodynic activity in the mouse capsaicin assay proved the σ1 antagonistic activity of 16b.

M100907 and BD 1047 attenuate the acute toxic effects of methamphetamine

There are no Food and Drug Administration approved pharmacotherapies for methamphetamine (METH) overdose, thus identifying novel drug targets to prevent this devastating adverse event is a public-health imperative. Previous research suggests that serotonin and sigma receptors may contribute to the adverse effects of METH. The present study assessed whether pretreatment with the 5-HT2A receptor antagonist M100907 or the sigma 1 (σ1) receptor antagonist BD 1047 attenuated METH-induced lethality, hyperthermia, convulsions, and seizures. Male, Swiss-Webster mice received intraperitoneal injections of M100907 (1 and 10 mg/kg), BD 1047 (10 mg/kg), or a combination of M100907 (1 mg/kg) and BD 1047 (10 mg/kg) prior to treatment with METH (78 mg/kg). Convulsions and lethality were assessed by observation, core body temperature was assessed by surgically implanted telemetric probes, and seizures were assessed by electroencephalography. M100907 reduced METH-elicited lethality from 67% to 33%, BD1047 reduced METH-elicited lethality from 67% to 50%, and combined administration of both agents eliminated lethality in all mice tested. Similarly, both agents and their combination reduced METH-elicited seizures and convulsions. None of the treatments decreased METH-induced hyperthermia. This research suggests that reducing METH-induced seizures is an important factor in reducing lethality associated with METH overdose. However, future studies should examine whether M100907 and BD 1047 modulate METH-induced hypertension and other adverse effects that may also contribute to METH overdose. Our data support the continued investigation of compounds that target 5-HT2A and σ1 receptors in METH-induced overdose, including their potential to yield emergency reversal agents.

Investigation of the Role of Chirality in the Interaction with σ Receptors and Effect on Binge Eating Episode of a Potent σ1 Antagonist Analogue of Spipethiane

The enantiomers of the potent σ1 receptor antagonist (±)-1 were synthesized and evaluated for their affinity at σ1, σ2 receptors and dopamine transporter (DAT). Analogously to (±)-1, both of the enantiomers showed very high affinity for the σ1 receptor and unprecedented selectivity over both the σ2 receptor and DAT. The lack of enantioselectivity between (+)-1 and (-)-1 indicated that the center of chirality in the 2-position of the benzothiochromane nucleus does not play a crucial role in the interaction with any of the studied targets. Docking studies confirmed that the configuration of the enantiomers has only marginal effects on the molecular interactions with the σ1 receptor. In in vivo studies in a female rat model of binge eating, (±)-1 dose-dependently decreased the binge eating episode elicited by a history of intermittent food restriction and stress, confirming and strengthening the important role played by the σ1 receptor in bingeing-related eating disorders.

Interaction of sigma-1 receptor modulators with seizure development in pentylenetetrazole-induced kindled mice

This study aimed to investigate the effects of sigma receptor modulators, opipramol and BD-1063, on epileptogenesis in pentylenetetrazole (PTZ)-kindling model of epilepsy. Mice (n = 6/group) were received PTZ (30 mg/kg), PTZ plus opipramol (5 or 10 mg/kg), PTZ plus opipramol (5 mg/kg) plus BD-1063 (5 mg/kg, a selective sigma-1 receptor antagonist), and PTZ plus BD-1063 on alternate days for 15 days. Opipramol (5 and 10 mg/kg) + PTZ groups became fully kindled and had higher seizure scores compared to the PTZ group. In contrast, the PTZ plus BD-1063 and the PTZ plus opipramol (5 mg/kg) plus BD-1063 group did not show full kindling. These findings indicate that opipramol has a pro-convulsant effect, which is possibly mediated through activation of sigma-1 receptors.

Sigma-1 Receptor Antagonist (BD1047) Decreases Cathepsin B Secretion in HIV-Infected Macrophages Exposed to Cocaine

Pathogenesis of HIV-associated neurocognitive disorders (HAND) is mediated through the infiltration of perivascular macrophages into the brain with the secretion of viral, neurotoxic and inflammatory proteins. One of these proteins is cathepsin B (CATB), a lysosomal cysteine protease that induces neuronal apoptosis, and increases in plasma and cerebrospinal fluid from HIV-1 infected patients (Cantres-Rosario et al. AIDS 27(3):347-356, 2013). Cocaine further potentiates CATB neurotoxicity in vitro and in vivo (Zenón et al. J NeuroImmune Pharmacol 9(5):703-715, 2014). Modulation of sigma-1 (Sig1R) by cocaine increases oxidative species, cytokines and other factors that promote lysosomal disruption. However, the role of Sig1R in CATB secretion and HIV-1 replication in macrophages exposed to cocaine is unknown. We hypothesized that pharmacological modulation of Sig1R would alter CATB secretion from HIV-1 infected macrophages in vitro and in vivo. To test our hypothesis, monocyte derived-macrophages (MDM) from HIV-1 seronegative donors were isolated, infected with HIV-1ADA, and pretreated with Sig1R antagonist (BD1047) or Sig1R agonist (PRE-084) prior to cocaine exposure and followed for 3,6,9 and 11 days post-infection (dpi). Experiments in vivo were conducted using the HIV encephalitis mouse model (HIVE) with BD1047 treatments prior to cocaine for 14 days. Results demonstrate that in presence of cocaine, BD1047 decreases CATB secretion at 11 dpi, while PRE-084 did not have an effect. In the mouse model, BD1047 treatment prior to cocaine decreased CATB expression, cleaved caspase-3 an p24 antigen levels, reduced astrocytosis, but did not increase MAP-2 or synaptophysin. Results demonstrate that Sig1R plays a role in the modulation of CATB levels in HIV-1 infected MDM exposed to cocaine in vitro and in vivo. Graphical Abstract ᅟ.

Sigma-1 Receptor Antagonists Haloperidol and Chlorpromazine Modulate the Effect of Glutoxim on Na+ Transport in Frog Skin

Using voltage-clamp technique, the involvement of sigma-1 receptors in the regulation of Na+ transport in frog skin by the immunomodulatory drug glutoxim was investigated. We have shown for the first time that preincubation of the frog skin with the sigma-1 receptor antagonists haloperidol and chlorpromazine attenuates the stimulatory effect of glutoxim on the Na+ transport. The results suggest the possible involvement of the sigma-1 receptors in the regulation of Na+ transport in frog skin epithelium by glutoxim.

Sigma-1 receptor antagonist PD144418 suppresses food reinforced operant responding in rats

Sigma-1 (σ1) receptors have been investigated for their involvement in learning, rewarding and motivational processes, particularly as it relates to substances of abuse. Few studies have examined the effects of σ1 receptor agonists and antagonists on the rewarding and motivational properties of natural reinforcers, such as food. Studies that have investigated σ1 receptor agonists and antagonists has produced conflicting results. σ1 receptor antagonist PD144418 has been found to produce a dose-dependent attenuation of locomotor activity induced by cocaine, and by itself, does not suppress basal locomotor activity in mice. However, its effects on reward and motivation as it relates to food are unknown. The present study examined the involvement of σ1 receptors in mediating the rewarding and motivational properties of food using an operant task. The results indicated that at the highest dose (10 μmol/kg), PD144418 significantly attenuated the number of active lever responses for chow pellets but did not decrease the number of active lever responses for sucrose pellets under a fixed ratio (FR2) schedule of reinforcement. However, under a progressive ratio (PR) reinforcement schedule, 10 μmol/kg of PD14418 significantly reduced the breakpoint, a measure indicative of effort or motivation, for both chow and sucrose pellets. When ad libitum chow or sucrose pellets were made freely available (i.e. no lever press required) inside the operant chamber, 10 μmol/kg, PD144418 did not have an effect on number of pellets consumed. These findings indicate that PD144418 reduces the motivational effort of a food reinforced behavior.

Effects of fluvoxamine on nerve growth factor-induced neurite outgrowth inhibition by dexamethasone in PC12 cells

In the present study, we examined the effects of fluvoxamine on nerve growth factor (NGF)-induced neurite outgrowth inhibition by dexamethasone (DEX) in PC12 cells. Fluvoxamine increased NGF-induced neurite outgrowth. Compared with co-treatment with NGF and fluvoxamine, p-Akt levels were higher than the values without fluvoxamine. The phosphorylated extracellular regulated kinase 1/2 levels were slightly increased by co-treatment with NGF and fluvoxamine. Fluvoxamine concentration-dependently improved NGF-induced neurite outgrowth inhibition by DEX. Fluvoxamine also improved the decrease in the NGF-induced p-Akt level caused by DEX. Interestingly, the sigma-1 receptor antagonist NE-100 blocked the improvement effects of fluvoxamine on NGF-induced neurite outgrowth inhibition by DEX. The selective sigma-1 receptor agonist PRE-084 also improved NGF-induced neurite outgrowth inhibition by DEX, which is blocked by NE-100. These results indicate that the improvement effects of fluvoxamine on NGF-induced neurite outgrowth inhibition by DEX may be attributable to the phosphorylation of Akt and the sigma-1 receptor.

Synthesis and Biological Evaluation of Sigma-1 (σ1 ) Receptor Ligands Based on Phenyl-1,2,4-oxadiazole Derivatives

In this study, a series of phenyl-1,2,4-oxadiazole derivatives were synthesized and evaluated for anti-allodynic activity. Structure-activity relationship studies identified 1-{4-[3-(2,4-dichlorophenyl)-1,2,4-oxadiazol-5-yl]butyl}piperidine (39) with excellent affinity for the σ1 receptor and selectivity for the σ2 receptor, with poor activity to other central nervous system neurotransmitter receptors and transporters associated with pain. Compound 39 exhibited dose-dependent efficacy in suppressing the formalin-induced flinching and attenuating mechanical allodynia in chronic constriction injury-induced neuropathic rats. These results suggest that compound 39 exerts potent antihyperalgesic activity and could be considered as a promising candidate for treating neuropathic pain.

May a sigma-1 antagonist improve neuropathic signs induced by cisplatin and vincristine in rats?

BACKGROUND

The antineoplastic drugs cisplatin and vincristine induce peripheral neuropathies. The sigma-1 receptor (σ1R) is expressed in areas of pain control, and its blockade with the novel selective antagonist MR-309 has shown efficacy in nociceptive and neuropathic pain models. Our goal was to test whether this compound reduces neuropathic signs provoked by these antitumoural drugs.

METHODS

Rats were treated with cisplatin or vincristine to induce neuropathies. The effects of acute or repeated administration of MR-309 were tested on mechanical and thermal sensitivity, electrophysiological activity of Aδ-primary afferents in the rat skin-saphenous nerve preparation, and gastrointestinal or cardiovascular functions.

RESULTS

Rats treated with antitumourals developed tactile allodynia, while those treated with vincristine also developed mechanical hyperalgesia. These in vivo modifications correlated with electrophysiological hyperactivity (increased spontaneous activity and hyperresponsiveness to innocuous and noxious mechanical stimulation). Animals treated with cisplatin showed gastrointestinal impairment and those receiving vincristine showed cardiovascular toxicity. A single dose of MR-309 strongly reduced both nociceptive behaviour and electrophysiological changes. Moreover, its concomitant administration with the antitumourals blocked the development of neuropathic symptoms, thus restoring mechanical sensitivity, improving the impairment of feeding behaviour and gastrointestinal transit in the cisplatin-treated group along with ameliorating the altered vascular reactivity recorded in rats treated with vincristine.

CONCLUSION

σ1R antagonist, MR-309, reduces sensorial and electrophysiological neuropathic signs in rats treated with cisplatin or vincristine and, in addition, reduces gastrointestinal and cardiovascular side effects.

SIGNIFICANCE

σ1R antagonism could be an interesting and new option to palliate antitumoural neuropathies.

Sigma-1 Receptor Agonists Induce Oxidative Stress in Mitochondria and Enhance Complex I Activity in Physiological Condition but Protect Against Pathological Oxidative Stress

The sigma1 receptor (σ1R) is a chaperone protein residing at mitochondria-associated endoplasmic reticulum (ER) membranes (MAMs), where it modulates Ca2+ exchange between the ER and mitochondria by interacting with inositol-1,4,5 trisphosphate receptors (IP3Rs). The σ1R is highly expressed in the central nervous system and its activation stimulates neuromodulation and neuroprotection, for instance in Alzheimer's disease (AD) models in vitro and in vivo. σ1R effects on mitochondria pathophysiology and the downstream signaling are still not fully understood. We here evaluated the impacts of σ1R ligands in mouse mitochondria preparations on reactive oxygen species (ROS) production, mitochondrial respiration, and complex activities, in physiological condition and after direct application of amyloid Aβ1-42 peptide. σ1R agonists (2-(4-morpholinethyl)-1-phenylcyclohexanecarboxylate hydrochloride (PRE-084), tetrahydro-N,N-dimethyl-5,5-diphenyl-3-furanmethanamine (ANAVEX1-41, AN1-41), (S)-1-(2,8-dimethyl-1-thia-3,8-diazaspiro[4.5]dec-3-yl)-3-(1H-indol-3-yl)propan-1-one (ANAVEX3-71, AN3-71), dehydroepiandrosterone-3 sulfate (DHEA), donepezil) increased mitochondrial ROS in a σ1R antagonist-sensitive manner but decreased Aβ1-42-induced increase in ROS. σ1R ligands (agonists or antagonists) did not impact respiration but attenuated Aβ1-42-induced alteration. σ1R agonists (PRE-084, AN1-41, tetrahydro-N,N-dimethyl-2,2-diphenyl-3-furanmethanamine hydrochloride (ANAVEX2-73, AN2-73), AN3-71) increased complex I activity, in a Ca2+-dependent and σ1R antagonist-sensitive manner. σ1R ligands failed to affect complex II, III, and IV activities. The increase in complex I activity explain the σ1R-induced increase in ROS since ligands failed to affect other sources of ROS accumulation in mitochondria and homogenates, namely NADPH oxidase (NOX) and superoxide dismutase (SOD) activities. Furthermore, Aβ1-42 significantly decreased the activity of complexes I and IV and σ1R agonists attenuated the Aβ1-42-induced complex I and IV dysfunctions. σ1R activity in mitochondria therefore results in a Ying-Yang effect, by triggering moderate ROS increase acting as a physiological signal and promoting a marked anti-oxidant effect in pathological (Aβ) conditions.

Cardiac sigma receptors - an update

More than four decades passed since sigma receptors were first mentioned. Since then, existence of at least two receptor subtypes and their tissue distributions have been proposed. Nowadays, it is clear, that sigma receptors are unique ubiquitous proteins with pluripotent function, which can interact with so many different classes of proteins. As the endoplasmic resident proteins, they work as molecular chaperones - accompany various proteins during their folding, ensure trafficking of the maturated proteins between cellular organelles and regulate their functions. In the heart, sigma receptor type 1 is more dominant. Cardiac sigma 1 receptors regulate response to endoplasmic reticulum stress, modulates calcium signaling in cardiomyocyte and can affect function of voltage-gated ion channels. They contributed in pathophysiology of cardiac hypertrophy, heart failure and many other cardiovascular disorders. Therefore, sigma receptors are potential novel targets for specific treatment of cardiovascular diseases.

Cholinesterase inhibitor rivastigmine enhances nerve growth factor-induced neurite outgrowth in PC12 cells via sigma-1 and sigma-2 receptors

Rivastigmine (Riv) is a potent and selective cholinesterase (acetylcholinesterase, AChE and butyrylcholinesterase, BuChE) inhibitor developed for the treatment of Alzheimer's disease (AD). To elucidate whether Riv causes neuronal differentiation, we examined its effect on nerve growth factor (NGF)-induced neurite outgrowth in PC12 cells. At concentrations of 0-100 μM, Riv was non-toxic in PC12 cells. Riv caused dose-dependent (10-100 μM) enhancement of NGF-induced neurite outgrowth, which was completely inhibited by the TrkA antagonist GW-441756. By contrast, Riv-mediated enhancement of neurite outgrowth was not blocked by the acetylcholine receptor antagonists, scopolamine and hexamethonium. However, the sigma-1 receptor (Sig-1R) antagonist NE-100 and sigma-2 receptor (Sig-2R) antagonist SM-21 each blocked about half of the Riv-mediated enhancement of NGF-induced neurite outgrowth. Interestingly, the simultaneous application of NE-100 and SM-21 completely blocked the enhancement of NGF-induced neurite outgrowth by Riv. These findings suggest that both Sig-1R and Sig-2R play important roles in NGF-induced neurite outgrowth through TrkA and that Riv may contribute to neuronal repair via Sig-1R and Sig-2R in AD therapy.

Sigma 1 Receptor Antagonists Inhibit Manic-Like Behaviors in Two Congenital Strains of Mice

Background

Several currently available animal models reproduce select behavioral facets of human mania as well as the abnormal glutamatergic neurotransmission and dysregulation of glycogen synthase kinase 3β that accompanies this disease.

Methods

In this study, we addressed the therapeutic potential of ligands of sigma receptor type 1 (σ1R) in 2 putative models of mania: the "manic" Black Swiss outbred mice from Taconic farms (BStac) and mice with the 129 genetic background and histidine triad nucleotide-binding protein 1 (HINT1) deletion (HINT1-/- mice) that exhibit bipolar-like behaviors.

Results

The activity of control mice, which do not exhibit manic-like behaviors in the forced swim test, was significantly enhanced by MK801, an inhibitor of glutamate N-methyl-D-aspartate receptor activity, an effect that was not or barely observed in manic-like mice. Typical mood stabilizers, such as glycogen synthase kinase 3β inhibitors, but not σ1R ligands, reduced the N-methyl-D-aspartate receptor-mediated behaviors in control mice. Notably, σ1R antagonists S1RA, PD144418, BD1047, and BD1063, but not σ1R agonists PRE084 and PPCC, attenuated the manic-like behaviors of BStac and HINT1-/- mice by increasing antiactivity behaviors. The antimanic effects of a single administration of σ1R antagonists persisted for at least 24 hours, and these drugs did not alter the behavior of the "bipolar" HINT1-/- mice during pro-depressive episodes.

Conclusions

σ1R antagonists exhibit a selective normalizing effect on specific behavioral domains of mania without altering control (normal) or depressive-like behaviors.

Benzomorphan skeleton, a versatile scaffold for different targets: A comprehensive review

Despite the fact that the benzomorphan skeleton has mainly been employed in medicinal chemistry for the development of opioid analgesics, it is a versatile structure. Its stereochemistry, as well as opportune modifications at the phenolic hydroxyl group and at the basic nitrogen, play a pivotal role addressing the benzomorphan-based compounds to a specific target. In this review, we describe the structure activity-relationships (SARs) of benzomorphan-based compounds acting at sigma 1 receptor (σ1R), sigma 2 receptor (σ2R), voltage-dependent sodium channel, N-Methyl-d-Aspartate (NMDA) receptor-channel complex and other targets. Collectively, the SARs data have highlighted that the benzomorphan nucleus could be regarded as a useful template for the synthesis of drug candidates for different targets.

Modality-specific peripheral antinociceptive effects of μ-opioid agonists on heat and mechanical stimuli: Contribution of sigma-1 receptors

Morphine induces peripherally μ-opioid-mediated antinociception to heat but not to mechanical stimulation. Peripheral sigma-1 receptors tonically inhibit μ-opioid antinociception to mechanical stimuli, but it is unknown whether they modulate μ-opioid heat antinociception. We hypothesized that sigma-1 receptors might play a role in the modality-specific peripheral antinociceptive effects of morphine and other clinically relevant μ-opioid agonists. Mechanical nociception was assessed in mice with the paw pressure test (450 g), and heat nociception with the unilateral hot plate (55 °C) test. Local peripheral (intraplantar) administration of morphine, buprenorphine or oxycodone did not induce antinociception to mechanical stimulation but had dose-dependent antinociceptive effects on heat stimuli. Local sigma-1 antagonism unmasked peripheral antinociception by μ-opioid agonists to mechanical stimuli, but did not modify their effects on heat stimulation. TRPV1+ and IB4+ cells are segregated populations of small neurons in the dorsal root ganglia (DRG) and the density of sigma-1 receptors was higher in IB4+ cells than in the rest of small nociceptive neurons. The in vivo ablation of TRPV1-expressing neurons with resiniferatoxin did not alter IB4+ neurons in the DRG, mechanical nociception, or the effects of sigma-1 antagonism on local morphine antinociception in this type of stimulus. However, it impaired the responses to heat stimuli and the effect of local morphine on heat nociception. In conclusion, peripheral opioid antinociception to mechanical stimuli is limited by sigma-1 tonic inhibitory actions, whereas peripheral opioid antinociception to heat stimuli (produced in TRPV1-expressing neurons) is not. Therefore, sigma-1 receptors contribute to the modality-specific peripheral effects of opioid analgesics.

Targeting immune-driven opioid analgesia by sigma-1 receptors: Opening the door to novel perspectives for the analgesic use of sigma-1 antagonists

Immune cells have a known role in pronociception, since they release a myriad of inflammatory algogens which interact with neurons to facilitate pain signaling. However, these cells also produce endogenous opioid peptides with analgesic potential. The sigma-1 receptor is a ligand-operated chaperone that modulates neurotransmission by interacting with multiple protein partners, including the μ-opioid receptor. We recently found that sigma-1 antagonists are able to induce opioid analgesia by enhancing the action of endogenous opioid peptides of immune origin during inflammation. This opioid analgesia is seen only at the inflamed site, where immune cells naturally accumulate. In this article we review the difficulties of targeting the opioid system for selective pain relief, and discuss the dual role of immune cells in pain and analgesia. Our discussion creates perspectives for possible novel therapeutic uses of sigma-1 antagonists as agents able to maximize the analgesic potential of the immune system.

Sigma-1 Receptor Antagonist Haloperidol Attenuates Store-Dependent Ca2+ Entry in Macrophages

Using Fura-2AM microfluorimetry, we have shown for the first time that preincubation of macrophages with sigma-1 receptor antagonist haloperidol leads to a significant inhibition of the store-dependent Ca2+ entry induced by endoplasmic Ca2+-ATPase inhibitors thapsigargin or cyclopiazonic acid in rat peritoneal macrophages. The results suggest the involvement of the sigma-1 receptor in the regulation of storedependent Ca2+ entry in macrophages.

Sigma 1 receptor mediated HMGB1 expression in spinal cord is involved in the development of diabetic neuropathic pain

No study has been conducted to examine the interactions of sigma-1 receptor (Sigma-1R) and high mobility group box 1 protein (HMGB1) in the development of diabetic peripheral neuropathy. Thus, we examined the effects of streptozotocin (STZ) treatment on expression of HMGB1 in subcellular levels in the dorsal root ganglion (DRG) in both wild-type and Sigma-1R-/- mice and evaluated the effects of repeated intrathecal administrations of selective Sigma-1R antagonists BD1047, agonist PRE-084, or HMGB1 inhibitor glycyrrhizin on peripheral neuropathy in wild-type mice. We found that STZ-induced tactile allodynia and thermal hyperalgesia was associated with increased total HMGB1 expression in DRG. STZ treatment promoted the distribution of HMGB1 into cytoplasm. Furthermore, STZ induced modest peripheral neuropathy and did not alter HMGB1 levels in DRG or the distribution of either cytoplasmic or nuclear HMGB1 in Sigma-1R-/- mice compared to sham control mice. Additionally, repeated stimulation of Sigma-1R in the spinal cord induced tactile allodynia and thermal hyperalgesia at 1 week. This phenomenon was associated with increased cytoplasmic HMGB1 translocation and HMGB1 expression in DRG. Finally, we found that repeated blockade of either Sigma-1R or HMGB1 in the spinal cord after STZ treatment prevent the development of tactile allodynia and thermal hyperalgesia at 1 week. These effects were associated with decreased cytoplasmic HMGB1 translocation and HMGB1 expression in DRG. Taken together, our results suggest that Sigma-1R-mediated enhancement of HMGB1 expression in the DRG is critical for the development of peripheral neuropathy in type 1 diabetes.

Small-Molecule Sigma1 Modulator Induces Autophagic Degradation of PD-L1

Emerging evidence suggests that Sigma1 (SIGMAR1, also known as sigma-1 receptor) is a unique ligand-regulated integral membrane scaffolding protein that contributes to cellular protein and lipid homeostasis. Previously, we demonstrated that some small-molecule modulators of Sigma1 alter endoplasmic reticulum (ER)-associated protein homeostasis pathways in cancer cells, including the unfolded protein response and autophagy. Programmed death-ligand 1 (PD-L1) is a type I integral membrane glycoprotein that is cotranslationally inserted into the ER and is processed and transported through the secretory pathway. Once at the surface of cancer cells, PD-L1 acts as a T-cell inhibitory checkpoint molecule and suppresses antitumor immunity. Here, we demonstrate that in Sigma1-expressing triple-negative breast and androgen-independent prostate cancer cells, PD-L1 protein levels were suppressed by RNAi knockdown of Sigma1 and by small-molecule inhibition of Sigma1. Sigma1-mediated action was confirmed by pharmacologic competition between Sigma1-selective inhibitor and activator ligands. When administered alone, the Sigma1 inhibitor decreased cell surface PD-L1 expression and suppressed functional interaction of PD-1 and PD-L1 in a coculture of T cells and cancer cells. Conversely, the Sigma1 activator increased PD-L1 cell surface expression, demonstrating the ability to positively and negatively modulate Sigma1 associated PD-L1 processing. We discovered that the Sigma1 inhibitor induced degradation of PD-L1 via autophagy, by a mechanism distinct from bulk macroautophagy or general ER stress-associated autophagy. Finally, the Sigma1 inhibitor suppressed IFNγ-induced PD-L1. Our data demonstrate that small-molecule Sigma1 modulators can be used to regulate PD-L1 in cancer cells and trigger its degradation by selective autophagy.Implications: Sigma1 modulators sequester and eliminate PD-L1 by autophagy, thus preventing functional PD-L1 expression at the cell surface. This posits Sigma1 modulators as novel therapeutic agents in PD-L1/PD-1 blockade strategies that regulate the tumor immune microenvironment.Visual Overview: http://mcr.aacrjournals.org/content/molcanres/16/2/243/F1.large.jpg Mol Cancer Res; 16(2); 243-55. ©2017 AACR.

Multifunctional thiosemicarbazones and deconstructed analogues as a strategy to study the involvement of metal chelation, Sigma-2 (σ2) receptor and P-gp protein in the cytotoxic action: In vitro and in vivo activity in pancreatic tumors

The aggressiveness of pancreatic cancer urgently requires more efficient treatment options. Because the sigma-2 (σ2) receptor was recently proposed as a promising target for pancreatic cancer therapy, we explored our previously developed multifunctional thiosemicarbazones, designed to synergistically impair cell energy levels, by targeting σ2 and P-gp proteins and chelating Iron. A deconstruction approach was herein applied by removing one function at a time from the potent multifunctional thiosemicarbazones 1 and 2, to investigate the contribution to cytotoxicity of each target involved. The results from in vitro (panel of pancreatic tumor cells) and in vivo experiments (C57BL/6 bearing KP02 tumor), suggest that while the multifunctional activity was not required for the antitumor activity of these thiosemicarbazones, σ2-targeting appeared to allow alternative tumor cell death mechanisms, leading to potent and less toxic off-targets toxicities compared to other thiosemicarbazones devoid of σ2-targeting.

Efficacy of a Novel Sigma-1 Receptor Antagonist for Oxaliplatin-Induced Neuropathy: A Randomized, Double-Blind, Placebo-Controlled Phase IIa Clinical Trial

This trial assessed the efficacy of MR309 (a novel selective sigma-1 receptor ligand previously developed as E-52862) in ameliorating oxaliplatin-induced peripheral neuropathy (oxaipn). A discontinuous regimen of MR309 (400 mg/day, 5 days per cycle) was tested in patients with colorectal cancer receiving FOLFOX in a phase II, randomized, double-blind, placebo-controlled, multicenter clinical trial. Outcome measures included changes in 24-week quantitative measures of thermal sensitivity and total neuropathy score. In total, 124 patients were randomized (1:1) to MR309 or placebo. Sixty-three (50.8%) patients withdrew prematurely before completing 12 planned oxaliplatin cycles. Premature withdrawal because of cancer progression was less frequent in the MR309 group (7.4% vs 25.0% with placebo; p = 0.054). MR309 significantly reduced cold pain threshold temperature [mean treatment effect difference (SE) vs placebo: 5.29 (1.60)°C; p = 0.001] and suprathreshold cold stimulus-evoked pain intensity [mean treatment effect difference: 1.24 (0.57) points; p = 0.032]. Total neuropathy score, health-related quality-of-life measures, and nerve-conduction parameters changed similarly in both arms, whereas the proportion of patients with severe chronic neuropathy (National Cancer Institute Common Terminology Criteria for Adverse Events ≥ 3) was significantly lower in the MR309 group (3.0% vs 18.2% with placebo; p = 0.046). The total amount of oxaliplatin delivered was greater in the active arm (1618.9 mg vs 1453.8 mg with placebo; p = 0.049). Overall, 19.0% of patients experienced at least 1 treatment-related adverse event (25.8% and 11.9% with MR309 and placebo, respectively). Intermittent treatment with MR309 was associated with reduced acute oxaipn and higher oxaliplatin exposure, and showed a potential neuroprotective role for chronic cumulative oxaipn. Furthermore, MR309 showed an acceptable safety profile.

Novel Sigma-1 receptor antagonists: from opioids to small molecules: what is new?

Sigma-1 (σ1) receptor has been identified as a chaperone protein that interacts with other proteins, such as N-methyl-D-aspartate (NMDA) and opioid receptors, modulating their activity. σ1 receptor antagonists have been developed to obtain useful compounds for the treatment of psychoses, pain, drug abuse and cancer. Some interesting compounds such as E-5842 (5) and MS-377 (24), haloperidol and piperazine derivatives, respectively, were endowed with high affinity for σ1 receptors (Ki σ1 = 4 and 73 nM; Ki σ2 = 220 and 6900, respectively). They were developed for the treatment of psychotic disorders and 5 also underwent Phase II clinical trials suggesting interesting potential therapeutic applications. Here, σ1 receptor antagonists have been grouped based on chemical structure and reviewed according to structure-activity relationship and potential therapeutic role.

Solid-phase organic synthesis of chiral, non-racemic 1,2,4-trisubstituted 1,4-diazepanes with high σ1 receptor affinity

The aim of this work was to transfer the established chiral-pool synthesis of 1,2,4-trisubstituted 1,4-diazepanes in solution on the solid phase. For this purpose, (S)-configured amino acids, (S)-alanine, and (S)-leucine, with a small methyl and a larger isobutyl moiety were attached to the solid support 9 by reductive amination. After five reaction steps on the solid support, the 1,4-diazepanes (S)-19a,b were cleaved off and reductively alkylated to afford the 1,2,4-trisubstituted 1,4-diazepanes (S)-20a and (S)-21b, respectively. Both compounds show high σ1 affinity and selectivity over the σ2 subtype.

circHIPK2-mediated σ-1R promotes endoplasmic reticulum stress in human pulmonary fibroblasts exposed to silica

Silicosis is characterized by fibroblast accumulation and excessive deposition of extracellular matrix. Although the roles of SiO2-induced chemokines and cytokines released from alveolar macrophages have received significant attention, the direct effects of SiO2 on protein production and functional changes in pulmonary fibroblasts have been less extensively studied. Sigma-1 receptor, which has been associated with cell proliferation and migration in the central nervous system, is expressed in the lung, but its role in silicosis remains unknown. To elucidate the role of sigma-1 receptor in fibrosis induced by silica, both the upstream molecular mechanisms and the functional effects on cell proliferation and migration were investigated. Both molecular biological assays and pharmacological techniques, combined with functional experiments, such as migration and proliferation, were applied in human pulmonary fibroblasts from adults to analyze the molecular and functional changes induced by SiO2. SiO2 induced endoplasmic reticulum stress in association with enhanced expression of sigma-1 receptor. Endoplasmic reticulum stress promoted migration and proliferation of human pulmonary fibroblasts-adult exposed to SiO2, inducing the development of silicosis. Inhibition of sigma-1 receptor ameliorated endoplasmic reticulum stress and fibroblast functional changes induced by SiO2. circHIPK2 is involved in the regulation of sigma-1 receptor in human pulmonary fibroblasts-adult exposed to SiO2. Our study elucidated a link between SiO2-induced fibrosis and sigma-1 receptor signaling, thereby providing novel insight into the potential use of sigma-1 receptor/endoplasmic reticulum stress in the development of novel therapeutic strategies for silicosis treatment.

Neuroprotective Effect of σ1-Receptors on the Cell Model of Huntington's Disease

Huntington's disease is a hereditary neurodegenerative disease that primarily affects striatal neurons. Recent studies demonstrated abnormalities in calcium regulation in striatal neurons in Huntington's disease, which leads to elimination of synaptic connections between cortical and striatal neurons. In the present study, we focused on the neuroprotective properties of σ1-receptor, because one of its main functions is associated with modulation of calcium homeostasis in cells. The application of selective σ1-receptor agonists to the corticostriatal cell culture restores synaptic connections between the cortical and striatal neurons. Based on the obtained data, we assume that σ1-receptor is a promising target for the development of drugs for the therapy of Huntington's disease.

Haloperidol Decreases Hyperalgesia and Allodynia Induced by Chronic Constriction Injury

Neuropathic pain has proven to be a difficult condition to treat, so investigational therapy has been sought that may prove useful, such as the use of sigma-1 antagonists. Haloperidol (HAL) is a compound that shows a high affinity with these receptors, acting as an antagonist. Therefore, the objective of this study was to demonstrate its effect in an experimental model of neuropathic pain and corroborate its antagonistic action of the sigma-1 receptors under these conditions. BD-1063 was used as a sigma-1 antagonist control, and gabapentin (Gbp) was used as a positive control. The antihyperalgesic and anti-allodynic effects of the drugs were determined after single-dose trials. In every case, the effects increased in a dose-dependent manner. HAL had the same efficacy as both BD-1063 and Gbp. In the analysis of pharmacological potency, in which the ED50 were compared, HAL was the most potent drug of all. The effect of HAL on chronic constriction injury (CCI) rats was reversed by the sigma-1 agonist (PRE-084). HAL reversed the hyperalgesic and allodynic effects of PRE-084 in naïve rats. The dopamine antagonist, (-)-sulpiride, showed no effect in CCl rats. These results suggest that HAL presents an antinociceptive effect via sigma-1 receptor antagonism at the spinal level in the CCl model.

N-(2-morpholin-4-yl-ethyl)-2-(1naphthyloxy)acetamide inhibits the chronic constriction injury-generated hyperalgesia via the antagonism of sigma-1 receptors

The most used therapeutic treatment to relieve neuropathic pain is that of neuromodulators such as anti-epileptics or anti-depressants; however, there are alternatives that may be potentially useful. The sigma-1 receptor is a therapeutic target that has shown favorable results at preclinical levels. The aim of this study was to evaluate the anti-hyperalgesic effect of N-(2-morpholin-4-yl-ethyl)-2-(1-naphthyloxy) acetamide (NMIN) in a chronic constriction injury model (CCI) and compare it both a sigma-1 antagonist (BD-1063) and also Gabapentin, as well as determine its possible role as an antagonist of sigma-1 receptors. The anti-hyperalgesic effects of Gabapentin (10.0, 17.8, 31.6, 56.2 and 100mg/kg, s.c.), BD-1063 (5.6, 10.0, 17.8, 31.6 and 56.2mg/kg, s.c.) and NMIN (31.6, 10.0, 316mg/kg and 562mg/kg, s.c.) were determined after single-doses, using the von Frey test in the CCI model. NMIN had the same efficacy as BD-1063, but both show less efficacy than Gabapentin. In an analysis of pharmacological potency, the ED50 were compared with it being found that BD-1063 is the most potent drug, followed by Gabapentin and NMIN. The anti-hyperalgesic effect of NMIN on CCI rats was reversed by (+)-pentazocine (s.c. route) and by PRE-084 (i.t. route), both sigma-1 agonists. Furthermore, NMIN reversed the hyperalgesic effect of PRE-084 in naïve rats. These results suggest that NMIN has an anti-hyperalgesic effect on the CCI model, and that one of its mechanisms of action is as a sigma-1 antagonist, being a significant role the blocking of these receptors at the spinal level.

New consensus multivariate models based on PLS and ANN studies of sigma-1 receptor antagonists

The treatment of neuropathic pain is very complex and there are few drugs approved for this purpose. Among the studied compounds in the literature, sigma-1 receptor antagonists have shown to be promising. In order to develop QSAR studies applied to the compounds of 1-arylpyrazole derivatives, multivariate analyses have been performed in this work using partial least square (PLS) and artificial neural network (ANN) methods. A PLS model has been obtained and validated with 45 compounds in the training set and 13 compounds in the test set (r2training = 0.761, q2 = 0.656, r2test = 0.746, MSEtest = 0.132 and MAEtest = 0.258). Additionally, multi-layer perceptron ANNs (MLP-ANNs) were employed in order to propose non-linear models trained by gradient descent with momentum backpropagation function. Based on MSEtest values, the best MLP-ANN models were combined in a MLP-ANN consensus model (MLP-ANN-CM; r2test = 0.824, MSEtest = 0.088 and MAEtest = 0.197). In the end, a general consensus model (GCM) has been obtained using PLS and MLP-ANN-CM models (r2test = 0.811, MSEtest = 0.100 and MAEtest = 0.218). Besides, the selected descriptors (GGI6, Mor23m, SRW06, H7m, MLOGP, and μ) revealed important features that should be considered when one is planning new compounds of the 1-arylpyrazole class. The multivariate models proposed in this work are definitely a powerful tool for the rational drug design of new compounds for neuropathic pain treatment. Graphical abstract Main scaffold of the 1-arylpyrazole derivatives and the selected descriptors.

Haloperidol, a sigma receptor 1 antagonist, promotes ferroptosis in hepatocellular carcinoma cells

Ferroptosis is a novel form of cell death, which is characterized by accumulation of reactive oxygen species (ROS). Sigma 1 receptor (S1R) has been suggested to function in oxidative stress metabolism. Both erastin and sorafenib significantly induced S1R protein expression. Haloperidol strongly promoted erastin- and sorafenib-induced cell death, which was blocked by ferrostatin-1 but not ZVAD-FMK or necrosulfonamide. During ferroptosis, haloperidol substantially increased the cellular levels of Fe2+, GSH and lipid peroxidation. Furthermore, several ferroptosis-related protein targets were up-regulated in the absence of haloperidol. Thus, Our study identified an association between haloperidol and ferroptosis for the first time. Our analyses of a combination of drugs may provide a novel strategy of hepatocellular carcinoma (HCC) therapy.

Role of sigma 1 receptor in high fat diet-induced peripheral neuropathy

The neurobiological mechanisms of obesity-induced peripheral neuropathy are poorly understood. We evaluated the role of Sigma-1 receptor (Sig-1R) and NMDA receptor (NMDARs) in the spinal cord in peripheral neuropathy using an animal model of high fat diet-induced diabetes. We examined the expression of Sig-1R and NMDAR subunits GluN2A and GluN2B along with postsynaptic density protein 95 (PSD-95) in the spinal cord after 24-week HFD treatment in both wild-type and Sig-1R-/- mice. Finally, we examined the effects of repeated intrathecal administrations of selective Sig-1R antagonists BD1047 in HFD-fed wild-type mice on peripheral neuropathy. Wild-type mice developed tactile allodynia and thermal hypoalgesia after 24-week HFD treatment. HFD-induced peripheral neuropathy correlated with increased expression of GluN2A and GluN2B subunits of NMDARs, PDS-95, and Sig-1R, as well as increased Sig-1R-NMDAR interaction in the spinal cord. In contrast, Sig-1R-/- mice did not develop thermal hypoalgesia or tactile allodynia after 24-week HFD treatment, and the levels of GluN2A, GluN2B, and PSD-95 were not altered in the spinal cord of HFD-fed Sig-1R-/- mice. Finally, repeated intrathecal administrations of selective Sig-1R antagonists BD1047 in HFD-fed wild-type mice attenuated peripheral neuropathy. Our results suggest that obesity-associated peripheral neuropathy may involve Sig-1R-mediated enhancement of NMDAR expression in the spinal cord.

Sigma Receptor (σR) Ligands with Antiproliferative and Anticancer Activity

Sigma receptor (σR) ligands have proven to be useful as cancer diagnostics and anticancer therapeutics and their ligands have been developed as molecular probes in oncology. Moreover, various σR ligands generate cancer cell death in vitro and in vivo. These σR ligands have exhibited promising results against numerous human and rodent cancers and are investigated under preclinical and clinical study trials, indicating a new category of drugs in cancer therapy.

Sigma 2 Receptor/Tmem97 Agonists Produce Long Lasting Antineuropathic Pain Effects in Mice

Neuropathic pain is an important medical problem with few effective treatments. The sigma 1 receptor (σ1R) is known to be a potential target for neuropathic pain therapeutics, and antagonists for this receptor are effective in preclinical models and are currently in phase II clinical trials. Conversely, relatively little is known about σ2R, which has recently been identified as transmembrane protein 97 (Tmem97). We generated a series of σ1R and σ2R/Tmem97 agonists and antagonists and tested them for efficacy in the mouse spared nerve injury (SNI) model. In agreement with previous reports, we find that σ1R ligands given intrathecally (IT) produce relief of SNI-induced mechanical hypersensitivity. We also find that the putative σ2R/Tmem97 agonists DKR-1005, DKR-1051, and UKH-1114 (Ki ∼ 46 nM) lead to relief of SNI-induced mechanical hypersensitivity, peaking at 48 h after dosing when given IT. This effect is blocked by the putative σ2R/Tmem97 antagonist SAS-0132. Systemic administration of UKH-1114 (10 mg/kg) relieves SNI-induced mechanical hypersensitivity for 48 h with a peak magnitude of effect equivalent to 100 mg/kg gabapentin and without producing any motor impairment. Finally, we find that the TMEM97 gene is expressed in mouse and human dorsal root ganglion (DRG) including populations of neurons that are involved in pain; however, the gene is also likely expressed in non-neuronal cells that may contribute to the observed behavioral effects. Our results show robust antineuropathic pain effects of σ1R and σ2R/Tmem97 ligands, demonstrate that σ2R/Tmem97 is a novel neuropathic pain target, and identify UKH-1114 as a lead molecule for further development.

The Sigma-1 Receptor Antagonist, S1RA, Reduces Stroke Damage, Ameliorates Post-Stroke Neurological Deficits and Suppresses the Overexpression of MMP-9

The glutamate N-methyl-D-aspartate receptor (NMDAR) plays an essential role in the excitotoxic neural damage that follows ischaemic stroke. Because the sigma-1 receptor (σ1R) can regulate NMDAR transmission, exogenous and putative endogenous regulators of σ1R have been investigated using animal models of ischaemic stroke. As both agonists and antagonists provide some neural protection, the selective involvement of σ1Rs in these effects has been questioned. The availability of S1RA (E-52862/MR309), a highly selective σ1R antagonist, prompted us to explore its therapeutic potential in an animal model of focal cerebral ischaemia. Mice were subjected to right middle cerebral artery occlusion (MCAO), and post-ischaemic infarct volume and neurological deficits were determined across a range of intervals after the stroke-inducing surgery. Intracerebroventricular or intravenous treatment with S1RA significantly reduced the cerebral infarct size and neurological deficits caused by permanent MCAO (pMCAO). Compared with the control/sham-operated mice, the neuroprotective effects of S1RA were observed when delivered up to 5 h prior to surgery and 3 h after ischaemic onset. Interestingly, neither mice with the genetic deletion of σ1R nor wild-type mice that were pre-treated with the σ1R agonist PRE084 showed beneficial effects after S1RA administration with regard to stroke infarction. S1RA-treated mice showed faster behavioural recovery from stroke; this finding complements the significant decreases in matrix metalloproteinase-9 (MMP-9) expression and reactive astrogliosis surrounding the infarcted cortex. Our data indicate that S1RA, via σ1R, holds promising potential for clinical application as a therapeutic agent for ischaemic stroke.

Sigma-1 receptors control immune-driven peripheral opioid analgesia during inflammation in mice

Sigma-1 antagonism potentiates the antinociceptive effects of opioid drugs, so sigma-1 receptors constitute a biological brake to opioid drug-induced analgesia. The pathophysiological role of this process is unknown. We aimed to investigate whether sigma-1 antagonism reduces inflammatory pain through the disinhibition of the endogenous opioidergic system in mice. The selective sigma-1 antagonists BD-1063 and S1RA abolished mechanical and thermal hyperalgesia in mice with carrageenan-induced acute (3 h) inflammation. Sigma-1-mediated antihyperalgesia was reversed by the opioid antagonists naloxone and naloxone methiodide (a peripherally restricted naloxone analog) and by local administration at the inflamed site of monoclonal antibody 3-E7, which recognizes the pan-opioid sequence Tyr-Gly-Gly-Phe at the N terminus of most endogenous opioid peptides (EOPs). Neutrophils expressed pro-opiomelanocortin, the precursor of β-endorphin (a known EOP), and constituted the majority of the acute immune infiltrate. β-endorphin levels increased in the inflamed paw, and this increase and the antihyperalgesic effects of sigma-1 antagonism were abolished by reducing the neutrophil load with in vivo administration of an anti-Ly6G antibody. The opioid-dependent sigma-1 antihyperalgesic effects were preserved 5 d after carrageenan administration, where macrophages/monocytes were found to express pro-opiomelanocortin and to now constitute the majority of the immune infiltrate. These results suggest that immune cells harboring EOPs are needed for the antihyperalgesic effects of sigma-1 antagonism during inflammation. In conclusion, sigma-1 receptors curtail immune-driven peripheral opioid analgesia, and sigma-1 antagonism produces local opioid analgesia by enhancing the action of EOPs of immune origin, maximizing the analgesic potential of immune cells that naturally accumulate in painful inflamed areas.

Quantification of highly selective sigma-1 receptor antagonist CM304 using liquid chromatography tandem mass spectrometry and its application to a pre-clinical pharmacokinetic study

An ultra-performance liquid chromatography-tandem mass spectrometry (UPLC-MS/MS) method was developed and validated for quantification of CM304, a novel and highly selective sigma-1 receptor antagonist that has recently entered into human clinical trials. A structural analogue of CM304, SN56, was used as the internal standard (IS). Chromatographic separation was achieved on an Acquity UPLC™ BEH C18 (1.7 μm, 2.1 mm × 50 mm) column using a mobile phase [water:methanol (0.1%v/v formic acid; 50:50, %v/v)] at a flow rate of 0.2 mL/min. Mass spectrometric detection was performed in the positive ionization mode with multiple reaction monitoring (MRM) using m/z transitions of 337 > 238 for CM304 and 319 > 220 for the IS. The method was found to be linear and reproducible with a regression coefficient consistently >0.99 for the calibration range of 3 to 3000 ng/mL. The extraction recovery ranged from 91.5 to 98.4% from spiked (7.5, 300 and 2526 ng/mL) plasma quality control samples. The precision (%RSD; 1.1 to 2.9%) and accuracy (%RE; -1.9 to 1.8%) were within acceptable limit. The validated method was successfully applied to a single dose oral and intravenous (I.V.) pharmacokinetic study of CM304 in rats. Following I.V. administration, the compound exhibited adequate exposure along with high extravascular distribution and insignificant amount of extra hepatic metabolism. Copyright © 2016 John Wiley & Sons, Ltd.

The activity of selective sigma-1 receptor ligands in seizure models in vivo

Sigma-1 receptor (Sig1R) is a ligand-regulated protein which, since its discovery, has been widely studied as a novel target to treat neurological disorders, including seizures. However, the roles and mechanisms of Sig1R in the regulation of seizures are not fully understood. The aim of the present study was to test and compare effects of often used selective Sig1R ligands in models of experimentally induced seizures. The anti-seizure activities and interactions of selective Sig1R agonist PRE-084, selective Sig1R antagonist NE-100 and novel positive allosteric Sig1R modulator E1R were evaluated in pentylenetetrazol (PTZ) and (+)-bicuculline (BIC)-induced seizure models in mice. Sig1R antagonist NE-100 at a dose of 25mg/kg demonstrated pro-convulsive activity on PTZ-induced seizures. Agonist PRE-084 did not change the thresholds of chemoconvulsant-induced seizures. Positive allosteric modulator E1R at a dose of 50mg/kg showed anti-convulsive effects on PTZ- and BIC-induced clonic and tonic seizures. The anti-seizure activity of E1R was blocked by NE-100. Surprisingly, NE-100 at a dose of 50mg/kg induced convulsions, but E1R significantly alleviated the convulsive behaviour induced by NE-100. In conclusion, the selective Sig1R antagonist NE-100 induced seizures that could be partially attenuated by positive allosteric Sig1R modulator. Our results confirm that Sig1R could be a novel molecular target for new anti-convulsive drugs.

Novel small molecule guanidine Sigma1 inhibitors for advanced prostate cancer

Prostate cancer is the most frequently diagnosed malignancy and the leading cause of cancer related death in men. First line therapy for disseminated disease relies on androgen deprivation, leveraging the addiction of these tumors on androgens for both growth and survival. Treatment typically involves antagonizing the androgen receptor (AR) or blocking the synthesis of androgens. Recurrence is common and within 2-3years patients develop castration resistant tumors that become unresponsive to AR-axis targeted therapies. In order to provide a more effective treatment, we are utilizing an approach that targets a key scaffolding protein, Sigma1 (also known as sigma-1 receptor), a unique 26-kilodalton integral membrane protein that is critical in stabilizing the AR. Herein we report on a new series of Sigma1 compounds for lead optimization derived from a hybrid pharmacophore approach.

Sigma-1 Receptor Regulates Mitochondrial Function in Glucose- and Oxygen-Deprived Retinal Ganglion Cells

Purpose

Understanding the role of mitochondria in retinal ganglion cells (RGCs) is relevant to human disease as studies have shown mitochondrial abnormalities in primary open-angle glaucoma patients. This study seeks to determine the effects of the sigma-1 receptor (σ-1r) and its agonists on mitochondrial function in oxygen- and glucose- deprived (OGD) purified neonatal RGCs.

Methods

Retinal ganglion cells were isolated from rat pups and subjected to OGD in varying conditions in the presence or absence of σ-1r agonist and antagonist and following addition of an AAV2-σ-1r vector that was used to increase σ-1r expression. Western blots and immunofluorescence microscopy validated findings. Mitochondrial function was determined by measuring mitochondrial membrane potential (Δψm) using the dye, fluorescence tetraethylbenzimidazolylcarbocyanineiodide (JC-1), and determination of cytochrome c oxidase activity using a cytochrome c oxidase assay kit. Caspase 3 and 7 activities were also measured using a luminescent assay kit.

Results

Oxygen and glucose deprivation in RGCs resulted in decreased mitochondrial membrane potential and cytochrome c oxidase activity when compared with normoxic RGCs. σ-1r agonists or overexpression of the σ-1r restored the mitochondrial membrane potential comparable to normoxic conditions, while σ-1r antagonists abolished these effects. Oxygen and glucose depreavtation induced decreases in cytochrome c activity were partially restored by overexpression or activation of σ-1r. Caspase activity was increased in response to OGD and was decreased by the addition of σ-1r agonist, pentazocine, and following σ-1r overexpression.

Conclusions

These data suggest that activation and/or overexpression of σ-1r restores RGCs mitochondrial function following OGD and that mitochondrial function is vital to the function of RGCs.

Sigma1 Targeting to Suppress Aberrant Androgen Receptor Signaling in Prostate Cancer

Suppression of androgen receptor (AR) activity in prostate cancer by androgen depletion or direct AR antagonist treatment, although initially effective, leads to incurable castration-resistant prostate cancer (CRPC) via compensatory mechanisms including resurgence of AR and AR splice variant (ARV) signaling. Emerging evidence suggests that Sigma1 (also known as sigma-1 receptor) is a unique chaperone or scaffolding protein that contributes to cellular protein homeostasis. We reported previously that some Sigma1-selective small molecules can be used to pharmacologically modulate protein homeostasis pathways. We hypothesized that these Sigma1-mediated responses could be exploited to suppress AR protein levels and activity. Here we demonstrate that treatment with a small-molecule Sigma1 inhibitor prevented 5α- dihydrotestosterone-mediated nuclear translocation of AR and induced proteasomal degradation of AR and ARV, suppressing the transcriptional activity and protein levels of both full-length and splice-variant AR. Consistent with these data, RNAi knockdown of Sigma1 resulted in decreased AR levels and transcriptional activity. Furthermore, Sigma1 physically associated with ARV7 and ARv567es as well as full-length AR. Treatment of mice xenografted with ARV-driven CRPC tumors with a drug-like small-molecule Sigma1 inhibitor significantly inhibited tumor growth associated with elimination of AR and ARV7 in responsive tumors. Together, our data show that Sigma1 modulators can be used to suppress AR/ARV-driven prostate cancer cells via regulation of pharmacologically responsive Sigma1-AR/ARV interactions, both in vitro and in vivoCancer Res; 77(9); 2439-52. ©2017 AACR.

Structure-constrained endomorphin analogs display differential antinociceptive mechanisms in mice after spinal administration

We previously reported a series of novel endomorphin analogs with unnatural amino acid modifications. These analogs display good binding affinity and functional activity toward the μ opioid receptor (MOP). In the present study, we further investigated the spinal antinociceptive activity of these compounds. The analogs were potent in several nociceptive models. Opioid antagonists and antibodies against several endogenous opioid peptides were used to determine the mechanisms of action of these peptides. Intrathecal pretreatment with naloxone and β-funaltrexamine (β-FNA) effectively inhibited analog-induced analgesia, demonstrating that activity of the analogs is regulated primarily through MOP. Antinociception induced by analog 2 through 4 was not reversed by δ opioid receptor (DOP) or κ opioid receptor (KOP) antagonist; antibodies against dynorphin-A (1-17), dynorphin-B (1-13), and Leu⁵/Met⁵-enkephalin had no impact on the antinociceptive effects of these analogs. In contrast, antinociceptive effects induced by a spinal injection of the fluorine substituted analog 1 were significantly reversed by KOP antagonism. Furthermore, intrathecal pretreatment with antibodies against dynorphin-B (1-13) attenuated the antinociceptive effect of analog 1. These results indicate that the antinociceptive activity exerted by intrathecally-administered analog 1 is mediated, in part, through KOP with increased release of dynorphin-B (1-13). The chemical modifications used in the present study may serve as a useful tool to gain insight into the mechanisms of endomorphins activity.

Spinal D-Serine Increases PKC-Dependent GluN1 Phosphorylation Contributing to the Sigma-1 Receptor-Induced Development of Mechanical Allodynia in a Mouse Model of Neuropathic Pain

We have recently shown that spinal sigma-1 receptor (Sig-1R) activation facilitates nociception via an increase in phosphorylation of the N-methyl-D-aspartate (NMDA) receptor GluN1 subunit (pGluN1). The present study was designed to examine whether the Sig-1R-induced facilitative effect on NMDA-induced nociception is mediated by D-serine, and whether D-serine modulates spinal pGluN1 expression and the development of neuropathic pain after chronic constriction injury (CCI) of the sciatic nerve. Intrathecal administration of the D-serine degrading enzyme, D-amino acid oxidase attenuated the facilitation of NMDA-induced nociception induced by the Sig-1R agonist, 2-(4-morpholinethyl)1-phenylcyclohexane carboxylate. Exogenous D-serine increased protein kinase C (PKC)-dependent (Ser896) pGluN1 expression and facilitated NMDA-induced nociception, which was attenuated by preteatment with the PKC inhibitor, chelerythrine. In CCI mice, administration of the serine racemase inhibitor, L-serine O-sulfate potassium salt or D-amino acid oxidase on postoperative days 0 to 3 suppressed CCI-induced mechanical allodynia (MA) and pGluN1 expression on day 3 after CCI surgery. Intrathecal administration of D-serine restored MA as well as the GluN1 phosphorylation on day 3 after surgery that was suppressed by the Sig-1R antagonist, N-[2-(3,4-dichlorophenyl)ethyl]-N-methyl-2-(dimethylamino)ethylamine dihydrobromide or the astrocyte inhibitor, fluorocitrate. In contrast, D-serine had no effect on CCI-induced thermal hyperalgesia or GluN1 expression. These results indicate that spinal D-serine: 1) mediates the facilitative effect of Sig-1R on NMDA-induced nociception, 2) modulates PKC-dependent pGluN1 expression, and 3) ultimately contributes to the induction of MA after peripheral nerve injury.

PERSPECTIVE

This report shows that reducing D-serine suppresses central sensitization and significantly alleviates peripheral nerve injury-induced chronic neuropathic pain and that this process is modulated by spinal Sig-1Rs. This preclinical evidence provides a strong rationale for using D-serine antagonists to treat peripheral nerve injury-induced neuropathy.

Anti-anhedonic effect of selective serotonin reuptake inhibitors with affinity for sigma-1 receptors in picrotoxin-treated mice

BACKGROUND AND PURPOSE

Prefrontal dopamine release by the combined activation of 5-HT1A and sigma-1 (σ1 ) receptors is enhanced by the GABAA receptor antagonist picrotoxin in mice. Here, we examined whether this neurochemical event was accompanied by behavioural changes.

EXPERIMENTAL APPROACH

Male mice were treated with picrotoxin to decrease GABAA receptor function. Their anhedonic behaviour was measured using the female encounter test. The expression of c-Fos was determined immunohistochemically.

KEY RESULTS

Picrotoxin caused an anxiogenic effect on three behavioural tests, but it did not affect the immobility time in the forced swim test. Picrotoxin decreased female preference in the female encounter test and attenuated the female encounter-induced increase in c-Fos expression in the nucleus accumbens. Picrotoxin-induced anhedonia was ameliorated by fluvoxamine and S-(+)-fluoxetine, selective serotonin reuptake inhibitors with high affinity for the σ1 receptor. The effect of fluvoxamine was blocked by a 5-HT1A or a σ1 receptor antagonist, and co-administration of the σ1 receptor agonist (+)-SKF-10047 and the 5-HT1A receptor agonist osemozotan mimicked the effect of fluvoxamine. By contrast, desipramine, duloxetine and paroxetine, which have little affinity for the σ1 receptor, did not affect picrotoxin-induced anhedonia. The effect of fluvoxamine was blocked by a dopamine D2/3 receptor antagonist. Methylphenidate, an activator of the prefrontal dopamine system, ameliorated picrotoxin-induced anhedonia.

CONCLUSION AND IMPLICATIONS

Picrotoxin-treated mice show anhedonic behaviour that is ameliorated by simultaneous activation of 5-HT1A and σ1 receptors. These findings suggest that the increased prefrontal dopamine release is associated with the anti-anhedonic effect observed in picrotoxin-treated mice.

Pharmacological Modulation of the Sigma 1 Receptor and the Treatment of Pain

There is a critical need for new analgesics acting through new mechanisms of action, which could increase the efficacy with respect to existing therapies and reduce their unwanted effects. Current preclinical evidence supports the modulatory role of sigma-1 receptors (σ1R) in nociception, mainly based on the pain-attenuated phenotype of σ1R knockout mice and on the antinociceptive effect exerted by σ1R antagonists on pains of different etiologies. σ1R is highly expressed in different pain areas of the CNS and the periphery (particularly dorsal root ganglia), and interacts and modulates the functionality of different receptors and ion channels . The antagonism of σ1R leads to decreased amplification of pain signaling within the spinal cord (central sensitization), but recent data also support a role at the periphery. σ1R antagonists have consistently demonstrated efficacy in neuropathic pain , but also in other types of pain including inflammatory, orofacial, visceral, and post-operative pain. Apart from acting alone, when combined with opioids, σ1R antagonists enhance opioid analgesia but not opioid-induced unwanted effects. Interestingly, unlike opioids, σ1R antagonists do not modify normal sensory mechanical and thermal sensitivity thresholds but they exert antihypersensitive effects in sensitizing conditions, enabling the reversal of nociceptive thresholds back to normal values. Accordingly, σ1R antagonists are not strictly analgesics; they are antiallodynic and antihyperalgesic drugs acting when the system is sensitized following prolonged noxious stimulation or persistent abnormal afferent input (e.g., secondary to nerve injury). These are distinctive features allowing σ1R antagonists to exert a modulatory effect specifically in pathophysiological conditions such as chronic pain .

Blockade of sigma 1 receptors alleviates sensory signs of diabetic neuropathy in rats

BACKGROUND

E-52862 (S1RA, 4-[2-[[5-methyl-1-(2-naphthalenyl)-1H-pyrazol-3-yl]oxy]ethyl]-morpholine), a novel selective sigma 1 receptor (σ1R) antagonist, has demonstrated efficacy in nociceptive and neuropathic pain models. Our aim was to test if σ1R blockade with E-52862 may modify the signs of neuropathy in Zucker diabetic fatty (ZDF) rats, a type 2 diabetes model.

METHODS

Mechanical and thermal response thresholds were tested on 7-, 13-, 14- and 15-week-old ZDF rats treated with saline or with E-52862 acutely administered on week 13, followed by sub-chronic administration (14 days). Axonal peripheral activity (skin-saphenous nerve preparation) and isolated aorta or mesenteric bed reactivity were analysed in 15-week-old ZDF rats treated with saline or E-52862 and in LEAN rats.

RESULTS

Zucker diabetic fatty rats showed significantly decreased thermal withdrawal latency and threshold to mechanical stimulation on week 13 compared to week 7 (prediabetes) and with LEAN animals; single-dose and sub-chronic E-52862 administration restored both parameters to those recorded on week 7. Regarding axonal peripheral activity, E-52862 treatment increased the mean mechanical threshold (77.3 ± 21 mN vs. 19.6 ± 1.5 mN, saline group) and reduced the response evoked by mechanical increasing stimulation (86.4 ± 36.5 vs. 352.8 ± 41.4 spikes) or by repeated mechanical supra-threshold steps (39.4 ± 1.4 vs. 83.5 ± 0.9). E-52862 treatment also restored contractile response to phenylephrine in aorta and mesenteric bed.

CONCLUSIONS

E-52862 administration reverses neuropathic (behavioural and electrophysiological) and vascular signs in the ZDF rat.

SIGNIFICANCE

Blockade of σ1R avoids the development of diabetic neuropathy in rats, and may represent a potentially useful therapeutic approach to peripheral neuropathies in diabetic patients. WHAT DOES THIS STUDY ADD?: This study presents evidences for the potential usefulness of sigma receptor blockade on diabetic neuropathy in rats. The methodology includes behavioural evidences, electrophysiological data and vascular-isolated models.

Gaining in pan-affinity towards sigma 1 and sigma 2 receptors. SAR studies on arylalkylamines

Sigma Receptor (SR) modulators are involved in different signal transduction pathways, representing important pharmacological/therapeutic tools in several pathological conditions, such as neurodegenerative diseases and cancers. To this purpose, numerous compounds have been developed in order to target selectively one of the two subtypes (S1R and S2R) as chemotherapeutic agent. However, experiments have also shown that ligands which are able to bind both SR subtypes can be useful for the diagnosis and/or the treatment of cancers. Therefore, the discovery of compounds with good affinity towards both S1R and S2R ('pan-modulators') is also of great interest and still represents a challenge up to now. For this reason, we synthesized novel arylalkylamines with the aim to obtain compounds with S1R and S2R affinity in the nM range and, by modeling quantitative structure-activity relationships (QSARs), we identified the essential structural features to obtain promising pan-compounds.

Sigma-1 Receptor and Pain

There is a critical need for new analgesics acting through new mechanisms of action, which could increase the efficacy respect to existing therapies and/or reduce their unwanted effects. Current preclinical evidence supports the modulatory role of the sigma-1 receptor (σ1R) in nociception, mainly based on the pain-attenuated phenotype of σ1R knockout mice and on the antinociceptive effect exerted by σ1R antagonists on pain of different etiology, very consistently in neuropathic pain, but also in nociceptive, inflammatory, and visceral pain. σ1R is highly expressed in different pain areas of the CNS and the periphery, particularly dorsal root ganglia (DRG), and interacts and modulates the functionality of different receptors and ion channels. Accordingly, antinociceptive effects of σ1R antagonists both acting alone and in combination with other analgesics have been reported at both central and peripheral sites. At the central level, behavioral, electrophysiological, neurochemical, and molecular findings support a role for σ1R antagonists in inhibiting augmented excitability secondary to sustained afferent input. Moreover, the involvement of σ1R in mechanisms regulating pain at the periphery has been recently confirmed. Unlike opioids, σ1R antagonists do not modify normal sensory mechanical and thermal sensitivity thresholds but they exert antihypersensitivity effects (antihyperalgesic and antiallodynic) in sensitizing conditions, enabling the reversal of nociceptive thresholds back to normal values. These are distinctive features allowing σ1R antagonists to exert a modulatory effect specifically in pathophysiological conditions such as chronic pain.

Sigma-1 Receptor Antagonists: A New Class of Neuromodulatory Analgesics

The sigma-1 receptor is a unique ligand-operated chaperone present in key areas for pain control, in both the peripheral and central nervous system. Sigma-1 receptors interact with a variety of protein targets to modify their function. These targets include several G-protein-coupled receptors such as the μ-opioid receptor, and ion channels such as the N-methyl-D-aspartate receptor (NMDAR). Sigma-1 antagonists modify the chaperoning activity of sigma-1 receptor by increasing opioid signaling and decreasing NMDAR responses, consequently enhancing opioid antinociception and decreasing the sensory hypersensitivity that characterizes pathological pain conditions. However, the participation in pain relief of other protein partners of sigma-1 receptors in addition to opioid receptors and NMDARs cannot be ruled out. The enhanced opioid antinociception by sigma-1 antagonism is not accompanied by an increase in opioid side effects , including tolerance, dependence or constipation, so the use of sigma-1 antagonists may increase the therapeutic index of opioids. Furthermore, sigma-1 antagonists (in the absence of opioids) have been shown to exert antinociceptive effects in preclinical models of neuropathic pain induced by nerve trauma or chemical injury (the antineoplastic paclitaxel), and more recently in inflammatory and ischemic pain. Although most studies attributed the analgesic properties of sigma-1 antagonists to their central actions, it is now known that peripheral sigma-1 receptors also participate in their effects. Overwhelming preclinical evidence of the role of sigma-1 receptors in pain has led to the development of the first selective sigma-1 antagonist with an intended indication for pain treatment, which is currently in Phase II clinical trials.