Sigma-1 Receptor Inhibition Reduces Mechanical Allodynia and Modulate Neuroinflammation in Chronic Neuropathic Pain

Neuropathic pain is one of the most debilitating forms of chronic pain, resulting from an injury or disease of the somatosensory nervous system, which induces abnormal painful sensations including allodynia and hyperalgesia. Available treatments are limited by severe side-effects and reduced efficacy in the chronic phase of the disease. Sigma-1 receptor (σ1R) has been identified as a chaperone protein, which modulate opioid receptors activities and the functioning of several ion channels, exerting a role in pain transmission. As such, it represents a druggable target to treat neuropathic pain. This study aims at investigating the therapeutic potential of the novel compound (+)-2R/S-LP2, a σ1R antagonist, in reducing painful behaviour and modulating the neuroinflammatory environment. We showed that repeated administration of the compound significantly inhibited mechanical allodynia in neuropathic rats, increasing the withdrawal threshold as compared to CCI-vehicle rats. Moreover, we found that (+)-2R/S-LP2-mediated effects resolve the neuroinflammatory microenvironment by reducing central gliosis and pro-inflammatory cytokines expression levels. This effect was coupled with a significant reduction of connexin 43 (Cx43) expression levels and gap junctions/hemichannels mediated microglia-to-astrocyte communication. These results suggest that inhibition of σ1R significantly attenuates neuropathic pain chronicization, thus representing a viable effective strategy.

Sigma-1 Receptor Signaling: In Search of New Therapeutic Alternatives for Cardiovascular and Renal Diseases

Cardiovascular and renal diseases are among the leading causes of death worldwide, and regardless of current efforts, there is a demanding need for therapeutic alternatives to reduce their progression to advanced stages. The stress caused by diseases leads to the activation of protective mechanisms in the cell, including chaperone proteins. The Sigma-1 receptor (Sig-1R) is a ligand-operated chaperone protein that modulates signal transduction during cellular stress processes. Sig-1R interacts with various ligands and proteins to elicit distinct cellular responses, thus, making it a potential target for pharmacological modulation. Furthermore, Sig-1R ligands activate signaling pathways that promote cardioprotection, ameliorate ischemic injury, and drive myofibroblast activation and fibrosis. The role of Sig-1R in diseases has also made it a point of interest in developing clinical trials for pain, neurodegeneration, ischemic stroke, depression in patients with heart failure, and COVID-19. Sig-1R ligands in preclinical models have significantly beneficial effects associated with improved cardiac function, ventricular remodeling, hypertrophy reduction, and, in the kidney, reduced ischemic damage. These basic discoveries could inform clinical trials for heart failure (HF), myocardial hypertrophy, acute kidney injury (AKI), and chronic kidney disease (CKD). Here, we review Sig-1R signaling pathways and the evidence of Sig-1R modulation in preclinical cardiac and renal injury models to support the potential therapeutic use of Sig-1R agonists and antagonists in these diseases.

Long-Lasting Nociplastic Pain Modulation by Repeated Administration of Sigma-1 Receptor Antagonist BD1063 in Fibromyalgia-like Mouse Models

Sigma-1 receptor (σ1R) ligands have been shown to be effective at relieving neuropathic and inflammatory pain, but have not yet been tested in experimental models of fibromyalgia. The objective of this study was to evaluate the effect of a σ1R antagonist (BD1063) compared to pregabalin. ICR-CD1 female mice were subjected to either six repeated injections of reserpine, to cause reserpine-induced myalgia (RIM6), or acidified saline intramuscular injections (ASI). In these two models, we evaluated the effect of BD1063 and pregabalin on thermal hypersensitivity, anxiety-like and depression-like behaviors, and on spinal cord gliosis. BD1063 exerted an antinociceptive effect on both reflexive (thermal hyperalgesia) and nonreflexive (anxiety- and depression-like) pain behaviors, and reduced spinal astroglial and microglial reactivity, following repeated treatment for 2 weeks. Interestingly, the effects of BD1063 were long-term, lasting several weeks after treatment discontinuation in both fibromyalgia-like models. Similar results were obtained with pregabalin, but the effects on pain behaviors lasted for a shorter length of time, and pregabalin did not significantly modulate spinal glial reactivity. The inhibitory and long-lasting effect of pharmacological blockade of σ1Rs on both sensory and affective dimensions of nociplastic-like pain and spinal cord gliosis in two experimental models of fibromyalgia support the application of this therapeutic strategy to treat fibromyalgia.

Dual Sigma-1 receptor antagonists and hydrogen sulfide-releasing compounds for pain treatment: Design, synthesis, and pharmacological evaluation

The development of σ1 receptor antagonists hybridized with a H2S-donor is here reported. We aimed to obtain improved analgesic effects when compared to σ1 receptor antagonists or H2S-donors alone. In an in vivo model of sensory hypersensitivity, thioamide 1a induced analgesia which was synergistically enhanced when associated with the σ1 receptor antagonist BD-1063. The selective σ1 receptor agonist PRE-084 completely reversed this effect. Four thioamide H2S-σ1 receptor hybrids (5a-8a) and their amide derivatives (5b-8b) were synthesized. Compound 7a (AD164) robustly released H2S and showed selectivity for σ1 receptor over σ2 and opioid receptors. This compound induced marked analgesia that was reversed by PRE-084. The amide analogue 7b (AD163) showed only minimal analgesia. Further studies showed that 7a exhibited negligible acute toxicity, together with a favorable pharmacokinetic profile. To the best of our knowledge, compound 7a is the first dual-acting ligand with simultaneous H2S-release and σ1 antagonistic activities.

Pharmacokinetics and brain σ1 receptor occupancy of MR309, a selective σ1 receptor antagonist

AIMS

Preclinical studies of MR309, a selective sigma-1 receptor (σ1R) antagonist, support a potential role in treating neuropathic pain. We report 2 studies that provide insight into the pharmacokinetics (PK) and brain σ1R binding of MR309.

METHODS

Steady-state PK of MR309 (400 mg once daily and 200 mg twice-daily [BID] for 10 days; EudraCT 2015-001818-99 [PK study]) and the relationship between MR309 plasma exposure and brain σ1R occupancy (EudraCT 2017-000670-11 [positron emission tomography study]) were investigated in healthy volunteers. Positron emission tomography using the σ1R ligand [11 C]SA4503 was conducted at baseline, and 2 and 8 hours after a single dose of MR309 (200-800 mg). The relationship between brain σ1R occupancy and MR309 exposure was explored using data-driven model fitting.

RESULTS

MR309 was well tolerated, brain σ1R occupancy ranged between 30.5 and 74.9% following single-dose MR309 (n = 7). MR309 BID provided a plasma PK profile with less fluctuation than once daily dosing (n = 16). MR309 200 mg BID yielded average steady state plasma concentrations between 2000 and 4000 ng/mL in the PK study, which corresponded to an estimated brain σ1R occupancy of 59-74%.

CONCLUSION

MR309 200 mg BID dose was below the 75% σ1R occupancy threshold expected to elicit maximal antinociceptive effect as observed in neuropathic pain models. Further investigations of MR309 for neuropathic pain will require higher brain σ1R occupancy, and establish the optimal dose by elucidating the clinical impact of a broad range of brain σ1R occupancy across different neuropathic pain indications.

Development of novel phenoxyalkylpiperidines as high-affinity Sigma-1 (σ1) receptor ligands with potent anti-amnesic effect

The sigma-1 (σ1) receptor plays a significant role in many normal physiological functions and pathological disease states, and as such represents an attractive therapeutic target for both agonists and antagonists. Here, we describe a novel series of phenoxyalkylpiperidines based on the lead compound 1-[ω-(4-chlorophenoxy)ethyl]-4-methylpiperidine (1a) in which the degree of methylation at the carbon atoms alpha to the piperidine nitrogen was systematically varied. The affinity at σ1 and σ2 receptors and at Δ8-Δ7 sterol isomerase (SI) ranged from subnanomolar to micromolar Ki values. While the highest-affinity was displayed at the σ1, the increase of the degree of methylation in the piperidine ring progressively decreased the affinity. The subnanomolar affinity 1a and 1-[ω-(4-methoxyphenoxy)ethyl]-4-methylpiperidine (1b) displayed potent anti-amnesic effects associated with σ1 receptor agonism, in two memory tests. Automated receptor-small-molecule ligand docking provided a molecular structure-based rationale for the agonistic effects of 1a and 1b. Overall, the class of the phenoxyalkylpiperidines holds potential for the development of high affinity σ1 receptor agonists, and compound 1a, that appears as the best in class (exceeding by far the activity of the reference compound PRE-084) deserves further investigation.

Examination of the Novel Sigma-1 Receptor Antagonist, SI 1/28, for Antinociceptive and Anti-allodynic Efficacy against Multiple Types of Nociception with Fewer Liabilities of Use

Neuropathic pain is a significant problem with few effective treatments lacking adverse effects. The sigma-1 receptor (S1R) is a potential therapeutic target for neuropathic pain, as antagonists for this receptor effectively ameliorate pain in both preclinical and clinical studies. The current research examines the antinociceptive and anti-allodynic efficacy of SI 1/28, a recently reported benzylpiperazine derivative and analog of the S1R antagonist SI 1/13, that was 423-fold more selective for S1R over the sigma-2 receptor (S2R). In addition, possible liabilities of respiration, sedation, and drug reinforcement caused by SI 1/28 have been evaluated. Inflammatory and chemical nociception, chronic nerve constriction injury (CCI) induced mechanical allodynia, and adverse effects of sedation in a rotarod assay, conditioned place preference (CPP), and changes in breath rate and locomotor activity were assessed after i.p. administration of SI 1/28. Pretreatment with SI 1/28 produced dose-dependent antinociception in the formalin test, with an ED50 (and 95% C.I.) value of 13.2 (7.42-28.3) mg/kg, i.p. Likewise, SI 1/28 produced dose-dependent antinociception against visceral nociception and anti-allodynia against CCI-induced neuropathic pain. SI 1/28 demonstrated no impairment of locomotor activity, conditioned place preference, or respiratory depression. In summary, SI 1/28 proved efficacious in the treatment of acute inflammatory pain and chronic neuropathy without liabilities at therapeutic doses, supporting the development of S1R antagonists as therapeutics for chronic pain.

Sigma-1 receptor increases intracellular calcium in cultured astrocytes and contributes to mechanical allodynia in a model of neuropathic pain

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 naïve 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 naïve 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.

Optimization of bifunctional piperidinamide derivatives as σ1R Antagonists/MOR agonists for treating neuropathic pain

Here, we describe the optimization, synthesis, and associated pharmacological analgesic activities of a new series of bifunctional piperidinamide derivatives as sigma-1 receptor (σ1R) antagonists and mu opioid receptor (MOR) agonists. The new compounds were evaluated in vitro in σ1R and MOR binding assays. The most promising compound 114 (also called HKC-126), showed superior affinities for σ1R and MOR and good selectivity to additional receptors related to pain. Compound 114 showed powerful dose-dependent analgesic effects in the acetic acid writhing test, formalin test, hot plate test, and chronic constriction injury (CCI) neuropathic pain model. In contrast to an equianalgesic dose of fentanyl, compound 114 produced fewer opioid-like side effects, such as reward liability, respiratory depression, physical dependence, and sedation. Lastly, the pharmacokinetic properties of this drug were also acceptable, and these results suggest that compound 114, as a mixed σ1R/MOR ligand, has potential for treating neuropathic pain.

Bifunctional μ opioid and σ1 receptor ligands as novel analgesics with reduced side effects

Opioid analgesics are highly effective painkillers for the treatment of moderate or severe pain, but they are associated with a number of undesirable adverse effects, including the development of tolerance, addiction, constipation and life-threatening respiratory depression. The development of new and safer analgesics with innovative mechanisms of action, which can enhance the efficacy in comparison to available treatments and reduce their side effects, is urgently needed. The sigma-1 receptor (σ1R), a unique Ca2+-sensing chaperone protein, is expressed throughout pain-modulating tissues and affects neurotransmission by interacting with different protein partners, including molecular targets that participate in nociceptive signalling, such as the μ-opioid receptor (MOR), N-methyl-d-aspartate receptor (NMDAR) and cannabinoid 1 receptor (CB1R). Overwhelming pharmacological and genetic evidence indicates that σ1R antagonists induce anti-hypersensitive effects in sensitising pain conditions (e.g. chemically induced, inflammatory and neuropathic pain) and enhance opioid analgesia but not opioid-mediated detrimental effects. It has been suggested that balanced modulation of MORs and σ1Rs may improve both the therapeutic efficacy and safety of opioids. This review summarises the functional profiles of ligands with mixed MOR agonist and σ1R antagonist activities and highlights their therapeutic potentials for pain management. Dual MOR agonism/σ1R antagonism represents a promising avenue for the development of potent and safer analgesics.

The Peripheral Role of CCL2 in the Anti-Nociceptive Effect of Sigma-1 Receptor Antagonist BD1047 on Inflammatory Hyperalgesia in Rats

Our recent study demonstrated that the CC-chemokine ligand 2 (CCL2) present in primary afferent fibers (PAFs) plays an important role in the microglia-dependent neuronal activation associated with zymosan-induced inflammatory pain. The present study was aimed to evaluate whether BD1047 (a prototypical sigma-1 receptor (Sig-1R) antagonist) is capable of modifying elevated levels of inflammation-evoked CCL2 as a peripheral antinociceptive mechanism. In DRG primary culture, zymosan dose-dependently increased CCL2 release from isolectin B4 (IB4)-positive DRG neurons, a process that was inhibited by co-culture with BD1047. Single treatment of BD1047 before intraplantar injection of zymosan in rats significantly reduced thermal hyperalgesia and mechanical hyperalgesia, as well as CCL2 expression in DRG neurons and microglia activation in the spinal dorsal horn. In the Complete Freund's adjuvant (CFA)-induced inflammation model, repeated administration of BD1047 dramatically attenuated thermal hyperalgesia and mechanical hyperalgesia, and significantly diminished CCL2 immunoreactivity and microglia activation. Notably, CFA-induced inflammation significantly increased Sig-1R immunoreactivity in DRG neurons, which was co-localized with CCL2 and IB4, respectively. Taken together, our results suggest that BD1047's anti-nociceptive property was substantially mediated by the inhibition of CCL2 release in unmyelinated PAFs and that this may, in turn, have attenuated the spinal microglia activation that is associated with inflammatory pain.

Novel High Affinity Sigma-1 Receptor Ligands from Minimal Ensemble Docking-Based Virtual Screening

Sigma-1 receptor (S1R) is an intracellular, multi-functional, ligand operated protein that also acts as a chaperone. It is considered as a pluripotent drug target in several pathologies. The publication of agonist and antagonist bound receptor structures has paved the way for receptor-based in silico drug design. However, recent studies on this subject payed no attention to the structural differences of agonist and antagonist binding. In this work, we have developed a new ensemble docking-based virtual screening protocol utilizing both agonist and antagonist bound S1R structures. This protocol was used to screen our in-house compound library. The S1R binding affinities of the 40 highest ranked compounds were measured in competitive radioligand binding assays and the sigma-2 receptor (S2R) affinities of the best S1R binders were also determined. This way three novel high affinity S1R ligands were identified and one of them exhibited a notable S1R/S2R selectivity.

Propionamide Derivatives as Dual μ-Opioid Receptor Agonists and σ1 Receptor Antagonists for the Treatment of Pain

A new series of propionamide derivatives was developed as dual μ-opioid receptor agonists and σ1 receptor antagonists. Modification of a high-throughput screening hit originated a series of piperazinylcycloalkylmethyl propionamides, which were explored to overcome the challenge of achieving balanced dual activity and convenient drug-like properties. The lead compound identified, 18g, showed good analgesic effects in several animal models of both acute (paw pressure) and chronic (partial sciatic nerve ligation) pain, with reduced gastrointestinal effects in comparison with oxycodone.

Antagonism of Sigma-1 receptor blocks heavy alcohol drinking and associated hyperalgesia in male mice

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-naïve 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.

Discovery of a σ1 receptor antagonist by combination of unbiased cell painting and thermal proteome profiling

Phenotypic screening for bioactive small molecules is typically combined with affinity-based chemical proteomics to uncover the respective molecular targets. However, such assays and the explored bioactivity are biased toward the monitored phenotype, and target identification often requires chemical derivatization of the hit compound. In contrast, unbiased cellular profiling approaches record hundreds of parameters upon compound perturbation to map bioactivity in a broader biological context and may link a profile to the molecular target or mode of action. Herein we report the discovery of the diaminopyrimidine DP68 as a Sigma 1 (σ1) receptor antagonist by combining morphological profiling using the Cell Painting assay and thermal proteome profiling. Our results highlight that integration of complementary profiling approaches may enable both detection of bioactivity and target identification for small molecules.

Identification and characterization of MAM03055A: A novel bivalent sigma-2 receptor/TMEM97 ligand with cytotoxic activity

Sigma-2 receptor/transmembrane protein 97 (TMEM97) is upregulated in cancer cells compared to normal cells. Traditional sigma-2 receptor agonists induce apoptosis and autophagy, making them of interest in cancer therapy. Recently, we reported a novel metabolically stimulative function of the sigma-2 receptor, showing increased 3-(4,5 dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) reduction and stimulation of glycolytic hallmarks. 6-Substituted analogs of the canonical sigma-2 receptor antagonist, 6-acetyl-3-(4-(4-(4-fluorophenyl)piperazin-1-yl)butyl)benzo[d]oxazol-2(3H)-one (SN79), produce both metabolically stimulative and cytotoxic effects. Here, we compare the activities of two related compounds: 6-amino-3-(4-(4-(4-fluorophenyl)piperazin-1-yl)butyl)benzo[d]oxazol-2(3H)-one (CM571), the 6-amino derivative of SN79, which binds with high affinity to both sigma-1 and sigma-2 receptors, and 1,3-bis(3-(4-(4-(4-fluorophenyl)piperazin-1-yl)butyl)-2-oxo-2,3-dihydrobenzo[d]oxazol-6-yl)thiourea (MAM03055A), a homo-bivalent dimer of CM571. MAM03055A resulted from the degradation of 3-(4-(4-(4-fluorophenyl)piperazin-1-yl)butyl)-6-isothiocyanatobenzo[d]oxazol-2(3H)-one (CM572), the cytotoxic 6-isothiocyanato SN79 derivative. MAM03055A exhibited high affinity and strong preference for sigma-2 receptors (sigma-1 K_i = 3371 nM; sigma-2 receptor K_i = 55.9 nM). Functionally, MAM03055A treatment potently induced cell death in SK-N-SH neuroblastoma, MDA-MB-231 breast, and both SW48 and SW480 colorectal cancer cell lines, causing proapoptotic BH3 interacting-domain death agonist (BID) cleavage in SK-N-SH cells. Conversely, CM571 induced metabolic stimulation. CM571 bound reversibly to both receptors, while MAM03055A bound pseudo-irreversibly to sigma-2 receptors and caused residual cytotoxic activity after acute exposure and removal of the compound from the media. Interestingly, MAM03055A induced a time-dependent loss of sigma-2 receptor/TMEM97 protein from cells, whereas monomer CM571 had no effect on receptor levels. These results suggest that monovalent and bivalent sigma-2 receptor ligands in this series interact differently with the receptor, thus resulting in divergent effects.

Tricyclic Triazoles as σ1 Receptor Antagonists for Treating Pain

The synthesis and pharmacological activity of a new series of 5a,7,8,8a-tetrahydro-4H,6H-pyrrolo[3,4-b][1,2,3]triazolo[1,5-d][1,4]oxazine derivatives as potent sigma-1 receptor (σ1R) ligands are reported. A lead optimization program aimed at improving the aqueous solubility of parent racemic nonpolar derivatives led to the identification of several σ1R antagonists with a good absorption, distribution, metabolism, and excretion in vitro profile, no off-target affinities, and characterized by a low basic pKa (around 5) that correlates with high exposure levels in rodents. Two compounds displaying a differential brain-to-plasma ratio distribution profile, 12lR and 12qS, exhibited a good analgesic profile and were selected as preclinical candidates for the treatment of pain.

Normalization of Calcium Balance in Striatal Neurons in Huntington's Disease: Sigma 1 Receptor as a Potential Target for Therapy

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 receptor antagonist (BD-1063) potentiates the antinociceptive effect of quercetin in neuropathic pain induced by chronic constriction injury

Neuropathic pain is characterized by the presence of hyperalgesia and allodynia. Pharmacological treatments include the use of antiepileptics such as pregabalin or gabapentin, as well as antidepressants; however, given the role of the sigma-1 receptor in the generation and maintenance of pain, it has been suggested that sigma-1 receptor antagonists may be effective. There are also other alternatives that have been explored, such as the use of flavonoids such as quercetin. Due to the relevance of drug combinations in therapeutics, the objective of this work was to evaluate the effect of the combination of BD-1063 with quercetin in a chronic sciatic nerve constriction model using the "Surface of Synergistic Interaction" analysis method. The combination had preferable additive or synergistic effects, with BD-1063 (17.8 mg/kg) + QUER (5.6 mg/kg) showing the best antinociceptive effects. The required doses were also lower than those used individually to obtain the same level of effect. Our results provide the first evidence that the combination of a sigma-1 receptor antagonist and the flavonoid quercetin may be useful in the treatment of nociceptive behaviors associated with neuropathic pain, suggesting a new therapeutic alternative for this type of pain.

Observational study of haloperidol in hospitalized patients with COVID-19

BACKGROUND

Haloperidol, a widely used antipsychotic, has been suggested as potentially useful for patients with COVID-19 on the grounds of its in-vitro antiviral effects against SARS-CoV-2, possibly through sigma-1 receptor antagonist effect.

METHODS

We examined the associations of haloperidol use with intubation or death and time to discharge home among adult patients hospitalized for COVID-19 at Assistance Publique-Hôpitaux de Paris (AP-HP) Greater Paris University hospitals. Study baseline was defined as the date of hospital admission. The primary endpoint was a composite of intubation or death and the secondary endpoint was discharge home among survivors in time-to-event analyses. In the primary analyses, we compared these two outcomes between patients receiving and not receiving haloperidol using univariate Cox regression models in matched analytic samples based on patient characteristics and other psychotropic medications. Sensitivity analyses included propensity score analyses with inverse probability weighting and multivariable Cox regression models.

RESULTS

Of 15,121 adult inpatients with a positive COVID-19 PT-PCR test, 39 patients (0.03%) received haloperidol within the first 48 hours of admission. Over a mean follow-up of 13.8 days (SD = 17.9), 2,024 patients (13.4%) had a primary end-point event and 10,179 patients (77.6%) were discharged home at the time of study end on May 1st. The primary endpoint occurred in 9 patients (23.1%) who received haloperidol and 2,015 patients (13.4%) who did not. The secondary endpoint of discharge home occurred in 16 patients (61.5%) who received haloperidol and 9,907 patients (85.8%) who did not. There were no significant associations between haloperidol use and the primary (HR, 0.80; 95% CI, 0.39 to 1.62, p = 0.531) and secondary (HR, 1.30; 95% CI, 0.74 to 2.28, p = 0.355) endpoints. Results were similar in multiple sensitivity analyses.

CONCLUSION

Findings from this multicenter observational study suggest that haloperidol use prescribed at a mean dose of 4.5 mg per day (SD = 5.2) for a mean duration of 8.4 days (SD = 7.2) may not be associated with risk of intubation or death, or with time to discharge home, among adult patients hospitalized for COVID-19.

Haloperidol potentiates antinociceptive effects of morphine and disrupt opioid tolerance

Haloperidol is an antipsychotic agent recently described as an antinociceptive drug able to mediate the antagonism of sigma-1 receptors while morphine is an opioid used in the treatment of neuropathic pain. The objectives of this work were to determine the type of interaction generated by the combination of morphine and haloperidol in neuropathic pain induced by chronic constriction injury and to evaluate morphine tolerance and side effects. The antiallodynic and anti-hyperalgesic effects of morphine (0.01-3.16 mg/kg, s.c.) and haloperidol (0.0178-0.1778 mg/kg, s.c.) were determined after single-doses, in monotherapy and combined, using the acetone and von Frey tests, respectively. Evaluations were performed until 10-days postsurgery. Data were processed using "Surface of Synergic Interaction analysis". The rotarod test was used to evaluate motor coordination, and the constipation test was performed using 5% charcoal. The effects of haloperidol and BD-1063, sigma-1 receptor antagonists, naloxone and PRE-084 (sigma-1 agonist) were determined using the morphine-tolerance model. Morphine (0.0316 mg/kg)+haloperidol (0.0178 mg/kg) was determined to be the optimal combination. Morphine-tolerance was observed on day 5 after 11 administrations, although in animals that received the combination, tolerance was delayed until day 8. PRE-084 and naloxone administered on day 5 in animals treated with the combination resulted in a blockade of its antiallodynic effects. Adverse effects of constipation or motor incoordination were not shown in animals treated with morphine + haloperidol. In conclusion, haloperidol enhances the antinociceptive effects of morphine without significant adverse effects, as it is able to disrupt or delay the morphine-tolerance in neuropathic pain.

Novel σ1 antagonists designed for tumor therapy: Structure - activity relationships of aminoethyl substituted cyclohexanes

Depending on the substitution pattern and stereochemistry, 1,3-dioxanes 1 with an aminoethyl moiety in 4-position represent potent σ1 receptor antagonists. In order to increase the stability, a cyclohexane ring first replaced the acetalic 1, 3-dioxane ring of 1. A large set of aminoethyl substituted cyclohexane derivatives was prepared in a six-step synthesis. All enantiomers and diastereomers were separated by chiral HPLC at the stage of the primary alcohol 7, and their absolute configuration was determined by CD spectroscopy. Neither the relative nor the absolute configuration had a large impact on the σ1 affinity. The highest σ1 affinity was found for cis-configured benzylamines (1R,3S)-11 (Ki = 0.61 nM) and (1S,3R)-11 (Ki = 1.3 nM). Molecular dynamics simulations showed that binding of (1R,3S)-11 at the σ1 receptor is stabilized by the typical polar interaction of the protonated amino moiety with the carboxy group of E172 which is optimally oriented by an H-bond interaction with Y103. The lipophilic interaction of I124 with the N-substituent also contributes to the high σ1 affinity of the benzylamines. The antagonistic activity was determined in a Ca2+ influx assay in retinal ganglion cells. The enantiomeric cis-configured benzylamines (1R,3S)-11 and (1S,3R)-11 were able to inhibit the growth of DU145 cells, a highly aggressive human prostate tumor cell line. Moreover, cis-11 could also inhibit the growth of further human tumor cells expressing σ1 receptors. The experimentally determined logD7.4 value of 3.13 for (1R,3S)-11 is in a promising range regarding membrane penetration. After incubation with mouse liver microsomes and NADPH for 90 min, 43% of the parent (1R,3S)-11 remained unchanged, indicating intermediate metabolic stability. Altogether, nine metabolites including one glutathione adduct were detected by means of LC-MS analysis.

Synergistic interaction between haloperidol and gabapentin in a model of neuropathic nociception in rat

Preclinical studies have reported that sigma-1 receptor antagonists may have efficacy in neuropathic pain states. The sigma-1 receptor is a unique ligand-operated chaperone present in crucial areas for pain control, in both the peripheral and central nervous system. This study assesses the synergistic antihyperalgesic and antiallodynic effect of haloperidol, a sigma-1 antagonist, combined with gabapentin in rats with peripheral neuropathy. Wistar rats male were subjected to chronic constriction injury (CCI) of the sciatic nerve. The effects of systemic administration of gabapentin and the sigma-1 receptor antagonist, haloperidol, were examined at 11 days post-CCI surgery. An analysis of Surface of Synergistic Interaction was used to determine whether the combination's effects were synergistic. Twelve combinations showed various degrees of interaction in the antihyperalgesic and antiallodynic effects. In hyperalgesia, three combinations showed additive effects, four combinations showed supra-additive effects, and three combinations produced an effect limited by the maximum effect. In allodynia, five combinations showed additive effects, two combinations showed supra-additive effects, and five combinations produced antihyperalgesic effects limited by the maximum effect. These findings indicate that the administration of some specific combination of gabapentin and haloperidol can synergistically reduce nerve injury-induced allodynia and hyperalgesia. This suggests that the haloperidol-gabapentin combination can improve the antiallodynic and antihyperalgesic effects in a neuropathic pain model.

Novel Sigma 1 Receptor Antagonists as Potential Therapeutics for Pain Management

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.

Synthesis, binding, and functional properties of tetrahydroisoquinolino-2-alkyl phenones as selective σ2R/TMEM97 ligands

Sigma-2 receptor (σ2R/TMEM97) has been implicated to play important roles in multiple cellular dysfunctions, such as cell neoplastic proliferation, neuro-inflammation, neurodegeneration, etc. Selective σ2 ligands are believed to be promising pharmacological tools to regulate or diagnose various disorders. As an ongoing effort of discovery of new and selective σ2 ligands, we have synthesized a series of tetrahydroisoquinolino-2-alkyl phenone analogs and identified that 10 of them have moderate to potent affinity and selectivity for σ2R/TMEM97. Especially, 4 analogs showed Ki values ranging from 0.38 to 5.1 nM for σ2R/TMEM97 with no or low affinity for sigma-1 receptor (σ1R). Functional assays indicated that these 4 most potent analogs had no effects on intracellular calcium concentration and were classified as putative σ2R/TMEM97 antagonists according to current understanding. The σ2R/TMEM97 has been suggested to play important roles in the central nervous system. Based on published pharmacological and clinical results from several regarded σ2R/TMEM97 antagonists, these analogs may potentially be useful for the treatment of various neurodegenerative diseases.

Sigma-1 receptor: A drug target for the modulation of neuroimmune and neuroglial interactions during chronic pain

Immune and glial cells play a pivotal role in chronic pain. Therefore, it is possible that the pharmacological modulation of neurotransmission from an exclusively neuronal perspective may not be enough for adequate pain management, and the modulation of complex interactions between neurons and other cell types might be needed for successful pain relief. In this article, we review the current scientific evidence for the modulatory effects of sigma-1 receptors on communication between the immune and nervous systems during inflammation, as well as the influence of this receptor on peripheral and central neuroinflammation. Several experimental models of pathological pain are considered, including peripheral and central neuropathic pain, osteoarthritic, and cancer pain. Sigma-1 receptor inhibition prevents peripheral (macrophage infiltration into the dorsal root ganglion) and central (activation of microglia and astrocytes) neuroinflammation in several pain models, and enhances immune-driven peripheral opioid analgesia during painful inflammation, maximizing the analgesic potential of peripheral immune cells. Therefore, sigma-1 antagonists may constitute a new class of analgesics with an unprecedented mechanism of action and potential utility in several painful disorders.

Discovery of EST73502, a Dual μ-Opioid Receptor Agonist and σ1 Receptor Antagonist Clinical Candidate for the Treatment of Pain

The synthesis and pharmacological activity of a new series of 4-alkyl-1-oxa-4,9-diazaspiro[5.5]undecane derivatives as potent dual ligands for the σ1 receptor (σ1R) and the μ-opioid receptor (MOR) are reported. A lead optimization program over the initial 4-aryl analogues provided 4-alkyl derivatives with the desired functionality and good selectivity and ADME profiles. Compound 14u (EST73502) showed MOR agonism and σ1R antagonism and a potent analgesic activity, comparable to the MOR agonist oxycodone in animal models of acute and chronic pain after single and repeated administration. Contrary to oxycodone, 14u produces analgesic activity with reduced opioid-induced relevant adverse events, like intestinal transit inhibition and naloxone-precipitated behavioral signs of opiate withdrawal. These results provide evidence that dual MOR agonism and σ1R antagonism may be a useful strategy for obtaining potent and safer analgesics and were the basis for the selection of 14u as a clinical candidate for the treatment of pain.

Small Molecules Selectively Targeting Sigma-1 Receptor for the Treatment of Neurological Diseases

The sigma-1 (σ1) receptor, an enigmatic protein originally classified as an opioid receptor subtype, is now understood to possess unique structural and functional features of its own and play critical roles to widely impact signaling transduction by interacting with receptors, ion channels, lipids, and kinases. The σ1 receptor is implicated in modulating learning, memory, emotion, sensory systems, neuronal development, and cognition and accordingly is now an actively pursued drug target for various neurological and neuropsychiatric disorders. Evaluation of the five selective σ1 receptor drug candidates (pridopidine, ANAVEX2-73, SA4503, S1RA, and T-817MA) that have entered clinical trials has shown that reaching clinical approval remains an evasive and important goal. This review provides up-to-date information on the selective targeting of σ1 receptors, including their history, function, reported crystal structures, and roles in neurological diseases, as well as a useful collation of new chemical entities as σ1 selective orthosteric ligands or allosteric modulators.

EST64454: a Highly Soluble σ1 Receptor Antagonist Clinical Candidate for Pain Management

The synthesis and pharmacological activity of a new series of pyrazoles that led to the identification of 1-(4-(2-((1-(3,4-difluorophenyl)-1H-pyrazol-3-yl)methoxy)ethyl)piperazin-1-yl)ethanone (9k, EST64454) as a σ1 receptor (σ1R) antagonist clinical candidate for the treatment of pain are reported. The compound 9k is easily obtained through a five-step synthesis suitable for the production scale and shows an outstanding aqueous solubility, which together with its high permeability in Caco-2 cells will allow its classification as a BCS class I compound. It also shows high metabolic stability in all species, linked to an adequate pharmacokinetic profile in rodents, and antinociceptive properties in the capsaicin and partial sciatic nerve ligation models in mice.

Inhibition of sigma-1 receptors substantially modulates GABA and glutamate transport in presynaptic nerve terminals

Sigma-1 receptors (Sig-1Rs) have been implicated in many neurological and psychiatric disorders and are a novel target for the treatment of such disorders. Sig-1R expression/activity deficits are linked to neurodegeneration, whereas the mechanisms mediated by Sig-1R are still unclear. Here, presynaptic [3H]GABA and L-[14C]glutamate transport was analysed in rat brain nerve terminals (synaptosomes) in the presence of the Sig-1R antagonist NE-100. NE-100 at doses of 1 and 10 μM increased the initial rate of synaptosomal [3H]GABA uptake, whereas 50 and 100 μM NE-100 decreased this rate, exerting a biphasic mode of action.Antagonists of GABAA and GABAB receptors, flumazenil and saclofen, respectively, prevented an increase in [3H]GABA uptake caused by 10 μM NE-100. L-[14C]glutamate uptake was decreased by 10-100 μM NE-100. A decrease in the uptake of both neurotransmitters mediated by NE-100 (50-100 μM) may have resulted from simultaneous antagonist-induced membrane depolarization, which was measured using the potential-sensitive fluorescent dye rhodamine 6G. The extracellular level of [3H]GABA was decreased by 1-10 μM NE-100, but that of L-[14C]glutamate remained unchanged. The tonic release of [3H]GABA measured in the presence of NO-711 was not changed by the antagonist, suggesting that NE-100 did not disrupt membrane integrity. The KCl- and FCCP-induced transporter-mediated release of L-[14C]glutamate was decreased by the antagonist; this may underlie the neuroprotective action of the antagonist in hypoxia/ischaemia. NE-100 (10-100 μM) decreased the KCl-evoked exocytotic release of [3H]GABA and L-[14C]glutamate, whereas the induction of the release of both neurotransmitters by the Ca2+ ionophore ionomycin was not affected by the antagonist; therefore, the mitigation of KCl-evoked exocytosis was associated with the NE-100-induced dysfunction of potential-dependent Ca2+ channels. Therefore, the Sig-1R antagonist can specifically act in an acute manner at the presynaptic level through the modulation of GABA and glutamate uptake, transporter-mediated release and exocytosis.

Setup and Validation of a Reliable Docking Protocol for the Development of Neuroprotective Agents by Targeting the Sigma-1 Receptor (S1R)

Sigma-1 receptor (S1R) is a promising molecular target for the development of novel effective therapies against neurodegenerative diseases. To speed up the discovery of new S1R modulators, herein we report the development of a reliable in silico protocol suitable to predict the affinity of small molecules against S1R. The docking method was validated by comparing the computational calculated Ki values of a test set of new aryl-aminoalkyl-ketone with experimental determined binding affinity. The druggability profile of the new compounds, with particular reference to the ability to cross the blood-brain barrier (BBB) was further predicted in silico. Moreover, the selectivity over Sigma-2 receptor (S2R) and N-methyl-D-aspartate (NMDA) receptor, another protein involved in neurodegeneration, was evaluated. 1-([1,1'-biphenyl]-4-yl)-4-(piperidin-1-yl)butan-1-one (12) performed as the best compound and was further investigated for acetylcholinesterase (AchE) inhibitor activity and determination of antioxidant activity mediated by aquaporins (AQPs). With a good affinity against both S1R and NMDA receptor, good selectivity over S2R and favorable BBB penetration potential together with its AChE inhibitory activity and its ability to exert antioxidant effects through modulation of AQPs, 12 represents a viable candidate for further development as a neuroprotective agent.

Deferred Administration of Afobazole Induces Sigma1R-Dependent Restoration of Striatal Dopamine Content in a Mouse Model of Parkinson's Disease

Previously, we demonstrated that the immediate administration of multitarget anxiolytic afobazole slows down the progression of neuronal damage in a 6-hydroxidodamine (6-OHDA) model of Parkinson's disease due to the activation of chaperone Sigma1R. The aim of the present study is to evaluate the therapeutic potential of deferred afobazole administration in this model. Male ICR mice received a unilateral 6-OHDA lesion of the striatum. Fourteen days after the surgery, mice were treated with afobazole, selective Sigma1R agonist PRE-084, selective Sigma1R antagonist BD-1047, and a combination of BD-1047 with afobazole or PRE-084 for another 14 days. The deferred administration of afobazole restored the intrastriatal dopamine content in the 6-OHDA-lesioned striatum and facilitated motor behavior in rotarod tests. The action of afobazole accorded with the effect of Sigma1R selective agonist PRE-084 and was blocked by Sigma1R selective antagonist BD-1047. The present study illustrates the Sigma1R-dependent effects of afobazole in a 6-OHDA model of Parkinson's disease and reveals the therapeutic potential of Sigma1R agonists in treatment of the condition.

Sigma-1 antagonism inhibits binge ethanol drinking at adolescence

BACKGROUND

Ethanol use during adolescence is a significant health problem, yet the pharmacological treatments to reduce adolescent binge drinking are scarce. The present study assessed, in male and female adolescent Wistar rats, if the sigma-1 receptor (S1-R) antagonists S1RA or BD-1063 disrupted ethanol drinking.

METHODS

Three times a week, for two weeks, the rats received the S1-R antagonists. Thirty min later they were exposed, for 2 h, to a bottle of 8% or 10 % v/v ethanol. A 24 h, two-bottle, ethanol intake test was conducted after termination of these procedures. A subset of these rats was tested for recognition memory via the novel object recognition test.

RESULTS

The rats given 64 mg/kg S1RA drank, in each binge session, significantly less than vehicle counterparts. Male rats given 4 or 16 mg/kg S1RA drank significantly less than those given 0 mg/kg in session 3 or in session 1 and 2, respectively; whereas female rats given 4 or 16 mg/kg drank significantly less than females given 0 mg/kg in session 2-5 or in sessions 2-6, respectively. Administration of 32 mg/kg, but not of 2 or 8 mg/kg, BD-1063 suppressed, across sessions, ethanol drinking. S1-R antagonism reduced absolute ethanol drinking at the two-bottle choice post-test. Recognition memory was not affected by the ethanol exposure.

CONCLUSIONS

The results indicate that S1-R antagonists may be promising targets to prevent increases in ethanol intake at adolescence. The persistent effect of S1-R antagonism in free-choice drinking suggests that modulation of the S1-R is altering plastic effects associated with ethanol exposure.

Sigma-1 (σ1) receptor activity is necessary for physiological brain plasticity in mice

The sigma-1 receptor (S1R) is a membrane-associated protein expressed in neurons and glia at mitochondria-associated endoplasmic reticulum (ER) membranes (MAMs). S1R interacts with different partners to regulate cellular responses, including ER stress, mitochondrial physiology and Ca2+ fluxes. S1R shapes cellular plasticity by directly modulating signaling pathways involved in inflammatory responses, cell survival and death. We here analyzed its impact on brain plasticity in vivo, in mice trained in a complex maze, the Hamlet test. The device, providing strong enriched environment (EE) conditions, mimics a small village. It has a central agora and streets expanding from it, leading to functionalized houses where animals can Drink, Eat, Hide, Run, or Interact. Animals were trained in groups, 4 h/day for two weeks, and their maze exploration and topographic memory could be analyzed. Several groups of mice were considered: non-trained vs. trained; repeatedly administered with saline vs. NE-100, a selective S1R antagonist; and wildtype vs. S1R KO mice. S1R inactivation altered maze exploration and prevented topographic learning. EE induced a strong plasticity measured through resilience to behavioral despair or to the amnesic effects of scopolamine, and increases in S1R expression and bdnf mRNA levels in the hippocampus; increases in neurogenesis (proliferation and maturation); and increases of histone acetylation in the hippocampus and cortex. S1R inactivation altered all these parameters significantly, showing that S1R activity plays a major role in physiological brain plasticity. As S1R is a major resident protein in MAMs, modulating ER responses and mitochondrial homeostasy, MAM physiology appeared impacted by enriched environment.

Urinary bladder sigma-1 receptors: A new target for cystitis treatment

No adequate treatment is available for painful urinary bladder disorders such as interstitial cystitis/bladder pain syndrome, and the identification of new urological therapeutic targets is an unmet need. The sigma-1 receptor (σ1-R) modulates somatic pain, but its role in painful urological disorders is unexplored. The urothelium expresses many receptors typical of primary sensory neurons (e.g. TRPV1, TRPA1 and P2X3) and high levels of σ1-R have been found in these neurons; we therefore hypothesized that σ1-R may also be expressed in the urothelium and may have functional relevance in this tissue. With western blotting and immunohistochemical methods, we detected σ1-R in the urinary bladder in wild-type (WT) but not in σ1-R-knockout (σ1-KO) mice. Interestingly, σ1-R was located in the bladder urothelium not only in mouse, but also in human bladder sections. The severity of histopathological (edema, hemorrhage and urothelial desquamation) and biochemical alterations (enhanced myeloperoxidase activity and phosphorylation of extracellular regulated kinases 1/2 [pERK1/2]) that characterize cyclophosphamide-induced cystitis was lower in σ1-KO than in WT mice. Moreover, cyclophosphamide-induced pain behaviors and referred mechanical hyperalgesia were dose-dependently reduced by σ1-R antagonists (BD-1063, NE-100 and S1RA) in WT but not in σ1-KO mice. In contrast, the analgesic effect of morphine was greater in σ1-KO than in WT mice. Together these findings suggest that σ1-R plays a functional role in the mechanisms underlying cyclophosphamide-induced cystitis, and modulates morphine analgesia against urological pain. Therefore, σ1-R may represent a new drug target for urinary bladder disorders.

Sigma-1 receptor antagonists: promising players in fighting neuropathic pain

Sigma-1 receptors (S1Rs) are strongly correlated to neuropathic pain (NP), since their inactivation may decrease allodynia or dysesthesia, promoting analgesic effects. In the recent patent landscape, S1R antagonists endowed with nanomolar S1Rs affinity emerged as potent antinociceptive agents. So far, three patented compounds have been proposed for counteracting NP. Particularly PV-752 and AV1066, disclosed by the University of Pavia (Italy) and Anavex, respectively, showed good analgesic activity in preclinical studies. Moreover, E-52862 developed by Esteve (Spain) has been proved to be effective, both in preclinical and Phase II clinical trials, against several symptoms of NP. These patents ascertain S1R antagonists as potential drugs, alone or in combination with other analgesic drugs, for managing NP in humans.

Exploiting the Power of Stereochemistry in Drug Action: 3-[(2S,6S,11S)-8-Hydroxy-6,11-dimethyl-1,4,5,6-tetrahydro-2,6-methano-3-benzazocin-3(2H)-yl]-N-phenylpropanamide as Potent Sigma-1 Receptor Antagonist

(+)-(2S,6S,11S)- and (-)-(2R,6R,11R)-Benzomorphan derivatives have a different binding affinity for sigma-1 (σ1R) and opioid receptors, respectively. In this study, we describe the synthesis of the (+)-enantiomer [(+)-LP1] of the benzomorphan MOR agonist/DOR antagonist LP1 [(-)-LP1]. The binding affinity of both (+)-LP1 and (-)-LP1 for σ1R and sigma-2 receptor (σ2R) was tested. Moreover, (+)-LP1 opioid receptor binding affinity was also investigated. Finally, (+)-LP1 was tested in a mouse model of inflammatory pain. Our results showed a nanomolar σ1R and binding affinity for (+)-LP1. Both (+)-LP1 and (-)-LP1 elicited a significant analgesic effect in a formalin test. Differently from (-)-LP1, the analgesic effect of (+)-LP1 was not reversed by naloxone, suggesting a σ1R antagonist profile. Furthermore, σ1R agonist PRE-084 was able to unmask the σ1R antagonistic component of the benzomorphan compound. (+)-LP1 could constitute an useful lead compound to develop new analgesics based on mechanisms of action alternative to opioid receptor activation.

Piperidine propionamide as a scaffold for potent sigma-1 receptor antagonists and mu opioid receptor agonists for treating neuropathic pain

We designed and synthesized a novel series of piperidine propionamide derivatives as potent sigma-1 (σ1) receptor antagonists and mu (μ) opioid receptor agonists, and measured their affinity for σ1 and μ receptors in vitro through binding assays. The basic scaffold of the new compounds contained a 4-substituted piperidine ring and N-aryl propionamide. Compound 44, N-(2-(4-(4-fluorobenzyl) piperidin-1-yl) ethyl)-N-(4-methoxy-phenyl) propionamide, showed the highest affinity for σ1 receptor (Ki σ1 = 1.86 nM) and μ receptor (Ki μ = 2.1 nM). It exhibited potent analgesic activity in the formalin test (ED50 = 15.1 ± 1.67 mg/kg) and had equivalent analgesic effects to S1RA (σ1 antagonist) in a CCI model. Therefore, Compound 44, which has mixed σ1/μ receptor profiles, may be a potential candidate for treating neuropathic pain.

Fenfluramine acts as a positive modulator of sigma-1 receptors

OBJECTIVE

Adjunctive fenfluramine hydrochloride, classically described as acting pharmacologically through a serotonergic mechanism, has demonstrated a unique and robust clinical response profile with regard to its magnitude, consistency, and durability of effect on seizure activity in patients with pharmacoresistant Dravet syndrome. Recent findings also support long-term improvements in executive functions (behavior, emotion, cognition) in these patients. The observed clinical profile is inconsistent with serotonergic activity alone, as other serotonergic medications have not been demonstrated to have these clinical effects. This study investigated a potential role for σ1 receptor activity in complementing fenfluramine's serotonergic pharmacology.

METHODS

Radioligand binding assays tested the affinity of fenfluramine for 47 receptors associated with seizures in the literature, including σ receptors. Cellular function assays tested fenfluramine and norfenfluramine (its major metabolite) activity at various receptors, including adrenergic, muscarinic, and serotonergic receptors. The σ1 receptor activity was assessed by the mouse vas deferens isometric twitch and by an assay of dissociation of the σ1 receptor from the endoplasmic reticulum stress protein binding immunoglobulin protein (BiP). In vivo mouse models assessed fenfluramine activity at σ1 receptors in ameliorating dizocilpine-induced learning deficits in spatial and nonspatial memory tasks, alone or in combination with the reference σ1 receptor agonist PRE-084.

RESULTS

Fenfluramine and norfenfluramine bound ≥30% to β2-adrenergic, muscarinic M1, serotonergic 5-HT1A, and σ receptors, as well as sodium channels, with a Ki between 266 nM (σ receptors) and 17.5 μM (β-adrenergic receptors). However, only σ1 receptor isometric twitch assays showed a positive functional response, with weak stimulation by fenfluramine and inhibition by norfenfluramine. Fenfluramine, but not the 5-HT2C agonist lorcaserin, showed a positive modulation of the PRE-084-induced dissociation of σ1 protein from BiP. Fenfluramine also showed dose-dependent antiamnesic effects against dizocilpine-induced learning deficits in spontaneous alternation and passive avoidance responses, which are models of σ1 activation. Moreover, low doses of fenfluramine synergistically potentiated the low-dose effect of PRE-084, confirming a positive modulatory effect at the σ1 receptor. Finally, all in vivo effects were blocked by the σ1 receptor antagonist NE-100.

SIGNIFICANCE

Fenfluramine demonstrated modulatory activity at σ1 receptors in vitro and in vivo in addition to its known serotonergic activity. These studies identify a possible new σ1 receptor mechanism underpinning fenfluramine's central nervous system effects, which may contribute to its antiseizure activity in Dravet syndrome and positive effects observed on executive functions in clinical studies.

Design and synthesis of N‑(benzylpiperidinyl)‑4‑fluorobenzamide: A haloperidol analog that reduces neuropathic nociception via σ1 receptor antagonism

AIMS

Haloperidol is a neuroleptic drug with high affinity towards the σ1 receptor (σ1R), acting as antagonist that decreases neuropathic pain, but has CNS side effects. This work describes the design and synthesis of a novel analog N‑(1‑benzylpiperidin‑4-yl)‑4‑fluorobenzamide (LMH-2), which produced antihyperalgesic and antiallodynic effects in rats with neuropathy induced by chronic constriction injury of the sciatic nerve (CCI), being more active than gabapentin (The most widely used drug for the treatment of neuropathic pain).

MAIN METHODS

LMH-2 was designed as haloperidol analog. Its structure was characterized by spectroscopic (1H and 13C NMR) and spectrometric mass (electronic impact) techniques. Additionally, in silico predictions of pharmacokinetic, pharmacodynamic and toxicological properties were obtained, with promising results. A competitive binding assay using radioligands was employed to evaluate the in vitro affinity for σ1R, whereas in vivo antihyperalgesic and antiallodynic activities were investigated using Wistar rats with CCI.

KEY FINDINGS

LMH-2 showed high affinity for σ1R in an in vitro binding assay, with a Ki = 6.0 nM and a high σ1R/σ2R selectivity ratio. Molecular docking studies were carried out to determine the binding energy and to analyze LMH-2-protein interactions. Through an in silico pharmacological consensus analysis, LMH-2 was considered safe for in vivo evaluation. Thus, LMH-2 had dose-dependent antiallodynic and antihyperalgesic activities; its efficacy was comparable to that of gabapentin, but its potency was 2-times higher than this drug.

SIGNIFICANCE

LMH-2 administration produced antihyperalgesic and antiallodynic effects by the antagonism of σ1R, suggesting its potential use as an analgesic drug for neuropathic pain.

4-Aryl-1-oxa-4,9-diazaspiro[5.5]undecane Derivatives as Dual μ-Opioid Receptor Agonists and σ1 Receptor Antagonists for the Treatment of Pain

The synthesis and pharmacological activity of a new series of 1-oxa-4,9-diazaspiro[5.5]undecane derivatives as potent dual ligands for the sigma-1 receptor (σ1R) and the μ-opioid receptor (MOR) are reported. The different positions of the central scaffold, designed using a merging strategy of both target pharmacophores, were explored using a versatile synthetic approach. Phenethyl derivatives in position 9, substituted pyridyl moieties in position 4 and small alkyl groups in position 2 provided the best profiles. One of the best compounds, 15au, showed a balanced dual profile (i.e., MOR agonism and sigma antagonism) and a potent analgesic activity, comparable to the MOR agonist oxycodone in the paw pressure test in mice. Contrary to oxycodone, as expected from the addition of σ1R antagonism, 15au showed local, peripheral activity in this test, which was reversed by the σ1R agonist PRE-084. At equianalgesic doses, 15au showed less constipation than oxycodone, providing evidence that dual MOR agonism and σ1R antagonism may be a useful strategy for obtaining potent and safer analgesics.

Pharmacological characterization of high-affinity σ1 receptor ligands with spirocyclic thienopyran and thienofuran scaffold

OBJECTIVES

In this study, the pharmacological properties of six spirocyclic piperidines 1-6 showing very high σ1 receptor affinity (Ki  = 0.2-16 nm) were investigated.

METHODS

In vitro receptor binding studies, retinal ganglion assay and in vivo capsaicin assay were used to determine the affinity, selectivity and activity. Influence on human tumour cell growth (cell lines A427, LCLC-103H, 5637 and DAN-G) was determined in different assays. The effect on the ergosterol and cholesterol biosynthesis was determined by GLC/MS analysis.

KEY FINDINGS

Receptor binding studies demonstrated high selectivity for the σ1 receptor. The increased Ca2+ influx mediated by 2 and the analgesic activity of 1, 4, 5 and 6 confirm σ1 receptor antagonistic activity. Inhibition of human tumour cell growth further supports the σ1 antagonistic effects. Treatment of A427 tumour cells with 2 led to cell detachment and cell degradation. Whereas the ergosterol biosynthesis was not affected, the sterol C14-reductase, a key enzyme in the cholesterol biosynthesis, was weakly inhibited.

CONCLUSIONS

Due to the high selectivity, off-target effects are not expected. The antiallodynic activity underlines the clinical potential of the spirocyclic piperidines for the treatment of neuropathic pain. Due to the antiproliferative activity, the spirocyclic σ1 antagonists represent promising antitumour agents.

Preliminary in Vitro Assessment of the Potential of EST64454, a Sigma-1 Receptor Antagonist, for Pharmacokinetic Drug-Drug Interactions

EST64454 is a selective sigma-1 receptor ligand intended for orally administered pain treatment that showed a promising profile in the lead optimization process. As part of the preliminary compound profiling, the potential for future drug-drug interactions was explored in vitro. Both direct and time-dependent CYP inhibition for CYP1A2, 2C9, 2C19, 2D6 and 3A4 was studied in human liver microsomes. EST64454 showed a low potential for CYP inhibition (IC50 between 100 and 1000 µM) and as time-dependent inhibitor (IC50 shift mainly around 1). CYP induction studies with HepaRG™ cells revealed no CYP induction at concentrations ≤50 µM, as shown by the CYP1A2, 3A4 and 2B6 activities measured. Reaction phenotyping was assessed after incubation with recombinant human enzymes. Although a very low metabolism was observed, several enzymes catalyzed the formation of metabolites, including CYP3A4, 2C19 and flavin monooxygenases (FMO) 1 and 3. EST64454 was not a P-glycoprotein (P-gp) substrate and was highly permeable in Caco-2 cells. P-gp inhibition was only observed at 200 µM, the highest concentration studied. Preliminary studies suggest that neither CYP nor P-gp interaction of EST64454 would be of any concern for further development. At later stages, the interaction kinetics and the clinical relevance of these findings will be thoroughly evaluated.

Chaperone Sigma1R mediates the neuroprotective action of afobazole in the 6-OHDA model of Parkinson's disease

Parkinson's disease (PD) is a progressive neurodegenerative disease with limited treatment options. Therefore, the identification of therapeutic targets is urgently needed. Previous studies have shown that the ligand activation of the sigma-1 chaperone (Sigma1R) promotes neuroprotection. The multitarget drug afobazole (5-ethoxy-2-[2-(morpholino)-ethylthio]benzimidazole dihydrochloride) was shown to interact with Sigma1Rs and prevent decreases in striatal dopamine in the 6-hydroxydopamine (6-OHDA)-induced parkinsonism model. The aim of the present study was to elucidate the role of Sigma1Rs in afobazole pharmacological activity. Using ICR mice we found that administration of afobazole (2.5 mg/kg, i.p.) or selective agonist of Sigma1R PRE-084 (1.0 mg/kg, i.p.) over 14 days normalizes motor disfunction and prevents decreases in dopamine in the 6-OHDA-lesioned striatum. Afobazole administration also prevents the loss of TH + neurons in the substantia nigra. The pre-administration of selective Sigma1R antagonist BD-1047 (3.0 mg/kg, i.p.) abolishes the activity of either afobazole or PRE-084, as determined using the rotarod test and the analysis of striatal dopamine content. The current study demonstrates the contribution of Sigma1Rs in the neuroprotective effect of afobazole in the 6-OHDA model of Parkinson's disease and defines the therapeutic perspective of Sigma1R agonists in the clinic.

Sigma-1 receptor antagonist, PD144418, selectively reduces female motivation for food during negative energy balance

Sigma-1 (σ1) receptors have been investigated for their involvement in learning, rewarding and motivational processes. PD144418, a σ1 receptor antagonist, 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. Moreover, PD144418 decreases the motivational effort of a food-reinforced behavior in male rats, without altering appetite or food palatability. It remains unknown whether the PD144418 can alter the motivational effort of a food-reinforced behavior in response to altered energy homeostasis, as is the case under 24 -h food deprivation. Additionally, while the previous experiments indicate effects in male rats, there has been no research examining the effects of PD144418, or any other σ1 receptor antagonist, on motivational aspects of feeding in females. The present study examined the effects of PD144418 on motivational aspects of feeding in male and female rats using an operant task under sated or food deprived conditions. Results indicated that when animals are sated, at the highest dose (10 μmol/kg), under a progressive ratio (PR) reinforcement schedule, PD144418 significantly attenuated the breakpoint and the number of active lever responses for sucrose pellets in both males and females. When animals are in a state of energy deficit, as is the case following 24-hr food deprivation, PD144418 does not alter motivationally driven operant responding as measured by the breakpoint in either sex but does alter the number of earned reinforcers responses in females.

Sigma-1 receptor ligand PD144418 and sigma-2 receptor ligand YUN-252 attenuate the stimulant effects of methamphetamine in mice

RATIONALE

Previous research indicates that the selective sigma-1 receptor ligand PD144418 and the selective sigma-2 ligands YUN-252 can inhibit cocaine-induced hyperactivity. The effects of these ligands on other stimulants, such as methamphetamine, have not been reported.

OBJECTIVES

The present study examined the effects of PD144418 and YUN-252 pretreatment on methamphetamine-induced hyperactivity after acute treatment.

METHODS

Mice (n = 8-14/group) were injected with PD144418 (3.16, 10, or 31.6 μmol/kg), YUN-252 (0.316, 3.16, 31.6 μmol/kg), or saline. After 15 min, mice injected with 2.69 μmol/kg methamphetamine or saline vehicle, where distance traveled during a 60-min period was recorded. Additionally, the effect of PD144418 on the initiation and expression of methamphetamine sensitization was determined by treating mice (n = 8-14/group) with PD144418, methamphetamine or saline repeatedly over a 5-day period, and testing said mice with a challenge dose after a 7-day withdrawal period.

RESULTS

Results indicate that both PD144418 and YUN-252, in a dose-dependent manner, attenuated hyperactivity induced by an acute methamphetamine injection. Specifically, 10 μmol/kg or 31.6 μmol/kg of PD144418 and 31 μmol/kg of YUN-252 suppressed methamphetamine-induced hyperactivity. In regard to methamphetamine sensitization, while 10 μmol/kg PD144418 prevented the initiation of methamphetamine sensitization, it did not have an effect on the expression.

CONCLUSIONS

Overall, the current results suggest an intriguing potential for this novel sigma receptor ligand as a treatment for the addictive properties of methamphetamine. Future analysis of this novel sigma receptor ligand in assays directly measuring reinforcement properties will be critical.

Chronic inhibition of the sigma-1 receptor exacerbates atrial fibrillation susceptibility in rats by promoting atrial remodeling

AIMS

This study aimed to evaluate the effects of the sigma-1 receptor (S1R) on atrial fibrillation (AF) susceptibility in rats.

MAIN METHODS

Rats were randomly assigned into three groups for intraperitoneal treatment with saline (CTL group), BD1047 (an antagonist of the S1R, BD group) or BD1047 plus fluvoxamine (an agonist of the S1R, BD + F group) for 4 weeks. The heart rate variability (HRV) and atrial electrophysiological parameters were measured via the PowerLab system and analyzed by LabChart 8.0 software. Atrial histology was determined with Masson staining. The protein levels of connexin (Cx) 40, Cav1.2, S1R, eNOS, p-eNOS, and p-AKT were detected by western blot assays.

KEY FINDINGS

Our results showed that BD1047 significantly shortened the atrial effective refractory period (ERP) and action potential duration (APD), increased AF inducibility and duration, augmented sympathetic activity, depressed parasympathetic activity, and reduced heart rate variability (HRV) compared with the CTL group. Masson staining also showed a significant increase in atrial fibrosis in the BD group. Furthermore, the expressions of S1R, Cx40, Cav1.2, p-eNOS, and p-AKT were dramatically reduced in the BD group compared with the CTL group (all P < 0.01). However, fluvoxamine administration mitigated most of the abovementioned alterations.

SIGNIFICANCE

Our findings indicated that S1R inhibition contributed to atrial electrical remodeling, cardiac autonomic remodeling and atrial fibrosis, which could be attenuated by fluvoxamine, thus providing new insights into the relationship between the S1R and AF.

Sigma-1 receptor modulates neuroinflammation associated with mechanical hypersensitivity and opioid tolerance in a mouse model of osteoarthritis pain

BACKGROUND AND PURPOSE

Osteoarthritic pain is a chronic disabling condition lacking effective treatment. Continuous use of opioid drugs during osteoarthritic pain induces tolerance and may result in dose escalation and abuse. Sigma-1 (σ1) receptors, a chaperone expressed in key areas for pain control, modulates μ-opioid receptor activity and represents a promising target to tackle these problems. The present study investigates the efficacy of the σ1 receptor antagonist E-52862 to inhibit pain sensitization, morphine tolerance, and associated electrophysiological and molecular changes in a murine model of osteoarthritic pain.

EXPERIMENTAL APPROACH

Mice received an intra-knee injection of monoiodoacetate followed by 14-day treatment with E-52862, morphine, or vehicle, and mechanical sensitivity was assessed before and after the daily doses.

KEY RESULTS

Monoiodoacetate-injected mice developed persistent mechanical hypersensitivity, which was dose-dependently inhibited by E-52862. Mechanical thresholds assessed before the daily E-52862 dose showed gradual recovery, reaching complete restoration by the end of the treatment. When repeated treatment started 15 days after knee injury, E-52862 produced enhanced short-term analgesia, but recovery to baseline threshold was slower. Both a σ1 receptor agonist and a μ receptor antagonist blocked the analgesic effects of E-52862. An acute, sub-effective dose of E-52862 restored morphine analgesia in opioid-tolerant mice. Moreover, E-52862 abolished spinal sensitization in osteoarthritic mice and inhibited pain-related molecular changes.

CONCLUSION AND IMPLICATIONS

These findings show dual effects of σ1 receptor antagonism alleviating both short- and long-lasting antinociception during chronic osteoarthritis pain. They identify E-52862 as a promising pharmacological agent to treat chronic pain and avoid opioid tolerance.

High-affinity sigma-1 (σ1) receptor ligands based on the σ1 antagonist PB212

Aim: The σ1 receptor is a druggable target involved in many physiological processes and diseases. To clarify its physiology and derive therapeutic benefit, nine analogs based on the σ1 antagonist PB212 were synthesized replacing the 4-methylpiperidine with basic moieties of varying size and degree of conformational freedom. Results & methodology: 3-Phenylpyrrolidine, 4-phenylpiperidine or granatane derivatives displayed the highest affinity (Ki.#x00A0;= 0.12, 0.31 or 1.03 nM). Calcium flux assays in MCF7σ1 cells indicated that the highest σ1 receptor affinity are σ1 antagonists. Molecular models provided a structural basis for understanding the σ1 affinity and functional activity of the analogs and incorporated Glennon's σ1 pharmacophore model. Conclusion: Herein, we identify new compounds exploitable as therapeutic drug leads or as tools to study σ1 receptor physiology.

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.