Pharmacology and therapeutic potential of sigma(1) receptor ligands

Two Targets, One Mission: Heterobivalent Metal-Based Radiopharmaceuticals for Prostate Cancer Imaging and Therapy

Prostate cancer (PCa) is a significant healthcare challenge, associated with considerable mortality and morbidity among men, particularly in developed countries. PCa mortality and morbidity are primarily related to its most advanced form, metastatic castration-resistant PCa (mCRPC), for which there is presently no cure. Therefore, novel therapeutic approaches to increase mCRPC survival are critically needed. Due to PCa tumor heterogeneity and a complex tumor microenvironment, the efficacy of single-target radiopharmaceuticals, such as the Food and Drug Administration-approved [177Lu]Lu-PSMA-617, is currently under reassessment. The design and development of PCa dual-target radiopharmaceuticals have garnered considerable attention, due to their benefits over single-target counterparts, namely increased therapeutic specificity and efficacy, as well as the ability to overcome the challenge of inconsistent tumor visualization caused by variable receptor expression across diverse lesions, thereby enabling more comprehensive imaging. Several PCa biomarkers are currently being investigated as potential targets for dual-target radiopharmaceuticals, including prostate-specific membrane antigen, gastrin-releasing peptide receptor, integrin αvβ3 receptor, fibroblast activation protein, sigma-1 receptor, as well as albumin, the radiosensitive cell nucleus, and mitochondria. This review explores recent advancements in heterobivalent metal-based radiopharmaceuticals for dual targeting in PCa, highlighting their significance in theranostic and personalized medicine.

Plant-derived compounds and neurodegenerative diseases: Different mechanisms of action with therapeutic potential

Neurodegenerative diseases are a group of disorders characterized by progressive degeneration of discrete groups of neurons causing severe disability. The main risk factor is age, hence their incidence is rapidly increasing worldwide due to the rise in life expectancy. Although the causes of the disease are not identified in about 90% of the cases, in the last decades there has been great progress in understanding the basis for neurodegeneration. Different pathological mechanisms including oxidative stress, mitochondrial dysfunction, alteration in proteostasis and inflammation have been addressed as important contributors to neuronal death. Despite our better understanding of the pathophysiology of these diseases, there is still no cure and available therapies only provide symptomatic relief. In an effort to discover new therapeutic approaches, natural products have aroused interest among researchers given their structural diversity and wide range of biological activities. In this review, we focus on three plant-derived compounds with promising neuroprotective potential that have been traditionally used by folk medicine: the flavonoid quercetin (QCT), the phytocannabinoid cannabidiol (CBD)and the tryptamine N,N-dimethyltryptamine (DMT). These compounds exert neuroprotective effects through different mechanisms of action, some overlapping, but each demonstrating a principal biological activity: QCT as an antioxidant, CBD as an anti-inflammatory, and DMT as a promoter of neuroplasticity. This review summarizes current knowledge on these activities, potential therapeutic benefits of these compounds and their limitations as candidates for neuroprotective therapies. We envision that treatments with QCT, CBD, and DMT could be effective either when combined or when targeting different stages of these diseases.

Sigma 1 Receptor and Its Pivotal Role in Neurological Disorders

Sigma 1 receptor (S1R) is a multifunctional, ligand-activated protein located in the membranes of the endoplasmic reticulum (ER). It mediates a variety of neurological disorders, including epilepsy, amyotrophic lateral sclerosis, Alzheimer's disease, Huntington's disease. The wide neuroprotective effects of S1R agonists are achieved by a variety of pro-survival and antiapoptotic S1R-mediated signaling functions. Nonetheless, relatively little is known about the specific molecular mechanisms underlying S1R activity. Many studies on S1R protein have highlighted the importance of maintaining normal cellular homeostasis through its control of calcium and lipid exchange between the ER and mitochondria, ER-stress response, and many other mechanisms. In this review, we will discuss S1R different cellular localization and explain S1R-associated biological activity, such as its localization in the ER-plasma membrane and Mitochondrion-Associated ER Membrane interfaces. While outlining the cellular mechanisms and important binding partners involved in these processes, we also explained how the dysregulation of these pathways contributes to neurodegenerative disorders.

Therapeutic targeting of neuroinflammation in methamphetamine use disorder

Methamphetamine (METH) is a highly addictive illicit psychostimulant with a significant annual fatality rate. Emerging studies highlight its role in neuroinflammation and a range of neurological disorders. This review examines the current landscape of potential drug targets for managing neuroinflammation in METH use disorders (MUDs), with a particular focus on the rationale behind targeting Toll-like receptor 4 (TLR4), the NLR family pyrin domain containing 3 (NLRP3) inflammasome, and other promising targets. Given the multifactorial neurological effects of METH, including cognitive impairment and neurodegeneration, addressing METH-induced neuroinflammation has shown considerable promise in partially mitigating the damaging effects on the central nervous system and improving behavioral outcomes. This article provides an overview of the existing understanding while charting a promising path forward for developing innovative MUD treatments, focusing on neuroinflammation as a therapeutic target. Targeting neuroinflammation in METH-induced neurological disorders shows significant promise in mitigating cognitive impairment and neurodegeneration, offering a potential therapeutic strategy for improving outcomes in MUD. While challenges remain in optimizing treatments, ongoing research into combination therapies, novel drug delivery systems, and neuroprotective agents suggests a positive outlook for more effective interventions.

PSMA and Sigma-1 receptor dual-targeted peptide mediates superior radionuclide imaging and therapy of prostate cancer

Radionuclide therapy, in particular peptide receptor radionuclide therapy (PRRT), has emerged as a valuable means to combat malignant tumors. The specific affinity of ACUPA peptide toward prostate-specific membrane antigen (PSMA) renders the successful development of PRRT for prostate cancer. The clinical outcome of PRRT is, however, generally challenged by moderate tumor uptake and off-target toxicity. Here, we report on a novel design of Sigma-1 receptor and PSMA dual-receptor targeted peptide (S1R/PSMA-P) for superior radionuclide imaging and therapy of prostate cancer. S1R/PSMA-P was acquired with good purity and could efficiently be labeled with 177Lu to yield 177Lu-S1R/PSMA-P with high specific activity and radiostability. Interestingly, 177Lu-S1R/PSMA-P revealed greatly enhanced affinity to LNCaP cells over single-targeted control 177Lu-PSMA-617. The single photon emission computed tomography (SPECT) imaging demonstrated exceptional uptake and retention of 177Lu-S1R/PSMA-P in LNCaP tumor, affording about 2-fold better tumor accumulation while largely reduced uptake by most normal tissues compared to 177Lu-PSMA-617. The selective uptake in LNCaP tumor was also visualized by positron emission tomography (PET) with 68Ga-S1R/PSMA-P. In accordance, a single and low dosage of 177Lu-S1R/PSMA-P at 11.1 MBq effectively suppressed tumor growth without causing apparent side effects. This dual-targeting strategy presents an appealing radionuclide therapy for malignant tumors.

Exploring the Role of Sigma Receptors in the Treatment of Cancer: A Narrative Review

This study investigated the association of sigma receptors (SRs) and their selective ligands (because the molecular characteristics of the same SRs, particularly sigma-2 receptor {S2R}, are not completely clear) in carcinogenesis, their potential use as antitumor agents, and their great utility in tumor imaging. The ion channels and transporters enhance the cell's ability to adapt to the metabolic conditions encountered in the tumor tissue. The high expression of SRs in the proliferating cells compared with those at rest indicates that this is a significant clinical biomarker for determining the proliferative status of solid tumors using functional PET imaging techniques. The association of SRs in the pathophysiology of cancer cells is a result of the high concentration of S1R and S2R binding sites observed in various tumor cell lines and tissues. It would also be remarkable to determine if SRs are involved in metastasis and other metastatic cell behaviors such as adhesion, secretion, motility, and penetration. An absolute challenge for research in this field is to develop an integrated model that describes the molecular mechanisms of sigma receptors, incorporating their known biological and pathophysiological roles.

The proof of concept of 2-{3-[N-(1-benzylpiperidin-4-yl)propyl]amino}-6-[N-methyl-N-(prop-2-yn-1-yl)amino]-4-phenylpyridine-3,5-dicarbonitrile for the therapy of neuropathic pain

In the search for new small molecules for the therapy of neuropathic pain, we found that 2-{3-[N-(1-benzylpiperidin-4-yl)propyl]amino}-6-[N-methyl-N-(prop-2-yn-1-yl)amino]-4-phenylpyridine-3,5-dicarbonitrile (12) induced a robust antiallodynic effect in capsaicin-induced mechanical allodynia, a behavioural model of central sensitization, through σ1R antagonism. Furthermore, administration of compound 12 to neuropathic animals, fully reversed mechanical allodynia, increasing its mechanical threshold to levels that were not significantly different from those found in paclitaxel-vehicle treated mice or from basal levels before neuropathy was induced. Ligand 12 is thus a promising hit-compound for the therapy of neuropathic pain.

Novel drug treatments for pain in advanced cancer and serious illness: a focus on neuropathic pain and chemotherapy-induced peripheral neuropathy

Drugs that are commercially available but have novel mechanisms of action should be explored as analgesics. This review will discuss haloperidol, miragabalin, palmitoylethanolamide (PEA), and clonidine as adjuvant analgesics or analgesics. Haloperidol is a sigma-1 receptor antagonist. Under stress and neuropathic injury, sigma-1 receptors act as a chaperone protein, which downmodulates opioid receptor activities and opens several ion channels. Clinically, there is only low-grade evidence that haloperidol improves pain when combined with morphine, methadone, or tramadol in patients who have cancer, pain from fibrosis, radiation necrosis, or neuropathic pain. Miragabalin is a gabapentinoid approved for the treatment of neuropathic pain in Japan since 2019. In randomized trials, patients with diabetic neuropathy have responded to miragabalin. Its long binding half-life on the calcium channel subunit may provide an advantage over other gabapentinoids. PEA belongs to a group of endogenous bioactive lipids called ALIAmides (autocoid local injury antagonist amides), which have a sense role in modulating numerous biological processes in particular non-neuronal neuroinflammatory responses to neuropathic injury and systemic inflammation. Multiple randomized trials and meta-analyses have demonstrated PEA's effectiveness in reducing pain severity arising from diverse pain phenotypes. Clonidine is an alpha2 adrenoceptor agonist and an imidazoline2 receptor agonist, which is U.S. Federal Drug Administration approved for attention deficit hyperactivity disorder in children, Tourette's syndrome, adjunctive therapy for cancer-related pain, and hypertension. Clonidine activation at alpha2 adrenoceptors causes downstream activation of inhibitory G-proteins (Gi/Go), which inhibits cyclic Adenosine monophosphate (AMP) production and hyperpolarizes neuron membranes, thus reducing allodynia. Intravenous clonidine has been used in terminally ill patients with poorly controlled symptoms, in particular pain and agitation.

Ethanol drinking at adulthood is sensitive to S1-R antagonism and is promoted by binge ethanol self-administration at adolescence

BACKGROUND

Binge drinking at adolescence is a risk factor for problematic alcohol (ethanol) consumption later in life, yet the murine studies that modelled this phenomenon via ethanol self-administration have provided mixed findings. Antagonism of the sigma-1 receptor (S1-R) system at adolescence modulates ethanol's motivational effects and intake. It is still unknown, however, whether this antagonism would protect against enhanced ethanol intake at adulthood after adolescent binge ethanol exposure.

METHODS

Exp. 1 and 2 tested adults male or female Wistar rats -exposed or not to ethanol self-administration at adolescence (postnatal days 31-49; nine 2-hour sessions of access to 8-10% ethanol)- for ethanol intake using 24-h two-bottle choice test (Exp. 1) or time restricted, single-bottle, tests (Exp. 2). Experiments 2-5 evaluated, in adolescent or adult rats, the effects of the S1-R antagonist S1RA on ethanol intake and on ethanol-induced conditioned taste or place aversion. Ancillary tests (e.g., novel object recognition, ethanol-induced locomotor activity) were also conducted.

RESULTS

Adolescent ethanol exposure promoted ethanol consumption at both the restricted, single-bottle, and at the two-bottle choice tests conducted at adulthood. S1RA administration reduced ethanol intake at adulthood and facilitated the development of ethanol-induced taste (but not place) aversion.

CONCLUSIONS

S1RA holds promise for lessening ethanol intake after chronic and substantial ethanol exposure in adolescence that results in heightened ethanol exposure at adulthood. This putative protective effect of S1-R antagonism may relate to S1RA exacerbating the aversive effects of this drug.

Design, Synthesis, and Cytotoxic Assessment of New Haloperidol Analogues as Potential Anticancer Compounds Targeting Sigma Receptors

Sigma receptors (SRs), including SR1 and SR2 subtypes, have attracted increasing interest in recent years due to their involvement in a wide range of activities, including the modulation of opioid analgesia, neuroprotection, and potential anticancer activity. In this context, haloperidol (HAL), a commonly used antipsychotic drug, also possesses SR activity and cytotoxic effects. Herein, we describe the identification of novel SR ligands, obtained by a chemical hybridization approach. There wereendowed with pan-affinity for both SR subtypes and evaluated their potential anticancer activity against SH-SY5Y and HUH-7 cancer cell lines. Through a chemical hybridization approach, we identified novel compounds (4d, 4e, 4g, and 4j) with dual affinity for SR1 and SR2 receptors. These compounds were subjected to cytotoxicity testing using a resazurin assay. The results revealed potent cytotoxic effects against both cancer cell lines, with IC50 values comparable to HAL. Interestingly, the cytotoxic potency of the novel compounds resembled that of the SR1 antagonist HAL rather than the SR2 agonist siramesine (SRM), indicating the potential role of SR1 antagonism in their mechanism of action. The further exploration of their structure-activity relationships and their evaluation in additional cancer cell lines will elucidate their therapeutic potential and may pave the way for the development of novel anticancer agents that target SRs.

Antinociceptive effect of LMH-2, a new sigma-1 receptor antagonist analog of haloperidol, on the neuropathic pain of diabetic mice

This study evaluates the antiallodynic and antihyperalgesic effects of LMH-2, a new haloperidol (HAL) analog that acts as sigma-1 receptor (σ1 R) antagonist, in diabetic mice using a model of neuropathic pain induced by chronic hyperglycemia. Additionally, we compared its effects with those of HAL. Hyperglycemia was induced in mice by nicotinamide-streptozotocin administration (NA-STZ, 50-130 mg/kg). Four weeks later, mechanical allodynia was assessed using the up-down method, and hyperalgesia was evoked with formalin 0.5%. We evaluated antiallodynic and antihyperalgesic effects of LMH-2 (5.6-56.2 mg/kg), HAL (0.018-0.18 mg/kg) and gabapentin (GBP, 5.6-56.2 mg/kg). The results showed that LMH-2 had a more significant antiallodynic effect compared to HAL and GBP (90.4±8.7 vs 75.1±3.1 and 41.9±2.3%, respectively; P<0.05), as well as an antihyperalgesic effect (96.3±1.2 vs 86.9±7.41 and 86.9±4.8%, respectively; P<0.05). Moreover, the antiallodynic and antihyperalgesic effect of both LMH-2 and HAL were completely abolished by PRE-084 (σ1 R agonist); and partially by pramipexole (a D2-like receptor agonist). Finally, the effect of all treatments on the rotarod test, barra, open field and exploratory behaviors showed that LMH-2 did not alter the animals' balance or the exploratory behavior, unlike as HAL or GBP. The molecular docking included indicate that LMH-2 has lower affinity to the D2R than HAL. These results provide evidence that LMH-2 exerts its antinociceptive effects as a σ1 R antagonist without the adverse effects induced by HAL or GBP. Consequently, LMH-2 can be considered a good and safe strategy for treating neuropathic pain caused by hyperglycemia in patients with diabetes.

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.

Bispecific Sigma1R-Antagonist/MOR-Agonist Compounds for Pain

Recent research has significantly advanced an understanding of sigma receptors, which consist of two distinct subtypes designated as S1R and S2R (s1R and s2R gene products, respectively). Both subtypes have recently been cloned and their crystal structures have been published. As a result, highly selective S1R and S2R agonist and antagonist ligands are now available. Unlike the confusion generated from prior use of non-selective 'sigma' compounds, these tool compounds have begun to add clarity about the function of sigma receptors in health and disease.  The discovery of compounds with high-affinity (nM range) S1R/S2R or S2R/S1R subtype selectivity (>100-fold), and selectivity over off-target sites (>1,000-fold) has brought the study of sigma receptor pharmacology into the modern era. Computer modeling has contributed to a better understanding of the binding processes, structural requirements for chemical synthesis, and potential therapeutic uses. Several lines of evidence converge on pain as a therapeutic target for S1R-antagonists (as single mechanism or as part of a multi-mechanistic approach). We highlight here some compounds reported over the past few years that have promise for use as analgesics, specifically some mono-mechanistic S1R-antagonists, and some that are 'bispecific', i.e., have more than one mechanism of action, for example, complementary action of the mu-opioid receptor (MOR). We concentrate on some compounds that are further along in development, in particular, some of the bispecific S1R-antagonist/MOR-agonist compounds.

A facile synthesis of precursor for the σ-1 receptor PET radioligand [18 F]FTC-146 and its radiofluorination

The σ-1 receptor is a non-opioid transmembrane protein involved in various human pathologies including neurodegenerative diseases, inflammation, and cancer. The previously published ligand [18 F]FTC-146 is among the most promising tools for σ-1 molecular imaging by positron emission tomography (PET), with a potential for application in clinical diagnostics and research. However, the published six- or four-step synthesis of the tosyl ester precursor for its radiosynthesis is complicated and time-consuming. Herein, we present a simple one-step precursor synthesis followed by a one-step fluorine-18 labeling procedure that streamlines the preparation of [18 F]FTC-146. Instead of a tosyl-based precursor, we developed a one-step synthesis of the precursor analog AM-16 containing a chloride leaving group for the SN 2 reaction with 18 F-fluoride. 18 F-fluorination of AM-16 led to a moderate decay-corrected radiochemical yield (RCY = 7.5%) with molar activity (Am ) of 45.9 GBq/μmol. Further optimization of this procedure should enable routine radiopharmaceutical production of this promising PET tracer.

[18F]Fluspidine-A PET Tracer for Imaging of σ1 Receptors in the Central Nervous System

σ1 receptors play a crucial role in various neurological and neurodegenerative diseases including pain, psychosis, Alzheimer's disease, and depression. Spirocyclic piperidines represent a promising class of potent σ1 receptor ligands. The relationship between structural modifications and σ1 receptor affinity and selectivity over σ2 receptors led to the 2-fluoroethyl derivative fluspidine (2, Ki = 0.59 nM). Enantiomerically pure (S)-configured fluspidine ((S)-2) was prepared by the enantioselective reduction of the α,β-unsaturated ester 23 with NaBH4 and the enantiomerically pure co-catalyst (S,S)-24. The pharmacokinetic properties of both fluspidine enantiomers (R)-2 and (S)-2 were analyzed in vitro. Molecular dynamics simulations revealed very similar interactions of both fluspidine enantiomers with the σ1 receptor protein, with a strong ionic interaction between the protonated amino moiety of the piperidine ring and the COO- moiety of glutamate 172. The 18F-labeled radiotracers (S)-[18F]2 and (R)-[18F]2 were synthesized in automated syntheses using a TRACERlab FX FN synthesis module. High radiochemical yields and radiochemical purity were achieved. Radiometabolites were not found in the brains of mice, piglets, and rhesus monkeys. While both enantiomers revealed similar initial brain uptake, the slow washout of (R)-[18F]2 indicated a kind of irreversible binding. In the first clinical trial, (S)-[18F]2 was used to visualize σ1 receptors in the brains of patients with major depressive disorder (MDD). This study revealed an increased density of σ1 receptors in cortico-striato-(para)limbic brain regions of MDD patients. The increased density of σ1 receptors correlated with the severity of the depressive symptoms. In an occupancy study with the PET tracer (S)-[18F]2, the selective binding of pridopidine at σ1 receptors in the brain of healthy volunteers and HD patients was shown.

Sigma-1 receptor agonism exacerbates immune-driven nociception: Role of TRPV1 + nociceptors

The analgesic effects of sigma-1 antagonists are undisputed, but the effects of sigma-1 agonists on pain are not well studied. Here, we used a mouse model to show that the administration of the sigma-1 agonists dextromethorphan (a widely used antitussive drug), PRE-084 (a standard sigma-1 ligand), and pridopidine (a selective drug being investigated in clinical trials for the treatment of neurodegenerative diseases) enhances PGE2-induced mechanical hyperalgesia. Superficial plantar incision induced transient weight-bearing asymmetry at early time points, but the mice appeared to recover at 24 h, despite noticeable edema and infiltration of neutrophils (a well-known cellular source of PGE2) at the injured site. Sigma-1 agonists induced a relapse of weight bearing asymmetry in a manner dependent on the presence of neutrophils. The effects of sigma-1 agonists were all reversed by administration of the sigma-1 antagonist BD-1063 in wild-type mice, and were absent in sigma-1 knockout mice, supporting the selectivity of the effects observed. The proalgesic effects of sigma-1 agonism were also abolished by the TRP antagonist ruthenium red and by in vivo resiniferatoxin ablation of TRPV1 + peripheral sensory neurons. Therefore, sigma-1 agonism exacerbates pain-like responses in mice with a mild inflammatory state through the action of TRPV1 + nociceptors. We also show that sigma-1 receptors are present in most (if not all) mouse and human DRG neurons. If our findings translate to humans, further studies will be needed to investigate potential proalgesic effects induced by sigma-1 agonism in patients treated with sigma-1 agonists.

Novel object recognition test as an alternative approach to assessing the pharmacological profile of sigma-1 receptor ligands

BACKGROUND

Although the terms "agonist" and "antagonist" have been used to classify sigma-1 receptor (σ1R) ligands, an unambiguous definition of the functional activity is often hard. In order to determine the pharmacological profile of σ1R ligands, the most common method is to assess their potency to alleviate opioid analgesia. It has been well established that σ1R agonists reduce opioid analgesic activity, while σ1R antagonists have been demonstrated to enhance opioid analgesia in different pain models.

METHODS

In the present study, we evaluated the pharmacological profile of selected σ1R ligands using a novel object recognition (NOR) test, to see if any differences in cognitive functions between σ1R agonists and antagonists could be observed. We used the highly selective PRE-084 and S1RA as reference σ1R agonist and antagonist, respectively. Furthermore, compound KSK100 selected from our ligand library was also included in this study. KSK100 was previously characterized as a dual-targeting histamine H3/σ1R antagonist with antinociceptive and antiallodynic activity in vivo. Donepezil (acetylcholinesterase inhibitor and σ1R agonist) was used as a positive control drug.

RESULTS

Both tested σ1R agonists (donepezil and PRE-084) improved learning in the NOR test, which was not observed with the σ1R antagonists S1RA and KSK100.

CONCLUSIONS

The nonlinear dose-response effect of PRE-084 in this assay does not justify its use for routine assessment of the functional activity of σ1R ligands.

An Emerging Role for Sigma Receptor 1 in Personalized Treatment of Breast Cancer

Despite the major progress in treating breast cancer, recurrence remains a problem and types such as triple-negative breast cancer still lack targeted medicine. The orphan Sigma receptor1 (SigmaR1) has emerged as a target in breast cancer, but its mechanism of action is unclear and hinders clinical utility. SigmaR1 is widely expressed in organ tissues and localized to various sub-cellular compartments, particularly the endoplasmic reticulum (ER), the mitochondrial-associated membranes (MAMs) and the nuclear envelope. As such, it involves diverse cellular functions, including protein quality control/ER stress, calcium signaling, cholesterol homeostasis, mitochondrial integrity and energy metabolism. Consequently, SigmaR1 has been implicated in a number of cancers and degenerative diseases and thus has been intensively pursued as a therapeutic target. Because SigmaR1 binds a number of structurally unrelated ligands, it presents an excellent context-dependent therapeutic target. Here, we review its role in breast cancer and the current therapies that have been considered based on its known functions. As SigmaR1 is not classified as an oncoprotein, we propose a model in which it serves as an oligomerization adaptor in key cellular pathways, which may help illuminate its association with variable diseases and pave the way for clinical utility in personalized medicine.

Effect of moderate prenatal ethanol exposure on the differential expression of two histamine H3 receptor isoforms in different brain regions of adult rat offspring

We have reported that prenatal alcohol exposure (PAE) elevates histamine H3 receptor (H3R) agonist-mediated inhibition of glutamatergic neurotransmission in the dentate gyrus. Here, we hypothesized that PAE alters the expression of two prominent H3R isoforms namely, the rH3A and rH3C isoforms, which have differing intrinsic activities for H3R agonists, in a manner that may contribute to heightened H3R function in PAE rats. In contrast to our predictions, we found different effects of sex and PAE in various brain regions with significant interactions between sex and PAE in dentate gyrus and entorhinal cortex for both isoforms. Subsequently, to confirm the PAE-and sex-induced differences on H3R isoform mRNA expression, we developed a polyclonal antibody selective for the rH3A inform. Western blots of rH3A mRNA-transfected HEK-293 cells identified a  ~ 48 kDa band of binding consistent with the molecular weight of rH3A, thus confirming antibody sensitivity for rH3A protein. In parallel, we also established a pan-H3R knockout mice line to confirm antibody specificity in rodent brain membranes. Both qRT-PCR and H3R agonist-stimulated [35S]-GTPγS binding confirmed the absence of mH3A mRNA and H3 receptor-effector coupling in H3R knockout (KO) mice. Subsequent western blotting studies in both rat and mouse brain membranes were unable to detect rH3A antibody binding at ~48 kDa. Rather, the H3RA antibody bound to a  ~ 55 kDa band in both rat and mouse membranes, including H3R KO mice, suggesting H3RA binding was not specific for H3Rs in rodent membranes. Subsequent LC/MS analysis of the ~55 kDa band in frontal cortical membranes identified the highly abundant beta subunit of ATPase in both WT and KO mice. Finally, LC/MS analysis of the ~48 kDa band from rH3A mRNA-transfected HEK-293 cell membranes was able to detect rH3A protein, but its presence was below the limits of quantitative reliability. We conclude that PAE alters rH3A and rH3C mRNA expression in some of the same brain regions where we have previously reported PAE-induced alterations in H3R-effector coupling. However, interpreting the functional consequences of altered H3R isoform expression was limited given the technical challenges of measuring the relatively low abundance of rH3A protein in native membrane preparations.

Development of a Novel σ1 Receptor Biosensor Based on Its Heterodimerization with Binding Immunoglobulin Protein in Living Cells

The σ₁ receptor (S1R) is a ligand-regulated non-opioid intracellular receptor involved in several pathological conditions. The development of S1R-based drugs as therapeutic agents is a challenge due to the lack of simple functional assays to identify and classify S1R ligands. We have developed a novel nanoluciferase binary technology (NanoBiT) assay based on the ability of S1R to heteromerize with the binding immunoglobulin protein (BiP) in living cells. The S1R-BiP heterodimerization biosensor allows for rapid and accurate identification of S1R ligands by monitoring the dynamics of association-dissociation of S1R and BiP. Acute treatment of cells with the S1R agonist PRE-084 produced rapid and transient dissociation of the S1R-BiP heterodimer, which was blocked by haloperidol. The effect of PRE-084 was enhanced by calcium depletion, leading to a higher reduction in heterodimerization even in the presence of haloperidol. Prolonged incubation of cells with S1R antagonists (haloperidol, NE-100, BD-1047, and PD-144418) increased the formation of S1R-BiP heteromers, while agonists (PRE-084, 4-IBP, and pentazocine) did not alter heterodimerization under the same experimental conditions. The newly developed S1R-BiP biosensor is a simple and effective tool for exploring S1R pharmacology in an easy cellular setting. This biosensor is suitable for high-throughput applications and a valuable resource in the researcher's toolkit.

The sigma-1 receptor curtails endogenous opioid analgesia during sensitization of TRPV1 nociceptors

BACKGROUND AND PURPOSE

Peripheral sensitization contributes to pathological pain. While prostaglandin E2 (PGE2) and nerve growth factor (NGF) sensitize peptidergic C-nociceptors (TRPV1+), glial cell line-derived neurotrophic factor (GDNF) sensitizes non-peptidergic C-neurons (IB4+). The sigma-1 receptor (sigma-1R) is a Ca²⁺ -sensing chaperone known to modulate opoid analgesia. This receptor binds both to TRPV1 and the μ opioid receptor, although the functional repercussions of these physical interactions in peripheral sensitization are unknown.

EXPERIMENTAL APPROACH

We tested the effects of sigma-1 antagonism on PGE2-, NGF-, and GDNF-induced mechanical and heat hyperalgesia in mice. We used immunohistochemistry to determine the presence of endomorphin-2, an endogenous μ receptor agonist, on dorsal root ganglion (DRG) neurons. Recombinant proteins were used to study the interactions between sigma-1R, μ- receptor, and TRPV1. We used calcium imaging to study the effects of sigma-1 antagonism on PGE2-induced sensitization of TRPV1+ nociceptors.

KEY RESULTS

Sigma1 antagonists reversed PGE2- and NGF-induced hyperalgesia but not GDNF-induced hyperalgesia. Endomorphin-2 was detected on TRPV1+ but not on IB4+ neurons. Peripheral opioid receptor antagonism by naloxone methiodide or administration of an anti-endomorphin-2 antibody to a sensitized paw reversed the antihyperalgesia induced by sigma-1 antagonists. Sigma-1 antagonism transfers sigma-1R from TRPV1 to μ receptors, suggesting that sigma-1R participate in TRPV1-μ receptor crosstalk. Moreover, sigma-1 antagonism reversed, in a naloxone-sensitive manner, PGE2-induced sensitization of DRG neurons to the calcium flux elicited by capsaicin, the prototypic TRPV1 agonist.

CONCLUSION AND IMPLICATIONS

Sigma-1 antagonism harnesses endogenous opioids produced by TRPV1+ neurons to reduce hyperalgesia by increasing μ receptor activity.

The Sigma Enigma: A Narrative Review of Sigma Receptors

The sigma-1 and sigma-2 receptors were first discovered in the 1960s and were thought to be a form of opioid receptors initially. Over time, more was gradually learned about these receptors, which are actually protein chaperones, and many of their unique or unusual properties can contribute to a range of important new therapeutic applications. These sigma receptors translocate in the body and regulate calcium homeostasis and mitochondrial bioenergetics and they also have neuroprotective effects. The ligands to which these sigma receptors respond are several and dissimilar, including neurosteroids, neuroleptics, and cocaine. There is controversy as to their endogenous ligands. Sigma receptors are also involved in the complex processes of cholesterol homeostasis and protein folding. While previous work on this topic has been limited, research has been conducted in multiple disease states, such as addiction, aging. Alzheimer's disease, cancer, psychiatric disorders, pain and neuropathic pain, Parkinson's disease, and others. There is currently increasing interest in sigma-1 and sigma-2 receptors as they provide potential therapeutic targets for many disease indications.

The Tetrahydroisoquinoline Scaffold in ABC Transporter Inhibitors that Act as Multidrug Resistance (MDR) Reversers

BACKGROUND

The failure of anticancer chemotherapy is often due to the development of resistance to a variety of anticancer drugs. This phenomenon is called multidrug resistance (MDR) and is related to the overexpression of ABC transporters, such as P-glycoprotein, multidrug resistance- associated protein 1 and breast cancer resistance protein. Over the past few decades, several ABC protein modulators have been discovered and studied as a possible approach to evade MDR and increase the success of anticancer chemotherapy. Nevertheless, the co-administration of pump inhibitors with cytotoxic drugs, which are substrates of the transporters, does not appear to be associated with an improvement in the therapeutic efficacy of antitumor agents. However, more recently discovered MDR reversing agents, such as the two tetrahydroisoquinoline derivatives tariquidar and elacridar, are characterized by high affinity towards the ABC proteins and by reduced negative properties. Consequently, many analogs of these two derivatives have been synthesized, with the aim of optimizing their MDR reversal properties.

OBJECTIVE

This review aims to describe the MDR modulators carrying the tetraidroisoquinoline scaffold reported in the literature in the period 2009-2021, highlighting the structural characteristics that confer potency and/or selectivity towards the three ABC transport proteins.

RESULTS AND CONCLUSION

Many compounds have been synthesized in the last twelve years showing interesting properties, both in terms of potency and selectivity. Although clear structure-activity relationships can be drawn only by considering strictly related compounds, some of the compounds reviewed could be promising starting points for the design of new ABC protein inhibitors.

Veratramine ameliorates pain symptoms in rats with diabetic peripheral neuropathy by inhibiting activation of the SIGMAR1-NMDAR pathway

CONTEXT

Veratramine may have a potential therapeutic effect for diabetic peripheral neuropathy (DPN).

OBJECTIVE

To evaluate whether veratramine ameliorates neuropathic pain in a rat diabetic model.

MATERIALS AND METHODS

Sprague-Dawley rats were used for a diabetic model induced by a streptozotocin + high-fat diet. Two months after the induction of the diabetic model, the rats with DPN were screened according to the mechanical pain threshold. The rats with DPN were divided into a model group (n = 12) and a treated group (n = 12). Rats with diabetes, but without peripheral neuropathy, were used in the vehicle group (n = 9). The treatment group received 50 μg/kg veratramine via the tail vein once a day for 4 weeks. During modelling and treatment, rats in all three groups were fed a high-fat diet.

RESULTS

The mechanical withdrawal threshold increased from 7.5 ± 1.9 N to 17.9 ± 2.6 N in DPN rats treated with veratramine. The tolerance time of the treated group to hot and cold ectopic pain increased from 11.8 ± 4.2 s and 3.4 ± 0.8 s to 20.4 ± 4.1 s and 5.9 ± 1.7 s, respectively. Veratramine effectively alleviated L4-L5 spinal cord and sciatic nerve pathological injury. Veratramine inhibited the expression of SIGMAR1 and the phosphorylation of the N-methyl-d-aspartate receptor (NMDAR) Ser896 site in spinal cord tissue, as well as inhibited the formation of SIGMAR1-NMDAR and NMDAR-CaMKII complexes.

DISCUSSION AND CONCLUSIONS

Veratramine may alleviate the occurrence of pain symptoms in rats with DPN by inhibiting activation of the SIGMAR1-NMDAR pathway.

SKF83959 Attenuates Memory Impairment and Depressive-like Behavior during the Latent Period of Epilepsy via Allosteric Activation of the Sigma-1 Receptor

Memory impairment and emotional disorder are two common clinical comorbidities in patients with epilepsy. It is imperative to develop a novel therapeutic agent or a strategy. 6-Chloro-7,8-dihydroxy-3-methyl-1-(3-methylphenyl)-2,3,4,5-tetrahydro-1H-3-benzazepine (SKF83959) is a dopamine-1 receptor agonist and sigma-1 receptor allosteric modulator, which displays the neuron-protective and anti-neuroinflammation activity. We examined the effect of SKF83959 on the memory impairment and emotional disorder in the latent period of epilepsy using the mice post-status epilepticus model. We found that SKF83959 ameliorated memory impairment and depressive-like mood, alleviated the neuron damage and the formation of gliosis in hippocampus, suppressed the rise of pro-inflammatory cytokines, including tumor necrosis factor-α and interleukin-1β, and induced nitric oxide synthase in the latent period of epilepsy. Additionally, SKF83959 significantly inhibited the activity of calcineurin and glycogen synthase kinase-3β. All of these protective actions were reversed by BD1047 (a sigma-1 receptor antagonist). In addition, the intra-hippocampus injection of ketoconazole (a dehydroepiandrosterone synthesis inhibitor) also reversed the protective activity of SKF83959. Thus, we concluded that SKF83959 ameliorated the memory impairment and depressive-like mood in epilepsy via allosterically activating the sigma-1 receptor and subsequently inhibiting the calcineurin/glycogen synthase kinase-3β pathway.

Comparative Analyses of Poly(ADP-Ribose) Polymerase Inhibitors

Poly(ADP-ribose) polymerase inhibitors (PARPi) are approved as monotherapies in BRCA1/2-mutated (m BRCA1/2) metastatic breast and ovarian cancers, and in advanced pancreatic and metastatic castration-resistant prostate cancers. Differential safety profiles across PARPi necessitate improved mechanistic understanding of inhibitor differences, especially with expansion of PARPi indications and drug combinations. Here, we report in vitro evaluations of PARPi (–/+ PARP trapper temozolomide, TMZ) with reference to total clinical mean concentration average or maximum (tCavg, tCmax), to elucidate contributions of primary pharmacology and structural differences to clinical efficacy and safety. In biochemical assays, rucaparib and niraparib demonstrated off-target secondary pharmacology activities, and in selectivity assays, talazoparib, olaparib, and rucaparib inhibited a broader panel of PARP enzymes. In donor-derived human bone marrow mononuclear cells, only olaparib both increased early apoptosis and decreased the cell viability half inhibitory concentration (IC50) at ≤ tCavg, whereas other PARPi only did so in the presence of TMZ. In cancer cell lines with DNA damage repair mutations, all PARPi decreased cell viability in H1048 but not TK6 cells, and only talazoparib decreased cell growth in DU145 cells at ≤ tCavg concentrations. When combined with low dose TMZ, only talazoparib left-shifted the functional consequences of PARP trapping (S-phase arrest, apoptosis, S-phase double-stranded breaks) and reduced cell viability/growth in TK6 and DU145 cell lines at ≤ tCavg, whereas the other inhibitors required high-dose TMZ. Our study suggests structural differences across PARPi may contribute to differences in PARP selectivity and off-target activities, which along with distinct pharmacokinetic properties, may influence inhibitor-specific toxicities in patients.

Novel N-normetazocine Derivatives with Opioid Agonist/Sigma-1 Receptor Antagonist Profile as Potential Analgesics in Inflammatory Pain

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

Effect of AXS-05 (Dextromethorphan-Bupropion) in Major Depressive Disorder: A Randomized Double-Blind Controlled Trial

OBJECTIVE

Altered glutamatergic neurotransmission is implicated in the pathogenesis of major depressive disorder. AXS-05 (dextromethorphan-bupropion) is an oral NMDA receptor antagonist and sigma-1 receptor agonist, which utilizes inhibition of CYP2D6 to increase its bioavailability. This phase 2 trial assessed the efficacy and safety of dextromethorphan-bupropion in the treatment of major depressive disorder.

METHODS

This randomized, double-blind, multicenter, parallel-group trial evaluated dextromethorphan-bupropion versus the active comparator sustained-release bupropion in patients 18-65 years old with a diagnosis of major depressive disorder of moderate or greater severity. Patients were randomly assigned to receive either dextromethorphan-bupropion (45 mg/105 mg tablet) or bupropion (105 mg tablet), once daily for the first 3 days and twice daily thereafter, for a total of 6 weeks. The primary endpoint was overall treatment effect on Montgomery-Åsberg Depression Rating Scale (MADRS) score (average of the change from baseline for weeks 1-6), assessed in all randomized patients whose diagnosis and severity were confirmed by an independent assessor and who received at least one dose of study medication and had at least one postbaseline assessment.

RESULTS

Of 97 patients randomized, 17 did not have a confirmed diagnosis and severity based on the independent assessment, resulting in 80 patients in the efficacy population (dextromethorphan-bupropion, N=43; bupropion, N=37). The mean change from baseline in MADRS score over weeks 1-6 (overall treatment effect) was significantly greater with dextromethorphan-bupropion than with bupropion (-13.7 points vs. -8.8 points; least-squares mean difference=-4.9; 95% CI=-3.1, -6.8). MADRS score change with dextromethorphan-bupropion was significantly greater than with bupropion at week 2 and every time point thereafter (week 6: -17.3 vs. -12.1 points; least-squares mean difference=-5.2, 95% CI=-1.1, -9.3). Remission rates were significantly greater with dextromethorphan-bupropion at week 2 and every time point thereafter (week 6: 46.5% vs. 16.2%; least-squares mean difference=30.3%, 95% CI=11.2, 49.4). Response rates (≥50% decrease in MADRS score from baseline) at week 6 were 60.5% with dextromethorphan-bupropion and 40.5% with bupropion (least-squares mean difference=19.9%, 95% CI=-1.6, 41). Most secondary outcomes favored dextromethorphan-bupropion. The most common adverse events with dextromethorphan-bupropion were dizziness, nausea, dry mouth, decreased appetite, and anxiety. Dextromethorphan-bupropion was not associated with psychotomimetic effects, weight gain, or sexual dysfunction.

CONCLUSIONS

In patients with major depression, dextromethorphan-bupropion (AXS-05) significantly improved depressive symptoms compared with bupropion and was generally well tolerated.

Three Naturally-Occurring Psychedelics and Their Significance in the Treatment of Mental Health Disorders

Classical psychedelics represent a family of psychoactive substances with structural similarities to serotonin and affinity for serotonin receptors. A growing number of studies have found that psychedelics can be effective in treating various psychiatric conditions, including post-traumatic stress disorder, major depressive disorder, anxiety, and substance use disorders. Mental health disorders are extremely prevalent in the general population constituting a major problem for the public health. There are a wide variety of interventions for mental health disorders, including pharmacological therapies and psychotherapies, however, treatment resistance still remains a particular challenge in this field, and relapse rates are also quite high. In recent years, psychedelics have become one of the promising new tools for the treatment of mental health disorders. In this review, we will discuss the three classic serotonergic naturally occurring psychedelics, psilocybin, ibogaine, and N, N-dimethyltryptamine, focusing on their pharmacological properties and clinical potential. The purpose of this article is to provide a focused review of the most relevant research into the therapeutic potential of these substances and their possible integration as alternative or adjuvant options to existing pharmacological and psychological therapies.

Design, synthesis and biological evaluation of novel aminopropylcarboxamide derivatives as sigma ligands

In our continuing effort to develop novel sigma receptor (SR) ligands, we present the design, synthesis and binding studies of a small library of aminopropylcarboxamide derivatives, obtained from a deconstruction of the piperidine ring of previously synthesized piperidine-based compounds. The best results were achieved with benzofuran (5c, 5g) and quinoline (5a, 5e) derivatives. These compounds revealed the highest affinity for both receptor subtypes. In particular, the 3,4-dimethoxyphenyl derivatives 5e and 5g showed the highest selectivity profile for S2R, especially the quinoline derivative 5e exhibited a 35-fold higher affinity for S2R subtype. The cytotoxic activity of aforementioned compounds was evaluated against SKBR3 and MCF7 cell lines, widely used for breast cancer studies. Whereas the potency of 5g was similar that of Siramesine and Haloperidol in both cell lines, compounds 5a, 5c and 5e exhibited a potency at least comparable to that of Haloperidol in SKBR3 cells. A molecular modelling evaluation towards the S2R binding site, confirmed the strong interaction of compound 5e thus justifying its highest S2R affinity.

Long COVID, neuropsychiatric disorders, psychotropics, present and future

Long COVID refers to the lingering symptoms which persist or appear after the acute illness. The dominant long COVID symptoms in the two years since the pandemic began (2020-2021) have been depression, anxiety, fatigue, concentration and cognitive impairments with few reports of psychosis. Whether other symptoms will appear later on is not yet known. For example, dopamine-dependent movement disorders generally take many years before first symptoms are seen. Post-stroke depression and anxiety may explain many of the early long COVID cases. Hemorrhagic, hypoxic and inflammatory damages of the central nervous system, unresolved systematic inflammation, metabolic impairment, cerebral vascular accidents such as stroke, hypoxia from pulmonary damages and fibrotic changes are among the major causes of long COVID. Glucose metabolic and hypoxic brain issues likely predispose subjects with pre-existing diabetes, cardiovascular or lung problems to long COVID as well. Preliminary data suggest that psychotropic medications may not be a danger but could instead be beneficial in combating COVID-19 infection. The same is true for diabetes medications such as metformin. Thus, a focus on sigma-1 receptor ligands and glucose metabolism is expected to be useful for new drug development as well as the repurposing of current drugs. The reported protective effects of psychotropics and antihistamines against COVID-19, the earlier reports of reduced number of sigma-1 receptors in post-mortem schizophrenic brains, with many antidepressant and antipsychotic drugs being antihistamines with significant affinity for the sigma-1 receptor, support the role of sigma and histamine receptors in neuroinflammation and viral infections. Literature and data in all these areas are accumulating at a fast rate. We reviewed and discussed the relevant and important literature.

Sigma-1 Receptor Ligands Chlorpromazine and Trifluoperazine Attenuate Ca2+ Responses in Rat Peritoneal Macrophages

Sigma-1 receptors are ubiquitous multifunctional ligand-regulated molecular chaperones in the endoplasmic reticulum membrane with a unique history, structure, and pharmacological profile. Sigma-1 receptors bind ligands of different chemical structure and pharmacological action and modulate a wide range of cellular processes in health and disease, including Ca2+ signaling. To elucidate the involvement of sigma-1 receptors in the processes of Ca2+ signaling in macrophages we studied the effect of sigma-1 receptor ligands, phenothiazine neuroleptics chlorpromazine and trifluoperazine, on Ca2+ responses induced by inhibitors of endoplasmic Ca2+-ATPases thapsigargin and cyclopiazonic acid, as well as by disulfide-containing immunomodulators Glutoxim and Molixan in rat peritoneal macrophages. Using Fura-2AM microfluorimetry we showed for the first time that chlorpromazine and trifluoperazine inhibit both phases of Ca2+ responses induced by Glutoxim, Molixan, thapsigargin, and cyclopiazonic acid in rat peritoneal macrophages. The data obtained indicate the participation of sigma-1 receptors in a complex signaling cascade caused by Glutoxim or Molixan and leading to an increase in intracellular Ca2+ concentration in macrophages. The results also indicate the involvement of sigma-1 receptors in the regulation of store-dependent Ca2+entry in macrophages.

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.

Dissecting the Mechanism of Action of Spiperone-A Candidate for Drug Repurposing for Colorectal Cancer

Simple Summary

Despite advances in primary and adjuvant treatments, approximately 50% of colorectal cancer (CRC) patients still die from recurrence and metastatic disease. Thus, alternative and more effective therapeutic approaches are expected to be developed. Drug repurposing is increasing interest in cancer therapy, as it represents a cheaper and faster alternative strategy to de novo drug synthesis. Psychiatric medications are promising as a new generation of antitumor drugs. Here, we demonstrate that spiperone—a licensed drug for the treatment of schizophrenia—induces apoptosis in CRC cells. Our data reveal that spiperone’s cytotoxicity in CRC cells is mediated by phospholipase C activation, intracellular calcium homeostasis dysregulation, and irreversible endoplasmic reticulum stress induction, resulting in lipid metabolism alteration and Golgi apparatus damage. By identifying new targetable pathways in CRC cells, our findings represent a promising starting point for the design of novel therapeutic strategies for CRC.

Abstract

Approximately 50% of colorectal cancer (CRC) patients still die from recurrence and metastatic disease, highlighting the need for novel therapeutic strategies. Drug repurposing is attracting increasing attention because, compared to traditional de novo drug discovery processes, it may reduce drug development periods and costs. Epidemiological and preclinical evidence support the antitumor activity of antipsychotic drugs. Herein, we dissect the mechanism of action of the typical antipsychotic spiperone in CRC. Spiperone can reduce the clonogenic potential of stem-like CRC cells (CRC-SCs) and induce cell cycle arrest and apoptosis, in both differentiated and CRC-SCs, at clinically relevant concentrations whose toxicity is negligible for non-neoplastic cells. Analysis of intracellular Ca²⁺ kinetics upon spiperone treatment revealed a massive phospholipase C (PLC)-dependent endoplasmic reticulum (ER) Ca²⁺ release, resulting in ER Ca²⁺ homeostasis disruption. RNA sequencing revealed unfolded protein response (UPR) activation, ER stress, and induction of apoptosis, along with IRE1-dependent decay of mRNA (RIDD) activation. Lipidomic analysis showed a significant alteration of lipid profile and, in particular, of sphingolipids. Damage to the Golgi apparatus was also observed. Our data suggest that spiperone can represent an effective drug in the treatment of CRC, and that ER stress induction, along with lipid metabolism alteration, represents effective druggable pathways in CRC.

Sigma-1 receptor activity in primary sensory neurons is a critical driver of neuropathic pain

The Sigma-1 receptor (σ1R) is highly expressed in the primary sensory neurons (PSNs) that are the critical site of initiation and maintenance of pain following peripheral nerve injury. By immunoblot and immunohistochemistry, we observed increased expression of both σ1R and σ1R-binding immunoglobulin protein (BiP) in the lumbar (L) dorsal root ganglia (DRG) ipsilateral to painful neuropathy induced by spared nerve injury (SNI). To evaluate the therapeutic potential of PSN-targeted σ1R inhibition at a selected segmental level, we designed a recombinant adeno-associated viral (AAV) vector expressing a small hairpin RNA (shRNA) against rat σ1R. Injection of this vector into the L4/L5 DRGs induced downregulation of σ1R in DRG neurons of all size groups, while expression of BiP was not affected. This was accompanied by attenuation of SNI-induced cutaneous mechanical and thermal hypersensitivity. Whole-cell current-clamp recordings of dissociated neurons showed that knockdown of σ1R suppressed neuronal excitability, suggesting that σ1R silencing attenuates pain by reversal of injury-induced neuronal hyperexcitability. These findings support a critical role of σ1R in modulating PSN nociceptive functions, and that the nerve injury-induced elevated σ1R activity in the PSNs can be a significant driver of neuropathic pain. Further understanding the role of PSN-σ1R in pain pathology may open routes to exploit this system for DRG-targeted pain therapy.

Synthesis of aminoethyl substituted piperidine derivatives as σ1 receptor ligands with antiproliferative properties

A series of novel σ₁ receptor ligands with a 4‐(2‐aminoethyl)piperidine scaffold was prepared and biologically evaluated. The underlying concept of our project was the improvement of the lipophilic ligand efficiency of previously synthesized potent σ₁ ligands. The key steps of the synthesis comprise the conjugate addition of phenylboronic acid at dihydropyridin‐4(1H)‐ones 7, homologation of the ketones 8 and introduction of diverse amino moieties and piperidine N‐substituents. 1‐Methylpiperidines showed particular high σ₁ receptor affinity and selectivity over the σ₂ subtype, whilst piperidines with a proton, a tosyl moiety or an ethyl moiety exhibited considerably lower σ₁ affinity. Molecular dynamics simulations with per‐residue binding free energy deconvolution demonstrated that different interactions of the basic piperidine‐N‐atom and its substituents (or the cyclohexane ring) with the lipophilic binding pocket consisting of Leu105, Thr181, Leu182, Ala185, Leu186, Thr202 and Tyr206 are responsible for the different σ₁ receptor affinities. Recorded logD_7.4 and calculated clogP values of 4a and 18a indicate low lipophilicity and thus high lipophilic ligand efficiency. Piperidine 4a inhibited the growth of human non‐small cell lung cancer cells A427 to a similar extent as the σ₁ antagonist haloperidol. 1‐Methylpiperidines 20a, 21a and 22a showed stronger antiproliferative effects on androgen negative human prostate cancer cells DU145 than the σ₁ ligands NE100 and S1RA.

Present and future antipsychotic drugs: a systematic review of the putative mechanisms of action for efficacy and a critical appraisal under a translational perspective

Antipsychotics represent the mainstay of schizophrenia pharmacological therapy, and their role has been expanded in the last years to mood disorders treatment. Although introduced in 1952, many years of research were required before an accurate picture of how antipsychotics work began to emerge. Despite the well-recognized characterization of antipsychotics in typical and atypical based on their liability to induce motor adverse events, their main action at dopamine D2R to elicit the "anti-psychotic" effect, as well as the multimodal action at other classes of receptors, their effects on intracellular mechanisms starting with receptor occupancy is still not completely understood. Significant lines of evidence converge on the impact of these compounds on multiple molecular signaling pathways implicated in the regulation of early genes and growth factors, dendritic spine shape, brain inflammation, and immune response, tuning overall the function and architecture of the synapse. Here we present, based on PRISMA approach, a comprehensive and systematic review of the above mechanisms under a translational perspective to disentangle those intracellular actions and signaling that may underline clinically relevant effects and represent potential targets for further innovative strategies in antipsychotic therapy.

The acid sphingomyelinase/ceramide system in COVID-19

Acid sphingomyelinase (ASM) cleaves sphingomyelin into the highly lipophilic ceramide, which forms large gel-like rafts/platforms in the plasma membrane. We showed that SARS-CoV-2 uses these platforms for cell entry. Lowering the amount of ceramide or ceramide blockade due to inhibitors of ASM, genetic downregulation of ASM, anti-ceramide antibodies or degradation by neutral ceramidase protected against infection with SARS-CoV-2. The addition of ceramide restored infection with SARS-CoV-2. Many clinically approved medications functionally inhibit ASM and are called FIASMAs (functional inhibitors of acid sphingomyelinase). The FIASMA fluvoxamine showed beneficial effects on COVID-19 in a randomized prospective study and a prospective open-label real-world study. Retrospective and observational studies showed favorable effects of FIASMA antidepressants including fluoxetine, and the FIASMA hydroxyzine on the course of COVID-19. The ASM/ceramide system provides a framework for a better understanding of the infection of cells by SARS-CoV-2 and the clinical, antiviral, and anti-inflammatory effects of functional inhibitors of ASM. This framework also supports the development of new drugs or the repurposing of "old" drugs against COVID-19.

Chlorpromazine Efficiently Treats the Crisis of Pheochromocytoma: Four Case Reports and Literature Review

Pheochromocytoma multisystem crisis (PMC) is a potentially lethal emergency due to catecholamine secretion. The condition manifests as severe hypertension to intractable cardiogenic shock and has a high mortality rate. This study explored the efficacy and safety of applying chlorpromazine on PMC patients. The study included seven patients (median age, 42 years; range, 14–57 years) diagnosed with pheochromocytoma. Four consecutive PMC patients were admitted to our critical care unit between 2016 and 2020 due to abdominal or waist pain, nausea, and vomiting. Their blood pressure (BP) fluctuated between 200–330/120–200 and 40–70/30–50 mmHg. Chlorpromazine (25 or 50 mg) was injected intramuscularly, followed by continuous intravenous infusion (2–8 mg/h). The patients' BP decreased to 100–150/60–100 mmHg within 1–3 h and stabilized within 3–5 days. Two weeks later, surgical tumor resection was successfully performed in all four patients. Similar clinical outcomes were also obtained in three patients with sporadic PMC reported in the literature who received chlorpromazine treatment, which reduced their BP readings from >200/100 mmHg to 120/70 mmHg. Our observations, combined with sporadic reports, showed that chlorpromazine efficiently controlled PMC. Thus, future studies on the use of chlorpromazine are warranted.

Fluvoxamine for the Early Treatment of SARS-CoV-2 Infection: A Review of Current Evidence

SARS-CoV-2 infection causes COVID-19, which frequently leads to clinical deterioration and/or long-lasting morbidity. Academic and governmental experts throughout the USA met in 2021 to discuss the potential for use of fluvoxamine as early treatment of SARS-CoV-2 infection. Fluvoxamine is a selective serotonin reuptake inhibitor (SSRI) that is a strong sigma-1 receptor agonist, and this may effectively reduce cytokine production, preventing clinical deterioration. This repurposed psychiatric medication has a well-known safety record, is inexpensive, easy to use, and widely available, all of which are advantages during this global COVID-19 pandemic. At the meeting, experts reviewed the existing published literature on the use of fluvoxamine as experimental COVID-19 treatment, as well as prior research on the potential mechanisms for anti-inflammatory effects of fluvoxamine, including for other conditions including sepsis. Investigators shared current trials underway and existing gaps in knowledge. Two randomized controlled trials and one observational study examining the effect of fluvoxamine in COVID-19 treatment have found high efficacy. Four larger randomized clinical trials are currently underway, including three in the USA and Canada. More data are needed on dosing and mechanisms of effect; however, fluvoxamine appears to have substantial potential as a safe and widely available medication that could be repurposed to ameliorate serious COVID-19-related morbidity and mortality. As of April 2021, fluvoxamine was mentioned in the NIH COVID-19 treatment guidelines, although no recommendation is made for or against use. Available data may warrant clinician discussion of fluvoxamine as a treatment option for COVID-19, using shared decision making. Video Abstract.

Research progress in pharmacological activities and structure-activity relationships of tetralone scaffolds as pharmacophore and fluorescent skeleton

The tetralone and tetralone derivatives, as crucial structural scaffolds of potential novel drugs targeted at multiple biological end-points, are normally found in several natural compounds and also, it can be used as parental scaffold and/or intermediate for the synthesis of a series of pharmacologically active compounds with a broad-spectrum of bioactivities including antibacterial, antitumor, CNS effect and so on. Meanwhile, SAR information of its analogues has drawn attentions among medicinal chemists, which could contribute to the further research related to tetralone derivatives aimed at multiple targets. This review encompasses pharmacological activities, SAR analysis and docking study of tetralone and its derivatives, expecting to provide a general retrospect and prospect on tetralone derivatives.

S1R agonist modulates rat platelet eicosanoid synthesis and aggregation

Sigma-1 receptor (S1R) is detected in different cell types and can regulate intracellular signaling pathways. S1R plays a role in the pathomechanism of diseases and the regulation of neurotransmitters. Fluvoxamine can bind to S1R and reduce the serotonin uptake of neurons and platelets. We therefore hypothesized that platelets express S1R, which can modify platelet function. The expression of the SIGMAR1 gene in rat platelets was examined with a reverse transcription polymerase chain reaction and a quantitative polymerase chain reaction. The receptor was also visualized by immunostaining and confocal laser scanning microscopy. The effect of S1R agonist PRE-084 on the eicosanoid synthesis of isolated rat platelets and ADP- and AA-induced platelet aggregation was examined. S1R was detected in rat platelets both at gene and protein levels. Pretreatment with PRE-084 of resting platelets induced elevation of eicosanoid synthesis. The rate of elevation in thromboxane B₂ and prostaglandin D₂ synthesis was similar, but the production of prostaglandin E₂ was higher. The concentration-response curve showed a sigmoidal form. The most effective concentration of the agonist was 2 µM. PRE-084 increased the quantity of cyclooxygenase-1 as detected by ELISA. PRE-084 also elevated the ADP- and AA-induced platelet aggregation. S1R of platelets might regulate physiological or pathological functions.

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.

Tumor-Associated Fibroblast-Targeting Nanoparticles for Enhancing Solid Tumor Therapy: Progress and Challenges

Even though nanoparticle drug delivery systems (nanoDDSs) have improved antitumor efficacy by delivering more drugs to tumor sites compared to free and unencapsulated therapeutics, achieving satisfactory distribution and penetration of nanoDDSs inside solid tumors, especially in stromal fibrous tumors, remains challenging. As one of the most common stromal cells in solid tumors, tumor-associated fibroblasts (TAFs) not only promote tumor growth and metastasis but also reduce the drug delivery efficiency of nanoparticles through the tumor's inherent physical and physiological barriers. Thus, TAFs have been emerging as attractive targets, and TAF-targeting nanotherapeutics have been extensively explored to enhance the tumor delivery efficiency and efficacy of various anticancer agents. The purpose of this Review is to opportunely summarize the underlying mechanisms of TAFs on obstructing nanoparticle-mediated drug delivery into tumors and discuss the current advances of a plethora of nanotherapeutic approaches for effectively targeting TAFs.

Chemoenzymatic synthesis of 2,6-disubstituted tetrahydropyrans with high σ1 receptor affinity, antitumor and analgesic activity

1,3-Dioxanes 1 and cyclohexanes 2 bearing a phenyl ring and an aminoethyl moiety in 1,3-relationship to each other represent highly potent σ1 receptor antagonists. In order to increase the chemical stability of the acetalic 1,3-dioxanes 1 and the polarity of the cyclohexanes 2, tetrahydropyran derivatives 3 equipped with the same substituents were designed, synthesized and pharmacologically evaluated. The key step of the synthesis was a lipase-catalyzed enantioselective acetylation of the alcohol (R)-5 leading finally to enantiomerically pure test compounds 3a-g. With respect to σ1 receptor affinity and selectivity over a broad range of related (σ2, PCP binding site) and further targets, the enantiomeric benzylamines 3a and cyclohexylmethylamines 3b represent the most promising drug candidates of this series. However, the eudismic ratio for σ1 binding is only in the range of 2.5-3.3. Classical molecular dynamics (MD) simulations confirmed the same binding pose for both the tetrahydropyran 3 and cyclohexane derivatives 2 at the σ1 receptor, according to which: i) the protonated amino moiety of (2S,6R)-3a engages the same key polar interactions with Glu172 (ionic) and Phe107 (π-cation), ii) the lipophilic parts of (2S,6R)-3a are hosted in three hydrophobic regions of the σ1 receptor, and iii) the O-atom of the tetrahydropyran derivatives 3 does not show a relevant interaction with the σ1 receptor. Further in silico evidences obtained by the application of free energy perturbation and steered MD techniques fully supported the experimentally observed difference in receptor/ligand affinities. Tetrahydropyrans 3 require a lower dissociative force peak than cyclohexane analogs 2. Enantiomeric benzylamines 3a and cyclohexylmethylamines 3b were able to inhibit the growth of the androgen negative human prostate cancer cell line DU145. The cyclohexylmethylamine (2S,6R)-3b showed the highest σ1 affinity (Ki(σ1) = 0.95 nM) and the highest analgesic activity in vivo (67%).

Development of New Benzylpiperazine Derivatives as σ1 Receptor Ligands with in Vivo Antinociceptive and Anti-Allodynic Effects

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

Histamine 3 receptor inverse agonist Samelisant (SUVN-G3031): Pharmacological characterization of an investigational agent for the treatment of cognitive disorders

BACKGROUND

Central histamine H3 receptors are a family of presynaptic auto and heteroreceptors. Blockade of the presynaptic H3 receptors activates the downstream pathway(s) involved in the processes of learning and memory, making it a potential therapeutic option for ameliorating cognitive dysfunction. Samelisant (SUVN-G3031) is a potent and selective inverse agonist at the H3 receptors.

AIM

The aim of this research is to study the effects of Samelisant in diverse animal models of cognitive functions.

METHODS

The effects of Samelisant on cognitive functions were studied using social recognition, object recognition and Morris water maze tasks. Neurochemical and electrophysiological effects of Samelisant were monitored using microdialysis and electroencephalography techniques.

RESULTS

Samelisant showed procognitive effects in diverse animal models of cognition at doses ranging from 0.3 to 3 mg/kg, per os (p.o.) (social recognition and object recognition task). Samelisant significantly increased the brain acetylcholine levels in the cortex at doses of 10 and 20 mg/kg, p.o. In the Morris water maze task, combined administration of suboptimal doses of Samelisant and donepezil resulted in procognitive effects significantly larger than the either treatment. Similarly, Samelisant significantly potentiated the effects of donepezil on pharmacodynamic biomarkers of cognition i.e. acetylcholine levels in brain and neuronal theta oscillations.

CONCLUSION

Samelisant may have potential utility in the treatment of cognitive deficits associated with hypocholinergic state.