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.

From Plant to Chemistry: Sources of Antinociceptive Non-Opioid Active Principles for Medicinal Chemistry and Drug Design

Pain is associated with many health problems and a reduced quality of life and has been a common reason for seeking medical attention. Several therapeutics are available on the market, although side effects, physical dependence, and abuse limit their use. As the process of pain transmission and modulation is regulated by different peripheral and central mechanisms and neurotransmitters, medicinal chemistry continues to study novel ligands and innovative approaches. Among them, natural products are known to be a rich source of lead compounds for drug discovery due to their chemical structural variety and different analgesic mechanisms. Numerous studies suggested that some chemicals from medicinal plants could be alternative options for pain relief and management. Previously, we conducted a literature search aimed at identifying natural products interacting either directly or indirectly with opioid receptors. In this review, instead, we have made an excursus including active ingredients derived from plants whose mechanism of action appears from the literature to be other than the modulation of the opioid system. These substances could, either by themselves or through synthetic and/or semi-synthetic derivatives, be investigated in order to improve their pharmacokinetic characteristics and could represent a valid alternative to the opioid approach to pain therapy. They could also be the basis for the study of new mechanisms of action in the approach to this complex and disabling pathology.

Discovery of a novel series of potent carbonic anhydrase inhibitors with selective affinity for μ Opioid receptor for Safer and long-lasting analgesia

In this study, we investigated the development of dual-targeted ligands that bind to both μ-opioid receptor (MOR) and carbonic anhydrase (CA) enzymes, using fentanyl structure as a template. We synthesized and evaluated 21 novel compounds with dual-targeted affinity identifying the lead candidate compound 8, showing selective affinity for MOR and potent inhibition of several cytosolic CA isoforms. By means of repeated treatment of 3 daily administrations for 17 days, fentanyl (0.1 mg/kg, subcutaneously) led to tolerance development, pain threshold alterations and withdrawal symptoms in CD-1 mice, as well as astrocyte and microglia activation in the dorsal horn of the lumbar spinal cord. In contrast, compound 8 (0.32 mg/kg s.c.) maintained stable during days its analgesic effect at the higher dose tested with fewer withdrawal symptoms, allodynia development and glial cells activation. Our results suggest that targeting both MOR and CA enzymes can lead to the development of new class of potent analgesic agents with fewer side effects and reduced tolerance development. Further studies are needed to explore the potential mechanisms underlying these effects and to further optimize the therapeutic potential of these compounds.

Discovery of first novel sigma/HDACi dual-ligands with a potent in vitro antiproliferative activity

Designing and discovering compounds for dual-target inhibitors is challenging to synthesize new, safer, and more efficient drugs than single-target drugs, especially to treat multifactorial diseases such as cancer. The simultaneous regulation of multiple targets might represent an alternative synthetic approach to optimize patient compliance and tolerance, minimizing the risk of target-based drug resistance due to the modulation of a few targets. To this end, we conceived for the first time the design and synthesis of dual-ligands σR/HDACi to evaluate possible employment as innovative candidates to address this complex disease. Among all synthesized compounds screened for several tumoral cell lines, compound 6 (Kiσ1R = 38 ± 3.7; Kiσ2R = 2917 ± 769 and HDACs IC50 = 0.59 µM) is the most promising candidate as an antiproliferative agent with an IC50 of 0.9 µM on the HCT116 cell line and no significant toxicity to normal cells. Studies of molecular docking, which confirmed the affinity over σ1R and a pan-HDACs inhibitory behavior, support a possible balanced affinity and activity between both targets.

From Plant to Chemistry: Sources of Active Opioid Antinociceptive Principles for Medicinal Chemistry and Drug Design

Pain continues to be an enormous global health challenge, with millions of new untreated or inadequately treated patients reported annually. With respect to current clinical applications, opioids remain the mainstay for the treatment of pain, although they are often associated with serious side effects. To optimize their tolerability profiles, medicinal chemistry continues to study novel ligands and innovative approaches. Among them, natural products are known to be a rich source of lead compounds for drug discovery, and they hold potential for pain management. Traditional medicine has had a long history in clinical practice due to the fact that nature provides a rich source of active principles. For instance, opium had been used for pain management until the 19th century when its individual components, such as morphine, were purified and identified. In this review article, we conducted a literature survey aimed at identifying natural products interacting either directly with opioid receptors or indirectly through other mechanisms controlling opioid receptor signaling, whose structures could be interesting from a drug design perspective.

New Insights into the Opioid Analgesic Profile of cis-(-)-N-Normetazocine-derived Ligands

In this work, we report on the in vitro and in vivo pharmacological properties of LP1 analogs to complete the series of structural modifications aimed to generate compounds with improved analgesia. To do that, the phenyl ring in the N-substituent of our lead compound LP1 was replaced by an electron-rich or electron-deficient ring and linked through a propanamide or butyramide spacer at the basic nitrogen of the (-)-cis-N-normetazocine skeleton. In radioligand binding assays, compounds 3 and 7 were found to display nanomolar binding affinity for the μ opioid receptor (MOR) (K_i = 5.96 ± 0.08 nM and 1.49 ± 0.24 nM, respectively). In the mouse vas deferens (MVD) assay, compound 3 showed an antagonist effect against DAMGO ([D-Ala², N-MePhe⁴, Gly-ol]-enkephalin), a highly selective MOR prototype agonist, whereas compound 7 produced naloxone reversible effect at MOR. Moreover, compound 7, as potent as LP1 and DAMGO at MOR, was able to reduce thermal and inflammatory pain assessed by the mouse tail-flick test and rat paw pressure thresholds (PPTs) measured by a Randall-Selitto test.

Synthesis, Computational Insights, and Evaluation of Novel Sigma Receptors Ligands

The development of diazabicyclo[4.3.0]nonane and 2,7-diazaspiro[3.5]nonane derivatives as sigma receptors (SRs) ligands is reported. The compounds were evaluated in S1R and S2R binding assays, and modeling studies were carried out to analyze the binding mode. The most notable compounds, 4b (AD186, K_iS1R = 2.7 nM, K_iS2R = 27 nM), 5b (AB21, K_iS1R = 13 nM, K_iS2R = 102 nM), and 8f (AB10, K_iS1R = 10 nM, K_iS2R = 165 nM), have been screened for analgesic effects in vivo, and their functional profile was determined through in vivo and in vitro models. Compounds 5b and 8f reached the maximum antiallodynic effect at 20 mg/kg. The selective S1R agonist PRE-084 completely reversed their action, indicating that the effects are entirely dependent on the S1R antagonism. Conversely, compound 4b sharing the 2,7-diazaspiro[3.5]nonane core as 5b was completely devoid of antiallodynic effect. Interestingly, compound 4b fully reversed the antiallodynic effect of BD-1063, indicating that 4b induces an S1R agonistic in vivo effect. The functional profiles were confirmed by the phenytoin assay. Our study might establish the importance of 2,7-diazaspiro[3.5]nonane core for the development of S1R compounds with specific agonist or antagonist profile and the role of the diazabicyclo[4.3.0]nonane in the development of novel SR ligands.

Design, synthesis, in vitro evaluation, and molecular modeling studies of N-substituted benzomorphans, analogs of LP2, as novel MOR ligands

6,7-Benzomorphans have been investigated in medicinal chemistry for developing new drugs. This nucleus could be considered a versatile scaffold. The physicochemical properties of benzomorphan N-substituent are crucial in achieving a definite pharmacological profile at opioid receptors. Thus, the dual-target MOR/DOR ligands LP1 and LP2 were obtained through N-substituent modifications. Specifically, LP2, bearing as N-substituent the (2R/S)-2-methoxy-2- phenylethyl group, is a dual-target MOR/DOR agonist and is successful in animal models of inflammatory and neuropathic pain. To obtain new opioid ligands, we focused on the design and synthesis of LP2 analogs. First, the 2-methoxyl group of LP2 was replaced by an ester or acid functional group. Then, spacers of different lengths were introduced at N-substituent. In-vitro, their affinity profile versus opioid receptors has been performed through competition binding assays. Molecular modeling studies were conducted to deeply analyze the binding mode and the interactions between the new ligands and all opioid receptors.

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.

The Multimodal MOPr/DOPr Agonist LP2 Reduces Allodynia in Chronic Constriction Injured Rats by Rescue of TGF-β1 Signalling

Neuropathic pain is one of the most disabling forms of chronic pain and it is characterized by hyperalgesia and allodynia linked to an aberrant processing of pain transmission and to neuroinflammation. Transforming growth factor-β1 (TGF-β1) is an anti-inflammatory cytokine, which protects against neuroinflammation. It has been demonstrated that TGF-β1 and opioid receptors signalling crosstalk results in an improvement of endogenous opioid analgesia, but it is not known whether mu opioid peptide receptor (MOPr) or delta opioid peptide receptor (DOPr) agonists can positively modulate TGF-β1 pathway. In the present study, we examined the correlation between anti-allodynic effect of LP2, a dual-target MOPr/DOPr agonist, and TGF-β1 signalling in the chronic constriction injury (CCI) model. We detected a significant decrease of active TGF-β1 and of its type II receptor TGFβ-R2 levels in the spinal cord from CCI rats and a selective deficit of TGF-β1 in microglia cells both at days 11 and 21 post-ligature, as assessed by immunofluorescence analysis. LP2, when administered from the 11 days post-ligature to 21 days, was able to reduce CCI-induced mechanical allodynia by rescue of TGF-β1 and TGFβ-R2 levels. Our data suggest that the rescue of TGF-β1 signalling by dual-target MOPr/DOPr agonist LP2 could be mediated by DOPr activation in spinal microglia, thus the dual-target approach could represent a novel pharmacological approach to increase the analgesic efficacy of MOPr agonists.

LP1 and LP2: Dual-Target MOPr/DOPr Ligands as Drug Candidates for Persistent Pain Relief

Although persistent pain is estimated to affect about 20% of the adult population, current treatments have poor results. Polypharmacology, which is the administration of more than one drug targeting on two or more different sites of action, represents a prominent therapeutic approach for the clinical management of persistent pain. Thus, in the drug discovery process the "one-molecule-multiple targets" strategy nowadays is highly recognized. Indeed, multitarget ligands displaying a better antinociceptive activity with fewer side effects, combined with favorable pharmacokinetic and pharmacodynamic characteristics, have already been shown. Multitarget ligands possessing non-opioid/opioid and opioid/opioid mechanisms of action are considered as potential drug candidates for the management of various pain conditions. In particular, dual-target MOPr (mu opioid peptide receptor)/DOPr (delta opioid peptide receptor) ligands exhibit an improved antinociceptive profile associated with a reduced tolerance-inducing capability. The benzomorphan-based compounds LP1 and LP2 belong to this class of dual-target MOPr/DOPr ligands. In the present manuscript, the structure-activity relationships and the pharmacological fingerprint of LP1 and LP2 compounds as suitable drug candidates for persistent pain relief is described.

Intercellular communication and ion channels in neuropathic pain chronicization

BACKGROUND

Neuropathic pain is caused by primary lesion or dysfunction of either peripheral or central nervous system. Due to its complex pathogenesis, often related to a number of comorbidities, such as cancer, neurodegenerative and neurovascular diseases, neuropathic pain still represents an unmet clinical need, lacking long-term effective treatment and complex case-by-case approach.

AIM AND METHODS

We analyzed the recent literature on the role of selective voltage-sensitive sodium, calcium and potassium permeable channels and non-selective gap junctions (GJs) and hemichannels (HCs) in establishing and maintaining chronic neuropathic conditions. We finally focussed our review on the role of extracellular microenvironment modifications induced by resident glial cells and on the recent advances in cell-to-cell and cell-to-extracellular environment communication in chronic neuropathies.

CONCLUSION

In this review, we provide an update on the current knowledge of neuropathy chronicization processes with a focus on both neuronal and glial ion channels, as well as on channel-mediated intercellular communication.

Novel N-Substituted Benzomorphan-Based Compounds: From MOR-Agonist/DOR-Antagonist to Biased/Unbiased MOR Agonists

Modifications at the basic nitrogen of the benzomorphan scaffold allowed the development of compounds able to segregate physiological responses downstream of the receptor signaling, opening new possibilities in opioid drug development. Alkylation of the phenyl ring in the N-substituent of the MOR-agonist/DOR-antagonist LP1 resulted in retention of MOR affinity. Moreover, derivatives 7a, 7c, and 7d were biased MOR agonists toward ERK1,2 activity stimulation, whereas derivative 7e was a low potency MOR agonist on adenylate cyclase inhibition. They were further screened in the mouse tail flick test and PGE2-induced hyperalgesia and drug-induced gastrointestinal transit.

Lipid Nanoparticle Inclusion Prevents Capsaicin-Induced TRPV1 Defunctionalization

BACKGROUND

Capsaicin (CPS) is a highly selective agonist of the transient receptor potential vanilloid type 1 (TRPV1) with a nanomolar affinity. High doses or prolonged exposure to CPS induces TRPV1 defunctionalization and, although this effect is currently used for the treatment of thermal hyperalgesia in chronic pain conditions, it is responsible of detrimental effects, such as denervation of sensory fibers. The aim of the present study was to formulate CPS loaded lipid nanocarriers (CPS-LN) in order to optimize CPS release, thus preventing TRPV1 internalization and degradation.

METHODS

CPS-LNs were formulated and characterized by in vitro studies. The activation of TRPV1 receptors after CPS-LN administration was evaluated by measuring spontaneous pain that was induced by local injection into the plantar surface of the mouse hind-paw. Moreover, the expression of TRPV1 in the skin was evaluated by western blot analysis in CPS-LN injected mice and then compared to a standard CPS solution (CPS-STD).

RESULTS

CPS inclusion in LN induced a lower pain response when compared to CPS-STD; further, it prevented TRPV1 down-regulation in the skin, while CPS-STD induced a significant reduction of TRPV1 expression.

CONCLUSIONS

Drug encapsulation in lipid nanoparticles produced an optimization of CPS release, thus reducing mice pain behavior and avoiding the effects that are caused by TRPV1 defunctionalization related to a prolonged activation of this receptor.

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.

Progress in the development of more effective and safer analgesics for pain management

Opioid analgesics have been used for thousands of years in the treatment of pain and related disorders, and have become among the most widely prescribed medications. Among opioid analgesics, mu opioid receptor (MOR) agonists are the most commonly used and are indicated for acute and chronic pain management. However, their use results in a plethora of well-described side-effects. From selective delta opioid receptor (DOR) and kappa opioid receptor (KOR) agonists to multitarget MOR/DOR and MOR/KOR ligands, medicinal chemistry provided different approaches aimed at the development of opioid analgesics with an improved pharmacological and tolerability fingerprint. The emergent medicinal chemistry strategy to develop ameliorated opioid analgesics is based upon the concept that functional selectivity for G-protein signalling is necessary for the therapeutic effect, whether β-arrestin recruitment is mainly responsible for the manifestation of side effects, including the development of tolerance after repeated administrations. This review summarises most relevant biased MOR, DOR, KOR and multitarget MOR/DOR ligands synthesised in the last decade and their pharmacological profile in "in vitro" and "in vivo" studies. Such biased ligands could have a significant impact on modern drug discovery and represent a new strategy for the development of better-tolerated drug candidates.

Rescue of Noradrenergic System as a Novel Pharmacological Strategy in the Treatment of Chronic Pain: Focus on Microglia Activation

Different types of pain can evolve toward a chronic condition characterized by hyperalgesia and allodynia, with an abnormal response to normal or even innocuous stimuli, respectively. A key role in endogenous analgesia is recognized to descending noradrenergic pathways that originate from the locus coeruleus and project to the dorsal horn of the spinal cord. Impairment of this system is associated with pain chronicization. More recently, activation of glial cells, in particular microglia, toward a pro-inflammatory state has also been implicated in the transition from acute to chronic pain. Both α2- and β2-adrenergic receptors are expressed in microglia, and their activation leads to acquisition of an anti-inflammatory phenotype. This review analyses in more detail the interconnection between descending noradrenergic system and neuroinflammation, focusing on drugs that, by rescuing the noradrenergic control, exert also an anti-inflammatory effect, ultimately leading to analgesia. More specifically, the potential efficacy in the treatment of neuropathic pain of different drugs will be analyzed. On one side, drugs acting as inhibitors of the reuptake of serotonin and noradrenaline, such as duloxetine and venlafaxine, and on the other, tapentadol, inhibitor of the reuptake of noradrenaline, and agonist of the µ-opioid receptor.

Simultaneous Activation of Mu and Delta Opioid Receptors Reduces Allodynia and Astrocytic Connexin 43 in an Animal Model of Neuropathic Pain

Neuropathic pain is a chronic condition triggered by lesions to the somatosensory nervous system in which pain stimuli occur spontaneously or as pathologically amplified responses. In this scenario, the exchange of signaling molecules throughout cell-to-cell and cell-to-extracellular environment communications plays a key role in the transition from acute to chronic pain. As such, connexin 43 (Cx43), the core glial gap junction and hemichannel-forming protein, is considered a triggering factor for disease chronicization in the central nervous system (CNS). Drugs targeting μ opioid receptors (MOR) are currently used for moderate to severe pain conditions, but their use in chronic pain is limited by the tolerability profile. δ opioid receptors (DOR) have become attractive targets for the treatment of persistent pain and have been associated with the inhibition of pain-sustaining factors. Moreover, it has been shown that simultaneous targeting of MOR and DOR leads to an improved pharmacological fingerprint. Herein, we aimed to study the effects of the benzomorphan ligand LP2, a multitarget MOR/DOR agonist, in an experimental model of neuropathic pain induced by the unilateral sciatic nerve chronic constriction injury (CCI) on male Sprague-Dawley rats. Results showed that LP2 significantly ameliorated mechanical allodynia from the early phase of treatment up to 21 days post-ligatures. We additionally showed that LP2 prevented CCI-induced Cx43 alterations and pro-apoptotic signaling in the CNS. These findings increase the knowledge of neuropathic pain development and the role of spinal astrocytic Cx43, suggesting new approaches for the treatment of neuropathic pain.

Synthesis, in vitro and in vivo characterization of new benzoxazole and benzothiazole-based sigma receptor ligands

A new set of 5-chlorobenzoxazole- and 5-chlorobenzothiazole-based derivatives containing the azepane ring as a basic moiety was designed, synthesized and evaluated through binding assays to measure their affinity and selectivity towards σ₁ and σ₂ receptors. Compounds 19, 22 and 24, with a four units spacer between the bicyclic scaffold and the azepane ring, showed nanomolar affinity towards both receptor subtype and the best K_i values (K_i σ₁ = 1.27, 2.30, and 0.78 and K_i σ₂ = 7.9, 3.8, and 7.61 nM, respectively). Evaluation of cytotoxic and apoptotic effects in MCF-7 human cancer cells was useful to assess σ₂ receptor activity, while an in vivo mice model of inflammatory pain allowed to analyze σ₁ receptor pharmacological properties. In vitro and in vivo results suggested that compound 19 is a σ₁/σ₂ agonist, compound 24 a σ₁ antagonist/σ₂ agonist, whereas compound 22 might act as σ₁ antagonist/σ₂ partial agonist. Due to their pharmacological profile, a potential therapeutic application in cancer of aforesaid novel σ₁/σ₂ receptor ligands, especially 22 and 24, is proposed.

Neuroprotective effects of Rosmarinus officinalis L. extract in oxygen glucose deprivation (OGD)-injured human neural-like cells

Rosmarinus officinalis L. (RO), an aromatic plant used as food condiment and in traditional medicine, exerts numerous beneficial properties including antioxidant, analgesic and neuroprotective effects. Onset and progression of homeostatic imbalances observed in the early phases of a number of neurodegenerative diseases, have been associated with a gap junction (GJ)-dependent increased membrane permeability and alterations of connexins (Cxs), including Cx43. Here, we evaluate spray-dried RO extract (SDROE)-mediated effects on cell viability, apoptosis and Cx43-based intercellular communication using human SH-SY5Y neuron-like and human A-172 glial-like cells in an in vitro model of oxygen glucose deprivation (OGD) injury. We found that SDROE exerts a protective action in OGD-injured cells, increasing cell viability and metabolic turnover and decreasing Cx43-based cell coupling. These data suggest that SDROE-mediated Cx43 reduction may be the molecular basis for its beneficial effects to be exploited for preventive treatment against the risk of some neurodegenerative disorders.

Simultaneous targeting of MOR/DOR: A useful strategy for inflammatory pain modulation

Development of new analgesics endowed with mu/delta opioid receptor (MOR/DOR) activity represents a promising alternative to MOR selective compounds because of their better therapeutic and tolerability profile. Lately, we have synthetized the MOR/DOR agonist LP2 that showed a long lasting antinociceptive activity in the tail flick test, an acute pain model. Here, we investigate whether LP2 is also effective in the mouse formalin test, a model of inflammatory pain sustained by mechanisms of central sensitization. Moreover, we evaluated a possible peripheral component of LP2 analgesic activity. Different doses of LP2 were tested after either intraperitoneal (i.p.) or intraplantar (i.pl.) administration. LP2 (0.75-1.00 mg/kg, i.p.), dose-dependently, counteracted both phases of the formalin test after i.p. administration. The analgesic activity of LP2 (0.75-1.00 mg/kg) was completely blocked by a pretreatment with the opioid antagonist naloxone (3 mg/kg, i.p.). Differently, the pretreatment with naloxone methiodide (5 mg/kg, i.p.), a peripherally restricted opioid antagonist, completely blocked the lower analgesic dose of LP2 (0.75 mg/kg) but only partially relieved the antinociceptive effects of LP2 at the dose of 1.00 mg/kg, thus revealing a peripheral analgesic component of LP2. I.pl. injections of LP2 (10-20 μg/10 μl) were also performed to investigate a possible effect of LP2 on peripheral nerve terminals. Nociceptive sensitization, which occur both at peripheral and central level, is a fundamental step for pain chronicization, thus LP2 is a promising drug for pain conditions characterized by nociceptive sensitization.

Tumor necrosis factor-related apoptosis-inducing ligand reduces the expression of the neuroprotective Na+ /Ca2+ exchanger isoform NCX3 in human neuroblastoma SH-SY5Y cells

Tumor necrosis factor-related apoptosis-inducing ligand (TRAIL), a cytokine belonging to the TNF superfamily, is regarded as a mediator of neurotoxicity. The constitutively expressed ion exchanger Na⁺ /Ca²⁺ exchanger isoform-3 (NCX3) has been shown to protect neurons from injury. Its expression is induced by nerve growth factor (NGF) through activation of its tyrosine kinase receptor trkA. The latter, in turn, activates downstream kinases, such as extracellular signal-regulated kinase (ERK) and the survival-related kinase protein kinase B (AKT). Here, we verified whether TRAIL could influence the expression of NCX3 via modulation of the NGF/trkA system. Differentiated human neuroblastoma SH-SY5Y cells were incubated with TRAIL and, subsequently, the expression of the NCX3 protein was studied at different times by means of western blot analysis. Then, the expression of the phosphorylated forms of either trkA, ERK or AKT was analyzed at identical intervals. Western blot analysis revealed that the expression of NCX3 protein decreased in a time-dependent fashion in SH-SY5Y cells treated with TRAIL, to reach its minimum at 48 h. On the other hand, p-trkA, p-ERK, and p-AKT expression was increased in cells treated with TRAIL after 6 and 16 h; then it declined to nearly undetectable levels after 48 h. Results indicate that the increase in TRAIL expression occurring during neuronal damage may be responsible of NCX3 down-regulation and weakens its neuroprotective effects. The TRAIL system could thus represent a potential target for treatment of neuronal damage characterized by NCX3 function impairment.

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

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

In Vitro Evaluation of Sunscreen Safety: Effects of the Vehicle and Repeated Applications on Skin Permeation from Topical Formulations

The evaluation of UV-filter in vitro percutaneous absorption allows the estimation of the systemic exposure dose (SED) and the margin of safety (MoS) of sunscreen products. As both the vehicle and pattern of application may affect sunscreen safety and efficacy, we evaluated in vitro release and skin permeation of two widely used UV-filters, octylmethoxycinnamate (OMC) and butylmethoxydibenzoylmethane (BMBM) from topical formulations with different features (oil in water (O/W) emulsions with different viscosity, water in oil (W/O) emulsion, oils with different lipophilicity). To mimic in-use conditions, we carried out experiments repeating sunscreen application on the skin surface for three consecutive days. BMBM release from all these vehicles was very low, thus leading to poor skin permeation. The vehicle composition significantly affected OMC release and skin permeation, and slight increases of OMC permeation were observed after repeated applications. From skin permeation data, SED and MoS values of BMBM and OMC were calculated for all the investigated formulations after a single application and repeated applications. While MoS values of BMBM were always well beyond the accepted safety limit, the safety of sunscreen formulations containing OMC may depend on the vehicle composition and the application pattern.

Idebenone: Novel Strategies to Improve Its Systemic and Local Efficacy

The key role of antioxidants in treating and preventing many systemic and topical diseases is well recognized. One of the most potent antioxidants available for pharmaceutical and cosmetic use is Idebenone (IDE), a synthetic analogue of Coenzyme Q10. Unfortunately, IDE's unfavorable physicochemical properties such as poor water solubility and high lipophilicity impair its bioavailability after oral and topical administration and prevent its parenteral use. In recent decades, many strategies have been proposed to improve IDE effectiveness in the treatment of neurodegenerative diseases and skin disorders. After a brief description of IDE potential therapeutic applications and its pharmacokinetic and pharmacodynamic profile, this review will focus on the different approaches investigated to overcome IDE drawbacks, such as IDE incorporation into different types of delivery systems (liposomes, cyclodextrins, microemulsions, self-micro-emulsifying drug delivery systems, lipid-based nanoparticles, polymeric nanoparticles) and IDE chemical modification. The results of these studies will be illustrated with emphasis on the most innovative strategies and their future perspectives.

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

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

Connexins in the Central Nervous System: Physiological Traits and Neuroprotective Targets

Cell-to-cell interaction and cell-to-extracellular environment communication are emerging as new therapeutic targets in neurodegenerative disorders. Dynamic expression of connexins leads to distinctive hemichannels and gap junctions, characterized by cell-specific conduction, exchange of stimuli or metabolites, and particular channel functions. Herein, we briefly reviewed classical physiological traits and functions of connexins, hemichannels, and gap junctions, in order to discuss the controversial role of these proteins and their mediated interactions during neuroprotection, with a particular focus on Cx43-based channels. We pointed out the contribution of connexins in neural cells populations during neurodegenerative processes to explore potential neuroprotective therapeutic applications.

Resveratrol-Loaded Lipid Nanocarriers: Correlation between In Vitro Occlusion Factor and In Vivo Skin Hydrating Effect

Lipid nanocarriers show occlusive properties that may be related to their ability to improve skin hydration. The aim of this work was to evaluate the relationship between in vitro occlusion factor and in vivo skin hydration for three types of lipid nanocarriers: nanoemulsions (NEs), solid lipid nanoparticles (SLNs) and nanostructured lipid carriers (NLCs). These lipid nanocarriers were loaded with trans-resveratrol (RSV) and incorporated in gel vehicles. In vitro occlusion factor was in the order SLNs > NLCs > NEs. Gels containing unloaded or RSV loaded lipid nanocarriers were applied on the back of a hand of 12 healthy volunteers twice a day for one week, recording skin hydration changes using the instrument Soft Plus. An increase of skin hydration was observed for all lipid nanocarriers (SLNs > NLCs > NEs). RSV loading into these nanocarriers did not affect in vitro and in vivo lipid nanocarriers effects. A linear relationship (r² = 0.969) was observed between occlusion factor and in vivo increase of skin hydration. Therefore, the results of this study showed the feasibility of using the occlusion factor to predict in vivo skin hydration resulting from topical application of different lipid nanocarriers loading an active ingredient with no inherent hydrating activity.

Rosemary Essential Oil-Loaded Lipid Nanoparticles: In Vivo Topical Activity from Gel Vehicles

Although rosemary essential oil (EO) shows many biological activities, its topical benefits have not been clearly demonstrated. In this work, we assessed the effects on skin hydration and elasticity of rosemary EO after topical application via gel vehicles in human volunteers. To improve its topical efficacy, rosemary EO was loaded into lipid nanoparticles (NLCs) consisting of cetyl palmitate as a solid lipid, and non-ionic surfactants. Such NLCs were prepared using different ratios of EO/solid lipid and those containing EO 3% w/w and cetyl pamitate 7% w/w were selected for in vivo studies, showing the best technological properties (small particle size, low polydispersity index and good stability). Gels containing free EO or EO-loaded NLCs were applied on the hand skin surface of ten healthy volunteers twice a day for one week. Skin hydration and elasticity changes were recorded using the instrument Soft Plus. Gels containing EO-loaded NLCs showed a significant increase in skin hydration in comparison with gels containing free EO. Skin elasticity increased, as well, although to a lesser extent. The results of this study point out the usefulness of rosemary EO-loaded NLCs for the treatment of cutaneous alterations involving loss of skin hydration and elasticity.

Chronic Treatment with Fluoxetine Induces Sex-Dependent Analgesic Effects and Modulates HDAC2 and mGlu2 Expression in Female Mice

Gender and sex differences in pain recognition and drug responses have been reported in clinical trials and experimental models of pain. Among antidepressants, contradictory results have been observed in patients treated with selective serotonin reuptake inhibitors (SSRIs). This study evaluated sex differences in response to the SSRI fluoxetine after chronic administration in the mouse formalin test. Adult male and female CD1 mice were intraperitoneally injected with fluoxetine (10 mg/kg) for 21 days and subjected to pain assessment. Fluoxetine treatment reduced the second phase of the formalin test only in female mice without producing behavioral changes in males. We also observed that fluoxetine was able to specifically increase the expression of metabotropic glutamate receptor type-2 (mGlu2) in females. Also a reduced expression of the epigenetic modifying enzyme, histone deacetylase 2 (HDAC2), in dorsal root ganglia (DRG) and dorsal horn (DH) together with an increase histone 3 acetylation (H3) level was observed in females but not in males. With this study we provide evidence that fluoxetine induces sex specific changes in HDAC2 and mGlu2 expression in the DH of the spinal cord and in DRGs and suggests a molecular explanation for the analgesic effects in female mice.

Wilms' tumor gene 1 silencing inhibits proliferation of human osteosarcoma MG-63 cell line by cell cycle arrest and apoptosis activation

Wilms’ tumor gene 1 (WT1) plays complex roles in tumorigenesis, acting as tumor suppressor gene or an oncogene depending on the cellular context. A high WT1 expression level was described in various types of human bone and soft-tissue sarcomas, including osteosarcoma (OS), but its function in carcinogenesis is not yet well understood. This study investigated WT1 both in human OS tissues and in human OS MG-63 cell line in which WT1 gene is up-regulated. The results demonstrated that WT1 is expressed in 50% of human OS cases. WT1-silenced MG-63 cells showed deregulation of proteins of cell cycle and down-regulation of PI3K/AKT pathway. Induction of apoptotic programme was also established by activation of caspase-3 and increase of Bax/Bcl2 ratio and p53 protein. This study provided new findings on role of WT1 and indicated an association between WT1 expression, cell cycle and apoptotic machinery. In conclusion, WT1 acts as a tumour promoter in osteosarcoma and it could be a potential therapeutic target.

Sigma-2 receptor ligands QSAR model dataset

The data have been obtained from the Sigma-2 Receptor Selective Ligands Database (S2RSLDB) and refined according to the QSAR requirements. These data provide information about a set of 548 Sigma-2 (σ₂) receptor ligands selective over Sigma-1 (σ₁) receptor. The development of the QSAR model has been undertaken with the use of CORAL software using SMILES, molecular graphs and hybrid descriptors (SMILES and graph together). Data here reported include the regression for σ₂ receptor pK_i QSAR models. The QSAR model was also employed to predict the σ₂ receptor pK_i values of the FDA approved drugs that are herewith included.

Inhibition of Cx43 mediates protective effects on hypoxic/reoxygenated human neuroblastoma cells

Olfactory ensheathing cells (OECs), a special population of glial cells, are able to synthesise several trophic factors exerting a neuroprotective action and promoting growth and functional recovery in both in vitro and in vivo models. In the present work, we investigated the neuroprotective effects of OEC-conditioned medium (OEC-CM) on two different human neuron-like cell lines, SH-SY5Y and SK-N-SH (neuroblastoma cell lines), under normoxic and hypoxic conditions. In addition, we also focused our attention on the role of connexins (Cxs) in the neuroprotective processes. Our results confirmed OEC-CM mediated neuroprotection as shown by cell adherence, proliferation and cellular viability analyses. Reduced connexin 43 (Cx43) levels in OEC-CM compared to unconditioned cells in hypoxic conditions prompted us to investigate the role of Cx43-Gap junctions (GJs) and Cx43-hemichannels (HCs) in hypoxic/reoxygenation injury using carbenoxolone (non-selective GJ inhibitor), ioxynil octanoato (selective Cx43-GJ inhibitor) and Gap19 (selective Cx43-HC inhibitor). We found that Cx43-GJ and Cx43-HC inhibitors are able to protect SH-SY5Y and allow to these cultures to overcome the injury. Our findings support the hypothesis that both OEC-CM and the inhibition of Cx43-GJs and Cx43-HCs offer a neuroprotective effect by reducing Cx43-mediated cell-to-cell and cell-to-extracellular environment communications.

Multitarget Opioid/Non-opioid Ligands: A Potential Approach in Pain Management

Polypharmacology, or the associations between two or more drugs producing biological effects on two or more different sites of action could represent a possible therapeutic approach for the clinical management of acute and chronic pain. The multitude and complexity of neuronal mechanisms that contribute to pain transmission provide several possible targets for pharmacological intervention. Thus, multitarget ligands possessing opioid-opioid or non-opioid-opioid mechanisms of action are potential drug candidates for pain relief. In this perspective, the past medicinal chemistry paradigm "one-target, one-disease" has been reconsidered and converted into "one-molecule, multiple targets". Multitarget ligands in comparison with cocktail drugs, besides an improved analgesic effect, display a more predictable pharmacokinetic and pharmacodynamic profile coupled to a less incidence of side-effects. Thus, they ameliorate patient compliance and decrease the risk of drug-drug interactions. In our previous review multitarget ligands with an opioid-opioid mechanism of action were described. Here, we deal with multitarget ligands with opioid-non opioid mechanism of action as potential drug candidates for the management of different pain states.

(+)-and (-)-Phenazocine enantiomers: Evaluation of their dual opioid agonist/σ1 antagonist properties and antinociceptive effects

cis-N-Substituted N-normetazocine enantiomers possess peculiar pharmacological profiles. Indeed, dextro enantiomers bind with high affinity σ₁ receptor while opposite enantiomers bind opioid receptors. In spite of their stereochemistry, cis-N-2-phenylethyl N-normetazocine (phenazocine) enantiomers showed mixed opioid/σ₁ receptor profiles and a significant in vivo analgesia. To the best of our knowledge, there is no information available regarding the evaluation of σ₁ pharmacological profile in the antinociceptive effects of (+)- and (-)-phenazocine. Therefore, the present study was designed to ascertain this component by in vitro and in vivo studies. In particular, we tested the σ₁ affinity of both enantiomers by a predictive binding assay in absence or presence of phenytoin (DPH). Our results showed that DPH (1 mM) did not increase the σ₁ receptor affinity of (+)-and (-)-phenazocine (K_i = 3.8 ± 0.4 nM, K_i = 85 ± 2.0 nM, respectively) suggesting a σ₁ antagonist profile of both enantiomers. This σ₁ antagonistic component of two phenazocine enantiomers was corroborated by in vivo studies in which the selective σ₁ receptor agonist PRE-084, was able to unmask their σ₁ antagonistic component associated with the opioid activity. The σ₁ antagonistic component of (+)- and (-)-phenazocine may justify their analgesic activity and it suggests that they may constitute useful lead compounds to develop new ligands with this dual activity.

Repeated activation of delta opiod receptors counteracts nerve injury-induced TNF-α up-regulation in the sciatic nerve of rats with neuropathic pain: A possible correlation with delta opiod receptors-mediated antiallodinic effect

Despite mu opioid receptor agonists are the cornerstones of moderate-to-severe acute pain treatment, their effectiveness in chronic pain conditions is controversial. In contrast to mu opioid receptor agonists, a number of studies have reported the effectiveness of delta opioid receptor agonists on neuropathic pain strengthening the idea that delta opioid receptors gain importance when chronic pain develops. Among other effects, it has been shown that delta opioid receptor activation in optic nerve astrocytes inhibits tumor necrosis factor-α-mediated inflammation in response to severe hypoxia. Considering the involvement of tumor necrosis factor-α in the development and maintenance of neuropathic pain, with this study we sought to correlate the effect of delta opioid receptor agonist on the development of mechanical allodynia to tumor necrosis factor-α expression at the site of nerve injury in rats subjected to chronic constriction injury of the sciatic nerve. To this aim, we measured the levels of tumor necrosis factor-α in the sciatic nerve of rats with neuropathic pain after repeated injections with a delta opioid receptor agonist. Results obtained demonstrated that repeated administrations of the delta opioid receptor agonist SNC80 (10 mg/kg, i.p. for seven consecutive days) significantly inhibited the development of mechanical allodynia in rats with neuropathic pain and that the improvement of neuropathic symptom was timely related to the reduced expression of tumor necrosis factor-α in the rat sciatic nerve. We demonstrated also that when treatment with the delta opioid receptor agonist was suspended both allodynia and tumor necrosis factor-α up-regulation in the sciatic nerve of rats with neuropathic pain were restored. These results show that persistent delta opioid receptor activation significantly attenuates neuropathic pain and negatively regulates sciatic nerve tumor necrosis factor-α expression in chronic constriction injury rats.

New bifunctional antioxidant/σ1 agonist ligands: Preliminary chemico-physical and biological evaluation

We previously reported bifunctional sigma-1 (σ1) ligands endowed with antioxidant activity (1 and 2). In the present paper, pure enantiomers (R)-1 and (R)-2 along with the corresponding p-methoxy (6, 11), p-fluoro derivatives (7, 12) were synthesized. σ1 and σ2 affinities, antioxidant properties, and chemico-physical profiles were evaluated. Para derivatives, while maintaining strong σ1 affinity, displayed improved σ1 selectivity compared to the parent compounds 1 and 2. In vivo evaluation of compounds 1, 2, (R)-1, 7, and 12 showed σ1 agonist pharmacological profile. Chemico-physical studies revealed that amides 2, 11 and 12 were more stable than corresponding esters 1, 6 and 7 under our experimental conditions. Antioxidant properties were exhibited by fluoro derivatives 7 and 12 being able to increase total antioxidant capacity (TAC). Our results underline that p-substituents have an important role on σ1 selectivity, TAC, chemical and enzymatic stabilities. In particular, our data suggest that new very selective compounds 7 and 12 could be promising tools to investigate the disorders in which σ1 receptor dysfunction and oxidative stress are contemporarily involved.

Evaluation of N-substituent structural variations in opioid receptor profile of LP1

The benzomorphan scaffold has great potential as lead structure and the nature of the N-substituent is able to influence affinity, potency, and efficacy at all three opioid receptors. Building upon these considerations, we synthesized a new series of LP1 analogues by introducing naphthyl or heteroaromatic rings in propanamide side chain of its N-substituent (9-15). In vitro competition-binding assays in HEK293 cells stably expressing MOR, DOR or KOR showed that in compound 9 the 1-naphthyl ring led to the retention of MOR affinity (Ki(MOR)=38±4nM) displaying good selectivity versus DOR and KOR. In the electrically stimulated GPI, compound 9 was inactive as agonist but produced an antagonist potency value (pA2) of 8.6 in presence of MOR agonist DAMGO. Moreover, subcutaneously administered it antagonized the antinociceptive effects of morphine with an AD50=2.0mg/kg in mouse-tail flick test. Modeling studies on MOR revealed that compound 9 fit very well in the binding pocket but in a different way in respect to the agonist LP1. Probably the replacement of its N-substituent on the III, IV and V TM domains reflects an antagonist behavior. Therefore, compound 9 could represent a potential lead to further develop antagonists as valid therapeutic agents and useful pharmacological tools to study opioid receptor function.

Harpagophytum procumbens extract potentiates morphine antinociception in neuropathic rats

The association of opioids and non-steroidal anti-inflammatory drugs, to enhance pain relief and reduce the development of side effects, has been demonstrated. Given many reports concerning the antinociceptive and anti-inflammatory effects of Harpagophytum procumbens extracts, the aim of our study was to investigate the advantage of a co-administration of a subanalgesic dose of morphine preceded by a low dose of H. procumbens to verify this therapeutically useful association in a neuropathic pain model. Time course, registered with the association of the natural extract, at a dose that does not induce an antinociceptive effect, followed by a subanalgesic dose of morphine showed a well-defined antiallodynic and antihyperalgesic effect, suggesting a synergism as a result of the two-drug association. H. procumbens cooperates synergistically with morphine in resolving hyperalgesia and allodynia, two typical symptoms of neuropathic pain. The results support the strategy of using an adjuvant drug to improve opioid analgesic efficacy.

CHF5074 protects SH-SY5Y human neuronal-like cells from amyloidbeta 25-35 and tumor necrosis factor related apoptosis inducing ligand toxicity in vitro

Alzheimer's disease (AD) is contributed by multiple pathogenic causes. The anomalous protein amyloid-β (Aβ) is regarded as a pivotal factor in AD, and originates from enzymatic cleavage of a precursor protein by the secretase family. 1-(3',4'-Dichloro-2-fluoro[1,1'-biphenyl]-4-yl)-cyclopropanecarboxylic acid (CHF5074) is a non-steroidal antiinflammatory derivative able to inhibit Aβ deposition in the brain of transgenic mouse models of AD. The proapoptotic cytokine TRAIL has been reported to mediate Aβ-dependent neurotoxicity. Here, the effects of CHF5074 on Aβ25-35- triggered TRAIL toxicity were evaluated in the differentiated human neuroblastoma cell line SH-SY5Y in vitro. Cells were pre-treated 1h with CHF5074 at graded concentrations (range: 1 nM-1 uM) and then challenged for 72 h with either Aβ25-35 or TRAIL. Results show that CHF5074 treatment prevented apoptotic death in SH-SY5Y cell line in a concentration- dependent fashion. Its maximally active concentration was 10 nM. Then, investigation of related molecular mechanisms underlying such protective effect of CHF5074 suggested that the levels of caspases, as well as of various kinases, including stress and MAP kinases, are modulated by CHF5074. Finally, treatment of injured human neuroblastoma cell line SH-SY5Y with CHF5074 resulted in prominent protection from apoptotic death. The bulk of these data suggest that CHF5074 represents a potential candidate for pharmacological neuroprotective treatment in neurodegenerative disorders.

Wilms' tumor 1 (WT1) protein expression in human developing tissues

Several genes playing crucial roles in human development often reproduce a key role also during the onset and progression of malignant tumors. WT1, a transcription factor expressed with a dynamic pattern during human development, has either oncogenic or suppressor tumor properties. A detailed analysis of the immunohistochemical profile of WT1 protein in human developmental tissues could be exploitable as the rational for better understanding its role in cancerogenesis and planning innovative WT1-based therapeutic approaches. This review focuses on the dynamic immunohistochemical expression and distribution of WT1 protein during human ontogenesis, providing illustrations and discussion on the most relevant findings. The possibility that WT1 nuclear/cytoplasmic expression in some tumors mirrors its normal developmental regulation will be emphasized.

HDAC and HAT inhibitors differently affect analgesia mediated by group II metabotropic glutamate receptors

Background

Histone deacetylases (HDACs) and histone acetyltransferases (HATs) are key players in epigenetic regulation of gene expression. Analgesic activity by HDAC inhibitors has been reported in different pain models including inflammatory and neuropathic pain. These drugs interfere with gene expression through different mechanisms including chromatin remodeling and/or activation of transcription factors. Among other targets, HDAC inhibitors regulate metabotropic glutamate receptors type 2 (mGlu2) expression in central and peripheral central nervous system. However whether inhibition of HAT activity also regulates mGlu2 expression has not been reported.

Findings

Here we report that curcumin (CUR), a naturally occurring compound endowed with p300/CREB-binding protein HAT inhibitory activity, is able to induce a drastic down-regulation of the mGlu2 receptor in the mouse spinal cord after systemic administration together with a marked hypoacetylation of histones H3 and H4 in dorsal root ganglia (DRG). Furthermore, the analgesic activity of the mGlu2/3 agonist, LY379268 is lost after a 3-day treatment with CUR. Conversely the analgesic activity of LY379268 is potentiated in mice pretreated for 5 consecutive days with the HDAC inhibitor, Suberoylanilide Hydroxamic Acid (SAHA), known to induce mGlu2-upregulation.

Conclusions

Our results demonstrate that systemically injected CUR is able to inhibit H3 and H4 acetylation in the DRG and to down-regulate mGlu2 receptors in the spinal cord. We also demonstrate that long term modification of the mGlu2 expression affects the analgesic properties of the orthosteric mGlu2/3 agonist, LY379268. These data open up the possibility that epigenetic modulators might be given in combination with “traditional” drugs in a context of a multi target approach for a better analgesic efficacy.

Haloperidol metabolite II prodrug: asymmetric synthesis and biological evaluation on rat C6 glioma cells

In a previous work we reported the antiproliferative effects of (±)-MRJF4, a novel haloperidol metabolite II (HP-mII) (a sigma-1 antagonist and sigma-2 agonist) prodrug, obtained through conjugation to 4-phenylbutyric acid (PhBA) [a histone deacetylase inhibitor (HDACi)] via an ester bond. As a continuation of this work, here we report the asymmetric synthesis of compounds (R)-(+)-MRJF4 and (S)-(-)-MRJF4 and the evaluation of their biological activity on rat C6 glioma cells, derived from glioblastoma multiforme (GBM), which is the most common and deadliest central nervous system (CNS) invasive malignancy. Favourable physicochemical properties, high permeability in the parallel artificial membrane permeability assay (PAMPA), good enzymatic and chemical stability, in vivo anticancer activity, associated with the capacity to reduce cell viability and to increase cell death by apoptosis, render compound (R)-(+)-MRJF4 a promising candidate for the development of a useful therapeutic for gliomas therapy.

The antagonistic effect of the sigma 1 receptor ligand (+)-MR200 on persistent pain induced by inflammation

OBJECTIVE AND DESIGN

The sigma 1 (σ1) receptor, which is widely distributed in the CNS in areas that are known to be important for pain control, may play a role in persistent pain characterized by the hypersensitivity of nociceptive transmission. Here, we investigated the effect of σ1 blockade in an inflammatory pain model.

TREATMENT AND METHODS

An intraplantar injection of carrageenan (2 %) was used to induce paw inflammation. The effects of the σ1 antagonist (+)-MR200, given subcutaneously at a dose of 0.1, 0.25, 0.5,1, 1.5, and 2 mg/kg prior to injection of carrageenan, on inflammatory pain and inflammation were assessed. Mechanical allodynia with von Frey filaments, thermal hyperalgesia with the plantar test and edema evaluation with a plethysmometer were measured. Intergroup comparisons were assessed by one- or two-way analysis of variance when appropriate, followed by post-hoc tests (Dunnett's test for one-way or Bonferroni for two-way ANOVA).

RESULTS

(+)-MR200 dose-dependently prevented allodynia and hyperalgesia induced by carrageenan. Furthermore, it reduced paw edema with a significant inhibition percentage of 37.82 % at 3 h after carrageenan treatment.

CONCLUSIONS

The blockade of the σ1 receptor with the selective antagonist (+)-MR200 may contribute to the suppression of the typical symptoms of inflammatory pain.

Design and synthesis of new bifunctional sigma-1 selective ligands with antioxidant activity

Herein we report the synthesis of new bifunctional sigma-1 (σ1)-selective ligands with antioxidant activity. To achieve this goal, we combined the structure of lipoic acid, a universal antioxidant, with an appropriate sigma aminic moiety. Ligands 14 and 26 displayed high affinity and selectivity for σ1 receptors (Kiσ1 = 1.8 and 5.5 nM; Kiσ2/σ1 = 354 and 414, respectively). Compound 26 exhibited in vivo antiopioid effects on kappa opioid (KOP) receptor-mediated analgesia. In rat liver and brain mitochondria (RLM, RBM), this compound significantly reduced the swelling and the oxidation of thiol groups induced by calcium ions. Our results demonstrate that the tested compound has protective effects against oxidative stress.

The multitarget opioid ligand LP1's effects in persistent pain and in primary cell neuronal cultures

Persistent pain states, such as those caused by nerve injury or inflammation, are associated with altered sensations, allodynia and hyperalgesia, that are resistant to traditional analgesics. A contribution to development and maintenance in altered pain perception comes from nociceptive processing and descending modulation from supraspinal sites. A multitarget ligand seems to be useful for pain relief with a decreased risk of adverse events and a considerable analgesic efficacy. The multitarget MOR agonist-DOR antagonist LP1, (3-[(2R,6R,11R)-8-hydroxy-6,11-dimethyl-1,4,5,6-tetrahydro-2,6-methano-3-benazocin-3(2H)-yl]-N-phenylpropanamide, is a central acting antinociceptive agent with low potential to induce tolerance. LP1 was tested in models of neuropathic pain - induced by chronic constriction injury (CCI) of the left sciatic nerve - and inflammatory pain - produced by intraplantar injection of carrageenan. In CCI rats, subcutaneous (s.c.) LP1 (3 mg/kg) showed a significant antiallodynic effect, measured with von Frey filaments, and antihyperalgesic effect, evoked in response to a radiant heat stimulus with plantar test. Analogously, LP1 significantly reduced allodynic and hyperalgesic thresholds in a model of inflammatory pain induced by carrageenan. To evaluate the contribution of opioid receptor subtypes in LP1 antinociceptive effects, the multitarget LP1 profile was assessed using selective opioid antagonists. Moreover, functional electrophysiological in vitro assays, using primary cortical and spinal cord networks, allowed to define the "pharmacological fingerprint" of LP1. The EC₅₀ values in this functional screening seem to confirm LP1 as a potent opioid ligand (EC₅₀ = 0.35 fM and EC₅₀ = 44 pM in spinal cord and frontal cortex, respectively). Using a NeuroProof data-base of well characterised reference compounds, a similarity profile of LP1 to opioid and non-opioid drugs involved in pain modulation was detected. Our studies seem to support that multitarget ligand approach should be useful for persistent pain conditions in which mechanical allodynia and thermal hyperalgesia are significant components of the nociceptive response.

Antinociceptive profile of LP1, a non-peptide multitarget opioid ligand

AIMS

Opioid drugs are the principal treatment option for moderate to severe pain and exert their biological effects through interactions with opioid receptors that are widely distributed throughout the CNS and peripheral tissues. Ligands capable of simultaneously targeting different receptors could be successful candidates for the treatment of chronic pain. Enhanced antinociception coupled with a low incidence of side effects has been demonstrated for ligands possessing mixed mu-opioid receptor (MOR) and delta-opioid receptor (DOR) activity. We previously reported that 3-[(2R,6R,11R)-8-hydroxy-6,11-dimethyl-1,4,5,6-tetrahydro-2,6-methano-3-benzazocin-3(2H)-yl]-N-phenylpropanamide (LP1) acted as a MOR-DOR ligand in in vitro functional assays and moreover this drug produced a valid antinociception that was longer lasting than that of morphine. The aim of this work was to determine whether the antinociceptive effect produced by LP1 was central or peripheral and to assess which opioid receptor subtypes are involved in its effects.

MAIN METHODS

We explored the effects of naloxone methiodide (NX-M), a quaternary opioid antagonist, administered either intracerebroventricularly (i.c.v.) or subcutaneously (s.c.), on LP1-mediated antinociception in male Sprague-Dawley rats. In addition, we administered s.c. selective antagonists for MOR, DOR and kappa-opioid receptor (KOR) to investigate the effects of LP1. To characterise this drug's DOR profile better, we also investigated the effects of LP1 on DPDPE, a selective DOR agonist.

KEY FINDINGS

Data obtained by tail flick test showed that LP1 induced predominantly MOR-mediated supraspinal antinociception and was able to counteract DPDPE analgesia.

SIGNIFICANCE

LP1, a multitarget opioid ligand, is a supraspinal acting antinociceptive agent that is useful for the treatment of chronic pain.