Pain Therapeutics Research Articles

A small firm checks in at a big partner’s complex

The controversial approval of Biogen’s Aduhelm earlier this month spotlights the challenges for big companies developing antibody treatments for Alzheimer’s disease. The US Food and Drug Administration signed off on the drug, but many neurologists were unimpressed, if not frustrated, with the approval, viewing the antibody’s impact as marginal at best and the FDA’s vetting as substandard. Recent results from a Phase 2 clinical trial of a small-molecule Alzheimer’s disease treatment developed by the tiny biotech firm Cassava Sciences, however, suggest a new approach to halting the progress of the seemingly intractable neurodegenerative disease. “Clinical data around our compound is very promising,” says Remi Barbier, CEO of Austin, Texas–based Cassava, which Barbier founded as Pain Therapeutics in 1998. “If the data continues to replicate, then we are looking at a monster, monster commercial manufacturing opportunity.” Something of a David among pharma Goliaths, Cassava has signed with a giant among contract

Impacts of diphenylamine NSAID halogenation on bioactivation risks

Diphenylamine NSAIDs are highly prescribed therapeutics for chronic pain despite causing symptomatic hepatotoxicity through mitochondrial damage in five percent of patients taking them. Differences in toxicity are attributed to structural modifications to the diphenylamine scaffold rather than its inherent toxicity. We hypothesize that marketed diphenylamine NSAID substituents affect preference and efficiency of bioactivation pathways and clearance. We parsed the FDA DILIrank hepatotoxicity database and modeled marketed drug bioactivation into quinone-species metabolites to identify a family of seven clinically relevant diphenylamine NSAIDs. These drugs fell into two subgroups, i.e., acetic acid and propionic acid diphenylamines, varying in hepatotoxicity risks and modeled bioactivation propensities. We carried out steady-state kinetic studies to assess bioactivation pathways by trapping quinone-species metabolites with dansyl glutathione. Analysis of the glutathione adducts by mass spectrometry characterized structures while dansyl fluorescence provided quantitative yields for their formation. Resulting kinetics identified four possible bioactivation pathways among the drugs, but reaction preference and efficiency depended upon structural modifications to the diphenylamine scaffold. Strikingly, diphenylamine dihalogenation promotes formation of quinone metabolites through four distinct metabolic pathways with high efficiency, whereas those without aromatic halogen atoms were metabolized less efficiently through two or fewer metabolic pathways. Overall metabolism of the drugs was comparable with bioactivation accounting for 4–13% of clearance. Lastly, we calculated daily bioload exposure of quinone-species metabolites based on bioactivation efficiency, bioavailability, and maximal daily dose. The results revealed stratification into the two subgroups; propionic acid diphenylamines had an average four-fold greater daily bioload compared to acetic acid diphenylamines. However, the lack of sufficient study on the hepatotoxicity for all drugs prevents further correlative analyses. These findings provide critical insights on the impact of diphenylamine bioactivation as a precursor to hepatotoxicity and thus, provide a foundation for better risk assessment in drug discovery and development.

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.

Antinociceptive Profile of ARN19702, (2-Ethylsulfonylphenyl)-[(2S)-4-(6-fluoro-1,3-benzothiazol-2-yl)-2-methylpiperazin-1-yl]methanone, a Novel Orally Active N-Acylethanolamine Acid Amidase Inhibitor, in Animal Models.

N-Acylethanolamine acid amidase (NAAA) is an N-terminal cysteine hydrolase that stops the physiologic actions of palmitoylethanolamide, an endogenous lipid messenger that activates the transcription factor, peroxisome proliferator-activated receptor-α We have previously reported that the compound ARN19702 [(2-ethylsulfonylphenyl)-[(2S)-4-(6-fluoro-1,3-benzothiazol-2-yl)-2-methylpiperazin-1-yl]methanone] is an orally active, reversible NAAA inhibitor (IC50 on human NAAA = 230 nM) that produces remarkable protective effects against multiple sclerosis in mice. In the present study, we assessed the profile of ARN19702 in mouse and rat models of acute and neuropathic pain. Oral administration in male mice attenuated in a dose-dependent manner the spontaneous nocifensive response elicited by intraplantar formalin injection and the hypersensitivity caused by intraplantar carrageenan injection, paw incision, or sciatic nerve ligation. In male rats, ARN19702 reduced nociception associated with paclitaxel-induced neuropathy without development of subacute antinociceptive tolerance. Finally, ARN19702 (30 mg/kg, oral) did not produce place preference or alter exploratory motor behavior in male mice. The findings support the conclusion that NAAA is a suitable molecular target for the discovery of efficacious analgesic drugs devoid of rewarding potential. SIGNIFICANCE STATEMENT: This study evaluated the pharmacological profile of the orally bioavailable N-acylethanolamine acid amidase (NAAA) inhibitor (2-ethylsulfonylphenyl)-[(2S)-4-(6-fluoro-1,3-benzothiazol-2-yl)-2-methylpiperazin-1-yl]methanone (ARN19702) in mouse and rat models of neurogenic and inflammatory pain. The compound's potential rewarding and sedative effects were also examined. It is concluded that ARN19702 exhibits a broad analgesic profile that can be generalized across rodent species. The findings point to NAAA as a control node in the processing of neuropathic and inflammatory pain and to ARN19702 as a lead to uncover novel pain therapeutics devoid of addictive potential .

NIH HEAL Initiative: National Institute of Neurological Disorders and Stroke Preclinical Program for Non-Addictive Pain Therapeutic Development

Background: The NIH Helping to End Addiction Long-term (HEAL) Initiative aims to focus efforts on advancing scientific solutions to stem the opioid crisis, improving prevention and treatment of opioid misuse/addiction, and enhancing pain management. Goal: NINDS is charged with accelerating the discovery and development of new non-addictive pharmacologic and non-pharmacologic pain therapeutics as part of the HEAL Initiative. NINDS established the Preclinical Screening Platform for Pain (PSPP) to accelerate and enhance testing of novel, non-addictive pain therapeutics. This program will evaluate new, as well as repurposed, small molecules, biologics, devices, and natural products across a range of pain conditions. PSPP is accepting assets from academic and industry sponsors, worldwide. Here we describe efforts within the PSPP program. The overall goal of the PSPP program is to provide an efficient, rigorous, one-stop in vivo screening resource to accelerate identification and efficacy profiling of non-opioid therapeutics for the treatment of pain. Under NINDS direction, preclinical testing of submitted agents is performed by contract facilities on a blinded and confidential basis at no cost to the PSPP participants. Test candidates are evaluated in a suite of in vivo pain-related endpoints and models, following in vitro receptor profiling, pharmacokinetic and safety assessment. Importantly, test candidates are also evaluated in models of abuse liability. We will describe the advances made to date towards establishing program goals of evaluating assets in a rigorous and reproducible manner. Background: The NIH Helping to End Addiction Long-term (HEAL) Initiative aims to focus efforts on advancing scientific solutions to stem the opioid crisis, improving prevention and treatment of opioid misuse/addiction, and enhancing pain management. Goal: NINDS is charged with accelerating the discovery and development of new non-addictive pharmacologic and non-pharmacologic pain therapeutics as part of the HEAL Initiative. NINDS established the Preclinical Screening Platform for Pain (PSPP) to accelerate and enhance testing of novel, non-addictive pain therapeutics. This program will evaluate new, as well as repurposed, small molecules, biologics, devices, and natural products across a range of pain conditions. PSPP is accepting assets from academic and industry sponsors, worldwide. Here we describe efforts within the PSPP program. The overall goal of the PSPP program is to provide an efficient, rigorous, one-stop in vivo screening resource to accelerate identification and efficacy profiling of non-opioid therapeutics for the treatment of pain. Under NINDS direction, preclinical testing of submitted agents is performed by contract facilities on a blinded and confidential basis at no cost to the PSPP participants. Test candidates are evaluated in a suite of in vivo pain-related endpoints and models, following in vitro receptor profiling, pharmacokinetic and safety assessment. Importantly, test candidates are also evaluated in models of abuse liability. We will describe the advances made to date towards establishing program goals of evaluating assets in a rigorous and reproducible manner.

GPR171 Agonist, MS15203, Effectively Enhances Morphine Antinociception Without Modulating Detrimental Side Effects

Opioid drugs are limited in clinical effectiveness because of their propensity for tolerance, addiction, withdrawal, and respiratory depression. Nonetheless, this drug class is still readily prescribed for acute and chronic pain, often to the long-term detriment of patients. Safer pain therapeutics are desperately needed. One novel avenue of drug development is to search for a target capable of enhancing opioid antinociception without enhancing negative side effects. This would allow for increased opioid effectiveness with lower doses, thus minimizing negative side effects and postponing dose escalation. The previous orphan receptor, GPR171, is one such target. Our recent work showed that an agonist for GPR171, MS15203 enhances morphine antinociception in two rodent acute pain assays (McDermott et al., 2019). Combining these two drugs could potentially lead to greater antinociception with lower opioid doses. The next step in vetting MS15203 as a novel pain therapeutic is to determine its effect on negative opioid side effects. In this current study we utilized three rodent behavioral assays to assess MS15203 in tolerance development, opioid withdrawal, and reward liability. Additionally, we used immunohistochemistry to assess ex vivo MS15203-induced dopamine activation in the ventral tegmental area (VTA). Results from a hot plate dose-response show that MS15203 has no significant effect on morphine tolerance development in both males and females. However, MS15203 significantly decreases morphine tolerance in females on the tail flick test, suggesting a sex-specific and spinal-specific effect. Results from a naloxone precipitated withdrawal assay show that MS15203 does not significantly alter morphine withdrawal. Results from a conditioned place preference assay, show that MS15203 alone causes no significant place preference, and has no significant modulatory effect when paired with morphine. Similarly, MS15203, causes no significant VTA activation alone, and has no significant modulatory effect on morphine-induced activation. Taken together these results present GPR171 agonist MS15203 as an enhancer of morphine antinociception, and an overall neutral agent in morphine tolerance, withdrawal, and reward. Future studies should assess MS15203 on respiratory depression.

Structural Variations among Marketed Diphenylamine NSAIDs Determine Preference and Efficiency for Four Possible Bioactivation Pathways

Diphenylamine NSAIDs are highly prescribed therapeutics for chronic pain despite causing symptomatic hepatotoxicity through mitochondrial damage in roughly five percent of the patients taking them. Studies attribute differences in toxicities to minor structural modifications to the diphenylamine scaffold rather than inherent toxicity of diphenylamine itself. We hypothesize that substituents of marketed diphenylamine NSAIDs determine the preference and efficiency of bioactivation pathways relative to overall drug clearance. We tested the hypothesis through a novel integration of bioinformatic, computational, and experimental approaches. Initially, we parsed the FDA DILIrank database containing liver toxicity information on marketed drugs and modeled their potential bioactivation into quinones to identify a family of seven clinically relevant diphenylamine NSAIDs including the well-studied diclofenac. These drugs fell into two subgroups, i.e. acetic acid and propionic acid diphenylamines, varying in hepatotoxicity risks and modeled bioactivation propensities. Next, we carried out novel steady-state kinetic studies to assess bioactivation pathways by trapping quinones with dansyl glutathione. Analysis of the glutathione adducts by MS characterized structures while dansyl fluorescence provided quantitative yields for their formation over time. The resulting kinetics identified four possible bioactivation pathways among the drugs, but the preference and efficiency of reactions depended upon structural modifications to the diphenylamine scaffold. Strikingly, diphenylamine dihalogenation promotes the formation of quinone metabolites through four distinct metabolic pathways with high efficiency, whereas those without aromatic halogen atoms were metabolized less efficiently through two or fewer metabolic pathways. Despite differences in bioactivation, overall metabolism of the drugs was comparable with bioactivation accounting for 4 to 13% of clearance. Lastly, we calculated daily bioload exposure from the quinone metabolites based on bioactivation efficiency, drug bioavailability, and maximal daily dose. The results revealed stratification into the two diphenylamine subgroups; propionic acid diphenylamines had a nearly four-fold greater daily bioload on average compared to acetic acid diphenylamines. However, the lack of sufficient study on the corresponding liver toxicities for all drugs prevented a more correlative analysis. Future work will identify responsible enzymes to understand the role of these structural modifications in metabolic clearance and bioactivation and subsequent drug-induced liver injury. These findings will provide critical insights on the impact of diphenylamine bioactivation as a precursor to DILI and thus, provide a foundation for better risk assessment in drug discovery and development.

Development of an activated microglia cell line model for screening lipid nanoparticle formulations of BDNF siRNA for neuropathic pain therapy

Purpose Brain-derived neurotrophic factor (BDNF) released from activated spinal microglia via the ATP-P2 × 4R-BDNF signaling pathway plays a central role in initiating pain hypersensitivity in neuropathic pain. Therefore, knockdown of BDNF expression in microglia using molecules like siRNA can be a promising strategy for neuropathic pain therapy. Our lab is developing lipidoid nanoparticles (LNP) for the delivery of BDNF siRNA (siBDNF) for treating neuropathic pain. We characterized the Spontaneously Immortalized Microglia-A9 (SIM-A9) cell line and confirmed the expression of Iba1, P2 × 4R, and BDNF under resting (non-activated) and ATP-stimulated conditions. SIM-A9 cell line was cultured with and without external stimuli, adenosine triphosphate (ATP), and/or lipopolysaccharide (LPS) by varying parameters such as the concentration of stimuli, incubation time, and cell regeneration time post-activation. The cytocompatibility of SIM-A9 cells with ATP and LPS was determined using an ATP assay. Intracellular Iba1, P2 × 4R, and BDNF protein expression in the resting and stimulated cells were characterized using western blotting, in-cell western, and immunocytochemistry. In a pilot study, SIM-A9 cells were transfected with RNAiMAX (a commercial transfection agent)/siBDNF complexes and changes in BDNF expression were evaluated using western blotting. We present two novel findings: first, SIM-A9 cells expressed P2 × 4R and BDNF proteins. Second, ATP at a safe dose showed a time-dependent increase in Iba1 and BDNF expression without intracellular toxicity. At 40 nM siRNA concentration, RNAiMAX/siBDNF complexes showed about a 15% reduction in SIM-A9 BDNF expression. In preliminary studies, LNP/siBDNF at 40 nM were well-tolerated by SIM-A9 cells, however, they only showed negligible BDNF knockdown in activated SIM-A9 cells. Currently, we are optimizing LNP formulations and transfection conditions to increase the extent of BDNF gene silencing. We have developed an ATP-activated SIM-A9 cell line model system that can be utilized for screening of neuropathic pain therapeutics.

15727 KATP channel prodrugs as therapeutics for chronic pain and substance abuse disorders

ABSTRACT IMPACT: Pharmacological activation of KATP channels may provide analgesia and attenuate opioid tolerance and withdrawal OBJECTIVES/GOALS: Our long term goal is to develop therapeutics for the treatment of the overuse of opioids. The objective of this application is to test novel KATP channel-targeting prodrugs in rodent models of neuropathic and inflammatory pain in addition to opioid tolerance after chronic morphine administration. METHODS/STUDY POPULATION: In one study, two different measures for chronic pain were implemented in mice. Male and female mice (n=10) were subjected to spinal nerve ligation (SNL) or intraplantar injection of Complete Freund’s Adjuvant (CFA) to induce neuropathic and inflammatory pain, respectively. Administration of KATP channel prodrugs (60ug, it) attenuated mechanical hypersensitivity after SNL or CFA compared to vehicle (saline). In a separate study, changes in mechanical hypersensitivity were tested while mice undergo chronic morphine treatment (15mg/kg, 2x, 5 days) with administration of the prodrugs. Tolerance was measured as the loss of antinociception, and withdrawal is measured ˜24 hours after the final morphine injection. RESULTS/ANTICIPATED RESULTS: Intrathecal administration of either KATP channel prodrugs significantly attenuated mechanical hypersensitivity after SNL and significantly attenuated mechanical hypersensitivity after CFA in mice. We predict that intrathecal administration of these prodrugs will also attenuate morphine tolerance and withdrawal in mice. This hypothesis is based off our previous data indicating non-water soluble KATP channel agonists produce analgesia and attenuate morphine tolerance in mice. DISCUSSION/SIGNIFICANCE OF FINDINGS: Pharmaceutical strategies to utilize KATP channels for therapeutics have been hindered due to the low solubility and low ability to cross the neurovascular unit. Newly developed, water-soluble KATP channel openers could be useful pharmaceutical strategy to reduce chronic pain, opioid tolerance, and withdrawal in human populations.

Novel curcumin analog (cis-trans curcumin) as ligand to adenosine receptors A2A and A2B: potential for therapeutics

All four of the adenosine receptor (AR) subtypes mediate pain and have been targeted by pharmacologists to generate new therapeutics for chronic pain. The vanilloid phytochemicals, which include curcumin, capsaicin, and gingerol, have been shown to alleviate pain. However, there is little to no literature on the interaction of vanilloid phytochemicals with ARs. In this study, photochemical methods were used to generate a novel isomer of curcumin (cis-trans curcumin or CTCUR), and the interactions of both curcumin and CTCUR with the two Gs-linked AR subtypes were studied. Competitive binding assays, docking analysis, and confocal fluorescence microscopy were performed to measure binding affinity; cell survival assays were used to measure toxicity; and cAMP assays were performed to measure receptor activation. Competitive binding results indicated that CTCUR binds to both AR A2A and AR A2B with Ki values of 5 μM and 7 μM, respectively, which is consistent with our docking results. Fluorescence microscopy data also shows binding for A2B and A2A. Cell survival results show that CTCUR and CUR are nontoxic at the tested concentrations in these cell lines. Overall, our results suggest that vanilloid phytochemicals may be slightly modified to increase interaction with Gs-ARs, and thereby can be further explored to provide a novel class of non-opioid antinociceptives.

Comparison of quinazoline and benzoylpyrazoline chemotypes targeting the CaVα-β interaction as antagonists of the N-type CaV2.2 channel

ABSTRACT Structural studies with an α subunit fragment of voltage-gated calcium (CaV) channels in complex with the CaVβ subunits revealed a high homology between the various CaVα-β subunits, predicting that targeting of this interface would result in nonselective compounds. Despite this likelihood, my laboratory initiated a rational structure-based screening campaign focusing on “hot spots” on the alpha interacting domain (AID) of the CaVβ2a subunits and identified the small molecule 2-(3,5-dimethylisoxazol-4-yl)-N-((4-((3-phenylpropyl)amino)quinazolin-2-yl)methyl)acetamide ( IPPQ ) which selectively targeted the interface between the N-type calcium (CaV2.2) channel and CaVβ. IPPQ (i) specifically bound to CaVβ2a; (ii) inhibited CaVβ2 ‘s interaction with CaV.2-AID; (iii) inhibited CaV2.2 currents in sensory neurons; (iv) inhibited pre-synaptic localization of CaV2.2 in vivo; and (v) inhibited spinal neurotransmission, which resulted in decreased neurotransmitter release. IPPQ was anti-nociceptive in naïve rats and reversed mechanical allodynia and thermal hyperalgesia in rodent models of acute, neuropathic, and genetic pain. In structure–activity relationship (SAR) studies focused on improving binding affinity of IPPQ , another compound (BTT-369), a benzoyl‐3,4‐dihydro‐1'H,2 H‐3,4'‐bipyrazole class of compounds, was reported by Chen and colleagues, based on work conducted in my laboratory beginning in 2008. BTT-369 contains tetraaryldihydrobipyrazole scaffold – a chemotype featuring phenyl groups known to be significantly metabolized, lower the systemic half-life, and increase the potential for toxicity. Furthermore, the benzoylpyrazoline skeleton in BTT-369 is patented across multiple therapeutic indications. Prior to embarking on an extensive optimization campaign of IPPQ , we performed a head-to-head comparison of the two compounds. We conclude that IPPQ is superior to BTT-369 for on-target efficacy, setting the stage for SAR studies to improve on IPPQ for the development of novel pain therapeutics.

Patient phenotyping in clinical trials of chronic pain treatments: IMMPACT recommendations

There is tremendous interpatient variability in the response to analgesic therapy (even for efficacious treatments), which can be the source of great frustration in clinical practice. This has led to calls for “precision medicine” or personalized pain therapeutics (ie, empirically based algorithms that determine the optimal treatments, or treatment combinations, for individual patients) that would presumably improve both the clinical care of patients with pain and the success rates for putative analgesic drugs in phase 2 and 3 clinical trials. However, before implementing this approach, the characteristics of individual patients or subgroups of patients that increase or decrease the response to a specific treatment need to be identified. The challenge is to identify the measurable phenotypic characteristics of patients that are most predictive of individual variation in analgesic treatment outcomes, and the measurement tools that are best suited to evaluate these characteristics. In this article, we present evidence on the most promising of these phenotypic characteristics for use in future research, including psychosocial factors, symptom characteristics, sleep patterns, responses to noxious stimulation, endogenous pain-modulatory processes, and response to pharmacologic challenge. We provide evidence-based recommendations for core phenotyping domains and recommend measures of each domain.

Anti-inflammatory and antinociceptive effects of the selective cannabinoid CB2 receptor agonist ABK5

Cannabinoid receptors are a potential target for anti-inflammatory and pain therapeutics. There are two subtypes, CB1 and CB2, and Δ9-tetrahydrocannabinol activates both of them, providing an analgesic effect but also psychoactive side effects. The psychoactive side effects are considered to be caused by activation of CB1, but not CB2. ABK5 is a CB2 subtype selective agonist that has a very different structure from known cannabinoid receptor agonists. Here, we report anti-inflammatory effects of ABK5 using the T-cell line Jurkat cells, and antinociceptive effect in an inflammatory pain model in rats. Production of the cytokines IL-2 and TNF-α was measured in stimulated Jurkat cells and MOLT-4 cells, and CXCL12-mediated chemotaxis of Jurkat cells was evaluated by a transwell migration assay. Anti-inflammatory and antinociceptive effects of ABK5 were also evaluated in a hindpaw CFA model in rats. ABK5 significantly decreased production of IL-2 and TNF-α measured as both mRNA and protein levels, and reduced chemotaxis towards CXCL12. It also attenuated edema and increased mechanical threshold in the hindpaw of CFA-treated rats. These results suggest that ABK5 is a good lead compound for the development of potential anti-inflammatory and analgesic agents.

'Reinventing the wheel' to advance the development of pain therapeutics.

Chronic pain affects approximately one-third of the population worldwide. The primary goal of animal research is to understand the neural mechanisms underlying pain so better treatments can be developed. Despite an enormous investment in time and money, almost no novel treatments for pain have been developed. There are many factors that contribute to this lack of translation in drug development. The mismatch between the goals of drug development in animals (inhibition of pain-evoked responses) and treatment in humans (restoration of function) is a major problem. To solve this problem, a number of pain-depressed behavioral tests have been developed to assess changes in normal behavior in laboratory animals. The use of home cage wheel running as a pain assessment tool is especially useful in that it is easy to use, provides an objective measurement of the magnitude and duration of pain, and is a clinically relevant method to screen novel drugs. Pain depresses activity in humans and animals, and effective analgesic treatments restore activity. Unlike traditional pain-evoked tests (e.g., hot plate, tail flick, von Frey test), restoration of home cage wheel running evaluates treatments for both antinociceptive efficacy and the absence of disruptive side effects (e.g., sedation, paralysis, nausea). This article reviews the literature using wheel running to assess pain and makes the case for home cage wheel running as an effective and clinically relevant method to screen novel analgesics for therapeutic potential.

Sex differences in brain modular organization in chronic pain.

Men and women can exhibit different pain sensitivities, and many chronic pain conditions are more prevalent in one sex. Although there is evidence of sex differences in the brain, it is not known whether there are sex differences in the organization of large-scale functional brain networks in chronic pain. Here, we used graph theory with modular analysis and machine-learning of resting-state-functional magnetic resonance imaging data from 220 participants: 155 healthy controls and 65 individuals with chronic low back pain due to ankylosing spondylitis, a form of arthritis. We found an extensive overlap in the graph partitions with the major brain intrinsic systems (ie, default mode, central, visual, and sensorimotor modules), but also sex-specific network topological characteristics in healthy people and those with chronic pain. People with chronic pain exhibited higher cross-network connectivity, and sex-specific nodal graph properties changes (ie, hub disruption), some of which were associated with the severity of the chronic pain condition. Females exhibited atypically higher functional segregation in the mid cingulate cortex and subgenual anterior cingulate cortex and lower connectivity in the network with the default mode and frontoparietal modules, whereas males exhibited stronger connectivity with the sensorimotor module. Classification models on nodal graph metrics could classify an individual's sex and whether they have chronic pain with high accuracies (77%-92%). These findings highlight the organizational abnormalities of resting-state-brain networks in people with chronic pain and provide a framework to consider sex-specific pain therapeutics.

427 - HARMONY study: pimavanserin significantly reduces risk of relapse of dementia-related psychosis

AbstractDementia-related psychosis (DRP) is common among patients with Alzheimer’s disease (AD), Parkinson’s disease (PD), dementia with Lewy bodies (DLB), frontotemporal dementia (FTD), and vascular dementia (VaD) and is associated with poor outcomes. HARMONY (NCT03325556) was a Phase 3, placebo-controlled, randomized, relapse-prevention study evaluating the efficacy and safety of pimavanserin for treating hallucinations and delusions associated with DRP. Patients with dementia and moderate-severe psychosis received open-label (OL) pimavanserin for 12 weeks. Patients with a sustained response (≥30% reduction in Scale for the Assessment of Positive Symptoms hallucinations+delusions Total Score AND Clinical Global Impression-Improvement score of much/very much improved) at Weeks 8 and 12 were randomized 1:1 to continue pimavanserin or receive placebo for up to 26 weeks in the double-blind (DB) period. The primary endpoint was time from randomization to relapse of DRP. 392 patients enrolled. 217 (61.8%) eligible patients experienced sustained response and were randomized. OL response was similar regardless of dementia subtype (randomization rates: 59.8% AD, 71.2% PDD, 71.4% VaD, 45.5% DLB, 50.0% FTD), baseline disease characteristics, age, dementia severity, or previous drug therapy. The study stopped early for superior efficacy when a prespecified interim analysis revealed >2.8-fold reduction in risk of relapse with pimavanserin (hazard ratio: 0.353; 95% CI: 0.172, 0.727; 1-sided p=0.0023). Adverse event rates were low and balanced (OL: 36.2%; DB: 41.0% pimavanserin, 36.6% placebo). No negative trends for worsening in cognition (as assessed by the Mini-Mental State Examination) or motor function were observed. The HARMONY study demonstrated a robust decrease in hallucinations and delusions and significant maintenance of efficacy with pimavanserin treatment in DRP.Study Sponsored By: ACADIA Pharmaceuticals Inc.DisclosuresThis study was funded by ACADIA Pharmaceuticals Inc.Drs. Foff, McEvoy, and Stankovic are all employees of ACADIA Pharmaceuticals Inc. (San Diego, CA, USA).Dr Cummings has provided consultation to ACADIA, Accera, Actinogen, AgeneBio, Alkahest, Allergan, Alzheon, Avanir, Axsome, Binomics, BiOasis Technologies, Biogen, Bracket, Cassava, Denali, Diadem, EIP Pharma, Eisai, Genentech, Green Valley, Grifols, Hisun, Idorsia, Lundbeck, Merck, Otsuka, Pain Therapeutics, Probiodrug, Proclara, QR, Resverlogix, Roche, Samumed, Shinkei Therapeutics, Sunovion, Suven, Takeda, and United Neuroscience pharmaceutical and assessment companies. He owns stock in ADAMAS, BioAsis, MedAvante, and QR Pharma. Dr. Cummings owns the copyright of the Neuropsychiatric Inventory (NPI). Dr. Cummings is supported by a COBRE grant from NIH/NIGMS #P20GM109025 and Keep Memory Alive.Dr. Soto has provided consultation to ACADIA, Avanir, Eisai, Lundbeck, and Otsuka.

Pharmacological treatment of pain among persons with opioid addiction: A systematic review and meta-analysis with implications for drug development.

The clinical features and neurobiology of pain and opioid use disorder (OUD) are inextricably linked. Despite emerging evidence supporting the negative impact of ongoing pain in the treatment of OUD, the pharmacological management of pain in the presence of OUD has received limited attention. We sought to systematically review the studies investigating pharmacotherapies for pain among persons with OUD. Eligible studies had participants with OUD and outcomes including evoked or spontaneous pain. We searched Scopus, Cochrane Database of Systematic Reviews, Medline, and Embase. Out of 1,097 studies that met the search criteria, 12 studies provided data relevant to the research question-five laboratory studies and seven clinical trials. Random effects pooled estimates suggested no significant difference between groups at baseline but a response favoring the active treatment group over placebo, with nonsignificant heterogeneity between studies. Findings from these studies provide preliminary evidence for analgesic and antihyperalgesic effects of gabapentin, GABA agonists, and NMDA antagonists among persons with OUD. To establish the tradeoffs between the analgesic effects and abuse liability of these compounds, further well-controlled clinical trials are required among persons with OUD. This review also underscores the need for methodological enhancement in drug development for pain in OUD. Future research should address the clinical and neurobiological overlap between pain- and addiction-related phenomena. Transdisciplinary approaches may identify biomarkers of these shared phenomena and their neural substrates. The development of novel therapeutics for pain in OUD may be accelerated by such integration of pain and addiction research.

Biased Opioid Antagonists as Modulators of Opioid Dependence: Opportunities to Improve Pain Therapy and Opioid Use Management.

Opioid analgesics are effective pain therapeutics but they cause various adverse effects and addiction. For safer pain therapy, biased opioid agonists selectively target distinct μ opioid receptor (MOR) conformations, while the potential of biased opioid antagonists has been neglected. Agonists convert a dormant receptor form (MOR-μ) to a ligand-free active form (MOR-μ*), which mediates MOR signaling. Moreover, MOR-μ converts spontaneously to MOR-μ* (basal signaling). Persistent upregulation of MOR-μ* has been invoked as a hallmark of opioid dependence. Contrasting interactions with both MOR-μ and MOR-μ* can account for distinct pharmacological characteristics of inverse agonists (naltrexone), neutral antagonists (6β-naltrexol), and mixed opioid agonist-antagonists (buprenorphine). Upon binding to MOR-μ*, naltrexone but not 6β-naltrexol suppresses MOR-μ*signaling. Naltrexone blocks opioid analgesia non-competitively at MOR-μ*with high potency, whereas 6β-naltrexol must compete with agonists at MOR-μ, accounting for ~100-fold lower in vivo potency. Buprenorphine’s bell-shaped dose–response curve may also result from opposing effects on MOR-μ and MOR-μ*. In contrast, we find that 6β-naltrexol potently prevents dependence, below doses affecting analgesia or causing withdrawal, possibly binding to MOR conformations relevant to opioid dependence. We propose that 6β-naltrexol is a biased opioid antagonist modulating opioid dependence at low doses, opening novel avenues for opioid pain therapy and use management.

A Closer Look at Anandamide Interaction With TRPV1.

The transient receptor potential subfamily vanilloid type 1 ion channel (TRPV1), located in the peripheral nervous system has been implicated in the perception of pain and possesses the ability to be modulated by various cannabinoid ligands. Because of its location, TRPV1 is an ideal target for the development of novel pain therapeutics. Literature precedent suggests a wide range of cannabinoid ligands can activate TRPV1, but the location and mode of entry is not well understood. Understanding the modes in which cannabinoids can enter and bind to TRPV1 can aid in rational drug design. The first endogenous ligand identified for TRPV1 was the endocannabinoid, anandamide (AEA). The Molecular Dynamics (MD) studies discussed here investigate the entry mode of AEA into TRPV1. During the course of the 10+ microsecond MD simulations, two distinct binding modes were observed: AEA binding in the tunnel formed by the S1–S4 region, and AEA binding in the vanilloid binding pocket, with preference for the former. Unbiased MD simulations have revealed multiple spontaneous binding events into the S1–S4 region, with only one event of AEA binding the vanilloid binding pocket. These results suggest that AEA enters TRPV1 via a novel location between helices S1–S4 via the lipid bilayer.

Discovery of a Highly Selective Sigma-2 Receptor Ligand, 1-(4-(6,7-Dimethoxy-3,4-dihydroisoquinolin-2(1H)-yl)butyl)-3-methyl-1H-benzo[d]imidazol-2(3H)-one (CM398), with Drug-Like Properties and Antinociceptive Effects In Vivo.

The sigma-2 receptor has been cloned and identified as Tmem97, which is a transmembrane protein involved in intracellular Ca2+ regulation and cholesterol homeostasis. Since its discovery, the sigma-2 receptor has been an extremely controversial target, and many efforts have been made to elucidate the functional role of this receptor during physiological and pathological conditions. Recently, this receptor has been proposed as a potential target to treat neuropathic pain due to the ability of sigma-2 receptor agonists to relieve mechanical hyperalgesia in mice model of chronic pain. In the present work, we developed a highly selective sigma-2 receptor ligand (sigma-1/sigma-2 selectivity ratio > 1000), 1-(4-(6,7-dimethoxy-3,4-dihydroisoquinolin-2(1H)-yl)butyl)-3-methyl-1H- benzo[d]imidazol-2(3H)-one (CM398), with an encouraging in vitro and in vivo pharmacological profile in rodents. In particular, radioligand binding studies demonstrated that CM398 had preferential affinity for sigma-2 receptor compared with sigma-1 receptor and at least four other neurotransmitter receptors sites, including the norepinephrine transporter. Following oral administration, CM398 showed rapid absorption and peak plasma concentration (Cmax) occurred within 10min of dosing. Moreover, the compound showed adequate, absolute oral bioavailability of 29.0%. Finally, CM398 showed promising anti-inflammatory analgesic effects in the formalin model of inflammatory pain in mice. The results collected in this study provide more evidence that selective sigma-2 receptor ligands can be useful tools in the development of novel pain therapeutics and altogether, these data suggest that CM398 is a suitable lead candidate for further evaluation.