OBJECTIVES:The neurotrophin receptor TrkA is a clinically and genetically validated target in pain signaling. Anti-nerve growth factor (NGF) monoclonal antibodies have shown clinical efficacy but with side effects such as rapidly progressing osteoarthritis limiting their use, potentially mediated via inhibition of NGF/p75NTR signaling. Therefore, we sought to identify novel and selective small molecule negative allosteric modulators of tropomyosin receptor kinase A (TrkA) and to verify their analgesic effect in vivo. METHODS:We have identified ACD137 as a potent and selective negative allosteric modulator (NAM) of TrkA during a lead optimization program. The potency of ACD137 on TrkA and selectivity over TrkB was determined in cell-based assays. ACD137 was tested for its analgesic and anti-inflammatory effects in a model of chemotherapy induced peripheral neuropathy (CIPN) using paclitaxel and in the mono-iodo acetate (MIA)-induced osteoarthritis model in rats. RESULTS:ACD137 demonstrated an IC50-value on TrkA of 1.2 nM and showed approximately 17,300- and 17,600-fold selectivivity for TrkA over TrkB and TrkC, respectively. After oral administration in rats, ACD137 reduced mechanical allodynia in the CIPN model in a dose-dependent manner with maximal analgesic efficacy similar to the effect of gabapentin. In a comparative arthritis study using the anti-NGF antibody tanezumab as comparator, ACD137 reduced both evoked and non-evoked pain behavior as well as inflammation with similar efficacy as tanezumab. Surprisingly, ACD137 demonstrated a significant protective effect against knee joint deterioration, something that was not observed with tanezumab. CONCLUSIONS:The data demonstrates that ACD137 is a potent, selective and in vivo active negative allosteric modulator of TrkA exhibiting analgesic effects in models of neuropathic and nociceptive pain. The molecule possesses promising properties for further pre-clinical development.

BACKGROUND:The transient receptor potential cation channel subfamily V1 (TRPV1) receptor is an important factor in pain transmission. The present Phase 2a study investigated the effect on evoked pain and safety of a topically administered TRPV1-antagonist (ACD440 Gel) in patients with chronic peripheral neuropathic pain (PNP). METHODS:This was an exploratory, randomized, placebo-controlled double-blind crossover study in patients with probable or definite PNP demonstrating sensory hypersensitivity, assessed as evoked pain on suprathreshold sensory stimulation, i.e. hyperalgesia. The aetiologies included a mix of postherpetic neuralgia, postoperative neuropathic pains, and chemotherapy-induced pain. Patients administered ACD440 Gel twice daily onto the painful area(s) for 7 days. Primary endpoint was hyperalgesia to brush, cold, heat, and pinprick. Secondary endpoints included spontaneous pain and Neuropathic Pain Symptom Inventory Questionnaire (NPSI). Due to a significant period effect, a post hoc analysis was conducted, including only period 1 data, i.e. a parallel group comparison. RESULTS:Fourteen patients were enrolled and completed the study. ACD440 Gel reduced pain intensity evoked by a 40°C thermoroller stimulus in heat hyperalgesic patients, by ACD440 from median 6 (IQR 4.75, 7.75) to 1.5 (IQR 0.75, 2.25), i.e. by -5.0 (95%CI -11.2, 1.2) vs placebo from median 4 (IQR 3.5, 5.0) to median 5.0 (IQR 4.5, 6.5), i.e. by 1.3 (95%CI -1.5, 4.2), p = 0.029. There were no adverse events induced by study treatment. Evoked mechanical hyperalgesia and brush allodynia were not significantly affected, p = 0.07. CONCLUSION:ACD440 Gel demonstrated a significant analgesic effect on thermally evoked pain, especially in suprathreshold heat pain. This is congruent with an attenuation of thermal hyperalgesia in chronic neuropathic pain patients with C-fibre mediated pain, while there was no effect on evoked pain related to Aβ and Aδ stimuli. The results support further clinical development in patients with thermally induced C-fibre mediated pain.

BACKGROUND:The TRPV1 receptor is a key molecule in pain generation. Previous development of oral TRPV1-antagonists was halted due to systemic heat insensitivity and body temperature alterations. The present Phase 1b study investigated the efficacy, safety and plasma exposure of a topically administered TRPV1-antagonist (ACD440 Gel) in healthy subjects. METHODS:The study comprised two parts. In part 1, 24 healthy subjects were included in this randomized double-blind, placebo-controlled, crossover trial. ACD440 Gel or Placebo was applied once daily and wiped off after 1 h, for 5 consecutive days. Assessments were done in normal skin, skin optimized for penetration (by stripping and occlusive gel application) and UVB-irradiated skin. Pain induced by thermo-nociceptive CO2 laser impulses generated laser-evoked potentials (LEPs), with readouts of peak-to-peak (PtP) amplitude in vertex-EEG and pain assessments by VAS (0-100). Endpoints include effects at 1 hour post-dose, AUC(Days 1-5) and AUC(0-24, Day 4). In UVB-irradiated skin, also pain on pinprick and skin redness were assessed. Part 2 explored the plasma pharmacokinetics of ACD440. RESULTS:ACD440 Gel reduced LEP PtP amplitude and VAS pain, p < 0.001, in all skin conditions, versus placebo. In UVB-irradiated skin, pinprick pain was also reduced, p = 0.047. Effects were significant after 1 h, maintaining for at least 9 h. There were no adverse events or drug-induced erythema. Plasma exposures of ACD440 were too low to establish an elimination half-life of ACD400. CONCLUSIONS:Topical ACD440 Gel demonstrated a significant analgesic effect on LEP, VAS score and pinprick pain, with low systemic exposures, supporting further clinical development. SIGNIFICANCE:This study demonstrates that the topical administration of a TRPV1-antagonist, ACD440 Gel, has potential as a new treatment for painful conditions affecting the skin, such as chronic peripheral neuropathic pain, without any local or systemic side effects.

Purpose AlzeCure Pharma AB is developing novel positive allosteric modulators of Trk-receptors for treatment of Alzheimer’s disease, depression, other psychiatric conditions and other disorders where cognition is impaired. The preceding candidate drug ACD855 was shown to have a too long half-life in humans to allow further development. To de-risk the development of the follow-up compound ACD856, the oral single ascending dose study of ACD856 in humans was preceded by an intravenous microdose study, assessing the elimination half-life in plasma. Methods A phase 0 study with a microdose of ACD856 (0.100 mg), was conducted in six healthy male subjects all receiving ACD856. Sequentially, a randomized, placebo-controlled, double-blind Phase I single ascending oral dose study (1 – 150 mg) was conducted, including 56 healthy subjects. Both studies assessed the safety and tolerability, as well as the PK properties of ACD856 after single dose intravenous and oral administration. Results ACD856 was well tolerated with no treatment emergent, or dose related adverse events or other safety assessments. In the microdose study, ACD856 exhibited a bi-exponential plasma decline, low distribution volume, low plasma clearance with a half-life of approximately 20 hours. Orally, ACD856 exhibited rapid absorption, an almost complete bioavailability and a dose proportional increase in exposure. While the C max was lowered and delayed by food intake, the effect on plasma half-life and the overall bioavailability was low. No renal elimination of ACD856 was detected. Conclusion The prediction proved accurate demonstrating the value of conducting a microdose study prior to ascending dose studies. Trial registration NCT05783830 March 24, 2023 (microdose study, retrospectively registered) and NCT05077631 October 14, 2021 (single ascending dose study).

Neurotrophins are important regulators of neuronal and non-neuronal functions. As such, the neurotrophins and their receptors, the tropomyosin receptor kinase (Trk) family of receptor tyrosine kinases, has attracted intense research interest and their role in multiple diseases including Alzheimer's disease has been described. Attempts to administer neurotrophins to patients have been reported, but the clinical trials have so far have been hampered by side effects or a lack of clear efficacy. Thus, much of the focus during recent years has been on identifying small molecules acting as agonists or positive allosteric modulators (PAMs) of Trk receptors. Two examples of successful discovery and development of PAMs are the TrkA-PAM E2511 and the pan-Trk PAM ACD856. E2511 has been reported to have disease-modifying effects in preclinical models, whereas ACD856 demonstrates both a symptomatic and a disease-modifying effect in preclinical models. Both molecules have reached the stage of clinical development and were reported to be safe and well tolerated in clinical phase 1 studies, albeit with different pharmacokinetic profiles. These two emerging small molecules are interesting examples of possible novel symptomatic and disease-modifying treatments that could complement the existing anti-amyloid monoclonal antibodies for the treatment of Alzheimer's disease. This review aims to present the concept of positive allosteric modulators of the Trk receptors as a novel future treatment option for Alzheimer's disease and other neurodegenerative and cognitive disorders, and the current preclinical and clinical data supporting this new concept. Preclinical data indicate dual mechanisms, not only as cognitive enhancers, but also a tentative neurorestorative function.

Neurotrophins are important regulators of neuronal and non-neuronal functions. As such, the neurotrophins and their receptors, the tropomyosin receptor kinase (Trk) family of receptor tyrosine kinases, has attracted intense research interest and their role in multiple diseases including Alzheimer’s disease has been described. Attempts to administer neurotrophins to patients have been reported, but the clinical trials have so far have been hampered by side effects or a lack of clear efficacy. Thus, much of the focus during recent years has been on identifying small molecules acting as agonists or positive allosteric modulators (PAMs) of Trk receptors. Two examples of successful discovery and development of PAMs are the TrkA-PAM E2511 and the pan-Trk PAM ACD856. E2511 has been reported to have disease-modifying effects in preclinical models, whereas ACD856 demonstrates both a symptomatic and a disease-modifying effect in preclinical models. Both molecules have reached the stage of clinical development and were reported to be safe and well tolerated in clinical phase 1 studies, albeit with different pharmacokinetic profiles. These two emerging small molecules are interesting examples of possible novel symptomatic and disease-modifying treatments that could complement the existing anti-amyloid monoclonal antibodies for the treatment of Alzheimer’s disease. This review aims to present the concept of positive allosteric modulators of the Trk receptors as a novel future treatment option for Alzheimer’s disease and other neurodegenerative and cognitive disorders, and the current preclinical and clinical data supporting this new concept. Preclinical data indicate dual mechanisms, not only as cognitive enhancers, but also a tentative neurorestorative function.

ACD856 is a positive allosteric modulator of tropomyosin receptor kinase (Trk) receptors which has shown to have pro-cognitive and anti-depressant-like effects in various animal models. It is currently in clinical development for the treatment of Alzheimer’s disease and other disorders where cognition is impaired and is also considered for indications such as depression or other neuropsychiatric diseases. ACD856 has a novel mechanism of action modulating the activity of the Trk-receptors, resulting in increased stimulation of the neurotrophin signaling pathways. Previous studies applying single intravenous and oral doses of ACD856 indicate that ACD856 is safe and well-tolerated by healthy volunteer subjects, and that it has suitable safety and pharmacokinetic properties for further clinical development. To investigate the safety and tolerability of 7 days of treatment with multiple ascending oral doses of ACD856 in healthy subjects, and to characterize its pharmacokinetic (PK) properties. In addition, pharmacodynamic effects of ACD856 using quantitative electroencephalography (qEEG) as an indicator for central target engagement were assessed. This was a prospective, phase I, double-blind, parallel-group, placebo-controlled, randomized study of the safety, tolerability, PK and pharmacodynamics of multiple ascending oral doses of ACD856 in healthy subjects. ACD856 or placebo were administered in 3 ascending dose cohorts of 8 subjects. Within each cohort, subjects were randomized to receive either ACD856 (n=6) or placebo (n=2). The study was conducted at a First-in-Human unit in Sweden. Twenty-four healthy male and female subjects. The study medication was administered as an oral solution, with ACD856 or the same contents without the active ingredient (placebo). The dose levels ranged from 10 mg to 90 mg. ACD856 was administered once daily for 7 days, targeting steady state. Safety and tolerability assessments included adverse events, laboratory, vital signs, 12-lead electrocardiogram (ECG), physical examination, assessment of stool frequency and questionnaires to assess symptoms of anxiety, depression, as well as suicidal ideation and behavior. In addition, cardiodynamic ECGs were extracted to evaluate cardiac safety. PK parameters were calculated based on measured concentrations of ACD856 in plasma, urine, and cerebrospinal fluid (CSF) samples. Metabolite profiling, characterization and analysis was performed based on and urine samples. qEEG was recorded for patients in the two highest dose cohorts (30 and 90 mg/day) as a pharmacodynamic assessment to explore central target engagement. Treatment with ACD856 was well tolerated with no serious adverse events. No treatment emergent or dose related trends were observed for any of the safety assessments. ACD856 was rapidly absorbed and reached maximum plasma exposure at 30 to 45 minutes after administration. Steady state was reached before Day 6, with an elimination half-life at steady state of approximately 20 hours. At steady state, ACD856 exhibited accumulation ratios for Cmax and AUC of approximately 1.6 and 1.9 respectively. The exposure, Cmax and AUC0-24, increased proportionally with the dose. There was no unchanged ACD856 detected in urine. The metabolic pattern in urine and plasma was similar, and in alignment with the metabolites observed in preclinical toxicology studies. The level of ACD856 measured in CSF at steady state increased with dose, indicating Central Nervous System (CNS) exposure at relevant levels for pharmacodynamic effects. ACD856 demonstrated significant dose-dependent treatment-associated changes on qEEG parameters. Specifically, increase of the relative theta power and decrease of the fast alpha and beta power was observed, leading to an acceleration of the delta+theta centroid and an increase in the theta/beta ratio. ACD856 was well tolerated at the tested dose levels (10–90 mg/daily for 7 days) in healthy subjects. The compound has a robust pharmacokinetic profile, with rapid absorption and dose-dependent exposure. ACD856 was shown to pass the blood-brain-barrier, reach relevant exposure in the CNS and to induce dose-dependent treatment-related changes on qEEG parameters, indicating central target engagement.

ABSTRACT:Paradoxical heat sensation (PHS) is the perception of warmth when the skin is cooled. Paradoxical heat sensation rarely occurs in healthy individuals but more frequently in patients suffering from lesions or disease of the peripheral or central nervous system. To further understand mechanisms and epidemiology of PHS, we evaluated the occurrence of PHS in relation to disease aetiology, pain levels, quantitative sensory testing parameters, and Neuropathic Pain Symptom Inventory (NPSI) items in patients with nervous system lesions. Data of 1090 patients, including NPSI scores from 404 patients, were included in the analysis. We tested 11 quantitative sensory testing parameters for thermal and mechanical detection and pain thresholds, and 10 NPSI items in a multivariate generalised linear model with PHS, aetiology, and pain (yes or no) as fixed effects. In total, 30% of the neuropathic patients reported PHS in contrast to 2% of healthy individuals. The frequency of PHS was not linked to the presence or intensity of pain. Paradoxical heat sensation was more frequent in patients living with polyneuropathy compared with central or unilateral peripheral nerve lesions. Patients who reported PHS demonstrated significantly lower sensitivity to thermal perception, with lower sensitivity to normally painful heat and cold stimuli. Neuropathic Pain Symptom Inventory scores were lower for burning and electric shock-like pain quality for patients with PHS. Our findings suggest that PHS is associated with loss of small thermosensory fibre function normally involved in cold and warm perception. Clinically, presence of PHS could help screening for loss of small fibre function as it is straightforward to measure or self-reported by patients.

ACD856 is a novel positive allosteric modulator of Trk-receptors in clinical development for the treatment of Alzheimer’s disease and other disorders where cognition is impaired. The aim of this study was to assess the safety, tolerability, pharmacokinetics (PK) and pharmacodynamics (PD) of multiple ascending doses of ACD856. 24 healthy volunteer subjects were administered ACD856 or placebo as a daily oral solution over 7 days in 3 cohorts of stepwise ascending doses. After each dose, the safety, tolerability, and pharmacokinetics of ACD856 were assessed by an internal Safety Review Committee to decide on the escalation of dose to the next cohort. There were no clinically significant changes from baseline in mean ECG, vital signs, physical examination findings, clinical chemistry, haematology, coagulation, or urinalysis parameters after receiving the 7 daily doses of ACD856. Occasional individual abnormal laboratory values were observed but all were assessed as not clinically significant. Most of the reported adverse events were of mild intensity, only a few were of moderate intensity and none of severe intensity. No serious adverse events were reported. The pharmacokinetic data confirmed the findings from the previously performed single ascending dose (SAD) study, including that ACD856 has a rapid absorption, long half-life, high bioavailability, and a linear dose-dependent exposure. The C max at steady state was approximately 1.6-fold higher than the initial dose administration and no time-dependent clearance was observed. Moreover, initial CSF data confirms CNS exposure of ACD856. Further PK, CSF and pharmacodynamic data will be shown at the time of presentation. ACD856 was shown to be safe and well tolerated in man at the tested dose levels and with a suitable pharmacokinetic profile for further clinical development. In the next step, ACD856 will be evaluated in a phase Ib study with the aim to further assess pharmacodynamic effects.

Visceral pain is a prominent feature of various gastrointestinal diseases. The P2X7 receptor is expressed by multiple cell types including dorsal root ganglion satellite glial cells, macrophages and spinal microglia, all of which have been implicated in nociceptive sensitization. We have used the selective and CNS penetrant P2X7 receptor antagonist Lu AF27139 to explore this receptor’s role in distinct rat models of inflammatory and visceral hypersensitivity. Rats injected with CFA in the hindpaw displayed a marked reduction in hindpaw mechanical threshold, which was dose-dependently reversed by Lu AF27139 (3–30 mg/kg, p.o.). In rats injected with TNBS in the proximal colon, the colorectal distension threshold measured distally was significantly lower than sham treated rats at 7 days post-injection (P < 0.001), indicative of a marked central sensitization. Colonic hypersensitivity was also reversed by Lu AF27139 (10–100 mg/kg) and by the κ-opioid receptor agonist U-50,488H (3 mg/kg, s.c.). Moreover, both Lu AF27139 and U-50,488H prevented a TNBS-induced increase in spinal and brain levels of PGE2 and LTB4, as well as an increase in brain levels of PGF2α and TXB2. Lu AF27139 was well tolerated as revealed by a lack of significant effect on rotarod motor function and coordination at all doses tested up to 300 mg/kg. Thus, P2X7 receptor antagonism is efficacious in a rat model of visceral pain, via a mechanism which potentially involves attenuation of microglial function within spinal and/or supraspinal pain circuits, albeit a peripheral site of action cannot be excluded.

P2X7 receptor antagonists have potential for treating various central nervous system (CNS) diseases, including neuropathic pain, although none have been approved for clinical use. Reasons may include insufficient understanding of P2X7 receptor signalling in pain, and the lack of a corresponding preclinical mechanistic biomarker.Lu AF27139 is a highly selective and potent small molecule antagonist at rat, mouse and human forms of the P2X7 receptor, with excellent pharmacokinetic and CNS permeability properties. In the current experiments, we probed the utility of previously characterized and novel signalling cascades exposed to Lu AF27139 using cultured microglia combined with release assays. Subsequently, we assessed the biomarker potential of identified candidate molecules in the rat chronic constriction injury (CCI) model of neuropathic pain; study design limitations precluded their assessment in spared nerve injury (SNI) rats.Lu AF27139 blocked several pain-relevant pathways downstream of P2X7 receptors in vitro. At brain and spinal cord receptor occupancy levels capable of functionally blocking P2X7 receptors, it diminished neuropathic hypersensitivity in SNI rats, and less potently in CCI rats. Although tissue levels of numerous molecules previously linked to neuropathic pain and P2X7 receptor function (e.g. IL-6, IL-1β, cathepsin-S, 2-AG) were unaffected by CCI, Lu AF27139-mediated regulation of spinal PGE2 and miRNA (e.g. rno-miR-93-5p) levels increased by CCI aligned with its ability to diminish neuropathic hypersensitivity.We have identified a pain-relevant P2X7 receptor-regulated mechanism in neuropathic rats, which could hold promise as a translatable biomarker and by association enhance the clinical progression of P2X7 receptor antagonists in neuropathic pain.Sub-optimal translation of preclinical molecules has hindered the clinical development of novel mechanism of action analgesics. We have undertaken a comprehensive in vitro analysis of migroglial signalling mechanisms recruited upon P2X7 receptor activation, a number of which were shown to be modulated by a selective P2X7 receptor antagonist in a well characterized animal model of neuropathic pain. Subject to further confirmation in other neuropathic models, this opens up the possibility to investigate their clinical utility as potential pain biomarkers in patients.

Furthermore, the authors have not taken into consideration the natural course of events of the standardized Swedish IDT program, where patients are usually fully or partially on sickness absence. In the statistics section, it is described that the initial 90 days were excluded from the analysis. However, after participation in an IDT program, time at work is usually stepwise increased during the consecutive 0–12 months where patients are partially or fully on sick leave. The authors comment on this in the results as ‘Interdisciplinary treatment patients consistently had a higher probability than controls of receiving sickness absence benefits, with the largest differences observed in the first year’. The common practice of stepwise reintroduction to working life, mostly affecting IDT patients, has not been addressed. Consequently, the use of sickness absence as major endpoint in a study about chronic pain treatment is controversial and the conclusions drawn in this study about the value of IDT are problematic. We believe that these points need a further and wider discussion in the scientific as well as in the clinical community engaged in chronic pain management. We definitely do agree with the authors claim ‘Nonetheless, as IDT is an internationally recommended intervention that represents a considerable resource burden on the healthcare system, despite inconclusive evidence for its effects, this calls for more adequately powered randomized controlled trials and better designed epidemiological studies’. The authors declare that they have no conflict of interest.

The pathophysiology of pain in neuropathy is complex and may be linked to sensory phenotypes. Quantitative sensory testing, a standardized method to evaluate sensory profiles in response to defined stimuli, assesses functional integrity of small and large nerve fiber afferents and central somatosensory pathways. It has revealed detailed insights into mechanisms of neuropathy, yet it remains unclear if pain directly affects sensory profiles. The main objective of this study was to investigate sensory profiles in patients with various neuropathic conditions, including polyneuropathy, mononeuropathy, and lesions to the central nervous system, in relation to self-reported presence or absence of pain and pain sensitivity using the Pain Sensitivity Questionnaire. A total of 443 patients (332 painful and 111 painless) and 112 healthy participants were investigated. Overall, loss of sensation was equally prevalent in patients with and without spontaneous pain. Pain thresholds were equally lowered in both patient groups, demonstrating that hyperalgesia and allodynia are just as present in patients not reporting any pain. Remarkably, this was similar for dynamic mechanical allodynia. Hypoalgesia was more pronounced in painful polyneuropathy, whereas hyperalgesia was more frequent in painful mononeuropathy (compared with painless conditions). Self-reported pain sensitivity was significantly higher in painful than in painless neuropathic conditions. Our results reveal the presence of hyperalgesia and allodynia in patients with central and peripheral lesions of the somatosensory system not reporting spontaneous pain. This shows that symptoms and signs of hypersensitivity may not necessarily coincide and that painful and painless neuropathic conditions may mechanistically blend into one another.

Objective To test whether contralateral sensory abnormalities in the clinically unaffected area of patients with unilateral neuropathic pain are due to the neuropathy or pain mechanisms. Methods We analyzed the contralateral clinically unaffected side of patients with unilateral painful or painless neuropathy (peripheral nerve injury [PNI], postherpetic neuropathy [PHN], radiculopathy) by standardized quantitative sensory testing following a validated protocol. Primary outcome was the independent contribution of the following variables on the contralateral sensory function using generalized linear regression models: pain intensity, disease duration, etiology, body area, and sensory patterns in the most painful area. Results Among 424 patients (PNI n = 256, PHN n = 78, radiculopathy n = 90), contralateral sensory abnormalities were frequent in both painful (n = 383) and painless (n = 41) unilateral neuropathy, demonstrating sensory loss for thermal and mechanical nonpainful stimuli and both sensory loss and gain for painful test stimuli. Analysis by etiology revealed contralateral pinprick hyperalgesia in PHN and PNI. Analysis by ipsilateral sensory phenotype demonstrated mirror-image pinprick hyperalgesia in both mechanical and thermal hyperalgesia phenotypes. Pain intensity, etiology, and affected body region predicted changes in only single contralateral somatosensory parameters. Disease duration had no impact on the contralateral sensory function. Conclusion Mechanisms of sensory loss seem to spread to the contralateral side in both painful and painless neuropathies. Contralateral spread of pinprick hyperalgesia was restricted to the 2 ipsilateral phenotypes that suggest sensitization; this suggest a contribution of descending net facilitation from supraspinal areas, which was reported in rodent models of neuropathic pain but not yet in human patients.

ABSTRACT:Neuropathic pain highly affects quality of life, well-being, and function. It has recently been shown based on cluster analysis studies that most patients with neuropathic pain may be categorized into 1 of 3 sensory phenotypes: sensory loss, mechanical hyperalgesia, and thermal hyperalgesia. If these phenotypes reflect underlying pathophysiological mechanisms, they may be more relevant for patient management than underlying neurological diagnosis or pain intensity. The aim of this study was thus to examine the impact of these sensory phenotypes on mental health, functionality, and quality of life. Data of 433 patients from the IMI/EuroPain network database were analyzed, and results of HADS-D/A, Pain Catastrophizing Scale, Euro Quality of Life 5D/-VAS, Brief Pain Inventory, and Graded Chronic Pain Scale between the sensory phenotypes were compared using multiple regression analysis. There was no difference in chronic pain grade, pain intensity, depression, or anxiety scores between phenotypes. Pain interference (Brief Pain Inventory) was higher (P = 0.002); self-reported health state lower (Euro Quality of Life 5D VAS, P = 0.02); and problems regarding mobility (P = 0.008), usual activities (P = 0.004), and self-care (P = 0.039) more prominent (EQ5-D) in the sensory loss compared with the thermal hyperalgesia phenotype. Patients with sensory loss also showed higher pain catastrophizing scores (P = 0.006 and 0.022, respectively) compared with the 2 other groups. Sensory phenotype is associated with the impact of neuropathic pain conditions on well-being, daily functionality, and quality of life but is less associated with pain intensity. These results suggest that the somatosensory phenotype should be considered for personalized pain management.

Pain medication plays an important role in the treatment of acute and chronic pain conditions, but some drugs, opioids in particular, have been overprescribed or prescribed without adequate safeguards, leading to an alarming rise in medication-related overdose deaths. The NIH Helping to End Addiction Long-term (HEAL) Initiative is a trans-agency effort to provide scientific solutions to stem the opioid crisis. One component of the initiative is to support biomarker discovery and rigorous validation in collaboration with industry leaders to accelerate high-quality clinical research into neurotherapeutics and pain. The use of objective biomarkers and clinical trial end points throughout the drug discovery and development process is crucial to help define pathophysiological subsets of pain, evaluate target engagement of new drugs and predict the analgesic efficacy of new drugs. In 2018, the NIH-led Discovery and Validation of Biomarkers to Develop Non-Addictive Therapeutics for Pain workshop convened scientific leaders from academia, industry, government and patient advocacy groups to discuss progress, challenges, gaps and ideas to facilitate the development of biomarkers and end points for pain. The outcomes of this workshop are outlined in this Consensus Statement.

Background and Aims Healthy women have generally been found to have increased experimental pain perception and chronic pain has a higher prevalence in female as compared to male patients. However, no study has investigated whether pain intensity and pain perception thresholds are distinct or similar between sexes within various chronic pain entities. We investigated whether average pain intensities and pain thresholds assessed using quantitative sensory testing (QST) differed between women and men suffering from three distinct chronic pain conditions: Complex Regional Pain Syndrome (CRPS type I), peripheral nerve injury (PNI) or polyneuropathy (PNP), as compared to paired healthy volunteers. Methods QST data of 1,252 patients (669 female, 583 male) with PNI (n = 342), PNP (n = 571) or CRPS (n = 339), and average pain intensity reports from previously published studies were included. Absolute andz-values (adjusted for age and body region) of cold, heat, pressure (PPT) and pinprick pain thresholds were compared in generalized linear models with aetiology, duration of underlying pain disease and average pain intensity as fixed effects. Results Average pain intensity during the past four weeks did not differ between women and men, in both mean and range. In women absolute pain thresholds for cold, heat and pinprick were lower than in males across all diagnoses (p < .05). However, afterz-transformation these differences disappeared except for PPT in CRPS (p = .001). Discussion Pain thresholds in patients show only minor sex differences. However, these differences mimic those observed in healthy subjects and do not seem to be linked to specific pathophysiological processes. Significance Female healthy participants and female patients with neuropathic pain conditions or CRPS I report lower pain thresholds compared to males, but pain intensity is similar and there is no sex difference in the extent to which the thresholds are altered in neuropathic pain or CRPS. Thus, the sex differences observed in various chronic pain conditions mimic those obtained in healthy participants, indicating that these differences are not linked to specific pathophysiological processes and are of minor clinical relevance.

Tourette syndrome ( TS ) is a neuropsychiatric disorder characterised by multiple, persistent tics. These semi‐voluntary motor and phonic manifestations are typically aggravated by exposure to acute stress, yet the mechanisms underlying this exacerbation remain unclear. Using a well‐characterised animal model of TS , the D1 CT ‐7 mouse, we recently showed that acute stress increases tic‐like responses and causes sensorimotor gating deficits, as measured by the prepulse inhibition of the startle. We showed that these effects are promoted by the brain synthesis of the neurosteroid allopregnanolone ( AP ). In line with this idea, inhibition of AP synthesis by finasteride was found to suppress the tic‐exacerbating effects of stress; conversely, AP administration resulted in a marked enhancement of the number of tic‐like motor bursts. Given that the primary mechanism of AP is based on the positive allosteric modulation of GABA A receptors, in the present study, we hypothesised that the enhancement in tic‐like behaviours induced by either stress or AP may be countered by isoallopregnanolone (iso AP ), the natural 3β‐epimer of AP that acts as an antagonist to the AP ‐binding site within GABA A receptors. In agreement with our hypothesis, iso AP (5‐10 mg kg ‐1 , s.c. ) dose‐dependently reduced the number of tic‐like behaviours induced by stress in D1 CT ‐7 mice. These effects were comparable to those elicited by both the benchmark TS therapy haloperidol (0.3 mg kg ‐1 , i.p. ), as well as finasteride (25 mg kg ‐1 , i.p. ). Iso AP also countered the prepulse inhibition deficits secondary to stress in D1 CT ‐7 mice. Finally, iso AP opposed the enhancement of tic‐like behaviours induced by AP (15 mg kg ‐1 , i.p. ). Given that iso AP is well‐tolerated and has an optimal safety profile, these data suggest that this steroid may have therapeutic properties in TS .

BACKGROUND:The transient receptor potential cation channel subfamily V 1 (TRPV1) is involved in nociception and has thus been of interest for drug developers, as a target for novel analgesics. However, several oral TRPV1 antagonists have failed in development, and novel approaches to target TRPV1 with innovative chemistry are needed. METHOD:This work describes an intradermal microdosing approach in humans for pharmacodynamic deductions and pharmacological profiling of compounds. First, a human capsaicin model was developed, to generate pharmacodynamic translational data (Study Part A, n = 24). Then, three small molecule TRPV1 antagonists (AZ11760788, AZ12048189 and AZ12099548) were investigated in healthy volunteers (Study Part B, n = 36), applying the established model. Pain and flare were assessed by Visual Analogue Score and laser Doppler, respectively. RESULTS:The developed model proved useful for pharmacologic deductions; all compounds caused a dose-dependent inhibition of capsaicin-induced pain and flare responses, with a rank order potency of AZ11760788 > AZ12048189 ≫ AZ12099548. In addition, the dose-response data showed that the minimal antagonist concentrations needed to inhibit TRPV1 was ≥6-7 times the equilibrium dissociation constant for each compound. CONCLUSION:With careful design of a pharmacodynamic translational human pain model, it was possible to rank order TRPV1 efficacy among three investigational TRPV1 antagonists, and to estimate human efficacious concentrations. SIGNIFICANCE:This fast and cost-effective translational approach allows for generation of human target engagement information early in drug development. This could be of value for other development programmes where pharmacological targets are expressed in peripheral sensory nerves.