Nonopioid analgesics discovery and the Valley of Death: EMA401 from concept to clinical trial

The angiotensin II type 2 receptor antagonists, PD123,319 ((S-( +)-1-[(4-(dimethylamino)-3-methylphenyl)methyl]-5-(diphenylacetyl)-4,5,6,7-tetrahydro-1H-imidazo[4,5-c]pyridine-6-carboxylic acid), EMA300 (5-(2,2-diphenylacetyl)-4-[(4-methoxy-3-methylphenyl)methyl]-1,4,6,7-tetrahydroimidazo[4,5-c]pyridine-6-carboxylic acid) and EMA401 ((3S)-5-(benzyloxy)-2-(2,2-diphenylacetyl)-6-methoxy-1,2,3,4-tetrahydroisoquinoline-3-carboxylic acid), evoke pain relief in a varicella zoster virus-induced rat model of neuropathic pain

Post-herpetic neuralgia (PHN) is a type of neuropathic (nerve) pain that persists for more than 3 months after crusting of the last shingles lesion. It is difficult to relieve with analgesic/adjuvant medications, and so novel analgesics are needed. Our aim was to use a rat model of varicella zoster virus (VZV)-induced neuropathic pain to assess the pain relief efficacy of several small molecule angiotensin II type 2 (AT2) receptor antagonists (PD123,319, EMA300, and EMA401) relative to clinically used analgesic/adjuvant agents from four different pharmacological classes. Male Wistar rats received a unilateral intraplantar injection of VZV-infected MRC-5 cells (2 × 104 infected cells) and paw withdrawal thresholds (PWTs) in the ipsilateral hindpaws were assessed using von Frey filaments. Animals with PWTs ≤ 8 g received single doses of PD123,319 (0.03-3 mg/kg), EMA300 (0.3-5 mg/kg), EMA401 (0.03-1 mg/kg), gabapentin (10-60 mg/kg), amitriptyline (5-30 mg/kg), morphine (0.1-3 mg/kg), meloxicam (5-20 mg/kg) or vehicle and PWT versus time curves were generated. Single doses of PD123,319, EMA300, EMA401, gabapentin and morphine-evoked dose-dependent anti-allodynia in the hindpaws of VZV-rats. The mean (95% confidence intervals) ED50s were 0.57 (0.04-1.7), 2.5 (1.0-3.7) and 0.41 (0.12-0.87) mg/kg for PD123,319, EMA300, and EMA401, respectively. The ED50s for gabapentin and morphine were 39.9 (25.1-64.8) and 0.04 (0.16-2.09) mg/kg, respectively. In conclusion, the anti-allodynic efficacy of EMA401 in a VZV-rat model of neuropathic pain is aligned with its analgesic efficacy in a Phase 2a clinical trial in patients with PHN. This model has utility for anti-allodynic efficacy assessment of novel AT2 receptor antagonists from drug discovery.

Advancing Pain Understanding and Drug Discovery: Insights from Preclinical Models and Recent Research Findings

Despite major advancements in our understanding of its fundamental causes, pain-both acute and chronic-remains a serious health concern. Various preclinical investigations utilizing diverse animal, cellular, and alternative models are required and frequently demanded by regulatory approval bodies to bridge the gap between the lab and the clinic. Investigating naturally occurring painful disorders can speed up medication development at the preclinical and clinical levels by illuminating molecular pathways. A wide range of animal models related to pain have been developed to elucidate pathophysiological mechanisms and aid in identifying novel targets for treatment. Pain sometimes drugs fail clinically, causing high translational costs due to poor selection and the use of preclinical tools and reporting. To improve the study of pain in a clinical context, researchers have been creating innovative models over the past few decades that better represent pathological pain conditions. In this paper, we provide a summary of traditional animal models, including rodents, cellular models, human volunteers, and alternative models, as well as the specific characteristics of pain diseases they model. However, a more rigorous approach to preclinical research and cutting-edge analgesic technologies may be necessary to successfully create novel analgesics. The research highlights from this review emphasize new opportunities to develop research that includes animals and non-animals using proven methods pertinent to comprehending and treating human suffering. This review highlights the value of using a variety of modern pain models in animals before human trials. These models can help us understand the different mechanisms behind various pain types. This will ultimately lead to the development of more effective pain medications.

Targeting sensory neuron GPCRs for peripheral neuropathic pain

Despite the high prevalence of peripheral neuropathic pain (NP) conditions and significant progress in understanding its underlying mechanisms, the management of peripheral NP remains inadequate. Existing pharmacotherapies for NP act primarily on the central nervous system (CNS) and are often associated with CNS-related adverse effects, limiting their clinical effectiveness. Mounting preclinical evidence indicates that reducing the heightened activity in primary sensory neurons by targeting G-protein-coupled receptors (GPCRs), without activating these receptors in the CNS, relieves pain without central adverse effects. In this review, we focus on recent advancements in GPCR-mediated peripheral pain relief and discuss strategies to advance the development of more effective and safer therapies for peripheral NP by shifting from traditional CNS modulatory approaches toward selective targeting of GPCRs on primary sensory neurons.

Angiotensin II type 2 receptor signalling as a pain target: Bench, bedside and back-translation

Translating promising preclinical pain relief data for novel molecules from drug discovery to positive clinical trial outcomes is challenging. The angiotensin II type 2 (AT2) receptor is a clinically-validated target based upon positive proof-of-concept clinical trial data in patients with post-herpetic neuralgia. This trial was conducted because AT2 receptor antagonists evoked pain relief in rodent models of neuropathic pain. EMA401 was selected as the drug candidate based upon its suitable preclinical toxicity and safety profile and good pharmacokinetics. Herein, we provide an overview of the discovery, preclinical and clinical development of EMA401, for the alleviation of peripheral neuropathic pain.