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

Abstract

Translation of promising preclinical efficacy data for investigational analgesics to positive clinical trial outcomes is limited, despite the large collective effort to date. However, one target with positive proof-of-concept clinical trial data is the angiotensin II type 2 (AT2) receptor. This review addresses the obstacles impeding successful preclinical to clinical research translation in the novel analgesics field, and it also provides an overview of the discovery and development of EMA401, a peripherally restricted, highly selective, orally active, small-molecule AT2 receptor antagonist for relief of neuropathic pain. Multiple AT2 receptor antagonists evoked dose-dependent antiallodynia in the chronic constriction injury of the sciatic nerve rat model of neuropathic pain. In AT2 receptor knockout chronic constriction injury mice, antiallodynia was abolished, affirming the AT2 receptor as the target. Subsequently, AT2 receptor antagonists were shown to evoke pain relief in multiple rodent chronic pain models. EMA401 (sodium salt) was selected as the drug candidate based on its >10,000-fold binding selectivity c.f. the angiotensin II type 1 receptor, good potency, and favourable pharmacokinetics. Animal toxicology and safety testing along with phase 1 clinical trials in healthy volunteers showed that oral EMA401 was safe and well-tolerated. Based on these data, a proof-of-concept clinical trial of oral EMA401 was undertaken in patients with postherpetic neuralgia. This 4-week trial showed that EMA401 evoked superior relief of postherpetic neuralgia relative to placebo and there were no serious adverse events in the EMA401 group.