EST73502 hydrochloride is a selective, orally active and blood-brain barrier (BBB) penetrant dual μ-opioid receptor (MOR) agonist and σ1 receptor (σ1R) antagonist, with K i s of 64 nM and 118 nM for MOR and σ1R, respectively. EST73502 hydrochloride has antinociceptive activity with reduced opioid-induced relevant adverse events[1].

EST73502 hydrochloride administered orally (10-40 mg/kg) demonstrates a dose-dependent analgesic effect, achieving a peak reduction in pain of 64% with an Effective Concentration (EC 50) of 14 mg/kg in the paw pressure test on CD1 male mice [1]. Additionally, intraperitoneal injections of EST73502 hydrochloride (5 mg/kg; twice daily for 10 days) significantly mitigate mechanical allodynia caused by partial sciatic nerve ligation (PSNL) in these mice, showing a maximum efficacy of 56% [1]. This is observed in the same CD1 male mouse model using PSNL to simulate the condition [1].