MGM-9

HSK21542 is a peripherally-restricted kappa opioid receptor (KOR) agonist developed for pain treatment. Because of the CNS pharmacological concern of opioid receptor activation, such as physical dependence and addiction potential, an assessment of abuse potential of HSK21542 was required prior to marketing approval. The preclinical abuse potential assessments for HSK21542 included the following studies: 1) intravenous self-administration study to explore the relative reinforcing efficacy in rats self-administering remifentanil; 2) rat drug discrimination study to examine the pharmacological similarity of the interoceptive or subjective effects of HSK21542 in rats discriminating pentazocine; 3) rat conditioned place preference (CPP) paradigm to test the rewarding effects; 4) rat natural physical dependence-spontaneous withdrawal study in rats chronically treated with HSK21542; 5) naloxone-precipitated withdrawal assay following chronic HSK21542 exposure to evaluate its physical dependence potential. The results showed that HSK21542 was devoid of behavioral evidence of positive reinforcing effect and did not share similar discriminative stimulus effects with pentazocine. HSK21542 also did not produce CPP in rats. In addition, HSK21542 did not produce spontaneous withdrawal or naloxone-precipitated withdrawal in rats with chronic treatments. Collectively, these preclinical findings suggest that HSK21542 has no abuse potential in animals, which demonstrate low abuse potential in humans.

Kappa opioid receptor (KOR) agonists represent promising therapeutics for pain relief due to their analgesic properties along with lower abuse potential than opioids that act at the mu opioid receptor. However, typical KOR agonists produce sedation and dysphoria. Previous studies have shown that G protein signaling-biased KOR agonists may present a means to untangle the desired analgesic properties from undesired side effects. In this paper, we report a new series of G protein signaling-biased KOR agonists entailing -S- → -CH₂- replacement in a previously reported KOR agonist, triazole 1.1. With an optimized carbon linker in hand, further development of the scaffold was undertaken to investigate the appendages of the triazole core. The structure-activity relationship study of this series is described, including several analogues that display enhanced potency while maintaining G protein-signaling bias compared to triazole 1.1.