2,6-diazaspiro[3.4]octan-7-one derivatives as potent sigma-1 receptor antagonists that enhanced the antinociceptive effect of morphine and rescued morphine tolerance

Opioids are efficacious analgesics for pain treatments. However, their repeated use in large doses often leads to analgesic tolerance, which limits the clinical application. Sigma-1 receptor (σ1R) antagonists were reported to synergistically enhance the analgesic effect of mu opioid receptor (MOR) agonists without amplifying the adverse effects. Therefore, the σ1R is considered a promising drug target for pain management. Based on the recently elucidated co-crystal structure of σ1R with 4-IBP, we designed and developed a series of σ1R antagonists harboring the 2,6-diazaspiro[3.4]octan-7-one scaffold. Through a detailed structure-activity relationship study, we identified compound 32 as a potent σ1R antagonist, which significantly enhanced the antinociceptive effect of morphine and rescued morphine-induced analgesic tolerance. Our results support σ1R antagonism as a promising strategy to develop novel analgesics and highlight the therapeutic potential of compound 32 to prevent morphine tolerance.