DBPR116, a Prodrug of BPRMU191, in Combination with Naltrexone as a Safer Opioid Analgesic Than Morphine via Peripheral Administration

The development of opioid analgesics with reduced adverse effects is an unmet need. In a previous study, we discovered a unique combination of BPRMU191 and morphinan antagonists that produced potent antinociception with reduced adverse effects after central administration (intrathecal or intracerebroventricular). BPRMU191/naltrexone exhibits notable in vitro and in vivo pharmacological properties. However, the poor blood–brain barrier penetrative ability of BPRMU191 restricts its clinical application. In this study, we utilized a prodrug strategy to deliver sufficient brain concentrations of BPRMU191 and selected compound 2 (DBPR116) with the best physicochemical and pharmacological properties among other in vivo active prodrugs. The in vivo pharmacological studies of compound 2/naltrexone, including thermally stimulated pain, cancer pain, constipation, sedation, psychological dependence, heart rate, and respiratory frequency measurements, demonstrated that it was a safer opioid analgesic than morphine in pain control.