Papers of the Week

HSK21542, a potent and peripherally-restricted kappa opioid receptor (KOR) agonist, is currently being developed to treat postoperative pain and pruritus. Given that conventional opioids (MOR agonists) are widely recognized for their toxicological impacts on the reproductive system and embryonic development, we evaluated the effects of HSK21542 accordingly. The results showed that HSK21542 did not influence male and female fertility or early embryonic development in rats. HSK21542 also did not show significant manifestations of pre- and post-natal development toxicity in rats. In the embryo-fetal developmental study, even though there was a 3.5% increase in incidence of fetuses with incomplete ossification of thoracic vertebral centrum in the 4 mg/kg/day group, the plasma exposure of HSK21542 in rats at the no observed adverse effect level (NOAEL) was 82.3 times higher than that of human exposure at 1 μg/kg. On the other hand, exposure to HSK21542 during pregnancy in rabbits did not show any teratogenic risk, only causing a minor impact on bone ossification in fetuses. In conclusion, HSK21542 has a favorable safety profile with only minor effects on the embryo-fetal developmental outcomes.