Structural modification of salvinorin A, the active component of Salvia divinorum, has resulted in the synthesis of novel neoclerodane diterpenes with opioid receptor affinity and activity. We report in this study a nonnitrogenous neoclerodane diterpene with mu opioid receptor affinity (13) that is an agonist at mu opioid receptors. This represents the identification of a novel structural class of mu opioid receptor agonists.

G protein-coupled receptor desensitization and trafficking are important regulators of opioid receptor signaling that can dictate overall drug responsiveness in vivo. Furthermore, different -opioid receptor (OR) ligands can lead to varying degrees of receptor regulation, presumably because of distinct structural conformations conferred by agonist binding. For example, morphine binding produces a OR with low affinity for ␤-arrestin proteins and limited receptor internalization, whereas enkephalin analogs promote robust trafficking of both ␤-arrestins and the receptors. Here, we evaluate OR trafficking in response to activation by a novel -selective agonist derived from the naturally occurring plant product, salvinorin A. It is interesting that this compound, termed herkinorin, does not promote the recruitment of ␤-arrestin-2 to the OR and does not lead to receptor internalization. Moreover, whereas G protein-coupled receptor kinase overexpression can promote morphine-induced ␤-arrestin interactions and OR internalization, such manipulations do not promote herkinorin-induced trafficking. Studies in mice have shown that ␤-arrestin-2 plays an important role in the development of morphine-induced tolerance, constipation, and respiratory depression. Therefore, drugs that can activate the receptor without recruiting the arrestins may be a promising step in the development of opiate analgesics that distinguish between agonist activity and receptor regulation and may ultimately lead to therapeutics designed to provide pain relief without the adverse side effects normally associated with the opiate narcotics.

Salvinorin A, a potent hallucinogen isolated from the leaves of Salvia divinorum, has gained popularity among adolescents in the USA. No detailed study of the pharmacokinetics has been conducted in vivo. The present study investigates the in vivo pharmacokinetics of salvinorin A (0.032 mg/kg, i.v. bolus) in rhesus monkeys (n=4, 2 male, 2 female). The elimination t(1/2) was rapid (56.6+/-24.8 min) for all subjects. Pharmacokinetic differences (distribution t(1/2), elimination t(1/2), and AUC) were observed between males and females, suggesting potential sex differences in its pharmacologic effects. Salvinorin B, the presumed major metabolite, is observed to accumulate ex vivo; however, in this study it never reached the limit of detection.

Salvinorin A is a psychoactive natural product that has been found to be a potent and selective kappa opioid receptor agonist in vitro and in vivo. The activity of salvinorin A is unusual compared to other opioids such as morphine in that it mediates potent kappa opioid receptor signaling yet leads to less receptor downregulation than observed with other kappa agonists. Our initial chemical modifications of salvinorin A have yielded one analogue, herkinorin ( 1c), with high affinity at the microOR. We recently reported that 1c does not promote the recruitment of beta-arrestin-2 to the microOR or receptor internalization. Here we describe three new derivatives of 1c ( 3c, 3f, and 3i) with similar properties and one, benzamide 7b, that promotes recruitment of beta-arrestin-2 to the microOR and receptor internalization. When the important role micro opioid receptor regulation plays in determining physiological responsiveness to opioid narcotics is considered, micro opioids derived from salvinorin A may offer a unique template for the development of functionally selective mu opioid receptor-ligands with the ability to produce analgesia while limiting adverse side effects.