Discipline: Chemistry and Chemical Sciences
Subcategory: Chemistry (not Biochemistry)
Christian Loo - California State University, Long Beach
Co-Author(s): Sean Henry, University of Michigan, Ann Arbor, Michigan; Jack Twarozynski, University of Michigan, Ann Arbor, Michigan; Jessica Anand, University of Michigan, Ann Arbor, Michigan; John Traynor, University of Michigan, Ann Arbor, Michigan; Katarzyna Sobczyk-Kojiro, University of Michigan, Ann Arbor, Michigan; Henry Mosberg, University of Michigan, Ann Arbor, Michigan.
Opioid analgesics are valuable assets in the treatment of severe and chronic pain as they are capable of producing potent analgesia. Although commonly prescribed, opioids can generate tolerance, dependence, and respiratory depression. Opioids work by acting on up to three opioid receptors: mu-opioid receptor (MOR), delta-opioid receptor (DOR), and kappa-opioid receptor (KOR). Mixed efficacy mu-opioid receptor (MOR) agonist/delta-opioid receptor (DOR) antagonist peptidomimetics have shown great promise as of late in being able to produce antinociception with reduced tolerance and dependence.
Previously, it was found that peptidomimetics containing the pharmacophore regions of a dimethyl tyrosine and benzyl group linked by a benzylic core with an O-n-propyl substituent demonstrated the desired MOR-agonism/DOR-antagonism profile. Although moderately stable and highly efficacious at MOR in vitro, the compound was found to be inactive in vivo. In an attempt to enable in vivo activity, we replaced the benzyl pendant with various cyclic basic amine pendants which have been suggested to increase metabolic stability and promote MOR/DOR efficacy. To test these compounds in vitro, binding affinities (Ki (nM)) were obtained by competitive displacement of radiolabeled [3H] diprenorphine in membrane preparations expressing MOR, DOR, or KOR and efficacy data were obtained using agonist-induced stimulation of [35S] GTP?S binding. Initial tests of the O-n-propylated compounds containing the basic amine pendants have revealed that they demonstrate full agonism at MOR and partial to no stimulation at DOR. Given the promising MOR/DOR profile of these compounds, they will be submitted for in vivo testing to determine activity, duration of action, and metabolic stability. Future studies may investigate other either larger or smaller basic amine pendant substitutions to better elucidate the relationship between size and efficacy, binding, and potency at the opioid receptors. This study also included a probing molecule featuring a stereocenter that was previously found to enhance metabolic stability, but greatly reduce MOR-agonism. This was to test if the addition of a basic amine pendant could overcome this poor agonism. Initial in vitro tests of the probing molecule have found that the addition of the basic amine pendant lead to similar binding, decreased potency, and similar MOR-efficacy compared to the benzyl pendant analog. As the current probing molecule incorporated a piperidine pendant, a future study might test the inclusion of an isoindoline pendant instead as that was the pendant that generated the highest MOR stimulation.
Funder Acknowledgement(s): NSF Interdisciplinary Research Experience for Undergraduates Program; NIH MARC Program; NIDA Grant DA003910NIH Grant# DA033397
Faculty Advisor: Dr. Henry Mosberg, email@example.com
Role: For this project, I synthesized all five of the peptidomimetic compounds tested in vitro. Each of the five compounds required a multi-step synthesis which I performed. This also involved analyzing the NMR data after each step to confirm the identity of the product, purifying the final product by HPLC, and identifying the final product by both NMR and liquid chromatography-mass spectrometry. After receiving the in vitro data back from our pharmacology collaborator, I interpreted the results.