Exploring Dynorphin Analogs as Kappa Opioid Receptor Antagonists
Structures of arodyn and zyklophin.
Structural modifications from dynorphin A-(1-11) are highlighted in blue and red.
We have studied the SAR of the endogenous KOR agonist dynorphin A extensively and identified a number of analogs that are KOR antagonists. We demonstrated that the linear peptide arodyn exhibited KOR antagonist activity after direct injection into the brain in mice and could prevent stress-induced relapse to cocaine-seeking behavior. However, this linear peptide is susceptible to metabolism by proteases, and therefore we examined the cyclic dynorphin A analog zyklophin for its KOR antagonist activity in mice. This peptide exhibits enhanced stability to proteolytic degradation compared to linear peptides, and is active after systemic (subcutaneous) administration in mice. In spite of its large (>1400) molecular weight and polar structure it can cross the blood-brain barrier to antagonize KOR in the CNS at a dose of only 3 mg/kg s.c. and prevent stress-induced relapse of cocaine-seeking behavior. Importantly, the peptide exhibits the desired finite duration of KOR antagonist activity (<12 hours).
We are continuing to study zyklophin to explore how structural features of this peptide affect not only its KOR antagonist activity, but also its ability to cross the blood-brain barrier.
Zyklophin administered subcutaneously can block the antinociception of the selective KOR agonist U50,488 administered centrally (i.c.v.) in the mouse 55 oC warm-water tail withdrawal (WWTW) assay. (From Aldrich et al., Proc. Natl. Acad. Sci. U.S.A. 2009, 106, 18396-18401)
- A.A. Joshi, T.F. Murray, and J.V. Aldrich. Structure-Activity Relationships of the Peptide Kappa Opioid Receptor Antagonist Zyklophin. J. Med. Chem. 2015, 58, 8783-8795. https://www.ncbi.nlm.nih.gov/pubmed/26491810
- Aldrich, J. V.; Patkar, K. A.; McLaughlin, J. P. Zyklophin, a systemically active selective kappa opioid receptor peptide antagonist with short duration of action. Proc Natl Acad Sci U S A 2009, 106, 18396-18401
- P. Huang, T. Yakovleva, J.V. Aldrich, J. Tunis, C. Parry, L.Y. Liu-Chen. Two short-acting kappa opioid receptor antagonists (zyklophin and LY2444296) exhibited different behavioral effects from the long-acting antagonist norbinaltorphimine in mouse anxiety tests. Neruosci Lett. 2016, 615, 15-20. https://www.ncbi.nlm.nih.gov/pubmed/26780565
Optimization of RCM cyclization involving aromatic residues
We are exploring novel approaches to prepare cyclic analogs of arodyn, taking advantage of the sequence of aromatic amino acids in the N-terminus. We have examined cyclization using ring-closing metathesis (RCM) to constrain not only the peptide backbone, but also the aromatic side chains. A side reaction during the cyclization led to low yields of the desired cyclic peptides and linear byproducts. We have done extensive optimization of this cyclization reaction and are using it to prepare a variety of cyclic analogs for examination of their KOR antagonist activity. Analogs that maintain KOR affinity and selectivity have been identified, and we are continuing to use this methodology to prepare novel cyclic analogs of arodyn.
- S.A. Gisemba, J.V. Aldrich. Optimized Ring Closing Metathesis Reaction Conditions To Suppress Desallyl Side Products in the Solid-Phase Synthesis of Cyclic Peptides Involving Tyrosine(O-allyl). J. Org. Chem. 2020 [Epub ahead of print]. https://www.ncbi.nlm.nih.gov/pubmed/31880448
- W.J. Fang, T.F. Murray, J.V. Aldrich. Design, synthesis, and opioid activity of arodyn analogs cyclized by ring-closing metathesis involving Tyr(allyl). Bioorg Med Chem. 2018, 26, 1157-1161. https://www.ncbi.nlm.nih.gov/pubmed/29273415
- N. Carey, K. Borozny, J. V. Aldrich and J. P. McLaughlin, “Reinstatement of Cocaine Place-Conditioning Prevented by the Peptide Kappa Opioid Antagonist, Arodyn,” Eur. J. Pharmacol.2007, 569, 84-89. https://www.ncbi.nlm.nih.gov/pubmed/17568579