A structure-activity relationship study and combinatorial synthetic approach of C-terminal modified bifunctional peptides that are delta/mu opioid receptor agonists and neurokinin 1 receptor antagonists.
A series of bifunctional peptides with opioid agonist and substance P antagonist bioactivities were designed with the concept of overlapping pharmacophores. In this concept, the bifunctional peptides were expected to interact with each receptor separately in the spinal dorsal horn where both the opioid receptors and the NK1 receptors were found to be expressed, to show an enhanced analgesic effect, no opioid-induced tolerance, and to provide better compliance than coadministration of two drugs. Compounds were synthesized using a two-step combinatorial method for C-terminal modification. In the method, the protected C-terminal-free carboxyl peptide, Boc-Tyr( tBu)- d-Ala-Gly Phe-Pro-Leu-Trp(Boc)-OH, was synthesized as a shared intermediate using Fmoc solid phase chemistry on a 2-chlorotrityl resin. This intermediate was esterified or amidated in solution phase. The structure-activity relationships (SAR) showed that the C-terminus acted as not only a critical pharmacophore for the substance P antagonist activities, but as an address region for the opioid agonist pharmacophore that is structurally distant from the C-terminal. Among the peptides, H-Tyr- d -Ala-Gly-Phe-Pro-Leu-Trp-NH-Bzl ( 3) demonstrated high binding affinities at both delta and mu receptors ( K i = 10 and 0.65 nM, respectively) with efficient agonist functional activity in the mouse isolated vas deferens (MVD) and guinea pig isolated ileum (GPI) assays (IC 50 = 50 and 13 nM, respectively). Compound 3 also showed a good antagonist activity in the GPI assay with substance P stimulation ( K e = 26 nM) and good affinity for the hNK1 receptor ( K i = 14 nM). Consequently, compound 3 is expected to be a promising and novel type of analgesic with bifunctional activities.
Yamamoto
Takashi
T
Department of Chemistry and Pharmacology, University of Arizona, Tucson, Arizona 85721, USA.
Nair
Padma
P
Vagner
Josef
J
Largent-Milnes
Tally
T
Davis
Peg
P
Ma
Shou-Wu
SW
Navratilova
Edita
E
Moye
Sharif
S
Tumati
Suneeta
S
Lai
Josephine
J
Yamamura
Henry I
HI
Vanderah
Todd W
TW
Porreca
Frank
F
Hruby
Victor J
VJ
D000818:Animals; D002460:Cell Line; D045744:Cell Line, Tumor; D020650:Combinatorial Chemistry Techniques; D006224:Cricetinae; D003412:Cricetulus; D004558:Electric Stimulation; D006168:Guinea Pigs; D006801:Humans; D007082:Ileum / Q000187:drug effects / Q000502:physiology; D066298:In Vitro Techniques; D008297:Male; D051379:Mice; D009119:Muscle Contraction / Q000187:drug effects; D009130:Muscle, Smooth / Q000187:drug effects / Q000502:physiology; D064729:Neurokinin-1 Receptor Antagonists; D009842:Oligopeptides / Q000138:chemical synthesis* / Q000737:chemistry / Q000494:pharmacology; D011869:Radioligand Assay; D051381:Rats; D017465:Receptors, Opioid, delta / Q000819:agonists*; D017450:Receptors, Opioid, mu / Q000819:agonists*; D013329:Structure-Activity Relationship; D014649:Vas Deferens / Q000187:drug effects / Q000502:physiology
D064729:Neurokinin-1 Receptor Antagonists; D009842:Oligopeptides; D017465:Receptors, Opioid, delta; D017450:Receptors, Opioid, mu