Tetrapeptide derivatives of [D-Pen(2),D-Pen(5)]-enkephalin (DPDPE) lacking an N-terminal tyrosine residue are agonists at the mu-opioid receptor.
The Phe(1) cyclic tetrapeptide Phe-c[D-Cys-Phe-D-Pen]NH(2) (Et) (JH-54) has been shown previously to exhibit high affinity and selectivity for the mu-opioid receptor. To examine the role of the Phe(1) residue in the unexpected high affinity of this peptide, 11 analogs of JH-54 have been synthesized and evaluated for opioid ligand binding and for efficacy using the [(35)S]GTPgammaS assay. Alteration of the bridging groups between the D-Cys(2) and D-Pen(4) residues of JH-54 from dithioether to disulfide revealed the importance of the relative position of the aromatic rings of the first and third residues in determining mu- and delta-affinities. The one carbon distance between the alpha carbon and phenyl ring in the N-terminal residue was critical. Additional steric bulk in the N-terminal Phe(1) residue was accommodated without large reductions in affinity in two naphthyl analogs, but not with 3, 3-(diphenyl)alanine. Conformational restriction of the Calpha-Cbeta and/or Cbeta-Cgamma bonds had little effect on affinities in two peptides with 2-amino-2-carboxytetralin in position 1, but it abolished activity in an isoquinoline analog and differentially altered activity in four phenylproline(1)-containing peptides. Most surprisingly, replacement of the Phe(1) aromatic ring with cyclohexyl resulted in a peptide of moderate affinity (K(i) = 32.5 nM) and potency (EC(50) = 58.8 nM). Thus, the tyrosyl para-hydroxyl substituent and even aromaticity in the N-terminal amino acid of these tetrapeptides are shown to be important, but not critical, features for mu-opioid receptor affinity, agonist potency, and efficacy.
McFadyen
I J
IJ
Department of Pharmacology, The University of Michigan, Ann Arbor, Michigan 48109-0632, USA.
Sobczyk-Kojiro
K
K
Schaefer
M J
MJ
Ho
J C
JC
Omnaas
J R
JR
Mosberg
H I
HI
Traynor
J R
JR
D000818:Animals; D002478:Cells, Cultured; D020881:Enkephalin, D-Penicillamine (2,5)- / Q000031:analogs & derivatives*; D016244:Guanosine 5'-O-(3-Thiotriphosphate) / Q000378:metabolism; D006168:Guinea Pigs; D010456:Peptides, Cyclic / Q000494:pharmacology*; D011869:Radioligand Assay; D017450:Receptors, Opioid, mu / Q000819:agonists*; D013329:Structure-Activity Relationship; D014443:Tyrosine
C416951:JOM 6; D010456:Peptides, Cyclic; D017450:Receptors, Opioid, mu; D016244:Guanosine 5'-O-(3-Thiotriphosphate); D014443:Tyrosine; D020881:Enkephalin, D-Penicillamine (2,5)-