Selective, high affinity peptide antagonists of alpha-melanotropin action at human melanocortin receptor 4: their synthesis and biological evaluation in vitro.
Peptide Ac-Nle(4)-cyclo(5beta-->10epsilon)(Asp(5)-His(6)-D-(2')Nal(7)-Arg(8)-Trp(9)-Lys(10))-NH(2), compound 1, a cyclic derivative of alpha-melanotropin, is a nonselective high affinity antagonist at human melanocortin receptors 3 and 4, and an agonist at melanocortin receptors 1 and 5. To differentiate between the physiological functions of these receptors, antagonists with improved receptor selectivity are needed. In this study, analogues of compound 1 without Ac-Nle(4) or His(6) and/or the amino group of Asp(5) were prepared and tested in binding assays and in functional assays on CHO cells expressing hMC3-5R. Several of these peptides were to be selective, high affinity hMC-4R antagonists. The most interesting was compound 10, named MBP10, cyclo(6beta-->10epsilon)(succinyl(6)-D-(2')Nal(7)-Arg(8)-Trp(9)-Lys(10))-NH(2), an antagonist (IC(50) = 0.5 nM) with 125-fold selectivity over hMC-3R (and of >300-fold selectivity over MC-1RB). This compound had no agonist activity at hMC-3R or hMC-4R and only weak agonist activity at hMC-5R. Examination of the sequences of these new peptides revealed that the D-(2')Nal(7)-Arg(8)-Trp(9) segment of peptide 1 forms the "essential core" required for high affinity and high selectivity of analogues of peptide 1 at hMC-4R, but the "extended core", His(6)-D-(2')Nal(7)-Arg(8)-Trp(9), is necessary for the maximum affinity for hMC-3R and hMC-5R.
Bednarek
M A
MA
Department of Medicinal Chemistry, Merck Research Laboratories, Rahway, NJ 07065, USA. maria_bednarek@merck.com
MacNeil
T
T
Kalyani
R N
RN
Tang
R
R
Van der Ploeg
L H
LH
Weinberg
D H
DH
D000818:Animals; D001667:Binding, Competitive; D016466:CHO Cells; D002851:Chromatography, High Pressure Liquid; D006224:Cricetinae; D000242:Cyclic AMP / Q000378:metabolism; D006801:Humans; D008968:Molecular Conformation; D010456:Peptides, Cyclic / Q000138:chemical synthesis* / Q000737:chemistry / Q000378:metabolism; D044104:Receptor, Melanocortin, Type 3; D044105:Receptor, Melanocortin, Type 4; D018043:Receptors, Corticotropin / Q000037:antagonists & inhibitors* / Q000378:metabolism; D044101:Receptors, Melanocortin; D015398:Signal Transduction; D013329:Structure-Activity Relationship; D000521:alpha-MSH / Q000378:metabolism*
C438866:MBP10 peptide; D010456:Peptides, Cyclic; D044104:Receptor, Melanocortin, Type 3; D044105:Receptor, Melanocortin, Type 4; D018043:Receptors, Corticotropin; D044101:Receptors, Melanocortin; C086971:melanocortin 5 receptor; D000521:alpha-MSH; D000242:Cyclic AMP