Antagonistic properties of centrally truncated analogs of [D-Trp(32)]NPY.
We have previously shown that [D-Trp(32)]NPY can competitively antagonize NPY-induced feeding in rats (Balasubramaniam et al. J. Med. Chem. 1994, 37, 811-815). This peptide, however, did not bind to SK-N-MC cells with Y-1 receptors. Since centrally truncated NPY analogs have been shown to bind Y-1 receptors, we synthesized similar analogs of [D-Trp(32)]NPY and investigated their Y-1 (SK-N-MC) and Y-2 (SK-N-BE2) receptor affinities and their properties in human erythroleukemia (HEL) cells. None of the analogs with D-Trp(32) mobilized intracellular calcium, [Ca2]i, in HEL cells. Although Des-AA(6-24)[Aoc(6)]NPY and the corresponding D-Trp(32) analog exhibited no affinity to Y-1 receptors, Des-AA(7-24)[Aoc(6),D-Trp(32)] NPY(6) exhibited weak binding. Replacing Pro(5) in 6 with D-Ala to stabilize the central chain reversal, and hence the antiparallel alignment of the N- and C-terminal regions known to be important for Y-1 binding, resulted in an analog, Des-AA(7-24)[D-Ala(5),Aoc(6),D-Trp(32)]NPY (7), which exhibited moderate antagonist potency in attenuating NPY effects on cAMP and [Ca2+]i, in SK-N-MC and HEL cells, respectively. This analog also shifted the dose-response curve of NPY on blood pressure in anesthetized rats. Deletion of only the 7-17 and/or the incorporation of N-Me-Ala(5), superior beta-turn stabilizer, in 7 did not improve the Y-1 receptor affinity. Des-AA(7-24)[D-Ala(5), Gly(6),D-Trp(32)]NPY exhibited an affinity similar to that of 7, suggesting that a long spacer arm is not necessary for efficient Y-1 receptor interaction. Locking the antiparallel alignment via a 2/26 or 2/27 lactam bridge did not improve the binding. Finally, replacement of D-Ala(5) in 7 with D-Trp dramatically increased both the binding and the antagonistic potencies. Modeling based on the avian pancreatic polypeptide X-ray structure suggested that analogs which have the N- and C-terminal regions in close proximity might exhibit good binding, and that the D-Trp(32) substitution may induce a beta-turn that could be important for exhibiting antagonism. A systematic investigation has resulted in the development of relatively potent Y-1 receptor antagonists. Further structure-activity studies with these compounds and those previously reported by us and other investigators should result in the development of long-acting and receptor selective antagonists.
Balasubramaniam
A
A
Department of Surgery, Colleges of Medicine and Pharmacy, University of Cincinnati, Cincinnati, Ohio 45267-0558, USA.
Ujhelyi
M
M
Borchers
M
M
Huang
Y
Y
Zhai
W
W
Zhou
Y
Y
Johnson
M
M
Sheriff
S
S
Fischer
J E
JE
D000595:Amino Acid Sequence; D000818:Animals; D002118:Calcium / Q000378:metabolism; D006801:Humans; D004915:Leukemia, Erythroblastic, Acute; D008969:Molecular Sequence Data; D009478:Neuropeptide Y / Q000031:analogs & derivatives* / Q000037:antagonists & inhibitors* / Q000138:chemical synthesis / Q000737:chemistry / Q000378:metabolism / Q000494:pharmacology; D051381:Rats; D017207:Rats, Sprague-Dawley; D017476:Receptors, Neuropeptide Y / Q000378:metabolism; D014407:Tumor Cells, Cultured
D009478:Neuropeptide Y; D017476:Receptors, Neuropeptide Y; C098653:neuropeptide Y, des-AA(7-24)-(Ala(5)-Aoc(6)-Trp(32))-; C086545:neuropeptide Y, Trp(32)-; D002118:Calcium