SUBTYPE SELECTIVITY AND ANTAGONISTIC PROFILE OF THE NONPEPTIDE Y1 RECEPTOR ANTAGONIST BIBP-3226

In the present study, the subtype specificity and species selectivity of the nonpeptide BIBP 3226, as well as its in vitro antagonism of neu ropeptide Y (NPY)-mediated second messengers have been investigated. R adiolabeled NPY is potently displaced by BIBP 3226 nylacetyl)-N-[(4-hy droxy-phenyl)methyl]-D-arginine amide} on human Y1 receptor expressing Chinese hamster ovary-K1 cells (K-j = 0.47 +/- 0.07 nM), SK-N-MC huma n neuroblastoma cells (K-j = 5.1 +/- 0.5 nM) and the rat parietal cort ex membranes (K-j = 6.8 +/- 0.7 nM). The interaction of BIBP 3226 with the Y1 receptor is stereoselective, because the (S)-enantiomer of the (R)-configured BIBP 3226 displays almost no affinity (K-j > 10,000 nM ). In contrast, concentrations up to 10 mu M BIBP 3226 do not displace [I-125]NPY from the human Y2 receptor (neuroblastoma cell line SMS-KA N): the rabbit Y2 receptor (kidney) and the rat Y2 receptor (hippocamp us). Functional antagonism could be shown for the human Y1 receptor: 0 .1 mu M BIBP 3226 antagonizes the NPY induced Ca++ mobilization (pK(b) = 7.5 +/- 0.17) as well as the NPY-mediated inhibition of cyclic AMP synthesis (pK(b) = 8.2 +/- 0.24) in SK-N-MC cells. In contrast, none o f the formerly described putative antagonists PYX-2, [D-Trp(32)]NPY an d benextramine could be characterized as high affinity Y1 receptor ant agonists. The 18 aminoacid NPY analog EXBP 68 [Ile-Glu-Pro-Pro-Orn-Tyr -Arg-Leu-Arg-Tyr-NH2, cyclic (2,4'), (2',4)-diamide] displayed Y1-sele ctive affinity with in vitro antagonistic properties (K-j = 0.33 +/- 0 .04 nM and (K-j = 8.4 +/- 0.07) in SK-N-MC cells. Therefore, BIBP 3226 is the first potent and subtype-selective nonpeptide Y1 receptor anta gonist.