In vitro and in vivo pharmacological characterization of the novel UT receptor ligand [Pen(5),DTrp(7),Dab(8)]urotensin II(4–11) (UFP-803)

Abstract

1. The novel urotensin-II (U-II) receptor (UT) ligand, [Pen(5),DTrp(7),Dab(8)]U-II(4–11) (UFP-803), was pharmacologically evaluated and compared with urantide in in vitro and in vivo assays. 2. In the rat isolated aorta, UFP-803 was inactive alone but, concentration dependently, displaced the contractile response to U-II to the right, revealing a competitive type of antagonism and a pA(2) value of 7.46. 3. In the FLIPR [Ca(2+)](i) assay, performed at room temperature in HEK293(hUT) and HEK293(rUT) cells, U-II increased [Ca(2+)](i) with pEC(50) values of 8.11 and 8.48. Urantide and UFP-803 were inactive as agonists, but antagonized the actions of U-II by reducing, in a concentration-dependent manner, the agonist maximal effects with apparent pK(B) values in the range of 8.45–9.05. In a separate series of experiments performed at 37°C using a cuvette-based [Ca(2+)](i) assay and CHO(hUT) cells, urantide mimicked the [Ca(2+)](i) stimulatory effect of U-II with an intrinsic activity (α) of 0.80, while UFP-803 displayed a small (α=0.21) but consistent residual agonist activity. When the same experiments were repeated at 22°C (a temperature similar to that in FLIPR experiments), urantide displayed a very small intrinsic activity (α=0.11) and UFP-803 was completely inactive as an agonist. 4. In vivo in mice, UFP-803 (10 nmol kg(−1)) antagonized U-II (1 nmol kg(−1))-induced increase in plasma extravasation in various vascular beds, while being inactive alone. 5. In conclusion, UFP-803 is a potent UT receptor ligand which displays competitive/noncompetitive antagonist behavior depending on the assay. While UFP-803 is less potent than urantide, it displayed reduced residual agonist activity and as such may be a useful pharmacological tool