Urotensin-II (U-II) is a cyclic peptide now described as the most potent vasoconstrictor known. U-II binds to a specific G protein-coupled receptor, formerly the orphan receptor GPR14, now renamed urotensin receptor (UT receptor), and present in mammalian species. Palosuran (ACT-058362; 1-[2-(4-benzyl-4-hydroxy-piperidin-1-yl)-ethyl]-3-(2-methyl-quinolin-4-yl)-urea sulfate salt) is a new potent and specific antagonist of the human UT receptor. ACT-058362 antagonizes the specific binding of 125 Ilabeled U-II on natural and recombinant cells carrying the human UT receptor with a high affinity in the low nanomolar range and a competitive mode of antagonism, revealed only with prolonged incubation times. ACT-058362 also inhibits U-II-induced calcium mobilization and mitogen-activated protein kinase phosphorylation. The binding inhibitory potency of ACT-058362 is more than 100-fold less on the rat than on the human UT receptor, which is reflected in a pDЈ 2 value of 5.2 for inhibiting contraction of isolated rat aortic rings induced by U-II. In functional assays of short incubation times, ACT-058362 behaves as an apparent noncompetitive inhibitor. In vivo, intravenous ACT-058362 prevents the no-reflow phenomenon, which follows renal artery clamping in rats, without decreasing blood pressure and prevents the subsequent development of acute renal failure and the histological consequences of ischemia. In conclusion, the in vivo efficacy of the specific UT receptor antagonist ACT-058362 reveals a role of endogenous U-II in renal ischemia. As a selective renal vasodilator, ACT-058362 may be effective in other renal diseases.

From a high-throughput screening campaign aiming at the identification of novel S1P1 receptor agonists, the pyrazole derivative 2 emerged as a hit structure. Medicinal chemistry efforts focused not only on improving the potency of the compound but in particular also on resolving its inherent instability issue. This led to the discovery of novel bicyclo[3.1.0]hexane fused thiophene derivatives. Compounds with high affinity and selectivity for S1P1 efficiently reducing the blood lymphocyte count in the rat were identified. For instance, compound 85 showed EC50 values of 7 and 2880 nM on S1P1 and S1P3, respectively, had favorable pharmacokinetic properties in rat and dog, distributed well into brain tissue, and efficiently and dose dependently reduced the blood lymphocyte count in the rat. After oral administration to spontaneously hypertensive rats, the S1P1 selective compound 85 showed no effect on mean arterial blood pressure and affected the heart rate during the wake phase of the animals only.

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In preceding communications we summarized our medicinal chemistry efforts leading to the identification of potent, selective, and orally active S1P1 agonists such as the thiophene derivative 1. As a continuation of these efforts, we replaced the thiophene in 1 by a 2-, 3-, or 4-pyridine and obtained less lipophilic, potent, and selective S1P1 agonists (e.g., 2) efficiently reducing blood lymphocyte count in the rat. Structural features influencing the compounds' receptor affinity profile and pharmacokinetics are discussed. In addition, the ability to penetrate brain tissue has been studied for several compounds. As a typical example for these pyridine based S1P1 agonists, compound 53 showed EC50 values of 0.6 and 352 nM for the S1P1 and S1P3 receptor, respectively, displayed favorable PK properties, and penetrated well into brain tissue. In the rat, compound 53 maximally reduced the blood lymphocyte count for at least 24 h after oral dosing of 3 mg/kg.