GPR182 is an endothelium-specific atypical chemokine receptor that maintains hematopoietic stem cell homeostasis.

G protein-coupled receptor 182 (GPR182) has been shown to be expressed in endothelial cells; however, its ligand and physiological role has remained elusive. We found GPR182 to be expressed in microvascular and lymphatic endothelial cells of most organs and to bind with nanomolar affinity the chemokines CXCL10, CXCL12, and CXCL13. In contrast to conventional chemokine receptors, binding of chemokines to GPR182 did not induce typical downstream signaling processes, including Gq- and Gi-mediated signaling or ß-arrestin recruitment. GPR182 showed relatively high constitutive activity in regard to ß-arrestin recruitment and rapidly internalized in a ligand-independent manner. In constitutive GPR182-deficient mice, as well as after induced endothelium-specific loss of GPR182, we found significant increases in the plasma levels of CXCL10, CXCL12, and CXCL13. Global and induced endothelium-specific GPR182-deficient mice showed a significant decrease in hematopoietic stem cells in the bone marrow as well as increased colony-forming units of hematopoietic progenitors in the blood and the spleen. Our data show that GPR182 is a new atypical chemokine receptor for CXCL10, CXCL12, and CXCL13, which is involved in the regulation of hematopoietic stem cell homeostasis.

Substituted 4-phenylthiazoles: Development of potent and selective A1, A3 and dual A1/A3 adenosine receptor antagonists.

Adenosine acts as a powerful signaling molecule via four distinct G protein-coupled receptors, designated A1, A2A, A2B and A3 adenosine receptors (ARs). A2A and A2B ARs are Gs-coupled, while A1 and A3 ARs inhibit cAMP production via Gi proteins. Antagonists for A1 and A3 ARs may be useful for the treatment of (neuro)inflammatory diseases including acute kidney injury and kidney failure, pulmonary diseases, and Alzheimer's disease. In the present study, we optimized the versatile 2-amino-4-phenylthiazole scaffold by introducing substituents at N2 and C5 to obtain A1 and A3 AR antagonists including dual-target compounds. Selective A1 antagonists with (sub)nanomolar potency were produced, e.g. 11 and 13. These compounds showed species differences being significantly more potent at the rat as compared to the human A1 AR, and were characterized as inverse agonists. Several potent and selective A3 AR antagonists, e.g. 7, 8, 17 and 22 (Ki values of 5-9 nM at the human A3 AR) were prepared, which were much less potent at the rat orthologue. Moreover, dual A1/A3 antagonists (10, 18) were developed showing Ki values between 8 and 42 nM. Docking and molecule dynamic simulation studies using the crystal structure of the A1 AR and a homology model of the A3 AR were performed to rationalize the observed structure-activity relationships.

Selectivity is species-dependent: Characterization of standard agonists and antagonists at human, rat, and mouse adenosine receptors.

Adenosine receptors (ARs) have emerged as new drug targets. The majority of data on affinity/potency and selectivity of AR ligands described in the literature has been obtained for the human species. However, preclinical studies are mostly performed in mouse or rat, and standard AR agonists and antagonists are frequently used for studies in rodents without knowing their selectivity in the investigated species. In the present study, we selected a set of frequently used standard AR ligands, 8 agonists and 16 antagonists, and investigated them in radioligand binding studies at all four AR subtypes, A1, A2A, A2B, and A3, of three species, human, rat, and mouse. Recommended, selective agonists include CCPA (for A1AR of rat and mouse), CGS-21680 (for A2A AR of rat), and Cl-IB-MECA (for A3AR of all three species). The functionally selective partial A2B agonist BAY60-6583 was found to additionally bind to A1 and A3AR and act as an antagonist at both receptor subtypes. The antagonists PSB-36 (A1), preladenant (A2A), and PSB-603 (A2B) displayed high selectivity in all three investigated species. MRS-1523 acts as a selective A3AR antagonist in human and rat, but is only moderately selective in mouse. The comprehensive data presented herein provide a solid basis for selecting suitable AR ligands for biological studies.

Benzothiazinones: a novel class of adenosine receptor antagonists structurally unrelated to xanthine and adenine derivatives.

2-(Acyl)amino-4H-3,1-benzothiazin-4-ones and related thienothiazinones were identified as structurally novel antagonists at adenosine receptors (ARs). 6-Methyl-2-benzoylamino-4H-3,1-benzothiazin-4-one (10d) was found to be a balanced AR antagonist with affinity for all human (h) subtypes (K(i) hA(1) 65.6 nM; hA(2A) 120 nM; hA(2B) 360 nM; hA(3) 30.4 nM), while in rat (r), 10d was a highly potent A(1)-selective antagonist (rA(1) 7.7 nM; rA(2A) 546 nM; rA(2B) 679 nM, rA(3) >10000 nM). 2-(4-Methylbenzoylamino)-4H-3,1-benzothiazin-4-one (10g) was found to be a potent antagonist at human A(2A) (68.8 nM) and A(3) ARs (23.0 nM) with high selectivity versus the other human AR subtypes. In contrast to A(1) and A(3) ARs, A(2A) and A(2B) ARs tolerated bulky 2-acyl substituents. tert-Butyl (4-oxo-4H-3,1-benzothiazin-2-ylcarbamoyl)benzylcarbamate (15g, K(i) hA(2B) 186 nM; hA(2A) 603 nM) and 4-(4-benzylpiperazine-1-carbonyl)-N-(4-oxo-4H-3,1-benzothiazin-2-yl)benzamide (15k, hA(2A) 69.5 nM; hA(2B) 178 nM) were highly selective versus the other AR subtypes. 2-Acylamino-3,1-benzothiazin-4-ones represent novel scaffolds suitable for the development of potent and selective AR antagonists for each of the four receptor subtypes.