Synthesis and progesterone receptor antagonist activities of 6-aryl benzimidazolones and benzothiazolones

Novel 6-aryl benzimidazolones and benzothiazolones were prepared and examined as bioisosteres of the recently reported 6-aryl dihydroquinolines (1) for progesterone receptor (PR) antagonist activities. PR antagonist activities increased when compounds 9c-f possessed a more lipophilic group at position-1 and pendent aryl moiety para to NH moiety. Furthermore, conversion of carbonyl moiety of 9e,f to the thio-carbonyl led to benzoimidazolethiones 15a,b with significantly improved potency and binding affinity.

Cultured human vascular smooth muscle cells with functional thromboxane A2 receptors: measurement of U46619-induced 45calcium efflux

Thromboxane A2 (TXA2)/prostaglandin H2 (PGH2) are potent vasoconstrictors whose contractile effects are mediated by increases in cellular calcium. Stable analogues of these compounds have shown calcium ionophore activity at high concentrations. To determine if effects of TXA2/PGH2 analogues on 45Ca2+ fluxes are receptor mediated, the effects of the stable TXA2/PGH2 mimetic U46619 and the TXA2/PGH2 receptor antagonist I-PTA-OH on 45Ca/+ fluxes in cultured human vascular smooth muscle cells were studied. The smooth muscle cells were cultured from human saphenous vein explants, and they retained the morphologic and immunologic characteristics of vascular smooth muscle cells. U46619 stimulated 45Ca2+ efflux in a dose-dependent manner with an EC50 of 398 +/- 26 nM (n = 4). The maximal 45Ca2+ efflux in response to U46619 (5 microM) was significantly greater (p = 0.006) than the 45Ca2+ efflux induced by KCl (40 mM). I-PTA-OH inhibited the U46619-induced 45Ca2+ efflux but had no effect on KCl-induced 45Ca2+ efflux. These results suggest that the effects of U46619 in increasing vascular smooth muscle cell calcium efflux are receptor mediated. Furthermore, vascular smooth muscle cells with functional TXA2/PGH2 receptors were cultured from human saphenous veins and provide a potentially useful in vitro system for the further study of TXA2/PGH2 receptor-mediated phenomena in human vascular tissue.

A novel approach for the study of thromboxane A2 and prostaglandin H2 receptors using an 125I-labeled ligand

Previous studies of eicosanoid receptors have utilized 3H-labeled ligands. However, 125I has a higher theoretical specific activity (approximately 2000 Ci/mmole) than 3H (29 Ci/mmole), which provides a potential advantage for 125I ligand binding studies when the receptor density is low. Since eicosanoids do not possess an easily iodinatable structure (e.g. a phenol or imidazole ring), it is not feasible to directly incorporate 125I into the molecule. The thromboxane A2/prostaglandin H2 receptor antagonist, cis-7-(2-p-hydroxyphenylethanolaminocyclopentyl)-heptanoic acid (cis-APO), was synthesized to test the concept that it could be labeled with 125I and used as a ligand for binding studies. cis-APO is a structural analog of 13-azaprostanoic acid, a TXA2/PGH2 antagonist [G. C. Le Breton, D. L. Venton, S. E. Enke and P. V. Halushka, Proc. natn. Acad. Sci. U.S.A. 76, 4097 (1979)], in which the omega aliphatic chain was substituted with 2-p-hydroxyphenylethanol, which contains a phenolic group. [127I]cis-APO was synthesized by insertion of 127I (stable isotope) into the phenolic portion of the molecule under alkaline conditions. [125I]-cis-APO was synthesized via insertion of 125I (unstable isotope) into the molecule in the presence of chloramine T. cis-APO inhibited human platelet aggregation induced by the thromboxane mimetic U46619 [C. Malmsten, Life Sci. 18, 169 (1976)]. The IC50 for cis-APO was 6.4 +/- 0.7 microM and for [127I]-cis-APO was 9.8 +/- 1.3 microM (P less than 0.001). [125I]-cis-APO binding to a human platelet membrane preparation at 4 degrees was time and protein concentration dependent, saturable, and reduced or abolished by trypsin or boiling respectively. The Kd for iodo-cis-APO determined at equilibrium using a Scatchard analysis was 1.48 microM and the maximum binding capacity was 18.7 pmoles/mg protein. The forward rate constant (k+1) was 2.3 X 10(3) M-1 s-1 and the dissociation constant (k-1) was 2.12 X 10(-3) s-1. The Kd determined from k-1/k+1 was 0.92 microM. These observations show that the omega side chain of eicosanoid analogs can be substituted with a phenolic group, iodinated, and retain biological activity. These molecules may then be utilized to study thromboxane A2 or prostaglandin H2 receptors.