Peter K.S. Siegl

Potent imidazole angiotensinII antagonists: acyl sulfonamides and acyl sulfamides as tetrazole replacements

Abstract Acyl sulfonamides and acyl sulfamides were synthesized and their in vitro and in vivo biological properties evaluated. AT1 binding affinities for these potent AII antagonists were similar to their tetrazole analogs. An enhancement in AT2 potencies was observed, particularly with acyl sulfonamides or sulfamides bearing hydrophobic substituents.

Imidazo[4,5-b]pyridine-based AT1 / AT2 angiotensin II receptor antagonists

Abstract The structure-activity relationships of 6-amido-imidazol [4,5-b]pyridine-based angiostensin II antagonists ( V demonstrate that high affinity for the AT1 and AT2 receptors is largely dependent upon the R1 and R4 substituents. Of this series, L-162,441 and L-162,620 exhibits subnanomolar (IC50) binding affinities to both AT1 and AT2 receptors and potent antihypertensive effects in animals upon oral administration.

Antithrombotic activity of recombinant tick anticoagulant peptide and heparin in a rabbit model of venous thrombosis

An in vivo rabbit model of venous thrombosis which includes physiological blood flow was used to compare the efficacy of the potent and specific factor Xa inhibitor recombinant tick anticoagulant peptide (rTAP) with standard heparin in the prevention of venous thrombus formation. In anesthetized rabbits, an autologous thrombus was induced with thrombin in a jugular vein and the increase in thrombus size was determined by measuring the accretion of intravenously injected [125I]fibrin(ogen) onto the developing thrombus. The effects of rTAP on hemostasis were monitored by changes in APTT values and template bleeding times. Inhibition of thrombus formation by an intravenous bolus followed by infusion of either rTAP or heparin exhibited a dose-response relationship with an IC50 of 0.9 micrograms/kg/min and 0.12 units/kg/min, respectively. At the IC50 doses, both rTAP and heparin inhibited fibrin(ogen) deposition without any significant effect on APTT or bleeding times. Bleeding times were modestly elevated at the fully efficacious doses of rTAP and heparin. Significant changes in APTT (1.9 +/- 0.3 fold over baseline) were only evident at the highest dose of rTAP while heparin caused a significant dose-dependent increase from 1.3 +/- 0.2 to greater than 4.2 +/- 0.6 fold over baseline. Therefore, in this rabbit model of venous thrombosis, specific inhibition of factor Xa by rTAP is an effective antithrombotic mechanism that does not require changes in systemic hemostatic parameters.

A new class of balanced AT1/AT2 angiotensin II antagonists: quinazolinone AII antagonists with acylsulfonamide and sulfonylcarbamate acidic functionalities

Abstract The structure activity relationships of a series of 2-alkyl-6-(acylamino)-3-[((2′-acylaminosulfonyl)biphenyl-4-yl)methyl]quinazolin-4-(3H)-ones were studied in order to identify balanced angiotensin II antagonists capable of potent binding to both AT 1 and AT 2 angiotensin receptor subtypes. The optimization of the substitution pattern led to the discovery of a potent, balanced quinazolinone antagonist L-162,393 , which displayed long lasting blockade of angiotensin pressor response in rats, dogs and rhesus monkeys.

The SAR of 6-(N-alkyl-N-acyl)-2-propyl-3-[(2′-tetrazol-5-yl)biphen-4-yl)methyl]-quinazolinones as balanced affinity antagonists of the human AT1 and AT2 receptors

Abstract Modification of the 6-N-alkyl-N-acyl groups of L-159,689, 6 6-(N-benzoyl-N-pentyl)-amino-2-propyl-3-[(2′-(tetrazol-5-yl)biphen-4-yl)methyl]quinazolin-4-(3H)one led to the identification of the 6-(N-benzoyl-N-(3-pyridylmethyl)) analog (L-162,537). L-162,537 had improved aqueous solubility and oral bioavailability in the dog. The SAR of this class of AT1 and AT2 ligands is discussed.

In vitro pharmacology of an angiotensin AT1 receptor antagonist with balanced affinity for AT2 receptors

L-163,017 (6-[benzoylamino]-7-methyl-2-propyl-3-[[2-(N-(3-methyl-1-butoxy) carbonylaminosulfonyl) [1,1]-biphenyl-4-yl]methyl]-3H-imidazo[4,5-b]pyridine) inhibited specific 125I-[Sar1, Ile8]angiotensin II binding to angiotensin AT1 receptor (Ki = 0.11-0.20 nM) in rabbit aorta, rat adrenal and human angiotensin AT1 receptor in CHO (Chinese hamster ovary transformed) cells and to AT2 receptor (Ki = 0.14-0.23 nM) in rat adrenal and brain receptors. L-163,017 also had a high affinity in the presence of bovine serum albumin (2 mg/ml), for angiotensin AT1 and AT2 receptors on human adrenal (Ki 3.9 and 4.3 nM), aorta (Ki 0.45 and 0.96 nM) and kidney (Ki 3.6 and 2.3 nM). The much higher Ki values in human tissues were likely due to the presence of bovine serum albumin in the binding assay buffer since L-163,017 had Ki values of 0.13 +/- 0.04 and 2.0 +/- 0.04 nM in the absence and presence of bovine serum albumin, respectively, in inhibiting 125I-[Sar1,Ile8]angiotensin II binding to angiotensin AT1 receptor in rat adrenal membranes. Scatchard analysis of 125I-[Sar1,Ile8]angiotensin II binding in the presence of bovine serum albumin (2 mg/ml) in rabbit aorta and bovine cerebellum indicated a competitive interaction of L-163,017 with angiotensin AT1 and AT2 receptors (Ki values 2.5 and 2.1 nM respectively). L-163,017 inhibited angiotensin II-induced aldosterone release in rat adrenal demonstrating that L-163,017 acted as a competitive antagonist (pA2 = 9.9) and lacked agonist activity. L-163,017 also inhibited angiotensin II responses in rat vascular tissues. The specificity of L-163,017 was shown by its lack of activity on the above functional responses produced by other agonists and in several binding assays.

Development of angiotensin II antagonists with equipotent affinity for human AT1 and AT2 receptor subtypes.

Abstract The quinazoline sulfonylcarbamate L-163,579 (9) is a potent, balanced antagonist of the binding of angiotensin II (Ang II) to human AT 1 and AT 2 receptors. This antagonist produces a long-lasting blockade of Ang II-induced pressor response in both rats and dogs after oral administration.

In vivo pharmacology of a novel AT1 selective angiotensin II receptor antagonist, MK-996

MK-996, N-(4-(5,7-dimethyl-2-ethyl-3H-imidazo[4,5-b]pyridin-3-yl- methyl)1,1-biphenyl-2-yl)-sulfonylbenzamide, is a potent, orally active, highly selective, nonpeptide angiotensin II (AII) receptor antagonist. MK-996 prevents the pressor response to intravenous AII in the conscious rat, dog, and rhesus monkey (ED50, mg/kg; oral/intravenous = 0.067/0.014, 0.035/0.017, and 0.1/0.036, respectively). In the anesthetized chimpanzee, MK-996 (1 mg/kg, iv) produces 100% (peak) inhibition of the AII pressor response and is still active (52%) at 24 h. To our knowledge this pharmacologic profile in the rat, dog, rhesus monkey, and chimpanzee presents the least species variability of any AII receptor antagonist yet described. Responses to methoxamine and arginine vasopressin are not affected by MK-996. In aortic coarcted (high renin) rats, MK-996 (3 mg/kg, by mouth) reduces blood pressure to normotensive (< 120 mm Hg) levels without reflex tachycardia. This dose of MK-996 reduces blood pressure to approximately the same level as both losartan (3 mg/kg, by mouth) and enalapril (3 mg/kg, by mouth) in this model. The duration of antihypertensive activity of MK-996 is similar to enalapril and shorter than losartan at the doses tested. Additionally, in the rat MK-996 does not potentiate the vasodepressor response to bradykinin and completely prevents the ability of AII to stimulate an increase in plasma levels of aldosterone. Therefore, MK-996 is a potent, orally active, nonpeptide AII receptor antagonist with a long duration of action, little species variability, and anti-hypertensive activity.

Potent triazolinone-based angiotensin II receptor antagonists with equivalent affinity for both the AT1 and AT2 subtypes ☆

A series of subnanomolar (IC50 triazolinone-based AT1/AT2-balanced AII antagonists has been identified. The 70-240-fold gain in AT2 activity relative to prototype compounds was achieved by the introduction of a 5-acylamino group on the N2-aryl moiety and the addition of (3-F-5-Pr)biphenyl substituents on 4. These analogues exhibited AT2/AT1 IC50 rations of ≤1 in multiple assay systems including human adrenal.

In vivo pharmacology of an angiotensin AT1 receptor antagonist with balanced affinity for angiotensin AT2 receptors

Abstract L-163,017 (6-[benzoylamino]-7-methyl-2-propyl-3-[(2′-(N-(3-methyl-1-butoxy)carbonylaminosulfonyl)[1,1′]-biphenyl-4-yl]-methyl]-3H-imidazo-[4,5-b] is a potent, orally active, nonpeptide angiotensin II receptor antagonist. Conscious rats and dogs were dosed p.o. and i.v.; in both species the plasma bioequivalents are similar at the angiotensin AT1 and AT2 receptor sites indicating balanced activity is maintained in vivo. L-163,017 prevents the pressor response to intravenous (i.v.) angiotensin II in the conscious rat, dog, and rhesus monkey. L-163,017 also significantly reduces blood pressure in a renin-dependent model of hypertension, similar to an angiotensin converting enzyme inhibitor (Enalapril) and an angiotensin AT1 receptor-selective antagonist (L-159,282). These studies indicate that neither the angiotensin AT2 receptor nor bradykinin is important in the acute antihypertensive activity of angiotensin converting enzyme inhibitors or angiotensin II receptor antagonists.