DuP 532: a second generation of nonpeptide angiotensin II receptor antagonists

Copper-mediated pentafluoroethylation of organoboronates and terminal alkynes with TMSCF3

The TMSCF₃-derived CuCF₂CF₃ species has been successfully applied in pentafluoroethylation of organoboronates and terminal alkynes. By using 1,10-phenanthroline as a ligand, a broad range of (hetero)arylboronates and alkenylboronates were smoothly pentafluoroethylated under aerobic conditions. Furthermore, terminal alkynes can undergo aerobic cross-coupling with the TMSCF₃-derived CuCF₂CF₃ species in the absence of additional ligands.

Metallaphotoredox Perfluoroalkylation of Organobromides

Ruppert-Prakash type reagents (TMSCF₃, TMSC₂F₅, and TMSC₃F₇) are readily available, air-stable, and easy-to-handle fluoroalkyl sources. Herein, we describe a mild, copper-catalyzed cross-coupling of these fluoroalkyl nucleophiles with aryl and alkyl bromides to produce a diverse array of trifluoromethyl, pentafluoroethyl, and heptafluoropropyl adducts. This light-mediated transformation proceeds via a silyl-radical-mediated halogen atom abstraction pathway, which enables perfluoroalkylation of a broad range of organobromides of variable steric and electronic demand. The utility of the method is demonstrated through the late-stage functionalization of several drug analogues.

From C1 to C2 : TMSCF3 as a Precursor for Pentafluoroethylation

A highly efficient copper-mediated aromatic pentafluoroethylation method using TMSCF₃ as the sole fluoroalkyl source is described. The reaction proceeds by a key C₁ to C₂ process, that is, the generation of CuCF₃ from TMSCF₃ , followed by a subsequent spontaneous transformation into CuC₂ F₅ . Various aryl iodides were pentafluoroethylated with the TMSCF₃ -derived CuC₂ F₅ . This method represents the first practical and efficient method for pentafluoroethylation of aryl iodides using commercially available TMSCF₃ as a pentafluoroethyl precursor.

Does protein binding modulate the effect of angiotensin II receptor antagonists?

Introduction

Angiotensin II AT 1-receptor antagonists are highly bound to plasma proteins (≥ 99%). With some antagonists, such as DuP-532, the protein binding was such that no efficacy of the drug could be demonstrated clinically. Whether protein binding interferes with the efficacy of other antagonists is not known. We have therefore investigated in vitro how plasma proteins may affect the antagonistic effect of different AT1-receptor antagonists.

Methods

A radio-receptor binding assay was used to analyse the interaction between proteins and the ability of various angiotensin II (Ang II) antagonists to block AT1-receptors. In addition, the Biacore technology, a new technique which enables the real-time monitoring of binding events between two molecules, was used to evaluate the dissociation rate constants of five AT1-receptor antagonists from human serum albumin.

Results

The in vitro AT 1-antagonistic effects of different Ang II receptor antagonists were differentially affected by the presence of human plasma, with rightward shifts of the IC50 ranging from one to several orders of magnitude. The importance of the shift correlates with the dissociation rate constants of these drugs from albumin. Our experiments also show that the way that AT1-receptor antagonists bind to proteins differs from one compound to another. These results suggest that the interaction with plasma proteins appears to modulate the efficacy of some Ang II antagonists.

Conclusion

Although the high binding level of Ang II receptor antagonist to plasma proteins appears to be a feature common to this class of compounds, the kinetics and characteristics of this binding is of great importance. With some antagonists, protein binding interferes markedly with their efficacy to block AT1-receptors.

Medicinal applications of perfluoroalkylated chain-containing compounds

Compounds with polyfluorinated molecular fragments possess unique properties associated with the presence of a large number of fluorine atoms that affect lipophilicity and conformational rigidity of the parent molecule along with other effects. The aim of this review is to provide an overview of synthesized compounds possessing perfluoroalkylated or polyfluorinated chains that have been tested for bioactivity or as potential drug candidates for the treatment of various diseases. As far as the length of the perfluoroalkylated chain is concerned the focus is centered on the compound bearing perfluoroethyl or tetrafluoroethyl as well as longer chains. The perfluoroalkylated compounds discussed are classified according to their biological activity.

An update on non-peptide angiotensin receptor antagonists and related RAAS modulators

The renin-angiotensin-aldosterone-system (RAAS) is an important regulator of blood pressure and fluid-electrolyte homeostasis. RAAS has been implicated in pathogenesis of hypertension, congestive heart failure, and chronic renal failure. Aliskiren is the first non-peptide orally active renin inhibitor approved by FDA. Angiotensin Converting Enzyme (ACE) Inhibitors are associated with frequent side effects such as cough and angio-oedema. Recently, the role of ACE2 and neutral endopeptidase (NEP) in the formation of an important active metabolite/mediator of RAAS, ang 1-7, has initiated attempts towards development of ACE2 inhibitors and combined ACE/NEP inhibitors. Furukawa and colleagues developed a series of low molecular weight nonpeptide imidazole analogues that possess weak but selective, competitive AT1 receptor blocking property. Till date, many compounds have exhibited promising AT1 blocking activity which cause a more complete RAAS blockade than ACE inhibitors. Many have reached the market for alternative treatment of hypertension, heart failure and diabetic nephropathy in ACE inhibitor intolerant patients and still more are waiting in the queue. But, the hallmark of this area of drug research is marked by a progress in understanding molecular interaction of these blockers at the AT1 receptor and unraveling the enigmatic influence of AT2 receptors on growth/anti-growth, differentiation and the regeneration of neuronal tissue. Different modeling strategies are underway to develop tailor made molecules with the best of properties like Dual Action (Angiotensin And Endothelin) Receptor Antagonists (DARA), ACE/NEP inhibitors, triple inhibitors, AT2 agonists, AT1/TxA2 antagonists, balanced AT1/AT2 antagonists, and nonpeptide renin inhibitors. This abstract gives an overview of these various angiotensin receptor antagonists.

Pharmacology of AT1-receptor blockers

Angiotensin II mediates its haemodynamic effects by binding to specific cell-surface receptors. In humans, two receptor subtypes have been identified, designated AT1 and AT2. Because all major deleterious effects of angiotensin II are produced via binding to AT1-receptors, selective blockade of this receptor subtype should confer haemodynamic benefits, while allowing stimulation of the potentially beneficial effects mediated by AT2-receptors. Experimental studies using various models have consistently revealed marked differences in the receptor binding properties of different AT1-receptor blockers. The relative receptor binding affinities of currently available AT1-receptor blockers is candesartan > irbesartan > valsartan/EXP-3174/telmisartan > tasosartan > losartan > eprosartan. Candesartan is also released from the receptor more slowly than other available AT1-receptor blockers, with a half-life of approximately 152 min for the receptor-blocker complex, compared with 31 min for EXP-3 174, 17 min for irbesartan and 5 min for losartan. Candesartan therefore binds to the AT1-receptor more tightly and more persistently than other AT1-receptor blockers.

Functional and binding studies of insurmountable antagonism of 606A, a novel AT1-receptor antagonist in rabbit tissues

Angiotensin AT1-receptor antagonists can be classified into two types, surmountable and insurmountable ones, based on the way they inhibit angiotensin II (AII)-induced vasoconstriction. To elucidate the causes of the difference, we studied how several antagonists associate with and dissociate from AT1-receptor sites by using rabbit adrenal cortical membrane. Four antagonists, 606A, EXP3174, CV11974, and E4177, showed equipotent competitive antagonism when they were added simultaneous with [125I]-AII in binding experiments. However, in AII-induced contraction studies with rabbit aorta, 606A, EXP3174, and CV11974 inhibited the contraction noncompetitively, whereas E4177 inhibited competitively. The longer the pretreatment period with EXP3174 or CV11974, the more effectively the antagonists suppressed AII-induced contraction. However, the suppression of contraction by 606A and E4177 changed little with the length of the pretreatment period. AII-induced contraction of 606A- or E4177-treated aorta recovered easily by washout, but that of CV11974-treated aorta was hard to recover by washout. These results obtained in the aorta were consistent with their characteristics observed in the AII binding study in the rabbit adrenal cortical membrane in cases of EXP3174 and CV11974. The differences between association rate with and dissociation rate from the AT1 receptor of E4177 and 606A were slight, in spite of the clear difference between their action in the contraction study. Because of the variations observed with the four compounds, mechanisms of insurmountable antagonism may not be uniform among AT1-receptor antagonists.

Practical considerations of the pharmacology of angiotensin receptor blockers

A review of the drug class of angiotensin receptor blockers (ARBs) as well as the ARBs currently available by prescription in the United States is presented. The importance of angiotensin II production by non-angiotensin-converting enzyme (non-ACE) pathways, particularly human chymase, is discussed. Emphasis is placed on the mechanism of action of ARBs and the different binding kinetics of these agents. Although all ARBs, as a group, block the AT1 receptor, they may differ in the pharmacological characteristics of their binding and be classified as either surmountable or insurmountable antagonists. Mechanisms of surmountable and insurmountable antagonism as well as possible benefits of these blocking characteristics are discussed in relation to the various ARBs. The cardiovascular effects of activation of the two main subtypes of angiotensin receptors (AT1 and AT2) are presented. In addition to their treatment of hypertension, ACE inhibitors are recognized as being effective in the management of heart failure, left ventricular hypertrophy, recurrent myocardial infarctions, and renal disease. ARBs are currently indicated only for the treatment of hypertension; however, in vitro and in vivo pharmacological studies as well as preliminary clinical data suggest that ARBs, like ACE inhibitors, may also provide effective protection against end-organ damage in these conditions.

Renin-angiotensin system genes in kidney development

The renin-angiotensin system (RAS) plays a key role in cardiovascular homeostasis through the interactions of angiotensin II with its receptors. All components of the RAS are developmentally regulated in the kidney. The functions of the system in the maturing kidney overlap those of the adult, but higher levels of expression and novel locations of expression in the fetus suggest that the RAS has alternate functions as well. Increasing evidence suggests that the RAS may regulate renal growth and development by initiating a complex cascade of events, involving growth factors and proto-oncogenes and other unidentified factors. These same cascades may also be important in renal disease states. Recent advances in the field of molecular and cell biology are providing new tools and strategies to elucidate the intimate mechanism whereby the RAS regulates growth processes and disease states.

Sequential development of angiotensin receptors and angiotensin I converting enzyme during angiogenesis in the rat subcutaneous sponge granuloma

1. The vasoconstrictor peptide antiotensin II (AII) can stimulate angiogenesis, an important process in wound healing, tumour growth and chronic inflammation. To elucidate mechanisms underlying AII-enhanced angiogenesis, we have studied a subcutaneous sponge granuloma model in the rat by use of 133Xe clearance, morphometry and quantitative in vitro autoradiography. 2. When injected directly into the sponge, AII (1 nmol day-1) increased 133Xe clearance from, and fibrovascular growth in sponge granulomas, indicating enhanced angiogenesis 6 to 12 days after implantation. This AII-enhanced angiogenesis was inhibited by daily doses (100 nmol/sponge) of the specific but subtype non-selective AII receptor antagonist (Sar1, Ile8)AII, and by the selective non-peptide AT1 receptor antagonists losartan and DuP 532. In contrast, AII-enhanced neovascularization was not inhibited by the AT2 receptor antagonist PD123319, nor was it mimicked by the AT2 receptor agonist CGP42112A (each at 100 nmol/sponge day-1). 3. AI (1 nmol/sponge day-1), the angiotensin converting enzyme (ACE) inhibitors captopril (up to 100 micrograms/sponge day-1) and lisinopril (40 micrograms/sponge day-1), or AII receptor antagonists did not affect angiogenesis in the absence of exogenous AII. 4. [125I]-(Sar1, Ile8)AII binding sites with characteristics of AT1 receptors were localized to microvessels and to non-vascular cells within the sponge stroma from 4 days after implantation, and were at higher density than in skin throughout the study. 5. [125I]-(Sar1, Ile8)AII binding sites with characteristics of AT2 receptors were localized to non-vascular stromal cells, were of lower density and appeared later than did AT1 sites. 6. The ACE inhibitor [125I]-351A bound to sites with characteristics of ACE, 14 days after sponge implantation. [125I]-351A bound less densely to sponge stroma than to skin. 7. We propose that AII can stimulate angiogenesis, acting via AT1 receptors within the sponge granuloma. AT1 and AT2 receptors and ACE develop sequentially during microvascular maturation, and the role of the endogenous angiotensin system in angiogenesis will depend on the balanced local expression of its various components. Pharmacological modulation of this balance may provide novel therapeutic approaches in angiogenesis-dependent diseases.

Candesartan (CV-11974) dissociates slowly from the angiotensin AT1 receptor

The mechanisms of the insurmountable antagonism of 2-ethoxy-1-[[2'-(1H-tetrazol-5-yl)biphenyl-4-yl]methyl]1H-benzimid azole -7-carboxylic acid, candesartan (CV-11974), an angiotensin AT1 receptor antagonist, on angiotensin II-induced rabbit aortic contraction were examined in contraction and binding studies. Preincubation of the rabbit aorta with CV-11974 (0.1 nM) for 30 min reduced the maximal contractile response to angiostensin II by approximately 50%. This insurmountable antagonism of CV-11974 was reversed in the presence of losartan (1 microM), a surmountable angiotensin AT1 receptor antagonist. The inhibitory effect of CV-11974 on angiotensin II-induced contraction persisted longer after washing than did that of losartan but was irreversible. Scatchard analysis of [3H]CV-11974 binding in bovine adrenal cortical membranes indicated the existence of a single class of binding sites (Kd = 7.4 nM). Competition binding studies using angiotensin II receptor agonists and antagonists have demonstrated that [3H[CV-11974 binding sites may be identical to angiotensin AT1 receptors. The dissociation rate of [3H]CV-11974 binding (t1/2 = 66 min) was 5 times slower than that of [125I]angiotensin II binding (t1/2 = 12 min). These results suggest that the insurmountable antagonism by CV-11974 is due to its slow dissociation from angiotensin AT1 receptors.

DuP 532, an angiotensin II receptor antagonist: first administration and comparison with losartan

We investigated the tolerability and angiotensin II antagonist activity of oral DuP 532 in healthy male subjects. DuP 532 (1 to 200 mg) was well tolerated, with no effect on blood pressure or heart rate. Compared with losartan (100 mg), DuP 532 (200 mg) was a weak antagonist of pressor responses to intravenous angiotensin II. Maximum inhibition of diastolic pressor response was 86% (95% confidence interval [CI], 84%, 88%) approximately 4.6 hours after losartan and 48% (95% CI, 38%, 56%) 8.7 hours after DuP 532. Twenty-four hours after dosing, inhibition by losartan and DuP 532 was similar (40% to 45%). DUP 532 is extensively bound in human plasma, with an in vitro free fraction of 0.06. Although DuP 532 and EXP3174 (losartan's active metabolite) have similar AT1-receptor potency, and plasma concentrations of DuP 532 were much greater than losartan/EXP3174, the level of antagonism was much less for DuP 532. These results indicate that multiple factors determine the in vivo potency of angiotensin II antagonists, including affinity for and distribution to the receptor as modulated by plasma binding.

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.

Pharmacology and pharmacokinetics of a novel nonpeptide angiotensin II receptor antagonist--DMP 811

DMP 811 exhibited high binding affinity for the angiotensin II subtype receptor AT1 in rat adrenal tissues with an IC50 of 6 nM, but not for the subtype receptor AT2. In the isolated rabbit aorta, DMP 811 inhibited the contractile response to angiotensin II selectively and noncompetitively with a KB value of 0.1 nM. In conscious renal hypertensive rats, DMP 811 decreased blood pressure with i.v. and p.o. ED30s of 0.005 and 0.03 mg/kg, respectively (p.o. ED30 for losartan = 0.59 mg/kg). In conscious furosemide-treated dogs, DMP 811 given either at 0.3 or 1 mg/kg p.o. decreased blood pressure. DMP 811 has oral bioavailabilities of 7 and 29% in rats and dogs, respectively, after a solution dose and 8 and 13%, respectively, after a suspension or capsule dosing. Our study indicates that DMP 811 is a selective and insurmountable AT1 receptor antagonist and is a 20-fold more potent orally-active antihypertensive agent than losartan.

Pharmacology of CS-866, a novel nonpeptide angiotensin II receptor antagonist

CS-866, (5-methyl-2-oxo-1,3-dioxolen-4-yl)methoxy-4-(1-hydroxy-1- methylethyl)-2-propyl-1-(4-[2-(tetrazol-5-yl)-phenyl]phenyl)met hylimidazol- 5-carboxylate, a prodrug type angiotensin receptor antagonist, is deesterified to the active acid, RNH-6270. RNH-6270 inhibited [125I]angiotensin II binding to bovine adrenal cortical membranes (angiotensin AT1 receptors) with an IC50 value of 7.7 nM, but not [125I]angiotensin II binding to bovine cerebellar membranes (angiotensin AT2 receptors), indicating the selectivity of the compound for angiotensin AT1 receptors. In guinea pig aortas, RNH-6270 reduced the maximal response of the concentration-contractile curve for angiotensin II (pD'2 = 9.9), but had no effect on the contractile response induced by phenylephrine or KCl. In conscious rats, intravenously injected RNH-6270 inhibited angiotensin II-induced pressor responses in a dose-dependent manner, and orally administered CS-866 produced a long-lasting inhibition of angiotensin II pressor responses. SK&F-525A, a P-450 inhibitor, suppressed the angiotensin II inhibitory effect of losartan, but not that of CS-866. These results demonstrate that RNH-6270 is a potent and AT1-selective angiotensin receptor antagonist and that, after oral administration, CS-866 has a long-lasting angiotensin II inhibitory action which is not affected by drug metabolizing enzymes in the liver.

Pharmacology of a potent long-acting imidazole-5-acrylic acid angiotensin AT1 receptor antagonist

The angiotensin II antagonistic activity of SB 203220, [E-alpha-[[2-butyl-1-(4-carboxy-1-naphthalenyl)methyl]-1H- imidazol-5-yl]-methylene]-2-thiophene-propanic acid], was examined in several in vitro and in vivo assays. SB 203220 displaced [125I]angiotensin II binding from a variety of tissues including the cloned human AT1 receptor (IC(50)5-15 nM). SB 203220 (10 microM) did not interact with AT2, endothelin (ETA and ETB) or calcitonin gene-related peptide receptors. [3H]SB 203220 bound with high affinity to the AT1 receptor (Kd = 4.9 nM), but dissociated from the receptor at a much slower rate when compared to [3H]SK&F 108566. SB 203220 antagonized intracellular Ca2+ mobilization induced by angiotensin II in rat vascular smooth muscle cells and exhibited a selective and partially insurmountable antagonism of angiotensin II-induced contraction in isolated rabbit aorta. In the aorta, SB 203220 produced a concentration-dependent parallel shift in the concentration-response curve to angiotensin II [EC30 = 5.94 +/- 1.6 10(-11) M] and depressed the maximal contractile response to angiotensin II by approximately 35%. The antagonistic effect of SB 203220 in rabbit aorta was slowly reversible compared to SK&F 108566. SB 203220 displayed no agonist activity and had no effect on the contractile responses to KCl, endothelin-1 or norepinephrine. In rats, SB 203220 at 10 mg/kg i.v. inhibited angiotensin II-induced aldosterone release. Intraduodenal or oral administration of SB 203220 (1-10 mg/kg) to conscious rats and dogs inhibited the pressor responses to exogenous angiotensin II.(ABSTRACT TRUNCATED AT 250 WORDS)

Development and validation of column-switching high-performance liquid chromatographic methods for the determination of a potent AII receptor antagonist, TCV-116, and its metabolites in human serum and urine

Column-switching HPLC methods have been developed and validated for the determination of a new antihypertensive prodrug, TCV-116 (I), and its metabolites, CV-11974 (II) and CV-15959 (III), in human serum and urine. Initial sample cleanup was achieved by extracting the analytes into an organic solvent. After chromatographing on an ODS column with a mobile phase consisting of acetonitrile and an acidic phosphate buffer, the zone of the analyte's retention was heart-cut onto a second ODS column with a mobile phase of acetonitrile and a phosphate buffer at a higher pH. Complete separation of the analytes and the endogenous peaks was accomplished by the two-dimensional chromatography. Good precision and linearity of the calibration standards, as well as the inter-day and intra-day precision and accuracy of quality control samples, were achieved. The limit of quantitation (LOQ), using 0.5 ml of serum, was 2 ng/ml for I, 0.8 ng/ml for II, and 0.5 ng/ml for III. The LOQ for urine sample was 10 ng/ml for II and III. Stability of the analytes during storage, extraction, and chromatography processes was established. The results illustrate the versatile application of column switching to method development of multiple analytes in various biological matrices. The methods have been successfully used for the analyses of I and its metabolites in thousands of clinical samples to provide pharmacokinetic data.

Prodrugs to improve the oral bioavailability of a diacidic nonpeptide angiotensin II antagonist

DMP 811 is a diacidic angiotensin II antagonist. It has relatively low oral bioavailability in rats. A prodrug approach to improving oral bioavailability was tested. Five esters were synthesized and their stability in rat plasma in vitro was determined. The hydrolysis rates of these five esters ranged from almost immediate to negligible. A simple n-propyl ester was hydrolyzed very slowly (< 10% in 24 hr) in rat plasma in vitro, and after oral dosing in rats plasma prodrug concentrations were much greater than DMP 811 concentrations. A pivaloyloxymethyl ester (1) was hydrolyzed relatively rapidly in rat plasma in vitro. Prodrug 1 was rapidly hydrolyzed by the intestine in vitro, and the intestinal permeation of DMP 811 was increased. DMP 811 oral bioavailability was 47% in rats dosed with 10 mg/kg 1, compared to 11% for rats dosed with 10 mg/kg DMP 811. However, DMP 811 bioavailability was only 27% after a 2 mg/kg dose of 1. In vitro plasma hydrolysis of 1 was highly species-dependent, with a half-life of 13 hr in human plasma but only 1 min in rat plasma. The prodrug approach has potential for improving the oral bioavailability of DMP 811, but selection of the optimal prodrug must be done in humans or in a species, such as dogs, with hydrolysis characteristics closer to humans.

In vitro pharmacological characterization of UP 269-6, a novel nonpeptide angiotensin II receptor antagonist

f1p4in vitro pharmacology of UP 269-6, a novel nonpeptide angiotensin II antagonist, was examined in radioligand binding and functional isolated tissue assays. UP 269-6 bound selectively to AT1 receptors as evidenced by the inhibition of specific [125I] Sar1, Ile8-AII binding in rat adrenal membranes (IC50 = 35.8 nM) and in cultured vascular smooth muscle cells (IC50 = 23.8 nM). UP 269-6 displayed a very high selectivity for the AT1 compared to the AT2 receptor subtype (IC50 > 10,000 nM). UP 269-6 inhibited the AII-induced contraction of isolated rabbit aortic strips. The pattern of AII antagonism suggested competitive antagonism at low concentrations (10(-10), 3 x 10(-10), 10(-9) M) of UP 269-6 and insurmountable antagonism at higher concentrations (3 x 10(-9), 10(-8), 3 x 10(-8) M). Based on the calculated pA2 values, UP 269-6 (9.86 +/- 0.25) was an angiotensin II receptor antagonist as potent as L-158,809 (9.82 +/- 0.37) and much more potent than losartan (7.96 +/- 0.38). UP 269-6 was devoid of affinity (IC50 > 10,000 nM) for many other receptors, ion channels and uptake sites, demonstrating its high specificity for AII receptors. Furthermore, this compound did not affect the contractile response to KCl or phenylephrine in rabbit aorta and exhibited no effect on angiotensin converting enzyme activity. These data demonstrate that UP 269-6 is a highly potent, selective and specific AT1 receptor antagonist.

Pharmacology of LR-B/081, a new highly potent, selective and orally active, nonpeptide angiotensin II AT1 receptor antagonist

1. The pharmacological profile of LR-B/081, (methyl 2-[[4-butyl-2-methyl- 6-oxo-5-[[2'-(1H-tetrazol-5-yl)[1,1'-biphenyl]-4-yl]methyl]-1(6H)- pyrimidinyl]methyl]-3-thiophenecarboxylate), a novel antagonist at the angiotensin II (AII) AT1-receptor, was studied in vitro and in vivo. 2. In rabbit aortic strips incubated with LR-B/081 (1-1,000 nM), the concentration-response curve to AII was displaced to the right in a nonparallel fashion and the maximal contraction was progressively reduced, indicating that the compound is an insurmountable antagonist in this preparation (apparent pKB = 9.50 +/- 0.23). However, the interaction of LR-B/081 with AII receptors was found to be reversible, since the maximal response to AII was restored by coincubation with losartan, a surmountable AII AT1-antagonist. Contractions elicited by KCl or phenylephrine were not affected by 10 microM LR-B/081. 3. In rat isolated perfused kidney, LR-B/081 and losartan antagonized the AII-induced vasoconstriction [IC50 (95% confidence limits) = 17(13-24) and 39(32-54) nM, respectively]. The LR-B/081 antagonism was incompletely reversed by excess AII, while losartan was fully displaced. The IC50 values of LR-B/081 and losartan obtained against vasoconstriction induced by endothelin-1 and noradrenaline were two orders of magnitude higher. 4. In pithed rats, the intravenous administration of LR-B/081 (0.2-2 mumol kg-1) dose-dependently shifted to the right in a nonparallel fashion the dose-pressor response curve to AII. The maximal pressor response to AII was reduced by LR-B/081 in a dose-dependent fashion. The coadministration of losartan induced a progressive recovery of the maximal pressor response to All, indicating that in vivo the interaction of LR-B/081 with All receptors is reversible. LR-B/081 at 6 micromol kg-1, i.v. also did not affect the vasopressor response induced by noradrenaline in the pithed rat.5. In conscious normotensive rats, single oral administration of LR-B/081 at 6 micromol kg-1 markedly inhibited the All-induced pressor response; the inhibition lasted more than 24 h.6. In conscious renal hypertensive rats, intravenous LR-B/081 appeared as potent as losartan (ED40mmHg(95% confidence limits) = 0.50(0.36-0.70) and 0.86(0.57-1.3) micromol kg-1, respectively). A single intravenous(2 micromol kg-1) or oral (6 micromol kg-1) administration of LR-B/081 induced a marked fall in blood pressure which lasted for at least 12 h.7. In conscious spontaneously hypertensive rats, LR-B/081 at 20 micromol kg-1 , p.o., induced a marked and sustained fall in blood pressure. The duration of the antihypertensive effect was longer than 12 h.Heart rate was not modified by LR-B/081 treatment. Repeated oral administration of 17 micromol kg-1LR-B/081 for 16 days did not result in the development of tolerance.8 These results demonstrate that LR-B/081 is a potent, selective and orally active antagonist of All at the AT1-receptor subtype, which markedly lowers the blood-pressure in conscious renal and spontaneously hypertensive rats.

Biochemical effects of losartan, a nonpeptide angiotensin II receptor antagonist, on the renin-angiotensin-aldosterone system in hypertensive patients

We investigated the effects of angiotensin II (Ang II) type 1 receptor blockade with losartan on the renin-angiotensin-aldosterone system in hypertensive patients (supine diastolic blood pressure, 95 to 110 mm Hg). Qualifying patients (n = 51) were allocated to placebo, 25 or 100 mg losartan, or 20 mg enalapril. Blood pressure, plasma drug concentrations, and renin-angiotensin-aldosterone system mediators were measured on 4 inpatient days: end of placebo run-in, after first dose, and 2 and 6 weeks of treatment. Plasma drug concentrations were similar after the first and last doses of losartan. At 6 weeks, 100 mg losartan and 20 mg enalapril showed comparable antihypertensive activity. Four hours after dosing, compared with the run-in day, 100 mg losartan increased plasma renin activity 1.7-fold and Ang II 2.5-fold, whereas enalapril increased plasma renin activity 2.8-fold and decreased Ang II 77%. Both drugs decreased plasma aldosterone concentration. For losartan, plasma renin activity and Ang II increases were greater at 2 than at 6 weeks. Effects of losartan were dose related. After the last dose of losartan, plasma renin activity and Ang II changes were similar to placebo changes by 36 hours. These results indicate that long-term blockade of the feedback Ang II receptor in hypertensive patients produces modest increases of plasma renin activity and Ang II that do not appear to affect the antihypertensive response to the antagonist.

Glycyl-histidyl-lysine interacts with the angiotensin II AT1 receptor

Gly-His-Lys, a tripeptide isolated from human plasma that increases the growth rate of many cells, stimulated in dose-dependent fashion the activity of phosphorylase a in isolated rat hepatocytes. Such effect was associated to increases in both IP3 production and [Ca++]i. Interestingly, these effects of Gly-His-Lys were antagonized by losartan, a nonpeptide angiotensin II receptor antagonist (AT1 selective), which suggested that these receptors were involved in its effect. Binding competition experiments using the radioligand [125I][Sar1-Ile8]angiotensin II clearly indicated that Gly-His-Lys interacts with AT1 receptors. It was also observed that other histidine-containing tripeptides were also capable of interacting with these receptors.

BMS-180560, an insurmountable inhibitor of angiotensin II-stimulated responses: comparison with losartan and EXP3174

1. This study compares the activity of BMS-180560 (2-butyl-1-chloro-1-[[1-[2-(2H-tetrazol-5-yl)phenyl]-1H-indol-4- yl]methyl]-1H-imidazole-5-carboxylic acid), an insurmountable angiotensin II (AII) receptor antagonist, with that of losartan and EXP3174 in functional and biochemical models of AII-receptor activation. 2. BMS-180560 selectively inhibited [125I]-Sar1Ile8AII ([125I]SI-AII) binding to rat aortic smooth muscle (RASM) cell and rat adrenal cortical AT1 receptors (Ki = 7.6 +/- 1.2 and 18.4 +/- 3.9 nM respectively) compared to adrenal cortical AT2 receptors (Ki = 37.6 +/- 1.3 microM). The Ki values of BMS-180560 and EXP3174, but not losartan, varied as a function of the BSA concentration used in the assays, indicating that the diacid drugs bound to albumin. 3. BMS-180560 (3-300 nM) increased the KD of SI-AII for RASM cell AT1 receptors. Only at high concentrations of BMS-180560 (300 nM) were Bmax values decreased. 4. BMS-180560 inhibited AII-stimulated contraction of rabbit aorta with a calculated KB = 0.068 +/- 0.048 nM and decreased maximal AII-stimulated contraction at 1 nM BMS-180560 by 75%. In the presence of 0.1% BSA, a higher KB value (5.2 +/- 0.92 nM) was obtained. Losartan behaved as a competitive antagonist with a KB = 2.6 +/- 0.13 nM. Contraction stimulated by endothelin-1, noradrenaline, KCl, or the TXA2 receptor agonist U-46619 were unaffected by BMS-180560 (1 nM). 5. AII stimulated the acidification rates of RASM cells as measured by a Cytosensor microphysiometer with an EC50 of 18 nM. Losartan (30 nM) shifted the AII concentration-effect curves in a competitive manner whereas BMS-180560 (0.01 and 0.1 nM) decreased the maximum responses by 60 and 75% respectively. Inhibition by losartan and BMS-180560 could be reversed following washout although recovery took longer for BMS-180560. 6. In [3H]-myoinositol-labelled RASM cells, losartan (30 and 200 nM), shifted the EC50 for AII-stimulated [3H]-inositol monophosphaste formation to higher values, with no change in the maximal response. By contrast, EXP3174 (0.1 to 1 nM) decreased the maximal response in a concentration-dependent manner (17-55%). BMS-180560 (3 and 10 nM) increased the EC50 for AII and decreased the maximum response by 30 and 80% respectively. The inhibition by EXP3174 and BMS-180560 could be reversed by inclusion of losartan (200 nM) indicating that the inhibition was not irreversible. 7. In conclusion, BMS-180560 is a potent, specific, predominantly competitive, reversible All receptor antagonist, which displays insurmountable receptor antagonism. At concentrations of BMS-180560 which have no effect on receptor number, BMS-180560 produced insurmountable antagonism of AII-stimulated second messenger formation, extracellular acidification, and smooth muscle contraction.

Receptor binding radiotracers for the angiotensin II receptor: radioiodinated [Sar1, Ile8]Angiotensin II

The potential for imaging the angiotensin II receptor was evaluated using the radioiodinated peptide antagonist [125I][Sar1, Ile8)angiotensin II. The radioligand provides a receptor-mediated signal in several tissues in rat (kidneys, adrenal and liver). The receptor-mediated signal of 3% ID/g kidney cortex should be sufficient to permit imaging, at least via SPECT. The radiotracer is sensitive to reductions in receptor concentration and can be used to define in vivo dose-occupancy curves of angiotensin II receptor ligands. Receptor-mediated images of [123I][Sar1, Ile8]angiotensin II were obtained in the rat kidney and Rhesus monkey liver.

Comparative pharmacology of recombinant rat AT1A, AT1B and human AT1 receptors expressed by transfected COS-M6 cells

1. Currently available antagonists and agonists cannot distinguish between angiotensin AT1 receptor subtypes. 2. We synthesized a series of compounds selected on the basis of having the most diverse structural features with respect to losartan (DuP753), the prototype non-peptide AT1 receptor antagonist. Using a radioligand-receptor binding assay and membranes prepared from COS-M6 cells transfected with individual AT1 receptor subtypes, we determined whether any of these compounds could distinguish between the receptor subtypes. 3. The diversity of the structural features of this series of compounds was reflected by the wide range of affinities (pIC50 values) displayed towards competing with [125I]-Sar1Ile8 angiotensin II for binding to the AT1 receptors. 4. Direct comparisons of the pIC50 values of individual compounds for rat AT1A, AT1B and human AT1 receptors revealed only minor differences. 5. It is concluded that compounds based structurally on losartan are unlikely to distinguish between these receptors.

Effect of SR 47436, a novel angiotensin II AT1 receptor antagonist, on human vascular smooth muscle cells in vitro

Proliferation of smooth muscle cells within the intima plays a key role in vascular occlusive disorders such as atherosclerosis and restenosis following balloon angioplasty. Among the factors that may be important in the development of vascular lesions, several authors have reported that the local angiotensin system participates in modulating the proliferation of smooth muscle cells after arterial injury. This study was therefore designed to characterize the antagonistic properties and to investigate the antiproliferative effect of a newly developed non-peptide angiotensin II AT1 receptor antagonist, SR 47436. This compound is a potent and competitive antagonist of the binding of [125I]angiotensin II to its receptor on cultured human aortic smooth muscle cells, exhibiting an IC50 value of 1.7 +/- 0.6 nM. SR 47436 was 10-fold more potent than DuP 753 (Losartan) (IC50 = 20.8 +/- 3.7 nM). In these same cells, SR 47436 potently inhibited the angiotensin II-induced [Ca2+]i increase (IC50 = 0.53 +/- 0.13 vs. 7.4 +/- 1.3 nM for DuP 753). Angiotensin II is a potent mitogen for human aortic smooth muscle cells in culture, exhibiting a maximum proliferative response at 1 microM. SR 47436 and Losartan prevented angiotensin II-induced proliferation of these cells in a dose-dependent manner (IC50 = 0.32 +/- 0.09 and 0.71 +/- 0.08 microM, respectively). SR 47436 displayed a marked in vitro inhibition of serum-induced smooth muscle cell proliferation (IC50 = 5.5 +/- 0.8 microM). A selective AT2 receptor antagonist, PD 123177 did not affect angiotensin II-induced responses in these cells.(ABSTRACT TRUNCATED AT 250 WORDS)

Angiotensin II and non-angiotensin II displaceable binding sites for [3H]losartan in the rat liver

By virtue of the more than 1000-fold selectivity of losartan (DuP 753) for the AT1 angiotensin II (AII) receptor subtype compared with the AT2 subtype, [3H]losartan may be a useful radioligand for studies of the AT1 receptor subtype. Comparison of Bmax values in the liver obtained from saturation isotherms using [3H]losartan (Bmax = 194 pmol/g tissue) and [125I]sarcosine1,isoleucine8 angiotensin II (Bmax = 20 pmol/g tissue) indicated that the AII receptor concentration was approximately 10% that of the [3H]losartan binding sites. In addition, AII at concentrations as high as 10 microM displaced less than one-third of specific [3H]losartan binding in the liver and less than 80% in the whole adrenal. The presence of non-AII displaceable [3H]losartan binding in the liver did not appear to result from metabolism of the radioligand since HPLC analysis of free and bound 3H revealed that greater than 90% of the 3H eluted at the same time as the parent [3H]losartan. This suggests that [3H]losartan binds with high affinity to a site(s) other than angiotensin II receptors in the rat liver.

Pharmacological profile of valsartan: a potent, orally active, nonpeptide antagonist of the angiotensin II AT1-receptor subtype

1. The pharmacological profile of valsartan, (S)-N-valeryl-N-([2'-(1H-tetrazol-5-yl)biphenyl-4-yl]-methyl)-vali ne, a potent, highly selective, and orally active antagonist at the angiotensin II (AII) AT1-receptor, was studied in vitro and in vivo. 2. Valsartan competed with [125I]-AII at its specific binding sites in rat aortic smooth muscle cell membranes (AT1-receptor subtype) with a Ki of 2.38 nM, but was about 30,000 times less active in human myometrial membranes (AT2-receptor subtype). 3. In rabbit aortic rings incubated for 5 min with valsartan, at concentrations of 2, 20 and 200 nM, the concentration-response curve of AII was displaced to the right and the maximum response was reduced by 33%, 36% and 40%, respectively. Prolongation of the incubation time with valsartan to 1 h or 3 h, further reduced the maximum response by 48% or 59% (after 20 nM) and by 59% or 60% (after 200 nM) respectively. After 3 h incubation an apparent pKb value of 9.26 was calculated. Contractions induced by noradrenaline, 5-hydroxytryptamine, or potassium chloride were not affected by valsartan. No agonistic effects were observed in the rabbit aorta at concentrations of valsartan up to 2 microM. 4. In bovine adrenal glomerulosa, valsartan inhibited AII-stimulated aldosterone release without affecting the maximum response (pA2 8.4). 5. In the pithed rat, oral administration of valsartan (10 mg kg-1) shifted the AII-induced pressor response curves to the right, without affecting responses induced by the electrical stimulation of the sympathetic outflow or by noradrenaline. Animals treated with valsartan 24 h before pithing also showed significant inhibition of the response to AII. 6. In conscious, two-kidney, one-clip renal hypertensive rats (2K1C), valsartan decreased blood pressure in a dose-dependent manner after single i.v. or oral administration. The respective ED30 values were 0.06 mg kg-1 (i.v.) and 1.4 mg kg-1 (p.o.). The antihypertensive effect lasted for at least 24 h after either route of administration. After repeated oral administration for 4 days (3 and 10 mg kg-1 daily), in 2K1C renal hypertensive rats, systolic blood pressure was consistently decreased, but heart rate was not significantly affected. 7. In conscious, normotensive, sodium-depleted marmosets, valsartan decreased mean arterial pressure, measured by telemetry, after oral doses of 1-30 mg kg-1. The hypotensive effect persisted up to 12 h after 3 and 10 mg kg-1 and up to 24 h after 30 mg kg-1. 8. In sodium-depleted marmosets, the hypotensive effect of valsartan lasted longer than that of losartan(DuP 753). In renal hypertensive rats, both agents had a similar duration (24 h), but a different onset of action (valsartan at 1 h, losartan between 2 h and 24 h).9. These results demonstrate that valsartan is a potent, specific, highly selective antagonist of AII at theAT1-receptor subtype and does not possess agonistic activity. Furthermore, it is an efficacious, orally active, blood pressure-lowering agent in conscious renal hypertensive rats and in conscious normotensive,sodium-depleted primates.