Mercaptoacyl amino acid inhibitors of atriopeptidase. 1. Structure-activity relationship studies of methionine and S-alkylcysteine derivatives.

A broad series of N-(3-mercaptoacyl) amino acid derivatives was evaluated for their ability to inhibit atriopeptidase (neutral endopeptidase, EC 3.4.24.11) in vitro and in vivo. Structural parameters studied were (i) the substituent on the 2-position of the 3-mercaptopropionyl moiety, (ii) the amino acid component, (iii) the S-terminal derivative, and (iv) the C-terminal derivative. Optimum activity was observed for derivatives of methionine and S-alkylcysteines. N-[3-Mercapto-2(S)-[(2-methylphenyl)methyl]-1-oxopropyl]-L-methionine was identified as a highly effective inhibitor of atriopeptidase meriting evaluation as a potential cardiovascular therapeutic agent.

Localization and characterization of neutral metalloendopeptidase (EC 3.4.24.11), the degradative enzyme for atrial natriuretic peptide, in rat kidney using a radioiodinated neutral metalloendopeptidase inhibitor.

Atrial natriuretic peptide (ANP) is rapidly degraded by neutral metalloendopeptidase (EC 3.4.24.11, NEP), with the kidney being a major site of ANP clearance. NEP has been anatomically localized in the rat kidney by in vitro autoradiography and the active site studied by a radioinhibitor binding assay (RIBA) using a newly developed radioinhibitor as a radioligand. SCH47896 is a phenolic derivative of SCH39370, a potent specific inhibitor of NEP, which can be radioiodinated with 125I. NEP catalytic activity in the rat kidney was inhibited by SCH47896 and its di-iodo analog SCH48446. Specific binding of [125I]SCH47896 to renal plasma membranes fitted a single-site model with Kd = 43.3 nM and maximal binding site density = 13.8 pmol/mg protein. Thus, [125I]SCH47896 retains full enzymatic inhibitory activity and full binding to the active site of the NEP. Autoradiographs using [125I]SCH47896 demonstrated maximal binding to deep proximal renal tubules. This binding was displaced in a dose-dependent manner by NEP inhibitors. Renal NEP was inhibited by SCH39370. Inhibition of ANP degradation by NEP in the kidney by the new NEP or atriopeptidase inhibitors may explain their natriuretic and diuretic effect in the absence of changes in plasma ANP levels. These studies will allow investigation of the regulation of NEP and the role inhibition of tissue NEP plays in the actions of the new atriopeptidase inhibitors. Furthermore, this method of radioinhibitor binding is applicable to any enzyme, provided a suitable radioligand can be constructed.

7-Oxabicyclo[2.2.1]heptyl carboxylic acids as thromboxane A2 antagonists: aza omega-chain analogues.

A novel bicyclic prostaglandin analogue, [1S-[1 alpha, 2 alpha (Z), 3 alpha, 4 alpha]]-7-[3-[[[[(1- Oxoheptyl)amino]acetyl]amino]-methyl]-7-oxabicyclo[2.2.1]hept-2- yl]-5-heptenoic acid [-)-7) was found to be a potent and selective thromboxane A2 (TxA2) receptor antagonist. Unlike the related series of omega-chain allylic alcohols, amide 7 and its congeners were uniformly free of direct contractile activity in vitro (bovine coronary) and in vivo (anesthetized guinea pig). Amide 7 was effective in the inhibition of (a) arachidonic acid induced platelet aggregation of human platelet-rich plasma (I50 = 0.18 +/- 0.006 microM), (b) 11,9-epoxymethano-PGH2 induced platelet aggregation of human platelet-rich plasma (I50 = 0.24 microM), (c) 11,9-epoxymethano-PGH2 induced contraction of guinea pig trachea (Kb = 3.0 +/- 0.3 nM) or rat aorta (Kb = 8.8 +/- 1.1 nM), and (d) arachidonic acid induced bronchoconstriction in the anesthetized guinea pig (0.1-1.0 mg/kg iv). Amide 7 inhibited the binding of [5,6-3H2]-[1S- (1 alpha, 2 alpha (Z), 3 alpha, 4 alpha)]-7-[3-[[2-[(Phenyl- amino)carbonyl]hydrazino]methyl]-7-oxabicyclo[2.2.1]hept-2-yl]-5- heptenoic acid to human platelet membranes in a specific and saturable manner with a Kd = 49.6 +/- 1.4 nM.

9,11-epoxy-9-homoprosta-5-enoic acid analogues as thromboxane A2 receptor antagonists.

A novel bicyclic prostaglandin analogue, (1S)-[1 alpha, 2 alpha(Z),3 alpha(1E,3S*,4R*),4 alpha]-7-[3-(3-hydroxy-4-phenyl-1-pentenyl)-7- oxabicyclo[2.2.1]hept-2-yl]-5-heptenoic acid (4), was found to be a potent and selective thromboxane A2 (TxA2) receptor antagonist. Alcohol 4 was the only member in a series of allylic alcohols which did not display direct contractile activity in the rat stomach strip model. Alcohol 4 was effective in the inhibition of (a) arachidonic acid induced platelet aggregation of human platelet-rich plasma (I50 = 0.65 +/- 0.1 microM); (b) 11,9-epoxymethano-PGH2 induced contraction of guinea pig trachea (pA2 = 8.0 +/- 0.2) or rat aorta (pA2 = 8.1 +/- 0.2); and (c) arachidonic acid induced bronchoconstriction in the anesthetized guinea pig (1 mg/kg iv). A radioiodinated analogue of 4 bound in a specific and saturable manner to human platelet membranes with a Kd = 2.3 +/- 0.9 nM. Modification of the alpha-chain, in an attempt to minimize in vivo metabolism, resulted in TxA2 receptor antagonists of reduced in vitro potency.

Atrial natriuretic factor-potentiating and antihypertensive activity of SCH 34826. An orally active neutral metalloendopeptidase inhibitor.

The effects of SCH 34826, an orally active neutral metalloendopeptidase inhibitor, on responses to atrial natriuretic factor-(103-125) or -(99-126) and on blood pressure were evaluated in rats. SCH 34826 (10, 30, and 90 mg/kg s.c. and 90 mg/kg p.o.) potentiated the antihypertensive action of atrial natriuretic factor (30 micrograms/kg i.v.) in conscious spontaneously hypertensive rats. SCH 34826 (90 mg/kg) also potentiated the diuretic and natriuretic responses to atrial natriuretic factor (30 micrograms/kg i.v.) as well as the plasma levels achieved after peptide injection. SCH 34826 significantly reduced blood pressure in the conscious deoxycorticosterone acetate-salt hypertensive rat, at doses of 90 mg/kg s.c. (-35 +/- 12 mm Hg), 10 mg/kg p.o. (-30 +/- 7 mm Hg), and 90 mg/kg p.o. (-45 +/- 6 mm Hg). SCH 34826 was devoid of acute antihypertensive activity in the spontaneously hypertensive rat but reduced blood pressure by day 3 of a 5-day treatment schedule. SCH 34826 (90 mg/kg s.c.) enhanced urine volume output in the deoxycorticosterone acetate-salt rat (2.78 +/- 0.6 vs. 1.27 +/- 0.3 ml/100 g/3 hr in vehicle-control rats, p less than 0.05). SCH 34826 (90 mg/kg s.c.) increased plasma levels of atrial natriuretic factor at 1 hour (753 +/- 89 vs. 451 +/- 79 pg/ml in vehicle-treated rats, p less than 0.05) but not 3 hours after dosing. The renal excretion of atrial natriuretic factor (3,092 +/- 1,089 vs. 21 +/- 6 pg/100 g/3 hr in vehicle-treated rats, p less than 0.05) and cyclic guanosine monophosphate (2,131 +/- 509 vs. 879 +/- 168 pg/100 g/3 hr in vehicle-treated rats, p less than 0.05) was markedly elevated by SCH 34826 in deoxycorticosterone acetate-salt rats. These studies suggest that neutral endopeptidase inhibition may represent a new approach to treatment of some forms of hypertension.

SCH 39370, a neutral metalloendopeptidase inhibitor, potentiates biological responses to atrial natriuretic factor and lowers blood pressure in desoxycorticosterone acetate-sodium hypertensive rats.

SCH 39370 (N-[N-[1-(S)-carboxyl-3-phenylpropyl]-(S)-phenyl-alanyl]-(S)-isoserin e) is a potent and specific inhibitor of neutral metalloendopeptidase (NEP) from rabbit kidney (IC50 = 11.2 +/- 1.9 nM) and is devoid of angiotensin-converting enzyme inhibitory activity at 1 microM. We evaluated the effect of NEP inhibition with SCH 39370 on the inactivation of atrial natriuretic factor (ANF) and on cardiovascular function in rats. SCH 39370 effectively prevented in vitro degradation of ANF (99-126) by a purified rabbit kidney NEP. SCH 39370 (30 mg/kg s.c) significantly delayed the disappearance of immunoreactive (ir) ANF from plasma in rats after an i.v. infusion of ANF (1 microgram/kg/min for 30 min): the plasma ir ANF level at 15 min postinfusion was 1.5 +/- 0.3 ng/ml vs. 0.3 +/- 0.04 ng/ml in the control. SCH 39370 also delayed the disappearance of ir ANF after infusion of the peptide (0.1 microgram/kg/min for 30 min) which increased plasma levels to those observed during volume expansion. This effect was accentuated markedly in rats with bilateral nephrectomy. The hypotensive response to injection of ANF (30 micrograms/kg i.v.) in spontaneously hypertensive rats (-38 +/- 6 mm Hg vs. -13 +/- 2 mm Hg in the control) and the diuretic and natriuretic responses to ANF in normal rats were potentiated by SCH 39370 (30 mg/kg s.c.), respectively. The results suggest that NEP can play a role in ANF disposition in vivo and that potentiation of the biological activities of high doses of ANF by SCH 39370 may be consequent to its inhibitory effect on ANF degradation.(ABSTRACT TRUNCATED AT 250 WORDS)

Mechanism of cholesteryl ester transfer protein inhibition by a neutralizing monoclonal antibody and mapping of the monoclonal antibody epitope.

The plasma cholesteryl ester transfer protein (CETP, Mr 74,000) has a binding site for neutral lipid which can readily equilibrate with lipoprotein cholesteryl esters or triglycerides. Recently, a monoclonal antibody (TP2) was obtained which neutralizes the cholesteryl ester (CE) and triglyceride (TG) transfer activities of the CETP. In this report, the epitope of the inhibitory monoclonal antibody has been localized to a hydrophobic 26-amino acid sequence at the COOH terminus of CETP. The Fab fragments of TP2 caused partial (50%) inhibition of CE transfer and complete inhibition of TG transfer by the CETP. Similarly, the Fab fragments inhibited (37%) the binding of CE to the CETP and abolished the binding of TG to the CETP. Surprisingly, the TP2 Fab was also found to enhance the binding of CETP to plasma lipoproteins and to phospholipid vesicles. In conclusion, the TP2 monoclonal antibody inhibits lipid transfer by blocking the uptake of lipid by CETP. The COOH-terminal epitope may be in or near the neutral lipid binding site. Occupancy of this site by TP2 Fab fragments or by neutral lipid may result in a conformational change of CETP causing enhanced binding to lipoproteins or vesicles.

9,11-Epoxy-9-homo-14-oxaprosta-5-enoic acid derivatives. Novel inhibitors of fatty acid cyclooxygenase.

A novel bicyclic prostaglandin analogue, [1R-[l alpha,2 beta (5Z),3 beta,4 alpha]]-7-[3-[(hexyloxy)methyl]- 7-oxabicyclo[2.2.1]hept-2-yl]-5-heptenoic acid (1), and cogeners were found to be potent inhibitors of fatty acid cyclooxygenase. Compound 1 was the only stereoisomer out of eight possible structures that was active. Ether 1 was 20 times more potent than indomethacin (IND) in inhibiting arachidonic acid (AA) induced aggregation of human platelet-rich plasma. Compound 1 was also more potent than IND in several in vivo assays, AA-induced sudden death in the conscious mouse (2 times) and AA-induced bronchoconstriction in the anesthetized guinea pig (16-45 times).

Pharmacological actions of SQ 29,548, a novel selective thromboxane antagonist.

SQ 29,548, [1S-[1 alpha,2 beta (5Z),3 beta,4 alpha]-7-[3-[[2-[(phenylamino) carbonyl]hydrazino]methyl]-7-oxabicyclo[2.2.1] hept-2-yl]-5-heptenoic acid, and the racemic modification, +/- SQ 29,548, were identified as active inhibitors of human platelet aggregation induced by arachidonic acid, collagen, epinephrine (2 degrees phase) and the thromboxane A2 mimics, 9,11-azo prostaglandin (PG) H2 and 11,9-epoxymethano PGH2. SQ 29,548 did not inhibit aggregation induced by ADP, and it did not prevent PGD2 from inhibiting ADP-induced platelet aggregation. Inhibition of platelet function by +/- SQ 29,548 was not associated with inhibition of cyclooxygenase or thromboxane synthetase or with changes in platelet cyclic AMP. In guinea-pig trachea and rat aorta, +/- SQ 29,548 competitively antagonized the activity of 9,11-azo PGH2 with pA2 values of 7.8 and 8.4, respectively. The chiral compound, SQ 29,548 competitively antagonized contractions of guinea-pig tracheal spirals caused by 11,9-epoxymethano PGH2 with a pA2 value of 9.1. The +/- SQ 29,548 competitively antagonized tracheal responses to 11,9-epoxymethano PGH2 and PGD2 with pA2 values of 8.2 and 8.3, respectively, indicating that PGD2 and the thromboxane A2 mimic probably act at the same receptor in guinea-pig tracheal smooth muscle. Contractions of guinea-pig tracheal spirals induced by PGE2 were not antagonized, and those caused by PGF2 alpha were only partially antagonized by +/- SQ 29,548. The +/- SQ 29,548 also significantly inhibited the aorta contracting activity of 11,9-epoxymethano PGH2 (pA2 = 9.1) and thromboxane A2 released from perfused guinea-pig lungs upon arachidonic acid challenge.(ABSTRACT TRUNCATED AT 250 WORDS)

Thromboxane receptor antagonist properties of SQ 27,427 in the anesthetized guinea pig.

The TXA2 receptor antagonist properties of SQ 27,427 (a novel oxabicyclo[2.2.1]heptane derivative) were studied in vivo in the anesthetized guinea pig where changes in pulmonary resistance, dynamic compliance, and mean arterial blood pressure were measured. Both the bronchoconstrictor and pressor responses to arachidonic acid (AA) and to the stable TXA2 mimic 9,11-azoPGH2 (AZO) were taken as indices of in vivo TXA2 receptor activation. The administration of SQ 27,427 (0.1-1.0 mg/kg i.v., and 10.0 mg/kg p.o.) caused dose-related inhibitions of both AA- and AZO-induced bronchoconstriction. Relative specificity of this antagonism was evidenced by the failure of SQ 27,427 (1.0 mg/kg i.v.) to inhibit histamine-induced bronchoconstriction. In the same experiments the pressor response to AA was reversed to a depressor response by SQ 27,427. This reversal was abolished by indomethacin. The pressor response to AZO was antagonized by SQ 27,427, but not by indomethacin. The reversal of the pressor response to AA by SQ 27,427 may be due to the unmasking of the depressor effect of a cyclooxygenase product, i.e., prostacyclin. It is concluded that SQ 27,427 is a relatively specific TXA2 receptor antagonist in vivo in the guinea pig.

Effects of SQ 27,427, a thromboxane A2 receptor antagonist, in the human platelet and isolated smooth muscle.

The TxA2 receptor antagonist properties of SQ 27,427 [a cyclohexylcarbinol-7-oxabicyclo(2.2.1)heptenoic acid analog] were studied in vitro both in the human platelet and various isolated smooth muscle preparations. SQ 27,427 was found to be a potent inhibitor of human platelet aggregation induced by arachidonic acid, ADP, epinephrine, collagen and the stable TxA2 agonists 9,11-azoPGH2 and SQ 26,655. Inhibition of platelet aggregation was achieved at concentrations of SQ 27,427 which did not alter TxB2 levels. SQ 27,427 was found to weakly inhibit the formation of TxB2 from arachidonic acid and had no effect on the synthesis of PGE2 or PGI2 from arachidonic acid. SQ 27,427 was also found to be a weak stimulator of platelet adenylate cyclase, being 1000 times less potent than PGI2. In isolated smooth muscle experiments, SQ 27,427 was shown to be a potent and specific TxA2 receptor antagonist. It caused competitive antagonism of 9,11-azoPGH2-induced contractions of vascular, respiratory and gastrointestinal smooth muscles. This antagonism was specific, as responses to norepinephrine, serotonin, PGE2, PGI2, PGF2 alpha, histamine, carbachol and KCl were not altered by SQ 27,427.