Magdi M. Asaad

Effects of omapatrilat in low, normal, and high renin experimental hypertension

Combined inhibition of neutral endopeptidase (NEP) and angiotensin converting enzyme (ACE) produces cardiovascular effects greater than those elicited by selective inhibition of either enzyme alone. Dual metalloprotease inhibitors are single molecules that inhibit both NEP and ACE and produce cardiovascular effects in animal models similar to those elicited by the combination of NEP and ACE inhibitors. The purpose of this study was to determined the duration of antihypertensive activity of the dual metalloprotease inhibitor omapatrilat in rodent models of hypertension. Omapatrilat inhibited NEP (Ki = 9 nmol/L) and ACE (Ki = 6 nmol/L) activities in vitro and inhibited the pressor response to angiotensin I in rats after intravenous administration with a potency and duration of action similar to those of the long acting ACE inhibitor fosinoprilat. After single dose administration, omapatrilat lowered mean arterial blood pressure (aortic catheter) in sodium depleted spontaneously hypertensive rats (high renin model) from 148+/-5 to 106+/-3 mm Hg (baseline to 24 h), in deoxycorticosterone acetate-salt hypertensive rats (low renin) from 167+/-4 to 141+/-5 mm Hg and in spontaneously hypertensive rats (normal renin) from 162+/-4 to 138+/-3 mm Hg (P < .05 at 24 h v vehicle in all models). After oral administration, omapatrilat (100 micromol/kg/day) persistently lowered systolic blood pressure (tail cuff) in spontaneously hypertensive rats during 11 days of treatment; at 24 h after dosing on day 12, mean arterial pressure (aortic catheter) was lower (P < .05) in the group receiving omapatrilat (133+/-5 mm Hg) than in the group receiving vehicle (149+/-2 mm Hg). The results indicate that omapatrilat is a potent dual metalloprotease inhibitor of NEP and ACE with long lasting, oral antihypertensive effects in low, normal, and high renin models of hypertension. Omapatrilat has the potential to be an effective, broad spectrum antihypertensive agent.

POTENTIATION OF NATRIURETIC PEPTIDES BY NEUTRAL ENDOPEPTIDASE INHIBITORS

1. Inhibitors of neutral endopeptidase (NEP) EC 3.4.24.11 were developed to regulate endogenous levels of the natriuretic and vasodilatory hormone atrial natriuretic peptide (ANP). The selective NEP inhibitor SQ 28603 enhanced the increases in plasma ANP and urinary excretion of ANP, cyclic GMP and sodium stimulated by infusion of human ANP in conscious monkeys. SQ 28603 also potentiated the renal and depressor responses to rat brain natriuretic peptide (BNP) in conscious spontaneously hypertensive rats (SHR) and human BNP in conscious monkeys. Therefore, selective NEP inhibitors protected both natriuretic peptides from degradation in vivo and enhanced their biological activities.

Dual metalloprotease inhibitors. I. constrained peptidomimetics of mercaptoacyl dipeptides

Abstract A series of benzo-fused lactams were incorporated as conformationally restricted dipeptide mimetics of Ala-Pro in dual-acting ACE/NEP inhibitors 1 and 2. The result of this modification led to compounds possessing excellent inhibitory potency versus ACE and NEP both in vitro and in vivo.

Antihypertensive and renal activity of SQ 28,603, an inhibitor of neutral endopeptidase

SQ 28,603 is a potent and selective inhibitor of neutral endopeptidase 3.4.24.11 (NEP), an enzyme that degrades atrial natriuretic peptide (ANP). In conscious deoxycorticosterone acetate (DOCA)/salt hypertensive rats, 300 μmol/kg, i.v., of SQ 28,603 significantly lowered mean arterial pressure (MAP) from 177 ± 12 to 154 ± 8 mm Hg and increased urinary cyclic guanosine monophosphate (GMP) excretion from 204 ± 70 to 1,068 ± 326 pmol/kg/min within 2 h. Urinary sodium excretion increased within 20 min from a control 51.2 ± 17.3 to 102.1 ± 26.7 μEq/kg/min. Infusion of SQ 28,603 (3.7 μmol/kg/min) for 6 h in a separate group of conscious DOCA/salt hypetensive rats gradually reduced MAP from 180 ± 7 to 142 ± 7 mm Hg and increased urinary cyclic GMP excretion from 182 ± 36 pmol/kg/min to 1.009 ± 394 pmol/kg/min. Despite the continuous infusion of the inhibitor, the natriuretic response peaked during the first hour of treatment at 128 ± 18 μEq/kg/min (vehicle = 54 ± 10 μEq/min). Plasma ANP was significantly greater in the rats infused with SQ 28,603 than in those receiving vehicle (333 ± 108 and 98 ± 14 fmol/ml, respectively), SQ 28,603 also significnatly reduced NEP activity by 95% in the kidneys (1.28 ± 0.08 vs. 18.35 ± 0.61 μmol/min after SQ 28,603 and vehicle respectively) and by 77% in the lungs (0.29 ± 0.03 vs. 0.92 ± 0.14 μmol/kg after SQ 28,603 and vehicle, respectively). In conclusion, inhibition of NEP activity by SQ 28,603 significantly decreased MAP and increased plasma ANP concentrations and urinary excretion of cyclic GMP in conscious DOCA/salt hypertensive rats.

MERCAPTOACYL DIPEPTIDES AS DUAL INHIBITORS OF ANGIOTENSIN-CONVERTING ENZYME AND NEUTRAL ENDOPEPTIDASE PRELIMINARY STRUCTURE-ACTIVITY STUDIES

Abstract Mercaptoacyl dipeptides were prepared as dual-acting ACE/NEP inhibitors. Inhibition of each enzyme may be explained by different binding models. Structure-activity studies determined that, in this series of compounds, the mercaptopropanoyl dipeptide framework leads to increased affinity for NEP but diminished ACE activity in vivo .

N-Formyl hydroxylamine containing dipeptides: generation of a new class of vasopeptidase inhibitors

Four primary zinc-binding pharmacophores (thiols, carboxylates, phosphorus acids, and hydroxamates) have been utilized in generating inhibitors of zinc metalloproteases such as ACE, NEP, the MMPs, and ECE. Although compounds which inhibit the activity of both ACE and NEP (vasopeptidase inhibitors, VPIs) have been reported which incorporate a thiol, carboxylate, or phosphorus acid pharmacophore, the generation of hydroxamate based vasopeptidase inhibitors has remained elusive. Herein we report the first potent vasopeptidase inhibitors which were generated from the incorporation of conformationally restricted dipeptide mimetics to an N-formyl hydroxylamine zinc-binding group. Compounds such as 13c and 13d are among the most potent in this series, exhibiting in vitro activity comparable to other classes of inhibitors.

Dual metalloprotease inhibitors. II. Effect of substitution and stereochemistry on benzazepinone based mercaptoacetyls

Abstract A structure-activity study of dual-acting ACE/NEP inhibitor 1A was initiated in order to ascertain what parameters effect in vitro activity versus ACE and NEP. Unlike NEP, ACE was found to be remarkably tolerant to a wide variety of permutations with respect to both the lactam nucleus and the pharmacophore side chain.

Renal and Depressor Effects of SQ 29,072, a Neutral Endopeptidase Inhibitor, in Conscious Hypertensive Rats

Summary: The depressor and renal responses to the neutral endopeptidase (NEP) inhibitor, SQ 29,072, were characterized in both the conscious spontaneously hypertensive rat (SHR) and the conscious deoxycorticosterone acetate (DOCA)/salt hypertensive rat. Inhibition of tissue NEP activity by pharmacologically active doses was also ascertained in both hypertensive models. Intravenous administration of 300 μmol/kg of SQ 29,072 significantly reduced mean arterial pressure (MAP), produced modest natriuretic and diuretic responses, and inhibited renal NEP activity by approximately 40% in conscious SHR. Doses of 100 and 300 μmol/kg of SQ 29,072 elicited greater depressor responses (−36 ± 7 and −41 ± 8 mm Hg, respectively) in DOCA/salt hypertensive rats than in SHR (−11 ± 24 and −31 ± 5 mm Hg, respectively). SQ 29,072 (300 μmol/kg, i.v.) also inhibited renal NEP activity to a greater extent (70%) in DOCA/salt hypertensive rats. Similarly, the depressor responses to exogenous ANP 99–126 (1, 3, and 10 nmol/kg, i.v.) were greater in DOCA/salt hypertensive rats (−16 ± 4, −38 ± 6, and −73 ± 6 mm Hg, respectively) than in the SHR (0 ± 6, −17 ± 3, and −24 ± 3 mm Hg, respectively). Finally, equidepressor doses of SQ 29,072 and ANP 99–126 both increased urine volume as well as sodium and cyclic GMP excretion in conscious DOCA/salt hypertensive rats. In conclusion, the profile of depressor and renal activities produced by SQ 29,072 was consistent with potentiation of endogenous ANP by inhibition of NEP in conscious SHR and DOCA/salt hypertensive rats.

Synthesis of benzo-fused, 7,5- and 7,6-fused azepinones as conformationally restricted dipeptide mimetics

Abstract Methodology for the generation of novel conformationally restricted dipeptide mimetics 9 and 16 has been developed. The key step involved intramolecular addition of an oxonium ion to the proximal indoline/tetrahydroquinoline aromatic ring. A dramatic difference in reactivity was observed in the formation of the 7,5- versus the 7,6-fused azepinone nuclei. Application of these mimetics in the synthesis of dual-acting ACE/NEP inhibitors 1 and 2 is described.

Heart failure augments the cardiovascular and renal effects of neutral endopeptidase inhibition in rats.

We compared the cardiovascular and renal actions of the neutral endopeptidase (NEP) inhibitor, SQ 28,603, in normal rats and in rats with healed myocardial infarcts. The infarcted rats were studied in the conscious state 8 weeks after ligation of the left main coronary artery and 4 h after placement of cardiovascular and renal catheters. Infarct size was 39 ± 1.2% of left ventricle circumference; right ventricle and lung weight to body weight ratios were twice those of normal rats. These postmortem values were shown to be associated with elevated left ventricular end diastolic pressure and high plasma atrial natriuretic peptide (ANP) concentration in separate groups of rats. SQ 28,603 at 100 μmol/kg intravenously (i.v.) caused urine volume and sodium excretion to increase by 79 ± 11 (il/min and 8.2 ± 1.4 μEq/min, respectively, 20 min after injection in infarcted rats; these changes were significantly greater than those in normal rats (12 ± 5 μl/min and 1.6 μEq/min, respectively). Thoracic venous pressure decreased by 1.9 ± 0.4 mm Hg 80 min after SQ 28,603 in infarcted rats and by only 0.1 ± 0.1 mm Hg in normal rats (p < 0.05 vs. infarcted rats). SQ 28,603 had no effects on mean arterial pressure (MAP), cardiac output (CO), or glomerular filtration rate (GFR). The observation that NEP inhibition has more pronounced effects in animals with high ambient ANP level than in those with normal ANP is consistent with previous studies in a variety of animal models and supports the concept that NEP inhibition potentiates endogenous ANP.