Structure-based drug design: the discovery of novel nonpeptide orally active inhibitors of human renin.

BACKGROUND: The aspartic proteinase renin plays an important physiological role in the regulation of blood pressure. It catalyses the first step in the conversion of angiotensinogen to the hormone angiotensin II. In the past, potent peptide inhibitors of renin have been developed, but none of these compounds has made it to the end of clinical trials. Our primary aim was to develop novel nonpeptide inhibitors. Based on the available structural information concerning renin-substrate interactions, we synthesized inhibitors in which the peptide portion was replaced by lipophilic moieties that interact with the large hydrophobic S1/S3-binding pocket in renin. RESULTS: Crystal structure analysis of renin-inhibitor complexes combined with computational methods were employed in the medicinal-chemistry optimisation process. Structure analysis revealed that the newly designed inhibitors bind as predicted to the S1/S3 pocket. In addition, however, these compounds interact with a hitherto unrecognised large, distinct, sub-pocket of the enzyme that extends from the S3-binding site towards the hydrophobic core of the enzyme. Binding to this S3(sp) sub-pocket was essential for high binding affinity. This unprecedented binding mode guided the drug-design process in which the mostly hydrophobic interactions within subsite S3(sp) were optimised. CONCLUSIONS: Our design approach led to compounds with high in vitro affinity and specificity for renin, favourable bioavailability and excellent oral efficacy in lowering blood pressure in primates. These renin inhibitors are therefore potential therapeutic agents for the treatment of hypertension and related cardiovascular diseases.

Effects of a specific and long-acting renin inhibitor in the marmoset.

Inhibition of renin was induced in conscious marmosets with CGP 29 287, Z-Arg-Arg-Pro-Phe-His-Sta-Ile-His-Lys (Boc)-OMe, a renin inhibitor with a prolonged duration of action. In vitro, CGP 29 287 is a potent inhibitor of primate plasma renin (inhibitory concentration, 50%: human = 1 X 10(-9) M; marmoset = 5 X 10(-9) M) and less potent against dog (2 X 10(-7) M) or rat (3 X 10(-5) M) plasma renin. CGP 29 287 is a weak inhibitor of other aspartic proteases such as porcine pepsin or bovine cathepsin D (inhibitory concentration, 50% = 4 X 10(-5) M). In furosemide-treated marmosets, CGP 29 287 lowered blood pressure and inhibited plasma renin activity during intravenous infusion and after intravenous bolus injection. The duration of action after intravenous injection was dose dependent and ranged from 1 hour after 0.1 mg/kg to more than 3 hours after 10 mg/kg. High doses of CGP 29 287 (100 mg/kg) were active after oral administration. In all experiments a close relation between inhibition of plasma renin activity and reduction of blood pressure was found. A maximum hypotensive response to CGP 29 287 was associated with complete inhibition of plasma renin activity, and the recovery of blood pressure was accompanied by recovery of plasma renin activity. The hypotensive effects of CGP 29 287 were smaller in untreated than in furosemide-treated marmosets. CGP 29 287 had no influence on blood pressure in marmosets after bilateral nephrectomy or after pretreatment with a converting enzyme inhibitor.(ABSTRACT TRUNCATED AT 250 WORDS)

Beta-adrenergic blocking agents: substituted phenylalkanolamines. Effect of side-chain length on beta-blocking potency in vitro.

The synthesis of a group of potential beta-blockers bearing a new 5-ethoxysalicylamide substituent on nitrogen is described. These compounds were tested for beta-adrenergic blocking potency in vitro and compared with analogous compounds bearing a tert-butyl group on nitrogen. The new N-substituent increased the beta-blocking potency substantially. In a series of five homologous compounds of the type Ar(CH2)nCHOHCH2NHR (R = 5-ethoxysalicylamide; n = 0-4), two maxima of beta-blocking potency were found for n = 0 and 2. Moreover, the carbon isostere of the corresponding (aryloxy)propanolamine still proved to be a very potent beta-blocker. The ether oxygen in the side chain is therefore not an absolute requirement for activity. Structure-activity relationships are discussed.

Renin inhibitors. Synthesis of transition-state analogue inhibitors containing phosphorus acid derivatives at the scissile bond.

The synthesis of five amino phosphorus derivatives, 1a-e, is described. The derivatives were incorporated into a series (18) of analogues of the 5-14 portion of angiotensinogen, in most cases at the scissile Leu-Val bond. The resultant compounds were tested in vitro for their ability to inhibit human plasma renin. Replacement of the scissile bond with the phosphinic analogue of Leu10-Val11 (1b) gave the most potent inhibitors, having IC50 = 7.5 x 10(-8) M for H-Pro-His-Pro-Phe-His-(1b)-Ile-His-Lys-OH and IC50 = 1.0 x 10(-7) M for Z-Arg-Arg-Pro-Phe-His-(1b)-Ile-His-NH2. The shorter phosphonic acid sequence Z-Pro-Phe-His-(1d) retained biological activity with an IC50 = 6.4 x 10(-6) M.

Nonpeptidic angiotensin II antagonists: synthesis and in vitro activity of a series of novel naphthalene and tetrahydronaphthalene derivatives.

Starting from the structure of the novel nonpeptidic angiotensin II antagonist DuP 753, a series of more rigid analogues was prepared by replacing the biphenyl part of DuP 753 with a naphthalene ring. Five different regioisomers (compounds 6a-e) were synthesized, and receptor binding in rat smooth muscle cell preparations as well as inhibition of angiotensin II induced contraction of rabbit aortic rings was measured and the order of potency was compared with predictions made on the basis of a molecular modeling study. In good agreement with the predictions, the 2,6-substituted regioisomer 6d and its analogue 7 (isomeric at the imidazole substituent) were found to be most potent, but were still weaker than DuP 753. Tetrahydronaphthalene derivatives with and without an additional methyl group in the alpha-position to the acidic function and with this same 2,6-substitution pattern (compounds listed in Table III) were then prepared with the expectation of getting a further increase in potency. Whereas the carboxylic acid derivatives 13a,b showed activity in the expected potency range, surprisingly no further potency increase was observed after replacement of the carboxylic acid function by a tetrazole (compounds 18a,b). These results may indicate that the compounds do not bind to the AT1 receptor in the same way as DuP 753.

Synthesis and biological activity of some transition-state inhibitors of human renin.

A series of renin inhibitors containing the dipeptide transition state mimics (2S,4S,5S)-5-amino-4-hydroxy-2-isopropyl-7-methyloctanoic acid (Leu (OH)/Val) and (2S,4S,5S)-5-amino-4-hydroxy-2-isopropyl-6-cyclohexylhexanoic acid (CHa /(OH)/Val) was prepared. A structure-activity study with Boc-Phe-His-Leu (OH)/Val-Ile-His-NH2 (8a) as starting material led to N-[(2S)-2-[(tert-butylsulfonyl)methyl]-3-phenylpropionyl]-His-Cha (OH)/ Val- NHC4H9-n (8i) which has the length of a tetrapeptide and contains only one natural amino acid. Compound 8i had an IC50 of 2 x 10(-9) M against human renin and showed high enzyme specificity; IC50 values against the related aspartic proteinases pepsin and cathepsin D were (8 x 10(-6) and 3 x 10(-6) M, respectively). In salt-depleted marmosets, 8i inhibited plasma renin activity PRA and lowered blood pressure for up to 2 h after oral administration of a dose of 10 mg/kg.

5-Methyl-6-phenyl-1,3,5,6-tetrahydro-3,6-methano-1,5-benzodiazocine-2,4-dione (BA 41899): representative of a novel class of purely calcium-sensitizing agents.

BA 41899 (5-methyl-6-phenyl-1,3,5,6-tetrahydro-3,6-methano-1,5- benzodiazocine-2,4-dione, 6) is a structurally novel 1,5-benzodiazocine derivative and represents the prototype of a hitherto unknown class of positive inotropic Ca(2+)-sensitizing agents. It is completely devoid of phosphodiesterase (PDE) III inhibitory activity or any other known inotropic mechanism. BA 41899 (6) exhibits a pharmacological in vitro profile comprising Ca(2+)-sensitizing, positive inotropic, and negative chronotropic effects. CGP 48506 ((+)-6), the (+)-enantiomer of BA 41899 (6), enantiospecifically carries Ca2+ sensitization by up to a full pCa unit and a corresponding positive inotropic effect. Conversely, the negative chronotropic action resides in the corresponding (-)-enantiomer, CGP 48508 ((-)-6). All the effects are exerted in the low micromolar range. The positive inotropic action of CGP 48506 ((+)-6) is associated with a decelerating effect on contraction and, more prominently, relaxation dynamics in isolated guinea pig atria. In contrast to Ca(2+)-sensitizing PDE inhibitors, CGP 48506 ((+)-6) does not increase maximum Ca(2+)-activated force in myocardial skinned fibers.

Comparison of different drug interference with the renin-angiotensin system.

The hypotensive effects of inhibitors of renin or converting-enzyme (CE) were compared in normotensive sodium-depleted marmosets. Renin was inhibited by an antiserum or a monoclonal antibody against human kidney renin or by peptidic renin inhibitors. The fall in blood pressure after the administration of renin antibodies or inhibitors was accompanied by complete inhibition of plasma renin activity. Antiserum and monoclonal antibody induced a hypotensive response of similar magnitude as peptidic renin inhibitors but had a longer duration of action. Teprotide was used as a CE-inhibitor. Inhibition of renin or CE lowered blood pressure but did not affect heart rate. The magnitude of the hypotensive effect was comparable after renin- or CE-inhibition and depended on the pretreatment plasma renin activity. Inhibition of renin prevented the hypotensive response to inhibition of CE and vice versa. The results of these comparative studies suggest that, in states of sodium depletion, the acute hypotensive effects of renin- or CE-inhibitors are entirely due to their interference with the renin-angiotensin system.

CGP 22979A, a renal vasodilator with natriuretic properties.

Renal vasodilation might be an interesting new antihypertensive principle. In the present study, the prodrug approach was adopted to synthesize a preferential renal vasodilator. A hydralazine-like compound, CGP 18137A (2-hydrazino-5-n-butyl-pyridine), was substituted with an N-acetyl-gamma-glutamyl residue. The resulting derivative, CGP 22979A [N-acetyl-L-glutamic acid-N[N2-(5-n-butyl-2-pyridyl)hydrazide]], was inactive in the isolated perfused mesenteric artery, whereas the parent compound induced a dose-dependent inhibition of vasoconstrictor stimuli. When administered i.v. to anesthetized rats in doses between 1.0 and 10.0 mg/kg, CGP 22979A increased renal blood flow significantly, by up to 31% without affecting blood pressure. A dose of 4.0 mg/kg lowered renal vascular resistance by 25% but did not alter total systemic, mesenteric and iliac vascular resistance. A dose of 10.0 mg/kg increased glomerular filtration rate by up to 42%. In conscious rats, the same dose increased sodium excretion by 200%. Because CGP 22979A induces renal vasodilation in rats and has a preferential action on the afferent arterioles, it might be a useful tool for studying the antihypertensive potential of renal vasodilation.