alpha-Hydroxy phosphinyl-based inhibitors of human renin.

The design and application of alpha-hydroxy phosphonates, a new class of transition state analogs, toward the discovery of novel and potent inhibitors of the aspartyl protease renin is described. Tripeptidic alpha-hydroxy diethyl phosphonate 3, the first example in this series, was found to be a good inhibitor of human renin (IC50 = 29 nM), and preliminary studies led to the choice of alpha-hydroxy dimethyl phosphonate 15 (IC50 = 16 nM) as a base-line compound for further structure-activity relationship study. Corresponding phosphinate (28-30) and phosphine oxide (23 and 24) analogs of 15 were prepared to assess the steric and electronic requirements around the phosphorus center. Evaluation of these analogs suggested that the presence of at least one alkoxy group on phosphorus was a critical requirement for good activity. Inhibitors with leucine at P2 possessed better in vitro activity than the corresponding P2 histidine analogs (15, IC50 = 16 nM vs 37, IC50 = 220 nM; 33, IC50 = 8.5 nM vs 40, IC50 = 41 nM). Compound 34 (IC50 = 31 nM), the P3 aminocaproic analog of 15, showed complete and long-lasting inhibition of plasma renin activity while eliciting a 10-15 mmHg drop in mean arterial pressure when administered intravenously at 1 mumol/kg in conscious, sodium-depleted, cynomolgus monkeys. In summary, the alpha-hydroxy phosphonates represent a promising and structurally novel class of transition state analog inhibitors of human renin.

Activated ketone based inhibitors of human renin.

Application of the concept of activated ketones to the design of novel and potent transition-state analog inhibitors of the aspartyl protease renin is described. Three different classes of peptidic activated ketones were synthesized: 1,1,1-trifluoromethyl ketones, alpha-keto esters, and alpha-diketones. The corresponding alcohols were also evaluated as renin inhibitors in each series. While the trifluoromethyl alcohol 12 (I50 = 4000 nM) was equipotent to the simple methyl alcohol 7 (I50 = 3200 nM), the structurally similar alpha-hydroxy esters (32 and 30, I50's = 5.3 and 4.7 nM, respectively) and alpha-hydroxy ketones (41 and 42, I50 = 23 and 15 nM, respectively) were 150-300-fold more active. The hydrating capability of the activated ketone functionality was important for intrinsic potency in the case of trifluoromethyl ketones, as illustrated by the significantly better activity of trifluoromethyl ketone 13 (I50 = 250 nM) compared to its alcohol analog 12 (I50 = 4000 nM). It was however unimportant for the alpha-keto ester (20 and 31, I50 = 15 and 4.1 nM, respectively) and alpha-diketone (43 and 44, I50 = 52 and 28 nM, respectively) based inhibitors, since their activity was essentially similar to that of the corresponding alcohols. These results collectively suggest that, whereas the trifluoromethyl ketones derive their renin inhibitory potency primarily from their ability to become hydrated, this is not a critical feature for the activity of alpha-dicarbonyl-based inhibitors. The alpha-keto ester and alpha-diketone based renin inhibitors benefit predominantly from the hydrophobic and/or H-bonding type binding interactions of the neighboring ester or acyl group itself, rather than the ability of this group to deactivate the adjacent ketone group and thereby make it susceptible to hydration.

Perinephritis hypertension in Macaca fascicularis (cynomolgus monkey): studies of the renin-angiotensin-aldosterone axis and renal hemodynamic function.

The purpose of the present study was to characterize the etiology of bilateral perinephritis hypertension in the non-human primate. Hypertension was induced in female cynomolgus (Macaca fascicularis) monkeys by wrapping both kidneys under sterile surgical procedures. Mean arterial pressure (MAP), plasma renin activity (PRA), plasma aldosterone concentration (ALDO), para-aminohippurate (PAH) clearance, glomerular filtration rate (GFR), urine volume, and sodium and potassium excretion were measured before and weekly after induction of the hypertension. MAP increased progressively from 108 +/- 1 to 135 +/- 4 mmHg during the first 6 weeks; thereafter, MAP remained at this elevated level, PRA was elevated two- to fivefold for up to 10 weeks after the hypertension and ALDO was elevated during 1 (139%), 4 (60%), 6 (196%), 8 (249%) and 10 (148%) weeks of the hypertension. PAH clearance and GFR were significantly reduced during week 1 of the hypertension, but returned to control values by week 2. Urine volume was increased significantly during the first week of the hypertension, while sodium and potassium excretion were not changed. Captopril (15 mumol/kg, intravenously) normalized the blood pressure regardless of the severity or duration of the disease. Additionally, captopril lowered ALDO and increased PRA. It is concluded that bilateral perinephritis hypertension in the monkey is dependent on increased activity of the renin-angiotensin-aldosterone axis.

Affinity purification of endothia protease with a novel renin inhibitor SQ 32,970.

A novel tripeptidic renin inhibitor is described, SQ 32,970, that will potently inhibit endothia protease. This inhibitor can be coupled to Sepharose and will allow the affinity-purification of endothia protease in one step to greater than 95% purity as measured by SDS PAGE. The purified endothia protease cleaves the Lys-Pro-Ala-Glu-Phe-Nph-Arg-Leu substrate at the Phe-Nph bond with a Kcat/Km of 7445 (s-1 mM-1) at pH 3.1 and 4057 (s-1 mM-1) at pH 6.0. Affinity purified endothia protease can be crystallized in the pH range in which it is enzymatically active and can be inhibited by renin inhibitors.

Pharmacology of novel imidazole alcohol inhibitors of primate renin.

SQ 30,774 and SQ 31,844 are representatives of a novel class of renin inhibitors, the imidazole alcohols. These compounds, which contain an imidazole ring as part of their active site binding group are potent in vitro inhibitors of primate renin, but not rat, hog of dog renin. In conscious, sodium-depleted cynomolgus monkeys both compounds produced a dose-related inhibition of plasma renin activity (PRA) at doses ranging between 0.001 and 1.0 mumol/kg, intravenously, and total inhibition was observed after the highest dose. However, a reduction in blood pressure was observed only after an intravenous dose of 10 mumol/kg or when the compounds were administered by infusion. In sodium-replete monkeys, SQ 30,774 inhibited the rise in arterial pressure and PRA following administration of exogenous monkey renin. When the compounds were administered orally at 50 mumol/kg, only SQ 31,844 significantly inhibited PRA (80%). It is concluded that representatives of the imidazole alcohol class of renin inhibitors are potent inhibitors of renin in vitro and inhibit PRA and lower arterial pressure in vivo.

Rapid metabolic inactivation of tipredane, a structurally novel topical steroid.

[3H]Tipredane ([3H]TP), [3H]triamcinolone acetonide ([ 3H]TAAC), [3H]hydrocortisone ([3H]HC), and [3H]betamethasone-17 alpha-valerate ([3H]BMV), each at a concentration of 1 microM, were separately incubated with the 10,000 g supernatant fraction of the liver and skin homogenates of humans, rats and mice (BMV was studied only in human liver). Sequential samples were taken for up to 1 h during each incubation. The radioactivity in each sample was extracted with methanol, and the methanolic extracts were analyzed by high performance liquid chromatography. Among the four compounds studied, [3H]TP was most rapidly biotransformed by the liver preparations of the three species. The rates of in vitro biotransformation of TP were 2.5-30 times faster than those of TAAC, HC and BMV. In the human liver preparation, the rates of biotransformation were in the order of: TP greater than TAAC greater than HC = BMV. In the mouse and rat liver preparations, the orders were: TP greater than TAAC greater than HC and TP greater than HC greater than TAAC, respectively. In the skin preparations, little, if any, biotransformation of [3H]TP and [3H]TAAC was observed in any of the species studied; however, [3H]HC underwent a slow, steady biotransformation in the skin preparations of humans and rats but not of mice. [3H]TP was biotransformed by the liver preparations of all three species to numerous metabolites, thirteen of which have been identified. The biotransformation reactions included: (1) sulfoxidation; (2) elimination of either one or both alkylthio groups; and (3) hydroxylation of the steroid nucleus. Some metabolites were synthesized and tested for glucocorticoid receptor binding and anti-inflammatory activities; all were found to be much less potent than TP. The observed separation of local anti-inflammatory activity from systemic side effects of TP is most probably due to its rapid metabolic inactivation; the liver, rather than the skin, is mainly responsible for the metabolic inactivation of TP.

Androstene-17-thioketals. 1st communication: glucocorticoid receptor binding, antiproliferative and antiinflammatory activities of some novel 20-thiasteroids (androstene-17-thioketals).

The unique replacements of the alpha-hydroxyl and beta-ketol groups of corticoids at C17 with selected, simple alkylthio or (2-fluoroalkyl)thio groups resulted in the structurally novel steroids, C17-alkylthioketals of 9 alpha-fluoro-11 beta-hydroxy-androsta-1,4-diene-3,17-dione. The described androstene-17-thioketals (20-thiasteroids) had high affinities for the glucocorticoid receptor protein of rat liver cytosol. Most were more potent than triamcinolone acetonide, a clinically moderately potent corticoid, in antiproliferative and antiinflammatory activities in mice. Specifically, (11 beta, 17 alpha)-17-(ethylthio)-9 alpha-fluoro-11 beta-hydroxy-17-(methylthio) androsta-1,4-dien-3-one (tipredane, SQ 27,239) and (11 beta, 17 alpha)-17-(ethylthio)-9 alpha-fluoro-17-[2-(fluoroethyl)thio] - 11 beta - hydroxy-androsta-1,4-dien-3-one (SQ 28,300), topically applied, were as potent as halcinonide, a clinically highly potent corticoid, in inhibition of croton oil-induced edema in the mouse. It is suggested that both thiasteroids could be moderately to highly potent topical antiinflammatory agents in man.

Androstene-17-thioketals. 2nd communication: pharmacological profiles of tipredane and (11 beta, 17 alpha)-17-(ethylthio)-9 alpha-fluoro-17-[2-(fluoroethyl)thio]-11 beta-hydroxy-androsta-1,4-dien-3-one, structurally novel 20-thiasteroids possessing potent and selective topical antiinflammatory activity.

Two structurally novel alkylthio-substituted steroids, (11 beta, 17 alpha)-17-(ethylthio)-9 alpha-fluoro-11 beta-hydroxy-17-(methylthio)andro-1,4-dien-3-one (tipredane, SQ 27,239) and (11 beta, 17 alpha)-(ethylthio)-9 alpha-fluoro-17-[2-(fluoroethyl) thio]-11 beta-hydroxy-androsta-1,4-dien-3-one (SQ 28,300) were compared to presently available topical corticosteroids for in vitro and in vivo glucocorticoid and antiinflammatory activities. Based upon results of in vitro assays, in vivo antiinflammatory tests in mice, and human vasoconstriction measurements, the thiasteroids most closely resemble moderately potent to highly potent corticoids. These compounds display more modest activity in topical antiinflammatory assays using rats. Both tipredane and SQ 28,300 exhibit favorable separation of local antiinflammatory activity from systemic effects on thymus and hypothalamic-pituitary-adrenal axis function, most probably due to rapid metabolic inactivation. As such, these compounds represent potentially safer therapy for topical treatment of corticoid-responsive skin diseases and bronchopulmonary conditions in humans.

Antiallergic properties of SQ 13,847, an orally effective agent. II. Activity in vitro.

SQ 13,847, a pyrazolo[1,5-c]quinazoline with potent oral antiallergic activity in the rat, was compared with its principal oxidative metabolite, SQ 12,903, for ability to block the release of histamine from the rat mast cell in vitro. SQ 12,903, at concentrations in the range of 0.3 to 2 micrometer, produced 50% inhibition of histamine release reactions triggered by dextran, antirat immunoglobulin (Ig) E or polymyxin B, whereas SQ 13,847 concentration of 100 micrometer or greater were required to produce equivalent inhibitory effects. The greater potency of SQ 12,903 relative to that of SQ 13,847, both in vitro and in passive cutaneous anaphylaxis via the intravenous route, together with the structural similarity of SQ 13,847 is prodrug, requiring oxidation to SQ 12,903 for expression of maximum antiallergic activity. SQ 12,903, disodium cromoglycate and doxantrazole displayed similar time-dependent inhibition and cross-tachyphylaxis, suggesting that all three antiallergic agents block mast cell degranulation via a common mechanism.

Characteristics of successful natural enemies in models of biological control of insect pests.

Biological control of insect pests is characterised by a persistent, strong reduction in the pest population following the introduction of a natural enemy. Analysis of mathematical models suggests that differential exploitation of patches of the pest in a spatially heterogeneous environment provides the most likely mechanism to account for known successes.

Adrenal steroidogenic actions of cyclic nucleotide derivatives in the rat.

Fifteen 3',5'-cyclic nucleotides and related compounds were studied for ability to mimic the steroidogenic action of ACTH in rats in which secretion of ACTH and corticosterone were suppressed by treatment with betamethasone, or by hypophysectomy. Subcutaneous administration of 8-chloro-cAMP, at doses of 40 mg/kg or greater, elicited the secretion of corticosterone to normal plasma levels in both betamethasone-treated and hypophysectomized animals. Cyclic AMP, dbcAMP, 8-methylthio-cAMP, 8-hydroxy-cAMP and the 6-chloro-8-aminopurine cyclic ribotide analog of cAMP also displayed steroidogenic activity in the betamethasone-treated rat; cGMP, 8-bromo-cGMP and 8-benzylthio-cGMP were inactive. Each of the steroidogenic derivatives of cAMP also displayed ability to activate steroidogenesis in isolated rat adrenal cells. These experiments demonstrate that various derivatives of cAMP mimic the adrenal steroidogenic action of ACTH, in vivo. Structure-activity comparisons support a steroidogenic mechanism involving direct activation by the nucleotides of cAMP-dependent protein kinase of the adrenal cortex.

Modulators of cyclic AMP systems.

On the basis of the data reported here, one may conclude that although many agents that act in the central nervous system are modulators of the action of cyclic AMP, it is difficult to establish a direct connection between the pharmacologic activity and the levels of cyclic AMP in the brain. This lack of interrelation applies to the benzodiazepines as well as to the pyrazolopyridines. The data for members of the latter group are somewhat frustrating in this regard, since an excellent correlation has been shown to exist between the potency of inhibition of PDE and activity in the antianxiety test. In measurements of steroidogenesis in the isolated adrenal cell, the correlation between activity in vito and the conflict assay is even better. The data presented here and reported elsewhere (Shimizu et al., 1974; Kelly et al., 1974; Mayer and King, 1974; King and Mayer, 1974) provide evidence that agents that act as inhibitors of PDE in cell-free systems exert their influence on cyclic AMP in tissue slices of the brain of guinea pigs by mechanisms that seem not to be related to an effect on PDE. Papaverine, and possibly chlordiazepoxide, may act by releasing agonists that, in turn, stimulate the accumulation of cyclic AMP. This activity is blocked bo other inhibitors of PDE, such as theophyline. Results obtained by the use of platelets are refreshingly clear. Inhibition of aggregation has been shown to occur when the level of cyclic AMP is raised, and a suggestive exists that the most potent inhibitors of platelet PDE are the best potentiators of the action of PGE1 in blocking aggregation. The study utilizing drugs collected from a large number of therapeutic classes makes clear that it is difficult to attribute the mechanism of action for any of the classes studied to modulation of cyclic AMP. An unexpected finding of this study, however, was the fact that pharmacologic agents include an unusually large number of inhibitors of PDE as compared with agents chosen at random. This finding provides a powerful tool for the biochemical pharmacologist who is examining large numbers of compounds in the search for potential drugs.