Walter Fischli

Promotion of sleep by targeting the orexin system in rats, dogs and humans

Orexins are hypothalamic peptides that play an important role in maintaining wakefulness in mammals. Permanent deficit in orexinergic function is a pathophysiological hallmark of rodent, canine and human narcolepsy. Here we report that in rats, dogs and humans, somnolence is induced by pharmacological blockade of both orexin OX1 and OX2 receptors. When administered orally during the active period of the circadian cycle, a dual antagonist increased, in rats, electrophysiological indices of both non-REM and, particularly, REM sleep, in contrast to GABAA receptor modulators; in dogs, it caused somnolence and increased surrogate markers of REM sleep; and in humans, it caused subjective and objective electrophysiological signs of sleep. No signs of cataplexy were observed, in contrast to the rodent, dog or human narcolepsy syndromes. These results open new perspectives for investigating the role of endogenous orexins in sleep-wake regulation.

Pharmacology of Macitentan, an Orally Active Tissue-Targeting Dual Endothelin Receptor Antagonist

Macitentan, also called Actelion-1 or ACT-064992 [N-[5-(4-bromophenyl)-6-(2-(5-bromopyrimidin-2-yloxy)ethoxy)-pyrimidin-4-yl]-N′-propylaminosulfonamide], is a new dual ETA/ETB endothelin (ET) receptor antagonist designed for tissue targeting. Selection of macitentan was based on inhibitory potency on both ET receptors and optimization of physicochemical properties to achieve high affinity for lipophilic milieu. In vivo, macitentan is metabolized into a major and pharmacologically active metabolite, ACT-132577. Macitentan and its metabolite antagonized the specific binding of ET-1 on membranes of cells overexpressing ETA and ETB receptors and blunted ET-1-induced calcium mobilization in various natural cell lines, with inhibitory constants within the nanomolar range. In functional assays, macitentan and ACT-132577 inhibited ET-1-induced contractions in isolated endothelium-denuded rat aorta (ETA receptors) and sarafotoxin S6c-induced contractions in isolated rat trachea (ETB receptors). In rats with pulmonary hypertension, macitentan prevented both the increase of pulmonary pressure and the right ventricle hypertrophy, and it markedly improved survival. In diabetic rats, chronic administration of macitentan decreased blood pressure and proteinuria and prevented end-organ damage (renal vascular hypertrophy and structural injury). In conclusion, macitentan, by its tissue-targeting properties and dual antagonism of ET receptors, protects against end-organ damage in diabetes and improves survival in pulmonary hypertensive rats. This profile makes macitentan a new agent to treat cardiovascular disorders associated with chronic tissue ET system activation.

Local Angiotensin II Generation in the Rat Heart Role of Renin Uptake

To elucidate the local effects of renin in the coronary circulation, we examined local angiotensin (Ang) I and II formation, as well as coronary vasoconstriction in response to renin administration, and compared the effects with exogenous infused Ang I. We perfused isolated hearts from rats overexpressing the human angiotensinogen gene in a Langendorff preparation and measured the hemodynamic effects and the released products. We also investigated cardiac Ang I conversion, including the contribution of non-angiotensin-converting enzyme-dependent Ang II-generating pathways. Finally, we studied Ang I conversion in vitro in heart homogenates. Renin and Ang I infusion both generated Ang II. Ang II release and vasoconstriction continued after renin infusion was stopped, even though renin disappeared immediately from the perfusate. In contrast, after Ang I infusion, Ang II release and coronary flow returned to basal levels. Ang I conversion (Ang II/Ang I ratio) was higher after renin infusion (0.109+/-0.027 versus 0.026+/-0.003, 15 minutes, P<.02) compared with infused Ang I. Remikiren added to the renin infusion abolished Ang I and II; captopril suppressed only Ang II, whereas an AT1 receptor blocker did not affect Ang I and II formation. All the drugs prevented renin-induced coronary flow changes. Total cardiac Ang II-forming activity was only partially inhibited by cilazaprilat (4.1+/-0.1 fmol x min(-1) x mg[-1]) and on a larger extent by chymostatin (2.6+/-0.3 fmol x min(-1) x mg[-1]) compared with control values (5.6+/-0.4 fmol x min(-1) x mg[-1]). We conclude that renin can be taken up by cardiac or coronary vascular tissue and induces long-lasting local Ang II generation and vasoconstriction. Locally formed Ang I was converted more effectively than infused Ang I. Furthermore, the comparison of in vivo and in vitro Ang I conversion suggests that in vitro assays may underestimate the functional contribution of angiotensin-converting enzyme to intracardiac Ang II formation.

The Discovery of N-[5-(4-Bromophenyl)-6-[2-[(5-bromo-2-pyrimidinyl)oxy]ethoxy]-4-pyrimidinyl]-N′-propylsulfamide (Macitentan), an Orally Active, Potent Dual Endothelin Receptor Antagonist

Starting from the structure of bosentan (1), we embarked on a medicinal chemistry program aiming at the identification of novel potent dual endothelin receptor antagonists with high oral efficacy. This led to the discovery of a novel series of alkyl sulfamide substituted pyrimidines. Among these, compound 17 (macitentan, ACT-064992) emerged as particularly interesting as it is a potent inhibitor of ET(A) with significant affinity for the ET(B) receptor and shows excellent pharmacokinetic properties and high in vivo efficacy in hypertensive Dahl salt-sensitive rats. Compound 17 successfully completed a long-term phase III clinical trial for pulmonary arterial hypertension.

Substituted piperidines: Highly potent renin inhibitors due to induced fit adaptation of the active site

The identification, synthesis and activity of a novel class of piperidine renin inhibitors is presented. The most active compounds show activities in the picomolar range and are among the most potent renin inhibitors ever identified.

Piperidine-renin inhibitors compounds with improved physicochemical properties

Piperidine renin inhibitors with heterocyclic core modifications or hydrophilic attachments show improved physical properties (lower lipophilicity, improved solubility). Tetrahydroquinoline derivative rac-30 with a molecular weight of 517 and a log D(pH 7.4) of 1.9 displays potent and long lasting blood pressure lowering effects after oral administration to sodium depleted conscious marmosets.

Design and Preparation of Potent, Nonpeptidic, Bioavailable Renin Inhibitors

Starting from known piperidine renin inhibitors, a new series of 3,9-diazabicyclo[3.3.1]nonene derivatives was rationally designed and prepared. Optimization of the positions 3, 6, and 7 of the diazabicyclonene template led to potent renin inhibitors. The substituents attached at the positions 6 and 7 were essential for the binding affinity of these compounds for renin. The introduction of a substituent attached at the position 3 did not modify the binding affinity but allowed the modulation of the ADME properties. Our efforts led to the discovery of compound (+)-26g that inhibits renin with an IC(50) of 0.20 nM in buffer and 19 nM in plasma. The pharmacokinetics properties of this and other similar compounds are discussed. Compound (+)-26g is well absorbed in rats and efficacious at 10 mg/kg in vivo.

Effects of cilazapril, a novel angiotensin converting enzyme inhibitor, on the structure of pulmonary arteries of rats exposed to chronic hypoxia.

Chronic hypoxia is Known to be associated with a thickening of the media of pulmonary arteries. The goal of the present study was to assess if cilazapril. a novel long-acting angiotensin converting enzyme (ACE) inhibitor. could prevent this thickening. For this purpose. three groups of rats were studied. One group was kept in normal room air. Two other groups were exposed to chronic hypoxia sinspired fraction of oxygen equal to 8% during 4 weeks). One group of hypoxie rats was treated with placebo and the other group received cilazapril tas food admixture of 3 mg/kg/day). After 4 weeks. the rats were anesthetized and pulmonary artery pressure and hematocrit measured. Then the lungs were perfused and fixed and morphometry of the pulmonary arteries was performed. Hypoxia induced an increases in pulmonary artery pressure and hematocrit associated with a dramatic increase in the thickness of the media of the pulmonary arteries. Cilazapril completely prevented the thickening of the media of the pulmonary arteries but dit not significantly decrease the pulmonary artery pressure or right ventricular weight.

Cilazapril prevents hypertension in spontaneously hypertensive rats

Summary: Chronic daily administration of cilazapril (1 x 10 mg/kg/day p.o., from age 4 to 14 weeks) to young spontaneously hypertensive rats (SHR) prevented the development of hypertension. The antihypertensive effect of a single dose of cilazapril persisted >24 h. Discontinuation of long-term treatment resulted in an increase of systolic arterial blood pressure (SAP) to control hypertensive levels within 4 days. Following 10 weeks of drug administration, comparative hemodynamic studies were carried out on age-matched (14 weeks) control SHR and cilazapril-treated SHR. Cilazapril-treated SHR had a significantly lower mean arterial blood pressure (MAP) and total peripheral vascular resistance than did control SHR. The antihypertensive effect of cilazapril was not associated with changes in heart rate (HR). The myocardial performance parameters, cardiac output, and stroke volume, were similar in treated and control SHR, suggesting that the antihypertensive effect of cilazapril following chronic administration to SHR is mainly due to a reduction in peripheral vascular resistance. Vasopressor responses to angiotensin I were significantly lower in cilazapril-treated SHR than in control SHR. By contrast, pressor responses to angiotensin II and a high dose of norepinephrine (1.0 μg/kg i.v.) were significantly enhanced. Isoproterenol elicited a fall in blood pressure in both groups, the extent of which was dependent upon the magnitude of basal blood pressure levels. Chronic cilazapril treatment resulted in a reduction of heart weight, suggesting that the drug may prevent development of cardiac hypertrophy in SHR. Kidney and adrenal weights were unaffected by the chronic treatment. Specific renin activities (SRA) in tissues of SHR were increased by factors of 20 (plasma) or 2 (kidney and adrenal) following cilazapril administration. Five weeks after discontinuation of drug treatment, near normal values of SRA were reached, suggesting that chronic administration of cilazapril is associated with reversible changes in the renin-angiotensin system (RAS) of SHR.

Tetrahydroisoquinolines as orexin receptor antagonists: Strategies for lead optimization by solution-phase chemistry

Different techniques can be applied for the automated production of small and large compound collections. Large libraries that are often generated and tested during the lead-finding stage of a project are typically produced by solid-phase chemistry. Libraries that are significantly smaller in size are often synthesized in solution. Chemistry in solution is rather versatile, offers numerous advantages and is therefore often the method of choice for generating small libraries during a lead optimization process. Fast and reliable purification procedures are required to yield compounds of high quality that can be immediately used in biological as well as pharmacological assays. Solution-phase chemistry combined with automated purification was applied to optimize initial lead inhibitors for the two human orexin receptors OX1 and OX2. Starting from a submicro-molar OX1 selective lead compound, low nanomolar analogues with improved physico-chemical properties were synthesized that antagonize either one or both orexin receptors.