Cynthia A. Fink

Novel and potent BK channel openers: CGS 7181 and its analogs

This article discloses the identification of a novel series of the opener of the large‐conductance Ca2+‐activated K+ (BK) channel, CGS 7181, and its analogs, CGS 7184, CGS 7590, and CGS 7725. The stimulatory effects of these compounds on the channels were investigated at whole‐cell and single channel levels using the patch‐clamp technique in single smooth muscle cells from vascular (coronary artery) and non‐vascular (bladder detrusor) tissues of several animal species. With a threshold of submicromolar concentration, extracellularly applied CGS 7181 and CGS 7184 (0.5–50 μM) induced a concentration‐dependent stimulation of the whole‐cell BK current (IBK) and concomitant membrane hyperpolarization in porcine coronary artery cells. The activation was prevented and reversed by TEA, but unaffected by nifedipine, suggesting that the effect was not subsequent to Ca2+ entry. CGS 7184, CGS 7590, and CGS 7725 (0.1–50 μM) produced augmentation of IBK in a similar manner in cells from bladder detrusor of guinea pig, rat, and dog. The onset and offset of the drug actions were slow compared to the known BK channel opener NS004. The effects of compounds applied intracellularly were assessed on single BK channels in inside‐out patches. With threshold concentrations ranging between 0.01 and 0.1 μM, all compounds caused a drastic and reversible increase in channel open‐state probability. The onset and washout of drug actions were considerably faster in inside‐out patches than in whole cells. It is concluded that CGS 7181 and its analogs directly open BK channels from either side of the membrane with a combination of potency and efficacy superior to any known BK channel openers, and an internal site of action best accounts for the results of our studies. Drug Dev. Res. 41:10–21, 1997.

CGS 34226, a thiol-based dual inhibitor of endothelin converting enzyme-1 and neutral endopeptidase 24.11

Endothelins (ETs) are potent vasoconstrictors and have been implicated in the pathogenesis of various cardiovascular and renal diseases. In contrast, atrial natriuretic peptide (ANP) is a potent vasorelaxant and diuretic agent, which is mainly degraded by neutral endopeptidase 24.11 (NEP) in vivo. Thus, compounds that can suppress the biosynthesis of ETs by inhibiting endothelin converting enzymes (ECEs), which catalyse the final step of post-translational processing of the vasoconstrictors, while simultaneously potentiating the levels of ANP by inhibiting NEP may have novel therapeutic utility. Through targeted screening of our compound library and subsequent optimization, CGS 34226 was identified as a potent, dual inhibitor of ECE-1 and NEP, inhibiting the enzymes with respective IC(50) values of 11 and 4.6 nM. In vivo, CGS 34226 suppressed the big endothelin-1 (big ET-1)-induced pressor response dose-dependently. At 15 and 90 min after an intravenous dose of 30 mg/kg in anaesthetized rats, this compound inhibited the big ET-1-induced effect by 79% and 65% respectively. In addition, CGS 34226 increased plasma ANP immunoreactivity by 120% up to 4 h after an intravenous dose of 10 mg/kg in conscious rats infused with ANP at a rate of 450 ng/kg per min, intravenously. These results show that CGS 34226 is a potent dual inhibitor of ECE-1 and NEP in vitro and in vivo and that the compound may represent a novel agent for the treatment of cardiovascular and renal dysfunction.

Design and synthesis of potent thiol-based inhibitors of endothelin converting enzyme-1.

Through directed screening of compounds prepared as metalloprotease inhibitors a compound, CGS 30084, that had potent endothelin converting enzyme-1 (ECE-1) in vitro inhibitory activity (IC50 = 77 nM) was identified. Herein we report the synthesis and optimization of ECE-1 inhibitory activity of additional analogues from this lead. Compound 3c, the thioacetate methyl ester derivative of compound 4c, was found to be a long acting inhibitor of ECE-1 activity in rats after oral administration.

Section Review: Cardiovascular & Renal: Recent advances in the development of dual angiotensin-converting enzyme and neutral endopeptidase inhibitors

The development of single molecules which possess the ability to inhibit both of the membrane-bound zinc metalloproteases, angiotensin-converting enzyme EC 2.4.15.1 (ACE) and neutral endopeptidase EC 3.4.24.11 (NEP), has been the focus of much recent drug discovery effort. These agents represent a new class of cardiovascular agent that should be more effective in treating a broader range of hypertensive patient and in congestive heart failure (CHF). Dual ACE and NEP inhibitors are currently under clinical investigation for hypertension and CHF and several more are under preclinical study. This review focuses on ACE/NEP dual inhibitors reported in the patent and primary literature over the past four years.

Synthesis and biological activity of potent heterocyclic thiol-based inhibitors of endothelin-converting enzyme-1

Directed screening of metalloprotease inhibitors identified CGS 30084 (1) as a potent inhibitor of endothelin-converting enzyme-1 (ECE-1) in vitro (IC(50)=77 nM). Herein we report the syntheses and biological activities of analogues containing modified biphenyl moieties, bearing heterocyclic proximal rings. Compound 20, the thioacetate ethyl ester prodrug derivative of compound 19a, was found to be an orally active and potent inhibitor of ECE-1 activity in rats.

Synthesis and biological activity of novel potent endothelin-converting enzyme-1 inhibitors

Through directed screening of metalloprotease inhibitors, CGS 30084 (1) has been identified as a potent endothelin-converting enzyme-1 (ECE-1) inhibitor in vitro (IC50 = 77 nM). Herein we report the syntheses and biological activities of analogues derived from this lead, based on modifications of the biphenyl moiety. Compound 10, the thioacetate methyl ester prodrug derivative of compound 6m, was found to be an orally active and potent inhibitor of ECE-1 activity in rats.

Effects of the ECE/NEP inhibitor CGS 34225 on the big ET-1-induced pressor response and plasma atrial natriuretic peptide concentration in conscious rats

CGS 34226 is a thiol-containing, potent dual inhibitor of endothelin converting enzyme-1 (ECE-1) and neutral endopeptidase 24.11 (NEP) with IC(50) values of 11 and 5 nM respectively. The purpose of the present study was to characterize the inhibitory effects of CGS 34225, an orally active prodrug of CGS 34226, on ECE-1 and NEP in vivo. The effects on ECE-1 and NEP were assessed by determining the inhibition of big endothelin-1 (big ET-1)-induced increases in mean arterial pressure (MAP) and increases in plasma atrial natriuretic peptide (ANP) concentrations respectively, in conscious rats. Thirty and 120 min after the administration of vehicle, big ET-1 (0.3 nmol/kg, intravenously; i.v.) produced pressor responses of approximately 800 mmHg.min (area under the curve for change in MAPxtime). Treatment with CGS 34225 at 1 mgEq/kg, per os (p.o.), decreased the pressor effect of big ET-1 by 39 and 53% at 30 and 120 min respectively (P<0.05, both times). Increasing the dose of CGS 34255 to 30 mgEq/kg, p.o., resulted in greater inhibition, 84 and 92% (P<0.05) at 30 and 120 min respectively. Furthermore, at this higher dose, the inhibitory effect on ECE-1 was long-lasting, averaging 86, 75 and 30% (P<0.05, all times) at 4, 8 and 24 h respectively. In rats treated with vehicle, the infusion of ANP at 450 ng/kg per min i.v. resulted in plasma ANP concentrations of 3.9-4.8 ng/ml that remained relatively constant for 4 h. Treatment with CGS 34225 at 10 mgEq/kg, p.o., increased the ANP level to 7.7+/-1.0 and 10.6+/-1.8 ng/ml at 1 and 4 h after dosing (P<0.05, both times). These data demonstrate that CGS 34225 is a potent, orally active and long-acting inhibitor of ECE-1 and NEP in vivo. It is anticipated that compounds with this dual function may be useful in the treatment of cardiovascular diseases where the ET system plays a pathogenic role and the potentiation of ANP elicits therapeutic benefits.

Design and synthesis of thiol containing inhibitors of matrix metalloproteinases

A series of thiol containing derivatives was prepared. Several of these compounds were found to inhibit matrix metalloproteinases 1, 3, and 9 with selectivity towards 3 and 9. Compounds 15, 20, and 22 were administered to rats orally at 75 mumol/kg. Drug levels of compounds 20 and 22 in the plasma were found to exceed the IC50 values for MMP 3 and 9 four hours after administration.

α-Mercaptoacyl dipeptides that inhibit angiotensin converting enzyme and neutral endopeptidase 24.11

Abstract α-Mercaptoacyl dipeptides were prepared and found to inhibit angiotensin converting enzyme (ACE) and neutral endopeptidase 24.11 (NEP). Compounds with a proline as the C-terminal amino acid, and possessing the S-stereochemistry at the thiol bearing carbon were preferred for optimal ACE inhibition while, R-stereochemistry was preferred for optimal NEP inhibition. Compounds containing alternative amino acid residues at the C-terminal position displayed optimal dual ACE/NEP inhibition when the stereochemistry was ‘S’ at this carbon atom.