Antihypertensive Peptides

Endotheline is a powerful vasoconstrictor extracted from porcine aortic endothelium and this peptide which has been recently isolated comprises 21 amino acids, has 2 disulfide bridges and has the formula (SEQ ID NO. 14): ##STR1##

A novel potent vasoconstrictor peptide produced by vascular endothelial cells taught by Yanagisawa et al, Nature, (1988), Vol. 332, p. 411-415 is designated in what follows under the name of ET1. The nomenclature used is that of the IUPAC-IUB commission (1984) European J. Biochem., Vol. 183, pg. 9-37. This peptide which contains 21 amino-acid residues and 2 disulfide bridges is capable of contracting the smooth muscle cells (arteries and veins) of different species of mammals (man, dog, cat, pig, guinea-pig, rat, rabbit . . . ) at very low doses. Other prior art includes FEBS Letters, Vol. 256, No. 1 (Oct. 2, 1989), pg. 1 to 3 and Biochemical and Biophysical Research, Vol. 163, No. 1 (Aug. 30, 1989), pg. 424-429.

It is an object of the invention to provide novel peptides by shortening the chain of endotheline and replacing certain amino acids with other amino acids in which the vascoconstricting activity of endotheline is avoided while retaining the property of blocking and fixing itself on the natural receptors of endotheline.

It is another object of the invention to provide novel antihypertensive compositions and a novel method of inducing antihypertensive activity in warm-blooded animals.

These and other objects and advantages of the invention will become obvious from the following detailed description.

The novel peptides of the invention have the formula (SEQ ID NO. 1)

wherein X.sub.1 is the residue of leucine or arginine or glutamine, X.sub.2 is the residue of isoleucine or valine, X.sub.3 is a residue of tryptophan or amidotryptophan or D-naphthylalanine and R.sub.1 is a remainder of 15 amino-acids of the formula (SEQ ID NO. 2) ##STR2## X.sub.4 in 7-position is a residue of an amino acid selected from the group consisting of glycine, nor-leucine, valine, isoleucine, leucine, alanine, phenylalanine, beta-alanine and methionine, X.sub.5 in 12-position is a residue of valine or leucine or glutamic acid and the broken line represents an optional disulfide bridge between two cysteine residues with the proviso that X.sub.4 is not methionine residue when X.sub.5 is a valine residue or R.sub.1 is the remainder of 15 amino acids of the formula (SEQ ID NO. 3) ##STR3## X.sub.6 is a residue of leucine or valine and the broken line is an optional disulfide bridge between 2 cysteine residues with the proviso that X.sub.6 is not a leucine residue when X.sub.1 is a glutamine residue or R.sub.1 is remainder of 9 amino acids of the formula (SEQ ID NO. 4) ##STR4## X.sub.7 in 5-position is a nor-leucine residue and the broken line is an optional disulfide bridge between 2 cysteine residues or R.sub.1 is a remainder of 9 amino acids of the formula (SEQ ID NO. 5) ##STR5## X.sub.8 is a residue of cysteine or alanine or serine and the broken line is an optional disulfide bridge between 2 cysteine residues.

A preferred group of the peptides of the invention are those wherein X.sub.1 is a residue of leucine, arginine or glutamine, X.sub.2 is an isoleucine residue and X.sub.3 is a residue of tryptophan, amidotryptophan or D-naphthylalanine. Among the latter, preferably are those wherein R.sub.1 is a remainder of the amino-acids of formula Ia, X.sub.4 in 7-position is a residue of glycine, valine or beta-alanine and X.sub.5 in 12-position is a residue of valine or leucine and the broken line optionally is a disulfide bridge between 2 cysteine residues or R.sub.1 is a remainder of the 15 amino-acids of Formula Ib, X.sub.6 is a residue of leucine or valine, and the broken line optionally is a disulfide bridge between 2 cysteine residues.

Also preferred are those wherein R.sub.1 is a remainder of the 9 amino-acids of formula Ic, X.sub.7 in 5-position is a nor-leucine residue and the broken line optionally is a disulfide bridge between 2 cysteine residues, or R.sub.1 is a remainder of the 9 amino-acids of formula Id, X.sub.8 is a cysteine residue and the broken line optionally is a disulfide bridge between 2 cysteine residues.

Especially preferred peptides are those of the formulae ##STR6##

The novel process of the invention for the preparation of the peptides of the invention comprises forming a solid phase by sequentially introducing protected amino acids onto a cross-linked polystyrene resin type support with a coupling agent, deprotecting the amino acids, releasing the peptide chain from the support and optionally cyclizing the disulfide bridge(s).

In a preferred mode of the process of the invention, the cross-linked polystyrene type is Boc--Trp--CM type where Boc is tert-butoxycarbonyl, Trp is a tryptophyl and CM is the cross-linked polystyrene support, the coupling agent is Bop or (benzotriazol-1-yloxy)-tris(dimethylamino)-phosphonium hexafluorophosphate and the deprotection of the amino acids and release from the support is effected with hydrofluoric acid at low temperatures, especially at about 0.degree. C.

The novel antihypertensive compositions of the invention are comprised of an antihypertensively effective amount of at least one novel peptide of the invention and an inert pharmaceutical carrier or excipient. The compositions may be in the form of tablets, dragees, gelules, capsules, granules, suppositories, aerosols and injectable solutions or suspensions.

Examples of suitable excipients are talc, gum arabic, lactose, starch, magnesium stearate, cocoa butter, aqueous or non-aqueous vehicles, fatty substances of animal or vegetable origin, paraffin derivatives, glycols, various wetting, dispersing or emulsifying agents, and preservatives.

The compositions have a remarkable inhibiting effect against hypertension induced by endotheline and an antischemic activity without the vasoconstricting activity of endotheline. The compositions are useful in the treatment of all vascular spasms, in the treatment of post-brain hemorrhages, in the treatment of coronary spasms and peripheral vascular spasms and renal insufficiency.

The novel method of the invention for inducing antihypertensive activity in warm-blooded animals, including humans, comprises administering to warm-blooded animals an antihypertensively effective amount of a peptide of formula I. The peptide can be administered orally, rectally or parenterally and the usual daily dose is 0.013 to 4 mg/kg depending on the condition treated, the method of administration and the specific peptide.

In the following examples, there are described several preferred embodiments to illustrate the invention. However, it should be understood that the invention is not intended to be limited to the specific embodiments.

STAGE A: Assembly of the Peptide Chain

A "Boc--Trp--CM--support" type support was used in which Boc is a tert-butoxycarbonyl, Trp is a tryptophyl and CM-support is a cross-linked polystyrene support. The support containing 0.6 mmol Trp/g was prepared by the potassium fluoride method of Horiki et al (1978) Chemistry Lett., pg. 165-168. All the amino-acids were N-protected by tert-butylcarbonyl. The protector groups of the lateral chains were p-methyl benzyl for cysteine, cyclohexyl ester for aspartic acid and glutamic acid, benzyl for serine, o-chlorobenzyloxycarbonyl for lysine, 2,6-dichlorobenzyl for tyrosine, Nim-tertiobutyloxycarbonyl, tryptophan and methionine were not protected.

The coupling reactions were carried out using Bop or (benzotriazol-1-yloxy)-tris(dimethylamino)-phosphonium hexafluorophosphate). A coupling cycle can be summarized as follows:

1. Treatment with a 50% solution of trifluoroacetic acid in dichloromethane containing 3% of ethanedithiol for 1 minute.

2. Draining, then treatment with a 50% solution of trifluoroacetic acid in dichloromethane containing 3% of ethanedithiol for 30 minutes.

3. Draining, then washing with isopropanol containing 5% of ethanedithiol.

4. Washing with dichloromethane, twice.

1. Addition of Bop and Boc-amino acid.

2. Addition of diisopropylethylamine (6 equivalents), then of solvent (dichloromethane or dimethylformamide) with stirring.

3. After a negative reaction to ninhydrin, washing twice with dichloromethane.

Control tests using ninhydrin were carried out following the process described by Kaiser et al, (1970) Anal. Biochem., Vol. 24, pg. 595-598. Before treatment with hydrofluoric acid, the last group of Boc was eliminated with trifluoroacetic acid. From 2 g of "Boc--Trp--CM--resin" type resin, 5.25 g of protected peptide chain-resin complex was obtained by operating manually, which was used directly for the following step.

STEP B: Release of the Protected Peptide Chain--Resin Complex

1.5 g of protected peptide chain-resin complex were reacted for 60 minutes with 15 ml of hydrofluoric acid at 0.degree. C. in the presence of 1 ml of anisole and 0.5 ml of dimethylsulfide. The resin was washed with ether and the crude peptide was extracted with an aqueous solution of acetic acid at 20%. After lyophilization, 660 mg of non-cyclized crude product were obtained which were used directly for the following step.

STEP C: Cyclization and Purification

500 mg of the crude peptide of Step B were dissolved in 250 ml of water and the solution was vigorously stirred while diisopropyl ethylamine was added until a pH of 8 was obtained. A drop of mixture was collected every hour and added to a drop of a solution containing dithiobis (2-nitrobenzoic) acid in a molar buffer of K.sub.2 HPO.sub.4 (pH 8) to monitor the oxidation reaction. During the reaction, the pH was kept at 8 by the addition of diisopropylethylamine. The reaction was followed by high performance liquid chromatography (HPLC). After 28 hours, the absence of yellow coloration was observed in the test using dithiobis (2-nitrobenzoic) acid.

The product obtained was purified by high performance liquid chromatography (HPLC) on a M20 ODS.sub.3 Whatman column and eluted with a water-acetonitrile mixture containing 0.1% trifluoroacetic acid. The fraction was lyophilized to obtain 30 mg of the expected product whose amino-acid composition appears in Table I.

Using the procedure of Example 1 but with other amino-acids, 14 other micro-proteins were prepared which appear hereafter. However, for the products of Examples 2 to 15, at Step C of cyclization and purification, 500 ml of water per 500 mg of peptide were used.

(Gly-7)--ET1 derivative (SEQ ID NO. 11) ##STR7##

(Nle-7)-DiNaphtylalanine-21-ET1 derivative.

(Nle-7)-Amidotryptophan-21-ET1 derivative.

(Beta-alanine-7)-ET1 derivative.

(Val-7)-ET1 derivative.

Derivative of formula Ic (X.sub.7 =Nle, X.sub.1 =Leu, X.sub.2 =Ile, X.sub.3 =Trp with disulfide bridge between cysteines 1 and 9).

Derivative of Formula Id (X.sub.8 in position 1 and 9=Cys, X.sub.1 =Leu, X.sub.2 =Ile, X.sub.3 =Trp with disulfide bridge between cysteines 1 and 9).

Derivative of Formula Ib (X.sub.6 in position 12=Val, X.sub.1 =Leu, X.sub.2 =Ile, X.sub.3 =Trp with two disulfide bridges between cysteines 1-15 and 3-11).

Derivative of Formula Ia (X.sub.4 in position 7=Nle, X.sub.1 =Gln, X.sub.2 =Ile, X.sub.3 =Trp, X.sub.5 =Val with two disulfide bridges between cysteines 1-15 and 3-11).

Derivative of Formula Ia (X.sub.4 in position 7=Met, X.sub.5 in position 12=Leu, X.sub.1 =Gln, X.sub.2 =Ile, X.sub.3 =Trp with two disulfide bridges between cysteines 1-15 and 3-11).

Derivative of Formula Id (X.sub.8 in position 1 and 9=Ala, X.sub.1 =Leu, X.sub.3 =Trp).

Derivative of Formula Ib (X.sub.6 =Leu, X.sub.1 =Arg, X.sub.2 =Ile, X.sub.3 =Trp).

The amino-acid compositions are indicated in Table I.

An injectable solute was prepared comprising 1 mg of the product of Example 1 and sufficient sterile aqueous excipient for a solution of 2 ml.

Tablets were prepared containing 2 mg of the product of Example 1 and excipient of lactose, starch, talc and magnesium stearate for a final weight of 150 mg.

A membrane preparation was made from rat posterior cortex and brain and the tissue was ground with a POLYTRON in a 50 mM Tris buffer pH=7.4. After 30 minutes at 25.degree. C. (W.B.), the homogenate was centrifuged at 30,000 g for 15 minutes (2 centrifugations with intermediate taking up in the Tris buffer pH 7.4). The deposits were suspended in an incubation buffer (Tris 25 mM, pepstatine A 5 microg/ml, aprotinine 3 microg/ml, PMSF 0.1 mM, EDTA 3 mM, EGTA 1 mM pH 7.4). 2 ml aliquots were distributed in hemolysis tubes and .sup.125 I endotheline (approximately 50,000 dpm/tube) and the product to be studied were added. The product was first tested at 3.times.10.sup.-5 M in triplicate. When the product tested displaced more than 50% of radioactivity linked specifically to the receptor, it was tested again in a range of 7 concentrations to determine the concentration which inhibited the radioactivity linked specifically to the receptor by 50%. In this way, the 50% inhibiting concentration was determined.

The non-specific bond was determined by the addition of endotheline at 10.sup.-6 M (in triplicate) and the deposits were incubated at 25.degree. C. for 60 minutes, put in a water-bath at 0.degree. C. for 5 minutes, filtered under reduced pressure and rinsed with a Tris buffer 7.4 pH. The radioactivity was counted in the presence of scintillating Triton. The result was expressed directly as a 50% inhibiting concentration (IC50), or the concentration of product studied expressed in nM necessary to displace 50% of the specific radioactivity fixed on the receptor studied.

Result:

The IC50-s found for the products of Examples 1 to 15 are given in Table II in nanomoles.

Various modifications of the products and method of the invention may be made without departing from the spirit or scope thereof and it is to be understood that the invention is intended to be limited only as defined in the appended claims.