Immunostimulating peptides, a process for their preparation and pharmaceutical compositions containing them

Abstract

Tripeptides having general formula II Glu-Lys-Arg in which: Glu is a glutamic acid residue, Lys is a lysine residue and Arg is an arginine residue are described. The aminoacids composing the tripeptides of the invention may be either of the natural, L-series or of the D-series or a racemic mixture of the two said series, but the aminoacids are preferably selected from the L-forms even though D- or DL aminoacids may also be considered. The invention refers also to the process for the preparation of said peptides as well as to their use as immunostimulant agents.

Description

The present invention relates to tripeptides having general formula II Glu-Lys-Arg in which: Glu is a glutamic acid residue, Lys is a lysine residue and Arg is an arginine residue.

The aminoacids composing the tripeptides of the invention may be either of the natural, L-series or of the D-series or a racemic mixture of the two said series, but the aminoacids are preferably selected from the L-forms even though D- or DL aminoacids may also be considered.

The invention refers also to the process for the preparation of said peptides as well as to their use as immunostimulant agents.

The tripeptide Arg-Ala-Arg is known from the Italian patent application no. 20027 A/86 of 9.04.1986: it is endowed with immunostimulating activity and it is able to enhance both the T-cells maturation and functional abilities.

Also the Arg-Lys-Glu tripeptide (splenotritin) corresponding to the 32-34 fragment of splenopoietin, a polypeptide hormone extracted from the bovine spleen and originally referred to as thymopoietin III because of its high affinity with thymopoietins I and II isolated from thymus, has immunostimulating properties, involving the maturation and functionality of T-lymphocytes (Italian patent application no. 20026 A/86 of 9.04.1986; Diezel W. et al.: Biomed. Biochim. Acta 45, 1349, 1986).

Similarly, the peptide Arg-Lys-Asp, differing from Arg-Lys-Glu only in the C-terminal aminoacidic residue, displays a similar behaviour (EP-A-0067425) as well as Arg-Gly-Asp, disclosed in the Italian patent application no. 21575 A/87 of 4.08.1987.

The peptides according to the invention proved to be active as immunostimulating agents, being effective in in vitro experimental models in promoting the maturation of murine immature T-lymphocytes and in enhancing the functionality of human T-cells. The peptides are capable of restoring the immune function in nude athymic mice, when administered for 5 days, 2 or 6 weeks by oral or i.p. route.

Like Arg-Ala-Arg and Arg-Lys-Glu, also the tripeptides of the present invention are stable to the in vitro simulated gastric juice.

Analogously to the two peptides above mentioned, the stability of which in the simulated gastric juice is related to the activity after oral administration, it has been demonstrated that also the peptides of the invention are endowed with immunostimulating activity both after oral administration and after parenteral administration.

This fact represents a remarkable advantage in the therapeutic use, with particular reference to the treatment of children and of other patients who do not tolerate the parenteral administration and also as a consequence of a better patient's compliance to the prescribed therapy.

According to what above described, the compounds of the invention have such features so as to make them particularly useful in the clinical practice for the therapy both of primary and secondary deficiencies.

The clinical utilities of immunostimulating compounds are described for instance in Immun. Lett. Vol. 16, 363, 1987, JAMA Vol. 258, 3005, 1987 and Drug Discovery and Development, Eds. Williams M. and Malick J. B., Humana 1987, p. 227, which are herein incorporated by reference.

For the intended use, the tripeptides of the invention may be administered either alone or in admixture with pharmaceutically acceptable carrier, in suitable pharmaceutical formulations which are a further object of the invention.

Examples of said formulations, which may be prepared using well known methods and excipients, such as those described in "Remington's Pharmaceutical Sciences Handbook", Mack Pub. Co., N.Y. U.S.A., are tablets, capsules, syrups, and the like for the oral administration whereas for the parenteral administration suitable forms are sterile solutions or suspensions in acceptable liquids, implants, etc. The preferred dosage form is a unit dose comprising from about 0.1 to about 500 mg of a tripeptide of formula II or the equivalent of a pharmaceutically acceptable salt thereof, such as acetate, hydrochloride, trifluoroacetate, sulfate salts.

The posology will depend on several factors such as type and seriousness of the pathologic conditions to be treated, patient's weight and sex, etc. and will be easily determined by the skilled practitioner. Generally one to four administrations a day will be prescribed.

The tripeptides II are prepared according to conventional methods, well known in peptide chemistry, such as solid state synthesis on resins.

The following non limitative examples are given as a further illustration of the invention.

EXAMPLE 1

GENERAL PROCEDURE FOR THE SOLID PHASE SYNTHESIS OF TRIPEPTIDES

1. Preparation of resins substituted with Boc-aminoacids

Chloromethylated polystyrene (1% crosslinked; 200-400 mesh) is swelled in dimethylformamide (DMF) (about 8-10 ml per g of resin), then treated with the Boc-aminoacid (1 mole per g of resin), followed by potassium fluoride (2 moles per g of resin). A small amount of solvent (5-10 ml) is then distilled off under vacuum after which the mixture is heated to 80.degree.-100.degree. C. for 16-18 hours. While cooling, the resin is filtered, washed with DMF, DMF:H.sub.2 O 1:1, H.sub.2 O, ethanol, CH.sub.2 Cl.sub.2 and methanol and then dried under vacuum. Substitution (calculated by the weight increase)=0.4-0.6 moles per g.

2. General synthetic procedure

The suitable amount of resin substituted with the C-terminal Boc-aminoacid in the desired sequence is sequentially treated at room temperature (20.degree.-25.degree. C.) with:

a) CH.sub.2 Cl.sub.2 b) 50% CF.sub.3 COOH:CH.sub.2 Cl.sub.2 (v/v) c) 50% CF.sub.3 COOH:CH.sub.2 Cl.sub.2 for 25' d) CH.sub.2 Cl.sub.2 (3 times) e) isopropanol f) 10% triethylamine:CH.sub.2 Cl.sub.2 (v/v) (twice) g) CH.sub.2 Cl.sub.2 h) methanol (twice) i) CH.sub.2 Cl.sub.2 (twice) The contact time for each treatment is 3-5 minutes except treatment c).

About 10-15 ml of solvent or of solvent reagent mixture are used per g of resin in each step.

j) The resin is stirred with a solution of the suitably protected last but one, Boc-aminoacid of the desired sequence 3 equivalents in CH.sub.2 Cl.sub.2 Dicyclohexylcarbodiimide 3 equivalents is then added thereto in CH.sub.2 Cl.sub.2. The reaction time is at least 2-4 hours and it may last overnight (16-18 hours).

The resin to which the peptide is bound is filtered and washed with CH.sub.2 Cl.sub.2, methanol and CH.sub.2 Cl.sub.2 and the synthesis completion is checked by the ninhydrin reaction. If the synthesis is incomplete, the same aminoacid is coupled again using half amounts of the reagents. The cycle is repeated for each aminoacid of the sequence, until this is completed.

After removal of the N-terminal Boc group, the resin to which the peptide is bound is carefully washed and dried under vacuum.

The peptide is detached from the resin and contemporaneously deprotected by treatment with anhydrous hydrofluoric acid (about 10 ml per g of resin) containing anisole (10% v/v) for 1 h at 0.degree. C.

After evaporation of hydrofluoric acid under reduced pressure, the crude peptide is extracted by washing the resin with diluted aqueous acetic acid and the product is isolated by lyophilization.

3. Purification of the crude tripeptide

The crude tripeptides may be purified by reverse phase preparative HPLC using silanized silica with C18 chain with, for instance, a Waters Prep 500 instrument. Using a 5.times.30 cm column, equilibrated with the suitable aqueous buffer, such as aqueous 0,1% trifluoroacetic acid, the crude peptide (about 2 g) is applied on the column and eluted with a gradient containing increasing amounts of acetonitrile. The fractions are checked by analytical HPLC and those containing the product at the desired purity degree (>95%) are collected and lyophilized. Finally, the purified product is transformed in the desired salt by treatment with the desired salt form of an ion-exchange resin.

SYNTHETIC PROCEDURES

The following compounds have been synthesized and purified by the general synthetic procedure described in Example 1 of U.S. patent application Ser. No. 384,327:

1) GLU-LYS-ARG (Boc-N.sup.G -tosyl-L-arginine=a; Boc-epsilon-2-chlorobenzyloxycarbonyl-L-lysine=b; Boc-gamma-benzyl-L-glutamic acid=c) 2) D-GLU-LYS-ARG (a; b; Boc-gamma-benzyl-D-glutamic acid=d) 3) GLU-D-LYS-ARG (a; Boc-epsilon-2-chlorobenzyloxycarbonyl-D-lysine=e; c) 4) GLU-LYS-D-ARG (Boc-N.sup.G -tosyl-D-arginine=f; b; c) 5) D-GLU-D-LYS-ARG (a; e; d) 6) D-GLU-LYS-D-ARG (f; b; d) 7) GLU-D-LYS-D-ARG (f; e; c) 8) D-GLU-D-LYS-D-ARG (f; e; d)

CHEMICAL CHARACTERISTICS

All the compounds 1-8 exhibit a molecular weight of 431.5.

______________________________________Appearance: white powdersPeptide Peptide content (%)* Peptide purity**______________________________________1 71.2 +/- 3% >97%2 81.0 +/- 3% >96%3 71.4 +/- 3% >97%4 69.8 +/- 3% >96%5 81.0 +/- 3% >93%6 79.0 +/- 3% >94%7 76.0 +/- 3% >94%8 73.0 +/- 3% >92%______________________________________ *Determined after acidic hydrolysis by OPA derivatization **Determined by RPHPLC

BIOLOGICAL CHARACTERISTICS

RNA synthesis in human T lymphocytes stimulated in vitro with phytohemagglutinin

Human T lymphocytes incubated in vitro for 24 hrs in the presence of 0.5% phytohemagglutinin (PHA) and of different peptide concentrations, have been analyzed for the RNA synthesis by means of 3H-uridine labelling. The results show that the tripeptides of this invention are capable of stimulating RNA synthesis in PHA activated human lymphocytes.

______________________________________ 3-H URIDINECONCENTRATION INCORPORATION (cpm)PEPTIDE (mcg/ml) MEAN (+/- SE) .DELTA. %______________________________________-- 0.0 2756 (432) --1 0.1 5344 (556)* +94 1.0 8235 (244)* +1992 0.1 4870 (546)* +77 1.0 7599 (377)* +1763 0.1 5531 (613)* +101 1.0 6985 (480)* +1534 0.1 4824 (318)* +75 1.0 7328 (523)* +1665 0.1 5258 (451)* +91 1.0 8139 (571)* +1956 0.1 5613 (384)* +104 1.0 8515 (564)* +2097 0.1 4829 (479)* +75 1.0 7033 (451)* +1558 0.1 5011 (345)* +82 1.0 7492 (466)* +172______________________________________ *= p < 0.01 In vitro synthesis of RNA by human lymphocytes activated with anti-T3 monoclonal antibody

Human T lymphocytes activated in vitro with an activator more specific than PHA, i.e. the anti-T3 monoclonal antibody (1.56 ng/ml), were incubated with 1 mcg/ml of the tripeptides and the RNA synthesis was evaluated by means of the 3H-uridine incorporation.

As shown in the table, also in this case the peptides are capable of enhancing the RNA synthesis of the already activated cells.

______________________________________ 3H-URIDINE INCORPORATION (cpm)PEPTIDE MEAN (+/- SE) .DELTA. %______________________________________-- 1263 (125) --1 3626 (419)* +1872 2937 (263)* +1333 4127 (343)* +2274 3814 (338)* +2025 3822 (404)* +2036 3617 (414)* +1867 4382 (189)* +2478 3470 (316)* +175______________________________________ *= p < 0.01

In vitro DNA synthesis in human T lymphocytes stimulated by PHA

Human T lymphocytes incubated in vitro for 72 hrs in the presence of 0.5% PHA and different peptide concentrations were analyzed for the DNA synthesis (proliferation) by means of 3H-thymidine labelling. The results show that the peptides are able to stimulate the DNA synthesis.

______________________________________ 3H-THYMIDINECONCENTRATION INCORPORATION (cpm)PEPTIDE (mcg/ml) MEAN (+/- SE) .DELTA. %______________________________________-- 0.0 10338 (2987) --1 0.1 19476 (6505) +88 1.0 22915 (8326) +1222 0.1 18165 (4844) +76 1.0 23990 (7012) +1323 0.1 18653 (7555) +80 1.0 21547 (6897) +1084 0.1 17513 (5418) +69 1.0 23280 (7676) +1255 0.1 18054 (6587) +75 1.0 22366 (7074) +1166 0.1 16982 (4877) +64 1.0 21242 (8656) +1057 0.1 19549 (6542) +89 1.0 23125 (7395) +1248 0.1 18893 (7688) +83 1.0 22871 (7134) +121______________________________________

In vitro stimulation of ConA-induced proliferation

Peripheral blood mononuclear cells (PBMC), obtained from healthy volunteers, were incubated with ConA in order to evaluate the proliferation as labeled thymidine uptake. The peptides n. 1, 2, 4 and 8 were used at the concentration of 0.1 mcg/ml.

The Table shows that the peptides under examination were capable of stimulating the ConA-induced proliferation.

______________________________________ 3H-THYMIDlNE INCORPORATION (cpm)PEPTIDE MEAN (+/- SE) .DELTA. %______________________________________-- 67156 (6223) --1 87318 (13455) +302 88428 (12127) +324 86525 (18646) +298 89203 (14588) +33______________________________________

Stimulation of the in vitro IL-2 and IL-6 production by PHA activated cells

Human T lymphocytes have been incubated with PHA in the presence or in the absence of 1 mcg/ml of the peptides, for 24 hrs in the case of IL-2 and 72 h for IL-6. The supernatants were collected, filtered (0.2 .mu.m) and assayed for the activity of IL-2 or IL-6 by addition at different concentrations to fresh T lymphocytes or to B cells coming from long term cultures. The proliferative activity of said cells, depending on the presence of the corresponding growth factor, has been evaluated by 3H-thymidine incorporation.

The Tables show that the peptides 1-8 are capable of stimulating IL-2 and IL-6 production.

__________________________________________________________________________IL-2 PRODUCTION (cpm)SUPERNATANT PERCENTAGE:3.1 6.2 12.5 25PEPT. X +/- SE .DELTA. % X +/- SE .DELTA. % X +/- SE .DELTA. % X +/- SE .DELTA. %__________________________________________________________________________-- 2572 -- 4741 -- 12725 -- 18554 -- 603 710 663 37831 4346 +69 16118 +240 26307 +107 32108 +73 67 3922 2190 16112 3991 +55 16727 +253 22281 +75 29783 +61 731 1985 4361 24283 4452 +73 15949 +236 25405 +100 31064 +67 206 4421 3377 39656 4224 +64 15602 +229 24867 +95 30185 +63 248 2917 2908 36318 4568 +78 15450 +226 23881 +88 30699 +65 553 3547 1658 1252__________________________________________________________________________ __________________________________________________________________________IL-6 PRODUCTION (cpm)SUPERNATANT PERCENTAGE:3.1 6.2 12.5 25PEPT. X +/- SE .DELTA. % X +/- SE .DELTA. % X +/- SE .DELTA. % X +/- SE .DELTA. %__________________________________________________________________________-- 2976 -- 5765 -- 10187 -- 18846 -- 645 1875 3168 26641 5113 +72 14078 +144 19977 +96 24966 +32 1135 6143 5419 39552 4473 +50 13024 +126 21915 +115 26271 +39 1737 4503 7150 24283 4983 +67 15674 +172 20820 +104 26378 +40 939 5395 5188 31046 4966 +67 13183 +129 21730 +113 25311 +34 1399 5868 4967 41238 4343 +46 13341 +131 20137 +98 24673 +31 490 4934 6413 4757__________________________________________________________________________

In vitro IL-2 production by ConA-activated human cells

PBMC obtained from healthy volunteers were incubated overnight with the peptides 1-8 and analyzed for IL-2 production by means of an ELISA test, by reading the plates after 30 or 60 min. The cells were activated with 10 mcg/ml of ConA; the peptides were used at the concentration of 1 mcg/ml.

The results show that these peptides are capable of increasing IL-2 production.

______________________________________ IL-2 PRODUCTION AFTER: 30 min 60 minPEPTIDE U/ml .DELTA. % U/ml .DELTA. %______________________________________-- 1.5 -- 1.5 --1 2.4 +60 1.7 +132 2.5 +67 1.8 +203 2.2 +47 1.8 +204 2.3 +53 1.7 +135 2.0 +33 1.9 +276 2.4 +60 1.8 +207 2.3 +53 1.8 +208 2.2 +47 1.9 +27______________________________________

Ex-vivo stimulation of mitogen-induced proliferation

The stimulation of mitogen-induced proliferation has been investigated by oral or i.p. administration of the peptides to nude athymic mice (body weight 28 g) at the daily dosage of 10 mcg/mouse for 5 days or 6 weeks.

The animals were sacrificed 24 h after the last treatment and the proliferation was determined as labeled thymidine uptake by the spleen cells.

As it can be seen from the following Tables, the in vivo administration of the peptides stimulates the ex-vivo determined mitogen-induced proliferation.

__________________________________________________________________________ CONTROLS PEPT.1 PEPT.2 PEPT.4 PEPT.8MITOGEN X +/- SE X +/- SE .DELTA. % X +/- SE .DELTA. % X +/- SE .DELTA. % X +/- SE .DELTA.__________________________________________________________________________ %MITOGEN-INDUCED PROLIFERATION IN NUDE MICE TREATED ORALLY FOR 5 DAYSWITH 10 mcg/mouse OF THE PEPTIDES (cpm)PHA0.000 398 891 +124 693 +74 706 +77 973 +144 54 148 86 212 690.125 372 714 +92 713 +92 802 +116 1114 +199 47 144 33 117 4350.500 524 1645 +214 1493 +185 1526 +191 1921 +267 94 64 231 99 2142.000 3086 3708 +20 4015 +30 3537 +15 5144 +67 1476 68 201 80 1462PWM%0.000 583 908 +56 874 +50 891 +53 987 +69 166 68 155 42 300.125 407 2296 +464 1878 +361 2051 +404 2531 +522 69 101 412 265 4130.500 573 4673 +716 4423 +672 5690 +893 6301 +1000 14 821 553 771 10922.000 1133 5014 +343 5541 +389 4838 +327 5979 +428 487 2655 989 1556 1303ConAmcg/ml0.000 371 914 +146 1061 + 186 898 +142 1048 +182 40 27 236 185 4050.312 417 4523 +985 5146 +1134 4805 +1052 5503 +1220 98 564 164 1162 9550.625 478 10978 +2197 11652 +2338 12356 +2485 13372 +2697 74 742 2197 1375 38491.250 748 27895 +3629 29781 +3881 28171 +3666 31523 +4115 169 2385 3518 2554 5395MITOGEN-INDUCED PROLIFERATION IN NUDE MICE TREATED ORALLY FOR 6 WEEKSWITH 10 mcg/mouse OF THE PEPTIDES (cpm)PWM%0.000 1256 4005 +219 3886 +209 4294 +242 4679 +273 190 1142 1169 2202 3450.125 808 2397 +197 2265 +180 2236 +177 2627 +225 72 318 184 370 4671.000 1223 2632 +115 2923 +139 2525 +106 3495 +186 638 105 427 172 645MITOGEN-INDUCED PROLIFERATION IN NUDE MICE TREATED I.P. FOR 6 WEEKSWITH 10 mcg/mouse OF THE PEPTIDES (cpm)PWM%0.000 2088 2904 +39 2785 +33 2876 +38 3495 +67 200 113 308 198 3730.125 2351 3338 +42 3621 +54 3496 +49 3827 +63 385 1675 1198 1401 10700.250 3018 4189 +39 4005 +33 4338 +44 4471 +48 127 288 291 527 2740.500 2245 3648 +62 3894 + 73 3721 +66 4361 +94 714 406 249 345 2741.000 3339 3263 -2 3461 +4 3365 +1 3887 +16 425 988 1227 964 7782.000 2621 2627 0 2789 +6 2698 +3 2978 +14 464 534 531 564 293ConAmcg/ml0.00 2165 2686 +24 2747 +27 2322 +7 2617 +21 394 547 406 688 4150.25 2177 6671 +206 7009 +222 6768 +211 7165 +229 208 328 643 219 8860.50 2284 10428 +357 10656 +366 11549 +406 13564 +493 186 741 1565 653 14801.00 3187 16870 +429 17337 +444 16912 +431 19558 +514 304 1938 949 1399 9062.00 2707 9829 +263 10957 +305 11654 +331 13472 +398 733 1104 603 1047 11624.00 1827 2722 +49 2974 +63 2661 +46 3386 +85 276 800 898 904 1212__________________________________________________________________________

ACUTE TOXICITY

The tripeptides 1-8 of the invention have a LD50 higher than 1000 mg/kg i.p. in the mouse.

Claims

1. The tripeptide Glu-Lys-Arg or a pharmaceutically acceptable salt thereof wherein the aminoacids glutamic acid, lysine and arginine are of the D-, L- or DL series.

2. The tripeptide, according to claim 1 wherein said salt is the acetate, trifluoroacetate, sulfate, or hydrochloride salt.

3. A pharmaceutical composition having immunostimulating activity comprising as the active principle an effective amount of the tripeptide Glu-Lys-Arg or a pharmaceutically acceptable salt thereof in a mixture with an acceptable carrier.