Anti-thrombins

Abstract: A polypeptide derived from leeches of the species Hirudinaria manillensis has the following amino-acid sequence: X-Y-tyr-thr-asp-cys-thr-glu-ser-gly-gln-asn-tyr-cys-leu-cys-val-­ gly-ser-asn-val-cys-gly-glu-gly-asp-asn-cys-asn-D- gln-leu-ser-­ ser-ser-gly-asn-gln-cys-val-E-gly-glu-gly-thr- pro-F-pro-gln-­ ser-gln-thr-glu-gly-asp-phe-glu-glu-ile-pro-asp-glu-Z-ile-lys; wherein X indicates any amino acid reisude; Y indicates any amino acid residue; Z indicates any amino acid residue; D indicates cys or pro; and E indicates glu or asp or his; F indicates asp, lys or trp; or a pharmaceutically acceptable salt, derivative or bioprecursor thereof. The polypeptide, and fragments thereof, is a specific anti-thrombin useful as a medicament.

Description: The present invention is concerned with novel anti-thrombins and, in particular, novel anti-thrombins derived from leech tissue and leech secretions. Hirudin is a well known and well characterised polypeptide, which is known to be specific for thrombin, and which is obtained as an extract from leeches of the species Hirudo medicinalis . The polypeptide has a relatively low molecular weight (ca.7000) and is comprised of 65 amino acids. The sequence of first isoform of hirudin has been determined by Dodt, Muller, Seemuller and Chang ("The complete amino acid sequence of hirudin a thrombin-specific inhibitor"; FEBS 165 (1984): pp180-184) to be as follows: Two variants of hirudin have also been characterised and the amino acid sequence determined. A first variant is described by Dodt, Machleidt, Seemuller, Maschler and Fritz ("Isolation and characterisation of hirudin isoinhibitors and sequence analysis of hirudin PA"), Biol. Chem. Hoppe-Seyler, 367 (1986) pp803-811. This variant differs from the one described previously, in the following respects: 1. -Ile- at position 1 instead of -Val- 2. -Thr- at position 2 instead of -Val- 3. -Lys- at position 24 instead of -Gln- 4. -Asn- at position 33 instead of -Asp- 5. -Lys- at position 35 instead of -Glu- 6. -Gly- at position 36 instead of -Lys- 7. -Asn- at position 47 instead of -Lys- 8. -Glu- at position 49 instead of -Gln- 9. -Asn- at position 53 instead of -Asp- A second variant is described by Harvey, Degryse, Stefani, Schamber et al ("Cloning and expression of a cDNA coding for the anti-coagulant hirudin from the bloodsucking leech, Hirudo medicinalis "), Proc. Nat. Acad. Sci. U.S.A. (1986) pp1084-1088. This is identical to the first-mentioned variant from positions 1 to 32 and then has the following differences from the first-mentioned hirudin: 1. -Gln- at position 33 instead of -Asp- 2. -Lys- at position 35 instead of -Glu- 3. -Asp- at position 36 instead of -Lys- 4. -Gln- at position 53 instead of -Asp- 5. -Pro- at position 58 instead of -Glu- 6. -Asp- at position 62 instead of -Glu- 7. -Asp- at position 64 instead of -Leu- 8. -Glu- at position 65 instead of -Gln- As indicated above, hirudin has been derived from leeches of the species Hirudo medicinalis . Hirudinaria manillensis is similar to Hirudo medicinalis in that they are both able to feed on amphibian and mammalian blood. However, Hirudinaria is evolutionarily more advanced than Hirudo medicinalis . It cannot be predicted with any certainty whether or not an active substance present in the secretions of a first species of leech is likely to be found in a different species, and (if substances of similar activities are found) whether they are likely to have substantially identical amino acid sequences, or markedly different amino acid sequences. We have now isolated a novel anti-thrombin from Hirudinaria manillensis , the anti-thrombin having the following amino acid sequence: (wherein each of X, Y and Z indicates any amino acid residue, D represents Cys or Pro, E represents Glu or Asp or His, F represents Asp, Trp or Lys, and * denotes positions in the anti-thrombin molecule which differ from those in the above-mentioned first variant of hirudin). Comparison with the hirudin sequence indicates approximately 62% homology (that is, about 38% differences), which is a surprisingly substantial difference. There are, in particular, significant differences at the important C-terminus, and the following clear differences: at position 13 (-Tyr- instead of -Leu-); at position 17 (-Val- instead of -Glu-); at position 24 (-Glu- instead of -Gln-); at position 26 (-Asp- instead of -Asn-); at position 27 (-Asn- instead of -Lys-); at position 29 (-Asn- instead of -Ile-); at position 30 (-Pro- or -Cys- instead of -Leu-); at position 31 (-Gln- instead of -Gly-); at position 32 (-Leu- instead of -Ser-); at position 33 (-Ser- instead of -Asp-); at position 35 (-Ser- instead of -Gly-); at position 36 (-Gly- instead of -Lys-); at position 41 (-Glu- or -Asp- or -His- instead of -Thr-); at position 47 (-Asp-, -Lys- or -Trp- instead of -Pro-); at position 51 (-Gln- instead of -His-); at position 52 (-Thr- instead of -Asn-); at position 53 (-Glu- instead of -Asp-); at position 61 (-Asp- instead of -Glu-); at position 64 (-Ile- instead of -Leu-); at position 65 (-Lys- instead of -Gln-). The differences in positions 61 (aspartate instead of glutamate), 64 (iso-leucine instead of leucine), and 65 (Lysine instead of glutamine) are believed to be especially important because the sequence 55-64 is thought to be a critical domain for the inhibitory action of hirudin (see in this connection Owen et al, "N-terminal replacement of small peptide anti-coagulants based on hirudin", 1988, J.Med Chem. 31: pp.1009-1011). The presence of aspartate (-Asp-), iso-leucine (-Ile-) and lysine (-Lys-) in the anti-thrombin according to the invention results in a novel thrombin-inhibiting domain; the sequence 54-65 alone is believed to be novel per se and to have novel anti-thrombin properties. The invention therefore further comprises a polypeptide which specifically inhibits thrombin and which comprises the amino acid sequence: Gly-Asp-Phe-Glu-Glu-Ile-Pro-Asp-Glu-Z-Ile-Lys, wherein Z represents any amino acid residue, or a pharmaceutically acceptable salt, derivative, or bioprecursor thereof. The amino acid at position 63 (represented by Z in the above formula) may be tyrosine (Tyr), which is typically sulfated. (In contrast, recombinant hirudin is generally not sulfated at this position.) The leech-derived anti-thrombin according to the invention (and corresponding DNA sequences which can be extrapolated therefrom) is non-homologous with eglin, a known elastase/chymotrypsin inhibitor which is known to be present in the medicinal leech Hirudo medicinalis , and is described by Seemuller et al in "Eglin: elastase-cathepsin G inhibitor from leeches"; 1981 Meth. Enzymol. 80: pp.804-816. The anti-thrombin according to the invention is typically isolated either from the tissue of the species Hirudinaria manillensis by techniques involving solvent extraction and subsequent fractionation by chromatographic techniques or the like; alternatively, it may be isolated in a similar manner from secretions (such as saliva) of Hirudinaria manillensis . According to a further aspect of the invention, therefore, a polypeptide according to the invention is preferably derived from the tissue or secretions of leeches of the species Hirudinaria manillensis . The polyeptide is an anti-thrombin which is specific in its activity to thrombin. The present invention further comprises a recombinant or protein-engineered equivalent to the polypeptide according to the invention. The anti-thrombin according to the invention may be used in a pharmaceutical formulation, together with a pharmaceutically acceptable carrier or excipient therefor. Such a formulation is typically for intravenous administration (in which case the carrier is generally sterile saline or water of acceptable purity). The anti-thrombin according to the invention is suitable for treatment of thromboembolic events, such as the coagulation of blood. In one embodiment of the invention, the anti-thrombin is coadministered with a plasminogen activator, such as tissue plasminogen activator; the anti-thrombin according to the invention has been found to be compatible with the latter. Exemplary processes for isolation of anti-thrombin according to the invention from leech tissue will now be described in the following detailed Examples. Example 1 Step - Acetone Extraction 600 grams of Hirudinaria manillensis leeches were dehydrated in approximately 2 litres of 96% ethanol for 24 hours. The anterior region of the animal was dissected away from the remainder of the body and was further dehydrated in approximately 200 ml 96% ethanol for a further 24 hours. Dehydrated leech heads were finely chopped into small pieces and a mixture of 40 ml acetone and 60 ml water was added. The mixture was stirred for 30 min at room temperature, spun for 15 minutes at 2,700 rpm and the supernatant decanted. The pellet was resuspended in a further 100 ml of 40:60 acetone: water mixture, followed by stirring at room temperature for 30 minutes. The mixture was spun at 2,700 rpm for 15 minutes and the supernatant decanted and pooled with the initial supernatant. 80 ml acetone and 20 ml water were added to the pooled supernatant and the pH lowered with glacial acetic acid to 4.4. The mixture was spun at 2,700 rpm for 15 minutes and the supernatant decanted. The pH of this solution was adjusted to 6.0 using 30% ammonia. The volume was reduced to approximately 30 ml by rotary evaporation at 35°C. Trichloroacetic acid crystals were added to lower the pH of the solution to 1.8, followed by centrifuging to remove precipitates. The raw anti-thrombin was precipitated from the solution using a 9-fold excess volume of acetone. The mixture was spun at 2,700 rpm for 15 min and the supernatant discarded. The pellet was resuspended in 50 ml acetone and spun at 2,700 rpm for 10 min; the washings were discarded and the precipitate dried in a vacuum desiccator for one hour. Raw anti-thrombin was reconstituted in 4.0 ml of water. Protein was estimated by absorbance at 280 nm to be 78 mg/ml. The activity was estimated by the prevention of thrombin/fibrinogen clot to be 2400 anti-thrombin units/ml (or about 10,000 anti-thrombin units per 200 grams of chopped heads). The total activity was 9600 anti-thrombin units; and the specific activity was calculated as 30.7 anti-thrombin units/mg protein. Step 2 - Ethanol Extraction The raw anti-thrombin solution was cooled to 3°C. Six 1.2ml aliquots of ice cold 96% ethanol were added at 5 minute intervals. The mixture was then left at 3°C for a further 10 minutes and was then centrifuged at 2,400 rpm for 10 minutes; the supernatant was decanted and retained. The pellet was resuspended in 4 ml ice cold distilled water, mixed with 7.2 ml ice cold 96% ethanol. This was allowed to stand at 3°C for 30 minutes and then centrifuged at 2,400 rpm for 10 minutes. The supernatant was decanted off and pooled with the initial supernatant. The pellet was resuspended in a mixture of 4 ml ice cold 96% ethanol and left to stand for 30 minutes at 3°C. This was then spun at 2,400 rpm for 10 minutes and the supernatant decanted and pooled. The pool was cooled to 0°C on ice and then 50.7 ml ethanol containing 0.5% ammonium acetate at -10°C was added. This was left for 30 minutes and then spun for 10 minutes at 2400 rpm. The supernatant was discarded and the precipitate washed with 50 ml ice cold ethanol. The precipitate was then dried in a vacuum desiccator for one hour. This was then reconstituted in water tested for anti-thrombin activity, protein content and then vialed and freeze dried; the resulting volume was 1.5 ml. The protein was estimated at 19 mg/ml using absorbance at 280 nm. Activity was estimated as 1000 anti-thrombin units (ATU)/ml using the thrombin/fibrinogen clotting assay. The specific activity was calculated at 52.6 ATU/mg protein. Example 2 Step 1 as in Example 1 was repeated, followed by Steps 2 and 3 as follows. Step 2 - Cation Exchange Chromatography Raw anti-thrombin was reconstituted in 10mM Ammonium Acetate - Acetic Acid pH 4.0 and filtered to remove insolubles. A carboxymethyl cellulose gel, commercially available under the trade mark CM Sephadex C50, was preswollen in buffer (10mM Ammonium Acetate - Acetic Acid; pH 4.0) and packed into a 30cm long column of 2.6cm diameter. The sample was loaded onto the column. 100ml buffer was run through the column and collected as waste. The buffer was then altered to 10mM Ammonium Acetate pH 4.2. 10ml fractions were then collected and tested for anti-thrombin activity and protein content. The specific activity for each fraction was calculated and fractions over a threshold value of specific activity were pooled, frozen and freeze dried. Step 3 - Anion Exchange Chromatography Lyophilised crude extract, produced either with ethanol extraction or CM Sephadex extraction, was reconstituted with 10mM Tris/HCl buffer, pH 7.5 and chromatographed on a DEAE-Sephadex A-25 column (0.9 x 7cm), pre-equilibrated with the same buffer. The column was developed at a flow rate of 15 ml/hr until the absorbance of the effluent at 234nm was below 0.15. The bound material was then eluted with a linear gradient of 0-1 M NaCl in the equilibration buffer (60ml in each reservoir). The effluent was collected in 2ml fractions for measurement of absorbance and inhibitory activity. The elution profiles obtained are shown for ethanol extracted material (Fig 1) and CM Sephadex extracted material (Fig 2). The fractions containing with anti-thrombin activity were pooled, concentrated and desalted on Sephadex G-25 before further purification. The partially purified sample was further fractionated by affinity chromatography on thrombin Sepharose. The column was washed with the equilibration buffer (0.1 M Tris/HCl, pH 8.0) and the bound anti-thrombin eluted with 1M benzamidine. The eluted material was lyophilised and desalted as before. The material was then purified by high performance liquid chromatography. 50 microlitres of concentrated sample was applied to a microbore RP-300 C-8 column (3 x 0.21cm) pre-equilibrated with 0.1% TFA at room temperature. The bound material was eluted with a 0-100% linear gradient of 60% acetonitrile, containing 0.09% TFA, in 35 min at a flow rate of 0.25 ml/min. The absorbance of the effluent was monitored at 215nm. Each peak, or partially resolved peak, was collected as a separate fraction for measurement of its inhibitory activity. The elution profile obtained is shown in Fig 3 and shows that the peaks containing anti-thrombin activity (peaks 5,6,7) are separated from other peaks. Sequencing Major peaks containing anti-thrombin activity (equivalent to peaks 5,6 & 7 in Fig 3) were dried under vacuum and analyzed for N-terminal amino acid sequence on an automated Applied Biosystems gas phase sequencer (Model 470A) linked to an on-line analyser (Model 120) for identification of PTH amino acids. Purified anti-thrombin sample was loaded directly onto the filter for sequencing. Cysteine residues in the sequence were determined after derivatisation to pyridylethyl cysteine by reaction of the purified saple with dithiothreitol and 4-vinylpyridine. Tryptic digests of the reduced and pyridylethylated anti-thrombin were obtained with TPCK-trypsin. The reaction was carried out in 0.05M ammonium bicarbonate buffer at 37°C for 4hr and the reaction stopped by freeze-drying and resuspension in 0.1% TFA. Fragments were separated by reversed phase HPLC under conditions similar to that described below in Example 3, step 5. C-terminal sequencing was performed by combination of the carboxypeptidase Y digestion and DABS-Cl methods as described by Chang in FEBS letts (1983), 164 pp 307-313. The sequence thus determined was as given above. Example 3 Steps 1 and 2 as in Example 2 were repeated, followed by Steps 3 and 4 as follows: Step 3. Anion Exchange Chromatography The solution from Step 2 was adjusted to pH 7.0 with 0.1M NaOH, and applied to a column containing an anion exchanger commercially available under the trade name Q-Sepharose, equilibrated in 20mM Tris HCl, pH 7.0 buffer. Buffer was pumped through this column until unbound protein (detected by absorbance at 280nm) was removed and then a gradient of salt (NaCl in the same buffer) applied in a linear or stepwise manner to elute the bound anti-thrombin. A typical chromatographic profile is shown in Figure 4. Fractions containing anti-thrombin activity were pooled and concentrated by ultrafiltration to a volume of 25-50 ml. At this stage anti-thrombin preparations had a specific activity of 100-400 anti-thrombin units/mg protein. Step 4. Gel Filtration The solution from Step 3 was applied to a gel filtration column commercially available as Superdex 200 equilibrated and eluted with 50mM Tris HCl, 0.1M NaCl, pH 7.5. A typical chromatographic profile is shown in Figure 5. Fractions containing anti-thrombin activity were collected, pooled and lyophilised. At this stage, anti-thrombin preparations typically had a specific activity in the range of 1000-4000 anti-thrombin units/mg protein. Step 5. Final Purification Material from Step 4 was applied to an affinity column of thrombin-Sepharose equilibrated in 0.1M Tris HCl, pH 8.0 and the unbound material eluted with the same buffer. The bound anti-thrombin was eluted from the column with 1M benzamidine, lyophilised and then desalted using a column of Sephadex G25. Material purified by affinity chromatography was further purified by HPLC (high performance liquid chromatography) using a reverse-phase column (RP-300 C-8). In a typical example (Figure 6), sample is applied to a column equilibrated in 0.1% trifluoroacetic acid (TFA) at room temperature and the bound anti-thrombin eluted with a linear gradient of 60% acetonitrile containing 0.9% TFA. Peaks of protein (detected by absorbance at 215/280nm) are collected and those containing anti-thrombin dried under vacuum. Assay of Anti-thrombin Activity Antithrombin activity was determined by measuring the inhibitor of the clotting activity of thrombin upon fibrinogen essentially as described by Markwardt in Methods in Enzymology; XIX, pp924 ; "Hirudin as an inhibitor of Thrombin" (1970), or by measuring the inhibition of thrombin cleavage of specific para-nitrophenol derived chromogenic substrates such as S-238 (commercially available from Kabi). The activity of the anti-thrombin according to the invention was not neutralised by a high concentration of neutralising monoclonal antibodies specific for hirudin (this is further immunological confirmation that the anti-thrombin according to the invention and hirudin are dissimilar). The anti-thrombin according to the invention and hirudin do however, have similar partial thromboplastic times for equivalent doses. This suggests that they have similar anticoagulant properties towards human blood.

Claims: A polypeptide which specifically inhibits thrombin and which comprises the amino acid sequence: Gly-Asp-Phe-Glu-Glu-Ile-Pro-Asp-Glu-Z-Ile-Lys, wherein Z represents any amino acid residue, or a pharmaceutically acceptable salt, derivative, or bioprecursor thereof. A polypeptide according to claim 1, having the following amino acid sequence: wherein X indicates any amino acid residue; Y indicates any amino acid residue; Z indicates any amino acid residue; D indicates Cys or Pro; and E indicates Glu or Asp or His; F indicates Asp, Lys or Trp; or a pharmaceutically acceptable salt, derivative or bioprecursor thereof. A polypeptide according to claim 2, wherein X represents Val. A polypeptide according to claim 2 or 3, wherein Y represents Ser. A polypeptide according to any of claims 1 to 4, wherein Z represents Tyr or a sulfated derivative thereof. A polypeptide according to claim 1 or 2, which is derived from the tissue or secretions of leeches of the species Hirudinaria manillensis . A pharmaceutical formulation which comprises an aqueous solution of a polypeptide according to any of claims 1 to 5. Use of a polypeptide according to any of claims 1 to 6 for preparing a medicament for treatment of thromboembolic processes. Use of a polypeptide according to any of claims 1 to 6 for preparing a medicament or administration to a patient together with a plasminogen activator.

Inventors: ATKINSON ANTHONY, ELECTRICWALA ASGAR, POWELL-JONES CHRISTOPHER, SAWYER ROY, ATKINSON, ANTHONY, ELECTRICWALA, ASGAR, POWELL-JONES, CHRISTOPHER, SAWYER, ROY
Applicants: BIOPHARM LTD, BIOPHARM (UK) LIMITED
Application year: 1989
Main classification: C07K7
IPC codes: A61K38, C07K14, A61K35, C07K7, A61P7