Modified hIL-6

Abstract: Provided are PEGylated "interleukin-6" derivatives (PEG-IL-6) having an extended plasma half-life, as well as enhanced in vivo IL-6 biological activities. Methods for producing the modified glycosylated and unglycosylated IL-6 proteins or polypeptides, as well as, for their use in treating hematopoietic disorders and difficiencies, particularly acute thrombocytopenia, are also provided.

Description: FIELD OF THE INVENTION The present invention relates to modified glycosylated and unglycosylated proteins and polypeptides possessing interleukin-6 (hereafter referred to as IL-6) activities where the modification comprises chemical modification of at least one amino group or carboxyl group on the proteins and polypeptides. The invention also relates to a process for producing the modified proteins or polypeptides, and to their use in treating haematopoietic disorders and deficiencies, particularly acute thrombocytopenia. BACKGROUND OF THE INVENTION Interleukin-6 is a multifunctional cytokine (Kishimoto, T. and T. Hirano, Ann. Rev. Immunol ., 6:485 (1988)). Included among its diverse biological activities are the induction of the terminal differentiation of B cells to plasma cells, the differentiation of killer T cells and nerve cells, as well as the acute phase protein synthesis of hepatocytes. It also stimulates the growth of hybridoma/plasmacytoma/myeloma cells, T cells, and hematopoietic stem cells. Differentiation inducing activity on megakaryocytes, leading to the production of platelets, has also been reported recently (Ishibashi, T., et al., Blood 74:1241, (1989)). One example of glycosylated proteins or polypeptides possessing interleukin-6 activities is human interleukin-6 (hereafter referred to as hlL-6). There are a number of reports on processes for producing hlL-6; for example, production by human T cell hybridoma cells (Okada, M., et al., J. Exp. Med ., 157:583 (1983)) or by human T cells transformed with human T cell leukemia virus (Japanese patent application, KOKAI NO. 61-115024). Human IL-6 may also be produced by recombinant DNA technologies which comprise transforming mammalian or bacterial cells with a vector carrying a DNA sequence encoding hlL-6 and then culturing these cells to obtain recombinant hlL-6. The resultant hlL-6 is a glycosylated protein if produced by mammalian cells, and an unglycosylated polypeptide if produced by bacterial cells. Both forms have been demonstrated to have interleukin-6 activities (EP 257406; WO 88/00206). The mature fully functional hlL-6 polypeptide has 184 amino acid residues as predicted from the nucleotide sequence of its cDNA. However, polypeptides with one or more additional amino acid residues or (at most) 27 amino acid deletions at their N-terminus, as well as polypeptides with at most 50 amino acid deletions (or substitutions) at their C-terminus, are known to retain IL-6 activity (EP 257406; WO 88/00206; EP 363083; Brakenhoff, J.P.J., J. Immunol ., 143:1175 (1989)). Several methods have been used to try to prolong the plasma half-life of certain intravenously administered high molecular weight polypeptides. These include modification of the polypeptide with polyethylene glycol (PEG), dextran, poly[Glu-Lys], pullulan, modified polyaspartate, or fatty acids, as well as coupling with γ-globulin. The chemical modification with PEG (hereinafter referred to as PEGylation) of a few non-human derived enzymes, such as asparaginase, superoxide dismutase, or uricase, resulted in increased plasma half-life. However, a number of problems have been observed with PEGylation. Acylation of tyrosine residues on the protein can result in a lowering of the biological activity of the protein; certain PEG-protein conjugates are insufficiently stable and therefore find no pharmacological use; certain reagents used for PEGylation are insufficiently reactive and therefore require long reaction times during which protein denaturation and/or inactivation can occur. Also, the PEGylating agent may be insufficiently selective. Difficulties can also arise as a result of the hydrophobicity of the protein to be PEGylated; in an aqueous medium hydrophobic proteins resist PEGylation at physiological pH. The criteria for effective PEGylation include not only whether the conjugated molecule has a combination of increased serum half-life and decreased immunogenicity, but also whether it is in fact a more potent pharmacological agent than its unmodified parent molecule. Given the broad range of differences in the physical characteristics and pharmacokinetics among proteins, it is impossible to predict in advance whether a protein can be successfully PEGylated and/or whether the PEGylated protein will still retain its biological activity without inducing untoward immunological responses. For example, in WO87/00056, relating to the solubilization of proteins for pharmaceutical compositions using polymer conjugation, the adverse effect of PEGylation on the in vitro activity of IL-2 is described in Example IIB (Table I, page 20). Example IC (page 19) references the IL-2 cell proliferation bioassay used. The results demonstrate that as more amino groups of the IL-2 are substituted with PEG, the PEGylated IL-2 undergoes a nearly 10-fold decrease in activity as compared to the activity of unmodified IL-2. The covalent modification of lysine residues causes a reduction in bioactivity of certain proteins. Lysine modification with activated PEG-esters is random, difficult to control, and often results in reduced bioactivity of the modified protein (Goodson, R., et al., Bio/Technology , 8:343 (April 1990)). U.S. Patent No. 4,904,584 (February 27, 1990) (WO-A-89 05 824) describes a process for preparing PEGylated polypeptides. However, the process requires a pre-modification of the polypeptides by first preparing LDVs (lysine depleted variants) to obtain a polypeptide having a "suitable" number of reactive lysine residues. No evidence is presented that PEGylated derivatives were actually obtained; nor is their any evidence that these proposed modified polypeptides retained any biological activity. Further, there is no exemplification of the production of PEG-IL-6 nor any exemplification of retained activity. As the in vivo half-life of IL-6 in blood is very short (Castell, J.V. et al., Eur, J. Biochem., 177:357 (1988)), it is desirable to increase hIL-6 plasma half-life and to thereby improve the pharmacokinetics and therapeutic efficacy of IL-6. To date, however, no one has been successful in so doing. SUMMARY OF THE INVENTION The present invention provides PEG-IL-6 which has a higher platelet producing activity compared to unmodified IL-6, said PEG-IL-6 being characterised by; (a) an IL-6 polypeptide comprising the amino acid sequence of SEQ ID NO: 1, SEQ ID NO: 2 or SEQ ID NO: 3, or an amino acid sequence having a deletion of up to 27 amino acid residues at the N-terminus thereof, or an amino acid sequence having a deletion of up to 50 amino acid residues at the C-terminus thereof; and (b) PEG linked to the IL-6 polypeptide to provide PEGylation of the structure: or where R 1 is an alkyl group with 1 to 3 carbon atoms, n is an integer between 7 and 600, and X is an amino group (-NH-) of the IL-6 polypeptide. The present invention also provides PEG-IL-6 which has a higher platelet producing activity compared to unmodified IL-L, said preparation being obtainable by: treating IL-6 having the amino acid sequence of SEQ ID NO: 3 with cathepsin C to cleave off the N-terminal residues Met-Lys; reacting the resulting IL-6 with activated PEG1 (methoxypolyethylene glycol with an average molecular weight of 4,500 Da coupled to N-hydroxysuccinimide) under conditions to obtain active PEG-IL-6 fractions giving a major band with a molecular weight of 91 ("Fr45-1"), 68 ("Fr45-2"), 41 ("Fr45-3") or 26 ("Fr45-4") kDa upon SDS-PAGE analysis wherein the average number of free amino groups per molecule is 6.1, 6.8, 9.3 or 12.6 respectively; and recovering said active PEG-IL-6 fractions. The present invention also provides PEG-IL-6 which has a higher platelet producing activity compared to unmodified IL-6, said preparation being obtainable by: treating IL-6 having the amino acid sequence of SEQ ID NO: 3 with cathepsin C to cleave off the N-terminal residues Met-Lys; reacting the resulting IL-6 with activated PEG2 (two polyethylene glycol monoethylether molecules having an average molecular weight of 5,000 Da coupled with cyanuric chloride) under conditions to obtain active PEG-IL-6 fractions wherein the average number of free amino groups per molecule is 5.3 ("Fr100-1"), 7.4 ("Fr100-2"), 8.6 ("Fr100-3"), 9.4 ("Fr100-4") or 10.0 ("Fr100-5"); and recovering said active PEG-IL-6 fractions. The present invention further provides PEG-IL-6 which has a higher platelet producing activity compared to unmodified IL-6, said preparation being obtainable by: treating IL-6 having the amino acid sequence of SEQ ID NO: 3 with cathepsin C to cleave off the N-terminal residues Met-Lys; reacting the resulting IL-6 with activated PEG12M (methoxypolyethylene glycol succinate with an average molecular weight of 12,000 Da coupled to Nhydroxysuccinimide) under conditions to obtain active PEG-IL-6 fractions wherein the average number of free amino groups per molecule is 5.2 ("Fr120-2"), 7.6 ("Fr120-2"), 8.7 ("Fr120-3"), 9.2 ("Fr120-4") or 9.8 ("Fr120-5"); and recovering said active PEG-IL-6 fractions. Preferably the PEG-IL-6 further comprises a Met-Lys dipeptide at the Nterminus of the IL-6. According to the invention, lL-6 is derivatized with polyethylene glycol (PEG) to produce PEG-lL-6 having prolonged plasma half-life and enhanced in vivo lL-6 biological activity. The lL-6 may be either glycosylated lL-6, unglycosylated lL-6, or biologically active fragments of either glycosylated or unglycosylated lL-6. Preferred amino acid sequences for IL-6 are set forth in the Sequence Listing and identified as Sequence Id Nos. 1, 2, and 3. The lL-6 can be either naturally or synthetically produced, either by recombinant methods or other methods known to those skilled in the art including chemical syntheses. Naturally produced lL-6 can be the expression product of a prokaryotic or eukaryotic host cell transformed or transfected with a DNA sequence encoding lL-6 or encoding a biologically active lL-6 fragment. A preferred host cell includes E. coli. The activated PEG used to produce PEG-lL-6 can be any of many activated PEG known to those skilled in the art including activated polyethylene glycol (4500), activated polyethylene glycol (5000), activated polyethylene glycol (12000), and the like. The particular activated PEG chosen can be any of a broad range of molecular weights as known to those skilled in the art and as used herein includes the molecular weight range of 4,500 to 12,000. Particularly preferred activated PEG includes the succinimidyl succinate derivatives of PEG and the bis-PEG derivatives of cvanuric chloride. The PEG can be attached to the lL-6 via one or more amino groups. The number of PEG moieties per lL-6 protein, polypeptide or fragment can vary as can the molecular weight of the PEG moiety. Generally, the higher the degree of PEGylation, i.e., the greater the number of PEG groups per protein molecule, the greater the in vivo biological activity of the lL-6; similarly, the higher the molecular weight of the PEG used to PEGylate, the fewer the number of PEG groups per protein molecule required for in vivo activity. Generally, at least two, and preferably more than five PEG moieties, should be attached per lL-6 Other aspects and advantages of the present invention will be apparent upon consideration of the following detailed description thereof which includes numerous illustrative examples of the practice of the invention. DETAILED DESCRIPTION OF THE INVENTION Described below is the chemical modification with PEG of at least one amino group of polypeptides possessing IL-6 activities. This modification results in an increase in in vivo half-life in blood and an increase of in vivo platelet producing activity as compared to that of unmodified IL-6. Thus, in one aspect of the present invention, modified glycosylated and unglycosylated proteins or polypeptides (preferably polypeptides) possessing improved interleukin-6 activities, particularly platelet producing activity, in primates, and especially in humans, are provided where the modification comprises the attachment of PEG to the polypeptides. The attachment of PEG to the molecules possessing IL-6 activities is done via the amino groups present in the polypeptides. For PEGylation via amino groups, at least one hydrogen atom of an amino group of the protein or protein fragment to be PEGylated is substituted with a group as shown in formula 1 or 2: n: a positive integer between 7 and 600. R 1 : an alkyl group with one to three carbons. n,m: a positive integer between 7 and 600, and may be equal or different. R 1 ,R 2 : an alkyl group with one to three carbons, and may be the same or different. In the present invention, hlL-6 polypeptides having substantially the following amino acid sequence are preferred as either the glycosylated or unglycosylated proteins or polypeptides possessing IL-6 activities: As used herein "substantially" means that the polypeptides may have one or more amino acid modification(s) (deletions, additions, insertions, or substitutions) of the above amino acid sequence as long as the modification(s) does not have any adverse affect on the function and biological activity of the polypeptides. Examples of such modifications are described in published patent applications EP 257406, WO 88/00206 and EP 363083 as well as in Brakenhoff, J.P.J., ( J. Immunol ., 143:1175 (1989)). The polypeptides may be produced by a number of methods including genetic engineering; hlL-6 polypeptides produced by recombinant E. coli are preferred as they can be obtained in good purity and in large quantity. A polypeptide with exactly the above amino acid sequence or the above amino acid sequence with one methionine or a Met-Lys dipeptide added at the N-terminus is especially preferred. These hlL-6 polypeptides may be produced by the procedure disclosed in PCT patent application WO 88/00206 (Genetics Institute Incorporated). They may also be produced by first chemically synthesizing a DNA sequence encoding hlL-6 polypeptides (Haegeman, G., et al., Eur. J. Biochem ., 159:625 (1986)) and then expressing the DNA in E. coli by the method of Souza et al . (WO 87/01132) (U.S. Patent No. 4,810,643). As used herein in the formulae, m and n indicate average values; m and n may be equal or different, are preferably equal and between 7 and 600, more preferably between 7 and 250, and most preferably between 30 and 150. The average molecular weight of the PEG used in the present invention may be between 300 and 30,000; and is preferably between 1,000 and 20,000; and is most preferably 12,000. The protecting groups for the hydroxyl group of the PEG, indicated as R 1 and R 2 , may be alkyl groups, with one to three carbon atoms, such as methyl, ethyl, n -propyl or i -propyl groups, and are preferably methyl groups. As a further aspect of the present invention there are provided processes for producing the PEGylated glycosylated proteins or polypeptides possessing IL-6 activities. The PEGylation of the amino groups on polypeptides possessing IL-6 activities (hereafter referred to as IL-6 polypeptides) may be achieved via succinimide (formula 1 ) or triazine (formula 2), and is preferably via succinimide. In the PEGylation via succinimide, PEG shown in formula 3 is coupled with the compound shown in formula 4 to obtain the compound shown in formula 5, which is then coupled to IL-6 polypeptides. Some of the activated PEGs, represented by the generic formula 5, are commercially available from, for example, Nippon Oil & Fats Co. (Tokyo, Japan). Formula 5 is a generic formula representative of succinimidyl succinate derivatives of PEG. FORMULA 3: PEG HO-(CH 2 CH 2 O) n -R 1 n,R 1 : same as in formula 1. n,R 1 : same as in formula 1. The coupling of activated PEG (formula 5) to IL-6 polypeptides may be achieved by incubating in 0.25 M sodium borate buffer (pH 8.0-8.5) for one to three hours at 4°C. The activated PEG may be added to the reaction mixture serially in small quantities to avoid its degradation. After the reaction, the PEGylated IL-6 polypeptides can be separated from unreacted materials by gel filtration and ionexchange column chromatography. For PEGylation via triazine, PEG shown in formula 3 is coupled with the compound shown in formula 6 to obtain the compound shown in formula 7; the formula 7 activated PEG is then coupled to IL-6 polypeptides. Some of the compounds represented by the generic formula 7 are commercially available from, for example, Seikagaku Kogyo Co. (Tokyo, Japan). n,m,R 1 ,R 2 : same as in formula 2. The coupling of activated PEG (formula 7) and IL-6 polypeptides may be achieved by incubating in 0.25 M sodium borate buffer (pH 10.0) for two to twenty hours at 4°C to room temperature. The activated PEG may be added to the reaction mixture serially in small quantities to avoid its degradation. After the reaction, the PEGylated IL-6 polypeptides can be separated from unreacted materials by gel filtration and ion-exchange column chromatography. The PEGylation of the carboxyl groups on IL-6 polypeptides may be achieved by coupling the polypeptides with the PEG shown in formula 8. FORMULA 8 H 2 NCH 2 CH 2 CH 2 O-(CH 2 CH 2 O) n -CH 2 CH 2 CH 2 NH 2 n: same as in formula 1. As a general rule, the higher the degree of PEGylation, i.e., the greater the number of PEG groups per protein molecule, the better the in vivo activity; and, the higher the molecular weight of the PEG used to PEGylate, the fewer the number of PEG groups per protein molecule required for in vivo activity. Generally, at least two and preferably more than five PEG moieties should be attached per IL-6 protein. As used herein, the following abbreviations and terms include, but are not necessarily limited to, the following definitions. Activated PEG1 is a generic term used to indicate activated polyethylene glycol (4500); Activated PEG2 is a generic term used to indicate activated polyethylene glycol (5000); Activated PEG12M is a generic term used to indicate activated polyethylene glycol (12000); PEG(4500)IL-6 is a generic term used to indicate the product formed upon the reaction of the succinimidyl succinate derivatives of PEG(4500) with IL-6; PEG(10000)IL-6 is a generic term used to indicate the product formed upon the reaction of the bis-PEG (5000) derivatives of cyanuric chloride with IL-6; and PEG(12000)IL-6 is a generic term used to indicate the product formed upon the reaction of the succinimidyl succinate derivatives of PEG(12000) with IL-6. The numbers in parentheses, i.e., 4500, 5000, and 12000 refer to the average molecular weight of polyethylene glycol. As used herein, "haematopoietic disorders and deficiencies" include but are not limited to thrombocytopenia, granulocytopenia, and anemia. The PEGylated IL-6 of the present invention has a much longer plasma half-life and upon administration to mice has a far superior capacity to increase the number of platelets compared to unmodified IL-6 polypeptides or glycosylated IL-6; further, the PEGylated IL-6 of the invention has very low toxicity. Thus, in another aspect of the present invention, therapeutic agents for treating haematopoietic disorders, particularly acute thrombocytopenia, and deficiencies are provided. Such agents comprise a therapeutically effective amount of the PEGylated IL-6 of the present invention in an admixture with a pharmaceutically acceptable carrier. The agents may be administered orally as tablets or capsules, or parenterally by injection. Generally, the daily dosage regimen is in the range of 0.0001 -10 mg/kg weight (as polypeptide), and preferably in the range of 0.004-1 mg/kg. The following examples illustrate practice of the invention. Example 1 relates to the preparation of Fr45-0 from hlL-6 polypeptide and an activated PEG1 (methoxypolyethylene glycol (4500) succinimidyl succinate). Example 2 relates to the SDS-PAGE characterization of Fr45-0. Example 3 relates to the preparation of Fr100-0 from hlL-6 polypeptide and an activated PEG2 (bis-methoxypolyethylene glycol (5000) cyanuric chloride). Example 4 relates to the preparation of four fractions of PEGylated hlL-6 polypeptide: Fr45-1, Fr45-2, Fr45-3, and Fr45-4 from hlL-6 and the activated PEG1 of Example 1. Example 5 relates to the SDS-PAGE characterization of the four fractions of Example 4. Example 6 demonstrates the capacity of the four fractions obtained in Example 4 capacity to induce IgM production in a B cell leukemic cell-line. Example 7 compares the in vivo platelet producing activity of hlL-6, Fr45-0 and Fr100-0 (as prepared in Examples 1 and 3). Example 8 compares the in vivo platelet producing activity of hlL-6 and of the four fractions of Example 4. Example 9 relates to the subcutaneous administration of hlL-6 or PEGylated hIL-6(Fr45-2, produced in Example 4) to acute-thrombocytopenic mice following X-ray irradiation. Example 10 relates to the subcutaneous administration of hlL-6, or PEGylated hlL-6 (Fr45-2, produced in Example 4) to acute-thrombocytopenic mice following treatment with the chemical carcinostatic cyclophosphamide. Example 11 relates to the preparation of five fractions of PEGylated hlL-6 polypeptide, Fr100-1, Fr100-2, Fr100-3, Fr100-4, and Fr100-5, from hlL-6 and the activated PEG2 of Example 3. Example 12 relates to the coupling of hlL-6 polypeptide to an activated PEG12M (methoxypolyethylene glycol (12000) succinimidyl succinate) and the preparation therefrom of five fractions of PEGylated hlL-6 polypeptide: Fr120-1, Fr120-2, Fr120-3, Fr120-4, and Fr120-5. Example 13 provides the results of a study to compare the level of platelet production following the administration of the hlL-6 (produced in Example 4) or its PEGylated derivatives (produced in Examples 11 and 12). Example 14 relates to the subcutaneous administration of PEGylated hlL-6 (produced in Example 12: Fr120-1 to Fr120-5) to acute-thrombocytopenic mice following X-ray irradiation. Example 15 demonstrates the in vivo persistence of PEGylated hlL-6 (Fr45-2, Fr120-1, and Fr120-2 produced in Examples 4 and 12) as compared to unmodified hlL-6. Example 16 describes the preparation of five fractions of PEGylated hlL-6: Fr120'-1 to Fr120'-5 from the hlL-6 polypeptide of Example 4 (however, without the cathepsin C treatment) and the activated PEG12M of Example 12. Example 17 provides the results of an acute toxicity assay of the hlL-6 of Example 4 and its PEGylated derivatives Fr45-2, Fr100-2, and Fr120-2 (produced in Examples 4, 11, and 12). In Examples 7-10 and 13-17, the PEGylated hlL-6 polypeptides of the present invention were dissolved in PBS containing 0.1% normal mouse serum. The concentration of the solutions was adjusted so that the final volume administered was 100 µl. EXAMPLE 1 A DNA sequence encoding the hlL-6 polypeptide with the following amino acid sequence was chemically synthesized and then introduced and expressed in E. coli as described by Souza et al . (WO 87/01132). E. coli cells (300 g), that accumulated hlL-6 polypeptide, were harvested by centrifugation for 10 min at 3500g. The hlL-6 polypeptide was extracted, solubilized and refolded as described in EP 257406. Approximately 2.9 g of the hlL-6 polypeptide, which was a single band on SDS-PAGE and had the predicted molecular weight of 21K, was obtained. An activated PEG1 (a succinimidyl succinate derivative of polyethylene glycol, which is methoxypolyethylene glycol succinate with an average molecular weight of 4,500 and coupled to N-hydroxysuccinimide) was commercially obtained from Nippon Oil & Fats Co. (Tokyo, Japan). The hlL-6 polypeptide (200 µg) was incubated with 1.5 mg of the activated PEG1 in 370 µl of 0.25 M sodium borate buffer (pH 8.5) for two hours at 4°C. The reaction was stopped by lowering the pH by adding 2 N hydrochloric acid. The molar ratio of the activated PEG to the free amino groups on the IL-6 polypeptide was approximately two to one. The reaction mixture was applied to a gel filtration column equilibrated with phosphate buffered saline (PBS) to exchange the buffer and was then subjected to the separation procedure below. The buffer-exchanged solution (3.5 ml) was applied to an HPLC gel-filtration column filled with TSK-gel G3000SW (Toso Co., Tokyo, Japan). The PEGylated hlL-6 polypeptide, having one to three PEG moieties per molecule, was eluted in the first peak to give a yield of approximately 20 µg. The PEGylated hlL-6 polypeptide so obtained was termed Fr45-0. EXAMPLE 2 The Fr45-0 obtained in Example 1 was characterized by SDS-PAGE (Fast System, Pharmacia; 10-15% gradient gel). The polypeptides were stained with silver staining and the molecular weights were estimated by comparison with standard molecular weight markers (Bio-Rad, Richmond, CA, USA). The apparent molecular weights of Fr45-0 were 23K, 37K, and 50K. EXAMPLE 3 An activated PEG2 (an activated polyethylene glycol with an average molecular weight of 10,000; synthesized by coupling two polyethylene glycol (average molecular weight 5,000) monomethylether molecules with cyanuric chloride) was commercially obtained from Seikagaku Kogyo Co., Tokyo, Japan. The hlL-6 polypeptide (200 µg) obtained in Example 1 was incubated with 3.5 mg of the activated PEG2 in 370 µl of 0.25 M sodium borate buffer (pH 10.0) for two hours at room temperature. The reaction was stopped by lowering the pH by adding 2 N hydrochloric acid. The molar ratio of the activated PEG to the free amino groups on the IL-6 polypeptide was approximately two to one. The reaction mixture was applied to a gel filtration column equilibrated with PBS to exchange the buffer and then subjected to the separation procedure described in Example 1. The PEGylated hlL-6 polypeptide with one to two PEG moieties per molecule was eluted in the first peak to give a yield of approximately 20 µg. The PEGylated hlL-6 polypeptide so obtained was termed Fr100-0. The apparent molecular weights of Fr100-0 were determined to be 28K and 42K as described in Example 2. EXAMPLE 4 A DNA sequence encoding the hlL-6 polypeptide with the following amino acid sequence was chemically synthesized and then introduced and expressed in E. coli as described by Souza et al . (WO 87/01132). This amino acid sequence has N-terminal residues of Met-Lys-Ala-Pro- and thus can be conveniently converted to Ala-Pro-, the natural hlL-6 sequence, by cleaving off the Met-Lys using cathepsin C. E. coli cells (300 g), that had accumulated hlL-6 polypeptide, were harvested by centrifugation for 10 min at 3500g, and the hlL-6 polypeptide was extracted, solubilized and refolded as described in EP 257406. After changing the buffer to 20 mM sodium acetate buffer, the polypeptide was treated with 6 U of cathepsin C (Boeringer Mannheim GmBH, Mannheim, Germany) for one hour at room temperature. The reaction mixture was quick-chilled and sodium phosphate buffer (pH 6.0) was added to a final concentration of 2 mM. The mixture was applied to a hydroxyapatite column equilibrated with 2 mM sodium phosphate buffer (1300 mmho, pH 6.0), and the hlL-6 was eluted in a peak fraction of 1200 ml with the same buffer. This fraction was then applied to a CM-Sepharose column equilibrated with 20 mM sodium acetate buffer (pH 6.0). The column was washed with the same buffer, and the hlL-6 was eluted in a peak fraction of 580 ml with a linear gradient of 0-0.3 M NaCl in the same buffer. Approximately 1.5 g of the hlL-6 polypeptide, which was a single band on SDS-PAGE and had the predicted molecular weight of 21 K, was obtained. The N-terminal sequence was confirmed to be Ala-Pro-Val-Pro- by direct sequence analysis. The hlL-6 polypeptide (100 mg) was dissolved in 100 ml of 0.1 M sodium borate buffer (pH 8.5) and 1125 mg of the activated PEG1 of Example 1 was added to the solution in an ice bath with stirring. The activated PEG1 was added either all at one time or in five additions at 30 min intervals, and the latter was found to give a better yield of the coupled product. Accordingly, the subsequent purification steps were carried out on the reaction mixture to which the activated PEG1 was added in five separate, sequential additions. The reaction mixture was concentrated to 10 ml using YM10 ultrafiltration membrane (Amicon, Danvers, MA, USA) and was applied to a Sephadex G100 column equilibrated with 20 mM sodium acetate buffer (pH 6.0). The PEGylated hlL-6 polypeptide was eluted in four fractions (hereafter referred to as Fr45-1, Fr45-2, Fr45-3, Fr45-4) with the same acetate buffer. Upon SDS-PAGE analysis, each fraction gave a main band of 91K, 68K, 41K, and 26K; respectively. The yield of each fraction was 2.9 mg, 4.0 mg, 2.9 mg, and 2.5 mg; respectively. EXAMPLE 5 The four fractions obtained in Example 4 were characterized by determining the number of free amino groups and by SDS-PAGE analysis. The number of free amino groups was determined by the method of Stocks et al. (Anal. Biochem ., 154:232 (1986)). The PEGylated polypeptides were reacted with 7.5% fluorescamine in 0.1 M sodium phosphate (pH 8.0), and the number of free amino groups was determined by measuring the intensity of fluorescence at 475 nm (excited at 390 nm). SDS-PAGE analysis was carried out on a 10-20% gradient gel (Daiichi Pure Chemicals Co., Tokyo, Japan). The polypeptides were stained with CBB and the molecular weights were estimated by comparison with standard molecular weight markers (Pharmacia, Upsala, Sweden). Each band was quantified using an image analysis system (Immunomedica model TIF-64). The results are shown in Table 1 below. Molecular weight distribution (%) 21 K 26K 41K 68K >91K # of free NH 2 Fr45-1 23.0 77.0 6.1 Fr45-2 14.0 52.2 33.8 6.8 Fr45-3 12.0 56.4 28.2 3.4 9.3 Fr45-4 9.9 75.7 14.4 12.6 EXAMPLE 6 The four fractions obtained in Example 4 were tested for their capacity to induce IgM production in a B cell leukemic cell line SKW6-C14 (Hirano, T., et al., Proc. Natl. Acad. Sci. USA , 82:5490 (1985)). The PEGylated hlL-6 polypeptides were dissolved in RPMIL-640 medium containing 10% fetal calf serum. The concentration of the solution was adjusted so that the final volume of the solution added to reaction mixtures (200 µl) was 50 µl. The results are shown in Table 2. The PEGylated hlL-6 retained its activity to induce IgM production in SKW6-C14. IgM Production (ng/ml) PEGylated hlL-6 Dose(pg/ml) unmodified hlL-6 Fr45-1 Fr45-2 Fr45-3 Fr45-4 3750.0 910 250 335 175 200 937.5 890 120 162 118 175 58.5 545 82 78 70 90 7.5 120 72 73 70 75 EXAMPLE 7 The in vivo platelet producing activity of the hlL-6, Fr45-0, and Fr100-0, produced in Examples 1 and 3, was examined in mice. Either hlL-6, Fr45-0, Fr100-0, or the mixture of hlL-6 and PEG(4500) (in vehicle) was administered subcutaneously to three Balb/c mice (8 weeks old, female) at a dose of 10 µg/mouse (on the basis of polypeptide) once a day for five days. Control mice were administered only vehicle comprising PBS containing 0.1% % normal mouse serum. Blood samples were taken on the sixth day and platelets in peripheral blood were counted. The results are shown in Table 3. Fr45-0 and Fr100-0 induced an approximately 230% increase in the number of platelets produced, while unmodified hlL-6, or the mixture of hlL-6 and PEG(4500) induced only an approximately 150% increase. Number of platelets Vehicle 74.5 (100%) PEG(4500)IL-6 173.5 (233%) PEG(10000)IL-6 170.0 (228%) hlL-6 + PEG(4500) 117.9 (158%) hlL-6 113.5 (152%) EXAMPLE 8 The hlL-6 or its PEGylated derivatives (Fr45-1 to Fr45-4), produced in Example 4, were administered subcutaneously to four Balb/c mice (8 weeks old, female) once a day for five days. Control mice were administered only vehicle comprising PBS containing 0.1% % normal mouse serum. Blood samples were taken on the sixth day and platelets in peripheral blood were counted. The results are shown in Table 4. The results also demonstrate a positive dose response relationship. The PEGylated hlL-6 showed significantly higher platelet producing activity compared to the unmodified hlL-6. Number of platelets (% of control) PEGylated hlL-6 unmodified Dose hlL-6 Fr45-1 Fr45-2 Fr45-3 Fr45-4 10 126.6 250.9 214.4* 194.0 173.5 5 130.2 224.6 188.9 188.9 144.2 1 111.1 143.6 151.5 128.8 124.0 0.5 115.8 135.4 125.8 134.4 107.2 0.1 100.4 103.2 102.0 92.8 107.6 EXAMPLE 9 The hlL-6 or its PEGylated derivative (Fr45-2), produced in Example 4, was administered subcutaneously to four acutely thrombocytopenic mice once a day at a dose of 5 µg/mouse for 10 serial days following X-ray irradiation (600 rad). Blood samples were taken daily and platelets in peripheral blood were counted. The results are shown in Figure 1. PEGylated hlL-6 administration resulted in at least five days earlier recovery from the thrombocytopenia than the control vehicle administration, while unmodified hlL-6 administration resulted in one to two days earlier recovery. In another test, five X-ray irradiated mice were administered hlL-6 or the Fr45-2 once a day for 7 serial days at a dose of 5 or 50 µg/mouse as described above. Blood samples were taken on the eighth day when the acute decrease of platelets in vehicle administered mice reached the minimum, as is seen in Figure 1, and platelets in peripheral blood were counted. The results are shown in Table 5. The 5 µg/mouse administration of the Fr45-2 completely prevented the acute drop in the platelet number while even 50 µg/mouse administration of the unmodified hlL-6 did not result in significant recovery from the acute thrombocytopenia. Number of platelets Vehicle 40.8 ( 63%) Fr45-2 (5 µg) 83.0 (127%) hlL-6 (5 µg) 47.0 (72%) hlL-6 (50 µg) 53.1 ( 82%) Normal 65.1 (100%) EXAMPLE 10 The hlL-6 or its PEGylated derivative (Fr45-2), produced in Example 4, was administered subcutaneously to four acute-thrombocytopenic mice, that had been treated with 200 mg/kg of a chemical carcinostatic cyclophosphamide (CY), once a day at a dose of 5 µg/mouse for hlL-6 and 1 µg/mouse for PEGylated hlL-6 for 7 serial days following the CY administration. Blood samples were taken daily and platelets in peripheral blood were counted. The results are shown in Figure 2. PEGylated hlL-6 administration resulted in significantly earlier recovery from the thrombocytopenia than the control vehicle administration, while unmodified hlL-6 administration induced platelet increase but not early recovery. EXAMPLE 11 As described below, the hlL-6 polypeptide produced in Example 4 was coupled to the activated PEG2 of Example 3. The hlL-6 polypeptide (100 mg) was dissolved in 200 ml of 0.1 M sodium borate buffer (pH 10.0) and 2500 mg of the activated PEG2 was added to the solution in five additions at 30 min intervals at room temperature with stirring. The reaction mixture was concentrated to 8 ml using YM10 ultrafiltration membrane (Amicon, Danvers, MA, USA) to give a PEG(10000)IL-6 and 3.5 ml of the concentrate was applied to a Superdex G200 column (Pharmacia, Upsala, Sweden) equilibrated with PBS. The PEGylated hlL-6 polypeptide was eluted in five fractions (hereafter referred to as Fr100-1, Fr100-2, Fr100-3, Fr100-4, Fr100-5) with PBS. The yield of each fraction was 3.8 mg, 5.9 mg, 5.8 mg, 4.8 mg, and 4.5 mg; respectively. The five fractions obtained were characterized by determining the number of free amino acid groups as described in Example 5. The average number of free amino groups per molecule of each fraction was 5.3, 7.4, 8.6, 9.4, and 10.0; respectively. EXAMPLE 12 An activated PEG12M (a succinimidyl succinate derivative of polyethylene glycol, which is methoxypolyethylene glycol succinate with an average molecular weight of 12,000 and coupled to N-hydroxysuccinimide) was obtained from Nippon Oil & Fats Co. (Tokyo, Japan). The hlL-6 polypeptide produced in Example 4 was coupled to this activated PEG12M. The hlL-6 polypeptide (90 mg) was dissolved in 180 ml of 0.1 M sodium borate buffer (pH 8.5) and 1000 mg of the activated PEG12M was added to the solution in three additions at 30 min intervals in an ice bath with stirring. The reaction mixture was concentrated to 6 ml using YM10 ultrafiltration membrane to give a PEG(12000)IL-6 and was applied to a Superdex G200 column equilibrated with PBS. The PEGylated hlL-6 polypeptide was eluted in five fractions (hereafter referred to as Fr120-1, Fr120-2, Fr120-3, Fr120-4, Fr120-5) with PBS. The yield of each fraction was 1.6 mg, 2.8 mg, 3.5 mg, 3.7 mg, and 3.7 mg; respectively. The five fractions obtained were characterized by determining the number of free amino acid groups as described in Example 5. The average number of free amino groups per molecule of each fraction was 5.2, 7.6, 8.7, 9.2, and 9.8; respectively. EXAMPLE 13 The hlL-6 produced in Example 4 or its PEGylated derivatives produced in Examples 11 and 12 were administered subcutaneously to four Balb/c mice (8 weeks old, female) once a day for five days. Control mice were administered with the vehicle. Blood samples were taken on the sixth day and platelets in peripheral blood were counted. The results are shown in Tables 6 and 7. The PEGylated hlL-6 showed significantly higher platelet producing activity compared to the unmodified hIL-6. Generally, the PEGylated hlL-6 derivatives of Example 12 gave higher activity. Number of platelets (% of control) PEGylated hlL-6 unmodified Dose hlL-6 Fr100-1 Fr100-2 Fr100-3 Fr100-4 Fr100-5 10 143.0 211.1 250.8 204.4 203.2 202.4 5 129.4 205.9 212.7 226.5 225.9 1 100.0 148.9 141.1 142.5 142.8 0.5 107.9 113.7 138.7 111.3 Number of platelets (% of control) PEGylated hlL-6 unmodified Dose hlL-6 Fr120-1 Fr120-2 Fr120-3 Fr120-4 Fr120-5 10 126.7 201.3 213.2 221.4 200.4 235.9 5 246.3 244.3 243.1 229.0 224.8 1 221.5 233.2 242.7 221.4 225.4 0.5 215.5 227.8 205.9 203.4 191.5 0.1 141.3 167.4 170.1 161.5 154.1 EXAMPLE 14 The PEGylated hlL-6 produced in Example 12 (Fr120-1 to Fr120-5) were administered subcutaneously to five acute-thrombocytopenic mice (8 weeks old, female), once a day for 7 serial days following X-ray irradiation (600 rad). Blood samples were taken on the eighth day and platelets in peripheral blood were counted. The results are shown in Figure 3. All the PEGylated hlL-6 fractions induced prominent recovery from the acute thrombocytopenia. At doses of over 0.1 µg/mouse, the administration of any of the five fractions resulted in a significantly (P<0.01) higher number of platelets produced as compared to the control (vehicle administration only). Fr120-1 and Fr120-2 were chosen for further study. EXAMPLE 15 The in vivo persistence of the PEGylated hlL-6 in blood was investigated. The hlL-6 of Example 4 or its PEGylated derivatives (Fr45-2, Fr120-1, and Fr120-2, produced in Examples 4 and 12) were administered subcutaneously to Balb/c mice (8 weeks old, female) at a dose of 0.2 µg/mouse (as polypeptide). Blood samples were taken at intervals and the serum concentration of hlL-6 was determined immunochemically using Quantikine hlL-6 (R&D Systems, Minneapolis, MN, USA). The result is shown in Figure 4. The PEGylated hlL-6 could be immunochemically detected even 24 hours after the administration while the unmodified hlL-6 could not be detected 5 hours after administration. This demonstrates that the halflife of hlL-6 was increased by PEGylation. EXAMPLE 16 The hlL-6 polypeptide, with exactly the sequence shown in Example 4, was produced as described in Example 4 but without the cathepsin C treatment. Thus, this IL-6 has a Met-Lys at the amino terminus. Approximately 2.9 g of the hlL-6 polypeptide, which was a single band on SDS-PAGE and had the predicted molecular weight of 21K, was obtained. The N-terminal sequence was confirmed to be Met-Lys-Ala-Pro- with more than 99% purity by direct sequence analysis. This sequence was stable for at least for 4 months when stored at 4°C. The hlL-6 polypeptide was PEGylated with the activated PEG12M of Example 12 to give a PEG(12000)IL-6 termed PEG(12000)IL-6'. The five fractions obtained were termed as Fr120'-1 to Fr120'-5. The PEGylated hlL-6 Fr120'-2 was administered to five mice once a day for five days at a dose of 1 µg/mouse and blood samples were taken on the sixth day as described in Example 13. The number of peripheral platelets in the test mice showed a 285% increase (significant at P<0.001) compared to the control (vehicle administered) mice. EXAMPLE 17 The acute toxicity of PEGylated hlL-6 was investigated. The hlL-6 of Example 4 or its PEGylated derivatives (Fr45-2, Fr100-2, and Fr120-2), produced in Examples 4, 11, and 12, were administered subcutaneously to five Balb/c mice (6 weeks old, male, 21-23 g weight) at a dose of either 1, 5, or 10 mg/kg weight (as polypeptide). None of the mice was observed to die during the ten day period after the administration. Thus the acute LD 50 for the three PEGylated hlL-6 was over 10 mg/kg weight. The foregoing examples describe the PEGylation of IL-6 which substantially increases the biological half-life of IL-6 while still retaining the biological activity of IL-6. While the present invention has been described in terms of specific methods and compositions, it is understood that variations and modifications will occur to those skilled in the art upon consideration of the present invention. For example, it is anticipated that smaller protein fragments and peptides derived from any form of IL-6, whether glycosylated or unglycosylated, and that still retain IL-6 biological activity, would also be effective in their PEGylated forms. It is also anticipated that forms of PEG other than the succinimidyl succinate derivatives of PEG (formula 5), the bis-polyethylene glycol derivatives of cyanuric chloride (formula 7) and the polyoxyethylene diamines (formula 8), such as carbonyl dimidazole, phenylcarbonate, succinimidyl carbonate or maleimide derivatives of PEG and mono-polyethylene glycol derivatives of cyanuric chloride, as well as other polyoxyethylene derivatives such as polyoxyethylene monoamines, will also be effective as PEGylating agents. Although the preferred forms of PEGylated IL-6 are unglycosylated hlL-6 polypeptides PEGylated at amino groups with polyethylene glycol succinate, it is not intended to preclude other combinations of PEG and IL-6 that are effective in having improved biological halflife and in retaining IL-6 activity. Further, it is anticipated that the general method of the invention of preparing PEGylated forms of IL-6 can be used to prepare PEGylated forms of other proteins for which it is desired to improve the biological half-life while still retaining and/or enhancing biological activity. Such other proteins include interleukin-2, interleukin-3, G-CSF, adenosine deaminase, asparaginase, urokinase and superoxide dismutase. Numerous modifications and variations in the invention as described in the above illustrative examples are expected to occur to those skilled in the art and consequently only such limitations as appear in the appended claims should be placed thereon. Accordingly, it is intended in the appended claims to cover all such equivalent variations which come within the scope of the invention as claimed. SEQUENCE LISTINGS (1) INFORMATION FOR SEQ. ID. NO. 1 (i) SEQUENCE CHARACTERISTICS: (A) LENGTH: 185 (B) TYPE: Amino acid (C) STRANDEDNESS: N/A (D) TOPOLOGY: N/A (xi) SEQUENCE DESCRIPTION : SEQ. ID. NO:1: (2) INFORMATION FOR SEQ. ID. NO. 2 (i) SEQUENCE CHARACTERISTICS: (A) LENGTH: 186 (B) TYPE: Amino acid (C) STRANDEDNESS: N/A (D) TOPOLOGY: N/A (xi) SEQUENCE DESCRIPTION : SEQ. ID. NO. 2: (3) INFORMATION FOR SEQ. ID. NO. 3 (i) SEQUENCE CHARACTERISTICS: (A) LENGTH: 187 (B) TYPE: Amino acid (C) STRANDEDNESS: N/A (D) TOPOLOGY: N/A (xi) SEQUENCE DESCRIPTION : SEQ. ID. NO. 3:

Claims: Claims for the following Contracting States : AT, BE, CH, LI, DE, DK, FR, GB, IT, NL, SE PEG-IL-6 which has a higher platelet producing activity compared to unmodified IL-6, said PEG-IL-6 being characterised by; (a) an IL-6 polypeptide comprising the amino acid sequence of SEQ ID NO: 1, SEQ ID NO: 2 or SEQ ID NO: 3, or an amino acid sequence having a deletion of up to 27 amino acid residues at the N-terminus thereof, or an amino acid sequence having a deletion of up to 50 amino acid residues at the C-terminus thereof; and (b) PEG linked to the IL-6 polypeptide to provide PEGylation of the structure: or where R 1 is an alkyl group with 1 to 3 carbon atoms, n is an integer between 7 and 600, and X is an amino group (-NH-) of the IL-6 polypeptide. PEG-IL-6 according to claim 1 obtainable by: treating IL-6 having the amino acid sequence of SEQ ID NO: 3 with cathepsin C to cleave off the N-terminal residues Met-Lys; reacting the resulting IL-6 with activated PEG1 (methoxypolyethylene glycol with an average molecular weight of 4,500 Da coupled to N-hydroxysuccinimide) under conditions to obtain active PEG-IL-6 fractions giving a major band with a molecular weight of 91 ("Fr45-1"), 68 ("Fr45-2"), 41 ("Fr45-3") or 26 ("Fr45-4") kDa upon SDS-PAGE analysis wherein the average number of free amino groups per molecule is 6.1, 6.8, 9.3 or 12.6 respectively; and recovering said active PEG-IL-6 fractions. PEG-IL-6 according to claim 1 obtainable by: treating IL-6 having the amino acid sequence of SEQ ID NO: 3 with cathepsin C to cleave off the N-terminal residues Met-Lys; reacting the resulting IL-6 with activated PEG2 (two polyethylene glycol monoethylether molecules having an average molecular weight of 5,000 Da coupled with cyanuric chloride) under conditions to obtain active PEG-IL-6 fractions wherein the average number of free amino groups per molecule is 5.3 ("Fr100-1"), 7.4 ("Fr100-2"), 8.6 ("Fr100-3"), 9.4 ("Fr100-4") or 10.0 ("Fr100-5"); and recovering said active PEG-IL-6 fractions. PEG-IL-6 according to claim 1 obtainable by: treating IL-6 having the amino acid sequence of SEQ ID NO: 3 with cathepsin C to cleave off the N-terminal residues Met-Lys; reacting the resulting IL-6 with activated PEG12M (methoxypolyethylene glycol succinate with an average molecular weight of 12,000 Da coupled to N-hydroxysuccinimide) under conditions to obtain active PEG-IL-6 fractions wherein the average number of free amino groups per molecule is 5.2 ("Fr120-2"), 7.6 ("Fr120-2"), 8.7 ("Fr120-3"), 9.2 ("Fr120-4") or 9.8 ("Fr120-5"); and recovering said active PEG-IL-6 fractions. PEG-IL-6 according to claim 4 which further comprises a Met-Lys dipeptide at the N-terminus of the IL-6. PEG-IL-6 according to any one of the preceding claims, for use in the treatment of haematopoietic disorders in an organism. PEG-IL-6 according to claim 6 for use in promoting platelet production. A pharmaceutical composition comprising a pharmaceutically acceptable solvent, diluent, adjuvant or carrier and as an active ingredient, PEG-IL-6 as claimed in any one of claims 1 to 5. Claims for the following Contracting State : ES A process for the preparation of a PEG-IL-6 which has a higher platelet producing activity compared to unmodified IL-6, said process being characterised by linking PEG to an IL-6 polypeptide comprising the amino acid sequence of SEQ ID NO: 1, SEQ ID NO: 2 or SEQ ID NO: 3, or an amino acid sequence having a deletion of up to 27 amino acid residues at the N-terminus thereof, or an amino acid sequence having a deletion of up to 50 amino acid residues at the C-terminus thereof, to provide the structure: or where R 1 is an alkyl group with 1 to 3 carbon atoms, n is an integer between 7 and 600 and X is an amino group (-NH-) of the IL-6 polypeptide. A process according to claim 1 wherein: IL-6 having the amino acid sequence of SEQ ID NO: 3 is treated with cathepsin C to cleave off the N-terminal residues Met-Lys; the resulting IL-6 is reacted with activated PEG1 (methoxypolyethylene glycol with an average molecular weight of 4,500 Da coupled to N-hydroxysuccinimide) under conditions to obtain active PEG-IL-6 fractions giving a major band with a molecular weight of 91 ("Fr45-1"), 68 ("Fr45-2"), 41 ("Fr45-3") or 26 ("Fr45-4") kDa upon SDS-PAGE analysis wherein the average number of free amino groups per molecule is 6.1, 6.8, 9.3 or 12.6 respectively; and said active PEG-IL-6 fractions are recovered. A process according to claim 1 wherein: treating IL-6 having the amino acid sequence of SEQ ID NO: 3 is treated with cathepsin C to cleave off the N-terminal residues Met-Lys; the resulting IL-6 is reacted with activated PEG2 (two polyethylene glycol monoethylether molecules having an average molecular weight of 5,000 Da coupled with cyanuric chloride) under conditions to obtain active PEG-IL-6 fractions wherein the average number of free amino groups per molecule is 5.3 ("Fr100-1"), 7.4 ("Fr100-2"), 8.6 ("Fr100-3") , 9.4 ("Fr100-4") or 10.0 ("Fr100-5"); and said active PEG-IL-6 fractions are recovered. A process according to claim 1 wherein: IL-6 having the amino acid sequence of SEQ ID NO: 3 is treated with cathepsin C to cleave off the N-terminal residues Met-Lys; the resulting IL-6 is reacted with activated PEG12M (methoxypolyethylene glycol succinate with an average molecular weight of 12,000 Da coupled to N-hydroxysuccinimide) under conditions to obtain active PEG-IL-6 fractions wherein the average number of free amino groups per molecule is 5.2 ("Fr120-2"), 7.6 ("Fr120-2"), 8.7 ("Fr120-3"), 9.2 ("Fr120-4") or 9.8 ("Fr120-5"); and said active PEG-IL-6 fractions are recovered. A process according to claim 4 wherein a Met-Lys dipeptide is provided at the N-terminus of the IL-6. A process for the preparation of a pharmaceutical composition, comprising admixture of a pharmaceutically acceptable solvent, diluent, adjuvant or carrier and, as an active ingredient, PEG-IL-6 which has a higher platelet producing activity compared to unmodified IL-6, said PEG-IL-6 being characterised by; (a) an IL-6 polypeptide comprising the amino acid sequence of SEQ ID NO: 1, SEQ ID NO: 2 or SEQ ID NO: 3, or an amino acid sequence having a deletion of up to 27 amino acid residues at the N-terminus thereof, or an amino acid sequence having a deletion of up to 50 amino acid residues at the C-terminus thereof; and (b) PEG linked to the IL-6 polypeptide to provide PEGylation of the structure: or where R 1 is an alkyl group with 1 to 3 carbon atoms, n is an integer between 7 and 600, and X is an amino group (-NH-) of the IL-6 polypeptide. A process according to claim 6 wherein the said PEG-IL-6 is obtainable by: treating IL-6 having the amino acid sequence of SEQ ID NO: 3 with cathepsin C to cleave off the N-terminal residues Met-Lys; reacting the resulting IL-6 with activated PEG1 (methoxypolyethylene glycol with an average molecular weight of 4,500 Da coupled to N-hydroxysuccinimide) under conditions to obtain active PEG-IL-6 fractions giving a major band with a molecular weight of 91 ("Fr45-1"), 68 ("Fr45-2"), 41 ("Fr45-3") or 26 ("Fr45-4") kDa upon SDS-PAGE analysis wherein the average number of free amino groups per molecule is 6.1, 6.8, 9.3 or 12.6 respectively; and recovering said active PEG-IL-6 fractions. A process according to claim 6 wherein the said PEG-IL-6 is obtainable by: treating IL-6 having the amino acid sequence of SEQ ID NO: 3 with cathepsin C to cleave off the N-terminal residues Met-Lys; reacting the resulting IL-6 with activated PEG2 (two polyethylene glycol monoethylether molecules having an average molecular weight of 5,000 Da coupled with cyanuric chloride) under conditions to obtain active PEG-IL-6 fractions wherein the average number of free amino groups per molecule is 5.3 ("Fr100-1"), 7.4 ("Fr100-2"), 8.6 ("Fr100-3"), 9.4 ("Fr100-4") or 10.0 ("Fr100-5"); and recovering said active PEG-IL-6 fractions. A process according to claim 6 wherein the said PEG-IL-6 is obtainable by: treating IL-6 having the amino acid sequence of SEQ ID NO: 3 with cathepsin C to cleave off the N-terminal residues Met-Lys; reacting the resulting IL-6 with activated PEG12M (methoxypolyethylene glycol succinate with an average molecular weight of 12,000 Da coupled to N-hydroxysuccinimide) under conditions to obtain active PEG-IL-6 fractions wherein the average number of free amino groups per molecule is 5.2 ("Fr120-2"), 7.6 ("Fr120-2"), 8.7 ("Fr120-3"), 9.2 ("Fr120-4") or 9.8 ("Fr120-5"); and recovering said active PEG-IL-6 fractions. A process according to claim 9 wherein the said PEG-IL-6 further comprises a Met-Lys dipeptide at the N-terminus of the IL-6. A PEG-IL-6 as defined in any one of claims 6 to 10. PEG-IL-6 according to claim 11, for use in the treatment of haematopoietic disorders in an organism. PEG-IL-6 according to claim 12 for use in promoting platelet production. A pharmaceutical composition comprising a pharmaceutically acceptable solvent, diluent, adjuvant or carrier and as an active ingredient, PEG-IL-6 as defined in any one of claims 6 to 10.

Inventors: INOUE HIDEO, KADOYA TOSHIHIKO, KAKITANI MAKOTO, MIKAYAMA TOSHIFUMI, INOUE, HIDEO, KADOYA, TOSHIHIKO, KAKITANI, MAKOTO, MIKAYAMA, TOSHIFUMI
Applicants: KIRIN AMGEN INC, KIRIN-AMGEN, INC.
Application year: 1991
Main classification: C12N15
IPC codes: C12N15, A61P7, C07K14, C07K1, A61K38