Abstract:
Modifying TNF with polyethyleneglycol (PEG) having an approximate weight average molecular weight in the range of about 10,000 to about 40,000, preferably in the range of about 20,000 to 30,000, significantly increases the circulating half-life of the TNF while not increasing its toxicity. As a result, lower doses of the TNF may be administered to effectively treat tumors with fewer, accompanying adverse side effects to the patient.

Description:
RELATED APPLICATIONS 
     This application is a divisional of U.S. patent application Ser. No. 09/504,280, filed Feb. 15, 2000, which is a continuation-in-part of U.S. patent application Ser. No. 09/006,810, filed Jan. 14, 1998, which claims the benefit of U.S. Provisional Patent Application Ser. No. 60/035,521, filed Jan. 15, 1997, each of which in incorporated herein in its entirety. 
     This invention is directed, inter alia, to tumor necrosis factor, and several mutant forms of tumor necrosis factor, formulated with polyethylene glycol having a molecular weight in the range of 10,000 to 40,000 and methods for treating tumors using such modified tumor necrosis factor. 
    
    
     BACKGROUND OF THE INVENTION 
     Malignant melanoma (stage 3) is a fatal disease killing most patients within one year of diagnosis. The incidence of melanoma is rapidly increasing in the United States and is even higher in other countries, such as Australia. Effective treatments for patients suffering from melanoma are urgently needed. 
     Kidney cancer currently kills approximately 13,000 individuals in the United States each year. This form of cancer is frequently not detected until it is well advanced. The only form of treatment that significantly affects a patient&#39;s prognosis is surgical resection of the affected organ. Unfortunately, because this type of cancer is highly metastatic, complete removal of all the metastasis is difficult, if not impossible. 
     Colon cancer is one of the most prevalent forms of cancer and currently kills approximately 140,000 individuals in the United States each year. Although there have been a large number of traditional chemotherapeutic drugs developed to treat this disease, long term survival (defined as the percentage of patients surviving five years or more) has not appreciably changed in the last four decades. Furthermore, all of the traditional chemotherapeutic drugs developed are highly toxic, have deleterious and often fatal side effects, and are expensive. A curative, non-toxic treatment for this disease is urgently needed. 
     A hallmark of melanomas, kidney and colon tumors is that these tumors quickly develop resistance to traditional chemotherapies. Even though patients may initially respond to chemotherapeutic treatment, drug-resistant tumors quickly arise and often kill the patient. An alternative way to treat these tumors would be to identify an “Achilles Heel” in the tumors and to develop therapies that would selectively treat that target. One such potential target has been identified. Specifically, it has been noted that all three of these types of tumors require extensive vascularization of each of the metastacies in order for the cancers to grow. Therefore, one would predict that a therapeutic agent which would inhibit the vascularization of these tumors may provide a unique means of treating these tumors. 
     Tumor necrosis factor (TNF) is a cytokine originally named for its ability to kill tumors. There are at least two different mechanisms by which TNF is believed to kill tumors. First is by a direct effect on the tumor itself. Second, TNF can selectively disrupt the vascularization of tumors, thus depriving the tumor of nutrients and oxygen and in so doing killing the tumor indirectly. This latter mechanism of killing was described in the first scientific publication describing TNF. Carswell and Old reported that the METH A tumor cells were completely resistant to TNF in vitro.  J. Proc. Natl. Acad. Sci USA,  72:3666-3670 (1975). However, METH A tumors in mice were extremely sensitive to killing by TNF in vivo. It was later shown that TNF selectively disrupted the vascularization of these METH A tumors. Subsequently it was later shown that a factor (EMAP 2) is released by some tumors that renders the tumor vasculature susceptible to TNF killing. Thus, TNF can kill some tumors (such as METH A sarcomas) not by directly killing the tumor cells, but rather by killing the tumors&#39; vasculature that provides the tumor with blood, oxygen and other nutrients necessary to live and grow. 
     Early clinical trials attempted to utilize TNF as a direct tumoricidal agent. This coupled with the fact that because TNF has a very short circulating half life (less than 20 minutes) in the circulation, extremely high doses of TNF were used which induced “shock”-like symptoms characterized by a precipitous drop in blood pressure and often death of the patient. 
     An alternative method of using TNF would be to formulate it so that it remains in the circulation longer thus giving it more time to react with (and thus destroy) the vasculature of the tumors. Several other therapeutic proteins which had very short circulating half lives have been formulated with polyethylene glycol (PEG) so that they circulate longer and remain in the vasculature. These proteins include asparaginase, adenosine deaminase, and super oxide dismutase. See, for example, Harras, J. M., in “Polyethylene Glycol Chemistry: Biotechnical and Biochemical Applications,” Plenum Press (1992). 
     Relevant to the invention described here, a group of investigators in Japan (Tsutsumi et. al.) have described that TNF could be formulated with certain PEG and that the resulting material had substantially increased circulating half-life and greater anti-tumor activity. See, Tsutsumi, Y., et al.,  Jap. J. Cancer Res.,  85:9-12 (1994); Tsutsumi, Y., et al.,  Jap. J. Cancer Res.,  85:1185-1188 (1994); Tsutsumi, Y., et al.,  Jap. J. Cancer Res.,  87:1078-1085 (1997). However these investigators used only PEG with a molecular weight of 5000 (PEG5000) attached to the primary amines on TNF with a succinimidyl succinate linker and failed to determine not only the optimal method of attaching PEG to TNF but also the optimal attachment sites on the molecule. 
     SUMMARY OF THE INVENTION 
     It has now been found that TNF modified with polyethylene glycol (PEG) having an approximate weight average molecular weight much higher than that experimented with by Tsutsumi et al., namely, in the range of about 10,000 to about 40,000 and preferably in the range of about 20,000 to about 30,000, is a greatly and surprisingly enhanced tumoricidal agent. 
     For one thing, the PEG-modified TNF of this invention has a significantly longer circulating half life than the PEG5000-modified TNF of Tsutsumi et al. For example utilizing the technology discovered by Tsutsumi et al., the circulating half life of PEG-TNF was about 2 days. In contrast using the most preferred PEG-modified TNF described herein, the circulating half-life is greater than 16 days (an 8 fold increase). 
     The PEG-modified TNF of this invention also exhibits significantly and surprisingly enhanced tumoricidal activity compared to either native TNF or to TNF modifed as by Tsutsumi et al. For example, tests indicate that the anti-tumor ED50 of the most preferred embodiment of the invention (TNF modified by PEG-20000 through primary amine groups), is as little as 10-50 IU (0.01 ug), a 2000 fold improvement over the 1000-3000 IU (2 ug) ED50 for native TNF. 
     Also surprising is the discovery that the modified TNF of this invention, even though it is far more potent at curing tumors and circulates many times longer than native TNF, is actually much safer (and less toxic) to use than the TNF of Tsutsumi et al. Tests indicate that optimal formulation of PEG-TNF circulated 8 times longer, is 2000 fold more potent and about 500 fold less toxic than the PEG-TNF described by Tsutsumi et. al in their publications. Moreover, it has been shown that this optimal formulation methodology can be utilized with TNF of several species (mouse and human) and with both wild type TNF as well as several mutant TNF proteins. Thus the present invention has enormous versatility in being able to be applied to many different TNF molecules. 
     This invention, therefore, relates to the modified TNF, wherein TNF has been modified by covalently bonding to the TNF, either directly or through a biocompatible linking agent, and preferably through a primary amine on the protein, PEG molecules, each PEG molecule of has an approximate weight average molecular weight in the range of about 10,000 to about 40,000. Preferably, the TNF is modified with five to twelve of the PEG molecules, more preferably, with about five to nine PEG molecules. 
     This invention also relates to a method of treating a patient suffering from a tumor by administering to said patient a therapeutically effective amount of said modified TNF. 
     This invention further relates to a method of enhancing the circulating half life of TNF comprising modifying said TNF by covalently bonding to it, preferably through primary amines on the protein, between about five and twelve PEG molecules having an approximate weight average molecular weight in the range of about 10,000 to about 40,000. 
     This invention further relates to a method of enhancing the tumoricidal activity of TNF comprising modifying said TNF by covalently bonding to it, preferably through primary amines on the protein, between about five and twelve PEG molecules having an approximate weight average molecular weight in the range of about 10,000 to about 40,000. 
     This invention further relates to a method of enhancing the safety of TNF by covalently bonding to it, preferably through primary amines on the protein, five to twelve PEG molecules each molecule having a molecular weigh of 10,000 to 40,000. 
    
    
     
       DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a graph depicting the circulating half life in mouse serum of native TNF (open circles), SS 5,000 MW PEG-TNF (closed circles), and 20,000 MW PEG-TNF (open triangles). 
         FIG. 2  is a graph depicting the circulating half life in mouse serum of native TNF (open circles), SS 5,000 MW PEG-TNF (closed circles), SS 12,000 MW PEG-TNF (closed triangles), SS-20,000 MW PEG-TNF (open triangles), NHS 12,000 MW PEG-TNF (closed squares), and NHS 20,000 MW PEG-TNF (open squares). 
         FIG. 3  is the sequence of secreted (mature) mouse (SEQ ID NO:1) and human (SEQ ID NO:2) TNF. Position 1 is the N-terminus of the secreted TNF. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     “Tumor necrosis factor” or “TNF” as used herein encompasses either naturally derived protein, such as isolated human or mouse TNF proteins, or protein produced using recombinant technology, such as recombinant murine TNF and recombinant human TNF or various TNF mutant proteins. Although the TNF-α protein is preferred, the term “TNF” also encompasses TNF-β protein. The terms also encompass TNF proteins that have been mutated by deletion or alteration of amino acids without significantly impairing biological activity. As non-limiting examples, such mutations include (reference being made to the sequence of the secreted protein, as illustrated in  FIG. 3 ): the protein in which amino acids 1-9 (MSTESMIRD) (SEQ ID NO:3) of the human secreted protein are deleted; the protein in which lysine at position 166 is changed to alanine (SEQ ID NO:4): the protein in which lysine at positions 188 and 204 is changed to alanine (SEQ ID NO:5); and combinations of these mutations. 
     “Polyethylene glycol” or “PEG” refers to mixtures of condensation polymers of ethylene oxide and water, in a branched or straight chains, represented by the general formula H(OCH 2 CH 2 ) n OH. “Polyethylene glycol” or “PEG” is used in combination with a numeric suffix to indicate the approximate weight average molecular weight thereof of each molecule. For example, PEG 5,000 refers to polyethylene glycol having an approximate weight average molecular weight of about 5,000; PEG 12,000 refers to polyethylene glycol having an approximate weight average molecular weight of about 12,000; and PEG 20,000 refers to polyethylene glycol having an approximate weight average molecular weight of about 20,000. Such polyethylene glycols are available from several commercial sources, and are routinely referred to, as indicated above, by their weight average molecular weights. 
     “Melanoma” may be a malignant or benign tumor arising from the melanocytic system of the skin and other organs, including the oral cavity, esophagus, anal canal, vagina, leptomeningers, and/or the conjunctivae or eye. The term “melanoma” includes, for example, acral-lentginous melanoma, amelanotic melanoma, benign juvenile melanome, lentigo maligna melanoma, malignant melanoma, nodular melanoma, subungual melanoma and superficial spreading melanoma. 
     “Patient” refers to an animal, preferably a mammal, more preferably a human. 
     “Biocompatible” refers to materials or compounds which are generally not injurious to biological functions and which will not result in any degree of unacceptable toxicity, including allergenic and disease states. 
     “Circulating half life” refers to the period of time, after injection of the modified TNF into a patient, until a quantity of the TNF has been cleared to levels one half of the original peak serum level. Circulating half life may be determined in any relevant species, including humans or mice. 
     “Covalently bound” as used herein refers to a covalent bond linking the TNF protein to the PEG molecule, either directly or through a linker. 
     According to this invention, TNF is modified with polyethylene glycol having an approximate weight average molecular weight in the range of 10,000 to 40,000, preferably in the range of 20,000 to 30,000. Generally, polyethylene glycol with a molecular weight of 30,000 or more is difficult to dissolve, and yields of the formulated product are greatly reduced. The polyethylene glycol may be branched or straight chain, but is preferably a straight chain. 
     The polyethylene glycols may be bonded to the TNF through biocompatible linking groups. As discussed above, “biocompatible” indicates that the compound or group is non-toxic and may be utilized in vitro or in vivo without causing injury, sickness, disease or death. PEG may be bonded to the linking group, for example, via an ether bond, an ester bond, a thiol bond, or an amide bond. Suitable biocompatible linking groups include, for example, an ester group, an amide group, an imide group, a carbamate group, a carboxyl group, a hydroxyl group, a carbohydrate, a maleimide group (including, for example, succinimidyl succinate (S S), succinimidyl propionate (SPA), succinimidyl carboxymethylate (SCM), succinimidyl succinamide (SSA), or N-hydroxysuccinimidyl (NHS), an epoxide group, an oxycarbonylimidazole group (including, for example, nitrophenyl carbonate (NPC) or trichlorophenyl carbonate (TPC)), a trysylate group, an aldehyde group, an isocyante group, a vinylsulfone group, a tyrosine group, a cysteine group, a histidine group or a primary amine. Preferably, the biocompatible linking group is an ester group and/or a maleimide group and bonds to the TNF through a primary amine on the TNF protein. More preferably, the linking group is SS, SPA, SCM, SSA or NHS; with SS being the most preferred. 
     Alternatively, TNF may be coupled directly to PEG (i.e., without a linking group) through an amino group, a sulfhydryl group, a hydroxyl group, or a carboxyl group. 
     Methods for covalently bonding TNF to PEG, directly or via a biocompatible linking group, are known in the art, as described, for example, in Harras, J. M., in “Polyethylene Glycol Chemistry: Biotechnical and Biochemical Applications,” Plenum Press (1992), the disclosure of which is herein incorporated by reference. It is preferred that the TNF protein be covalently bonded to five to twelve PEG molecules. Methods for determining the number of PEG molecules bonded to the protein are known in the art, for example, Habeeb, A. F. S. A.,  Anal. Biochem.,  14:328-339 (1966); Harras, J.M., supra., herein incorporated by reference. The number of PEG molecules bonded to TNF will vary according to the linking group utilized, the length of reaction, and the molar ratios of TNF and PEG utilized in the reaction. 
     As one skilled in the art would recognize, the modified TNF of this invention may be administered in a number of ways, for example, orally, intranasally, intraperitoneally, parenterally, intravenously, intralymphatically, intratumorly, intramuscularly, interstitially, intrarterially, subcutaneously, intraocularly, intrasynoially, transepithelially, and transdermally. A therapeutically effective amount of one of the modified compounds of the present invention is an amount effective to inhibit tumor growth, and that amount may vary according to the method of administration. Generally, effective doses should be in the range of about 0.001 to 0.1 mg/kg, once a week. The modified TNF may be formulated with pharmaceutically acceptable carriers and diluents, as known in the art. For example, for intravenous? administration, the modified TNF may be mixed with a phosphate buffered saline solution, or any other appropriate solution known to those skilled in the art, prior to injection. Tests have shown that the modified TNF is particularly effective in treating melanoma, colon cancer, kidney cancer and breast cancer tumors. 
     The invention is further demonstrated in the following examples, which are for purposes of illustration, and are not intended to limit the scope of the present invention. 
     TNF used in the experiments described below was of mouse TNF and human TNF or human TNF mutants. The human TNF was produced in  E. coli  and  Pichea pasatoris , and murine TNF as well as the human TNF mutants were produced in  Pichea pastoris . Recombinant TNF was produced in  E. coli  or  Pichea  using methods similar to those described in Pennica, D., et al.,  Nature,  312:724-729 (1981); Streekishna, K., et al.,  Biochemistry,  28:4117-4125 (1989). The mouse TNF was produced in  E. coli  and in  Pichea.    
     EXAMPLE 1 
     Attachment of PEG to TNF 
     Coupling PEG to TNF was performed using the general methods described in Harras, J. M., cited above. To TNF (1 mg/ml in 100 mm phosphate buffer, pH 7.2-7.5), the SS-PEG, SP-PEG or NHS-PEG was added at a 10 to 50 molar excess and mixed for one hour at room temperature. This results in approximately 8-12 PEG molecules being attached to the primary amines of each molecule of TNF. Other PEG linkers and attachment sites required different pH, reaction times and amounts of PEG all of which must be empirically determined. All PEG-TNF formulations were purified by removing unreacted PEG and from the PEG-TNF by ultra filtration using a 100 kDa cut off filter. In each of the modifications referenced in this example, the TNF was modified with five to 15 molecules of PEG. 
     Purity of the PEG-TNF was assessed by SDS-PAGE and the percent of primary amines modified by this procedure was determined using florescamine as described by S. J. Stocks (Anal. Biochem. 154:232 (1986)). SDS-PAGE results indicated that very little, if any, native TNF remained in the preparation after pegylation. 
     EXAMPLE 2 
     Specific Activity of TNF 
     Prior to pegylation (native TNF), both human and mouse was tested for its biological activity using the L929 cytotoxicity assay originally described in the first publication on TNF and in detail below. The specific activity of the TNF was 10 6  I.U. units per milligram. The protein concentration was determined by the method of Bradford. Bradford, M. M.,  Anal. Biochem.,  72:248-254 (1976). BSA was used as a standard. Purity of the preparation was assessed by SDS-PAGE gel. All preparations used were &gt;99% pure (i.e. less than 1% of native TNF remained in the PEG-TNF. 
     EXAMPLE 3 
     L-929 Cytotoxicity Testing of PEG-TNF 
     The PEG-TNF were examined for in vitro cytotoxic activity using the L-929 cytotoxicity assay performed according to the procedure set forth below. The specific activity of the native TNF starting material was 1.5×10 6  units/mg a value. The specific activity of the PEG-TNF was most often less than one half of the specific activity of the native TNF. This experiment was repeated using a wide variety of PEG molecular weights, methods of attachment (linkers) and sites of attachment (see Table 1). 
     
       
         
               
             
               
               
               
               
             
               
               
               
               
             
           
               
                 TABLE 1 
               
             
             
               
                   
               
               
                 Effects of The Attachment Site, Linker Chemistry and 
               
               
                 PEG molecular Weight on the Biological Activity of TNF 
               
               
                 measured In Vitro (L-929 Cytotoxicity of PEG-TNF) 
               
             
          
           
               
                   
                   
                 Molecular Weight 
                 % Activity 
               
               
                 Attachment Site 
                 Linker 
                 of PEG 
                 Retained 
               
               
                   
               
             
          
           
               
                 Primary Amines 
                 SS-PEG 
                 5,000 mw 
                 55 
               
               
                   
                 SS-PEG 
                 12,000 mw  
                 53 
               
               
                   
                 SS-PEG 
                 20,000 mw  
                 56 
               
               
                   
                 SS-PEG 
                 30,000 mw  
                 54 
               
               
                   
                 SS-PEG 
                 40,000 mw  
                 55 
               
               
                   
                 SP-PEG 
                 5,000 mw 
                 51 
               
               
                   
                 SP-PEG 
                 20,000 mw  
                 52 
               
               
                   
                 PEG2-NHS 
                 10,000 mw  
                 49 
               
               
                   
                 PEG2-NHS 
                 20,000 mw  
                 52 
               
               
                   
                 PEG2-NHS 
                 40,000 mw  
                 54 
               
               
                 Hydroxyl groups 
                 Epoxy PEG 
                 5,000 mw 
                 38 
               
               
                   
                 Epoxy PEG 
                 8,000 mw 
                 38 
               
               
                   
                 Glycedal ether 
                 5,000 mw 
                 0 
               
               
                 Carboxyl groups 
                 Nitro Phenyl 
                 5,000 mw 
                 21 
               
               
                   
                 Trichloro 
                 5,000 mw 
                 11 
               
               
                   
                 Phenyl 
               
               
                   
                 Tresylate 
                 5,000 mw 
                 8 
               
               
                   
                 PEG aldehyde 
                 5,000 mw 
                 0 
               
               
                 Sulfhydral groups 
                 Vinyl sulfone 
                 5,000 mw 
                 12 
               
               
                   
                 Isocynate 
                 5,000 mw 
                 19 
               
               
                   
                 Maleimide 
                 5,000 mw 
                 43 
               
               
                   
               
             
          
         
       
     
     EXAMPLE 4 
     Determination of Serum Half Life of PEG-TNF 
     In order to measure the circulating half life (serum half life) of TNF and PEG-TNF, an ELISA assay for human and mouse TNF obtained from Genzyme was used. The kit was used as suggested by the manufacturer. Mice were injected with either TNF or PEG (100 units) i.p., and approximately 25 μl of serum was collected from retro-orbital bleeds at the times indicated in  FIG. 1 . A total of 5 mice (female, C57 bl6 mice, 20-25 g) were in each group. 
     The native TNF (open circles) was cleared very fast, and the only data point above baseline was 30 minutes post-injection. 
     The SS 5,000 MW peg-TNF (closed circles) had a half life of about 4 days. The half life of the 20,000 MW PEG-TNF (open triangles) was &gt;15 days. 
     This experiment was repeated using the treatment groups listed below, and the results presented in  FIG. 2 : native TNF (open circles); SS 5,000 MW PEG-TNF-α (closed triangles); SS 20,000 MW PEG-TNF (open triangles); NHS 12,000 MW PEG-TNF-α (closed squares). The serum half life for the different treatment groups was &gt;15 days for NHS 20,000 MW PEG-TNF and SS 20,000 MW PEG-TNF-α; approximately 4 days for SS 5,000 MW PEG-TNF; approximately 6 days for SS 12,000 MW PEG-TNF; approximately 8 days for NHS 12,000 MW PEG-TNF; and 30 min post-injection for native TNF. In summary, each PEG-TNF exhibited a much longer half life than native TNF; however, the NHS 20,000 MW PEG-TNF and the SS 20,000 MW PEG-TNF had significantly longer half lives (&gt;15 days) than the TNF modified with lower molecular weight PEG. 
     Data from these and other experiments performed with additional PEGs, linkers and sites of attachment are shown in Table 2. 
     
       
         
               
             
               
               
             
               
               
               
               
             
               
               
               
               
             
           
               
                 TABLE 2 
               
             
             
               
                   
               
               
                 Effects of The Attachment Site, Linker Chemistry 
               
               
                 and PEG molecular Weight on Circulating Half Life 
               
               
                 and In Vitro Cytotoxicity Using L-929 Cells 
               
             
          
           
               
                   
                 Serum Half-Life = 0.02 days (~20 minutes) 
               
             
          
           
               
                   
                   
                   
                 Serum 
               
               
                 Native Human TNF 
                   
                 Molecular Weight 
                 Half-Life 
               
               
                 Attachment Site 
                 Linker 
                 of PEG 
                 (days) 
               
               
                   
               
             
          
           
               
                 Primary Amines 
                 SS-PEG 
                 5,000 mw 
                 4 
               
               
                   
                 SS-PEG 
                 12,000 mw  
                 8 
               
               
                   
                 SS-PEG 
                 20,000 mw  
                 16 
               
               
                   
                 SS-PEG 
                 30,000 mw  
                 17 
               
               
                   
                 SS-PEG 
                 40,000 mw  
                 17 
               
               
                   
                 SP-PEG 
                 5,000 mw 
                 5 
               
               
                   
                 SP-PEG 
                 20,000 mw  
                 8 
               
               
                   
                 PEG2-NHS 
                 10,000 mw  
                 7 
               
               
                   
                 PEG2-NHS 
                 20,000 mw  
                 16 
               
               
                   
                 PEG2-NHS 
                 40,000 mw  
                 18 
               
               
                 Hydroxyl groups 
                 Epoxy PEG 
                 5,000 mw 
                 5 
               
               
                   
                 Epoxy PEG 
                 8,000 mw 
                 6 
               
               
                   
                 Glycedal ether 
                 5,000 mw 
                 12 
               
               
                 Carboxyl groups 
                 Nitro Phenyl 
                 5,000 mw 
                 5 
               
               
                   
                 Trichloro Phenyl 
                 5,000 mw 
                 5 
               
               
                   
                 PEG aldehyde 
                 5,000 mw 
                 21 
               
               
                 Sulfhydral groups 
                 Vinyl sulfone 
                 5,000 mw 
                 3 
               
               
                   
                 Isocynate 
                 5,000 mw 
                 3 
               
               
                   
                 Maleimide 
                 5,000 mw 
                 2 
               
               
                   
               
             
          
         
       
     
     These experiments illustrate that by attaching PEG to the primary amines and using PEG of 20,000 to 30,000 mw, the optimum retention of biological activity measured in vitro (L-929 cytoxicity) and the longest circulating half life in vivo are observed. However, a remaining concern is whether increasing the circulating half life of the PEG-TNF would greatly increase the toxicity of the TNF. 
     EXAMPLE 5 
     Lethality of the PEG-TNF 
     As a screen, two C57 bl6 mice (female, 20-25 g) were injected intraperitoneally (i.p.) with either native TNF or SS-PEG-TNF and survival of the animals was monitored. The doses used were 1, 5, and 10 thousand units of activity. 
     With native TNF, the following results were obtained: 
     10,000 I.U.—both mice dead the next morning 
     5,000 I.U.—one mouse dead next morning; the second mouse in obvious distress (hair ruffled and little movement) and dead after 2 days 
     1,000 I.U.—one mouse dead the next morning; the second mouse in distress (hair ruffled and little movement) and in such poor condition after 2 days that it was euthanized 
     With the SS-PEG-TNF, all mice at all doses remained in good health for two weeks following injection. Behavior was normal, as was eating and drinking. There was no change in coat (fur was not ruffled). All of the mice were euthanized 15 days post-injection. 
     TNF kills mice by causing an abrupt drop in blood pressure. Blood pressure in mice can be measured using a pressure cuff around the tail, much as blood pressure is measured using a pressure cuff around the arm of a human. Because it has been shown that TNF is more lethal to mice having tumors, than normal mice, the animals used in this experiment were implanted with METH A sarcomas grown to approximately 0.5 cm in diameter. In these experiments we injected mice (5 in each group) with various amounts of TNF or PEG-TNF and the blood pressure was measured 2 hours post treatment (the time of minimum blood pressure following treatment. In Table 3 below, the hypotension ED50 is the amount of TNF or modified TNF that caused 50% of the mice to experience hypotension or shock. 
     High doses of TNF can kill mice within 2 days following treatment. The amount of TNF required to kill half of the mice is calculated at the LD 50  (Lethal Dose that kills 50% of the mice). Long Term survival is affected by tumor growth and thus an effective Anti-Tumor dose of TNF Is defined as the lowest dose required to enable a treated mouse to live twice as long as a mouse that does not receive treatment. The amount of TNF or PEG-TNF required to double the life expectancy (by killing the tumor)of 50% of the animals is presented as the Anti-Tumor Activity ED 50  in Table 3. All amounts of TNF are expressed as the amount of TNF protein and dose not include the weight of the PEG. 
     An ideal formulation of TNF would result in a PEG-TNF that exhibiting a high LD50 (be less lethal), a high ED 50  for blood pressure decrease (not cause hypotension or shock), and a low ED 50  for Anti-Tumor Activity (that is, be very potent at killing the tumor). 
     In this experiment, succimimidyl succinamide (SS) linker was used to link PEG 20,000 to the primary amines of mouse, human and several biologically active TNF mutants, to see if this formulation technology could be applied to other forms of TNF. The results from these experiments are summarized in Table 3 below 
     
       
         
               
             
               
               
               
               
               
             
               
               
               
               
               
               
             
           
               
                 TABLE 3 
               
             
             
               
                   
               
               
                 How does Formulation With PEG Effect 
               
               
                 TNF Toxicity and Anti-Tumor Activity 
               
             
          
           
               
                   
                   
                   
                 Hypo- 
                 Anti-Tumor 
               
               
                 Species 
                   
                   
                 tension 
                 Activity 
               
               
                 of TNF 
                 Formulation 
                 LD 50   
                 (ED 50 ) 
                 (ED 50 ) 
               
               
                   
               
             
          
           
               
                 Murine 
                 Native TNF 
                  2 ug 
                 1 ug 
                 20 
                 ug 
               
               
                   
                 PEG TNF 
                 100 ug 
                 2 ug 
                 0.01 
                 ug 
               
               
                 Human 
                 Native TNF 
                  7 ug 
                 1 ug 
                 60 
                 ug 
               
               
                   
                 PEG TNF 
                 300 ug 
                 4 ug 
                 0.005 
                 ug 
               
               
                 Human 
                 Native TNF 
                  60 ug 
                 1 ug 
                 2 
                 ug 
               
               
                 -77-87 
                 PEG TNF 
                 100 ug 
                 5 ug 
                 0.002 
                 ug 
               
               
                 Human 
                 Native TNF 
                 300 ug 
                 100 ug  
                 2 
                 ug 
               
               
                 188, 204 K-A 
                 PEG TNF 
                 300 ug 
                 100 ug  
                 20 
                 ug 
               
               
                   
               
             
          
         
       
     
     EXAMPLE 6 
     Antitumor Activity of PEG-TNF 
     The results presented above indicate that modification of TNF with PEG according to this invention not only reduces the lethality of the TNF, but that especially the TNF modified with PEG having a molecular weight of approximately 20,000 exhibited a surprisingly enhanced circulating half life and surprisingly and significantly enhanced anti-tumor activity. 
     To test the anti tumor activity of the 20,000 mw PEG-TNF with that of the native TNF and the PEG-TNF described by Tsutsumi et al., a test was carried out utilizing the B16 murine melanoma model. C57 bl6 female mice (20-25 g) were injected with one million B16 melanoma cells, s.q. on flank. The tumors were allowed to grow for one week prior to treatment. There were 5 mice in each treatment group, and animals were treated once a week for three weeks. The number of days the animals survived was noted ( the experiment was terminated at 180 days and all animals were euthanized; however the animals that survived this amount of time were all tumor free and in good health), and the results are shown below in Table 4. 
                                                                                                                     TABLE 4                   Effect of Native TNF and PEG-TNF on Survival       of Mice Implanted with B16 Melanomas                    Average       Treatment Group   Survival Time (days)   Survival Time               Saline control   18, 18, 20, 21, 24   20.2 days       Native TNF            10   IU   17, 18, 19, 21, 21   20.2 days       100   IU   16, 18, 19, 19, 23   19.0 days            SS-PEG 5,000 mw TNF                    10   IU   20, 22, 24, 26, 27   23.6 days       100   IU   21, 22, 24, 26, 27   25.0 days       1000   IU   21, 49, 53, 180, 180   96.6 days            SS-PEG 20,000 mw TNF                    10   IU   38, 180, 180, 180, 180   96.6 days       100   IU   180, 180, 180, 180, 180    180 days       1000   IU   180, 180, 180, 180, 180    180 days                    
Note that all animals surviving 180 days were devoid of tumors and were euthanized.
 
     Similar experiments were performed using a variety of other tumors including kidney, colon leukemia and breast cancer. Mice were injected with 1×10 6  tumor cells and, two weeks later, were injected i.p. with the 20,000 mw PEG-TNF once a week, for three weeks. Cure was defined as the percent of animals surviving five times longer than untreated animals. Results are presented in Table 5 and indicate that the modified TNF of this invention is effective in treating melanoma tumors, kidney tumors, colon tumors, and breast tumors. 
     
       
         
               
             
               
               
               
               
               
               
             
               
               
               
               
               
               
             
           
               
                 TABLE 5 
               
             
             
               
                   
               
               
                 Identification of tumors most sensitive to TNF 
               
             
          
           
               
                   
                 Tumor Type 
                 Cell Line 
                   
                 Dose of PEG-TNF 
                 % cured 
               
               
                   
                   
               
             
          
           
               
                   
                 Kidney 
                 G401 
                 10 
                 IU 
                 80 
               
               
                   
                   
                   
                 30 
                 IU 
                 80 
               
               
                   
                 Colon 
                 HT29 
                 10 
                 IU 
                 40 
               
               
                   
                   
                   
                 30 
                 IU 
                 60 
               
               
                   
                   
                   
                 100 
                 IU 
                 80 
               
               
                   
                 Breast 
                 MCF7 
                 10 
                 IU 
                 0 
               
               
                   
                   
                   
                 30 
                 IU 
                 0 
               
               
                   
                   
                   
                 100 
                 IU 
                 20 
               
               
                   
                 Brain 
                 SW1088 
                 100 
                 IU 
                 0 
               
               
                   
                 Leukemia 
                 L1210 
                 100 
                 IU 
                 0 
               
               
                   
                 Hepatoma 
                 Hep3B 
                 100 
                 IU 
                 0 
               
               
                   
                   
               
             
          
         
       
     
     The results presented above are surprising for a number of reasons. First, there was no way to predict that modifying TNF with high molecular weight PEG would increase the circulating half-life of the TNF. Indeed, the clearance rate of proteins in general cannot be predicted based on their molecular weight. Second, although it had been previously shown that proteins modified with PEG circulate longer than proteins without PEG, it had not, to the inventor&#39;s knowledge, ever been shown or suggested that simply increasing the molecular weight of the PEG would can have a dramatic effect on the circulating half-life of the PEG protein. Third, it had not been previously shown or suggested that using 20,000-30,000 molecular weights of PEG would provide the optimal circulating half life. Fourth, it was unexpected that modification of TNF with high molecular weight PEG, although it decreases the in vivo activity of TNF in killing L-929 cells, would actually enhance the tumoricidal activity of the TNF in vivo. This is particularly surprising in view of the added stearic hindrance expected to be created by the high molecular weight modifier such that it would be unable to interact with TNF receptors. Finally, although one would have predicted that the modified TNF, because of its enhanced circulating half life, would have been even more toxic than the native TNF, this, surprisingly, was not the case. 
     Table 6, below, provides a comparison of the activity, half life, lethality and anti-tumor activity for native TNF, for PEG5000-modified TNF, as disclosed by Tstusumi et al., and for the preferred embodiment of this invention, PEG20,000-modified TNF. 
     
       
         
               
             
               
               
               
               
             
               
               
               
               
             
               
               
               
               
               
               
               
             
               
               
               
               
               
               
             
               
               
               
               
               
               
               
             
               
             
               
               
               
               
               
               
               
             
           
               
                 TABLE 6 
               
             
             
               
                   
               
               
                 Comparison of the Activities and Toxicities 
               
               
                 of Various PEG and Native TNF 
               
             
          
           
               
                   
                   
                 Tsutsumi&#39;s 
                 20,000 mw 
               
               
                   
                 Native TNF 
                 PEG-TNF 
                 PEG-TNF 
               
               
                   
                   
               
             
          
           
               
                 In vitro activity 
                 100% 
                 56% 
                 54-56% 
               
               
                 (L-929 Cell 
               
               
                 cytoxicity) 
               
             
          
           
               
                 Circulating half life 
                 20 
                 min 
                 3-5 
                 hours 
                 16-18 
                 days 
               
             
          
           
               
                 Lethality in Tumor 
                 20-70 
                 ug 
                 ND 
                 300 
                 ug 
               
               
                 free mice (LD 50 ) 
               
             
          
           
               
                 Mice with METH A 
                 1-2 
                 ug 
                 10 
                 ug 
                 300 
                 ug 
               
               
                 tumors 
               
             
          
           
               
                 Dose required to cure 50% of mice with tumors 
               
             
          
           
               
                 METH A sarcoma 
                 &gt;2 
                 ug 
                 10 
                 ug 
                 0.01 
                 ug 
               
               
                 B16 Melanoma 
                 &gt;2 
                 ug 
                 10 
                 ug 
                 0.01 
                 ug 
               
               
                   
               
             
          
         
       
     
     METHODS AND MATERIALS 
     In Vitro Cytotoxicity Assay 
     Materials
         L929 fibroblasts ATCC #CCL1 NCTC clone 929.   Dulbecco&#39;s Modified Essential Medium (DMEM) and Fetal Bovine   Serum (GIBCO Laboratories, Grand Island, N.Y. #16000-010)   Recombinant Human Tumor Necrosis Factor-α (TNF-α) (prepared in-house)   Microtiter Plate Reader (Molecular Devices Corp., Menlo Park, Calif., Emax)       

     Method B. Propagation of L929 Fibroblasts: 
     Cells were grown in DMEM supplemented with 10% Fetal Bovine Serum Incubate overnight in a 37° C., 5% CO 2  humidified incubator. Cells were planted in a 96 well plates (3,000 cells/well in 0.15 ml of DMEM containing Fetal Bovine Serum. After 24 hours of growth, TNF or PEG TNF was added to the wells and the plates were incubated an additional 24 hours the viability of the cells was determined by adding 20 μl of 3[4,5-dimethylthiazol-2-yl]-2,5-diphenyltetrazolium bromide (MTT) (25 mg/ml in phosphate buffered saline pH 7.4) to each well of the culture plate and incubating the cultures at 37° C. for four hours. After that time, the culture supernatents were discarded and 150 μl of DMSO was added to each well. The absorbance of each well at 570 nm was determined using a micro titer plate reader. Wells that exhibit an A 540  closest to 50% of the arithmetic mean of the control are considered to represent 50% lysis (1 unit) of the L929 cells. 
     Determination of Circulating Half Life of PEG-TNF 
     Materials
         ELISA Kits from Genzyme (Cambridge, Mass.),       

     Methods 
     The Elisa kits were used as suggested by the manufacturer. Serum samples were collected from retro orbital plexus using heparinized 50 μl capillary tubes. A pretreatment blood sample was collected just prior to i.v. injection with TNF or PEG-TNF formulations. Additional blood samples were collected at 30 minutes, 24 hours as well as 3, 7, 12 and 15 days post-treatment. The samples were centrifuged and the resulting supematant was stored frozen at −20° C. until being assayed.