Wound healing using IGF-II and TGF
This is a continuation of copending application Ser. No. 07/530,649, filed May 30, 1990, now abandoned; which in turn is a continuation-in-part of U.S. Ser. No. 196,975, filed May 20, 1988, now U.S. Pat. No. 4,983,581. 
    
    
     BACKGROUND OF THE INVENTION 
     This invention relates to healing wounds. 
     Growth factors are polypeptide hormones which stimulate a defined population of target cells. Examples of growth factors include platelet-derived growth factor (PDGF), insulin-like growth factor (IGF-I), transforming growth factor beta (TGF-β), transforming growth factor alpha (TGF-α), epidermal growth factor (EGF), and fibroblast growth factor (FGF). 
     TGF-β is a multifunctional regulatory polypeptide synthesized by many cell types and sequestered in human platelets in amounts similar to PDGF. The in vitro biological effects of TGF-β are dependent upon the presence of other growth factors: TGF-β in the presence of PDGF stimulates fibroblast growth, and in the presence of EGF inhibits fibroblasts (Roberts, et al. Proc. Natl. Acad. Sci, USA 82:119). TGF-β inhibits proliferation of epithelial cells in vitro (Shipley et al., 1986, Cancer Res. 46:2068), and in vivo stimulates DNA, total protein, and collegen synthesis when injected into wound chambers (Sporn et al., 1986, Science 219:1329). The breaking strength of incisional wounds increases in a dose dependent manner after application of TGF-β (Mustoe, et al., Science 237:1333). 
     IGF-I is synthesized de novo in the liver and secreted into the plasma. In vitro, IGF-I can promote DNA synthesis in both mesenchymal and epithelial cells (Van Wyk 1984, Hormonal Proteins and Peptides, Li, ed.). Addition of IGF-I in vivo by itself does not promote wound healing, but when added with PDGF the combination stimulates connective tissue and epithelial and bone cell proliferation (Lynch, et al., 1987, Proc. Natl. Acad. Sci., USA 84:7696, Lynch et al., 1987, J. Clin. Periodontol. 16:545). 
     SUMMARY OF THE INVENTION 
     In one aspect, the invention features healing an external wound in a mammal, e.g., a human patient, by applying to the wound an effective amount of a composition that includes a combination of purified TGF-β and purified IGF-I. Preferably, the TGF-β is human TGF-β, but can also be of another mammalian species, e.g., porcine. The TGF-β can be isolated from natural sources (e.g., platelets) or, more preferably, produced by recombinant cells. 
     In a second aspect, the invention features regenerating bone of a mammal, e.g., a human patient, by administering to the patient, preferably by application to the area of injured or depleted bone, an effective amount of a composition that includes purified Insulin-like growth factor-I and purified transforming growth factor beta. The composition aids in regeneration, at least in part, by promoting the growth of bone cells and bone matrix. Bone regeneration using the composition of the invention is more effective than that achieved in the absence of treatment (i.e., without applying exogenous agents) or by treatment with purified Insulin-like growth factor-I or purified transforming growth factor beta alone. 
     In preferred embodiments of this aspect of the invention, the composition is prepared by combining purified IGF-I and TGF-β. Most preferably, purified IGF-I and TGF-β are combined in a weight-to-weight ratio of between 25:1 and 1:25, preferably between 2:1 and 1:2, and more preferably 2:1 or 1:1. 
     In a third aspect, the invention features healing an external wound and regenerating bone of a mammal, e.g., a human patient, by applying an effective amount of a wound healing and bone regenerating composition including purified Insulin-like growth factor-II (IGF-II) and purified transforming growth factor beta. 
     In preferred embodiments of this aspect of the invention, the composition is prepared by combining purified IGF-II and TGF-β. Most preferably, purified IGF-II and TGF-β are combined in a weight-to-weight ratio of between 25:1 and 1:25, preferably between 2:1 and 1:2, and more preferably 2:1 or 1:1. 
     The term &#34;purified&#34; as used herein refers to IGF-I, IGF-II, or TGF-β which, prior to mixing with the other component, is 95% or greater, by weight, IGF-I, IGF-II, or TGF-β, i.e., is substantially free of other proteins, lipids, and carbohydrates with which it is naturally associated. 
     A purified protein preparation will generally yield a single major band on a polyacrylamide gel for each IGF-I, IGF-II, or TGF-β component. Most preferably, the purified IGF-I, IGF-II, or TGF-β used in the composition is pure as judged by amino-terminal amino acid sequence analysis. 
     IGF-I, IGF-II, and TGF-β are all commercially available and may be obtained using recombinant DNA technology or by solid phase peptide synthesis. The purified TGF-β may be obtained from human platelets or by recombinant DNA technology. Thus, by the terms &#34;IGF-I&#34;, &#34;IGF-II&#34;, &#34;TGF-β&#34;, we mean both platelet-derived and recombinant materials of mammalian, preferably primate, origin; most preferably, the primate is a human, but can also be a chimpanzee or other primate. Recombinant TGF-β can be recombinant monomer or homodimer, made by inserting into cultured prokaryotic or eukaryotic cells a DNA sequence encoding a subunit, and then allowing the translated subunits to be processed by the cells to form a homodimer. 
     The compositions of the invention provide a fast, effective method for healing external wounds of mammals, e.g., bed sores, lacerations and burns, and for regenerating bone, e.g., injured, infected, or malignant bone. The compositions enhance connective tissue formation compared to natural healing (i.e., with no exogenous agents added) or pure IGF-I, IGF-II, or TGF-β alone. The compositions promote a significant increase in new epithelial tissue and promote the synthesis of total protein and collagen. The epithelial layer obtained is thicker than that created by natural healing or by TFG-β alone, and also contains more epithelial projections connecting it to the new connective tissue; it is thus more firmly bound and protective. The compositions also promote significant increase in new bone formation, especially adjacent root and periosteal surfaces. 
     Other features and advantages of the invention will be apparent from the following description of the preferred embodiments thereof, and from the claims. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     We now describe preferred embodiments of the invention. 
     External wounds, e.g., bed sores and burns, or bone wounds following injury, infection, or malignancy, are treated, according to the invention, with IGF-I/TGF-β or with IGF-II/TGF-β. Recombinant human IGF-I is commercially available from Amgen Biologicals (Thousand Oaks, Calif.). IGF-II, also known as multiplication-stimulating activity, is commercially available from ICN Biomedicals (Cleveland, Ohio). Purified human and porcine TGF-β are commercially available from R&amp;D Systems, Inc. (Minnesota, Minn.). 
     TGF-β was purified from human or porcine platelets by the method of Assoian (1983, J. Biol. Chem. 258: 7155). Briefly, platelet-rich plasma (20-30 units, 2-5 days old) was centrifuged (3200×g 30 min, at 4° C.) to remove plasma proteins. The platelets were then washed twice in 500 ml portions of Tris-HCl/citrate buffer, and recentrifuged. The washed platelets were then added to a solution of acid ethanol and then immediately extracted in a homogenizer. After incubation overnight at 4° C., precipitated proteins were removed by centrifugation and the supernatant adjusted to pH 3 using NH 4  OH. TGF-β was precipitated by addition of ethanol (2 volumes at 0° C.) and ethyl ether (4 volumes at 0° C.). The precipitate was collected by centrifugation and suspended in 1M acetic acid (10 ml). The supernatant was separated from the precipitate by centrifugation and placed on a Bio-Gel P60 gel filtration column (4.4×115 cm), with a flow rate of 20 ml/hr, equilibrated in 1M acetic acid. Five milliliter fractions were collected and assayed for biological activity using growth inhibition of BALB/MK cells and anchorage-independent growth of non-neoplastic NRK fibroblasts. Fractions containing peak activity were pooled, lyophilized, and redissolved in 0.5 ml of 1M acetic acid containing 8M ultra-pure urea (Schwartz/Mann) and gel filtered at a flow rate of 3 ml/hr on a Bio-Gel P60 column (1.6×85 cm). Aliquots of column fractions were tested for TGF-β activity as described above. Fractions containing peak TGF-β activity were pooled, dialized against 1M acetic acid to remove urea, and added to a C-18 (synchropak) HPLC column in 0.1% triflouroacetic acid and eluted with a 20-50% acetonitrile gradient. Biologically active fractions were pooled, and final purity checked by SDS-PAGE and amino acid analysis for known properties of TGF-β. 
     Recombinant TGF-β can be prepared by standard techniques. For example, oligonucleotide probes designed on the basis of the protein sequence of TGF-β can be used for the isolation of TGF-β exons in a human genomic DNA or a cDNA library, using the technique described in Birynch (1985, Nature 316: 701). The gene for TGF-β is isolated, cloned into standard expression vectors, and transfected into mammalian cells, from which TGF-β is then purified using standard methods. 
     WOUND HEALING 
     To determine the effectiveness of IGF-I/TGF-β or IGF-II/TGF-β mixtures in promoting wound healing, the following experiments were performed. 
     Young white Yorkshire pigs (Parson&#39;s Farm, Hadley, Mass.) weighing between 10 and 15 kg were fasted for at least 6 hours prior to surgery and then anesthetized. Under aseptic conditions, the back and thoracic areas were clipped, shaved, and washed with mild soap and water. The area to be wounded was then disinfected with 70% alcohol. 
     Wounds measuring 1 cm×2 cm were induced at a depth of 0.5 mm using a modified Castroviejo electrokeratome (Storz, St. Louis, Mo., as modified by Brownells, Inc.). The wounds resulted in complete removal of the epithelium, as well as a portion of the underlying dermis (comparable to a second degree burn injury). Individual wounds were separated by at least 15 mm of unwounded skin. Wounds receiving identical treatment were organized as a group and separated from other groups by at least 3 cm. Wounds receiving no growth factor treatment were separated from wounds receiving such treatment by at least 10 cm. 
     The wounds were treated directly with a single application of the following growth factors suspended in biocompatible gel: 1) 500 ng pure human or porcine TGF-β; 2) 500 ng pure recombinant IGF-I alone; 3) 500 ng human or porcine TGF-β plus 500 ng pure recombinant IGF-I. 
     Following wounding, biopsy specimens were taken on days 3 through 10. Biopsy specimens for histologic evaluation were taken as wedges approximately 3 mm deep and placed in 10% formalin. Specimens for biochemical analysis were obtained using an electrokeratome. The final dimensions of the specimens were 1.5 mm×10 mm×1.5 mm. Three specimens per wound were collected for biochemical analysis. Following collection, the specimens ere frozen in liquid Nitrogen and stored at -80° C. 
     HISTOLOGIC EVALUATION 
     Histologic specimens were prepared using standard paraffin impregnating and embedding techniques. Four micron sections were made and stained using filtered Harris hemotoxylin and alcoholic eosin; they were then observed under a microscope. Computer-aided morphometric analyses were performed. The area of the new epithelial and connective tissue layers were assessed with the aid of a customized program (need details) for determining areas of histological specimens. 
     COLLAGEN DETERMINATION 
     The specimens for biochemical analysis were thawed and the newly synthesized wound tissue dissected from the surrounding tissue under a dissecting microscope. The samples were hydrolyzed in 6M HCl at 120° C. for 18 hours in sealed ampoules. Assay of the hydrolysate for hydroxyproline, an amino acid unique to collagen was then performed using the technique of Switzer and Summer, 1971, Anal. Biochem. 39:487. 
     RESULTS 
     The results from histologic evaluation indicated that wounds treated with TGF-β had a thinner epithelial layer than wounds receiving no treatment. In contrast, wounds treated with the combination of purified human or porcine TGF-β and recombinant human IGF-I had thicker connective tissue and epithelial layers, and more extensive epithelial projections connecting these layers, than wounds receiving no treatment, human or porcine TGF-β alone, or pure IGF-I alone. The IGF-I plus TGF-β-treated wounds also had greater total collagen content, as indicated by increased hydroxyproline, than wounds treated with TGF-β alone, IGF-I alone, or gel alone. 
     BONE REGENERATION 
     To determine the effectiveness of TGF-β/IGF-I preparations in promoting periodontium and/or bone growth, the following experiments may be performed. 
     Beagle dogs with naturally occurring periodontal disease are selected on the basis of an initial radiographic examination. The teeth which exhibit 30% to 80% bone loss are initially scaled using ultrasonic instruments. Surgical flaps and root planing techniques are then performed, and the experimental teeth are treated with a composition containing purified TGF-β and IGF-I in a pharmaceutically acceptable carrier substance, e.g., commercially available inert gels, e.g., methyl cellulose. Teeth in the remaining quadrants receive control gel alone, or pure TGF-β or IGF-I alone. Block biopsies of the teeth and bone are taken periodically following surgery and prepared for histologic evaluation using standard demineralizing and processing techniques. Histologic analysis of periodontal and bone specimens will indicate whether, adjacent to the root surfaces of experimental specimens (i.e., those treated with the TGF-β/IGF-I combination), distinct areas of new bone formation are present and whether a deposit resembling cementum is present on the root surface adjacent to the new bone. New bone may also be present on the periosteal surface of the specimens. In addition, abundant proliferation of osteoblast-like cells may be present adjacent to the newly formed bone and newly formed collagen fibers may insert into the newly formed cementum. 
     In contrast, the control specimens may appear as follows: there will be little evidence of new bone formation, an absence of new cementum-like deposits, and connective tissue may be oriented perpendicular to the bony surface appearing to form a &#34;cap&#34; over the original bone. 
     An IGF-II/TGF-β composition may be tested for effectiveness in healing wounds and regenerating bones by replacing IGF-I with IGF-II in the IGF/TGF-β composition described above. 
     DOSAGE 
     To determine the appropriate dosage of purified TGF-β, the above-described wound healing experiments were repeated except that the wounds were treated with 2.5 ng, 5.0 ng, and 10 ng of purified TGF-β per square millimeter of wound dispersed in 30 μl of biocompatible gel. The results showed that optimum effects were produced when the TGF-β content of a IGF-I/TGF-β mixture was 5.0 ng/mm 2  or higher. 
     To determine the optimal ratio of IGF-I to TGF-β, combinations in which the weight to weight ratio of IGF-I to TGF-β ranged from 25:1 to 1:25 were evaluated as described above. Optimum results were achieved with a ratio of between 2:1 and 1:2. 
     To determine the optimal ratio of IGF-I to TGF-β, combinations in which the weight to weight ratio of IGF-I to TGF-β range from 25:1 to 1:25 can be evaluated as described above for bone regeneration experiments. 
     To determine the optimal ratio of IGF-II to TGF-β, combinations in which the weight to weight ratio of IGF-II to TGF-β ranged from 25:1 to 1:25 can be evaluated as described above. 
     OTHER EMBODIMENTS 
     Other embodiments are within the following claims. For example, IGF-I, IGF-II, and TGF-β can be obtained by standard recombinant DNA technology using nucleic acid having a base sequence identical to that of the naturally occurring gene encoding IGF-I, IGF-II, or TGF-β in a human or other mammal. Further, this nucleic acid may be modified by conservative base substitutions such that it encodes the same amino acid sequence of naturally occurring IGF-I, IGF-II, or TGF-β; or modified with base substitutions which encode a different amino acid sequence to that naturally occurring, but the protein product of which has substantially the same wound healing properties as the naturally occurring proteins.