# Patent

## Title
Tropoelastins and uses thereof

## Abstract

The present invention relates to biocompatible polymeric scaffold materials, methods for making the materials and methods of using the materials. More particularly, the present invention relates to implants and grafts comprising polymeric scaffold materials of cross-linked human tropoelastin polypeptides and methods of making and using the same. In addition, the present invention provides alternatively spliced tropoelastin polynucleotides and polypeptides.

## Background
CROSS REFERENCE TO RELATED APPLICATIONS
This application claims the benefit under 35 U.S.C. §119(e) of U.S. Provisional Application No. 61/451,696, filed Sep. 30, 2011, which is incorporated by reference herein in its entirety.


STATEMENT REGARDING SEQUENCE LISTING
The Sequence Listing associated with this application is provided in text format in lieu of a paper copy, and is hereby incorporated by reference into the specification. The name of the text file containing the Sequence Listing is DERM—001 —01 US_ST25.txt. The text file is 369 KB, was created on Dec. 28, 2012, and is being submitted electronically via EFS-Web.
BACKGROUND
1. Technical Field
The present invention generally relates to tropoelastin polynucleotides and polypeptides and methods of making and using the same to prepare biocompatible polymeric scaffold materials. More particularly, the present invention relates to alternative spliced tropoelastin isoforms, and to implants and grafts comprising polymeric scaffold materials of cross-linked human tropoelastin polypeptides and methods of making and using the same.
2. Description of the Related Art
Regenerative medicine has the potential to repair or replace any diseased cell, tissue, or organ; thus revolutionizing the practice of medicine. One important goal of regenerative medicine is to repair, maintain, improve or even restore the function of damaged or diseased cells, tissues, and organs. However, to date, there have a limited number of successful examples applying these concepts in a human clinical setting. In addition, many of compositions and materials used in regenerative medicine are currently cost-prohibitive, inefficient, and/or unsafe.
Surgical means have been used to regenerate tissue in a certain, controlled manner. Common reasons for surgical intervention include, a fractured bone, the regeneration of new tissue to replace tissue lost due to traumatic or surgical causes or an infection, atrophy or for congenital reasons. Success of surgical interventions often requires that the affected tissue be separated from other tissues surrounding it and that around the tissue a certain space is created, to which tissue can regenerate.
The inadequacy of existing polymeric graft materials has constantly been challenged by the development of new materials, particularly those with more favorable physical properties. The use of polyurethane biomaterials has been limited by questions surrounding long-term stability of implanted materials. The combined susceptibility of polyurethanes to hydrolysis, cracking, enzymatic degradation, calcification and corrosion to varying degrees depending on the formulation (Santerre et al., (2005), Biomaterials, 26, 7457-70) has led to doubts regarding biostability and bi-product toxicity. The problems faced by polyurethane biomaterials are common to this field.
Currently available biocompatible membranes also lack ideal shapeability and rigidity. These two properties of biocompatible membranes are contrary to each other. For example, a biocompatible membrane must naturally be shaped to fit the tissue structure in such a manner that it separates the tissues from each other exactly as desired so as to allow the regenerating tissue to grow in the correct shape with no damage to the surrounding tissue. On the other hand, the membrane must be sufficiently rigid that its shape does not change under the pressure caused by the growing tissue or that possible external stress does not cause a movement hampering the healing of the tissue. The prior art does not provide a satisfactory solution to fulfilling both requirements.
For example, synthetic biocompatible membranes made of expanded polytetrafluoroethylene (ePTFE) such as GoreTex®, Impra, or Atrium have increased rigidity when supported by titanium support threads or other metal alloys. Such membranes are often rigid and therefore keep their form well under the pressure of tissue, but correspondingly, their shaping is arduous. In contrast shaping support thread-free PTFE membranes is quite easy, but their rigidity is not sufficient. Another significant problem with such membranes is that they require surgical removal from the organ system after the tissue has healed. Surgical removal of such membranes increases patient costs, discomfort, and adds to the patient's risk of obtaining an infection from the operation.
Biocompatible membranes made of biodegradable polymers need not be surgically removed from the organ system, as they dissipate slowly from the organ system via normal biochemical and metabolic pathways. A significant problem with biodegradable materials is that the thin, easily shaping membranes are not rigid enough to maintain space for the regenerating tissue to grow undisturbed. Thus, there is a significant risk the membrane bends under pressure against the healing tissue so that there is insufficient space for the regenerating tissue to adequately grow. To achieve sufficient rigidity, the membrane can naturally be made thicker. However, when the thickness of the membrane is increased to achieve a sufficient rigidity, the membrane becomes so thick that shaping it is very difficult and arduous.
It is clear that there is a large unmet need in regenerative medicine for a more biocompatible, durable, and clinically effective polymeric biomaterial. The compositions, implants, and methods of the present invention address these needs and offer other related advantages.
BRIEF SUMMARY
The present invention generally provides biocompatible polymeric scaffold materials comprising novel tropoelastin compositions, methods for making the materials and methods of using the materials.
In various embodiments, the present invention provides implants and grafts comprising polymeric scaffold materials of cross-linked human tropoelastin polypeptides. In various other embodiments, methods of making polymeric scaffold materials are provided. In addition, the present invention provides alternatively spliced tropoelastin polynucleotides and polypeptides and compositions comprising the same.
In various embodiments, the present invention contemplates, in part, a method for repairing, replacing, or regenerating an injured or damaged tissue comprising: providing an amount of one or more tropoelastin polypeptides; casting the tropoelastin polypeptides into a desired shape to form a scaffold; culturing cells on the shaped tropoelastin polymer scaffold to form an implant; and providing the implant to a subject; thereby repairing, replacing, or regenerating the injured or damaged tissue.
In one embodiment, at least one of the one or more tropoelastin polypeptides comprises an alternatively spliced tropoelastin polypeptide.
In a particular embodiment, at least one or more alternatively spliced tropoelastin polypeptides comprises an amino acid sequence as set forth in any one of SEQ ID NOs: 2-48.
In an additional embodiment, at least one or more alternatively spliced tropoelastin polypeptides comprises an amino acid sequence as set forth in any one of SEQ ID NOs: 13, 47, and 48.
In a certain embodiment, at least one or more alternatively spliced tropoelastin polypeptides comprises an amino acid sequence as set forth in SEQ ID NOs: 13.
In a further embodiment, the at least one or more alternatively spliced tropoelastin polypeptides comprises an N-terminal or C-terminal truncation of 1, 2, 3, 4, 5, 6, 7, 8, 9, or 10 amino acids.
In a particular embodiment, the tissue is selected from the group consisting of: odontic tissue, periodontal tissue, pancreatic tissue, neural tissue, cardiac tissue, bone marrow, muscle tissue, bone tissue, skin tissue, liver tissue, hair follicles, vascular tissue, adipose tissue, lung tissue, retinal tissue, corneal tissue, and kidney tissue.
In one embodiment, the scaffold comprises one or more co-polymers.
In another embodiment, the scaffold comprises one or more resorbable co-polymers.
In yet another embodiment, the scaffold comprises one or more non-resorbable co-polymers.
In still yet another embodiment, the scaffold comprises both a resorbable and a non-resorbable co-polymer.
In a certain embodiment, the one or more co-polymers comprises a collagen protein.
In a certain particular embodiment, the desired shape is a three dimensional shape
In another certain particular embodiment, the desired shape is a sheet or a tube.
In an additional particular embodiment, the cells comprise stem cells, progenitor cells, and/or differentiated cells.
In various embodiments, the present invention contemplates, in part, a method for making an implant comprising: providing an amount of one or more tropoelastin polypeptides; casting the tropoelastin polypeptides into a desired shape to form a scaffold; culturing cells on the shaped tropoelastin polymer scaffold to form an implant.
In one embodiment, at least one of the one or more tropoelastin polypeptides comprises an alternatively spliced tropoelastin polypeptide.
In a particular embodiment, at least one or more alternatively spliced tropoelastin polypeptides comprises an amino acid sequence as set forth in any one of SEQ ID NOs: 2-48.
In a certain embodiment, at least one or more alternatively spliced tropoelastin polypeptides comprises an amino acid sequence as set forth in any one of SEQ ID NOs: 13, 47, and 48.
In an additional embodiment, at least one or more alternatively spliced tropoelastin polypeptides comprises an amino acid sequence as set forth in SEQ ID NOs: 13.
In a further embodiment, the at least one or more alternatively spliced tropoelastin polypeptides comprises an N-terminal or C-terminal truncation of 1, 2, 3, 4, 5, 6, 7, 8, 9, or 10 amino acids.
In one embodiment, the scaffold comprises one or more co-polymers.
In another embodiment, the scaffold comprises one or more resorbable co-polymers.
In yet another embodiment, the scaffold comprises one or more non-resorbable co-polymers.
In still yet another embodiment, the scaffold comprises both a resorbable and a non-resorbable co-polymer.
In a further particular embodiment, the one or more co-polymers comprises a collagen protein.
In an additional particular embodiment, the desired shape is a three dimensional shape
In a certain particular embodiment, the desired shape is a sheet or a tube.
In one embodiment, the cells are stem/progenitor cells.
In a further embodiment, the stem/progenitor cells are selected from the group consisting of: bone marrow stem/progenitor cells, umbilical cord stem/progenitor cells, adipose tissue derived stem/progenitor cells, hematopoietic stem/progenitor cells (HSGs), mesenchymal stem/progenitor cells, muscle stem/progenitor cells, liver stem/progenitor cells, pancreatic stem/progenitor cells, skin stem/progenitor cells, neural stem/progenitor cells, kidney stem/progenitor cells, osteoblast stem/progenitor cells, and chondrocyte stem/progenitor cells
In an additional embodiment, the cells comprises one or more of odontic cells, periodontic cells, gingival cells, pancreatic islet cells, CNS cells, PNS cells, cardiac muscle cells, skeletal muscle cells, smooth muscle cells, hematopoietic cells, bone cells, liver cells, an adipose cells, renal cells, lung cells, chondrocyte, skin cells, keratinocytes, fibroblasts, follicular cells, vascular cells, epithelial cells, immune cells, and endothelial cells.
In various other embodiments, the present invention contemplates, in part, an implant comprising: a biocompatible polymer scaffold comprising one or more tropoelastin polypeptides; one or more populations of cells; and a co-polymer polypeptide, wherein the implant is substantially endotoxin free.
In a particular embodiment, at least one of the one or more tropoelastin polypeptides comprises an alternatively spliced tropoelastin polypeptide.
In an additional embodiment, the at least one or more alternatively spliced tropoelastin polypeptides comprises an amino acid sequence as set forth in any one of SEQ ID NOs: 2-48.
In a certain embodiment, the at least one or more alternatively spliced tropoelastin polypeptides comprises an amino acid sequence as set forth in any one of SEQ ID NOs: 13, 47, and 48.
In a further embodiment, the at least one or more alternatively spliced tropoelastin polypeptides comprises an amino acid sequence as set forth in SEQ ID NOs: 13.
In a particular additional embodiment, the at least one or more alternatively spliced tropoelastin polypeptides comprises an N-terminal or C-terminal truncation of 1, 2, 3, 4, 5, 6, 7, 8, 9, or 10 amino acids.
In a certain additional embodiment, the one or more co-polymers comprises a collagen protein.
In a further additional embodiment, the scaffold is cast into a desired shape.
In another further additional embodiment, the desired shape is a three dimensional shape.
In one embodiment, the cells are stem/progenitor cells.
In another embodiment, the stem/progenitor cells are selected from the group consisting of: bone marrow stem/progenitor cells, umbilical cord stem/progenitor cells, adipose tissue derived stem/progenitor cells, hematopoietic stem/progenitor cells (HSGs), mesenchymal stem/progenitor cells, muscle stem/progenitor cells, liver stem/progenitor cells, pancreatic stem/progenitor cells, skin stem/progenitor cells, neural stem/progenitor cells, kidney stem/progenitor cells, osteoblast stem/progenitor cells, and chondrocyte stem/progenitor cells
In yet another embodiment, the cells comprises one or more of odontic cells, periodontic cells, gingival cells, pancreatic islet cells, CNS cells, PNS cells, cardiac muscle cells, skeletal muscle cells, smooth muscle cells, hematopoietic cells, bone cells, liver cells, an adipose cells, renal cells, lung cells, chondrocyte, skin cells, keratinocytes, fibroblasts, follicular cells, vascular cells, epithelial cells, immune cells, and endothelial cells.
In various embodiments, the present invention contemplates, in part, a polynucleotide comprising a nucleotide sequence as set forth in any one of SEQ ID NOs: 50-86 or a variant thereof.
In a particular embodiment, the polynucleotide has a nucleotide sequence that is at least 95% identical to a nucleotide sequence as set forth in any one of SEQ ID NOs: 50-86.
In another particular embodiment, the polynucleotide encodes a tropoelastin polypeptide as set forth in any one of SEQ ID NOs: 2-48.
In a certain particular embodiment, at least one or more alternatively spliced tropoelastin polypeptides comprises an amino acid sequence as set forth in any one of SEQ ID NOs: 13, 47, and 48.
In an additional particular embodiment, the at least one or more alternatively spliced tropoelastin polypeptides comprises an amino acid sequence as set forth in SEQ ID NOs: 13.
In a further particular embodiment, the polynucleotide encodes a tropoelastin polypeptide that has an amino acid sequence that is at least 95% identical to an amino acid sequence as set forth in any one of SEQ ID NOs: 2-48.
In one embodiment, the nucleotide sequence is codon optimized for expression in Escherichia coli, yeast, or insect cells.
In various embodiments, the present invention contemplates, in part, a polypeptide encoded by a polynucleotide.
In one embodiment, the polypeptide comprises one or more amino acid substitutions, deletions, or insertions.
In a particular embodiment, the polypeptide comprises an N-terminal or C-terminal truncation of 1, 2, 3, 4, 5, 6, 7, 8, 9, or 10 amino acids.
In a certain embodiment, the polypeptide comprises a C-terminal truncation of 1, 2, 3, 4, 5, 6, 7, 8, 9, or 10 amino acids.



BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS
FIG. 1 shows an SDS PAGE analysis of tropoelastin expression. Lane 1 is a molecular weight marker; lane 2 is uninduced E. coli host cultures; and lanes 3-8 are induced E. coli host cultures. The arrow identifies the region of the gel corresponding to tropoelastin having a molecular weight (MW) of 62,000 Daltons.
FIG. 2 shows a chromatographic profile of tropoelastin protein purification.
FIG. 3 shows SEM images that illustrate the self-assembly and subsequent formation of tropoelastin fibers up to 30 μm in length in the presence of a succinimide-PEG crosslinking reaction.



BRIEF DESCRIPTION OF THE SEQUENCE IDENTIFIERS
SEQ ID NOs: 1-48 represent amino acid sequences of tropoelastin polypeptides.
SEQ ID NOs: 49-87 represent polynucleotide sequences of tropoelastin cDNAs.
DETAILED DESCRIPTION
All publications, patents and patent applications cited herein, whether supra or infra, are hereby incorporated by reference in their entirety.
The articles “a,” “an,” and “the” are used herein to refer to one or to more than one (i.e. to at least one) of the grammatical object of the article. By way of example, “an element” means one element or more than one element.
As used herein, the term “about” or “approximately” refers to a quantity, level, value, number, frequency, percentage, dimension, size, amount, weight or length that varies by as much as 15%, 10%, 9%, 8%, 7%, 6%, 5%, 4%, 3%, 2% or 1% to a reference quantity, level, value, number, frequency, percentage, dimension, size, amount, weight or length. In one embodiment, the term “about” or “approximately” refers a range of quantity, level, value, number, frequency, percentage, dimension, size, amount, weight or length±15%, ±10%, ±9%, ±8%, ±7%, ±6%, ±5%, ±4%, ±3%, ±2%, or ±1% about a reference quantity, level, value, number, frequency, percentage, dimension, size, amount, weight or length.
Throughout this specification, unless the context requires otherwise, the words “comprise”, “comprises” and “comprising” will be understood to imply the inclusion of a stated step or element or group of steps or elements but not the exclusion of any other step or element or group of steps or elements. By “consisting of” is meant including, and limited to, whatever follows the phrase “consisting of.” Thus, the phrase “consisting of” indicates that the listed elements are required or mandatory, and that no other elements may be present. By “consisting essentially of” is meant including any elements listed after the phrase, and limited to other elements that do not interfere with or contribute to the activity or action specified in the disclosure for the listed elements. Thus, the phrase “consisting essentially of” indicates that the listed elements are required or mandatory, but that no other elements are optional and may or may not be present depending upon whether or not they affect the activity or action of the listed elements
Reference throughout this specification to “one embodiment” or “an embodiment” means that a particular feature, structure or characteristic described in connection with the embodiment is included in at least one embodiment of the present invention. Thus, the appearances of the phrases “in one embodiment” or “in an embodiment” in various places throughout this specification are not necessarily all referring to the same embodiment. Furthermore, the particular features, structures, or characteristics may be combined in any suitable manner in one or more embodiments.
As noted above, the invention generally relates to alternatively spliced tropoelastins, and their production and use in biocompatible polymeric scaffold materials for regenerative medicine. The materials are shapeable into various forms, including, but not limited to sheets, tubes, and any other three-dimensional spatial pieces. The shapeable scaffolds are used in constructing grafts and implants to provide aspects of regenerative medicine and promote regeneration by repairing, replacing or restoring damaged tissues or organs.
An objective in the development of bioengineered materials for regenerative medicine is the generation of polymer scaffolds with desirable properties, including strength, elasticity, and biocompatibility. The use of natural or near-natural starting materials in the manufacture of polymer scaffolds with low resorption has the advantages of providing an established level of performance and congruence. Implants and grafts comprising such scaffolds are more biocompatible, last longer, provide a more efficient means of regeneration, and are less toxic than existing biomaterials. An important example of a natural polymer scaffold with low or slow resorption is human elastin. Elastin is one of the most abundant protein polymers in organs that require flexibility as part of their essential functions, including the skin, lungs, blood vessels, and bladder, among others.
Elastin is a polymer of tropoelastin. However, to date only a single form of tropoelastin has been studied and its properties characterized. The present inventors have discovered that many forms of tropoelastin exist in the human body. Clearly, an advantage exists for the human body to have evolved such a complex of multiple tropoelastin forms. These different forms differ in tensile strength, elasticity, stiffness, cross-linking potential, ability to attract populating cells (chemotaxis) and wound healing properties. In various embodiments, fibers composed of two or more tropoelastin isoforms display different and unique properties compared to those fibers composed of a single isoform.
Thus, one significant advantage of the invention is the development of elastins with unique properties, e.g., tensile strength, elasticity, and flexibiltiy/stiffness, generated by combining 2, 3, 4, 5, 6, 7, 8, 9, 10 or more individual tropoelastin isoforms, themselves having unique properties. Such unique elastins can be tailored for use at locations in the body where their unique properties are the most advantageous. For example, the strongest fibers can be used to repair muscles, the most elastic fibers can be used to construct bladders and other flexible organs, e.g, blood vessels, and the stiffest fibers can be used in cartilage repair.
A. Elastin
The elastin protein polymer is synthesized from tropoelastin monomers, soluble polypeptides of about 72 kDa (Parks et al., Am. J. Respir. Cell Mol. Biol. 2:399, 1990). During elastin synthesis, newly synthesized tropoelastin monomers are secreted into the extracellular space, assembled into functional fibers, and cross-linked to form insoluble elastin. Following secretion, tropoelastin monomers self-associate in a process called coacervation, which arises from hydrophobic interactions. Coacervation concentrates and aligns tropoelastin for cross-linking and is a precursor to fiber formation (fibrillogenesis). Fibrillogenesis takes place at unique sites close to the cell membrane where tropoelastin is secreted within microfibrillar bundles surrounding the cell. Lysyl oxidase then oxidizes terminal amino groups on lysine residues and cross-links form as the oxidized side chains undergo condensation reactions.
Elastin has been used in combination with other supporting components to form biocompatible structures. Elastin, digested from animal sources has been combined with gelatin, collagen (Buttafoco et al., (2006) Biomaterials, 27, 724-34) and polymers such as poly(lactide-co-glycolide) (Stitzel et al., (2006) Biomaterials, 27, 1088-94) using electrospinning and producing fibers with improved tensile characteristics. Elastin from porcine arteries has also been used as the scaffold for a graft material, reinforced by physically wrapping the construct with small intestinal submucosa (essentially decellularized collagen) (Hinds et al., (2006) J. Biomed. Mater. Res. Part A, 77, 458-69). However, these materials are limited by the low quality and supply of animal elastin, infectious organisms associated with animal tissue sources, and also by the thrombogenicity of the supporting material.
B. Tropoelastin
The human tropoelastin gene has been isolated and the sequence has been determined (Indik et al., P.N.A.S. USA (1987), 84, pp. 5680-5684; Indik et al., Connect. Tissue Res. (1987), 16; pp. 197-211). The human tropoelastin gene has at least 34 separate exons spanning a total of 45 kbp of genomic DNA. Previously, others have identified alternative splicing of 6 of the 34 exons, which leads to at least 11 alternatively spliced protein isoforms (e.g., polymorphic polypeptides) of human tropoelastin (Boyd et al. Matrix (1991), 11; pp. 235-241; Shapiro, Am. J. Respir. Crit. Care Med. (1994) 150; pp. S160-S164; Fazio et al. J. Invest. Dermatol. (1988), 91; pp. 458-464; Fazio et al. Lab. Invest. (1988), 58; pp. 270-277). Applicants have conducted a detailed polymorphism analysis of tropoelastin mRNAs obtained from four independent human fibroblast cell lines revealed the presence of many different exon mRNA polymorphisms (see, e.g., Example 1). Illustrative tropoelastin polypeptides, including alternatively spliced tropoelastins and tropoelastins having point mutations, are set in SEQ ID NOs: 2-48. Illustrative polynucleotides sequences that represent tropoelastin cDNAs are set in SEQ ID NOs: 50-86.
The various polymorphic forms of tropoelastin can interact in ways that enhance specific roles of the resulting fiber. For example, some forms can provide a higher degree of elasticity, while other forms can promote hydrophobic interactions, increased tensile strength or chemotaxis by skin cells. These different forms can display unique affinities for cell surface receptors or in their ability to bind other proteins during fibrillogenesis. For example, particular tropoelastin polymorphisms affect the tensile strength in vascular tissue. In addition, carotid artery elasticity parameters (distensibility and elastic modulus) correlates with the presence of a particular elastin polymorph. Individuals carrying this polymorph show a decrease in distensibility and an increase in the elastic modulus of the carotid artery, linking the elasticity and tensile strength of tissues to the presence of specific elastin polymorphisms.
C. Biocompatible Polymer Scaffolds
In various embodiments, a biocompatible polymer scaffold with desirable properties, including, but not limited to strength, elasticity and biocompatibility comprises one or more tropoelastin polypeptides, as discussed elsewhere herein. As used herein, the terms “tropoelastin,” “tropoelastin polypeptides,” “tropoelastin polymorphic polypeptides,” “tropoelastin polymorphs,” “alternatively spliced tropoelastin polypeptides,” “alternatively spliced tropoelastin isoforms,” and “tropoelastin protein isoforms” refer to any of a variety of different isolated or recombinant human tropoelastin polypeptides, e.g., SEQ ID NOs: 2-48, encoded by “normally” spliced mRNAs, alternatively spliced tropoelastin mRNAs or tropoelastin mRNAs comprising polymorphic exons or single nucleotide polymorphisms (SNPs), as well as fusion proteins thereof. In various embodiments, the term “tropoelastin polypeptides,” includes “normally” spliced tropoelastin, alternatively spliced tropoelastin, and variants and fragments thereof. The normally spliced form of tropoelastin includes all exons and for purposes of comparison, is set forth in SEQ ID NO: 1. A full length tropoelastin cDNA including 5′ and 3′ UTR and all exons is set forth in SEQ ID NO: 87. Additional illustrative embodiments of tropoelastin polypeptides includes the amino acid sequences set forth in SEQ ID NOs: 2-48.
In particular preferred embodiments, compositions and methods of the present invention comprise one or more tropoelastin polypeptides having an amino acid sequence as set forth in SEQ ID NO: 2-48, including variants thereof.
In particular embodiments, the polypeptides and biocompatible scaffolds are “endotoxin free.” As used herein, the term “endotoxin free” refers to compositions that contain at most trace amounts (i.e., amounts having no adverse physiological effects to a subject) of endotoxin, and preferably undetectable amounts of endotoxin. In one embodiment, the term “endotoxin free” or “substantially endotoxin free” refers to a composition that is at least 95%, at least 96%, at least 97%, at least 98%, at least 99%, or 100% endotoxin free. In one embodiment, the term “endotoxin free” refers to endotoxin levels or an endotoxin profile that may be less than about 0.001, 0.005, 0.01, 0.02, 0.03, 0.04, 0.05, 0.06, 0.08. 0.09, 0.1, 0.5, 1.0, 1.5, 2, 2.5, 3, 4, 5, 6, 7, 8, 9, or 10 endotoxin units (EU)/ml or EU/mg. Typically, 1 ng lipopolysaccharude (LPS) corresponds to about 1-10 EU.
In other embodiments, non-human tropoelastin may be employed; however, it is generally desirable to match the species of animal being treated to the species of the tropoelastin being used to ensure biocompatability.
In particular embodiments, a non-human tropoelastin polypeptide is isolated from; or a non-human tropoelastin cDNA is obtained from a bovine, an equine, a sheep, a goat, a pig, a dog, a cat, rodent, or a non-human primate.
In a preferred embodiment, the tropoelastin polypeptides are human.
In another preferred embodiment, the present invention provides human tropoelastins codon optimized for recombinant expression in various hosts, methods for recombinantly producing the codon optimized tropoelastins, and the recombinant tropoelastin polypeptides for use in preparing biocompatible polymer scaffolds.
Various properties of the polymer scaffold that can affect the strength, elasticity, cross-linking potential and other physical and biochemical behavior of tropoelastin polymers, include, but are not limited to, the number and identity of the tropoelastin polymorphs in the scaffold, co-polymers included in the tropoelastin polymer scaffold, the thickness and/or shape of the scaffold, and the degree of cross-linking, among others.
In one embodiment, the polymer scaffolds are tailored to suit particular needs in the human body. The properties of the scaffold are tailored by incorporation of tropoelastin isoforms having different properties in tensile strength, elasticity, and flexibility/rigidity. In this way, the scaffold can be reliably designed for a particular purpose. For example, highly flexible elastin can be used in the construction of vascular structures (e.g., veins and arteries). The ability of elastin polymers to attract the growth of capillaries and promote the population of the scaffolds by the migration and growth of nearby cells (chemotaxis) are an important advantage of the invention in the context of wound healing.
Mechanical tests, such as uniaxial tensile testing, ultimate stresses and linear moduli parameters, yield and failure energies, and other tests (e.g., creep tests) known to those skilled in the art can be used to determine the mechanical characteristics of the devices.
1. Number and Identity of Tropoelastin Polymorphs
In particular embodiments, a scaffold comprises a single type of tropoelastin polypeptide, or a combination of tropoelastin polypeptides. The combination of tropoelastin polypeptides can comprise 1, 2, 3, 4, 5, 6, 7, 9, 10, or more, different types of tropoelastin polypeptides. In another particular embodiment, the scaffold can comprise at least 1, at least 2, at least 3, at least 4, at least 5, at least 6, at least 7, at least 8, at least 9, at least 10 or more, different tropoelastin polypeptides. In another particular embodiment, the scaffold can comprise 1 or more, 2 or more, 3 or more, 4 or more, 5 or more, 6 or more, 7 or more, 8 or more, 9 or more, or 10 or more different types of tropoelastin polypeptides, e.g., SEQ ID NOs: 2-48.
In certain embodiments, a scaffold comprises a single tropoelastin polypeptide, such as an alternatively spliced tropoelastin, or a combination of alternatively spliced tropoelastin polypeptides, wherein the tropoelastin polypeptides are human. In other certain embodiments, the tropoelastin polypeptides are any number or combination of human, non-human primate, bovine, an equine, a sheep, a goat, a pig, a dog, a cat, or rodent tropoelastin polypeptides.
In other particular embodiments, suitable tropoelastin polypeptides for use in manufacturing biocompatible polymer scaffolds include tropoelastin polypeptides, polypeptides encoded by alternatively spliced tropoelastin mRNAs, polypeptides encoded by tropoelastin mRNAs with one or more polymorphic exons and/or amino acid mutations, and genetically engineered tropoelastin polypeptides (e.g., fusion polypeptides) including any of the foregoing tropoelastin polypeptides.
Furthermore, one having ordinary skill in the art would appreciate that varying the ratio and/or identity of each of the tropoelastin polymorphs present in a combination can generate tropoelastin-based scaffolds with desired elasticity, tensile strength, and shapeability. For example, polymers based on particular combinations of tropoelastin exons that resulted in 3 different polymorphic forms, displayed tensile strength and elasticity reflecting the presence or absence of certain portions of the tropoelastin molecules. Thus, the strength, elasticity, cross-linking potential and other physical and biochemical behavior of tropoelastin polymers can be varied and possibly controlled by incorporating various polymorphic forms of tropoelastin into polymeric scaffolds.
In another embodiment, the ratio and/or identity of each of the tropoelastin polymorphs present in a combination can be varied so as to match the tropoelastin polymorphs present in the tissue being repaired, replaced, or regenerated.
2. Co-Polymers
In particular embodiments, a biocompatible polymer scaffold comprises one or more tropoelastin polypeptides and a co-polymer. An exemplary and in some cases preferred co-polymer is collagen. The presence and association of tropoelastin with collagen in biocompatible polymer scaffolds can significantly increase the durability of the scaffolds and decrease the rate of collagen degradation and resorption, which is a major advance and benefit over current collagen membranes. In one embodiment, the co-polymer is resorbable. In another embodiment, the co-polymer is non-resorbable. In a particular embodiment, the scaffold comprises one or more resorbable and non-resorbable co-polymers and one or more tropoelastin polypeptides.
In particular embodiments, a collagen co-polymer suitable for use in the biocompatible polymer scaffolds, includes, but is not limited to Collagen Type I, Collagen Type II, Collagen Type III, Collagen Type IV, Collagen Type V, Collagen Type VI, Collagen Type VII, Collagen Type VIII, Collagen Type IX, Collagen Type X, Collagen Type XI, Collagen Type XII, Collagen Type XIII, Collagen Type XIV, Collagen Type XV, Collagen Type XVI, Collagen Type XVII, Collagen Type XVIII, Collagen Type XIX, Collagen Type XX, Collagen Type XXI, Collagen Type XXII, Collagen Type XXIII, Collagen Type XXIV, Collagen Type XXV, Collagen Type XXVI, Collagen Type XXVII, Collagen Type XXVIII, and Collagen Type XXIX.
In other particular embodiments, the collagen co-polymer is selected from the group consisting of Collagen Type I, Collagen Type II, Collagen Type III, and Collagen Type IV.
In other particular embodiments, the collagen co-polymer is selected from the group consisting of: Collagen Type I and Collagen Type III.
In other particular embodiments, the collagen co-polymer is Collagen Type I and/or Collagen Type III.
In other embodiments, a biocompatible polymer scaffolds comprises one or more tropoelastin polypeptides in combination with 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, or more collagens
One having skill in the art would appreciate that varying the ratio and/or identity of tropoelastin polypeptides and collagen co-polymers in a biocompatible polymer scaffold can generate scaffolds with desired elasticity, tensile strength, and shapeability and/or to match the tropoelastins and collagens present in the tissue being repaired, replaced, or regenerated.
In particular embodiments, exemplary molar ratios of tropoelastin to collagen include about 10:1, about 9:1, about 8:1, about 7:1, about 6:1, about 5:1, about 4:1, about 3:1, about 2:1, about 1:1, about 1:2, about 1:3, about 1:4, about 1:5, about 1:6, about 1:7, about 1:8, about 1:9, about 1:10 or any intervening ratio.
Other co-polymers suitable for use in particular embodiments, include hyaluronic acid, hyaluronates, chitosan, chitosan derivatives, polyrotaxane, polyrotaxane derivatives, polyglycolic acid, chitin, chitin derivatives, gelatin, fibronectin, heparin, laminin, and alginate
In particular embodiments, suitable co-polymers are resorbable synthetics including, but not limited to, polylactone, polylcaprolactone, polylactic acid, polyglycolic acid, or any combination thereof.
In certain embodiments, suitable copolymers are non-resorbable synthetics, including, but not limited to, metals, e.g., titanium, stainless steel, nickel, aluminum alloys, and alloys of nickel-iron, or any combination there of; ceramics e.g., silicon and silicon oxide, or any combination there of; plastics, e.g., polypropylene (PP), polystyrene (PS), nylon, high impact polystyrene (HIPS), acrylonitrile butadiene styrene (ABS), polyethylene terephthalate (PET), poly(vinyl chloride) (PVC), polyurethanes (PU), polycarbonate (PC), polyvinylidene chloride (PVDC), polyethylene (PE), polycarbonate/acrylonitrile butadiene styrene (PC/ABS), polymethyl methacrylate (PMMA), polytetrafluoroethylene (PTFE), and polyetheretherketone (PEEK), or any combination there of; and rubbers, e.g., polybutadiene, chloro isobutylene isoprene, polychloroprene, chlorosulphonated polyethylene, epichlorohydrin, epichlorohydrin, ethylene propylene, ethylene propylene diene, ethylene vinyl acetate, fluoronated hydrocarbon, hydrogenated nitrile butadiene, polyisoprene, isoprene butylene butyl, butadiene acrylonitrile, polyurethane, styrene butadiene, and poly-siloxane, or any combination there of.
3. Casts/Molds
In particular embodiments, a biocompatible polymer scaffold is formed into a desired shape, for example by casting in a mold or electrospinning. One having ordinary skill in the art would appreciate that the preferred shape will depend, in part, the particular tissue or organ being repaired, replaced, or regenerated.
In a certain embodiment, a biocompatible polymer scaffold is formed in a subject, in a wound or in an area of space wherein new tissue is needed. In particular embodiments, one or more cell populations may be mixed with one or more tropoelastin polypeptides and the implant formed in vivo. In another embodiment, the implants are formed from molds in vitro or ex vivo. In related embodiments, the mixture comprises a co-polymer, e.g., a collagen polypeptide.
Exemplary molds and casts can be formed from many different materials or their combinations including, but not limited to, metals, ceramics, plastics, rubbers, glass, and fiberglass. In one embodiment, the mold is formed from plastic or metal.
Illustrative examples of metals include, but are not limited to, titanium, stainless steel, nickel, aluminum alloys, and alloys of nickel-iron, or any combination there of.
Illustrative examples of ceramics include, but are not limited to, silicon and silicon oxide, or any combination there of.
Illustrative examples of plastics include, but are not limited to, polypropylene (PP), polystyrene (PS), nylon, high impact polystyrene (HIPS), acrylonitrile butadiene styrene (ABS), polyethylene terephthalate (PET), poly(vinyl chloride) (PVC), polyurethanes (PU), polycarbonate (PC), polyvinylidene chloride (PVDC), polyethylene (PE), polycarbonate/acrylonitrile butadiene styrene (PC/ABS), polymethyl methacrylate (PMMA), polytetrafluoroethylene (PTFE), and polyetheretherketone (PEEK), or any combination there of.
Illustrative examples of rubbers include, but are not limited to, polybutadiene, chloro isobutylene isoprene, polychloroprene, chlorosulphonated polyethylene, epichlorohydrin, epichlorohydrin, ethylene propylene, ethylene propylene diene, ethylene vinyl acetate, fluoronated hydrocarbon, hydrogenated nitrile butadiene, polyisoprene, isoprene butylene butyl, butadiene acrylonitrile, polyurethane, styrene butadiene, and poly-siloxane, or any combination there of.
Exemplary desired shapes of the biocompatible polymer scaffold, include, but are not limited to sheets, tubes, any other three dimensional shape. Scaffolds formed in the shape of a sheet can be used in the preparation of implants and grafts to provide reparative, replacement, and/or regenerative therapy for dermal tissues, membranes for tooth root coverage procedures, membranous tissues (e.g., dura mater), and the like. Scaffolds formed in the shape of a tube can be used in the preparation of implants and grafts to provide reparative, replacement, and/or regenerative therapy for arteries, veins, ureters, urethras, nerves, long bones, and the like. Scaffolds formed in the shape of any other three dimensional can be used in the preparation of implants and grafts to provide reparative, replacement, and/or regenerative therapy for organ transplants, bone remodeling or mending, dental implants, or for muscle, tendon, ligament, and cartilage grafts.
A biocompatible polymer scaffold formed, cast, or molded in the shape of a sheet, can be a flat sheet, or a sheet having curvatures to closely match the contours of the injured, damaged, or diseased tissue or organ being repaired, replaced, or regenerated. The sheets may be of any geometrical shape, including but not limited to squares, rectangles, trapezoids, triangles, circles, ellipses, and the like.
Exemplary areas of the sheets include areas of about 1 mm2 to about 1 m2, about 1 mm2 to about 50 cm2, about 1 mm2 to about 25 cm2, about 1 mm2 to about 10 cm2, about 1 mm2 to about 1 cm2, about 1 cm2 to about 1 m2, about 1 cm2 1 cm2 to about 500 cm2, 1 cm2 to about 250 cm2, 1 cm2 to about 200 cm2, 1 cm2 to about 150 cm2, to about 100 cm2, about 1 cm2 to about 50 cm2, about 1 cm2 to about 25 cm2, about 1 cm2 to about 10 cm2, about 1 cm2 to about 5 cm2, about 1 cm2 to about 2.5 cm2, about 10 mm2 to about 10 cm2, about 0.1 cm2 to about 10 cm2, about 0.1 cm2 to about 1 cm2, or any intervening range thereof. For example, the range of areas of 1 cm2 to 100 cm2 of an exemplary sheet includes about areas of about 1 cm2, about 5 cm2, about 10 cm2, about 20 cm2, about 30 cm2, about 40 cm2, about 50 cm2, about 60 cm2, about 70 cm2, about 80 cm2, about 90 cm2, and about 100 cm2.
Exemplary degrees of thickness of a biocompatible polymer scaffold formed, cast, or molded in the shape of a sheet, include a range of about 0.1 mm to about 10 mm, about 0.25 mm to about 7.5 mm, about 0.5 mm to about 5 mm, about 0.75 mm to about 2.5 mm, about 1 mm to about 2 mm or any intervening range thereof.
In another embodiment, the thickness can be about 0.1 mm, about 0.25 mm, about 0.5 mm, about 0.75 mm, about 1 mm, about 2 mm, about 3 mm, about 4 mm, about 5 mm, about 7.5 mm, or about 10 mm or more.
A biocompatible polymer scaffold formed, cast, or molded in the shape of a tube, can have any desired length, diameter, and thickness such that the size of the scaffold is suitable to repair, replace, and/or regenerate an injured, damaged, or diseased tissue or organ.
Exemplary lengths of the tube include about 0.5 cm, about 1 cm, about 2.5 cm, about 5 cm, about 10 cm, about 25 cm, about 50 cm, about 100 cm, about 150 cm, about 200 cm, about 250 cm, about 300 cm, about 350 cm, about 400 cm, about 450 cm, about 500 cm, or longer.
Exemplary diameters of the tube include about 0 mm (e.g., a solid fiber), 0.5 mm, about 1 mm, about 1.5 mm, about 2 mm, about 2.5 mm, about 3 mm, about 3.5 mm, about 4 mm, about 4.5 mm, about 5 mm, about 5.5 mm, about 6 mm, about 6.5 mm, about 7 mm, about 7.5 mm, about 8 mm, about 8.5 mm, about 9 mm, about 9.5 mm, about 10 mm, about 11 mm, about 12 mm or more mm in diameter. In a preferred embodiment, a tube of the invention has about 1 mm to about 10 mm diameter.
A biocompatible polymer scaffold formed, cast, or molded in the shape of other three dimensional objects can have any desired volume and/shape such that the size of the scaffold is suitable to repair, replace, and/or regenerate an injured, damaged, or diseased tissue or organ.
Exemplary volumes of the three dimensional shape scaffolds of about 100 mm3 to about 5 m3, about 100 mm3 to about 1000 cm3, about 1 cm3 to about 1000 cm3, about 1 cm3 to about 100 cm3, about 1 cm3 to about 10 cm3, about 10 cm3 to about 1000 m3, about 10 cm3 to about 100 cm3, about 500 cm3 to about 1000 cm3, about 100 mm3 to about 5 cm3, about 100 mm3 to about 2.5 cm3, about 1 cm3 to about 5 cm3, about 1 cm3 to about 2.5 cm3, about 750 cm3 to about 1250 cm3, about 850 cm3 to about 1150 cm3, about 950 cm3 to about 1050 cm3, about 900 cm3 to about 1000 cm3, or any intervening range thereof. For example, the range of volumes of 1 cm3 to 10 cm3 of an exemplary three dimensional shape includes about volumes of about 1 cm3, about 2 cm3, about 3 cm3, about 4 cm3, about 5 cm3, about 6 cm3, about 7 cm3, about 8 cm3, about 9 cm3, and about 10 cm3.
4. Polymer/Co-Polymer Cross-Linking Agents
In particular embodiments, polymer/co-polymer cross-linking agents agent are employed to modulate the porosity, hardness, density, rigidity, and/or elasticity of the biocompatible polymer scaffold.
In particular embodiments, the cross-linking agent is an enzyme. Exemplary enzymatic cross-linking agents include, but are not limited to, any lysyl oxidase capable of converting epsilon amines to adipic semi-aldehydes or through the enzyme catalysis of transglutaminase.
In other particular embodiments, the cross-linking agent is a chemical cross-linking agent. Exemplary chemical cross-linking agents include, but are not limited to, bipyridylruthenium(II) in the presence of ammonium persulfate and visible light, tris-Cobalt-60 γ-irradiation, Arthromyces ramosus peroxidase treatment, pyrroloqinoline quinone in the presence of copper, methacrylamide anhydride, dimethyl adipimidate, bis(sulfosuccinimidyl)suberate (BS3), 1-Ethyl-3-[3-dimethylaminopropyl]carbodiimide Hydrochloride) (EDC), glutaraldehyde, N-hydroxysuccinimide) (NHS), NHS-polyethylene glycol (NHS-PEG), NHS-PEG-NHS, and 1,6-diisocyanatohexane (HMDI) and combinations thereof.
Cross-linking may be performed at the time the scaffold is being cast. For example, cross-linking agents can be added to a tropoelastin polypeptide composition just prior to molding, at the time the scaffold is being molded, or after molding of the scaffold is completed.
In another embodiment, a modified version of tropoelastin polypeptide is provided which is not susceptible to cross-linking. The tropoelastin polypeptide may not be susceptible to cross-linking for a number of reasons including, mutating one or more lysine residues in the tropoelastin polypeptide. The high degree of cross-linking found in the elastic fibers contributes to their proper function. Lysyl oxidase is the enzyme that catalyzes the oxidative deamination of lysine residues leading to the non-enzymatic condensation of the modified lysine side chains. This same enzyme is involved in collagen cross-link formation as well. All but about 5 of the 34 lysine residues of tropoelastin participate in some form of cross-link resulting in a highly insoluble polymer (Rosenbloom et al., FASEB J. (1993), 7: p. 1208).
Thus, by modulating the lysine available for cross-linking provides another method for modulating the porosity, hardness, density, rigidity, and/or elasticity of the biocompatible polymer scaffold.
5. Strength and Elasticity
In particular embodiments, a biocompatible polymer scaffold is formed with a desired strength and elasticity. One having ordinary skill in the art would appreciate that the preferred strength and elasticity will depend, in part, the particular tissue or organ being repaired, replaced, or regenerated.
Without being bound to any particular theory, the present invention contemplates, in part, that the static and dynamic mechanical properties, including, but not limited to strength and elasticity, of biocompatible polymer scaffold comprising tropoelastins, including, but not limited to, sheets and tubes, can approximate the static and dynamic mechanical properties of the native target tissue or biological end location.
In one non-limiting example, the mechanical parameters of the native target tissue, e.g., stress/strain characteristics, Young's modulus, yield point, and any other biologically relevant mechanical parameter can be modeled and matched by the tropoelastin scaffold.
Illustrative mechanical parameters of the biocompatible polymer scaffolds of the invention can be about 25% to about 125%, about 50% to about 100%, about 75% to about 100% of the mechanical parameters of the corresponding native tissue or any intervening range thereof. In one embodiment, the mechanical parameters of the biocompatible polymer scaffolds of the invention can be about 10%, 20%, 30%, 40%, 50%, 60%, 70%, 80%, 90%, 100%, 110%, 120%, or more of the mechanical parameters of the corresponding native tissue or any intervening percentage thereof.
However, in some circumstances lower values or higher values may be required and necessary for end use of the implant. For example, end device design characteristics may require higher yield point or failure point values than normal healthy tissue due to disease processes within the patient.
D. Implants and Grafts
In various embodiments, an implant or graft is provided to promote repair, replacement, and/or regeneration of a damaged, injured, or diseased tissue or organ.
In one embodiment, an implant or graft comprises a cast or formed biocompatible polymer scaffold and a population of cells. The implant or graft can comprise one or more cell populations that are seeded, grown, or cultured on the scaffold. The cell populations can be developmentally mature or restricted, developmentally potent or plastic, or a combination of the foregoing cell types. As used herein, the terms “implant” and “graft” are used interchangeably and refer to a biocompatible natural and/or synthetic polymer scaffold that has any of the characteristics described for scaffolds, supra or infra, one or more tropoelastin polymorphs and one or more of co-polymers, cell populations, and other polypeptides, e.g., cytokines, growth factors, etc.
In particular embodiments, an implant or graft comprises a biocompatible polymer scaffold that can be molded into any suitable form or shape, as described elsewhere herein throughout. In a certain embodiment, an implant or graft is formed in a subject, in a wound, or in an area of space wherein new tissue is needed. In particular embodiments, one or more cell populations may be mixed with one or more tropoelastin polymorphic polypeptides and the implant formed in vivo. In related embodiments, the mixture comprises a co-polymer, e.g., a collagen polypeptide.
Thus, implants or grafts comprising biocompatible polymer scaffolds comprising one or more tropoelastin polymorphs and one or more populations of cells growing thereon, can accelerate tissue growth and regeneration and participate as a reinforcing material in a newly constructed, cell-based tissue, which usually lack elastin during adult tissue regeneration. The presence of elastin would more closely resemble the provisional matrix that is created during the development of tissues in utero.
Sheet-like implants and grafts provide reparative, replacement, and/or regenerative therapy for dermal tissues, membranes for tooth root coverage procedures, membranous tissues (e.g., dura mater), flat bones (e.g., skull, breast-bone) and the like. Tubular implants and grafts provide reparative, replacement, and/or regenerative therapy for arteries, veins, ureters, urethras, nerves, long bones (e.g., femur, fibula, tibia, humerus, radius, ulna, metacarpals, metatarsals, etc.) and the like. Other three dimensional implants and grafts provide reparative, replacement, and/or regenerative therapy for organ transplants (e.g., liver, lung, skin, heart, pancreas, etc.), bone remodeling or mending of all types of bones, dental implants, or for muscle, tendon, ligament, and cartilage grafts.
The physical properties of the tropoelastin polymers can be modulated to create scaffolds of specific strengths, elasticity, and density. Thus, in certain embodiments, implants or grafts comprising biocompatible polymer scaffolds comprising one or more tropoelastin polypeptides and one or more populations of cells growing thereon are stable in vivo and will remain in a patient's body for up to 1, 2, 3, 4, 5, 10, 15 or more years.
In various embodiments, implants or grafts disclosed herein, comprise at least one cell or population of cells.
In particular embodiments, a cell or population of cells is cultured in or seeded onto a biocompatible polymer scaffold to form an implant or graft. Such implants or grafts can also include, by way of non-limiting example, cytokines, growth factors, hormones, or other compounds/agents that may provide therapeutic benefit in a method of repairing, replacing, or regenerating a tissue or organ.
Exemplary growth factors and cytokines include, but are not limited to, brain derived neurotropihic factor (BDNF), bone morphogenetic protein 2 (BMP-2), bone morphogenetic protein 6 (BMP-6), bone morphogenetic protein 7 (BMP-7), cardiotrophin 1 (BMP-2), CD22, CD40, ciliary neurotrophic factor (CNTF), CCL1-CCL28, CXCL1-CXCL17, XCL1, XCL2, CX3CL1, vascular endothelial cell growth factor (VEGF), epidermal growth factor (EGF), FAS-ligand, fibroblast growth factor 1 (FGF-1), fibroblast growth factor 2 (FGF-2), fibroblast growth factor 4 (FGF-4), fibroblast growth factor 5 (FGF-5), fibroblast growth factor 6 (FGF-6), fibroblast growth factor 1 (FGF-7), fibroblast growth factor 1 (FGF-10), Flt-3, granulocyte colony-stimulating factor (G-CSF), granulocyte macrophage stimulating factor (GM-CSF), hepatocyte growth factor (HGF), interferon alpha (IFN-a), interferon beta (IFN-b), interferon gamma (IFNg), insulin-like growth factor 1(IGF-1), insulin-like growth factor 2 (IGF-2), interleukin 1 (IL-1), interleukin 2 (IL-2), interleukin 3 (IL-3), interleukin 4 (IL-4), interleukin 5 (IL-5), interleukin 6 (IL-6), interleukin 7 (IL-7), interleukin 8 (IL-8), interleukin 9 (IL-9), interleukin 10 (IL-10), interleukin 11 (IL-11), interleukin 12 (IL-12), interleukin 13 (IL-13), interleukin 15 (IL-15), interleukin 17 (IL-17), interleukin 19 (IL-19), macrophage colony-stimulating factor (M-CSF), monocyte chemotactic protein 1 (MCP-1), macrophage inflammatory protein 3a (MIP-3a), macrophage inflammatory protein 3b (MIP-3b), nerve growth factor (NGF), neurotrophin 3 (NT-3), neurotrophin 4 (NT-4), platelet derived growth factor AA (PDGF-AA), platelet derived growth factor AB (PDGF-AB), platelet derived growth factor BB (PDGF-BB), platelet derived growth factor CC(PDGF-CC), platelet derived growth factor DD (PDGF-DD), RANTES, stem cell factor (SCF), stromal cell derived factor 1 (SDF-1), transforming growth factor alpha (TGF-a), transforming growth factor beta (TGF-b), tumor necrosis factor alpha (TNF-a), WntI, Wnt2, Wnt2b/13, Wnt3, Wnt3a, Wnt4, Wnt5a, Wnt5b, Wnt6, Wnt7a, Wnt7b, Wnt7c, Wnt8, Wnt8a, Wnt8b, Wnt8c, WntIOa, WntIOb, WntII, WntI4, WntI5, or WntI6, Sonic hedgehog, Desert hedgehog, and Indian hedgehog.
Exemplary hormones include, but are not limited to, Antimullerian hormone (or mullerian inhibiting factor or hormone), Adiponectin, Adrenocorticotropic hormone (or corticotropin), Angiotensinogen and angiotensin, Antidiuretic hormone (or vasopressin, arginine vasopressin), Atrial-natriuretic peptide (or atriopeptin), Calcitonin, Cholecystokinin, Corticotropin-releasing hormone, Erythropoietin, Follicle-stimulating hormone, Gastrin, Ghrelin, Glucagon, Gonadotropin-releasing hormone, Growth hormone-releasing hormone, Human chorionic gonadotropin, Human placental lactogen, Growth hormone, Insulin-like growth factor 1, Insulin-like growth factor (or somatomedin), Leptin, Luteinizing hormone, Melanocyte stimulating hormone MSH, Orexin, Oxytocin, Parathyroid hormone, Prolactin, Relaxin, Secretin, Somatostatin, Thrombopoietin, Thyroid-stimulating hormone (or thyrotropin), and Thyrotropin-releasing hormone.
In particular embodiments, implants or grafts comprise cells that are genetically modified to express increased amounts of a particular extracellular material, cytokine, and/or growth factor to promote or facilitate the repair, regeneration, or replacement of a tissue or organ.
Alternatively, or in addition, particular embodiments provide implants or grafts comprising cells that natively express the desired cytokine, and/or growth factor to promote or facilitate the repair, regeneration, or replacement of a tissue, or organ.
In another embodiment, an implant or grafts comprises a biocompatible polymer scaffold, a population of multipotent or pluripotent stem cells, and hormones, growth factors, cytokines, morphogens (e.g., retinoic acid etc), extracellular matrix materials (e.g., fibronectin, laminin, collagen, etc.) or other materials (e.g., DNA, viruses, other cell types, etc.) that facilitate the differentiation of the cell population along a particular developmental pathway once the implant has been implanted in the patient. Alternatively, or in addition, the cells may be differentiated in vitro during cell culturing with the biocompatible polymer scaffold.
In various embodiments, an implant or graft comprising the inventive biocompatible polymer scaffold and a population of cells growing thereon supports guided tissue engineering and regeneration in a patient or subject. Thus, the present invention contemplates, in part, to use an implant or graft comprising a biocompatible polymer scaffold in combination a population of cells cultured thereon, and incorporating any of the features disclosed herein. The exact nature of the implant (e.g., the size, shape, elasticity, strength, cell type growing thereon, etc.) will vary according to the use desired.
In various embodiments, methods of providing reparative, replacement, or regenerative therapy to a site in vivo comprises introducing the implant or grafts into the individual at or near the site of tissue or organ injury, wherein the regenerative, restorative, preventative, or ameliorative therapy is desired and/or required.
For example, an implant or grafts of the present invention can be implanted or grafted in odontic tissue, periodontic tissue, pancreatic tissue, neural tissue, cardiac tissue, bone marrow, muscle tissue, bone tissue, skin tissue, liver tissue, hair follicles, vascular tissue, adipose tissue, lung tissue, retinal tissue, corneal tissue, and kidney tissue, as required to direct the appropriate therapy.
E. Cells
Various embodiments provide implants or grafts comprising one or more population of cells. The population of cells may be made up of any number and/or combination of homogenous or heterogeneous cell types, as described elsewhere herein or that are known to those having ordinary skill in the art. Those having ordinary skill in the art would appreciate that any of the cell types discussed herein, supra or infra, are suitable for seeding, growing, or culturing said cells on particular biocompatible polymer scaffolds as discussed elsewhere herein throughout.
The cell populations can be isolated primary cells or cell lines, either of which may further comprise one or more genetic modifications and/or transgenes.
In preferred embodiments, the cell population comprises mammalian cells. Illustrative examples of mammals include bovines, equines, sheep, goats, pigs, dogs, cats, primates, and rodents.
In particular embodiments, a population of cells seeded on, growing on, and/or cultured on a biocompatible polymer scaffold, as described elsewhere herein throughout, comprises one or more cell types selected from the group consisting of: a stem cell, a progenitor cell, a reprogrammed cell, and a differentiated cell. In other embodiments, a population of cells seeded on, growing on, and/or cultured on a biocompatible polymer scaffold comprises a mixture or combination of stem cells, progenitor cells, and differentiated cells.
In one embodiment, the population of cells is selected from adult, neonatal, or embryonic stem/progenitor cells.
In particular embodiments, the population of cells is selected from the group consisting of: mesodermal stem/progenitor cells, endodermal stem/progenitor cells, and ectodermal stem/progenitor cells.
In related embodiments, the population of cells comprises a mesodermal stem/progenitor cell. Illustrative examples of mesodermal stem/progenitor cells include, but are not limited to mesodermal stem/progenitor cells, endothelial stem/progenitor cells, bone marrow stem/progenitor cells, umbilical cord stem/progenitor cells, adipose tissue derived stem/progenitor cells, hematopoietic stem/progenitor cells (HSGs), mesenchymal stem/progenitor cells, muscle stem/progenitor cells, kidney stem/progenitor cells, osteoblast stem/progenitor cells, chondrocyte stem/progenitor cells, and the like.
In other related embodiments, the population of cells comprises an ectodermal stem/progenitor cell. Illustrative examples of ectodermal stem/progenitor cells include, but are not limited to neural stem/progenitor cells, retinal stem/progenitor cells, skin stem/progenitor cells, and the like.
In other related embodiments, the population of cells comprises an endodermal stem/progenitor cell. Illustrative examples of endodermal stem/progenitor cells include, but are not limited to liver stem/progenitor cells, pancreatic stem/progenitor cells, epithelial stem/progenitor cells, and the like.
In certain embodiments, the population of cells includes a heterogeneous or homogeneous population of cells selected from the group consisting of: odontic cells, periodontic cells, gingival cells, pancreatic islet cells, CNS cells, PNS cells, cardiac muscle cells, skeletal muscle cells, smooth muscle cells, hematopoietic cells, bone cells, liver cells, an adipose cells, renal cells, lung cells, chondrocyte, skin cells, keratinocytes, fibroblasts, follicular cells, vascular cells, epithelial cells, immune cells, endothelial cells, and the like.
In certain other embodiments, the population of cells comprises a cell isolated from an in vivo tissue selected from the group consisting of: odontic tissue, periodontic tissue, gingival tissue, pancreatic tissue, neural tissue, cardiac tissue, bone marrow, muscle tissue, bone tissue, skin tissue, liver tissue, hair follicles, vascular tissue, adipose tissue, lung tissue, retinal tissue, corneal tissue, and kidney tissue. The cell isolate from the foregoing in vivo tissues can be an adult stem cell, progenitor cell, or somatic cell.
In certain other embodiments, the population of cells comprises a cell isolated from an in vivo tissue selected from the group consisting of: odontic tissue, periodontic tissue, and gingival tissue. In related embodiments, the population of cells comprises: gingival fibroblasts, periodontal ligament fibroblasts, osteoblasts, and osteoblast like cells.
In certain other embodiments, the population of cells comprises a cell isolated from bone marrow. In related embodiments, the population of cells comprises: bone marrow stromal cells, bone marrow stem cells, hematopoietic stem cells, and/or mesenchymal stem cells.
In certain other embodiments, the population of cells comprises a cell isolated from the skin of an individual. In related embodiments, the population of cells comprises: keratinocytes and/or fibroblasts.
In other illustrative embodiments, implants comprise cell populations obtained from a different donor (allogeneic), obtained from the individual to be treated (autologous), or obtained from an entirely different species (xenogeneic).
One of ordinary skill in the art is familiar with methods for isolating and culturing the different types of cells described herein (e.g., Embryonic Stem Cells: Methods and Protocols (Methods in Molecular Biology) (Kurstad Turksen, Ed., 2002); Embryonic Stem Cell Protocols: Volume I: Isolation and Characterization (Methods in Molecular Biology) (Kurstad Turksen, Ed., 2006); Embryonic Stem Cell Protocols: Volume II: Differentiation Models (Methods in Molecular Biology) (Kurstad Turksen, Ed., 2006); Human Embryonic Stem Cell Protocols (Methods in Molecular Biology) (Kursad Turksen Ed., 2006); Mesenchymal Stem Cells: Methods and Protocols (Methods in Molecular Biology) (Darwin J. Prockop, Donald G. Phinney, and Bruce A. Bunnell Eds., 2008); Hematopoietic Stem Cell Protocols (Methods in Molecular Medicine) (Christopher A. Klug, and Craig T. Jordan Eds., 2001); Hematopoietic Stem Cell Protocols (Methods in Molecular Biology) (Kevin D. Bunting Ed., 2008) Neural Stem Cells: Methods and Protocols (Methods in Molecular Biology) (Leslie P. Weiner Ed., 2008)).
Cells may be cultured in growth-promoting conditions, which can include any set of conditions (temperature, atmosphere, growth medium composition, humidity, degree of agitation, etc.) under which cells normally proliferate. None of these conditions are critical. The temperature should be near that of normal human body temperature (i.e., about 37° C.), but can be any temperature at which cells can proliferate (e.g., 30 to 43° C.). Cells can be grown in an air atmosphere, or an air atmosphere supplemented with 5% CO2, for example. The growth medium can be any liquid medium which contains nutrients and factors sufficient to support proliferation of cells. Such media contain, for example, a carbon source (e.g., glucose) and minimal essential nutrients, and preferably contain one or more of a mammalian serum (e.g., fetal calf serum), an antibiotic (e.g., penicillin or streptomycin), and L-glutamine (i.e., to improve amino acid supply for protein biosynthesis).
Mammalian serum can be used at a concentration of 1% to 20%, by volume, of the total growth medium. The serum is preferably pre-screened to ensure that it supports vigorous growth of cells; some lots, even lots provided from the same supplier, do not support vigorous growth of cells. Alternatively, the mammalian serum can be replaced with one or more growth factors (e.g., fibroblast growth factor, platelet derived growth factor, insulin growth factor, or endothelial growth factor). The growth medium can, for example, be Minimal Essential Medium-alpha without deoxyribonucleotides or ribonucleotides, supplemented with fetal calf serum, antibiotics, and L-glutamine; Dulbecco's minimal essential medium; and others well known to one of ordinary skill in the art. The growth medium is preferably replaced one or more times (e.g., every 3 or 4 days) during culture of the cells.
F. Polynucleotides
The present invention also provides isolated tropoelastin polynucleotides and polynucleotides encoding tropoelastin polypeptides (e.g., tropoelastin polymorphic polypeptides from alternatively spliced transcripts or transcripts having exon polymorphisms, tropoelastin fusion polypeptides) of the invention, as described elsewhere herein, e.g., SEQ ID NOs: 2-48. Isolated polynucleotides of the present invention, include, but are not limited to, alternatively spliced tropoelastin polynucleotides (e.g., alternatively spliced exons 2, 3, 5, 6, 8, 10, 11, 13, 17, 19, 20, 22, 23, 24, 25, 26, 28, 31, 32, and 33). In addition, Applicants identified partially deleted isoforms of that represent tropoelastin cDNAs, tropoelastin cDNAs comprising deleted or partially deleted exons (e.g., tropoelastin exons 2, 6, 8, 10, 17, 20, 24, 26, and 28), and engineered tropoelastin cDNAs, as described elsewhere herein e.g., SEQ ID NOs: 50-86. Fusion polynucleotides that encode fusion polypeptides are also included in the present invention, as described elsewhere herein.
As used herein, the terms “polynucleotide” or “nucleic acid” refers to messenger RNA (mRNA), RNA, genomic DNA (gDNA), complementary DNA (cDNA) or DNA. The term typically refers to polymeric form of nucleotides of at least 100, at least 200, at least 300, at least 400, at least 500, at least 600, at least 700, at least 800, at least 900, at least 1000, at least 1250, at least 1500, at least 1750, at least 2000, at least 2250, at least 2500, at least 2750, at least 3000, at least 3250, at least 3500, at least 3750, at least 4000 or more bases in length, or any intermediate length of either ribonucleotides or deoxynucleotides or a modified form of either type of nucleotide. The term includes single and double stranded forms of DNA. The term also includes sense, non-sense, antisense DNA strands, and plus and minus RNA strands.
In particular embodiments, polynucleotides are provided by this invention that encode at least about 50, 100, 200, 250, 300, 400, 500, 600, 625, 650, 675, 700, 725, 750, 800, or 822 or more contiguous amino acid residues of a polypeptide of the invention, as well as all intermediate lengths. It will be readily understood that “intermediate lengths,” in this context, means any length between the quoted values, such as 650, 651, 652, 653, 654, 655, 656, 657, 658, 659, 660, 661, 662, 663, 664, 665, 666, 667, 668, 669, 670, 671, 672, 673, 674, and 675, etc., 675, 676, 677, 678, 679, 680, 681, 682, 683, 684, 685, 686, 687, 688, 689, 690, 691, 692, 693, 694, 695, 696, 697, 698, 699, and 700, etc.; and 700, 701, 702, 703, 704, 705, 706, 707, 708, 709, 710, 711, 712, 713, 714, 715, 716, 717, 718, 719, 720, 721, 722, 723, 724, 725, 726, 727, 728, 729, and 730, etc.
As used herein, the terms “polynucleotide variant” and “variant” and the like refer to polynucleotides displaying substantial sequence identity with a reference polynucleotide sequence or polynucleotides that hybridize with a reference sequence under stringent conditions that are defined hereinafter. These terms also encompass polynucleotides that are distinguished from a reference polynucleotide by the addition, deletion or substitution of at least one nucleotide. Accordingly, the terms “polynucleotide variant” and “variant” include polynucleotides in which one or more nucleotides have been added or deleted, or replaced with different nucleotides.
In certain embodiments, a variant tropoelastin polynucleotide encodes a polypeptide having an amino acid sequence having at least about 50%, 55%, 60%, 65%, 70%, 75%, 80%, 85%, 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98% or more identical to a corresponding sequence of a tropoelastin reference polypeptide, as described herein, and substantially retains the desired properties of that reference polypeptide. Also included are tropoelastin polynucleotide sequences that encode tropoelastin polypeptides having 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 30, 40, 50, 60, 70, 80, 90, 100, 110, 120, 130, 140, 150 or more amino acids additions, deletions, or substitutions, and that substantially retain the desired properties of that reference polypeptide. In certain embodiments, tropoelastin polynucleotides encode tropoelastin polypeptides having additions or deletions that occur at the C-terminal end and/or the N-terminal end of the reference polypeptide. In certain embodiments, tropoelastin polynucleotides encode tropoelastin polypeptides having 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 30, 40, 50 N-terminal and/or C-terminal amino acid deletions or additions. In certain embodiments polynucleotide variants encode tropoelastin polypeptides comprising 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 30, 40, 50 N-terminal and/or C-terminal amino acid deletions.
In this regard, it is well understood in the art that certain alterations inclusive of mutations, additions, deletions and substitutions can be made to a reference polynucleotide whereby the altered polynucleotide retains the biological function or activity of the reference polynucleotide.
In various illustrative embodiments, the present invention provides isolated polynucleotides as set forth in SEQ ID NOs: 50-86 that encode tropoelastin polypeptides of the invention, including, but not limited to those polypeptides set forth in SEQ ID NOs: 2-48. Tropoelastin polypeptides of the invention are used to direct cell-based compositions to a particular cellular environment to repair, replace, restore and/or regenerate damaged or diseased mammalian cells, tissues and organs.
Polynucleotides can be synthesized using protocols known in the art as described in Caruthers et al., 1992, Methods in Enzymology 211, 3-19; Thompson et al., International PCT Publication No. WO 99/54459; Wincott et al., 1995, Polynucleotides Res. 23, 2677-2684; Wincott et al., 1997, Methods Mol. Bio., 74, 59-68; Brennan et al., 1998, Biotechnol Bioeng., 61, 33-45; and Brennan, U.S. Pat. No. 6,001,311.
Polynucleotides and fusions thereof may be prepared, manipulated and/or expressed using any of a variety of well established techniques known and available in the art. For example, polynucleotide sequences which encode polypeptides of the invention, or fusion proteins or functional equivalents thereof, may be used in recombinant DNA molecules to direct expression of a polypeptide of the present invention. The polynucleotides of the present invention, regardless of the length of the coding sequence itself, may be combined with other DNA sequences, such as 5′ and 3′ untranslated sequences (UTRs), promoters, polyadenylation signals, additional restriction enzyme sites, multiple cloning sites, other coding segments, and the like, such that their overall length may vary considerably. It is therefore contemplated that a polynucleotide fragment of almost any length may be employed; with the total length preferably being limited by the ease of preparation and use in the intended recombinant DNA protocol.
Moreover, it will be appreciated by those of ordinary skill in the art that, as a result of the degeneracy of the genetic code, there are many nucleotide sequences that encode a polypeptide, or fragment of variant thereof, as described herein. Some of these polynucleotides bear minimal homology to the nucleotide sequence of any native gene. As will be understood by those of skill in the art, it may be advantageous in some instances to produce polypeptide-encoding nucleotide sequences possessing non-naturally occurring codons. For example, codons preferred by a particular prokaryotic or eukaryotic host can be selected to increase the rate of protein expression or to produce a recombinant RNA transcript having desirable properties, such as a half-life which is longer than that of a transcript generated from the naturally occurring sequence. Moreover, the polynucleotide sequences of the present invention can be engineered using methods generally known in the art in order to alter polypeptide encoding sequences for a variety of reasons, including but not limited to, alterations which modify the cloning, processing, expression and/or activity of the gene product. Further, alleles of the genes comprising the polynucleotide sequences provided herein may also be used. Alleles are endogenous genes that are altered as a result of one or more mutations, such as deletions, additions and/or substitutions of nucleotides.
In order to express a desired polypeptide, a nucleotide sequence encoding the polypeptide, or a functional equivalent, may be inserted into appropriate expression vector, i.e., a vector which contains the necessary elements for the transcription and translation of the inserted coding sequence. Methods which are well known to those skilled in the art may be used to construct expression vectors containing sequences encoding a polypeptide of interest and appropriate transcriptional and translational control elements. These methods include in vitro recombinant DNA techniques, synthetic techniques, and in vivo genetic recombination.
Such techniques are described in the literature. See, e.g., Ausubel et al., Short Protocols in Molecular Biology, 3rd ed., Wiley & Sons, 1995; Sambrook and Russell, Molecular Cloning: A Laboratory Manual (3rd Edition, 2001; Maniatis et al. Molecular Cloning: A Laboratory Manual (1982); DNA Cloning: A Practical Approach, vol. I & II (D. Glover, ed.); Oligonucleotide Synthesis (N. Gait, ed., 1984); Nucleic Acid Hybridization (B. Hames & S. Higgins, eds., 1985); Transcription and Translation (B. Hames & S. Higgins, eds., 1984); Perbal, A Practical Guide to Molecular Cloning (1984).
G. Polypeptides
As noted above, the present invention, in certain aspects, provides for the prevention, treatment, cure, amelioration, or mitigation of disease or injuries in humans by the introducing implants comprising a biocompatible polymer scaffold that comprises one or more tropoelastin polypeptides, e.g., alternatively spliced tropoelastin polypeptides as disclosed herein, and one or more populations of cells. In particular embodiments, the present invention provides therapeutic implants comprising tropoelastin polypeptides and methods of using the same to effect tissue, and or organ regenerative, preventative, restorative, and/or ameliorative therapy.
As used herein, the terms “polypeptide,” “peptide,” and “protein” are used interchangeably, unless specified to the contrary, and according to conventional meaning, i.e., as a sequence of amino acids. Polypeptides are not limited to a specific length, e.g., they may comprise a full length protein sequence or a fragment of a full length protein, and may include post-translational modifications of the polypeptide, for example, glycosylations, acetylations, phosphorylations and the like, as well as other modifications known in the art, both naturally occurring and non-naturally occurring. Polypeptides can be prepared using any of a variety of well known recombinant and/or synthetic techniques, illustrative examples of which are further discussed below. Illustrative examples of tropoelastin polypeptides for use in the present invention are set forth in SEQ ID NOs: 2-48. Tropoelastins can be selected according to the desired elasticity, tensile strength, and shapeability and/or to match the tropoelastins and collagens present in the tissue being repaired, replaced, or regenerated.
Tropoelastin polypeptides are often alternatively spliced polypeptides. The present invention contemplates, in part, a core tropoelastin polypeptide comprising exons that are present in most, if not all isoforms. In one embodiment, the core tropoelastin comprises exons 1, 4, 7, 9, 12, 14, 15, 16, 18, 21, 27, 29, and 34. In another embodiment, the present invention contemplates, in part, a core tropoelastin polypeptide comprising one or more exons that are partially deleted, but that are also included in many tropoelastin polypeptide isoforms. In one embodiment, the core tropoelastin comprises exons 1, 4, 6B, 7, 9, 12, 14, 15, 16, 18, 21, 24B, 26A, 27, 29, and 34.
As used herein, the term “partially deleted exon” refers to a exon that has at least one long form and at least one short form; the short form comprising a partial deletion long form. The naming convention used herein, for partially deleted exons names the long form the “A form” and the short or partially deleted form, the “B form.” For example, exon 2A refers to the tropoelastin exon that begins at nucleotide position 83 and ends at nucleotide position 133 of SEQ ID NO: 49 and exon 2B refers to the tropoelastin exon that begins at nucleotide position 122 and ends at nucleotide position 133 of SEQ ID NO: 49. Illustrative partially deleted exons include exons 2A/B, 6A/B, 8A/B, 10A/B, 17A/B, 24A/B, 26A/B, and 28A/B.
As used herein, the term “tropoelastin fragment,” refers to a fragment, e.g., biologically active fragment, of a reference polypeptide sequence. In particular embodiments, tropoelastin fragments comprise at least about 50, 100, 200, 250, 300, 400, 500, 600, 625, 650, 675, 700, 725, 750, 800, or 822 or more contiguous amino acid residues of a polypeptide of the invention, as well as all intermediate lengths. It will be readily understood that “intermediate lengths,” in this context, means any length between the quoted values, such as 650, 651, 652, 653, 654, 655, 656, 657, 658, 659, 660, 661, 662, 663, 664, 665, 666, 667, 668, 669, 670, 671, 672, 673, 674, and 675, etc., 675, 676, 677, 678, 679, 680, 681, 682, 683, 684, 685, 686, 687, 688, 689, 690, 691, 692, 693, 694, 695, 696, 697, 698, 699, and 700, etc.; and 700, 701, 702, 703, 704, 705, 706, 707, 708, 709, 710, 711, 712, 713, 714, 715, 716, 717, 718, 719, 720, 721, 722, 723, 724, 725, 726, 727, 728, 729, and 730, etc.
Also included are tropoelastin polypeptides having 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 30, 40, 50, 60, 70, 80, 90, 100, 110, 120, 130, 140, 150 or more amino acids additions, deletions, or substitutions, and that substantially retain the desired properties of that reference polypeptide. In certain embodiments, tropoelastin polypeptides have additions or deletions that occur at the C-terminal end and/or the N-terminal end of the reference polypeptide. In certain embodiments, tropoelastin polypeptides having 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 30, 40, 50 N-terminal and/or C-terminal amino acid deletions or additions. In certain embodiments, tropoelastin polypeptides comprise 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 30, 40, 50 N-terminal and/or C-terminal amino acid deletions.
In various embodiments, the invention contemplates polypeptide fragments that retain at least one biological activity of tropoelastin. Fragments may also be selected according to the tropoelastin properties desired, e.g., desired elasticity, tensile strength, and shapeability and/or to match the tropoelastins and collagens present in a tissue being repaired, replaced, or regenerated.
Polypeptides include polypeptide variants. Polypeptide variants may differ from a naturally occurring polypeptide in one or more substitutions, deletions, additions and/or insertions. Such variants may be naturally occurring or may be synthetically generated, for example, by modifying one or more of the above polypeptide sequences used in the methods of the invention and evaluating their effects using any of a number of techniques well known in the art. Preferably, polypeptides of the invention include polypeptides having at least about 65%, 70%, 75%, 85%, 90%, 95%, 98%, or 99% amino acid identity thereto.
Further, the present invention contemplates, tropoelastin polypeptides comprising one or more, two or more, three or more, four or more, or five or more amino acid substitutions in polypeptides encoded by particular exons. Illustrative example of exons and corresponding amino acid substitutions with reference to the unsubstituted polypeptide sequence set forth in SEQ ID NO: 1, include, without limitation: exon 8A, glycine (G) arginine→ (R), glycine (G)→ alanine (A), glycine (G)→ valine (V); exon 14, valine (V)→ methionine (M); exon 15, alanine (A)→ proline (P), alanine (A)→ threonine (T); exon 16, isoleucine (I)→ valine (V); exon 17B, lysine (K)→ threonine(T), alanine (A)→ glycine (G), alanine (A)→ serine (S), lysine (K)→glutamine (Q); exon 18, glycine (G)→alanine (A), glycine (G)→ serine (S), valine (V)→isoleucine (I); exon 20B, glycine (G)→ serine (S); exon 21, proline (P)→ alanine (A); exon 23, proline (P)→ alanine (A), lysine (K)→ glutamate (E), phenylalanine (F)→ tyrosine (Y), glutamine (Q)→ histidine (H); exon 26A, arginine (R)→ glycine (G), glycine (G)→ arginine (R); and exon 29, alanine (A)→ valine(V).
In certain embodiments, a variant will contain conservative substitutions. A “conservative substitution” is one in which an amino acid is substituted for another amino acid that has similar properties, such that one skilled in the art of peptide chemistry would expect the secondary structure and hydropathic nature of the polypeptide to be substantially unchanged. Modifications may be made in the structure of the polynucleotides and polypeptides of the present invention and still obtain a functional molecule that encodes a variant or derivative polypeptide with desirable characteristics, e.g., with an ability to modulate, induce and/or maintain pluripotency as described herein. When it is desired to alter the amino acid sequence of a polypeptide to create an equivalent, or even an improved, variant polypeptide of the invention, one skilled in the art, for example, can change one or more of the codons of the encoding DNA sequence, e.g., according to Table 1.







TABLE 1







AMINO ACID CODONS














One
Three







letter
letter














Amino Acids
code
code
Codons
















Alanine
A
Ala
GCA
GCC
GCG
GCU


 


Cysteine
C
Cys
UGC
UGU




 


Aspartic acid
D
Asp
GAC
GAU




 


Glutamic acid
E
Glu
GAA
GAG




 


Phenylalanine
F
Phe
UUC
UUU




 


Glycine
G
Gly
GGA
GGC
GGG
GGU


 


Histidine
H
His
CAC
CAU




 


Isoleucine
I
Iso
AUA
AUC
AUU



 


Lysine
K
Lys
AAA
AAG




 















Leucine
L
Leu
UUA
UUG
CUA
CUC
CUG
CUU


 


Methionine
M
Met
AUG







 


Asparagine
N
Asn
AAC
AAU






 


Proline
P
Pro
CCA
CCC
CCG
CCU




 


Glutamine
Q
Gln
CAA
CAG






 


Arginine
R
Arg
AGA
AGG
CGA
CGC
CGG
CGU


 


Serine
S
Ser
AGC
AGU
UCA
UCC
UCG
UCU


 


Threonine
T
Thr
ACA
ACC
ACG
ACU




 


Valine
V
Val
GUA
GUC
GUG
GUU




 


Tryptophan
W
Trp
UGG







 


Tyrosine
Y
Tyr
UAC
UAU









Guidance in determining which amino acid residues can be substituted, inserted, or deleted without abolishing biological activity can be found using computer programs well known in the art, such as DNASTARTM software. Preferably, amino acid changes in the protein variants disclosed herein are conservative amino acid changes, i.e., substitutions of similarly charged or uncharged amino acids. A conservative amino acid change involves substitution of one of a family of amino acids which are related in their side chains. Naturally occurring amino acids are generally divided into four families: acidic (aspartate, glutamate), basic (lysine, arginine, histidine), non-polar (alanine, valine, leucine, isoleucine, proline, phenylalanine, methionine, tryptophan), and uncharged polar (glycine, asparagine, glutamine, cystine, serine, threonine, tyrosine) amino acids. Phenylalanine, tryptophan, and tyrosine are sometimes classified jointly as aromatic amino acids. In a peptide or protein, suitable conservative substitutions of amino acids are known to those of skill in this art and generally can be made without altering a biological activity of a resulting molecule. Those of skill in this art recognize that, in general, single amino acid substitutions in non-essential regions of a polypeptide do not substantially alter biological activity (see, e.g., Watson et al. Molecular Biology of the Gene, 4th Edition, 1987, The Benjamin/Cummings Pub. Co., p. 224). Exemplary conservative substitutions are described in U.S. Provisional Patent Application No. 61/241,647, the disclosure of which is herein incorporated by reference.
In making such changes, the hydropathic index of amino acids may be considered. The importance of the hydropathic amino acid index in conferring interactive biologic function on a protein is generally understood in the art (Kyte and Doolittle, 1982, incorporated herein by reference). Each amino acid has been assigned a hydropathic index on the basis of its hydrophobicity and charge characteristics (Kyte and Doolittle, 1982). These values are: isoleucine (+4.5); valine (+4.2); leucine (+3.8); phenylalanine (+2.8); cysteine/cystine (+2.5); methionine (+1.9); alanine (+1.8); glycine (−0.4); threonine (−0.7); serine (−0.8); tryptophan (−0.9); tyrosine (−1.3); proline (−1.6); histidine (−3.2); glutamate (−3.5); glutamine (−3.5); aspartate (−3.5); asparagine (−3.5); lysine (−3.9); and arginine (−4.5).
It is known in the art that certain amino acids may be substituted by other amino acids having a similar hydropathic index or score and still result in a protein with similar biological activity, i.e., still obtain a biological functionally equivalent protein. In making such changes, the substitution of amino acids whose hydropathic indices are within ±2 is preferred, those within ±1 are particularly preferred, and those within ±0.5 are even more particularly preferred. It is also understood in the art that the substitution of like amino acids can be made effectively on the basis of hydrophilicity.
As detailed in U.S. Pat. No. 4,554,101, the following hydrophilicity values have been assigned to amino acid residues: arginine (+3.0); lysine (+3.0); aspartate (+3.0±1); glutamate (+3.0±1); serine (+0.3); asparagine (+0.2); glutamine (+0.2); glycine (0); threonine (−0.4); proline (−0.5±1); alanine (−0.5); histidine (−0.5); cysteine (−1.0); methionine (−1.3); valine (−1.5); leucine (−1.8); isoleucine (−1.8); tyrosine (−2.3); phenylalanine (−2.5); tryptophan (−3.4). It is understood that an amino acid can be substituted for another having a similar hydrophilicity value and still obtain a biologically equivalent, and in particular, an immunologically equivalent protein. In such changes, the substitution of amino acids whose hydrophilicity values are within ±2 is preferred, those within ±1 are particularly preferred, and those within ±0.5 are even more particularly preferred.
As outlined above, amino acid substitutions may be based on the relative similarity of the amino acid side-chain substituents, for example, their hydrophobicity, hydrophilicity, charge, size, and the like.
Polypeptide variants further include glycosylated forms, aggregative conjugates with other molecules, and covalent conjugates with unrelated chemical moieties (e.g., pegylated molecules). Covalent variants can be prepared by linking functionalities to groups which are found in the amino acid chain or at the N- or C-terminal residue, as is known in the art. Variants also include allelic variants, species variants, and muteins. Truncations or deletions of regions which do not affect functional activity of the proteins are also variants.
Optimal alignment of sequences for comparison may be conducted using the Megalign program in the Lasergene suite of bioinformatics software (DNASTAR, Inc., Madison, Wis.), using default parameters. Alternatively, optimal alignment of sequences for comparison may be conducted by the local identity algorithm of Smith and Waterman (1981) Add. APL. Math 2:482, by the identity alignment algorithm of Needleman and Wunsch (1970) J. Mol. Biol. 48:443, by the search for similarity methods of Pearson and Lipman (1988) Proc. Nat'l Acad. Sci. USA 85: 2444, by computerized implementations of these algorithms (GAP, BESTFIT, BLAST, FASTA, and TFASTA in the Wisconsin Genetics Software Package, Genetics Computer Group (GCG), 575 Science Dr., Madison, Wis.), or by inspection. Examples of algorithms that are suitable for determining percent sequence identity and sequence similarity are the BLAST and BLAST 2.0 algorithms, which are described in Altschul et al. (1977) Nucl. Acids Res. 25:3389-3402 and Altschul et al. (1990) J. Mol. Biol. 215:403-410, respectively.
Polypeptides of the present invention include fusion polypeptides. In preferred embodiments, fusion polypeptides and polynucleotides encoding fusion polypeptides are provided. Fusion polypeptides and fusion proteins refer to a polypeptide having at least two, three, four, five, six, seven, eight, nine, or ten polypeptide segments. Tropoelastin domains associated with desired properties may be multimerized or concatenated and used to provide a desired elasticity, tensile strength, and shapeability and/or to match the tropoelastins and collagens present in a tissue being repaired, replaced, or regenerated.
The polypeptide domains or segments of the fusion protein can be in any order. Fusion polypeptides or fusion proteins can also include conservatively modified variants, polymorphic variants, alleles, mutants, subsequences, and interspecies homologs, so long as the desired transcriptional activity of the fusion polypeptide is preserved.
Amino acids in polypeptides of the present invention that are essential for function can be identified by methods known in the art, such as site-directed mutagenesis or alanine-scanning mutagenesis (Cunningham and Wells, Science 244:1081-1085, 1989). The latter procedure introduces single alanine mutations at every residue in the molecule. The resulting mutant molecules are then tested for biological activity such as binding to a natural or synthetic binding partner (e.g., polynucleotide transcription factor binding site; EMSA assays). Furthermore, transcriptional activity of fusion polypeptides, mutants, and variants thereof can be assayed in vitro using CAT or luciferase reporter assays as generally described in the art. Sites that are critical for protein-DNA binding can also be determined by structural analysis such as crystallization, nuclear magnetic resonance or photoaffinity labeling (Smith et al., J. Mol. Biol. 224:899-904, 1992 and de Vos et al. Science 255:306-312,1992). Polypeptides may comprise a signal (or leader) sequence at the N-terminal end of the protein, which co-translationally or post-translationally directs transfer of the protein. The polypeptide may also be conjugated to a linker or other sequence for ease of synthesis, purification or identification of the polypeptide (e.g., poly-His), or to enhance binding of the polypeptide to a solid support.
The fusion partner may be designed and included for essentially any desired purpose provided they do not adversely affect the desired activity of the polypeptide. For example, a fusion partner comprises a sequence that assists in expressing the protein (an expression enhancer) at higher yields than the native recombinant protein. Other fusion partners may be selected so as to increase the solubility of the protein or to enable the protein to be targeted to desired intracellular compartments. Still further fusion partners include affinity tags, which facilitate purification of the protein. Fusion polypeptides may be produced by chemical synthetic methods or by chemical linkage between the two moieties or may generally be prepared using other standard techniques.
In general, polypeptides and fusion polypeptides (as well as polynucleotides encoding them) are isolated. An “isolated” polypeptide or polynucleotide is one that is removed from its original environment. For example, a naturally-occurring protein is isolated if it is separated from some or all of the coexisting materials in the natural system. Preferably, such polypeptides are at least about 90% pure, more preferably at least about 95% pure and most preferably at least about 99% pure. A polynucleotide is considered to be isolated if, for example, it is cloned into a vector that is not a part of the natural environment.
A variety of protocols for detecting and measuring the expression of polynucleotide-encoded products, using either polyclonal or monoclonal antibodies specific for the product are known in the art. Examples include enzyme-linked immunosorbent assay (ELISA), radioimmunoassay (RIA), and fluorescence activated cell sorting (FACS). These and other assays are described, among other places, in Hampton et al., Serological Methods, a Laboratory Manual (1990) and Maddox et al., J. Exp. Med. 158:1211-1216 (1983).
H. Methods
As noted above, the invention generally relates, in part, to production of implants and grafts comprising biocompatible polymeric scaffold materials and one or more cell populations for use in regenerative medicine. The implants or grafts are shapeable into various forms, including, but not limited to sheets, tubes, and any other three-dimensional spatial pieces. Further, the cells growing on the implants or grafts promote regeneration by repairing, replacing or restoring damaged tissues or organs.
1. Wound Treatment
In one embodiment, implants and grafts are used for treating wounds. Exemplary wounds that can be treated by implants and grafts described herein, include, but are not limited to: blast injuries suffered during combat such as blunt trauma, shrapnel wounds and burns; burns, cuts (superficial and deep), scrapes, abrasions, gashes, and punctures.
After a wound has been cleaned and disinfected, it is closed to promote healing and reduce the risk of infection. The most frequently used closures are sutures and staples. These devices have the advantages of excellent tensile strength, a low dehiscence rate and rapid and simple application. However, the disadvantages are requiring removal and leaving scars on the tissue. Sutures and staples cannot be used to completely close wounds that have gaps in their proximate edges and do not seal the wound nor promote wound healing.
Recently, adhesives such as cyanoacrylate glues and fibrin biological adhesives have been introduced to close traumatic injuries and surgical incisions. N-butyl-1,2-cyanoacrylate (Histoacryl) and 2-octyl-cyanoacrylate (Dermabond) are widely used to close surface wounds and incisions. These adhesives cure rapidly upon contact with water, provide excellent tensile strength (30.6 N) and are sloughed off during the healing process. Tooth enamel bonded with cyanoacrylate has a shear bond strength of up to 7 MPa.
However, the contraindications for their use are inadequate hemostasis, areas of the skin under high tension, such as over the joints, or proximity to moist areas, which reduces tensile strength. Because cyanoacrylate adhesives are toxic and release formaldehyde during their breakdown by the body, they are not recommended for closing deep incisions or wounds. Infected or heavily contaminated wounds should not be closed with these adhesives.
Fibrin sealants include fibrinogen and thrombin as separate components. When these two proteins are mixed, the fibrinogen is cleaved and a fibrin clot forms, sealing and closing the wound. Additional components such as human factor XIII and aprotinin are often included in the preparations to increase the tensile strength of the clot and reduce fibrinoloysis. However, fibrin sealants can be limited in their application as wound adhesives by their relatively low tensile strength (30 kPa). In addition, fibrin sealants do not have adequate tensile strength to close skin injuries. In some instances, adverse immunologic reactions are observed with repeated use of fibrin preparations that contain bovine blood products such as aprotinin.
Tropoelastin is synthesized as a natural monomer and then catalytically polymerized; thus, the monomer can be applied to the edges of a wound and polymerized in vivo on the surface or within the edges of a wound, physically closing and sealing the wound.
During polymerization, tropoelastin-based scaffolds, as described elsewhere herein, are conducive to cell attachment and growth, and can promote the wound healing process. Thus, in addition to performing as a strong wound adhesive and sealant, tropoelastin-based implants may also contribute to accelerated wound healing by attracting regenerative cells into a supporting scaffold that self-assembles during fibrillogenesis. Tropelastin itself can participate as a reinforcing material in a newly forming scar.
Thus, in one embodiment, an implant or graft comprising a biocompatible polymer scaffold comprising one or more tropoelastin polypeptides and one or more cell populations is grafted to a wound of a subject to repair, replace, or regenerate the wounded tissue.
Without wishing to be bound by any particular theory, the foregoing implant or graft provides a regenerative phase that continues for days, weeks, or months, and further provides an increased rate of epithelial cell growth that helps repair the wound with new tissue. Implants and grafts used in particular embodiments of the present invention provide more rapid wound healing, more perfect reconstruction of the damaged parts of the wound, and minimize wound contraction.
In a particular embodiment, a wound of a subject is treated by providing an implant or graft comprising a biocompatible polymer scaffold comprising one or more tropoelastin polypeptides. The scaffold or graft can be molded into any form. In one embodiment, the scaffold is cast as a sheet, with a thickness that matches that of the wounded area.
In another particular embodiment, the scaffold is cast directly in the wound.
In another particular, embodiment, the scaffold is seeded with one or more cell populations. In a related embodiment, the cell populations comprise fibroblasts, keratinocytes, and other cell types that can promote wound healing and tissues regeneration (e.g., stem cells).
In certain embodiments, the implant comprises growth factors, co-polymers, and a distribution of tropoelastin polypeptides similar to the wounded tissue.
Without wishing to be bound by any particular theory, it is contemplated that providing an implant comprising a tropoelastin polypeptide profile similar to the wounded tissue will result in a repaired wound whose tissue is indistinguishable from normal tissue, aesthetically and functionally.
2. Guided Tissue and Bone Regeneration
In various embodiments, the biocompatible polymer scaffolds described herein are used in regenerative medicine for osteopathic applications, including, but not limited to craniofacial, odontic, and periodontic applications.
In one embodiment, implants and grafts are provided that comprise biocompatible polymer scaffolds comprising one or more tropoelastin polypeptides for use in reconstruction and regeneration of oral and craniofacial tissues.
In particular embodiments, a biocompatible polymer scaffold comprises one or more tropoelastin polypeptides and a human collagen co-polymer. The resulting scaffolds are engineered for the desired surface topography, porosity, strength and elasticity.
In one embodiment, the biocompatible polymer scaffold is cast in the form of a sheet and can be used as a regenerative membrane in various clinical applications, e.g., guided tissue regeneration (GTR) or root coverage procedures.
In one embodiment, the biocompatible polymer scaffold is cast as a sheet and seeded with periodontal ligament cells (PDL) forming an implant or graft that is suitable for use in a root coverage procedure. Once the implant has formed, a surgeon engrafts the implant in a root coverage procedure using methods known to those having ordinary skill in the art.
In another embodiment, the biocompatible polymer scaffold is cast in a three dimensional shape for use as a bone filling material. Virtually any shape can be achieved because the unpolymerized scaffold material is in a shapeable putty-like form. Once molded, the scaffold can be hardened by cross-linking. In addition, the shapeable scaffold can support unique clinical applications in periodontal medicine for guided bone regeneration (GBR) procedures and eliminate the need for a bone filler and a membrane to contain the bone graft.
In a particular embodiment, an implant comprises a biocompatible polymer scaffold as described herein, molded into a desired shape, and one or populations of cells.
In a certain embodiment, an implant or graft comprises one or more cell populations comprises bone marrow stem cells, mesenchymal stem cells, or pre-osteoblast cells to facilitate tissue or bone regeneration. Additionally, the osteogenic potential of the shapeable scaffold/implant can be used as a sole therapy or in combination with currently available commercial bone filler products or primary autologous bone harvests.
One having ordinary skill in the art would recognize that any type of bones can be repaired, replace, or regenerated using the foregoing techniques.
3. Vasculature Regeneration
As noted above, in particular embodiments, biocompatible polymer scaffolds are cast into the form of tubes. The dimensions, elasticity, and strength of the tubular scaffolds can be engineered to be useful as arteries, veins, ducts, ureters, urethras, and virtually any other tubular structure in the body wherein reparative, replacement, or regenerative therapy is desired or required.
In one embodiment, an implant or graft is provided to repair, replacement or regenerate a vessel within the peripheral vascular system, cardiac vasculature, or cardiac tissue itself. The implant or graft can comprise a biocompatible polymer scaffold having one or more tropoelastin polypeptides, and one or more populations of cells. Exemplary cell populations used in an implant or graft to repair, replacement or regenerate a vessel within the vascular system comprise smooth muscle cells, fibroblasts, mesenchymal stem cells, bone marrow stem cells, and the like.
Thus, one significant advantage of the invention is the development of elastins with unique properties, e.g., tensile strength, elasticity, and flexibiltiy/stiffness, generated by combining 2, 3, 4, 5, 6, 7, 8, 9, 10 or more individual tropoelastin isoforms, themselves having unique properties. Such unique elastins can be tailored for use at locations in the body where their unique properties are the most advantageous. For example, the strongest fibers can be used to repair muscles, the most elastic fibers can be used to construct bladders and other flexible organs, e.g, blood vessels, and the stiffest fibers can be used in cartilage repair.
In particular embodiments, the vessel being repaired, replace, or regenerated is selected from the group consisting of: veins, venules, capillaries, arterioles, and arteries.
In other particular embodiments, the vessel being repaired, replace, or regenerated is selected from the group consisting of: coronary vessels, vessels in the brain, or any other vessel that has been damaged and/or injured and is in need of repair, replacement, or regeneration.
EXAMPLES
Example 1
Cloning and Sequence Analysis of Tropoelastin Isoforms
Genetic Analysis
Four non-fetal skin fibroblast cell lines from healthy donors were purchased from the Corriel Institute for Medical Research. Total RNA was extracted from the four cell lines. cDNA was synthesized from the RNA using reverse transcriptase, and the cDNA was amplified using PCR with specifically designed primers. The amplified DNA was then ligated into a plasmid and transformed into Escherichia coli (E. coli). Colonies containing the cloned cDNA were picked and the size of the inserted cDNA determined. Only colonies containing full length inserts were further evaluated. The cDNA was isolated from the host and subjected to full length DNA sequencing. A total of 96 distinct cDNA clones were sequenced.
A comparison of the sequences revealed that a total of 34 separate tropoelastin polymorphs were present in the mRNA from 4 human cell lines. A detailed polymorphism analysis of tropoelastin mRNAs obtained from four independent human fibroblast cell lines revealed the presence of many different exon mRNA polymorphisms. Applicants have discovered that at least 17 exons are involved in the alternative splicing of tropoelastin, including exons 2, 3, 5, 6, 8, 10, 11, 13, 17, 19, 20, 22, 23, 24, 25, 26, 28, 31, 32, and 33. In addition, Applicants identified partially deleted isoforms of exons 2, 6, 8, 10, 17, 20, 24, 26, and 28. In total, human tropoelastin comprises at least 29 exons, including partially deleted exons, that can be alternatively spliced; thus, potentially encoding a total of 841 alternatively spliced tropoelastin polypeptides. The following table shows the polynucleotide positions for each of the exons with reference to a tropoelastin cDNA, as set forth in SEQ ID NO: 49.







TABLE 2







human tropoelastin exons (to STOP codon)











Exon number
Start polynucleotide
End polynucleotide















 1
1
82



 2A
83
133



 2B
122
133



 3
134
163



 4
164
196



 5
197
232



 6A
233
352



 6B
260
352



 7
353
403



 8A
404
469



 8B
419
469



 9
470
511



10A
512
631



10B
560
631



11
632
661



12
662
733



13
734
775



14
776
835



15
836
889



16
890
979



17A
980
1039



17B
995
1039



18
1040
1186



19
1187
1240



20A
1241
1405



20B
1241
1381



21
1406
1447



22
1448
1534



23
1535
1591



24A
1592
1771



24B
1610
1771



25
1772
1816



26A
1817
2041



26B
1817
1942



27
2042
2080



28A
2081
2152



28B
2086
2152



29
2153
2212



30
2213
2287



31
2288
2326



32
2327
2380



33
2381
2425



34
2426
2469










Moreover, a number of amino acid substitutions were identified that further increases the diversity of the tropoelastin polypeptides disclosed by Applicants. Illustrative tropoelastin polypeptides, including alternatively spliced tropoelastins and tropoelastins having amino acids mutations, are set forth in SEQ ID NOs: 2-48.
Example 2
Design of Tropoelastin Gene for Optimization of Protein Expression
Tropoelastin Gene Optimization and Design
The sequence of the human tropoelastin gene was originally published in 1987 (Indik et al. P.N.A.S. USA (1987); 84: pp. 5680-5684.). The gene encoding tropoelastin is large, spanning more than 41.5 kilobases and contains an extensive number of tandem repeated nucleotides. Moreover, the codon usage of the tropoelastin gene is highly biased toward expression in human cells. All of these factors contribute to the difficulty of successfully synthesizing this protein in alternative hosts. As a result, attempts to express the human gene in E. coli have largely been unsuccessful and yield only small amounts of tropoelastin protein (Indik et al. Arch. Biochem. Biophys. (1990); 280: (1): pp. 80-86).
The highly biased codon usage in the human tropoelastin gene interferes with assembly of the protein during translation, because the necessary tRNA molecules are not abundant in alternative hosts such as bacteria, yeasts or plants. Therefore, the rate of tropoelastin synthesis during gene expression is limited by the concentration of the appropriate tRNAs. For example, there are 79 glycine codons that are encoded as GGA in the human tropoelastin gene (Fazio et al. J. Invest. Dermatol. (1988);91: pp. 458-464). However, in alternative hosts the glycine codons GGU, GGG and GGC are used more frequently than GGA; thus, the rate of tropoelastin synthesis in these alternative hosts is compromised.
In addition, the human tropoelastin gene contains other features that contribute to the inefficient translation of mRNA into protein, including a large number of tandem repeating identical codons and long stretches of AT/GC sequences. The human tropoelastin mRNA also contains several self-complementary regions, which is conducive to the formation of stable helical structures that impede translation of mRNA into protein. Previous attempts by others have been made to address the codon bias with a synthetic tropoelastin gene containing a more universal codon usage have been largely unsuccessful (Martin S L, Vrhovski B, Weiss A. Total synthesis and expression in Escherichia coli of a gene encoding human tropoelastin. Gene. 1995; 154: 159-166.). The previous methods are only effective at a laboratory scale, producing human tropoelastin sporadically and in very limited quantities.
Applicants took a more comprehensive approach and designed a human tropoelastin DNA sequence that simultaneously addressed biased codon usage, tandem repeats, AT/GC stretches and unwanted helix formation. A final DNA sequence was designed with putative improved functional characteristics in all known structural aspects by using an iterative algorithm.







TABLE 3







Examples of Codon Preference Optimization










Codon
Human Gene
Alternative Host
Optimized Gene














Glycine
GGA
43.3%
34.6%
34.3%



GGU
56.6%
33.7%
33.3%



GGG
0
15.4%
14.8%



GGC
0
16.2%
17.6%


Valine
GUA
0
18.6%
18.5%



GUU
 100%
40.3%
40.2%



GUG
0
24.2%
23.9%



GUC
0
16.9%
17.4%









The codon usage of the tropoelastin coding sequence was optimized to closely mimic the endogenous codon usage of the alternative host used for protein expression.
The number of tandem repeats of identical codons in the optimized sequence was simultaneously reduced during the gene design process. The original sequence contained 23 tandem repeats with up to 4 identical codons. The optimized sequence was engineered to contain 9 tandem repeats with 3 identical codons. Further, the number of AT/GC stretches was reduced from 62 stretches with more than 4 nucleotides to 38 stretches with more than 4 nucleotides. Secondary structure (Amarzguioui M, G. Brede E, Babaie M, Grotli B, Sproat H, Prydz E. Secondary structure prediction and in vitro accessibility of mRNA as tools in the selection of target sites for ribozymes. Nucleic Acids Res. 2000; 28(21): 4113-24.) was optimized by reducing the number of complimentary sequences that would tend to form helices by 36%.
One having skill in the art would appreciate that all of the tropoelastin polynucleotide sequences disclosed herein can be codon optimized for expression in any number of species.
Example 3
Expression of Tropoelastin Protein
Gene Synthesis and Expression
A codon optimized version of a human tropoelastin coding sequence, e.g., SEQ ID NOs: 84-86, was synthesized and was used to efficiently produce human tropoelastin, e.g., SEQ ID NOs: 47-48, in alternative hosts such as bacteria, yeasts and plants. The correct DNA sequence for the optimized tropoelastin polynucleotide was confirmed by sequencing, the optimized tropoelastin polynucleotide was ligated into an E. coli expression vector, and the optimized tropoelastin polynucleotide containing expression vector was transformed into E. coli. Several clones of the E. coli transformant were cultured, induced to express protein, and harvested. The expression of tropoelastin was analyzed by SDS PAGE. FIG. 1 shows that when the codon optimized version of the human tropoelastin coding sequence was expressed in E. coli, tropoelastin was efficiently expressed in the cell. The efficient expression of the optimized tropoelastin coding sequence validates the strategy used in re-designing the tropoelastin gene.
Example 4
Purification of Tropoelastin Protein
Protein Production and Purification
For use in composition and methods directed to guided regeneration, (e.g., guided tissue regeneration (GTR), guided bone regeneration (GBR)), we tropoelastin protein was produced at low cost and in large quantities using the following exemplary methods. A simple and efficient purification process was designed to purify tropoelastin protein in a few steps. A series of four histidine residues (“poly-His tag”) was incorporated at the carboxy terminus of the tropoelastin protein to facilitate purification of the protein.
Cell paste containing the expressed tropoelastin was homogenized, extracted, clarified by centrifugation, and the supernatant passed over a column containing a nickel resin (HiTrap). The tropoelastin protein was eluted from the column as a single peak with 250 millimolar (mM) imidazole. The resulting chromatographic profile is shown in FIG. 2. Column fractions containing the tropoelastin protein were pooled and analyzed for purity by SDS PAGE. This analysis demonstrated that the optimized tropoelastin as designed and synthesized was purified to over 95% homogeneity by the use of a single chromatographic step on a Ni resin. Approximately 100 milligrams (mg) (dry weight) of tropoelastin protein was recovered from 100 milliliters (mL) of cell extract in this example. The manufacturing is scalable up to kilogram (kg) quantities of purified material. One kg of purified tropoelastin is sufficient to produce about 10,000 cm3 of polymer membranes.
Example 5
Polymerization of Tropoelastin
Polymerization Studies
Purified tropoelastin was dialyzed into phosphate buffered saline (PBS) and polymerized with the crosslinking reagent N-hydroxy succinimide-PEG-N-hydroxy succinimide and allowed to react to completion. The reaction mixture was dried, fixed and prepared for SEM imaging. The images obtained from unreacted and crosslinked tropoelastin are shown in FIG. 3. These results indicated that purified tropoelastin formed cross-linkable fibers in vitro.
Example 6
Results of Clinical Trials with Tropoelastin Cream
Clinical Testing
A composition comprising purified tropoelastin protein was formulated with an emulsion cream carrier at a concentration of 200 μg tropoelastin protein per ounce of emulsion cream carrier and transferred to Clinical Research Laboratories, Inc. and the potential for dermal irritation and also dermal sensitization were assessed. A total of 54 adult subjects signed Informed Consent Forms in compliance with 21 CFR Part 50: “Protection of Human Subjects” and a HIPAA Authorization Form in compliance with 45 CFR Parts 160 and 164. All subjects completed a Subject Profile/Medical History Form provided by Clinical Research Laboratories, Inc. prior to the study.
Test Method
A patch comprising the tropoelastin in a carrier cream was applied to the upper back of the patients (between the scapulae) and allowed to remain in direct skin contact for a period of 24 hours.
Patches were Applied to the Same Site on Monday, Wednesday, and
Friday for a total of 9 applications during the Induction Period. The sites were graded by a CRL technician for dermal irritation 24 hours after removal of the patches on Tuesday and Thursday and 48 hours after removal of the patches on Saturday.
The sites were graded according to the following scoring system:
Dermal Scoring Scale














Score
Skin Reactions









0
No visible skin reaction



±
Barely perceptible erythema



+
Mild erythema



++
Well defined erythema



+++
Erythema and edema



++++
Erythema and edema with vesiculation










Following approximately a 2-week rest period, the challenge patches were applied to previously untreated test sites on the back. After 24 hours, the patches were removed by a CRL technician and the test sites were evaluated for dermal reactions. The test sites were re-evaluated at 48 and 72 hours.

Results
The results of the irritation study showed that the tropoelastin composition is non-irritating. None of the 54 subjects received an irritancy score above “0”. The results of the challenge study indicated that the tropoelastin composition is non-sensitizing. None of the 54 subjects received a challenge score above “0” after 24, 48 or 72 hours of observation. Therefore, the tropoelastin composition described above was non-irritating and non-sensitizing to patients.
Example 7
Recombinant Human Tropoelastins as a Material for Use in Wound Care
Recombinant human tropoelastin and/or tropoelastin polymorphs are characterized as a crossed-linked material for use in wound care. In vitro and in vivo tests are performed to evaluate the structure, tensile strength, and biocompatibility of the cross-linked tropoelastin material.
Scanning Electron Microscopy (SEM) is used to evaluate the surface structure of the cross-linked tropoelastin material using three different cross-linkers. Tensile strength of the three different tropoelastin cross-linked materials is characterized using an Instron device and is compared to currently available materials (e.g. Dermabond). A well characterized in vivo subcutaneous implant model in a rodent is used to evaluate the biocompatibility of the cross-linked tropoelastin materials. Standard outcome measures of fibrous capsule formation, activated tissue macrophages, foreign body giant cell presence, and the resulting vascular response to the material are evaluated (Kellar et al., Journal of Biomedical Materials Research. 61 (2): 226-233; 2002 and Kidd et al. Journal of Biomedical Materials Research. 59 (4): 682-689; 2002).
Example 8
Recombinant Human Tropoelastins as a Wound Adhesive
Recombinant human tropoelastin and/or tropoelastin polymorphs are cross-linked then evaluated as a wound adhesive. Currently available wound adhesives use synthetic components (e.g. cyanoacrylate) which have toxic properties to healing tissues. Other currently available options include biological solutions such as fibrin from animal sources. However, fibrin obtained from animal sources raises concerns for patient use based on animal-source disease transmission or allergies to animal-source materials. Human tropoelastin as a wound adhesive can help promote wound healing and thus reduces the incidence of infection in wounds.
In addition, a wound adhesive based on human tropoelastin and/or tropoelastin polymorphs can also accelerate healing and assist in wound edge approximation. The cross-linked tropoelastin material is tested for efficacy in vivo using an incisional wound model in the rat (Kapoor, M. et. al., Am. J. Path. 2004. 165: 299-307). Outcome measures that are evaluated in this wound model include: wound closure rates, re-epithelialization, wound strength, and scar formation.
Example 9
Generation and Characterization of Tropoelastin Scaffolds
Experimental Overview
Tropoelastin sheet scaffolds and tropoelastin shapeable scaffolds will be created. These two types of scaffolds will be evaluated using in vitro techniques to assay the affinity of periodontal ligament (PDL) cells and cryopreserved human bone marrow-derived mesenchymal stem cells (MSCs) for the respective scaffold prototypes.
PDL cells were selected for biocompatibility evaluation of the sheet scaffolds in guided tissue regeneration (GTR) applications such as dental root coverage procedures. Additionally, cryopreserved human bone marrow-derived MSCs were selected for applications incorporating stem cell therapies for GTR and guided bone regeneration (GBR) procedures.
Recombinant human tropoelastin can be cross-linked to create new materials suitable for use as membranes in GTR and GTB applications. The type and degree of crosslinking and presence of human collagen can alter the physical and biological characteristics of these new membranes.
Methods
The human extracellular matrix protein tropoelastin (monomeric) is co-polymerized with human collagen, and cross-linked membranes for guided tissue and bone regeneration are fabricated. The resulting structures are characterized for surface topography, porosity, strength and elasticity. Microscopy and mechanical testing are used to measure and compare mechanical properties and surface topography of tropoelastin polymer membranes with varying degrees of crosslinking and as a copolymer with human collagen.
Human tropoelastin monomer will be synthesized by and obtained by methods described herein. Tropoelastin monomer is cross-linked using bis(sulfosuccinimidyl) suberate (11.4 A° (Mithieux J, Rasko E, Weiss AS, Synthetic elastin hydrogels derived from massive elastic assemblies of self-organized human protein monomers. Biomaterials. 2004; 25: 4921-4927.) or dimethyl adipimidate (8.6 A° at crosslinker:tropoelastin molar ratios ranging from 2:1 to 10:1 and allowed to polymerize at 37° C., the temperature at which tropoelastin coacervates (Clark A. Arnspang E. Mithieux S. Korkmaz E. Braet P. Weiss A. Tropoelastin massively associates during coacervation to form quantized protein spheres. Biochemistry. 2006. 45: 9989-9996.).
In particular embodiments, tropoelastin monomer is mixed with human collagen (e.g., Fibrogen) at tropoelastin:collagen molar ratios ranging from about 10:1 to about 1:1 and crosslinked using bis suberate.
Polymerized structures are cast as membranes of varying thicknesses of about 0.5 mm to about 5 mm between glass sheets. Optimized selection of crosslinking and copolymerization conditions for GTR and GBR membranes is performed by characterizing the mechanical properties of the sample. Scanning Electron Microscopy and Atomic Force Microscopy are used to characterize the surface topography of the samples, which is important for fostering cell attachment. Uniaxial tensile testing is performed using a material testing apparatus designed specifically for biomaterials testing. Mechanical measurements are obtained from human tropoelastin membranes and membranes comprising copolymer blends of tropoelastin and collagen.
Results
The static and dynamic mechanical properties of each of the tropoelastin membranes will be evaluated as noted above. Crosslinked tropoelastin polymers and copolymers comprising collagen could exhibit variations in their mechanical properties.
Example 10
Tropoelastin Sheet Scaffolds Comprising Tropoelastin Polymorphs and PDLs
Experimental Overview
Tropoelastin sheet scaffolds are generated using tropoelastin polymorphs. The scaffold supports the growth and maintenance of PDL cells in in vitro tissue culture. The growth of PDL cells on these scaffolds indicates that the tropoelastin scaffolds comprising tropoelastin polymorphs can be used as GTR membranes for root coverage procedures. Recombinant tropoelastin scaffolds can support the growth and maintenance of PDL cells over currently available membrane technologies alone (e.g. AlloDerm®).
Methods
PDL cells are obtained from human teeth using routine extractions from consenting patients. Extracted teeth are stored in I-MEM (Biochrom, Berlin, Germany) at 37° C. PDL explants are dissected from the cervical root thirds using methods commonly known in the art. PDL cells will be cultured without enzymatic treatment according to Ragnarsson et al. (Ragnarsson B, Carr G, Daniel J C Isolation and growth of human periodontal ligament cells in vitro. Journal of Dental Research. 1985. 64: 1026-1030.) at 37° C. in a humidified incubator with 5% CO2/95% air. All cultures are incubated with a-minimum essential-medium (a-MEM) (Biochrom) supplemented with 10% heat-inactivated fetal calf serum (FCS) (Nunc,Wiesbaden, Germany), 2 mg/ml sodium hydrogencarbonate (Merck,Darmstadt, Germany), 100 mg/ml ascorbic acid (Merck), 50 mg/ml b-aminoproprionitrile (Sigma, Munich, Germany), 100 U/ml penicillin G (Sigma), 100 mg/ml streptomycin (Sigma) and 40 U/ml of nystatin (Sigma) at pH 7.4. Media is changed every three days and cells are subcultured at a density of 2500 cells/mm3. Typical cell passage conditions include incubating cell cultures in a solution of phosphate-buffered saline (PBS), without any Ca2+ or Mg2+ ions, containing 0.05% trypsin/0.02 (:)/0 EDTA (Nunc). This solution is inactivated with FCS prior to cell centrifugation (1200 r.p.m. for 5 minutes).
PDL cells are resuspended at a density of 105 cells per 3 ml of I-MEM. PDL cells are cultured on the tropoelastin sheet scaffolds that are the size of cell culture disk inserts that fit into 12-well tissue culture plates. Control tissue culture wells contain commercially available AlloDerm® (BioHorizons, Birmingham, Ala.). Cell culture experiments are performed in triplicate and are characterized for cell viability and number at 24, 48, 72 hours, and 1 week timepoints. Cell viability is monitored by trypan blue exclusion. Subsequently, the cells will be counted in triplicate in a Coulter Counter.
Results
Tropoelastin sheet scaffolds could support PDL cell growth and maintenance over the course of an experiment (24, 48, 72 hours, and 1 week). Initial cell populations will be compared to cell numbers at the various timepoints. Cell viability data is an important indicator of PDL cell affinity toward the tropoelastin sheet scaffold. Comparisons to AlloDerm® will be made at the various timepoints and could demonstrate equivalence of the tropoelastin scaffold to a well established, widely clinical-used periodontal membrane (Gapski R, Parks Calif., Wang H L. Acellular Dermal Matrix for Mucogingival Surgery: A Meta-Analysis. J Periodontol November 2005, Vol. 76, No. 11: 1814-1822; Papageorgakopoulos G, Greenwell H, Hill M, Vidal R, Scheetz JP. Root coverage using acellular dermal matrix and comparing a coronally positioned tunnel to a coronally positioned flap approach. J Periodontol. 2008 June; 79(6):1022-30; and Cummings L C, Kaldahl W B, Allen E P. Histologic evaluation of autogenous connective tissue and acellular dermal matrix grafts in humans. J Periodontol. 2005 February; 76(2):178-86).
Example 11
Tropoelastin Shapeable Scaffolds Comprising Tropoelastin Polymorphs and MSCs
Experimental Overview
Tropoelastin shapeable scaffolds are generated using tropoelastin polymorphs. Tropoelastin shapeable scaffolds support growth and maintenance of cryopreserved human bone marrow-derived mesenchymal stem cells (MSCs) in in vitro tissue culture. Tropoelastin shapeable scaffolds are manufactured in a variety of shapes and forms, as described elsewhere herein. The scaffolds are used as delivery vehicles for or as a sole therapy for repairing and/or regenerating bone in GBR and GTR procedures. Recombinant tropoelastin scaffolds comprising tropoelastin polymorphs support the growth and maintenance of cryopreserved MSCs over currently available bone filler materials alone (e.g. Grafton®).
Methods
Methods for culturing cryopreserved human bone marrow-derived MSCs are known to those having ordinary skill in the art, for example, in the methods published by Kundu et al. (Kundu A K, Khatiwala C B, Putnam A J. Extracellular Matrix Remodeling, Integrin Expression, and Downstream Signaling Pathways Influence the Osteogenic Differentiation of Mesenchymal Stem Cells on Poly(Lactide-Co-Glycolide) Substrates. Tissue Engineering. 2008. Part A, Vol 14. 1-11). Cells are purchased from Lonza (Walkersville, Md.) at passage 2. The manufacturer tests these cells for purity using flow cytometry and for their ability to differentiate into osteogenic, chondrogenic, and adipogenic lineages. The cells are positive for the cell surface markers CD105, CD166, CD29, and CD44 and negative for CD14, CD34, and CD45.
MSCs are routinely cultured and expanded in a non-differentiating growth medium consisting of Dulbecco's modified Eagle medium (DMEM) supplemented with 10% fetal bovine serum (FBS), 4 mM of L-glutamine, 100 units/mL of penicillin and 0.1 mg/mL of streptomycin. Cells are grown in a 5% CO2 atmosphere at 37° C., and the medium is renewed every 2 to 3 days. Before confluence, cells are trypsinized using trypsin-ethylenediaminetetraacetic acid (Tryp-EDTA; Invitrogen) and passaged 1:3 into fresh culture flasks. Experiments are conducted using cells below passage 8.
The osteogenic differentiation of MSCs on tropoelastin shapeable scaffolds vs. Grafton® (BioHorizons, Birmingham, Ala.) is monitored using an ALP activity assay and the von Kossa method to stain for deposited calcium phosphate mineral (Kundu A K and Putnam A J. Vitronectin and collagen I differentially regulate osteogenesis in mesenchymal stem cells. Biochem Biophys Res Commun. 2006. 347). For both assays, MSCs (2.5×104 cells/cm3) are seeded on shapeable tropoelastin scaffolds in 12 well culture dishes in serum-containing medium for 24 h. The culture medium is replaced with OS medium and is changed every other day.
For the ALP assay, MSCs are lysed after 7 and 14 days in passive lysis buffer (Promega Corporation) for 15 min at room temperature. Lysates are scraped from the wells of the tissue culture plates of tropoelastin shapeable scaffolds and Grafton® controls and then incubated with 50 mM of p-nitrophenylphosphate in assay buffer (containing 100 mM glycine, 1 mM MgCl2, pH 10.5) at 37° C. for 25 minutes. The reaction is stopped by adding 0.5 mL 0.1 N sodium hydroxide and the absorbance read at 405 nm. The specific ALP activity is determined using the extinction coefficient for p-nitrophenylphosphate (1.85×104/M per cm) and then expressed in units of ALP activity per mg of protein.
For von Kossa staining, a commercially available kit (American MasterTech Scientific Inc, Lodi, Calif.) is used to stain calcium phosphate mineral deposited by MSCs cultured on tropoelastin shapeable scaffolds in OS medium. As in the ALP assays, medium with fresh inhibitors is provided every other day. After 14 days, cells are washed twice with warmed PBS pH 7.4, followed by fixation using 4% formaldehyde in PBS at 25° C. for 40 min. Samples are then extensively rinsed with double distilled water and incubated in the presence of 5% silver nitrate, followed by exposure to ultraviolet light for 40 min. After extensive rinsing with water, the cells are treated with 5% sodium thiosulphate for 3 min, rinsed, and then incubated in Nuclear Fast Red stain for 5 min before a final rinse with water. Staining results are visualized on a Nikon E800 (Nikon, Melville, N.Y.) microscope using a 10× objective and the images compiled with using a standard image analysis software program.
Results
Tropoelastin shapeable scaffolds could demonstrate equal or superior ability to culture cryopreserved human bone marrow-derived MSCs and facilitate osteogenic differentiation than presently available methods. Results can be compared to Graftoecontrols, a commercially available bone graft material that has shapeable characteristics. The tropoelastin shapeable scaffolds could afford the same shapeable properties of existing methods with an added benefit of stable cross-linking which can eliminate the need for a secondary membrane covering.
Example 12
Cross-Linked Tropoelastin Material for Use as a Tissue Culture Scaffold
Experimental Overview
Recombinant tropoelastin and/or tropoelastin polymorphs are manufactured, cross-linked, and characterized for use as a tissue culture scaffold. Microscopy and mechanical testing are used to measure and compare mechanical properties and surface topography of three cross-linked tropoelastin polymorphs. The different cross-linked polymorphs can exhibit variation in mechanical properties.
Methods
The different tropoelastin polymorphs (monomeric) will be synthesized by and obtained by the methods described elsewhere herein. Each monomeric polymorph will be catalytically cross-linked either with the established bis(sulfosuccinimidyl) suberate (11.4 A° (Mithieux et al., 2004)), dimethyl adipimidate (8.6 A° or thiol-cleavable 3,3′′-dithiobis(sulfosuccinimidylpropionate) (12 A° at crosslinker:tropoelastin molar ratios ranging from 2:1 to 10:1 and allowed to polymerize at 37° C., the temperature at which tropoelastin coacervates (Clark et al., 2006).
Polymerized materials are cast as solid rods and barbells. SEM and Atomic Force Microscopy (AFM) are used to characterize the surface topography of the samples, which is important for fostering cell attachment. Uniaxial tensile testing is performed using a material testing apparatus designed specifically for biomaterials testing, capable of applying both static and dynamic loads with high accuracy at low forces and high strains. Such a device is necessary because tropoelastin is highly extensible, has an elastic modulus of 220−280 kPa, and the polymerized materials have a cross-sectional area on the order of about 5 mm3 to about 50 mm3.
Dynamic testing is used to measure fatigue and endurance properties of the samples under cyclic loading. Creep behavior is assessed by measuring strain while subjecting the sample to constant applied loads. These measurements are performed both with the sample dry as well as immersed in a fluid environment that can simulate biological conditions.
Mechanical measurements are performed on three types of polymerized tropoelastin materials. The first type of polymerized tropoelastin material is solid tropoelastin of a single polymorph, which is used for correlating mechanical properties with genetic variation. The second type of polymerized tropoelastin material is for testing is porous tropoelastin. Porosity and void volumes of fabricated biomaterials such as tropoelastin influence cell attachment, migration, and proliferation onto material surfaces. Different porosities and void volumes for each tropoelastin polymorphs are tested. The third type of polymerized tropoelastin material is a copolymer blend of multiple tropoelastin polymorphs, prepared in both solid and porous configurations. Different configurations of copolymer blends of multiple tropoelastin polymorphs are tested. Thorough characterization of the mechanical properties polymerized tropoelastin materials allows for optimized selection of materials for tissue culture scaffolds. Testing multiple blends of polymorphs allows for creating potentially novel optimal materials.
Results
Methods for evaluating the static and dynamic mechanical properties of each of the tropoelastin polymorphs are disclosed. The different tropoelastin polymorphs or combinations thereof, could exhibit variations in their mechanical properties due to the variations in genetic sequence.
Example 13
Biocompatibility of Tropoelastin Scaffolds
Experimental Overview
The biocompatibility is evaluated as a vehicle for tissue culture scaffolds for three different cross-linked tropoelastin scaffold prototypes, e.g., the scaffolds produced in Example 12. The current methods for culturing of various cell types, including pluripotent stem cell populations require specialized protein surfaces for cellular attachment. In the case of certain stem cell populations, feeder layers are also required. A novel tropoelastin scaffold provides an appropriate protein interface for cellular attachment and obviate the need for other more specialized scaffolds known in the art.
Methods
Commercially available fibroblasts are obtained and cultured using standard cell culture techniques. Established cell cultures are harvested and cultured onto the tropoelastin scaffold prototypes in 12 well plates. Cell populations are determined 24, 48, and 72 hours post-culture on the three different scaffold prototypes. Experiments are done in triplicate and means and standard deviations are calculated for comparisons.
In another embodiment, bone marrow-derived stem cells are harvested from rats, purified and frozen using existing protocols. Methods of subculture/expansion, analysis and cryopreservation of the whole stem cell fraction are evaluated and optimized. Additionally, clonal selection is performed to isolate pure cultures of stem cells. Researcher's Working Cell Banks (RWCB) are produced.
Briefly, male Sprague Dawley rats of various ages are anesthetized and both femurs are removed. The ends of each femur are cut off and flushed with 10-30 mL of sterile 10% FBS in Dulbecco's modified Eagle's Medium-Low Glucose (DMEM-LG). Bone spicules and clots are allowed to settle briefly after which the cell suspension is decanted into a sterile 50 mL tube. The bone marrow mononuclear cell (BMMNC) fraction is isolated using Ficoll density gradient centrifugation. The cells of the BMMNC fraction are plated at 1×105 cells per well in 24 well plates grown in an incubator at 37° C. with 5% CO2. The cells are trypsinized using 0.25% Trypsin-EDTA and subsequently counted using a coulter counter. Cells bearing CD34, CD90, and CD44 markers are identified and purified using dynal beads. Purity of the purified cells is verified using flow cytometry. The cells are labeled using both Dil and CFD SE.
Conditions are optimized for subculture, expansion, analysis, cryopreservation and subsequent revival of these cells. These procedures yield the cells of the RWCB.
Bone marrow-derived stem cells from the RWCB are grown on tropoelastin scaffolds. Ranging studies are performed to optimize culturing conditions (e.g. media composition, culture time). Engraftment of the stem cells onto tropoelastin scaffolds is visualized microscopically. Labeling of stem cells is used to trace cells in vitro and for in vivo experiments.
Labeling of the BMMNC cells in culture is performed using standards methods known to those having ordinary skill in the art. An exemplary method uses a commercially available Vybrant® CFDA SE (carboxyfluorescein diacetate, succinimidyl ester) Cell Tracer Kit provided by Invitrogen. This kit provides a versatile and well-retained cell-tracing reagent in a convenient and easy-to-use form. CFDA SE passively diffuses into cells. CFDA SE is colorless and nonfluorescent until undergoing cleavage of the acetate groups by intracellular esterases to yield highly fluorescent, amine-reactive carboxyfluorescein succinimidyl ester. The succinimidyl ester group reacts with intracellular amines, forming fluorescent conjugates that are well-retained and can be fixed with aldehyde fixatives. Excess unconjugated reagent and by-products passively diffuse to the extracellular medium, where they are washed away. The dye-protein adducts that form in labeled cells are retained by the cells throughout development, meiosis, and allow in vivo tracing.
Harvested BMMNC cells are centrifuged to obtain a cell pellet and the supernatant is aspirated. BMMNC cells are resuspended in prewarmed (37° C.) PBS containing the labeling probe. The BMMNC cells and the labeling probe are incubated together for 15 minutes at 37° C. The BMMNC cells are re-pelleted by centrifugation and resuspended in fresh prewarmed medium. The BMMNC cells are subsequently incubated for another 30 minutes to ensure complete modification of the probe and then the BMMNC cells are washed again. Visualization of the harvested BMMNC is possible within the tropoelastin scaffold.
Results
Methods for determining biocompatibility of the tropoelastin scaffolds using standard fibroblast cell culturing experiments are disclosed. A Researcher's Working Cell Bank of a mixed population of stem cells could be established in sufficient quantities to carryout the experiments described herein. In addition, this example shows that bone marrow-derived stem cells could be cultured on the tropoelastin scaffolds
Example 14
A Tropoelastin Scaffold Seeded with Bone Marrow-Derived Stem Cells as a Treatment for Chronic Heart Failure
Experimental Overview
Cell-seeded bioengineered tropoelastin scaffolds are evaluated as a regenerative medicine therapy in vivo. Treatment with tropoelastin scaffolds seeded with bone marrow-derived stem cells are used to improve measureable outcomes in an existing rat model of heart failure model.
Methods
The effect of a tropoelastin scaffold seeded with bone marrow-derived stem cells as a treatment for chronic heart failure is evaluated. Left coronary artery ligation is used to infarct rat hearts, thus creating a model of chronic heart failure. The 3 week timepoint has previously been shown as a point in time where chronic heart failure is established. These rats have stable heart failure with elevated LV-EDPs, dilated LV, with ventricular remodeling, decreased LV dP/dt, decreased cardiac output and decreased survival. A control group of infarcted-only rats is used as a control group. Hemodynamics of the coronary vessels, echocardiography, and histology of the heart tissue and vasculature will be evaluated in this study.
Results
Treatment of myocardial infarction with tropoelastin scaffolds seeded with bone marrow-derived stem cells could positively influence LV remodeling. Other positive treatment outcomes include, but are not limited to altered LV dilatation, an improved EF, a lower LV end-diastolic pressure, an improved cardiac output and a higher LV dP/dt. Treatment with tropoelastin scaffolds seeded with bone marrow-derived stem cells could alter infarct size and stimulate angiogenesis.
The various embodiments described above can be combined to provide further embodiments. All of the U.S. patents, U.S. patent application publications, U.S. patent applications, foreign patents, foreign patent applications and non-patent publications referred to in this specification and/or listed in the Application Data Sheet are incorporated herein by reference, in their entirety. Aspects of the embodiments can be modified, if necessary to employ concepts of the various patents, applications and publications to provide yet further embodiments.
These and other changes can be made to the embodiments in light of the above-detailed description. In general, in the following claims, the terms used should not be construed to limit the claims to the specific embodiments disclosed in the specification and the claims, but should be construed to include all possible embodiments along with the full scope of equivalents to which such claims are entitled. Accordingly, the claims are not limited by the disclosure.

## Claims

1. A complementary DNA (cDNA) comprising a nucleotide sequence that has at least 95% identity to a nucleotide sequence as set forth in any one of SEQ ID NOs: 84-86.

2. The cDNA of claim 1, wherein the cDNA has the nucleotide sequence set forth in any one of SEQ ID NOs: 84-86.

3. The cDNA of claim 1, wherein the cDNA encodes a tropoelastin polypeptide comprising an amino acid sequence as set forth in any one of SEQ ID NOs: 13, 47, and 48.

4. The cDNA of claim 1, wherein the cDNA encodes a tropoelastin polypeptide comprising an amino acid sequence as set forth in SEQ ID NO: 13.

5. The cDNA of claim 2, wherein the cDNA encodes a tropoelastin polypeptide comprising an amino acid sequence as set forth in any one of SEQ ID NOs: 13, 47, and 48.

6. The cDNA of claim 1, wherein the nucleotide sequence is codon optimized for expression in Escherichia coli, yeast, or insect cells.

7. A complementary DNA (cDNA) comprising a nucleotide sequence that has at least 85% identity to a nucleotide sequence as set forth in any one of SEQ ID NOs: 84-86.

8. A complementary DNA (cDNA) comprising a nucleotide sequence that has at least 90% identity to a nucleotide sequence as set forth in any one of SEQ ID NOs: 84-86.