WO2018157011A1 - Products and methods for treating burn wounds - Google Patents

Abstract

Disclosed are methods for treating burn wounds utilizing a debridement agent and a viable genetically-modified xenogeneic skin substitute, and combination products utilizing those treatment agents.

Description

PRODUCTS AND METHODS FOR TREATING BURN WOUNDS

CROSS REFERENCE TO RELATED APPLICATIONS

[0001] The present application claims the benefit of U.S. Provisional Application No. 62/463,275, filed on February 24, 2017, which is incorporated herein by reference in its entirety for all purposes under the law.

FIELD OF THE INVENTION

[0002] The present invention relates to the treatment of burn wounds with a debriding agent and a genetically-modified xenogeneic skin substitute.

BACKGROUND OF THE INVENTION

[0003] The skin performs many vital functions, allowing the human body to maintain homeostasis. These functions include preventing dessication via fluid loss, preventing electrolyte loss, and insulating the body against unchecked temperature loss. Following severe burn injury these functions are often interrupted, either due to gross skin loss or due to formation of eschar, a layer of nonviable burned skin.

[0004] As a result of losing these "barrier functions" as well as the overall burden of wounds that result from severe burns, metabolic derangements can be severe, including life- threatening dehydration, electrolyte imbalances, hypothermia, and the development of the "hypermetabolic response" to burns. It is known that debridement of necrotic tissue followed by temporary coverage helps to decrease this hypermetabolic response, but it is imperative that the wounds be covered with a product or method that recreates the barrier function of the skin, allowing homeostasis to resume.

[0005] Debridement of these wounds is typically done surgically. The two methods of surgical excision are tangential excision, which involves removal of thin layers of dermis until healthy tissue is visualized, and fascial excision, which involves removal of the full thickness of dermis down to the underlying fascia. Tangential excision allows less viable tissue to be removed with the necrotic tissue, but typically results in higher blood loss, is a larger physiologic stressor than fascial excision, and is more likely to result in "incomplete" debridement, with some devitalized tissue remaining in place. In fascial excision, blood loss and operative time are minimized, but often a large amount of healthy tissue is removed with the burned tissue.

[0006] For coverage of the resulting wound, there are many options of both biologic and synthetic origin (or a combination). The wound may be covered with autologous skin grafts (autografts), or if autografting is contraindicated or unnecessary, temporary coverage is obtained using one of several wound coverage products. These wound coverage products provide differing levels of wound protection and restoration of the skin barrier during healing.

[0007] Common commercially available products include synthetic and biologic products. Examples of synthetic products include, bandages, topical antimicrobial preparations, and other synthetic (such as nylon or similar polymer) products with or without nonviable cellular or protein components. Biologic products can be human or animal derived. Examples of human derived products include human acellular dermal matrices, various powdered lyophilized cell preparations, and split thickness cadaver allografts which may be cryopreserved or glycerol preserved. Cryopreserved allograft is the only product that contains viable cells, however its availability is limited. All currently commercially available animal products contain either no cellular components or nonviable cells. These include collagen matrices and glutaraldehyde-fixed (nonviable) dermal derived products. No currently commercially available skin substitute product contains viable non-human animal cells. No currently commercially available skin substitute product is composed of porcine skin preserved via glycerolization, which confers shipping and storage advantages over cryopreserved porcine skin and effectiveness advantages over glutaraldehyde-fixed porcine skin.

[0008] For partial thickness wounds, as would be seen after tangential excision, the skin's barrier has not been completely lost, and so either biologic or synthetic products are both acceptable. Primarily biologic products include human cadaver allograft and nonviable xenograft.

[0009] Human cadaver allograft is commonly used for recreating the skin's barrier. It adheres to the burn wound and, by virtue of containing viable cells, is able to survive at that site until it is rejected by the recipient's immune system, which typically takes about 1-3 weeks. Because it adheres well and survives, it is able to create a good barrier against fluid and electrolyte loss and prevent wound infection. Additionally, it is thought that the presence of non-crosslinked extracellular matrix proteins in the allograft functions to promote healing of the underlying wound. As a living tissue, its viability is tied to its access to nutrients, and thus, is dependent on maintaining good contact with the wound bed and that the wound bed contains viable tissue. Human cadaver allograft is commonly supplied in the United States as a cryopreserved graft containing viable cells, while in Europe it is commonly supplied as a glycerol preserved graft. Glycerol preservation allows the graft to maintain its favorable handling characteristics and leaves extracellular matrix proteins un-crosslinked. Studies have not demonstrated a difference between cryopreserved and glycerol-preserved allograft in clinical efficacy.

[00010] While live-cell products provide the highest level of barrier restoration, the use of live-cell xenogeneic products was halted by the FDA due to concerns surrounding zoonotic endogenous retroviruses. Thus, the available xenogeneic products for the treatment of burns are aldehyde-fixed, so they contain no viable cells, which alleviates the concern for retrovirus transmission. However, aldehyde cross-linking of cell surface molecules limits the potential efficacy of these products and renders them stiffer and less conformable. They function as a biologic wound coverage but do not adhere, restore the skin's barrier, or prevent infection to the same degree as live-cell products. Similar to allograft, these xenogeneic products are rejected by the recipient's immune system and typically require changing every several days.

[00011] There are many nonbiologic products for use in partial thickness burns. For example, BIOBRA E (Smith & Nephew) is a product consisting of a pliable nylon mesh impregnated with xenogeneic collagen. The manufacturer claims that this product effectively covers wounds and that the collagen peptides promote healing; however it does not restore the skin's barrier function to the same degree as biologies. There are also a number of antimicrobial creams and non-adherent gauzes that are available for the treatment of small burns.

[00012] For full thickness burn wounds, such as would be seen after fascial excision or tangential excision of a severe burn, biologic products are preferred when the wounds cover large areas. Human cadaver allograft is most often employed in these patients. Glutaraldehyde fixed xenograft is less commonly used in the treatment of full thickness burn wounds but are an option. Conversely, synthetic products such as BIOBRANE are rarely used as temporary coverage in these wounds. A combination of antimicrobial agents and negative pressure wound therapy can be used to manage smaller full thickness burn wounds, and do help to prevent infection, but do not restore the skin's barrier like allograft.

[00013] Therefore, there remains a need for a product and method of treatment that do not suffer from the drawbacks identified above

SUMMARY OF THE INVENTION

[00014] In one aspect, the present invention is directed to a method of treating a burn wound in a subject in need of such treatment, which comprises:

a) preparing the wound by subjecting the wound to an effective amount of a debriding agent, and b) covering the prepared wound with a viable genetically-modified xenogeneic skin substitute.

[00015] In another aspect, the present invention is directed to a system for treating a burn wound which comprises:

a) an effective amount of a debriding agent;

b) an effective amount of a viable genetically-modified xenogeneic skin substitute;

c) suitable packaging for components a) and b); and optionally

d) instructional material for use of the system.

DETAILED DESCRIPTION OF THE INVENTION

[00016] Described herein is (1) a method of treatment of burn wounds comprised of burn wound preparation with a debriding agent followed by wound coverage with a viable genetically modified xenogeneic skin substitute; and (2) a combination product comprising a debriding agent and a viable genetically modified xenogeneic skin substitute.

[00017] The debriding agent of the present invention comprises any agent that is capable of cleaning a burn wound by removing foreign material and dead tissue. Many such agents are known. Preferably, an enzymatic debridement agent is used. In enzymatic debridement, collagenases or other proteolytic enzymes are employed that break down proteins of the extracellular matrix, allowing devitalized tissue to be wiped away without the need for surgery while preferably leaving healthy tissue substantially intact.

[00018] By selecting for degradation of burned, necrotic tissue only, these agents have the potential to reshape burn care. In surgical debridement, fascial excision is often employed as a burned patient may not tolerate extensive tangential excision. Thus, while debridement is beneficial overall, it is often said to "turn a partial thickness wound into a full thickness wound." Enzymatic debridement agents are less of an insult to the patient's overall physiologic state and allow removal of only necrotic tissue, maximizing the amount of the patient's own healthy tissue that is retained. Furthermore, unlike tangential excision which often leaves behind areas of nonviable tissue that may result in healing difficulties later, enzymatic debridement is able to remove even small pockets of devitalized tissue, leaving the healthiest possible wound bed.

[00019] The enzymatic debridement agent may be a bromelain enriched enzyme product, but may also be another collagenase or other enzyme product that is capable of clearing devitalized tissue or wound debris. NexoBrid™ (MediWound Ltd.) is one such bromelain enriched product that specifically targets heat-denatured collagen for degradation, resulting in partial-thickness and full-thickness wounds requiring a wound coverage or dressing product. Such products and methods are described in U.S. Patent Nos. 8,540,983; 8, 119,124; 7,128,719; and 7,794,709, each of which is incorporated by reference herein, and U.S. Patent Application No. 11/571,880 (Publication No. US2009/0010910A1), which is incorporation by reference herein. The enzymatic agent is commonly provided in a dry powder form that is reconstituted prior to use, but it may also be provided in other forms, such as an ointment or cream.

[00020] There are many skin substitutes contemplated for use in the present invention that act to restore the skin's barrier function. As used herein, "viable" is meant to include skin products that are either unpreserved, or that have been preserved in a fashion that does not introduce significant cross-linking of the product's extracellular matrix proteins.

[00021] Suitable preservation techniques include cryopreservation, glycerol preservation, etc. In a preferred embodiment, the skin substitute comprises skin harvested from alpha- 1, 3 -galactosyltransf erase knockout swine, such as those described in U.S. Patent No. 7,547,816, the contents of which are incorporated herein by reference. Such Gal- knockout swine lack the epitope or marker responsible for eliciting the hyperacute rejection response. Instead, the recipient's immune system reacts to products from these swine in the same manner as it would react to allogeneic products. Skin harvested from these swine possesses all of the advantages of live-cell allograft products (such as cadaver allograft) in terms of clinical efficacy and duration of adherence prior to rejection, but avoid the logistical and ethical concerns surrounding the use of human tissues. While there are glutaraldehyde fixed xenogeneic products on the market today, they generally do not meet the clinical efficacy of live-cell and glycerol preserved cadaver allograft at restoring the skin's barrier function.

[00022] Xenotransplantation was halted for years due to concerns over infectious disease transmission. Since then, research in the field has largely addressed these concerns, and the FDA has released guidelines for xenotransplantation products. In spite of this, the rapid, hyperacute rejection that is seen when wild-type xenogeneic skin products are used in humans has prohibited their use. Even glutaraldehyde-fixed products last just a number of days before they must be changed.

[00023] Thus, in a particularly preferred embodiment, the xenogeneic skin substitute described herein is a product derived from the skin of GalT-knockout genetically modified swine, which is has not undergone aldehyde fixation or crosslinking. Skin substitute products derived from swine possessing this modification have been studied extensively in a pig-to- baboon model. See, e.g., U.S. Patent No. 9,883,939, the contents of which are incorporated herein by reference. These studies showed that the porcine skin substitute is able to vascularize in a manner similar to allograft, remain viable and adherent to the wound bed for a time comparable to allograft, and restore the skin's barrier function similarly to allograft when compared on the basis of preventing infection and minimizing fluid loss. Such skin substitutes may be obtained, stored and prepared as known in the art, or otherwise utilized as described in U.S. Patent No. 9,883,939 and Weiner et al., Xenotransplantation 2010, 17: 147- 152, the contents of which are incorporated by reference herein.

[00024] This product most often is a split thickness skin graft composed of the entire epidermis and superficial portion of the dermis, but may also be a full thickness skin graft composed of the entire epidermis and entire dermis, or a product composed of the dermis alone. The product most often is cryopreserved, but may also be preserved in a glycerol solution. The dimensions of the product will vary depending on the specific needs present in each individual case. The thickness of the product is dependent on the composition of the skin substitute (split thickness, full thickness, or dermis alone). Split thickness grafts are most commonly harvested at a thickness of 0.022 inches but may be thinner or thicker. The thickness of dermal and full thickness skin products is dependent on the dermal thickness of the individual swine donor.

[00025] Debridement leading to a clean, healthy wound bed free from residual necrotic tissue promotes healing and reduces infection, and the removal of just the minimum necessary amount of tissue results in a better cosmetic and functional outcome. As discussed above, enzymatic debridement accomplishes these results to a greater degree than surgical debridement.

[00026] The resulting wound bed is also different from a wound bed following surgical debridement. After surgical debridement, the wound bed typically has a relatively uniform contour as tissue is removed along a single plane. After enzymatic debridement, the tissue is more uneven, as every pocket of devitalized tissue is removed while leaving intervening healthy tissue. This results in a non-uniform wound bed with increased overall surface area, of which a higher proportion consists of exposed, healthy tissue.

[00027] The present wound coverage products are able to take advantage of this unique wound bed to different degrees. The use of cryopreserved, live-cell or glycerol- preserved xenogeneic skin grafts as coverage following enzymatic debridement is a novel method of treatment that is distinct from the use of cadaver allograft and results in better results than other non-allograft products. a. Cryopreserved and glycerol preserved xenografts maintain their pliability and conformability after storage, and are able to conform to the uneven contour of the enzymatically debrided wound bed more effectively than stiffer, aldehyde cross-linked products.

b. Live-cell xenograft (and allograft) exerts efficacy by adhering to the wound bed, vascularizing, and providing a living-tissue barrier against infection and fluid loss. All of these aspects are primarily dependent on being in contact with a healthy viable wound bed. Therefore, the wound bed provided by enzymatic debridement, in which necrotic tissue is removed more thoroughly and healthy, viable tissue is more effectively spared, provides a special advantage to live-cell xenografts that is not realized with the use of non-live-cell products - including terminally sterilized and/or aldehyde crosslinked xenografts - allowing them to be more effective at restoring the skin's barrier function.

c. Because nonbiologic products, such as gauzes, antimicrobial creams, and nylon meshes, do not exert their efficacy by the mechanisms described above, they do not benefit from the unique wound bed provided by enzymatic debridement to the same degree as a live-cell product.

d. Because the efficacy of glutaraldehyde fixed products is not dependent on being in contact with a healthy, viable wound bed (i.e. they do not exert their effect through readily vascularizing and instead act only by providing a biologic coverage, akin to a bandage) to the same degree as live-cell products, they do not benefit from the unique wound bed provided by enzymatic debridement to the same degree as a cryopreserved or glycerol preserved product.

[00028] The method of treatment described herein may be referred to as a "clean and cover" technique for the treatment of burn wounds. In use, the enzymatic debriding agent is prepared, mixed, or reconstituted as is appropriate, and its application is carried out in any suitable manner, e.g., according to the manufacturer's recommendations for that product. Such may include application of the debriding agent, followed by a period during which the product exerts its effect. That period may vary depending on the specific product and the nature of the wound to be treated.

[00029] Treatment times using the enzymatic debridement agent may range from minutes to several days depending on the exact debridement product used and number of serial applications required in order to achieve adequate wound debridement. Most commonly, Nexobrid, a bromelain based product, requires four hours per treatment, and multiple treatments are typically not necessary. After this period the wound may preferably be wiped, scraped, or otherwise cleaned in order to remove the residual product and any enzymatically digested tissue. Treatment in such manner results in a wound, which may be either partial thickness or full thickness, but is commonly a mixture of the two, which requires further management.

[00030] Next, coverage of the resulting wound is obtained using a skin substitute as described above. After debridement, the skin substitute is placed on the wound bed and secured in place using appropriate means, such as sutures, staples, bandages, or other similar methods. The skin substitute is left in place until such time as it either is rejected by the recipient's immune system, or is removed intentionally to allow further treatment. This further treatment may include placement of cadaver allograft or another burn care product, placement of autologous skin grafts for definitive closure, etc.

[00031] The combination product described herein is a product comprising a debridement agent and a skin substitute for the purpose of executing the method of treatment described above. Both the debridement agent and skin substitute may be supplied in various quantities and sizes for use on burn wounds of various sizes, so that a managing physician may make a determination regarding quantity required.

[00032] The products may be packaged together and sold together, packaged separately and sold together, or packaged separately and sold separately for the purpose of use together. The exact packaging for each will vary, depending on the specific product. For the skin substitute, the packaging is appropriate for the preservation method. For example, cryopreserved grafts are preserved in cryopreservation medium in a polypropylene (or similar) vial, tube, or other container that is specifically intended for cryopreservation purposes. Cryopreservation media contains a DMSO or glycerol protectant and may be mixed with human or porcine serum with or without antibiotics and other additives. Glycerol preserved grafts may be packaged in an appropriate sterile pouch, vial, tube, or other container with or without residual glycerol containing medium. Finally, the packaging may optionally include suitable instructional material for use of the combination product (e.g., package insert, printed instructions on container material, etc.).

[00033] The embodiments of the invention described above are intended to be merely exemplary; numerous variations and modifications will be apparent to those skilled in the art. All such variations and modifications are intended to be within the scope of the present invention as defined in any appended claims.

Claims

What is claimed is:

1) A method of treating a burn wound in a subject in need of such treatment, which comprises:

a) preparing the wound by subjecting the wound to an effective amount of a debriding agent, and

b) covering the prepared wound with a viable genetically-modified xenogeneic skin substitute.

2) The method of claim 1, wherein the subject is human, and the skin substitute comprises a genetically-modified porcine xenograft.

3) The method of claim 1, wherein the debriding agent comprises an enzymatic agent.

4) The method of claim 3, wherein the enzymatic agent comprises one or more of bromelain, collagenase, or combinations thereof.

5) The method of claim 1, wherein the genetically-modified xenogeneic skin substitute comprises a product derived from the skin of genetically-modified swine.

6) The method of claim 5, wherein the swine skin lacks an alpha-l,3-galactose epitope.

7) The method of claim 1, wherein prior to use, the skin substitute has been preserved.

8) The method of claim 7, wherein the preservation method comprises cryopreservation or glycerol preservation.

9) The method of claim 1, wherein the skin substitute is secured on the prepared wound.

10) The method of claim 9, wherein the skin substitute is secured using sutures, staples, or bandages. 11) The method of claim 1, wherein the skin substitute is left in place until it is rejected by the subject's immune system, or is removed in order to permit further therapy.

12) The method of claim 1, wherein the skin substitute comprises a split thickness skin graft.

13) The method of claim 1, wherein the skin substitute comprises a full thickness skin graft.

14) The method of claim 1, wherein the skin substitute comprises the dermis alone.

15) A system for treating a burn wound which comprises:

a) an effective amount of a debriding agent;

b) an effective amount of a viable genetically-modified xenogeneic skin substitute;

c) suitable packaging for components a) and b); and optionally d) instructional material for use of the system.

16) The system of claim 15, wherein the debriding agent comprises an enzymatic agent.

17) The system of claim 16, wherein the enzymatic agent comprises one or more of bromelain, collagenase, or combinations thereof.

18) The system of claim 15, wherein the genetically-modified xenogeneic skin substitute comprises a product derived from the skin of genetically-modified swine.

19) The system of claim 18, wherein the swine skin lacks an alpha-l,3-galactose epitope.

20) The system of claim 15, wherein the skin substitute has been preserved. 21) The system of claim 20, wherein the preservation method comprises cryopreservation or glycerol preservation.

22) The system of claim 15, wherein the skin substitute comprises a split thickness skin graft.

23) The system of claim 15, wherein the skin substitute comprises a full thickness skin graft.

24) The system of claim 15, wherein the skin substitute comprises the dermis