Multimodal Therapy for Approaching Difficult-to-Heal Wounds: Becaplermin in Combination with Sequential Living Skin Equivalent Applications in a Series of Patients with Multifactorial Leg Ulcers

Introduction
  The vast majority of leg ulcers occur in patients with venous insufficiency; however, most patients with venous insufficiency do not develop leg ulcers.¹ This observation suggests that additional factors may be involved in the etiology of leg ulcers. Data on leg ulcers from 1,380 patients revealed that over 70 percent of their ulcers could be classified as postthrombotic ulcers involving primary or secondary hypercoagulable states.^2,3

  Other causes of leg ulcers, which may present with or without venous disease, include a diverse group of disorders including connective tissue diseases, peripheral vascular disease, vasculitis, cryoglobulinemia, cryofibrinogenemia, and lymphoproliferative disorders. Leg ulcers due to these disorders are often unresponsive to conventional therapy and frequently become chronic, exacting a financial and psychosocial burden. The use of newer agents that provide safe and effective treatment options for these difficult-to-heal wounds should result in substantial cost savings and improved quality of life.⁴

  Although the precise molecular mechanisms involved in healing chronic skin wounds have not been completely elucidated, it is understood that specific cytokines and growth factors participate in the process. Cell types found within wounds synthesize and express growth factor receptors, and topical application of growth factors can accelerate wound repair in vivo. A physiologic basis for treating chronic human wounds with exogenous recombinant human platelet-derived growth factor-BB (rhPDGF-BB) has been identified with the discovery of PDGF receptors in normal skin and granulation tissue.⁵ Becaplermin gel* contains human PDGF-BB produced by recombinant DNA technology, and has biological activity similar to that of naturally occurring PDGF.⁶ In the United States, the indication for becaplermin is restricted to use as an adjunct to good ulcer care practices in the treatment of lower extremity diabetic neuropathic ulcers that extend into the subcutaneous tissue or beyond and have an adequate blood supply. The mechanism of action of becaplermin is thought to involve chemotactic recruitment and proliferation of endothelial cells and fibroblast-like cells in granulation tissue.

  A living skin equivalent (LSE) ** is an allogenic, bilayered living skin construct that has been developed for the treatment of chronic, difficult-to-heal ulcers. This tissue-engineered skin consists of a well-differentiated and stratified epidermal layer with a distinct stratum corneum and multilayer dermal matrix of collagen and fibroblasts. LSE is made from viable human dermal and epidermal cells derived from neonatal foreskin.⁷ The lack of professional antigen-presenting cells in LSE results in a low immunogenic profile, and there have been no clinically evident signs of rejection in patients treated with LSE.⁸ Because it contains living fibroblasts and keratinocytes, LSE produces cytokines, growth factors, and matrix proteins associated with normal wound healing.⁹ Biochemically, LSE expresses PDGF and at least 15 other cytokines and growth factors, which may act synergistically to promote healing. Recent studies indicate that cells within the wound bed of chronic ulcers are often unresponsive to growth-regulatory signals seen in normal wound healing, thus limiting the potential effectiveness of single growth factor agents.¹⁰ Application(s) of multiple growth factors in addition to the sequential use of single growth factors may accelerate the healing process of chronic wounds.¹¹

Discussion
  Ulcerations of the skin affect approximately 2.5 million individuals in the United States, a number that is likely to increase as the average age of the population rises.¹² Due to substantial medical resource utilization, the projected annual cost of treating just venous leg ulcers in the United States is approaching $1 billion.¹³ The economic impact of skin ulcers also entails indirect costs, including an estimated annual loss of two million work days in the United States.¹² Similarly, chronic skin ulcers adversely affect patients’ quality of life. In a study examining the impact of leg ulcers on psychosocial issues, the majority of patients reported feelings of anger, fear, depression, social isolation, and negative self image, in addition to experiencing severe pain.¹⁴

  Hypercoagulable states may exist with a variety of clinical syndromes, including heparin-induced thrombopathy, the myeloproliferative syndromes, and malignant disorders.¹⁵ Antiphospholipid antibody syndrome, characterized by circulating autoantibodies to negatively charged phospholipids, is an important risk factor for thrombosis in patients with systemic lupus erythematosus as well as other conditions.¹⁶

  Anticoagulants, fibrinolytic agents, and immunosuppressive drugs have been used to help correct underlying disease states that can cause leg ulcers.^17,18 In this study, a multimodal approach has been used with good success to treat chronic skin ulcers related to a variety of these diseases that had failed standard wound care treatment. By delivering rhPDGF-BB to the wound bed, application of becaplermin gel supported the formation of granulation tissue and coincided with easier debridement. A reduction in pain followed the application of LSE. LSE, a bioengineered human-skin equivalent, functions as an occlusive covering, maintains a moist wound environment, and produces multiple cytokines and growth factors (including PDGF) that are naturally occurring substances known to be involved in normal wound healing.

  LSE has been shown to be clinically effective for the treatment of several types of difficult-to-heal wounds. A multicenter pivotal trial for venous leg ulcers demonstrated that LSE was more effective than standard of care in both percentage of patients completely healed at six months and in median time to complete wound closure.⁸ LSE plus compression therapy was also superior to compression therapy alone in healing larger, deeper venous ulcers and ulcers of greater than one year’s duration.¹⁹

  LSE has also been proven effective in treating diabetic foot ulcers and recently received FDA approval for this indication. In the pivotal trial for diabetic foot ulcers, 56 percent (63/112) of ulcers treated with LSE were 100-percent closed by 12 weeks of treatment, compared to 39 percent (36/96) of ulcers treated with conventional therapy alone (p = .0026). The median time to 100-percent wound closure was 65 days for diabetic foot ulcers treated with LSE plus conventional therapy versus 90 days for ulcers treated with conventional therapy alone (p = .0026).⁷

  LSE is being evaluated for safety and efficacy for a variety of other skin wounds, including arterial ulcers, mixed arterial/venous ulcers, burns, pressure ulcers, epidermolysis bullosa, and posttraumatic/postsurgical wounds.²⁰

  In this case series, LSE and becaplermin appeared to work synergistically to promote healing of the most recalcitrant chronic leg ulcers that had failed to respond to previous conventional wound treatments. LSE/becaplermin application required little effort and no special equipment or surgery. However, when applying becaplermin gel over LSE, caution was exercised in order to avoid disturbing the beneficial interaction between the wound bed and the living skin equivalent. The combination therapy was not associated with any signs of infection or sensitization at the ulcer site. While the LSE/becaplermin multimodal therapy employed in these seven patients has shown promising results, larger studies are needed to thoroughly evaluate this type of combination therapy. This combination should only be considered for those multifactorial ulcers that do not respond to aggressive wound care (possibly including becaplermin or LSE as single agents), as it may only prove to be cost effective in those cases where the only alternative may be amputation.

  * Regranex® (Ortho-McNeil Pharmaceutical Inc, Raritan, New Jersey)

  ** Apligraf® (Novartis Pharmaceuticals Corporation, East Hanover, New Jersey)