Abstract:
The present invention features hydrogel drug delivery systems and methods of producing and using such systems for the treatment of wounds. The systems are based on a hydrogel into which a low concentration of growth factor, e.g., epidermal growth factor, is passively transferred from a dilute aqueous solution. When placed in contact with a wounded tissue, the growth factor passively transfers out of the contact lens to provide accelerated healing. The amount of growth factor absorbed into the hydrogel is low, e.g., ≦350 ppb, but this amount has surprisingly been found to be effective in producing a therapeutic effect. The systems are applicable to ocular and other wound treatments.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    In general, the invention relates to the fields of hydrogels, drug delivery systems, and wound healing.  
           [0002]    Corneal wounds caused by injury, disease, or surgery represent a serious medical condition that may lead to loss of sight. For example, persistent epithelial defects can lead to stromal melting, which causes serious visual dysfunction. Wound healing of corneal mucosal tissue has taken on increased importance with the advent of laser corrective surgery to re-establish normal vision for people who do not wish to wear contact lenses or spectacles. These laser surgical methods are used to correct vision for nearsightedness (myopia), farsightedness (hyperopia), and astigmatism. The methods include laser in situ keratomileusis (LASIK), laser epithelial keratomileusis (LASEK), and photo-refractive keratectomy (PRK).  
           [0003]    LASIK refers to the use of a laser to reshape the cornea without invading the adjacent cell layers. During the LASIK procedure, a microkeratome is used to separate the surface layers of the cornea and create a corneal flap (160-180 microns deep). This flap stays attached to the rest of the cornea and is folded back on one side to expose the stroma of the cornea. The laser delivers pulses of ultraviolet light onto the inner cornea (stroma). Each pulse removes a microscopic layer of the inner cornea to reshape the surface of the cornea. For nearsighted patients, the procedure flattens the cornea. For farsighted patients, the procedure increases the curvature of the cornea. For astigmatism, selected tissues are removed at certain angles to make the cornea more spherical in shape. After exposure to the laser is completed, the corneal flap is replaced where it bonds without the need for stitches. The anterior layers of the cornea (epithelium, Bowman&#39;s Layer) are largely preserved. Once the surgery is completed, the eye is left to heal normally with the exception of eye drops, which are used to prevent infection &amp; swelling, with varying degrees of success. Following the surgery, patients are able to see clearly without depending on glasses or contacts.  
           [0004]    During PRK, the surgeon removes the epithelium (the anterior layer of the cornea or Bowman&#39;s Layer), which is a thin layer of protective skin that covers the cornea. This layer can be removed with an excimer laser or a brush. During the procedure, the patient stares at a fixation light. In less than a minute, the laser removes the proper amount of tissue while it reshapes the surface of the cornea. The excimer laser delivers pulses of ultraviolet light into the cornea. This exposure to laser radiation reduces or eliminates nearsightedness by flattening the central cornea and relocating the focal point of the lens onto the retina rather than in front of it, which produces sharper vision. Following surgery, a bandage contact lens is placed on the eye for 2-3 days. Because the epithelium was removed, patients may experience blurry vision for three to five days. Eye drops and the contact lens are effective in reducing postoperative discomfort. The purpose of the contact lens given to PRK patients post-surgically is to protect the leading edge of the corneal epithelium that is regenerating along the surface of the eye, post-surgery. As patients blink, the newer leading edge of the epithelium may be removed. As a result, recovery takes longer and there is an increased risk of infection.  
           [0005]    LASEK is similar to PRK but the epithelium is detached by using an alcohol solution that weakens the epithelium and allows it to fold back into a flap. A laser is then used to re-shape the cornea and correct vision acuity.  
           [0006]    All three procedures can result in corneal epithelial defects, and inflammation and infection may also occur. These complications can lead to acuity regression or other adverse effects. Wound healing is thus of critical importance for the outcome of surgery. There exists a need, therefore, for devices that promote healing of corneal wounds.  
         SUMMARY OF THE INVENTION  
         [0007]    The present invention features hydrogel drug delivery systems and methods of producing and using such systems for the treatment of wounds. The systems are based on a hydrogel into which a growth factor, e.g., epidermal growth factor (EGF), is passively transferred from a dilute aqueous solution. When placed in contact with a wounded tissue, the growth factor passively transfers out of the hydrogel to provide accelerated healing and a concomitant reduction in pain. The amount of growth factor absorbed into the hydrogel is low, e.g., ≦350 ppb, but this amount surprisingly is effective in producing a therapeutic effect likely because the delivery system is localized and provides a sustained release of the factor. The systems are applicable to ocular wounds, especially after vision correcting surgery, as well as other wound treatments.  
           [0008]    Accordingly, in one aspect, the invention features a polymeric hydrogel that comprises a substantially pure growth factor, e.g., epidermal growth factor, platelet derived growth factor, hepatocytic growth factor, or combinations thereof, at a concentration of between 5 ppb and 350 ppb. The hydrogel has a water content of, for example, between 37.5% and 70% by weight. Exemplary hydrogel materials include a tetrapolymer of hydroxymethylmethacrylate, ethylene glycol, dimethylmethacrylate, and methacrylic acid. Other examples of hydrogels include those including an ionic or non-ionic polymer and those including etafilcon A, vifilcon A, or polymacon B. In various embodiments, the growth factor is capable of being passively released into an environment, e.g., an ocular environment, under ambient or existing conditions. In other embodiments, the hydrogel may be shaped as a contact lens, e.g., one capable of correcting vision. Such a contact lens may be capable of correcting vision in the range of +8.0 to −8.0 diopters, including plano, and may have a base curve between 8.0 and 9.0.  
           [0009]    The invention further features a method for making a hydrogel drug delivery system. This method includes the steps of providing a hydrogel; washing the hydrogel in an isotonic saline solution; partially desiccating the lens; and placing the washed and partially desiccated hydrogel in an aqueous solution, e.g., having a pH between 6.9 and 7.4, of between 0.01 and 10 ng growth factor, e.g., epidermal growth factor, platelet derived growth factor, hepatocytic growth factor, or combinations thereof, per μl, wherein growth factor is passively transferred into the hydrogel to produce the hydrogel drug delivery system. The concentration of growth factor in the hydrogel after soaking is, for example, between 5 and 350 ppb. In one embodiment, the hydrogel is placed in the solution of growth factor for at least 30 minutes.  
           [0010]    In another aspect, the invention features a method for treating a wound. The method includes the steps of providing a hydrogel containing a growth factor as described above; placing said hydrogel in contact with the wound, wherein the growth factor is passively released from the hydrogel to treat the wound. In one embodiment, the hydrogel further acts as a protective shield against mechanical abuse. In various embodiments, the wound is in endothelial tissue, epithelial tissue, the lung, the skin, or the digestive tract. The hydrogel may be placed in a body cavity. In another embodiment, the passively released growth factor causes a reduction in pain compared to a wound not contacted with the polymeric hydrogel.  
           [0011]    By “ambient conditions” is meant room temperature and pressure.  
           [0012]    By “existing conditions” is meant in situ, as in the eye or other body system.  
           [0013]    By “substantially pure” is meant having a purity of greater than 75% by weight. A growth factor of the invention is, for example, greater than 85%, 90%, 95%, or even 99% pure. Use of the term is intended to define purity from other biological compounds, e.g., proteins, carbohydrates, and lipids that are commonly associated with the growth factor in vivo.  
           [0014]    By “treating” is meant the medical management of a patient with the intent that a prevention, cure, stabilization, or amelioration of the symptoms will result. This term includes active treatment, that is, treatment directed specifically toward improvement of the disorder; palliative treatment, that is, treatment designed for the relief of symptoms rather than the curing of the disorder; preventive treatment, that is, treatment directed to prevention of the disorder; and supportive treatment, that is, treatment employed to supplement another specific therapy directed toward the improvement of the disorder. The term “treatment” also includes symptomatic treatment, that is, treatment directed toward constitutional symptoms of the disorder. The term further includes the promotion of wound closure or healing.  
           [0015]    By “wound” is meant an injury to any tissue. Examples of wounds include burns, lacerations, abrasions, bites, surgical wounds, puncture wounds, and ulcers.  
           [0016]    All percentages described in the present invention are by weight unless otherwise specified.  
         DETAILED DESCRIPTION OF THE INVENTION  
         [0017]    This invention provides a polymeric drug delivery system including a hydrogel containing a growth factor, e.g., EGF. Allowing passive transference of the growth factor from a dilute aqueous solution into the hydrogel produces the delivery system. The hydrogel, when placed in contact with a wound, delivers a low concentration of the growth factor over an extended period of time. This sustained delivery accelerates the wound healing process while avoiding potential damaging effects of localized delivery of high concentrations of compounds.  
           [0018]    Drug Delivery System  
           [0019]    Hydrogels. This invention may employ different polymer compositions that are useful in the treatment of a variety of tissues. For example, in the ocular environment, conventional soft contact lenses can be used and can be either ionic or non-ionic hydrogels containing between 37.5% -70% water by weight and can have any base curve, e.g. from 8.0 to 9.0. The contact lenses may also have the ability to correct vision, for example over a range of diopters of +8.0 to −8.0, including piano. Exemplary hydrogel contact lens materials include etafilcon A, vifilcon A, polymacon B, and a tetrapolymer of hydroxymethylmethacrylate, ethylene glycol, dimethylmethacrylate, and methacrylic acid. These materials may also be employed, in other physical forms, in treating wounds in other tissues. Other suitable hydrogel materials are known to those skilled in the art. The hydrogels may be insoluble or may dissolve over time in vivo, e.g., over one day or one week. The growth factor is passively delivered, for example, by diffusion out of the hydrogel or by release as the hydrogel dissolves.  
           [0020]    The drug delivery system is produced by partially desiccating a hydrated hydrogel (or equivalently partially hydrating a desiccated hydrogel). The desiccation step removes, for example, approximately (within ±2%) 5%, 10%, 15%, 20%, 25%, 30%, 40%, 50%, 60%, or 75% of the water in a hydrogel. Desiccation can occur, for example, by exposure of the hydrogel to ambient or humidity controlled air, by heating the hydrogel for a specific period of time, or by blowing dried gas, such as N 2 , over the hydrogel. In one embodiment, the hydrogel is saturated with physiological (isotonic) saline prior to desiccation. The partially desiccated hydrogel is then soaked, e.g., for at least 30 minutes, in a dilute aqueous solution of growth factor, e.g., at a pH between 6.9 to 7.4. The hydrogels may also be soaked for at least 1 hour, 6 hours, 12 hours, or 24 hours. The concentration of growth factor into which the hydrogel is placed is typically 10 ng/μl or less, e.g., at most 5 ng/μl, 1 ng/μl, 0.1 ng/μl, or 0.01 ng/μl. Higher concentrations may also be used, for example, to reduce the soaking time. The growth factor is passively transfered into the hydrogel. This transfer occurs at least in part by rehydrating the hydrogel. Diffusion of the growth factor into the water in the hydrogel may also occur.  
           [0021]    Typically, the concentration of growth factor transferred to the hydrogel is substantially lower than the solution in which the hydrogel is soaked. For example, the concentration of growth factor in the hydrogel is at least 2×, 5×, or 10× less than that of the soaking solution. The water content and type of hydrogel, time and conditions, e.g., temperature of soaking, composition of the soaking solution (e.g., ionic strength and pH), and type of growth factor employed also may influence the concentration of growth factor in the drug delivery system. The water content of the hydrogel also helps to determine the total amount of growth factor present in a hydrogel. Thus, the water content of a hydrogel represents another variable by which to control the amount of growth factor delivered to a tissue. The production of a hydrogel containing a specified amount of growth factor can be accomplished by routine experimentation by one skilled in the art. Exemplary hydrogels include between 5 and 350 ppb of growth factor, for example, between 5 and 250 ppb, 5 and 100 ppb, 5 and 50 ppb, or 5 and 10 ppb.  
           [0022]    Growth factors. Growth factors are a heterogeneous group of proteins capable of stimulating growth and the multiplication of cells. Exemplary growth factors include epidermal growth factor, platelet derived growth factor, hepatocytic growth factor, and combinations thereof. These growth factors may be natural, synthetic, or recombinant growth factors or growth factor derivatives from any animal, for example, humans, or any domesticated animal or pet species. Such growth factors also include biologically active growth factors and analogs. Peptide growth factors play important biological roles by regulating many of the processes involved in normal wound healing including migration, mitosis, and differentiation of cells. Growth factors are commercially available or may be isolated using methods known in the art.  
           [0023]    Other compounds. The hydrogels of the invention may also contain medicaments other than growth factors. These additional compounds include, without limitation, analgesics, anti-inflammatory drugs, antibodies, meganins, self-proteins, pharmaceutical drugs, and antibiotic compounds.  
           [0024]    The use of preservatives is non-ideal as they may transfer to a hydrogel disproportionately and cause cytotoxicity.  
           [0025]    Treatment. To treat a wound, a drug delivery system of the invention may be placed in contact with a damaged tissue. When the system is shaped as a contact lens, the lens may simply be placed in the eye normally in order to deliver the growth factor. In order to effect accelerated healing of other wounds, the hydrogel may be part of a bandage or may be adhered (e.g., by adhesives or sutures) to the wounded tissue. If the hydrogel is placed internally in a patient, the hydrogel is advantageously biodegradable.  
           [0026]    Hydrogels may be considered to be disposable and may be replaced after a specified period of time. Alternatively, a hydrogel that has a depleted amount of growth factor may be recycled by desiccating and soaking the hydrogel again.  
           [0027]    Treatment Approaches  
           [0028]    The invention may be used in conjunction with healing many types of wounds, including, without limitation, ocular, oral, lung, digestive tract, skin, large intestine, small intestine, colon, and other wounds to endothelial, mucosal, or epithelial tissues. As stated above, the invention provides accelerated healing by delivering a growth factor to an injured tissue. This delivery occurs by passive transfer and allows medications to be released into fluids of the body, e.g., ocular fluid. The growth factor stimulates proliferation of cells surrounding a wound to close the wound and replace damaged cells. Because the growth factor is localized by the hydrogel, which provides a timed release of the growth factor, a lesser amount of growth factor may in many cases be needed to effect wound healing than if, e.g., topical solutions, such as eye drops are used. Accelerated healing may also reduce the pain and inflammation associated with a particular wound and may help prevent infection. In addition, the hydrogel may also act as a physical barrier to provide protection from mechanical abuse and to prevent adherence of the healing tissue to adjacent tissues.  
           [0029]    Ocular Wounds. In one embodiment, the wound is an ocular wound, e.g., in epithelial, endothelial, or retinal tissue. The invention is of particular utility after vision correcting surgery, such as LASIK, PRK, or LASEK. Soft and collagen contact lenses may be utilized to minimize post-surgical epithelial trauma and provide a stable healing environment. PRK typically requires a therapeutic contact lens for 3-4 days, and post-operative therapeutic drops are often prescribed. In the present invention, the hydrogel may be shaped as a contact lens that acts as a reservoir for the growth factor and can serve to protect the leading edge of wound healing from normal mechanical abuse. The growth factor gradually delivered in a low concentration from the lens obviates the need for therapeutic drops. Therapeutic drops often include high concentrations of drugs because the majority of the drop is excreted from the eye in a short period of time. These high concentrations can cause additional damage to a wound, which is avoided by the use of the present, localized time-release drug delivery system.  
           [0030]    A further understanding of the invention may be obtained from the following non-limiting examples. 
       
    
    
     EXAMPLE 1  
       [0031]    Production of a Drug Delivery System.  
         [0032]    An exemplary drug delivery system was prepared as follows. Contact lenses were removed from their package and rinsed with saline to remove contact lens packing solution. The hydrogel lens materials were allowed to desiccate for 10-30 seconds. The hydrogel lens materials were placed into physiological saline that contained epidermal growth factor (EGF) at concentrations of 10 ng/μl or 5.0 ng/μl for at least 30 minutes. Lower concentrations may also be used. Longer passive transference times may also be used. Untreated or control lenses were placed in physiological saline without EGF.  
       EXAMPLE 2  
       [0033]    Healing of Ocular Tissue.  
         [0034]    Ocular cells were placed into a sterile plastic dish. This dish contained a 5-mm disk. The purpose of the disk was to prevent cells from growing in the covered area. When the disk was removed, a 5-mm “wound” or “hole” was present.  
         [0035]    Contact lenses were then added to these cell sheets with the wounds. The lenses were left in contact with the cell sheets for a minimum of 30 minutes. Minimal medium was used to maintain the cell cultures. Cells were incubated at 35° C.±2° C. in 5% CO 2 . Contact lenses with or without EGF were produced as in Example 1. The contact lenses used were polymacon B, vifilcon A, and lidofilcon A hydrogel polymers.  
         [0036]    The cell sheets were then viewed over time, and the diameter of the hole was measured.  
         [0037]    The results are expressed in terms of closure of the in vitro wound over time.  
         [0038]    Epithelial Cells and Tissue. Epithelial (rabbit corneal epithelial cells) cells were seeded on a dish and contacted with control and EGF-containing contact lenses. At 48 hours there was a 25% difference in the closure rate between the EGF-treated cells and the non-EGF treated cells. At 72 hours, there was a 43% difference in the closure rate between the EGF-treated epithelial tissue and the controls. The hydrogel material that was used was vifilcon A, an ionic polymer with a water content of 55%. The polymer had been incubated with 10 ng/μl for one hour at 4° C. prior to use in the experiments. The lens contained approximately 1 ng/μl of EGF.  
         [0039]    Closure rates were calculated by direct measurement of the diameter of the wound. Measurements were taken daily.  
         [0040]    In a related series of experiments, a vifilcon A lens was incubated under the same conditions as above with 5.0 ng/μl of EGF and then contacted with an epithelial “wound” as above. The lens contained approximately 0.5 ng/μl of EGF. At 48 hours, there was a 21% closure rate difference between controls and EGF treated hydrogel materials. At 72 hours, there was also a 21% difference in the closure rate. These results indicated that over a 72-hour period, the relative healing rates remained essentially the same for the treated and non-treated epithelial tissue, with the epithelial tissue treated with EGF always having an accelerated rate of healing.  
         [0041]    The rate of wound healing increased with increased exposure of the hydrogel material to the wound. Further, compared to a wound not contacted with any lens, at 48 hours there was a 31% difference in the healing rates. Healing for tissue exposed to a lens soaked in 10 ng/μl of EGF increased from 14% at 48 hours to 25% at 72 hours.  
         [0042]    Endothelial Cells and Tissue. Wounds caused in endothelial tissue (bovine corneal endothelial cells) were also healed by release of EGF from a vifilcon A lens. The lens, soaked in 10 ng/μl of EGF as above, showed a 73% difference in healing rates at 48 hours compared to a control. At 72 hours, the EGF-treated tissue had completely healed. In the control group, less than half (43%) of the tissue had healed. The same lens material exposed to 5 ng/μl of EGF showed a 31% difference in closure rate at 48 hours between the EGF treated group and the controls. At 72 hours, 53% of the tissue had healed in the EGF treated group, compared to 43% in the control.  
         [0043]    Lidofilcon A hydrogel (non-ionic, water content=70%) materials were evaluated for their ability to deliver EGF to endothelial tissue to close wounds. The concentration of EGF used in the soaking solution was 10 ng/μl. At 48 hours, the EGF treated tissue showed a 54% increase in the healing rate (wound closure rate) as compared to controls. At 72 hours, there was a difference of 44%.  
         [0044]    A third material, Polymacon B, that is non-ionic and has a water content of 38%, was also evaluated for the ability to deliver EGF to wounds. The lenses were prepared using a soaking solution of 10 ng/μl of EGF. At 48 hours, the wound was 60% closed in the treated group and 27% closed in the non-treated group. At 72 hours, the difference in closure between the treated and untreated groups was 62%. In the EGF treated group at 72 hours, the wound had closed by 80%, while in the untreated group, the wound had closed by 46.8%.  
         [0045]    Other Embodiments  
         [0046]    Modifications and variations of the described methods of the invention will be apparent to those skilled in the art without departing from the scope and spirit of the invention. Although the invention has been described in connection with specific desirable embodiments, it should be understood that the invention as claimed should not be unduly limited to such specific embodiments. Indeed, various modifications of the described modes for carrying out the invention, which are obvious to those skilled in the art, are intended to be within the scope of the invention.  
         [0047]    All publications, patents, and patent applications mentioned in this specification are herein incorporated by reference to the same extent as if each individual publication, patent, or patent application was specifically and individually to be incorporated by reference.  
         [0048]    Other embodiments are within the claims.