WO2008098027A2 - Treatment of ischemic retinal conditions with memantine - Google Patents

Abstract

Disclosed herein is the use of memantine for the manufacture of a medicament for preventing and treating retinal degeneration associated with vitrectomy and laser photocoagulation.

Description

TREATMENT OF ISCHEMIC RETINAL CONDITIONS WITH MEMANTINE by Inventors Adelekan O. Oyejide, James A. Burke, Brian G. Short, and Larry A. Wheeler

CROSS REFERENCE TO RELATED APPLICATIONS

[0001] The present application claims the benefit under 35 U. S. C. §119(e) to United States Provisional Patent Application Number 60/888,501 filed February 6, 2007, the entire contents of which are incorporated by reference herein.

FIELD OF THE INVENTION

[0002] The present invention relates generally to a method for the improvement of blood flow to the retina and choroid in order to halt or reverse the course of visual deterioration. More specifically, it relates to the treatment of ischemic retinal degeneration caused by increased intraocular pressure complications of vitrectomy and laser photocoagulation with memantine.

BACKGROUND OF THE INVENTION

[0003] The human retina includes three primary nuclear layers that include five major classes of neurons. The five major classes of neurons are: (i) photoreceptors (rods and cones); (ii) bipolar cells; (iii) horizontal cells; (iv) amacrine cells; and (v) ganglion cells. The outer nuclear layer (ONL) contains the photoreceptor cell bodies. The inner nuclear layer (INL) contains the cell bodies of the bipolar neurons, horizontal neurons, and amacrine neurons. Interplexiform neurons, displaced ganglion cells, and the glial cells of Muller are also located in the INL. The ganglion cell layer contains the cell bodies of most of the ganglion cells, displaced amacrine cells, and some astroglial cells.

[0004] Synaptic connections are made among the various classes of neurons, which result in the vertical and lateral flow of visual information in the retina. Both excitatory and inhibitory synaptic connections are present in the retina. Glutamate is probably the primary excitatory neurotransmitter. Gamma-aminobutyric acid (GABA) is probably a major inhibitory neurotransmitter. Other neurotransmitters are present among the various retinal neurons.

[0005] The retina is supplied with oxygen and nutrients by two vascular systems, one within the retina itself (central retinal artery) and one in the choroid (posterior ciliary artery). Interruption or impairment of either system leads to degeneration of the retina and ultimately to loss of vision. There are many diseases and conditions that affect retinal circulation and nutritional supply. Early improvement in blood flow or nutrient supply to the retina in some of these diseases and throughout the time course of others might be the key to slowing vision loss or eliminating it altogether.

[0006] Ophthalmic laser treatment is a treatment for many conditions of the eye, including age-related macular degeneration (AMD), macular edema, and photorefractive keratectomy (PRK). In addition, a number of diseases that involve macular degeneration that are potentially treated with lasers include Stargardt's disease, Best's disease, Batten's disease, Sjogren-Larsson syndrome, cone-rod dystrophy, and ovine ceroid lipofuscinosise, and Tay- Sach's disease. At least some types of AMD are caused by increased neovascularization.

[0007] Laser photocoagulation treatment utilizes thermal energy to destroy neovascular tissue. The energy of the laser heats the tissue and results in full-thickness retinal damage including secondary, collateral damage to the tissue surrounding the laser contact site. The secondary, collateral damage may result from physiological effects, such as excessive release of the neurotransmitter, glutamate, resulting from the primary damage caused by the laser. Additionally, the secondary, collateral damage may be attributed to phospholipid hydrolysis and arachidonic acid metabolites, oxygen free radicals, changes in intracellular and extracellular ion concentrations, and other excitotoxic mechanisms. The secondary damage may exacerbate the primary anatomical and physiological damage caused by the laser and may result in unwanted side effects, such as further vision loss, of the subject exposed to the laser. [0008] Ischemic retinal degeneration, or degeneration of the central part of the retina, is second only to glaucoma as a leading cause of blindness among people of all ages. It causes at least some loss of vision in 10 million people over the age of 50. This ischemic retinal degeneration is caused by various diseases, including diabetic retinopathy, glaucoma, sickle cell retinopathy, vascular abnormalities, obstructive arterial and venous retinopathies, venous capillary insufficiency, hypertensive retinopathy, inflammation, tumors, retinal detachment, etc.

[0009] Vitrectomy also induces retinal degeneration. The vitreous is a normally clear, gel-like substance that fills the center of the eye. It makes up approximately 2/3 of the eye's volume, giving it form and shape before birth. Certain problems affecting the back of the eye may require a vitrectomy, or surgical removal of the vitreous. During a vitrectomy, the surgeon creates small incisions/punctures in the eye (sclerotomies) for separate instruments. These incisions are placed in the pars plana of the eye, which is located just behind the iris but in front of the retina. The instruments which pass through these incisions include a light pipe, an infusion port, and the vitrectomy cutting device. Upon completion of pars plana vitrectomy, each sclerotomy site is closed. After a vitrectomy, the eye is filled with fluid until the vitreous is replaced as the eye secretes aqueous and nutritive fluids.

[0010] Some of the most common eye conditions that require vitrectomy include 1) complications from diabetic retinopathy, such as retinal detachment or bleeding, 2) macular hole, 3) retinal detachment, 4) pre-retinal membrane fibrosis, 5) bleeding inside the eye (vitreous hemorrhage), 6) injury or infection, and 7) certain problems related to previous eye surgery.

[0011] Glaucoma is a disease of the eye characterized by increased intraocular pressure. On the basis of its etiology, glaucoma has been classified as primary or secondary. For example, primary glaucoma in adults (congenital glaucoma) may be either open-angle or acute or chronic angle- closure. Secondary glaucoma results from pre-existing ocular diseases such as uveitis, intraocular tumor or an enlarged cataract. [0012] The underlying causes of primary glaucoma are not yet known. The increased intraocular tension is due to the obstruction of aqueous humor outflow. In chronic open-angle glaucoma, the anterior chamber and its anatomic structures appear normal, but drainage of the aqueous humor is impeded. In acute or chronic angle-closure glaucoma, the anterior chamber is shallow, the filtration angle is narrowed, and the iris may obstruct the trabecular meshwork at the entrance of the canal of Schlemm. Dilation of the pupil may push the root of the iris forward against the angle, and may produce pupilary block and thus precipitate an acute attack. Eyes with narrow anterior chamber angles are predisposed to acute angle-closure glaucoma attacks of various degrees of severity.

[0013] Secondary glaucoma is caused by any interference with the flow of aqueous humor from the posterior chamber into the anterior chamber and subsequently, into the canal of Schlemm. Inflammatory disease of the anterior segment may prevent aqueous escape by causing complete posterior synechia in iris bombe, and may plug the drainage channel with exudates. Other common causes are intraocular tumors, enlarged cataracts, central retinal vein occlusion, trauma to the eye, operative procedures and intraocular hemorrhage.

[0014] Considering all types together, glaucoma occurs in about 2% of all persons over the age of 40 and may be asymptotic for years before progressing to rapid loss of vision. Several topical ophthalmic therapeutic agents are currently administered to patients in an effort to reduce intraocular pressure, including prostaglandins and prostamides, α₂-adrenergic agonists, β-adrenergic antagonists, and others.

[0015] In addition to intraocular pressure reduction, a complimentary approach to the treatment of the sequelae of glaucoma is the administration of neuroprotective agents. Glaucoma is associated with an increase in the rate of retinal ganglion cell loss, resulting in vision loss. U.S. Pat. No. 6,482,854 and Sugrue (Journal of Medicinal Chemistry, 1997, Vol. 40, No. 18, 2793- 2809) teach the use of neuroprotective agents to treat glaucoma. While the exact mechanism of these neuroprotective agents may not be unambiguously established, it is believed that these compounds work as glutamate antagonists. Retinal ganglion cells, like other ganglion cells, have surface receptors for glutamate as well as other amino acids, which trigger neuronal excitation. However, excess amino acid associated neuroexcitation causes neuronal degeneration and cell death. In the case of glaucoma, vitreous concentrations of glutamate are double that of a healthy individual, and thus it is believed that the excess glutamate causes accelerated ganglion cell loss and accompanying loss of vision. There are several types of glutamate receptors which are classified based on their function and mechanism of action. One class of glutamate receptors, the ionotropic receptors, works through Ca²⁺-specific ion channels. This class can be divided into subclasses based upon their selective agonists. It is believed that adamantane-based amines act as antagonists to one of these subclasses of receptors, the N- methyl-D-aspartate (NMDA) receptor.

SUMMARY OF THE INVENTION

[0016] The present invention is applicable to the treatment or prevention of visual deterioration associated with diseases or conditions that cause retinal ischemia or decrease retinal or choroidal blood flow. Specifically, the present invention is directed to methods of treating vitrectomy and laser- photocoagulation-induced retinal degeneration with memantine.

[0017] In one embodiment, a method of treating vitrectomy-induced retinal degeneration is provided comprising administering a therapeutically effective amount of memantine to a mammal in need thereof. The memantine can be administered either before or after vitrectomy and can be administered as an oral dose, as a time-release depot or can be directly injected at the area of retinal degeneration.

[0018] In another embodiment, a method of treating laser photocoagulation-induced retinal degeneration is provided comprising administering a therapeutically effective amount of memantine to a mammal in need thereof. The memantine can be administered either before or after laser photocoagulation and can be administered as an oral dose, as a time-release depot or can be directly injected at the area of retinal degeneration.

BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 depicts retinal necrosis of pressure-induced ischemia which is abrogated by oral memantine (Figure 1A). Normal retina is depicted in Figure 1 B. Six months after placebo treatment and pressure-induced ischemia, there is collapse of the outer segment with marked degeneration and necrosis of the outer nuclear layer (ONL) and inner nuclear layer (INL) (Figure 1C). Hematoxylin and eosin, x200.

[0020] Figure 2 depicts retinal immunoreactivity with an antibody to neuron-specific enolase (NSE) (Figure 2A). In the Normal retina, NSE reactivity in the ganglion cell layer (GCL), ONL, and INL regions is strong (Figure 2B). Six months after placebo treatment and pressure-induced ischemia, there is marked reduction and disorderly arrangement of NSE- reactive cells in the ONL and INL (Figure 2C). Hematoxylin and eosin, x 200.

[0001] Figure 3 depicts retinal glial fibrillary acidic protein (GFAP) immunoreactivity (Figure 3A). In normal retina, an orderly arrangement of glial fibers extend from just below the inner limiting membrane to the outer plexiform layer (OPL) (Figure 2B). Six months after placebo treatment and pressure-induced ischemia, GFAP-immunoreactive bands of glial fibers twist around the entire atrophic retina (Figure 2C). Hematoxylin and eosin, x400.

[0021] Figure 4 depicts retinal anti-macrophage antibody (RAM11) reactivity (Figure 4A). The normal retina shows no reactivity with RAM11 (Figure 4B). Six months after placebo treatment and pressure-induced ischemia, hypertrophic retinal pigment epithelial (RPE) cells and macrophages/migratory RPE cells (arrow) scattered through the retina were strongly immunoreactive with RAM11 (Figure 4C). Following memantine treatment, occasional RPE cell aggregates (arrow) remained strongly RAM11- positive. Hematoxylin and eosin, x400.

DEFINITIONS OF TERMS [0022] In this specification and in the claims which follow, reference will be made to a number of terms which shall be defined to have the following meanings:

[0023] "Decreased blood flow" as used herein refers to choroidal or retinal blood flow that is below normal human retinal blood flow. Normal blood flow has been reported in the range of 8.1 to 18.5 μl/min/mg tissue.

[0024] "Ischemic retinal degeneration" is the degeneration of the retina and occurs as a result of the impairment or interruption of the supply of oxygen or other nutrients to the retina via the central retinal artery or to the choroid via the posterior ciliary artery. Such impairment or interruption may result from various diseases and conditions such as diabetic retinopathy, glaucoma, sickle cell retinopathy, vascular abnormalities, obstructive arterial and venous retinopathies, venous capillary insufficiency, hypertensive retinopathy, inflammation, tumors, and retinal detachment.

[0025] "Pharmaceutical composition" refers to a composition containing the pharmaceutically active substance. The composition may also contain a pharmaceutically acceptable vehicle.

[0026] "Pharmaceutically active substance" as used herein refers to a substance that has been shown to be useful in the treatment of decreased ocular blood flow. In the present invention, pharmaceutically active substances include droperidol.

[0027] "Prevention" refers to the treatment of patients with decreased retinal and/or choroidal blood flow to avoid visual deterioration (prophylaxis).

[0028] "Therapeutically effective amount" as used herein refers to an amount of a pharmaceutically active substance useful in the prevention or treatment of visual deterioration.

[0029] "Treatment" as used herein refers to the reduction or elimination of visual deterioration resulting from decreased blood flow to the retina and choroid (therapy). DETAILED DESCRIPTION OF THE INVENTION

[0030] The present invention is applicable to the treatment or prevention of visual deterioration associated with diseases or conditions that cause retinal ischemia or decrease retinal or choroidal blood flow. Memantine has been shown to prevent loss of retinal cells following pressure-induced retinal ischemia. Low tension glaucoma and ischemic retinal degeneration appear to be associated with decreased ocular blood flow. Accordingly, the use of memantine affords a method for treating these disorders. Additionally, memantine does not produce local irritation to the eyes.

[0031] Memantine (Namenda™) (1-amino-3,5-dimethyl adamantane), which is disclosed, e.g., in U.S. Pat. Nos. 4,122,193; 4,273,774; and 5,061 ,703, is a systemically-active non-competitive NMDA receptor antagonist having low to moderate affinity for the receptor and strong voltage dependency and rapid blocking/unblocking kinetics.

[0032] The present invention is directed to the use of memantine in the therapy or prevention of vitrectomy- and laser photocoagulation-induced retinal degeneration. In a method of treatment of retinal degeneration, a therapeutically effective amount of the memantine is administered to a patient in need thereof.

[0033] The administration of memantine can be via any of the accepted modes of administration of pharmaceutical compositions. These methods include topical administration of solutions, suspension ointments or gels, parenteral injection, oral administration, direct injection at the site of retinal degeneration or implantation of a time-release depot adjacent to the site of retinal degeneration.

[0034] Depending on the intended mode of administration, the compositions may be in the form of solid, semi-solid or liquid dosage forms, such as for example, tablets, pills, capsules, powders, liquids, suspensions, or the like, preferably in unit dosage forms suitable for single administration of precise dosages. The compositions will include a conventional pharmaceutical vehicle and, in addition, may include other medicinal agents, pharmaceutical agents, carriers, adjuvants, diluents, etc. The amount of active compound administered will, of course, be dependent on the subject being treated, the manner of administration and the judgment of the prescribing physician.

[0035] The conventional pharmaceutical vehicle should be compatible with the pharmaceutically active substance of the pharmaceutical composition. Suitable vehicles for ocular use are, for example, sterile isotonic solutions such as isotonic sodium chloride or boric acid solutions. These vehicles typically contain sodium chloride or boric acid, respectively, as well as benzalkonium chloride and sterile distilled or purified water. Also useful is phosphate buffered saline (PBS), pH 7.4. Other suitable vehicular constituents include phenylmercuric nitrate, sodium sulfate, sodium sulfite, disodium phosphate and monosodium phosphate.

[0036] The compositions may also contain auxiliary substances, i.e. antimicrobial agents such as chlorobutanol, parabens or organic mercurial compounds; pH adjusting agents such as sodium hydroxide, hydrochloric acid or sulfuric acid; and viscosity increasing agents such as methylcelluiose. One of ordinary skill in the art will easily find substitutes for the above auxiliary substances. The final composition should be sterile, essentially free of foreign particles, and have a pH that allows for optimum drug stability. Generally, pH values in the range of 5-8 will find use with the subject composition. Preferably, the pH will be as close to the pH of tear fluid, i.e. 7.4 as possible.

[0037] Typically, the compositions of the subject invention are prepared as solutions, suspensions, ointments, gels, or ocular delivery devices such as drug-impregnated solid carriers (depots) that are inserted into the eye. If such a carrier is used, the above-mentioned vehicles are unnecessary. A variety of polymers can be used to formulate ophthalmic drug carriers. Saettone, M. F., et al., J. Pharm. Pharmocol (1984) 36:229, and Park, K. et al., in Recent Advances in Drug Delivery Systems, Anderson et al., eds., Plenum Press (1984) 163-183, describe such polymers, the disclosures of which are incorporated herein by reference in their entirety. Drug release is generally effected via dissolution or bioerosion of the polymer, osmosis, or combinations thereof. The depot should be formulated to release the drug at a rate that does not significantly disrupt the tonicity of tear fluid.

[0038] More specifically, several matrix-type delivery systems can be used with the subject invention. These systems are described in detail in Ueno et al., "Ocular Pharmacology of Drug Release Devices", in Controlled Drug Delivery, Bruck, ed., vol. II, Chap 4 CRC Press Inc. (1983), the disclosure of which is incorporated herein by reference in its entirety. Such systems include hydrophilic soft contact lenses impregnated or soaked with the desired drug, as well as biodegradable or soluble depots that need not be removed after placement in the eye. These soluble ocular inserts can be composed of any degradable substance that can be tolerated by the eye and that is compatible with the drug to be administered. Such substances include but are not limited to polyvinyl alcohol), polymers and copolymers of polyacrylamide, ethylacrylate, and vinylpyrrolidone, as well as cross-linked polypeptides or polysaccharides, such as chitin.

[0039] The composition of the invention may comprise memantine and at least one pharmaceutically acceptable excipient. An exemplary oral composition comprises memantine, a diluent, a binder, a disintegrant, a glidant, a surfactant, a lubricant, and a coating. Preferably, the memantine is in the form of memantine hydrochloride, which, more preferably, is present in an amount of between about 2 to about 6 percent, preferably, about 3 to about 5 percent by weight of the composition.

[0040] Disclosed herein is a method of treating retinal ischemia comprising administering a therapeutically effective amount of memantine to a mammal in need thereof. In one embodiment, the ischemia is acute ischemia. In another embodiment, memantine is administered before onset of acute ischemia. In another embodiment, the ischemia is associated with photoreceptor cell loss.

[0041] For the purposes of this disclosure, "treat," "treating," or "treatment" refer to the use of a compound, composition, therapeutically active agent, or drug in the diagnosis, cure, mitigation, treatment, or prevention of disease or other undesirable condition.

[0042] The terms "memantine", "amantadine", and "rimantadine" as used herein refer to the free base forms of the amine, or any of the various salts, such as memantine hydrochloride, which can be prepared by the addition of an acid to the free base. The determination of the amount of memantine used in the compositions disclosed herein is well within the ability of one having ordinary skill in the art. An "effective" amount of memantine is an amount which has a detectable effect over a similar composition or method which comprises no memantine or any other active ingredient which would be expected to have an effect similar to that of memantine.

[0043] In referring to concentrations of memantine herein, the numeric value for the concentration is understood to be the concentration of the free base, regardless of the form in which the memantine is used. Since there is a large range of concentrations or amounts at which memantine is effective, the concentration or amount of memantine as used herein may vary. One embodiment comprises from 0.05 to 5% memantine. Other embodiments comprise from 0.05% to 2% memantine. Some compositions comprise from 0.05% to 2.5% memantine. Another composition comprises from 0.2% to 3% memantine. Some compositions comprise from 0.1 to 2% memantine. Other compositions comprise from 0.5% to 2% memantine. Another embodiment comprises from 0.5% to 3.5% memantine. Other embodiments comprise from 0.3% to 1.5%. Another composition comprises from 0.5% to 1.3% memantine. Other embodiments comprise from 0.1% to 1 % memantine. Another embodiment comprises from about 0.5% to about 1 % memantine. Other composition comprise about 0.5% memantine. Other compositions comprise about 1% memantine.

[0044] The compositions can also include a polyanionic polymer. The term "polyanionic polymer" refers, in the broadest sense understood in the art, to a polymer comprising several anionic moieties. While not intending to limit the scope of the invention in any way, typical examples of polyanionic polymers are carboxymethylcellulose, hyaluronic acid, carboxymethylamylose, anionic polymers derived from acrylic acid (meaning to include polymers from acrylic acid, acrylates and the like and mixtures thereof), anionic polymers derived from methacrylic acid (meaning to include polymers from methacrylic acid, methacrylates, and the like and mixtures thereof), poly(methacrylic acid) derivatives, polyphospazene derivatives, poly(aspartic acid), anionic polymers of amino acids (meaning to include polymers of amino acids, amino acid salts, and the like and mixtures thereof), acidic gelatin, and anionic polymers derived from alginic acid (meaning to include alginic acid, alginates, and the like and mixtures thereof). In one embodiment, the polyanionic polymer comprises carboxymethylcellulose. Carboxymethylcellulose is a polyanionic species, and thus may have one or more countering cations, by which it may be referred. For example, sodium carboxymethylcellulose refers to a carboxymethylcellulose having sodium as the counterion.

[0045] While not intending to limit the scope of the invention in any way, it is often useful to include a buffer in ophthalmic compositions to maintain the pH from about 6 to about 8 for optimal comfort. Buffers used are those known to those skilled in the art, and, while not intending to be limiting, some examples are acetate, borate, carbonate, citrate, and phosphate buffers. Tonicity agents such as glycerin, mannitol, sorbitol, sodium chloride, and other electrolytes may also be used in ophthalmic compositions to adjust the concentration of dissolved material to the desired isotonic range. Surfactants such as polysorbates, poloxamers, alcohol ethoxylates, ethylene glycol- propylene glycol block copolymers, fatty acid amides, alkylphenol ethoxylates, or phospholipids may also be used in ophthalmic compositions. Chelating agents may also be used in ophthalmic compositions to enhance preservative effectiveness. While not intending to be limiting, some useful chelating agents are edetate salts, like edetate disodium, edetate calcium disodium, edetate sodium, edetate trisodium, and edetate dipotassium. The foregoing discussion of compounds typically used in ophthalmic compositions is given purely for purposes of example, to more readily enable a person of ordinary skill in the art to carry out the methods disclosed herein, and is not intended to limit the scope of the invention in any way.

[0046] Dosages and desired drug concentrations of memantine may vary depending on the particular use envisioned. The determination of the appropriate dosage or route of administration is well within the skill of an ordinary physician. Animal experiments provide reliable guidance for the determination of effective doses for human therapy. Interspecies scaling of effective doses can be performed following the principles laid down by Mardenti, J. and Chappell, W. "The use of interspecies scaling in toxicokinetics" In Toxicokinetics and New Drug Development, Yacobi et al, Eds., Pergamon Press, New York 1989, pp. 42-96. The term "therapeutically effective" amount as used herein refers to the amount needed to perform the particular treatment such as, for example, cancer. "Treatment" refers to both therapeutic treatment and prophylactic or preventative measures, wherein the object is to prevent or slow down (lessen) the targeted pathologic condition or disorder. Those in need of treatment include those already with the disorder as well as those prone to have the disorder or those in whom the disorder is to be prevented.

[0047] Diseases associated with ischemia that may be treated by the present method include acute glaucoma, including acute angle closure glaucoma, retinitis pigmentosa, age-related macular degeneration, Stargardt's disease, and inherited retinal degeneration, acute angle glaucoma, vitrectomy-induced retinal degeneration, laser photocoagulation-induced retinal degeneration and retinal degeneration induced by increased intraocular pressure.

[0048] In particular the treatment may involve treating photoreceptor loss associated with one of these conditions. Some clinical conditions that involve loss of photoreceptor cells include macular degeneration, retinitis pigmentosa (RP), Stargardt's disease, Best's vitelliform macular dystrophy, choroideremia, rod-cone dystrophy, congenital stationary night blindness and Leber's congenital amaurosis. [0049] Macular degeneration is a blinding disease caused by the death of the photoreceptor cells in that part of the retina known as the macula. The macula is a circular area, approximately 3 mm or about 1/10 inch in diameter, that is located next to the optic nerve. In the age-related form of macular degeneration (ARMD), photoreceptor cells within the macula die off slowly, thus accounting for the progressive loss of vision that usually begins after the fifth or sixth decade of life. As one moves toward the center of the macula, the percentage of cones rises sharply, and reaches 100% in the center of a specialized region called the fovea. It is the degeneration of photoreceptor cells, primarily in the macula, that accounts for the loss of central vision and fine detail vision that defines ARMD.

[0050] Retinitis pigmentosa causes the degeneration of photoreceptor cells in the retina. Photoreceptor cells capture and process light helping a person to see. As these cells degenerate and die, patients experience progressive vision loss.

[0051] Stargardt's disease is a severe form of macular degeneration that begins in late childhood, leading to legal blindness. Stargardt's disease is symptomatically similar to age-related macular degeneration, and it affects approximately one in 10,000 children.

[0052] Lesions in Best's vitelliform macular dystrophy (affects central vision at an early age) are restricted to the eye. No systemic associations exist. Abnormalities in the eye result from a disorder in the retinal pigment epithelium (RPE). Lipofuscin (periodic acid-Schiff [PAS] positive) accumulates within the RPE cells and in the sub-RPE space, particularly in the foveal area. The RPE appears to have degenerative changes in some cases, and secondary loss of photoreceptor cells has been noted. Based on our data, memantine may be able to stop or slow down RPE degeneration and photoreceptor cell loss.

[0053] Choroideremia is a rare inherited disorder that causes progressive loss of vision due to degeneration of the choroid and retina. [0054] Rod-Cone Dystrophy is the name given to a wide range of eye conditions. The common link is a problem with the rod and cone photoreceptors. Photoreceptor cells convert light into nerve signals that ultimately get transmitted to our brain through our optic nerve. There are two types of photoreceptor cells; cones which help us detect color and fine details and account for our central vision; while the rods help us see in low light and help us with night and peripheral vision. With Rod-Cone Dystrophy, one's photoreceptor cells may not work from childhood, or may lose their ability to function over time.

[0055] Congenital stationary night blindness is an inherited eye disorder that is not progressive ("stationary") and principally affects the rod photoreceptors in the retina, impairing night vision. There may also be moderate to high myopia (short sightedness).

[0056] Leber's congenital Aamaurosis (LCA; RP at birth) is a degenerative disease that results in a severe loss of vision. This disease is thought to be caused by abnormal development of photoreceptor cells in the retina or perhaps the extremely premature degeneration of the retinal cells. Typically a baby with LCA will have very reduced vision at birth although the retina may appear normal when first examined. Within months, however, parents will usually notice nystagmus - an involuntary, rhythmical, repeated movement of the eyes. Children with LCA account for 10-18% of all cases of congenital blindness.

Example 1

[0057] Memantine hydrochloride, a moderate affinity N-methyl-D- aspartate (NMDA)-receptor antagonist, has shown retinal neuroprotective effects in short-term studies in a variety of rodent models. Repeated dosing also conferred neuroprotection in glaucomatous monkeys. The purpose of this study was to evaluate the effects of a single oral dose of memantine (20 mg/kg) on retinal histology 6 months after an acute retinal ischemic insult in rabbits. [0058] Four Dutch-belted rabbits weighing approximately 2.5 kg each were used, in accordance with the ARVO Statement for the Use of Animals in Ophthalmic and Vision Research and protocols approved by the Institutional Animal Care and Use Committee of Allergan, Inc. Each rabbit received either a single oral dose of 20 mg/kg memantine (n = 2) or 50 mg sugar (placebo) (n = 2) in a gelatin capsule. Two hours later, rabbits were anesthetized with isofluorane, and unilateral acute retinal ischemia was induced by raising intraocular pressure to 120 mm Hg for 45 minutes following gravity-flow injection of phosphate-buffered saline into the anterior chamber. At six months, animals were humanely sacrificed and ocular tissues harvested into Davidson's fixative. Histopathological evaluation was performed on sections of the central retina stained with hematoxylin and cosin. Additional sections were analyzed for immunoreactivity with the following antibodies: neuron- specific enolase (NSE) (Dako North America, Inc.; Carpinteria, CA), mouse anti— glial fibrillary acidic protein (GFAP) (Lab Vision Corp.; Fremont, CA), and mouse anti-rabbit macrophage (RAM11) (Dako, Inc.). Purified IgG served as a negative control. Sections were incubated with diluted primary antibodies overnight at 4°C. Immunoreactivity was detected with biotinylated goat anti- rabbit, goat anti-mouse, or Mouse On Mouse biotinylated anti-mouse IgG secondary antibodies and the avidin-biotin-peroxidase complex (Vector Laboratories, Inc; Burlingame, CA). An immunoreactive signal was developed using diaminobenzidine (DAB) (Zymed Laboratories; San Francisco, CA). Photomicrographs were taken with an Olympus AX70 microscope equipped with the RT Color Spot Camera system (Diagnostic Instruments, Inc; Sterling Heights, Ml). Histopathologic lesions and immunoreactivity were scored on a semiquantitative scale from 1+ (minimal severity/reactivity) to 4+ (marked severity/reactivity).

[0059] Pressure-induced global ischemia caused marked retinal injury in vehicle-treated eyes. At six months, the ischemic lesion was characterized by severe disorganization, degeneration, and necrosis of cells in all retinal layers, resulting in moderate to severe attenuation of the retina (Figure 1B). There was mild (2+) reduction in the number of nuclei in the ganglion cell layer (GCL) (Table 1). The inner nuclear layer (INL) was reduced to 1 or 2 cell layers thick, while the outer nuclear layer (ONL) was severely and diffusely degenerate and necrotic. The photoreceptor layer was most severely (4+) and consistently affected, showing diffuse absence. The retinal pigment epithelium (RPE) showed multifocal areas of irregularity, hypertrophy, and hyperplasia (Figure 1 B). These RPE changes were especially prominent in areas of focal retinal detachment. In contrast, memantine-treated animals subjected to pressure induced ocular ischemia showed significantly better preservation of retinal cells in all layers. While nuclei in the GCL were slightly fewer than in the ischemic, placebo-treated eyes, neuronal nuclei in the INL and ONL showed comparable or only slightly reduced density when memantine-treated ischemic eyes were compared to the placebo-treated, nonischemic retina (Figures 1A, 1C). However, minimal RPE proliferation persisted in the memantine-treated ischemic eyes up to 6 months (Table 1).

OD = ischemic eye; OS = normal eye; INL = inner nuclear layer; ONL = outer nuclear layer,

PRL = photoreceptor layer, Deg = degeneration

Lesion Severity Score: 0 = none; 1+ = minimal; 2+ = mild; 3+ = moderate; 4+ = marked

[0060] Placebo-treated rabbits with superimposed retinal ischemia showed minimal (1+) NSE immunoreactivity in comparison to placebo-treated, nonischemic eyes, which showed marked (4+) NSE immunoreactivity (Table 2; Figure 2). Thus, acute retinal ischemia resulted in neuronal loss at all levels of the retina, which apparently progressed and persisted up to six months. The photoreceptor layer showed diffuse pallor and lack of NSE reactivity. Memantine was associated with only minimal loss of NSE reactivity in the ONL and GCL layers, consistent with the histologic evidence of neuronal loss in these layers. NSE immunoreactivity in the INL of memantine-treated ischemic eyes was only slightly lower than in the INL of placebo-treated, nonischemic eyes (Table 2; Figures 2C, 2A).

[0061] In retinas from placebo-treated, nonischemic eyes, GFAP immunoreactivity was moderate and confined to the cell bodies and axons of ganglion cells and neurites in the inner plexiform layer (IPL), with extensions sometimes reaching to the distal end of the INL (Figure 3A). By contrast, there was a marked increase in GFAP immunoreactivity (Table 2; Figure 3B) in retinal sections from placebo treated ischemic eyes, and the thickened immunoreactive glial fibers were irregularly dispersed across the attenuated retinal thickness in a manner reminiscent of glial scar tissue. Retinal GFAP immunoreactivity in the memantine-treated, ischemic group was similar to that described for the placebo-treated, nonischemic eyes (Table 2), except that in the memantine group, a slight increase in GFAP labeling (and therefore glial activity) was apparent in the IPL (Figure 3C). Thus, the severe retinal gliosis of pressure-induced ischemia was largely abrogated by memantine.

[0062] Presumptive macrophages (anti-RAM 11 -labeled cells) were not seen in placebo-treated, nonischemic retinas, indicating the absence of residual inflammation. By contrast, anti-macrophage antibody was moderately (3+) immunoreactive for swollen, hypertrophic, "activated" RPE cells in placebo-treated, ischemic retinas (Table 2; Figure 4B). Within the atrophic retinal layers, similarly immunoreactive cells likely representing presumptive migrating RPE/macrophages were observed (Figure 4B). The RPE layer of memantine-treated animals showed significantly reduced numbers of these hypertrophic and macrophage antibody immunoreactive "activated" cells (Table 2; Figure 4C). Thus, although minimal in severity, RPE proliferation persisted in the memantine-treated ischemic eyes up to six months.

Table 2. Retinal Immunoreactivity

Animal NSE GFAP RAM11

OD = ischemic eye; OS = normal eye;

Immunoreactivity Score: O = none; 1+ = minimal; 2+ = mild; 3+ = moderate; 4+ = marked

[0063] In this study, pressure-induced ischemia resulted in various degrees of damage to the retina, lmmunohistochemistry confirmed that proliferative glial cells repaired the damaged retina, and neurons and nerve fibers could not regenerate. Furthermore, ischemia-induced retinal damage was significantly inhibited by a single 20 mg oral dose of memantine. The neuroprotective effect of memantine manifested histologically in a variety of ways, including inhibition of neuronal cell death, prevention of glial cell proliferation, inhibition of retinal detachment, and deactivation of RPE/macrophage proliferation. Neuronal cell loss is readily explained by glutamatergic excitotoxicity. The stimuli for glial cell proliferation, on the other hand, are potentially myriad. For example, retinal microglia may respond to hypoxia and ischemia with hypertrophy, enhanced enzymatic activity, and transient increase in density, and gliosis may also occur in direct response to retinal ganglion cell damage, axonal degeneration, photoreceptor degeneration, or RPE proliferation. As expected, activated RPE cells were immunoreactive for antimacrophage antibody; this is consistent with previous data indicating that constitutive expression of macrophage epitopes by neuroectodermally-derived RPE cells extends their immunophenotypic similarities with mesenchymally-derived mononuclear phagocytes. As a noncompetitive, moderate affinity, NMDA-receptor antagonist, the therapeutic value of memantine hinges on its ability to transiently block NMDA receptors and prevent glutamatergic excitotoxicity. Memantine may be expected to provide therapeutic retinal neuroprotection in rabbits with dysregulated glutamatergic neurotransmission because two major cell types, photoreceptors and ganglion cells, are known to be glutamatergic in adult rabbits. Thus, data presented here confirm earlier findings regarding the neuroprotective potential of memantine and suggest that oral memantine may protect the retina against the degenerative and necrotic lesions classically associated with acute ischemic insult.

[0064] In rabbits, pressure-induced ischemia caused ganglion cell, INL, ONL, and photoreceptor cell degeneration and necrosis, accompanied by retinal detachment and RPE proliferation that persisted up to six months in the central retina.

[0065] lmmunohistochemistry confirmed that proliferative glial cells repaired the damaged retina, and neurons and nerve fibers could not regenerate. Ischemia-induced retinal damage was largely abrogated by a single 20 mg oral dose of memantine administered two hours prior to the ischemic insult.

[0066] Oral memantine protects the retina against the degenerative and necrotic lesions classically associated with acute ischemia. Memantine is useful in preservation/restoration of retinal histology in preexisting retinal ischemia. These results show that memantine protects and rescues photoreceptor cells from acute ischemic injury.

[0067] Unless otherwise indicated, all numbers expressing quantities of ingredients, properties such as molecular weight, reaction conditions, and so forth used in the specification and claims are to be understood as being modified in all instances by the term "about." Accordingly, unless indicated to the contrary, the numerical parameters set forth in the specification and attached claims are approximations that may vary depending upon the desired properties sought to be obtained by the present invention. At the very least, and not as an attempt to limit the application of the doctrine of equivalents to the scope of the claims, each numerical parameter should at least be construed in light of the number of reported significant digits and by applying ordinary rounding techniques. Notwithstanding that the numerical ranges and parameters setting forth the broad scope of the invention are approximations, the numerical values set forth in the specific examples are reported as precisely as possible. Any numerical value, however, inherently contains certain errors necessarily resulting from the standard deviation found in their respective testing measurements.

[0068] The terms "a," "an," "the" and similar referents used in the context of describing the invention (especially in the context of the following claims) are to be construed to cover both the singular and the plural, unless otherwise indicated herein or clearly contradicted by context. Recitation of ranges of values herein is merely intended to serve as a shorthand method of referring individually to each separate value falling within the range. Unless otherwise indicated herein, each individual value is incorporated into the specification as if it were individually recited herein. All methods described herein can be performed in any suitable order unless otherwise indicated herein or otherwise clearly contradicted by context. The use of any and all examples, or exemplary language (e.g., "such as") provided herein is intended merely to better illuminate the invention and does not pose a limitation on the scope of the invention otherwise claimed. No language in the specification should be construed as indicating any non-claimed element essential to the practice of the invention.

[0069] Groupings of alternative elements or embodiments of the invention disclosed herein are not to be construed as limitations. Each group member may be referred to and claimed individually or in any combination with other members of the group or other elements found herein. It is anticipated that one or more members of a group may be included in, or deleted from, a group for reasons of convenience and/or patentability. When any such inclusion or deletion occurs, the specification is deemed to contain the group as modified thus fulfilling the written description of all Markush groups used in the appended claims.

[0070] Certain embodiments of this invention are described herein, including the best mode known to the inventors for carrying out the invention. Of course, variations on these described embodiments will become apparent to those of ordinary skill in the art upon reading the foregoing description. The inventor expects skilled artisans to employ such variations as appropriate, and the inventors intend for the invention to be practiced otherwise than specifically described herein. Accordingly, this invention includes all modifications and equivalents of the subject matter recited in the claims appended hereto as permitted by applicable law. Moreover, any combination of the above-described elements in all possible variations thereof is encompassed by the invention unless otherwise indicated herein or otherwise clearly contradicted by context.

[0071] Furthermore, numerous references have been made to patents and printed publications throughout this specification. Each of the above-cited references and printed publications are individually incorporated herein by reference in their entirety.

[0072] In closing, it is to be understood that the embodiments of the invention disclosed herein are illustrative of the principles of the present invention. Other modifications that may be employed are within the scope of the invention. Thus, by way of example, but not of limitation, alternative configurations of the present invention may be utilized in accordance with the teachings herein. Accordingly, the present invention is not limited to that precisely as shown and described.

Claims

What is claimed is:

1. A method of treating vitrectomy-induced retinal degeneration comprising administering a therapeutically effective amount of memantine to a mammal in need thereof.

2. The method of claim 1 wherein said memantine is administered before vitrectomy.

3. The method of claim 1 wherein said memantine is administered after vitrectomy.

4. The method of claim 1 wherein the step of administering a therapeutically effective amount of memantine comprises administration of an oral dosage of memantine.

5. The method of claim 1 wherein the step of administering a therapeutically effective amount of memantine comprises implantation of a memantine-containing time-release depot.

6. The method of claim 1 wherein the step of administering a therapeutically effective amount of memantine comprises injection of memantine at a site of retinal degeneration.

7. A method of treating laser photocoagulation-induced retinal degeneration comprising administering a therapeutically effective amount of memantine to a mammal in need thereof.

8. The method of claim 7 wherein said memantine is administered before laser photocoagulation.

9. The method of claim 7 wherein said memantine is administered after laser photocoagulation.

10. The method of claim 7 wherein the step of administering a therapeutically effective amount of memantine comprises implantation of a memantine-containing time-release depot.

11. The method of claim 7 wherein the step of administering a therapeutically effective amount of memantine comprises injection of memantine at a site of retinal degeneration.