EP1067922A1 - Agents et procedes de modulation du transfert du zinc a l'aide de metallothioneine - Google Patents

Agents et procedes de modulation du transfert du zinc a l'aide de metallothioneine

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Publication number
EP1067922A1
EP1067922A1 EP99916366A EP99916366A EP1067922A1 EP 1067922 A1 EP1067922 A1 EP 1067922A1 EP 99916366 A EP99916366 A EP 99916366A EP 99916366 A EP99916366 A EP 99916366A EP 1067922 A1 EP1067922 A1 EP 1067922A1
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EP
European Patent Office
Prior art keywords
zinc
glutathione
metallothionein
chelates
release
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EP99916366A
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German (de)
English (en)
Inventor
Bert L. Vallee
Wolfgang Maret
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Endowment for Research in Human Biology Inc
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Endowment for Research in Human Biology Inc
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    • A—HUMAN NECESSITIES
    • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
    • A61K—PREPARATIONS FOR MEDICAL, DENTAL OR TOILETRY PURPOSES
    • A61K31/00—Medicinal preparations containing organic active ingredients
    • A61K31/70—Carbohydrates; Sugars; Derivatives thereof
    • A61K31/7042—Compounds having saccharide radicals and heterocyclic rings
    • A61K31/7048—Compounds having saccharide radicals and heterocyclic rings having oxygen as a ring hetero atom, e.g. leucoglucosan, hesperidin, erythromycin, nystatin, digitoxin or digoxin
    • A—HUMAN NECESSITIES
    • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
    • A61K—PREPARATIONS FOR MEDICAL, DENTAL OR TOILETRY PURPOSES
    • A61K31/00—Medicinal preparations containing organic active ingredients
    • A—HUMAN NECESSITIES
    • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
    • A61K—PREPARATIONS FOR MEDICAL, DENTAL OR TOILETRY PURPOSES
    • A61K31/00—Medicinal preparations containing organic active ingredients
    • A61K31/13—Amines
    • A61K31/145—Amines having sulfur, e.g. thiurams (>N—C(S)—S—C(S)—N< and >N—C(S)—S—S—C(S)—N<), Sulfinylamines (—N=SO), Sulfonylamines (—N=SO2)
    • A—HUMAN NECESSITIES
    • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
    • A61K—PREPARATIONS FOR MEDICAL, DENTAL OR TOILETRY PURPOSES
    • A61K31/00—Medicinal preparations containing organic active ingredients
    • A61K31/185—Acids; Anhydrides, halides or salts thereof, e.g. sulfur acids, imidic, hydrazonic or hydroximic acids
    • A61K31/19—Carboxylic acids, e.g. valproic acid
    • A61K31/195—Carboxylic acids, e.g. valproic acid having an amino group
    • A61K31/197—Carboxylic acids, e.g. valproic acid having an amino group the amino and the carboxyl groups being attached to the same acyclic carbon chain, e.g. gamma-aminobutyric acid [GABA], beta-alanine, epsilon-aminocaproic acid or pantothenic acid
    • A61K31/198—Alpha-amino acids, e.g. alanine or edetic acid [EDTA]
    • A—HUMAN NECESSITIES
    • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
    • A61K—PREPARATIONS FOR MEDICAL, DENTAL OR TOILETRY PURPOSES
    • A61K31/00—Medicinal preparations containing organic active ingredients
    • A61K31/33—Heterocyclic compounds
    • A61K31/335—Heterocyclic compounds having oxygen as the only ring hetero atom, e.g. fungichromin
    • A61K31/35—Heterocyclic compounds having oxygen as the only ring hetero atom, e.g. fungichromin having six-membered rings with one oxygen as the only ring hetero atom
    • A61K31/352—Heterocyclic compounds having oxygen as the only ring hetero atom, e.g. fungichromin having six-membered rings with one oxygen as the only ring hetero atom condensed with carbocyclic rings, e.g. methantheline 
    • A61K31/353—3,4-Dihydrobenzopyrans, e.g. chroman, catechin
    • A61K31/355—Tocopherols, e.g. vitamin E
    • A—HUMAN NECESSITIES
    • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
    • A61K—PREPARATIONS FOR MEDICAL, DENTAL OR TOILETRY PURPOSES
    • A61K31/00—Medicinal preparations containing organic active ingredients
    • A61K31/33—Heterocyclic compounds
    • A61K31/335—Heterocyclic compounds having oxygen as the only ring hetero atom, e.g. fungichromin
    • A61K31/365—Lactones
    • A61K31/375—Ascorbic acid, i.e. vitamin C; Salts thereof
    • A—HUMAN NECESSITIES
    • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
    • A61K—PREPARATIONS FOR MEDICAL, DENTAL OR TOILETRY PURPOSES
    • A61K31/00—Medicinal preparations containing organic active ingredients
    • A61K31/33—Heterocyclic compounds
    • A61K31/38—Heterocyclic compounds having sulfur as a ring hetero atom
    • A61K31/385—Heterocyclic compounds having sulfur as a ring hetero atom having two or more sulfur atoms in the same ring
    • A—HUMAN NECESSITIES
    • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
    • A61K—PREPARATIONS FOR MEDICAL, DENTAL OR TOILETRY PURPOSES
    • A61K31/00—Medicinal preparations containing organic active ingredients
    • A61K31/33—Heterocyclic compounds
    • A61K31/395—Heterocyclic compounds having nitrogen as a ring hetero atom, e.g. guanethidine or rifamycins
    • A61K31/41—Heterocyclic compounds having nitrogen as a ring hetero atom, e.g. guanethidine or rifamycins having five-membered rings with two or more ring hetero atoms, at least one of which being nitrogen, e.g. tetrazole
    • A—HUMAN NECESSITIES
    • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
    • A61K—PREPARATIONS FOR MEDICAL, DENTAL OR TOILETRY PURPOSES
    • A61K31/00—Medicinal preparations containing organic active ingredients
    • A61K31/33—Heterocyclic compounds
    • A61K31/555—Heterocyclic compounds containing heavy metals, e.g. hemin, hematin, melarsoprol
    • A—HUMAN NECESSITIES
    • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
    • A61K—PREPARATIONS FOR MEDICAL, DENTAL OR TOILETRY PURPOSES
    • A61K31/00—Medicinal preparations containing organic active ingredients
    • A61K31/70—Carbohydrates; Sugars; Derivatives thereof
    • A61K31/7042—Compounds having saccharide radicals and heterocyclic rings
    • A61K31/7052—Compounds having saccharide radicals and heterocyclic rings having nitrogen as a ring hetero atom, e.g. nucleosides, nucleotides
    • A61K31/706—Compounds having saccharide radicals and heterocyclic rings having nitrogen as a ring hetero atom, e.g. nucleosides, nucleotides containing six-membered rings with nitrogen as a ring hetero atom
    • A61K31/7064—Compounds having saccharide radicals and heterocyclic rings having nitrogen as a ring hetero atom, e.g. nucleosides, nucleotides containing six-membered rings with nitrogen as a ring hetero atom containing condensed or non-condensed pyrimidines
    • A61K31/7076—Compounds having saccharide radicals and heterocyclic rings having nitrogen as a ring hetero atom, e.g. nucleosides, nucleotides containing six-membered rings with nitrogen as a ring hetero atom containing condensed or non-condensed pyrimidines containing purines, e.g. adenosine, adenylic acid
    • A—HUMAN NECESSITIES
    • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
    • A61K—PREPARATIONS FOR MEDICAL, DENTAL OR TOILETRY PURPOSES
    • A61K38/00—Medicinal preparations containing peptides
    • A61K38/04—Peptides having up to 20 amino acids in a fully defined sequence; Derivatives thereof
    • A61K38/06—Tripeptides
    • A61K38/063—Glutathione
    • A—HUMAN NECESSITIES
    • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
    • A61K—PREPARATIONS FOR MEDICAL, DENTAL OR TOILETRY PURPOSES
    • A61K45/00—Medicinal preparations containing active ingredients not provided for in groups A61K31/00 - A61K41/00
    • A61K45/06—Mixtures of active ingredients without chemical characterisation, e.g. antiphlogistics and cardiaca

Definitions

  • the present invention relates to control of zinc metabolism mediated by metallothioneins.
  • Metallothioneins are both the predominant cellular reservoir for bioavailable zinc and the primary shuttle for zinc transfer among biomolecules.
  • Agents are provided that enhance or prevent the release of zinc from metallothioneins and thereby affect metabolic pathways that depend on the availability or uptake of zinc.
  • MT-1 and MT-2 are the two prevalent forms, which are expressed, but whose physiological functions are unknown.
  • MT-3 was discovered only recently in brains from patients afflicted with Alzheimer's disease (Uchida, Y., Takio, K., Titani, K., Ihara, Y., and Tomonaga, M. (1991) Neuron 7, 337). Its discovery was based on the fact that it inhibits the growth of neurons. Thus far. it is the only MT that is known to exhibit such a specific biological function. This isoform contains zinc and copper(I), but not cadmium or other metals. Multiple factors among them members of the nuclear hormone receptor family, interferons, inducers of the acute phase response, and metalloregulatory proteins, affect tissue- and isoprotein-specific gene expression.
  • AD Alzheimer's disease
  • Parkinson's disease involves degeneration of pigmented neuronal systems in the brain stem that leads to neuromediator dysfunction.
  • the principal cytoskeletal pathology associated with Parkinson's disease is the Lewy body which predominately occurs in aminergic and other subcortical, spinal cord, and sympathetic ganglia neurons, and also to a lesser extent in the cerebral cortex.
  • Lewy bodies in Parkinson's disease lead to a degeneration of the dopaminergic pathway of the pigmented neuronal systems as well as to a degeneration of other neuronal systems, and this degeneration leads to a complex set of functional deficits (M. Ebadi et al., 1996, Progr. Neurobiol., 48, 1, and references therein).
  • EPILEPSY Epilepsy is broadly used to describe a group of disorders that are characterized by transient, recurrent, spontaneous paroxysms of a hyperactive brain resulting in seizures.
  • the interictal (between seizures) state of the epileptogenic cortex displays brief, high-amplitude electrical impulses. Seizures are characterized by loss of inhibitory signals so as to foster hyperexcitability and hyperactivity.
  • Apoptosis is a physiological process whereby cells die without swelling, necrosis, or inflammation (J. F. R. Kerr et al, 1972, Brit. J. Cancer, 26, 239). Apoptosis, in a non-pathological context, is considered responsible for the selective deletion of cells during embryogenesis and for homeostasis in continuously renewing tissues (S. Sen, 1992, Biol. Rev., 67, 287). In a pathological context, apoptosis is exhibited by cells in response to irradiation, oxidative stress, and to various chemical stimuli such as glucocorticoids (M. J.
  • Apoptosis has also been implicated as a process leading to aging (Z. Zakeri and R. A. Lockshin, 1994, Ann. Rev. NY Acad. Sci., 719, 212) and cancer (J. F. R. Kerr et al, 1994, Cancer, 73, 2013).
  • Biophysical and morphological indicators of apoptosis include fragmentation of endonuclear and chromatin DNA (Arends et al, 1990, Amer. J. Pathol., 136, 593) and compaction of cytoplasmic organelles into so-called "apoptotic bodies" (A. H. Wyllie et al, 1980, Int. Rev. Cytol., 68, 251).
  • neoplasm or tumor
  • benign or malignant Benign tumors generally remain localized. Malignant tumors are collectively termed cancers.
  • malignant generally means that the tumor can invade and destroy neighboring body structures and spread to distant sites to cause death (for review, see Robbins and Angell, 1976. Basic Pathology, 2d Ed., W.B. Saunders Co., Philadelphia, 68). Effective treatment and prevention of cancer remains a long-felt need, and a major goal of biomedical research.
  • Autoimmune diseases are estimated to affect from 1 to 2 percent of the human population. Such diseases fall into two broad categories: organ-specific, and systemic diseases. Organ-specific autoimmune diseases include myasthenia gravis, Grave's disease, juvenile insulin-dependent diabetes, Addison's disease, and a host of others. Systemic autoimmune diseases include rheumatoid arthritis, systemic lupus erythematosus, scleroderma, rheumatic fever, as well as others. Such diseases result from a breakdown of immune tolerance to self-antigens. Such breakdown may be due to any of one or several organ-specific autoimmune diseases. Organ-specific autoimmune diseases include myasthenia gravis, Grave's disease, juvenile insulin-dependent diabetes, Addison's disease, and a host of others. Systemic autoimmune diseases include rheumatoid arthritis, systemic lupus erythematosus, scleroderma, rheumatic fever, as well as others. Such diseases result
  • Systemic lupus erythematosus is characterized by inflammation in many different organ systems, as well as by excessive production of antibodies to nuclear, cytoplasmic and membrane antigens.
  • Viruses are obligate intracellular parasites whose replication in a host cell is at the molecular level (A. K. Field, 1994, Encyclopedia of Virology, R. G. Webster and A. Granoff, Eds., Academic Press, 42). Viruses are dependent on the host cell energy for metabolism and macromolecular synthesis, particularly with respect to reproduction of their genomes in the hostile environment of the host cell (id.).
  • the cycle of viral replication involves attachment of a virion to a host cell, penetration of the host cell, initiation of expression of viral genes, and use of the host cell biosynthetic apparatus to generate viral proteins and nucleic acids and packaging so as to generate and release progeny virions.
  • Antiviral agents for general and specific viral diseases have been proposed that target each of the stages in the viral replication cycle (id.).
  • HIV Human immunodeficiency virus
  • AIDS acquired immunodeficiency syndrome
  • HIV-1 Barre-Sinoussi et al., 1983, Science 220, 868; Gallo et al., 1984, Science 224, 500
  • HIV-2 Clavel et al., 1986, Science 233, 343; Guyader et al., 1987, Nature 326, 662
  • HIV replication occurs prominently in CD4 + T lymphocyte populations, and HIV infection leads to depletion of this cell type and eventually to immune incompetence, opportunistic infections, neurological dysfunctions, neoplastic growth, and ultimately death.
  • Retroviruses are small enveloped viruses that contain a single-stranded RNA genome, and replicate via a DNA intermediate produced by a virally-encoded reverse transcriptase, an RNA-dependent DNA polymerase
  • retroviruses include, for example, oncogenic viruses such as human T-cell leukemia viruses (HTLV- 1,-11, -III), and feline leukemia virus.
  • HTLV- 1,-11, -III human T-cell leukemia viruses
  • feline leukemia virus feline leukemia virus
  • HIV-1 infects T lymphocytes, monocyte-macrophages, dendritic cells, and glia within the central nervous system (e.g., microglia, astrocytes) (Gartner et al, 1986, Science 233, 215; Koenig et al, 1986, Science 233, 1089; Pope et al, 1994, Cell 78, 389; Weissman et al, 1995, Proc. Natl. Acad. Sci. USA 92, 826; Schmidtmayerova et al. 1996, Proc Natl. Acad. Sci. USA, 93, 700).
  • CD4 glycoprotein which serves as a receptor for HIV-1 and HIV-2 (Dalgleish et al, 1984, Nature 312, 763; Klatzmann et al, 1984, Nature 312, 767; Maddon et al, 1986, Cell 47, 333).
  • HIV like other enveloped viruses, introduces viral genetic material into the host cell through a viral-envelope mediated fusion of viral and target membranes. HIV-1 infection is mediated through the binding of the virus to the CD4 glycoprotein and other co- receptors.
  • the HIV-1 envelope glycoproteins gp41 (a transmembrane protein) and gpl20 (a cell surface protein) direct this binding.
  • gpl20 is non-covalently attached to gp41, which is anchored in the viral lipid bilayer.
  • HIV-1 entry is mediated by the high-affinity binding of gpl20 to the amino-terminal domain of the CD4 glycoprotein, causing conformational changes in gpl20 (McDougal et al, 1986, Science 231, 382; Helseth et al, 1990, J. Virol. 64, 2416; Wain-Hobson, 1996, Nature 384, 1 17) and subsequent binding of gpl20 to co- receptors, such as CXC-CKR4 and CC-CKR5 (Wu et al, 1996, Nature 384, 179; Trkola et al, 1996, Nature, 384, 184; Wain-Hobson, 1996, Nature 384, 117).
  • HIV infection is pandemic and HIV-associated diseases represent a major world health problem.
  • considerable effort is being put into the design of effective compounds, currently no curative anti-retroviral drugs against AIDS exist.
  • several stages of the HIV life cycle have been considered as targets for therapeutic intervention (Mitsuya, H. et al, 1991, FASEB J., 5, 2369-2381).
  • Many viral targets for intervention with HIV life cycle have been suggested, as the prevailing view is that interference with a host cell protein would have deleterious side effects.
  • virally encoded reverse transcriptase has been one focus of drug development.
  • a number of reverse-transcriptase-targeted drugs, including 2',3'-dideoxynucleoside analogs such as
  • CD4 the cell surface receptor for HIV.
  • Recombinant soluble CD4 has been shown to inhibit infection of CD4 + T cells by some HIV-1 strains (Smith, D.H. et al, 1987, Science,
  • Late stage processing is dependent on the activity of a viral protease, and drugs are being developed which inhibit this protease (Erickson, J., 1990, Science, 249, 527).
  • the clinical sample is being developed which inhibit this protease (Erickson, J., 1990, Science, 249, 527).
  • HIV-1 envelope proteins (gpl60, gpl20, gp41) have been shown to be the major antigens for anti-HIV antibodies present in AIDS patients (Barin, et al, 1985, Science, 228, 1094). Thus far. therefore, these proteins seem to be the most promising
  • Alfalfa mosaic virus (A1MV) and the related ilarviruses such as tobacco streak virus are economically important pathogens whose coat proteins contain zinc-finger domains. To be infectious, such viruses require genome activation by a few molecules of the coat proteins or nucleic acids coding for them. These viruses are of economic significance because crop infections by them result in losses to alfalfa, tobacco, clover, pea, potato, pepper, tomato celery and prune farmers.
  • HPV Human papilloma viruses
  • Semliki Forest Virus is a mosquito-borne pathogen that in humans, can cause arthralgia, rash and fever. Along with Sindbis virus, it is a member of the Togaviridae Alphavirus genus. It has been isolated in Africa, India and Southeast Asia, and is primarily found in small wild animals, birds and subhuman primates.
  • Hepatitis C is the major etiological agent of human parenterally and community-acquired non-A and non-B hepatitis. Chronic hepatitis C is estimated to be carried by 300 million humans worldwide, and is more prevalent in Europe and Japan than either Hepatitis A or B. Protective vaccination is not available for Hepatitis C, and no truly effective treatment is available for the disease.
  • MEASLES Measles viral infection in non-immune humans causes fever, cough, conjunctivitis and a rash. Complications of the disease can lead to pneumonia and immunodepression that leads to bacterial invasion of the lungs; occasionally, post-infectious encephalitis may result and can lead to demyelination with risk of mortality or loss of intellectual function. There are no known chemotherapeutics effective against measles infection, although hyperimmune serum globulin can prevent or modify the disease if given within 5 days of exposure.
  • Drug addiction or dependence involves repeated, compulsive use of a drug in order to receive its chemical rewarding effects or to avoid the punishing effects of drug withdrawal (C. Page and M. J. Curtis, 1997, "Integrated Pharmacology", Mosby International, London, ch. 30; A.J. Roberts and G.F. Koob, 1997, Alcohol Health and Research World, 21, 101-106; J. Blundell, 1991, TiPS, 12, 147-157). All drugs that produce dependence have chemical effects within the brain and provide pleasurable sensations or rewards, such as anti-fatigue, relaxation, or euphoria.
  • reward system Such rewarding sensations (hereinafter “reward system”) are due to potentiation of neurotransmitters in the brain; neurotransmitters implicated in this process are ⁇ -aminobutyric acid (hereinafter, “GABA”), dopamine, norepinephrine, acetylcholine, glutamate, endorphin, and serotonin (id.).
  • GABA ⁇ -aminobutyric acid
  • dopamine norepinephrine
  • acetylcholine glutamate
  • endorphin endorphin
  • serotonin serotonin
  • Ebselen (2-phenyl-l,2-benzisoselenazol-3(2H)-one is known for the treatment of rheumatism (DE-OS 3027073; U.S. Pat. No. 4,352,799) and for the treatment of oxidative stress (DE-OS 3616923).
  • Ebselen solid drug pharmaceutical preparations are also known (U.S. Pat. No. 5,021,242. None of these disclosures, however, suggest in any
  • the present invention is directed to therapeutic methods and compositions that control metallothionein mediated zinc transfer.
  • a method is disclosed for modulating the release of zinc from metallothionein within a cell comprising altering the concentrations of glutathione and glutathione disulfide within a cell.
  • a method is disclosed of promoting the release of zinc from metallothionein within a cell comprising increasing the concentration of glutathione disulfide within the cell.
  • a method is disclosed of promoting the release of zinc from metallothionein within a cell comprising increasing the concentration of glutathione disulfide within the cell in the presence of naturally occurring glutathione.
  • Methods are disclosed of promoting the release of zinc from metallothionein within a cell comprising administering to the cell a zinc-releasing amount of an oxidizing agent.
  • the oxidizing agent is selected from the group consisting of ebselen, selenocystine, selenocystamine, selenoglutathione disulfide, iron(III) chelates, dehydroascorbate, disulfides, including but not limited to glutathione and coenzyme A disulfides and cystamine, FAD, NAD , copper (II) chelates, and combinations thereof.
  • Methods are also disclosed of inhibiting the release of zinc from metallothionein within a cell comprising increasing the concentration of glutathione within the cell.
  • Methods are also disclosed of inhibiting the release of zinc from metallothionein within a cell comprising administering to the cell an amount of a reducing agent effective to inhibit the release of zinc from metallothionein.
  • the reducing agent is selected from the group consisting of selenocysteine, selenoglutathione, selenocysteamine, iron(II) chelates, ascorbate, glutathione, coenzyme A, cysteamine, FADH 2 , NADH, copper(I) chelates, vitamin E, N-acetyl-L-cysteine, ⁇ -lipoate, and combinations thereof.
  • the invention provides for treatment of disorders of cell fate or differentiation by administration of a therapeutic compound of the invention.
  • therapeutic compounds include but are not limited to: ebselen, cytochrome c, ascorbate, dehydroascorbate, GSH, GSSG, coenzyme A, cystamine, cysteamine, FAD, FADH 2 , azurin, vitamin E, N-acetyl-L-cysteine, ⁇ -lipoate, and combinations thereof.
  • a method for treatment of a pathological condition in which zinc homeostasis is perturbed involves administration of an effective amount of a compound, where administration of the compound changes the cellular oxidation state to effect an action selected from the group consisting of causing a release of zinc from MT and prevention of a release of zinc from MT.
  • the disclosed method is applicable to classes of disorders and disorders including but not limited to : Alzheimer's disease; neurodegenerative diseases including Parkinson's disease, Huntington's disease and amyotrophic lateral sclerosis; epilepsy; addictions; severe mental illness including depression and schizophrenia; eating disorders including anorexia nervosa, bulimia and obesity; inflammatory diseases including colitis, ileitis, common cold, dermatitis, asthma and endotoxic shock; disorders of the endocrine system including prostate cancer and hypertrophy, diseases of the thyroid, parathyroid, pituitary and thymus, diseases of the ovaries and diseases of the adrenal glands; pathological apoptosis; carcinogenesis; autoimmune diseases including systemic lupus ery hematosus; viral diseases including infection by HIV, hepatitis C, measles, papilloma and Semliki Forest virus.
  • the method also includes co-administration of a cofactor to better target the molecule to which zinc is released. Cofactor
  • Tris tris(hydroxymethyl)aminomefhane
  • SDH sorbitol dehydrogenase (EC 1.1.1.14);
  • apo-SDH zinc-depleted SDH
  • GSH glutathione;
  • GSSG glutathione disulfide;
  • CPA carboxypeptidase
  • a AP alkaline phosphatase
  • HQSA 8-hydroxyquinoline-5-sulfonic acid
  • DTNB 5,5'-dithiobis-(2-nitrobenzoic acid)
  • Hepes 4-(2-hydroxyethyl)piperazine-l-ethanesulfonic acid
  • DsbA protein disulfide isomerase from E. coli
  • the term compound means any molecule, salt, metal, or any other combination of one or more atoms, including but not limited to covalently bonded molecules, ionic materials, metallic materials, crystalline materials, atoms or molecules or ions in solution, atoms or molecules or ions in the gas phases, and combinations of any of the preceding.
  • chelate refers to a complex between one or more metal atoms and one or more ligands where the bonds between the metal and ligand may include any coordinative, dative, ionic, Lewis-basic or covalent interaction, and where at least one ligand occupies at least two coordination sites on at least one metal atom.
  • ligands forming chelates include but are not limited to nitrogen and oxygen macrocycles such as porphines, chorines, porphyrazines and crown ethers, ⁇ -keto carbonyl anionic compounds such as acetylacetonate, multi-dentate amines such as ethylene diamine, bipyridines, and phenanthrolines, polycarboxylate and mixed carboxylate/amine ligands such as EDTA, cyclopentadienyl anion, ⁇ -diimines (l,4-diaza-l,3-butadiene derivatives), multidentate phosphines such as diphos and diars, as well as other multi-dentate ligands well known to those of ordinary skill in coordination chemistry; any such ligand may be substituted or unsubstituted, and may be part of a larger molecule such as a polypeptide or protein, and may be immobilized, for example, on a non-polymeric or polymeric support (
  • FIG. 3 Reconstitution of apo-SDH with free zinc (A) and MT-1 (B). Free zinc or MT-1 was incubated with apo-SDH (1.7 ⁇ M) under different ratios of zinc to apo-SDH monomers in 0.2 M Tris-HCl, pH 7.4 for 30 min (or 60 min for MT-1). Aliquots (10 ⁇ l) were withdrawn from this mixture and assayed for enzymatic activity.
  • FIG. 6 Radiochromatograms of 65 Zn-MT-2 with apo-SDH in the absence or presence of GSH and GSSG.
  • MT-2 was incubated with apo-SDH (molar ratio between zinc and apo- SDH of 1.0) for 60 min and then the mixture was analyzed by radiochromatography as described under Materials and Methods.
  • A in the absence of GSH and GSSG;
  • the radiochromatograms were integrated from fractions 14-17.
  • Figure 9 Reconstitution of apo-AP with Zn 7 MT-2 in the presence of oxidizing agents.
  • Apo-AP 0.5 ⁇ M
  • Zn 7 MT-2 0.29 ⁇ M
  • various concentrations of DTNB (- ⁇ -) and GSSG (- ⁇ -) in 10 mM Tris, pH 8.0 Aliquots were taken after two hours and assayed spectrophotometrically for enzymatic activity. 100 % AP activity corresponds to reactivated apo-AP in the absence of oxidizing agents under otherwise identical conditions.
  • Figure 1 Reaction of MT-2 with PAR in the presence of selenite and selenocystamine.
  • MT-2 0.5 ⁇ M, was incubated with PAR, 100 ⁇ M, in the absence (-•-) and presence of 50 ⁇ M sodium selenite (- ⁇ -) and 50 ⁇ M selenocystamine (- ⁇ -).
  • FIG. 14 Zinc release from MT by ebselen.
  • A Time dependence of zinc transfer from MT-2 (0.5 ⁇ M) to PAR (100 ⁇ M) in the absence (- ⁇ -) and presence (- ⁇ -) of ebselen (10 ⁇ M in methanol) in 20 mM Hepes, pH 7.5 at 25 °C.
  • B Zinc transfer from MT (0.2 ⁇ M) to the apoform of carboxypeptidase A (1 ⁇ M) as a function of the concentration of ebselen under the same conditions as in (A).
  • FIG. 15 Kinetics of zinc release from MT-2 induced by the glutathione redox couple.
  • MT 1.3 ⁇ M
  • PAR 100 ⁇ M
  • 0.2 M Tris-HCl, pH 7.4 in the absence of glutathione, squares; in the presence of 1.5 mM GSH and 3 mM GSSG, circles.
  • Zinc release was followed by measuring the formation of Zn(PAR) 2 at 500 nm.
  • FIG. 1 Kinetics of zinc release from MT by dithiodipyridine and concomitant sulfhydryl oxidation.
  • MT 0.5 ⁇ M
  • MT was dissolved in degassed, 20 mM Hepes, pH 7.5 and incubated with 100 ⁇ M zincon (to measure zinc release, right ordinate, circles) and 50 ⁇ M dithiodipyridine (to measure thiol oxidation, left ordinate, squares).
  • FIG. 1 Kinetics of the reaction of MT-2 with protein disulfide isomerase (DsbA).
  • MT (0.75 ⁇ M) was incubated with the indicated amounts of DsbA and PAR (90 ⁇ M) in 40 mM Hepes, pH 7.4; MT control, squares; one equivalent of DsbA, circles; two equivalents of DsbA, diamonds; three equivalents of DsbA, triangles.
  • FIG. 1 Kinetics of the reaction of ebselen with MT followed by UV-VIS spectroscopy.
  • A MT-2 (0.5 ⁇ M) and ebselen (10 ⁇ M) in 20 mM Hepes, pH 7.5 at 25 °C between 0 and 24 sec.
  • B Difference spectra calculated from the spectra shown in (A).
  • Figure 20 Stopped-flow kinetics of the reactions between ebselen and MT (A) and ebselen and glutathione (B). (Conditions are given in the legends on the printouts.)
  • FIG. 22 Zinc release (left ordinate, - ⁇ -) from yeast alcohol dehydrogenase by ebselen and concomitant decrease of enzymatic activity (right ordinate, - ⁇ -) .
  • Yeast alcohol dehydrogenase 0.5 ⁇ M was reacted with increasing aliquots of ebselen in 20 mM Hepes (nitrogen-saturated), pH 7.5 in the presence of the indicator PAR (100 ⁇ M).
  • FIG. 23 Catalytic activity of selenocystine.
  • 0.5 ⁇ M MT (rabbit) was added to a nitrogen purged solution of 100 ⁇ M PAR in 20 mM Hepes, pH 7.5 in a quartz cuvette.
  • 'BuOOH (10 mM stock in water) was added to a final concentration of 100 ⁇ M and catalytic amounts of DL-selenocystine (1 mM stock in 0.01 M HCl, pH 2.0) were added.
  • the cuvette was closed by laboratory film and the solution was mixed by gently turning the closed cuvette.
  • the cuvette was inserted into a Cary IE spectrophotometer (Varian) thermostated 6 x 6 cell holder (25°C) and changes in absorption at 500 nm were recorded.
  • FIG. 24 Zinc transfer from human Zn 7 -MT to apo-SDH in the presence of ATP ( ⁇ ), AMPPNP ( ⁇ ) and ADP ( ⁇ ), and in the absence of nucleotides (D ).
  • Apo-SDH (1.7 ⁇ M) was incubated with 0.24 ⁇ M MT in 0.2 M Tris-HCl, pH 7.4 at 22.5 °C in the absence or presence of nucleotide (1 mM). Aliquots were withdrawn periodically and assayed for enzymatic activity.
  • FIG. 25 Electronic absorption difference spectra of binding of ATP to MT.
  • the difference spectra of reactions of human MT-2 (2.5 ⁇ M) with different concentrations of ATP were recorded on a Cary model IE high performance UV-Vis spectrophotometer (Varian) using Tandem cuvets as desribed in Material and Methods.
  • FIG. 26 Spectrophotometric detection of ATP binding to rabbit Cd,Zn MT-2 by the Hummel-Dreyer method.
  • MT 142 ⁇ M MT
  • Figure 27 Scatchard plot of ATP binding to rabbit Cd,Zn MT-2. Conditions as described in Figure 26.
  • FIG. 28 Quenching of fluorescent e-ATP by rabbit Cd,Zn MT-2.
  • e-ATP (20 ⁇ M) was dissolved in 0.2 M Tris-HCl, pH 7.4. Aliquots of MT were added and emission spectra recorded with excitation at 274 nm (5 nm slits).
  • FIG 29 ATP binding to MT in the presence of glutathione. ATP (100 ⁇ M) was incubated with rabbit Cd,Zn MT-2 (142 ⁇ M) in 50 mM Hepes, pH 7.4 in the absence of glutathione or in the presence of either GSH (120 ⁇ M) or GSSG (500 ⁇ M). Binding was evaluated as described in Figure 26.
  • Figure 30A,B Reactivity of thiols of MT in the absence and presence of ATP.
  • Human MT-2 (10 ⁇ M) was incubated with ( ⁇ ) or without (D) ATP (1 mM) and DTNB (4 ⁇ M) in 0.2 M Tris, pH 7.4 and the reaction followed spectrophotometrically.
  • FIG 31 The effect of ATP on elution behavior of MT in gel filtration.
  • Cd,Zn MT-2 (0.5 mg) was dissolved in 50 mM Hepes, pH 7.4, 10 mM NaCl in the presence or absence of 1 mM ATP, and subjected to gel filtration on a Sephadex G-75 column (100 x 1 cm) at 25 °C an a flow rate of 6.7 mL/h Elution of MT (- ⁇ -); elution of MT/ATP complex (- ⁇ -).
  • the present invention relates to therapeutic methods and compositions that alter zinc metabolism by means of an increase or decrease in zinc transfer between metallothionein and cellular and extracellular zinc acceptors.
  • the invention provides for treatment pathological conditions in which zinc is perturbed including those delineated in Table 1 , below.
  • Such therapeutic compounds include but are not limited to: ebselen, cytochrome c, ascorbate and dehydroascorbate, GSH and GSSG, coenzyme A, cystamine and cysteamine, FAD and FADH 2 , azurin, vitamin E, and pro-GSH agents such as N-acetyl-L-cysteine and ⁇ -lipoate.
  • ebselen cytochrome c
  • ascorbate and dehydroascorbate GSH and GSSG
  • coenzyme A cystamine and cysteamine
  • FAD and FADH 2 FAD and FADH 2
  • azurin azurin
  • vitamin E azurin
  • pro-GSH agents such as N-acetyl-L-cysteine and ⁇ -lipoate.
  • Preferred among these compounds are ebselen, ascorbate and dehydroascorbate,
  • GSH and GSSG GSH and GSSG, cystamine and cysteamine, azurin, vitamin E, and pro-GSH agents such as N-acetyl-L-cysteine and ⁇ -lipoate.
  • the compound most preferred is ebselen.
  • Alzheimer's disease central nervous Neurodegenerative diseases including Parkinson's disease, system Huntington's disease, and amyotrophic lateral sclerosis
  • Severe mental illness including depression and schizophrenia Eating disorders including anorexia nervosa, bulimia and obesity
  • Zinc in MT is bound extremely tightly (K D about 10 "13 M).
  • Zinc in contrast to copper or iron, is redox-inert.
  • the properties of zinc complexes are not altered by valence changes of the central atom in a manner akin to those in iron or copper complexes.
  • the redox state of the sulfur ligands can be changed.
  • the cluster structure of MT provides the chemical basis by which the cysteine ligands can induce oxidoreductive properties.
  • the cluster structure focuses on the significance of zinc/cysteine thiolate coordination in MT as the critical arrangement for zinc in this molecule to render the complex oxidoreductive. This allows for thermodynamic stability of zinc in MT while permitting zinc to retain kinetic lability.
  • Zinc plays a central role in cellular metabolism, and zinc performs regulatory functions. Zinc is a modulator of synaptic transmission, which is an extracellular regulatory function. It is quite likely that zinc also is an intracellular regulator that operates at concentrations different from those of calcium and hence coordinates different sets of biochemical processes.
  • the present invention is directed to a novel and surprising exploitation of the heretofore unknown relationship between cellular redox state and MT-mediated zinc transfer. The sections below discuss the relationship of zinc to certain disease states. It must be emphasized that nowhere in the literature is there a suggestion of treatment or prevention of disease by regulation of zinc homeostasis through regulation of the MT redox state.
  • the present invention is directed toward the up-regulation and down-regulation of intra- and extracellular zinc by specific regulation of the redox state of metallothionein.
  • Increase in the oxidation potential of the environment surrounding MT will favor release of zinc so as to increase the amount of zinc available for biochemical processes, while decrease in the oxidation potential of the MT environment will favor retention of zinc by MT so as to decrease the amount of zinc available for biochemical processes.
  • zinc signatures are available for zinc transfer to particular apoproteins and enzymes (B. Vallee and D. S. Auld, 1993, Ace. Chem. Res.,26, 543).
  • zinc-containing active sites are not at the apoprotein surface, a specific interaction between MT and the apoprotein determines the target. Such interactions are due in some cases to ATP, GTP or GSH binding to the surface of MT which binding provides a recognition factor for the target protein.
  • the active sites are often at the surface, and the recognition may involve other + influences than binding of GSH and/or ATP or GTP.
  • the methods described below preferably further comprise prior administration or coadministration of a zinc salt, MT, or a combination of a zinc salt and MT.
  • a zinc salt, MT, or a combination of a zinc salt and MT is preferable because release of zinc from MT requires administration of oxidizing compounds, and subjects suffering from a zinc deficiency typically are already undergoing oxidative stress.
  • Such prior or coadministration of zinc salts and/or MT will reduce the oxidative stress in a zinc-deficient subject, and thereby permit administration of oxidizing compounds without unduly contributing to further oxidative stress in the zinc-deficient subject.
  • Zinc is concentrated in vesicles of the pre-synaptic terminals of certain glutamatergic neurons and is released during high-frequency neuronal firing, and metallothionein-III ("MT-III") is abundant in these neurons (J. C. Erikson et al, 1997, J. Neuroscience, 17, 1271-1281, and references therein).
  • Zinc is known to have a wide variety of neuromodulatory functions, and to be involved in the pathophysiology of several neurological disorders (id.). Zinc has been found to be neurotoxic, and its intracellular accumulation may contribute to nerve death in seizure disorders (id.).
  • the invention provides a method of treating a subject having a disease of the central nervous system comprising administering to the subject a reducing agent that inhibits release of zinc from metallothionein in an amount effective for treatment of the disease of the central nervous system.
  • a major component of senile plaques in the AD brain is A ⁇ M0 , a 40 residue polypeptide whose precipitation from cerebrospinal fluid leads to the formation of A ⁇ amyloid plaque.
  • a ⁇ ,. 40 has been shown to bind zinc saturably, and the Zn-A ⁇ M0 complex has been shown to precipitate out of cerebrospinal fluid at physiological zinc concentrations
  • prevention of accumulation or further accumulation of the amyloid plaques characteristic of Alzheimer's disease is effectuated by treatment with reducing and shuttle agent compounds of the present invention.
  • Particularly preferred among the compounds of the current invention for this embodiment are certain thiols, and citrate and dehydroascorbate derivatives.
  • the invention provides a method of treating a subject having Alzheimer's disease comprising administering to the subject a reducing agent that inhibits release of zinc from metallothionein in an amount effective for treatment of the Alzheimer's disease.
  • NEURODEGENERATIVE DISEASES Various neurodegenerative disorders are associated with free radicals (J. A. Knight, 1997, Annal. Clin. Lab. Sci., 27, 11). For example, amyotrophic lateral sclerosis (Lou Gehrig's disease), Parkinson's disease, Down's syndrome and multiple sclerosis have all been found to be associated with excess free radicals, particularly oxygen-based free radicals (id.).
  • a compound is administered to a cell so as to maintain a reducing potential in the MT environment.
  • the maintenance of MT in its reduced state prevents the release of zinc, thereby preventing damage from zinc influx.
  • the invention provides a method of treating a subject having a neurodegenerative disease comprising administering to the subject a reducing agent that inhibits release of zinc from metallothionein in an amount effective for treatment of the neurodegenerative disease.
  • the neurodegenerative disease may be selected from the group consisting of Parkinson's disease, Huntington's disease, and amyotrophic lateral sclerosis, etc.
  • the invention provides a method of treating a subject having Parkinson's disease comprising administering to the subject a reducing agent that inhibits release of zinc from metallothionein in an amount effective for treatment of the Parkinson's disease.
  • Zinc has been found to diminish synaptic inhibition by ⁇ -aminobutyric acid (“GABA”) in a rat model for epilepsy.
  • GABA ⁇ -aminobutyric acid
  • One condition associated with epilepsy is hyperexcitability of synapses in the mammalian forebrain (P. A. Schwartzkroin, Ed., 1993, Epilepsy: Models, Mechanisms, and Concepts, Cambridge Univ. Press). This hyperexcitability is favored by a reduction in synaptic inhibition, and synaptic inhibition is primarily mediated by GABA.
  • Zinc is associated with synaptic inhibition in epilepsy.
  • the dentate gyrus of several experimental models, as well as of humans suffering from temporal lobe epilepsy ("TLE") exhibits a distinctive aberrant sprouting of mossy fibers (S. Otis, et al, 1994, Proc. Natl. Acad. Sci. U.S.A., 91, 7698).
  • the Wistar rat kindling model for epilepsy has enhanced functional inhibition of GABA (id.).
  • the mossy fibers of this and other models, as well as those of humans, are loaded with Zn 2+ that can be released on stimulation (C. J. Fredrickson and D. W. Moncrief, 1994, Biol. Signals, 3, 127).
  • Zn 2+ has been shown to inhibit certain types of GABA receptors, particularly during early development (T. G. Smart et al, 1994, Prog. Neurobiol., 42, 393).
  • Zn 2+ has been shown
  • MT-III is a growth-inhibitory factor and is expressed by zinc-containing neurons.
  • MT-III has been suggested to be involved in seizure disorders (J. C. Erickson et al, 1997, J. Neurosci., 17, 1271), and MT-III knockout mice have been found to be more susceptible to seizures induced by treatment with kainic acid (id.).
  • reducing compounds are administered to patients suffering from epilepsy so as to prevent the release of zinc from
  • the invention provides a method of treating an epileptic subject comprising administering to the subject a reducing agent that inhibits release of zinc from metallothionein in an amount effective for treatment of the epilepsy.
  • Zinc metabolism has been related to alcoholism. For example, the concentration of zinc has been shown to be altered in the tissues of alcoholics (M. Ebadi et al, 1995, Neurochem. Int., 27, 1-22).
  • oxidizing compounds are administered along with disulfiram so as to promote release of zinc from MT. Without committing to any particular theory or mechanism, it is believed that such zinc release from MT in conjunction with disulfiram leads to improved anti-drinking effects as compared to disulfiram alone.
  • Zinc metabolism is also related to withdrawal from cocaine (D. J. Ennulat and B. M. Cohen, 1997, Brain Res. Mol. Brain. Res., 49, 299-302).
  • Cocaine treated rats have been shown to have repressed levels of mRNA coding for a zinc-finger protein transcriptional regulator. After 2 days without cocaine, the level of this mRNA was found to have returned to normal. At the same time mRNA for a different zinc-finger protein transcriptional regulator was found to be induced by cocaine treatment (id.).
  • oxidative compounds are administered to maintain high levels of available zinc. Without committing to any particular theory or mechanism of action, it is believed that such high levels of available zinc interferes with the biochemical reward system (C. Page and M.J. Curtis, 1997, "Integrated Pharmacology", Mosby International, London, ch. 30; A.J. Roberts and G.F. Koob, 1997, Alcohol Health and Research World, 21, 101-106; J. Blundell, 1991, TiPS, 12,
  • the invention provides a method of treating a subject having a drug or alcohol addiction comprising administering to the subject an oxidizing agent that promotes release of zinc from metallothionein in an amount effective for treatment of the addiction.
  • the invention provides method of treating a subject with severe mental illness comprising administering to the subject an oxidizing agent that promotes release of zinc from metallothionein in an amount effective for treatment of the severe mental illness.
  • Zinc is associated with energy metabolism and has been implicated in several eating disorders. For example, zinc is believed to be associated with the energy homeostasis of obesity via its interaction with dietary fat consumption (M. D. Chen et al, 1996, Biol. Trace. Elem. Res., 52, 125-32). Support for this belief is found, for example, in the correlation between hair zinc concentration and obesity (S. K. Taneja et al, 1996, Experientia, 52, 31-3).
  • the invention provides a method for treating a subject having an eating disorder selected from the group consisting of anorexia nervosa, bulimia and obesity by administering to the subject an amount of a compound effective to treat said condition, wherein the compound changes the cellular oxidation state to effect an action selected from the group consisting of causing a release of zinc from metallothionein and preventing release of zinc from metallothionein.
  • the invention provides A method of treating a subject with anorexia nervosa comprising administering to the subject an oxidizing agent that promotes release of zinc from metallothionein in an amount effective for treatment of the anorexia nervosa.
  • the invention provides a method of treating an obese subject comprising administering to the subject a reducing agent that inhibits release of zinc from metallothionein in an amount effective for treatment of the obesity.
  • ICAM-1 intercellular adhesion molecule 1
  • Zinc has also been shown to enhance the expression of ICAM-1 in cells actively involved in inflammatory response (S. Martinotti et al, 1995, Biochem. Biophys. Acta, 1261, 107-14).
  • the invention provides a method of treating a subject with an inflammatory disease comprising administering to the subject an oxidizing agent that promotes release of zinc from metallothionein in an amount effective for treatment of the inflammatory disease.
  • Colitis and Crohn's disease reveal decreased zinc superoxide dismutase activity (L. Lih-Brody et al, 1996, Digest. Dis. Sci., 41, 2078-86) and colitis has been experimentally successfully treated in rats using a zinc chelate compound (T. Yoshikawa et al, 1997, Digestion, 58, 464-8).
  • Lung epithelial tissue in asthmatics furthermore, has been shown to have reduced zinc-specific activity, perhaps due to inflammatory responses.
  • the invention provides a method for treating a subject with colitis or Crohn's disease comprising administering to the subject an oxidizing agent that promotes release of zinc from metallothionein in an amount effective for treatment of the inflammatory disease.
  • oxidizing compounds are administered by inhalation so as to treat asthma.
  • Prostate glands of most mammals are known to contain among the highest levels of zinc of any tissues.
  • zinc levels are increased over normal prostate levels and are known to inhibit androgen metabolism (S. Dutkiewicz, 1995, Materia Medica Polona, 27, 15).
  • Antioxidant enzyme expression is reduced in malignant (neoplastic) prostate glands (A. M. Baker et al, 1997, Prostate, 32, 229).
  • the invention provides a method of treating a subject suffering from a disorder of the endocrine system comprising administering to the subject a reducing agent that inhibits release of zinc from metallothionein in an amount effective for treatment of the disorder of the endocrine system.
  • a reducing agent that inhibits release of zinc from metallothionein in an amount effective for treatment of the disorder of the endocrine system.
  • prostate cancer prostate hypertrophy
  • a disorder of the thyroid a disorder of the parathyroid, a disorder of the ovaries, and a disorder of the adrenal gland.
  • reducing compounds are supplied to hyperplastic or neoplastic prostate glands so as to reduce release of zinc from
  • Zinc is believed to play a role in pathological apoptosis. Where mice or rats have been fed a zinc-deficient diet, "massive" increase in apoptotic bodies has been
  • mice 20 observed in mucosal cells of their small intestines (M. Elmes, 1977, J. Pathol., 123, 219-23), and thymic atrophy and defective T helper cell function have also been observed (P. J. Fraker et al, 1971, J. Nutr., 107, 1889-95). Furthermore, zinc-deprived mice also have been found to exhibit skin lesions and stunted growth that are linked to apoptosis (G. Fernandes et al, 1979, Proc. Natl. Acad. Sci., 76, 457-61).
  • oxidizing compounds are administered to effect release of zinc from MT in order to combat pathological apoptosis.
  • the invention provides a method of treating a subject with pathological apoptosis comprising administering to the subject an oxidizing agent that promotes release of zinc from metallothionein in an amount effective for treatment of the pathological apoptosis.
  • a compound of the invention is administered to treat a cancerous condition, or to prevent progression from a pre-neoplastic or non-malignant state (e.g. , metaplastic condition) into a neoplastic or a malignant state.
  • a pre-neoplastic or non-malignant state e.g. , metaplastic condition
  • oxidizing compounds are administered so as to release zinc from MT at the site of a cancerous condition and thereby induce apoptosis of selected cells.
  • the invention provides a method of treating a subject with cancer, said method comprising administering to the subject an oxidizing agent that promotes release of zinc from metallothionein in an amount effective for inducing apoptosis of the cells of the cancer.
  • reducing compounds are administered so as to inhibit release of zinc from MT, thereby limiting the bioavailability of zinc as would be required for cellular proliferation, and thus reducing the proliferation of selected cells.
  • the invention provides a method of treating a subject with cancer, said method comprising administering to the subject a reducing agent that inhibits release of zinc from metallothionein in an amount effective for inhibiting proliferation of the cells of the cancer.
  • oxidizing compounds are administered to subjects at risk for or experiencing autoimmune diseases so as to promote the release of zinc from MT and thus ameliorate the disease.
  • the invention provides a method of treating a subject with an
  • - 28 autoimmune disease comprising administering to the subject an oxidizing agent that promotes release of zinc from metallothionein in an amount effective for treatment of the autoimmune disease.
  • Systemic lupus erythematosus has been associated with dietary zinc deficiency (id.).
  • oxidizing compounds are administered to subjects at risk for or experiencing systemic lupus erythematosus so as to promote the release of zinc from MT and thus ameliorate the disease.
  • the invention provides a method of treating a subject with systemic lupus erythematosus comprising administering to the subject an oxidizing agent that promotes release of zinc from metallothionein in an amount effective for treatment of the lupus erythematosus.
  • HIV-1 integration requires cleavage of two nucleotides from the 3' ends of viral DNA by HIV-1 integrase.
  • HIV-1 integrase contains three distinct domains (J. Kukosky and A. M. Skalka, 1994, Pharmacol. Ther., 61, 185), one of which (the N-terminal domain) is known to bind zinc (M. S. Johnson et al, 1986, Proc. Natl. Acad. Sci. USA, 83, 7468).
  • Zinc binding has been shown to play important structural and functional roles in integrase activity (S.P. Lee et al, 1997, Biochemistry, 36, 173).
  • NCPO mature HIV-1 nucleocapsid protein
  • reducing compounds are administered to a patient infected with HIV so as to prevent zinc transfer from MT to HIV-1 integrase and thus to inhibit HIV-1 integrase activity and also so as to prevent transfer of zinc from NCP to T, so as to interrupt the HIV-1 life cycle.
  • the invention provides a method of treating a subject suffering from an infection with HIV
  • reducing compounds are administered to plants at risk for or undergoing ilarviral and related viral infection such as A1MV so as to prevent transfer of zinc from MT to the viral capsid protein and thereby reduce or prevent infection.
  • the invention provides a method of treating a plant or plant cell infected with an ilarvirus or a mosaic virus comprising administering to the subject a reducing agent that inhibits release of zinc from metallothionein amount effective for treatment of the infection with the ilarvirus or the mosaic virus.
  • PAPILLOMA VIRAL CARCINOGENESIS E7 proteins of cancer-involved HPVs are cysteine-rich zinc-binding proteins.
  • reducing compounds of the present invention are administered to a patient infected with or in danger of infection with cancer-involved HPVs so as to prevent transfer of zinc from MT to the HPV E7 protein and thereby to prevent or mitigate cervical cancer.
  • the invention provides a method of treating a subject infected with papilloma virus, said method comprising administering to the subject an oxidizing agent that promotes release of zinc from metallothionein in an amount effective for treatment of the papilloma virus.
  • Zn 2+ has been shown to in vitro to inhibit SFV-liposome fusion due to interference with El protein trimer formation (J. Corver et al, 1997, Virology, 238, 14).
  • an animal in need of treatment for SFV infection is treated with an oxidizing therapeutic so as to induce zinc transfer from metallothionein to the SFV El protein and thereby to inhibit access of SFV to the host cytosol.
  • the invention provides a method of treating a subject infected with Semliki Forest virus comprising administering to the subject an oxidizing agent that promotes release of zinc from metallothionein in an amount effective for treatment of the Semliki Forest virus.
  • HEPATITIS C Several Hepatitis C (HCV) non-structural proteinases (NSP) exhibit zinc- dependent activity (A. Grakoui et al, 1993, J. Virol., 67, 2832; M. Hijikata et al, 1993, J. Virol., 67, 4665). Activity of these proteinases is necessary for the replication of the HCV genome. At least one of the NSP, NS3 has a zinc-binding site (R. A. Love et al, 1996, Cell, 87, 332).
  • reducing compounds are administered to a patient infected with HCV so as to prevent MT transfer of zinc to HCV NS3, and thereby to inhibit further replication of the HCV genome.
  • the invention provides a method of treating a subject infected with hepatitis C virus comprising administering to the subject a reducing agent that inhibits release of zinc from metallothionein in an amount effective for treatment of the hepatitis C virus.
  • MV V protein is believed to play a role in transcription and/or replication of MV genome.
  • V protein binds zinc (P. Liston and D. J. Briedis, 1994, Virol., 198, 399).
  • a reducing compound is administered to a patient who has been exposed to measles so as to prevent the transfer of zinc from MT to MV V protein.
  • the invention provides a method of treating a subject infected with measles virus comprising administering to the subject a reducing agent that inhibits release of zinc from metallothionein in an amount effective for treatment of the measles virus.
  • cofactors may be co-administered concurrently with or within a time period just prior to administration of the compound in order to provide target specificity to the zinc released.
  • the cofactors are administered from 0.01 seconds to 24 hours prior to administration of the compound.
  • Cofactors useful for co-administration with the compounds of the present invention include but are not limited to ATP, GTP and GSH. :
  • the invention provides methods of treatment (and prophylaxis) by administration to a subject of an effective amount of a compound described above.
  • the subject is preferably an animal, including but not limited to animals such as cows, pigs, chickens, primates, etc., and is preferably a mammal, and most preferably human.
  • Various delivery systems are known and can be used to administer a compound according to the invention, e.g., encapsulation in liposomes, microparticles, microcapsules, etc.
  • Methods of introduction include but are not limited to intradermal, intramuscular, intraperitoneal, intravenous, subcutaneous, intranasal, and oral routes.
  • the compounds may be administered by any convenient route, for example by infusion or bolus injection, by absorption through epithelial or mucocutaneous linings (e.g., oral mucosa, rectal and intestinal mucosa, etc.) and may be administered together with other biologically active agents. Administration can be systemic or local.
  • compositions of the invention may be desirable to administer locally to the area in need of treatment; this may be achieved by, for example, and not by way of limitation, local infusion during surgery, topical application, e.g., in conjunction with a wound dressing after surgery, by injection, by means of a catheter, by means of a suppository, or by means of an implant, said implant being of a porous, non-porous, or gelatinous material, including membranes, such as sialastic membranes, or fibers.
  • administration can be by direct
  • compositions comprise a therapeutically effective amount of a compound, and a pharmaceutically acceptable carrier or excipient.
  • a carrier includes but is not limited to saline, buffered saline, dextrose, water, glycerol, ethanol, and combinations thereof.
  • the carrier and composition can be sterile. The formulation should suit the mode of administration.
  • the composition can also contain wetting or emulsifying agents, or pH buffering agents.
  • the composition can be a liquid solution, suspension, emulsion, tablet, pill, capsule, sustained release formulation, or powder.
  • the composition can be formulated as a suppository, with traditional binders and carriers such as triglycerides.
  • Oral formulation can include standard carriers such as pharmaceutical grades of mannitol, lactose, starch, magnesium stearate, sodium saccharine, cellulose, magnesium carbonate, etc.
  • the composition is formulated in accordance with routine procedures as a pharmaceutical composition adapted for intravenous administration to human beings.
  • compositions for intravenous administration are solutions in sterile isotonic aqueous buffer.
  • the composition may also include a solubilizing agent and a local anesthetic such as lignocaine to ease pain at the site of the injection.
  • the ingredients are supplied either separately or mixed together in unit dosage form, for example, as a dry lyophilized powder or water free concentrate in a hermetically sealed container such as an ampoule or sachette indicating the quantity of active agent.
  • the composition is to be administered by infusion, it can be dispensed
  • compositions are administered by injection, an ampoule of sterile water for injection or saline can be provided so that the ingredients may be mixed prior to administration.
  • the compounds of the invention can be formulated as neutral or salt forms.
  • Pharmaceutically acceptable salts include those formed with free amino groups such as those derived from hydrochloric, phosphoric, acetic, oxalic, tartaric acids, etc., and those formed with free carboxyl groups such as those derived from sodium, potassium, ammonium, calcium, ferric hydroxides, isopropylamine, triethylamine, 2-efhylamino ethanol, histidine, procaine, etc.
  • the therapeutic compounds according to the invention may also be immobilized, for example, on a biologically-inert non-polymeric or polymeric support.
  • Non-limiting examples of such supports include functionalized polystyrene or other polymeric beads, fibers, sheets, etc, and functionalized cellulosic materials such as paper, cotton thread, and the like. Immobilization may involve covalent attachment to the support, or inclusion, adsorption or absorption on or into a porous, non-porous or swellable support. Such immobilization permits easy introduction of the compounds to a specific site by administering the compound on the support, and also provides for easy later removal by removal of the support.
  • the compounds of the invention may also be formulated for transdermal and transmucosal administration.
  • One of ordinary skill would understand that there are numerous technologies available for carrying out such transdermal and transmucosal administration.
  • the amount of the compound of the invention which will be effective in the treatment of a particular disorder or condition will depend on the nature of the disorder or condition, and can be determined by standard clinical techniques.
  • in vitro assays may optionally be employed to help identify optimal dosage ranges.
  • the precise dose to be employed in the formulation will also depend on the route of administration, and the seriousness of the disease or disorder, and should be decided according to the judgment of the practitioner and each patient's circumstances.
  • suitable dosage ranges for intravenous administration are generally about 20-500 micrograms of active compound per kilogram body weight.
  • Suitable dosage ranges for intranasal administration are generally about 0.01 pg/kg body weight to 1 mg/kg body weight.
  • Effective doses may be extrapolated from dose-response curves derived from in vitro or animal model test systems.
  • Suppositories generally contain active ingredient in the range of 0.5% to 10% by weight; oral formulations preferably contain 10% to 95% active ingredient.
  • the invention also provides a pharmaceutical pack or kit comprising one or more containers filled with one or more of the ingredients of the pharmaceutical compositions of the invention.
  • a pharmaceutical pack or kit comprising one or more containers filled with one or more of the ingredients of the pharmaceutical compositions of the invention.
  • Optionally associated with such container(s) can be a notice in the form prescribed by a governmental agency regulating the manufacture, use or sale of pharmaceuticals or biological products, which notice reflects approval by the agency of manufacture, use or sale for human administration.
  • MT metallothionein
  • a 1 : 1 molar ratio of MT to sorbitol dehydrogenase is required for full reactivation, indicating that only one of the seven zinc atoms of MT is transferred in this process.
  • Reduced glutathione (GSH) and glutathione disulfide (GSSG) are critical modulators of both the rate of zinc transfer and the ultimate number of zinc atoms transferred. GSSG increases the rate of zinc transfer 3-fold and its concentration is the major determinant for efficient zinc transfer.
  • GSH has a dual function: In the absence of GSSG, it inhibits zinc transfer from MT, indicating that MT is in a latent state under the relatively high cellular concentrations of GSH. In addition, it primes MT for the reaction with GSSG by enhancing the rate of zinc transfer 10-fold and by increasing the number of zinc atoms transferred to four. 65 Zn-labeling experiments confirm the release of one zinc from MT in the absence of glutathione and the more effective release of zinc in the presence of GSH and GSSG. In vivo, MT may keep the cellular concentrations of free zinc very low and, acting as a temporary cellular reservoir, release zinc in a process that is dynamically controlled by its interactions with both GSH and GSSG.
  • the protein plays a role in the biological function of zinc, a paradigm quite different from that in most other zinc proteins where zinc plays a role in the biological function of the protein.
  • the compounds of the present invention take advantage of the tight binding of zinc to MT and the ability to control its release.
  • the present invention is directed to glutathione disulfide mediated zinc release in the
  • GSH pyridine-2,6-dicarboxylic acid (dipicolinic acid), Coomassie Brilliant Blue G, 2-carboxyl-2'-hydroxy-5'-sulfoformazylbenzene (Zincon) and carbonic anhydrase (bovine erythrocytes) were from Sigma; sorbitol and 4-(2- pyridylazo)resorcinol (PAR) from Aldrich; 65 ZnCl 2 (77.7-103.6 Gbq/g) from Dupont/NEN. Preparation and Characterization of Human MT.
  • Human MT-1 and MT-2 isoforms were prepared in this laboratory according to established procedures known to those of ordinary skill (see, for example, M. Vasak, 1991, Methods Enzymol. 205, 41-44) and converted to their apoforms and reconstituted with Zn 2+ to result in the respective Zn 7 -MT isoforms (see, W. Maret, 1994, Proc. Natl. Acad. Sci. USA, 91, 237-241). Excess zinc was removed by gel filtration through a Sephadex G-50 fine column (30 x 0.5 cm) and the MT isoforms were characterized by metal analyses, determinations of sulfhydryl groups with dithiodipyridine, and amino acid analyses.
  • Loosely bound zinc in MT solutions was assayed spectrophotometrically at 620 nm with Zincon.
  • Addition of 10 ⁇ l of 10 mM Zincon to 890 ⁇ l of 10 mM Tris-HCl, pH 8.6 identifies the existence of less than 4% of loosely bound zinc.
  • SDH and Zinc-depleted SDH Sheep liver SDH was obtained as a lyophilized powder from Boehringer Mannheim and stock solutions were prepared by dissolving enzyme in 1 ml of 0.2 M Tris-HCl, pH 7.4. As is standard in the art, enzyme concentrations were determined with a Coomassie Blue protein-dye binding assay with bovine serum albumin as a standard (see, R. K. Scopes, 1982, Protein Purification (Springer, New York), p 266).
  • Zinc-depleted SDH (apo-SDH) was prepared according to standard procedures familiar to those of ordinary skill, in Centricon-10 centrifugal microcdncentrators (Amicon) using 0.2 M phosphate buffer, pH 7.0, containing 10 mM dipicolinic acid to remove zinc (see, for example, W. Maret, 1989, Biochemistry, 28, 9944-9949).
  • the apoform had 2.0% residual enzymatic activity compared with the native zinc enzyme and contained 0.015 g- atom zinc/subunit.
  • the amount of zinc in native SDH was 1 g-atom/subunit, in agreement with the expected value (J. Jeffery et al, 1984, EMBO J. 3, 357-360).
  • Mammalian SDH was used an exemplary cellular zinc acceptor.
  • Mammalian SDH is a tetramer of four identical subunits with an overall molecular mass of 152 kDa and one catalytic zinc atom per subunit (J. Jeffery, et al, 1984, EMBO J., 3, 357-360; J. Jeffery, et
  • MT-2 reactivates apo-SDH to 13% (data not shown) and is therefore slightly less effective in transferring zinc than MT-1.
  • the second-order rate constants for MT-1 and MT-2 are 24 and 16 M “ 's " ', respectively (Table 3). These slightly different rates and degrees of reactivation with MT-1 and -2 are in accord with data reported for carbonic anhydrase and rat liver MT isoforms (D. R. Winge and K. A. (Miklossy, 1982, Arch. Biochem.
  • GSSG is known to mobilize all seven zinc atoms from MT at pH 8.6 (W. Maret, 1994, Proc. Natl. Acad. Sci. USA, 91, 237-241). We therefore tested how GSSG effects the transfer of zinc atoms at pH 7.4. Adding MT to apo-SDH in the presence of GSSG generates activity faster and to a greater extent than in its absence. Thus, incubation of apo-SDH with MT-1 (equimolar zinc) for one hour in the presence of GSSG leads to 31% reactivation, almost twice that achieved without GSSG (Figure 4).
  • GSH and GSSG Neither GSH nor GSSG at the concentrations employed affects the activity of SDH in the absence of MT. Nevertheless, GSH strongly influences the capacity of MT-2 to reconstitute apo-SDH in the presence of GSSG (Table 4). Thus, it further modulates the enhancement of zinc transfer from MT to apo-SDH by GSSG ( Figure 4).
  • Figure 4 At a constant concentration of 3.0 mM GSSG, the rate and extent of zinc transfer from MT-2 to apo-SDH increase until a plateau is reached at the GSH concentration of 1.5 mM ( Figure 5A & Table 4). Under these conditions, the rate constant is increased 10-fold and the amount of zinc transferred is 5-fold greater than that in the absence of GSH and GSSG.
  • the concentration of GSH was kept constant at 1.5 mM and the concentration of GSSG was varied, the rate and extent of zinc transfer increased linearly with increasing concentrations of GSSG ( Figure 5B & Table 4).
  • GSH stimulates the rate of zinc transfer in the apo-SDH/MT/GSSG system, signifying control of the MT molecule by glutathione with important implications regarding modulation of zinc transfer by the GSH/GSSG redox couple in vivo (see below).
  • GSH and GSSG could i) bind to SDH and affect its activity, ii) control the amount of free zinc available once it is released from MT, or iii) bind to MT and affect its conformation and zinc binding. Our data strongly favor the last mechanism.
  • GSH binding would protect MT from the loss of Zn-2, thereby inhibiting its transfer, while providing a reactive thiol for the reaction with GSSG and resulting in zinc transfer through a process that is strictly proportional to and dependent on the concentration of GSSG ( Figure
  • MT Controls Cellular Free Zinc.
  • the reactivation of apo-SDH with Zn-MT occurs at a rate that is slower than that with free zinc ions ( Figure 1). Specifically, the rate constant for zinc transfer from MT to apo-SDH is three orders of magnitude less than that of about
  • Intracellular zinc concentrations are exceedingly low, i.e. ⁇ 100 pM (E. J. Peck and W. J. Ray, 1971, J. Biol. Chem., 246, 1160-1167; T. J. B. Simons, 1991, J. Membr. Biol, 3, 63-7; D. Atar et al,
  • MT may not transfer zinc to apo-proteins in the normal cellular environment where, the GSH/GSSG redox ratio is between 30: 1 to 100: 1 (C. Hwang et al, 1992, Science 257, 1496-1502). It is noteworthy that these are steady-state conditions under which there may not be any need for zinc in the cell, and where the role of MT is to sequester zinc, not to distribute it. Hence, this condition must be perturbed in order to change the role of MT from that of an acceptor to that of a donor when zinc is needed in events such as cell proliferation, for example.
  • Zinc can be transferred in both directions, i.e. from the enzymes to thionein, the apo-form of MT, and from MT to the apo-enzymes.
  • Agents that mediate or enhance zinc transfer have been identified which provide kinetic pathways in either direction.
  • MT does not transfer all of its seven zinc atoms to an apo-enzyme, but apparently contains at least one that is more prone to transfer than the others.
  • Zinc transfer from zinc enzymes to thionein is mediated by zinc chelating agents such as Tris buffer, citrate or glutathione.
  • Redox-agents are asymmetrically involved in both directions of zinc transfer. For example, reduced glutathione mediates zinc transfer from enzymes to thionein, while glutathione disulfide oxidizes MT with enhanced release of zinc and transfer of zinc to apo-enzymes. Therefore, the cellular redox state and the concentration of other biological chelating agents might well determine the direction of zinc transfer and ultimately affect zinc distribution.
  • Metallothionein is a protein that has long been in search of a function. Its composition and structure (Margoshes, M. and B. L. Vallee, 1957, J. Am. Chem. Soc, 79,
  • T has been shown to block the action of zinc-dependent transcription factors, e.g. TF IIIA and Spl, presumably via metal chelation (J. Zeng et al, 1991, FEBS Lett., 279, 310-312; J. Zeng et al, 1991, Proc. Natl. Acad. Sci. USA, 88, 9984-9988).
  • MT transfers at least some of its complexed zinc ions to a number of apo-proteins (A. O. Udom and F. O. Brady, 1980, Biochem. J., 187, 329-335).
  • AP is a dimer containing one catalytic and one co-catalytic zinc atom, as well as one magnesium atom per monomer (W. F. Bosron et
  • CPA requires only one zinc atom per molecule to achieve full activity. The distinct differences between the two enzymes are important to rule out specific interactions between MT and either one of them.
  • T prepared this way can be stored at -180°C under nitrogen for more than three months without loss of thiol groups.
  • Zinc transfer from Zn 7 MT-2 to apo-alkaline phosphatase Stock solutions of AP and apo-AP in 10 mM Tris, pH 8.0 were diluted with the same buffer to make 0.5 ⁇ M working solutions. A solution of 100 mM p-nitrophenyl phosphate in water was diluted with 10 mM Tris, pH 8.0 to obtain a 1 mM substrate working solution. Enzyme (50 ⁇ l) and substrate were rapidly mixed in an acid- washed quartz cuvet and the formation of p- nitrophenolate monitored at 400 nm for 2 min (A. O. Udom and F. O. Brady, 1980, Biochem. J., 187, 329-335). A linear best fit was used to calculate the turnover rates between 50 s and 150 s for slow and between 20 s and 60 s for fast reactions. Unless otherwise stated, activity is expressed as percent of that measured for native AP.
  • Zinc transfer experiments were conducted by pre-incubation of T and AP, or apo-AP with Zn 7 MT-2 or Cd 5 Zn 2 MT-2 and potential agents that enhance transfer in 10 mM Tris, pH 8.0, for two hours at 20°C and subsequent activity analysis.
  • CPA apo-carboxypeptidase A.
  • CPA was purified on a CABS-Sepharose column (L. B. Cueni et al, 1980, Anal. Biochem., 107, 341-349) and stored as a crystal suspension in 10 mM Tris, pH 7.5, at 4°C.
  • Apo-CPA was prepared from CPA crystals (D. S. Auld, 1988, Methods Enzymol., 158, 71-79) and stored as a suspension at 4°C.
  • the purity of CPA and its apo-form was at least 95 % as determined by SDS-PAGE (see above).
  • CPA activity was measured by changes in the fluorescence of the substrate Dns-G-G-W (17) with a
  • Zinc transfer from CPA to T was measured by incubating the enzyme and T in 1 M Tris, pH 8.0, for 90 min at 20°C and subsequently determining the CPA activity.
  • the activity of a reconstituted zinc enzyme is a measure of the extent of metal transfer from MT- 2 to the apo-enzyme.
  • the phosphotransferase activity of the apo-AP preparation used in these experiments was less than 10 % of that of the native enzyme.
  • a 4-fold molar excess of zinc sulfate fully reactivates apo-AP, corresponding to a stoichiometric amount of zinc (four zinc ions, two catalytic and two cocatalytic, per enzyme dimer are required).
  • Zn 7 MT-2 also reactivates the apo-enzyme, but somewhat slower than zinc sulfate (>15 min vs. 5 min). However, maximal activation requires more than a 15-fold molar excess of Zn 7 MT-2 ( Figure 8). Thus, on average, less than one zinc atom is transferred from Zn 7 MT-2 to the apo-enzyme.
  • Disulfides interact with MT-2 and release zinc ions (infra). These reagents also would be expected to enhance zinc transfer from MT-2 to apo-enzymes, hence reactivation of apo-AP in the presence of two such reagents, DTNB and GSSG, was investigated.
  • DTNB is highly reactive and consequently it reacts at a much lower excess and orders of magnitude faster than GSSG (infra; T. Y. Li et al, 1981, Biochem. J., 193, 441-446; M. M. Savas et al, 1993, J. Inorg. Biochem., 52, 235-249).
  • Micromolar concentrations of DTNB more than triple the reactivation efficiency of Zn 7 MT-2, whereas millimolar concentrations of GSSG are required to achieve the same effect (Figure 9).
  • Reactivity of thionein a) zinc transfer from alkaline phosphatase to thionein.
  • T the apoform of MT.
  • cysteine thiols the reactivity of its cysteine thiols is a critical parameter for our understanding of the reactivity of the zinc- sulfur bonds in MT.
  • T is stable if stored at -180°C in liquid nitrogen and that it can be employed for several hours in biochemical studies without significant oxidation of its thiols. This has allowed us to investigate T in reactions in which it acts as a metal acceptor toward a zinc enzyme, and in redox reactions with disulfides.
  • the activity of AP depends critically on the concentration of buffer ions. In the presence of Tris, citrate or glutathione (GSH) the catalytic activity of AP decreases over time (Table 5). These agents also influence zinc transfer from AP to T. Addition of T to AP in 10 mM Tris, pH 8.0 only marginally affects the activity of the enzyme but when the identical experiment is performed in 1 M Tris, pH 8.0, AP activity decreases to below 10 % of its original value within approximately 30 min ( Figure 12). The concentration of T at which 50 % of the original activity of AP is inhibited (IC 50 ) is about 0.25 ⁇ M in 1 M Tris,
  • T The effects of T on CPA activity are comparable to those on AP activity: First, addition of T to CPA in 1 M Tris, pH 8.0 progressively decreases the enzyme's activity (data not shown). Second, at substoichiometric amounts of T, the inactivation reaction reaches equilibrium within 30 min (IC 50 of 0.4 ⁇ M). Third, loss of enzyme activity is also most likely due to removal of Zn(II) from the active site since addition of a 100-fold excess of zinc sulfate restores 65 % of the enzyme's original activity.
  • reaction 2 is based on two assumptions. One is that MT has a metal transfer potential of seven based on cooperative binding of seven zinc ions all with similar binding constants. The other is that the products do not undergo further reactions and thereby shift the equilibrium to the right. To date, most reports have accepted that zinc binds cooperatively and that only T and Zn 7 MT-2 exist without stable intermediates (K. B. Nielson and D. R. Winge, 1983, J.
  • the stability constant of Zn 7 MT-2 is too high to account for zinc transfer from a thermodynamically relatively stable system (MT-2) to others that are orders of magnitude more labile (CPA, AP) under stoichiometric concentrations of the reactants. If the binding constants were the same for all seven zinc atoms in MT-2, only a negligible fraction of zinc should be transferred. Indeed, without a driving force, the occurrence of zinc transfer would be a surprising result.
  • the observed metal transfer potential of MT-2 is approximately one in the case of CPA and perhaps less than that in the case of AP.
  • MT exhibits high structural flexibility, and cadmium exchange inside the ⁇ -cluster and between the ⁇ -clusters of two MT molecules is fast (J. D. Otvos et al, 1993, in Metallothionein III, eds. Suzuki, K. T., Imura, N. & Kimura, M. (Birkhauser, Basel),
  • the release of one zinc ion by metal-exchange requires one cadmium or cuprous ion. Since in most organisms both cadmium and copper are far less
  • Thiol modification reactions are particularly attractive as a means to release zinc since they affect the zinc ligands of MT (Fliss, H. & Menard, M. (1992) Arch. Biochem. Biophys. 293, 195-199; W. Maret, 1994, Proc. Natl. Acad. Sci. USA, 91, 237-241) and are biochemically feasible.
  • Such reactions possibly involving cellular GSSG, would not only facilitate release but also increase the number of zinc ions transferred per MT molecule (with the thiolation reaction as the rate-determining step) in vivo.
  • DTNB thiol/disulfide-exchange reagents
  • GSSG thiol/disulfide-exchange reagents
  • DTNB is a highly reactive thiolation agent. It rapidly thiolates the sulfhydryl groups of MT-2, with concomitant release of ionic zinc. Moreover, it significantly increases the number of zinc ions transferred per MT-2 molecule.
  • the reactivation of apo-CPA or -AP in the presence of micromolar concentrations of DTNB is more than three times as great as in its absence, indicating that only three to four, but not all seven zinc ions become available for transfer.
  • GSSG has similar effects, although it requires millimolar concentrations to achieve the same enhancement.
  • MT-2 W. Maret, 1994, Proc. Natl. Acad. Sci. USA, 91, 237-241
  • DTNB T. Y. Li et al, 1981, Biochem. J., 193, 441-446; M. M. Savas et al, 1993, J. Inorg. Biochem., 52, 235-249
  • DTNB also increases the extent of zinc transfer while no clear effect was seen with GSSG up to 1 mM.
  • selenium compounds as possible agents that increase the rate of zinc transfer from MT to an acceptor at micromolar concentrations of reagents.
  • Selenium is an essential trace element that is involved in the regulation and maintenance of the cellular thiol redox state. Our experiments indicate that zinc transfer reactions may well be a possible target for the molecular action of selenium.
  • reaction 5 In the absence of a driving force for the forward or backward reaction, the equilibrium of removal of zinc from a zinc protein by T (reaction 5) should be controlled hermodynamically. Since for most proteins the binding constant for zinc is at least 1,000 fold lower than that for T, zinc transfer from zinc enzymes to T should be preferred thermodynamically .
  • T does not appear to sequester significant amounts of zinc from the active site of the enzyme.
  • T does not necessarily act as a strong chelating agent toward enzymes. If this were so, then the induction of T in the cell might interfere with many zinc-dependent enzymatic processes.
  • T does inactivate AP in the presence of buffer ions such as Tris or citrate.
  • buffer ions help deplete the enzyme of its zinc, and thereby act to shuttle zinc between the enzyme and T. The fact that T is ineffective in 10 mM Tris strongly suggests that there is no direct interaction of T and the zinc enzyme.
  • Tris and citrate lower the stability constant of AP.
  • Tris is not only a buffer ion, but also a co-substrate for AP (M. Sone et al, 1997, J. Biol. Chem., 272, 6174-6178; J. E. Coleman and P. Gettins, 1983, Adv. Enzymol. Relat. Areas Mol. Biol., 55, 381-4801) and a chelating agent.
  • Zinc chelating agents such as citrate and GSH occur in the cytosol in millimolar concentrations (A.
  • T is a very strong reductant. It reacts significantly faster with disulfides than does MT. The reactivity of T toward disulfides and other oxidizing agents is efficiently quenched in the presence of zinc (Figure 13). Whether or not such reducing power of T is needed in the cell and whether or not such reducing power, or as a matter of fact the reductive functions of any cellular thiols, are controlled by binding of zinc is currently unknown.
  • Agent AP Activity in the AP Activity in the added* mM Absence of T, % Presence of T, %
  • MT Metallothionein
  • This function likely controls and distributes zinc in the cell. Its function in this regard is specific and mitigates the idea that MT is a scavenger of radicals or a detoxifier of heavy metals. It seems unlikely that MT would be primarily a site of sequestration of toxic metals in the cell, since the redox reactivity of its cysteine ligands would render its heavy metal complexes similarly susceptible to mobilization by oxidative reactions. The biological significance of the widespread use of cysteine as a ligand of zinc in proteins would seem to reside in the capacity of thiols to bind zinc very tightly and of oxidized thiols to bind it weakly.
  • This concept integrates biologically redox-inert zinc, not only in MT but possibly in zinc finger or other proteins, into the redox chemistry of the cell and suggests a new mechanism of cellular control, in which a high reducing power is related to zinc binding while a low reducing power is related to zinc mobilization.
  • MT Metallothionein
  • cysteine constitutes one third of its amino acids and histidine and aromatic amino acids are absent. All twenty cysteines bind zinc such that each metal atom has a complement of four cysteine ligands. The zinc atoms are arranged into two discrete clusters each with bridging cysteines. In one cluster nine cysteines bind three zincs, and in the other eleven bind four. This constellation, unique so far, is encountered solely in MTs. The physiology of MT has remained unknown and its three-dimensional structure was established only less than a decade ago ((M + )
  • the sulfur ligands in the MT clusters are crucial for the dynamic state of zinc.
  • the zinc sulfur-cluster chemistry might be sensitive to changes of the cellular redox state and that oxidizing conditions induce the transfer of zinc from its binding sites in MT to those of lower affinity in other proteins.
  • Spectrophotometric assays Reactions between MT and oxidizing agents were monitored by two types of assays.
  • the other assay is based on the reduction of oxidizing agents with suitable chromophoric properties. Redox reactions were measured at 25 °C with a Cary IE spectrophotometer (Varian) by following the reduction of the oxidizing agent at its absorption maximum.
  • Redox Reagent n Redox Reaction References Potential* with MT* 00 glutathione disulfide/ 2 - 240 E 0 ' + W. Maret, 1994, Proc. Natl. Acad. Sci. USA, 91, 237-241; W. ⁇ glutathione Maret, 1995, Neurochem. Int., 7, 111-1 17.
  • the redox potential derived from measured GSH/GSSG ratios of 30: 1 to 100: 1 in the cytosol has been calculated to fall between -221 and -236 mV (C. Hwang et al, 1992, Science, 257, 1496- 1502).
  • the GSH/GSSG ratio is in the range from 1 :1 to 3: 1 (C. Hwang et al, 1992, Science, 257, 1496-1502) corresponding to redox potentials of -133 to -165 mV, respectively (for a total glutathione concentration of 1 mM).
  • an oxidizing power stronger than indicated by the midpoint potential can be attained, particularly in a compartmentalized redox environment.
  • the physiological reactant could well be a disulfide other than GSSG or a particular disulfide of a given protein or proteins
  • GSSG indeed is the cellular disulfide involved, then its reaction with MT might be enzyme catalyzed
  • the family of thiol/disulfide oxidoreductases includes thioredoxins and protein disulfide isomerases; we have selected DsbA for study as it has the highest redox potential (-125 mV) (F.
  • Selenium compounds are preferred as oxidizing and reducing agents for control of zinc release from metallothionein.
  • Non-limiting examples of such preferred selenium compounds include as oxidizing agents, ebselen, selenocystine, selenocystamine, selenoglutathione, and as reducing agents, selenocysteine, selenoglutathione, selenocysteamine.
  • Ebselen is a preferred oxidizing agent for the release of zinc from metallothionein in the present invention.
  • the ability of ebselen to release zinc from metallothionein has been demonstrated as described in the following sections.
  • Selenium compounds oxidize the thiolate ligands in the zinc clusters of metallothionein and release zinc. This hitherto unrecognized chemistry defines new cellular targets for selenium compounds and suggests important interactions between the two essential elements zinc and selenium. In attempts to delineate further the redox chemistry of biological zinc complexes with thiolate ligands, we found that the selenium-containing drug ebselen (2-phenyl-l,2-benzisoselenazol-3(2H)-one) releases zinc from metallothionein.
  • ebselen 2-phenyl-l,2-benzisoselenazol-3(2H)-one
  • the reaction is very rapid (t 1/2 ⁇ 1 min) and proceeds through opening of the isoselenazol ring and formation of a selenenyl sulfide with metallothionein.
  • the reaction with glutathione is even faster (t 1/2 ⁇ 1 s) and first forms a selenol and then a diselenide derivative of ebselen.
  • the reaction with metallothionein is stoichiometric and not affected by hydrogen peroxide.
  • ebselen is not a glutathione peroxidase mimic in this reaction.
  • it illustrates the functional potential of active site selenocysteines in selenoproteins in general.
  • the biological oxidizing agents that induce zinc release from MT feature prominently disulfides, selenium salts, and selenocystamine. Unlike their sulfur analogs, selenium compounds are particularly effective at stoichiometric concentrations (Jacob, C,
  • Ebselen reacts with thiols first by opening the isoselenazol ring while forming a sulfur-selenium bond. Excess thiols then reduce ebselen to a selenol derivative followed by the formation of a disulfide (Haenen, G. R. M. M., De Rooij, B. M., Vermeulen, N. P. E., & Bast A. (1990) Mol Pharmac. 37, 412-422).
  • Ebselen (98+ % pure) was obtained from Sigma (St. Louis, MO) and is of sufficiently low zinc content not to interfere with the zinc transfer assay.
  • the extinction coefficients of ebselen in methanol (Sigma, sequencing grade) were determined as 14,400 M-'cm “1 (262 nm) and 6,000 M " 'cm " ' (330 nm) (Morgenstern, R., Cotgreave, I. A., & Engman, L. (1992) Chem.-Biol Interactions 84, 77-84).
  • Rabbit MT-1 and MT-2 isoforms were converted from the cadmium-containing to the zinc-containing species (Vasak, M. (1991) Meth. Enzymol. 205, 41-44) and characterized by titration of thiols with 2,2'- dithiodipyridine and zinc analyses.
  • Yeast alcohol dehydrogenase (Sigma) was subjected
  • UV-VIS Spectroscopy Spectra were recorded with either Varian Cary 1 or Cary 50 spectrophotometers thermostatted at 25 °C. Stopped-flow kinetics were performed with a Biosequential SX-18MV reaction analyzer (Applied Photophysics, Leatherhead, U.K.). Selenol intermediates were assayed with l-chloro-2,4-dinitrobenzene (CDNB) (Cotgreave, I. A., Morgenstern, R., Engman, L., & Ahokas, J. (1992) Chem.-Biol Interactions 84, 69- 76).
  • CDNB l-chloro-2,4-dinitrobenzene
  • Ebselen at equimolar concentrations with respect to the twenty thiol ligands of MT affects a rapid (t 1/2 ⁇ 1 min) and complete transfer of zinc to either PAR (Fig. 14A) or apo-CPA (Fig. 14B) acting as zinc acceptors.
  • the initial reactivation of carboxypeptidase A ("CPA") in the absence of ebselen is due to the residual activity of apo-CPA and zinc transfer from MT which can transfer up to one zinc atom (Jacob, C, Maret, W., & Vallee, B. L. (1998) Proc. Natl. Acad. Sci.
  • Ebselen and its metabolites exhibit absorption spectra that are quite sensitive to chemical changes at the selenium atom (Ackerboom, T. P. M., Sies, H., & Ziegler, D. M. (1995) Arch. Biochem. Biophys. 316, 220-226).
  • ebselen and MT When the reaction between ebselen and MT is followed directly by wavelengths scans, two isosbestic points at 259 and 318 nm, characteristic of the interconversion of two absorbing species, are observed (Fig. 19A).
  • the reactivity of MT is between that of free thiols and that of a complex in which all thiolates are bound as terminal ligands, suggesting that the presence of bridging thiolate ligands in the clusters increase the reactivity MT.
  • ebselen may react preferrentially with MT in vivo. Reaction of Ebselen with MT in the Presence of Glutathione. Ebselen reacts efficiently with thiols such as glutathione to form a selenodisulfide (Sies, H. (1993) Free Radical Biol. Med. 14, 313-323).
  • ebselen forms a rather stable adduct and the consecutive reaction, the formation of a disulfide bond in MT and the concomitant release of a reduced selenol derivative of ebselen, seems to be rather slow if it occurs at all.
  • Ebselen shows little catalytic activity toward the hydrogen peroxide-induced zinc release from MT-2, also indicating the absence of a selenol intermediate.
  • the reaction of ebselen with MT is not catalytic and ebselen does not act as a glutathione peroxidase mimic in this reaction.
  • ebselen reacts reversibly in the presence of hydrogen peroxide and, hence will be available for the irreversible reaction with MT in the presence of glutathione.
  • ebselen whose properties as a glutathione peroxidase mimic involve both reduction of peroxides and oxidation of thiols.
  • the mechanism of action of ebselen as a therapeutic drug is not understood fully. In the reaction with MT, ebselen oxidizes thiols in MT and, therefore, actually acts as an oxidant. Controlled release of zinc, which itself is also considered an antioxidant (Bray, T. M. & Bettger, W. J. (1990) Free Radical Biol. Med. 8, 281-291), could contribute to the overall antioxidant action of ebselen.
  • Selenocysteine is a natural occurring amino acid which forms the active center of a number of enzymes, notably glutathione peroxidase and thyroid deiodinase. While the reaction of diselenides with glutathione has been studied previously, virtually nothing is known about the interactions of diselenides with zinc-sulfur bonds. Therefore oxidative zinc release from MT was studied in the presence of D,L-selenocystine. This reagent releases zinc from MT in the absence of an additional oxidant. However, they were also found to enhance zinc transfer from MT to PAR (4-(2-pyridylazo)resorcinol) when 'butylhydroperoxide ('BuOOH) was used as mild oxidizing agent.
  • PAR 4-(2-pyridylazo)resorcinol
  • D,L-selenocystine and 'BuOOH were obtained from Sigma (St. Louis, MO) and are of sufficiently low zinc content not to interfere with the zinc transfer assay.
  • Rabbit MT- 1 and MT-2 isoforms were converted from the cadmium-containing to the zinc-containing species (Vasak, M. (1991) Meth. Enzymol. 205, 41-44) and characterized by titration of thiols with 2,2'-dithiodipyridine and zinc analysis.
  • UV-VIS Spectroscopy Spectra were recorded with a Varian Cary 1 spectrophotometer thermostatted at 25°C.
  • D,L-Selenocystine Kinetics of the reaction of D,L-Selenocystine with Metallothionein.
  • D,L-selenocystine at equimolar concentrations with respect to the twenty thiol ligands of MT affects transfer of zinc to PAR.
  • zinc transfer under those conditions cannot be quenched by even a 30 fold excess of glutathione.
  • This observation might indicate some specificity of D,L-selenocystine (or intermediates) towards MT in comparison to glutathione.
  • substoichiometric amounts of D,L-selenocystine enhance zinc transfer in the presence
  • GTP has almost identical effects.
  • the corresponding di- or monophosphates and pyrimidine nucleotides neither bind as strongly as ATP nor do they enhance zinc transfer. Carbamylation of lysines of MT abolishes the binding of ATP, indicating that the highly conserved lysines are part of the binding site.
  • the binding of ATP is affected by glutathione and glutathione disulfide, both of which modulate zinc release and its transfer from MT (Jiang, L. J., Maret, W. & Vallee, B. L. (1998) Proc. Natl. Acad. Sci. USA, 95, 3483-3488). Glutathione decreases ATP binding whereas glutathione disulfide increases it.
  • the thermodynamic stabilities and kinetic labilities of zinc in MT are the consequence of ligand exchange and redox reactions of the cysteine sulfur donor atoms (Maret, W., Larsen, K.
  • Nucleotides, 5,5'-dithiobis(2-nitrobenzoic acid) (DTNB) and rabbit liver Cd,Zn- metallothionein II (Cd,Zn-MT-2) were obtained from Sigma; 65 ZnCl 2 (77.7-103.6 Gbq/g) from Dupont NEN; sheep liver sorbitol dehydrogenase (SDH) from Boehringer Mannheim; adenosine 5'-[ ⁇ , ⁇ -imido]triphosphate (AMP-PNP) from Fluka; and 1 ,N 6 -ethenoadenosine 5'-triphosphate (e-ATP) from Molecular Probes.
  • Zinc-depleted sorbitol dehydrogenase (apo-SDH) and human Zn 7 -MT-2 were prepared and characterized as described (Jiang, L. J., Maret, W. & Vallee, B. L. (1998) Proc. Natl. Acad. Sci. USA, 95, 3483-3488). Lysine Modification. Lysines in MT were modified by dissolving rabbit liver Cd,Zn-MT-2 in 0.2 ml of saturated sodium borate, pH 9.2, adding solid potassium cyanate to a final concentration of 1 M and incubating the reaction mixture for 40 h at 37 °C (Zeng, J. (1991) Meth. Enzymol., 205, 433-437).
  • Radioactivity in each fraction was measured by ⁇ -emission spectroscopy with a Searle model 1185 Automatic Gamma system operating at a 0.12-1.2 MeV energy range.
  • Reactivity of MT in the presence of nucleotides was determined using DTNB under pseudo-first order rate conditions where [DTNB] ⁇ [MT] (Cismowski, M. J., & Huang, P. C. (1991) Biochemistry, 30, 6626-6632). Under these conditions two equivalents of thiobenzoate are formed, since the inter- or intramolecular disulfide of MT is favored over the mixed disulfide (Savas, M. M., Shaw, C. F.
  • ATP binding a) Electronic absorption difference spectra. Double difference spectra of Zn-MT (2.5 ⁇ M) with different concentrations of ATP were recorded in 0.2 M Tris, pH 7.4 on a Cary model IE high performance UV-Vis spectrophotometer (Varian) using tandem cuvets (Roustan, C, Kassab, R., Pradel, L. A., & Thoai, N. V. (1968) Biochim. Biophys. Acta, 167, 326-338). ATP and MT were separated in the two chambers of the reference cuvet. while they were mixed in the chambers of the sample cuvet.
  • Spectra were recorded (spectrum 1), the samples in the two chambers of the reference cuvet were mixed, and the spectra were recorded again (spectrum 2). Double difference spectra were obtained by subtracting spectrum 2 from spectrum 1.
  • Hummel-Dreyer method Hummel, J. P., & Dreyer, W. J. (1962) Biochim. Biophys. Acta, 63, 530-532.
  • a Sephadex G-25 column (1 x 30 cm) was equilibrated with 50 mM Hepes buffer, pH 7.4 containing ATP (100 ⁇ M). Cd,Zn-MT was dissolved in this buffer and then applied to the column.
  • the resulting elution profile will exhibit a peak at the position where MT elutes, and a trough, representing the depletion of ATP in the buffer, at the position where ATP would elute. From the area of the trough and the known amount of protein applied, the binding ratio was determined at each concentration of ATP.
  • the comparison of rate constants is based on the assumption that in both cases only one zinc atom is transferred. In fact, however, in the presence of ATP at least five zinc atoms are released from MT and transferred to apo-SDH. The enhancement of zinc transfer depends on the concentration of ATP; 10 ⁇ M ATP leads to 21% and 100 ⁇ M to 36% reactivation, respectively (data not shown).
  • These effects are of the same order of magnitude as those observed with the glutathione/glutathione disulfide system (Jiang, L. J., Maret, W. & Vallee, B. L. (1998) Proc. Natl. Acad. Sci. USA, 95, 3483-3488).
  • other purine nucleotides e.g. ADP (Fig. 24), AMP, GMP, cAMP and cGMP or pyrimidine nucleotides such as CTP or UTP, do not enhance zinc transfer from MT at all.
  • ATP often binds to other biomolecules in the form of a Mg or Ca complex. Hence, these possibilities were examined. However, neither calcium nor magnesium ions at concentrations of up to 1 mM affected the reaction in any way. ATP analogs such as ATP- ⁇ -S and AMP-PNP are hydrolyzed poorly and therefore are commonly employed to examine whether or not ATP hydrolysis is a component or accompaniment of a physiological process. The reactivation of apo-SDH by MT in the presence of AMP-PNP closely resembles that in the presence of ATP, indicating that ATP hydrolysis is not essential for zinc transfer from MT (Fig. 24). Vanadate, a potent ATPase inhibitor does not affect zinc transfer.
  • ATP is a relatively weak zinc-chelating reagent
  • PAR 4-(2-pyridylazo)resorcinol
  • [ATP B ]/ [ATP F ][MT] 0 -[ATP B ] / K d [MT] 0 + n / K d
  • [ATP B ] and [ATP F ] are the concentrations of bound and free ATP, respectively
  • [MT] 0 the initial concentration of MT
  • n the number of identical and independent binding sites of MT
  • K d the dissociation constant.
  • the linear Scatchard plot gave a value of 0.93 for n (Fig. 27) - indicating that MT binds one molecule of ATP with a K d of 176 (+/- 33) ⁇ M, close to the value estimated by double difference spectrophotometry (Fig. 25).
  • lysine residues are relatively highly conserved in mammalian MT-1/-2 isoforms. Since they might participate in ATP binding, they were modified by carbamoylation (Zeng, J. (1991) Meth. Enzymol., 205, 433-437). ATP binding to lysine- modified MT is essentially abolished as assayed by the Hummel-Dreyer method. Further, ATP does not enhance zinc transfer of lysine-modified MT to apo-SDH, demonstrating that ATP binding is a prerequisite for the enhancement of zinc transfer. Since phosphate binds to Lys-31 (Robbins, A. H., McRee, D. E., Williamson, M., Collett, S. A.
  • e-ATP a fluorescent analogue of ATP
  • Fig. 28 When it binds to MT quenching of fluorescence is observed (Fig. 28). The magnitude of the quenching is likely due to the cadmium in MT, since a significantly smaller quenching is observed when Zn- MT was used in an analogous experiment.
  • Half-maximal quenching occurs at 20 ⁇ M of e- ATP, which is about one seventh of the K d value observed for ATP.
  • Binding of the analogue therefore, is significantly stronger as has been observed in other instances where this was explained on the basis of the additional hydrophobic surface in comparison with ATP (Sigel, H. and Song, B. (1996) in Interactions of Metal Ions with Nucleotides, Nucleic Acids, and Their Constituents eds., Sigel, A. & Sigel, H., Metal Ions in Biological Systems, 32, 135-205, Marcel Dekker, New York). ATP binding in the presence of glutathione. It has been suggested that the zinc content of MT is controlled by the cellular glutathione redox state (Maret, W. (1994) Proc. Natl. Acad. Sci.
  • the binding is specific for purine nucleotide triphosphates, since binding of other nucleotides could not be detected. Also, the binding data correlate well with the data for zinc transfer from MT to apo-SDH. It is perhaps of significance that only the purine nucleotides show these effects. They are known to form more stable complexes with zinc due to the formation of a macrochelate involving N-7 of the base (Sigel, H. and Song, B. (1996) in Interactions of Metal Ions with Nucleotides, Nucleic Acids, and Their Constituents eds., Sigel, A. & Sigel, H., Metal Ions in Biological Systems, 32, 135-205, Marcel Dekker, New York).
  • lysines could also be part of a nuclear translocation sequence.
  • Nuclear translocation of MT requires energy and the "nucleophilic" distribution of MT in human tumor cells is related to the ATP state (Woo, E. S., Kondo, Y., Watkins, S. C, Hoyt, D. G., & Lazo, J. S. (1996) Experimental Cell Research, 224, 365-371). Given the relatively low affinity of ATP for MT, the question arises whether or not
  • MT is associated with ATP in the cell. If one takes into account that the cytosolic concentration of ATP is under tight control and is almost always in the millimolar range (Peters, G. J., De Arbreu, R. A., Oosterhof, A., & Veerkamp, J. H. (1983) Biochim. Biophys. Acta, 759, 7-15; Rauch, U., Schulze, K., Witzenbichler, B., & Schultheiss, H. P. (1994) Circulation Res., 75, 760) while MT is present in the micromolar range or below (Krezoski, S. K., Villalobos, J., Shaw III, C. F., & Petering, D.
  • ATP could change the conformation of MT (maybe the small binding energy is sufficient for inducing a large conformational change in a rather flexible small protein such as MT), thereby influencing the reactivity of the zinc clusters.
  • the observation that zinc transfer is observed only in the presence of apo-SDH indicates that ATP "loosens the conformation" for more efficient zinc transfer.
  • ATP modulates the redox behavior of MT in a manner that is analogous to that of GSH.
  • GSH has been proposed to bind to the ⁇ -domain of MT by displacing a thiol ligand (Brouwer, M. Brouwer, T. H., & Cashon, R. E. (1993) Biochem. J., 294, 219-225).
  • the following experiment illustrates a relatively significant change in the shape of MT when ATP is bound.
  • the MT/ATP complex elutes about 20 min later than MT ( Figure 31 ). It was already known that MT itself, owing to the prolate ellipsoid shape of the molecule,

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Abstract

L'invention concerne un procédé destiné au traitement des maladies végétales et animales lorsque ces maladies impliquent un dysfonctionnement de l'homéostasie du zinc. Ledit procédé consiste à administrer des agents thérapeutiques modifiant le potentiel d'excitation cellulaire de manière à oxyder la métallothionéine, et donc à libérer des ions de zinc, ou de manière à maintenir la métallothionéine dans un état réduit pour empêcher le transfert du zinc de la métallothionéine aux accepteurs de zinc.
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US20040110691A1 (en) * 2001-11-13 2004-06-10 Stamler Jonathan S. Thiol reactive agents as a therapeutic modality
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US20160101079A1 (en) * 2014-10-09 2016-04-14 Albert Crum Protective metallothionein analog compounds, their compositions and use thereof in the treatment of pathogenic diseases
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