Patent Application
20070009537
The invention relates to antibody-mediated generation of reactive oxygen species from singlet oxygen and to therapeutic compositions and methods for treating microbial infections by using such antibodies.
Research throughout the last century has led to a consensus as to the role of antibodies in the immune system. The essence of this consensus is that the antibody molecule does not directly kill, or otherwise generate a product that could adversely affect, its target. Instead, the antibody molecule has been perceived as a binding molecule that merely tags its target or that activates other molecules or biological systems to respond to an antibody-antigen complex. Hence, antibodies themselves have been perceived as not possessing any destructive ability but as only marking foreign substances for removal by the complement cascade and/or phagocytosis (Arlaud et al., Immunol. Today, 8, 106-111 (1987); Sim & Reid, Immunol. Today 12, 307-311 (1991)).
However, antibodies with catalytic activities that can directly destroy their targets would have utility for many applications, for example, for directly killing microbes.
The invention provides methods for utilizing newly discovered abilities of antibodies to produce reactive oxygen species. According to the invention, antibodies can kill microbes by converting singlet oxygen (1O2*) into reactive oxygen species. Antibodies perform such conversion without the need for any other component of the immune system, that is, without the need for the complement cascade or phagocytosis.
Hence, according to the invention, antibodies have anti-microbial activity as a result of the production of powerful reactive oxygen species, including but not limited to superoxide radical (O2−), hydroxyl radical (OH●), hydrogen peroxide H2O2 or ozone (O3). Such activity resides in antibodies and in antibody-coated mammalian leukocytes such as neutrophils.
Thus, the invention is directed to an anti-microbial composition consisting essentially of a pharmaceutically acceptable carrier and an isolated antibody that can bind to a microbe, wherein the antibody can generate a reactive oxygen species when singlet oxygen (1O2) is present. The anti-microbial composition can also contain a sensitizer molecule that can generate singlet oxygen (1O2). In some embodiments, such a sensitizer can generate singlet oxygen (1O2) in the presence of light. Examples of sensitizer molecule include a pterin, a flavin, a hematoporphyrin, a tetrakis(4-sulfonatophenyl) porphyrin, a bipyridyl ruthenium(II) complex, a rose Bengal dye, a quinone, a rhodamine dye, a phthalocyanine, a hypocrellin, rubrocyanin, pinacyanol, allocyanin or a chlorin. Such sensitizer molecules can be attached to the antibody. In some embodiments, the antibody is a human or a humanized antibody.
Reactive oxygen species generated by the antibodies of the invention include superoxide radicals, hydroxyl radicals, hydrogen peroxide, ozone and other reactive oxygen species. In some embodiments, the reactive oxygen species is ozone.
The invention also provides methods to utilize antibodies to produce reactive oxygen species from singlet oxygen to treat infections, diseases and other conditions. The invention also contemplates therapeutic compositions comprising antibody compositions that can combat microbial infections. Such antibody compositions can be engineered to exhibit increased oxidative function.
For example, in some embodiments, the invention is directed to a method of treating a microbial infection in a mammal that involves administering to the mammal an anti-microbial composition consisting essentially of an antibody that can bind to a microbe and a pharmaceutically acceptable carrier, wherein the antibody can generate a reactive oxygen species when singlet oxygen (1O2) is present. The composition can also contain a sensitizer molecule that can generate singlet oxygen (1O2). As described above, such sensitizer molecules can be attached to the antibody.
In other embodiments, the invention is directed to a method of generating a reactive oxygen species to inhibit the growth of a microbe that involves contacting the microbe with an antibody that can bind to the microbe and a source of singlet oxygen (1O2). In some embodiments, the source of singlet oxygen (1O2) is a sensitizer molecule. As described above, such sensitizer molecules can be attached to the antibody.
For
FIGS. 21A-B provide bar graphs illustrating the bactericidal activity of the S. typhimurium-specific antibody 6B5. The mean colony forming units (n=3) are shown at time zero (t=0, blue) and at after one hour (t=1 h, magenta) incubation of live S. typhimurium with the 6B5 antibody preparation under different conditions.
The present invention concerns the discovery that antibodies, as a class of molecules, have the ability to convert singlet oxygen to reactive oxygen species. According to the invention, such reactive oxygen species can kill microbes. Examples of reactive oxygen species generated by antibodies include, but are not limited to ozone (O3), superoxide radical (O2−), hydrogen peroxide (H2O2) or hydroxyl radical (OH•).
The ability of antibodies to convert singlet oxygen to reactive oxygen species, regardless of source or antigenic specificity of the antibody, links the previously appreciated binding properties of antibodies with an ability to destroy their target. The present invention therefore provides methods for inhibiting microbial growth that involve contacting a microbe with an antibody that can generate a reactive oxygen species.
Definitions
Abbreviations: (HP) hematoporphyrin; (PBS) phosphate buffered saline; (OVA) chick-egg ovalbumin; (SOD) superoxide dismutase; (PO) peroxidase enzymes; (phox) phagocyte oxidase; (HRP) horseradish peroxidase; (MS) mass spectroscopy; (AES) ICP-atomic emission spectroscopy; (MS) mass-spectral, (QC) quantum chemical.
The term “agent” herein is used to denotes a chemical compound, a mixture of chemical compounds, a biological macromolecule, or an extract made from biological materials such as bacteria, plants, fungi, or animal (particularly mammalian) cells or tissues. Agents are evaluated for potential activity as antibody or neutrophil modulatory agents by screening assays described herein.
The terms “effective amount,” “effective reducing amount,” “effective ameliorating amount”, “effective bactericidal amount,” “effective tissue injury inhibiting amount”, “therapeutically effective amount” and the like terms as used herein are terms to identify an amount sufficient to obtain the desired physiological effect, e.g., treatment of a condition, disorder, disease and the like or reduction in symptoms of the condition, disorder, disease and the like. Such an effective amount of an antibody in the context of therapeutic methods is an amount that results in reducing, reversing, ameliorating, or inhibiting a microbial infection.
An “engineered antibody molecule” is a polypeptide that has been produced through recombinant techniques. Such molecules can include a reactive center that can catalyze the production of at least one reactive oxygen species from singlet oxygen. Such engineered antibody molecules may have a reactive indole contained within a polypeptide structure. The indole of such a molecule may be present as a tryptophan residue. Engineered antibody molecules may also contain non-natural amino acids and linkages as well as peptidomimetics. Engineered antibody molecules also include antibodies that are modified to eliminate the reaction center such that they are substantially unable to generate reactive oxygen species.
As used herein, the term “epitope” means any antigenic determinant on an antigen to which the paratope of an antibody binds. Epitopic determinants usually consist of chemically active surface groupings of molecules such as amino acids or sugar side chains and usually have specific three-dimensional structural characteristics, as well as specific charge characteristics. Antigens can include polypeptides, fatty acids, lipoproteins, lipids, chemicals, hormones and the like. In some embodiments, antigens include, but are not limited to, proteins from microbes such as bacteria or viruses such as human immunodeficiency virus, influenza virus, herpesvirus, papillomavirus, human T-cell leukemia virus and the like. In other embodiments, antigens include, but are not limited to, proteins expressed on cancer cells such as lung cancer, prostate cancer, colon cancer, cervical cancer, endometrial cancer, bladder cancer, bone cancer, leukemia, lymphoma, brain cancer and the like. Antigens of the invention also include chemicals such as ethanol, tetrahydrocanabinol, LSD, heroin, cocaine and the like.
The term “modulate” refers to the capacity to either enhance or inhibit a functional property of an antibody or engineered antibody molecule of the invention. Such modulation may increase or decrease production of at least one reactive oxygen species by the antibody, neutrophil or engineered antibody molecule.
A “non-natural” amino acid includes D-amino acids as well as amino acids that do not occur in nature, as exemplified by 4-hydroxyproline, γ-carboxyglutamate, O-phosphoserine, N-acetylserine, N-formylmethionine, 3-methylhistidine, 5-hydroxylysine and other such amino acids and imino acids.
The term “peptidomimetic” or “peptide mimetic” describes a peptide analog, such as those commonly used in the pharmaceutical industry as non-peptide drugs, with properties analogous to those of the template peptide. (Fauchere, J., Adv. Drug Res., 15: 29 (1986) and Evans et al., J. Med. Chem., 30:1229 (1987)). Generally, peptidomimetics are structurally similar to a paradigm polypeptide (i.e., a polypeptide that has a biochemical property or pharmacological activity), but have one or more peptide linkages optionally replaced by a linkage such as, —CH2NH—, —CH2S—, —CH2—CH2—, —CH═CH— (cis and trans), —COCH2—, —CH(OH)CH2—, and —CH2SO—, by methods known in the art. Advantages of peptide mimetics over natural polypeptide embodiments may include more economical production, greater chemical stability, altered specificity, reduced antigenicity, and enhanced pharmacological properties such as half-life, absorption, potency and efficacy.
As used herein, the terms “pharmaceutically acceptable,” “physiologically tolerable” and grammatical variations thereof, as they refer to compositions, carriers, diluents and reagents, are used interchangeably and represent that such materials are capable of administration to or upon a mammal without the production of undesirable physiological effects such as nausea, dizziness, gastric upset and the like.
The terms “protein” and “polypeptide” are used to describe a native protein, a peptide, a protein fragment, or an analog of a protein or polypeptide. These terms may be used interchangeably.
As used herein the term “reactive oxygen species” means antibody-generated oxygen species. These reactive oxygen species can possess one or more unpaired electrons or are otherwise reactive because they are readily react with other molecules. Such reactive oxygen species include but are not limited to superoxide free radicals, hydrogen peroxide, hydroxyl radical, peroxyl radical, ozone and other short-lived trioxygen adducts that have the same chemical signature as ozone.
Catalytic Activity of Antibodies
According to the invention, antibodies, regardless of source or antigenic specificity, can convert singlet oxygen into reactive oxygen species such as to ozone (O3), superoxide radical (O2−), hydrogen peroxide (H2O2) or hydroxyl radical (OH•). Such enzymatic action, joined with the high affinity targeting capabilities of antibodies, makes them into singular entities that can effectively destroy their targets. The antibody is therefore more properly perceived to be a remarkable adaptor molecule, having evolved both targeting and catalytic functions that place it at the frontline of the vertebrate defense against foreign invaders.
The ability to produce reactive oxygen species from singlet oxygen is present in intact immunoglobulins and well as in antibody fragments such as Fab, F(ab′)2 and Fv fragments (see examples). This activity does not reside in other molecules, including RNaseA, superoxide dismutase, and Bowman-Birk inhibitor protein that can be oxidized (example I and Table 1). Also, the activity is not associated with the presence of disulfides in a molecule, even though such disulfides are sufficiently electron rich that they can be oxidized (Bent et al., J. Am. Chem. Soc. 87:2612-2619 (1975)).
The ability of an antibody to generate a reactive oxygen species from singlet oxygen is abolished if the antibody is denatured. This indicates that the three dimensional structure of the antibody is relevant to the reduction process used to generate reactive oxygen species.
The ability to produce reactive oxygen species in an efficient and long term manner from singlet oxygen is present in immunoglobulins and in the T-cell receptor (example II,
Structural studies also indicate that a conserved tryptophan residue found in T-cell receptors resides in a domain similar to that found in antibodies. While antibodies and T-cell receptors both have such a tryptophan. β2-Macroglobulin, which lacks this conserved tryptophan residue, does not have the ability to generate ozone, superoxide or hydrogen peroxide. The sequence and structure surrounding this tryptophan residue is highly conserved between antibodies and T-cell receptors, indicating that those surrounding structures may also play a role in allowing catalysis of singlet oxygen to hydrogen peroxide, ozone, and/or superoxide.
The discovery of the bactericidal activity of antibodies in the presence of 1O2* is the first direct evidence that they can destroy their antigenic targets in the absence of complement or phagocytes. This is the first evidence that antibodies may play a role in host defense against bacterial or microbial infection.
Endogenous Production of Singlet Oxygen
The role of the newly discovered chemical potential of antibodies in vivo is dependent on the availability of the key substrate 1O2*. However, 1O2* is produced during a variety of physiological events and is available in vivo. See J. F. Kanofsky Chem.-Biol. Interactions 70, 1 (1989) and references therein. For example, 1O2* is produced including reperfusion. X. Zhai and M. Ashraf Am. J. Physiol., 269 (Heart Circ. Physiol., 38) H1229 (1995). Also, 1O2* is produced in neutrophil activation during phagocytosis. J. R. Kanofsky, H. Hoogland, R. Wever, S. J. Weiss J. Biol. Chem., 263, 9692 (1988); Babior et al., Amer. J. Med., 109:33-34 (2000). Singlet oxygen (1O2) also results from irradiation by light of metal-free porphyrin precursors that are present in the skin of porphyria sufferers.
Moreover, the substrate 1O2* is generated by phagocytosis or reperfusion in amounts that are sufficient for antibodies to produce detectable levels of reactive oxygen species. For example, the volume of the phagosome is approximately 1.0×10−15 liters. Hence, the reactions identified herein need not be highly efficient because only a few hundred molecules comprise micromolar concentrations in such a small volume. In fact, the concentration of 1O2* has been calculated to be as high as a molar concentration within the phagosome. E. P. Reeves et al., Nature 416, 291 (2002). The same estimates can be made regarding the number of antibody molecules from titrations with bacteria and fluorescently-labeled antibodies and the immuno-gold studies (
Singlet molecular oxygen (1O2) is also generated during microbicidal processes in both direct and indirect ways. Singlet molecular oxygen (1O2) is generated directly, for example, via the action of flavoprotein oxidases (Allen, R. C., Stjernholm, R. L., Benerito, R. R. & Steele, R. H., eds. Cormier, M. J., Hercules, D. M. & Lee, J. (Plenum, New York), pp. 498-499 (1973); Klebanoff, S. J. in The Phagocytic Cell in Host Resistance (National Institute of Child Health and Human Development, Orlando, Fla.) (1974)). Alternatively, 1O2 can be generated indirectly during microbicidal processes such as the nonenzymatic disproportionation of O2•− in solutions at low pH, like those found in the phagosome (Stauff, J., Sander, U. & Jaeschke, W., Chemiluminescence and Bioluminescence, eds., Williams, R. C. & Fudenberg, H. H. (Intercontinental Medical Book Corp., New York), pp. 131-141 (1973); Allen, R. C., Yevich, S. J., Orth, R. W. & Steele, R. H., Biochem. Biophys. Res. Commun., 60, 909-917 (1974)).
Because 1O2 is so highly reactive, it was previously considered to be an endpoint in the cascade of oxygen-scavenging agents. However, it has been found that antibodies, as a class of proteins, have the ability to intercept 1O2 and efficiently reduce it to reactive oxygen species, thus offering a mechanism by which 1O2 can be rescued and recycled during phagocyte action, and thereby potentiating the microbial action of the immune system.
Therapeutic Methods
The invention provides methods, for the production of reactive oxygen species when their production is warranted, such as for inhibiting microbial infection, in promoting wound healing, lysing bacteria, eliminating viruses, targeting cancer cells for oxidant-induced lysis and the like processes. For example, the invention provides antibody mediated generation of reactive oxygen species to supplement the local concentration of superoxide concentration generated by phagocytic neutrophils and to combat a bacterial infection or viral infection. The reactive oxygen species acts as an anti-microbial agent destroying the bacteria, viruses or other microbes. Thus, to enhance this process, one would use the method of this invention to provide an antibody composition to the area to cause an increase in the local concentration of reactive oxygen species.
A. Providing Antibody Activity
Therapeutic methods contemplated by the invention that are based on using an antibody that can generate reactive oxygen species include 1) inhibiting proliferation of a microbe, or targeting and killing a microbe in a patient where the antibody recognizes and immunoreacts with an antigen expressed on the microbe, 2) inhibiting proliferation of a cancer cell, or targeting and killing a cancer cell in a patient where the antibody recognizes and immunoreacts with an antigen expressed on the cancer cell, 3) inhibiting tissue injury associated with neutrophil mediated inflammation in a subject, for example where the inflammation results from a bacterial infection or when the subject has an autoimmune disease, 4) enhancing the bactericidal effectiveness of a phagocyte in a subject, 5) promoting wound healing in a subject having a open wound where the reactive oxygen species stimulates fibroblast proliferation and/or the immune response further includes lymphocyte proliferation, 6) stimulating cell proliferation, such as stimulating fibroblast proliferation in a wound in a subject, and similar situations.
In some embodiments, the invention provides therapeutic methods for treating microbial infections and other diseases that benefit from enhanced production of a reactive oxygen species such as a superoxide radical, hydroxyl radical, ozone or hydrogen peroxide. Such methods can employ any antibody to generate reactive oxygen species in a situation where the production of such a reactive oxygen species is warranted. In some embodiments, the specifically targeted to bind to the microbe, so that production of reactive oxygen species is localized.
Moreover, such methods can employ an antibody that has been engineered to generate increased levels of reactive oxygen species, for example, because the antibody has an additional reactive site for converting singlet oxygen to reactive oxygen species. The use of engineered antibody molecules having more than two reductive centers compared to a non-engineered antibody having the two conserved tryptophan residues is warranted when enhanced production of a reactive oxygen species such as a superoxide radical, hydroxyl radical, ozone or hydrogen peroxide is needed.
In still further aspects, the antibody is a recombinant antibody that is provided as described herein or, alternatively, is expressed from an expression vector delivered to the cell. The expression vector in this context can also express a sensitizer molecule (see below).
The minimum requirement for generating a reactive oxygen species by an antibody is the presence of oxygen, i.e., aerobic conditions are generally required. The biological conversion of singlet oxygen to reactive oxygen species occurs in light, including visible light, infrared light and under ultraviolet irradiation conditions. When visible light conditions are employed, the production of singlet oxygen can be enhanced using other molecules that can provide a source of singlet oxygen. Molecules that generate singlet oxygen include molecules that generate singlet oxygen without the need for other factors or inducers as well as “sensitizer” molecules that can generate singlet oxygen after exposure to an inducer. Examples of molecules that can generate singlet oxygen without the need for other factors or inducers include, but are not limited to, endoperoxides. In some embodiments, the endoperoxide employed can be an anthracene-9,10-dipropionic acid endoperoxide. Examples of sensitizer molecules include, but are not limited to, pterins, flavins, hematoporphyrins, tetrakis(4-sulfonatophenyl)porphyrin, bipyridyl ruthenium(II) complexes, rose Bengal dyes, quinones, rhodamine dyes, phthalocyanines, hypocrellins, rubrocyanins, pinacyanols or allocyanines.
Sensitizer molecules can be induced to generate singlet oxygen when exposed to an inducer. One such inducer is light. Such light can be visible light, ultraviolet light, or infrared light, depending upon the type and structure of the sensitizer.
The invention further contemplates the therapeutic use of an antibody to create ozone, superoxide, hydroxyl radical or hydrogen peroxide in an environment where such reactive oxygen species are needed or are substantially absent. In one embodiment, the invention contemplates a method for inhibiting the growth of a microbe where the microbe is contacted with a composition including an antibody able to generate such a reactive oxygen species from singlet oxygen. The method is successful when nonspecific or immunospecific (antigen binding), whole or fragment antibodies are used. Such antibody fragments include single chain antibodies as well as the engineered molecules and antibodies described herein. However, when localized activity against a microbe is desired, the antibody can be specific for an antigen associated with the microbe. For example, the antibody can bind selectively to an antigen on the surface of the microbe.
The antibody composition can be delivered in vivo to a subject with a microbial infection or other disease or condition that may benefit from exposure to a reactive oxygen species. Preferred in vivo delivery methods include administration intravenously, topically, by inhalation, by cannulation, intracavitally, intramuscularly, transdermally, subcutaneously or by liposome containing the antibody.
Exemplary concentrations of antibody at the cell surface range from 0.01 to 50 micromolar. However, the concentration may vary depending on the desired outcome where the amount of antibody provided is that amount of antibody that is sufficient to obtain the desired physiological effect, i.e., the generation of a reactive oxygen species such as hydrogen peroxide, ozone, a superoxide radical or a derivative oxidant thereof to generate oxidative stress. Dosing and timing of the therapeutic treatments with antibody compositions are compatible with those described for antioxidants below.
The methods of the invention further contemplate exposing an antibody or antibody-antigen complex to irradiation with ultraviolet, infrared or visible light in the method of generating antibody-mediated reactive oxygen species such as hydrogen peroxide, ozone, superoxide radicals or derivative oxidants thereof.
To enhance the production of a reactive oxygen species, a reactive oxygen species-generating amount of a sensitizer, for example, a photosensitizer, can be utilized in the therapeutic methods described herein. As defined herein, a sensitizer is any molecule that induces or increases the concentration of singlet oxygen. Sensitizers can be used in the presence of irradiation, the process of which includes exposure to ultraviolet, infrared or visible light for a period sufficient to activate the sensitizer. Exemplary exposure times and conditions are described in the examples.
A reactive oxygen species-generating amount of sensitizer is the amount of sensitizer that is sufficient to obtain the desired physiological effect, e.g., generation of a reactive oxygen species such as superoxide, ozone or hydrogen peroxide from singlet oxygen, mediated by an antibody in any situation where the presence of such reactive oxygen species and the derivatives thereof is warranted. In some embodiments, a sensitizer is conjugated to the antibody. An antibody conjugated to a sensitizer is generally capable of binding to a antigen, i.e., the antibody retains an active antigen binding site, allowing for antigen recognition and complexing to occur.
Exemplary sensitizers include but are not limited to pterins, flavins, hematoporphyrin, tetrakis(4-sulfonatophenyl)porphyrin, bipyridyl ruthemium(II) complexes, rose bengal dye, quinones, rhodamine dyes, phtalocyanine, and hypocrellins.
In a further embodiment, generation of a reactive oxygen species is enhanced by administering a means to enhance production of singlet oxygen. Reduced singlet oxygen is the source of reactive oxygen species such as hydrogen peroxide, ozone, superoxide radicals or derivative oxidants thereof. One means to enhance production of singlet oxygen is a prodrug that includes any molecule, compound, or reagent that is useful in generating singlet oxygen. Such a prodrug is administered with, or at a time subsequent to, the administering or contacting of an antibody with a desired target cell, tissue or organ as described herein. When a prodrug is administered after antibody administration, the antibody has already had an opportunity to immunoreact with its target antigen and may have formed an antibody-antigen complex. A means to enhance production of singlet oxygen can then enhance the generation of reactive oxygen species such as hydrogen peroxide, ozone, superoxide radicals or derivative oxidants thereof, at the site of antibody-antigen recognition. This embodiment has particular advantages, for example, the ability to create increased local accumulation of therapeutically desirable superoxide, ozone or hydrogen peroxide at a desired site or location.
A preferred prodrug is endoperoxide, for example, at a concentration of about 1 micromolar to about 50 micromolar. A preferred concentration of endoperoxide to achieve at the antibody-antigen complex site is about 10 micromolar.
An antigenic target of the antibodies of the invention can be any antigen known or available to one of skill in the art. The antigen can be any antigen that is present on or in a cell, tissue or organ where the presence of reactive oxygen species and the antibody mediated process of producing it is warranted. The antigen can be in solution, for example, in extracellular fluids. An antigen can be, for example, a protein, a peptide, a fatty acid, a low density lipoprotein, an antigen associated with inflammation, a cancer cell antigen, a bacterial antigen, a viral antigen or a similar molecule.
Cells on which antigens are associated include but are not limited to microbial, endothelial, interstitial, epithelial, muscle, phagocytic, blood, dendritic, connective tissue and nervous system cells.
Hence, for example, infections of the following target microbial organisms can be treated by the antibodies of the invention: Aeromonas spp., Bacillus spp., Bacteroides spp., Campylobacter spp., Clostridium spp., Enterobacter spp., Enterococcus spp., Escherichia spp., Gastrospirillum sp., Helicobacter spp., Klebsiella spp., Salmonella spp., Shigella spp., Staphylococcus spp., Pseudomonas spp., Vibrio spp., Yersinia spp., and the like. Infections that can be treated by the antibodies of the invention include those associated with staph infections (Staphylococcus aureus), typhus (Salmonella typhi), food poisoning (Escherichia coli, such as O157:H7), bascillary dysentery (Shigella dysenteria), pneumonia (Psuedomonas aerugenosa and/or Pseudomonas cepacia), cholera (Vivrio cholerae), ulcers (Helicobacter pylori), Salmonella typhimurium and others. E. coli serotype O157:H7 has been implicated in the pathogenesis of diarrhea, hemorrhagic colitis, hemolytic uremic syndrome (HUS) and thrombotic thrombocytopenic purpura (TTP). The antibodies of the invention are also active against drug-resistant and multiply-drug resistant strains of bacteria, for example, multiply-resistant strains of Staphylococcus aureus and vancomycin-resistant strains of Enterococcus faecium and Enterococcus faecalis.
In some embodiments, the anti-microbial compositions of the invention are used against gram negative bacteria. In further embodiments, the anti-microbial compositions can be used against Escherichia spp., Pseudomonas spp., and/or Salmonella spp. For example, the anti-microbial compositions can be used against different types of Escherichia coli, Salmonella typhimurium, Psuedomonas aerugenosa and other related bacteria.
The anti-microbial compositions of the invention are also effective against viruses. The term “virus” refers to DNA and RNA viruses, viroids, and prions. Viruses include both enveloped and non-enveloped viruses, for example, hepatitis A virus, hepatitis B virus, hepatitis C virus, human immunodeficiency virus (HIV), poxviruses, herpes viruses, adenoviruses, papovaviruses, parvoviruses, reoviruses, orbiviruses, picomaviruses, rotaviruses, alphaviruses, rubivirus, influenza virus type A and B, flaviviruses, coronaviruses, paramyxoviruses, morbilliviruses, pneumoviruses, rhabdoviruses, lyssaviruses, orthmyxoviruses, bunyaviruses, phleboviruses, nairoviruses, hepadnaviruses, arenaviruses, retroviruses, enteroviruses, rhinoviruses and the filovirus.
Other therapeutic conditions that would benefit from the creation or enhancement of reactive oxygen species in a cell, tissue, organ or extracellular compartment are known by those of ordinary skill in the art. For example, such conditions are further described in McCord, Am. J. Med., 108:652-659 (2000), the disclosure of which are hereby incorporated by reference.
Anti-microbial activity can be evaluated against these varieties of microbes using methods available to one of skill in the art. Anti-microbial activity, for example, is determined by identifying the minimum inhibitory concentration (MIC) of an antibody of the present invention that prevents growth of a particular microbial species. In one embodiment, anti-microbial activity is the amount of antibody that kills 50% of the microbes when measured using standard dose or dose response methods.
Methods of evaluating therapeutically effective dosages for treating a microbial infection with antibodies described herein include determining the minimum inhibitory concentration of an antibody preparation at which substantially no microbes grow in vitro. Such a method permits calculation of the approximate amount of antibody needed per volume to inhibit microbial growth or to kill 50% of the microbes. Such amounts can be determined, for example, by standard microdilution methods. For example, a series of microbial culture tubes containing the same volume of medium and the substantially the same amount of microbes are prepared, and an aliquot of antibody is added. The aliquot contains differing amounts of antibody in the same volume of solution. The microbes are cultured for a period of time corresponding to one to ten generations and the number of microbes in the culture medium is determined.
The optical density of the cultural medium can also be used to estimate whether microbial growth has occurred—if no significant increase in optical density has occurred, then no significant microbial growth has occurred. However, if the optical density increases, then microbial growth has occurred. To determine how many microbial cells remain alive after exposure to the antibody, a small aliquot of the culture medium can be removed at the time when the antibody is added (time zero) and then at regular intervals thereafter. The aliquot of culture medium is spread onto a microbial culture plate, the plate is incubated under conditions conducive to microbial growth and, when colonies appear, the number of those colonies is counted.
B. Inhibiting Unwanted Oxidation
The invention also provides methods for ameliorating the negative effects of antibody-mediated production of reactive oxygen species.
The use of molecules that effect the antibody-mediated production of reactive oxygen species is applicable to any situation in which unwanted, deleterious, damaging production of reactive oxidant species that are generated by antibodies. The molecules that are useful in these situations are referred to generally as “antioxidants,” defined as any molecule that has an antagonist effect to an oxidant. An antioxidant so defined includes 1) inhibitors of antibody-mediated superoxide generation, 2) inhibitors of antibody-mediated hydrogen peroxide generation, 3) inhibitors of antibody-mediated ozone generation, 4) inhibitors of the reactions converting hydrogen peroxide into derivative reactive oxidants; and 5) inhibitors of the reactive oxygen species themselves.
Such antioxidants include those that inhibit the activation of oxygen producing reactive oxidants as well as those neutralizing those already formed. The antioxidant effect can occur by any mechanism, including catalysis. Antioxidants as a category include oxygen scavengers or free radical scavengers. Antioxidants may be of different types so they are available if and when they are needed. In view of the presence of oxygen throughout an aerobic organism, antioxidants may be available in different cellular, tissue, organ and extracellular compartments. The latter include extracellular fluid spaces, intraocular fluids, synovial fluid, cerebrospinal fluid, gastrointestinal secretions, interstitial fluid, blood and lymphatic fluid. Antioxidants are present within an organism but are also provided by supplementing the diet and by use of the methods of this invention. In some embodiments, the antioxidants employed include but are not limited to ascorbic acid, α-tocopherol, γ-glutamylcysteinylglycine, γ-glutamyl transpeptidase, α-lipoic acid, dihydrolipoate, Bacetyl-5-methoxytyptamine, flavones, flavonenes, flavanols, catalase, peroxidase, superoxide dismutase, metallothionein, and butylated hydroxytoluene. In other embodiments, the molecule that has the capacity to function as an antioxidant in the context of the methods of this invention is an engineered antibody in which the ability to generate superoxide free radical from reducing singlet oxygen is diminished or preferably absent altogether. Such antibody molecules are described herein.
The use of antioxidants is directed to situations in which an antioxidant is required to prevent, control, minimize, reduce, or inhibit the damage of an oxidant or a reactive oxygen product. Thus, the invention contemplates the use of an antioxidant for reducing the antibody-mediated production of reactive oxygen species in tissues, for example, in healthy tissues surrounding the site treated with antibodies. In such situations, without intervention, the cellular damage may result, for example, in inflammatory conditions, in trauma conditions, in organ transplantation and the like.
In the context of using an engineered antibody as an antioxidant, the antibody, having diminished or substantially no ability to generate reactive oxygen species such as superoxide, ozone or hydrogen peroxide since it lacks the reductive centers that reduce singlet oxygen, provides a therapeutic benefit in promoting a desired immune response without inducing additional tissue damage resulting from excess superoxide production. Engineered therapeutic antibody compositions can retain their antigen-binding site so that targeting to a particular antigen is achieved in concert with the desired therapeutic benefits.
The present invention further contemplates a method of ameliorating oxidative stress in a subject as well as alleviating a symptom in a subject where the symptom is associated with production of oxidant. Exemplary of conditions in which the therapeutic methods of inhibiting the antibody mediated production of reactive oxygen species with an antioxidant of the present invention include but are not limited to inhibiting aberrant smooth muscle disorder, inhibiting liver disease, proliferation of cancer cells, inhibiting inflammation in cancer patients receiving radiotherapy, inflammatory diseases (arthritis, vasculitis, glomerulonephritis, systemic lupus erythematosus, and adult respiratory distress syndrome), ischemic diseases (heart disease, stroke, intestinal ischemia, and reperfusion injury), hemochromatosis, acquired immunodeficiency syndrome, emphysema, organ transplantation, gastric ulcers, hypertension, preeclampsia, neurological diseases (multiple sclerosis, Alzheimer's disease, Parkinson's disease, amyotrophic lateral sclerosis, and muscular dystrophy) alcoholism and smoking-related diseases.
Cells in which oxidative stress is deleterious include but are not limited to endothelial, interstitial, epithelial, muscle (smooth, skeletal or cardiac), phagocytic (including neutrophils and macrophages), white blood cells, dendritic, connective tissue and nervous system cells. Effected tissues include but are not limited to muscle, nervous, skin, glandular, mesenchymal, splenic, sclerous, epithelial and endothelial tissues.
Useful references that describe the use of antioxidants and oxygen scavengers to treat various conditions induced by oxidative stress, other than that relating to the generation of oxidants by an antibody as described in the present invention, include the disclosures of U.S. Pat. Nos. 5,362,492; 5,599,712; 5,637,315; 5,647,315; 5,747,026; 5,848,290; 5,994,339; 6,030,611 and 6,040,611, the disclosures of which patents are hereby incorporated by reference. Such references support the therapeutic uses of antioxidants in the present invention.
Antibodies
The invention provides therapeutic antibodies. All antibody molecules belong to a family of plasma proteins called immunoglobulins. Their basic building block, the immunoglobulin fold or domain, is used in various forms in many molecules of the immune system and other biological recognition systems. A typical immunoglobulin has four polypeptide chains, contains an antigen binding region known as a variable region, and contains a non-varying region known as the constant region. An antibody contemplated for use in the present invention can be in any of a variety of forms, including a whole immunoglobulin, Fv, Fab, F(ab′)2 other fragments, and a single chain antibody that includes the variable domain complementarity determining regions (CDR), or other forms. All of these terms fall under the broad term “antibody” as used herein. The present invention contemplates the use of any specificity of an antibody, polyclonal or monoclonal, and is not limited to antibodies that recognize and immunoreact with a specific antigen. In preferred embodiments, in the context of both the therapeutic and screening methods described herein, an antibody or fragment thereof is used that is immunospecific for an antigen.
The term “antibody” as used in this invention includes intact molecules as well as fragments thereof, such as Fab, F(ab′)2, and Fv, which are capable of binding an epitope. These antibody fragments retain some ability to selectively bind with its antigen or receptor and are defined as follows:
(1) Fab, the fragment, which contains a monovalent antigen-binding fragment of an antibody molecule, can be produced by digestion of whole antibody with the enzyme papain to yield an intact light chain and a portion of one heavy chain;
(2) Fab′, the fragment of an antibody molecule can be obtained by treating whole antibody with pepsin, followed by reduction, to yield an intact light chain and a portion of the heavy chain; two Fab′ fragments are obtained per antibody molecule;
(3) F(ab′)2, the fragment of the antibody that can be obtained by treating whole antibody with the enzyme pepsin without subsequent reduction; F(ab′)2 is a dimer of two Fab′ fragments held together by two disulfide bonds;
(4) Fv, defined as a genetically engineered fragment containing the variable region of the light chain and the variable region of the heavy chain expressed as two chains; and
(5) Single chain antibody (“sFv”), defined as a genetically engineered molecule containing the variable region of the light chain, the variable region of the heavy chain, linked by a suitable polypeptide linker as a genetically fused single chain molecule.
The preparation of polyclonal antibodies is well-known to those skilled in the art. See, for example, Green, et al., Production of Polyclonal Antisera, in: Immunochemical Protocols (Manson, ed.), pages 1-5 (Humana Press); Coligan, et al., Production of Polyclonal Antisera in Rabbits, Rats Mice and Hamsters, in: Current Protocols in Immunology section 2.4.1 (1992), which are hereby incorporated by reference.
The preparation of monoclonal antibodies is also conventional. See, for example, Kohler & Milstein, Nature, 256:495 (1975); Coligan, et al., sections 2.5.1-2.6.7; and Harlow, et al., in: Antibodies: A Laboratory Manual, page 726 (Cold Spring Harbor Pub. (1988)), which are hereby incorporated by reference. Monoclonal antibodies can be isolated and purified from hybridoma cultures by a variety of well-established techniques. Such isolation techniques include affinity chromatography with Protein-A Sepharose, size-exclusion chromatography, and ion-exchange chromatography. See, e.g., Coligan, et al., sections 2.7.1-2.7.12 and sections 2.9.1-2.9.3; Barnes, et al., Purification of Immunoglobulin G (IgG), in: Methods in Molecular Biology, Vol. 10, pages 79-104 (Humana Press (1992).
The present invention also contemplates engineered therapeutic molecules including engineered antibodies that have been altered to contain an additional reductive center. Such engineered antibody molecules can be used where an insufficient amount of antibody or reactive oxygen species is present. Such engineered therapeutic molecules can be engineered to have an increased number of reductive centers relative to those that were naturally occurring in the molecule or antibody.
Introduction of a reductive center in a engineered molecule or antibody is accomplished by methods well known to one of ordinary skill in the art. Preferred means including recombinant expression methods and well as direct protein synthesis methods have been previously described. The choice of method is necessarily dependent on the length of the molecule being engineered. Regardless of the methods employed, the positioning, i.e., the location, of the engineered reductive center is based upon the ability of the engineered molecule to exhibit reducing activity on singlet oxygen. Preferably, the incorporated reductive centers are positioned such that they are deeply buried in the folded molecule and so reactive oxygen species production is retained or augmented. In one embodiment, an engineered antibody retains antigen-binding function, and the location of an engineered reductive center is adjacent to a variable binding domain. In certain aspects, one reductive center is contemplated. In other aspects, two reductive centers are contemplated. Still, in other aspects, more than three reductive centers are contemplated. Preferably, the reductive centers comprise indole. Also contemplated are reductive centers having indole moieties such as those present in tryptophan residue. Any technique to engineer such reductive centers in a molecule or antibody is contemplated for use in the present invention. In a preferred embodiment, the reductive centers are introduced by site-directed mutagenesis of nucleotide sequences encoding the engineered antibody such that the substituted nucleotides encode tryptophan residues at predetermined locations in the encoded molecule.
In the embodiment of preparing an engineered molecule such as an antibody to include desired reductive centers, a molecule that is produced by recombinant technology is also contemplated to be in the form of a fusion conjugate, where the conjugate can provide a sensitizer molecule as described herein for use in therapeutic methods as described herein.
Engineered antibodies or other molecules, which can be any protein or polypeptide that contains reductive centers that function according to the methods of the invention and/or sensitizer molecules, are contemplated for any of the methods as described herein.
Methods of in vitro and in vivo manipulation of monoclonal antibodies are well known to those skilled in the art. One particular manipulation involves the process of humanizing a monoclonal antibody by recombinant means to generate antibodies containing human specific and recognizable sequences. See, for review, Holmes, et al., J. Immunol. 158:2192-2201 (1997) and Vaswani, et al., Annals Allergy, Asthma & Immunol., 81:105-115 (1998).
Methods of making antibody fragments are known in the art (see for example, Harlow and Lane, Antibodies: A Laboratory Manual, Cold Spring Harbor Laboratory, New York, (1988), incorporated herein by reference). Antibody fragments of the present invention can be prepared by proteolytic hydrolysis of the antibody or by expression in E. coli of DNA encoding the fragment. Antibody fragments can be obtained by pepsin or papain digestion of whole antibodies conventional methods. For example, antibody fragments can be produced by enzymatic cleavage of antibodies with pepsin to provide a 5S fragment denoted F(ab′)2. This fragment can be further cleaved using a thiol reducing agent, and optionally a blocking group for the sulfhydryl groups resulting from cleavage of disulfide linkages, to produce 3.5S Fab′ monovalent fragments. Alternatively, an enzymatic cleavage using pepsin produces two monovalent Fab′ fragments and an Fc fragment directly. These methods are described, for example, in U.S. Pat. No. 4,036,945 and U.S. Pat. No. 4,331,647, and references contained therein. These patents are hereby incorporated in their entireties by reference.
Other methods of cleaving antibodies, such as separation of heavy chains to form monovalent light-heavy chain fragments, further cleavage of fragments, or other enzymatic, chemical, or genetic techniques may also be used, so long as the fragments bind to the antigen that is recognized by the intact antibody. For example, Fv fragments comprise an association of VH and VL chains. This association may be noncovalent or the variable chains can be linked by an intermolecular disulfide bond or cross-linked by chemicals such as glutaraldehyde. Preferably, the Fv fragments comprise VH and VL chains connected by a peptide linker. These single-chain antigen binding proteins (sFv) are prepared by constructing a structural gene comprising DNA sequences encoding the VH and VL domains connected by an oligonucleotide. The structural gene is inserted into an expression vector, which is subsequently introduced into a host cell such as E. coli. The recombinant host cells synthesize a single polypeptide chain with a linker peptide bridging the two V domains. Methods for producing sFvs are described, for example, by Whitlow, et al., Methods: a Companion to Methods in Enzymology Vol. 2, page 97 (1991); Bird, et al., Science, 242:423-426 (1988); Ladner, et al, U.S. Pat. No. 4,946,778; and Pack, et al., Bio/Technology, 11:1271-77 (1993).
Another form of an antibody fragment is a peptide coding for a single complementarity-determining region (CDR). CDR peptides (“minimal recognition units”) can be obtained by constructing genes encoding the CDR of an antibody of interest. Such genes are prepared, for example, by using the polymerase chain reaction to synthesize the variable region from RNA of antibody-producing cells. See, for example, Larrick, et al., Methods: a Companion to Methods in Enzymology, Vol. 2, page 106 (1991).
The invention contemplates human and humanized forms of non-human (e.g. murine) antibodies. Such humanized antibodies are chimeric immunoglobulins, immunoglobulin chains or fragments thereof (such as Fv, Fab, Fab′, F(ab′)2 or other antigen-binding subsequences of antibodies) that contain minimal sequence derived from non-human immunoglobulin. For the most part, humanized antibodies are human immunoglobulins (recipient antibodies) in which residues from a complementary determining region (CDR) of the recipient are replaced by residues from a CDR of a nonhuman species (donor antibody) such as mouse, rat or rabbit having the desired specificity, affinity and capacity.
In some instances, Fv framework residues of the human immunoglobulin are replaced by corresponding non-human residues. Furthermore, humanized antibodies may comprise residues that are found neither in the recipient antibody nor in the imported CDR or framework sequences. These modifications are made to further refine and optimize antibody performance. In general, humanized antibodies will comprise substantially all of at least one, and typically two, variable domains, in which all or substantially all of the CDR regions correspond to those of a non-human immunoglobulin and all or substantially all of the FR regions are those of a human immunoglobulin consensus sequence. The humanized antibody optimally also will comprise at least a portion of an immunoglobulin constant region (Fc), typically that of a human immunoglobulin. For further details, see: Jones et al., Nature 321, 522-525 (1986); Reichmann et al., Nature 332, 323-329 (1988); Presta, Curr. Op. Struct. Biol. 2, 593-596 (1992); Holmes, et al., J. Immunol., 158:2192-2201 (1997) and Vaswani, et al., Annals Allergy, Asthma & Immunol., 81:105-115 (1998).
The invention also provides methods of mutating antibodies to optimize their affinity, selectivity, binding strength, reactive oxygen species production or other desirable property. A mutant antibody refers to an amino acid sequence variant of an antibody. In general, one or more of the amino acid residues in the mutant antibody is different from what is present in the reference antibody. Such mutant antibodies necessarily have less than 100% sequence identity or similarity with the reference amino acid sequence. In general, mutant antibodies have at least 75% amino acid sequence identity or similarity with the amino acid sequence of either the heavy or light chain variable domain of the reference antibody. Preferably, mutant antibodies have at least 80%, more preferably at least 85%, even more preferably at least 90%, and most preferably at least 95% amino acid sequence identity or similarity with the amino acid sequence of either the heavy or light chain variable domain of the reference antibody.
One method of mutating antibodies involves affinity maturation using phage display. Affinity maturation using phage display refers to a process described in Lowman et al., Biochemistry 30(45): 10832-10838 (1991), see also Hawkins et al., J. Mol. Biol. 254: 889-896 (1992). While not strictly limited to the following description, this process can be described briefly as involving mutation of several antibody hypervariable regions in a number of different sites with the goal of generating all possible amino acid substitutions at each site. The antibody mutants thus generated are displayed in a monovalent fashion from filamentous phage particles as fusion proteins. Fusions are generally made to the gene III product of M13. The phage expressing the various mutants can be cycled through several rounds of selection for the trait of interest, e.g. binding affinity or selectivity. The mutants of interest are isolated and sequenced. Such methods are described in more detail in U.S. Pat. No. 5,750,373, U.S. Pat. No. 6,290,957 and Cunningham, B. C. et al., EMBO J. 13(11), 2508-2515 (1994).
The preparation of a therapeutic antibody (or fragment thereof) of this invention can be accomplished by recombinant expression techniques as well as protein synthesis, methods of which are well known to one of ordinary skill in the art. For recombinant approaches, mutation of a nucleic acid that encodes an antibody or fragment thereof can be conducted by a variety of means, but is most conveniently conducted using mutagenized oligonucleotides that are designed to introduce mutations at predetermined sites that then encode an altered amino acid sequence in the expressed molecule. Such alterations include substitutions, additions, and/or deletions of particular nucleotide sequences that similarly encode substitutions, additions, and/or deletions of the encoded amino acid residue sequence. Site-directed mutagenesis, also referred to as oligonucleotide-directed mutagenesis and variations thereof, and the subsequent cloning of the altered genes are well known techniques (Sambrook et al., Molecular Cloning: A Laboratory Manual 2nd ed., Chapter 15, Cold Spring Harbor Laboratory Press, (1989)). Another recombinant approach includes synthesizing the gene encoding a therapeutic molecule of this invention by combining long oligonucleotide strands that are subsequently annealed and converted to double-stranded DNA suitable for cloning and expression (Ausebel et al., Current Protocols in Molecular Biology Units 10 and 15, Wiley and Sons, Inc. (2000)). Such techniques can be used to create engineered molecules that contain a reduction center and are able to generate hydrogen peroxide or superoxide from singlet oxygen. It is contemplated that such engineered molecules can be designed based on antibody structure and on the T-cell receptor, in the case of hydrogen peroxide.
Thus, the present invention contemplates an antibody that has been engineered to generate more superoxide free radical, ozone or hydrogen peroxide in a desired location. The antibody is engineered to contain additional reductive centers that increase the reduction of singlet molecular oxygen to superoxide free radical or hydrogen peroxide, as described in examples I and II herein. The invention also contemplates an antibody that has been engineered to have at least a diminished capacity to generate superoxide free radical or hydrogen peroxide from singlet oxygen. In that context, the antibody lacks at least one of its reductive centers and preferably is substantially free of a reductive center. Such antibody compositions are readily prepared with methods well known to one of ordinary skill in the art.
If desired, polyclonal or monoclonal antibodies prepared for use as therapeutic compositions or in the methods of invention can be further purified, for example, by binding to and elution from a matrix to which the polypeptide or a peptide to which the antibodies were raised is bound. Those of skill in the art will know of various techniques common in the immunology arts for purification and/or concentration of polyclonal antibodies, as well as monoclonal antibodies (Coligan, et al., Unit 9, Current Protocols in Immunology, Wiley Interscience, (1991)).
Compositions
The antibodies, antioxidants and oxygen scavengers of the invention may be formulated into a variety of acceptable compositions. Such pharmaceutical compositions can be administered to a mammalian host, such as a human patient, in a variety of forms adapted to the chosen route of administration, i.e., orally or parenterally, by intravenous, intramuscular, topical or subcutaneous routes.
In cases where compounds, for example, antioxidant and oxygen scavenger compounds, are sufficiently basic or acidic to form stable nontoxic acid or base salts, administration of such compounds as salts may be appropriate. Examples of pharmaceutically acceptable salts are organic acid addition salts formed with acids that form a physiological acceptable anion, for example, tosylate, methanesulfonate, acetate, citrate, malonate, tartarate, succinate, benzoate, ascorbate, α-ketoglutarate, and α-glycerophosphate. Suitable inorganic salts may also be formed, including hydrochloride, sulfate, nitrate, bicarbonate, and carbonate salts.
Pharmaceutically acceptable salts are obtained using standard procedures well known in the art, for example by reacting a sufficiently basic compound such as an amine with a suitable acid affording a physiologically acceptable anion. Alkali metal (for example, sodium, potassium or lithium) or alkaline earth metal (for example calcium) salts of carboxylic acids also are made.
Thus, the present antibodies and compounds may be systemically administered, e.g., orally, in combination with a pharmaceutically acceptable vehicle such as an inert diluent or an assimilable edible carrier. They may be enclosed in hard or soft shell gelatin capsules, may be compressed into tablets, or may be incorporated directly with the food of the patient's diet. For oral therapeutic administration, the antibodies, antioxidants and oxygen scavengers may be combined with one or more excipients and used in the form of ingestible tablets, buccal tablets, troches, capsules, elixirs, suspensions, syrups, wafers, and the like. Such compositions and preparations should contain at least 0.1% of active compound. The percentage of the compositions and preparations may, of course, be varied and may conveniently be between about 2 to about 60% of the weight of a given unit dosage form. The amount of antibodies, antioxidants or oxygen scavengers in such therapeutically useful compositions is such that an effective dosage level will be obtained.
The tablets, troches, pills, capsules, and the like may also contain the following: binders such as gum tragacanth, acacia, corn starch or gelatin; excipients such as dicalcium phosphate; a disintegrating agent such as corn starch, potato starch, alginic acid and the like; a lubricant such as magnesium stearate; and a sweetening agent such as sucrose, fructose, lactose or aspartame or a flavoring agent such as peppermint, oil of wintergreen, or cherry flavoring may be added. When the unit dosage form is a capsule, it may contain, in addition to materials of the above type, a liquid carrier, such as a vegetable oil or a polyethylene glycol. Various other materials may be present as coatings or to otherwise modify the physical form of the solid unit dosage form. For instance, tablets, pills, or capsules may be coated with gelatin, wax, shellac or sugar and the like. A syrup or elixir may contain the active compound, sucrose or fructose as a sweetening agent, methyl and propylparabens as preservatives, a dye and flavoring such as cherry or orange flavor. Of course, any material used in preparing any unit dosage form should be pharmaceutically acceptable and substantially non-toxic in the amounts employed. In addition, the active compound may be incorporated into sustained-release preparations and devices.
For wound healing, topical application to a wound on a subject can be employed. A composition containing an antibody can be applied directly to the wound or applied to a bandage and then applied to the wound.
The active compound may also be administered intravenously or intraperitoneally by infusion or injection. Solutions of the active compound or its salts may be prepared in water, optionally mixed with a nontoxic surfactant. Dispersions can also be prepared in glycerol, liquid polyethylene glycols, triacetin, and mixtures thereof and in oils. Under ordinary conditions of storage and use, these preparations contain a preservative to prevent the growth of microorganisms.
The pharmaceutical dosage forms suitable for injection or infusion can include sterile aqueous solutions or dispersions or sterile powders comprising the active ingredient that are adapted for the extemporaneous preparation of sterile injectable or infusible solutions or dispersions, optionally encapsulated in liposomes. In all cases, the ultimate dosage form should be sterile, fluid and stable under the conditions of manufacture and storage. The liquid carrier or vehicle can be a solvent or liquid dispersion medium comprising, for example, water, ethanol, a polyol (for example, glycerol, propylene glycol, liquid polyethylene glycols, and the like), vegetable oils, nontoxic glyceryl esters, and suitable mixtures thereof. The proper fluidity can be maintained, for example, by the formation of liposomes, by the maintenance of the required particle size in the case of dispersions or by the use of surfactants. The prevention of the action of microorganisms can be brought about by various antibacterial and antifungal agents, for example, parabens, chlorobutanol, phenol, sorbic acid, thimerosal, and the like. In many cases, it will be preferable to include isotonic agents, for example, sugars, buffers or sodium chloride. Prolonged absorption of the injectable compositions can be brought about by the use in the compositions of agents delaying absorption, for example, aluminum monostearate and gelatin.
Sterile injectable solutions are prepared by incorporating the antibodies, antioxidants or oxygen scavengers in the required amount in the appropriate solvent with various of the other ingredients enumerated above, as required, followed by filter sterilization. In the case of sterile powders for the preparation of sterile injectable solutions, the preferred methods of preparation are vacuum drying and the freeze drying techniques, which yield a powder of the antibodies, antioxidants or oxygen scavengers plus any additional desired ingredient present in the previously sterile-filtered solutions.
For topical administration, the antibodies, antioxidants or oxygen scavengers may be applied in pure form, i.e., when they are liquids. However, it will generally be desirable to administer them to the skin as compositions or formulations, in combination with a dermatologically acceptable carrier, which may be a solid or a liquid.
Useful solid carriers include finely divided solids such as talc, clay, microcrystalline cellulose, silica, alumina and the like. Useful liquid carriers include water, alcohols or glycols or water-alcohol/glycol blends, in which the present antibodies, antioxidants or oxygen scavengers can be dissolved or dispersed at effective levels, optionally with the aid of non-toxic surfactants. Adjuvants such as fragrances and additional antimicrobial agents can be added to optimize the properties for a given use. The resultant liquid compositions can be applied from absorbent pads, used to impregnate bandages and other dressings, or sprayed onto the affected area using pump-type or aerosol sprayers.
Thickeners such as synthetic polymers, fatty acids, fatty acid salts and esters, fatty alcohols, modified celluloses or modified mineral materials can also be employed with liquid carriers to form spreadable pastes, gels, ointments, soaps, and the like, for application directly to the skin of the user.
Examples of useful dermatological compositions that can be used to deliver the antibodies, antioxidants or oxygen scavengers of the present invention to the skin are known to the art; for example, see Jacquet et al. (U.S. Pat. No. 4,608,392), Geria (U.S. Pat. No. 4,992,478), Smith et al. (U.S. Pat. No. 4,559,157) and Wortzman (U.S. Pat. No. 4,820,508).
Useful dosages of the antibodies, antioxidants or oxygen scavengers of the present invention can be determined by comparing their in vitro activity, and in vivo activity in animal models. Methods for the extrapolation of effective dosages in mice, and other animals, to humans are known to the art; for example, see U.S. Pat. No. 4,938,949.
Generally, the concentration of the antibodies, antioxidants or oxygen scavengers of the present invention in a liquid composition, such as a lotion, will be from about 0.1-25 wt-%, preferably from about 0.5-10 wt-%. The concentration in a semi-solid or solid composition such as a gel or a powder will be about 0.1-5 wt-%, preferably about 0.5-2.5 wt-%.
The amount of the antibodies, antioxidants or oxygen scavengers, or an active salt or derivative thereof, required for use in treatment will vary not only with the particular salt selected but also with the route of administration, the nature of the condition being treated and the age and condition of the patient and will be ultimately at the discretion of the attendant physician or clinician.
In general, however, a suitable dose will be in the range of from about 0.5 to about 100 mg/kg, e.g., from about 10 to about 75 mg/kg of body weight per day, such as 3 to about 50 mg per kilogram body weight of the recipient per day, preferably in the range of 6 to 90 mg/kg/day, most preferably in the range of 15 to 60 mg/kg/day.
The antibodies, antioxidants or oxygen scavengers are conveniently administered in unit dosage form; for example, containing 5 to 1000 mg, conveniently 10 to 750 mg, most conveniently, 50 to 500 mg of active ingredient per unit dosage form.
Ideally, the antibodies, antioxidants or oxygen scavengers should be administered to achieve peak plasma concentrations of the active compound of from about 0.5 to about 75 μM, preferably, about 1 to 50 μM, most preferably, about 2 to about 30 μM. This may be achieved, for example, by the intravenous injection of a 0.05 to 5% solution of the antibodies, antioxidants or oxygen scavengers, optionally in saline, or orally administered as a bolus containing about 1-100 mg of the antibodies, antioxidants or oxygen scavengers. Desirable blood levels may be maintained by continuous infusion to provide about 0.01-5.0 mg/kg/hr or by intermittent infusions containing about 0.4-15 mg/kg of the antibodies, antioxidants or oxygen scavengers.
The desired dose may conveniently be presented in a single dose or as divided doses administered at appropriate intervals, for example, as two, three, four or more sub-doses per day. The sub-dose itself may be further divided, e.g., into a number of discrete loosely spaced administrations; such as multiple inhalations from an insufflator or by application of a plurality of drops into the eye.
In a preferred embodiment, an antioxidant enters the cell and reacts with the reactive oxygen species thereby reducing the concentration of reactive oxygen species in the cell. In an alternative embodiment, an antioxidant enters the cell or is present in the surrounding extracellular milieu and reacts with the oxidants generated from reactive oxygen species.
The therapeutic compositions of this invention, the antioxidants described herein, antibodies that include both engineered antibodies and other molecules containing additional reductive centers as described herein for promoting antibody activity, are administered in a manner compatible with the dosage formulation, and in a therapeutically effective amount. The quantity to be administered and timing depends on the subject to be treated, capacity of the subject's system to utilize the active ingredient, and degree of therapeutic effect desired. Precise amounts of active ingredient required to be administered depend on the judgement of the practitioner and are peculiar to each individual. However, suitable dosage ranges for various types of applications depend on the route of administration. Suitable regimes for administration are also variable, but are typified by an initial administration followed by repeated doses at intervals to result in the desired outcome of the therapeutic treatment.
Antibodies, antioxidants or oxygen scavengers contemplated for use in the present invention can be delivered to the site of interest to mediate the desired outcome in a composition such as a liposome, the preparation of which is well known to one of ordinary skill in the art of liposome-mediated delivery. Alternative delivery means include but are not limited to administration intravenously, topically, orally, by inhalation, by cannulation, intracavitally, intramuscularly, transdermally, and subcutaneously.
Therapeutic compositions of the present invention contain a physiologically tolerable carrier together with an antioxidant as described herein or an antibody as described herein for providing antibody activity, dissolved or dispersed therein as an active ingredient. In a preferred embodiment, the therapeutic composition is not immunogenic when administered to a mammal or human patient for therapeutic purposes.
The preparation of a pharmacological composition that contains active ingredients dissolved or dispersed therein is well understood in the art and need not be limited based on formulation. Typically such compositions are prepared as injectables either as liquid solutions or suspensions, however, solid forms suitable for solution, or suspensions, in liquid prior to use can also be prepared. The preparation can also be emulsified.
The active ingredients can be mixed with excipients that are pharmaceutically acceptable and compatible with the active ingredient and in amounts suitable for use in the therapeutic methods described herein. Suitable excipients are, for example, water, saline, dextrose, glycerol, ethanol or the like and combinations thereof. In addition, if desired, the composition can contain minor amounts of auxiliary substances such as wetting or emulsifying agents, pH buffering agents and the like which enhance the effectiveness of the active ingredient.
The therapeutic compositions of the present invention can include pharmaceutically acceptable salts of the components therein. Pharmaceutically acceptable salts include the acid addition salts (formed with the free amino groups of the polypeptide) that are formed with inorganic acids such as, for example, hydrochloric or phosphoric acids, or such organic acids as acetic, tartaric, mandelic and the like. Salts formed with the free carboxyl groups can also be derived from inorganic bases such as, for example, sodium, potassium, ammonium, calcium or ferric hydroxides, and such organic bases as isopropylamine, trimethylamine, 2-ethylamino ethanol, histidine, procaine and the like.
Physiologically tolerable carriers are well known in the art. Exemplary of liquid carriers are sterile aqueous solutions that contain no materials in addition to the active ingredients and water, or contain a buffer such as sodium phosphate at physiological pH value, physiological saline or both, such as phosphate-buffered saline. Still further, aqueous carriers can contain more than one buffer salt, as well as salts such as sodium and potassium chlorides, dextrose, polyethylene glycol and other solutes.
Liquid compositions can also contain liquid phases in addition to and to the exclusion of water. Exemplary of such additional liquid phases are glycerin, vegetable oils such as cottonseed oil, and water-oil emulsions.
Other therapeutic conditions that would benefit from the antioxidant inhibition of antibody mediated oxidant production in a cell, tissue, or organs as well as extracellular compartments are well known to those of ordinary skill in the art and have been reviewed by McCord, Am. J. Med. 108:652-659 (2000) and Babior et al., Am. J. Med., 109:33-44 (2000), the disclosures of which are hereby incorporated by reference.
The invention is further described in detail by reference to the non-limiting examples that follow. While the invention has been described in detail with reference to certain preferred embodiments thereof, it will be understood that modifications and variations are within the spirit and scope of that which is described and claimed.
Antibodies:
The following whole antibodies were obtained from PharMingen: 49.2 (mouse IgG2b κ), G155-178 (mouse IgG2a κ), 107.3 (mouse IgG1 κ), A95-1 (rat IgG2b), G235-2356 (hamster IgG), R3-34 (rat IgG κ), R35-95 (rat IgG2a κ), 27-74 (mouse IgE), A110-1 (rat IgG1 λ), 145-2C11 (hamster IgG group 1 κ), M18-254 (mouse IgA κ), and MOPC-315 (mouse IgA λ). The following were obtained from Pierce: 31243 (sheep IgG), 31154 (human IgG), 31127 (horse IgG), and 31146 (human IgM).
The following F(ab′)2 fragments were obtained from Pierce: 31129 (rabbit IgG), 31189 (rabbit IgG), 31214 (goat IgG), 31165 (goat IgG), and 31203 (mouse IgG). Protein A, protein G, trypsin-chymotrypsin inhibitor (Bowman-Birk inhibitor), β-lactoglobulin A, α-lactalbumin, myoglobin, β-galactosidase, chicken egg albumin, aprotinin, trypsinogen, lectin (peanut), lectin (Jacalin), BSA, superoxide dismutase, and catalase were obtained from Sigma. Ribonuclease IA was obtained from Amersham Pharmacia. The following immunoglobulins were obtained in-house using hybridoma technology: OB2-34C12 (mouse IgG1 κ), SHO1-41G9 (mouse IgG1 κ), OB3-14F1 (mouse IgG2a κ), DMP-15G12 (mouse IgG2a κ), AD1-19G1 (mouse IgG2b κ), NTJ-92C12 (mouse IgG1 κ), NBA-5G9 (mouse IgG1 κ), SPF-12H8 (mouse IgG2a κ), TIN-6C11 (mouse IgG2a κ), PRX-1B7 (mouse IgG2a κ), HA5-19A11 (mouse IgG2a κ), EP2-19G2 (mouse IgG1 κ), GNC-92H2 (mouse IgG1 κ), WD1-6G6 (mouse IgG1 κ), CH2-5H7 (mouse IgG2b κ), PCP-21H3 (mouse IgG1 κ), and TM1-87D7 (mouse IgG1 κ). DRB polyclonal (human IgG) and DRB-b12 (human IgG) were supplied by Dennis R. Burton (The Scripps Research Institute). 1D4 Fab (crystallized) was supplied by Ian A. Wilson (The Scripps Research Institute).
All assays were carried out in PBS (10 mM phosphate/60 mM sodium chloride, pH 7.4). Commercial protein solution samples were dialyzed into PBS as necessary. Amplex Red hydrogen peroxide assay kits (A-12212) were obtained from Molecular Probes.
Antibody/Protein Irradiation.
Unless otherwise stated, the assay solution (100 μl, 6.7 μM protein in PBS, pH 7.4) was added to a glass vial, sealed with a screw-cap, and irradiated with either UV (312 nm, 8000 μWcm−2 Fischer-Biotech transilluminator) or visible light.
Quantitative Assay for Hydrogen Peroxide.
An aliquot (20 μl) from the protein solution was removed and added into a well of a 96-well microtiter plate (Costar) containing reaction buffer (80 μl). Working solution (100 μl/400 μM Amplex Red reagent 1/2 units/ml horseradish peroxidase) was then added, and the plate was incubated in the dark for 30 min. The fluorescence of the well components was then measured using a CytoFluor Multiwell Plate Reader (Series 4000, PerSeptive Biosystems, Framingham, Mass.; Ex/Em: 530/580 nm). The hydrogen peroxide concentration was determined using a standard curve. All experiments were run in duplicate, and the rate is quoted as the mean of at least two measurements.
Sensitization and Quenching Assays.
A solution of 31127 (100 μl of horse IgG, 6.7 μM) in PBS (pH 7.4, 4% dimethylformamide) and hematoporphyrin IX (40 μM) was placed in proximity to a strip light. Hydrogen peroxide concentration was determined as described herein. The assay was also performed in the presence of NaN3 (100 mM) or PBS in D2O.
Oxygen Dependence.
A solution of 31127 (1.6 ml, horse IgG, 6.7 μM) in PBS (pH 7.4) was rigorously degassed using the freeze/thaw method under argon. Aliquots (100 μl) were introduced into septum-sealed glass vials that had been purged with the appropriate O2/Ar mixtures (0-100%) via syringe. Dissolved oxygen concentrations were measured with an Orion 862A dissolved oxygen meter. These solutions were then vortexed vigorously, allowed to stand for 20 min, and then vortexed again. A syringe containing the requisite O2/Ar mixture was used to maintain atmospheric pressure during the course of the experiment. Aliquots (20 μl) were removed using a gas-tight syringe and hydrogen peroxide concentration measured as described herein. The data from three separate experiments were collated and analyzed using the Enzyme Kinetics v1.1 computer program (for determination of Vmax and Km parameters).
Antibody Production of Hydrogen Peroxide in the Dark, Using a Chemical 1O2 Source.
A solution of sheep IgG 31243 (100 μl, 20 μM) in PBS (pH 7.4) and the endoperoxide of disodium 3,3N-(1,4naphthylidene) dipropionate (25 mM in D2O) were placed in a warm room (37 EC) for 30 min in the dark. Hydrogen peroxide concentration was determined as described herein.
Hydrogen Peroxide Formation by the Fab1D4 Crystal.
A suspension of crystals of the Fab fragment of 1D4 (2 μl) was diluted with PBS (198 μl, pH 7.4) and vortexed gently. Following centrifugation, the supernatant was removed, and the washing procedure was repeated twice further. The residual crystal suspension was then diluted into PBS, pH 7.4 (100 μl), and added into a well of a quartz ELISA plate. Following UV irradiation for 30 min, Amplex Red working solution (100 μl) was added, and the mixture was viewed on a fluorescence microscope.
Antibody Fluorescence Versus Hydrogen Peroxide Formation.
A solution of 31127 (1.0 ml of horse IgG, 6.7 μM) in PBS (pH 7.4) was placed in a quartz cuvette and irradiated with UV light for 40 min. At 10-min intervals, the fluorescence of the solution was measured using an SPF-500C spectrofluorimeter (SLM-Aminco, Urbana, Ill.; Ex/Em, 280/320). At the same time point, an aliquot (20 μl) of the solution was removed, and the hydrogen peroxide concentration was determined as described herein.
Consumption of Hydrogen Peroxide by Catalase.
A solution of EP2-19G12 (100 μl of mouse IgG, 20 μM in PBS, pH 7.4) was irradiated with UV light for 30 min, after which time the concentration of hydrogen peroxide was determined by stick test (EM Quant Peroxide Test Sticks) to be 2 mg/liter. Catalase [1 μl, Sigma, 3.2 M (NH4)2SO4, pH 6.0] was added, and after 1 min, the concentration of H2O2 was found to be 0 mg/liter.
Denaturation.
IgG 19G12 (100 μl, 6.7 μM) was heated to 100 EC in an Eppendorf tube for 2 min. The resultant solution was transferred to a glass, screw-cap vial and irradiated with UV light for 30 min. The concentration of H2O2 was determined after 30 min.
The measured values for the initial rate of formation of hydrogen peroxide by a panel of intact immunoglobulins and antibody fragments are collected in Table 1. It is believed that Ig-generated O2•− dismutates spontaneously into H2O2, which is then utilized as a cosubstrate with N-acetyl-3,7-dihydroxyphenazine 1 (Amplex Red) for horseradish peroxidase, to produce the highly fluorescent resorufin 2 (excitation maxima 563 nm, emission maxima 587 nm) (
*Assay conditions are described in Materials and Methods.
HMean values of at least two determinations. The background rate of H2O2 formation is 0.005 nmol/min in PBS and 0.003 nm/min in PBS with SOD.
The rates of hydrogen peroxide formation were linear for more than 10% of the reaction, with respect to the oxygen concentration in PBS under ambient condition (275 μM). With sufficient oxygen availability, the antibodies can generate at least 40 equivalents of H2O2 per protein molecule without either a significant reduction in activity or structural fragmentation. An example of the initial time course of hydrogen peroxide formation in the presence or absence of antibody 19G2 is shown in
The data in Table 1 reveal a universal ability of antibodies to generate H2O2 from 1O2. This function seems to be shared across a range of species and is independent of the heavy and light chain compositions investigated or antigen specificity. The initial rates of hydrogen peroxide formation for the intact antibodies are highly conserved, varying from 0.15 nmol/min/mg [clone A95-1 (rat IgG2b)] to 0.97 nmol/min/mg (clone PCP-21H3, a murine monoclonal IgG) across the whole panel. Although the information available is more limited for the component antibody fragments, the activity seems to reside in both the Fab and F(ab′)2 fragments.
If this activity were due to a contaminant, it would have to be present in every antibody and antibody fragment obtained from diverse sources. However, to further rule out contamination, crystals of the murine antibody 1D4 Fab from which high-resolution x-ray structures have been obtained (at 1.7 D) were investigated for their ability to generate H2O2 (
Investigations into this antibody transformation support singlet oxygen as the intermediate being reduced. No formation of hydrogen peroxide occurs with antibodies under anaerobic conditions either in the presence or absence of UV irradiation. Furthermore, no generation of hydrogen peroxide occurs under ambient aerobic conditions without irradiation. Irradiation of antibodies with visible light in the presence of a known photosensitizer of 3O2 in aqueous solutions hematoporphyrin (HP) (Kreitner, M., Alth, G., Koren, H., Loew, S. & Ebermann, R., Anal. Biochem., 213, 63-67 (1993)), leads to hydrogen peroxide formation (
Furthermore, incubation of sheep antibody 31243 in the dark at 37 EC, with a chemical source of 1O2 [the endoperoxide of 3N,3N-(1,4naphthylidene) dipropionate] leads to hydrogen peroxide formation.
The rate of formation of H2O2, by horse IgG with HP (40 μM) in visible light, is increased in the presence of D2O and reduced with the 1O2 quencher NaN3 (40 mM) (
The rate of hydrogen peroxide formation is proportional to IgG concentration between 0.5 and 20 μM but starts to curve at higher concentrations (
Significantly, the effect of oxygen concentration on the observed rate of H2O2 production shows a significant saturation about 200 μM of oxygen (
The mechanism by which antibodies reduce 1O2 is still being determined. However, the participation of a metal-mediated redox process has been largely discounted because the activity of the antibodies remains unchanged after exhaustive dialysis in PBS containing EDTA (4 mM). This leaves the intrinsic ability of the amino acid composition of the antibodies themselves. Aromatic amino acids such as tryptophan (Trp) can be oxidized by 1O2 via electron transfer (Grossweiner, L. I., Curr. Top. Radiat. Res. O. 11, 141-199 (1976)). In addition, disulfides are sufficiently electron rich that they can also be oxidized (Bent. D. V. & Hayon, E., J. Am. Chem. Soc., 87, 2612-2619 (1975)). Therefore, there is the potential that Trp residues and/or the intrachain or interchain disulfide bonds homologous to all antibodies are responsible for 1O2 reduction. To both investigate to what extent this ability of antibodies is shared by other proteins and to probe the mechanism of reduction, a panel of other proteins was studied (
Whereas other proteins can convert 1O2 into O2•−, in contrast to antibodies it is by no means a universal property. RNase A and superoxide dismutase, which do not possess Trp residues but have several disulfide bonds, do not reduce 1O2. Similarly, the Bowman-Birk inhibitor protein (Voss, R.-H., Ermler, U., Essen, L.-O., Wenzl, G., Kim, Y.-M. & Flecker, P., Eur. J. Biochem. 242, 122-131 (1996); Baek, J. & Kim, S., Plant Physiol., 102, 687 (1993)) that has seven disulfide bonds and zero Trp residues does not reduce 1O2. In contrast, chick ovalbumin, which has only 2 Trp residues (Feldhoff, R. & Peters, T. J., Biochem. J., 159, 529-533 (1976)), is one of the most efficient proteins at reducing 1O2.
Given the loss of antibody activity upon denaturation, the location of key residues in the protein is likely to be more critical than their absolute number. Because the majority of aromatic residues in proteins are generally buried to facilitate structural stability (Burley, S. K. & Petsko, G. A., Science, 229, 23-28 (1985)), the nature of the reduction process was explored in terms of relative contribution of surface and buried residues by fluorescence-quenching experiments. Aromatic amino acids in proteins are modified by the absorption of ultraviolet light, especially in the presence of sensitizing agents such as molecular oxygen or ozone (Foote, C. S., Science, 162, 963-970 (1968); Foote, C. S., Free Radicals Biol., 2, 85-133 (1976); Gollnick, K., Adv. Photochem., 6, 1-122 (1968)). Trp reacts with 1O2 via a [2+2] cycloaddition to generate N-formylkynurenine or kynurenine, which are both known to significantly quench the emission of buried Trp residues (Mach, H., Burke, C. J., Sanyal, G., Tsai, P.-K, Volkin, D. B. & Middaugh, C. R. in Formulation and Delivery of Proteins and Peptides, eds. Cleland, J. L. & Langer, R. (American Chemical Society, Denver, Colo.) (1994)). The intrinsic fluorescence of horse IgG is rapidly quenched to 30% of its original value during a 40-min irradiation, whereas hydrogen peroxide generation is linear throughout (r2=0.998) (
Throughout nature, organisms have defended themselves by production of relatively simple chemicals. At the level of single molecules, this mechanism has thought to be largely abandoned with the appearance in vertebrates of the immune system. It was considered that once a targeting device had evolved, the killing mechanism moved elsewhere. The present results realign recognition with killing within the same molecule. In a certain sense this chemical immune system parallels the purely chemical defense mechanism of lower organisms, with the exception that a more sophisticated and diverse targeting element is added.
Given the constraints that an ideal killing system must use host molecules in a localized fashion while minimizing self damage, one can hardly imagine a more judicious choice than 1O2. Because one already has such a reactive molecule, it is important to ask what might be the advantage of its further conversion by the antibody. The key issue is that by conversion of the transient singlet oxygen molecule (lifetime 4 μs) into the more stable O2•−, one now has access to hydrogen peroxide and all of the toxic products it can generate. In addition, superoxide is the only molecular oxygen equivalent remaining at the end of the oxygen-scavenging cascade. Therefore, this “recycling” may serve as a crucial mechanism for potentiation of the microbicidal process. Another benefit of singlet molecular oxygen is that it is only present when the host is under assault, thereby making it an “event-triggered” substrate. Also, because there are alternative ways to defend that use accessory systems, this chemical arm of the immune system might be silent under many circumstances. This said, however, there may be many disease states where antibody and singlet oxygen find themselves juxtaposed, thereby leading to cellular and tissue damage. Given that diverse events in man lead to the production of singlet oxygen, its activation by antibodies may lead to a variety of diseases ranging from autoimmunity to reperfusion injury and atherosclerosis (Skepper et al., Microsc. Res. Tech., 42, 369-385 (1998)).
Crystallography:
IgG 4C6 was digested with papain and the Fab′ fragment purified using standard protocols (Harlow and Lane). The Fab′ was crystallized from 13-18% PEG 8 K, 0.2 M ZnAc, 0.1 M cacodylate, pH 6.5. Crystals were pressurized under xenon gas at 200 psi for two minutes (Soltis et al., J. Appl. Cryst., 30, 190, (1997)) and then flash cooled in liquid nitrogen. Data were collected to 2.0 Å resolution at SSRL BL9-2. The structure was solved by molecular replacement using coordinates from the native 4C6 structure, and xenon atom sites were identified from strong peaks in the difference Fourier map. Refinement of the structure was done in CNS (Brünger et al., Acta. Crystallogr., D54, 905 (1998)) to final R=23.1% and Rfree=25.7%. The occupancies of the two xenon atoms were refined after fixing their B values fifty percent higher than the B factors of the immediately surrounding protein. The FIG.s were generated in Bobscript (R. M. Esnouf, Acta Crystallog., D55, 938 (1999)).
Scanning of the Kabat Database:
The Kabat database of human and mouse sequences was analyzed to determine the number of Trp, Tyr, Cys, Met in their structures. Sequences were rejected if there were too many residue deletions or missing fragments. This allowed a high certainty analysis for 2068 of the 3894 sequences available. The values are reported as the mean totals with the range in parentheses of the CH, VH, CL and VL (κ and λ) regions: Trp 15.5 (14 to 31), Tyr 30.4 (13 to 47), Cys 19.3 (15 to 29), Met 11.6 (7 to 32), His 13.3 (8 to 28). Grand total=90.1 (49 to 167).
Inductively Coupled Plasma Atomic Emission Spectroscopy:
Inductively coupled plasma atomic emission spectroscopy (ICP-AES) of mAb PCP21H3 was performed on a Varian, Axial Vista Simultaneous ICP-AES spectrometer. Mouse monoclonal antibody (PCP21H3) was exhaustively dialyzed into sodium phosphate buffered saline (PBS, 50 mM pH 7.4) with 20 mM EDTA. In a typical assay 300 μL of a 10.5% HNO3 solution was added to 100 μL of a 10 mg/mL antibody solution and was incubated at 70° C. for 14 hours. This solution was then diluted to 2 mL with MQH2O and then analyzed by comparison to standards. ICP-AES analysis results are reported in parts per million (μg/mL): Ag 0.0026 (0.0072 atoms per antibody molecule); Al 0.0098 (0.113 atoms per antibody molecule); As 0.0062 (0.025 atoms per antibody molecule); Ba below level of detection; Ca 0.0355 (0.266 atoms per antibody molecule).
The high Ca concentration observed was a result of contamination of the phosphate buffer system utilized in the assay system. To investigate the effect of Ca(II) on the rate of antibody-mediated H2O2, the irradiation of antibody samples was performed using the assay procedure outlined in the legend of
Oxygen Isotope Experiments:
In a typical experiment, a solution of antibody (6.7 μM, 100 μL) or non-immunoglobulin protein (50 μM, 100 μL) in PB (160 mM phosphate; pH 7.4) was lyophilized to dryness and then dissolved in H2O2 (100 μL, 98%). Sodium chloride was excluded to minimize signal suppression in the MS. The higher concentration of non-immunoglobulin protein was necessary to generate a detectable amount of H2O2 for the MS assay. This protein solution was irradiated on a UV-transilluminator under saturating 16O2 aerobic conditions in a sealed quartz cuvette for 8 hours at 20 EC. The H2O2 concentration was determined after 8 hours using the Amplex Red assay (Zhou et al., Anal. Biochem., 253, 162 (1997)). The sample was then filtered by centrifugation through a microcon (size-exclusion filter) to remove the protein and the H2O2 concentration re-measured. TCEP (freshly prepared 20 mM stock in H218O) was added (ca. 2 mol eq relative to H2O2) and the solution was left to stand at 37° C. for 15 minutes, after which time all the H2O2 had reacted. The TCEP solution in H218O was prepared fresh prior to every assay because 18O is slowly incorporated into the carboxylic acids of TCEP (over days). During the time course of the assay, no incorporation of 18O occurs due to this pathway. Furthermore, there is no incorporation of 18O from H218O into the 16O phosphine oxide. The peak at 249 m/z is the (M−H)− of TCEP. The peak at 249 is observed in all the MS because an excess of TCEP (twofold) relative to H2O2 is used in the assay.
The reproducibility of the 16O/18O ratio from protein samples lyophilized together was reasonable (±10%). However, problems with removing protein-bound water molecules during the lyophilization process meant that the observed ratios could vary between samples from different lyophilization batches by as much as 2:1 to 4:1 (when lyophilizing from H216O). It is, therefore, important that rigorous lyophilization and degassing procedures were followed. In this regard, the 18O2 and H216O experiments exhibited far less inter-assay variability due to the relative ease of removing protein-bound oxygen molecules.
Antibodies from different species give similar ratios within the experimental constraints detailed below: 16O:18O: WD1-6G6 mIgG (murine) 2.1:1; poly-IgG (horse) 2.2:1; poly-IgG (sheep) 2.2:1; EP2-19G2 mIgG (murine) 2.1:1; CH2-5H7 mIgG (murine) 2.0:1; poly-IgG (human) 2.1:1. Ratios were based on the mean value of duplicate determinations except for poly-IgG (horse), which was the mean value of ten measurements. All assays and conditions were as described above.
In a typical experiment, a solution of sheep or horse poly-IgG (6.7 μM, 100 μL) in PB (160 mM phosphate; pH 7.4) was degassed under an argon atmosphere for 30 min. This solution was then saturated with 18O2 (90%) and irradiated as described above. Assays and procedures are then as described herein.
Assay for H2O2 Production as a Function of the Efficiency of 1O2 Formation Via 3O2 Sensitization with Hematoporphyrin IX:
The assay is a modification of a procedure developed by H. Sakai and co-workers, Proc. SPIE-Int. Soc. Opt. Eng., 2371, 264 (1995). In brief, the horse poly-IgG (1 mg/mL) in PBS (50 mM, pH 7.4) and hematoporphyrin IX (40 μM) was irradiated with white light from a transilluminator. Aliquots were removed (50 μL) and the concentration of H2O2 and 3-aminophthalic acid measured simultaneously. H2O2 concentration was measured by the amplex red assay (Zhou et al., Anal. Biochem. 253, 162 (1997)). 3-Aminophthalic acid concentration was measured by reversed-phase HPLC on a Hitachi D4000 series machine with an Adsorbosphere-C18 column, a UV detector at 254 nm, and a mobile phase of acetonitrile/water (0.1% TFA) of 18:82 at 1 mL/min (retention time of luminol=7.4 min and of 3-aminophthalic acid=3.5 min). The concentrations of luminol and 3-aminophthalic acid were determined by comparison of peak height and area to control samples. The experimental data yielded the amount of 1O2 formed by hematoporphyrin IX (being directly proportional to the amount of 3-aminophthalic acid formed) and the amount of H2O2 formed by the antibody. There was no significant amount of 1O2 formed by antibodies without hematoporphyrin IX in white light.
Any concerns that the amplex red assay was detecting protein-hydroperoxide derivatives in addition to H2O2 were discounted because the apparent H2O2 concentration measured using this method was independent of whether irradiated protein was removed from the sample (by size-exclusion filtration).
Quantum Chemical Methods:
All QC calculations were carried out with Jaguar [Jaguar 4.0, Schrödinger, Inc. Portland, Ore., 1998. See B. H. Greeley, T. V. Russo, D. T. Mainz, R. A. Friesner, J.-M. Langlois, W. A. Goddard III, R. E. Donnelly, J. Chem. Phys., 101, 4028 (1994)] using the B3LYP flavor of density functional theory (DFT) [J. C. Slater in Quantum Theory of Molecules and Solids, Vol. 4: The Self-Consistent Field of Molecules and Solids, McGraw Hill, New York, (1974)], that included the generalized gradient approximation and exact exchange. The 6-31G** basis set was used on all atoms. All geometries were fully optimized. Vibrational frequencies were calculated to ensure that each minimum was a true local minimum (only positive frequencies) and that each transition state (TS) had only a single imaginary frequency (negative eigenvalue of the Hessian). Such QC calculations have been demonstrated to have an accuracy of about 3 kcal/mol for simple organic molecules. Non-closed shell molecules such as O2 and 3O2 were expected to have larger errors. However, such errors were expected to be systematic such that the mechanistic implications of the QC results would be correct. All energetics were reported in kcal/mol without correcting for zero point energy or temperature.
Antibodies are capable of generating hydrogen peroxide (H2O2) from singlet molecular oxygen (1O2). However, it was not known until reported herein, that the process was catalytic. It is now shown that antibodies are unique as a class of proteins in that they can produce up to 500 mole equivalents of H2O2 from 1O2, without a reduction in rate, in the absence of any discernible cofactor and electron donor. Based on isotope incorporation experiments and kinetic data, it is proposed that antibodies are capable of facilitating an unprecedented addition of H2O to 1O2 to form H2O3 as the first intermediate in a reaction cascade that eventually leads to H2O2. X-ray crystallographic studies with xenon point to conserved oxygen binding sites within the antibody fold where this chemistry could be initiated. These findings suggest a unique protective function of immunoglobulins against 1O2 and raise the question of whether the need to detoxify 1O2 has played a decisive role in the evolution of the immunoglobulin fold.
Antibodies, regardless of source or antigenic specificity, generate hydrogen peroxide (H2O2) from singlet molecular oxygen (1O2) thereby potentially aligning defensive recognition and killing within the same molecule (Wentworth et al., Proc. Natl. Acad. Sci. U.S.A., 97, 10930 (2000)). Given the potential chemical and biological significance of this discovery, the mechanistic basis and structural location within the antibody of this process has been investigated. These combined studies reveal that, in contrast to other proteins, antibodies may catalyze an unprecedented set of chemical reactions between water and singlet oxygen.
Kinetic Studies.
Long term UV irradiation studies reveal that antibody-mediated H2O2 production is a much more efficient process than is the case for the non-immunoglobulin proteins (
In contrast to other proteins, antibodies are able to resume photo-production of H2O2 at the same initial rate as at the start of the experiment if the H2O2 generated during the assay is removed by catalase, as shown for murine monoclonal IgG PCP21H3 (
Inhibition of the catalytic function of an enzyme either by substrates, transition state analogs or reaction products is often taken as strong evidence for an active site phenomenon. It has already been noted that the antibody-mediated photo-production of H2O2 is saturable with molecular oxygen (Kmapp (O2) 187 μM) (Wentworth et al., Proc. Natl. Acad. Sci. U.S.A., 97, 10930 (2000)). This formal product inhibition of H2O2 provides further evidence for such a binding site phenomenon.
An earlier report concerning the photo-production of H2O2 by antibodies did not probe the maximum amount of H2O2 that could be generated (Wentworth et al., Proc. Natl. Acad. Sci. U.S.A., 97, 10930 (2000)). This issue has been examined by repetitive cycles of UV irradiation of antibody samples followed by removal of the generated H2O2 by catalase (
The antibody structure is remarkably inert against the oxidizing effects of H2O2. When exposed to standard UV irradiation conditions for 6 hours in the presence of H2O2 (at a concentration high enough to fully inhibit H2O2 production), a polyclonal horse IgG antibody sample becomes fully active once the inhibitory H2O2 has been destroyed by catalase (
To ensure that there was no change in the protein structure in the presence of H2O2 (that may be contributing to the apparent inhibitory effect of H2O2) even at the level of side-chain position, x-ray crystal structures of Fab 4C6 were determined in the presence and absence of H2O2. Fab 4C6 was selected because its native crystals diffract to a higher resolution than any other published antibody (˜1.3 D). The root mean square difference (RMSD) of key structural parameters was compared for the 4C6 structure before and after a soak experiment with 3 mM H2O2. RMSD of all atoms=0.412 D, RMSD Cα atoms=0.327 D, RMSD main chain atoms=0.328 D, RMSD side-chain atoms=0.488 D. The overlayed native and H2O2-treated structures of murine Fab 4C6 (Li et al., J. Am. Chem. Soc., 117, 3308 (1995)) were superimposable, reinforcing the evidence of stability of the antibody fold to H2O2 (
An action spectrum of the antibody-mediated photo-production of H2O2 and the corresponding absorbance spectrum of the antibody protein for the same wavelength range (260-320 nm) are juxtaposed in
Probing the efficiency of H2O2 production by horse IgG as a function of the efficiency of 1O2 formation via 3O2 sensitization with hematoporphyrin IX (φA=0.22 in phosphate buffer pH 7.0) and visible light reveals that for every 275±25 mole equivalents of 1O2 generated by sensitization, 1 mole equivalent of H2O2 is generated by the antibody molecule (Wilkinson et al., J. Phys. Chem. Ref. Data 22, 113 (1993); Sakai et al., Proc. SPIE-Int. Soc. Opt. Eng., 2371, 264 (1995)).
The Question of the Electron Source.
The mechanism problem posed by the antibody-mediated H2O2 production from singlet oxygen can be divided into two sub-problems: one referring to the electron source for the process and the other concerning the chemical mechanism of the process. Given that the conversion of 1O2 to H2O2 requires two mole equivalents electrons, the fact that antibodies can generate>500 equivalents of H2O2 per equivalent of antibody molecule raises an acute electron inventory problem. The search for this electron source began with the most distinct possibilities. Electron transfer through proteins can occur with remarkable facility and over notably large distances (Winkler et al., Pure & Appl. Chem., 71, 1753 (1999); Winkler, Curr. Opin. Chem. Biol., 4, 192 (2000)). The first electron source considered was a collection of the residues typically implicated as electron donors and cited in normal protein photo-oxidation processes. The nearly constant rate of H2O2 production by antibodies and αβ-TCR during repetitive cycles of irradiation and catalase treatment (
Normal protein photo-oxidation is a complex cascade of processes that leads to the generation of 1O2 and other reactive oxygen species (ROS), such as superoxide anion (O2•−), peroxyl radical (HO2•) and H2O2 (Foote, Science 162, 963 (1968)). Present mechanistic thinking links the sensitivity of proteins to photo-oxidation with up to five amino acids: tryptophan (Trp), tyrosine (Tyr), cysteine (and cystine), methionine (Met), and histidine (His) (Straight and Spikes, in Singlet O2, A. A. Frimer, Ed. (CRC Press, Inc., Boca Raton, Fla., 1985), vol IV9, pp. 91-143; Michaeli and Feitelson, Photochem. Photobiol., 59, 284 (1994)). The photo-production of H2O2 by Trp and molecular oxygen is a well-characterized process that involves, at least in part, the formation and reduction of 1O2 to O2• that spontaneously dismutates into H2O2 and 3O2 (McMormick and Thompson, J. Am. Chem. Soc., 100, 312 (1978)). Tryptophan, both as an individual amino-acid and as a constituent of proteins, is particularly sensitive to near-UV irradiation (300-375 nm) under aerobic conditions, owing to its conversion to N,N-formylkynurenine (NFK) that is a particularly effective near-UV (λmax 320 nm) photosensitizer (Walrant and Santus, Photochem. Photobiol., 19, 411 (1974)). However, Trp photo-oxidation is accompanied by sub-stoichiometric production of H2O2 (ca. 0.5 mole equivalents) during near-UV irradiation (
Scanning of the Kabat database of human and mouse antibody heavy- and light-chain sequences (2068 of 3894 sequences were analyzed) revealed that antibodies rarely have more than 15 Trp residues in their entire structure (mean value=15.5 with a range of 14 to 31 Trp residues) (Kabat et al., Sequences of Proteins of Immunological Interest (US Department of Health and Human Services, Public Health Service, NIH, ed. 5th, 1991); Martin, PROTEINS: Struct., Funct. and Genet., 25, 130 (1996)). In fact, even if all of the amino acids that are implicated in protein photo-oxidation processes vide supra are collectively involved in antibody-mediated H2O2-production, there is still an insufficient number of these residues (mean value=90.1 with a range of 49 to 167 reactive residues) to account for the 500 mole equivalents of H2O2 generated.
The potential of chloride ion (present at 150 mM in PBS) as a reducing equivalent was then investigated given that chloride ion is known to be a suitable electron source for photo-production of H2O2 via a triplet excited state of an anthraquinone (Scharf and Weitz, Symp. Quantum Chem. Biochem., Jerusalem vol. 12 (Catal. Chem. Biochem.: Theory Exp.), pp. 355-365 (1979)). This possibility was quickly discounted when the rate of H2O2 production by immunoglobulins was found to be independent of chloride ion concentration (
The possible role of metal ions was investigated. While such ions could hardly be present in antibodies in such amounts that they could serve as an electron source, trace amounts of them might play a central role as catalytic redox centers. Experiments were performed that, for all practical purposes, allowed the involvement of trace metals in this process to be ruled out. For example, the rate of antibody-mediated photo-production of H2O2 was unchanged before and after exhaustive dialysis of antibody samples with EDTA-containing buffer (
All of the observations thus far forcibly pointed towards the need to identify an electron source that would not involve deactivation of the protein catalyst and that could account for the high turnover numbers and hence, for a quasi unlimited source of electrons.
A more broad consideration of the chemical potential of 1O2 was done. The participation of this energized form of molecular oxygen in the antibody-mediated mechanism was clearly inferred from a previous report (Wentworth et al., Proc. Natl. Acad. Sci. U.S.A., 97, 10930 (2000)). In brief, the antibody-mediated rate of H2O2 photo-production is increased in D2O and reduced in the presence of the 1O2 quencher, sodium azide. Furthermore, antibodies have been shown to generate H2O2 via sensitization of 3O2 with hematoporphyrin IX in visible light, and in the dark with the endoperoxide of disodium 3N,3N-(1,4-naphthylidene) dipropionate (a chemical 1O2 source). The involvement of 1O2 is also consistent with the close similarity of the action spectrum of antibody-mediated H2O2 production and the absorbance spectrum of antibody constituent tryptophans (
Given that the known chemistry of 1O2 can be conceptualized as the chemistry of the super-electrophile “dioxa-ethene” (Foote, Acc. Chem. Res., 1, 104 (1968), the heretofore unknown possibility was considered that a molecule of water may, in the presence of an antibody, add as a nucleophile to 1O2 and form H2O3 as an intermediate. Thus, water becoming oxidized to H2O2 would fulfill the role of the electron source.
Oxygen isotope experiments were undertaken to test the hypothesis of an antibody-catalyzed photo-oxidation of H2O by 1O2 through determination of the source of oxygen found in the H2O2. Contents of 16O/18O in H2O2 were measured by modification of a standard H2O2 detection method (Han et al., Anal. Biochem., 234, 107 (1996)). Briefly, this method involves reduction with tris carboxyethyl phosphine (TCEP), followed by mass-spectral (MS) analysis of the corresponding phosphine oxides (
These experiments revealed that UV-irradiation of antibodies, in the presence of oxygen, leads to oxygen incorporation from water into H2O2 (
The following control experiments were performed. First, under conditions of 16O2 and H216O, irradiation of poly-IgG (horse) generated H216O2 (
Isotope experiments were also performed with β-galactosidase, the most efficient non-immunoglobulin protein at generating H2O2, as well as 3-methylindole. In both cases, photo-oxidation led to negligible 18O incorporation into the H2O2 (
This view is further supported by observations that irradiation of 3-methylindole generates H2O2 but the H2O2 generated does not include oxygen incorporation from H218O. The same experiment performed with tryptophan does give rise to exchange with a ratio 16O/18O 1.2:1. This result is thought to be due to the ammonium functionality acting as an intramolecular general acid that protonates the internal oxygen of a diastereomeric mixture of 3′-hydroperoxides. It should be noted that while this is interesting from a chemical point of view, it cannot account for the catalytic production of H2O2 by antibodies both because it is a stoichiometric process and Trp residues in proteins do not possess a free ammonium group.
The Chemical Mechanism.
All antibodies studied can catalyze the oxidation of water by singlet oxygen. The thermodynamic balance between reactants and products for the oxidation of H2O by 1O2 (heat of reaction, ΔHr=+28.1 kcal/mol) (D. R. Lide, in Hanbook of Chemistry and Physics 73rd ed. (CRC, 1992)), demands a stoichiometry in which more than one molecule of 1O2 would have to participate per molecule of oxidized water during its conversion into two molecules of H2O2. This stoichiometry assumes that no further light energy before that involved in the production of singlet from triplet oxygen is participating in the process. Qualitative chemical reasoning on hypothetical mechanistic pathways, together with thermodynamic considerations, makes the likely overall stoichiometries as in either equations 1b or c (all energetics are calculated from gas phase experimental heats of formation and are reported in kcal/mol):
1O2+2H2O→2H2O2; ΔHr°=28.1 (1a)
2 1O2+2H2O→2H2O2+3O2; ΔHr°=5.6 (1b)
3 1O2+2H2O→2H2O2+2 3O2; ΔHr°=−16.9 (1c)
A recent report of a transition metal-catalyzed conversion of 1O2 and water into hydrogen peroxide, via a tellurium-mediated redox process (Detty and Gibson, J. Am. Chem. Soc., 112, 4086 (1990)), provides experimental evidence for a process in which 1O2 and H2O can be converted into H2O2 and, hence that the energetic demands of this process can be overcome. It is thought that the mechanism for the antibody-mediated photo-oxidation process involves the addition of a molecule water to a molecule of 1O2 to form dihydrogen trioxide as the first intermediate on the way to H2O2. The antibody's function as a catalyst would have to be the supply of a specific molecular environment that would stabilize the critical intermediate relative to its reversible formation and, or, would accelerate the consumption of the intermediate by channeling its conversion to H2O2. An essential feature of such an environment might consist of a special constellation of organized water molecules at an active site conditioned by an antibody-specific surrounding.
While H2O3 has not yet been detected in biological systems, its chemistry in vivo has been a source of considerable speculation and its in vitro properties have been the subject of numerous experimental and theoretical treatments (C. Deby, La Recherche 228, 378 (1991); Sawyer, in Oxygen Chemistry (Oxford University Press, Oxford, 1991); Cerkovnik and Plesnicar, J. Am. Chem. Soc., 115, 12169 (1993); Vincent and Hillier, J. Phys. Chem., 99, 3109 (1995); Plesnicar et al., Chem. Eur. J., 6, 809 (2000); Corey et al., J. Am. Chem. Soc., 108, 2472 (1986); Koller and Plesnicar, J. Am. Chem. Soc., 118, 2470 (1996); Cacace et al., Science, 285, 81 (1999)). Plesnicar and co-workers have shown that H2O3, reductively generated from ozone, decomposes into H2O and 1O2 (Koller and Plesnicar, J. Am. Chem. Soc. 118, 2470 (1996)). Applying the principle of microscopic reversibility, it was surmised that the reverse reaction should also be catalyzed by one or more molecules of water. To delineate plausible reaction routes and energetics of such a process, first principles quantum chemical (QC) methods were used (B3LYP Density Functional Theory) as described herein. The results are illustrated in equations 2a-c (all energetics are in kcal/mol):
The direct reaction of water and 1O2 to give H2O3 is quite unfavorable, with an activation barrier of 70 kcal/mol (Eqn. 2a). However, with the addition of a second or third water molecule a concerted process is found that decreases the activation barrier to 31.5 and 15.5 kcal/mol respectively. Indeed these additional waters do play the role of a catalyst (in equation. 2b the H of the 2nd water goes to the product HOOOH, simultaneous with the H of the 1st water replacing it). These barriers are small compared with the first HO bond energy of water (119 kcal/mol) and the bond energy of 1O2 (96 kcal/mol). Note that the reverse reaction in Eqn. 2b and Eqn. 2c has a barrier of only 15.5 or 0 kcal/mol respectively, suggesting that H2O3 is not stable in bulk water or water rich systems. Thus, the best site within the antibody structure for producing and utilizing H2O3 is expected to be one in which there are localized waters and water dimers next to hydrophobic regions without such waters.
The 16O/18O ratio in the phosphine oxide derived from the antibody-catalyzed photo-oxidation of water poses a significant constraint to the selection of reaction paths by which this primary intermediate H2O3 would to convert to the final product H2O2. The ratio is primarily determined by the number of 1O2 molecules that chemically participate in the production of two moles of H2O2 from two moles of H2O as well as by mechanistic details of this process. A ratio of 2.2:1 would coincide exactly with the value predicted for certain mechanisms in which two molecules of 1O2 and two molecules of H2O are transformed into two molecules of H2O2 and one molecule of molecular oxygen (which would have to be 3O2 for thermodynamic reasons). An example of such a mechanism is an SN2-type disproportionation of two molecules of H2O3 into H2O4 and H2O2, followed by the decomposition of the former into H2O2 and 3O2. The complex problem of defining theoretically feasible reaction pathways for the conversion of H2O3 into H2O2 with or without the participation of 1O2 has been tackled in a systematic way using quantum chemical methods (B3LYP Density Functional Theory). These studies show extensive docking calculations of H2O3 and the transition states for its formation and conversion into H2O2 to a number of proteins. Indeed there are unique sites of stabilizing these species in a region of antibodies (and the αβ-T cell receptor) in a region with isolated waters and next to hydrophobic regions. This extended study revealed the potential existence of a whole spectrum of theoretically feasible chemical pathways for the H2O3 to H2O2 conversion.
Structural Studies of Xenon Binding to Antibodies.
Given the conserved ability of antibodies, regardless of origin or antigen specificity, or of the αβ-TCR to mediate this reaction, X-ray structural studies were instigated to search for a possible conserved reaction site within these immunoglobulin fold proteins. A key constraint for any potential locus is that molecular oxygen (either 1O2 or triplet with a potential sensitizing residue in proximity, preferably tryptophan) and water must be able to co-localize, and the transition-states and intermediates along the pathway must be stabilized either within the site or in close proximity.
There is strong evidence to support the notion that Xe and O2 co-localize in the same cavities within proteins (Tilson et al., J. Mol. Biol., 199, 195 (1988); Schoenborn et al., Nature, 207, 28 (1965)). Accordingly, xenon gas was used as a heavy atom tracer to locate cavities within the murine monoclonal antibody 4C6 that may be accessible to molecular oxygen (Li et al., J. Am. Chem. Soc., 117, 3308 (1995)).
Three xenon sites were identified (
The xenon I binding site (Xe1 site) has been analyzed here in more detail because it is conserved in all antibodies and the αβ TCR (
The contacting side chains for Xe1 in Fab 4C6 are AlaL19, IleL21, LeuL73, and IleL75, which are highly conserved aliphatic side chains in all antibodies (Kabat et al., Sequences of Proteins of Immunological Interest (US Department of Health and Human Services, Public Health Service, NIH, ed. 5th, 1991)). Additionally, only slight structural variation was observed in this region in all antibodies surveyed. Notably, several other highly conserved and invariant residues are in the immediate vicinity of this xenon site, including TrpL35, PheL62, TyrL86, LeuL104, and the disulfide-bridge between CysL23 and CysL88. TrpL35 stacks against the disulfide-bridge and is only 7 from the xenon atom. In this structural context, TrpL35 may be a putative molecular oxygen sensitizer, since it is the closest Trp to Xe1. Comparison with the 2C αβ TCR structure and all available TCR sequences shows that this Xe1 hydrophobic pocket is also highly conserved in TCRs (
Human β2-microglobulin, which does not generate H2O2, does not have the same detailed structural characteristics that define the antibody Xe1 binding pocket, despite its overall immunoglobulin fold. Also, β2-microglobulin does not contain the conserved Trp residue that occurs there in both antibodies and TCRs. If TrpL35 (antibodies) or Trpα34 (TCR) is the oxygen sensitizer, the lack of a corresponding Trp in β2-microglobulin may relate to the finding that it does not catalyze the oxidation of water.
Thus, the xenon experiments have identified at least one site that is both accessible to molecular oxygen and is in a conserved region (VL) in close proximity to an invariant Trp; an equivalent conserved site is also possible in the fold of VH. The structure and sequence around the Xe1 site is almost exactly reproduced in the VH domain by the pseudo two-fold rotation axis that relates VL to VH. Although a xenon binding-site was not located in this domain, it is thought that molecular oxygen can still access the corresponding cavity in VH. The proposed heavy chain xenon site may not have been found because the crystals were pressurized for only two minutes, which may have been insufficient time to establish full equilibrium, or simply because xenon is too large compared to oxygen for the corresponding cavity on the VH side, or due to crystal packing. In other antibody experiments, Xe binding sites were found in only one of the two molecules of the asymmetric unit that suggests that crystal packing can modulate access of Xe in crystals. Analysis of the sequence and structure around these sites shows that they are highly conserved in both antibodies and TCRs thus providing a possible understanding of why the Ig-fold in antibodies and the TCR can be involved in this unusual chemistry.
Antibodies are unique among proteins in their ability to catalytically convert 1O2 into H2O2. It is thought that this process participates in killing by event-related production of H2O2. Alternatively, antibodies can fulfill the function of defending an organism against 1O2. This would require the further processing of hydrogen peroxide into water and triplet oxygen by catalase.
This Example illustrates that antibodies directed against bacteria can kill those bacteria by generating reactive oxygen species.
Antibody and Cell Preparations
Sheep (31243) and horse (31127) polyclonal IgG were obtained from Pierce and used without further purification. The E. coli O112a,c-specific murine monoclonal antibody (15404) was obtained from QED biosciences and was used without further purification. The E. coli non-specific murine monoclonal antibodies 33F12 and 84G3 were obtained from the Scripps Hybridoma lab and used at>98% purity (based on SDS-PAGE analysis). Monoclonal 33F12 is a murine monoclonal IgG that catalyzes the aldol reaction. Wagner et al., Science 270, 1797 (1995). E. coli XL1-B was obtained from Stratagene. E. coli O112a,c (ATCC 12804) is an enteroinvasive strain which can infect malnourished and immuno-compromised individuals. L. Siegfried, M. Kmetove, H. Puzova, M. Molokacova, J. Filka, J. Med. Microbiol. 41, 127 (1994).
The following antibody preparations were prepared in-house by the following methods.
Rabbit Polyclonal IgG Specific for E. coli XL-1 Blue.
On the day of immunization (Day 0), New Zealand White rabbits, (2.5 kg) were pre-bled 10 ml from each ear and then injected subcutaneously with heat killed (65° C., 15 min), chemically competent E. coli XL-1 (OD600=1) (650 μl and 350 μl of phosphate buffered saline, PBS ph 7.4). Fourteen days after immunization (Day 14), the rabbits received a second injection in the same manner as the first. Twenty eight days after immunization (Day 28), the rabbits received a third injection in the the same manner as the first and second injections. At thirty five days after immunization (Day 35), the rabbits were bled 50 ml from an ear. At forty two days after immunization, (Day 42), the rabbits were bleed 50 ml from an ear.
Sera were allowed to stand at room temperature for 1-2 h, then placed at 4° C. overnight and spun at 2500-3500 rpm for 15 min. The supernatants were transferred to a new round bottom tube (50 ml) and spun at 9-10 K rpm for 15 min. These supernatants were transferred to a clean conical (50 ml) tube and stored at −10° C. Sera were then tested by ELISA (see below), diluted 1:1 in PBS and then filtered through a 0.2 μM filter. The protein concentration (Abs280) of sera samples was measured. Sera samples were then loaded onto a protein G column (Amersham Gamma-Bind G, 10 mg protein/ml bead). The bound antibody was washed with 3 column volumes of PBS pH 7.4 and then eluted with 2 column volumes of acetic acid (0.1 M, pH 3.0). The elution peak was neutralized with Tris buffer (1 M, pH 9.0) (0.5 ml in 4 ml fraction) and then dialyzed back into PBS.
Murine Monoclonal IgGs Specific for E. coli XL-1 Blue
At Day 0, 129 Gix+ mice (6-8 weeks, 4 per group) received intraperitoneal injections of heat killed (65° C., 15 min), chemically competent E. coli XL-1 at OD600=1 in a volume of 150 μl with 50 μl of phosphate buffered saline, PBS pH 7.4. At Day 14, the mice received a second injection in the same manner as the first. At Day 28, the mice received a third injection in the same manner as the first and second injections. At Day 35 mice were bled via intraocular puncture.
Twelve monoclonal antibodies specific for XL-1 blue were prepared using standard protocols. Antibody preparations were purified by ammonium sulfate precipitation followed by loading onto a protein G column (Amersham Gamma-Bind G, 10 mg protein/ml bead). The bound antibody was washed with 3 column volumes of PBS pH 7.4 and then eluted with two column volumes of acetic acid (0.1 M, pH 3.0). The elution peak was neutralized with Tris buffer (1 M, pH 9.0) (0.5 ml in 4 ml fraction) and then dialyzed back into PBS.
Generic ELISA for Determining Antibody-Binding to Live or Killed E. coli
The OD600 of a frozen glycerol stock of E. coli XL1-blue was read and the live bacterial stock was diluted in PBS to OD600=1.0. Twenty-five microliter aliquots of bacteria were placed in wells of a 96-well hi-bind ELISA plate and allowed to dry overnight at 37° C. Plates were gently washed twice with dH2O. Plate wells were blocked with BLOTTO (50 μl/well) for 30 min at room temperature and this blocking solution was removed by shaking. The antibody-containing sample to be assayed was then diluted into BLOTTO and 25 μl of this solution was placed in each well. Plates were incubated at 37° C. for 1 h in a moist chamber, washed with dH2O (10×) and 25 μl of a secondary antibody (HRP-goat anti-rabbit conjugate, 1:2000) in BLOTTO was added to each well. Plates were incubated at 37° C. for 1 h in a moist chamber and washed gently with dH2O (10×). Developer substrate (50 μl/well) was added and the plates were read at 450 nm after 30 min.
Dead bacterial samples were also used for ELISA. These samples were handled in the same manner as above, but before addition and adherence to ELISA microtiter plates, the E. coli are heat killed (65° C., 15 min).
Bactericidal Assays
In a typical experiment, a culture of E. coli (in log phase growth, OD600=0.2-0.3) was repeatedly pelleted (3×3,500 rpm) and resuspended in PBS (pH 7.4). The PBS suspended cells were then added to glass vials and cooled to 4° C. Hematoporphyrin IX (40 μM) and antibody (20 μM) were added and the vials were either placed on a light box (visible light, 2.8 mW cm−2) or in the dark at 4° C. and incubated for 1 h. Viability was determined by recovery of colony forming units (CFUs) on agar plates. Each experiment was performed at least in duplicate.
Microscopy Studies
Samples were prepared for electron microscopy as follows. Cells were fixed with paraformaldehyde (2% w/v), glutaraldehyde (2.5% w/v) in cacodylate (0.1 M) at 0° C. for 1.75 h and then pelleted. The cell pellet was resuspended in OsO4 (1% w/v) in cacodylate (0.1 M), allowed to stand for 30 min and then pelleted. The pellet was then sequentially dehydrated with ethanol and propylene oxide, embedded in resin and then sectioned. The sections were stained with uranyl acetate and lead citrate. For gold labeling studies, the procedure used was as detailed above with the addition of the following steps. First, samples were pelleted and washed with fresh isotonic buffer to remove unbound primary antibody. Second, the pellet was resuspended in a solution of goat anti-mouse antibody that had been covalently modified with 12 nm gold particles, and incubated for 90 min.
Decomposition of O3 Under Aqueous Conditions
The rate of decomposition of O3 under the aqueous conditions employed was measured by the following method. Ozone, produced by a passage of O2 through a Polymetrics ozonizer, was bubbled for 2 min through a phosphate buffered saline (PBS, pH 7.4) solution in a quartz cuvette (1 cm2) at room temperature. The time-dependent change in optical density was then measured at 260 nm (ε=2,700 M−1 cm−1) for at least 5 half lives in a Hitachi u.v./vis spectrophotometer equipped with a thermostatted rack at 22° C. See Takeuchi et al., Anal. Chim. Acta. 230, 183 (1990). The half-life of O3 was then determined graphically (t½=66 sec) from a plot of OD vs. time using Graphpad Prism V 3.0 software (data not shown). The sensitivity of the assay was limited by spectrophotometer accuracy to±0.1% (˜1 μM) of the OD at t=0.
Assay for Ozone
In a typical experiment, a solution of indigo carmine 1 (1 mM) in PBS (pH 7.4) was irradiated on a transilluminator (312 nm, 0.8 mWcm−2) at room temperature in the presence or absence of antibody (20 μM) with or without catalase (13 mU/mL) in a quartz microtiter plate (final volume 200 μL), in duplicate. At various time-points a sample is removed (20 μL) and quenched into phosphate buffer (100 mM, pH 3.0, 180 μL). The OD was measured at 610 nm in a microtiter plate reader (Spectramax). Production of isatin sulfonic acid 2 was determined by LC-MS (Hitachi D-7000 HPLC linked to a Hitachi M-8000 ion-trap electrospray mass-spectrometer (in the negative-ion detection mode). LC conditions were a Spherisorb RP-C18 column and acetonitrile water (30:70) mobile phase at 1 mL/min. An in-line splitter was used to divert 0.2 mL/min of column effluent into the MS. Isatin sulfonic acid 2 RT=3.4 min, [MH]—226.
A variety of reactive species were tested to ascertain whether indigo carmine 1 could be converted to isatin sulfonic acid 2 by species other than ozone.
aOxidation was determined by following the absorbance change at 610 nm in a microtitre plate reader before and after addition of the respective oxidant to indigo carmine 1 (1 mM) in phosphate buffer (PB, pH 7.4) at room temperature under the conditions specified.
b18O incorporation was determined by performing the oxidation of indigo carmine 1 in PB (100 mM, pH 7.4) with H218O (>95% labeled) under the conditions specified for each oxidant and monitoring the isotopic profile of cyclic α-ketoamide 2 by negative ion electrospray mass spectrometry. Under the conditions of the assay the label installed into the amide carbonyl of α-ketoamide 2 does not exchange with water.
cIndigo carmine (1, 1 mM) was added to a solution of ozone (˜600 μM) in PB (100 mM, pH 7.0).
dThe effect of 1O2* was investigated by irradiation of an hematoporphyrin IX (40 μM) solution and 1 (1 mM) in PB with visible light (2.7 mW/cm−2) for 1 h.
eSee ref. 42.
fPotassium superoxide (10 mM) in DMSO was added to a solution of 1 in PB (100 mM, pH 7.0) such that the final organic cosolvent was 5%.
gFinal concentration 2 mM in PB.
hNot determined.
iIndigo carmine (1, 1 mM) was added to a solution of NaOCl (20 mM) in PBS (pH 7.4) and formation of cyclic α-ketoamide 2 was determined by HPLC after complete bleaching of the solution occurred.
Preliminary studies revealed that, rapid and reversible exchange of the oxygen of the lactam carbonyl of cyclic α-ketoamide 2 with water occurred in the presence of u.v. light (312 nm, 0.8 mW cm−2). However, in white light no discernable exchange occurred during the experiment. Thus, all 18O isotope incorporations experiments were carried out using hematoporphyrin IX (40 μM and white light (2.7 mW cm−2) as the 1O2* source.
Further studies were performed using the following additional chemical probes that contained a normal carbon-carbon double bond.
The choice of the probes, 3- and 4-vinyl-benzoic acid (3 and 4 respectively), was guided by their aqueous solubility coupled with ease of detection by HPLC. In a typical experiment, a solution of 3-vinyl benzoic acid 3 (1 mM) or 4-vinyl benzoic acid 4 (1 mM) in PBS (pH 7.4) was irradiated (312 nm, 0.8 mW/cm−2) at room temperature in the presence or absence of antibody 4C6, or sheep polyclonal antibody (20 μM). Timed aliquots were removed (20 μL) and diluted 1:3 into acetonitrile:water (1:1). Product composition was determined by reversed-phase HPLC.
Conventional ozonolysis of 3-vinyl benzoic acid 3 (1 mM) in PBS (pH 7.4) at room temperature leads to the production of the benzaldehyde derivative 5a with minor production of the corresponding epoxide 6a in a ratio of˜10:1. Similarly, ozonolysis of 4, under the same conditions as described above, leads to 4-carboxybenzaldehyde 5b and the corresponding oxirane 5b in a ratio of˜9:1. In a typical experiment, a solution of 3 or 4 (1 mM) in PBS (pH 7.4) was added to a solution of O3 in PBS (600 μM) at room temperature and allowed to stand for 5-10 min. The ozonolysis of 3 and 4 was performed in this manner rather than by bubbling an O3/O2 mixture through the aqueous reaction solution to prevent further oxidation of 3 and 4 that leads to hydroxylation and fragmentation of the aromatic ring. The product mixture and substrate conversion was elucidated by reversed-phase HPLC. HPLC analysis was performed on a Hitachi D-7000 machine with a Spherisorb RP-18 column and a mobile phase of acetonitrile and water (0.1% TFA) (30:70) at a flow rate of 1 mL/min. Localization was performed by u.v. detection (254 nm) (RT 3=7.84 min; RT 5a=4.02 min; RT 6a=3.82 min; RT 4 8.50 min;; RT 5b=3.72 min; RT 6b=4.25 min). Peak areas were converted to concentration by comparison to standard curves.
Antibody Detection on Neutrophils
Neutrophils are known to have antibodies on their cell surface. Fluorescence activated cell sorting (FACS) was used to measure the number of immunoglobulin molecules per cell present under resting and activated conditions. Under resting conditions there are approximately 50,000 antibody molecules per cell, which increased to approximately 65,000 antibody molecules per cell upon activation.
Antimicrobial Activity of Antibodies
As illustrated above, antibodies catalyze the generation of hydrogen peroxide (H2O2) from singlet molecular oxygen (1O2*) and water by a process that proceeds via dihydrogen trioxide (H2O3) intermediate. Results provided in this Example illustrate that antibodies can utilize this process to efficiently kill bacteria.
Initial bactericidal studies utilized two strains of the gram-negative bacteria E. coli (XL1-blue and O-112a,c). E. coli XL1-B was obtained from Stratagene. E. coli O112a,c (ATCC 12804) is an enteroinvasive strain which can infect malnourished and immuno-compromised individuals. Siegfried et al., J. Med. Microbiol. 41, 127 (1994).
The 1O2* ion has bactericidal action. Berthiaume et al., Biotechnology 12, 703 (1994). However, initiation of H2O2 production by antibodies requires exposure to the substrate 1O2*. Wentworth et al., Proc. Natl. Acad. Sci. U.S.A. 97, 10930 (2000). Therefore, a 1O2* generating system was used that would not, on its own, kill E. coli. Antibodies can utilize 1O2* generated by either endogenous or exogenous sensitizers or chemical sources, using u.v. or white light, or thermal decomposition of e.g. anthracene-9,10-dipropionic acid endoperoxide respectively. Therefore, the choice of a 1O2* generating system is guided solely by experimental considerations such as reaction efficiency and cellular or substrate sensitivity to irradiation. In these experiments, hematoporphyrin IX (HPIX, 40 μM) was selected as an efficient sensitizer of 3O2. Wilkinson et al., J. Phys. Chem. Ref. Data 22, 113 (1993). When irradiated with white light (light flux 2.7 mW cm−2) for 1 h in phosphate buffered saline (PBS, pH 7.4) at 4±1° C., hematoporphyrin IX has negligible bactericidal activity against the two E. coli serotypes (˜107 cells/mL).
In a typical experiment, a culture of E. coli (in log phase growth, OD600=0.2-0.3) was repeatedly washed in PBS by pelleting (3×3,500 rpm) the cells and resuspending them in PBS (pH 7.4). The PBS suspended cells were then added to glass vials and cooled to 4° C. Hematoporphyrin IX (40 μM) and antibody (20 μM) were added and the vials were either placed on a light box (visible light, 2.8 mW cm−2) or in the dark at 4° C. and incubated for 1 h. Viability was determined by recovery of colony forming units (CFUs) on agar plates. Each experiment was performed at least in duplicate.
Addition of monoclonal antibodies (20 μM) to a mixture of hematoporphyrin IX and bacteria resulted in killing of>95% of the bacteria (
Antibody-mediated bactericidal activity increased both as a function of irradiation time (
Controls indicated that cold shock and hematoporphyrin IX toxicity were not responsible for an appreciable loss of colony forming units (CFUs). Furthermore, confocal microscopy revealed that antibody mediated bacterial cell aggregation was also not contributing to a lack of CFUs in the antibody-treated groups. Fluorescence analysis of the bacterial cells indicated that the amount of membrane-associated sensitizer in the hematoporphyrin IX-treated E. coli cells was not increased by antibody binding. Finally, while it is difficult to rule out the potential role of trace metals in the bactericidal action of antibodies, the presence of EDTA (2 mM) had no effect on the survival of bacteria in the assay system employed.
The bactericidal potential of antibodies appeared to be in general phenomenon. All twelve murine monoclonal antibodies (1×κγ, 7×κγ2a, 3×κγ2b, 1×κγ3 isotypes) and one rabbit polyclonal IgG (titer 120,000) sample that were tested were bactericidal. Nonspecific antibodies also were able to generate bactericidal agents. Only 1O2* was required for the activation of the water oxidation pathway—such activation was independent of the antibody-antigen union. In this regard, 10 non-specific murine monoclonal antibodies, one non-specific sheep antibody preparation and one horse polyclonal IgG sample with no specificity for E. coli cell-surface antigens were studied and all possessed bactericidal activity. The potency of the bactericidal activity of antigen non-specific antibodies was observed to be very similar to antigen-specific antibodies. Typically 20 μM of antibody (non-specific) was>95% bactericidal in the assay system. The bactericidal action of antibodies was not simply a non-specific protein effect as bovine serum albumin (BSA, 20 μM) exhibited no bacterial killing in the assay system.
To gain insight into the nature of the observed bacterial killing the morphology of killed bacteria was studied by electron microscopy. Gold-labeled secondary antibodies were used to correlate the morphological damage to sites on the bacterial cell wall where antibodies were bound.
The killing is associated with the production of holes in the bacterial cell wall at the sites of antigen-antibody union (
The bacterium is under an internal pressure of about 30 atmospheres, hence any weakening of the membrane can lead to catastrophic rupture. The process appeared to begin with slight disruptions observed at the interface between the cell wall and cytoplasm (
The Chemical Nature of the Bactericidal Agents(s)
If H2O2 was the ultimate product of the antibody-catalyzed oxidation of water pathway (Wentworth et al., Proc. Natl. Acad. Sci. U.S.A. 97, 10930 (2000); P. Wentworth, Jr. et al Science 293, 1806 (2001)), then H2O2 alone would be the killing agent. This conclusion was strengthened by observations that catalase, which converts H2O2 to water (H2O) and molecular oxygen (O2), offered complete protection against the bactericidal activity of non-specific antibodies (
The amount of H2O2 generated by non-specific antibodies was 35±5 μM. The amount of H2O2 generated by specific antibodies was variable. The issue of proximity made a direct comparison between the effects of H2O2 in solution and H2O2 generated on the surface of the bacterial membrane complicated. For example, the protective effect of catalase (13 mU/mL) against the bactericidal activity of 11 E. coli antigen-specific murine monoclonal antibodies and 11 E. coli non-specific murine monoclonal antibodies was studied. In all cases with non-specific antibodies, catalase completely attenuated the bactericidal activity. For the antigen-specific antibodies however, extent of protection by catalase was dependent on the monoclonal antibody used and varied over a wide range. Therefore, proximity of H2O2 generation (directly on the surface of the bacterial membrane or in solution) affected the degree of protection offered by catalase. Hence, the effects of H2O2 in solution were compared only with H2O2 generated by antigen non-specific antibodies.
The mean rate of H2O2 formation (35±5 μM/h) generated by non-specific antibodies (20 μM) during the irradiation of a mixture containing hematoporphyrin IX (40 μM) with visible light (2.7 mW cm31 2) for 1 h at 4° C. in PBS (pH 7.4) was highly conserved. This mean value was determined from ten murine monoclonal IgGs and a sheep and horse polyclonal IgG (n=12).
However, when the toxicity of H2O2 on the two E. coli cell lines was quantified it became apparent that the amount of H2O2 generated by non-specific antibodies, 35±5 μM, could not alone account for the potency of the bactericidal activity (
The combination of H2O2 with antibodies and/or H2O2 with hematoporphyrin IX was not more toxic to bacteria than H2O2 alone. These variables were tested to ascertain whether some interaction might occur between H2O2 and other components in the assay that would account for the potency of the bactericidal activity. In particular, the following combination of conditions were tested for bactericidal activity against E. coli O112a,c:
The finding that the toxicity of H2O2 to E. coli was below that generated by antibodies, necessitated re-examination of the experiments with catalase. One possibility was that H2O2 reacted with some other chemical species that was also generated by the antibody, to produce other bactericidal molecule(s) and thus, by destroying H2O2, catalase prevented formation of that other chemical species. Another alternative was that the bactericidal species that were formed on the way to H2O2 was also a substrate for catalase.
Further experimentation indicated that ozone (O3) was generated by antibodies. Under the aqueous conditions employed, ozone is quite long lived (t½=6 sec). Thus, ozone is sufficiently long lived to be detected by chemical probes such as indigo carmine 1, a sensitive reagent for the detection of O3 in aqueous systems. Takeuchi et al., Anal. Chem., 61, 619 (1989); Takeuchi et al., Anal. Chim. Acta. 230, 183 (1990). Conventional ozonolysis of indigo carmine 1 in aqueous solution led to bleaching of the characteristic absorbance of indigo carmine 1 (γmax610 nm, ε=20,000 LM−1 cm−1) and the formation of the cyclic α-ketoamide 2 (
To prove that ozone is produced by antibodies, the following experiments were performed. A solution of indigo carmine 1 (1 mM) in PBS (pH 7.4) was irradiated with u.v. light (312 nm, 0.8 mW cm−2) with no antibodies present. No bleaching was observed. However, when the same experiment was carried out in the presence of either a sheep polyclonal antibody (20 μM) or the murine monoclonal antibody 33F12 (20 μM) bleaching of indigo carmine 1 was observed (
The oxidative cleavage of the C═C double bond of indigo carmine 1 is a sensitive probe for ozone detection. Takeuchi et al., Anal. Chem., 61, 619 (1989); Takeuchi et al., Anal. Chim. Acta. 230, 183 (1990). However, such cleavage was not specific for ozone. Further experiments with the oxidants listed in Table 2 were performed under the specified conditions to test whether those oxidants could also oxidize indigo carmine 1. Such experimentation confirmed that singlet oxygen (1O2) could bleach solutions of indigo carmine 1 to form cyclic α-ketoamide 2 by oxidative double bond cleavage. 1O2* is generated by antibodies upon u.v.-irradiation. Wentworth et al., Proc. Natl. Acad. Sci. U.S.A. 97, 10930 (2000); Wentworth et al., Science 293, 1806 (2001). An analytical differentiation between oxidative cleavage of indigo carmine 1 to cyclic α-ketoamide 2 by 1O2* versus one by O3 was therefore sought.
Further experimentation indicated that cleavage by O3 could be distinguished from cleavage by 1O2* by observing 18O incorporation into the lactam carbonyl groups of cyclic α-ketoamide 2 when ozone is the oxidant. No such 18O incorporation into the lactam carbonyl group of cyclic α-ketoamide 2 occurred when 1O2* was the oxidant. Isotope incorporation experiments were therefore carried out in H218O (>95% 18O) containing phosphate buffer (PB, 100 mM, pH 7.4) (Table 2 and
When indigo carmine 1 (100 μM) was irradiated with visible light (2.8 mW cm−2) in the presence of sheep IgG (20 μM) and hematoporphyrin IX (40 μM), oxidized product 2 was formed that possesses a mass spectrum demonstrating exchange of 18O of water into the lactam carbonyl (
To further substantiate that ozone was generated by antibodies, the following additional chemical probes that contained a normal carbon-carbon double bond were tested.
In a typical experiment, a solution of 3-vinyl benzoic acid 3 (1 mM) or 4-vinyl benzoic acid 4 (1 mM) in PBS (pH 7.4) was irradiated (312 nm, 0.8 mW/cm−2) at room temperature in the presence or absence of antibody 4C6, or sheep polyclonal antibody (20 μM). Timed aliquots were removed (20 μL) and diluted 1:3 into acetonitrile:water (1:1). Product composition was determined by reversed-phase HPLC.
Irradiation of solutions of compounds 3 and 4 (1 mM) with u.v. light (312 nm, 0.8 mW cm−2), in the presence of a sheep polyclonal IgG (20 μM), led to the formation of 3-carboxybenzaldehyde 5a and 3-oxiranyl benzoic acid 6a (ratio 15:1, 1.5% conversion of 3 after 3 h) and 4-carboxybenzaldehyde 5b and 4-oxiranyl-benzoic acid 6b (ratio of 10:1, 2% conversion to 4 after 3 h) respectively. These products are also observed when compounds 3 and 4 are ozonolized in a conventional way. Moreover, these results were similar to those observed for indigo carmine 1 irradiated with u.v. light in the presence of either a sheep polyclonal antibody or the murine monoclonal antibody 33F12 where bleaching of indigo carmine 1 was observed (
In sharp contrast, 1O2* generated by hematoporphyrin IX (40 μM) and visible light (2.7 mW cm−2), did not cause any detectable oxidation of either 3 or 4 under similar conditions. Therefore, 3-vinyl benzoic acid 3 and 4-vinyl benzoic acid 4 are selective for ozone and the ozone must be produced by the antibodies present in the reaction.
Evidence for Ozone Production by Activated Neutrophils
Neutrophils are central to a host's defense against bacteria and are known to have antibodies on their cell surface and the ability, upon activation, to generate a cocktail of powerful oxidants including 1O2*. Steinbeck et al., J. Biol. Chem., 267, 13425 (1992); Steinbeck et al., J. Biol. Chem., 268, 15649 (1993). Thus, these cells therefore offer both a non-photochemical, biological source of 1O2* and the antibodies capable of processing this substrate by the water-oxidation pathway. Most areas of the body do not have access to photochemical energy. Hence, if neutrophils provide a cellular source of 1O2, an analysis of the oxidants expelled by antibody-coated neutrophils after activation could provide an indication as to whether ozone or or H2O2 production by such antibodies may have a physiological relevance.
Human neutrophils were prepared as described by M. Markert, P. C. Andrews, and B. M. Babior Methods Enzymol. 105, 358 (1984). Following activation with phorbol myristate (1 μg/mL), the neutrophils (1.5×107 cells/mL) produced an oxidant species that oxidatively cleaves indigo carmine 1 to isatin sulfonic acid 2 (
This Example illustrates that antibodies directed against Salmonella typhimurium can kill those bacteria by generating reactive oxygen species.
Salmonella typhimurium (ATCC 12804) was obtained from ATCC. Salmonella non-specific murine monoclonal antibodies 33F12 and 84G3 were obtained from the Scripps Hybridoma lab and used at>98% purity (based on SDS-PAGE analysis).
Murine Monoclonal Antibodies Generated for Bacterial Killing Studies
Gix+ mice that were 6-8 weeks old were used for generating antibodies against heat killed (65° C., 15 min) Salmonella typhimurium. The following immunization schedule was employed.
Day 0, 129 Gix+ mice (4 per group) each received an i.p. injection of heat killed, chemically competent Salmonella typhimurium (OD600=1) (150 μl bacteria and 50 μl of phosphate buffered saline, PBS pH 7.4).
Day 14, the mice received a second injection of the same bacterial solution.
Day 28, the mice received a third injection, the same as 1st and 2nd injection.
Day 35, the mice are bled via intraocular puncture.
Monoclonal antibodies were prepared following these immunization protocols using standard protocols. Purification of these antibodies involved ammonium sulfate precipitation followed by loading onto a protein G column (Amersham Gamma-Bind G, 10 mg protein/ml bead). The bound antibody was washed with 3 column volumes of PBS pH 7.4 and then eluted with 2 column volumes of acetic acid (0.1 M, pH 3.0). The elution peak was neutralized with Tris buffer (1 M, pH 9.0) (0.5 ml in 4 ml fraction) and then dialyzed back into PBS.
ELISA Assay for Antibody-Binding to Live or Killed Salmonella typhimurium
Live Bacteria:
The OD600 of a frozen glycerol stock of S. typhimurium was used to assess bacterial cell concentration and the bacterial suspension was diluted in PBS to OD600=1.0. The diluted bacterial suspension was aliquoted (25 μl/well) into a 96-well hi-bind ELISA plate and allow to dry overnight at 37° C. The plate was gently washed with distilled water two times and the well were blocked with BLOTTO (50 μl/well) for 30 min at room temperature. The BLOTTO was removed by shaking. Antibody-containing samples in BLOTTO (25 μl/well) were then added and the plates were incubated at 37° C. for 1 h in a moist chamber. The wells were washed ten times with distilled water and a secondary antibody (HRP-goat anti-rabbit conjugate, 1:2000, 25 μl well) in BLOTTO was added. The plates were then incubated at 37° C. for 1 h in a moist chamber and washed gently with distilled water ten times. The developer substrate was then added (50 μl/well). Plates were read at 450 nm after 30 min.
Dead Bacteria:
The same procedure as described above was used for dead bacteria, but the bacteria are heat killed (65° C., 15 min) prior to addition to the ELISA plate.
Bactericidal Assays
In a typical experiment, a culture of S. typhimurium in log phase growth at OD600=0.2-0.3 was repeatedly pelleted (3×3,500 rpm) and resuspended in PBS (pH 7.4). The PBS suspended cells were then added to glass vials and cooled to 4° C. hematoporphyrin IX solution (40 μM) and antibody (20 μM) were added. The vials were placed either on a light box (visible light, 2.8 mW cm−2) or in the dark at 4° C. Incubation was for 1 hour. Viability was determined by recovery of colony forming units (CFUs) on agar plates. Each experiment was performed with at least duplicate samples.
A panel of S. typhimurium-specific murine monoclonal antibodies were raised and tested for bactericidal activity. Each antibody examined was bactericidal, exhibiting greater than 50% killing of S. typhimurium after one hour irradiation in the presence of a hematoporphyrin IX solution (120 μM) so long as the antibody was present at a concentration of greater than 5 μM (
Controls indicated that cold shock and hematoporphyrin IX toxicity are not responsible for an appreciable loss of CFUs. Furthermore, confocal microscopy revealed that antibody-mediated bacterial cell aggregation was not contributing to a lack of CFUs in the antibody-treated groups. Fluorescence analysis of the bacterial cells indicated that the amount of membrane-associated sensitizer in the hematoporphyrin IX-treated E. coli cells was not increased by antibody binding. The bactericidal action of antibodies was not a non-specific protein effect as bovine serum albumin (BSA, 20 μM) exhibited no bacterial killing in the assay. Finally, the presence of EDTA (2 mM) had no effect on the survival of bacteria in the assay system detailed above.
All patents and publications referenced or mentioned herein are indicative of the levels of skill of those skilled in the art to which the invention pertains, and each such referenced patent or publication is hereby incorporated by reference to the same extent as if it had been incorporated by reference in its entirety individually or set forth herein in its entirety. Applicants reserve the right to physically incorporate into this specification any and all materials and information from any such cited patents or publications.
The specific methods and compositions described herein are representative of preferred embodiments and are exemplary and not intended as limitations on the scope of the invention. Other objects, aspects, and embodiments will occur to those skilled in the art upon consideration of this specification, and are encompassed within the spirit of the invention as defined by the scope of the claims. It will be readily apparent to one skilled in the art that varying substitutions and modifications may be made to the invention disclosed herein without departing from the scope and spirit of the invention. The invention illustratively described herein suitably may be practiced in the absence of any element or elements, or limitation or limitations, which is not specifically disclosed herein as essential. The methods and processes illustratively described herein suitably may be practiced in differing orders of steps, and that they are not necessarily restricted to the orders of steps indicated herein or in the claims. As used herein and in the appended claims, the singular forms “a,” “an,” and “the” include plural reference unless the context clearly dictates otherwise. Thus, for example, a reference to “a host cell” includes a plurality (for example, a culture or population) of such host cells, and so forth. Under no circumstances may the patent be interpreted to be limited to the specific examples or embodiments or methods specifically disclosed herein. Under no circumstances may the patent be interpreted to be limited by any statement made by any Examiner or any other official or employee of the Patent and Trademark Office unless such statement is specifically and without qualification or reservation expressly adopted in a responsive writing by Applicants.
The terms and expressions that have been employed are used as terms of description and not of limitation, and there is no intent in the use of such terms and expressions to exclude any equivalent of the features shown and described or portions thereof, but it is recognized that various modifications are possible within the scope of the invention as claimed. Thus, it will be understood that although the present invention has been specifically disclosed by preferred embodiments and optional features, modification and variation of the concepts herein disclosed may be resorted to by those skilled in the art, and that such modifications and variations are considered to be within the scope of this invention as defined by the appended claims.
The invention has been described broadly and generically herein. Each of the narrower species and subgeneric groupings falling within the generic disclosure also form part of the invention. This includes the generic description of the invention with a proviso or negative limitation removing any subject matter from the genus, regardless of whether or not the excised material is specifically recited herein.
Other embodiments are within the following claims. In addition, where features or aspects of the invention are described in terms of Markush groups, those skilled in the art will recognize that the invention is also thereby described in terms of any individual member or subgroup of members of the Markush group.
This application claims priority to provisional Application Ser. No. 60/426,242, filed Nov. 14, 2001. This application is related to PCT Application No. PCT/US01/29165, filed Sep. 17, 2001, Provisional Application Ser. No. 60/315,906, filed Aug. 29, 2001, Provisional Application Ser. No. 60/235,475, filed Sep. 26, 2000, and Provisional Application Ser. No. 60/232,702, filed Sep. 15, 2001.
Work contributing to this invention was supported by a grant from the National Institutes of Health, GM43858, PO1CA277489. Accordingly, the United States government has certain rights in the invention.
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/EP03/12709 | 11/13/2003 | WO | 6/5/2006 |
| Number | Date | Country | |
|---|---|---|---|
| 60426242 | Nov 2002 | US |
