Patent Application
20130005666
Oxidative stress is a major contributor to aging, insulin resistance, and neurodegeneration. An emergent strategy for restoring redox homeostasis involves activation of the transcription factor, Nrf2 (nuclear factor erythroid 2-related factor 2), a member of the cap'n'collar family of basic leucine zipper transcription factors that regulates a coordinated adaptive gene program (MOI et al., Proc Natl Acad Sci USA, 91: 9926-9930 (1994)). Indeed, activators of the Nrf2 response are beneficial for the treatment and prevention of chronic degenerative diseases, while inhibitors of its activation may help to fight cancer (CALABRESE et al., Neurochem Res, 33: 2444-2471 (2008); HAYES et al., Trends Biochem Sci, 34, 176-188 (2009); LAU et al., Pharmacol Res, 58: 262-270 (2008)). A major challenge in the development of effective Nrf2 activators is to identify those that lead specifically to Nrf2 stabilization and consequent promoter activation, without imposing general oxidative/electrophilic stress.
Nrf2 is sequestered under homeostatic conditions by binding to its inhibitory protein, Keap1 (Kelch-like ECH-associated protein-1) (MOTOHASHI et al., Trends Mol Med, 10: 549-557 (2004); ITOH et al., Genes Dev 13: 76-86 (1999)). Keap1 serves as a bridge between Nrf2 and the Cul3-Rbx1 E3 ubiquitin ligase, leading to Nrf2 ubiquitination and thereby targeting Nrf2 for degradation by the 26S proteasome (KOBAYASHI et al., Mol Cell Biol, 24: 7130-7139 (2004); CULLINAN et al., Mol Cell Biol, 24: 8477-8486 (2004); ZHANG et al., Mol Cell Biol, 24: 10941-10953 (2004)). Upon exposure to oxidative stress, xenobiotics, or electrophilic compounds, the Nrf2 protein is released from its complex with Keap1 and translocates to the nucleus. There, it forms heterodimers with other transcription regulators, such as small Maf proteins, and induces the expression of antioxidant genes controlled by the antioxidant response element (ARE) (KASPAR et al., Free Radic Biol Med, 47: 1304-1309 (2009)).
Nrf2 is composed of Neh1-Neh6 domains, among which Neh2 is the putative negative regulatory domain that interacts with Keap1, Neh4 and Neh5 are transactivation domains, and Neh1 is the binding domain for ARE (TONG et al., Biol Chem, 387: 1311-1320 (2006b)). The functional domains of Keap1 are the Broad complex, Tramtrack and Bric-a-Brac (BTB), the intervening region (IVR), the double glycine repeats domain (DGR), and the C-terminal region (CTR) (TONG et al., Biol Chem, 387: 1311-1320 (2006b)). Two motifs in the Neh2 domain, e.g. ETGE and DLG, are recognized by the Keap1 homodimer in a hinge-latch mode (TONG et al., Mol Cell Biol, 26: 2887-2900 (2006a); TONG et al., Biol Chem, 387: 1311-1320 (2006b); TONG et al., Mol Cell Biol., 27: 7511-7521 (2007)). Keap1 mediates polyubiquitination of the positioned lysines within the central α-helix of the Neh2 domain under homeostatic conditions. Under oxidative/electrophilic stress reactive cysteines within Keap1 are modified and thus Keap1 undergoes conformational changes which lead to the detachment of the weak-binding DLG, resulting in Nrf2 stabilization. However, debate remains as to whether Nrf2 is completely released from its complex with Keap1 (ZHANG, Drug Metab Rev, 38: 769-789 (2006)) or not. Nrf2 activators identified so far are represented by potent alkylating agents (DINKOVA-KOSTOVA et al., Methods Enzymol, 382: 423-448 (2004)) and redox active compounds like diphenols, aminophenols and phenylene diamines, the precise mechanism of action of which is controversial. Recent data shows an enhanced effect of these compounds in the presence of exogenously added copper (WANG et al., Chem Biol, 17: 75-85 (2010)).
Current techniques for monitoring Nrf2 activation include the ARE-luciferase (MOEHLENKAMP et al., Arch Biochem Biophys, 363: 98-106 (1999)), Nrf2 responsive element-luciferase (Westerink et al., Mutat Res 696, 21-40 (2010)), or ARE-human placental alkaline phosphatase reporter systems (Son et al., J Neurochem 112, 1316-1326 (2010)).
Recently, a GFP fusion protein with the Nrf2 ZIP domain was utilized to study Nrf2 nuclear translocation (THEODORE et al., J Biol Chem, 283: 8984-8994 (2008)), while GFP fusion with the C. elegans Nrf2 analog was used to analyze Nrf2 activation by proteasomal dysfunction (KAHN et al., J. Biochem, 409: 205-213 (2008)). The ARE-GFP reporter assay was used to screen the library of 2,000 biologically active compounds (Spectrum library) and 45 hits identified (SHAW et al., UK Patent Application #0918626.3, Priority Date (Oct. 24, 2008), Publ Date (May 5, 2010)), with andrographolide being the most potent. The use of ARE-luciferase reporter for high throughput screening (HTS) purposes has been recently published (HUR et al., Chem Biol, 17, 537-547 (2010)). The screen of 1.5 million compounds resulted in discovery of novel alkylating agents targeting Cys 151 in Keap1 as well as a dozen other cellular proteins including phosphatase 2a, and HDAC1 and HDAC2 (HUR et al., Chem Biol, 17, 537-547 (2010)).
ITOH et al., Genes Dev 13: 76-86 (1999) disclosed a NEH2+ reporter construct, and used it to assay NRF2 activity. This paper describes a chicken Neh2 construct, and a mouse Neh2 construct. The latter is 1-73 aa residues of mouse Neh2 attached to GFP. As shown in
This disclosure presents a novel reporter construct, in which the Neh2 domain is fused to a luciferase gene (Neh2-luc), as a new powerful tool for the high throughput screening and real time monitoring of Nrf2 activation. It is demonstrated herein that a 97 aa Neh2 sequence is sufficient for recognition, ubiquitination and degradation of the fusion where the reporter in attached to C-terminus of Neh2. This disclosure also demonstrates the utility of the Neh2-luc model to identify and classify novel compounds capable of inducing Nrf2-specific astrocyte-dependent neuroprotection from oxidative stress.
In the following description, reference is made to the accompanying drawings that form a part hereof, and in which is shown by way of illustration specific embodiments which may be practiced. These embodiments are described in detail to enable those skilled in the art to practice the invention, and it is to be understood that other embodiments may be utilized and that logical changes may be made without departing from the scope of the present invention. The following description of example embodiments is, therefore, not to be taken in a limited sense, and the scope of the present invention is defined by the appended claims.
The Abstract is provided to comply with 37 C.F.R. §1.72(b) to allow the reader to quickly ascertain the nature and gist of the technical disclosure. The Abstract is submitted with the understanding that it will not be used to interpret or limit the scope or meaning of the claims.
For convenience, before further description of the present invention, certain terms employed in the specification, examples, and appendant claims are collected here. These definitions should be read in light of the entire disclosure and understood as by a person of skill in the art.
The articles “a” and “an” are used herein to refer to one or to more than one (i.e., to at least one) of the grammatical object of the article. By way of example, “an element” means one element or more than one element.
The term “nucleic acid” refers to a polymeric form of nucleotides, either ribonucleotides or deoxynucleotides or a modified form of either type of nucleotide. The terms should also be understood to include, as equivalents, analogs of either RNA or DNA made from nucleotide analogs, and, as applicable to the embodiment being described, single-stranded (such as sense or antisense) and double-stranded polynucleotides.
The term “operably linked”, when describing the relationship between two nucleic acid regions, refers to a juxtaposition wherein the regions are in a relationship permitting them to function in their intended manner. For example, a control sequence “operably linked” to a coding sequence is ligated in such a way that expression of the coding sequence is achieved under conditions compatible with the control sequences, such as when the appropriate molecules (e.g., inducers and polymerases) are bound to the control or regulatory sequence(s).
The term “amino acid” is intended to embrace all molecules, whether natural or synthetic, which include both an amino functionality and an acid functionality and capable of being included in a polymer of naturally-occurring amino acids. Exemplary amino acids include naturally-occurring amino acids; analogs, derivatives and congeners thereof; amino acid analogs having variant side chains; and all stereoisomers of any of any of the foregoing.
The term “protein”, and the terms “polypeptide” and “peptide” which are used interchangeably herein, refers to a polymer of amino acids. Exemplary polypeptides include gene products, naturally-occurring proteins, homologs, orthologs, paralogs, fragments, and other equivalents, variants and analogs of the foregoing.
The terms “recombinant protein” or “recombinant polypeptide” refer to a polypeptide which is produced by recombinant DNA techniques. An example of such techniques includes the case when DNA encoding the expressed protein is inserted into a suitable expression vector which is in turn used to transform a host cell to produce the protein or polypeptide encoded by the DNA.
A “fusion protein” or “fusion polypeptide” refers to a chimeric protein as that term is known in the art and may be constructed using methods known in the art. In many examples of fusion proteins, there are two different polypeptide sequences, and in certain cases, there may be more. The sequences may be linked in frame. A fusion protein may include a domain which is found (albeit in a different protein) in an organism which also expresses the first protein, or it may be an “interspecies”, “intergenic”, etc. fusion expressed by different kinds of organisms. In various embodiments, the fusion polypeptide may comprise one or more amino acid sequences linked to a first polypeptide. In the case where more than one amino acid sequence is fused to a first polypeptide, the fusion sequences may be multiple copies of the same sequence, or alternatively, may be different amino acid sequences. The fusion polypeptides may be fused to the N-terminus, the C-terminus, or the N- and C-terminus of the first polypeptide. Exemplary fusion proteins include polypeptides comprising a glutathione S-transferase tag (GST-tag), histidine tag (His-tag), an immunoglobulin domain or an immunoglobulin binding domain.
The term “reporter gene” or “reporter” is known in the art and as used in the present invention with respect to a DNA sequence means any DNA sequence encoding a peptide, a protein or a polypeptide or nucleic acid that can give rise to a signal that can be detected, traced, or measured. As used in the present invention with respect to a DNA sequence, “reporter” will generally means a cDNA sequence (although in some cases a reporter gene may have introns) that encodes a protein or polypeptide or nucleic acid that is used in the art to provide a measurable phenotype that can be distinguished over background signals. The product of said reporter gene may also be referred to a “reporter” and may be mRNA, a peptide, a polypetide, or protein, and may also be readily measured by any mRNA or protein quantification technique known in the art. “Reporter” may also refer to a tag or label that is affixed to a protein or peptide after it is expressed and may be any such tag or label known in the art. The reporter may, in a preferred embodiment, be a fluorophore.
A “fluorophore” is a component of a molecule which causes a molecule to be fluorescent. It is a functional group in a molecule which will absorb energy of a specific wavelength and re-emit energy at a specific wavelength. The amount and wavelength of the emitted energy depend on both the fluorophore and the chemical environment of the fluorophore. Fluorescein isothiocyanate (FITC), a reactive derivative of fluorescein, has been one of the most common fluorophores chemically attached to other, non-fluorescent molecules to create new fluorescent molecules for a variety of applications. Other historically common fluorophores are derivatives of rhodamine (TRITC), coumarin, and cyanine. Newer generations of fluorophores such as the CF dyes, the FluoProbes dyes, the DyLight Fluors, the Oyester dyes, the Atto dyes, the HiLyte Fluors, and the Alexa Fluors are also known in the art.
The term “modulate” or “modulation”, when used in reference to a functional property or biological activity or process (e.g., enzyme activity or receptor binding), refers to the capacity to either up regulate (e.g., activate or stimulate), down regulate (e.g., inhibit or suppress) or otherwise change a quality of such property, activity or process. Therefore, an Nrf2 activator means a molecule that up regulates (e.g., activates, stimulates or enhances) a functional property or activity of Nrf2, such as one or more of the functions or activities known to be associated with Nrf2.
For example, Nrf2 has been shown to be a critical factor for the basal and inducible expression of many families of cytoprotective and detoxication genes (RAMOS-GOMEZ et al., Proc Natl Acad Sci USA, 98: 3410-3415 (2001); CHANAS et al., J. Biochem, 365: 405-16 (2002); THIMMULAPPA et al., Cancer Res, 62: 5196-203 (2002); MCMAHON et al., Cancer Res, 61: 3299-307 (2001); KWAK et al., J Biol Chem, 278: 8135-45 (2003); KWAK et al., Mol Med, 7: 135-45 (2001)). The diseases that could be treated or prevented by Nrf2 activation seem extensive as most have an etiology in oxidative stress.
In addition to conjugating and antioxidative genes, Nrf2 regulates other protective mechanisms including anti-inflammatory responses, the molecular chaperones/stress response system, and expression of the ubiquitin/proteasome system (KWAK et al., J Biol Chem, 278: 8135-45 (2003)). For this reason, activation of Nrf2 constitutes a broad protective response, making Nrf2 and its interacting partners important targets for anti-aging agents, as well as cancer chemoprevention.
Nrf2 activators have been investigated as anti-cancer drugs, and some have been shown to inhibit cancer formation in a variety of rodent organs, including the bladder, blood, colon, kidney, liver, lung, pancreas, stomach, and trachea, skin, and mammary tissue (ZHANG et al., Mol Cell Biol, 24: 10941-10953 (2004)).
In addition to cancer, Nrf2-regulated protective mechanisms may defend against and treat respiratory diseases such as hyperoxic lung injury (CHO et al., Am J Respir Cell Mol Biol, 26: 175-82 (2002)), emphysema (ISHII et al., J Immunol, 175: 6968-75 (2005)), asthma (RANGASAMY et al., J Exp Med, 202: 47-59 (2005)).
Nrf2 also plays a key role in the antioxidant defense of the central nervous system and has been shown to be important for neuroprotection in several acute and chronic neuropathological conditions (CALKINS et al., Proc Natl Acad Sci USA, 102: 244-9 (2005); BURTON et al., Neurotoxicology, 27(6): 1094-100 (2006)). Relevant CNS conditions include but are not limited to, stroke (both acute and chronic), multiple sclerosis, amyotrophic lateral sclerosis, the paroxysmal disorders (e.g., the epilepsies), autonomic nervous system dysfunction (e.g., arterial hypertension), movement disorders (e.g., hyperkinetic disorders, dyskinesias (resting tremor), basal ganglia hyperkinetic disorders (e.g., Huntington's chorea, hemiballismus), neuropsychiatric disorders (e.g., mania, psychosis obsessive compulsive disorder, and addiction), Alzheimer's disease, Parkinson's disease, hypothalamic disorders such as hyperlactemia, craniopharyngioma, gondotrophin deficiency, growth hormone deficiency, vassopressin deficiancy, prolactinomas, obesity, neuropathic pain syndromes, acrodynia, Charcot-Marie-Tooth disease, diabetic neuropathies, nerve compression syndromes, neuralgias, neuromuscular junction diseases, POEMS syndrome, optical nerve injury diseases (e.g., glaucoma), olfactory disorders such as anosmia, hyponosmia, hypernosmia and impaired olfactory learning and memory and various retinal degenerative diseases (e.g., retinitis pigmentosa, macular degeneration).
Nrf2 has been shown to be important in cardiovascular diseases as well, such as cerebral ischemia (SHIH et al., J Neurosci, 25: 10321-10335 (2005)), and several other cardiac disorders (ZHU et al., FEBS Lett, 579: 3029-36 (2005)).
NRf2 activators have been investigated in the context of metabolic disease and diabetes, including insulin resistance and chronic kidney disease (CKD) in patients with diabetes mellitus. It has been established that there is a clear relationship between oxidative stress and inflammation and the various pathologies associated with diabetes, including diabetic nephropathy and chronic kidney disease. (BROWNLEE, Nature, 414 (6865): 813-20 (2001)).
The term “condition that is susceptible to treatment with a compound that upregulates NRF2” refers to any medical disease or condition for which there is evidence that NRF2 activity may be beneficial. Said condition may involve the nervous system, including the central nervous system.
The term “treating” as used herein is intended to encompass curing as well as ameliorating at least one symptom of any condition or disease.
A “patient,” “subject” or “host” is intended to include human and non-human animals. Non-human animals includes all vertebrates, e.g., mammals and non-mammals, such as non-human primates, sheep, dogs, cats, cows, horses, chickens, amphibians, and reptiles, although mammals are preferred, such as non-human primates, sheep, dogs, cats, cows and horses. The subject may also be livestock such as, cattle, swine, sheep, poultry, and horses, or pets, such as dogs and cats. The subject may be male or female, and may be elderly, an adult, adolescent, child, or infant. The term “juvenile” shall refer to infants, children, adolescents—any organism from the time between its birth and the maturation of its nervous system. The human subject may be caucasian, african, asian, semitic, or of other or mixed racial background. Preferred subjects include human patients suffering from or at risk for the neural diseases, conditions, and disorders described herein.
The term “sequence homology” refers to the proportion of base matches between two nucleic acid sequences or the proportion of amino acid matches between two amino acid sequences. When sequence homology is expressed as a percentage, e.g., 50%, the percentage denotes the proportion of matches over the length of sequence from a desired sequence that is compared to some other sequence. Gaps (in either of the two sequences) are permitted to maximize matching; gap lengths of 15 bases or less are usually used, 6 bases or less are used more frequently, with 2 bases or less used even more frequently. The term “sequence identity” means that sequences are identical (i.e., on a nucleotide-by-nucleotide basis for nucleic acids or amino acid-by-amino acid basis for polypeptides) over a window of comparison. The term “percentage of sequence identity” is calculated by comparing two optimally aligned sequences over the comparison window, determining the number of positions at which the identical amino acids occurs in both sequences to yield the number of matched positions, dividing the number of matched positions by the total number of positions in the comparison window, and multiplying the result by 100 to yield the percentage of sequence identity. Methods to calculate sequence identity are known to those of skill in the art and described in further detail below.
The term “NRF2” is an abbreviation for “nuclear factor (erythroid-derived 2)-like 2” or “NF-E2-related factor 2” or “NFE2-related factor 2” or “nuclear factor erythroid-derived 2-like 2.” All terms are used interchangeably by those of skill in the art. Other terms used by those of skill in the art to refer to human NRF2 proteins include “NFE2L2”, “HEBP1”, “OTTHUMP00000205251”, or “OTTHUMP00000207980.” Nrf2 belongs to the Cap'n'Collar (CNC) family of transcription factors that contain a conserved basic region-leucine zipper structure. The Online Mendelian Inheritance in Man reference number for NRF2 is 600492. The term includes mutated NRF2 proteins.
The term “NEH2” is an abbreviation for “Nrf2-ECH homology 2”. Neh2 is located at the N terminus of Nrf2 and acts as the regulatory domain for cellular stress response. There are two evolutionarily conserved motifs within the Neh2 domain among the CNC protein family. The DLG motif, which locates at the N-terminal region, has been reported to be important for ubiquitination and degradation of Nrf2, while the ETGE motif is essential for interacting with Keap1. In addition, seven lysine residues of the Neh2 domain, which reside upstream of the ETGE motif, have been shown to be indispensable for Keap1-dependent polyubiquitination and degradation of Nrf2.
The term “vector” refers to a nucleic acid capable of transporting another nucleic acid to which it has been linked. One type of vector which may be used in accord with the invention is an episome, i.e., a nucleic acid capable of extra-chromosomal replication. Other vectors include those capable of autonomous replication and expression of nucleic acids to which they are linked. Vectors capable of directing the expression of genes to which they are operatively linked are referred to herein as “expression vectors”. In general, expression vectors of utility in recombinant DNA techniques are often in the form of “plasmids” which refer to circular double stranded DNA molecules which, in their vector form are not bound to the chromosome. Infectious expression vectors, such as recombinant baculoviruses, are used to express proteins in cultured cells. Other infectious expression vectors, such as recombinant adenoviruses and vaccinia viruses, are used as vaccines to express foreign antigens in vaccines. However, the invention is intended to include such other forms of expression vectors which serve equivalent functions and which become known in the art subsequently hereto.
Unless otherwise indicated, all numbers expressing quantities of ingredients, reaction conditions, and so forth used in the specification and claims are to be understood as being modified in all instances by the term “about.” Accordingly, unless indicated to the contrary, the numerical parameters set forth in this specification and attached claims are approximations that may vary depending upon the desired properties sought to be obtained by the present invention.
Construction and Validation of Neh2-luc Reporter
This reporter construct of this invention is composed of a nucleic acid encoding a fusion protein between an Neh2 domain and a reporter protein.
Neh2 domains suitable for use in the present reporter construct include Neh2 domains from naturally occurring Nrf2 molecules of a mammal, such as human, mouse, chicken, among others.
In some embodiments, the Neh2 domain used in the reporter construct is the Neh2 domain of human Nrf2. In a specific embodiment, this Neh2 domain of human Nrf2 is composed of amino acids 1-97 of human Nrf2, as shown in SEQ ID NO: 11. Naturally occurring allelic variants and functional derivatives of SEQ ID NO: 11 are also suitable for use in the reporter construct of this invention.
In other embodiments, the Neh2 domain used in the reporter construct is the Neh2 domain of murine Nrf2 or chicken Nrf2. The native Neh2 domains of these molecules are set forth in SEQ ID NO: 15 and SEQ ID NO: 17, respectively. Naturally occurring allelic variants and functional derivatives of these naturally occurring Neh2 domains are also suitable for use in the reporter construct of this invention.
As used herein, a “functional derivative” of a naturally occurring Neh2 domain maintains characteristic structural features of a Neh2 domain attributable to its function (e.g., interacting with Keap1). In this context, relevant characteristic structural features of a Neh2 domain include the DLG motif and the ETGE motif and the lysine residues between them. For purposes of this invention, these motifs should be intact to preserve the function of the Neh2 domain (e.g., its ability to interact with Keap1), while amino acid residues outside of these motifs are relatively more tolerant to modifications (such as substitutions, including both conservative and non-conservative substitutions, and deletions or insertions at the N or C-terminus of the Neh2 domain).
The DLG motif refers to the peptide sequence, LXXQDXDLG (SEQ ID NO: 12), which is widely conserved in CNC factors. See, e.g., Katoh et al. (Arch Biochm Biophys 43: 342-350 (2005). The residue “X” at position 2 is often a bulky hydrophobic residue such as W or Y; “X” at position 3 is a positively charged residue such as R or K; and “X” at position 6 is a hydrophobic residue such as I or V. The ETGE motif refers to the peptide, ETGE (SEQ ID NO: 13). Thus, suitable functional derivatives of a naturally occurring Neh2 domain include, for example, peptides that share at least 95%, 96%, 97%, 98% or 99% of sequence identity with SEQ ID NO: 11, or have 1, 2, 3, 4, or 5 amino acid differences from SEQ ID NO: 11, where the differences occur outside of the DLG and ETGE motifs. Preferably, the differences consist of conservative amino acid substitutions at internal locations of an Neh2 domain, or deletions or additions at the N- or C-terminus. As examples of deletions at the N or C terminus, peptide composed of 92, 93, 94, 95, or 96 contiguous amino acids of SEQ ID NO: 11 may be suitable for use in this invention. Examples of conservative substitutions include the substitution of a non-polar (hydrophobic) residue such as I, V, L or M for another; the substitution of one polar (hydrophilic) residue for another polar residue, such as R for K, Q for N, G for S, or vice versa; and the substitution of a basic residue such as K, R or H for another or the substitution of one acidic residue such as D or E for another. Examples of non-conservative substitutions include the substitution of a non-polar (hydrophobic) residue such as I, V, L, A, M for a polar (hydrophilic) residue such as C, Q, D, K and/or vice versa.
In the reporter construct of this invention, a nucleic acid encoding an Neh2 domain is linked to a reporter gene. A variety of reporter genes can be used which are capable of generating a detectable signal. Examples of suitable reporter genes include, but are not limited to, luciferase gene, lactosidase gene, green fluorescent protein gene, or a yellow fluorescent protein gene, or cyan fluorescent gene, or red fluorescent gene.
In some embodiments, a nucleotide sequence encoding an amino acid linker is included in a reporter construct between the Neh2 domain and the reporter. Use of linkers in making fusion proteins is well documented in the art. Linkers are generally short peptides composed of small amino acid residues such as Glycine and Serine.
A nucleic acid which codes for an Neh2-reporter fusion is placed in an operable linkage to a promoter functional in a recipient cell, which can be a constitutive promoter or an inducible promoter to drive the expression of the Neh2-reporter fusion molecule in the recipient cell. A CMV promoter and a SV40 promoter are examples of promoters that can drive strong expression in a wide spectrum of cell types and are suitable for use in the reporter constructs of this invention.
A nucleic acid construct or vector, which carries an Neh2-reporter fusion nucleic acid, can be introduced into an appropriate host cell by various means available in the art, such as liposome-mediated transfection, electroporation, calcium phosphate precipitation, DEAE-Detxan followed by polyethylene glycol, among others. While the examples disclosed herein exemplify a human neuroblastoma cell line as a recipient cell, a variety of mammalian cell lines including human cell lines are available for use. The resulting cell line can be used to screen for useful compounds, such as Nrf2 modulators (activators or inhibitors), as further disclosed hereinbelow.
In a specific embodiment, the Pcmv-driven Neh2-luc reporter supports the constitutive, intracellular synthesis of a novel fusion protein composed of amino acid 1-97 of human Nrf2 (containing the Neh2 domain) and firefly luciferase. Since the Neh2 domain is known to be sufficient for recognition by the ubiquitin-ligase complex and subsequent ubiquitination of the fusion protein, the recombinant luciferase labeled protein should undergo proteasomal degradation. The steady-state concentration of the fusion protein should correspond to the equilibrium between its synthesis and degradation (
The overexpressed Neh2-luciferase fusion protein successfully competes with endogenous Nrf2 for Keap1 binding and thus, rescues endogenous Nrf2 from degradation: the reporter cell line shows a 4-6-fold increase in mRNA for Nrf2-regulated genes such as HO-1 and GSLM (
Canonical activators of Nrf2 such as 15-deoxy-prostaglandin J2 (15d-PGJ2) (ITOH et al., Mol Cell Biol 24: 36-45 (2004)), sulforaphane (MYZAK et al., Cancer Lett, 233: 208-218 (2006)) and tert-butylhydroquinone (TBHQ) (MOEHLENKAMP et al., Arch Biochem Biophys, 363: 98-106 (1999)) disrupt the interaction in the Neh2luc-Keap1-Cul3 complex leading to a measureable increase in luciferase activity and protein (
If compared to commonly used ARE-luc reporter, the newly developed one has an obvious advantage to monitor immediate changes upon the addition of Nrf2 activators: the response of ARE-luc reporter to TBHQ is 3 h delayed (
The Neh2-luc reporter system is a novel tool to monitor the direct effect of a particular compound on the first step controlling Nrf2 stability, i.e. Nrf2-Keap1 and/or Keap1-Cul3 interaction. Validation studies further performed using traditional approaches (
In contrast to the previously utilized ARE-based promoter-reporter constructs, the novel reporter provides real time monitoring of Nrf2 stabilization and can be successfully used for high throughput screening purposes (see below) as well as in vivo bioluminescent imaging.
Pilot HTS of Spectrum library
In a further aspect, reporter cells line disclosed herein are used to screen for compounds, such as Nrf2 modulators (activators or inhibitors). In some embodiments, compounds being tested are small molecule compounds, e.g., organic compounds having a molecular weight of less than 1500 Dalton, 1200 Dalton, 1000 Dalton or even 800 Dalton. Peptides or other classes of molecules may also be screened.
In accordance with this invention, the level of expression of the reporter gene from a Neh2-reporter construct, hence the amount of signal detected, reflects the ability and extent a compound can modulate Nrf2. Thus, an Nrf2 modulator can be identified by contacting a reporter cell line with candidate compounds, detecting signals generated from the reporter, and comparing the amount of signals with a control. In some embodiments, the control represents the amount of signals detected from a reporter cell line in the absence of a candidate compound under identical conditions. In other embodiments, the control represents the amount of signals detected from a reporter cell line in the presence of a known activator compound under identical conditions, as exemplified hereinbelow.
The exemplary reporter cell line generated herein was stable for more than a year providing constant readings for all control Nrf2 activators. It has been shown to be suitable for HTS purposes: the results of a pilot screen of the Spectrum library using the novel Neh2-luc reporter cell line with 10 μM tert-butylhydroquinone (TBHQ) as a positive control are presented below. TBHQ has been used in vivo for prophylaxis against ischemic stroke (SHIH et al., J Neurosci, 25: 10321-10335 (2005)). TBHQ was chosen among other canonical activators tested since the concentration titration curve had no peaks and showed a saturation plateau (
The screen revealed 224 hits exhibiting Neh2-luc reporter activity equal or higher than 25% of TBHQ; among those, 100 showed activation of at least 75% of that induced by TBHQ. Thus, 5% of biologically active compounds and drugs presented in the Spectrum library are at least 75% as potent as TBHQ in activation of Nrf2. The prevalence of hits may reflect the important role that Nrf2 plays in xenobiotic detoxification of a large number of chemical entities.
As a further test of specificity of the identified Nrf2 activators, the inventors compared 200 putative Nrf2 activators to almost 30 hits from HTS of the same library found using a HIF1 ODD-luc reporter, HIF-1α oxygen degradable domain fused to luciferase, as described (SMIRNOVA et al., Chem Biol, 17: 380-391 (2010)). Upon hydroxylation at proline 564 in normoxia, the ODD-luciferase recruits the E3 Ubiquitin Ligase, Von Hippel Lindau protein, and targets the ODD-luciferase for proteasomal degradation (SMIRNOVA et al., Chem Biol, 17: 380-391 (2010)). The observation that the Nrf2 (Neh2-luc) or HIF1 (ODD-luc) screens of the identical 2,000 compound library give hits that do not overlap is the strongest evidence for specific chemical control of the stability of both reporters. The findings suggest that rate-limiting step in reporter activation is determined by Neh2 (of Nrf2) or ODD (of HIF1α) and not by proteasomal degradation. In other words, the reporters select unique activators of Nrf2 and HIF1, respectively, and not common inhibitors of proteosomal degradation.
Well-known drugs and hormones were found in the screen as potent activators of the Neh2-luc reporter, for example minocycline (KUANG et al., Brain Res, 1286: 174-184 (2009)), sulindac, auranofin (KATAOKA et al., J Biol Chem, 276: 34074-34081 (2001)), teniposide, podophyllotoxin derivatives, which showed 200% activation over the canonical TBHQ-induced Neh2-luc response. Purpurogallin carboxylates (
The hits included phenolic antioxidants; diphenols (
Structure-activity relationship studies for flavones indicate the necessary presence of 3-hydroxy-group, since 3′,4′-dimethoxy-3-hydroxyflavone and kaempferol (3,5,7,4′-tetrahydroxyflavone) are 2.5-fold less effective than quercetin and fisetin. Luteolin (5,7,3′,4′-tetrahydroxyflavone) has an effect similar to kaempferol and thus, is much lesser active than fisetin and quercetin, although they all have two adjacent hydroxy-groups on a freely rotating phenyl ring. Additionally, double Michael reaction acceptors such as curcumins showing more than 200% activation (
Of the 45 hits from the ARE-GFP screen of the same library (SHAW et al., UK Patent Application #0918626.3, Priority Date (Oct. 24, 2008), Publ Date (May 5, 2010)), 37 of those were among our hits. The conditions of HTS were very different, in particular the incubation time (24 h ARE-GFP vs 3 h Neh2-luc), so some of the hits missed were likely to induce extremely delayed effects. The lesser number of hits in the ARE-GFP screen could reflect both prolonged incubation and lesser sensitivity of the assay: the cell number per well was at least 7 times higher and ebselen as a positive control induced only a 3-fold increase in the reporter signal (SHAW et al., UK Patent Application #0918626.3, Priority Date (Oct. 24, 2008), Publ Date (May 5, 2010)) compared to more than 10-fold activation by TBHQ in the case of Neh2-luc reporter (
Novel Classes of Nrf2 Activators
The previously unknown classes of hits included:
(1) all members of gedunin/khivorin family (18 compounds) were among the hits (see
(2) planar Zn2+ chelators such as 8-hydroxyquinoline and chloroacetoxyquinoline (60% activation). The presence of Zn2+-atom in Keap1 was documented for the recombinant protein produced in E. coli, and an estimate for Zn2+ binding constant was on the order of pM (DINKOVA-KOSTOVA et al., Biochemistry, 44: 6889-6899 (2005)). We recently identified a number of novel branched oxyquinolines as inhibitors of the HIF prolyl hydroxylases (SMIRNOVA et al., Chem Biol, 17: 380-391 (2010)). None of these compounds (which are also zinc chelators with Ki below 200 nM) showed any Neh2-luciferase activation, pointing to specific structural requirements for oxyquinoline zinc chelators as Nrf2 activators. 3-Hydroxyflavone was found as a modest Nrf2 activator and is known to bind zinc better than 5-hydroxyflavone or 3′4′-dihydroxyflavone (LAPOUGE et al., J Phys Chem A, 110: 12494-12500 (2006)).
(3) adenosine, azathioprine, bromonitroindazole were modest hits in our screen: they resemble the recently published structures of novel Nrf2 inducers supposedly targeting the intervening region of Keap1 (WU et al., Chem Biol Drug Des, 75: 475-480 (2010)) (see
Time-Course of Reporter Activation as a Tool for Hit Classification
As mentioned, the novel reporter provides the possibility of real time monitoring for changes in the stability of Nrf2 in the form of the luciferase labeled Neh2 domain for the first time. By following the kinetics of reporter activation one may expect to discriminate the mechanism of action of various Nrf2 activators, i.e. direct activators will exert immediate effects, while those acting indirectly will show lag-periods of different durations.
The mechanism of Nrf2 activation has been postulated to occur due to the chemical modification of key thiols in Keap1. Accordingly, all alkylating agents tested were hits. The exact mechanism of action of redox-cycling compounds like ortho- or para-dihydroxy-phenols is not known, although they are supposed to undergo oxidation resulting in formation of potential alkylating compounds.
Among well-known classes of hits, particularly those of catechol-type, with two adjacent hydroxy-groups, e.g. fisetin, quercetin, but not luteolin (class IV,
We decided to undertake a separate study to use the kinetics of reporter activation to compare the mechanism of action of our best hits using the Neh2-luc reporter system. In addition to providing a novel categorization of Nrf2 activators, our central interest was to further characterize our best hits, which exhibited a very steep concentration response over a very narrow range of concentrations (
For the comparative studies we selected a number of hits, suspected to work via different mechanisms: TBHQ, ortho-phenylene diamine (oPD), o-catechol, NDGA, quercetin, and fisetin as representatives of redox-cycling compounds; sulforaphane, and pyrithione as alkylating compounds; Cd2+, as a heavy metal of unknown mechanism of action; geldanamycin, specific inhibitor of Hsp90 working via blockade of ATP-binding site (OBERMANN et al., J Cell Biol, 143: 901-910 (1998)), trichostatin A (TSA), a general inhibitor of HDACs resulting in destabilization of Hsp90, and gedunin, which is supposed to disrupt the association of Cdc37 and Hsp90 (Brandt et al. 2008).
In accord with the time-course of reporter activation (
The similar behavior of TBHQ, sulforaphane, auranofin, pyrithione and gedunin permits their classification into one group of “alkylators”. Catechol is likely to undergo quick transformation and then also works as an “alkylator”. Apparently oPD and catechol behave differently: oPD has a clearly defined short lag-period, which may reflect the additional modification step of the inducer, such as enzymatic oxidation with copper-dependent enzymes (WANG et al., Chem Biol, 17: 75-85 (2010)): oPD is possibly the one working through redox cycling.
The effect of Cd2+ is more than 1 hour-delayed, so it either has problems with getting into the cell, or more likely, has an indirect effect on the system via inactivation of thiol-disulfide exchange by inhibiting thioredoxin reductase/thioredoxin system. It is of interest to note that increased concentrations of Cd2+ shorten the lag-period, while in the case of oPD, the lag-period duration barely depends on the inducer concentration.
The activation effect observed with geldanamycin, a selective Hsp90 inhibitor was rather modest (2-3 fold in the range of 0.5-1.5 μM) with toxicity dominating at increased concentrations. A characteristic feature of geldanamycin induced Neh2-luciferase stabilization was an extremely prolonged (up to 3 h) lag-period, similar to that observed for the global histone deacetylase inhibitor, TSA (
As an independent approach to test the mechanism of action of selected hits in comparison with the well-known controls we performed Keap1 labeling experiments (
Neuroprotective Effects of the Best Hits
To confirm that the Neh2-luc activators newly identified from our screen induce a neuroprotective response, we examined the biological effects of these activators on astrocyte-dependent neuroprotection using an astrocyte-neuron coculture model of oxidative stress. Specifically, Nrf2 activation in astrocytes induces non cell autonomous neuroprotection via the transcriptional regulation of genes involved generally in the antioxidant response, including those involved in the biosynthesis, use and export of the major antioxidant glutathione (GSH) (SHIH et al., J Neurosci 23: 3394-3406 (2003)). Glutamate or homocysteic acid (HCA, glutamate analog) treatment of immature neurons leads to substantial glutathione depletion in neurons and astrocytes and subsequent oxidative stress-induced death of immature neurons; since astrocytes possess ten times as much glutathione as neurons, HCA treated astrocytes remain viable (HASKEW-LAYTON et al., Proc Natl Acad Sci USA, in press (2010)). Thus primary cultured astrocytes were pretreated with NDGA, fisetin or gedunin for 24 hr followed by the addition of adjacent neurons in the presence of the GSH-depleting compound, HCA. Pretreatment of the astrocytes with NDGA, fisetin or gedunin induced significant neuroprotection (
To confirm that the astrocyte-dependent neuroprotective effects were specific to the activation of Nrf2, astrocytes were pretreated with siRNAs targeted against Nrf2. Three separate Nrf2 siRNA sequences lead to reduced Nrf2 mRNA and protein levels (FIGS. 13B,C) and reduced levels of Nrf2-regulated HO-1 protein levels (
As electrophiles, many of the canonical Nrf2 activators are potential neurotoxins. Even a low level of electrophilic stress would not be ideal for many neurological conditions where oxidative stress is a contributor to disease pathology. Thus the identification of non-electrophilic activators of Nrf2 is a high priority. Importantly, in contrast to the neurotoxic effects of the canonical Nrf2 activators such as TBHQ, the hits from our screen (NDGA, fisetin or gedunin) did not induce toxicity in isolated neurons using a sensitive assay of neuronal vulnerability (
Previous reporters of Nrf2 activation have utilized the antioxidant response element (ARE) fused to coding regions of firefly luciferase or human alkaline phosphatase in vitro or in vivo. The ARE-GFP construct was used to screen Spectrum library and 45 hits were identified (SHAW et al., UK Patent Application #0918626.3, Priority Date (Oct. 24, 2008), Publ Date (May 5, 2010)). The Are-based reporters allow monitoring of 24 h and more delayed effects of antioxidant response induced by Nrf2 stabilization. We have constructed a new reporter system that allows immediate monitoring of drug-induced Nrf2 stabilization in the form of Neh2-luciferase fusion protein. The reporter appears to be a physiological surrogate for Nrf2 based on several observations:
1) Keap1 overexpression inhibits the reporter activity, while Keap1 depletion stabilizes the reporter (
2) Canonical activators of Nrf2, which have been shown to act by alkylating Keap1, lead to expected increases in the Neh2-luciferase activity and protein (
3) Representatives of all previously known classes of Nrf2 activators as well as the majority of ARE-GFP screen hits (SHAW et al., UK Patent Application #0918626.3, Priority Date (Oct. 24, 2008), Publ Date (May 5, 2010)) were identified in the Spectrum library using the novel reporter, further validating the assay (
4) Novel activators of Nrf2 defined in this screen protect neurons from oxidative death via an Nrf2-dependent mechanism in astrocytes (
The power of the new reporter allowed us to discriminate between direct and indirect effects on reporter stabilization induced by compounds tested in HTS, and for the first time identify gedunin as a direct activator of Nrf2. Recent studies suggest that gedunins are potent Hsp90 inhibitors (BRANDT et al., J Med Chem, 51: 6495-6502 (2008)). Celastrol, a quinone methide triterpenoid, is known as Hsp90 inhibitor (ZHANG et al., J Biol Chem, 284: 35381-35389 (2009); ZHANG et al., Mol Cancer Ther, 7: 162-170 (2008)) as well, and its derivative, dihydrocelastrol, was also found as a modest hit in the screen. Based only on structural similarities between gedunin and celastrol, it is possible that gedunin utilizes a similar mechanism of action via disrupting the interaction between Hsp90 and Cdc37, the co-chaperone providing a bridge between Hsp90 and client tyrosine kinases (ZHANG et al., J Biol Chem, 284: 35381-35389 (2009); ZHANG et al., Mol Cancer Ther, 7: 162-170 (2008)), which being detached from the Hsp90 complex undergo fast inactivation (usually within 40-45 min). Of note, triterpenoids have been described as Nrf2 activators using ARE-reporter mice and NQO1 induction levels (YATES et al., Mol Cancer Ther, 6: 154-162 (2007)), and induce neuroprotection in a transgenic model of Huntington's disease (STACK et al., Free Radic Biol Med., 49:147-158 (2010)). Withanolides, closer analogs of gedunins, have been long known as inducers of NQO1 (DINKOVA-KOSTOVA et al., Methods Enzymol, 382: 423-448 (2004)), and are also known to disrupt Hsp90-Cdc37 interaction (YU et al., Biochem Pharmacol, 79: 542-551 (2010)).
If gedunin works via the same mechanism as the above compounds, we should observe the delayed effect of Hsp90 down-regulation with all three compounds, e.g. gedunin, geldanamycin and TSA. However, the latter two show 3 h lag-period in reporter activation, in contrast to the immediate effect induced by gedunin (
An important unanswered question is the mechanism of “switch” effect demonstrated for our best hits, fisetin and NDGA. The time-course of NDGA and fisetin clearly shows that they exert an immediate effect upon addition to the reporter cell line, therefore they act “as is”, without prior chemical modification. Both NDGA and fisetin have adjacent hydroxy-groups on a freely rotating phenyl ring. We could suggest that these adjacent hydroxy groups lead to reduction of a critical disulfide bond. However, there is some doubt that fisetin and NDGA work via this mechanism since the flavones are strong reducing agents capable of immediate reduction of dithionitrobenzoate, a model disulfide, while NDGA is not. In addition, luteolin, a flavone with potent reducing properties, with 3′,4′-dihydroxy-phenyl group present in fisetin, but hydroxyl group in position 5, not 3, is a very poor Nrf2 activator. Moreover, catechol, being a very potent reducing agent, does show a 20 min lag-period, which may reflect initial “priming”, most likely oxidation that results in formation of its form capable of alkylating Keap1. The fact that luteolin and catechol do not behave the same way argues against this potential mechanism and points out to the special structural requirements for a “switch” mechanism of Nrf2 activation.
A common and intriguing feature of our most promising hits, fisetin and NDGA, is their steep concentration response, reminiscent of a ligand binding to a receptor. Of note, a common feature of these hits is that they all have been reported to act as inhibitors of protein tyrosine kinases, and NDGA in particular was reported to target IGF1-R kinase. We also identified genistein (100% reporter activation), which is well known for targeting this class of enzymes. Phosphorylation of Tyr141 in Keap1 is catalyzed by an unknown protein tyrosine kinase and is critical for Keap1 stability (JAIN et al., J Biol Chem 283: 17712-17720 (2008)). Protein tyrosine kinases are also known to be stabilized by Hsp90, inhibitors of which also came out in our screen as hits.
The analysis of kinetics of individual hits leads to the model scheme of Nrf2 regulation shown in
Canonical activators of Nrf2 such as TBHQ, isothiocyanates, and the recently identified AL-I (HUR et al., Chem Biol, 17, 537-547 (2010)) appear to act by modifying key cysteines in Keap1, the negative regulator of Nrf2 stability. A major potential problem with electrophile activators of Nrf2 is their ability to induce toxicity, particularly in cells vulnerable to redox stress such as neurons afflicted by ischemia or neurodegeneration. The challenge is to find Nrf2 activators which do not add to the overall oxidative load, and the novel reporter provides a valuable resource for future developments towards such medications. Here we identify a number of novel Nrf2 activators that are non-toxic to neurons over the range of concentrations optimal for reporter activation (
Activation of Nrf2 by TBHQ, sulforaphane, or CDDO-triterpenoid plays a key role in the antioxidant defense of the central nervous system and has been shown to be important for neuroproteciton in several acute and chronic neuropathological conditions such as stroke, intracerebral hemorrhage, Parkinson's disease, Huntington's disease and amyotrophic lateral sclerosis, and yet Nrf2 activators are only now making their way into the clinic (SHIH et al., J Neurosci, 25: 10321-10335 (2005); CHEN et al., Mol Cell, 34: 663-673 (2009); VARGAS et al., J Neurosci, 28: 13574-13581 (2008)). These findings highlight the biological and clinical importance of a real-time assay for screening and design of Nrf2 activators. The newly developed Neh2-luciferase reporter is perfectly suitable for HTS purposes, for studying the mechanistic details of drug action, and by analogy with HIF ODD-luc system (SAFRAN et al., Proc Natl Acad Sci USA, 103: 105-110 (2006)), we are confident that the new reporter may be successfully used for in vivo imaging of Nrf2 activators in animals.
Genetic antioxidant responses activated by electrophiles are currently monitored via the use of reporters such as firefly luciferase, human alkaline phosphatase, or GFP driven by a canonical antioxidant response element (ARE). Activators of this pathway lead to the stabilization of Nrf2 and induction of dozens of genes that have been shown to prevent cancer, neurodegeneration, proinflammatory states, and combat atherosclerosis. There is a lack of compelling bioassay to ensure real-time monitoring of antioxidant response. We present a novel reporter based on a principle different than the widely used ARE-luciferase. The newly developed reporter constitutively expresses the Neh2 domain of Nrf2 fused to firefly luciferase. The steady-state concentration of Nrf2 (as represented by Neh2 luciferase) established in cells can be manipulated by the addition of compounds affecting the individual steps controlling the Nrf2 stability. The novel reporter allows monitoring the antioxidant response in real-time, right after drug administration, and is suitable both for high throughput screening and elucidation of the mechanism of drug action. The power of the new reporter is illustrated by its application for screening of Spectrum library followed by real-time monitoring of action of selected hits: in addition to the identification of new Nrf2 activators, we for the first time make an insight into the mechanistic details of their action and offer a strategy to discriminate between the action of direct activators such as alkylating agents and those requiring additional transformation steps such as prior oxidation (catechols and diamines) or manipulation of upstream regulatory pathways (via Hsp90 inhibition). Gedunins and their structural analogs were identified as a novel pharmacological class of Nrf2 activators. We also provide biological evidence for Nrf2-dependent neuroprotective roles played by newly identified Nrf2 activators—fisetin, nordihydroguaiaretic acid, and gedunin—in an established model of oxidative stress in neuron-astrocyte coculture.
The present invention also provides a method for the prevention or treatment of a disease characterized by insufficient or overabundance of NRF2 activity in a subject, by administering to the subject a composition comprising a therapeutically effective amount of a modulator of NRF2 and a pharmaceutically acceptable excipient.
In another aspect, the present invention provides pharmaceutically acceptable compositions which comprise a therapeutically-effective amount of one or more of the modulators of NRF2, as described above, formulated together with one or more pharmaceutically acceptable excipients. In another aspect, the present invention provides pharmaceutically acceptable compositions which comprise a therapeutically-effective amount of one or more of the modulators of NRF2, as described above, formulated together with one or more pharmaceutically acceptable excipients and other therapeutically effective medications known in the art allowing for but not limited to combination therapies to improve overall efficacy of each individual therapeutic or to limit the concentration of either therapeutic to avoid side effects and maintain efficacy. The active ingredient and excipient(s) may be formulated into compositions and dosage forms according to methods known in the art. As described in detail below, the pharmaceutical compositions of the present invention may be specially formulated for administration in solid or liquid form, including those adapted for the following: (1) oral administration, for example, tablets, capsules, powders, granules, pastes for application to the tongue, aqueous or non-aqueous solutions or suspensions, drenches, or syrups; (2) parenteral administration, for example, by subcutaneous, intramuscular or intravenous injection as, for example, a sterile solution or suspension; (3) topical application, for example, as a cream, ointment or spray applied to the skin, lungs, or mucous membranes; or (4) intravaginally or intrarectally, for example, as a pessary, cream or foam; (5) sublingually or buccally; (6) ocularly; (7) transdermally; or (8) nasally.
A therapeutically effective amount of the pharmaceutical composition of the present invention is sufficient to treat or prevent a disease characterized by symptoms comprising insufficient or overabundance of NRF2 activity. The dosage of active ingredient(s) may vary, depending on the reason for use and the individual subject. The dosage may be adjusted based on the subject's weight, the age and health of the subject, and tolerance for the compound or composition.
The phrase “pharmaceutically acceptable” is employed herein to refer to those compounds, materials, compositions, and/or dosage forms which are, within the scope of sound medical judgment, suitable for use in contact with the tissues of the subject with toxicity, irritation, allergic response, or other problems or complications, commensurate with a reasonable benefit/risk ratio.
The phrase “pharmaceutically-acceptable excipient” as used herein refers to a pharmaceutically-acceptable material, composition or vehicle, such as a liquid or solid filler, diluent, carrier, manufacturing aid (e.g., lubricant, talc magnesium, calcium or zinc stearate, or steric acid), solvent or encapsulating material, involved in carrying or transporting the therapeutic compound for administration to the subject. Each excipient should be “acceptable” in the sense of being compatible with the other ingredients of the formulation and not injurious to the subject. Some examples of materials which can serve as pharmaceutically-acceptable excipients include: sugars, such as lactose, glucose and sucrose; starches, such as corn starch and potato starch; cellulose and its derivatives, such as sodium carboxymethyl cellulose, ethyl cellulose and cellulose acetate; gelatin; talc; waxes; oils, such as peanut oil, cottonseed oil, safflower oil, sesame oil, olive oil, corn oil and soybean oil; glycols, such as ethylene glycol and propylene glycol; polyols, such as glycerin, sorbitol, mannitol and polyethylene glycol; esters, such as ethyl oleate and ethyl laurate; agar; buffering agents; water; isotonic saline; pH buffered solutions; and other non-toxic compatible substances employed in pharmaceutical formulations. If desired, certain sweetening and/or flavoring and/or coloring agents may be added. Other suitable excipients can be found in standard pharmaceutical texts, e.g. in “Remington's Pharmaceutical Sciences”, The Science and Practice of Pharmacy, 19th Ed. Mack Publishing Company, Easton, Pa., (1995).
Excipients are added to the composition for a variety of purposes. Diluents increase the bulk of a solid pharmaceutical composition, and may make a pharmaceutical dosage form containing the composition easier for the patient and caregiver to handle. Diluents for solid compositions include, for example, microcrystalline cellulose (e.g. Avicel®), microfine cellulose, lactose, starch, pregelatinized starch, calcium carbonate, calcium sulfate, sugar, dextrates, dextrin, dextrose, dibasic calcium phosphate dihydrate, tribasic calcium phosphate, kaolin, magnesium carbonate, magnesium oxide, maltodextrin, mannitol, polymethacrylates (e.g. Eudragit®), potassium chloride, powdered cellulose, sodium chloride, sorbitol and talc.
Solid pharmaceutical compositions that are compacted into a dosage form, such as a tablet, may include excipients whose functions include helping to bind the active ingredient and other excipients together after compression. Binders for solid pharmaceutical compositions include acacia, alginic acid, carbomer (e.g. carbopol), carboxymethylcellulose sodium, dextrin, ethyl cellulose, gelatin, guar gum, hydrogenated vegetable oil, hydroxyethyl cellulose, hydroxypropyl cellulose (e.g. Klucel®), hydroxypropyl methyl cellulose (e.g. Methocel®), liquid glucose, magnesium aluminum silicate, maltodextrin, methylcellulose, polymethacrylates, povidone (e.g. Kollidon®, Plasdone®), pregelatinized starch, sodium alginate and starch.
The dissolution rate of a compacted solid pharmaceutical composition in the subjects's stomach may be increased by the addition of a disintegrant to the composition. Disintegrants include alginic acid, carboxymethylcellulose calcium, carboxymethylcellulose sodium (e.g. Ac Di Sol®, Primellose®), colloidal silicon dioxide, croscarmellose sodium, crospovidone (e.g. Kollidon®, Polyplasdone®), guar gum, magnesium aluminum silicate, methyl cellulose, microcrystalline cellulose, polacrilin potassium, powdered cellulose, pregelatinized starch, sodium alginate, sodium starch glycolate (e.g. Explotab®) and starch.
Glidants can be added to improve the flowability of a non compacted solid composition and to improve the accuracy of dosing. Excipients that may function as glidants include colloidal silicon dioxide, magnesium trisilicate, powdered cellulose, starch, talc and tribasic calcium phosphate.
When a dosage form such as a tablet is made by the compaction of a powdered composition, the composition is subjected to pressure from a punch and dye. Some excipients and active ingredients have a tendency to adhere to the surfaces of the punch and dye, which can cause the product to have pitting and other surface irregularities. A lubricant can be added to the composition to reduce adhesion and ease the release of the product from the dye. Lubricants include magnesium stearate, calcium stearate, glyceryl monostearate, glyceryl palmitostearate, hydrogenated castor oil, hydrogenated vegetable oil, mineral oil, polyethylene glycol, sodium benzoate, sodium lauryl sulfate, sodium stearyl fumarate, stearic acid, talc and zinc stearate.
In liquid pharmaceutical compositions of the present invention, the modulator of and any other solid excipients are dissolved or suspended in a liquid carrier such as water, water-for-injection, vegetable oil, alcohol, polyethylene glycol, propylene glycol or glycerin.
Liquid pharmaceutical compositions may contain emulsifying agents to disperse uniformly throughout the composition an active ingredient or other excipient that is not soluble in the liquid carrier. Emulsifying agents that may be useful in liquid compositions of the present invention include, for example, gelatin, egg yolk, casein, cholesterol, acacia, tragacanth, chondrus, pectin, methyl cellulose, carbomer, cetostearyl alcohol and cetyl alcohol.
Liquid pharmaceutical compositions of the present invention may also contain a viscosity enhancing agent to improve the mouth feel of the product and/or coat the lining of the gastrointestinal tract. Such agents include acacia, alginic acid bentonite, carbomer, carboxymethylcellulose calcium or sodium, cetostearyl alcohol, methyl cellulose, ethylcellulose, gelatin guar gum, hydroxyethyl cellulose, hydroxypropyl cellulose, hydroxypropyl methyl cellulose, maltodextrin, polyvinyl alcohol, povidone, propylene carbonate, propylene glycol alginate, sodium alginate, sodium starch glycolate, starch tragacanth and xanthan gum.
Sweetening agents such as sorbitol, saccharin, sodium saccharin, sucrose, aspartame, fructose, mannitol and invert sugar may be added to improve the taste.
Flavoring agents and flavor enhancers may make the dosage form more palatable to the patient. Common flavoring agents and flavor enhancers for pharmaceutical products that may be included in the composition of the present invention include maltol, vanillin, ethyl vanillin, menthol, citric acid, fumaric acid, ethyl maltol and tartaric acid.
Preservatives and chelating agents such as alcohol, sodium benzoate, butylated hydroxy toluene, butylated hydroxyanisole and ethylenediamine tetraacetic acid may be added at levels safe for ingestion to improve storage stability.
According to the present invention, a liquid composition may also contain a buffer such as guconic acid, lactic acid, citric acid or acetic acid, sodium guconate, sodium lactate, sodium citrate or sodium acetate. Selection of excipients and the amounts used may be readily determined by the formulation scientist based upon experience and consideration of standard procedures and reference works in the field.
Solid and liquid compositions may also be dyed using any pharmaceutically acceptable colorant to improve their appearance and/or facilitate patient identification of the product and unit dosage level.
The dosage form of the present invention may be a capsule containing the composition, for example, a powdered or granulated solid composition of the invention, within either a hard or soft shell. The shell may be made from gelatin and optionally contain a plasticizer such as glycerin and sorbitol, and an opacifying agent or colorant.
A composition for tableting or capsule filling may be prepared by wet granulation. In wet granulation, some or all of the active ingredients and excipients in powder form are blended and then further mixed in the presence of a liquid, typically water, that causes the powders to clump into granules. The granulate is screened and/or milled, dried and then screened and/or milled to the desired particle size. The granulate may then be tableted, or other excipients may be added prior to tableting, such as a glidant and/or a lubricant.
A tableting composition may be prepared conventionally by dry blending. For example, the blended composition of the actives and excipients may be compacted into a slug or a sheet and then comminuted into compacted granules. The compacted granules may subsequently be compressed into a tablet.
As an alternative to dry granulation, a blended composition may be compressed directly into a compacted dosage form using direct compression techniques. Direct compression produces a more uniform tablet without granules. Excipients that are particularly well suited for direct compression tableting include microcrystalline cellulose, spray dried lactose, dicalcium phosphate dihydrate and colloidal silica. The proper use of these and other excipients in direct compression tableting is known to those in the art with experience and skill in particular formulation challenges of direct compression tableting.
A capsule filling may include any of the aforementioned blends and granulates that were described with reference to tableting, however, they are not subjected to a final tableting step.
The present description is further illustrated by the following examples, which should not be construed as limiting in any way. The contents of all cited references (including literature references, issued patents, published patent applications as cited throughout this application) are hereby expressly incorporated by reference.
Cell Lines, Primary Neuronal and Astrocyte Cultures
Human neuroblastoma SH-SY5Y cells were transfected with 1 mg of pcDNA3-Neh2LUC10, pcDNA3-ODDLUC8, pcDNA3-LUC3, and ARE-LUC/pcDNA3 (5:1) by using Lipofectamine—2000 (Invitrogen). Transfected cells were grown in the presence of 500 mg/ml Geneticin (GIBCO-Invitrogen) on DMEM/F12+ GlitaMAX (Dulbecco's modified Eagle medium Nutrient Mixture F-12 (Ham)(1:1) 1×, GIBCO 10565) medium.
Primary neuronal and astrocyte cultures. All animal procedures were performed according to protocols approved by the Institutional Animal Care and Use Committee of the Weill Medical College of Cornell University. Primary astrocyte cultures were prepared from the cerebral cortices of Sprague-Dawley rat pups (P1-3). Primary neuronal cultures were prepared from the forebrains of Sprague-Dawley rat embryos (E17). Following removal of the meninges, the cultures were dissociated as described by Ratan et al. (RATAN et al., Methods Enzymol, 352: 183-90 (2002)). In brief, the brain tissue was dissociated using the protease Papain (Worthington Biochemical Corp). Astrocyte cultures were then seeded at a low density (15,000/mL) on Primaria™ plates (BD Falcon) and grown for ˜2 weeks to confluency in minimal essential medium (MEM—Invitrogen) supplemented with 10% horse serum and 25 units/ml penicillin plus 25 g/ml streptomycin. Upon reaching confluency the astrocytes were treated with 8 μM cytosine-D-arabinofuranoside (Ara-C), a mitotic inhibitor, for ˜3 days to kill off contaminating cells. The astrocytes were used for experiments at 2-3 weeks in culture. GFAP staining confirmed greater than ˜95% purity of the astrocyte cultures. Neuronal enriched cultures were plated at a density of 500,000 cells/mL directly on top of a confluent monolayer of astrocytes in MEM supplemented with 10% horse serum, 2.5% fetal bovine serum and 25 units/ml penicillin plus 25 g/ml streptomycin. Under these conditions, the cultured immature neurons lack glutamate receptors and are therefore not susceptible to glutamate-mediated excitotoxicity. (RATAN et al., Methods Enzymol, 352: 183-90 (2002))
Reporter Plasmid Construction.
DNA fragment encoding 1-97 a.a. residues of Neh2 domain of NRF2 was the product of PCR with a cDNA template obtained from total RNA isolated from SH-SY5Y cells by using NucleoSpin RNAII kit (Macherey-Nagel) and used for cDNA synthesis by SuperScript III First-Strand Synthesis System for RT-PCR (Invitrogen). Neh2 fragment flanked with HindIII and NarI sites was amplified using Advantage 2 polymerase mix (Clontech) and the following primers
Then it was inserted into HindIII and NarI sites of pGL3-control (Promega) to obtain pGL3NEH2LUC. The HindIII-XbaI DNA fragment of pGL3NEH2LUC encoding fusion protein Neh2-luciferase was cloned into corresponding sites of pcDNA3 (Invitrogen) to obtain pcDNA3-Neh2LUC10. The HIF ODDLUC encoding plasmid pcDNA3-ODDLUC8 was constructed as described previously (SMIRNOVA et al., Chem Biol, 17: 380-391 (2010)). pcDNA3-LUC3 encoding plain luciferase was made by insertion of HindIII-XbaI fragment of pGL3-control into HindIII-XbaI sites of pcDNA3. The ARE-luciferase construct contained an ARE promoter consensus sequence as derived from the human NADPH quinone oxidoreductase gene (5′CTCAGCCTTCCAAATCGCAGTCACAGTGACTCAGCAGAATC-3′, SEQ ID NO: 3), upstream of a luciferase reporter (MOEHLENKAMP et al., Arch Biochem Biophys, 363: 98-106 (1999)).
HTS Optimization and SAR Analysis
The assay was optimized for HTS format to provide Z values above 0.7. SH-SY5Y-Neh2-luc cells were plated into 384 well, white, flat-bottom plates at 7000 cell/well in 30 μl serum and incubated overnight at 37° C., 5% CO2. The next day compounds were added to two final concentrations of 16 μM and 32 μM, plates were incubated for 3 hr at 37° C., and luciferase activity was measured using SteadyGlo™ reagent (Promega). Each plate had two internal standards, TBHQ (100%) and DMSO (0%). The reporter activation (%) was calculated as a ratio (L-LDMSO)/(LTBHQ-LDMSO). Hits were defined as those greater than 25%. HTS of 2,000 compounds was performed at Rockefeller University HTS Resource Center. A total of 224 hits from the initial screen have been tested in duplicate, and 210 were confirmed. Classification into structural clusters has been done manually. The line expressing wild-type luciferase under the same promoter was used to evaluate the effect of all compounds from Spectrum library on luciferase activity. None were found to inhibit or enhance the luciferase activity under the experimental conditions, while 46 compounds were found to be toxic at 3 h incubation and were excluded from consideration. The previously described HIF1 ODD-luc reporter line (SMIRNOVA et al., Chem Biol, 17: 380-391 (2010)) was used as a control for specificity.
Summary information on the assay is found in the following table:
Extended SAR Analysis
Selected hits were tested in 96-format white, flat-bottom plates with varied concentrations of an inhibitor (0.05-25 μM). Cells were plated at the density of 25,000 cell per well using a WellMate multichannel dispenser from Matrix (Thermo Fisher Scientific) and grown overnight on DMEM/F12+GlutaMAX (100 μl per well). Then the inhibitor was added, and the plates were incubated for a fixed time interval; the medium was removed, cells lysed in 20 μL (out of which 4 μL were taken for protein measurement), then BrightGlo™ reagent (Promega) was added to the wells and luciferase activity measured on a luminometer Lmax11384 (Molecular Devices). The reporter activation was normalized to the background luminescence divided by protein concentration. Kinetics of reporter activation were measured by adding varied fixed concentrations of an inhibitor at different time points followed by simultaneous cell lysis, protein determination, and luciferase activity measurement in the whole 96-well plate; this assay format minimizes experimental error originating from the well-known instability of luciferase reagent.
Computer Modeling
Docking experiments were performed using the CDOCKER algorithm, followed by force field minimization and binding energy calculations using the molecular mechanics algorithm CHARMm (as implemented in Discovery Studio 2.5, Accelrys, San Diego, Calif.). The crystal structure of human Keap1 kelch domain with the bound 16-mer peptide of human Neh2 (2FLU.pdb) with hydrogen atoms added was used as the starting template structure.
Si RNA Keap1 Knockdown
SiRNA against human Keap1 and control non-specific siRNA were purchased from Thermo Scientific Dharmacon. Neroblastoma SH-SYSY cells carried pcDNA3-Neh2LUC10 or pcDNA3-LUC3 were plated at 3×105 cells per well in 6 well plate. Next day cells were transfected with On-Targetplus Smartpool siRNA Keap1 and ON-TARGETplus Non-Targeting Pool using Lipofectomine 2000 (Invitrogen) according protocol. Transfected cells were probed in luciferase assays and quantitative real-time PCR analysis 24, 48, 72 h after transfection with siRNA.
Real-Time Polymerase Chain Reaction
Total RNA was isolated from SH-SY5Y cells by using NucleoSpin RNAII kit (Macherey-Nagel) and used for cDNA synthesis by SuperScript III First-Strand Synthesis System for RT-PCR (Invitrogen). Quantitative real-time PCR analyses of human KEAP1, GCLC, GCLM, HO-1 and NQO1 were performed by using the corresponding primers and probe set from Applied Biosystems on the ABI 7500 Fast Real Time PCR TaqMan system (Applied Biosystems). GAPDH was used for normalization.
MTT assay
Cell death was monitored simultaneously with luciferase assays by plating cells, in parallel, in the transparent bottom plates and performing two independent assays of cell viability along with luciferase: MTT reduction and phase contrast observation. In all cases, MTT agreed with our morphological assay. The range of concentrations used was chosen to minimize the possibility of cell death in the time interval and concentration range shown. The use of robotics for cell plating results in uniform concentration of cells along the plate, and we have found after validation no need to continue normalization to the cell protein. Additional manipulations in the same well result in increasing the errors in following activity measurements as we established during the HTS optimization.
Redox active glutathione measurements. (PINTO et al., J Chromatogr B Analyt Technol Biomed Life Sci., 877(28): 3434-3441 (2009))
Concentrations of the redox-active glutathione were measured without prior derivatization by high performance liquid chromatography (HPLC) coupled with a coulometric detector. The HPLC system consisted of an ESA Liquid Chromatograph equipped with an 8-channel coulometric array (CoulArray) detector (ESA, Inc., Chelmsford, Mass.). Following rinsing of cell media from cultured cells with PBS, astrocytes were harvested from culture plates by scraping and collected into Eppendoff tubes. Cells were spun at 900×g for 5 minutes, the PBS rinse removed and cell pellets frozen in dry ice. Prior to HPLC analysis, cells were lyzed by addition of 50 μL of ice-cold, de-ionized water followed by addition of 12.5 μL of 25% (w/v) metaphosphoric acid (MPA) with vortexing. Samples were held in an ice bath for 15 minutes and then centrifuged at 50 C. for 10 minutes at 13,000 g in a microfuge to sediment coagulated protein. Protein precipitates were dissolved in 70 μL of 0.1 N NaOH and protein was quantitated by a spectrophotometric method using bicinchoninic acid (BCA) reagent (Pierce Chemical Co., Rockford, Ill.). In many cases, supernatant fractions were analyzed immediately after removal of denatured protein for GSH determination using HPLC separation (see below). The supernatant fractions from 5% MPA homogenates were injected directly onto a Bio-Sil ODS-5S, 5-μm particle size, 4.0×250 mm, C18 column (Bio-Rad, Life Science Research Group, Hercules, Calif.) and eluted with a mobile phase consisting of 50 mM NaH2PO4, 0.05 mM octane sulfonic acid, and 3% (v/v) acetonitrile (pH 2.62) at a flow rate of 1 ml/min. PEEKTM (polyetheretherketone) tubing was used throughout the HPLC system, and 0.2μ PEEKTM filters were placed pre- and post-column to protect both column and flow cells, respectively, from any potential particulate matter. A Rheodyne injection valve with a 5-μl sample loop was used to manually introduce samples. The 8-channel CoulArray detectors were set at 175, 250, 325, 400, 475, 550, 650, and 750 mV, respectively. Peak areas were analyzed using ESA, Inc. software. Concentration of glutathione was obtained from appropriate standard curves, and was normalized as nmol/mg protein.
Western Blotting
Cell cultures were rinsed in PBS then lysed and scraped in RIPA buffer (Boston BioProducts) with 1% Protease Inhibitor Cocktail (Sigma). Lysates were vortexed, incubated on ice for 15 min, sonicated, and stored at −80° C. Protein concentration was determined using BCA Protein Assay Kit (Pierce/Thermo Scientific, Rockford, Ill.). Samples were diluted in water to equalize protein concentration, mixed with Laemmli SDS sample buffer (reducing, 4×), boiled at 100° C. for 5 min, cooled on ice, and centrifuged at 13,000 g for 1 minute immediately before gel loading. Samples were resolved by SDS-PAGE using 10% gels run at 120V for 2 h and transferred onto nitrocellulose membranes at 100V for 1 h. Quantitative Western blots were performed according to the Western Blot Analysis protocol supplied by L1-COR Biosciences (Doc#988-09288). Primary antibodies used were mouse monoclonal antibody for luciferase sc-74548 diluted 1:1000 (Santa Cruz), rabbit polyclonal antibody for beta-actin A2066 diluted 1:10,000 (Sigma), and a rabbit polyclonal antibody for heme oxygenase-1 (Stressgen, 1:1,000). Secondary antibodies used were goat anti-Rabbit IR dye 680 and goat anti-mouse IRDye 800CW (L1-COR Biosciences).
Western Blot for Nrf2.
Whole cell lysates of astrocytes overexpressing Nrf2 (50 μg) were loaded in a precast NuPAGE gel with 4-12% gradient (Invitrogen), run and transferred to nitrocellulose membrane with 100V for 1 hour at 4° C. The membrane was incubated with L1-COR Odissey blocking buffer, L1-COR Biosciences, overnight at 4° C. and for 2 hours at room temperature with the Nrf2 antibody (Abcam, dilution 1:500) and beta-actin antibody (Sigma, dilution 1:5000). The membranes were developed with the L1-COR system (L1-COR Biosciences).
Keap1 Labeling by sulfoxythiocarbate-alkyne (STCA) in Cells
Keap1 labeling experiments were performed as described previously (AHN et al., Proc. Natl. Acad. Soc. USA., 107: 9590-9595 (2010)) with following modifications. HEK293 cells transiently expressing FLAG-Keap1 were incubated with 200 μM competing compounds (sulforaphane, fisetin, quercetin, gedunin, TBHQ, ciclopirox, geldanamycin) in serum-free DMEM for 1 h. After washing with PBS, cells were further incubated with 10 μM sulfoxythiocarbate-alkyne (STCA) for 30 min at 37° C. FLAG-Keap1 was immunoprecipitated from cell lysates, subjected to click reaction with biotin azide on beads, and eluted with SDS-loading buffer. Eluted samples were immunoblotted with Streptavidin-HRP (Pierce) and anti-FLAG antibodies (Sigma).
Adenoviral Transduction
Adenoviral vectors containing cDNA for Nrf2 or Keap1 were obtained from the laboratory of Timothy H. Murphy. Nrf2 was driven by a CMV promoter and a separate CMV promoter also drove the expression of GFP. Keap1 was driven by a CMV promoter and contained a FLAG tag. Cells were treated with the adenoviral plasmids at a multiplicity of infection (MOI)=25 for 4 hr in serum free Opti-MEM media and used ˜24-48 hr following transduction.
Neuronal Viability
Neuronal viability was quantified using a modified protocol (Carrier et al. 2006). Astrocyte-neuron cocultures were 4% paraformaldehyde fixed for 0.5 h at 37° C., then incubated with anitibodies against the neuronal specific marker microtubule associated protein 2 (polyclonal anti-MAP2, 1:500, in 4% normal goat serum and 0.3% triton-x 100) overnight at 4° C. Then the cells were incubated with rabbit secondary antibodies conjugated with horseradish peroxidase (anti-rabbit-HRP, 1:1250, in 4% normal goat serum and 0.3% triton-x 100) for 0.5 h at RT. The fixed cells were incubated with a reaction buffer containing 150 μM Amplex Red and 800 μM H2O2 made up in basal media (135 mM NaCl, 3.8 mM KCl, 1.2 mM MgSO4, 1.3 CaCl2, 1.2 mM KH2PO4, 10 mM D-glucose, 10 mM HEPES, pH=7.4) for approximately 0.5 h at RT; the formation of resorufin was measured on a Spectramax Plus 384 (Molecular Devices) at 560 nm at RT. To account for the non-specific binding of MAP2 to astrocytes, values determined for astrocytes alone were subtracted from coculture values.
MMDLELPPPGLPSQQDMDLIDILWRQDIDLGVSREVEDFSQRRKEYELEKQKKLEKERQEQLQKEQEKAF
FAQLQLDEETGEFLPIQPAQHIQSETS
GSANYSQVAHIPKSDALYFDDCMQLLAQTFPFVDDNEVSSATF
MMDLELPPPG LQSQQDMDLI DILWRQDIDL GVSREVFDFS QRQKDYELEK QKKLEKERQE
QLQKEQEKAF FAQFQLDEET GEFLPIQPAQ HIQTDTS
GSA SYSQVAHIPK QDALYFEDCM
MNLIDILWRQ DIDLGARREV FDFSQRQKEY ELEKQKKLEK ERQEQLQKER EKALLAQLVL
DEETGEFVPA QPAQRVQSEN AEPPISFSQS TDTS
KPEEAL SFDDCMQLLA EAFPFIDDNE
This application claims the benefit of priority from U.S. Provisional Application No. 61/502,600, filed Jun. 29, 2011, the entire contents of which are incorporated herein by reference.
This invention was made with Government support of the Winifred Masterson Burke Relief Foundation, the Adelson Foundation for Neurorehabilitation and Repair, NYS DOH Center of Research Excellence #CO19772, and Thomas Hartman Foundation for Parkinson's Research.
| Number | Date | Country | |
|---|---|---|---|
| 61502600 | Jun 2011 | US |
