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EP1368499A2 - Genes de rats en rapport avec la toxicologie, et leurs utilisations - Google Patents

Genes de rats en rapport avec la toxicologie, et leurs utilisations

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Publication number
EP1368499A2
EP1368499A2 EP02728330A EP02728330A EP1368499A2 EP 1368499 A2 EP1368499 A2 EP 1368499A2 EP 02728330 A EP02728330 A EP 02728330A EP 02728330 A EP02728330 A EP 02728330A EP 1368499 A2 EP1368499 A2 EP 1368499A2
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EP
European Patent Office
Prior art keywords
rct
phase
protein
alpha
genes
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EP02728330A
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German (de)
English (en)
Inventor
Georgia Farris
Samuel H. Hicken
Spencer B. Farr
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Phase-1 Molecular Toxicology Inc
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Phase-1 Molecular Toxicology Inc
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Publication of EP1368499A2 publication Critical patent/EP1368499A2/fr
Withdrawn legal-status Critical Current

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    • C—CHEMISTRY; METALLURGY
    • C07—ORGANIC CHEMISTRY
    • C07K—PEPTIDES
    • C07K14/00—Peptides having more than 20 amino acids; Gastrins; Somatostatins; Melanotropins; Derivatives thereof
    • C07K14/435—Peptides having more than 20 amino acids; Gastrins; Somatostatins; Melanotropins; Derivatives thereof from animals; from humans
    • C07K14/46—Peptides having more than 20 amino acids; Gastrins; Somatostatins; Melanotropins; Derivatives thereof from animals; from humans from vertebrates
    • C07K14/47—Peptides having more than 20 amino acids; Gastrins; Somatostatins; Melanotropins; Derivatives thereof from animals; from humans from vertebrates from mammals
    • C—CHEMISTRY; METALLURGY
    • C12—BIOCHEMISTRY; BEER; SPIRITS; WINE; VINEGAR; MICROBIOLOGY; ENZYMOLOGY; MUTATION OR GENETIC ENGINEERING
    • C12Q—MEASURING OR TESTING PROCESSES INVOLVING ENZYMES, NUCLEIC ACIDS OR MICROORGANISMS; COMPOSITIONS OR TEST PAPERS THEREFOR; PROCESSES OF PREPARING SUCH COMPOSITIONS; CONDITION-RESPONSIVE CONTROL IN MICROBIOLOGICAL OR ENZYMOLOGICAL PROCESSES
    • C12Q1/00—Measuring or testing processes involving enzymes, nucleic acids or microorganisms; Compositions therefor; Processes of preparing such compositions
    • C12Q1/68—Measuring or testing processes involving enzymes, nucleic acids or microorganisms; Compositions therefor; Processes of preparing such compositions involving nucleic acids
    • C12Q1/6876—Nucleic acid products used in the analysis of nucleic acids, e.g. primers or probes
    • C—CHEMISTRY; METALLURGY
    • C12—BIOCHEMISTRY; BEER; SPIRITS; WINE; VINEGAR; MICROBIOLOGY; ENZYMOLOGY; MUTATION OR GENETIC ENGINEERING
    • C12Q—MEASURING OR TESTING PROCESSES INVOLVING ENZYMES, NUCLEIC ACIDS OR MICROORGANISMS; COMPOSITIONS OR TEST PAPERS THEREFOR; PROCESSES OF PREPARING SUCH COMPOSITIONS; CONDITION-RESPONSIVE CONTROL IN MICROBIOLOGICAL OR ENZYMOLOGICAL PROCESSES
    • C12Q2600/00—Oligonucleotides characterized by their use
    • C12Q2600/142—Toxicological screening, e.g. expression profiles which identify toxicity
    • C—CHEMISTRY; METALLURGY
    • C12—BIOCHEMISTRY; BEER; SPIRITS; WINE; VINEGAR; MICROBIOLOGY; ENZYMOLOGY; MUTATION OR GENETIC ENGINEERING
    • C12Q—MEASURING OR TESTING PROCESSES INVOLVING ENZYMES, NUCLEIC ACIDS OR MICROORGANISMS; COMPOSITIONS OR TEST PAPERS THEREFOR; PROCESSES OF PREPARING SUCH COMPOSITIONS; CONDITION-RESPONSIVE CONTROL IN MICROBIOLOGICAL OR ENZYMOLOGICAL PROCESSES
    • C12Q2600/00—Oligonucleotides characterized by their use
    • C12Q2600/158—Expression markers

Definitions

  • TECHNICAL FIELD This invention is in the field of toxicology. More specifically, the invention provides a set of rat genes useful for determining toxicological responses to various agents.
  • FDA Food and Drug Administration
  • Toxicological studies are an important part of drug development but toxicity studies traditionally have required long periods of clinical trials, using both animal models and humans, and are quite often very expensive to conduct.
  • a two year toxicity study in rats can cost approximately $800,000. See, for example, Casarett and Doull's Toxicology, 4th Edition, M.O. Amdur et al., eds. Pergamon Press, New York, N.Y. p. 37 (1991).
  • traditional toxicology studies are no longer sufficient to assess toxicity of a drug or compound because there are too many compounds derived from high throughput screening of combinatorial chemical libraries.
  • traditional toxicological methods have offered little insight into molecular mechanisms of toxicity, which makes extrapolation of toxicity results from animal models to humans difficult.
  • toxicogenetics In recent years, a new field of toxicogenetics has emerged whereby toxicological responses to drugs or compound are studied at a molecular level, e.g., differential gene expression.
  • One major focus of toxicogenetics is the study of differential gene expression induced as an response to chemical or environmental stress.
  • One major goal of most applied toxicology studies is to identify the organ or organs, system, or systems that are damaged by exposure to a drug or other environmental agent. Examples of some major toxic target organs include but are not limited to the liver, kidney, pancreas, heart, lung, brain, fhymus, and hypothalamus.
  • major toxic target systems include but are not limited to the immune, nervous, digestive and circulatory systems.
  • toxicity manifested at the organism level is preceded by altered expression of related genes, then detection of altered gene expression may serve as an early warning for subsequent deleterious outcomes.
  • Altered gene expression may precede organ or system outcomes by weeks, months or even years.
  • measuring the alterations in gene expression may reduce reliance on the observing delayed manifestations of toxicity.
  • Better understanding of molecular mechanisms through toxicogenetics may also improve the predictive accuracy of animal models to humans, and in vitro systems to in vivo settings. A molecular approach to toxicology could save time, money and animal resources.
  • Differential gene expression technology involves detecting the change in gene expression of cells exposed to various stimuli.
  • the stimulus can be in the form of growth factors, receptor-ligand binding, transcription factors, or exogenous factors such as drugs, chemicals, or pharmaceutical compounds.
  • PCR polymerase chain reaction
  • RT-PCR reverse transcriptase polymerase chain reaction
  • microarray technology provides a faster and more efficient method of detecting differential gene expression. Differential gene expression analysis by microarrays involves nucleotides immobilized on a substrate whereby nucleotides from cells which have been exposed to a stimulus can be contacted with the immobilized nucleotides to generate a hybridization pattern.
  • This microarray technology has been used for detecting secretion and membrane-associated gene products, collecting pharmacological information about cancer, stage specific gene expression in Plasmodium falciparum malaria, translation products in eukaryotes, and a number of other scientific inquiries. See, for example, Diehn M, et al. Nat Genet. 25(1): 58-62 (1993); Scherf, U., et al. Nat Genet. 24(3): 236-44 (1993); Hayward R.E., et al. MolMicrobiol 35(1): 6-14 (1993); Johannes G., et al. Proc Natl Acad Sci USA 96(23): 13118-23 (1993).
  • Microarray technology has also been used in exploring drug- induced alterations in gene expression in Mycobacterium tuberculosis. See, for example, Wilson M., et al. Proc Natl Acad Sci. 96(22): 12833-8 (1999).
  • the invention provides toxic response genes and uses thereof.
  • the invention provides a method of evaluating the toxicity of an agent by (a) exposing a test animal to the agent; (b) measuring the expression of one or more toxic response genes selected from the genes corresponding to the partial gene sequences in Tables 6, 7, 8, 9, and 10 in the test animal in response to the agent, thereby generating a test expression profile; and (c) comparing the test expression profile with a reference expression profile indicative of toxicity, wherein toxicity of the agent is evaluated by determining whether a significant correlation exists between the test expression profile and the reference expression profile.
  • the group of genes corresponding to the partial gene sequences is responsive in kidney, liver, spleen, heart, lung, testis, or brain.
  • the test animal is a rat, dog, non-human primate, or a human.
  • the agent is administered at various dosages or for various lengths of time.
  • the invention provides a method of evaluating the toxicity of an agent by (a) exposing a test animal to the agent; (b) measuring the expression of one or more toxic response genes selected from the genes corresponding to the partial gene sequences in Tables 6, 7, and 8 in the test animal in response to the agent, thereby generating a test expression profile; and (c) comparing the test expression profile with a reference expression profile indicative of toxicity, wherein toxicity of the agent is evaluated by determining whether a significant correlation exists between the test expression profile and the reference expression profile.
  • the group of genes corresponding to the partial gene sequences is responsive in kidney, liver, spleen, heart, lung, testis, or brain.
  • the test animal is a rat, dog, non-human primate, or a human.
  • the agent is administered at various dosages or for various lengths of time.
  • the invention provides a method of evaluating the toxicity of a agent by (a) exposing a test animal to the agent; (b) measuring the expression of one or more toxic response genes selected from the genes corresponding to the partial gene sequences in Table 4 in the test animal in response to the agent, thereby generating a test expression profile; and (c) comparing the test expression profile with a reference expression profile indicative of toxicity, wherein toxicity of the agent is evaluated by determining whether a significant correlation exists between the test expression profile and the reference expression profile.
  • the set of toxicologically relevant genes consists of at least 25 genes.
  • the set of toxicologically relevant genes consists of at least 50 genes.
  • the set of toxicologically relevant genes consists of at least 100 genes.
  • the invention provides an array which includes one or more polynucleotides selected from the genes corresponding to the partial gene sequences in Tables 6, 7, 8, 9, and 10 or fragments of at least 20 nucleotides thereof.
  • the group of genes corresponding to the partial gene sequences is responsive in kidney, liver, spleen, heart, lung, testis, or brain.
  • the invention provides an array which includes one or more polynucleotides selected from the genes corresponding to the partial gene sequences in Tables 6, 7, and 8 or fragments of at least 20 nucleotides thereof.
  • the group of genes corresponding to the partial gene sequences is responsive in kidney, liver, spleen, heart, lung, testis, or brain.
  • the invention provides an array which includes one or more polynucleotides selected from the group consisting of the genes corresponding to the partial gene sequences in Table 4 or fragments of at least 20 nucleotides thereof.
  • the set of toxic response genes consists of at least 25 genes.
  • the set of toxic response genes consists of at least 50 genes.
  • the set of toxic response genes consists of at least 100 genes.
  • the invention provides an array which includes a set of polynucleotides of at least 20 nucleotides in length substantially homologous to a set of toxic response genes selected from the genes corresponding to the partial gene sequences in Tables 6, 7, and 8.
  • the invention provides an array which includes one or more polynucleotides which are homologous to the polynucleotides contained in the array which includes one or more polynucleotides selected from the genes corresponding to the partial gene sequences in Tables 6, 7, and 8 or fragments of at least 20 nucleotides thereof.
  • the polynucleotides correspond to human, murine, non- human primate, or canine genes.
  • Figure 2 depicts the similar differential gene expression response in two different organs from two rats given the same treatment of lipopolysaccharide (LPS)- treated rats at 6 hours post-exposure.
  • the data shown is liver data from two rats (the first and second bars for each gene) and kidney data from two rats (the third and forth bar for each gene).
  • LPS lipopolysaccharide
  • Figure 3 depicts the progression of toxicity-induced differential gene expression in rat liver over time. Rats were treated with lipopolysaccharide (8 mg/kg) by a single intraperitoneal injection.
  • Figure 6 depicts a correlation matrix of four mechanistic classes of toxic compounds.
  • the gene expression data from a rat CT array tested in rat liver was identified by successive pairwise gene identification. The areas of white boxes signify higher correlations.
  • the abbreviations are as follows: PAH: Polyaromatic Hydrocarbons, TCDD, Benzo(a)pyrene, Dimethylbenzanthracene; PP: Peroxisome Proliferators, Gemfibrozil, Diethylhexyl phthalate, Wy 14,643; CS: Corticosteroids, Prednisone, Triamcinolone; NM: Nitrogen Mustards, Mechlorethamine, Cyclophosphamide, Melphalan, Chlorambucil.
  • Figure 7 depicts the very similar response of the gene cytochrome P450 1 A2 using the microarray platform (O symbols and dashed line) and the the TacMan real time PCR platform ( ⁇ symbols and solid lines).
  • Figure 8 depicts the very similar response of the gene fatty acid synthase using the microarray platform (O symbols and dashed line) and the TacMan real time PCR 0 platform (D symbols and solid lines).
  • Figure 9 depicts the very similar response of the gene multidrug resistant protein- 1 using the microarray platform (O symbols and dashed line) and the the TacMan real time PCR platform (D symbols and solid lines).
  • Table 1 is a list of pharmaceutical agents which can potentially cause greatly heightened toxic responses in some individuals.
  • Table 2 is a list of industrial agents which can potentially cause greatly heightened toxic responses in some individuals.
  • Table 3 is a list of the drugs and chemicals used to generate the data shown in tables 7, 8, 9, and 10. These compounds were selected for their ability to induce the following pathologies: liver degeneration/necrosis, hepatocyte hypertrophy, hepatocyte vacuoles, renal tubular degeneration/necrosis, renal glomerular necrosis, myocardial degeneration, myocardial inflammation, splenic lymphoid depletion / apoptosis, splenic lymphoid hyperplasia, neurotoxicity, skeletal muscle degeneration and inflammation, multiple tissue necrosis and inflammation, repair, including proliferation.
  • Table 4 is a list of the 700 rat genes and/or gene sequences that have been determined to be toxic response genes.
  • Sequences using Ml 3 reverse primer include: TAATACGACTCACTATAGGGAATTTGGCCCTCGAGGCCAAGAATTC (SEQ ID NO: 701) which can be followed by an insert which can also be followed by
  • ATTAACCCTCACTAAAGGGAATAAGCTTGCGGCCGC (SEQ ID NO: 703) which can be followed by an insert which can also be followed by
  • the third set of genes in this table refer to the genes chosen on the basis of their possible role in critical cellular pathways and empirical data toxicity responsiveness.
  • the clones for this third set of genes used the pCRII-TOPO vector.
  • the gene sequences in this Table 4 may include a small portion of vector in the sequence. Portions of the following vector sequence are what may be included in the sequence listed in Table 4 and should not be included when referring to the gene or gene sequence itself.
  • Sequences using T7 promoter as primer include: ATATCTGCAGAATTCGCCCTT
  • Table 6 is a list of the genes discovered by testing of 17,241 genes on a 17,241 gene microarray and the response data that provided the basis for choosing each gene. These 400 genes were selected after a first filtering of all gene data for acceptable fold induction values (>2), coefficient of variance (CON, ⁇ 30), and fluorescent value (fluor, >400) then ranking the genes that met these criteria by the number of experiments in which the gene responded, COV between duplicate slides, and fold induction. The name of the gene is followed by the list of compounds that induced an acceptable response (passed the filters) and the specifics of the tissue evaluated, the dose of the drug or chemical, and the timepoint that the animal was sacrificed after intraperitoneal injection of the compound.
  • Table 7 is a list which shows the tissue specific response of the toxicology genes chosen empirically from the 17,241 gene set. The data evaluated for. this tissue response was obtained by dosing rats with the compounds listed in Table 3 and then determining the differential gene expression to compile a database with approximately 2500 experiments (i.e., data from one microarray). The tissue response is greater than 2 fold in 1% of the experiments for the specific tissue for liver and kidney and greater than 2 fold in 2% of the experiments for the specific tissue for heart, lung, spleen, testis, and brain. This table is organized by data for each gene.
  • Table 8 is a list which shows tissue specific response of the toxicology genes in Table 7 with organization by tissue.
  • Table 9 is a list which shows the tissue specific response of the toxicology genes chosen by description of their role in critical cellular pathways.
  • the data evaluated for this tissue response was obtained by dosing rats with the compounds listed in Table 3 and determining the differential gene expression to compile a database with approximately 2500 experiments.
  • the tissue response is greater than 2 fold in 1% of the experiments for the specific tissue for liver and kidney and greater than 2 fold in 2% of the experiments for the specific tissue for heart, lung, spleen, testis, and brain. This table is organized by data for each gene.
  • Table 10 is a list which shows tissue specific response of the toxicology genes in Table 9 with organization by tissue.
  • the present invention provides a set of toxicologically relevant rat genes which can be used to evaluate a toxic response to drugs, chemicals, and/or compounds.
  • Toxicity refers to the exaggerated microscopic or macroscopic responses of cells, tissues, organs or systems to low or average doses of an agent.
  • frank toxicity refers to toxicity in which macroscopic responses can be observed. Examples of frank toxicity responses include but are not limited to clinical observations, serum chemistry values, hematology values, urinalysis values, histopathology results, or gross appearance of the tissues and organs at necropsy.
  • a “toxicological response” refers to a cellular, tissue, organ or system level response to exposure to an agent and includes, but is not limited to, the differential expression of genes and/or proteins encompassing both the up- and down-regulation of such genes; the up- or down-regulation of genes which encode proteins associated with the repair or regulation of cell damage; or the regulation of genes which respond to the presence of an agent.
  • toxicity gene(s) "toxicologically relevant gene(s)”, and “toxic response gene(s)” as used herein are interchangeable. These terms can be defined as a gene whose message or protein level is altered by adverse stimuli. The specific set of genes that cells induce is dependent upon, inter alia, the type of damage or toxic threat caused by the agent and which organs are the most threatened.
  • Gene expression indicative of toxicological response refers to the relative levels of expression of a toxicity gene or toxic response gene.
  • Profiles of gene expression profiles may be measured in a sample, such as samples comprising a variety of cell types, different tissues, different organs, or fluids (e.g., blood, urine, spinal fluid or serum). These profiles can include “test expression profile” and “reference expression profile”.
  • Substantially homologous or “substantially identical” refers to sequence homology wherein at least 70%, preferably at least 80%, preferably at least 85%, and more preferably at least 90% nucleotide or amino acid residue identity, when compared
  • nucleotide can be compared over their full-length (e.g., the length of the shorter of
  • test sequences typically one sequence acts as a reference sequence, to which test sequences are
  • test and reference sequences are compared.
  • subsequence coordinates are designated, if necessary, and
  • a further indication that two nucleic acid sequences or polypeptides are substantially identical is that the first polypeptide (e.g., a polypeptide encoded by the first nucleic acid) is immunologically cross reactive with the second polypeptide (e.g., a polypeptide encoded by the second nucleic acid).
  • a polypeptide is typically substantially identical to a second polypeptide, for example, where the two peptides differ only by conservative substitutions.
  • gene refers to polynucleotide sequences which encode protein products and encompass RNA, mRNA, cDNA, single stranded DNA, double stranded DNA, complement strands, and fragments thereof. Genes can include introns and exons.
  • gene sequence(s) refers to gene(s), full-length genes or any portion thereof.
  • arrays and “microarray” are interchangeable and refer to an arrangement of a collection of nucleotide sequences in a centralized location.
  • Arrays can be on a solid substrate, such as a glass slide, or on a semi-solid substrate, such as nitrocellulose membrane.
  • the nucleotide sequences can be DNA, RNA, any permutations thereof, and include nucleotide analogs.
  • the nucleotide sequences can also be partial sequences from a gene, primers, whole gene sequences, non-coding sequences, coding sequences, published sequences, known sequences, or novel sequences.
  • An "agent" to which an individual can exhibit a toxicological response can include, for example, drugs, pharmaceutical compounds, household chemicals, industrial chemicals, environmental chemicals, and other chemicals and compounds to which individuals may be exposed. Exposure to an agent can constitute physical contact as well as secondary contact, such as inhalation and environmental exposure.
  • Differential expression refers to the change in expression levels of genes, and/or proteins encoded by said genes, in cells, tissues, organs or systems upon exposure to an agent.
  • differential gene expression includes differential transcription and translation, as well as message stabilization. Differential gene expression encompasses both up- and down-regulation of gene expression.
  • Rat refers to a mammal from the Rattus genus which can include any one of numerous rodents (Rattus and related genera) differing from related mice by considerably larger size and by structural details (e.g., size of teeth). Rats strains which may be used include but are not limited to Sprague-Dawley, Wistar, and Fisher.
  • sample refers to substances supplied by an individual.
  • the samples may comprise cells, tissue, parts of tissues, organs, parts of organs, or fluids (e.g., blood, urine or serum). Samples are characterized in a preferred embodiment by comprising at least two different genes and may also include genes from multiple cell types. Samples include, but are not limited to, those of eukaryotic, mammalian or human origin.
  • the terms "protein”, “polypeptide”, and “peptide” are used interchangeably herein to refer to polymers of amino acids of any length.
  • the polymer may be linear or branched, it may comprise modified amino acids, and it may be interrupted by non- amino acids.
  • polypeptides containing one or more analogs of an amino acid including, for example, unnatural amino acids as well as other modifications known in the art.
  • the term "significant correlation” has the normal meaning in the art and means that the probability of the observed difference (or in the case of "similar” measurements, the probability of a observed absence of difference) occurring by chance (the p-value) is less than some predetermined level, i.e., a p-value that is ⁇ 0.05, preferably ⁇ 0.01 and more preferably ⁇ 0.001.
  • a p-value that is ⁇ 0.05, preferably ⁇ 0.01 and more preferably ⁇ 0.001.
  • suitable statistical methods are well known to those of skill can be used to measure statistical significance (e.g., standard statistical methods such as Student t-tests ⁇ for comparing two samples ⁇ ,
  • ANOVA analysis of variance ⁇ , and confidence interval analysis; software such as the SAS System Version 8 (SAS Institute Inc., Gary, NC, USA) can be used for analysis).
  • mammals include, but are not limited to, farm animals, sport animals, pets, primates, mice and rats. III. Identifying a set of toxicologically relevant genes
  • Identification of a set of toxicologically relevant genes can be achieved by several methods.
  • One method which can be used is to clone genes previously described to be potentially relevant in toxicology. Using published sequences, for example in literature or from GenBank, primers can be made and then used to PCR amplify from a relevant library to obtain the candidate toxicologically relevant gene of interest which can then be cloned into a plasmid or an expression vector, depending on the use desired.
  • the gene sequence (full or partial) can be placed amongst other toxicologically relevant genes in a microarray for high-throughput testing, as disclosed infra.
  • a plasmid may be used to grow high copies of the candidate toxicologically relevant gene of interest which can then be purified by any commercially available kit (e.g., from Qiagen or Promega).
  • the purified candidate toxicologically relevant gene may be used for "spotting" in a microarray or alternatively, the purified nucleic acid can then be inserted into an expression vector, transfected into mammalian cells, e.g., rat cells, and then the cells can be exposed to a compound and observed for toxicological responses.
  • Frank toxicity may be ascertained by , observing changes in cell morphology or re-arrangement of cytoskeleton, which can be determined by examination under a microscope, or alternatively, cell apoptosis or necrosis.
  • "transcriptome profiling" described in greater detail below, may be used whereby nucleic acid can be isolated from both the exposed and unexposed cells and examined to determine which level of the compound causes the up-regulation or down-regulation of the toxicologically relevant gene of interest.
  • Another method which can be used to identify a set of toxicologically relevant genes is to test available rat genes, of which there are approximately 17,421 known rat genes, for the genes' response using tissues from rat toxicity studies and select those with differential expression. Differential expression may be assessed by any number of methods.
  • One method which may be used is by microarray analysis.
  • Provided herein are methods of using microarray analysis to determine differential gene expression.
  • Another method of determining differential gene expression is by reverse transcriptase- polymerase chain reaction (RT-PCR), e.g., Taqman® technology.
  • RT-PCR reverse transcriptase- polymerase chain reaction
  • Taqman® technology Provided herein are methods of using Taqman® technology.
  • Yet another method which could be used to detect differential gene expression is Invader® technology, commercially available from Third Wave.
  • One method which can be used to identify a set of toxicologically relevant genes is to use an "open system" to compare gene expression profiles from control rats and rats treated with an agent to select responsive genes.
  • comparisons between gene expression profiles from control rat cells (or rat cell lines) and rat cells (or rat cell lines) treated with an agent can be used to select responsive genes.
  • This is referred to herein as "transcriptome profiling”.
  • This method empirically determines which genes are toxicologically relevant by analyzing differential gene expression.
  • experimental rats are divided into two groups. One group is exposed to one or more agent(s) at different concentrations for different lengths of time. Another group of rats is not exposed to any agent and serves as the control group.
  • Rats are then sacrificed and organs such as liver, spleen, kidney, testes, heart, lung, and thymus are harvested for cells to perform molecular analysis of gene expression.
  • organs such as liver, spleen, kidney, testes, heart, lung, and thymus are harvested for cells to perform molecular analysis of gene expression.
  • analysis of serum proteins in the circulating blood can provide another measure to compare with unexposed rats.
  • RNA of both groups is isolated and reverse transcribed in PCR reactions to generate cDNA which in turn is amplified to generate double stranded DNA.
  • the PCR is performed in the presence of a radioactive DNA substrate that is incorporated into the double stranded
  • DNA On a polyacrylamide gel, the DNA derived from the treated cells is separated by length next to the DNA derived from untreated population. The intensity of the resulting band or bands is compared between the treated and untreated groups of cells. Bands that show different radioactive intensity are excised from the gel, amplified by PCR, cloned, and sequenced. The sequences are compared with known gene sequences in the public databases such as GenBank. In this manner, novel rat genes, in addition to known rat genes with varying degrees of similarity, which are toxicologically relevant are discovered and identified. The examples disclosed herein illustrates how this aspect of the invention may be practiced by the skilled artisan.
  • a full-length gene is obtained by using the portion of the rat gene sequence which is known to make primers and then use the primers in combination with random primers in PCR reactions with a rat cDNA library. The PCR reaction are run on a standard agarose gel and amplified bands are identified, excised from the gel, and sequenced.
  • the agent to be tested can selected on the basis of different criteria.
  • the basis of a compound to test is damage observed in specific organs.
  • cisplatin, amphotericin B and gentamicin are selected because they have been observed to cause kidney tubular epithelial cell damage.
  • clofibrate, gemfibrozil, and WY 14643 are selected because liver peroxisome proliferation has been observed to be affected by clofibrate, gemfibrozil, and WY 14643.
  • a basis for selection is function.
  • cisplatin causes apoptosis and reactive oxygen species
  • amphotericin B causes increased permeability of cell membranes to ions and renal vasoconstriction
  • gentamicin causes phospholipid accumulation in lysosomes.
  • kidney toxicants include but are not limited to cisplatin, gentamicin, puromycin, and amphotericin B.
  • Liver toxicant include but are not limited to chlorpromazine, clofibrate, diflunisal, tetracycline, erythromycin, and ethanol.
  • Immunotoxicants include but are not limited to cyclosporin A, lipopolysaccharide (LPS), hydroxyurea, phenylhydrazine, dexamethasone, estradiol, and tamoxifen.
  • Heart toxicant includes but is not limited to doxorubicin.
  • Multiorgan toxicants include but are not limited to methotrexate and cadmium chloride.
  • Dosages of agents to use in rat experiments can be determined using several methods. In one aspect, reported dosages are used as a starting point and dose incrementally above and below the reported dosage. Increments can be at least about
  • Upregulation or downregulation of markers in the blood including but not limited to: serum chemistry
  • hematology values and hematology values can be used to determine if toxicity has been reached.
  • examining the histopathology of organs, in particular, organs which are the specific targets of the compound of interest may be used to determine if a
  • pathological changes include liver degeneration/necrosis, hepatocyte hypertrophy, hepatocyte vacuoles, renal tubular degeneration/necrosis, renal glomerular necrosis, myocardial degeneration, myocardial inflammation, splenic lymphoid depletion / apoptosis, splenic lymphoid hyperplasia, neurotoxicity, skeletal muscle degeneration and inflammation, multiple tissue necrosis and inflammation, repair, including proliferation.
  • the molecular changes in response to administration of different doses of one or more agents is determined by
  • a low dosage level of the agent is added and then in a step-wise manner, the dosage is increased as well as length of time exposed to the agent. If the agent is lipophilic and easily crosses the lipid bilayer of cells, a lower initial concentration may be used and/or shorter length of time exposed to the agent.
  • the agent possesses the nature that would not cross the cell barrier easily and would need to be actively or passively transported across cell membranes, then a slighter higher initial concentration may be used and/or longer length of time exposed to the agent.
  • Increasing dosage step- wise while monitoring toxicological response and morphology of the cells, rate of death of the cells, and growth patterns allows the skilled artisan to determine the dosage at which a toxicological response occurs.
  • toxicological responses may occur which are visible changes, including but not limited to, physical structure and integrity of the cells (e.g., morphology, growth pattern, etc.).
  • Monitoring for cellular toxic responses as well as molecular toxic responses, e.g., differential gene expression increases the likelihood of finding preferable dosages.
  • Changes in gene expression are toxicologically significant at that dosage at which removal or diminishment of the treatment no longer results in a return to normalcy, i.e., the state of a cell, organ, or system that existed prior to the treatment with the compound. Treatments beyond a certain dosages or time period may commit the cell to a toxicologically-relevant fate. This toxic dosage is reflected by an identifiable gene expression pattern, which is distinct from the pattern observed below the toxic dosage.
  • the route can vary, and can be intraperitoneal, intravenous, subcutaneous, transcutaneously, intramuscular, enterally, transdermally, transmucously, sustained release polymer compositions (e.g., a lactide polymer or co-polymer microparticle or implant), perfusion, pulmonary (e.g., inhalation), nasal, oral, etc.
  • Injectables can be prepared in conventional forms, either as liquid solutions or suspension, solid forms suitable for solution or suspension in liquid prior to injection, or as emulsions.
  • the agents can be administered in a pharmaceutically acceptable form, for example, with an excipient.
  • Suitable excipients include, for example, water, saline, aqueous dextrose, glycerol, ethanol or the like.
  • Formulations for parenteral and nonparenteral delivery of one or more agents are known in the art and described in greater detail in Remington: The Science and Practice of Pharmacy, Mack Publishing (2000).
  • a carrier is used to administer the agent, the carrier must be acceptable in the sense of being compatible with the agent to be tested and not deleterious (i.e., harmful) to the rat to be treated.
  • conventional non-toxic carriers include, for example mannitol, lactose, starch, magnesium stearate, magnesium carbonate, sodium saccharin, talcum, cellulose, glucose, sucrose, pectin, dextrin, tragacanth,
  • methyl cellulose sodium carboxymethyl cellulose, a low-melting wax, cocoa butter,
  • the active compound as defined above may be formulated as suppositories using, for example, polyalkylene glycols, for example, propylene glycol
  • the agent to be administered will preferably contain a quantity of the agent in an amount sufficient to effect some sort of toxicological response in the rat,
  • rat genes which are candidate toxicologically relevant genes have
  • cD ⁇ A library can be made from different rat cells, obtained ex vivo or from a commercial source, for example, American Type Culture Collection (ATCC).
  • ATCC American Type Culture Collection
  • the generation of a cD ⁇ A involves reverse transcribing isolated R ⁇ A and is well-known in the art (see for
  • the rat gene fragments, amplified by PCR, are cloned into any standard plasmid expression vector which can be obtained from numerous commercial sources (e.g., Promega, InVitrogen, New England BioLabs, etc.) and sequenced.
  • the resulting sequence information is then compared to the GenBank database to confirm that the cloned DNA is the specific rat gene for which the primers were designed.
  • the amplified gene is then added to the panel of genes to be included in the array.
  • non-rat e.g., human
  • Primers to these toxicologically relevant non-rat genes are designed, synthesized, and are subsequently used in PCR reaction with rat cDNA libraries to amplify the homologous rat gene.
  • the homologous rat gene may or may not be the exact sequence as the non-rat gene with which the primers were designed. Amplified rat gene is then added to the panel of genes to be included in the array.
  • rat genes or gene sequences which are toxicologically relevant or are candidate toxicologically relevant genes are used to determine toxicologically relevant genes in other rodents, e.g., mice.
  • target sequences for inclusion in a rat a ⁇ ay are obtained by de novo synthesis of nucleotides which are immobilized on a substrate, e.g., a glass slide.
  • the target sequences are from genes which can indicate one or more toxicological responses.
  • differential display can be used to identify genes of interest. Differential gene expression can be observed by using techniques involving gel electrophoresis and polynucleotide microarrays or commercially available technologies, e.g., Invader® or Taqman®.
  • the results of PCR synthesis of mRNA isolated from tissues of treated and control rats or cell lines are subjected to gel electrophoresis, and the bands produced by these mRNA populations are compared. Bands present on an image of one gel from one mRNA population, and not present on another, correspond to the presence of a particular mRNA in one population and not in the other, and thus indicate a gene that is likely to be differentially expressed.
  • RNA derived from control and treated rat or cell lines can be compared by using arbitrary oligonucleotide sequences often nucleotides (random 10-mers) as a 5' primer and a set of 12 oligonucleotides complimentary to the poly A tail as a 3' fluorescent labeled "anchor primer". These primers are then used to amplify partial sequences of mRNAs with the addition of deoxyribonucleotides. These amplified sequences are then resolved on a sequencing gel such that each sequencing gel has a sequence of 50-100 mRNAs. The sequencing gels are then compared to each other to determine which amplified segments are expressed differentially (Liang, P. et al. Science 257:967, 1992; Welsh, J. et al., Nucl. Acid Res. 20:4965, 1992; Liang, P., et al.,
  • Rat cells can be obtained from various sources including, but are not limited to, tissue samples, organs, blood, skin, biological fluids (e.g., urine, spinal fluid, semen, etc.), and cell lines. Transcriptome profiling may also be obtained in rats dosed in vivo. Immortalized cell lines are obtained from commercial sources, e.g., Gibco BRL Life Sciences, or from other sources, e.g., American Type Culture Collection (ATCC). Other methods of obtaining rat cells include isolating cells obtained from tissue biopsies, blood, skin, or biological fluids, for example from rats dosed in vivo. As is well known to one of skill in the art, isolating cells from tissue samples can be achieved using any variety of techniques.
  • Sources from which cells are obtained can be any number of organs, including but not limited to liver, lung, heart, testis, kidney, spleen, thymus, and brain.
  • liver cells may be used for toxicity studies where the agent to be administered is known or thought to induce liver malfunctions or liver toxicity.
  • the use of cells deriving from the target organ may yield more beneficial information regarding toxicological responses than if a tissue were selected at random.
  • a panel of cells isolated from different sources may be used.
  • liver cells may be used in the absence of knowledge of the agent's target of action because the liver is known to process many toxins.
  • liver cells may be used that toxicologically relevant genes may be identified and then subsequently tested on other organs to determine toxicity in the other organs or alternatively, to identify which organ(s) is the target for the agent.
  • Time would be saved testing cells from one tissue source (liver in this situation) instead of isolating cells from many tissue sources. Rat cells obtained ex vivo or from a commercial or non-commercial source can be used fresh from a necropsy or frozen for storage and then cultured in media at time of experimentation.
  • basal cell-sustaining media that can be used to keep the pH of the liquid in a range that promotes survival of rat cells.
  • basal cell-sustaining media include F12/DMEM, Ham's F10 (Sigma), CMRL-1066, Minimal essential medium (MEM, Sigma), RPMI-1640 (Sigma), Dulbecco's Modified Eagle's Medium
  • DMEM fetal calf serum
  • IMEM Iscove's Modified Eagle's Medium
  • Cells can be grown in plates or in flasks. Cells are grown and expanded to a level desired and needed for DNA or RNA isolation. Cells are removed from the plate or flask to isolate DNA or RNA. If the cells are adherent, trypsin or another equivalent may be used to release the cells from the plate or flask.
  • At least about lxlO 2 cells are used as sources for DNA and RNA.
  • rats are dosed, tissues harvested (and nucleic acids isolated) after exposure to toxic doses of drugs/chemicals in vivo. This embodiment is further described in the Examples.
  • the isolated nucleic acid is then amplified to generate a product which can be attached to a substrate.
  • the substrate is a solid substrate (e.g. , glass slide).
  • the amplification process involves using primers which have a reactive group (e.g., amine group or derivative thereof) on one end of the primer, which is incorporated into the amplification product.
  • a reactive group e.g., amine group or derivative thereof
  • One example of reactive primers that can be used is Amine Primers from Synthegen.
  • the gene fragments which are attached to the glass slide can vary in length. The more nucleotides of a gene that are in the array, the tighter the binding and the greater the specificity in binding can occur.
  • the desired length of a gene or a fragment thereof that is to be included in the array should take into consideration the balance between a high specificity of binding obtained with a long (e.g., >1 kb) gene sequence with the high mutational rate associated with a longer fragment.
  • the gene fragments attached to the glass slide are at least about 25 base pairs
  • the gene fragments are about 500 bp in length.
  • the region of a gene that is used to attach to a solid substrate to generate an array can be any portion of the gene, coding, non-coding, 5' end, 3' end, etc. In a preferred embodiment, about 500 base pairs of the 3' end of rat gene related to toxicological responses are selected to be included in an array.
  • a method is to attach an amine group, a derivative of an amine group, another group with a positive charge or another group which is reactive to one end of a primer that is used to amplify a gene or a gene fragment to be included in the array. Subsequent amplification of a PCR product will then incorporate this reactive group onto one end of the product.
  • the amplified product is then contacted with a solid substrate, such as a glass slide, which is coated with an aldehyde or another reactive group which will form a covalent link with the reactive group that is on the amplified PCR product and become covalently attached to the glass slide.
  • a solid substrate such as a glass slide
  • an aldehyde or another reactive group which will form a covalent link with the reactive group that is on the amplified PCR product and become covalently attached to the glass slide.
  • arrays of polymers, such as nucleic acids, immobilized on a solid substrate are disclosed, for example, in U.S. Pat.
  • NHL Algorithms for analysis and evaluation of toxicologically relevant genes A multi-step approach can be used in ranking candidate genes from rat genes, for example, a' set of 17,421 rat genes, known herein as "17K array", for possible inclusion on a comprehensive toxicity (CT) array.
  • 17K array a' set of 17,421 rat genes, known herein as "17K array”
  • CT comprehensive toxicity
  • three cutoff criteria can be specified for individual gene values from whatever experiments result from using the 17K array: 1) Fold Induction/Repression level, 2) Average Fluorescence level of the replicate spots (reflection of the expression level) and 3) Coefficient of Variation of the replicate spots.
  • the initial screening to make the "cut” may be based on expression level and measurement quality.
  • gene values that would made the cut were aggregated into overall scores, and ranked for each gene, may be based on six ranking criteria: 1) Number of slides on which that gene met the cutoff criteria (NC), 2) Percent of consistency between slides (% of time the gene value made the cutoff criteria on the replicate slide for that initial slide) (CC), 3) Average magnitude (absolute value) of fold induction for all occurrences where that gene made the cutoff criteria (FI), 4) Coefficient of Variation of those fold induction scores (unlike all the other ranking criteria, lower is deemed better) (CV), 5) Average fluorescence value of all replicate spots of occurrences where that gene made the cutoff criteria (FL), and 6) Tissue consistency (what percent of cutoff-meeting occurrences of the gene were in the same tissue) (CT).
  • NC Number of slides on which that gene met the cutoff criteria
  • CC Percent of consistency between slides (% of time the gene value made the cutoff criteria on the replicate slide for that initial slide)
  • FI Average magnitude (absolute value) of
  • Each gene was assigned a score between 0 and 100 for each ranking criterion.
  • Each ranking criterion score was computed as follows: The range of values for all genes was computed for the criterion by subtracting the lowest value present among all scores from the highest. The score for each gene was then calculated by subtracting the lowest value present from the value for that gene, then dividing by the range and multiplying by 100. In other words, the score for each gene is the percent above the minimum present toward the maximum. For example, if a gene's score was three-fourths of the way between the minimum present and the maximum for that criterion, its score would be 75%. Since for the CV factor (coefficient of variation of fold inductions) lower was deemed better, the score thus computed was subtracted from 100 to invert the percentage.
  • the final ranking score for each gene can be computed via a weighted combination of its score on the six ranking criteria. If a score could not be computed for a particular criterion, the entire value of that criterion would be removed from the equation, and ranking was based solely on the remaining factors. IX. Methods of using toxicologically relevant genes
  • the test expression profile includes genes or gene sequences from Tables 4, 6, 7, 8, 9, or 10.
  • the reference profile includes one or more expression profiles which have been empirically derived, for example, from Table 4, 6, 7, 8, 9, or 10.
  • the test gene expression profile may be compared with a reference gene expression profile stored in a database, for example, a comprehensive toxicity (CT) database.
  • CT comprehensive toxicity
  • the gene expression profiles are associated with responsiveness in a particular organ, for example, kidney, liver, spleen, heart, lung, testis, or brain.
  • rat toxicologically relevant genes are used to obtain an array comprising polynucleotides which are selected from genes corresponding to partial gene sequences of toxicologically relevant genes.
  • the array includes genes or partial gene sequences of at least 20 nucleotides each. In another embodiment, the array includes genes or partial gene sequences of at least 50 nucleotides, at least 100 nucleotides, at least 200 nucleotides, at least 300 nucleotides, or at least 500 nucleotides each. In another embodiment, the array comprises toxicologically relevant genes corresponding to the partial gene sequences in Table 4. In other embodiments, the array comprises toxicologically relevant genes corresponding to partial gene sequences in Table 6, 7, 8, 9, or 10. In yet another embodiment, the array comprises toxicologically relevant genes corresponding to partial gene sequences associated with responsiveness in a particular organ, for example, kidney, liver, spleen, heart, lung, testis, or brain.
  • toxicologically relevant gene sequences from non-rat animals can be obtained by using the arrays described herein to select for sequences which are substantially homologous.
  • homology may be determined by using computerized sequence alignment, as described above, or by hybridization techniques. Nucleic acids will hybridize will depend upon factors such as their degree of complementarity as well as the stringency of the hybridization reaction conditions. Stringent conditions can be used to identify nucleic acid duplexes with a high degree of complementarity. Means for adjusting the stringency of a hybridization reaction are well-known to those of skill in the art.
  • conditions that increase stringency include higher temperature, lower ionic strength and presence or absence of solvents; lower stringency is favored by lower temperature, higher ionic strength, and lower or higher concentrations of solvents. Identifying toxicologically relevant genes in other non-rat animals may assist in determining which species is best suited for animal models by assessing which species is most susceptible to toxic responses.
  • gene expression profiles of rats can be compared when dosed with one drug and then compared to a second gene expression profile when dosed with another drug.
  • the toxicologically relevant data may be correlated using the algorithms disclosed herein.
  • the effects of drug-drug interaction may induce a similar set of genes to be up-regulated or down-regulated. The effect may be additive or multiplicative.
  • the effects of the drug-drug interaction may induce different set of genes which are not related in function.
  • the methods and set of toxicologically relevant genes disclosed herein allow target organs and toxic doses therein to be determined, as shown in Table 7, 8, 9, and 10. This is useful in drug design where the drug may have an intended target of one organ but have toxic multi- organ effects.
  • the methods and set of toxicologically relevant genes may be used to predict toxic response to agents which may take repeated exposure over a period of time for frank toxicity to appear.
  • agents are one-hit carcinogens (e.g., afiatoxin Bl, dimethylnitrosamine, ENU, etc.) or multi- dose carcinogens (e.g., phenobarbital and WY 14643).
  • the molecular toxic response to these carcinogens may be determined in advance of any macroscopic changes which may occur in response to exposure to these agents.
  • X. Method of using toxicological response data to generate a toxicological database By collecting data from cells, tissues, or organs from rats in response to one or more agents at different dosages and/or at different time points, a database can be built with collection of information about toxicological responses, e.g., reference expression profiles. With the database, it will be possible to evaluate toxicological response to specific agents or combinations thereof.
  • One practical application of toxicogenetics is to help rank a series of agents based upon gene expression. Initial ranking is done by determining the average percent of maximum alteration for a set of genes indicative of a specific stress or damage, for example, DNA damage (e.g., waf-1, DNA Pol beta, c-abl, cyclin G, Ape, and Mg t).
  • Another method to use gene expression data for prioritizing lead agents is to construct a thorough dose-response curve for all the genes of interest.
  • the EC 5 o's for each gene induced beyond a threshold level is determined (the EC 50 is the concentration that induces a gene to half-maximum for that agent).
  • Agents can then be ranked by the EC 50 average for the genes of interest. Agents with the lowest EC 5 o's would be considered as more toxic.
  • the rat gene array can also generate information that can be used to predict downstream effects, such as which pathways are affected by certain agents. This is accomplished by looking at the differential gene expression and analyzing which pathways contain the toxicological response genes and also which pathways the genes can affect. This information in turn can be used to predict tissue responses, whole organ responses, and/or system responses. The ability to predict whole organ responses has great potential in the development of drugs, pharmaceutical compounds, and even in the use of chemicals.
  • Example 1 Discovery and characterization of toxicology relevant genes by empirical data Section 1. Preparation and printing available rat genes on a microarray a. Polymerase chain reaction
  • Ml 3 forward primer was CTCAAGGCGATTAAGTTGGGTAAC (SEQ ID NO:709) and the sequence of the Ml 3 reverse primer was
  • the Ml 3 reverse primer had a C12 amine link attached to insure binding of the sense strand (5'- 3') of the PCR product to the glass microarray slide.
  • the amine linker can be added during synthesis of a primer at several any commercial sources, e.g., Synthegen.
  • the following ingredients were combined for the PCR reaction: 21 ⁇ l H 2 0, 2.5 ⁇ l 10X PCR buffer, 0.12 ⁇ l of lOmM dNTPs, 1 ⁇ l of 25 ng/ ⁇ l M13 forward primer, 1 ⁇ l of 25 ng/ ⁇ l M13 reverse primer, a sample of the clone from glycerol stock, and 0.5 ⁇ l Taq polymerase for a total volume of 25 ⁇ l.
  • the reaction mix was run at 95°C for 5 minutes and then cycled 35 times under the conditions of 95° C for 30 seconds, 45°C for 30 seconds, 72° C for 30 seconds, and followed by 72° C for 5 minutes and finally
  • the amplified product was purified by a standard ethanol precipitation method and alternatively by commercial PCR clean-up kits, e.g. Millipore, Qiagen.
  • PCR product was spotted on the coated glass slide using an MD Generation II Array Spotter.
  • Spotting Chamber Area of spotter enclosed in glass which houses the pins, plates, trays and most spotter machinery.
  • N2 Tank 5 ft. high steel gas tank labeled "Nitrogen, Compressed” N2 : The N2 gas from the N2 tank
  • Air Conditioner Kenmore air conditioner installed in window of spotting chamber
  • Humidifier 1 Essick 2000 Evaporative Cooler against the window
  • Humidifier 2 Bemis Airflow with white flexible duck into the Spotter Unit
  • Humidifier 3 Bemis Airflow against the wall Humidifier 4: Kenmore QuietComfort 7 Vacuum Pump: Gast Laboratory Oilless Piston Vacuum Pump Dampbox: The plastic sealable container containing an NaCl / water slurry
  • the temperature control was adjusted to 60°.
  • the spotter chambers were adjusted to be greater than 39 % relative humidity and less than 65° C.
  • the spotting pins were pre-washed for 20 cycles.
  • the glass slides were first each blown with N2 gas for about 2 seconds per side.
  • the slides were inserted into the Spotter following Array Spotter Run Values.
  • the slides were aligned using a clean narrow rod orienting it on the center right edge of the slide and gently pushed to the left until the slide was aligned vertically against the metal pins. After slides were loaded and straightened, a visual check was done to make sure no more debris had fallen.
  • the humidity was confirmed to be greater than 39% relative humidity.
  • the MD spotter recognizes 16 plates as a maximum for a run and will pause automatically after 8 plates.
  • the MD spotter also advances sequentially to plates in an invariable order and is not programmable to accommodate unique plate sourcing scheme. Therefore, it was important to manually rotate (or shuffle) plates to accomplish the spotting for the rat arrays.
  • the genes (PCR products) were spotted in duplicate on each slide and a total of 3000 genes were printed on a single slide (total 6000 spots). There were 6 slides in a set for inclusion of all 17,241 genes.
  • the printed (spotted) microarrays were examined for quality control purposes under a phase contrast microscope to evaluate spot morphology and presence of all genes.
  • This blocking procedure is important because it reduces the non-specific background signals.
  • the amounts provided in this protocol are for 19 slides, however, a skilled artisan may make modifications accordingly. More staining dishes and slide racks will be required if more than 19 slides are to be blocked.
  • a clean glass container was obtained and filled with Nanopure H20. The container was placed on a hot plate and heated to a high temperature.
  • a blocking solution was made by adding 2.5 ml of 20%) SDS to 500mL blocking solution bottle. The blocking solution was warmed in microwave for 2.5 minutes and checked to determine if the temperature had reached 50°C. If the temperature of the solution was not at yet 50°C, then the solution was warmed in the microwave at 10 second intervals until it reached the desired temperature.
  • Rats are divided into treated rats that receive a specific concentration of the compound and the control rats that only receive the vehicle in which the compound is mixed into solution or suspension (e.g., saline). Where possible, saline was used as the vehicle.
  • Rats are injected with a drug, compound, or appropriate vehicle intraperitoneal with a volume of lOml/kg body weight. The concentrations of each drug or chemical dosed are the dose at which toxicity has been documented by traditional toxicology methods (e.g.
  • histopathology, serum chemistry, hematology) and a second dose is 25% of the toxic dose.
  • the rats are dosed after not having food for 10 hours and then sacrificed at 6h, 24h, and 72h later.
  • Three control rats and three treated rats are euthanized at each timepoint for each drug.
  • Each rat is heavily sedated with an overdose of CO2 by inhalation and then a maximum amount of blood drawn. This blood is separated into a clot tube for isolation of serum, and into a heparinized tube for isolation of blood lymphocytes. Exsanguination of the rat by this drawing of blood kills the rat.
  • the method of collecting the tissues is very important and ensures preserving the quality of the mRNA in the tissues.
  • the body of the rat is then opened up and several prosectors rapidly remove the specified organs/tissues and immediately place them into liquid nitrogen.
  • Blood lymphocytes, serum, urine, liver, lung, heart, testes, spleen, bone marrow, brain, and other targets that may be specific targets of the drug/chemical were harvested. All of the organs/tissues are completely frozen within 3 minutes of the death of the animal to ensure that mRNA does not degrade.
  • the organs/tissues are then packaged into well-labeled plastic freezer quality bags and stored at -80 degrees until needed for isolation of the mRNA from a portion of the organ/tissue sample.
  • Serum chemistry changes were evaluated at 24 hours and 72 hours. Histopathology was evaluated by a pathologist at 72 hours for evidence of toxicity.
  • RNA samples To isolate high quality and high purity total RNA from tissue samples, the following materials are used: Qiagen RNeasy midi kits, 2-mercaptoethanol, liquid N 2 , tissue homogenizer, dry ice.
  • RNA isolation technique is used for RNA isolation from animal tissue and can be modified to accommodate smaller samples. If tissue needs to be broken, it can be placed on a double layer of aluminum foil which is placed within a weigh boat containing a small amount of liquid nitrogen. The aluminum foil was placed around the tissue and then a blunt force was applied to the tissue with a small foil-wrapped hammer. For liver or kidney, about 0.15-0.20 g of tissue was weighed and placed in a 15 ml conical tube. All tissue were kept on dry ice when other samples were being weighed.
  • RLT buffer about 3.8 ml of RLT buffer was added to the tube containing the sample.
  • the RLT buffer® from Qiagen can be prepared beforehand by adding 10 ⁇ l betamercaptoethanol to each 1.0 ml of lysis buffer needed.
  • the tissue was homogenized using the rotor-stator homogenizer for 45 seconds.
  • a IKA Ultra Turrax T25 homogenizer set at speed 4 with the S25N-10G dispersing element can be used.
  • a Virtishear Cyclone 750W rotor/stator homogenizer (Virtis item # 278077) can be used with the 7 mm microfine sawtooth shaft and generator (195 mm long with a processing range of 0.25 ml to 20 ml, item # 372718).
  • samples were stored on ice until all samples were homogenized.
  • the tip was first run for a few seconds in 95 % ethanol and then rinsed by squirting with fresh 95% ethanol. This process was repeated with nanopure water.
  • the tissue lysate was centrifuged at room temperature for 10 minutes at 3700- 3800 rpm in a Beckman GS-6 (or equivalent) centrifuge to remove nuclei thus reducing DNA contamination.
  • the supernatant of the lysate was transferred to a clean 15 ml conical tubes containing an equal volume of 70% EtOH in DEPC treated H 2 O, being careful not to include any of the pellet or fatty layer and mixed.
  • About 3.8 ml of sample was added to the RNeasy spin column placed in a 15 ml centrifuge tube and centrifuged at 3000 x g (3690-3710 rpm, Beckman GS-6) for 5 min. The flow-through was discarded. The remaining sample was added to the appropriate column and spun at 3000 x g for 5 minutes and the flow-through was discarded.
  • Buffer RW1 (Qiagen®) was added to the column and spun as before then about 2.5 ml of buffer RPE (Qiagen®) was added to column and spun at 3000 x g (3690-3710 rpm, Beckman GS-6) for 2 minutes.
  • RPE buffer was supplied as a concentrate so 4 volumes of 95% EtOH was added before use.
  • about 220 ml of 95% EtOH would be added to 55 ml of RPE.
  • Another 2.5 ml of buffer RPE was added and spun for 5 minutes to also dry out column. The column, including the tip, should be dry for the next elution step.
  • the column that has the RNA bound to a clean 15 ml tube was transferred and 200 ⁇ l of RNase-free water was added to the column, allowed to sit for 1 minute, and spun for 3 minutes at 3000 x g (3690-3710 rpm, Beckman GS-6). This step was repeated into the same tube but with 200 ⁇ l RNase-free water. c. Removal of contaminant DNA
  • Isolated RNA samples can be precipitated using the following lithium chloride (LiCl) process either before or after measuring absorbance reading for quantitation purposes. The volume of the sample was measured. To this, about 1/3 volume of LiCl
  • PPT Solution from Ambion (Cat # 9480) was added and mixed by inverting the tube.
  • the LiCl should be in solution. If not, it may be necessary to adjust the pH to 8.0.
  • RNA storage buffer (Ambion Cat # 7000).
  • the contaminant DNA was removed by incorporating the DNAse step in Qiagen® midi kit procedure as described in the instructions for the kit.
  • Fluorescence-labeled first strand cDNA probe was made from total or mRNA by first isolating RNA from control and treated cells, disclosed supra. This probe is hybridized to microarray slides spotted with DNA specific for toxicologically relevant genes.
  • the materials needed to practice this example are: total or messenger RNA, primer, Superscript II buffer, dithiothreitol (DTT), nucleotide mix, Cy3 or Cy5 dye,
  • the volume of each sample that would contain 20 ⁇ g of total RNA (or 2 ⁇ g of mRNA) was calculated.
  • the amount of DEPC water needed to bring the total volume of each RNA sample to 14 ⁇ l was also calculated. If RNA is too dilute, the samples are concentrated to a volume of less than 14 ⁇ l in a speedvac without heat. The speedvac must be capable of generating a vacuum of 0 Milli-Torr so that samples can freeze dry under these conditions. Sufficient volume of DEPC water was added to bring the total volume of each RNA sample to 14 ⁇ l.
  • Each PCR tube was labeled with the name of the sample or control reaction. The appropriate volume of DEPC water and 8 ⁇ l of anchored oligo dT mix (stored at -20°C) was added to each tube.
  • Eppendorf tubes containing 600 ⁇ l of ethanol precipitation mixture 600 ⁇ l was used to rinse the PCR tubes. The tubes were inverted to mix.
  • Samples were placed in -80°C freezer for at least 20-30 minutes. If desired, samples
  • the completed RT reaction contains • impurities that must be removed. These impurities include excess primers, nucleotides, and dyes.
  • impurities include excess primers, nucleotides, and dyes.
  • One method of removing the impurities was by following the instructions in the QIAquick PCR purification kit (Qiagen catalog #120016).
  • the completed RT reactions were cleaned of impurities by ethanol precipitation and resin bead binding. The samples were centrifuged for 15 minutes at 20800 x g (14000 rpm in Eppendorf model 5417C) and carefully the supernatant was decanted. A visible pellet was seen (pink/red for Cy3, blue for Cy5).
  • hybrid was denatured by heating for 5 minutes at 95°C in a heat block and flash spun.
  • Binding Resin was added to each well of the filter plate that was used. If this was done with a multi-channel pipette, wide orifice pipette tips would have been used to prevent clogging. It is highly preferable not to touch or puncture the membrane of the filter
  • a consistent amount of cDNA is pipeted into each well of the 384-well, 100 ⁇ l assay plate (Falcon Microtest cat#35-3980) plate because readings will vary with volume. Controls or identical samples should be pooled at this step, if required.
  • the probes were transferred from the Millipore 96 well plate to every other well of the 384 well assay plate. This was done using a multi-channel pipette. For replicate samples that have been pooled, 60 ⁇ l aliquots were transferred into wells of the assay plate.
  • the Cy-3 and Cy-5 fluorescence was analyzed using the Wallac Victor 1420 Multilabel counter workstation programmed for reading Cy3-Cy-5 in the 384-well
  • Lamp filter D642 samarium slot B7
  • Concentration of the cDNA probes is often necessary so that they can be resuspended in hybridization buffer at the appropriate volume.
  • a sample of control cDNA (Cy-5) is mixed with each test cDNA (Cy-3). This is very important because it allows hybridization of treated and the appropriate control cDNA samples on the same microarray.
  • Eppendorf tubes were labeled for each test sample and the mixed cDNA samples were added to the appropriate tubes. These tubes were placed in a speed-vac to dry down, with foil covering any windows on the speed vac. At this point, heat (45°C)
  • Hybridization Buffer for 100 ⁇ l:
  • the solution was filtered through 0.2 ⁇ m syringe filter, then the volume was
  • the hybridization buffer was made up as:
  • Hybridization Buffer for 101 ul:
  • DNA (5 ⁇ g/ ⁇ l), 0.5 ⁇ l poly A (5 ⁇ g/ ⁇ l), 0.25 ⁇ l Yeast tRNA (10 ⁇ g/ ⁇ l) was added per
  • the probe remained in the dark for 10-15 minutes at room temperature and then was gently vortexed for several seconds and then was flash spun in the microfuge. The probes were boiled for 5 minutes and centrifuged for 3 min
  • all non-specifically bound cDNA probe should be removed from the array. Removal of all non-specifically bound cDNA probe was accomplished by washing the array and using the following materials: slide holder, glass washing dish, SSC, SDS, and nanopure water. It is highly preferable that great caution be used with the standard wash conditions as deviations can greatly affect data.
  • the stainless steel slide carriers were placed in the second dish and filled with 2X SSC, 0.1%SDS. Then the slides were removed from glass slide holders and placed in the stainless steel holders submerged in 2X SSC, 0.1%SDS and soaked for 5 minutes. The slides were transferred in the stainless steel slide carrier into the next glass dish containing 0. IX SSC and 0.1 %SDS for 5 minutes. Then the slides are transferred in the stainless steel carrier to the next glass dish containing only 0.1X SSC for 5 minutes. The slides, still in the slide carrier, were transferred into nanopure water (18 megaohms) for 1 second. To dry the slides, the stainless steel slide carriers were placed on micro-carrier plates with a folded paper towel underneath. The top of the slides was gently dabbed with a tissue. Then the slides were spun in a centrifuge (Beckman GS-6 or equivalent) for 5 minutes at 1000 rpm. It is very important that the slides spin dry instead of air dry, as air drying leads to increased background.
  • Sprague-Dawley male rats approximately 2.5 months old, were used for toxicity testing. Tliree rats were injected intraperitoneally with a drug/chemical at each dose per sacrifice timepoint and three other rats were used as control animals as described above in section (a) of Toxicity studies.
  • the drugs/chemicals dosed for the testing of the 17,241 gene array were as follows:
  • tissue samples shown in the table above along with the corresponding tissue from a rat injected with the vehicle were processed for cDNA with dye incorporated as described in section 2.
  • the set of 6 microarray slides these cDNA samples were hybridized on was described in section 1 and the target spotted on them were the PCR products from 17,421 genes.
  • the washed and dried hybridized slides were scanned on Axon Instruments Inc. GenePix 4000A Micro Array Scanner and the fluorescent readings from this scanner converted into quantitation files on a computer using GenePix software.
  • the three cutoff criteria were: fold induction/repression level, average fluorescence of the replicate spots used to calculate expression level, and coefficient of variation of the replicate spots.
  • fold induction/repression level the stored induction repression level of a gene in a particular experiment has been calculated as follows: 5 1). arrive at a treatment score for the gene.
  • the treatment score was represented by the amount of Cy3 labeled cDNA from a treated source (e.g., laboratory animals dosed with a compound) that had bound to a complementary target DNA spot of the microarray slide.
  • the amount of Cy3 labeled cDNA was detected by a microarray laser scanner at a wavelength of 532nm. 0 2) arrive at a control score for the gene.
  • the control score was represented by the amount of Cy5 labeled cDNA from an untreated source that had bound to a complementary target DNA spot of the microarray slide.
  • the amount of Cy5 labeled cDNA was detected by a microarray laser scanner at a wavelength of 635nm.
  • the unit of measure was the pixel intensity or the average of several pixel intensities reported by a microarray laser scanner at coordinate on a microarray slide.
  • the pixel intensity at that location was proportional to the number of photons detected by a photomultiplier tube when a spot of target DNA labeled with fluorescent probe was illuminated by a laser with a wavelength to which the dye is sensitive.
  • a photomultiplier tube When a spot of target DNA labeled with fluorescent probe was illuminated by a laser with a wavelength to which the dye is sensitive.
  • the average fluorescence level of the replicate spots used to calculate the expression level is accomplished by a simple average of the four treated replicate values used in any experiment to calculate the expression level of a gene.
  • the coefficient of variation of the replicate spots was a conventional measure of variability, expressed as a percentage, that in this case was derived by dividing the standard deviation of the four replicate treated-to-control ratios by the average of the four replicated treated-to-control ratios.
  • the latter criteria represent useful measures of data quality.
  • initial screening is based on expression level and measurement quality.
  • Algorithms were written specifically to perform the entire process of ranking genes to be included from the 17K array on to the CT array. In the initial part of the program, the three criteria above were “ended” together, so that in order to "make the first cut” the gene would have to meet all three criteria. This was considered the first tier in the program.
  • the criteria are adjustable within the algorithms. For the actual ranking of the 17k array, the following criteria were used: induction/repression level: 2; fluorescence level: 400; and a coefficient of variation: 30%.
  • induction/repression level 2
  • fluorescence level 400
  • a coefficient of variation 30%.
  • To make the first cut and be selected as a potential toxicologically relevant gene a gene only had to meet the 3 criteria within one experiment stored in the 17K warehouse of data. Likewise, relevant values for the gene would have been included each time it met the criteria within a different experiment.
  • the data for genes that made the cut (and hence were selected as potential toxicologically relevant genes) and each time the genes made the cut were stored in a separate, temporary data table for ranking (the second tier in the process). A gene's data could be included more than once: one time for each experiment in which that gene met the three criteria.
  • NC is a simple count of the number of different compounds (not experiments, as duplicate experiments were performed for each compound) in which that gene met the 3 criteria, 2) Percent of consistency between slides (% time the gene value made the cutoff criteria on the replicated slide for that initial slide) (CC).
  • CC Percent of consistency between slides (% time the gene value made the cutoff criteria on the replicated slide for that initial slide) (CC).
  • NC number of compounds
  • CC compound consistency
  • CV coefficient of variation of those fold induction scores (unlike all the other ranking criteria, a lower coefficient of variation is deemed better)
  • Tissue consistency i.e., what percent of cutoff-meeting occurrences of the gene were in the same tissue (CT).
  • Each gene was assigned a score between 0 and 100 for each ranking criterion.
  • Each ranking criterion score was computed as follows: The range of values for all genes was computed for the criterion by subtracting the lowest value present among all scores from the highest.
  • the temporary data table compiled from the 17K warehouse included scores for every gene that had met the initial 3 cutoff criteria. A gene would be present in the table with values for each experiment in which it had met or surpassed the 3 cutoff criteria. Scores were then aggregated from the gene occurrences of each gene into an overall score for that gene for each of the six criteria described above. For example, if Gene A made the cut in three experiments with respective induction scores of 4, 6, and 8 then the aggregated induction score for Gene A would be 6 (the average of the three values).
  • the final ranking score for each gene was computed via a weighted combination of its score on the six ranking criteria. If a score could not be computed for a particular criterion, the entire value of that criterion was removed from the equation , and ranking was based solely on the remaining factors.
  • Each of the ranking criteria could be weighted between 0 and 5, and weightings are relative, so that 2:2:2:2:2 would be the same as 4:4:4:4:4:4, etc.
  • a zero weighting would drop the factor from the equation. For example, suppose that Gene A had the following scores: NC: 75%, CC: 50%, FT. 80%, CV: 25%, FL: 50%, and CT: 30%. Using the weightings described above (3, 1, 5, 0, 0, 0) the final score for Gene A would be calculated as follows:
  • 675/9 75 would be the final score for Gene A.
  • a score was then computed for each discrete gene based on aggregating the individual values for that gene from one or more experiments where that gene had made the initial cut.
  • the list of genes was then rank-ordered on the basis of final scores.
  • the objective determination of how many genes to take from the top of the list to be added to the CT array was based on the number of experiments that genes showed a response in. At about gene number 450 on the list of rank-ordered genes the number of experiments that genes showed a response in started of often be only one experiment or one compound. It was desired that most genes on the array have response to different mechanisms of toxicity or different in different tissues. Therefore, the number of genes chosen from the top of the list of rank-ordered genes was 450.
  • Section 4 Evaluation of empirical data on specific tissue response of rat genes corresponding to the partial sequence discovered from the 17,241 gene set.
  • Microarrays were printed with the 400 genes discovered empirically following the description for PCR and spotting slides in Section 1 of Materials and Methods. The washed and dried hybridized slides were scanned on Axon Instruments Inc. GenePix 4000A MicroArray Scanner and the fluorescent readings from this scanner converted into quantitation files on a computer using GenePix software. c. Analysis of quantitation files to evaluate toxicologically relevant genes Quantitation files were imported into Phase- 1 Matrix Express Software designed for analysis of differential gene expression data. The ratios if the fluorescent values of the treated and control cDNA samples hybridized on the same slide were determined for each spot and termed fold induction values (positive value for induction of gene response and negative value for suppression of gene response).
  • the fold inductions for each gene is an average of the fold inductions for the 4 spots on the slide for each gene. If the coefficient of variance for the 4 spots is greater than 50% then the data for the gene is not entered for that gene on that slide.
  • the Matrix Express software allows development of a warehouse containing the fold induction data from multiple experiments (microarrays). A warehouse was constructed by importing quantitation files and analyzing fold inductions for rats treated with drugs and chemicals listed in table 3. In addition, most samples were hybridized in duplicate and the data from 2 high-quality slides was averaged in the warehouse. For rats treated with every compound the liver and kidneys were always processed and evaluated for gene expression.
  • Spleen, heart, testes, lung samples were evaluated the multiple organ toxicants. Spleen was evaluated for all immunotoxicants and 5 non-immunotoxicants, heart samples were evaluated for all heart toxicants, testes was evaluated for flutamide and all steroid compounds, lung was evaluated for all lung toxicants, and brain was evaluated for all brain toxicants.
  • This warehouse contained approximately 2500 final experiments (primarily averages of 2 duplicate experiments to make 1 final experiment) at the time of evaluation for tissue specific response of the genes.
  • a gene was determined to be response in liver if it had a 2-fold induction (stimulation or suppression) in more than 1% of the experiments for liver samples.
  • a gene was determined responsive in the kidney if it had a 2-fold induction in more than 1% of the experiments for kidney samples.
  • a 1% cut-off was a generous cutoff for liver and kidney because these organs were evaluated for all toxicants (including non-hepatic or renal toxicants).
  • a gene was determined to be responsive in the heart, spleen, lung, testis, or brain if it had a 2-fold induction in more than 2% of the experiments for the respective organs.
  • the heart, spleen, lung, testis, and brain cut-off was higher at 2% compared to 1% because there were fewer total experiments in the warehouse for each of these organs and a higher cut-off minimizes false positive results when dealing with this smaller number of experiments.
  • the toxicology database contained approximately 2500 final experiments (primarily averages of 2 duplicate experiments to make 1 final experiment), based on the compounds listed in Table 3, at the time of evaluation for tissue specific response of the " genes.
  • Table 7 shows the tissue specific response of toxicology genes chosen empirically from the 17,241 gene set demonstrated for each gene and Table 8 shows the same information from Table 7 with the genes with tissue specific response listed by tissue.
  • Figures 1 through 6 show the differential gene expression of rats dosed with toxic compounds from this toxicology database. The differential expression between replicate microarrays, over time, between organs, and between different compounds is demonstrated in the figures showing the power of having a set of toxicology relevant genes to process rat toxicity studies with.
  • Example 2 Production and characterization of known genes for toxicity response Section 1. Production of clones a.
  • Identifying and isolating toxicologically relevant genes from rat or human databases One method that was used to identify and isolate toxicologically relevant genes for inclusion in a rat array was to search a public database (e.g., GenBank) for genes that have been identified as part of critical cellular pathways (e.g. metabolism, DNA synthesis). ' Once these genes were identified, primers were designed and used in an amplification process with cDNA library made from rat liver cells. The amplified product was cloned into an expression vector and sequenced to confirm that the sequence matched or was substantially similar to the gene sequence information obtained from GenBank. Confirmed amplified gene products were then incorporated into a rat array using the methods described in Example 1, section 1. Potential toxicologically relevant genes which have been identified and isolated in this manner are included in Table 4.
  • GenBank public database
  • Another method used to identify and isolate genes with some evidence of roles in critical cellular pathways was by first finding the sequence a public database (e.g., GenBank) and sequences corresponding within these genes were synthesized de novo and used in amplification reactions. The amplified product was cloned into an expression vector and sequenced to confirm that the sequence matched or was substantially similar to the gene sequence information obtained from GenBank. Confirmed amplified gene products were then incorporated into a rat array using the methods disclosed herein to immobilize the gene product, or target sequence, to a glass slide.
  • GenBank public database
  • sequences corresponding within these genes were synthesized de novo and used in amplification reactions.
  • the amplified product was cloned into an expression vector and sequenced to confirm that the sequence matched or was substantially similar to the gene sequence information obtained from GenBank. Confirmed amplified gene products were then incorporated into a rat array using the methods disclosed herein to immobilize the gene product, or target sequence, to a glass
  • Table 9 shows the tissue specific response of genes with potential roles in critical cellular pathways demonstrated for each gene
  • Table 10 shows the same information from Table 9 with the genes with tissue specific response listed by tissue.
  • Figures 1 through 6 show the differential gene expression of rats dosed with toxic compounds from this toxicology database. The differential expression between replicate microarrays, over time, between organs, and between different compounds is demonstrated in the figures showing the power of having a set of toxicology relevant genes to process rat toxicity studies with.
  • RNA isolation Liver tissue from a rat sacrificed 24h after intraperitoneal injection of a toxic dose of aflatoxin Bl (1 mg/kg) and the appropriate liver tissue from the saline injected vehicle control rat were used to determine the differentially expressed genes in a rat exposed to a liver toxicant (aflatoxin).
  • RNA was isolated from both liver samples using an RNA isolation kit from Qiagen (RNeasy Midi kit) followed by use of a Messageclean ® kit from Genhunter ® . The protocols from the MessageClean ® kit were modified to generate more optimal conditions for removing DNA contamination.
  • these ingredients were added: 50 ⁇ l total RNA, 5.7 ⁇ l lOx reaction buffer, 1.0 ⁇ l DNase 1 (10 units/ ⁇ l) for a total volume of 56.7 ⁇ l.
  • the ingredients were mixed well and incubated for 30 minutes at 37° Celsius.
  • 40 ⁇ l phenol/chloroform mixture (1:1 volume) was added and the mixture was vortexed for 30 seconds and allowed to sit on ice for 10 minutes.
  • the tube containing the mixture was spun in an Eppendorf centrifuge at 4 degrees for 5 minutes at maximum speed. The upper phase was collected, transferred to a new tube and 5 ⁇ l of 3M NaOAc and 200 ⁇ l 95% ethanol was added to the upper phase.
  • RNAimage ® kits were used and protocols from the RNAimage ® kits were altered to optimize more successful mRNA differential display. The following section describes the method by which this was accomplished:
  • dATP 2000 Ci/mmole
  • Taq DNA polymerase from PE Biosystems for a total volume of 20 ⁇ l.
  • the tube containing all these ingredients were mixed well by pipetting up and down and placed in a fhermocycler at 95°C for 5 minutes and then amplified for 40 cycles under the conditions of 94°C for 30 seconds, 40°C for 2 minutes, 72°C for 30 seconds and finally held at 4°C until the samples are removed from the thermocycler.
  • a 6% denaturing polyacrylamide gel in TBE was prepared and allowed to polymerize for at least 2 hours before using. Then the gel was run for about 30 minutes before any samples were loaded. It is important for all the sample wells in the gel to be flushed and cleared of all urea prior to loading any samples in the wells. About 3.5 ⁇ l of each sample was mixed with 2 ⁇ l of loading dye and incubated at 80°C for 2 minutes immediately before loading onto the 6% gel.
  • the loading dye was xylene and after the gel was loaded with the samples obtained from the rounds of PCR, the gel was run at 60 watts of constant power until the xylene dye was about 6 inches from the bottom of the gel.
  • the gel was blotted onto a large sheet of exposed autoradiograph film.
  • the gel was covered with plastic wrap and under dark conditions, the gel was placed in a large autoradiograph cassette with a new sheet of unexposed film, marked for orientation, and the film was exposed to the gel at -80°C.
  • the exposure period can be anywhere from overnight to 72 hours.
  • PCR to amplify gel band PCR was set up to amplify the gel band.
  • the re-amplification should be done using the same primer set and PCR conditions except the dNTP concentrations should be at 20 ⁇ M.
  • the following ingredients were combined for the PCR reaction: 20.4 ⁇ l H 2 0, 4 ⁇ l 10X PCR buffer, 3.2 ⁇ l of 250 ⁇ M dNTPs , 4 ⁇ l of 2 ⁇ M H-AP primers, 4 ⁇ l of 2 ⁇ M H-TnM, 4 ⁇ l template (out of the 100 ⁇ l containing gel band), and 0.5 ⁇ l Taq polymerase for a total volume of 40 ⁇ l.
  • products from different sources may be used to achieve the desired cloned product.
  • InVitrogen's TOPO TA Cloning Kit® was used and the following material was combined in a reaction tube: 2 ⁇ l of freshly run PCR product, 2 ⁇ l of sterile H 2 0, 1 ⁇ l of PCR-TOPO vector for a final volume of 5 ⁇ l. The combined ingredients were mixed gently and incubated for 5 minutes at room temperature. Then 1 ⁇ l of 6x TOPO Cloning Stop Solution was added and all combined ingredients were mixed for about 10 seconds at room temperature and then set on ice. One ShotTM cells were thawed on ice.
  • PCR Screening colonies for correct recombinant plasmids PCR was used to ascertain whether the white colonies selected contained the correct recombinant plasmid.
  • the following ingredients were combined for the PCR reaction: 21 ⁇ l H 2 0, 2.5 ⁇ l 10X PCR buffer, 0.12 ⁇ l of lOmM dNTPs, 1 ⁇ l of 25 ng/ ⁇ l T7 primer, 1 ⁇ l gene specific left or right primer at 25 ng/ ⁇ l, template (a toothpick was " used to transfer colony from transformation plate to tube by swishing the toothpick around in the reaction mix), and 0.5 ⁇ l Taq polymerase for a total volume of 25 ⁇ l.
  • the reaction mix was run at 95°C for 5 minutes and then cycled 35 times under the conditions of 95° C for 30 seconds, 45°C for 30 seconds, 72° C for 30 seconds, and followed by 72° C for 5 minutes and finally 4°C until samples are removed from the thermocycler. About 4 ⁇ l of the PCR product was removed and run on a 1% agarose gel to ascertain the success of the PCR reaction. Bacterial colonies corresponding to the colonies which yielded positive PCR results were grown overnight in LB media containing 100 ⁇ g/ ⁇ l ampicillin at 37° C with constant shaking. Plasmid DNA were isolated from the overnight cultures and sequenced using a T7 primer.
  • Results RCT-289 and RCT-290 are the two toxicologically relevant genes identified using methods disclosed in this example.
  • the gene sequences are listed in Table 4.
  • RNA was isolated from tissues and/or organs from rats dosed with toxic compounds listed in Example 1, Section 3, and then the mRNA within this total RNA
  • reaction mixture 6 ⁇ l of 5x first strand buffer, 3 ⁇ l 0.1 DTT, 1.5 ⁇ l 1 OmM dNTPs, 1.5
  • RT-PCR Real Time PCR
  • Taqman® Universal PCR Master Mix available from Applied Biosystem
  • target and control primers /probes and cDNA.
  • This method measures PCR product accumulation with a dual-labeled fluorogenic probe.
  • the probes are labeled with 6-FAM on the 5' end and TAMRA on the 3' end.
  • TAMRA is a quencher dye.
  • This assay exploits the 5'- 3' exonuclease property of Taq polymerase. When the probe hybridizes to its target the reporter dye (FAM) is cleaved by the 5' exonuclease activity of the Taq polymerase and can emit a fluorescent signal. With increasing cycles of amplification, more signal is emitted and detected using an ABI 7700 sequence detector.
  • primer and probe sets For each gene, a set of two primers and a fluorogenic probe are designed and synthesized. For quantitation of mRNA, optimal design for probes and primers requires primers to be positioned over exoh-intron junctions. This step rules out amplification of contaminating genomic DNA.
  • primer and probe sets have been designed for 16 genes that are part of the 700 rat toxicologically relevant gene array, also referred to herein as "comprehensive toxicity anay" or "CT anay”. These genes were up-regulated or down-regulated by toxic drugs/chemicals in rats exposed in vivo or rat cells exposed in culture. The probes and primer sets were tested for their ability to amplify genomic DNA
  • RNA of high quality and high purity was isolated from cultured cells by using Qiagen RNeasy midi kits and 2-mercaptoethanol. Precautions were taken to minimize the risk of RNA degradation by RNases by wearing gloves, treating work areas and equipment with an RNase inhibitor, for example, RNase Zap (Ambion® Products, Austin, TX) and keeping samples on ice. This total RNA isolation technique
  • HepG2 human hepatocyte cells in T-75 flasks and maxi kit RNA isolation for cells in
  • T-175 flasks Cells were checked under the microscope to make sure that they were viable.
  • Cells were dosed with an agent, which could be a drug, chemical, or pharmaceutical
  • composition when they reached 60-80% confluence. It is preferable to avoid isolating
  • RLT buffer (RLT buffer requires the addition of 10 ⁇ l beta mercaptoethanol for each 1.0 ml RLT) was added directly to the cell culture flask.
  • T-75 flasks received 3 ml RLT buffer and T-175 flasks received 5.0 ml RLT buffer. It is preferable to lightly agitate the flasks at this point. Flasks were lightly agitated to distribute the RLT buffer and the cells became a gelatinous layer. The cells were allowed to sit for 4 minutes, then fluid was withdrawn and placed in RNase- free tubes. An equivalent volume of 70% ethanol was added to each tube and vortexed to distribute evenly. If a precipitate with a string ⁇
  • the fluid was applied to a spin column and spun for 5 min at 3650 rpm in the Beckman
  • GS-6 (or a similar centrifuge).
  • the flow-through was discarded.
  • About 4 or 15 ml (T- 75 or T-175, respectively) of RWl buffer was applied and spun for 5 min at 3650 RPM.
  • the flow through was discarded.
  • About 2.5 ml RPE buffer (midi columns) or 10 ml RPE buffer (maxi columns) was applied and centrifuged for 3 minutes.
  • the flow- through was discarded.
  • Another 2.5 or 10 ml buffer RPE was applied and centrifuged for 5 minutes to dry out column before proceeding to the elution step.
  • the column, including the tip should be dry for the next step.
  • the column that has the RNA bound to it was transferred to a clean tube for elution. Then 150 ⁇ l of RNase-free water was added to midi columns and 500 ⁇ l of RNase-free water to columns, allowed to sit for 2-4 minutes and spun for 3 min at 3000 x g (3690-3710 rpm, Beckman GS-6 or a similar centrifuge). The elution was repeated with another 150 ⁇ l or 500 ⁇ l of RNase-free water into the same tube. The elution was precipitated using the LiCl precipitation protocol, exemplified in Example 2, and resuspended in RNA storage buffer.
  • the O.D. reading was taken at 260 nm. About 2.0 ⁇ l RNA was added to 98 ⁇ l H2O and the O.D. reading was taken and calculated as follows:

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Abstract

L'invention porte sur un ensemble de gènes de rats en rapport avec la toxicologie et s'avérant utiles pour déterminer les réponses toxicologiques.
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