WO2005051310A2 - Genes ctps utilises en tant que modificateurs de la voie pten et procedes d'utilisation associes - Google Patents

Genes ctps utilises en tant que modificateurs de la voie pten et procedes d'utilisation associes Download PDF

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WO2005051310A2
WO2005051310A2 PCT/US2004/039206 US2004039206W WO2005051310A2 WO 2005051310 A2 WO2005051310 A2 WO 2005051310A2 US 2004039206 W US2004039206 W US 2004039206W WO 2005051310 A2 WO2005051310 A2 WO 2005051310A2
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ctps
assay
pten
agent
cell
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WO2005051310A3 (fr
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Michael R. Costa
Garth Joseph Mcgrath
Lynn Margaret Bjerke
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Exelixis, Inc.
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    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N33/00—Investigating or analysing materials by specific methods not covered by groups G01N1/00 - G01N31/00
    • G01N33/48—Biological material, e.g. blood, urine; Haemocytometers
    • G01N33/50—Chemical analysis of biological material, e.g. blood, urine; Testing involving biospecific ligand binding methods; Immunological testing
    • G01N33/5005—Chemical analysis of biological material, e.g. blood, urine; Testing involving biospecific ligand binding methods; Immunological testing involving human or animal cells
    • G01N33/5008—Chemical analysis of biological material, e.g. blood, urine; Testing involving biospecific ligand binding methods; Immunological testing involving human or animal cells for testing or evaluating the effect of chemical or biological compounds, e.g. drugs, cosmetics
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N2333/00—Assays involving biological materials from specific organisms or of a specific nature
    • G01N2333/90—Enzymes; Proenzymes
    • G01N2333/9015—Ligases (6)
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N2500/00—Screening for compounds of potential therapeutic value
    • G01N2500/10—Screening for compounds of potential therapeutic value involving cells

Definitions

  • the AKT signaling pathway is frequently hyperactivated by a variety of mechanisms in a wide range of human cancers, including melanoma, breast, lung, prostate, and ovarian tumors (see Vivanco I and Sawyers CL (2002) Nat Rev Cancer. 2(7):489-501; Scheid MPand Woodgett JR (2001) J Mammary Gland Biol Neoplasia. 6(l):83-99).
  • the AKT protein kinase activity can be elevated by amplification and overexpression of the AKT2 gene, or by increased production of phosphatidylinositol (3, 4, 5) trisphosphate (PIP 3 ), which activates AKT by recruitment to the plasma membrane.
  • PIP 3 In normal phosphoinositide metabolism, phosphatidylinositol (3, 4) bisphosphate (PIP 2 ) is phosphorylated by phosphatidylinositol 3-kinase (PI3K) to generate PIP 3 , and PIP 3 is dephosphorylated back to PIP 2 by the lipid phosphatase PTEN.
  • PIP 3 levels in tumors can be enhanced by amplification and overexpression of PI3K, or by hyperactivation of the PI3K activator IGF receptor. Most commonly, however, PLP 3 levels in tumor cells are elevated by mutation or deletion of the PTEN tumor suppressor, at rates as high as 40-50% of prostate cancers.
  • the AKT pathway promotes tumor progression by enhancing cell proliferation, growth, survival, and motility, and by suppressing apoptosis. These effects are mediated by several AKT substrates, including the related transcription factors FKHR and AFX, for which phosphorylation by AKT mediates nuclear export. All of the major AKT pathway components have structural and functional orthologs in C. elegans that function in dauer larva formation (see Wolkow CA et al. (2002) J Biol Chem 277(51):49591-7; Paradis S et al (1999) Genes Dev. 13(11): 1438-52.).
  • dauer-constitutive (Daf-c) phenotype Normally, environmental cues of low food (bacteria) levels, high dauer pheromone concentration, and high temperature trigger a developmental decision that signals alternative differentiation pathways in all tissues and entry into a diapause (dauer) arrest.
  • inactivating mutations in the PTEN ortholog daf- 18, or the FKHR and AFX ortholog daf-16 generate a dauer-defective (Daf-d) phenotype and prevent dauer formation regardless of environmental conditions.
  • a daf-18 deletion mutant fully suppresses the Daf-c phenotype of age-1 and daf-2 mutations (Gil EB et al (1999) Proc Natl Acad Sci U S A. 96(6):2925-30.; Mihaylova VT et al (1999) Proc Natl Acad Sci U S A.
  • daf-18 ep496
  • daf-18 ep497
  • the Daf-d phenotype of double mutants daf-18 (ep496); daf-2 (el370) and daf-18 (ep497); and daf-2 (el 370) can be reverted to a Daf-c phenotype by RNAi of akt-1 or age-1, indicating that the double mutants display increased AKT signaling.
  • the catalytic conversion of UTP to CTP is accomplished by the enzyme cytidine- 5-prime-triphosphate synthetase (CTPS).
  • CTPS is important in the biosynthesis of phospholipids and nucleic acids, and plays a key role in cell growth, development, and tumorigenesis.
  • the region to which the CTPS gene has been mapped is the location of breakpoints involved in several tumor types.
  • CTPS2 catalyzes the formation of CTP from UTP with the concomitant deamination of glutamine to glutamate.
  • CTPS2 is the rate- limiting enzyme in the synthesis of cytosine nucleotides, which play an important role in various metabolic processes and provide the precursors necessary for the synthesis of RNA and DNA. Cancer cells that exhibit increased cell proliferation also exhibit an increased activity of CTPS2.
  • CTPS2 may be an attractive target for selective chemotherapy.
  • Two alternatively spliced transcript variants encoding CTPS2 have been described.
  • the ability to manipulate the genomes of model organisms such as C. elegans provides a powerful means to analyze biochemical processes that, due to significant evolutionary conservation, have direct relevance to more complex vertebrate organisms.
  • a genetic screen can be carried out in an invertebrate model organism having underexpression (e.g. knockout) or overexpression of a gene (referred to as a "genetic entry point") that yields a visible phenotype. Additional genes are mutated in a random or targeted manner. When a gene mutation changes the original phenotype caused by the mutation in the genetic entry point, the gene is identified as a "modifier" involved in the same or overlapping pathway as the genetic entry point.
  • CTPS cytidine-5-prime-triphosphate synthetase
  • CTPS -modulating agents are nucleic acid modulators such as antisense oligomers and RNAi that repress CTPS gene expression or product activity by, for example, binding to and inhibiting the respective nucleic acid (i.e. DNA or mRNA).
  • CTPS modulating agents may be evaluated by any convenient in vitro or in vivo assay for molecular interaction with a CTPS polypeptide or nucleic acid.
  • candidate CTPS modulating agents are tested with an assay system comprising a CTPS polypeptide or nucleic acid. Agents that produce a change in the activity of the assay system relative to controls are identified as candidate PTEN modulating agents.
  • the assay system may be cell-based or cell-free.
  • CTPS-modulating agents include CTPS related proteins (e.g. dominant negative mutants, and biotherapeutics); CTPS -specific antibodies; CTPS -specific antisense oligomers and other nucleic acid modulators; and chemical agents that specifically bind to or interact with CTPS or compete with CTPS binding partner (e.g. by binding to a CTPS binding partner).
  • a small molecule modulator is identified using a synthase assay.
  • the screening assay system is selected from a binding assay, an apoptosis assay, a cell proliferation assay, an angiogenesis assay, and a hypoxic induction assay.
  • candidate PTEN pathway modulating agents are further tested using a second assay system that detects changes in the PTEN pathway, such as angiogenic, apoptotic, or cell proliferation changes produced by the originally identified candidate agent or an agent derived from the original agent.
  • the second assay system may use cultured cells or non-human animals.
  • the secondary assay system uses non-human animals, including animals predetermined to have a disease or disorder implicating the PTEN pathway, such as an angiogenic, apoptotic, or cell proliferation disorder (e.g. cancer).
  • the invention further provides methods for modulating the CTPS function and/or the PTEN pathway in a mammalian cell by contacting the mammalian cell with an agent that specifically binds a CTPS polypeptide or nucleic acid.
  • the agent may be a small molecule modulator, a nucleic acid modulator, or an antibody and may be administered to a mammalian animal predetermined to have a pathology associated with the PTEN pathway.
  • CTPS-modulating agents that act by inhibiting or enhancing CTPS expression, directly or indirectly, for example, by affecting a CTPS function such as enzymatic (e.g., catalytic) or binding activity, can be identified using methods provided herein.
  • CTPS modulating agents are useful in diagnosis, therapy and pharmaceutical development.
  • CTPS polypeptide refers to a full-length CTPS protein or a functionally active fragment or derivative thereof.
  • a "functionally active" CTPS fragment or derivative exhibits one or more functional activities associated with a full-length, wild- type CTPS protein, such as antigenic or immunogenic activity, enzymatic activity, ability to bind natural cellular substrates, etc.
  • a functionally active CTPS polypeptide is a CTPS derivative capable of rescuing defective endogenous CTPS activity, such as in cell based or animal assays; the rescuing derivative may be from the same or a different species.
  • functionally active fragments also include those fragments that comprise one or more structural domains of a CTPS, such as a binding domain.
  • Protein domains can be identified using the PFAM program (Bateman A, et al., Nucleic Acids Res, 1999, 27:260-2).
  • the synthase domain (PFAM 06418) of CTPS from GIs# 4503133 and 28559085 (SEQ ID NOs:3 and 4, respectively) is located at approximately amino acid residues 1 to 284 and 1 to 287, respectively.
  • Methods for obtaining CTPS polypeptides are also further described below.
  • preferred fragments are functionally active, domain- containing fragments comprising at least 25 contiguous amino acids, preferably at least 50, more preferably 75, and most preferably at least 100 contiguous amino acids of a CTPS.
  • the fragment comprises the entire functionally active domain.
  • CTPS nucleic acid refers to a DNA or RNA molecule that encodes a CTPS polypeptide.
  • the CTPS polypeptide or nucleic acid or fragment thereof is from a human, but can also be an ortholog, or derivative thereof with at least 70% sequence identity, preferably at least 80%, more preferably 85%, still more preferably 90%, and most preferably at least 95% sequence identity with human CTPS.
  • Methods of identifying orthlogs are known in the art. Normally, orthologs in different species retain the same function, due to presence of one or more protein motifs and/or 3-dimensional structures.
  • Orthologs are generally identified by sequence homology analysis, such as BLAST analysis, usually using protein bait sequences. Sequences are assigned as a potential ortholog if the best hit sequence from the forward BLAST result retrieves the original query sequence in the reverse BLAST (Huynen MA and Bork P, Proc Natl Acad Sci (1998) 95:5849-5856; Huynen MA et al, Genome Research (2000) 10:1204-1210). Programs for multiple sequence alignment, such as CLUSTAL (Thompson JD et al, 1994, Nucleic Acids Res 22:4673-4680) may be used to highlight conserved regions and/or residues of orthologous proteins and to generate phylogenetic trees.
  • CLUSTAL Thinson JD et al, 1994, Nucleic Acids Res 22:4673-4680
  • orthologous sequences from two species generally appear closest on the tree with respect to all other sequences from these two species.
  • Structural threading or other analysis of protein folding e.g., using software by ProCeryon, Biosciences, Salzburg, Austria
  • protein folding may also identify potential orthologs.
  • a gene duplication event follows speciation, a single gene in one species, such as C. elegans, may correspond to multiple genes (paralogs) in another, such as human.
  • the term "orthologs" encompasses paralogs.
  • percent (%) sequence identity with respect to a subject sequence, or a specified portion of a subject sequence, is defined as the percentage of nucleotides or amino acids in the candidate derivative sequence identical with the nucleotides or amino acids in the subject sequence (or specified portion thereof), after aligning the sequences and introducing gaps, if necessary to achieve the maximum percent sequence identity, as generated by the program WU-BLAST-2.0al9 (Altschul et al, J. Mol. Biol. (1997) 215:403-410) with all the search parameters set to default values.
  • the HSP S and HSP S2 parameters are dynamic values and are established by the program itself depending upon the composition of the particular sequence and composition of the particular database against which the sequence of interest is being searched.
  • a % identity value is determined by the number of matching identical nucleotides or amino acids divided by the sequence length for which the percent identity is being reported. "Percent (%) amino acid sequence similarity" is determined by doing the same calculation as for determining % amino acid sequence identity, but including conservative amino acid substitutions in addition to identical amino acids in the computation. A conservative amino acid substitution is one in which an amino acid is substituted for another amino acid having similar properties such that the folding or activity of the protein is not significantly affected.
  • Aromatic amino acids that can be substituted for each other are phenylalanine, tryptophan, and tyrosine; interchangeable hydrophobic amino acids are leucine, isoleucine, methionine, and valine; interchangeable polar amino acids are glutamine and asparagine; interchangeable basic amino acids are arginine, lysine and histidine; interchangeable acidic amino acids are aspartic acid and glutamic acid; and interchangeable small amino acids are alanine, serine, threonine, cysteine and glycine.
  • an alignment for nucleic acid sequences is provided by the local homology algorithm of Smith and Waterman (Smith and Waterman, 1981, Advances in Applied Mathematics 2:482-489; database: European Bioinformatics Institute; Smith and Waterman, 1981, J. of MolecBiol., 147:195-197; Nicholas et al., 1998, "A tutorial on Searching Sequence Databases and Sequence Scoring Methods” (www.psc.edu) and references cited therein.; W.R. Pearson, 1991, Genomics 11:635-650).
  • This algorithm can be applied to amino acid sequences by using the scoring matrix developed by Dayhoff (Dayhoff: Atlas of Protein Sequences and Structure, M. O. Dayhoff ed., 5 suppl.
  • Derivative nucleic acid molecules of the subject nucleic acid molecules include sequences that hybridize to the nucleic acid sequence of a CTPS.
  • the stringency of hybridization can be controlled by temperature, ionic strength, pH, and the presence of denaturing agents such as formamide during hybridization and washing.
  • a nucleic acid molecule of the invention is capable of hybridizing to a nucleic acid molecule containing the nucleotide sequence of a CTPS under high stringency hybridization conditions that are: prehybridization of filters containing nucleic acid for 8 hours to overnight at 65° C in a solution comprising 6X single strength citrate (SSC) ( ⁇ i SSC is 0.15 M NaCl, 0.015 M Na citrate; pH 7.0), 5X Denhardt's solution, 0.05% sodium pyrophosphate and 100 ⁇ g/ml herring sperm DNA; hybridization for 18-20 hours at 65° C in a solution containing 6X SSC, IX Denhardt's solution, 100 g/ml yeast tRNA and 0.05% sodium pyrophosphate; and washing of filters at 65° C for lh in a solution containing 0.
  • SSC single strength citrate
  • moderately stringent hybridization conditions are used that are: pretreatment of filters containing nucleic acid for 6 h at 40° C in a solution containing 35% formamide, 5X SSC, 50 mM Tris-HCl (pH7.5), 5mM EDTA, 0.1% PVP, 0.1% Ficoll, 1% BSA, and 500 ⁇ g/ml denatured salmon sperm DNA; hybridization for 18-20h at 40° C in a solution containing 35% formamide, 5X SSC, 50 mM Tris-HCl (pH7.5), 5mM EDTA, 0.02% PVP, 0.02% Ficoll, 0.2% BSA, 100 ⁇ g/ml salmon sperm DNA, and 10% (wt/vol) dextran sulfate; followed by washing twice for 1 hour at 55° C in a solution containing 2X SSC and 0.1% SDS.
  • low stringency conditions can be used that are: incubation for 8 hours to overnight at 37° C in a solution comprising 20% formamide, 5 x SSC, 50 mM sodium phosphate (pH 7.6), 5X Denhardt's solution, 10% dextran sulfate, and 20 jug/ml denatured sheared salmon sperm DNA; hybridization in the same buffer for 18 to 20 hours; and washing of filters in 1 x SSC at about 37° C for 1 hour.
  • Isolation, Production, Expression, and Mis-expression of CTPS Nucleic Acids and Polypeptides are useful for identifying and testing agents that modulate CTPS function and for other applications related to the involvement of CTPS in the PTEN pathway.
  • CTPS nucleic acids and derivatives and orthologs thereof may be obtained using any available method. For instance, techniques for isolating cDNA or genomic DNA sequences of interest by screening DNA libraries or by using polymerase chain reaction (PCR) are well known in the art.
  • PCR polymerase chain reaction
  • the particular use for the protein will dictate the particulars of expression, production, and purification methods. For instance, production of proteins for use in screening for modulating agents may require methods that preserve specific biological activities of these proteins, whereas production of proteins for antibody generation may require structural integrity of particular epitopes. Expression of proteins to be purified for screening or antibody production may require the addition of specific tags (e.g., generation of fusion proteins).
  • CTPS protein for assays used to assess CTPS function, such as involvement in cell cycle regulation or hypoxic response, may require expression in eukaryotic cell lines capable of these cellular activities.
  • Techniques for the expression, production, and purification of proteins are well known in the art; any suitable means therefore may be used (e.g., Higgins SJ and Hames BD (eds.) Protein Expression: A Practical Approach, Oxford University Press Inc., New York 1999; Stanbury PF et al., Principles of
  • recombinant CTPS is expressed in a cell line known to have defective PTEN function.
  • the recombinant cells are used in cell-based screening assay systems of the invention, as described further below.
  • the nucleotide sequence encoding a CTPS polypeptide can be inserted into any appropriate expression vector.
  • the necessary transcriptional and translational signals can derive from the native CTPS gene and/or its flanking regions or can be heterologous.
  • a variety of host-vector expression systems may be utilized, such as mammalian cell systems infected with virus (e.g. vaccinia virus, adenovirus, etc.); insect cell systems infected with virus (e.g. baculovirus); microorganisms such as yeast containing yeast vectors, or bacteria transformed with bacteriophage, plasmid, or cosmid DNA.
  • virus e.g. vaccinia virus, adenovirus, etc.
  • insect cell systems infected with virus e.g. baculovirus
  • microorganisms such as yeast containing yeast vectors, or bacteria transformed with bacteriophage, plasmid, or cosmid DNA.
  • An isolated host cell strain that modulates the expression of, modifies, and/or specifically processes the gene product may be used.
  • the expression vector can comprise a promoter operably linked to a CTPS gene nucleic acid, one or more origins of replication, and, one or more selectable markers (e.g. thymidine kinase activity, resistance to antibiotics, etc.).
  • selectable markers e.g. thymidine kinase activity, resistance to antibiotics, etc.
  • recombinant expression vectors can be identified by assaying for the expression of the CTPS gene product based on the physical or functional properties of the CTPS protein in in vitro assay systems (e.g. immunoassays).
  • the CTPS protein, fragment, or derivative may be optionally expressed as a fusion, or chimeric protein product (i.e.
  • a chimeric product can be made by ligating the appropriate nucleic acid sequences encoding the desired amino acid sequences to each other using standard methods and expressing the chimeric product.
  • a chimeric product may also be made by protein synthetic techniques, e.g. by use of a peptide synthesizer (Hunkapiller et al, Nature (1984) 310:105-111). Once a recombinant cell that expresses the CTPS gene sequence is identified, the gene product can be isolated and purified using standard methods (e.g.
  • CTPS proteins can be purified from natural sources, by standard methods (e.g. immunoaffinity purification). Once a protein is obtained, it may be quantified and its activity measured by appropriate methods, such as immunoassay, bioassay, or other measurements of physical properties, such as crystallography.
  • the methods of this invention may also use cells that have been engineered for altered expression (mis-expression) of CTPS or other genes associated with the PTEN pathway.
  • mis-expression encompasses ectopic expression, over- expression, under-expression, and non-expression (e.g. by gene knock-out or blocking expression that would otherwise normally occur).
  • Genetically modified animals Animal models that have been genetically modified to alter CTPS expression may be used in in vivo assays to test for activity of a candidate PTEN modulating agent, or to further assess the role of CTPS in a PTEN pathway process such as apoptosis or cell proliferation.
  • the altered CTPS expression results in a detectable phenotype, such as decreased or increased levels of cell proliferation, angiogenesis, or apoptosis compared to control animals having normal CTPS expression.
  • the genetically modified animal may additionally have altered PTEN expression (e.g. PTEN knockout).
  • Preferred genetically modified animals are mammals such as primates, rodents (preferably mice or rats), among others.
  • Preferred non-mammalian species include zebrafish, C.
  • Preferred genetically modified animals are transgenic animals having a heterologous nucleic acid sequence present as an extrachromosomal element in a portion of its cells, i.e. mosaic animals (see, for example, techniques described by Jakobovits, 1994, Curr. Biol. 4:761-763.) or stably integrated into its germ line DNA (i.e., in the genomic sequence of most or all of its cells).
  • Heterologous nucleic acid is introduced into the germ line of such transgenic animals by genetic manipulation of, for example, embryos or embryonic stem cells of the host animal. Methods of making transgenic animals are well-known in the art (for transgenic mice see Brinster et al., Proc. Nat.
  • the transgenic animal is a "knock-out" animal having a heterozygous or homozygous alteration in the sequence of an endogenous CTPS gene that results in a decrease of CTPS function, preferably such that CTPS expression is undetectable or insignificant.
  • Knock-out animals are typically generated by homologous recombination with a vector comprising a transgene having at least a portion of the gene to be knocked out. Typically a deletion, addition or substitution has been introduced into the transgene to functionally disrupt it.
  • the transgene can be a human gene (e.g., from a human genomic clone) but more preferably is an ortholog of the human gene derived from the transgenic host species.
  • a mouse CTPS gene is used to construct a homologous recombination vector suitable for altering an endogenous CTPS gene in the mouse genome.
  • mice Detailed methodologies for homologous recombination in mice are available (see Capecchi, Science (1989) 244:1288-1292; Joyner et al, Nature (1989) 338:153-156). Procedures for the production of non-rodent transgenic mammals and other animals are also available (Houdebine and Chourrout, supra; Pursel et al, Science (1989) 244:1281-1288; Simms et al, Bio/Technology (1988) 6:179-183).
  • knock-out animals such as mice harboring a knockout of a specific gene, may be used to produce antibodies against the human counterpart of the gene that has been knocked out (Claesson MH et al., (1994) Scan J Immunol 40:257-264; DeclerckPJ et al., (1995) J Biol Chem. 270:8397-400).
  • the transgenic animal is a "knock-in" animal having an alteration in its genome that results in altered expression (e.g., increased (including ectopic) or decreased expression) of the CTPS gene, e.g., by introduction of additional copies of CTPS, or by operatively inserting a regulatory sequence that provides for altered expression of an endogenous copy of the CTPS gene.
  • a regulatory sequence include inducible, tissue-specific, and constitutive promoters and enhancer elements.
  • the knock- in can be homozygous or heterozygous.
  • Transgenic nonhuman animals can also be produced that contain selected systems allowing for regulated expression of the transgene.
  • cre/loxP recombinase system of bacteriophage PI (Lakso et al., PNAS (1992) 89:6232-6236; U.S. Pat. No. 4,959,317). If a cre/loxP recombinase system is used to regulate expression of the transgene, animals containing transgenes encoding both the Cre recombinase and a selected protein are required.
  • Such animals can be provided through the construction of "double" transgenic animals, e.g., by mating two transgenic animals, one containing a transgene encoding a selected protein and the other containing a transgene encoding a recombinase.
  • a recombinase system is the FLP recombinase system of Saccharomyces cerevisiae (O'Gorman et al. (1991) Science 251:1351-1355; U.S. Pat. No. 5,654,182).
  • both Cre-LoxP and Flp-Frt are used in the same system to regulate expression of the transgene, and for sequential deletion of vector sequences in the same cell (Sun X et al (2000) Nat Genet 25:83-6).
  • the genetically modified animals can be used in genetic studies to further elucidate the PTEN pathway, as animal models of disease and disorders implicating defective PTEN function, and for in vivo testing of candidate therapeutic agents, such as those identified in screens described below.
  • the candidate therapeutic agents are administered to a genetically modified animal having altered CTPS function and phenotypic changes are compared with appropriate control animals such as genetically modified animals that receive placebo treatment, and/or animals with unaltered CTPS expression that receive candidate therapeutic agent.
  • appropriate control animals such as genetically modified animals that receive placebo treatment, and/or animals with unaltered CTPS expression that receive candidate therapeutic agent.
  • CTPS function animal models having defective PTEN function (and otherwise normal CTPS function), can be used in the methods of the present invention.
  • a mouse with defective DAF18 function can be used to assess, in vivo, the activity of a candidate DAF18 modulating agent identified in one of the in vitro assays described below.
  • Transgenic mice with defective DAF18/PTEN function have been described in literature- (DiCristofano A et al (1998) Nat genet 19:348-355).
  • the candidate PTEN modulating agent when administered to a model system with cells defective in PTEN function, produces a detectable phenotypic change in the model system indicating that the PTEN function is restored, i.e., the cells exhibit normal cell cycle progression.
  • the invention provides methods to identify agents that interact with and/or modulate the function of CTPS and/or the PTEN pathway. Modulating agents identified by the methods are also part of the invention. Such agents are useful in a variety of diagnostic and therapeutic applications associated with the PTEN pathway, as well as in further analysis of the CTPS protein and its contribution to the PTEN pathway. Accordingly, the invention also provides methods for modulating the PTEN pathway comprising the step of specifically modulating CTPS activity by administering a CTPS- interacting or -modulating agent.
  • a "CTPS -modulating agent” is any agent that modulates CTPS function, for example, an agent that interacts with CTPS to inhibit or enhance CTPS activity or otherwise affect normal CTPS function.
  • CTPS function can be affected at any level, including transcription, protein expression, protein localization, and cellular or extra-cellular activity.
  • the CTPS - modulating agent specifically modulates the function of the CTPS.
  • the phrases "specific modulating agent”, “specifically modulates”, etc., are used herein to refer to modulating agents that directly bind to the CTPS polypeptide or nucleic acid, and preferably inhibit, enhance, or otherwise alter, the function of the CTPS. These phrases also encompass modulating agents that alter the interaction of the CTPS with a binding partner, substrate, or cofactor (e.g. by binding to a binding partner of a CTPS, or to a protein/binding partner complex, and altering CTPS function).
  • the CTPS- modulating agent is a modulator of the PTEN pathway (e.g. it restores and/or upregulates PTEN function) and thus is also a PTEN-modulating agent.
  • Preferred CTPS-modulating agents include small molecule compounds; CTPS- interacting proteins, including antibodies and other biotherapeutics; and nucleic acid modulators such as antisense and RNA inhibitors.
  • the modulating agents may be formulated in pharmaceutical compositions, for example, as compositions that may comprise other active ingredients, as in combination therapy, and/or suitable carriers or excipients. Techniques for formulation and administration of the compounds may be found in "Remington's Pharmaceutical Sciences” Mack Publishing Co., Easton, PA, 19 t'h edition.
  • Small molecule modulators Small molecules are often preferred to modulate function of proteins with enzymatic function, and/or containing protein interaction domains.
  • Chemical agents referred to in the art as "small molecule” compounds are typically organic, non-peptide molecules, having a molecular weight up to 10,000, preferably up to 5,000, more preferably up to 1,000, and most preferably up to 500 daltons.
  • This class of modulators includes chemically synthesized molecules, for instance, compounds from combinatorial chemical libraries. Synthetic compounds may be rationally designed or identified based on known or inferred properties of the CTPS protein or may be identified by screening compound libraries.
  • modulators of this class are natural products, particularly secondary metabolites from organisms such as plants or fungi, which can also be identified by screening compound libraries for CTPS-modulating activity. Methods for generating and obtaining compounds are well known in the art (Schreiber SL, Science (2000) 151: 1964-1969; Radmann J and Gunther J, Science (2000) 151:1947-1948). Small molecule modulators identified from screening assays, as described below, can be used as lead compounds from which candidate clinical compounds may be designed, optimized, and synthesized. Such clinical compounds may have utility in treating pathologies associated with the PTEN pathway.
  • candidate small molecule modulating agents may be improved several-fold through iterative secondary functional validation, as further described below, structure determination, and candidate modulator modification and testing.
  • candidate clinical compounds are generated with specific regard to clinical and pharmacological properties.
  • the reagents may be derivatized and re-screened using in vitro and in vivo assays to optimize activity and minimize toxicity for pharmaceutical development.
  • Protein Modulators Specific CTPS-interacting proteins are useful in a variety of diagnostic and therapeutic applications related to the PTEN pathway and related disorders, as well as in validation assays for other CTPS-modulating agents.
  • CTPS- interacting proteins affect normal CTPS function, including transcription, protein expression, protein localization, and cellular or extra-cellular activity.
  • CTPS-interacting proteins are useful in detecting and providing information about the function of CTPS proteins, as is relevant to PTEN related disorders, such as cancer (e.g., for diagnostic means).
  • a CTPS-interacting protein may be endogenous, i.e. one that naturally interacts genetically or biochemically with a CTPS, such as a member of the CTPS pathway that modulates CTPS expression, localization, and/or activity.
  • CTPS-modulators include dominant negative forms of CTPS-interacting proteins and of CTPS proteins themselves.
  • Yeast two-hybrid and variant screens offer preferred methods for identifying endogenous CTPS-interacting proteins (Finley, R. L. et al. (1996) in DNA Cloning-Expression
  • An CTPS-interacting protein may be an exogenous protein, such as a CTPS- specific antibody or a T-cell antigen receptor (see, e.g., Harlow and Lane (1988) Antibodies, A Laboratory Manual, Cold Spring Harbor Laboratory; Harlow and Lane (1999) Using antibodies: a laboratory manual. Cold Spring Harbor, NY: Cold Spring Harbor Laboratory Press).
  • CTPS antibodies are further discussed below.
  • a CTPS-interacting protein specifically binds a CTPS protein.
  • a CTPS-modulating agent binds a CTPS substrate, binding partner, or cofactor.
  • the protein modulator is a CTPS specific antibody agonist or antagonist.
  • the antibodies have therapeutic and diagnostic utilities, and can be used in screening assays to identify CTPS modulators.
  • the antibodies can also be used in dissecting the portions of the CTPS pathway responsible for various cellular responses and in the general processing and maturation of the CTPS.
  • Antibodies that specifically bind CTPS polypeptides can be generated using known methods.
  • the antibody is specific to a mammalian ortholog of CTPS polypeptide, and more preferably, to human CTPS.
  • Antibodies may be polyclonal, monoclonal (mAbs), humanized or chimeric antibodies, single chain antibodies, Fab fragments, F(ab').sub.2 fragments, fragments produced by a FAb expression library, anti- idiotypic (anti-Id) antibodies, and epitope-binding fragments of any of the above.
  • Epitopes of CTPS which are particularly antigenic can be selected, for example, by routine screening of CTPS polypeptides for antigenicity or by applying a theoretical method for selecting antigenic regions of a protein (Hopp and Wood (1981), Proc. Nati. Acad. Sci. U.S.A. 78:3824-28; Hopp and Wood, (1983) Mol. Immunol.
  • Antibodies may be generated against crude cell extracts of CTPS or substantially purified fragments thereof. If CTPS fragments are used, they preferably comprise at least 10, and more preferably, at least 20 contiguous amino acids of a CTPS protein. In a particular embodiment, CTPS-specific antigens and/or immunogens are coupled to carrier proteins that stimulate the immune response.
  • the subject polypeptides are covalently coupled to the keyhole limpet hemocyanin (KLH) carrier, and the conjugate is emulsified in Freund's complete adjuvant, which enhances the immune response.
  • KLH keyhole limpet hemocyanin
  • An appropriate immune system such as a laboratory rabbit or mouse is immunized according to conventional protocols.
  • the presence of CTPS-specific antibodies is assayed by an appropriate assay such as a solid phase enzyme-linked immunosorbant assay (ELIS A) using immobilized corresponding CTPS polypeptides.
  • Other assays such as radioimmunoassays or fluorescent assays might also be used.
  • Chimeric antibodies specific to CTPS polypeptides can be made that contain different portions from different animal species.
  • a human immunoglobulin constant region may be linked to a variable region of a murine mAb, such that the antibody derives its biological activity from the human antibody, and its binding specificity from the murine fragment.
  • Chimeric antibodies are produced by splicing together genes that encode the appropriate regions from each species (Morrison et al.,
  • Humanized antibodies which are a form of chimeric antibodies, can be generated by grafting complementary-determining regions (CDRs) (Carlos, T. M., J. M. Harlan. 1994. Blood 84:2068-2101) of mouse antibodies into a background of human framework regions and constant regions by recombinant DNA technology (Riechmann LM, et al., 1988 Nature 323: 323-327).
  • CDRs complementary-determining regions
  • Humanized antibodies contain ⁇ 10% murine sequences and -90% human sequences, and thus further reduce or eliminate immunogenicity, while retaining the antibody specificities (Co MS, and Queen C. 1991 Nature 351: 501-501; Morrison SL. 1992 Ann. Rev. Immun. 10:239-265).
  • Humanized antibodies and methods of their production are well-known in the art (U.S. Pat. Nos. 5,530,101, 5,585,089, 5,693,762, and 6,180,370).
  • CTPS-specific single chain antibodies which are recombinant, single chain polypeptides formed by linking the heavy and light chain fragments of the Fv regions via an amino acid bridge, can be produced by methods known in the art (U.S. Pat. No.
  • antibodies will be labeled by joining, either covalently or non-covalently, a substance that provides for a detectable signal, or that is toxic to cells that express the targeted protein (Menard S, et al., hit J. Biol Markers (1989) 4:131-134).
  • labels and conjugation techniques are known and are reported extensively in both the scientific and patent literature. Suitable labels include radionuclides, enzymes, substrates, cofactors, inhibitors, fluorescent moieties, fluorescent emitting lanthanide metals, chemiluminescent moieties, bioluminescent moieties, magnetic particles, and the like (U.S. Pat. Nos.
  • recombinant immunoglobulins may be produced (U.S. Pat. No. 4,816,567).
  • Antibodies to cytoplasmic polypeptides may be delivered and reach their targets by conjugation with membrane-penetrating toxin proteins (U.S. Pat. No. 6,086,900).
  • the antibodies of the subject invention are typically administered parenterally, when possible at the target site, or intravenously. The therapeutically effective dose and dosage regimen is determined by clinical studies.
  • the amount of antibody administered is in the range of about 0.1 mg/kg -to about 10 mg/kg of patient weight.
  • a unit dosage injectable form e.g., solution, suspension, emulsion
  • a pharmaceutically acceptable vehicle e.g., water, saline, Ringer's solution, dextrose solution, and 5% human serum albumin.
  • Nonaqueous vehicles such as fixed oils, ethyl oleate, or liposome carriers may also be used.
  • the vehicle may contain minor amounts of additives, such as buffers and preservatives, which enhance isotonicity and chemical stability or otherwise enhance therapeutic potential.
  • the antibodies' concentrations in such vehicles are typically in the range of about 1 mg/ml to aboutlO mg/ml. Immunotherapeutic methods are further described in the literature (US Pat. No. 5,859,206; WO0073469).
  • nucleic Acid Modulators comprise nucleic acid molecules, such as antisense oligomers or double stranded RNA (dsRNA), which generally inhibit CTPS activity.
  • Preferred nucleic acid modulators interfere with the function of the CTPS nucleic acid such as DNA replication, transcription, translocation of the CTPS RNA to the site of protein translation, translation of protein from the CTPS RNA, splicing of the CTPS RNA to yield one or more mRNA species, or catalytic activity which may be engaged in or facilitated by the CTPS RNA.
  • the antisense oligomer is an oligonucleotide that is sufficiently complementary to a CTPS mRNA to bind to and prevent translation, preferably by binding to the 5' untranslated region.
  • CTPS-specific antisense oligonucleotides preferably range from at least 6 to about 200 nucleotides.
  • the oligonucleotide is preferably at least 10, 15, or 20 nucleotides in length.
  • the oligonucleotide is preferably less than 50, 40, or 30 nucleotides in length.
  • the oligonucleotide can be DNA or RNA or a chimeric mixture or derivatives or modified versions thereof, single-stranded or double-stranded.
  • the oligonucleotide can be modified at the base moiety, sugar moiety, or phosphate backbone.
  • the oligonucleotide ' may include other appending groups such as peptides, agents that facilitate transport across the cell membrane, hybridization-triggered cleavage agents, and intercalating agents.
  • the antisense oligomer is a phosphothioate morpholino oligomer (PMO).
  • PMOs are assembled from four different morpholino subunits, each of which contain one of four genetic bases (A, C, G, or T) linked to a six-membered morpholine ring. Polymers of these subunits are joined by non-ionic phosphodiamidate intersubunit linkages.
  • CTPS nucleic acid modulators are double-stranded RNA species mediating RNA interference (RNAi).
  • RNAi is the process of sequence-specific, post-transcriptional gene silencing in animals and plants, initiated by double-stranded RNA (dsRNA) that is homologous in sequence to the silenced gene.
  • dsRNA double-stranded RNA
  • Methods relating to the use of RNAi to silence genes in C. elegans, Drosophila, plants, and humans are known in the art (Fire A, et al, 1998 Nature 391:806-811; Fire, A. Trends Genet. 15, 358-363 (1999); Sharp, P. A. RNA interference 2001. Genes Dev. 15, 485-490 (2001); Hammond, S. M., et al., Nature Rev. Genet. 2, 110-1119 (2001); Tuschl, T. Chem. Biochem.
  • Nucleic acid modulators are commonly used as research reagents, diagnostics, and therapeutics.
  • antisense oligonucleotides which are able to inhibit gene expression with extraordinar specificity, are often used to elucidate the function of particular genes (see, for example, U.S. Pat. No. 6,165,790).
  • Nucleic acid modulators are also used, for example, to distinguish between functions of various members of a biological pathway.
  • antisense oligomers have been employed as therapeutic moieties in the treatment of disease states in animals and man and have been demonstrated in numerous clinical trials to be safe and effective (Milligan JF, et al, Current Concepts in Antisense Drug Design, J Med Chem.
  • a CTPS-specific nucleic acid modulator is used in an assay to further elucidate the role of the CTPS in the PTEN pathway, and/or its relationship to other members of the pathway.
  • a CTPS- specific antisense oligomer is used as a therapeutic agent for treatment of PTEN-related disease states.
  • Assay Systems The invention provides assay systems and screening methods for identifying specific modulators of CTPS activity.
  • an "assay system” encompasses all the components required for performing and analyzing results of an assay that detects and/or measures a particular event.
  • primary assays are used to identify or confirm a modulator's specific biochemical or molecular effect with respect to the CTPS nucleic acid or protein.
  • secondary assays further assess the activity of a CTPS modulating agent identified by a primary assay and may confirm that the modulating agent affects CTPS in a manner relevant to the PTEN pathway. In some cases, CTPS modulators will be directly tested in a secondary assay.
  • the screening method comprises contacting a suitable assay system comprising a CTPS polypeptide or nucleic acid with a candidate agent under conditions whereby, but for the presence of the agent, the system provides a reference activity (e.g. synthase activity), which is based on the particular molecular event the screening method detects.
  • a reference activity e.g. synthase activity
  • a statistically significant difference between the agent-biased activity and the reference activity indicates that the candidate agent modulates CTPS activity, and hence the PTEN pathway.
  • the CTPS polypeptide or nucleic acid used in the assay may comprise any of the nucleic acids or polypeptides described above.
  • Primary Assays The type of modulator tested generally determines the type of primary assay.
  • screening assays are used to identify candidate modulators. Screening assays may be cell-based or may use a cell-free system that recreates or retains the relevant biochemical reaction of the target protein (reviewed in Sittampalam GS et al, Curr Opin Chem Biol (1997) 1:384-91 and accompanying references).
  • cell-based refers to assays using live cells, dead cells, or a particular cellular fraction, such as a membrane, endoplasmic reticulum, or mitochondrial fraction.
  • cell free encompasses assays using substantially purified protein (either endogenous or recombinantly produced), partially purified or crude cellular extracts. Screening assays may detect a variety of molecular events, including protein-DNA interactions, protein-protein interactions (e.g., receptor-ligand binding), transcriptional activity (e.g., using a reporter gene), enzymatic activity (e.g., via a property of the substrate), activity of second messengers, immunogenicty and changes in cellular morphology or other cellular characteristics.
  • Appropriate screening assays may use a wide range of detection methods including fluorescent, radioactive, colorimetric, spectrophotometric, and amperometric methods, to provide a read-out for the particular molecular event detected.
  • Cell-based screening assays usually require systems for recombinant expression of CTPS and any auxiliary proteins demanded by the particular assay.
  • Appropriate methods for generating recombinant proteins produce sufficient quantities of proteins that retain their relevant biological activities and are of sufficient purity to optimize activity and assure assay reproducibihty.
  • Yeast two-hybrid and variant screens, and mass spectrometry provide preferred methods for determining protein-protein interactions and elucidation of protein complexes.
  • the binding specificity of the interacting protein to the CTPS protein may be assayed by various known methods such as substrate processing (e.g. ability of the candidate CTPS-specific binding agents to function as negative effectors in CTPS-expressing cells), binding equilibrium constants (usually at least about 10 7 M " ⁇ preferably at least about 10 8 M "1 , more preferably at least about 10 9 M " ), and immunogenicity (e.g. ability to elicit CTPS specific antibody in a heterologous host such as a mouse, rat, goat or rabbit).
  • substrate processing e.g. ability of the candidate CTPS-specific binding agents to function as negative effectors in CTPS-expressing cells
  • binding equilibrium constants usually at least about 10 7 M " ⁇ preferably at least about 10 8 M "1 , more preferably at least about 10 9 M "
  • immunogenicity e.g. ability to elicit CTPS specific antibody in a heterologous host such as a mouse, rat, goat or rabbit.
  • binding may be assayed by,
  • the screening assay may measure a candidate agent's ability to specifically bind to or modulate activity of a CTPS polypeptide, a fusion protein thereof, or to cells or membranes bearing the polypeptide or fusion protein.
  • the CTPS polypeptide can be full length or a fragment thereof that retains functional CTPS activity.
  • the CTPS polypeptide may be fused to another polypeptide, such as a peptide tag for detection or anchoring, or to another tag.
  • the CTPS polypeptide is preferably human CTPS, or is an ortholog or derivative thereof as described above.
  • the screening assay detects candidate agent-based modulation of CTPS interaction with a binding target, such as an endogenous or exogenous protein or other substrate that has CTPS -specific binding activity, and can be used to assess normal CTPS gene function.
  • a binding target such as an endogenous or exogenous protein or other substrate that has CTPS -specific binding activity
  • Suitable assay formats that may be adapted to screen for CTPS modulators are known in the art.
  • Preferred screening assays are high throughput or ultra high throughput and thus provide automated, cost-effective means of screening compound libraries for lead compounds (Fernandes PB, Curr Opin Chem Biol (1998) 2:597-603; Sundberg SA, Curr Opin Biotechnol 2000, 11:47-53).
  • screening assays uses fluorescence technologies, including fluorescence polarization, time-resolved fluorescence, and fluorescence resonance energy transfer. These systems offer means to monitor protein-protein or DNA-protein interactions in which the intensity of the signal emitted from dye-labeled molecules depends upon their interactions with partner molecules (e.g., Selvin PR, Nat Struct Biol (2000) 7:730-4; Fernandes PB, supra; Hertzberg RP and Pope AJ, Curr Opin Chem Biol (2000) 4:445-451).
  • partner molecules e.g., Selvin PR, Nat Struct Biol (2000) 7:730-4; Fernandes PB, supra; Hertzberg RP and Pope AJ, Curr Opin Chem Biol (2000) 4:445-45.
  • a variety of suitable assay systems may be used to identify candidate CTPS and PTEN pathway modulators (e.g. U.S. Pat. Nos.
  • Apoptosis assays Apoptosis or programmed cell death is a suicide program is activated within the cell, leading to fragmentation of DNA, shrinkage of the cytoplasm, membrane changes and cell death. Apoptosis is mediated by proteolytic enzymes of the caspase family. Many of the altering parameters of a cell are measurable during apoptosis. Assays for apoptosis may be performed by terminal deoxynucleotidyl transferase- mediated digoxigenin-11-dUTP nick end labeling (TUNEL) assay.
  • TUNEL terminal deoxynucleotidyl transferase- mediated digoxigenin-11-dUTP nick end labeling
  • the TUNEL assay is used to measure nuclear DNA fragmentation characteristic of apoptosis ( Lazebnik et al, 1994, Nature 371, 346), by following the incorporation of fluorescein-dUTP (Yonehara et al, 1989, J. Exp. Med. 169, 1747). Apoptosis may further be assayed by acridine orange staining of tissue culture cells (Lucas, R., et al., 1998, Blood 15:4730-41). Other cell- based apoptosis assays include the caspase-3/7 assay and the cell death nucleosome ELISA assay.
  • the caspase 3/7 assay is based on the activation of the caspase cleavage activity as part of a cascade of events that occur during programmed cell death in many apoptotic pathways.
  • the caspase 3/7 assay commercially available Apo-ONETM Homogeneous Caspase-3/7 assay from Promega, cat# 67790
  • lysis buffer and caspase substrate are mixed and added to cells.
  • the caspase substrate becomes fluorescent when cleaved by active caspase 3/7.
  • the nucleosome ELISA assay is a general cell death assay known to those skilled in the art, and available commercially (Roche, Cat# 1774425).
  • This assay is a quantitative sandwich-enzyme-immunoassay which uses monoclonal antibodies directed against DNA and histones respectively, thus specifically determining amount of mono- and oligonucleosomes in the cytoplasmic fraction of cell lysates.
  • Mono and oligonucleosomes are enriched in the cytoplasm during apoptosis due to the fact that DNA fragmentation occurs several hours before the plasma membrane breaks down, allowing for accumalation in the cytoplasm. Nucleosomes are not present in the cytoplasmic fraction of cells that are not undergoing apoptosis.
  • the Phospho-histone H2B assay is another apoptosis assay, based on phosphorylation of histone H2B as a result of apoptosis.
  • Fluorescent dyes that are associated with phosphohistone H2B may be used to measure the increase of phosphohistone H2B as a result of apoptosis.
  • Apoptosis assays that simultaneously measure multiple parameters associated with apoptosis have also been developed. In such assays, various cellular parameters that can be associated with antibodies or fluorescent dyes, and that mark various stages of apoptosis are labeled, and the results are measured using instruments such as CellomicsTM ArrayScan ® HCS System.
  • the measurable parameters and their markers include anti-active caspase-3 antibody which marks intermediate stage apoptosis, anti-PARP-p85 antibody (cleaved PARP) which marks late stage apoptosis, Hoechst labels which label the nucleus and are used to measure nuclear swelling as a measure of early apoptosis and nuclear condensation as a measure of late apoptosis, and TOTO-3 fluorescent dye which labels DNA of dead cells with high cell membrane permeability.
  • An apoptosis assay system may comprise a cell that expresses a CTPS, and that optionally has defective PTEN function (e.g. PTEN is over-expressed or under-expressed relative to wild-type cells).
  • a test agent can be added to the apoptosis assay system and changes in induction of apoptosis relative to controls where no test agent is added, identify candidate PTEN modulating agents.
  • an apoptosis assay may be used as a secondary assay to test a candidate PTEN modulating agents that is initially identified using a cell-free assay system.
  • An apoptosis assay may also be used to test whether CTPS function plays a direct role in apoptosis.
  • an apoptosis assay may be performed on cells that over- or under-express CTPS relative to wild type cells. Differences in apoptotic response compared to wild type cells suggests that the CTPS plays a direct role in the apoptotic response.
  • Apoptosis assays are described further in US Pat. No. 6,133,437.
  • Cell proliferation and cell cycle assays may be assayed via bromodeoxyuridine (BRDU) incorporation.
  • BRDU bromodeoxyuridine
  • This assay identifies a cell population undergoing DNA synthesis by incorporation of BRDU into newly-synthesized DNA. Newly-synthesized DNA may then be detected using an anti-BRDU antibody (Hoshino et al, 1986, Int. J. Cancer 38, 369; Campana et al, 1988, J. Immunol. Meth. 107, 79), or by other means.
  • Cell proliferation is also assayed via phospho-histone H3 staining, which identifies a cell population undergoing mitosis by phosphorylation of histone H3.
  • Incorporation can then be measured by standard techniques such as by counting of radioisotope in a scintillation counter (e.g., Beckman LS 3800 Liquid Scintillation Counter).
  • a scintillation counter e.g., Beckman LS 3800 Liquid Scintillation Counter.
  • Another proliferation assay uses the dye Alamar Blue (available from
  • MTS assay is based on in vitro cytotoxicity assessment of industrial chemicals, and uses the soluble tetrazolium salt, MTS.
  • MTS assays are commercially available, for example, the Promega CellTiter 96 ® AQueous Non-Radioactive Cell Proliferation Assay (Cat.# G5421).
  • Cell proliferation may also be assayed by colony formation in soft agar, or clonogenic survival assay (Sambrook et al., Molecular Cloning, Cold Spring Harbor (1989)). For example, cells transformed with CTPS are seeded in soft agar plates, and colonies are measured and counted after two weeks incubation. Cell proliferation may also be assayed by measuring ATP levels as indicator of metabolically active cells. Such assays are commercially available, for example Cell Titer-GloTM, which is a luminescent homogeneous assay available from Promega. Involvement of a gene in the cell cycle may be assayed by flow cytometry (Gray JW et al.
  • a cell proliferation or cell cycle assay system may comprise a cell that expresses a CTPS, and that optionally has defective PTEN function (e.g. PTEN is over-expressed or under-expressed relative to wild-type cells).
  • a test agent can be added to the assay system and changes in cell proliferation or cell cycle relative to controls where no test agent is added, identify candidate PTEN modulating agents.
  • the cell proliferation or cell cycle assay may be used as a secondary assay to test a candidate PTEN modulating agents that is initially identified using another assay system such as a cell-free assay system.
  • a cell proliferation assay may also be used to test whether CTPS function plays a direct role in cell proliferation or cell cycle.
  • a cell proliferation or cell cycle assay may be performed on cells that over- or under- express CTPS relative to wild type cells. Differences in proliferation or cell cycle compared to wild type cells suggests that the CTPS plays a direct role in cell proliferation or cell cycle.
  • Angiogenesis Angiogenesis may be assayed using various human endothelial cell systems, such as umbilical vein, coronary artery, or dermal cells.
  • angiogenesis assay system may comprise a cell that expresses a CTPS, and that optionally has defective PTEN function
  • angiogenesis assay e.g. PTEN is over-expressed or under-expressed relative to wild-type cells.
  • a test agent can be added to the angiogenesis assay system and changes in angiogenesis relative to controls where no test agent is added, identify candidate PTEN modulating agents.
  • the angiogenesis assay may be used as a secondary assay to test a candidate PTEN modulating agents that is initially identified using another assay system.
  • An angiogenesis assay may also be used to test whether CTPS function plays a direct role in cell proliferation. For example, an angiogenesis assay may be performed on cells that over- or under-express CTPS relative to wild type cells.
  • hypoxia inducible factor- 1 The alpha subunit of the transcription factor, hypoxia inducible factor- 1 (HEF-1), is upregulated in tumor cells following exposure to hypoxia in vitro. Under hypoxic conditions, HLF-1 stimulates the expression of genes known to be important in tumour cell survival, such as those encoding glyolytic enzymes and VEGF.
  • hypoxic induction assay system may comprise a cell that expresses a CTPS, and that optionally has defective PTEN function (e.g. PTEN is over-expressed or under- expressed relative to wild-type cells).
  • a test agent can be added to the hypoxic induction assay system and changes in hypoxic response relative to controls where no test agent is added, identify candidate PTEN modulating agents.
  • the hypoxic induction assay may be used as a secondary assay to test a candidate PTEN modulating agents that is initially identified using another assay system.
  • a hypoxic induction assay may also be used to test whether CTPS function plays a direct role in the hypoxic response.
  • a hypoxic induction assay may be performed on cells that over- or under-express CTPS relative to wild type cells. Differences in hypoxic response compared to wild type cells suggests that the CTPS plays a direct role in hypoxic induction.
  • Cell adhesion assays measure adhesion of cells to purified adhesion proteins, or adhesion of cells to each other, in presence or absence of candidate modulating agents.
  • Cell-protein adhesion assays measure the ability of agents to modulate the adhesion of cells to purified proteins. For example, recombinant proteins are produced, diluted to 2.5g/mL in PBS, and used to coat the wells of a microtiter plate. The wells used for negative control are not coated. Coated wells are then washed, blocked with 1% BSA, and washed again. Compounds are diluted to 2x final test concentration and added to the blocked, coated wells. Cells are then added to the wells, and the unbound cells are washed off.
  • Retained cells are labeled directly on the plate by adding a membrane-permeable fluorescent dye, such as calcein-AM, and the signal is quantified in a fluorescent microplate reader.
  • a membrane-permeable fluorescent dye such as calcein-AM
  • Cell-cell adhesion assays measure the ability of agents to modulate binding of cell adhesion proteins with their native ligands. These assays use cells that naturally or recombinantly express the adhesion protein of choice.
  • cells expressing the cell adhesion protein are plated in wells of a multiwell plate.
  • Cells expressing the ligand are labeled with a membrane-permeable fluorescent dye, such as BCECF , and allowed to adhere to the monolayers in the presence of candidate agents.
  • Unbound cells are washed off, and bound cells are detected using a fluorescence plate reader.
  • High-throughput cell adhesion assays have also been described. In one such assay, small molecule ligands and peptides are bound to the surface of microscope slides using a microarray spotter, intact cells are then contacted with the slides, and unbound cells are washed off. In this assay, not only the binding specificity of the peptides and modulators against cell lines are determined, but also the functional cell signaling of attached cells using immunofluorescence techniques in situ on the microchip is measured (Falsey JR et al., Bioconjug Chem. 2001 May-Jun;12(3):346-53).
  • Tubulogenesis assays monitor the ability of cultured cells, generally endothelial cells, to form tubular structures on a matrix substrate, which generally simulates the environment of the extracellular matrix.
  • exemplary substrates include MatrigelTM (Becton Dickinson), an extract of basement membrane proteins containing laminin, collagen IV, and heparin sulfate proteoglycan, which is liquid at 4° C and forms a solid gel at 37° C.
  • Other suitable matrices comprise extracellular components such as collagen, fibronectin, and/or fibrin. Cells are stimulated with a pro-angiogenic stimulant, and their ability to form tubules is detected by imaging.
  • Tubules can generally be detected after an overnight incubation with stimuli, but longer or shorter time frames may also be used.
  • Tube formation assays are well known in the art (e.g., Jones MK et al., 1999, Nature Medicine 5:1418-1423). These assays have traditionally involved stimulation with serum or with the growth factors FGF or VEGF. Serum represents an undefined source of growth factors.
  • the assay is performed with cells cultured in serum free medium, in order to control which process or pathway a candidate agent modulates.
  • different target genes respond differently to stimulation with different pro-angiogenic agents, including inflammatory angiogenic factors such as TNF-alpa.
  • a tubulogenesis assay system comprises testing a CTPS's response to a variety of factors, such as FGF, VEGF, phorbol myristate acetate (PMA), TNF-alpha, ephrin, etc.
  • factors such as FGF, VEGF, phorbol myristate acetate (PMA), TNF-alpha, ephrin, etc.
  • An invasion/migration assay tests the ability of cells to overcome a physical barrier and to migrate towards pro-angiogenic signals.
  • Migration assays are known in the art (e.g., Paik JH et al., 2001, J Biol Chem 276:11830-11837).
  • cultured endothelial cells are seeded onto a matrix-coated porous lamina, with pore sizes generally smaller than typical cell size.
  • the matrix generally simulates the environment of the extracellular matrix, as described above.
  • the lamina is typically a membrane, such as the transwell polycarbonate membrane (Corning Costar Corporation, Cambridge, MA), and is generally part of an upper chamber that is in fluid contact with a lower chamber containing pro-angiogenic stimuli. Migration is generally assayed after an overnight incubation with stimuli, but longer or shorter time frames may also be used. Migration is assessed as the number of cells that crossed the lamina, and may be detected by staining cells with hemotoxylin solution (VWR Scientific, South San Francisco, CA), or by any other method for determining cell number. In another exemplary set up, cells are fluorescently labeled and migration is detected using fluorescent readings, for instance using the Falcon HTS FluoroBlok (Becton Dickinson).
  • a preferred assay system for migration/invasion assays comprises testing a CTPS's response to a variety of pro-angiogenic factors, including tumor angiogenic and inflammatory angiogenic agents, and culturing the cells in serum free medium.
  • a sprouting assay is a three-dimensional in vitro angiogenesis assay that uses a cell-number defined spheroid aggregation of endothelial cells ("spheroid"), embedded in a collagen gel-based matrix.
  • the spheroid can serve as a starting point for the sprouting of capillary-like structures by invasion into the extracellular matrix (termed “cell sprouting") and the subsequent formation of complex anastomosing networks (Korff and Augustin, 1999, J Cell Sci 112:3249-58).
  • cell sprouting the extracellular matrix
  • spheroids are prepared by pipetting 400 human umbilical vein endothelial cells into individual wells of a nonadhesive 96-well plates to allow overnight spheroidal aggregation (Korff and Augustin: J Cell Biol 143: 1341-52, 1998).
  • Spheroids are harvested and seeded in 900 l of methocel-collagen solution and pipetted into individual wells of a 24 well plate to allow collagen gel polymerization. Test agents are added after 30 min by pipetting 100 ⁇ l of 10-fold concentrated working dilution of the test substances on top of the gel. Plates are incubated at 37°C for 24h. Dishes are fixed at the end of the experimental incubation period by addition of paraformaldehyde. Sprouting intensity of endothelial cells can be quantitated by an automated image analysis system to determine the cumulative sprout length per spheroid.
  • Primary assays for antibody modulators For antibody modulators, appropriate primary assays test is a binding assay that tests the antibody's affinity to and specificity for the CTPS protein. Methods for testing antibody affinity and specificity are well known in the art (Harlow and Lane, 1988, 1999, supra).
  • the enzyme-linked immunosorbant assay (ELISA) is a preferred method for detecting CTPS-specific antibodies; others include FACS assays, radioimmunoassays, and fluorescent assays. In some cases, screening assays described for small molecule modulators may also be used to test antibody modulators.
  • primary assays may test the ability of the nucleic acid modulator to inhibit or enhance CTPS gene expression, preferably mRNA expression.
  • expression analysis comprises comparing CTPS expression in like populations of cells (e.g., two poojs of cells that endogenously or recombinantly express CTPS) in the presence and absence of the nucleic acid modulator.
  • Methods for analyzing mRNA and protein expression are well known in the art. For instance, Northern blotting, slot blotting, ribonuclease protection, quantitative RT-PCR (e.g., using the TaqMan®, PE Applied
  • CTPS mRNA expression may be confirmed in cells treated with the nucleic acid modulator (e.g., Current Protocols in Molecular Biology (1994) Ausubel FM et al, eds., John Wiley & Sons, Inc., chapter 4; Freeman WM et al, Biotechniques (1999) 26:112-125; Kallioniemi OP, Ann Med 2001, 33:142-147; Blohm DH and Guiseppi-Elie, A Curr Opin Biotechnol 2001, 12:41-47). Protein expression may also be monitored. Proteins are most commonly detected with specific antibodies or antisera directed against either the CTPS protein or specific peptides.
  • the nucleic acid modulator e.g., Current Protocols in Molecular Biology (1994) Ausubel FM et al, eds., John Wiley & Sons, Inc., chapter 4; Freeman WM et al, Biotechniques (1999) 26:112-125; Kallioniem
  • CTPS-modulating agents encompass candidate clinical compounds or other agents derived from previously identified modulating agent.
  • Secondary assays can also be used to test the activity of a modulating agent on a particular genetic or biochemical pathway or to test the specificity of the modulating agent's interaction with CTPS. Secondary assays generally compare like populations of cells or animals (e.g., two pools of cells or animals that endogenously or recombinantly express CTPS) in the presence and absence of the candidate modulator. In general, such assays test whether treatment of cells or animals with a candidate CTPS-modulating agent results in changes in the PTEN pathway in comparison to untreated (or mock- or placebo-treated) cells or animals. Certain assays use "sensitized genetic backgrounds", which, as used herein, describe cells or animals engineered for altered expression of genes in the PTEN or interacting pathways.
  • Cell based assays may detect endogenous PTEN pathway activity or may rely on recombinant expression of PTEN pathway components. Any of the aforementioned assays may be used in this cell-based format.
  • Candidate modulators are typically added to the cell media but may also be injected into cells or delivered by any other efficacious means.
  • Models for defective PTEN pathway typically use genetically modified animals that have been engineered to mis-express (e.g., over- express or lack expression in) genes involved in the PTEN pathway. Assays generally require systemic delivery of the candidate modulators, such as by oral administration, injection, etc. In a preferred embodiment, PTEN pathway activity is assessed by monitoring neovascularization and angiogenesis. Animal models with defective and normal PTEN are used to test the candidate modulator's affect on CTPS in Matrigel® assays.
  • Matrigel® is an extract of basement membrane proteins, and is composed primarily of laminin, collagen IV, and heparin sulfate proteoglycan. It is provided as a sterile liquid at 4° C, but rapidly forms a solid gel at 37° C. Liquid Matrigel® is mixed with various angiogenic agents, such as bFGF and VEGF, or with human tumor cells which over-express the CTPS. The mixture is then injected subcutaneously(SC) into female athymic nude mice (Taconic, Germantown, NY) to support an intense vascular response. Mice with Matrigel® pellets may be dosed via oral (PO), intraperitoneal (IP), or intravenous (IV) routes with the candidate modulator.
  • PO oral
  • IP intraperitoneal
  • IV intravenous
  • mice are euthanized 5 - 12 days post-injection, and the Matrigel® pellet is harvested for hemoglobin analysis (Sigma plasma hemoglobin kit). Hemoglobin content of the gel is found to correlate the degree of neovascularization in the gel.
  • the effect of the candidate modulator on CTPS is assessed via tumorigenicity assays.
  • Tumor xenograft assays are known in the art (see, e.g., Ogawa K et al., 2000, Oncogene 19:6043-6052). Xenografts are typically implanted SC into female athymic mice, 6-7 week old, as single cell suspensions either from a preexisting tumor or from in vitro culture.
  • the tumors which express the CTPS endogenously are injected in the flank, 1 x 10 5 to 1 x 10 7 cells per mouse in a volume of 100 ⁇ L using a 27 gauge needle. Mice are then ear tagged and tumors are measured twice weekly.
  • Candidate modulator treatment is initiated on the day the mean tumor weight reaches 100 mg.
  • Candidate modulator is delivered TV, SC, IP, or PO by bolus administration. Depending upon the pharmacokinetics of each unique candidate modulator, dosing can be performed multiple times per day.
  • the tumor weight is assessed by measuring perpendicular diameters with a caliper and calculated by multiplying the measurements of diameters in two dimensions. At the end of the experiment, the excised tumors maybe utilized for biomarker identification or further analyses.
  • xenograft tumors are fixed in 4% paraformaldehyde, 0.1M phosphate, pH 7.2, for 6 hours at 4°C, immersed in 30% sucrose in PBS, and rapidly frozen in isopentane cooled with liquid nitrogen.
  • tumorogenicity is monitored using a hollow fiber assay, which is described in U.S. Pat No. US 5,698,413.
  • the method comprises implanting into a laboratory animal a biocompatible,- semi-permeable encapsulation device containing target cells, treating the laboratory animal with a candidate modulating agent, and evaluating the target cells for reaction to the candidate modulator.
  • Implanted cells are generally human cells from a pre-existing tumor or a tumor cell line.
  • Tumorogenicity and modulator efficacy may be evaluated by assaying the quantity of viable cells present in the macrocapsule, which can be determined by tests known in the art, for example, MTT dye conversion assay, neutral red dye uptake, trypan blue staining, viable cell counts, the number of colonies formed in soft agar, the capacity of the cells to recover and replicate in vitro, etc.
  • a tumorogenicity assay use a transgenic animal, usually a mouse, carrying a dominant oncogene or tumor suppressor gene knockout under the control of tissue specific regulatory sequences; these assays are generally referred to as transgenic tumor assays.
  • tumor development in the transgenic model is well characterized or is controlled.
  • the "RIPl-Tag2" transgene comprising the S V40 large T-antigen oncogene under control of the insulin gene regulatory regions is expressed in pancreatic beta cells and results in islet cell carcinomas (Hanahan D, 1985, Nature 315:115-122; Parangi S et al, 1996, Proc Natl Acad Sci USA 93: 2002-2007; Bergers G et al, 1999, Science 284:808-812).
  • An "angiogenic switch,” occurs at approximately five weeks, as normally quiescent capillaries in a subset of hyperproliferative islets become angiogenic.
  • the RTP1-TAG2 mice die by age 14 weeks.
  • Candidate modulators may be administered at a variety of stages, including just prior to the angiogenic switch (e.g., for a model of tumor prevention), during the growth of small tumors (e.g., for a model of intervention), or during the growth of large and/or invasive tumors (e.g., for a model of regression).
  • Tumorogenicity and modulator efficacy can be evaluating life-span extension and/or tumor characteristics, including number of tumors, tumor size, tumor morphology, vessel density, apoptotic index, etc.
  • the invention also provides methods for modulating the PTEN pathway in a cell, preferably a cell pre-determined to have defective or impaired PTEN function (e.g. due to overexpression, underexpression, or misexpression of PTEN, or due to gene mutations), comprising the step of administering an agent to the cell that specifically modulates CTPS activity.
  • the modulating agent produces a detectable phenotypic change in the cell indicating that the PTEN function is restored.
  • function is restored means that the desired phenotype is achieved, or is brought closer to normal compared to untreated cells.
  • cell proliferation and/or progression through cell cycle may normalize, or be brought closer to normal relative to untreated cells.
  • the invention also provides methods for treating disorders or disease associated with impaired PTEN function by administering a therapeutically effective amount of a CTPS -modulating agent that modulates the PTEN pathway.
  • the invention further provides methods for modulating CTPS function in a cell, preferably a cell pre-determined to have defective or impaired CTPS function, by administering a CTPS -modulating agent.
  • the invention provides a method for treating disorders or disease associated with impaired CTPS function by administering a therapeutically effective amount of a CTPS -modulating agent.
  • CTPS is implicated in PTEN pathway provides for a variety of methods that can be employed for the diagnostic and prognostic evaluation of diseases and disorders involving defects in the PTEN pathway and for the identification of subjects having a predisposition to such diseases and disorders.
  • Various expression analysis methods can be used to diagnose whether CTPS expression occurs in a particular sample, including Northern blotting, slot blotting, ribonuclease protection, quantitative RT-PCR, and microarray analysis, (e.g., Current
  • Tissues having a disease or disorder implicating defective PTEN signaling that express a CTPS are identified as amenable to treatment with a CTPS modulating agent.
  • the PTEN defective tissue overexpresses a CTPS relative to normal tissue.
  • a Northern blot analysis of mRNA from tumor and normal cell lines, or from tumor and matching normal tissue samples from the same patient, using full or partial CTPS cDNA sequences as probes, can determine whether particular tumors express or overexpress CTPS.
  • the TaqMan® is used for quantitative RT-PCR analysis of CTPS expression in cell lines, normal tissues and tumor samples (PE Applied Biosystems).
  • CTPS oligonucleotides
  • antibodies directed against a CTPS as described above for: (1) the detection of the presence of CTPS gene mutations, or the detection of either over- or under-expression of CTPS mRNA relative to the non-disorder state; (2) the detection of either an over- or an under-abundance of CTPS gene product relative to the non-disorder state; and (3) the detection of perturbations or abnormalities in the signal transduction pathway mediated by CTPS.
  • Kits for detecting expression of CTPS in various samples comprising at least one antibody specific to CTPS, all reagents and/or devices suitable for the detection of antibodies, the immobilization of antibodies, and the like, and instructions for using such kits in diagnosis or therapy are also provided.
  • the invention is drawn to a method for diagnosing a disease or disorder in a patient that is associated with alterations in CTPS expression, the method comprising: a) obtaining a biological sample from the patient; b) contacting the sample with a probe for CTPS expression; c) comparing results from step (b) with a control; and d) determining whether step (c) indicates a likelihood of the disease or disorder.
  • the disease is cancer, most preferably a cancer as shown in TABLE 2.
  • the probe may be either DNA or protein, including an antibody.
  • I. C. elegans PTEN screen We designed a genetic screen to identify suppressor genes that, when inactivated, decrease signaling through the AKT pathway.
  • the function of individual genes was inactivated by RNAi in the daf-18 (ep496); daf-2 (el370) double mutant by soaking LI larvae in double-stranded RNA for each gene. Subsequently, the larvae were grown on bacteria at 25°C and scored for a statistically significant increase in dauer formation as compared to larvae treated without RNA (approximately 0-2% dauers).
  • Suppressor genes were counter-screened to eliminate those that showed allele-specific suppression of the ep496 nonsense mutation but not the ep497 missense mutation by performing RNAi on the daf-18 (ep497); daf-2 (el370) double mutant and scoring for enhanced dauer formation at 25°C. daf-16 mutations provide a test for pathway specificity since they fully suppress the Daf-c phenotype of all known AKT pathway mutants but, at most, only weakly suppress the Daf-c phenotype of mutants in the daf-7 (TGF-D) and daf-11 (cGMP signaling) pathways.
  • CTPS symbol and “CTPS name aliases” provide a symbol and the known name abbreviations for the Targets, where available, from Genbank.
  • CTPS RefSeq_NA or GI_NA provide the reference DNA sequences for the CTPSs as available from National Center for Biology Information (NCBI), CTPS protein Genbank identifier number (GI#), CTPS name, and CTPS description, all available from Genbank, respectively.
  • NCBI National Center for Biology Information
  • GI# CTPS protein Genbank identifier number
  • CTPS name and CTPS description, all available from Genbank, respectively.
  • the length of each amino acid is in the "CTPS Protein Length” column. Names and Protein sequences of C. elegans modifiers of PTEN from screen
  • Example I are represented in the "Modifier Name” and “Modifier GI_AA” column by GI#, respectively.
  • the cell lysate is incubated with 25 ⁇ l of M2 beads (Sigma) for 2 h at 4 °C with gentle rocking. After extensive washing with lysis buffer, proteins bound to the beads are solubilized by boiling in SDS sample buffer, fractionated by SDS-polyacrylamide gel electrophoresis, transferred to polyvinylidene difluoride membrane and blotted with the indicated antibodies. The reactive bands are visualized with horseradish peroxidase coupled to the appropriate secondary antibodies and the enhanced chemiluminescence (ECL) Western blotting detection system (Amersham Pharmacia Biotech).
  • ECL enhanced chemiluminescence
  • RNA samples Single stranded cDNA was then synthesized by reverse transcribing the RNA samples using random hexamers and 500ng of total RNA per reaction, following protocol 4304965 of Applied Biosystems (Foster City, CA).
  • Primers for expression analysis using TaqMan® assay were prepared according to the TaqMan® protocols, and the following criteria: a) primer pairs were designed to span introns to eliminate genomic contamination, and b) each primer pair produced only one product. Expression analysis was performed using a 7900HT instrument.
  • TaqMan® reactions were carried out following manufacturer's protocols, in 25 ⁇ l total volume for 96-well plates and 10 ⁇ l total volume for 384-well plates, using 300nM primer and 250 nM probe, and approximately 25ng of cDNA.
  • the standard curve for result analysis was prepared using a universal pool of human cDNA samples, which is a mixture of cDNAs from a wide variety of tissues so that the chance that a target will be present in appreciable amounts is good.
  • the raw data were normalized using 18S rRNA (universally expressed in all tissues and cells). For each expression analysis, tumor tissue samples were compared with matched normal tissues from the same patient.
  • a gene was considered overexpressed in a tumor when the level of expression of the gene was 2 fold or higher in the tumor compared with its matched normal sample.
  • a universal pool of cDNA samples was used instead.
  • a gene was considered overexpressed in a tumor sample when the difference of expression levels between a tumor sample and the average of all normal samples from the same tissue type was greater than 2 times the standard deviation of all normal samples (i.e., Tumor - average(all normal samples) > 2 x STDEV(all normal samples) ). Results are shown in Table 2. Number of pairs of tumor samples and matched normal tissue from the same patient are shown for each tumor type. Percentage of the samples with at least two-fold overexpression for each tumor type is provided.
  • a modulator identified by an assay described herein can be further validated for therapeutic effect by administration to a tumor in which the gene is overexpressed.
  • a decrease in tumor growth confirms therapeutic utility of the modulator.
  • the likelihood that the patient will respond to treatment can be diagnosed by obtaining a tumor sample from the patient, and assaying for expression of the gene targeted by the modulator.
  • the expression data for the gene(s) can also be used as a diagnostic marker for disease progression.
  • the assay can be performed by expression analysis as described above, by antibody directed to the gene target, or by any other available detection method. Table 2

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Abstract

L'invention concerne des gènes CTPS humains identifiés en tant que modulateurs de la voie PTEN, qui constituent par conséquent des agents thérapeutiques destinés au traitement de troubles associés à une fonction déficiente de PTEN. L'invention concerne également des procédés d'identification de modulateurs de PTEN, consistant à cribler des agents qui modulent l'activité des gènes CTPS.
PCT/US2004/039206 2003-11-24 2004-11-23 Genes ctps utilises en tant que modificateurs de la voie pten et procedes d'utilisation associes WO2005051310A2 (fr)

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Non-Patent Citations (2)

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GHAREHBAGHI ET AL: 'Studies on the antitumor activity and biochemical actions of cyclopentenyl cytosine against human colon carcinoma HT-29 in vitro and in vivo.' LIFE SCIENCES. vol. 64, no. 2, 1999, pages 103 - 112, XP002994574 *
VERSCHUUR ET AL: 'Cyclopentenyl cytosine inhibits cytidine triphosphate synthetase in paediatric acute non-lymphocytic leukaemia: a promising target for chemotherapy.' EUROPEAN JOURNAL OF CANCER. vol. 36, 2000, pages 627 - 635, XP002994575 *

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