Patent Application
20110117551
The present invention relates to the area of cancer diagnostics and therapeutics. In particular, it relates to methods and kits for identifying, diagnosing, prognosing and monitoring lung cancer. These methods include determining the methylation status or the expression levels of particular genes, or a combination thereof. In particular, the lung cancer relates to non-small cell lung cancer.
Lung cancer is the most common cause of cancer-related death and causes over one million deaths worldwide each year (Greenlee et al, 2001). Lung cancer is clinically subdivided into small cell lung cancer (SCLC; comprise about 20% of lung cancers), the most aggressive form of lung cancer, and non-small cell lung cancer (NSCLC, the most common lung cancer accounting for about 80%), consisting of adenocarcinoma, squamous cell carcinoma, large cell carcinoma, and miscellaneous other types such as carcinoids, pleomorphic and mixed carcinomas and a range of neuroendocrine cancers (Travis, 2002).
The first signs of cancer usually come from one or more of the following sources: presentation of symptoms, visual detection or direct palpation, histopathological analysis of a biopsy specimen, remote imaging or the detection of a cancer biomarker in a tissue or bodily fluid specimen. The rather late appearance of symptomatology associated with lung cancer, and the poor accessibility to the lung tissue thwart the timely detection of malignancy, contributing to high mortality rates (Ganti et al., 2006; Greenberg et al., 2007). Therefore, remote imaging and the development of cancer biomarkers offers the best hope for early detection of lung cancer.
Cancer biomarkers have been described in literature. One can distinguish between immunological markers and genetic markers. Genetic markers are based on detection of mutation in distinct genes in particular in tumor suppressor genes. More recently, DNA methylation markers are evaluated as potential genetic markers for detection of cancer because they offer certain advantages when compared to mutation markers. One of the most important features is that they occur at the early stages of cancer development and in many cases are tissue- and tumor-type specific (Esteller et al. 2001). A further advantage, methylation profile is preserved in purified isolated DNA and methylation changes appear to precede apparent malignancy in many cases. In addition, methylation markers may serve for predictive purposes as they often reflect the sensitivity to therapy or duration of patient survival.
DNA methylation is a chemical modification of DNA performed by enzymes called methyltransferases, in which a methyl group (m) is added to certain cytosines (C) of DNA. This non-mutational (epigenetic) process (mC) is a critical factor in gene expression regulation. See, J. G. Herman, Seminars in Cancer Biology, 9: 359-67, 1999. By turning genes off that are not needed, DNA methylation is an essential control mechanism for the normal development and functioning of organisms. Alternatively, abnormal DNA methylation is one of the mechanisms underlying the changes observed with aging and development of many cancers.
Although the phenomenon of gene methylation has attracted the attention of cancer researchers for some time, its true role in the progression of human cancers is just now being recognized. In normal cells, methylation occurs predominantly in regions of DNA that have few CG base repeats, while CpG islands, regions of DNA that have long repeats of CG bases, remain non-methylated. Gene promoter regions that control protein expression are often CpG island-rich. Aberrant methylation of these normally non-methylated CpG islands in the promoter region causes transcriptional inactivation or silencing of certain tumor suppressor expression in human cancers.
Genes that are hypermethylated in tumor cells are strongly specific to the tissue of origin of the tumor. Molecular signatures of cancers of all types can be used to improve cancer detection, the assessment of cancer risk and response to therapy. Promoter hypermethylation events provide some of the most promising markers for such purposes.
An early diagnosis is critical for the successful treatment of many types of cancer, including lung cancer. If the exact methylation profiles of lung tumors are available and drugs targeting the specific genes are obtainable, then the treatment of lung cancer could be more focused and rational. Therefore, the detection and mapping of novel methylation markers is an essential step towards improvement of lung cancer prevention, screening and treatment.
There is a continuing need in the art to identify methylation markers that can be used for improved assessment of lung cancer.
According to one embodiment of the invention a method is provided for identifying lung cancer or its precursor, or predisposition to lung cancer. Epigenetic modification of at least one gene selected from the group consisting of ACSL6, ALS2CL, APC2, ARTS-1, BEX1, BMP7, BNIP3, CBR3, CD248, CD44, CHD5, DLK1, DPYSL4, DSC2, EDNRB, EPB41L3, EPHB6, ERBB3, FBLN2, FBN2, FOXL2, GNAS, GSTP1, HS3ST2, HPN, IGFBP7, IRF7, JAM3, LOX, LY6D, LY6K, MACF1, MCAM, NCBP1, NEFH, NID2, PCDHB15, PCDHGA12, PFKP, PGRMC1, PHACTR3, PHKA2, POMC, PRKCA, PSEN1, RASSF1A, RASSF2, RBP1, RRAD, SFRP1, SGK, SOD3, SOX17, SULF2, TIMP3, TJP2, TRPV2, UCHL1, WDR69, ZFP42, ZNF442, and ZNF655 is detected in a test sample containing lung cells or nucleic acids from lung cells. The test sample is identified as containing cells that are neoplastic, precursor to neoplastic, or predisposed to neoplasia, or as containing nucleic acids from cells that are neoplastic, precursor to neoplastic, or predisposed to neoplasia.
According to another embodiment of the invention a kit is provided for assessing lung cancer or its precursor, or predisposition to lung cancer in a test sample containing lung cells or nucleic acids from lung cells. The kit comprises in a package: a reagent that (a) modifies methylated cytosine residues but not non-methylated cytosine residues, or that (b) modifies non-methylated cytosine residues but not methylated cytosine residues; and at least one pair of oligonucleotide primers that specifically hybridizes under amplification conditions to a region of a gene selected from the group consisting of ACSL6, ALS2CL, APC2, ARTS-1, BEX1, BMP7, BNIP3, CBR3, CD248, CD44, CHD5, DLK1, DPYSL4, DSC2, EDNRB, EPB41L3, EPHB6, ERBB3, FBLN2, FBN2, FOXL2, GNAS, GSTP1, HS3ST2, HPN, IGFBP7, IRF7, JAM3, LOX, LY6D, LY6K, MACF1, MCAM, NCBP1, NEFH, NID2, PCDHB15, PCDHGA12, PFKP, PGRMC1, PHACTR3, PHKA2, POMC, PRKCA, PSEN1, RASSF1A, RASSF2, RBP1, RRAD, SFRP1, SGK, SOD3, SOX17, SULF2, TIMP3, TJP2, TRPV2, UCHL1, WDR69, ZFP42, ZNF442, and ZNF655. The region is within about 3 kb of said gene's transcription start site.
Another embodiment of the invention provides a second kit for assessing lung cancer or its precursor, or predisposition to lung cancer in a test sample containing lung cells or nucleic acids from lung cells. The kit comprises in a package: at least two pairs of oligonucleotide primers that specifically hybridize under amplification conditions to a region of a gene selected from the group consisting of ACSL6, ALS2CL, APC2, ARTS-1, BEX1, BMP7, BNIP3, CBR3, CD248, CD44, CHD5, DLK1, DPYSL4, DSC2, EDNRB, EPB41L3, EPHB6, ERBB3, FBLN2, FBN2, FOXL2, GNAS, GSTP1, HS3ST2, HPN, IGFBP7, IRF7, JAM3, LOX, LY6D, LY6K, MACF1, MCAM, NCBP1, NEFH, NID2, PCDHB15, PCDHGA12, PFKP, PGRMC1, PHACTR3, PHKA2, POMC, PRKCA, PSEN1, RASSF1A, RASSF2, RBP1, RRAD, SFRP1, SGK, SOD3, SOX17, SULF2, TIMP3, TJP2, TRPV2, UCHL1, WDR69, ZFP42, ZNF442, and ZNF655. The region is within about 3 kb of said gene's transcription start site.
An additional aspect of the invention provides an isolated polynucleotide. The polynucleotide comprises a nucleotide sequence selected from the group consisting of SEQ ID NO: 1-449.
These and other embodiments which will be apparent to those of skill in the art upon reading the specification provide the art with reagents and methods for detecting lung cancer, early lung cancer, or predisposition to lung cancer.
The inventors have found that cytosines within CpG dinucleotides of DNA from particular genes isolated from a test sample are differentially methylated in human lung cancer tissue samples and normal lung tissue control samples. The cancer tissues samples are hypermethylated or hypomethylated with respect to the normal samples (collectively termed epigenetic modification). The differential methylation has been found in genomic DNA of ACSL6, ALS2CL, APC2, ARTS-1, BEX1, BMP7, BNIP3, CBR3, CD248, CD44, CHD5, DLK1, DPYSL4, DSC2, EDNRB, EPB41L3, EPHB6, ERBB3, FBLN2, FBN2, FOXL2, GNAS, GSTP1, HS3ST2, HPN, IGFBP7, IRF7, JAM3, LOX, LY6D, LY6K, MACF1, MCAM, NCBP1, NEFH, NID2, PCDHB15, PCDHGA12, PFKP, PGRMC1, PHACTR3, PHKA2, POMC, PRKCA, PSEN1, RASSF1A, RASSF2, RBP1, RRAD, SFRP1, SGK, SOD3, SOX17, SULF2, TIMP3, TJP2, TRPV2, UCHL1, WDR69, ZFP42, ZNF442, and ZNF655. These genes are all known in the art and fully described by sequence in publicly available databases, e.g., Entrez Gene of the National Center for Biotechnology Information. See Gene ID references provided in Table 1 and Table 3, each of which is incorporated by reference herein.
Epigenetic modification of a gene can be determined by any method known in the art.
One method is to determine that a gene which is expressed in normal cells or other control cells is less expressed or not expressed in tumor cells. Conversely, a gene can be more highly expressed in tumor cells than in control cells in the case of hypomethylation. This method does not, on its own, however, indicate that the silencing or activation is epigenetic, as the mechanism of the silencing or activation could be genetic, for example, by somatic mutation. One method to determine that silencing is epigenetic is to treat with a reagent, such as DAC (5′-deazacytidine), or with a reagent which changes the histone acetylation status of cellular DNA or any other treatment affecting epigenetic mechanisms present in cells, and observe that the silencing is reversed, i.e., that the expression of the gene is reactivated or restored. Another means to determine epigenetic modification is to determine the presence of methylated CpG dinucleotide motifs in the silenced gene or the absence of methylation CpG dinucleotide motifs in the activated gene. Typically these methylated motifs reside near the transcription start site, for example, within about 3 kbp, within about 2.5 kbp, within about 2 kbp, within about 1.5 kbp, within about 1 kbp, within about 750 bp, or within about 500 bp. CpG dinucleotides susceptible to methylation are typically concentrated in the promoter region, intron region or exon region of human genes. Thus, the methylation status of the promoter and/or intron and/or exon region of at least one gene can be assessed. Once a gene has been identified as the target of epigenetic modification in tumor cells, determination of reduced or enhanced expression can be used as an indicator of epigenetic modification.
Expression of a gene can be assessed using any means known in the art. Typically expression is assessed and compared in test samples and control samples which may be normal, non-malignant cells. The test samples may contain cancer cells or pre-cancer cells or nucleic acids from them. For example the sample may contain lung adenoma cells, lung advanced adenoma cells, or lung adenocarcinoma cells. Samples may contain squamous cells, and large cell carcinoma. Samples may contain mixtures of different types and stages of lung cancer cells. Either mRNA (nucleic acids) or protein can be measured to detect epigenetic modification. Methods employing hybridization to nucleic acid probes can be employed for measuring specific mRNAs. Such methods include using nucleic acid probe arrays (microarray technology), in situ hybridization, and using Northern blots. Messenger RNA can also be assessed using amplification techniques, such as RT-PCR. In some embodiments oligonucleotide probes are covalently linked to primers for amplification. Advances in genomic technologies now permit the simultaneous analysis of thousands of genes, although many are based on the same concept of specific probe-target hybridization. Sequencing-based methods are an alternative; these methods started with the use of expressed sequence tags (ESTs), and now include methods based on short tags, such as serial analysis of gene expression (SAGE) and massively parallel signature sequencing (MPSS). Differential display techniques provide yet another means of analyzing gene expression; this family of techniques is based on random amplification of cDNA fragments generated by restriction digestion, and bands that differ between two tissues identify cDNAs of interest. Specific proteins can be assessed using any convenient method including immunoassays and immunocytochemistry but are not limited to that. Most such methods will employ antibodies which are specific for the particular protein or protein fragments. The sequences of the mRNA (cDNA) and proteins of the markers of the present invention are known in the art and publicly available.
Methylation-sensitive restriction endonucleases can be used to detect methylated CpG dinucleotide motifs. Such endonucleases may either preferentially cleave methylated recognition sites relative to non-methylated recognition sites or preferentially cleave non-methylated relative to methylated recognition sites. Examples of the former are Acc III, Ban I, BstN I, Msp I, and Xma I. Examples of the latter are Acc II, Ava I, BssH II, BstU I, Hpa II, and Not I. Alternatively, chemical reagents can be used which selectively modify either the methylated or non-methylated form of CpG dinucleotide motifs.
Modified products can be detected directly, or after a further reaction which creates products which are easily distinguishable. Means which detect altered size and/or charge can be used to detect modified products, including but not limited to electrophoresis, chromatography, and mass spectrometry. Examples of such chemical reagents for selective modification include hydrazine and bisulfite ions. Hydrazine-modified DNA can be treated with piperidine to cleave it. Bisulfite ion-treated DNA can be treated with alkali. Other means which are reliant on specific sequences can be used, including but not limited to hybridization, amplification, sequencing, and ligase chain reaction, Combinations of such techniques can be uses as is desired.
The principle behind electrophoresis is the separation of nucleic acids via their size and charge. Many assays exist for detecting methylation and most rely on determining the presence or absence of a specific nucleic acid product. Gel electrophoresis is commonly used in a laboratory for this purpose.
One may use MALDI mass spectrometry in combination with a methylation detection assay to observe the size of a nucleic acid product. The principle behind mass spectrometry is the ionizing of nucleic acids and separating them according to their mass to charge ratio. Similar to electrophoresis, one can use mass spectrometry to detect a specific nucleic acid that was created in an experiment to determine methylation. See (Tost, J. et al. 2003).
One form of chromatography, high performance liquid chromatography, is used to separate components of a mixture based on a variety of chemical interactions between a substance being analyzed and a chromatography column. DNA is first treated with sodium bisulfite, which converts an unmethylated cytosine to uracil, while methylated cytosine residues remain unaffected. One may amplify the region containing potential methylation sites via PCR and separate the products via denaturing high performance liquid chromatography (DHPLC). DHPLC has the resolution capabilities to distinguish between methylated (containing cytosine) and unmethylated (containing uracil) DNA sequences. (Deng, D. et al. 2002)
Hybridization is a technique for detecting specific nucleic acid sequences that is based on the annealing of two complementary nucleic acid strands to form a double-stranded molecule. One example of the use of hybridization is a microarray assay to determine the methylation status of DNA. After sodium bisulfite treatment of DNA, which converts an unmethylated cytosine to uracil while methylated cytosine residues remain unaffected, oligonucleotides complementary to potential methylation sites can hybridize to the bisulfite-treated DNA. The oligonucleotides are designed to be complimentary to either sequence containing uracil (thymine) or sequence containing cytosine, representing unmethylated and methylated DNA, respectively. Computer-based microarray technology can determine which oligonucleotides hybridize with the DNA sequence and one can deduce the methylation status of the DNA. Similarly primers can be designed to be complimentary to either sequence containing uracil (thymine) or sequence containing cytosine. Primers and probes that recognize the converted methylated form of DNA are dubbed methylation-specific primers or probes (MSP).
An additional method of determining the results after sodium bisulfite treatment involves sequencing the DNA to directly observe any bisulfite-modifications. Pyrosequencing technology is a method of sequencing-by-synthesis in real time. It is based on an indirect bioluminometric assay of the pyrophosphate (PPi) that is released from each deoxynucleotide (dNTP) upon DNA-chain elongation. This method presents a DNA template-primer complex with a dNTP in the presence of an exonuclease-deficient Klenow DNA polymerase. The four nucleotides are sequentially added to the reaction mix in a predetermined order. If the nucleotide is complementary to the template base and thus incorporated, PPi is released. The PPi and other reagents are used as a substrate in a luciferase reaction producing visible light that is detected by either a luminometer or a charge-coupled device. The light produced is proportional to the number of nucleotides added to the DNA primer and results in a peak indicating the number and type of nucleotide present in the form of a pyrogram. Pyrosequencing can exploit the sequence differences that arise following sodium bisulfite-conversion of DNA.
A variety of amplification techniques may be used in a reaction for creating distinguishable products. Some of these techniques employ PCR. Other suitable amplification methods include the ligase chain reaction (LCR) (Barringer et al, 1990), transcription amplification (Kwoh et al. 1989; WO88/10315), selective amplification of target polynucleotide sequences (U.S. Pat. No. 6,410,276), consensus sequence primed polymerase chain reaction (U.S. Pat. No. 4,437,975), arbitrarily primed polymerase chain reaction (WO90/06995), nucleic acid based sequence amplification (NASBA) (U.S. Pat. Nos. 5,409,818; 5,554,517; 6,063,603), microsatellite length polymorphism (MLP), and nick displacement amplification (WO2004/067726).
Sequence variation that reflects the methylation status at CpG dinucleotides in the original genomic DNA offers two approaches to PCR primer design. In the first approach, the primers do not themselves “cover” or hybridize to any potential sites of DNA methylation; sequence variation at sites of differential methylation are located between the two primers. Such primers are used in bisulfite genomic sequencing, COBRA, Ms-SNuPE. In the second approach, the primers are designed to anneal specifically with either the methylated or unmethylated version of the converted sequence. If there is a sufficient region of complementarity, e.g., 12, 15, 18, or 20 nucleotides, to the target, then the primer may also contain additional nucleotide residues that do not interfere with hybridization but may be useful for other manipulations. Exemplary of such other residues may be sites for restriction endonuclease cleavage, for ligand binding or for factor binding or linkers or repeats. The oligonucleotide primers may or may not be such that they are specific for modified methylated residues
One way to distinguish between modified and unmodified DNA is to hybridize oligonucleotide primers which specifically bind to one form or the other of the DNA. After hybridization, an amplification reaction can be performed and amplification products assayed. The presence of an amplification product indicates that a sample hybridized to the primer. The specificity of the primer indicates whether the DNA had been modified or not, which in turn indicates whether the DNA had been methylated or not. For example, bisulfate ions modify non-methylated cytosine bases, changing them to uracil bases. Uracil bases hybridize to adenine bases under hybridization conditions. Thus an oligonucleotide primer which comprises adenine bases in place of guanine bases would hybridize to the bisulfite-modified DNA, whereas an oligonucleotide primer containing the guanine bases would hybridize to the non-modified (methylated) cytosine residues in the DNA. Amplification using a DNA polymerase and a second primer yield amplification products which can be readily observed. Such a method is termed MSP (Methylation Specific PCR; U.S. Pat. Nos. 5,786,146; 6,017,704; 6,200,756). The amplification products can be optionally hybridized to specific oligonucleotide probes which may also be specific for certain products. Alternatively, oligonucleotide probes can be used which will hybridize to amplification products from both modified and nonmodified DNA.
In one particular embodiment, primers useful in MSP carried out on the gene selected from ACSL6, ALS2CL, APC2, ARTS-1, BEX1, BMP7, BNIP3, CBR3, CD248, CD44, CHD5, DLK1, DPYSL4, DSC2, EDNRB, EPB41L3, EPHB6, ERBB3, FBLN2, FBN2, FOXL2, GNAS, GSTP1, HS3ST2, HPN, IGFBP7, IRF7, JAM3, LOX, LY6D, LY6K, MACF1, MCAM, NCBP1, NEFH, NID2, PCDHB15, PCDHGA12, PFKP, PGRMC1, PHACTR3, PHKA2, POMC, PRKCA, PSEN1, RASSF1A, RASSF2, RBP1, RRAD, SFRP1, SGK, SOD3, SOX17, SULF2, TIMP3, TJP2, TRPV2, UCHL1, WDR69, ZFP42, ZNF442, and ZNF655 are provided. Primers of the invention preferably are designed to amplify the genomic sequences in the regions under investigation. Preferred regions may comprise, consist essentially of or consist of the sequences represented by SEQ ID NO. 129-192 and/or SEQ ID NO. 193-256 and/or SEQ ID NO. 315-329 and/or SEQ ID NO. 330-344 and/or SEQ ID NO. 408-428 and/or SEQ ID NO. 429-449 and/or SEQ ID NO. 271-277 and/or SEQ ID NO. 278-284. Preferred sense primers (5′-3′) may comprise, consist essentially of or consist of the sequences represented by SEQ ID NO. 1-64 and/or SEQ ID NO. 285-299 and/or SEQ ID NO. 345-365 and/or SEQ ID NO. 257-263. Preferred antisense primers (5′-3′) comprise, consist essentially of or consist of the sequences represented by SEQ ID NO. 65-128 and/or SEQ ID NO. 300-314 and/or SEQ ID NO. 366-386 and/or SEQ ID NO. 264-270.
Another way to distinguish between modified and nonmodified DNA is to use oligonucleotide probes which may also be specific for certain products. Such probes can be hybridized directly to modified DNA or to amplification products of modified DNA. Oligonucleotide probes can be labeled using any detection system known in the art. These include but are not limited to fluorescent moieties, radioisotope labeled moieties, bioluminescent moieties, luminescent moieties, chemiluminescent moieties, enzymes, substrates, receptors, or ligands.
In one particular embodiment, probes useful in MSP carried out on the gene selected from ACSL6, ALS2CL, APC2, ARTS-1, BEX1, BMP7, BNIP3, CBR3, CD248, CD44, CHD5, DLK1, DPYSL4, DSC2, EDNRB, EPB41L3, EPHB6, ERBB3, FBLN2, FBN2, FOXL2, GNAS, GSTP1, HS3ST2, HPN, IGFBP7, IRF7, JAM3, LOX, LY6D, LY6K, MACF1, MCAM, NCBP1, NEFH, NID2, PCDHB15, PCDHGA12, PFKP, PGRMC1, PHACTR3, PHKA2, POMC, PRKCA, PSEN1, RASSF1A, RASSF2, RBP1, RRAD, SFRP1, SGK, SOD3, SOX17, SULF2, TIMP3, TJP2, TRPV2, UCHL1, WDR69, ZFP42, ZNF442, and ZNF655 are provided. Probes of the invention preferably are designed to bind to genomic sequences in the regions under investigation. Preferred regions may comprise, consist essentially of or consist of the sequences represented by SEQ ID NO. 129-192 and/or SEQ ID NO. 193-256 and/or SEQ ID NO. 315-329 and/or SEQ ID NO. 330-344 and/or SEQ ID NO. 408-428 and/or SEQ ID NO. 429-449 and/or SEQ ID NO. 271-277 and/or SEQ ID NO. 278-284. Preferred probes (5′-3′) may comprise, consist essentially of or consist of the sequences represented by SEQ ID NO. 387-407.
Still another way for the identification of methylated CpG dinucleotides utilizes the ability of the MBD domain of the McCP2 protein to selectively bind to methylated DNA sequences (Cross et al, 1994; Shiraishi et al, 1999). Restriction enconuclease digested genomic DNA is loaded onto expressed His-tagged methyl-CpG binding domain that is immobilized to a solid matrix and used for preparative column chromatography to isolate highly methylated DNA sequences.
Real time chemistry allows for the detection of PCR amplification during the early phases of the reactions, and makes quantitation of DNA and RNA easier and more precise. A few variations of the real-time PCR are known. They include the TaqMan™ (Roche Molecular Systems) system and Molecular Beacon™ system which have separate probes labeled with a fluorophore and a fuorescence quencher. In the Scorpion™ system the labeled probe in the form of a hairpin structure is linked to the primer. In addition, the Amplifluor™ (Chemicon International) system and the Plexor™ (Promega) system can be used.
DNA methylation analysis has been performed successfully with a number of techniques which include the MALDI-TOFF, MassARRAY, MethyLight, Quantitative analysis of ethylated alleles (QAMA), enzymatic regional methylation assay (ERMA), HeavyMethyl, QBSUPT, MS-SNuPE, MethylQuant, Quantitative PCR sequencing, and Oligonucleotide-based microarray systems.
Subsets of genes for all aspects and embodiments of the invention include ACSL6, ALS2CL, APC2, ARTS-1, BEX1, BMP7, BNIP3, CBR3, CD248, CD44, CHD5, DLK1, DPYSL4, DSC2, EDNRB, EPB41L3, EPHB6, ERBB3, FBLN2, FBN2, FOXL2, GNAS, GSTP1, HS3ST2, HPN, IGFBP7, IRF7, JAM3, LOX, LY6D, LY6K, MACF1, MCAM, NCBP1, NEFH, NID2, PCDHB15, PCDHGA12, PFKP, PGRMC1, PHACTR3, PHKA2, POMC, PRKCA, PSEN1, RASSF1A, RASSF2, RBP1, RRAD, SFRP1, SGK, SOD3, SOX17, SULF2, TIMP3, TJP2, TRPV2, UCHL1, WDR69, ZFP42, ZNF442, and ZNF655. By “gene” is meant any gene which is taken from the family to which the named “gene” belongs and includes according to all aspects of the invention not only the particular sequences found in the publicly available database entries, but also encompasses transcript and nucleotide variants of these sequences, with the proviso that methylation or another epigenetic modification of the gene is linked to lung cancer. The number of genes whose modification is tested and/or detected can vary: one, two, three, four, five, or more genes can be tested and/or detected. In some cases at least two genes are selected. In other embodiments at least three genes are selected.
Testing can be performed diagnostically or in conjunction with a therapeutic regimen.
Testing can be used to monitor efficacy of a therapeutic regimen, whether a chemotherapeutic agent or a biological agent, such as a polynucleotide. Testing can also be used to determine what therapeutic or preventive regimen to employ on a patient. Moreover, testing can be used to stratify patients into groups for testing agents and determining their efficacy on various groups of patients. The detection may also link to a cancer stage or grade. The “Stage” refers to how far a cancer has progressed anatomically, while the “grade” refers to cell appearance (differentiation) and DNA make up.
Test samples and normal samples for diagnostic, prognostic, or personalized medicine uses can be obtained from surgical samples, such as biopsies or fine needle aspirates, from paraffin embedded lung, or other organ tissues, from a body fluid such as blood, serum, lymph, saliva, sputum, urine, pleural fluid, bronchoalveolar lavage fluid. Such sources are not meant to be exhaustive, but rather exemplary. A test sample obtainable from such specimens or fluids includes detached tumor cells and/or free nucleic acids that are released from dead or damaged tumor cells. Nucleic acids include RNA, genomic DNA, mitochondrial DNA, single or double stranded, and protein-associated nucleic acids. Any nucleic acid specimen in purified or non-purified form obtained from such specimen cell can be utilized as the starting nucleic acid or acids. The test samples may contain cancer cells or pre-cancer cells or nucleic acids from them. For example the sample may contain lung adenoma cells, lung advanced adenoma cells, or lung adenocarcinoma cells. Samples may contain squamous cells or large cell carcinoma. Samples may contain mixtures of different types and stages of lung cancer cells.
The test sample is generally obtained from a (human) subject suspected of being tumorigenic. Alternatively the test sample is obtained from a subject undergoing routine examination and not necessarily being suspected of having a disease. Thus patients at risk can be identified before the disease has a chance to manifest itself in terms of symptoms identifiable in the patient. Alternatively the sample is obtained from a subject undergoing treatment, or from patients being checked for recurrence of disease.
Demethylating agents can be contacted with cells in vitro or in vivo for the purpose of restoring normal gene expression to the cell. Suitable demethylating agents include, but are not limited to 5-aza-2′-deoxycytidine, 5-aza-cytidine, Zebularine, procaine, and L-ethionine. This reaction may be used for diagnosis, for determining predisposition, and for determining suitable therapeutic regimes.
Although diagnostic and prognostic accuracy and sensitivity may be achieved by using a combination of markers, such as 5 or 6 markers, or 9 or 10 markers, practical considerations may dictate use of smaller combinations. Any combination of markers for a specific cancer may be used which comprises 2, 3, 4, or 5 markers. Combinations of 2, 3, 4, or 5 markers can be readily envisioned given the specific disclosures of individual markers provided herein. Preferably, the invention involves detecting an epigenetic change in a panel of genes comprising a combination of 2, 3, 4 or 5 markers. Preferably, the panel comprises RASSF1A and/or SOX17 and/or HS3ST2-nor and/or NID2 and/or SFRP1.
Kits according to the present invention are assemblages of reagents for testing methylation. They are typically in a package which contains all elements, optionally including instructions. The package may be divided so that components are not mixed until desired. Components may be in different physical states. For example, some components may be lyophilized and some in aqueous solution. Some may be frozen. Individual components may be separately packaged within the kit. The kit may contain reagents, as described above for differentially modifying methylated and non-methylated cytosine residues. Desirably the kit will contain oligonucleotide primers which specifically hybridize to regions within 3 kb of the transcription start sites of the genes/markers: ACSL6, ALS2CL, APC2, ARTS-1, BEX1, BMP7, BNIP3, CBR3, CD248, CD44, CHD5, DLK1, DPYSL4, DSC2, EDNRB, EPB41L3, EPHB6, ERBB3, FBLN2, FBN2, FOXL2, GNAS, GSTP1, HS3ST2, HPN, IGFBP7, IRF7, JAM3, LOX, LY6D, LY6K, MACF1, MCAM, NCBP1, NEFH, NID2, PCDHB15, PCDHGA12, PFKP, PGRMC1, PHACTR3, PHKA2, POMC, PRKCA, PSEN1, RASSF1A, RASSF2, RBP1, RRAD, SFRP1, SGK, SOD3, SOX17, SULF2, TIMP3, TJP2, TRPV2, UCHL1, WDR69, ZFP42, ZNF442, and ZNF655. Additional markers may be used. Typically the kit will contain both a forward and a reverse primer for a single gene or marker. If there is a sufficient region of complementarity, e.g., 12, 15, 18, or 20 nucleotides, then the primer may also contain additional nucleotide residues that do not interfere with hybridization but may be useful for other manipulations. Exemplary of such other residues may be sites for restriction endonuclease cleavage, for ligand binding or for factor binding or linkers or repeats. The oligonucleotide primers may or may not be such that they are specific for modified methylated residues. The kit may optionally contain oligonucleotide probes. The probes may be specific for sequences containing modified methylated residues or for sequences containing non-methylated residues. The kit may optionally contain reagents for modifying methylated cytosine residues. The kit may also contain components for performing amplification, such as a DNA polymerase (particularly a thermostable DNA polymerase) and deoxyribonucleotides. Means of detection may also be provided in the kit, including detectable labels on primers or probes. Kits may also contain reagents for detecting gene expression for one of the markers of the present invention (Table 1 and Table 3). Such reagents may include probes, primers, or antibodies, for example. In the case of enzymes or ligands, substrates or binding partners may be sued to assess the presence of the marker. Kits may contain 1, 2, 3, 4, or more of the primers or primer pairs of the invention. Kits that contain probes may have them as separate molecules or covalently linked to a primer for amplifying the region to which the probes hybridize. Other useful tools for performing the methods of the invention or associated testing, therapy, or calibration may also be included in the kits, including buffers, enzymes, gels, plates, detectable labels, vessels, etc.
In one aspect of this embodiment, the gene is contacted with hydrazine, which modifies cytosine residues, but not methylated cytosine residues, then the hydrazine treated gene sequence is contacted with a reagent such as piperidine, which cleaves the nucleic acid molecule at hydrazine modified cytosine residues, thereby generating a product comprising fragments. By separating the fragments according to molecular weight, using, for example, an electrophoretic, chromatographic, or mass spectrographic method, and comparing the separation pattern with that of a similarly treated corresponding non-methylated gene sequence, gaps are apparent at positions in the test gene contained methylated cytosine residues. As such, the presence of gaps is indicative of methylation of a cytosine residue in the CpG dinucleotide in the target gene of the test cell.
Bisulfite ions, for example, sodium bisulfite, convert non-methylated cytosine residues to bisulfite modified cytosine residues. The bisulfite ion treated gene sequence can be exposed to alkaline conditions, which convert bisulfite modified cytosine residues to uracil residues. Sodium bisulfite reacts readily with the 5,6-double bond of cytosine (but poorly with methylated cytosine) to form a sulfonated cytosine reaction intermediate that is susceptible to deamination, giving rise to a sulfonated uracil. The sulfonate group can be removed by exposure to alkaline conditions, resulting in the formation of uracil. The DNA can be amplified, for example, by PCR, and sequenced to determine whether CpG sites are methylated in the DNA of the sample. Uracil is recognized as a thymine by Taq polymerase and, upon PCR, the resultant product contains cytosine only at the position where 5-methylcytosine was present in the starting template DNA. One can compare the amount or distribution of uracil residues in the bisulfite ion treated gene sequence of the test cell with a similarly treated corresponding non-methylated gene sequence. A decrease in the amount or distribution of uracil residues in the gene from the test cell indicates methylation of cytosine residues in CpG dinucleotides in the gene of the test cell. The amount or distribution of uracil residues also can be detected by contacting the bisulfite ion treated target gene sequence, following exposure to alkaline conditions, with an oligonucleotide that selectively hybridizes to a nucleotide sequence of the target gene that either contains uracil residues or that lacks uracil residues, but not both, and detecting selective hybridization (or the absence thereof) of the oligonucleotide.
Test compounds can be tested for their potential to treat cancer. Expression of a gene selected from those listed in Table 1 and Table 3 is determined and if it is increased or decreased by the compound in the cell or if methylation of the gene is decreased or increased by the compound in the cell, one can identify it as having potential as a treatment for cancer. The candidate compound will have the effect of reversing the expression/or methylation modification found in the cancer cell.
The above disclosure generally describes the present invention. All references disclosed herein are expressly incorporated by reference. A more complete understanding can be obtained by reference to the following specific examples which are provided herein for purposes of illustration only, and are not intended to limit the scope of the invention.
Using re-expression profiles of lung cancer cell lines, candidate genes were identified and the most promising markers were tested on tissue using the Base5 methylation profiling platform (Straub et al. 2007). Differential methylation of the particular genes was assessed using Base5 methylation profiling platform as follows: DNA was extracted from lung samples, bisulfite converted, and selected regions of the particular genes were amplified using primers whose sequence represented converted or non-converted DNA sequences. Amplification was monitored in real-time set up using cybergreen. Two robust data analyses designed to cope with inherent variance (i.e., noise) in measured Ct and Tm values were applied to withhold 64 different assays for detecting differential methylation of ACSL6, ALS2CL, APC2, BEX1, BMP7, CBR3, CD248, CD44, CHD5, DLK1, DPYSL4, DSC2, EPB41L3, EPHB6, ERBB3, FBLN2, FBN2, FOXL2, GSTP1, HS3ST2, IGFBP7, IRF7, JAM3, LOX, LY6D, LY6K, MACF1, MCAM, NEFH, NID2, PCDHB15, PHACTR3, POMC, PRKCA, PSEN1, RBP1, RRAD, SFRP1, SOD3, SOX17, SULF2, TIMP3, TJP2, TRPV2, UCHL1, WDR69, ZFP42, ZNF442, and ZNF655 in lung cancer tissue samples.
Promoter sequences were linked with gene expression to identify epigenetically silenced genes. An established pharmacologic unmasking strategy (5-aza-2′-deoxycytidine [DAC] and trichostatin A [TSA]) for re-expression analysis of epigenetically targeted genes was combined with proprietary advanced bioinformatics tools to identify genes prone to promoter methylation. To identify differentially methylated markers associated with non-small cell lung cancer (NSCLC), the information derived from 11 cell lines (ATCC, at domain lgcpromochem-atcc.com/, 2006) was used:
1. NCI-H23: adenocarcinoma, cell line derived from a smoker
2. NCI-H1568: adenocarcinoma, cell line derived from a smoker
3. NCI-H1993: adenocarcinoma, cell line derived from a smoker
4. NCI-H2023: adenocarcinoma, cell line derived from a non-smoker
5. NCI-H2085: adenocarcinoma, cell line derived from a non-smoker
6. NCI-H2228: adenocarcinoma, cell line derived from a non-smoker
7. NCI-H520: squamous cell carcinoma, cell line
8. NCI-H838: adenocarcinoma, cell line derived from a smoker
9. NCI-H2170: squamous cell carcinoma, cell line derived from a non-smoker
10. NCI-H1869: squamous cell carcinoma, cell line derived from a smoker
11. SK-MES-1: squamous cell carcinoma, cell line
Cell culture, microarray and data analysis was done as described in Schuebel et al, 2007. In short, the cell lines were cultured with 5-aza-2′-deoxycytidine (AZA) and with trichostatin A (TSA) in parallel. Control cells underwent mock treatment. Total RNA was harvested from AZA-, TSA- and mock-treated cells. Amplification and labeling of the RNA were carried out using the Low RNA Input Linear Amplification kit (Agilent Technologies). The complementary labeled RNA was hybridized and processed according the Agilent microarray protocol. All calculations and normalizations of the expression data were performed using the R statistical computing platform (Ihaka et al., 1996) and packages from Bioconductor bioinformatics software (Gentleman et al., 1996).
A gene was selected as a good candidate if it met the following criteria:
1. Re-expressed under AZA treatment; a gene was termed as a top tier gene if the expression is up regulated by more than two-fold in the AZA treated versus mock sample on the Agilent whole human genome expression microarray platform; if it showed an enrichment between 1.4 and 2 fold it was termed as a next tier gene
2. Silent, i.e., having no basal expression, in the mock cells
3. No response to TSA treatment alone
Following this initial candidate selection, 2 main strategies were taken to further select good gene candidates susceptible to hypomethylation and/or hypermethylation: a computational strategy and a verification strategy based on cell lines and primary tumors.
This strategy was applied on the top and next tier genes of the first 6 cell lines (NCI-H23, NCI-H1568, NCI-H1993, NCI-H2023, NCI-H2085, and NCI-H2228).
Different steps were taken towards identification of good candidate genes susceptible to hypomethylation and/or hypermethylation:
Step 1: The promoters of all the selected and clearly annotated top tier genes were separately mapped on the genome-wide alignment of all promoter associated CpG islands. The genes were selected if they were located less than 9 ancestral nodes from an established list of 56 markers (see BROAD analysis). Using this approach, 100 genes were identified.
BROAD analysis: Genome-wide Promoter Alignment
The “Database of Transcription Start Sites” (DBTSS) (Suzuki et al., 2004) mapped each transcript sequence on the human draft genome sequence to identify its transcriptional start site, providing more detailed information on distribution patterns of transcriptional start sites and adjacent regulatory regions. From ˜14,500 well-characterized human genes present in the Affymetrix GeneChip Human Genome U133A Arrays 8793 sequences were extracted from the DBTSS [5, 6] (DBTSS, version 3.0 based on human assembly build 31). The remaining genes (14,500−8793=5707) on the Affymetrix array contained no reported transcriptional start site (TSS) according to DBTSS. All the promoter sequences were subsequently aligned by clustalw algorithm (Li 2003; Thompson et al., 1994) Treeillustrator (Trooskens et al., 2005) was used to visualize the large guide tree in addition to indicating the location of the known markers. Some regions on the “circle” are denser in known markers than others, indicating that there might be a sequence mechanism located in the small region around the TSS which makes certain genes more methylation-prone.
Step 2: As shown by Schuebel et al. and based on the sequencing project from Sjöblom et al. (Sjöblom et al., 2006), promoter CpG island methylation and subsequent gene silencing of genes known to be mutated in cancer is more frequent than the mutations themselves. Therefore the genes identified by Sjöblom et al. were used to identify possible extra targets from the top or next tiers with a known genetic background in either colon or breast cancer. Taking into account all 6 cell lines, 22 extra genes were found to adhere to this category.
Step 3: A final batch of genes was selected based on their appearance in multiple top tiers of the colorectal cell lines from Schuebel et al. and at least one top tier of the lung cancer cell lines. The same approach was used based on multiple breast cancer cell lines, i.e. MDA-MB-231, MDA-MB-468, MCF7 and T-47D. The next tiers of the breast cancer cell lines were also used, since the overlap between multiple top tiers of these breast cancer cell lines and the top tiers of the lung cancer cell lines was minimal compared to the overlap with the colon cancer cell lines. Sixteen genes were selected out of the colon screen and another 17 out of the breast screen.
After removing the duplicates of genes obtained by these different approaches, a list of in total 144 genes was identified by this strategy.
This strategy was applied on a selection of the top and next tier genes of 4 adenocarcinoma cell lines (NCI-H23, NCI-H1568, NCI-H1993, and NCI-H838) and 4 squamous cell carcinoma cell lines (NCI-1520, NCI-H2170, NCI-H1869, and SK-MES-1). These genes were verified in cell lines and/or primary tumors and normal lung samples for expression by reverse transcription-PCR and promoter methylation by MSP. Using this strategy, a list of in total 63 was identified.
Duplicates, imprinted genes and genes for which primer design was not possible were excluded from both lists. This final selection of genes was further analyzed on the Base5 methylation profiling platform (Straub et al. 2007).
A total of 132 samples (64 lung cancer samples, the majority derived from lung adenocarcinoma and sqaumous cell carcinomas; and 68 corresponding normal tissues) were used to find markers which distinguish cancer from non-cancer tissue based on methylation status.
A high throughput, real-time methylation specific detection platform was applied on two groups of samples totaling 132 genomic DNA samples. The two groups of samples consisted of 64 samples isolated from lung cancer tissue and 68 samples isolated from corresponding normal lung tissue.
From each sample, up to 1 μg of genomic DNA was converted using a bisulfite based protocol (EZ DNA Methylation Kit™, ZYMO Research, Orange, Calif.).
After conversion and purification the equivalent of 25-75 ng of the starting material was applied per sub-array of an OpenArray™ plate on a real-time qPCR system (BioTrove Inc.) using the DNA double strand-specific dye SYBRgreen for signal detection.
The cycling conditions were: 90° C.-10 seconds, (43° C. 18 seconds, 49° C. 60 seconds, 77° C. 22 seconds, 72° C. 70 seconds, 95° C. 28 seconds) for 40 cycles, 70° C. for 200 seconds, 45° C. for 5 seconds. A melting curve was generated in a temperature range between 45° C. and 94° C. Methylation specific PCR (MSP) primers were designed for each of the genes assessed for hypermethylation.
For each combination of assays and samples two parameters were collected using an algorithm which is part of the standard data analysis package offered by the supplier. The parameters were the Ct value (threshold cycle number) of the assessed amplicon and the melting temperature of the assessed amplicon.
The following data analysis workflow was applied to the results created by the software which came with the system OpenArray™ system. Data was collected for each combination of assays and samples in the two sets of samples used. Results were filtered using the following approach. Read outs from not loaded reaction spaces were removed from analysis. Technical Control assays were removed from the data set. Assays known to not work for other than biological reasons were removed from the analysis. Samples for which Ct calls for the gene beta-Actin were not present were removed from the analysis. Ct values >0 for each gene were normalized using the Ct values collected for the gene beta-Actin. This resulted in two files containing the results for each set of sample.
Two robust data analyses designed to cope with inherent variance (i.e., noise) in measured Ct and Tm values were applied which have common features and data analysis steps. Based on the original data, a p-value was assigned to each marker that corresponds to the probability of obtaining Ct/Tm values at least as favorable assuming these values were the result of chance alone. Next, robustness of the above p-value was computed by introducing increasing levels of noise in the data and recomputing the p-value (pVal) as above. The noise level on the x-axis was plotted against (1−pVal) on the y-axis, and the area under the resulting curve was used as the final score for a particular marker. With robust markers, the initial p-value survives for a while, hence (1−pVal) will stay high for a while, hence the area under the curve (AUC) will tend to be high. With not-so-robust markers an initial (1−pVal) will drop quickly with increasing noise levels on the x-axis, which will result in a lower AUC.
The two analysis methods, called “Ranks” and “Squares,” differ only in the way the p-values for each noise level are applied.
For computing p-values with the Ranks method for a particular marker, four lists of ranks of samples are generated: two based on the Ct values determined for each assay applied to all samples (cancer samples as well as non cancer samples) resulting in one ascending list of ranks and on one descending list of ranks; and two based on the Tm values determined for each assay applied to all samples (cancer samples as well as non-cancer samples) resulting in one ascending list of ranks and on one descending list of ranks.
For each of these four lists of ranks, the sum of the ranks of the cancer samples are calculated. The lowest of these four sums is kept. Depending on this lowest sum, we label the marker as a positive/negative Ct/Tm marker. For instance, if the lowest sum is found with the descending Ct ranking, we label the marker as a negative Ct ranker; alternatively, in case the lowest sum is found with the descending Tm ranking, the marker is labeled as a positive Tm ranker.
Next, the rank sum of the cancers is recorded for 10,000 random rankings. The fraction of cases where this sum is at least as low as the rank sum of the cancers in the original ranking is taken to be the p-value.
In order to asses the correlation between added noise and resulting p-values, random noise is introduced into the list Ct values and Tm values and the ranking procedure is repeated. This process resulted in a series of p-values with increasing levels of noise which was used to determine an AUC score. Assays are ranked based on their AUC from high to low.
Applying this method, a lower and/or upper limit is imposed on the Ct and/or Tm values determined for all samples. Such limits correspond to a “square” imposed on the scatter plot of samples where Ct forms the x-axis and Tm forms the y-axis. When considering all possible squares in this scatter plot, we are in fact exploring all combinations of a lower and/or upper limit in the Ct dimension on the one hand and the Tm dimension on the other hand. The sensitivity and specificity for the detection of cancers is determined for the set of all possible squares as defined above.
Next, for each square, the p-value is computed using the Fisher exact test. The square resulting in the highest sensitivity and specificity for determining methylation in cancer and normal samples can thus be determined for each marker candidate.
To test quality of the best square, an increasing amount of noise is injected as described above, and the p-value is recomputed using the Fisher exact test. When plotting the correlation between injected noise and the resulting p-values, the AUC can be determined. The most optimal square will result in the highest AUC. Assays are ranked based on the maximal AUC achievable.
The results of the applied analysis methods are “zipped” together in the following way. The results of applying the two analysis methods described above to two different sample sets are included into four different lists called “sample_set—1_ranks”, “sample_set—2_ranks”, “sample_set—1_squares”, and “sample_set—2_squares”
A new “zipped” list is created by taking the highest scoring assay from the list “sample_set—1_ranks,” followed by a comparison of the highest scoring assay from list “sample_set—2_ranks.” If the marker is already present in the zipped list, this finding is noted and the next highly scoring marker of the list “sample_set—2_ranks” is used. This selection procedure is applied comparing the highest scoring assay of lists “sample_set—1_squares,” noting down if the assay already has scored in the zipped list up to this step. The “sample_set—2_squares” list is used as the source for the next markers in the zipped list. The sequence of lists is maintained until all the assays in all the lists have been assessed.
The cut-offs 0.832, 0.909, 0.687 and 0.743 were applied on the “AUC” determined for each assay and rank in the lists sample_set—1_ranks, sample_set—2_ranks, sample_set—1_squares, and sample_set—2_squares. This resulted in 10 different genes.
Results
A high throughput, real-time methylation specific detection platform was applied on two groups of samples isolated from lung cancer tissue and from corresponding normal lung tissue. In this study it was shown that a number of genes are differentially methylated in lung cancer, in particular in non-small cell lung cancer, more particularly in lung adenocarcinoma or squamous cell carcinoma. We identified 64 different assays for detecting 49 different genes being differentially methylated in human lung cancer tissue and normal lung tissue control samples. The genes identified are ACSL6, ALS2CL, APC2, BEX1, BMP7, CBR3, CD248, CD44, CHD5, DLK1, DPYSL4, DSC2, EPB41L3, EPHB6, ERBB3, FBLN2, FBN2, FOXL2, GSTP1, HS3ST2, IGFBP7, IRF7, JAM3, LOX, LY6D, LY6K, MACF1, MCAM, NEFH, NID2, PCDHB15, PHACTR3, POMC, PRKCA, PSEN1, RBP1, RRAD, SFRP1, SOD3, SOX17, SULF2, TIMP3, TJP2, TRPV2, UCHL1, WDR69, ZFP42, ZNF442, ZNF655.
The resulting assays have the assay details provided in Table 1.
Finally a total number of 80 different assays (62 different genes), comprising:
Differential methylation was assessed using the Base 5 platform; genes were ranked based on the best selectivity (sensitivity and specificity) between human lung cancer tissue and normal lung tissue samples. The investigated genes were ACSL6, ALS2CL, APC2, ARTS-1, BEX1, BMP7, BNIP3, CBR3, CD248, CD44, CHD5, DLK1, DPYSL4, DSC2, EDNRB, EPB41L3, EPHB6, ERBB3, FBLN2, FBN2, FOXL2, GNAS, GSTP1, HS3ST2, HPN, IGFBP7, IRF7, JAM3, LOX, LY6D, LY6K, MACF1, MCAM, NCBP1, NEFH, NID2, PCDHB15, PCDHGA12, PFKP, PGRMC1, PHACTR3, PHKA2, POMC, PRKCA, PSEN1, RASSF1A, RASSF2, RBP1, RRAD, SFRP1, SGK, SOD3, SOX17, SULF2, TIMP3, TJP2, TRPV2, UCHL1, WDR69, ZFP42, ZNF442, ZNF655.
Primer and amplicon sequences for the 49 genes are summarized in Table 1 and 2. Primer and amplicon sequences for the remainder 13 genes are listed in Table 3 and Table 4.
Twenty three assays issuing from the Base 5 analysis were selected and transferred to the Lightcycler platform in order to confirm the Base 5 results using 3 independent sample sets (JHU, Baltimore, USA; UMCG, Groningen, The Netherlands and Ulg, Liège, Belgium) and to define the best lung cancer methylation markers (Table 5). A beta-actin (ACTB) assay was included as an internal control. The assays were applied on a 384 well plate. The samples were randomized per plate. On this platform Ct values (cycle number at which the amplification curves cross the threshold value, set automatically by the software) and melting curves (Tm) were generated on the Roche LightCycler 480 using SYBR green as detector and for verification of the melting temperature. The size of the amplicon and intensity of the signal detected were analyzed using the Caliper LabChip electrophoretic separation system. Well-defined cut offs were set up on Ct, Tm, amplicon size and signal to get similar methylation calls when using the final Molecular Beacon (MB) detection system for further verification of the markers. DNA methylation calls were compared between 146 lung cancer and 58 normal tissue samples. DNA was isolated using proteinase K digestion and phenol/chloroform extraction method. DNA concentration was measured using NanoDrop Spectrophotometer. From each sample, up to 3 μg of genomic DNA was converted using a bisulphite based protocol (EZ DNA Methylation Kit™, ZYMO Research). After conversion and purification the equivalent of 20 ng of gDNA was used per reaction. An assay ranking was generated and the results are summarized in a methylation table (
A sample was considered methylated if Ct is under 40 and if Tm and amplicon size are within the boundaries of Tm+/−2 degrees and amplicon size+/−10 bp. The intensity of the band detected by capillary electrophoresis had to be higher than 20. Those cut offs were set up to get similar methylation calls after Lightcycler analysis and real time PCR with Beacon detection system.
DNA methylation calls were compared between lung cancer tissue and normal lung tissue. An assay ranking with the set of samples was generated and the results are summarized in a methylation table (
A general overview of the ranking is given in Table 6.
A comparison between the results coming from the Base 5 and the Lightcycler platforms has been performed.
Most of the interesting assays discovered on the Base 5 platform were confirmed on the Lightcycler platform.
Nineteen genes (APC2, BMP7, BNIP3, DLK1, DPYSL4, GSTP1, HS3ST2, JAM3, LOX, LY6K, NID2, PCDHGA12, PGRMC1, PHKA2, RASSF1A, RASSF2, SFRP1, SOX17, SULF2), were further selected based on the ranking on the Base 5 and/or Lightcycler platforms (marker discovery). For these assays, qMSPs using molecular beacons as detection system were designed (3 designs are evaluated per assay) and tested on control samples (cell lines). Several parameters (background, dynamic of the curve, highest range in fluorescence between beginning of the amplification and plateau phase, etc) were checked. In this phase of assay development, PCR material was used for generating the standard curves (instead of plasmids).
These assays were further verified on lung tissue samples collected by Ulg (Liège, Belgium), VUmc (Amsterdam, The Netherlands), UMCG (Groningen, The Netherlands) and Durham VA Medical Center (Durham, N.C., USA) (normal PE tissue samples #60, cancer PE tissue samples #86 (adenocarcinoma #30, squamous cell carcinoma #15, large cell carcinoma #6, carcinoid #1, neuroendocrine #1, NSCLC #33)). DNA was isolated from the lung tissue samples using a phenol-chloroform procedure, quantified using the picogreen method and 1 μg of DNA was bisulphite treated using the ZYMO kit.
The primers and molecular beacons used for the different qMSPs are summarized in Table 7. The amplicons are summarized in Table 8. qMSPs were carried out in a total volume of 12 μl in 384 well plates in an ABI PRISM 7900HT instrument (Applied Biosystems). The final reaction mixture consisted of in-house qMSP buffer (including 80.4 nmol of MgCl2), 60 nmol of each dNTPs, 0.5 U of Jump Start Taq polymerase (SIGMA), 72 ng of forward primer, 216 ng of reverse primer, 1.92 pmol of molecular beacon, 6.0 pmol of ROX (passive reference dye) and 50 ng of bisulphite converted genomic DNA. Thermal cycling was initiated with an incubation step of 5 minutes at 95° C., followed by 45 cycles (95° C. for 30 seconds, 57° C. for 30 seconds, 72° C. for 30 seconds). The last step was performed at 72° C. for 5 minutes. These conditions were similar for all the test genes as well as for ACTB.
Ct values were determined using the SDS software (version 2.2.2) supplied by Applied Biosystems with automatic baseline settings and threshold. The slopes and R2 values for the different standard curves were determined after exporting data into excel.
As an example,
In addition to the test genes, the independent reference gene ACTB was also measured.
The ratios between the test genes and ACTB were calculated to generate the test result. The samples were classified as methylated, unmethylated, or invalid based on the decision tree shown in
The highest methylation value of the normal tissue specimens was taken as a directive to define a cut off above which the cases were considered to be methylated. The analytical cut off was finally set to give the highest possible specificity and/or above 3 times STDEV (Normal) (excluding outliers).
The one-tailed Fisher's exact test as described above was used as a scoring function to rank the candidate markers (Journal of Statistical Software, vol. 08, issue i21, 2003).
Table 9 summarizes the results obtained for JAM3. Table 10 summarizes the results obtained for all the tested markers on tissue samples. The individual performances of the assays are shown in
The control sputum samples were collected from the Lung Cancer Clinical Collaborative Research Agreement study of ONCO with the UMCG hospital (Groningen, The Netherlands). These samples were taken from participants to the NELSON screening program (a randomized controlled screening trial for lung cancer using multi-slice low-dose CT in high risk subjects—current smokers (55%) and former smokers (45%) who (had) smoked at least 16 cigarettes a day for at least 26 years or at least 11 cigarettes a day for at least 31 years).
The cancer sputum samples (stage IA #2, stage IIIA #3, stage IIIB #1, stage IV #1, stage unknown #1) were collected from the Lung Cancer Clinical Collaborative Research Agreement study of ONCO with Durham VA Medical Center (Durham, N.C., USA). Patients with histologically proven NSCLC or patients suspected of having NSCLC planning to undergo resection and who have a predicted probability of 75% or more of having NSCLC (e.g., using nomograms such as at the worldwide web domain chestx-ray.com, at the page SPN/SPNProb.html) were included in the study.
Subjects were provided with a sterile cup containing Saccomanno's fixative and instructed to take a deep breath, cough deeply, and expectorate into the cup for 3 consecutive days. The samples were centrifuged at 1500×g for 15 min to sediment all cellular material, the supernatants were removed and the cell pellet was washed with PBS. DNA was extracted from the sputum cells using standard salt-chloroform extraction and ethanol precipitation for high molecular DNA and dissolved in 250 μL TE buffer (10 mM Tris; 1 mM EDTA (pH 8.0)). DNA was quantified using the picogreen method and 20 μg (or maximum amount if less than 20 μg recovered from DNA extraction) of DNA was bisulphite treated using the EpiTect bisulfite kit (QIAGEN).
QMSP was performed after bisulphite treatment on denatured genomic DNA. The assays were carried out as described above, except that 960 ng of bisulphite converted genomic DNA was added in the reaction mixture. The samples were classified as methylated, unmethylated, or invalid as described above. The results based on ratio (copy number gene tested/copy number ACTB) and based on copy number obtained for all the tested markers on sputum samples from lung cancer patients and from control patients were ranked according their p-value (Fisher's exact test) (Table 11—ratio, Table 12—copy number).
Several combinations of markers were investigated to maximize sensitivity of detection, without significantly compromising specificity. The samples were classified as methylated if at least one of the tested markers scored positive based on ratio or based on copy number. Examples of the performance of combination of markers are summarized in Table 13 (ratio) and in Table 14 (copy number). Specificity above 90% is obtained for some combinations of markers (based on ratio and copy number). Sensitivity of 100% is obtained for some combinations of markers (based copy number).
The disclosure of each reference cited in this disclosure is expressly incorporated herein.
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/US2009/034531 | 2/19/2009 | WO | 00 | 12/22/2010 |
| Number | Date | Country | |
|---|---|---|---|
| 61029693 | Feb 2008 | US |
