CN118291616A

CN118291616A - Composition for detecting lung cancer and application thereof

Info

Publication number: CN118291616A
Application number: CN202310005985.6A
Authority: CN
Inventors: 聂海珍; 王晶; 吴振
Original assignee: Biochain Beijing Science and Technology Inc
Current assignee: Biochain Beijing Science and Technology Inc
Filing date: 2023-01-03
Publication date: 2024-07-05

Abstract

The application provides a composition for detecting lung cancer and application thereof, wherein the composition comprises the following components: a nucleic acid for detecting methylation status of a target gene, wherein the target gene is one, two, or three of an OSR1 gene, a LOC648987 gene, and a LOC643977 gene. The application also provides a kit comprising the composition and application of the composition in preparing a kit for detecting lung cancer in vitro.

Description

Composition for detecting lung cancer and application thereof

Technical Field

The application belongs to the field of molecular biology, relates to gene detection, and in particular relates to a nucleic acid composition for detecting methylation of lung cancer related genes, and a corresponding kit and application thereof.

Background

Cancer is a disease caused by abnormal cell proliferation and is also a major public health problem. Lung cancer is one of the cancers with the highest global morbidity and mortality. In China, the incidence rate and death rate of lung cancer are also the first, and the lung cancer is one of diseases seriously threatening the health of people.

The lung cancer is hidden, the cancer focus of most early lung cancer patients cannot be found in time, most lung cancer patients are found and diagnosed, the disease is advanced to middle and late stages, the best opportunity for operation or treatment is lost, and the lung cancer is one of the reasons for high and inexperienced lung cancer mortality. According to the study published by the national cancer center in the journal of Lancet-Global health (Lancet Global Health), the survival rate of the lung cancer patients diagnosed in 2012 to 2015 of China is lower in total 5 years and is 19.7 percent. Lung cancer patients are often found and diagnosed at an advanced stage, losing optimal treatment opportunities. If the disease can be found and treated early, the prognosis of the patient can be effectively improved, the survival rate of 5 years can be improved, and the death rate can be reduced. However, lung cancer still lacks ideal early-stage auxiliary diagnosis means at present.

The current technical means applied to early screening and diagnosis of lung cancer mainly comprise imaging examination, hematological examination, pathological examination and the like, but the means have certain limitations: if lung cancer tissue is obtained through operation or puncture to carry out pathological examination, the lung cancer tissue is the gold standard for lung cancer diagnosis, but the problems of high operation difficulty, high trauma to a patient, tissue detection heterogeneity and the like exist; at present, the imaging examination mainly uses low-dose spiral CT (LD-CT) for chest scanning, and the technology can reduce the overall lung cancer mortality rate by improving the detection rate of early lung cancer, but simultaneously, the high false positive rate and possible radiation injury and the like are worried; clinical serological tumor markers such as lung cancer five items (CEA, CYFRA21-1, SCC, pro-GRP, NSE) are commonly used as auxiliary diagnostic means of lung cancer, but the traditional serological tumor markers have low detection sensitivity on early lung cancer and cannot meet the requirement of early screening.

In recent years, more and more researches indicate that DNA methylation is closely related to the occurrence and development of diseases such as lung cancer. As one of the important research points in the field of epigenetic science, DNA methylation refers to the process of converting 5 'cytosine in CpG dinucleotides on genomic DNA sequences to 5' methylcytosine under the catalysis of DNA methyltransferases. It has been demonstrated that abnormal hypermethylation of the promoter region of the cancer suppressor gene inhibits transcription of the corresponding cancer suppressor gene, which reduces or silences gene expression, resulting in reduced or absent cancer suppressing function of the gene, and thus promotes the occurrence and development of lung cancer. Abnormal methylation of DNA usually occurs in the ultra-early stage of cancer, is a seed factor for tumor growth, and the methylation state of DNA can also dynamically change along with the development of the course of cancer, so that the growth condition of tumor focus can be directly reflected, and therefore, the early screening and auxiliary diagnosis of lung cancer by using DNA methylation detection has great application potential.

One important way to achieve early screening of lung cancer is liquid biopsy based on genetic sequencing technology, where the samples used for detection are mostly circulating free DNA (cfDNA) in peripheral blood. Part of cfDNA is produced and released during apoptosis or necrosis of cancer cells, and is called circulating tumor DNA (Circulating tumor DNA, ctDNA), and methylation abnormality at specific sites on ctDNA characterizes the occurrence and development of cancer. Therefore, the early screening and auxiliary diagnosis of lung cancer can be realized by taking the blood plasma cfDNA as a detection sample and matching with a methylation gene marker with high sensitivity and high specificity for lung cancer detection.

Disclosure of Invention

Based on the problems of inconvenient detection, high false positive, low sensitivity, high diagnosis omission ratio, high cost and incapability of early diagnosis of the existing lung cancer detection technology, the application provides a composition for detecting lung cancer, the composition provided by the application can sensitively and specifically detect lung cancer, and a kit comprising the composition and application of the composition in detecting lung cancer. The kit provided by the application has good lung cancer detection sensitivity and specificity, and can conveniently, rapidly and effectively detect lung cancer.

The application provides a composition for detecting lung cancer in vitro, a kit and application thereof, a method for detecting based on the kit, and application for detecting lung cancer.

In particular, the application relates to the following:

1. A composition for detecting lung cancer in vitro, the composition comprising:

Nucleic acid for detecting methylation status of a target gene,

Wherein the methylation state of the target gene is characterized by methylation of the target sequence of the target gene,

Wherein the target gene is one, two or three of OSR1 gene, LOC648987 gene and LOC643977 gene.

2. The composition of item 1, wherein the target sequence of the OSR1 gene is as set forth in SEQ ID NO:1 or SEQ ID NO:2 or SEQ ID NO:3 or SEQ ID NO: 4.

3. The composition of item 1, wherein the target sequence of the LOC648987 gene is set forth in SEQ ID NO:5 or SEQ ID NO:6 or SEQ ID NO:7 or SEQ ID NO: shown at 8.

4. The composition of item 1, wherein the target sequence of the LOC643977 gene is set forth in SEQ ID NO:9 or SEQ ID NO:10 or SEQ ID NO:11 or SEQ ID NO: shown at 12.

5. The composition according to any one of items 1 to 4, wherein the nucleic acid for detecting methylation status of a target gene comprises:

a primer which is a fragment of at least 9 nucleotides in a target sequence of the target gene,

The fragment comprises at least one CpG dinucleotide sequence.

6. The composition according to any one of items 1 to 5, wherein the nucleic acid for detecting methylation status of a target gene comprises:

A probe which is a fragment of at least 15 nucleotides hybridised to the target sequence of the target gene under moderately stringent or stringent conditions,

The fragment comprises at least one CpG dinucleotide sequence.

7. The composition according to any one of items 1 to 6, further comprising:

an agent that converts an unmethylated cytosine base at position 5 of a target sequence of a target gene to uracil.

8. The composition of any one of items 1-7, wherein the nucleic acid for detecting the methylation state of a target gene further comprises:

Blocking agents that preferentially bind to target sequences in the unmethylated state.

9. The composition according to item 8, wherein,

The at least 9 nucleotide fragment, which is SEQ ID NO:13 and SEQ ID NO:14, or it is SEQ ID NO:17 and SEQ ID NO:18, or it is SEQ ID NO:21 and SEQ ID NO: 22;

The at least 15 nucleotide fragment, which is SEQ ID NO:15, or SEQ ID NO:19, or SEQ ID NO: 23;

The sequence of the blocker is SEQ ID NO:16, the sequence of SEQ ID NO:20, or SEQ ID NO: 24.

10. An oligonucleotide for detecting lung cancer in vitro, comprising:

The SEQ ID NO:1 or SEQ ID NO:2 or SEQ ID NO:3 or SEQ ID NO:4 or a fragment of at least 9 nucleotides in its complement comprising at least one CpG dinucleotide sequence; and/or

The SEQ ID NO:5 or SEQ ID NO:6 or SEQ ID NO:7 or SEQ ID NO:8 or a fragment of at least 9 nucleotides in its complement comprising at least one CpG dinucleotide sequence; and/or

The SEQ ID NO:9 or SEQ ID NO:10 or SEQ ID NO:11 or SEQ ID NO:12 or a complementary sequence thereof and comprises at least one CpG dinucleotide sequence.

11. The oligonucleotide of item 10, further comprising:

Hybridization to the SEQ ID NO:1 or SEQ ID NO:2 or SEQ ID NO:3 or SEQ ID NO:4 or a fragment of at least 15 nucleotides in its complement comprising at least one CpG dinucleotide sequence; and/or

Hybridization to the SEQ ID NO:5 or SEQ ID NO:6 or SEQ ID NO:7 or SEQ ID NO:8 or a fragment of at least 15 nucleotides in its complement comprising at least one CpG dinucleotide sequence; and/or

Hybridization to the SEQ ID NO:9 or SEQ ID NO:10 or SEQ ID NO:11 or SEQ ID NO:12 or a complementary sequence thereof and comprises at least one CpG dinucleotide sequence.

12. The oligonucleotide of item 11, further comprising:

13. An oligonucleotide for detecting lung cancer in vitro, comprising:

SEQ ID NO:13 and SEQ ID NO: 14.

14. The oligonucleotide of item 13, further comprising: SEQ ID NO: 15.

15. The oligonucleotide of item 14, further comprising: SEQ ID NO: 16.

16. An oligonucleotide for detecting lung cancer in vitro, comprising:

SEQ ID NO:17 and SEQ ID NO: 18.

17. The oligonucleotide of item 16, further comprising: SEQ ID NO: 19.

18. The oligonucleotide of item 17, further comprising: SEQ ID NO: 20.

19. An oligonucleotide for detecting lung cancer in vitro, comprising:

SEQ ID NO:21 and SEQ ID NO: 22.

20. The oligonucleotide of item 19, further comprising: SEQ ID NO: 23.

21. The oligonucleotide of item 20, further comprising: SEQ ID NO: 24.

Use of osr1 gene in the preparation of a kit for in vitro detection of lung cancer.

Use of loc648987 gene in the preparation of a kit for in vitro detection of lung cancer.

Use of loc643977 gene in the preparation of a kit for in vitro detection of lung cancer.

25. A kit comprising the composition of any one of claims 1-9 or comprising the oligonucleotide of any one of claims 10-21.

26. The kit of item 25, further comprising at least one additional component selected from the group consisting of:

nucleoside triphosphates, DNA polymerase and buffers required for the function of the DNA polymerase.

27. The kit of item 25 or 26, further comprising: and (3) a specification.

28. Use of the composition of any one of claims 1-9 or the oligonucleotide of any one of claims 10-21 for the preparation of a kit for detecting lung cancer in vitro.

29. The use according to any one of claims 22-24 and 28, wherein the kit for in vitro detection of lung cancer detects lung cancer by a method comprising the steps of:

1) Isolating a DNA sample comprising a target sequence of a target gene or a fragment thereof from a biological sample to be tested;

2) Determining the methylation status of the target sequence of the target gene;

3) And judging the state of the biological sample according to the detection result of the methylation state of the target sequence of the target gene, thereby realizing in-vitro detection of lung cancer.

30. The use according to item 29, wherein the method comprises the steps of:

extracting genome DNA of a biological sample to be detected;

treating the extracted genomic DNA with a reagent to convert the unmethylated cytosine base at position 5 to uracil or other bases;

Contacting the reagent-treated DNA sample with a DNA polymerase and a primer for a target sequence of a target gene of interest, and performing DNA polymerization in the presence of a blocking agent that preferentially binds to the target sequence in an unmethylated state;

Detecting the amplified product with a probe; and

Determining the methylation status of at least one CpG dinucleotide of the target sequence of the target gene of interest based on the presence or absence of the amplification product.

31. The use according to item 30, wherein the reagent is a bisulphite reagent.

32. A method of detecting lung cancer comprising the steps of:

Isolating a DNA sample comprising a target sequence of a target gene or a fragment thereof from a biological sample to be tested;

determining the methylation status of the target sequence of the target gene; and

And judging the state of the biological sample according to the detection result of the methylation state of the target sequence of the target gene, thereby realizing in-vitro detection of lung cancer.

33. A method of detecting lung cancer comprising the steps of:

extracting genome DNA of a biological sample to be detected;

Detecting the amplified product with a probe; and

34. The method of item 32 or 33, wherein,

The target gene is one, two or three of OSR1 gene, LOC648987 gene and LOC643977 gene.

35. The method of item 34, wherein the OSR1 gene has a target sequence as set forth in SEQ ID NO:1 or SEQ ID NO:2 or SEQ ID NO:3 or SEQ ID NO: 4.

36. The method of item 34, wherein the target sequence of the LOC648987 gene is set forth in SEQ ID NO:5 or SEQ ID NO:6 or SEQ ID NO:7 or SEQ ID NO: shown at 8.

37. The method of item 34, wherein the target sequence of the LOC643977 gene is set forth in SEQ ID NO:9 or SEQ ID NO:10 or SEQ ID NO:11 or SEQ ID NO: shown at 12.

38. The method of item 33, wherein the reagent is a bisulphite reagent.

39. The method of item 33, wherein the primer is:

40. The method of item 33, wherein the blocking agent is one that preferentially binds to the target sequence in the unmethylated state.

41. The method of item 33, wherein the probe is:

42. The method of item 39, wherein the primer is SEQ ID NO:13 and SEQ ID NO:14, or it is SEQ ID NO:17 and SEQ ID NO:18, or it is SEQ ID NO:21 and SEQ ID NO: 22.

43. The method of item 40, wherein the blocker is SEQ ID NO:16, the sequence of SEQ ID NO:20, or SEQ ID NO: 24.

44. The method of item 41, wherein the probe is SEQ ID NO:15, or SEQ ID NO:19, or SEQ ID NO: 23.

The application has the following beneficial effects:

By detecting the target sequences of three lung cancer methylation genes, namely OSR1 gene, LOC648987 gene and/or LOC643977 gene, the methylation states of the 3 genes can be sensitively and specifically detected, so that the detection method can be used for detecting peripheral blood episomal DNA. The detection of peripheral blood samples of lung cancer patients and normal control individuals shows that: the composition and the detection method described by the application can sensitively and specifically detect lung cancer, including common lung cancer of two different cell types: adenocarcinoma and squamous carcinoma, thereby ensuring the correctness and reliability of the detection result. Therefore, the application provides a composition and a detection method for detecting lung cancer in vitro, and the composition and the detection method have important clinical application value.

Other features and advantages of the application will be described with reference to the following detailed description and claims.

Drawings

The above and other features of the present application will be further explained with reference to the drawings and the detailed description thereof. It is appreciated that these drawings depict only several exemplary embodiments according to the application and are therefore not to be considered limiting of its scope.

FIG. 1 is a graph showing the results of comparison of the average methylation levels of OSR1 gene in lung adenocarcinoma (LUAD), lung squamous carcinoma (LUSC), normal human plasma free DNA (cfDNA) and normal human White Blood Cells (WBC).

FIG. 2 is a graph showing the results of comparison of the average methylation levels of the LOC648987 gene in lung adenocarcinoma (LUAD), lung squamous carcinoma (LUSC), normal human plasma free DNA (cfDNA) and normal human White Blood Cells (WBC).

FIG. 3 is a graph showing the results of comparison of the average methylation levels of the LOC643977 gene in lung adenocarcinoma (LUAD), lung squamous carcinoma (LUSC), normal human plasma free DNA (cfDNA) and normal human White Blood Cells (WBC).

FIG. 4 shows the results of the detection of positive control samples (mixture of HeLa cell line DNA and normal human leukocyte cell line DNA, in which HeLa cell line DNA is in a highly/fully methylated state and can be used as a detection target; normal human leukocyte cell line DNA is in a low/unmethylated state and can be used as a detection background) and negative control samples (normal human leukocyte cell line DNA, normal human leukocyte cell line DNA is usually in a low/unmethylated state and can be used as a negative control) using the composition and the detection method of the present application. The results show that: the composition and the detection method provided by the application are positive to the detection result of a positive control sample and negative to the detection result of the cell line DNA of normal human leucocytes, wherein the methylation state detection result of OSR1, LOC648987 and LOC643977 genes in the positive control sample is shown in the upper part of FIG. 4, and the methylation state detection result of OSR1, LOC648987 and LOC643977 genes in the cell line DNA of normal human leucocytes is shown in the lower part of FIG. 4.

Detailed Description

The application will be further illustrated with reference to the following examples, which are to be understood as merely further illustrating and explaining the application and are not to be construed as limiting the application.

Reagents and materials used in the present application are commercially available unless otherwise indicated.

The practice of the present application will employ, unless otherwise indicated, conventional techniques of molecular biology (including recombinant techniques), microbiology, cell biology, biochemistry and genetics, which are within the skill of the art. Such techniques are described in detail in the literature as Molecular Cloning: a Laboratory Manual, second edition (Sambrook et al, 1989); oligonucleotide Synthesis (M.J.Gait, 1984); ANIMAL CELL Culture (R.I. Freshney, 1987); methods in Enzymology books (american academic press limited); current Protocols in Molecular Biology (F.M. Ausubel et al, 1987 edition, and periodic updates); and (2) PCR: the Polymerase ChainReaction (Mullis et al, 1994 edition). Primers, probes, blockers and kits useful in the present application can be prepared using standard techniques well known in the art.

Unless defined otherwise, technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs.

Definition of the definition

"Precancerous" in the present application means a cell at an early stage of or prone to be transformed into a cancer cell. Such cells may exhibit one or more phenotypic traits characteristic of cancer cells.

"Stringent hybridization conditions" and "high stringency" in the present application refer to conditions under which a probe hybridizes to its target sequence, typically in a complex mixture of nucleic acids. Stringent conditions are sequence-dependent and will be different in different circumstances. Longer sequences hybridize specifically at higher temperatures. For detailed guidance on nucleic acid hybridization, reference may be made to Tijssen, biochemical and molecular biological techniques-nucleic acid probe hybridization, "review of hybridization principles and nucleic acid assay strategies. Typically, stringent conditions are those about 5-10deg.C below the melting point (Tm) for a specific nucleic acid at a defined ionic strength pH. At Tm temperatures (at defined ionic strength, pH and nucleic acid concentration), 50% of the probes complementary to the target hybridize uniformly to the target sequence. Stringent conditions can also be achieved with the addition of destabilizing agents. For selective or specific hybridization, the positive signal is twice, preferably 10 times, that of the background hybridization. Exemplary stringent hybridization conditions are as follows: hybridization was performed at 42℃in a solution of 50% formamide, 5 XSSC and 1% SDS, or at 65℃in a solution of 5 XSSC and 1% SDS, followed by washing at 65℃in a solution of 0.2XSSC and 0.1% SDS.

Also, if the polypeptides encoded by the nucleic acids are substantially similar, the nucleic acids are substantially similar even if they are not capable of hybridizing under stringent conditions. In this case, the nucleic acid is typically hybridized under moderately stringent hybridization conditions. As an example, "moderately stringent hybridization conditions" include hybridization in a solution of 40% formamide, 1M sodium chloride and 1% SDS at 37 ℃ and washing in a solution of 1xSSC at 45 ℃. It will be apparent to one of ordinary skill in the art that guidance in achieving the conditions to achieve the same stringency is available in the prior art. For PCR, temperatures around 36℃are typically suitable for low stringency amplification, while annealing temperatures range between 32℃and 48℃based on the length of the primer. For highly stringent PCR amplification, it is typically at 62℃and the annealing temperature for highly stringent hybridization ranges between 50℃and 65℃based on the length and specificity of the primers. For cycling conditions of high stringency and low stringency amplification, typically, include: the denaturation phase is continued for 30 seconds to 2 minutes at 90-95 ℃, the annealing phase is continued for 30 seconds to 2 minutes, and the extension phase is continued for 1 to 2 minutes at about 72 ℃. Tools and guidelines for low and high stringency amplification reactions are available in the prior art.

"Oligonucleotide" in the present application refers to a molecule consisting of two or more nucleotides, preferably three or more nucleotides, the exact size of which may depend on a number of factors, which in turn are determined by the ultimate function and use of the oligonucleotide. In certain embodiments, the oligonucleotide may comprise a length of 10 nucleotides to 100 nucleotides. In certain embodiments, the oligonucleotides may comprise a length of 10 nucleotides to 30 nucleotides, or may have lengths of 20 and 25 nucleotides. In some particular embodiments, oligonucleotides shorter than these lengths are also suitable.

"Primer" according to the present application means an oligonucleotide capable of acting as a starting point for synthesis, whether it is naturally occurring in a purified restriction digest or synthetically produced, when placed under conditions that induce synthesis of a primer extension product complementary to a nucleic acid strand, i.e., in the presence of a nucleotide and an inducer such as a DNA or RNA polymerase and at a suitable temperature and pH. The primer may be single-stranded or double-stranded and must be long enough to prime the synthesis of the desired extension product in the presence of the primer. The exact length of the primer depends on a variety of factors, including temperature, primer source and method used. For example, for diagnostic and prognostic applications, an oligonucleotide primer will typically contain at least or more than about 9,10, or 15, or 20, or 25 or more nucleotides, depending on the complexity of the target sequence, but it may contain fewer nucleotides or more nucleotides. Factors involved in determining the appropriate length of the primer are well known to those skilled in the art.

"Primer pair" according to the present application means a primer pair which hybridizes to the opposite strand of a target DNA molecule or to a region of the target DNA flanked by nucleotide sequences to be amplified.

"Primer site" in the present application refers to a region of target DNA or other nucleic acid to which a primer hybridizes.

The "probe" of the present application, when referring to a nucleic acid sequence, is used in its ordinary sense to denote a selected nucleic acid sequence that hybridizes to a target sequence under defined conditions and can be used to detect the presence of the target sequence. Those skilled in the art will appreciate that in some cases, probes may also be used as primers, and primers may be used as probes.

"DNA methylation" according to the application refers to the addition of a methyl group to the 5-position of cytosine (C), which is usually (but not necessarily) the case in CpG (cytosine followed by guanine) dinucleotides. As used herein, "increased degree of methylation" or "substantial degree of methylation" refers to the presence of at least one methylated cytosine nucleotide in a DNA sequence, wherein the corresponding C in a normal control sample (e.g., a DNA sample extracted from a non-cancerous cell or tissue sample or a DNA sample treated for methylation of DNA residues) is unmethylated, and in certain embodiments, at least 2, 3, 4, 5, 6, 7, 8, 9, 10, or more C can be methylated, wherein the C at these positions in the control DNA sample is unmethylated.

In embodiments, a variety of different methods may be used to detect DNA methylation changes. Methods for detecting DNA methylation include, for example, methylation-sensitive restriction endonuclease (MSRE) assays using southern or Polymerase Chain Reaction (PCR) assays, methylation-specific or methylation-sensitive PCR (MS-PCR), methylation-sensitive single nucleotide primer extension (MS-SnuPE), high Resolution Melting (HRM) assays, bisulfite sequencing, pyrosequencing, methylation-specific single strand conformation assays (MS-SSCA), combinatorial bisulfite restriction assays (COBRA), methylation-specific gradient gel electrophoresis (MS-DGGE), methylation-specific melting curve assays (MS-MCA), methylation-specific high performance liquid chromatography (MS-DHPLC), methylation-specific Microarray (MSO). These assays may be PCR assays, quantitative assays using fluorescent markers or southern blot assays.

"Methylation determination" in the context of the present application refers to any determination of the methylation status of one or more CpG dinucleotide sequences within a DNA sequence.

"Detecting" according to the present application means any process of observing a marker or a change in a marker (e.g. a change in the methylation state of a marker or the expression level of a nucleic acid or protein sequence) in a biological sample, whether or not the marker or the change in the marker is actually detected. In other words, the act of detecting the marker or a change in the marker of the sample is "detecting" even if the marker is determined to be absent or below the sensitivity level. The detection may be quantitative, semi-quantitative, or non-quantitative observation, and may be based on comparison to one or more control samples. It is to be understood that detecting lung cancer as disclosed herein includes detecting pre-cancerous cells that begin to develop into, or are about to develop into, or have an increased propensity to develop into, lung cancer cells. Detecting lung cancer may also include detecting a possible probability of death or a possible prognosis of a disease condition.

"Homology", "identity" and "similarity" in the present application refer to sequence similarity between 2 nucleic acid molecules. The positions in each sequence can be compared to determine "homology", "identity" or "similarity", and the sequences can be aligned for comparison purposes. When an equivalent position in the compared sequences is occupied by the same base, the molecules are identical at that position; when an equivalent site is occupied by the same or a similar amino acid (e.g., similar in steric or charged properties) residue, the molecule may be said to be homologous (similar) at that position. Expression of homology/similarity or percent identity refers to a function of the number of identical or similar amino acids at positions shared by the compared sequences. "unrelated" or "non-homologous" sequences share less than 40% identity, preferably less than 25% identity, with the sequences of the present application. The absence of residues (amino acids or nucleic acids) or the presence of redundant residues also reduces identity and homology/similarity when comparing 2 sequences. In specific embodiments, for two or more sequences or subsequences, as determined using BLAST or BLAST 2.0 sequence comparison algorithms having default parameters described below, or as determined by manual alignment and visual inspection provided on-line, e.g., by the national center for Biotechnology information (National Center for Biotechnology Information (NCBI)), when compared and aligned for maximum correspondence over a comparison window or designated region, if their sequences are about 60% identical over the designated region, Or about 65%, 70%, 75%, 80%, 85%, 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99% or more, may be considered substantially or significantly homologous, similar or identical. The definition also relates to or can be used to test the complement of a sequence. Thus, for example, if a nucleotide sequence can be predicted to occur naturally in a DNA duplex, or can occur naturally in the form of one or both of the complementary strands, the nucleotide sequence that is complementary to a specified target sequence or variant thereof is itself considered "similar" to the target sequence, and when reference is made to a "similar" nucleic acid sequence, includes single-stranded sequences, their complementary sequences, double-stranded strand complexes, sequences capable of encoding the same or similar polypeptide products, and any permissible variants of any of the foregoing, to the extent permitted by the context herein. The circumstances in which similarity must be limited to analysis of a single nucleic acid strand sequence may include, for example, detection and quantification of expression of a particular RNA sequence or coding sequence in a cell. The definition also includes sequences with deletions and/or additions, as well as sequences with substitutions. In embodiments, identity or similarity may be over a region of at least about 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 10, 21, 22, 23, 24, 25 or more nucleotides in length, or over a region of more than about 10, 15, 20, 25, 30, 35, 40, 45, 50, 55, 60, 65, 70, 75, 80, 85, 90, 95 or more than about 100 nucleotides in length.

"Amplification" according to the present application means the process of obtaining multiple copies from one specific locus of a nucleic acid, such as genomic DNA or cDNA. Amplification may be accomplished using any of a variety of known means including, but not limited to, polymerase Chain Reaction (PCR), transcription-based amplification, and Strand Displacement Amplification (SDA).

The "fluorescence-based real-time PCR" of the present application means a method of: and adding a fluorescent group into the PCR reaction system, monitoring the whole PCR process in real time by utilizing fluorescent signal accumulation, and finally quantitatively analyzing the unknown template through a standard curve. In this PCR technique, there is a very important concept, the cycle threshold, also called Ct value. C represents Cycle, t represents threshold, and Ct has the meaning of: the number of cycles that the fluorescent signal within each reaction tube experiences when reaching a set threshold. For example, the fluorescence threshold (threshold) is set as follows: the fluorescent signal of the first 15 cycles of the PCR reaction served as the fluorescent background signal, and the default (default) setting of the fluorescent threshold was 10 times the standard deviation of the fluorescent signal of 3-15 cycles.

The "cut off value of real-time PCR" of the present application means a critical Ct value for a biomarker that determines whether a sample is negative or positive. According to some embodiments of the present application, the "critical Ct value (Cut Off value) is obtained based on statistical processing from a certain number of sample data, and may be different depending on the required sensitivity or specificity requirements.

The "sensitivity" of the present application means the ratio of cancers detected from a certain cancer sample, and the calculation formula is: sensitivity= (detected cancer/all cancers), whereas "specificity" indicates the normal proportion detected in a certain normal human sample, the formula is specificity= (undetected negative/total negative).

A "label" or "detectable moiety" according to the present application is a component that is detectable by spectroscopic, photochemical, biochemical, immunochemical, chemical or other physical means. For example, useful labels include 32P, fluorescent dyes, electron dense reagents, enzymes (e.g., enzymes commonly used in ELISA), biotin, digoxin, or haptens, and proteins that can be prepared to be detectable, e.g., by incorporating a radiolabel into the peptide or for detecting antibodies that specifically react with the peptide.

Nucleic acid molecules can be detected using a variety of different methods. Nucleic acid detection methods include, for example, PCR and nucleic acid hybridization (e.g., southern blot, northern blot, or in situ hybridization). In particular, oligonucleotides (e.g., oligonucleotide primers) capable of amplifying a target nucleic acid may be used in a PCR reaction. The PCR method generally comprises the steps of: obtaining a sample, isolating nucleic acids (e.g., DNA, RNA, or both) from the sample, and contacting the nucleic acids with one or more oligonucleotide primers that specifically hybridize to a template nucleic acid under conditions that enable amplification of the template nucleic acid to occur. In the presence of a template nucleic acid, amplification products are produced. Conditions for nucleic acid amplification and detection of amplification products are known to those skilled in the art. Various improvements to the basic PCR technique have been developed, including, but not limited to, anchored PCR, RACE PCR, RT-PCR, and Ligase Chain Reaction (LCR). The primer pairs in the amplification reaction must anneal to the opposite strand of the template nucleic acid and should be kept at a suitable distance from each other so that the polymerase can efficiently polymerize across the region and so that the amplified product can be easily detected, for example, using electrophoresis. For example, oligonucleotide primers may be designed using a computer program such as OLIGO (Molecular Biology Insights inc., cascades, colo.) to aid in designing primers with similar melting temperatures. Typically, the oligonucleotide primers are 9-30 or 40 or 50 nucleotides in length (e.g., 9、10、11、12、13、14、15、16、17、18、19、20、21、22、23、24、25、26、27、28、29、30、31、32、33、34、35、36、37、38、39、40、41、42、43、44、45、46、47、48、49 or 50 nucleotides in length), but the oligonucleotide primers may be longer or shorter as long as appropriate amplification conditions are used.

Detection of the amplification product or hybridization complex is typically accomplished using a detectable label. The term "label", when referring to a nucleic acid, is intended to include direct labeling of the nucleic acid by coupling (i.e., physically linking) a detectable substance to the nucleic acid, as well as indirect labeling of the nucleic acid by reaction with another reagent that directly labels the detectable substance. Detectable substances include various enzymes, prosthetic groups, fluorescent materials, luminescent materials, bioluminescent materials, and radioactive materials. Examples of suitable enzymes include horseradish peroxidase, alkaline phosphatase, beta-galactosidase, or acetylcholinesterase; examples of suitable prosthetic groups include streptavidin/biotin and avidin/biotin; examples of suitable fluorescent materials include umbelliferone, fluorescein isothiocyanate, rhodamine, dichlorotriazinylamine fluorescein, dansyl chloride or phycoerythrin; examples of luminescent materials include luminol; examples of bioluminescent materials include luciferase, luciferin and aequorin. Examples of indirect labeling include end-labeling a nucleic acid with biotin such that the nucleic acid can be detected with fluorescently labeled streptavidin.

SUMMARY

In one aspect, the application provides a composition for detecting lung cancer in vitro, the composition comprising a nucleic acid for detecting methylation status within a target sequence of a target gene, wherein the methylation status of the target gene is characterized by methylation of the target sequence of the target gene, wherein the target gene is one, two or three of an OSR1 gene, a LOC648987 gene and a LOC643977 gene.

The application provides a group of target sequences of target genes for emitting abnormal methylation in lung cancer, which comprise target sequences of an OSR1 gene, a LOC648987 gene and a LOC643977, wherein the target sequences of the OSR1 gene are shown as SEQ ID NO:1-4, the target sequence of the LOC648987 gene is shown as SEQ ID NO:5-8, the target sequence of the LOC643977 gene is shown as SEQ ID NO: 9-12.

It will also be appreciated by those skilled in the art that the target sequences for the OSR1 gene, LOC648987 gene, and LOC643977 are not limited to the specific sequences listed above. The target sequence of the OSR1 gene should cover a sequence identical to SEQ ID NO:1-4, comprising one or two or more nucleotide mutations, but substantially still functionally identical thereto, as well as sequences identical to those of SEQ ID NOs: 1-4, a sequence having 95%, 96%, 97%, 98% or 99% sequence identity to the sequence set forth in any one of claims 1-4. The target sequence of the LOC648987 gene should cover a sequence identical to SEQ ID NO:5-8, comprising one or two or more nucleotide mutations, but substantially still functionally identical thereto, as well as sequences identical to those of SEQ ID NO:5-8, a sequence having 95%, 96%, 97%, 98% or 99% sequence identity to the sequence set forth in any one of figures. The target sequence of LOC643977 should cover a sequence identical to SEQ ID NO:9-12, comprising one or two or more nucleotide mutations, but substantially still functionally identical thereto, as well as sequences identical to those of SEQ ID NOs: 9-12, a sequence having 95%, 96%, 97%, 98% or 99% sequence identity to the sequence set forth in any one of claims.

The target sequence (5 '-3') of the OSR1 gene is as follows:

SEQ ID NO：1

the sequence (5 '-3') of the target sequence of the OSR1 gene after bisulfite treatment is as follows:

SEQ ID NO：2

The complementary sequences (5 '-3') of the target sequence of the OSR1 gene are as follows:

SEQ ID NO：3

the sequence complementary to the target sequence of the OSR1 gene after bisulfite treatment (5 '-3') is as follows:

SEQ ID NO：4

The target sequence (5 '-3') of the LOC648987 gene is as follows:

SEQ ID NO：5

the sequence (5 '-3') of the target sequence of the LOC648987 gene after bisulfite treatment is as follows: SEQ ID NO:6

The complementary sequence (5 '-3') of the target sequence of the LOC648987 gene is as follows:

SEQ ID NO：7

The sequence (5 '-3') of the complementary sequence of the target sequence of the LOC648987 gene after bisulfite treatment is as follows:

SEQ ID NO：8

The target sequence (5 '-3') of the LOC643977 gene is as follows:

SEQ ID NO：9

The sequence (5 '-3') of the target sequence of the LOC643977 gene after bisulfite treatment is as follows:

SEQ ID NO：10

the complementary sequence (5 '-3') of the target sequence of the LOC643977 gene is as follows:

SEQ ID NO：11

The sequence (5 '-3') of the complementary sequence of the target sequence of the LOC643977 gene after bisulfite treatment is as follows: SEQ ID NO:12

Target sequences and related sequences of the OSR1 gene, LOC648987 gene, and LOC643977 gene are shown in table 1:

Table 1: target sequences of OSR1 gene, LOC648987 gene and LOC643977 gene and related sequences

Preferably, the nucleic acid for detecting methylation status of a gene of interest comprises a fragment of at least 9 nucleotides in a target sequence of the gene of interest, wherein the fragment comprises at least one CpG dinucleotide sequence. In certain preferred embodiments, the nucleic acid for detecting the methylation state of a target gene comprises a fragment of at least 9 nucleotides, preferably a fragment of at least 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22 or more nucleotides in a sequence of the target gene after bisulfite conversion, such as by bisulfite conversion of the sample DNA.

More preferably, the nucleic acid for detecting methylation status of a gene of interest comprises a fragment of at least 15 nucleotides that hybridizes under moderate stringency or stringent conditions to a target sequence of said gene of interest, wherein said fragment of nucleotides comprises at least one CpG dinucleotide sequence. In certain preferred embodiments, the nucleic acid for detecting the methylation state of a target gene, such as by converting a test sample DNA using bisulfite, comprises a fragment of at least 15 nucleotides, preferably a fragment of at least 16, 17, 18, 19, 20, 21, 22 or more nucleotides, in a sequence following bisulfite conversion of the target sequence of the target gene under moderately stringent or stringent conditions, wherein the fragment of nucleotides comprises at least one CpG dinucleotide sequence.

Preferably, the composition further comprises an agent that converts an unmethylated cytosine base at position 5 of the target sequence of the target gene to uracil. More preferably, the reagent is bisulphite.

Preferably, the nucleic acid for detecting the methylation state of the target gene further comprises a blocking agent that preferentially binds to the DNA in the unmethylated state.

Preferably, the composition comprises one or more of the optimal primers, probes, and/or blocking agents shown in table 2, and/or table 4:

Table 2: optimal primer, probe and blocker sequences for use in the present application

"_F" in Table 2 represents a forward primer; "_R" represents the reverse primer; "_P" represents a probe; "_B" represents a blocking agent.

Table 3: the probe sequence used in the application and a fluorescence labeling mode

Table 4: blocking agent and marking mode adopted by the application

In another aspect, the application provides an oligonucleotide for detecting lung cancer in vitro comprising: SEQ ID NO:1 or SEQ ID NO:2 or SEQ ID NO:3 or SEQ ID NO:4 or a fragment of at least 9 nucleotides in its complement comprising at least one CpG dinucleotide sequence; and/or SEQ ID NO:5 or SEQ ID NO:6 or SEQ ID NO:7 or SEQ ID NO:8 or a fragment of at least 9 nucleotides in its complement comprising at least one CpG dinucleotide sequence; and/or SEQ ID NO:9 or SEQ ID NO:10 or SEQ ID NO:11 or SEQ ID NO:12 or a complementary sequence thereof and comprises at least one CpG dinucleotide sequence.

Preferably the oligonucleotide for in vitro detection of lung cancer comprises: for SEQ ID NO:1 or SEQ ID NO:2 or SEQ ID NO:3 or SEQ ID NO:4 or a complementary sequence thereof, a fragment of at least 9 nucleotides in the bisulfite converted sequence; and/or to SEQ ID NO:5 or SEQ ID NO:6 or SEQ ID NO:7 or SEQ ID NO:8 or a complementary sequence thereof, and comprising at least 9 nucleotides of a CpG dinucleotide sequence; and/or to SEQ ID NO:9 or SEQ ID NO:10 or SEQ ID NO:11 or SEQ ID NO:12 or a complement thereof, and comprising at least one CpG dinucleotide sequence.

The oligonucleotide for detecting lung cancer in vitro of the present application further comprises: hybridization to the SEQ ID NO:1 or SEQ ID NO:2 or SEQ ID NO:3 or SEQ ID NO:4 or a fragment of at least 15 nucleotides in its complement comprising at least one CpG dinucleotide sequence; and/or hybridizes to the SEQ ID NO:5 or SEQ ID NO:6 or SEQ ID NO:7 or SEQ ID NO:8 or a fragment of at least 15 nucleotides in its complement comprising at least one CpG dinucleotide sequence; and/or hybridizes to the SEQ ID NO:9 or SEQ ID NO:10 or SEQ ID NO:11 or SEQ ID NO:12 or a complementary sequence thereof and comprises at least one CpG dinucleotide sequence.

Preferably the oligonucleotide for in vitro detection of lung cancer comprises: hybridization to SEQ ID NO:1 or SEQ ID NO:2 or SEQ ID NO:3 or SEQ ID NO:4 or a complementary sequence thereof, and comprising at least 15 nucleotides of a CpG dinucleotide sequence; and/or hybridizes under moderately stringent or stringent conditions to the sequence set forth in SEQ ID NO:5 or SEQ ID NO:6 or SEQ ID NO:7 or SEQ ID NO:8 or a complementary sequence thereof, and comprising at least 15 nucleotides of a CpG dinucleotide sequence; and/or hybridizes under moderately stringent or stringent conditions to the sequence set forth in SEQ ID NO:9 or SEQ ID NO:10 or SEQ ID NO:11 or SEQ ID NO:12 or a complement thereof, and comprising at least one CpG dinucleotide sequence.

The oligonucleotide for detecting esophageal cancer in vitro of the application further comprises: blocking agents that preferentially bind to DNA in the unmethylated state.

In a specific embodiment, an oligonucleotide for detecting lung cancer in vitro, comprising: SEQ ID NO:13 and SEQ ID NO: 14. It also includes: SEQ ID NO: 15. It also includes: SEQ ID NO: 16.

In another specific embodiment, an oligonucleotide for detecting lung cancer in vitro, comprising: SEQ ID NO:17 and SEQ ID NO: 18. It also includes: SEQ ID NO: 19. It also includes: SEQ ID NO: 20.

In another specific embodiment, an oligonucleotide for detecting lung cancer in vitro, comprising: SEQ ID NO:21 and SEQ ID NO:22, which further comprises: SEQ ID NO: 23. It also includes: SEQ ID NO: 24.

In another aspect, the application provides a kit comprising the composition. The kit further comprises at least one additional component selected from the group consisting of: nucleoside triphosphates, DNA polymerase and buffers required for the function of the DNA polymerase.

The application also relates to application of the OSR1 gene and/or the LOC648987 gene and/or the LOC643977 gene in preparing a kit for detecting lung cancer in vitro.

Wherein, the OSR1 gene, english name protein odd-SKIPPED RELATED 1, is located in the p24.1 region of human chromosome 2, codes a transcription factor, belonging to zinc finger transcription factor family. The transcription factor may be involved in regulating the development of the heart, genitourinary organs, etc. of the embryo.

LOC648987 and LOC643977 genes each encode a long non-coding RNA (longnon-codingRNA) and are both located in the p12 region of chromosome 5 in humans.

In yet another aspect, the present application provides a method for detecting lung cancer in vitro, the method comprising the steps of:

1) Separating target sequences of target genes or fragments thereof in a biological sample to be detected;

According to certain preferred embodiments, the method further comprises the steps of:

1) Extracting genome DNA of a biological sample to be detected;

2) Treating the DNA sample obtained in step 1) with a reagent to convert the 5-unmethylated cytosine base into uracil or another base, i.e., to convert the 5-unmethylated cytosine base of the target sequence of the target gene into uracil or another base, the converted base being different from the 5-unmethylated cytosine base in hybridization performance and being detectable;

3) Contacting the DNA sample treated in step 2) with a DNA polymerase and primers for the target sequence of the target gene such that the treated target sequence of the target gene is amplified to produce amplified products or not; the treated target sequence of the target gene produces amplified products if DNA polymerization occurs; the treated target gene sequence is not amplified if DNA polymerization does not occur;

4) Detecting the amplified product with a probe; and

5) Determining the methylation status of at least one CpG dinucleotide of the target sequence of the target gene of interest based on the presence or absence of the amplification product.

Preferably, typical primers comprise fragments of the target sequence of the target gene comprising a sequence that hybridizes to a sequence selected from the group consisting of SEQ ID NOs: 1-4, any one of SEQ ID NOs: 5-8 and SEQ ID NO: a fragment of at least 9 nucleotides of any one of 9-12.

Preferably, a typical probe comprises a fragment of said target sequence of the target gene comprising a sequence which hybridizes to a sequence selected from the group consisting of SEQ ID NOs: 1-4, any one of SEQ ID NOs: 5-8 and SEQ ID NO:9-12 of any one of the following.

Preferably, a typical blocker is one that preferentially binds to DNA in the unmethylated state.

Preferably, one or more of the primers, probes are as set forth in table 2 above. One or more of the blocking agents are as set forth in table 2 or table 4 above.

And, the contacting or amplifying comprises using at least one of the following methods: using a thermostable DNA polymerase as the amplification enzyme, using a polymerase lacking 5'-3' exonuclease activity, using Polymerase Chain Reaction (PCR), producing an amplification product nucleic acid molecule with a detectable label.

According to certain preferred embodiments, the methylation status of at least one CpG dinucleotide in the target sequence of the gene of interest is determined from the critical Ct value of the real-time PCR reaction. The method for analyzing DNA in the biological sample by utilizing the real-time PCR reaction can conveniently realize the detection of the methylation state of the target sequence of the target gene, and can rapidly and conveniently judge whether the detected sample is positive according to the critical Ct value of the PCR reaction, thereby providing a noninvasive and rapid lung cancer in-vitro detection method.

The biological sample is selected from the group consisting of a cell line, a histological section, a tissue biopsy/paraffin-embedded tissue, a body fluid, stool, a colonic outflow, urine, plasma, serum, whole blood, isolated blood cells, cells isolated from blood, or a combination thereof.

A preferred biological sample is plasma.

The application also provides a kit comprising the composition. Typically, the kit comprises a container for holding a biological sample of a patient. And, the kit also includes instructions for use and interpretation of the test results.

The application provides a method for noninvasively detecting lung cancer in vitro by detecting methylation state of target sequences of target genes. The inventors found that there are significant differences in the methylation status of OSR1 gene, LOC648987 gene and LOC643977 gene target sequences in lung cancer tissue and the methylation status of the gene target sequences of normal lung tissue: in lung cancer tissues, the OSR1 gene, LOC648987 gene, and LOC643977 gene target sequences were methylated, whereas in normal lung tissues, the OSR1 gene, LOC648987 gene, and LOC643977 gene target sequences were not methylated. Therefore, the application provides a method for detecting lung cancer in vitro by detecting the methylation states of OSR1 gene, LOC648987 gene and LOC643977 gene target sequences in a sample, and the method provided by the application can be used for detecting lung cancer noninvasively and rapidly.

The application also provides a composition capable of sensitively and specifically detecting the methylation state of the target sequence of the target gene; and a method and a kit for non-invasively detecting lung cancer in vitro.

The following description is of examples of compositions, kits, nucleic acid sequences, and detection methods of the application.

In certain embodiments, the composition further comprises an agent that converts an unmethylated cytosine base at position 5 of the gene to uracil. Preferably, the agent is bisulphite. Bisulfite modification of DNA is a known tool for assessing CpG methylation status. In eukaryotic DNA, 5-methylcytosine is the most common covalent base modification. 5-methylcytosine cannot be identified by sequencing because 5-methylcytosine has the same base pairing behavior as cytosine. Furthermore, the epigenetic information carried by 5-methylcytosine is completely lost during PCR amplification. The most commonly used method for analyzing DNA for the presence of 5-methylcytosine is based on the specific reaction of bisulfite with cytosine; after subsequent alkaline hydrolysis, unmethylated cytosines are converted to uracil which corresponds to thymine in pairing behavior; but under these conditions 5-methylcytosine remains unmodified. The original DNA is thus converted in such a way that the 5-methylcytosine, which was originally indistinguishable from cytosine in its hybridization behavior, can now be detected as the only cytosine remaining by conventional known molecular biological techniques, for example by amplification and hybridization. All of these techniques are now fully utilized based on different base pairing properties. Thus, typically, the present application provides for the use of bisulfite technology in combination with one or more methylation assays for determining the methylation state of CpG dinucleotide sequences within a target sequence of a gene of interest. Furthermore, the method of the application is suitable for analyzing heterogeneous biological samples, such as low concentrations of tumor cells in blood or stool. Thus, when analyzing the methylation status of CpG dinucleotide sequences in such samples, one skilled in the art can use quantitative assays to determine the methylation level (e.g., percentage, fraction, ratio, proportion or degree) of a particular CpG dinucleotide sequence, rather than the methylation status. Accordingly, the term methylation status or methylation status shall also be taken to mean a value reflecting the methylation status of a CpG dinucleotide sequence.

In certain embodiments, the methods of the present application specifically comprise: 1) Extracting genome DNA of a biological sample to be detected; 2) Treating the DNA sample obtained in step 1) with a reagent to convert the 5-unmethylated cytosine base into uracil or another base, i.e., to convert the 5-unmethylated cytosine base of the target sequence of the target gene into uracil or another base, the converted base being different from the 5-unmethylated cytosine base in hybridization performance and being detectable; 3) Contacting the DNA sample treated in step 2) with a DNA polymerase and primers for the target sequence of the target gene such that the treated target sequence of the target gene is amplified to produce amplified products or not; the treated target sequence of the target gene produces amplified products if DNA polymerization occurs; the treated target gene sequence is not amplified if DNA polymerization does not occur; 4) Detecting the amplified product with a probe; 5) And determining the methylation status of at least one CpG dinucleotide of the target sequence of the target gene of interest based on the presence or absence of the amplification product.

Typically, the contacting or amplifying comprises using at least one of the following methods: using a thermostable DNA polymerase as the amplification enzyme; using a polymerase lacking 5'-3' exonuclease activity; PCR was used; producing an amplification product nucleic acid molecule with a detectable label. Preferably, the methylation status is determined by means of PCR, such as "fluorescence-based real-time PCR technique", methylation sensitive single nucleotide primer extension reaction (Ms-SNuPE), methylation Specific PCR (MSP), and methylation CpG island amplification (MCA), etc., is used to determine the methylation status of at least one CpG dinucleotide of the target sequence of the gene of interest. Among these, the "fluorescence-based real-time PCR" assay is a high throughput quantitative methylation assay that uses fluorescence-based real-time PCR (TaqMan) techniques, requiring no further manipulation after the PCR step. Briefly, the "fluorescence-based real-time PCR" method starts with a mixed sample of genomic DNA that is converted into a mixed pool of methylation-dependent sequence differences in a sodium bisulfite reaction according to standard procedures. Fluorescence-based PCR was then performed in an "offset" (biased) reaction (using PCR primers overlapping known CpG dinucleotides). Sequence differences can be produced at the amplification level and at the fluorescence detection amplification level. The "fluorescence-based real-time PCR" assay can be used as a quantitative test for methylation status in genomic DNA samples, where sequence discrimination occurs at the level of probe hybridization. In this quantitative format, the PCR reaction provides methylation specific amplification in the presence of fluorescent probes that overlap specific CpG dinucleotides. An unbiased control for the amount of starting DNA is provided by the following reaction: wherein neither the primer nor the probe covers any CpG dinucleotide. The "fluorescence-based real-time PCR" method can be used with any suitable probe, such as "TaqMan", "Lightcycler", etc. The TaqMan probe is double labeled with a fluorescent reporter (RLOC 648987 rter) and a Quencher (Quencher) and is designed to be specific for a relatively high GC content region such that it melts at a temperature about 10℃higher than the forward or reverse primer during the PCR cycle. This allows the TaqMan probe to remain fully hybridized during the PCR annealing/extension step. When Taq polymerase enzymatically synthesizes a new strand in PCR, it eventually encounters an annealed TaqMan probe. Taq polymerase 5 'to 3' endonuclease activity will then displace the TaqMan probe by digesting it, thereby releasing the fluorescent reporter molecule for quantitative detection of its now unquenched signal using a real-time fluorescent detection system. Typical reagents for "fluorescence-based real-time PCR" analysis may include, but are not limited to: PCR primers for target sequences of target genes; a non-specific amplification blocker; taqMan or Lightcycler probes; optimized PCR buffers and deoxynucleotides; taq polymerase, and the like.

Examples

Example 1

By analyzing the genome-wide methylation chip (HumanMethylation k chip from Illumina corporation) data of 413 lung adenocarcinoma tissue samples and 332 lung squamous carcinoma tissue samples with 656 normal human WBC (white blood cell) samples and 23 normal human plasma samples, the inventors found that the methylation rates of OSR1, LOC648987 and LOC643977 genes in lung adenocarcinoma and lung squamous carcinoma tissues were significantly higher than those of normal human plasma and normal human WBC (results are shown in fig. 1-3).

Further, the present inventors found out the sequence fragments of these three target genes with the most obvious methylation differences in lung cancer tissues and normal human WBCs and plasma samples by analyzing the probe sequences of OSR1, LOC648987 and LOC643977 genes on the whole genome methylation chip and the corresponding methylation rate data, thereby determining the target sequences of these three target genes. Target sequences and related sequences of the OSR1 gene, LOC648987 gene and LOC643977 gene are shown in Table 1 above.

Example 2

Designing primers, probes and blocking agents according to target sequences of the OSR1 gene, the LOC648987 gene and the LOC643977 gene, wherein the designed optimal primer probe sequences are shown in tables 2 and 5; the blocker sequences are shown in the foregoing tables 2 and 4:

Table 5: optimal primers and probes for OSR1, LOC648987 and LOC643977 genes

Sequence numbering	Sequence name
		SEQ ID NO：13	OSR1_F
SEQ ID NO：14	OSR1_R
		SEQ ID NO：15	OSR1_P
SEQ ID NO：17	LOC648987_F
		SEQ ID NO：18	LOC648987_R
SEQ ID NO：19	LOC648987_P
		SEQ ID NO：21	LOC643977_F
SEQ ID NO：22	LOC643977_R
		SEQ ID NO：23	LOC643977_P

The cell line DNA of normal human leukocytes is normally in a low/unmethylated state and can be used as a negative control, with an amount of 15.75 ng/reaction in this embodiment; the Hela cell line DNA was in a highly/fully methylated state, in this embodiment a positive control was made of a mixture of Hela cell line DNA and normal human leukocyte cell line DNA, wherein the amounts of Hela cell line DNA and normal human leukocyte cell line DNA added in each PCR reaction were 175 pg/reaction and 15.75ng, respectively.

The DNA sample is firstly subjected to bisulphite conversion, and the converted BisDNA (bisulphite converted DNA) is used as a template to carry out real-time PCR amplification by using the primer probe. The beta Actin (ACTB) gene is used as an internal reference, a beta actin gene amplicon is created by using a primer complementary to the beta actin gene sequence, and the beta actin gene amplicon is detected with a specific probe. Each sample is subjected to at least one real-time PCR, and in some embodiments, two or three real-time PCR assays are performed.

When the primer and the amplification enzyme of the present application are used to amplify the treated DNA fragments, several DNA fragments can be amplified simultaneously in the same reaction vessel. Preferably, the amplification product is 100 to 2,000 base pairs in length. When the genomic DNA of the biological sample to be detected is a mixture of methylated and unmethylated state, especially if the DNA in the methylated state is far less than the DNA in the unmethylated state, such as: in order to improve the amplification specificity of PCR amplification primers, the application adopts a blocker specific to target sequences of target genes in a PCR reaction system. The 5 'end of the blocker nucleotide sequence has an overlap region of greater than or equal to 5 nucleotides with the 3' end nucleotide sequence of the forward (F) or reverse (R) primer; the blocker is complementary to the same strand of the target sequence DNA of the target gene of interest as either the forward (F) or reverse (R) primer; the melting temperature of the blocker is higher than that of the forward (F) or reverse (R) primer by more than (including) 5 ℃; the nucleotide sequence of the blocker comprises at least one CpG dinucleotide sequence and is complementary to the sequence of the unmethylated target gene sequence DNA after bisulfite conversion. Thus, when the genomic DNA of the biological sample to be detected is a mixture of methylated and unmethylated, especially in the case where the DNA in the methylated state is far less than the DNA in the unmethylated state, the DNA in the unmethylated state is subjected to bisulfite conversion and preferentially binds to the blocker, thereby inhibiting the binding of the DNA template to the PCR primer and thus not causing PCR amplification, and the DNA in the methylated state is not bound to the blocker and thus to the primer and thus causing PCR amplification. The fragments obtained by amplification are then detected, directly or indirectly. Preferably the label is in the form of a fluorescent label, radionuclide or attachable molecular fragment.

Table 6: composition of the PCR System used in the present application

"_F" in Table 6 represents a forward primer; "_R" represents the reverse primer; "_P" represents a probe; "_B" represents a blocking agent.

In the present application, real-time PCR detection can be performed using standard procedures according to the prior art on a variety of commercial real-time PCR instrumentation. According to certain embodiments, detection of real-time PCR is performed on a life technologies instrument (7500). The PCR reaction mixture is prepared from 25pg-100ng and 300-600nM primer and blocker, 150-300nM probe, 1-10UTaq polymerase, 50-400. Mu.M of each dNTP, 1-10 mM MgCl ₂ and ddH ₂ O to a final volume of 20. Mu.l to 100. Mu.l, preferably 50. Mu.l. One composition of the PCR system used in the present application is shown in Table 6. The sample was amplified with a pre-cycle at 90 to 99 ℃ for 3-60 minutes followed by a 35-55 cycle anneal at 50 to 72 ℃ for 1 to 30 seconds, an anneal and extension at 50 to 72 ℃ for 5 to 90 seconds, and denaturation at 90 to 99 ℃ for 5 to 90 seconds. The DNA template used may be added with reference gene, positive control or negative control, as required. The preferred PCR amplification procedure used is: 94 ℃ for 20min; (93 ℃,30s;65 ℃,35 s-read fluorescent signal) 45 cycles; 40℃for 10s.

As a result, as shown in FIG. 4, when the positive control sample was used as a template, the OSR1, LOC648987 and LOC643977 genes were amplified efficiently; when the low/unmethylated DNA is used as a template, the target genes except the reference gene ACTB are not amplified.

Example 3

3.1 Genomic DNA was extracted from 16 lung cancer tissue samples (8 lung adenocarcinoma and 8 lung squamous carcinoma) and 24 normal human WBC samples, converted to BisDNA by bisulfite, and methylation of OSR1, LOC648987 and LOC643977 genes was detected according to the PCR reaction system and reaction procedure in example 2 with a template amount of 10 ng/reaction. The extraction and treatment of the DNA may be performed by any standard means known in the art, and in particular, in this example, all sample DNA extraction and bisulphite DNA modification are performed by using the plasma treatment kit of boer honest.

Finally, ct values (cut off values) of real-time PCR of 16 lung cancer tissues and 24 normal human WBC samples on target sequences of the target genes are measured. According to the PCR result, the critical values of Ct values (cut off values) of the three genes were all selected to be ct=37, and as shown in table 7, the sensitivities of detecting lung cancer by OSR1, LOC648987, and LOC643977 genes alone were 93.8%, 62.5%, and 68.8%, respectively; the sensitivity of the combined interpretation of the three genes reaches 93.8 percent. Methylation of target sequences of the target genes has good specificity, the specificity of LOC648987 and LOC643977 is 100%, the specificity of OSR1 is 91.7%, and therefore the specificity of joint interpretation is 91.7%, and the results are shown in Table 8.

Table 7: sensitivity of detecting lung cancer using OSR1, LOC648987 and/or LOC643977 genes

TABLE 8

The specific calculation formula in table 8: specificity = number of negative detected/total number of negative, as in table 8 the specificity of the third column OSR1 is the number of negative detected 22 divided by the total number of normal samples 24, i.e. 22/24 = 91.7%.

3.2 Plasma free DNA was extracted from 15 lung cancer and 20 normal human plasma samples (3.5 mL) as samples, converted to BisDNA by bisulfite, and methylation of OSR1, LOC648987 and LOC643977 genes was detected according to the PCR reaction system and reaction procedure in example 2. The results are shown in Table 9, with sensitivities of 73.3%, 46.7% and 46.7% for lung cancer detection by OSR1, LOC648987 and LOC643977 genes, respectively; the sensitivity of the combined interpretation of the three genes reaches 86.7 percent. Methylation of target sequences of the target genes has good specificity, the specificity of LOC648987 and LOC643977 reach 100%, the specificity of OSR1 is 95%, and therefore the specificity of joint interpretation is 95%, and the results are shown in Table 10.

Table 9: sensitivity of detecting lung cancer using OSR1, LOC648987 and/or LOC643977 genes

Table 10

The above experimental results show that the methylated DNA of the target sequence of the target gene is an indicator of lung cancer. The detection of the target sequence methylated DNA of the target gene can realize the noninvasive detection of lung cancer in vitro and can improve the detection rate of lung cancer.

In summary, the composition, the nucleic acid sequence, the kit and the application thereof and the detection method realize in vitro detection of lung cancer by using the methylation biomarker of the target gene target sequence through detecting the methylation nucleic acid sequence of the target gene target sequence and fragments thereof, thereby effectively improving the sensitivity of in vitro detection of lung cancer and maintaining high specificity of detection. By using the method for analyzing the free DNA of the plasma sample by the real-time PCR, the methylation state of the target sequence of the target gene can be conveniently detected, and whether the sample is positive can be rapidly and conveniently judged according to the Ct value of the real-time PCR, so that the noninvasive and convenient lung cancer in-vitro detection method is provided.

Although various aspects and embodiments of the present application are disclosed herein, other aspects and embodiments will be apparent to those skilled in the art. The various aspects and embodiments disclosed herein are presented for purposes of illustration only and not limitation.

Claims

Nucleic acid for detecting methylation status of a target gene,

2. The composition of claim 1, wherein the OSR1 gene has a target sequence as set forth in SEQ ID NO:1 or SEQ ID NO:2 or SEQ ID NO:3 or SEQ ID NO: 4.

3. The composition of claim 1, wherein the LOC648987 gene has a target sequence as set forth in SEQ ID NO:5 or SEQ ID NO:6 or SEQ ID NO:7 or SEQ ID NO: shown at 8.

4. The composition of claim 1, wherein the LOC643977 gene has a target sequence as set forth in SEQ ID NO:9 or SEQ ID NO:10 or SEQ ID NO:11 or SEQ ID NO: shown at 12.

5. The composition of any one of claims 1 to 4, wherein the nucleic acid for detecting methylation status of a target gene comprises:

The fragment comprises at least one CpG dinucleotide sequence.

6. The composition of any one of claims 1-5, wherein the nucleic acid for detecting methylation status of a target gene comprises:

The fragment comprises at least one CpG dinucleotide sequence.

7. The composition of any one of claims 1-6, further comprising:

8. The composition of any one of claims 1-7, wherein the nucleic acid for detecting methylation status of a gene of interest further comprises:

9. The composition of claim 8, wherein,

The at least 15 nucleotide fragment, which is SEQ ID NO:15, or SEQ ID NO:19, or SEQ ID NO: 23.

10. Use of a composition according to any one of claims 1 to 9 for the preparation of a kit for in vitro detection of lung cancer.