Patent Application
20190256921
This disclosure relates generally to tumour detection. More particularly, this disclosure relates to tumour-specific DNA methylation detection.
Cancer screening and monitoring has helped to improve outcomes over the past few decades simply because early detection leads to a better outcome as the cancer can be eliminated before it has spread. In the case of breast cancer, for instance, physical breast exams, mammography, ultrasound and MRI (in high risk patients) have all played a role in improving early diagnosis. The cost/benefit of these modalities for general screening, particularly in relatively younger women, has been controversial.
A primary issue for any screening tool is the compromise between false positive and false negative results (or specificity and sensitivity) which lead to unnecessary investigations in the former case, and ineffectiveness in the latter case. An ideal test is one that has a high Positive Predictive Value (PPV), minimizing unnecessary investigations but detecting the vast majority of cancers. Another key factor is what is called “detection sensitivity”, to distinguish it from test sensitivity, and that is the lower limits of detection in terms of the size of the tumour. Screening mammography in breast cancer, for instance, is considered to have a sensitivity from 80 to 90% with a specificity of 90%. However the mean size of tumours detected by mammography remains in the range of 15 to 19 mm. It has been suggested that only 3-13% of women derive an improved treatment outcome from this screening suggesting that the detection of smaller tumours would provide increased benefit. For women at high risk of developing breast cancer the use of MRI has offered some benefit with sensitivities in the range of 75 to 97% and specificities in the area of 90 to 96% and in combination with mammography offering 93-94% sensitivity and 77 to 96% specificities. However, MRI is acknowledged to have a poor PPV, in the area of 10-20%, leading to a large number of false positives and as a consequence unnecessary invasive investigations. All of these screens have likely reached their limit of detection sensitivity (or size of the tumour) and in the case of mammography still involve exposure to radiation, which may be of particular concern in women with familial mutations which render them more sensitive to radiation damage. There are no effective blood based screens for breast cancer based on circulating analytes.
While the above discussion focusses on breast cancer as an example, many of the same challenges exist for other types of cancers as well.
The detection of circulating tumour DNA is increasingly acknowledged as a viable “liquid biopsy” allowing for the detection and informative investigation of tumours in a non-invasive manner. Typically using the identification of tumour specific mutations these techniques have been applied to colon, breast and prostate cancers. Due to the high background of normal DNA present in the circulation these techniques can be limited in sensitivity. As well, the variable nature of tumour mutations in terms of occurrence and location (such as p53 and KRAS mutations) has generally limited these approaches to detecting tumour DNA at 1% of the total DNA in serum. Advanced techniques such as BEAMing have increased sensitivity, but are still limited overall. Even with these limitations the detection of circulating tumour DNA has recently been shown to be useful for detecting metastasis in breast cancer patients.
The detection of tumour specific methylation in the blood has been proposed to offer distinct advantages over the detection of mutations1-5. A number of single or multiple methylation biomarkers have been assessed in cancers including lung6-10, colon11,12 and breast13-16. These have suffered from low sensitivities as they have tended to be insufficiently prevalent in the tumours. Several multi-gene assays have been developed with improved performance. A more advanced multi-gene system using a combination of 10 different genes has been reported and uses a multiplexed PCR based assay17. It offers combined sensitivity and specificity of 91% and 96% respectively, due to the better coverage offered and it has been validated in a small cohort of stage IV patients. However, it has a very high background in normal blood which will limit its detection sensitivity. Methylated markers have been used to monitor the response to neoadjuvant therapy18,19, and recently a methylation gene signature associated with metastatic tumours has been identified20.
There remains a need for more sensitive and specific screening tools, as well as for straightforward tests that allow for the assessment of tumour burden, chemotherapy response, detection of residual disease, relapse and primary screening in high risk populations.
It is an object of this disclosure to obviate or mitigate at least one disadvantage of previous approaches.
In a first aspect, this disclosure provides a method for detecting a tumour, comprising: extracting DNA from a cell-free sample obtained from a subject, bisulphite converting at least a portion of the DNA, amplifying regions methylated in cancer from the bisulphite converted DNA, generating sequencing reads from the amplified regions, and detecting tumour signals comprising at least two adjacent methylated sites within a single sequencing read, wherein the detection of at least one of the tumour signals is indicative of a tumour.
In another aspect, there is provided a use of the method for determining response to treatment.
In another aspect, there is provided a use of the method for monitoring tumour load.
In another aspect, there is provided a use of the method for detecting residual tumour post-surgery.
In another aspect, there is provided a use of the method for detecting relapse.
In another aspect, there is provided a use of the method as a secondary screen.
In another aspect, there is provided a use of the method as a primary screen.
In another aspect, there is provided a use of the method for monitoring cancer development.
In another aspect, there is provided a use of the method for monitoring cancer risk.
In another aspect, there is provided a kit for detecting a tumour comprising reagents for carrying out the method, and instructions for detecting the tumour signals.
Other aspects and features of this disclosure will become apparent to those ordinarily skilled in the art upon review of the following description of specific embodiments in conjunction with the accompanying figures.
Embodiments of this disclosure will now be described, by way of example only, with reference to the attached Figures.
Generally, this disclosure provides a method for detecting a tumour that can be applied to cell-free samples, e.g., to detect cell-free circulating tumour DNA. The method utilizes detection of adjacent methylation signals within a single sequencing read as the basic “positive” tumour signal.
In one aspect, there is provided a method for detecting a tumour, comprising: extracting DNA from a cell-free sample obtained from a subject, bisulphite converting at least a portion of the DNA, amplifying regions methylated in cancer from the bisulphite converted DNA, generating sequencing reads from the amplified regions, and detecting tumour signals comprising at least two adjacent methylated sites within a single sequencing read, wherein the detection of at least one of the tumour signals is indicative of a tumour.
By “cell-free DNA (cfDNA)” is meant DNA in a biological sample that is not contained in a cell. cfDNA may circulate freely in in a bodily fluid, such as in the bloodstream.
“Cell-free sample”, as used herein, is meant a biological sample that is substantially devoid of intact cells. This may be a derived from a biological sample that is itself substantially devoid of cells, or may be derived from a sample from which cells have been removed. Example cell-free samples include those derived from blood, such as serum or plasma; urine; or samples derived from other sources, such as semen, sputum, feces, ductal exudate, lymph, or recovered lavage.
“Circulating tumour DNA”, as used herein, accordingly refers to cfDNA originating from a tumour.
By “region methylated in cancer” is meant a segment of the genome containing methylation sites (CpG dinucleotides), methylation of which is associated with a malignant cellular state. Methylation of a region may be associated with more than one different type of cancer, or with one type of cancer specifically. Within this, methylation of a region may be associated with more than one subtype, or with one subtype specifically.
The terms cancer “type” and “subtype” are used relatively herein, such that one “type” of cancer, such as breast cancer, may be “subtypes” based on e.g., stage, morphology, histology, gene expression, receptor profile, mutation profile, aggressiveness, prognosis, malignant characteristics, etc. Likewise, “type” and “subtype” may be applied at a finer level, e.g., to differentiate one histological “type” into “subtypes”, e.g., defined according to mutation profile or gene expression.
By “adjacent methylated sites” is meant two methylated sites that are, sequentially, next to each other. It will be understood that this term does not necessarily require the sites to actually be directly beside each other in the physical DNA structure. Rather, in a sequence of DNA including spaced apart methylation sites A, B, and C in the context A-(n)n-B-(n)n-C, wherein (n)n refers to the number of base pairs (bp) (e.g., up to 300 bp), sites A and B would be recognized as “adjacent” as would sites B and C. Sites A and C, however, would not be considered to be adjacent methylated sites.
In one embodiment, the regions methylated in cancer comprise CpG islands.
“CpG islands” are regions of the genome having a high frequency of CpG sites. CpG islands are usually 300-3000bp in length and are found at or near promotors of approximately 40% of mammalian genes. They show a tendency to occur upstream of so-called “housekeeping genes”. A concrete definition is elusive, but CpG islands may be said to have an absolute GC content of at least 50%, and a CpG dinucleotide content of at least 60% of what would be statistically expected. Their occurrence at or upstream of the 5′ end of genes may reflect a role in the regulation of transcription, and methylation of CpG sites within the promoters of genes may lead to silencing. Silencing of tumour suppressors by methylation is, in turn, a hallmark of a number of human cancers.
In one embodiment, the regions methylated in cancer comprise CpG shores.
“CpG shores” are regions extending short distances from CpG islands in which methylation may also occur. CpG shores may be found in the region 0 to 2 kb upstream and downstream of a CpG island.
In one embodiment, the regions methylated in cancer comprise CpG shelves.
“CpG shelves” are regions extending short distances from CpG shores in which methylation may also occur. CpG shelves may generally be found in the region between 2 kb and 4 kb upstream and downstream of a CpG island (i.e., extending a further 2 kb out from a CpG shore).
In one embodiment, the regions methylated in cancer comprise CpG islands and CpG shores.
In one embodiment, the regions methylated in cancer comprise CpG islands, CpG shores, and CpG shelves.
In one embodiment, the regions methylated in cancer comprise CpG islands and sequences 0 to 4 kb upstream and downstream. The regions methylated in cancer may also comprise CpG islands and sequences 0 to 3 kb upstream and downstream, 0 to 2 kb upstream and downstream, 0 to 1 kb upstream and downstream, 0 to 500 bp upstream and downstream, 0 to 400 bp upstream and downstream, 0 to 300 bp upstream and downstream, 0 to 200 bp upstream and downstream, or 0 to 100 bp upstream and downstream.
In one embodiment, the step of amplifying is carried out with primers designed to anneal to bisulphite converted target sequences having at least one methylated site therein. Bisulphite conversion results in unmethylated cytosines being converted to uracil, while 5-methylcytosine is unaffected. “Bisulphite converted target sequences” are thus understood to be sequences in which cytosines known to be methylation sites are fixed as “C” (cytosine), while cytosines known to be unmethylated are fixed as “U” (uracil; which can be treated as “T” (thymine) for primer design purposes). Primers designed to target such sequences may exhibit a degree of bias towards converted methylated sequences. However, in one embodiment, the primers are designed without preference as to location of the at least one methylated site within target sequences. Often, to achieve optimal discrimination, it may be desirable to place a discriminatory base at the ultimate or penultimate 3′ position of an oligonucleotide PCR primer. In this embodiment, however, no preference is given to the location of the discriminatory sites of methylation, such that overall primer design is optimized based on sequence (not discrimination). This results in a degree of bias for some primer sets, but usually not complete specificity towards methylated sequences (some individual primer pairs, however, may be specific if a discriminatory site is fortuitously placed). As will be described herein, this permits some embodiments of the method to be quantitative or semi-quantitative.
In one embodiment, the PCR primers are designed to be methylation specific. This may allow for greater sensitivity in some applications. For instance, primers may be designed to include a discriminatory nucleotide (specific to a methylated sequence following bisulphite conversion) positioned to achieve optimal discrimination, e.g. in PCR applications. The discriminatory may be positioned at the 3′ ultimate or penultimate position.
In one embodiment, the primers are designed to amplify DNA fragments 75 to 150 bp in length. This is the general size range known for circulating DNA, and optimizing primer design to take into account target size may increase the sensitivity of the method according to this embodiment. The primers may be designed to amplify regions that are 50 to 200, 75 to 150, or 100 or 125 bp in length.
In some embodiments, concordant results provide additional confidence in a positive tumour signal. By “concordant” or “concordance”, as used herein, is meant methylation status that is consistent by location and/or by repeated observation. As has already been stated, the basic “tumour signal” defined herein comprises at least two adjacent methylated sites within a single sequencing read. However, additional layers of concordance can be used to increase confidence for tumour detection, in some embodiments, and not all of these need be derived from the same sequencing read. Layers of concordance that may provide confidence in tumor detection may include, for example:
(a) detection of methylation of at least two adjacent methylation sites;
(b) detection of methylation of more than two adjacent methylation sites;
(c) detection of methylation at adjacent sites within the same section of a target region amplified by one primer pair;
(d) detection of methylation at non-adjacent sites within the same section of a region amplified by one primer pair;
(e) detection of methylation at adjacent sites within the same target region;
(f) detection of methylation at non-adjacent sites within the same target region;
(g) any one of (a) to (f) in the same sequencing read;
(h) any one of (a) to (f) in at least two sequencing reads;
(i) any one of (a) to (f) in a plurality of sequencing reads;
(j) detection over methylation at sets of adjacent sites that overlap;
(k) repeated observation of any one of (a) to (j); or
(l) any combination or subset of the above.
In one embodiment, each of the regions is amplified in sections using multiple primer pairs. In one embodiment, these sections are non-overlapping. The sections may be immediately adjacent or spaced apart (e.g. spaced apart up to 10, 20, 30, 40, or 50 bp). Since target regions (including CpG islands, CpG shores, and/or CpG shelves) are usually longer than 75 to 150 bp, this embodiment permits the methylation status of sites across more (or all) of a given target region to be assessed.
A person of ordinary skill in the art would be well aware of how to design primers for target regions using available tools such as Primer3, Primer3Plus, Primer-BLAST, etc. As discussed, bisulphite conversion results in cytosine converting to uracil and 5′-methyl-cytosine converting to thymine. Thus, primer positioning or targeting may make use of bisulphite converted methylate sequences, depending on the degree of methylation specificity required.
Target regions for amplification are designed to have at least two CpG dinucleotide methylation sites. In some embodiments, however, it may be advantageous to amplify regions having more than one CpG methylation site. For instance, the amplified regions may have 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, or 15 CpG methylation sites. In one embodiment, the primers are designed to amplify DNA fragments comprising 3 to 12 CpG methylation sites. Overall this permits a larger number of adjacent methylation sites to be queried within a single sequencing read, and provides additional certainty (exclusion of false positives) because multiple concordant methylations can be detected within a single sequencing read. In one embodiment, the tumour signals comprise more than two adjacent methylation sites within the single sequencing read. Detecting more than two adjacent methylation sites provides additional concordance, and additional confidence that the tumour signal is not a false positive in this embodiment. For example, a tumour signal may be designated as 3, 4, 5, 6, 7, 8, 9, 10 or more adjacent detected methylation sites within a single sequencing read. In one embodiment, the detection of more than one of the tumour signals is indicative of a tumour. Detection of multiple tumour signals, in this embodiment, can increase confidence in tumour detection. Such signals can be at the same or at different sites. In one embodiment, the detection of more than one of the tumour signals at the same region is indicative of a tumour. Detection of multiple tumour signals indicative of methylation at the same site in the genome, in this embodiment, can increase confidence in tumour detection. So too can detection of methylation at adjacent sites in the genome, even if the signals are derived from different sequencing reads. This reflects another type of concordance. In one embodiment, the detection of adjacent or overlapping tumour signals across at least two different sequencing reads is indicative of a tumour. In one embodiment, the adjacent or overlapping tumour signals are within the same CpG island. In one embodiment, the detection of 5 to 25 adjacent methylated sites is indicative of a tumour.
Methylated regions can be selected according to the purpose of the intended assay. In one embodiment, the regions comprise at least one region listed Table 1 and/or Table 2. In one embodiment, the regions comprise all regions listed in Table 1 and/or Table 2.
Likewise, primer pairs can be designed based on the intended target regions.
In one embodiment, the step of amplification is carried out with more than 100 primer pairs. The step of amplification may be carried out with 10, 20, 30, 40, 50, 60, 70, 80, 90, 100, 110, 120, 130, 140, 150, or more primer pairs. In one embodiment, the step of amplification is a multiplex amplification. Multiplex amplification permits large amount of methylation information to be gathered from many target regions in the genome in parallel, even from cfDNA samples in which DNA is generally not plentiful. The multiplexing may be scaled up to a platform such as ION AmpliSeq™, in which, e.g. up to 24,000 amplicons may be queried simultaneously. In one embodiment, the step of amplification is nested amplification. A nested amplification may improve sensitivity and specificity.
The nested reaction may be part of a next generation sequencing approach. Barcode and/or sequencing primers may be added in the second (nested) amplification. Alternatively, these may added in the first amplification.
In one embodiment, the method further comprises quantifying the tumour signals, wherein a number in excess of a threshold is indicative of a tumour. In one embodiment, the steps of quantifying and comparing are carried out independently for each of the sites methylated in cancer. Accordingly, a count of positive tumour signals may be established for each site. In one embodiment, the method further comprises determining a proportion of the sequencing reads containing tumour signals, wherein the proportion in excess of a threshold is indicative of a tumour. In one embodiment, the step of determining is carried out independently for each of the sites methylated in cancer.
By “threshold”, as used herein, is meant a value that is selected to discriminate between a disease (e.g., malignant) state, and a non-disease (e.g., healthy) state. Thresholds can be set according to the disease in question, and may be based on earlier analysis, e.g., of a training set. Thresholds may also be set for a site according to the predictive value of methylation at a particular site. Thresholds may be different for each methylation site, and data from multiple sites can be combined in the end analysis.
Various design parameters may be used to select the regions subject to amplification in some embodiments. In one embodiment, the regions are not methylated in healthy tissue. Healthy tissue would be understood to be non-malignant. Healthy tissue is often selected based on the origin of the corresponding tumour.
Regions may be selected based on desired aims or required specificity, in some embodiments. For instance, it may be desirable to screen for more than one cancer type. Thus, in one embodiment, the regions are collectively methylated in more than one tumour type. It may be desirable to include regions methylated generally in a group of cancers, and regions methylated in specific cancers in order to provide different tiers of information. Thus, in one embodiment, the regions comprise regions that are specifically methylated in specific tumours, and regions that are methylated in more than one tumour type. Likewise, it may be desirably to include a second tier of regions that can differentiate between tumour types. In one embodiment, the regions specifically methylated in specific tumours comprise a plurality of groups, each specific to one tumour type. However, it may be desirable in some contexts to have a test that is focused on one type of cancer. Thus, in one embodiment, the regions are methylated specifically in one tumour type. In one embodiment, the regions are selected from those listed in Table 3 and the tumour is one carrying a BRCA1 mutation.
More specifically, in some embodiments regions may be selected that are methylated in particular subtypes of a cancer exhibiting particular histology, karyotype, gene expression (or profile thereof), gene mutation (or profile thereof), staging, etc. Accordingly, the regions to be amplified may comprise one or more groups of regions, each being established to be methylated in one particular cancer subtype. In one embodiment the regions to be amplified may be methylated in a cancer subtype bearing particular mutations. With breast cancer in mind, one example subtype defined by mutation is cancer bearing BRCA1 mutations. Another subtype is cancer bearing BRCA2 mutations. Other breast cancer subtypes for which methylated regions may be determined include Basal, Luminal A, Luminal B, HER2 and Normal-like tumours. For uveal melanoma, for example, subtypes may include tumours that have retained or lost chromosome 3 (monosomy 3).
Within the context of such a test of some embodiments, information about not only the presence, but also the pattern and distribution of tumour signals both within specific regions and between different regions may help to detect or validate the presence of a form of cancer. In one embodiment, the method further comprises determining a distribution of tumour signals across the regions, and comparing the distribution to at least one pattern associated with a cancer, wherein similarity between the distribution and the pattern is indicative of the cancer.
“Distribution”, as used herein in this context, is meant to indicate the number and location of tumour signals across the regions. Statistical analysis may be used to compare the observed distribution with, e.g., pre-established patterns (data) associated with a form of cancer. In other embodiments, the distribution may be compared to multiple patterns. In one embodiment, the method further comprises determining a distribution of tumour signals across the regions, and comparing the distribution to a plurality of patterns, each one associated with a cancer type, wherein similarity between the distribution and one of the plurality of patterns is indicative of the associated cancer type.
In one embodiment, the step of generating sequencing reads is carried out by next generation sequencing. This permits a very high depth of reads to be achieved for a given region. These are high-throughput methods that include, for example, Ilumina (Solexa) sequencing, Roche 454 sequencing, Ion Torrent sequencing, and SOLiD sequencing. The depth of sequencing reads may be adjusted depending on desired sensitivity.
In one embodiment, the step of generating sequencing reads is carried out simultaneously for samples obtained from multiple patients, wherein the amplified CpG islands from is barcoded for each patient. This permits parallel analysis of a plurality of patients in one sequencing run.
A number of design parameters may be considered in the selection of regions methylated in cancer, according to some embodiments. Data for this selection process may be from a variety of sources such as, e.g., The Cancer Genome Atlas (TCGA) (http://cancergenome.nih.gov/), derived by the use of, e.g., Illumina Infinium HumanMethylation450 BeadChip (http://www.illumina.com/products/methylation450beadchipkits.html) for a wide range of cancers, or from other sources based on, e.g., bisulphite whole genome sequencing, or other methodologies. For instance, “methylation value” (understood herein as derived from TCGA level 3 methylation data, which is in turn derived from the beta-value, which ranges from −0.5 to 0.5) may be used to select regions. In one embodiment, the step of amplification is carried out with primer sets designed to amplify at least one methylation site having a methylation value of below -0.3 in normal issue. This can be established in a plurality of normal tissue samples, for example 4. The methylation value may be at or below −0.1, −0.2, −0.3, −0.4, or −0.5. In one embodiment, the primer sets are designed to amplify at least one methylation site having a difference between the average methylation value in the cancer and the normal tissue of greater than 0.3. The difference may be greater than 0.1, 0.2, 0.3, 0.4, or 0.5. Proximity of other methylation sites that meet this requirement may also play a role in selecting regions, in some embodiments. In one embodiment, the primer sets include primer pairs amplifying at least one methylation site having at least one methylation site within 200 bp that also has a methylation value of below −0.3 in normal issue, and a difference between the average methylation value in the cancer and the normal tissue of greater than 0.3. In another embodiment the adjacent site having these features may be 300 bp. The adjacent site may be within 100, 200, 300, 400, or 500 bp.
In some embodiments, target regions may be selected for amplification based on the number of tumours in the validation set having methylation at that site. For example, a region may be selected if it is methylated in at least 50%, 55%, 60%, 65%, 70%, 75%, 80, 85%, 90, or 95% of tumours tested. For example, regions may be selected if they are methylated in at least 75% of tumours tested, including within specific subtypes. For some validations, it will be appreciated that tumour-derived cell lines may be used for the testing.
In another embodiment, the method further comprises oxidative bisulphite conversion. In addition to the analysis of methylation of CpG residues, additional information that may be of clinical significance may be derived from the analysis of hydroxymethylation. Bisulphite sequencing results in the conversion of unmethylated cytosine residues into uracil/thymidine residues, while both methylated and hydroxymethylated cytosines remain unconverted. However, oxidative bisulphite treatment allows for the conversion of hydroxymethylated cytosines to uracil/thymidine allowing for the differential analysis of both types of modifications. By comparison of bisulphite to oxidative bisulphite treatments the presence of hydroxymethylation can be deduced. This information may be of significance as its presence or absence may be correlated with clinical features of the tumor which may be clinically useful either as a predictive or prognostic factor. Accordingly, in some embodiments, information about hydroxymethylation could additionally be used in the above-described embodiments.
In one aspect, the presence of specific patterns of methylation is linked to underlying characteristics of particular tumours. In these cases, the methylation patterns detected by the method are indicative of clinically relevant aspects of the tumours such as aggressiveness, likelihood of recurrence, and response to various therapies. Detection of these patterns in the blood may thus provide both prognostic and predictive information related to a patient's tumor.
In another aspect, the forgoing method may be applied to clinical applications involving the detection or monitoring of cancer.
In one embodiment, the forgoing method may be applied to determine and/or predict response to treatment.
In one embodiment, the forgoing method may be applied to monitor and/or predict tumour load.
In one embodiment, the forgoing method may be applied to detect and /or predict residual tumour post-surgery.
In one embodiment, the forgoing method may be applied to detect and/or predict relapse.
In one aspect, the forgoing method may be applied as a secondary screen.
In one aspect, the forgoing method may be applied as a primary screen.
In one aspect, the forgoing method may be applied to monitor cancer development.
In one aspect, the forgoing method may be applied to monitor and/or predict cancer risk.
In another aspect, there is provided a kit for detecting a tumour comprising reagents for carrying out the aforementioned method, and instructions for detecting the tumour signals. Reagents may include, for example, primer sets, PCR reaction components, and/or sequencing reagents.
In one embodiment of the forgoing methods, the regions comprise C2CD4A, COL19A1, DCDC2, DHRS3, GALNT3, HES5, KILLIN, MUC21, NR2E1/OSTM1, PAMR1, SCRN1, and SEZ6, and the tumour is uveal melanoma. In one embodiment, the probes comprise C2C5F, COL2F, DCD5F, DGR2F, GAL1F, GAL3F, HES1F, HES3F, HES4F, KIL5F, KIL6F, MUC2F, OST3F, OST4F, PAM4F, SCR2F, SEZ3F, and SEZ5F.
In one embodiment, the regions comprise ADCY4, ALDH1L1, ALOX5, AMOTL2, ANXA2, CHST11, EFS, EPSTI1, EYA4, HAAO, HAPLN3, HCG4P6, HES5, HIF3A, HLA-F, HLA-J, HOXA7, HSF4, KLK4, LOC376693, LRRC4, NBR1, PAH, PON3, PPM1H, PTRF, RARA, RARB, RHCG, RND2,TMP4, TXNRD1, and ZSCAN12, and the tumour is prostate cancer. In one embodiment, the probes comprise ADCY4-F, ALDH1L1-F, ALOX5-F, AMOTL2-F, ANXA2-F, CHST11-F, EFS-F, EPSTI1-F, EYA4-F, HAAO-F, HAPLN3-F, HCG4P6-F, HES5-F, HIF3A-F, HLA-F-F, HLA-J-1-F, HLA-J-2-F, HOXA7-F, HSF4-F, KLK4-F, LOC376693-F, LRRC4-F, NBR1-F, PAH-F, PON3-F, PPM1H-F, PTRF-F, RARA-F, RARB-F, RHCG-F, RND2-F,TMP4-F, TXNRD1-F, and ZSCAN12-F. In one embodiment, the probes additionally include C1Dtrim, C1Etrim, CHSAtrim, DMBCtrim, FOXAtrim, FOXEtrim, SFRAtrim, SFRCtrim, SFREtrim, TTBAtrim, VWCJtrim, and VWCKtrim.
In one embodiment, the regions comprise ASAP1, BC030768, C18orf62, C6orf141, CADPS2, CORO1C, CYP27A1, CYTH4, DMRTA2, EMX1, HFE, HIST1H3G/1H2BI, HMGCLL1, KCNK4, KJ904227, KRT78, LINC240, Me3, MIR1292, NBPF1, NHLH2, NRN1, PPM1H, PPP2R5C, PRSS3, SFRP2, SLCO4C1, SOX2OT, TUBB2B, USP44, Intergenic (Chr1), Intergenic (Chr2), Intergenic (Chr3), Intergenic (Chr4), Intergenic (Chr8), and Intergenic (Chr10), and the tumour is aggressive prostate cancer. In one embodiment, the aggressive prostate cancer has a Gleason Score greater than 6. In one embodiment, the aggressive prostate cancer has a Gleason Score of 9 or greater. In one embodiment, the probes comprise ASAP1/p, BC030768/p, C18orf62/p, C6orf141/p-1, C6orf141/p-2, CADPS2/p, CORO1C/p-1, CORO1C/p-2, CYP27A1/p, CYTH4/p, DMRTA2/p, EMX1/p, HFE/p-1, HFE/p-2, HIST1H3G/1H2BI/p, HMGCLL1/p, KCNK4/p, KJ904227/p, KRT78/p, LINC240/p-1, LINC240/p-2, Me3/p-1, Me3/p-2, MIR129, NBPF1/p, NHLH2/p, NRN1/p, PPM1H/p-1, PPM1H/p-2, PPP2R5C/p, PRSS3/p, SFRP2/p-1, SFRP2/p-2, SLCO4C1/p, SOX2OT/p, TUBB2B/p, USP44/p, Chr1/p-1, Chr2/p-1, Chr3/p-1, Chr4/p-1, Chr8/p-1, and Chr10/p-1.
In one embodiment, the regions comprise the regions depicted in
In one embodiment, the regions comprise ALX1, ACVRL1, BRCA1,C1orf114, CA9, CARD11, CCL28, CD38, CDKL2, CHST11, CRYM, DMBX1, DPP10, DRD4, ERNA4, EPSTI1, EVX1, FABP5, FOXA3, GALR3, GIPC2, HINF1B, HOXA9, HOXB13, Intergenic5, Intergenic 8, IRF8, ITPRIPL1, LEF1,LOC641518, MAST1, BARHL2, BOLL, C5orf39, DDAH2, DMRTA2, GABRA4, ID4, IRF4, NTSE, SIM1, TBX15, NFIC, NPHS2, NR5A2, OTX2, PAX6, GNG4, SCAND3, TAL1, PDX1, PHOX2B, POU4F1,PFIA3, PRDM13, PRKCB, PRSS27, PTGDR, PTPRN2, SALL3, SLC7A4, SOX2OT, SPAG6, TCTEX1D1, TMEM132C, TMEM90B, TNFRSF10D, TOP2P1, TSPAN33, TTBK1, UDB, and VWC2., and the tumour is triple negative breast cancer (TNBC). In one embodiment, the probes comprise ALX1, AVCRL1, BRCA1-A, C1Dtrim, C1Etrim, CA9-A, CARD11-B, CCL28-A, CD38, CDKL2-A, CHSAtrim, CRYM-A, DMBCtrim, DMRTA2exp-A, DPP10-A, DPP10-B, DPP10-C, DRD4-A, EFNA4-B, EPSTI1, EVX1, FABP5, FOXAtrim, FOXEtrim, GALR3-A, GIPC2-A, HINF C trim, HOXAAtrim, HOXACtrim, HOXB13-A, Int5, Int8, IRF8-A, ITRIPL1, LEF1-A, MAST1 A trim, mbBARHL2 Trim, mbBOLL Trim, mbC5orf Trim, mbDDAH Trim, mbDMRTA Trim, mbGABRA A Trim, mbGABRA B Trim, mbGNG Trim, mbID4 Trim, mbIRF Trim, mbNT5E Trim, mbSIM A Trim, mbTBX15 Trim, NFIC-B, NFIC-A, NPSH2-B, NR5A2-B, OTX2-A, PAX6-A, pbDMRTA Trim, pbGNG Trim, pbSCAND Trim, pbTAL Trim, PDX1exp-B, PHOX2B-A, POU4F1 A trim, PPFIA3-A, PRDM13, PRKCB-A, PRKCB-C, PRSS27-A, PTGDR, PTPRN2-A, PTPRN2-B, SALL3-A, SALL3-B, SLC7A4-A, SOX2OT-B, SPAG6 A trim, TCTEX1D1-A, TMEM-A, TMEM-B, TMEM90B-A, TNFRSF10D, TOP2P1-B, TSPAN33-A, TTBAtrim, UBD-A, VWCJtrim, and VWCKtrim.
In one embodiment, each region is amplified with primer pairs listed for the respective region in Table 15.
In one embodiment, the method further comprises administering a treatment for the tumour detected.
In one aspect, there is provided a method for identifying a methylation signature indicative of a biological characteristic, the method comprising: obtaining data for a population comprising a plurality of genomic methylation data sets, each of said genomic methylation data sets associated with biological information for a corresponding sample, segregating the methylation data sets into a first group corresponding to one tissue or cell type possessing the biological characteristic and a second group corresponding to a plurality of tissue or cell types not possessing the biological characteristic, matching methylation data from the first group to methylation data from the second group on a site-by-site basis across the genome, identifying a set of CpG sites that meet a predetermined threshold for establishing differential methylation between the first and second groups, identifying, using the set of CpG sites, target genomic regions comprising at least two differentially methylated CpGs with 300 bp that meet said predetermined criteria, extending the target genomic regions to encompass at least one adjacent differentially methylated CpG site that does not meet the predetermined criteria, wherein the extended target genomic regions provide the methylation signature indicative of the biological trait.
In one embodiment, the method further comprises validating the extended target genomic regions by testing for differential methylation within the extended target genomic regions using DNA from at least one independent sample possessing the biological trait and DNA from at least one independent sample not possessing the biological sample.
In one embodiment, the step of identifying further comprises limiting the set of CpG sites to CpG sites that further exhibit differential methylation with peripheral blood mononuclear cells from a control sample.
In one embodiment, the plurality of tissue or cell types of the second group comprises at least some tissue or cells of the same type as the first group.
In one embodiment, the plurality of tissue or cell types of the second group comprises a plurality of non-diseased tissue or cell types.
In one embodiment, the predetermined threshold is indicative of methylation in the first group and non-methylation in the second group.
In one embodiment, the predetermined threshold is at least 50% methylation in the first group.
In one embodiment, the predetermined threshold is a difference in average methylation between the first and second groups of 0.3 or greater.
In one embodiment, the biological trait comprises malignancy.
In one embodiment, the biological trait comprises a cancer type.
In one embodiment, the biological trait comprises a cancer classification.
In one embodiment, the cancer classification comprises a cancer grade.
In one embodiment, the cancer classification comprises a histological classification.
In one embodiment, the biological trait comprises a metabolic profile.
In one embodiment, the biological trait comprises a mutation.
In one embodiment, the mutation is a disease-associated mutation.
In one embodiment, the biological trait comprises a clinical outcome.
In one embodiment, the biological trait comprises a drug response.
In one embodiment, the method further comprises designing a plurality of PCR primers pairs to amplify portions of the extended target genomic regions, each of the portions comprising at least one differentially methylated CpG site.
In one embodiment, the step of designing the plurality of primer pairs comprising converting non-methylated cytosines uracil, to simulate bisulphite conversion, and designing the primer pairs using the converted sequence.
In one embodiment, the primer pairs are designed to have a methylation bias.
In one embodiment, the primer pairs are methylation-specific.
In one embodiment, the primer pairs have no CpG residues within them having no preference for methylation status.
In one aspect, there is provided a method for synthesizing primer pairs specific to a methylation signature, the method comprising: carrying out the forgoing method, and synthesizing the designed primer pairs.
In one aspect, there is provided a non-transitory computer-readable medium comprising instructions that direct a processor to carry out the forgoing method.
In one aspect, there is provided a computing device comprising the computer-readable medium.
Concept Summary
The embodiments detect circulating tumour DNA using a highly sensitive and specific methylation based assay with detection limits 100 times better than other techniques.
Generally “probe” is used herein to refer to a target region for amplification and/or the ensuing amplified PCR product. It will be understood that each probe is amplified by a “primer set” or “primer pair”.
Multiple methylation-biased PCR primer pairs can be created, which are able to preferentially amplify these regions. These multiple regions are sequenced using next generation sequencing (NGS) at a high read depth to detect multiple tumour specific methylation patterns in a single sample. As described herein, features have been incorporated into a blood based cancer detection system that provides advantages over other tests which have been developed, and provides an unprecedented level of sensitivity and specificity as well as enables the detection of minute quantities of DNA (detection sensitivity).
Probe and Primer Set Development
The detection of circulating tumour DNA is hampered by both the presence of large amounts of normal DNA as well as by the very low concentrations of tumour DNA in the blood. Compounding this issue, both PCR and sequencing based approaches suffer from the introduction of single nucleotide changes due to the error prone nature of these processes. To deal with these issues, regions of the genome have been identified that exhibit concerted tumour specific methylation over a significant expanse of DNA so that each CpG residue is concordant21. Methylation-biased PCR primer pairs were designed for multiple segments of DNA across these regions each containing multiple CpG residues. Sample protocols for selection of differentially methylated regions and design of region specific PCR primers are provided.
Protocol For the Selection of Differentially Methylated Regions
Use of TCGA DATA For Identifying Breast Specific Probes
Level 3 (processed) Illumina Infinium HumanMethylation450 BeadChip array data (http://www.illumina.com/techniques/microarrays/methylation-arrays.html) was downloaded from The Tumour Genome Atlas (TCGA) site (https://tcga-data.nci.nih.gov/tcga/tcgaHome2.jsp) for the appropriate tumour types (e.g., breast, prostate, colon, lung, etc.). Tumour and normal samples were separated and the methylation values (from −0.5 to +0.5) for each group were averaged. The individual methylation probes were mapped to their respective genomic location. Probes that fulfilled the following example criteria were then identified:
1. The average methylation values for the normal breast, prostate, colon and lung tissues all below −0.3;
2. The difference between the average breast tumour and average breast normal values greater than 0.3, or at least 50% methylation in the tumour group; and
3. Two probes within 300 bp of each other fulfill criteria 1 and 2.
These criteria establish that the particular probe is not methylated in normal tissue, that the difference between the tumour and normal is significant, and that multiple probes in a relatively small area are co-ordinately methylated. Regions which had multiple positive consecutive probes (i.e., 3 or more) were prioritized for further analysis. Average values for approximately 10 other probes to either side of the positive region were plotted for all tumour and normal tissue samples to define the region exhibiting differential methylation. Regions exhibiting concerted differential methylation between tumour and normal for single or multiple tumour types were identified.
A secondary screen for a lack of methylation of these regions in blood was carried out by examining the methylation status of the defined regions in multiple tissues using nucleotide level genome wide bisulphite sequencing data. Specifically the UCSC Genome Browser (https://genome.ucsc.edu/) was used to examine methylation data from multiple sources.
Data was processed by the method described in Song Q, et al., A reference methylome database and analysis pipeline to facilitate integrative and comparative epigenomics. PLOS ONE 2013 8(12): e81148 (http://journals.plos.org/plosone/article?id=10.1371/journal.pone.0081148) for use in the UCSC Browser and to identify hypo-methylated regions (above blue lines).
The following data sources were used:
Gertz J, et al., Analysis of DNA methylation in a three-generation family reveals widespread genetic influence on epigenetic regulation. PLoS Genet. 2011 7(8):e1002228 (http://journals.plos.org/plosgenetics/article?id=10.1371/journal.pgen.1002228).
Heyn H, et al., Distinct DNA methylomes of newborns and centenarians. Proc. Natl. Acad. Sci. U.S.A. 2012 109(26):10522-7 (http://www.pnas.org/content/109/26/10522).
Hon G C, et al., Global DNA hypomethylation coupled to repressive chromatin domain formation and gene silencing in breast cancer. Genome Res. 2012 22(2):246-58 (http://genome.cshlp.org/content/22/2/246).
Heyn H, et al., Whole-genome bisulfite DNA sequencing of a DNMT3B mutant patient. Epigenetics. 2012 7(6):542-50 (http://www.tandfonline.com/doi/abs/10.4161/epi.20523#.VsS_gdIUVIw).
Hon G C, et al., Global DNA hypomethylation coupled to repressive chromatin domain formation and gene silencing in breast cancer. Genome Res. 2012 22(2):246-58 (http://genome.cshlp.org/content/22/2/246).
All of the regions identified exhibited hypo-methylation in normal blood cells including Peripheral Blood Mononuclear Cells (PBMC), the prime source of non-tissue DNA in plasma.
Protocol For the Design of Region Specific Primers For PCR Amplification and Next Generation Sequencing
For regions identified as being differentially methylated in tumours, PCR primers were designed that are able to recognize bisulphite converted DNA which is methylated. Using Methyprimer Express™ or PyroMark™, or other web based programs, the DNA sequence of the region was converted to the sequence obtained when fully methylated DNA is bisulphite converted (i.e., C residues in a CpG dinucleotide remain Cs, while all other C residues are converted to T residues). The converted DNA was then analysed using PrimerBlast™ (http://www.ncbi.nlm.nih.gov/tools/primer-blast/) to generate optimal primers. Primers were not expressly selected to contain CpG residues but due to the nature of the regions, generally CpG islands, most had 1 to 3 CpGs within them. This renders them biased towards the amplification of methylated DNA but in many cases they do recognize and amplify non-methylated DNA as well. The region between the primers includes 2 or more CpG residues. Primers were chosen to amplify regions from 75 to 150 base pairs in size with melting temperatures in the range of 52-68° C. Multiple primers were designed for each region to provide increased sensitivity by providing multiple opportunities to detect that region. Adapter sequences (CS1 and CS2) were included at the 5′ end of the primers to allow for barcoding and for sequencing on multiple sequencing platforms by the use of adaptor primers for secondary PCR.
Primers were characterized by PCR amplification of breast cancer cell line DNA and DNA from various primary tumours. PCR amplification was done with individual sets of primers and Next Generation Sequencing carried out to characterize the methylation status of specific regions. Primer sets exhibiting appropriate tumour specific methylation were then combined into a multiplex PCR reaction containing many primers.
Results
Selection of Regions For Cancer and Cancer Types
For breast cancer, 52 regions in the genome were identified that are highly methylated in tumours but where multiple normal tissues do not exhibit methylation of these regions. These serve as highly specific markers for the presence of a tumour with little or no background signal.
Table 1 depicts regions selected for breast cancer screening.
In Table 1, ‘Start’ and ‘End’ designate the coordinates of the target regions in the hg18 build of the human genome reference sequence. The ‘General Location’ field gives the name of one or more gene or ORF in the vicinity of the target region. Examination of these sequences relative to nearby genes indicates that they were found, e.g., in upstream, in 5′ promoters, in 5′ enhancers, in introns, in exons, in distal promoters, in coding regions, or in intergenic regions. The ‘Tumour’ field indicates whether a region is methylated in prostate (P), breast (B), colon (C), and/or lung (L) cancers. The ‘Size’ field indicates the size of the target region.
In the discussion here, it should be recognized that reference to genes such as CHST11, FOXA, and NT5 are not intended to be indicative of the genes in question per se, but rather to the associated methylated regions described in Table 1.
In total, 52 regions were found to be methylated in association with breast cancer, 17 were found to be methylated in association with prostate cancer, 9 were found to be methylated in association with prostate cancer, and 1 region was found to be methylated in association with lung cancer. Thus, some regions appear to be generally indicative of the various types of cancers assessed. Other regions methylated in subgroups of these, while others are specific for cancers. In the context of this assay and the types of cancers examined, 25 regions may be described as being “specifically methylated in breast cancer”. However, it is noted that the same approach may be used to identify regions methylated specifically in other cancers.
Assays may be developed for cancer generally, or to detect groups of cancers or specific cancers. A multi-tiered assay may be developed using “general” regions (methylated in multiple cancers) and “specific” regions (methylated in only specific cancers). A multi-tiered test of this sort may be run together in one multiplex reaction, or may have its tiers executed separately.
Probes For Breast Cancer
Over 150 different PCR primer pairs were developed to the 52 different regions in the genome shown to exhibit extensive methylation in multiple breast cancer samples from the TOGA database but with no or minimal methylation in multiple normal tissues and in blood cells (Peripheral Blood Mononuclear Cells and others).
As proof of concept, these were then used to amplify bisulphite converted DNA from breast cancer cell lines MCF-7 (ER+, PR+), T47-D (ER+, PR+), SK-BR-3 (HER2+), MDA-MD-231 (Triple Negative) and normal breast lines MCF-10A and 184-hTERT. Sequencing adapters were added and Next Generation Sequencing carried out on an Ion Torrent sequencer. The sequencing reads were then separated by region and the sequence reads were analyzed using the BiqAnalyzer HT program.
Results
Example results of methylation analysis will be discussed herein. CHST11 is an example of a region methylated in prostate, breast, and colon cancer. FOXA is a region methylated in breast and prostate cancer. NT5 is a region methylated specifically in breast cancer.
When sequenced, these probes produced strong concordant signals that consisted of multiple methylated CpGs (5 to 25) where there is a strong correlation between individual sites being methylated in tumours. This eliminates false positive results due to PCR and sequencing errors. These tumour specific multiple methylated sites can be detected against a high background of normal DNA, being limited only by the read depth of the sequencing. Based on bioinformatic analysis of TCGA tumours, this essentially eliminates false positive signals.
These results exemplify probes of differing specificities that can be selected using the approach outlined herein.
Probes For Uveal Cancer
Using the above-described methodologies, regions were selected for uveal cancer screening. Table 2 depicts these regions.
Tests For Breast Cancer Subtypes
The screen that has been described above, which originally incorporated all breast tumours in the TCGA database, can also be done on subsets of the tumour database.
BRCA1 carriers were taken out of the dataset and analyzed individually to identify target methylated regions specific to this subgroup. Breast cancer can also be divided in other ways: e.g., into five subtypes, Basal, Luminal A., Luminal B, HER2 and Normal-like. Patients in each of these groups were identified and analyzed to identify target methylated regions for each subset.
The screen can also be changed to look at individual patients using the previously described criteria to see who are positive or negative. Target methylated regions can then be ranked based on how many individuals are positive. This can help to remove biasing due to amalgamation (averaging). Targets can then be selected, e.g., if they are present in greater than 75% of patients for each subtype, and then rationalize amongst these.
Test For BRCA Carriers
Current monitoring practices for women at high risk of developing breast cancer due to familial BRCA1 or 2 mutations involve yearly MRI, however the high false positive rates result in a large number of unnecessary biopsies. Using the methodology described herein, a test may be developed to serve as a secondary screen, e.g., to be employed after a positive MRI finding; or to be used for primary screening of high risk patients. The blood test is designed to detect all types of breast cancer but because ER+ breast cancer is the most frequent it is biased towards these cancers, though some of the constituent probes do recognize HER2+ and TNBC tumours. In order to provide optimal sensitivity for the monitoring of BRCA1 and 2 an assay optimized for these patients may be developed.
Both TNBC and BRCA1 and 2 patients were selected from the TCGA 450 k methylation database. Generally, most BRCA1 and 2 tumours will present as TNBC but many non-familial cancers are also TNBC. These patients were analyzed using the above-described tumour specific methylation region protocol on both the overall TNBC population and on the BRCA1 and 2 patients. 85 tumour specific regions were identified for TNBC, 67 for BRCA1 and 13 for BRCA2 populations. Of these 39 were present in any two populations and they constitute the starting point for the development of this assay. Appropriate regions for a BRCA1 specific test were identified and assessed in individual patients with known mutations. This population is surprisingly uniform and most patients are recognized by a large number of probes. AUCs for individual probes are for the most part very high. Based on these results, an assay can be developed to detect all three, i.e., TNBC, BRCA1 and 2. If additional detection sensitivity is required, then individual tests can be constructed. For high risk women who are BRCA1 or 2 mutation carriers, their mutation status should be known so that the appropriate test can be applied.
Test For BRCA1 Carriers
Probes have been developed for the detection of cancer in carriers of the BRCA1 mutation. Methylation data from the TCGA Breast cancer cohort were selected from patients known to be carriers of pathogenic BRCA1 mutations. This data was then analyzed as described to identify regions of the genome specifically methylated in this sub-set of breast cancers. Table 3 lists appropriate regions identified and their genomic locations.
52 different probes were then developed to various parts of these regions and the methylation pattern in tumor cell lines was characterized, including MDA-MB-436 and HCC1937 which are known to carry BRCA1 mutations. These probes will be combined with previously characterized probes to other regions which are also methylated in tumours from BRCA1 patients. This would provide for a highly sensitive assay able to detect cancer in these high risk women at the earliest possible stage.
Tests For Other Subtypes
A number of breast cell lines from women with known BRCA1 mutations have been isolated such as MDA-MB-436, HCC1937 and HCC1395 (all available from ATCC). These may be used to validate the assay as was done for the general blood test. For BRCA2 mutant lines there is only one ATCC cell line at present, HCC1937. There are several BRCA2 mutant ovarian cancer lines that have been identified and they may be used if the bioinformatic analysis confirms that these methylation markers are also found in ovarian cancer. The development of a single assay that detects both breast and ovarian cancer in BRCA2 carriers represents a distinct advantage as it would simultaneously monitor the two primary cancer risks in these patients.
The development of these assays follows the same course the above-described general assay proceeding from TCGA data to cells lines to patient samples. Tumour banks (some of which have mutation data) can be used for this, and analysis of these tumours provides an indication of their likely BRCA mutation. These samples can also be sequenced to confirm the prediction.
Testing of Cell-Free Samples
Proof of concept testing was carried out using cell lines for ease of analysis. However, the assay can be applied to test for cell-free DNA, e.g., circulating cell-free tumour DNA in blood, and finds wide application in this context. A sample protocol for circulating tumour DNA is provided.
Sample Protocol: Test For Circulating Tumour DNA
DNA Preparatio
The following example protocol may be used to detect circulating tumour DNA (tDNA).
Obtain DNA to be used for bisulfite conversion and downstream PCR amplification (i.e., cell line, tumour or normal DNA). Determine DNA purity on 0.8% agarose gel.
Determine genomic DNA (gDNA) for concentration in ug/uL by UV spectrophotometry.
Prepare a 1:100 dilution with TE buffer.
Remove RNA contaminates, if necessary, using the purification protocol for the GenElute Mammalian Genomic DNA Miniprep Kit, Sigma Aldrich, CAT #G1N350 (http://www.sigmaaldrich.com/technical-documents/protocols/biology/genelute-mammalian-genomic-dna-miniprep-kit.html). Follow purification protocol from steps A: 2a-3a, step 4-9.
OPTIONAL: For gDNA from a cell line, sonicate gDNA to approximately 90-120 bp (this represents general size of circulating tDNA). To do this, sonicate 5-10 ug of sample (50-100 ng/100 uL) using a sonicator. Use setting 4, and 15 pulses for 30 seconds with 30 seconds rest on ice in between. Determine sonicated DNA purity and bp size on 0.8% agarose gel.
Bisulfite convert DNA—EpiTect Fast Bisulfite Conversion Kit, QIAgen, CAT #59824 (https://www.qiagen.com/us/resources/resourcedetail?id=15863f2d-9d1c-4f12-b2e8-a0c6a82b2b1e&lang=en). Follow bisulfite conversion protocol on pages 1-18, 19-23. Refer to trouble shooting guide pages 30-32. Modifications to the protocol include: 1. Prepare reactions in 1.5 mL tubes, 2. High concentration samples at 2 ug, and low concentration samples at 500 ng-1 ug, 3. Perform the bisulfite conversion using 2 heat blocks set at 95° C. and 60° C., 4. Incubation at 60° C. extended to 20 minutes, to achieve complete bisulfite conversion, 5a Elute DNA in 10-20 uL of elution buffer for −50-100 ng/uL final concentration, and 5b Dilute DNA to 10 ng/uL for use in PCR.
Perform nested PCR with Hot Star Taq Plus DNA Polymerase, Qiagen, CAT #203605 (https://www.qiagen.com/ca/resources/resourcedetail?id=c505b538-7399-43b7-ad10-d27643013d10&lang=en).
Singleplex PCR Amplification
For singleplex PCR amplification of individual probes, carry out a primary PCR reaction with methylation-biased primers (MBP), (primer forward and reverse).
Table 4 recites reaction components.
Table 5 lists thermocycler conditions.
Carry out a secondary PCR reaction with universal primers CS1 (Barcode) and CS2 (P1 Adapter). To do this, remove an aliquot from the primary reaction, use as template DNA, this method serves as a two-step dilution PCR reaction
Table 6 recites reaction components.
Table 7 recites thermocycler conditions.
Determine PCR specificity on 2% agarose gel. Run the methylation-biased PCR product and the CS1 CS2 sequencing PCR product beside one another on the agarose to visualize the banding pattern and increase in bp size. PCR product should be between 200-300 bp
For Singleplex PCR products, pool 5-10 uL of each PCR reaction (CS1 CS2 Secondary RXN) into a single tube for each sample type. Purify the pooled PCR with Agencourt AMPure XP beads at a 1.2:1 ratio (90 uL beads+75 uL sample), e.g., as below.
Agencourt Ampure XP Bead Purification
Use freshly prepared 70% ethanol. Allow the beads and pooled DNA to equilibrate to room temperature.
1. Add indicated volume of Agencourt AMPure XP beads to each sample: 90 uL beads+75 uL Pool (1.2:1)
2. Pipet up and down 5 times to thoroughly mix the bead suspension with the DNA. Incubate the suspension at RT for 5 minutes.
3. Place the tube on a magnet for 5 minutes or until the solution clears. Carefully remove the supernatant and store until purified library has been confirmed.
4. Remove the tube from the magnet; add 200 uL of freshly prepared 70% EtOH. Place the tube back on the magnet and incubate for 30 seconds; turn the tube around twice in the magnet to move the beads through the EtOH solution. After the solution clears, remove and discard the supernatant without disturbing the pellet.
5. Repeat step #4 for a second EtOH wash.
6. To remove residual EtOH, pulse-spin the tube. Place the tube back on the magnet, and carefully remove any remaining EtOH with a 20 uL Pipette, without disturbing the pellet.
7. Keeping the tube on the magnet, air-dry the beads at RT for ˜5 minutes.
8. Remove the tube from the magnet; add 50 uL of TE directly to the pellet. Flick the tube to mix thoroughly. Incubate at RT for 5 minutes.
9. Pulse-spin and place the tube back on the magnet for ˜2 minutes or until the solution clears. Transfer the supernatant containing the eluted DNA to a new 1.5 mL Eppendorf LoBind tube.
10. Remove the tube from the magnet; add 50 uL of TE directly to the pellet. Flick the tube to mix thoroughly. Store the beads, along with the supernatant, at 4° C. until purified library has been confirmed.
11. Visualize the sample pre- and post-purification on an 8% acrylamide gel (higher resolution). Pooled PCR product should be visualized as multiple bands (as each PCR product is a slightly different bp size). Purified sample should eliminate product beneath 150 bp.
12. Perform nested PCR with Multiplex PCR Plus Kit, Qiagen, CAT #206152 (https://www.qiagen.com/ca/resources/resourcedetail?id=beb1f99e-0580-42c5-85d4-ea5f37573c07&lang=en), e.g., as below.
Multiplex PCR Amplification of Up to 50 Probes in a Single Reaction
Create multiplex primer mix by aliquot 1 uL of each forward and reverse primer at 10 pmol/uL into a single 1.5 mL tube. Calculate the final concentration of each primer by dividing the initial primer concentration by the final volume of primer mix in the tube, i.e., 15 probes to be multiplexed into a single reaction, would total 30 primers and at 1 uL each, 30 uL final volume. Thus ((10 pmol)(1 uL))/30 uL=0.333 pmol. Primer concentration requires optimization during PCR amplification, as the number of primers in a single reaction can influence the efficiency of the product, e.g.
15 primer sets ˜2 pmol final [ ] in PCR
50 primer sets ˜0.5 pmol final [ ] in PCR
Carry out primary PCR reaction with methylation-biased primers.
Table 8 lists reaction components for multiple amplifications of 15 probes, and Table 9 lists reaction components for multiple amplifications of 50 probes. Table 10 list reaction conditions.
Determine PCR specificity on 2% agarose gel. Multiplex products should be visualized with multiple banding pattern between 100-300 bp.
Pooling is not required for multiplex products, as the probes have already been combined and amplified into a single tube/reaction.
Purify the pooled PCR with Agencourt AMPure XP beads at a 1.2:1 ratio (60 uL beads+50 uL sample) (refer within document for purification protocol).
After PCR amplification, along with pooling and purifying, the samples can be quantified by qPCR, e.g., Ion Library Quantification Kit, TaqMan assay quantification of Ion Torrent libraries, Thermo Fisher Scientific, CAT #4468802 (https://tools.thermofishercom/content/sfs/manuals/4468986_IonLibraryQuantitationKit_UG.pdf)
1. Create a standard curve of 6.8 pM, 0.68 pM, 0.068 pM, 0.0068 pM
2. Dilute samples 1:1000, and run in duplicate
3. Perform qPCR assay on the Step One Plus Real Time machine by Life Technologies
4. Sample libraries quantified ≥100 pM can proceed to be sequenced on the Life Technologies Ion Torrent Sequencing platform
Life Technologies Ion Torrent PGM Sequencing
Ion PGM Template OT2 200.
Perform template reaction with Ion PGM Template OT2 200 Kit, Thermo Fisher Scientific, CAT #4480974. Kit contents to be used on the One Touch 2 and Enrichment system (https://tools.thermofisher.com/content/sfs/manuals/MAN0007220_Ion_PGM_Template_OT2_200_Kit_UG.pdf—
Utilizing library quant. obtained from qPCR, dilute libraries appropriately to 100 pM. Follow Life Technologies guide on how to further dilute libraries for input into final template reaction.
Follow reference guide to complete template reaction
Ion PGM Sequencing 200
Perform sequencing reaction with Ion PGM Sequencing 200 kit, Thermo Fisher Scientific, CAT #4482006. Kit contents to be used on the Ion PGM system (https://tools.thermofishercom/content/sfs/manuals/MAN0007273_IonPGMSequenc_200Kit_v2_UG.pdf).
Plan sequencing run
Follow reference guide to complete PGM sequencing
Sequencing data analysis and work flow
Obtain run report generated by the PGM and Torrent Browser
Run report includes the following information
Obtain uBAM files generated by the PGM, available for download to an external hard drive
Bioinformatics data analysis
Uveal Melanoma Test
The molecular biology of uveal melanoma (UM) is simpler than that of breast cancer, with minimal mutations and rearrangements, and only two major sub-types which correspond to the retention or loss of chromosome 3p. A test was developed for UM which is superior to current state of the art blood assays.
Analysis of 450 k methylation TCGA data for 80 UMs allowed for the identification of regions of tumour specific methylation in both 3p- and 3pWT tumours using our algorithm. Table 11 shows 16 hypermethylated regions in both 3p- and 3pWT tumours used for probe development and testing, according to one embodiment.
The top 14 of these common regions were carried forward for probe development and a total of 26 different probes were characterized, with several regions having up to three probes targeting them. Each of these probes was then validated using six different UM cell lines to assess their methylation status. As negative controls, DNA from peripheral blood mononuclear cells (PBMCs), which are the main source of contaminating DNA in blood samples, as well as a pool of cell free DNA (cfDNA) from 16 individuals, were also tested (
The validated regions were C2CD4A, COL19A1, DCDC2, DHRS3, GALNT3, HES5, KILLIN, MUC21, NR2E1/OSTM1, PAMR1, SCRN1, and SEZ6. The validated probes were C2C5F, COL2F, DCD5F, DGR2F, GAL1F, GAL3F, HES1F, HES3F, HES4F, KIL5F, KIL6F, MUC2F, OST3F, OST4F, PAM4F, SCR2F, SEZ3F, and SEZ5F.
These patients were previously tested using the pyrophosphorolysis-activated polymerization (PAP) assay26, which detects the frequent GNAQ or GNA11 mutations in UM27. In all cases the test detected cancer in these patients even when the PAP assay failed to register a signal (
Prostate Cancer Test
An important aspect of any test is that it should be applicable to all patients. Based on our experience it is essential to consider specific subtypes of a given cancer to ensure that all patients are detected by the assay. The TCGA analysis of a large prostate cohort revealed sub-groups based on specific mutations and transcriptional profiles28. Four subtypes were identified based on the overall pattern of methylation found in these tumours. In this example the TCGA prostate cohort was divided into groups based on the methylation pattern and subjected to methylation analysis.
Table 12 lists 40 regions associated with all sub-types of prostate cancer.
These regions common to all four methylation subtypes were identified and a total of 38 probes from 33 regions were selected and appropriate “biased” PCR probes were generated. These were characterized using four different prostate cancer lines. DU145 is an androgen receptor (AR−) negative cell line that is able to generate metastases in the mouse. PC3 is also AR− and also metastatic. LNCaP is an androgen receptor positive line (AR+) that is non-metastatic in the mouse while RWPE cells are AR+ and non-metastatic. DNA from PBMC was also tested as this represents the primary source of cell free DNA in the circulation.
A total of 34 probes from 33 regions were validated in that they showed little or no methylation in PBMCs while showing large scale methylation in one or more of the tumour cell lines (
The validated regions were ADCY4, ALDH1L1, ALOX5, AMOTL2, ANXA2, CHST11, EFS, EPSTI1, EYA4, HAAO, HAPLN3, HCG4P6, HES5, HIF3A, HLA-F, HLA-J, HOXA7, HSF4, KLK4, LOC376693, LRRC4, NBR1, PAH, PON3, PPM1H, PTRF, RARA, RARB, RHCG, RND2,TMP4, TXNRD1, and ZSCAN12.
The validated probes were ADCY4-F, ALDH1L1-F, ALOX5-F, AMOTL2-F, ANXA2-F, CHST11-F, EFS-F, EPSTI1-F, EYA4-F, HAAO-F, HAPLN3-F, HCG4P6-F, HES5-F, HIF3A-F, HLA-F-F, HLA-J-1-F, HLA-J-2-F, HOXA7-F, HSF4-F, KLK4-F, LOC376693-F, LRRC4-F, NBR1-F, PAH-F, PON3-F, PPM1H-F, PTRF-F, RARA-F, RARB-F, RHCG-F, RND2-F, TMP4-F, TXNRD1-F, and ZSCAN12-F.
To these 34 probes an additional 12 probes (from 7 regions) were added that had previously been characterized in breast cancer, which were also able to detect prostate cancer, for a total of 46 probes.
The added probes were C1Dtrim, C1Etrim, CHSAtrim, DMBCtrim, FOXAtrim, FOXEtrim, SFRAtrim, SFRCtrim, SFREtrim, TTBAtrim, VWCJtrim, and VWCKtrim.
These probes were multiplexed together and were then used to analyze plasma samples from five patients before they had initiated androgen deprivation therapy (ADT) and 12 months after starting treatment. These patients were part of a small cohort (˜40 patients) being followed for depression and the plasma samples at 0.5 ml were much smaller than normally used for the assay (2 mls). All of the patients were MO with no sign of metastatic disease when placed on ADT.
A variety of probes were positive depending on the particular patient (
Based on the literature, three of these regions appear to have prognostic significance as well. C1orf114 or CCDC1 has been shown to be correlated with biochemical relapse. HES5 is a transcription factor that is regulated by the Notch pathway and methylation of its promoter occurs early in prostate cancer development. KLK5 is part of the Kallikrein gene complex that includes KLK3 (the PSA gene). We can demonstrate that KLK5 expression is correlated with methylation and KLK5 expression has previously been shown to be increased in higher grade tumours. These results strongly suggest that the examination of a large number of methylation markers may yield significant insight into the specific processes involved in prostate cancer development and produce diagnostic and prognostic information that would be vital for management of the disease.
Predictive Prostate Cancer Methylation Biomarkers
The 50 region assay according to embodiments described herein is sufficiently sensitive to easily detect metastatic disease and to follow changes in tumour size over time and, as indicated, has predictive value in itself. As described above, at least three regions, KLK5, HER5, and C1orf114 have potential to predict progression. In order to develop additional probes that are able to predict outcome in this patient population, the prostate cancer TCGA data was reanalysed to divide the patients by Gleason score. An inter-cohort comparison was conducted to identify regions frequently methylated in higher score cancers. Initially, Gleason grades 6 and 9 were compared as these typically represent less and more aggressive tumours and both groups had sufficient numbers of patients to ensure significance of the results. Probe development was carried out under the same criteria as with the original probe sets so that they could be used with ctDNA. No single probe will be absolutely specific for a given grade but a number of the probes showed excellent division between Gleason scores with the proportion of the cohort positive for a given grade increasing with increasing grade (
The probes were ASAP1/p, BC030768/p, C18orf62/p, C6orf141/p-1, C6orf141/p-2, CADPS2/p, CORO1C/p-1, CORO1C/p-2, CYP27A1/p, CYTH4/p, DMRTA2/p, EMX1/p, HFE/p-1, HFE/p-2, HIST1H3G/1H2BI/p, HMGCLLI/p, KCNK4/p, KJ904227/p, KRT78/p, LINC240/p-1, LINC240/p-2, Me3/p-1, Me3/p-2, MIR129, NBPF1/p, NHLH2/p, NRN1/p, PPM1H/p-1, PPM1H/p-2, PPP2R5C/p, PRSS3/p, SFRP2/p-1, SFRP2/p-2, SLCO4C1/p, SOX2OT/p, TUBB2B/p, USP44/p, Chr1/p-1, Chr2/p-1, Chr3/p-1, Chr4/p-1, Chr8/p-1, and Chr10/p-1.
It is expected that it will be an overall pattern of hypermethylation, rather than a single probe, that will have the greatest predictive power.
Breast Cancer Test
One approach described herein for identifying hypermethylated regions in breast cancer focused on the most frequently methylated regions within the TOGA database. Due to the large number of LumA and LumB patients in this dataset there was a significant under-detection particularly of the Basal class of tumours.
Accordingly, the data were reanalyzed based on the four molecular subtypes LumA, LumB, Her2 and Basal. The Normal-like subtype is not very frequent in the dataset and as expected is very close to normal tissue, however a small number of regions recognizing this subtype were also included. Overall, methods and probes were developed and tested for over 230 different regions (some with multiple probes), and these have been validated using a variety of breast cancer cell lines and tumour samples. Some regions are subtype-specific but most recognize multiple subtypes. These have been assembled into a single test incorporating 167 different probes which recognize all subtypes (
Another test specific for the triple negative breast cancer (TNBC) subtype was developed from the larger set of general regions identified as described above. This test incorporates 86 probes from 71 regions, listed in Table 14.
The probes were ALX1, AVCRL1, BRCA1-A, C1Dtrim, C1Etrim, CA9-A, CARD11-B, CCL28-A, CD38, CDKL2-A, CHSAtrim, CRYM-A, DMBCtrim, DMRTA2exp-A, DPP10-A, DPP10-B, DPP10-C, DRD4-A, EFNA4-B, EPSTI1, EVX1, FABP5, FOXAtrim, FOXEtrim, GALR3-A, GIPC2-A, HINF C trim, HOXAAtrim, HOXACtrim, HOXB13-A, Int5, Int8, IRF8-A, ITRIPL1, LEF1-A, MAST1 A trim, mbBARHL2 Trim, mbBOLL Trim, mbC5orf Trim, mbDDAH Trim, mbDMRTA Trim, mbGABRA A Trim, mbGABRA B Trim, mbGNG Trim, mbID4 Trim, mbIRF Trim, mbNT5E Trim, mbSIM A Trim, mbTBX15 Trim, NFIC-B, NFIC-A, NPSH2-B, NR5A2-B, OTX2-A, PAX6-A, pbDMRTA Trim, pbGNG Trim, pbSCAND Trim, pbTAL Trim, PDX1exp-B, PHOX2B-A, POU4F1 A trim, PPFIA3-A, PRDM13, PRKCB-A, PRKCB-C, PRSS27-A, PTGDR, PTPRN2-A, PTPRN2-B, SALL3-A, SALL3-B, SLC7A4-A, SOX2OT-B, SPAG6 A trim, TCTEX1D1-A, TMEM-A, TMEM-B, TMEM90B-A, TNFRSF10D, TOP2P1-B, TSPAN33-A, TTBAtrim, UBD-A, VWCJtrim, and VWCKtrim.
The ability of this test to detect TNBC was validated by the analysis of 14 TNBC primary tumours as well as matched normal tissue from four of these patients. Large scale methylation was observed for the majority of probes and was distinctly different from the normal samples (
Sensitivity of the Tests
The tests described herein are designed to detect less than one genome's worth of DNA in a sample through the use of multiple regions where a single probe out of many can signal the presence of a tumour. The more regions and probes incorporated into a test the greater is the sensitivity. This is in contrast to mutation detection where the presence of a single mutation per genome equivalent means that random sampling effects rapidly limit sensitivity when the concentration of the tumour DNA falls below one genome equivalent per sample. The presence of large amounts of normal DNA in fluid samples also creates problems for the detection of mutations through the relatively high error rates for PCR and sequencing. To assess the limits of methods and tests described herein, a dilution experiment was performed wherein DNA from a TNBC cell line (HCC1937 DNA) was diluted into a constant amount of PBMC DNA (10 ng) from a normal patient (
Discussion
The sensitivity of mutation based detection tests is limited by their detection of single unknown mutations in genes, such as p53 or ras. As only a single mutation is present per genome equivalent, this dramatically limits the sensitivity of these assays. Once the concentration of tumour DNA in the blood decreases to less than one genome equivalent per volume of blood analysed, the probability of detecting a mutation decreases dramatically as that particular segment of DNA may not be present in the blood sample. The assay described herein incorporates multiple probes for multiple regions from across the genome to dramatically increase sensitivity. For example, up to 100 or more probes may be incorporated into the assay, making it up to 100 or more times more sensitive than mutation based tests.
Circulating tumour DNA may be produced by the apoptotic or necrotic lysis of tumour cells. This produces very small DNA fragments in the blood. With this in mind, PCR primer pairs were designed to detect DNA in the range of 75 to 150 bp in length, which is optimal for the detection of circulating tumour DNA.
The use of DNA methylation offers one more advantage over mutation based approaches. Mutated genes are typically expressed in the cells (such as p53). They are thus in loosely compacted euchromatin, in comparison to methylated DNA which is in tightly compacted heterochromatin. This methylated and compacted DNA may be protected from apoptotic nucleases, increasing its concentration in the blood in comparison to these less compacted genes.
Extensive analysis of the genome wide methylation patterns in breast, colon, prostate and lung cancers and normal tissue in each of these organs based on TCGA data was carried out. 52 regions were identified for breast cancer which fulfill design criteria, which looks for an optimal difference in methylation between tumour and normal breast tissue, and where there is no methylation in any of the other normal tissues. As well, there should optimally be at least 2 CpG residues within 200 basepairs of each other. This ensured that regions of coordinated tumour specific methylation have been identified.
Within these 52 regions, 17 were found in common with colon cancer, and 9 in common with prostate cancer. Interestingly there were few appropriate regions identified in lung cancer, with only 1 overlapping with breast cancer. Most of these regions are associated with specific genes, though several are distantly intergenic, and almost all were found in CpG islands of various sizes. Probes were first developed for those regions with some commonality between cancers and designed PCR primers which recognize the methylated DNA sequence. This provides a bias in the amplification process for tumour DNA, enriching the tumour signal. These primer pairs amplify regions of 75 to 150 bp in accordance with our design criteria. Typically these regions contain from 3 to 12 CpG residues each, ensuring a robust positive signal when these regions are sequenced. Multiple non-overlapping probes were used as the CpG islands are generally larger than 150 bp, allowing for multiple probes for each appropriate region, providing more power to detect these regions and increasing the detection sensitivity of the assay.
Six different breast cancer lines were used in this validation analysis that have been shown to generally retain tumour specific methylation patterns22. MCF-7 and T47D lines are classic ER+positive cell lines representing the most frequent class of breast cancer. SK-BR-3 cells are a HER2+ line and MDA-MB-231 cells represent a Triple Negative Breast cancer (TNBC), thus the 3 main categories of breast cancer are represented covering 95% of all tumours. Two “normal” lines were also used, the MCF10A line, though this line has been shown to contain some genomic anomalies, and the karyotypically normal 184-hTERT line. DNA was bisulphite converted, and the probes were amplified individually, barcoded then pooled according to cell line and subject to Next Generation Sequencing on an Ion Torrent sequencer. Not all PCR primer pairs produced a product due to the methylation-based nature of the primers, but in general, where a signal was detected, around 1000 reads were obtained per probe for each cell line. These reads were processed through our NGS pipeline using Galaxy and then loaded into the NGS methylation program BiqAnalyzer23,24. This program extracts probe specific reads, aligns them against the probe reference sequence, and calls methylated and unmethylated CpGs. It also carries out quality control measures related to bisulphite conversion and alignment criteria. In all of these probes there are several CpG residues within the primer sequence producing a bias towards amplifying methylated DNA. The analysis shown only includes CpGs outside of the primers which are solely representative of the methylation status of the sample being analysed.
Validation work continues to validate potential probe regions. A further 24 regions were characterized using 52 different probes in the cell lines as an initial screen for their suitability.
It has been noted that there does appear to be a population of patients with relatively few positive probes. This is not subtype specific and other probes specific for this population have been identified. As appropriate, additional probes will be developed for all suitable regions and expanded to include other parts of the associated CpG islands. Overall it is expected that 100-150 separate probes in the assay will provide optimal sensitivity.
The next step in validating each of these probes was to examine their methylation patterns in actual patient tumour samples. A small cohort of patient samples was used to investigate GR methylation. From this group three ER+ tumours (one of which is positive for GR methylation), one HER2+ tumour and two TNBC tumours were chosen, as well as their corresponding normal controls. Taking the CHST11A probe as an example,
Initial proof of concept work involved mixing experiments where non-methylated and methylated DNA was mixed in increasing ratios. This demonstrated that based in the presence of multiple CpG signatures methylated DNA could easily be detected in the presence of at least a 500 fold excess of unmethylated DNA. These probes were amplified with PCR primers that were not methylation specific or biased, and the probes developed to date do incorporate a bias towards methylated DNA, which further increases the detection sensitivity. However, they do amplify non-methylated DNA (in part because primers were designed with no preference as to the location of methylation sites within the primers). This was done intentionally as it provides for a potential quantitative aspect to this assay. Some of the circulating normal DNA in blood samples is likely from the lysis of nucleated blood cells, which is why serum is preferred over plasma as a source of DNA. However the ratio of tumour to normal DNA in blood may provide some quantitation of the actual concentration of tumour DNA present in the blood, which is thought to be correlated with tumour load. Since tumour can be distinguished from normal DNA reads, the ratio between them can be used as a proxy for the tumour DNA concentration. The number of tumour specific reads per volume of blood, regardless of the number of normal reads, may also prove to be closely linked to circulating tumour DNA levels.
Optimizing this test may include multiplexing to allow all of the probes the opportunity to amplify their targets in a given sample of DNA. Through the use of limited concentrations of primers and cycles, excellent amplification of all probes was obtained within a set of 17 primer pairs. Expanding this to include all of the optimized primers is not expected to be an issue.
The test may be implemented as a blood based breast cancer detection system in patient blood samples.
Based on development and validation work to date, the assay offers significant advantages other current and developing tests based on sensitivity, specificity, and detection sensitivity.
Some potential applications of the embodiments described herein are listed below by level of detection sensitivity:
Determining response to neo-adjuvant chemotherapy;
Monitoring tumour load in diagnosed patients;
Detecting residual disease post-surgery;
Detecting relapse;
Secondary screen after positive MRI in high risk patients;
Direct monitoring of high risk patients; and
Primary population screening.
The analysis of patients with active breast cancer offers the ability to assess a number of different aspects of this blood based test. Patients with locally advanced disease can be recruited preferentially, as these patients generally have larger tumours, receive neo-adjuvant therapy, are more likely to have residual disease and are at higher risk of relapse. By analysing blood samples from these patients upon diagnosis, after any neo-adjuvant treatments, pre-surgery, and at followup visits post-surgery it is possible to follow the relative tumour burden in these patients over the course of treatment. This will allow the tumour size and type to be correlated with the results of the test described herein.
Patients can be recruited in the clinic after a biopsy confirmed positive diagnosis. Blood can be drawn in conjunction with other routine blood work at diagnosis, after neo-adjuvant treatment, before surgery, within a month after surgery and every 3-6 months following that. Blood from 50 aged matched women without disease can also be collected from the community to provide control samples for the patient cohort. Relevant clinical data can be collected including radiological assessments and/or pathology reports. In particular, the receptor status of the tumours, the size of the tumour based on both radiological assessment and examination of the excised tumour, as well as treatments and response to therapy can be correlated with the circulating DNA analysis.
The assay described herein is expected to be quantitative at different levels. At very low levels of tumour DNA, the random presence of the tumour DNA in a sample will result in a subset of individual probes being positive, with the number of positive probes increasing with greater tumour DNA levels. At higher levels of tumour DNA the number of tumour specific reads will increase, either as an absolute number or in relation to the number of normal DNA reads. As a result methylation data can be treated in three ways:
(1) As a binary outcome where each probe will be considered to be positive if it has any tumour specific methylation pattern present;
(2) An individual threshold of methylation will be established for each probe based on the minimum number of reads required to call a tumour; or
(3) Tumour specific reads per number of normal reads for each probe (or, e.g., per 100,000 total reads).
Each of these approaches may be used to carry out logistic regression on the patient and control sets. Receiver Operating Characteristic (ROC) analysis may be used to define thresholds for each probe that maximizes the sensitivity and sensitivity of the assay. The performance of the entire assay may be characterized using Area Under the Curve (AUC) analysis for overall sensitivity, specificity, classification accuracy and likelihood ratio. Pearson or Spearman correlations may be used to compare patient parameters with the test outcomes.
Changes in methylation may be important drivers of breast cancer development and that these occur very early during the process of transformation. This may explain why many of the observed methylations are common amongst different breast cancer sub-types, while some are even common to other cancers. This may mean that these changes predate the development of full malignancy and suggests that they could also have value in assessing the risk of a women developing breast cancer. It is envisaged that the assay described herein can be used to track the accumulation of risk in the form of increasing gene specific methylation levels and could be used to develop a risk assessment tool. This would be useful for the development and assessment of risk mitigation and prevention strategies.
Table 15 lists the primers used herein for each probe.
indicates data missing or illegible when filed
The above-described embodiments are intended to be examples only. Alterations, modifications and variations can be effected to the particular embodiments by those of skill in the art. The scope of the claims should not be limited by the particular embodiments set forth herein, but should be construed in a manner consistent with the specification as a whole.
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All references referred to herein are expressly incorporated by reference in their entireties.
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/CA2017/000111 | 5/4/2017 | WO | 00 |
| Number | Date | Country | |
|---|---|---|---|
| 62331585 | May 2016 | US |
