Patent Grant
9187785
MicroRNAs (miRNA) are a recently discovered class of small non-coding RNAs (17-14 nucleotides). Due to their function as regulators of gene expression they play a critical role both in physiological and in pathological processes, such as cancer (Calin and Croce 2006; Esquela-Kerscher and Slack 2006; Zhang, Pan et al. 2007; Sassen, Miska et al. 2008).
There is increasing evidence that miRNAs are not only found in tissues but also in human blood both as free circulating nucleic acids (also called circulating miRNAs) and in mononuclear cells. A recent proof-of-principle study demonstrated miRNA expression pattern in pooled blood sera and pooled blood cells, both in healthy individuals and in cancer patients including patients with lung cancer (Chen, Ba et al, 2008). In addition, a remarkable stability of miRNAs in human sera was recently demonstrated (Chen, Ba et al. 2008; Gilad, Meiri et al. 2008). These findings make miRNA a potential tool for diagnostics for various types of diseases based on blood analysis.
Multiple sclerosis (MS), also known as disseminated sclerosis or encephalomyelitis disseminata) is an inflammatory autoimmune disease of the central nervous system (CNS). Causing MS appears to be a combination of immunological, genetic and environmental factors. It is a chronic demyelinating disease, which primarily affects young adults and is characterized by a highly variable course. The heterogeneous presentation of MS is characterized by a variety of clinical problems arising from multiple regions of demyelination and inflammation along axonal pathways. The signs and symptoms of MS are determined by the location of the affected regions.
Mostly, the disease begins in the third or fourth decade of life. Its initial course is characterized by acute episodes of neurological dysfunction, such as decreased vision, followed by subsequent recovery. This course is known as relapsing-remitting MS. Over time, the improvement after attacks may be incomplete and the relapsing-remitting course may evolve into one of increasing progression of disability, termed secondary progressive MS.
The diagnosis of MS generally relies on the presence of a neurological problem that remits and then returns at an unrelated site. This is confirmed by magnetic resonance imaging (MRI) or functional evidence of lesions in a particular pathway by abnormal evoked potentials. The histological hallmark of MS at postmortem exam is multiple lesions at different sites showing loss of myelin and infiltration by a characteristic complement of inflammatory cells.
The key to identifying predictive markers is a deeper understanding of the factors that underlie the therapeutic response. Identification of biomarkers will in turn allow for stratification of MS patients for their response to a specific treatment, ultimately leading to improved therapeutic benefits and a personalized treatment approach for MS patients.
Identification of reliable biomarkers in MS sclerosis patients bears the potential for an improved MS diagnosis, monitoring the disease activity and progression and also to evaluate response to treatments. The field of biomarker discovery has gradually shifted from the aim to find the perfect surrogate marker to the construction of composite markers with higher performances, taking advantage of technologies allowing unbiased screening, including microarray analyses. However, suitable biomarker sets allowing for a non-invasive diagnosis of MS based on peripheral profiles have not been detected, so far.
Various markers have been proposed to indicate specific types of disorders such as cancer or MS. However, there is still a need for more efficient and effective methods and compositions for the diagnosis of diseases.
The present invention provides novel methods for diagnosing diseases based on the determination of specific miRNAs that have altered expression levels in disease states compared to healthy or other relevant controls. The present invention particularly provides novel methods for the diagnosis and/or prognosis and/or monitoring of multiple sclerosis or related diseases in human individuals based on miRNA analysis from samples derived from blood.
A first subject-matter of the invention is a method for diagnosing multiple sclerosis, comprising the steps
A “biological sample” in terms of the invention means a sample of biological tissue or fluid. Examples of biological samples are sections of tissues, blood, blood fractions, plasma, serum, etc. A biological sample may be provided by removing a sample of cells from a subject, but can also be provided by using a previously isolated sample. For example, a tissue sample can be removed from a subject suspected of having a disease by conventional biopsy techniques. In a preferred embodiment, a blood sample is taken from the subject. In one embodiment, the blood or tissue sample is obtained from the subject prior to initiation of radiotherapy, chemotherapy or other therapeutic treatment. According to the invention, the biological sample preferably is a blood, plasma, or PBMC (peripheral blood mononuclear cell), or a serum sample. Further, it is also preferred to use blood cells, e.g. erythrocytes, leukocytes or thrombocytes.
A biological sample from a patient means a sample from a subject suspected to be affected by a disease. As used herein, the term “subject” refers to any mammal, including both human and other mammals. Preferably, the methods of the present invention are applied to human subjects.
In step (a) of the method of the invention, an expression profile of a predetermined set of miRNAs is determined. The determination may be carried out by any convenient means for determining nucleic acids. For expression profiling, qualitative, semi-quantitative and preferably quantitative detection methods can be used. A variety of techniques are well known to those of skill in the art. In particular, the determination may comprise nucleic acid hybridization and/or nucleic acid amplification steps.
Nucleic acid hybridization may for example be performed using beads, a solid phase nucleic acid biochip array, in particular a microarray, beads, or in situ hybridization. The miRNA microarray technology affords the analysis of a complex biological sample for all expressed miRNAs. Nucleotides with complementarity to the corresponding miRNAs are spotted, or synthesized on coated carriers. E.g., miRNAs isolated from the sample of interest may be labelled, e.g. fluorescently labelled, so that upon hybridization of the miRNAs to the complementary sequences on the carrier the resulting signal indicates the occurrence of a distinct miRNA. Preferably, microarray methods are employed that do not require labeling of the miRNAs prior to hybridization (
Further, quantitative real-time polymerase chain reaction (RT-PCR) can be used to detect also low abandoned miRNAs. Furthermore, bead-based assays, e.g. the luminex platform, are also suitable.
Furthermore, bead-based assays, e.g. the Luminex platform, are also suited to carry out the present invention.
Alternative methods for obtaining expression profiles may also contain sequencing, next generation sequencing or mass spectroscopy.
The predetermined set of miRNAs in step (a) of the method of the invention depends on the disease to be diagnosed. The inventors found out that single miRNA biomarkers lack sufficient accuracy, specificity and sensitivity, and therefore it is preferred to analyze more complex miRNA expression patterns, so-called miRNA signatures. The predetermined set of miRNAs comprises one or more, preferably a larger number of miRNAs (miRNA signatures) that are differentially regulated in samples of a patient affected by a particular disease compared to healthy or other relevant controls.
The expression profile determined in step (a) is subsequently compared to a reference expression profile or a relevant reference in step (b). This reference may be a mathematical function or algorithm that allows for the diagnosis of the disease. This mathematical function or algorithm has been developed on the basis of a plurality of reference expression profiles. The reference expression profile is the expression profile of the same set of miRNAs in a biological sample originating from the same source as the biological sample from a patient but obtained from a healthy subject. Preferably, both the reference expression profile and the expression profile of step (a) are determined in a blood or serum sample including whole blood, plasma, serum or fractions thereof, or in a sample of peripheral blood mononuclear cells, erythrocytes, leukocytes and/or thrombocytes. It is understood that the reference expression profile is not necessarily obtained from a single healthy subject but may be an average expression profile of a plurality of healthy subjects. It is preferred to use a reference expression profile obtained from a person of the same gender, and a similar age as the patient. It is also understood that the reference expression profile is not necessarily determined for each test. Appropriate reference profiles stored in databases may also be used. These stored references profiles may, e.g., be derived from previous tests. The reference profile may also be a mathematical function or algorithm which is developed on a plurality of measured reference profiles.
The inventors succeeded in developing a generally applicable approach to arrive at miRNA signatures that are correlated with a particular disease. The general work flow is depicted in
The inventors surprisingly found out that the described approach yields in miRNA signatures that provide high diagnostic accuracy, specificity and sensitivity in the determination of multiple sclerosis or related disease states/clinical conditions.
According to a preferred embodiment of the invention, the disease to be determined is multiple sclerosis. Surprisingly, the inventors found out that miRNAs are differentially regulated in samples from MS patients as compared to health controls. A complete overview of all miRNAs that are found to be differentially regulated in blood samples of multiple sclerosis patients is provided in the tables shown in
Preferably, the predetermined set of miRNAs for the diagnosis of multiple sclerosis comprises one or more nucleic acids selected from the deregulated miRNAs presented in the tables in
Thus, preferably the predetermined set of miRNAs for the diagnosis of MS comprises one or more nucleic acids selected from the 24 most deregulated miRNAs hsa-miR-145, hsa-miR-186, hsa-miR-664, hsa-miR-584, hsa-miR-20b, hsa-miR-223, hsa-miR-422a, hsa-miR-142-3p, hsa-let-7c, hsa-miR-151-3p, hsa-miR-491-5p, hsa-miR-942, hsa-miR-361-3p, hsa-miR-22*, hsa-miR-140-5p, hsa-miR-216a, hsa-miR-1275, hsa-miR-367, hsa-miR-146a, hsa-miR-598, hsa-miR-613, hsa-miR-18a*, hsa-miR-302b, hsa-miR-501-5p. Preferably, the predetermined set of miRNAs comprises at least 7, preferably at least 10, 15, 20 or all of the above-indicated nucleic acids. Most preferably, the predetermined set of miRNAs comprises those miRNAs that were most significantly deregulated: hsa-miR-145, hsa-miR-186, hsa-miR-664, hsa-miR-584, hsa-miR-20b, hsa-miR-223, hsa-miR-422a, hsa-miR-142-3p, hsa-let-7c.
In another embodiment, the predetermined set of miRNAs for the diagnosis of MS comprises at least one preferred signature 1-84 as shown in Table 1. It should be noted that preferred diagnostic sets may also comprise one or more miRNAs of the miRNAs disclosed in Table 1 and any combination of the miRNAs together with one or more further diagnostically relevant miRNA from
Another embodiment of the present invention is a kit for diagnosing a disease, comprising means for determining an expression profile of a predetermined set of miRNAs in a biological sample, in particular in a blood, plasma, and/or serum sample including whole blood, plasma, serum or fractions thereof, or in a sample comprising peripheral blood mononuclear cells, erythrocytes, leukocytes and/or thrombocytes. Preferably, one or more reference expression profiles or a relevant reference which may be a mathematical function or algorithm—which allows for the diagnosis of the disease—are also provided which show the expression profile of the same set of miRNAs in the same type of biological sample, in particular in a blood and/or serum sample, obtained from one or more healthy subjects. A comparison to said reference expression profile(s) or relevant reference incl. a mathematical function or algorithm allows for the diagnosis of the disease.
The kit is preferably a test kit for detecting a predetermined set of miRNAs in sample by nucleic acid hybridisation and optionally amplification such as PCR or RT-PCR. The kit preferably comprises probes and/or primers and enzymes and reagents, including also reagent for cDNA-synthesis from miRNAs prior to real-time PCR for detecting a predetermined set of miRNAs. Further, the kit may comprise enzymes and reagents, e.g. for cDNA synthesis from miRNAs prior to RT-PCR.
A preferred embodiment of the present invention is a kit for diagnosing multiple sclerosis, comprising means for determining the expression profile of one or more relevant miRNAs presented in the table in
In a preferred embodiment the kit comprises means for determining at least seven, preferably at least 10, 15, 20 or all of the indicated miRNAs. It is particularly preferred to include means for determining the 24, 20, 15, 10 or at least 7 first mentioned miRNAs in the order of their diagnostic significance as represented by their order in the table in
The means for determining a predetermined set of miRNAs may for example comprise a microarray comprising miRNA-specific oligonucleotide probes. In a preferred embodiment, the microarray comprises miRNA-specific oligonucleotide probes for one or more miRNAs oligonucleotide probes for one or more miRNAs. Depending on the intended use of the microarray in the diagnostic of a particular disease, probes for different miRNAs may be included.
A microarray intended for use in the diagnosis of multiple sclerosis preferably comprises miRNA specific oligonucleotide probes for one or more miRNAs presented in the table in
In a preferred embodiment the microarray comprises oligonucleotide probes for determining at least 7, preferably at least 10, 15, 20 or all of the indicated miRNAs. It is particularly preferred to include oligonucleotide probes for determining the most significant miRNAs, which is represented by their order in the table depicted in
The microarray can comprise oligonucleotide probes obtained from known or predicted miRNA sequences. The array may contain different oligonucleotide probes for each miRNA, for example one containing the active mature sequence and another being specific for the precursor of the miRNA. The array may also contain controls such as one or more sequences differing from the human orthologs by only a few bases, which can serve as controls for hybridization stringency conditions. It is also possible to include viral miRNAs or putative miRNAs as predicted from bioinformatic tools. Further, it is possible to include appropriate controls for non-specific hybridization on the microarray.
The invention also relates to sets of oligo- or polynucleotides for diagnosing multiple sclerosis comprising the sequences of at least 7, preferably at least 10, 15, 20 or all of the indicated mIRNAs, and/or the complement of such sequences. It is particularly preferred to include oligo- or polynucleotides for detecting the most significant miRNAs, which are represented by their order in the table depicted in
Another embodiment of the present invention relates to a method for the assessment of a clinical condition related to multiple sclerosis of a patient.
Recent developments have shown that there is a tendency towards smaller sets of biomarkers for the detection of diseases. However, for single biomarkers and small biomarker sets, there is only a basic understanding whether these biomarkers are specific for only the single diseases or whether they occur in any other disease.
Therefore, the present inventors developed a novel class of diagnostic tests improving the current test scenarios. The inventors found out that a variety of diseases are correlated with a specific expression profile of miRNAs. In case a patient is affected by a particular disease, several miRNAs are present in larger amounts compared to a healthy normal control, whereas the amount of other miRNAs is decreased. Interestingly, the amount of some miRNAs is deregulated, i.e. increased or decreased, in more than one disease. The miRNA profile for a particular disease therefore shows conformity with the miRNA profile of other diseases in regard of individual miRNAs while other miRNAs show significant differences. If the expression profile of a large variety of miRNAs in a biological sample of a patient is measured, the comparison of the expression profile with a variety of reference expression profiles which are each characteristic for different diseases makes it possible to obtain information about the clinical condition of a certain patient and to determine, which disease(s) is/are present in said patient.
A further subject matter of the invention is a method for the assessment of a clinical condition related to multiple sclerosis of a patient comprising the steps
The inventors found out that the above method for the assessment of a clinical condition makes it possible to carry out an integrative diagnosis of a wide variety of diseases, particularly including multiple sclerosis. Comparing a miRNA profile obtained from a biological sample of a patient whose clinical condition is not known with a plurality of reference profiles characteristic for different diseases enables the diagnosis of a wide variety of diseases with high specificity and sensitivity.
A “biological sample” in terms of the invention means a sample of biological tissue or fluid as described hereinabove. Examples of biological samples are sections of tissues, blood, blood fractions, plasma, serum, urine or samples from other peripheral sources.
The set of miRNAs determined in step (d) preferably includes a large number of different miRNAs. It is particularly preferred to use at least 10, 20, 30, 50, preferably at least 100, 200, 500 or 1,000 miRNAs. Most preferably, all known miRNAs are included in the set of miRNAs determined in step (b) Such a complex set of miRNA-biomarkers enables a diagnosis with higher specificity and sensitivity compared to single biomarkers or sets of only a few dozens of such markers.
The determination of the set of miRNAs can be done as described herein above. Preferably, the determination is done on an experimental platform which shows a high degree of automation to minimize experimental variations, measure results time- and cost-efficiently, measures results highly reproduceably and be able for measuring more than one sample at once in order to ensure a high throughput.
Step (c) preferably includes a comparison of the miRNA profile measured for a patient with a large number of different reference profiles to provide information about the presence of as many different diseases as possible. The reference expression profiles may be laid down in a database, e.g. an Internet database, a centralized or a decentralized database. The reference profiles do not necessarily have to include information about all miRNAs included in step (b), which are determined in the sample of the patient. It is, according to the invention, sufficient if the reference profile provides information on those miRNAs which are altered to a large extent compared to the condition of a healthy individual in case of the presence of a disease. Alternatively, the said relevant reference may be a mathematical function or algorithm.
Preferably, an miRNA reference profile or the relevant reference according to the invention provides information on miRNA expression characteristic for a particular disease in the same type of biological sample as used in step (b) for determining a predetermined set of miRNAs in a sample from a patient. This means that, if a patient with an unknown disease is to be classified with the analysis of a blood sample, the comparison is preferably made with miRNA reference expression profiles, which do also relate to the miRNA expression pattern in a blood sample.
The reference profiles or the relevant reference characteristic for particular diseases provide information on one or more miRNAs, which are, in case of the disease, highly deregulated, for example strongly increased or decreased, as compared to a healthy condition. It is not necessary for the reference profiles to provide information about all miRNAs included in the set of biomarkers determined in step (b). However, the more miRNAs are included in the reference profile or relevant reference, the more precise the diagnosis will be. If, for example, a reference profile for lung cancer is included, it is preferred to include the characteristic miRNAs for lung cancer. Equivalently, it is preferred to include into a reference profile for multiple sclerosis the characteristic miRNAs for multiple sclerosis as described hereinabove as well.
Another embodiment of this aspect of the invention is a kit for the assessment of a clinical condition related to multiple sclerosis of a patient comprising
(a) means for determining a predetermined set of miRNAs in a biological sample from a patient, and
(b) a plurality of miRNA reference expression profiles characteristic for different diseases or a mathematical function that allows for the diagnosis on the basis of the data derived from the miRNA expression profiles of a patient.
The set of miRNAs to be determined in a biological sample from a patient preferably includes a large number of different miRNAs. It is particularly preferred to include all known miRNAs in the set of miRNAs to be determined. In each case, said predetermined set of miRNAs should include those miRNAs for which information is provided in the reference profiles characteristic for particular diseases. It is understood that only in case the set of miRNAs determined in a biological sample from a patient comprises those miRNAs included in the reference profile/reference for a disease, a diagnosis regarding this particular disease can be provided or otherwise the diagnosis may be less informative.
The assessment of a clinical condition of a patient according to the invention is suitable for diagnosing any diseases which are correlated with a characteristic miRNA profile. Accordingly, the kit for the assessment of a clinical condition preferably includes reference profiles/references for a plurality of diseases that are correlated with a characteristic miRNA profile. It is understood that all miRNAs that are significantly deregulated in the disease states for which reference profiles are provided should be included in the set of miRNAs to be determined in a biological sample from a patient. If the kit for the assessment of a clinical condition of a patient should provide information regarding, e.g. lung cancer or multiple sclerosis, a reference profile should be available providing information about the significantly deregulated miRNAs compared to a normal or any other relevant control individual or any other relevant control individual(s). A kit for the assessment of a clinical condition shall provide information on the presence of multiple sclerosis, a reference profile characteristic for multiple sclerosis should be included. Said reference profile preferably includes information on those miRNAs that are most significantly deregulated in the case of MS. The relevant miRNAs are as disclosed hereinabove.
The invention will now be illustrated by the following figures and the non-limiting experimental examples.
Scheme of a miRNA hybridization assay for use in the invention.
miRNA capture probes consist of 1 miRNA probe sequence stretch that is linked to support via 3′-end or alternatively by 5′-end (not depicted here)
the miRNA probe sequence stretches are complementary to miRNA target sequences
each miRNA capture probe can bind 1 miRNA target sequences
the miRNA target sequences are labeled prior to hybridisation (e.g, by biotin labeling)
Scheme of an miRNA tandem hybridization assay for use in the invention
miRNA capture probes consist of 2 DNA-based miRNA probe sequence stretches that are linked to each other by a spacer element
the miRNA probe sequence stretches are complementary to miRNA target sequences
each miRNA capture probe can bind 2 miRNA target sequences
the spacer sequence consists of 0-8 nucleotides the miRNA target sequences are labeled prior to hybridisation (e.g. by biotin labeling)
miRNA RAKE-Assay for use in the invention (PT Nelson et al., Nature Methods, 2004, 1(2), 1)
the miRNA capture probes consist of one miRNA probe sequence stretch (green) and one elongation element (orange)
probes are oriented 5′→3′, presenting a free terminal 3′-OH
the miRNA probe sequence stretch (preen) is complementary to miRNA target sequences (dark green)
the elongation sequences (orange) can be freely chosen and is typically between 1-12 nucleotides long, preferably a homomeric sequence
each miRNA capture probe can bind 1 miRNA target sequence
the miRNA target sequences are NOT labeled prior to hybridisation
Labeling occurs after hybridisation during elongation by polymerase extension reaction
Biochip is not reusable due to exonuclease treatment
miRNA MPEA-Assay for use in the invention (Vorwerk S. et al., Microfluidic-based enzymatic on-chip labeling of miRNAs, N. Biotechnol. 2008; 25(2-3):142-9. Epub 2008 Aug. 20)
the miRNA capture probes consist of one miRNA probe sequence stretch (green) and one elongation element (orange)
probes are oriented 3′→5′, presenting a free terminal 5′-OH the miRNA probe sequence stretch (green) is complementary to miRNA target sequences (dark green)
the elongation sequences (orange) can be freely chosen and is typically between 1-12 nucleotides long, preferably a homomeric sequence
each miRNA capture probe can bind 1 miRNA target sequences
the miRNA target sequences are NOT labeled prior to hybridisation
Labeling occurs after hybridisation during elongation by polymerase extension reaction
Biochip is reusable after removal of target/elongated target
miRNA capture probe design (design MPEA/RAKE)
Depicted is the design of a capture probe for the exemplary miRNA human mature miRNA let-7a for use in the various types of hybridization assays shown in
Spacer Element.
Capture probes for use in e.g. a tandem hybridization assay as shown in
Elongation element (Design Probe MPEA/RAKE)
A capture probe, e.g. for use in a RAKE or MPEA assay as shown in
Pearson Correlation Coefficient depending on the number of elongated nucleotides in capture probes in an MPEA assay.
Diagram describing the general approach for determining miRNA signatures for use as biomarkers in disease diagnosis.
Overview of all miRNAs that are found to be differentially regulated in blood samples of MS patients, grouped according to their diagnostic information represented by the respective area under the curve (AUC) value in receiver-operator characteristic curves. The first 193 entries represent miRNAs with t-test p-values<0.05.
Overview of all miRNAs that are found to be differentially regulated in blood samples of MS patients, grouped according to their diagnostic information represented by the t-test significance. The first 165 entries represent miRNAs with t-test p-values<0.05. The grouping is based on additional information derived from further patients (compared to
A further list of 308 entries representing miRNAs with t-test p-values<0.05. The grouping is based on additional information derived from further patients (compared to
Histogram plots of the logarithm of fold quotions, the raw t-test p-values and the adjusted p-values. The histogram plots show in the upper part a histogram of logarithmized fold changes, detailing a manifold up-regulated miRNAs in Multiple Sclerosis compared to healthy subjects. The middle and lower part of the Figure describe raw significance values and adjusted significance values providing evidence for a wide variety of deregulated miRNAs that are well suited for MS detection.
This Figure presents for two miRNAs, namely miR-145 and miR-186, the intensity values for all MS (left part) and control (right part) samples. Both miRNAs show a significant up-regulation in MS.
The Box-plots denote the accuracy, specificity and sensitivity of the diagnostic test of the invention. In comparison, random classification results are shown, providing evidence for a decreased classification accuracy of about 50% (corresponding to random guessing). Furthermore, the graphic shows that the true classification scenario is more stable while the random classifications entail high variances.
This graph illustrates a disease network containing nodes for each disease as blue-colored rhombs (lung cancer, multiple sclerosis, pancreatic cancer, melanoma and Wilm tumor). Additionally, it contains differentially colored and sized nodes, representing biomarker sets. The size of these nodes represents the number of biomarkers inside the set (additionally the number of biomarkers is given inside the corresponding circles). The color represents the information on the number of diseases that are significant for the biomarkers in the set. The nodes are connected to the respective diseases, e.g., each green colored node contains biomarkers, significant for two diseases and thus each green node is connected to two disease nodes. (blue=significant to one disease, rose=significant for 3 diseases, purple=significant to 5 diseases).
The bar graphs in
1.1 Materials and Methods
1.1.1 Samples
Blood samples were obtained with patients' informed consent.
1.1.2 miRNA Microarray Screening
Blood of MS patients and volunteers without known disease was extracted in PAXgene Blood RNA tubes (BD, Franklin Lakes, N.J. USA). For each blood donor, 5 ml of peripheral blood were obtained. Total RNA was extracted from blood cells using the miRNeasy Mini Kit (Qiagen GmbH, Hilden, Germany) and the RNA has been stored at −70° C. Samples were analyzed with the Geniom Realtime Analyzer (GRTA, febit GmbH, Heidelberg, Germany) using the Geniom Biochip miRNA homo sapiens. Each array contains 7 replicates of 866 miRNAs and miRNA star sequences as annotated in the Sanger mirBase 12.0. Sample labelling with Biotine has been carried out by multifluidic-based enzymatic on-chip labelling of miRNAs (MPEA).
Following hybridization for 16 hours at 42° C. the biochip was washed automatically and a program for signal enhancement was processed with the GRTA. The resulting detection pictures were evaluated using the Geniom Wizard Software. For each array, the median signal intensity was extracted from the raw data file such that for each miRNA seven intensity values have been calculated corresponding to each replicate copy of mirBase on the array. Following background correction, the seven replicate intensity values of each miRNA were summarized by their median value. To normalize the data across different arrays, quantile normalization was applied and all further analyses were carried out using the normalized and background subtracted intensity values.
1.1.3 Statistical Analysis
After having verified the normal distribution of the measured data, a parametric t-test (unpaired, two-tailed) was carried out for each miRNA separately, to detect miRNAs that show a different behavior in different groups of blood donors. The resulting p-values were adjusted for multiple testing by Benjamini-Hochberg adjustment.
To find relations of the detected miRNAs to other diseases the Human miRNA Disease Database was used. In more detail, a bipartite network was built where nodes correspond either to a miRNA or to a diseases. Only edges between miRNA and diseases nodes are allowed, where an edge between miRNA A and disease B means that the miRNA A is differentially regulated in disease B. Since for MS no deregulated miRNAs are known the node “MultipleSclerosis” was added to this network and linked to all miRNAs that were significant in the analysis.
In addition to the single biomarker analysis and network analysis, classification of samples using miRNA patterns was carried out using Support Vector Machines (SVM,) as implemented in the R e1071 package. In detail, different kernel (linear, polynomial, sigmoid, radial basis function) Support Vector Machines were evaluated, where the cost parameter was sampled from 0.01 to 10 in decimal powers. The measured miRNA profiles were classified using 100 repetitions of standard 10-fold cross-validation. As a subset selection technique we applied a filter approach based on t-test. In detail, the s miRNAs with lowest p-values were computed on the training set in each fold of the cross validation, where s was sampled from 1 to 866. The respective subset was used to train the SVM and to carry out the prediction of the test samples. As result, the mean accuracy, specificity, and sensitivity were calculated together with the 95% Confidence Intervals (95% CI) for each subset size. To check for overtraining permutation tests were applied. Here the class labels were sampled randomly and classifications were carried out using the permuted class labels. All statistical analyzes were performed using R.
1.2 Results
1.2.1 miRNA Experiments
The expression of 866 miRNAs and miRNA star sequences was analyzed in blood cells of 22 patients with MS. As a control blood cells of 22 volunteers without known disease were used.
Following RNA isolation and the novel on-chip labeling technique, the miRNA expression profiles were measured by the Geniom Bioship miRNA homo sapiens in the GRTA (febit GmbH, Heidelberg). Following intensity value computation and quantile normalization of the miRNA profiles, a mean correlation value of 0.97 for technical replicates was determined by using purchased total RNA from Ambion (four heart and four liver replicates). For the biological replicates the different tumor samples were compared between each other and the different normal samples were compared between each other. The biological replicates showed a mean correlation of 0.87 and a variance of 0.009.
1.2.2 Ruling Out the Influence of Age and Gender
To cross-check that age and gender do not have an influence on our analysis, t-tests for the normal samples were computed. In the case of males versus females there were no statistically significant deregulated miRNA. The most significant miRNA, hsa-miR-423, showed an adjusted significance level of 0.78.
To test for the influence of donor age the profiles obtained from samples obtained from the oldest versus youngest patients were compared by splitting the group in half based on age. Here, the most significant miRNA, miR-890, obtained an adjusted p-value of 0.87. As for gender, there were no deregulated miRNAs, thus providing evidence that age and gender do not have a substantial influence on the miRNA profiles.
Additionally, we checked the influence of a therapy. Patients were either treated with glatiramer acetate (n=9), or interferon-β (n=10), or did not get a therapy (n=1). We compared the group of patients treated with glatiramer acetate to the group treated with interferon-β. As for the gender and the age we did not find any significant miRNA.
1.2.3 Single Deregulated miRNAs
Hypothesis testing was applied to identify miRNAs deregulated in the blood cells of MS patients as compared to the blood cells of the controls. Following verification of an approximately normal distribution, two-tailed unpaired t-tests were performed for each miRNA. The respective p-values were adjusted for multiple testing by the Benjamini-Hochberg approach. In total 193 miRNAs significantly deregulated in blood cells of MS patients as compared to the controls were detected. Histogram plots of the logarithm of fold quotients, the raw t-test p-values and the adjusted p-values are presented in
Notably, all the above-mentioned miRNAs showed a significant up-regulation in MS besides miR-20b. Table 2 shows the 24 most deregulated miRNAs. Of these 91.7% were up-regulated in MS while 8.3% were down-regulated, providing evidence for an overall up-regulation of miRNAs in MS.
Additionally for the best miRNAs receiver operator characteristic curves (ROC) and the area under the curve value (AUC) were computed. The higher the AUC, the better the miRNA biomarker is, where a maximal value of 1 for miRNA A would mean that the highest control reactivity would be lower than the lowest MS intensity of miRNA A. For the best miRNA hsa-miR-145 an AUC value of 0.96 was obtained and four of the 44 samples were wrong classified (2 Ms sera as controls, so-called False Negatives, and 2 controls classified as MS samples, so-called False Positives).
1.2.4 Relation to Other Diseases
Since there is no evidence for de-regulated miRNAs in MS patients in the literature, it was checked whether the detected 193 miRNAs are already related to other human diseases. To this end, the Human microRNA Disease Database (HMDD) was grasped. This comprehensive database contains for over 100 human diseases information on deregulated miRNAs. Altogether, over 2000 relations are included in the HMDD. To analyze the respective data, a bipartite graph was created were nodes are either miRNAs or human diseases, and edges between a miRNA and a disease mean that the respective miRNA is deregulated in the respective disease.
Thereby, a network containing 452 nodes was created, 137 belonging to diseases and 315 to miRNAs. The network also contained 1617 unique edges (some relations between miRNAs and diseases have been published in multiple papers). As mentioned previously, MS is not included as disease in this network. Thus, the network was modified as followings: a disease node “MultipleSclerosis” was added and edges between this node and all significant miRNAs were created. Additionally, all disease nodes that are not linked to any MS miRNA and all miRNAs belonging only to removed disease nodes were removed. The novel network thus contains only those miRNAs that are significant in MS and other diseases and those that are significant in MS, only. This shrunken network contained 77 disease nodes together with the 193 significant miRNAs. Remarkably, only 43 of the 193 (22%) miRNAs were related to a disease other than MS while the remaining 78% miRNAs were only connected to MS. Of these 146 miRNAs, 36 were so-called star sequences.
Altogether, these results provide strong evidence that the detected complex miRNA profile is not disease specific but rather specific for MS.
1.2.5 Evaluating Complex Fingerprints
As discussed in Section 1.2.3, the best miRNA suffices to classify 20 of 22 MS samples and 20 of 22 control samples correctly. This obviously corresponds to a high specificity, sensitivity and accuracy of 90.8%. However, these results are not validated by a re-sampling technique as bootstrapping or cross-validation and are based only on a single marker. In order to improve the already high classification accuracy and the statistical reliability the predictive power of multiple miRNAs was combined by using statistical learning techniques. In detail, Support Vector Machines with different kernels (linear, polynomial, sigmoid, radial basis function) were applied to the data and a hypothesis test based subset selection was carried out as described in Material and Methods. To gain statistical significance 100 repetitions of 10-fold cross validation were carried out. Likewise, 100 repetitions for the permutation tests were computed where samples with randomly assigned class labels were investigated.
The best results were obtained with radial basis function Support Vector Machines and a subset of 24 miRNAs (see Table 2). These miRNAs allowed for the discrimination between blood samples of MS patients and blood samples of controls with an accuracy of 95.5% a specificity of 95.5%, and a sensitivity of 95.5%.
The permutation tests showed significantly decreased accuracy, specificity, and sensitivity rates, as detailed in
Additionally, it was checked whether the relevant miRNAs were linked to one of over 100 other diseases as annotated in the HMDD. Remarkable over 80% of the respective miRNAs have not been linked to other diseases, so far.
For the molecular clinical thermometer, an arbitrary machine learning (feature extraction/classification/regression/clustering) technique can be applied. The workflow does not depend on the applied method that can be seen as a black box.
First, a sophisticated large set of samples for the diseases to be investigated has to be measured using a larger amount of biomarkers. This set, consisting of a p×n matrix where n is the number of samples and p the number of biomarkers, is commonly denoted as training data set.
Now, a combination of feature extraction and supervised learning techniques (the process can be also carried out with slight modifications using unsupervised techniques) is applied to generate a statistical model, which describes the training data well. Here, it is essential to control the model complexity in order to avoid so-called overtraining of the statistical models. Although, in general, multi-class cases can be carried out, we focus on two class comparisons, i.e., normal versus cancer 1, normal versus cancer 2, cancer 1 versus cancer 2.
Given the trained models and a new biomarker profile, the statistical model can be used to compute the probability for each class and this new sample. Only one example are support vector machines, where the distance of a sample to the seperating hyperplane can be used to estimate the class probability via a regression approach. The specificity and sensitivity can be trade-off by shifting the probability threshold (which usually should be 0.5 or 50%).
The probabilities in the previously described step can be used to generate so-called disease probability plots (DPP). These plots contain for each class and a single sample the probabilities to belong to a certain class. In detail, each class is described by a colored line of length 100 (representing a percentage range), where the lower rate is colored green (representing small probabilities) and the higher range red (higher probabilities). For each class, an arrow marks the probability for the patient and the respective disease. For class “normal” the minimal and maximal probability to be normal are shown.
The DPPs thus allow for visualizing the complex statistical evaluation in a simple and well interpretable way.
| Number | Date | Country | Kind |
|---|---|---|---|
| 09015668 | Dec 2009 | EP | regional |
This application is a 35 U.S.C. 371 National Phase Entry Application from PCT/EP2010/057943, filed Jun. 7, 2010, which claims the benefit of U.S. Provisional Applications Nos. 61/184,452 filed Jun. 5, 2009, 61/213,971 filed Aug. 3, 2009, 61/287,521 filed Dec. 17, 2009 and European Patent Application No. 09015668.8 filed on Dec. 17, 2009, the disclosures of which are incorporated herein in their entirety by reference.
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| PCT/EP2010/057943 | 6/7/2010 | WO | 00 | 2/28/2012 |
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| WO2010/139811 | 12/9/2010 | WO | A |
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| 20020172968 | Liu et al. | Nov 2002 | A1 |
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| 20090131356 | Bader et al. | May 2009 | A1 |
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| 2327800 | Jun 2011 | EP |
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