Patent Application
20210278413
The present invention relates to an evaluation method for genomic abnormalities in cells, and more specifically, to a simple, rapid and non-invasive evaluation method for genomic abnormalities in cells without requiring expertise in the evaluation.
Pluripotent stem cells such as iPS cells and ES cells can differentiate into any cell types constituting the body, and are attracting a great deal of attention as a cell supply source for regenerative medicine. In order to use these cells for regenerative medicine, it is necessary to culture a large amount of iPS cells and ES cells. On the other hand, it is known that repeated division of these cells increases the risk of genomic abnormalities [chromosome numerical abnormalities, chromosome morphological abnormalities (abnormalities in which a part of a chromosome moves to another chromosome, and abnormalities in which the orientation of a part of a chromosome is reversed)] (Non-Patent Literature 1 and 2). Since cells with genomic abnormalities are more likely to cause canceration, it is necessary to check whether these genomic abnormalities occur before cell transplantation.
As a method of analyzing chromosomes, a method in which, after a certain number of cells are cultured, division is stopped with a colcemid solution, the cells are treated with a hypotonic solution, and then fixed with methanol/acetic acid, and then a specimen is prepared on a slide glass, a Giemsa staining or G band/Q band treatment is performed, and observation under a microscope is then performed is general. Refer to Non-Patent Literature 3 (the Japanese Association for Chromosome and Gene Analysis Vol. 32 No. 1 2014, pp 60-89).
In JP2010-508815 (WO2008/066655), a method in which components in a culture medium when oocytes are cultured for fertilization and implantation are analyzed, and chromosome abnormalities are diagnosed is disclosed. In this literature, target cells are oocytes, and there is no disclosure for pluripotent stem cells.
The chromosome analysis method disclosed in Non-Patent Literature 3 requires expertise for evaluation because procedures including a pretreatment operation are complicated and also visual observation under a microscope is necessary. Therefore, analysis and evaluation by outsourcing are general. In this case, several weeks to several months are required to obtain analysis results.
In addition, in all of the above analysis methods, it is necessary to perform invasive treatment on cells. Therefore, after chromosomes are analyzed, it is not possible to use the cells used for the evaluation for another purpose, for example, as a cell source for regenerative medicine.
An objective of the present invention is to provide a simple, rapid and non-invasive evaluation method for genomic abnormalities in cells without requiring expertise in the evaluation.
The inventors conducted extensive studies, and as a result, completed the present invention by finding that it is possible to evaluate genomic abnormalities in cells based on the abundance of a specific indicator in a culture supernatant.
The present invention includes the following inventions.
(1) An evaluation method for genomic abnormalities, wherein is evaluated whether test cells have genomic abnormalities using pluripotent stem cells cultured in a culture medium or cells induced to differentiate from pluripotent stem cells as the test cells, the method including: a step of measuring an abundance of an indicator in a culture supernatant of test cells; and a step of evaluating whether the test cells have genomic abnormalities based on the abundance of the indicator, wherein the indicator is at least one selected from the group consisting of deoxycytidine, kynurenine, putrescine, alanine, cysteine, cystathionine, and threonic acid, and wherein it is evaluated whether the test cells have genomic abnormalities based on the abundance of the at least one indicator.
(2) The evaluation method for genomic abnormalities according to (1), further including a step of measuring an abundance of the indicator in a culture supernatant of control cells known to have normal chromosomes, wherein, for the at least one indicator, it is evaluated whether the test cells have genomic abnormalities by comparing the abundance of the indicator in the culture supernatant of the test cells with the abundance of the indicator in the culture supernatant of the control cells.
(3) The evaluation method for genomic abnormalities according to (2), wherein, for the at least one indicator, based on determination of whether the ratio of the abundance of the indicator in the culture supernatant of the test cells to the abundance of the indicator in the culture supernatant of the control cells is at a predetermined threshold value or more, or at the predetermined threshold value or less, it is evaluated whether the test cells have genomic abnormalities.
(4) The evaluation method for genomic abnormalities according to (3), wherein, when the indicator is deoxycytidine, kynurenine, putrescine, cystathionine, or threonic acid, it is evaluated whether the test cells have genomic abnormalities based on determination of whether the ratio is at the predetermined threshold value or less.
(5) The evaluation method for genomic abnormalities according to claim 3, wherein, when the indicator is alanine or cysteine, it is evaluated whether the test cells have genomic abnormalities based on determination of whether the ratio is at the predetermined threshold value or more.
(6) The evaluation method for genomic abnormalities according to any one of (1) to (4), wherein among the indicators, at least one selected from the group consisting of putrescine, deoxycytidine, and kynurenine is selected as the indicator.
(7) The evaluation method for genomic abnormalities according to any one of (1) to (6), wherein among the indicators, two or more indicators are selected.
(8) The evaluation method for genomic abnormalities according to any one of (1) to (7), wherein it is evaluated whether there are abnormalities on the 18th chromosome.
(9) The evaluation method for genomic abnormalities according to any one of (1) to (8), wherein the abundance of the indicator in the culture supernatant is evaluated by liquid chromatography-mass spectrometry (LC-MS).
A cell culture method including a process of selecting the test cells based on the results of evaluating genomic abnormalities by the method according to any one of (1) to (9).
In the evaluation method for genomic abnormalities of the present invention, pluripotent stem cells cultured in a culture medium or cells induced to differentiate from pluripotent stem cells are used as the test cells. However, without being limited to pluripotent stem cells, the method can also be applied to general cells cultured in a culture medium. The pluripotent stem cells include embryonic stem cells (ES cells), induced pluripotent stem cells (iPS cells), and the like.
In the present invention, the abundance of the indicator in the culture supernatant may be measured using any method. Representative methods include, for example, a gas chromatographic analysis method (GC), a liquid chromatographic analysis method (LC), mass spectrometry (MS), liquid chromatography-mass spectrometry (LC-MS), and gas chromatography-mass spectrometry (GC-MS).
According to the present invention, since it is only necessary to collect the culture supernatant for analyzing chromosomes of cells, it is possible to obtain analysis results in a short time without requiring complicated pretreatment as in the related art. In addition, since it is not necessary to perform invasive treatment on cells as in the related art, it is possible to use test cells as a cell source for regenerative medicine or the like after chromosomes are analyzed.
That is, according to the present invention, as in the related art, visual chromosome observation using a microscope is not necessary, and expertise for visual chromosome observation is not necessary. In addition, the evaluation procedure is simple and it is possible to evaluate genomic abnormalities rapidly.
An evaluation method for genomic abnormalities of the present invention is an evaluation method for genomic abnormalities in which it is evaluated whether test cells have genomic abnormalities using pluripotent stem cells cultured in a culture medium or cells induced to differentiate from pluripotent stem cells as the test cells, including a step of measuring an abundance of an indicator in a culture supernatant of test cells; and a step of evaluating whether the test cells have genomic abnormalities based on the abundance of the indicator. The indicator, that is, a biomarker, is at least one selected from the group consisting of deoxycytidine, kynurenine, putrescine, alanine, cysteine, cystathionine, and threonic acid. In the evaluation step, it is evaluated whether the test cells have genomic abnormalities based on the abundance of the at least one indicator.
In the present invention, the test cells are pluripotent stem cells cultured in a culture medium or cells induced to differentiate from pluripotent stem cells. The pluripotent stem cells include embryonic stem cells (ES cells) induced pluripotent stem cells (iPS cells), and the like. Such pluripotent stem cells are repeatedly divided while being cultured in a culture medium and a risk of genomic abnormalities [chromosome numerical abnormalities, chromosome morphological abnormalities (abnormalities in which a part of a chromosome moves to another chromosome, and abnormalities in which the orientation of a part of a chromosome is reversed)] increases. Therefore, it is necessary to check whether cells have genomic abnormalities.
In a preferable aspect of the present invention, the evaluation method for genomic abnormalities further includes a step of measuring an abundance of an indicator in a culture supernatant of control cells known to have normal chromosomes. In this aspect, in the evaluation step, for the at least one indicator, it is evaluated whether the test cells have genomic abnormalities by comparing the abundance of the indicator in the culture supernatant of the test cells with the abundance of the corresponding indicator in the culture supernatant of the control cells.
In still another aspect of the present invention, in the evaluation method for genomic abnormalities, in place of a step of measuring an abundance of an indicator in a culture supernatant of control cells known to have normal chromosomes, abundances of indicators in a culture supernatant of control cells known to have normal chromosomes may be registered in a library in advance, and the abundance of an indicator in a culture supernatant of control cells based on this library prepared in advance may be used. In this case, the culture conditions for the test cells need to be the same as or similar to the culture conditions used for preparing the library.
Regarding a culture medium used for culturing test cells and culturing control cells, a culture medium generally used for culturing stem cells, for example, DMEM/F12 or a culture medium containing DMEM/F12 as a main component (for example, mTeSR1, TeSR-E8, and Essential-8) can be used. Table 1 shows components constituting DMEM/F12.
In the present invention, the indicator is at least one selected from the group consisting of deoxycytidine, kynurenine, putrescine, alanine, cysteine, cystathionine, and threonic acid.
Among these indicators, amounts of deoxycytidine, kynurenine, putrescine, cystathionine or threonic acid tend to decrease when the test cells have genomic abnormalities compared with normal cells having no genomic abnormalities. On the other hand, among these indicators, amounts of alanine or cysteine tend to increase when the test cells have genomic abnormalities compared with normal cells having no genomic abnormalities.
In a preferable aspect of the present invention, in the evaluation method for genomic abnormalities, for the at least one indicator, based on determination of whether the ratio of the abundance of the indicator in the culture supernatant of the test cells to the abundance of the indicator in the culture supernatant of the control cells is at a predetermined threshold value or more, or at the predetermined threshold value or less, it is evaluated whether the test cells have genomic abnormalities.
Ratio=(abundance of the indicator in the culture supernatant of the test cells)/(abundance of the indicator in the culture supernatant of the control cells).
If the indicator is deoxycytidine, kynurenine, putrescine, cystathionine, or threonic acid, when the test cells have genomic abnormalities, the amount of the indicator tends to decrease compared with normal cells having no genomic abnormalities. Therefore, based on determination of whether the ratio is at the predetermined threshold value or less, it is possible to evaluate whether the test cells have genomic abnormalities.
If the indicator is alanine or cysteine, when the test cells have genomic abnormalities, the amount of the indicator tends to increase compared with normal cells having no genomic abnormalities. Therefore, based on determination of whether the ratio is at the predetermined threshold value or more, it is possible to evaluate whether the test cells have genomic abnormalities.
In these aspects, the threshold value can be determined by those skilled in the art in advance. The threshold value may vary depending on test cell lines to be cultured.
In the present invention, in order to allow a significant difference in the abundance between normal cells having no genomic abnormalities and cells having genomic abnormalities to be ascertained, it is recommended to select at least one selected from the group consisting of putrescine, deoxycytidine, and kynurenine among these indicators as an indicator.
In addition, in the present invention, among the indicators, it is preferable to select two or more of these indicators. In this case, when it is evaluated whether test cells have genomic abnormalities based on the abundance of two or more indicators, it is possible to perform evaluation more accurately.
In the present invention, particularly it is possible to evaluate whether there are abnormalities on the 18th chromosome.
In addition, in another aspect of the present invention, in place of cells known to have normal chromosomes, cells known to have certain atypical chromosomes may be used as control cells. In this aspect, this evaluation method for genomic abnormalities may further include a step of measuring an abundance of an indicator in a culture supernatant of control cells known to have certain atypical chromosomes. Alternatively, abundances of indicators in a culture supernatant of control cells known to have certain atypical chromosomes may be registered in a library in advance, and the abundance of an indicator in a culture supernatant of control cells based on this library prepared in advance may be used. In this case, the culture conditions for the test cells need to be the same as or similar to the culture conditions used for preparing the library.
Then, when cells known to have certain atypical chromosomes are used as control cells, in the evaluation step, for the at least one indicator, it is evaluated whether the test cells have genomic abnormalities by comparing the abundance of the indicator in the culture supernatant of the test cells with the abundance of the corresponding indicator in the culture supernatant of the control cells. That is, if the abundance of the indicator in the test cells is similar to the abundance of the corresponding indicator in the control cells, it can be determined that the test cells have the same specific abnormal chromosome as abnormal chromosomes of the control cells. If the abundance of the indicator in the test cells is different from the abundance of the corresponding indicator in the control cells, it can be determined that the test cells do not have the abnormal chromosomes of the control cells. In this case, it can be determined that the test cells have normal chromosomes or may have abnormal chromosomes different from the abnormal chromosomes of the control cells.
Regarding a method of measuring the abundance of the indicator in the culture supernatant, quantitative analysis using a gas chromatographic analysis instrument (GC), a liquid chromatographic analysis instrument (LC), or a mass spectrometer can be used, and particularly, quantitative analysis by liquid chromatography mass spectrometry (LC-MS) or gas chromatography-mass spectrometry (GC-MS) can be preferably used, but the method is not limited thereto. For example, a sample obtained by carrying out a predetermined pretreatment on a culture supernatant may be caused to flow through a column of a liquid chromatographic (LC) device together with an eluate, and the abundance of the indicator contained in the sample may be determined from results obtained by detecting components separated and eluted from the column with a detector such as an ultraviolet-visible spectroscopic detector or an infrared spectroscopic detector. In addition, a reagent that allows each of the indicators to specifically develop a color or emit light may be added to the culture supernatant, and the abundance of the indicator may be determined based on the intensity of color development or light emission.
Regarding the abundance of the indicator, in a gas chromatographic analysis method (GC), a liquid chromatographic analysis method (LC), gas chromatography-mass spectrometry (GC-MS), or liquid chromatography-mass spectrometry (LC-MS), a peak area value (area) of the indicator or a concentration of the indicator in the culture supernatant calculated from the peak area value (area) of the indicator can be used. Alternatively, “Area/Confluency,” and “Concentration/Confluency” corrected (standardized) with confluency of cells; and “Area/Cell Number,” and “Concentration/Cell Number” corrected with the number of cells (Cell Number, or Cell Count) may be used. When the value corrected (standardized) with the confluency of cells or the number of cells (Cell Number, or Cell Count) is used, even if there is a difference in the proliferation rates between control cells and test cells, it is possible to compare the peak area value (Area/Confluency) of the indicator or the concentration (Concentration/Confluency) of the indicator per cell number. Therefore, it is possible to perform comparison with high accuracy in which metabolisms of control cells and test cells are also taken into account, and it is possible to evaluate whether test cells have genomic abnormalities with higher accuracy.
While the present invention will be described with reference to the following examples, the present invention is not limited to the examples.
One example of evaluating whether there are genomic abnormalities in cells by the method of the present invention will be described.
In this example, four samples cultured from the same human iPS cells line [human iPS cells line samples having normal chromosomes (A, B, and C) and human iPS cells line sample having abnormalities on the 18th chromosome (D)] were used. That is, in this example, control cell samples A, B, and C from iPS cells lines having normal chromosomes and the test cell sample D from iPS cells lines having chromosomal abnormalities were used. Hereinafter, a procedure from cell culture to culture supernatant analysis in this example will be described.
The control cells were inoculated into 5 wells of a 6-well plate (well diameter of 35 mm) coated with Vitronectin-N (commercially available from Life Technologies) and cultured (in
The test cells were inoculated into 5 wells of a 6-well plate (well diameter of 35 mm) coated with Vitronectin-N (commercially available from Life Technologies) and cultured (in
20 μL of a 0.5 mM isopropylmalic acid aqueous solution was added as an internal standard to 50 μL of each of the samples, and 260 μL of methanol was additionally added to modify proteins contained in the sample. Proteins were removed by a filtration filter and the filtrate was collected.
After the samples subjected to the above pretreatment were frozen and dried and incubated in a pyridine solution containing methoxyamine hydrochloride, MSTFA
(N-methyl-N-trimethylsilyltrifluoroacetamide) was additionally added to the samples, and thus compounds in the samples were trimethylsilylated. Then, these derivatized samples were subjected to analysis by GC-MS. “Smart Metabolites Database” (commercially available from Shimadzu Corporation) was used for analysis of the analysis results. This database is a collection of data obtained by analyzing various compound reference materials subjected to the same derivatization treatment as above by GC-MS. Compound identification was performed using an index indicating whether a difference between the retention index (a value relative to the retention time) set in the database and the retention index of the derivatized compound in the sample was within ±5 and whether both quantitative ions and confirmed ions present in the database were detected in the derivatized compound in the sample. On the other hand, quantification of the compound was performed by a method of calculating an area of the mass chromatogram for characteristic ions for each derivatized compound in the sample according to conditions set in the database.
An appropriate amount of ultrapure water (Milli-Q (registered trademark) water, commercially available from Merck) was added to the samples subjected to the above pretreatment, dilution was performed, and the samples were analyzed by LC-MS. In the LC-MS analysis, compounds in the samples were temporally separated by gradient elution using a reverse phase separation column and then mass analysis was performed in a multiple reaction monitoring (MRM) mode. Analysis conditions in the MRM mode were set using a reference material for the compound. The compound was identified based on determination of whether the difference between the retention time of the reference material and the retention time of the compound in the sample was within ±0.1 minutes. In addition, the compound was quantified by a method of calculating an area of the mass chromatogram for characteristic ions for each compound in the sample.
Device used: ultra high-performance liquid chromatograph Nexera X2 series (commercially available from Shimadzu Corporation)
Column: Discovery HS F5-3* (2.1 mm I.D.×150 mmL, particle size: 3 μm, Sigma-Aldrich)
Device used: ultra-high speed triple quadrupole mass spectrometer LCMS-8060 (commercially available from Shimadzu Corporation)
In addition to the analysis by GC-MS and the analysis by LC-MS, analysis can also be performed by LC, and using the results, according to the same procedures as below, data analysis can be performed and genomic abnormalities can be evaluated.
The well was imaged on each culture day using Biostudio (commercially available from Nikon), and an area proportion of cells in the well was calculated as a cell coverage.
For the culture supernatant samples A, B, C, and D collected on each culture day, a value (area ratio) was calculated by dividing the quantitative value (area value) of each indicator compound (marker) determined by performing the above LC-MS analysis by the quantitative value (area value) of the internal standard. Then, for each of the control cells and the test cells, a value obtained by subtracting the area ratio of the control sample from the area ratio obtained from the results obtained by analyzing the culture supernatant collected from the 5 wells by LC-MS was calculated, and additionally, the corrected value corrected with a cell coverage was compared as an index value of the amount of substance produced or consumed by one cell during 24 hour-culture. Specifically, when the value obtained by subtracting the area ratio of the control sample from the area ratio determined for the control cells was set as [a], the value obtained by subtracting the area ratio of the control sample from the area ratio determined for the test cells was set as [b], the rate of increase in the cell coverage of target cells for every 24-hour culture was set as [c], and the rate of increase in the cell coverage of test cells for every 24-hour culture was set as [d], if confidence intervals of [a]/[c] and [b]/[d] did not overlap, it was determined that there was no significant difference in the amount of substance produced or consumed by one cell during 24-hour culture between the culture supernatant of the control cells and the culture supernatant of the test cells.
First, the results obtained from the area ratio are shown below.
Here, the control cells (sample C) and the test cells (sample D) had substantially the same cell proliferation rate in culturing, that is, the numbers of cells over time were substantially the same.
In
On the other hand, in
Next, the results obtained from a corrected value (Area ratio/Confluency) determined by correcting the value of the area ratio with the cell coverage (confluency) are shown below.
Here, as described above, in
In
On the other hand, in
A method of calculating a confidence interval of ΔArea ratio/ΔConfluency is as follows.
ΔArea ratio=(area ratio determined for control cells on the 3rd day)−(area ratio of control sample on the 3rd day)
ΔConfluency=(cell coverage determined for control cell on the 3rd day)−(cell coverage determined for control cells C on the 2nd day)
Here, for the normal control cells, the confidence interval was calculated using all the measured values of the target cells (samples A, B, and C).
Table 3 shows the 95% confidence interval for the indicators, and Table 4 shows the 90% confidence interval for the indicators.
In Table 3 and Table 4, when the value obtained by subtracting the area ratio of the control sample from the area ratio determined for the control cell samples A, B, and C was set as [a], the value obtained by subtracting the area ratio of the control sample from the area ratio determined for the test cells was set as [b], the rate of increase in the cell coverage of target cells for every 24-hour culture was set as [c], and the rate of increase in the cell coverage of test cells for every 24-hour culture was set as [d], if confidence intervals of [a]/[c] and [b]/[d] did not overlap, it was determined that there was a significant difference in the amount of substance produced or consumed by one cell during 24-hour culture between the culture supernatant of the control cells and the culture supernatant of the test cells. When such a determination was performed, more accurate determination was possible.
For the culture supernatant samples collected on each culture day, regarding the area value of each indicator compound (marker) determined by performing the above LC-MS analysis, from the LC-MS analysis results of the indicator compounds with known concentrations, the concentration value of each indicator compound was calculated by an external standard method. Then, for each of the control cell samples and test cell samples, a value (ΔConc) obtained by subtracting the concentration value of the control sample from the concentration value obtained from the results obtained by analyzing the culture supernatant collected from the 5 wells by LC-MS was calculated, and additionally, the corrected value (ΔConc/ΔConfluency) corrected with the amount of change in the cell coverage (ΔConfluency) was compared as an index value of the amount of substance produced or consumed by one cell during 24-hour culture.
ΔConc=(concentration value determined for culture supernatant sample on the 3rd day)−(concentration value of control sample on the 3rd day)
ΔConfluency=(cell coverage determined for culture supernatant sample on the 3rd day)−(cell coverage determined for culture supernatant sample on the 2nd day)
Here, for the normal control cell sample, the average value of ΔConc/ΔConfluency of the target cell samples A, B, and C was used.
Accordingly, even if comparison was performed not only with the area ratio but also the concentration ratio, similarly, the results in which there was a significant difference between normal cells and cells having abnormalities were obtained.
In the above example, a case in which cell lines A, B, and C were used as control cells and the cell lines D were used as test cells has been described. The present invention can also be applied to a case in which other cell lines are used as control cells and other cell lines are used as test cells. This will be understood by those skilled in the art that, according to the above example, the indicator (that is, the marker) can be used for determining genomic abnormalities. In addition, it can be clearly understood that the culture medium for cells is not limited to those used in the example, but various culture mediums can be used.
When a process of selecting the test cells is performed based on the results of evaluating genomic abnormalities by the method of the present invention, only normal cells can be continuously cultured in a non-invasive manner.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2018-115655 | Jun 2018 | JP | national |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/JP2019/023962 | 6/17/2019 | WO | 00 |
