Patent Application
20130052650
At least two biological dyes, termed a dye blend, that bound preferentially and non-specifically to double stranded DNA (dsDNA), exhibited higher fluorescence and lower inhibition of DNA polymerase than that exhibited by each dye alone, even when each dye alone was used at a higher concentration than the concentration of that dye in the dye blend. The dye blend increased the maximum fluorescence signal at the PCR endpoint, decreased the quantification cycle (Cq), and did so without compromising polymerase catalytic activity. That is, the dye blend enhanced PCR signal detection, improved PCR detection threshold, and reduced PCR inhibition. By overcoming single dye inhibition of DNA polymerase, the dye blend saturated dsDNA to a higher percentage, which is important for HRM analysis.
The dyes bound non-specifically to DNA in that they did not require a specific DNA sequence to bind to. The dyes bound preferentially to dsDNA over single stranded DNA (ssDNA). The dye blends were evaluated at various concentrations and under various conditions to determine performance in a quantitative polymerase chain reaction assay (qPCR, also referred to as real-time PCR (rt-PCR) or real-time quantitative PCR (rt-qPCR), and a high resolution melt (HRM) analysis, also referred to as a saturation binding profile.
The dye blend, in addition to utility in qPCR and/or HRM assays, was applicable in other assays using fluorescent DNA binding dyes, including but not limited to gel electrophoresis, DNA quantification, cell staining, etc.
The patent or application file contains at least one drawing executed in color. Copies of this patent or patent application publication with color drawing(s) will be provided by the Office upon request and payment of the necessary fee.
One embodiment is a polymerase chain reaction assay and/or a high resolution melting assay containing a fluorescent complex resulting from non-specific, non-covalent binding of a test nucleic acid to at least two and up to ten double stranded DNA binding dyes, the test nucleic acid being at least one of a control nucleic acid for quantitative PCR (qPCR), a nucleic acid amplified by qPCR, or a double-stranded DNA (dsDNA), where the dsDNA binding dyes have substantially similar excitation and emission spectra such that each of the at least two dsDNA binding dyes can be excited, and its resulting emissions detected, simultaneously, and where the combination of the dyes exhibits≧50% saturation of the test nucleic acid. The excitation and emission spectra may be substantially similar when a single instrument configuration can excite and measure emission from the dyes in a single measurement. The single instrument configuration comprises a filter set selecting a range of excitation and emission wavelengths. In one embodiment, the excitation is 488 nm±10 nm and the emission is 525 nm±10 nm. In one embodiment, the excitation is 488 nm±2 nm and the emission is 525 nm±20 nm. In one embodiment, the excitation is 488 nm±40 nm and the emission is 525 nm±40 nm. In one embodiment, the assay uses two dyes. The dyes may be ethidium bromide, SYBR® Green, LCGREEN®, SYTO® 9, EVAGREEN®, RESOLIGHT®, Chromofy, BOXTO, monomethine dyes, and/or Canon Life Science dyes.
One embodiment is a method for quantitating and/or detecting a target nucleic acid in a biological sample. This method comprises performing a quantitative polymerase chain reaction (qPCR) on a target nucleic acid to generate an amplified target nucleic acid in the presence of at least two and up to 10 dsDNA binding dyes, exposing the biological sample containing the amplified target nucleic acid to light at a wavelength absorbed by each compound; and detecting a fluorescent emission intensity from the compounds where the intensity is proportional to the quantity of the amplified target nucleic acid in the sample.
One embodiment is a method for quantitating and/or detecting a target nucleic acid in a biological sample. This method comprises performing a quantitative polymerase chain reaction (qPCR) on a target nucleic acid to generate an amplified target nucleic acid in the presence of at least two and up to ten dsDNA binding dyes, exposing the biological sample containing the amplified target nucleic acid to light at a wavelength absorbed by each compound; and detecting a fluorescent emission intensity from the compounds where the intensity is proportional to the quantity of the amplified target nucleic acid in the sample, and where the at least two dsDNA binding dyes have substantially similar excitation and emission spectra such that the at least two dsDNA binding dyes can be excited, and their resulting emissions detected, simultaneously, where the dyes result in ≧50% saturation of the test nucleic acid. The excitation and emission properties of the dyes may be substantially similar when a single instrument configuration is able to excite and measure emission from the at least two dsDNA binding dyes in a single measurement. The single instrument configuration comprises a filter set which selects a range of excitation and emission wavelengths. In one embodiment, the excitation is 488 nm±10 nm and the emission is 525 nm±10 nm. In one embodiment, the excitation is 488 nm±2 nm and the emission is 525 nm±20 nm. In one embodiment, the excitation is 488 nm±40 nm and the emission is 525 nm±40 nm. In one embodiment, the method uses two dyes. The dyes may be ethidium bromide; SYBR® Green, LCGREEN®, SYTO® 9, EVAGREEN®, RESOLIGHT®, Chromofy, BOXTO, monomethine dyes, and/or Canon Life Science dyes. In one embodiment, the target nucleic acid is a ribonucleic acid (RNA), and the method reverse transcribes the RNA into DNA prior to performing qPCR.
One embodiment is a method of analyzing a target double-stranded deoxyribonucleic acid (dsDNA). The method comprises heating the dsDNA target to a melting temperature in the presence of at least two and up to ten dsDNA binding dyes, plotting the melting temperatures against fluorescence emitted from the dyes to generate a melting curve, and identifying a genotype of the target dsDNA from the melting curve by melting temperature, melting curve slope, and/or melting curve shape. In one embodiment, the melting curve of the target dsDNA is compared with a melting curve of a reference dsDNA to determine a genotype of the target dsDNA. The excitation and emission properties of the dyes may be substantially similar when a single instrument configuration is able to excite and measure emission from the at least two dsDNA binding dyes in a single measurement. The single instrument configuration comprises a filter set which selects a range of excitation and emission wavelengths. In one embodiment, the excitation is 488 nm±10 nm and the emission is 525 nm±10 nm. In one embodiment, the excitation is 488 nm±2 nm and the emission is 525 nm±20 nm. In one embodiment, the excitation is 488 nm±40 nm and the emission is 525 nm±40 nm. In one embodiment, the method uses two dyes. The dyes may be ethidium bromide; SYBR® Green, LCGREEN®, SYTO® 9, EVAGREEN®, RESOLIGHT®, Chromofy, BOXTO, monomethine dyes, and/or Canon Life Science dyes.
One embodiment is a method of detecting mutations in a target nucleic acid by performing a quantitative polymerase chain reaction (qPCR) in the presence of at least two and up to ten double-stranded DNA binding dyes to generate an amplicon, heating the amplicon to generate a melting curve, and analyzing melting temperature, melting curve slope, and/or melting curve shape to detect a mutation in a target sample.
One embodiment is a method of analyzing a target nucleic acid by (a) first performing quantitative polymerase chain reaction (qPCR) on a target nucleic acid in a biological sample in the presence of a reaction mixture comprising at least two and up to ten dsDNA binding dyes resulting in an amplified target nucleic acid, (b) exposing the sample containing the amplified target nucleic acid to light at a wavelength absorbed by each of the dyes, and (c) detecting a fluorescent emission intensity from the dyes where the intensity is proportional to the quantity of the amplified target nucleic acid in the sample; and (d) subsequently determining a genotype of the target nucleic acid in the sample by heating the amplified target to generate a melting curve, and analyzing the melting curve to determine the genotype of the target nucleic acid in the absence of additional components to the reaction mixture.
One embodiment is a method for nucleic acid analysis by combining a target nucleic acid and at least two and up to ten double stranded DNA binding dyes and an unlabeled probe configured to hybridize to a portion of the target nucleic acid to result in a mixture, incubating the mixture under conditions to hybridize the unlabeled probe to the target nucleic acid to form a probe/target duplex, measuring fluorescence from the dyes as the mixture is heated, generating a melting curve for the probe/target duplex, and analyzing the shape of the melting curve including generating a derivative curve and analyzing the shape and location of one or more melting peaks on the derivative melting curve. In one embodiment, the target nucleic acid contains at least one point mutation and the method detects the point mutation.
One embodiment is a kit comprising at least two and up to ten double stranded DNA binding dyes. The kit contains instructions for performing each of high resolution melting of a target nucleic and quantitative polymerase chain reaction using components of the kit. The kit may contain a reference nucleic acid encoding a CFTR, BRCA1, BRCA2, MFN2, HTT, SMPD1, or NOD2 gene. Both qPCR and HRM may be performed using the kit.
One embodiment is a method of saturating double stranded DNA (dsDNA) with at least two and up to ten double stranded DNA binding dyes at concentrations not inhibitory to quantitative polymerase chain reaction (qPCR). The method comprises providing the dyes to a dsDNA at a concentration that provides at least 90% maximal fluorescent signal, where the concentration of the dyes does not substantially inhibit qPCR of the dsDNA, and where the blend of dsDNA-binding fluorescent dyes is selected from at least two and up to ten of ethidium bromide; SYBR® Green, LCGREEN®, SYTO® 9, EVAGREEN®, RESOLIGHT®, Chromofy, BOXTO, monomethine dyes, and Canon Life Science dyes.
One embodiment is a polymerase chain reaction assay and/or a high resolution melting assay containing a fluorescent complex resulting from non-specific, non-covalent binding of a test nucleic acid to at least two and up to ten double stranded DNA binding dyes selected from ethidium bromide, SYBR® Green, LCGREEN®, SYTO® 9, EVAGREEN®, RESOLIGHT®, Chromofy, BOXTO, monomethine dyes, and/or Canon Life Science dyes, where the test nucleic acid is at least one of a control nucleic acid for quantitative PCR (qPCR), a nucleic acid amplified by qPCR, or a double-stranded DNA (dsDNA), and where the dyes have substantially similar excitation and emission spectra such that each dye is excited, and its resulting emission detected, simultaneously, and where the dyes provide≧50% saturation of the test nucleic acid.
One embodiment is a method for quantitating and/or detecting a target nucleic acid in a biological sample. The method comprises performing a quantitative polymerase chain reaction (qPCR) on a target nucleic acid to generate an amplified target nucleic acid in the presence of at least two and up to ten double stranded DNA binding dyes, exposing the biological sample containing the amplified target nucleic acid to light at a wavelength absorbed by dyes; and detecting a fluorescent emission intensity from the dyes where the intensity is proportional to the quantity of the amplified target nucleic acid in the sample, and where the at dyes have substantially similar excitation and emission spectra such that the dyes are excited, and their resulting emissions detected, simultaneously, where the dyes provide≧50% saturation of the test nucleic acid.
When using dsDNA binding dyes to quantitate DNA, higher concentrations of dsDNA generally result in higher fluorescence. The amplicons that result from qPCR can be analyzed by melt curve analysis, e.g., a standard melt curve or HRM assay, to distinguish their sizes or characteristics, e.g., polymorphisms. While qPCR monitors fluorescence increase, HRM assays monitor fluorescence decrease as the dsDNA separates and the compound is no longer bound. When dye concentrations are used that are less than saturating, HRM assay results are equivocal; this is because the dye released upon melting tends to simply move to regions of the DNA that remain dsDNA. Dye relocation obscures potential sequence differences in the dsDNA templates. Thus, saturating concentrations of dyes are used in both qPCR and HRM assays to increase fluorescence signal and saturate dsDNA, resulting in a more sensitive assay that detected fewer/smaller differences in dsDNA.
In qPCR, increased dye binding to dsDNA permits quantifying dsDNA by measuring the quantification cycle (Cq). Cq is the cycle at which fluorescence crosses a certain value during DNA amplification. A lower Cq indicates a greater quantity of DNA at the start of amplification. The higher fluorescence signal resulting from increased dye concentration in the amplification reaction permits DNA quantitation at a lower Cq value, e.g., the assay becomes more sensitive.
An increased concentration of dsDNA binding dye in qPCR provides benefits, but also inhibits the DNA polymerase enzyme in the reaction mixture in a concentration-dependent manner. Increasing a dye concentration beyond an optimal value quickly inhibits DNA polymerase, resulting in reduced product synthesis and, in turn, reduced yield, lower qPCR endpoint, and increased Cq, i.e., reduced assay sensitivity and efficiency.
The inventive dye blends provided increased assay sensitivity and increased efficiency to both qPCR and HRM assays.
Combinations of at least two structurally similar dyes, and combinations of at least two structurally distinct dyes were evaluated to determine if blending or mixing dyes having differing binding mechanisms, characteristics, modes led to enhanced performance in either qPCR and/or high resolution melting (HRM) assays. The dyes in the blends can have similar, complimentary, or different properties and structures. The dye blends have substantially similar excitation and emission spectra. Excitation and emission spectra are substantially similar when the dyes can be excited and detected at the same time by an instrument; a single instrument configuration can excite and measure emission from the at least two dsDNA binding dyes in a single measurement. A single instrument configuration has a filter set that selects a range of excitation and emission wavelengths. The spectra can be read in the same channel/same filter set of an instrument. In one embodiment, the channel/filter set is a SYBR Green channel/filter set. In one embodiment, the channel/filter set provides excitation at 488 nm±40 nm and emission at 525 nm±40 nm. In one embodiment, the channel/filter set provides excitation at 488 nm±20 nm and emission at 525 nm±20 nm. In one embodiment, the channel/filter set provides excitation at 488 nm±10 nm and emission at 525 nm±10 nm. In one embodiment, any blend of from two dyes and up to ten dyes, where each dye in the blend has an absorbance maximum close to 488 nm and emission maximum close to 525 nm are used. In one embodiment, two dyes are used in the dye blend. In one embodiment, more than two dyes are used in the dye blend. In one embodiment, three dyes are used in the dye blend. In one embodiment, four dyes are used in the dye blend. In one embodiment, five dyes are used in the dye blend. In one embodiment, six dyes are used in the dye blend. In one embodiment, seven dyes are used in the dye blend. In one embodiment, eight dyes are used in the dye blend. In one embodiment, nine dyes are used in the dye blend. In one embodiment, ten dyes are used in the dye blend.
Quantitative PCR applications include research (quantitative gene transcription, DNA changes over time responsive to various environments or agents, progression of cell differentiation) and clinical diagnostics (e.g., DNA present in infectious diseases, cancer, genetic abnormalities). Quantitative-PCR amplifies a target DNA or a copy DNA derived from RNA by reverse transcription, to simultaneously detect it and quantify it in real time, i.e., as amplification occurs rather than when amplification is complete. In qPCR the quantity is reported as an absolute number, or as the number of copies, or as a relative amount when normalized to either the amount of DNA at the outset of the PCR (DNA input), or the amount of DNA produced from housekeeping genes. Use of qPCR in combination with reverse transcription (RT) permits quantification of ribonucleic acid, both coding RNA (messenger RNA (mRNA)), and non-coding RNAs.
Products of qPCR are typically detected by one of two methods: (1) measuring non-specific fluorescence from dyes that intercalate with any dsDNA; or (2) measuring specific fluorescence from probes that bind to specific DNA sequences and that are labeled with a fluorescent dye (reporter) that is detectable only when the probe is hybridized with its complementary DNA target.
In method (1), the dye binds non-specifically to, and/or intercalates with, dsDNA causing the dye to fluoresce. As the dsDNA is amplified during qPCR cycles, the fluorescence increases and is determined at each amplification cycle, and the fluorescence increase is used to determine the DNA concentration in comparison to a standard dilution series of known dsDNA, or to a relative concentration in comparison to another target, such as a stably expressed reference gene. The reagents are prepared as with standard PCR, and adding a fluorescent dye. The PCR analyzer includes a fluorescence detector.
In method (2), an oligonucleotide probe is added to the qPCR reaction mixture. The oligonucleotide sequence of the probe is substantially complementary to a region of the target DNA, and the probe contains a dye whose fluorescence is detected or enhanced only if the probe is hybridized to the target DNA. As the quantity of target DNA is increased during amplification cycles, the quantity of probe that can hybridize to the target sequence is increased and hence fluorescence is increased. The increase in fluorescence is used to determine the DNA concentration in the sample by comparing it to a standard dilution series of a known DNA, or to a relative concentration in comparison to another target, such as a stably expressed reference gene. The reagents are prepared as with standard PCR, and adding a fluorescently-labeled probe. The PCR analyzer includes a fluorescence detector.
There are instances when the above detection methods are combined. One example is probes labeled with an indirectly excitable fluorophore can be used in conjunction with a fluorescent dye that intercalates into dsDNA and when the probe hybridizes to a target strand in the reaction mixture and the dsDNA binding dye is excited, the fluorophore of the probe emits (U.S. Pat. No. 7,632,642). Another example is the use of a probe oligonucleotide labeled with dsDNA binding dye (U.S. Published Patent Application No. 2008/0220415 A1)
In either method, relative DNA concentrations during the exponential PCR phase are determined by plotting fluorescence versus PCR cycle number on a logarithmic scale; the exponentially-increasing DNA quantity results in a straight line. The threshold for detecting fluorescence above background is determined. The cycle at which the sample fluorescence exceeds this threshold is termed the quantitation cycle threshold, Cq. The DNA quantity theoretically doubles every cycle during the exponential phase, permitting calculation of the relative amount of DNA. For example, if Cq of sample A is reached three times sooner than Cq of sample B, sample A contains 23=8 times more DNA template.
High resolution melt (HRM) analysis detects genetic aberrations in dsDNA. It characterizes dsDNA based on thermal dissociation behavior to determine and identify differences in sequence, length, GC content, and/or strand complementarity. HRM analysis exceeds traditional DNA dissociation analysis, also termed DNA melting curve analysis, in the quality and quantity of the resulting information. HRM analysis detects genetic aberrations such as mutations, including single base changes (single nucleotide polymorphisms or SNPs), polymorphisms, epigenetic differences, etc. It thus is used for mutation discovery (gene scanning), screening for loss of heterozygosity, DNA fingerprinting, SNP genotyping, characterization of haplotype blocks, DNA methylation analysis, DNA mapping, species identification, somatic acquired mutation ratios, HLA compatibility typing, allelic prevalence in a population, and identification of candidate predisposition genes. HRM is more cost effective than DNA sequencing, is applicable to large scale rapid and accurate genotyping, and is a relatively simple technique.
In one embodiment, HRM analysis is performed after amplifying a DNA region of interest (e.g., one containing a mutation) after qPCR. This amplified region, amplicon, is heated from about 50° C. to about 95° C. and, at a point during this heating process, the amplicon melting temperature is reached and the two strands of DNA separate (“melt” apart). The melting temperature, Tm, is the temperature at which one-half of the DNA strands are double-stranded and one-half are single-stranded. Tm depends on both the DNA length and its specific nucleotide sequence composition. The precise temperature, determined to a fraction of a degree, at which melting occurs is monitored using a fluorescent dye that binds and/or intercalates specifically to only dsDNA; dye bound to dsDNA exhibits intense fluorescence, while dye in the presence of single stranded DNA (ssDNA) or “melted” DNA exhibits minimal fluorescence. Thus, at the outset of HRM analysis, the sample exhibits high fluorescence due to numerous amplicons. Upon heating, the fluorescence in the sample decreases due to DNA melting and dye un-binding.
A fluorometer measures emitted fluorescence, which is plotted against temperature to generate a melting curve. The temperature at which dsDNA separates (“melts”) depends upon its base sequence. For example, two samples with the same amplicon yield identical melting curves because each amplicon has the identical sequence. However, if an amplicon contains a sequence with a mutation, the temperature at which the dsDNA separates (“melts”) differs, yielding a different melting curve from the sample containing a non-mutated amplicon.
In one embodiment, HRM analysis is performed on genomic DNA to determine if a mutation is present. Genomic DNA contains two alleles, leading to three mutation outcomes: (1) neither allele contains a mutation (wild type), (2) one allele contains a mutation (heterozygote), (3) both alleles contain a mutation (homozygote). HRM analysis of genomic DNA under each mutation outcome yields a different melting curve. Thus, when analyzing genomic DNA, a mutation in a gene associated with, e.g., breast cancer, can be screened for and the patient can be assessed as having a wild type, homozygous, or heterozygous genotype. Examples of genetic mutations correlated with a disease, and detectable with HRM analysis, include but are not limited to mutations in cystic fibrosis transmembrane conductance regulator (CFTR), BRCA1/2 (breast cancer), mitofusin-2 (MFN2; Charcot-Marie-Tooth disease), Huntingtin (HTT; Huntington's disease), sphingomyelin phosphodiesterase 1 (SMPD1; Niemann-Pick disease), NOD2 (nucleotide-binding oligomerization domain containing 2; Crohn's disease), etc.
Because dsDNA with no mis-matches has 100% base pair affinity, a first temperature is required to separate the strands, but where the dsDNA has mis-matches, and thus has less than 100% base pair affinity, a second temperature is required to separate the strands. The second temperature may be less than or greater than the first temperature, depending upon the specific DNA composition, e.g., a G→A mutation could lower the overall Tm. A method to detect mutations in a target nucleic acid performs qPCR in the presence of at least a dye blend to generate an amplicon, then heating the amplicon to generate a melting curve, and then analyzing the melting temperature Tm, melting curve slope, and/or melting curve shape to detect a mutation in a target sample. Analysis software plots the relative fluorescence unit (RFU) data collected during generation of the melting curve as a function to of temperature. Melting curves can be normalized adjusting pre-melt and post-melt regions with sliders. For better visual identification the adjusted region of the melting curve can be generated to a difference curve. Difference curve analysis shows the difference in fluorescence between a well and the fluorescence of a reference curve. The reference curve is generated from the average fluorescence of all the curves within a selected reference group.
HRM melting curves can discriminate between samples based on curve shape and/or curve shift. Curve shape analysis utilizes detailed shapes in the curve itself. Curve shift analysis utilizes thermal offset, or shift, of a curve from other curves.
Raw data may be normalized before being used in HRM curves; typical plots are fluorescence units (ordinate) versus temperature (abscissa), similar to PCR amplification plots substituting temperature (abscissa) for cycle number (abscissa). In HRM analysis plots, as with rt-PCR plots, fluorescence is normalized to a 0% to 100% scale. In one embodiment, the temperature (abscissa) is also normalized to compensate for well-to-well temperature measurement variations among samples. In one embodiment, differences in melting curve shape are analyzed by subtracting each curve from a reference curve, which results in automatic clustering the samples into groups with similar melting curves e.g., samples with heterozygote gene mutations versus samples with homozygote mutations. Information and recommendations how HRM data should be analyzed are known in the art, e.g., van der Stoep et al., 2009, Diagnostic guidelines for High-Resolution Melting Curve (HRM) Analysis: An Interlaboratory Validation of BRCA1 Mutation Scanning Using the 96-Well LightScanner™, Human Mutation 30 (6): 899-909; Montgomery et al., 2007, Simultaneous mutation scanning and genotyping by high-resolution DNA melting analysis, Nature Protocols (2) 1: 59-66; Liew et al. 2004, Genotyping of single-nucleotide polymorphisms by high-resolution melting of small amplicons, Clin Chem 50: 1156-1164; and Wittwer et al. 2003, High-resolution genotyping by amplicon melting analysis using LCGreen. Clin Chem 49: 853-860.
Commercially available instruments that contain software programs for each of these analyses are typically used, e.g., Viia 7, Stepone Plus or 7500 Real-Time PCR System (Applied Biosystems); Lightcyler 480 System (Roche); PikoReal Real-Time PCR system (Thermo Scientific); Rotorgene Q (Qiagen); CFX Real-Time Detection Systems (BioRad); Eco Real-Time PCR System (Illumina); or LightScanner System (Idaho Technology).
A hypothetical melt curve plots temperature versus fluorescence, where dsDNA binding dyes fluoresce in the presence of dsDNA but either do not fluoresce or have substantially decreased fluorescence in the presence of ssDNA. A melt curve plot typically shows the transition from dsDNA high fluorescence initial, pre-melt, phase, through the sharp fluorescence decrease of the melt phase where dsDNA is separated forming ssDNA, to base fluorescence at the final, post-melt, phase where only ssDNA is present. Fluorescence decreases as DNA intercalating dye is released from dsDNA as it separates into ssDNA. The midpoint of the melt phase, at which the rate of change in fluorescence is greatest, defines the melting temperature Tm of the specific DNA fragment being analyzed.
Intercalating dyes that saturate dsDNA result in homogeneous staining of homo-or heteroduplex DNA (
In one embodiment, the dsDNA binding dyes of the blend are selected from at least one of the following classes of dsDNA binding dyes: ethidium bromide, SYBR® Green (Life Technologies, U.S. Pat. Nos. 5,436,134, 5,658,751; PCT/US94/04127 published as WO 94/24213, each of which is hereby incorporated by reference herein in its entirety), LCGREEN® (Idaho Technology, U.S. Pat. Nos. 7,456,281, 7,387,887, each of which is hereby incorporated by reference herein in its entirety), SYTO 9 (Molecular Probes), EVAGREEN® (Biotium U.S. Pat. No. 7,776,567, which is hereby incorporated by reference in its entirety), RESOLIGHT® (Roche), Chromofy (TAATA Biocenter), BOXTO (TAATA Biocenter), monomethine dyes (Dyomics, PCT/US08/78277 published as WO 2009/046010, which is hereby incorporated by reference in its entirety), Canon Life Science dyes (U.S. Published Patent Application No. 20100167279, which is hereby incorporated by reference in its entirety). In one embodiment, the dsDNA binding dyes of the blend are selected from the compounds in Deligeorgivez et al. Intercalating Cyanine Dyes for Nucleic Acid Detection, Recent Patents on Material Science, 2009, 2, 1-26. In one embodiment, the dsDNA binding dyes of the blend are selected from Thiazole Orange (TO), Oxazole Yellow (YO), homodimeric styrylcyanine dyes (Abbott Laboratories); PO-PRO-1 (λex/em=435/455 nm), BO-PRO-1 (λex/em=462/481 nm), YO-PRO-1 (λex/em=491/509 nm), TO-PRO-1 (λex/em=515/531 nm), SYTO, SYTOX, SYBR Gold, SYBR Green I, SYBR Green II, BEBO, BETO, BOXTO, BOXBO, PO-PRO-3 (λex/em=539/567 nm), BO-PRO-3 (λex/em=575/599 nm), YO-PRO-3 (λex/em=612/631 nm), TO-PRO-3 (λex/em=642/661 nm), TO-PRO-5 (λex/em=745/720 nm), YOYO-1 (λex/λem=491/509 nm), TOTO-1 (λex/λem=514/533 nm), POPO-1 (λex/em=434/456 nm), BOBO-1 (λex/em=462/481 nm), POPO-3 (λex/em=534/570 nm), BOBO-3 (λex/em=570/602 nm), YOYO-3 (λex/em=612/631 nm), TOTO-3 (λex/em=642/660 nm), JO-PRO-1 (λex/em=530/545 nm), LO-PRO-1 (λex/em=567/580 nm), JOJO-1 (λex/em=529/545 nm), LOLO-1 (λex/em=565/579 nm), LDS-751 (Life Technologies Inc.); EvaGreen (Biotium); LCGreen (Idaho Technology); Thiazole Blue, Thiazole Orange and Thiazole Blue heterodimer (TOTAB), Thiazole Orange-ethidium heterodimer (TOED), and Thiazole Orange and Thiazole Indolenine heterodimer (TOTIN).
In one embodiment, at least one of the dsDNA binding dyes of the blend is a compound having the formula
where each of R1-R10 and R12 is independently H or a linear or branched hydrocarbon, optionally containing one or more heteroatoms;
R1 and R2, R2 and R3, R3 and R4, R4 and R5, R7 and R8, R8 and R9, R9 and R10 or R6 and R12 are substituents capable of forming an aliphatic chain or ring, or an aromatic ring;
R11 is a linear or branched hydrocarbon, optionally containing one or more heteroatoms;
R13 is selected from
X is selected from the group consisting of O, S, Se, NR16 where R16 is H or a hydrocarbon optionally containing one or more heteroatoms, and CR17R18 where R17 and R18 are the same or different and are independently a hydrocarbon optionally containing one or more heteroatoms, or in combination complete a five, six, or seven membered saturated ring, optionally containing one or more heteroatoms;
n is an integer from 0 to 3; and anion is a counterion.
In one embodiment, at least one of the dsDNA binding dyes of the blend is selected from the following compounds
In one embodiment, at least one of the dsDNA binding dyes of the blend is a compound having the formula
wherein BRIDGE is a substantially aliphatic, substantially neutral linker comprising from about 8 to about 150 non-hydrogen atoms; Q1 is a dye constituent selected from a fluorescent nucleic acid dye constituent, a non-fluorescent nucleic acid dye constituent, a fluorescent non-nucleic acid dye constituent, and a non-fluorescent non-nucleic acid dye constituent; Q2 is a dye constituent selected from a fluorescent nucleic acid dye constituent, a non-fluorescent nucleic acid dye constituent, a fluorescent non-nucleic acid dye constituent, and a non-fluorescent non-nucleic acid dye constituent; at least one dye constituent of the Q1 dye constituent and the Q2 dye constituent is a reporter dye constituent; at least one dye constituent of the Q1 dye constituent and the Q2 dye constituent is a fluorescent nucleic acid dye constituent or a non-fluorescent nucleic acid dye constituent; and the reporter dye constituent and the fluorescent nucleic acid dye constituent are optionally the same, wherein
R1 represents where BRIDGE attaches to the structure; and ψ is an anion; or
wherein R1′ of Formula II is H; alkyl or alkenyl having 1 carbon to 6 carbons, inclusive; a halogen; —OR9; —SR10; —CN; —NH(C═O)R13; —NHS(═O)2R14; —C(═O)NHR15; or a substituent associated with minor groove binding; or represents where BRIDGE attaches to the structure;
when R1′ of Formula II comprises at least one of R9, R10, R11, R12, R13, R14 and R15, any said one of R9, R10, R11, R12, R13, R14 and R15, independently, is H or alkyl having 1 carbon to 12 carbons, inclusive, optionally incorporating 1 to 2 nitrogen(s), inclusive, or an aryl;
when R1′ of Formula II comprises R11 and R12, R11 and R12 may in combination form a 5- or 6-membered saturated or unsaturated ring, which optionally comprises at least one hetero atom selected from N and O;
X of Formula II is selected from O and S; n of Formula II is selected from 0, 1, and 2;
R6 of Formula II is H; alkyl or alkenyl having 1 carbon to 10 carbons, inclusive, optionally comprising at least one hetero atom selected from N, O, and S; a halogen; —OR16; —SR16; —NR16R17; or a substituted or an unsubstituted aryl, optionally comprising 1 to 3 hetero atom(s), inclusive, selected from N, O, and S; or represents where BRIDGE attaches to the structure;
R7 of Formula II is H; alkyl or alkenyl having 1 carbon to 10 carbons, inclusive, optionally comprising an aryl and at least one hetero atom selected from N, O, and S; or a substituted or an unsubstituted aryl optionally comprising 1 to 3 hetero atom(s), inclusive, selected from N, O, and S; or represents where BRIDGE attaches to the structure;
R8 and R8′ of Formula II in combination form a fused aromatic ring, which may be further substituted 1 to 4 time(s), inclusive, independently, by C1-C2, inclusive, alkyl, C1-C2, inclusive, alkoxy, C1-C2, inclusive, alkylmercapto, or a halogen;
each of R16 and R17 independently is H; alkyl having 1 carbon to 12 carbons, inclusive, optionally incorporating 1 to 2 nitrogen(s) or an aryl; or
R16 and R17 may in combination form a 5- or 6-membered saturated or unsaturated ring, which optionally comprises at least one hetero atom selected from N and O;
only one of R1′, R6 and R7 of Formula II represents where BRIDGE attaches to the structure; and
ψ f Formula II is an anion; or when either Q1 or Q2 is an acridine dye, at least one dye constituent of the Q1 and Q2 dye constituents has the structure of Formula III:
wherein each R1 of Formula III is independently, is H or a C1-C2, inclusive, alkyl; one of R2 and R3 of Formula III represents where BRIDGE attaches to the structure;
when R2 of Formula III represents where BRIDGE attaches to the structure, R3 is H or —CH3;
when R3 of Formula III represents where BRIDGE attaches to the structure, R2 is selected from H, —CH3, —NH2, —NHCH3, —CN, and —C(═O)NH2;
each R6 of Formula III independently, is H or a C1-C2, inclusive, alkyl;
each R7 of Formula III independently, is H or a C1-C2, inclusive, alkyl; for each pair of adjacent R6 or R7 and R1, independently, R6 or R7 and R1 may in combination form a 5- or 6-membered, saturated or unsaturated ring; and ψ of Formula III is an anion.
In one embodiment, at least one of the dsDNA binding dyes of the blend is a compound of the formula
wherein the moiety Y represents an optionally-substituted fused monocyclic or polycyclic aromatic ring or an optionally-substituted fused monocyclic or polycyclic nitrogen-containing heteroaromatic ring; X is oxygen, sulfur, selenium, tellurium or a moiety selected from C(CH3)2 and NR1, where R1 is hydrogen or C1-6alkyl; R2 is selected from the group consisting of C1-6alkyl, C3-8 cycloalkyl, aryl, aryl(C1-3 alkyl), hydroxyalkyl, alkoxy-alkyl, aminoalkyl, mono and dialkylaminoalkyl, trialky-lammoniumalkyl, alkylenecarboxylate, alkylenecarboxamide, alkylenesulfonate, optionally substituted cyclic heteroatom-containing moieties, and optionally substituted acyclic heteroatom-containing moieties; t=0 or 1; Z is a charge selected from 0 or 1;
R3 is selected from the group consisting of hydrogen, C1-6 alkyl, and arylcarbonyl, or R2 and R3 are taken together to form —CH2)w—, wherein w is 1 to 5;
R9 and R13 are each independently selected from the group consisting of hydrogen, C1-6 alkyl, and arylcarbonyl; n=0, 1, or 2; and v=0 or 1; with the proviso that v=0 when R2 and R3 are not taken together to form —(CH2)w—; wherein when v=0, Q is an heterocycle selected from the group of structures consisting of:
and
wherein when v=1, Q is an heterocycle selected from the group of structures consisting of:
wherein R4, R5, R6, R7, R8, R12, and R13 are independently selected from the group consisting of hydrogen, halogen, alkyl, cycloalkyl, heteroalkyl, heterocycloalkyl, alkenyl, polyalkenyl, alkynyl, polyalkynyl, alkenylalkynyl, alkylnitrilethio, aryl, heteroaryl, alkoxy, arylcarbonylthio, cycloheteroalkylcarbonylthio, dialkylaminoalkylcarbonylthio, dialkylamino, cycloalkylthio, cycloheteroalkylthio, trialkylammoniumalkylthio, trialkylammoniumalkylcarbonylthio, and nucleosidylthio, each of which may be optionally substituted; an acyclic heteroatom-containing moiety, a cyclic heteroatom-containing moiety, a BRIDGE-DYE, and a reactive group, each of which optionally includes a quaternary ammonium moiety.
In one embodiment, at least one of the dsDNA binding dyes of the blend is a compound having the formula
characterized in that either all of A1, A2, A3 and A4 are H or one of A1, A2, A3 and A4 is a substituent which is a halogenyl, and the others are H; B is selected from a group consisting of S, O, N—R, and C—(R)2 wherein R is C1-C6-Alkyl; D is either an unsubstituted or a substituted C1-C6-alkyl; X is either H or a methoxy-group; Y is selected from a group consisting of S, O, N—R wherein R is C1-C6-Alkyl, and Z1-C═C-Z2, wherein Z1 and Z2 independently from each other are either H or a methoxy-group; L is either CH3 or phenyl; and M is either phenyl or a substituted or unsubstituted C1-C18 amino-alkyl.
In one embodiment, at least one of the dsDNA binding dyes of the blend is a compound having the formula
wherein A is
wherein X is O or S; R1, R2, R3, R4, R5, R6 and R7 are independently hydrogen, halogen, thiol, optionally substituted alkyl, optionally substituted alkoxy, optionally substituted alkenyl, optionally substituted polyalkenyl, optionally substituted alkynyl, optionally substituted polyalkynyl, optionally substituted thioalkyl, optionally substituted aminoalkyl, optionally substituted aryl, optionally substituted heteroaryl and optionally substituted arylalkyl; R1 and/or R2 carry one or more positive charges such that the sum of the positive charge(s) on R1 and R2 is 1, 2 or 3; and R3, and/or R4, and/or R5, and/or R6 and/or R7 carry one or more positive charges such that the sum of the positive charge(s) on R3, R4, R5, R6 and R7 is 1, 2 or 3.
In one embodiment, at least one of the dsDNA binding dyes of the blend is a compound having the formula
wherein each R1 is independently H; or an alkyl group having from 1-6 carbons; or a trifluoromethyl; or a halogen; or —OR8, —SR8 or —(NR8R9) where R8 and R9, which can be the same or different, are independently H; or alkyl groups having 1-6 carbons; or 1-2 allyclic, heteroalicyclic, aromatic or heterouromatic nngs, containing 1-4 heteroatoms, wherein the hetero atoms are O, N or S; or R8 and R9 taken in combination are —(CH2)2-L-(CH2)2— where L=a single bond, —O—, —CH2—, or —NR10—, where R10 is H or an alkyl group having 1-6 carbons; and t=1-4; R2 is an alkyl group having 1-6 carbons;
X is O, S, Se or —NR15, where R16 is H or an alkyl group having 1-6 carbons; or X is CR16RI7 where R16 and RI7, which may be the same or different, are independently alkyl groups having 1-6 carbons, or R16 and R17 taken in combination complete a five or six membered saturated ring; n=0, 1 or 2; Z is a biologically compatible counterion; Q has the formula Q1 or Q2
wherein Y is —CR3═CR4—; p and m=0 or 1, such that p+m=t; R5 is an alkyl, alkenyl, polyalkenyl, alkynyl or polyailkynyl group having 1-6 carbons; or R5 is a OMEGA; R3, R4, R6 and R7, which may be the same or different, are independently H; or an alkyl, alkenyl, polyalkenyl, alkynyl or polyaticynyl group having 1-6 carbons; or a halogen; or —OH, —OR8, —SR8, —(NR8R9); or —OSO2R19 where R19 is alkyl having 1-6 carbons, or perfluoroalkyl having 1-6 carbons, or aryl; or an OMEGA; or R6 and R7, taken in combination are —(CH2)v— where v=3 or 4, or R6 and R7 form a fused aromatic ring according to formula Q2; R11, R12, R13, and R14, which may be the same or different, are independently H, or an alkyl, alkenyl, polyalkenyl, alkynyl or polyalkynyl group having 1-6 carbons; or a halogen; or an OMEGA; or —OH, —OR8, —SR8, or —(NR8R9); OMEGA is a cyclohexyl, cyclohexenyl, morpholino, piperidinyl, naphthyl, phenyl, thienyl, benzothiazolyl, furanyl, oxazolyl, benzoxazolyl or pyridinyl that is unsubstituted or optionally substituted one or more times, independently, by halogen, alkyl, perfluoroalkyl, areinc, alkylamino, dialkylamino, alkoxy or carboxyalkyl, having 1-6 carbons, and that is attached as R3, R3, R4, R5, R6, R7, R11, R12, R13, or R14 by a single bond; such that at least one of R3, R4, R5, R6, R7, R11, R12, R13, and R14, is an OMEGA, and, where more than one of R3, R4, R5, R6, R7, R11, R12, R13, and R14 is an OMEGA, each OMEGA is optionally the same or different; and such that when 0 has the formula Q1, n=O.
In one embodiment, at least one of the dsDNA binding dyes of the blend is a compound having the formula
wherein each R1 is independently H; or an alkyl group having from 1-6 carbons; an alkoxy group having from 1-6 carbons; or a trifluoromethyl; or a halogen; and t=1-4; R2 is an alkyl group having 1-6 carbons; X is O, S, Se or NR15, where R15 is H or an alkyl group having 1-6 carbons; or X is CR16R17 where R16 and R17, which may be the same or different, are independently alkyl groups having 1-6 carbons, or R16 and R17 taken in combination complete a five or six membered saturated ring; n=0, 1 or 2; P is a biologically compatible counterion; Q has the formula Q1 or Q2
wherein Y is —CR3═CR4—; p and m=0 or 1, such that p+m=l; R5 is an alkyl, alkenyl polyalkenyl, alkynyl or polyalkynyl group having 1-6 carbons; or R5 is a cyclic substituent that is a substituted or unsubstituted aryl or heteroaryl; or a substituted or unsubstituted cycloalkyl having 3-10 carbons; or R5 is a TAIL; R3, R4, R6 and R7, which may be the same or different, are independently H; or an alkyl, alkenyl. polyalkenyl, alkynyl or polyalkynyl group having 1-6 carbons; or a halogen; or a substituted or unsubstituted aryl or heteroaryl; or a substituted or unsubstituted cycloalkyl having 3-10 carbons; or —OR8, —SR8, —(NR8R9); or —OSO2R19; or a TAIL; where R8 and R9, which can be the same or different, are independently H; or alkyl groups having 1-6 carbons; or 1-2 alicyclic or aromatic rings; or R8 and R9 taken in combination are —(CH2)4— or —(CH2)5— to give a 5 or 6 membered ring; and where R19 is alkyl having 1-6 carbons, or perfluoroalkyl having 1-6 carbons, or aryl; or R6 and R7, taken in combination are —(CH2)v—, where v=3 or 4, or R6 and R7 form a fused aromatic ring according to formula Q2; R11, R12, R13, and R14, which may be the same or different, are independently H; or an alkyl, alkenyl, polyalkenyl, alkynyl or polyalkynyl group having 1-6 carbons; or a halogen; or a TAIL; or —OH, —OR8, —SR8, or —(NR8R9); TAIL is a heteroatom-containing moiety having the formula LINK-SPACER-CAP; wherein LINK is a single covalent bond, —O—, —S—, or —NR20—; where R20 is H, a linear or branched alkyl having 1-8 carbons, or R20 is —SPACER′-CAP′; SPACER and SPACER′, which may be the same or different, are covalent linkages, linear or branched, cyclic or heterocyclic, saturated or unsaturated, each having 1-16 nonhydrogen atoms selected from the group consisting of C, N, P, O and S, such that the linkage contains any combination of ether, thioether, amine, ester, amide bonds; or single, double, triple or aromatic carbon-carbon bonds; or phosphorus-oxygen, phosphorus-sulfur bonds, nitrogen-nitrogen or nitrogen-oxygen bonds; or aromatic or heteroaromatic bonds; CAP and CAP′, which may be the same or different, are —O—R21, —S—R21, —NR21R22, or —N+R21R22R23ψ−; wherein R21, R22, and R23 are independently H, or a linear or branched alkyl or cycloalkyl having 1-8 carbons, optionally further substituted by hydroxy, alkoxy having 1-8 carbons, carboxyalkyl having 1-8 carbons, or phenyl, where phenyl is optionally further substituted by halogen, hydroxy, alkoxy having 1-8 carbons, aminoalkyl having 1-8 carbons, or carboxyalkyl having 1-8 carbons; or, one or more of R21, R22 and R23, taken in combination with SPACER or SPACER′ or R20 forms a 5- or 6-membered aromatic, heteroaromatic, alicyclic or heteroalicyclic ring, the heteroatoms selected from O, N or S; where ψ− is a biologically compatible counterion; or CAP and CAP′ are independently
where R21, R22 and ψ− are as defined previously; such that at least one of R3, R4, R5, R6, R7, R11, R12, R13, and R14 is a TAIL; and when R5 is a TAIL, LINK is a single bond; and where only R5 is a TAIL, R3 or R4 is not hydrogen; and, where more than one of R2, R3, R4, R5, R6, R7, R11, R12, R13, and R14 is a TAIL, each TAIL is optionally the same or different.
Dye saturation is a consideration when selecting dye blends, because a dye with a high percent saturation performs better in HRM analysis. Dye saturation is defined as the fluorescence at a certain dye concentration, typically the concentration usable for qPCR and typically 1×, as a percentage of the maximum fluorescence obtained when dsDNA is titrated with an increasing dye concentration. When a predetermined concentration of dsDNA is titrated with increasing concentrations of a dsDNA-binding dye, the fluorescence increases until all the dye-binding sites on the dsDNA are occupied. At this point, the fluorescence plateaus or decreases because the dsDNA is saturated with dye. Individual dyes are primarily designed for either qPCR or HRM; using a dye blend provides optimal properties for both qPCR and HRM.
The disclosed dye blends have properties that each dye alone does not provide. A blend of dsDNA binding dyes provided improved properties compared with the individual dyes alone, e.g., higher fluorescence and the same or lower Cq compared to each dye alone. In embodiments, dye blends were used at a concentration of the individual dyes that was generally lower than would be used if the dyes were used alone. Using a relatively lower dye concentrations is generally less inhibitory to other processes, e.g., PCR. However, the dyes in the dye blends provided an enhanced effect on dsDNA saturation, where saturation is increased using dye concentrations that were not inhibitory to qPCR. For example, a dye blend may contain two dyes, each at a concentration that, if used alone, would provide about 60% DNA saturation, but the dye blend provided about 90% or greater DNA saturation. Thus, the dye blends showed a synergistic effect by improving performance beyond the performance of each dye alone. This synergistic effect may reflect different binding modes on the dsDNA by the different dyes forming the dye blend.
Without being bound to a specific theory, the improved characteristics of the described dsDNA binding dye blends may increase the design space for dye concentration in a mix for HRM and qPCR. Using the blend of dsDNA binding dyes permits fluorescence maxima to be achieved at a lower concentration of each dye than using each individual dye alone, and at a concentration that is less inhibitory to DNA polymerase enzymes. The dye blends improved the fluorescence characteristics of qPCR and HRM, and also overcame the problems of qPCR inhibition associated with saturating concentrations of dsDNA binding dyes.
In one embodiment, a dye blend of two dyes blends was as follows: structurally similar dyes V11-02190 and V11-03001, and structurally distinct dyes V11-02190 and Eva Green.
Although the manufacturer does not provide the exact structure of Eva Green®, it is thought to be two homo-monomers linked by a bridge.
The performance of the dye blend in qPCR was compared in triplicate qPCR reactions across a series of 10-fold dilutions of human genomic DNA (hgDNA; Roche, Cat#. 1691112) from 50 ng-50 pg per reaction using a glyceraldehyde phosphate dehydrogenase (GAPDH) 94 assay GAPDH 94 F 5′ ACAGTCAGCCGCATCTTCTT 3′ (SEQ ID. NO: 1); GAPDH 94 R 5′ ACGACCAAATCCGTTGACTC 3′ (SEQ ID. NO: 2); final concentration each primer 400 nM).
PCR reactions, 15 μl, comprised 10 mM Tris pH 8.2; 500 mM KCl; 0.01 mM EDTA; 3 mM MgCl2; 200 pM of each dNTP (Thermo Fisher Scientific); 0.01% Tween 20; 0.005 U/pl Thermo-start DNA polymerase (Thermo Fisher Scientific). Molecular grade reagents were from Sigma unless otherwise stated.
A blend of two structurally similar dyes and two structurally dissimilar dyes were selected as representative dyes. The two structurally similar dyes were V11-02190 and V11-03001, as disclosed in PCT/US08/78277, incorporated by reference herein in its entirety. The two structurally dissimilar dyes were V11-02190 and Eva Green®. Each dye in the respective dye blend was included in the reaction mixtures at the concentrations described. Each dye was added alone at each of the different concentrations as control reactions. All of the described dyes are non-specific dsDNA binding dyes. Single dyes were included as controls at 0.5× to 2× optimum concentration of each dye, which was 8 μM V11-02190, 1 μM V11-03001, 1× Eva Green. Reactions were cycled on a Roche LC480 thermal cycler using a 384 well block with the following conditions: 95° C. for 15 minutes, followed by 50 cycles of 95° C. for 15 seconds, 60° C. for 20 seconds, 72° C. for 20 seconds during which fluorescence data was acquired, following which a melting curve was acquired at 65° C.-95° C. Fluorescence data were generated by exciting the dye(s), whether a single dye or a dye blend, at a single excitation wavelength and measuring emission at a single emission wavelength. As is known in the art, a single excitation or emission wavelength may comprise a narrow range of excitation and/or emission wavelengths, such as a range of about 1 nm to about 20 nm.
A blend of V11-02190 and V11-03001, at various concentrations, was compared with each dye separately, at various concentrations, in generating either an amplification curve or a melting peak, using the above-described method and as shown in
Some dye blends showed improved characteristics compared with individual dye conditions. Tm peaks, as shown in
Several blends showed higher endpoints and lower Cq than single dyes alone (controls) even at increased concentrations, e.g. 8 μM V11-2190 with either 1 μM V11-3001 or 2 μM V11-3001.
The amplification curves comparing V11-02190N11-03001 blends with single dyes were analyzed to determine mean Cq using the fit points/threshold/Cq call method (which are user-defined on the Roche Lightcycler 480 software) as shown in
Using the fit points/threshold/Cq call method, dye blends that produced the combined highest RFU and lowest Cq results were 8 μM V11-02190 and 2 μM V11-0301; and 8 μM V11-02190 and 1 μM V11-03001.
The results of the V11-02190 and V11-03001 dye blend showed that blending dyes increased endpoint fluorescence compared with individual dyes alone. For example, even using an increased concentration (16 μM) of dye V11-02190 alone, there was a lower endpoint fluorescence when compared to a dye blend containing 8 μM V11-02190 and 2 μM VI 1-03001. Dye blends also improved Cq compared to Cq with individual dyes alone. For example, a dye blend of V11-02190 and V11-03001 showed lower Cq than an equivalent concentration of V11-02190 alone and lower or approximately equivalent concentration of V11-03001 alone. The dye blends provided a compromise and provided properties that neither dye alone could provide. Cq calculated using the second derivative method appeared to penalize dye blends with higher endpoints due to the steeper amplification curve; Cq calculated using fit points/threshold/Cq call method provided more representative results based on analysis of the amplification plots. Thus, the dye blends avoided qPCR inhibition from increasing a single dye on its own, while providing improved saturation data.
In addition to dye blends exhibiting improved properties compared to single dyes, the dye blends also exhibited minimal PCR inhibition, as demonstrated by the lack of increase in Cq value, and only at the highest concentrations of each dye in the blend. For example, dye V11-02190 at a concentration of 16 μM exhibited significant PCR inhibition; V11-03001 at a concentration of 2 μM exhibited significant PCR inhibition, shown in
A dye blend of V11-02190 and a commercially available dye Eva Greene (Biotium) were evaluated at various concentrations, and the blend was compared with each dyes alone at various concentrations, in both qPCR and melting curve analysis using the methods described above. The results are shown in
Some dye blends showed improved characteristics compared with individual dye conditions. Tm peaks, as shown in
Specific dye blends were further analyzed, and the data are shown in
The amplification curves comparing a blend of V11-02190 and Eva Greene with single dyes alone were analyzed to determine mean Cq, using the fit points/threshold/Cq call method, as shown in
Using the fit points/threshold/Cq call method, dye blends that produced the combined highest RFU and lowest Cq results were 8 μM V11-02190 and 2× Eva Green®; 16 μM V11-02190 and 0.5× Eva Green®; and 16 μM V11-02190 and 1× Eva Green®. The results showed that blending dyes increased endpoint fluorescence compared with individual dyes alone, and improved Cq compared with individual dyes alone (V11-02190 control, Eva Green® control), see
Dye saturation of selected dye blends from qPCR was compared to the individual dyes alone as an indication of potential performance in HRM analysis. Higher dye saturation provides less dye redistribution to non-denatured regions of the DNA during melting and thus results in higher melt sensitivity. To evaluate dye saturation, triplicate 25 μL samples were evaluated that contained 10 mM Tris pH 8.2; 500 mM KCl; 0.01 mM EDTA; and 10 ng/μl human genomic DNA (Roche cat#.1691112). Each dye blend was added at the following concentrations: 20×, 10×, 5×, 2.5×, 1×, 0.5×, 0.25×, 0.1×, and 0.01×; 1× is the concentration previously tested in qPCR. Fluorescence measurements were determined on BMG FluoSTAR Galaxy, using 485 nm excitation and 520 nm emission filters blanked using 10 mM Tris pH 8.2; 500 mM KCl; 0.01 mM EDTA buffer. Fluorescence values of control reactions (no dsDNA added) were subtracted from reactions containing dsDNA to produce fluorescence values normalized to remove any background fluorescence from unbound dye.
Dye blend 8 μM V11-02190 and 2 μM V11-03001 showed increased dye saturation, compared with V11-03001 controls, and a smaller increase compared with V11-02190 controls. Selected results from
Dye blend 8 μM V11-02190 and 2× Eva Green®, and dye blend 16 μM V11-02190 and 1× Eva Green®, showed increased saturation compared with either dye alone (V11-02190 control and Eva Green® control. Selected results from
A dye blend of V11-02190 and a commercially available dye LC Green® (Idaho Technology) were evaluated at various concentrations, and the blend was compared with each dyes alone at various concentrations, in HRM analysis, with qRCR data of V11-02190 shown in
A dye blend of EVAGREEN® and LCGREEN® (Idaho Technology) was evaluated at various concentrations. Each dye was added alone at each of the different concentrations as control reactions. Single dyes were included as controls at 0.25× to 0.75× and 0.5× to 2× optimum concentrations of each dye of EVAGREEN® and LCGREEN®, respectively. Reactions were cycled on Corbett Rotor Gene 6000 thermal cycler using a 72 well block with the following conditions: 95° C. for 10 minutes, followed by 40 cycles of 95° C. for 10 seconds, 60° C. for 15 seconds during which fluorescence data was acquired, following which a melting curve was acquired at 70° C.-85° C., rising by 0.1° C. each step. The performance of the dye blend in HRM was compared in qPCR reactions using primer set that detects a 108 bp region (ACTGGGTAAA TGTCACAAAA GAAGTGGTCT ACCACTGTGC CACAGAACGG CAAATTGAAC ATGGCTGTCA CATGGAGAAC TGCCATAGTC AGACCAATGC CAAAGGAC (SEQ ID. NO: 8) of the OR10J5 gene, with a forward primer sequence of 5′ GTC CTT TGG CAT TGG TCT GAC TA 3′ (SEQ ID. NO: 9); and reverse primer sequence of 5′ ACT GGG TAA ATG TCA CAA AAG AAG TG 3′ (SEQ ID. NO: 10); the final concentration of each primer was 500 nM. Triplicate reactions from 10 ng, about 2900 copies, of three human genomic DNA samples, each known to contain one of each of 3 SNP genotypes, GG, AG or AA, as well as negative template control reactions.
Using HRM analysis, the dye blend that produced the combined highest RFU were 0.5× EVAGREEN® and 0.5× LCGREEN®.
The disclosed dye blends have properties that each dye alone does not provide.
As one example, dye blend V11-03001 and V11-02190 improved the fluorescence signal and, although to a lesser extent, improved Cq without increasing the concentration of either dye alone to a concentration that would be inhibitory, thus providing an improved dye composition for qPCR. Dye blend V11-03001 and V11-02190 provided a small improvement in dye saturation, thus providing an improved dye composition for HRM assays.
As one example, dye blend V11-02190 and EVAGREEN® improved the fluorescence signal compared with either dye alone, and improved Cq compared with EVAGREEN® alone. Dye blend V11-02190 and EVAGREEN® greatly improved dye saturation, thus providing an improved dye composition for HRM assays. Without being held to a single theory, it is believed that this effect may indicate that dyes having different structures in a dye blend have different modes of binding to dsDNA, and that the higher saturation results from an additive effect.
Mixing two different dsDNA binding dyes demonstrated improved properties compared with the individual dyes alone. The dye blends had higher fluorescence, and the same or lower Cq compared to each dye alone. The dye blends resulted in an additive effect on dsDNA saturation, which was achieved at dye concentrations that were not inhibitory to qPCR. The dye blends showed an additional effect beyond simply increasing the concentration of the individual dyes which, due to higher concentrations of either dye alone, exceeded the optimal concentration and inhibited DNA polymerase. The dye blends showed a synergistic effect by improving performance beyond the performance of each dye alone. This synergistic effect may reflect different binding modes on the dsDNA, as this effect was demonstrated to a greater extent when two structurally dissimilar dyes were in the dye blend, e.g., V11-02190 and EvaGreen.
As one example, dye blend V11-02190 and LCGREEN® improved the fluorescence signal and improved Cq compared to each dye alone. It provided an improved dye composition for HRM assay. This indicated that two structurally different dyes in a dye blend have different modes of binding to dsDNA, as the result of a dye blend shows a synergistic effect.
As one example, dye blend EVAGREEN® and LCGREEN® improved the dye saturation percentage, thus providing an improved dye composition for HRM assays. The dye blends showed a synergistic effect by improving performance beyond the HRM performance of each dye alone.
Without being bound to a single theory, the improved characteristics of the described dsDNA binding dye blends may increase the design space for dye concentration in a mix for HRM and qPCR. Using the blend of dsDNA binding dyes permits fluorescence maxima to be achieved at a lower concentration of each dye than using each individual dye alone, and at a concentration that is less inhibitory to DNA polymerase enzymes. The dye blends improved the fluorescence characteristics of qPCR and HRM, and also overcame the problems of qPCR inhibition associated with saturating concentrations of dsDNA binding dyes.
The embodiments shown and described in the specification are only specific embodiments of inventors who are skilled in the art and are not limiting in any way. Therefore, various changes, modifications, or alterations to those embodiments may be made without departing from the spirit of the invention in the scope of the following claims.
All references, including U.S. Pat. Nos. 7,776,567; 7,456,281; 5,436,134; and 5,658,751, and U.S. Published Patent Application No. 20100167279 are expressly incorporated by reference herein in their entirety.
Applicants incorporate by reference the material contained in the accompanying computer readable Sequence Listing identified as Sequence_Listing_ST25.txt, having a file creation date of Aug. 15, 2012 12:01 P.M. and file size of 2.37 kilobytes.
This application claims priority to co-pending U.S. application Ser. No. 61/528,315 filed Aug. 29, 2011, which is expressly incorporated by reference herein in its entirety.
| Number | Date | Country | |
|---|---|---|---|
| 61528315 | Aug 2011 | US |
