WO2009046010A2

WO2009046010A2 - Monomethine dyes

Info

Publication number: WO2009046010A2
Application number: PCT/US2008/078277
Authority: WO
Inventors: Charles Brush; Jianqin Liu; Peter Czerney; Matthias Wenzel
Original assignee: Charles Brush; Jianqin Liu; Peter Czerney; Matthias Wenzel
Priority date: 2007-10-02
Filing date: 2008-09-30
Publication date: 2009-04-09
Also published as: EP2201009A2; US20100285470A1; EP2436780A2; EP2436780A3; WO2009046010A3; EP2201009A4; US8378115B2; EP2201009B1; EP2436780B1; EP3118201A1

Abstract

Monomethine dyes that have no or minimal fluorescence in buffer or in the presence of single stranded DNA or RNA, but strongly fluoresce in the presence of double-stranded DNA. In one embodiment, the dye is useful in quantitative RT-PCR.

Description

MONOMETHINE DYES

This application claims priority to co-pending U.S. application Serial No. 60/976,822, filed October 2, 2007, and is hereby incorporated by reference in its entirety. BACKGROUND

A polymethine dye is a dye having a linearly conjugated system with an odd number of methine (-CH=) groups, where the terminal heteroatoms N, O, or S, eventually are included in two terminal heterocycles Het| and Het₂. As described herein, polymethines are a delocalized π (pi) electron system, represented by at least in two equivalent formulas shown below:

A monomethine dye has n = 0, thus having a single -C= between the heterocycles. When n = 1, the dye is a trimethine, and so on.

Numerous monomethine dyes are known. Some monomethine dyes have the characteristic of no or minimal fluorescence in buffer or in the presence of single stranded DNA (ssDNA) or RNA, but strong fluorescence in the presence of double-stranded DNA (dsDNA). Examples of such dyes, which are commercially useful because of this characteristic, include SYBR Green, Thiazole Orange, BOXTO, Eva Green, and LC Green. SYBR Green, the structure of which is shown below,

is one the most commonly used fluorescent dyes.

Benzopyrylium monomethines are known, but none has the side chain needed for utility in fluorescence studies, and none has been used in dsDNA binding assays.

Other such dyes are desirable. BRIEF DESCRIPTION OF THE DRAWINGS

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.

FIG. 1 shows the general structure of benzopyrylium monomethine compounds. FIGS. 2A and 2B show the general structures of two classes of monomethine dyes: FIG. 2A having a benzthiazole moiety, and FIG. 2B having a benzoxazole moiety.

FIG. 3 shows the structure of one type of benzopyrylium monomethine dye.

FIG. 4A, 4B, and 4C show the structure of other types of benzopyrylium monomethine dyes.

FIG. 5A shows the fluorescent spectra of V02-07015.

FIG. 5B shows the fluorescent spectra of V02-07027.

FIG. 5C shows the fluorescent spectra of V13-01184.

FIG. 5D shows the fluorescent spectra of V11 -03001.

FIG. 6 shows quantitative real time polymerase chain reaction (qRT-PCR) data using V02-07027 dye

FIG. 7 shows qRT-PCR data using V02-07015 dye.

FIG. 8 shows data from a melting experiment with V02-07027 dye.

FIG. 9 shows fluorescence spectra of V11-03001 in the presence of DNA or RNA.

FIG. 10 shows low range RNA quantification using V11-03001.

FIG. 11 shows high resolution screening data of a representative dye.

FIG. 12 shows high resolution melting curves with commercial dyes.

DETAILED DESCRIPTION

Compounds and their compositions, also referred to herein as dyes, are disclosed. The disclosed dyes have enhanced fluorescence, in some cases fluorescence comparable to commercially available dsDNA binding dyes. They have enhanced selective binding to double stranded DNA (dsDNA) compared to single stranded DNA (ssDNA), that is, they have minimal fluorescence in the absence of dsDNA and significance fluorescence in the presence of dsDNA. They have enhanced brightness, and are used to detect PCR amplicons in quantitative real time polymerase chain reaction (qRT-PCR). In embodiments, the dyes may exhibit affinity for RNA.

To produce such dyes, a series of monomethine compounds that include the benzopyrylium moiety were synthesized. The general chemical structure of the benzopyrylium monomethine compound is shown in FIG. 1; substitutions for R in addition to alkyl, aryl, and aralkyl are possible.

More specifically, these compounds have the formula

anion 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 R^B, 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 ore more heteroatoms;

R¹³is selected from a linear or branched hydrocarbon that is saturated or unsaturated, optionally containing one or more heteroatoms, optionally containing a tetraalkylammonium group; aryl or pyrimidyl; or NR¹⁴R¹⁵ where R¹⁴ and R¹⁵ are the same or different and are independently H or a hydrocarbon, optionally containing one or more heteroatoms, optionally containing a tetraalkylammonium group, or R¹⁴ and R¹⁵ in combination complete a five, six, or seven membered saturated ring, optionally containing one or more heteroatoms, and optionally containing a quaternary ammonium group; or R¹³ is a linker connecting the rest of the molecule to another benzopyrylium methine dye, forming a dimer dye structure. The dyes of the dimer may be the same or different.

X is selected from the group consisting of O, S, Se, NR¹⁶ where R¹⁶ is H or a hydrocarbon optionally containing one ore 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 inclusive; and anion is a counterion.

The general structures of two classes of monomethine dyes is shown in FIGS. 2A and 2B; FIG. 2A shows a compound with a benzthiazole moiety, and FIG. 2B shows a compound with a benzoxazole moiety.

Benzopyrylium monomethine compounds were synthesized generally by condensation of an activated methyl group on the benzopyrylium moiety and an activated sulfide on the other heterocycle in the presence of a tertiary amine. An example of the reaction is shown below

Synthesis and properties of representative compounds was as follows. V02-07027

1 2

100 mg (240 μmol) benzopyrylium-salt 1 and 93 mg (312 μmol) of 2-(ethylthio)-3-methyl-1 ,3-benzothiazol- 3-ium tetrafluoroborate 2 were mixed in 10 mL ethanol. Ethyldiisopropylamine (53 μl_ (312 μmol)) was added and the mixture was refluxed for two hours. The reaction mixture was then cooled and the ethanol was removed under vacuum. The yellow/brown residue was purified by column chromatography. Yield: 40 % C₂₈H₃₇N₄OS⁴BF₄ M = 564.50 g/mol λ_maχ = 477 nm (ethanol) ε = 60,000 L/mol^*cm

V13-01184

100 mg (232 μmol) benzopyrylium-salt 1 and 93 mg (312 μmol) of 2-(ethylthio)-3-methyl-1 ,3-benzothiazol-

3-ium tetrafluoroborate 2 were mixed in 10 mL ethanol. Ethyldiisopropylamine (53 μl_ (312 μmol)) was added and the mixture was refluxed for two hours. The reaction mixture was then cooled and the ethanol was removed under vacuum. The yellow/brown residue was purified by column chromatography.

Yield: 42 %

C₂₈H₃₅N₄O₂S⁴BF₄

M = 578.48 g/mol λm_ax = 481 nm (ethanol) ε = 83,000 L/mol*cm

V02-07015

100 mg (286 μmol) benzopyrylium-salt and 87 mg (286 μmol) 2-(ethylthio)-3-ethyl-1,3-benzothiazol-3-ium tetrafluoroborate were dissolved in 10 mL ethanol, followed by addition of 49 μl_ (286 μmol) ethyldiisopropylamine. The mixture was refluxed for about one hour, cooled to ambient temperature (about 2O⁰C to about 22⁰C), then the ethanol was removed under vacuum. The brown residue was purified by column chromatography. Yield: 20 % C₃₀H₄₀N₃OS*CIO₄ M = 590.12 g/mol λ_max = 522 nm (ethanol) ε = 50,000 L/mol^*cm

V13-01026

100 mg (232 μmol) benzopyrylium-salt 1 and 83 mg (232 μg) benzopyrylium-salt 2 were mixed in 10 mL ethanol. Ethyldiisopropylamine (40 μL (232 μmol)) was added and the mixture was refluxed for one hour.

After cooling to ambient temperature (about 2O⁰C to about 22⁰C), the resulting red precipitate was filtered off, washed with diethylether, and dried.

Yield: 15 %

C₃₄H₃₇N₄(VBF₄

M = 630.57 g/mol λ_max = 585 nm (ethanol) ε = 50,000 L/mol*cm

V02-06187

1 2 '

100 mg (264 μmol) benzopyrylium-salt 1 and 82 mg (264 μmol) 2-(ethylthio)-3-ethyl-1 ,3-benzothiazol-3- ium tetrafluoroborate 2 were mixed in 10 mL ethanol. Ethyldiisopropylamine (40 μL (232 μmol)) was added and the mixture was refluxed for one hour, followed by addition of 80 mg (528 μmol) sodium iodide. After cooling to ambient temperature (about 2O⁰C to about 22⁰C), the resulting orange precipitate was filtered off, washed with diethylether, and dried.

Yield: 25 %

C₂₉H₂₉N₂OS*!

M = 580.53 g/mol λm_ax = 550 nm (ethanol) ε = 55,000 L/mol*cm

V02-06188

100 mg (264 μmol) benzopyrylium-salt 1 and 78 mg (264 μmol) 2-(ethylthio)-3-ethyl-1 ,3-benzoxazol-3-ium tetrafluoroborate 2 were mixed in 10 mL ethanol. Ethyldiisopropylamine (40 μl_ (232 μmol)) was added and the mixture was refluxed for one hour followed by addition of 80 mg (528 μmol) sodium iodide. After cooling to ambient temperature (about 2O⁰C to about 22⁰C), the resulting orange precipitate was filtered off, washed with diethylether, and dried.

Yield: 15 %

C₂₉H₂₉N₂O₂ ⁴BF₄

M = 524.36 g/mol λmax = 520 nm (ethanol) ε = 55,000 L/mol^*cm

V02-07108

1 2

100 mg (240 μmol) benzopyrylium-salt 1 and 93 mg (312 μmol) of 2-(ethylthio)-3-methyl-1,3-benzothiazol- 3-ium tetrafluoroborate 2 were mixed in 10 mL ethanol. Ethyldiisopropylamine (53 μL (312 μmol)) was added and the mixture was refluxed for two hours. The reaction mixture was then cooled and the ethanol was removed under vacuum. The yellow/brown residue was purified by column chromatography. Yield: 40 % C₂₈H₃₇N₄OS⁴BF₄ M = 564.50 g/mol λmax = 498 nm (ethanol) ε = 50,000 L/mol*cm In embodiments, the monomethine compounds may also include a tetralkylammonium and/or quaternary ammonium group. Examples of such compounds include

V11-03001

V11-02190

BF₄

V13-02162

Side chains useful for dsDNA binding, such as dimethylaminopropylmethylamine and analogues that provide a positive charge at the pH used in assays, were appended to the general dye.

The resulting structures are grouped as Groups A, B, C, D, and E, shown below. Substituents for X, R7, R9, R10, R12, and R13 are shown in Table 1 below.

In embodiments, the monomethine compounds may also include dimers of the disclosed structures. Examples of such compounds include

V13-01170

and

These compounds were dissolved in a biocompatible excipient, such as a buffer, and were evaluated in assays for fluorescence in the presence of ssDNA (40mer ssDNA), and in the presence of two kinds of dsDNA (40mer dsDNA and λDNA), as explained below.

Stock solutions (8 mM) of each dye were prepared by dissolving each compound in dimethylsulfoxide (DMSO). Stock dye solutions were diluted to a desired concentration in tris-EDTA (TE) buffer (10 mM Tris, 1 mM EDTA, pH 8.0) immediately prior to use.

Stock solutions of λ DNA and 40mer synthetic oligonucleotides (dsDNA and ssDNA), each at a concentration of 40 μM, were prepared in TE buffer. All DNA concentrations described are in base pairs of nucleotides. The DNA stock solutions were diluted to a desired concentration in TE buffer before being mixed with diluted dye solutions.

Absorption spectra of the each dye alone (8 μM solutions in TE buffer) were measured on a Perkin Elmer LS55 fluorimeter. Absorption spectra of each dye-DNA complex were obtained by incubating 8 μM dye with 8 μM DNA in TE buffer for ten minutes. Optical densities were determined at the absorbance maxima and the extinction coefficients were calculated using Beer's law.

Fluorescence enhancement measurements of each dye were obtained by incubating dyes with λDNA, 40mer dsDNA, or 40mer ssDNA at a final concentration of 0.8 μM dye and 3.2 μM DNA for one minute. Fluorescence scans of the samples were performed with excitation wavelengths corresponding to the absorption maxima of the dyes. The resulting fluorescence intensities were compared to fluorescence intensities of Thiazole Orange (TO) and a compound equivalent to SYBR Green without the side chain (V02-06101), shown below,

TO V02-06101 binding to λDNA, 40mer dsDNA, or 40mer ssDNA at a final concentration of 0.8 μM TO and 3.2 μM DNA for one minute, the same as for the tested dyes. The discrimination ratio between dsDNA and ssDNA was calculated by comparing the fluorescence intensities.

Final candidate compounds were then synthesized with the dimethylaminopropyl)methyiamine side chain. A preliminary evaluation of these candidate compounds was conducted assessing fluorescence upon binding to the 240mer PCR amplicon or λ DNA. The most promising candidates were tested in quantitative real time polymerase chain reactions (qRT-PCR) on a commercially available instrument, using either commercially available mastermixes of reagents or individually prepared reagents.

Results for the disclosed dyes were evaluated in comparison to the following parameters of the known dye, SYBR Green: absorption ± 3 nm of SYBR Green (λ_max (abs) = 494 nm) emission ± 3 nm of SYBR Green (λ_max (em) = 524 nm) extinction coefficient (ε) not less than 68,000 (SYBR Green ε = 73,000) ratio of fluorescence with dsDNA to ssDNA 25 : 1 fluorescence > SYBR Green compatibility with same buffers used with SYBR Green no inhibition of PCR. Results for fluorescence induced by benzopyrylium monomethine dyes binding to dsDNA are shown in Table 1

Each of the benzopyrylium monomethines of FIGS. 2A, 2B, 3, 4A, 4B, and 4C exhibited strong fluorescence in the presence of dsDNA; some approached the fluorescence of SYBR Green. The compound shown in FIG. 3 had about 50% of the fluorescence of SYBR Green in the presence of dsDNA. It was evaluated in qRT PCR.

Compounds V02-07015, V13-01184, V13-01170, V02-07108, V11-03001 , V02-07027 and V12- 02144 were evaluated.

Among these compounds, V13-01184, V11-03001 , V02-07015 and V02-07027 showed increased fluorescence in the presence of DNA compared to other compounds, as shown in FIGs. 5A-5D, with the dyes in the presence of TE buffer, 40mer ssDNA, 40mer dsDNA, λ DNA , and rRNA, as indicated. The fluorescence intensities were 4 to 8 times higher than that for the reference Thiazole Orange Dye (Table 3). Dye V13-01184, V11 -03001 , V02-07015 and V02-07027 also showed discrimination between dsDNA and ssDNA. The fluorescence intensities in the presence of dsDNA were 1.4 - 3.7 times higher than corresponding intensities in the presence of ssDNA (Table 3). It was noted that substitution of long amino side chain on the R10 or R7 position in Group B dyes increased the fluorescence intensity in the presence of DNA (for example dye V02-07015 and V02-07027). Substitution the R10 group with pyperazine ethanol side chain increased the fluorescence significantly (dye V13-01184 and V11-03001). Among all the dyes studied, dye V11-03001 showed the strongest fluorescence enhancement, which was comparable to that for SYBR Green dye.

Table 1. Spectral characterization

Table 2. Absorption spectra characterization in the presence of DNA

Table 3. Fluorescence spectral characterization in the presence of DNA

Dyes were investigated for RNA binding, some of which showed fluorescence enhancement in the presence of rRNA. Dyes V13-01184 and V11-03001 showed significant fluorescence enhancement when bound with RNA. V11-03001 showed the brightest fluorescence among all tested dyes and also showed a 12 nm red shift between RNA and DNA binding. The spectral properties are provided in Tables 4 and 5.

Table 4. S ectral characterization of the d es in the presence of DNA/RNA

Table 5. Fluorescence characterization of dyes in the presence of DNA

Real-time PCR was performed in 25 μL volumes on a Stratagene^® MX3005p (Stratagene, La JoIIa CA). The following PCR protocol was used to amplify a 94 base pair (bp) product from the Human GAPDH gene; 95⁰C x 10 min, followed by 45 cycles of 95⁰C x 20 sec, 60⁰C x 20 sec, and 72⁰C x 22 sec (data collected at 72°C step). Each amplification reaction (25 μL) included 10 ng of Human Genomic DNA template (Sigma), 200 μM of each dNTP, 3 mM MgCI₂, 5OmM KCL, 10 μm EDTA, 10 mM Tris, 5% DMSO, 70 nM of both forward (5¹ ACA GTC AGC CGC ATC TTC TT) and reverse (5' ACG ACC AAA TCC GTT GAC TC) primers, and 0.625 units of Taq DNA polymerase (Thermo Scientific). The dyes were included at varying concentrations. ABsolute™ QPCR SYBR^® Green master mix (Thermo Scientific) was used for amplification when SYBR^® Green I was required as the indicator. No template control (NTC) reactions without DNA were also included. The fluorescent signal was monitored in the following five channels (nm excitation/nm emission): 492/516, 535/555, 545/568, 585/610, and 635/665. Presence of amplicon was determined using post-amplification melt-curve analysis (95°C x 60 sec x 1 cycle, 6O⁰C x 30 sec x 1 cycle followed by 95°C x 30 sec (with continuous data collection during ramping)) and agarose gel electrophoresis. All reactions were performed in triplicate but are shown as a single curve (average of the three individual reactions).

To evaluate the ability of the dyes to detect PCR products in real-time, a 94 bp fragment of the human GAPDH gene was amplified from 10 ng of human genomic DNA. Each of dyes V02-07027 and V02-07015 at 80 ng, 120 ng, and 160 ng were included in 25 μL amplification reactions (previous experiments were used to narrow the testing range of the dyes).

FIG. 6 shows the monitored fluorescent signal from the varying concentrations of the dye V02- 07027 to optimize the amount of dye to be used when monitored using the 492/516 nm filter set. The increase in fluorescence after each cycle, for all the dye concentrations, followed the predicted shape of a typical real-time PCR amplification (that of a sigmoid curve) and also resembled that observed from the amplification mixture containing SYBR^® Green I. No increase in fluorescence was detected for the NTC reactions. Dye amounts greater than 80 ng inhibited PCR. No increase in fluorescence was detected when using any of the other monitored filter sets.

FIG. 7 shows the monitored fluorescent signal from varying concentrations of the dye V02-07015 when monitored using the 535/555 nm filter set. The increase in fluorescence after each cycle, for all the dye concentrations, followed the predicted shape of a typical real-time PCR amplification (that of a sigmoid curve). Amplification of product using the SYBR^® Green I mixture was not detected when fluorescence was monitored in this wavelength. No increase in fluorescence was detected for the NTC reactions. No inhibition of PCR was observed with increasing amounts of dye. No increase in fluorescence was detected when using any of the other monitored filter sets.

The disclosed dyes can also be used to confirm the presence of specific amplicon when using post-amplification melt curve analysis. As shown in FIG. 8, the derivative plot of the melt curve analysis, there was a single peak corresponding to a single amplicon produced during PCR. No peaks were observed in the NTC reactions.

Compound V02-07027 was also used to detect the formation of longer PCR amplicons using qRT-PCR: The following bp fragments were used: 110 bp and 925 bp fragments from human β-actin gene, a 309 bp fragment from human Survivin gene, and a 413 bp fragment from human lntegrin α5 gene. Real time PCR was performed on a Stratagene^® MX3000 (Stratagene, La JoIIa CA) instrument using an excitation wavelength of 492 nm and an emission wavelength of 516 nm. Each amplification reaction (25 μl) contained 10 ng or 100 ng of human Genomic DNA, 200 μM of each dNTP, 1.5 mM MgCI₂, 5OmM KCL, 10 mM Tris-HCI, 400 nM of each of forward and reverse primers, and 2.5 units of Taq DNA polymerase (Thermo Fisher Scientific (Milwaukee Wl)). Varying amounts of V02-07027 or a dye such as SYBR® Green (Invitrogen) were added to the reaction mix. Reactions were performed in triplicate and the data points represented the average signal.

The dye VO2-07027, at concentrations ranging between 20 ng to 60 ng, bound to amplified DNA fragments, generating a fluorescent signal. The dye bound to varying lengths of amplicons (example 110 bp, 309 bp, 413 bp, and 925 bp) generating a fluorescent signal. The dye was able to bind to amplicons derived from varying amounts of the starting template (example, 10 ng, 100 ng). The dye could be used to measure the product of the amplification reaction based on the fluorescent signal generated upon dye binding to dsDNA. The increase in fluorescent signal during the PCR amplification corresponded to the increase in the amplified DNA that was generated in the reaction.

Detecting and quantifying small amounts of RNA is important in many determinations such as quantitating in vitro transcription yields and quantitating RNA concentration before performing RNA containing assays. RNA is typically quantitated by determining absorbance at 260 nm (λ₂6o), but disadvantages include protein interference, DNA absorbance, and the need for high concentration of RNA (> 4 μg/ml). More sensitive fluorescence methods must be used to quantitate small amounts of RNA. A widely used RNA quantitation dye is RiboGreen^® (Invitrogen), where 1 ng/ml of RNA can be detected and quantitated with a standard fluorometer, fluorescence microplate reader, or filter fluorometer.

In one embodiment, the inventive composition binds RNA. In one embodiment, compounds are provided that bind RNA in the absence of DNA. In one embodiment, the absence of DNA means substantially free of DNA and may be accomplished by methods known to a person of ordinary skill in the art such as treatment with a DNA nuclease. In one embodiment, the compounds exhibit increased fluorescence in the presence of RNA. In one embodiment, the compounds may be used to quantitate the amount of RNA present in a solution. For example, following the method of U.S. Patent Publication 20070072229, which is hereby incorporated by reference in its entirety, the resulting RNA may be quantitated using at least one of the present compounds. In one embodiment, at least one of compounds V11-03001 , V11-02190, and V13-02162 exhibit affinity for RNA and may be used to detect and/or quantitate RNA.

In one embodiment, the V11-03001 compound may be used to quantitate RNA. The V11-03001 compound is not fluorescent by itself, as shown in FIG. 9, but in the presence of rRNA, the dye shows strong fluorescence with maximum emission at 552 nm (A₅₅₂). The dye also shows fluorescence in the presence of DNA, however, the maximum for dye/DNA complex is shifted to 540 nm, as shown in FIG. 9. Additionally, with V11-03001 there was a linear relationship between fluorescence intensity and total RNA concentration in the low range RNA assay, as shown in FIG. 10. Fluorescence intensities were comparable to those using RiboGreen^®.

In one embodiment, the dyes can be used in high resolution melting (HRM) curve analysis after qRT-PCR to verify, for example, that the desired product was amplified. In one embodiment, the dyes could be used to detect the presence of genetic variation, including heterozygous single base changes. Heteroduplex and homoduplex detection may be used for a variety of analyses, including mutation scanning and genotyping. Scanning is the process in which a nucleic acid fragment is compared to a reference nucleic acid fragment to detect the presence of any difference in sequence. A positive value indicates the presence of a sequence difference but may not necessarily reflect the exact nature of the sequence variance or its position on the nucleic acid fragment. Genotyping includes the detection and determination of known nucleic acid sequence variances, including but not limited to, SNPs, base deletions, base insertions, sequence duplications, rearrangements, inversions, base methylations, number of short tandem repeats; and in the case of a diploid genome, whether the genome is a homozygote or a heterozygote of the sequence variance, as well as the cis/trans positional relationship of two or more sequence variances on a DNA strand (haplotyping).

Single nucleotide polymorphisms (SNPs) are common genetic variations where a variation occurs only in a single base. The alteration may cause an amino acid change in a protein, alter rates of transcription, affect mRNA spicing, or have no apparent effect on cellular processes. In some cases, even if the change is silent (e.g., when the amino acid for which it codes does not change), SNP genotyping may still be valuable if the alteration is associated with a unique phenotype caused by another genetic alteration. Methods for genotyping SNPs include gel electrophoresis, mass spectrometry, and fluorescence. Fluorescence techniques that are homogeneous, and do not require adding reagents after commencement of amplification or physical sampling of the reactions for analysis are desirable.

High resolution melting is a rapid, high-throughput method for mutation scanning and genotyping, based on the melting point (T_m ) DNA being inversely proportional to the hydrogen bonding strength of the constituent base pairs. Single base pair changes are detected by analyzing the shift in T_m of the melting curves due to differences in hydrogen bonding strength. The amplicons are denatured and, using a highly sensitive optical detector, the dsDNA binding to one of the disclosed dyes is tracked by monitoring fluorescence across an accurately controlled temperature range. The resulting melting profiles can identify the presence of sequence variations within the amplicon.

In one embodiment, dyes used for HRM are saturation dyes. Saturation dyes are generally dyes that do not significantly inhibit PCR when present at concentrations that provide maximum fluorescence signal for an amount of dsDNA typically generated by PCR in the absence of dye. Although saturation dyes are identified by their compatibility with PCR at near saturating concentrations, it is understood that the dyes can be used at much lower concentrations. In embodiments, the dye can be added, e.g., after the PCR reaction. Thus, dyes that do inhibit PCR at or near saturating concentrations may be used.

FIG. 11 shows a representative dye binding to three different DNA samples, permitting discrimination among single base pair changes among these DNA samples. FIG. 12 shows melting curves for wild type DNA and heterozygote mutant DNA treated with LCGreen^® Plus or SYBR^® Green I. The melting curves were analyzed by generating a derivative curve and analyzing the shape and location of one or more melting peaks on the derivative melting curve, as known to a person of ordinary skill in the art. The negative first derivative of the melting curve is plotted on the y axis, with temperature plotted on the x axis. Expressed in another way, a melting temperature profile may be graphically represented by plotting -dF/dT against T, where dF is the change in measured fluorescence emission, dT is the change in temperature of the nucleic acid, and T is the temperature of the nucleic acid. Such a graphic representation will show peaks at temperatures at which the most rapid changes in fluorescence occur, indicating melting temperatures. By accurately measuring the melting temperature, the presence of a heteroduplex, for example, created by a mutation, which would effect the melting temperature, is determined. The heteroduplex that is formed during PCR due to the heterozygous mutant was detected using LCGreen^® Plus, but was not detected using SYBR^® Green I. These results indicated that LCGreen^® Plus had higher sensitivity than SYBR^® Green I. Similar results are obtained using the disclosed dyes. In one embodiment, a method is provided that requires only a standard PCR mixture, including reagents such as a thermostable polymerase, such as Taq, and deoxyribonucleotide triphosphates (dNTPs), primers, and addition, prior to PCR, of one of the inventive dsDNA binding dyes. In one embodiment, scanning or genotyping is performed by melting curve analysis in the presence of one or more unlabeled probes and at least one of the disclosed double-stranded binding dyes. The melting curve analysis may take place during or subsequent to amplification, or in the absence of amplification. The dye may be at a saturating concentration.

In one embodiment, the dye may be added prior to PCR. When dye is added prior to a PCR reaction, it is often desirable that the dye does not interfere with the PCR reaction. In such embodiments, the dye may be a saturation dye. In one embodiment, the dye may be added after PCR. In such embodiments, a saturation dye and/or saturating concentrations of the dye need not necessarily be used.

While the disclosed dyes have been described in the context of real-time quantitative PCR analyses and melting curve analysis, it is understood that the inventive dyes may be used for a variety of methods such as nucleic acid quantitation, determination of initial nucleic acid concentration, testing for the presence of a nucleic acid, multiplexing with labeled probes, and other PCR-based methods.

In one embodiment, the disclosed dyes are used to label nucleic acids such as dsDNA in the nucleus of a cell. For example, the dyes can be used to label nucleic acids in samples that either contain, or are capable of containing, nucleic acids; such samples include, but are not limited to, cell lysate, tissue lysate, tissue culture, forensic samples, etc. When used to stain cells or tissues, the cells or tissues may be either live or fixed (e.g., histologically preserved). The sample was combined with the dye at an appropriate concentration and under appropriate conditions (e.g., temperature, pH, etc.) to evaluate fluorescence and hence to qualitatively detect the presence of nucleic acid in the sample. The concentration of nucleic acid in the sample may be quantitated by combining the sample with a biocompatible composition of the compound, incubating under conditions sufficient to result in a dye-nucleic acid complex yielding a detectable fluorescent signal, and quantitating nucleic acid by comparing fluorescence of the sample with fluorescence of a known quantity of nucleic acid.

In one embodiment, the disclosed dyes are used to specifically stain cell organelles. As one example, V02-06132 may be used as an RNA specific dye in cell organelles and may be used to monitor patterns and/or kinetics of gene expression and RNA transport. In one embodiment, the dye is reconstituted in dimethyl sulfoxide (DMSO) at about 1 mg/ml and then added to cells at a final concentration ranging from about 30 nM to about 1 μM. The cells are then incubated with the dye for a time and at a temperature that optimizes staining. In one embodiment, the cells may be incubated with the dye for about 15 minutes to about 1 hour at about 37⁰C and then imaged. In one embodiment, the cells are first fixed and then subjected to staining with the dye. In one embodiment, the cells are fixed with 4% paraformaldehyde, washed, and then incubated with dye for 15 minutes, followed by cell imaging.

As one example, V02-07027 may be used as a DNA specific stain in cell organelles. It may be used to assess, e.g., DNA content, chromosome staining, localization, compartmentalization, cell proliferation, cell viability, cytotoxicity, etc. In one embodiment, the dye is reconstituted in DMSO at about 1 mg/ml and then added to the cells at a final concentration ranging from about 30 nM to about 1 μM. The cells are then incubated with the dye for a time and at a temperature that optimizes staining. In one embodiment, the cells may be incubated with the dye for about 15 minutes to about 1 hour at about 37⁰C and then imaged. In one embodiment, the cells are first fixed and then subjected to staining with the dye. In one embodiment, the cells are fixed with 4% paraformaldehyde, washed, and then incubated with dye for 15 minutes, followed by cell imaging.

As other examples, V13-01026, V02-06136, and V02-06139 may be mitochondria specific stains and may be used, e.g., to track mitochondrial changes during apoptosis, investigate mitochondrial toxicity, uncoupling, anoxia, etc. Mitochondrial specific dyes may be combined with a mitochondrial membrane potential sensor and used to monitor effects of drugs on mitochondrial membrane potential. In one embodiment, the dye is reconstituted in DMSO at about 1 mg/ml and then added at a final ccncentration ranging from about 30 nM to about 1 μM to the cells. In one embodiment, the cells are incubated with dye at a concentration in the range of about 0.8 μM to about 2.5 μM. The cells are then incubated with the dye for a time period and at a temperature which optimizes staining. In one embodiment, the cells may be incubated with the dye for about 15 minutes to about 1 hour at about 37⁰C and then imaged. In one embodiment, the cells are first fixed and then subjected to staining with the dye. In one embodiment, the cells are fixed with 4% paraformaldehyde, washed, and then incubated with dye for 15 minutes, followed by cell imaging.

As one example, V13-01035 may be a lysosome specific stain.

The embodiments and examples described are only illustrative and are not limiting in any way. As one example, the benzoxazole compound VO2-06188 was tested and had a slight preference for binding to dsDNA over binding to ssRNA. Other benzoxazole compounds will likely also bind to dsDNA to a greater extent than will bind to ssDNA or RNA. As other examples, some aryl, oxazole, thiazole, 4-quinoline, 4-benzopyrylo, and 2- benzopyrylo compounds and dye compositions will likely bind to dsDNA to a greater extent that will bind to ssDNA or RNA. Therefore, various changes, modifications or alterations to these embodiments may be made without departing from the spirit of the invention and the scope of the following claims.

What is claimed is:

Claims

A compound having a formula selected from at least one of

or

Anion - wherein 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 ore more heteroatoms; R¹³ is selected from a linear, cyclic, or branched hydrocarbon that is saturated or unsaturated, optionally containing one or more heteroatoms, optionally containing a tetraalkylammonium group; aryl or pyrimidyl; or

NR¹⁴R¹⁵ where R¹⁴ and R¹⁵ are the same or different and are independently H or a hydrocarbon, optionally containing one or more heteroatoms optionally containing a tetraalkylammonium group, or R¹⁴ and R^1S in combination complete a five, six, or seven membered saturated ring, optionally containing one or more heteroatoms optionally containing a quaternary ammonium group; or

R¹³ is a linker connecting the rest of the molecule to another benzopyrylium methine dye, forming a dimer dye structure. The dyes of the dimer may be the same or different. X is selected from the group consisting of O, S, Se, NR¹⁶ where R¹⁶ is H or a hydrocarbon optionally containing one ore 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.

2. A composition comprising a compound having the formula selected from at least one of

R¹ and R², R² and R³, R³ and R⁴, R⁴ and R⁵, R⁷ and R^s, 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, cyclic, or branched hydrocarbon, optionally containing one ore more heteroatoms;

R¹³ is selected from a linear or branched hydrocarbon that is saturated or unsaturated, optionally containing one or more heteroatoms optionally containing a tetraalkylammonium group; aryl or pyrimidyl; or NR¹⁴R¹⁵ where R¹⁴ and R¹⁵ are the same or different and are independently H or a hydrocarbon, optionally containing one or more heteroatoms optionally containing a tetraalkylammonium group, or R¹⁴ and R¹⁵ in combination complete a five, six, or seven membered saturated ring, optionally containing one or more heteroatoms optionally containing a quaternary ammonium group; or

R¹³ is a linker connecting the rest of the molecule to another benzopyrylium methine dye, forming a dimer dye structure. The dyes of the dimer may be the same or different.

X is selected from the group consisting of O, S, Se, NR¹⁶ where R¹⁶ is H or a hydrocarbon optionally containing one ore 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, and a biocompatible excipient.

3. The compound of claim 1 or the composition of claim 2 wherein the compound is selected from the group consisting of

and

4. An method for detecting double stranded deoxyribonucleic acid (dsDNA), the method comprising, providing a sample capable of containing dsDNA and a compound having a formula selected from at least one of

Anion -

wherein each of R¹ - R¹⁰ and R¹² is independently H or a linear or branched hydrocarbon, optionally containing one or more heteroatoms;

R¹¹ is a linear or branched hydrocarbon, optionally containing one ore more heteroatoms; R¹³ is selected from a linear, cyclic, or branched hydrocarbon that is saturated or unsaturated, optionally containing one or more heteroatoms optionally containing a tetraalkylammonium group; aryl or pyrimidyl; or

NR¹⁴R¹⁵ where R¹⁴ and R¹⁵ are the same or different and are independently H or a hydrocarbon, optionally containing one or more heteroatoms optionally containing a tetraalkylammonium group, or R¹⁴ and R¹⁵ in combination complete a five, six, or seven membered saturated ring, optionally containing one or more heteroatoms optionally containing a quaternary ammonium group; or

R¹³ is a linker connecting the rest of the molecule to another benzopyrylium methine dye, forming a dimer dye structure. The dyes of the dimer may be the same or different. X is selected from the group consisting of O, S, Se, NR¹⁶ where R¹⁶ is H or a hydrocarbon

■>17_D18 , optionally containing one ore more heteroatoms, and CR^R¹⁰ where R i1¹7' a . nd 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 under conditions sufficient for the compound to bind to dsDNA, and assaying the sample for fluorescence indicating binding of the compound to dsDNA.

5. The method claim 4 wherein the compound is selected from the group consisting of

and

6. The method of claim 4 wherein quantitation of fluorescence in the sample quantitates dsDNA in the sample.

7. The method of claim 4 performed in a quantitative polymerase chain reaction (qPCR) or a real time polymerase chain reaction (qRT-PCR).

8. A fluorescent complex comprising a nucleic acid non-covalently bound to at least one compound of claim 1.

9. A method of quantitating nucleic acids in a sample, the method comprising combining a sample with the composition of claim 2, incubating the sample and composition under conditions sufficient for the compound to combine with the nucleic acid to form a dye-nucleic acid complex that yields a detectable fluorescent signal; and quantitating the nucleic acid in the sample by comparing the fluorescent signal with the signal from a known quantity of nucleic acid.

10. The method of claim 9 wherein the nucleic acid is double stranded deoxyribonucleic acid (dsDNA).

11. The method of claim 9 wherein the nucleic acid is ribonucleic acid (RNA).

12. A compound having a structure selected from the group consisting of

BF₄

BF, and

13. A composition comprising a compound having at least one of the structures of claim 12 and at least one biocompatible excipient.

14. A PCR reaction mixture composition, the composition comprising a target nucleic acid, PCR reagents, a pair of oligonucleotide primers configured for amplifying a portion of the target nucleic acid to produce an amplicon, and the composition of claim 2, wherein PCR reagents comprise a thermostable polymerase and deoxyribonucleotide triphosphates (dNTPs).

15. A method of nucleic acid analysis, the method comprising the steps of melting a target nucleic acid in the presence of a dsDNA binding dye to generate a melting curve, and using the melting curve to identify the genotype, wherein the dsDNA binding dye is a compound of claim 1.

16. A method of detecting mutations in a target nucleic acid, the method comprising providing an amplification mixture comprising a nucleic acid sample, a pair of primers configured for amplifying a locus of the target nucleic acid, a thermostable polymerase, and a dsDNA binding dye, amplifying the nucleic acid sample to generate an amplicon, melting the amplicon to generate a melting curve, and analyzing the shape of the melting curve to detect mutations in a target sample, wherein the dsDNA binding dye is a compound of claims 1.

17. A method for nucleic acid analysis, the method comprising combining a target nucleic acid, a dsDNA binding dye of claim 1 , 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 permit the unlabeled probe to hybridize to the target nucleic acid to form a probe/target duplex, measuring fluorescence from the dsDNA binding dye as the mixture is heated, generating a melting curve for the probe/target duplex, and analyzing the shape of the melting curve.