COMPETITIVE COMPOSITIONS OF NUCLEIC ACID MOLECULES FOR ENRICHMENT OF RARE-ALLELE-BEARING SPECIES

Abstract

The present disclosure describes the thermodynamic design and concentrations necessary to design probe compositions with desired optimal specificity that enable enrichment, detection, quantitation, purification, imaging, and amplification of rare-allele-bearing species of nucleic acids (prevalence <1%) in a large stoichiometric excess of a dominant-allele-bearing species (wildtype). Being an enzyme-free and homogeneous nucleic acid enrichment composition, this technology is broadly compatible with nearly all nucleic acid-based biotechnology, including plate reader and fluorimeter readout of nucleic acids, microarrays, PCR and other enzymatic amplification reactions, fluorescence barcoding, nanoparticle-based purification and quantitation, and in situ hybridization imaging technologies.

Claims

1. A nucleic acid detection composition comprising: a target nucleic acid probe comprising a first target probe oligonucleotide and a second target probe oligonucleotide, wherein the first target probe oligonucleotide comprises a target probe complement region that is complementary to a target nucleic acid sequence, wherein the second target probe oligonucleotide comprises a target probe protector region that is complementary to a first target probe complement subsequence of the target probe complement region thereby providing a target double-stranded probe portion and a target single-stranded probe portion, wherein the target double-stranded probe portion comprises the first target probe complement subsequence and the target probe protector region, and the target single-stranded probe portion comprises a second target probe complement subsequence of the target probe complement region; a target auxiliary oligonucleotide, wherein the target auxiliary oligonucleotide is the second target probe oligonucleotide separate from the target nucleic acid probe; a variant nucleic acid probe comprising a first variant probe oligonucleotide and a second variant probe oligonucleotide, wherein the first variant probe oligonucleotide comprises a variant probe complement region that is complementary to a variant nucleic acid sequence, wherein the second variant probe oligonucleotide comprises a variant probe protector region that is complementary to a first variant probe complement subsequence of the variant probe complement region thereby providing a variant double-stranded probe portion and a variant single-stranded probe portion, wherein the variant double-stranded probe portion comprises the first variant probe complement subsequence and the variant probe protector region, and the variant single-stranded probe portion comprises a second variant probe complement subsequence of the variant probe complement region, wherein the target probe complement region and the variant probe complement region share at least two conserved sequences separated by a non-conserved sequence; and a variant auxiliary oligonucleotide, wherein the variant auxiliary oligonucleotide is the second variant oligonucleotide separate from the variant nucleic acid probe.

2. The composition of claim 1 wherein the non-conserved sequence is a single nucleotide.

3. The composition of claim 1 wherein the target probe complement region and the variant probe complement region share two conserved sequences separated by a non-conserved sequence.

4. The composition of claim 3 wherein the non-conserved sequence is a single nucleotide.

5. The composition of claim 1 wherein the first target probe oligonucleotide comprises a detectable label or a capture moiety conjugated thereto.

6. The composition of claim 5 wherein the second target probe oligonucleotide comprises a quencher sufficient to prevent detection of the detectable label or capture of the capture moiety.

7. The composition of claim 1 further comprising a third target probe oligonucleotide hybridized to a target probe non-complement region of the first target probe oligonucleotide, wherein the third target probe oligonucleotide comprises a detectable label or a capture moiety conjugated thereto, and a fourth target probe oligonucleotide hybridized to a target probe non-protector region of the second target probe oligonucleotide, wherein the fourth target probe oligonucleotide comprises a quencher sufficient to prevent detection of the detectable label or capture of the capture moiety.

8. The composition of claim 1 wherein the concentration of the variant nucleic acid probe relative to the concentration of the target nucleic acid probe is from greater than 1:1 to about less than 100000:1.

9. The composition of claim 1 wherein the concentration of the target auxiliary oligonucleotide relative to the concentration of the target nucleic acid probe is from greater than 1:1000 to less than 100000:1.

10. The composition of claim 1 wherein the concentration of the variant auxiliary oligonucleotide relative to the concentration of the variant nucleic acid probe is from greater than 1:1000 to less than 100000:1.

11. The composition of claim 1 wherein the target nucleic acid probe has a target reaction standard free energy (ΔG°.sub.rxn1), wherein the variant nucleic acid probe has a variant reaction standard free energy (ΔG°.sub.rxn2), and wherein ΔG°.sub.rxn1 is greater than the sum of ΔG°.sub.rxn2+1 kcal/mol.

12. The composition of claim 1 wherein the target nucleic acid probe has a concentration-adjusted target reaction standard free energy defined as ΔG°.sub.rxn1+Rτ ln([P.sub.t]/[P.sub.tC.sub.t]), wherein the variant nucleic acid probe has a variant reaction standard free energy defined as ΔG°.sub.rxn2+Rτ ln([P.sub.v]/[P.sub.vC.sub.v]), where R is the ideal gas constant, τ is the temperature in Kelvin, P.sub.t is the initial concentration of the target auxiliary oligonucleotide, P.sub.tC.sub.t is the initial concentration of the target nucleic acid probe, P.sub.v is the initial concentration of the variant auxiliary oligonucleotide, P.sub.vC.sub.v is the initial concentration of the variant nucleic acid probe, wherein the concentration-adjusted reaction standard free energy of the target nucleic acid probe is greater than the sum of the concentration-adjusted reaction standard free energy of the variant nucleic acid probe +1 kcal/mol.

13. The composition of claim 1 wherein the target nucleic acid probe has a target reaction standard free energy (ΔG°.sub.rxn1), wherein the variant nucleic acid probe has a variant reaction standard free energy (ΔG°.sub.rxn2), and wherein ΔG°.sub.rxn1 is greater than ΔG°.sub.rxn2, and ΔG°.sub.rxn2 is greater than −7 kcal/mol.

14. The composition of claim 1 wherein the target nucleic acid probe further comprises a third oligonucleotide and a fourth oligonucleotide, wherein the third oligonucleotide comprises a first target probe oligonucleotide-specific subsequence and a fourth oligonucleotide specific subsequence, wherein the first target probe oligonucleotide-specific subsequence is complementary to a target probe non-complement region of the first target probe oligonucleotide, wherein the fourth oligonucleotide comprises a second target probe oligonucleotide-specific subsequence and a third oligonucleotide-specific subsequence, wherein the second target probe oligonucleotide-specific subsequence is complementary to a target probe non-protector region of the second target probe oligonucleotide, wherein the target probe non-protector region of the second target probe oligonucleotide does not overlap with the target probe protector region, wherein the fourth oligonucleotide-specific subsequence is complementary to the third oligonucleotide-specific subsequence, and wherein the target auxiliary oligonucleotide further comprises the fourth oligonucleotide.

15. The composition of claim 14 wherein the fourth oligonucleotide-specific subsequence of the third oligonucleotide comprises a detectable label or a capture moiety conjugated thereto, and wherein the third oligonucleotide-specific subsequence of the fourth oligonucleotide comprises a quencher sufficient to prevent detection of the detectable label or capture of the capture moiety.

16. The composition of claim 1 wherein the variant nucleic acid probe further comprises a third oligonucleotide and a fourth oligonucleotide, wherein the third oligonucleotide comprises a first variant probe oligonucleotide-specific subsequence and a fourth oligonucleotide specific subsequence, wherein the first variant probe oligonucleotide-specific subsequence is complementary to a variant probe non-complement region of the first variant probe oligonucleotide, wherein the fourth oligonucleotide comprises a second variant probe oligonucleotide-specific subsequence and a third oligonucleotide-specific subsequence, wherein the second variant probe oligonucleotide-specific subsequence is complementary to a variant probe non-protector region of the second variant probe oligonucleotide, wherein the variant probe non-protector region of the second variant probe oligonucleotide does not overlap with the variant probe protector region, wherein the fourth oligonucleotide-specific subsequence is complementary to the third oligonucleotide-specific subsequence, and wherein the variant auxiliary oligonucleotide further comprises the fourth oligonucleotide.

17. A nucleic acid detection composition comprising: a target nucleic acid probe comprising a first target probe oligonucleotide and a second target probe oligonucleotide, wherein the first target probe oligonucleotide comprises a target probe complement region that is complementary to a target nucleic acid sequence, wherein the second target probe oligonucleotide comprises a target probe protector region that is complementary to a first target probe complement subsequence of the target probe complement region thereby providing a target double-stranded probe portion and a target single-stranded probe portion, wherein the target double-stranded probe portion comprises the first target probe complement subsequence and the target probe protector region, and the target single-stranded probe portion comprises a second target probe complement subsequence of the target probe complement region; a target auxiliary oligonucleotide, wherein the target auxiliary oligonucleotide is the second target probe oligonucleotide separate from the target nucleic acid probe; and a variant nucleic acid probe comprising a first variant probe oligonucleotide, wherein the first variant probe oligonucleotide comprises a variant probe complement region that is complementary to a variant nucleic acid sequence, wherein the target probe complement region and the variant probe complement region share at least two conserved sequences separated by a non-conserved sequence.

18. The composition of claim 17 wherein the target nucleic acid probe further comprises a third oligonucleotide and a fourth oligonucleotide, wherein the third oligonucleotide comprises a first target probe oligonucleotide-specific subsequence and a fourth oligonucleotide specific subsequence, wherein the first target probe oligonucleotide-specific subsequence is complementary to a target probe non-complement region of the first target probe oligonucleotide, wherein the fourth oligonucleotide comprises a second target probe oligonucleotide-specific subsequence and a third oligonucleotide-specific subsequence, wherein the second target probe oligonucleotide-specific subsequence is complementary to a target probe non-protector region of the second target probe oligonucleotide, wherein the target probe non-protector region of the second target probe oligonucleotide does not overlap with the target probe protector region, wherein the fourth oligonucleotide-specific subsequence is complementary to the third oligonucleotide-specific subsequence, and wherein the target auxiliary oligonucleotide further comprises the fourth oligonucleotide.

19. A nucleic acid detection composition comprising: a target nucleic acid probe comprising a first target probe oligonucleotide, wherein the first target probe oligonucleotide comprises a target probe complement region that is complementary to a target nucleic acid sequence; a variant nucleic acid probe comprising a first variant probe oligonucleotide and a second variant probe oligonucleotide, wherein the first variant probe oligonucleotide comprises a variant probe complement region that is complementary to a variant nucleic acid sequence, wherein the second variant probe oligonucleotide comprises a variant probe protector region that is complementary to a first variant probe complement subsequence of the variant probe complement region thereby providing a variant double-stranded probe portion and a variant single-stranded probe portion, wherein the variant double-stranded probe portion comprises the first variant probe complement subsequence and the variant probe protector region, and the variant single-stranded probe portion comprises a second variant probe complement subsequence of the variant probe complement region, wherein the target probe complement region and the variant probe complement region share at least two conserved sequences separated by a non-conserved sequence; and a variant auxiliary oligonucleotide, wherein the variant auxiliary oligonucleotide is the second variant oligonucleotide separate from the variant nucleic acid probe.

20. The composition of claim 19 wherein the variant nucleic acid probe further comprises a third oligonucleotide and a fourth oligonucleotide, wherein the third oligonucleotide comprises a first variant probe oligonucleotide-specific subsequence and a fourth oligonucleotide specific subsequence, wherein the first variant probe oligonucleotide-specific subsequence is complementary to a variant probe non-complement region of the first variant probe oligonucleotide, wherein the fourth oligonucleotide comprises a second variant probe oligonucleotide-specific subsequence and a third oligonucleotide-specific subsequence, wherein the second variant probe oligonucleotide-specific subsequence is complementary to a variant probe non-protector region of the second variant probe oligonucleotide, wherein the variant probe non-protector region of the second variant probe oligonucleotide does not overlap with the variant probe protector region, wherein the fourth oligonucleotide-specific subsequence is complementary to the third oligonucleotide-specific subsequence, and wherein the variant auxiliary oligonucleotide further comprises the fourth oligonucleotide.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0049] FIG. 1: Competitive Composition invention overview. The nucleic acid probe compositions of the present disclosure (also referred to as Competitive Composition) 2 is a reagent mixture that comprises target nucleic acid probe (Probe) that is specific to a Target species T and a variant nucleic acid probe (Sink) that is specific to a Variant species V. Here, the Probe binds more favorably to the Target than the Variant, and the Sink binds more favorably to the Variant than to the Target. The nucleic acid compositions of the present disclosure are used to isolate, identify, quantify, or detect a Target in a heterogeneous mixture of nucleic acids sample 1. The initial concentration ratio of the Variant to the Target in the sample is X. Upon completion of the reaction 3, the ratio of the amount of Target that is bound to the Probe (T.Math.Probe) to the amount of Variant that is bound to be Probe (V.Math.Probe) Y will be enriched relative to the initial ratio of Target and Variant in the Sample.

[0050] FIG. 2: Potential morphologies of Competitive Composition components. The Competitive Composition comprises a target nucleic acid probe (referred to hereinafter generally as “Probe”) and a variant nucleic acid probe (referred to herein generally as “Sink”). Each can adopt one of a number of different nucleic acid molecule morphologies previously reported in literature, or yet to be reported. This figure shows a partial list of morphologies the Probe may adopt. Morphologies the Sink can adopt are similar. Importantly, the morphology of the Probe and the Sink may be different. Both the Probe and the Sink can comprises single Block or double Blocks, where a Block is either a strand or a complex that comprises 2 or more oligonucleotides formed through Watson-Crick hybridization reactions. The left panel shows the reaction between a Target and a single-Block Probe 4 that comprises a Target-binding Block (TB-Block). The right panel shows the reaction between a Target and a double-Block Probe 10 that comprises a Target-binding Block (TB-Block) and an Auxiliary Block (A-Block). The expended panel displaces exemplary structures of single-Block (5-9) and double-Block Probes (11-15). The black dots between strands represent base pairs within each Block, while the vertical black lines represent base pairs between Blocks and between the Target-binding Block and the bound Target (T.Math.Probe). The thick black portions of the Probe represent the nucleotide(s) dependent on the polymorphic nucleotide(s) that differ between the Target and Variant species. The half-arrow at one end of each strand represents the 3′ end.

[0051] FIG. 3: Primary reactions between the Sample and an exemplary Competitive Composition 16. Here each oligonucleotide strand is subdivided into regions denoted by numbers. Each region comprises contiguous nucleotide bases, and acts as a functional unit in hybridization and disassociation. The four primary reactions are (1) the Target T binding to the Probe, (2) the Variant V binding to the Sink, (3) the Variant V binding to the Probe, and (4) the Target T binding to the Sink. Each of these reactions has a corresponding reaction standard free energy ΔG°.sub.rxn that characterizes their favorability. The first two reactions are desirable reactions that properly pair the Target to the Probe and the Variant to the Sink, and the latter two reactions are undesirable.

[0052] FIG. 4A: depicts reaction equilibrium behavior of the Probe and Sink at a first reaction standard free energy value. The analytical dependence of the equilibrium binding yield to the Probe (assuming excess Probe) on reaction ΔG°.sub.rxn is shown, as well as the yields for ΔG°.sub.rxn1=0.5 kcal/mol and ΔG°.sub.rxn3=+2.5 kcal/mol, corresponding to a ΔΔG°.sub.1 of 3.0 kcal/mol. There is an almost 50-fold difference in binding yield between the Target and the Variant to the Probe for these values.

[0053] FIG. 4B depicts reaction equilibrium behavior of the Probe and Sink at a second reaction standard free energy value different from that in FIG. 4A. The analytical dependence of the equilibrium binding yield to the Sink based on reaction ΔG°.sub.rxn follows a sigmoid. Because the intent of the Sink is to deplete the Variant concentration without too much impact on the Target concentration, a different set of ΔG°.sub.rxn values are desirable than for the Probe. Here, ΔG°.sub.rxn2=3 kcal/mol and ΔG°.sub.rxn4=+1 kcal/mol, resulting in 98% depletion of Variant (2% remaining) and 29% depletion of the Target (71% remaining). This set of values would improve the enrichment factor by over 30-fold (71%/2%).

[0054] FIG. 5: An embodiment of Competitive Compositions 16 using an X-Probe as Probe and a toehold probe as Sink, in which the Probe exhibits conditional fluorescence upon hybridization to Target T or Variant V. Conditional fluorescence is achieved because a fluorophore (shown as star) is initially in close proximity to a quencher (shown as large dot); after reaction, the quencher is delocalized and fluorescence increases. There are three contributions to observed fluorescence: the fluorescence due to Target bound to the Probe (f.sub.A), the fluorescence due to Variant bound to the Probe (f.sub.C), and the fluorescence of the unbound Probe due to incomplete quenching (f.sub.B).

[0055] FIG. 6: Example Competitive Composition 41 (SEQ ID NOS 2, 45, 1, 46, 47 and 48, respectively, in order of appearance) for fluorescent detection of the rare EGFR L858R (c.2573T>G) mutation (T) (SEQ ID NO: 43) in a background of EGFR wildtype sequence (V) (SEQ ID NO: 44). The polymorphic nucleotide is shown in bold. The differential fluorescence responses of Variant alone (1500 nM) and Variant (1500 nM) with a small amount of Target (0.5 nM) are shown. The latter conditions correspond to X=3000-fold excess of Variant over Target, and comparison of f.sub.A and f.sub.C values suggest a 2781-fold binding affinity difference (as measured by β) of Target bound to Probe as compare to Variant bound to Probe. Experiments were performed at 37° C. in 5×PBS buffer using synthetic oligonucleotides of the given sequences.

[0056] FIG. 7: Example Competitive Composition 42 (SEQ ID NOS 2, 249, 1, 250, 251 and 252, respectively, in order of appearance) for fluorescent detection of the rare TP53 R248Q (c.743G>A) mutation (T) (SEQ ID NO: 247) in a background of TP53 wildtype sequence (V) (SEQ ID NO: 248). Experiments were performed at 37° C. in 5×PBS buffer using synthetic oligonucleotides of the given sequences.

[0057] FIG. 8: Example Competitive Composition 43 (SEQ ID NOS 2, 147, 1, 148, 143 and 144, respectively, in order of appearance) for fluorescent detection of the rare NRAS G12D (c.35G>A) mutation (T) (SEQ ID NO: 145) in a background of NRAS wildtype sequence (V) (SEQ ID NO: 146). Experiments were performed at 37° C. in 5×PBS buffer using synthetic oligonucleotides of the given sequences.

[0058] FIG. 9A provides the morphologies of the Probe and Sink used in the Competitive Composition to test 44 different cancer-related single nucleotide polymorphisms. The sequences for the probes and target/variant sequences used are shown in Tables 1-3.

[0059] FIG. 9B provides a summary of binding affinity fold-change β from experimental results for 44 different cancer-related Target/Variant pairs using Competitive Compositions of FIG. 9A. Here the sample Variant/Target ratio is 1000:1. The binding affinity fold-change varied between 200 and 2420, with a median of roughly 1000.

[0060] FIG. 9C provides a comparison of fold-change β from experimental results for the same 44 different Target/Variant pairs using only the Probe component of the Competitive Composition without the Sink as compared to the Competitive Composition with Probe and Sink. Here the sample Variant/Target ratio is X=100, a factor of 10 lower than for the Competitive Composition. The median fold-change β is roughly 30, consistent with the best previously reported designs. Thus, the Competitive Composition has improved enrichment by roughly a further factor of 30 to 1000, enabling rare allele detection down to 0.1% load. This is the first report of reliable enzyme-free and homogeneous detection of rare alleles at this sensitivity.

[0061] FIG. 9D provides an exemplary distribution of optimal ΔG°.sub.rxn combinations at 1 hour reaction time. The figure shows optimal ΔG°.sub.rxn1 and ΔG°.sub.rxn2 values given by ordinary differential equation simulation for the 44 mutations discussed in FIG. 9A-9C with ΔΔG° values ranging from +1.8 kcal/mol to +5.9 kcal/mol at 37° C. Probe and Sink with ΔG°.sub.rxn in those values exhibit maximum specificity at 1 hour. As can be seen, optimal ΔG°.sub.rxn values shift significantly for different ΔΔG° values. For the 44 SNV/WT pairs we have tested, optimal ΔG°.sub.rxn1 and ΔG°.sub.rxn2 values can vary from −1.6 to −0.6 kcal/mol and −6.4 to −2.8 kcal/mol, respectively.

[0062] FIG. 10A provides an experimental workflow diagram for Competitive Composition assays on PCR amplicons of human genomic DNA samples. Two extracted DNA samples from Coriell Cell Repository (NA18537 and NA18546) bearing single nucleotide polymorphisms at the SMAD7 locus are mixed 48 at 100:0, 99:1, 90:10, 10:90, 1:99, and 0:100 ratios to total concentrations of 2 ng/μL (50 μL), and amplified by asymmetric non-allele-specific PCR 49 to generate single-stranded amplicon 50. Competitive Compositions 51 that are designed to each allele are mixed with the assigned PCR product for detection 52.

[0063] FIG. 10B provides the fluorescence responses of Competitive Composition to each SNP for the experiment diagramed in FIG. 10A. In each experiment, 0.5 nM Probe and 10 nM Sink were reacted with 40 μL PCR product. Allele frequencies of SMAD7-C (as shown in black) and SMAD7-T (as shown in grey) in genomic DNA mixture prior to PCR are displayed in parentheses.

[0064] FIG. 11: List of incidental species present in the example Competitive Composition consisting of a conditionally fluorescent X-probe as Probe and a toehold probe as Sink. The additional species in solution are due to the formulation of the Probe 46 and Sink 47, which intentionally result in excess of certain species. All species shown here are considered and modeled in simulations.

[0065] FIG. 12A provides simulations of the Competitive Composition reacting with a low fraction (0.01%) of Target. These simulations are performed based on the Ordinary Differential Equation model described in the text of the example conditionally fluorescent system. Shown are binding affinity fold-change β due to the low quantity of Target after 1 hour of reaction, 4 hours of reaction, and 48 hours of reaction, due to varying values of ΔG°.sub.rxn1 and ΔG°.sub.rxn2. Longer reaction times broaden the range of ΔG°.sub.rxn values that yield high β.

[0066] FIG. 12B provides a three-dimensional representation of the 13 value shown in FIG. 12A based on ΔG°.sub.rxn1 and ΔG°.sub.rxn2 after 1 hour of reaction.

[0067] FIG. 12C demonstrates the maximum 13 value that can be achieved following different durations of reaction time based on the simulation of FIG. 12A.

[0068] FIG. 13: Competitive composition 53 with different Probe and Sink component morphologies, here a biotin-functionalized (Bio) hairpin probe for the Probe and a Yin-Yang probe for the Sink. With the probes properly designed based on thermodynamics, the fraction of Target T to Variant V that will be captured by a streptavidin-coated surface 54 will be highly enriched over the original sample. Due to the single-stranded nature of the hairpin probe, there is an additional Rτ ln([Probe]) term in the evaluation of optimal ΔG°.sub.rxn1. The black dots between strands represent base pairs within each Block, while the vertical black lines represent base pairs between Blocks and between the Target-binding Block and the bound Target or Variant.

[0069] FIG. 14: Competitive Composition 55 with unfunctionalized Probe and Sink components. Instead the enrichment capabilities are realized via a functionalized nucleic acid molecule 57 of universal sequence that is complementary to an additional region of the Probe (region 56). The indirect linkage between the Probe and the functionalized oligonucleotide need not be through only one hybridization interaction: for example, the Probe could be hybridized partially to an unfunctionalized strand, which is itself hybridized partially to a secondary functionalized strand. The product that a colocalized with the functionalized group will simultaneously or sequentially be captured 58, imaged 59, or assayed through any other methods, while the rest of the molecules will usually be washed away 60.

[0070] FIG. 15: Competitive Composition for enrichment of allele-specific enzymatic amplification. The Target and Variant species are based on the antisense strands for the EGFR L858R (c.2573T>G) mutation 61 and the corresponding wildtype sequence 62. Values of ΔG°.sub.rxn shown are calculated at 60° C. in 0.18 M Na.sup.t, consistent with the environment of a typical PCR anneal step. The Probe 63 is the only species that is not blocked at the 3′ end by a non-extensible group, and capable of serving as primer. Thus, the enrichment of Target to Variant in binding to the Probe serves to increase the fraction of Target that is amplified by PCR. FIG. 15 discloses SEQ ID NOS 277-282, respectively, in order of appearance.

DESCRIPTION OF THE INVENTION

[0071] In the present disclosure, a novel reagent mixture composition (referred to herein as a “Competitive Composition) is provided. The Competitive Composition reacts with a heterogeneous sample mixture containing at last two closely related nucleic acid species: a dominant-allele-bearing species (Variant) and a rare-allele-bearing species (Target), with the former typically in excess of the latter (FIG. 1). The Variant and the Target molecules contain a highly similar subsequence, with length between, for example, 5 and 200 nucleotides, that differs by at least 1 nucleotide, known as the polymorphic nucleotide(s).

[0072] The Competitive Composition comprises a target nucleic acid probe (Probe) and a variant nucleic acid probe (Sink), with the later in excess concentration of the former, with the Sink reacting more favorably with the Variant than with the Target (due to the Sink's complementarity to the dominant allele nucleotide(s)) and the Probe reacting more favorably with the Target than with the Variant (due to the Probe's complementarity to the rare allele nucleotide(s)).

[0073] Mathematically, the concentration ratio of Variant to Target ([Variant]/[Target]) in the initial sample is here denoted as X, and the concentration ratio of Variant to Target that is bound to the Probe after the reaction is denoted as Y. By using Competitive Compositions designed based on the guidelines described here, Y will be much smaller than X; our experimental data across 44 different cancer-related mutations shows an average enrichment ratio (X/Y) of around 1000.

[0074] This enrichment ratio for the present Competitive Composition is significantly higher than prior art regarding the use of a single probes alone. In addition to showing experimental results that compare favorably to prior art, the present disclosure additionally includes validated theoretical analysis and simulations explaining why the Competitive Compositions described here provide an advantage over strategies.

Components of Competitive Composition

[0075] There components of the Competitive Composition comprise a target nucleic acid probe (Probe), a variant nucleic acid probe (Sink), and a target auxiliary oligonucleotide and a target auxiliary oligonucleotide. Both the Probe and Sink can comprise single or double Blocks, where a Block is either a strand or a complex that comprises 2 or more oligonucleotides formed through Watson-Crick hybridization reactions. Single-Block Probe or Sink comprises Target-binding Block, while double-Block Probe or Sink further comprises an Auxiliary Block in addition to the Target-binding Block. The Auxiliary Block releases from the Target-binding Block concurrently with the hybridization of the Target or Variant. Each of these components is a nucleic acid molecule and can adopt any of a number of different morphologies (FIG. 2). Example single-Block embodiments of the Probe and the Sink include (but are not limited to) molecular beacons, hairpin probes, and triple-stem probe. Example double-Block embodiments of the Probe and the Sink include (but are not limited to) Yin-Yang probes, toehold probes, and X-probes.

[0076] Each of these designs generally possesses some degree of tunability in reaction favorability with their intended target (i.e. Target for Probe, Variant for Sink). For example, the standard free energy of hybridization (ΔG°.sub.rxn) can be modulated via the length of the single-stranded toehold regions for Yin-Yang probes, toehold probes, X-probes, and hairpin probes; the length of nonhomologous regions for toehold probes and X-probes. For single-stranded components (e.g. molecular beacons, hairpin probes, triple-stem probes), reaction favorability can be tuned via component concentration.

[0077] For purposes of illustrating one embodiment of the present disclosure, a particular exemplary Competitive Composition comprising an X-probe for the Probe and an toehold probe for the Sink will be described. It should be understood that this specific embodiment is to provide an example of the Competitive Composition, and is not meant to limit the Competitive Composition to this embodiment.

[0078] As shown in FIG. 3, for example, in one embodiment, the target nucleic acid probe (Probe) is an X-probe and the non-target nucleic acid probe (Sink) is a toehold probe. Here, the X-probe (Probe) comprises four oligonucleotides or strands as follows: the first target oligonucleotide comprising subsequences 19, 18, 21, and 27; the second target oligonucleotide comprising subsequences 17, 20, and 25; the third oligonucleotide comprising subsequences 23 and 26; and the fourth oligonucleotide comprising subsequences 22 and 24. The first target nucleotide can be further characterized as including a target sequence region which is directed to subsequences 18 and 19 (and in some instances 20). It should also be noted that not all of the subsequences for each oligonucleotide are required for proper function. For example, subsequences 20-23 could be removed, or just subsequences 20 and 21 could be removed, or moreover, subsequences 22 and 23 could be removed. Each subsequence, represented by a number in FIG. 3, denotes a portion of the oligonucleotide that functionally acts as a unit in hybridization or dissociation. One subsequence is said to be complementary to another subsequence if the nucleotides of each subsequence can simultaneously form several Watson-Crick base pairs with each other. In this particular example, the first and second target oligonucleotides are designed such that subsequence 17 is partially or fully complementary to subsequence 18 thereby forming a first double-stranded region of the probe; optional subsequence 20 is partially or fully complementary to region 21 thereby forming a second double-stranded region of the probe (or simply an extension of the first double-stranded region); subsequence 26 is partially or fully complementary to region 27 thereby forming a third double-stranded region of the probe; optional subsequence 22 is partially or fully complementary to region 23 thereby forming a fourth double-stranded region of the probe; and subsequence 24 is partially or fully complementary to region 25 thereby forming a fifth double-stranded region of the probe. In addition, the first target oligonucleotide comprises a single-stranded region comprising subsequence 19 that is complementary to the target nucleic acid sequence (as is subsequence 18). Although not depicted in FIG. 3, subsequences 22 and 23 (or optionally subsequence 26 and 24 in the instance the probe is not designed with subsequences 22 and 23) provide sites for conjugation of detectable labels and quenchers thereof.

[0079] As the X-probe is introduced into a sample containing target T and under the proper temperature and buffer conditions as shown in FIG. 3, subsequences 18 and 19 of the first target oligonucleotide hybridize to subsequences 33 and 34, respectively, of the target T. Upon such hybridization, the third oligonucleotide bearing subsequence 26 will remain hybridized to subsequence 27 of the first target oligonucleotide (“target complex”) whereas second target oligonucleotide and forth oligonucleotide (the “protector complex”) will dissociate from the target complex. In the instance a fluorophore F is conjugated to the end of second oligonucleotide at subsequence 23 and a quencher Q is conjugated to the of the fourth oligonucleotide at subsequence 22, the dissociation of the protector complex from the target complex upon binding to the target will remove the quencher Q and allow the fluorophore F to fluoresce as the third oligonucleotide remains hybridized to subsequence 27 of the first target oligonucleotide.

[0080] Continuing with FIG. 3, in one embodiment, the Sink comprises a toehold or ultra-specific probe. The Sink comprises a first non-target oligonucleotide comprising subsequences 32, 29, and 30, and a second non-target oligonucleotide comprising subsequences 28 and 31. As can be appreciated in FIG. 3, the sink forms at least a first double-stranded region resulting from the hybridization of subsequences 28 and 29 and a second double-stranded region resulting from the hybridization of subsequences 31 and 32. This leaves the first non-target oligonucleotide having a single-stranded region of subsequence 30. Upon exposure to a sample comprising the target T and non-target nucleic acid variant V, subsequences 29 and 30 will hybridize to subsequences 36 and 37, respectively of variant V thereby causing release of the second non-target oligonucleotide from the probe complex. As discussed above, the Sink can comprise a label on the first non-target oligonucleotide and a quencher on the second non-target nucleotide at the end of subsequences 32 and 31, respectively. In this instance, the label will become detectable upon the first non-target oligonucleotide binding to variant V as the second non-target oligonucleotide bearing the quencher is displaced.

[0081] Although not shown in FIG. 3, the composition may comprise a target auxiliary oligonucleotide and a non-target auxiliary oligonucleotide. The target auxiliary oligonucleotide, in certain embodiments, comprises the second target oligonucleotide hybridized to the fourth oligonucleotide separate and free from the probe complex. Thus, the target auxiliary oligonucleotide or complex is in excess of the first target oligonucleotide and third oligonucleotide thereby resulting in an initial concentration of free first target oligonucleotide complexed with the third oligonucleotide. Similarly, the non-target auxiliary oligonucleotide, in this embodiment, comprises the second non-target oligonucleotide separate and free from the Sink probe complex. Stated another way, the second non-target oligonucleotide will be in excess of the first non-target oligonucleotide.

[0082] In another embodiment, the target nucleic acid probe of the competitive composition may comprise a toehold probe instead of a X-probe, and the non-target nucleic acid probe or Sink probe may comprise a toehold probe or an X-probe. In yet another embodiment, the target nucleic acid probe may comprise a toehold probe or an X probe and the non-target nucleic acid probe or Sink probe may comprise a single oligonucleotide. In yet another embodiment, the target nucleic acid probe may comprise a single oligonucleotide and the Sink probe may comprise either a toehold probe or a X-probe.

[0083] As explained in more detail below, based on its sequence, the target nucleic acid probe (Probe) has a target reaction standard free energy with the target nucleic acid sequence T defined as ΔG°.sub.rxn1, whereas the reaction of the Probe with the variant or non-target nucleic acid strand V will have a reaction standard free energy ΔG°.sub.rxn3 that will be weaker (more positive or less negative) than ΔG°.sub.rxn1 due to the mismatch base. Moreover, the Sink will act in the opposite fashion where its reaction standard free energy with the target (ΔG°.sub.rxn4) will be weaker that its reaction standard free energy with the variant (ΔG°.sub.rxn2) due to the mismatch base in the target T. Moreover, in certain embodiments, ΔG°.sub.rxn1 will be weaker (more positive or less negative) then ΔG°.sub.rxn2. More specifically, in certain embodiments, the relationship between ΔG°.sub.rxn1 and ΔG°.sub.rxn2 can be defined as, for example, ΔG°.sub.rxn1 is greater than the sum of ΔG°.sub.rxn2+1 kcal/mol, or alternatively ΔG°.sub.rxn1 is greater than ΔG°.sub.rxn2 where ΔG°.sub.rxn2 is greater than −7 kcal/mol. As used herein, the term “greater than” as used in connection with the standard reaction free energies of the Probe to target T and Sink to variant V means more positive or less negative (e.g. −4 kcal/mol is “greater than”−7 kcal/mol). Thus, in many instances, the composition of the present disclosure comprises a target nucleic acid probe that interacts with the target nucleic acid T less favorably than the non-target nucleic acid probe (Sink) interacts with the non-target nucleic acid variant V. In most samples in which the competitive compositions described above will be used, the non-target nucleic acid species or variant V is present on the dominant allele and will therefore be in excess of the target nucleic acid species T present on the rare allele.

[0084] In any of the above embodiments, any one of the strands of the probe may further comprise a synthetic nucleic acid analog such as LNA, PNA, 2′O-methyl substituted RNA, L-DNA, and speigelmers. In an alternative, any one of the strands of the probe may further comprise synthetic or natural analogs such as isosine, methylated nucleotides, iso-cytosine and iso-guanine, spiegelmer nucleotides, and xDNA.

[0085] The terms “polynucleotide,” “nucleic acid,” “oligonucleotide,” “nucleic acid species,” and “nucleic acid molecule” are used interchangeably. They refer to a polymeric form of nucleotides of any length, either deoxyribonucleotides or ribonucleotides, or analogs thereof. Polynucleotides may have any three-dimensional structure, and may perform any function. The following are non-limiting examples of polynucleotides: coding or non-coding regions of a gene or gene fragment, loci (locus) defined from linkage analysis, exons, introns, messenger RNA (mRNA), transfer RNA, ribosomal RNA, ribozymes, cDNA, recombinant polynucleotides, branched polynucleotides, plasmids, vectors, isolated DNA of any sequence, isolated RNA of any sequence, nucleic acid probes, and primers. A polynucleotide may comprise modified nucleotides, such as methylated nucleotides and nucleotide analogs. If present, modifications to the nucleotide structure may be imparted before or after assembly of the polymer. A polynucleotide may be further modified, such as by conjugation with a labeling component.

[0086] A process for preparing an X-probe is provided. In one embodiment, the third oligonucleotide (A), the fourth oligonucleotide (B), the second target (or non-target) oligonucleotide (P), and the first target (or non-target) oligonucleotide (C) are mixed together in aqueous solution. In one embodiment, the concentration of the first target (or non-target) oligonucleotide C is in excess of the third oligonucleotide A, the concentration of the second target (or non-target) oligonucleotide (P) is in excess of the first target (or non-target) oligonucleotide (C), and the concentration of the fourth oligonucleotide (B) is in excess of the protector strand such that a probe mixture is formed comprising complex BPCA, complex BPC, complex BP, and strand B. In another embodiment, the concentration of P is in excess of B, the concentration of C is in excess of P, and the concentration of A is in excess of C such that a probe mixture formed comprises complex BPCA, complex PCA, complex CA, and strand A.

[0087] In any of the above embodiments, the probe components are thermally annealed following mixing. In one embodiment, the thermal annealing includes heating the mixture to a temperature no less than 65° C., and cooling to a temperature no higher than 45° C. In another embodiment, the thermal annealing includes heating the mixture to a temperature no less than 80° C., and cooling to a temperature no higher than 60° C. In yet another embodiment, the thermal annealing includes heating the mixture to a temperature no less than 95° C., and cooling to a temperature no higher than 75° C.

[0088] In an alternative embodiment, the probe components are isothermally annealed through addition of salt or high salinity solutions. In yet another embodiment, the probe components are isothermally annealed through removal or dilution of formamide or other denaturants.

[0089] The probes of the present disclosure can be used in a variety of assays including, but not limited to the following: specific DNA or RNA detection or quantitation via fluorescence; specific DNA or RNA imaging via fluorescence; specific DNA or RNA detection, quantitation, or imaging via chromagenic methods (e.g. haptenated probes, and subsequent antibody-based recruitment of horseradish peroxidase (HRP) or alkaline phosphate (AP).

Competitive Composition Reactions

[0090] FIG. 3 shows the target T, variant V, Probe, and Sink decomposed as a number of regions or subsequences, denoted by numbers. Each region is a number of continuous nucleotide bases that act as a unit in hybridization and dissociation. Regions may be partially or fully Watson-Crick complementary to other regions (e.g. region 17 to region 18), and different regions may possess identical sequences to each other (e.g. regions 34 and 37).

[0091] The Variant and the Target species are here assumed to differ only from each other by a single polymorphic nucleotide, shown as a thick black line segment or black circle. In this example, the polymorphic nucleotide resides in the 33 and 36 regions. Here, it was assumed that regions 18 and 29 differ in sequence only at the nucleotide complementary to the polymorphic nucleotide, and that regions 19 and 30 are identical in sequence. In actuality, this does not need to be the case: for example, the complements to polymorphic nucleotide could reside in region 2 of the Probe and in region 30 of the Sink that is to say, the positions in which the Probe binds the Target/Variant need not be the same as the positions in which the Sink binds the Variant/Target. Regions 35 and 38 on the Variant and Target in FIG. 3 are optional and may not exist for short Variant and Target. If they do exist, however, region 35 and 38 are specifically not complementary to regions 21 and 23 of the Probe and region 32 of the Sink. Four distinct primary reactions occur between the two pairs of species: (1) the Target with the Probe, (2) the Variant with the Sink, (3) the Variant with the Probe, and (4) the Target with the Sink. From the point of view of enriching the fraction of Target bound to the Probe, the first two reactions are desirable: reaction (1) is the proper binding of the Target to the Probe, and reaction (2) reduces the amount of Variant available to bind to the Probe. In contrast, the other two are undesirable; reaction (3) is the improper binding of Variant to the Probe, and reaction (4) reduces the amount of Target available to bind to the Probe. The standard free energies of the four reactions are defined as ΔG°.sub.rxn1, ΔG°.sub.rxn2, ΔG°.sub.rxn3, ΔG°.sub.rxn4, respectively.

[0092] Hypothetically, it would be desirable for ΔG°.sub.rxn1 and ΔG°.sub.rxn2 to be as negative (favorable) as possible, and simultaneously ΔG°.sub.rxn3 and ΔG°.sub.rxn4 should be as positive (unfavorable) as possible. However, these values are necessarily coupled:

ΔΔG°.sub.1=ΔG°.sub.rxn3−ΔG°.sub.rxn1

ΔΔG°.sub.2=ΔG°.sub.rxn4−ΔG°.sub.rxn2

[0093] The values of ΔΔG°.sub.1 and ΔΔG°.sub.2, in turn, are influenced by the relative thermodynamics of a single-base mismatch (in general, ΔΔG°.sub.1≠ΔΔG°.sub.2). Based on experimental data and analysis, it has been determined that optimal values of ΔG°.sub.rxn1 and ΔG°.sub.rxn2 depend to some degree on ΔΔG° values.

[0094] One way to conceptualize the coupling between the different ΔG°.sub.rxn terms and their effects on the Competitive Composition performance is to consider the equilibrium for each of the Probe's and the Sink's individual reactions with the Target and the Variant. In such a simplified scenario, each reaction yield (defined as the fraction of the Target or Variant that is hybridized to the Probe or Sink at equilibrium) can be analytically computed based on the value of ΔG°.sub.rxn (FIGS. 4A and 4B). When there exists a large excess of Variant over Target, it is desirable from the point of view of enrichment for the Probe to possess higher specificity while the Sink possesses higher sensitivity.

Design Principles

[0095] The values of ΔΔG°.sub.1 and ΔΔG°.sub.2 are influenced by the single-base mismatch bubbles generated between the Variant-Probe complex (V.Math.Probe) and the Target-Sink complex (T.Math.Sink), respectively. Larger values of these two terms offer greater potential enrichment, but this potential can only be tapped via proper design of Probe and Sink with optimized ΔG°.sub.rxn1 and ΔG°.sub.rxn2 values.

[0096] Referring back to FIG. 3 and FIGS. 4A and 4B, an important tradeoff between specificity and sensitivity needs to be considered. For example, maximization of only the enrichment factor (X/Y), a proxy for the specificity, results from values of ΔG°.sub.rxn1 and ΔG°.sub.rxn2 being +∞ and −∞, respectively; unfortunately, such a Competitive Composition design would give no yield of either the Target or Variant bound to the Probe. Such a result is clearly undesirable from an application perspective of rare allele detection, quantitation, imaging, and purification, as this Competitive Composition would have zero sensitivity to the Target.

[0097] To explore these tradeoffs in realistic settings, the conditionally fluorescent X-Probe was considered as a model application for Target detection. The Binding affinity fold-change β=(f.sub.A.Math.X)/(f.sub.B+f.sub.C) represents the detectable fluorescence difference due to a small amount of the Target. Given the large number of species and reaction parameters in the Competitive Composition, analytical solution and optimization is unlikely to yield simple solutions conducive to intuitive understanding. Therefore, ordinary differential equation (ODE) simulations of the Competitive Composition system were performed in order to examine the landscape of Binding affinity fold-change due to various factors. The simulation follows the rate laws of chemical reaction and integrates the reaction process numerically.

[0098] For accuracy, modeled incidental species in the Probe and Sink components were also considered (FIG. 11). Additional investigations suggest these have very minor impact on the overall behavior of the system. The chemical reactions modeled are:

[00001]$R+\mathrm{FQPC}\underset{k_{1-}}{\stackrel{k_{1+}}{\rightleftharpoons }}\mathrm{FC}.Math.R+\mathrm{PQ}$$R+P_s{C}_s\underset{k_{2-}}{\stackrel{k_{2+}}{\rightleftharpoons }}{C}_s.Math.R+P_s$$D+\mathrm{FQPC}\underset{k_{3-}}{\stackrel{k_{3+}}{\rightleftharpoons }}\mathrm{FC}.Math.D+\mathrm{PQ}$$D+P_s{C}_s\underset{k_{4-}}{\stackrel{k_{4+}}{\rightleftharpoons }}{C}_s.Math.D+P_s$$R+\mathrm{QPC}\underset{k_{5-}}{\stackrel{k_{5+}}{\rightleftharpoons }}C.Math.R+\mathrm{PQ}$$D+\mathrm{QPC}\underset{k_{6-}}{\stackrel{k_{6+}}{\rightleftharpoons }}C.Math.D+\mathrm{PQ}$

where R represents the Target, D represents the Variant, k+ and k− represent the forward and the reverse rate constants respectively. The names and structures of other species are illustrated in FIG. 11. The values of all forward reaction rate constants k+ are assumed to be 3×10.sup.5M.sup.−1s.sup.−1; this is estimated based on previous studies and our own calibration experiments (data not shown). The values of the reverse reaction rate constants k− are calculated based on k.sub.+ on the ΔG° of the reaction:

[00002]$k_{-}=\frac{k_{+}}{K_{\mathrm{eq}}}=\frac{k_{+}}{e^{-\Delta G_{\mathrm{rxn}}^{\circ }/R_T}}$

[0099] For k.sub.1−, ΔG°.sub.rxn1 was used; for k.sub.2−, ΔG°.sub.rxn2; for k.sub.3−, ΔG°.sub.rxn3 ≡ΔG°.sub.rxn1+ΔΔG°.sub.1; for k.sub.4−, ΔG°.sub.rxn4≡ΔG°.sub.rxn2+ΔΔG°.sub.2, for k.sub.5−, ΔG°.sub.rxn5≡ΔG°.sub.rxn1+ΔG°.sub.NH; for k.sub.6−, ΔG°.sub.rxn6 ≡ΔG°.sub.rxn1+ΔΔG°.sub.1+ΔG°.sub.NH. The term ΔG°.sub.NB denotes the nonhomologous region that is missing for the incomplete QPC species of the Probe, and has value −8.46 kcal/mol. For all simulations here, ΔΔG°.sub.1=+3 kcal/mol and ΔΔG°.sub.2=+4 kcal/mol. The ODE simulation of the above reactions consists of the following rate law equations:

[00003]$\frac{d\left[R\right]}{\mathrm{dt}}=-k_1+\left[\mathrm{FQPC}\right]\left[R\right]+k_{1-}\left[\mathrm{FC}.Math.R\right]\left[\mathrm{PQ}\right]-k_{2+}\left[P_s{C}_s\right]\left[R\right]+k_{2-}\left[C_s.Math.R\right]\left[P_s\right]-k_{5+}\left[\mathrm{QPC}\right]\left[R\right]+k_{5-}\left[C.Math.R\right]\left[\mathrm{PQ}\right]$$\frac{d\left[D\right]}{\mathrm{dt}}=-k_3+\left[\mathrm{FQPC}\right]\left[D\right]+k_{3-}\left[\mathrm{FC}.Math.D\right]\left[\mathrm{PQ}\right]-k_{4+}\left[P_s{C}_s\right]\left[D\right]+k_{4-}\left[C_s.Math.D\right]\left[P_s\right]-k_{6+}\left[\mathrm{QPC}\right]\left[D\right]+k_{6-}\left[C.Math.D\right]\left[\mathrm{PQ}\right]$$\frac{d\left[\mathrm{PQ}\right]}{\mathrm{dt}}=k_1+\left[\mathrm{FQPC}\right]\left[R\right]-k_{1-}\left[\mathrm{FC}.Math.R\right]\left[\mathrm{PQ}\right]+k_{3+}\left[\mathrm{FQPC}\right]\left[D\right]-k_{3-}\left[\mathrm{FC}.Math.D\right]\left[\mathrm{PQ}\right]+k_{5+}\left[\mathrm{QPC}\right]\left[R\right]-k_{5-}\left[C.Math.R\right]\left[\mathrm{PQ}\right]+k_{6+}\left[\mathrm{QPC}\right]\left[D\right]-k_{6-}\left[C.Math.D\right]\left[\mathrm{PQ}\right]$$\frac{d\left[\mathrm{FQPC}\right]}{\mathrm{dt}}=-k_{1+}\left[\mathrm{FQPC}\right]\left[R\right]+k_{1-}\left[\mathrm{FC}.Math.R\right]\left[\mathrm{PQ}\right]-k_{3+}\left[\mathrm{FQPC}\right]\left[D\right]+k_{3-}\left[\mathrm{FC}.Math.D\right]\left[\mathrm{PQ}\right]$$\frac{d\left[P_s\right]}{\mathrm{dt}}=k_{2+}\left[P_s{C}_s\right]\left[R\right]-k_{2-}\left[C_s.Math.R\right]\left[P_s\right]+k_{4+}\left[P_s{C}_s\right]\left[D\right]-k_{4-}\left[C_s.Math.D\right]\left[P_s\right]$$\frac{d\left[P_s{C}_s\right]}{\mathrm{dt}}=-k_{2+}\left[P_s{C}_s\right]\left[R\right]+k_{2-}\left[C_s.Math.R\right]\left[P_s\right]-k_{4+}\left[P_s{C}_s\right]\left[D\right]+k_{4-}\left[C_s.Math.D\right]\left[P_s\right]$$\frac{d\left[\mathrm{FC}.Math.R\right]}{\mathrm{dt}}=k_{1+}\left[\mathrm{FQPC}\right]\left[R\right]-k_{1-}\left[\mathrm{FC}.Math.R\right]\left[\mathrm{PQ}\right]$$\frac{d\left[\mathrm{FC}.Math.D\right]}{\mathrm{dt}}=k_{3+}\left[\mathrm{FQPC}\right]\left[D\right]-k_{3-}\left[\mathrm{FC}.Math.D\right]\left[\mathrm{PQ}\right]$$\frac{d\left[C_s.Math.R\right]}{\mathrm{dt}}=k_{2+}\left[P_s{C}_s\right]\left[R\right]-k_{2-}\left[C_s.Math.R\right]\left[P_s\right]$$\frac{d\left[C_s.Math.D\right]}{\mathrm{dt}}=k_{4+}\left[P_s{C}_s\right]\left[D\right]-k_{4-}\left[C_s.Math.D\right]\left[P_s\right]$$\frac{d\left[\mathrm{QPC}\right]}{\mathrm{dt}}=-k_{5+}\left[\mathrm{QPC}\right]\left[R\right]+k_{5-}\left[C.Math.R\right]\left[\mathrm{PQ}\right]-k_{6+}\left[\mathrm{QPC}\right]\left[D\right]+k_{6-}\left[C.Math.D\right]\left[\mathrm{PQ}\right]$$\frac{d\left[C.Math.R\right]}{\mathrm{dt}}=k_{5+}\left[\mathrm{QPC}\right]\left[R\right]-k_{5-}\left[C.Math.R\right]\left[\mathrm{PQ}\right]$$\frac{d\left[C.Math.D\right]}{\mathrm{dt}}=k_{6+}\left[\mathrm{QPC}\right]\left[D\right]-k_{6-}\left[C.Math.D\right]\left[\mathrm{PQ}\right]$

[0100] FIG. 12 shows summary simulation results for the Competitive Composition system. For these simulations, the initial concentration of species were [Target]=0.15 nM, [Variant]=1500 nM, [FQPC]=2.5 nM, [QPC]=1.25 nM, [QP]=3.75 nM, [P.sub.SC.sub.S]=2250 nM, and [P.sub.S]=450 nM. The background fluorescence f.sub.B is equivalent to the fluorescence from 0.04 nM of unquenched fluorophore-labeled strands, and is consistent with observed values in experiments (FIG. 6-9).

[0101] There is an optimal value range for ΔG°.sub.rxn1 and ΔG°.sub.rxn2 that yields high Binding affinity fold-change (FIG. 12AB). When the longer reaction times are allowed, the range of desirable ΔG°.sub.rxn1 and ΔG°.sub.rxn2 values broadens slightly: For example, after 1 hour of reaction, Signal Increase is high when ΔG°.sub.rxn1 is between 0 and −1.5 kcal/mol and ΔG°.sub.rxn2 is between −2.5 and −4.5 kcal/mol. After 48 hours, the range broadens to between 0 and −4.5 kcal/mol for ΔG°.sub.rxn1 and between −2.5 and −7 kcal/mol for ΔG°.sub.rxn2.

[0102] Furthermore, FIG. 12C shows that the maximum signal increase achievable increases with reaction time, though improvement becomes marginal after about 4 hours. In many applications, rapid assays and reactions are desirable; thus there is a tradeoff between short and long reaction times. It is expected that between 30 minutes and 4 hours will be typical.

[0103] In the above simulations, ΔΔG°.sub.1 and ΔΔG°.sub.2 were assumed to be +3 and +4 kcal/mol. Through the course of our simulations and investigations, it has been determined that the optimal ΔG°.sub.rxn1 and ΔG°.sub.rxn2 ranges are relatively insensitive to parameters such as Probe concentration [FQPC], Sink concentration [P.sub.SC.sub.S], reaction time, and background fluorescence level f.sub.B. They are, however, sensitive to the stoichiometric ratios ([QP]/[FQPC]), ([P.sub.S]/[P.sub.SC.sub.S]), and ΔΔG° values, consistent with prior art on double-stranded probes.

[0104] Consequently, the following ranges of ΔG°.sub.rxn values are reasonable for this embodiment (X-Probe as Probe, ultraspecific probes as Sink) of Competitive Compositions:

−4 kcal/mol≤ΔG°.sub.rxn1+Rτ ln([QP]/[FQPC]])≤+3 kcal/mol

−7 kcal/mol≤ΔG°.sub.rxn2+Rτ ln([P.sub.S]/[P.sub.SC.sub.S])≤+1 kcal/mol  (1)

where R is the ideal gas constant and τ is the temperature in Kelvin, and concentrations shown are initial concentrations before addition of sample. As can be seen, high performance is generally observed when the Sink binds more favorably to the Variant than the Probe to the Target (ΔG°.sub.rxn1<ΔG°.sub.rxn2). Competitive Compositions utilizing other Probe and Sink morphologies that result in auxiliary species release follow the same range guidelines for ΔG°.sub.rxn values. Use of Probe morphologies that do not release auxiliary species (e.g. molecular beacons, hairpin probes, and triple-stem probes instead follows:

−4 kcal/mol≤ΔG°.sub.rxn1−Rτ ln([Probe])≤+3 kcal/mol  (2)

Similarly, use of Sink morphologies that do not release auxiliary species follows:

−7 kcal/mol≤ΔG°.sub.rxn2−Rτ ln([Sink])≤+1 kcal/mol  (3)

[0105] The values of ΔG°.sub.rxn1 and ΔG°.sub.rxn2 for a given Probe and Sink design can be calculated using software such as NUPACK or mFold based on their sequences; such calculations are described in more detail in literature describing the component probes themselves and is considered accessible by people of ordinary skill in the art of thermodynamics-guided nucleic acid probe design. Simultaneous use of multiple Probes with different morphologies targeting the same Target species is not recommended; simultaneous use of multiple Sinks with different morphologies targeting the same Variant species is not recommended.

[0106] For example, the standard reaction free energy of the interaction between the target nucleic acid probe (Probe) and target nucleic acid T of FIG. 3 may be expressed as:

ΔG°.sub.rxn1=ΔG°.sub.34-19−ΔG°.sub.22-23−ΔG°.sub.20-21−ΔG°.sub.ML+(ΔG°.sub.33-18−ΔG°.sub.17-18)−ΔG°.sub.label

where ΔG°.sub.34-19 is the standard free energy of the hybridization between subsequence 34 and subsequence 19, ΔG°.sub.22-23 is the standard free energy of the hybridization between subsequence 22 and subsequence 23, ΔG°.sub.20-21 is the standard free energy of the hybridization between subsequence 20 and subsequence 21, ΔG°.sub.ML is the standard free energy of the hybridization in the multi-loop provided at the intersection of the four oligonucleotides, ΔG°.sub.33-18 is the standard free energy of the hybridization between subsequence 33 and subsequence 18, ΔG°.sub.17-18 is the standard free energy of the hybridization between subsequence 17 and subsequence 18, and ΔG°.sub.label is the standard free energy difference between the thermodynamic contribution of the label on the third oligonucleotide when it is in close proximity to the label on the fourth oligonucleotide (not shown) versus when they are delocalized.

[0107] Additionally, the standard reaction free energy of the interaction between the non-target nucleic acid probe (Sink) and non-target nucleic acid V of FIG. 3 may be expressed as:

ΔG°.sub.rxn2=ΔG°.sub.t-TC+ΔG°.sub.nh-PC+(ΔG°.sub.v-TC−ΔG°.sub.h-Pc)

where ΔG°.sub.t-TC is the standard free energy of the hybridization between subsequence 37 and subsequence 30, ΔG°.sub.nh-PC is the standard free energy of the hybridization between subsequence 31 and subsequence 32, ΔG°.sub.v-TC is the standard free energy of the hybridization between subsequence 36 and subsequence 29, ΔG°.sub.nh-PC is the standard free energy of the hybridization between subsequence 28 and subsequence 29.

[0108] Finally, although Signal Increase is a metric specific to conditionally fluorescent Competitive Compositions for detection of Target, other applications that utilize the enrichment capabilities of the Competitive Composition, such as in situ hybridization-based imaging or enzyme-based amplification, likely also face a tradeoff between specificity and sensitivity, so that the guidelines for ΔG°.sub.rxn1 and ΔG°.sub.rxn2 are likely to be generally suitable.

Other Applications of Competitive Compositions

[0109] Another example embodiment of Competitive Composition involves indirect linkage of the Probe species to a functionalized oligo (known as a Universal Functionalized Strand) via one or more hybridization interactions on additional domains (FIG. 14). The Target and Variant molecules that react with the Probe become colocalized to the Universal Functionalized Strand, which facilitates the enrichment of Target via surface or nanoparticle capture, or enables detection/imaging via direct or downstream fluorescence, metallic precipitation, or chemoluminescence. Target and Variant molecules not bound to the Probe, in some embodiments, are dark or washed away prior to downstream reaction.

[0110] Another example embodiment of Competitive Composition involves the usage of the Probe as a primer for enzymatic amplification (FIG. 15). The Target may be a biological sequence bearing a rare mutation or allele, and the Variant may represent the wildtype sequence. In this example, the 3′ end of the Sink is functionalized with a chemical moiety that prevents enzymatic extension, such as a dideoxy nucleotide, a 3-carbon spacer group, or a minor groove binder.

Design Process

[0111] Many potential design processes can be used to generate the sequences employed in a Competitive Composition. The following provides one example.

[0112] 1) Select the Target and Variant as subsequences from a target nucleic acid. The Target and Variant must contain the polymorphic nucleotide(s) of interest, and are otherwise identical. Considerations, such as Target and Variant secondary structure, can be used to inform Target and Variant sequence selection.

[0113] (2) Determine operation conditions, including temperature, buffer salinity, crowding/denaturing agents, reaction time, and readout mechanism.

[0114] (3) Select morphologies of the Probe and the Sink. Considerations, such as cost and complexity of the components, can be used to guide/inform morphology selection.

[0115] (4) Calculate or estimate ΔΔG°.sub.1 and ΔΔG°.sub.2 based on the Target and Variant sequences at desired operation conditions. Thermodynamic values for DNA-DNA and RNA-RNA mismatch bubbles for certain operation conditions are available in literature; for other nucleic acids or conditions, ΔΔG° values can only be coarsely estimated.

[0116] (5) Determine optimal values of ΔG°.sub.rxn1 and ΔG°.sub.rxn2 via ordinary differential equation simulations, such as described in this document. Binding affinity fold-change (or other relevant metric) will be calculated for many different ΔG°.sub.rxn values based on ΔΔG° values, predetermined background signal, Target and Variant concentrations, and Probe and Sink concentrations.

[0117] (6) Design Target-specific Probe based on selected morphology and selected ΔG°.sub.rxn1 value, with iterative fine-tuning of sequence as necessary. Other considerations such as oligonucleotide lengths, functionalizations utilized, etc. can be used for further guide and inform Probe sequence selection.

[0118] (7) Design Variant-specific Sink based on selected morphology and selected ΔG°.sub.rxn2 value, with iterative fine-tuning of sequence as necessary. Other considerations such as oligonucleotide lengths, functionalizations utilized, etc. can be used for further guide and inform Sink sequence selection.

Examples

Experimental Results on Conditionally Fluorescent Competitive Compositions

[0119] To experimentally validate the ability for Competitive Compositions to enrich Target over Variant in binding to the probe, experiments were designed and performed on a conditionally fluorescent version of the Probe (FIG. 5). The Probe is natively dark until it hybridizes to either the Target or the Variant. By observing the fluorescence response of a sample of Variant with a small amount (load) of Target, and comparing to the response of the same quantity of Variant in absence of Target, it can be inferred that the enrichment is provided by the Competitive Composition.

[0120] Referring now to FIG. 5, four major products are formed via the reactions described in FIG. 3; of these, the two products involving the Probe yield high fluorescence. The fluorescence generated by the Target bound to the Probe is denoted by f.sub.A, the fluorescence generated by the Variant bound to the Probe is denoted by f.sub.C, and the total background fluorescence due to incomplete quenching, dark current of the photon detector, autofluorescence of the cuvettes and water Roman spectra is denoted by f.sub.B.

[0121] FIG. 6-8 show the sequence designs for the Probe, Sink, Target, and Variant based on 3 different cancer-related mutation sequences, drawn from the COSMIC database. In each of these, the Variant is the wildtype gene sequence, and the Target is a single nucleotide variant; the concentration of Variant was 3000 times that of the concentration of Target in each case (X=3000), yet the 0.033% load of the Target contributed similar additional fluorescence signal as the Variant. This indicates that of the molecules bound to the Probe, the Target has been enriched by a factor of over 1000.

[0122] A different metric to utilize is “Binding affinity fold-change β”, defined as (f.sub.A.Math.X)/(f.sub.B+f.sub.C). Binding affinity fold-change is likely the most reproducible and robust metric because the background fluorescence level f.sub.B may vary due to autofluorescence from different cuvettes, or differences in sample holder positions, or other changes. A lower bound for the enrichment factor (X/Y) can be calculated as the Binding affinity fold-change.

[0123] Similar experiments to FIG. 6-8 were conducted for 44 different cancer-related mutations for Competitive Compositions with X=1000 using the Probe and Sink morphologies shown in FIG. 9A. Tables 1-3 below represents the sequences used in these experiments where: P—first target probe oligonucleotide; C—second target probe oligonucleotide; F—third target probe oligonucleotide with label; Q—fourth target probe oligonucleotide with quencher; P.sub.s—first variant probe oligonucleotide; C.sub.s—second variant probe oligonucleotide; T—target nucleic acid sequence; V—variant nucleic acid species. It should be noted that the third and fourth target probe oligonucleotides were commonly with every Probe (Probe for each experiment comprises P-C-F-Q complex with only the P-C sequences varying). The F and P functionalized strands were post-synthesis HPLC purified by IDT; all other strands were ordered with standard desalt and not purified. In functionalized sequences, /3Rox N/ denotes the IDT entry code for the 3′ ROX (carboxy-X-rhodamine) fluorophore functionalized by NHS ester chemistry, and /5IAbRQ/ the IDT entry code for the 5′ Iowa Black Red Quencher group.

TABLE-US-00001 TABLE 1 Sequences for the Probes, Sinks, Targets, and Variants used in the Experiments of FIG. 9A-9D. SEQ ID Allele dG°rxn1 dG°rxn2 Species NO. Sequence SMAD 7-C −1.38 −4.33 P 5 AAGGACGAGCAAATGTACCTG CACTCATCCAAAAGAGGAAA C 6 GGGTCCTGTTTCCTCTTTTGGATGAGTG GTCTACTATCCACGATTTAAC Ps 7 CGACTCTCATCCAAAAGAGGAA Cs 8 GGGTCCTATTTCCTCTTTTGGATGAGAGTCG SMAD7-T −0.90 −5.07 P 9 AAGGACGAGCAAATGTACCTG CACTCATCCAAAAGAGGAA C 10 GGGTCCTATTTCCTCTTTTGGATGAGTG GTCTACTATCCACGATTTAAC Ps 11 ACACACTCATCCAAAAGAGGAAA Cs 12 GGGTCCTGTTTCCTCTTTTGGATGAGTGTGT BRAF-D594G −0.66 −2.35 T 13 ATAGGTGGTTTTGGTCTAGCTACAGTGAAA (c.1781A>G) V 14 ATAGGTGATTTTGGTCTAGCTACAGTGAAA P 15 AAGGACGAGCAAATGTACCTG CAAGGTGGTTTTGGTCTAGC C 16 TTCACTGTAGCTAGACCAAAACCACCTTG GTCTACTATCCACGATTTAAC Ps 17 TGTTAATAAGGTGATTTTGGTCTAGC Cs 18 TCACTGTAGCTAGACCAAAATCACCTTATTAACA BRAF-V600E −1.59 −4.29 T 19 ATAGGTGATTTTGGTCTAGCTACAGAGAAA (c.1799T>A) V 20 ATAGGTGATTTTGGTCTAGCTACAGTGAAA P 21 AAGGACGAGCAAATGTACCTG CAAGGTGATTTTGGTCTAG C 22 TCTCTGTAGCTAGACCAAAATCACCTTG GTCTACTATCCACGATTTAAC Ps 23 CGCAGGTGATTTTGGTCTAGC Cs 24 TCACTGTAGCTAGACCAAAATCACCTGCG EGFR-G719A 0.35 −5.21 T 25 TTCAAAAAGATCAAAGTGCTGGCCTCCGGT (c.2156G>C) V 26 TTCAAAAAGATCAAAGTGCTGGGCTCCGGT P 27 AAGGACGAGCAAATGTACCTG CACAAAAAGATCAAAGTGCTGG C 28 CGGAGGCCAGCACTTTGATCTTTTTGTG GTCTACTATCCACGATTTAAC Ps 29 AGGCAAAAAGATCAAAGTGCTGG Cs 30 CGGAGCCCAGCACTTTGATCTTTTTGCCT EGFR-S7681 −0.72 −5.18 T 31 GCCTACGTGATGGCCATCGTGGACAACCCC (c.2303G>T) V 32 GCCTACGTGATGGCCAGCGTGGACAACCCC P 33 AAGGACGAGCAAATGTACCTG CACTACGTGATGGCCATCGT C 34 GGTTGTCCACGATGGCCATCACGTAGTG GTCTACTATCCACGATTTAAC Ps 35 AGTTCTACGTGATGGCCAGCGTG Cs 36 GGTTGTCCACGCTGGCCATCACGTAGAACT EGFR-T790M −0.10 −2.75 T 37 GTGCAGCTCATCATGCAGCTCATGCCCTTC (c.2369C>T) V 38 GTGCAGCTCATCACGCAGCTCATGCCCTTC P 39 AAGGACGAGCAAATGTACCTG CAGCAGCTCATCATGCAGCTC C 40 AGGGCATGAGCTGCATGATGAGCTGCTG GTCTACTATCCACGATTTAAC Ps 41 TGTTAATAGCAGCTCATCACGCAGCTC Cs 42 AGGGCATGAGCTGCGTGATGAGCTGCTATTAACA EGFR-L858R −1.28 −2.69 T 43 ATGTCAAGATCACAGATTTTGGGCGGGCCA (c.2573T>G) V 44 ATGTCAAGATCACAGATTTTGGGCTGGCCA P 45 AAGGACGAGCAAATGTACCTG CAGTCAAGATCACAGATTTTGG C 46 GCCCGCCCAAAATCTGTGATCTTGACTG GTCTACTATCCACGATTTAAC Ps 47 TGTTAATAGTCAAGATCACAGATTTTGG Cs 48 GCCAGCCCAAAATCTGTGATCTTGACTATTAACA EGFR-L861Q −0.39 −4.45 T 49 TGGCCAAACAGCTGGGTGCGGAAGAGAAAG (c.2582T>A) V 50 TGGCCAAACTGCTGGGTGCGGAAGAGAAAG P 51 AAGGACGAGCAAATGTACCTG CAGCCAAACAGCTGGGTGCG C 52 TTTCTCTTCCGCACCCAGCTGTTTGGCTG GTCTACTATCCACGATTTAAC Ps 53 TAGTTGCCAAACTGCTGGGTGCG Cs 54 TTCTCTTCCGCACCCAGCAGTTTGGCAACTA ERBB2-S310F −0.41 −3.90 T 55 ACTACCTTTCTACGGACGTGGGATTCTGCA (c.929C>T) V 56 ACTACCTTTCTACGGACGTGGGATCCTGCA P 57 AAGGACGAGCAAATGTACCTG CATACCTTTCTACGGACGTG C 58 CAGAATCCCACGTCCGTAGAAAGGTATG GTCTACTATCCACGATTTAAC Ps 59 TGTTAATATACCTTTCTACGGACGTG Cs 60 CAGGATCCCACGTCCGTAGAAAGGTATATTAACA ERBB2-L755S −1.44 −4.49 T 61 TTCCAGTGGCCATCAAAGTGTCGAGGGAAA (c.2264T>C) V 62 TTCCAGTGGCCATCAAAGTGTTGAGGGAAA P 63 AAGGACGAGCAAATGTACCTG CACCAGTGGCCATCAAAGTG C 64 TCCCTCGACACTTTGATGGCCACTGGTG GTCTACTATCCACGATTTAAC Ps 65 GTTAATACCAGTGGCCATCAAAGTG Cs 66 TCCCTCAACACTTTGATGGCCACTGGTATTAAC ERBB2-V842I −0.84 −4.92 T 67 GGATGTGCGGCTCATACACAGGGACTTGGC (c.2524G>A) V 68 GGATGTGCGGCTCGTACACAGGGACTTGGC P 69 AAGGACGAGCAAATGTACCTG CAATGTGCGGCTCATACACA C 70 CAAGTCCCTGTGTATGAGCCGCACATTG GTCTACTATCCACGATTTAAC Ps 71 GTTAATAATGTGCGGCTCGTACACA Cs 72 CAAGTCCCTGTGTACGAGCCGCACATTATTAAC KRAS-G12A −1.99 −3.40 T 73 CTTGTGGTAGTTGGAGCTGCTGGC (c.35G>C) V 74 CTTGTGGTAGTTGGAGCTGGTGGC P 75 AAGGACGAGCAAATGTACCTG CAACTTGTGGTAGTTGGAG C 76 GCCAGCAGCTCCAACTACCACAAGTTG GTCTACTATCCACGATTTAAC Ps 77 CCGCTGTGGTAGTTGGA Cs 78 CACCAGCTCCAACTACCACAGCGC KRAS-G12C 1.28 −3.40 T 79 CTTGTGGTAGTTGGAGCTTGTGGC (c.34G>T) V 80 CTTGTGGTAGTTGGAGCTGGTGGC P 81 AAGGACGAGCAAATGTACCTG CAACTTGTGGTAGTTGGAGC C 82 GCCACAAGCTCCAACTACCACAAGTTG GTCTACTATCCACGATTTAAC Ps 83 CCGCTGTGGTAGTTGGA Cs 84 CACCAGCTCCAACTACCACAGCGC KRAS-G12D −0.66 −3.77 T 85 CTTGTGGTAGTTGGAGCTGATGGC (c.35G>A) V 86 CTTGTGGTAGTTGGAGCTGGTGGC P 87 AAGGACGAGCAAATGTACCTG CAACTTGTGGTAGTTGGAG C 88 GCCATCAGCTCCAACTACCACAAGTTG GTCTACTATCCACGATTTAAC Ps 89 GCATCTGTGGTAGTTGGA Cs 90 CACCAGCTCCAACTACCACAGATGC KRAS-G12R 0.26 −3.40 T 91 CTTGTGGTAGTTGGAGCTCGTGGC (c.34G>C) V 92 CTTGTGGTAGTTGGAGCTGGTGGC P 93 AAGGACGAGCAAATGTACCTG CAACTTGTGGTAGTTGGAGC C 94 GCCACGAGCTCCAACTACCACAAGTTG GTCTACTATCCACGATTTAAC Ps 95 CCGCTGTGGTAGTTGGA Cs 96 CACCAGCTCCAACTACCACAGCGC KRAS-G12S −0.34 −3.40 T 97 CTTGTGGTAGTTGGAGCTAGTGGC (c.34G>A) V 98 CTTGTGGTAGTTGGAGCTGGTGGC P 99 AAGGACGAGCAAATGTACCTG CAACTTGTGGTAGTTGGAG C 100 GCCACTAGCTCCAACTACCACAAGTTG GTCTACTATCCACGATTTAAC Ps 101 CCGCTGTGGTAGTTGGA Cs 102 CACCAGCTCCAACTACCACAGCGC KRAS-G12V −0.92 −3.40 T 103 CTTGTGGTAGTTGGAGCTGTTGGC (c.35G>T) V 104 CTTGTGGTAGTTGGAGCTGGTGGC P 105 AAGGACGAGCAAATGTACCTG CAACTTGTGGTAGTTGGAG C 106 GCCAACAGCTCCAACTACCACAAGTTG GTCTACTATCCACGATTTAAC Ps 107 CCGCTGTGGTAGTTGGA Cs 108 CACCAGCTCCAACTACCACAGCGC KRAS-G13C −0.92 −2.85 T 109 CTTGTGGTAGTTGGAGCTGGTTGC (c.37G>T) V 110 CTTGTGGTAGTTGGAGCTGGTGGC P 111 AAGGACGAGCAAATGTACCTG CAACTTGTGGTAGTTGGAG C 112 GCAACCAGCTCCAACTACCACAAGTTG GTCTACTATCCACGATTTAAC Ps 113 CAGGCTGTGGTAGTTGGA Cs 114 CACCAGCTCCAACTACCACAGCCTG KRAS-G13D −0.69 −6.06 T 115 CTTGTGGTAGTTGGAGCTGGTGACGTAGGC (c.38G>A) V 116 CTTGTGGTAGTTGGAGCTGGTGGCGTAGGC P 117 AAGGACGAGCAAATGTACCTG CATGTGGTAGTTGGAGCTGG C 118 CTACGTCACCAGCTCCAACTACCACATG GTCTACTATCCACGATTTAAC Ps 119 TTAATATGTGGTAGTTGGAGCTGGT Cs 120 CTACGCCACCAGCTCCAACTACCACATATTAA KRAS-G13V −0.69 −6.32 T 121 CTTGTGGTAGTTGGAGCTGGTGTCGTAGGC (c.38G>T) V 122 CTTGTGGTAGTTGGAGCTGGTGGCGTAGGC P 123 AAGGACGAGCAAATGTACCTG CATGTGGTAGTTGGAGCTGG C 124 CTACGACACCAGCTCCAACTACCACATG GTCTACTATCCACGATTTAAC Ps 125 AGGTGTGGTAGTTGGAGCTGGT Cs 126 CTACGCCACCAGCTCCAACTACCACACCT KRAS-Q61H −0.64 −3.29 T 127 GCAGGTCACGAGGAGTACAGTGCAATGAGG (c.183A>C) V 128 GCAGGTCAAGAGGAGTACAGTGCAATGAGG P 129 AAGGACGAGCAAATGTACCTG CAAGGTCACGAGGAGTACAG C 130 TCATTGCACTGTACTCCTCGTGACCTTG GTCTACTATCCACGATTTAAC Ps 131 TGTTAATAAGGTCAAGAGGAGTACAG Cs 132 TCATTGCACTGTACTCCTCTTGACCTTATTAACA MAP2K1-K57N −0.32 −5.87 T 133 ACCCAGAATCAGAAGGTGGGAGAACTGAAG (c.171G>T) V 134 ACCCAGAAGCAGAAGGTGGGAGAACTGAAG P 135 AAGGACGAGCAAATGTACCTG CACCAGAATCAGAAGGTGGG C 136 TTCAGTTCTCCCACCTTCTGATTCTGGTG GTCTACTATCCACGATTTAAC Ps 137 AGGCCAGAAGCAGAAGGTGGG Cs 138 TCAGTTCTCCCACCTTCTGCTTCTGGCCT NRAS-G12C 0.20 −5.30 T 139 GTGGTTGGAGCATGTGGTGTTGGGAAAAGC (c.34G>T) V 140 GTGGTTGGAGCAGGTGGTGTTGGGAAAAGC P 141 AAGGACGAGCAAATGTACCTG CAGGTTGGAGCATGTGGTGTT C 142 CTTTTCCCAACACCACATGCTCCAACCTG GTCTACTATCCACGATTTAAC Ps 143 AGGGGTTGGAGCAGGTGGTGT Cs 144 TTTTCCCAACACCACCTGCTCCAACCCCT NRAS-G12D 0.20 −5.30 T 145 GTGGTTGGAGCAGATGGTGTTGGGAAAAGC (c.35G>A) V 146 GTGGTTGGAGCAGGTGGTGTTGGGAAAAGC P 147 AAGGACGAGCAAATGTACCTG CAGGTTGGAGCAGATGGTGTT C 148 CTTTTCCCAACACCATCTGCTCCAACCTG GTCTACTATCCACGATTTAAC Ps 149 AGGGGTTGGAGCAGGTGGTGT Cs 150 TTTTCCCAACACCACCTGCTCCAACCCCT NRAS-G12S 0.55 −5.24 T 151 TACAAACTGGTGGTGGTTGGAGCAAGTGGT (c.34G>A) V 152 TACAAACTGGTGGTGGTTGGAGCAGGTGGT P 153 AAGGACGAGCAAATGTACCTG CTCAAACTGGTGGTGGTTGGA C 154 CACTTGCTCCAACCACCACCAGTTTGAG GTCTACTATCCACGATTTAAC Ps 155 CGATCAAACTGGTGGTGGTTGGA Cs 156 CACCTGCTCCAACCACCACCAGTTTGATCG NRAS-G13D 0.20 −5.30 T 157 GTGGTTGGAGCAGGTGATGTTGGGAAAAGC (c.38G>A) V 158 GTGGTTGGAGCAGGTGGTGTTGGGAAAAGC P 159 AAGGACGAGCAAATGTACCTG CAGGTTGGAGCAGGTGATGTT C 160 CTTTTCCCAACATCACCTGCTCCAACCTG GTCTACTATCCACGATTTAAC Ps 161 AGGGGTTGGAGCAGGTGGTGT Cs 162 TTTTCCCAACACCACCTGCTCCAACCCCT NRAS-Q61H −0.80 −3.40 T 163 ATACTGGATACAGCTGGACATGAAGAGTAC (c.183A>T) V 164 ATACTGGATACAGCTGGACAAGAAGAGTAC P 165 AAGGACGAGCAAATGTACCTG CAACTGGATACAGCTGGAC C 166 ACTCTTCATGTCCAGCTGTATCCAGTTG GTCTACTATCCACGATTTAAC Ps 167 TGTTAATAACTGGATACAGCTGGAC Cs 168 ACTCTTCTTGTCCAGCTGTATCCAGTTATTAACA NRAS-Q61K −0.28 −3.40 T 169 ATACTGGATACAGCTGGAAAAGAAGAGTAC (c.181C>A) V 170 ATACTGGATACAGCTGGACAAGAAGAGTAC P 171 AAGGACGAGCAAATGTACCTG CAACTGGATACAGCTGGAA C 172 ACTCTTCTTTTCCAGCTGTATCCAGTTG GTCTACTATCCACGATTTAAC Ps 173 TGTTAATAACTGGATACAGCTGGAC Cs 174 ACTCTTCTTGTCCAGCTGTATCCAGTTATTAACA NRAS-Q61L −0.89 −4.12 T 175 GGACATACTGGATACAGCTGGACTAGAAGA (c.182A>T) V 176 GGACATACTGGATACAGCTGGACAAGAAGA P 177 AAGGACGAGCAAATGTACCTG CAACATACTGGATACAGCT C 178 TTCTAGTCCAGCTGTATCCAGTATGTTG GTCTACTATCCACGATTTAAC Ps 179 GTTAATAACATACTGGATACAGCTG Cs 180 TTCTTGTCCAGCTGTATCCAGTATGTTATTAAC NRAS-Q61R −0.20 −1.98 T 181 ATACTGGATACAGCTGGACGAGAAGAGTAC (c.182A>G) V 182 ATACTGGATACAGCTGGACAAGAAGAGTAC P 183 AAGGACGAGCAAATGTACCTG CAACTGGATACAGCTGGACG C 184 TACTCTTCTCGTCCAGCTGTATCCAGTTG GTCTACTATCCACGATTTAAC Ps 185 GTGTTAATAACTGGATACAGCTGGAC Cs 186 ACTCTTCTTGTCCAGCTGTATCCAGTTATTAACAC PIK3CA-E542K −0.52 −4.79 T 187 CTCTCTAAAATCACTGAGCAGGAGAAAGAT (c.1624G>A) V 188 CTCTCTGAAATCACTGAGCAGGAGAAAGAT P 189 AAGGACGAGCAAATGTACCTG CACTCTAAAATCACTGAGCA C 190 TCTTTCTCCTGCTCAGTGATTTTAGAGTG GTCTACTATCCACGATTTAAC Ps 191 AGGCTCTGAAATCACTGAGCA Cs 192 CTTTCTCCTGCTCAGTGATTTCAGAGCCT PIK3CA-E545K −0.36 −5.25 T 193 AGATCCTCTCTCTGAAATCACTAAGCAGGA (c.1633G>A) V 194 AGATCCTCTCTCTGAAATCACTGAGCAGGA P 195 AAGGACGAGCAAATGTACCTG CAATCCTCTCTCTGAAATCAC C 196 CCTGCTTAGTGATTTCAGAGAGAGGATTG GTCTACTATCCACGATTTAAC Ps 197 TTAATAATCCTCTCTCTGAAATCAC Cs 198 CTGCTCAGTGATTTCAGAGAGAGGATTATTAA PIK3CA-H1047L −0.81 −3.47 T 199 TGATGCACTTCATGGTGGCTGGACAACAAA (c.3140A>T) V 200 TGATGCACATCATGGTGGCTGGACAACAAA P 201 AAGGACGAGCAAATGTACCTG CAATGCACTTCATGGTGGCT C 202 TGTTGTCCAGCCACCATGAAGTGCATTG GTCTACTATCCACGATTTAAC Ps 203 TGTTAATAATGCACATCATGGTGGCT Cs 204 TGTTGTCCAGCCACCATGATGTGCATTATTAACA PIK3CA-H1047R −0.81 −2.05 T 205 TGATGCACGTCATGGTGGCTGGACAACAAA (c.3140A>G) V 206 TGATGCACATCATGGTGGCTGGACAACAAA P 207 AAGGACGAGCAAATGTACCTG CAATGCACGTCATGGTGGCT C 208 TGTTGTCCAGCCACCATGACGTGCATTG GTCTACTATCCACGATTTAAC Ps 209 GTGTTAATAATGCACATCATGGTGGCT Cs 210 TGTTGTCCAGCCACCATGATGTGCATTATTAACAC STK11-Q37* 1.02 −3.70 T 211 ATCGACTCCACCGAGGTCATCTACTAGCCG (c.109C>T) V 212 ATCGACTCCACCGAGGTCATCTACCAGCCG P 213 AAGGACGAGCAAATGTACCTG CACGACTCCACCGAGGTCAT C 214 GCTGGTAGATGACCTCGGTGGAGTCGTG GTCTACTATCCACGATTTAAC Ps 215 CACCACGACTCCACCGAGGTCAT Cs 216 GCTGGTAGATGACCTCGGTGGAGTCGTGGTG STK11-P281L 0.34 −3.56 T 217 ATCCCGGGCGACTGTGGCCCCCTGCTCTCT (c.842C>T) V 218 ATCCCGGGCGACTGTGGCCCCCCGCTCTCT P 219 AAGGACGAGCAAATGTACCTG CACCCGGGCGACTGTGGCCCC C 220 AGAGCAGGGGGCCACAGTCGCCCGGGTG GTCTACTATCCACGATTTAAC Ps 221 TGTTAATACCCGGGCGACTGTGGCCCC Cs 222 AGAGCGGGGGGCCACAGTCGCCCGGGTATTAACA STK11-F354L 0.33 −3.75 T 223 AGGACCTCTTGGACATCGAGGATGACATCA (c.1062C>G) V 224 AGGACCTCTTCGACATCGAGGATGACATCA P 225 AAGGACGAGCAAATGTACCTG CAGACCTCTTGGACATCGAG C 226 ATGTCATCCTCGATGTCCAAGAGGTCTG GTCTACTATCCACGATTTAAC Ps 227 GTTAATAGACCTCTTCGACATCGAG Cs 228 ATGTCATCCTCGATGTCGAAGAGGTCTATTAAC TP53-R175H 0.00 −4.23 T 229 GTTGTGAGGCACTGCCCCCACCATGAGCGC (c.524G>A) V 230 GTTGTGAGGCGCTGCCCCCACCATGAGCGC P 231 AAGGACGAGCAAATGTACCTG CATGTGAGGCACTGCCCCCAC C 232 GCTCATGGTGGGGGCAGTGCCTCACATG GTCTACTATCCACGATTTAAC Ps 233 GTCGAGGCGCTGCCCCCACCATG Cs 234 AGCGCTCATGGTGGGGGCAGCGCCTCGAC TP53-R213* −1.46 −3.54 T 235 ACTTTTTGACATAGTGTGGTGGTGCCCTAT (c.637C>T) V 236 ACTTTTCGACATAGTGTGGTGGTGCCCTAT P 237 AAGGACGAGCAAATGTACCTG CATTTTTGACATAGTGTGGTG C 238 AGGGCACCACCACACTATGTCAAAAATG GTCTACTATCCACGATTTAAC Ps 239 AAGACAATTTTCGACATAGTGTGGTG Cs 240 AGGGCACCACCACACTATGTCGAAAATTGTCTT TP53-Y220C 0.08 −2.92 T 241 CGACATAGTGTGGTGGTGCCCTGTGAGCCG (c.659A>G) V 242 CGACATAGTGTGGTGGTGCCCTATGAGCCG P 243 AAGGACGAGCAAATGTACCTG CAACATAGTGTGGTGGTGCCC C 244 GCTCACAGGGCACCACCACACTATGTTG GTCTACTATCCACGATTTAAC Ps 245 TGTTAATAACATAGTGTGGTGGTGCC Cs 246 GCTCATAGGGCACCACCACACTATGTTATTAACA TP53-R248Q −0.38 −6.06 T 247 TTCCTGCATGGGCGGCATGAACCAGAGGCC (c.743G>A) V 248 TTCCTGCATGGGCGGCATGAACCGGAGGCC P 249 AAGGACGAGCAAATGTACCTG CACCTGCATGGGCGGCATGA C 250 CCTCTGGTTCATGCCGCCCATGCAGGTG GTCTACTATCCACGATTTAAC Ps 251 GCCCTGCATGGGCGGCATGAAC Cs 252 CCTCCGGTTCATGCCGCCCATGCAGGGC TP53-R248W −0.26 −2.91 T 253 ATGAACTGGAGGCCCATCCTCACCATCATC (c.742C>T) V 254 ATGAACCGGAGGCCCATCCTCACCATCATC P 255 AAGGACGAGCAAATGTACCTG CAGAACTGGAGGCCCATCCT C 256 TGATGGTGAGGATGGGCCTCCAGTTCTG GTCTACTATCCACGATTTAAC Ps 257 TGTTAATAGAACCGGAGGCCCATCCT Cs 258 TGATGGTGAGGATGGGCCTCCGGTTCTATTAACA TP53-R273C 0.18 −3.18 T 259 ACGGAACAGCTTTGAGGTGTGTGTTTGTGC (c.817C>T) V 260 ACGGAACAGCTTTGAGGTGCGTGTTTGTGC P 261 AAGGACGAGCAAATGTACCTG CAGGAACAGCTTTGAGGTGT C 262 ACAAACACACACCTCAAAGCTGTTCCTG GTCTACTATCCACGATTTAAC Ps 263 TGTTAATAGGAACAGCTTTGAGGTGC Cs 264 ACAAACACGCACCTCAAAGCTGTTCCTATTAACA TP53-R273H −1.24 −5.54 T 265 AGGTGCATGTTTGTGCCTGTCCTGGGAGAG (c.818G>A) V 266 AGGTGCGTGTTTGTGCCTGTCCTGGGAGAG P 267 AAGGACGAGCAAATGTACCTG CAGTGCATGTTTGTGCCTGT C 268 CTCCCAGGACAGGCACAAACATGCACTG GTCTACTATCCACGATTTAAC Ps 269 AGTTGTGCGTGTTTGTGCCTGTC Cs 270 CTCCCAGGACAGGCACAAACACGCACAACT TP53-R282W 0.28 −3.81 T 271 GGGAGAGACTGGCGCACAGAGGAAGAGAAT (c.844C>T) V 272 GGGAGAGACCGGCGCACAGAGGAAGAGAAT P 273 AAGGACGAGCAAATGTACCTG CAGAGAGACTGGCGCACAGA C 274 TCTCTTCCTCTGTGCGCCAGTCTCTCTG GTCTACTATCCACGATTTAAC Ps 275 GTTAATAGAGAGACCGGCGCACAGA Cs 276 TCTCTTCCTCTGTGCGCCGGTCTCTCTATTAAC

TABLE-US-00002 TABLE 2 Sequences used for the Third Oligonucleotide (F) and Fourth Oligonucleotide (Q) used with the Probe Sequences of Table 1. SEQ ID Species NO. Sequence F 1 GTTAAATCGTGGATAGTAGAC TTCGCAC/3Rox N/ Q 2 /5IAbRQ/GTGCGAA CAGGTACATTTGCTCGTCCTT

TABLE-US-00003 TABLE 3 Sequences non-allele specific primers at SMAD7 gene locus. SEQ ID Primer NO. Sequence Forward 3 CCATGCTCACAGCCTCATC Primer Reverse 4 TGTTTCCTGAGGAGTCTGAGG Primer

[0124] The results are summarized in FIG. 9B. β values higher than 400 are showed non-linearly for clarity. As can be seen all experiments imply enrichment factors of over 200, with a median of around 1000. FIG. 9C shows comparison of Competitive Composition experiments and experiments for the same 44 different Target/Variant pairs at X=100 given just the Probe, with no Sink. Performance for Probe only experiments was highly variable, and median enrichment was significantly lower, with median of about 30, consistent with prior reports. Thus, the Competitive Composition significantly improves the enrichment of Target in a homogeneous, enzyme-free manner, facilitating applications in rare allele detection.

[0125] The primary reason for the improvement of the Competitive Composition over a good Target-specific Probe alone is that the Competitive Composition captures the enrichment power of both ΔΔG°.sub.1 and ΔΔG°.sub.2, whereas the Target-specific Probe alone captures only ΔΔG°.sub.1.

[0126] FIG. 10 shows Competitive Composition assays on PCR amplicons of human genomic DNA samples. Two extracted DNA samples from Coriell Cell Repository (NA18537 and NA18546) bearing single nucleotide polymorphisms at the SMAD7 gene locus are mixed at various ratios to total concentrations of 2 ng/μL (50 μL), and amplified by asymmetric non-allele-specific PCR to generate single-stranded amplicon. Competitive Compositions that are designed to each allele are mixed with the assigned PCR product for detection. As can be seen, Competitive Composition can reliably detect intended Target post PCR down to 1%.

[0127] Therefore, the present invention is well adapted to attain the ends and advantages mentioned as well as those that are inherent therein. While numerous changes may be made by those skilled in the art, such changes are encompassed within the spirit of this invention as illustrated, in part, by the appended claims.