PCR Blocker Oligonucleotides for Low-VAF Mutation Detection
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Solution Overview
Problem
Existing molecular assays struggle to effectively discriminate low variant allele frequencies (VAF) in samples dominated by wild-type alleles, particularly in regions of hypermutability, leading to inefficient use of reagents and challenges in detecting minor nucleotide differences and mutations.
Innovation Solution
The use of specially configured blocker oligonucleotides, known as mutant enhancing oligonucleotide walls (MEOWs), with a 5′ exonuclease resister end and a 3′ extension blocker modification, to inhibit non-specific amplification of wild-type sequences and enhance amplification of low-abundant target sequences in PCR assays.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional PCR assays are used to detect mutant sequences in samples dominated by wild-type alleles, then the assay can amplify both wild-type and mutant sequences, but the sensitivity to detect low variant allele frequencies is insufficient due to reagent waste on abundant wild-type templates
Solution Approach 1:
The invention extracts and removes the wild-type sequence from the amplification reaction by using a blocker oligonucleotide that specifically binds to and prevents amplification of wild-type templates. This allows the PCR reagents to be focused exclusively on amplifying the mutant sequences, thereby improving detection sensitivity without wasting reagents on abundant wild-type DNA.
Solution Approach 2:
The blocker oligonucleotide acts as an intermediary agent that selectively interferes with wild-type sequence amplification. By introducing this mediator component, the system achieves differential amplification where wild-type sequences are blocked while mutant sequences proceed normally, resolving the sensitivity issue without requiring changes to the core PCR chemistry.
2Measurement precision
If standard oligonucleotides are used for target discrimination, then the assay can bind to both reference and target sequences, but the ability to discriminate single nucleotide differences is insufficient
Solution Approach 1:
The blocker oligonucleotide is designed with local quality enhancement through modified bases (such as LNA or E-ice modifications) at specific positions that correspond to the mutant nucleotide. These localized modifications create high-affinity binding only to the mutant sequence, enabling single nucleotide discrimination without requiring complex assay designs across the entire oligonucleotide length.
Solution Approach 2:
The invention changes the chemical parameters of the oligonucleotide by incorporating modified bases that alter binding affinity and specificity. These parameter changes allow the blocker to distinguish single nucleotide differences through differential binding stability, achieving high discrimination capability while maintaining relatively simple assay design.
3Reliability
If unmodified 5′ end oligonucleotides are used for blocking, then the oligonucleotide can be hydrolyzed by Taq polymerase to prevent reference sequence detection, but the reference sequence continues to be amplified during PCR
Solution Approach 1:
The blocker oligonucleotide is designed with a 5′ modification (such as phosphorothioate bonds, LNA, or other nuclease-resistant modifications) that prevents hydrolysis by Taq polymerase before the blocking function is executed. This preliminary protection ensures the blocker remains intact throughout the PCR reaction, maintaining reliable reference sequence blocking while allowing mutant sequences to be efficiently amplified.
Solution Approach 2:
The blocker oligonucleotide combines different material properties: a modified 5′ end for nuclease resistance and a modified interior region for high-affinity mutant-specific binding. This composite structure integrates multiple functions into a single oligonucleotide component, achieving both reliable blocking and efficient mutant amplification without requiring separate components.
4Measurement precision
If two different fluorophores are used in drop-off assays to target mutation and reference regions, then signal detection can be achieved, but the assay complexity increases and targets per well are reduced
Solution Approach 1:
The invention uses a universal fluorophore-labeled probe that can detect both wild-type and mutant sequences. By combining this universal probe with the blocker oligonucleotide system, a single fluorescence channel is used to distinguish between wild-type (blocked, no signal) and mutant (amplified, signal present) outcomes, eliminating the need for multiple fluorophores while maintaining detection capability and reducing assay complexity.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
MEOWs significantly increase the sensitivity and specificity of PCR assays, allowing detection of low variant allele frequencies down to 0.1% with a 1.6 to 64-fold improvement in sensitivity compared to conventional methods, and reduce non-specific amplification by up to 99%, facilitating accurate detection of mutations in complex samples.
Implementation Method 1
a 5′ exonuclease resister; wherein the reference binding region is configured to hybridize to a binding reference region of the reference sequence
Implementation Method 2
a labelled probe comprising a fluorophore and a quencher, wherein the labelled probe has a shared sequence region configured to hybridize to a shared region of the target sequence and the reference sequence
Data Source
AI summary
Provided herein are methods, kits, and related compositions useful for detecting from a biological sample a low variant allele frequency (VAF) by conventional PCR methods by use of two or more specially configured probes. A first universal-type labelled probe would, normally, when hybridized to a sequence, generate an optically-detectable signal by PCR. Provided herein, however, are specially configured oligonucleotides that, when bound, either prevents non-specific binding of labelled probe to the sequence and/or inhibits reference sequence synthesis by PCR. In this manner, even very low populations of sequences in the presence of another population of sequence that could differ by as little as one nucleotide, can be reliably detected by commercially-available PCR systems.