Oligonucleotide Primer Blocking for Mutant DNA Detection
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Solution Overview
Problem
Current methods for detecting and quantifying circulating tumor cells (CTCs) and circulating tumor DNA (ctDNA) are hindered by their rarity and the difficulty in distinguishing tumor DNA from normal DNA, leading to high background noise and false positive results due to the vast excess of normal cell DNA.
Innovation Solution
The use of specific oligonucleotide primers that selectively amplify mutant DNA over wild-type DNA by competing with blocking oligonucleotides, preventing polymerase extension on wild-type templates and allowing for the specific detection of tumor-associated DNA markers.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If nucleic acid amplification methods such as PCR are used to detect tumor cell DNA, then amplification of target DNA is achieved, but the method lacks sufficient sensitivity to distinguish tumor cell DNA from normal cell DNA due to the very large excess of normal cell DNA leading to high background noise
Solution Approach 1:
The patent applies local quality by designing primers with specific local sequence characteristics that differ between tumor and normal DNA. The primers contain regions of perfect complementarity to tumor-specific sequences and regions of mismatch with normal DNA, creating localized binding specificity that enables discrimination against the background of normal cell DNA.
Solution Approach 2:
The patent employs parameter changes by optimizing primer characteristics including length, melting temperature, and sequence composition to enhance specificity. The primers are designed with specific Tm ranges and GC content to ensure selective binding to tumor DNA while minimizing non-specific amplification of normal DNA, thereby reducing background noise.
2Measurement precision
If existing methods are used to detect circulating tumor cells, then detection capability is limited, but the methods are difficult and expensive to perform because CTCs are very rare (1 in 10^6-10^7 leukocytes)
Solution Approach 1:
The patent applies segmentation by dividing the detection process into distinct stages: enrichment of tumor DNA through selective primer binding, amplification of enriched DNA, and detection. This segmented approach simplifies the overall process by focusing on specific molecular targets rather than attempting to detect entire rare cells among millions of leukocytes.
Solution Approach 2:
The patent uses intermediary molecules (specifically designed primers and probes) that mediate between the rare tumor DNA targets and the detection system. These intermediaries provide high-affinity binding to tumor-specific sequences and serve as templates for amplification, making the detection of rare CTCs feasible without requiring complex isolation procedures.
3Measurement precision
If primers are designed to amplify tumor-specific DNA sequences, then specificity for mutant DNA is improved, but the primers may also bind to wild-type DNA reducing amplification specificity
Solution Approach 1:
The patent applies asymmetry by designing primers with asymmetric binding characteristics: one region of the primer has perfect complementarity to the mutant sequence while another region contains deliberate mismatches with the wild-type sequence. This asymmetric design ensures high-affinity binding to mutant DNA while creating thermodynamic barriers to wild-type DNA binding, thereby preventing false positives.
Solution Approach 2:
The patent employs preliminary anti-action by incorporating mismatch nucleotides in the primer sequences that pre-emptively prevent binding to wild-type DNA. These intentional mismatches are positioned to create unstable hybridization with wild-type sequences before amplification begins, thereby preventing false positive amplification of normal DNA.
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
This approach enhances the detection of tumor-associated DNA while reducing background signals from normal DNA, enabling more accurate identification and monitoring of cancer progression and therapeutic efficacy.
Implementation Method 1
a blocking oligonucleotide having a blocking moiety that prevents polymerase extension, where the blocking oligonucleotide is perfectly complementary to and binds a region within the wild-type target polynucleotide
Implementation Method 2
a forward primer that is perfectly complementary to and binds the mutant variant
Implementation Method 3
contacting a mixture of wild-type and mutant variant target polynucleotides with dNTPs a polymerase, a primer pair capable of hybridizing with and amplifying said target polynucleotides
Data Source
AI summary
In one aspect, the invention features a combination of oligonucleotides comprising a forward primer oligonucleotide and a blocking oligonucleotide. The forward primer oligonucleotide has a 3′ end region, where the 3′ end region includes a portion complementary to a mutation positioned in a region within a polynucleotide. The blocking oligonucleotide contains a blocking moiety and has a 5′ end region, where the 5′ end region includes a portion complementary to a wild-type sequence of the region corresponding to the position of the mutation. In other aspects, the invention provides kits including the combination of primer oligonucleotides and methods of using the oligonucleotides to detect a mutation in a polynucleotide.