Blocked recombinase polymerase amplification for mutation analysis of PIK3CA gene

A multiplexed, allele-specific recombinase polymerase amplification assay with lateral flow readout for sickle cell disease detection

Isothermal nucleic acid amplification tests have the potential to improve disease diagnosis at the point of care, but it remains challenging to develop multiplexed tests that can detect ≥3 targets or to detect point mutations that may cause disease. These capabilities are critical to enabling informed clinical decision-making for many applications, such as sickle cell disease (SCD). To address this, we describe the development of a multiplexed allele-specific recombinase polymerase amplification (RPA) assay with lateral flow readout. We first characterize the specificity of RPA using primer design strategies employed in PCR to achieve point mutation detection, and demonstrate the utility of these strategies in achieving selective isothermal amplification and detection of genomic DNA encoding for the healthy βA globin allele, or genomic DNA containing point mutations encoding for pathologic βS and βC globin alleles, which are responsible for most sickle cell disorders. We then optimize reaction conditions to achieve multiplexed amplification and identification of the three alleles in a single reaction. Finally, we perform a small pilot study with 20 extracted genomic DNA samples from SCD patients and healthy volunteers - of the 13 samples with valid results, the assay demonstrated 100% sensitivity and 100% specificity for detecting pathologic alleles, and an overall accuracy of 92.3% for genotype prediction. This multiplexed assay is rapid, minimally instrumented, and when combined with point-of-care sample preparation, could enable DNA-based diagnosis of SCD in low-resource settings. The strategies reported here could be applied to other challenges, such as detection of mutations that confer drug resistance.

Ultrafast and Highly Specific Detection of One-Base Mutated Cell-Free DNA at a Very Low Abundance

Liquid biopsy as well as genotyping plays important roles in guiding the use of tumor-targeted drugs and monitoring the generation of drug resistance. However, current methods, such as next-generation sequencing (NGS) and pyrosequencing, require long analysis time and complicated steps. To achieve ultrafast and highly specific detection of cell-free DNA (cfDNA) from blood, we improved our recently developed FEN1-aided RPA (FARPA), which combined flap endonuclease 1 (FEN1)-catalyzed invasive reactions with recombinase polymerase amplification (RPA) by inactivating the RPA enzymes before invasive reactions, designing short RPA primers, and changing invasive reaction conditions. Using the L858R and T790M mutations as examples, FARPA was sensitive to detect 5 copies of targeted mutants, specific to sense the mutants with an abundance as low as 0.01% from blood, and ultrafast to get results within 40 min. The method was readily expended to genotyping, and 15 min was enough to report the allele species directly from oral swab samples by coupling quick DNA extraction reagents. Validation was carried out by detecting clinical samples, including 20 cfDNA from patients with non-small cell lung cancer (NSCLC) for liquid biopsy and 43 human genomic DNA (gDNA) purified from blood (33) or lysed from oral swabs (10) for genotyping, giving 100% agreement with NGS and pyrosequencing, respectively. Furthermore, a portable battery-driven device with dual-channel fluorescence detection was successfully constructed to facilitate point-of-care testing (POCT) of liquid biopsy and genotyping, providing doctors with a potential tool to achieve genotyping- or mutant-guided personalized medicine at emergency or source-limited regions.

Molecular Mechanisms Underlying CRISPR/Cas-Based Assays for Nucleic Acid Detection

Applied to investigate specific sequences, nucleic acid detection assays can help identify novel bacterial and viral infections. Most up-to-date systems combine isothermal amplification with Cas-mediated detection. They surpass standard PCR methods in detection time and sensitivity, which is crucial for rapid diagnostics. The first part of this review covers the variety of isothermal amplification methods and describes their reaction mechanisms. Isothermal amplification enables fast multiplication of a target nucleic acid sequence without expensive laboratory equipment. However, researchers aim for more reliable results, which cannot be achieved solely by amplification because it is also a source of non-specific products. This motivated the development of Cas-based assays that use Cas9, Cas12, or Cas13 proteins to detect nucleic acids and their fragments in biological specimens with high specificity. Isothermal amplification yields a high enough concentration of target nucleic acids for the specific signal to be detected via Cas protein activity. The second part of the review discusses combinations of different Cas-mediated reactions and isothermal amplification methods and presents signal detection techniques adopted in each assay. Understanding the features of Cas-based assays could inform the choice of an optimal protocol to detect different nucleic acids.

Bioplatforms in liquid biopsy: advances in the techniques for isolation, characterization and clinical applications

Tissue biopsy analysis has conventionally been the gold standard for cancer prognosis, diagnosis and prediction of responses/resistances to treatments. The existing biopsy procedures used in clinical practice are, however, invasive, painful and often associated with pitfalls like poor recovery of tumor cells and infeasibility for repetition in single patients. To circumvent these limitations, alternative non-invasive, rapid and economical, yet sturdy, consistent and dependable, biopsy techniques are required. Liquid biopsy is an emerging technology that fulfills these criteria and potentially much more in terms of subject-specific real-time monitoring of cancer progression, determination of tumor heterogeneity and treatment responses, and specific identification of the type and stages of cancers. The present review first briefly revisits the state-of-the-art technique of liquid biopsy and then proceeds to address in detail, the advances in the potential clinical applications of four major biological agencies present in liquid biopsy samples (circulating tumor DNA (ctDNA), circulating tumor cells (CTCs), exosomes and tumor-educated platelets (TEPs)). Finally, the authors conclude with the limitations that need to be addressed in order for liquid biopsy to effectively replace the conventional invasive biopsy methods in the clinical settings.

Critical insight into recombinase polymerase amplification technology

INTRODUCTION

Recombinase polymerase amplification (RPA) is a promising and emerging technology for rapidly amplifying target nucleic acid from minimally processed samples and through small portable instruments. RPA is suitable for point-of-care testing (POCT) and on-site field testing, and it is compatible with microfluidic devices. Several detection assays have been developed, but limited research has dug deeper into the chemistry of RPA to understand its kinetics and fix its shortcomings.

AREAS COVERED

This review provides a detailed introduction of RPA molecular mechanism, kits formats, optimization, application, pros, and cons. Moreover, this critical review discusses the nonspecificity issue of RPA, highlights its consequences, and emphasizes the need for more research to resolve it. This review discusses the reaction kinetics of RPA in relation to target length, product quantity, and sensitivity. This critical review also questions the novelty of recombinase-aided amplification (RAA). In short, this review discusses many aspects of RPA technology that have not been discussed previously and provides a deeper insight and new perspectives of the technology.

EXPERT OPINION

RPA is an excellent choice for pathogen detection, especially in low-resource settings. It has a potential to replace PCR for all purposes, provided its shortcomings are fixed and its reagent accessibility is improved.

From saliva to SNP: non-invasive, point-of-care genotyping for precision medicine applications using recombinase polymerase amplification and giant magnetoresistive nanosensors

Genetic testing is considered a cornerstone of the precision medicine paradigm. Genotyping of single nucleotide polymorphisms (SNPs) has been shown to provide insights into several important issues, including therapy selection and drug responsiveness. However, a scarcity of widely deployable and cost-effective genotyping tools has limited the integration of precision medicine into routine clinical practice. The objective of our work was to develop a portable, cost-effective, and automated platform that performs SNP genotyping at the point-of-care (POC). Using recombinase polymerase amplification (RPA) and giant magnetoresistive (GMR) nanosensors, we present a highly automated and multiplexed point-of-care platform that utilizes direct saliva for the qualitative genotyping of four SNPs (rs4633, rs4680, rs4818, rs6269) along the catechol-O-methyltransferase gene (COMT), which is associated with the modulation of pain sensitivity and perioperative opioid use. Using this approach, we successfully amplify, detect, and genotype all four of the SNPs, demonstrating 100% accordance between the experimental results obtained using the automated RPA and GMR genotyping assay and the results obtained using a COMT PCR genotyping assay that was formerly validated using pyrosequencing. This automated, portable, and multiplexed RPA and GMR assay shows great promise as a solution for SNP genotyping at the POC and reinforces the broad applications of magnetic nanotechnology in biomedicine.

Design of Oligonucleotides for Allele-Specific Amplification Based on PCR and Isothermal Techniques

Single-nucleotide variations have been associated to various genetic diseases, variations on drug efficiency, and differences in cancer prognostics. The detection of these changes in nucleic acid sequences from patient samples is particularly useful for accurate diagnosis, therapeutics, and disease management. A reliable allele-specific amplification is still an important challenge for molecular-based diagnostic technologies. In the last years, allele-specific primers have been designed for promoting the enrichment of certain variants, based on a higher stability of primer/template duplexes. Also, several methods are based on the addition of a blocking oligonucleotide that prevent the amplification of a specific variant, enabling that other DNA variants can be observed. In this context, genotyping methods based on isothermal amplification techniques are increasing, especially those assays aimed to be deployed at point-of-care applications. The correct selection of target sequences is crucial for reaching the required analytical performances, in terms of reaction time, amplification yield, and selectivity. The present chapter describes the design criteria for the selection of primers and blockers for relevant PCR approaches and novel isothermal strategies. Several successful examples are provided in order to highlight the main design restrictions and the potential to be extended to other applications.

A genosensor for detecting single-point mutations in dendron chips after blocked recombinase polymerase amplification

Dendron–probe conjugates were effectively immobilized on chip surfaces, improving assay sensitivity and simplifying coupling reactions. Combined with an isothermal amplification, the array method accurately detects single-base changes.

Protein or ribonucleoprotein-mediated blocking of recombinase polymerase amplification enables the discrimination of nucleotide and epigenetic differences between cell populations

Isothermal DNA amplification, such as recombinase polymerase amplification (RPA), is well suited for point-of-care testing (POCT) as it does not require lengthy thermal cycling. By exploiting DNA amplification at low temperatures that do not denature heat-sensitive molecules such as proteins, we have developed a blocking RPA method to detect gene mutations and examine the epigenetic status of DNA. We found that both nucleic acid blockers and nuclease-dead clustered regularly interspaced short palindromic repeats (CRISPR) ribonucleoproteins suppress RPA reactions by blocking elongation by DNA polymerases in a sequence-specific manner. By examining these suppression events, we are able to discriminate single-nucleotide mutations in cancer cells and evaluate genome-editing events. Methyl-CpG binding proteins similarly inhibit elongation by DNA polymerases on CpG-methylated template DNA in our RPA reactions, allowing for the detection of methylated CpG islands. Thus, the use of heat-sensitive molecules such as proteins and ribonucleoprotein complexes as blockers in low-temperature isothermal DNA amplification reactions markedly expands the utility and application of these methods.

Fujita et al. investigate the use of oligoribonucleotides, proteins, and ribonucleoprotein complexes as sequence-specific blockers of DNA extension by DNA polymerases. They demonstrate the value of proteins and ribonucleoprotein complexes as blockers in low-temperature isothermal DNA amplification reactions for discrimination of nucleotide and epigenetic differences.

Highly Sensitive Detection of Low-Abundance BRAF V600E Mutation in Fine-Needle Aspiration Samples by Zip Recombinase Polymerase Amplification

Papillary thyroid carcinoma (PTC) is the most common thyroid cancer with high incidence in endocrine tumors, which emphasizes the significance of accurate diagnostics. Still, the commonly used cytological method (fine-needle aspiration (FNA) cytology) and molecular diagnostic methods (such as PCR and sequencing) are limited in terms of diagnostic time, sensitivity, and user-friendliness. In this study, we introduce a novel Zip recombinase polymerase amplification (Z-RPA) strategy to efficiently detect rare mutant alleles in PTC fine-needle aspiration samples, which is sensitive, fast, and simple to manipulate. Using Zip nucleic acid (ZNA) probes to clamp the mutation region, the phi 29 polymerase could selectively displace mismatched ZNA probes and start amplification, while leaving complementary ZNA probes untouched and blocking amplification according to genotype. We demonstrated the good sensitivity and specificity of this strategy with optimized conditions and design, which enabled detection of BRAF V600E mutation in a total 4 ng of genomic DNA within 40 min (≈1 copy). Robust behavior in clinical specimen analysis was also demonstrated. The Z-RPA strategy provides a pragmatic approach to rapidly, sensitively, and easily detect BRAF V600E mutation in clinical fine-needle aspiration samples, which is a promising method for early cancer diagnosis and treatment guideline.

Developments in integrating nucleic acid isothermal amplification and detection systems for point-of-care diagnostics

Early disease detection through point-of-care (POC) testing is vital for quickly treating patients and preventing the spread of harmful pathogens. Disease diagnosis is generally accomplished using quantitative polymerase chain reaction (qPCR) to amplify nucleic acids in patient samples, permitting detection even at low target concentrations. However, qPCR requires expensive equipment, trained personnel, and significant time. These resources are not available in POC settings, driving researchers to instead utilize isothermal amplification, conducted at a single temperature, as an alternative. Common isothermal amplification methods include loop-mediated isothermal amplification, recombinase polymerase amplification, rolling circle amplification, nucleic acid sequence-based amplification, and helicase-dependent amplification. There has been a growing interest in combining such amplification methods with POC detection methods to enable the development of diagnostic tests that are well suited for resource-limited settings as well as developed countries performing mass screenings. Exciting developments have been made in the integration of these two research areas due to the significant impact that such approaches can have on healthcare. This review will primarily focus on advances made by North American research groups between 2015 and June 2020, and will emphasize integrated approaches that reduce user steps, reliance on expensive equipment, and the system's time-to-result.

A novel hotspot specific isothermal amplification method for detection of the common PIK3CA p.H1047R breast cancer mutation

Breast cancer (BC) is a common cancer in women worldwide. Despite advances in treatment, up to 30% of women eventually relapse and die of metastatic breast cancer. Liquid biopsy analysis of circulating cell-free DNA fragments in the patients' blood can monitor clonality and evolving mutations as a surrogate for tumour biopsy. Next generation sequencing platforms and digital droplet PCR can be used to profile circulating tumour DNA from liquid biopsies; however, they are expensive and time consuming for clinical use. Here, we report a novel strategy with proof-of-concept data that supports the usage of loop-mediated isothermal amplification (LAMP) to detect PIK3CA c.3140 A > G (H1047R), a prevalent BC missense mutation that is attributed to BC tumour growth. Allele-specific primers were designed and optimized to detect the p.H1047R variant following the USS-sbLAMP method. The assay was developed with synthetic DNA templates and validated with DNA from two breast cancer cell-lines and two patient tumour tissue samples through a qPCR instrument and finally piloted on an ISFET enabled microchip. This work sets a foundation for BC mutational profiling on a Lab-on-Chip device, to help the early detection of patient relapse and to monitor efficacy of systemic therapies for personalised cancer patient management.

Applying a Linear Amplification Strategy to Recombinase Polymerase Amplification for Uniform DNA Library Amplification

Recombinase polymerase amplification (RPA) is an isothermal DNA amplification method with broad applications as a point-of-care test and in molecular biology techniques. Currently, most of the applications are focused on target-specific amplification. Because RPA has the advantage of amplifying DNA under isothermal conditions, we utilized RPA as a DNA library amplification tool. In this study, we used a sheared genomic DNA library and an oligonucleotide (oligo) library for the comparison of polymerase chain reaction and RPA. For the sheared DNA library, we observed biased amplification after RPA was conducted. Thus, to amplify the size-variable DNA library uniformly, we introduced a linear amplification strategy with RPA and successfully improved the uniformity. On the other hand, using the same-sized oligo library, we confirmed that RPA amplified this library uniformly without modification of the protocol. These results demonstrate that RPA can be applied not only to amplify a specific target as previously demonstrated but also to amplify a complex DNA library composed of a large number of different DNA molecules.

Review: a comprehensive summary of a decade development of the recombinase polymerase amplification

RPA is a versatile complement or replacement of PCR, and now is stepping into practice.