Name: single droplet digital polymerase chain reaction for comprehensive and simultaneous detection of mutations in hotspot regions
Uploaded: 2018-09-25T14:00:00
Description: Watch this Scientific Journal Video about Single Droplet Digital Polymerase Chain Reaction for Comprehensive and Simultaneous Detection of Mutations in Hotspot Regions at JoVE.com

This work was supported by Institut Curie SiRIC (grant INCa- DGOS-4654).&#160;The authors wish also to thank Caroline Hego for her contribution to the video.

The protocol presented here follows the ethics guidelines of the Institut Curie. All human samples were obtained from patients enrolled, after informed consent, in studies approved by the Institutional Review Board at Institut Curie.
1. Blood Collection, Plasma Storage and Cell-free DNA Extraction
NOTE: DNA extracted from any type of &#8220;tissue&#8221; can be used (e.g., fresh or formaldehyde-fixed paraffin embedded (FFPE) tissues, cells in culture or blood...

<ol>
	<li>Alexandrov, L. B., Nik-Zainal, S., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Signatures+of+mutational+processes+in+human+cancer.">Signatures of mutational processes in human cancer.</a> Nature. 500 (7463), 415-421 (2013).</li><li>Amado, R. G., Wolf, M., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Wild-Type+KRAS+Is+Required+for+Panitumumab+Efficacy+in+Patients+With+Metastatic+Colorectal+Cancer.">Wild-Type KRAS Is Required for Panitumumab Efficacy in Patients With Metastatic Colorectal Cancer.</a> Journal of Clinical Oncology. 26 (10), 1626-1634 (2008).</li><li>Karapetis, C. S., Khambata-Ford, S., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=K-ras+mutations+and+benefit+from+cetuximab+in+advanced+colorectal+cancer.">K-ras mutations and benefit from cetuximab in advanced colorectal cancer.</a> New England Journal of Medicine. 359 (17), 1757-1765 (2008).</li><li>Postel, M., Roosen, A., Laurent-Puig, P., Taly, V., Wang-Renault, S. -. F. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Droplet-based+digital+PCR+and+next+generation+sequencing+for+monitoring+circulating+tumor+DNA:+a+cancer+diagnostic+perspective.">Droplet-based digital PCR and next generation sequencing for monitoring circulating tumor DNA: a cancer diagnostic perspective.</a> Expert Review of Molecular Diagnostics. 18 (1), 7-17 (2018).</li><li>Saliou, A., Bidard, F. -. C., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Circulating+tumor+DNA+for+triple-negative+breast+cancer+diagnosis+and+treatment+decisions.">Circulating tumor DNA for triple-negative breast cancer diagnosis and treatment decisions.</a> Expert Review of Molecular Diagnostics. 16 (1), 39-50 (2015).</li><li>Decraene, C., Silveira, A. B., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Multiple+Hotspot+Mutations+Scanning+by+Single+Droplet+Digital+PCR.">Multiple Hotspot Mutations Scanning by Single Droplet Digital PCR.</a> Clinical chemistry. 64 (2), 317-328 (2018).</li><li>Untergasser, A., Cutcutache, I., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Primer3--new+capabilities+and+interfaces.">Primer3--new capabilities and interfaces.</a> Nucleic Acids Research. 40 (15), e115 (2012).</li><li>Snyder, M. W., Kircher, M., Hill, A. J., Daza, R. M., Shendure, J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Cell-free+DNA+Comprises+an+In+Vivo+Nucleosome+Footprint+that+Informs+Its+Tissues-Of-Origin.">Cell-free DNA Comprises an In Vivo Nucleosome Footprint that Informs Its Tissues-Of-Origin.</a> Cell. 164 (1-2), 57-68 (2016).</li><li>Bidshahri, R., Attali, D., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Quantitative+Detection+and+Resolution+of+BRAF+V600+Status+in+Colorectal+Cancer+Using+Droplet+Digital+PCR+and+a+Novel+Wild-Type+Negative+Assay.">Quantitative Detection and Resolution of BRAF V600 Status in Colorectal Cancer Using Droplet Digital PCR and a Novel Wild-Type Negative Assay.</a> The Journal of Molecular Diagnostics. 18 (2), 190-204 (2016).</li><li>Attali, D., Bidshahri, R., Haynes, C., Bryan, J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=ddpcr:+an+R+package+and+web+application+for+analysis+of+droplet+digital+PCR+data.">ddpcr: an R package and web application for analysis of droplet digital PCR data.</a> F1000Research. 5, (2016).</li><li>Forbes, S. A., Beare, D., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=COSMIC:+somatic+cancer+genetics+at+high-resolution.">COSMIC: somatic cancer genetics at high-resolution.</a> Nucleic Acids Research. 45 (D1), D777-D783 (2017).</li></ol>

To design an efficient drop-off ddPCR assay, optimization is crucial, and the protocol must be followed carefully. Each combination of primers and probes has a unique PCR reaction efficiency. Thus, an individual assay has to be carefully validated on control samples before being used on valuable test samples. Optimization and validation are important to certify peak signal detection and assess specificity and sensitivity. As described in the protocol, all mutations located in a target region covered by the &#34;probe 2&#...

Thousands of somatic mutations related to cancer development have been reported1. Among these, a few are predictive markers of the efficacy of targeted therapy 2,3 and genetic screening of these mutations is now routine clinical practice. Droplet digital PCR (ddPCR) technology can be used to monitor for the presence or the absence of mutations with high detection accuracy and is highly compatible with non-invasive liquid biopsies4,5. However, current ddPCR assays are primarily designed to detect mutations known a priori. This severely limits the use of ddPCR as a discovery tool when the mutation is unknown. Indeed, in the conventional ddPCR design, a hydrolysis probe recognizing the wild-type allele (WT Probe) competes with a specific probe recognizing the mutant allele (MUT Probe) (Figure 1A). The probe with higher affinity hybridizes to the template and releases its fluorophore, indicating the nature of the corresponding allele. The fluorescence data obtained for each droplet can be visualized in a scatter plot representing the fluorescence emitted by the WT and MUT probes in different dimensions. A schematic representation of a typical result for a conventional ddPCR assay is presented in Figure 1A. In this example, the blue cloud corresponds to the droplets containing WT alleles identified by the WT probe, whereas the red cloud corresponds to droplets in which the MUT allele has been amplified and identified by the MUT probe. Depending on the quantity of DNA loaded in the reaction, double positive droplets containing both WT and MUT amplicons can appear (green cloud). The light grey cloud corresponds to empty droplets.
Since most platforms allow for the detection of a limited number of fluorophores (usually 2, but up to 5), throughput of conventional ddPCR is limited. Therefore, targeting regions with multiple adjacent mutations requires design of technically challenging multiplex ddPCR assays or the use of multiple reactions targeting each mutation in parallel. The drop-off ddPCR strategy, overcomes this limitation as it can potentially detect any genetic alteration within a target region using a unique pair of WT hydrolysis probes. The first probe (Probe 1) covers a non-variable sequence, adjacent to the target region and the second probe (Probe 2) is complementary to the WT sequence of the target region where mutations are expected (Figure 1B). While the first probe quantifies the total amount of amplifiable molecules in the reaction, the second probe discriminates WT and MUT alleles by sub-optimal hybridization to mutant sequences. Probe 2 can identify multiple types of mutations in the target region (single or multiple nucleotide substitutions, deletion, etc.)6. As in conventional ddPCR, the light grey cloud corresponds to droplets containing no DNA molecules. It is important to recall that in this type of assay, optimal separation of WT and MUT clouds is dependent on the quantity of DNA loaded in the reaction, since droplets containing both WT and MUT target alleles cannot be distinguished from droplets containing only the WT form. Therefore, this assay requires that most droplets contain no more than one copy of the targeted gene.

<table>
	<tbody>
		<tr>
			<td>K2EDTA tube (color code : lavender)</td>
			<td>BD</td>
			<td>367863</td>
			<td>EDTA tubes are used to obtain a whole blood or EDTA plasma sample</td>
		</tr>
		<tr>
			<td>QIAamp Circulating Nucleic Acid Kit (manual protocol)</td>
			<td>Qiagen</td>
			<td>55114</td>
			<td>For isolation of free-circulating DNA from human plasma</td>
		</tr>
		<tr>
			<td>QIAsymphony DSP Circulating DNA Kit (automated protocol)</td>
			<td>Qiagen</td>
			<td>937556</td>
			<td>For isolation of free-circulating DNA from human plasma</td>
		</tr>
		<tr>
			<td>QIAsymphony SP system</td>
			<td>Qiagen</td>
			<td>9001297</td>
			<td>fully integrated and automated system for cfDNA, DNA or RNA purification</td>
		</tr>
		<tr>
			<td>QIAvac 24 Plus</td>
			<td>Qiagen</td>
			<td>19413</td>
			<td>For purification of up to 24 cfDNAs simultaneously</td>
		</tr>
		<tr>
			<td>Qubit fluorometer</td>
			<td>Invitrogen</td>
			<td>Q33226</td>
			<td>The Qubit fluorometer is a benchtop fluorometer for the quantitation of DNA</td>
		</tr>
		<tr>
			<td>QX100 or QX200 reader</td>
			<td>Bio-Rad</td>
			<td>186-3003 or186-4003, respectively</td>
			<td>The reader measures fluorescence intensity of each droplet and detects the size and shape as droplets pass the detector</td>
		</tr>
		<tr>
			<td>QX100 or QX200 droplet generator</td>
			<td>Bio-Rad</td>
			<td>186-3002 or 186-4002, respectively</td>
			<td>Instrument used for droplet generation</td>
		</tr>
		<tr>
			<td>C1000 thermal cycler</td>
			<td>Bio-Rad</td>
			<td>1851196</td>
			<td>Modular thermal cycler platform, includes C1000 Touch thermal cycler chassis, 96-well fast reaction module</td>
		</tr>
		<tr>
			<td>Plate sealer</td>
			<td>Bio-Rad</td>
			<td>181-4000</td>
			<td>PX1&#8482; PCR plate sealer</td>
		</tr>
		<tr>
			<td>DG8 cartridge holder</td>
			<td>Bio-Rad</td>
			<td>186-3051</td>
			<td>Positions and holds the DG8 cartridge in the instrument for droplet generation</td>
		</tr>
		<tr>
			<td>Droplet generator cartridges and gaskets</td>
			<td>Bio-Rad</td>
			<td>186-4007</td>
			<td>Microfluidic DG8 cartridge used to mix sample and oil to generate droplets; DG8 gaskets seal the cartridge to prevent evaporation and apply the pressure required for droplet formation</td>
		</tr>
		<tr>
			<td>PCR supermix</td>
			<td>Bio-Rad</td>
			<td>186-3010</td>
			<td>ddPCR supermix for probes (no dUTP)</td>
		</tr>
		<tr>
			<td>96-well PCR plates</td>
			<td>Eppendorf</td>
			<td>951020362</td>
			<td>96-well semi-skirted plates</td>
		</tr>
		<tr>
			<td>Foil seal</td>
			<td>Bio-Rad</td>
			<td>181-4040</td>
			<td>Pierceable foil heat seal</td>
		</tr>
		<tr>
			<td>ddPCR Droplet Reader Oil</td>
			<td>Bio-Rad</td>
			<td>186-3004</td>
			<td>oil used in the read</td>
		</tr>
		<tr>
			<td>Droplet Generation Oil for Probes</td>
			<td>Bio-Rad</td>
			<td>186-3005</td>
			<td>oil for droplet generation</td>
		</tr>
		<tr>
			<td>DNA loBind Tube 1.5 mL</td>
			<td>Eppendorf</td>
			<td>0030 108.051</td>
			<td>Eppendorf LoBind Tubes maximize sample recovery by significantly reducing sample-to-surface binding</td>
		</tr>
		<tr>
			<td>Multiplex I cfDNA Reference Standard Set</td>
			<td>HORIZON</td>
			<td>HD780</td>
			<td>The Multiplex I cfDNA Reference Standards are highly-characterized, biologically-relevant reference materials used to assess the performance of cfDNA assays that detect somatic mutations</td>
		</tr>
		<tr>
			<td>QUBIT DSDNA HS ASSAY KIT, 500</td>
			<td>Life Technologies</td>
			<td>Q32854</td>
			<td>The HS assay is highly selective for double-stranded DNA (dsDNA) over RNA and is designed to be accurate for initial sample concentrations from 10 pg/&#181;L to 100 ng/&#181;L</td>
		</tr>
		<tr>
			<td>Qubit Assay Tubes</td>
			<td>Life Technologies</td>
			<td>Q32856</td>
			<td>Qubit assay tubes are 500 &#181;L thin-walled polypropylene tubes for use with the Qubit Fluorometer</td>
		</tr>
	</tbody>
</table>

single droplet digital polymerase chain reaction for comprehensive and simultaneous detection of mutations in hotspot regions

Droplet digital polymerase chain reaction (ddPCR) is a highly sensitive quantitative polymerase chain reaction (PCR) method based on sample fractionation into thousands of nano-sized water-in-oil individual reactions. Recently, ddPCR has become one of the most accurate and sensitive tools for circulating tumor DNA (ctDNA) detection. One of the major limitations of the standard ddPCR technique is the restricted number of mutations that can be screened per reaction, as specific hydrolysis probes recognizing each possible allelic version are required. An alternative methodology, the drop-off ddPCR, increases throughput, since it requires only a single pair of probes to detect and quantify potentially all genetic alterations in the targeted region. Drop-off ddPCR displays comparable sensitivity to conventional ddPCR assays with the advantage of detecting a greater number of mutations in a single reaction. It is cost-effective, conserves precious sample material, and can also be used as a discovery tool when mutations are not known a priori.

In a proof-of-concept study, KRAS exon 2 mutations (codons 12 and 13) and EGFR exon 19 deletions were investigated in FFPE tissues and plasma samples from cancer patients using the drop-off ddPCR strategy6.
The KRAS drop-off probe interrogated a 16 bp region encompassing multiple mutations in exon 2 of the KRAS gene, which harbor more than 95% of the known KRAS </em...

Watch this Scientific Journal Video about Single Droplet Digital Polymerase Chain Reaction for Comprehensive and Simultaneous Detection of Mutations in Hotspot Regions at JoVE.com

Single Droplet Digital Polymerase Chain Reaction for Comprehensive and Simultaneous Detection of Mutations in Hotspot Regions

Here, we present a protocol to accurately quantify multiple genetic alterations of a target region in a single reaction using drop-off ddPCR and a unique pair of hydrolysis probes.

Droplet digital polymerase chain reaction (ddPCR) is a highly sensitive quantitative polymerase chain reaction (PCR) method based on sample fractionation ...

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