Obtaining high-quality genomic DNA from tumor tissues is an essential first step for analyzing genetic alterations using next generation sequencing. In this article, we present a simple and rapid method to enrich tumor cells and obtain intact DNA from touch imprint cytology specimens.
The overall goal of this protocol is to obtain high-quality tumor DNA from clinical samples. This method can help answer key questions in basic and clinical science such as cancer research, diagnosis, and treatment decisions. The main advantage of this technique is that we can obtain tumor DNA more simply and quickly than with previous methods.
To begin the protocol, touch the tumor surface of a previously prepared and resected tissue onto a normal glass slide several times with gloved hands. Visually confirm that the touched area is covering more than 80%of the glass slide. Lightly press the normal glass slide against a Polyethylene Naphthalate or PEN membrane slide and rub it gently two to three times with gloved hands.
Visually confirm that the cells are transferred from the normal glass slide to the PEN membrane slide. Air dry both the glass and PEN membrane slides for five minutes at room temperature. After drying, stain the normal glass slide for direct cytological examination.
Dip the glass slides into fixative solution for five seconds and then stain with Giemsa staining solution for 15 seconds. Assess and screen the tumor contents and cellularity on the normal glass slide entirely with a microscope for quick assessment. Evaluate tumor cells based on several criteria.
If the sample shows tumor cellularity over 60%by quick microscopic assessment from the previous section, cut the tumor-touched film of the PEN membrane slides for DNA extraction with a knife and gloved hands. Transfer the cut film to a sterile microcentrifuge tube with a pin set and gloved hands. Store the film-containing microcentrifuge tube at four degrees Celsius until DNA extraction.
Open the software and plan the run condition and set the run parameter within the software. Click the plan tab and select template, then select the appropriate run method. Select the application and technique type and click next.
Select the instrument, sample preparation kit, library kit type, template kit, sequencing kit, base calibration mode, chip type, control sequence, and barcode set and click next. Select plugins and click next. Select project and click next.
Then select default reference and BED files of the targeted region. Type the sample name, select the barcode, and click plan run. Next, perform template preparation and chip loading in an automated instrument according to the manufacturer's instructions.
Thaw the reagent cartridge at room temperature for 45 minutes before use. Dilute the undiluted library with nuclease-free water according to the library concentration calculated in step 6.8 and make 20 picomolar libraries. Prepare a pooled library for sequencing and store it on ice.
Add 25 microliters of the pooled library with a 100 microliter pipette to the bottom of the sample tube. Turn on the power and open the cover of the automated instrument. Place the sequencing chip, chip adapter, enrichment cartridge, tip cartridge, PCR plate, PCR frame seal, recovery tube, solution cartridge, and reagent cartridge to the appropriate position of the automated instrument.
Touch set up run and step by step on the screen. Close the cover and touch start check on the screen. After the deck scan process, touch next.
Check the display contents, kit type, chip ID, sample ID, chip type, plans. Set the time and touch OK.After finishing the chip loading, touch next and open the cover. Unload the sequencing chip from the chip adapter with gloved hands.
Place the chip into the chip container, wrap it with parafilm, and store the chip at four degrees Celsius until the sequencing reaction. Then remove the enrichment cartridge, PCR plate, PCR frame seal, recovery tube, solution cartridge, and reagent cartridge from the appropriate position of the automated instrument with gloved hands. Transfer an empty tip cartridge to the waste tip position of the automated instrument with gloved hands.
Touch next and close the cover. Then touch start and clean the automated instrument with ultraviolet rays for four minutes. Dissolve a sodium chlorite tablet in 1, 000 milliliters of ultra-pure water and filter the solution with a 0.22 micron filter.
Once the sequencing instrument has warmed up, touch clean and next on the screen of the sequencing instrument. Clean the sequencing instrument with 250 milliliters of filter-sterilized sodium chlorite solution, then 250 milliliters of ultra-pure water. Then touch initialize and select the appropriate sequencing kit on the screen.
Install a gray shipper with gloved hands. Initialize the sequencing instrument with the wash solution, the pH adjustment solution, and the pH standard solution. Next, add 20 microliters of DATP, DGTP, DCTP, and DTTP nucleotides in 50 milliliter tubes with a 100 microliter pipette.
Install a gray shipper at the appropriate location with gloved hands. Load the 50 milliliter tube and screw it onto the sequencing instrument. Select next on the screen to start the initialization step.
After completing the initialization step, touch run on the screen and select the appropriate library preparation instrument. Scan the two-dimensional barcode of the chip. Insert the sequencing chip in the appropriate position.
Close the chip clamp and instrument door and touch chip check, next, and OK on the screen to start the sequencing run. After the sequencing reaction, transfer the data and perform data analyzing pipeline on the sequencing server. The absolute DNA quantities and the RQ value, an indicator of the degradation level of genomic DNA, show that a higher DNA yield is achieved using the TIC specimens compared with the FFPE specimens.
In addition, the RQ values from the TIC DNA were significantly higher compared with that of the FFPE DNA across different tumor types. APC Q1367*was identified in both FFPE and TIC DNA extracted from site one and APC S1356*KRAS G12D, and TP53 M237i were detected in both FFPE and TIC DNA extracted from site two, three, and four suggesting that the identical somatic mutations were identified in paired FFPE and TIC DNA samples prepared from the same tumor site. Notably, the same somatic mutations were detected between primary colorectal cancer and two metastatic liver cancer samples suggesting that the tumor clones from site two metastasized to liver.
After its development, this technique paved the way for researchers in the field of molecular and medical research to identify genetic cancers.
