Remember how they created the #JurassicPark (in the famous film!)? Yes, they got the dinosaur DNA from a mosquito trapped in tens of millions years old Amber, which happened to have suck blood from one of the dinosaurs.
FIG: The amber with the mosquito trapped into it. #JurassicPark #amber
Well! in #liquidbiopsy, the Dinosaur is the #cancer patient, the mosquito is the clinician, and yes there isn't a formation of another Dinosaur, but the patient's genomic profile. In blood, there are certain components like cell-free DNA (#cfDNA), circulating tumor DNA (#ctDNA), circulating tumor cells (#CTCs) and #exosomes that, when analysed can open up directed avenues of treatments.
Why not Solid tissue biopsy?
•is a Surgical procedure, invasive
•from a part of solid primary tumor underestimates and overlooks the genomic complexity of the cell population
•Repeated longitudinal sampling is not feasible
• Psychological and economic challenges associated
Why Liquid biopsy?
•is a minimally invasive technique, no recovery time and hospital stay needed
•Cheaper than solid biopsy
•Repeated longitudinal sampling is possible
•It surrogates for biological activity of underlying tumors: #RealTimeBiopsy
•It has a #decreased_diagnosis_bias from #tumor_heterogeneity and dynamically reflects tumor progression
•Molecular characterization of Patient’s tumor signature is possible which has prognostic value
•Best tool for #early_detection and monitoring of therapeutic response
•Less trauma and generally less risk to patients, especially to those who are not candidates for invasive biopsy.
FIG: Schematic representation of the advantage of Liquid biopsy over the solid variant. #egfrmutation #brafmutation #nrasmutation #cancerrelapse
Circulating Tumor Cells (CTCs)
#Ashworth first identified tumor cells in the bloodstream in 1869 released by solid tumor and named it as #circulating_tumor_cells (CTCs). These are products of #EpithelialMesenchymalTransition (EMT) and can participate in micro-metastases and reverse EMT or MET while surviving in the blood for
CTCs can be detected in vitro from #BuffyCoat by #FACS (immunoselection targeting EpCAM+, CD45-) or by biophysical characteristics like size, density, deformity and bioelectric properties. In vivo detection relies on administration of certain harmless CTC-specific reporter tags (eg. #nanoparticles) in the bloodstream and detection by #laserbeam, photodetector etc. Nevertheless their count , marker proteins on the membrane, DNA Mutations and #methylation patterns, also different kinds of RNA holds great #theranostics value.
TABLE: Advantages and limitations of analyzing CTCs by #liquidbiopsy.
Circulating Tumor DNA (ctDNA)
ctDNA's half life in the bloodstream is <2 hours which makes it an ideal choice for Real Time monitoring of tumor progression. These are characteristically 70-200bp long stretches of DNA found in the patient's bloodstream at a concentration of 180ng/mL.
The point mutations present in the patient plasma DNA, were quantified by bidirectional pyrophosphorolysis-activated polymerization PCR (Bi-PAP) and droplet digital PCR (ddPCR) assay. These have a sensitivity of >0.1% mutant DNA diluted in normal DNA. Techniques like standard/ modified NGS and BEAMing (Beads, Emulsion, Amplification, Magnetics-ing) which is a highly sensitive digital PCR method combining emulsion PCR and flow cytometry to identify and quantify specific somatic mutations, are also used to study ctDNA from patients.
TABLE: Advantages and limitations of looking into #ctDNA
Exosomes
The small lipid bilayer membarne vesicles born out #endocytosis tell great stories about their parent cells. These 50-100 nm diameter vesicles can contain 9769 #proteins, 3408 #mRNAs and 2838 #miRNAs on an average and can be found in the bloodstream at a concentration of 1.13-1.19g/mL. As these #exosomes are means of communication between cells and have been proved to play pivotal roles in Cancer initiation and progression, they are the natural contenders of CTCs and ctDNA in liquid biopsy.
Most of the detection techniques we have discussed here can be applied to study exosomes and their enrichment and extraction protocols are also well established.
TABLE: Summarizing why #exosomes are the best choice in #liquidbiopsy
What else to consider?
Although it has a lot of advantages over the conventional technologies,
•Collection of sample, detection of molecular signatures and analysis is still largely based on probability
•Strong connection between the analytes and diseases still being established
•Sensitivity of current technologies still have not reached to clinical levels
•This is a relatively new area (2015-), so skilled manpower is scarce.
Let's hope for further advancements!
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