[Frontiers in Bioscience, Landmark, 25, 874-892, Jan 1, 2020]

Applications of RNA characterisation in circulating tumour cells

Sara Hassan1-3, Tony Blick1-3, Elizabeth D. Williams1,2,4, Erik W. Thompson1-3

1School of Biomedical Sciences and Institute of Health and Biomedical Innovation (IHBI), Faculty of Health, Queensland University of Technology (QUT), Brisbane, Australia, 2Translational Research Institute, Brisbane, Australia, 3Invasion and Metastasis Unit, IHBI, QUT, Brisbane, Australia, 4Australian Prostate Cancer Research Centre – Queensland (APCRC-Q) and Queensland Bladder Cancer Initiative (QBCI), Brisbane, Australia

TABLE OF CONTENTS

1. Abstract
2. Introduction
3. Beyond enumeration: RNA analysis of CTCs
4. Methodologies for RNA studies
    4.1. RT-qPCR
    4.2. RNA-ISH
    4.3. RNAseq
5. CTC-RNA signatures
6. Concluding remarks
7. References

1. ABSTRACT

Circulating tumour cells (CTCs) are shed into the bloodstream from both primary and secondary tumours and provide a non-invasive means to study tumor progression and response to treatment. Assessment of ribonucleic acid (RNA) and monitoring dynamic changes in gene expression profiles of CTCs extends their clinical and prognostic power and establish their role in guiding treatment. Among these methods, droplet digital (RT-ddPCR) technique provides a high sensitivity and detectibility of CTCs. RNA-sequencing (RNAseq) is the most comprehensive method, that would allow the simultaneous measurement of a large number of genes and theoretically the whole transcriptome. Since CTCs are heterogeneous in nature, single cell RNAseq methods are very valuable in assessing population dynamics and functional states of CTCs. While RNA in situ hybridization (RNA-ISH) is used relatively less frequently, it also allows for the assessment of expression of multiple genes within individual CTCs. Epithelial to Mesenchymal Transition (EMT) or Plasticity (EMP) is a major contributor to metastasis, providing a mechanism to allow cells to become migratory and invasive, and to survive in the bloodstream. Monitoring CTCs undergoing EMT may lead to improvement in their prognostic and predictive power. Here, we review various RNA analysis of CTCs and those that undergo EMT and their application in diagnosis, prognosis and treatment of cancers.

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Abbreviations AR: androgen receptor cDNA: complementary DNA CTC: circulating tumour cell ctDNA: circulating tumour DNA EGFR: epidermal growth factor receptor EMP: epithelial mesenchymal plasticity EMT: epithelial mesenchymal transition ER: oestrogen receptor HCC: hepatocellular carcinoma HER2: human epidermal growth factor receptor 2 ICC: immunocytochemistry MET: mesenchymal epithelial transition NHV: normal healthy volunteer OS: overall survival PFS: progression-free survival PSA: prostate specific antigen RNA: ribonucleic acid RNA-ISH: RNA- in situ hybridisation RNAseq: RNA sequencing RT-ddPCR: reverse transcriptase-droplet digital polymerase chain reaction RT-qPCR: reverse transcriptase-quantitative polymerase chain reaction SNP: single nucleotide polymorphism

Key Words: CTC, Metastasis, EMT, Tumour Heterogeneity, RNA analysis, CTC score, Review

Send correspondence to: Sara Hassan, School of Biomedical Sciences and Institute of Health & Biomedical Innovation (IHBI), Faculty of Health, Queensland University of Technology (QUT), Brisbane, Australia, Tel: 61 424500957, E-mail: sara.hassan@hdr.qut.edu.au