Defining the landscape of circRNAs in non-small cell lung cancer and their potential as liquid biopsy biomarkers: a complete review including current methods

Abstract

Despite the significant decrease in population-level mortality of lung cancer patients as reflected in the Surveillance Epidemiology and End Results program national database, lung cancer, with non-small cell lung cancer (NSCLC) in the lead, continues to be the most commonly diagnosed cancer and foremost cause of cancer-related death worldwide, primarily due to late-stage diagnosis and ineffective treatment regimens. Although innovative single therapies and their combinations are constantly being tested in clinical trials, the five-year survival rate of latestage lung cancer remains only 5% (Cancer Research, UK). Henceforth, investigation in the early diagnosis of lung cancer and prediction of treatment response is critical for improving the overall survival of these patients. Circular RNAs (circRNAs) are a re-discovered type of RNAs featuring stable structure and high tissue-specific expression. Evidence has revealed that aberrant circRNA expression plays an important role in carcinogenesis and tumor progression. Further investigation is warranted to assess the value of EV-and platelet-derived circRNAs as liquid biopsy-based readouts for lung cancer detection. This review discusses the origin and biology of circRNAs, and analyzes their present landscape in NSCLC, focusing on liquid biopsies to illustrate the different methodological

Multiplex Analysis of CircRNAs from Plasma Extracellular Vesicle-Enriched Samples for the Detection of Early-Stage Non-Small Cell Lung Cancer

“…CircRNAs are highly enriched in EVs [ 7 ] and show a relatively high stability compared to other forms of RNA [ 8 ]. Several studies have highlighted their potential as liquid biopsy biomarkers [ 12 ] but current limitations in circRNA quantification methods are limiting their implementation in the clinical setting. Consequently, new, and robust protocols for circRNA analysis are needed.…”

“…Moreover, it has been reported that aberrant expression of certain circRNAs can promote cancer development and progression [ 11 ]. Additionally, some circRNAs have been investigated as liquid biopsy biomarkers for the early detection of lung cancer and other solid tumors [ 12 , 13 ]. However, the lack of consensus on a robust and standardized protocol for circRNA quantification is holding back the development of clinically applicable assays.…”

Liquid biopsy and non-small cell lung cancer: are we looking at the tip of the iceberg?

“…Extracellular vescicles are also a source of more abundant genetic information when compared with ctDNA and they are characterised by high stability, even though DNA extraction procedures are technically more complex. Finally, microRNA are small non-coding RNA, frequently deregulated in tumours and they can be detected and analysed in plasma, even though several technical issues have to be faced before validation for clinical practice [ 168 – 170 ].…”

Digital multiplexed analysis of circular RNAs in FFPE and fresh non‐small cell lung cancer specimens

“…circRNAs are a newly re‐defined type of endogenous RNA molecules originated by a noncanonical process called ‘back‐splicing’. Through this mechanism, the 5′ splice donor covalently links to the 3′ end of an upstream exon, resulting in a single‐stranded circular structure which can include one or different exonic/intronic regions [ 1 ]. This particular assembly lacking a poly(A) tail makes them very stable and resistant to exonuclease‐mediated degradation when compared to their linear counterparts [ 2 ].…”

“…RT‐qPCR is widely used as a quantification tool for circRNA expression studies. While its sensitivity and short turnaround time proves beneficial for circRNA research, several events such as template switching, rolling circle amplification, or the bias attached to this technique may hinder the results [ 13 ]. In addition, it does not allow high‐throughput analysis, which is necessary for biomarker discovery.…”