Detection of colorectal cancer associated circular RNAs hsa_circ_0031263, hsa_circ_0072715, and hsa_circ_0136666 in plasma with nanowire chips

Rationale: Colorectal cancer (CRC) is one of the most prevalent oncological diseases with high mortality. Invasive optical (endoscopic) colono- scopy has been recognized as a golden standard for the CRC diagnostics. A promising area is the development of non-invasive tools for CRC diagnosis with circular RNA (circRNA). One of the most sensitive non-invasive tools for detection of cancer RNA markers is considered to be the biosensor methods with the use of nanowire chips with oDNA probes (fragments of DNA oligonucleotides) immobilized on their surface. It has been previously shown that circRNA hsa_circ_0136666_CBC1, hsa_circ_0031263_CBC1, and hsa_circ_0072715_CBC1 are associated with CRC. Aim: To determine the lower limit of concentration sensitivity of detection of CRC-associated circRNA with nanowire chips with immobilized oDNA probes, to demonstrate the usability of these chips for non-invasive detection of circRNA in plasma in the CRC diagnostics, and to establish the potential for the use of nanowire chips for the early CRC diagnosis. Methods: To ensure biospecific binding of the circRNA hsa_circ_0136666_CBC1, hsa_circ_0031263_CBC1, and hsa_circ_0072715_CBC1 (the CRC markers), oDNA probes with the nucleotide sequences complementary to the target circRNA have been immobilized on the nanowire surface. At the study step 1, we detected the lower concentration limit for detection of the target molecules with the use of their analogues, i.e. synthetic model oDNA with the nucleotide sequences complementary to oDNA probes. At the study step 2, we used the nanowire chips with immobilized oDNA probes to detect the circRNA in plasma of the patients with confirmed CRC. Plasma samples from non-cancer patients were used as controls. Results: The lower concentration limit for the detection of DNA analogues of the circRNA hsa_circ_0136666_CBC1, hsa_circ_0031263_CBC1, and hsa_circ_0072715_CBC1 with nanowire chips with oDNA probes was 10-16 М. The analysis of total RNA isolated from plasma of the CRC patients showed a significant increase in the signal from the sensory elements of the nanowire chip. The analysis of plasma samples from the non-cancer patients, the nanowire signal changes were non-significant indicating the absence of detectable concentrations of the circRNA in plasma of the non-cancer patients. Conclusion: We have identified the minimal detectable concentration of the circRNA hsa_circ_0136666_CBC1, hsa_circ_0031263_CBC1, and hsa_circ_0072715_CBC1, associated to the development of CRC, with nanowire chips with immobilized oDNA probes: it was 10-16 М. The experiment showed the usability of such nanowire chips for non-invasive detection of the given circRNA markers in total RNA samples isolated from plasma of CRC patients.