Evaluation of CD73, PD-1, circHIPK3, and circNRIP1 expression in the peripheral blood of patients with colorectal cancer.

Introduction: Colorectal cancer (CRC) is known to have an association with circular RNAs (circRNAs) and immune checkpoint factors. This study sought to examine the expression levels of hsa_circ_0000284 and hsa_circ_0004771 molecules and the programmed cell death 1 protein (PD-1) and ecto-5'-nucleotidase (CD73) immune checkpoints in the peripheral blood of patients with CRC as well as the ratios of circular to linear forms of homeodomain-interacting protein kinase 3 (HIPK3) and nuclear receptor interacting protein 1 (NRIP1).

Methods: Real-time polymerase chain reaction (PCR) and flow cytometry were used to assess quantitatively the expression level of circRNAs, CD73, and PD-1 in blood samples from patients with CRC and healthy control individuals. The expression of CD73 and PD-1 molecules was analyzed using FlowJo software, and the expression levels of circRNAs, CD73, and PD-1 were calculated with real-time PCR analysis.

Results: Real-time PCR analysis revealed a statistically significant increase in the linear form of hsa_circ_0004771 (linNRIP1) and PD-1 gene expression in patients' blood compared with control individuals. In addition, the circHIPK3:linHIPK3 and circNRIP1:linNRIP1 ratios are statistically significantly higher in patients than in healthy control individuals. The flow cytometry assessment indicated a statistically significant increase in PD-1 on the surface of lymphocytes and monocytes and an increase in CD73 on the granulocytes of patients compared with the healthy control individual.

Discussion: Based on these findings, hsa_circ_0000284, hsa_circ_0004771, PD-1, and CD73 were statistically significantly increased in our cancer group. If further research were done, these blood markers could potential be biomarkers for CRC progression.