Cytokine MicroRNA regulatory networks in colorectal cancer: Contemporary research insights and mechanistic analysis.

Colorectal cancer (CRC) remains a leading cause of cancer-related mortality worldwide. Effective CRC screening in the United States has reduced incidence of CRC in populations over 50 years of age. Early-onset CRC is emerging as a significant issue. There is need for better understanding of CRC biology to develop screening techniques, diagnostic markers and novel therapies to improve outcomes. MicroRNAs (miRNAs) are involved in several cellular processes and function as tumor suppressors and oncogenes. The miRNA/cytokine networks play a critical role in CRC pathogenesis by contributing to an extended period of inflammation which promotes tumorigenesis, tumor progression, and immune evasion. Certain miRNAs such as miR-21 and miR-155 are pro-inflammatory while others like miR-34, miR-143, miR-145 and mi146a are protective against cancer. When using miRNAs as therapeutics in CRC, the therapies rely on miRNA inhibitors to either suppress the miRNAs that have a role in activating oncogenic pathways or replacing miRNAs with mimics that can upregulate tumor suppressors which have been dysregulated due to cancerous mutations. Key immune checkpoint pathways such as PD-1/PD-L1, NF-κB, MAPK, PI3/AKT, and Wnt/β-catenin signaling cascades are regulated by miRNAs. A number of miRNAs are also tested as therapeutic co-targets for boosting immunotherapy effectiveness. Several clinical trials are underway to incorporate miRNAs into CRC screening or detecting early recurrence. Since the administration of targeted treatments can result in an immune-related adverse effect, growing interest has focused on exosomes as alternative carriers for miRNA-based therapeutics. Overall, applications of miRNAs have the potential to improve CRC outcomes.