Circulating MicroRNAs as Cancer Biomarkers in Liquid Biopsies.

Biological fluids such as blood, saliva, and urine offer a rich source of biomarkers that have the potential to change the paradigm of cancer management. By allowing routine noninvasive sampling that can offer new insights into cancer progression and response to treatment so-called liquid biopsies can play an important role in personalized medicine. MicroRNAs (miRNAs) are a particularly attractive class of biomarkers as they are not only resistant to the high levels of RNases found in biological fluids, but also able to confer clinically useful information about the disease relating to diagnosis, prognosis, and the response to treatment. Circulating miRNAs are either associated with proteins or extracellular vesicles (EV) and although their origin and implied functions as intracellular messengers remain somewhat controversial, they are implicated in the progression and the establishment of metastatic niches. In this chapter, we review the rapidly emerging field of circulating miRNA cancer biomarkers, their origin and function, techniques to detect these molecules, and the use of bioinformatic tools to derive implied regulatory function, as well as the challenges that lie ahead for their clinical implementation.

Integrated mRNA and miRNA Transcriptomic Analyses Reveals Divergent Mechanisms of Sunitinib Resistance in Clear Cell Renal Cell Carcinoma (ccRCC).

The anti-angiogenic therapy sunitinib remains the standard first-line treatment for meta static clear cell renal cell carcinoma (ccRCC). However, acquired resistance develops in nearly all responsive patients and represents a major source of treatment failure. We used an integrated miRNA and mRNA transcriptomic approach to identify miRNA:target gene interactions involved in sunitinib resistance. Through the generation of stably resistant clones in three ccRCC cell lines (786-O, A498 and Caki-1), we identified non-overlapping miRNA:target gene networks, suggesting divergent mechanisms of sunitinib resistance. Surprisingly, even though the genes involved in these networks were different, they shared targeting by multiple members of the miR-17~92 cluster. In 786-O cells, targeted genes were related to hypoxia/angiogenic pathways, whereas, in Caki-1 cells, they were related to inflammatory/proliferation pathways. The immunotherapy target PD-L1 was consistently up-regulated in resistant cells, and we demonstrated that the silencing of this gene resulted in an increase in sensitivity to sunitinib treatment only in 786-O-resistant cells, suggesting that some ccRCC patients might benefit from combination therapy with PD-L1 checkpoint inhibitors. In summary, we demonstrate that, although there are clearly divergent mechanisms of sunitinib resistance in ccRCC subtypes, the commonality of miRNAs in multiple pathways could be targeted to overcome sunitinib resistance.