Gene Silencing Agents in Breast Cancer

MicroRNAs (miRs) are a class of non-coding RNAs, approximately 20–25 nucleotides long, discovered in the nematode, Caenorhabditis elegans , in 1993. There are two primary categories of non-coding RNA (ncRNA): (1) short interfering RNAs (siRNA) and (2) microRNAs (miRs). In general, miRs control protein production via partially complementary binding of the mRNA 3′UTRs. Both siRNAs and miRNAs are critical regulators of developmental and homeostatic processes as well as disease pathogenesis. While the treatment of advanced stage breast cancer presents several challenges, the development of therapeutic resistance contributes to a high mortality rate. Dysregulation of miR expression has been implicated in progression of breast cancer disease. Moreover, miRs have been found to play a role in the development of drug resistance. In this context, one of the therapeutic potentials of miRNAs is the correlation of circulating miR levels with breast cancer progression stages and disease phenotypes. Secondly, researchers are investigat-ing novel delivery strategies for the substitution or silencing of ncRNAs involved in the disease. This chapter describes both the general miRNA mechanism of actions and the miRNAs related to breast cancer research. It is specifically designed for breast cancer researchers with expertise in gene delivery, clinicians, and clinical translational scientists.