Let-7 Family miRNAs Represent Potential Broad-Spectrum Therapeutic Molecules for Human Cancer

miRNAs are a class of small non-coding RNAs that modulate gene expression. Let-7 was first discovered in Caenorhabditis elegans and is one of the most extensively studied miRNAs. The human let-7 family contains 13 miRNAs. The expression of these miRNAs is decreased in most human cancers and contributes to carcinogenesis and progression. Thus, the let-7 family of miRNAs has attracted the attention of researchers in various fields. Exogenous let-7 restoration has been confirmed to show antitumor efficacy in many human cancers. Let-7 functions as a tumor suppressor by acting upon several multi-signaling pathways and multiple downstream target oncogenes that are involved in most human cancers. Let-7 shows potential for modulation of chemoresistance and radiation sensitivity in human cancers. miRNAs in the let-7 family represent potential broad-spectrum antitumor molecules for human cancer therapy, and miRNAs in this family have been studied intensively for their therapeutic potential. However, most previous studies have been limited to a single functional aspect or focused on a single effect in a particular type of cancer. Here, we review the latest research on let-7 and discuss its potential value as a broadspectrum antitumor molecule.