Cell-based assay to detect small molecules restoring levels of let-7 miRNAs.

Blockage of miRNA biogenesis by LIN28, or other mechanisms, results in derepression of target genes, some of which are oncogenic (e.g., ) potentially contributing to tumor progression and drug resistance. We have developed a cell-based assay to identify small molecules that increase levels of mature functional let-7 miRNAs by inhibiting the function of Lin28B protein or by other means. This system consists of a reporter gene (GFP) regulated by the tTR-KRAB repressor protein which in turn is regulated by processed miRNAs. Using this system, we screened approximately 4000 small molecules and identified more than a dozen compounds capable of augmenting levels of mature miRNAs. Among those compounds, Kenpaullone and BIO were shown to increase miRNA levels with consequent suppression of MYCN protein in neuroblastoma cell lines. This novel strategy provides an additional cell-based assay for candidate cancer drug screening in a high throughput setting and will facilitate the identification of anti-cancer drugs. Moreover, this assay could be used to screen shRNA and CRISPR libraries to identify novel components of the LIN28- axis which may provide new therapeutic targets.