Highlights d Development of two potent FTO inhibitors with IC 50 values in the low nanomolar range d KD of FTO or pharmacological inhibition of FTO suppresses LSC/LIC self-renewal d Targeting FTO suppresses immune checkpoint gene expression and immune evasion d Targeting FTO by potent inhibitors holds therapeutic promise against various cancers

Circular RNAs (circRNAs) are long, non-coding RNAs that result from the non-canonical splicing of linear premRNAs. However, the characteristics and the critical role of circRNA in co-/post-transcriptional regulation were not well recognized until the "microRNA sponge" function of circRNA is discovered. Recent studies have mainly been devoted to the function of the circular RNA sponge for miR-7 (ciRS-7) and sex-determining region Y (SRY) by targeting microRNA-7 (miR-7) and microRNA-138 (miR-138), respectively. In this review, we illustrate the specific role of circRNAs in a wide variety of cancers and in regulating the biological behavior of cancers via miR-7 or miR-138 regulation. Furthermore, circRNA, together with its gene silencing ability, also shows its potential in RNA interference (RNAi) therapy by binding to target RNAs, which provides a novel perspective in cancer treatment. Thus, this review concerns the biogenesis, biological function, oncogenesis, progression and possible therapies for cancer involving circRNAs.