Mini-reviewMicroRNAs as novel targets and tools in cancer therapy

- MicroRNAs are both relevant molecular targets and therapeutic targets in cancer.
- Diverse synthetic antagonists have been developed and can be used to target miRNAs in vivo.
- The delivery of miRNA mimics and inhibitors to specific organs is still a therapeutic challenge.
- A liposome-based miR-34 mimic is the first cancer-targeted microRNA drug to enter phase I clinical trials in human patients.

MicroRNAs (miRNAs) are currently experiencing a renewed peak of attention not only as diagnostics but also especially as highly promising novel targets or tools for clinical therapy in several different malignant diseases. Moreover, the recent discovery of competing endogenous RNAs (ceRNAs) as novel miRNA-regulators has contributed exciting insights in this regard. Therefore, this review summarizes and discusses the latest findings on (1) how miRNAs have become therapeutic targets of diverse synthetic antagonists, (2) how novel endogenous regulators of miRNAs such as ceRNAs or pseudogenes could emerge as therapeutics scavenging oncogenic miRNAs and (3) how miRNAs themselves are already, and will increasingly be, used as therapeutics. Recent advances on the importance of miRNA-target affinity and the subcellular localization of miRNAs are also discussed. The potential of these developments in different tumor entities and particular hallmarks of cancer such as metastasis, disease progression, interactions with the tumor microenvironment, or cancer stem cells are equally highlighted.