Drug repositioning trends in rare and intractable diseases.

Drug repositioning (DR) is an effective way for developing drugs for rare and intractable diseases (RIDs). Preparation of the ontology is essential for drug development in RIDs, in which disease names have been inconsistently used worldwide. Ontology-based analysis of clinical trial data revealed that DR occurs actively in RIDs. Drugs and their target genes are keys to explore repositionable drugs, because shared target genes between diseases indicate a common mechanism of drug action. This approach visualizes a DR landscape that facilitates drug development. Here, we review the current situation of ontology in RIDs, the trends in drug development, and an efficient strategy for DR based on drug target gene information.