Despite standard
cancer therapies such as
chemotherapy and targeted
therapy have shown some efficacies, the
cancer in many cases eventually relapses and metastasizes upon stopping the treatment. There is a small subpopulation of
cancer cells within
tumor, with specific characters similar to those found in stem cells. This group of
cancer cells is known as
tumor-initiating or cancer stem cells (CSCs), which have an ability to self-renew and give rise to
cancer cell progeny. CSCs are related with drug resistance,
metastasis and relapse of
cancer, hence emerging as a crucial
drug target for eliminating
cancer. Rapid advancement of CSC biology has enabled researchers to isolate and culture CSCs in vitro, making the cells amenable to high-throughput
drug screening. Recently,
drug repositioning, which utilizes existing drugs to develop potential new indications, has been gaining popularity as an alternative approach for the
drug discovery. As existing drugs have favorable bioavailability and safety profiles,
drug repositioning is now actively exploited for prompt development of
therapeutics for many serious diseases, such as
cancer. In this review, we will introduce latest examples of attempted
drug repositioning targeting CSCs and discuss potential use of the repositioned drugs for
cancer therapy.