Expansion of Human Hematopoietic Stem Cells (HSCs) is a rapidly advancing field showing great promise for clinical applications. Recent evidence has implicated the nervous system and glial family ligands (GFLs) as potential drivers of hematopoietic survival and self-renewal in the bone marrow niche, but how to apply this to HSC maintenance and expansion is yet to be explored. We demonstrate a role for the GFL receptor, RET, at the cell surface of HSCs, in mediating sustained cellular growth, resistance to stress and improved cell survival throughout in vitro expansion. HSCs treated with the key RET ligand/co-receptor complex, GDNF/GFRa1, show improved progenitor function at primary transplantation and improved long-term HSC function at secondary transplantation. Finally, we demonstrate that RET drives a multi-faceted intracellular signalling pathway, including key signalling intermediates AKT, ERK1/2, NFkB and p53, responsible for a wide range of cellular and genetic responses which improve cell growth and survival under culture conditions.

The cancer stem cell (CSC) model suggests that a subpopulation of cells within the tumor, the CSCs, is responsible for cancer relapse and metastasis formation. CSCs hold unique characteristics, such as self-renewal, differentiation abilities, and resistance to chemotherapy, raising the need for discovering drugs that target CSCs. Previously we have found that the antihypertensive drug spironolactone impairs DNA damage response in cancer cells. Here we show that spironolactone, apart from inhibiting cancerous cell growth, is also highly toxic to CSCs. Notably, we demonstrate that CSCs have high basal levels of DNA double-strand breaks (DSBs). Mechanistically, we reveal that spironolactone does not damage the DNA but impairs DSB repair and induces apoptosis in cancer cells and CSCs while sparing healthy cells. In vivo, spironolactone treatment reduced the size and CSC content of tumors. Overall, we suggest spironolactone as an anticancer reagent, toxic to both cancer cells and, particularly to, CSCs.