Drug Repurposing for Targeting Cancer Stem-like Cells in Glioblastoma

Glioblastoma (GBM) is one of the deadliest types of cancer, characterized by a short life expectancy after diagnosis, mostly related to therapy resistance and recurrence. GBM stem-like cells (GSCs) reside within the tumor and contribute to these features; therefore, finding drugs that specifically target such cells holds promise to halt GBM progression. The primary objective of this work is to comprehensively review and discuss the potential of hard drug repurposing to target GSCs. Several studies evaluating drugs showing anti-GSC activity, originally approved for non-cancer indications, were identified. These mainly included antidiabetics (e.g., Metformin, Phenformin, and Sitagliptin), antihypertensives (e.g., Nicardipine, Doxazosin, and Prazosin), antimicrobials (e.g., Pyrvinium pamoate, Flubendazole, and Clofazimine), and central nervous system-acting drugs (e.g., Chlorpromazine, Fluvoxamine, and Disulfiram). Relevant candidates include those that disrupt GSC metabolism, namely impairing mitochondrial function, such as Metformin, Chlorpromazine, and Pyrvinium pamoate. Multiple signaling pathways may be involved, namely the Wnt, PI3K/AKT, and STAT3 pathways, among others. Also significant were those drugs tested in combination, resulting in increased sensitivity to Temozolomide (TMZ), the standard pharmacological treatment available for GBM. Some repurposed agents, such as Disulfiram and Metformin, have already reached clinical testing, although none have yet been incorporated into clinical practice. Importantly, major translational barriers remain, like limited blood-brain barrier penetration and the lack of robust clinical trials. In conclusion, drug repurposing is an affordable and suitable strategy to target GSCs, impairing cell viability, reducing stemness, and enhancing their sensitivity to TMZ, which has potential that should be further explored to improve patients' clinical outcomes.