APLN and glioblastoma: Apelin was identified as a central regulator of endothelium-dependent tumour initiation and maintenance in GBM cells with stem-like properties, and the apelin receptor antagonist, MM54, was used to successfully reduce tumour expansion and lengthen survival in a GBM xenograft mouse model (Harford-Wright et al., 2017; Harford-Wright and Gavard, 2018).