PROKR1 and glioblastoma: We have chosen compound PKRA7 for our experiments because it could potently inhibit PK2 receptors, with IC50 values of 5.0 and 8.2 nM for PKR1 and PKR2, respectively (Figure S1), and, more importantly, it could penetrate the blood-brain barrier, a feature that could be critical for the treatment of glioblastoma.