RB1 and astrocytoma (excluding glioblastoma): After this evidence, experimental variables were analyzed to set up a protocol in order to (a) increase RB uptake by amino acids starvation, thus reducing the RB molar amount of administration; (b) pharmacologically block the extracellular release of RB by GW4869; and (c) identify suitable PDT time-interval conditions to efficiently stimulate RB photo-activation in astrocytoma cells vs. normal astrocytes.