The present study addresses two related questions: (i) whether the up-regulation of p-Erk and p-Akt proteins induced by MEK inhibition can be prevented by concomitant Hsp90 inhibition and (ii) whether the MEK inhibition can enhance the radiosensitizing effect of the Hsp90 inhibitor NVP-AUY922 in 2 tumor cell lines, i.e. lung carcinoma A549 and glioblastoma SNB19. Here, AKT1 is linked to glioblastoma.