CTH and glioblastoma: Because the transsulfuration pathway is the primary route for biosynthesis of the antioxidants cysteine and glutathione and because CTH and its downstream partner CBS also produce the protumoral gaseous transmitter hydrogen sulfide (H2S), another ROS scavenger, as a byproduct of their enzymatic activity, we next investigated whether GBM cells lacking CTH are less invasive due to a limited supply of these 3 factors produced downstream of CTH.