SLC44A1 and central nervous system cancer: Although definitive evidence for CTL1-mediated transport of choline or choline-like drugs across the BBB is lacking, it has been explored as a target for NP-based drug delivery for two reasons: (i) its expression in glioma cells [211]; (ii) the low physiological plasma concentration of choline (~25% of the Michaelis–Menten constant, Km), which leaves CTL1 relatively unoccupied, potentially enabling the facilitated transport of choline derivatives without significantly disrupting endogenous choline homeostasis [208].