P-retigabine: an N-propargyled retigabine with improved brain distribution and enhanced antiepileptic activity

Retigabine (RTG, [ethyl N-[2-amino-4-[(4-fluorophenyl)methyl]amino] phenyl] carbamate]) is a first-in-class antiepileptic drug that acts by potentiating neuronal KCNQ potassium channels; however, it has less than optimal brain distribution. In this study, we report that P-RTG (ethyl N-[2-amino-4-((4-fluorobenzyl)(prop-2-ynyl)amino)phenyl]carbamate), an RTG derivative that incorporates a propargyl group at the N position of the RTG linker, exhibits an inverted brain distribution compared with RTG. The brain-to-plasma concentration ratio of P-RTG increased to 2.30 compared with 0.16 for RTG. However, the structural modification did not change the drug's potentiation potency, subtype selectivity, or RTG molecular determinants on KCNQ channels. In addition, in cultured hippocampal neurons, P-RTG exhibited a similar capability as RTG for suppressing both induced and spontaneous action potential firing. Notably, P-RTG antiepileptic activity in the maximal electroshock (MES)-induced mouse seizure model was significantly enhanced to a value 2.5 times greater than that of RTG. Additionally, the neurotoxicity of P-RTG in the rotarod test was comparable with that of RTG. Collectively, our results indicate that the incorporation of a propargyl group significantly improves the RTG brain distribution, supporting P-RTG as a promising antiepileptic drug candidate. The strategy for improving brain-to-plasma distribution of RTG might be applicable for the drug development of other central nervous system diseases.