In Vitro: Leu-AMS is proved to be a potent inhibitor of Leucyl-tRNA Synthetase (LRS) with an IC50 value of 22.34 nM. Leu-AMS is highly cytotoxic in both cancer cells and normal cells. Leu-AMS does not affect S6 kinase (S6K) phosphorylation at all. Leu-AMS inhibits the catalytic activity of LRS but does not affect the leucine-induced mTORC1 activation.