JPH203 (KYT-0353, JPH-203SBECD), a selective L-type amino acid transporter 1 inhibitor, shows a dramatic inhibition of leucine uptake (IC50=0.06 µM) and cell growth (IC50=4.1 µM) in human colon cancer cells (HT-29), human oral cancer cells (YD-38) and leukemic cells.