L‐type amino acid transporter 1 (LAT1) inhibition selectively impairs growth and decreases viability of MB cells. A, Proliferation assay of HD‐MB03 and DAOY cells treated or not with 20 or 30 µmol/L of JPH203 for 72 h. Control (Ct) conditions were treated with DMSO for the same time period. B, Viability assay of HD‐MB03 and DAOY cells treated or not with 20 or 30 µmol/L of JPH203 for 72 h. Control (Ct) conditions were treated with DMSO for the same time period. C, Viability assay of murine primary astrocytes (C8‐D1A) and primary cortical neurons (PCN) treated with 30 µmol/L of JPH203 or DMSO (control, Ct) for 72 h. D, In vitro 3‐D growth assay of HD‐MB03 and DAOY cells. Spheroids generated with HD‐MB03 or DAOY cells were treated with 20 or 30 µmol/L of JPH203 or DMSO (control, Ct) for 12 d. E, Spheroid growth measurements over time. The surface area of spheroids was measured at the indicated time points and normalized by the initial size of the control (■), 20 µmol/L JPH203 (▲) and 30 µmol/L JPH203 (●) spheroids. Data points indicate mean ± SEM from at least three independent experiments (***P < 0.001; **P < 0.01; *P < 0.05; ns: P > 0.05, Student's t test)