Anti-Tumor Potential of Selective L-Type Amino Acid Transporter (LAT1) Inhibitor, JPH203, in Patient-Derived Canine Bladder Cancer Organoids

L-type amino acid transporter 1 (LAT1), which controls the neutral amino acid uptake across the cell membranes, has been frequently overexpressed in various human cancers. Overexpression of LAT1 is associated with higher proliferation and shorter patient survival in tumors. Here, upregulated LAT1 expression was observed in patient-derived canine bladder cancers (BCs), and a small-molecule LAT1 inhibitor (JPH203) successfully reduced BC tumor growth both in vitro and in vivo. Patient-derived cancer cells were collected from dogs with naturally occurring tumors at veterinary clinics in Japan, and the 2.5D cancer organoid culture system was generated following our previous studies. Compared with other canine cancers or normal bladder cells, the increased LAT1 expression was observed in 2 strains of BC organoids. JPH203 inhibited boronophenylalanine (BPA) uptake activity by more than 90% and suppressed cell proliferation dose-dependently. Deprivation of BPA uptake activity by JPH203 also regulated the phosphorylation of mTOR-related proteins. Furthermore, intraperitoneal administration of JPH203 decreased the growth and tumor weight of BC organoid-derived xenograft in immunodeficient mice with an induction of apoptosis and a decrease in LAT1 expression compared to vehicle-administered mice. Therefore, the present study demonstrates that JPH203 exerts anti-tumor effects in canine BC through modulation of the mTOR signaling pathway and supports further investigation of LAT1-targeted therapy for canine BC.