Amino acid transporter LAT1 is expressed on cancer cell-derived exosomes with potential as a diagnostic and prognostic biomarker

L-type amino acid transporter 1 (LAT1) is upregulated in various cancers and contributes to the growth and proliferation of cancer cells. Previous clinicopathological studies have revealed associations between the high expression of LAT1 and the poor prognosis in multiple cancer types. However, in those studies, the expression of LAT1 has been evaluated solely by immunohistochemistry on resected tumors or tissue biopsies. Cancer cell-derived exosomes are attracting increasing attention as a resource of diagnostic, prognostic, and therapeutic biomarkers. In this study, we revealed the expression of LAT1 on exosomes from pancreatic cancer T3M-4 cells by western blotting, immunoprecipitation, and immuno-transmission electron microscopy. LAT1 was generally detected by western blotting and ELISA on exosomes from several pancreatic, biliary tract, and ovarian cancer cells. Notably, similar trends existed between the abundance of exosomal LAT1 and the cellular LAT1 expression levels. The expression of LAT1 on exosomes in vivo was verified using the peritoneal wash from intraperitoneal T3M-4 tumor-bearing mice. These results indicate that exosomal LAT1 released from cancer cells holds significant potential as a novel biomarker for diagnosis and prognosis.