Sustained reductions in valine and isoleucine mediate anti-cancer pharmacological effects of inhibiting amino acid transporter LAT1 in cancer cells.

[BACKGROUND] L-type amino acid transporter 1 (LAT1; SLC7A5), which preferentially transports large neutral amino acids (LNAAs), is highly upregulated in various cancers and represents a promising therapeutic target. The first-in-class LAT1-specific inhibitor, nanvuranlat (JPH203, KYT-0353), has exhibited potent anti-cancer effects and is under clinical evaluation. However, alterations in the amino acid availability in cancer cells underlying its pharmacological activities remain to be elucidated.

[METHODS] Amino acids in nanvuranlat-treated cancer cells were measured by high-performance liquid chromatography. LAT1 knockdown was performed using siRNA. To mimic LAT1 inhibition, cancer cells were incubated in culture media lacking specific LNAA(s) reduced by nanvuranlat. The consequences of these treatments were compared by cell-based assays, including analyses of amino acid contents, cell growth, amino acid-related signaling pathways, cell cycle, ATP production rate, and transcriptomes by RNA sequencing. Metabolome of nanvuranlat-treated and untreated cells was compared by mass spectrometry. The effects of nanvuranlat on amino acid composition were also examined in three-dimensional cancer cell spheroids.

[RESULTS] Both pharmacological and genetic inhibition of LAT1 preferentially and continuously reduced valine, isoleucine, and tryptophan in pancreatic cancer MIA PaCa-2 cells. Nanvuranlat induced similar alterations in intracellular amino acids in multiple cancer cell lines. Depletion of these amino acids from culture media selectively lowered their intracellular concentrations, recapitulating the effects of nanvuranlat on cell growth, amino acid-related mTORC1/GAAC signaling pathways, and cell cycle. Deprivation of valine or isoleucine exhibited more pronounced impacts than tryptophan in all assays. As a novel pharmacological action of nanvuranlat mediated by the reductions in valine and isoleucine, we revealed downregulation of multiple genes in the TCA cycle and respiratory chain, accompanied by a decreased mitochondrial ATP production rate. Consistently, metabolomics revealed broad decreases in the TCA cycle intermediates by LAT1 inhibition. Nanvuranlat also similarly influenced the amino acid levels in cancer cell spheroids.

[CONCLUSIONS] Reductions in valine and isoleucine in cancer cells primarily account for the multifaceted anti-cancer pharmacological activities of LAT1 inhibition by nanvuranlat. This study establishes the molecular basis for LAT1-targeted therapy and highlights growth-promoting processes in cancer cells that can be exploited pharmacologically by modulating the availability of specific amino acids.