BackgroundThe L-type amino acid transporter 1 (LAT1/SLC7A5) transports essential amino acids across the plasma membrane. While LAT1 is overexpressed in a variety of human neoplasms, its expression and its role in thyroid cancer is currently unknown. Anaplastic thyroid carcinoma (ATC) is a highly aggressive malignancy for which no effective therapy exists. The purpose of this study was to explore whether the inhibition of LAT1 in ATC would affect tumor growth both in vitro and in vivo.MethodsLAT1 was pharmacologically blocked by JPH203 in human ATC and papillary thyroid cancer (PTC) cell lines. The effects on proliferation and mTORC1 activity were addressed in vitro. A genetically engineered mouse model of ATC was used to address the effect of blocking LAT1 on tumor growth in vivo. SLC7A5 transcription was measured in patient-derived ATC samples to address the clinical relevance of the findings.ResultsLAT1 block by JPH203 reduced proliferation and mTORC1 signaling in human thyroid cancer cell lines. SLC7A5 transcription was upregulated in ATC tissues derived from a genetically engineered mouse model and in ATC samples recovered from patients. JPH203 treatment induced thyroid tumor growth arrest in vivo in a fully immunocompetent mouse model of thyroid cancer. Additionally, analysis of publicly available datasets of thyroid carcinomas revealed that high LAT1 expression is associated with potentially untreatable PTC presenting reduced NIS/SLC5A5 transcription and with ATC.ConclusionsThese preclinical results show that LAT1 inhibition is a novel therapeutic approach in the context of thyroid cancers, and more interestingly in untreatable thyroid cancers.Electronic supplementary materialThe online version of this article (10.1186/s13046-018-0907-z) contains supplementary material, which is available to authorized users.

Adequate amino acid (AA) supply is vital especially for highly proliferative tissues like the placenta. Other tissues which are critical for nutrient absorption and transport, such as the intestine and liver, mainly use the efficient sodium (Na +)-dependent uptake maintained by System A transporters, 1 such as the SNAT family. 2 The heteromeric SLC7 AA transporters, a subgroup of the System L-exchanger

A series of derivatives of the substrate amino acid l-tryptophan have been investigated for inhibition of the L-type amino acid transporter LAT1 (SLC7A5), which is an emerging target in anticancer drug discovery. Of the four isomeric 4-, 5-, 6-, or 7benzyloxy-l-tryptophans, the 5-substituted derivative was the most potent, with an IC 50 of 19 μM for inhibition of [ 3 H]-lleucine uptake into HT-29 human colon carcinoma cells. The replacement of the carboxy group in 5-benzyloxy-l-tryptophan by a bioisosteric tetrazole moiety led to a complete loss in potency. Likewise, the corresponding tetrazolide derived from l-tryptophan itself was found to be neither a substrate nor an inhibitor of the transporter. Increasing the steric bulk at the 5position, while reasonably well tolerated in some cases, did not result in an improvement in potency. At the same time, none of these derivatives was found to be a substrate for LAT1mediated transport.

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