We have been studying the SAR of the L-type amino acid transporter 1 (LAT1, SLC7A5) for use in targeted drug delivery to tissues in which it is highly expressed (e.g., brain and tumors) and for its importance in cancer cell signaling and metabolism. We and others have shown that LAT1 substrate SAR is surprisingly tolerant of side chain substitution with various functional groups (e.g., amines, carboxylic acids, esters, amides) and that even non-amino acids (i.e., hydroxamic acids and small esters) can be substrates. However, LAT1 is size restrictive, as we found that amino acids with two or more aromatic rings have diminished cell uptake rates with a concomitant increase in potency of inhibition that generally correlates with lipophilicity. While trying to probe the size limitations of LAT1 SAR, we synthesized and tested in cell assays a series of ketoprofen-phenylalanine conjugates based on analogs that had previously been described in the literature as substrates. In our hands, these larger amino acid prodrugs were potent inhibitors (IC50 = 1.2 μM) that demonstrated poor cell uptake in a LAT1-expressing cell line. Our SAR studies revealed that orientation of a carbonyl linker connecting phenylalanine to ketoprofen and related derivatives had a significant effect on potency, which led to our discovery of inhibitor 1 (IC50 = 310 nM). We will present our recent findings on LAT1 substrates and inhibitors as well as our use of cryo-EM structure-based models to rationally prepare a focused library to optimize ligand potency. These results could be useful for designing amino acid prodrugs for transport across the blood-brain barrier or into tumors or to increase LAT1 inhibitor potency for blocking cancer cells.

Employing a carbonyl group to increase inhibitor potency for the L-type amino acid transporter 1

ACS Fall 2021

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