RESUMEN
A sweet taste receptor is composed of heterodimeric G-protein-coupled receptors T1R2 and T1R3. Although there are many sweet tastants, only a few compounds have been reported as negative allosteric modulators (NAMs), such as lactisole, its structural derivative 2,4-DP, and gymnemic acid. In this study, candidates for NAMs of the sweet taste receptor were explored, focusing on the structural motif of lactisole. Ibuprofen, a nonsteroidal anti-inflammatory drug (NSAID), has an α-methylacetic acid moiety, and this structure is also shared by lactisole and 2,4-DP. When ibuprofen was applied together with 1 mM aspartame to the cells that stably expressed the sweet taste receptor, it inhibited the receptor activity in a dose-dependent manner. The IC50 value of ibuprofen against the human sweet taste receptor was calculated as approximately 12 µM, and it was almost equal to that of 2,4-DP, which is known as the most potent NAM for the receptor to date. On the other hand, when the inhibitory activities of other profens were examined, naproxen also showed relatively potent NAM activity against the receptor. The results from both mutant analysis for the transmembrane domain (TMD) of T1R3 and docking simulation strongly suggest that ibuprofen and naproxen interact with T1R3-TMD, similar to lactisole and 2,4-DP. However, although 2,4-DP and ibuprofen had almost the same inhibitory activities, these activities were acquired by filling different spaces of the ligand pocket of T1R3-TMD; this knowledge could lead to the rational design of a novel NAM against the sweet taste receptor.