Molecular basis for the activation of the bitter taste receptor TAS2R14 by Ritonavir

Ritonavir is a protease inhibitor used in combination with other antiretroviral drugs to treat HIV, especially in children. It enhances the effectiveness of these drugs by inhibiting the cytochrome P450-3A4 enzyme, thereby increasing their bioavailability. Ritonavir is also being investigated for cancer treatment due to its mechanism of action. However, its intense bitterness, particularly in liquid formulations, can be intolerable for some children. This bitterness is attributed to its activation of bitter taste receptors, including TAS2R14 (also named T2R14), as demonstrated in our previous study. In this study, we utilized molecular modeling, site-directed mutagenesis, and cell-based calcium mobilization assays to characterize the key residues involved in TAS2R14 activation by ritonavir. Eight critical residues for ritonavir interacting with the receptor were discovered. The results indicate two potential binding sites for ritonavir in TAS2R14 receptor, including orthosteric and allosteric sites. These findings can be useful for developing bitter blockers targeting TAS2R14 to eliminate or reduce the bitter taste of ritonavir.