Quercetin is a flavonoid with antioxidant, antiviral, antimicrobial, and anti-inflammatory properties. Therefore, it has been postulated as a molecule with great therapeutic potential. The renoprotective capacity of quercetin against various toxins that produce oxidative stress, in both in vivo and in vitro models, has been shown. However, it is not clear whether quercetin itself or any of its metabolites are responsible for the protective effects on the kidney. Although the pharmacokinetics of quercetin have been widely studied and the complexity of its transit throughout the body is well known, the metabolic processes that occur in the kidney are less known. Because of that, the objective of this review was to delve into the molecular and cellular events triggered by quercetin and/or its metabolites in the tubular cells, which could explain some of the protective properties of this flavonoid against oxidative stress produced by toxin administration. Thus, the following are analyzed: (1) the transit of quercetin to the kidney; (2) the uptake mechanisms of quercetin and its metabolites from plasma to the tubular cells; (3) the metabolic processes triggered in those cells, which affect the accumulation of metabolites in the intracellular space; and (4) the efflux mechanisms of these compounds and their subsequent elimination through urine. Finally, it is discussed whether those processes that are mediated in the tubular cells and that give rise to different metabolites are related to the antioxidant and renoprotective properties observed after the administration of quercetin.

Quercetin, a flavonoid with promising therapeutic potential, has been shown to protect from cisplatin nephrotoxicity in rats following intraperitoneal injection, but its low bioavailability curtails its prospective clinical utility in oral therapy. We recently developed a micellar formulation (P-quercetin) with enhanced solubility and bioavailability, and identical nephroprotective properties. As a first aim, we herein evaluated the oral treatment with P-quercetin in rats, which displayed no nephroprotection. In order to unravel this discrepancy, quercetin and its main metabolites were measured by HPLC in the blood and urine after intraperitoneal and oral administrations. Whilst quercetin was absorbed similarly, the profile of its metabolites was different, which led us to hypothesize that nephroprotection might be exerted in vivo by a metabolic derivate. Consequently, we then aimed to evaluate the cytoprotective capacity of quercetin and its main metabolites (quercetin 3-O-glucoside, rutin, tamarixetin, isorhamnetin and quercetin 3-O-glucuronide) against cisplatin toxicity, in HK-2 and NRK-52E tubular cell lines. Cells were incubated for 6 h with quercetin, its metabolites or vehicle (pretreatment), and subsequently 18 h in cotreatment with 10–300 μM cisplatin. Immediately after treatment, cell cultures were subject to the MTT technique as an index of cytotoxicity and photographed under light microscopy for phenotypic assessment. Quercetin afforded no direct cytoprotection and quercetin-3-O-glucuronide was the only metabolite partially preventing the effect of cisplatin in cultured tubule cells. Our results identify a metabolic derivative of quercetin contributing to its nephroprotection and prompt to further explore exogenous quercetin-3-O-glucuronide in the prophylaxis of tubular nephrotoxicity.

G protein-coupled receptors (GPCRs) are a therapeutically privileged family of receptors, involved in a wide variety of pathophysiological conditions and the successful target for ∼34% of FDA-approved drugs. However, a significant percentage of GPCRs remain orphan, i.e. the endogenous ligands that modulate receptor function are unknown, and hence knowledge about their functional role and the generation of new therapeutics lag behind. During recent years, the use of cryo-electron microscopy has revolutionized GPCR structural biology including its application to orphan GPCRs, especially those displaying constitutive activity in cellular model systems. Such efforts have resulted in the description of new modes of in-built agonists that include the ECL2 and N-terminal regions, as well as identifying ubiquitous endogenous ligands readily bound to GPCRs. These results position structural determination as a new key component in GPCR deorphanization, shedding light on new signaling mechanisms, bringing questions about their functional regulation and opening new avenues for drug design.

Dopamine D2 receptor (D2R) regulates key aspects of motor control, cognition, and reward. Its function depends not only on ligand binding and signaling efficacy but also on the dynamic control of receptor localization at the cell surface. Neuronal calcium sensor 1 (NCS-1) interacts with D2R in a Ca2+-dependent manner. Using in vitro and cellular assays, we found that NCS-1 promotes D2R trafficking to the plasma membrane through active exocytosis while preserving canonical receptor pharmacology. A screen of FDA-approved drugs identified protein–protein interaction (PPI) modulators targeting the NCS-1/D2R interface. Azilsartan medoxomil, atorvastatin, and vilazodone disrupt this interaction, reducing D2R surface expression. Structural studies revealed that these compounds target NCS-1, overlap the D2R binding site, and perturb the dynamics of the regulatory helix H10. These findings reveal an unexploited intracellular mechanism to modulate D2R function via PPI modulation, offering a novel strategy to fine-tune dopaminergic tone beyond receptor blockade or direct agonism.

A data-driven, automation-assisted, customizable framework for fragment-to-hit progression that directly delivers structurally validated hit series primed for rapid SAR exploration and exploits high-throughput crystallography at synchrotrons.

Efficient drug discovery relies on workflows that integrate structural insights with rapid and cost-effective exploration of chemical space. Here, we present a data-driven fragment-based lead discovery approach to target Neuronal Calcium Sensor 1 (NCS-1) protein-protein interactions (PPIs). This study represents a complete implementation of a single high-value design-make-test-analyze cycle that directly yields compounds with micromolar affinity with the potential to modulate NCS-1 interactions with key targets, including the G-protein chaperone Ric-8A and the dopamine D ₂ and cannabinoid CB ₁ receptors. X-ray crystallographic fragment screening (CFS) revealed diverse interaction patterns within the NCS-1 hydrophobic crevice. Algorithmically guided fragment evolution and automated synthesis enabled the rapid generation of over 250 derivatives, with biophysical validation using LC-MS and Grating-coupled interferometry. Structural analyses highlighted key pharmacophores, with selected compounds exhibiting favorable drug-like properties and potential blood-brain barrier penetration, making them promising candidates for neurodegenerative and neurodevelopmental disorders. Our results demonstrate the feasibility of accelerated hit-to-lead development at synchrotrons, demonstrating a robust, scalable platform for PPI-targeting drug discovery. The generated chemically diverse scaffolds provide a strong foundation for future therapeutic optimization.