Virtual Screening, Synthesis and In Vitro Characterization of Histamine H₄ Receptor Ligands Based on Pyrimidine...

Histamine is a biologically active monoamine acting through four G protein-coupled receptors (H₁R-H₄R), which represent attractive therapeutic targets for a range of diseases. Nowadays, H₄R is recognized as a key player in inflammation and cancer. Here, we describe the design, syntheses and characterization of new H₄R ligands containing pyrido[2,3-d]pyrimidine or pyrimidine scaffold. Candidate structures were scored in silico by docking to the structure of the human inactive H₄R. Favorable structures were synthesized and, after confirmation of identity, their affinities were verified in in vitro screenings. Tested compounds did not exhibit any relevant cytotoxic (PrestoBlue) or antiproliferative (BrdU incorporation) effects at concentrations used in the functional assays. In a radioligand displacement assay (H₄R affinity) the pyrimidine series showed lower binding, whereas several pyrido[2,3-d]pyrimidine derivatives and one pyrimidine analog produced >60% inhibition at 1 µM. Two similar compounds with the highest and moderate affinities were selected for further studies. In the G_i-cAMP pathway, both compounds behaved as moderate H₄R antagonists, but in contrast, their profiles diverged in the β-arrestin pathway. These findings suggest ligand-dependent biased differences in signaling across G-protein and β-arrestin pathways at H₄R. Overall, YAN-153 emerges as a promising lead structure for further optimization and for more detailed in vitro (e.g., metabolic stability, selectivity) and in vivo studies.