Tailoring the biological activity of oxorhenium(V) complexes through Chrysin ligand functionalization

Chrysin, structurally one of the simplest flavonoids, shows a broad spectrum of biological activities, particularly its anticancer potential. Additionally, it has the possibility of coordination to metal ions as a bidentate chelate ligand, forming highly stable metal complexes. This synergism of metal ions and Chrysin led to a significant improvement in its diverse biological activities. Chrysin (HL1) and its derivatives (methoxy (HL2), benzyloxy (HL3), acetylated (HL4), and silylated (HL5)) were coordinated as OO-bidentate ligands to the rhenium(V) ion, and all five complexes crystallized in the form of monocrystals. The stability studies in PBS and human blood plasma solution were performed for those compounds, indicating that all complexes underwent precipitation in PBS, whereas no precipitation was observed in plasma. Moreover, the spectral profiles recorded in plasma indicate that plasma components exert a significant stabilizing effect on the rhenium complexes. The antiproliferative activity of complexes 1-5 was evaluated against the human ovarian carcinoma (A2780), colorectal carcinoma (HCT116), and the non-malignant HEK293 cell line. No direct relationship could be established between the complex precipitation in plasma and its cytotoxic activity. Complex 3 displayed pronounced spectral modifications in plasma while remaining essentially inactive in all cell lines tested, whereas 1 exhibited comparatively limited spectral changes despite being among the most active compounds of the series. The most active complexes 5, 1, and 2 displayed significant selectivity, with lower cytotoxicity toward non-tumorigenic HEK293 cells than A2780 and HCT116 cancer cells.