N-heterocyclic carbene (NHC) ligands are known for their exceptional versatility and applications, being good σ-donors, sterically tunable and quite stables at different thermic, pH and oxidative conditions. Furthermore, they have been proved to be excellent ligands for transition metals and, particularly, gold (Au) and silver (Ag) complexes have been intensively studied for their biomedical and therapeutic applications. Both NHC-Au- and -Ag complexes have been shown to target selectively cancer cells or bacteria, without exerting side or unwanted effects on the normal cells' viability. Herein we reported the design, synthesis and biological evaluation of a new series of NHC-Au and -Ag complexes, adopting nucleobases, that is guanine and guanosine, as NHC precursors. The individuated lead, which contains gold, was able to hamper, particularly, the growth of MDA-MB-231 breast cancer cells, inducing genomic DNA damage and apoptosis. Additionally, the same complex exerted an antiviral activity in bronchial epithelial cells infected with influenza virus A/H1N1. The disclosed double biological activity offers new hints in the field of synthesis and pharmaceutical use of biohybrid organometallic complexes, as valid scaffolds for the potential treatment of oncologic patients with viral infection complications or viceversa to hamper the tumor onset after viral infections.