Synthesis, Characterization, and Biological Evaluation of New Ru(II) Polypyridyl Photosensitizers for Photodynamic Therapy

Two Ru(II) polypyridyl complexes, Ru(DIP)2(bdt) (1) and [Ru(dqpCO2Me)(ptpy)]2+ (2) (DIP = 4,7-diphenyl-1,10-phenanthroline, bdt = 1,2-benzenedithiolate, dqpCO2Me = 4-methylcarboxy-2,6-di(quinolin-8-yl)pyridine), ptpy = 4′-phenyl-2,2′:6′,2″-terpyridine) have been investigated as photosensitizers (PSs) for photodynamic therapy (PDT). In our experimental settings, the phototoxicity and phototoxic index (PI) of 2 (IC50(light): 25.3 μM, 420 nm, 6.95 J/cm2; PI >4) and particularly of 1 (IC50(light): 0.62 μM, 420 nm, 6.95 J/cm2; PI: 80) are considerably superior compared to the two clinically approved PSs porfimer sodium and 5-aminolevulinic acid. Cellular uptake and distribution of these complexes was investigated by confocal microscopy (1) and by inductively coupled plasma mass spectrometry (1 and 2). Their phototoxicity was also determined against the Gram-(+) Staphylococcus aureus and Gram-(−) Escherichia coli for potential antimicrobial PDT (aPDT) applications. Both complexes showed significant aPDT activity (420 nm, 8 J/cm2) against Gram-(+) (S. aureus; >6 log10 CFU reduction) and, for 2, also against Gram-(−) E. coli (>4 log10 CFU reduction).