| Summary: | The water-soluble ruthenium complex cis-[Ru(dcbpyH)2(PTAH)2]Cl2⋅3H2O (1) (dcbpy = 4,4′-dicarboxy-2,2′-
bipyridine; PTA = 1,3,5-triaza-7-phosphaadamantane) has been synthesized and characterised by NMR, IR
spectroscopy, elemental analysis, and single-crystal X-ray diffraction. The optical properties of 1 were studied,
including photoactivation under visible light, as well as its biological properties, together with those of the
previously published Ru complexes cis-[Ru(bpy)2(PTA)2]Cl2 (2), trans-[Ru(bpy)2(PTA)2](CF3SO3)2 (3) and cis-
[Ru(bpy)2(H2O)(PTA)](CF3SO3)2 (4) (bpy = 2,2′-bipyridine). Anticancer activities of the complexes against
human lung (A549), cervical (HeLa) and prostate (PC3) carcinoma cells were evaluated under dark conditions
and upon photoactivation with visible light. None of the complexes exhibited cytotoxic activity in the absence of
light irradiation (IC50 > 100 μM). However, after photoactivation, the cytotoxicity of complexes 1, 2 and 3
against the three cell lines markedly increased, resulting in IC50 values between 25.3 μM and 9.3 μM. Notably,
these complexes did not show toxicity against red blood cells. These findings show the potential of complexes 1,
2 and, particularly, 3 for selective and controlled cancer photochemotherapy. The reactivity of the Ru complexes
against DNA under UV–Vis irradiation was studied by analysing plasmid mobility. Experimental data shows that
4 unfolds supercoiled DNA (SC DNA) both in the dark and under visible irradiation, while 1 and 3 are only active
under light, being 2 inactive in either case. The unfolding activities of complexes 3 and 4 were dependent on the
air present in the reaction. The measured intracellular levels of reactive oxygen species (ROS) upon irradiation
with complexes 1, 2 and 3 suggest that their mechanism of action is related to oxidative stress.
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