Evaluation of the Medicinal Potential of Two Ruthenium(II) Polypyridine Complexes as One‐ and Two‐Photon Photodynamic Therapy Photosensitizers

Abstract

Two [Ru(phen)₂ dppz]²⁺ derivatives (phen=1,10-phenantroline, dppz=dipyrido[3,2-a:2',3'-c]phenazine) with different functional groups on the dppz ligand [dppz-7,8-(OMe)₂ (1), dppz-7,8-(OH)₂ (2)] have been synthesized, characterized and investigated as photosensitizers (PSs) for photodynamic therapy (PDT) against cancer. Both complexes showed intense red phosphorescence and promising singlet oxygen (¹ O₂ ) quantum yields of 75 % (1) and 54 % (2) in acetonitrile. Complex 1 (logP_o/w =-0.52, 2.4 nmol Ru per mg protein) was found to be more lipophilic, having also a higher cellular uptake efficiency compared to 2 (logP_o/w =-0.20, 0.9 nmol Ru per mg protein). Complex 1 localized evenly in HeLa cells whereas 2, was mainly visualized in the cell membrane by confocal microscopy. In the dark, complex 1 (IC₅₀ =36.5 μm) was found to be more toxic than complex 2 (IC₅₀ >100 μm) on a HeLa cells monolayer. Importantly, in view of PDT applications, both complexes were found to be non-toxic in the dark towards multicellular HeLa spheroids (IC₅₀ >100 μm). Upon one-photon irradiation (420 nm, 9.27 J cm^-2 ), 1 exhibited higher phototoxicity (IC₅₀ =3.1 μm) than 2 (IC₅₀ =16.7 μm) on HeLa cell monolayers. When two-photon irradiation (800 nm, 9.90 J cm^-2 ) was applied, only 1 (IC₅₀ =9.5 μm) was found to be active toward HeLa spheroids. This study demonstrates that the functional group on the intercalative ligand has a strong influence on the cellular localization and anticancer activity of Ru^II polypyridyl complexes.