A red light-activable hetero-bimetallic [Fe(III)-Ru(II)] complex as a dual-modality PDT tool for anticancer therapy

We developed a novel red light activable hetero-bimetallic [Fe(III)-Ru(II)] complex by combining hydroxyl radical-generating Fe(III)-catecholate as type I PDT and singlet oxygen generating Ru(II)-paracymene complex as type II PDT agents and potentially function as a dual modality PDT tool for enhanced phototherapeutic applications. The bridging linker 2-amino-3-(3,4-dihydroxyphenyl)-N-(1,10-phenanthrolin-5-yl)propenamide (L2) acted as bridging linker. The single pot synthesis of hetero-bimetallic [Fe(III)-Ru(II)] complex was carried out through acid-amine coupling. Various photophysical assays confirmed the photo-activated production of (●OH) radicals and (1O2) oxygen generation upon activation of the [Fe(III)-Ru(II)] complex by red light (600-720 nm, 30 J cm-2), and resulted in enhanced cytotoxicity with photo-index ~45. The complex, [Fe(III)-Ru(II)] potentially bonded to the DNA binding by ruthenium moiety was responsible for minimal dark toxicity. The cytotoxic potential of the complex under red light was a result of the photo-induced accumulation of reactive oxygen species through both type I and type II photodynamic therapy (PDT) mechanisms in A549 and HeLa cells, while non-cancerous HPL1D cells remained unaffected. We probed the caspase 3/7-dependent apoptosis of the complex, [Fe(III)-Ru(II)], in vitro. Overall, the hetero-bimetallic [Fe(III)-Ru(II)] complex offered an ideal example of a red light activable dual-modality next-generation PDT tool for phototherapeutic anticancer therapy.