Evaluation of light-activated Ru(II) prodrugs and their photoproducts as potential anti-cancer agents

Abstract

Photoactivated chemotherapy (PACT) has emerged as a new method for targeted cancer therapy. Strained ruthenium based complexes with octahedral geometry may undergo ligand dissociation once irradiated, forming aquated photoproducts that are greatly cytotoxic compared to their prodrug complex. The current study evaluates light-activated ruthenium prodrugs and their photoproducts as potential anti-cancer agents. The complexes being investigated are: [Ru(bpy)2phen]Cl2 (unstrained), [Ru(bpy)2BC]Cl2, [Ru(bpy)2dpphen]Cl2. Both strained complexes showed a 𝜆max≅ 450 nm in the visible range, accordingly, blue LED light (460 nm) was used for their photoactivation. [Ru(bpy)2BC]Cl2 was synthesized, purified and characterized by NMR and investigated for its mechanistic potential against cancer. The aquated photoproduct of [Ru(bpy)2dpphen]Cl2 was purified, characterized using ESI/MS and NMR, and shown to be essential for the exhibited toxicity when its prodrug and light irradiated complex were tested on human melanoma (A375) cancer cells. The uptake of [Ru(bpy)2BC]Cl2, assessed by ICP/MS, started immediately post incubation and plateaued after 24 hours. The uptake was mainly attributed to occur via active transport. Cytotoxicity assays on A375 showed a mean phototoxicity index of 340 at 72 hours, presenting the intracellular aquated photoproducts being effective rather than the dissociating ligands. A significant increase in ROS production and DNA damage was also observed. Flow cytometry results revealed the induction of apoptosis. Western blot analysis of pro- and anti-apoptotic protein revealed apoptosis to be mediated through both intrinsic and extrinsic pathways, as well as via inhibition of the MAPK and PI3K pathways. [Ru(bpy)2BC]Cl2 (with and without photoactivation), and [Ru(bpy)(dpphen)H2O]Cl2 were also investigated for their in vivo anticancer activity using a 7,12-Dimethylbenz[a] anthracene/12-O-Tetradecanoylphorbol 13-acetate skin carcinogenesis mice model. All complexes reduced significantly tumor growth 3 weeks post treatment when compared to non-treated mice. In conclusion, this study demonstrates that [Ru(bpy)2BC]Cl2 is a multi-mechanistic PACT drug which exhibits promising in vitro and in vivo anti-cancer potentials. It also reveals that [Ru(bpy)(dpphen)H2O]Cl2, the aquated form of [Ru(bpy)2dpphen]Cl2 photoproduct, has in vitro and in vivo anticancer activity and could be used as a chemotherapeutic agent.