The role of ancillary ligands on benzodipyridophenazine-based Ru(ii)/Ir(iii) complexes in dark and light toxicity against TNBC cells†‡

In this study, we investigated the impact of ancillary ligands on the anticancer activity of benzodipyridophenazine-based Ru(II) and Ir(III) complexes (Ru1, Ru2, Ir1, and Ir2). These metal complexes displayed three significant absorption bands attributed to the ligand-centered (LC) transitions, ligand-to-ligand charge transfer (LLCT), and metal-to-ligand charge transfer (MLCT). Binding studies of biomolecules were performed with the complexes along with the ligand, and it was found that after binding with Ru(II)/Ir(III), the properties of the ligands were enhanced. In vitro screening revealed that complex [(η⁵-Cp*)IrIIICl(κ²-N,N-benzo[i]dipyrido[3,2-a:2′,3′-c])phenazine] (Ir1) exhibited the highest potency and selectivity (IC₅₀ ∼ 2.14 μM, PI > 13) under yellow light irradiation. The photo-toxicity trend was Ir1 > Ru1 > Ir2 ≫ Ru2, which was found to be directly correlated with the singlet oxygen quantum yield (¹O₂). Chloro-substituted complexes (Ir1 and Ru1) were effective for hypoxic tumor treatment, particularly Ir1, which could generate high amounts of reactive oxygen species (ROS, type I PDT) in cells under photo irradiation. The high value of fluorescence quantum yield (f_φ = 0.26) and significant emission at λ = 571 nm of Ir1 were certainly useful for bio-imaging applications. Colocalisation and DCFDA studies of Ir1 revealed that it can accumulate in the mitochondria, leading to depolarization of the mitochondrial membrane. These studies confirm that the complex Ir1 is a promising candidate for TNBC treatment in hypoxic tumors, with efficacy comparable to the current PDT drug Photofrin.