Anticancer efficacy of bis-heteroleptic iridium(iii) complexes with difluoro-substituted phenylpyridine ligands

A series of iridium(iii) complexes (Ir1-Ir3) with the formula [Ir(F₂ppy)₂(L)] (F₂ppy = 2-(2,4-difluoro-phenyl)pyridine, L = pyridine-2-aldoxime, 2-pyridylamidoxime and di-2-pyridylketoxime) were synthesized through the reaction of [(F₂ppy)₂Ir(μ-Cl)₂Ir(F₂ppy)₂] (SM1) and the respective ancillary ligands (L). All the complexes were characterised by FT-IR, ¹H & ¹⁹F-NMR analysis, electronic absorption-emission spectroscopy and cyclic voltammetric studies. Molecular structures of complexes Ir1 and Ir3 were determined by interpreting single crystal X-ray data. All the complexes were found to be luminescent with low quantum yields. Anticancer studies on cancer cell lines MDAMB, HT-29 and LN-229 revealed their effectiveness as antiproliferative agents. The cytotoxicity of the complexes was evaluated using the MTT assay and complex Ir2 showed activity similar to that of cisplatin towards the three cancer cells. The elevated level of reactive oxygen species (ROS) in the iridium complex-treated cancer cells further supported the antiproliferation efficacy of Ir1-Ir3. Further, the effectiveness of Ir1-Ir3 on cancer cells was established through a cell migration study and apoptotic induction assay on LN-229 and a colony formation assay on HT-29 cancer cells. Immunocytochemistry analysis of LN-229 cancer cells revealed apoptosis through the p53-dependent pathway.