Cytotoxic properties of fac-Re(CO)₃ complexes with quinoline coligands: Insights on the mode of cell death and DNA fragmentation

Four tricarbonyl rhenium(I) complexes featuring quinoline ligands (1–4) were examined for their potential cytotoxicity properties against three malignant cell lines and one normal cell line of different origins. The most cytotoxic compound among the synthesized complexes was complex 2, which was formed when [ReBr(CO)₃(N^∧O)] (N^∧O = quinoline-2-carboxaldehyde) (1) and para-amino phenol reacted. Its IC₅₀ values are in the range of 26.05–30.33 μg/mL. Complex 4, decorated with benzimidazole moiety, has been demonstrated to be harmless to normal mice splenocytes. The cellular localization of 1–4 was investigated using fluorescence microscopy to provide insight into their biotargets, cellular localization, and modes of action. Among the evaluated malignant cell lines, complex 2 exhibited the highest levels of apoptotic and necrotic alterations in the MCF-7 cell line. Re(I) complexes appeared to gather inside intercellular connections and around cellular membranes, as seen in the fluorescence microscopy images. Along the cell membrane, the compounds accumulated as well, anticipating their entry.