Synthesis, characterization, DNA interaction, and anticancer studies of novel <i>facial</i> tricarbonylrhenium(<scp>i</scp>) complexes with uracil-derived ligands

Herein, we report the formation and characterisation of novel rhenium(i) complexes with bidentate uracil chelating ligands. Three metal complexes including <i>fac</i>-[Re(CO)₃(urda)Cl] (1) (urda = 5, 6-diamino-1, 3-dimethyluracil), <i>fac</i>-[Re(CO)₃(uramb)Br] (2) (uramb = amino-5-((2-aminobenzylidene)amino)-1,3-dimethyluracil) and <i>fac</i>-[Re(CO)₃(urqn)Br] (3) (urqn = amino-5-((isoquinolin-3-ylmethylene)amino)-1,3-dimethyluracil) were spectroscopically characterized. Structural elucidations were corroborated by single-crystal X-ray crystallography, TOF mass spectrometry, and elemental analysis. These metal complexes retain their structural integrity in aqueous media during UV-Vis spectrophotometric titrations. Anticancer screening of the metal complexes was done in two cancer cell lines, HCC70 and HeLa, as well as in a benign MCF12A cell line. In particular, while complex 1 was highly cytotoxic towards HeLa cells and was non-toxic to HCC70 TNBC and MCF12A non-cancerous cells, complex 2 displayed low micromolar toxicity in all three cell lines and was selected for further analysis. This metal complex exhibits dual DNA intercalation and groove-binding modes, however this did not lead to DNA damage as assessed by a comet assay. In addition, metal complex 2 did not appear to inhibit topoisomerase activity, suggesting a different mechanism of action from that reported for ruthenium complexes with topoisomerase inhibitory activities.