Spectroscopy and mechanisms of redox-active copper-based anticancer complexes

Copper complexes are increasingly gaining prominence as potential anticancer agents. However, an ongoing challenge to their continued development is characterization of their fundamental behaviours in physiological environments and their mechanisms of action. This work has addressed these issues through: i) development of new Cu(II) anticancer candidates with functional ligand architectures, ii) implementation of novel spectroscopic approaches to characterize the biochemical behaviour of these compounds, and iii) correlation of these approaches with biological studies to develop structure-activity relationships. The complexes developed in these studies include benzimidazole and Schiff-base ligand scaffolds, with systematic derivatization to modify properties such as lipophilicity and reduction potentials. A particular focus was given to tuning the electronics of the Cu(II) compounds to examine their suitability as hypoxia (lower oxygen level) targeting metallodrugs. To determine the biologically active species, ligand exchange processes and interactions with biological molecules were characterized using magnetic resonance methods. The interactions of Cu(II) compounds with serum proteins, important for in vivo transport following administration, were studied using both frozen-solution and room-temperature electron paramagnetic resonance (EPR) experiments. For a series of hypoxia targeting fluorinated Cu(II) theranostic (therapeutic + diagnostic) compounds, 19F nuclear magnetic resonance (NMR) and magnetic resonance imaging (MRI) were employed to characterize the oxidized and reduced species, and novel NMR experiments demonstrated selective accumulation of a copper species in hypoxic cellular nuclei. Given the nuclear accumulation, the ability of Cu(II) compounds to interact with and cleave DNA through the generation of reactive oxygen species (ROS) was determined using both spectroscopic and molecular biology techniques. In a final study, non-conventional NMR methods were employed to characterize the interactions of a hydrophobic, first-in-class, chemotherapeutic with metal ions. Experiments utilizing both paramagnetic Cu(II) and diamagnetic Zn(II) ions facilitated the assignment of the coordination of the therapeutic to the metal ions. These results explained how the metal-ion interactions promoted increased aqueous solubility, a desirable property for further clinical development.