Copper complexes in cancer therapy

Copper homeostasis is tightly regulated in both prokaryotic and eukaryotic cells to ensure sufficient amounts for cuproprotein biosynthesis, while limiting oxidative stress production and toxicity. Over the last century, copper complexes have been developed as antimicrobials and for treating diseases involving copper dyshomeostasis (e.g., Wilson's disease). There now exists a repertoire of copper complexes that can regulate bodily copper through a myriad of mechanisms. Furthermore, many copper complexes are now being appraised for a variety of therapeutic indications (e.g., Alzheimer's disease and amyotrophic lateral sclerosis) that require a range of copper-related pharmacological affects. Cancer therapy is also drawing considerable attention since copper has been recognized as a limiting factor for multiple aspects of cancer progression including growth, angiogenesis, and metastasis. Consequently, 'old copper complexes' (e.g., tetrathiomolybdate and clioquinol) have been repurposed for cancer therapy and have demonstrated anticancer activity in vitro and in preclinical models. Likewise, new tailor-made copper complexes have been designed based on structural and biological features ideal for their anticancer activity. Human clinical trials continue to evaluate the therapeutic efficacy of copper complexes as anticancer agents and considerable progress has been made in understanding their pharmacological requirements. In this chapter, we present a historical perspective on the main copper complexes that are currently being repurposed for cancer therapy and detail several of the more recently developed compounds that have emerged as promising anticancer agents. We further provide an overview of the known mechanisms of action, including molecular targets and we discuss associated clinical trials.