Recent advances in metal complexes for the photodynamic therapy of cancer

Abstract

Photodynamic therapy is a non-invasive medical approach that employs a source of light together with a photosensitizer for the treatment of several diseases. Photodynamic therapy makes use of reactive oxygen species such as cytotoxic singlet oxygen for the induction of apoptotic cell death in cancerous cells. Anticancer chemotherapeutic treatments use the cytotoxicity of metallodrugs, wherein all the cells (both cancer and normal cells) in a patient are subjected to similar cytotoxic effects, which results in severe undesirable side effects. During the last couple of decades, metal complexes based on transition metal ions/atoms have displayed exciting cytotoxicity as photodynamic therapeutic agents. Photodynamic therapy serves as an effective localized approach for cancer treatment, wherein metal complexes are employed as photosensitizers. In response to the growing investigations on the utility of metal complexes as photosensitizers in the photodynamic therapy of cancer, we attempted to review the recent advances in the utilization of metal complexes in this field of research. We critically reviewed the in vitro and in vivo studies pertaining to the development of metal complexes based on ruthenium, iridium, osmium, platinum, cobalt, zinc and rhenium, among others, as effective agents for the photodynamic therapy of cancer. Besides, the intervention of nanotechnology for enhancing the anticancer photodynamic therapeutic profiles of metal complexes is described. Importantly, the current status of metal complexes in clinical trials for the photodynamic therapy of cancer is highlighted. Finally, existing challenges in the development of effective photoactive metallodrugs are outlined, and future outlooks for research on the development of effective photoactive metallodrugs are mentioned.