Metal dipyrrin complexes as potential photosensitizers for photodynamic therapy

Over the last decades, the use of photodynamic therapy (PDT) for the treatment of various types of cancer as well fungal, viral and bacterial infections has received increasing attention. Despite its clinical success, the currently approved photosensitizers (PSs) are associated with poor water solubility, aggregation, low photostability and a long excretion time. To overcome these limitations, much research is devoted towards the development of PSs based on transition metal complexes. However, the majority of metals used for this purpose are rare and expensive. Therefore, it would be of high interest to develop effective PDT PSs based on cheap and abundant metals. In this article, the use of Cu(II) and Ni(II) dipyrrin complexes as potential PDT PSs against cancer is presented. As required for PDT applications, these complexes were found to have a strong absorption in the green spectrum and to be stable in an aqueous solution in the dark as well as upon light irradiation. Biological studies revealed that the complexes have a very low cytotoxic effect in the dark with a slight effect upon irradiation at 510 nm in human cervical carcinoma (HeLa) cells.