Chlorin derivatives sterically-prevented from self-aggregation with high antitumor activity for photodynamic therapy

In this study two new chlorin derivatives sterically prevented from aggregation were synthesised by the Diels-Alder reaction between protoporphyrin IX dimethyl ester and 1-(2-hydroxyethyl)maleimide. The compounds were fully characterised by 1H NMR, 13C NMR, UV-Vis and high-resolution mass spectroscopy (HRMS) and their photochemical properties such as singlet oxygen quantum yield (ϕ0), fluorescence quantum yield (ϕf) and photodegradation were also evaluated. Furthermore, the partition coefficient (log P) revealed that these compounds present amphiphilic properties. Studies of the photodynamic action in tumour cells (HEp-2 and HeLa) and non-tumour cells (Vero) were also performed in order to confirm the photodynamic therapy (PDT) activity that was indicated by the preliminary photophysical studies. Those phototoxicity results were 55-77% higher than the results obtained with the commercial photosensitiser verteporfin. Finally, cytotoxic assays were performed with the new photosensitiser candidates and cell death was determined using fluorescence microscopy, which provided information about the mechanisms of cell death. In general, we have obtained improved and accessible compounds for PDT studies, as highlighted by the research presented here.