Acridin-3,6-dialkyldithiourea hydrochlorides as new photosensitizers for photodynamic therapy of mouse leukemia cells

[Display omitted] •Photocytotoxicity of new proflavines useful in the anticancer therapy was examined.•Irradiation at 365nm increased cytotoxicity of new proflavines about ten times.•Intracellular distribution of the new photosensitizers (PS) was investigated.•Sequestration of these compounds in lysosomes and mitochondria was confirmed. Acridin-3,6-dialkyldithiourea hydrochlorides (AcrDTUs) have been evaluated as a new group of photosensitizers (PSs) for photodynamic antitumor therapy (PDT). Mouse leukemia cells L1210 were used for testing of AcrDTUs as the new PSs. The irradiation (UV-A light (365nm), 1.05J/cm2) increased cytotoxicity of all derivatives against L1210 cells more than ten times. The highest photocytotoxicity was found for propyl-AcrDTU with IC50=0.48±0.03μM after 48h incubation. A generation of the superoxide radical anion upon UV-A irradiation of propyl-AcrDTU was confirmed by in situ photochemical EPR experiments. To explain a mechanism of photocytotoxic action of AcrDTUs, an intracellular distribution of propyl-AcrDTU has been studied. It was found that AcrDTU in non-irradiated cells was not present in their nucleus but in the lysosomes and partly in the mitochondria, and sequestration of propyl-AcrDTU was dependent on pH in lysosomes. After irradiation, the cell death was induced by oxidative damage of lysosomal and mitochondrial membranes. Concerning the cell cycle, flow cytometry after PDT with propyl-AcrDTU showed a significant increase of the cells in the subG0 phase. Observed signs of necrosis, apoptosis, and autophagy indicate that PDT/AcrDTU leads to multiple cell death types (caspase independent apoptosis, necrosis, and autophagy).