A photosensitive tricarbonyl Mn(I) CO-releasing molecule of 6-mercaptopurine: Genotoxicity and mode of cell death

Two photosensitive tricarbonyl manganese(I) complexes [MnX(bpy)(CO)₃]^0/+ (X = Br (1) and 6-mercaptopurine (2); bpy = 2,2′-bipyridine) were tested for their antiproliferative effects against six normal and malignant cell lines of various origins under dark and 468 nm light exposure. 6-Mercaptopurine is a widely recognised therapeutic drug used to treat human leukaemia. Compound 1 was highly toxic to the THP-1 cell line, with an IC₅₀ value of 13.6 ± 1.2 μM in light and 3.0 ± 0.1 μM in dark, while 2 had no effect on it. On the other hand, 2 demonstrated slighlty toxicity towards HepG2 cells, with IC₅₀ values of about 100 μM under dark and light conditions. The illumination at 468 nm increased the formation of the reactive oxygen species (ROS) of both 1 and 2 in comparison to the dark ones. Complex 1 had the greater capacity for apoptosis, which was the predominant mode of cell death. The Comet assay confirmed the genotoxicity of both complexes and the light conditions caused significant genotoxic damage compared to the dark conditions.