CASP9 and lung cancer: Similarly, activation and increased expression of caspase-9 and the cell cycle checkpoint protein p53 were reported in lung cancer cells treated with nickel ferrite nanoparticles [77]; the authors also revealed that the apoptotic effect of their ferrites depended on the cell type [78], which corresponds to our own observations, the activation of caspase-9 being clearly more pronounced in A375 cells.