Iodinated chlorin p₆ copper complex induces anti-proliferative effect in oral cancer cells through elevation of intracellular reactive oxygen species

We investigated the anticancer chemotoxicity of previously reported iodinated chlorin p₆ copper complex (ICp₆-Cu), a novel chlorophyll derivative in which copper is attached to the side chain carboxylate groups via coordination. Human oral carcinoma cells NT8e, 4451 and the non-cancerous keratinocyte HaCaT cells were treated with ICp₆-Cu for 48 h in dark and cell viability, proliferation and morphological alterations were examined. ICp₆-Cu showed pronounced cytotoxicity in cancer cells with IC₅₀ ∼40 μM, whereas, the viability of HaCaT cells was not affected. Cell proliferation assay revealed that ICp₆-Cu at IC₅₀ concentration led to complete inhibition of cell proliferation in both the cell lines. Cell morphology studied by confocal microscopy showed absence of cell death via necrosis or apoptosis. Instead, the treated cells displayed distinct features of non-apoptotic death such as highly vacuolated cytoplasm, lysosomal membrane permeabilization and damage to cytoskeleton F-actin filaments. In addition, ICp₆-Cu treatment led to time dependent increase in the intracellular level of reactive oxygen species (ROS) and the cytotoxicity of ICp₆-Cu was significantly inhibited by pre-treatment of cells with antioxidants (glutathione and trolox). These findings revealed that ICp₆-Cu is a potent chemotoxic agent which can induce cytotoxic effect in cancer cells through elevation of intracellular ROS. It is suggested that ICp₆-Cu may provide tumor selective chemotoxicity by exploiting difference of redox environment in normal and cancer cells.