Type of cell death induced by alpha-trifluoromethyl acyloins in oral squamous cell carcinoma

We previously reported that alpha-trifluoromethyl acyloins (TFs) induced various types of cell death, depending on the target cancer cell line. We investigated here what type of cell death is induced by a-trifluoromethyl acyloins in two human oral squamous cell carcinoma cell lines (HSC-2, HSC-4). TFs produced few TUNEL-positive cells. TFs induced annexin V/PI-double positive HSC-2 cells and annexin V-positive/PI-negative HSC-4 cells, respectively, but failed to activate caspase-3, capase-8 and caspase-9 in both HSC-2 and HSC-4 cells. On the other hand, TFs induced the formation of acidic organelles (detected by acridine orange staining) in both HSC-2 and HSC-4 cells. When HSC-2 and HSC-4 cells that had been transfected with expression vector encording the microtubule-associated protein 1 light chain 3 (LC3) gene fused to green fluorescent protein (GFP) were treated with TFs, LC3-GFP fusion protein was accumulated as granular dots in autophagosomes. Pretreatment with 3-methyladenine, an inhibitor of autophagy, partially inhibited the cytotoxicity of TFs, the formation of acidic organelles and LC3 accumulation in the autophagosome. These data suggest that alpha-trifluoromethyl acyloins may induce autophagic cell death in HSC-2 and HSC-4 cells following the early stage of necrosis or apoptosis, respectively.