Induction of autophagy by sphingosine kinase 1 inhibitor PF-543 in head and neck squamous cell carcinoma cells

Sphingosine kinase 1 (SphK1) overexpressed in head and neck squamous cell carcinoma (SCC) regulates tumor growth. The effects of PF-543, a specific SphK1 inhibitor, on human SCC cells were examined. The proportion of viable cells after PF-543 treatment decreased in a time- and dose-dependent manner, and cell death occurred in SphK1-expressing SCC cells. Flow cytometry analysis revealed that PF-543 induced both necrosis and apoptosis. PF-543 also induced granular accumulation of LC3 and conversion from LC3-I to LC3-II, which was blocked by autophagy inhibitors, wortmannin, 3-methyladenine (3-MA), and bafilomycin A1. Treatment of head and neck SCC cells with autophagy inhibitors and PF-543 increased the proportion of cells with necrosis and apoptosis, indicating that autophagy acts to promote cell survival. Reactive oxygen species (ROS) scavenger reduced the cytotoxicity of PF-543. These results demonstrated that PF-543 induces apoptosis, necrosis, and autophagy in human head and neck SCC cells, and that autophagy antagonizes either necrosis or apoptosis.