Lipids are a broad class of molecules that, besides being a major form of energy storage and components of cell membranes, act as bioactive signalling molecules. N-acyl taurines are structurally related to endocannabinoids that are known to exert antiproliferative actions in a variety of cancer cells. We have evaluated the cytotoxicity of N-oleoyl taurine and N-arachidonoyl taurine and found N-acyl taurines to reduce proliferation of prostate cancer cells.

The sphingolipids ceramide and sphingosine act as tumour suppressors. We found selenite treatment to cause reduced viability, induction of neutral sphingomyelinase activity and accumulation of ceramide in the liver cancer cells. Inhibition of sphingosine kinase 1 (SK1) sensitized the cells to selenite treatment with regards to ceramide accumulation, arrest of cells in the G1/S phases of the cell cycle and formation of reactive oxygen species. Whereas combined selenite treatment and SK1 inhibition synergistically reduced the number of viable cells, the non-tumorigenic hepatocyte cell line, remained unaffected.

Furthermore, we studied the involvement of sphingolipid metabolism in bladder cancer cells treated with Bacillus Calmette-Guérin (BCG), and found BCG to induce formation of nitric oxide and upregulation of nitric oxide synthase 2 as well as SK1 protein levels. Additionally, pharmacological inhibition of SK1 enhanced the viability reduction, ceramide accumulation and induction of apoptosis observed following BCG treatment.

In conclusion, our findings have shown that N-acyl taurines exert antiproliferative effects on prostate cancer cells. Furthermore, sphingolipids were shown to be involved in cytotoxic treatment with selenite and BCG in liver cancer and bladder cancer cells respectively, and inhibition of SK1 increased the cytotoxicity. Our findings raise the possibility that modulation of ceramide-metabolizing enzymes could be used to enhance the effects of selenite and BCG in these cancer cell types.