Ian Hayes

Targeting inflammatory diseases via apoptotic mechanisms.

Induction of apoptosis in immune cells is a crucial mechanism used by the body to produce immune resolution. The homeostatic mechanisms employed are currently being identified and, to date, studies have highlighted some of the signals that regulate the immune response. The exposure of phosphatidylserine on the surface of an apoptotic neutrophil is sufficient to limit the immune response in acute inflammation, whereas apoptosis of key effector cells can limit the response in chronic inflammation. Other therapeutic approaches that are being investigated include the inhibition of apoptosis by blocking the caspase cascade. This approach will be of particular relevance for the treatment of inflammatory central nervous system diseases and sepsis. An alternative approach being examined is forced resolution, whereby apoptosis is induced in effector cells, principally T cells, through activation-induced cell death mediated by Fas receptors. Inhibitors of this mechanism have been identified and targeted in several studies.

The anticancer drug mithramycin A sensitises tumour cells to apoptosis induced by tumour necrosis factor (TNF)

In this report we show that mithramycin considerably increases the direct cytotoxic effect of tumour necrosis factor (TNF) on tumour cells in vitro. Sensitisation to TNF-induced apoptosis was prevented by the broad caspase inhibitor zVAD-fmk, whereas overexpression of Bcl-2 had no effect. Mithramycin also potentiated cell death induced by Fas agonistic antibodies. In contrast, mithramycin reduced the percentage of cells undergoing apoptosis due to factor withdrawal. TNF-induced activation of NF-kappaB (NF-κB)-dependent gene expression was not modulated by mithramycin treatment. Concomitantly with the increased sensitivity, the protein level of the short-spliced cFLIP variant was downregulated. These results indicate that mithramycin enhances TNF-induced cell death in an NF-κB-independent manner, and suggest that the Fas-associated death domain protein plays a crucial role in the TNF-sensitising effect of mithramycin.