Discussion and conclusion In this study, we have investigated whether induction of TRAIL/zVAD/CHX induced programmed necrosis rep resents a viable strategy for the elimination of tumor cells. Necrosis has long been regarded as an accidental, non physiologic form of cell death, whereas caspase dependent apoptosis EPZ-5676 price was considered to be the only form of programmed Inhibitors,Modulators,Libraries and thus physiologically occurring cell death. This view has however been challenged by nu merous studies which have provided Inhibitors,Modulators,Libraries evidence for the ex istence of programmed forms of necrosis that do not depend on caspases but nevertheless follow defined molecular steps. While caspase dependent apoptosis is the major pathway leading to PCD, programmed ne crosis can act as a backup system when the apoptotic machinery fails or is inactivated.

It has been shown that programmed necrosis exerts critical functions in mul tiple patho physiological Inhibitors,Modulators,Libraries settings, e. g. the regulation of bone growth, ovulation, negative selection of Inhibitors,Modulators,Libraries lymphocytes, pancreatitis, epilepsy, ischemia reperfusion injury, Parkinsons, Huntingtons and Alzheimers disease, and cell destruction by Salmonella, Shigella, HIV and vaccinia virus. In contrast to apoptosis, a comprehensive pic ture of the signaling pathways of programmed necrosis is not yet available. In the most extensively studied model, TNF R1 elicits programmed necrosis via activation of RIPK1 and RIPK3, a step which is stimulated by the deubiquitinase CYLD and the deacetylase SIRT2, but nega tively regulated by the proteins FADD, FLIP, caspase 8 and members of the cIAP family.

Downstream of RIPK3, the proteins MLKL and PGAM5 Inhibitors,Modulators,Libraries contribute to programmed necrosis by promoting mitochondrial fragmentation. We have previously demonstrated that ceramide acts as an additional key molecule in death receptor mediated pro grammed necrosis. Furthermore, enzymes of the en ergy metabolism, the Bcl 2 family member Bmf and production of reactive oxygen species have been implicated as additional factors in programmed necrosis. The capacity to elicit programmed necrosis appears to be an intrinsic feature of death receptors and has been reported not only for TNF R1, but also for Fas/ CD95 and ectodermal dysplasia receptor. Inde pendently, we and others have demonstrated the ability to trigger programmed necrosis for human and murine TRAIL receptors.

In contrast to programmed ne crosis, the efficacy of TRAIL in the apoptotic elimination of tumor cells has been extensively demonstrated in clin ical trials employing mono or combination therapies. Consistent with the finding that TRAIL elicits apop tosis selectively in tumor but not primary cells, TRAIL was well normally tolerated in preclinical models at serum con centrations that were shown to be effective against cancer cells, as were agonistic TRAIL receptor anti bodies applied to patients in clinical trials using mono or combination therapies.