Molecular mechanisms of death in cells with defective apoptotic pathways

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The body protects itself from cancer by killing any cell that poses a risk of becoming a tumour. The body kills these cells via a carefully orchestrated sequence (or pathway) of events, however many cancer cells have defects in cell death pathways that has permitted them to survive even though they have been told to die. In this proposal we set out a research program to investigate how to kill cancer cells that don't want to die. Various tumour cells have been shown to have increased levels of Bcl-2, a proto-oncogene that blocks cell death induced by diverse stimuli. Cells that over-express Bcl-2 are also resistant to cytotoxic drugs. Understanding how to bypass Bcl-2 (or proteins that block cell death in tumours) will lead to a better understanding of cell death-cell survival and allow us to explore the possibility of tailoring treatment for patients in which specific defects in death pathways have been identified in their cancer cells. Cytotoxic lymphocytes (CL) are cells of the immune system that defend the body from cancer by specifically attacking and killing tumor cells. We have been pioneering studies of CL:tumour interactions in which we can define the morphology and kinetics of critical events in cell death and have shown that CL have the ability to kill target cells that over-express Bcl-2. Following the aims in this proposal, we will understand the mechanisms by which cytotoxic lymphocytes kill target cells that have defects in classical cell death pathways. These studies will therefore define alternative pathways to cell death in the event that a key component of the preferential pathway to cell death is inoperative. Since cytotoxic lymphocytes use a variety of ways to kill their targets and tumors may contain multiple defects in cell death pathways, we will explore which are the key defects, or the combination of multiple defects, in cell death pathways that prevent cytotoxic lymphocyte mediated cell death and permit tumour survival in vivo.