Systems biological analysis of mitochondrial apoptosis synergies evoked by 2nd generation TRAIL receptor agonists and cardic glycosides

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TRAIL receptor agonists are cancer cell-selective agents that trigger mitochondrial apoptosis through the activation of the BH3-only protein Bid, but so far demonstrated limited clinical efficacy. We found that non-toxic concentrations of therapeutically relevant cardiac glycosides (CGs), such as digitoxin, cause complex changes in apoptosis protein amounts and synergistically enhance cell death via the mitochondrial Bcl-2 family-dependent pathway. Here, we will investigate these processes, using a systems biological approach of integrated experimental and mathematical analyses. We will develop prototype tools for case-specifically predicting responsiveness to combination treatments with a superior 2nd generation TRAIL receptor agonist (IZI1551) and CGs in cell lines and in vivo models of colorectal cancer (CRC). To this end, we will (i) study changes in the quantitative composition of the signalling networks that control TRAIL and Bcl-2 family signalling in well characterised CRC model cell lines upon CG exposure, (ii) investigate which signalling cascades drive CG-induced apoptosis protein deregulation, (iii) employ mathematical pathway models to predict the consequences that these changes will have for apoptosis signal transduction and to identify optimal treatment schedules, and (iv) validate mathematical predictions on apoptosis responsiveness by flow-cytometric and microscopic real-time measurements in cellulo and by CRC xenograft models in vivo. Besides detailed novel insight into the complexity of apoptosis signal transduction and cell death regulation, this work will also provide the basis for the optimal further development and exploitation of mitochondrial apoptosis synergies evoked by IZI1551/CG co-treatments for future translational studies.