Nonlinear regulation of commitment to apoptosis by simultaneous inhibition of Bcl-2 and XIAP in leukemia and lymphoma cells

Abstract

Apoptosis is a complex pathway regulated by the concerted action of multiple pro- and anti-apoptotic molecules. The intrinsic (mitochondrial) pathway of apoptosis is governed up-stream of mitochondria, by the family of Bcl-2 proteins, and down-stream of mitochondria, by low-probability events, such as apoptosome formation, and by feedback circuits involving caspases and inhibitor of apoptosis proteins (IAPs), such as XIAP. All these regulatory mechanisms ensure that cells only commit to death once a threshold of damage has been reached and the anti-apoptotic reserve of the cell is overcome. As cancer cells are invariably exposed to strong intracellular and extracellular stress stimuli, they are particularly reliant on the expression of anti-apoptotic proteins. Hence, many cancer cells undergo apoptosis when exposed to agents that inhibit anti-apoptotic Bcl-2 molecules, such as BH3 mimetics, while normal cells remain relatively insensitive to single agent treatments with the same class of molecules. Targeting different proteins within the apoptotic network with combinatorial treatment approaches often achieves even greater specificity. This led us to investigate the sensitivity of leukemia and lymphoma cells to a pro-apoptotic action of a BH3 mimetic combined with a small molecule inhibitor of XIAP. Using the computational probabilistic model of the apoptotic pathway, verified by experimental results from human leukemia and lymphoma cell lines, we show that inhibition of XIAP has a non-linear effect on sensitization towards apoptosis induced by the BH3 mimetic HA14-1. This study justifies further ex vivo and animal studies on the potential of the treatment of leukemia and lymphoma with a combination of BH3 mimetics and XIAP inhibitors.

Heat shock protein 90 mediates the apoptosis and autophage in nicotinic-mycoepoxydiene-treated HeLa cells

“…To explore whether NMD-induced Cyt c release was correlated with mitochondrial dysfunction [20], we applied both fluorescence microscopy and flow cytometry to evaluate the mitochondrial membrane potential (MMP) change by probing MMP with the sensitive dye JC-1. It was found that the color of JC-1 staining changed from orange to green in HeLa cells after NMD treatment (Fig.…”

Monte Carlo Study Elucidates the Type 1/Type 2 Choice in Apoptotic Death Signaling in Healthy and Cancer Cells

“…Our previous studies elucidated mechanisms for slow activation and generation of cell-to-cell variability through the type 2 pathway: (1) effective small number of reactant molecules generated due to the action of inhibitory molecules such as Bcl2 and XIAP [10,13] and (2) low probability reaction events such as the apoptosome formation [7]. These parameters are varied here to study their impact on the type 1/type 2 choice.…”

“…It is reasonable to expect that the multi-molecular complex apoptosome will have significantly reduced mobility and its P diff is assumed to be zero. Kinetic reaction rates (such as k on /k off ) and molecular concentrations (Table A1, Table A2 in Appendix I) are obtained from values reported in the literature and utilized in our previous work [7,9,10,12,13] (unless specified otherwise). Probabilistic reaction rate constants used in this study are obtained from kinetic rate constants using a previously described parameter-mapping scheme [7,38].…”

“…Both types of cell-to-cell variability can have important ramifications for diseases characterized by dysregulated apoptosis. In cancer, for example, cellular variation in anti-apoptotic protein levels (such as the Bcl2 concentration) as well as effective low number of molecules generated by over-expressed apoptotic inhibitors contribute to large cell-to-cell variability in apoptotic activation [10,13,14]. …”

“…Incomplete activation of the type 2 pathway may lead to generation of more resistant phenotypes. Therefore, it is important to search for strategies that would eliminate cell-to-cell variability in cancer cell apoptosis [13,14,16]. In addition, such strategies need to selectively target cancer cells.…”